Author name code: toth
ADS astronomy entries on 2022-09-14
author:"Toth, Gabor"
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Title: Simulation of Magnetospheric Sawtooth Oscillations: The Role
of Kinetic Reconnection in the Magnetotail
Authors: Wang, Xiantong; Chen, Yuxi; Tóth, Gábor
Bibcode: 2022GeoRL..4999638W
Altcode:
Magnetospheric sawtooth oscillations are observed during strong and
steady solar wind driving conditions. The simulation results of our
global magnetohydrodynamics (MHD) model with embedded kinetic physics
show that when the total magnetic flux carried by constant solar wind
exceeds a threshold, sawtooth-like magnetospheric oscillations are
generated. Different from previous works, this result is obtained
without involving time-varying ionospheric outflow in the model. The
oscillation period and amplitude agree well with observations. The
simulated oscillations cover a wide range of local times, although
the distribution of magnitude as a function of longitude is different
from observations. Our comparative simulations using ideal or Hall MHD
models do not produce global time-varying features, which suggests that
kinetic reconnection physics in the magnetotail is a major contributing
factor to sawtooth oscillations.
Title: Global Magnetohydrodynamic Magnetosphere Simulation With an
Adaptively Embedded Particle-In-Cell Model
Authors: Wang, Xiantong; Chen, Yuxi; Tóth, Gábor
Bibcode: 2022JGRA..12730091W
Altcode:
We perform a geomagnetic event simulation using a newly developed
magnetohydrodynamic with adaptively embedded particle-in-cell
(MHD-AEPIC) model. We have developed effective criteria to identify
reconnection sites in the magnetotail and cover them with the PIC
model. The MHD-AEPIC simulation results are compared with Hall MHD and
ideal MHD simulations to study the impacts of kinetic reconnection at
multiple physical scales. At the global scale, the three models produce
very similar SYM-H and SuperMag Electrojet indexes, which indicates
that the global magnetic field configurations from the three models
are very close to each other. We also compare the ionospheric solver
results and all three models generate similar polar cap potentials and
field-aligned currents. At the mesoscale, we compare the simulations
with in situ Geotail observations in the tail. All three models
produce reasonable agreement with the Geotail observations. At the
kinetic scales, the MHD-AEPIC simulation can produce a crescent
shape distribution of the electron velocity space at the electron
diffusion region, which agrees very well with MMS observations near
a tail reconnection site. These electron scale kinetic features are
not available in either the Hall MHD or ideal MHD models. Overall,
the MHD-AEPIC model compares well with observations at all scales, it
works robustly, and the computational cost is acceptable due to the
adaptive adjustment of the PIC domain. It remains to be determined
whether kinetic physics can play a more significant role in other
types of events, including but not limited to substorms.
Title: SOFIE (Solar-wind with Field-lines and Energetic-particles):
A data-driven and self-consistent SEP modeling and forecasting tool
Authors: Zhao, Lulu; Manchester, Ward, IV; Sokolov, Igor; Van der
Holst, Bart; Toth, Gabor; Tenishev, Valeriy; Gombosi, Tamas; Mays,
M. Leila; Huang, Zhenguang; Whitman, Kathryn; Sachdeva, Nishtha
Bibcode: 2022cosp...44.1190Z
Altcode:
We present a data-driven and self-consistent SEP model, SOFIE,
to simulate the acceleration and transport processes of energetic
particles using the Space Weather Modeling Framework (SWMF) developed
at the University of Michigan. In this model, the background solar
wind plasma in the solar corona and interplanetary space is modeled
by the Alfven Wave Solar-atmosphere Model(-Realtime) (AWSoM(-R)),
which is driven by the near-real-time hourly updated GONG (bihourly
ADAPT-GONG) magnetogram. In the background solar wind, the CMEs
are launched employing the Eruptive Event Generator using Gibson-Low
configuration (EEGGL), by inserting a flux rope estimated from the free
magnetic energy in the active region. The acceleration and transport
processes are then modeled self-consistently by the multiple magnetic
field line tracker (M-FLAMPA) and the Adaptive Mesh Particle Simulator
(AMPS). We will demonstrate the capability of SOFIE to demystify the
acceleration processes by the CME-driven shock in the low corona and the
modulation of energetic particles by the solar wind structures. Besides,
using selected historical SEP events, e.g. 2013 Apr 11 event, we will
illustrate the progresses toward a faster-than-real-time prediction
of SEPs.
Title: The helicity sign of flux transfer events flux ropes and
its relationship to the guide field and Hall physics in magnetic
reconnection at the magnetopause
Authors: Dahani, Souhail; Toth, Gabor; Cassak, . Paul; Fear, Robert;
Burch, James; Giles, . Barbara; Genot, Vincent; Lavraud, Benoit;
Torbert, Roy; Gershman, Dan; Chen, Yuxi; Kieokaew, Rungployphan;
Fargette, Naïs; Marchaudon, Aurelie
Bibcode: 2022cosp...44.1618D
Altcode:
Flux Transfer Events (FTEs) are transient magnetic flux ropes
typically found at the Earth's magnetopause on the dayside. While
it is known that FTEs are generated by magnetic reconnection, it
remains unclear how the details of magnetic reconnection controls
their properties. A recent study showed that the helicity sign of
the FTEs positively correlates with the east-west (By) component of
the Interplanetary Magnetic Field (IMF). With data from the Cluster
and Magnetospheric MultiScale missions, we performed a statistical
study of 166 quasi force-free FTEs. We focus on their helicity sign
and possible correlations with upstream solar wind conditions and
local magnetic reconnection properties. Using both in situ data and
the Maximum Magnetic Shear model, we find that FTEs whose helicity
sign positively correlates with the IMF By show moderate magnetic
shears while those uncorrelated to the IMF By have higher magnetic
shears. We propose that for small IMF By, which corresponds to high
shear and low guide field, the Hall pattern of magnetic reconnection
determines the FTE core field and helicity sign. This work highlights
a fundamental connection between the kinetic processes at work in
magnetic reconnection and the macroscale structure of FTEs.
Title: Can Physics-Based SWx Models Predict Space Weather Variations?
Authors: Gombosi, Tamas; Manchester, Ward, IV; Sokolov, Igor; Van
der Holst, Bart; Toth, Gabor; Huang, Zhenguang; Zhao, Lulu; Sachdeva,
Nishtha; Wang, Xiantong
Bibcode: 2022cosp...44.3217G
Altcode:
Over the space age, we have accumulated extensive knowledge of the
regions of space surrounding the Earth and the Sun, and the governing
physical processes controlling space weather in these regions. However,
this knowledge has not been translated into an operational forecast
capability. By combining our expertise in space weather modeling and
data science/machine learning we can not only address the "holy grail"
of space weather prediction and extend the forecast horizon from
minutes to days, but also transition the results to space weather
operations. The current space weather predictive capabilities are
either short term and/or not accurate and reliable. How can we forecast
the severity of the terrestrial impact (geo-effectiveness) of solar
storms? When an active region on the Sun will produce eruptions, and
how large these will be? We only learn about the magnetic field and
exact timing at the L1 point (about 1 million miles away) when the
eruption reaches the ACE or DSCOVR satellites, which provides only
a 20 minute to 1 hour forecast time, depending on the CME speed. We
initiated a research program that aims to answer these questions using
a unique combination of modeling, computation, and massive amounts of
space weather data collected by satellites that will be used to train
state-of-the-art machine learning algorithms.
Title: NOAA SWPC's Operational Geospace Model: Assessing and Improving
Performance
Authors: Singer, Howard; Millward, George; Toth, Gabor; Huang,
Zhenguang; Cash, Michele; Balch, Christopher; Camporeale, Enrico;
Adamson, Eric
Bibcode: 2022cosp...44.3445S
Altcode:
Since 2016, in the United States, the National Oceanic and Atmospheric
Administration's (NOAA) Space Weather Prediction Center (SWPC) has
been continuously running an operational Geospace model. The coupled
model developed at the University of Michigan, and part of their Space
Weather Modeling Framework (SWMF), is driven by solar wind observations
measured at L1 to provide short-term regional predictions of magnetic
variations in space and at Earth's surface. The surface magnetic
variations, when combined with Earth conductivity models, can be used
to model geoelectric fields that drive geomagnetically induced currents
(GICs) in long-line conductors such as power grids. The model is an
important tool, useful for predicting space weather impacts on the
power grids--one of societies top priority space weather problems. In
this presentation, we will describe the continuous activities needed
to assess model performance and to validate and improve model skill to
more accurately determine regional activity that supports space weather
customers. We will discuss the processes within NOAA for model upgrades
as well as current model performance, pathways for future improvements
and the challenges for both the research and operational communities.
Title: Magnetospheric storm and substorm simulations using the MHD
with Adaptively Embedded Particle-in-Cell (MHD-AEPIC) model
Authors: Toth, Gabor; Wang, Xiantong; Chen, Yuxi
Bibcode: 2022cosp...44.1725T
Altcode:
The Magnetohydrodynamic with Embedded Particle-In-Cell (MHD-EPIC) model
has been developed and applied successfully to Earth, Mercury, Mars
and Ganymede magnetosphere simulations. While MHD-EPIC is many orders
of magnitude faster than a fully kinetic global model, it can become
prohibitively slow if the potential region of interest where kinetic
phenomena, such as magnetic reconnection, can occur is large. This is
due to the fact that the PIC domain in MHD-EPIC is restricted to a set
of static Cartesian boxes. For example, a very large PIC box would be
needed to accommodate the flapping motion of the magnetotail current
sheet during a geomagnetic storm simulation. To tackle this problem,
we have developed a new MHD with Adaptively Embedded Particle-In-Cell
(MHD-AEPIC) model. MHD-AEPIC inherits all numerical algorithms from
MHD-EPIC and incorporates a new adaptive PIC model, the Flexible
Kinetic Simulator (FLEKS). FLEKS allows the PIC cells to be activated
and deactivated during a simulation. The coupling between the MHD
model and the adaptive PIC grid has been developed and implemented
into the Space Weather Modeling Framework. We have also developed
physics-based criteria to identify potential reconnection sites,
which makes the adaptation fully automatic. In this work, we apply
the new MHD-AEPIC model to geomagnetic storm and substorm simulations
and demonstrate how adaptation makes this simulation feasible. In
particular, we demonstrate that MHD-AEPIC is capable of reproducing
global sawtooth oscillations as well as electron-scale physics.
Title: Michigan Sun-to-Earth Model with Data Assimilation and
Quantified Uncertainty
Authors: Toth, Gabor
Bibcode: 2022cosp...44.3440T
Altcode:
As part of the Space Weather with Quantified Uncertainty NSF program,
we have been developing the Michigan Sun-to-Earth Model with Data
Assimilation and Quantified Uncertainty (MSTEM-QUDA). The main
goal of the project is to provide useful probabilistic forecast of
major space weather events about 24 hours before the geospace impact
occurs. We are using the first-principles models in the Space Weather
Modeling Framework in combination with uncertainty quantification and
data assimilation. Using sophisticated experimental design and fully
automated scripts, we have performed about a thousand simulations with
our solar corona and heliosphere model generating steady state solar
wind solutions and coronal mass ejections. Based on these simulations,
we have performed the uncertainty quantification analysis. One important
finding is that the physically meaningful range of the background solar
wind model parameters depends on the solar cycle. Our CME simulations
show reasonably good arrival times and velocity structures. While the
amplitude of the magnetic field is similar to the observations, the
temporal profiles are challenging to match. Data assimilation provides
an opportunity to improve the predictions. We are using in-situ
observations at L1 prior to the CME and coronal while-light image
observations right after the eruption to find the optimal parameters
for the ensemble simulations. To make ensemble simulations feasible, the
model should take advantage of GPUs. We have already ported the Geospace
model, a large part of MSTEM-QUDA, to run efficiently on a GPU. The
operational Geospace model can run on a single GPU significantly faster
than real time at the same speed as using about 100 CPU cores. The
Michigan Sun-to-Earth Model is available as an open-source distribution
at https://github.com/MSTEM-QUDA to the entire community.
Title: Global Driving of Auroral Precipitation: 1. Balance of Sources
Authors: Mukhopadhyay, Agnit; Welling, Daniel; Liemohn, Michael;
Ridley, Aaron; Burleigh, Meghan; Wu, Chen; Zou, Shasha; Connor,
Hyunju; Vandegriff, Elizabeth; Dredger, Pauline; Tóth, Gabor
Bibcode: 2022JGRA..12730323M
Altcode:
The accurate determination of auroral precipitation in global models has
remained a daunting and rather inexplicable obstacle. Understanding
the calculation and balance of multiple sources that constitute
the aurora, and their eventual conversion into ionospheric
electrical conductance, is critical for improved prediction of
space weather events. In this study, we present a semi-physical
global modeling approach that characterizes contributions by
four types of precipitation—monoenergetic, broadband, electron,
and ion diffuse—to ionospheric electrodynamics. The model uses a
combination of adiabatic kinetic theory and loss parameters derived
from historical energy flux patterns to estimate auroral precipitation
from magnetohydrodynamic (MHD) quantities. It then converts them into
ionospheric conductance that is used to compute the ionospheric feedback
to the magnetosphere. The model has been employed to simulate the 5-7
April 2010 Galaxy15 space weather event. Comparison of auroral fluxes
show good agreement with observational data sets like NOAA-DMSP and
OVATION Prime. The study shows a dominant contribution by electron
diffuse precipitation, accounting for ∼74% of the auroral energy
flux. However, contributions by monoenergetic and broadband sources
dominate during times of active upstream solar conditions, providing
for up to 61% of the total hemispheric power. The study also finds
a greater role played by broadband precipitation in ionospheric
electrodynamics which accounts for ∼31% of the Pedersen conductance.
Title: MHD simulation of solar wind interaction with Mars and
comparison with MAVEN observations
Authors: Ma, Yingjuan; Luhmann, Janet G.; Russell, C. T.; Nagy,
Andrew; Toth, Gabor; Fang, Xiaohua
Bibcode: 2022cosp...44..936M
Altcode:
Since Mars has no global intrinsic magnetic field, the solar wind plasma
interacts with the Martian upper atmosphere/ionosphere in a more direct
manner. Therefore, it is important to incorporate ionospheric processes
into global interaction models so that ionospheric responses/changes
can be captured self-consistently. There are two well-known numerical
challenges in modeling the global interaction of the solar wind
with Mars: 1) resolve the ionospheric structure with sufficient
radial resolution; and 2) include the effect of the Martian crustal
field. Various missions to Mars, especially the ongoing MAVEN mission,
provide excellent datasets to improve our understanding of solar wind
interactions with Mars and to validate numerical models of Mars. In
this presentation, we will discuss some recent advances in MHD modeling
efforts, including time dependent MHD, multi-fluid MHD, multi-fluid
MHD with electronic pressure equations, and global MHD with embedded
PIC model, and the comparison with spacecraft observation.
Title: MSWIM2D: Two-dimensional Outer Heliosphere Solar Wind Modeling
Authors: Keebler, Timothy B.; Tóth, Gábor; Zieger, Bertalan;
Opher, Merav
Bibcode: 2022ApJS..260...43K
Altcode:
The vast size of the Sun's heliosphere, combined with sparse
spacecraft measurements over that large domain, makes numerical
modeling a critical tool to predict solar wind conditions where there
are no measurements. This study models the solar wind propagation
in 2D using the BATSRUS MHD solver to form the MSWIM2D data set of
solar wind in the outer heliosphere. Representing the solar wind
from 1 to 75 au in the ecliptic plane, a continuous model run from
1995-present has been performed. The results are available for free
at http://csem.engin.umich.edu/mswim2d/. The web interface extracts
output at desired locations and times. In addition to solar wind ions,
the model includes neutrals coming from the interstellar medium to
reproduce the slowing of the solar wind in the outer heliosphere and
to extend the utility of the model to larger radial distances. The
inclusion of neutral hydrogen is critical to recreating the solar
wind accurately outside of ~4 au. The inner boundary is filled by
interpolating and time-shifting in situ observations from L1 and
STEREO spacecraft when available. Using multiple spacecraft provides
a more accurate boundary condition than a single spacecraft with time
shifting alone. Validations of MSWIM2D are performed using MAVEN and
New Horizons observations. The results demonstrate the efficacy of
this model to propagate the solar wind to large distances and obtain
practical, useful solar wind predictions. For example, the rms error
of solar wind speed prediction at Mars is only 66 km s-1
and at Pluto is a mere 25 km s-1.
Title: Energy-momentum tensor and duality symmetry of linearized
gravity in the Fierz formalism
Authors: Tóth, Gábor Zsolt
Bibcode: 2022CQGra..39g5003T
Altcode: 2021arXiv210802124T
A formulation of linearized gravity in flat background, based on the
Fierz tensor as a counterpart of the electromagnetic field strength,
is discussed in detail and used to study fundamental properties of the
linearized gravitational field. In particular, the linearized Einstein
equations are written as first order partial differential equations
in terms of the Fierz tensor, in analogy with the first order Maxwell
equations. An energy-momentum tensor $({{T}_{\mathrm{lg}}}^{ab})$
with favourable properties and exhibiting remarkable similarity to the
standard energy-momentum tensor of the electromagnetic field is found
for the linearized gravitational field. ${{T}_{\mathrm{lg}}}^{ab}$
is quadratic in the Fierz tensor (which is constructed from the first
derivatives of the linearized metric), traceless, and satisfies the
dominant energy condition in a gauge that contains the transverse
traceless (TT) gauge. It is further shown that in suitable gauges,
including the TT gauge, linearized gravity in the absence of matter has
a duality symmetry that maps the Fierz tensor, which is antisymmetric
in its first two indices, into its dual. Conserved currents associated
with the gauge and duality symmetries of linearized gravity are also
determined. These currents show good analogy with the corresponding
currents in electrodynamics.
Title: AWSoM Magnetohydrodynamic Simulation of a Solar Active Region
with Realistic Spectral Synthesis
Authors: Shi, Tong; Manchester, Ward, IV; Landi, Enrico; van der
Holst, Bart; Szente, Judit; Chen, Yuxi; Tóth, Gábor; Bertello,
Luca; Pevtsov, Alexander
Bibcode: 2022ApJ...928...34S
Altcode:
For the first time, we simulate the detailed spectral line emission
from a solar active region (AR) with the Alfvén Wave Solar Model
(AWSoM). We select an AR appearing near disk center on 2018 July 13
and use the National Solar Observatory's Helioseismic and Magnetic
Imager synoptic magnetogram to specify the magnetic field at the
model's inner boundary. To resolve small-scale magnetic features, we
apply adaptive mesh refinement with a horizontal spatial resolution
of 0°.35 (4.5 Mm), four times higher than the background corona. We
then apply the SPECTRUM code, using CHIANTI spectral emissivities,
to calculate spectral lines forming at temperatures ranging from 0.5
to 3 MK. Comparisons are made between the simulated line intensities
and those observed by Hinode/Extreme-ultraviolet Imaging Spectrometer
where we find close agreement across a wide range of loop sizes and
temperatures (about 20% relative error for both the loop top and
footpoints at a temperature of about 1.5 MK). We also simulate and
compare Doppler velocities and find that simulated flow patterns are
of comparable magnitude to what is observed. Our results demonstrate
the broad applicability of the low-frequency AWSoM for explaining the
heating of coronal loops.
Title: The Solar Wind with Hydrogen Ion Exchange and Large-scale
Dynamics (SHIELD) Code: A Self-consistent Kinetic-Magnetohydrodynamic
Model of the Outer Heliosphere
Authors: Michael, A. T.; Opher, M.; Tóth, G.; Tenishev, V.;
Borovikov, D.
Bibcode: 2022ApJ...924..105M
Altcode:
Neutral hydrogen has been shown to greatly impact the plasma flow in
the heliosphere and the location of the heliospheric boundaries. We
present the results of the Solar Wind with Hydrogen Ion Exchange
and Large-scale Dynamics (SHIELD) model, a new, self-consistent,
kinetic-MHD model of the outer heliosphere within the Space Weather
Modeling Framework. The charge exchange mean free path is on the
order of the size of the heliosphere; therefore, the neutral atoms
cannot be described as a fluid. The numerical code SHIELD couples
the MHD solution for a single plasma fluid to the kinetic solution
for neutral hydrogen atoms streaming through the system. The kinetic
code is based on the Adaptive Mesh Particle Simulator, a Monte Carlo
method for solving the Boltzmann equation. The numerical code SHIELD
accurately predicts the increased filtration of interstellar neutrals
into the heliosphere. In order to verify the correct implementation
within the model, we compare the results of the numerical code SHIELD
to those of other, well-established kinetic-MHD models. The numerical
code SHIELD matches the neutral hydrogen solution of these studies
as well as the shift in all heliospheric boundaries closer to the
Sun in comparison with the multi-fluid treatment of neutral hydrogen
atoms. Overall the numerical code SHIELD shows excellent agreement with
these models and is a significant improvement to the fluid treatment
of interstellar hydrogen.
Title: Effect of different simulation configurations on the
prediction performance of the Space Weather Modeling Framework on
ground magnetic perturbations
Authors: Kwagala, Norah; Tenfjord, Paul; Norgren, Cecilia; Hesse,
Michael; Moretto Jorgensen, Therese; Toth, Gabor; Kolsto, Hakon;
Fl Spinnangr, Susanne; Perez-Coll Jimenez, Judit; Kuniyoshi, Hidetaka
Bibcode: 2021AGUFMSH55C1850K
Altcode:
This study investigates how different simulation configurations of
the Space Weather Modeling Framework (SWMF) affect the predicted
magnetic perturbations (dB and dB/dt) on the ground. The SWMF
configurations investigated include numerical integration schemes and
grid resolutions. Different simulations of two historic geomagnetic
storms are studied: the extreme activity halloween storm on 29 October
2003 and a relatively low activity storm on 31 August 2001. Our region
of investigation is the northern hemisphere above 50 degrees magnetic
latitude using all 88 available geomagnetic ground stations provided
by the superMAG network. The performance of the model predictions
with the different parameter settings is compared using different
metrics including the normalised root mean square error, correlation
coefficient, probability of detection, probability of false detection,
Heidke skill score, and frequency bias.
Title: A Predictive Geoelectric Field Model: Development, Results,
and Challenges
Authors: Singer, Howard; Balch, Christopher; Camporeale, Enrico;
Adamson, Eric; Millward, George; Cash, Michele; Toth, Gabor; Huang,
Zhenguang; Kelbert, Anna; Rigler, Erin
Bibcode: 2021AGUFMSM41A..02S
Altcode:
Historically, there are numerous documented examples of geomagnetic
storms causing geomagnetically induced currents (GICs) in power
grids resulting in power outages, service disruption, and impacts on
routine operations. As a result, space weather impacts on the power
grids are one of the top priority problems in today's society. To
address this problem, NOAAs Space Weather Prediction Center (SWPC)
has provided products and services that forecast, warn, and alert
power grid operators of impending geomagnetic storms. However, during
a meeting with grid operators in 2011, nowcasts and forecasts of the
surface geoelectric field were identified as the key input needed for
determining GICs since the regional geoelectric field can be used
as input to power grid system models for determining the level of
geomagnetically induced currents. SWPC, working with our partners has
addressed this problem by: 1) working with the University of Michigan in
2016 to transition into operations a Geospace Model that was driven by
solar wind observations at L1 to provide short-term regional predictions
of magnetic variations at Earths surface that drive the geoelectric
field; and 2) working with partners at the US Geological Survey (USGS)
in 2020 to introduce a near real-time Geoelectric Model that used
ground-based magnetometer data from the USGS and Natural Resources
Canada (NRCan), along with a 3D empirical ground conductivity model,
to estimate the regional geoelectric field in the US. Then, in June
2021, instead of using near-real time ground observed magnetic field
data to drive the geoelectric model, we use predicted magnetic fields
from the Geospace Model to drive the Geoelectric Model in a predictive
mode. In this presentation, we show the first results from the coupled
Geospace/Geoelectric model that can provide short-term predictions of
the regional geoelectric field to support power grid operators. First
results indicate that the model does surprisingly well at predicting
the more slowly varying geoelectric field (many minutes); however,
as expected, the model does not do as well with minute-by-minute
variations. In addition to showing these results, we discuss model
limitations, next steps towards producing useful geoelectric products,
and the challenges for the research community to improve geoelectric
forecasting.
Title: Simulating the dawn-dusk asymmetry of Mercurys magnetotail
reconnection with MHD-AEPIC model
Authors: Chen, Yuxi; Jia, Xianzhe; Toth, Gabor; Dong, Chuanfei; Sun,
Weijie; Slavin, James; Li, Changkun; Wang, Xiantong
Bibcode: 2021AGUFMSM55C1788C
Altcode:
Since the kinetic scales of Mercury's magnetospheric plasma can be
comparable to Mercury's radius, kinetic effects play an important role
in Mercury's magnetosphere. Chen et al. (2019) studied the dawn-dusk
asymmetries of Mercurys magnetotail using the magnetohydrodynamics
with embedded particle-in-cell (MHD-EPIC) simulations, and showed
the asymmetries of the tail current-sheet thickness, plasma density
and electron pressure clearly. The MHD-EPIC simulations also show the
asymmetries of reconnection products, the dipolarization events and
planetward reconnection jets, but the asymmetries are less obvious
than MESSENGER observations. To further explore the physics behind
the reconnection asymmetries, we use the newly developed MHD with
adaptively embedded particle-in-cell (MHD-AEPIC) model to simulate
Mercurys magnetotail dynamics. The MHD-AEPIC model supports a PIC
region of any shape so that Mercurys inner magnetosphere can be also
covered by the PIC code. Compared to Chen et al. (2019), the larger
PIC region in the MHD-AEPIC model allows us to study the evolution of
the dipolarization events and reconnection jets after they penetrate
into the inner magnetosphere. Since the ion-electron mass ratio may
be crucial for the dawn-dusk asymmetries, we will examine its role by
varying this model parameter in a series of simulations.
Title: Predicting the Optimal Poynting Flux for Different Solar
Activity Conditions for Realtime Solar Wind Prediction
Authors: Huang, Zhenguang; Toth, Gabor; Gombosi, Tamas; Sachdeva,
Nishtha; Zhao, Lulu; Manchester, Ward; van der Holst, Bart; Sokolov,
Igor
Bibcode: 2021AGUFMSH45D2395H
Altcode:
Its critical to have an accurate solar wind background in the inner
heliosphere for space weather prediction, from the arrival of Corotating
Interaction Regions (CIRs), to the Coronal Mass Ejections (CMEs),
and Solar Energetic Particles (SEPs). In the space weather community,
there are two major approaches to predict the solar wind background:
one uses empirical or semi-empirical models, e.g., the Wang-Sheeley-Arge
(WSA) model; the other is based on first-principles model, e.g., the
Alfven Wave Solar atmosphere Model (AWSoM) developed at the University
of Michigan. In the past, it was difficult for physics models to
perform real-time solar wind predictions, because the computational
cost is much higher for physics-based models than for empirical or
semi-empirical models, and the optimal input parameters could be
different for different solar rotations in which case the user would
need to run the model with different input parameters to best predict
the solar wind. Nowadays, the computational cost is not a big issue
as super computers are much more powerful than before. The remaining
issue is that the input parameters could vary. In real-time solar
wind prediction, it is necessary to have optimal input parameters in
advance. In this presentation, we study the relation between one of the
most important parameters for AWSoM, the Poynting flux at the inner
boundary, and the magnetic field structure of the solar corona. We
obtain the optimal Poynting flux value for nine Carrington rotations
in the last solar cycle and correlate it with various characteristics
of the solar magnetic field, such as open flux, area of coronal holes,
etc.. The preliminary results are encouraging, and suggest that the
optimal parameter can be estimated from the magnetograms.
Title: SOFIE (Solar-wind with Field-lines and Energetic-particles):
A data-driven and self-consistent SEP modeling and forecasting tool
Authors: Zhao, Lulu; Sokolov, Igor; Gombosi, Tamas; Tenishev, Valeriy;
Huang, Zhenguang; Toth, Gabor; Sachdeva, Nishtha; Manchester, Ward;
van der Holst, Bart
Bibcode: 2021AGUFMSH55F1900Z
Altcode:
We present a data-driven and self-consistent SEP model, SOFIE, to
simulate the acceleration and transport processes of energetic particles
using the Space Weather Modeling Framework (SWMF). In this model, the
background solar wind plasma in the solar corona and interplanetary
space are modeled by the Alfven Wave Solar-atmosphere Model(-Realtime)
(AWSoM(-R)) driven by the near-real-time hourly updated GONG (bihourly
ADAPT-GONG) magnetograms. In the background solar wind, the CMEs
are launched employing the Eruptive Event Generator using Gibson-Low
configuration (EEGGL), by inserting a flux rope estimated from the free
magnetic energy in the active region. The acceleration and transport
processes are then modeled self-consistently by the multiple magnetic
field line tracker (M-FLAMPA) and the Adaptive Mesh Particle Simulator
(AMPS). We will demonstrate the capability of SOFIE to demystify the
acceleration processes by the CME-driven shock in the low corona and the
modulation of energetic particles by the solar wind structures. Besides,
using selected historical SEP events, e.g. 2013 Apr 11 event, we will
illustrate the progresses toward a faster-than-real-time prediction
of SEPs.
Title: 2D Michigan Solar Wind Propagation Model for the Outer
Heliosphere
Authors: Keebler, Timothy; Toth, Gabor; Opher, Merav; Zieger, Bertalan
Bibcode: 2021AGUFMSH25C2105K
Altcode:
Modeling of the solar wind propagation through the Outer Heliosphere
is critical for comparison with limited spacecraft data and to fill
in an area with sparse in-situ observations. Following the MSWiM
one-dimensional solar wind advection model, the Michigan Solar WInd
Model in 2D (MSWIM2D) is presented to improve solar wind representation
for the outer heliosphere in the ecliptic plane. This model is driven
using data from observatories at the first Earth-Sun Lagrangian point,
as well as the STEREO spacecraft, to fill the inner boundary at 1
AU. By time-shifting the point observations and interpolating between
multiple observatories, the entire inner boundary of Earth's orbit
can be constantly populated by solar wind observations, permitting
the driving of a 2D model. Interstellar neutrals are also included to
interact with the solar wind, extending the model utility to larger
radial distances. Validation at Mars using MAVEN data shows good
agreement, and validation at New Horizons is presented here to assess
model performance over longer propagations. The model output is publicly
accessible for use by the broader planetary and heliospheric community,
available at http://csem.engin.umich.edu/mswim2d. This interface allows
interpolation of the model results along user-defined trajectories
at one hour output cadence. Timeseries along the trajectories can be
created between 1995 and 2020, and include solar wind density, vector
velocity, vector magnetic field, and ion temperature.
Title: A comparison of heliotail configurations arising from different
treatments of non-ideal MHD effects with ENA maps at IBEX energies
Authors: Kornbleuth, Marc; Opher, Merav; Baliukin, Igor; Dayeh,
Maher; Zirnstein, Eric; Gkioulidou, Matina; Dialynas, Kostas; Galli,
Andre; Richardson, John; Izmodenov, Vladislav; Zank, Gary; Fuselier,
Stephen A.; Michael, Adam; Toth, Gabor; Tenishev, Valeriy; Alexashov,
Dmitry; Drake, James
Bibcode: 2021AGUFMSH21B..02K
Altcode:
The role of the solar magnetic field in the heliosheath has long
been considered passive, but recent studies indicate it may play an
active role in collimating the heliosheath plasma into two lobes at
high latitudes. We compare results from two MHD models, the BU and
Moscow models, which treat non-ideal MHD effects differently. The BU
model allows for magnetic reconnection at the heliopause between the
solar and interstellar magnetic fields, while the Moscow model does not
allow for direct communication between the solar wind and interstellar
medium. We use the same boundary conditions, 22-year averaged solar
cycle conditions from 1995 to 2017. An important result is that
both models show that the plasma in the heliosheath and heliotail is
confined by the solar magnetic field in two lobes. The plasma solutions
in the nose of the heliosphere are similar. However, the Moscow model
displays a long, thousands of AU comet-like tail whereas the BU model
shows the heliotail is shortened to about 400 AU where the interstellar
medium flows between the two lobes. The ENA maps from the two models
show both qualitative and quantitative agreement at IBEX energies,
despite the different configurations of the heliotail. The modeled
ENA maps agree qualitatively, but not quantitatively, with IBEX ENA
observations. At higher energies the ENA maps from the two models
differ, so higher energy ENA data (from INCA or IMAP) may be able to
determine which model heliotail best fits the data.
Title: Magnetosphere Energy Dynamics in 3D, Comparison to the Virial
Theorem and Quantification of Macro Scale Dynamics During a Simulated
Storm Event
Authors: Brenner, Austin; Pulkkinen, Tuija; Al Shidi, Qusai; Toth,
Gabor
Bibcode: 2021AGUFMSM35C1984B
Altcode:
Ground magnetic perturbations are due to dynamics within the
magnetosphere ionosphere system as well as coupling with the solar
wind. Global simulation is well suited to study the entire system
at once with self-consistent physics. In this work the magnetopause
location is identified from Space Weather Modeling Framework (SWMF)
output at 1min cadence for a simulated event to a fixed downstream
distance. Preliminary results of total energy integrated over the
magnetosphere volume correlates well with Disturbance Storm Time
(DST) index (attached figure). Following up on the initial results the
magnetosphere volume is analyzed for spatial distribution of energy
in terms of total energy, as well as hydrodynamic energy and magnetic
energy. The relative contribution to magnetic perturbation at the
Earth's center is determined for subregions and energy types using
the Biot-Savart law and Virial Theorem. Comparisons with in situ and
ground based observations are made to identify areas of high and low
simulation confidence.
Title: AWSoM MHD simulation of a solar active region with realistic
spectral synthesis
Authors: Manchester, Ward; Shi, Tong; Landi, Enrico; Szente, Judit;
van der Holst, Bart; Chen, Yuxi; Toth, Gabor; Bertello, Luca; Pevtsov,
Alexander
Bibcode: 2021AGUFMSH12B..02M
Altcode:
For the first time, we simulate the detailed spectral line emission
from a solar active region (AR) with the Alfven Wave Solar Model
(AWSoM). We select an active region appearing near disk center on
2018 July 13 and use an NSO-HMI synoptic magnetogram to specify the
magnetic field at the model's inner boundary. To resolve smaller-scale
magnetic features, we apply adaptive mesh refinement to resolve the
AR with a spatial resolution of 0.37 degrees, four times higher than
the background corona. We then apply the SPECTRUM code informed with
Chianti spectral emissivities to calculate more than a dozen spectral
lines forming at temperatures ranging from 0.5 to 3+ MK. Comparisons
are made between these simulated line profiles and those observed by
the Hinode/EIS instrument where we find close agreement (within a
20% margin of error of peak intensity) across a wide range of loop
sizes and temperatures. We also compare the differential emission
measure calculated from both the simulation and EIS observation to
further show the model's ability to capture the plasma temperature and
density. Finally, we simulate and compare Doppler velocities and find
that simulated flow patterns to be of comparable magnitude to what
is observed. Our results demonstrate the broad applicability of the
low-frequency Alfven wave balanced turbulence theory for explaining
the heating of coronal loops.
Title: Magnetohydrodynamic with Adaptively Embedded Particle-in-Cell
model: MHD-AEPIC
Authors: Shou, Yinsi; Tenishev, Valeriy; Chen, Yuxi; Toth, Gabor;
Ganushkina, Natalia
Bibcode: 2021JCoPh.44610656S
Altcode: 2021arXiv210805425S
Space plasma simulations have seen an increase in the use of
magnetohydrodynamic (MHD) with embedded Particle-in-Cell (PIC)
models. This combined MHD-EPIC algorithm simulates some regions
of interest using the kinetic PIC method while employing the MHD
description in the rest of the domain. The MHD models are highly
efficient and their fluid descriptions are valid for most part of
the computational domain, thus making large-scale global simulations
feasible. However, in practical applications, the regions where the
kinetic effects are critical can be changing, appearing, disappearing
and moving in the computational domain. If a static PIC region is used,
this requires a much larger PIC domain than actually needed, which
can increase the computational cost dramatically. To address the
problem, we have developed a new method that is able to dynamically
change the region of the computational domain where a PIC model is
applied. We have implemented this new MHD with Adaptively Embedded PIC
(MHD-AEPIC) algorithm using the BATS-R-US Hall MHD and the Adaptive
Mesh Particle Simulator (AMPS) as the semi-implicit PIC models. We
describe the algorithm and present a test case of two merging flux
ropes to demonstrate its accuracy. The implementation uses dynamic
allocation/deallocation of memory and load balancing for efficient
parallel execution. We evaluate the performance of MHD-AEPIC compared
to MHD-EPIC and the scaling properties of the model to large number
of computational cores.
Title: Dependence of Mercurys magnetopause reconnection on the
upstream conditions: 3D Hall-MHD simulations
Authors: Li, Changkun; Jia, Xianzhe; Chen, Yuxi; Zhou, Hongyang;
Toth, Gabor; Slavin, James; Sun, Weijie
Bibcode: 2021AGUFM.P24B..03L
Altcode:
Observations from NASAs MESSENGER spacecraft reveal that Mercury
has a miniature magnetosphere arising from the interaction of its
intrinsic dipole field with the inner heliosphere solar wind. Compared
to the terrestrial magnetosphere, Mercurys magnetosphere appears to be
more dynamic in that the global timescales for plasma and magnetic
flux circulation are much shorter, and the dayside magnetopause
reconnection occurs at higher rates and under a wider range of
magnetic shear angles. As a product of multiple X-line reconnection,
flux transfer events (FTEs) are found to arise much more frequently
with an occurrence rate of about 50 times higher than that detected
at Earth. MESSENGER observations suggest that the different upstream
solar wind conditions are likely the cause for large differences
in reconnection-driven dynamics between Mercurys magnetosphere
and Earths. In order to understand how reconnection rate and the
characteristics of resultant FTEs vary with the upstream conditions,
we have employed the BATSRUS Hall-MHD model with a high-resolution
grid to simulate Mercurys magnetopause dynamics under a wide range of
upstream solar wind and IMF conditions. Flux ropes are found to form
due to multiple X-line reconnection in all our time-dependent Hall MHD
simulations under fixed wind conditions, but their properties, such
as occurrence rate and spatial scale, vary depending on the upstream
parameters. We have developed automated techniques to identify and
analyze FTEs in our simulations. The results of our analyses are
compared directly with MESSENGER observations (e.g., Sun et al. 2020)
and the comparison yields generally good agreement in terms of FTE
spatial size, occurrence frequency, flux content, etc. The carefully
designed Hall-MHD simulations allow us to examine how the properties of
FTEs depend on parameters such as the solar wind Alfvenic Mach number,
IMF orientation, and the magnetosheath plasma . With the global model,
we also evaluate the global reconnection rate and the contribution
of FTEs to the global circulation of magnetic flux at Mercury and how
these properties vary in response to changes in the external conditions.
Title: A Turbulent Heliosheath Driven by Rayleigh Taylor Instability
Authors: Opher, Merav; Drake, James; Zank, Gary; Toth, Gabor; Powell,
Erick; Kornbleuth, Marc; Florinski, Vladimir; Izmodenov, Vladislav;
Giacalone, Joe; Fuselier, Stephen A.; Dialynas, Kostas; Loeb, Abraham;
Richardson, John
Bibcode: 2021AGUFMSH21B..06O
Altcode:
The heliosphere is the bubble formed by the solar wind as it interacts
with the interstellar medium (ISM). Studies show that the solar
magnetic field funnels the heliosheath solar wind (the shocked solar
wind at the edge of the heliosphere) into two jet-like structures
(1-2). Magnetohydrodynamic simulations show that these heliospheric
jets become unstable as they move down the heliotail (1-3) and drive
large-scale turbulence. However, the mechanism that produces of this
turbulence had not been identified. Here we show that the driver of
the turbulence is the Rayleigh-Taylor (RT) instability caused by the
interaction of neutral H atoms streaming from the ISM with the ionized
matter in the heliosheath (HS). The drag between the neutral and ionized
matter acts as an effective gravity which causes a RT instability to
develop along the axis of the HS magnetic field. A density gradient
exists perpendicular to this axis due to the confinement of the solar
wind by the solar magnetic field. The characteristic time scale of
the instability depends on the neutral H density in the ISM and for
typical values the growth rate is ~ 3 years. The instability destroys
the coherence of the heliospheric jets and magnetic reconnection ensues,
allowing ISM material to penetrate the heliospheric tail. Signatures of
this instability should be observable in Energetic Neutral Atom (ENA)
maps from future missions such as IMAP (4). The turbulence driven by the
instability is macroscopic and potentially has important implications
for particle acceleration.
Title: Geomagnetic storm event simulation using a global MHD with
Adaptively Embedded Particle-In-Cell (MHD-AEPIC) model
Authors: Wang, Xiantong; Chen, Yuxi; Toth, Gabor
Bibcode: 2021AGUFMSM42C..09W
Altcode:
The MHD with Embedded Particle-In-Cell (MHD-EPIC) model has been
successfully applied to Earth, Mercury, Mars and Ganymede magnetosphere
simulations to study reconnection physics in a global context. However,
the PIC region in MHD-EPIC is restricted to be a Cartesian box, which
is not flexible enough to cover the whole domain of interest due to
massive computational cost. For example, a very large PIC box would be
needed to accommodate the flapping motion of the magnetotail current
sheet during a geomagnetic storm simulation. To tackle this problem,
we have developed a new MHD with Adaptively Embedded Particle-In-Cell
(MHD-AEPIC) model that inherits all numerical algorithms from MHD-EPIC,
and also accommodates an adaptive PIC grid that allows PIC cells to
be turned on and off during the simulation. We have also developed
physics-based criteria for the identification of reconnection sites
that makes the adaptation fully automatic. In this work, we apply the
MHD-AEPIC model to a geomagnetic storm simulation and demonstrate how
adaptation works in a real-world scenario. Furthermore, we provide
comparison with observations ranging from electron scales to global
scales.
Title: A Time-Dependent Split Tail Heliosphere
Authors: Powell, Erick; Opher, Merav; Toth, Gabor; Tenishev, Valeriy;
Michael, Adam; Kornbleuth, Marc; Richardson, John
Bibcode: 2021AGUFMSH15F2075P
Altcode:
There is a current debate on the shape of the heliosphere. Current
models provide different solutions to the heliotail. These
models assume different numerical techniques as well as physical
assumptions. Kornbleuth et al. (2021) show that both BU and Moscow
models show collimation of the heliotail plasma by the magnetic
field as first found by Opher et al. (2015). The BU model has the
ISM plasma flowing between the two lobes at around 400AU downtail,
what is known as the croissant-like heliosphere. The BU model was
first extended to include a treatment to the neutral H in a kinetic
fashion by Michael et al. (2021) where they show that the croissant-like
heliotail remain. In this work, within the SHIELD project, we extend
the work of Michael et al. (2021) with the newly updated BU model to
investigate the effect of time dependent solar wind conditions on the
two-lobed heliotail. The BU model in this work was a kinetic-MHD model
that self consistently coupled an MHD treatment of ions to a kinetic
treatment of the neutrals in a long-term solution. We have improved
the statistics in the BU model, through implementation of a lookup
table for the charge exchange rate and resulting source terms for the
plasma, that is more computationally efficient and allows us to capture
shorter time scales necessary to accurately model the evolution of the
time-dependent heliotail. We extend the work of Michael et al. (2021)
with the newly updated SHIELD model to investigate the effect of time
dependent solar wind conditions on the two-lobed heliotail. We comment
on the structure of the heliotail and the differences between long-term
and and time-dependent solutions.
Title: Formation and evolution of the large-scale magnetic fields
in Venus Ionosphere: Results from a 3D global multi-species MHD model
Authors: Ma, Yingjuan; Toth, Gabor; Nagy, Andrew; Luhmann, Janet;
Russell, Christopher
Bibcode: 2021AGUFMSM52C..04M
Altcode:
Large-scale magnetic fields have been observed at Venus ionosphere by
both the Pioneer Venus Orbiter (PVO) and Venus Express spacecraft. In
this study, we examine the formation and evolution of the large-scale
magnetic field in the Venus ionosphere using a sophisticated
global multi-species MHD model that has been developed for Venus. A
time-dependent model run is performed under varying solar wind dynamic
pressure. Based on model results, we find that: 1) Both the locations
of plasma boundaries (such as bow shock and induced magnetospheric
boundary) and plasma conditions in the magnetosheath and the outer part
of the induced magnetosphere adjust quickly (~ minutes) to solar wind
dynamic pressure change; 2) a large-scale magnetic field gradually forms
in the ionosphere during the time when the solar wind dynamic pressure
exceeds the ionospheric thermal pressure; 3) both the penetration and
decay of the large-scale magnetic field in the ionosphere are slow (~
hours); 4) the ion escape rate has a non-linear response to the change
of solar wind dynamic pressure.
Title: Global Sensitivity Analysis for Solar-Wind Simulations in
the Space Weather Modelling Framework
Authors: Jivani, Aniket; Huan, Xun; Chen, Yang; van der Holst, Bart;
Zou, Shasha; Huang, Zhenguang; Sachdeva, Nishtha; Iong, Daniel;
Manchester, Ward; Toth, Gabor
Bibcode: 2021AGUFMSH55C1851J
Altcode:
The Space Weather Modelling Framework (SWMF) offers efficient and
flexible sun-to-earth simulations based on coupled first principles
and/or empirical models. This encompasses computing the quiet solar
wind, generating a coronal mass ejection (CME), propagating the CME
through the heliosphere, and calculating the magnetospheric impact via
geospace models. The predictions from these different steps and models
are affected by uncertainty and variation of many model inputs and
parameters, such as the Poynting flux emanating from the photosphere
and driving and heating the solar wind. In this presentation, as part
of the NextGen SWMF project funded by NSF, we perform uncertainty
quantification (UQ) for the quiet solar wind simulations produced by
our Alfven Wave Solar atmosphere Model (AWSoM). We first catalogue
the various sources of uncertainty and their distributions, and then
propagate the uncertainty to key predictive quantities of interest, the
in-situ solar wind and magnetic field at 1 au, through space-filling
designs of high-fidelity simulations. Using this dataset, we then
build polynomial chaos surrogate models that offer a convenient route
to global sensitivity analysis, which quantifies the contribution
of each input parameters uncertainty towards the variability of the
QoIs. The resulting Sobol sensitivity index allows us to rank and retain
only the most impactful parameters going forward, thereby achieving
dimension-reduction of the stochastic space. We have performed this
UQ analysis for both solar maximum and solar minimum conditions,
and we will summarize our findings in this presentation.
Title: Terrestrial Impacts of Global Geospace Modeling of an Ensemble
of Storms
Authors: Al Shidi, Qusai; Pulkkinen, Tuija; Brenner, Austin; Toth,
Gabor; Zou, Shasha; Gombosi, Tamas
Bibcode: 2021AGUFMSH45E2408A
Altcode:
Modeling the terrestrial impacts of the sun's solar wind is critical
to understanding geomagnetic storms. We use a database of 144 storms
from 2010-2019 and showed how these storms affect magnetometers on
the ground. We also extracted profiles of the magnetic field along the
magnetotail. Skill scores are assigned to the individual stations on
the ground based on how well they can forecast magnetic indeces like
SYM-H and AL. We us our Space Weather Modeling Framework's geospace
configuration. Our model includes coupling of 3D MHD solver (BATSRUS),
the Rice Convection Model, and the Ridley Ionospheric Model. We have
found that all stations have a positive Heidke Skill Score which is
encouraging in terms of space weather forecasting.
Title: Developing the Michigan Sun-to-Earth Model with Data
Assimilation and Quantified Uncertainty
Authors: Toth, Gabor; Chen, Yang; Huan, Xun; van der Holst, Bart;
Zou, Shasha; Jivani, Aniket; Iong, Daniel; Sachdeva, Nishtha; Huang,
Zhenguang; Chen, Yuxi; Gaenko, Alexander; Manchester, Ward
Bibcode: 2021AGUFMSH53B..06T
Altcode:
As part of the Space Weather with Quantified Uncertainty program, our
project, funded by NSF, has been working on developing the Michigan
Sun-to-Earth Model with Data Assimilation and Quantified Uncertainty
(MSTEM-QUDA). In this talk we will summarize the main goals of the
project and report our progress. Using sophisticated experimental
design and fully automated scripts, we have performed many hundreds
of simulations with our solar corona and heliosphere model generating
steady state solar wind solutions. Based on these simulations, we have
completed the uncertainty quantification analysis. One important finding
is that the physically meaningful range of certain model parameters
depends on the solar cycle. We will use an ensemble of background
solar wind model solutions as a starting point for simulating coronal
mass ejections. Our preliminary model runs show promising accuracy for
the CME arrival time. We have also ported the Geospace model, a large
part of MSTEM-QUDA, to run efficiently on a GPU. In fact, we can run
the operational Geospace model on a single GPU significantly faster
than real time at the same speed as using about 100 CPU cores. The
Michigan Sun-to-Earth Model is available as an open-source distribution
at https://github.com/MSTEM-QUDA to the entire community.
Title: How will the crustal magnetic field affect the tail
reconnection process at Mars?
Authors: Ma, Yingjuan; Toth, Gabor; Chen, Yuxi; Nagy, Andrew; Russell,
Christopher
Bibcode: 2021AGUFM.P45F2498M
Altcode:
We use a fully coupled global MHD model with an embedded Particle in
Cell (PIC) code to further understand the magnetic reconnection process
on Mars and its consequences, especially how will the crustal magnetic
field affect the tail reconnection process. This two-way coupled
MHD-EPIC model has been applied to Mars and performed a detailed
study for a tail reconnection event observed by MAVEN [Harada et al.,
2015]. In this study, four more cases will be studied with the same
solar wind condition but for different crustal field orientations. The
subsolar longitude for the baseline case is at 73.1 east longitude. For
the four cases, the subsolar longitude is set to 0, 90, 180 and 270
degrees east longitude, with the strong crustal field located in
the nightside, dawn, dayside and dusk side, respectively. Detailed
analysis of the model results will then be presented to show the
relation between crustal field and tail reconnection process at Mars.
Title: The Development of a Split-tail Heliosphere and the Role of
Non-ideal Processes: A Comparison of the BU and Moscow Models
Authors: Kornbleuth, M.; Opher, M.; Baliukin, I.; Gkioulidou, M.;
Richardson, J. D.; Zank, G. P.; Michael, A. T.; Tóth, G.; Tenishev,
V.; Izmodenov, V.; Alexashov, D.; Fuselier, S.; Drake, J. F.;
Dialynas, K.
Bibcode: 2021ApJ...923..179K
Altcode: 2021arXiv211013962K
Global models of the heliosphere are critical tools used in the
interpretation of heliospheric observations. There are several
three-dimensional magnetohydrodynamic (MHD) heliospheric models that
rely on different strategies and assumptions. Until now only one paper
has compared global heliosphere models, but without magnetic field
effects. We compare the results of two different MHD models, the BU
and Moscow models. Both models use identical boundary conditions to
compare how different numerical approaches and physical assumptions
contribute to the heliospheric solution. Based on the different
numerical treatments of discontinuities, the BU model allows for the
presence of magnetic reconnection, while the Moscow model does not. Both
models predict collimation of the solar outflow in the heliosheath
by the solar magnetic field and produce a split tail where the solar
magnetic field confines the charged solar particles into distinct north
and south columns that become lobes. In the BU model, the interstellar
medium (ISM) flows between the two lobes at large distances due to
MHD instabilities and reconnection. Reconnection in the BU model at
the port flank affects the draping of the interstellar magnetic field
in the immediate vicinity of the heliopause. Different draping in the
models cause different ISM pressures, yielding different heliosheath
thicknesses and boundary locations, with the largest effects at high
latitudes. The BU model heliosheath is 15% thinner and the heliopause is
7% more inwards at the north pole relative to the Moscow model. These
differences in the two plasma solutions may manifest themselves in
energetic neutral atom measurements of the heliosphere.
Title: Simulating Solar Maximum Conditions Using the Alfvén Wave
Solar Atmosphere Model (AWSoM)
Authors: Sachdeva, Nishtha; Tóth, Gábor; Manchester, Ward B.; van
der Holst, Bart; Huang, Zhenguang; Sokolov, Igor V.; Zhao, Lulu;
Shidi, Qusai Al; Chen, Yuxi; Gombosi, Tamas I.; Henney, Carl J.;
Lloveras, Diego G.; Vásquez, Alberto M.
Bibcode: 2021ApJ...923..176S
Altcode:
To simulate solar coronal mass ejections (CMEs) and predict their
time of arrival and geomagnetic impact, it is important to accurately
model the background solar wind conditions in which CMEs propagate. We
use the Alfvén Wave Solar atmosphere Model (AWSoM) within the the
Space Weather Modeling Framework to simulate solar maximum conditions
during two Carrington rotations and produce solar wind background
conditions comparable to the observations. We describe the inner
boundary conditions for AWSoM using the ADAPT global magnetic maps
and validate the simulated results with EUV observations in the low
corona and measured plasma parameters at L1 as well as at the position
of the Solar Terrestrial Relations Observatory spacecraft. This
work complements our prior AWSoM validation study for solar minimum
conditions and shows that during periods of higher magnetic activity,
AWSoM can reproduce the solar plasma conditions (using properly
adjusted photospheric Poynting flux) suitable for providing proper
initial conditions for launching CMEs.
Title: Predicting the Background Solar Wind for Solar Maximum
Conditions with the Alfven Wave Solar atmosphere model (AWSoM)
Authors: Sachdeva, Nishtha; Toth, Gabor; Manchester, Ward; van der
Holst, Bart; Huang, Zhenguang; Sokolov, Igor; Zhao, Lulu; Al Shidi,
Qusai; Chen, Yuxi; Gombosi, Tamas; Henney, Carl
Bibcode: 2021AGUFMSH45D2396S
Altcode:
For physics-based simulations of the coronal mass ejections (CMEs)
it is essential to start with realistic background solar wind
conditions. To achieve this goal, we use the 3D extended MHD Alfven
Wave Solar atmosphere Model (AWSoM) to simulate the background plasma
environment during the magnetically active phase of solar cycle 24 and
validate the results with in situ and remote observations. Representing
the solar maximum conditions by two Carrington Rotations, we use the
ADAPT-HMI photospheric magnetic-field maps to drive AWSoM and simulate
the solar wind from the low corona to Earths orbit. We compare the AWSoM
predicted solar wind with EUV observations near the Sun as well as with
observed plasma and magnetic field parameters at L1 and at the STEREO
spacecraft location. We find that the optimal value for the Poynting
flux parameter of the model depends on the solar activity: for solar
maximum it has to be reduced by about a factor of two compared to the
solar minimum. Using properly adjusted Poynting flux parameters for the
solar maximum period results in a reasonable match with observations
for which quantitative comparisons show small margins of error. These
provide a reasonably accurate background solar wind into which a CME
will be launched.
Title: Stormtime energetics: Energy transport across the magnetopause
in a global MHD simulation
Authors: Brenner, Austin; Pulkkinen, Tuija I.; Al Shidi, Qusai;
Toth, Gabor
Bibcode: 2021FrASS...8..180B
Altcode:
Coupling between the solar wind and magnetosphere can be expressed
in terms of energy transfer through the separating boundary known as
the magnetopause. Geospace simulation is performed using the Space
Weather Modeling Framework (SWMF) of a multi-ICME impact event on
February 18-20, 2014 in order to study the energy transfer through
the magnetopause during storm conditions. The magnetopause boundary
is identified using a modified plasma β and fully closed field
line criteria to a downstream distance of −20Re. Observations
from Geotail, Themis, and Cluster are used as well as the Shue 1998
model to verify the simulation field data results and magnetopause
boundary location. Once the boundary is identified, energy transfer
is calculated in terms of total energy flux K, Poynting flux S,
and hydrodynamic flux H. Surface motion effects are considered and
the spatial distribution is explored in terms of dayside (X > 0),
flank (X < 0), and tail cap (X = Xmin) regions. It is found that
total integrated energy flux over the boundary is nearly balanced
between injection and escape, and flank contributions dominate the
Poynting flux injection. Poynting flux dominates net energy input,
while hydrodynamic flux dominates energy output. Surface fluctuations
contribute significantly to net energy transfer and comparison with
the Shue model reveals varying levels of cylindrical asymmetry in
the magnetopause flank throughout the event. Finally existing energy
coupling proxies such as the Akasofu ε parameter and Newell coupling
function are compared with the energy transfer results.
Title: Challenges in Modeling the Outer Magnetosphere
Authors: Tóth, Gábor; Chen, Yuxi; Huang, Zhenguang; van der Holst,
Bart
Bibcode: 2021GMS...259..717T
Altcode:
No abstract at ADS
Title: Multi Fluid MHD Simulations of Europa's Plasma Interaction
Under Different Magnetospheric Conditions
Authors: Harris, Camilla D. K.; Jia, Xianzhe; Slavin, James A.; Toth,
Gabor; Huang, Zhenguang; Rubin, Martin
Bibcode: 2021JGRA..12628888H
Altcode:
Europa hosts a periodically changing plasma interaction driven
by the variations of Jupiter's magnetic field and magnetospheric
plasma. We have developed a multi fluid magnetohydrodynamic (MHD)
model for Europa to characterize the global configuration of the
plasma interaction with the moon and its tenuous atmosphere. The model
solves the multi fluid MHD equations for electrons and three ion fluids
(Jupiter's magnetospheric O+, as well as O+ and
O2+ originating from Europa's atmosphere) while
incorporating sources and losses in the MHD equations due to electron
impact and photo ionization, charge exchange, recombination and other
relevant collisional effects. Using input parameters constrained by the
Galileo magnetic field and plasma observations, we first demonstrate the
accuracy of our model by simulating the Galileo E4 and E14 flybys, which
took place under different upstream conditions and sampled different
regions of Europa's interaction. Our model produces 3D magnetic field
and plasma bulk parameters that agree with and provide context for the
flyby observations. We next present the results of a parameter study of
Europa's plasma interaction at three different excursions from Jupiter's
central plasma sheet, for three different global magnetospheric states,
comprising nine steady state simulations. By separately tracking
multiple ion fluids, our MHD model allows us to quantify the access of
the Jovian magnetospheric plasma to Europa's surface and determine how
that access is affected by changing magnetospheric conditions. We find
that the thermal magnetospheric O+ precipitation rate ranges
from (1.8-26) × 1024 ions/s, and that the precipitation
rate increases with the density of the ambient magnetospheric plasma.
Title: What sustained multi-disciplinary research can achieve:
The space weather modeling framework
Authors: Gombosi, Tamas I.; Chen, Yuxi; Glocer, Alex; Huang, Zhenguang;
Jia, Xianzhe; Liemohn, Michael W.; Manchester, Ward B.; Pulkkinen,
Tuija; Sachdeva, Nishtha; Al Shidi, Qusai; Sokolov, Igor V.; Szente,
Judit; Tenishev, Valeriy; Toth, Gabor; van der Holst, Bart; Welling,
Daniel T.; Zhao, Lulu; Zou, Shasha
Bibcode: 2021JSWSC..11...42G
Altcode: 2021arXiv210513227G
Magnetohydrodynamics (MHD)-based global space weather models have
mostly been developed and maintained at academic institutions. While
the "free spirit" approach of academia enables the rapid emergence
and testing of new ideas and methods, the lack of long-term stability
and support makes this arrangement very challenging. This paper
describes a successful example of a university-based group, the Center
of Space Environment Modeling (CSEM) at the University of Michigan,
that developed and maintained the Space Weather Modeling Framework
(SWMF) and its core element, the BATS-R-US extended MHD code. It took
a quarter of a century to develop this capability and reach its present
level of maturity that makes it suitable for research use by the space
physics community through the Community Coordinated Modeling Center
(CCMC) as well as operational use by the NOAA Space Weather Prediction
Center (SWPC).
Title: Kinetic Modeling in the Magnetosphere
Authors: Markidis, Stefano; Olshevsky, Vyacheslav; Tóth, Gábor;
Chen, Yuxi; Peng, Ivy Bo; Lapenta, Giovanni; Gombosi, Tamas
Bibcode: 2021GMS...259..607M
Altcode: 2020arXiv201206669M
This paper presents the state of the art of kinetic modeling
techniques for simulating plasma kinetic dynamics in magnetospheres. We
describe the critical numerical techniques for enabling large-scale
kinetic simulations of magnetospheres: parameter scaling, implicit
Particle-in-Cell schemes, and fluid-kinetic coupling. We show an
application of these techniques to study particle acceleration
and heating in asymmetric magnetic reconnection in the Ganymede
magnetosphere.
Title: Estimating Maximum Extent of Auroral Equatorward Boundary
Using Historical and Simulated Surface Magnetic Field Data
Authors: Blake, Seán. P.; Pulkkinen, Antti; Schuck, Peter W.; Glocer,
Alex; Tóth, Gabor
Bibcode: 2021JGRA..12628284B
Altcode:
The equatorward extent of the auroral oval, the region which separates
the open field polar cap regions with the closed field subauroral
regions, is an important factor to take into account when assessing the
risk posed by space weather to ground infrastructure. During storms, the
auroral oval is known to move equatorward, accompanied by ionospheric
current systems and significant magnetic field variations. Here we
outline a simple algorithm which can be used to estimate the maximum
extent of the auroral equatorward boundary (MEAEB) using magnetic
field data from ground based observatories. We apply this algorithm
to three decades of INTERMAGNET data, and show how the auroral oval
in the Northern hemisphere moves South with larger (more negative Dst)
storms. We simulate a number of storms with different magnitudes using
the Space Weather Modeling Framework (SWMF), and apply the same auroral
boundary detection algorithm. For SWMF simulated storms with Dst >
-600nT, the estimates of the MEAEB are broadly in line with the same
estimates for historical events. For the extreme scaled storms (with
Dst < -1,000 nT), there is considerable scatter in the estimated
location of the auroral equatorward boundary. Our largest storm
simulation was calculated using Carrington like estimates for the
solar wind conditions. This resulted in a minimum Dst = -1,142 nT,
and a minimum estimated auroral boundary of 35.5° MLAT in places.
Title: Threaded-field-line Model for the Low Solar Corona Powered
by the Alfvén Wave Turbulence
Authors: Sokolov, Igor V.; Holst, Bart van der; Manchester, Ward B.;
Su Ozturk, Doga Can; Szente, Judit; Taktakishvili, Aleksandre; Tóth,
Gábor; Jin, Meng; Gombosi, Tamas I.
Bibcode: 2021ApJ...908..172S
Altcode:
We present an updated global model of the solar corona, including the
transition region. We simulate the realistic three-dimensional (3D)
magnetic field using the data from the photospheric magnetic field
measurements and assume the magnetohydrodynamic (MHD) Alfvén wave
turbulence and its nonlinear dissipation to be the only source for
heating the coronal plasma and driving the solar wind. In closed-field
regions, the dissipation efficiency in a balanced turbulence is
enhanced. In the coronal holes, we account for a reflection of the
outward-propagating waves, which is accompanied by the generation
of weaker counterpropagating waves. The nonlinear cascade rate
degrades in strongly imbalanced turbulence, thus resulting in colder
coronal holes. The distinctive feature of the presented model is the
description of the low corona as almost-steady-state low-beta plasma
motion and heat flux transfer along the magnetic field lines. We trace
the magnetic field lines through each grid point of the lower boundary
of the global corona model, chosen at some heliocentric distance,
R = Rb ∼ 1.1R⊙, well above the transition
region. One can readily solve the plasma parameters along the magnetic
field line from 1D equations for the plasma motion and heat transport
together with the Alfvén wave propagation, which adequately describe
the physics within the heliocentric distance range R⊙
< R < Rb, in the low solar corona. By interfacing
this threaded-field-line model with the full MHD global corona model
at r = Rb, we find the global solution and achieve a
faster-than-real-time performance of the model on ∼200 cores.
Title: Advances and challenges in global magnetosphere simulations.
Authors: Kuznetsova, Maria; Sibeck, David; Toth, Gabor; Rastaetter,
Lutz; Chen, Li-Jen
Bibcode: 2021cosp...43E1079K
Altcode:
Global magnetospheric simulation is an essential tool that enables
researches to put data from fleets of multi-spacecraft missions such
as Cluster, THEMIS, MMS into a global context. The presentation will
discuss utilization of magnetosphere missions to review the state of
global magnetosphere modeling. High resolution observations of electron
diffusion region crossings by MMS can be utilized to validate global
magnetosphere models' capability to simulate locations of separatrix
surfaces and magnetic reconnection sites. Multi-spacecraft observations
can be utilized to evaluate capabilities to simulate reconnection sites
motion and plasmoid dynamics. The presentation will include overview of
new tools, services and models implemented at the Community Coordinated
Modeling Center (CCMC) to facilitate magnetospheric mission science. We
will discuss advances and challenges in global magnetosphere simulations
for moderate and extreme solar wind driving conditions. Strong solar
wind driving can push the magnetopause boundary into inner magnetosphere
and even upper atmosphere where single fluid MHD approach is not
applicable. One of the major challenges is to quantify the interaction
between global evolution of the magnetosphere and microphysical
kinetic processes in diffusion regions near reconnection sites. Our
past studies of magnetosphere dynamics during moderate steady southward
driving demonstrated that incorporation of kinetic nongyrotropic effects
near reconnection sites in magnetotail significantly alter the global
magnetosphere evolution. To study characteristics of loading/unloading
cycle in response to extreme solar wind driving we utilize the global
MHD component of the Space Weather Modeling Framework (SWMF) with
incorporated kinetic corrections.
Title: Structure of the Heliotail
Authors: Opher, Merav; Richardson, John; Krimigis, Stamatios;
Toth, Gabor; Tenishev, Valeriy; Zank, Gary; Drake, James; Izmodenov,
Vladislav; Fuselier, Stephen; Dialynas, Konstantinos; Baliukin, Igor;
Dayeh, Maher A.; Zieger, Bertalan; Michael, Adam; Kornbleuth, Marc;
Gkioulidou, Matina
Bibcode: 2021cosp...43E.880O
Altcode:
The canonical view of the structure of the heliosphere is that it
has a long comet-like tail. This view is not universally accepted and
there is vigorous debate as to whether it possesses a long comet-like
structure, is bubble shaped, or is "croissant"-like, a debate that
is driven by observations and modeling. Opher et al. (2015) suggest a
heliosphere with two lobes, described as "croissant"-like. An extension
of the single ion global 3D MHD model that treats PUIs created in
the supersonic solar wind as a fluid separate and distinct from the
thermal solar wind plasma yields a heliosphere that is reduced in
size and rounder in shape (Opher et al. 2020). In contrast, Izmodenov
et al. 2020 argue that a long/extended tail confines the plasma. One
direct way to probe the structure of the tail is through energetic
neutral atom (ENA) maps. ENA images of the tail by Interstellar
Boundary Explorer (IBEX) at energies of 0.5-6keV exhibit a multi-lobe
structure. These lobes are attributed to signatures of slow and fast
wind within the extended heliospheric tail as part of the 11-year
solar cycle (McComas et al. 2013; Zirnstein et al. 2017). Higher
energy ENA observations (>5.2 keV) from the Cassini spacecraft, in
conjunction with >28 keV in-situ ions from V1&2/LECP (Dialynas
et al. 2017), in contrast, support the interpretation of bubble-like
heliosphere, with few substantial tail-like features, although there are
interpretations otherwise (Bzowski & Schwadron 2018). Regardless of
the shape of the heliotail, there is an agreement between models that
the solar magnetic field in the inner heliosheath (IHS) possesses a
"slinky-like" structure (Opher et al. 2015; Pogorelov et al. 2015;
Izmodenov et al. 2015) that helps confine the plasma in the IHS. In
this work, as part of a recently funded project SHIELD (Solar-wind
with Hydrogen Ion Exchange and Large-scale Dynamics), we revisit
two different MHD models (Izmodenov et al. 2018; Opher et al. 2020)
and investigate instabilities possibly responsible for the different
solutions. We investigate how the different physical assumptions are
manifested in ENA maps derived from IBEX and Cassini ENA data and
predict what could be observed by the upcoming IMAP mission.
Title: The Impact of Kinetic Neutrals on the Heliotail
Authors: Michael, A. T.; Opher, M.; Tóth, G.; Tenishev, V.; Drake,
J. F.
Bibcode: 2021ApJ...906...37M
Altcode:
The shape of the heliosphere is thought to resemble a long, comet
tail, however, recently it has been suggested that the heliosphere is
tailless with a two-lobe structure. The latter study was done with
a three-dimensional (3D) magnetohydrodynamic code, which treats the
ionized and neutral hydrogen atoms as fluids. Previous studies that
described the neutrals kinetically claim that this removes the two-lobe
structure of the heliosphere. In this work, we use the newly developed
Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD)
model. SHIELD is a self-consistent kinetic-MHD model of the outer
heliosphere that couples the MHD solution for a single plasma fluid from
the BATS-R-US MHD code to the kinetic solution for neutral hydrogen
atoms solved by the Adaptive Mesh Particle Simulator, a 3D, direct
simulation Monte Carlo model that solves the Boltzmann equation. We
use the same boundary conditions as our previous simulations using
multi-fluid neutrals to test whether the two-lobe structure of the
heliotail is removed with a kinetic treatment of the neutrals. Our
results show that despite the large difference in the neutral hydrogen
solutions, the two-lobe structure remains. These results are contrary
to previous kinetic-MHD models. One such model maintains a perfectly
ideal heliopause and does not allow for communication between the
solar wind and interstellar medium. This indicates that magnetic
reconnection or instabilities downtail play a role for the formation
of the two-lobe structure.
Title: The Structure of the Heliosphere as revealed by modeled ENA
maps at IBEX energies
Authors: Kornbleuth, Marc; Opher, Merav; Toth, Gabor; Tenishev,
Valeriy; Izmodenov, Vladislav; Baliukin, Igor; Michael, Adam
Bibcode: 2021cosp...43E.896K
Altcode:
The heliosphere is indirectly probed in all directions by energetic
neutral atom (ENA) observations by spacecraft such as the Interstellar
Boundary Explorer (IBEX). Energetic neutral atom (ENA) modeling is
an important tool in understanding these ENA observations. Most MHD
models describe the ionized components as a single ion characterized by
a single Maxwellian distribution. This is clearly an approximation,
a "recipe" is needed to translate the single ion to the full ion
distribution present in the solar wind. In this work, we explore how
different treatment of ions in ENA models and heliospheric solutions
from two separate MHD models manifest in ENA maps. Here we use two
different models: one from Boston University (Michael et al. 2020;
2019) and the other from Moscow University (Izmodenov & Alexashov
2018) to probe the effect of the MHD solution in the ENA maps. The
two MHD models treat the heliospheric boundaries differently, with
the Moscow University model suppressing all non-ideal MHD effects
such as reconnection and instabilities. We use same the boundary
conditions (corresponding to solar minima) and same ISM conditions and
investigate the differences in the modeled ENA maps, and whether IBEX
can observe these features. The treatment of ions in the ENA model is
also crucial. Including multiple ion species, such as using several
pick-up ion (PUI) populations, has been shown to provide the best
agreement between ENA models and IBEX observations. Ion propagation
across the termination shock and downstream in the heliosheath is an
important element in ENA production, yet there are various methods for
modeling this propagation. We compare two separate ENA map "recipes"
to understand the role of each population in contributing to IBEX
observations.
Title: Understanding the Limitations of System Models for Geomagnetic
Index Prediction
Authors: Brenner, A.; Pulkkinen, T. I.; Al Shidi, Q.; Toth, G.;
Gombosi, T. I.
Bibcode: 2020AGUFMSA0210021B
Altcode:
The WINDMI physics based system model is an "instant" prediction tool
that takes solar wind input data and predicts geomagnetic indices such
as Dst. It does this by modeling the solar wind-magnetosphere-ionosphere
system as a connected set of circuit elements. These components take
into account the average amount of energy contained in a region and
estimate an effective resistance, capacitance, or inductance. The Space
Weather Modeling Framework (SWMF) couples several models to create
a self-consistent system mostly derived from first principles. By
using SWMF to reconstruct and analyze the energy contained in the
various circuit elements of the WINDMI model allows us to make a
direct comparison to understand under what conditions the circuit
assumption performs well, and what features are missing. First,
geomagnetic indices are compared for the two models along with OMNI
data for a real series of events beginning on Feb 18, 2014. Then,
several circuit elements are recreated within SWMF and compared over
the simulation time. We discuss implications and limitations for the
use of system models as prediction tools, along with suggestions for
a possible new application of machine learning.
Title: How Pickup Ions Generate Turbulence in the Inner Heliosheath:
A Multi-Fluid Approach
Authors: Zieger, B.; Opher, M.; Toth, G.; Florinski, V. A.
Bibcode: 2020AGUFMSH0160017Z
Altcode:
The solar wind in the inner heliosheath beyond the termination
shock (TS) is a non-equilibrium collisionless plasma consisting of
thermal solar wind ions, suprathermal pickup ions and electrons. In
such multi-ion plasma, two fast magnetosonic wave modes exist: the
low-frequency fast mode that propagates in the thermal ion component
and the high-frequency fast mode that propagates in the suprathermal
pickup ion component. Both fast modes are dispersive on fluid and
ion scales, which results in nonlinear dispersive shock waves. We
present high-resolution three-fluid simulations of the TS and the inner
heliosheath up to 2.2 AU downstream of the TS. We show that downstream
propagating nonlinear fast magnetosonic waves grow until they steepen
into shocklets, overturn, and start to propagate backward in the frame
of the downstream propagating wave. The counter-propagating nonlinear
waves result in 2-D fast magnetosonic turbulence, which is driven
by the ion-ion hybrid resonance instability. Energy is transferred
from small scales to large scales in the inverse cascade range and
enstrophy is transferred from large scales to small scales in the direct
cascade range. We validate our three-fluid simulations with in-situ
high-resolution Voyager 2 magnetic field observations in the inner
heliosheath. Our simulations reproduce the observed magnetic turbulence
spectrum with a spectral slope of -5/3 in frequency domain. However,
the fluid-scale turbulence spectrum is not a Kolmogorov spectrum in
wave number domain because Taylor's hypothesis breaks down in the
inner heliosheath. The magnetic structure functions of the simulated
and observed turbulence follow the Kolmogorov-Kraichnan scaling,
which implies self-similarity.
Title: Geomagnetic simulation using MHD with Adaptively Embedded
PIC model
Authors: Wang, X.; Chen, Y.; Toth, G.
Bibcode: 2020AGUFMSM0050004W
Altcode:
The MHD with embedded PIC (MHD-EPIC) model makes it feasible
to incorporate kinetic physics into a global simulation. Still,
this requires a large enough box-shaped PIC domain to accommodate
the movement and changes of the magnetic reconnection regions over
time. This wastes computational resources on simulating regions with
the expensive PIC model where MHD would be sufficient to describe
the physics. We have developed a new MHD with Adaptively Embedded PIC
(MHD-AEPIC) algorithm that couples the BATS-R-US MHD model with the
new FLexible Exascale Kinetic Simulator (FLEKS) PIC code. In the new
coupled model the PIC domains can move with the magnetic reconnection
regions and adapt to them with an arbitrary shape. In this work, we
will first introduce the algorithms for selecting the reconnection
regions in the MHD model that need to be resolved with the kinetic PIC
model. Then we will compare simulations obtained with MHD-EPIC using
fixed PIC regions versus MHD-AEPIC employing adaptive PIC regions to
verify that the new model generates reliable results. Finally, we will
apply the MHD-AEPIC model to a global magnetic storm simulation and
demonstrate the improved efficiency.
Title: How does planetary magnetic field impact on Ion escape rate?
Authors: Ma, Y.; Russell, C. T.; Toth, G.; Nagy, A. F.; Brain, D.
Bibcode: 2020AGUFMSM043..05M
Altcode:
We use an advanced multi-fluid MHD model of Mars to examine the
planetary magnetic field impact on the ion escape rate. The multi-fluid
MHD model has been recently improved by solving an additional electron
pressure equation [Ma et al., 2019], and is the first global model
that enables a self-consistent calculation of both ion and electron
temperatures and pressure gradient force terms. The improved model has
also been validated with a MAVEN event study, and is found to match
the best with corresponding MAVEN plasma observations as compared
with previous versions of the code. To examine the effect of planetary
magnetic field, we use the new model to run a total of ten simulation
cases with identical solar wind parameters but different planetary
dipole moments with surface equatorial field strengths ranging from
0 to 5000 nT. We also examine how different IMF orientations modulate
the impact of planetary magnetic field on the ion escape rates.
Title: Modeling sources of magnetospheric plasma during storms
and substorms
Authors: Glocer, A.; Chappell, C. R.; Fok, M. C. H.; Welling, D. T.;
Huddleston, M.; Toth, G.
Bibcode: 2020AGUFMSM045..01G
Altcode:
It is well accepted that all of the plasma in Earth's magnetosphere
derives from either the solar wind or the planet itself via the
processes of ionospheric outflow. Indeed, the presence of O+ in the
magnetosphere, which can only come from the ionosphere, is a clear
indicator of an ionospheric source of plasma. Unlike O+ which only
has one source of plasma, H+ can come from both the solar wind and the
ionosphere. The solar wind H+ must enter the magnetosphere through the
dayside magnetopause interactions, whereas ionospheric H+ is constantly
flowing out of the ionosphere where can either be recirculated in the
magnetosphere or lost down the magnetotail. In this presentation we
will use merged global models combining ionospheric outflow (PWOM),
multi-fluid MHD (BATS-R-US), and a ring current model (CIMI) to examine
the relative importance of ionospheric and solar wind plasma in defining
magnetospheric composition. We will moreover examine the pathways ions
take to reach different regions of the magnetosphere and timescales
required for different source populations to be effective contributors
to magnetospheric composition in that region. The simulations presented
consider a real event case study (2018-08-25/28) which features a
large storm with comparisons to MMS observations. We also consider
an idealized substorm using idealized inputs and both isotropic and
anisotropic outflow conditions.
Title: Time-dependent global MHD simulations of Jupiter's
magnetosphere with a realistic internal field model
Authors: Sarkango, Y.; Jia, X.; Toth, G.; Chen, Y.
Bibcode: 2020AGUFMSM0540005S
Altcode:
Jupiter's internal field, which has strong higher-order components,
together with the fast rotation of the planet introduces a periodic
modulation ("wobbling") to the magnetosphere which has been observed
in the crossing of the Jovian current sheet by in-situ spacecraft. Our
understanding of the current sheet is largely based on in-situ data
that has limited spatial coverage and empirical models, which consider
two main factors in fitting the magnetic field observations. Firstly,
it is known that information about the changing magnetic field would
propagate at a finite speed through the inhomogeneous, ambient plasma
environment. Secondly, it was shown that the inclusion of current
sheet hinging, which limits the latitudinal excursions of the current
sheet beyond a certain distance, improves the fit to observations. In
particular, better fits were obtained by assuming that the degree
of hinging changes along the Sun-Jupiter line, rather than radial
distance. This hints that current sheet hinging is likely due to
solar-wind influence on the outer magnetosphere. In this work, we
incorporate a non-axisymmetric internal field model into our Jupiter
global simulation to understand the contribution of the two factors
described above in a self-consistent manner. Our simulation includes
the mass loading due to Io in the form of source and loss terms in
the MHD equations and solves the semi-relativistic MHD equations
using the BATSRUS code (Sarkango et al., 2019). To understand how
solar wind forcing influences the hinging of the current sheet,
we drive our simulations with time-dependent solar wind input and
systematically analyze the response of the current sheet to varying
solar wind conditions.
Title: Simulating Solar Maximum Conditions with the Alfven Wave
Solar Atmosphere Model (AWSoM)
Authors: Sachdeva, N.; van der Holst, B.; Toth, G.; Manchester, W.;
Sokolov, I.
Bibcode: 2020AGUFMSH0290015S
Altcode:
The Alfven Wave Solar atmosphere Model (AWSoM) within the Space Weather
Modeling Framework (SWMF) is a physics-based solar corona model
that solves magnetohydrodynamic (MHD) equations along with Alfven
wave turbulence, radiative cooling and heat conduction. The Alfven
wave pressure and dissipation account for solar wind acceleration and
heating. AWSoM extends from the upper chromosphere up to 1 AU and beyond
and includes the description of electron temperature and perpendicular
and parallel proton temperature. AWSoM is driven by observations of the
photospheric magnetic field, which are applied at the inner boundary. In
this study, we use the ADAPT (Air Force Data Assimilative Photospheric
Flux Transport) synchronic maps to drive our solar corona model. The
ADAPT model uses observations of the solar photospheric magnetic field
to produce an ensemble of magnetic field maps using a flux-transport
model and data assimilation. We simulate solar maximum conditions using
AWSoM and compare the results with SDO/AIA observations in the low
corona and observations of solar wind density, speed and magnetic field
at 1 AU (OMNI data). The background solar wind derived from our model
provides the plasma environment into which Coronal Mass Ejections (CMEs)
can be launched. We use the Gibson-Low Flux Rope model to initiate a
CME and propagate it into the inner heliosphere. We validate the CME
simulation by comparing the results with remote as well as in-situ
observations from SOHO, SDO, STEREO, and WIND.
Title: The Effect of Changing Solar Magnetic Field Intensity on
ENA Maps
Authors: Kornbleuth, M. Z.; Opher, M.; Michael, A. T.; Sokol, J. M.;
Toth, G.; Tenishev, V.
Bibcode: 2020AGUFMSH0230008K
Altcode:
Opher et al. (2015) showed that the solar magnetic field can confine and
collimate the solar wind plasma in the heliosheath. IBEX observations
of the heliotail have shown the presence of two high latitude
lobes of enhanced ENA flux in the heliotail at high energies (>2
keV). Numerous studies have investigated how the latitudinal variation
of the solar wind during the solar cycle affects the latitudinal profile
of ENAs in the heliotail. Kornbleuth et al. (2020) showed that while
the solar wind profile does contribute to the high latitude lobes
observed by IBEX in the heliotail, the solar magnetic field plays a
significant role as well. In this work we use steady state MHD solutions
corresponding to solar wind conditions from particular years to isolate
how conditions corresponding to different periods of the solar cycle
influence ENA maps. We find the variations in the intensity of the
solar magnetic field play an important role in not only influencing
observations of the heliotail, but also in affecting the thickness
of the heliosheath in the direction of the nose. The variations not
only affect the ENA intensity observed in the high latitude tail, but
also the size and location of the high latitude lobes. Additionally,
as noted by previous studies, we find the changes in the solar wind
dynamic pressure influence the observed ENA flux and that asymmetries
in the dynamic pressure can be discerned from ENA maps.
Title: Flexible Kinetic Coupling Model with FLEKS for Simulating
Ganymede's Magnetosphere
Authors: Zhou, H.; Jia, X.; Chen, Y.; Toth, G.
Bibcode: 2020AGUFMSM0540015Z
Altcode:
To capture the local kinetic processes within fluid simulations,
we couple the MHD model BATS-R-US to the recently developed implicit
kinetic particle-in-cell (PIC) model Flexible Exascale Kinetic Simulator
(FLEKS). This new model allows the users to set flexible PIC regions
based on geometric and physical criteria, and is more efficient in doing
large scale parallelized simulations. The coupled model is applied to
the magnetosphere simulation of Ganymede, with the high-resolution PIC
region covering the entire magnetopause and tail current sheet. The
prolific outputs of electrons and ions from kinetic simulation shed
light on the reconnection driven physics across the entire magnetosphere
that are not available in the simplified fluid description.
Title: NextGen Space Weather Modeling Framework Using Physics,
Data Assimilation, Uncertainty Quantification and GPUs
Authors: Toth, G.; Zou, S.; Chen, Y.; Huan, X.; van der Holst, B.;
Manchester, W.; Liemohn, M. W.; Chen, Y.; Huang, Z.; Gaenko, A.
Bibcode: 2020AGUFMSM015..05T
Altcode:
We have been recently awarded a major NSF/NASA grant from the SWQU
program to develop the NextGen Space Weather Modeling Framework that
will employ computational models from the surface of the Sun to the
surface of Earth in combination with assimilation of observational
data to provide optimal probabilistic space weather forecasting. The
model will run efficiently on the next generation of supercomputers
to predict space weather about one day or more before the impact
occurs. The new project will concentrate on forecasting major space
weather events generated by coronal mass ejections (CMEs). Current space
weather prediction tools employ first-principles and/or empirical
models. While these provide useful information, their accuracy,
reliability and forecast window need major improvements. Data
assimilation has the potential to significantly improve model
performance, as it has been successfully done in terrestrial weather
forecast. To allow for the sparsity of satellite observations, however,
a different data assimilation method will be employed. The new model
will start from the Sun with an ensemble of simulations that span
the uncertain observational and model parameters. Using real time and
past observations, the model will strategically down-select to a high
performing subset. Next, the down-selected ensemble will be extended by
varying uncertain parameters and the simulation continued to the next
data assimilation point. The final ensemble will provide a probabilistic
forecast of the space weather impacts. While the concept is simple,
finding the optimal algorithm that produces the best prediction with
minimal uncertainty is a complex and very challenging task that requires
developing, implementing and perfecting novel data assimilation and
uncertainty quantification methods. To make these ensemble simulations
run faster than real time, the most expensive parts of the model
need to run efficiently on the current and future supercomputers,
which employ graphical processing units (GPUs) in addition to the
traditional multi-core CPUs. The main product of this project will be
the Michigan Sun-To-Earth Model with Quantified Uncertainty and Data
Assimilation (MSTEM-QUDA) that will be made available to the space
physics community with an open source license. We will describe the
main concept of the project and our initial progress.
Title: Role of Inductive Electric Field on the Build-up of Storm
Time Ring Current
Authors: Liu, J.; Ilie, R.; Toth, G.
Bibcode: 2020AGUFMSM037..11L
Altcode:
During geomagnetic storms, plasma is energized and transported from
the night side plasma sheet to the inner magnetosphere, resulting in a
build-up of plasma density and pressure. The magnetic gradient-curvature
further drives the energetic ions westward, therefore creating
a pressure accumulation in the evening sector. Continuous inward
adiabatic transport from the plasma sheet to the inner magnetosphere
can be a major contributor to the pressure build up on night side,
which suggests that convection electric field plays a significant
role in developing the storm time ring current. However, during the
storm time, the inductive nature can overwhelm the electrostatic
nature of convection electric field, due to the temporal change of
magnetic field. Thus, regarding the electrostatic component of electric
field as the total convection field is not sufficient nor accurate for
modeling the dynamics of inner magnetosphere system, and it may lead to
mis-estimation of the transport and energization of ring current hot
ion species, and associated storm time ring current build-up. Both
theoretical and numerical modifications to an inner magnetosphere
kinetic model --- Hot Electron-Ion Drift Integrator (HEIDI) has been
made to account for the effect of inductive electric field, in order
to assess how much inductive electric is relative to electro-static
field, in addition with investigating the role of inductive electric
field on the build-up and evolution of storm time inner magnetospheric
ring current. We found that, during the intensifying southward IMF
period, magnetic field is stretched away from dipole, and the associated
inductive electric field further accumulates ion pressure in the evening
sector and depletes ion pressure in the morning sector. The reverse
is true as the magnetic field dipolarizes back to dipole configuration.
Title: Heliospheric Ly α Absorption in a Split Tail Heliosphere
Authors: Powell, E.; Opher, M.; Michael, A. T.; Kornbleuth, M. Z.;
Wood, B. E.; Izmodenov, V.; Toth, G.; Tenishev, V.; Richardson, J. D.
Bibcode: 2020AGUFMSH0170013P
Altcode:
Neutral hydrogen in the hydrogen wall and heliosheath absorb wavelengths
of light near Ly α from nearby stars. Heliospheric models are essential
to understand these observations since the observations are an indirect
method of probing the the heliosphere. Opher et al. (2015) suggested
that the solar magnetic field can collimate the solar wind plasma,
resulting in a heliosphere with a split tail. We compare the Ly α
predictions made by multi-fluid kinetic-MHD models of Opher et al. 2020,
Michael et al. 2020 that present a "Croissant-like" (split tail)
shape with long tail models used in Izmodenov et al. 2018. Previous
studies have shown that the interstellar magnetic field can affect the
distribution of neutral hydrogen in the hydrogen wall just outside
the heliosphere. In this study our models use a grid that extends
1500 AU downwind and vary the Interstellar magnetic field strength
and direction. The split tail model successfully reproduce the LY α
profiles in upwind and sidewind line of sights and have good agreement
in downwind line of sights. We comment on the differences between
the two MHD models and which directions can be more sensitive to the
heliospheric shape as well from the interstellar magnetic field.
Title: Multi-fluid MHD Modeling of Europa's Plasma Interaction
Authors: Harris, C. D. K.; Jia, X.; Toth, G.; Huang, Z.; Slavin,
J. A.; Rubin, M.
Bibcode: 2020AGUFMSM049..06H
Altcode:
Europa hosts a periodically changing plasma interaction driven by the
variations of Jupiter's magnetic field and magnetospheric plasma. We
have developed a multi-fluid MHD model for the plasma interaction to
investigate its response to these magnetic field and plasma variations
at Europa's orbit. The model solves the multi-fluid MHD equations
for electrons and three ion fluids (magnetospheric O+ as
well as O+ and O2+ originating from
Europa's ionosphere) while incorporating sources and losses in the
fluid equations due to ionization, electron heat conduction, charge
exchange, recombination and other relevant collisional effects. Using
input parameters constrained by the Galileo MAG and PLS observations,
we first demonstrate the accuracy of our model's representation of the
plasma interaction by simulating the Galileo E4 and E14 flybys, which
took place under different upstream conditions and sampled different
regions of Europa's interaction. Our model produces 3D magnetic field
and plasma bulk parameters that agree with and provide context for
the flyby observations. We next present the results of a parameter
study of Europa's plasma interaction at three different System-III
longitudes within Jupiter's magnetosphere, for three different
global magnetospheric states, comprising 9 steady-state simulations
in total. We describe how Europa's ionosphere is self-consistently
generated in response to the external plasma conditions, and show how
the relative strengths of the magnetospheric plasma versus Europa's
ionosphere control Europa's global interaction with Jupiter's
magnetosphere.
Title: Quantitative Investigation of the Effect on Ground Magnetic
Perturbations of IMF Bx
Authors: Kwagala, N. K.; Moretto, T.; Hesse, M.; Tenfjord, P.; Norgren,
C.; Toth, G.; Gombosi, T. I.; Kolsto, H.; Flø Spinnangr, S.
Bibcode: 2020AGUFMSH0030007K
Altcode:
In this work, we investigate quantitatively the effect of IMF Bx on
magnetospheric dynamics, ionospheric currents, and the resulting
magnetic perturbations measured at magnetometer stations on the
ground. Using the University of Michigan's space weather modeling
framework (SWMF), two historic geomagnetic storms are simulated and
compared to ground-based magnetic observations. For each storm two
separate simulations are carried out, one with IMF Bx artificially
set to zero throughout the event and the other keeping the measured
variable IMF Bx in the driving conditions. The difference between the
outputs from the two runs in the magnetosphere, ionosphere and magnetic
perturbations on the ground will be presented and discussed.
Title: The lunar crustal magnetic anomalies were not produced by
impact plasmas
Authors: Oran, R.; Weiss, B. P.; Shprits, Y.; Miljkovic, K.; Toth, G.
Bibcode: 2020AGUFMGP015..01O
Altcode:
The crusts of the Moon, Mercury, Mars, and many meteorites parent bodies
are magnetized. Although the magnetizing field is commonly attributed
to that of an ancient core dynamo, a longstanding hypothesized
alternative is that the remanent magnetization may have been produced
by impact plasmas that can transiently induce fields or amplify the
background interplanetary magnetic field. However, the dynamics of
such impact-plasma fields have not been studied self-consistently in
the context of the coupled interaction of the impact plume, solar wind,
and the non-uniform electrical resistivity inside the body. To address
this gap, we combined hydrocode impact-physics and magnetohydrodynamic
(MHD) simulations to study impact field generation and amplification on
the Moon. Considering a diversity of different impact and solar wind
conditions 3.5-4 Ga ago, we demonstrate that the resulting fields are
weaker than previously predicted. Field strengths are limited due to
solar wind variability, the formation of a diamagnetic cavity around
the moon by the expanding plasma cloud, and the fact that the induced
field is dissipated by ohmic dissipation in the crust. As a result,
the maximum crustal field is at least 3 orders of magnitude too weak
to explain the magnetization. The elimination of impact plasmas as
the sole source of lunar magnetism leaves a core dynamo as the only
plausible source of the majority of magnetization on the Moon. This
result may challenge impact-magnetization scenarios considered for
other bodies, such as Mercury.
Title: A Statistical Comparison of Global MHD Simulations and
Geomagnetic Storm Indices
Authors: Al Shidi, Q. A.; Pulkkinen, T. I.; Brenner, A.; Toth, G.;
Zou, S.
Bibcode: 2020AGUFMSM022..07A
Altcode:
Space weather monitoring and predictions largely rely on ground
magnetic measurements and geomagnetic indices such as the Disturbance
Storm Time index (Dst or SYM-H), Auroral Electrojet Index (AL) or the
Polar Cap Index (PCI) all constructed using the individual station
data. The global MHD simulations such as the Space Weather Modeling
Framework (SWMF) can give predictions of these indices, driven by
solar wind observations obtained at L1 giving roughly one hour lead
time. The accuracy of these predictions especially during geomagnetic
storms is a key metric for the model performance, and critical to
operational space weather forecasts. In this presentation, we
perform the largest statistical study of global simulation results
using a database of 140 storms with minimum Dst below -50 nT during
the years from 2010 to 2020. We compare SWMF results with indices
derived from the SuperMAG network, which with its denser station
network provides a more accurate representation of the true level
of activity in the ring current and in the auroral electrojets. We
show that the SWMF generally gives good results for the SYM-H index,
whereas the AL index is typically underestimated by the model with
the model predicting lower than observed ionospheric activity. We
also examine the Cross Polar Cap Potential (CPCP) and compare it with
a model derived using the PCI (Ridley et al., 2004) as well as with
results obtained from the SuperDARN network. We show that the Ridley
et al. CPCP model is much closer to the SWMF values. The results are
used to discuss factors governing energy dissipation in magnetosphere -
ionosphere system as well as possibilities to improve on the operational
space weather forecasts.
Title: FLEKS: A Flexible Particle-in-Cell code for Multi-Scale Space
Plasma Simulations
Authors: Chen, Y.; Toth, G.; Wang, X.
Bibcode: 2020AGUFMSM0050003C
Altcode:
The Magnetohydrodynamics with embedded particle-in-cell (MHD-EPIC)
model has been successfully applied to global magnetospheric simulations
in recent years. However, the PIC region was restricted to be a box,
and it is not always feasible to cover the whole physical structure
of interest with a box due to the limitation of the computational
resources. The FLexible Exascale Kinetic Simulator (FLEKS), which is
a new PIC code and allows a PIC region of any shape, is designed to
break this restriction and extend the capabilities of the MHD-EPIC
model. FLEKS uses the Gauss's law satisfying energy-conserving
semi-implicit method (GL-ECSIM) as the base PIC solver. We have
also designed extra numerical techniques, such as the adaptive time
stepping and particle resampling algorithms, to further improve the
accuracy and flexibility of the PIC solver. The grid of FLEKS has to
be Cartesian, but the active PIC region is not necessarily to be a
box anymore since any Cartesian cells can be turned off. Furthermore,
FLEKS supports switching on or switching off grid cells adaptively
during a simulation. The initial conditions and boundary conditions
of the active PIC region are provided by the coupled MHD code. FLEKS
and the coupled MHD code constitute the MHD with adaptively embedded
particle-in-cell (MHD-AEPIC) model. FLEKS is implemented in C++ in the
object-oriented design, and it is based on a third-party open source
library AMReX, which provides FLEKS high-performance parallel data
structures. We will present the numerical and implementation details,
show its parallel performance, and demonstrate its capabilities with
3D magnetospheric simulations.
Title: 3D Hall-MHD Simulations of Mercury's Dayside Magnetopause
Reconnection and Its Impact on the Global Magnetospheric Dynamics
Authors: Li, C.; Jia, X.; Chen, Y.; Zhou, H.; Toth, G.; Slavin, J. A.;
Sun, W.
Bibcode: 2020AGUFMP078.0004L
Altcode:
Observations from NASA's MESSENGER spacecraft reveal that Mercury has
a miniature magnetosphere arising from the interaction of its dipolar
intrinsic field with the inner heliosphere solar wind. Compared to the
terrestrial magnetosphere, Mercury's magnetosphere appears to be more
dynamic in that the typical timescales for global plasma and magnetic
flux circulation are much shorter, and the dayside magnetopause
reconnection occurs at faster rates and under a wider range of
magnetic shear angles. As a product of multiple X-line reconnection,
flux transfer events (FTEs) are found to arise much more frequently
with occurrence rates of about 50 times higher than detected at
Earth. MESSENGER observations suggest that aside from the apparent
difference in system size, the large differences in reconnection-driven
dynamics between Mercury's magnetosphere and the Earth's are likely
related to the upstream solar wind conditions. In order to obtain a
quantitative, global understanding of how magnetopause reconnection
occurs at Mercury and its large-scale consequences, we have used the
BATSRUS Hall-MHD code with a high resolution grid that resolves ion
kinetic scales to simulate Mercury's magnetopause dynamics under a
variety of upstream solar wind and IMF conditions. Flux ropes are found
to form in all of our time-dependent Hall MHD simulations under steady
solar wind conditions, but their properties, such as occurrence rate
and spatial structure, vary depending on the upstream parameters. We
have developed techniques to identify flux ropes in our simulations and
extract their magnetic field and plasma properties that can be compared
directly with MESSENGER observations of FTEs. The set of carefully
designed Hall MHD simulations allow us to examine how the properties of
FTEs depend on such parameters as the solar wind Alfvénic Mach number,
IMF orientation, and the magnetosheath plasma . With the global model,
we also evaluate the contribution of FTEs to the global circulation of
plasma and magnetic flux at Mercury and how it might vary in response
to changes in the external conditions.
Title: Comparing the best ADAPT realizations from WSA, AWSoM and
AWSoM-R
Authors: Huang, Z.; Sokolov, I.; van der Holst, B.; Toth, G.; Arge,
C. N.; Sachdeva, N.; Jones, S. I.; Manchester, W.; Gombosi, T. I.
Bibcode: 2020AGUFMSH0290028H
Altcode:
Solar corona models are typically driven by global photospheric
magnetic field maps assembled from magnetograms. Magnetic field maps
derived from different magnetogram sources (e.g. MDI, GONG, etc)
can produce different results when used as boundary conditions. One
of the commonly used synchronic maps is provided by the ADAPT (Air
Force Data Assimilative Photospheric Flux Transport) model, which
makes use of a flux transport model to evolve the regions where there
are no observations. The ADAPT model uses the ensemble least-squares
data assimilation method that account for model and observational
uncertainties and provides 12 different realizations for a given
moment in time. Previous studies have shown the same solar corona
model running with 12 different realizations also provide different
predicted solar wind values at 1 AU. In this presentation, we will
use the ADAPT maps to drive the WSA (Wang-Sheeley-Arge) model, the
AWSoM (Alfven-Wave driven Solar atmosphere Model) and the AWSoM-R
(Alfven-Wave driven Solar atmosphere Model - Realtime) model. The
coronal portion of the WSA model makes use of the coupled potential
field source surface and Schatten current sheet models to derive the
global coronal magnetic field from global maps of the photospheric
field. The model then applies empirical formulas to specify the solar
wind at the outer coronal boundary and a 1D kinematic model to predict
solar wind speed and interplanetary magnetic polarity anywhere in
the inner heliosphere. AWSoM is a physics-based model solving the
MHD equations together with radiative cooling, heat conduction and a
phenomenological Alfven wave turbulence and dissipation model including
wave reflection (proportional to the Alfvén speed gradients) and
turbulent dissipation from the chromosphere to the heliosphere. The
AWSoM-R model uses 1-D field line threads to simulate the region in
the lower chromosphere to speed up the simulations. We will compare
the predicted solar wind values at 1 AU with observations and use the
WSA Prediction Metric developed at NASA Goddard Space Flight Center to
select the best ADAPT map realization(s) for the three models. We will
investigate whether we can improve the prediction capability of the
complex physics-based models like AWSoM and AWSoM-R using the insight
gained from the inexpensive empirical WSA model.
Title: A Gray-Box Model for a Probabilistic Estimate of Regional
Ground Magnetic Perturbations: Enhancing the NOAA Operational Geospace
Model With Machine Learning
Authors: Camporeale, E.; Cash, M. D.; Singer, H. J.; Balch, C. C.;
Huang, Z.; Toth, G.
Bibcode: 2020JGRA..12527684C
Altcode: 2019arXiv191201038C
We present a novel algorithm that predicts the probability that the
time derivative of the horizontal component of the ground magnetic
field dB/dt exceeds a specified threshold at a given location. This
quantity provides important information that is physically relevant to
geomagnetically induced currents (GICs), which are electric currents
associated with sudden changes in the Earth's magnetic field due
to space weather events. The model follows a "gray-box" approach
by combining the output of a physics-based model with machine
learning. Specifically, we combine the University of Michigan's
Geospace model that is operational at the National Oceanic and
Atmospheric Administration (NOAA) Space Weather Prediction Center,
with a boosted ensemble of classification trees. We discuss the
problem of recalibrating the output of the decision tree to obtain
reliable probabilities. The performance of the model is assessed by
typical metrics for probabilistic forecasts: Probability of Detection
and False Detection, True Skill Statistic, Heidke Skill Score, and
Receiver Operating Characteristic curve. We show that the ML-enhanced
algorithm consistently improves all the metrics considered.
Title: A Case Study on the Origin of Near-Earth Plasma
Authors: Glocer, A.; Welling, D.; Chappell, C. R.; Toth, G.; Fok,
M. -C.; Komar, C.; Kang, S. -B.; Buzulukova, N.; Ferradas, C.; Bingham,
S.; Mouikis, C.
Bibcode: 2020JGRA..12528205G
Altcode:
This study presents simulations of the coupled space environment
during a geomagnetic storm that separates the different sources
of near-Earth plasma. These simulations include separate fluids
for solar wind and ionospheric protons, ionospheric oxygen, and the
plasmasphere. Additionally, they include the effects of both a hot ring
current population and a cold plasmaspheric population simultaneously
for a geomagnetic storm. The modeled ring current population represents
the solution of bounce-averaged kinetic solution; the core plasmaspheric
model assumes a fixed temperature of 1 eV and constant pressure along
the field line. We find that during the storm, ionospheric protons can
be a major contributor to the plasmasheet and ring current and that
ionospheric plasma can largely displace solar wind protons in much of
the magnetosphere under certain conditions. Indeed, the ionospheric
source of plasma cannot be ignored. Significant hemispheric asymmetry
is found between the outflow calculated in the summer and winter
hemispheres, consistent with past observations. That asymmetric
outflow is found to lead to asymmetric filling of the lobes, with
the northern (summer) lobe receiving more outflow that has a higher
proportion of O+ and the southern (winter) lobe receiving
less outflow with a higher proportion of H+. We moreover
find that the inclusion of the plasmasphere can have a system-wide
impact. Specifically, when the plasmasphere drainage plume reaches the
magnetopause, it can reduce the reconnection rate, suppress ionospheric
outflow and change its composition, change the composition in the
magnetosphere, and reduce the ring current intensity.
Title: Magnetohydrodynamic With Embedded Particle-In-Cell Simulation
of the Geospace Environment Modeling Dayside Kinetic Processes
Challenge Event
Authors: Chen, Yuxi; Tóth, Gábor; Hietala, Heli; Vines, Sarah K.;
Zou, Ying; Nishimura, Yukitoshi; Silveira, Marcos V. D.; Guo, Zhifang;
Lin, Yu; Markidis, Stefano
Bibcode: 2020E&SS....701331C
Altcode: 2020arXiv200104563C
We use the magnetohydrodynamic (MHD) with embedded particle-in-cell
model (MHD-EPIC) to study the Geospace Environment Modeling (GEM)
dayside kinetic processes challenge event at 01:50-03:00 UT on 18
November 2015, when the magnetosphere was driven by a steady southward
interplanetary magnetic field (IMF). In the MHD-EPIC simulation, the
dayside magnetopause is covered by a PIC code so that the dayside
reconnection is properly handled. We compare the magnetic fields
and the plasma profiles of the magnetopause crossing with the MMS3
spacecraft observations. Most variables match the observations well in
the magnetosphere, in the magnetosheath, and also during the current
sheet crossing. The MHD-EPIC simulation produces flux ropes, and we
demonstrate that some magnetic field and plasma features observed by
the MMS3 spacecraft can be reproduced by a flux rope crossing event. We
use an algorithm to automatically identify the reconnection sites from
the simulation results. It turns out that there are usually multiple
X-lines at the magnetopause. By tracing the locations of the X-lines,
we find that the typical moving speed of the X-line endpoints is
about 70 km/s, which is higher than but still comparable with the
ground-based observations.
Title: Dispersive Fast Magnetosonic Waves and Shock-Driven
Compressible Turbulence in the Inner Heliosheath
Authors: Zieger, Bertalan; Opher, Merav; Tóth, Gábor; Florinski,
Vladimir
Bibcode: 2020JGRA..12528393Z
Altcode:
The solar wind in the inner heliosheath beyond the termination
shock (TS) is a nonequilibrium collisionless plasma consisting of
thermal solar wind ions, suprathermal pickup ions, and electrons. In
such multi-ion plasma, two fast magnetosonic wave modes exist,
the low-frequency fast mode and the high-frequency fast mode. Both
fast modes are dispersive on fluid and ion scales, which results
in nonlinear dispersive shock waves. We present high-resolution
three-fluid simulations of the TS and the inner heliosheath up to a few
astronomical units (AU) downstream of the TS. We show that downstream
propagating nonlinear fast magnetosonic waves grow until they steepen
into shocklets, overturn, and start to propagate backward in the frame
of the downstream propagating wave. The counterpropagating nonlinear
waves result in 2-D fast magnetosonic turbulence, which is driven
by the ion-ion hybrid resonance instability. Energy is transferred
from small scales to large scales in the inverse cascade range, and
enstrophy is transferred from large scales to small scales in the
direct cascade range. We validate our three-fluid simulations with in
situ high-resolution Voyager 2 magnetic field observations in the inner
heliosheath. Our simulations reproduce the observed magnetic turbulence
spectrum with a spectral slope of -5/3 in frequency domain. However,
the fluid-scale turbulence spectrum is not a Kolmogorov spectrum in
wave number domain because Taylor's hypothesis breaks down in the
inner heliosheath. The magnetic structure functions of the simulated
and observed turbulence follow the Kolmogorov-Kraichnan scaling,
which implies self-similarity.
Title: Coupled MHD - Hybrid Simulations of Space Plasmas
Authors: Moschou, S. P.; Sokolov, I. V.; Cohen, O.; Toth, G.; Drake,
J. J.; Huang, Z.; Garraffo, C.; Alvarado-Gómez, J. D.; Gombosi, T.
Bibcode: 2020JPhCS1623a2008M
Altcode: 2019arXiv191108660M
Heliospheric plasmas require multi-scale and multi-physics
considerations. On one hand, MHD codes are widely used for global
simulations of the solar-terrestrial environments, but do not provide
the most elaborate physical description of space plasmas. Hybrid
codes, on the other hand, capture important physical processes, such
as electric currents and effects of finite Larmor radius, but they can
be used locally only, since the limitations in available computational
resources do not allow for their use throughout a global computational
domain. In the present work, we present a new coupled scheme which
allows to switch blocks in the block-adaptive grids from fluid MHD to
hybrid simulations, without modifying the self-consistent computation
of the electromagnetic fields acting on fluids (in MHD simulation)
or charged ion macroparticles (in hybrid simulation). In this way,
the hybrid scheme can refine the description in specified regions of
interest without compromising the efficiency of the global MHD code.
Title: Reconnection-Driven Dynamics at Ganymede's Upstream
Magnetosphere: 3-D Global Hall MHD and MHD-EPIC Simulations
Authors: Zhou, Hongyang; Tóth, Gábor; Jia, Xianzhe; Chen, Yuxi
Bibcode: 2020JGRA..12528162Z
Altcode:
The largest moon in the solar system, Ganymede, is the only moon known
to possess a strong intrinsic magnetic field and a corresponding
magnetosphere. Using the latest version of Space Weather Modeling
Framework (SWMF), we study the upstream plasma interactions and dynamics
in this sub-Alfvénic system. Results from the Hall magnetohydrodynamics
(MHD) and the coupled MHD with embedded particle-in-cell (MHD-EPIC)
models are compared. We find that under steady upstream conditions,
magnetopause reconnection occurs in a nonsteady manner, and the
energy partition between electrons and ions is different in the
two models. Flux ropes of Ganymede's radius in length form on the
magnetopause at a rate about 3 min and create spatiotemporal variations
in plasma and field properties. Upon reaching proper grid resolutions,
the MHD-EPIC model can resolve both electron and ion kinetics at the
magnetopause and show localized nongyrotropic behavior inside the
diffusion region. The estimated global reconnection rate from the
models is about 80 kV with 60% efficiency, and there is weak evidence
of ∼1 min periodicity in the temporal variations due to the dynamic
reconnection process.
Title: The Confinement of the Heliosheath Plasma by the Solar Magnetic
Field as Revealed by Energetic Neutral Atom Simulations
Authors: Kornbleuth, M.; Opher, M.; Michael, A. T.; Sokół, J. M.;
Tóth, G.; Tenishev, V.; Drake, J. F.
Bibcode: 2020ApJ...895L..26K
Altcode: 2020arXiv200506643K
Traditionally, the solar magnetic field has been considered to have
a negligible effect in the outer regions of the heliosphere. Recent
works have shown that the solar magnetic field may play a crucial role
in collimating the plasma in the heliosheath. Interstellar Boundary
Explorer (IBEX) observations of the heliotail indicated a latitudinal
structure varying with energy in the energetic neutral atom (ENA)
fluxes. At energies ∼1 keV, the ENA fluxes show an enhancement at
low latitudes and a deficit of ENAs near the poles. At energies >2.7
keV, ENA fluxes had a deficit within low latitudes, and lobes of higher
ENA flux near the poles. This ENA structure was initially interpreted
to be a result of the latitudinal profile of the solar wind during
solar minimum. We extend the work of Kornbleuth et al. by using solar
minimum-like conditions and the recently developed Solar-wind with
Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model. The
SHIELD model couples the magnetohydrodynamic plasma solution with
a kinetic description of neutral hydrogen. We show that while the
latitudinal profile of the solar wind during solar minimum contributes
to the lobes in ENA maps, the collimation by the solar magnetic
field is important in creating and shaping the two high-latitude
lobes of enhanced ENA flux observed by IBEX. This is the first work
to explore the effect of the changing solar magnetic field strength
on ENA maps. Our findings suggest that IBEX is providing the first
observational evidence of the collimation of the heliosheath plasma
by the solar magnetic field.
Title: Formation and Evolution of the Large-Scale Magnetic Fields
in Venus' Ionosphere: Results From a Three Dimensional Global
Multispecies MHD Model
Authors: Ma, Yingjuan; Toth, Gabor; Nagy, Andrew; Luhmann, Janet;
Russell, Christopher
Bibcode: 2020GeoRL..4787593M
Altcode:
Large-scale magnetic fields have been observed in Venus'
ionosphere by both the Pioneer Venus Orbiter (PVO) and Venus
Express spacecraft. In this study, we examine the formation and
evolution of the large-scale magnetic field in the Venus ionosphere
using a sophisticated global multispecies Magnetohydrodynamics
(MHD) model that has been developed for Venus (Ma et al., 2013, https://doi.org/10.1029/2012JA018265).
A time-dependent model run is performed under varying solar wind
dynamic pressure. Based on model results, we find that (1) the initial
response of the induced magnetosphere is fast (~min), (2) a large-scale
magnetic field gradually forms in the ionosphere when the solar wind
dynamic pressure suddenly exceeds the ionospheric thermal pressure,
(3) both the penetration and decay of the large-scale magnetic field
in the ionosphere are slow (~hr), and (4) the ion escape rate has a
nonlinear response to the change of solar wind dynamic pressure.
Title: Validating the Space Weather Modeling Framework (SWMF)
for applications in northern Europe. Ground magnetic perturbation
validation
Authors: Kwagala, Norah Kaggwa; Hesse, Michael; Moretto, Therese;
Tenfjord, Paul; Norgren, Cecilia; Tóth, Gabor; Gombosi, Tamas;
Kolstø, Håkon M.; Spinnangr, Susanne F.
Bibcode: 2020JSWSC..10...33K
Altcode:
In this study we investigate the performance of the University of
Michigan's Space Weather Modeling Framework (SWMF) in prediction of
ground magnetic perturbations (ΔB) and their rate of change with
time (dB/dt), which is directly connected to geomagnetically induced
currents (GICs). We use the SWMF set-up where the global magnetosphere
provided by the Block Adaptive Tree Solar-wind Roe-type Upwind Scheme
(BATS-R-US) MHD code, is coupled to the inner magnetosphere and the
ionospheric electrodynamics. The validation is done for ΔB and dB/dt
separately. The performance is evaluated via data-model comparison
through a metrics-based approach. For ΔB, the normalized root mean
square error (nRMS) and the correlation coefficient are used. For dB/dt,
the probability of detection, the probability of false detection,
the Heidke skill score, and the frequency bias are used for different
dB/dt thresholds. The performance is evaluated for eleven ground
magnetometer stations located between 59° and 85° magnetic latitude
and spanning about five magnetic local times. Eight geomagnetic storms
are studied. Our results show that the SWMF predicts the northward
component of the perturbations better at lower latitudes (59°-67°)
than at higher latitudes (>67°), whereas for the eastward component,
the model performs better at high latitudes. Generally, the SWMF
performs well in the prediction of dB/dt for a 0.3 nT/s threshold,
with a high probability of detection ≈0.8, low probability of false
detection (<0.4), and Heidke skill score above zero. To a large
extent the model tends to predict events as often as they are actually
occurring in nature (frequency bias 1). With respect to the metrics
measures, the dB/dt prediction performance generally decreases as the
threshold is raised, except for the probability of false detection,
which improves.
Title: MHD Predictions of Plasma Conditions Above Insight Landing
Site based on MAVEN observations
Authors: Ma, Yingjuan; Russell, Chris; Yu, Yanan; Nagy, Andrew; Toth,
Gabor; Jakosky2, Bruce
Bibcode: 2020EGUGA..2220751M
Altcode:
The Interior Exploration using Seismic Investigations, Geodesy
and Heat Transport (InSight) mission was launched on 5 May 2018 and
successfully landed at Elysium Planitia (4.5oN, 135.9oE)on Mars on 26
November 2018. The InSight Lander carries a magnetometer to measure
disturbances from the Martian ionosphere. In order to understand the
daily variations in the magnet field measurements on Martian surface,
in this study, we use the time-dependent MHD model to study how plasma
conditions vary with local time above insight landing site using solar
wind condition from MAVEN observation. Significant diurnal variations
can be seen in all plasma quantities due to solar wind interactions and
planetary rotation. The induced magnetic field is mainly in the same
direction as the upstream IMF. However, it seems that the variations
seen by the Insight magnetometer cannot be only due to the interaction
of the solar wind. We also add a neutral wind effect in our simulations
to further investigate possible causes of surface field changes.
Title: Predicting Solar Flares with Machine Learning: Investigating
Solar Cycle Dependence
Authors: Wang, Xiantong; Chen, Yang; Toth, Gabor; Manchester, Ward
B.; Gombosi, Tamas I.; Hero, Alfred O.; Jiao, Zhenbang; Sun, Hu; Jin,
Meng; Liu, Yang
Bibcode: 2020ApJ...895....3W
Altcode: 2019arXiv191200502W
A deep learning network, long short-term memory (LSTM), is used to
predict whether an active region (AR) will produce a flare of class
Γ in the next 24 hr. We consider Γ to be ≥M (strong flare), ≥C
(medium flare), and ≥A (any flare) class. The essence of using LSTM,
which is a recurrent neural network, is its ability to capture temporal
information on the data samples. The input features are time sequences
of 20 magnetic parameters from the space weather Helioseismic and
Magnetic Imager AR patches. We analyze ARs from 2010 June to 2018
December and their associated flares identified in the Geostationary
Operational Environmental Satellite X-ray flare catalogs. Our results
produce skill scores consistent with recently published results using
LSTMs and are better than the previous results using a single time
input. The skill scores from the model show statistically significant
variation when different years of data are chosen for training and
testing. In particular, 2015-2018 have better true skill statistic and
Heidke skill scores for predicting ≥C medium flares than 2011-2014,
when the difference in flare occurrence rates is properly taken into
account.
Title: Publisher Correction: A small and round heliosphere suggested
by magnetohydrodynamic modelling of pick-up ions
Authors: Opher, Merav; Loeb, Abraham; Drake, James; Toth, Gabor
Bibcode: 2020NatAs...4..719O
Altcode: 2020NatAs.tmp...96O
An amendment to this paper has been published and can be accessed via
a link at the top of the paper.
Title: Is the Relation Between the Solar Wind Dynamic Pressure and
the Magnetopause Standoff Distance so Straightforward?
Authors: Samsonov, A. A.; Bogdanova, Y. V.; Branduardi-Raymont, G.;
Sibeck, D. G.; Toth, G.
Bibcode: 2020GeoRL..4786474S
Altcode:
We present results of global magnetohydrodynamic simulations which
reconsider the relationship between the solar wind dynamic pressure
(Pd) and magnetopause standoff distance (RSUB). We
simulate the magnetospheric response to increases in the dynamic
pressure by varying separately the solar wind density or velocity
for northward and southward interplanetary magnetic field (IMF). We
obtain different values of the power law indices N in the relation
RSUB∼Pd-1>/N depending on which parameter, density, or velocity,
has been varied and for which IMF orientation. The changes in the
standoff distance are smaller (higher N) for a density increase for
southward IMF and greater (smaller N) for a velocity increase. An
enhancement of the solar wind velocity for a southward IMF increases
the magnetopause reconnection rate and Region 1 current that move
the magnetopause closer to the Earth than it appears in the case of
density increase for the same dynamic pressure.
Title: The Solar-wind with Hydrogen Ion Exchange and Large-scale
Dynamics (SHIELD) model: A Self-Consistent Kinetic-MHD Model of the
Outer Heliosphere
Authors: Michael, Adam T.; Opher, Merav; Toth, Gabor; Tenishev,
Valeriy; Borovikov, Dmitry
Bibcode: 2020arXiv200401152M
Altcode:
Neutral hydrogen has been shown to greatly impact the plasma flow in
the heliopshere and the location of the heliospheric boundaries. We
present the results of the Solar-wind with Hydrogen Ion Exchange
and Large-scale Dynamics (SHIELD) model, a new, self-consistent,
kinetic-MHD model of the outer heliosphere within the Space Weather
Modeling Framework. The charge-exchange mean free path is on order
of the size of the heliosphere; therefore, the neutral atoms cannot
be described as a fluid. The SHIELD model couples the MHD solution
for a single plasma fluid to the kinetic solution from for neutral
hydrogen atoms streaming through the system. The kinetic code is based
on the Adaptive Mesh Particle Simulator (AMPS), a Monte Carlo method for
solving the Boltzmann equation. The SHIELD model accurately predicts the
increased filtration of interstellar neutrals into the heliosphere. In
order to verify the correct implementation within the model, we compare
the results of the SHIELD model to other, well-established kinetic-MHD
models. The SHIELD model matches the neutral hydrogen solution of these
studies as well as the shift in all heliospheric boundaries closer
to the Sun in comparison the the multi-fluid treatment of the neutral
hydrogen atoms. Overall the SHIELD model shows excellent agreement to
these models and is a significant improvement to the fluid treatment
of interstellar hydrogen.
Title: A small and round heliosphere suggested by magnetohydrodynamic
modelling of pick-up ions
Authors: Opher, Merav; Loeb, Abraham; Drake, James; Toth, Gabor
Bibcode: 2020NatAs...4..675O
Altcode: 2020NatAs.tmp...55O; 2020NatAs.tmp...90O
As the Sun moves through the surrounding partially ionized medium,
neutral hydrogen atoms penetrate the heliosphere, and through charge
exchange with the supersonic solar wind, create a population of hot
pick-up ions (PUIs). Until recently, the consensus was that the shape
of the heliosphere is comet-like. The termination shock crossing by
Voyager 2 demonstrated that the heliosheath (the region of shocked
solar wind) pressure is dominated by PUIs; however, the impact of
the PUIs on the global structure of the heliosphere has not been
explored. Here we use a novel magnetohydrodynamic model that treats
the PUIs as a separate fluid from the thermal component of the solar
wind. The depletion of PUIs, due to charge exchange with the neutral
hydrogen atoms of the interstellar medium in the heliosheath, cools the
heliosphere, `deflating' it and leading to a narrower heliosheath and
a smaller and rounder shape, confirming the shape suggested by Cassini
observations. The new model reproduces both the properties of the PUIs,
based on the New Horizons observations, and the solar wind ions, based
on the Voyager 2 spacecraft observations as well as the solar-like
magnetic field data outside the heliosphere at Voyager 1 and Voyager 2.
Title: The surface distributions of the production of the
major volatile species, H2O, CO2, CO and
O2, from the nucleus of comet 67P/Churyumov-Gerasimenko
throughout the Rosetta Mission as measured by the ROSINA double
focusing mass spectrometer
Authors: Combi, Michael; Shou, Yinsi; Fougere, Nicolas; Tenishev,
Valeriy; Altwegg, Kathrin; Rubin, Martin; Bockelée-Morvan, Dominique;
Capaccioni, Fabrizio; Cheng, Yu-Chi; Fink, Uwe; Gombosi, Tamas;
Hansen, Kenneth C.; Huang, Zhenguang; Marshall, David; Toth, Gabor
Bibcode: 2020Icar..33513421C
Altcode: 2019arXiv190902082C
The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis
(ROSINA) suite of instruments operated throughout the over two
years of the Rosetta mission operations in the vicinity of comet
67P/Churyumov-Gerasimenko. It measured gas densities and composition
throughout the comet's atmosphere, or coma. Here we present
two-years' worth of measurements of the relative densities of the
four major volatile species in the coma of the comet, H2O,
CO2, CO and O2, by one of the ROSINA sub-systems
called the Double Focusing Mass Spectrometer (DFMS). The absolute
total gas densities were provided by the Comet Pressure Sensor (COPS),
another ROSINA sub-system. DFMS is a very high mass resolution and
high sensitivity mass spectrometer able to resolve at a tiny fraction
of an atomic mass unit. We have analyzed the combined DFMS and COPS
measurements using an inversion scheme based on spherical harmonics
that solves for the distribution of potential surface activity of
each species as the comet rotates, changing solar illumination, over
short time intervals and as the comet changes distance from the sun
and orientation of its spin axis over long time intervals. We also
use the surface boundary conditions derived from the inversion scheme
to simulate the whole coma with our fully kinetic Direct Simulation
Monte Carlo model and calculate the production rates of the four major
species throughout the mission. We compare the derived production rates
with revised remote sensing observations by the Visible and Infrared
Thermal Imaging Spectrometer (VIRTIS) as well as with published
observations from the Microwave Instrument for the Rosetta Orbiter
(MIRO). Finally we use the variation of the surface production of the
major species to calculate the total mass loss over the mission and,
for different estimates of the dust/gas ratio, calculate the variation
of surface loss all over the nucleus.
Title: 3D global Hall-MHD simulations of Mercury's magnetopause
dynamics
Authors: Li, C.; Jia, X.; Chen, Y.; Toth, G.; Slavin, J. A.; Sun, W.
Bibcode: 2019AGUFMSM33D3217L
Altcode:
As the innermost planet of the solar system, Mercury's magnetosphere
has long been considered a very unique system due to its proximity to
Sun. At Mercury's orbit, the solar wind plasma density, ram pressure,
and IMF strength typically are much higher than those encountered
by the terrestrial magnetosphere. Because of the small size of the
magnetosphere, the low Alfven Mach number upstream flow and resultant
low-beta magnetosheath plasma, the interaction between Mercury's
magnetosphere and the solar wind is extremely dynamic and the dynamics
is dominated by effects associated with magnetic reconnection. Previous
analyses of the MESSENGER observations have revealed extraordinarily
high occurrence rate of Flux Transfer Events (FTEs) at the magnetopause,
which were observed to arise on a timescale of a few seconds (e.g.,
Slavin et al., 2012). In order to gain a better understanding of the
generation mechanism of the frequently observed FTEs and the overall
magnetopause dynamics, we have employed the BATSRUS Hall-MHD code to
simulate Mercury's interaction with the solar wind. A high-resolution
grid with cell size of ~ 30 km (or ~ 0.01 RM) is used at the
dayside magnetopause in order to resolve ion-scale physics, which is
important for reconnection. Our Hall-MHD model also includes Mercury's
interior that allows us to self-consistently simulate the induction
effects of the conducting core (Jia et al., 2015, 2019). Our initial
simulations using steady solar wind with southward IMF conditions show
that reconnection at the magnetopause occurs in a non-steady fashion,
which then leads to flux ropes of varying sizes being generated on
timescale of seconds, which is generally consistent with what has
been reported based on MESSENGER observations. The dynamic behavior
of the magnetopause is not seen in ideal MHD simulations that use
the same input parameters. The differences between these two sets of
simulations suggest that the Hall physics may play an important role
in magnetopause reconnection and large-scale dynamics at Mercury.
Title: Systematic Study of the Magnetopause Reconnection and FTEs
from 3D Simulations of Ganymede's Magnetosphere
Authors: Zhou, H.; Toth, G.; Jia, X.
Bibcode: 2019AGUFMSM41B..09Z
Altcode:
The largest moon in the solar system, Ganymede, is also the only
moon known to possess a strong intrinsic magnetic field and a
corresponding magnetosphere. Previous results have shown that
even under steady upstream conditions, magnetopause reconnection
at Ganymede occurs in a non-steady manner. Simulation results from
Hall MHD and MHD-E(mbedded)Particle-In-Cell models have shown clear
signatures of flux ropes on the magnetopause, with a fluctuation of
global reconnection rate in the 20min runs. In this study, we will
present a detailed comparison on the direct and indirect reconnection
rate calculation from several numerical models and give insights into
the flux transfer events (FTEs) and the responses from Ganymede's
magnetosphere. With the techniques of tracking the reconnection
sites, the relation between spatiotemporal variations in plasma and
field properties across the magnetopause, the flux rope generation,
and the reconnection rate will be discussed. These would be useful
for the future JUICE mission for aiding the in-situ measurements and
detecting plasma interaction processes.
Title: The response of Jupiter's coupled magnetosphere-ionosphere
system to changes in the solar wind and the release of plasmoids in
the magnetotail: Results from global MHD simulations
Authors: Sarkango, Y.; Jia, X.; Toth, G.
Bibcode: 2019AGUFMSM33G3289S
Altcode:
Joint observations by the HST and in situ spacecraft have shown that
the brightness of Jupiter's aurora appears to be correlated with
solar wind dynamic pressure enhancement, despite theoretical work
predicting the opposite. In this study, we use a time-dependent global
MHD model (Sarkango et al., 2019, JGR) to investigate the response
of Jupiter's coupled magnetosphere-ionosphere system to different
types of changes in the upstream conditions, such as IMF rotation
and forward interplanetary shock. Our model solves the single fluid
semi-relativistic ideal MHD equations and self-consistently includes
the mass loading associated with the Io plasma torus through the
addition of source and loss terms. Using our model, we show that
the response of the corotation enforcement currents (which we assume
are a proxy for auroral brightness) to a shock-induced compression
varies significantly with local time, with currents being depleted
on the dayside and moderately enhanced on the nightside. Plasmoids
are frequently seen in our model due to tail reconnection and plasmoid
release occurs more frequently during periods of high solar wind dynamic
pressure. The release of plasmoids is often accompanied with reduction
of the net open flux in the polar regions as well as decrease in the
intensity of corotation enforcement currents, consistent with the
idea that the magnetosphere returns to a less stressed state after
plasmoid release. Plasmoids originating on closed field lines are
found to temporarily create a region of closed flux deep inside the
polar cap that originally only contains open magnetic field lines,
which diminishes in size as the plasmoid moves tailward and interacts
with the surrounding plasma. Our results together show that the polar
regions of Jupiter are highly dynamic and the formation and release
of plasmoids further complicates the dynamics through large-scale
reconfiguration of the magnetic field topology.
Title: Exploring the physics of sawtooth oscillations from MHD-EPIC
simulations
Authors: Chen, Y.; Toth, G.; Wang, X.; Gombosi, T. I.; Welling, D. T.;
Henderson, M. G.; Markidis, S.; Cassak, P.
Bibcode: 2019AGUFMSM21B3144C
Altcode:
The sawtooth events are global magnetospheric oscillations with a 2~4
hour period identified by the saw blade like signature of the energetic
particle flux and magnetic field near geosynchronous orbit. Previous
global numerical simulations suggest that the oscillations are generated
by the ionospheric O + outflows (Brambles et al. [2011]). However,
recent satellite observations demonstrated the ionospheric outflow is
neither a necessary nor a sufficient condition for the generation of the
sawtooth oscillations (Liao et al. [2014], Lund et al. [2017]). We use
the MHD with embedded particle-in-cell (MHD-EPIC) model, which simulates
Earth's magnetotail with a PIC code, to show the periodic magnetospheric
oscillations can be generated even without the ionospheric outflow. We
show that the magnetotail reconnection is not fast enough to balance
the incoming magnetic flux during the stretching phase of a sawtooth,
and the dipolarization phase is triggered by the onset of reconnection
around x=-20 R E , where the reconnection rate is fast enough to
release the magnetic flux due to the high ambient magnetic field
strength. We will present the spatial features and temporal variations
of the sawtooth oscillations from the MHD-EPIC simulation results,
and compare the simulations with the observations.
Title: How small changes in the magnetopause current help trap the
ring current population
Authors: Ilie, R.; Liu, J.; Chen, L., , Dr; Zhu, H.; Toth, G.; Bashir,
M. F.; Liemohn, M. W.
Bibcode: 2019AGUFMSM41D3272I
Altcode:
Particle energization is one of the open questions in heliophysics
research, whether it pertains to coronal heating, polar wind outflow,
or magnetospheric transport. The terrestrial magnetosphere acts as
an efficient particle accelerator, as it can rapidly accelerate
charged particles up to very high energies over relatively short
times and distances. While the magnetic field topology is critical for
understanding the particle drifts, knowing the source and structure of
the electric field is crucial for interpreting the flow of particles
in this region. Assessing the relative contribution of potential
versus inductive electric fields at the energization of the hot ion
population in the inner magnetosphere is only possible by thorough
examination of the time varying magnetic field and current systems
using global modeling of the entire system. Based on the Helmholtz
vector decomposition of the motional electric field as calculated by
the BATS-R-US model, we differentiate the electric field based on its
source (electrostatic vs. inductive). Electric field coupling between
the BATS-R-US and the Hot Electron and Ion Drift Integrator model
reveals the crucial role of time varying magnetic fields, and hence the
inductive electric field, in trapping of energetic particle and in the
overall particle energization. We show that inductive electric
fields, even if not impulsive in nature, contribute significantly
to the total field, and in the absence of strong dipolarizations,
most of the contribution comes from the intensification of the
magnetopause current. In addition, the inductive electric field acts
to stabilize the ring current, and it plays a significant role in
particle trapping. These results indicate a potential paradigm shift in
our knowledge of particle energization in the context of ring current
development and decay.
Title: Global Magnetospheric Model with Microscopic Physics: MHD-EPIC
Authors: Toth, G.; Chen, Y.; Zhou, H.; Wang, X.; Tenishev, V.; Shou,
Y.; Markidis, S.
Bibcode: 2019AGUFMSM12B..06T
Altcode:
In the last 5 years we have developed and implemented the
magnetohydrodynamics with embedded particle-in-cell (MHD-EPIC)
model. MHD-EPIC allows performing global MHD simulations two-way
coupled with local PIC simulations covering one or more regions where
kinetic effects are important, such as magnetic reconnection sites. We
have improved the PIC algorithm to conserve energy and satisfy Gauss'
law at the same time, generalized the MHD-PIC coupling to arbitrary
MHD grids and rotated PIC regions, and improved the efficiency of the
coupler. We have also studied the technique of artificially increasing
the kinetic scales by changing the mass per charge ratio for the ions
and electrons, and we found that the global solution remains essentially
the same as long as the global and kinetic scales are reasonably well
separated. The combination of these new technologies and insights
enabled us to perform MHD-EPIC simulations for several magnetospheres,
including Ganymede, Mercury, Mars, Earth and Saturn. In this talk we
will demonstrate these capabilities for modeling Earth's magnetosphere
with the PIC region covering the dayside or tail reconnection sites. On
the dayside we compare the model with observations of flux transfer
events and kinetic scale observations by the MMS space craft. For the
magnetotail we study the dynamics of the reconnection process that
appears to reproduce several features of sawtooth events for strong
but steady driving with negative Bz field. Our work is supported by
the NSF INSPIRE and PRE-EVENTS grants.
Title: Modeling an Extreme Coronal Mass Ejection and its Consequences
for the Earth's Inner Magnetosphere
Authors: Komar, C. M.; Kang, S. B.; Oliveira, D. M.; Bhaskar, A. T.;
Fok, M. C. H.; Glocer, A.; Buzulukova, N.; Toth, G.
Bibcode: 2019AGUFMSM13E3356K
Altcode:
Interplanetary coronal mass ejections (CMEs) can have a variety of
different impacts upon Geospace. The most extreme CME on record to have
struck the Earth is the well-known Carrington event of 1859. However,
in the sixty or so years since the Space Age began, we have thus
far been exceptionally lucky that no extreme CME has impacted the
Earth's space environment. The work by Tsurutani and Lakhina, GRL, 2014
estimates some of the potential impacts that an extreme CME could have
on Geospace. Tsurutani and Lakhina, 2014 utilize empirical relations
to provide best estimates of: (1) the magnetopause's location, (2)
the sudden impulse intensity, and (3) the magnetospheric electric
field. The CME conditions described by Tsurutani and Lakhina, 2014
is the most extreme CME conceived by our current theoretical and
empirical knowledge; such a CME is likely to be MORE extreme than
the Carrington event. Global magnetospheric models are now capable
of simulating such events to give insight into the effects of extreme
space weather conditions. This work will present the results of
simulations with the Space Weather Modeling Framework using the global
magnetohydrodynamic (MHD) Block Adaptive Tree Solar wind Roe-type
Upwind Scheme (BATS-R-US) code. The simulation uses the exact extreme
CME conditions presented in Tsurutani and Lakhina, 2014 to model the
impact of an extreme CME on the magnetosphere. We will present the
successful simulation of these extreme space weather conditions. We will
directly compare and contrast the predicted values from the empirical
relations presented in Tsurutani and Lakhina, 2017 with the results of
the MHD simulations: the sudden impulse dB/dt, magnetopause location,
and the magnetospheric electric field. We will discuss the response
of the inner magnetospheric system to extreme space weather events.
Title: Multi-fluid MHD Modeling of Europa's Plasma Interaction:
Effects of Asymmetric Density in the Neutral Atmosphere
Authors: Harris, C. D. K.; Jia, X.; Slavin, J. A.; Toth, G.; Rubin, M.
Bibcode: 2019AGUFMSM33F3279H
Altcode:
Europa orbits Jupiter within the Jovian magnetosphere, that region
of space dominated by the planetary magnetic field and by plasma
originating from Jupiter's moon Io. Europa's subsurface ocean and weak
atmosphere interact with Jupiter's magnetic field and magnetospheric
plasma. Here we investigate the role of Europa's neutral O2
atmosphere in the generation of Europa's ionosphere and its interaction
with Jupiter's magnetosphere. We have developed a 3D multi-fluid
magnetohydrodynamic (MHD) model for the plasma interaction that solves
for the bulk properties of 3 ion fluids (magnetospheric O+,
ionospheric O+ and O2+), an electron
fluid, and the electromagnetic fields near the moon. We include
a static distribution of neutral O2 that represents
Europa's atmosphere and provides the neutral source for ionization
and charge exchange source terms that populate the ionosphere in our
simulation. We use our MHD model to demonstrate the effects of variation
in the neutral atmosphere on the plasma interaction during two different
flybys conducted by the Galileo mission. During the E4 flyby Europa was
located outside the plasma sheet and the trailing hemisphere was sunlit,
while during the E15 flyby Europa was embedded within the plasma sheet
and the trailing hemisphere was in shadow. By comparing our simulation
results to the in situ magnetometer and plasma data collected by the
Galileo spacecraft, we show that the E4 flyby is readily modeled with a
neutral atmosphere with enhanced O2 density on the trailing
hemisphere; conversely, the E15 flyby is better modeled by a neutral
atmosphere that is enhanced on the leading hemisphere. This finding is
consistent with results from recent modeling of Europa's atmosphere that
incorporates the effects of solar illumination on Europa's spatially
non-uniform atmosphere as the moon rotates (Oza et al., 2019). Our
work demonstrates that the state of Europa's neutral atmosphere is a
crucial factor in the generation of Europa's ionosphere and, ultimately,
the magnetic field perturbations associated with the plasma interaction.
Title: The Current State of Operational Geospace Modeling Efforts
at NOAA SWPC
Authors: Cash, M. D.; Singer, H. J.; Balch, C. C.; Millward, G. H.;
Camporeale, E.; Toth, G.; Huang, Z.
Bibcode: 2019AGUFMSM12B..01C
Altcode:
The operational Geospace model, which has been running in real-time
at NOAA's Space Weather Prediction Center (SWPC) since 2016,
will undergo a significant upgrade in 2020 to a higher resolution
version. The Geospace model is comprised of three coupled components
from University of Michigan's Space Weather Modeling Framework (SWMF),
and having run the model continuously for the past three years, we
have been able to assess the strengths and limitations of running
the model in such a real-time mode. In this presentation, we discuss
the successes and limitations experienced running with the current
low-resolution version of the model, and present examples of the
expected model improvements associated with upgrading the model to
a higher resolution. In particular, we will discuss improvements to
our regional forecasting capabilities and the implications that such
improvements have on down-stream modeling efforts such as predicting
the regional geoelectric field in a predictive mode using output from
the Geospace model.
Title: Global modeling of the drivers and impacts of storm-time
plasma composition
Authors: Glocer, A.; Welling, D. T.; Toth, G.; Fok, M. C. H.; Chappell,
C. R.; Kang, S. B.; Komar, C. M.; Buzulukova, N.; Ferradas, C.
Bibcode: 2019AGUFMSM11A..06G
Altcode:
Earth's space environment system is comprised of a myriad of plasma
populations. These populations encompass characteristic energies ranging
over 6 orders of magnitude; from sub-eV plasma in the ionosphere, to
10-100 keV plasma in the ring current, and MeV and higher particles in
the radiation belts. Further complicating this picture is the fact that
the origin of near-Earth plasma, be it the ionosphere or solar wind,
remains a subject of significant debate. Simulating these disparate
plasma populations in a single global simulation requires a fusion of
fluid and kinetic models. In this presentation we present an improved
coupling of the Polar Wind Outflow Model (PWOM), the Comprehensive
Ionosphere Magnetosphere Interaction (CIMI) model, and BATSRUS model
of the magnetosphere. These models are coupled together using the Space
Weather Modeling Framework (SWMF), and represent a comprehensive model
of the Earth's space environment. The improved coupling allows us to
investigate the origin of near-Earth plasma by separately tracking
solar wind plasma (H+) from ionospheric plasma (highlatitude H+ and
O+, as well as plasmaspheric H+). Focusing on storm-time simulations,
we will examine hemispheric asymmetries in the outflow, the relative
role of wave-particle interactions and solar EUV in driving ionospheric
outflow, and the impact on the ring current and radiation belts. We
will moreover highlight the kinetic features embedded in the model
and discuss current limitations future directions.
Title: Predicting Solar Flares using Time Sequence Based Machine
Learning Models
Authors: Wang, X.; Toth, G.; Chen, Y.; Manchester, W.; Jiao, Z.; Sun,
H.; Sun, Z.; Hero, A. O.; Gombosi, T. I.
Bibcode: 2019AGUFMSH34A..03W
Altcode:
In the last few years machine learning methods are becoming popular
for predicting solar flares. We use the Space-weather HMI Active Region
Patches (SHARP) dataset to analyze thousands of active regions' magnetic
field and derived parameters (total unsigned flux, free magnetic
energy, etc) using various machine learning algorithms. In this work
we first use the SHARP summary parameters to predict the maximum flare
intensity in a certain time window through a Long Short-Term Memory
(LSTM) algorithm, which is a particular type of a recurrent neural
network. The dataset we are using contains 3399 active regions from
2010 to 2015. Furthermore, we will use the full vector magnetogram
images to train a combined LSTM and feature extraction convolutional
neural network (CNN). This approach allows capturing more detailed
spatial-temporal features of the magnetic field. Our results show
that using a time sequence to predict the maximum flare intensity can
achieve a better Heidke Skill Score (HSS) than using a single frame
as the input. The HSS for predicting the maximum flare class in the
next 24 hours is about 0.35 for M/X flares and 0.55 for C/M/X flares.
Title: Validation of the Alfvén Wave Solar Atmosphere Model (AWSoM)
with Observations from the Low Corona to 1 au
Authors: Sachdeva, Nishtha; van der Holst, Bart; Manchester, Ward B.;
Tóth, Gabor; Chen, Yuxi; Lloveras, Diego G.; Vásquez, Alberto M.;
Lamy, Philippe; Wojak, Julien; Jackson, Bernard V.; Yu, Hsiu-Shan;
Henney, Carl J.
Bibcode: 2019ApJ...887...83S
Altcode: 2019arXiv191008110S
We perform a validation study of the latest version of the Alfvén
Wave Solar atmosphere Model (AWSoM) within the Space Weather Modeling
Framework. To do so, we compare the simulation results of the model
with a comprehensive suite of observations for Carrington rotations
representative of the solar minimum conditions extending from the
solar corona to the heliosphere up to the Earth. In the low corona
(r < 1.25 {\text{}}{R}⊙ ), we compare with EUV
images from both Solar-Terrestrial Relations Observatory-A/EUVI
and Solar Dynamics Observatory/Atmospheric Imaging Assembly and to
three-dimensional (3D) tomographic reconstructions of the electron
temperature and density based on these same data. We also compare the
model to tomographic reconstructions of the electron density from
Solar and Heliospheric Observatory/Large Angle and Spectrometric
Coronagraph observations (2.55 < r < 6.0{\text{}}{R}⊙
). In the heliosphere, we compare model predictions of solar wind
speed with velocity reconstructions from InterPlanetary Scintillation
observations. For comparison with observations near the Earth, we use
OMNI data. Our results show that the improved AWSoM model performs
well in quantitative agreement with the observations between the inner
corona and 1 au. The model now reproduces the fast solar wind speed
in the polar regions. Near the Earth, our model shows good agreement
with observations of solar wind velocity, proton temperature, and
density. AWSoM offers an extensive application to study the solar
corona and larger heliosphere in concert with current and future solar
missions as well as being well suited for space weather predictions.
Title: Preferential Ion Heating and Particle Acceleration Downstream
of Dispersive Shock Waves in Collisionless Multi-Ion Plasma
Authors: Zieger, B.; Toth, G.; Opher, M.
Bibcode: 2019AGUFMSH23B3396Z
Altcode:
We briefly review the theory of dispersive shock waves in collisionless
multi-ion plasma. In such plasma, two (or more) fast magnetosonic wave
modes exist: the high-frequency fast mode that propagates in the ion
component with the higher thermal speed and the low-frequency fast mode
that propagates in the ion component with the lower thermal speed [Toida
and Aota, 2013; Zieger et al., 2015]. Both fast modes are dispersive
on fluid and ion scales, which results in nonlinear dispersive shock
waves. A negative dispersive wave mode produces a trailing wave
train downstream of the shock, while a positive dispersive wave mode
produces a precursor wave train upstream of the shock [Biskamp, 1973;
Hoefer, 2014]. Here we present high-resolution three-fluid simulations
of dispersive shock waves in two-ion-species plasma. We show that
downstream propagating nonlinear magnetosonic waves grow until they
steepen into shocklets (thin current sheets), overturn, and start to
propagate backward in the frame of the downstream propagating wave, as
predicted by theory [McKenzie et al., 1993; Dubinin et al, 2006]. The
counter-propagating nonlinear waves result in fast magnetosonic
turbulence far downstream of the shock. Interestingly, energy is
transferred from small scales to large scales (inverse energy cascade)
in the high-frequency fast mode, and from large scales to small scales
(direct energy cascade) in the low-frequency fast mode as the turbulence
develops in time. We show that the ion species with the lower thermal
speed is preferentially heated by the turbulence. Forward shocklets
can efficiently accelerate both ions and electrons to high energies
through the shock drift acceleration mechanism. We can conclude that
fast magnetosonic turbulence in collisionless multi-ion plasma will move
the plasma towards a state where the thermal speeds of different ion
species are comparable. Our theoretical and numerical simulation results
could help to explain the observed preferential heating of heavy ions
in the solar corona, the acceleration of energetic particles downstream
of interpanetary shocks in the multi-ion solar wind, the non-adiabatic
cooling of solar wind ions and pickup ions in the outer heliosphere,
and the unfolding of the anomalous cosmic ray energy spectra in the
heliosheath, downstream of the termination shock.
Title: Validating the Space Weather Modeling Framework (SWMF)
for applications in northern Europe: Ground magnetic perturbation
validation
Authors: Kwagala, N. K.; Hesse, M.; Tenfjord, P.; Norgren, C.; Moretto,
T.; Toth, G.; Gombosi, T. I.
Bibcode: 2019AGUFMSM13F3373K
Altcode:
This study evaluates the performance of the University of Michigan's
Space Weather Modeling Framework (SWMF) in the prediction of ground
magnetic perturbations in the northern Europe region. The SWMF
consists of an MHD code which is a Block Adaptive Tree Solar-wind
Roe-type Upwind Scheme (BATS-R-US), with several other models
which can be coupled together. We use the the global magnetosphere,
ionosphere electrodynamics and inner magnetosphere coupled SWMF. The
SWMF is currently used for space weather forecast by the by the
NOAA Space Weather Prediction Centre (SWPC) and at the Community
Coordinated Modeling Centre (CCMC). The SWMF was selected to transit
to operation after a series of community-wide validations of several
numerical models on a global scale. In our study we further validate
the SWMF for applications in the northern Europe region. The model
predictions are done for selected ground magnetometer stations between
59o - 78o magnetic latitudes spanning 5 magnetic
local hours. The performance is quantified using the metrics-based
analyses, normalized root-mean-square error and cross correlation
coefficient. The different metrics are derived from contingency
tables built for each event and station. Investigated metrics include
the probability of detection, probability of false alarm detection,
Heidke Skill Score and frequency bias of the model. The variation of
the model performance is investigated from event to event, and for
different magnetic latitudes, and magnetic local times.
Title: Impact of Non-MHD Effects on Global Magnetosphere Dynamics
for Extreme Solar Wind Driving
Authors: Kuznetsova, M. M.; Toth, G.; Rastaetter, L.
Bibcode: 2019AGUFMSM11A..04K
Altcode:
The presentations will address challenges in global magnetosphere
simulations for extreme driving conditions. Strong solar wind driving
can push the magnetopause boundary into inner magnetosphere and even
upper atmosphere where single fluid MHD approach is not applicable. For
extreme driving the magnetopause can move close to the earthward
boundary of the simulation domain that can lead to increased sensitivity
to parameters and assumptions at the inner boundary. Ionosphere
conductance models are typically trained on observational data sets
that do not include time periods with extreme driving. Another major
challenge is to quantify the interaction between global evolution of the
magnetosphere and microphysical kinetic processes in diffusion regions
near reconnection sites. Our past studies of magnetosphere dynamics
during moderate steady southward driving demonstrated that incorporation
of kinetic nongyrotropic effects near reconnection sites in magnetotail
significantly alter the global magnetosphere evolution. To study
characteristics of loading/unloading cycle in response to extreme solar
wind driving we utilize the global MHD component of the Space Weather
Modeling Framework (SWMF) with incorporated kinetic corrections. We
also discuss relative impact of kinetic effects at the reconnection
site and conditions at the inner boundary.
Title: The Two-Lobe Structure of the Heliosphere Persists in the
SHIELD Model, a K-MHD Model of the Outer Heliosphere
Authors: Michael, A.; Opher, M.; Toth, G.; Tenishev, V.; Borovikov, D.
Bibcode: 2019AGUFMSH51B..07M
Altcode:
The canonical view of the shape of the heliosphere resembles a long
comet tail, however, our research group at BU, led by Dr. Merav
Opher, has suggested that the heliosphere is tailless with a
two-lobe structure. This study was done with a state-of-the-art 3D
magnetohydrodynamic (MHD) code that treats the ionized and neutral
hydrogen atoms as fluids. Previous studies that have described the
neutrals kinetically have claimed that this removes the two-lobe
structure of the heliosphere. In this work, we will use the newly
developed Solar-wind with Hydrogen Ion Exchange and Large-scale
Dynamics (SHIELD) model, a self-consistent kinetic-MHD model of the
outer heliosphere. The SHIELD model couples the Outer Heliosphere
(OH) and Particle Tracker (PT) components within the Space Weather
Modeling Framework (SWMF). The OH component utilizes the Block-Adaptive
Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) MHD code, a highly
parallel, 3D, and block-adaptive solver. The PT component is based
on the Adaptive Mesh Particle Simulator (AMPS) model, a 3D, direct
simulation Monte Carlo model that solves the Boltzmann equation to
model the neutral distribution function throughout the domain. The
SHIELD model couples the MHD solution for a single plasma fluid to the
kinetic solution from for neutral hydrogen atoms streaming through the
system. We use the same boundary conditions as Opher et al. (2015), the
seminal work on the two-lobe structure, within the SHIELD model to test
whether the two-lobe structure of the heliotail is removed. Our results
show that despite the large difference in the neutral solution between
the fluid and kinetic treatment of the neutral hydrogen, the two-lobe
structure remains even when the neutral hydrogen atoms are modeled
kinetically. These results are contrary to Izmodenov et al (2018),
whose model maintains a perfectly ideal heliopause and does not allow
for communication between the solar wind and interstellar medium . This
indicates that magnetic reconnection downtail and/or instabilities
play a crucial role for the formation of the two-lobe structure.
Title: Role of the Inductive Electric Field to the Ring Current
Particle Energization and Trapping
Authors: Liu, J.; Ilie, R.; Toth, G.
Bibcode: 2019AGUFMSM13F3372L
Altcode:
The dynamic nature of magnetic field within inner magnetosphere region
plays an important role in the transport and energization process of
ring current ion species, by altering the local gradient-curvature drift
of trapped ring current ion population, changing the bounce path length
of trapped particles, and inducing a global inductive electric field,
as described by Faraday's law, that accelerates particles within a
short period of time. Quantifying the effect brought by the dynamic
nature of magnetic field is crucial for providing a realistic and
accurate description of the dynamic and time-evolution of terrestrial
ring current, especially during storm time, when the dynamic nature of
magnetic field is prominent. The motions of different particle
population trapped within inner magnetosphere are both energy and
pitch-angle dependent, so standard single fluid treatment of plasma
cannot provide adequate description of the inner magnetosphere. To
accurately simulate this closed field lines region, a kinetic model
solving the energy and pitch-angle dependent particle drift of hot ions
and electrons is needed. The Hot Electron Ion Drift Integrator (HEIDI)
kinetic model is able to separate the contribution from different
aspects of the dynamic nature of magnetic field, to particle drift,
energization rate and pitch-angle scattering. We present here, for the
first time, an assessment of the role the inductive electric field
plays in trapping particles in the inner magnetosphere, and in the
intensification of the ring current. Comparison results on the
drift, energization rate and pitch-angle change obtained from HEIDI,
by both coupling it with BATS-R-US and running stand alone, have been
obtained to analyze the effect of different aspects of time-changing
magnetic field on the ring-current ion dynamics. In coupled mode,
BATS-R-US provides HEIDI with self-consistent electric (separated by
source) and magnetic field information, while in stand-alone mode, HEIDI
itself is able to calculate a self-consistent inductive electric field
generated by a time varying analytic stretching dipole magnetic field.
Title: Limitations of global MHD models of the Earth's magnetosphere
Authors: Rastaetter, L.; Moretto, T.; Hesse, M.; Kuznetsova, M. M.;
Toth, G.; Raeder, J.; Lyon, J.; Honkonen, I. J.
Bibcode: 2019AGUFMSM12B..02R
Altcode:
Global MHD models are an important asset in the collection of models
that forecast and specify space weather effects in the near-Earth space
environment. To further improve space weather forecasting accuracy, it
is necessary to not only improve skill scores in a variety of model-data
comparisons but also improve the models' performance by comparing
model results with expectations derived from fundamental physics
principles. For example, ideal MHD models are expected to have the same
electric potential on conjugate foot points of closed magnetic field
lines. We test the degree of non-idealness in 4 global MHD models (SWMF,
OpenGGCM, LFM and GUMICS) at the Community Coordinated Modeling Center
using magnetosphere-ionosphere mapping tools. Field-line resonances seen
at ULF wave frequencies are another challenge where model responses
can be measured. The analysis of the causes of disagreements between
models and between models and observations can be used to improve the
way models are run in the community (through the CCMC and elsewhere).
Title: MESSENGER observations and global simulations of highly
compressed magnetosphere events at Mercury
Authors: Jia, X.; Slavin, J. A.; Poh, G.; DiBraccio, G. A.; Toth,
G.; Chen, Y.; Raines, J. M.; Gombosi, T. I.
Bibcode: 2019AGUFMSM51A..03J
Altcode:
Mercury's comparatively weak intrinsic field, lack of an appreciable
atmosphere and its close proximity to the Sun lead to a magnetosphere
that undergoes more direct space-weathering interactions than other
planets. The shielding effect due to the induction currents in
the planetary core and erosion of the dayside magnetosphere due to
magnetopause reconnection, compete against each other for dominance in
controlling the large-scale structure of Mercury's magnetosphere. Here
weidentify and examine all MESSENGER crossings of Mercury's dayside
magnetopause with magnetospheric field intensities >= 300 nT. A
total of 8 such events have been identified, all of which occurred under
highly compressed magnetosphere (HCM) conditions. Our analysis suggests
that the 8 HCM events represent the highest solar wind dynamic pressures
for which the MESSENGER's orbit still passed below the magnetopause
and provided measurements of the dayside magnetosphere. Using the
magnetohydrodynamic model by Jia et al.(2015) that electromagnetically
couples Mercury's interior with its magnetosphere, a series of global
simulations are conducted to quantitatively characterize the response of
Mercury's magnetosphere to solar wind forcing. Combining the MESSENGER
observations with the simulations, we have obtained a consistent picture
of how Mercury's dayside magnetospheric configuration is controlled,
separately and in combination, by induction-driven shielding and
reconnection-driven erosion. For solar wind pressures of ~ 40-90 nPa,
compared with the average ~ 10-15 nPa at Mercury's orbit, the shielding
effects of induction in Mercury's core in standing-off the solar
wind typically exceeds the erosion of the dayside magnetosphere due to
reconnection for these events, most of which occurred under low magnetic
shear conditions. For high magnetic shear across the magnetopause
our simulation predicts that reconnection would dominate. Mercury's
effective magnetic moment as inferred from magnetopause stand-off
distance ranges from 170 to 250 nT-RM3 for these
events. These findings, presented in Jia et al. (2019), are of crucial
importance for understanding the space weathering at Mercury and its
contribution to the generation of Mercury's exosphere.
Title: The Structure of the Heliotail as probed by a Kinetic-MHD,
a Multi-Ion Description of the Heliosphere and Energetic Neutral Maps
Authors: Opher, M.; Michael, A.; Kornbleuth, M. Z.; Drake, J. F.;
Loeb, A.; Toth, G.
Bibcode: 2019AGUFMSH53A..04O
Altcode:
A critical question regarding the heliosphere is its veryshape and the
structure of the heliotail (whether it has a long comet-like shape,
is bubble shaped, or "croissant"-like), prompted by observations
and modeling (Opher et al. 2015; Pogorelov et al. 2015; Izmodenov
& Alexashov 2015; Dialynas et al. 2017; Schwadron & Bzowski
2018). Opher et al. (2015) show that the magnetic tension of the solar
magnetic field organizes the solar wind in the heliosheath into two
jet-like structures, giving the heliosphere a "croissant"-like shape
where the distance to the heliopause downtail is almost the same as
that towards the nose. There have been arguments that with a
kinetic treatment of the neutral H, the heliotail extends to large
distances (Izmodenov et al. 2018; Pogorelov et al. 2015). We recently
developed the Solar-wind with Hydrogen Ion Exchange and Large-scale
Dynamics (SHIELD) model, a self-consistent kinetic-MHD model of the
outer heliosphere within the SWMF framework (Toth et al. 2012). The
SHIELD model couples the MHD solution for a single plasma fluid to
the kinetic solution for neutral hydrogen atoms streaming through
the system. Our results show that even when the neutral H atoms
are treated kinetically, the two-lobe structure remains (Michael et
al. 2019). Their results indicate that magnetic reconnection downtail
and/or instabilities play a crucial role in the formation of the
two-lobe structure. We will present globally distributed flux (GDF)
ENA maps from the SHIELD model, including a latitudinal variation of
the solar wind corresponding to the conditions in the year 2008 using
solar wind data from Sokol et al. (2015). The GDF ENA maps replicate
the IBEX observations for solar minima conditions. We have also
recently extended our global MHD model (Opher et al. 2019) to treat the
pick-up ions (PUIs) created in the supersonic solar wind as a separate
fluid from the thermal component of the solar wind. The PUIs charge
exchange with the cold neutral H atoms of the ISM in the heliosheath
and are quickly depleted. The depletion of PUIs cools the heliosphere
downstream of the TS, "deflating" it and leading to a narrower HS and a
smaller and rounder shape. With this model, we reproduce the IBEX ENA
observations along Voyager 2, as well the magnetic field observations
at Voyager 1 and 2 ahead of the heliosphere.
Title: Validating the Alfven Wave Solar Atmosphere (AWSoM) Model
from the Low Corona to 1 AU
Authors: Sachdeva, N.; van der Holst, B.; Manchester, W.; Toth, G.;
Lloveras, D. G.; Vásquez, A. M.; Lamy, P.; Jackson, B. V.; Henney,
C. J.
Bibcode: 2019AGUFMSH51A..04S
Altcode:
The coronal/solar wind model, the Alfven Wave Solar atmosphere Model
(AWSoM) a component within the Space Weather Modeling Framework (SWMF)
follows a self-consistent physics-based global description of coronal
heating and solar wind acceleration. AWSoM includes a description
of low-frequency forward and counter-propagating Alfven waves that
non-linearly interact resulting in a turbulent cascade and dissipative
heating. In addition, there are separate temperatures for electrons and
protons with collisional and collisionless heat conduction applied only
to electrons and radiative losses based on the Chianti model. AWSoM
extends from the base of the transition region where the strong
density gradient necessitates self-consistent treatment of Alfven wave
reflection and balanced turbulence. It includes a stochastic heating
model as well as a description of proton parallel and perpendicular
temperatures and kinetic instabilities based on temperature anisotropy
and plasma beta.To validate AWSoM, we model Carrington rotations
representative of solar minimum conditions and compare the simulation
results with a comprehensive suite of observations. In the low corona
(r < 1.25 Rs), we compare with EUV images from both STEREOA/EUVI
and SDO/AIA and to three-dimensional tomographic reconstructions of
the electron temperature and density based on these same data. We
also compare the model to tomographic reconstructions of the electron
density from SOHO/LASCO observations (2.55 < r < 6 Rs). In
the heliosphere, we compare model predictions of solar wind speed
with velocity reconstructions from Interplanetary Scintillation
observations. For comparison with observations near the Earth, we
use OMNI data. Our results show that the AWSoM model performs well
in quantitative agreement with the observations between the inner
corona and 1 AU. In the lower corona, the model and the tomographic
reconstructions agree within 20%-30% on average. The model also
reproduces the fast solar wind speed in the polar regions. Near the
Earth, our model shows good agreement with observations of solar wind
velocity, electron temperature and density. The AWSoM model provides
a comprehensive tool to study the solar corona and larger heliosphere
with current and future solar missions as well as being well suited
for space weather predictions.
Title: Importance of Ambipolar Electric Field in Driving Ion Loss
From Mars: Results From a Multifluid MHD Model With the Electron
Pressure Equation Included
Authors: Ma, Y. J.; Dong, C. F.; Toth, G.; van der Holst, B.; Nagy,
A. F.; Russell, C. T.; Bougher, S.; Fang, Xiaohua; Halekas, J. S.;
Espley, J. R.; Mahaffy, P. R.; Benna, M.; McFadden, J.; Jakosky, B. M.
Bibcode: 2019JGRA..124.9040M
Altcode:
The multifluid (MF) magnetohydrodynamic model of Mars is improved
by solving an additional electron pressure equation. Through the
electron pressure equation, the electron temperature is calculated
based on the effects from various electron-related heating and
cooling processes (e.g., photoelectron heating, electron-neutral
collision, and electron-ion collision), and thus, the improved model
can calculate the electron temperature and the electron pressure force
terms self-consistently. Model results of a typical case using the MF
with electron pressure equation included model are compared in detail
to identical cases using the MF and multispecies models to identify the
effect of the improved physics. We find that when the electron pressure
equation is included, the general interaction patterns are similar to
those with no electron pressure equation. However, the MF with electron
pressure equation included model predicts that the electron temperature
is much larger than the ion temperature in the ionosphere, consistent
with both Viking and Mars Atmosphere and Volatile EvolutioN (MAVEN)
observations. Using our numerical model, we also examined in detail
the relative importance of different forces in the plasma interaction
region. All three models are also applied to a MAVEN event study using
identical input conditions; overall, the improved model matches best
with MAVEN observations. All of the simulation cases are examined in
terms of the total ion loss, and the results show that the inclusion of
the electron pressure equation increases the escape rates by 50-110%
in total mass, depending on solar condition and strong crustal field
orientation, clearly demonstrating the importance of the ambipolar
electric field in facilitating ion escape.
Title: Studying Dawn-Dusk Asymmetries of Mercury's Magnetotail Using
MHD-EPIC Simulations
Authors: Chen, Yuxi; Tóth, Gábor; Jia, Xianzhe; Slavin, James A.;
Sun, Weijie; Markidis, Stefano; Gombosi, Tamas I.; Raines, Jim M.
Bibcode: 2019JGRA..124.8954C
Altcode: 2019arXiv190406753C
MESSENGER has observed a lot of dawn-dusk asymmetries in Mercury's
magnetotail, such as the asymmetries of the cross-tail current sheet
thickness and the occurrence of flux ropes, dipolarization events, and
energetic electron injections. In order to obtain a global pictures
of Mercury's magnetotail dynamics and the relationship between these
asymmetries, we perform global simulations with the magnetohydrodynamics
with embedded particle-in-cell (MHD-EPIC) model, where Mercury's
magnetotail region is covered by a PIC code. Our simulations show that
the dawnside current sheet is thicker, the plasma density is larger,
and the electron pressure is higher than the duskside. Under a strong
interplanetary magnetic field driver, the simulated reconnection
sites prefer the dawnside. We also found the dipolarization events
and the planetward electron jets are moving dawnward while they are
moving toward the planet, so that almost all dipolarization events and
high-speed plasma flows concentrate in the dawn sector. The simulation
results are consistent with MESSENGER observations.
Title: Numerical investigation of the dynamics of linear spin s fields
on a Kerr background: Late-time tails of spin s =±1 ,±2 fields
Authors: Csukás, Károly; Rácz, István; Tóth, Gábor Zsolt
Bibcode: 2019PhRvD.100j4025C
Altcode: 2019arXiv190509082C
The time evolution of linear fields of spin s =±1 and s =±2 on Kerr
black hole spacetimes are investigated by solving the homogeneous
Teukolsky equation numerically. The applied numerical setup is based
on a combination of conformal compactification and the hyperbolic
initial value problem. The evolved basic variables are expanded in
terms of spin-weighted spherical harmonics, which allows us to evaluate
all angular derivatives analytically, whereas the evolution of the
expansion coefficients in the time-radial section is determined by
applying the method of lines implemented in a fourth order accurate
finite differencing stencil. Concerning the initialization, in all
of our investigations, single mode excitations—either static or
purely dynamical-type initial data—are applied. Within this setup
the late-time tail behavior is investigated. Because of the applied
conformal compactification, the asymptotic decay rates are determined at
three characteristic locations—in the domain of outer communication,
at the event horizon, and at future null infinity—simultaneously. A
recently introduced new type of "energy" and "angular momentum" balance
relations are also applied in order to demonstrate the feasibility
and robustness of the developed numerical schema and also to verify
the proper implementation of the underlying mathematical model.
Title: Identifying Solar Flare Precursors Using Time Series of
SDO/HMI Images and SHARP Parameters
Authors: Chen, Yang; Manchester, Ward B.; Hero, Alfred O.; Toth,
Gabor; DuFumier, Benoit; Zhou, Tian; Wang, Xiantong; Zhu, Haonan;
Sun, Zeyu; Gombosi, Tamas I.
Bibcode: 2019SpWea..17.1404C
Altcode: 2019arXiv190400125C
In this paper we present several methods to identify precursors that
show great promise for early predictions of solar flare events. A data
preprocessing pipeline is built to extract useful data from multiple
sources, Geostationary Operational Environmental Satellites and Solar
Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI),
to prepare inputs for machine learning algorithms. Two classification
models are presented: classification of flares from quiet times
for active regions and classification of strong versus weak flare
events. We adopt deep learning algorithms to capture both spatial
and temporal information from HMI magnetogram data. Effective feature
extraction and feature selection with raw magnetogram data using deep
learning and statistical algorithms enable us to train classification
models to achieve almost as good performance as using active region
parameters provided in HMI/Space-Weather HMI-Active Region Patch
(SHARP) data files. Case studies show a significant increase in the
prediction score around 20 hr before strong solar flare events.
Title: High Resolution Finite Volume Method for Kinetic Equations
with Poisson Brackets
Authors: Sokolov, Igor V.; Sun, Haomin; Toth, Gabor; Huang, Zhenguang;
Tenishev, Valeriy; Zhao, Lulu; Kota, Jozsef; Cohen, Ofer; Gombosi,
Tamas
Bibcode: 2019arXiv191012636S
Altcode:
Simulation of plasmas in electromagnetic fields requires numerical
solution of a kinetic equation that describes the time evolution
of the particle distribution function. In this paper we propose a
finite volume scheme based on integral relation for Poisson brackets
to solve the Liouville equation, the most fundamental kinetic
equation. The proposed scheme conserves the number of particles,
maintains the total-variation-diminishing (TVD) property, and provides
high-quality numerical results. Other types of kinetic equations may
be also formulated in terms of Poisson brackets and solved with the
proposed method including the transport equations describing the
acceleration and propagation of Solar Energetic Particles (SEPs),
which is of practical importance, since the high energy SEPs produce
radiation hazards. The proposed scheme is demonstrated to be accurate
and efficient, which makes it applicable to global simulation systems
analyzing space weather.
Title: Embedded Kinetic Simulation of Ganymede's Magnetosphere:
Improvements and Inferences
Authors: Zhou, Hongyang; Tóth, Gábor; Jia, Xianzhe; Chen, Yuxi;
Markidis, Stefano
Bibcode: 2019JGRA..124.5441Z
Altcode:
The largest moon in the solar system, Ganymede, is also the only moon
known to possess a strong intrinsic magnetic field and a corresponding
magnetosphere. Using the new version of Hall magnetohydrodynamic
with embedded particle-in-cell model with a self-consistently coupled
resistive body representing the electrical properties of the moon's
interior, improved inner boundary conditions, and the flexibility of
coupling different grid geometries, we achieve better match of magnetic
field with measurements for all six Galileo flybys. The G2 flyby
comparisons of plasma bulk flow velocities with the Galileo Plasma
Subsystem data support the oxygen ion assumption inside Ganymede's
magnetosphere. Crescent shape, nongyrotropic, and nonisotropic ion
distributions are identified from the coupled model. Furthermore, we
have derived the energy fluxes associated with the upstream magnetopause
reconnection of ∼10-7W/cm2 based on our model
results and found a maximum of 40% contribution to the total peak
auroral emissions.
Title: Global MHD simulations of the Response of Jupiter's
Magnetosphere and Ionosphere to Changes in the Solar Wind and IMF
Authors: Sarkango, Yash; Jia, Xianzhe; Toth, Gabor
Bibcode: 2019JGRA..124.5317S
Altcode:
We have developed a new global magnetohydrodynamic (MHD) model for
Jupiter's magnetosphere based on the BATSRUS code and an ionospheric
electrodynamics solver. Our model includes the Io plasma torus at
its appropriate location and couples the global magnetosphere with
the planetary ionosphere through field-aligned currents. Through
comparisons with available particle and field observations as well
as empirical models, we show that the model captures the overall
configuration of the magnetosphere reasonably well. In order to
understand how the magnetosphere responds to different solar wind
drivers, we have carried out time-dependent simulations using various
kinds of upstream conditions, such as a forward shock and a rotation
in the interplanetary magnetic field (IMF). Our model predicts that
compression of the magnetosphere by a forward shock of typical strength
generally weakens the corotation enforcement currents on the dayside
and produces an enhancement on the nightside. However, the global
response varies depending on the IMF orientation. A forward shock
with a typical Parker-spiral IMF configuration has a larger impact
on the magnetospheric configuration and large-scale current systems
than with a parallel IMF configuration. Plasmoids are found to form
in the simulation due to tail reconnection and have complex magnetic
topology, as they evolve and propagate down tail. For a fixed mass
input rate in the Io plasma torus, the frequency of plasmoid occurrence
in our simulation is found to vary depending on the upstream solar
wind driving.
Title: SPECTRUM: Synthetic Spectral Calculations for Global Space
Plasma Modeling
Authors: Szente, J.; Landi, E.; Manchester, W. B., IV; Toth, G.;
van der Holst, B.; Gombosi, T. I.
Bibcode: 2019ApJS..242....1S
Altcode:
High-resolution spectroscopy is the most accurate tool for measuring
the properties of the solar corona. However, interpreting measured
line intensities and line profiles emitted by the optically thin solar
corona is complicated by line-of-sight (LOS) integration, which leads to
measuring weighted averages of the plasma properties along the LOS. LOS
integration effects can be removed by combining CHIANTI spectral
emissivities with a 3D global model of the solar corona to calculate
the contribution of all structures along the LOS to the measured
intensities. In this paper, we describe SPECTRUM, a postprocessing tool
that can calculate the emission from the optically thin solar corona
by combining 3D magnetohydrodynamic (MHD) space plasma simulation
results with the CHIANTI database. Doppler-shifted, nonthermal line
broadening due to low-frequency Alfvén waves and anisotropic proton
and isotropic electron temperatures can be individually taken into
account during calculations. Synthetic spectral calculations can then
be used for model validation, for interpretation of solar observations,
and for forward modeling purposes. SPECTRUM is implemented within the
Space Weather Modeling Framework (SWMF) and is therefore publicly
available. In this paper, we describe the SPECTRUM module and show
its applications by comparing synthetic spectra using simulation data
by the 3D MHD Alfvén Wave Solar Model with observations done by the
Hinode/Extreme-ultraviolet Imaging Spectrometer during Carrington
rotations 2063 and 2082.
Title: MESSENGER observations and global simulations of highly
compressed magnetosphere events at Mercury
Authors: Jia, Xianzhe; Slavin, James; Poh, Gangkai; DiBraccio, Gina;
Toth, Gabor; Chen, Yuxi; Raines, Jim; Gombosi, Tamas
Bibcode: 2019EGUGA..2111922J
Altcode:
We identify and examine all MESSENGER crossings of Mercury's dayside
magnetopause with magnetospheric field intensities >= 300 nT. The 8
such events, which occurred under highly compressed magnetosphere (HCM)
conditions, are analyzed in the identical manner utilized by Slavin et
al. (2014). The results suggest that the 8 HCM events represent the
highest solar wind dynamic pressures for which the MESSENGER's orbit
still passed below the magnetopause and provided measurements of the
dayside magnetosphere. Using the magnetohydrodynamic model by Jia et
al. (2015) that electromagnetically couples Mercury's interior with
its magnetosphere, a series of global simulations are conducted to
quantitatively characterize the response of Mercury's magnetosphere
to solar wind forcing. Combining the MESSENGER observations with the
simulations, we have obtained a consistent picture of how Mercury's
dayside magnetospheric configuration is controlled, separately and in
combination, by induction-driven shielding and reconnection-driven
erosion. For solar wind pressures of ∼ 40-90 nPa, compared with
the average ∼ 10-15 nPa at Mercury's orbit, the shielding events of
induction in Mercury's core in standing-off the solar wind typically
exceeds the erosion of the dayside magnetosphere due to reconnection
for these events, most of which occurred under low magnetic shear
conditions. For high magnetic shear across the magnetopause our
simulation predicts that reconnection would dominate. Mercury's
effective magnetic moment as inferred from magnetopause stand-off
distance ranges from 170 to 250 nT-RM3 for these events. These findings,
presented in Jia et al. (2019, JGR), are of crucial importance for
understanding the space weathering at Mercury and its contribution to
the generation of Mercury's exosphere.
Title: The Surface Distributions of the Production of the Major
Volatile Species, H2O, CO2, CO and O2, from the Nucleus of Comet
67P/Churyumov-Gerasimenko throughout the Rosetta Mission
Authors: Combi, Michael; Shou, Yinsi; Fougere, Nicolas; Altwegg,
Kathrin; Rubin, Martin; Bocklee-Morvan, Dominique; Gombosi, Tamas;
Hansen, Kenneth C.; Huang, Zhenguang; Toth, Gabor; Tenishev, Valeriy
Bibcode: 2019EGUGA..2118635C
Altcode:
The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis
(ROSINA) suite of instruments operated throughout the just over two
years of the Rosetta mission operations in the vicinity of comet
67P/Churyumov-Gerasimenko. It measured gas densities and composition
throughout the comet's atmosphere, or coma. Here we present two-years'
worth of measurements of the four major volatile species in the coma
of the comet, H2O, CO2, CO and O2, by one of the ROSINA sub-systems
called the Double Focusing Mass Spectrometer (DFMS). DFMS is a very high
mass resolution and high sensitivity mass spectrometer able to resolve
at a tiny fraction of an atomic mass unit. We have analyzed the DFMS
measurements using an inversion scheme based on spherical harmonics
that solves for the distribution of potential surface activity of
each species as the comet rotates, changing solar illumination, over
short time intervals and as the comet changes distance from the sun
and orientation of its spin axis over long time intervals. We also
use the surface boundary conditions derived from the inversion scheme
to simulate the whole coma with our fully kinetic Direct Simulation
Monte Carlo model and calculate the production rates of the four major
species throughout the mission. We compare the derived production rates
with remote sensing observations by the Visible and Infrared Thermal
Imaging Spectrometer (VIRTIS) as well as with published observations
from the Microwave Instrument for the Rosetta Orbiter (MIRO). Finally
we use the variation of the surface production of the major species to
calculate the total mass loss distribution over the surface throughout
the mission.
Title: A Predicted Small and Round Heliosphere
Authors: Opher, Merav; Loeb, Abraham; Drake, James; Toth, Gabor
Bibcode: 2019EGUGA..2111837O
Altcode:
The shape of the solar wind bubble within the interstellar medium, the
so-called heliosphere, has been explored over six decades (Davis 55;
Parker '61; Axford '72; Baranov & Malama '93). As the Sun moves
through the surrounding partially-ionized medium, neutral hydrogen
atoms penetrate the heliosphere, and through charge-exchange with
the supersonic solar wind, create a population of hot pick-up ions
(PUIs). The Voyager 2 (V2) data demonstrated that the heliosheath
pressure is dominated by PUIs. Here we use a novel magnetohydrodynamic
model that treats the PUIs as a separate fluid from the thermal
component of the solar wind. Unlike previous models, the new model
reproduces the properties of the PUIs and solar wind ions based on
the New Horizon (McComas et al. 2017) and V2 (Richardson et al. 2008)
spacecraft observations. The model significantly changes the energy
flow in the outer heliosphere, leading to a smaller and rounder shape
than previously predicted, in agreement with energetic neutral atom
observations by the Cassini spacecraft (Dialynas et al. 2017). We
will discuss the consequences of this new shape for draping of the
interstellar magnetic field and conditions at Voyager 1 and 2 in the
local interstellar medium.
Title: Validating the Alfven Wave Solar Model (AWSoM) from the lower
corona to 1 AU
Authors: Sachdeva, Nishtha; Manchester, Ward; van der Holst, Bart;
Toth, Gabor; Vasquez, Alberto; Jackson, Bernard; Lloveras, Diego G.;
Mac Cormack, Cecilia; Yu, Hsiu-Shan
Bibcode: 2019EGUGA..21.1465S
Altcode:
We examine the steady state three-dimensional MHD simulations of the
solar corona carried out with the new version of the Alfven Wave Solar
Model (AWSoM) within the Space Weather Modeling framework (SWMF). AWSoM
addresses the acceleration and heating of the solar corona via the
interaction between counter-propagating Alfven waves. This non-linear
interaction between the outward propagating low-frequency Alfven waves
and those partially reflected by the speed gradients results in a
turbulent energy cascade. The model uses physics-based partitioning
of wave-dissipated heat between isotropic electron and anisotropic
proton temperatures. To validate the AWSoM model, we select rotations
representative of the solar minimum and maximum conditions and compare
our simulation results with a comprehensive suite of observations. We
use three-dimensional tomographic reconstructions of the electron
temperature and density in the inner corona (r < 1.25 Rsun) based
on multi-wavelength extreme ultraviolet images from STEREO/EUVI
and SDO/AIA. For comparison with observations made near the Earth,
we compare the model with OMNI data. At different radial distances
between 20 Rsun and 1 AU, we compare the model with reconstructions
made with Interplanetary Scintillation (IPS) observations. Observations
are compared with the simulated model results of plasma mass density,
velocity, and magnetic fields, temperature anisotropy, and wave
turbulence. Our results at solar minimum show that the improved AWSoM
model performs well in agreement with the observations between inner
corona and 1 AU. In the lower corona the model and the tomographic
reconstructions match within a 20 % accuracy. Near the Earth, our model
shows good agreement with observations of solar wind velocity, electron
temperature and magnetic field. However, the electron density at 1 AU
is overpredicted by the model for the solar minimum simulations. While
this model version is already an improvement over previous predictions,
we plan to validate our model using more Carrington rotations. The AWSoM
model presents an extensive application to study the solar corona and
larger heliosphere in concert with current and future solar missions.
Title: Five-moment Two-Electron Plasma Simulation for Comet
67P/Churyumov-Gerasimenko
Authors: Huang, Zhenguang; Toth, Gabor; Gombosi, Tamas; Jia, Xianzhe;
Combi, Michael; Hansen, Kenneth; Shou, Yinsi; Tenishev, Valeriy;
Altwegg, Kathrin.; Rubin, Martin
Bibcode: 2019EGUGA..2118127H
Altcode:
One of the key investigations of the Rosetta mission is to understand
the interactions between the solar wind and the cometary magnetosphere
of comet 67P/Churyumov-Gerasimenko (CG). Extensive numerical
modeling work based on fluid, hybrid and fully kinetic models have
been carried out and provided valuable context for interpreting
various features of the cometary environment observed by different
instruments. Fluid-type models have proven to be a useful tool for
investigating how the solar wind interacts with comets on a global
scale. However, in previous fluid models (e.g., MHD models), electrons
are either treated as part of the plasma fluid or simulated with an
additional electron pressure equation, without having their own the
continuity and momentum equations. Such an approach cannot represent
any of the electron kinetic features properly. Besides, previous MHD
models could not simulate multiple electron fluids. In this study, we
present the first five-moment two-electron plasma simulation of a comet,
by introducing the continuity and momentum equations respectively for
the solar wind and cometary electrons, in which case the Hall effect
is included automatically and the electron dynamics and resulting
electric field are simulated self-consistently. As will be shown in
this presentation, our five-moment two-electron simulation captures
the separate bulk motions of the solar wind electrons and the cometary
electrons, which is consistent with the results of the Particle-In-Cell
(PIC) simulation performed by Deca et al. (2017).
Title: End-of-Mission ROSINA/COPS observation of the innermost coma
of comet 67P/Churyumov-Gerasimenko
Authors: Tenishev, Valeriy; Rubin, Martin; Tzou, Chia-yu; Shi, Xian;
Combi, Michael; Altwegg, Kathrin; Gombosi, Tamas; Shou, Yinsi; Huang,
Zhenquang; Toth, Gabor; Sierks, Holger; Hofstadter, Mark
Bibcode: 2019EGUGA..2118885T
Altcode:
End-of-mission pressure measurements performed with ROSINA/COPS
presented a unique chance to probe the coma of 67P/Churyumov-Gerasimenko
in the altitude range starting from tens of kilometers down to
the surface of the nucleus of the comet. That is an unprecedented
opportunity to uncover effects that topology and activity of the nucleus
have on the structure of the coma very close to the nucleus. The primary
focus of the presented study is analyzing these measurements using the
numerical modeling of the comet environment. At the end of the Rosetta
mission, 67P/Churyumov-Gerasimenko was at a heliocentric distance of 3.8
AU where the coma is collisionless. That makes it possible to apply the
Liouville theorem to characterize the distribution of volatiles in the
coma, as we have done in our analysis. We have used the SHAP7 nucleus
model to account for the topology of the volatile source. Spacecraft
trajectory and the instrument pointing relative to the comet's nucleus
have been determined with the SPICE library. Here, we present the
results of our analysis and discuss the effects of the surface topology
and that of the local surface volatile injection on the distribution
of gas in the innermost coma of comet 67P/Churyumov-Gerasimenko.
Title: The Formation and Evolution of Large Scale Magnetic Fields
in Venus Ionosphere
Authors: Ma, Y. J.; Toth, G.; Nagy, A. F.; Russell, C. T.
Bibcode: 2019LPI....50.2903M
Altcode:
In this study, we use a multi-species MHD model to understand the
formation and evolution of large scale magnetic fields in Venus
ionosphere.
Title: MESSENGER Observations and Global Simulations of Highly
Compressed Magnetosphere Events at Mercury
Authors: Jia, Xianzhe; Slavin, James A.; Poh, Gangkai; DiBraccio,
Gina A.; Toth, Gabor; Chen, Yuxi; Raines, Jim M.; Gombosi, Tamas I.
Bibcode: 2019JGRA..124..229J
Altcode:
We identify and examine all MErcury Surface Space ENvironment,
GEochemistry, and Ranging (MESSENGER) crossings of Mercury's
dayside magnetopause with magnetospheric field intensities
≥300 nT. The eight such events, which occurred under
highly compressed magnetosphere conditions, are analyzed
in the identical manner utilized by Slavin et al. (2014, https://doi.org/10.1002/2014JA020319).
The results suggest that the eight highly compressed magnetosphere
events represent the highest solar wind dynamic pressures for
which the MESSENGER's orbit still passed below the magnetopause
and provided measurements of the dayside magnetosphere. Using
the magnetohydrodynamic model by Jia et al. (2015, https://doi.org/10.1002/2015JA021143)
that electromagnetically couples Mercury's interior with its
magnetosphere, a series of global simulations are conducted to
quantitatively characterize the response of Mercury's magnetosphere
to solar wind forcing. Combining the MESSENGER observations with the
simulations, we have obtained a consistent picture of how Mercury's
dayside magnetospheric configuration is controlled, separately and
in combination, by induction-driven shielding and reconnection-driven
erosion. For solar wind pressures of ∼40-90 nPa, compared with the
average ∼10-15 nPa at Mercury's orbit, the shielding effects of
induction in Mercury's core in standing-off the solar wind typically
exceed the erosion of the dayside magnetosphere due to reconnection
for these events, most of which occurred under low magnetic shear
conditions. For high magnetic shear across the magnetopause our
simulation predicts that reconnection would dominate. Mercury's
effective magnetic moment as inferred from magnetopause standoff
distance ranges from 170 to 250 nT-RM3 for these events. These findings
are of crucial importance for understanding the space weathering at
Mercury and its contribution to the generation of Mercury's exosphere.
Title: Soft X-ray Emission Scenarios of Comet 46P/Wirtanen for its
2018 Apparition in Accordance with HXMT Observation
Authors: Lai, I. L.; Huo, Z. X.; Huang, P. S.; Rubin, M.; Gombosi,
T. I.; Toth, G.; Ip, W. H.
Bibcode: 2018AGUFM.P23G3514L
Altcode: 2018AGUFM.P23G3514R
Comet 46P/Wirtanen was the original destination of the Rosetta mission
but replaced by Comet 67P/Churyumov-Gerasimenko soon after the launch
delay in 2003. As a result, the research work about Comet 46P has been
very limited over the past decade. In this December, 46P will reach
its perihelion ( 1.05 AU) making a very close approach to Earth with
the comet-earth distance about 30 times of earth-moon distance. It is
predicted to reach naked-eye brightness around this great apparition
due to its hyperactivity, which provides an excellent opportunity to
study it in detail. The Insight-HXMT (Hard X-ray Modulation Telescope)
is the first Chinese X-ray astronomy satellite and will be used to
observe as a target of opportunity. Models and simulation works of the
X-ray emission of 46P as a result of solar-wind interaction during the
close approach phase to be presented in this work would greatly assist
the design of the HXMT observations and subsequent data analysis. The
observational procedure and data processing pipeline established also
will be invaluable for future mission opportunities.
Title: Impact of the September 2017 Solar Flare and ICME Events
on Mars
Authors: Ma, Y.; Fang, X.; Pawlowski, D. J.; Halekas, J. S.; Russell,
C. T.; Luhmann, J. G.; Xu, S.; Lillis, R. J.; Thiemann, E.; Bougher,
S. W.; Toth, G.; Nagy, A. F.; Dong, C.; Espley, J. R.; Jakosky, B. M.;
Lee, C. O.
Bibcode: 2018AGUFM.P51H2970M
Altcode:
The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observed
a strong X-class solar flare impacting Mars on 10 September 2017,
followed by a fast interplanetary coronal mass ejection (ICME). These
solar events provide a great opportunity to advance our understanding of
space weather events and their impact on Mars. In this study, the impact
of the solar flare and ICME events on the Martian system is examined in
detail using a sophisticated multi-species global MHD model. We found
that the main features of the interaction can be reasonably captured by
the model for both the solar flare and the ICME events. The results of
the MHD model coupled with Mars Global Ionosphere-Thermosphere Model
(MGITM) reproduce the density enhancement caused by the solar flare,
consistent with MAVEN observations. Using derived solar wind proxy,
our time-dependent run of the ICME event is able to reproduce some
detailed structures observed by MAVEN. Our calculations show that the
solar flare has an important impact on the ionosphere and the upper
atmosphere, but has little effect at the solar wind-Mars interaction. In
contrast, the ICME greatly disturbs the plasma enviorment of Mars,
especially the induced magnetosphere. The ICME-driven distrubances
include variations of various plasma boundaries and large enhancement
of atmospheric erosion.
Title: Global dipole magnetic field: Boon or bane for the Martian
atmospheric retention?
Authors: Dong, C.; Luhmann, J. G.; Ma, Y.; Lingam, M.; Bhattacharjee,
A.; Lee, Y.; Bougher, S. W.; Wang, L.; Glocer, A.; Strangeway, R. J.;
Curry, S.; Fang, X.; Toth, G.; Nagy, A. F.; Lillis, R. J.; Mitchell,
D. L.; Brain, D.; Jakosky, B. M.
Bibcode: 2018AGUFM.P31C3736D
Altcode:
The absence of global dipole magnetic fields at terrestrial planets
is widely perceived as a major impediment in protecting planetary
atmospheres from being eroded by stellar winds. In this work,
we re-examine this idea by focusing on the rate of atmospheric
ion escape from Mars for nominal solar wind parameters and an
extreme ``Carrington-type'' space weather event. We carry out
extensive numerical simulations using a sophisticated multi-fluid
magnetohydrodynamics (MHD) model, thereby demonstrating that the escape
rate is a non-monotonic function of the Martian dipole magnetic field
strength, and that it varies by more than an order of magnitude in
certain instances. Our work illustrates, for the very first time using
the state-of-the-art global simulations, that the lack of dipole fields
is not necessarily a disadvantage from the viewpoint of atmospheric
losses. We are led to the conclusion that the ion escape rates from
Mars may have actually been higher when it possessed stronger magnetic
moment in the past. We conclude our analysis by briefly exploring the
ensuing implications for Martian and exoplanetary habitability.
Title: Loss of the Martian atmosphere to space: Present-day loss rates
determined from MAVEN observations and integrated loss through time
Authors: Jakosky, B. M.; Brain, D.; Chaffin, M.; Curry, S.; Deighan,
J.; Grebowsky, J.; Halekas, J.; Leblanc, F.; Lillis, R.; Luhmann,
J. G.; Andersson, L.; Andre, N.; Andrews, D.; Baird, D.; Baker, D.;
Bell, J.; Benna, M.; Bhattacharyya, D.; Bougher, S.; Bowers, C.;
Chamberlin, P.; Chaufray, J. -Y.; Clarke, J.; Collinson, G.; Combi,
M.; Connerney, J.; Connour, K.; Correira, J.; Crabb, K.; Crary, F.;
Cravens, T.; Crismani, M.; Delory, G.; Dewey, R.; DiBraccio, G.; Dong,
C.; Dong, Y.; Dunn, P.; Egan, H.; Elrod, M.; England, S.; Eparvier, F.;
Ergun, R.; Eriksson, A.; Esman, T.; Espley, J.; Evans, S.; Fallows,
K.; Fang, X.; Fillingim, M.; Flynn, C.; Fogle, A.; Fowler, C.; Fox,
J.; Fujimoto, M.; Garnier, P.; Girazian, Z.; Groeller, H.; Gruesbeck,
J.; Hamil, O.; Hanley, K. G.; Hara, T.; Harada, Y.; Hermann, J.;
Holmberg, M.; Holsclaw, G.; Houston, S.; Inui, S.; Jain, S.; Jolitz,
R.; Kotova, A.; Kuroda, T.; Larson, D.; Lee, Y.; Lee, C.; Lefevre,
F.; Lentz, C.; Lo, D.; Lugo, R.; Ma, Y. -J.; Mahaffy, P.; Marquette,
M. L.; Matsumoto, Y.; Mayyasi, M.; Mazelle, C.; McClintock, W.;
McFadden, J.; Medvedev, A.; Mendillo, M.; Meziane, K.; Milby, Z.;
Mitchell, D.; Modolo, R.; Montmessin, F.; Nagy, A.; Nakagawa, H.;
Narvaez, C.; Olsen, K.; Pawlowski, D.; Peterson, W.; Rahmati, A.;
Roeten, K.; Romanelli, N.; Ruhunusiri, S.; Russell, C.; Sakai, S.;
Schneider, N.; Seki, K.; Sharrar, R.; Shaver, S.; Siskind, D. E.;
Slipski, M.; Soobiah, Y.; Steckiewicz, M.; Stevens, M. H.; Stewart,
I.; Stiepen, A.; Stone, S.; Tenishev, V.; Terada, N.; Terada, K.;
Thiemann, E.; Tolson, R.; Toth, G.; Trovato, J.; Vogt, M.; Weber,
T.; Withers, P.; Xu, S.; Yelle, R.; Yiğit, E.; Zurek, R.
Bibcode: 2018Icar..315..146J
Altcode:
Observations of the Mars upper atmosphere made from the Mars Atmosphere
and Volatile Evolution (MAVEN) spacecraft have been used to determine
the loss rates of gas from the upper atmosphere to space for a complete
Mars year (16 Nov 2014 - 3 Oct 2016). Loss rates for H and O are
sufficient to remove ∼2-3 kg/s to space. By itself, this loss would
be significant over the history of the planet. In addition, loss rates
would have been greater early in history due to the enhanced solar
EUV and more-active Sun. Integrated loss, based on current processes
whose escape rates in the past are adjusted according to expected
solar evolution, would have been as much as 0.8 bar CO2
or 23 m global equivalent layer of H2O; these losses are
likely to be lower limits due to the nature of the extrapolation of
loss rates to the earliest times. Combined with the lack of surface
or subsurface reservoirs for CO2 that could hold remnants
of an early, thick atmosphere, these results suggest that loss of
gas to space has been the dominant process responsible for changing
the climate of Mars from an early, warmer environment to the cold,
dry one that we see today.
Title: Specification of the near-Earth space environment with SHIELDS
Authors: Jordanova, V. K.; Delzanno, G. L.; Henderson, M. G.; Godinez,
H. C.; Jeffery, C. A.; Lawrence, E. C.; Morley, S. K.; Moulton,
J. D.; Vernon, L. J.; Woodroffe, J. R.; Brito, T. V.; Engel, M. A.;
Meierbachtol, C. S.; Svyatsky, D.; Yu, Y.; Tóth, G.; Welling, D. T.;
Chen, Y.; Haiducek, J.; Markidis, S.; Albert, J. M.; Birn, J.; Denton,
M. H.; Horne, R. B.
Bibcode: 2018JASTP.177..148J
Altcode:
Predicting variations in the near-Earth space environment that can lead
to spacecraft damage and failure is one example of "space weather" and
a big space physics challenge. A project recently funded through the
Los Alamos National Laboratory (LANL) Directed Research and Development
(LDRD) program aims at developing a new capability to understand, model,
and predict Space Hazards Induced near Earth by Large Dynamic Storms,
the SHIELDS framework. The project goals are to understand the dynamics
of the surface charging environment (SCE), the hot (keV) electrons
representing the source and seed populations for the radiation belts,
on both macro- and micro-scale. Important physics questions related
to particle injection and acceleration associated with magnetospheric
storms and substorms, as well as plasma waves, are investigated. These
challenging problems are addressed using a team of world-class experts
in the fields of space science and computational plasma physics, and
state-of-the-art models and computational facilities. A full two-way
coupling of physics-based models across multiple scales, including
a global MHD (BATS-R-US) embedding a particle-in-cell (iPIC3D)
and an inner magnetosphere (RAM-SCB) codes, is achieved. New data
assimilation techniques employing in situ satellite data are developed;
these provide an order of magnitude improvement in the accuracy in the
simulation of the SCE. SHIELDS also includes a post-processing tool
designed to calculate the surface charging for specific spacecraft
geometry using the Curvilinear Particle-In-Cell (CPIC) code that can
be used for reanalysis of satellite failures or for satellite design.
Title: Modeling Martian Atmospheric Losses over Time: Implications
for (Exo)Planetary Climate Evolution and Habitability
Authors: Dong, Chuanfei; Lee, Yuni; Ma, Yingjuan; Lingam, Manasvi;
Bougher, Stephen; Luhmann, Janet; Curry, Shannon; Toth, Gabor; Nagy,
Andrew; Tenishev, Valeriy; Fang, Xiaohua; Mitchell, David; Brain,
Dave; Jakosky, Bruce
Bibcode: 2018DPS....5030311D
Altcode:
Mars has always represented an important target from the standpoint
of planetary science, especially on account of its long-term climate
evolution. One of the most striking differences between ancient and
current Mars is that the former had a thicker atmosphere compared
to the present-day value, thereby making Noachian Mars potentially
more conducive to hosting life. This discrepancy immediately raises
the question of how and when the majority of the Martian atmosphere
was lost, as well as the channels through which it occurred. There
are compelling observational and theoretical reasons to believe that
the majority of atmospheric escape must have occurred early in the
planet's geological history, when the extreme ultraviolet (EUV) flux
and the solar wind from the Sun were much stronger than today. Our
understanding of present-day Martian atmospheric escape has improved
greatly thanks to observations undertaken by, e.g., the MAVEN in
conjunction with detailed theoretical modeling. In this study, we
adopted the one-way coupled framework, which has been employed to study
the ion and photochemical losses at the current epoch. We adopted the
3-D Mars thermosphere from the Mars Global Ionosphere Thermosphere Model
(M-GITM) and the hot atomic oxygen density from the Mars exosphere Monte
Carlo model Adaptive Mesh Particle Simulator (AMPS) as the input for
the 3-D BATS-RUS Mars multi-fluid MHD (MF-MHD) model. The Mars AMPS hot
oxygen corona and the associated photochemical loss rate were calculated
based on the thermospheric/ionospheric background from M-GITM. Our
simulations indicate that the total photochemical and ion atmospheric
losses over the span 0-4 Ga are approximately equal to each other, and
their sum amounts to 0.1 bar being lost over this duration. If we assume
that the oxygen lost through a combination of ion and photochemical
escape mechanisms was originally derived from surface water, we find
3.8 × 10^17 kg of water has been lost from Mars between 0 and 4 Ga;
this mass corresponds to a global surface depth of 2.6 m. This study
offers fresh insights concerning the long-term climate evolution and
habitability of the increasing number of exoplanets discovered yearly
due to atmospheric losses.
Title: Integration of RAM-SCB into the Space Weather Modeling
Framework
Authors: Welling, Daniel T.; Toth, Gabor; Jordanova, Vania K.;
Yu, Yiqun
Bibcode: 2018JASTP.177..160W
Altcode:
Numerical simulations of the ring current are a challenging
endeavor. They require a large set of inputs, including electric and
magnetic fields and plasma sheet fluxes. Because the ring current
broadly affects the magnetosphere-ionosphere system, the input set is
dependent on the ring current region itself. This makes obtaining a set
of inputs that are self-consistent with the ring current difficult. To
overcome this challenge, researchers have begun coupling ring current
models to global models of the magnetosphere-ionosphere system. This
paper describes the coupling between the Ring current Atmosphere
interaction Model with Self-Consistent Magnetic field (RAM-SCB)
to the models within the Space Weather Modeling Framework. Full
details on both previously introduced and new coupling mechanisms are
defined. The impact of self-consistently including the ring current
on the magnetosphere-ionosphere system is illustrated via a set of
example simulations.
Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth
System
Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan;
Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao,
Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa,
Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale;
Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland,
Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander;
Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens,
Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent;
Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet,
Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth,
Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha
Bibcode: 2018arXiv181008728N
Altcode:
The authors of this report met on 28-30 March 2018 at the New Jersey
Institute of Technology, Newark, New Jersey, for a 3-day workshop
that brought together a group of data providers, expert modelers, and
computer and data scientists, in the solar discipline. Their objective
was to identify challenges in the path towards building an effective
framework to achieve transformative advances in the understanding
and forecasting of the Sun-Earth system from the upper convection
zone of the Sun to the Earth's magnetosphere. The workshop aimed to
develop a research roadmap that targets the scientific challenge
of coupling observations and modeling with emerging data-science
research to extract knowledge from the large volumes of data (observed
and simulated) while stimulating computer science with new research
applications. The desire among the attendees was to promote future
trans-disciplinary collaborations and identify areas of convergence
across disciplines. The workshop combined a set of plenary sessions
featuring invited introductory talks and workshop progress reports,
interleaved with a set of breakout sessions focused on specific topics
of interest. Each breakout group generated short documents, listing
the challenges identified during their discussions in addition to
possible ways of attacking them collectively. These documents were
combined into this report-wherein a list of prioritized activities
have been collated, shared and endorsed.
Title: Noether currents for the Teukolsky master equation
Authors: Tóth, Gábor Zsolt
Bibcode: 2018CQGra..35r5009T
Altcode: 2018arXiv180104710T
Conserved currents associated with the time translation and axial
symmetries of the Kerr spacetime and with scaling symmetry are
constructed for the Teukolsky master equation (TME). Three partly
different approaches are taken, of which the third one applies
only to the spacetime symmetries. The results yielded by the three
approaches, which correspond to three variants of Noether’s theorem,
are essentially the same, nevertheless. The construction includes
the embedding of the TME into a larger system of equations, which
admits a Lagrangian and turns out to consist of two TMEs with opposite
spin weight. The currents thus involve two independent solutions of
the TME with opposite spin weights. The first approach provides an
example of the application of an extension of Noether’s theorem to
nonvariational differential equations. This extension is also reviewed
in general form. The variant of Noether’s theorem applied in the
third approach is a generalization of the standard construction of
conserved currents associated with spacetime symmetries in general
relativity, in which the currents are obtained by the contraction
of the symmetric energy-momentum tensor with the relevant Killing
vector fields. Symmetries and conserved currents related to boundary
conditions are introduced as well, and Noether’s theorem and
its variant for nonvariational differential equations are extended
to them. The extension of the latter variant is used to construct
conserved currents related to the Sommerfeld boundary condition.
Title: Modeling Martian Atmospheric Losses Over Time: Implications
for (Exo)Planetary Climate Evolution and Habitability
Authors: Dong, C. F.; Lee, Y.; Ma, Y. J.; Lingam, M.; Bougher, S. W.;
Luhmann, J. G.; Curry, S. M.; Toth, G.; Nagy, A. F.; Tenishev, V.;
Fang, X.; Mitchell, D. L.; Brain, D. A.; Jakosky, B. M.
Bibcode: 2018LPICo2065.2052D
Altcode:
We make use of the one-way coupled framework (linking our GCM, DSMC,
and MHD models), known to accurately reproduce MAVEN observations,
for studying the atmospheric ion and photochemical escape rates and
climate evolution over the history of Mars.
Title: Solar Wind Interaction With the Martian Upper Atmosphere:
Roles of the Cold Thermosphere and Hot Oxygen Corona
Authors: Dong, Chuanfei; Bougher, Stephen W.; Ma, Yingjuan; Lee,
Yuni; Toth, Gabor; Nagy, Andrew F.; Fang, Xiaohua; Luhmann, Janet;
Liemohn, Michael W.; Halekas, Jasper S.; Tenishev, Valeriy; Pawlowski,
David J.; Combi, Michael R.
Bibcode: 2018JGRA..123.6639D
Altcode: 2018arXiv180400937D
We study roles of the thermosphere and exosphere on the Martian
ionospheric structure and ion escape rates in the process of the
solar wind-Mars interaction. We employ a four-species multifluid
magnetohydrodynamic model to simulate the Martian ionosphere
and magnetosphere. The cold thermosphere background is taken
from the Mars Global Ionosphere Thermosphere Model, and the hot
oxygen exosphere is adopted from the Mars exosphere Monte Carlo
model—Adaptive Mesh Particle Simulator. A total of four cases with
the combination of 1-D (globally averaged) and 3-D thermospheres
and exospheres are studied. The ion escape rates calculated by
adopting 1-D and 3-D atmospheres are similar; however, the latter
are required to adequately reproduce the ionospheric observations by
the Mars Atmosphere and Volatile EvolutioN mission. In addition, our
simulations show that the 3-D hot oxygen corona plays an important role
in preventing planetary molecular ions (O<mrow></mrow>2+
and CO<mrow></mrow>2+) escaping from Mars, mainly resulting
from the mass loading of the high-altitude exospheric O+
ions. The cold thermospheric oxygen atom, however, is demonstrated to
be the primary neutral source for O+ ion escape during the
relatively weak solar cycle 24.
Title: A Predicted Small and Round Heliosphere
Authors: Opher, Merav; Loeb, Abraham; Drake, James; Toth, Gabor
Bibcode: 2018arXiv180806611O
Altcode:
The shape of the solar wind bubble within the interstellar medium,
the so-called heliosphere, has been explored over six decades. As the
Sun moves through the surrounding partially-ionized medium, neutral
hydrogen atoms penetrate the heliosphere, and through charge-exchange
with the supersonic solar wind, create a population of hot pick-up
ions (PUIs). The Termination Shock (TS) crossing by Voyager 2 (V2)
data demonstrated that the heliosheath (HS) (the region of shocked
solar wind) pressure is dominated by suprathermal particles. Here we
use a novel magnetohydrodynamic model that treats the freshly ionized
PUIs as a separate fluid from the thermal component of the solar
wind. Unlike previous models, the new model reproduces the properties of
the PUIs and solar wind ions based on the New Horizon and V2 spacecraft
observations. The PUIs charge exchange with the cold neutral H atoms of
the ISM in the HS and are quickly depleted. The depletion of PUIs cools
the heliosphere downstream of the TS, "deflating" it and leading to a
narrower HS and a smaller and rounder shape, in agreement with energetic
neutral atom observations by the Cassini spacecraft. The new model, with
interstellar magnetic field orientation constrained by the IBEX ribbon,
reproduces the magnetic field data outside the HP at Voyager 1(V1). We
present the predictions for the magnetic field outside the HP at V2.
Title: The Impact and Solar Wind Proxy of the 2017 September ICME
Event at Mars
Authors: Ma, Yingjuan; Fang, Xiaohua; Halekas, Jasper S.; Xu, Shaosui;
Russell, Christopher T.; Luhmann, Janet G.; Nagy, Andrew F.; Toth,
Gabor; Lee, Christina O.; Dong, Chuanfei; Espley, Jared R.; McFadden,
James P.; Mitchell, David L.; Jakosky, Bruce M.
Bibcode: 2018GeoRL..45.7248M
Altcode:
We study a large interplanetary coronal mass ejection event impacting
Mars in mid-September 2017 numerically. During this time period,
MAVEN remained inside the Martian bow shock and therefore could not
measure the solar wind directly. We first simulate the event using three
steady state cases with estimated solar wind conditions and find that
these cases were able to reproduce the general features observed by
MAVEN. However, these time-stationary runs cannot capture the response
of the system to large variations in the solar wind associated with
the event. To address this problem, we derive a solar wind proxy based
on MAVEN observations in the sheath region and their comparison with
steady state magnetohydrodynamic model results. The derived solar
wind proxy is then used to drive a time-dependent magnetohydrodynamic
model, and we find that the data-model comparison is greatly improved,
especially in the magnetosheath. We are able to reproduce some detailed
structures observed by MAVEN during the period, despite the lack of a
direct measurement of the solar wind, indicating that the derived solar
wind conditions are reliable. Finally, we examine in detail the impact
of the event on the Martian system: including variations of the three
typical plasma boundaries and the ion loss rates. Our results show that
these plasma boundary locations varied drastically during the event, and
the total ion loss rate was enhanced by more than an order of magnitude.
Title: The Astrosphere and Mass-Loss Ratio of Proxima Centauri
Authors: Opher, Merav; Toth, Gabor; Loeb, Abraham
Bibcode: 2018cosp...42E2514O
Altcode:
Our understanding about the heliosphere dramatically evolved from
the results from Voyager, Cassini and Interstellar Boundary Explorer
(IBEX). With the rapid discovery of exoplanets in other stellar systems
it is important to understand how this new acquired knowledge affects
the astrospheres around other stars. In particular, recently the shape
of the Heliosphere is being challenged by theoretical and observation
work (Opher et al. 2015; Diyalinas et al. 2017). The nearest star to the
Sun, Proxima Centauri, is particularly interesting as it was recently
discovered to host an Earth-size planet in its "habitable zone", Proxima
b. Here we investigate the astrosphere around Proxima Centauri. As the
star moves through the surrounding partially-ionized medium, neutral
hydrogen atoms penetrate the astrospheres and through charge-exchange
with the supersonic stellar wind creating a population of hot pick-up
ions (PUIs). We present global magnetohydrodynamic simulations that
treats the PUIs as a separate fluid. Most global models treat the PUI
and thermal component as a single fluid. Planetary atmospheres are
affected by particle fluxes from their host stars. The only means
by which coronal winds of Sun-like stars have ever been probed is
by the circumstellar H Lyman-alpha absorption fin the interaction
region between the wind and the interstellar medium, namely the
"astrospheres". The Lyman-alpha constrains on the stellar wind based
on Hubble Space Telescope measurements rely on prior hydrodynamical
models. Here we revisit the constraints on the mass-loss of Proxima
Centauri (Wood et al. 2011) with improved theoretical predictions and
discuss the implications for Space Weather effects on Proxima b.
Title: NOAA SWPC's Operational Geospace Model Performance during
Earth-Affecting Events
Authors: Cash, Michele; Singer, . Howard; Millward, George; Toth,
Gabor; Welling, Daniel; Balch, Christopher
Bibcode: 2018cosp...42E.524C
Altcode:
The Geospace model was first transitioned into real-time operations at
the NOAA Space Weather Prediction Center (SWPC) in October 2016 and
has been upgraded once since going operational. The Geospace model
is a part of the Space Weather Modeling Framework (SWMF) developed
at the University of Michigan, and the model simulates the full
time-dependent 3D Geospace environment (Earth's magnetosphere, ring
current and ionosphere) and predicts global and local space weather
parameters such as induced magnetic perturbations in space and on
Earth's surface. The current version of the Geospace model uses three
coupled components of SWMF: the BATS-R-US global magnetosphere model,
the Rice Convection Model (RCM) of the inner magnetosphere, and the
Ridley Ionosphere electrodynamics Model (RIM). In the operational mode,
SWMF/Geospace runs continually using real-time solar wind data from a
satellite at L1, either DSCOVR or ACE. We present an analysis of the
overall performance of the Geospace model during the Earth-affecting
events that occurred since the Geospace model went operational. We
also use past large Earth-affecting events to evaluate how well the
current operational version of the model would have performed during
enhanced storm periods.
Title: The effects of Pick-up Ions on the Shape of The Heliosphere
Authors: Opher, Merav; Toth, Gabor; Loeb, Abraham
Bibcode: 2018cosp...42E2513O
Altcode:
As the Sun moves through the surrounding partially-ionized medium,
neutrals hydrogen atom penetrate the heliosphere and through
charge-exchange with the supersonic solar wind create a population of
hot pick-up ions (PUIs). With the crossing of the termination shock by
Voyager 2 it became clear that the heliosheath pressure is dominated
by the PUIs while the bulk thermal solar wind is much colder. Recently
the shape of the Heliosphere is being challenged by theoretical and
observation work (Opher et al. 2015; Diyalinas et al. 2017). Previously
we had explored the effects of PUIs in the termination shock crossing
(Zieger et al. 2015). In this work, we explore the effects of PUIs on
the shape of the heliosphere. We present global magnetohydrodynamic
simulations that treats the PUIs a separate fluid. Most global models
treat the PUI and thermal component as a single fluid. We comment
on the effect of the global structure as well as the properties of
the heliosheath.
Title: Quantifying the access of Jupiter's magnetospheric plasma to
Europa's surface through a multi-fluid MHD model
Authors: Harris, Camilla; Toth, Gabor; Rubin, Martin; Jia, Xianzhe;
Slavin, A. James
Bibcode: 2018cosp...42E1383H
Altcode:
Europa's space environment is controlled by the wobbling of Jupiter's
magnetic field, the magnetic response to this wobbling induced in
the conducting subsurface ocean, and the interaction of Jupiter's
magnetosphere with Europa's ionosphere and extended exosphere. We have
developed a multi-fluid MHD model for Europa's plasma interaction which
self-consistently solves for the bulk properties of 3 ion fluids and
the electromagnetic fields in the vicinity of the moon. To validate our
model, we have simulated the Galileo E4 Flyby using the observed plasma
and magnetic field conditions. Our model has accurately reproduced
Galileo magnetometer observations along the flyby trajectory, and
provides full 3D density and velocity fields for O^+ and O_2^+ ionized
from Europa's neutral O_2 exosphere, and the thermal, corotating O^+
from Jupiter's magnetosphere. Based on the three-ion-fluid MHD model,
we have mapped the distribution of the magnetospheric plasma that was
able to penetrate the plasma interaction to reach Europa's surface. We
find that while the majority of downward flux impinges on the upstream
hemisphere, the surface impact by the ambient magnetospheric O^+ ions
exhibits a slight preference towards the anti-jovian hemisphere due to
the influence of the convectional electric field. Under the E4 flyby
conditions, we estimate that about 13% of the available upstream O^+
ions precipitate to Europa's surface. Most of the ambient plasma is
instead diverted around the moon due to the plasma interaction with the
ionosphere. This precipitation represents the contribution of thermal
plasma to the sputtering interaction with Europa's icy surface which
replenishes the O_2 exosphere.
Title: MHD Simulations of the Impact of the September 2017 Major
Solar Flare and ICME Events on Mars
Authors: Ma, Yingjuan; Luhmann, Janet G.; Russell, C. T.; Bougher,
Stephen; Nagy, Andrew; Toth, Gabor; Lee, Christina O.; Pawlowski,
David; Lillis, Robert; Fang, Xiaohua; Jakosky, Bruce; Halekas, Jasper;
Espley, Jared; Thiemann, Edward; Connerney, John; Xu, Shaosui; Dong,
Chuanfei
Bibcode: 2018cosp...42E2103M
Altcode:
We study the impact of the September 2017 extreme solar flare
and interplanetary coronal mass ejection events on Mars using a
sophisticated multi-species MHD model. The flare impact is examined by
coupling with the Mars Global Ionosphere-Thermosphere Model. A great
challenge of the study is that MAVEN was mostly inside the Martian
bow shock during the events, and thus no direct solar wind measurement
was available. To carry out reasonable simulations, we first simulate
the events using steady-state assumptions with rough solar wind
estimates. Although these simplistic time-stationary runs are able to
capture the general features observed by MAVEN, they cannot represent
the details of the large perturbations associated with the events. To
describe the time variation during the space weather events, we estimate
upstream solar wind conditions by fitting steady-state MHD model results
to MAVEN observations in the sheath region. The obtained solar wind
proxies are then used to drive a time-dependent MHD simulation. It is
found that the data-model comparison is greatly improved, especially
in the magnetosheath region. We are able to reproduce many detailed
structures observed by MAVEN during the period despite the fact
that no direct measurement of the solar wind is available. This
model-data agreement confirms the validity of the derived upstream
solar wind conditions. Using the time-dependent results, we examine
in detail the impact of the events on the Martian system, including
three plasma boundaries (Bow Shock, induced magnetosphere and ion
composition boundaries) and ion loss rates. It is found that these
plasma boundaries vary dramatically during the ICME and total planetary
ion loss rates are enhanced by more than an order of magnitude.
Title: Consequences of Treating the Solar Magnetic Field as a Dipole
on the Global Structure of the Heliosphere and Heliosheath
Authors: Michael, A. T.; Opher, M.; Tóth, G.
Bibcode: 2018ApJ...860..171M
Altcode:
We investigate the effect of including the heliospheric current sheet
on global modeling of the heliosphere. Due to inherent numerical
dissipation in the current handling of the heliospheric current sheet,
models have chosen to remove it to avoid numerical problems. We compare
a model where the polarity of the Parker spiral is the same in both
hemispheres (unipolar) to a dipole description of the solar magnetic
field, with the magnetic and rotational axes aligned forming a flat
heliospheric current sheet. The flat current sheet is pulled into the
northern hemisphere, which reduces the magnetic field strength at the
Voyager 1 trajectory over the last 22% of the heliosheath. The decrease
in magnetic field intensity is transferred into the thermal energy of
the plasma causing the dipole model to predict an entirely thermally
dominated heliosheath; this is a stark contrast to the magnetically
dominated region ahead of the heliopause in the unipole model. We
find that the two-lobe structure of the solar wind magnetic field
persists within the dipole model, with the flat current sheet not
able to fully erode the magnetic tension force. However, there is a
large amount of magnetic dissipation in the tail between the lobes,
which affects the structure of the plasma in the region. Furthermore,
the draped interstellar magnetic field in the dipole model is strongly
affected by reconnection at the nose of the heliosphere, yielding a
distinctly different draping pattern than that observed at Voyager 1.
Title: Reconnection in the Martian Magnetotail: Hall-MHD With Embedded
Particle-in-Cell Simulations
Authors: Ma, Yingjuan; Russell, Christopher T.; Toth, Gabor; Chen,
Yuxi; Nagy, Andrew F.; Harada, Yuki; McFadden, James; Halekas, Jasper
S.; Lillis, Rob; Connerney, John E. P.; Espley, Jared; DiBraccio, Gina
A.; Markidis, Stefano; Peng, Ivy Bo; Fang, Xiaohua; Jakosky, Bruce M.
Bibcode: 2018JGRA..123.3742M
Altcode:
Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observations show
clear evidence of the occurrence of the magnetic reconnection process in
the Martian plasma tail. In this study, we use sophisticated numerical
models to help us understand the effects of magnetic reconnection
in the plasma tail. The numerical models used in this study are
(a) a multispecies global Hall-magnetohydrodynamic (HMHD) model and
(b) a global HMHD model two-way coupled to an embedded fully kinetic
particle-in-cell code. Comparison with MAVEN observations clearly shows
that the general interaction pattern is well reproduced by the global
HMHD model. The coupled model takes advantage of both the efficiency
of the MHD model and the ability to incorporate kinetic processes of
the particle-in-cell model, making it feasible to conduct kinetic
simulations for Mars under realistic solar wind conditions for the
first time. Results from the coupled model show that the Martian
magnetotail is highly dynamic due to magnetic reconnection, and the
resulting Mars-ward plasma flow velocities are significantly higher
for the lighter ion fluid, which are quantitatively consistent with
MAVEN observations. The HMHD with Embedded Particle-in-Cell model
predicts that the ion loss rates are more variable but with similar
mean values as compared with HMHD model results.
Title: An Integrated Modeling Suite for Simulating the Core Induction
and Kinetic Effects in Mercury's Magnetosphere
Authors: Jia, X.; Slavin, J.; Chen, Y.; Poh, G.; Toth, G.; Gombosi, T.
Bibcode: 2018LPICo2047.6082J
Altcode:
We present results from state-of-the-art global models of Mercury's
space environment capable of self-consistently simulating the induction
effect at the core and resolving kinetic physics important for magnetic
reconnection.
Title: Modeling Martian Atmospheric Losses over Time: Implications
for Exoplanetary Climate Evolution and Habitability
Authors: Dong, Chuanfei; Lee, Yuni; Ma, Yingjuan; Lingam, Manasvi;
Bougher, Stephen; Luhmann, Janet; Curry, Shannon; Toth, Gabor; Nagy,
Andrew; Tenishev, Valeriy; Fang, Xiaohua; Mitchell, David; Brain,
David; Jakosky, Bruce
Bibcode: 2018ApJ...859L..14D
Altcode: 2018arXiv180505016D
In this Letter, we make use of sophisticated 3D numerical simulations
to assess the extent of atmospheric ion and photochemical losses from
Mars over time. We demonstrate that the atmospheric ion escape rates
were significantly higher (by more than two orders of magnitude) in the
past at ∼4 Ga compared to the present-day value owing to the stronger
solar wind and higher ultraviolet fluxes from the young Sun. We found
that the photochemical loss of atomic hot oxygen dominates over the
total ion loss at the current epoch, while the atmospheric ion loss
is likely much more important at ancient times. We briefly discuss the
ensuing implications of high atmospheric ion escape rates in the context
of ancient Mars, and exoplanets with similar atmospheric compositions
around young solar-type stars and M-dwarfs.
Title: Including Kinetic Ion Effects in the Coupled Global Ionospheric
Outflow Solution
Authors: Glocer, A.; Toth, G.; Fok, M. -C.
Bibcode: 2018JGRA..123.2851G
Altcode:
We present a new expansion of the Polar Wind Outflow Model to include
kinetic ions using the particle-in-cell (PIC) approach with Monte Carlo
collisions. This implementation uses the original hydrodynamic solution
at low altitudes for efficiency and couples to the kinetic solution
at higher altitudes to account for kinetic effects important for
ionospheric outflow. The modeling approach also includes wave-particle
interactions, suprathermal electrons, and a hybrid parallel computing
approach combining shared and distributed memory paralellization. The
resulting model is thus a comprehensive, global, model of ionospheric
outflow that can be run efficiently on large supercomputing clusters. We
demonstrate the model's capability to study a range of problems
starting with the comparison of kinetic and hydrodynamic solutions
along a single field line in the sunlit polar cap, and progressing
to the altitude evolution of the ion conic distribution in the cusp
region. The interplay between convection and the cusp on the global
outflow solution is also examined. Finally, we demonstrate the impact
of these new model features on the magnetosphere by presenting the
first two-way coupled ionospheric outflow-magnetosphere calculation
including kinetic ion effects.
Title: Hall effect in the coma of 67P/Churyumov-Gerasimenko
Authors: Huang, Z.; Tóth, G.; Gombosi, T. I.; Jia, X.; Combi, M. R.;
Hansen, K. C.; Fougere, N.; Shou, Y.; Tenishev, V.; Altwegg, K.;
Rubin, M.
Bibcode: 2018MNRAS.475.2835H
Altcode: 2018arXiv180103991H
Magnetohydrodynamics simulations have been carried out in studying the
solar wind and cometary plasma interactions for decades. Various plasma
boundaries have been simulated and compared well with observations
for comet 1P/Halley. The Rosetta mission, which studies comet
67P/Churyumov-Gerasimenko, challenges our understanding of the
solar wind and comet interactions. The Rosetta Plasma Consortium
observed regions of very weak magnetic field outside the predicted
diamagnetic cavity. In this paper, we simulate the inner coma with the
Hall magnetohydrodynamics equations and show that the Hall effect is
important in the inner coma environment. The magnetic field topology
becomes complex and magnetic reconnection occurs on the dayside when
the Hall effect is taken into account. The magnetic reconnection on the
dayside can generate weak magnetic field regions outside the global
diamagnetic cavity, which may explain the Rosetta Plasma Consortium
observations. We conclude that the substantial change in the inner coma
environment is due to the fact that the ion inertial length (or gyro
radius) is not much smaller than the size of the diamagnetic cavity.
Title: A Spectroscopic Study of the Energy Deposition in the Low
Corona: Connecting Global Modeling to Observations
Authors: Szente, J.; Landi, E.; Toth, G.; Manchester, W.; van der
Holst, B.; Gombosi, T. I.
Bibcode: 2017AGUFMSH41C..06S
Altcode:
We are looking for signatures of coronal heating process using a
physically consistent 3D MHD model of the global corona. Our approach is
based on the Alfvén Wave Solar atmosphere Model (AWSoM), with a domain
ranging from the upper chromosphere (50,000K) to the outer corona,
and the solar wind is self-consistently heated and accelerated by the
dissipation of low-frequency Alfvén waves. Taking into account separate
electron and anisotropic proton heating, we model the coronal plasma
at the same time and location as observed by Hinode/EIS, and calculate
the synthetic spectra that we compare with the observations. With
the obtained synthetic spectra, we are able to directly calculate
line intensities, line width, thermal and nonthermal motions, line
centroids, Doppler shift distributions and compare our predictions
to real measurements. Our results directly test the extent to which
Alfvénic heating is present in the low corona.
Title: Gas Production at Comet 67P/Churyumov-Gerasimenko as Measured
by the ROSINA Instrument: Long Term Trends and Correlations with
H2O and CO2
Authors: Hansen, K. C.; Altwegg, K.; Berthelier, J. J.; Combi, M. R.;
De Keyser, J.; Fiethe, B.; Fougere, N.; Fuselier, S. A.; Gombosi,
T. I.; Huang, Z.; Rubin, M.; Tenishev, V.; Toth, G.; Tzou, C. Y.
Bibcode: 2017AGUFM.P54D..03H
Altcode:
The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)
instrument onboard the Rosetta spacecraft measured the in situ gas
density of comet 67P/Churyumov-Gerasimenko during the full perihelion
passage of the comet within 3.5au. During this time, ROSINA sampled the
neutral coma, measuring the broad range of cometary species including
both the major constituents such as H2O, CO2, CO as well as many other
species that are interesting to the general astrophysical community,
such as O2, Xe, Si and even amino acids. Many of these species are hard
to detect and therefore measurements are limited to when the spacecraft
was close to the comet or the production rate was high. In contrast,
in this work we will consider species that are most easily measured due
to either their higher production rates or the ease with which their
mass peaks are located (H2O, CO2, CO, O2, 18OH, HDO, OCS, SO2, H2S, CN,
HCN, NH3, CH4, C2H2, C2H3, CH3OH and F). The advantage of examining
these species is that we are able to present measurements over the
entire perihelion passage at reasonably high time resolution. In this
work we will present two important results. First, we will examine the
long-term trend and heliocentric distance dependence of the production
of these species over the entire perihelion passage of 67P. Second we
will consider the correlation of the production of each species with
the production of H2O and CO2. The study will consider both the long
term correspondence between production of different species as well
as the shorter term correlation.
Title: Influence of the solar wind and IMF on Jupiter's magnetosphere:
Results from global MHD simulations
Authors: Sarkango, Y.; Jia, X.; Toth, G.; Hansen, K. C.
Bibcode: 2017AGUFMSM33C2679S
Altcode:
Due to its large size, rapid rotation and presence of substantial
internal plasma sources, Jupiter's magnetosphere is fundamentally
different from that of the Earth. How and to what extent do the external
factors, such as the solar wind and interplanetary magnetic field (IMF),
influence the internally-driven magnetosphere is an open question. In
this work, we solve the 3D semi-relativistic magnetohydrodynamic (MHD)
equations using a well-established code, BATSRUS, to model the Jovian
magnetosphere and study its interaction with the solar wind. Our
global model adopts a non-uniform mesh covering the region from 200
RJ upstream to 1800 RJ downstream with the inner boundary placed at a
radial distance of 2.5 RJ. The Io plasma torus centered around 6 RJ is
generated in our model through appropriate mass-loading terms added to
the set of MHD equations. We perform systematic numerical experiments
in which we vary the upstream solar wind properties to investigate
the impact of solar wind events, such as interplanetary shock and
IMF rotation, on the global magnetosphere. From our simulations,
we extract the location of the magnetopause boundary, the bow shock
and the open-closed field line boundary (OCB), and determine their
dependence on the solar wind properties and the IMF orientation. For
validation, we compare our simulation results, such as density,
temperature and magnetic field, to published empirical models based
on in-situ measurements.
Title: Space Weather Forecasting at NOAA with Michigan's Geospace
Model: Results from the First Year in Real-Time Operations
Authors: Cash, M. D.; Singer, H. J.; Millward, G. H.; Balch, C. C.;
Toth, G.; Welling, D. T.
Bibcode: 2017AGUFMSM11E..07C
Altcode:
In October 2016, the first version of the Geospace model was
transitioned into real-time operations at NOAA Space Weather Prediction
Center (SWPC). The Geospace model is a part of the Space Weather
Modeling Framework (SWMF) developed at the University of Michigan,
and the model simulates the full time-dependent 3D Geospace environment
(Earth's magnetosphere, ring current and ionosphere) and predicts global
space weather parameters such as induced magnetic perturbations in space
and on Earth's surface. The current version of the Geospace model uses
three coupled components of SWMF: the BATS-R-US global magnetosphere
model, the Rice Convection Model (RCM) of the inner magnetosphere, and
the Ridley Ionosphere electrodynamics Model (RIM). In the operational
mode, SWMF/Geospace runs continually in real-time as long as there is
new solar wind data arriving from a satellite at L1, either DSCOVR or
ACE. We present an analysis of the overall performance of the Geospace
model during the first year of real-time operations. Evaluation metrics
include Kp, Dst, as well as regional magnetometer stations. We will
also present initial results from new products, such as the AE index,
available with the recent upgrade to the Geospace model.
Title: The contribution of inductive electric fields to particle
energization in the inner magnetosphere
Authors: Ilie, R.; Toth, G.; Liemohn, M. W.; Chan, A. A.
Bibcode: 2017AGUFMSM23A2586I
Altcode:
Assessing the relative contribution of potential versus inductive
electric fields at the energization of the hot ion population in the
inner magnetosphere is only possible by thorough examination of the
time varying magnetic field and current systems using global modeling of
the entire system. We present here a method to calculate the inductive
and potential components of electric field in the entire magnetosphere
region. This method is based on the Helmholtz vector decomposition of
the motional electric field as calculated by the BATS-R-US model, and is
subject to boundary conditions. This approach removes the need to trace
independent field lines and lifts the assumption that the magnetic field
lines can be treated as frozen in a stationary ionosphere. In order to
quantify the relative contributions of potential and inductive electric
fields at driving plasma sheet ions into the inner magnetosphere,
we apply this method for the March 17th, 2013 geomagnetic storm. We
present here the consequences of slow continuous changes in the
geomagnetic field as well as the strong tail dipolarizations on the
distortion of the near-Earth magnetic field and current systems. Our
findings indicate that the inductive component of the electric field
is comparable, and even higher at times than the potential component,
suggesting that the electric field induced by the time varying magnetic
field plays a crucial role in the overall particle energization in
the inner magnetosphere.
Title: Are "Habitable" Exoplanets Really Habitable? -A perspective
from atmospheric loss
Authors: Dong, C.; Huang, Z.; Jin, M.; Lingam, M.; Ma, Y. J.; Toth,
G.; van der Holst, B.; Airapetian, V.; Cohen, O.; Gombosi, T. I.
Bibcode: 2017AGUFM.P42B..02D
Altcode:
In the last two decades, the field of exoplanets has witnessed a
tremendous creative surge. Research in exoplanets now encompasses
a wide range of fields ranging from astrophysics to heliophysics
and atmospheric science. One of the primary objectives of studying
exoplanets is to determine the criteria for habitability, and whether
certain exoplanets meet these requirements. The classical definition
of the Habitable Zone (HZ) is the region around a star where liquid
water can exist on the planetary surface given sufficient atmospheric
pressure. However, this definition largely ignores the impact of
the stellar wind and stellar magnetic activity on the erosion of
an exoplanet's atmosphere. Amongst the many factors that determine
habitability, understanding the mechanisms of atmospheric loss is
of paramount importance. We will discuss the impact of exoplanetary
space weather on climate and habitability, which offers fresh insights
concerning the habitability of exoplanets, especially those orbiting
M-dwarfs, such as Proxima b and the TRAPPIST-1 system. For each case,
we will demonstrate the importance of the exoplanetary space weather
on atmospheric ion loss and habitability.
Title: Solar Atmosphere to Earth's Surface: Long Lead Time dB/dt
Predictions with the Space Weather Modeling Framework
Authors: Welling, D. T.; Manchester, W.; Savani, N.; Sokolov, I.;
van der Holst, B.; Jin, M.; Toth, G.; Liemohn, M. W.; Gombosi, T. I.
Bibcode: 2017AGUFMSH34B..05W
Altcode:
The future of space weather prediction depends on the community's
ability to predict L1 values from observations of the solar
atmosphere, which can yield hours of lead time. While both
empirical and physics-based L1 forecast methods exist, it is not
yet known if this nascent capability can translate to skilled
dB/dt forecasts at the Earth's surface. This paper shows results
for the first forecast-quality, solar-atmosphere-to-Earth's-surface
dB/dt predictions. Two methods are used to predict solar wind and
IMF conditions at L1 for several real-world coronal mass ejection
events. The first method is an empirical and observationally based
system to estimate the plasma characteristics. The magnetic field
predictions are based on the Bz4Cast system which assumes that the
CME has a cylindrical flux rope geometry locally around Earth's
trajectory. The remaining plasma parameters of density, temperature
and velocity are estimated from white-light coronagraphs via a variety
of triangulation methods and forward based modelling. The second is
a first-principles-based approach that combines the Eruptive Event
Generator using Gibson-Low configuration (EEGGL) model with the Alfven
Wave Solar Model (AWSoM). EEGGL specifies parameters for the Gibson-Low
flux rope such that it erupts, driving a CME in the coronal model
that reproduces coronagraph observations and propagates to 1AU. The
resulting solar wind predictions are used to drive the operational
Space Weather Modeling Framework (SWMF) for geospace. Following the
configuration used by NOAA's Space Weather Prediction Center, this
setup couples the BATS-R-US global magnetohydromagnetic model to the
Rice Convection Model (RCM) ring current model and a height-integrated
ionosphere electrodynamics model. The long lead time predictions
of dB/dt are compared to model results that are driven by L1 solar
wind observations. Both are compared to real-world observations from
surface magnetometers at a variety of geomagnetic latitudes. Metrics
are calculated to examine how the simulated solar wind drivers
impact forecast skill. These results illustrate the current state
of long-lead-time forecasting and the promise of this technology for
operational use.
Title: End-of-mission ROSINA/COPS measurements as a probe of the
innermost coma of comet 67P/Churyumov-Gerasimenko
Authors: Tenishev, V.; Fougere, N.; Rubin, M.; Tzou, C. Y.; Combi,
M. R.; Altwegg, K.; Gombosi, T. I.; Shou, Y.; Huang, Z.; Hansen,
K. C.; Toth, G.
Bibcode: 2017AGUFM.P51D2634T
Altcode:
A cometary coma is a unique phenomenon in the Solar system that
represents an example of a planetary atmosphere influenced by little
or no gravity. Due to the negligible gravity of a comet's nucleus, a
coma has a characteristic size that exceeds that of the nucleus itself
by many orders of magnitude. An extended dusty gas cloud that forms
a coma is affected mainly by molecular collisions, radiative cooling,
and photolytic, charge-exchange, and impact-ionization reactions. Such
an environment has been extensively observed during the recent Rosetta
mission, which was the first mission that escorts a comet along its way
through the Solar system for an extended amount of time with the main
scientific objectives of characterizing comet's nucleus, determining the
surface composition, and studying the comet's activity development. The
ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis)
Comet Pressure Sensor (COPS) onboard the Rosetta spacecraft has
performed one of the most exciting observations of the innermost coma
during the spacecraft descend maneuver during the last ten hours of
the mission when the random and outflow directed pressures in the coma
have been measured all the way down to the comet's surface. Performed
at such close proximity to the nucleus, these observations can help
to characterize effects due to topological features and/or the gas
local conditions at the surface of the nucleus. The major focus
of the presented study is analyzing of the end-of-mission pressure
measurements by the ROSINA/COPS instrument. Because the coma at a
heliocentric distance of 3.8 AU was in a collisionless regime, it
can be described by solving the Liouville equation, as we have done
in our analysis. We have used the SHAP5 nucleus model to account for
the topology of the volatile source. Spacecraft trajectory and the
instrument pointing with respect to the comet's nucleus have been
obtained with the SPICE library. Here, we present results of our
analysis and discuss the effects of the surface topology and that of
the local surface volatile injection on the distribution of gas in
the innermost coma of comet 67P/Churyumov-Gerasimenko.
Title: Global Magnetosphere Modeling With Kinetic Treatment of
Magnetic Reconnection
Authors: Toth, G.; Chen, Y.; Gombosi, T. I.; Cassak, P.; Markidis,
S.; Peng, B.; Henderson, M. G.
Bibcode: 2017AGUFMSM22B..04T
Altcode:
Global magnetosphere simulations with a kinetic treatment of magnetic
reconnection are very challenging because of the large separation of
global and kinetic scales. We have developed two algorithms that can
overcome these difficulties: 1) the two-way coupling of the global
magnetohydrodynamic code with an embedded particle-in-cell model
(MHD-EPIC) and 2) the artificial increase of the ion and electron
kinetic scales. Both of these techniques improve the efficiency
of the simulations by many orders of magnitude. We will describe
the techniques and show that they provide correct and meaningful
results. Using the coupled model and the increased kinetic scales,
we will present global magnetosphere simulations with the PIC domains
covering the dayside and/or tail reconnection sites. The simulation
results will be compared to and validated with MMS observations.
Title: Five-moment multi-fluid plasma simulation for comet
67P/Churyumov-Gerasimenko
Authors: Huang, Z.; Toth, G.; Gombosi, T. I.; Jia, X.; Hansen,
K. C.; Combi, M. R.; Tenishev, V.; Shou, Y.; Fougere, N.; Rubin, M.;
Altwegg, K.
Bibcode: 2017AGUFM.P51D2629H
Altcode:
Understanding the interactions between the solar wind and
cometary magnetosphere was one of the key topics in the Rosetta
mission. Numerical simulations have been widely carried out to
investigate these interactions and the results agree well with
observations. There are three different kinds of models: fluid models
(in which both the ions and electrons are treated as fluids), hybrid
models (in which the ions are considered as particles while the
electrons are considered as a fluid) and fully kinetic models (in
which both the ions and electrons are treated as particles). Fluid
models can well simulate the large-scale boundaries of the solar
wind-comet interaction, such as the bow shock position and the size of
the diamagnetic cavity, and typically have much lower computational
cost than hybrid and fully kinetic models. In previous fluid models,
electrons are usually simulated with an electron pressure equation,
without specifying the continuity and momentum equations. Such
an approach cannot represent any of the electron kinetic features
properly. In this study, we present the first five-moment multi-fluid
plasma simulation of a comet, by introducing the continuity and
momentum equations for the electrons, in which case the electrons
and electric field are simulated more self-consistently than the
classical multi-fluid MHD simulations and the Hall effect is included
automatically. We compare the five-moment multi-fluid simulation
results with those of a multi-fluid Hall MHD simulation and discuss
the new features observed in the five-moment multi-fluid model.
Title: The Structure of the Heliosphere with Solar Cycle and Its
Effect on the Conditions in the Local ISM
Authors: Opher, M.; Drake, J. F.; Toth, G.; Swisdak, M.; Michael,
A.; Kornbleuth, M. Z.; Zieger, B.
Bibcode: 2017AGUFMSH54B..04O
Altcode:
We argued (Opher et al. 2015, Drake et al. 2015) that the magnetic
tension of the solar magnetic field plays a crucial role in
organizing the solar wind in the heliosheath into two jet-like
structures. The heliosphere then has a "croissant"-like shape where
the distance to the heliopause downtail is almost the same as towards
the nose. Regardless of whether the heliospheric tail is split in two
or has a long comet shape there is consensus that the magnetic field
in the heliosheath behaves differently than previously expected -
it has a "slinky" structure and is turbulent. In this presentation,
we will discuss several aspects related with this new model. We will
show that this structure persists when the solar magnetic field is
treated as a dipole. We show how the heliosphere, with its "Croissant"
shape, evolves when the solar wind with solar cycle conditions are
included and when the neutrals are treated kinetically (with our new
MHD-Kinetic code). Due to reconnection (and turbulence of the jets)
there is a substantial amount of heliosheath material sitting on open
field lines. We will discuss the impact of artificial dissipation
of the magnetic field in driving mixing and how it evolves with the
solar cycle. We will discuss as well the development of turbulence
in the jets and its role in mixing the plasma in the heliosheath and
LISM and controlling the global structure of the heliosphere. We will
discuss how the conditions upstream of the heliosphere, in the local
interstellar medium are affected by reconnection in the tail and how it
evolves with solar cycle. Recently we established (Opher et al. 2017)
that reconnection in the eastern flank of the heliosphere is responsible
for the twist of the interstellar magnetic field (BISM) acquiring a
strong east-west component as it approaches the Heliopause. Reconnection
drives a rotational discontinuity (RD) that twists the BISM into the
-T direction and propagates upstream in the interstellar medium toward
the nose. The consequence is that the N component of BISM is reduced in
a band upstream of the HP. We show how the location of the RD upstream
of the heliopause is affected by the solar cycle.
Title: A New Global Multi-fluid MHD Model of the Solar Corona
Authors: van der Holst, B.; Chandran, B. D. G.; Alterman, B. L.;
Kasper, J. C.; Toth, G.
Bibcode: 2017AGUFMSH32A..09V
Altcode:
We present a multi-fluid generalization of the AWSoM model, a global
magnetohydrodynamic (MHD) solar corona model with low-frequency Alfven
wave turbulence (van der Holst et al., 2014). This new extended
model includes electron and multi-ion temperatures and velocities
(protons and alpha particles). The coronal heating and acceleration
is addressed via outward propagating low-frequency Alfven waves that
are partially reflected by Alfven speed gradients. The nonlinear
interaction of these counter-propagating waves results in turbulent
energy cascade. To apportion the wave dissipation to the electron and
ion temperatures, we employ the results of the theories of linear wave
damping and nonlinear stochastic heating as described by Chandran et
al. (2011, 2013). This heat partitioning results in a more than mass
proportional heating among ions.
Title: Multi-fluid MHD simulations of Europa's interaction with
Jupiter's magnetosphere
Authors: Harris, C. D. K.; Jia, X.; Slavin, J. A.; Rubin, M.; Toth, G.
Bibcode: 2017AGUFMSM41C..04H
Altcode:
Several distinct physical processes generate the interaction between
Europa, the smallest of Jupiter's Galilean moons, and Jupiter's
magnetosphere. The 10˚ tilt of Jupiter's dipole causes time varying
magnetic fields at Europa's orbit which interact with Europa's
subsurface conducting ocean to induce magnetic perturbations around the
moon. Jovian plasma interacts with Europa's icy surface to sputter off
neutral particles, forming a tenuous exosphere which is then ionized
by impact and photo-ionization to form an ionosphere. As jovian plasma
flows towards the moon, mass-loading and interaction with the ionosphere
slow the flow, producing magnetic perturbations that propagate along
the field lines to form an Alfvén wing current system, which connects
Europa to its bright footprint in Jupiter's ionosphere. The Galileo
mission has shown that the plasma interaction generates significant
magnetic perturbations that obscure signatures of the induced field
from the subsurface ocean. Modeling the plasma-related perturbations
is critical to interpreting the magnetic signatures of Europa's
induction field, and therefore to magnetic sounding of its interior,
a central goal of the upcoming Europa Clipper mission. Here we model
the Europa-Jupiter interaction with multi-fluid magnetohydrodynamic
simulations to understand quantitatively how these physical processes
affect the plasma and magnetic environment around the moon. Our
model separately tracks the bulk motion of three different ion fluids
(exospheric O2+, O+, and magnetospheric O+), and includes sources and
losses of mass, momentum and energy to each of the ion fluids due to
ionization, charge-exchange and recombination. We include calculations
of the electron temperature allowing for field-aligned electron
heat conduction, and Hall effects due to differential ion-electron
motion. Compared to previous simulations, this multi-fluid model allows
us to more accurately determine the precipitation flux of jovian plasma
to Europa's surface, which has significant implications for space
weathering at the moon. Including the Hall effect in our simulations
enables us to determine the effects of separate ion-electron bulk
motion throughout the interaction, and our simulations reveal noticeable
asymmetries and small-scale features in the Alfvén wings.
Title: Impacts of Extreme Space Weather Events on Power Grid
Infrastructure: Physics-Based Modelling of Geomagnetically-Induced
Currents (GICs) During Carrington-Class Geomagnetic Storms
Authors: Henderson, M. G.; Bent, R.; Chen, Y.; Delzanno, G. L.;
Jeffery, C. A.; Jordanova, V. K.; Morley, S.; Rivera, M. K.; Toth,
G.; Welling, D. T.; Woodroffe, J. R.; Engel, M.
Bibcode: 2017AGUFMSA22A..01H
Altcode:
Large geomagnetic storms can have devastating effects on power
grids. The largest geomagnetic storm ever recorded - called the
Carrington Event - occurred in 1859 and produced Geomagnetically Induced
Currents (GICs) strong enough to set fires in telegraph offices. It
has been estimated that if such a storm occurred today, it would
have devastating, long-lasting effects on the North American power
transmission infrastructure. Acutely aware of this imminent threat,
the North American Electric Reliability Corporation (NERC) was recently
instructed to establish requirements for transmission system performance
during geomagnetic disturbance (GMD) events and, although the benchmarks
adopted were based on the best available data at the time, they suffer
from a severely limited physical understanding of the behavior of GMDs
and the resulting GICs for strong events. To rectify these deficiencies,
we are developing a first-of-its-kind data-informed modelling capability
that will provide transformational understanding of the underlying
physical mechanisms responsible for the most harmful intense localized
GMDs and their impacts on real power transmission networks. This work
is being conducted in two separate modes of operation: (1) using
historical, well-observed large storm intervals for which robust
data-assimilation can be performed, and (2) extending the modelling
into a predictive realm in order to assess impacts of poorly and/or
never-before observed Carrington-class events. Results of this work
are expected to include a potential replacement for the current NERC
benchmarking methodology and the development of mitigation strategies
in real power grid networks. We report on progress to date and show
some preliminary results of modeling large (but not yet extreme) events.
Title: Numerical simulation of the kinetic effects in the solar wind
Authors: Sokolov, I.; Toth, G.; Gombosi, T. I.
Bibcode: 2017AGUFMSH14B..07S
Altcode:
Global numerical simulations of the solar wind are usually based on
the ideal or resistive MagnetoHydroDynamics (MHD) equations. Within
a framework of MHD the electric field is assumed to vanish in
the co-moving frame of reference (ideal MHD) or to obey a simple
and non-physical scalar Ohm's law (resistive MHD). The Maxwellian
distribution functions are assumed, the electron and ion temperatures
may be different. Non-disversive MHD waves can be present in this
numerical model. The averaged equations for MHD turbulence may be
included as well as the energy and momentum exchange between the
turbulent and regular motion. With the use of explicit numerical
scheme, the time step is controlled by the MHD wave propagtion time
across the numerical cell (the CFL condition) More refined approach
includes the Hall effect vie the generalized Ohm's law. The Lorentz
force acting on light electrons is assumed to vanish, which gives the
expression for local electric field in terms of the total electric
current, the ion current as well as the electron pressure gradient
and magnetic field. The waves (whistlers, ion-cyclotron waves etc)
aquire dispersion and the short-wavelength perturbations propagate with
elevated speed thus strengthening the CFL condition. If the grid size
is sufficiently small to resolve ion skindepth scale, then the timestep
is much shorter than the ion gyration period. The next natural step
is to use hybrid code to resolve the ion kinetic effects. The hybrid
numerical scheme employs the same generalized Ohm's law as Hall MHD
and suffers from the same constraint on the time step while solving
evolution of the electromagnetic field. The important distiction,
however, is that by sloving particle motion for ions we can achieve
more detailed description of the kinetic effect without significant
degrade in the computational efficiency, because the time-step is
sufficient to resolve the particle gyration. We present the fisrt
numerical results from coupled BATS-R-US+ALTOR code as applied to
kinetic simulations of the solar wind.
Title: Global Three-dimensional Simulation of the Solar
Wind-Magnetosphere Interaction Using a Two-way Coupled
Magnetohydrodynamics with Embedded Particle-in-Cell Model
Authors: Chen, Y.; Toth, G.; Cassak, P.; Jia, X.; Gombosi, T. I.;
Slavin, J. A.; Welling, D. T.; Markidis, S.; Peng, I. B.; Jordanova,
V. K.; Henderson, M. G.
Bibcode: 2017AGUFMSM24A..05C
Altcode:
We perform a three-dimensional (3D) global simulation of Earth's
magnetosphere with kinetic reconnection physics to study the interaction
between the solar wind and Earth's magnetosphere. In this global
simulation with magnetohydrodynamics with embedded particle-in-cell
model (MHD-EPIC), both the dayside magnetopause reconnection region
and the magnetotail reconnection region are covered with a kinetic
particle-in-cell code iPIC3D, which is two-way coupled with the global
MHD model BATS-R-US. We will describe the dayside reconnection related
phenomena, such as the lower hybrid drift instability (LHDI) and the
evolution of the flux transfer events (FTEs) along the magnetopause,
and compare the simulation results with observations. We will also
discuss the response of the magnetotail to the southward IMF. The
onset of the tail reconnection and the properties of the magnetotail
flux ropes will be discussed.
Title: 3D Hall MHD-EPIC Simulations of Ganymede's Magnetosphere
Authors: Zhou, H.; Toth, G.; Jia, X.
Bibcode: 2017AGUFMSM33D2700Z
Altcode:
Fully kinetic modeling of a complete 3D magnetosphere is still
computationally expensive and not feasible on current computers. While
magnetohydrodynamic (MHD) models have been successfully applied to a
wide range of plasma simulation, they cannot capture some important
kinetic effects. We have recently developed a new modeling tool
to embed the implicit particle-in-cell (PIC) model iPIC3D into
the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme (BATS-R-US)
magnetohydrodynamic model. This results in a kinetic model of the
regions where kinetic effects are important. In addition to the
MHD-EPIC modeling of the magnetosphere, the improved model presented
here is now able to represent the moon as a resistive body. We use
a stretched spherical grid with adaptive mesh refinement (AMR) to
capture the resistive body and its boundary. A semi-implicit scheme is
employed for solving the magnetic induction equation to allow time steps
that are not limited by the resistivity. We have applied the model to
Ganymede, the only moon in the solar system known to possess a strong
intrinsic magnetic field, and included finite resistivity beneath the
moon`s surface to model the electrical properties of the interior in
a self-consistent manner. The kinetic effects of electrons and ions
on the dayside magnetopause and tail current sheet are captured with
iPIC3D. Magnetic reconnections under different upstream background
conditions of several Galileo flybys are simulated to study the global
reconnection rate and the magnetospheric dynamics
Title: A new hybrid particle/fluid model for cometary dust
Authors: Shou, Y.; Combi, M. R.; Tenishev, V.; Toth, G.; Hansen,
K. C.; Huang, Z.; Gombosi, T. I.; Fougere, N.; Rubin, M.
Bibcode: 2017AGUFM.P51D2641S
Altcode:
Cometary dust grains, which originate from comets, are believed to
contain clues to the formation and the evolution of comets. They
also play an important role in shaping the cometary environment,
as they are able to decelerate and heat the gas through collisions,
carry charges and interact with the plasma environment, and possibly
sublimate gases. Therefore, the loss rate and behavior of dust
grains are of interest to scientists. Currently, mainly two types of
numerical dust models exist: particle models and fluid models have
been developed. Particle models, which keep track of the positions
and velocities of all gas and dust particles, allow crossing dust
trajectories and a more accurate description of returning dust grains
than the fluid model. However, in order to compute the gas drag
force, the particle model needs to follow more gas particles than dust
particles. A fluid model is usually more computationally efficient and
is often used to provide simulations on larger spatial and temporal
scales. In this work, a new hybrid model is developed to combine the
advantages of both particle and fluid models. In the new approach a
fluid model based on the University of Michigan BATSRUS code computes
the gas properties, and feeds the gas drag force to the particle
model, which is based on the Adaptive Mesh Particle Simulator (AMPS)
code, to calculate the motion of dust grains. The coupling is done
via the Space Weather Modeling Framework (SWMF). In addition to the
capability of simulating the long-term dust phenomena, the model can
also designate small active regions on the nucleus for comparison with
the temporary fine dust features in observations. With the assistance
of the newly developed model, the effect of viewing angles on observed
dust jet shapes and the transportation of heavy dust grains from the
southern to the northern hemisphere of comet 67P/Churyumov-Gerasimenko
will be studied and compared with Rosetta mission images. Preliminary
results will be presented. Support from contracts JPL #1266314 and
#1266313 from the US Rosetta Project and grant NNX14AG84G from the
NASA Planetary Atmospheres Program are gratefully acknowledged.
Title: Surface Activity Distributions of Comet
67P/Churyumov-Gerasimenko Derived from VIRTIS Images
Authors: Fougere, N.; Combi, M. R.; Tenishev, V.; Migliorini,
A.; Bockelée-Morvan, D.; Fink, U.; Filacchione, G.; Rinaldi, G.;
Capaccioni, F.; Toth, G.; Gombosi, T. I.; Hansen, K. C.; Huang, Z.;
Shou, Y.
Bibcode: 2017AGUFM.P51D2642F
Altcode:
The outgassing mechanism of comets still remains a critical question to
better understand these objects. The Rosetta mission gave some insight
regarding the potential activity distribution from the surface of
the nucleus of comet 67P/Churyumov-Gerasimenko, Fougere et al. (2016)
used a spherical harmonics inversion scheme with in-situ measurements
from the ROSINA instrument to derive mapping of the broad distribution
of potential activity at the surface of the nucleus. Marschall et
al. (2017) based on the appearance of dust active areas suggested
that the so-called "neck" region and regions with fractured cliffs
and locally steep slopes show more activity than the rest of comet
67P's nucleus. Using in situ ROSINA measurements from a distance makes
it difficult to distinguish between these two scenarios because the
fast expansion of the gas and large molecular mean free paths prevents
distinguishing small outgassing features even when the spacecraft was in
bound orbits within 10 km from the nucleus. In this paper, we present a
similar numerical inversion approach using VIRTIS images, which should
better probe the very inner coma of comet 67P and give more detailed
information about the outgassing activity. Support from contracts JPL
#1266314 and #1266313 from the US Rosetta Project and grant NNX14AG84G
from the NASA Planetary Atmospheres Program are gratefully acknowledged.
Title: Importance of Ambipolar Electric Field in the Ion Loss from
Mars- Results from a Multi-fluid MHD Model with the Electron Pressure
Equation Included
Authors: Ma, Y.; Dong, C.; van der Holst, B.; Nagy, A. F.; Bougher,
S. W.; Toth, G.; Cravens, T.; Yelle, R. V.; Jakosky, B. M.
Bibcode: 2017AGUFM.P11B2509M
Altcode:
The multi-fluid (MF) magnetohydrodynamic (MHD) model of Mars is further
improved by solving an additional electron pressure equation. Through
the electron pressure equation, the electron temperature is calculated
based on the effects from various electrons related heating and cooling
processes (e.g. photo-electron heating, electron-neutral collision
and electron-ion collision), and thus the improved model is able to
calculate the electron temperature and the electron pressure force
self-consistently. Electron thermal conductivity is also considered in
the calculation. Model results of a normal case with electron pressure
equation included (MFPe) are compared in detail to an identical case
using the regular MF model to identify the effect of the improved
physics. We found that when the electron pressure equation is included,
the general interaction patterns are similar to that of the case
with no electron pressure equation. The model with electron pressure
equation predicts that electron temperature is much larger than the ion
temperature in the ionosphere, consistent with both Viking and MAVEN
observations. The inclusion of electron pressure equation significantly
increases the total escape fluxes predicted by the model, indicating the
importance of the ambipolar electric field(electron pressure gradient)
in driving the ion loss from Mars.
Title: Results from the OH-PT model: a Kinetic-MHD Model of the
Outer Heliosphere within SWMF
Authors: Michael, A.; Opher, M.; Tenishev, V.; Borovikov, D.; Toth, G.
Bibcode: 2017AGUFMSH23C2676M
Altcode:
We present an update of the OH-PT model, a kinetic-MHD model of the
outer heliosphere. The OH-PT model couples the Outer Heliosphere (OH)
and Particle Tracker (PT) components within the Space Weather Modeling
Framework (SWMF). The OH component utilizes the Block-Adaptive Tree
Solarwind Roe-type Upwind Scheme (BATS-R-US) MHD code, a highly
parallel, 3D, and block-adaptive solver. As a stand-alone model,
the OH component solves the ideal MHD equations for the plasma and
a separate set of Euler's equations for the different populations of
neutral atoms. The neutrals and plasma in the outer heliosphere are
coupled through charge-exchange. While this provides an accurate
solution for the plasma, it is an inaccurate description of the
neutrals. The charge-exchange mean free path is on the order of the
size of the heliosphere; therefore the neutrals cannot be described
as a fluid. The PT component is based on the Adaptive Mesh Particle
Simulator (AMPS) model, a 3D, direct simulation Monte Carlo model
that solves the Boltzmann equation for the motion and interaction of
multi-species plasma and is used to model the neutral distribution
functions throughout the domain. The charge-exchange process occurs
within AMPS, which handles each event on a particle-by-particle basis
and calculates the resulting source terms to the MHD equations. The
OH-PT model combines the MHD solution for the plasma with the kinetic
solution for the neutrals to form a self-consistent model of the
heliosphere. In this work, we present verification and validation of
the model as well as demonstrate the codes capabilities. Furthermore we
provide a comparison of the OH-PT model to our multi-fluid approximation
and detail the differences between the models in both the plasma
solution and neutral distribution functions.
Title: Modeling of Ion and Photochemical Losses to Space Over the
Martian History: Implications for Exoplanetary Climate Evolution
and Habitability
Authors: Dong, C. F.; Lee, Y.; Ma, Y. J.; Bougher, S. W.; Luhmann,
J. G.; Jakosky, B. M.; Curry, S. M.; Brain, D. A.; Toth, G.; Nagy,
A. F.
Bibcode: 2017LPICo2042.4023D
Altcode:
This study informs our understanding of the long-term evolution of the
Martian climate due to atmospheric losses to space, and has implications
for analogous change on exoplanets. Thus, it offers fresh insights
concerning the habitability of exoplanets.
Title: Are "Habitable" Exoplanets Really Habitable? A Perspective
from Atmospheric Loss
Authors: Dong, C. F.; Huang, Z. G.; Jin, M.; Lingam, M.; Ma, Y. J.;
Toth, G.; van der Holst, B.; Airapetian, V.; Cohen, O.; Gombosi, T.
Bibcode: 2017LPICo2042.4021D
Altcode:
We will discuss the impact of exoplanetary space weather on the
climate and habitability, which offers fresh insights concerning the
habitability of exoplanets, especially those orbiting M-dwarfs, such
as Proxima b and the TRAPPIST-1 system.
Title: A New 3D Multi-fluid Dust Model: A Study of the Effects
of Activity and Nucleus Rotation on Dust Grain Behavior at Comet
67P/Churyumov-Gerasimenko
Authors: Shou, Y.; Combi, M.; Toth, G.; Tenishev, V.; Fougere, N.;
Jia, X.; Rubin, M.; Huang, Z.; Hansen, K.; Gombosi, T.
Bibcode: 2017ApJ...850...72S
Altcode:
Improving our capability to interpret observations of cometary dust
is necessary to deepen our understanding of the role of dust in the
formation of comets and in altering the cometary environments. Models
including dust grains are in demand to interpret observations and
test hypotheses. Several existing models have taken into account the
gas-dust interaction, varying sizes of dust grains and the cometary
gravitational force. In this work, we develop a multi-fluid dust
model based on the BATS-R-US code. This model not only incorporates
key features of previous dust models, but also has the capability
of simulating time-dependent phenomena. Since the model is run in
the rotating comet reference frame, the centrifugal and Coriolis
forces are included. The boundary conditions on the nucleus surface
can be set according to the distribution of activity and the solar
illumination. The Sun revolves around the comet in this frame. A newly
developed numerical mesh is also used to resolve the real-shaped
nucleus in the center and to facilitate prescription of the outer
boundary conditions that accommodate the rotating frame. The inner
part of the mesh is a box composed of Cartesian cells and the outer
surface is a smooth sphere, with stretched cells filled in between the
box and the sphere. Our model achieved comparable results to the Direct
Simulation Monte Carlo method and the Rosetta/OSIRIS observations. It
is also applied to study the effects of the rotating nucleus and the
cometary activity and offers interpretations of some dust observations
of comet 67P/Churyumov-Gerasimenko.
Title: Venus Ionosphere and Induced Magnetosphere Responses to Solar
Wind Dynamic Pressure and IMF Direction
Authors: Ma, Yingjuan; Toth, Gabor; Nagy, Andew; Russell, Chris
Bibcode: 2017DPS....4950501M
Altcode:
In this study, we focus on the responses of the ionosphere and the
induced magnetosphere of Venus to two typical changes in the solar wind:
solar wind dynamic pressure changes and the interplanetary magnetic
field (IMF) direction changes. Often regarded as the Earth’s ‘sister
planet’, Venus has similar size and mass as Earth. But it is also
remarkably different from Earth in many respects. Even though we have
some basic knowledge of the solar wind interaction with Venus based on
spacecraft observations, little is known about how the interaction
and the resulting plasma escape rates vary in response to solar
wind variations due to the lack of coordinated observations of both
upstream solar wind conditions and simultaneous plasma properties in
the Venus ionosphere. Furthermore, recent observations suggest that
plasma escape rates are significantly enhanced during stormy space
weather in response to solar wind pressure pulses (Edberg et al.,
2011). Thus it is important to understand the plasma interaction under
varying solar wind conditions. We use a sophisticated multi-species
MHD model that has been recently developed for Venus (Ma et al.,
2013) to characterize the changes of the ionosphere and the induced
magnetosphere for varying solar wind conditions. Based on model results,
we discuss the perturbations of the magnetic field in the ionosphere
and its variation with altitude; the variation of the total plasma
escape-rate; and the time scale of the Venus ionosphere and induced
magnetosphere in responding to both types of changes in the solar wind.
Title: Global Three-Dimensional Simulation of Earth's Dayside
Reconnection Using a Two-Way Coupled Magnetohydrodynamics With
Embedded Particle-in-Cell Model: Initial Results
Authors: Chen, Yuxi; Tóth, Gábor; Cassak, Paul; Jia, Xianzhe;
Gombosi, Tamas I.; Slavin, James A.; Markidis, Stefano; Peng, Ivy Bo;
Jordanova, Vania K.; Henderson, Michael G.
Bibcode: 2017JGRA..12210318C
Altcode: 2017arXiv170403803C
We perform a three-dimensional (3-D) global simulation of Earth's
magnetosphere with kinetic reconnection physics to study the
flux transfer events (FTEs) and dayside magnetic reconnection
with the recently developed magnetohydrodynamics with embedded
particle-in-cell model. During the 1 h long simulation, the FTEs are
generated quasi-periodically near the subsolar point and move toward the
poles. We find that the magnetic field signature of FTEs at their early
formation stage is similar to a "crater FTE," which is characterized
by a magnetic field strength dip at the FTE center. After the FTE core
field grows to a significant value, it becomes an FTE with typical
flux rope structure. When an FTE moves across the cusp, reconnection
between the FTE field lines and the cusp field lines can dissipate the
FTE. The kinetic features are also captured by our model. A crescent
electron phase space distribution is found near the reconnection
site. A similar distribution is found for ions at the location where
the Larmor electric field appears. The lower hybrid drift instability
(LHDI) along the current sheet direction also arises at the interface of
magnetosheath and magnetosphere plasma. The LHDI electric field is about
8 mV/m, and its dominant wavelength relative to the electron gyroradius
agrees reasonably with Magnetospheric Multiscale (MMS) observations.
Title: Analysis of the ROSINA/COPS end-of-mission measurements of
the coma of comet 67P/Churyumov-Gerasimenko
Authors: Tenishev, Valeriy; Combi, Michael R.; Fougere, Nicolas;
Rubin, Martin; Tzou, Chia-Yu; Shou, Yinsi; Gombosi, T. I.; Altwegg,
Kathrin; Huang, Zhenguang; Toth, Gabor; Hansen, Kenneth C.
Bibcode: 2017DPS....4950905T
Altcode:
A cometary coma is a unique phenomenon in the Solar system that
represents an example of a planetary atmosphere influenced by little
or no gravity. Due to the negligible gravity of a comet’s nucleus, a
coma has a characteristic size that exceeds that of the nucleus itself
by many orders of magnitude. An extended dusty gas cloud that forms
a coma is affected mainly by molecular collisions, radiative cooling,
and photolytic, charge-exchange, and impact-ionization reactions.Such
an environment has been extensively observed during the recent Rosetta
mission, which was the first mission that escorts a comet along its
way through the Solar system for an extended amount of time with
the main scientific objectives of characterizing comet’s nucleus,
determining the surface composition, and studying the comet’s activity
development.The ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral
Analysis) Comet Pressure Sensor (COPS) onboard the Rosetta spacecraft
has performed one of the most exciting observations of the innermost
coma during the spacecraft descend maneuver during the last ten hours of
the mission when the random and outflow directed pressures in the coma
have been measured all the way down to the comet’s surface. Performed
at such close proximity to the nucleus, these observations can help
to characterize effects due to topological features and/or the gas
local conditions at the surface of the nucleus.The major focus of
the presented study is analyzing of the end-of-mission pressure
measurements by the ROSINA/COPS instrument. Because the coma at a
heliocentric distance of 3.8 AU was in a collisionless regime, it
can be described by solving the Liouville equation, as we have done
in our analysis. We have used the SHAP5 nucleus model to account
for the topology of the volatile source. Spacecraft trajectory and
the instrument pointing with respect to the comet’s nucleus have
been obtained with the SPICE library. Here, we present results of our
analysis and discuss the effects of the surface topology and that of
the local surface volatile injection on the distribution of gas in
the innermost coma of comet 67P/Churyumov-Gerasimenko.
Title: Surface Activity Distributions of Comet
67P/Churyumov-Gerasimenko Derived from VIRTIS Images
Authors: Fougere, Nicolas; Combi, Michael R.; Tenishev, Valeriy;
Migliorini, Alessandra; Bockelee-Morvan, Dominique; Fink, Uwe;
Filacchione, Gianrico; Rinaldi, Giovanna; Capaccioni, Fabrizio; Toth,
Gabor; Gombosi, T. I.; Hansen, Kenneth C.; Huang, Zhenguang; Shou,
Yinsi; VIRTIS Team
Bibcode: 2017DPS....4941501F
Altcode:
The outgassing mechanism of comets still remains a critical question
to better understand these objects. The Rosetta mission gave some
insight regarding the potential activity distribution from the
surface of the nucleus of comet 67P/Churyumov-Gerasimenko, Fougere
et al. (2016, Astronomy & Astrophysics, Volume 588, id.A134, 11
pp and Monthly Notices of the Royal Astronomical Society, Volume 462,
Issue Suppl_1, p.S156-S169) used a spherical harmonics inversion scheme
with in-situ measurements from the ROSINA instrument to derive mapping
of the broad distribution of potential activity at the surface of the
nucleus. Marschall et al. (2016, Astronomy & Astrophysics, doi:
10.1051/0004-6361/201730849) based on the appearance of dust active
areas suggested that the so-called “neck” region and regions with
fractured cliffs and locally steep slopes show more activity than the
rest of comet 67P’s nucleus. Using in situ ROSINA measurements from a
distance makes it difficult to distinguish between these two scenarios
because the fast expansion of the gas and large molecular mean free
paths prevents distinguishing small outgassing features even when the
spacecraft was in bound orbits within 10 km from the nucleus. In this
paper, we present a similar numerical inversion approach using VIRTIS
images, which should better probe the very inner coma of comet 67P and
give more detailed information about the outgassing activity. Support
from contracts JPL #1266314 and #1266313 from the US Rosetta Project
and grant NNX14AG84G from the NASA Planetary Atmospheres Program are
gratefully acknowledged.
Title: Scaling the Ion Inertial Length and Its Implications for
Modeling Reconnection in Global Simulations
Authors: Tóth, Gábor; Chen, Yuxi; Gombosi, Tamas I.; Cassak, Paul;
Markidis, Stefano; Peng, Ivy Bo
Bibcode: 2017JGRA..12210336T
Altcode:
We investigate the use of artificially increased ion and electron
kinetic scales in global plasma simulations. We argue that as long
as the global and ion inertial scales remain well separated, (1) the
overall global solution is not strongly sensitive to the value of the
ion inertial scale, while (2) the ion inertial scale dynamics will also
be similar to the original system, but it occurs at a larger spatial
scale, and (3) structures at intermediate scales, such as magnetic
islands, grow in a self-similar manner. To investigate the validity and
limitations of our scaling hypotheses, we carry out many simulations
of a two-dimensional magnetosphere with the magnetohydrodynamics with
embedded particle-in-cell (MHD-EPIC) model. The PIC model covers
the dayside reconnection site. The simulation results confirm that
the hypotheses are true as long as the increased ion inertial length
remains less than about 5% of the magnetopause standoff distance. Since
the theoretical arguments are general, we expect these results to
carry over to three dimensions. The computational cost is reduced
by the third and fourth powers of the scaling factor in two- and
three-dimensional simulations, respectively, which can be many orders
of magnitude. The present results suggest that global simulations
that resolve kinetic scales for reconnection are feasible. This is a
crucial step for applications to the magnetospheres of Earth, Saturn,
and Jupiter and to the solar corona.
Title: The Dehydration of Water Worlds via Atmospheric Losses
Authors: Dong, Chuanfei; Huang, Zhenguang; Lingam, Manasvi; Tóth,
Gábor; Gombosi, Tamas; Bhattacharjee, Amitava
Bibcode: 2017ApJ...847L...4D
Altcode: 2017arXiv170901219D
We present a three-species multi-fluid magnetohydrodynamic model
(H+, H2O+, and e -),
endowed with the requisite atmospheric chemistry, that is capable
of accurately quantifying the magnitude of water ion losses from
exoplanets. We apply this model to a water world with Earth-like
parameters orbiting a Sun-like star for three cases: (I) current normal
solar wind conditions, (II) ancient normal solar wind conditions,
and (III) one extreme “Carrington-type” space weather event. We
demonstrate that the ion escape rate for (II), with a value of 6.0 ×
1026 s-1, is about an order of magnitude higher
than the corresponding value of 6.7 × 1025 s-1
for (I). Studies of ion losses induced by space weather events, where
the ion escape rates can reach ∼1028 s-1,
are crucial for understanding how an active, early solar-type star
(e.g., with frequent coronal mass ejections) could have accelerated
the depletion of the exoplanet’s atmosphere. We briefly explore
the ramifications arising from the loss of water ions, especially
for planets orbiting M-dwarfs where such effects are likely to be
significant.
Title: Noether's theorems and conserved currents in gauge theories
in the presence of fixed fields
Authors: Tóth, Gábor Zsolt
Bibcode: 2017PhRvD..96b5018T
Altcode: 2016arXiv161003281T
We extend the standard construction of conserved currents for
matter fields in general relativity to general gauge theories. In
the original construction, the conserved current associated with
a spacetime symmetry generated by a Killing field hμ
is given by √{-g }Tμ νhν , where Tμ
ν is the energy-momentum tensor of the matter. We show that if
in a Lagrangian field theory that has gauge symmetry in the general
Noetherian sense some of the elementary fields are fixed and are
invariant under a particular infinitesimal gauge transformation, then
there is a current Bμ that is analogous to √{-g }Tμ
νhν and is conserved if the nonfixed fields satisfy
their Euler-Lagrange equations. The conservation of Bμ
can be seen as a consequence of an identity that is a generalization of
∇μTμ ν=0 and is a consequence of the gauge
symmetry of the Lagrangian. This identity holds in any configuration of
the fixed fields if the nonfixed fields satisfy their Euler-Lagrange
equations. We also show that Bμ differs from the relevant
canonical Noether current by the sum of an identically conserved current
and a term that vanishes if the nonfixed fields are on shell. For an
example, we discuss the case of general, possibly fermionic, matter
fields propagating in fixed gravitational and Yang-Mills background. We
find that in this case the generalization of ∇μTμ
ν=0 is the Lorentz law ∇μTμ ν-Fa
ν λJa λ=0 , which holds as a consequence of the
diffeomorphism, local Lorentz and Yang-Mills gauge symmetry of the
matter Lagrangian. For a second simple example, we consider the case
of general fields propagating in a background that consists of a
gravitational and a real scalar field.
Title: Spectral Analysis of Heating Processes in the Alfvén Wave
Driven Global Corona Model
Authors: Szente, Judit; Toth, Gabor; Landi, Enrico; Manchester, Ward;
van der Holst, Bart; Gombosi, Tamas
Bibcode: 2017shin.confE..78S
Altcode:
Among numerous theories explaining the existence of the hot solar
corona and continuous solar wind, one of the most successful one is
based on wave heating. This approach describes Alfvén waves traveling
along the magnetic field lines carrying sufficient energy to heat the
corona and accelerate the solar wind. The wave energy is deposited
through turbulent dissipation, which leaves identifiable traces in the
plasma. Spectral observations have suggested the existence of wave
heating: via the decrease of non-thermal spectral line broadening,
and via charge state ratios of specific minor-ions reflecting the
heating history of the solar wind plasma. We determine the extent
to which Alfvén-waves drive the solar corona using a combination of
spectral modeling and observational techniques. In this study,
we reevaluate observational evidence of the coronal heating process:
we simulate observations of the global corona and its spectral line
emission with the Alfvén Wave Solar Model (AWSoM) and compare the
synthetic data with observations.
Title: Consequences of treating the solar magnetic field as a dipole
on the global structure of the heliosphere and an update on the
OH-PT model
Authors: Michael, Adam Thomas; Opher, Merav; Toth, Gabor; Tenishev,
Valeriy; Borovikov, Dmitry
Bibcode: 2017shin.confE.168M
Altcode:
Through the use of numerical models, we have begun to realize the
importance the solar magnetic field has on the heliosphere. The aim
of all outer heliosphere simulations is to accurately model the solar
magnetic field, including a self-consistent approach to the heliospheric
current sheet. We investigate the effect that including the heliospheric
current sheet has on our global 3D MHD model of the heliosphere. We
compare the unipolar model, where the polarity of the Parker spiral
is the same in both hemispheres, to the dipole description of the
solar magnetic field with the magnetic and rotational axes aligned
forming a flat heliospheric current sheet, defined as a discontinuity
between polarities. The flat current sheet is pulled into the northern
hemisphere, avoiding the stagnation region, and reduces the magnetic
field strength at the Voyager 1 trajectory over the last 22.5% of the
heliosheath. The decrease in magnetic field intensity is transferred
into the thermal energy of the plasma causing the dipole model to
predict an entirely thermally dominated heliosheath, a stark contrast
to the magnetically dominated region ahead of the heliopause in the
unipole model. The jet that forms within the current sheet increases
the radial velocity and ram pressure just downstream of the heliopause
causing the heliopause to be asymmetric and located further in the
northern hemisphere. We find that the two-lobe structure of the solar
wind magnetic field persists within the dipole model with the flat
current sheet not able to fully erode the magnetic tension force. We
also present an update of the OH-PT model within SWMF. The OH-PT model
is a kinetic-MHD model that couples the BATS-R-US MHD solver to AMPS,
a DSMC code used to solve the Boltzmann equation for the distribution
function of the neutrals and energetic neutral atoms streaming through
the heliosphere.
Title: Calculating the inductive electric field in the terrestrial
magnetosphere
Authors: Ilie, Raluca; Daldorff, Lars K. S.; Liemohn, Michael W.;
Toth, Gabor; Chan, Anthony A.
Bibcode: 2017JGRA..122.5391I
Altcode:
This study presents a theoretical approach to calculate the inductive
electric field, and it is further applied to global MHD simulations
of the magnetosphere. The contribution of the inductive component to
the total electric field is found by decomposing the motional electric
field into a superposition of an irrotational and a solenoidal vector
and assuming that the time-varying magnetic field vanishes on the
boundary. We find that a localized change in the magnetic field
generates an inductive electric field whose effect extends over all
space, meaning that the effect of the inductive electric field is global
even if the changes in the magnetic field are localized. Application
of this formalism to disturbed times provides strong evidence that
during periods of increased activity the electric field induced
by the localized change in magnetic field can be comparable to (or
larger than) the potential electric fields in certain regions. This
induced field exhibits significant spatial and temporal variations,
which means that particles that drift into different regions of space
are being exposed to different means of acceleration. These results
suggest that the inductive electric field could have a substantial
contribution to particle energization in the near-Earth region even
though the changes in the magnetic fields occur at distances of several
tens of Earth radii. This finding is particularly important for ring
current modeling which in many cases excludes inductive contributions
to the total particle drift.
Title: Effects of electric field methods on modeling the midlatitude
ionospheric electrodynamics and inner magnetosphere dynamics
Authors: Yu, Yiqun; Jordanova, Vania K.; Ridley, Aaron J.; Toth,
Gabor; Heelis, Roderick
Bibcode: 2017JGRA..122.5321Y
Altcode:
We report a self-consistent electric field coupling between the
midlatitude ionospheric electrodynamics and inner magnetosphere dynamics
represented in a kinetic ring current model. This implementation in
the model features another self-consistency in addition to its already
existing self-consistent magnetic field coupling with plasma. The
model is therefore named as Ring current-Atmosphere interaction
Model with Self-Consistent magnetic (B) and electric (E) fields,
or RAM-SCB-E. With this new model, we explore, by comparing with
previously employed empirical Weimer potential, the impact of using
self-consistent electric fields on the modeling of storm time global
electric potential distribution, plasma sheet particle injection,
and the subauroral polarization streams (SAPS) which heavily rely on
the coupled interplay between the inner magnetosphere and midlatitude
ionosphere. We find the following phenomena in the self-consistent
model: (1) The spatially localized enhancement of electric field is
produced within 2.5 < L < 4 during geomagnetic active time in the
dusk-premidnight sector, with a similar dynamic penetration as found in
statistical observations. (2) The electric potential contours show more
substantial skewing toward the postmidnight than the Weimer potential,
suggesting the resistance on the particles from directly injecting
toward the low-L region. (3) The proton flux indeed indicates that the
plasma sheet inner boundary at the dusk-premidnight sector is located
further away from the Earth than in the Weimer potential, and a "tongue"
of low-energy protons extends eastward toward the dawn, leading to
the Harang reversal. (4) SAPS are reproduced in the subauroral region,
and their magnitude and latitudinal width are in reasonable agreement
with data.
Title: Variability of Jupiter's IR H3+ aurorae
during Juno approach
Authors: Moore, L.; O'Donoghue, J.; Melin, H.; Stallard, T.; Tao,
C.; Zieger, B.; Clarke, J.; Vogt, M. F.; Bhakyapaibul, T.; Opher,
M.; Tóth, G.; Connerney, J. E. P.; Levin, S.; Bolton, S.
Bibcode: 2017GeoRL..44.4513M
Altcode:
We present ground-based observations of Jupiter's
H3+ aurorae over four nights in April 2016
while the Juno spacecraft was monitoring the upstream interplanetary
magnetic field. High-precision maps of auroral H3+
densities, temperatures, and radiances reveal significant variabilities
in those parameters, with regions of enhanced density and emission
accompanied by reduced temperature. Juno magnetometer data,
combined with solar wind propagation models, suggest that a shock
may have impacted Jupiter in the days preceding the observation
interval but that the solar wind was quiescent thereafter. Auroral
H3+ temperatures reveal a downward temporal trend,
consistent with a slowly cooling upper atmosphere, such as might follow
a period of shock recovery. The brightest H3+
emissions are from the end of the period, 23 April. A lack of
definitive signatures in the upstream interplanetary magnetic field
lends supporting evidence to the possibility that this brightening
event may have been driven by internal magnetospheric processes.
Title: MHD Coupling with PIC to Study the Magnetic Reconnection
Process in the Martian Plasma Tail
Authors: Ma, Yingjuan; Russell, Christopher; Toth, Gabor; Chen,
Yuki; Nagy, Andrew; Harada, Yuki; McFadden, James; Halekas, Jasper;
Connerney, Jack; Jakosky, Bruce; Markidis, Stefano; Peng, Ive
Bibcode: 2017EGUGA..1910180M
Altcode:
Mars Atmosphere and Volatile EvolutioN Mission (MAVEN) observations
showed clear evidence that magnetic reconnection happens in the Martian
plasma tail. We use both the HALL MHD model and the two-way coupled
MHD-PIC model to study a MAVEN magnetotail reconnection event based
on the observed solar wind conditions to understand the reconnection
process and quantify its global consequences. The coupled approach takes
advantage of both MHD and PIC models, making it feasible to conduct
kinetic simulations under realistic solar wind conditions. Model results
show that the Martian magnetotail is highly dynamic and the Marsward
plasma flow velocities due to magnetic reconnection are higher for
the lighter ion fluid, which are quantatively consistent with MAVEN
observations. The effect of the magnetic reconnection on the total
ion loss rate will also be discussed based on model results.
Title: The Twist of the Draped Interstellar Magnetic Field Ahead
of the Heliopause: A Magnetic Reconnection Driven Rotational
Discontinuity
Authors: Opher, M.; Drake, J. F.; Swisdak, M.; Zieger, B.; Toth, G.
Bibcode: 2017ApJ...839L..12O
Altcode: 2017arXiv170206178O
Based on the difference between the orientation of the interstellar B
ISM and the solar magnetic fields, there was an expectation
that the magnetic field direction would rotate dramatically across
the heliopause (HP). However, the Voyager 1 spacecraft measured
very little rotation across the HP. Previously, we showed that the B
ISM twists as it approaches the HP and acquires a strong
T component (east-west). Here, we establish that reconnection in the
eastern flank of the heliosphere is responsible for the twist. On the
eastern flank the solar magnetic field has twisted into the positive N
direction and reconnects with the southward pointing component of the
B ISM. Reconnection drives a rotational discontinuity (RD)
that twists the B ISM into the -T direction and propagates
upstream in the interstellar medium toward the nose. The consequence is
that the N component of B ISM is reduced in a finite width
band upstream of the HP. Voyager 1 currently measures angles (δ ={\sin
}-1({B}N/B)) close to solar values. We present MHD
simulations to support this scenario, suppressing reconnection in the
nose region while allowing it in the flanks, consistent with recent
ideas about reconnection suppression from diamagnetic drifts. The
jump in plasma β (the plasma to magnetic pressure) across the nose
of HP is much greater than in the flanks because the heliosheath β is
greater there than in the flanks. Large-scale reconnection is therefore
suppressed in the nose but not at the flanks. Simulation data suggest
that B ISM will return to its pristine value 10-15 au past
the HP.
Title: Variations of the Martian plasma environment during the ICME
passage on 8 March 2015: A time-dependent MHD study
Authors: Ma, Y. J.; Russell, C. T.; Fang, X.; Dong, C. F.; Nagy,
A. F.; Toth, G.; Halekas, J. S.; Connerney, J. E. P.; Espley, J. R.;
Mahaffy, P. R.; Benna, M.; McFadden, J.; Mitchell, D. L.; Andersson,
L.; Jakosky, B. M.
Bibcode: 2017JGRA..122.1714M
Altcode:
The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft observed
a strong interplanetary coronal mass ejection (ICME) impacting Mars on
8 March 2015. We use a time-dependent global MHD model to investigate
the response of the Martian ionosphere and induced magnetosphere to the
large solar wind disturbance associated with the ICME. Taking observed
upstream solar wind conditions from MAVEN as inputs to the MHD model,
the variations of the Martian plasma environments are simulated
realistically in a time period from 2.5 h prior to the arrival of
the ICME shock to about 12 h after the impact. Detailed comparisons
between the model results and the relevant MAVEN plasma measurements
are presented, which clearly show that the time-dependent multispecies
single-fluid MHD model is able to reproduce the main features observed
by the spacecraft during the ICME passage. Model results suggest
that the induced magnetosphere responds to solar wind variation on
a very short time scale (approximately minutes). The variations of
the plasma boundaries' distances from the planet along the subsolar
line are examined in detail, which show a clear anticorrelation with
the magnetosonic Mach number. Plasma properties in the ionosphere
(especially the induced magnetic field) varied rapidly with solar
wind changes. Model results also show that ion escape rates could be
enhanced by an order of magnitude in response to the high solar wind
dynamic pressure during the ICME event.
Title: Coronal Jets Simulated with the Global Alfvén Wave Solar Model
Authors: Szente, J.; Toth, G.; Manchester, W. B., IV; van der Holst,
B.; Landi, E.; Gombosi, T. I.; DeVore, C. R.; Antiochos, S. K.
Bibcode: 2017ApJ...834..123S
Altcode:
This paper describes a numerical modeling study of coronal jets to
understand their effects on the global corona and their contribution
to the solar wind. We implement jets into a well-established
three-dimensional, two-temperature magnetohydrodynamic (MHD) solar
corona model employing Alfvén-wave dissipation to produce a realistic
solar-wind background. The jets are produced by positioning a compact
magnetic dipole under the solar surface and rotating the boundary plasma
around the dipole's magnetic axis. The moving plasma drags the magnetic
field lines along with it, ultimately leading to a reconnection-driven
jet similar to that described by Pariat et al. We compare line-of-sight
synthetic images to multiple jet observations at EUV and X-ray
bands, and find very close matches in terms of physical structure,
dynamics, and emission. Key contributors to this agreement are the
greatly enhanced plasma density and temperature in our jets compared
to previous models. These enhancements arise from the comprehensive
thermodynamic model that we use and, also, our inclusion of a dense
chromosphere at the base of our jet-generating regions. We further
find that the large-scale corona is affected significantly by the
outwardly propagating torsional Alfvén waves generated by our polar
jet, across 40° in latitude and out to 24 R⊙. We estimate
that polar jets contribute only a few percent to the steady-state
solar-wind energy outflow.
Title: Chromosphere to 1 AU Simulation of the 2011 March 7th Event:
A Comprehensive Study of Coronal Mass Ejection Propagation
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Sokolov, I.;
Tóth, G.; Vourlidas, A.; de Koning, C. A.; Gombosi, T. I.
Bibcode: 2017ApJ...834..172J
Altcode: 2016arXiv161108897J
We perform and analyze the results of a global magnetohydrodynamic
simulation of the fast coronal mass ejection (CME) that occurred
on 2011 March 7. The simulation is made using the newly developed
Alfvén Wave Solar Model (AWSoM), which describes the background
solar wind starting from the upper chromosphere and extends to
24 R⊙. Coupling AWSoM to an inner heliosphere model
with the Space Weather Modeling Framework extends the total domain
beyond the orbit of Earth. Physical processes included in the model
are multi-species thermodynamics, electron heat conduction (both
collisional and collisionless formulations), optically thin radiative
cooling, and Alfvén-wave turbulence that accelerates and heats the
solar wind. The Alfvén-wave description is physically self-consistent,
including non-Wentzel-Kramers-Brillouin reflection and physics-based
apportioning of turbulent dissipative heating to both electrons and
protons. Within this model, we initiate the CME by using the Gibson-Low
analytical flux rope model and follow its evolution for days, in which
time it propagates beyond STEREO A. A detailed comparison study is
performed using remote as well as in situ observations. Although the
flux rope structure is not compared directly due to lack of relevant
ejecta observation at 1 au in this event, our results show that the
new model can reproduce many of the observed features near the Sun
(e.g., CME-driven extreme ultraviolet [EUV] waves, deflection of the
flux rope from the coronal hole, “double-front” in the white light
images) and in the heliosphere (e.g., shock propagation direction,
shock properties at STEREO A).
Title: Data-constrained Coronal Mass Ejections in a Global
Magnetohydrodynamics Model
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Sokolov, I.;
Tóth, G.; Mullinix, R. E.; Taktakishvili, A.; Chulaki, A.; Gombosi,
T. I.
Bibcode: 2017ApJ...834..173J
Altcode: 2016arXiv160505360J
We present a first-principles-based coronal mass ejection (CME)
model suitable for both scientific and operational purposes by
combining a global magnetohydrodynamics (MHD) solar wind model with
a flux-rope-driven CME model. Realistic CME events are simulated
self-consistently with high fidelity and forecasting capability by
constraining initial flux rope parameters with observational data from
GONG, SOHO/LASCO, and STEREO/COR. We automate this process so that
minimum manual intervention is required in specifying the CME initial
state. With the newly developed data-driven Eruptive Event Generator
using Gibson-Low configuration, we present a method to derive Gibson-Low
flux rope parameters through a handful of observational quantities so
that the modeled CMEs can propagate with the desired CME speeds near
the Sun. A test result with CMEs launched with different Carrington
rotation magnetograms is shown. Our study shows a promising result
for using the first-principles-based MHD global model as a forecasting
tool, which is capable of predicting the CME direction of propagation,
arrival time, and ICME magnetic field at 1 au (see the companion paper
by Jin et al. 2016a).
Title: A new 3D multi-fluid dust model: a study of the effects of
activity and nucleus rotation on the dust grains' behavior in the
cometary environment
Authors: Shou, Y.; Combi, M. R.; Toth, G.; Fougere, N.; Tenishev,
V.; Huang, Z.; Jia, X.; Hansen, K. C.; Gombosi, T. I.; Bieler, A. M.;
Rubin, M.
Bibcode: 2016AGUFM.P43A2099S
Altcode:
Cometary dust observations may deepen our understanding of the role
of dust in the formation of comets and in altering the cometary
environment. Models including dust grains are in demand to interpret
observations and test hypotheses. Several existing models have taken
into account the gas-dust interaction, varying sizes of dust grains and
the cometary gravitational force. In this work, we develop a multi-fluid
dust model based on BATS-R-US in the University of Michigan's Space
Weather Modeling Framework (SWMF). This model not only incorporates
key features of previous dust models, but also has the capability
of simulating time-dependent phenomena. Since the model is running
in the rotating comet reference frame with a real shaped nucleus in
the computational domain, the fictitious centrifugal and Coriolis
forces are included. The boundary condition on the nucleus surface
can be set according to the distribution of activity and the solar
illumination. The Sun, which drives sublimation and the radiation
pressure force, revolves around the comet in this frame. A newly
developed numerical mesh is also used to resolve the real shaped nucleus
in the center and to facilitate prescription of the outer boundary
conditions that accommodate the rotating frame. The inner part of the
grid is a box composed of Cartesian cells and the outer surface is a
smooth sphere, with stretched cells filled in between the box and the
sphere. The effects of the rotating nucleus and the activity region on
the surface are discussed and preliminary results are presented. This
work has been partially supported by grant NNX14AG84G from the NASA
Planetary Atmospheres Program, and US Rosetta contracts JPL #1266313,
JPL #1266314 and JPL #1286489.
Title: Increased electron pressure as possible origin of magnetic
field dropouts observed by RPC-MAG of comet 67P/Churyumov-Gerasimenko
Authors: Huang, Z.; Toth, G.; Gombosi, T. I.; Bieler, A. M.; Combi,
M. R.; Hansen, K. C.; Jia, X.; Fougere, N.; Shou, Y.; Cravens, T.;
Tenishev, V.; Altwegg, K.; Rubin, M.
Bibcode: 2016AGUFM.P43A2091H
Altcode:
The Rosetta Plasma Consortium MAGnetometer (RPC-MAG) has observed
signatures of magnetic field dropouts in the inner coma region of comet
67P/Churyumov-Gerasimenko at distances from 30km to 400km, which is
larger than what has been predicted by numerical simulations of the
cometary plasma environment. It is still unclear how these magnetic
field dropouts form in the inner coma region. In the present work, we
use our newly developed multi-fluid plasma-neutral interaction model
(Huang et al. 2016) to investigate this problem. The model solves the
governing multi-ion MHD equations for the cometary and solar wind ions
and electrons, and the Euler equations for the neutral gas fluid. We
show that a strong local increase of electron pressure is capable
to generate the features of the magnetic field dropouts observed by
RPC-MAG: the simulation results show that a low magnetic field region
is formed and the recovery phase of the magnetic field magnitude is
faster than the declining phase, which suggests that the mechanism
proposed here based on localized enhancement of electron pressure may
provide a possible explanation for the unusually large distance of
the observed magnetic field dropouts.
Title: How Numerical Magnetic Dissipation at the Heliospheric
Current Sheet Affects Model Predictions at Voyager 1 and Results
from a Kinetic-MHD Model of the Heliosphere within SWMF
Authors: Michael, A.; Opher, M.; Toth, G.; Borovikov, D.; Tenishev,
V.; Provornikova, E.
Bibcode: 2016AGUFMSH41C2544M
Altcode:
Several studies suggest that there is a need to move beyond ideal MHD
in order to explain the Voyager 1 and 2 observations (Richardson et
al. 2013; Michael et al. 2015). In the numerical simulations there
is inherent and unavoidable numerical dissipation in the heliospheric
current sheet that greatly exceeds the realistic dissipation rates. The
magnetic dissipation inherent in modeling the heliospheric current
sheet offers us a chance to explore non-ideal MHD effects in the
heliosphere and heliosheath. In this work we investigate the role
magnetic dissipation has on the overall structure of the heliosheath
by comparing models describing the solar magnetic field both as a
unipole and a dipole. We show that magnetic dissipation reduces the
solar wind magnetic field strength over a significant fraction of
the heliosheath. The region affected by the dissipation is increased
when 11-year solar cycle variations in the solar wind are included
and we discuss how this alters our prediction for Voyager 1 and 2
observations. We also present a new kinetic-MHD model of the outer
heliosphere, which couples the Outer Heliosphere (OH) and Particle
Tracker (PT) components within the Space Weather Modeling Framework
(SWMF). The OH component uses the BATS-R-US MHD solver, a highly
parallel, 3D, and block-adaptive code. The PT component is based on the
Adaptive Mesh Particle Simulator (AMPS) model, a 3D, direct simulation
Monte Carlo model that solves the Boltzmann equation for the motion and
interaction of a multi-species gas within a plasma. The neutrals and
plasma in the outer heliosphere are coupled through charge-exchange;
the OH-PT model combines the MHD solution for the plasma with the
kinetic solution for the neutrals to form a self-consistent model
of the heliosphere. We present preliminary results of this model and
discuss the implications on the structure of the heliosphere.
Title: Multi-fluid MHD study of the solar wind interaction with Pluto
Authors: Dong, C.; Ma, Y.; McComas, D. J.; Bhattacharjee, A.;
Zirnstein, E.; Toth, G.; Luhmann, J. G.; Wang, L.
Bibcode: 2016AGUFMSM51E2558D
Altcode:
The study of the solar wind interaction with Pluto's upper atmosphere
has triggered a great of interest in recent years. The Solar Wind
Around Pluto (SWAP) instrument onboard New Horizon (NH) spacecraft
has provided a wealth of detailed and quantitative information about
Pluto and its interaction with the tenuous solar wind out at 33 AU. The
SWAP data reveals Pluto's unique interaction with the solar wind as a
hybrid of comet-like and the Venus/Mars-like interactions. While SWAP
data has provided many of the key results, a lot of details are still
missing merely based on NH flyby observations. In order to further
investigate the solar wind-Pluto interaction from a global point of
view, we develop a 3-D multi-fluid MHD (MF-MHD) model. The MF-MHD
model solves separate continuity, momentum and energy equations for
each ion species. We adopt the 1-D modeled neutral atmosphere, which
is based on NH observations, as the MF-MHD input. Photoionization,
charge exchange and electron impact ionization are all included in
the MF-MHD model. We will study the ion escape rate, and Pluto's
magnetosphere and heavy ion tail structure. We will also do some
data-model comparisons. This work has the potential to improve our
understanding of present day Pluto's unique solar wind interaction
and thus enhance the science returned from the NH mission.
Title: Probing the nature of pick-up ions (and kappa distribution)
in the heliosheath through global ENA measurements and in-situ
measurements
Authors: Opher, M.; Zieger, B.; Drake, J. F.; Kornbleuth, M. Z.;
Toth, G.
Bibcode: 2016AGUFMSH13D..01O
Altcode:
Both Voyager and IBEX are providing us with an un-precedent view of
the nature of the heliosheath through in situ and global ENA maps. Both
their measurements indicated that the thermodynamic of the heliosheath
is dominated by the presence of pick-up ions (PUIs). Kappa distributions
are routinely used to capture the presence of PUIs. Recently we
investigated the nature of the crossing of the termination shock
by the presence of the pick-up ions (Zieger et al. 2015). We were
able to constrain the properties of the PUI in the heliosheath by
matching the Voyager observations to the properties of the non-linear
structures created by the multi-fluid nature of the solar wind called
"oscilliton". Here we will review these results as well as our recent
effort on understanding the nature of the turbulence of the heliosheath
by the presence of pick-up ions. We will review as well our recent
proposed scenario where that the structure of the heliosphere might be
very different than we previously thought (Opher et al. 2015). We showed
(Opher et al. 2015, Drake et al. 2015) that the magnetic tension of the
solar magnetic field plays a crucial role on organizing the solar wind
in the heliosheath into two jet-like structures. The global ENA maps
provide another window in constraining the pick-up ions and heating
in the heliosheath (Opher et al. 2013). We will discuss the resultant
maps from the "heliosphere with jets" and the constrains on the nature
of the pick-up ions in the heliosheath.
Title: Validation of 2D and 3D MHD with embedded PIC (MHD-EPIC)
simulations against MMS observations
Authors: Chen, Y.; Toth, G.; Gombosi, T. I.; Markidis, S.; Peng,
I. B.; Cassak, P.; Hietala, H.
Bibcode: 2016AGUFMSM14B..06C
Altcode:
We carry out 2D and 3D global simulations of Earth's magnetosphere with
the recently developed MHD-EPIC model, which is a two-way coupling of
the extended magnetohydrodynamic (XMHD) code BATS-R-US with the implicit
Particle-in-Cell (PIC) model iPIC3D. The PIC model covers both the
dayside and tail reconnection regions, while the global Hall MHD code
handles the rest of the computational domain. We use several 2D global
simulations to demonstrate that the size and dynamics of flux ropes
at the dayside do not depend on either ion mass or grid resolution as
long as the MHD quantities are fixed. Increasing the ion mass allows
the kinetic physics to be resolved with reasonable computational
resources. Similar to the MMS observations, the crescent-shape electron
phase space distribution is found near the reconnection site in the
global 2D simulations. The tail reconnection site is also covered
by PIC model for these 2D cases. The difference between the dayside
reconnection and the tail reconnection is compared. We also carry out
3D MHD-EPIC global simulations for MMS events with varying solar wind
conditions. Since MHD-EPIC simulations provide both electron and ion
information, we can compare the kinetic property of particles with
MMS observation besides electromagnetic fields.
Title: Effects of Induction and Magnetopause Reconnection on Mercury's
Magnetosphere: MESSENGER Observations and Global MHD Simulations
with Coupled Planetary Interior
Authors: Jia, X.; Slavin, J. A.; Poh, G.; Toth, G.; Gombosi, T. I.
Bibcode: 2016AGUFMSM41C2455J
Altcode:
It has long been suggested that two processes, i.e., erosion of the
dayside magnetosphere due to strong magnetopause reconnection and the
shielding effect of the induction currents at the planetary core,
compete against each other in governing the structure of Mercury's
magnetosphere. We have combined analysis of MESSENGER data during
extreme solar wind conditions with global MHD simulations to assess
the relative importance of the two processes. Following the study of
Slavin et al. (2014), we have analyzed an additional set of MESSENGER
magnetopause crossings to determine the dependence of the magnetopause
standoff distance on solar wind parameters. We have also employed
the global MHD model of Jia et al. (2015) that electromagnetically
couples Mercury's interior to the surrounding space environment
to simulate the response of the system to solar wind forcing for a
wide range of solar wind and IMF conditions. We find that while the
magnetopause standoff distance decreases with increasing solar wind
pressure, just as expected, its dependence on the external pressure
follows closely a power-law relationship with an index of -1/6,
rather than a steeper power-law falling-off expected for the case
with only induction present. Our results suggest that for the external
conditions examined, induction and magnetopause reconnection appear to
play equally important roles in determining the global configuration
of Mercury's magnetosphere, consistent with the finding obtained by
Slavin et al. (2014). We also find that the magnetospheric current
systems produce magnetic perturbations that are spatially non-uniform in
nature, resulting in induced magnetic field at the core that contains
significant power in both the dipole and high order moments. Based
on the simulation results, we determine how the induced field varies
with the solar wind conditions, and provide quantitative constraints
on the ability of Mercury's core to shield the planetary surface from
direct solar wind impact.
Title: MHD Modeling of Jupiter's Magnetosphere using the Space
Weather Modeling Framework (SWMF): Preliminary Results
Authors: Sarkango, Y.; Jia, X.; Toth, G.; Hansen, K. C.
Bibcode: 2016AGUFMSM51E2532S
Altcode:
Jupiter's magnetosphere is driven predominantly by its rapid
rotation and high rate of internal plasma loading arising from the
moon, Io. Modeling this system using magnetohydrodynamics (MHD)
provides a means to understand magnetospheric dynamics from a global
perspective. However, MHD modeling of Jupiter's magnetosphere is
computationally challenging mainly due to the system size and the
large wave speeds close to the planet. Using the Space Weather Modeling
Framework, we have modeled the Jovian magnetosphere with a single-fluid
approach and a combined explicit and implicit scheme that enables large
time steps making it feasible to simulate the magnetosphere for long
periods of time at acceptable computational cost. Unlike previous MHD
models that assume the magnetic dipole to be aligned with the spin axis,
our model includes the 10° tilt of Jupiter's dipole in order to capture
the periodic modulations driven by this non-axisymmetric internal
field, one of the fundamental features of the Jovian magnetosphere. Our
simulation also includes effects of mass loading based on an empirical
neutral gas distribution peaked around Io's orbit, which is ionized and
added as source terms in the MHD equations. As a first step, we drive
our simulation with steady solar wind conditions in order to establish
a physical picture of the global configuration of the magnetosphere,
such as the global convection pattern and large-scale current systems
present in the magnetosphere. We observe that the magnetosphere consists
of distinguishable regions with varying degrees of corotation. Moreover,
the central plasma sheet is found to exhibit oscillatory behavior due to
the tilt of the dipole axis. We compare the model output with Galileo
particle and field measurements, such as plasma density, velocity,
and magnetic field, in order to validate our model.
Title: Collisionless Asymmetric Magnetic Reconnection in 3D MHD-EPIC
Global Simulations
Authors: Markidis, S.; Peng, I. B.; Chen, Y.; Toth, G.; Gombosi,
T. I.; Erkisson, E.; Johlander, A.; Khotyaintsev, Y. V.; Vaivads,
A.; Laure, E.
Bibcode: 2016AGUFMSM21A2413M
Altcode:
Kinetic simulations that are embedded in global MHD simulations
(MHD-EPIC) enable the study of collisionless magnetic reconnection
in realistic configurations. The MHD simulation solves the global
interaction of solar wind with the planet magnetosphere over the whole
domain while the kinetic simulations are performed only in the selected
regions where kinetic physics plays a critical role. The coupling
between MHD and kinetic simulations is two-way as the MHD simulation
provides boundary conditions to the kinetic simulations while the
results of the kinetic simulations overwrite the results of the MHD
simulations. One of the main applications of this simulation technique
is the study of magnetic reconnection with local kinetic simulations
only in the magnetopause and the magnetotail regions. We carry out 3D
local iPIC3D Particle-in-Cell (PIC) simulations in global BATS-R-US Hall
MHD simulations using the SWMF coupling framework to study the kinetic
features of driven asymmetric magnetic reconnection. Because the PIC
simulations are initialized and coupled with Hall MHD simulations,
the PIC simulations of asymmetric reconnection are carried out
in a realistic initial configuration of the electric and magnetic
fields and with a realistic driver from the boundaries. The 3D PIC
simulations resolve the electron inertial length of the system to
accurately describe the physics in the electron diffusion region
during asymmetric reconnection. The 3D PIC simulations show the
development of flux ropes as results of magnetic reconnection and the
presence of instabilities and strong wave activities in proximity of
the current sheet. In particular, electron outflow jets are unstable
against Kelvin-Helmholtz instability and lower-hybrid drift waves are
present in proximity of the current sheet. The PIC simulations also
allow us to study the electron distribution functions in the electron
diffusion region and to identify crescent-shaped electron distribution
functions as recently observed by the MMS spacecrafts. The results
of the embedded 3D PIC simulations provide a realistic picture of
collisionless asymmetric magnetic reconnection that can be used for
further understanding the observations from MMS.
Title: A New 3D Multi-fluid Model: A Study of Kinetic Effects and
Variations of Physical Conditions in the Cometary Coma
Authors: Shou, Y.; Combi, M.; Toth, G.; Tenishev, V.; Fougere, N.;
Jia, X.; Rubin, M.; Huang, Z.; Hansen, K.; Gombosi, T.; Bieler, A.
Bibcode: 2016ApJ...833..160S
Altcode:
Physics-based numerical coma models are desirable whether to interpret
the spacecraft observations of the inner coma or to compare with the
ground-based observations of the outer coma. In this work, we develop a
multi-neutral-fluid model based on the BATS-R-US code of the University
of Michigan, which is capable of computing both the inner and outer
coma and simulating time-variable phenomena. It treats H2O,
OH, H2, O, and H as separate fluids and each fluid has
its own velocity and temperature, with collisions coupling all fluids
together. The self-consistent collisional interactions decrease the
velocity differences, re-distribute the excess energy deposited by
chemical reactions among all species, and account for the varying
heating efficiency under various physical conditions. Recognizing
that the fluid approach has limitations in capturing all of the
correct physics for certain applications, especially for very
low density environment, we applied our multi-fluid coma model to
comet 67P/Churyumov-Gerasimenko at various heliocentric distances
and demonstrated that it yields comparable results to the Direct
Simulation Monte Carlo (DSMC) model, which is based on a kinetic
approach that is valid under these conditions. Therefore, our model may
be a powerful alternative to the particle-based model, especially for
some computationally intensive simulations. In addition, by running the
model with several combinations of production rates and heliocentric
distances, we characterize the cometary H2O expansion
speeds and demonstrate the nonlinear dependencies of production rate
and heliocentric distance. Our results are also compared to previous
modeling work and remote observations, which serve as further validation
of our model.
Title: Studying the thermodynamics of coronal jets through modeling-
and observational diagnostics techniques
Authors: Szente, J.; Manchester, W.; Landi, E.; Toth, G.; van der
Holst, B.; Gombosi, T. I.; DeVore, C. R.; Antiochos, S. K.
Bibcode: 2016AGUFMSH21E2577S
Altcode:
We present a comprehensive study of simulated and observed coronal jets
using EUV and soft X-ray narrow-band images and EUV high resolution
spectra. The goal of our study is to understand the thermodynamics
and time evolution of jets and their impact on the coronal plasma. We
simulate jets with a full 3D MHD coronal model with separate electron
and proton temperatures and heating due to Alfvén wave turbulence. Due
to the fast dynamics of the small-scale eruptive reconnections at the
footpoint of the jet, it is essential to undertake this effort with a
model with separate electron and proton temperatures to interpret the
observed signatures in EUV and soft X-ray bands. The obtained synthetic
images are compared to observations done by the instrumentations of
SDO, STEREO and Hinode space crafts. The turbulence in this model is
ideally suited to analyze the spectroscopic signatures, such as line
broadening. The 3-hour long simulation of jets interacting with the
global solar corona shows plasma responses potentially being observed
with the upcoming Solar Probe Plus mission.
Title: Dispersive Magnetosonic Waves and Turbulence in the
Heliosheath: Multi-Fluid MHD Reconstruction of Voyager 2 Observations
Authors: Zieger, B.; Opher, M.; Toth, G.
Bibcode: 2016AGUFMSH41C2542Z
Altcode:
Recently we demonstrated that our three-fluid MHD model of the solar
wind plasma (where cold thermal solar wind ions, hot pickup ions, and
electrons are treated as separate fluids) is able to reconstruct the
microstructure of the termination shock observed by Voyager 2 [Zieger
et al., 2015]. We constrained the unknown pickup ion abundance and
temperature and confirmed the presence of a hot electron population at
the termination shock, which has been predicted by a number of previous
theoretical studies [e.g. Chasei and Fahr, 2014; Fahr et al., 2014]. We
showed that a significant part of the upstream hydrodynamic energy is
transferred to the heating of pickup ions and "massless" electrons. As
shown in Zieger et al., [2015], three-fluid MHD theory predicts two
fast magnetosonic modes, a low-frequency fast mode or solar wind ion
(SW) mode and a high-frequency fast mode or pickup ion (PUI) mode. The
coupling of the two ion populations results in a quasi-stationary
nonlinear mode or oscilliton, which appears as a trailing wave
train downstream of the termination shock. In single-fluid plasma,
dispersive effects appear on the scale of the Debye length. However,
in a non-equilibrium plasma like the solar wind, where solar wind
ions and PUIs have different temperatures, dispersive effects become
important on fluid scales [see Zieger et al., 2015]. Here we show that
the dispersive effects of fast magnetosonic waves are expected on the
scale of astronomical units (AU), and dispersion plays an important
role producing compressional turbulence in the heliosheath. The
trailing wave train of the termination shock (the SW-mode oscilliton)
does not extend to infinity. Downstream propagating PUI-mode waves
grow until they steepen into PUI shocklets and overturn starting to
propagate backward. The upstream propagating PUI-mode waves result
in fast magnetosonic turbulence and limit the downstream extension of
the oscilliton. The overturning distance of the PUI-mode, where these
waves start to propagate backward, depends on the maximum growth rate
of the PUI-mode. We discuss our simulations in light of the Voyager
2 observations in the heliosheath.
Title: Resolving the Kinetic Reconnection Length Scale in Global
Magnetospheric Simulations with MHD-EPIC
Authors: Toth, G.; Chen, Y.; Cassak, P.; Jordanova, V.; Peng, B.;
Markidis, S.; Gombosi, T. I.
Bibcode: 2016AGUFMSM23C..03T
Altcode:
We have recently developed a new modeling capability: the
Magnetohydrodynamics with Embedded Particle-in-Cell (MHD-EPIC) algorithm
with support from Los Alamos SHIELDS and NSF INSPIRE grants. We have
implemented MHD-EPIC into the Space Weather Modeling Framework (SWMF)
using the implicit Particle-in-Cell (iPIC3D) and the BATS-R-US extended
magnetohydrodynamic codes. The MHD-EPIC model allows two-way coupled
simulations in two and three dimensions with multiple embedded PIC
regions. Both BATS-R-US and iPIC3D are massively parallel codes. The
MHD-EPIC approach allows global magnetosphere simulations with embedded
kinetic simulations. For small magnetospheres, like Ganymede or
Mercury, we can easily resolve the ion scales around the reconnection
sites. Modeling the Earth magnetosphere is very challenging even with
our efficient MHD-EPIC model due to the large separation between the
global and ion scales. On the other hand the large separation of
scales may be exploited: the solution may not be sensitive to the
ion inertial length as long as it is small relative to the global
scales. The ion inertial length can be varied by changing the ion mass
while keeping the MHD mass density, the velocity, and pressure the same
for the initial and boundary conditions. Our two-dimensional MHD-EPIC
simulations for the dayside reconnection region show in fact, that the
overall solution is not sensitive to ion inertial length. The shape,
size and frequency of flux transfer events are very similar for a wide
range of ion masses. Our results mean that 3D MHD-EPIC simulations for
the Earth and other large magnetospheres can be made computationally
affordable by artificially increasing the ion mass: the required grid
resolution and time step in the PIC model are proportional to the ion
inertial length. Changing the ion mass by a factor of 4, for example,
speeds up the PIC code by a factor of 256. In fact, this approach
allowed us to perform an hour-long 3D MHD-EPIC simulations for the
Earth magnetosphere.
Title: Multi-ion Multi-fluid Simulations of the Effects of Pick-up
Ions on the Global Structure of the Heliosphere
Authors: Bambic, C. J.; Opher, M.; Zieger, B.; Michael, A.; Kornbleuth,
M. Z.; Toth, G.
Bibcode: 2016AGUFMSH41C2543B
Altcode:
We present the first 3D MHD multi-ion, multi-fluid simulations
including pick-up ions as a separate fluid on the global structure of
the heliosphere. Pick-up ions, formed by charge exchange between the
solar wind and local interstellar medium, are thought to account for
the missing thermal energy measured by Voyager 2 at the crossing of the
Termination Shock. By treating the pick-up ions as a separate fluid
(with an isotropic distribution) from the solar wind thermal plasma,
we are able to isolate the properties of the suprathermal pick-up
ion plasma from that of the thermal solar wind. In addition to the
two charged ion fluids, we include four neutral fluids which interact
via charge exchange with the pick-up ion plasma. We show that pick-up
ions are dynamically important in the outer heliosphere, thinning and
heating the heliosheath. Since the neutral fluids are imprinted with the
properties of the plasma they are born from, this work has implications
for the Energetic Neutral Atom (ENA) maps of the global heliosphere. We
discuss briefly the effects on the global ENA maps of the heliosphere
in addition to measurements along the Voyager 1 and 2 trajectories.
Title: Operationalizing the Space Weather Modeling Framework:
Challenges and Resolutions
Authors: Welling, D. T.; Gombosi, T. I.; Toth, G.; Singer, H. J.;
Millward, G. H.; Balch, C. C.; Cash, M. D.
Bibcode: 2016AGUFMSM23C..06W
Altcode:
Predicting ground-based magnetic perturbations is a critical step
towards specifying and predicting geomagnetically induced currents
(GICs) in high voltage transmission lines. Currently, the Space
Weather Modeling Framework (SWMF), a flexible modeling framework for
simulating the multi-scale space environment, is being transitioned from
research to operational use (R2O) by NOAA's Space Weather Prediction
Center. Upon completion of this transition, the SWMF will provide
localized time-varying magnetic field (dB/dt) predictions using
real-time solar wind observations from L1 and the F10.7 proxy for EUV
as model input. This presentation chronicles the challenges encountered
during the R2O transition of the SWMF. Because operations relies on
frequent calculations of global surface dB/dt, new optimizations were
required to keep the model running faster than real time. Additionally,
several singular situations arose during the 30-day robustness test that
required immediate attention. Solutions and strategies for overcoming
these issues will be presented. This includes new failsafe options for
code execution, new physics and coupling parameters, and the development
of an automated validation suite that allows us to monitor performance
with code evolution. Finally, the operations-to-research (O2R) impact
on SWMF-related research is presented. The lessons learned from this
work are valuable and instructive for the space weather community as
further R2O progress is made.
Title: The role of inductive electric fields in the ring current
enhancement during the March 17th, 2013 geomagnetic storm
Authors: Ilie, R.; Toth, G.; Liemohn, M. W.; Chan, A. A.
Bibcode: 2016AGUFMSM11A2128I
Altcode:
The terrestrial magnetosphere has the capability to rapidly accelerate
charged particles up to very high energies over relatively short
times and distances. These energetic particles are injected
from the magnetotail into the inner magnetosphere through two
primary mechanisms. One transport method is the potential-driven
convection during periods of southward IMF, which allows part of the
dawn-to-dusk solar wind electric field to effectively map down to
the polar ionosphere. The second transport process involves a sudden
reconfiguration of the magnetic field and the creation of transient
induced electric fields. However, it is not possible to distinguish
the two terms by only measuring the electric field. Assessing the
relative contribution of potential versus inductive electric fields at
the energization of the hot ion population in the inner magnetosphere
is only possible by thorough examination of the time varying magnetic
field and current systems using global modeling of the entire system. We
developed a novel method to calculate the inductive and potential
components of electric field in the entire magnetosphere domain. This
approach removes the need to trace independent field lines and lifts
the assumption that the magnetic field lines can be treated as frozen
in a stationary ionosphere. We quantify the relative contributions of
potential and inductive electric fields at driving plasma sheet ions
into the inner magnetosphere during the March 17th, 2103 geomagnetic
storm. The consequence of these injections on the distortion of
the near-Earth magnetic field and current systems have been rarely
separated in order to determine their relative effectiveness from a
global perspective.
Title: New Space Weather Forecasting at NOAA with Michigan's
Geospace Model
Authors: Singer, H. J.; Millward, G. H.; Balch, C. C.; Cash, M. D.;
Onsager, T. G.; Toth, G.; Welling, D. T.; Gombosi, T. I.
Bibcode: 2016AGUFMSH11C2259S
Altcode:
We will present first results from the University of Michigan's Geospace
model that is transitioning, during 2016, from a research capability
into operations at the NOAA Space Weather Prediction Center. The
first generation of space weather products from this model will be
described. These initial products will support power grid operators,
as well as other users, with both global and regional, short-term
predictions of geomagnetic activity. The Geospace model is a coupled
system including three components: the BATS-R-US magnetohydrodynamic
(MHD) model of the magnetosphere; the Ridley ionosphere electrodynamics
model (RIM); and the Rice Convection Model (RCM), an inner magnetosphere
ring-current model developed at Rice University. The model is driven by
solar wind data from a satellite at L1 (now NOAA's DSCOVR satellite)
and F10.7, a proxy for solar extreme ultra-violet radiation. The
Geospace model runs continuously, driven by the 1-minute cadence
real-time L1 data that is propagated to the inflow boundary of the
MHD code. The model steps back to an earlier time and then continues
forward if high-speed solar wind overtakes slower solar wind. This
mode of operation is unique among the models at NOAA's National
Center for Environment Prediction's Central Operations (NCO), and it
is also different from the typical scientific simulation mode. All
of this work has involved 3D graphical model displays and validation
tools that are being developed to support forecasters and web-based
external users. Lessons learned during the transition process will
be described, as well as the iterative process that occurs between
Research and Operations and the scientific challenges for future model
and product improvements.
Title: Specification of the Surface Charging Environment with SHIELDS
Authors: Jordanova, V.; Delzanno, G. L.; Henderson, M. G.; Godinez,
H. C.; Jeffery, C. A.; Lawrence, E. C.; Meierbachtol, C.; Moulton,
J. D.; Vernon, L.; Woodroffe, J. R.; Brito, T.; Toth, G.; Welling,
D. T.; Yu, Y.; Albert, J.; Birn, J.; Borovsky, J.; Denton, M.; Horne,
R. B.; Lemon, C.; Markidis, S.; Thomsen, M. F.; Young, S. L.
Bibcode: 2016AGUFMSM23C..02J
Altcode:
Predicting variations in the near-Earth space environment that can
lead to spacecraft damage and failure, i.e. "space weather", remains
a big space physics challenge. A recently funded project through the
Los Alamos National Laboratory (LANL) Directed Research and Development
(LDRD) program aims at developing a new capability to understand, model,
and predict Space Hazards Induced near Earth by Large Dynamic Storms,
the SHIELDS framework. The project goals are to understand the dynamics
of the surface charging environment (SCE), the hot (keV) electrons
representing the source and seed populations for the radiation belts,
on both macro- and microscale. Important physics questions related to
rapid particle injection and acceleration associated with magnetospheric
storms and substorms as well as plasma waves are investigated. These
challenging problems are addressed using a team of world-class experts
in the fields of space science and computational plasma physics, and
state-of-the-art models and computational facilities. In addition to
physics-based models (like RAM-SCB, BATS-R-US, and iPIC3D), new data
assimilation techniques employing data from LANL instruments on the Van
Allen Probes and geosynchronous satellites are developed. Simulations
with the SHIELDS framework of the near-Earth space environment where
operational satellites reside are presented. Further model development
and the organization of a "Spacecraft Charging Environment Challenge"
by the SHIELDS project at LANL in collaboration with the NSF Geospace
Environment Modeling (GEM) Workshop and the multi-agency Community
Coordinated Modeling Center (CCMC) to assess the accuracy of SCE
predictions are discussed.
Title: Real-time SWMF-Geospace at CCMC: assessing the quality of
output from continuous operational simulations
Authors: Liemohn, M. W.; Welling, D. T.; De Zeeuw, D.; Kuznetsova,
M. M.; Rastaetter, L.; Ganushkina, N. Y.; Ilie, R.; Toth, G.; Gombosi,
T. I.; van der Holst, B.
Bibcode: 2016AGUFMSH31C..03L
Altcode:
The ground-based magnetometer index Dst is a decent measure of the
near-Earth current systems, in particular those in the storm-time
inner magnetosphere. The ability of a large-scale, physics-based
model to reproduce, or even predict, this index is therefore a
tangible measure of the overall validity of the code for space
weather research and space weather operational usage. Experimental
real-time simulations of the Space Weather Modeling Framework (SWMF)
are conducted at the Community Coordinated Modeling Center (CCMC),
with results available there (http://ccmc.gsfc.nasa.gov/realtime.php),
through the CCMC Integrated Space Weather Analysis (iSWA) site
(http://iswa.ccmc.gsfc.nasa.gov/IswaSystemWebApp/), and the Michigan
SWMF site (http://csem.engin.umich.edu/realtime). Presently,
two configurations of the SWMF are running in real time at
CCMC, both focusing on the geospace modules, using the BATS-R-US
magnetohydrodynamic model, the Ridley Ionosphere Model, and with and
without the Rice Convection Model for inner magnetospheric drift
physics. While both have been running for several years, nearly
continuous results are available since July 2015. Dst from the model
output is compared against the Kyoto real-time Dst. Various quantitative
measures are presented to assess the goodness of fit between the models
and observations. In particular, correlation coefficients, RMSE and
prediction efficiency are calculated and discussed. In addition,
contingency tables are presented, demonstrating the ability of the
model to predict "disturbed times" as defined by Dst values below
some critical threshold. It is shown that the SWMF run with the inner
magnetosphere model is significantly better at reproducing storm-time
values, with prediction efficiencies above 0.25 and Heidke skill
scores above 0.5. This work was funded by NASA and NSF grants, and
the European Union's Horizon 2020 research and innovation programme
under grant agreement 637302 PROGRESS.
Title: Forecasting CMEs at 1AU with a Flux Rope-Driven Model
Authors: Manchester, W.; Jin, M.; van der Holst, B.; Toth, G.;
Mullinix, R.; Taktakishvili, A.; Chulaki, A.; Gombosi, T. I.
Bibcode: 2016AGUFMSH11C2249M
Altcode:
Until recently, operational models of coronal mass ejection (CME)
propagation omitted magnetic drivers and imposed CMEs with field-free
flows. While capable of predicting the arrival times of solar wind
disturbances, such models are incapable of predicting the magnetic
ejecta of a CME, which is the fundamental driver of large geomagnetic
storms. Here, we report on a significant advancement in the development
and delivery of a magnetic flux rope-driven operational CME model
Eruptive Event Generator Gibson-Low EEGGL that was recently installed
at the Community Coordinated Modeling Center (CCMC). This new model
simulates the propagation of CMEs from Sun to 1AU by combining the
analytical Gibson & Low (GL) flux rope model with the state-of-art
Alfven Wave Solar Model. Using synoptic magnetcogram and coronagraph
observations, the model can predict the long-term evolution of the CME
magnetic fields in interplanetary space. Following the work of Jin et
al. (2016), we examine case studies of CMEs at 1 AU to illustrate the
capabilities and limitations of this space weather forecasting tool.
Title: The Heliosphere with Jets and its implications for the global
Energetic Neutral Atoms Maps throughout the Solar Cycle and its
impact on the large-scale draping of the interstellar magnetic field
Authors: Opher, M.; Drake, J. F.; Kornbleuth, M. Z.; Michael, A.;
Zieger, B.; Swisdak, M.; Toth, G.
Bibcode: 2016AGUFMSH23A..05O
Altcode:
Recently we proposed a scenario (Opher et al. 2015) that the
structure of the heliosphere might be very different than we previously
thought. The standard picture of the heliosphere is a comet-shape like
structure with the tail extending for 1000's of AUs. This standard
picture stems from a view where magnetic forces are negligible and the
solar magnetic field is convected passively down the tail. We showed
(Opher et al. 2015, Drake et al. 2015) that the magnetic tension
of the solar magnetic field plays a crucial role on organizing the
solar wind in the heliosheath into two jet-like structures. The two
heliospheric jets are separated by the interstellar medium that
flows between them. The heliosphere then has a ``croissant"-like
shape where the distance to the heliopause downtail is almost the
same as towards the nose. Here we present the implications of this
"croissant-like structure" for the global Energetic Neutral Atoms
maps as measured by IBEX in the heliotail and its variation with
solar cycle. We include solar cycle variations of the solar wind
(density and speed and magnetic intensity) while keeping a unipolar
configuration to minimize spurious magnetic dissipation that erodes
the solar magnetic field. We discuss as well the consequences on the
draping and reconnection of the interstellar magnetic field across the
heliopause. We show that reconnection in the flanks and tail control the
draping and the orientation of the interstellar magnetic field (BISM)
ahead of the heliopause and can explain the Voyager 1 observations. The
BISM twists as it approaches the HP and acquires a strong T component
(East-West) as shown in Opher & Drake (2013). Only after some
significant distance outside the HP is the direction of the interstellar
field distinguishably different from that of the Parker spiral.
Title: Direct Simulation Monte Carlo modelling of the major species
in the coma of comet 67P/Churyumov-Gerasimenko
Authors: Fougere, Nicolas; Altwegg, K.; Berthelier, J. -J.; Bieler,
A.; Bockelée-Morvan, D.; Calmonte, U.; Capaccioni, F.; Combi, M. R.;
De Keyser, J.; Debout, V.; Erard, S.; Fiethe, B.; Filacchione, G.;
Fink, U.; Fuselier, S. A.; Gombosi, T. I.; Hansen, K. C.; Hässig,
M.; Huang, Z.; Le Roy, L.; Leyrat, C.; Migliorini, A.; Piccioni, G.;
Rinaldi, G.; Rubin, M.; Shou, Y.; Tenishev, V.; Toth, G.; Tzou, C. -Y.
Bibcode: 2016MNRAS.462S.156F
Altcode:
We analyse the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis
(ROSINA) - the Double Focusing Mass Spectrometer data between 2014
August and 2016 February to examine the effect of seasonal variations
on the four major species within the coma of 67P/Churyumov-Gerasimenko
(H2O, CO2, CO, and O2), resulting from
the tilt in the orientation of the comet's spin axis. Using a numerical
data inversion, we derive the non-uniform activity distribution at the
surface of the nucleus for these species, suggesting that the activity
distribution at the surface of the nucleus has not significantly been
changed and that the differences observed in the coma are solely due to
the variations in illumination conditions. A three-dimensional Direct
Simulation Monte Carlo model is applied where the boundary conditions
are computed with a coupling of the surface activity distributions and
the local illumination. The model is able to reproduce the evolution
of the densities observed by ROSINA including the changes happening at
equinox. While O2 stays correlated with H2O as it
was before equinox, CO2 and CO, which had a poor correlation
with respect to H2O pre-equinox, also became well correlated
with H2O post-equinox. The integration of the densities
from the model along the line of sight results in column densities
directly comparable to the VIRTIS-H observations. Also, the evolution
of the volatiles' production rates is derived from the coma model
showing a steepening in the production rate curves after equinox. The
model/data comparison suggests that the seasonal effects result in the
Northern hemisphere of 67P's nucleus being more processed with a layered
structure while the Southern hemisphere constantly exposes new material.
Title: Evolution of water production of 67P/Churyumov-Gerasimenko:
An empirical model and a multi-instrument study
Authors: Hansen, Kenneth C.; Altwegg, K.; Berthelier, J. -J.; Bieler,
A.; Biver, N.; Bockelée-Morvan, D.; Calmonte, U.; Capaccioni, F.;
Combi, M. R.; de Keyser, J.; Fiethe, B.; Fougere, N.; Fuselier, S. A.;
Gasc, S.; Gombosi, T. I.; Huang, Z.; Le Roy, L.; Lee, S.; Nilsson,
H.; Rubin, M.; Shou, Y.; Snodgrass, C.; Tenishev, V.; Toth, G.; Tzou,
C. -Y.; Simon Wedlund, C.; Rosina Team
Bibcode: 2016MNRAS.462S.491H
Altcode:
We examine the evolution of the water production of comet
67P/Churyumov-Gerasimenko during the Rosetta mission (2014 June-2016
May) based on in situ and remote sensing measurements made by Rosetta
instruments, Earth-based telescopes and through the development of an
empirical coma model. The derivation of the empirical model is described
and the model is then applied to detrend spacecraft position effects
from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis
(ROSINA) data. The inter-comparison of the instrument data sets shows
a high level of consistency and provides insights into the water and
dust production. We examine different phases of the orbit, including
the early mission (beyond 3.5 au) where the ROSINA water production does
not show the expected increase with decreasing heliocentric distance. A
second important phase is the period around the inbound equinox, where
the peak water production makes a dramatic transition from northern to
southern latitudes. During this transition, the water distribution is
complex, but is driven by rotation and active areas in the north and
south. Finally, we consider the perihelion period, where there may be
evidence of time dependence in the water production rate. The peak water
production, as measured by ROSINA, occurs 18-22 d after perihelion at
3.5 ± 0.5 × 1028 water molecules s-1. We show
that the water production is highly correlated with ground-based dust
measurements, possibly indicating that several dust parameters are
constant during the observed period. Using estimates of the dust/gas
ratio, we use our measured water production rate to calculate a uniform
surface loss of 2-4 m during the current perihelion passage.
Title: A possible mechanism for the formation of magnetic field
dropouts in the coma of 67P/Churyumov-Gerasimenko
Authors: Huang, Z.; Tóth, G.; Gombosi, T. I.; Bieler, A.; Combi,
M. R.; Hansen, K. C.; Jia, X.; Fougere, N.; Shou, Y.; Cravens, T. E.;
Tenishev, V.; Altwegg, K.; Rubin, M.
Bibcode: 2016MNRAS.462S.468H
Altcode:
The Rosetta Plasma Consortium MAGnetometer (RPC-MAG) has
detected signatures of diamagnetic regions associated with comet
67P/Churyumov-Gerasimenko at distances from 30 to 400 km at different
heliocentric distances, which is larger than what has been predicted by
numerical simulations of the cometary plasam environment. The physical
mechanism behind these diamagnetic regions is still unknown. In
this work, we use our newly developed multifluid plasma-neutral
model to explore a possible physical mechanism that might create such
regions. The model solves the governing multifluid magnetohydrodynamic
equations for cometary and solar wind ions and electrons, and the Euler
equations for the neutral gas fluid. We find that a local increase
of electron thermal pressure is capable of generating many of the
observed features of the diamagnetic regions observed by RPC-MAG. The
simulation results show that a magnetic field-free region is formed
and the recovery phase of the magnetic field magnitude is faster than
the declining phase.
Title: A new 3D multi-fluid model: a study of kinetic effects and
variations of physical conditions in the cometary coma
Authors: Shou, Yinsi; Combi, Michael R.; Toth, Gabor; Huang, Zhenguang;
Jia, Xianzhe; Fougere, Nicolas; Tenishev, Valeriy; Gombosi, T. I.;
Hansen, Kenneth C.; Bieler, Andre
Bibcode: 2016DPS....4821705S
Altcode:
Physics-based numerical coma models are desirable whether to interpret
the spacecraft observations of the inner coma or to compare with
the ground-based observations of the outer coma. In this work,
we develop a multi-neutral-fluid model based on BATS-R-US in the
University of Michigan's SWMF (Space Weather Modeling Framework),
which is capable of computing both the inner and the outer coma and
simulating time-variable phenomena. It treats H2O, OH,
H2, O, and H as separate fluids and each fluid has its
own velocity and temperature, with collisions coupling all fluids
together. The self-consistent collisional interactions decrease the
velocity differences, re-distribute the excess energy deposited by
chemical reactions among all species, and account for the varying
heating efficiency under various physical conditions. Recognizing
that the fluid approach has limitations in capturing all of the
correct physics for certain applications, especially for very low
density environment, we applied our multi-fluid coma model to comet
67P/Churyumov-Gerasimenko (CG) at various heliocentric distances
and demonstrated that it is able to yield comparable results as
the Direct Simulation Monte Carlo (DSMC) model, which is based on
a kinetic approach that is valid under these conditions. Therefore,
our model may be a powerful alternative to the particle-based model,
especially for some computationally intensive simulations. In addition,
by running the model with several combinations of production rates and
heliocentric distances, we can characterize the cometary H2O
expansion speeds and demonstrate the nonlinear effect of production
rates or photochemical heating. Our results are also compared to
previous modeling work (e.g., Bockelee-Morvan & Crovisier 1987) and
remote observations (e.g., Tseng et al. 2007), which serve as further
validation of our model. This work has been partially supported by
grant NNX14AG84G from the NASA Planetary Atmospheres Program, and US
Rosetta contracts JPL #1266313, JPL #1266314 and JPL #1286489.
Title: Data Constrained Coronal Mass Ejections in A Global
Magnetohydrodynamics Model
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Sokolov, I.;
Toth, G.; Mullinix, R. E.; Taktakishvili, A.; Chulaki, A.; Gombosi,
T. I.
Bibcode: 2016usc..confE.120J
Altcode:
We present a first-principles-based coronal mass ejection (CME)
model suitable for both scientific and operational purposes by
combining a global magnetohydrodynamics (MHD) solar wind model with
a flux rope-driven CME model. Realistic CME events are simulated
self-consistently with high fidelity and forecasting capability by
constraining initial flux rope parameters with observational data from
GONG, SDO/HMI, SOHO/LASCO, and STEREO/COR. We automate this process
so that minimum manual intervention is required in specifying the CME
initial state. With the newly developed data-driven Eruptive Event
Generator Gibson-Low (EEGGL), we present a method to derive Gibson-Low
(GL) flux rope parameters through a handful of observational quantities
so that the modeled CMEs can propagate with the desired CME speeds near
the Sun. A test result with CMEs launched with different Carrington
rotation magnetograms are shown. Our study shows a promising result
for using the first-principles-based MHD global model as a forecasting
tool, which is capable of predicting the CME direction of propagation,
arrival time, and ICME magnetic field at 1 AU.
Title: Direct Simulation Monte-Carlo Modeling of the Major Volatile
Species of Comet 67P/Churyumov-Gerasimenko observed by ROSINA
and VIRTIS
Authors: Fougere, Nicolas; altwegg, kathrin; Berthelier, Jean-Jacques;
Bieler, Andre; Bockelee-Morvan, Dominique; Calmonte, Ursina;
Capaccioni, Fabrizio; Combi, Michael R.; De Keyser, Johan; Debout,
Vincent; Erard, Stéphane; Fiethe, Björn; Filacchione, Gianrico;
Fink, Uwe; Fuselier, Stephen; Gombosi, T. I.; Hansen, Kenneth C.;
Hässig, Myrtha; Huang, Zhenguang; Le Roy, Léna; Migliorini,
Alessandra; Piccioni, Giuseppe; Rinaldi, Giovanna; Rubin, Martin;
Shou, Yinsi; Tenishev, Valeriy; Toth, Gabor; Tzou, Chia-Yu; VIRTIS
Team and ROSINA Team
Bibcode: 2016DPS....4811610F
Altcode:
During the past few decades, modeling of cometary coma has known
tremendous improvements notably with the increase of computer
capacity. While the Haser model is still widely used for interpretation
of cometary observations, its rather simplistic assumptions such as
spherical symmetry and constant outflow velocity prevent it to explain
some of the coma observations. Hence, more complex coma models have
emerged taking full advantage of the numerical approach. The only method
that can resolve all the flow regimes encountered in the coma due to the
drastic changes of Knudsen numbers is the Direct Simulation Monte-Carlo
(DSMC) approach.The data acquired by the instruments on board of the
Rosetta spacecraft provides a large amount of observations regarding the
spatial and temporal variations of comet 67P/Churyumov-Gerasimenko's
coma. These measurements provide constraints that can be applied to
the coma model in order to describe best the rarefied atmosphere of
67P. We present the last results of our 3D multi-species DSMC model
using the Adaptive Mesh Particle Simulator (Tenishev et al. 2008 and
2011, Fougere 2014). The model uses a realistic nucleus shape model from
the OSIRIS team and takes into account the self-shadowing created by
its concavities. The gas flux at the surface of the nucleus is deduced
from the relative orientation with respect to the Sun and an activity
distribution that enables to simulate both the non-uniformity of the
surface activity and the heterogeneities of the outgassing.The model
results are compared to the ROSINA and VIRTIS observations. Progress
in incorporating Rosetta measurements from the last half of the mission
into our models will be presented. The good agreement between the model
and these measurements from two very different techniques reinforces
our understanding of the physical processes taking place in the coma.
Title: An empirical model of H2O, CO2
and CO coma distributions and production rates for comet
67P/Churyumov-Gerasimenko based on ROSINA/DFMS measurements and
AMPS-DSMC simulations
Authors: Hansen, Kenneth C.; Altwegg, Kathrin; Bieler, Andre;
Berthelier, Jean-Jacques; Calmonte, Ursina; Combi, Michael R.; De
Keyser, Johan; Fiethe, Björn; Fougere, Nicolas; Fuselier, Stephen;
Gombosi, T. I.; Hässig, Myrtha; Huang, Zhenguang; Le Roy, Léna;
Rubin, Martin; Tenishev, Valeriy; Toth, Gabor; Tzou, Chia-Yu;
ROSINA Team
Bibcode: 2016DPS....4811623H
Altcode:
We have previously used results from the AMPS DSMC (Adaptive Mesh
Particle Simulator Direct Simulation Monte Carlo) model to create an
empirical model of the near comet water (H2O) coma of comet
67P/Churyumov-Gerasimenko. In this work we create additional empirical
models for the coma distributions of CO2 and CO. The AMPS
simulations are based on ROSINA DFMS (Rosetta Orbiter Spectrometer
for Ion and Neutral Analysis, Double Focusing Mass Spectrometer)
data taken over the entire timespan of the Rosetta mission. The
empirical model is created using AMPS DSMC results which are extracted
from simulations at a range of radial distances, rotation phases and
heliocentric distances. The simulation results are then averaged over
a comet rotation and fitted to an empirical model distribution. Model
coefficients are then fitted to piecewise-linear functions of
heliocentric distance. The final product is an empirical model of
the coma distribution which is a function of heliocentric distance,
radial distance, and sun-fixed longitude and latitude angles. The model
clearly mimics the behavior of water shifting production from North to
South across the inbound equinox while the CO2 production
is always in the South.The empirical model can be used to de-trend
the spacecraft motion from the ROSINA COPS and DFMS data. The ROSINA
instrument measures the neutral coma density at a single point and the
measured value is influenced by the location of the spacecraft relative
to the comet and the comet-sun line. Using the empirical coma model
we can correct for the position of the spacecraft and compute a total
production rate based on single point measurements. In this presentation
we will present the coma production rates as a function of heliocentric
distance for the entire Rosetta mission.This work was supported by
contracts JPL#1266313 and JPL#1266314 from the US Rosetta Project and
NASA grant NNX14AG84G from the Planetary Atmospheres Program.
Title: Coronal response to EUV jets modeled with the Alfvén Wave
Solar Model
Authors: Szente, Judith; Toth, Gabor; Manchester, Ward B., IV; van der
Holst, Bartholomeus; Landi, Enrico; Gombosi, Tamas; DeVore, Carl R.;
Antiochos, Spiro K.
Bibcode: 2016usc..confE..72S
Altcode:
We study the thermodynamics of jet phenomena with the use of multiple
wavelength SDO-AIA observations [e.g. Adams (2014) and Moore (2015)]
combined with advanced numerical simulations made with AWSoM coronal
model [van der Holst (2014)]. AWSoM provides a fully three-dimensional,
magnetohydrodynamic description of the solar atmosphere heated by the
dissipation of kinetic Alfvén waves in a self-consistent manner. In
addition, the model's multi-species thermodynamics with electron
heat conduction provides for the accurate construction of synthetic
line-of-sight images of phenomena. We implement our jets in the solar
wind with a magnetic dipole twisted about axis, resulting in EUV jets
similar in topology and dynamics as being observed. We show that the
coronal atmosphere responds at a large-scale as torsional Alfvén waves
propagate into the outer corona (up to 24 solar radii and 40 degrees in
latitude), introduced by the small-scale eruptive reconnection events
at the footpoint of the jet.
Title: A Possible Mechanism for the Formation of Magnetic
Field Dropouts Observed by RPC-MAG in the Inner Coma of Comet
67P/Churyumov-Gerasimenko
Authors: Huang, Zhenguang; Toth, Gabor; Gombosi, T. I.; Bieler,
Andre; Combi, Michael R.; Hansen, Kenneth C.; Jia, Xianzhe; Fougere,
Nicolas; Shou, Yinsi; Cravens, Thomas; Tenishev, Valeriy; Rubin,
Martin; altwegg, kathrin
Bibcode: 2016DPS....4811620H
Altcode:
The Rosetta Plasma Consortium MAGnetometer (RPC-MAG) has detected
signatures of a diamagnetic cavity associated with the comet
67P/Churyumov-Gerasimenko at a distance of 170 km, which is two to three
times larger than what has been predicted by numerical simulations of
the cometary plasma environment. It remains unclear how this extended
diamagnetic cavity forms. In the present work, we investigate this
problem with our newly developed multi-fluid plasma-neutral interaction
model (Huang et al., 2016). The multi-fluid model solves the governing
multifluid MHD equations (for the cometary ions, the solar wind protons
and the electrons) and the Euler equations for the neutral gas fluid. We
find that a strong increase of electron pressure along a magnetic flux
tube is capable of generating similar features of the diamagnetic
cavity as those observed by the RPC-MAG. Direct comparison of our
model results with the RPC observations shows reasonable agreement
in terms of key characteristics of the cavity crossings, such as
the duration and the magnetic field variations, suggesting that the
mechanism proposed here based on localized enhancement of electron
pressure may provide a possible explanation for the unusually large
distance of the observed cavity.This work was supported by contracts
JPL#1266313 and JPL#1266314 from the US Rosetta Project and NASA grant
NNX14AG84G from the Planetary Atmospheres Program.
Title: Threaded-Field-Lines Model for the Low Solar Corona Powered
by the Alfven Wave Turbulence
Authors: Sokolov, Igor V.; van der Holst, Bart; Manchester, Ward B.;
Ozturk, Doga Can Su; Szente, Judit; Taktakishvili, Aleksandre; Tóth,
Gabor; Jin, Meng; Gombosi, Tamas I.
Bibcode: 2016arXiv160904379S
Altcode:
We present an updated global model of the solar corona, including
the transition region. We simulate the realistic tree-dimensional
(3D) magnetic field using the data from the photospheric magnetic
field measurements and assume the magnetohydrodynamic (MHD) Alfvén
wave turbulence and its non-linear dissipation to be the only source
for heating the coronal plasma and driving the solar wind. In closed
field regions the dissipation efficiency in a balanced turbulence
is enhanced. In the coronal holes we account for a reflection of
the outward propagating waves, which is accompanied by generation of
weaker counter-propagating waves. The non-linear cascade rate degrades
in strongly imbalanced turbulence, thus resulting in colder coronal
holes. The distinctive feature of the presented model is the description
of the low corona as almost-steady-state low-beta plasma motion and
heat flux transfer along the magnetic field lines. We trace the magnetic
field lines through each grid point of the lower boundary of the global
corona model, chosen at some heliocentric distance, $R=R_{b}\sim1.1\
R_\odot$ well above the transition region. One can readily solve the
plasma parameters along the magnetic field line from 1D equations for
the plasma motion and heat transport together with the Alfvén wave
propagation, which adequately describe physics within the heliocentric
distances range, $R_{\odot}<R<R_{b}$, in the low solar corona. By
interfacing this threaded-field-lines model with the full MHD global
corona model at $r=R_{b}$, we find the global solution and achieve a
faster-than-real-time performance of the model on $\sim200$ cores.
Title: Effects of Numerical Magnetic Dissipation on the
Characteristics of the Heliosphere
Authors: Michael, Adam Thomas; Opher, Merav; Provornikova, Elena;
Toth, Gabor
Bibcode: 2016shin.confE.125M
Altcode:
Through the use of numerical models, we have recently begun to
realize the importance the solar wind"s magnetic field has on the
location of the termination shock (Izmodenov and Alexashov 2015)
as well as the shape of the heliosphere (Opher et al. 2015) and
thickness of the heliosheath (Drake et al. 2015). Several studies
suggest that there should be a need to move beyond ideal MHD in order
to explain the Voyager 1 and 2 observations (Richardson et al. 2013;
Michael et al. 2015). In the numerical simulations there is inherent
numerical dissipation in the helispheric current sheet that an ideal
MHD model cannot control. In a sense the dissipated magnetic energy
can be transferred to thermal heating or to ram pressure. The magnetic
dissipation inherent in modeling the heliospheric current sheet offers
us a chance to explore non-ideal MHD effects in the heliosphere
and heliosheath. Solar cycle models that include the reversal of
the magnetic field have inherently a large fraction of magnetic
dissipation. In this work we investigate the role magnetic dissipation
has on the overall structure of the heliosheath. We describe the solar
magnetic field both as a dipole, with the magnetic and rotational axes
aligned, as well as a unipole. We have seen in Opher et al. 2016 that
the use of a dipole magnetic field, in the case without any motion
through the ISM, reduces the confinement of the plasma at the current
sheet. We investigate how the magnetic dissipation affects the shape and
thickness of the heliosheath and heliosphere. Furthermore, we explore
how these effects are altered when 11-year solar cycle variations in
the solar wind are included and comment on how magnetic dissipation
alters the prediction for Voyager 1 and 2 observations.
Title: Validating Physics-based Space Weather Models for Operational
Use
Authors: Gombosi, Tamas; Singer, Howard; Millward, George; Toth,
Gabor; Welling, Daniel
Bibcode: 2016cosp...41E.696G
Altcode:
The Geospace components of the Space Weather Modeling Framework
developed at the University of Michigan is presently transitioned to
operational use by the NOAA Space Weather Prediction Center. This talk
will discuss the various ways the model is validated and skill scores
are calculated.
Title: Do we know the actual magnetopause position for typical solar
wind conditions?
Authors: Samsonov, A. A.; Gordeev, E.; Tsyganenko, N. A.; Å
afránková, J.; Němeček, Z.; Å imůnek, J.; Sibeck, D. G.;
Tóth, G.; Merkin, V. G.; Raeder, J.
Bibcode: 2016JGRA..121.6493S
Altcode:
We compare predicted magnetopause positions at the subsolar point and
four reference points in the terminator plane obtained from several
empirical and numerical MHD models. Empirical models using various
sets of magnetopause crossings and making different assumptions about
the magnetopause shape predict significantly different magnetopause
positions (with a scatter >1 RE) even at the subsolar
point. Axisymmetric magnetopause models cannot reproduce the cusp
indentations or the changes related to the dipole tilt effect,
and most of them predict the magnetopause closer to the Earth than
nonaxisymmetric models for typical solar wind conditions and zero
tilt angle. Predictions of two global nonaxisymmetric models do not
match each other, and the models need additional verification. MHD
models often predict the magnetopause closer to the Earth than the
nonaxisymmetric empirical models, but the predictions of MHD simulations
may need corrections for the ring current effect and decreases of the
solar wind pressure that occur in the foreshock. Comparing MHD models
in which the ring current magnetic field is taken into account with
the empirical Lin et al. model, we find that the differences in the
reference point positions predicted by these models are relatively
small for Bz=0. Therefore, we assume that these predictions
indicate the actual magnetopause position, but future investigations
are still needed.
Title: The interaction between the solar wind and the heterogeneous
neutral gas coma of comet 67P/Churyumov-Gerasimenko
Authors: Rubin, Martin; Toth, Gabor; Tenishev, Valeriy; Fougere,
Nicolas; Huang, Zhenguang
Bibcode: 2016cosp...41E1660R
Altcode:
Comets are surrounded by an extended gas and dust coma. Neutral
particles are continuously ionized by solar irradiation and then
picked-up by the solar wind. This leads to a complex interaction between
the neutral gas coma and the solar wind, which changes over the course
of the comet's orbit around the Sun. The European Space Agency's Rosetta
spacecraft has been in orbit around comet 67P/Churyumov-Gerasimenko
since August 2014. Rosetta carries several instruments to investigate
the comet's nucleus and surrounding neutral gas coma and plasma. Part
of the payload is the Rosetta Orbiter Spectrometer for Ion and Neutral
Analysis (ROSINA) that consists of two mass spectrometers and a pressure
sensor. ROSINA was designed to measure the neutral gas abundance and
composition and low energy ions in the coma in situ. ROSINA observations
have shown that the coma is very heterogeneous both in total density and
composition of the neutral gas. This heterogeneity is driven in large
part by the complex shape of the nucleus and the varying illumination
conditions associated with the comet's rotation. In this presentation
we will show the time-dependent distribution of the major volatiles
around the comet constrained by ROSINA observations. Furthermore we
will investigate the impact of the highly non-symmetric neutral gas
coma on the interaction of the solar wind with the comet.
Title: FDIPS: Finite Difference Iterative Potential-field Solver
Authors: Toth, Gabor; van der Holst, Bartholomeus; Huang, Zhenguang
Bibcode: 2016ascl.soft06011T
Altcode:
FDIPS is a finite difference iterative potential-field solver that
can generate the 3D potential magnetic field solution based on a
magnetogram. It is offered as an alternative to the spherical harmonics
approach, as when the number of spherical harmonics is increased, using
the raw magnetogram data given on a grid that is uniform in the sine
of the latitude coordinate can result in inaccurate and unreliable
results, especially in the polar regions close to the Sun. FDIPS is
written in Fortran 90 and uses the MPI library for parallel execution.
Title: Four-fluid MHD simulations of the plasma and neutral gas
environment of comet 67P/Churyumov-Gerasimenko near perihelion
Authors: Huang, Zhenguang; Tóth, Gábor; Gombosi, Tamas I.; Jia,
Xianzhe; Rubin, Martin; Fougere, Nicolas; Tenishev, Valeriy; Combi,
Michael R.; Bieler, Andre; Hansen, Kenneth C.; Shou, Yinsi; Altwegg,
Kathrin
Bibcode: 2016JGRA..121.4247H
Altcode:
The neutral and plasma environment is critical in understanding the
interaction of the solar wind and comet 67P/Churyumov-Gerasimenko
(CG), the target of the European Space Agency's Rosetta mission. To
serve this need and support the Rosetta mission, we have developed a
3-D four-fluid model, which is based on BATS-R-US (Block-Adaptive Tree
Solarwind Roe-type Upwind Scheme) within SWMF (Space Weather Modeling
Framework) that solves the governing multifluid MHD equations and the
Euler equations for the neutral gas fluid. These equations describe the
behavior and interactions of the cometary heavy ions, the solar wind
protons, the electrons, and the neutrals. This model incorporates
different mass loading processes, including photoionization and
electron impact ionization, charge exchange, dissociative ion-electron
recombination, and collisional interactions between different fluids. We
simulated the plasma and neutral gas environment near perihelion
in three different cases: an idealized comet with a spherical body
and uniform neutral gas outflow, an idealized comet with a spherical
body and illumination-driven neutral gas outflow, and comet CG with a
realistic shape model and illumination-driven neutral gas outflow. We
compared the results of the three cases and showed that the simulations
with illumination-driven neutral gas outflow have magnetic reconnection,
a magnetic pileup region and nucleus directed plasma flow inside
the nightside reconnection region, which have not been reported in
the literature.
Title: The Coma of Comet 67P/Churyumov-Gerasimenko Pre- and Post-
Equinox
Authors: Fougere, Nicolas; Altwegg, Kathrin; Berthelier, Jean-Jacques;
Bieler, Andre; Bockelee-Morvan, Dominique; Calmonte, Ursina;
Capaccioni, Fabrizio; Combi, Mike; Dekeyser, Johan; Debout, Vincent;
Erard, Stephane; Fiethe, Bjorn; Fillacchione, Gianrico; Fink, Uwe;
Fuselier, Stephen; Gombosi, Tamas; Hansen, Kenneth; Hassig, Myrtha;
Huang, Zhenguang; Leroy, Lena; Leyrat, Cedric; Migliorini, Alessandra;
Piccioni, Giuseppe; Rinaldi, Giovanna; Rubin, Martin; Tenishev,
Valeriy; Toth, Gabor; Tzou, Chia-Yu; Shou, Yinsi
Bibcode: 2016EGUGA..1817897F
Altcode:
As the Rosetta spacecraft escorts comet 67P/Churyumov-Gerasimenko
(67P) during its journey in the Solar System, it monitors the
evolution of the neutrals' distribution in the coma of 67P. Indeed,
while the comet orbits around the Sun, the energy input received
by the different regions of the nucleus varies, directly impacting
67P's outgassing pattern. We model the H2O, CO2, and CO coma of Comet
67P/Churyumov-Gerasimenko (67P) pre- and post- equinox using a 3D Direct
Monte-Carlo Simulation approach. The use of a kinetic method enables
us to model the coma from the nucleus' surface to a few hundreds of
kilometers even in the regions where collisions cannot maintain a
fluid regime. The activity at the surface of the nucleus is described
using a spherical harmonic expansion with 25 terms constrained by
ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis)
observations. The model outputs contain information about numerous
macroscopic parameters such as number densities, velocities, and
temperatures of each species. Then, the results from the simulations
are integrated along the line of sight to be compared with the remote
sensing observations from the VIRTIS (Visible and Infrared Thermal
Imaging Spectrometer) instrument. The model shows a good agreement
with the data, giving a clear evidence of our understanding of the
physics of the coma of comet 67P.
Title: Four-fluid MHD Simulations of the Plasma and Neutral Gas
Environment of Comet 67P/Churyumov-Gerasimenko Near Perihelion
Authors: Huang, Zhenguang; Toth, Gabor; Gombosi, Tamas; Jia, Xianzhe;
Rubin, Martin; Fougere, Nicolas; Tenishev, Valeriy; Combi, Michael;
Bieler, Andre; Hansen, Kenneth; Shou, Yinsi; Altwegg, Kathrin
Bibcode: 2016EGUGA..18.2214H
Altcode:
The neutral and plasma environment is critical in understanding the
interaction of the solar wind and comet 67P/Churyumov-Gerasimenko
(CG), the target of the European Space Agency's Rosetta mission. In
this study, we have developed a 3-D four-fluid model, which is based
on BATS-R-US (Block-Adaptive Tree Solarwind Roe-type Upwind Scheme)
within SWMF (Space Weather Modeling Framework) that solves the governing
multi-fluid MHD equations and the Euler equations for the neutral
gas fluid. These equations describe the behavior and interactions
of the cometary heavy ions, the solar wind protons, the electrons,
and the neutrals. We simulated the plasma and neutral gas environment
of comet CG with SHAP5 model near perihelion and we showed that the
plasma environment in the inner coma region have some new features:
magnetic reconnection in the tail region, a magnetic pile-up region on
the nightside, and nucleus directed plasma flow inside the nightside
reconnection region.
Title: Pre- and Post-equinox ROSINA production rates calculated using
a realistic empirical coma model derived from AMPS-DSMC simulations
of comet 67P/Churyumov-Gerasimenko
Authors: Hansen, Kenneth; Altwegg, Kathrin; Berthelier, Jean-Jacques;
Bieler, Andre; Calmonte, Ursina; Combi, Michael; De Keyser, Johan;
Fiethe, Björn; Fougere, Nicolas; Fuselier, Stephen; Gombosi, Tamas;
Hässig, Myrtha; Huang, Zhenguang; Le Roy, Lena; Rubin, Martin;
Tenishev, Valeriy; Toth, Gabor; Tzou, Chia-Yu
Bibcode: 2016EGUGA..1817905H
Altcode:
We have previously used results from the AMPS DSMC (Adaptive Mesh
Particle Simulator Direct Simulation Monte Carlo) model to create an
empirical model of the near comet coma (<400 km) of comet 67P for
the pre-equinox orbit of comet 67P/Churyumov-Gerasimenko. In this work
we extend the empirical model to the post-equinox, post-perihelion
time period. In addition, we extend the coma model to significantly
further from the comet (~100,000-1,000,000 km). The empirical model
characterizes the neutral coma in a comet centered, sun fixed reference
frame as a function of heliocentric distance, radial distance from the
comet, local time and declination. Furthermore, we have generalized
the model beyond application to 67P by replacing the heliocentric
distance parameterizations and mapping them to production rates. Using
this method, the model become significantly more general and can be
applied to any comet. The model is a significant improvement over
simpler empirical models, such as the Haser model. For 67P, the
DSMC results are, of course, a more accurate representation of the
coma at any given time, but the advantage of a mean state, empirical
model is the ease and speed of use. One application of the empirical
model is to de-trend the spacecraft motion from the ROSINA COPS and
DFMS data (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis,
Comet Pressure Sensor, Double Focusing Mass Spectrometer). The ROSINA
instrument measures the neutral coma density at a single point and
the measured value is influenced by the location of the spacecraft
relative to the comet and the comet-sun line. Using the empirical coma
model we can correct for the position of the spacecraft and compute a
total production rate based on the single point measurement. In this
presentation we will present the coma production rate as a function
of heliocentric distance both pre- and post-equinox and perihelion.
Title: Three-dimensional direct simulation Monte-Carlo modeling of
the coma of comet 67P/Churyumov-Gerasimenko observed by the VIRTIS
and ROSINA instruments on board Rosetta
Authors: Fougere, N.; Altwegg, K.; Berthelier, J. -J.; Bieler, A.;
Bockelée-Morvan, D.; Calmonte, U.; Capaccioni, F.; Combi, M. R.;
De Keyser, J.; Debout, V.; Erard, S.; Fiethe, B.; Filacchione, G.;
Fink, U.; Fuselier, S. A.; Gombosi, T. I.; Hansen, K. C.; Hässig,
M.; Huang, Z.; Le Roy, L.; Leyrat, C.; Migliorini, A.; Piccioni, G.;
Rinaldi, G.; Rubin, M.; Shou, Y.; Tenishev, V.; Toth, G.; Tzou, C. -Y.
Bibcode: 2016A&A...588A.134F
Altcode:
Context. Since its rendezvous with comet 67P/Churyumov-Gerasimenko
(67P), the Rosetta spacecraft has provided invaluable information
contributing to our understanding of the cometary environment. On
board, the VIRTIS and ROSINA instruments can both measure gas
parameters in the rarefied cometary atmosphere, the so-called coma,
and provide complementary results with remote sensing and in situ
measurement techniques, respectively. The data from both ROSINA and
VIRTIS instruments suggest that the source regions of H2O
and CO2 are not uniformly distributed over the surface of
the nucleus even after accounting for the changing solar illumination
of the irregularly shaped rotating nucleus. The source regions of
H2O and CO2 are also relatively different
from one another.
Aims: The use of a combination of a formal
numerical data inversion method with a fully kinetic coma model is a
way to correlate and interpret the information provided by these two
instruments to fully understand the volatile environment and activity
of comet 67P.
Methods: In this work, the nonuniformity of the
outgassing activity at the surface of the nucleus is described by
spherical harmonics and constrained by ROSINA-DFMS data. This activity
distribution is coupled with the local illumination to describe
the inner boundary conditions of a 3D direct simulation Monte-Carlo
(DSMC) approach using the Adaptive Mesh Particle Simulator (AMPS)
code applied to the H2O and CO2 coma of comet
67P.
Results: We obtain activity distribution of H2O
and CO2 showing a dominant source of H2O in the
Hapi region, while more CO2 is produced in the southern
hemisphere. The resulting model outputs are analyzed and compared with
VIRTIS-M/-H and ROSINA-DFMS measurements, showing much better agreement
between model and data than a simpler model assuming a uniform surface
activity. The evolution of the H2O and CO2
production rates with heliocentric distance are derived accurately
from the coma model showing agreement between the observations from
the different instruments and ground-based observations.
Conclusions: We derive the activity distributions for H2O
and CO2 at the surface of the nucleus described in
spherical harmonics, which we couple to the local solar illumination
to constitute the boundary conditions of our coma model. The model
presented reproduces the coma observations made by the ROSINA and VIRTIS
instruments on board the Rosetta spacecraft showing our understanding
of the physics of 67P's coma. This model can be used for further data
analyses, such as dust modeling, in a future work.
Title: Response of Mercury's Magnetosphere to Solar Wind Forcing:
Results of Global MHD Simulations with Coupled Planetary Interior
Authors: Jia, Xianzhe; Slavin, James; Poh, Gangkai; Toth, Gabor;
Gombosi, Tamas
Bibcode: 2016EGUGA..18.5291J
Altcode:
As the innermost planet, Mercury arguably undergoes the most direct
space weathering interactions due to its weak intrinsic magnetic field
and its close proximity to the Sun. It has long been suggested that two
processes, i.e., erosion of the dayside magnetosphere due to intense
magnetopause reconnection and the shielding effect of the induction
currents generated at the conducting core, compete against each other
in governing the large-scale structure of Mercury's magnetosphere. An
outstanding question concerning Mercury's space weather is which
of the two processes is more important. To address this question,
we have developed a global MHD model in which Mercury's interior is
electromagnetically coupled to the surrounding space environment. As
demonstrated in Jia et al. (2015), the new modeling capability allows
for self-consistently characterizing the dynamical response of the
Mercury system to time-varying external conditions. To assess the
relative importance of induction and magnetopause reconnection in
controlling the magnetospheric configuration, especially under
strong solar driving conditions, we have carried out multiple
global simulations that adopt a wide range of solar wind dynamic
pressure and IMF conditions. We find that, while the magnetopause
standoff distance decreases with increasing solar wind pressure,
just as expected, its dependence on the solar wind pressure follows
closely a power-law relationship with an index of ~ -1/6, rather
than a steeper power-law falling-off expected for the case with only
induction present. This result suggests that for the range of solar wind
conditions examined, the two competing processes, namely induction and
reconnection, appear to play equally important roles in determining
the global configuration of Mercury's magnetosphere, consistent
with the finding obtained by Slavin et al. (2014) based on MESSENGER
observations. We also find that the magnetic perturbations produced by
the magnetospheric current systems are spatially non-uniform in nature,
and consequently they result in an induced magnetic field at the core
that contains significant power in not only the dipole but also high
order moments. Based on the simulation results, we determine how the
induced magnetic field varies with the external solar wind conditions,
and provide quantitative constraints on the ability of Mercury's core
to shield the planetary surface from direct solar wind impact.
Title: Extended Magnetohydrodynamics with Embedded Particle-in-Cell
(XMHD-EPIC) Simulations of Magnetospheric Reconnection
Authors: Toth, Gabor; Gombosi, Tamas; Jia, Xianzhe; Welling, Daniel;
Chen, Yuxi; Haiducek, John; Jordanova, Vania; Peng, Ivy Bo; Markidis,
Stefano; Lapenta, Giovanni
Bibcode: 2016EGUGA..18.2344T
Altcode:
We have recently developed a new modeling capability to embed the
implicit Particle-in-Cell (PIC) model iPIC3D into the BATS-R-US
extended magnetohydrodynamic model. The PIC domain can cover the
regions where kinetic effects are most important, such as reconnection
sites. The BATS-R-US code with its block-adaptive grid can efficiently
handle the rest of the computational domain where the MHD or Hall MHD
description is sufficient. The current implementation of the MHD-EPIC
model allows two-way coupled simulations in two and three dimensions
with multiple embedded PIC regions. The MHD and PIC grids can have
different grid resolutions and grid structures. The MHD variables
and the moments of the PIC distribution functions are interpolated
and message passed in an efficient manner through the Space Weather
Modeling Framework (SWMF). Both BATS-R-US and iPIC3D are massively
parallel codes fully integrated into, run by and coupled through
the SWMF. We have successfully applied the MHD-EPIC code to model
Ganymede's and Mercury's magnetospheres. We compared our results with
Galileo and MESSENGER magnetic observations, respectively, and found
good overall agreement. We will report our progress on modeling the
Earth magnetosphere with MHD-EPIC with the goal of providing direct
comparison with and global context for the MMS observations.
Title: Responses of Venus Ionosphere and Induced Magnetosphere to
Solar Wind Pressure Variations
Authors: Ma, Yingjuan; Toth, Gabor; Nagy, Andrew F.; Russell,
Christopher T.
Bibcode: 2016EGUGA..18.9743M
Altcode:
Often regarded as the Earth's 'sister planet', Venus has similar size
and mass as Earth. But it is also remarkably different from Earth in
many respects. Even though we have some basic knowledge of the solar
wind interaction with Venus based on spacecraft observations, little
is known about how the interaction and the resulting plasma escape
rates vary in response to solar wind variations due to the lack of
coordinated observations of both upstream solar wind conditions and
simultaneous plasma properties in the Venus ionosphere. Furthermore,
recent observations suggest that plasma escape rates are significantly
enhanced during stormy space weather in response to solar wind pressure
pulses (Edberg et al., 2011). Thus it is important to understand the
plasma interaction under varying solar wind conditions. In this study,
we use a sophisticated multi-species MHD model that has been recently
developed for Venus (Ma et al., 2013) to characterize the responses
of the ionosphere and the induced magnetosphere of Venus to a typical
variation of the solar wind: dynamic pressure change. We will examine
the response of the ionosphere and the induced magnetosphere to both
pressure enhancements and decreases. We will quantify the total plasma
escape-rate change in response to such variations and to identify the
underlying driver for changes in escape rate. We will also quantify
the time scale of the Venus ionosphere and induced magnetosphere in
responding to the pressure change of the external solar wind driver.
Title: Extended magnetohydrodynamics with embedded particle-in-cell
simulation of Ganymede's magnetosphere
Authors: Tóth, Gábor; Jia, Xianzhe; Markidis, Stefano; Peng, Ivy Bo;
Chen, Yuxi; Daldorff, Lars K. S.; Tenishev, Valeriy M.; Borovikov,
Dmitry; Haiducek, John D.; Gombosi, Tamas I.; Glocer, Alex; Dorelli,
John C.
Bibcode: 2016JGRA..121.1273T
Altcode:
We have recently developed a new modeling capability to embed
the implicit particle-in-cell (PIC) model iPIC3D into the
Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme magnetohydrodynamic
(MHD) model. The MHD with embedded PIC domains (MHD-EPIC) algorithm
is a two-way coupled kinetic-fluid model. As one of the very first
applications of the MHD-EPIC algorithm, we simulate the interaction
between Jupiter's magnetospheric plasma and Ganymede's magnetosphere. We
compare the MHD-EPIC simulations with pure Hall MHD simulations
and compare both model results with Galileo observations to assess
the importance of kinetic effects in controlling the configuration
and dynamics of Ganymede's magnetosphere. We find that the Hall
MHD and MHD-EPIC solutions are qualitatively similar, but there are
significant quantitative differences. In particular, the density and
pressure inside the magnetosphere show different distributions. For our
baseline grid resolution the PIC solution is more dynamic than the Hall
MHD simulation and it compares significantly better with the Galileo
magnetic measurements than the Hall MHD solution. The power spectra of
the observed and simulated magnetic field fluctuations agree extremely
well for the MHD-EPIC model. The MHD-EPIC simulation also produced a
few flux transfer events (FTEs) that have magnetic signatures very
similar to an observed event. The simulation shows that the FTEs
often exhibit complex 3-D structures with their orientations changing
substantially between the equatorial plane and the Galileo trajectory,
which explains the magnetic signatures observed during the magnetopause
crossings. The computational cost of the MHD-EPIC simulation was only
about 4 times more than that of the Hall MHD simulation.
Title: What Controls the Structure and Dynamics of Earth's
Magnetosphere?
Authors: Eastwood, J. P.; Hietala, H.; Toth, G.; Phan, T. D.;
Fujimoto, M.
Bibcode: 2016mssf.book..271E
Altcode:
No abstract at ADS
Title: Separator reconnection at the magnetopause for predominantly
northward and southward IMF: Techniques and results
Authors: Glocer, A.; Dorelli, J.; Toth, G.; Komar, C. M.; Cassak, P. A.
Bibcode: 2016JGRA..121..140G
Altcode:
In this work, we demonstrate how to track magnetic separators
in three-dimensional simulated magnetic fields with or without
magnetic nulls, apply these techniques to enhance our understanding
of reconnection at the magnetopause. We present three methods for
locating magnetic separators and apply them to 3-D resistive MHD
simulations of the Earth's magnetosphere using the Block-Adaptive-Tree
Solar-wind Roe-type Upwind Scheme code. The techniques for finding
separators and determining the reconnection rate are insensitive to
interplanetary magnetic field (IMF) clock angle and can in principle
be applied to any magnetospheric model. Moreover, the techniques
have a number of advantages over prior separator finding techniques
applied to the magnetosphere. The present work examines cases of high
and low resistivity for two clock angles. We go beyond previous work
examine the separator during Flux Transfer Events (FTEs). Our analysis
of reconnection on the magnetopause yields a number of interesting
conclusions: Reconnection occurs all along the separator even during
predominately northward IMF cases. Multiple separators form in
low-resistivity conditions, and in the region of an FTE the separator
splits into distinct branches. Moreover, the local contribution to the
reconnection rate, as determined by the local parallel electric field,
drops in the vicinity of the FTE with respect to the value when there
are none.
Title: Multi-fluid MHD Study of the Solar Wind Interaction with Mars'
Upper Atmosphere during the 2015 March 8th ICME Event
Authors: Dong, C.; Ma, Y.; Bougher, S. W.; Toth, G.; Nagy, A. F.;
Halekas, J. S.; Dong, Y.; Curry, S.; Luhmann, J. G.; Brain, D. A.;
Connerney, J. E. P.; Espley, J. R.; Mahaffy, P. R.; Benna, M.;
McFadden, J. P.; Mitchell, D. L.; DiBraccio, G. A.; Lillis, R. J.;
Jakosky, B. M.; Grebowsky, J. M.
Bibcode: 2015AGUFM.P21A2083D
Altcode:
The 3-D Mars multi-fluid BATS-R-US MHD code is used to study the solar
wind interaction with the Martian upper atmosphere during the 2015
March 8th interplanetary coronal mass ejection (ICME). We studied
four steady-state cases, corresponding to three major ICME phases:
pre-ICME phase (Case 1), sheath phase (Cases 2--3), and ejecta
phase (Case 4). Detailed data-model comparisons demonstrate that
the simulation results are in good agreement with Mars Atmosphere
and Volatile EvolutioN (MAVEN) measurements, indicating that the
multi-fluid MHD model can reproduce most of the features observed by
MAVEN, thus providing confidence in the estimate of ion escape rates
from its calculation. The total ion escape rate is increased by an
order of magnitude, from 2.05×1024 s-1 (pre-ICME phase) to 2.25×1025
s-1 (ICME sheath phase), during this time period. The calculated ion
escape rates were used to examine the relative importance of the two
major ion loss channels from the planet: energetic pickup ion loss
through the dayside plume and cold ionospheric ion loss through the
nightside plasma wake region. We found that the energetic pickup ions
escaping from the dayside plume could be as much as ~23% of the total
ion loss prior to the ICME arrival. Interestingly, the tailward ion
escape rate is significantly increased at the ejecta phase, leading
to a reduction of the dayside ion escape to ~5% of the total ion
loss. Under such circumstance, the cold ionospheric ions escaping
from the plasma wake comprise the majority of the ion loss from the
planet. Furthermore, by comparing four simulation results along the
same MAVEN orbit, we note that there is no significant variation in
the Martian lower ionosphere. Finally, both bow shock and magnetic
pileup boundary (BS, MPB) locations are decreased from (1.2 RMars, 1.57
RMars) at the pre-ICME phase to (1.16 RMars, 1.47 RMars) respectively
during the sheath phase along the dayside Sun-Mars line. MAVEN has
provided a great opportunity to study the evolution of the Martian
atmosphere and climate over its history. A large quantity of useful
data has been returned for future studies. These kinds of data-model
comparisons can help the community to better understand the Martian
upper atmosphere response to the (extreme) variation in the solar wind
and its interplanetary environment from a global perspective.
Title: Four-fluid MHD Simulations of the Plasma and Neutral Gas
Environment of Comet Churyumov-Gerasimenko Near Perihelio
Authors: Huang, Z.; Toth, G.; Gombosi, T. I.; Jia, X.; Rubin, M.;
Hansen, K. C.; Fougere, N.; Bieler, A. M.; Shou, Y.; Altwegg, K.;
Combi, M. R.; Tenishev, V.
Bibcode: 2015AGUFM.P31E2116H
Altcode:
The neutral and plasma environment is critical in understanding the
interaction of comet Churyumov-Gerasimenko (CG), the target of the
Rosetta mission, and the solar wind. To serve this need and support
the Rosetta mission, we develop a 3-D four fluid model, which is
based on BATS-R-US within the SWMF (Space Weather Modeling Framework)
that solves the governing multi-fluid MHD equations and the Euler
equations for the neutral gas fluid. These equations describe the
behavior and interactions of the cometary heavy ions, the solar wind
protons, the electrons, and the neutrals. This model incorporates
different mass loading processes, including photo and electron impact
ionization, charge exchange, dissociative ion-electron recombination,
and collisional interactions between different fluids. We simulate the
near nucleus plasma and neutral gas environment near perihelion with
a realistic shape model of CG and compare our simulation results with
Rosetta observations.
Title: Solar Wind Prediction at Pluto During the New Horizons Flyby:
Results From a Two-Dimensional Multi-fluid MHD Model of the Outer
Heliosphere
Authors: Zieger, B.; Toth, G.; Opher, M.; Gombosi, T. I.
Bibcode: 2015AGUFMSM31D2539Z
Altcode:
We adapted the outer heliosphere (OH) component of the Space Weather
Modeling Framework, which is a 3-D global multi-fluid MHD model of the
outer heliosphere with one ion fluid and four neutral populations, for
time-dependent 2-D multi-fluid MHD simulations of solar wind propagation
from a heliocentric distance of 1 AU up to 50 AU. We used this model to
predict the solar wind plasma parameters as well as the interplanetary
magnetic field components at Pluto and along the New Horizons trajectory
during the whole calendar year of 2015 including the closest approach
on July 14. The simulation is run in the solar equatorial plane in the
heliographic inertial frame (HGI). The inner boundary conditions along
a circle of 1 AU radius are set by near-Earth solar wind observations
(hourly OMNI data), assuming that the global solar wind distribution
does not change much during a Carrington rotation (27.2753 days). Our
2-D multi-fluid MHD code evolves one ion fluid and two neutral fluids,
which are the primary interstellar neutral atoms and the interstellar
neutral atoms deflected in the outer heliosheath between the slow bow
shock and the heliopause. Spherical expansion effects are properly
taken into account for the ions and the solar magnetic field. The
inflow parameters of the two neutral fluids (density, temperature,
and velocity components) are set at the negative X (HGI) boundary at 50
AU distance, which are taken from previous 3-D global multi-fluid MHD
simulations of the heliospheric interface in a much larger simulation
box (1500x1500x1500 AU). The inflow velocity vectors of the two neutral
fluids define the so-called hydrogen deflection plane. The solar wind
ions and the interstellar neutrals interact through charge exchange
source terms included in the multi-fluid MHD equations, so the two
neutral populations are evolved self-consistently. We validate our
model with the available plasma data from New Horizons as well as
with Voyager 2 plasma and magnetic field observations within the
heliocentric distance of 50 AU. Our new time-dependent 2-D multi-fluid
MHD model is generally applicable for solar wind predictions at any
outer planet (Jupiter, Saturn, Uranus, Neptune) or spacecraft in the
outer heliosphere where charge exchange between solar wind ions and
interstellar neutrals play an important role.
Title: Modeling AWSoM CMEs with EEGGL: A New Approach for Space
Weather Forecasting
Authors: Jin, M.; Manchester, W.; van der Holst, B.; Sokolov, I.;
Toth, G.; Vourlidas, A.; de Koning, C. A.; Gombosi, T. I.
Bibcode: 2015AGUFMSH43C..02J
Altcode:
The major source of destructive space weather is coronal mass ejections
(CMEs). However, our understanding of CMEs and their propagation in the
heliosphere is limited by the insufficient observations. Therefore,
the development of first-principals numerical models plays a vital
role in both theoretical investigation and providing space weather
forecasts. Here, we present results of the simulation of CME propagation
from the Sun to 1AU by combining the analytical Gibson & Low (GL)
flux rope model with the state-of-art solar wind model AWSoM. We also
provide an approach for transferring this research model to a space
weather forecasting tool by demonstrating how the free parameters of
the GL flux rope can be prescribed based on remote observations via
the new Eruptive Event Generator by Gibson-Low (EEGGL) toolkit. This
capability allows us to predict the long-term evolution of the CME
in interplanetary space. We perform proof-of-concept case studies to
show the capability of the model to capture physical processes that
determine CME evolution while also reproducing many observed features
both in the corona and at 1 AU. We discuss the potential and limitations
of this model as a future space weather forecasting tool.
Title: Combining DSMC Simulations and ROSINA/COPS Data of Comet
67P/Churyumov-Gerasimenko to Develop a Realistic Empirical Coma
Model and to Determine Accurate Production Rates
Authors: Hansen, K. C.; Fougere, N.; Bieler, A. M.; Altwegg, K.;
Combi, M. R.; Gombosi, T. I.; Huang, Z.; Rubin, M.; Tenishev, V.;
Toth, G.; Tzou, C. Y.
Bibcode: 2015AGUFM.P31E2104H
Altcode:
We have previously published results from the AMPS DSMC (Adaptive
Mesh Particle Simulator Direct Simulation Monte Carlo) model and its
characterization of the neutral coma of comet 67P/Churyumov-Gerasimenko
through detailed comparison with data collected by the ROSINA/COPS
(Rosetta Orbiter Spectrometer for Ion and Neutral Analysis/COmet
Pressure Sensor) instrument aboard the Rosetta spacecraft [Bieler,
2015]. Results from these DSMC models have been used to create an
empirical model of the near comet coma (<200 km) of comet 67P. The
empirical model characterizes the neutral coma in a comet centered,
sun fixed reference frame as a function of heliocentric distance,
radial distance from the comet, local time and declination. The
model is a significant improvement over more simple empirical models,
such as the Haser model. While the DSMC results are a more accurate
representation of the coma at any given time, the advantage of a mean
state, empirical model is the ease and speed of use. One use of such
an empirical model is in the calculation of a total cometary coma
production rate from the ROSINA/COPS data. The COPS data are in situ
measurements of gas density and velocity along the ROSETTA spacecraft
track. Converting the measured neutral density into a production rate
requires knowledge of the neutral gas distribution in the coma. Our
empirical model provides this information and therefore allows us to
correct for the spacecraft location to calculate a production rate as
a function of heliocentric distance. We will present the full empirical
model as well as the calculated neutral production rate for the period
of August 2014 - August 2015 (perihelion).
Title: A multifluid magnetohydrodynamic simulation of the interaction
between Jupiter's magnetosphere and its moon Europa
Authors: Rubin, M.; Jia, X.; Altwegg, K.; Combi, M. R.; Daldorff,
L. K. S.; Gombosi, T. I.; Khurana, K. K.; Kivelson, M.; Tenishev,
V.; Toth, G.; van der Holst, B.; Wurz, P.
Bibcode: 2015AGUFM.P21B..01R
Altcode:
Jupiter's moon Europa is believed to contain a subsurface water
ocean whose finite electrical conductance imposes clear induction
signatures on the magnetic field in its surroundings. The evidence
rests heavily on measurements performed by the magnetometer on board
the Galileo spacecraft during multiple flybys of the moon. Europa's
interaction with the Jovian magnetosphere has become a major target
of research in planetary science, partly because of the potential
of a salty ocean to harbor life outside our own planet. Thus it is
of considerable interest to develop numerical simulations of the
Europa-Jupiter interaction that can be compared with data in order
to refine our knowledge of Europa's subsurface structure. In this
presentation we show aspects of Europa's interaction with the Jovian
magnetosphere extracted from a multifluid magnetohydrodynamics (MHD)
code BATS-R-US recently developed at the University of Michigan. The
model dynamically separates magnetospheric and pick-up ions and is
capable of capturing some of the physics previously accessible only to
kinetic approaches. The model utilizes an adaptive grid to maintain the
high spatial resolution on the surface required to resolve the portion
of Europa's neutral atmosphere with a scale height of a few tens of
kilometers that is in thermal equilibrium. The model also derives the
electron temperature, which is crucial to obtain the local electron
impact ionization rates and hence the plasma mass loading in Europa's
atmosphere. We compare our results with observations made by the plasma
particles and fields instruments on the Galileo spacecraft to validate
our model. We will show that multifluid MHD is able to reproduce the
basic features of the plasma moments and magnetic field observations
obtained during the Galileo E4 and E26 flybys at Europa.
Title: Using the 11-year Solar Cycle to Predict the Heliosheath
Environment at Voyager 1 and 2
Authors: Michael, A.; Opher, M.; Provornikova, E.; Richardson, J. D.;
Toth, G.
Bibcode: 2015AGUFMSH41A2373M
Altcode:
As Voyager 2 moves further into the heliosheath, the region of subsonic
solar wind plasma in between the termination shock and the heliopause,
it has observed an increase of the magnetic field strength to large
values, all while maintaining magnetic flux conservation. Dr. Burlaga
will present these observations in the 2015 AGU Fall meeting
(abstract ID: 59200). The increase in magnetic field strength could
be a signature of Voyager 2 approaching the heliopause or, possibly,
due to solar cycle effects. In this work we investigate the role the
11-year solar cycle variations as well as magnetic dissipation effects
have on the heliosheath environments observed at Voyager 1 and 2 using
a global 3D magnetohydrodynamic model of the heliosphere. We use time
and latitude-dependent solar wind velocity and density inferred from
SOHO/SWAN and IPS data and solar cycle variations of the magnetic
field derived from 27-day averages of the field magnitude average
of the magnetic field at 1 AU from the OMNI database as presented in
Michael et al. (2015). Since the model has already accurately matched
the flows and magnetic field strength at Voyager 2 until 93 AU,
we extend the boundary conditions to model the heliosheath up until
Voyager 2 reaches the heliopause. This work will help clarify if the
magnetic field observed at Voyager 2 should increase or decrease
due to the solar cycle. We describe the solar magnetic field both
as a dipole, with the magnetic and rotational axes aligned, and as
a monopole, with magnetic field aligned with the interstellar medium
to reduce numerical reconnection within the heliosheath, due to the
removal of the heliospheric surrent sheet, and at the solar wind -
interstellar medium interface. A comparison of the models allows for
a crude estimation of the role that magnetic dissipation plays in the
system and whether it allows for a better understanding of the Voyager
2 location in the heliosheath.
Title: Overview of the SHIELDS Project at LANL
Authors: Jordanova, V.; Delzanno, G. L.; Henderson, M. G.; Godinez,
H. C.; Jeffery, C. A.; Lawrence, E. C.; Meierbachtol, C.; Moulton,
D.; Vernon, L.; Woodroffe, J. R.; Toth, G.; Welling, D. T.; Yu, Y.;
Birn, J.; Thomsen, M. F.; Borovsky, J.; Denton, M.; Albert, J.; Horne,
R. B.; Lemon, C. L.; Markidis, S.; Young, S. L.
Bibcode: 2015AGUFMSM31E..04J
Altcode:
The near-Earth space environment is a highly dynamic and coupled
system through a complex set of physical processes over a large range
of scales, which responds nonlinearly to driving by the time-varying
solar wind. Predicting variations in this environment that can affect
technologies in space and on Earth, i.e. "space weather", remains
a big space physics challenge. We present a recently funded project
through the Los Alamos National Laboratory (LANL) Directed Research
and Development (LDRD) program that is developing a new capability to
understand, model, and predict Space Hazards Induced near Earth by Large
Dynamic Storms, the SHIELDS framework. The project goals are to specify
the dynamics of the hot (keV) particles (the seed population for the
radiation belts) on both macro- and micro-scale, including important
physics of rapid particle injection and acceleration associated with
magnetospheric storms/substorms and plasma waves. This challenging
problem is addressed using a team of world-class experts in the fields
of space science and computational plasma physics and state-of-the-art
models and computational facilities. New data assimilation techniques
employing data from LANL instruments on the Van Allen Probes and
geosynchronous satellites are developed in addition to physics-based
models. This research will provide a framework for understanding of key
radiation belt drivers that may accelerate particles to relativistic
energies and lead to spacecraft damage and failure. The ability to
reliably distinguish between various modes of failure is critically
important in anomaly resolution and forensics. SHIELDS will enhance
our capability to accurately specify and predict the near-Earth space
environment where operational satellites reside.
Title: Initial Predictions of Outflow Rates from Jupiter's Ionosphere
Authors: Garcia-Sage, K.; Glocer, A.; Bell, J. M.; Toth, G.; Khazanov,
G. V.
Bibcode: 2015AGUFMSM31C2518G
Altcode:
Although Voyager 2 observations of H3+ in Jupiter's magnetosphere
indicate an ionospheric source of plasma, very little work has been
done to predict outflow rates from Jupiter's ionosphere. We use the
Polar Wind Outflow Model (PWOM), originally developed for Saturn and
Earth, to model outflow at Jupiter. We use a neutral atmosphere and
atmosphere-ionosphere chemistry from the Jupiter-Global Ionosphere
and Thermosphere Model (J-GITM) model and solve the field-aligned
gyrotropic transport equations along open flux tubes. The model includes
the effects of topside electron heat flux, collisional heating, and
photoionization. We describe a new modeling approach that includes
a kinetic description of superthermal photoelectrons and secondary
electron production. We show the preliminary results for vertical
transport and outflow of ionospheric H+, H2+, and H3+. These results
provide initial predictions for ion populations that Juno may observe
over Jupiter's polar regions.
Title: Modeling of the Inner Coma of Comet 67P/Churyumov-Gerasimenko
Constrained by VIRTIS and ROSINA Observations
Authors: Fougere, N.; Combi, M. R.; Tenishev, V.; Bieler, A. M.;
Migliorini, A.; Bockelée-Morvan, D.; Toth, G.; Huang, Z.; Gombosi,
T. I.; Hansen, K. C.; Capaccioni, F.; Filacchione, G.; Piccioni, G.;
Debout, V.; Erard, S.; Leyrat, C.; Fink, U.; Rubin, M.; Altwegg, K.;
Tzou, C. Y.; Le Roy, L.; Calmonte, U.; Berthelier, J. J.; Rème, H.;
Hässig, M.; Fuselier, S. A.; Fiethe, B.; De Keyser, J.
Bibcode: 2015AGUFM.P31E2105F
Altcode:
As it orbits around comet 67P/Churyumov-Gerasimenko (CG), the Rosetta
spacecraft acquires more information about its main target. The
numerous observations made at various geometries and at different
times enable a good spatial and temporal coverage of the evolution of
CG's cometary coma. However, the question regarding the link between
the coma measurements and the nucleus activity remains relatively open
notably due to gas expansion and strong kinetic effects in the comet's
rarefied atmosphere. In this work, we use coma observations made by
the ROSINA-DFMS instrument to constrain the activity at the surface
of the nucleus. The distribution of the H2O and CO2 outgassing is
described with the use of spherical harmonics. The coordinates in the
orthogonal system represented by the spherical harmonics are computed
using a least squared method, minimizing the sum of the square residuals
between an analytical coma model and the DFMS data. Then, the previously
deduced activity distributions are used in a Direct Simulation Monte
Carlo (DSMC) model to compute a full description of the H2O and CO2
coma of comet CG from the nucleus' surface up to several hundreds of
kilometers. The DSMC outputs are used to create synthetic images,
which can be directly compared with VIRTIS measurements. The good
agreement between the VIRTIS observations and the DSMC model, itself
constrained with ROSINA data, provides a compelling juxtaposition of
the measurements from these two instruments. Acknowledgements Work at
UofM was supported by contracts JPL#1266313, JPL#1266314 and NASA grant
NNX09AB59G. Work at UoB was funded by the State of Bern, the Swiss
National Science Foundation and by the ESA PRODEX Program. Work at
Southwest Research institute was supported by subcontract #1496541 from
the JPL. Work at BIRA-IASB was supported by the Belgian Science Policy
Office via PRODEX/ROSINA PEA 90020. The authors would like to thank ASI,
CNES, DLR, NASA for supporting this research. VIRTIS was built by a
consortium formed by Italy, France and Germany, under the scientific
responsibility of the IAPS of INAF, which guides also the scientific
operations. The consortium includes also the LESIA of the Observatoire
de Paris, and the Institut für Planetenforschung of DLR. The authors
wish to thank the RSGS and the RMOC for their continuous support.
Title: MHD Model Results of Solar Wind Interaction with Mars and
Comparison with MAVEN Plasma Observations
Authors: Ma, Y.; Russell, C. T.; Nagy, A. F.; Fang, X.; Dong, Y.;
Toth, G.; Halekas, J. S.; Connerney, J. E. P.; Espley, J. R.; Mahaffy,
P. R.; Benna, M.; McFadden, J. P.; Mitchell, D. L.; Jakosky, B. M.
Bibcode: 2015AGUFM.P13D..06M
Altcode:
The Mars Atmosphere and Volatile Evolution mission (MAVEN), launched on
November 18, 2013, is now in its primary science phase. The mission was
designed to study the upper atmosphere, ionosphere, and magnetosphere
of Mars, the response to solar and solar-wind input, and the ability
of atmospheric molecules and atoms to escape to space. In this study,
we use a time-dependent MHD model to interpret plasma observations
made by MAVEN particle and field instruments. Detailed comparisons
between the model and the relevant plasma observations from MAVEN
are presented for an entire Mars rotation under relatively quiet
solar wind conditions. Through comparison along MAVEN orbits, we
find that the time-dependent multi-species single-fluid MHD model is
able to reproduce the main features of the plasma environment around
Mars. Using the model results, we find that photoionization beyond
the terminator is the dominant ion source as compared with day-night
transport in maintaining the nightside ionosphere. Model results
also show that both the time-varying solar wind conditions and the
continuously rotating crustal field work together to control the ion
escape variation with time.
Title: Modeled Interaction of Comet 67P/Churyumov-Gerasimenko with
the Solar Wind Inside 2 AU
Authors: Rubin, M.; Gombosi, T. I.; Hansen, K. C.; Ip, W. -H.;
Kartalev, M. D.; Koenders, C.; Tóth, G.
Bibcode: 2015EM&P..116..141R
Altcode: 2015EM&P..tmp...20R
Periodic comets move around the Sun on elliptical orbits. As such
comet 67P/Churyumov-Gerasimenko (hereafter 67P) spends a portion of
time in the inner solar system where it is exposed to increased solar
insolation. Therefore given the change in heliocentric distance, in
case of 67P from aphelion at 5.68 AU to perihelion at ~1.24 AU, the
comet's activity—the production of neutral gas and dust—undergoes
significant variations. As a consequence, during the inbound portion,
the mass loading of the solar wind increases and extends to larger
spatial scales. This paper investigates how this interaction changes
the character of the plasma environment of the comet by means of
multifluid MHD simulations. The multifluid MHD model is capable of
separating the dynamics of the solar wind ions and the pick-up ions
created through photoionization and electron impact ionization in the
coma of the comet. We show how two of the major boundaries, the bow
shock and the diamagnetic cavity, form and develop as the comet moves
through the inner solar system. Likewise for 67P, although most likely
shifted back in time with respect to perihelion passage, this process
is reversed on the outbound portion of the orbit. The presented model
herein is able to reproduce some of the key features previously only
accessible to particle-based models that take full account of the ions'
gyration. The results shown herein are in decent agreement to these
hybrid-type kinetic simulations.
Title: Magnetospheric Simulations With the Three-Dimensional
Magnetohydrodynamics With Embedded Particle-in-Cell Model
Authors: Toth, G.; Jia, X.; Chen, Y.; Markidis, S.; Peng, B.;
Daldorff, L. K. S.; Tenishev, V.; Borovikov, D.; Haiducek, J. D.;
Gombosi, T. I.; Glocer, A.; Dorelli, J.; Lapenta, G.
Bibcode: 2015AGUFMSM54A..07T
Altcode:
We have recently developed a new modeling capability to embed the
implicit Particle-in-Cell (PIC) model iPIC3D into the BATS-R-US
magnetohydrodynamic model. The PIC domain can cover the regions where
kinetic effects are most important, such as reconnection sites. The
BATS-R-US code, on the other hand, can efficiently handle the rest
of the computational domain where the MHD or Hall MHD description is
sufficient with its block-adaptive grid. The current implementation
of the MHD-EPIC model allows two-way coupled simulations in two and
three dimensions with multiple embedded PIC regions. The MHD and
PIC grids can have different grid resolutions. The MHD variables
and the moments of the PIC distribution functions are interpolated
and message passed in an efficient manner through the Space Weather
Modeling Framework (SWMF). Both BATS-R-US and iPIC3D are massively
parallel codes fully integrated into, run by and coupled through
the SWMF. We have successfully applied the MHD-EPIC code to model
Ganymede's magnetosphere. Using four PIC regions we have in effect
performed a fully kinetic simulation of the moon's mini-magnetosphere
with a grid resolution that is about 5 times finer than the ion inertial
length. The Hall MHD model provides proper boundary conditions for the
four PIC regions and connects them with each other and with the inner
and outer outer boundary conditions of the much larger MHD domain. We
compare our results with Galileo magnetic observations and find good
overall agreement with both Hall MHD and MHD-EPIC simulations. The
power spectrum for the small scale fluctuations, however, agrees with
the data much better for the MHD-EPIC simulation than for Hall MHD. In
the MHD-EPIC simulation, unlike in the pure Hall MHD results, we also
find signatures of flux transfer events (FTEs) that agree very well with
the observed FTE signatures both in terms of shape and amplitudes. We
will also highlight our ongoing efforts to model the magnetospheres
of Mercury and Earth with the MHD-EPIC model.
Title: Magnetohydrodynamics with Embedded Particle-in-Cell Simulation
of Mercury's Magnetosphere
Authors: Chen, Y.; Toth, G.; Jia, X.; Gombosi, T. I.; Markidis, S.
Bibcode: 2015AGUFMSM31A2474C
Altcode:
Mercury's magnetosphere is much more dynamic than other planetary
magnetospheres because of Mercury's weak intrinsic magnetic field and
its proximity to the Sun. Magnetic reconnection and Kelvin-Helmholtz
phenomena occur in Mercury's magnetopause and magnetotail at higher
frequencies than in other planetary magnetosphere. For instance,
chains of flux transfer events (FTEs) on the magnetopause, have been
frequentlyobserved by the the MErcury Surface, Space ENvironment,
GEochemistry and Ranging (MESSENGER) spacecraft (Slavin et al.,
2012). Because ion Larmor radius is comparable to typical spatial
scales in Mercury's magnetosphere, finite Larmor radius effects need
to be accounted for. In addition, it is important to take in account
non-ideal dissipation mechanisms to accurately describe magnetic
reconnection. A kinetic approach allows us to model these phenomena
accurately. However, kinetic global simulations, even for small-size
magnetospheres like Mercury's, are currently unfeasible because of the
high computational cost. In this work, we carry out global simulations
of Mercury's magnetosphere with the recently developed MHD-EPIC model,
which is a two-way coupling of the extended magnetohydrodynamic
(XMHD) code BATS-R-US with the implicit Particle-in-Cell (PIC) model
iPIC3D. The PIC model can cover the regions where kinetic effects are
most important, such as reconnection sites. The BATS-R-US code, on the
other hand, can efficiently handle the rest of the computational domain
where the MHD or Hall MHD description is sufficient. We will present
our preliminary results and comparison with MESSENGER observations.
Title: Nowcasting Ground Magnetic Perturbations with the Space
Weather Modeling Framework
Authors: Welling, D. T.; Toth, G.; Singer, H. J.; Millward, G. H.;
Gombosi, T. I.
Bibcode: 2015AGUFMSM13F..07W
Altcode:
Predicting ground-based magnetic perturbations is a critical step
towards specifying and predicting geomagnetically induced currents
(GICs) in high voltage transmission lines. Currently, the Space Weather
Modeling Framework (SWMF), a flexible modeling framework for simulating
the multi-scale space environment, is being transitioned from research
to operational use (R2O) by NOAA's Space Weather Prediction Center. Upon
completion of this transition, the SWMF will provide localized B/t
predictions using real-time solar wind observations from L1 and the
F10.7 proxy for EUV as model input. This presentation describes the
operational SWMF setup and summarizes the changes made to the code
to enable R2O progress. The framework's algorithm for calculating
ground-based magnetometer observations will be reviewed. Metrics
from data-model comparisons will be reviewed to illustrate predictive
capabilities. Early data products, such as regional-K index and grids
of virtual magnetometer stations, will be presented. Finally, early
successes will be shared, including the code's ability to reproduce
the recent March 2015 St. Patrick's Day Storm.
Title: The impact of exospheric neutral dynamics on ring current decay
Authors: Ilie, R.; Liemohn, M. W.; Skoug, R. M.; Funsten, H. O.;
Gruntman, M.; Bailey, J. J.; Toth, G.
Bibcode: 2015AGUFMSA32A..01I
Altcode:
The geocorona plays an important role in the energy budget of the
Earth's inner magnetosphere since charge exchange of energetic ions
with exospheric neutrals makes the exosphere act as an energy sink
for ring current particles. Long-term ring current decay following a
magnetic storm is mainly due to these electron transfer reactions,
leading to the formation energetic neutral atoms (ENAs) that leave
the ring current system on ballistic trajectories. The number of ENAs
emitted from a given region of space depends on several factors,
such as the energy and species of the energetic ion population
in that region and the density of the neutral gas with which the
ions undergo charge exchange. However, the density and structure
of the exosphere are strongly dependent on changes in atmospheric
temperature and density as well as charge exchange with the ions
of plasmaspheric origin, which depletes the geocorona (by having a
neutral removed from the system). Moreover, the radiation pressure
exerted by solar far-ultraviolet photons pushes the geocoronal hydrogen
away from the Earth in an anti-sunward direction to form a tail of
neutral hydrogen. TWINS ENA images provide a direct measurement of
these ENA losses and therefore insight into the dynamics of the ring
current decay through interactions with the geocorona. We assess the
influence of geocoronal neutrals on ring current formation and decay by
analysis of the predicted ENA emissions using 6 different geocoronal
models and simulations from the HEIDI ring current model during storm
time. Comparison with TWINS ENA images shows that the location of
the peak ENA enhancements is highly dependent on the distribution of
geocoronal hydrogen density. We show that the neutral dynamics has a
strong influence on the time evolution of the ring current populations
as well as on the formation of energetic neutral atoms.
Title: Global Multi-fluid Solar Corona Model with Temperature
Anisotropy
Authors: van der Holst, B.; Chandran, B. D. G.; Kasper, J. C.; Szente,
J.; Sokolov, I.; Toth, G.; Gombosi, T. I.
Bibcode: 2015AGUFMSH13C2448V
Altcode:
The mechanisms that heat and accelerate the fast and slow wind have
not yet been conclusively identified. Plasma properties of Helium
in the solar wind are critical tracers for both processes so that
understanding them is key towards gaining insight in the solar wind
phenomenon, and being able to model it and predict its properties. We
present a generalization of the AWSoM model, a global solar corona model
with low-frequency Alfvén wave turbulence (van der Holst et al., 2014)
to include alpha-particle dynamics. To apportion the wave dissipation
to the isotropic electron temperature, parallel and perpendicular ion
temperatures, we employ the results of the theories of linear wave
damping and nonlinear stochastic heating as described by Chandran
et al. (2011, 2013). We account for the instabilities due to the
developing temperature anisotropies for the protons (Meng et al.,
2012) and alpha particles (Verscharen et al., 2013). We discuss the
feasibility for Alfvén wave turbulence to simultaneously address the
coronal heating and alpha-proton differential streaming.
Title: A study of the variation of physical conditions in the cometary
coma based on a 3D multi-fluid model
Authors: Shou, Y.; Combi, M. R.; Fougere, N.; Tenishev, V.; Toth,
G.; Gombosi, T. I.; Huang, Z.; Jia, X.; Bieler, A. M.; Hansen, K. C.
Bibcode: 2015AGUFM.P31E2114S
Altcode:
Physics-based numerical coma models are desirable whether to
interpret the spacecraft observations of the inner coma or to
compare with the ground-based observations of the outer coma. One
example is Direct Simulation Monte Carlo (DSMC) method, which has
been successfully adopted to simulate the coma under various complex
conditions. However, for bright comets with large production rates,
the time step in DSMC model has to be tiny to accommodate the small
mean free path and the high collision frequency. In addition a truly
time-variable 3D DSMC model would still be computationally difficult
or even impossible under most circumstances. In this work, we develop
a multi-neutral-fluid model based on BATS-R-US in the University of
Michigan's SWMF (Space Weather Modeling Framework), which can serve
as a useful alternative to DSMC methods to compute both the inner
and the outer coma and to treat time-variable phenomena. This model
treats H2O, OH, H2, O, H and CO2 as separate fluids and each fluid
has its own velocity and temperature. But collisional interactions
can also couple all fluids together. Collisional interactions tend to
decrease the velocity differences and are also able to re-distribute
the excess energy deposited by chemical reactions among all species. To
compute the momentum and energy transfer caused by such interactions
self-consistently, collisions between fluids, whose efficiency is
proportional to the densities, are included as well as heating from
various chemical reactions. By applying the model to comets with
different production rates (i.e. 67P/Churyumov-Gerasimenko, 1P/Halley,
etc.), we are able to study how the heating efficiency varies with
cometocentric distances and production rates. The preliminary results
and comparison are presented and discussed. This work has been partially
supported by grant NNX14AG84G from the NASA Planetary Atmospheres
Program, and US Rosetta contracts JPL #1266313, JPL #1266314 and
JPL #1286489.
Title: Dynamics of Polar Jets from the Chromosphere to the Corona:
Mass, Momentum and Energy Transfer
Authors: Szente, J.; Toth, G.; Manchester, W.; van der Holst, B.;
Landi, E.; DeVore, C. R.; Gombosi, T. I.
Bibcode: 2015AGUFMSH23D..05S
Altcode:
Coronal jets, routinely observed by multiple instruments at
multiple wavelengths, provide a unique opportunity to understand
the relationships between magnetic field topology, reconnection, and
solar wind heating and acceleration. We simulate coronal jets with the
Alfvén Wave Solar Model (AWSoM) [van der Holst (2014)] and focus our
study on the thermodynamical evolution of the plasma. AWSoM solves
the two-temperature MHD equations with electron heat conduction,
which not only addresses the thermodynamics of individual species,
but also allows for the construction of synthetic images from the EUV
and soft X-ray wavelength range. Our jet model takes the form of a
slowly rotating bipole field imbedded in the open magnetic field of
a coronal hole; a topology suggested by observations. We follow the
formation and evolution of polar jets starting from the chromosphere
and extending into the outer corona. The simulations show small-scale
eruptive reconnection events that self-consistently heat and accelerate
the solar wind. Our results provide a quantitative comparison to
observations made in the EUV and X-ray spectrum.
Title: Magnetized Jets Driven by the Sun, the Structure of the
Heliosphere Revisited: Consequences for Draping of BISM ahead of
the HP and Time Variability of ENAs
Authors: Opher, M.; Drake, J. F.; Zieger, B.; Michael, A.; Toth, G.;
Swisdak, M.; Gombosi, T. I.
Bibcode: 2015AGUFMSH41A2371O
Altcode:
Recently we proposed (Opher et al. 2015) that the structure of the
heliosphere might be very different than we previously thought. The
classic accepted view of the heliosphere is a quiescent, comet-like
shape aligned in the direction of the Sun's travel through the
interstellar medium (ISM) extending for thousands of astronomical
units. We have shown, based on magnetohydrodynamic (MHD) simulations,
that the tension force of the twisted magnetic field of the Sun
confines the solar wind plasma beyond the termination shock and drives
jets to the north and south very much like astrophysical jets. These
heliospheric jets are deflected into the tail region by the motion of
the Sun through the ISM. As in some astrophysical jets the interstellar
wind blows the two jets into the tail but is not strong enough to force
the lobes into a single comet-like tail. Instead, the interstellar wind
flows around the heliosphere and into the equatorial region between
the two jets. We show that the heliospheric jets are turbulent (due
to large-scale MHD instabilities and reconnection) and strongly mix
the solar wind with the ISM. The resulting turbulence has important
implications for particle acceleration in the heliosphere. The two-lobe
structure is consistent with the energetic neutral atom (ENA) images of
the heliotail from IBEX where two lobes are visible in the north and
south and the suggestion from the Cassini ENAs that the heliosphere
is "tailless." The new structure of the heliosphere is supported by
recent analytic work (Drake et al. 2015) that shows that even in high
β heliosheath the magnetic field plays a crucial role in funneling the
solar wind in two jets. Here we present these recent results and show
that the heliospheric jets mediate the draping of the magnetic field
and the conditions ahead of the heliopause. We show that reconnection
between the interstellar and solar magnetic field both at the flanks of
the jets and in between them twist the interstellar magnetic field in a
small layer ahead of the HP in agreement with Voyager 1 observations (as
seen in Opher & Drake 2013). We present results of the heliospheric
jets for a weaker magnetic field, representative of the 2010-2012
period and what is expected to be seen in the ENA maps with solar cycle.
Title: Testing the magnetotail configuration based on observations
of low-altitude isotropic boundaries during quiet times
Authors: Ilie, R.; Ganushkina, N.; Toth, G.; Dubyagin, S.; Liemohn,
M. W.
Bibcode: 2015JGRA..12010557I
Altcode:
We investigate the configuration of the geomagnetic field on the
nightside magnetosphere during a quiet time interval based on National
Oceanic and Atmospheric Administration Polar Orbiting Environment
Satellites Medium Energy Proton and Electron Detector (NOAA/POES
MEPED) measurements in combination with numerical simulations of the
global terrestrial magnetosphere using the Space Weather Modeling
Framework. Measurements from the NOAA/POES MEPED low-altitude data
sets provide the locations of isotropic boundaries; those are used to
extract information regarding the field structure in the source regions
in the magnetosphere. In order to evaluate adiabaticity and mapping
accuracy, which is mainly controlled by the ratio between the radius
of curvature and the particle's Larmor radius, we tested the threshold
condition for strong pitch angle scattering based on the MHD magnetic
field solution. The magnetic field configuration is represented by
the model with high accuracy, as suggested by the high correlation
coefficients and very low normalized root-mean-square errors between
the observed and the modeled magnetic field. The scattering criterion,
based on the values of k=<mfrac>Rcρ</mfrac> ratio at
the crossings of magnetic field lines, associated with isotropic
boundaries, with the minimum B surface, predicts a critical value of
kCR∼33. This means that, in the absence of other scattering
mechanisms, the strong pitch angle scattering takes place whenever the
Larmor radius is ∼33 times smaller than the radius of curvature of the
magnetic field, as predicted by the Space Weather Modeling Framework.
Title: New Publicly Available EEGGL Tool for Simulating Coronal
Mass Ejections.
Authors: Sokolov, I.; Manchester, W.; van der Holst, B.; Gombosi,
T. I.; Jin, M.; Mullinix, R.; Taktakishvili, A.; Chulaki, A.; Toth, G.
Bibcode: 2015AGUFMSH21B2403S
Altcode:
We present and demonstrate a new tool, EEGGL (Eruptive Event Generator
using Gibson-Low configuration) for simulating CMEs (Coronal Mass
Ejections). CMEs are among the most significant space weather events,
producing the radiation hazards (via the diffuse shock acceleration
of the Solar Energetic Particles - SEPs), the interplanetary shock
waves as well as the geomagnetic activity due to the drastic changes of
the interplanetary magnetic field within the "magnetic clouds" ("flux
ropes"). Some of this effects may be efficiently simulated using the
"cone model", which is employed in the real-time simulations of the
ongoing CMEs at the NASA-Goddard Space Flight Center. The cone model
provides a capability to predict the location, time, width and shape of
the hydrodynamic perturbation in the upper solar corona (at ~0.1 AU),
which can be used to drive the heliospheric simulation (with the ENLIL
code, for example). At the same time the magnetic field orientation
in this perturbation is uncertain within the cone model, which limits
the capability of the geomagnetic activity forecast. The new EEGGL
tool http://ccmc.gsfc.nasa.gov/analysis/EEGGL/recently developed at
the Goddard Space Flight Center in collaboration with the University
of Michigan provides a new capability for both evaluating the magnetic
field configuration resulting from the CME and tracing the CME through
the solar corona. In this way not only the capability to simulate the
magnetic field evolution at 1 AU may be achieved, but also the more
extensive comparison with the CME observations in the solar corona may
be achieved. Based on the magnetogram and evaluation of the CME initial
location and speed, the user may choose the active region from which
the CME originates and then the EEGGL tools provides the parameters
of the Gibson-Low magnetic configuration to parameterize the CME. The
recommended parameters may be used then to drive the simulation of CME
propagation from the low solar corona to 1 AU using the global code
for simulating the solar corona and inner heliosphere. The Community
Coordinated Modeling Center (CCMC) provides the capability for CME
runs-on-request, to the heliophysics community.
Title: Alfvén wave solar model (AWSoM): proton temperature anisotropy
and solar wind acceleration
Authors: Meng, X.; van der Holst, B.; Tóth, G.; Gombosi, T. I.
Bibcode: 2015MNRAS.454.3697M
Altcode:
Temperature anisotropy has been frequently observed in the solar corona
and the solar wind, yet poorly represented in computational models
of the solar wind. Therefore, we have included proton temperature
anisotropy in our Alfvén wave solar model (AWSoM). This model solves
the magnetohydrodynamic equations augmented with low-frequency Alfvén
wave turbulence. The wave reflection due to Alfvén speed gradient
and field-aligned vorticity results in turbulent cascade. At the
gyroradius scales, the apportioning of the turbulence dissipation into
coronal heating of the protons and electrons is through stochastic
heating. This paper focuses on the impacts of the proton temperature
anisotropy on the solar wind. We apply AWSoM to simulate the steady
solar wind from the corona to 1 AU using synoptic magnetograms. The
Alfvén wave energy density at the inner boundary is prescribed with
a uniform Poynting flux per field strength. We present the proton
temperature anisotropy distribution, and investigate the firehose
instability in the heliosphere from our simulations. In particular, the
comparisons between the simulated and observed solar wind properties
at 1 AU during the ramping-up phase and the maximum of solar cycle 24
imply the importance of addressing the proton temperature anisotropy
in solar wind modelling to capture the fast solar wind speed.
Title: Ganymede as a Laboratory for Multiscale Physics
Authors: Glocer, A.; Dorelli, J.; Toth, G.; Daughton, W. S.; Le, A.
Bibcode: 2015AGUFMSM54A..03G
Altcode:
There are multiple scales on which the local physics of collisionless
magnetic reconnection operate. These include the ion scale and
electron scales defined by the associated inertial lengths. In
Earth's magnetosphere, even the ion scale is inaccessible to even
very large-scale numerical simulations, as it is just a tiny fraction
of the total system size. Therefore we primarily rely on resistive
MHD simulations when studying Earth's magnetosphere. In contrast,
Ganymede's magnetosphere is much smaller, and the ion inertial
length is much larger compared to the system's size. The relatively
large scales make it possible to model Ganymede's magnetosphere with
more sophisticated approaches while adequately resolving the relevant
physical scales. Ganymede is therefore an ideal laboratory for studying
both the multiple scales involved in collisionless reconnection as
well as the consequences for the global magnetosphere; it is a real
magnetosphere with available in situ data that is also accessible to
multiple modeling approaches. We present recent Hall MHD simulations
with the BATSRUS code, and comparisons to Galileo observations, of this
small magnetosphere and demonstrate the global importance of ion scale
effects. We further extract magnetic separators and compare the results
with resistive MHD, Hybrid and PIC results. As with the GEM reconnection
challenge, we find that including ion scale physics is the minimum
extension of MHD to capture most basic features of the magnetosphere.
Title: Modeling of the VIRTIS-M Observations of the Coma of Comet
67P/Churyumov-Gerasimenko
Authors: Fougere, Nicolas; Combi, Michael R.; Tenishev, Valeriy;
Bieler, Andre; Migliorini, Alessandra; Piccioni, Giuseppe; Capaccioni,
Fabrizio; Filacchione, Gianrico; Toth, Gabor; Huang, Zhenguang;
Gombosi, Tamas; Hansen, Kenneth; Bockelee-Morvan, Dominique; Debout,
Vincent; Erard, Stephane; Leyrat, Cedric; Fink, Uwe; Rubin, Martin;
Altwegg, Kathrin; Tzou, Chia-Yu; Le Roy, Lena; Calmonte, Ursina;
Berthelier, Jean-Jacques; Reme, Henri; Hassig, Myrtha; Fuselier,
Stephen; Fiethe, Bjorn; De Keyser, Johan
Bibcode: 2015DPS....4741306F
Altcode:
The recent images of the inner coma of 67P/Churyumov-Gerasimenko (CG)
made by the infrared channel of the VIRTIS-M instrument on board the
Rosetta spacecraft show the gas distribution as it expands in the
coma (Migliorini et al. 2015, DPS abstract).Since VIRTIS is a remote
sensing instrument, a proper modeling of these observations requires
the computation of the full coma of comet CG, which necessitates the
use of a kinetic approach due to the rather low gas densities. Hence,
we apply a Direct Simulation Monde Carlo (DSMC) method to solve the
Boltzmann equation and describe CG’s coma from the nucleus surface
up to a few hundreds of kilometers. The model uses the SHAP5 nucleus
shape model from the OSIRIS team. The gas flux distribution takes into
account solar illumination, including self-shadowing. The local activity
at the surface of the nucleus is given by spherical harmonics expansion
reproducing best the ROSINA-DFMS data. The densities from the DSMC model
outputs are then integrated along the line-of-sight to create synthetic
images that are directly comparable with the VIRTIS-M column density
measurements.The good agreement between the observations and the model
illustrates our continuously improving understanding of the physics
of the coma of comet CG.AcknowledgementsWork at UofM was supported by
contracts JPL#1266313, JPL#1266314 and NASA grant NNX09AB59G. Work
at UoB was funded by the State of Bern, the Swiss National Science
Foundation and by the European Space Agency PRODEX Program. Work at
Southwest Research institute was supported by subcontract #1496541 from
the JPL. Work at BIRA-IASB was supported by the Belgian Science Policy
Office via PRODEX/ROSINA PEA 90020. The authors would like to thank ASI,
CNES, DLR, NASA for supporting this research. VIRTIS was built by a
consortium formed by Italy, France and Germany, under the scientific
responsibility of the IAPS of INAF, which guides also the scientific
operations. The consortium includes also the LESIA of the Observatoire
de Paris, and the Institut für Planetenforschung of DLR. The authors
wish to thank the RSGS and the RMOC for their continuous support.
Title: The Plasma Environment in Comets Over a Wide Range of
Heliocentric Distances: Application to Coment C/2006 P1 (McNaught)
Authors: Shou, Yinsi; Combi, Michael; Jia, Yingdong; Gombosi, Tamas;
Toth, Gabor; Rubin, Martin
Bibcode: 2015DPS....4741519S
Altcode:
On 2007 January 12, comet C/2006 P1 (McNaught) passed its perihelion at
0.17 AU. Abundant remote observations offer plenty of information on the
neutral composition and neutral velocities within 1 million kilometers
of the comet nucleus. In early February, the Ulysses spacecraft made
an in situ measurement of the ion composition, plasma velocity, and
magnetic field when passing through the distant ion tail and the ambient
solar wind. The measurement by Ulysses was made when the comet was
at around 0.8 AU. With the constraints provided by remote and in situ
observations, we simulated the plasma environment of Comet C/2006 P1
(McNaught) using a multi-species comet MHD model over a wide range of
heliocentric distances from 0.17 to 1.75 AU. The solar wind interaction
of the comet at various locations is characterized and typical subsolar
standoff distances of the bow shock and contact surface are presented
and compared to analytic solutions. We find the variation in the bow
shock standoff distances at different heliocentric distances is smaller
than the contact surface. In addition, we modified the multi-species
model for the case when the comet was at 0.7 AU and achieved comparable
water group ion abundances, proton densities, plasma velocities, and
plasma temperatures to the Ulysses/SWICS and SWOOPS observations. We
discuss the dominating chemical reactions throughout the comet-solar
wind interaction region and demonstrate the link between the ion
composition near the comet and in the distant tail as measured by
Ulysses. The work at the University of Michigan was supported by the
NASA Planetary Atmospheres grant NNX14AG84G.
Title: Solar wind Mars interaction during the MAVEN Deep Dip
campaigns: multi-fluid MHD simulations based upon the SWIA, NGIMS
and MAG measurements
Authors: Dong, Chuanfei; Bougher, Stephen W.; Ma, Yingjuan; Toth,
Gabor; Curry, Shannon M.; Nagy, Andrew F.; Halekas, Jasper S.; Luhmann,
Janet G.; Mahaffy, Paul; Benna, Mehdi; Connerney, Jack E. P.; Espley,
Jared; Mitchell, David L.; Brain, David A.; Jakosky, Bruce M.
Bibcode: 2015DPS....4741913D
Altcode:
The 3-D Mars multi-fluid Block Adaptive Tree Solar-wind Roe
Upwind Scheme (BATS-R-US) MHD code is used to study the solar wind
interaction with the Martian upper atmosphere during the MAVEN Deep Dip
campaigns. MAVEN made the first comprehensive measurements of Martian
thermosphere and ionosphere composition, structure, and variability at
altitudes down to ~130 km in the subsolar region during the second of
its Deep Dip campaigns. MAVEN will start its fourth Deep Dip campaign
this September and a large quantity of useful data will be returned
for this study as well. In this study we adopt the MAVEN measurements
as the multi-fluid MHD inputs. The estimated solar wind density and
velocity, the estimated interplanetary magnetic field (IMF), and the
exactly measured neutral atmosphere profile are taken from the SWIA,
MAG and NGIMS instruments, respectively. We will compare the calculated
ionosphere ion profiles with the NGIMS measurements. In the meantime,
we will show the calculations of the global ion escape rates based
upon actual measured neutral atmosphere profiles during the MAVEN Deep
Dip campaigns.
Title: Comparison of 3D kinetic and hydrodynamic models to ROSINA-COPS
measurements of the neutral coma of 67P/Churyumov-Gerasimenko
Authors: Bieler, Andre; Altwegg, Kathrin; Balsiger, Hans; Berthelier,
Jean-Jacques; Calmonte, Ursina; Combi, Michael; De Keyser, Johan;
Fiethe, Björn; Fougere, Nicolas; Fuselier, Stephen; Gasc, Sébastien;
Gombosi, Tamas; Hansen, Kenneth; Hässig, Myrtha; Huang, Zhenguang;
Jäckel, Annette; Jia, Xianzhe; Le Roy, Lena; Mall, Urs A.; Rème,
Henri; Rubin, Martin; Tenishev, Valeriy; Tóth, Gábor; Tzou, Chia-Yu;
Wurz, Peter
Bibcode: 2015A&A...583A...7B
Altcode:
67P/Churyumov-Gerasimenko (67P) is a Jupiter-family comet and the object
of investigation of the European Space Agency mission Rosetta. This
report presents the first full 3D simulation results of 67P's neutral
gas coma. In this study we include results from a direct simulation
Monte Carlo method, a hydrodynamic code, and a purely geometric
calculation which computes the total illuminated surface area on the
nucleus. All models include the triangulated 3D shape model of 67P as
well as realistic illumination and shadowing conditions. The basic
concept is the assumption that these illumination conditions on the
nucleus are the main driver for the gas activity of the comet. As a
consequence, the total production rate of 67P varies as a function of
solar insolation. The best agreement between the model and the data
is achieved when gas fluxes on the night side are in the range of 7%
to 10% of the maximum flux, accounting for contributions from the
most volatile components. To validate the output of our numerical
simulations we compare the results of all three models to in situ gas
number density measurements from the ROSINA COPS instrument. We are
able to reproduce the overall features of these local neutral number
density measurements of ROSINA COPS for the time period between early
August 2014 and January 1 2015 with all three models. Some details in
the measurements are not reproduced and warrant further investigation
and refinement of the models. However, the overall assumption that
illumination conditions on the nucleus are at least an important
driver of the gas activity is validated by the models. According to
our simulation results we find the total production rate of 67P to be
constant between August and November 2014 with a value of about 1 ×
1026 molecules s-1.
Title: MHD model results of solar wind interaction with Mars and
comparison with MAVEN plasma observations
Authors: Ma, Y. J.; Russell, C. T.; Fang, X.; Dong, Y.; Nagy, A. F.;
Toth, G.; Halekas, J. S.; Connerney, J. E. P.; Espley, J. R.; Mahaffy,
P. R.; Benna, M.; McFadden, J. P.; Mitchell, D. L.; Jakosky, B. M.
Bibcode: 2015GeoRL..42.9113M
Altcode:
The Mars Atmosphere and Volatile EvolutioN mission (MAVEN), launched
on 18 November 2013, is now in its primary science phase, orbiting
Mars with a 4.5 h period. In this study, we use a time-dependent MHD
model to interpret plasma observations made by MAVEN particle and
field instruments. Detailed comparisons between the model and the
relevant plasma observations from MAVEN are presented for an entire
Mars rotation under relatively quiet solar wind conditions. Through
comparison along MAVEN orbits, we find that the time-dependent
multispecies single-fluid MHD model is able to reproduce the main
features of the plasma environment around Mars. Using the model results,
we find that photoionization beyond the terminator is the dominant
ion source as compared with day-night transport in maintaining the
nightside ionosphere. Model results also show that both the time-varying
solar wind conditions and the continuously rotating crustal field work
together to control the ion escape variation with time.
Title: Three-dimensional kinetic modeling of the neutral and charged
dust in the coma of Rosetta’s target comet 67P/Churyumov-Gerasimenko
Authors: Tenishev, Valeriy; Borovikov, Dmitry; Combi, Michael R.;
Fougere, Nicolas; Huang, Zhenguang; Bieler, Andre; Hansen, Kenneth;
Toth, Gabor; Jia, Xianzhe; Shou, Yinsi; Gombosi, Tamas; Rubin, Martin;
Rotundi, Alessandra; Della Corte, Vincenzo
Bibcode: 2015DPS....4750309T
Altcode:
Rosetta is the first mission that escorts a comet along its way
through the Solar System for an extended amount of time. As a result,
the target of the mission, comet 67P/Churyumov-Gerasimenko, is an
object of great scientific interest.Dust ejected from the nucleus
is entrained into the coma by the escaping gas. Interacting with the
ambient plasma the dust particles are charged by the electron and ion
collection currents. The photo and secondary emission currents can also
change the particle charge. The resulting Lorentz force together with
the gas drag, gravity, and radiation pressure define the dust particle
trajectories.At altitudes comparable to those of the Rosetta trajectory,
direction of a dust particle velocity can be significantly different
from that in the innermost vicinity of the coma near the nucleus. At
such altitudes the angular distribution of the dust grains velocity has
a pronounced tail-like structure. This is consistent with Rosetta’s
GIADA dust observations showing dust grains moving in the anti-sunward
direction.Here, we present results of our model study of the neutral
and charged dust in the coma of comet 67P/Churyumov-Gerasimenko,
combining the University of Michigan AMPS kinetic particle model and the
BATSRUS MHD model. Trajectories of dust particles within the observable
size range of Rosetta’s GIADA dust instrument have been calculated
accounting for the radiation pressure, gas drag, the nucleus gravity,
the Lorentz force, and the effect of the nucleus rotation. The dust
grain electric charge is calculated by balancing the collection currents
at the grain’s location. We present angular velocity distribution
maps of these charged dust grains for a few locations representative
of Rosetta's trajectory around the comet.This work was supported by
US Rosetta project contracts JPL-1266313 and JPL-1266314 and NASA
Planetary Atmospheres grant NNX14AG84G
Title: Multifluid MHD study of the solar wind interaction with Mars'
upper atmosphere during the 2015 March 8th ICME event
Authors: Dong, Chuanfei; Ma, Yingjuan; Bougher, Stephen W.; Toth,
Gabor; Nagy, Andrew F.; Halekas, Jasper S.; Dong, Yaxue; Curry, Shannon
M.; Luhmann, Janet G.; Brain, David; Connerney, Jack E. P.; Espley,
Jared; Mahaffy, Paul; Benna, Mehdi; McFadden, James P.; Mitchell,
David L.; DiBraccio, Gina A.; Lillis, Robert J.; Jakosky, Bruce M.;
Grebowsky, Joseph M.
Bibcode: 2015GeoRL..42.9103D
Altcode:
We study the solar wind interaction with the Martian upper atmosphere
during the 8 March 2015 interplanetary coronal mass ejection (ICME)
by using a global multifluid MHD model. Comparison of the simulation
results with observations from Mars Atmosphere and Volatile EvolutioN
(MAVEN) spacecraft shows good agreement. The total ion escape rate
is increased by an order of magnitude, from 2.05 × 1024
s-1 (pre-ICME phase) to 2.25 × 1025
s-1 (ICME sheath phase), during this time period. Two major
ion escape channels are illustrated: accelerated pickup ion loss through
the dayside plume and ionospheric ion loss through the nightside plasma
wake region. Interestingly, the tailward ion loss is significantly
increased at the ejecta phase. Both bow shock and magnetic pileup
boundary (BS and MPB) locations are decreased from (1.2RM,
1.57RM) at the pre-ICME phase to (1.16RM,
1.47RM), respectively, during the sheath phase along the
dayside Mars-Sun line. Furthermore, both simulation and observational
results indicate that there is no significant variation in the Martian
ionosphere (at altitudes ≲ 200 km, i.e., the photochemical region)
during this event.
Title: 3D DSMC Modeling of the Coma of Comet 67P/Churyumov-Gerasimenko
Observed by the VIRTIS and ROSINA instruments
Authors: Fougere, N.; Combi, M. R.; Tenishev, V.; Bieler, A.; Toth, G.;
Huang, Z.; Gombosi, T. I.; Hansen, K. C.; Capaccioni, F.; Filacchione,
G.; Migliorini, A.; Bockelée-Morvan, D.; Debout, V.; Erard, S.;
Leyrat, C.; Fink, U.; Rubin, M.; Altwegg, K.; Tzou, C. -Y.; Le Roy, L.
Bibcode: 2015EPSC...10..344F
Altcode:
Since its rendez-vous with comet 67P/Chruryumov- Gerasimenko (CG),
the Rosetta spacecraft has provided invaluable information contributing
to our understanding of the cometary environment. On board, the VIRTIS
and ROSINA instruments can both measure gas parameters in the rarefied
cometary atmosphere, the coma, and provide complementary results with
remote sensing and in-situ measurements, respectively. The use of
a numerical model is a way to correlate the information provided by
both VIRTIS and ROSINA to fully understand the volatile environment
of comet CG. To describe the entire coma including the regions where
collisions cannot maintain the flow in a fluid regime, the use of a
kinetic method is necessary. Here, the Direct Simulation Monte-Carlo
(DSMC) approach is applied to the cometary coma to solve the Boltzmann
equation [1] using the Adaptive Mesh Particle Simulator (AMPS) code [2],
[3], [4], [5], and then compared with VIRTIS and ROSINA data.
Title: Four-fluid MHD Simulations of the Plasma and Neutral Gas
Environment of Comet Churyumov-Gerasimenko Near Perihelion
Authors: Huang, Z.; Toth, G.; Gombosi, T.; Jia, X.; Rubin, M.;
Fougere, N.; Tenishev, V.; Combi, M.; Bieler, A.; Hansen, K.; Shou,
Y.; Altwegg, K.
Bibcode: 2015EPSC...10..406H
Altcode:
We develop a 3-D four fluid model to study the plasma environment of
comet Churyumov- Gerasimenko (CG), which is the target of the Rosetta
mission. Our model is based on BATS-R-US within the SWMF (Space Weather
Modeling Framework) that solves the governing multifluid MHD equations
and and the Euler equations for the neutral gas fluid. These equations
describe the behavior and interactions of the cometary heavy ions,
the solar wind protons, the electrons, and the neutrals. This model
incorporates mass loading processes, including photo and electron
impact ionization, furthermore taken into account are charge exchange,
dissociative ion-electron recombination, as well as collisional
interactions between different fluids. We simulate the near nucleus
plasma and neutral gas environment with a realistic shape model of
CG near perihelion and compare our simulation results with Rosetta
observations.
Title: MHD Model Results of Solar Wind Plasma Interaction with
Mars and Comparison with MAVEN Observations during Quiet Solar
Wind Conditions
Authors: Ma, Y.; Russell, C.; Nagy, A. F.; Toth, G.; Halekas, J. S.;
Connerney, J. E. P.; Espley, J. R.; Mahaffy, P. R.; Benna, Mhedi;
McFadden, James
Bibcode: 2015EPSC...10..316M
Altcode:
The Mars Atmosphere and Volatile Evolution mission (MAVEN), launched
on November 18, 2013, is now in its primary science phase, orbiting
Mars with a 4.5 hour period. In this presentation, we show detailed
comparisons between the MHD model results and the relevant plasma
observations from MAVEN during quiet solar wind conditions. Through
comparison with relevant observation along MAVEN orbits, we find that
in general, the time-dependent multi-species MHD model reproduces very
well the plasma interaction process around Mars.
Title: Constraining the pickup ion abundance and temperature through
the multifluid reconstruction of the Voyager 2 termination shock
crossing
Authors: Zieger, Bertalan; Opher, Merav; Tóth, Gábor; Decker,
Robert B.; Richardson, John D.
Bibcode: 2015JGRA..120.7130Z
Altcode:
Voyager 2 observations revealed that the hot solar wind ions (the
so-called pickup ions) play a dominant role in the thermodynamics
of the termination shock and the heliosheath. The number density and
temperature of this hot population, however, have remained unknown,
since the plasma instrument on board Voyager 2 can only detect the
colder thermal ion component. Here we show that due to the multifluid
nature of the plasma, the fast magnetosonic mode splits into a
low-frequency fast mode and a high-frequency fast mode. The coupling
between the two fast modes results in a quasi-stationary nonlinear
wave mode, the "oscilliton," which creates a large-amplitude trailing
wave train downstream of the thermal ion shock. By fitting multifluid
shock wave solutions to the shock structure observed by Voyager 2,
we are able to constrain both the abundance and the temperature of
the undetected pickup ions. In our three-fluid model, we take into
account the nonnegligible partial pressure of suprathermal energetic
electrons (0.022-1.5 MeV) observed by the Low-Energy Charged Particle
Experiment instrument on board Voyager 2. The best fitting simulation
suggests a pickup ion abundance of 20 ± 3%, an upstream pickup ion
temperature of 13.4 ± 2 MK, and a hot electron population with an
apparent temperature of ~0.83 MK. We conclude that the actual shock
transition is a subcritical dispersive shock wave with low Mach number
and high plasma β.
Title: Solar wind interaction with the Martian upper atmosphere:
Crustal field orientation, solar cycle, and seasonal variations
Authors: Dong, Chuanfei; Bougher, Stephen W.; Ma, Yingjuan; Toth,
Gabor; Lee, Yuni; Nagy, Andrew F.; Tenishev, Valeriy; Pawlowski,
Dave J.; Combi, Michael R.; Najib, Dalal
Bibcode: 2015JGRA..120.7857D
Altcode:
A comprehensive study of the solar wind interaction with the Martian
upper atmosphere is presented. Three global models: the 3-D Mars
multifluid Block Adaptive Tree Solar-wind Roe Upwind Scheme MHD
code (MF-MHD), the 3-D Mars Global Ionosphere Thermosphere Model
(M-GITM), and the Mars exosphere Monte Carlo model Adaptive Mesh
Particle Simulator (M-AMPS) were used in this study. These models
are one-way coupled; i.e., the MF-MHD model uses the 3-D neutral
inputs from M-GITM and the 3-D hot oxygen corona distribution from
M-AMPS. By adopting this one-way coupling approach, the Martian
upper atmosphere ion escape rates are investigated in detail with
the combined variations of crustal field orientation, solar cycle,
and Martian seasonal conditions. The calculated ion escape rates are
compared with Mars Express observational data and show reasonable
agreement. The variations in solar cycles and seasons can affect the
ion loss by a factor of ∼3.3 and ∼1.3, respectively. The crustal
magnetic field has a shielding effect to protect Mars from solar wind
interaction, and this effect is the strongest for perihelion conditions,
with the crustal field facing the Sun. Furthermore, the fraction of cold
escaping heavy ionospheric molecular ions [(O2+
and/or O2+)/Total] are inversely proportional
to the fraction of the escaping (ionospheric and corona) atomic
ion [O+/Total], whereas O2+ and
O2+ ion escape fractions show a positive linear
correlation since both ion species are ionospheric ions that follow
the same escaping path.
Title: The Plasma Environment in Comets over a Wide Range of
Heliocentric Distances: Application to Comet C/2006 P1 (McNaught)
Authors: Shou, Y.; Combi, M.; Jia, Y. -D.; Gombosi, T.; Toth, G.;
Rubin, M.
Bibcode: 2015ApJ...809..156S
Altcode:
On 2007 January 12, comet C/2006 P1 (McNaught) passed its perihelion
at 0.17 AU. Abundant remote observations offer plenty of information
on the neutral composition and neutral velocities within 1 million
kilometers of the comet nucleus. In early February, the Ulysses
spacecraft made an in situ measurement of the ion composition, plasma
velocity, and magnetic field when passing through the distant ion
tail and the ambient solar wind. The measurement by Ulysses was made
when the comet was at around 0.8 AU. With the constraints provided by
remote and in situ observations, we simulated the plasma environment of
Comet C/2006 P1 (McNaught) using a multi-species comet MHD model over
a wide range of heliocentric distances from 0.17 to 1.75 AU. The solar
wind interaction of the comet at various locations is characterized
and typical subsolar standoff distances of the bow shock and contact
surface are presented and compared to analytic solutions. We find the
variation in the bow shock standoff distances at different heliocentric
distances is smaller than the contact surface. In addition, we modified
the multi-species model for the case when the comet was at 0.7 AU
and achieved comparable water group ion abundances, proton densities,
plasma velocities, and plasma temperatures to the Ulysses/SWICS and
SWOOPS observations. We discuss the dominating chemical reactions
throughout the comet-solar wind interaction region and demonstrate
the link between the ion composition near the comet and in the distant
tail as measured by Ulysses.
Title: Solar Cycle Variation of the Magnetic Field Strength and
Magnetic Dissipation Effects in the Heliosheath
Authors: Michael, Adam Thomas; Opher, Merav; Provornikova, Elena;
Richardson, John; Toth, Gabor
Bibcode: 2015shin.confE..81M
Altcode:
We investigate the role the 11-year solar cycle variation of the
magnetic field strength as well as magnetic dissipation effects have on
the flows within the heliosheath using a global 3D magnetohydrodynamic
model of the heliosphere. We use time and latitude-dependent solar
wind velocity and density inferred from SOHO/SWAN and IPS data and
implemented solar cycle variations of the magnetic field derived from
27-day averages of the field magnitude average of the magnetic field at
1 AU from the OMNI database. This model predicts Voyager 1 (V1) and 2
(V2) will observe similar plasma parameters within the HS. While this
model accurately predicts the observations at V2, it does not reproduce
the decrease in radial velocity or drop in magnetic flux observed by
V1. This implies that the solar cycle variations in solar wind magnetic
field observed at 1 AU do not cause the order of magnitude decrease
in magnetic flux observed in the V1 data. We describe the solar wind
magnetic field as a monopole, to remove the heliospheric current sheet
(HCS), with the magnetic field aligned with that of the interstellar
medium. This diminishes any numerical reconnection at the ISM - solar
wind interface as well as within the heliosheath itself. We compare
our model to the same model describing the solar wind magnetic field
as a dipole. In the dipole case, there is an intrinsic loss of magnetic
energy near the HCS due to reconnection. This reconnection is numerical
since we do not include real resistivity in the model. The comparison of
the two models allows for an estimation of the effects of reconnection
in the HS. We compare both models to observations along V1 and V2 and
discuss whether magnetic dissipation is a significant process affecting
the flows within the heliosheath.
Title: The role of the Hall effect in the global structure and
dynamics of planetary magnetospheres: Ganymede as a case study
Authors: Dorelli, J. C.; Glocer, Alex; Collinson, Glyn; Tóth, Gábor
Bibcode: 2015JGRA..120.5377D
Altcode: 2015arXiv150100501D
We present high-resolution Hall MHD simulations of Ganymede's
magnetosphere demonstrating that Hall electric fields in ion-scale
magnetic reconnection layers have significant global effects not
captured in resistive MHD simulations. Consistent with local kinetic
simulations of magnetic reconnection, our global simulations show
the development of intense field-aligned currents along the magnetic
separatrices. These currents extend all the way down to the moon's
surface, where they may contribute to Ganymede's aurora. Within the
magnetopause and magnetotail current sheets, Hall J × B forces
accelerate ions to the local Alfvén speed in the out-of-plane
direction, producing a global system of ion drift belts that
circulates Jovian magnetospheric plasma throughout Ganymede's
magnetosphere. We discuss some observable consequences of these
Hall-induced currents and ion drifts: the appearance of a sub-Jovian
"double magnetopause" structure, an Alfvénic ion jet extending across
the upstream magnetopause, and an asymmetric pattern of magnetopause
Kelvin-Helmholtz waves.
Title: Polar Jet Simulation with the Alfvén Wave Solar Model (AWSoM)
Authors: Szente, Judit; Toth, Gabor; van der Holst, Bart; DeVore,
C. Richard; Gombosi, Tamas
Bibcode: 2015shin.confE..87S
Altcode:
Coronal jets are being observed by multiple instruments at multiple
wavelengths (SOHO, Yohkoh, STEREO, Hinode [Paraschiv (2010,
2015)]). Studying polar jets can lead to an improved understanding
of the relations between magnetic field topology and reconnection
as well as solar wind heating and acceleration.The thermodynamical
evolution of the plasma is the focus of our work. We introduce a
slowly accelerated rotating bipole field in the open region of the
background magnetic field. Similar magnetic topology is also implied in
observations. Our aim is to implement the formation and evolution of
polar jets in the coronal hole region starting from the chromosphere
up to the outer corona. The simulations show small-scale eruptive
reconnection events. The self-consistent heating and acceleration of
the solar wind in the AWSoM model [van der Holst (2014)] provides the
opportunity to study the energetics of the jet phenomena. This study
leads to the possibility of quantitative comparison of the simulation
results to X-ray, EUV or white light observations.
Title: The two-way relationship between ionospheric outflow and the
ring current
Authors: Welling, D. T.; Jordanova, V. K.; Glocer, A.; Toth, G.;
Liemohn, M. W.; Weimer, D. R.
Bibcode: 2015JGRA..120.4338W
Altcode:
It is now well established that the ionosphere, because it acts as a
significant source of plasma, plays a critical role in ring current
dynamics. However, because the ring current deposits energy into the
ionosphere, the inverse may also be true: the ring current can play a
critical role in the dynamics of ionospheric outflow. This study uses
a set of coupled, first-principles-based numerical models to test
the dependence of ionospheric outflow on ring current-driven region
2 field-aligned currents (FACs). A moderate magnetospheric storm
event is modeled with the Space Weather Modeling Framework using
a global MHD code (Block Adaptive Tree Solar wind Roe-type Upwind
Scheme, BATS-R-US), a polar wind model (Polar Wind Outflow Model),
and a bounce-averaged kinetic ring current model (ring current
atmosphere interaction model with self-consistent magnetic field,
RAM-SCB). Initially, each code is two-way coupled to all others except
for RAM-SCB, which receives inputs from the other models but is not
allowed to feed back pressure into the MHD model. The simulation
is repeated with pressure coupling activated, which drives strong
pressure gradients and region 2 FACs in BATS-R-US. It is found that
the region 2 FACs increase heavy ion outflow by up to 6 times over
the noncoupled results. The additional outflow further energizes the
ring current, establishing an ionosphere-magnetosphere mass feedback
loop. This study further demonstrates that ionospheric outflow is not
merely a plasma source for the magnetosphere but an integral part in
the nonlinear ionosphere-magnetosphere-ring current system.
Title: Global MHD simulations of Mercury's magnetosphere with coupled
planetary interior: Induction effect of the planetary conducting
core on the global interaction
Authors: Jia, Xianzhe; Slavin, James A.; Gombosi, Tamas I.; Daldorff,
Lars K. S.; Toth, Gabor; Holst, Bart
Bibcode: 2015JGRA..120.4763J
Altcode:
Mercury's comparatively weak intrinsic magnetic field and its close
proximity to the Sun lead to a magnetosphere that undergoes more direct
space-weathering interactions than other planets. A unique aspect of
Mercury's interaction system arises from the large ratio of the scale
of the planet to the scale of the magnetosphere and the presence of a
large-size core composed of highly conducting material. Consequently,
there is strong feedback between the planetary interior and the
magnetosphere, especially under conditions of strong external
forcing. Understanding the coupled solar wind-magnetosphere-interior
interaction at Mercury requires not only analysis of observations but
also a modeling framework that is both comprehensive and inclusive. We
have developed a new global MHD model for Mercury in which the
planetary interior is modeled as layers of different electrical
conductivities that electromagnetically couple to the surrounding plasma
environment. This new modeling capability allows us to characterize
the dynamical response of Mercury to time-varying external conditions
in a self-consistent manner. Comparison of our model results with
observations by the MErcury Surface, Space ENvironment, GEochemistry,
and Ranging (MESSENGER) spacecraft shows that the model provides
a reasonably good representation of the global magnetosphere. To
demonstrate the capability to model induction effects, we have performed
idealized simulations in which Mercury's magnetosphere is impacted by
a solar wind pressure enhancement. Our results show that due to the
induction effect, Mercury's core exerts strong global influences on the
way Mercury responds to changes in the external environment, including
modifying the global magnetospheric structure and affecting the extent
to which the solar wind directly impacts the surface. The global MHD
model presented here represents a crucial step toward establishing a
modeling framework that enables self-consistent characterization of
Mercury's tightly coupled planetary interior-magnetosphere system.
Title: Assessing the role of oxygen on ring current formation and
evolution through numerical experiments
Authors: Ilie, R.; Liemohn, M. W.; Toth, G.; Yu Ganushkina, N.;
Daldorff, L. K. S.
Bibcode: 2015JGRA..120.4656I
Altcode:
We address the effect of ionospheric outflow and magnetospheric ion
composition on the physical processes that control the development
of the 5 August 2011 magnetic storm. Simulations with the Space
Weather Modeling Framework are used to investigate the global
dynamics and energization of ions throughout the magnetosphere
during storm time, with a focus on the formation and evolution of
the ring current. Simulations involving multifluid (with variable
H+/O+ ratio in the inner magnetosphere) and
single-fluid (with constant H+/O+ ratio in
the inner magnetosphere) MHD for the global magnetosphere with inner
boundary conditions set either by specifying a constant ion density or
by physics-based calculations of the ion fluxes reveal that dynamical
changes of the ion composition in the inner magnetosphere alter the
total energy density of the magnetosphere, leading to variations in
the magnetic field as well as particle drifts throughout the simulated
domain. A low oxygen to hydrogen ratio and outflow resulting from a
constant ion density boundary produced the most disturbed magnetosphere,
leading to a stronger ring current but misses the timing of the storm
development. Conversely, including a physics-based solution for the
ionospheric outflow to the magnetosphere system leads to a reduction
in the cross-polar cap potential (CPCP). The increased presence of
oxygen in the inner magnetosphere affects the global magnetospheric
structure and dynamics and brings the nightside reconnection point
closer to the Earth. The combination of reduced CPCP together with
the formation of the reconnection line closer to the Earth yields
less adiabatic heating in the magnetotail and reduces the amount of
energetic plasma that has access to the inner magnetosphere.
Title: Stellar winds on the main-sequence. I. Wind model
Authors: Johnstone, C. P.; Güdel, M.; Lüftinger, T.; Toth, G.;
Brott, I.
Bibcode: 2015A&A...577A..27J
Altcode: 2015arXiv150306669J
Aims: We develop a method for estimating the properties of
stellar winds for low-mass main-sequence stars between masses of 0.4
M⊙ and 1.1 M⊙ at a range of distances from the
star.
Methods: We use 1D thermal pressure driven hydrodynamic
wind models run using the Versatile Advection Code. Using in situ
measurements of the solar wind, we produce models for the slow and
fast components of the solar wind. We consider two radically different
methods for scaling the base temperature of the wind to other stars:
in Model A, we assume that wind temperatures are fundamentally linked
to coronal temperatures, and in Model B, we assume that the sound speed
at the base of the wind is a fixed fraction of the escape velocity. In
Paper II of this series, we use observationally constrained rotational
evolution models to derive wind mass loss rates.
Results: Our
model for the solar wind provides an excellent description of the real
solar wind far from the solar surface, but is unrealistic within the
solar corona. We run a grid of 1200 wind models to derive relations
for the wind properties as a function of stellar mass, radius, and
wind temperature. Using these results, we explore how wind properties
depend on stellar mass and rotation.
Conclusions: Based on our
two assumptions about the scaling of the wind temperature, we argue that
there is still significant uncertainty in how these properties should
be determined. Resolution of this uncertainty will probably require
both the application of solar wind physics to other stars and detailed
observational constraints on the properties of stellar winds. In the
final section of this paper, we give step by step instructions for how
to apply our results to calculate the stellar wind conditions far from
the stellar surface.
Title: Self-consistent multifluid MHD simulations of Europa's
exospheric interaction with Jupiter's magnetosphere
Authors: Rubin, M.; Jia, X.; Altwegg, K.; Combi, M. R.; Daldorff,
L. K. S.; Gombosi, T. I.; Khurana, K.; Kivelson, M. G.; Tenishev,
V. M.; Tóth, G.; Holst, B.; Wurz, P.
Bibcode: 2015JGRA..120.3503R
Altcode:
The Jovian moon, Europa, hosts a thin neutral gas atmosphere, which
is tightly coupled to Jupiter's magnetosphere. Magnetospheric ions
impacting the surface sputter off neutral atoms, which, upon ionization,
carry currents that modify the magnetic field around the moon. The
magnetic field in the plasma is also affected by Europa's induced
magnetic field. In this paper we investigate the environment of Europa
using our multifluid MHD model and focus on the effects introduced
by both the magnetospheric and the pickup ion populations. The model
self-consistently derives the electron temperature that governs
the electron impact ionization process, which is the major source
of ionization in this environment. The resulting magnetic field is
compared to measurements performed by the Galileo magnetometer, the
bulk properties of the modeled thermal plasma population is compared
to the Galileo Plasma Subsystem observations, and the modeled surface
precipitation fluxes are compared to Galileo Ultraviolet Spectrometer
observations. The model shows good agreement with the measured magnetic
field and reproduces the basic features of the plasma interaction
observed at the moon for both the E4 and the E26 flybys of the Galileo
spacecraft. The simulation also produces perturbations asymmetric
about the flow direction that account for observed asymmetries.
Title: What Controls the Structure and Dynamics of Earth's
Magnetosphere?
Authors: Eastwood, J. P.; Hietala, H.; Toth, G.; Phan, T. D.;
Fujimoto, M.
Bibcode: 2015SSRv..188..251E
Altcode: 2014SSRv..tmp...20E
Unlike most cosmic plasma structures, planetary magnetospheres
can be extensively studied in situ. In particular, studies of the
Earth's magnetosphere over the past few decades have resulted in
a relatively good experimental understanding of both its basic
structural properties and its response to changes in the impinging
solar wind. In this article we provide a broad overview, designed
for researchers unfamiliar with magnetospheric physics, of the main
processes and parameters that control the structure and dynamics of
planetary magnetospheres, especially the Earth's. In particular, we
concentrate on the structure and dynamics of three important regions:
the bow shock, the magnetopause and the magnetotail. In the final part
of this review we describe the current status of global magnetospheric
modelling, which is crucial to placing in situ observations in the
proper context and providing a better understanding of magnetospheric
structure and dynamics under all possible input conditions. Although
the parameter regime experienced in the solar system is limited, the
plasma physics that is learned by studying planetary magnetospheres
can, in principle, be translated to more general studies of cosmic
plasma structures. Conversely, studies of cosmic plasma under a wide
range of conditions should be used to understand Earth's magnetosphere
under extreme conditions. We conclude the review by discussing this
and summarizing some general properties and principles that may be
applied to studies of other cosmic plasma structures.
Title: Plasma and wave properties downstream of Martian bow shock:
Hybrid simulations and MAVEN observations
Authors: Dong, Chuanfei; Winske, Dan; Cowee, Misa; Bougher, Stephen
W.; Andersson, Laila; Connerney, Jack; Epley, Jared; Ergun, Robert;
McFadden, James P.; Ma, Yingjuan; Toth, Gabor; Curry, Shannon; Nagy,
Andrew; Jakosky, Bruce
Bibcode: 2015TESS....130502D
Altcode:
Two-dimensional hybrid simulation codes are employed to investigate
the kinetic properties of plasmas and waves downstream of the Martian
bow shock. The simulations are two-dimensional in space but three
dimensional in field and velocity components. Simulations show that
ion cyclotron waves are generated by temperature anisotropy resulting
from the reflected protons around the Martian bow shock. These proton
cyclotron waves could propagate downward into the Martian ionosphere
and are expected to heat the O+ layer peaked from 250 to
300 km due to the wave-particle interaction. The proton cyclotron wave
heating is anticipated to be a significant source of energy into the
thermosphere, which impacts atmospheric escape rates. The simulation
results show that the specific dayside heating altitude depends on the
Martian crustal field orientations, solar cycles and seasonal variations
since both the cyclotron resonance condition and the non/sub-resonant
stochastic heating threshold depend on the ambient magnetic field
strength. The dayside magnetic field profiles for different crustal
field orientation, solar cycle and seasonal variations are adopted
from the BATS-R-US Mars multi-fluid MHD model. The simulation results,
however, show that the heating of O+ via proton cyclotron
wave resonant interaction is not likely in the relatively weak crustal
field region, based on our simplified model. This indicates that
either the drift motion resulted from the transport of ionospheric
O+, or the non/sub-resonant stochastic heating mechanism are
important to explain the heating of Martian O+ layer. We
will investigate this further by comparing the simulation results
with the available MAVEN data. These simulated ion cyclotron waves
are important to explain the heating of Martian O+ layer
and have significant implications for future observations.
Title: Lifetime of the Fossil Field in Titan's Ionosphere
Authors: Ma, Yingjuan; Russell, Christopher T.; Wei, Hanying; Nagy,
Andrew F.; Toth, Gabor; Dougherty, Michele K.; Coates, Andrew J.;
Wahlund, Jan-Erik; Edberg, Niklas J. T.
Bibcode: 2015EGUGA..17.6940M
Altcode:
Cassini spacecraft has made more than 100 Titan flybys since October
2004. Among these flybys, there are a few special ones (T32, T42, T85,
T96). During or shortly before periapsis on these encounters, Titan was
found to be outside the Saturnian magnetosphere, in the magnetosheath
region or directly exposed in the solar wind. During the T32 flyby,
the first magnetosheath encounter, simulation results and observations
clearly demonstrated the existence of fossil field, because the magnetic
field direction in the magnetosheath region was opposite to the field
orientation surrounding Titan when it had been inside the Saturnian
magnetosphere. However, because Cassini passed by Titan shortly after
the magnetopause crossing, this flyby only provides a lower limit of
the lifetime of the fossil field. Quantifying the lifetime of the fossil
field has important implications for understanding the magnetic field of
other Titan flybys. Since the plasma is highly dynamic in Saturn's outer
magnetosphere, even though the ambient plasma condition is not changing
as dramatically as discussed in the presented flyby, Titan's ionosphere
could still record some of those changes so that the observed field in
the deep ionosphere might have very complicated signatures. The same
behavior could also occur at Venus and Mars (in the weak crustal field
region), which would help us to understand the complicated magnetic
signatures in un-magnetized planetary ionospheres. In this paper,
we present observations and simulation results for the other three
Titan flybys to provide a better constraint on the lifetime of the
fossil field in Titan's ionosphere.
Title: Magnetic Flux Conservation in the Heliosheath Including Solar
Cycle Variations of Magnetic Field Intensity
Authors: Michael, A. T.; Opher, M.; Provornikova, E.; Richardson,
J. D.; Tóth, G.
Bibcode: 2015ApJ...803L...6M
Altcode:
In the heliosheath (HS), Voyager 2 has observed a flow with constant
radial velocity and magnetic flux conservation. Voyager 1, however,
has observed a decrease in the flow’s radial velocity and an order of
magnitude decrease in magnetic flux. We investigate the role of the 11
yr solar cycle variation of the magnetic field strength on the magnetic
flux within the HS using a global 3D magnetohydrodynamic model of the
heliosphere. We use time and latitude-dependent solar wind velocity
and density inferred from Solar and Heliospheric Observatory/SWAN
and interplanetary scintillations data and implemented solar cycle
variations of the magnetic field derived from 27 day averages of
the field magnitude average of the magnetic field at 1 AU from the
OMNI database. With the inclusion of the solar cycle time-dependent
magnetic field intensity, the model matches the observed intensity
of the magnetic field in the HS along both Voyager 1 and 2. This is
a significant improvement from the same model without magnetic field
solar cycle variations, which was over a factor of two larger. The
model accurately predicts the radial velocity observed by Voyager 2;
however, the model predicts a flow speed ∼100 km s-1
larger than that derived from LECP measurements at Voyager 1. In the
model, magnetic flux is conserved along both Voyager trajectories,
contrary to observations. This implies that the solar cycle variations
in solar wind magnetic field observed at 1 AU does not cause the order
of magnitude decrease in magnetic flux observed in the Voyager 1 data.
Title: Real-time SWMF-Geospace: A New Website Enabling Community Use
Authors: Liemohn, Michael; De Zeeuw, Darren; Kopmanis, Jeff;
Ganushkina, Natalia; Welling, Daniel; Toth, Gabor; Ridley, Aaron;
Ilie, Raluca; Gombosi, Tamas; Kuznetsova, Maria M.; Maddox, Marlo;
Rastaetter, Lutz
Bibcode: 2015TESS....120005L
Altcode:
An experimental real-time simulation of the Space Weather Modeling
Framework (SWMF) is conducted at the Community Coordinated Modeling
Center (CCMC), (http://ccmc.gsfc.nasa.gov/realtime.php) and also
through the CCMC's Integrated Space Weather Analysis (iSWA) site
(http://iswa.ccmc.gsfc.nasa.gov/IswaSystemWebApp/). Presently,
two configurations of the SWMF are running in real time at
CCMC, both focusing on the geospace modules, using the BATS-R-US
magnetohydrodynamic model, the Ridley Ionosphere Model, and with
and without the Rice Convection Model for inner magnetospheric
drift physics. The model output includes result extractions along
satellite trajectories as well as magnetic perturbation vectors
at ground-based station locations. Here we unveil a new website
(http://csem.engin.umich.edu/realtime) to highlight these real-time
model results conducted by the CCMC, present some basic data-model
comparisons with real-time observations, and archive the accuracy of
this continuously-available simulation.
Title: Instantaneous configuration of the geomagnetic field inferred
from the low-altitude isotropic boundaries: modeling and observations
Authors: Ilie, Raluca; Ganushkina, Natalia; Toth, Gabor; Liemohn,
Michael
Bibcode: 2015TESS....120601I
Altcode:
Understanding the interplay between ionospheric, auroral and
magnetospheric phenomena requires detailed knowledge of Earth’s
magnetic field geometry under various solar wind conditions. This
geometry is directly relevant to the magnetic field mapping between
different regions of near-Earth space.To evaluate the instantaneous
geomagnetic field configuration we probe the isotropic boundaries (IB)
of energetic particles measured at low altitudes. Those are interpreted
as the boundary between the regions of adiabatic and stochastic particle
motion in the equatorial magnetotail and provide information regarding
the degree of magnetic field stretching.We investigate the topology and
dynamics of the magnetotail current during active and quiet times as
de- pendent on solar wind and IMF parameters based on NOAA/POES MEPED
and DMSP SSJ/4 measurements in combination with global magnetospheric
simulations using the Space Weather Modeling Framework (SWMF).The
extensive NOAA/POES MEPED low-altitude data sets give the locations of
isotropic boundaries, which are used to extract information regarding
particle distributions and field structure in the source regions in
the magnetosphere.We present a comparison between the magnetic field
lines with the observed IB latitude and those com- puted from the SWMF
using the theoretical relation for IB locations in the magnetotail,
i.e. where the ratio between curvature radius and Larmor radius is
close to 8. This investigation assesses the accuracy of the model
magnetic field and the structure of the magnetotail. The results are
examined in relation to the solar wind and IMF conditions to determine
the corresponding configuration and dynamics of the magnetotail.
Title: The Heterogeneous Coma of Comet 67P/Churyumov-Gerasimenko
from Rosetta Observations
Authors: Fougere, Nicolas; Tenishev, Valeriy; Bieler, Andre; Combi,
Michael; Gombosi, Tamas; Toth, Gabor; Hansen, Kenneth; Shou, Yinsi;
Huang, Zhenguang; Jia, Xianzhe; Rubin, Martin; Altwegg, Kathrin; Wurz,
Peter; Balsiger, Hans; Jaeckel, Annette; Le Roy, Lena; Gasc, Sebastien;
Calmonte, Ursina; Tzou, Chia-Yu; Hässig, Myrtha; Fuselier, Stephen;
De Keyser, Johan; Berthelier, Jean-Jacques; Mall, Urs; Rème, Henri;
Fiethe, Bjorn
Bibcode: 2015EGUGA..17.4695F
Altcode:
Since its orbit insertion around comet 67P/Churyumov-Gerasimenko (CG),
the Rosetta spacecraft has revealed invaluable information regarding
the cometary coma environment. The prolonged period of observation
enabled a relatively extensive spatial coverage of comet CG's coma,
which showed distinct spatial distributions for different species. We
introduce a fully 3D kinetic model performed with the Direct Simulation
Monte-Carlo approach of the H2O, CO, and CO2 coma of comet CG using
the Adaptive Mesh Particle Simulator code with the shape model of the
Rosetta nucleus. The model allows the description of the full coma of
comet CG including the regions where collisions cannot maintain a flow
that can be described by a fluid. The model is constrained by Rosetta
observations giving clues regarding the gas release of the different
species. This constitutes the most advanced coma model of comet CG,
which is critical to interpret instrument data and for further mission
planning.
Title: MHD Model Results of Solar Wind Plasma Interaction with Mars
and Comparison with MAVEN Observations
Authors: Ma, Y. J.; Russell, C. T.; Nagy, A. F.; Toth, G.; Halekas,
J. S.; Connerney, J. E. P.; Espley, J. R.; Mahaffy, P. R.
Bibcode: 2015LPI....46.1202M
Altcode: 2015LPICo1832.1202M
This study investigates in detail how plasma properties in Mars
ionosphere are influenced locally by the crustal field and its rotation.
Title: A 3D Description of the Coma of Comet 67P/Churyumov-Gerasimenko
Constrained by Rosetta Observations
Authors: Fougere, N.; Tenishev, V.; Bieler, A. M.; Combi, M. R.;
Gombosi, T. I.; Hansen, K. C.; Jia, X.; Shou, Y.; Huang, Z.; Toth, G.;
Altwegg, K.; Wurz, P.; Balsiger, H.; Jäckel, A.; Le Roy, L.; Gasc,
S.; Calmonte, U.; Rubin, M.; Tzou, C. Y.; Hässig, M.; Fuselier, S.;
De Keyser, J.; Berthelier, J. J.; Mall, U. A.; Rème, H.; Fiethe, B.
Bibcode: 2014AGUFM.P41C3930F
Altcode:
For the first time, the Rosetta spacecraft stays with a comet over an
extended period of time during its journey in the inner the solar
system. The data provided by the suite of instruments on board
the Rosetta spacecraft, notably the ROSINA mass spectrometers and
the pressure sensor, provides critical information concerning comet
67P/Churyumov-Gerasimenko (CG) and its environment. These measurements
reinforce our knowledge of comet CG and enable us to describe the
nucleus and the sources with more details. The observations allow us
to better constrain and accordingly develop much more realistic models
of the comet's coma. We show a 3D simulation of the gas and dust coma
of comet CG using a Direct Simulation Monte-Carlo model performed with
the Adaptive Mesh Particle Simulator (Tenishev et al. 2008, 2011). The
coma model presented includes a realistic nucleus shape, with a gas
flux distribution and a surface temperature that takes into account
irregularities and concavities of the nucleus. Along with the gas drag,
the gravity field drives the dust dynamics and is therefore accurately
computed around the irregular nucleus shape. This constitutes the
state-of-the-art of cometary coma models, which are crucial to interpret
instrument data and for further mission planning. Acknowledgement:This
work was supported by contracts JPL#1266313 and JPL#1266314 from
the US Rosetta Project and NASA grant NNX09AB59G from the Planetary
Atmospheres Program. References:Tenishev et al. 2008 ApJ 685:659,
and 2011 ApJ 732:104
Title: Counter-streaming alpha proton plasmas in an eroding magnetic
cloud: new insights into space plasma evolution from Wind
Authors: Szente, J.; Toth, G.; Manchester, W.; van der Holst, B.;
Landi, E.; DeVore, C. R.; Gombosi, T. I.
Bibcode: 2014AGUFMSH23D..05S
Altcode:
Coronal jets, routinely observed by multiple instruments at
multiple wavelengths, provide a unique opportunity to understand
the relationships between magnetic field topology, reconnection, and
solar wind heating and acceleration. We simulate coronal jets with the
Alfvén Wave Solar Model (AWSoM) [van der Holst (2014)] and focus our
study on the thermodynamical evolution of the plasma. AWSoM solves
the two-temperature MHD equations with electron heat conduction,
which not only addresses the thermodynamics of individual species,
but also allows for the construction of synthetic images from the EUV
and soft X-ray wavelength range. Our jet model takes the form of a
slowly rotating bipole field imbedded in the open magnetic field of
a coronal hole; a topology suggested by observations. We follow the
formation and evolution of polar jets starting from the chromosphere
and extending into the outer corona. The simulations show small-scale
eruptive reconnection events that self-consistently heat and accelerate
the solar wind. Our results provide a quantitative comparison to
observations made in the EUV and X-ray spectrum.
Title: 3D Direct Simulation Monte Carlo Modeling of the Spacecraft
Environment of Rosetta
Authors: Bieler, A. M.; Tenishev, V.; Fougere, N.; Gombosi, T. I.;
Hansen, K. C.; Combi, M. R.; Huang, Z.; Jia, X.; Toth, G.; Altwegg,
K.; Wurz, P.; Jäckel, A.; Le Roy, L.; Gasc, S.; Calmonte, U.; Rubin,
M.; Tzou, C. Y.; Hässig, M.; Fuselier, S.; De Keyser, J.; Berthelier,
J. J.; Mall, U. A.; Rème, H.; Fiethe, B.; Balsiger, H.
Bibcode: 2014AGUFM.P41C3931B
Altcode:
The European Space Agency's Rosetta mission is the first to escort
a comet over an extended time as the comet makes its way through the
inner solar system. The ROSINA instrument suite consisting of a double
focusing mass spectrometer, a time of flight mass spectrometer and a
pressure sensor, will provide temporally and spatially resolved data on
the comet's volatile inventory. The effect of spacecraft outgassing is
well known and has been measured with the ROSINA instruments onboard
Rosetta throughout the cruise phase. The flux of released neutral
gas originating from the spacecraft cannot be distinguished from the
cometary signal by the mass spectrometers and varies significantly
with solar illumination conditions. For accurate interpretation of
the instrument data, a good understanding of spacecraft outgassing is
necessary. In this talk we present results simulating the spacecraft
environment with the Adaptive Mesh Particle Simulator (AMPS) code. AMPS
is a direct simulation monte carlo code that includes multiple species
in a 3D adaptive mesh to describe a full scale model of the spacecraft
environment. We use the triangulated surface model of the spacecraft
to implement realistic outgassing rates for different areas on the
surface and take shadowing effects in consideration. The resulting
particle fluxes are compared to the measurements of the ROSINA
experiment and implications for ROSINA measurements and data analysis
are discussed. Spacecraft outgassing has implications for future space
missions to rarefied atmospheres as it imposes a limit on the detection
of various species.
Title: The Mars Magnetosphere in the Tail of Comet C/2013 A1(Siding
Spring)
Authors: Ma, Y.; Jia, Y. D.; Russell, C. T.; Nagy, A. F.; Toth, G.;
Combi, M. R.; Yelle, R. V.; Dong, C.; Bougher, S. W.
Bibcode: 2014AGUFM.P43A3971M
Altcode:
Comet C/2013 A1 (Siding Spring) is an Oort cloud comet with an open
path. In October 2014, comet Siding Spring passes about 12 Mars radii
from the center of the planet. Carrying multiple active spacecraft,
Mars is expected to enter the plasma tail of the comet, providing a
unique opportunity to study the response of the Mars magnetosphere
to the supersonic cometary tail. We use our multi-fluid MHD model,
which has been successfully applied to various comets, to simulate the
composition of plasma trailing the comet. We include the effects of the
decomposition, ionization, and charge exchange of major ion species
around the comet in the model. The model result is then extracted
along Mars orbit into a time dependent plasma distribution. Second,
we simulate the real-time response of the Mars magnetosphere in
the comet tail using a multi-fluid model of Mars. The comet tail
plasma distribution is used as the upstream boundary conditions for
the Mars model. The simulation results will be used to quantify the
perturbations of the plasma environment around Mars and provide a
baseline for interpreting plasma observations along the MAVEN orbit
during the comet passage.
Title: Global Multi-Fluid Solar Corona and Inner Heliosphere Model
for Solar Probe Plus and Solar Orbite
Authors: van der Holst, B.; Sokolov, I.; Toth, G.; Gombosi, T. I.
Bibcode: 2014AGUFMSH21B4095V
Altcode:
The mechanisms that heat and accelerate the fast and slow wind have
not yet been conclusively identified, and their understanding is one of
the major science goals of the Solar Orbiter (SO) and Solar Probe Plus
(SPP) missions. Helium abundance and properties in the solar wind are
critical tracers for both processes so that understanding them is key
towards gaining insight in the solar wind phenomenon, and being able
to model it and predict its properties. SO and SPP will carry critical
instrumentation to measure the properties of Helium in the solar wind
at distances between within 10 solar radii up to 1 AU. We present
a generalization of the recently developed global solar corona and
inner heliosphere model with low-frequency Alfvenic turbulence [van
der Holst et al. (2014)] to include alpha-particle dynamics. This new
multi-fluid model uses the stochastic heating mechanism to partition
the turbulence dissipation into coronal heating of the electrons and
ions. The momentum and energy exchange rates due to Coulomb collisions
are accounted for. We discuss the feasibility for Alfvenic turbulence
to simultaneously address the coronal heating and proton-alpha particle
differential streaming.
Title: Solar Wind Interaction with the Martian Upper Atmosphere at
Early Mars/Extreme Solar Conditions
Authors: Dong, C.; Bougher, S. W.; Ma, Y.; Toth, G.; Lee, Y.; Nagy,
A. F.; Tenishev, V.; Pawlowski, D. J.; Combi, M. R.
Bibcode: 2014AGUFM.P53C4032D
Altcode:
The investigation of ion escape fluxes from Mars, resulting from
the solar wind interaction with its upper atmosphere/ionosphere, is
important due to its potential impact on the long-term evolution of
Mars atmosphere (e.g., loss of water) over its history. In the present
work, we adopt the 3-D Mars cold neutral atmosphere profiles (0 ~
300 km) from the newly developed and validated Mars Global Ionosphere
Thermosphere Model (M-GITM) and the 3-D hot oxygen profiles (100 km
~ 5 RM) from the exosphere Monte Carlo model Adaptive Mesh Particle
Simulator (AMPS). We apply these 3-D model output fields into the 3-D
BATS-R-US Mars multi-fluid MHD (MF-MHD) model (100 km ~ 20 RM) that can
simulate the interplay between Mars upper atmosphere and solar wind by
considering the dynamics of individual ion species. The multi-fluid MHD
model solves separate continuity, momentum and energy equations for
each ion species (H+, O+, O2+, CO2+). The M-GITM model together with
the AMPS exosphere model take into account the effects of solar cycle
and seasonal variations on both cold and hot neutral atmospheres. This
feature allows us to investigate the corresponding effects on the Mars
upper atmosphere ion escape by using a one-way coupling approach, i.e.,
both the M-GITM and AMPS model output fields are used as the input for
the multi-fluid MHD model and the M-GITM is used as input into the AMPS
exosphere model. In this study, we present M-GITM, AMPS, and MF-MHD
calculations (1-way coupled) for 2.5 GYA conditions and/or extreme
solar conditions for present day Mars (high solar wind velocities,
high solar wind dynamic pressure, and high solar irradiance conditions,
etc.). Present day extreme conditions may result in MF-MHD outputs that
are similar to 2.5 GYA cases. The crustal field orientations are also
considered in this study. By comparing estimates of past ion escape
rates with the current ion loss rates to be returned by the MAVEN
spacecraft (2013-2016), we can better constrain the total ion loss to
space over Mars history, and thus enhance the science returned from
the MAVEN mission.
Title: MHD-Epic: Embedded Particle-in-Cell Simulations of Reconnection
in Global 3D Extended MHD Simulations
Authors: Daldorff, L. K. S.; Toth, G.; Borovikov, D.; Gombosi, T. I.;
Lapenta, G.
Bibcode: 2014AGUFMSM13B4161D
Altcode:
With the new modeling capability in the Space Weather Modeling Framework
(SWMF) of embedding an implicit Particle-in-Cell (PIC) model iPIC3D
into the BATS-R-US magnetohydrodynamics model (Daldorff et al. 2014,
JCP, 268, 236) we are ready to locally handle the full physics of the
reconnection and its implications on the full system where globally,
away from the reconnection region, a magnetohydrodynamic description is
satisfactory. As magnetic reconnection is one of the main drivers in
magnetospheric and heliospheric plasma dynamics, the self-consistent
description of the electron dynamics in the coupled MHD-EPIC model is
well suited for investigating the nature of these systems. We will
compare the new embedded MHD-EPIC model with pure MHD and Hall MHD
simulations of the Earth's magnetosphere.
Title: The Multi-fluid Nature of the Termination Shock
Authors: Zieger, B.; Opher, M.; Toth, G.
Bibcode: 2014AGUFMSH21D..05Z
Altcode:
After the crossing of the termination shock by the Voyager spacecraft,
it became clear that pickup ions (PUIs) dominate the thermodynamics
of the heliosheath. Particle-in-cell simulations by Wu et al. [2010]
have shown that the sum of the thermal solar wind and non-thermal PUI
distributions downstream of the termination shock can be approximated
with a 2-Maxwellian distribution. Therefore the heliosheath can be
described as multi-fluid plasma comprising of cold thermal solar
wind ions, hot pickup ions (PUI) and electrons. The abundance of
the hot pickup ion population has remained unknown, since the plasma
instrument on board Voyager 2 can only detect the colder thermal ion
component. Upstream of the termination shock, where the solar wind bulk
flow is quasi-perpendicular to the Parker spiral-like heliospheric
magnetic field, the two ion fluids are fully coupled. However, in
the heliosheath, where the ion flows start to divert from the radial
direction, PUIs and thermal solar wind ions become decoupled in the
parallel direction, resulting in differential ion flow velocities. This
multi-fluid nature of the heliosheath cannot be captured in current
single-fluid MHD models of the heliosphere. Here we present our new
multi-ion Hall MHD model of the termination shock, which is able to
resolve finite gyroradius effects [Zieger et al., 2014]. The addition
of hot PUIs to the mixture of thermal solar wind protons and cold
electrons results in the mode splitting of fast magnetosonic waves
into a high-frequency fast mode (or PUI mode) and a low-frequency fast
mode (or thermal proton mode). We show that the multi-fluid nature of
the solar wind predicts two termination shocks, one in the thermal
and the other in the pickup ion component. We demonstrate that the
thermal ion shock is a dispersive shock wave, with a trailing wave
train, which is a quasi-stationary nonlinear wave mode, also known
as oscilliton. We constrain the previously unknown PUI abundance and
the PUI temperature by fitting simulated multi-fluid termination shock
profiles to Voyager 2 observations. Our model provides self-consistent
energy partitioning between the ion species across the termination shock
and predicts the preferential heating of the thermal ion component. The
nonlinear oscilliton mode can be a source of compressional turbulence
in the heliosheath.
Title: Global impact of collisionless magnetic reconnection on the
structure of planetary magnetospheres
Authors: Dorelli, J.; Glocer, A.; Collinson, G.; Toth, G.
Bibcode: 2014AGUFMSM13B4159D
Altcode:
While the local physics of collisionless magnetic reconnection
has been well studied, the consequences for global magnetospheric
structure remain largely unexplored. It is well known, for example,
that Hall electric fields generate a new system of field-aligned
currents propagating from the reconnection site along the magnetic
separatrices; but it is not known how these currents contribute to the
global region 1 and region 2 current systems or to auroral substorm
features. In this presentation, we show that collisionless reconnection
has a significant impact on the large scale structure of planetary
magnetospheres. Using global Hall MHD simulations, we demonstrate
that field-aligned currents generated at the reconnection sites (and
carried by whistler or kinetic Alfven waves) extend all the way down
to the surface of the magnetized body and must therefore be included
in the magnetosphere-ionosphere coupling physics (e.g., Harang-like
discontinuities in the ionospheric convection pattern -- absent in
MHD -- are introduced, and the current densities are large enough to
produce auroral emission). More surprisingly, ions and electrons pick up
magnetic drifts (due to JxB forces in the ion diffusion regions) that
significantly alter the global magnetospheric convection pattern. Ions
in the plasma sheet drift duskward while electrons drift dawnward,
producing large asymmetries in the plasma sheet structure even in the
absense of solar wind asymmetry, asymmetric ionospheric conductance
or co-rotation. We discuss the implications of these effects for the
reconnection-driven magnetospheres of Ganymede, Mercury and Earth.
Title: Global MHD Simulation of the Coronal Mass Ejection on 2011
March 7: from Chromosphere to 1 AU
Authors: Jin, M.; Manchester, W.; van der Holst, B.; Sokolov, I.;
Toth, G.; Vourlidas, A.; de Koning, C. A.; Gombosi, T. I.
Bibcode: 2014AGUFMSH43A4176J
Altcode:
Performing realistic simulations of solar eruptions and validating
those simulations with observations are important goals in order
to achieve accurate space weather forecasts. Here, we perform and
analyze results of a global magnetohydrodyanmic (MHD) simulation of the
fast coronal mass ejection (CME) that occurred on 2011 March 7. The
simulation is made using the newly developed Alfven Wave Solar Model
(AWSoM), which describes the background solar wind starting from the
upper chromosphere and expands to 24 Rs. Coupling of AWSoM to an inner
heliosphere (IH) model with the Space Weather Modeling Framework (SWMF)
extends the total domain beyond the orbit of Earth. Physical processes
included in the model are multi-species thermodynamics, electron heat
conduction (both collisional and collisionless formulations), optically
thin radiative cooling, and Alfven-wave pressure that accelerates
the solar wind. The Alfven-wave description is physically consistent,
including non-WKB reflection and physics-based apportioning of turbulent
dissipative heating to both electrons and protons. Within this model,
we initiate the CME by using the Gibson-Low (GL) analytical flux rope
model and follow its evolution for days, in which time it propagates
beyond 1 AU. A comprehensive validation study is performed using
remote as well as in-situ observations from SDO, SOHO, STEREOA/B,
and OMNI. Our results show that the new model can reproduce many
of the observed features near the Sun (e.g., CME-driven EUV waves,
deflection of the flux rope from the coronal hole, "double-front"
in the white light images) and in the heliosphere (e.g., CME-CIR
interaction, shock properties at 1 AU). The CME-driven shock arrival
time is within 1 hour of the observed arrival time, and nearly all the
in-situ parameters are correctly simulated, which suggests the global
MHD model as a powerful tool for the space weather forecasting.
Title: Time-dependent MHD modeling of Titan's plasma interaction
during T32, T85 and T96 and comparison to Cassini data
Authors: Ma, Y.; Nagy, A. F.; Toth, G.; Bertucci, C.; Dougherty,
M. K.; Coates, A. J.; Wahlund, J. E.
Bibcode: 2014AGUFMSM33A..07M
Altcode:
The Cassini Spacecraft flew past Titan on June 13, 2007 and found
Titan was outside Saturn's magnetopause. During this pass (T32),
observations showed dramatic changes of magnetic field orientation as
well as plasma flow parameters during inbound and outbound segments. We
have studied Titan's ionospheric responses to such a sudden change in
the upstream plasma conditions, using a sophisticated multi-species
global MHD model. Simulation results of three different cases (steady
state; simple current sheet crossing and magnetopause crossing) are
presented and compared against Cassini Magnetometer (MAG), Langmuir
Probe (LP) and Cassini Plasma Spectrometer (CAPS) observations. The
simulation results provide clear evidence of the existence of fossil
field. The MAG data can be well reproduced with a simple current sheet
crossing. The Cassini plasma observations can only be reproduced by the
magnetopause crossing case using plasma conditions constrained by CAPS
observations. Real-time simulation also reveals how the fossil field
formed during the interaction and shows the coexistence of two pile-up
regions with opposite magnetic orientation, the formation of a pair of
new Alfven wings and tail disconnection during magnetopause crossing
process. During two recent Titan flybys T85 and T96, Titan was found
to be in the magnetosheath region of Saturn and in the solar wind,
respectively. We present simulation results for those two flybys and
compare features of Titan's plasma interaction in different plasma
environments.
Title: High Order Schemes in Bats-R-US for Faster and More Accurate
Predictions
Authors: Chen, Y.; Toth, G.; Gombosi, T. I.
Bibcode: 2014AGUFMSM31A4161C
Altcode:
BATS-R-US is a widely used global magnetohydrodynamics model that
originally employed second order accurate TVD schemes combined with
block based Adaptive Mesh Refinement (AMR) to achieve high resolution
in the regions of interest. In the last years we have implemented
fifth order accurate finite difference schemes CWENO5 and MP5 for
uniform Cartesian grids. Now the high order schemes have been extended
to generalized coordinates, including spherical grids and also to
the non-uniform AMR grids including dynamic regridding. We present
numerical tests that verify the preservation of free-stream solution and
high-order accuracy as well as robust oscillation-free behavior near
discontinuities. We apply the new high order accurate schemes to both
heliospheric and magnetospheric simulations and show that it is robust
and can achieve the same accuracy as the second order scheme with much
less computational resources. This is especially important for space
weather prediction that requires faster than real time code execution.
Title: The role of superthermal electrons in high latitude ionospheric
outflows
Authors: Glocer, A.; Khazanov, G. V.; Liemohn, M. W.; Toth, G.;
Gombosi, T. I.
Bibcode: 2014AGUFMSM44A..06G
Altcode:
It is well accepted that the ionosphere is a critical source of plasma
for the magnetosphere, providing O+, H+, and He+ which can have wide
ranging consequences for the space environment system. Changing ion
composition affects magnetic reconnection in the magnetosphere, the ring
current, and the wave environment which is important for high energy
radiation belt electrons. Of the myriad of mechanisms that are important
in determining the ionospheric outflow solution at high latitudes,
we focus on the role of superthermal electron populations. It has
been demonstrated in multiple studies that even small concentrations
of superthermal electrons can have a dramatic effect on the outflow
solution. In this presentation, we present simulation results using
our Polar Wind Outflow Model (PWOM) and our SuperThermal Electron
Transport (STET) code. We describe recent results on superthermal
electrons role in defining the quiet time solar wind solution with
comparisons to observations. We also discuss preliminary results that
combine the PWOM and STET codes for a more comprehensive treatment of
the impact of superthermal electrons.
Title: Magnetic Dissipation Effects on the Flows within the
Heliosheath
Authors: Michael, A.; Opher, M.; Provornikova, E.; Toth, G.
Bibcode: 2014AGUFMSH11B4041M
Altcode:
We investigate the effect that magnetic dissipation has on the
flows within the heliosheath (HS), the subsonic plasma in between
the termination shock (TS) and the heliopause (HP). We use a global
3D multi-fluid magnetohydrodynamic (MHD) model of the heliosphere,
which has a grid resolution of 0.5 AU within the heliosphere along
both Voyager 1 and Voyager 2 trajectories. We describe the solar
wind magnetic field as a monopole, to remove the heliospheric current
sheet, with the magnetic field aligned with that of the interstellar
medium (ISM) to diminish any numerical reconnection at the ISM -
solar wind interface. This configuration of the solar wind magnetic
field also reduces any numerical magnetic dissipation effects in the
HS. We compare our model to the same model describing the solar wind
magnetic field as a dipole. In the dipole case, there is an intrinsic
loss of magnetic energy near the heliospheric current sheet (HCS)
due to reconnection. This reconnection is numerical since we do not
include real resistivity in the model. The comparison of the two models
will allow for an estimation of the effects of reconnection in the HS
since there is no numerical dissipation of the magnetic field in the
monopole model. We compare steady state solutions and the role magnetic
dissipation has on the global characteristics of the heliosphere. We
find that the monopole model of the solar wind magnetic field removes
the asymmetry observed in the TS and predicted for the HP. Furthermore,
the TS is considerably closer to the Sun in the monopole model due
to the build up of magnetic filed at the HP. We also investigate
magnetic dissipation effects in the 11-year solar cycle variations
of the solar wind in a 3D time-dependent model. This model includes
3D latitudinal and temporal variations of the solar wind density
and velocity taken from SOHO/SWAN and IPS data from 1990 to 2012 as
described in Provornikova et al. 2014. We additionally include a time
varying magnetic field obtained from the OMNI database. We compare
both models to observations along Voyager 1 and Voyager 2 and discuss
whether magnetic dissipation is a significant process affecting the
flows within the HS.
Title: Storm time plasma transport in a unified and inter-coupled
global magnetosphere model
Authors: Ilie, R.; Liemohn, M. W.; Toth, G.
Bibcode: 2014AGUFMSM14A..03I
Altcode:
We present results from the two-way self-consistent coupling between
the kinetic Hot Electron and Ion Drift Integrator (HEIDI) model and
the Space Weather Modeling Framework (SWMF). HEIDI solves the time
dependent, gyration and bounced averaged kinetic equation for the phase
space density of different ring current species and computes full pitch
angle distributions for all local times and radial distances. During
geomagnetic times the dipole approximation becomes unsuitable even in
the inner magnetosphere. Therefore the HEIDI model was generalized
to accommodate an arbitrary magnetic field and through the coupling
with SWMF it obtains a magnetic field description throughout the
HEIDI domain along with a plasma distribution at the model outer
boundary from the Block Adaptive Tree Solar Wind Roe Upwind Scheme
(BATS-R-US) magnetohydrodynamics (MHD) model within SWMF. Electric field
self-consistency is assured by the passing of convection potentials
from the Ridley Ionosphere Model (RIM) within SWMF. In this study we
test the various levels of coupling between the 3 physics based models,
highlighting the role that the magnetic field, plasma sheet conditions
and the cross polar cap potential play in the formation and evolution
of the ring current. We show that the dynamically changing geospace
environment itself plays a key role in determining the geoeffectiveness
of the driver. The results of the self-consistent coupling between
HEIDI, BATS-R-US and RIM during disturbed conditions emphasize the
importance of a kinetic self-consistent approach to the description
of geospace.
Title: MHD-EPIC: Extended Magnetohydrodynamics with Embedded
Particle-in-Cell Simulation of Ganymede's Magnetosphere.
Authors: Toth, G.; Daldorff, L. K. S.; Jia, X.; Gombosi, T. I.;
Lapenta, G.
Bibcode: 2014AGUFMSM23D..03T
Altcode:
We have recently developed a new modeling capability to
embed theimplicit Particle-in-Cell (PIC) model iPIC3D into the
BATS-R-USmagnetohydrodynamic model. The PIC domain can cover the
regions wherekinetic effects are most important, such as reconnection
sites. TheBATS-R-US code, on the other hand, can efficiently
handle the rest ofthe computational domain where the MHD or Hall
MHD description issufficient. As one of the very first applications
of the MHD-EPICalgorithm (Daldorff et al. 2014, JCP, 268, 236) we
simulate theinteraction between Jupiter's magnetospheric plasma with
Ganymede'smagnetosphere, where the separation of kinetic and global
scalesappears less severe than for the Earth's magnetosphere. Because
theexternal Jovian magnetic field remains in an anti-parallel
orientationwith respect to Ganymede's intrinsic magnetic field,
magneticreconnection is believed to be the major process that
couples the twomagnetospheres. As the PIC model is able to describe
self-consistentlythe electron behavior, our coupled MHD-EPIC model
is well suited forinvestigating the nature of magnetic reconnection
in thisreconnection-driven mini-magnetosphere. We will compare the
MHD-EPICsimulations with pure Hall MHD simulations and compare both
modelresults with Galileo plasma and magnetic field measurements
to assess therelative importance of ion and electron kinetics in
controlling theconfiguration and dynamics of Ganymede's magnetosphere.
Title: A Multi-neutral-fluid model of comet 67P/Churyumov-Gerasimenko
Authors: Shou, Y.; Combi, M. R.; Gombosi, T. I.; Jia, X.; Toth, G.;
Hansen, K. C.; Tenishev, V.; Fougere, N.
Bibcode: 2014AGUFM.P41C3924S
Altcode:
As comet 67P/Churyumov-Gerasimenko, the Rosetta mission target, is
approaching perihelion, the OSIRIS instrument observed the nucleus'
very unique dumbbell-like shape recently. It arouses an interesting
question as to what the coma will look like with the combination of the
irregular shape and the rotation of the nucleus, as a result of solar
radiation. A physics-based three dimensional coma model is highly
desirable to study this topic. One candidate is Direct Simulation
Monte Carlo (DSMC) method, and it has been successfully applied to
such problems. However, since the comet may be considerably active
closer to perihelion and the gas near the nucleus is dense, the time
step in DSMC model has to be tiny to accommodate the small mean free
path and the high collision frequency, which can make time-variable
DSMC modeling computationally expensive. In this work, we develop
a multi-neutral-fluid model based on BATS-R-US in the University of
Michigan's SWMF (Space Weather Modeling Framework), which can serve as
a useful alternative to DSMC methods to compute the inner coma. This
model treats cometary heavy neutrals, hydrogen atoms and dusts of
different particle sizes as separate fluids. In the model, we include
different momentum and energy transfer coefficients for different
fluids, heating from chemical reactions and frictions between gas and
dust. With other necessary physics considered, it is able to give us
a more physical picture than one fluid model. The preliminary results
are presented and discussed. This work has been partially supported
by NASA Planetary Atmospheres program grant NNX14AG84G and US Rosetta
contracts JPL #1266313 and JPL #1266314.
Title: High Resolution Magnetotail Simulations of Bursty Bulk Flows
Authors: Buzulukova, N.; Dorelli, J.; Glocer, A.; Fok, M. C. H.;
Toth, G.
Bibcode: 2014AGUFMSM23C4236B
Altcode:
We present the results of high resolution resistive MHD simulations of
bursty bulk flows using the BATSRUS magnetosphere model. We performed
a number of runs with three levels of constant resistivity. For each
resistivity level, we studied the dependence on tail resolution and
looked for solutions where numerical resistivity was small compared
to the set physical resistivity. For constant solar wind driving
(southward Bz IMF), we found the formation of bursty bulk flows (BBFs)
and dipolarization fronts when the resistivity was below a critical
value. We extracted virtual s/c data through dipolarization fronts and
BBFs and compared with observed properties of BBFs. We also studied
the ionospheric response to BBF formation. By switching on/off the
ring current module (CRCM) in the BATSRUS, we examined relationship
between BBFs and ring current injections.
Title: Consequences of Kinetic Effects in Nonsymmetric Reconnection
Configurations on Large-Scale Dynamical Processes in Magnetosphere
and Solar Plasma
Authors: Kuznetsova, M. M.; Hesse, M.; Aunai, N.; Wendel, D. E.;
Rastaetter, L.; Glocer, A.; Toth, G.
Bibcode: 2014AGUFMSM44B..04K
Altcode:
One of the major conclusions of the GEM Reconnection Challenge at the
dawn of the millennium was that reconnection rate is independent of the
electron mass. This finding allowed to reduce the problem to hall-less
pair plasma fluid description and reproduce kinetic reconnection
rates in large-scale single-fluid simulations by incorporating
kinetic non-gyrotropic corrections to the induction equation. It was
demonstrated that nongyrotropic effects incorporated into symmetric
magnetotail reconnection could significantly alter the global
magnetosphere evolution. In this paper we will extend the approach to
non-symmetric configurations relevant to planetary magnetospheres and
solar corona. We will examine the applicability of the non-gyrotropic
fluid approach to nonsymmetric magnetic reconnection and demonstrate
consequences of local kinetic effects on global evolution.
Title: Magnetic reconnection in 3D magnetosphere models: magnetic
separators and open flux production
Authors: Glocer, A.; Dorelli, J.; Toth, G.; Komar, C. M.; Cassak, P.
Bibcode: 2014AGUFMSM42A..03G
Altcode:
There are multiple competing definitions of magnetic reconnection
in 3D (e.g., Hesse and Schindler [1988], Lau and Finn [1990], and
Boozer [2002]). In this work we focus on separator reconnection. A
magnetic separator can be understood as the 3D analogue of a 2D x
line with a guide field, and is defined by the line corresponding
to the intersection of the separatrix surfaces associated with
the magnetic nulls. A separator in the magnetosphere represents
the intersection of four distinct magnetic topologies: solar wind,
closed, open connected to the northern hemisphere, and open connected
to the southern hemisphere. The integral of the parallel electric
field along the separator defines the rate of open flux production,
and is one measure of the reconnection rate. We present three methods
for locating magnetic separators and apply them to 3D resistive MHD
simulations of the Earth's magnetosphere using the BATS-R-US code. The
techniques for finding separators and determining the reconnection rate
are insensitive to IMF clock angle and can in principle be applied to
any magnetospheric model. The present work examines cases of high and
low resistivity, for two clock angles. We also examine the separator
during Flux Transfer Events (FTEs) and Kelvin-Helmholtz instability.
Title: Multifluid MHD Simulations of the Plasma Environment of Comet
Churyumov-Gerasimenko at Different Heliocentric Distances
Authors: Huang, Z.; Jia, X.; Rubin, M.; Fougere, N.; Gombosi, T. I.;
Tenishev, V.; Combi, M. R.; Bieler, A. M.; Toth, G.; Hansen, K. C.;
Shou, Y.
Bibcode: 2014AGUFM.P41C3928H
Altcode:
We study the plasma environment of the comet Churyumov-Gerasimenko,
which is the target of the Rosetta mission, by performing large scale
numerical simulations. Our model is based on BATS-R-US within the
Space Weather Modeling Framework that solves the governing multifluid
MHD equations, which describe the behavior of the cometary heavy ions,
the solar wind protons, and electrons. The model includes various mass
loading processes, including ionization, charge exchange, dissociative
ion-electron recombination, as well as collisional interactions between
different fluids. The neutral background used in our MHD simulations
is provided by a kinetic Direct Simulation Monte Carlo (DSMC) model. We
will simulate how the cometary plasma environment changes at different
heliocentric distances.
Title: Plasma environment of a weak comet - Predictions for Comet
67P/Churyumov-Gerasimenko from multifluid-MHD and Hybrid models
Authors: Rubin, M.; Koenders, C.; Altwegg, K.; Combi, M. R.;
Glassmeier, K. -H.; Gombosi, T. I.; Hansen, K. C.; Motschmann, U.;
Richter, I.; Tenishev, V. M.; Tóth, G.
Bibcode: 2014Icar..242...38R
Altcode:
The interaction of a comet with the solar wind undergoes various
stages as the comet's activity varies along its orbit. For a comet like
67P/Churyumov-Gerasimenko, the target comet of ESA's Rosetta mission,
the various features include the formation of a Mach cone, the bow
shock, and close to perihelion even a diamagnetic cavity. There are
different approaches to simulate this complex interplay between the
solar wind and the comet's extended neutral gas coma which include
magnetohydrodynamics (MHD) and hybrid-type models. The first treats
the plasma as fluids (one fluid in basic single fluid MHD) and the
latter treats the ions as individual particles under the influence of
the local electric and magnetic fields. The electrons are treated as a
charge-neutralizing fluid in both cases. Given the different approaches
both models yield different results, in particular for a low production
rate comet. In this paper we will show that these differences can be
reduced when using a multifluid instead of a single-fluid MHD model
and increase the resolution of the Hybrid model. We will show that some
major features obtained with a hybrid type approach like the gyration
of the cometary heavy ions and the formation of the Mach cone can be
partially reproduced with the multifluid-type model.
Title: Plasma Flows in the Heliosheath along the Voyager 1 and 2
Trajectories due to Effects of the 11 yr Solar Cycle
Authors: Provornikova, E.; Opher, M.; Izmodenov, V. V.; Richardson,
J. D.; Toth, G.
Bibcode: 2014ApJ...794...29P
Altcode:
We investigate the role of the 11 yr solar cycle variations in the
solar wind (SW) parameters on the flows in the heliosheath using a new
three-dimensional time-dependent model of the interaction between the
SW and the interstellar medium. For boundary conditions in the model we
use realistic time and the latitudinal dependence of the SW parameters
obtained from SOHO/SWAN and interplanetary scintillation data for the
last two solar cycles (1990-2011). This data set generally agrees with
the in situ Ulysses measurements from 1991 to 2009. For the first ~30
AU of the heliosheath the time-dependent model predicts constant radial
flow speeds at Voyager 2 (V2), which is consistent with observations
and different from the steady models that show a radial speed decrease
of 30%. The model shows that V2 was immersed in SW with speeds of
500-550 km s-1 upstream of the termination shock before
2009 and in wind with upstream speeds of 450-500 km s-1
after 2009. The model also predicts that the radial velocity along
the Voyager 1 (V1) trajectory is constant across the heliosheath,
contrary to observations. This difference in observations implies that
additional effects may be responsible for the different flows at V1
and V2. The model predicts meridional flows (VN) higher than those
observed because of the strong bluntness of the heliosphere shape in
the N direction in the model. The modeled tangential velocity component
(VT) at V2 is smaller than observed. Both VN and VT essentially depend
on the shape of the heliopause.
Title: Effects of crustal field rotation on the solar wind plasma
interaction with Mars
Authors: Ma, Yingjuan; Fang, Xiaohua; Russell, Christopher T.;
Nagy, Andrew F.; Toth, Gabor; Luhmann, Janet G.; Brain, Dave A.;
Dong, Chuanfei
Bibcode: 2014GeoRL..41.6563M
Altcode:
The crustal remnant field on Mars rotates with the planet at
a period of 24 h 37 min, constantly varying the magnetic field
configuration interacting with the solar wind. Until now, there has
been no self-consistent modeling investigation on how this varying
magnetic field affects the solar wind plasma interaction. Here we
include the rotation of this localized crustal field in a multispecies
single-fluid MHD model of Mars and simulate an entire day of solar
wind interaction under normal solar wind conditions. The MHD model
results are compared with Mars Global Surveyor (MGS) magnetic field
observations and show very close agreement, especially for the field
strength along almost all of the 12 orbits on the day simulated. Model
results also show that the ion escape rates slowly vary with rotation,
generally anticorrelating with the strength of subsolar magnetic crustal
sources, with some time delay. In addition, it is found that in the
intense crustal field regions, the densities of heavy ion components
enhance significantly along the MGS orbit, implying strong influence
of the crustal field on the ionospheric structures.
Title: High Order Schemes in BATS-R-US: Is it OK to Simplify Them?
Authors: Tóth, G.; Chen, Y.; van der Holst, B.; Daldorff, L. K. S.
Bibcode: 2014ASPC..488..273T
Altcode:
We describe a number of high order schemes and their simplified variants
that have been implemented into the University of Michigan global
magnetohydrodynamics code BATS-R-US. We compare the various schemes
with each other and the legacy 2nd order TVD scheme for various test
problems and two space physics applications. We find that the simplified
schemes are often quite competitive with the more complex and expensive
full versions, despite the fact that the simplified versions are only
high order accurate for linear systems of equations. We find that all
the high order schemes require some fixes to ensure positivity in the
space physics applications. On the other hand, they produce superior
results as compared with the second order scheme and/or produce the
same quality of solution at a much reduced computational cost.
Title: Global Magnetohydrodynamics Simulation of the Coronal Mass
Ejection on 2011 March 7: from Chromosphere to 1 AU
Authors: Jin, Meng; Manchester, W. B.; van der Holst, B.; Sokolov,
I.; Toth, G.; Vourlidas, A.; de Koning, C.; Gombosi, T. I.
Bibcode: 2014shin.confE..10J
Altcode:
Performing realistic simulations of solar eruptions and validating
those simulations with observations are important goals in order to
achieve accurate space weather forecasts. Here, we analyze results
of a global magnetohydrodyanmic (MHD) simulation of the fast coronal
mass ejection (CME) that occurred on 2011 March 7. The simulation is
made using the newly developed Alfven Wave Solar Model (AWSoM), which
describes the background solar wind starting from the upper chromosphere
and expends to 24 Rs. Coupling of AWSoM to an inner heliosphere (IH)
model with the Space Weather Modeling Framework extends the total domain
beyond the orbit of Earth. Physical processes included in the model are
multi-species thermodynamics, electron heat conduction (both collisional
and collisionless formulation), optically thin radiative cooling and
Alfven-wave pressure that accelerates the solar wind. The Alfven-wave
description is physically self-consistent, including non-WKB reflection
and physics-based apportioning of turbulent dissipative heating to both
electrons and protons. Within this model, we initiate the CME by using
the Gibson-Low (GL) analytical flux rope model and follow its evolution
for days, in which time it propagates beyond 1 AU. A comprehensive
validation study is performed using remote as well as the in situ
observations from SDO, SOHO, STEREOA/B, and OMNI. Our results show
that the new model can reproduce many of the observed features near
the Sun (e.g., CME-driven EUV waves, deflection of the flux rope from
the coronal hole, double-front in the white light images) and in the
heliosphere (e.g., CME-CIR interaction, shock properties at 1 AU). By
fitting the CME speeds near the Sun with observations, the CME-driven
shock arrival time is within 1 hour of the observed arrival time and
all the in situ parameters are correctly simulated, which suggests the
global MHD model as a powerful tool for the space weather forecasting.
Title: The behavior of the flows within the heliosheath
Authors: Michael, Adam; Opher, Merav; Provornikova, Elena; Toth, Gabor
Bibcode: 2014shin.confE..61M
Altcode:
The current Voyager measurements of the plasma flows reveal the complex
nature of the heliosheath, the last boundary between the Solar System
and the interstellar medium. These measurements are challenging
the standard theories and models. We use a global 3D multi-fluid
magnetohydrodynamic (MHD) model of the heliosphere to study the flows
within the heliosheath. Our model has a grid resolution of 0.5 AU within
the heliosphere, along both Voyager 1 and Voyager 2 trajectories,
and describes the solar wind magnetic field as a monopole to avoid
any numerical magnetic dissipation effects in the heliosheath. We find
that the model predicts the heliosheath to be split into two regions,
first a thermally dominated region downstream of the termination
shock followed by a magnetically dominated region (? < 1) just
before the heliopause. We compare the solution to the same model
with dipole description of the solar wind magnetic field. The dipole
solar wind magnetic field includes a flat heliospheric current sheet
where reconnection occurs due to numerical dissipation. The two models
predict a considerably different heliosheath. We compare both models
to observations along V1 and V2 and discuss whether we can use these
models to predict when Voyager 2 is approaching the heliopause.
Title: Effects of Crustal Field Rotation on the Solar Wind Plasma
Interaction with Mars
Authors: Ma, Yingjuan; Fang, Xiaohua; Russell, Christopher; Brain,
Dave; Nagy, Andrew; Toth, Gabor; Luhmann, Janet; Dong, Chuanfei
Bibcode: 2014EGUGA..16.8381M
Altcode:
The crustal field on Mars rotates constantly with the planet at a
period of 24 h 37 min. In this study, we include the rotation of the
crustal field in the multi-species single fluid MHD model of Mars
and simulated one entire day of May 15, 2005 using normal solar
wind condition to investigate how this rotation affects the solar
wind plasma interaction. The MHD model results are compared with MGS
magnetic field observations and show remarkably good agreement along
almost all of the 12 orbits on that day. Model results also show that
the ion escape fluxes vary slowly with rotation, anti-correlating with
the strength of subsolar magnetic crustal sources. It is also found
that near intense crustal field regions, the densities of the heavy
ion components increase significantly, implying a strong influence of
the crustal field on the low-altitude ionosphere.
Title: Solar wind interaction with Mars upper atmosphere: Results
from the one-way coupling between the multifluid MHD model and the
MTGCM model
Authors: Dong, Chuanfei; Bougher, Stephen W.; Ma, Yingjuan; Toth,
Gabor; Nagy, Andrew F.; Najib, Dalal
Bibcode: 2014GeoRL..41.2708D
Altcode:
The 3-D multifluid Block Adaptive Tree Solar-wind Roe Upwind
Scheme (BATS-R-US) MHD code (MF-MHD) is coupled with the 3-D Mars
Thermospheric general circulation model (MTGCM). The ion escape
rate from the Martian upper atmosphere is investigated by using a
one-way coupling approach, i.e., the MF-MHD model incorporates the
effects of 3-D neutral atmosphere profiles from the MTGCM model. The
calculations are carried out for two cases with different solar cycle
conditions. The calculated total ion escape flux (the sum of three
major ionospheric species, O+, O2+, and CO2+) for solar
cycle maximum conditions (6.6×1024 s-1) is
about 2.6 times larger than that of solar cycle minimum conditions
(2.5×1024 s-1). Our simulation results show
good agreement with recent observations of 2-3×1024
s-1 (O+, O2+, and CO2+) measured near solar
cycle minimum conditions by Mars Express. An extremely high solar
wind condition is also simulated which may mimic the condition of
coronal mass ejections or corotating interaction regions passing
Mars. Simulation results show that it can lead to a significant value
of the escape flux as large as 4.3×1025s-1.
Title: Martian ionospheric responses to dynamic pressure enhancements
in the solar wind
Authors: Ma, Y. J.; Fang, X.; Nagy, A. F.; Russell, C. T.; Toth, Gabor
Bibcode: 2014JGRA..119.1272M
Altcode:
As a weakly magnetized planet, Mars ionosphere/atmosphere interacts
directly with the shocked solar wind plasma flow. Even though many
numerical studies have been successful in reproducing numerous features
of the interaction process, these earlier studies focused mainly on
interaction under steady solar wind conditions. Recent observations
suggest that plasma escape fluxes are significantly enhanced in
response to solar wind dynamic pressure pulses. In this study, we
focus on the response of the ionosphere to pressure enhancements
in the solar wind. Through modeling of two idealized events using a
magnetohydrodynamics model, we find that the upper ionosphere of Mars
responds almost instantaneously to solar wind pressure enhancements,
while the collision dominated lower ionosphere (below ~150 km) does
not have noticeable changes in density. We also find that ionospheric
perturbations in density, magnetic field, and velocity can last more
than an hour after the solar wind returns to the quiet conditions. The
topside ionosphere forms complicated transient shapes in response, which
may explain unexpected ionospheric behaviors in recent observations. We
also find that ionospheric escape fluxes do not correlate directly with
simultaneous solar wind dynamic pressure. Rather, their intensities
also depend on the earlier solar wind conditions. It takes a few hours
for the ionospheric/atmospheric system to reach a new quasi-equilibrium
state.
Title: Comet 1P/Halley Multifluid MHD Model for the Giotto Fly-by
Authors: Rubin, M.; Combi, M. R.; Daldorff, L. K. S.; Gombosi, T. I.;
Hansen, K. C.; Shou, Y.; Tenishev, V. M.; Tóth, G.; van der Holst,
B.; Altwegg, K.
Bibcode: 2014ApJ...781...86R
Altcode:
The interaction of comets with the solar wind has been the focus of
many studies including numerical modeling. We compare the results
of our multifluid MHD simulation of comet 1P/Halley to data obtained
during the flyby of the European Space Agency's Giotto spacecraft in
1986. The model solves the full set of MHD equations for the individual
fluids representing the solar wind protons, the cometary light and
heavy ions, and the electrons. The mass loading, charge-exchange,
dissociative ion-electron recombination, and collisional interactions
between the fluids are taken into account. The computational domain
spans over several million kilometers, and the close vicinity of the
comet is resolved to the details of the magnetic cavity. The model
is validated by comparison to the corresponding Giotto observations
obtained by the Ion Mass Spectrometer, the Neutral Mass Spectrometer,
the Giotto magnetometer experiment, and the Johnstone Plasma Analyzer
instrument. The model shows the formation of the bow shock, the
ion pile-up, and the diamagnetic cavity and is able to reproduce the
observed temperature differences between the pick-up ion populations and
the solar wind protons. We give an overview of the global interaction
of the comet with the solar wind and then show the effects of the
Lorentz force interaction between the different plasma populations.
Title: Alfvén Wave Solar Model (AWSoM): Coronal Heating
Authors: van der Holst, B.; Sokolov, I. V.; Meng, X.; Jin, M.;
Manchester, W. B., IV; Tóth, G.; Gombosi, T. I.
Bibcode: 2014ApJ...782...81V
Altcode: 2013arXiv1311.4093V
We present a new version of the Alfvén wave solar model, a global model
from the upper chromosphere to the corona and the heliosphere. The
coronal heating and solar wind acceleration are addressed with
low-frequency Alfvén wave turbulence. The injection of Alfvén
wave energy at the inner boundary is such that the Poynting flux is
proportional to the magnetic field strength. The three-dimensional
magnetic field topology is simulated using data from photospheric
magnetic field measurements. This model does not impose open-closed
magnetic field boundaries; those develop self-consistently. The
physics include the following. (1) The model employs three different
temperatures, namely the isotropic electron temperature and the
parallel and perpendicular ion temperatures. The firehose, mirror,
and ion-cyclotron instabilities due to the developing ion temperature
anisotropy are accounted for. (2) The Alfvén waves are partially
reflected by the Alfvén speed gradient and the vorticity along the
field lines. The resulting counter-propagating waves are responsible
for the nonlinear turbulent cascade. The balanced turbulence due to
uncorrelated waves near the apex of the closed field lines and the
resulting elevated temperatures are addressed. (3) To apportion the
wave dissipation to the three temperatures, we employ the results
of the theories of linear wave damping and nonlinear stochastic
heating. (4) We have incorporated the collisional and collisionless
electron heat conduction. We compare the simulated multi-wavelength
extreme ultraviolet images of CR2107 with the observations from
STEREO/EUVI and the Solar Dynamics Observatory/AIA instruments. We
demonstrate that the reflection due to strong magnetic fields in the
proximity of active regions sufficiently intensifies the dissipation
and observable emission.
Title: Effects of Solar wind Pressure Enhancement and the Diurnal
Rotation of the Crustal Field on the Solar Wind Plasma Interaction
with Mars
Authors: Ma, Yingjuan; Russell, C. T.; Bougher, Stephen; Nagy, Andrew;
Toth, Gabor; Fang, Xiaohua
Bibcode: 2014cosp...40E1926M
Altcode:
As Mars is a weakly magnetized planet, its ionosphere/atmosphere
interacts directly with the shocked solar wind plasma flow. Recent
observations suggest that plasma escape fluxes are significantly
enhanced in response to solar wind dynamic pressure pulses. In this
presentation, based on multi-species single-fluid MHD numerical
simulations, we show the response of the ionosphere to pressure
enhancements in the solar wind. We find that the upper ionosphere
of Mars responds almost instantaneously to solar wind pressure
enhancements, while the collision dominated lower ionosphere (below
~150 km) does not have noticeable changes in density. We also find
that ionospheric perturbations in density, magnetic field, and
velocity can last more than an hour after the solar wind returns
to the quiet conditions. The topside ionosphere forms complicated
transient shapes in response, which may explain unexpected ionospheric
behavior in recent observations. We also find that ionospheric escape
fluxes do not correlate directly with simultaneous solar wind dynamic
pressure. Rather, their intensities depend in part on the earlier
solar wind conditions. We also include the diurnal rotation of the
crustal field in the MHD model to investigate how this rotation
affects the solar wind plasma interaction. The MHD model results are
compared with MGS magnetic field observations and show remarkably good
agreement between the two. Model results also show that the ion escape
fluxes vary slowly with rotation, anti-correlating with the strength
of subsolar magnetic crustal sources. It is found that near intense
crustal field regions, the densities of heavy ion components increase
significantly, implying a strong influence on the upper ionosphere by
the crustal field.
Title: Study of solar cycle effects in the heliosheath in the model
based on SWAN/SOHO and IPS data at 1 AU
Authors: Provornikova, Elena; Richardson, John; Opher, Merav; Toth,
Gabor; Izmodenov, Vladislav
Bibcode: 2014cosp...40E2636P
Altcode:
Observations of plasma in the heliosheath by Voyager 1 and 2 showed
highly variable and very different plasma flows. Voyager 2 has been
observing nearly constant radial flow ~110 km/s indicating that
the spacecraft is still far from the heliopause. Plasma velocity
components determined from LECP on Voyager 1 rapidly decreased across
the heliosheath to zero values in the stagnation region near the
HP. Steady state models of the outer heliosphere do not explain such
different flows. These puzzling observational data motivate us to
explore different physical effects at the edges of the heliosphere in
the models. In this work we focus on time-dependent effects related to
11- year solar cycle. We use a 3D MHD multi-fluid model of interaction
of the solar wind with the local interstellar medium (BATSRUS) with
time-dependent boundary conditions for the supersonic solar wind. Used
realistic boundary conditions (plasma density and velocity) at 1 AU were
derived from the measurements of intensities of Lyman-alpha emission
on SOHO/SWAN, OMNI data (in the ecliptic plane) and interplanetary
scintillations data over two full solar cycles. We present results of
the time-dependent model and discuss effects of realistic variations
of the solar wind parameters on the flow in the heliosheath and in the
vicinity of the heliopause. From comparison of model results with the
Voyager 1 and 2 observations we found that the solar cycle effects can
explain constant radial flow along the Voyager 2 but do not reproduce
the decrease of radial flow to zero seen at Voyager 1.
Title: Predicting the time derivative of local magnetic perturbations
Authors: Tóth, Gábor; Meng, Xing; Gombosi, Tamas I.; Rastätter, Lutz
Bibcode: 2014JGRA..119..310T
Altcode:
Some of the potentially most destructive effects of severe
space weather storms are caused by the geomagnetically induced
currents. Geomagnetically induced currents (GICs) can cause failures
of electric transformers and result in widespread blackouts. GICs
are induced by the time variability of the magnetic field and are
closely related to the time derivative of the local magnetic field
perturbation. Predicting dB/dt is rather challenging, since the local
magnetic perturbations and their time derivatives are both highly
fluctuating quantities, especially during geomagnetic storms. The
currently available first principles-based and empirical models cannot
predict the detailed minute-scale or even faster time variation of
the local magnetic field. On the other hand, Pulkkinen et al. (2013)
demonstrated recently that several models can predict with positive
skill scores whether the horizontal component of dB/dt at a given
magnetometer station will exceed some threshold value in a 20 min
time interval. In this paper we investigate if one can improve the
efficiency of the prediction further. We find that the Space Weather
Modeling Framework, the best performing among the five models compared
by Pulkkinen et al. (2013), shows significantly better skill scores
in predicting the magnetic perturbation than predicting its time
derivative, especially for large deviations. We also find that there is
a strong correlation between the magnitude of dB/dt and the magnitude
of the horizontal magnetic perturbation itself. Combining these two
results one can devise an algorithm that gives better skill scores for
predicting dB/dt exceeding various thresholds in 20 min time intervals
than the direct approach.
Title: Geomagnetic Environment Modeling at the Community Coordinated
Modeling Center: Successes, Challenges and Perspectives.
Authors: Kuznetsova, Maria; Toth, Gabor; Hesse, Michael; Rastaetter,
Lutz; Glocer, Alex
Bibcode: 2014cosp...40E1723K
Altcode:
The Community Coordinated Modeling Center (CCMC,
http://ccmc.gsfc.nasa.gov) hosts an expanding collection of modern
space science and space weather models developed by the international
space science community. The goals of the CCMC are to support the
research and developmental work necessary to substantially increase
the present-day space environment modeling capability and to maximize
scientific return on investments into model development. CCMC is
servicing models through interactive web-based systems, supporting
community-wide research projects and designing displays and tools
customized for specific applications. The presentation will review the
current state of the geomagnetic environment modeling, highlight resent
progress, and showcase the role of state-of-the-art magnetosphere
models in advancing our understanding of fundamental phenomena in
magnetosphere plasma physics.
Title: Multi-fluid MHD Study of the Solar Wind Induced Plasma Escape
from the Martian Atmosphere
Authors: Ma, Y.; Russell, C. T.; Nagy, A. F.; Toth, G.; Dong, C.;
Bougher, S. W.
Bibcode: 2013AGUFM.P13C..05M
Altcode:
In this study, the multi-fluid MHD model (Najib et al., 2011)
is further improved to include an electron pressure equation to
self-consistently calculate the electron temperature. The electron
pressure equation included in the improved model can accurately
calculate the electron temperature and the electron pressure
force. The electron temperature is also needed to calculate rates
of some electron temperature dependent chemical reactions such as
dissociative recombination and electron impact ionization. So the
improvement of the model leads to a more accurate evaluation of the
ion density in the ionosphere and a more accurate description of the
interaction process. Model results of a typical case with electron
pressure equation included are compared in detail to an identical case
without the electron pressure equation to identify the effect of the
improved physics. The two cases will be examined to identify changes
in the global interaction patterns. Electron temperature will also
be compared for the two cases to identify regions where temperatures
differs the most. The ion density profiles at different locations
will be compared to identify the changes of plasma density due to
changes of recombination rates and impact ionization rates caused by
different electron temperatures. The calculated electron temperature
profile will also be compared to the only available pre-MAVEN electron
observations from the Viking Retarding Potential Analyzer (RPA) (Hansen
et al., 1977). Based on model results, two-dimensional maps of the ion
densities and fluxes are to be generated in the tail region at various
distances to locate the intense region for plasma bulk escape. We will
also plan to fly through the 3D MHD model results using planned MAVEN
orbits to predict when and where the spacecraft will pass different
plasma boundaries (such as the bow shock, MPB, and ionopause), and
the typical range of the plasma parameters in different regions.
Title: Global MHD simulations of Mercury's interaction with the
solar wind: Influence of the planetary conducting core on the
magnetospheric interaction
Authors: Jia, X.; Slavin, J. A.; Gombosi, T. I.; Daldorff, L.; Toth, G.
Bibcode: 2013AGUFMSM21A2139J
Altcode:
Mercury's comparatively weak intrinsic magnetic field and its close
proximity to the Sun lead to a mini-magnetosphere that undergoes more
direct space-weathering interactions than other planets. A unique
aspect of the Mercury interaction system relates to the large ratio
of the scale of the planet to the scale of the tiny magnetosphere and
the presence of a large-size core (with radius ~ 80% of the planetary
radius) composed of highly conducting material, implying that there
is potentially strong feedback between the planet's interior and
the magnetosphere, especially under conditions of strong solar wind
driving. Understanding the solar wind-magnetosphere-exosphere-interior
interaction at Mercury as a highly coupled system requires not only
analysis of spacecraft data but also a modeling framework that is
both comprehensive and inclusive. To this end, we have developed a new
global MHD model of Mercury's interaction with the solar wind based on
the BATSRUS code in which the interior of the planet (modeled as layers
of different electric conductivities) is electrodynamically coupled to
the surrounding space plasma environment. The new modeling capability
allows for self-consistently characterizing the dynamical response of
the Mercury system to time-varying external conditions. In particular,
we have applied the coupled model to assess quantitatively the effect
of induction arising from the planet's conducting core on the global
magnetosphere. A set of idealized simulations have been carried out in
which Mercury's magnetosphere is impacted by solar wind disturbances
with different levels of pressure enhancement. Our results show that
due to the induction effect, Mercury's core can impose strong global
influences on the way Mercury responds to changes in the external
environment, including modifying the global magnetospheric structure
and affecting the extent to which the solar wind directly impacts the
planetary surface. By applying the model to simulate extreme events,
such as those observed by MESSENGER during impact of Coronal Mass
Ejections (Slavin et al., 2013), we aim to obtain a deeper understanding
of the tightly coupled Mercury system, and thereby to develop further
constraints on the properties of the planet's interior.
Title: Two-way self-consistent coupling of HEIDI in SWMF
Authors: Ilie, R.; Liemohn, M. W.; Toth, G.
Bibcode: 2013AGUFMSM43A2281I
Altcode:
In this study we present results from the two-way coupling between
the kinetic Hot Electron and Ion Drift Integrator (HEIDI) model and
the Space Weather Modeling Framework (SWMF). HEIDI solves the time
dependent, gyration and bounced averaged kinetic equation for the phase
space density of different ring current species and computes full pitch
angle distributions for all local times and radial distances. This
model was generalized to accommodate an arbitrary magnetic field
and, through the coupling with SWMF, it obtains the magnetic field
description along with the plasma distribution at the model boundaries
from the Block Adaptive Tree Solar Wind Roe Upwind Scheme (BATS-R-US)
magnetohydrodynamics (MHD) model within the SWMF. Electric field
self-consistency is assured by the passing of convection potentials
from the Ridley Ionosphere Model (RIM) within SWMF. Our study tests
the various levels of coupling between the 3 models, highlighting the
roles that the magnetic field, plasma sheet conditions and the cross
polar cap potential play in the formation and evolution of the ring
current. The results of the self-consistent coupling between HEIDI,
BATSRUS and RIM during disturbed conditions emphasize the importance of
a kinetic self-consistent approach to the description of the geospace.
Title: Evaluating the Importance of Outflow Velocity at the MHD
Inner Boundary
Authors: Welling, D. T.; Liemohn, M. W.; Toth, G.; Glocer, A.
Bibcode: 2013AGUFMSA41A2105W
Altcode:
Including an ionospheric source of magnetospheric plasma in global
magnetohydrodynamic models (MHD) is an exercise in setting inner
boundary mass density and radial velocity. Recently, in order to account
for the complex processes that accelerate plasmas up from ionospheric
altitudes to MHD inner boundary altitudes (typically 2.5 to 3 Earth
Radii), empirical and first-principles-based models have been developed
to set inner boundary conditions in a dynamic and activity-dependent
manner. However, such measures are not necessary to achieve outflowing
fluences of the order observed by various spacecraft. Spatially and
temporally constant boundary conditions, even with zero radial velocity,
have been shown to produce dynamic outflow patterns and supply the
bulk of magnetospheric plasma. Noteworthy of this approach is the
inherent assumption that no acceleration has occurred between the
ionosphere and the inner boundary, that is, the ionosphere is simply
a mass reservoir. This assumption is contrary to our understanding of
the magnetosphere-ionosphere system, yet the net result - outflowing
heavy and light ions that populate the rest of geospace - is similar
to that when a more realistic outflow specification is applied. The
implication is that radial velocity matters little when supplying
outflow to global MHD models. This paper investigates the importance
of radial velocity at the inner boundary of MHD codes in driving
ionospheric outflows into the greater domain. Multi-fluid BATS-R-US
is used to simulate an idealized storm, first using zero radial
velocity at the inner boundary, then non-zero constant values, and
finally with spatially and temporally dynamic values driven by the
Polar Wind Outflow Model (PWOM), which sets radial velocity and number
density based on physics-based modeling of gap region populations. The
results, in terms of total fluence, spatial outflowing flux patterns,
and overall magnetospheric response, are compared to investigate how
the simulation depends on this value. Magnetospheric implications are
evaluated via density, temperature, and composition within the lobes,
plasmasheet, and ring current regions. MHD-derived global indices,
such as DST and CPCP, will also be leveraged. The results of this
study are a systematic test of the importance of sub-magnetosphere
acceleration of ionospheric plasma in magnetospheric dynamics.
Title: The Challenge of Incorporating Charged Dust in the Physics
of Flowing Plasma Interactions
Authors: Jia, Y.; Russell, C. T.; Ma, Y.; Lai, H.; Jian, L.; Toth, G.
Bibcode: 2013AGUFMSM53A2212J
Altcode:
The presence of two oppositely charged species with very different mass
ratios leads to interesting physical processes and difficult numerical
simulations. The reconnection problem is a classic example of this
principle with a proton-electron mass ratio of 1836, but it is not
the only example. Increasingly we are discovering situations in which
heavy, electrically charged dust particles are major players in a plasma
interaction. The mass of a 1mm dust particle is about 2000 proton masses
and of a 10 mm dust particle about 2 million proton masses. One example
comes from planetary magnetospheres. Charged dust pervades Enceladus'
southern plume. The saturnian magnetospheric plasma flows through
this dusty plume interacting with the charged dust and ionized plume
gas. Multiple wakes are seen downstream. The flow is diverted in one
direction. The field aligned-current systems are elsewhere. How can
these two wake features be understood? Next we have an example from
the solar wind. When asteroids collide in a disruptive collision, the
solar wind strips the nano-scale charged dust from the debris forming
a dusty plasma cloud that may be over 106km in extent and
containing over 100 million kg of dust accelerated to the solar wind
speed. How does this occur, especially as rapidly as it appears to
happen? In this paper we illustrate a start on understanding these
phenomena using multifluid MHD simulations but these simulations are
only part of the answer to this complex problem that needs attention
from a broader range of the community.
Title: Solar wind interaction with Mars' upper atmosphere: Results
from 3-D studies using one-way coupling between the Multi-fluid MHD,
the M-GITM and the AMPS models
Authors: Dong, C.; Bougher, S. W.; Ma, Y.; Toth, G.; Lee, Y.; Nagy,
A. F.; Tenishev, V.; Pawlowski, D. J.; Meng, X.; Combi, M. R.
Bibcode: 2013AGUFM.P12A..01D
Altcode:
The study of the solar wind interaction with Mars upper
atmosphere/ionosphere has triggered a great of interest in recent
years. Among the large number of topics in this research area,
the investigation of ion escape fluxes has become increasingly
important due to its potential impact on the long-term evolution
of Mars atmosphere (e.g., loss of water) over its history. In the
present work, we adopt the 3-D Mars cold neutral atmosphere profiles
(0~300 km) from the newly developed and validated Mars Global Ionosphere
Thermosphere Model (M-GITM) and the 3-D hot oxygen profiles (100km~5RM)
from the exosphere Monte Carlo model Adaptive Mesh Particle Simulator
(AMPS). We apply these 3-D model outputs fields into the 3-D BATS-R-US
Mars multi-fluid MHD model (100km~20RM) that can better simulate the
interplay between Mars upper atmosphere and solar wind by considering
the dynamics of individual ion species. The multi-fluid model solves
separate continuity, momentum and energy equations for each ion species
(H+, O+, O2+, CO2+). The M-GITM model together with the AMPS exosphere
model take into account the effects of solar cycle and seasonal
variations on both cold and hot neutral atmospheres, allowing us to
investigate the corresponding effects on the Mars upper atmosphere ion
escape by using a one-way coupling approach, i.e., both the M-GITM
and AMPS model outputs are used as the inputs for the multi-fluid
model and M-GITM is used as input into the AMPS exosphere model. The
calculations are carried out for selected cases with different nominal
solar wind, solar cycle and crustal field orientation conditions. This
work has the potential to provide predictions of ion escape rates for
comparison to future data to be returned by the MAVEN primary mission
(2014-2016) and thereby improve our understanding of present day escape
processes. Acknowledgments: The work presented here was supported by
NASA grants NNH10CC04C, NNX09AL26G, NSF grant ATM-0535811.
Title: Modeling comet 1P/Halley's plasma environment using multifluid
MHD
Authors: Rubin, M.; Combi, M. R.; Daldorff, L. K. S.; Gombosi, T. I.;
Hansen, K. C.; Shou, Y.; Tenishev, V. M.; Tóth, G.; van der Holst,
B.; Altwegg, K.
Bibcode: 2013EPSC....8...87R
Altcode:
Observations by ESA's Giotto spacecraft at comet 1P/Halley on March
14, 1986, allowed a detailed glance into the interaction between the
neutral gas coma and the solar wind. For a highly productive comet
such as 1P/Halley the plasma environment is remarkably diverse when
probed at various cometocentric distances. We apply a global scale
multifluid magnetohydrodynamics (MHD) approach in which the individual
plasma components are treated as a set of coupled magnetized fluids
([1], [2]). This is a continuation of our previous work using a single
species model ([3], [4]) and provides insight on some of the involved
dynamical processes that might otherwise only be accessible by Monte
Carlo Hybrid-type models.
Title: Pressure anisotropy in global magnetospheric simulations:
Coupling with ring current models
Authors: Meng, X.; Tóth, G.; Glocer, A.; Fok, M. -C.; Gombosi, T. I.
Bibcode: 2013JGRA..118.5639M
Altcode:
We have recently extended the global magnetohydrodynamic (MHD)
model BATS-R-US to account for pressure anisotropy. Since the inner
magnetosphere dynamics cannot be fully described even by anisotropic
MHD, we coupled our anisotropic MHD model with two inner magnetospheric
models: the Rice Convection Model (RCM) and the Comprehensive Ring
Current Model (CRCM). The coupled models provide better representations
of the near-Earth plasma, especially during geomagnetic storms. In this
paper, we present the two-way coupling algorithms with both ring current
models. The major difference between these two couplings is that the
RCM assumes isotropic and constant pressures along closed field lines,
while the CRCM resolves pitch angle anisotropy. For model validation,
we report global magnetosphere simulations performed by the coupled
models. The simulation results are compared to the results given by
the coupled isotropic MHD and ring current models. We find that in
the global MHD simulations coupled with ring current models, pressure
anisotropy results in a thinner magnetosheath, a shorter tail, a much
smaller Earthward plasma jet from the tail reconnection site, and is
also important in controlling the magnetic field configuration. The
comparisons with satellite data for the magnetospheric event simulations
show improvements on reproducing the measured tail magnetic field and
inner magnetospheric flow velocity when including pressure anisotropy
in the ring current model coupled global MHD model.
Title: Ionospheric Responses to Discontinuities in the Solar Wind
Authors: Ma, Y.; Russell, C. T.; Nagy, A. F.; Toth, G.
Bibcode: 2013EPSC....8..845M
Altcode:
The solar wind plasma flow and associated IMF are highly variable. Past
studies about Mars mainly focus on its interactions with steady solar
wind conditions. However recent study found that the total escape
fluxes can be significantly enhanced during solar wind pressure pulses
[1]. This study focuses on ionosphere response to solar wind 1) density
variation and 2) magnetic field direction change. Through numerical
modeling, we found that the upper ionosphere of Mars responses almost
instantaneously to solar wind density enhancement, while the lower
ionosphere (below ~150 km) do not have any noticeable changes in
density. Current sheet crossing can cause only moderate changes in the
upper ionosphere of Mars with several min time delays. We also found
that perturbations in density and integrated escape fluxes caused by
the solar wind variations could last more than an hour.
Title: Numerical Simulations of Coronal Mass Ejection on 2011 March 7:
One-temperature and Two-temperature Model Comparison
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Oran, R.;
Sokolov, I.; Toth, G.; Liu, Y.; Sun, X. D.; Gombosi, T. I.
Bibcode: 2013ApJ...773...50J
Altcode:
During Carrington rotation (CR) 2107, a fast coronal mass ejection (CME;
>2000 km s-1) occurred in active region NOAA 11164. This
event is also associated with a solar energetic particle event. In
this study, we present simulations of this CME with one-temperature
(1T) and two-temperature (2T: coupled thermodynamics of the electron
and proton populations) models. Both the 1T and 2T models start from
the chromosphere with heat conduction and radiative cooling. The
background solar wind is driven by Alfvén-wave pressure and heated
by Alfvén-wave dissipation in which we have incorporated the balanced
turbulence at the top of the closed field lines. The magnetic field of
the inner boundary is set up using a synoptic map from Solar Dynamics
Observatory/Helioseismic and Magnetic Imager. The Titov-Démoulin
flux-rope model is used to initiate the CME event. We compare the
propagation of fast CMEs and the thermodynamics of CME-driven shocks in
both the 1T and 2T CME simulations. Also, the synthesized white light
images are compared with the Solar and Heliospheric Observatory/Large
Angle and Spectrometric Coronagraph observations. Because there is no
distinction between electron and proton temperatures, heat conduction
in the 1T model creates an unphysical temperature precursor in front
of the CME-driven shock and makes the shock parameters (e.g., shock
Mach number, compression ratio) incorrect. Our results demonstrate
the importance of the electron heat conduction in conjunction with
proton shock heating in order to produce the physically correct CME
structures and CME-driven shocks.
Title: Plasma flow in the outer heliosphere due to variations of
the solar wind structure at 1 AU in 11-year solar cycle
Authors: Provornikova, Elena; Opher, Merav; Izmodenov, Vlad; Toth,
Gabor
Bibcode: 2013shin.confE..67P
Altcode:
Recent observations at Voyager 1 and 2 in the heliosheath - region
of hot subsonic solar wind flow at the heliosphere boundary - show
complex and very different plasma flows. Voyager 2 has been observing
a constant radial flow 110 km/s indicating that the spacecraft is far
from the heliopause. Meanwhile, in 2011 Voyager 1 entered a stagnation
region at 120 AU with small/near-zero flow velocity components meaning
that Voyager 1 may be very close to the HP. Steady state models of the
outer heliosphere do not explain such different flows. These puzzling
observational data motivate us to explore different physical effects
at the edges of the heliosphere in the models. In this work we focus
on time-dependent effects related to 11- year solar cycle. We use a
global 3D MHD multi-fluid model of interaction of the solar wind with
the local interstellar medium with time-dependent boundary conditions
for the supersonic solar wind. Realistic boundary conditions (plasma
density and velocity) at 1 AU were obtained from the measurements of
intensities of Lyman-alpha emission on SOHO/SWAN, OMNI data (in the
ecliptic plane) and interplanetary scintillations data over two full
solar cycles. We present results of the time-dependent model and discuss
effects of realistic variations of the solar wind parameters on the
flow in the heliosheath and in the vicinity of the heliopause. From
comparison of model results with the Voyager 1 and 2 observations we
found that the solar cycle effects can explain constant radial flow
along the Voyager 2 but do not reproduce the decrease of radial flow
to zero seen at Voyager 1.
Title: A slow bow shock ahead of the heliosphere
Authors: Zieger, B.; Opher, M.; Schwadron, N. A.; McComas, D. J.;
Tóth, G.
Bibcode: 2013GeoRL..40.2923Z
Altcode:
Current estimates of plasma parameters in the local interstellar
medium indicate that the speed of the interstellar wind, i.e.,
the relative speed of the local interstellar cloud with respect to
the Sun, is most likely less than both the fast magnetosonic speed
(subfast) and the Alfvén speed (sub-Alfvénic) but greater than
the slow magnetosonic speed (superslow). In this peculiar parameter
regime, MHD theory postulates a slow magnetosonic shock ahead of the
heliosphere, provided that the angle between the interstellar magnetic
field and the interstellar plasma flow velocity is quite small (e.g.,
15° to 30°). In this likely scenario, our multifluid MHD model of
the heliospheric interface self-consistently produces a spatially
confined quasi-parallel slow bow shock. Voyager 1 is heading toward
the slow bow shock, while Voyager 2 is not, which means that the two
spacecraft are expected to encounter different interstellar plasma
populations beyond the heliopause. The slow bow shock also affects
the density and spatial extent of the neutral hydrogen wall.
Title: Simulation of the Coronal Mass Ejection on 2011 March 7:
from Chromosphere to 1 AU
Authors: Jin, Meng; Manchester, Ward; van der Holst, Bart; Oran, Rona;
Sokolov, Igor; Toth, Gabor; Gombosi, Tamas I.; Vourlidas, Angelos;
Liu, Yang; Sun, Xudong
Bibcode: 2013shin.confE...4J
Altcode:
On 2011 March 7, a fast CME (> 2000 km/s) occurred in NOAA
11164. This event is also associated with a Solar Energetic Particle
(SEP) event. In this study, we present the magnetohydrodynamics
simulation results of this event by using the newly developed Alfven
Wave SOlar Model (AWSOM) in Space Weather Modeling Framework (SWMF). The
background solar wind starts from chromosphere with heat conduction
and radiative cooling. The solar wind is driven by Alfven-wave pressure
and heated by Alfven-wave dissipation. The magnetic field of the inner
boundary is specified with a synoptic magnetogram from SDO/HMI. We
initiate the CME by using the Gibson-Low flux rope model. In order to
produce physically correct CME structures and CME-driven shocks, the
electron and proton temperatures are separated so that the electron
heat conduction is explicitly treated in conjunction with proton
shock heating. We simulate the CME propagation to 1 AU. Comprehensive
validation work is done by using the remote as well as the in-situ
observation from SOHO, SDO, STEREOA/B, ACE, and WIND. Our results show
that the new model can reproduce most of the observed features near the
Sun and in the heliosphere. The CME-driven shock is well reproduced,
which is important for modeling the SEP event with diffusive shock
acceleration. We also try to compare the differences and similarities
between this event and previous simulated extreme events (e.g., the
2003 Halloween CMEs).
Title: Time-dependent solar wind flows in the heliosheath
Authors: Provornikova, E.; Opher, M.; Izmodenov, V.; Toth, G.
Bibcode: 2013AGUSMSH21A..02P
Altcode:
Recent observations on Voyager 1 and 2 spacecraft show complex and
very different solar wind flows in the heliosheath region. Voyager
2 has been observing constant radial flows (Richardson and Wang
2013). At the beginning of 2011 Voyager 1 entered a region with zero
and even negative radial velocity of the plasma flow (Krimigis et
al. 2011). Since mid 2012 Voyager 1 continues observing a new region
in the heliosheath with fast changing of intensities of anomalous and
galactic cosmic rays. These puzzling observational data motivate us
to explore different physical effects at the edges of the heliosphere
in the models. In order to separate spatial from temporal effects the
investigation of time-dependent effects are crucial. In this work we
focus on time-dependent effects of the 11-year solar cycle. We use
a global MHD multi-fluid model of interaction of the solar wind with
the local interstellar medium with time-dependent boundary conditions
for the supersonic solar wind. Realistic boundary conditions (plasma
density and velocity) at 1 AU for the plasma were obtained from the
measurements of Ly-alpha intensities on SOHO/SWAN, OMNI data and
interplanetary scintillations data. We present effects of realistic
variations of the solar wind dynamic pressure on the solar wind flow in
the heliosheath and in the vicinity of the heliopause. Comparing the
results of time-dependent model along the Voyager 1 and 2 trajectory
with observational data we describe effects of solar cycle on the
flows that Voyager measures.
Title: Structure of the Heliosheath and Heliopause
Authors: Opher, M.; Drake, J. F.; Swisdak, M. M.; Toth, G.
Bibcode: 2013AGUSMSH24A..06O
Altcode:
We discuss the structure of the heliosheath (HS) and and heliopause (HP)
when reconnection is taken place within the sector region. Observational
constrains of reconnection within the sector are challenged by
the resolution limitations of the magnetometer. However, indirect
constraints such as the lack of conservation of magnetic flux in
the heliosheath (Richardson et al. 2013) and the correlation of the
variability of energetic particles with the sector region (Hill et
al. 2013) indicate that reconnection might be taking place within
the sector (Opher et al. 2011). The reconnected sector region in
high beta plasma has a multitude of islands and is very similar to
a crossing of a normal sector in terms of the overall configuration
of the magnetic field and intensity. However, there is substantial
reduction of magnetic tension. We show, that Rayleigh-Taylor (RT)
instabilities can take place within the sector region where there is
no magnetic tension to stabilize the interchange instability (Opher et
al. 2013). The RT instability produces elongated flow structures that
disturb the heliosheath flow pattern. This instability can explain the
large differences between the flows at Voyager 1 and 2. V1 measurements
indicate a constant decrease in the radial speed until a region with
zero radial speeds while V2 radial speeds are constant. The structure of
the HP has been explored with 2-D PIC simulations (Swisdak et al. 2013)
to understand what underlies the complex particle and magnetic data
seen by V1 in the latter half of 2012. We show using a global MHD
model that because of draping the direction of the magnetic field
in the interstellar medium (ISM) does not differ significantly from
the azimuthal heliospheric field measured in the HS. Magnetic field
profiles from cuts of the MHD simulation across the HP are used as
input into the initial conditions of the PIC simulation. However, the
HS in the PIC simulation is taken to have a sectored structure with a
population of pickup ions.The sectored field reconnects first, forming
magnetic islands with scales of the order of the sector spacing. These
islands then begin reconnecting with the ISM across the HP, slowed
by the higher density plasma in the ISM. The HP eventually develops a
complex magnetic structure with nested magnetic islands where HS and
ISM plasma has mixed. Multiple sharp jumps in the number density of
the ISM plasma are seen in cuts across the HP which is revealed not
as a single boundary but as a series of boundaries. The jumps occur at
separatrices of magnetic islands that exhibit jumps in the population
density but no jumps in the magnetic field direction. This important
result is consistent with the striking absence of rotation of the
magnetic field data seen during jumps in the ACR and GCR intensities
seen by V1. Based on these simulation results and the Voyager magnetic
and particle data we have constructed the possible magnetic structure
of the HP boundary region, which includes a series of nested magnetic
islands and separatrices, that produce a porous boundary. The jump
in the magnetic field strength measured by Voyager on its approach to
the HP very likely arises from the leakage of high pressure HS plasma
across this porous boundary into the ISM where it is lost.
Title: Propagation into the heliosheath of a large-scale solar wind
disturbance bounded by a pair of shocks
Authors: Provornikova, E.; Opher, M.; Izmodenov, V.; Toth, G.
Bibcode: 2013A&A...552A..99P
Altcode: 2013arXiv1303.5105P
Context. After the termination shock (TS) crossing, the Voyager
2 spacecraft has been observing strong variations of the magnetic
field and solar wind parameters in the heliosheath. Anomalous cosmic
rays, electrons, and galactic cosmic rays present strong intensity
fluctuations. Several works suggested that the fluctuations might be
attributed to spatial variations within the heliosheath. Additionally,
the variability of the solar wind in this region is caused by different
temporal events that occur near the Sun and propagate to the outer
heliosphere.
Aims: To understand the spatial and temporal
effects in the heliosheath, it is important to study these effects
separately. In this work we explore the role of shocks as one type
of temporal effects in the dynamics of the heliosheath. Although
currently plasma in the heliosheath is dominated by solar minima
conditions, with increasing solar cycle shocks associated with
transients will play an important role.
Methods: We used a
3D MHD multi-fluid model of the interaction between the solar wind
and the local interstellar medium to study the propagation of a pair
of forward-reverse shocks in the supersonic solar wind, interaction
with the TS, and propagation to the heliosheath.
Results: We
found that in the supersonic solar wind the interaction region between
the shocks expands, the shocks weaken and decelerate. The fluctuation
amplitudes of the plasma parameters vary with heliocentric distance. The
interaction of the pair of shocks with the TS creates a variety of
new waves and discontinuities in the heliosheath, which produce a
highly variable solar wind flow. The collision of the forward shock
with the heliopause causes a reflection of fast magnetosonic waves
inside the heliosheath. A movie is available in electronic form
at http://www.aanda.org
Title: Saturnian Local Time Effects in Titan's Interaction- A
multi-fluid MHD study
Authors: Ma, Yingjuan; Russell, Chris; Nagy, Andrew; Toth, Gabor;
Dougherty, Michele; Cravens, Tom
Bibcode: 2013EGUGA..15.3509M
Altcode:
We use a multi-fluid MHD model to study the effects of Saturnian
Local Time(SLT). The multi-fluid model improves the previously used
7-species single-fluid MHD model by solving the density, velocity and
pressure equations for each of the seven ion fluids. This model allows
the motion of the different ion fluids to be decoupled. The model is
first applied to an idealized case and the results are compared in
detail with that of the 7-species single-fluid MHD model to illustrate
the importance of the multi-fluid effects. Simulation results show
that the multi-fluid model is able to reproduce asymmetric results
along the convection electric field direction. The velocities patterns
are different for different mass ion fluids. The heavier the ion is,
the more significant is the flow along the convection electric field
direction. Also the multi-fluid MHD model predicts that more heavy
ions are escaping from the satellite as compared with the single-fluid
model. We also apply the model to test the effects of SLT and find
that the escaping fluxes of heavy ions vary significantly with SLT.
Title: CRCM + BATS-R-US two-way coupling
Authors: Glocer, A.; Fok, M.; Meng, X.; Toth, G.; Buzulukova, N.;
Chen, S.; Lin, K.
Bibcode: 2013JGRA..118.1635G
Altcode:
We present the coupling methodology and validation of a fully coupled
inner and global magnetosphere code using the infrastructure provided
by the Space Weather Modeling Framework (SWMF). In this model,
the Comprehensive Ring Current Model (CRCM) represents the inner
magnetosphere, while the Block-Adaptive-Tree Solar-Wind Roe-Type
Upwind Scheme (BATS-R-US) represents the global magnetosphere. The
combined model is a global magnetospheric code with a realistic ring
current and consistent electric and magnetic fields. The computational
performance of the model was improved to surpass real-time execution
by the use of the Message Passing Interface (MPI) to parallelize the
CRCM. Initial simulations under steady driving found that the coupled
model resulted in a higher pressure in the inner magnetosphere and an
inflated closed field-line region as compared to simulations without
inner-magnetosphere coupling. Our validation effort was split into two
studies. The first study examined the ability of the model to reproduce
Dst for a range of events from the Geospace Environment Modeling (GEM)
Dst Challenge. It also investigated the possibility of a baseline shift
and compared two approaches to calculating Dst from the model. We
found that the model did a reasonable job predicting Dst and Sym-H
according to our two metrics of prediction efficiency and predicted
yield. The second study focused on the specific case of the 22 July
2009 moderate geomagnetic storm. In this study, we directly compare
model predictions and observations for Dst, THEMIS energy spectragrams,
TWINS ENA images, and GOES 11 and 12 magnetometer data. The model did
an adequate job reproducing trends in the data. Moreover, we found
that composition can have a large effect on the result.
Title: A global multispecies single-fluid MHD study of the plasma
interaction around Venus
Authors: Ma, Y. J.; Nagy, A. F.; Russell, C. T.; Strangeway, R. J.;
Wei, H. Y.; Toth, G.
Bibcode: 2013JGRA..118..321M
Altcode:
This paper reports a new global multispecies single-fluid MHD model that
was recently developed for Venus. This model is similar to the numerical
model that has been successfully applied to Mars. Mass densities of
proton and three important ionospheric ion species (O+,
O2+, and CO2+) are
self-consistently calculated in the model by including related
chemical reactions and ion-neutral collision processes. The simulation
domain covers the region from 100 km altitude above the surface
up to 24 RV in the tail. An adaptive spherical grid
structure is constructed with radial resolution of about 5 km in the
lower ionosphere. Bow shock locations are well reproduced for both
solar-maximum and solar-minimum conditions using appropriate solar wind
parameters for each case. It is shown that the shock locations are
farther from the planet during the solar maximum condition, because
of both the enhanced solar radiation strength and the relatively
small Mach number. The simulation results also agree well with Venus
Express observations, as shown by comparisons between model results
with magnetic fields observed by the spacecraft.
Title: Predicting the time derivative of local magnetic perturbations
with physics based models
Authors: Toth, G.; Meng, X.; Liemohn, M. W.; Gombosi, T. I.
Bibcode: 2012AGUFMSM23C2330T
Altcode:
The Space Weather Prediction Center (SWPC) expressed interest in
predicting the time derivative of the local magnetic field perturbations
(dB/dt). The dB/dt quantity is closely related to the geomagnetically
induced currents (GIC) which is one of the most important quantities
that the end-users of SWPC would like to receive. The Community
Coordinated Modeling Center (CCMC) has run several models for several
events to evaluate the predictive capabilities of the models. It
was clear from the beginning that one cannot hope to predict the
instantaneous value of dB/dt with the current models. For this
reason it was decided that the models will attempt to predict if
some component of dB/dt exceeds or not some threshold values in a
time period. The models showed some success in doing so, and achieved
positive (better than random) skill scores. Here we investigate if one
can improve the efficiency of the prediction further. The idea is that
the magnitude of dB/dt is quite strongly correlated to the magnitude
of the magnetic perturbation dB. Our model, the Space Weather Modeling
Framework, shows significantly better skill scores in predicting the
magnetic perturbation than predicting dB/dt, especially for large
deviations. This suggests that one can use the predicted value of dB
to improve on the prediction accuracy of dB/dt. We find that this is
indeed the case.
Title: Hall MHD Simulations of Comet 67P/Churyumov-Gerasimenko
Authors: Shou, Y.; Combi, M. R.; Rubin, M.; Hansen, K. C.; Toth, G.;
Gombosi, T. I.
Bibcode: 2012AGUFM.P43C1932S
Altcode:
Comets have highly eccentric orbits and a wide range of gas production
rates and thus they are ideal subjects to study the interaction between
the solar wind and nonmagnetized bodies. Hansen et al. (2007, Space
Sci. Rev. 128, 133) used a fluid-based MHD model and a semi-kinetic
hybrid particle model to study the plasma environment of comet
67P/Churyumov-Gerasimenko (CG), the Rosetta mission target comet,
at different heliocentric distances. They showed that for such a
weak comet at a large heliocentric distance, the length scales of the
cometosheath and the bow shock are comparable to or smaller than the ion
gyroradius, which violates the underlying assumption for a valid fluid
description of the plasma. As a result, the classical ideal MHD model
is not able to always give physical results, while the hybrid model,
which accounts for the kinetic effects of ions with both cometary
and solar wind origin, is more reliable. However, hybrid models are
computationally expensive and the results can be noisy. A compromise
approach is Hall MHD [Toth et al., 2008], which includes the Hall
term in the MHD equations and allows for the decoupling of the ion and
electron fluids. We use a single ion species Hall MHD model to simulate
the plasma environment of comet 67P/CG and compare the results with
the two models mentioned above. We find that the Hall effect is capable
of reproducing some features of the hybrid model and thus extends the
applicability of MHD. In addition, this study helps to identify the
conditions and regions in the cometary plasma where the Hall effect
is not negligible. This work is supported by NSF Planetary Astronomy
grant AST0707283 and JPL subcontract 1266313 under NASA grant NMO710889.
Title: Probing the Nature of the Heliosheath with the Heliospheric
Neutral Atom Spectra Measured by IBEX in the Voyager 1 Direction
Authors: Opher, M.; Prested, C. L.; McComas, D. J.; Schwadron, N. A.;
Toth, G.
Bibcode: 2012AGUFMSH13D..04O
Altcode:
The Interstellar Boundary Explorer (IBEX) has been making detailed
observations of neutrals from the boundaries of the heliosphere from
0.2-6 keV. Recent studies using the accumulated measurements of three
years of observations extended the IBEX spectra down to lower energies
(Fusielier et al. ApJ 2012). We compare the modeled ENA spectra to
the ones measured by IBEX in order to explore the sensitivity to the
heliosheath flows and temperatures along the Voyager 1 trajectory. The
models explored are: (a) single-ion, multi-fluid (SI-MF) (Opher
et al. 2009) that includes the ionized thermal plasma (solar wind
plus pick-up ions (PUIs) plus the neutral H atoms) in a multi-fluid
approximation; and our recent model (b) multi-ion, multi-fluid (MI-MF)
that treats the PUIs and the thermal ions as separate fluids with
maxwellian distributions (Prested et al. 2012). The use of a maxwellian
distribution for the transmitted PUIs is supported by works such as
Wu et al. (2010). Additionally, in the modeled ENA spectra we account
for effects, not present in the models, from: a) the zero flows in
the stagnation region (Decker et al. Nature 2012), as from our model
that included the sector region (Opher et al. ApJ 2012) 15-20AU before
the heliopause; b) extra heating in the stagnation region equivalent
to the missing ram pressure; c) extra heating due to reconnection
in the stagnation region (Drake et al. 2010; Opher et al. 2011);
d) kappa ion distribution with power spectra (~ 1.5 - 2.0) in the
heliosheath as produced by models such as Gloeckler and Fisk (2010);
e) kappa ion distribution in the outer heliosheath. We find that the
models that invoked extra heating in the stagnation region (as in case
(b)-(c)) best agree with the low energy IBEX data. We evaluate model
results in terms of the number of free parameters versus the level of
agreement and comment on the implications of the models.
Title: Space Weather Model Validations Using dBH/dt at High and
Mid-Latitude Magnetometer Locations
Authors: Rastaetter, L.; Kuznetsova, M. M.; Pulkkinen, A.; Toth, G.;
Raeder, J.; Wiltberger, M. J.
Bibcode: 2012AGUFMSM23B2305R
Altcode:
As part to the model validation efforts performed at the Community
Coordinated Modeling Center (CCMC), a Research-to-Operation (R2O)
modeling challenge was started in 2010 to investigate the performance of
first-principles and statistical models of the magnetosphere-ionosphere
system to predict magnetic disturbances that can trigger geomagnetically
induced currents. These models have to be able to run in real-time on
a small-sized computer cluster in order to be able to support space
weather operations. The outputs of the models are the horizontal
magnetic perturbations ("delta-BH") at a given list of magnetometer
stations that cover the high, middle and low latitudes. The "R2O
challenge" is a continuation of the 2008 GEM challenge and involves
the Space Weather Modeling Framework (SWMF), the OpenGGCM and the Lyon
Fedder Mobarry (LFM) models of the global magnetosphere-ionosphere
system and the Weimer and Weigel delta-BH specification models. These
5 models have been run for 6 events of at least a day's length that
include 2 strong storms, 3 intermediate sized storms and one weak
event. We compared model outputs with 12 magnetometers that were
selected for the original 2008 GEM challenge. In this paper we describe
the calculation of the delta-BH values for the magnetosphere-ionosphere
models that include currents in the ionosphere, field-aligned currents
and the magnetosphere portions of the simulations. To validate the
calculations performed at CCMC we compared our results to delta-BH
computed during run-time by the Space Weather Modeling Framework (SWMF)
model. We present the role and intensity of the contributions to the
delta-BH signal coming from the three current systems. The evaluation
of the model results is based on an event-based metric using counts of
how often the observed or modeled time derivative of delta-BH ("dBH/dt")
exceeds a threshold at least once in each of the time windows that cover
the storm events. The resulting contingency table (number of hits, false
alarms, misses and predicted non-events) for each threshold value and
window length is converted to a single skill, such as the Heidke Skill
Score that will be used to select models for space weather operations.
Title: The inner magnetosphere as simulated by the anisotropic
BATS-R-US - CRCM model
Authors: Meng, X.; Toth, G.; Glocer, A.; Fok, M. H.; Gombosi, T. I.;
Buzulukova, N.
Bibcode: 2012AGUFMSM41A2191M
Altcode:
We have recently developed the two-way coupling between anisotropic
BATS-R-US and the CRCM. The coupled model provides us an opportunity to
examine the effects of pressure anisotropy on the inner magnetospheric
dynamics self-consistently, especially during geomagnetic disturbed
time. From the aspect of the CRCM, we investigate the differences
between the isotropic-MHD-driven and anisotropic-MHD-driven
simulations. We validate the coupled model through comparing the
simulated pressure anisotropy, energy flux and other model outputs
with TWINS and other satellite observations.
Title: New Adventures with the Space Weather Modeling Framework
Authors: Gombosi, T. I.; Toth, G.; van der Holst, B.; Sokolov, I.;
Manchester, W. B.; Daldorff, L.; DeZeeuw, D.; Welling, D. T.; Ridley,
A. J.; Liemohn, M. W.; Oran, R.; Meng, X.; Jin, M.
Bibcode: 2012AGUFMSM22D..03G
Altcode:
This talk will present new capabilities implemented in the Space Weather
Modeling Framework (SWMF) and new validation studies that were recently
carried out at the University of Michigan. We will focus on four new
developments: 1) the recently developed anisotropic plasma pressure
simulation technique that made it possible to implement a sophisticated
two-way coupling of the CRCM ring current model, 2) the newly developed
solar wind model that starts at the chromosphere and extends beyond
Earth orbit, 3) regional space weather impact modeling capability and 4)
new validation studies using various magnetospheric storms.
Title: Solar wind flow in the heliosheath due to latitudinal and
time variations over the solar cycle
Authors: Provornikova, E.; Opher, M.; Izmodenov, V.; Toth, G.
Bibcode: 2012AGUFMSH11B2203P
Altcode:
Recent observations by Voyager 2 in the heliosheath showed strong
variations of the solar wind density, velocity and temperature. Magnetic
field fluctuates considerably as observed on both Voyager 1 and
2. Anomalous and galactic cosmic rays also present large fluctuations
of intensity. Spatial variations and temporal effects in the solar
wind due to solar cycle attribute to the observed fluctuations. In
this work we aim to explore effects of realistic solar cycle on the 3D
solar wind flow in the outer heliosphere. We use time and latitudinal
variations of the solar wind density and velocity over two last solar
cycles as the boundary conditions in a 3D MHD multi-fluid model of the
interaction between the solar wind and interstellar medium based on
BATSRUS code. These realistic boundary conditions at 1 AU for the plasma
were obtained on the base of the measurements of Ly-alpha intensities
on SOHO/SWAN and interplanetary scintillations data (IPS). In our
simulation a numerical spatial grid is highly refined along the Voyager
2 trajectory in order to capture disturbances propagating in the
solar wind and compare the model with the observations. To validate
the model and used boundary conditions we compare our results with
Voyager 2 plasma data. In particular we focus on the time-dependent
plasma flow in the heliosheath.
Title: Simulate the Coronal Mass Ejection on 2011 March 7 from
Chromosphere to 1 AU
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Oran, R.;
Sokolov, I.; Toth, G.; Gombosi, T. I.; Vourlidas, A.; Liu, Y.; Sun, X.
Bibcode: 2012AGUFMSH33E..04J
Altcode:
On 2011 March 7, a fast CME (> 2000 km/s) occurred in NOAA
11164. This event is also associated with a Solar Energetic Particle
(SEP) event. In this study, we present the magnetohydrodynamics
simulation results of this event. We initiate the CME by using the
Titov-Demoulin flux rope model. The background solar wind starts
from chromosphere with heat conduction and radiative cooling. The
solar wind is driven by Alfven-wave pressure and heated by Alfven-wave
dissipation. The magnetic field of the inner boundary is specified with
a synoptic magnetogram from SDO/HMI. In order to produce the physically
correct CME structures and CME-driven shocks, the electron and proton
temperatures are separated so that the electron heat conduction
is explicitly treated in conjunction with proton shock heating. We
simulate the CME propagation to 1 AU. A comprehensive validation work
is done by using the remote as well as the in-situ observation from
SOHO, STEREOA/B, ACE, and WIND. Our result shows that the new model
can reproduce most of the observed features near the Sun and in the
heliosphere. The CME-driven shock is well reproduced, which is important
for modeling the SEP event with diffusive shock acceleration.
Title: Solar wind interaction with Mars Upper atmosphere: Results
from the one-way coupling between the Multi-fluid MHD model and the
M-TGCM model
Authors: Dong, C.; Bougher, S. W.; Ma, Y.; Toth, G.; Nagy, A. F.;
Brain, D. A.; Najib, D.
Bibcode: 2012AGUFM.P21G..02D
Altcode:
The study of the solar wind interaction with Mars upper
atmosphere/ionosphere has triggered great interest in recent
years. Among the large number of topics in this research area, the
investigation of ion escape rates has become increasingly important due
to its potential impact on the long-term evolution of Mars atmosphere
(e.g., loss of water) over its history. In the present work, we adopt
the 3D Mars neutral atmosphere profiles from the well-regarded Mars
Thermospheric Global Circulation Model (M-TGCM) and one-way couple it
with the 3D BATS-R-US Mars multi-fluid MHD model that solves separate
momentum equations for each ion species. The M-TGCM model takes into
account the effects of the solar cycle (solar minimum: F10.7=70 and
solar maximum: F10.7=200 with equinox condition: Ls=0), allowing
us to investigate the effects of the solar cycle on the Mars upper
atmosphere ion escape by using a one-way coupling, i.e., the M-TGCM
model outputs are used as inputs for the multi-fluid MHD model. A case
for solar maximum with extremely high solar wind parameters is also
investigated to estimate how high the escape flux can be for such an
extreme case. Moreover, the ion escape flux along a satellite trajectory
will be studied. This has the potential to provide predictions of ion
escape rates for comparison to future data to be returned by the MAVEN
mission (2012-2016). In order to make the code run more efficiently,
we adopt a more appropriate grid structure compared to the one used
previously. This new grid structure will benefit us to investigate
the effects of some dynamic events (such as CME and dust storm) on
the ion escape flux.
Title: Multi-fluid MHD study of Titan's plasma interaction
Authors: Ma, Y.; Russell, C. T.; Nagy, A. F.; Toth, G.; Dougherty,
M. K.; Cravens, T. E.
Bibcode: 2012AGUFMSM32B..06M
Altcode:
We study the plasma interaction around Titan using a three dimensional
multi-fluid MHD model. The model calculates densities, velocities,
and pressures of seven ion species which are important in either
Titan's ionosphere or in the ambient plasma. The code uses a
spherical grid structure with high radial resolution ~ 30 km in the
lower ionosphere. The model is applied to an idealized case of Titan
and the results are compared in detail with that of multi-species but
single fluid model using the same set of plasma parameters. It is shown
that the multi-fluid model is able to produce the flow separation of
different ion fluids along the convection electric field direction. Also
the multi-fluid model is in favor of the escape of the heavier ion
species. The multi-fluid MHD model is also applied to a recent Titan
flyby and compared with plasma observations of Cassini.
Title: Multi-Scale Simulations of Magnetospheric Dynamics for Steady
Solar Wind Driving
Authors: Kuznetsova, M.; Rastaetter, L.; Glocer, A.; Hesse, M.; Toth,
G.; Gombosi, T. I.
Bibcode: 2012AGUFMSM21E..03K
Altcode:
The variety of magnetopsheric convection patterns for steady solar wind
conditions is one of the major challenges in undertanding underlying
mechanisms driving the magnetopshere. We utilize the multi-scale
and multi-species global MHD code BATSRUS to analyse the relative
contribution of solar wind conditions, ionosphere conductance pattern,
plasma composition in inner magnetosphere and local conditions at
the reconnection sites on the global magnetosphere dynamics. The
primary mechanism controlling the dissipation in the vicinity of the
reconnection site is incorporated into MHD description in terms of
non-gyrotropic corrections to induction and energy equations. The
non-gyrotropic terms reflecting ion kinetic effects depend on the
local plasma and field parameters and ion Larmor radii. The varying
plasma composition is incorporated into the multi-species description
through the effective ion mass. Transitions between different modes
of convection will be analysed.
Title: Viscosity in Global Magnetosphere Simulations
Authors: Daldorff, L.; Toth, G.; Meng, X.; Gombosi, T. I.
Bibcode: 2012AGUFMSM21B2280D
Altcode:
The multiple scales involved in the magnetic reconnection process
give rise to many instabilities. Unfortunately we are not able to
capture these processes with today's global magnetosphere models. The
mixing of the unstable regions can behave in a "viscous" fashion on
larger scales. We therefore implemented viscosity into the BATS-R-US
global magnetohydrodynamic code to look at how numerical and physical
viscosity will influence the global magnetosphere simulations in
addition to magnetic dissipation. Our long term goal is to obtain
physically reasonable approximations of reconnection on large scales
that do not depend on the grid resolution and numerical dissipation.
Title: Does a slow magnetosonic bow shock exist in the local
interstellar medium?
Authors: Zieger, B.; Opher, M.; Schwadron, N. A.; McComas, D. J.;
Toth, G.
Bibcode: 2012AGUFMSH11B2200Z
Altcode:
The currently accepted best estimates of plasma parameters in the
local interstellar medium suggest that the speed of the interstellar
wind (i.e. the relative speed of the local interstellar cloud with
respect to the Sun) is very slow (i.e., sub-Alfvenic; Opher et al.,
Science, 2009; Schwadron et al., ApJ, 2011). This means that no fast
magnetosonic bow shock can be formed in the local interstellar medium
upstream of the heliosphere, [McComas et al., Science, 2012]. However,
the existence of a slow magnetosonic bow shock may be possible. With
current LISM parameters, the Mach number for upstream propagating slow
magnetosonic waves in the pristine LISM is ~2.1, which suggests that a
weak quasi-parallel slow bow shock (SBS) in front of our heliopshere
may exist in some regions. Our new multi-ion, multi-fluid MHD model
of the heliospheric interface [Prested et al., ApJ, 2012] produces
such a slow magnetosonic bow shock only in the quasi-parallel region
where theta_Bn (i.e. the angle between the interstellar magnetic field
and the normal to the slow magnetosonic surface; SMS) is less than
45 degrees. The SBS divides the LISM into two distinct regions with
different plasma populations. One is the pristine LISM and the other
is the hotter and slower compressed plasma population of the outer
heliosheath that is spatially restricted to the downstream region of
the quasi-parallel shock. Slow magnetosonic shocks are generally not
observed in space plasmas due to their lack of stability. However,
the plasma in the local interstellar medium exists in a regime not
commonly observed in interplanetary space. We discuss the possible
existence of the magnetosonic bow shock in front of the heliosphere,
the arguments for and against its stability, and its implications for
heliospheric measurements.
Title: Multi-ion, multi-fluid 3-D magnetohydrodynamic simulation of
the outer heliosphere
Authors: Prested, Christina; Opher, Merav; Toth, Gabor
Bibcode: 2012arXiv1211.1908P
Altcode:
Data from the Voyager probes and the Interstellar Boundary Explorer
have revealed the importance of pick-up ions (PUIs) in understanding
the character and behavior of the outer heliosphere, the region of
interaction between the solar wind and the interstellar medium. In
the outer heliosphere PUIs carry a large fraction of the thermal
pressure, which effects the nature of the termination shock, and
they are a dominate component of pressure in the heliosheath. This
paper describes the development of a new multi-ion, multi-fluid 3-D
magnetohydrodynamic model of the outer heliosphere. This model has the
added capability of tracking the individual fluid properties of multiple
ion populations. For this initial study two ion populations are modeled:
the thermal solar wind ions and PUIs produced in the supersonic solar
wind. The model also includes 4 neutral fluids that interact through
charge-exchange with the ion fluids. The new multi-ion simulation
reproduces the significant heating of PUIs at the termination shock,
as inferred from Voyager observations, and provides properties of PUIs
in the 3-D heliosheath. The thinning of the heliosheath due to the loss
of thermal energy in the heliosheath from PUI and neutral interaction is
also quantified. In future work the multi-ion, multi-fluid model will
be used to simulate energetic neutral atom (ENA) maps for comparison
with the Interstellar Boundary Explorer, particularly at PUI energies
of less than 1 keV.
Title: TwoDSSM: Self-gravitating 2D shearing sheet
Authors: Gammie, Charles F.; McKinney, Jonathan C.; Noble, Scott C.;
Tóth, Gábor; Del Zanna, Luca
Bibcode: 2012ascl.soft10025G
Altcode:
TwoDSSM solves the equations of self-gravitating hydrodynamics in
the shearing sheet, with cooling. TwoDSSM is configured to use a
simple, exponential cooling model, although it contains code for a
more complicated (and perhaps more realistic) cooling model based on a
one-zone vertical model. The complicated cooling model can be switched
on using a flag.
Title: A Numerical Study of Comet Mcnaught over a Wide Range of
Heliocentric Distances
Authors: Shou, Yinsi; Combi, M. R.; Rubin, M.; Toth, G.
Bibcode: 2012DPS....4431412S
Altcode:
A numerical study of Comet McNaught over a wide range of heliocentric
distances Yinsi Shou, Michael R. Combi, Martin Rubin, Gabor Toth The
Comet C/2006 P1 (McNaught) has a small perihelion distance (0.17 AU)
and had a very high production rate during its passage close to the Sun
in January and February of 2007. During that period, it was monitored by
both ground- and space-based observatories, which provided substantial
information about the comet. In early February, the Ulysses spacecraft
encountered its ion tail and gave clues to the surrounding solar wind
conditions and to the cometary environment. Therefore, Comet McNaught
is an ideal object to study the cometary structures under extreme
conditions and the solar wind-comet interaction over a wide range of
heliocentric distances. A numerical study of Comet McNaught combining
two models is conducted. First, a single species magnetohydrodynamics
(MHD) [Gombosi et al. (1996, JGR 101, 15233)] simulation is performed
using a set of ‘observed’ comet parameters as input. Then a
chemistry model [Häberli et al. (1997, Icarus 130, 373)] extracts
the streamlines from the MHD model and calculates the densities of
different species accounting for photo-dissociation, photo-ionization,
electron recombination, ion-molecule and charge-exchange reactions. The
MHD results are able to give the diamagnetic cavity sizes and shock
distances at various heliocentric distances while the chemistry model
better resolves the distribution of the major chemical species in the
cometary plasma environment. The combination of the two models allows
us to obtain detailed information on the chemical composition of a
much wider range of atoms and molecules compared to multi-species or
multi-fluid MHD models and at much lower computational expense. Some
preliminary results are presented and discussed. This work has been
partially supported by grant AST-0707283 from the NSF Planetary
Astronomy program and NASA Planetary Atmospheres program grant
NNX09AB59G.
Title: HARM: A Numerical Scheme for General Relativistic
Magnetohydrodynamics
Authors: Gammie, Charles F.; McKinney, Jonathan C.; Tóth, Gábor
Bibcode: 2012ascl.soft09005G
Altcode:
HARM uses a conservative, shock-capturing scheme for evolving the
equations of general relativistic magnetohydrodynamics. The fluxes are
calculated using the Harten, Lax, & van Leer scheme. A variant of
constrained transport, proposed earlier by Tóth, is used to maintain a
divergence-free magnetic field. Only the covariant form of the metric
in a coordinate basis is required to specify the geometry. On smooth
flows HARM converges at second order.
Title: Do Corotating Interaction Region Associated Shocks Survive
When They Propagate into the Heliosheath?
Authors: Provornikova, E.; Opher, M.; Izmodenov, V.; Toth, G.
Bibcode: 2012ApJ...756L..37P
Altcode:
During the solar minimum at the distance of 42-52 AU from the Sun,
Voyager 2 observed recurrent sharp, shock-like increases in the
solar wind speed that look very much like forward shocks (Lazarus
et al.). The shocks were produced by corotating interaction regions
(CIRs) that originated near the Sun. After the termination shock
(TS) crossing in 2007, Voyager 2 entered the heliosheath and
has been observing the plasma emanated during the recent solar
minima. Measurements show high variable flow, but there were no
shocks detected in the heliosheath. When CIR-driven shocks propagate
to the outer heliosphere, their structure changes due to collision
and merging processes of CIRs. In this Letter, we explore an effect
of the merging of CIRs on the structure of CIR-associated shocks. We
use a three-dimensional MHD model to study the outward propagation of
the shocks with characteristics similar to those observed by Voyager 2
at ~45 AU (Lazarus et al. 1999). We show that due to merging of CIRs
(1) reverse shocks disappear, (2) forward shocks become weaker due
to interaction with rarefaction regions from preceding CIRs, and (3)
forward shocks significantly weaken in the heliosheath. Merged CIRs
produce compression regions in the heliosheath with small fluctuations
of plasma parameters. Amplitudes of the fluctuations diminish as
they propagate deeper in the sheath. We conclude that interaction
of shocks and rarefaction regions could be one of the explanations,
why shocks produced by CIRs are not observed in the heliosheath by
Voyager 2 while they were frequently observed upstream the TS.
Title: The Coupled Evolution of Electrons and Ions in Coronal Mass
Ejection-driven shocks
Authors: Manchester, W. B., IV; van der Holst, B.; Tóth, G.; Gombosi,
T. I.
Bibcode: 2012ApJ...756...81M
Altcode:
We present simulations of coronal mass ejections (CMEs) performed with
a new two-temperature coronal model developed at the University of
Michigan, which is able to address the coupled thermodynamics of the
electron and proton populations in the context of a single fluid. This
model employs heat conduction for electrons, constant adiabatic index
(γ = 5/3), and includes Alfvén wave pressure to accelerate the solar
wind. The Wang-Sheeley-Arge empirical model is used to determine the
Alfvén wave pressure necessary to produce the observed bimodal solar
wind speed. The Alfvén waves are dissipated as they propagate from
the Sun and heat protons on open magnetic field lines to temperatures
above 2 MK. The model is driven by empirical boundary conditions that
includes GONG magnetogram data to calculate the coronal field, and
STEREO/EUVI observations to specify the density and temperature at
the coronal boundary by the Differential Emission Measure Tomography
method. With this model, we simulate the propagation of fast CMEs and
study the thermodynamics of CME-driven shocks. Since the thermal speed
of the electrons greatly exceeds the speed of the CME, only protons
are directly heated by the shock. Coulomb collisions low in the corona
couple the protons and electrons allowing heat exchange between the
two species. However, the coupling is so brief that the electrons never
achieve more than 10% of the maximum temperature of the protons. We find
that heat is able to conduct on open magnetic field lines and rapidly
propagates ahead of the CME to form a shock precursor of hot electrons.
Title: Multi-fluid MHD study of the solar wind interaction with
Venus at Solar max and Solar min conditions.
Authors: Ma, Y. J.; Nagy, A. F.; Russell, C. T.; Najib, D.; Toth, G.
Bibcode: 2012epsc.conf..137M
Altcode: 2012espc.conf..137M
We study the solar wind interaction with Venus, using a new advanced
multi-fluid MHD model that has been developed recently. The model is
similar to the numerical model that was successfully applied to Mars
(Najib et al., 2011). Mass densities, velocities and pressures of the
protons and three important ionosphere ion species (O+, O2+ and CO2+)
are self-consistently calculated by solving the individual coupled
continuity, momentum and energy equations. The various chemical
reactions and ion-neutral collision processes are considered in the
model. The simulation domain covers the region from 100 km altitude
above the surface up to 16 RV in the tail. An adaptive spherical
grid structure is constructed with radial resolution of about 10 km
in the lower ionosphere. The model is applied to both solar-maximum
and solar-minimum conditions and model results are compared in detail
with multi-species single fluid model results and VEX observations.
Title: Test of the weak cosmic censorship conjecture with a charged
scalar field and dyonic Kerr-Newman black holes
Authors: Tóth, Gábor Zsolt
Bibcode: 2012GReGr..44.2019T
Altcode: 2012GReGr.tmp...85T; 2011arXiv1112.2382Z
A thought experiment considered recently in the literature, in which
it is investigated whether a dyonic Kerr-Newman black hole can be
destroyed by overcharging or overspinning it past extremality by a
massive complex scalar test field, is revisited. Another derivation of
the result that this is not possible, i.e. the weak cosmic censorship
is not violated in this thought experiment, is given. The derivation
is based on conservation laws, on a null energy condition, and on
specific properties of the metric and the electromagnetic field of
dyonic Kerr-Newman black holes. The metric is kept fixed, whereas
the dynamics of the electromagnetic field is taken into account. A
detailed knowledge of the solutions of the equations of motion is
not needed. The approximation in which the electromagnetic field
is fixed is also considered, and a derivation for this case is also
given. In addition, an older version of the thought experiment, in
which a pointlike test particle is used, is revisited. The same result,
namely the non-violation of the cosmic censorship, is rederived in a
way which is simpler than in earlier works.
Title: Pressure anisotropy in global magnetospheric simulations:
A magnetohydrodynamics model
Authors: Meng, X.; Tóth, G.; Liemohn, M. W.; Gombosi, T. I.; Runov, A.
Bibcode: 2012JGRA..117.8216M
Altcode: 2012JGRA..11708216M
In order to better describe the space plasmas where pressure anisotropy
has prominent effects, we extend the BATS-R-US magnetohydrodynamics
(MHD) model to include anisotropic pressure. We implement the
anisotropic MHD equations under the double adiabatic approximation with
an additional pressure relaxation term into BATS-R-US and perform global
magnetospheric simulations. The results from idealized magnetospheric
simulations confirm previous studies: pressure anisotropy widens the
magnetosheath, increases the density depletion in the vicinity of the
magnetopause, enhances the nightside plasma pressure, and introduces an
eastward ring current. In addition, we find that the flow speed in the
magnetotail is significantly reduced by including pressure anisotropy
in MHD simulations. Our model is validated through comparing the
simulations to the THEMIS data on both the dayside and nightside of
the magnetosphere during quiet times. The comparison to the results
from isotropic MHD simulations implies that although anisotropic MHD
is comparable to isotropic MHD in matching the measurement, it improves
the simulated plasma velocity in some cases.
Title: What did we learn about the 3D Global Structure of the
Heliosphere with Voyager and IBEX
Authors: Opher, Merav; Provornikova, Elena; Toth, Gabor; Drake, James;
Swisdak, Marc; Izmodenov, Vladislav
Bibcode: 2012cosp...39.1407O
Altcode: 2012cosp.meet.1407O
In this talk I will review what we have learned in the past couple
of years about the global structure of the heliosphere. The recent
measurements in-situ by the Voyager spacecrafts, combined with the
all-sky images of the heliospheric boundaries by the Interstellar
Boundary Explorer (IBEX) mission have transformed radically our
knowledge of the boundaries of the heliosphere. Concepts that resisted
decades are being revisited due to their puzzling measurements. In
this talk, I will cover some of these puzzles and what are learning
regarding the dynamic nature of the heliosphere and heliosheath. When
uncovering the structure of the heliosheath it is crucial to separate
spatial from temporal variations. We were fortunate that the extended
solar minima conditions minimized temporal effects in the heliosphere
and allowed us to uncover the spatial variations. With the increased
solar activity becomes a challenge to incorporate temporal effects. I
will review some of the puzzled observations of by Voyager spacecraft in
the heliosheath indicating that the presence of the heliospheric current
sheet might play a crucial role on organizing the heliosheath; affecting
both the flows and transport of energetic particles. I will review
as well our attempts to estimate the temporal effects that Corotating
Interacting Regions have in the heliosheath. Finally, I will address how
knowledge gained from missions such as Ulysses and future out of the
ecliptic mission concepts as well as theoretical analysis of physical
parameters that may be observed from the solar polar orbit will allow
us a better understanding of the global structure of the heliosphere,
in particular with its interaction with the interstellar medium.
Title: VAC: Versatile Advection Code
Authors: Tóth, Gábor; Keppens, Rony
Bibcode: 2012ascl.soft07003T
Altcode:
The Versatile Advection Code (VAC) is a freely available general
hydrodynamic and magnetohydrodynamic simulation software that works in
1, 2 or 3 dimensions on Cartesian and logically Cartesian grids. VAC
runs on any Unix/Linux system with a Fortran 90 (or 77) compiler and
Perl interpreter. VAC can run on parallel machines using either the
Message Passing Interface (MPI) library or a High Performance Fortran
(HPF) compiler.
Title: 3D Global Structure of the Heliosheath with the Sector Region
Authors: Opher, Merav; Toth, Gabor; Drake, James; Swisdak, Marc
Bibcode: 2012cosp...39.1406O
Altcode: 2012cosp.meet.1406O
No abstract at ADS
Title: Magnetohydrodynamics with Anisotropic Ion Pressure
Authors: Meng, X.; Tóth, G.; Gombosi, T. I.
Bibcode: 2012ASPC..459..340M
Altcode:
To simulate the pressure anisotropy of space plasmas, we extended the
global magnetohydrodynamics (MHD) model BATS-R-US based on the study
of MHD with anisotropic ion pressure and isotropic electron pressure
under both the classical and semirelativistic approximation. We
derived the characteristic wave speeds for determining time steps and
calculating numerical fluxes. Simulations of the Earth's magnetosphere
validated the model's ability to reproduce the pressure anisotropy in
the magnetosheath.
Title: MHD Modeling of Solar Wind Interaction with Mars
Authors: Ma, Yingjuan; Russell, C. T.; Najib, Dalal; Nagy, Andrew;
Toth, Gabor
Bibcode: 2012cosp...39.1139M
Altcode: 2012cosp.meet.1139M
No abstract at ADS
Title: Simulating radiative shocks in nozzle shock tubes
Authors: van der Holst, B.; Tóth, G.; Sokolov, I. V.; Daldorff,
L. K. S.; Powell, K. G.; Drake, R. P.
Bibcode: 2012HEDP....8..161V
Altcode: 2011arXiv1109.4332V
We use the recently developed Center for Radiative Shock Hydrodynamics
(CRASH) code to numerically simulate laser-driven radiative shock
experiments. These shocks are launched by an ablated beryllium disk
and are driven down xenon-filled plastic tubes. The simulations
are initialized by the two-dimensional version of the Lagrangian
Hyades code which is used to evaluate the laser energy deposition
during the first 1.1 ns. Later times are calculated with the CRASH
code. CRASH solves for the multi-material hydrodynamics with separate
electron and ion temperatures on an Eulerian block-adaptive-mesh
and includes a multi-group flux-limited radiation diffusion and
electron thermal heat conduction. The goal of the present paper is to
demonstrate the capability to simulate radiative shocks of essentially
three-dimensional experimental configurations, such as circular and
elliptical nozzles. We show that the compound shock structure of
the primary and wall shock is captured and verify that the shock
properties are consistent with order-of-magnitude estimates. The
synthetic radiographs produced can be used for comparison with future
nozzle experiments at high-energy-density laser facilities.
Title: Modeling of heliosphere and magnetic reconnection in the
heliosheath
Authors: Opher, Merav; Drake, Jim; Swisdak, Marc; Schoeffller, Kevin;
Toth, Gabor
Bibcode: 2012shin.confE..53O
Altcode:
The recent measurements in-situ by the Voyager spacecrafts,
combined with the all-sky images of the heliospheric boundaries by
the Interstellar Boundary Explorer (IBEX) mission have transformed
radically our knowledge of the boundaries of the heliosphere. Concepts
that resisted decades are being revisited due to their puzzling
measurements. In particular after the crossing of the termination
shock (TS) by V1 and then by V2, one of the first surprises was that
both Voyager found no evidence for the acceleration of the anomalous
cosmic rays at the TS as expected for approximately 25 years. Another
challenge are the energetically particles intensities that are
dramatically different at Voyager 1 and 2. In this talk I will review
the state-of-the art of numerical modeling of the global heliosphere as
well as our recent model that propose that reconnection is happening in
the heliosheath within the sector region. All current global models of
the heliosphere are based on the assumption that the magnetic field in
the heliosheath is laminar. Recently, we proposed that the annihilation
of the 'sectored' magnetic field within the heliosheath as it is
compressed on its approach to the heliopause produces anomalous cosmic
rays and also energetic electrons. As a product of the annihilation
of the sectored magnetic field, densely packed magnetic islands (which
further interact to form magnetic bubbles) are produced. These magnetic
islands/bubbles will be convected with ambient flows as the sector
region is carried to higher latitudes filling the heliosheath. As
a result, the magnetic field in the heliosheath sector region will
be disordered. I will review results from our three-dimensional MHD
simulation for the first time included self-consistently the sector
region and particle-in-cells simulations that followed the kinetic
evolution of the reconnection of the multiple current sheets. We show
that due to the high pressure of the interstellar magnetic field
a north-south asymmetry develops such that the disordered sectored
region fills a large portion of the northern part of the heliosphere
with a smaller extension in the southern hemisphere. I will review
observations that support this scenario indicating that the presence of
the heliospheric current sheet, where the magnetic field reconnected
might play a crucial role on organizing the heliosheath; affecting
both the flows and transport of energetic particles.
Title: Simulating the long-term evolution of radiative shocks in
shock tubes
Authors: van der Holst, B.; Toth, G.; Sokolov, I. V.; Torralva, B. R.;
Powell, K. G.; Drake, R. P.
Bibcode: 2012arXiv1206.1370V
Altcode:
We present the latest improvements in the Center for Radiative Shock
Hydrodynamics (CRASH) code, a parallel block-adaptive-mesh Eulerian
code for simulating high-energy-density plasmas. The implementation can
solve for radiation models with either a gray or a multigroup method
in the flux-limited-diffusion approximation. The electrons and ions are
allowed to be out of temperature equilibrium and flux-limited electron
thermal heat conduction is included. We have recently implemented
a CRASH laser package with 3-D ray tracing, resulting in improved
energy deposition evaluation. New, more accurate opacity models are
available which significantly improve radiation transport in materials
like xenon. In addition, the HYPRE preconditioner has been added to
improve the radiation implicit solver. With this updated version of
the CRASH code we study radiative shock tube problems. In our set-up,
a 1 ns, 3.8 kJ laser pulse irradiates a 20 micron beryllium disk,
driving a shock into a xenon-filled plastic tube. The electrons emit
radiation behind the shock. This radiation from the shocked xenon
preheats the unshocked xenon. Photons traveling ahead of the shock
will also interact with the plastic tube, heat it, and in turn this
can drive another shock off the wall into the xenon. We are now able
to simulate the long term evolution of radiative shocks.
Title: Sensitivity of ENA emission to various plasma properties in
the outer heliosphere: insight from MHD models
Authors: Prested, Christina Lee; Opher, M.; Toth, G.; Schwadron, N.
Bibcode: 2012shin.confE..52P
Altcode:
Using our new 3D multi-ion, multi-fluid MHD model of the outer
heliosphere, we probe the nature of energetic neutral atom (ENA)
emission in the heliosheath. How does ENA emission vary through the
heliosheath and what properties of the plasma and neutrals is it
most sensitive to? Where are the majority of ENA's produced and how
does this insight affect our interpretation of the IBEX all-sky ENA
maps? From this analysis we begin to answer these questions and engage
in a dialogue on linking the MHD models of the outer heliosphere with
the IBEX ENA maps.
Title: How does merging of CIRs affect shocks in the outer
heliosphere?
Authors: Provornikova, Elena; Opher, Merav; Izmodenov, Vlad; Toth,
Gabor
Bibcode: 2012shin.confE..56P
Altcode:
Observations of the solar wind in the outer heliosphere by Voyager 2
exhibit many examples of shocks. During the solar minimum in 1994-1997
near the distance 45 AU from the Sun Voyager 2 observed recurrent
shocks and shock-like structures that were produced by corotating merged
interaction regions. Measurements of the heliosheath plasma, emanated
during the recent solar minima, do not show existence of shocks in the
heliosheath. We explore an effect of merging of corotating interaction
regions (CIRs) in the solar wind on the structure of CIR associated
shocks. Using a 3D MHD model of the solar wind interaction with the
local interstellar medium, we show that due to interaction of shocks
and rarefaction waves in a process of merging of CIRs, the shocks
strongly weaken in the outer heliosphere. Presented study suggests
that merging process could be one of the explanations why Voyager
2 did not observe CIR associated shocks in the heliosheath while it
showed several examples of shocks in the solar wind upstream the TS.
Title: Numerical Simulations of Coronal Mass Ejection on 2011 March 7:
One-Temperature and Two-Temperature Model Comparison
Authors: Jin, Meng; Manchester, W. B.; van der Holst, B.; Oran, R.;
Sokolov, I.; Toth, G.; Gombosi, T. I.
Bibcode: 2012shin.confE..42J
Altcode:
During Carrington Rotation 2107, a fast CME (> 2000 km/s) occurred
in NOAA 11164. This event is also associated with a Solar Energetic
Particle (SEP) event. In this study, we present simulations of this
CME with one-temperature (1T) and two-temperature ( 2T: coupled
thermodynamics of the electron and proton populations) models. Both
the 1T and 2T models start from chromosphere with heat conduction
and radiative cooling. The background solar wind is driven by
Alfven-wave pressure and heated by Alfven-wave dissipation in which
the counter-propagating waves are included. The magnetic field of the
inner boundary is set up using the magnetogram from SDO/HMI. The Titov
Demoulin flux-rope model is used to initiate the CME event. We compare
the propagation of fast CMEs and the thermodynamics of CME-driven
shocks in both the 1T and 2T CME simulations. Our results emphasize
the importance of the explicit treatment of electron heat conduction
in conjunction with proton shock heating in the CME simulation in order
to produce the physically correct CME structures and CME-driven shocks.
Title: Near the Boundary of the Heliosphere: A Flow Transition Region
Authors: Opher, M.; Drake, J. F.; Velli, M.; Decker, R. B.; Toth, G.
Bibcode: 2012ApJ...751...80O
Altcode:
Since April of 2010, Voyager 1 has been immersed in a region of near
zero radial flows, where the solar wind seems to have stopped. The
existence of this region contradicts current models that predict
that the radial flows will go to zero only at the heliopause. These
models, however, do not include the sector region (or include it in
a kinematic fashion), where the solar magnetic field periodically
reverses polarity. Here we show that the presence of the sector region
in the heliosheath, where reconnection occurs, fundamentally alters
the flows, giving rise to a Flow Transition Region (FTR), where the
flow abruptly turns and the radial velocity becomes near zero or
negative. We estimate, based on a simulation, that at the Voyager 1
location, the thickness of the FTR is around 7-11 AU.
Title: Magnetospheric configuration and dynamics of Saturn's
magnetosphere: A global MHD simulation
Authors: Jia, Xianzhe; Hansen, Kenneth C.; Gombosi, Tamas I.; Kivelson,
Margaret G.; Tóth, Gabor; DeZeeuw, Darren L.; Ridley, Aaron J.
Bibcode: 2012JGRA..117.5225J
Altcode: 2012JGRA..11705225J
We investigate the solar wind interaction with Saturn's magnetosphere by
using a global magnetohydrodynamic simulation driven by an idealized
time-varying solar wind input that includes features of Corotating
Interaction Regions typically seen at Saturn. Our model results indicate
that the compressibility of Saturn's magnetosphere is intermediate
between the Earth's and Jupiter's, and the magnetopause location
appears insensitive to the orientation of the interplanetary magnetic
field. The modeled dependences of both the magnetopause and bow shock
locations on the solar wind dynamic pressure agree reasonably well
with those of data-based empirical models. Our model shows that
the centrifugal acceleration of mass-loaded flux tubes leads to
reconnection on closed field lines forming plasmoids, an intrinsic
process (“Vasyliūnas-cycle”) in Saturn's magnetosphere taking
place independent of the external conditions. In addition, another type
of reconnection process involving open flux tubes (“Dungey-cycle”)
is also seen in our simulation when the external condition is favorable
for dayside reconnection. Under such circumstances, plasmoid formation
in the tail involves reconnection between open field lines in the lobes,
producing stronger global impacts on the magnetosphere and ionosphere
compared to that imposed by the Vasyliūnas-cycle directly. Our
model also shows that large-scale tail reconnection may be induced
by compressions driven by interplanetary shocks. In our simulation,
large-scale tail reconnection and plasmoid formation take place in a
quasi-periodic manner but the recurrence rate tends to be higher as the
dynamic pressure becomes higher. While large-scale plasmoid release
clearly is an important process in controlling the magnetospheric
dynamics, it appears insufficient to account for all the losses of
plasma added by the magnetospheric sources. We find that a large
fraction of the planetary plasma is lost through the magnetotail
near the flanks probably through relatively small-scale plasmoids,
a situation that may also exist at Jupiter.
Title: Multi-fluid MHD study of the solar wind interaction with
Venus at Solar max and Solar min conditions
Authors: Ma, Y.; Nagy, A. F.; Russell, C. T.; Najib, D.; Toth, G.
Bibcode: 2012EGUGA..1411974M
Altcode:
We study solar wind interaction with Venus using a new advanced
multi-fluid MHD model that has recently been developed. The model
is similar to the numerical model that was successfully applied to
Mars (Najib et al., 2011). Mass densities, velocities and pressures
of the protons and major ionosphere ion species (O+, O2+ and CO2+)
are self-consistently calculated by solvng the individual coupled
continuity, momentum and energy equations. The various chemical
reactions and ion-neutral collision processes are considered in the
model. The simulation domain covers the region from 100 km altitude
above the surface up to 16 RV in the tail. An adaptive spherical
grid structure is constructed with radial resolution of about 10 km
in the lower ionosphere. The model is applied to both solar-maximum
and solar-minimum conditions and model results are compared in detail
with multi-species single fluid model results and observations.
Title: Kinetic model of the inner magnetosphere with arbitrary
magnetic field
Authors: Ilie, Raluca; Liemohn, Michael W.; Toth, Gabor; Skoug, Ruth M.
Bibcode: 2012JGRA..117.4208I
Altcode: 2012JGRA..11704208I
Theoretical and numerical modifications to an inner magnetosphere
model—Hot Electron Ion Drift Integrator (HEIDI)—were
implemented, in order to accommodate for a nondipolar arbitrary
magnetic field. While the dipolar solution for the geomagnetic
field during quiet times represents a reasonable assumption in the
near-Earth closed field region, during storm activity this assumption
becomes invalid. HEIDI solves the time-dependent, gyration- and
bounce-averaged kinetic equation for the phase space density of
one or more ring current species. New equations are derived for the
bounce-averaged coefficients for the distribution function, and their
numerical implementation is discussed. Also, numerically solving
all the bounce-averaged coefficients for the dipole case does not
change the results significantly from the analytical approximation
of Ejiri (1978). However, distorting the magnetic field changes all
bounce-averaged coefficients that make up the kinetic equation. Initial
simulations show that changing the magnetic field changes the whole
topology of the ring current. This is because the drifts are altered due
to dayside compression and nightside stretching of the field. Therefore,
at certain locations, the nondipolar magnetic drifts can dominate the
convective drifts, considerably altering the pressure distribution in
the equatorial plane.
Title: Modeling solar zenith angle effects on the polar wind
Authors: Glocer, A.; Kitamura, N.; Toth, G.; Gombosi, T.
Bibcode: 2012JGRA..117.4318G
Altcode: 2012JGRA..11704318G
We use the Polar Wind Outflow Model (PWOM) to study the geomagnetically
quiet conditions in the polar cap during solar maximum. The PWOM solves
the gyrotropic transport equations for O+, H+,
and He+ along several magnetic field lines in the polar
region in order to reconstruct the full 3D solution. We directly
compare our simulation results to the data based empirical model
of Kitamura et al. (2011) of electron density which is based on 63
months of Akebono satellite observations. The modeled ion and electron
temperatures are also compared with a statistical compilation of quiet
time data obtained by the EISCAT Svalbard Radar (ESR) and Intercosmos
Satellites. The data and model agree reasonably well, albeit with some
differences. This study shows that photoelectrons play an important
role in explaining the differences between sunlit and dark results
of electron density, ion composition, as well as ion and electron
temperatures of the quiet time polar wind solution. Moreover, these
results provide an initial validation of the PWOM's ability to model
the quiet time “background” solution.
Title: Perpendicular flow deviation in a magnetized counter-streaming
plasma
Authors: Jia, Y. -D.; Ma, Y. J.; Russell, C. T.; Lai, H. R.; Toth,
G.; Gombosi, T. I.
Bibcode: 2012Icar..218..895J
Altcode:
Charged dust exists in various regions in the Solar System. How
this charged dust interacts with the surrounding plasma is not well
understood. In this study we neglect the charging process and treat
the charged dust as a fluid interacting with the ambient magnetized
plasma fluid. The model reproduces the expected plasma deceleration
with both positively charged and negatively charged dust, but a new
effect arises. Negatively charged dust causes the magnetic field to
bend in the direction of the convection electric field, while positively
charged dust causes the opposite magnetic field bending. Consequently,
the interaction does not only result in a perpendicular shift in the
downstream current system, but also a rotation in these currents. We
present quantitative results using the multi-fluid MHD code BATSRUS
for both subsonic and supersonic interactions. We find that the same
perpendicular bending exists for all counter-streaming interaction
problems, independent of the shape of the dust cloud. The new model can
be applied to plasma interaction studies including, but not limited to,
charged dust particles in the solar wind, cometary plasma, the Enceladus
plume, and active plasma releases, such as the Active Magnetospheric
Particle Tracer Experiment (AMPTE) mission. The predicted behavior is
consistent with observations at Enceladus.
Title: A Global Two-temperature Corona and Inner Heliosphere Model:
A Comprehensive Validation Study
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Gruesbeck,
J. R.; Frazin, R. A.; Landi, E.; Vasquez, A. M.; Lamy, P. L.; Llebaria,
A.; Fedorov, A.; Toth, G.; Gombosi, T. I.
Bibcode: 2012ApJ...745....6J
Altcode:
The recent solar minimum with very low activity provides us a unique
opportunity for validating solar wind models. During CR2077 (2008
November 20 through December 17), the number of sunspots was near
the absolute minimum of solar cycle 23. For this solar rotation,
we perform a multi-spacecraft validation study for the recently
developed three-dimensional, two-temperature, Alfvén-wave-driven
global solar wind model (a component within the Space Weather Modeling
Framework). By using in situ observations from the Solar Terrestrial
Relations Observatory (STEREO) A and B, Advanced Composition Explorer
(ACE), and Venus Express, we compare the observed proton state (density,
temperature, and velocity) and magnetic field of the heliosphere with
that predicted by the model. Near the Sun, we validate the numerical
model with the electron density obtained from the solar rotational
tomography of Solar and Heliospheric Observatory/Large Angle and
Spectrometric Coronagraph C2 data in the range of 2.4 to 6 solar
radii. Electron temperature and density are determined from differential
emission measure tomography (DEMT) of STEREO A and B Extreme Ultraviolet
Imager data in the range of 1.035 to 1.225 solar radii. The electron
density and temperature derived from the Hinode/Extreme Ultraviolet
Imaging Spectrometer data are also used to compare with the DEMT as
well as the model output. Moreover, for the first time, we compare
ionic charge states of carbon, oxygen, silicon, and iron observed in
situ with the ACE/Solar Wind Ion Composition Spectrometer with those
predicted by our model. The validation results suggest that most of the
model outputs for CR2077 can fit the observations very well. Based on
this encouraging result, we therefore expect great improvement for the
future modeling of coronal mass ejections (CMEs) and CME-driven shocks.
Title: Multi-fluid MHD simulation of the solar wind interaction
with Venus
Authors: Nagy, A. F.; Najib, D.; Ma, Y.; Russell, C. T.; Toth, G.
Bibcode: 2011AGUFMSA13A1865N
Altcode:
This paper reports on a new advanced multi-fluid MHD model that
has recently been developed for Venus. The model is similar to the
numerical model that was successfully applied to Mars (Najib et al.,
2011). Mass densities, velocities and pressures of the protons and
major ionosphere ion species (O+, O2+ and CO2+) are self-consistently
calculated by solving the individual coupled continuity, momentum
and energy equations. The various chemical reactions and ion-neutral
collision processes are considered in the model. The simulation domain
covers the region from 100 km altitude above the surface up to 16 RV
in the tail. An adaptive spherical grid structure is constructed with
radial resolution of about 10 km in the lower ionosphere. The model
is applied to both solar-maximum and solar-minimum conditions and
model results are compared in detail with multi-species single fluid
model results.
Title: 3D MHD modeling of non-stationary flow in the heliosheath
Authors: Provornikova, E.; Opher, M.; Izmodenov, V.; Toth, G.; Oran, R.
Bibcode: 2011AGUFMSH11A1910P
Altcode:
Both Voyager 1 and 2 data show that the heliosheath region is highly
dynamic. As we climb out of the extended solar minima, time variations
will be more and more important. The variations in the solar wind
parameters in the heliosheath can be affected by the propagation of
different interplanetary disturbances to the outer heliosphere. Using
a 3D MHD multi-fluid code based on BATS-R-US (Opher et al. 2009),
with a highly resolved spatial grid in Voyager 2 direction (size of a
cell 0.48 AU) we study the propagation of the solar wind large-scale
structures in the heliosheath region. We present our first results on
the propagation of a forward-reverse shock pair and an abrupt pulse of
solar wind dynamic pressure in the heliosheath region. We discuss in
details the structure of the flow in the heliosheath and the response
of the heliopause to the disturbances. We analyze the intensity of
variations of the plasma parameters (magnetic field and speed) as
measured in Voyager 2. We conclude that reflected waves appear in
the heliosheath and they may contribute to the variations in solar
wind parameters measured at Voyager spacecrafts. We present as well
the initial results from a realistic propagation of a global merged
interaction regions (GMIR) from the Sun to the heliospheric boundaries
using a new coupled inner heliosphere-to outer heliosphere module.
Title: Multi-fluid MHD study of Ion Loss from Titan's Atmosphere
Authors: Ma, Y.; Russell, C. T.; Nagy, A. F.; Toth, G.; Dougherty,
M. K.; Cravens, T. E.
Bibcode: 2011AGUFMSM21B2014M
Altcode:
We study the plasma interaction around Titan using our new three
dimensional multi-fluid MHD model similar to the one that was used
recently to study Mars [Najib et al., 2011]. The multi-fluid MHD model
of Titan is solved using the Michigan BATSRUS code. The model calculates
densities, velocities, and pressures of seven ion species which are
important in either Titan's ionosphere or in the ambient plasma. The
code uses a spherical grid structure with high radial resolution ~ 30
km in the lower ionosphere. The model is applied to an idealized case
of Titan and the results are compared in detail with that of a single
fluid model using the same set of plasma parameters to illustrate the
importance of multi-fluid effects near Titan. We present the calculated
ion escape rates from both models and discuss the differences.
Title: Flow Transition Region in the Heliosheath
Authors: Opher, M.; Drake, J. F.; Velli, M.; Toth, G.
Bibcode: 2011AGUFMSH11A1908O
Altcode:
The tilt between the solar rotation and magnetic axes creates a
sector region. Recently, we argued that the magnetic field in the
sector region in the heliosheath has reconnected (Opher et al. 2011)
and is filled with magnetic structures disconnected from the sun,
called "bubbles". Here we show, that the sector region affects the
flows in the heliosheath such as to create a region where the flow
abruptly turns and the radial flow is near zero or negative. We dub
this the flow transition region (FTR). The FTR is formed due to several
effects that we have explored. The sector region in the heliosheath
defines two flows: the flow within the sector region (region 1)
behaves like an un-magnetized flow while the flow outside the sector
(region 2) is connected to the larger heliosphere through the laminar
magnetic field. The region 1 flow is dominantly affected by the blunt
heliopause ahead of it and is mostly radial. As the flow streamlines
approach the heliopause they turn abruptly, creating the FTR.This
region didn't exist in previous simulations with no sectors where the
flows downstream of the termination shock turn almost immediately to
the sides and to higher latitudes. The thickness of FTR varies and is
thinner in the southern hemisphere. We estimate, based on a recent 3D
MHD simulation (Opher et al. 2011) that at the Voyager 1 location the
thickness of FTR is 10-12AU. The simulations accurately reproduce the
Voyager 1 flows. Since 2010 Voyager 1 has been immersed in the FTR,
based on the negligible flows detected (Krimigis et al. 2011). If no
other temporal dependent effects change the overall structure of the
heliosphere, Voyager 1 is expected to cross the heliopause in the
next 3-5 years. The FTR is much narrower in the southern hemisphere
and Voyager 2 is expected to enter that region in the next couple years.
Title: Modeling the quiet time outflow solution in the polar cap
Authors: Glocer, A.; Kitamura, N.; Gombosi, T. I.; Toth, G.
Bibcode: 2011AGUFMSM44A..05G
Altcode:
We use the Polar Wind Outflow Model (PWOM) to study the geomagnetically
quiet conditions in the polar cap during solar maximum. The PWOM solves
the gyrotropic transport equations for O+, H+, and
He+ along several magnetic field lines in the polar region
in order to reconstruct the full 3D solution. We directly compare our
simulation results to the data based empirical model of Kitamura et
al. [2011] of electron density, which is based on 63 months of Akebono
satellite observations. The modeled ion and electron temperatures
are also compared with a statistical compilation of quiet time data
obtained by the EISCAT Svalbard Radar (ESR) and Intercosmos Satellites
(Kitamura et al. [2011]). The data and model agree reasonably well. This
study shows that photoelectrons play an important role in explaining
the differences between sunlit and dark results, ion composition, as
well as ion and electron temperatures of the quiet time polar wind
solution. Moreover, these results provide validation of the PWOM's
ability to model the quiet time "background" solution.
Title: The heliospheric structure during the recent solar minimum:
shocks in the lower corona and the magnetic field structure in
the heliosheath
Authors: Opher, M.; Drake, J. F.; Evans, R.; Provornikova, E.; Swisdak,
M. M.; Schoeffler, K. M.; van der Holst, B.; Toth, G.
Bibcode: 2011AGUFMSH23D..06O
Altcode:
In this talk we review the recent heliospheric structure as
affected by the recent solar minimum. We will focus especially on
two frontiers areas: a) evolution of shocks in the lower corona and
b) the heliosheath. In particular, we will focus on how the recent
extended minimum allowed us to separate spatial and temporal effects
in the outer heliosphere. We will describe new phenomena that we were
able to explore, the reconnection of the sectored magnetic field in the
heliosheath. Very little is known on how shocks thought to be driven by
CMEs, form and evolve in the lower corona. This is a crucial area since
its has been shown by observations that they form low in the corona
(1-4Rs) and coincide with the acceleration to GeV energies. We will
describe our recent attempts (e.g., Evans et al. 2011; Das et al.;
2011) to uncover the evolution of CMEs at these locations. All the
current global models of the heliosphere are based on the assumption
that the magnetic field in the heliosheath, in the region close to
the heliopause is laminar and connect back to the Sun. We argue
recently, based on Voyager observations that in that region the
heliospheric magnetic field is not laminar but instead consists of
magnetic bubbles, or magnetic structures disconnected from the Sun
(Opher et al. 2011). The consequence is that the heliopause might
be a porous membrane instead of a shield. As the sun increased its
activity, it will be more complicated to disentangle temporal from
spatial and global structure. We will comment on how the increased
solar activity might affect the sector structure in the heliosheath as
well as the implication for our understanding of how galactic cosmic
rays enter the heliosphere. Due to the slow flows in the heliosheath,
the heliosheath has a long time memory of solar activity. Moreover,
Corotating Interaction Regions and Global Merged Interacting Regions
are known to disturb the termination shock and heliopause as well
as the heliosheath flows and fields. For example it is still poorly
understood how temporal effects propagate in the heliosheath and affect
the level of turbulence. We will present some of our recent work trying
to understand how temporal effects, such as CIRs propagates from the
sun into the outer heliosphere.
Title: Modeling Solar Wind and Coronal Mass Ejection During Carrington
Rotation 2107
Authors: Jin, M.; Manchester, W. B.; van der Holst, B.; Gruesbeck,
J. R.; Frazin, R. A.; Landi, E.; Vasquez, A. M.; Toth, G.; Gombosi,
T. I.
Bibcode: 2011AGUFMSH53C..08J
Altcode:
With the starting of solar cycle 24, the Sun begins to show more
activity. New observations from Solar Dynamics Observatory (SDO) give
us a great opportunity to test and validate our solar corona model
for space weather forecasts. During Carrington Rotation 2107, an M3.7
flare occurred in NOAA 11164 on 2011 March 7 with a fast CME (> 2000
km/s). There is also a Solar Energetic Particle (SEP) event associated
with this CME. In this study, we will first model the steady state solar
wind using a newly developed three-dimensional Alfven-wave-driven global
solar wind model within the Space Weather Modeling Framework (SWMF),
which includes counter propagating Alfven waves. The magnetic field of
the inner boundary is set up using the magnetogram from SDO/HMI. The
inner boundary condition for density and temperature are specified
from the Differential Emission Measure Tomography (DEMT) of SDO/AIA
data. A flux rope is then applied to the active region NOAA 11164 to
initiate the CME event. The properties of CME-driven shocks in the
model output are studied in detail, which will be used to simulate the
related SEP event in the future. By using multispacecraft observations,
we perform a validation study for the model results.
Title: Variation of Pick-up Ion Pressure throughout the Heliosheath:
3-Dimensional Multi-ion, Multi-fluid Magnetohydrodynamic Simulation
of the Outer Heliosphere
Authors: Prested, C. L.; Opher, M.; Toth, G.; Schwadron, N. A.
Bibcode: 2011AGUFMSH21C..07P
Altcode:
The interaction between the solar system and interstellar medium (ISM)
involves multiple populations of ions and neutrals of both heliosphere
and local interstellar origin. Of special interest is the pick-up ion
population generated in the inner heliosphere, as it carries upwards of
80% the plasma pressure in the outer heliosphere [Richardson et al.,
2008]. The Interstellar Boundary Explorer (IBEX) global energetic
neutral atom (ENA) maps of the interstellar-heliosphere interaction
show temporal variation in the interaction region upwards of 15% in ENA
emission over a time scale of < 6 months. The short time scale and
magnitude of the variation implies that the origin of this variation
comes from the solar system plasma, which has considerable solar
cycle variation, and likely not from variability in the interstellar
medium. The dynamic properties of the pressure dominant pick-up ions
are a likely candidate for this temporal variation. We ask, how does
the pick-up ion pressure vary through the heliosheath, spatially
and temporally? In previous 3-dimensional magnetohydrodynamic (MHD)
simulations of the outer heliosphere, a single plasma fluid was used
to describe the behavior of the solar wind plasma and the pick-up
ions. For simulating ENA maps, the single plasma fluid was assumed
to have a kappa distribution, describing the thermal core of solar
wind plasma and the suprathermal tail of pick-up ions [Prested et
al., 2008]. These simulations captured the global structure of the
heliosphere but lost information on how the pick-up ion population and
the pressure it carries evolve through the ISM-heliosphere interaction
region. This information is vital for understanding the energy-dependent
temporal and spatial variations observed in the IBEX global maps. We
have extended our previous 3-d MHD multifluid model [Opher et al., 2009]
to include the solar wind and pick-up ions as 2 separate ion fluids
[i.e. Glocer et al., 2009 ], in addition to treating 4 separate neutral
populations. Additionally, we introduce temporal variation by simulating
the global heliosphere with solar-minimum and solar-maximum solar wind
conditions. We quantify how the pick-up ion pressure varies through the
heliosheath under these conditions and validate our results through
comparison with the Voyager 1 and 2 heliosheath measurements. From
our analysis of the two extreme solar wind cases, we conclude whether
or not variation in pick-up ion pressure could be responsible for the
6-month, large scale variation seen in the IBEX global maps.
Title: Controlling Reconnection in Global Magnetospheric Simulations
Authors: Toth, G.; Meng, X.; Daldorff, L.; Ridley, A. J.; Gombosi,
T. I.
Bibcode: 2011AGUFMSM31B2108T
Altcode:
Magnetic reconnection plays a major role in determining the dynamics
of the magnetosphere. Yet, the reconnection rate in most global
magnetosphere models relies on numerical resistivity. This means,
unfortunately, that the simulation results are sensitive to the
numerical parameters, such as grid resolution and the choice of the
numerical scheme. We are exploring how we can control the resistivity in
a better way. As a preliminary study, we do grid convergence studies of
reconnection with constant resistivity in 2 dimensions. We establish the
relationship between the grid resolution and the achievable magnetic
Reynolds number. Based on these results we can estimate the effective
numerical resistivity in global magnetospheric simulations, and use
an explicit resistivity to better control the reconnection rate.
Title: Anisotropic BATSRUS and CRCM two way coupling
Authors: Meng, X.; Toth, G.; Glocer, A.; Fok, M. H.; Gombosi, T. I.
Bibcode: 2011AGUFMSM51B2061M
Altcode:
As a newly extended capability of the BATSRUS code, anisotropic
MHD can solve for the anisotropic ion pressure and isotropic
electron pressure. It does a good job on simulating the quiet time
magnetosphere, and the coupling with the Rice Convection Model (RCM)
produces reasonable solutions for geomagnetic storms. However, RCM
assumes the isotropic distribution of particles, which ignores the
anisotropy information from BATSRUS. In order to better represent
the near-Earth magnetosphere especially during disturbed times, we
couple the anisotropic BATSRUS to the Comprehensive Ring Current Model
(CRCM), which resolves the pitch-angle distribution. We present the
preliminary results here, including the coupling algorithm and some
validation tests.
Title: Spatial and temporal signatures of flux transfer events in
global simulations of magnetopause dynamics
Authors: Kuznetsova, M. M.; Sibeck, D. G.; Hesse, M.; Berrios, D.;
Rastaetter, L.; Toth, G.; Gombosi, T. I.
Bibcode: 2011AGUFMSM53B..01K
Altcode:
Flux transfer events (FTEs) were originally identified by transient
bipolar variations of the magnetic field component normal to the nominal
magnetopause centered on enhancements in the total magnetic field
strength. Recent Cluster and THEMIS multi-point measurements provided
a wide range of signatures that are interpreted as evidence for FTE
passage (e.g., crater FTEs, traveling magnetic erosion regions). We use
the global magnetohydrodynamic (MHD) code BATS-R-US developed at the
University of Michigan to model the global three-dimensional structure
and temporal evolution of FTEs during multi-spacecraft magnetopause
crossing events. Comparison of observed and simulated signatures and
sensitivity analysis of the results to the probe location will be
presented. We will demonstrate a variety of observable signatures
in magnetic field profile that depend on space probe location with
respect to the FTE passage. The global structure of FTEs will be
illustrated using advanced visualization tools developed at the
Community Coordinated Modeling Center.
Title: Simulating the one-dimensional structure of Titan's upper
atmosphere: 3. Mechanisms determining methane escape
Authors: Bell, Jared M.; Bougher, Stephen W.; Waite, J. Hunter, Jr.;
Ridley, Aaron J.; Magee, Brian A.; Mandt, Kathleen E.; Westlake,
Joseph; DeJong, Anna D.; Bar-Nun, Akiva; Jacovi, Ronen; Toth, Gabor;
De La Haye, Virginie; Gell, David; Fletcher, Gregory
Bibcode: 2011JGRE..11611002B
Altcode:
This investigation extends the work presented by Bell et al. (2010a,
2010b). Using the one-dimensional (1-D) configuration of the
Titan Global Ionosphere-Thermosphere Model (T-GITM), we quantify
the relative importance of the different dynamical and chemical
mechanisms that determine the CH4 escape rates calculated
by T-GITM. Moreover, we consider the implications of updated Huygens
Gas Chromatograph Mass Spectrometer (GCMS) determinations of both the
40Ar mixing ratios and 15N/14N isotopic
ratios in work by Niemann et al. (2010). Combining the GCMS constraints
in the lower atmosphere with the Ion Neutral Mass Spectrometer (INMS)
measurements in work by Magee et al. (2009), our simulation results
suggest that the optimal CH4 homopause altitude is located
at 1000 km. Using this homopause altitude, we conclude that topside
escape rates of 1.0 × 1010 CH4 m-2
s-1 (referred to the surface) are sufficient to reproduce
the INMS methane measurements in work by Magee et al. (2009). These
escape rates of methane are consistent with the upper limits to
methane escape (1.11 × 1011 CH4 m-2
s-1) established by both the Cassini Plasma Spectrometer
(CAPS) and Magnetosphere Imaging Instrument (MIMI) measurements of
Carbon-group ions in the near Titan magnetosphere.
Title: Numerical investigation of the late-time Kerr tails
Authors: Rácz, István; Tóth, Gábor Zs
Bibcode: 2011CQGra..28s5003R
Altcode: 2011arXiv1104.4199R
The late-time behavior of a scalar field on fixed Kerr background
is examined in a numerical framework incorporating the techniques of
conformal compactification and hyperbolic initial value formulation. The
applied code is 1+(1+2) as it is based on the use of the spectral
method in the angular directions while in the time-radial section
fourth order finite differencing, along with the method of lines, is
applied. The evolution of various types of stationary and non-stationary
pure multipole initial states are investigated. The asymptotic decay
rates are determined not only in the domain of outer communication but
along the event horizon and at future null infinity as well. The decay
rates are found to be different for stationary and non-stationary
initial data, and they also depend on the fall off properties of
the initial data toward future null infinity. The energy and angular
momentum transfers are found to show significantly different behavior
in the initial phase of the time evolution. The quasinormal ringing
phase and the tail phase are also investigated. In the tail phase, the
decay exponents for the energy and angular momentum losses at I^{\,+}
are found to be smaller than at the horizon which is in accordance
with the behavior of the field itself and it means that at late times
the energy and angular momentum falling into the black hole become
negligible in comparison with the energy and angular momentum radiated
toward I^{\,+} . The energy and angular momentum balances are used as
additional verifications of the reliability of our numerical method.
Title: The importance of thermal electron heating in Titan's
ionosphere: Comparison with Cassini T34 flyby
Authors: Ma, Y. J.; Russell, C. T.; Nagy, A. F.; Toth, G.; Dougherty,
M. K.; Wellbrock, A.; Coates, A. J.; Garnier, P.; Wahlund, J. -E.;
Cravens, T. E.; Richard, M. S.; Crary, F. J.
Bibcode: 2011JGRA..11610213M
Altcode:
We use a new magnetohydrodynamic (MHD) model to study the effects of
thermal-electron heating in Titan's ionosphere. This model improves the
previously used multispecies MHD model by solving both the electron
and ion pressure equations instead of a single plasma pressure
equation. This improvement enables a more accurate evaluation of ion
and electron temperatures inside Titan's ionosphere. The model is
first applied to an idealized case, and the results are compared in
detail with those of the single-pressure MHD model to illustrate the
effects of the improvement. Simulation results show that the dayside
ionosphere thermal pressure is larger than the upstream pressure
during normal conditions, when Titan is located in the dusk region;
thus Saturn's magnetic field is shielded by the highly conducting
ionosphere, similar to the interaction of Venus during solar maximum
conditions. This model is also applied to a special flyby of Titan,
the T34 flyby, which occurred near the dusk region. It is shown that
better agreement with the magnetometer data can be achieved using
the two-fluid MHD model with the inclusion of the effects of thermal
electron heating. The model results clearly demonstrate the importance
of thermal-electron heating in Titan's ionosphere.
Title: A 3D Multi-fluid MHD Study of the Interaction of the Solar
Wind with the Ionosphere/Atmosphere System of Venus.
Authors: Najib, D.; Nagy, A.; Toth, G.; Ma, Y. -J.
Bibcode: 2011epsc.conf..158N
Altcode: 2011DPS....43..158N
We use the latest version of our four species multifluid model to
study the interaction of the solar wind with Venus. The model solves
simultaneously the continuity, momentum and energy equations of the
different ions. The lower boundary of our model is at 100 km, below
the main ionospheric peak, and the radial resolution is about 10 km in
the ionosphere, thus the model does a very good job in reproducing the
ionosphere and the associated processes. We carry out calculations for
high and low solar activity conditions and establish the importance
of mass loading by the extended exosphere of Venus. We demonstrate
the importance of using the multi-fluid rather than a single fluid
model. We also calculate the atmospheric escape of the ionospheric
species and compare our model results with the observed parameters
from Pioneer Venus and Venus Express.
Title: Perpendicular Flow Separation in a Magnetized Counterstreaming
Plasma: Application to the Dust Plume of Enceladus
Authors: Jia, Y. -D.; Ma, Y. J.; Russell, C. T.; Toth, G.; Gombosi,
T. I.; Dougherty, M. K.
Bibcode: 2011epsc.conf...99J
Altcode: 2011DPS....43...99J
The interaction of charged dust with a magnetized flowing plasma
can be treated with a multi-fluid MHD simulation. We examine the
interaction of the corotating Saturnian plasma with the charged-dust
plume of Enceladus. The model produces plasma deceleration with both
positively and negatively charged dust. In addition, the negatively
charged dust causes plasma deflection in the direction of the motional
electric field and a kink in the magnetic field extending in the
same direction. Positively charged dust causes the opposite plasma
deflection and the opposite magnetic field bending. These results agree
with the magnetic signatures observed on Cassini plume flybys. The
code has been tested on both subsonic and supersonic interactions and
is applicable to solar wind dust pickup, ICME interactions with dust
trails, cometary plasma pickup, active plasma releases such as the
AMPTE barium release as well as the Enceladus plume.
Title: Rapid rebuilding of the outer radiation belt
Authors: Glocer, A.; Fok, M. -C.; Nagai, T.; Tóth, G.; Guild, T.;
Blake, J.
Bibcode: 2011JGRA..116.9213G
Altcode:
Recent observations by the radiation monitor (RDM) on the spacecraft
Akebono have shown several cases of >2.5 MeV radiation belt electron
enhancements occurring on timescales of less than a few hours. Similar
enhancements are also seen in detectors on board the NOAA/POES and
TWINS 1 satellites. These intervals are shorter than typical radial
diffusion or wave-particle interactions can account for. We choose two
so-called “rapid rebuilding” events that occur during high speed
streams (4 September 2008 and 22 July 2009) and simulated them with the
Space Weather Modeling Framework configured with global magnetosphere,
radiation belt, ring current, and ionosphere electrodynamics model. Our
simulations produce a weaker and delayed dipolarization as compared
to observations, but the associated inductive electric field in the
simulations is still strong enough to rapidly transport and accelerate
MeV electrons resulting in an energetic electron flux enhancement that
is somewhat weaker than is observed. Nevertheless, the calculated
flux enhancement and dipolarization is found to be qualitatively
consistent with the observations. Taken together, the modeling results
and observations support the conclusion that storm-time dipolarization
events in the magnetospheric magnetic field result in strong radial
transport and energization of radiation belt electrons.
Title: Reducing numerical diffusion in magnetospheric simulations
Authors: Tóth, Gábor; Meng, Xing; Gombosi, Tamas I.; Ridley, Aaron J.
Bibcode: 2011JGRA..116.7211T
Altcode:
Physics-based global magnetosphere modeling requires large computational
resources. It is still impractical to resolve the computational domain
to the point where numerical errors become negligible. One possible
way of reducing numerical diffusion is the “Boris correction”:
the semirelativistic magnetohydrodynamics equations are solved with an
artificially reduced speed of light. Here we introduce a new alternative
approach, an Implicit Scheme with Limited Numerical Dissipation
(ISLND). The fully implicit time stepping provides stability, and the
wave speeds are limited in the dissipative numerical fluxes only. This
limiting only affects the numerical scheme, and it does not modify the
equations being solved. This approach can be employed for most total
variation diminishing schemes. The differences between the Boris
and ISLND schemes are demonstrated in simple numerical tests. We
also perform several simulations for two magnetic storms using the
global magnetosphere, the ionosphere electrodynamics, and the inner
magnetosphere models of the Space Weather Modeling Framework, and we
compare the Boris scheme with the limited numerical dissipation method
and also with the unmodified base scheme at various grid resolutions. We
find that for these particular simulations the Boris scheme and the
ISLND scheme produce comparable results, both being significantly less
diffusive than the unmodified scheme.
Title: A Global Two-Temperature Corona and Inner Heliosphere Model:
A Validation Study
Authors: Jin, Meng; Manchester, W. B.; van der Holst, B.; Gruesbeck,
J.; Frazin, R. A.; Vasquez, A. M.; Lamy, P. L.; Llebaria, A.; Fedorov,
A.; Toth, G.; Gombosi, T. I.
Bibcode: 2011shin.confE..12J
Altcode:
The recent solar minimum with very low activity provides us a unique
opportunity for validating solar wind models. During CR2077 (2008,
November 20 through December 17), the sunspots number reaches the
absolute minimum of solar cycle 23. For this solar rotation, we
perform a multi-spacecraft validation study for the recently developed
three-dimensional, two-temperature, Alfven-wave-driven global solar wind
model (a component within the Space Weather Modeling Framework). By
using in situ observations from STEREO A and B, ACE/WIND and Venus
Express, we compare the observed proton state (density, temperature and
velocity) and magnetic field of the heliosphere with that predicted
by the model. Near the Sun, we validate the numerical model with the
electron density obtained from the solar rotational tomography of
SOHO/LASCO-C2 data in the range of 2.4 to 6 solar radii. Electron
temperature and density are determined from differential emission
measure tomography of STEREO A and B EUVI data in the range of 1.035 to
1.225 solar radii. Moreover, we compare ionic charge states of carbon,
oxygen, silicon, and iron observed in situ with ACE/SWICS and that
predicted by our model. The validation results suggest that most of
the model outputs for CR2077 can fit the observations very well. Based
on this encouraging result, we therefore expect great improvement for
the modeling of CMEs and CME-driven shocks in the future.
Title: Is the Magnetic Field in the Heliosheath Laminar or a Turbulent
Sea of Bubbles?
Authors: Opher, M.; Drake, J. F.; Swisdak, M.; Schoeffler, K. M.;
Richardson, J. D.; Decker, R. B.; Toth, G.
Bibcode: 2011ApJ...734...71O
Altcode: 2011arXiv1103.2236O
All current global models of the heliosphere are based on the assumption
that the magnetic field in the heliosheath, in the region close to
the heliopause (HP), is laminar. We argue that in that region the
heliospheric magnetic field is not laminar but instead consists of
magnetic bubbles. We refer to it as the bubble-dominated heliosheath
region. Recently, we proposed that the annihilation of the "sectored"
magnetic field within the heliosheath as it is compressed on its
approach to the HP produces anomalous cosmic rays and also energetic
electrons. As a product of the annihilation of the sectored magnetic
field, densely packed magnetic islands (which further interact to form
magnetic bubbles) are produced. These magnetic islands/bubbles will be
convected with ambient flows as the sector region is carried to higher
latitudes filling the heliosheath. We further argue that the magnetic
islands/bubbles will develop upstream within the heliosheath. As a
result, the magnetic field in the heliosheath sector region will be
disordered well upstream of the HP. We present a three-dimensional
MHD simulation with very high numerical resolution that captures the
north-south boundaries of the sector region. We show that due to the
high pressure of the interstellar magnetic field a north-south asymmetry
develops such that the disordered sectored region fills a large portion
of the northern part of the heliosphere with a smaller extension in the
southern hemisphere. We suggest that this scenario is supported by the
following changes that occurred around 2008 and from 2009.16 onward: (1)
the sudden decrease in the intensity of low energy electrons (0.02-1.5
MeV) detected by Voyager 2, (2) a sharp reduction in the intensity of
fluctuations of the radial flow, and (3) the dramatic differences in
intensity trends between galactic cosmic ray electrons (3.8-59 MeV) at
Voyager 1 and 2. We argue that these observations are a consequence of
Voyager 2 leaving the sector region of disordered field during these
periods and crossing into a region of unipolar laminar field.
Title: Kinetic versus Multi-fluid Approach for Interstellar Neutrals
in the Heliosphere: Exploration of the Interstellar Magnetic Field
Effects
Authors: Alouani-Bibi, Fathallah; Opher, Merav; Alexashov, Dimitry;
Izmodenov, Vladislav; Toth, Gabor
Bibcode: 2011ApJ...734...45A
Altcode: 2011arXiv1103.3202A
We present a new three-dimensional (3D) self-consistent two-component
(plasma and neutral hydrogen) model of the solar wind interaction with
the local interstellar medium (LISM). This model (K-MHD) combines
the magnetohydrodynamic treatment of the solar wind and the ionized
LISM component with a kinetic model of neutral interstellar hydrogen
(LISH). The local interstellar magnetic field (B LISM)
intensity and orientation are chosen based on an early analysis of the
heliosheath flows. The properties of the plasma and neutrals obtained
using the K-MHD model are compared to previous multi-fluid and kinetic
models. The new treatment of LISH revealed important changes in the
heliospheric properties not captured by the multi-fluid model. These
include a decrease in the heliocentric distance to the termination
shock (TS), a thinner heliosheath, and a reduced deflection angle (θ)
of the heliosheath flows. The asymmetry of the TS, however, seems to
be unchanged by the kinetic aspect of the LISH.
Title: CRASH: A Block-adaptive-mesh Code for Radiative Shock
Hydrodynamics—Implementation and Verification
Authors: van der Holst, B.; Tóth, G.; Sokolov, I. V.; Powell, K. G.;
Holloway, J. P.; Myra, E. S.; Stout, Q.; Adams, M. L.; Morel, J. E.;
Karni, S.; Fryxell, B.; Drake, R. P.
Bibcode: 2011ApJS..194...23V
Altcode: 2011arXiv1101.3758V
We describe the Center for Radiative Shock Hydrodynamics (CRASH)
code, a block-adaptive-mesh code for multi-material radiation
hydrodynamics. The implementation solves the radiation diffusion model
with a gray or multi-group method and uses a flux-limited diffusion
approximation to recover the free-streaming limit. Electrons and ions
are allowed to have different temperatures and we include flux-limited
electron heat conduction. The radiation hydrodynamic equations are
solved in the Eulerian frame by means of a conservative finite-volume
discretization in either one-, two-, or three-dimensional slab geometry
or in two-dimensional cylindrical symmetry. An operator-split method
is used to solve these equations in three substeps: (1) an explicit
step of a shock-capturing hydrodynamic solver; (2) a linear advection
of the radiation in frequency-logarithm space; and (3) an implicit
solution of the stiff radiation diffusion, heat conduction, and
energy exchange. We present a suite of verification test problems
to demonstrate the accuracy and performance of the algorithms. The
applications are for astrophysics and laboratory astrophysics. The
CRASH code is an extension of the Block-Adaptive Tree Solarwind Roe
Upwind Scheme (BATS-R-US) code with a new radiation transfer and
heat conduction library and equation-of-state and multi-group opacity
solvers. Both CRASH and BATS-R-US are part of the publicly available
Space Weather Modeling Framework.
Title: Obtaining Potential Field Solutions with Spherical Harmonics
and Finite Differences
Authors: Tóth, Gábor; van der Holst, Bart; Huang, Zhenguang
Bibcode: 2011ApJ...732..102T
Altcode: 2011arXiv1104.5672T
Potential magnetic field solutions can be obtained based on the
synoptic magnetograms of the Sun. Traditionally, a spherical harmonics
decomposition of the magnetogram is used to construct the current-
and divergence-free magnetic field solution. This method works
reasonably well when the order of spherical harmonics is limited to
be small relative to the resolution of the magnetogram, although some
artifacts, such as ringing, can arise around sharp features. When the
number of spherical harmonics is increased, however, using the raw
magnetogram data given on a grid that is uniform in the sine of the
latitude coordinate can result in inaccurate and unreliable results,
especially in the polar regions close to the Sun. We discuss here
two approaches that can mitigate or completely avoid these problems:
(1) remeshing the magnetogram onto a grid with uniform resolution in
latitude and limiting the highest order of the spherical harmonics to
the anti-alias limit; (2) using an iterative finite difference algorithm
to solve for the potential field. The naive and the improved numerical
solutions are compared for actual magnetograms and the differences
are found to be rather dramatic. We made our new Finite Difference
Iterative Potential-field Solver (FDIPS) a publicly available code
so that other researchers can also use it as an alternative to the
spherical harmonics approach.
Title: Three-dimensional, multifluid, high spatial resolution MHD
model studies of the solar wind interaction with Mars
Authors: Najib, Dalal; Nagy, Andrew F.; Tóth, Gábor; Ma, Yingjuan
Bibcode: 2011JGRA..116.5204N
Altcode:
Our newly developed 3-D, multifluid MHD model is used to study the
interaction of the solar wind with Mars. This model is based on the
BATS-R-US code, using a spherical grid and a radial resolution equal
to 10 km in the ionospheric regions. We solve separate continuity,
momentum, and energy equations for each ion fluid and run our model
for both solar minimum and maximum conditions. We obtain asymmetric
densities, velocities, and magnetic pileup in the plane containing both
the direction of the solar wind and the convective electric field. These
asymmetries are the result of the decoupling of the individual ions;
therefore, our model is able to account for the respective dynamics
of the ions and to show new physical processes that could not be
observed by the single-fluid model. Our results are consistent with
the measured bow shock and magnetic pileup locations and with the
Viking-observed ion densities. We also compute the escape fluxes for
both solar minimum and solar maximum conditions and compare them to
the single-fluid results and the observed values from Mars Express.
Title: The effects of dynamic ionospheric outflow on the ring current
Authors: Welling, D. T.; Jordanova, V. K.; Zaharia, S. G.; Glocer,
A.; Toth, G.
Bibcode: 2011JGRA..116.0J19W
Altcode:
The importance of ionospheric O+ on the development of the
storm time ring current is recognized but not well understood. The
addition of this outflow in global MHD models has the potential
to change the magnetic field configuration, particle densities and
temperatures, and the convection electric field. This makes including
heavy ion outflow in ring current simulations difficult, as this
addition cannot be easily decoupled from a host of other changes. This
study attempts to overcome this problem by using three coupled models,
PWOM, RIM, and BATS-R-US, to drive a ring current model, RAM-SCB. The
differences in drivers when outflow is included and is not included are
compared to see how outflow changes ring current input. It is found
that including this outflow reduces the convection electric field,
lowers the plasma sheet number density and temperature, and increases
the complexity of the plasma sheet ion composition both temporally and
spatially. These changes cause an overall reduction in ring current
energy density. Further simulations that attempt to isolate these
effects find that the most important change in terms of ring current
development is the drop in convection electric field. Local time
dependencies of O+ injections are found to be nontrivial
as well. Capturing all of these effects requires a whole system,
first-principles approach.
Title: CRASH: A Block-Adaptive-Mesh Code for Radiative Shock
Hydrodynamics
Authors: van der Holst, B.; Toth, G.; Sokolov, I. V.; Powell, K. G.;
Holloway, J. P.; Myra, E. S.; Stout, Q.; Adams, M. L.; Morel, J. E.;
Drake, R. P.
Bibcode: 2011ascl.soft01008V
Altcode:
CRASH (Center for Radiative Shock Hydrodynamics) is a block
adaptive mesh code for multi-material radiation hydrodynamics. The
implementation solves the radiation diffusion model with the gray or
multigroup method and uses a flux limited diffusion approximation
to recover the free-streaming limit. The electrons and ions are
allowed to have different temperatures and we include a flux limited
electron heat conduction. The radiation hydrodynamic equations are
solved in the Eulerian frame by means of a conservative finite volume
discretization in either one, two, or three-dimensional slab geometry
or in two-dimensional cylindrical symmetry. An operator split method
is used to solve these equations in three substeps: (1) solve the
hydrodynamic equations with shock-capturing schemes, (2) a linear
advection of the radiation in frequency-logarithm space, and (3)
an implicit solve of the stiff radiation diffusion, heat conduction,
and energy exchange. We present a suite of verification test problems
to demonstrate the accuracy and performance of the algorithms. The
CRASH code is an extension of the Block-Adaptive Tree Solarwind Roe
Upwind Scheme (BATS-R-US) code with this new radiation transfer and
heat conduction library and equation-of-state and multigroup opacity
solvers. Both CRASH and BATS-R-US are part of the publicly available
Space Weather Modeling Framework (SWMF).
Title: BATSRUS with Anisotropic Ion Pressure
Authors: Meng, X.; Toth, G.; Gombosi, T. I.
Bibcode: 2010AGUFMSM51B1816M
Altcode:
We extend the capability of BATSRUS code to simulate anisotropic
pressure. Several events are presented here, including quiet time as
well as storms. The comparison with measurements, primarily Cluster
and THEMIS data are shown. We also investigate the possibility of
including a separate evolution equation for the (isotropic) electron
pressure. The assumption of isotropy for electrons is reasonable
for most space applications. We describe our progress with the
implementation and testing.
Title: Simulating the one-dimensional structure of Titan's upper
atmosphere: 2. Alternative scenarios for methane escape
Authors: Bell, Jared M.; Bougher, Stephen W.; Waite, J. Hunter, Jr.;
Ridley, Aaron J.; Magee, Brian A.; Mandt, Kathleen E.; Westlake,
Joseph; Dejong, Anna D.; de La Haye, Virginie; Bar-Nun, Akiva; Jacovi,
Ronen; Toth, Gabor; Gell, David; Fletcher, Gregory
Bibcode: 2010JGRE..11512018B
Altcode:
In Bell et al. (2010) (paper 1), we provide a series of
benchmark simulations that validate a newly developed Titan Global
Ionosphere-Thermosphere Model (T-GITM) and calibrate its estimates of
topside escape rates with recent work by Cui et al. (2008), Strobel
(2009), and Yelle et al. (2008). Presently, large uncertainties exist
in our knowledge of the density and thermal structure of Titan's
upper atmosphere between the altitudes of 500 km and 1000 km. In this
manuscript, we explore a spectrum of possible model configurations of
Titan's upper atmosphere that are consistent with observations made by
the Cassini Ion-Neutral Mass Spectrometer (INMS), Composite Infrared
Spectrometer, Cassini Plasma Spectrometer, Magnetospheric Imaging
Instrument, and by the Huygens Gas Chromatograph Mass Spectrometer
and Atmospheric Science Instrument. In particular, we explore the
ramifications of multiplying the INMS densities of Magee et al. (2009)
by a factor of 3.0, which significantly alters the overall density,
thermal, and dynamical structures simulated by T-GITM between 500 km
and 1500 km. Our results indicate that an entire range of topside
CH4 escape fluxes can equivalently reproduce the INMS
measurements, ranging from ∼108 - 1.86 × 1013
molecules m-2 s-1 (referred to the surface). The
lowest topside methane escape rates are achieved by scaling the INMS
densities by a factor of 3.0 and either (1) increasing the methane
homopause altitude to ∼1000 km or (2) including a physicochemical loss
referred to as aerosol trapping. Additionally, when scaling the INMS
densities by a factor of 3.0, we find that only Jeans escape velocities
are required to reproduce the H2 measurements of INMS.
Title: A Data-driven, Two-temperature Solar Wind Model with Alfvén
Waves
Authors: van der Holst, B.; Manchester, W. B., IV; Frazin, R. A.;
Vásquez, A. M.; Tóth, G.; Gombosi, T. I.
Bibcode: 2010ApJ...725.1373V
Altcode:
We have developed a new three-dimensional magnetohydrodynamic
(MHD) solar wind model coupled to the Space Weather Modeling
Framework (SWMF) that solves for the different electron and proton
temperatures. The collisions between the electrons and protons are
taken into account as well as the anisotropic thermal heat conduction
of the electrons. The solar wind is assumed to be accelerated by
the Alfvén waves. In this paper, we do not consider the heating of
closed magnetic loops and helmet streamers but do address the heating
of the protons by the Kolmogorov dissipation of the Alfvén waves in
open field-line regions. The inner boundary conditions for this solar
wind model are obtained from observations and an empirical model. The
Wang-Sheeley-Arge model is used to determine the Alfvén wave energy
density at the inner boundary. The electron density and temperature
at the inner boundary are obtained from the differential emission
measure tomography applied to the extreme-ultraviolet images of the
STEREO A and B spacecraft. This new solar wind model is validated
for solar minimum Carrington rotation 2077 (2008 November 20 through
December 17). Due to the very low activity during this rotation,
this time period is suitable for comparing the simulated corotating
interaction regions (CIRs) with in situ ACE/WIND data. Although we do
not capture all MHD variables perfectly, we do find that the time of
occurrence and the density of CIRs are better predicted than by our
previous semi-empirical wind model in the SWMF that was based on a
spatially reduced adiabatic index to account for the plasma heating.
Title: Is the Magnetic Field in the Heliosheath Sector Region and
in the Outer Heliosheath Laminar?
Authors: Opher, M.; Drake, J. F.; Swisdak, M. M.; Toth, G.
Bibcode: 2010AGUFMSH23D..04O
Altcode:
All the current global models of the heliosphere are based on the
assumption that the magnetic field in the outer heliosheath close to
the heliopause is laminar. We argue that in the outer heliosheath the
heliospheric magnetic field is not laminar but instead consists of
nested magnetic islands. Recently, we proposed (Drake et al. 2009)
that the annihilation of the ``sectored'' magnetic field within the
heliosheath as it is compressed on its approach to the heliopause
produces the anomalous cosmic rays (ACRs) and also energetic
electrons. As a product of the annihilation of the sectored magnetic
field, densly-packed magnetic islands are produced. These magnetic
islands will be convected with the ambient flows as the sector boundary
is carried to higher latitudes filling the outer heliosheath. We
further argue that the magnetic islands will develop upstream (but
still within the heliosheath) where collisionless reconnection is
unfavorable -- large perturbations of the sector structure near the
heliopause will cause compressions of the current sheet upstream,
triggering reconnection. As a result, the magnetic field in the
heliosheath sector region will be disordered well upstream of the
heliopause. We present a 3D MHD simulation with unprecedent numerical
resolution that captures the sector boundary. We show that due to
the high pressure of the interstellar magnetic field the disordered
sectored region fills a large portion of the northern part of the
heliosphere with a smaller extension in the southern hemisphere. We
test these ideas with observations of energetic electrons, which
because of their high velocity are most sensitive to the structure of
the magnetic field. We suggest that within our scenario we can explain
two significant anomalies in the observations of energetic electrons
in the outer heliosphere: the sudden decrease in the intensity of low
energy electrons (0.02-1.5MeV) from the LECP instrument on Voyager 2 in
2008 (Decker 2010); and the dramatic differences in intensity trends
between Galactic Cosmic Ray Electrons (3.8-59MeV) at Voyager 1 and 2
(McDonald 2010). We argue that these observations are a consequence
of Voyager 2 leaving the sector region of disordered field in mid 2008
and crossing into a region of unipolar laminar field.
Title: Global MHD simulations of the interaction between Saturn's
magnetosphere and the solar wind (Invited)
Authors: Jia, X.; Hansen, K. C.; Gombosi, T. I.; Kivelson, M. G.;
Toth, G.; de Zeeuw, D.; Ridley, A. J.
Bibcode: 2010AGUFMSM31C..01J
Altcode:
At Saturn, both the external (the solar wind) and the internal (the
planet’s rotation and internal plasma source) conditions play an
important role in affecting the global structure and dynamics of the
magnetosphere. We have used 3D global MHD simulations to investigate
the global configuration and dynamics of Saturn’s mass-loaded
magnetosphere under different solar wind conditions. Our present
model (BATSRUS) adopts a high-resolution, non-uniform spherical grid,
which is crucial for capturing fine structures of the large-scale
magnetospheric currents responsible for the coupling between the
magnetosphere and the ionosphere. In order to examine the effects
of the solar wind driving on dynamics of Saturn’s magnetosphere,
we have used an idealized solar wind input with features typical of
those of Corotating Interaction Regions (CIRs) seen at Saturn’s
orbit. Our simulation results indicate that periodic large-scale
plasmoid formation occurs in Saturn’s magnetotail, independent of
the IMF conditions. However, the periodicity of plasmoid formation in
the tail appears to be strongly affected by the upstream solar wind
conditions. In this talk, we will compare the global magnetospheric
configuration under different solar wind dynamic pressure and IMF
conditions. In particular, we will discuss the interplay between the
so-called “Vasyliunas-cycle” and “Dungey-cycle” in controlling
the global plasma convection in Saturn’s magnetosphere. We will
also show the ionospheric response to the solar wind driving, such
as changes in the field-aligned currents and convection pattern,
and discuss their relationship with dynamics in the magnetosphere.
Title: Modeling Ionospheric Outflows In Global Models (Invited)
Authors: Glocer, A.; Toth, G.; Fok, M. H.; Gombosi, T. I.; Welling,
D. T.
Bibcode: 2010AGUFMSA33C..01G
Altcode:
The magnetosphere contains a significant amount of ionospheric O+,
particularly during geomagnetically active times. The presence
of this ionospheric plasma has a notable impact on magnetospheric
composition and processes. We present our methodology for including
an ionospheric mass source into global models, and for tracking the
consequences for the space environment system. An overview of our
recent efforts is provided. In particular, we illustrate the effect
that plasma of ionospheric origin can have on the magnetosphere by
simulating extreme geospace events when the fraction of O+ is largest,
and contrast those results with simulations of more moderate events. We
also compare different techniques of modeling/tracking ionospheric
outflow, and explore the implications for the storm-time ring current
and magnetospheric magnetic field configuration.
Title: Numerical Simulation of Earth Directed CMEs with an Advanced
Two-Temperature Coronal Model (Invited)
Authors: Manchester, W. B.; van der Holst, B.; Frazin, R. A.; Vasquez,
A. M.; Toth, G.; Gombosi, T. I.
Bibcode: 2010AGUFMSH32A..02M
Altcode:
We present progress on modeling Earth-directed CMEs including
the December 12, 2008 CME and the May 13, 2005 campaign event from
initiation to heliospheric propagation. Our earlier work on the 2005
event followed the CME to the orbit of Saturn employing the coronal
model of Cohen et al. (2007), which relies on a spatially varying
adiabatic index (gamma) to produce the bimodal solar wind. This
model was able to reproduce several features of the observed event,
but suffered from artifacts of the artificially thermodynamics. We
will examine results of a recent simulation performed with a new
two-temperature solar corona model developed at the University of
Michigan. This model employs heat conduction for both ion and electron
species, constant adiabatic index (=5/3), and includes Alfven waves
to drive the solar wind. The model includes SOHO/MDI magnetogram data
to calculate the coronal field, and also uses SOHO/EIT observations
to specify the density and temperature at the coronal boundary by
the Differential Emission Measure Tomography (DEMT) method. The
Wang-Sheeley-Arge empirical model is used to determine the Alfven
wave pressure necessary to produce the observed solar wind speeds. We
find that the new model is much better able to reproduce the solar
wind densities, and also correctly captures the compression at the
CME-driven shock due to the fixed adiabatic index.
Title: Component Reconnexion at the Heliopause
Authors: Moore, T. E.; Alouani-Bibi, F.; Opher, M.; Toth, G.; McComas,
D. J.
Bibcode: 2010AGUFMSH21A1795M
Altcode:
Extended X lines of component reconnection at the heliopause are derived
from 3D MHD simulations of the steady state heliosphere (Alouani-Bibi
et al 2010, Opher et al 2009). A similar study established this
technique to describe the extended shape of reconnection X-lines at
the magnetosphere, as result of its interaction with the interplanetary
field of varying orientation (Moore et al., 2002). At the heliopause,
reconnection X-line candidates are derived on the basis of geometrical
criteria, allowing for shear angles between the interacting fields of
less than 180 degree (Cowley 1976) and properties of the magnetic fields
and flows outside (interstellar medium) and inside (interplanetary space
beyond the termination shock) the heliopause. Kinetic effects addressed
by Swisdak et al. (2009) and Opher et al. (2010) can inhibit large
scale component reconnection, leading to more localized and nearly
anti-parallel reconnection, possibly accounting for the persistent
hot spot in IBEX heliopause ribbon.
Title: Multi-Scale Modeling of Global Magnetosphere Structure and
Dynamics
Authors: Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.;
de Zeeuw, D.; Gombosi, T. I.
Bibcode: 2010AGUFMSM31B1868K
Altcode:
To understand the role of magnetic reconnection in global evolution of
magnetosphere and to place spacecraft observations into global context
it is essential to perform global simulations with physically motivated
model of dissipation that is capable to reproduce reconnection rates
predicted by kinetic models. In our efforts to bridge the gap between
small scale kinetic modeling and global simulations we introduced an
approach that allows to quantify the interaction between large-scale
global magnetospheric dynamics and microphysical processes in diffusion
regions near reconnection sites. We utilized the high resolution global
MHD code BATSRUS and incorporated primary mechanism controlling the
dissipation in the vicinity of reconnection sites in terms of kinetic
corrections to induction and energy equations. One of the key elements
of the multiscale modeling of magnetic reconnection is identification
of reconnection sites and boundaries of surrounding diffusion regions
where non-MHD corrections are required. Reconnection site search in the
equatorial plane implemented in our previous studies is extended to cusp
and magnetpause reconnection, as well as for magnetotail reconnection
in realistic asymmetric configurations. The role of feedback between
the non-ideal effects in diffusion regions and global magnetosphere
structure and dynamics will be discussed.
Title: Hydrogen deflection in the heliosphere and the effect of
local interstellar magnetic field
Authors: Alouani-Bibi, F.; Opher, M.; Alexashov, D.; Toth, G.;
Izmodenov, V.
Bibcode: 2010AGUFMSH21A1800A
Altcode:
The interaction of solar wind plasma with the local interstellar
medium is studied using a coupled 3D Kinetic-MHD model. We show that
the deflection of hydrogen atoms that penetrates the heliosphere is
affected by the orientation and magnitude of the local interstellar
magnetic field (BLISM) as well as by the kinetic treatment of neutral H
atoms. We show that the observed deflection by Lallement et al (2005,
2010) of interstellar neutral hydrogen flow at the inner-heliosphere
is attained for different orientations and magnitudes of BLISM. The
hydrogen deflection plane (HDP, that is the plane containing the He and
H vector directions) is not a unique indicator for defining both the
BLISM orientation and magnitude. This study is done for a high intensity
field, BLISM (4.4µG), based on the analysis of the heliospheric
asymmetries (Opher et al. 2009) which used multi-fluid model of
solar wind and local interstellar interaction. Comparisons between
the kinetic and multi-fluid treatments of neutrals showed substantial
reduction in the hydrogen deflection for the kinetic approach.
Title: 3D, multi-fluid, MHD calculations of Mars interaction with
the solar wind
Authors: Najib, D.; Toth, G.; Nagy, A. F.; Curry, S.; Ma, Y.
Bibcode: 2010AGUFM.P53E1571N
Altcode:
We use our 3D multi-fluid MHD model to simulate the interaction of the
solar wind with non-magnetized planets, Mars in particular. We set
the lower boundary to 100 km and consider photo and electron impact
ionization as well as charge exchange in our chemistry. We also add
more realistic physical processes to our model, and test it against
different solar wind conditions. In addition, we are solving for
the electron pressure and therefore for the electron fluid. We also
calculate the escape fluxes and compare our results to observations.
Title: Numerical simulation of the solar wind disturbances propagating
to the distant heliosphere
Authors: Provornikova, E. A.; Opher, M.; Izmodenov, V.; Toth, G.
Bibcode: 2010AGUFMSH51D1721P
Altcode:
The propagation of waves in the solar wind plasma from 1 AU to the
heliospheric boundaries is studied. First we consider the simple
1D spherically symmetric model of the solar wind interaction with
the local interstellar medium to describe the wave evolution in
the supersonic solar wind flow in which parameters change with
heliocentric distance. The hydrodynamics solution and the influence of
the interstellar H atoms on the wave structure in the solar wind is
discussed. The 2D kinetic-gasdynamic model (Izmodenov et al., 2005,
2008) and 3D MHD model (Opher et al. 2009) are used to study the
interaction of the different types of waves in the solar wind with
the the termination shock and heliopause.
Title: Hall MHD Study of the Solar wind Interaction with Venus
Authors: Nagy, A. F.; Ma, Y.; Russell, C. T.; Zhang, T.; Wei, H.;
Strangeway, R. J.; Toth, G.
Bibcode: 2010AGUFMSM33D..01N
Altcode:
A multi-species, global, Hall MHD model is used to study the solar
wind interaction with Venus ionosphere/atmosphere. This model is
based on the numerical model that has been successfully applied to
Mars (Ma et al., 2004), with Hall effect included. A self-consistent
Venus ionosphere is calculated in the model with three ion species
(O+, O2+ and CO2+). The related chemical reactions and collision
processes are also considered. Our simulation domain covers the region
from 100km altitude to 16 Rv in the tail. An adaptive spherical grid
structure is used with radial resolution of about 15 km in the lower
ionosphere. Mass-loading effect is examined for both solar maximum
and solar minimum conditions. The importance of the Hall effect will
be discussed. We also show comparisons between our model results
with the magnetic fields observed by the magnetometer carried aboard
Venus Express.
Title: Two Way Coupling RAM-SCB to the Space Weather Modeling
Framework
Authors: Welling, D. T.; Jordanova, V. K.; Zaharia, S. G.; Toth, G.
Bibcode: 2010AGUFMSA41B1720W
Altcode:
The Ring current Atmosphere interaction Model with Self-Consistently
calculated 3D Magnetic field (RAM-SCB) has been used to successfully
study inner magnetosphere dynamics during different solar wind and
magnetosphere conditions. Recently, one way coupling of RAM-SCB
with the Space Weather Modeling Framework (SWMF) has been achieved
to replace all data or empirical inputs with those obtained through
first-principles-based codes: magnetic field and plasma flux outer
boundary conditions are provided by the Block Adaptive Tree Solar wind
Roe-type Upwind Scheme (BATS-R-US) MHD code, convection electric field
is provided by the Ridley Ionosphere Model (RIM), and ion composition
is provided by the Polar Wind Outflow Model (PWOM) combined with a
multi-species MHD approach. These advances, though creating a powerful
inner magnetosphere virtual laboratory, neglect the important mechanisms
through which the ring current feeds back into the whole system,
primarily the stretching of the magnetic field lines and shielding of
the convection electric field through strong region two Field Aligned
Currents (FACs). In turn, changing the magnetosphere in this way changes
the evolution of the ring current. To address this shortcoming, the
coupling has been expanded to include feedback from RAM-SCB to the
other coupled codes: region two FACs are returned to the RIM while
total plasma pressure is used to nudge the MHD solution towards the
RAM-SCB values. The impacts of the two way coupling are evaluated on
three levels: the global magnetospheric level, focusing on the impact on
the ionosphere and the shape of the magnetosphere, the regional level,
examining the impact on the development of the ring current in terms
of energy density, anisotropy, and plasma distribution, and the local
level to compare the new results to in-situ measurements of magnetic
and electric field and plasma. The results will also be compared to past
simulations using the one way coupling and no coupling whatsoever. This
work is the first to fully couple an anisotropic kinetic ring current
code with a self-consistently calculated magnetic field to a set of
global models.
Title: Modeling the Rapid Rebuilding of the Radiation Belts During
High Speed Streams
Authors: Glocer, A.; Fok, M. H.; Nagai, T.; Toth, G.
Bibcode: 2010AGUFMSM24A..07G
Altcode:
Recent observations by Akebono/RDM have shown several cases of
>2.5 MeV radiation belt electron enhancements occuring on time
scales of less than a few hours. These intervals are shorter than
typical radial diffusion or wave-particle interactions can account
for. We choose two so-called "rapid rebuilding'' events that occur
during high speed streams (July 22, 2009 and September 4, 2008) and
simulated them with the coupled BATSRUS-RBE model. We demonstrate
that strong dipolarization events in the magnetospheric magnetic field
result in strong radial transport and energization of radiation belt
electrons. The modeled enhancment, time scales, and commencment time
are shown to be consistent with Akebono/RDM observations.
Title: Simulating the one-dimensional structure of Titan's upper
atmosphere: 1. Formulation of the Titan Global Ionosphere-Thermosphere
Model and benchmark simulations
Authors: Bell, Jared M.; Bougher, Stephen W.; Waite, J. Hunter;
Ridley, Aaron J.; Magee, Brian A.; Mandt, Kathleen E.; Westlake,
Joseph; DeJong, Anna D.; Bar–Nun, Akiva; Jacovi, Ronen; Toth, Gabor;
De La Haye, Virginie
Bibcode: 2010JGRE..11512002B
Altcode:
We employ a newly developed Navier-Stokes model, the Titan Global
Ionosphere-Thermosphere Model (T-GITM) to address the one dimensional
(1-D) coupled composition, dynamics, and energetics of Titan's upper
atmosphere. Our main goals are to delineate the details of this new
theoretical tool and to present benchmark calibration simulations
compared against the Ion-Neutral Mass Spectrometer (INMS) neutral
density measurements. First, we outline the key physical routines
contained in T-GITM and their computational formulation. Then, we
compare a series of model simulations against recent 1-D work by Cui
et al. (2008), Strobel (2008, 2009), and Yelle et al. (2008) in order
to provide a fiducial for calibrating this new model. In paper 2 and a
future paper, we explore the uncertainties in our knowledge of Titan's
atmosphere between ∼500 km and 1000 km in order to determine how
the present measurements constrain our theoretical understanding of
atmospheric structures and processes.
Title: The effect of the magnetic field stretching on the development
of the ring current
Authors: Ilie, R.; Toth, G.; Liemohn, M. W.; Skoug, R. M.
Bibcode: 2010AGUFMSM31B1871I
Altcode:
While the dipolar solution for the geomagnetic field during quiet
times represents a reasonable assumption, during storm activity this
assumption becomes invalid. Theoretical and numerical modifications to
an inner magnetosphere - Hot Electron Ion Drift Integrator (HEIDI)-
model are implemented, in order to accommodate for a non-dipolar
arbitrary magnetic field. HEIDI solves the time dependent, gyration and
bounced averaged kinetic equation for the phase space density of one
or more ring current species. In this study the effect of the magnetic
field stretching on the build-up of the ring current is examined for
both real and idealized input conditions.
Title: Self-consistent inner magnetosphere simulation driven by a
global MHD model
Authors: Zaharia, Sorin; Jordanova, V. K.; Welling, D.; Tóth, G.
Bibcode: 2010JGRA..11512228Z
Altcode:
We present results from a one-way coupling between the kinetic Ring
Current Atmosphere Interactions Model with Self-Consistent B field
(RAM-SCB) and the Space Weather Modeling Framework (SWMF). RAM-SCB
obtains plasma distribution and magnetic field at model boundaries
from the Block Adaptive Tree Solar Wind Roe Upwind Scheme (BATS-R-US)
magnetohydrodynamics (MHD) model and convection potentials from the
Ridley Ionosphere Model within SWMF. We simulate the large geomagnetic
storm of 31 August 2005 (minimum SYM-H of -116 nT). Comparing SWMF
output with Los Alamos National Laboratory geostationary satellite
data, we find SWMF plasma to be too cold and dense if assumed to
consist only of protons; this problem is alleviated if heavier ions are
considered. With SWMF inputs, we find that RAM-SCB reproduces well storm
time magnetosphere features: ring current morphology, dusk side peak,
pitch angle anisotropy, and total energy. The RAM-SCB ring current and
Dst are stronger than the SWMF ones and reproduce observations much
better. The calculated field-aligned currents (FAC) compare reasonably
well with 2 h averaged pictures from Iridium satellite data. As the
ring current peak rotates duskward in the storm main phase, the region
2 FACs rotate toward noon, a feature also seen in observations. Finally,
the RAM-SCB magnetic field outperforms both the dipole and the BATS-R-US
field at Cluster and Polar spacecraft locations. This study shows the
importance of a kinetic self-consistent approach and the sensitive
dependence of the storm time inner magnetosphere on plasma sheet
conditions and the cross polar cap potential. The study showcases the
RAM-SCB capability as an inner magnetosphere module coupled with a
global MHD model.
Title: Improving the physics models in the Space Weather Modeling
Framework
Authors: Toth, G.; Fang, F.; Frazin, R. A.; Gombosi, T. I.; Ilie,
R.; Liemohn, M. W.; Manchester, W. B.; Meng, X.; Pawlowski, D. J.;
Ridley, A. J.; Sokolov, I.; van der Holst, B.; Vichare, G.; Yigit,
E.; Yu, Y.; Buzulukova, N.; Fok, M. H.; Glocer, A.; Jordanova, V. K.;
Welling, D. T.; Zaharia, S. G.
Bibcode: 2010AGUFMSM51A1757T
Altcode:
The success of physics based space weather forecasting depends on
several factors: we need sufficient amount and quality of timely
observational data, we have to understand the physics of the Sun-Earth
system well enough, we need sophisticated computational models,
and the models have to run faster than real time on the available
computational resources. This presentation will focus on a single
ingredient, the recent improvements of the mathematical and numerical
models in the Space Weather Modeling Framework. We have developed a
new physics based CME initiation code using flux emergence from the
convection zone solving the equations of radiative magnetohydrodynamics
(MHD). Our new lower corona and solar corona models use electron heat
conduction, Alfven wave heating, and boundary conditions based on solar
tomography. We can obtain a physically consistent solar wind model from
the surface of the Sun all the way to the L1 point without artificially
changing the polytropic index. The global magnetosphere model can now
solve the multi-ion MHD equations and take into account the oxygen
outflow from the polar wind model. We have also added the options
of solving for Hall MHD and anisotropic pressure. Several new inner
magnetosphere models have been added to the framework: CRCM, HEIDI
and RAM-SCB. These new models resolve the pitch angle distribution
of the trapped particles. The upper atmosphere model GITM has been
improved by including a self-consistent equatorial electrodynamics
and the effects of solar flares. This presentation will very briefly
describe the developments and highlight some results obtained with
the improved and new models.
Title: Two-fluid Mhd Study On Ion Loss From Titan'S Atmosphere
Authors: Ma, Yingjuan; Russell, C. T.; Nagy, A. F.; Toth, G.;
Dougherty, M. K.; Cravens, T. E.; Wellbrock, A.; Coates, A. J.;
Garnier, P.; Wahlund, J.; Crary, F. J.
Bibcode: 2010DPS....42.3617M
Altcode: 2010BAAS...42.1068M
This presentation report progress on modeling of Titan's plasma
interaction. The single fluid model is improved by including an
electron energy equation in the Hall MHD model so that both electron
temperature and ion temperature are self-consistently calculated. The
plasma interaction with Titan is expected to vary as the moon moves
around its orbit. Using the improved model, we compare the structure
of the interaction under two extreme conditions, corresponding to
upstream flow interacting with the nightside and dayside ionosphere
respectively. Model results show that the dayside ionosphere is more
extended and the flow is more disturbed in the 6 SLT case than in
the 18 SLT case. We also calculate the ion escape rates under these
conditions and compare with Cassini observations of the available low
altitudes Cassini flybys in corresponding SLTs.
Title: Multi-Ion Magnetohydrodynamics
Authors: Toth, G.; Glocer, A.; Ma, Y.; Najib, D.; Gombosi, T.
Bibcode: 2010ASPC..429..213T
Altcode:
We derive and numerically solve the full set of magnetohydrodynamic
equations with multiple ion fluids. The numerical difficulties and the
algorithmic solutions are discussed. We show some preliminary results
for the interaction of Mars' ionosphere with the solar wind.
Title: Comparison of the open-closed separatrix in a global
magnetospheric simulation with observations: The role of the ring
current
Authors: Rae, I. J.; Kabin, K.; Lu, J. Y.; Rankin, R.; Milan, S. E.;
Fenrich, F. R.; Watt, C. E. J.; Zhang, J. -C.; Ridley, A. J.; Gombosi,
T. I.; Clauer, C. R.; Tóth, G.; DeZeeuw, D. L.
Bibcode: 2010JGRA..115.8216R
Altcode: 2010JGRA..11508216R
The development of global magnetospheric models, such as Space
Weather Modeling Framework (SWMF), which can accurately reproduce
and track space weather processes has high practical utility. We
present an interval on 5 June 1998, where the location of the
polar cap boundary, or open-closed field line boundary (OCB), can be
determined in the ionosphere using a combination of instruments during
a period encompassing a sharp northward to southward interplanetary
field turning. We present both point- and time-varying comparisons
of the observed and simulated boundaries in the ionosphere and
find that when using solely the coupled ideal magnetohydrodynamic
magnetosphere-ionosphere model, the rate of change of the OCB to a
southward turning of the interplanetary field is significantly faster
than that computed from the observational data. However, when the inner
magnetospheric module is incorporated, the modeling framework both
qualitatively, and often quantitatively, reproduces many elements of
the studied interval prior to an observed substorm onset. This result
demonstrates that the physics of the inner magnetosphere is critical
in shaping the boundary between open and closed field lines during
periods of southward interplanetary magnetic field (IMF) and provides
significant insight into the 3-D time-dependent behavior of the Earth's
magnetosphere in response to a northward-southward IMF turning. We
assert that during periods that do not include the tens of minutes
surrounding substorm expansion phase onset, the coupled SWMF model may
provide a valuable and reliable tool for estimating both the OCB and
magnetic field topology over a wide range of latitudes and local times.
Title: Including gap region field-aligned currents and magnetospheric
currents in the MHD calculation of ground-based magnetic field
perturbations
Authors: Yu, Yiqun; Ridley, Aaron J.; Welling, Dan T.; Tóth, Gabor
Bibcode: 2010JGRA..115.8207Y
Altcode: 2010JGRA..11508207Y
Many high-latitude modeling studies utilize the horizontal ionospheric
Hall current in calculating ground-based magnetic perturbations, but
low-latitude and midlatitude studies should include current systems such
as the magnetospheric, field-aligned, and Pedersen currents. Recently,
by including all these current systems, a more precise ground-based
perturbation calculator has been implemented in the Space Weather
Modeling Framework. Using this new method, ground-based perturbations
generated by different current systems are analyzed at low, middle,
and high latitudes. As a result of the current systems, MLT-UT maps
of ground-based perturbations are studied. Furthermore, nine storms
events are simulated at more than 20 low-latitude and midlatitude
magnetometer locations and compared with observational ground-based
perturbations. These studies show that for specifying the northward
component of the ground magnetic perturbations, the inclusion of
magnetospheric, field-aligned, and Pedersen current is important
and improves the prediction significantly over the prediction only
considering the Hall current in the calculation. The improvement is
the most during the storm main phase. However, for the vertical and
eastward components of the perturbations, which were typically smaller
than the northward component, the inclusion of these current systems
actually made the specifications worse because the ring current in
the model rotates more toward the dayside than in reality.
Title: Dynamics of ring current and electric fields in the inner
magnetosphere during disturbed periods: CRCM-BATS-R-US coupled model
Authors: Buzulukova, N.; Fok, M. -C.; Pulkkinen, A.; Kuznetsova, M.;
Moore, T. E.; Glocer, A.; Brandt, P. C.; Tóth, G.; Rastätter, L.
Bibcode: 2010JGRA..115.5210B
Altcode: 2010JGRA..11505210B
We present simulation results from a one-way coupled global MHD model
(Block-Adaptive-Tree Solar-Wind Roe-Type Upwind Scheme, BATS-R-US) and
kinetic ring current models (Comprehensive Ring Current Model, CRCM,
and Fok Ring Current, FokRC). The BATS-R-US provides the CRCM/FokRC
with magnetic field information and plasma density/temperature at the
polar CRCM/FokRC boundary. The CRCM uses an electric potential from
the BATS-R-US ionospheric solver at the polar CRCM boundary in order
to calculate the electric field pattern consistent with the CRCM
pressure distribution. The FokRC electric field potential is taken
from BATS-R-US ionospheric solver everywhere in the modeled region,
and the effect of Region II currents is neglected. We show that for
an idealized case with southward-northward-southward Bz IMF turning,
CRCM-BATS-R-US reproduces well known features of inner magnetosphere
electrodynamics: strong/weak convection under the southward/northward
Bz; electric field shielding/overshielding/penetration effects; an
injection during the substorm development; Subauroral Ion Drift or
Polarization Jet (SAID/PJ) signature in the dusk sector. Furthermore,
we find for the idealized case that SAID/PJ forms during the substorm
growth phase, and that substorm injection has its own structure of
field-aligned currents which resembles a substorm current wedge. For
an actual event (12 August 2000 storm), we calculate ENA emissions and
compare with Imager for Magnetopause-to-Aurora Global Exploration/High
Energy Neutral Atom data. The CRCM-BATS-R-US reproduces both the
global morphology of ring current and the fine structure of ring
current injection. The FokRC-BATS-R-US shows the effect of a realistic
description of Region II currents in ring current-MHD coupled models.
Title: Interaction of Saturn's magnetosphere and its moons:
1. Interaction between corotating plasma and standard obstacles
Authors: Jia, Y. -D.; Russell, C. T.; Khurana, K. K.; Toth, G.;
Leisner, J. S.; Gombosi, T. I.
Bibcode: 2010JGRA..115.4214J
Altcode: 2010JGRA..11504214J
The interaction of Saturn's inner magnetosphere with its moons ranges
from the addition of significant quantities of gas, dust, and plasma,
causing significant consequences for the dynamics and energetics
of the entire Saturnian magnetosphere, to the simple absorption of
plasma and energetic particles by the icy moons with non-electrically
conducting interiors. The interaction with these moons is complex with
the contribution of many physical processes, depending on the geometry
of any plume, the structure of the atmosphere, and its interaction with
the surface and interior of the moon, the latter by induced fields. Our
ultimate goal is to understand the complexities of this interaction
and its temporal variations, especially at Enceladus. In this paper
we use magnetohydrodynamics (MHD) code for addressing the flow around
obstacles that are simpler than the Enceladus interaction. These
simulations both help us understand the interaction with other icy moons
and prepare us for the simulation of the flow around Enceladus. The
processes involved include ordinary collisions, impact ionization,
photoionization, and charge exchange. We examine a series of simple
canonical interactions before we later apply our simulation where
the multiple processes are occurring simultaneously with asymmetric
geometries. We apply our 3-D MHD model to simulate the interaction
between the Saturnian corotational plasma flow for the following cases:
an absorbing body having an insulating surface; ion pickup via photo and
impact ionization from a spherically symmetric neutral cloud; charge
exchange with such a neutral cloud; and ion pickup at an insulating,
absorbing body with an atmosphere acted upon by the sum of the three
ionization processes. In addition to validating the model and obtaining
a deeper understanding of the consequences of each interaction, we can
immediately make some conclusions about the Enceladus interaction. We
find that the magnetometer data are most consistent with the surface
of Enceladus being absorbing and insulating, rather than the surface
being reflecting and electrically conducting. For the conditions in
the corotating flow at Enceladus, the perturbation to the plasma flow
produced by photo/impact ionization is an order of magnitude smaller
than that produced by charge exchange. Moreover, the perturbation to the
magnetic field Bz component by a spherically symmetric mass
loading source alone is an order of magnitude smaller than that observed
in the neighborhood of the plume. Thus, the perturbation observed
in the magnetometer data is primarily due to the mass loading in the
plume, which is primarily ion-neutral charge exchange. The geometry
and source strength of the plume are investigated in a following paper.
Title: The Space Weather Modeling Framework (SWMF): Models and
Validation
Authors: Gombosi, Tamas; Toth, Gabor; Sokolov, Igor; de Zeeuw, Darren;
van der Holst, Bart; Ridley, Aaron; Manchester, Ward, IV
Bibcode: 2010cosp...38.4166G
Altcode: 2010cosp.meet.4166G
In the last decade our group at the Center for Space Environment
Modeling (CSEM) has developed the Space Weather Modeling Framework
(SWMF) that efficiently couples together different models describing
the interacting regions of the space environment. Many of these domain
models (such as the global solar corona, the inner heliosphere or the
global magneto-sphere) are based on MHD and are represented by our
multiphysics code, BATS-R-US. SWMF is a powerful tool for coupling
regional models describing the space environment from the solar
photosphere to the bottom of the ionosphere. Presently, SWMF contains
over a dozen components: the solar corona (SC), eruptive event generator
(EE), inner heliosphere (IE), outer heliosphere (OH), solar energetic
particles (SE), global magnetosphere (GM), inner magnetosphere (IM),
radiation belts (RB), plasmasphere (PS), ionospheric electrodynamics
(IE), polar wind (PW), upper atmosphere (UA) and lower atmosphere
(LA). This talk will present an overview of SWMF, new results obtained
with improved physics as well as some validation studies.
Title: A 3D Multi-fluid MHD Study of the Interaction of the Solar
Wind with the Ionosphere/Atmosphere System of Mars.
Authors: Najib, Dalal; Nagy, Andrew; Toth, Gabor; Ma, Yingjuan
Bibcode: 2010cosp...38.1406N
Altcode: 2010cosp.meet.1406N
We use our new four species multi-fluid model to study the interaction
of the solar wind with Mars. The lower boundary of our model is at
100 km, below the main ionospheric peak, and the radial resolution is
about 10 km in the ionosphere, thus the model does a very good job in
reproducing the ionosphere and the associated processes. We carry out
calculations for high and low solar activity conditions and establish
the importance of mass loading by the extended exosphere of Mars. We
also calculate the atmospheric escape of the ionospheric species,
including pick up ions. Finally, we compare our model results with
the Viking, MGS and Mars Express observations.
Title: Exploring the Effects of Ionospheric Outflow on the Inner
Magnetosphere using RAM-SCB
Authors: Welling, Daniel; Jordanova, Vania; Zaharia, Sorin; Toth, Gabor
Bibcode: 2010cosp...38.2212W
Altcode: 2010cosp.meet.2212W
The Ring current Atmosphere interactions Model with Self-Consistently
calculated 3D Mag-netic field (RAM-SCB) has been used to successfully
study inner magnetosphere dynamics during different solar wind and
magnetosphere conditions. Historically, this numerical model has relied
on empirical formulations to provide magnetic field boundary conditions,
ionospheric electric potential, and to specify heavy ion composition at
the outer boundary. Either empirical models or observations typically
specify plasma density and temperature at the boundary. Re-cently,
RAM-SCB has been integrated into the Space Weather Modeling Framework,
a flexible system that creates real time, two-way coupling between
RAM-SCB, the multi-species version of BATS-R-US global MHD and the
Polar Wind Outflow Model. Through these couplings, RAM-SCB receives
first-principle derived magnetic and plasma boundary conditions as
well as convective electric potentials from the SWMF and returns inner
magnetosphere plasma pres-sure to correct the MHD solution. This
work uses the newly coupled system to explore the relationship
between ionospheric outflow and ring current plasma distribution and
composition. Data-model comparisons of magnetic field and particle
fluxes are used to investigate how well the coupled system represents
real world conditions.
Title: Global Asymmetries in the Heliosphere: Signature of the
Interstellar Magnetic Field
Authors: Opher, Merav; Alouani-Bibi, Fathallah; Izmodenov, Vladislav;
Richardson, John; Toth, Gabor; Gombosi, Tamas
Bibcode: 2010cosp...38.1604O
Altcode: 2010cosp.meet.1604O
In recent years it become clear that magnetic field effects, plays an
important role in the Heliosphere, from shaping it and possible being
responsible for the asymmetries observed in the Voyager data (e.g.,
Opher et al. 2007, 2009). However, the strength and orientation of
the field in the local interstellar medium near the heliosphere has
been poorly constrained. Previous estimates of the field strength
range from 1.8-2.5 G and the field was thought to be parallel to the
Galactic plane or inclined by 38-60 (Lallement et al. 2005) or 60-90
(Opher et al. 2007) to this plane. These estimates relied either on
indirect observational inferences or modeling in which the interstellar
neutral hydrogen was not taken into account. We will discuss recent
work that indicate that based on asymmetries detected by Voyager 1
and 2 and measurements of the deflection of the solar wind plasma
flows in the heliosheath (Opher et al. 2009) indicate that the field
strength in the local interstellar medium is strong, between 4-5 G
(Other works such as Izmodenov 2009; Pogorelov et al. 2009; Ratkiewickz
et al. 2009 found similar strength). The field is tilted 20-30 from
the interstellar medium flow direction (resulting from the peculiar
motion of the Sun in the Galaxy) and is at an angle of about 30 from
the Galactic plane. We will discuss the effect of such magnetic field
in the global asymmetries of the heliosphere. We further will comment
on the effect on asymmetries of our recent model of Kinetic-MHD model
treating the neutrals in kinetic fashion (Alouani-Bibi et al. 2010). We
will relate our findings with the most recent results of IBEX that
indicate that the interstellar magnetic field has a strong signature
in the emission of energetic neutrals.
Title: Magnetosphere modeling using MHD with anisotropic pressure
Authors: Toth, Gabor; Meng, Xing; van der Holst, Bart; Gombosi, Tamas
Bibcode: 2010cosp...38.2066T
Altcode: 2010cosp.meet.2066T
In several space physics systems, including the magnetosphere,
the parallel and perpendicular (with respect to the magnetic
field) components of the pressure tensor can become significantly
different. The BATS-R-US code has recently been extended with the
capability of solving the magnetohydrodynamic equations with an
anisotropic ion pressure. The anisotropy is limited by instabilities
and particle-particle and particle-wave interactions. These effects
are taken into account as parameterized source terms. We use the total
energy equation in combination with the two pressure equations so that
we use a conservative scheme as much as possible. This is important to
correctly capture the bow shock. We also have the option of allowing the
electron temperature to be different from the ion temperature(s). In
our current model the separate electron temperature is assumed to be
isotropic. Our preliminary results indicate that using anisotropic ion
pressure instead of isotropic pressure gives significantly different
results. In this talk we will present a systematic comparison between
the isotropic and anisotropic MHD models. We will use observational
data from the WIND and Cluster satellites to validate our new model
for the quiet magnetosphere as well as for magnetic storms.
Title: Hybrid simulation of interstellar wind interaction with solar
wind plasma
Authors: Izmodenov, V.; Alouani Bibi, F.; Opher, M.; Aleksashov, D.;
Toth, G.
Bibcode: 2009AGUFMSH21A1496I
Altcode:
Iterative Hybrid (Kinetic / MHD) approach is used to study the
interaction of the partly ionized interstellar wind with the fully
ionized solar wind plasma. Charged and neutral components are coupled
though charge exchange. The location and topology (e.g. asymmetries) of
the Heliospheric boundaries (BS, HP and TS) are analyzed and compared
to previous multi-fluid approach, where the kinetic description of
neutrals was approximated by hydrodynamic multi neutral species (4
species). Based on analysis of global heliospheric asymmetries, we use
our best estimate for the interstellar magnetic field orientation and
intensity. The iterative scheme is performed using the ionized fluid
properties obtained with our 3D MHD code as a source term for the
neutral H, which is treated by solving the Boltzmann Kinetic equation,
the output of the later is fed back to the MHD code as plasma source
terms. Each of these phases is allowed to reach a steady state before
each iteration.
Title: Ion Loss from Titan's Atmosphere versus Local Time: A two-fluid
MHD Study
Authors: Ma, Y.; Russell, C. T.; Nagy, A. F.; Toth, G.; Dougherty,
M. K.; Cravens, T. E.; Wellbrock, A.; Coates, A. J.; Garnier, P.;
Wahlund, J.; Crary, F. J.
Bibcode: 2009AGUFM.P13D..06M
Altcode:
This presentation report recent progress on modeling of plasma
interaction around Titan. The single fluid MHD model reproduces only
the sum of the electron temperature and ion temperature. Our recent
modeling includes an electron energy equation in the Hall MHD model so
that both electron temperature and ion temperature ARE self-consistently
calculated. The plasma interaction with Titan is expected to vary as the
moon moves around its orbit. Using the improved model, we compare the
structure of the interaction under two extreme conditions, corresponding
to upstream flow interacting with the nightside and dayside ionosphere
respectively. Model results show that the dayside ionosphere is more
extended and the flow is more disturbed in the 6 SLT case than in the
18 SLT case. We calculate the ion escape rates under these conditions
and compare with Cassini observations of the only two available low
altitudes Cassini flybys in Saturn's dawn (T5 flyby) and dusk (T34
flyby) sectors.
Title: Global simulations of dynamic magnetosphere response to steady
southward IMF driving
Authors: Patel, K.; Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.;
Toth, G.; de Zeeuw, D.; Gombosi, T. I.
Bibcode: 2009AGUFMSM13B1608P
Altcode:
We utilize the global MHD model BATS-R-US with incorporated
nongyrotropic effects in diffusion regions to investigate the dynamic
magnetosphere response to southward interplanetary magnetic field (IMF)
driving. We analyze relative importance of the solar wind conditions,
ionosphere conductance and dissipation mechanisms supporting the
magnetotail reconnection in controlling the mode of magnetic energy
release. The conditions for the quasi-periodic loading/unloading
sawtooth response will be discussed.
Title: A new method for global magnetosphere simulations: an implicit
scheme with limited numerical diffusion
Authors: Toth, G.; Meng, X.; Gombosi, T. I.
Bibcode: 2009AGUFMSM51A1321T
Altcode:
We are introducing a new scheme to model the global magnetosphere
with less numerical diffusion. The new scheme combines the stability
of an implicit solver with a limited diffusive numerical flux. The
new scheme is an alternative to the standard "Boris correction"
that solves the semi-relativistic MHD equations with an artificially
reduced speed of light. While the Boris correction is an efficient and
well established method, it changes the time dependent behavior of the
equations, since it artificially reduces the propagation speeds. The
new scheme on the other hand does not modify the physics, only the
numerical algorithm. We are comparing the limited numerical diffusion
scheme with the Boris correction for idealized problems as well as
for magnetic storm simulations.
Title: A 3D Multi-fluid MHD Study of the Interaction of the Solar
Wind with the Ionosphere/Atmosphere System of Mars
Authors: Najib, D.; Nagy, A. F.; Ma, Y.; Toth, G.
Bibcode: 2009AGUFM.P11B1213N
Altcode:
We use our new four species multi-fluid model to study the interaction
of the solar wind with Mars. The lower boundary of our model is at
100 km, below the main ionospheric peak, and the radial resolution
is about 10 km in the ionosphere, thus the model does a very good
job in reproducing the ionosphere and the associated processes. We
carry out calculations for high and low solar activity conditions and
establish the importance of the extended exosphere of Mars. We also
calculate the atmospheric escape of the ionospheric species and the
added contributions from charge exchange in the exosphere. Finally,
we compare our model results with the Viking, MGS and Mars observations.
Title: Coupling HEIDI into the SWMF
Authors: Ilie, R.; Liemohn, M. W.; Toth, G.; Ridley, A. J.
Bibcode: 2009AGUFMSM11A1546I
Altcode:
In this study we will present results from the Hot Electron and Ion
Drift Integrator (HEIDI) model, which has been recently coupled into
the Space Weather Modeling Framework (SWMF). HEIDI solves the time
dependent, gyration and bounced averaged kinetic equation for the
phase space density of different ring current species. An advantage
of using HEIDI is that it computes full pitch angle distributions
for all local times and radial distances. The largest modification
and improvement to HEIDI is the inclusion of a non-dipolar, time
dependent magnetic field. The bounce-averaged coefficients, which
make up the bounce-averaged kinetic equation, have been rewritten to
account for an arbitrary magnetic field. The gradient/curvature drift
includes both azimuthal and radial components. Moreover, arbitrary grid
sizes in radial, azimuthal, energy and pitch angle are allowed. HEIDI
receives full and realistic magnetic field distributions from BATSRUS
and the electric potential from the ionospheric electrodynamics model,
through couplers within SWMF. Preliminary results of the self-consistent
coupling between HEIDI and BATSRUS during idealized and realistically
drive time-periods will be presented.
Title: Multifluid Block-Adaptive-Tree Solar wind Roe-type Upwind
Scheme: Magnetospheric composition and dynamics during geomagnetic
storms—Initial results
Authors: Glocer, A.; Tóth, G.; Ma, Y.; Gombosi, T.; Zhang, J. -C.;
Kistler, L. M.
Bibcode: 2009JGRA..11412203G
Altcode:
The magnetosphere contains a significant amount of ionospheric
O+, particularly during geomagnetically active times. The
presence of ionospheric plasma in the magnetosphere has a notable
impact on magnetospheric composition and processes. We present a
new multifluid MHD version of the Block-Adaptive-Tree Solar wind
Roe-type Upwind Scheme model of the magnetosphere to track the fate
and consequences of ionospheric outflow. The multifluid MHD equations
are presented as are the novel techniques for overcoming the formidable
challenges associated with solving them. Our new model is then applied
to the May 4, 1998 and March 31, 2001 geomagnetic storms. The results
are juxtaposed with traditional single-fluid MHD and multispecies MHD
simulations from a previous study, thereby allowing us to assess the
benefits of using a more complex model with additional physics. We
find that our multifluid MHD model (with outflow) gives comparable
results to the multispecies MHD model (with outflow), including a more
strongly negative Dst, reduced CPCP, and a drastically improved magnetic
field at geosynchronous orbit, as compared to single-fluid MHD with
no outflow. Significant differences in composition and magnetic field
are found between the multispecies and multifluid approach further away
from the Earth. We further demonstrate the ability to explore pressure
and bulk velocity differences between H+ and O+,
which is not possible when utilizing the other techniques considered.
Title: The link between pick-up ions and energetic neutral atoms
Authors: Alouani Bibi, F.; Opher, M.; Prested, C. L.; Schwadron,
N. A.; Toth, G.
Bibcode: 2009AGUFMSH21B1508A
Altcode:
We study the source (starting inside the termination shock) and
transport of pick-up ions (PUI) linked to the generation of energetic
neutral atoms (ENA). We use a three dimensional multi-fluid (seven
populations: thermal protons, four neutral populations, PUI ions and
ENA) magneto-hydrodynamic model. PUIs are injected into the simulation
grid as an inner-boundary condition at 30 AU and appropriate PUI source
terms are included inside the heliopause. At the inner-boundary, the
PUI initial density and temperature are derived analytically assuming
a Vasyliunas-Siscoe distribution function for these suprathermal
particles. PUI production beyond the heliopause is neglected. The
variations in the non-thermal solar wind pressure inside the heliopause
as a result of PUI production and convection are analyzed. Implications
of these pressure variations on the heliospheric boundaries and
resulting ENA maps are discussed.
Title: Comparing Different Approaches of Modeling Magnetospheric
Composition
Authors: Glocer, A.; Toth, G.; Fok, M. H.; Gombosi, T. I.; Yu, Y.;
Moore, T.
Bibcode: 2009AGUFMSM22A..08G
Altcode:
The magnetosphere contains a significant amount of ionospheric O+,
particularly during geomagnetically active times. The presence of this
ionospheric plasma has a notable impact on magnetospheric composition
and processes. There currently exist only a handful of approaches to
model magnetospheric composition: multi-fluid MHD, multi-species MHD,
and individual particle tracing techniques. We present an overview
of the advantages and disadvantages of these different approaches
and provide a direct comparison of their results. Details of the new
multi-fluid and multi-species MHD versions of the BATS-R-US model of
the magnetosphere are given. The multi-fluid and multi-species MHD
approaches are directly compared for May 4, 1998 and March 31, 2001
geomagnetic storms. These approaches yield comparable results, namely
a more strongly negative Dst, reduced CPCP, and a drastically improved
magnetic field at geosynchronous orbit, as compared to single-fluid
MHD with no ionospheric outflow. We also simulate the October 2002
geomagnetic storm and directly compare our multi-fluid and multi-species
simulations to the particle tracing approach used by Fok et al, [2008].
Title: Orientation and Magnitude of the Interstellar Magnetic Field
from Heliosheath Flows
Authors: Opher, M.; Alouani Bibi, F.; Toth, G.; Richardson, J. D.;
Izmodenov, V.; Gombosi, T. I.
Bibcode: 2009AGUFMSH32A..04O
Altcode:
We show that the heliosheath flows can be used as a new and highly
important data set to determine the interstellar magnetic field
orientation and magnitude. We use a new three-dimensional model
that includes both the plasma and the neutral H atoms as well as the
interplanetary and interstellar magnetic fields. The field orientation
and magnitude that we derive differ substantially from the those
previously reported (Opher et al. 2006, 2007). We comment on the
consequences of this result on the heliospheric global asymmetries (such
as the field-aligned streaming of low energy particles, the distance of
the termination shock, and the shape of the heliopause). We comments
as well on the inference on the conditions on the local interstellar
medium. We study the effect of numerical resolution and non-stationary
on the model shock and find them to be negligible. We also comment
on the possible effects of the tilt of current sheet, not included
currently in the model (which at the time of the termination shock
crossings of Voyager 1 and 2 was about 30 degrees). We present a
simulation with a scaled down heliosphere which includes a dynamic
time dependent current sheet.
Title: Coupling RAM-SCB to a Magnetospheric GCM and Polar Wind
Outflow Model
Authors: Welling, D. T.; Jordanova, V.; Zaharia, S. G.; Toth, G.
Bibcode: 2009AGUFMSM13C1617W
Altcode:
The Ring current Atmosphere interaction Model with Self-Consistently
calculated 3D Magnetic field (RAM-SCB) has been used to successfully
study inner magnetosphere dynamics during different solar wind and
magnetosphere conditions. Historically, this numerical model has
relied on empirical formulations to provide magnetic field boundary
conditions, ionospheric electric potential, and to specify heavy ion
content at the outer boundary. Either empirical models or observations
typically specify plasma density at the boundary. Recently, RAM-SCB
has been integrated into the Space Weather Modeling Framework,
a flexible system that creates real time, two-way coupling between
RAM-SCB, the multi-species version of BATS-R-US global MHD and the
Polar Wind Outflow Model. Through these couplings, RAM-SCB receives
first-principle derived magnetic and plasma boundary conditions from
the SWMF and returns inner magnetosphere plasma pressure to correct the
MHD solution. This paper summarizes the methodology used and presents
simulation results of magnetospheric storms using the coupled codes. The
impact of the coupling, especially the delivery of heavy ionospheric
ions to RAM-SCB, on plasma pressure, energy density, and anisotropy
in the inner magnetosphere are explored. Data-model comparisons are
used to investigate how well the coupled system represents real world
conditions.
Title: BATSRUS with Hall MHD and anisotropic pressure
Authors: Meng, X.; Toth, G.; Gombosi, T. I.
Bibcode: 2009AGUFMSM51A1344M
Altcode:
We describe our progress in extending the capabilities of the BATS-R-US
MHD code to model anisotropic pressure. In several space physics
applications the assumption of isotropic pressure is not valid, and
the parallel and perpendicular (with respect to the magnetic field)
components of the pressure tensor can become significantly different. We
will describe the equations and our progress with the implementation
and testing of this new capability.
Title: A strong, highly-tilted interstellar magnetic field near the
Solar System
Authors: Opher, M.; Bibi, F. Alouani; Toth, G.; Richardson, J. D.;
Izmodenov, V. V.; Gombosi, T. I.
Bibcode: 2009Natur.462.1036O
Altcode:
Magnetic fields play an important (sometimes dominant) role in the
evolution of gas clouds in the Galaxy, but the strength and orientation
of the field in the interstellar medium near the heliosphere has
been poorly constrained. Previous estimates of the field strength
range from 1.8-2.5μG and the field was thought to be parallel to the
Galactic plane or inclined by 38-60° (ref. 2) or 60-90° (ref. 3)
to this plane. These estimates relied either on indirect observational
inferences or modelling in which the interstellar neutral hydrogen was
not taken into account. Here we report measurements of the deflection of
the solar wind plasma flows in the heliosheath to determine the magnetic
field strength and orientation in the interstellar medium. We find that
the field strength in the local interstellar medium is 3.7-5.5μG. The
field is tilted ~20-30° from the interstellar medium flow direction
(resulting from the peculiar motion of the Sun in the Galaxy) and is
at an angle of about 30° from the Galactic plane. We conclude that
the interstellar medium field is turbulent or has a distortion in the
solar vicinity.
Title: Integration of the radiation belt environment model into the
space weather modeling framework
Authors: Glocer, A.; Toth, G.; Fok, M.; Gombosi, T.; Liemohn, M.
Bibcode: 2009JASTP..71.1653G
Altcode:
We have integrated the Fok radiation belt environment (RBE) model
into the space weather modeling framework (SWMF). RBE is coupled
to the global magnetohydrodynamics component (represented by the
Block-Adaptive-Tree Solar-wind Roe-type Upwind Scheme, BATS-R-US,
code) and the Ionosphere Electrodynamics component of the SWMF,
following initial results using the Weimer empirical model for
the ionospheric potential. The radiation belt (RB) model solves the
convection-diffusion equation of the plasma in the energy range of 10
keV to a few MeV. In stand-alone mode RBE uses Tsyganenko's empirical
models for the magnetic field, and Weimer's empirical model for
the ionospheric potential. In the SWMF the BATS-R-US model provides
the time dependent magnetic field by efficiently tracing the closed
magnetic field-lines and passing the geometrical and field strength
information to RBE at a regular cadence. The ionosphere electrodynamics
component uses a two-dimensional vertical potential solver to provide
new potential maps to the RBE model at regular intervals. We discuss the
coupling algorithm and show some preliminary results with the coupled
code. We run our newly coupled model for periods of steady solar wind
conditions and compare our results to the RB model using an empirical
magnetic field and potential model. We also simulate the RB for an
active time period and find that there are substantial differences in
the RB model results when changing either the magnetic field or the
electric field, including the creation of an outer belt enhancement
via rapid inward transport on the time scale of tens of minutes.
Title: Multiscale Modeling of Reconnection: Effects on CME Dynamics
Authors: Evans, Rebekah Minnel; Kuznetsova, Maria M.; Opher, Merav;
Toth, Gabor; Gombosi, Tamas I.
Bibcode: 2009shin.confE.189E
Altcode:
Magnetic reconnection is believed to play a crucial role in
the initiation and liftoff of a CME, and could continue during
propagation. However, the best tool to study these events - advanced
global MHD models - operates in the fluid regime and therefore is
limited to unphysical numerical and/or ad hoc anomalous reconnection
terms. Recently, efforts to include kinetic reconnection effects in a
global MHD code were successfully implemented into the BATS-R-US model
for the magnetotail. By applying the same techniques used in multiscale
modeling of magnetospheric reconnection, we simulate for the first time
the dissipation of magnetic energy of a CME as it propagates through
the interplanetary medium and the feedback on the background solar
wind. We initiate the CME using a modified Titov-Demoulin flux rope
with the Space Weather Modeling Framework and determine the effects
of the nongyrotropic corrections on the evolution out to 3Rsun.
Title: Modeling ionospheric outflows and their impact on the
magnetosphere, initial results
Authors: Glocer, A.; Tóth, G.; Gombosi, T.; Welling, D.
Bibcode: 2009JGRA..114.5216G
Altcode: 2009JGRA..11405216G
Ionospheric outflow has been shown to be a significant contributor to
the plasma population of the magnetosphere during active geomagnetic
conditions. We present the results of new efforts to model the source
and effects of out-flowing plasma in the Space Weather Modeling
Framework (SWMF). In particular, we develop and use the Polar Wind
Outflow Model (PWOM), a field-aligned, multifluid, multifield line polar
wind code to simulate the ionospheric outflow. The PWOM is coupled to
the ionosphere electrodynamics and global magnetosphere components of
the SWMF, so we can calculate the outflow and its resulting impact on
magnetospheric composition and dynamics. By including the outflow as
part of a coupled system, we study the consequences of outflow on the
larger space environment system. We present our methodology for the
magnetosphere-ionosphere coupling, as well as the effect of outflow on
the magnetosphere during two geomagnetic storms. Moreover, we explore
the use of multispecies MHD to track the resulting plasma composition
in the magnetosphere. We find that, by including ionospheric outflow
during geomagnetic storms, we can reduce the RMS error in the simulated
magnetic field as compared with various GOES satellites by as much as
50%. Additionally, we find that the outflow causes a strong decrease
in Dst and in the cross-polar cap potential.
Title: Cavities of weak magnetic field strength in the wake of FTEs:
Results from global magnetospheric MHD simulations
Authors: Kuznetsova, M. M.; Sibeck, D. G.; Hesse, M.; Wang, Y.;
Rastaetter, L.; Toth, G.; Ridley, A.
Bibcode: 2009GeoRL..3610104K
Altcode:
We use the global magnetohydrodynamic (MHD) code BATS-R-US
to model multipoint observations of Flux Transfer Event (FTE)
signatures. Simulations with high spatial and temporal resolution
predict that cavities of weak magnetic field strength protruding
into the magnetosphere trail FTEs. These predictions are consistent
with recently reported multi-point Cluster observations of traveling
magnetopause erosion regions (TMERs).
Title: Modeling the Radiation Belts During a Geomagnetic Storm
Authors: Glocer, A.; Fok, M.; Toth, G.
Bibcode: 2009AGUSMSM72A..07G
Altcode:
We utilize the Radiation Belt Environment (RBE) model to simulate the
radiation belt electrons during a geomagnetic storm. Particularly,
we focus on the relative contribution of whistler mode wave-particle
interactions and radial diffusion associated with rapid changes in the
magnetospheric magnetic field. In our study, the RBE model obtains a
realistic magnetic field from the BATS-R-US magnetosphere model at a
regular, but adjustable, cadence. We simulate the storm with and without
wave particle interactions, and with different frequencies for updating
the magnetic field. The impacts of the wave-particle interactions,
and the rapid variations in the magnetospheric magnetic field, can
then be studied. Simulation results are also extracted along various
satellite trajectories for direct comparison where appropriate.
Title: Simulations of Radiative Shocks in the Regime of SN Breakout
Shocks.
Authors: Drake, R. Paul; Doss, F. W.; Fryxell, B.; Grosskopf, M. J.;
Holloway, J. P.; van der Holst, B.; Huntington, C.; Kuranz, C. C.;
Myra, E. S.; Powell, K. G.; Sokolov, I. V.; Stout, Q. F.; Toth, G.;
Visco, A. J.
Bibcode: 2009AAS...21442706D
Altcode:
We have entered an era when detection of shock breakout from SNe
will become routine. Such shocks are radiative, as radiative energy
transport is a dominant aspect of their dynamics. They are for a
time in the regime where the system is optically thin outward from
the density jump but optically thick inward. Accurate simulations of
such shocks will be a challenge, as their radiation transport occurs
on multiple scales and their hydrodynamics is unstable. In our Center
for Radiative Shock Hydrodynamics we are developing a simulation code
to simulate experimental radiative shocks that are in the regime of the
SN breakout shocks. The code will feature block-adaptive hydrodynamics,
realistic treatment of materials, and a variety of radiation transport
options. We plan in due course to apply this code to SN breakout
shocks. We will describe the code and show results of initial
simulations of the experiments. The experiments produce such shock
waves in Xe or Ar by using a laser to shock, ionize, and accelerate
a Be plate into a gas-filled shock tube at above 100 km/s. We will
discuss and show how structure develops in these systems due to both
radiative energy transfer and hydrodynamic instability. Supported
by the DOE NNSA under the Predictive Sci. Academic Alliance Program
by grant DE-FC52-08NA28616, the Stewardship Sci. Academic Alliances
program by grant DE-FG52-04NA00064, and the Nat. Laser User Facility
by grant DE-FG03-00SF22021.
Title: The Space Weather Modeling Framework
Authors: Toth, G.
Bibcode: 2009AGUSMSH22A..03T
Altcode:
The Center for Space Environment Modeling (CSEM) at the University
of Michigan has developed the Space Weather Modeling Framework
(SWMF) that integrates independently developed models into a high
performance simulation tool. The SWMF models a dozen physics domains
spanning from the solar corona and heliosphere to the magnetosphere,
ionosphere and thermosphere of the Earth. The SWMF can perform a
realistic Sun-to-thermosphere simulation faster than real time on
today's supercomputers. We also use subsets of the SWMF components
to model various space physics systems. I will describe the current
status of the SWMF and our plans for future development.
Title: 3D, Multi-fluid, MHD Calculations of the Solar Wind Interaction
with Mars and the Associated Plasma Escape.
Authors: Najib, D.; Nagy, A.; Toth, G.; Ma, Y. -J.
Bibcode: 2009EGUGA..11.2219N
Altcode:
We have used our new 3D, multi-fluid, MHD model to study the interaction
of the solar wind with Mars. Our lower boundary is set at 100 km and
we have a radial grid resolution of about 10 km in the ionosphere. We
consider both photo and electron impact ionization, as well as charge
exchange processes. We compare a number of calculated and measured
parameters, such as bow shock and MPB locations. We also calculate the
plasma escape fluxes, for a variety of solar and upstream conditions. We
compare our calculated escape fluxes with the published, measured
values obtained by the ASPERA instrument carried by Mars Express.
Title: Hall MHD on Block-Adaptive Grids
Authors: Tóth, G.; Ma, Y. -J.; Gombosi, T. I.
Bibcode: 2009ASPC..406..287T
Altcode:
This proceedings paper is based on a much longer research paper that
was published during the conference (Toth et al. 2008). We present
a conservative second order accurate finite volume discretization
of the magnetohydrodynamics equations including the Hall term on
three dimensional block adaptive grids with Cartesian or generalized
coordinates. Both explicit and implicit time integration schemes are
developed. The parallel scaling and robustness are demonstrated by
three dimensional simulations of planetary magnetospheres.
Title: Breakout Coronal Mass Ejection or Streamer Blowout: The
Bugle Effect
Authors: van der Holst, B.; Manchester, W., IV; Sokolov, I. V.; Tóth,
G.; Gombosi, T. I.; DeZeeuw, D.; Cohen, O.
Bibcode: 2009ApJ...693.1178V
Altcode:
We present three-dimensional numerical magnetohydrodynamic (MHD)
simulations of coronal mass ejections (CMEs) initiated by the breakout
mechanism. The initial steady state consists of a bipolar active region
embedded in the solar wind. The field orientation of the active region
is opposite to that of the overarching helmet streamer, so that this
pre-eruptive region consists of three arcades with a magnetic null
line on the leading edge of the central arcade. By applying footpoint
motion near the polarity inversion line of the central arcade, the
breakout reconnection is turned on. During the eruption, the plasma in
front of the breakout arcade gets swept up. The latter effect causes
a pre-event swelling of the streamer. The width of the helmet streamer
increases in time and follows a "bugle" pattern. In this paper, we will
demonstrate that if this pre-event streamer swelling is insufficient,
reconnection on the sides of the erupting breakout arcade/flux rope
sets in. This will ultimately disconnect the helmet top, resulting in
a streamer blowout CME. On the other hand, if this pre-event swelling
is effective enough, the breakout reconnection will continue all the
way to the top of the helmet streamer. The breakout mechanisms will
then succeed in creating a breakout CME.
Title: Confronting Observations and Modeling: The Role of the
Interstellar Magnetic Field in Voyager 1 and 2 Asymmetries
Authors: Opher, M.; Richardson, J. D.; Toth, G.; Gombosi, T. I.
Bibcode: 2009SSRv..143...43O
Altcode: 2008SSRv..tmp..178O
Magnetic effects are ubiquitous and known to be crucial in space physics
and astrophysical media. We have now the opportunity to probe these
effects in the outer heliosphere with the two spacecraft Voyager 1
and 2. Voyager 1 crossed, in December 2004, the termination shock and
is now in the heliosheath. On August 30, 2007 Voyager 2 crossed the
termination shock, providing us for the first time in-situ measurements
of the subsonic solar wind in the heliosheath. With the recent in-situ
data from Voyager 1 and 2 the numerical models are forced to confront
their models with observational data. Our recent results indicate
that magnetic effects, in particular the interstellar magnetic field,
are very important in the interaction between the solar system and
the interstellar medium. We summarize here our recent work that
shows that the interstellar magnetic field affects the symmetry of
the heliosphere that can be detected by different measurements. We
combined radio emission and energetic particle streaming measurements
from Voyager 1 and 2 with extensive state-of-the art 3D MHD modeling, to
constrain the direction of the local interstellar magnetic field. The
orientation derived is a plane ∼60°-90° from the galactic
plane. This indicates that the field orientation differs from that
of a larger scale interstellar magnetic field, thought to parallel
the galactic plane. Although it may take 7-12 years for Voyager 2 to
leave the heliosheath and enter the pristine interstellar medium,
the subsonic flows are immediately sensitive to the shape of the
heliopause. The flows measured by Voyager 2 in the heliosheath indicate
that the heliopause is being distorted by local interstellar magnetic
field with the same orientation as derived previously. As a result of
the interstellar magnetic field the solar system is asymmetric being
pushed in the southern direction. The presence of hydrogen atoms tend
to symmetrize the solutions. We show that with a strong interstellar
magnetic field with our most current model that includes hydrogen atoms,
the asymmetries are recovered. It remains a challenge for future works
with a more complete model, to explain all the observed asymmetries
by V1 and V2. We comment on these results and implications of other
factors not included in our present model.
Title: Time-dependent global MHD simulations of Cassini T32 flyby:
From magnetosphere to magnetosheath
Authors: Ma, Y. J.; Russell, C. T.; Nagy, A. F.; Toth, G.; Bertucci,
C.; Dougherty, M. K.; Neubauer, F. M.; Wellbrock, A.; Coates, A. J.;
Garnier, P.; Wahlund, J. -E.; Cravens, T. E.; Crary, F. J.
Bibcode: 2009JGRA..114.3204M
Altcode: 2009JGRA..11403204M
When the Cassini spacecraft flew by Titan on 13 June 2007,
at 13.6 Saturn local time, Titan was directly observed to be
outside Saturn's magnetopause. Cassini observations showed dramatic
changes of magnetic field orientation as well as other plasma flow
parameters during the inbound and outbound segments. In this paper,
we study Titan's ionospheric responses to such a sudden change in
the upstream plasma conditions using a sophisticated multispecies
global MHD model. Simulation results of three different cases (steady
state, simple current sheet crossing, and magnetopause crossing)
are presented and compared against Cassini Magnetometer, Langmuir
Probe, and Cassini Plasma Spectrometer observations. The simulation
results provide clear evidence for the existence of a fossil field
that was induced in the ionosphere. The main interaction features,
as observed by the Cassini spacecraft, are well reproduced by the
time-dependent simulation cases. Simulation also reveals how the fossil
field was trapped during the interaction and shows the coexistence of
two pileup regions with opposite magnetic orientation, as well as the
formation of a pair of new Alfven wings and tail disconnection during
the magnetopause crossing process.
Title: Confronting Observations and Modeling: The Role of the
Interstellar Magnetic Field in Voyager 1 and 2 Asymmetries
Authors: Opher, M.; Richardson, J. D.; Toth, G.; Gombosi, T. I.
Bibcode: 2009fohl.book...43O
Altcode:
Magnetic effects are ubiquitous and known to be crucial in space physics
and astrophysical media. We have now the opportunity to probe these
effects in the outer heliosphere with the two spacecraft Voyager 1
and 2. Voyager 1 crossed, in December 2004, the termination shock and
is now in the heliosheath. On August 30, 2007 Voyager 2 crossed the
termination shock, providing us for the first time in-situ measurements
of the subsonic solar wind in the heliosheath. With the recent in-situ
data from Voyager 1 and 2 the numerical models are forced to confront
their models with observational data. Our recent results indicate
that magnetic effects, in particular the interstellar magnetic field,
are very important in the interaction between the solar system and
the interstellar medium. We summarize here our recent work that
shows that the interstellar magnetic field affects the symmetry of
the heliosphere that can be detected by different measurements. We
combined radio emission and energetic particle streaming measurements
from Voyager 1 and 2 with extensive state-of-the art 3D MHD modeling, to
constrain the direction of the local interstellar magnetic field. The
orientation derived is a plane ∼60°-90° from the galactic
plane. This indicates that the field orientation differs from that
of a larger scale interstellar magnetic field, thought to parallel
the galactic plane. Although it may take 7-12 years for Voyager 2 to
leave the heliosheath and enter the pristine interstellar medium,
the subsonic flows are immediately sensitive to the shape of the
heliopause. The flows measured by Voyager 2 in the heliosheath indicate
that the heliopause is being distorted by local interstellar magnetic
field with the same orientation as derived previously. As a result of
the interstellar magnetic field the solar system is asymmetric being
pushed in the southern direction. The presence of hydrogen atoms tend
to symmetrize the solutions. We show that with a strong interstellar
magnetic field with our most current model that includes hydrogen atoms,
the asymmetries are recovered. It remains a challenge for future works
with a more complete model, to explain all the observed asymmetries
by V1 and V2. We comment on these results and implications of other
factors not included in our present model.
Title: Investigating the Earth's magnetosphere response to IMF Bz
magnitude using SWMF
Authors: Cai, X.; Clauer, R. C.; Ridley, A. J.; Toth, G.
Bibcode: 2008AGUFMSM23B1693C
Altcode:
Observations indicate that the magnitude of southward interplanetary
magnetic field (IMF) contributes to different magnetosphere response
modes. Using the University of Michigan Space Weather Modeling
Framework (SWMF), including a global magnetosphere model, coupled with
an inner magnetosphere model and an ionosphere electrodynamics model,
we attempt to quantify the role of the IMF Bz in determining the level
of activity in the magnetosphere. In separate experiments, the IMF Bz
component is set to -2.5 nT, - 5 nT, -10 nT, -15 nT and -20 nT while
keeping the other input solar wind parameters constant. We have found
that the magnetosphere becomes more and more active as IMF Bz becomes
more negative. The average vertical magnetic field at geosynchronous
orbit, at all local times, decrease systematically, i.e., the inner
magnetosphere becomes more stretched as the IMF Bz becomes more
negative. The standard deviation also becomes larger, implying that the
magnetosphere shows more variability. When the IMF is weak (-2.5 nT),
the magnetic field at local midnight is quasi-steady. The magnetosphere
starts to show quasi- periodic (~ 2 hours) dipolarizations when IMF
is -5 nT and stronger. However, as the IMF Bz becomes more negative,
increased turbulence develops around the inner magnetosphere and appears
to disrupt the periodic formation of the night side reconnection.
Title: Improvements in the Space Weather Modeling Framework
Authors: Ridley, A. J.; Liemohn, M.; Dezeeuw, D.; Ilie, R.; Sokolov,
I.; Toth, G.; Yu, Y.
Bibcode: 2008AGUFMSA51A1530R
Altcode:
The magnetosphere within the Space Weather Modeling Framework (SWMF)
has been represented by a global magnetosphere model (BATSRUS), an
inner magnetosphere model (the Rice Convection Model) and a model of
the ionospheric electrodynamics. We present significant improvements
in the SWMF: (1) We have implemented a spherical grid within BATSRUS
and have utilized this for modeling the magnetosphere; (2) We have
significantly improved the physics of the auroral oval within the
ionospheric electrodynamics code, modeling a self-consistent diffuse and
discrete auroral oval; (3) We utilize the multifluid MHD code within
BATSRUS to allow for more accurate specification and differentiation
of the density within the magnetosphere; and (4) we have incorporated
the Hot Electron and Ion Drift Integrator (HEIDI) ring current code
within the SWMF. We will present these improvements and show the
quantitative differences within the model results when comparing to
a suite of measurements for a number of different intervals.
Title: Magnetic Storm Simulation With Multiple Ion Fluids: Algorithm
Authors: Toth, G.; Glocer, A.; Gombosi, T.
Bibcode: 2008AGUFMSM11A1568T
Altcode:
We describe our progress in extending the capabilities of the
BATS-R-US MHD code to model multiple ion fluids. We solve the full
multiion equations with no assumptions about the relative motion
of the ion fluids. We discuss the numerical difficulties and the
algorithmic solutions: the use of a total ion fluid in combination
with the individual ion fluids, the use of point-implicit source
terms with analytic Jacobian, using a simple criterion to separate
the single-ion and multiion regions in our magnetosphere applications,
and an artificial friction term to limit the relative velocities of the
ion fluids to reasonable values. This latter term is used to mimic the
effect of two-stream instabilities in a crude manner. The new code is
fully integrated into the Space Weather Modeling Framework and it has
been coupled with the ionosphere, inner magnetosphere and polar wind
models to simulate the May 4 1998 magnetic storm.
Title: Non-steady Reconnection in Global Simulations of Magnetosphere
Dynamics.
Authors: Kuznetsova, M.; Hesse, M.; Sibeck, D.; Rastaetter, L.; Toth,
G.; Ridley, A.
Bibcode: 2008AGUFMSM23C..04K
Altcode:
To analyze the non-steady magnetic reconnection during quasi-steady
solar wind driving we employed high resolution global MHD model
BATSRUS with non-MHD corrections in diffusion regions around the
reconnection sites. To clarify the role of small-scale non-MHD effects
on the global magnetospheric dynamic we performed simulations with
different models of dissipation. We found that magnetopause surface is
not in steady state even during extended periods of steady solar wind
conditions. The so-called tilted reconnection lines become unstable
due to formation of pressure bubbles, strong core field flux tubes,
vortices, and traveling magnetic field cavities. Non-steady dayside
reconnection results in formation of flux tubes with bended axis
magnetically connecting magnetic field cavities generated at flanks
and strong core segments formed near the subsolar region. We found
that the rate of magnetic flux loading to the tail lobes is not very
sensitive to the dissipation mechanism and details of the dayside
reconnection. On the other hand the magnetotail reconnection rate,
the speed of the reconnection site retreat and the global magnetotail
dynamics strongly depend on the model of dissipation. THEMIS and Cluster
observations are consistent with signatures predicted by simulations.
Title: Breakout coronal mass ejection or streamer blowout: the
bugle effect
Authors: van der Holst, B.; Manchester, C.; Sokolov, I.; Toth, G.;
Gombosi, T.; Dezeeuw, D.; Cohen, O.
Bibcode: 2008AGUFMSH23B1640V
Altcode:
We present three-dimensional numerical magnetohydrodynamic
simulations of coronal mass ejections (CMEs) initiated by the breakout
mechanism. The initial steady state consists of a bipolar active region
embedded in the solar wind. The field orientation of the active region
is opposite to that of the overarching helmet streamer, so that this
pre-eruptive region consists of three arcades with a magnetic null
line on the leading edge of the central arcade. By applying footpoint
motion near the polarity inversion line of the central arcade, the
breakout reconnection is turned on. During the eruption, the plasma in
front of the breakout arcade gets swept up. The latter effect causes
a pre-event swelling of the streamer. The width of the helmet streamer
increases in time and follows a "bugle" pattern. In this paper, we will
demonstrate that if this pre- event streamer swelling is insufficient,
reconnection on the sides of the erupting breakout arcade/flux rope
sets in. This will ultimately disconnect the helmet top, resulting in
a streamer blowout CME. On the other hand, if this pre-event swelling
is effective enough, the breakout reconnection will continue all the
way to the top of the helmet streamer. The breakout mechanisms will
then succeed in creating a breakout CME.
Title: 3D, Multi-fluid, MHD Calculations Of Plasma Escape From Mars
Authors: Najib, D.; Toth, G.; Nagy, A.; Ma, Y.
Bibcode: 2008AGUFMSM13A1670N
Altcode:
We use our new multi-fluid, MHD model to calculate plasma escape from
Mars. Our lower boundary is set at 100 km and we have a radial grid
resolution of about 10 km in the ionosphere. We consider both photo
and electron impact ionization, as well as charge exchange processes
in calculating the escape fluxes, using a variety of solar and upstream
conditions.
Title: Storm-time Inner Magnetosphere: Self-consistent Kinetic
Simulation Driven by the Space Weather Modeling Framework
Authors: Zaharia, S. G.; Jordanova, V. K.; Toth, G.
Bibcode: 2008AGUFMSM14A..03Z
Altcode:
Accurately modeling inner magnetosphere dynamics requires proper
treatment of both the kinetic drift physics as well as the interaction
between particles and fields. Observations consistently show the inner
magnetosphere magnetic field to be significantly depressed during
geomagnetic storms. The field changes are caused by large amounts of
injected ring current plasma, which in turn strongly influence the
dynamic evolution of the plasma. We have developed a self-consistent
inner magnetosphere code that treats this self- consistent interaction,
through coupling a kinetic ring current model (RAM) with an Euler
potential-based 3D plasma equilibrium code; in our approach, the
magnetic field is computed in force balance with the kinetic model
anisotropic pressures (anisotropy being critically important for the
excitation of EMIC waves), and then fed back into the kinetic code. Here
we report results from simulating a geomagnetic storm using this model,
with plasma and magnetic field on the boundary supplied from the global
BATSRUS MHD code from the Space Weather Modeling Framework (SWMF);
we focus in particular on the following aspects: 1). the effect of
the MHD model boundary vs. observation-based (from LANL satellites)
boundary conditions; 2). the effect of magnetic self-consistency on
ring current plasma pressure, anisotropy and EMIC wave instability;
and 3). the relative magnitude of the induced vs. convective electric
fields in the inner magnetosphere during the storm.
Title: Magnetic storm simulation with multiple ion fluids: results
and analysis
Authors: Glocer, A.; Toth, G.; Gombosi, T.
Bibcode: 2008AGUFMSM11A1569G
Altcode:
Ionosheric outflow can be a significant contributor to the plasma
population of the magnetosphere during active geomagnetic conditions. We
present preliminary results and analysis of new efforts to model the
source and effects of out-flowing plasma in the Space Weather Modeling
Framework (SWMF). In particular, we use the Polar Wind Outflow Model
(PWOM), a field-aligned multi-fluid polar wind code to study the
ionospheric outflow, and a newly developed multi-fluid version of
the BATS-R-US model of the magnetosphere to track the fate of that
outflow. We present our methodology and a description of the evolution
of magnetospheric composition during the May 4th 1998 geomagnetic storm.
Title: Balancing Act: The Role of The Interstellar Magnetic Field
and Neutral H in Voyager 1 and 2 Asymmetries
Authors: Opher, M.; Stone, E. C.; Toth, G.; Izmodenov, V.; Alexashov,
V.; Gombosi, T. I.
Bibcode: 2008AGUFMSH14A..07O
Altcode:
We present results from recently developed 5 fluid MHD model (4
neutral fluids and 1 ionized fluid). We present a benchmark comparison
between our model and the kinetic Moscow model for the case of strong
interstellar magnetic field, and no interplanetary field. The presence
of neutral H, as pointed out by previous works, has the effect of
diminishing the global heliospheric asymmetries. With a stronger
interstellar field, however, the asymmetries are increased. Results
of the 5-fluid MHD model have been employed as an starting point for a
new kinetic-MHD model that combines the BATS-R-US MHD code with the 3D
Monte- Carlo Moscow code. We present first results of this new coupled
model. We discuss these results and compare with our previous work
(Opher et al. 2006, 2007). Our goal is to constrain the orientation
and intensity of the interstellar magnetic field that can satisfy
the different constraints from the observed asymmetries (energetic
particles streaming (east- west); the 10AU differences between V1 and
V2 crossing; radio emission; and neutral H deflection).
Title: Inner magnetosphere--global MHD coupled code: initial results
Authors: Buzulukova, N.; Fok, M.; Kuznetsova, M.; Pulkkinen, A.;
Rastaetter, L.; Brandt, P.; Toth, G.
Bibcode: 2008AGUFMSM11A1571B
Altcode:
We present results of a one-way coupling between a global MHD model
(BATSRUS) and a ring current model with ionosphere feedback (CRCM). The
MHD model provides magnetic field in all computational regions
and electric field potential, temperature and density at the outer
boundary. The ring current model calculates the plasma distribution (H+
and e-) in the energy range 1-200keV, field-aligned currents of Region-2
and electric fields. We consider inner magnetosphere dynamics during an
idealized case with south-north-south Bz turning as well as a real event
during the 12 August 2000 storm. For the idealized case, we reproduce
basic features of the electric field in the inner magnetosphere:
strong convection during southward IMF and shielding, weak convection
during northward IMF and overshielding. Additionally, we estimate
characteristic times for shielding/overshielding formation. For the 12
August 2000 event we calculate ring current 3D fluxes and reconstruct
energetic neutral atom (ENA) images. We compare the modeled ENA images
with those observed by IMAGE HENA imager and investigate global ring
current dynamics during 12 August 2000 event.
Title: Three-dimensional MHD Simulation of the 2003 October 28
Coronal Mass Ejection: Comparison with LASCO Coronagraph Observations
Authors: Manchester, Ward B., IV; Vourlidas, Angelos; Tóth, Gábor;
Lugaz, Noé; Roussev, Ilia I.; Sokolov, Igor V.; Gombosi, Tamas I.;
De Zeeuw, Darren L.; Opher, Merav
Bibcode: 2008ApJ...684.1448M
Altcode: 2008arXiv0805.3707M
We numerically model the coronal mass ejection (CME) event of 2003
October 28 that erupted from AR 10486 and propagated to Earth in less
than 20 hr, causing severe geomagnetic storms. The magnetohydrodynamic
(MHD) model is formulated by first arriving at a steady state corona
and solar wind employing synoptic magnetograms. We initiate two
CMEs from the same active region, one approximately a day earlier
that preconditions the solar wind for the much faster CME on the
28th. This second CME travels through the corona at a rate of
over 2500 km s-1, driving a strong forward shock. We
clearly identify this shock in an image produced by the Large Angle
Spectrometric Coronagraph (LASCO) C3 and reproduce the shock and its
appearance in synthetic white-light images from the simulation. We
find excellent agreement with both the general morphology and the
quantitative brightness of the model CME with LASCO observations. These
results demonstrate that the CME shape is largely determined by its
interaction with the ambient solar wind and may not be sensitive to the
initiation process. We then show how the CME would appear as observed
by wide-angle coronagraphs on board the Solar Terrestrial Relations
Observatory (STEREO) spacecraft. We find complex time evolution of
the white-light images as a result of the way in which the density
structures pass through the Thomson sphere. The simulation is performed
with the Space Weather Modeling Framework (SWMF).
Title: MHD Simulations of CME-Driven Shocks: Structures Relevant to
Particle Acceleration
Authors: Manchester, W. B.; Toth, G.; Sokolov, I.; Zurbuchen, T. H.;
Kota, J.
Bibcode: 2008AIPC.1039..273M
Altcode:
Fast Coronal Mass Ejections (CMEs) drive strong shocks from the corona
through interplanetary space where these large-scale disturbances
accelerate particles typically associated with gradual events. The
acceleration of solar energetic particles (SEPs) is strongly dependent
on shock speed and geometry, which may exhibit significant temporal
and spatial variations as the CME propagates. Here, we examine
three-dimensional (3-D) magnetohydrodynamic simulations of CMEs,
and find that the ambient solar wind structure strongly affects
the evolution of CME-driven shocks. Variations in wind speed
deform the shock front, resulting in strong meridional flows and
compressions in the CME sheath. We also find that CMEs can cause stream
interactions that result in high-latitude reverse shocks Sunward of the
CME. Understanding and predicting such CME driven shocks is a necessary
step in building a quantitative model of SEP acceleration and transport
that can be used to forecast and mitigate radiation hazards.
Title: Hall magnetohydrodynamics on block-adaptive grids
Authors: Tóth, Gábor; Ma, Yingjuan; Gombosi, Tamas I.
Bibcode: 2008JCoPh.227.6967T
Altcode:
We present a conservative second order accurate finite volume
discretization of the magnetohydrodynamics equations including the Hall
term. The scheme is generalized to three-dimensional block-adaptive
grids with Cartesian or generalized coordinates. The second order
accurate discretization of the Hall term at grid resolution changes
is described in detail. Both explicit and implicit time integration
schemes are developed. The stability of the explicit time integration is
ensured by including the whistler wave speed for the shortest discrete
wave length into the numerical dissipation, but then second order
accuracy requires the use of symmetric limiters in the total variation
diminishing scheme. The implicit scheme employs a Newton Krylov Schwarz
type approach, and can achieve significantly better efficiency than
the explicit scheme with an appropriate preconditioner. The second
order accuracy of the scheme is verified by numerical tests. The
parallel scaling and robustness are demonstrated by three-dimensional
simulations of planetary magnetospheres.
Title: Modeling Ionospheric Outflows and Magnetosphere Composition
During Quiet and Active Times
Authors: Glocer, A.; Toth, G.; Gombosi, T.
Bibcode: 2008AGUSMSM41A..03G
Altcode:
Ionosheric outflow can be a significant contributor to the
plasma population of the magnetosphere during active geomagnetic
conditions. Most Magnetosphere- Ionosphere Coupling (MIC) models
do not include this outflow in a physical manner; instead they rely
on pressure gradient terms to draw plasma off the inner boundary of
the magnetosphere. We present preliminary results of new ef- forts to
model the source and effects of out-flowing plasma in the Space Weather
Modeling Framework (SWMF). In particular, we use the Polar Wind Outflow
Model (PWOM), a field-aligned multi-fluid polar wind code, coupled to
the Iono- sphere Electrodynamics (IE), and Global Magnetosphere (GM)
components of the SWMF. We present our methodology for the MIC, as well
as the evolution of the outflow during a geomagnetic storm. Moreover,
we explore the use of multi-species and multi-fluid MHD to track the
resulting plasma composition in the magnetosphere.
Title: Multi-Fluid Simulations of a Coupled Ionosphere-Magnetosphere
System
Authors: Gombosi, T. I.; Glocer, A.; Toth, G.; Ridley, A. J.; Sokolov,
I. V.; de Zeeuw, D. L.
Bibcode: 2008AGUSMSM33A..02G
Altcode:
In the last decade we have developed the Space Weather Modeling
Framework (SWMF) that efficiently couples together different models
describing the interacting regions of the space environment. Many
of these domain models (such as the global solar corona, the inner
heliosphere or the global magnetosphere) are based on MHD and are
represented by our multiphysics code, BATS-R-US. BATS-R-US can solve the
equations of "standard" ideal MHD, but it can also go beyond this first
approximation. It can solve resistive MHD, Hall MHD, semi-relativistic
MHD (that keeps the displacement current), multispecies (different
ion species have different continuity equations) and multifluid (all
ion species have separate continuity, momentum and energy equations)
MHD. Recently we added two-fluid Hall MHD (solving the electron
and ion energy equations separately) and are working on an extended
magnetohydrodynamics model with anisotropic pressures. Ionosheric
outflow can be a significant contributor to the plasma population of
the magnetosphere during active geomagnetic conditions. This talk
will present preliminary results of our simulations when we couple
a new field- aligned multi-fluid polar wind code to the Ionosphere
Electrodynamics (IE), and Global Magnetosphere (GM) components of the
SWMF. We use multi-species and multi-fluid MHD to track the resulting
plasma composition in the magnetosphere.
Title: Effects of Heavy Ions on Ring Current Dynamics from Dipolar,
Empirical, or Self-Consistent Magnetic Field Simulations
Authors: Jordanova, V. K.; Zaharia, S.; Toth, G.
Bibcode: 2008AGUSMSM44A..04J
Altcode:
The plasma composition in the near-Earth magnetosphere varies
significantly with geomagnetic and solar activity, with H+ being the
dominant ring current ion species during quiet time, and O+ contributing
mostly during active time. We use our kinetic ring current-atmosphere
interactions model (RAM) that has been recently extended for
non-dipolar magnetic field geometry to investigate the effects of
various O+/H+ composition ratios applied at the outer boundary on
ring current dynamics. The RAM is coupled with a 3-D equilibrium
model that calculates self-consistently the magnetic field in force
balance with the anisotropic ring current ion distributions. Such
anisotropy is critically important for the excitation of EMIC waves,
whose characteristics depend strongly on the presence of both cold and
energetic heavy ions (mainly He+ and O+) in the plasmas. We simulate
the sunward transport, acceleration, and loss of ring current ions
during a geomagnetic storm using this newly improved model with plasma
and magnetic field boundary conditions supplied from the global BATSRUS
model from the SWMF. Ring current development and EMIC wave instability
during various storm phases are presented and their dependence on ion
composition is discussed. The effect of non-dipolar magnetic field
geometry and the feedback of a self-consistently computed magnetic
field on ring current dynamics are investigated.
Title: Parallel Explicit/Implicit Time Stepping Scheme on
Block-Adaptive Grids
Authors: Tóth, G.; de Zeeuw, D. L.; Ma, Y. -J.; Gombosi, T. I.;
Powell, K. G.
Bibcode: 2008ASPC..385..237T
Altcode:
This proceedings paper is mostly based on a much longer research
paper tet{Toth2006}. We present a parallel explicit/implicit time
integration scheme well suited for block-adaptive grids. Load balancing
and the optimal choice of the time step for speed and robustness are
discussed. The parallel efficiency of the scheme is demonstrated for
a three-dimensional Hall magnetohydrodynamics problem.
Title: Role of periodic loading-unloading in the magnetotail versus
interplanetary magnetic field Bz flipping in the ring
current buildup
Authors: Taktakishvili, A.; Kuznetsova, M. M.; Hesse, M.; Fok, M. -C.;
RastäTter, L.; Maddox, M.; Chulaki, A.; Tóth, G.; Gombosi, T. I.;
de Zeeuw, D. L.
Bibcode: 2008JGRA..113.3206T
Altcode:
Introducing kinetic corrections into the to BATSRUS code in the
magnetotail region leads to fast reconnection rates observed in
kinetic simulations and quasi-periodic loading-unloading cycles in the
magnetotail during a long period of steady southward interplanetary
magnetic field (IMF) Bz (Kuznetsova et al., 2006, 2007). We
use the global MHD code BATSRUS output to drive the Fok Ring Current
(FRC) model, which then exhibits quasi-periodic oscillations of
geosynchronous energetic particle fluxes, similar to "sawtooth"
injection profiles. We compare these results with the results of the FRC
model driven by BATSRUS for periodically flipping IMF Bz
component, without kinetic corrections. The comparison shows the
dominant role of quasi-periodic loading-unloading in the tail over
the role of flipping IMF Bz component in the formation
of geosynchronous fluxes for various energies. This same result is
confirmed by the analysis of particle number and energy content within
geosynchronous orbit.
Title: Sun to Earth Simulation of 15-May-2005 Space Weather Event
Authors: Yuan, Xingqiu; Trichtchenko, Larisa; Rankin, Robert; Kabin,
Konstantin; Toth, Gabor; Manchester, Ward, IV
Bibcode: 2008cosp...37.3570Y
Altcode: 2008cosp.meet.3570Y
The numerical simulation of typical space weather events is a necessary
step towards developing real-time space weather forecasting. It
can help us to evaluate the physical model, to enhance the speed of
calculations with reasonable reduced resolution, and provide a global
picture of the transient disturbance interacting with the background
solar wind. In this paper, the well-defined halo-CME space weather
events of 15-May-2005 are chosen to investigate the propagation of
the solar disturbance in the moderately fast background solar wind
environment, and its successive geoeffectiveness. Detailed comparisons
of the simulation results with the groundand satellitebased observations
are presented. It is found that the simulation results are qualitatively
in good agreement with the observations.
Title: Modeling Ionospheric Outflows and Magnetosphere Composition
During Quiet and Active Times
Authors: Glocer, Alex; Toth, Gabor; Gombosi, Tamas
Bibcode: 2008cosp...37.1029G
Altcode: 2008cosp.meet.1029G
Ionosheric outflow can be a significant contributor to the
plasma population of the magnetosphere during active geomagnetic
conditions. Most Magnetosphere-Ionosphere Coupling (MIC) models do
not include this outflow in a physical manner; instead they rely on
pressure gradient terms to draw plasma off the inner boundary of the
magnetosphere. We present preliminary results of new efforts to model
the source and effects of out-flowing plasma in the Space Weather
Modeling Framework (SWMF). In particular, we use the Polar Wind Outflow
Model (PWOM), a field-aligned multi-fluid polar wind code, coupled
to the Ionosphere Electrodynamics (IE), and Global Magnetosphere (GM)
components of the SWMF. We present our methodology for the MIC, as well
as the evolution of the outflow during a geomagnetic storm. Moreover,
we explore the use of multi-species and multi-fluid MHD to track the
resulting plasma composition in the magnetosphere.
Title: Simulating the interaction of the 2007 April 19 CME with
Comet Encke
Authors: Manchester, Ward, IV; Gombosi, Tamas; Frazin, Richard;
Vourlidas, Angelos; Toth, Gabor; Cohen, Ofer; Hansen, Kenneth; Sokolov,
Igor; van der Holst, Bart
Bibcode: 2008cosp...37.1896M
Altcode: 2008cosp.meet.1896M
We model the propagation of a coronal mass ejection (CME) that was
observed with LASCO on April 19, 2007. The resulting ICME was observed
with SECCHI (STEREO A) to impact comet Encke on April 20. We compare the
results of our three-dimensional global MHD simulation of this event
with both sets of coronagraph observations. In particular, we make
synthetic Thomson-scattered white light images from the simulation to
quantitatively compare to the coronagraph images made with LASCO and
SECCHI. We then propagate the CME into interplanetary space where it
interacts with comet Encke. We simulate the complex response of the
cometary plasma to the CME impact.
Title: When Magnetized Winds Collide: Role of the Interstellar
Magnetic Field Shaping the Heliosphere
Authors: Opher, Merav; Stone, Edward; Richardson, John; Toth, Gabor;
Alexashov, Dmitry; Izmodenov, Vladislav; Gombosi, Tamas
Bibcode: 2008cosp...37.2295O
Altcode: 2008cosp.meet.2295O
Magnetic effects are ubiquitous and known to be crucial in space
physics and astrophysical media; Space physics is an excellent
plasma laboratory and provide observational data that add crucial
constraints to theoretical models. Voyager 1 crossed in Dec 2004,
the termination shock and is now in the heliosheath. On August 30,
2007 Voyager 2 crossed the termination shock providing us for the
first time with in-situ measurements of the subsonic solar wind in
the heliosheath. In this talk I will review our recent results that
indicate that magnetic effects, in particular the interstellar magnetic
field, are very important in the interaction between the solar system
and the interstellar medium. Recently, combining radio emission and
energetic particle streaming measurements from Voyager 1 and 2 with
extensive state-of-the art 3D MHD modeling, we were able to constrain
the direction of the local interstellar magnetic field. Although might
take 7-12 years for Voyager 2 to leave the heliosheath and enter the
pristine interstellar medium, the subsonic flows are immediately
sensitive to the shape of the heliopause. We show that the flows
measured by Voyager 2 from days 258-350 indicate that the heliopause
is being distorted by a local interstellar magnetic field 60° -90°
from the galactic plane. This confirms our earlier prediction that
the field orientation in the Local Interstellar Cloud differs that of
a larger scale interstellar magnetic field, thought to parallel the
galactic plane. As a result of the interstellar magnetic field the
solar system is asymmetric being pushed in the southern direction. I
will comment on these results and present preliminary results of the
effect of H neutrals on our previous MHD results.
Title: Global MHD Simulations of Magnetospheric and Ionospheric
Responses to the 5th June 1998 Event
Authors: Lu, Jianyong; Rae, Ian; Rankin, Robert; Zhang, Jichun; Kabin,
Konstantin; Gombosi, T.; de Zeeuw, D. L.; Toth, G.
Bibcode: 2008cosp...37.1831L
Altcode: 2008cosp.meet.1831L
Using WIND and ACE solar wind data, we have simulated the magnetospheric
and ionospheric responses to the 5th June 1998 event with global
MHD model SWMF. The chosen time period in our calculations includes
a sharp northward turning and a southward turning in the IMF,
followed by a period of relatively stead condition, respectively. We
first investigate the calculation influence of running the code in
different ways: (1) with or without RICE convection model, and (2)
time-accurate run or local time stepping or some combinations of both
to drive to a steady state before time-varying solar wind. We show that
the simulated magnetospheric and ionospheric responses, such as the
location of the polar cap boundary and ionospheric currents, can be
significantly affected by the treatment of the steady conditions. We
conclude that, with appropriate treatment of the true magnetospheric
configuration, the modelling framework SWMF can accurately reflect the
dynamic features of the solar wind-magnetosphere-ionosphere coupling
and provide reliable results for estimating magnetic field topology
and ionospheric responses.
Title: Multi-physics simulations of space weather
Authors: Gombosi, Tamas; Toth, Gabor; Sokolov, Igor; de Zeeuw, Darren;
van der Holst, Bart; Cohen, Ofer; Glocer, Alex; Manchester, Ward,
IV; Ridley, Aaron
Bibcode: 2008cosp...37.1047G
Altcode: 2008cosp.meet.1047G
Presently magnetohydrodynamic (MHD) models represent the "workhorse"
technology for simulating the space environment from the solar
corona to the ionosphere. While these models are very successful in
describing many important phenomena, they are based on a low-order
moment approximation of the phase-space distribution function. In the
last decade our group at the Center for Space Environment Modeling
(CSEM) has developed the Space Weather Modeling Framework (SWMF) that
efficiently couples together different models describing the interacting
regions of the space environment. Many of these domain models (such
as the global solar corona, the inner heliosphere or the global
magnetosphere) are based on MHD and are represented by our multiphysics
code, BATS-R-US. BATS-R-US can solve the equations of "standard"
ideal MHD, but it can also go beyond this first approximation. It
can solve resistive MHD, Hall MHD, semi-relativistic MHD (that keeps
the displacement current), multispecies (different ion species have
different continuity equations) and multifluid (all ion species have
separate continuity, momentum and energy equations) MHD. Recently we
added two-fluid Hall MHD (solving the electron and ion energy equations
separately) and are working on extended magnetohydrodynamics with
anisotropic pressures. This talk will show the effects of added physics
and compare space weather simulation results to "standard" ideal MHD.
Title: D Breakout Coronal Mass Ejections in the Solar Wind
Authors: van der Holst, Bart; Toth, Gabor; Sokolov, Igor; Gombosi,
Tamas; Manchester, Ward, IV; Cohen, Ofer; de Zeeuw, Darren
Bibcode: 2008cosp...37.3281V
Altcode: 2008cosp.meet.3281V
The initiation and evolution of coronal mass ejections (CMEs) is
studied by means of the breakout model embedded in a 3D solar wind in
the framework of numerical magnetohydrodynamics. The initial steady
equilibrium contains a pre-eruptive region consisting three arcades
with alternating magnetic flux polarity and with correspondingly three
neutral lines on the phtosphere. The magnetic tension of the overlying
closed magnetic field of the helmet streamer keeps this structure
in place. The most crucual element in the initial breakout topology
is the existence of an X-point on the leading edge of the central
arcade. By applying shear flow, the reconnection with the overlying
helmet streamer field is turned on. The breakout reconnection opens
the overlying field in an energetically efficient way. Initially,
this process will speed up the CME. The simulations will exploit the
new spherical grids in BATS-R-US to accurately capture the dynamics.
Title: Investigating the periodicity of sawtooth events using the
Space Weather Modeling Framework (SWMF) - preliminary results
Authors: Cai, X.; Clauer, C. R.; Ridley, A. J.; Toth, G.; Liemohn,
M. W.; Gombosi, T. I.; Kuznetsova, M. M.
Bibcode: 2007AGUFMSM32A..06C
Altcode:
By introducing a non-gyrotropic correction to the induction equation
in a BATS-R-US simulation, it has been reported that periodic
dipolarizations similar to sawtooth oscillations are seen at
geosynchronous orbit in the magnetosphere. However the simulated
periodicity reported is around 60 minutes, while the observed
periodicity, obtained from a analysis of around 400 individual teeth,
is about 180 minutes. We report here preliminary results from an
investigation that examines how solar wind parameters may affect the
periodicity using a series of Space Weather Modeling Framework (SWMF)
simulations which includes the non-gyrotropic BATS-R-US model. We
examine the effects of the external driving conditions by systematically
changing the magnitude of solar wind dynamic pressure and interplanetary
magnetic field (IMF) southward component (Bz) in the simulations.
Title: Validating SWMF Particle Density and Energy: Initial Results
Authors: Welling, D. T.; Ridley, A. J.; Gombosi, T. I.; de Zeeuw,
D.; Toth, G.
Bibcode: 2007AGUFMSM43E..01W
Altcode:
First principle-based models can be a powerful tool for scientific
and operational space weather forecasting and analysis. A key step
for improving current models and preparing them for operational
use is thorough data-model comparisons. Of particular interest
is particle density and energy distribution in the magnetosphere,
which are key values for spacecraft surface charging calculations. In
this study, we compare particle density and energy spectrum values
generated by the Space Weather Modeling Framework (SWMF) to in situ
LANL geosynchronous measurements. The SWMF is configured to use a
self-consistent ionospheric electrodynamics model, the BATSRUS global
MHD model, and the Rice Convection Model (RCM). Coupling these models
allows for tracing the magnetic field lines from the MHD solution to
provide the RCM with an improved open/closed field line boundary. It
also allows for the extraction of the RCM solution along any satellite
trajectory by tracing the magnetic field line from the 3D location
of the satellite to the 2D RCM ionospheric grid. The SWMF is further
configured to run in near-real time on 32 Columbia SGI processors,
creating a solution that better reflects the SWMF's capabilities in
an operational environment. This study is an extension of previous
work to validate the SWMF's modeled magnetic field.
Title: Modeling STEREO White-Light Observations of CMEs with 3D
MHD Simulations
Authors: Manchester, M. B.; Vourlidas, A.; Toth, G.; Lugaz, N.;
Sokolov, I.; Gombosi, T.; de Zeeuw, D.; Opher, M.
Bibcode: 2007AGUFMSH32A0785M
Altcode:
We model the Thomson-scattered white-light appearance of a variety of
3D MHD models of CMEs during solar minimum to reproduce large-scale
features of SECCHI observations. We create a gallery of expected CME
shapes at large elongations as seen by SECCHI. We examine evidence of
shock propagation, magnetic clouds, CME pancaking, and complex time
evolution as CMEs propagate at large elongation past the Thomson
sphere. A key point is to determine how the structure of CMEs and
CME-driven shocks are affected by interaction with the ambient solar
wind. MHD models are performed with BATSRUS and SWMF, and formulated
by first arriving at a steady state corona and solar wind employing
synoptic magnetograms. We initiate CMEs from active regions low in
the corona with magnetic flux ropes.
Title: The Orientation of the Local Interstellar Magnetic Field and
Induced Asymmetries of the Heliosphere: Neutrals-MHD model
Authors: Opher, M.; Stone, E. C.; Izmodenov, V.; Malama, Y.; Alexashov,
D.; Toth, G.; Gombosi, T.
Bibcode: 2007AGUFMSH12B..03O
Altcode:
We present the results of a 3D Neutral-MHD model of the heliosphere. The
neutrals are treated in a multi-fluid approach coupled to the ionized
component by charge exchange. Comparisons are made with previous studies
that showed that the local interstellar magnetic field introduces
asymmetries in the heliosphere that are consistent with Voyager 1 and
2 observations of radio emissions and energetic particle streaming
(Opher et al. Science 2007; Opher et al. ApJL 2006). We present,
additionally, preliminary results of a 3D Kinetic-MHD model. The
main advantage of this model is a rigorous kinetic description of
interstellar H atoms, especially at the Bow Shock, Heliopause and
Termination Shock interfaces. Differences of kinetic and multi-fluid
approaches are discussed. The new model should provide refined estimates
of the strength and direction of the local interstellar field and of
the resulting distortions of the shape of the heliosphere.
Title: The Michigan Space Weather Modeling Framework (SWMF)
Authors: de Zeeuw, D.; Gombosi, T.; Ridley, A.; Toth, G.
Bibcode: 2007AGUFMSM41A0310D
Altcode:
The Space Weather Modeling Framework (SWMF) developed at the
University of MIchigan has been used to model a wide variety of space
environments. It is especially well suited to space weather modeling
and can follow the complete system from CME initiation to interaction
with the upper atmosphere at Earth. A graphical user interface (GUI)
has been developed to facilitate setup, execution, and visualization
of model runs. This GUI has been enhanced to allow more complete
visualization and model result analysis, including comparisons with
data. Examples will be shown of the SWMF use through the GUI for a
variety of space weather events.
Title: Numerical Simulations of the Interaction of Enceladus'
Interaction With Saturn's Magnetosphere Using a 3D Multi-Species,
Hall MHD Model
Authors: Najib, D.; Nagy, A. F.; Toth, G.; Combi, M. R.; Ma, Y. J.;
Khurana, K.; Crary, F. F.; Coates, A. J.
Bibcode: 2007AGUFM.P43A1009N
Altcode:
We have used our new multi-species, Hall MHD model to study the
interaction of Saturn's magnetosphere with Enceladus. We used neutral
densities, consistent with the values observed during the Cassini's
July 14, 2005 flyby of Enceladus. We used a simple ion chemistry
scheme and approximated the upstream conditions from CAPS and MAG
observations. We compare our calculated plasma and magnetic field
values with the observed ones.
Title: Modeling Ionospheric Outflow During a Geomagnetic Storm
Authors: Glocer, A.; Toth, G.; Gombosi, T.
Bibcode: 2007AGUFMSA51B0521G
Altcode:
Ionosheric outflow can be a significant contributor to the
plasma population of the magnetosphere during active geomagnetic
conditions. Most Magnetosphere-Ionosphere Coupling (MIC) models do
not include this outflow in a physical manner; instead they rely
on pressure gradient terms to draw plasma off the inner boundary
of the magnetosphere. We present preliminary results of new efforts
to model the source and effects of out-flowing plasma in the Space
Weather Modeling Framework (SWMF). In particular, we use the Polar
Wind Outflow Model (PWOM), a field-aligned multi-fluid polar wind code,
coupled to the Ionosphere Electrodynamics (IE), and Global Magnetosphere
(GM) components of the SWMF. We present our methodology for the MIC,
as well as the evolution of the outflow during a geomagnetic storm.
Title: Integration of the Radiation Belt Environment Model Into the
Space Weather Modeling Framework
Authors: Toth, G.; Glocer, A.; Fok, M.; Gombosi, T.
Bibcode: 2007AGUFMSM12A..07T
Altcode:
We have integrated the Fok Radiation Belt Environment model (RBE) into
the Space Weather Modeling Framework (SWMF). RBE is coupled to the
global magnetohydrodynamics component (represented by BATSRUS) of the
SWMF. The radiation belt model solves the convection-diffusion equation
of the plasma in the range of 10keV to a few MeV. In stand-alone mode
RBE uses Tsyganenko's empirical models for the magnetic field. In the
SWMF the BATSRUS model provides the time dependent magnetic field
by efficiently tracing the closed magnetic field lines and passing
the geometrical and field strength information to RBE at a regular
cadence. We discuss the coupling algorithm and show some preliminary
results with the coupled code. We run our new coupled model for periods
of steady northward and southward IMF and compare our results to the
radiation belt model using an empirical magnetic field model. We also
simulate the radiation belts for an event of active time period.
Title: 3D global multi-species Hall-MHD simulation of the Cassini
T9 flyby
Authors: Ma, Ying-Juan; Nagy, Andrew F.; Toth, Gabor; Cravens, Thomas
E.; Russell, Christopher T.; Gombosi, Tamas I.; Wahlund, Jan-Erik;
Crary, Frank J.; Coates, Andrew J.; Bertucci, César L.; Neubauer,
Fritz M.
Bibcode: 2007GeoRL..3424S10M
Altcode:
The wake region of Titan is an important component of Titan's
interaction with its surrounding plasma and therefore a thorough
understanding of its formation and structure is of primary interest. The
Cassini spacecraft passed through the distant downstream region of
Titan on 18:59:30 UT Dec. 26, 2005, which is referred to as the T9
flyby and provided a great opportunity to test our understanding of the
highly dynamic wake region. In this paper we compare the observational
data (from the magnetometer, plasma analyzer and Langmuir probe) with
numerical results using a 7-species Hall MHD Titan model. There is a
good agreement between the observed and modeled parameters, given the
uncertainties in plasma measurements and the approximations inherent
in the Hall MHD model. Our simulation results also show that Hall MHD
model results fit the observations better than the non-Hall MHD model
for the flyby, consistent with the importance of kinetic effects in
the Titan interaction. Based on the model results, we also identify
various regions near Titan where Hall MHD models are applicable.
Title: Multiscale modeling of magnetospheric reconnection
Authors: Kuznetsova, M. M.; Hesse, M.; RastäTter, L.; Taktakishvili,
A.; Toth, G.; de Zeeuw, D. L.; Ridley, A.; Gombosi, T. I.
Bibcode: 2007JGRA..11210210K
Altcode:
In our efforts to bridge the gap between small-scale kinetic modeling
and global simulations, we introduced an approach that allows to
quantify the interaction between large-scale global magnetospheric
dynamics and microphysical processes in diffusion regions near
reconnection sites. We use the global MHD code BATS-R-US and replace
an ad hoc anomalous resistivity often employed by global MHD models
with a physically motivated dissipation model. The primary kinetic
mechanism controlling the dissipation in the diffusion region in
the vicinity of the reconnection site is incorporated into the MHD
description in terms of nongyrotropic corrections to the induction
equation. We developed an algorithm to search for reconnection
sites in north-south symmetric magnetotail. Spatial scales of
the diffusion region and magnitude of the reconnection electric
field are calculated consistently using local MHD plasma and field
parameters. The locations of the reconnection sites are constantly
updated during the simulations. To clarify the role of nongyrotropic
effects in the diffusion region on the global magnetospheric dynamics,
we perform simulations with steady southward interplanetary magnetic
field driving of the magnetosphere. Ideal MHD simulations with
magnetic reconnection supported by numerical resistivity often produce
quasi-steady configuration with almost stationary near-Earth neutral
line (NENL). Simulations with nongyrotropic corrections demonstrate
dynamic quasi-periodic response to the steady driving conditions. Fast
magnetotail reconnection supported by nongyrotropic effects results
in tailward retreat of the reconnection site with average speed of
the order of 100 km/s followed by a formation of a new NENL in the
near-Earth thin current sheet. This approach allowed to model for
the first time loading/unloading cycle frequently observed during
extended periods of steady low-mach-number solar wind with southward
interplanetary magnetic field.
Title: Leakage of photospheric acoustic waves into non-magnetic
solar atmosphere
Authors: Erdélyi, R.; Malins, C.; Tóth, G.; de Pontieu, B.
Bibcode: 2007A&A...467.1299E
Altcode:
Aims:This paper aims to look at the propagation of synthetic
photospheric oscillations from a point source into a two-dimensional
non-magnetic solar atmosphere. It takes a particular interest in
the leakage of 5-min global oscillations into the atmosphere, and
aims to complement efforts on the driving of chromospheric dynamics
(e.g. spicules and waves) by 5-min oscillations.
Methods: A
model solar atmosphere is constructed based on realistic temperature
and gravitational stratification. The response of this atmosphere to
a wide range of adiabatic periodic velocity drivers is numerically
investigated in the hydrodynamic approximation.
Results: The
findings of this modelling are threefold. Firstly, high-frequency waves
are shown to propagate from the lower atmosphere across the transition
region experiencing relatively low reflection and transmitting energy
into the corona. Secondly, it is demonstrated that driving the upper
solar photosphere with a harmonic piston driver at around the 5 min
period may generate three separate standing modes with similar periods
in the chromosphere and transition region. In the cavity formed
by the chromosphere and bounded by regions of low cut-off period
at the photospheric temperature minimum and the transition region
this is caused by reflection, while at either end of this region in
the lower chromosphere and transition region the standing modes are
caused by resonant excitation. Finally, the transition region becomes
a guide for horizontally propagating surface waves for a wide range
of driver periods, and in particular at those periods which support
chromospheric standing waves. Crucially, these findings are the results
of a combination of a chromospheric cavity and resonant excitation in
the lower atmosphere and transition region.
Title: The Michigan Space Weather Modeling Framework (SWMF) Graphical
User Interface
Authors: de Zeeuw, D.; Gombosi, T.; Toth, G.; Ridley, A.
Bibcode: 2007AGUSMSM23A..09D
Altcode:
The Michigan Space Weather Modeling Framework (SWMF) is a powerful tool
available for the community that has been used to model from the Sun
to Earth and beyond. As a research tool, however, it still requires
user experience with parallel compute clusters and visualization
tools. Thus, we have developed a graphical user interface (GUI) that
assists with configuring, compiling, and running the SWMF, as well as
visualizing the model output. This is accomplished through a portable
web interface. Live examples will be demonstrated and visualization
of several archived events will be shown.
Title: Coupling a polar wind model to the Space Weather Modeling
Framework (SWMF)
Authors: Glocer, A.; Gombosi, T.; Toth, G.; Hansen, K.; Ridley, A.
Bibcode: 2007AGUSMSA33A..05G
Altcode:
Polar wind and other ionospheric outflows are a vital source of
plasma to the magnetosphere. Ambipolar electric fields, Field Aligned
Currents (FACs), Joule heating, centrifugal acceleration, wave-particle
interactions, and other physical phenomenon accelerate plasma and
can lead to mass flow from the ionosphere to the magnetosphere. Most
Magnetosphere-Ionosphere Coupling (MIC) in models ignores these
processes instead relying on pressure gradient terms to draw plasma
off the inner boundary of the magnetosphere. We present preliminary
results of new efforts to incorporate this important physics into the
Space Weather Modeling Framework (SWMF). In particular, we use the
Polar Wind Outflow Model (PWOM), a field-aligned multi-fluid polar
wind code, and describe efforts to couple it to the Upper Atmosphere
(UA), Ionosphere Electrodynamics (IE), and Global Magnetosphere (GM)
components of the SWMF. We present our methodology for the MIC, as
well as several controlled numerical experiments demonstrating the
importance of different physical processes.
Title: Simulated CMEs and Predictions for STEREO
Authors: Manchester, M. B.; Vourlidas, A.; Gombosi, T.; Sokolov,
I. V.; Cohen, O.; Toth, G.
Bibcode: 2007AGUSMSH41A..06M
Altcode:
We compare results of our global MHD simulations of CMEs propagating
from Sun-to-Earth to observations made with STEREO. We model a number
of events of varying degree of complexity, and model the observations
that are made by the SECCHI coronagraph suite and in situ observations
by IMPACT and PLASTIC. We make synthetic Thomson-scattered white light
images from the simulations as they would appear to the COR1, COR2,
and wide-angle coronagraphs HI1 and HI2. We identify shock structures
in the coronagraph images and follow their evolution to Earth orbit. At
large elongation, we find complex time evolution of the white- light
images as a result of three-dimensional structures encountering large
variations in scattering efficiency as they pass through the Thomson
sphere. We then compare the modeled ICME plasma structures with
observations from PLASTIC. We also model solar energetic particles
and compare them with IMPACT observations.
Title: Comparison of Hall MHD and the non-gyrotropic resistivity
model in the global magnetohydrodynamic code BATSRUS
Authors: Toth, G.; Ma, Y.; Gombosi, T. I.; Kuznetsova, M. M.
Bibcode: 2007AGUSMSM51A..12T
Altcode:
We have recently added Hall MHD to the global magnetohydrodynamic
code BATSRUS. Compared to ideal or resistive MHD, Hall MHD provides
a more realistic modeling of the interaction of the solar wind with
unmagnetized bodies and the reconnection process in magnetospheres. On
the other hand accurate modeling of reconnection is rather expensive
due to the required resolution and the stiffness of the Hall MHD
equations. The non-gyrotropic resistivity model of Kuznetsova et al. is
a phenomenological approximation based on the results of particle
simulations. It provides an inexpensive but surprisingly accurate
model for the reconnection process. We will systematically compare
the two approaches within the BATSRUS code.
Title: Numerical Investigation of the Homologous Coronal Mass Ejection
Events from Active Region 9236
Authors: Lugaz, N.; Manchester, W. B., IV; Roussev, I. I.; Tóth,
G.; Gombosi, T. I.
Bibcode: 2007ApJ...659..788L
Altcode:
We present a three-dimensional compressible magneto-hydrodynamics
(MHD) simulation of the three coronal mass ejections (CMEs) of 2000
November 24, originating from NOAA active region 9236. These three
ejections, with velocities around 1200 km s-1 and associated
with X-class flares, erupted from the Sun in a period of about 16.5
hr. In our simulation, the coronal magnetic field is reconstructed
from MDI magnetogram data, the steady-state solar wind is based on a
varying polytropic index model, and the ejections are initiated using
out-of-equilibrium semicylindrical flux ropes with a size smaller than
the active region. The simulations are carried out with the Space
Weather Modeling Framework. We are able to reproduce the shape and
velocity of the CMEs as observed by the LASCO C3 coronograph. The
complex ejecta resulting from the interaction of the three CMEs is
preceded at Earth by a single shock wave, which, in our simulation,
arrives at Earth 10 hr later than the shock observed by the Wind
spacecraft. This article discusses the three-dimensional aspects
of the propagation, interaction, and merging of the forward shock
waves associated with the three ejections. Synthetic images from the
Heliospheric Imagers onboard the STEREO spacecraft are produced, and we
predict that the large density jump associated with the interaction of
the shocks should be observed by those coronographs in the near future.
Title: Understanding storm-time ring current development through
data-model comparisons of a moderate storm
Authors: Zhang, Jichun; Liemohn, Michael W.; de Zeeuw, Darren L.;
Borovsky, Joseph E.; Ridley, Aaron J.; Toth, Gabor; Sazykin, Stanislav;
Thomsen, Michelle F.; Kozyra, Janet U.; Gombosi, Tamas I.; Wolf,
Richard A.
Bibcode: 2007JGRA..112.4208Z
Altcode: 2007JGRA..11204208Z
With three components, global magnetosphere (GM), inner magnetosphere
(IM), and ionospheric electrodynamics (IE), in the Space Weather
Modeling Framework (SWMF), the moderate storm on 19 May 2002 is
globally simulated over a 24-hour period that includes the sudden
storm commencement (SSC), initial phase, and main phase of the
storm. Simulation results are validated by comparison with in situ
observations from Geotail, GOES 8, GOES 10, Polar, LANL MPA, and
the Sym-H and Dst indices. It is shown that the SWMF is reaching a
sophistication level for allowing quantitative comparison with the
observations. Major storm characteristics at the SSC, in the initial
phase, and in the main phase are successfully reproduced. The simulated
plasma parameters exhibit obvious dawn-dusk asymmetries or symmetries
in the ring current region: higher density near the dawn and higher
temperature in the afternoon and premidnight sectors; the pressure is
highest on the nightside and exhibits a near dawn-dusk symmetry. In
addition, it is found in this global modeling that the upstream solar
wind/IMF conditions control the storm activity and an important
plasma source of the ring current is in the solar wind. However,
the ionospheric outflow can also affect the ring current development,
especially in the main phase. Activity in the high-latitude ionosphere
is also produced reasonably well. However, the modeled cross polar
cap potential drop (CPCP) in the Southern Hemisphere is almost always
significantly larger than that in the Northern Hemisphere during the
May storm.
Title: Polar wind outflow model: Saturn results
Authors: Glocer, A.; Gombosi, T. I.; Toth, G.; Hansen, K. C.; Ridley,
A. J.; Nagy, A.
Bibcode: 2007JGRA..112.1304G
Altcode: 2007JGRA..11201304G
The Saturnian system's configuration and dynamics are to a large
extent controlled by the planet's rapid rotation and the plasma in
the magnetosphere. Therefore characterizing the relative importance
of the various plasma sources is crucial to understanding Saturn's
magnetosphere. Most research in this area focuses on the addition of
mass from the icy satellites, the rings, and Titan, while comparatively
little attention has been paid to the ionospheric source. We investigate
the ionospheric source at high latitude using multifluid numerical
simulations of Saturn's polar wind and find that the magnitude
of the particle source rate out of the polar cap is between 2.1
× 1026 and 7.5 × 1027 s-1. Our
multifluid simulations are carried out using the Polar Wind Outflow
Model (PWOM). This new model is capable of calculating the polar wind
at Earth and Saturn by solving the gyrotropic transport equations. The
polar wind at Saturn is modeled from below the peak ionospheric
density to an altitude of one Saturn radius, yielding fluxes for
H3+, H+, and electrons. Because the
neutral temperature is ill constrained, we calculate source rates
for various Saturnian atmospheric profiles corresponding to neutral
temperatures of 420, 600, 800, 1000, 1500 K. We compare the results with
those calculated from other models and measurements where appropriate.
Title: Parallel Adaptive Solution of the MHD Equations and Its Role
in the Space-Weather Modeling Framework
Authors: Powell, K. G.; Gombosi, T. I.; Stout, Q. F.; de Zeeuw, D. L.;
Tóth, G.; Sokolov, I. V.; Ridley, A. J.; Hansen, K. C.; Manchester,
W. B.; Roussev, I. I.
Bibcode: 2006ASPC..359...33P
Altcode:
Over the last ten years, a collaboration of researchers in space
physics, computer science and computational fluid dynamics has grown
into the Center for Space Environment Modeling at the University of
Michigan. The group has partnered with researchers at Rice, Stanford,
NCAR, and NASA Goddard, among other institutions, to develop a
first-principles-based software framework for modeling space-weather
events. In this paper, a solution-adaptive method for solving the
MHD equations in a highly efficient manner on parallel computers is
presented. In addition, an overview of the broader effort to develop
the Space Weather Modeling Framework is given.
Title: The Polar Wind Outflow Model: Saturn Results
Authors: Nagy, A.; Glocer, A.; Gombosi, T.; Toth, G.; Hansen, K.;
Ridley, A.
Bibcode: 2006AGUFMSM31C..03N
Altcode:
The Saturnian system's configuration and dynamics are to a large
extent controlled by the planet's rapid rotation and the plasma in
the magnetosphere. Therefore, characterizing the relative importance
of the various plasma sources is crucial to understanding Saturn's
magnetosphere. Most research in this area focuses on the addition of
mass from the icy satellites, the rings, and Titan, while comparatively
little attention has been paid to the ionospheric source. We investigate
the ionospheric source at high latitude using multi-fluid numerical
simulations of Saturn's polar wind, and find that the magnitude of
the particle source rate out of the polar cap is between 2.1×10^{26}
and 7.5×10^{27} s-1. Our multi-fluid simulations are carried out
using the Polar Wind Outflow Model (PWOM). This new model is capable of
calculating the polar wind at Earth and Saturn by solving the gyrotropic
transport equations. The polar wind at Saturn is modeled from below the
peak ionospheric density to an altitude of one Saturn radius, yielding
fluxes for H3+, H+, and electrons. Because the neutral temperature
is ill constrained, we calculate source rates for various Saturnian
atmospheric profiles corresponding to neutral temperatures of 420,
600, 800, 1000, 1500 K. We compare the results with those calculated
from other models and measurements where appropriate.
Title: 3D Global MHD Simulation of Titan's interaction with its
surrounding plasma
Authors: Ma, Y.; Nagy, A. F.; Toth, G.; Najib, D.; Cravens, T. E.;
Crary, F.; Coates, A. J.; Bertucci, C.; Neubauer, F. M.
Bibcode: 2006AGUFM.P21B..07M
Altcode:
The interaction of Titan's ionosphere with its surrounding plasma
flow is more complex than analogous solar wind-planet interactions,
because of Titan's varying relative location in the Sun-Saturn
system. We have studied the role of the angle between the direction
of the solar radiation and the corotating plasma flow using our 3D
multi-species MHD model. We also present results from a comparison
between our model simulations and the observations corresponding to
the T9 flyby of Cassini, using the measured upstream plasma parameters.
Title: Hall MHD Simulations on Block Adaptive Grids
Authors: Toth, G.; Ma, Y.; Gombosi, T. I.; Sokolov, I. V.
Bibcode: 2006AGUFMSM34B..02T
Altcode:
We have recently extended the global magnetohydrodynamic (MHD) code
BATSRUS to include the physics of Hall MHD. The numerical algorithm
is developed on a block adaptive grid with explicit and implicit time
integration. We discuss the algorithm, numerical tests, and initial
simulation results applied to magnetospheric simulations. The effects
of Hall MHD on the reconnection process is of particular initerest at
the day-side magnetopause and in the magnetotail region.
Title: Collisionless Reconnection in Global Modeling of Magnetospheric
Dynamics
Authors: Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Gombosi, T.;
de Zeeuw, D.; Toth, G.
Bibcode: 2006AGUFMSM34B..03K
Altcode:
Recent advances in small-scale kinetic modeling of magnetic reconnection
significantly improved our understanding of physical mechanisms
controlling the dissipation in the vicinity of the reconnection site in
collisionless plasma. However the progress in studies of small-scale
geometries was not very helpful for large scale simulations. Global
magnetosphere simulations usually include non-ideal processes in
terms of numerical dissipation and/or ad hoc anomalous resistivity. To
understand the role of magnetic reconnection in global evolution of
magnetosphere and to place spacecraft observations into global context
it is desirable to perform global simulations with physically motivated
model of dissipation that are capable to reproduce reconnection rates
observed in kinetic models. In our efforts to bridge the gap between
small scale kinetic modeling and global simulations we introduced an
approach that allows to quantify the interaction between large-scale
global magnetospheric dynamics and microphysical processes in diffusion
regions near reconnection sites. We utilized the global MHD code BATSRUS
and incorporate primary mechanism controlling the dissipation in the
vicinity of the reconnection site in terms of non-gyrotropic corrections
to the induction equation. We demonstrated that nongyrotropic effects
can significantly alter the global magnetosphere evolution. Our approach
allowed for the first time to model loading/unloading cycle in response
to steady southward IMF driving. We will extend our approach to cases
with nonzero IMF By and analyze the effects of solar wind parameters and
ionospheric conductance on reconnection rate and global magnetosphere
dynamics.
Title: Ring Current Decay of Moderate Storms at Solar Maximum:
Global Modeling Using Superposed Epoch Upstream Conditions
Authors: Zhang, J.; Wolf, R. A.; Sazykin, S.; Toffoletto, F. R.;
Liemohn, M. W.; de Zeeuw, D. L.; Ridley, A. J.; Toth, G.; Gombosi,
T. I.
Bibcode: 2006AGUFMSM33D..06Z
Altcode:
This study is an extension of our previous high-performance storm
simulation with the coupled BATS-R-US (Block Adaptive Tree Solar-wind
Roe-type Upwind Scheme) global magnetohydrodynamics (MHD) model, Rice
Convection Model (RCM), and Ridley Ionosphere Model (RIM). In this
work, the superposed epoch recovery phase of 34 moderate storms at
solar maximum (July, 1999 -- June, 2002) is simulated for averaged
upstream solar wind conditions with the standalone RCM and also
with the coupled codes. Superposed epoch averages of Dst, Sym-H, and
the Los Alamos Magnetospheric Plasma Analyzer (MPA) observations at
geosynchronous orbit are used to validate the modeling results. In
addition, parameters in the standalone RCM and the coupled codes are
adjusted to systematically study the effects of interchange instability,
charge exchange rate, particle drift intensity, and particle energy
levels on the ring current decay. Computer experiments will also
explore how magnetic field changes and time-dependent plasma-sheet
density affect the recovery phase.
Title: Modeling the "gap" region between the ionosphere and
magnetosphere
Authors: Glocer, A.; Gombosi, T.; Toth, G.; Hansen, K.; Ridley, A.
Bibcode: 2006AGUFMSA41B1419G
Altcode:
The gap region refers to the 2-3 Re space between the outer boundary of
most ionosphere models, and the inner boundary of most magnetosphere
models. Ambipolar electric fields, Field Aligned Currents (FACs),
Joule heating, centrifugal acceleration, wave-particle interactions,
and other physical phenomenon in the gap region accelerate plasma and
can lead to mass flow from the ionosphere to the magnetosphere. Most
Magnetosphere-Ionosphere Coupling (MIC) models ignore these processes
instead relying on pressure gradient terms to draw plasma off the
inner boundary of the magnetosphere. We present preliminary results of
new efforts to model the "gap" region in the Space Weather Modeling
Framework (SWMF). In particular, we use the Polar Wind Outflow Model
(PWOM), a field-aligned multi-fluid polar wind code, and describe
efforts to couple it to the Upper Atmosphere (UA), Ionosphere
Electrodynamics (IE), and Global Magnetosphere (GM) components of
the SWMF. We present our methodology for the MIC, as well as several
controlled numerical experiments demonstrating the importance of
different physical processes in the gap region.
Title: 3D Global MHD Simulation of the Saturn Magnetospheric Plasma
Interaction with Titan's Ionosphere
Authors: Ma, Yingjuan; Nagy, A. F.; Cravens, T. E.; Toth, G.; Crary,
F. J.; Coates, A. J.; Dougherty, M. K.
Bibcode: 2006DPS....38.2703M
Altcode: 2006BAAS...38..527M
The interaction between Titan's ionosphere and its surrounding plasma
is simulated using our 3D multi-species MHD model.We compare the
simulation results with the observations obtained during the T9 flyby,
using the upstream plasma parameters measured during the flyby. The
Hall term (JXB) is also included in the model to investigate the ion
gyro-radii effect.
Title: Enhancement of Photospheric Meridional Flow by Reconnection
Processes
Authors: Cohen, O.; Fisk, L. A.; Roussev, I. I.; Toth, G.; Gombosi,
T. I.
Bibcode: 2006ApJ...645.1537C
Altcode:
We simulate the two-dimensional transport of the open magnetic flux
on the surface of the Sun. The temporal evolution of the flux density
depends on the advective motions due to solar differential rotation
and poleward meridional flow and on an effective spatial diffusive
motion. The latter is a result of the uniform diffusion of field line
footpoints in the network lanes and a nonuniform diffusion of field
lines due to reconnection of open field lines with closed loops on the
solar surface. The gradient of the diffusion coefficient represents an
effective velocity in addition to the advective velocity. We investigate
the behavior of the steady state solution for solar minimum and solar
maximum conditions with spatially uniform and nonuniform diffusion
coefficients. We find that for solar minimum conditions, the effect of
spatial diffusion resulting from reconnection processes enhances the
poleward meridional flow due to the large-scale preferred direction
in the gradient of the diffusion coefficient. For solar maximum
conditions, the net effect of spatial diffusion is minimal because of
the isotropic and local gradients of the diffusion coefficient. Our
simulation demonstrates that magnetic reconnection processes on the
solar surface can be a mechanism to vary motions on the photosphere,
in particular, poleward meridional flow.
Title: Understanding Ring Current Sources of Moderate and Intense
Storms at Solar Maximum: Global Modeling Using Superposed Epoch
Upstream Conditions
Authors: Zhang, J.; Liemohn, M. W.; de Zeeuw, D. L.; Borovsky, J. E.;
Ridley, A. J.; Toth, G.; Sazykin, S.; Thomsen, M. F.; Kozyra, J. U.;
Gombosi, T. I.; Wolf, R. A.
Bibcode: 2006AGUSMSM53A..07Z
Altcode:
With the Space Weather Modeling Framework (SWMF), we conduct storm
simulations for superposed epoch upstream solar wind conditions of
34 moderate storms and 64 intense storms at solar maximum (July,
1999 - June, 2002). In comparison with superposed epoch averages of
Dst, Sym-H, and the Los Alamos Magnetospheric Plasma Analyzer (MPA)
observations at geosynchronous orbit, modeling results are validated. It
is shown that the SWMF is sophisticated enough to make quantitative
data-model comparisons. The major storm characteristics are successfully
reproduced. With the two levels of storm intensity and different SWMF
parameter settings, the influences on storms of upstream conditions,
ionospheric outflow and ionospheric conductance are assessed. It
is shown that the integrated energy input for a storm is much more
important than the short-lived peaks in the upstream solar wind
values. Consistent with the MPA averaged measurements, it is found that
in the inner magnetosphere in the simulated main phase plasmas become
denser near dawn than around duskside; plasma temperature is higher in
the afternoon and pre-midnight sectors; but enhanced plasma pressure
is always symmetric on the nightside with a peak at midnight. Possible
reasons for these plasma parameter asymmetries and symmetries are
investigated and discussed. personal.umich.edu/~jichunz/
Title: The global ionosphere thermosphere model
Authors: Ridley, A. J.; Deng, Y.; Tóth, G.
Bibcode: 2006JASTP..68..839R
Altcode: 2006JATP...68..839R
The recently created global ionosphere thermosphere model (GITM)
is presented. GITM uses a three-dimensional spherical grid that
can be stretched in both latitude and altitude, while having a fixed
resolution in longitude. GITM is nontraditional in that it does not use
a pressure-based coordinate system. Instead it uses an altitude-based
grid and does not assume a hydrostatic solution. This allows the model
to more realistically capture physics in the high-latitude region, where
auroral heating is prevalent. The code can be run in a one-dimensional
(1-D) or three-dimensional (3-D) mode. In 3-D mode, the modeling region
is broken into blocks of equal size for parallelization. In 1-D mode,
a single latitude and longitude is modeled by neglecting any horizontal
transport or gradients, except in the ionospheric potential. GITM
includes a modern advection solver and realistic source terms for the
continuity, momentum, and energy equations. Each neutral species has
a separate vertical velocity, with coupling of the velocities through
a frictional term. The ion momentum equation is solved for assuming
steady-state, taking into account the pressure, gravity, neutral
winds, and external electric fields. GITM is an extremely flexible
code—allowing different models of high-latitude electric fields,
auroral particle precipitation, solar EUV inputs, and particle energy
deposition to be used. The magnetic field can be represented by an
ideal dipole magnetic field or a realistic APEX magnetic field. Many
of the source terms can be controlled (switched on and off, or values
set) by an easily readable input file. The initial state can be set
in three different ways: (1) using an ideal atmosphere, where the user
inputs the densities and temperature at the bottom of the atmosphere;
(2) using MSIS and IRI; and (3) restarting from a previous run. A 3-D
equinox run and a 3-D northern summer solstice run are presented. These
simulations are compared with MSIS and IRI to show that the large-scale
features are reproduced within the code. We conduct a second equinox
simulation with different initial conditions to show that the runs
converge after approximately 1.5 days. Additionally, a 1-D simulation
is presented to show that GITM works in 1-D and that the dynamics are
what is expected for such a model.
Title: Multi-Scale Modeling of Magnetospheric Reconnection.
Authors: Kuznetsova, M. M.; Hesse, M.; Rastatter, L.; Toth, G.;
Dezeeuw, D. L.; Gombosi, T. I.
Bibcode: 2006AGUSMSM21A..04K
Altcode:
One of the major challenges in modeling the magnetospheric magnetic
reconnection is to quantify the interaction between large-scale global
magnetospheric dynamics and microphysical processes in diffusion regions
near reconnection sites. There is still considerable debate as to what
degree microphysical processes on kinetic scales affect the global
evolution and how important it is to substitute numerical dissipation
and/or ad hoc anomalous resistivity by a physically motivated model
of dissipation. Comparative studies of magnetic reconnection in small
scale geometries demonstrated that MHD simulations that included
non-ideal processes in terms of a resistive term η J did not produce
the fast reconnection rates observed in kinetic simulations. For a broad
range of physical parameters in collisionless magnetospheric plasma,
the primary mechanism controlling the dissipation in the vicinity of
the reconnection site is non-gyrotropic effects with spatial scales
comparable with the particle Larmor radius. We utilize the global MHD
code BATSRUS and incorporate nongyrotropic effects in diffusion regions
in terms of corrections to the induction equation. We developed an
algorithm to search for magnetotail reconnection sites, specifically
where the magnetic field components perpendicular to the local current
direction approaches zero and form an X-type configuration. Spatial
scales of the diffusion region and magnitude of the reconnection
electric field are calculated self-consistently using MHD plasma
and field parameters in the vicinity of the reconnection site. The
location of the reconnection sites is updated during the simulations. To
clarify the role of nongyrotropic effects in diffusion region on the
global magnetospheric dynamic we perform simulations with steady
southward IMF driving of the magnetosphere. Ideal MHD simulations
with magnetic reconnection supported by numerical resistivity
produce steady configuration with almost stationary near-earth
neutral line (NENL). Simulations with non-gyrotropic corrections
demonstrate dynamic quasi-periodic response to the steady driving
condition. The loading/unloading cycle in non-gyrotropic MHD results
has a non-stationary reconnection site in the magnetotail, with the
retreating during the stretching phase and then a new NENL forming in
the resulting thin plasma sheet. We expect that this model will lead
to improved representations of space weather event in the magnetosphere.
Title: Simulation of the Ejections From NOAA AR 9236 With the SWMF
Authors: Lugaz, N.; Manchester, W.; Toth, G.; Gombosi, T. I.
Bibcode: 2006AGUSMSA23A..01L
Altcode:
NOAA active region 9236 produced a series of 5 X-class flares and
5 full halo CMEs between November 24 and November 27, 2000. Some of
these ejections interacted on their way to Earth and produced a complex
ejecta observed by the ACE satellite. We performed a MHD simulation of
the ejections of November 24 using the Space Weather Modeling Framework
(SWMF). We are able to reproduce LASCO C2 and C3 coronograph images with
good agreement and to get a better understanding of the interaction
of multiple CMEs resulting in the formation of a long-lived magnetic
storm at Earth.
Title: Understanding Ring Current Sources of Moderate and Intense
Storms at Solar Maximum: Global Modeling Using Superposed Epoch
Upstream Conditions
Authors: Zhang, J. -C.; Liemohn, M. W.; de Zeeuw, D. L.; Borovsky,
J. E.; Ridley, A. J.; Toth, G.; Sazykin, S.; Thomsen, M. F.; Kozyra,
J. U.; Gombosi, T. I.; Swmf; Mpa Team
Bibcode: 2006cosp...36.3321Z
Altcode: 2006cosp.meet.3321Z
With the Space Weather Modeling Framework SWMF we conduct storm
simulations for superposed epoch upstream solar wind conditions of 34
moderate storms and 64 intense storms at solar maximum July 1999 -
June 2002 In comparison with superposed epoch averages of Dst Sym-H
and the Los Alamos Magnetospheric Plasma Analyzer MPA observations
at geosynchronous orbit modeling results are validated It is shown
that the SWMF is sophisticated enough to make quantitative data-model
comparisons The major storm characteristics are successfully reproduced
With the two levels of storm intensity and different SWMF parameter
settings the influences on storms of upstream conditions ionospheric
outflow and ionospheric conductance are assessed It is shown that the
integrated energy input for a storm is much more important than the
short-lived peaks in the upstream solar wind values Consistent with the
MPA averaged measurements it is found that in the inner magnetosphere
in the simulated main phase plasmas become denser near dawn than
around duskside plasma temperature is higher in the afternoon and
pre-midnight sectors but enhanced plasma pressure is always symmetric on
the nightside with a peak at midnight Possible reasons for these plasma
parameter asymmetries and symmetries are investigated and discussed
Title: Space weather simulations with the Space Weather Modeling
Framework
Authors: Gombosi, T.; Toth, G.; Sokolov, I.; Ridley, A.; de Zeeuw,
D.; Manchester, W.; Clauer, R.
Bibcode: 2006cosp...36.1541G
Altcode: 2006cosp.meet.1541G
The Space Weather Modeling Framework SWMF aims at providing a flexible
framework for physics based space weather simulations The SWMF combines
numerical models of the Solar Corona which includes the Eruptive
Event Generator the Inner Heliosphere Solar Energetic Particles
Global Magnetosphere Inner Magnetosphere Radiation Belt Ionosphere
Electrodynamics and Upper Atmosphere into a parallel high performance
model All the components can be replaced with alternatives and one has
the option to use only a subset of the components The SWMF enables us
to do simulations that were not possible with the individual components
We highlight some numerical simulations obtained with the SWMF
Title: Kelvin-Helmholtz Instability and Turbulence Forming Behind
a CME-driven Shock.
Authors: Manchester, W. B.; Opher, M.; Gombosi, T.; Dezeeuw, D.;
Sokolov, I.; Toth, G.
Bibcode: 2005AGUFMSH53A1245M
Altcode:
We have found that a fast CME propagating through a bimodal solar wind
produces variety of unexpected results. By means of a three-dimensional
(3-D) numerical ideal magnetohydrodynamics (MHD) model we explore the
interaction of a fast CME with a solar wind that possesses fast and
slow speed solar wind at high and low latitude respectively. Within
this model system, a CME erupts from the coronal streamer belt with
an initial speed in excess of 1000 km/s which naturally drives a
forward shock. An indentation in the shock forms at low latitude
where it propagates through the slow solar wind. This indentation
causes the fast-mode shock to deflect the flow toward the impinging
flux rope. The plasma flow then must reverses direction to move around
the rope, resulting in strong velocity shears. The shear flow is shown
to be susceptible to the Kelvin-Helmholtz instability, which results
in significant turbulence producing an environment very conducive to
particle acceleration.
Title: Understanding Storm-time Ring Current Sources through
Data-Model Comparisons of a Moderate Storm, an Intense Storm and
a Super-storm
Authors: Zhang, J.; Liemohn, M. W.; Dezeeuw, D. L.; Borovsky, J. E.;
Ridley, A. J.; Toth, G.; Sazykin, S.; Thomsen, M. F.; Kozyra, J. U.;
Gombosi, T. I.; Wolf, R. A.
Bibcode: 2005AGUFMSM22A..08Z
Altcode:
With the Space Weather Modeling Framework (SWMF), the moderate
storm on 19 May 2002, the intense storm on 11 May 2002, and the
super-storm on 20 November 2003 are simulated. In comparison with
in-situ observations from Wind, Geotail, Polar, Goes8, Goes10, Goes12,
LANL MPA, and measured Sym-H, simulation results are validated. It is
shown that the SWMF is sophisticated enough to make quantitative data-
model comparisons. The major characteristics of the three storms are
successfully reproduced. Observations and modeling results match better
in the outer than inner magnetosphere; they match better during the
quiet than disturbed times. With different SWMF parameter settings and
storm sizes, the influences on storms of upstream solar wind conditions,
ionospheric outflow and ionospheric conductance are assessed. Results
from `virtual satellites', placed at geosynchronous orbit in the SWMF,
show that plasma temperature and entropy are asymmetric on the nightside
with a peak at 7:00 - 8:00 PM local time. After the solar wind shock
hits the magnetosphere, the nightside plasma becomes denser closer
to dawn and dusk. Possible reasons for the number density peaks are
investigated and discussed.
Title: Statistical Study of the Probability of Titan Being in the
Solar Wind or in Saturn's Magnetosheath
Authors: Lundberg, E. T.; Hansen, K. C.; Gombosi, T. I.; Toth, G.
Bibcode: 2005AGUFM.P43A0957L
Altcode:
We present the results of a statistical study of the location of
Titan relative to the bow shock and the magnetopause of Saturn's
magnetosphere. Using statistical distributions of solar wind ram
pressure at Saturn's orbit and the dependence of the magnetosphere's
boundaries on this pressure we are able to calculate the probability of
finding Titan in the solarwind, the magnetosheath or the magnetosphere
for each point along its orbit. As a preliminary example consider Titan
at the sub-solar point for 2004 solar wind conditions. We find that
Titan would have spent 56.7% of its time in the magnetosphere, 42.1%
in the magnetosheath and 1.3% in the solarwind for these conditions
when at the sub-solar point. We will present statistics for Titan at
a set of local times along its orbit as well as integrated over its
entire orbit. We obtain solar wind conditions at the orbit of Saturn
by propagating ACE and other spacecraft measurements of the solar wind
conditions at the Earth radially outward using a 1D MHD model. The
propagation is validated against Voyager, Pioneer and Cassini data. For
our calculations, we use different models for the shape of the bow
shock and magnetopause. These include the traditional Slavin model as
well as a new boundary model generated by fitting geometric surfaces
to a global 3D MHD model of Saturn's magnetosphere.
Title: Magnetic Reconnection in Global MHD Modeling of Magnetosphere
Dynamics
Authors: Kuznetsova, M. M.; Hesse, M.; Rastatter, L.; Toth, G.;
de Zeeuw, D.; Gombosi, T.
Bibcode: 2005AGUFMSM31B0418K
Altcode:
One of the major challenges in global MHD modeling of magnetosphere
dynamics is to find an accurate description of the reconnection rate. We
will take advantage of recent progress in small-scale kinetic studies
of magnetic reconnection, which demonstrated that the reconnection
rate is controlled by ion nongyrotropic behavior near the reconnection
site. It can then be expressed in terms of nongyrotropic corrections to
the electric field. We will demonstrate that the reconnection electric
field can be estimated as a convection electric field v x B at the edge
of the non-MHD diffusion region. The BATSRUS adaptive grid structure
allows to perform global simulations with spatial resolution near the
reconnection site comparable with ion kinetic scales. To reproduce
fast reconnection rates observed in kinetic simulations we modified
the global MHD code BATSRUS by introducing nongyrotropic corrections
to the magnetic induction equation. The role of the nongyrotropic
effects near the reconnection site on the global magnetospheric
dynamics will be analyzed. Testing the ability of global MHD models
to describe magnetospheric dynamics is one of the elements of science
based validation efforts at the Community Coordinated Modeling Center.
Title: Space Weather Modeling Framework: A new tool for the space
science community
Authors: Tóth, GáBor; Sokolov, Igor V.; Gombosi, Tamas I.; Chesney,
David R.; Clauer, C. Robert; de Zeeuw, Darren L.; Hansen, Kenneth
C.; Kane, Kevin J.; Manchester, Ward B.; Oehmke, Robert C.; Powell,
Kenneth G.; Ridley, Aaron J.; Roussev, Ilia I.; Stout, Quentin F.;
Volberg, Ovsei; Wolf, Richard A.; Sazykin, Stanislav; Chan, Anthony;
Yu, Bin; Kóta, József
Bibcode: 2005JGRA..11012226T
Altcode:
The Space Weather Modeling Framework (SWMF) provides a high-performance
flexible framework for physics-based space weather simulations, as well
as for various space physics applications. The SWMF integrates numerical
models of the Solar Corona, Eruptive Event Generator, Inner Heliosphere,
Solar Energetic Particles, Global Magnetosphere, Inner Magnetosphere,
Radiation Belt, Ionosphere Electrodynamics, and Upper Atmosphere into a
high-performance coupled model. The components can be represented with
alternative physics models, and any physically meaningful subset of the
components can be used. The components are coupled to the control module
via standardized interfaces, and an efficient parallel coupling toolkit
is used for the pairwise coupling of the components. The execution
and parallel layout of the components is controlled by the SWMF. Both
sequential and concurrent execution models are supported. The SWMF
enables simulations that were not possible with the individual physics
models. Using reasonably high spatial and temporal resolutions in all
of the coupled components, the SWMF runs significantly faster than
real time on massively parallel supercomputers. This paper presents
the design and implementation of the SWMF and some demonstrative
tests. Future papers will describe validation (comparison of model
results with measurements) and applications to challenging space
weather events. The SWMF is publicly available to the scientific
community for doing geophysical research. We also intend to expand
the SWMF in collaboration with other model developers.
Title: Magnetic Reconnection Rate in Collisionless Plasma.
Authors: Patel, K.; Kuznetsova, M. M.; Hesse, M.; Rastatter, L.;
Toth, G.; Gombosi, T.
Bibcode: 2005AGUFMSH51D..06P
Altcode:
The physical processes controlling the magnetic reconnection rate are of
principle importance for many phenomena in space plasma. Comparative
study of magnetic reconnection in kinetic and fluid simulations
demonstrated that the reconnection rate is controlled by ion
nongyrotropic behavior near the reconnection site. We will demonstrate
that reconnection electric field can be estimated as a convection
electric field v x B at the edge of the non-MHD diffusion region and
can be incorporated into the MHD description. We employ small scale
and global MHD simulation codes and introduce non-ideal corrections
to the induction equation in terms of nongyrotropic corrections to
the electric field. The role of the nongyrotropic effects near the
reconnection site on the global dynamics will be analyzed.
Title: Multiple Scales in the Solar Wind Interaction with the
Magnetosphere
Authors: Gombosi, T. I.; Ridley, A. J.; de Zeeuw, D. L.; Sokolov,
I. V.; Toth, G.
Bibcode: 2005AGUFMSM34A..01G
Altcode:
The solar wind interaction with the magnetosphere takes place on many
scales ranging from global scale current systems to mesoscale processes
like ionospheric outflows, to microscale phenomena involving kinetic
effects and reconnection. This talk will discuss a new computational
tool, the Space Weather Modeling Framework (SWMF), that was specifically
designed to self-consistently couple different physics domains described
by different approximate models. SWMF can couple global MHD codes to
kinetic drift physics models (such as RCM), as well as other mesoscale
and/or microscale codes. We will show several simulations and data
comparisons investigating the effects of various processes on the
configuration and dynamics of the magnetosphere.
Title: Numerical Simulation of Transport of Open Magnetic Flux on
the Solar Surface
Authors: Cohen, O.; Fisk, L. A.; Gombosi, T. I.; Roussev, I. I.;
Toth, G.
Bibcode: 2005AGUFMSH41A1116C
Altcode:
Following Fisk (2005), we simulate the transport and evolution
of the open magnetic flux on the surface of the sun. The temporal
evolution of the flux density depends on the convective motion due
to solar differential rotation and poleward meridional flow, and an
effective diffusive motion. The latter is a result of the diffusion
of field-lines footpoints in the network lanes, and the diffusion of
field-lines due to reconnection of open field lines with closed loops
on the solar surface. The diffusion coefficient of the network lanes
motion is constant everywhere, while the diffusion coefficient due
to the reconnection process is non-uniform, and depends on the open
flux density and the rate of emergence of the new magnetic loops. The
gradient of the diffusion coefficient due to reconnection represents an
effective velocity in addition to the convective motion. We investigate
the behavior of the steady-state solution with constant and spatial
diffusion coefficient; we also examine the behavior of the effective
velocity due to the non-uniform diffusion coefficient. In the future,
we plan to extend the current 2D model to a 3D geometry in order
to investigate the role of the open flux in the evolution of the
large-scale solar magnetic field and in solar wind acceleration,
in the extent of a global model.
Title: Sun-to-Thermosphere Simulation of the October 28, 2003 Event
With the Space Weather Modeling Framework
Authors: Toth, G.; de Zeeuw, D. L.; Gombosi, T. I.; Manchester, W. B.;
Ridley, A. J.; Roussev, I. I.; Sokolov, I. V.
Bibcode: 2005AGUFMSM11A..05T
Altcode:
Space weather forecasting requires faster than real-time simulations
of the entire Sun-to-Earth model chain at high enough spatial and
temporal resolution to resolve the important geoeffective features in
the solar wind and the magnetosphere-ionosphere-thermosphere system. We
present a complete end-to-end simulation of one of the most intensive
solar storms, the October 28, 2003 CME. The physical domain models
spanning from the Solar Corona model to the Upper Atmosphere model
are self-consistently coupled together by the high-performance Space
Weather Modeling Framework (SWMF). We discuss technological advances
enabling the faster than real-time operation of the SWMF with high
resolution. We also compare the simulation results with observations.
Title: Magnetotail Current Sheet Thinning in Global Simulations of
Magnetosphere Dynamics.
Authors: Taktakishvili, A.; Kuznetsova, M.; Hesse, M.; Rastatter,
L.; Toth, G.; de Zeeuw, D.; Gombosi, T.
Bibcode: 2005AGUFMSM23B0430T
Altcode:
We perform simulations of magnetotail dynamics using the global MHD
models at the Community Coordinated Modeling Center (CCMC). We select
solar wind conditions which drive the accumulation of magnetic field in
the tail lobes and subsequent magnetotail current sheet thinning. We
will demonstrate the formation of bifurcated and triple-peak current
sheets during this phase. In addition, we will analyze the dependence
of the thin current sheet structure, location, rate of the thinning
and timing of reconnection onset on solar wind conditions. Finally,
we will discuss the role of dayside reconnection rate, of diffusion
at the flanks, and of distant tail processes on the dynamics of the
current sheet thinning.
Title: The Polar Wind as a Mass Source for Saturn's Magnetosphere
Authors: Glocer, A.; Gombosi, T.; Toth, G.; Hansen, K.; Ridley, A.
Bibcode: 2005AGUFM.P52A..06G
Altcode:
Characterizing the relative importance of the various mass sources
is crucial to understanding Saturn's magnetosphere. Most research in
this area focuses on the addition of mass from the icy satellites and
rings. Comparatively little attention has been paid to the ionospheric
source. Our study addresses this issue by using multi-fluid numerical
simulations of Saturn's polar wind to determine the magnitude of the
contribution. We introduce a model capable of calculating the polar wind
at Earth and Saturn, solving the gyrotropic transport equations. The
polar wind at Saturn is calculated from below the peak ionospheric
density to an altitude of one Saturn radius, giving fluxes for H3+,
H+, and electrons. Similarly, at Earth the calculation ranges from
200 km to approximately one Earth radius, providing fluxes for O+, H+,
and He+. We calculate source rates for various atmospheric profiles,
and compare the results with those calculated from other models and
measurements where appropriate.
Title: Transport and Acceleration of Electrons from the Outer to
the Inner Magnetosphere
Authors: Schriver, D.; Ashour-Abdalla, M.; Zelenyi, L.; Gombosi, T.;
Ridley, A.; Toth, G.; Travnicek, P.
Bibcode: 2005AGUFMSM33C0469S
Altcode:
To examine the transport and acceleration of electrons throughout the
Earth's magnetosphere, a global model that follows electron motion
in magnetic and electric fields representative of the magnetospheric
configuration has been developed. The goal is to understand the
formation of the seed electron population with energies > keV located
at about 10 R_E from the Earth in the equatorial plane. The results show
that electrons launched in the outer magnetospere are adibatically
compressed as they convect towards the magnetic midplane in the
magnetotail forming a heated central plasma sheet towards the Earth. A
group of electrons accelerated near a reconnection region located in the
deep magnetotail also contributes to the plasma sheet population and the
heated distribution function that forms in the seed region (at about 10
R_E) is a combination of electrons that are accelerated adiabatically
and non-adiabatically. The results also show that the seed electron
distribution is highly anisotropic with the perpendicular temperature
about 2 times the parallel temperature. Results that consider different
magnetic activity levels will be discussed and comparisions with Cluster
satellite data in the near-Earth plasma sheet region will be presented.
Title: Numerical simulations of vertical oscillations of a solar
coronal loop
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Wang, T. J.;
Tóth, G.
Bibcode: 2005A&A...440..385S
Altcode:
We consider the impulsive excitation of fast vertical kink standing
waves in a solar coronal loop that is embedded in a potential
arcade. The two-dimensional numerical model we implement includes the
effects of field line curvature and nonlinearity on the excitation
and damping of standing fast magnetosonic waves. The results of the
numerical simulations reveal wave signatures which are characteristic
of vertical loop oscillations seen in recent TRACE observational data.
Title: Global MHD simulations of Saturn's magnetosphere at the time
of Cassini approach
Authors: Hansen, K. C.; Ridley, A. J.; Hospodarsky, G. B.; Achilleos,
N.; Dougherty, M. K.; Gombosi, T. I.; Tóth, G.
Bibcode: 2005GeoRL..3220S06H
Altcode:
We present the results of a 3D global magnetohydrodynamic simulation
of the magnetosphere of Saturn for the period of Cassini's initial
approach and entry into the magnetosphere. We compare calculated bow
shock and magnetopause locations with the Cassini measurements. In order
to match the measured locations we use a substantial mass source due
to the icy satellites (~1 × 1028 s-1 of water
product ions). We find that the location of bow shock and magnetopause
crossings are consistent with previous spacecraft measurements,
although Cassini encountered the surfaces further from Saturn than
the previously determined average location. In addition, we find that
the shape of the model bow shock and magnetopause have smaller flaring
angles than previous models and are asymmetric dawn-to-dusk. Finally,
we find that tilt of Saturn's dipole and rotation axes results in
asymmetries in the bow shock and magnetopause and in the magnetotail
being hinged near Titan's orbit (~20 RS).
Title: Cross-Disciplinary Modeling of Heliospheric Phenomena with
the Space Weather Modeling Framework
Authors: Gombosi, T. I.; Toth, G.; Sokolov, I. V.; Stout, Q. F.;
Clauer, C. R.; de Zeeuw, D. L.; Hansen, K. C.; Manchester, W. B.;
Powell, K. G.; Ridley, A. J.; Roussev, I. I.
Bibcode: 2005AGUSMSH11B..01G
Altcode:
The Space Weather Modeling Framework (SWMF) aims at providing a
high-performance flexible plug-and-play type framework for physics
based space weather simulations, as well as for various space physics
applications. The SWMF combines numerical models of the Solar Corona,
Eruptive Event Generator, Inner Heliosphere, Solar Energetic Particles,
Global Magnetosphere, Inner Magnetosphere, Radiation Belt, Ionosphere
Electrodynamics and Upper Atmosphere into a high performance coupled
model. All the components can be replaced with alternatives, and one
can use only a subset of the components. The components are coupled
to the control module via standardized interfaces, and an efficient
parallel coupling toolkit can be used for the pairwise coupling of
the components. The SWMF enables us to do simulations that were not
possible with the individual components. Using reasonably high spatial
and temporal resolutions in all the coupled components, the SWMF can
still run significantly faster than real time on massively parallel
supercomputers. This talk presents the design and implementation of
the SWMF with a demonstrative application to a space weather event.
Title: Fast Magnetotail Reconnection: Challenge to Global MHD Modeling
Authors: Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.;
de Zeeuw, D.; Gombosi, T.
Bibcode: 2005AGUSMSM33A..02K
Altcode:
Representation of fast magnetotail reconnection rates during substorm
onset is one of the major challenges to global MHD modeling. Our
previous comparative study of collisionless magnetic reconnection
in GEM Challenge geometry demonstrated that the reconnection rate is
controlled by ion nongyrotropic behavior near the reconnection site
and that it can be described in terms of nongyrotropic corrections
to the magnetic induction equation. To further test the approach we
performed MHD simulations with nongyrotropic corrections of forced
reconnection for the Newton Challenge setup. As a next step we employ
the global MHD code BATSRUS and test different methods to model fast
magnetotail reconnection rates by introducing non-ideal corrections
to the induction equation in terms of nongyrotropic corrections,
spatially localized resistivity, or current dependent resistivity. The
BATSRUS adaptive grid structure allows to perform global simulations
with spatial resolution near the reconnection site comparable with
spatial resolution of local MHD simulations for the Newton Challenge. We
select solar wind conditions which drive the accumulation of magnetic
field in the tail lobes and subsequent magnetic reconnection and
energy release. Testing the ability of global MHD models to describe
magnetotail evolution during substroms is one of the elements of science
based validation efforts at the Community Coordinated Modeling Center.
Title: Evolution of CME-driven Shocks in the Lower Corona for the
October-November 2003 Events
Authors: Opher, M.; Manchester, W.; Gombosi, T.; Liewer, P.; Roussev,
I.; Sokolov, I.; Dezeeuw, D.; Toth, G.
Bibcode: 2005AGUSMSH13B..03O
Altcode:
While it is generally accepted that the largest energetic particle
events are created by CME-driven shocks in interplanetary space, the
relative importance of CME-driven shocks versus flare-related processes
in creating energetic particles low in the corona is not understood
and is an area of active research. We analyzed the formation of CME
driven shocks in the lower corona for the Halloween Space Storms
that occurred in late October and early November 2003. We used the
Space Weather Modeling Framework (SWMF) developed at the University
of Michigan to create a realistic corona. The CME was modeled as an
out of equilibrium flux rope lying under a closed field region in the
AR 10486. The MHD code was first used to create realistic background
corona using observed photospheric fields for boundary conditions for
the Carrington rotation 2008. The background corona was validated by
comparing results from the model with in situ solar wind observations
from ACE/WIND. We discuss the magnetosonic speed profile in the lower
corona and the consequences for the CME shock formation. Consequences
for the acceleration of particles to GeV/nucleon are discussed. The
computational runs were performed at the supercomputer Columbia at
NASA/AMES.
Title: Are high-latitude forward-reverse shock pairs driven by
over-expansion?
Authors: Manchester, W. B.; Zurbuchen, T. H.; Gombosi, T. I.; de Zeeuw,
D. L.; Sokolov, I. V.; Toth, G.
Bibcode: 2005AGUSMSH52A..04M
Altcode:
During its passage through the high-latitude heliosphere, Ulysses
observed Interplanetary CMEs (ICMEs) bounded by shocks. These
forward-reverse shock pairs have only been observed at high latitude in
the fast solar. It has been suggested (e.g. Gosling et al. 1995) that
these shock pairs are the result of the expansion of the coronal mass
ejection in the ambient solar wind, so called "over-expansion". Here
we demonstrate and alternative explanation for forward-reverse
shock pairs by means of a three-dimensional (3-D) numerical ideal
magnetohydrodynamics (MHD) model of a CME interacting with the solar
wind. Our global steady-state coronal model possesses fast and slow
speed solar wind at high and low latitude respectively reminiscent of
near solar minimum conditions. Within this model system, a CME erupts
from the coronal streamer belt with an initial speed in excess of 1000
km/s which naturally drives a forward shock. When the CME is greater
than 40 Rs from the Sun, we find that a reverse shock forms poleward of
the CME as a result of the interaction of the CME with the bimodal solar
wind. In front of the CME, the slow wind is deflected to higher latitude
while behind the CME, fast wind is deflected to low latitude. The
deflected streams collide to form a reverse shock. The shock pair
formed in this way naturally forms at high latitude in the fast wind
stream. We will discuss these model results in the context of in situ
solar wind data and make testable predictions based on this model.
Title: Effects of a Tilted Heliospheric Current Sheet in the
Heliosheath
Authors: Opher, M.; Liewer, P.; Velli, M.; Gombosi, T.; Manchester,
W.; Dezeeuw, D.; Toth, G.
Bibcode: 2005AGUSMSH23A..07O
Altcode:
Effects of a Tilted Heliospheric Current Sheet in the Heliosheath
Recent observations indicate that Voyager 1, now beyond 90 AU, is in a
region unlike any encountered in it's 26 years of exploration. There
is currently a controversy as to whether Voyager 1 has already
crossed the Termination Shock, the first boundary of the Heliosphere
(Krimigis et al. 2003; McDonald et al. 2003, Burlaga et al. 2003). An
important aspect of this controversy is our poor understanding
of this region. The region between the Termination Shock and the
Heliopause, the Helisheath, is one of the most unknown regions
theoretically. In the Heliosheath magnetic effects are crucial,
as the solar magnetic field is compressed at the Termination Shock
by the slowing flow. Therefore, to accurately model the heliosheath
the inclusion of the solar magnetic field is crucial. Recently, our
simulations showed that the Heliosheath presents remarkable dynamics,
with turbulent flows and a presence of a jet flow at the current sheet
that is unstable due to magnetohydrodynamic instabilities (Opher et
al. 2003; 2004). We showed that to capture these phenomena, spatial
numerical resolution is a crucial ingredient, therefore requiring the
use of an adaptive mesh refinement (AMR). These previous works assumed
that the solar rotation and the magnetic axis were aligned. Here we
present including, for the first time, the tilt of the heliocurrent
sheet using a 3D MHD AMR simulation with BATS-R-US code. We discuss
the effects on the global structure of the Heliosheath, the flows,
turbulence and magnetic field structure. We access the consequences for
the observations measured by Voyager 1 since mid-2002. This intensive
computational run was done at the supercomputer Columbia at NASA/AMES
Title: Validation of the Space Weather Modeling Framework for
Northward IMF Conditions
Authors: Toth, G.; Ridley, A. J.; Oieroset, M.; de Zeeuw, D. L.;
Gombosi, T. I.
Bibcode: 2005AGUSMSM42A..01T
Altcode:
We have simulated the magnetosphere and the ionosphere for an extended
period of northward interplanetary magnetic field (IMF) conditions
that occurred between 17:00 UT October 22 2003 and 00:00 UT October
24 2003. The Space Weather Modeling Framework (SWMF) is run with the
coupled global magnetosphere (BATSRUS), inner magnetosphere (RCM)
and ionosphere electro-dynamics (Ridley) components. The simulation
results are compared with the magnetic field measurements of the GOES
10, GOES 12, Polar, Wind and Geotail satellites, and with the density,
temperature, magnetic field and velocity measured by the Cluster
satellites. We examine the effects of the grid resolution, Joule
heating, resistivity, and coupling with the Inner Magnetosphere. It
is found that the coupling with the RCM significantly improves the
agreement between the observed and simulated magnetic fields near
the Earth. In order to better match the far-tail Wind observations,
resistivity needs to be added to the simulation. This indicates that
the numerical resistivity in the code is most likely too low in the
reconnection sites. In addition, it is shown that the amount of Joule
heating in the reconnection site has a strong influence on the density
and temperature of the plasma sheet. This series of simulations also
serve as a validation of the SWMF.
Title: Coronal Mass Ejection Shock and Sheath Structures Relevant
to Particle Acceleration
Authors: Manchester, W. B., IV; Gombosi, T. I.; De Zeeuw, D. L.;
Sokolov, I. V.; Roussev, I. I.; Powell, K. G.; Kóta, J.; Tóth, G.;
Zurbuchen, T. H.
Bibcode: 2005ApJ...622.1225M
Altcode:
Most high-energy solar energetic particles are believed to be
accelerated at shock waves driven by coronal mass ejections (CMEs). The
acceleration process strongly depends on the shock geometry and the
structure of the sheath that forms behind the shock. In an effort
to understand the structure and time evolution of such CME-driven
shocks and their relevance to particle acceleration, we investigate
the interaction of a fast CME with the ambient solar wind by means
of a three-dimensional numerical ideal MHD model. Our global steady
state coronal model possesses high-latitude coronal holes and a
helmet streamer structure with a current sheet near the equator,
reminiscent of near solar minimum conditions. Fast and slow solar
winds flow at high and low latitude, respectively, and the Archimedean
spiral geometry of the interplanetary magnetic field is reproduced by
solar rotation. Within this model system, we drive a CME to erupt by
introducing a Gibson-Low magnetic flux rope that is embedded in the
helmet streamer in an initial state of force imbalance. The flux rope
rapidly expands and is ejected from the corona with maximum speeds
in excess of 1000 km s-1, driving a fast-mode shock from
the inner corona to a distance of 1 AU. We find that the ambient solar
wind structure strongly affects the evolution of the CME-driven shocks,
causing deviations of the fast-mode shocks from their expected global
configuration. These deflections lead to substantial compressions of
the plasma and magnetic field in their associated sheath region. The
sudden postshock increase in magnetic field strength on low-latitude
field lines is found to be effective for accelerating particles to
the GeV range.
Title: Modelling gravity gradient variation due to water mass
fluctuations
Authors: Völgyesi, L.; Tóth, G.
Bibcode: 2005ggsm.conf..364V
Altcode:
No abstract at ADS
Title: Determination of gravity anomalies from torsion balance
measurements
Authors: Völgyesi, L.; Tóth, G.; Csapó, G.
Bibcode: 2005ggsm.conf..292V
Altcode:
No abstract at ADS
Title: A Physics-Based Software Framework for Sun-Earth Connection
Modeling
Authors: Toth, G.; Volberg, O.; Ridley, A. J.; Gombosi, T. I.;
de Zeeuw, D.; Hansen, K. C.; Chesney, D. R.; Stout, Q. F.; Powell,
K. G.; Kane, K. J.; Oehmke, R. C.
Bibcode: 2005mcsp.conf..383T
Altcode:
No abstract at ADS
Title: Electron Transport in the Earth's Outer and Inner Magnetosphere
Authors: Schriver, D.; Ashour-Abdalla, M.; Zelenyi, L.; Gombosi, T.;
Ridley, A. J.; Dezeeuw, D.; Toth, G.; Monostori, G.
Bibcode: 2004AGUFMSM33B..06S
Altcode:
As electrons are transported from the solar wind and through the
Earth's magnetosphere, they can be accelerated to energies >
10 keV when they reach the so-called seed region located at about 10
RE radially from the Earth in the equatorial plane. As these
seed electrons move closer to the Earth, wave-particle interactions
can cause further acceleration of electrons to relativistic (MeV)
energies. This process occurs during the recovery of magnetic storms,
where relativistic electron fluxes are usually observed to be enhanced
over pre-storm values in the inner magnetosphere near geosynchronous
orbit. In this study, the transport of electrons from the solar wind and
outer magnetosphere towards the seed region is examined. This is done
by following electron trajectories from different starting points in a
global model for the magnetospheric magnetic and electric fields. The
electron particle trajectories are followed based on the guiding center
approximation and both an empirical and an MHD model (BATS-R-US code)
are used for the global magnetospheric fields. In regions where
the local fields are very weak (e.g., near reconnection regions),
non-adiabatic effects could be important and this is included when
following electrons by switching from the guiding center approximation
to a full trajectory calculation using the Lorentz force equation in
these localized regions of space. Electron distribution functions
formed at different locations in the magnetotail as well as in the
seed region will be discussed.
Title: New Simulations of Saturn's Polar Wind
Authors: Glocer, A.; Gombosi, T.; Hansen, K.; Toth, G.
Bibcode: 2004AGUFM.P51A1417G
Altcode:
We present preliminary results of a new simulation of Saturn's
polar wind. The results include new vertical ion and electron density
profiles, fluxes, and net source rates. Our model solves the 13 moment
gyrotropic transport equations. The gyration dominated assumption
allows us to assume that the flow is field aligned, and justifies the
use of a one dimensional model. Furthermore, the effect of solar zenith
angle and optical depth on the solar flux is taken into account. While
capable of modeling transient behavior, only steady state results are
presented. Similarly, the ability to include field aligned currents
is built into the model, but their effect is not yet studied. By
combining polar wind model output with a global MHD simulation of
the magnetosphere-ionosphere system, we are able to calculate the net
ionospheric source due to the polar wind. Like Earth, we expect that
Saturn's ionosphere is an important source of magnetospheric plasma. The
recent arrival of Cassini is giving unprecedented amounts of data. The
time is therefore ripe for an attempt to characterize the ionospheric
source at Saturn, and this simulation will help further this objective.
Title: Coupling of a global MHD code and an inner magnetospheric
model: Initial results
Authors: de Zeeuw, Darren L.; Sazykin, Stanislav; Wolf, Richard A.;
Gombosi, Tamas I.; Ridley, Aaron J.; Tóth, Gabor
Bibcode: 2004JGRA..10912219D
Altcode:
This paper describes the coupling of BATS-R-US (Block Adaptive Tree
Solar-wind Roe-type Upwind Scheme), a magnetohydrodynamics (MHD) code
representing the Earth's global magnetosphere and its coupling to
the ionosphere and solar wind, and the Rice Convection Model (RCM),
which represents the inner magnetosphere and its coupling to the
ionosphere. The MHD code provides a time-evolving magnetic field model
for the RCM as well as continuously updated boundary conditions for
the electric potential and plasma. The RCM computes the distribution
functions of inner magnetospheric particles, including transport of
inner plasmasheet and ring current particles by gradient/curvature
drifts; it thus calculates more accurate inner magnetospheric pressures,
which are frequently passed to the MHD model and used to nudge the
MHD values. Results are presented for an initial run with the coupled
code for the case of uniform ionospheric conductance with steady
solar wind and southward interplanetary magnetic field (IMF). The
results are compared with those for a run of the MHD code alone. The
coupled-code run shows significantly higher inner magnetospheric
particle pressures. It also exhibits several well-established
characteristics of inner magnetospheric electrodynamics, including
strong region-2 Birkeland currents and partial shielding of the inner
magnetosphere from the main force of the convection electric field. A
sudden northward turning of the IMF causes the ring current to become
more nearly symmetric. The inner magnetosphere exhibits an overshielding
(dusk-to-dawn) electric field that begins about 10 min after the
northward turning reaches the magnetopause and lasts just over an hour.
Title: Space Weather Modeling Framework: Modeling the Sun-Earth
System Faster Than Real Time
Authors: Toth, G.; Sokolov, I. V.; Kane, K. J.; Gombosi, T. I.; de
Zeeuw, D. L.; Ridley, A. J.; Volberg, O.; Hansen, K. C.; Manchester,
W. B.; Roussev, I. I.; Stout, Q. F.; Powell, K. G.
Bibcode: 2004AGUFMSH53B0325T
Altcode:
The Space Weather Modeling Framework (SWMF) aims at providing a
flexible plug-and-play type framework for physics based space weather
simulations, as well as for various space physics applications. The SWMF
combines numerical models of the Solar Corona (including an Eruptive
Event Generator), the Inner Heliosphere, Solar Energetic Particles,
Global Magnetosphere, Inner Magnetosphere, Radiation Belt, Ionosphere
Electrodynamics and Upper Atmosphere into a high performance coupled
model. All the components can be replaced with alternatives, and one can
use only a subset of the components. The configuration, compilation and
execution of the framework can be done with a user friendly Graphical
User Interface. The components are coupled to the control module via
standardized interfaces, and an efficient parallel coupling toolkit
is used for the pairwise coupling of the components. The execution
and parallel layout of the components is controlled by the SWMF. Both
sequential and concurrent execution models are supported. The SWMF
enables us to do simulations that were not possible with the individual
components. Using reasonably high spatial and temporal resolutions in
all the coupled components, the SWMF can still run significantly faster
than real time on massively parallel super computers. We highlight
some numerical simulations obtained with the SWMF.
Title: Effects of a Tilted Heliospheric Current Sheet in the
Heliosheath: 3D MHD Modeling
Authors: Opher, M.; Liewer, P.; Velli, M.; Gombosi, T.; Manchester,
W.; Dezeeuw, D.; Toth, G.
Bibcode: 2004AGUFMSH42A..02O
Altcode:
Recent observations indicate that Voyager 1, now beyond 90 AU, is in
a region unlike any encountered in it's 26 years of exploration. There
is currently a controversy as to whether Voyager 1 has already crossed
the Termination Shock, the first boundary of the Heliosphere (Krimigis
et al. 2003; McDonald et al. 2003, Burlaga et al. 2003). An important
aspect of this controversy is our poor understanding of this region. The
region between the Termination Shock and the Heliopause, the Helisheath,
is one of the most unknown regions theoretically. In the Heliosheath
magnetic effects are crucial, as the solar magnetic field is compressed
at the Termination Shock by the slowing flow. Therefore, to accurately
model the Heliosheath the inclusion of the solar magnetic field is
crucial. Recently, our simulations showed that the Heliosheath presents
remarkable dynamics, with turbulent flows and a presence of a jet
flow at the current sheet that is unstable due to magnetohydrodynamic
instabilities (Opher et al. 2003; 2004). We showed that to capture
these phenomena, spatial numerical resolution is a crucial ingredient,
therefore requiring the use of an adaptive mesh refinement (AMR). These
previous works assumed that the solar rotation and the magnetic axis
were aligned. Here we present for the first time results including
the tilt of the heliocurrent sheet using a 3D MHD AMR simulation, with
BATS-R-US code. We discuss the effects on the global structure of the
Heliosheath, the flows, turbulence and magnetic field structure. We
assess the consequences for the observations measured by Voyager 1
since mid-2002.
Title: 3D Density Structure and LOS Observations of a Model CME
Authors: Manchester, W. B.; Lugaz, N.; Gombosi, T.; de Zeeuw, D.;
Sokolov, I.; Toth, G.
Bibcode: 2004AGUFMSH21D..04M
Altcode:
We present synthetic Thomson-scattered white-light images of a simulated
coronal mass ejection (CME). The simulations are based on a 3-D MHD
model of a CME propagating through a bimodal solar wind characteristic
of solar minimum. The CME is driven by a 3-D Gibson-Low flux rope
inserted in the helmet streamer of the steady-state corona. Synthetic
coronograph images are produced that follow the evolution of the CME
to 1 AU from several points of view. The white light images provide
a basis for comparison with wide angle coronographs, like those of
SMEI or STEREO. We find that a large amount of plasma is swept up
from the solar wind by the CME-driven shock wave, which dominates the
density structure far from the Sun. We also find that the shape of
this compressed plasma is highly distorted by the variation in speed
of the ambient solar wind. Comparisons of 2-D integrated images to the
3-D density structure show that the viewing angle severely effects the
line-of-sight appearance of the CME, as well as the estimated mass of
the CME from such 2D images.
Title: CME Shock and Sheath Structures Relevant to Particle
Acceleration
Authors: Manchester, W. B.; Kota, J.; Gombosi, T.; Igor, S. V.;
Roussev, I.; de Zeeuw, D.; Powell, K.; Toth, G.; Zurbuchen, T.
Bibcode: 2004AGUFMSH33A1188M
Altcode:
Most high-energy solar energetic particles (SEPs) are believed to be
accelerated at shock waves driven by coronal mass ejections (CMEs). The
acceleration process strongly depends on the shock geometry, and the
structure of the sheath that forms behind the shock. In an effort
to understand the structure and time evolution of such CME-driven
shocks and their relevance to particle acceleration, we investigate
the interaction of a fast CME with the ambient solar wind by means of
a three-dimensional (3-D) numerical ideal magnetohydrodynamics (MHD)
model. Our global steady-state coronal model possesses high-latitude
coronal holes and a helmet streamer structure with a current sheet
near the equator, reminiscent of near solar minimum conditions. Fast
and slow speed solar wind flow at high and low latitude respectively
and the Archimedian spiral geometry of the interplanetary magnetic
field is reproduced by solar rotation. Within this model system, we
drive a CME to erupt by the introduction of a Gibson-Low magnetic flux
rope that is embedded in the helmet streamer in an initial state of
force imbalance. The flux rope rapidly expands and is ejected from the
corona with maximum speeds in excess of 1000 km/s driving a fast-mode
shock from the inner corona to a distance of 1 astronomical unit
(AU). We find that the ambient solar wind structure strongly affects
the evolution of the CME-driven shocks causing deviations of the of
the fast-mode shocks from their expected global configuration. These
deflections lead to substantial compressions of the plasma and magnetic
field in their associated sheath region. The sudden post-shock increase
in magnetic field strength on low latitude field lines is found to be
effective for accelerating particles to the GeV range.
Title: Effects of a Tilted Heliospheric Current Sheet at the Edge
of the Solar System
Authors: Opher, M.; Liewer, P.; Manchester, W.; Gombosi, T.; DeZeeuw,
D.; Toth, G.
Bibcode: 2004AAS...205.4306O
Altcode: 2004BAAS...36.1412O
Recent observations indicate that Voyager 1, now beyond 90 AU, is in
a region unlike any encountered in it's 26 years of exploration. There
is currently a controversy as to whether Voyager 1 has already crossed
the Termination Shock, the first boundary of the Heliosphere (Krimigis
et al. 2003; McDonald et al. 2003, Burlaga et al. 2003). An important
aspect of this controversy is our poor understanding of this region. The
region between the Termination Shock and the Heliopause, the Helisheath,
is one of the most unknown regions theoretically. In the Heliosheath
magnetic effects are crucial, as the solar magnetic field is compressed
at the Termination Shock by the slowing flow. Therefore, to accurately
model the heliosheath the inclusion of the solar magnetic field is
crucial.Recently, our simulations showed that the Heliosheath presents
remarkable dynamics, with turbulent flows and a presence of a jet
flow at the current sheet that is unstable due to magnetohydrodynamic
instabilities (Opher et al. 2003; 2004). We showed that to capture
these phenomena, spatial numerical resolution is a crucial ingredient,
therefore requiring the use of an adaptive mesh refinement (AMR). These
previous works assumed that the solar rotation and the magnetic axis
were aligned. Here we present for the first time results including the
tilt of the heliocurrent sheet using a 3D MHD AMR simulation , with
BATS-R-US code. We discuss the effects on the global structure of the
Heliosheath, the flows, turbulence and magnetic field structure. We
access the consequences for the observations measured by Voyager 1
since mid-2002.
Title: Space Weather Modeling Framework: An Overview and Application
to the October 29, 2003 Storm
Authors: Ridley, A. J.; Gombosi, T.; Toth, G.; Sokolov, I. V.; de
Zeeuw, D.; Chesney, D.; Volberg, O.; Powell, K.; Stout, Q.; Hansen,
K.; Kane, K.
Bibcode: 2004AGUFMSA41B..04R
Altcode:
The University of Michigan's Space Weather Modeling Framework
(SMWF) aims at providing framework for physics based space weather
simulations, as well as for various space physics applications. The
SWMF combines numerical models of the Solar Corona, Inner Heliosphere,
Solar Energetic Particles, Global Magnetosphere, Inner Magnetosphere,
Radiation Belts, Ionosphere and Upper Atmosphere into a parallel, high
performance model. We present SWMF results from the October 29, 2003
storm, in which the global magnetosphere (BATSRUS), inner magnetosphere
(RCM), ionospheric electrodynamics, and upper atmospheric models (GITM)
are run together driven by data from the upstream ACE satellite. We
will present comparisons between the simulation results and data from
different magnetospheric satellites. We will further present model
comparisons between the global magnetosphere run with and without the
inner magnetosphere coupling.
Title: Space Environment Forecasting for the Exploration Initiative
with the Space Weather Modeling Framework
Authors: Gombosi, T. I.; Toth, G.; Sokolov, I. V.; de Zeeuw, D. L.;
Ridley, A. J.; Kane, K.; Volberg, O.; Hansen, K. C.; Manchester,
W. B.; Roussev, I. I.; Clauer, C. R.; Powell, K. G.; Stout, Q. F.
Bibcode: 2004AGUFMSH53C..05G
Altcode:
Robotic and human exploration of the solar system poses the challenge
to model and eventually forecast the plasma and energetic particle
environment throughout the inner heliosphere. This talk will describe
the recently developed Space Weather Modeling Framework (SWMF) that
combines numerical models of the solar corona (the global structure
is determined by synoptic magnetograms), magnetically driven solar
eruptions, the inner heliosphere out to Saturn's orbit, solar
energetic particles, the global magnetosphere, the particle drift
physics controlled inner magnetosphere, the radiation belts, the
ionospheric electrodynamics and the upper atmosphere and ionosphere
into a high performance coupled simulation. This powerful simulation
tool is presently capable of running faster than real-time from the
Sun to Earth and it will be further developed into a space weather
forecasting tool for the Exploration initiative. Particular attention
will be paid to predicting solar energetic particle spectra and fluxes
throughout the inner heliosphere. The SWMF is capable of simulating
the acceleration and transport of energetic particles together with a
self-consistent description of interplanetary transients that generate
and accelerate the SEP population.
Title: Three-dimensional MHD simulations of the magnetosphere
of Uranus
Authors: Tóth, GáBor; KováCs, DáNiel; Hansen, Kenneth C.; Gombosi,
Tamas I.
Bibcode: 2004JGRA..10911210T
Altcode:
We have successfully simulated the magnetosphere of Uranus for the
time period of the Voyager 2 flyby in January 1986. On the basis of the
Voyager measurements, a self-consistent numerical solution is obtained
with the parallel block adaptive three-dimensional (3-D) MHD code
BATS-R-US. The time-dependent simulation has been carried out with a
new explicit-implicit time integration scheme. By comparing corotating
steady state solutions and a fully time-dependent 3-D simulation
with the Voyager data, we show that the magnetosphere of Uranus at
the time of the flyby can be regarded as stationary relative to the
frame corotating with the planet. We obtained excellent agreement with
the observed magnetic field vector along the whole path of the flyby,
which includes the near-Uranus offset dipole field as well as several
current sheet crossings in the tail. The location of the bow shock and
the magnetopause also agree to high accuracy. We are confident that our
numerical solution is a good representation of the three-dimensional
magnetosphere of Uranus during the flyby. The numerical solution shows
a twisted magnetotail with field lines that are also stretched due to
the flow of plasma in the magnetotail.
Title: On the evolution of the solar wind between 1 and 5 AU at the
time of the Cassini Jupiter flyby: Multispacecraft observations of
interplanetary coronal mass ejections including the formation of a
merged interaction region
Authors: Hanlon, P. G.; Dougherty, M. K.; Forsyth, R. J.; Owens,
M. J.; Hansen, K. C.; Tóth, G.; Crary, F. J.; Young, D. T.
Bibcode: 2004JGRA..109.9S03H
Altcode:
The Cassini flyby of Jupiter occurred at a time near solar
maximum. Consequently, the pre-Jupiter data set reveals clear and
numerous transient perturbations to the Parker Spiral solar wind
structure. Limited plasma data are available at Cassini for this period
due to pointing restrictions imposed on the instrument. This renders
the identification of the nature of such structures ambiguous,
as determinations based on the magnetic field data alone are
unreliable. However, a fortuitous alignment of the planets during this
encounter allowed us to trace these structures back to those observed
previously by the Wind spacecraft near the Earth. Of the phenomena that
we are satisfactorily able to trace back to their manifestation at
1 AU, two are identified as being due to interplanetary coronal mass
ejections. One event at Cassini is shown to be a merged interaction
region, which is formed from the compression of a magnetic cloud by two
anomalously fast solar wind streams. The flux-rope structure associated
with this magnetic cloud is not as apparent at Cassini and has most
likely been compressed and deformed. Confirmation of the validity of the
ballistic projections used here is provided by results obtained from a
one-dimensional magnetohydrodynamic projection of solar wind parameters
measured upstream near the Earth. It is found that when the Earth and
Cassini are within a few tens of degrees in heliospheric longitude,
the results of this one-dimensional model predict the actual conditions
measured at 5 AU to an impressive degree. Finally, the validity of the
use of such one-dimensional projections in obtaining quasi-solar wind
parameters at the outer planets is discussed.
Title: Dual spacecraft observations of a compression event within
the Jovian magnetosphere: Signatures of externally triggered
supercorotation?
Authors: Hanlon, P. G.; Dougherty, M. K.; Krupp, N.; Hansen, K. C.;
Crary, F. J.; Young, D. T.; Tóth, G.
Bibcode: 2004JGRA..109.9S09H
Altcode:
By using Cassini as an upstream solar wind monitor, we are able to
infer increases in the interplanetary dynamic pressure upstream of
Jupiter as the spacecraft approached the planet. Observations are made
of the effect that these pressure increases had upon both the fields
and particles within the Jovian magnetosphere as measured by the
Galileo orbiter, which had subsequently reentered the magnetosphere
on the duskside. As the external pressure increased, so too did
the total field magnitude at Galileo (in particular the Bz and Bϕ
components). In addition, strongly leading field angles were observed
following the onset of the compression and strongly lagging fields
during reexpansion. These observations are consistent with the concept
of external control of the angular velocity of the magnetospheric plasma
due to conservation of angular momentum within the system. Heating of
the plasma can be seen as a pronounced increase in particle flux as
measured by the Energetic Particles Detector (EPD) instrument aboard
Galileo. Changes in plasma velocity inferred from energetic particle
anisotropies at Galileo appear to be consistent with the behavior of the
changing magnetic field angle. The overall behavior and response time of
the system appears to be consistent with recently published theoretical
modeling of the Jovian magnetosphere-ionosphere coupling system.
Title: Magnetic Effects Change Our View of the Heliosheath
Authors: Opher, M.; Liewer, P. C.; Velli, M.; Gombosi, T. I.;
Manchester, W.; Dezeeuw, D. L.; Toth, G.; Sokolov, I.
Bibcode: 2004AIPC..719..105O
Altcode: 2004astro.ph..6184O
There is currently a controversy as to whether Voyager 1 has
already crossed the termination Shock, the first boundary of the
heliosphere. The region between the termination shock and the
heliopause, the heliosheath, is one of the most unknown regions
theoretically. In the heliosheath magnetic effects are crucial,
as the solar magnetic field is compressed at the termination shock
by the slowing flow. Recently, our simulations showed that the
heliosheath presents remarkable dynamics, with turbulent flows and
the presence of a jet flow at the current sheet that is unstable due
to magnetohydrodynamic instabilities. In this paper we review these
recent results, and present an additional simulation with constant
neutral atom background. In this case the jet is still present but with
reduced intensity. Further study, e.g., including neutrals and the tilt
of the solar rotation from the magnetic axis, is required before we can
definitively address how the heliosheath behaves. Already we can say
that this region presents remarkable dynamics, with turbulent flows,
indicating that the heliosheath might be very different from what we
previously thought.
Title: Magnetic Effects at the Edge of the Solar System: MHD
Instabilities, the de Laval Nozzle Effect, and an Extended Jet
Authors: Opher, M.; Liewer, P. C.; Velli, M.; Bettarini, L.; Gombosi,
T. I.; Manchester, W.; DeZeeuw, D. L.; Toth, G.; Sokolov, I.
Bibcode: 2004ApJ...611..575O
Altcode: 2004astro.ph..6182O
To model the interaction between the solar wind and the interstellar
wind, magnetic fields must be included. Recently, Opher et al. found
that by including the solar magnetic field in a three-dimensional
high-resolution simulation using the University of Michigan BATS-R-US
code, a jet-sheet structure forms beyond the solar wind termination
shock. Here we present an even higher resolution three-dimensional case
in which the jet extends for 150 AU beyond the termination shock. We
discuss the formation of the jet due to a de Laval nozzle effect and
its subsequent large-period oscillation due to magnetohydrodynamic
(MHD) instabilities. To verify the source of the instability, we
also perform a simplified two-dimensional geometry MHD calculation
of a plane fluid jet embedded in a neutral sheet with the profiles
taken from our three-dimensional simulation. We find remarkable
agreement with the full three-dimensional evolution. We compare both
simulations and the temporal evolution of the jet, showing that the
sinuous mode is the dominant mode that develops into a velocity-shear
instability with a growth rate of 5×10-9s-1=0.027
yr-1. As a result, the outer edge of the heliosphere presents
remarkable dynamics, such as turbulent flows caused by the motion of
the jet. Further study, including neutrals and the tilt of the solar
rotation from the magnetic axis, is required before we can definitively
address how this outer boundary behaves. Already, however, we can say
that the magnetic field effects are a major player in this region,
changing our previous notion of how the solar system ends.
Title: Magnetic Effects and our Changing View of the Heliosheath
Authors: Liewer, P. C.; Opher, M.; Velli, M.; Gombosi, T. I.;
Manchester, W.; DeZeeuw, D. L.; Toth, G.; Sokolov, I.
Bibcode: 2004AAS...204.7208L
Altcode: 2004BAAS...36R.799L
The Sun traveling through the interstellar medium carves out a
bubble of solar wind called the Heliosphere. Recent observations
indicate that Voyager 1, now beyond 90 AU, is in a region unlike
any encountered in it's 26 years of exploration. There is currently
a controversy as to whether or not Voyager 1 has already crossed the
Termination Shock, the first boundary of the Heliosphere (Krimigis et
al. 2003; McDonald et al. 2003, Burlaga et al. 2003). The controversy
stems from different interpretations of observations from several
instruments. Contributing to this controversy is our poor understanding
of the outer heliosphere. The region between the Termination Shock and
the Heliopause, the Heliosheath, is one of the most unknown regions
theoretically. In the Heliosheath magnetic effects are crucial, as
the solar magnetic field is compressed at the Termination Shock by the
slowing flow. Recently, our simulations showed that the Heliosheath is
remarkably dynamic, with turbulent flows resulting from an unstable
jet flow at the current sheet (Opher et al. 2003; 2004). In this
talk we review these recent results, and present additional results
from simulations of the unstable jet with a constant neutral atom
background. Further studies which include additional effects such
as the tilt between the solar rotation axis and the magnetic axis,
are required before we can definitively address the structure and
dynamics of the outer heliosphere. Already we can say that this region
presents remarkable dynamics, with turbulent flows, indicating that
the Heliosheath might be very different from what we previously thought.
Title: Learning from our Sun: The Interaction of Stellar with
Interstellar Winds
Authors: Opher, M.; Liewer, P. C.; Velli, M.; Gombosi, T. I.;
Manchester, W.; DeZeeuw, D. L.; Toth, G.; Sokolov, I. V.
Bibcode: 2004AAS...204.0303O
Altcode: 2004BAAS...36..671O
Stars have winds which interact with the interstellar medium. The
intensity of the winds can be 10 million times greater than that of
the solar wind. The magnetic fields of these stars can be orders of
magnitude greater than that of the Sun. The rotation periods can be
appreciably different from that of the Sun. A detailed description of
the interaction of stellar winds with the interstellar winds has never
been made. The interaction between the Sun and Interstellar Medium
creates three major structures: Termination Shock, Heliopause and
Bow Shock. Recently, we found (Opher et al. 2003, 2004) that beyond
the region where the solar wind become subsonic, the Termination
Shock, a jet-sheet structure forms in the equatorial plane of the
Sun rotation axis. This structure forms due to the compression of the
solar magnetic field by the interstellar wind. The structure of the
jet-sheet resembles a the "brim of a baseball cap"- it extends beyond
the Termination Shock for 150 AU (almost touching the Bow Shock) and
has a width of 10AU. This result is due to a novel application of a
state-of-art 3D Magnetohydrodynamic (MHD) code with a highly refined
grid (0.75 AU 4 orders of magnitude smaller than the physical dimensions
of the system). The jet-sheet is unstable and oscillates up and down
due to a velocity shear instability. We showed that the sinuous mode
is the dominant mode that develops into a velocity-shear-instability
with a growth rate of 0.027 years-1. We are the first to
predict the formation of this structure at the equatorial region in
the interaction of magnetized rotating star and an external wind (for
a stellar rotation and magnetic field axis aligned). In this work,
we extend our previous solar studies and investigate the effect in
other solar-like stars. We present the dependence of the jet-sheet
structure and the velocity-shear instability on the star mass-loss rate
and magnetic field. We discuss further applications to other stellar
wind interactions and the observational limits for the detection of
this structure.
Title: Modeling the Carrington Event: sun-to-earth propagation of
a very fast CME
Authors: Manchester, W. B.; Ridley, A. J.; Gombosi, T.; de Zeeuw,
D.; Sokolov, I. V.; Toth, G.
Bibcode: 2004AGUSMSH43A..06M
Altcode:
We present a three-dimensional (3D) numerical ideal magnetohydrodynamics
(MHD) model describing the time-dependent propagation of a CME from the
solar corona to Earth in just 18 hours. The simulations are performed
using the BATS-R-US (Block Adaptive Tree Solarwind Roe Upwind Scheme)
code. We begin by developing a global steady-state model of the corona
that possesses high-latitude coronal holes and a helmet streamer
structure with a current sheet at the equator. The Archimedian spiral
topology of the interplanetary magnetic field is reproduced along with
fast and slow speed solar wind. Within this model system, we drive a
CME to erupt by the introduction of a Gibson-Low magnetic flux rope
that is embedded in the helmet streamer in an initial state of force
imbalance. The flux rope rapidly expands driving a very fast CME with
an initial speed of in excess of 4000 km/s and slowing to a speed of
nearly 2000 km/s at Earth. We find our model predicts a thin sheath
around the flux rope, passing the earth in only two hours. Shocked solar
wind temperatures at 1 AU are in excess of 10 million degrees. Physics
based AMR allows us to capture the structure of the CME focused on a
particular Sun-Earth line with high spatial resolution given to the
bow shock ahead of the flux rope.
Title: Parallel field line and stream line tracing algorithms for
space physics applications
Authors: Toth, G.; de Zeeuw, D.; Monostori, G.
Bibcode: 2004AGUSMSM54A..04T
Altcode:
Field line and stream line tracing is required in various space physics
applications, such as the coupling of the global magnetosphere and inner
magnetosphere models, the coupling of the solar energetic particle and
heliosphere models, or the modeling of comets, where the multispecies
chemical equations are solved along stream lines of a steady state
solution obtained with single fluid MHD model. Tracing a vector field is
an inherently serial process, which is difficult to parallelize. This
is especially true when the data corresponding to the vector field is
distributed over a large number of processors. We designed algorithms
for the various applications, which scale well to a large number of
processors. In the first algorithm the computational domain is divided
into blocks. Each block is on a single processor. The algorithm folows
the vector field inside the blocks, and calculates a mapping of the
block surfaces. The blocks communicate the values at the coinciding
surfaces, and the results are interpolated. Finally all block surfaces
are defined and values inside the blocks are obtained. In the second
algorithm all processors start integrating along the vector field inside
the accessible volume. When the field line leaves the local subdomain,
the position and other information is stored in a buffer. Periodically
the processors exchange the buffers, and continue integration of the
field lines until they reach a boundary. At that point the results
are sent back to the originating processor. Efficiency is achieved
by a careful phasing of computation and communication. In the third
algorithm the results of a steady state simulation are stored on a hard
drive. The vector field is contained in blocks. All processors read in
all the grid and vector field data and the stream lines are integrated
in parallel. If a stream line enters a block, which has already been
integrated, the results can be interpolated. By a clever ordering
of the blocks the execution speed can be increased dramatically. The
communication occurs via file in an asynchronous manner. Disk access
efficiency is improved by caching the data in memory.
Title: Modeling a space weather event from the Sun to the Earth:
CME generation and interplanetary propagation
Authors: Manchester, Ward B.; Gombosi, Tamas I.; Roussev, Ilia;
Ridley, Aaron; de Zeeuw, Darren L.; Sokolov, I. V.; Powell, Kenneth
G.; Tóth, GáBor
Bibcode: 2004JGRA..109.2107M
Altcode:
We present a three-dimensional (3-D) numerical ideal
magnetohydrodynamics (MHD) model describing the time-dependent expulsion
of a coronal mass ejection (CME) from the solar corona propagating
to 1 astronomical unit (AU). The simulations are performed using the
Block Adaptive Tree Solar-Wind Roe Upwind Scheme (BATS-R-US) code. We
begin by developing a global steady-state model of the corona that
possesses high-latitude coronal holes and a helmet streamer structure
with a current sheet at the equator. The Archimedean spiral topology
of the interplanetary magnetic field is reproduced along with fast
and slow speed solar wind. Within this model system, we drive a CME
to erupt by the introduction of a Gibson-Low magnetic flux rope that
is anchored at both ends in the photosphere and embedded in the helmet
streamer in an initial state of force imbalance. The flux rope rapidly
expands and is ejected from the corona with maximum speeds in excess
of 1000 km/s. Physics-based adaptive mesh refinement (AMR) allows us to
capture the structure of the CME focused on a particular Sun-Earth line
with high spatial resolution given to the bow shock ahead of the flux
rope as well as to the current sheet behind. The CME produces a large
magnetic cloud at 1 AU (>100 R⊙) in which Bz undergoes
a full rotation from north to south with an amplitude of 20 nT. In a
companion paper, we find that the CME is very effective in generating
strong geomagnetic activity at the Earth in two ways. First, through
the strong sustained southward Bz (lasting more than 10 hours) and,
second, by a pressure increase associated with the CME-driven shock
that compresses the magnetosphere.
Title: Three-dimensional MHD simulation of a flux rope driven CME
Authors: Manchester, Ward B.; Gombosi, Tamas I.; Roussev, Ilia; de
Zeeuw, Darren L.; Sokolov, I. V.; Powell, Kenneth G.; Tóth, GáBor;
Opher, Merav
Bibcode: 2004JGRA..109.1102M
Altcode:
We present a three-dimensional (3-D) numerical ideal
magnetohydrodynamics (MHD) model, describing the time-dependent
expulsion of plasma and magnetic flux from the solar corona that
resembles a coronal mass ejection (CME). We begin by developing a
global steady-state model of the corona and solar wind that gives
a reasonable description of the solar wind conditions near solar
minimum. The model magnetic field possesses high-latitude coronal
holes and closed field lines at low latitudes in the form of a
helmet streamer belt with a current sheet at the solar equator. We
further reproduce the fast and slow speed solar wind at high and low
latitudes, respectively. Within this steady-state heliospheric model,
conditions for a CME are created by superimposing the magnetic field
and plasma density of the 3-D Gibson-Low flux rope inside the coronal
streamer belt. The CME is launched by initial force imbalance within
the flux rope resulting in its rapid acceleration to a speed of over
1000 km/s and then decelerates, asymptotically approaching a final
speed near 600 km/s. The CME is characterized by the bulk expulsion of
∼1016 g of plasma from the corona with a maximum of ∼5 ×
1031 ergs of kinetic energy. This energy is derived from the
free magnetic energy associated with the cross-field currents, which is
released as the flux rope expands. The dynamics of the CME are followed
as it interacts with the bimodal solar wind. We also present synthetic
white-light coronagraph images of the model CME, which show a two-part
structure that can be compared with coronagraph observations of CMEs.
Title: First 3D MHD simulations of the inner magnetosphere with an
embedded drift physics model: The October 22-23, 1996 magnetic storm
Authors: de Zeeuw, D. L.; Gombosi, T. I.; Liemohn, M. W.; Ridley,
A. J.; Tóth, G.; Sazykin, S.; Wolf, R. A.
Bibcode: 2004cosp...35...75D
Altcode: 2004cosp.meet...75D
This paper describes the coupling of BATS-R-US, a magnetohydrodynamics
(MHD) code representing the Earth's global magnetosphere and its
coupling to the ionosphere and solar wind, and the Rice Convection Model
(RCM), which represents the inner magnetosphere and its coupling to the
ionosphere. The MHD code provides a time-evolving magnetic field model
for the RCM as well as continuously updated boundary conditions for
the electric potential and plasma. The RCM computes the distribution
functions of inner magnetospheric particles, including transport of
inner plasmasheet and ring-current particles by gradient/curvature
drifts; it thus calculates more accurate inner magnetospheric pressures,
which are frequently passed to the MHD model and used to nudge the
MHD values. Results are presented with the coupled code first for
the case of uniform ionospheric conductance with steady solar wind
and southward IMF. The results are compared with those from a run
of the MHD code alone. The coupled-code run shows significantly
higher inner magnetospheric particle pressures. It also exhibits
several well-established characteristics of inner magnetospheric
electrodynamics, including strong region-2 Birkeland currents and
partial shielding of the inner magnetosphere from the main force of
the convection electric field. A sudden northward turning of the IMF
causes the ring current to become more nearly symmetric. The inner
magnetosphere exhibits an overshielding (dusk-to-dawn) electric field
that begins about 10 minutes after the northward turning reaches
the magnetopause and lasts just over an hour. A second coupled-code
run was made for a moderate storm (Oct 22-23 1996). This event
is characterized by a long period of mildly (5-10nT) Southward IMF
followed by a Northward turning and roughly 600km/s velocities. While
the maximum field aligned current in the coupled code was often larger
than for MHD alone, the ionospheric cross polar cap potentials were
smaller due to current closure through the enhanced region 2 current
region. Many of the features described in the simpler first case above
are also evident here, including significant stretching of the tail.
Title: A virtual upstream solar wind monitor for the Cassini mission
at Saturn
Authors: Hansen, K. C.; Glocer, A.; Toth, G.; Gombosi, T. I.
Bibcode: 2004cosp...35.3063H
Altcode: 2004cosp.meet.3063H
In order to provide solar wind conditions upstream of Saturn, we
have developed a method to propagate the solar wind radially outward
from the Earth to Saturn using a 1D MHD code. We will present the
initial results and validation studies of our method. Having upstream
solar wind conditions will add significant value to the Cassini
measurements by allowing correlation studies between solar wind
and magnetospheric phenomena. In order to understand the response of
Saturn's magnetosphere to solar wind driving, we must have knowledge of
the solar wind conditions while at the same time making magnetospheric
measurements. These could be either remote measurements of the aurora or
in situ measurements in the magnetosphere. During Cassini's nominal four
year mission, a favorable alignment where Cassini can measure the solar
wind while at the same time imaging the aurora will occur only for a
few month period during the first orbit. In addition, it is obvious that
Cassini cannot make solar wind measurements and in situ magnetospheric
measurements simultaneously. In order to overcome these limitations and
to provide solar wind conditions more often during the Cassini mission,
we have developed a method to propagate solar wind conditions measured
at the Earth out to Saturn using a 1D MHD code. Because the method does
not take into account solar longitudinal variations, this method is
expected to work reasonably well only during the period where the Sun,
the Earth and Saturn are aligned (opposition). We have validated the
model and the time range around opposition of its applicability using
Cassini data from the Jupiter flyby (Dec. 2000) and from more recent
Cassini measurements (Jan. 2004). In addition, using ISEE3 (1979-1982)
data as input at 1AU, we have been able to model 10 opposition periods
and compare model results with Pioneer 11, Voyager 1 and Voyager
2 data. During this time, the three spacecraft were at a range of
radial distances between Jupiter and Saturn. We have shown the model to
work reasonably well during a period of roughly a month, centered at
opposition. We will discuss the strength and weaknesses of the model
during solar maximum and solar minimum conditions as well as ways to
extend the model after the launch of Stereo near the end of 2005.
Title: Eruption of a Buoyantly Emerging Magnetic Flux Rope
Authors: Manchester, W. B.; Fan, Y.; Gombosi, T.; de Zeeuw, D.;
Sokolov, I.; Toth, G.
Bibcode: 2003AGUFMSH22A0178M
Altcode:
We present a three-dimensional numerical ideal magnetohydrodynamic
simulation designed to model the emergence of magnetic flux passing
from below the photosphere into the corona. For the initial state, we
prescribe a plane parallel atmosphere that comprises the convection
zone, isothermal photosphere and chromosphere, and isothermal
corona. Embedded in this system is a isolated horizontal magnetic
flux rope located 10 photospheric pressure scale heights below the
photosphere. The flux rope is uniformly twisted with plasma temperature
inside the tube reduced to compensate for the magnetic pressure. Density
is reduced in the middle of the rope so that this section buoyantly
rises. The early evolution of precedes with the middle of the rope
rising to the photosphere and expanding into the corona. Just as it
seems the system might approach equilibrium, the upper part of the
flux rope begins to separate from the lower, mass ladened part. The
separation occurs by stretching of the field to form a current sheet
where reconnection severs the field lines to form a new system of closed
flux. This flux then erupts into the corona. Essential to the eruption
process are shearing motions driven by the Lorentz force which naturally
occurs as the rope expands in the pressure stratified atmosphere. The
shearing motions transport axial flux and energy to the expanding
portion of the magnetic field which contributes to the eruption. Once
the axial flux is largely transported from the submerged field, the
expansion of the magnetic field in the corona begins to decelerate.
Title: Dual Spacecraft Observations of a Compression Event Within
the Jovian Magnetosphere
Authors: Hanlon, P. G.; Dougherty, M. K.; Krupp, N.; Hansen, K. C.;
Crary, F. J.; Young, D. T.; Toth, G.
Bibcode: 2003AGUFMSM31C1125H
Altcode:
By using Cassini as an upstream solar wind monitor we were able to
infer increases in the interplanetary dynamic pressure upstream of
Jupiter as the spacecraft approached the planet. Observations are made
of the effect that these pressure increases had upon both the fields
and particles within the Jovian magnetosphere as measured by the
Galileo orbiter, which had subsequently re-entered the magnetosphere
on the dusk side. As the external pressure increased, so too did the
total field magnitude at Galileo (in particular the B-z and B-phi
components). In addition strongly leading field angles were observed
subsequent to the onset of the compression and strongly lagging fields
during re-expansion, this being consistent with the concept of external
control of the angular velocity of the magnetospheric plasma due to
conservation of angular momentum within the system. Heating of the
plasma can be seen clearly as a pronounced increase in particle flux
as measured by the EPD instrument aboard Galileo. Changes in plasma
velocity as inferred from energetic particle anisotropies at Galileo
appear to be well correlated with the behavior of the changing magnetic
field angle. The overall behavior and response time of the system
appears to be comparable to that predicted by recent theoretical
modeling of the Jovian magnetosphere-ionosphere coupling system.
Title: MHD Simulations of the Magnetosphere of Uranus: Successful
Comparison With Voyager 2
Authors: Tóth, G.; Tóth, G.; Kovacs, D.; Hansen, K. C.; Gombosi,
T. I.
Bibcode: 2003AGUFMSM31C1130T
Altcode:
We have successfully simulated the magnetosphere of Uranus for the time
period of the Voyager 2 flyby in January 1986. Based on the Voyager
measurements, a self-consistent numerical solution is obtained with the
parallel block adaptive 3D MHD code BATSRUS. By comparing corotating
steady state solutions and fully time dependent 3D simulations with the
Voyager data we show that the magnetosphere of Uranus at the time of the
flyby can be regarded as stationary relative to the frame corotating
with the planet. We obtained excellent agreement with the observed
magnetic field along the whole path of the flyby, which includes the
close by offset dipole field as well as several current sheet crossings
in the tail. The location of the bow shock and the magnetopause also
agree to high accuracy. We are confident that our numerical solution
is a good representation of the 3 dimensional magnetosphere of Uranus
during the flyby. The numerical solution shows a twisted magnetotail
and field lines are also stretched due to the flow of plasma in the
magnetotail. The time dependent simulations were carried out with an
explicit-implicit time integration scheme, while stationary solutions
were obtained with the local time stepping scheme. Even with these
advanced numerical schemes the time dependent simulation required a
full day on 30 CPU-s.
Title: Modeling the May 1, 1998 CME propagation from the Sun to
the Earth
Authors: Manchester, W. B.; Roussev, I.; Sokolov, I.; Ridley, A.;
Gombosi, T.; de Zeeuw, D.; Hansen, K.; Toth, G.
Bibcode: 2003AGUFMSM11D..01M
Altcode:
We present a three-dimensional numerical ideal magnetohydrodynamics
model describing the halo coronal mass ejection (CME) of May 1, 1998
propagating from the solar corona to 1 A.U. We begin by developing a
realistic global steady-state model of the corona and solar wind in
which the magnetic field is derived from synoptic magnetograms. The
Archimedian spiral topology of the interplanetary magnetic field is
reproduced along with fast and slow speed solar wind. Within this model
system, we drive the CME eruption by placing a Gibson-Low magnetic
flux rope in the helmet streamer of the pre-event active region. The
flux rope is in an initial state of force imbalance and expands at
such a rate as to approximate the observed speed of the May 1, 1998
CME. Physics based AMR of the BATS-R-US (Block Adaptive Tree Solarwind
Roe Upwind Scheme) code allows us to capture the structure of the
CME on a particular Sun-Earth line with high spatial resolution. In
particular, we highly resolve the the bow shock ahead of the flux
rope as well as to the current sheet behind. We compare our model
CME plasma parameters at 1 AU to observed values. In a companion
paper, we use the model CME-perturbed solar wind as input for an
Earth-Magnetospheric/Ionosphere/Thermosphere simulation and compare
the geoffectiveness of the Earth-system model to observations.
Title: Doing It In The SWMF Way: From Separate Space Physics
Simulation Programs To The Framework For Space Weather Simulation.
Authors: Volberg, O.; Toth, G.; Sokolov, I.; Ridley, A. J.; Gombosi,
T. I.; de Zeeuw, D. C.; Hansen, K. C.; Chesney, D. R.; Stout, Q. F.;
Powell, K. G.; Kane, K. J.; Oehmke, R. C.
Bibcode: 2003AGUFMSM22A0223V
Altcode:
The NASA-funded Space Weather Modeling Framework (SWMF) is developed
to provide "plug and play" type Sun-to-Earth simulation capabilities
serving the space physics modeling community. In its fully developed
form, the SWMF will comprise a series of interoperating models of
physics domains, ranging from the surface of the Sun to the upper
atmosphere of the Earth. In its current form the SWMF links together
five models: Global Magnetosphere, Inner Heliosphere, Ionosphere
Electrodynamics, Upper Atmosphere, and Inner Magnetosphere. The
framework permits to switch models of any type. The SWMF is a structured
collection of software building blocks that can be used or customized
to develop Sun-Earth system modeling components, and to assemble them
into application. The SWMF consist of utilities and data structures
for creating model components and coupling them. The SWMF contains
Control Model, which controls initialization and execution of the
components. It is responsible for component registration, processor
layout for each component and coupling schedules. A component is
created from the user-supplied physics code by adding a wrapper,
which provides the control functions and coupling interface to
perform the data exchange with other components. Both the wrapper and
coupling interface are constructed from the building blocks provided
by the framework itself. The current SWMF implementation is based on
the latest component technology and uses many important concepts of
Object-Oriented Programming emulated in Fortran 90. Currently it works
on Linux Beowulf clusters, SGI Origin 2000 and Compaq ES45 machines.
Title: Entry and Acceleration of Solar Wind Electrons in the Earth's
Outer Magnetosphere
Authors: Schriver, D.; Ashour-Abdalla, M.; Zelenyi, L.; Gombosi, T.;
Ridley, A.; de Zeeuw, D.; Toth, G.; Monostori, G.
Bibcode: 2003AGUFMSH42A0484S
Altcode:
It is well known that during the recovery of magnetic storms,
relativistic electron fluxes are usually enhanced over pre-storm values
in the inner magnetosphere near geosynchronous orbit. Although the
final acceleration of electrons to MeV energies most likely occurs
in the inner magnetosphere, observations indicate that an enhanced
flux of energized electrons (> 10 keV) forms in the so-called
seed region located at about 10 RE radially from the Earth in the
equatorial plane. To examine the acceleration of electrons from the
solar wind to the seed region, a study is being undertaken whereby
electron trajectories are followed starting upstream of the bow shock,
through the magnetopause and throughout the outer magnetosphere. The
entry locations of electrons will be examined along with acceleration
mechanisms that occur between the solar wind and seed region. The
electron particle trajectories are followed based on the guiding center
approximation in a global MHD model of the solar wind interaction with
the Earth's magnetosphere for various interplanetary magnetic field
(IMF) conditions.
Title: Magnetic Effects at the Edge of the Solar System: MHD
Instabilities, the de Laval nozzle effect and an Extended Jet
Authors: Opher, M.; Liewer, P.; Velli, M.; Bettarini, L.; Gombosi,
T. I.; Manchester, W.; Dezeeuw, D. L.; Toth, G.; Sokolov, I.
Bibcode: 2003AGUFMSH11C1114O
Altcode:
To model the interaction between the solar system and the interstellar
wind magnetic fields, ionized and neutral components besides cosmic
rays must be included. Recently (Opher et al. ApJL 2003) found, that
by including the solar magnetic field in an high resolution run with
the University of Michigan BATS-R-US code, a jet-sheet structure forms
beyond the Termination Shock. Here we discuss the formation of the jet
and its subsequent large period oscillation due to magnetohydrodynamic
instabilities. We perform in a simplified two dimensional geometry
resistive magnetohydrodynamic calculation of a plane fluid jet embedded
in a neutral sheet with the profiles taken from our simulation. We
find remarkable agreement with the full three dimensional evolution. We
present an even higher resolution three dimensional case where the jet
extends for 150AU beyond the Termination Shock. We compare the temporal
evolution of the jet showing that the sinuous mode is the dominant mode
that develops into a velocity-shear-instability with a growth rate of
5 x 10-9 sec-1=0.027 years-1. As a
result the outer edge of the heliosphere presents remarkable dynamics,
such as turbulence and flows caused by the motion of the jet. Further
study, e.g., including neutrals and the tilt of the solar rotation
from the magnetic axis, is required before we can definitively address
how this outer boundary behaves. Already, however, we can say that the
magnetic field effects are a major player in this region changing our
previous notion of how the solar system ends.
Title: A Three-dimensional Model of the Solar Wind Incorporating
Solar Magnetogram Observations
Authors: Roussev, I. I.; Gombosi, T. I.; Sokolov, I. V.; Velli, M.;
Manchester, W., IV; DeZeeuw, D. L.; Liewer, P.; Tóth, G.; Luhmann, J.
Bibcode: 2003ApJ...595L..57R
Altcode:
We present a new compressible MHD model for simulating the
three-dimensional structure of the solar wind under steady state
conditions. The initial potential magnetic field is reconstructed
throughout the computational volume using the source surface method, in
which the necessary boundary conditions for the field are provided by
solar magnetogram data. The solar wind in our simulations is powered
by the energy interchange between the plasma and large-scale MHD
turbulence, assuming that the additional energy is stored in the
``turbulent'' internal degrees of freedom. In order to reproduce
the observed bimodal structure of the solar wind, the thermodynamic
quantities for the initial state are varied with the heliographic
latitude and longitude depending on the strength of the radial
magnetic field.
Title: Parallel, Adaptive-Mesh-Refinement MHD for Global Space-Weather
Simulations
Authors: Powell, Kenneth G.; Gombosi, Tamas I.; de Zeeuw, Darren L.;
Ridley, Aaron J.; Sokolov, Igor V.; Stout, Quentin F.; Tóth, Gábor
Bibcode: 2003AIPC..679..807P
Altcode:
The first part of this paper reviews some issues representing
major computational challenges for global MHD models of the space
environment. These issues include mathematical formulation and
discretization of the governing equations that ensure the proper jump
conditions and propagation speeds, regions of relativistic Alfvén
speed, and controlling the divergence of the magnetic field. The
second part of the paper concentrates on modern solution methods that
have been developed by the aerodynamics, applied mathematics and DoE
communities. Such methods have recently begun to be implemented
in space-physics codes, which solve the governing equations
for a compressible magnetized plasma. These techniques include
high-resolution upwind schemes, block-based solution-adaptive grids
and domain decomposition for parallelization. We describe the space
physics MHD code developed at the University of Michigan, based on
the developments listed above.
Title: Probing the Edge of the Solar System: Formation of an Unstable
Jet-Sheet
Authors: Opher, Merav; Liewer, Paulett C.; Gombosi, Tamas I.;
Manchester, Ward; DeZeeuw, Darren L.; Sokolov, Igor; Toth, Gabor
Bibcode: 2003ApJ...591L..61O
Altcode: 2003astro.ph..5420O
The Voyager spacecraft is now approaching the edge of the solar
system. Near the boundary between the solar system and the interstellar
medium we find that an unstable ``jet-sheet'' forms. The jet-sheet
oscillates up and down because of a velocity shear instability. This
result is due to a novel application of a state-of-the-art
three-dimensional MHD code with a highly refined grid. We assume
as a first approximation that the solar magnetic and rotation axes
are aligned. The effect of a tilt of the magnetic axis with respect
to the rotation axis remains to be seen. We include in the model
self-consistently magnetic field effects in the interaction between
the solar and interstellar winds. Previous studies of this interaction
had poorer spatial resolution and did not include the solar magnetic
field. This instability can affect the entry of energetic particles
into the solar system and the intermixing of solar and interstellar
material. The same effect found here is predicted for the interaction
of rotating magnetized stars possessing supersonic winds and moving
with respect to the interstellar medium, such as O stars.
Title: Adaptive Mesh Refinement for conservative systems:
multi-dimensional efficiency evaluation
Authors: Keppens, R.; Nool, M.; Tóth, G.; Goedbloed, J. P.
Bibcode: 2003CoPhC.153..317K
Altcode: 2004astro.ph..3124K
Obtainable computational efficiency is evaluated when using an Adaptive
Mesh Refinement (AMR) strategy in time accurate simulations governed
by sets of conservation laws. For a variety of 1D, 2D, and 3D hydro-
and magnetohydrodynamic simulations, AMR is used in combination with
several shock-capturing, conservative discretization schemes. Solution
accuracy and execution times are compared with static grid simulations
at the corresponding high resolution and time spent on AMR overhead
is reported. Our examples reach corresponding efficiencies of 5
to 20 in multi-dimensional calculations and only 1.5-8% overhead is
observed. For AMR calculations of multi-dimensional magnetohydrodynamic
problems, several strategies for controlling the ∇.B=0 constraint
are examined. Three source term approaches suitable for cell-centered B
representations are shown to be effective. For 2D and 3D calculations
where a transition to a more globally turbulent state takes place, it
is advocated to use an approximate Riemann solver based discretization
at the highest allowed level(s), in combination with the robust
Total Variation Diminishing Lax-Friedrichs method on the coarser
levels. This level-dependent use of the spatial discretization acts
as a computationally efficient, hybrid scheme.
Title: Interpreting Coronagraph Data used Simulated White Light
Images and 3D MHD Models of CMEs
Authors: Liewer, P. C.; Opher, M.; Velli, M.; Manchester, W.; DeZeeuw,
D.; Gombose, T.; Roussev, I.; Sokolov, I.; Toth, G.; Powell, K.
Bibcode: 2003SPD....34.0511L
Altcode: 2003BAAS...35Q.816L
We use a 3D time-dependent MHD model of a CME to try to understand the
relationship between the CME structure and the bright features seen
in coronagraph images. Questions addressed include whether the bright
leading edge seen in LASCO coronagraph images of CMEs corresponds to
compressed coronal material or shocked solar wind. We will analyze
the evolution of the density and magnetic field as the CME propagates
for CMEs of various field strengths and initial speeds. Coronagraph
line-of-sight (LOS) images show 2D projections of the 3D density
structure of the CME. Synthetic coronagraph images will be computed
for the various CME cases to relate the structure to the LOS images. We
use the University of Michigan BATS-R-US time-dependent adaptive grid
MHD code to compute the CME evolution. The CME is created by inserting
a flux-rope CME into a steady-state solution for the corona. The flux
rope is anchored at both ends in the photosphere and embedded in a
helmet streamer; it is not initially in equilibrium. The subsequent
evolution of the flux rope - its expansion and propagation through the
corona to 1 AU - is computed self-consistently with the evolution of
the background corona and solar wind.
Title: The Formation of an Unstable Jet-Sheet at the Edge of the
Solar System
Authors: Opher, M.; Liewer, P.; Velli, M.; Gombosi, T.; Manchester,
W.; DeZeeuw, D.; Sokolov, I.; Toth, G.
Bibcode: 2003SPD....34.0604O
Altcode: 2003BAAS...35Q.818O
We find that the boundary between the solar system and the interstellar
medium an unstable jet-sheet forms. The jet is unstable and oscillates
up and down due to Kelvin-Helmholtz type instability. We use a
state-of-art 3D MHD code art with an adaptive grid mesh especially
designed to refine the region at the current sheet and in the region
between the termination shock and the heliopause. In the present study
we assume as a first approximation that the solar magnetic field and
rotation axis are aligned. We include in the model self-consistently
magnetic field effects in the interaction between the solar and
interstellar winds. Previous studies of this interaction had poorer
spatial resolution and did not include the solar magnetic field. We
present results from three different resolutions (ranging from 0.5AU to
6AU at the current sheet) and discuss the effect of resolution on the
characteristics of the jet such as strength and width. We show that in
order to resolve the jet, there is a need of a resolution higher than
3-4AU, the resolution used in previous studies. The neutrals interacting
with the plasma component by charge-exchange interactions can affect
the formation of the jet and we present results discussing their effect.
Title: HARM: A Numerical Scheme for General Relativistic
Magnetohydrodynamics
Authors: Gammie, Charles F.; McKinney, Jonathan C.; Tóth, Gábor
Bibcode: 2003ApJ...589..444G
Altcode: 2003astro.ph..1509G
We describe a conservative, shock-capturing scheme for evolving the
equations of general relativistic magnetohydrodynamics. The fluxes are
calculated using the Harten, Lax, & van Leer scheme. A variant of
constrained transport, proposed earlier by Tóth, is used to maintain
a divergence-free magnetic field. Only the covariant form of the metric
in a coordinate basis is required to specify the geometry. We describe
code performance on a full suite of test problems in both special
and general relativity. On smooth flows we show that it converges at
second order. We conclude by showing some results from the evolution
of a magnetized torus near a rotating black hole.
Title: Modeling a space weather event from the Sun to the Earth:
Magnetospheric Storm Results
Authors: Ridley, A.; de Zeeuw, D.; Gombosi, T.; Hansen, K.; Manchester,
W.; Sokolov, I.; Toth, G.
Bibcode: 2003EAEJA.....7651R
Altcode:
This papers shows magnetospheric results from one of the first ever
Sun to Earth MHD simulations. The University of Michigan's BATSRUS
MHD code was used to launch a Coronal Mass Ejection (CME) near
the solar surface and simulate the propagation of the CME through
interplanetary space. Because the CME was tracked using adaptive mesh
refinement, the resolution within the shock was 1/8 of a solar radius
(14 Earth radii, or R_e) at 1 AU. The CME had large field strengths
(27 nT), densities (35 cm-3), and velocities (540 km/s)
at 1 AU. Two dimensional results from the CME simulation at 1 AU were
used to drive the magnetospheric simulation. This allowed gradients and
correct propagation planes to be resolved at the upstream boundary. The
magnetospheric simulation was run using a maximum resolution of 1/8
R_e at the inner boundary, which was set to 2.5 R_e, and a minimum
resolution of 8 R_e near the side and outflow boundaries. The location
of the dayside magnetopause was tracked over time as well latitude of
the last closed field line. The strength of the auroral precipitation
and cross polar cap were also investigated. The magnetospheric and
ionospheric results from this simulation will be presented.
Title: On the evolution of the Solar Wind between 1 and 5 AU at
solar maximum and its effect upon Jovian auroral emission
Authors: Hanlon, P. G.; Dougherty, M. K.; Forsyth, R. J.; Hansen,
K. C.; Pryor, W.; Crary, F.; Tóth, G.
Bibcode: 2003EAEJA....12234H
Altcode:
The Cassini fly-by of Jupiter occurred at a time of solar maximum,
and as a consequence, the in-situ measurements taken in the Solar Wind
upstream of the planet, reveal numerous Interplanetary Coronal Mass
Ejections (ICMEs). A fortuitous alignment of the planets allowed us
to trace these events back to observations taken at the Earth. In
particular one event observed by Cassini is shown to be a Merged
Interaction Region (MIR), created from the coalescence of multiple
ICMEs between 1 and 5 AU. We examine results from a one dimensional
Magneto-hydrodynamic (MHD) simulation of the Solar Wind at Earth
propagated out to Cassini and compare with the in-situ data taken. It
is found that by integrating along the nominal Parker Spiral field we
can to some extent, correct for the changing angular offset between the
two points of observation by obtaining a fractional increase or decrease
in the propagation time of the events observed. The results of this MHD
simulation are then allowed to propagate further to the planet allowing
comparisons to be made between the state of the Solar Wind and remote
observations of the planetary aurorae that were taken simultaneously.
Title: Modeling a space weather event from the sun to earth: CME
generation and interplanetary propagation
Authors: Manchester, W.; de Zeeuw, D.; Gombosi, T.; Hansen, K.;
Ridley, A.; Roussev, I.; Sokolov, I.; Toth, G.
Bibcode: 2003EAEJA.....6645M
Altcode:
We present a three-dimensional (3D) numerical ideal magnetohydrodynamics
(MHD) model describing the time-dependent expulsion of a CME from the
solar corona propagating all the way to 1 A.U.. The simulations are
performed using the BATS-R-US (Block Adaptive Tree Solarwind Roe Upwind
Scheme) code. We begin by developing a global steady-state model of the
corona that possesses high-latitude coronal holes and a helmet streamer
structure with a current sheet at the equator. The Archimedian spiral
topology of the interplanetary magnetic field is reproduced along with
fast and slow speed solar wind. Within this model system, we drive a
CME to erupt by the introduction of a Gibson-Low magnetic flux rope that
is anchored at both ends in the photosphere and embedded in the helmet
streamer in an initial state of force imbalance. The flux rope rapidly
expands and is ejected from the corona with maximum speeds in excess
of 1500 km/sec. Physics based AMR allows us to capture the structure
of the CME focused on a particular Sun-Earth line with high spatial
resolution given to the bow shock ahead of the flux rope as well as
to the current sheet behind. We find our model CME plasma parameters
at 1 AU to be geoeffective and use this as solar wind input for an
Earth-Magnetospheric simulation in a companion paper.
Title: Global flow patterns and ionospheric convection in Jupiter's
magnetosphere
Authors: Hansen, K. C.; de Zeeuw, D. L.; Gombosi, T. I.; Ridley,
A. J.; Toth, G.; Sokolov, I.
Bibcode: 2003EAEJA.....6812H
Altcode:
The size and configuration of Jupiter's magnetosphere is controlled
by the ambient solar wind conditions, Jupiter's strong rotation
and intrinsic magnetic field and the plasma sources internal to the
magnetosphere. We will examine the relative importance of each of these
factors using our 3D global magnetohydrodynamic (MHD) model of the
Jovian magnetosphere. This model uses adaptive mesh refinement (AMR)
to model the global Jovian system, including the mass loading region
near Io's orbit. The inner boundary of the MHD model, at 3 R_J, is
coupled to a height integrated ionospheric electric potential model. We
will present results of the coupled model and show similarities
and differences to other planetary magnetospheres. We will show
that Jupiter's magnetosphere without mass loading and rotation is
Earth-like in all but size. Adding rotation determines, to a large
extent, the flow pattern in the magnetosphere. The addition of mass
loading, although extremely important, does not change the character
or topology of the magnetospheric convection but instead modifies
the locations of magnetospheric features such as the bow shock, the
magnetopause and the location of reconnection sites. In addition, we
will show how features like the magnetospheric "wings" [Song, ASR, 2001]
at the Earth are manifest and modified in the magnetosphere of Jupiter.
Title: 3D MHD description of the region beyond the termination shock:
The behaviour of the Current Sheet
Authors: Opher, M.; Liewer, P.; Gombosi, T.; Manchester, W.; Dezeeuw,
D. L.; Powell, K.; Sokolov, I.; Toth, G.; Velli, M.
Bibcode: 2002AGUFMSH21A0485O
Altcode:
A fully self consistent MHD study of the heliosheath region is carried
out, using BATSRUS, a three dimensional time dependent adaptive grid
magnetohydrodynamic (MHD) model. The heliosheath, located between
the termination shock and the heliopause, has not been studied in
detail. At the termination shock the solar wind passes from a supersonic
to a subsonic regime decelerating until it reaches the heliopause
where it is diverted to the heliotail. This region is intersected
in the equatorial plane (assuming a no-tilt for the dipole field)
by a current sheet as the solar magnetic field changes polarity. One
of the major questions is whether the current sheet remains at the
equatorial plane. The magnetic field of the solar wind is included. In
order to isolate the effects at this region we assumed no magnetic
field in the interstellar medium. We observe a much faster flow of the
current sheet, where the compressed azimuthal magnetic field is absent,
leading to large velocity shear. With BATSRUS, we were able to obtain
high resolution needed to analyze the behavior of this complicated
regime, in particular the stability of the current sheet. We report
the results and comment on the major processes responsible.
Title: 3D MHD Simulation of CME Propagation from Solar Corona to 1 AU
Authors: Manchester, W. B.; Roussev, I.; Opher, M.; Gombosi, T.;
Dezeeuw, D.; Toth, G.; Sokolov, I.; Powell, K.
Bibcode: 2002AGUFMSH21A0501M
Altcode:
We present a three-dimensional (3D) numerical ideal magnetohydrodynamics
(MHD) model describing the time-dependent expulsion of a CME from
the solar corona propagating all the way to 1 A.U.. The simulations
are performed using the BATS-R-US (Block Adaptive Tree Solarwind Roe
Upwind Scheme) code. We begin by developing a global steady-state
model of the corona that possesses high-latitude coronal holes and
a helmet streamer structure with a current sheet at the equator. The
Archimedian spiral topology of the interplanetary magnetic field is
reproduced along with fast and slow speed solar wind at high and
low latitudes respectively. Within this model system, we drive a
CME to erupt by the introduction of a Gibson-Low magnetic flux rope
that is anchored at both ends in the photosphere and embedded in the
helmet streamer in an initial state of force imbalance. The flux rope
then rapidly accelerates to speeds in excess of 1500 km/sec driving
a strong MHD shock as part of the CME. We find that both the shock
front and the flux rope are strongly effected by bi-modal solar wind
as the CME travels to 1 AU. Physics based AMR allows us to capture
the complexity of the CME development and propagation focused on a
particular Sun-Earth line. The applied numerical algorithm is designed
to use optimal computational resources for the sake of tracing CMEs
with very high spatial resolution all the way from Sun to Earth. We
compare the model CME plasma parameters at 1 AU to observations and
find the event to be geoeffective.
Title: University of Michigan MHD results of the Geospace Global
Circulation Model metrics challenge
Authors: Ridley, A. J.; Hansen, K. C.; Tóth, G.; de Zeeuw, D. L.;
Gombosi, T. I.; Powell, K. G.
Bibcode: 2002JGRA..107.1290R
Altcode:
We present University of Michigan MHD code results of the "metrics
challenge." We have simulated the magnetospheric and ionospheric
configuration during the 16-17 April 1999 CME, the 10-11 December 1998
time period, and the 5-6 November 1998 time period. The simulation
results were compared to the DMSP cross-track velocities, and the RMS
differences were examined. We have found that the code reproduces the
DMSP data quite accurately except for the sharpness of the gradients
and the transients which were observed. The cross polar cap potential
was well matched, as was the location of the convection reversal
boundary. In addition, the code reproduced features of statistical
models of the ionospheric electric potential.
Title: BAIKAL experiment: status report
Authors: Osipova, E.; Pavlov, A.; Pańkov, L.; Panfilov, A.;
Pliskovsky, E.; Klimov, A.; Pokhil, P.; Polecshuk, V.; Popova, E.;
Prosin, V.; Rosanov, M.; Rubtzov, V.; Semeney, Y.; Spiering, C.;
Streicher, O.; Tarashanky, B.; Thon, T.; Toth, G.; Vasiliev, R.;
Wischnewski, R.; Yashin, I.; Zhukov, V.
Bibcode: 2002NuPhS.110..504O
Altcode: 2001astro.ph.12446D
We review the present status of the Baikal Neutrino Project and present
the results obtained with the deep underwater neutrino telescope NT-200.
Title: Towards an Operational Sun-to-Earth Model for Space Weather
Forecasting
Authors: Gombosi, T. I.; Clauer, C. R.; De Zeeuw, D. L.; Hansen,
K. C.; Manchester, W. B.; Powell, K. G.; Ridley, A. J.; Roussev, I.;
Sokolov, I. V.; Toth, G.; Wolf, R. A.; Sazykin, S.; Holzer, T. E.;
Low, B. C.; Richmond, A. D.; Roble, R. G.
Bibcode: 2002AGUSMSH51B..06G
Altcode:
We are presently developing a physics based, modular, large-scale
model of the solar-terrestrial environment simulating space weather
phenomena and providing a framework to test theories and explore the
possibility of operational use in space weather forecasting. This talk
will describe the main components of the model (a global MHD code,
an upper atmosphere and ionosphere model, and the inner magnetosphere
drift physics model). We will also discuss the testing and transitioning
the model through CCMC to operational use by NOAA SEC and the Air
Force. Particular attention will be paid to the need of validation
and metrics studies.
Title: Studying the Complexity in Dynamics and Magnetic Topology of
CME with 3D MHD Simulations Involving Dynamic AMR
Authors: Roussev, I. I.; Manchester, W. B.; Gombosi, T. I.; De Zeeuw,
D. L.; Sokolov, I. V.; Toth, G.
Bibcode: 2002AGUSMSH21A..01R
Altcode:
It is of fundamental importance in solar, heliospheric,
and magnetospheric physics to explore the high degree of
variability and complex internal magnetic and plasma structure of
CMEs. Three-dimensional (3D) magnetohydrodynamic (MHD) simulations
provide excellent grounds for studying the complexity in dynamics of
this and other solar phenomena. We present some results on state-of-art
numerical experiments of CME propagation, including dynamic Adaptive
Mesh Refinement (AMR). All computations presented here are carried out
using the BATS-R-US (Block Adaptive Tree Solarwind Roe Upwind Scheme)
code and involve 3D MHD. The CME is initiated through an eruption of
twisted flux rope in the solar corona. The MHD shock created ahead of
the CME is essential in determining geoeffective events. The physics
based AMR allows to reveal the complexity of the CME development and
propagation on the particular ray Sun-Earth. The applied numerical
algorithm is designed to use optimal computational resources for the
sake of tracing CMEs with very high spatial resolution all the way
from Sun to Earth, and beyond. We further discuss the differences in
using various criteria for mesh refinement on the overall physical
picture of the CME dynamics.
Title: 3D MHD Simulations of Flux Rope Driven CMEs
Authors: Manchester, W. B.; Roussev, I.; Opher, M.; Gombosi, T.;
DeZeeuw, D.; Toth, G.; Sokolov, I.; Powell, K.
Bibcode: 2002AGUSMSH22D..03M
Altcode:
We present a three-dimensional (3D) numerical ideal magnetohydrodynamics
(MHD) model describing the time-dependent expulsion of a CME from
the solar corona propagating all the way to 1 A.U.. The simulations
are performed using the BATS-R-US (Block Adaptive Tree Solarwind Roe
Upwind Scheme) code. We begin by developing a global steady-state
model of the corona that possesses high-latitude coronal holes and
a helmet streamer structure with a current sheet at the equator. The
Archimedian spiral topology of the interplanetary magnetic field is
reproduced along with fast and slow speed solar wind at high and low
latitudes respectively. Within this model system,we drive a CME to erupt
by the introduction of a twisted magnetic flux rope that is anchored at
both ends in the photosphere and embedded in the helmet streamer. The
flux rope configuration that we employ was first developed by Gibson
and Low as part of a 3D self-similar model of a CME. In this case,
the flux rope has the form of a spherical ball of twisted magnetic
field distorted to a tear shape by a stretching transformation. The
stretch transformation produces an outward radially directed Lorentz
force within the flux rope that rapidly accelerates the leading edge of
the rope to speeds of 1800 km/sec, driving a strong shock as part of
the CME. We follow the evolution of the CME from the low corona as it
makes its way through the heliosphere. We explore the dynamics of the
expanding flux rope as it interacts with the rotating, bi-modal solar
wind to determine significant MHD effects. Finally we present synthetic
white-light coronagraph images of the model CME which show a three-part
structure that can be compared with observations of CME structure.
Title: 3D adaptive grid MHD simulations of the global heliosphere
with self- consistent fluid neutral hydrogen
Authors: Opher, M.; Liewer, P.; Gombosi, T.; Manchester, W.; Dezeeuw,
D.; Powell, K.; Sokolov, I.; Toth, G.
Bibcode: 2002cosp...34E.835O
Altcode: 2002cosp.meetE.835O
A three dimensional adaptive grid magnetohydrodynamic (MHD) model of
the interaction of the solar wind with the local interstellar medium
is presented. The code used is the BATS-R-US time-dependent adaptive
grid three-dimensional magnetohydrodynamic, which is similar to the
code used by Linde et al. JGR, 103, 1889 (1998). The magnetic field
of both the solar wind and the interstellar medium are included. The
latitute dependence of the solar wind is also taken into account. The
neutral atoms are included self-consistently as a fluid, without
assuming constant the density, velocity or temperature as previous
3D MHD studies. The location of the termination shock and heliopause
in the steady state solution for different values and directions of
interstellar magnetic field are presented and compared with previous
results. We also present results where we isolated the effects of
neutrals and magnetic field showing their relative importance, in
particular the heliopause.
Title: Simulations of erupting flux rope driven CMEs
Authors: Manchester, W.; Gombosi, T.; de Zeeuw, D.; Powell, K.;
Roussev, I.; Sokolov, I.; Toth, G.
Bibcode: 2002cosp...34E2635M
Altcode: 2002cosp.meetE2635M
We present a three-dimensional (3D) numerical ideal magnetohydrodynamics
(MHD) model describing the time-dependent expulsion of a CME from
the solar corona. We begin by developing a global steady-state model
of the corona that possesses highlatitude coronal holes and a helmet
streamer structure with a current sheet at the equator. The Archimedian
spiral topology of the interplanetary magnetic field is reproduced
along with fast and slow speed solar wind at high and low latitudes
respectively. Within this model system, we drive a CME to erupt by
the introduction of a twisted magnetic flux rope that is anchored at
both ends in the photosphere and embedded in the helmet streamer. The
flux rope configuration that we employ was first developed by Gibson
and Low as part of a 3D self-similar model of a CME. In this case,
the flux rope has the form of a spherical ball of twisted magnetic
field distorted to a tear shape by a stretching transformation. The
stretch transformation produces an outward radially directed Lorentz
force within the flux rope that rapidly accelerates the leading edge
of the rope to speeds of 1200 km/sec, driving strong shock as part
of the CME. We follow the evolution of the CME from the low corona as
it makes its way through the heliosphere. We explore the dynamics of
the expanding flux rope as it interacts with the rotating, bi-modal
solar wind to determine significant MHD effects. Finally we present
synthetic white-light coronagraphs images of the model CME to determine
the degree to which they match observations of CME structure.
Title: Development of an Integrated Predictive MHD Space Weather
Model from the Solar Surface to the Earth's Upper Atmosphere
Authors: Clauer, C. R.; Gombosi, T. I.; Powell, K. G.; Stout, Q. F.;
Toth, G.; Dezeeuw, D.; Ridley, A. J.; Wolf, R. A.; Roble, R. G.;
Holzer, T. E.
Bibcode: 2002swsm.conf..149C
Altcode:
No abstract at ADS
Title: Using dynamic AMR to simulate geoeffective interplanetary
transients
Authors: Roussev, I.; Manchester, W.; Gombosi, T.; de Zeeuw, D.;
Sokolov, I.; Toth, G.
Bibcode: 2002cosp...34E.555R
Altcode: 2002cosp.meetE.555R
It is of fundamental importance for solar, heliospheric, and
magnetospheric physics to explore the complex dynamic evolution and
geoeffectiveness of coronal transients, commonly known as CMEs, all the
way from their origin at the Sun, through the interplanetary space, to
Earth. In this light, three-dimensional (3D) magnetohydrodynamic (MHD)
simulations provide excellent grounds for studying the complexity in
dynamics of this and other solar phenomena. We present some results
on state-of-art numerical experiments of CME propagation, including
dynamic Adaptive Mesh Refinement (AMR). All computations presented here
are carried out using the BATS-R-US (Block Adaptive Tree Solarwind
Roe Upwind Scheme) code and involve 3D time-dependent MHD. The
CME is initiated through an eruption of double-twisted magnetic
flux rope originating from the solar corona. The MHD shock formed
ahead of the solar transient is essential in determining geoeffective
events. The physics based AMR allows us to examine in great detail the
complexity of the CME development and propagation on the particular
ray Sun-Earth. The applied numerical algorithm is designed to use
optimal computational resources for the sake of tracing CMEs with very
high spatial resolution all the way from Sun to Earth, and beyond. We
further discuss the differences in using various criteria for mesh
refinement on the overall physical picture of the CME dynamics.
Title: Pulsar wind nebulae in supernova remnants. Spherically
symmetric hydrodynamical simulations
Authors: van der Swaluw, E.; Achterberg, A.; Gallant, Y. A.; Tóth, G.
Bibcode: 2001A&A...380..309V
Altcode:
A spherically symmetric model is presented for the interaction of
a pulsar wind with the associated supernova remnant. This results
in a pulsar wind nebula whose evolution is coupled to the evolution
of the surrounding supernova remnant. This evolution can be divided
in three stages. The first stage is characterised by a supersonic
expansion of the pulsar wind nebula into the freely expanding ejecta
of the progenitor star. In the next stage the pulsar wind nebula is
not steady; the pulsar wind nebula oscillates between contraction and
expansion due to interaction with the reverse shock of the supernova
remnant: reverberations which propagate forward and backward in
the remnant. After the reverberations of the reverse shock have
almost completely vanished and the supernova remnant has relaxed to
a Sedov solution, the expansion of the pulsar wind nebula proceeds
subsonically. In this paper we present results from hydrodynamical
simulations of a pulsar wind nebula through all these stages in
its evolution. The simulations were carried out with the Versatile
Advection Code.
Title: 3D Global MHD Simulations of Flux-Rope-Driven CMEs
Authors: Gombosi, T. I.; Manchester, W. B.; De Zeeuw, D. L.; Toth,
G.; Powell, K. G.; Sokolov, I.
Bibcode: 2001AGUFMSH12B0759G
Altcode:
We present a three-dimensional (3D) numerical ideal magnetohydrodynamics
(MHD) model describing the time-dependent expulsion of a CME form the
solar corona. We begin by developing a 3D MHD model of a steady-state
helmet streamer enveloped by a solar wind. We then drive the helmet
streamer to erupt in a CME by introduction of a twisted magnetic flux
rope that is anchored at both ends in the photosphere and embedded
in the helmet streamer. We follow the evolution of the CME from the
low corona as it makes its way through heliosphere. We explore the
dynamics of the expanding flux rope as it interacts with the rotating,
bi-modal solar wind to determine significant MHD effects such as
shock formation. Finally we present synthetic white-light coronagraphs
images of the model CME to determine the degree to which they match
observations of CME structure.
Title: Inner Magnetosphere Simulations - Coupling the Michigan MHD
Model with the Rice Convection Model.
Authors: De Zeeuw, D.; Sazykin, S.; Ridley, A.; Toth, G.; Gombosi,
T.; Powell, K.; Wolf, D.
Bibcode: 2001AGUFMSM42A0830D
Altcode:
The adaptive-grid Michigan MHD model (BATSRUS) has been coupled to a
new high performance Rice Convection Model (RCM). This fully coupled
code allows us to self-consistently simulate the physics in the
inner magnetosphere, including Region 1 and Region 2 currents. We will
describe the two models and how they are coupled, report on the results
of a synthetic event with the coupled code and show a comparison with
and without coupling.
Title: 3D MHD Simulation of a Coronal Arcade Eruption by Self-Induced
Shearing
Authors: Manchester, W. B.; Toth, G.; De Zeeuw, D. L.; Gombosi, T. I.;
Powell, K. G.
Bibcode: 2001AGUFMSH12B0758M
Altcode:
We present the results of a three-dimensional time-dependent
magnetohydrodynamic(MHD) simulation of the nonlinear development of
instabilities of a magnetically-sheared arcade and show how it relates
to coronal mass ejections (CMEs). To model the arcade eruption, we
capitalize on a family of analytical solutions for initial states, which
describe magnetic arcades in uniform gravity that are characterized
by magnetic shear. In our simulations we find that such an arcade is
unstable when subjected to small velocity perturbations and responds
by slowly rising and expanding. Most significantly, we find shearing
motions naturally arise in conjunction with the instability. This
field line shearing is in response to the Lorentz, force which drives
large amplitude Alfvén waves, which transport magnetic shear from the
lower to the upper extremities of the arcade. The self-induced shear
Alfvén waves, coupled with magnetic buoyancy, provide a powerful
feedback mechanism that drives the arcades to a loss of equilibrium
and eruption following a long period of expansion. The simulation
of the arcade eruption is significant with regard to CME initiation
for two major reasons. First, the arcade eruption is the result of
undriven MHD instabilities and second, magnetic field line shearing
is an intrinsic aspect of the instability that occurs spontaneously.
Title: Combined Explicit-Implicit Techniques for Faster than Real-Time
Space Weather Simulations
Authors: Toth, G.; Powell, K. G.; De Zeeuw, D. L.; Gombosi, T. I.
Bibcode: 2001AGUSM..SM52A03T
Altcode:
The Alfvén speed can approach the speed of light near the Earth. This
poses a severe problem for numerical modeling of the magnetosphere,
since the time steps of an explicit time integration scheme are
limited by the CFL numerical stability condition: the waves must not
propagate more than one cell size in one time step. In a well resolved
simulation, the cell size may be as small as several 100 km-s, which
limits the time step to be less than 0.01 or even 0.001 seconds. On
the other hand, typical time scales of the magnetosphere are on the
order of minutes. This discrepancy calls for the use of implicit
time stepping techniques, which are not limited by the CFL stability
condition. We are reporting our preliminary results with a newly
implemented Newton-Krylov-Schwarz type implicit time stepping scheme
in our block-adaptive parallel 3D MHD code. The linear problems arising
from the Newton scheme are solved with a parallel Krylov subspace type
iterative scheme using a Schwarz type preconditioner. We also explore
the possibility of combining the implicit and explicit time stepping
schemes: the expensive but stable implicit scheme is used near the
Earth where the wave speeds are high, while the inexpensive explicit
scheme is employed where the stability condition on the time step is
not restrictive.
Title: Results of the Michigan MHD Metrics Challenge
Authors: Ridley, A. J.; Gombosi, T.; De Zeeuw, D.; Toth, G.; Powell, K.
Bibcode: 2001AGUSM..SM32A06R
Altcode:
We present University of Michigan MHD code results of the so-called
"Metrics Challenge". We have simulated the magnetospheric and
ionospheric configuration during the CME of April 16 - 17, 1999. The
simulation results were compared with DMSP cross track velocities
and the RMS differences were examined. We have found that the code
reproduces the DMSP data accurately except for the sharpness of the
gadients and the transients which were observed. The cross polar cap
potential was well matched, as was the location of the convection
reversal boundary.
Title: Coupled MHD-Inner Magnetosphere Simulations of Geomagnetic
Storms
Authors: De Zeeuw, D.; Sazykin, S.; Ridley, A.; Toth, G.; Gombosi,
T.; Clauer, B.; Powell, K.; Wolf, D.; Spiro, B.
Bibcode: 2001AGUSM..SM32A02D
Altcode:
The adaptive-grid Michigan MHD model (BATSRUS) has been coupled to a
new high Rice Convection Model (RCM). This fully coupled code gives
the possibility to realistically undertake global MHD simulations of
a magnetic storm and the computation of both Region 1 and Region 2
currents. We will review details of the two models and their coupling,
and report on the results of our first storm time simulation with the
coupled code and show a comparison with observations. We will discuss
the global observations provided by arrays of magnetometers which
measure the temporal and spatial development of the ring current as
well as high latitude global electrodynamic parameters derived from
the AMIE and LiMIE data inversion techniques.
Title: Adaptive mesh refinement MHD for global simulations
Authors: Gombosi, T. I.; Tóth, G.; de Zeeuw, D. L.; Powell, K. G.;
Stout, Q. F.
Bibcode: 2001sps..proc...88G
Altcode:
Techniques that have become common in aerodynamics codes have
recently begun to be implemented in space-physic codes, which solve
the governing equations for a compressible plasma. These techniques
include high-resolution upwind schemes, block-based solution-adaptive
grids and domain decomposition for parallelization. While some
of these techniques carry over relatively straightforwardly from
aerodynamics to space physics, space physics simulations pose some new
challenges. This paper gives a brief review of the state-of-the-art in
modern space-physics codes, including a validation study of several of
the techniques in common use. A remaining challenge is that of flows
that include regions in which relativistic effects are important;
some background and preliminary results for these problems are
given. 1 Governing equations The governing equations for an ideal,
non-relativistic, compressible plasma may be written in a number of
different forms. In primitive variables, the governing equations,
which represent a combination of the Euler equations of gasdynamics
and the Maxwell equations of electromagnetics, may be written as:
∂ρ ∂t + u · ρ + ρ · u = 0 ρ ∂u ∂t + ρu · u + p -
j × B = 0 ∂B ∂t + × E = 0 ∂p ∂t + u · p + γp · u = 0
(1) where the current density j and the electric field vector E are
related to the magnetic field B by Amp`ere's law and Ohm's
Title: Storage of a Strong Magnetic Field Below the Solar Convection
Zone (CD-ROM Directory: contribs/rempel)
Authors: Rempel, M.; Schüssler, M.; Moreno-Insertis, F.; Tóth, G.
Bibcode: 2001ASPC..223..738R
Altcode: 2001csss...11..738R
No abstract at ADS
Title: Pulsar wind nebulae in supernova remnants
Authors: van der Swaluw, E.; Achterberg, A.; Gallant, Y. A.; Tóth, G.
Bibcode: 2000astro.ph.12440V
Altcode:
A spherically symmetric model is presented for the interaction of
a pulsar wind with the associated supernova remnant. This results
in a pulsar wind nebula whose evolution is coupled to the evolution
of the surrounding supernova remnant. This evolution can be divided
in three stages. The first stage is characterised by a supersonic
expansion of the pulsar wind nebula into the freely expanding ejecta
of the progenitor star. In the next stage the pulsar wind nebula is
not steady; the pulsar wind nebula oscillates between contraction and
expansion due to interaction with the reverse shock of the supernova
remnant: reverberations which propagate forward and backward in
the remnant. After the reverberations of the reverse shock have
almost completely vanished and the supernova remnant has relaxed to
a Sedov solution, the expansion of the pulsar wind nebula proceeds
subsonically. In this paper we present results from hydrodynamical
simulations of a pulsar wind nebula through all these stages in
its evolution. The simulations were carried out with the Versatile
Advection Code.
Title: Storage of magnetic flux at the bottom of the solar convection
zone
Authors: Rempel, M.; Schüssler, M.; Tóth, G.
Bibcode: 2000A&A...363..789R
Altcode:
We consider the mechanical equilibrium of a layer of axisymmetric
toroidal magnetic field located in a subadiabatically stratified
region near the bottom of the solar convection zone, with particular
emphasis on the effects of spherical geometry. We determine equilibrium
configurations and simulate numerically how these are reached from a
non-equilibrium initial situation. While a subadiabatic stratification
is essential for suppressing the buoyancy force, the latitudinal
component of the magnetic curvature force is balanced by a latitudinal
pressure gradient (in the case of a large subadiabaticity, as in the
radiative interior) or by the Coriolis force due to a toroidal flow
along the field lines (in the case of small subadiabaticity, as in
a layer of convective overshoot). The latter case is found relevant
for storing the magnetic flux generated by the solar dynamo. The
corresponding equilibrium properties are similar to those of isolated
magnetic flux tubes. Significant variations of the differential rotation
at the bottom of the convection zone in the course of the solar cycle
are expected for such a kind of equilibrium.
Title: Solar Physics Simulations with the Versatile Advection Code
Authors: Tóth, G.
Bibcode: 1999ESASP.448..389T
Altcode: 1999mfsp.conf..389T; 1999ESPM....9..389T
No abstract at ADS
Title: Wave Heating and Nonlinear Dynamics of Coronal Loops
Authors: Beliën, A. J. C.; Martens, P. C. H.; Keppens, R.; Tóth, G.
Bibcode: 1999ASPC..184..248B
Altcode:
We present the first results of 2.5D nonlinear magnetohydrodynamic
wave heating simulations of solar coronal loops with inclusion
of the modeling of the coupling to the transition region and
chromosphere. Magnetic flux tubes with fixed lengths are considered
but the coronal extent of the loops as situated in between the two
transition regions can vary dynamically. The numerical simulations
were carried out with the Versatile Advection Code. The loops are
excited with linearly polarized Alfvén waves at the chromospheric
base. The main finding is that resonant absorption is not efficient
since most of the Poynting flux that enters the loop will be used to
support all the nonlinearly generated magnetoacoustic motions and the
corresponding compression of coronal plasma.
Title: On the Azimuthal Stability of Shock Waves around Black Holes
Authors: Molteni, Diego; Tóth, Gábor; Kuznetsov, Oleg A.
Bibcode: 1999ApJ...516..411M
Altcode: 1998astro.ph.12453M
Analytical studies and numerical simulations of time-dependent axially
symmetric flows onto black holes have shown that it is possible
to produce stationary shock waves with a stable position for both
ideal inviscid and moderately viscous accretion disks. We perform
several two-dimensional numerical simulations of accretion flows in
the equatorial plane to study shock stability against nonaxisymmetric
azimuthal perturbations. We find a peculiar new result. A very small
perturbation seems to produce an instability as it crosses the shock,
but after some small oscillations, the shock wave suddenly transforms
into an asymmetric closed pattern and stabilizes with a finite radial
extent, despite the fact that the inflow and outflow boundary conditions
are perfectly symmetric. The main characteristics of the final flow are:
(1) The deformed shock rotates steadily without any damping. It is
a permanent feature, and the thermal energy content and the emitted
energy vary periodically with time. (2) This behavior is also stable
against further perturbations. (3) The average shock is still very
strong and well defined, and its average radial distance is somewhat
larger than that of the original axially symmetric circular shock. (4)
Shocks obtained with larger angular momentum exhibit more frequencies
and beating phenomena. (5) The oscillations occur in a wide range
of parameters, so this new effect may have relevant observational
consequences, such as (quasi-) periodic oscillations, for the accretion
of matter onto black holes. Typical timescales for the periods are 0.01
and 1000 s for black holes with 10 and 106 Msolar,
respectively.
Title: Nonlinear dynamics of Kelvin-Helmholtz unstable magnetized
jets: Three-dimensional effects
Authors: Keppens, R.; Tóth, G.
Bibcode: 1999PhPl....6.1461K
Altcode: 1999astro.ph..1383K
A numerical study of the Kelvin-Helmholtz instability in compressible
magnetohydrodynamics is presented. The three-dimensional simulations
consider shear flow in a cylindrical jet configuration, embedded in
a uniform magnetic field directed along the jet axis. The growth of
linear perturbations at specified poloidal and axial mode numbers
demonstrate intricate nonlinear coupling effects. The physical
mechanisms leading to induced secondary Kelvin-Helmholtz instabilities
at higher mode numbers are identified. The initially weak magnetic
field becomes locally dominant in the nonlinear dynamics before
and during saturation. Thereby, it controls the jet deformation
and eventual breakup. The results are obtained using the Versatile
Advection Code [G. Tóth, Astrophys. Lett. Commun. 34, 245 (1996)],
a software package designed to solve general systems of conservation
laws. An independent calculation of the same Kelvin-Helmholtz unstable
jet configuration using a three-dimensional pseudospectral code gives
important insights into the coupling and excitation events of the
various linear mode numbers.
Title: Numerical simulation of prominence oscillations
Authors: Schutgens, N. A. J.; Tóth, G.
Bibcode: 1999A&A...345.1038S
Altcode: 1999astro.ph..3128S
We present numerical simulations, obtained with the Versatile Advection
Code, of the oscillations of an inverse polarity prominence. The
internal prominence equilibrium, the surrounding corona and the inert
photosphere are well represented. Gravity and thermodynamics are not
taken into account, but it is argued that these are not crucial. The
oscillations can be understood in terms of a solid body moving through
a plasma. The mass of this solid body is determined by the magnetic
field topology, not by the prominence mass proper. The model also
allows us to study the effect of the ambient coronal plasma on the
motion of the prominence body. Horizontal oscillations are damped
through the emission of slow waves while vertical oscillations are
damped through the emission of fast waves.
Title: Simulations of small-scale explosive events on the Sun
Authors: Innes, D. E.; Tóth, G.
Bibcode: 1999SoPh..185..127I
Altcode: 1999astro.ph..1342I
Small-scale explosive events or microflares occur throughout the
chromospheric network of the Sun. They are seen as sudden bursts of
highly Doppler-shifted spectral lines of ions formed at temperatures
in the range 2×104−5×105 K. They tend to occur near regions of
cancelling photospheric magnetic fields and are thought to be directly
associated with magnetic field reconnection. Recent observations have
revealed that they have a bi-directional jet structure reminiscent
of Petschek reconnection. In this paper compressible MHD simulations
of the evolution of a current sheet to a steady Petschek, jet-like
configuration are computed using the Versatile Advection Code. We
obtain velocity profiles that can be compared with recent ultraviolet
line-profile observations. By choosing initial conditions representative
of magnetic loops in the solar corona and chromosphere, it is possible
to explain the fact that jets flowing outward into the corona are more
extended and appear before jets flowing towards the chromosphere. This
model can reproduce the high Doppler-shifted components of the line
profiles, but the brightening at low velocities, near the center of
the bi-directional jet, cannot be explained by this simple MHD model.
Title: Growth and saturation of the Kelvin-Helmholtz instability
with parallel and antiparallel magnetic fields
Authors: Keppens, Rony; Tóth, G.; Westermann, R. H. J.; Goedbloed,
J. P.
Bibcode: 1999JPlPh..61....1K
Altcode: 1999astro.ph..1166K
Available from http://journals.cambridge.org/bin/bladerunner?REQUNIQ=1105385252&REQSESS=958582&118000REQEVENT=&REQINT1=18471&REQAUTH=0
Title: A high Reynolds number algorithm for polytropic accretion
disk studies
Authors: Nauta, Michiel D.; Toth, Gabor
Bibcode: 1998A&A...336..791N
Altcode:
An algorithm is proposed to study two-dimensional vortices in thin,
polytropic accretion disks. It is based on a method which has been
used to study vortices in planetary atmospheres. It is special in
that it conserves both energy and potential enstrophy in the absence
of dissipation. This leads to desirable stability properties which
permit calculations at relatively high Reynolds numbers. The algorithm
is tested and compared to existing methods, in particular with a Total
Variation Diminishing method.
Title: Implicit and semi-implicit schemes in the Versatile Advection
Code: numerical tests
Authors: Toth, G.; Keppens, R.; Botchev, M. A.
Bibcode: 1998A&A...332.1159T
Altcode:
We describe and evaluate various implicit and semi-implicit
time integration schemes applied to the numerical simulation of
hydrodynamical and magnetohydrodynamical problems. The schemes were
implemented recently in the software package Versatile Advection
Code, which uses modern shock capturing methods to solve systems of
conservation laws with optional source terms. The main advantage
of implicit solution strategies over explicit time integration is
that the restrictive constraint on the allowed time step can be
(partially) eliminated, thus the computational cost is reduced. The
test problems cover one and two dimensional, steady state and time
accurate computations, and the solutions contain discontinuities. For
each test, we confront explicit with implicit solution strategies.
Title: Nonlinear MHD Simulations of Wave Dissipation in Flux Tubes
Authors: Poedts, S.; Tóth, G.; Beliën, A. J. C.; Goedbloed, J. P.
Bibcode: 1997SoPh..172...45P
Altcode: 1997ESPM....8...45P
The phase mixing and resonant dissipation of Alfvén waves is studied in
both the 'closed' magnetic loops and the 'open' coronal holes observed
in the hot solar corona. The resulting energy transfer from large
to small length scales contributes to the heating of these magnetic
structures. The nonlinear simulations show that the periodically varying
shear flows that occur in the resonant layers are unstable. In coronal
holes, the phase mixing of running Alfvén waves is speeded up by the
'flaring out' of the magnetic field lines in the lower chromosphere.
Title: Numerical Simulation of Magnetohydrodynamic Flows
Authors: Toth, G.
Bibcode: 1997CoKon.100..259T
Altcode: 1997CoKon..12..259T
This review deals with the numerical simulation of magnetohydrodynamic
flows. A general overview of the different numerical techniques
compares their advantages, disadvantages and points to the appropriate
application areas. Some specific schemes, and their implementation in
the Versatile Advection Code are discussed in more detail.
Title: A General Code for Modeling MHD Flows on Parallel Computers:
Versatile Advection Code
Authors: Tóth, G.
Bibcode: 1996ApL&C..34..245T
Altcode:
No abstract at ADS
Title: A General Code for Modeling MilD Flows on Parallel Computers:
VersatileAdvection Code
Authors: Toth, G.
Bibcode: 1996mpsa.conf..471T
Altcode: 1996IAUCo.153..471T
No abstract at ADS
Title: Simulations of the Wardle Instability of C-Type Shock Waves
Authors: Tóth, G.
Bibcode: 1995Ap&SS.233..301T
Altcode:
C-type shocks in the partially ionized ISM are modelled by numerical
simulations. Under certain conditions the shocks are subject to the
Wardle instability, which initially makes the shock front rippled, then
in the non-linear stage can produce density variations in both the ion
and neutral fluids. A systematic search in the numerically accessible
parameter space is done to determine the wave vector kmax
and the growth rates max of the fastest growing modes. The
neutral Alfvén number, and the angleθ sbetween the shock
normal and the upstream magnetic field determine the strength and
obliqueness of the shock, as well as the dimensionless parameters of
the fastest growing mode. The results confirm and extend Wardle's linear
analysis. The non-linear evolution shows saturation of the instability
and the formation of high density regions that detach from the shock
front with the downstream flow. Numerical difficulties are partially
solved by an implicit treatment of the ion-neutral friction terms,
but strong shocks still can not be modelled efficiently. A fully
implicit method for the ions and the magnetic field is used to model
C-type shocks with low fractional ionization and high ion Alfvén speed.
Title: Simulations of the Wardle instability of C-type shock waves
Authors: Toth, Gabor
Bibcode: 1995MNRAS.274.1002T
Altcode:
C-type shocks in the partially ionized interstellar medium (ISM) are
modelled by numerical simulations. Under certain conditions the shocks
are subject to the Wardle instability, which initially makes the shock
front rippled, and then, in the non-linear stage, can produce density
enhancements in both the ion and neutral fluids. A systematic search in
the numerically accessible parameter space is carried out to determine
the wave vector k_max and the growth rate s_max of the fastest growing
modes. The neutral Alfven number, A^(n)=v_s/v^(n)A, where v_s is the
shock speed and v^(n)A is the Alfven speed in the limit of strong
coupling between the two fluids, and the angle theta_s between the
shock normal and the upstream magnetic field determine the strength and
obliqueness of the shock, as well as the dimensionless parameters of
the fastest growing mode. The results confirm and extend Wardle's linear
analysis. The non-linear evolution shows saturation of the instability
and the formation of regions with enhanced density that detach from
the shock front with the downstream flow. Numerical difficulties are
partially solved by an implicit treatment of the ion-neutral friction
terms, but strong shocks still cannot be modelled efficiently. A fully
implicit method for the ions and the magnetic field is used to model
C-type shocks with low fractional ionization and high ion Alfven speed.
Title: Numerical Study of Two-Fluid C-Type Shock Waves
Authors: Toth, Gabor
Bibcode: 1994ApJ...425..171T
Altcode:
C-type magnetohydrodynamic shocks in the partially ionized interstellar
medium are studied in the two-fluid approximation. The ionized fluid
can move along the magnetic field lines, while it interacts with the
neutral fluid via ion-neutral elastic scattering. I use an explicitly
flux-conserving two-dimensional Eulerian flux-corrected transport code
to study the dynamics of two-fluid shocks. A numerical instability
intrinsic to two-fluid problems was discovered, and a solution to
the problem is proposed. The code can successfully simulate C-type
shocks. The results of the linear stability analysis by Wardle are
confirmed, and the nonlinear behavior of the instability is explored.
Title: Instability of C-shocks in the ISM.
Authors: Tóth, G.
Bibcode: 1994nsa..book..224T
Altcode:
C-type MHD shocks in the partially ionized ISM are studied in the
two-fluid approximation. The ionized fluid can move along the magnetic
field lines, while it interacts with the neutral fluid via ion-neutron
elastic scattering. The author uses an explicitly flux conserving
2-dimensional Eulerian FCT (Flux Corrected Transport) code to study
the dynamics of two-fluid shocks. A numerical instability intrinsic
to two-fluid problems was discovered, and a fix to the problem is
proposed. The code can successfully simulate C-type shocks. The
results of the linear stability analysis by Wardle are confirmed,
and the non-linear behavior of the instability is explored.
Title: Oscillatory Instability of Radiative Shocks with Transverse
Magnetic Field: Linear Analysis and Nonlinear Simulations
Authors: Toth, G.; Draine, B. T.
Bibcode: 1993ApJ...413..176T
Altcode:
We examine the stability of plane-parallel radiative shocks with
a transverse magnetic field, for radiative cooling laws in which
Lambda varies as rho-squared T exp alpha; the instability is a global
thermal one driving a periodic oscillation of the shock front, and
corresponding oscillation in the instantaneous shock speed. The two
dimensionless parameters determining the stability of the system are
alpha, the exponent of the power law, and the Alfven Mach number MA. We
determine the stable and unstable regions of this 2D parameter space
for the fundamental mode and the first seven overtone modes through
linear analysis of the hydrodynamical equations. As expected, the
magnetic field has a stabilizing influence. For alpha greater than
0, even a relatively weak magnetic field can stabilize against all
modes. For alpha greater than 0.5, even weaker fields are sufficient
to suppress thermal instability. We also determine the linear growth
rates and frequencies of the fundamental mode and the first and second
overtones for 12 pairs of the parameters alpha and MA.
Title: Instability of Radiative and C-Type MHD Shock Waves
Authors: Toth, Gabor
Bibcode: 1993PhDT........30T
Altcode:
Radiative shocks with a cooling law Lambda ~ rho^2T^alpha can be subject
to a global thermal instability which drives a periodic oscillation of
the shock front. The stabilizing effect of a transverse magnetic field
is examined. The two dimensionless parameters determining the stability
of the system are alpha and the Alfven Mach number MA. The
stable and unstable regions of this two-dimensional parameter space are
determined through linear analysis. For alpha > 0 even a relatively
weak magnetic field (MA < 8) can stabilize against all
modes. The results are confirmed by means of numerical simulations. The
simulations show saturation or secondary shock formation in the
non-linear regime. Radiative shocks with v_{s } _sp{~}< 160km s^{-1}
radiative shocks in the "warm ISM" may be magnetically stabilized. In
higher density gas, however, the magnetic field is not strong enough
to appreciably affect the shock stability. Next the dynamics of C-type
MHD shocks in the partially ionized ISM are studied in the two-fluid
approximation by an explicitly flux conserving two-dimensional
Eulerian FCT code. A numerical instability intrinsic to two-fluid
problems is discovered, and a fix to the problem is proposed. The code
can successfully simulate a rippling instability of the shock front
discovered by Wardle through linear analysis. Numerical simulations are
presented to find the wave vector vec kmax and the growth
rate smax of the fastest growing modes. For perpendicular
shocks the analytic calculations are confirmed, while for oblique
shocks k_ {|} equiv k cos phik, the component of the wave
vector lying in the plane of the magnetic field and the shock normal,
is found to be the critical parameter determining smax. The
phimax angle is only weakly constrained. These results
confirm and generalize the predictions of the linear analysis. The
simulation of a weak perpendicular shock shows that saturation of the
Wardle-instability occurs only when the density perturbations reach
an amplitude comparable to the total density jump through the shock
front. The simulations show a strong transient amplification of the
initial perturbations, thus to some extent the amplitude and spectrum
of the seed perturbations in the ambient ISM will contribute to the
selection of the dominant growing mode.
Title: Instability of radiative and C-type MHD shock waves
Authors: Tóth, Gábor
Bibcode: 1993PhDT.......130T
Altcode:
No abstract at ADS
Title: Oscillatory instability of radiative shocks with transverse
magnetic field: linear analysis and nonlinear simulations.
Authors: Tóth, G.; Draine, B. T.
Bibcode: 1992BAAS...24.1261T
Altcode:
No abstract at ADS
Title: Oscillatory Instability of Radiative Shocks with Transverse
Magnetic Field: Linear Analysis and Nonlinear Simulations
Authors: Toth, G.; Draine, B. T.
Bibcode: 1992AAS...181.8605T
Altcode:
We examine the stability of plane-parallel radiative shocks with
a transverse magnetic field, for radiative cooling laws Lambda ~
rho (2) T(alpha ). The instability of interest is a global thermal
instability which drives a periodic oscillation of the shock front,
and corresponding oscillation in the instantaneous shock speed. The two
dimensionless parameters determining the stability of the system are
alpha , the exponent of the power law, and the Alfven Mach number
M_Aequiv v_s/v_A, where v_s is the average shock speed and v_A is
the Alfven velocity in the preshock medium. We determine the stable
and unstable regions of this two dimensional parameter space for
the fundamental mode and the first seven overtone modes through
linear analysis of the hydrodynamical equations. As expected, the
magnetic field has a stabilizing influence. For alpha >0 even a
relatively weak magnetic field (M_A < 8) can stabilize against
all modes. For alpha > 0.5 even weaker fields (M_A < 33) are
sufficient to suppress thermal instability. We also determine the
linear growth rates and frequencies of the fundamental mode and the
first and second overtones for twelve pairs of the parameters alpha
and M_A. A fully dynamical numerical simulation of these twelve cases
confirms the results of the linear analysis, and also explores the
nonlinear behavior of the oscillations. In most of the unstable cases
the amplitude of the shock front oscillation saturates at a level of 5%
to 10% of the length of the cooling region. In the least stable cases,
however, the flow develops multiple shocks. Using a simple approximation
to the cooling function for shocked interstellar gas, we show that v_s
< ~= 160kms(-1) radiative shocks in interstellar gas with n_H <
~eq0.4cm(-3) (the "warm ionized medium" or "warm neutral medium") may
be magnetically stabilized. In higher density gas, however, the magnetic
field is not strong enough to appreciably affect the shock stability.
Title: Oscillatory Instability of Radiative Shocks with Transverse
Magnetic Field: Linear Analysis and Nonlinear Simulations
Authors: Tóth, G.; Draine, B. T.
Bibcode: 1992AAS...181.8505T
Altcode: 1992BAAS...24.1259T
No abstract at ADS
Title: Galactic Disks, Infall, and the Global Value of Omega
Authors: Toth, G.; Ostriker, J. P.
Bibcode: 1992ApJ...389....5T
Altcode:
The thinness and coldness of galactic disks can be used to set
stringent limits on the current rate of infall of satellite systems
onto spiral galaxies. After reviewing the literature concerning
numerical results, we develop analytical arguments which confirm
and considerably extend prior work. For infalling satellites on
isotropically oriented circular orbits, we show that, due to scattering,
the thermal energy gain of the disk exceeds the satellite energy loss
from dynamical friction by a factor of 1.6, with 25% deposited in
z motion and 75% in planar motions. This factor almost compensates
for the frictional loss to the halo, with halo-to-disk loss rates
being approximately 2.87rρ_h_(r)/{SIGMA}_d_(r). For our chosen
Galactic model this corresponds to 62% of the energy deposited in
the spherical component at the solar radius. While satellite infall
will thicken disks by perturbing the stellar orbits, it will cause
adiabatic contraction too. If there is gas infall, this makes the disk
thinner by settling down in the galactic plane. However, the first
effect dominates, the ratio between stellar heating and gas cooling
being 0.11(v_rot/σ_normal_)^2^~7 for equal masses added in stars
and gas. Applying these arguments to current models for our Galaxy,
we find that no more than 4% of its mass inside the solar radius
can have accreted within the last 5 billion years, or else its scale
height and its Toomre Q-parameter would exceed observed values. We
find that tidal stripping of infalling dwarfs is not a large effect
unless core radii significantly exceed 1 kpc. In standard cold dark
matter-dominated models for the growth of structure with {OMEGA}_tot_
= 1, the mass accreted in dark matter lumps rises faster than t^2/3^
and would exceed 28% in the last 5 Gyr. If our Galaxy is typical (and
the prevalence of spiral structure indicates that this is so), then
such models for the growth of structure may be ruled out. There is
no such difficulty in open universes, since accretion declines after
a time t_1/2_= H^-1^_0pi{OMEGA}_0_/(1 - {OMEGA}^3/2^, nor
is there a problem if {OMEGA} = 1 in the form of radiation, {LAMBDA},
or a hot component which would not accrete. Heating from satellite
infall may account for a substantial fraction of the increase of
velocity dispersion and scale height with age that is observed in our
Galaxy. In addition, since the satellite infall events are discrete, the
age-velocity dispersion relation should reflect this, and the velocity
distribution will have a non-Gaussian tail, which will contribute to
a thick disk.
Title: Three-Point Correlations of Galaxy Clusters
Authors: Toth, Gabor; Hollosi, Joseph; Szalay, Alexander S.
Bibcode: 1989ApJ...344...75T
Altcode:
We estimate the irreducible angular three-point correlation function
of Abell clusters in distance classes 5 and 6 with Galactic latitude
|b^II^| >= 40^deg^ from the Abell and Abell, Corwin, and Olowin
catalog and of clusters identified in the Shane-Wirtanen catalog
(Shectman). We find that the distribution of these clusters satisfies
a relation between the two- and three-point correlation functions:
Title: Angular Cross-Correlation of Abell Clusters in Different
Distance Classes
Authors: Szalay, A. S.; Hollosi, J.; Toth, G.
Bibcode: 1989ApJ...339L...5S
Altcode:
We estimate the angular autocorrelation and cross-correlation functions
of the D = 1... 4, D = 5, and D = 6 distance class Abell clusters. While
the autocorrelation functions can be described by a power-law form w(θ)
is proportional to θ^-1^, the cross-correlations are found to be much
flatter. Moreover, there is a strong anticorrelation between the most
distant D = 6 and the closest D = 1... 4 subsamples. We believe this to
be an artifact of the cluster identification process presumably due to
the finite angular size of the cluster. This anticorrelation seems to
contradict some recent estimations of projection contaminations in the
Abell catalog. We suggest that the angular proximity of a foreground
cluster may have caused a background cluster not to be counted as it
was thought to be a subcluster or it was erroneously assigned to a
nearer distance class.
Title: Three-Point Correlations of Abell Clusters
Authors: Toth, Gabor; Hollosi, Joseph; Szalay, Alex S.
Bibcode: 1988LNP...310..195T
Altcode: 1988lssu.work..195T
The irreducible three-point correlations of Abell clusters are estimated
using all distance class 5 + 6 clusters with a latitude greater than
or equal to 40 deg. It is found that the clusters satisfy a relation
between the two- and three-point correlation functions similar to that
for galaxies. There is a strong discrepancy between the northern and
southern galactic caps.
Title: Three-point correlations of Abell clusters.
Authors: Tóth, G.; Hollósi, J.; Szalay, A. S.
Bibcode: 1988lssu.conf..195T
Altcode:
The authors estimate the irreducible three-point correlations of
Abell clusters using all distance class 5+6 clusters with latitude
|bII| ≥ 40°. They find that these clusters satisfy a
relation between the two- and three-point correlation functions:
ζ(r,s,u) ≈ Q(ξ(r)ξ(s) + ξ(s)ξ(u) + ξ(u)ξ(r)) similar to
that for galaxies. The value of Q has large uncertainties: Q =
0.9±0.5. Higher order terms seem to be absent in ζ. Several error
estimation methods are applied.
Title: Book Reviews
Authors: Hodgson, R. G.; Smith, R. J.; Brasch, K. R.; Tóth, G.;
McIntosh, P. S.; Trusell, F. C.
Bibcode: 1963StAst..17...74H
Altcode: 1963JALPO..17...74H
Six books are reviewed: The System of Minor Planets by Günter
D. Roth; Star Gazing with Telescope and Camera by George T. Keene;
Der Sternhimmel 1963, Edited by Robert A. Naef; The Physics of the
Moon by P. Hedervari; Solar Research, by Giorgio Abetti; and Soviet
Science of Interstellar Space, by S. Pikelner.