Author name code: bourdin
ADS astronomy entries on 2022-09-14
author:"Bourdin, Philippe-A."
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Title: Electromotive force and helicity estimation of an iCME observed
by SolarOrbiter
Authors: Bourdin, Philippe-A.
Bibcode: 2022cosp...44.1369B
Altcode:
Inter-planetary coronal mass ejections that are faster than the ambient
solar wind are known to push a bow shock in front of them. Such fronts
usually feature strongly oscillating magnetic fields that are similar
to magneto-hydrodynamic turbulence or dynamo action. The electromotive
force is one way of estimating the turbulent nature of such fronts,
giving a way to identify the exact arrival time, even without knowing
the complete following magnetic field structures. The magnetic
helicity within the iCME is largely conserved during the travel of
the iCME through the heliosphere. Also this handedness should be the
same as found in the solar corona during the actual outbreak. We aim
to estimate the handedness of the magnetic helicity by using in-situ
observations from SolarOrbiter MAG and SWA-PAS data of the event
around 4th of November 2021. To this end, we compute the electromotive
force from the fluctuations of the magnetic field and proton velocity
moments. Finally, we infer the handedness of the magnetic helicity
and compare the magnitude of the electromotive force to our previous
study of Helios observations in the inner heliosphere between 0.28 and
1 au. This allows us to compare the turbulent magnitude of the November
2021 event to a decade worth of inner-heliospheric observations from
the Helios database. We show how the SolarOrbiter observation fits to
a scaling law for the decay of the electromotive force that we deduced
from Helios data.
Title: Heating and cooling in an atmospheric model of the solar corona
Authors: Pandey, Vartika; Bourdin, Philippe-A.
Bibcode: 2022cosp...44.2482P
Altcode:
We investigate the solar coronal heating problems. We aim to model
the field-line braiding mechanism with magnetic foot-points that are
shuffled to generate an upward Poynting flux. The magnetic energy then
travels into the corona. These perturbations induce electric currents
that later heat the coronal plasma through Ohmic dissipation. The
initial condition for large-scale magneto-hydrodynamic simulations
is an atmospheric stratification but as the numerical and analytical
derivatives are not identical the initial hydrodynamic equilibrium
is inexact. It would not be cost-effective to settle the initial
in-equilibrium in a large-scale 3D model. Therefore, we use a 1D
model that spans from the solar interior to the corona for finding the
numerical equilibrium under the actual MHD simulation parameters, like
mass diffusion, heat conduction, viscosity, and radiative losses. This
new 1D atmospheric stratification will be used as the initial condition
for our large 3D simulation runs. Also, we implement an artificial
heating function for the corona that compensates for a lack of heating
in the early phase of the model, where the observational driving
sets in and takes at least Alfvèn travel time for the perturbation
to reach the corona. This way, we avoid the collapse of solar corona
due to insufficient heating. This function also compensates for the
natural and numerical energy losses.This allows us to start the 3D
model with the most realistic physics and keep the vertical settling
motions at a minimum, in particular below some m/s, which is also
the observable Doppler shift magnitude in the corona.We also discuss
the effects of the coronal heating and cooling mechanisms and their
importance in different atmospherical layers, such as compressional
heating, viscous heating, radiative losses, as well as how they balance
out. This procedure finally allows us to start large-scale 3D models
and get realistic vertical velocities without numerical effects, which
can then be compared with Doppler shifts observed by the Hinode/EIS
instrument in the corona.
Title: Influence of the kinematic viscosity on solar convection
simulations
Authors: Tschernitz, Johannes; Bourdin, Philippe-A.
Bibcode: 2022cosp...44.2553T
Altcode:
Numerical simulations can give insights into solar plasma processes,
that would not be possible otherwise. While the computing power of
modern supercomputers has increased over time, the spatial resolution
is still limited. Diffusion parameters like kinematic viscosity play
a major role in the numerical stability of magneto-hydrodynamic
simulations. Generally, larger viscosity can make a simulation
more stable, while in return it suppresses small scale turbulent
motions. Therefore, the value of the simulated viscosity is often by
several orders of magnitude larger than the realistic one. We perform
hydrodynamic 2D simulations of solar convection with the Pencil Code in
order to study the effect of different values of the kinematic viscosity
on the numerical stability, the spatial scale of the convection,
and the vertical velocities. Our convection simulations also include a
large part of the solar atmosphere, up to 25 Mm above the surface, while
including 20 Mm of the solar convection layer. We use a box of 512×384
grid points, resulting in a spatial resolution of about 125 km. Our
initial condition matches the density and temperature stratification
of the Sun, including a realistic gravity profile. The atmosphere is
kept at the initial temperature profile by a Newton-cooling scheme,
while we drive the convection from the bottom with a realistic
heat input. We find that convection starts in two different regions
separately after some time. The first region lies at the solar surface,
where the convection is driven by cooling. The second region lies at
the bottom of the box, where the convection cells are driven by the
heating from below. We run the simulation setup several times with
varying values of the kinematic viscosity in the range of $\sim$10$
^{-7}$ to $\sim$10$ ^{10}$ m$ ^{2}$/s. We find that the cells at the
top are dependent on the kinematic viscosity, if it is above $\sim$10$
^{8}$ m$ ^{2}$/s, with larger values resulting in larger cells. Below
this value, the size of the cells is practically constant around 2.5 Mm
in diameter, and not varying for lower viscosity values. The numerical
stability is affected for small viscosities and the simulation crashes
before the completion of 24 hours solar time. Diffusion constants like
the kinematic viscosity have to be chosen carefully for a specific
problem to avoid numerical problems in the simulation domain. We find
that there is an optimal choice of the viscosity with good numerical
stability and only small changes of the physical behavior in the upper
layers of the convection zone.
Title: The Pencil Code, a modular MPI code for partial differential
equations and particles: multipurpose and multiuser-maintained
Authors: Pencil Code Collaboration; Brandenburg, Axel; Johansen,
Anders; Bourdin, Philippe; Dobler, Wolfgang; Lyra, Wladimir;
Rheinhardt, Matthias; Bingert, Sven; Haugen, Nils; Mee, Antony; Gent,
Frederick; Babkovskaia, Natalia; Yang, Chao-Chin; Heinemann, Tobias;
Dintrans, Boris; Mitra, Dhrubaditya; Candelaresi, Simon; Warnecke,
Jörn; Käpylä, Petri; Schreiber, Andreas; Chatterjee, Piyali;
Käpylä, Maarit; Li, Xiang-Yu; Krüger, Jonas; Aarnes, Jørgen;
Sarson, Graeme; Oishi, Jeffrey; Schober, Jennifer; Plasson, Raphaël;
Sandin, Christer; Karchniwy, Ewa; Rodrigues, Luiz; Hubbard, Alexander;
Guerrero, Gustavo; Snodin, Andrew; Losada, Illa; Pekkilä, Johannes;
Qian, Chengeng
Bibcode: 2021JOSS....6.2807P
Altcode: 2021JOSS....6.2807C; 2020arXiv200908231B
The Pencil Code is a highly modular physics-oriented simulation code
that can be adapted to a wide range of applications. It is primarily
designed to solve partial differential equations (PDEs) of compressible
hydrodynamics and has lots of add-ons ranging from astrophysical
magnetohydrodynamics (MHD) to meteorological cloud microphysics and
engineering applications in combustion. Nevertheless, the framework
is general and can also be applied to situations not related to
hydrodynamics or even PDEs, for example when just the message passing
interface or input/output strategies of the code are to be used. The
code can also evolve Lagrangian (inertial and noninertial) particles,
their coagulation and condensation, as well as their interaction with
the fluid.
Title: Derfflinger's Sunspot Observations: Primary Dataset to
Understand the Dalton Minimum
Authors: Hayakawa, Hisashi; Besser, Bruno P.; Imada, Shinsuke; Arlt,
Rainer; Iju, Tomoya; Bourdin, Philippe; Kraml, Amand; Uneme, Shoma
Bibcode: 2021cosp...43E.915H
Altcode:
As various predictions indicate possible arrival of depressed solar
cycles or even a secular/grand solar minimum, it is increasingly
important to understand the actual solar activity during the existing
solar secular/grand minima. The Dalton Minimum is arguably one of such
solar secular/grand minima within the coverage of telescopic sunspot
observations, while its sunspot group number has been differently
reconstructed by various studies and its butterfly diagram has not been
reconstructed. Here, we examine the original observational records
of Derfflinger in Krememünster Observatory, spanning from 1802 to
1824, covering the core period of the Dalton Minimum. We revise his
sunspot group number and reconstruct the butterfly diagram. These
reconstructions show that the Dalton Minimum was significantly different
from the Maunder Minimum, both in terms of amplitude of its solar
cycles and sunspot distributions.
Title: Life-time evolution and magnetic structure of coronal holes
Authors: Heinemann, Stephan; Pomoell, Jens; Temmer, Manuela; Bourdin,
Philippe
Bibcode: 2021cosp...43E1024H
Altcode:
The study of the evolution of coronal holes (CHs) is especially
important in the context of high--speed solar wind streams
emanating from them. Slow and high speed stream interaction
regions may deliver large amount of energy into the Earth's
magnetosphere-termosphere-ionosphere system system, cause geomagnetic
storms, and shape interplanetary space. The open magnetic structure,
its evolution and interplay with the local and global fields strongly
defines the coronal and solar wind properties. Only by understanding
these we can attempt to create a full picture of our heliosphere. By
statistically investigating the long--term evolution of 16 well
observed CHs, which are distributed in time over a full solar cycle,
we aim to reveal processes that drive the observed changes in the
CH parameters. We use remote sensing image data from SDO and focus
on coronal, morphological and underlying photospheric magnetic field
characteristics as well as investigate the evolution of the associated
high--speed streams from in-situ measurements. The analysis of the
observational data is supported by modeling, based on synthetic data
in order to simulate the small-scale magnetic field topology in 3
dimensions. We find that the CH area evolution mostly shows a rough
trend of growing to a maximum followed by a decay. No correlation of
the area evolution to the evolution of the signed magnetic flux and
signed magnetic flux density enclosed in the projected coronal hole
area was found. From this we conclude that the magnetic flux within
the extracted coronal hole boundaries is not the main cause for its
area evolution. This is supported by the model results. Change rates
of the signed mean magnetic flux density and the signed magnetic flux
are derived to be dependent on the solar cycle rather than on the
evolution of the individual CH. This clearly hints towards that the
global magnetic field gives significant contribution to the evolution
of open magnetic field structures on the Sun. The velocities of the
high speed streams emanating from the CHs are found to be linearly
related to the area of the individual CH, however the slopes vary.
Title: Investigating Mercury's Environment with the Two-Spacecraft
BepiColombo Mission
Authors: Milillo, A.; Fujimoto, M.; Murakami, G.; Benkhoff, J.; Zender,
J.; Aizawa, S.; Dósa, M.; Griton, L.; Heyner, D.; Ho, G.; Imber,
S. M.; Jia, X.; Karlsson, T.; Killen, R. M.; Laurenza, M.; Lindsay,
S. T.; McKenna-Lawlor, S.; Mura, A.; Raines, J. M.; Rothery, D. A.;
André, N.; Baumjohann, W.; Berezhnoy, A.; Bourdin, P. A.; Bunce,
E. J.; Califano, F.; Deca, J.; de la Fuente, S.; Dong, C.; Grava,
C.; Fatemi, S.; Henri, P.; Ivanovski, S. L.; Jackson, B. V.; James,
M.; Kallio, E.; Kasaba, Y.; Kilpua, E.; Kobayashi, M.; Langlais, B.;
Leblanc, F.; Lhotka, C.; Mangano, V.; Martindale, A.; Massetti, S.;
Masters, A.; Morooka, M.; Narita, Y.; Oliveira, J. S.; Odstrcil, D.;
Orsini, S.; Pelizzo, M. G.; Plainaki, C.; Plaschke, F.; Sahraoui, F.;
Seki, K.; Slavin, J. A.; Vainio, R.; Wurz, P.; Barabash, S.; Carr,
C. M.; Delcourt, D.; Glassmeier, K. -H.; Grande, M.; Hirahara, M.;
Huovelin, J.; Korablev, O.; Kojima, H.; Lichtenegger, H.; Livi, S.;
Matsuoka, A.; Moissl, R.; Moncuquet, M.; Muinonen, K.; Quèmerais,
E.; Saito, Y.; Yagitani, S.; Yoshikawa, I.; Wahlund, J. -E.
Bibcode: 2020SSRv..216...93M
Altcode: 2022arXiv220213243M
The ESA-JAXA BepiColombo mission will provide simultaneous measurements
from two spacecraft, offering an unprecedented opportunity to
investigate magnetospheric and exospheric dynamics at Mercury as
well as their interactions with the solar wind, radiation, and
interplanetary dust. Many scientific instruments onboard the two
spacecraft will be completely, or partially devoted to study the
near-space environment of Mercury as well as the complex processes
that govern it. Many issues remain unsolved even after the MESSENGER
mission that ended in 2015. The specific orbits of the two spacecraft,
MPO and Mio, and the comprehensive scientific payload allow a wider
range of scientific questions to be addressed than those that could
be achieved by the individual instruments acting alone, or by previous
missions. These joint observations are of key importance because many
phenomena in Mercury's environment are highly temporally and spatially
variable. Examples of possible coordinated observations are described in
this article, analysing the required geometrical conditions, pointing,
resolutions and operation timing of different BepiColombo instruments
sensors.
Title: Driving solar coronal MHD simulations on high-performance
computers
Authors: Bourdin, Philippe-A.
Bibcode: 2020GApFD.114..235B
Altcode: 2019arXiv190808557B
The quality of today's research is often tightly limited to
the available computing power and scalability of codes to many
processors. For example, tackling the problem of heating the solar
corona requires a most realistic description of the plasma dynamics and
the magnetic field. Numerically solving such a magneto-hydrodynamical
(MHD) description of a small active region (AR) on the Sun requires
millions of computation hours on current high-performance computing
(HPC) hardware. The aim of this work is to describe methods for an
efficient parallelisation of boundary conditions and data input/output
(IO) strategies that allow for a better scaling towards thousands
of processors (CPUs). The Pencil Code is tested before and after
optimisation to compare the performance and scalability of a coronal
MHD model above an AR. We present a novel boundary condition for
non-vertical magnetic fields in the photosphere, where we approach
the realistic pressure increase below the photosphere. With that,
magnetic flux bundles become narrower with depth and the flux density
increases accordingly. The scalability is improved by more than one
order of magnitude through the HPC-friendly boundary conditions and
IO strategies. This work describes also the necessary nudging methods
to drive the MHD model with observed magnetic fields from the Sun's
photosphere. In addition, we present the upper and lower atmospheric
boundary conditions (photospheric and towards the outer corona),
including swamp layers to diminish perturbations before they reach
the boundaries. Altogether, these methods enable more realistic 3D MHD
simulations than previous models regarding the coronal heating problem
above an AR - simply because of the ability to use a large amount of
CPUs efficiently in parallel.
Title: Thaddäus Derfflinger's Sunspot Observations during 1802-1824:
A Primary Reference to Understand the Dalton Minimum
Authors: Hayakawa, Hisashi; Besser, Bruno P.; Iju, Tomoya; Arlt,
Rainer; Uneme, Shoma; Imada, Shinsuke; Bourdin, Philippe-A.; Kraml,
Amand
Bibcode: 2020ApJ...890...98H
Altcode: 2020arXiv200102367H
As we are heading toward the next solar cycle, presumably with
a relatively small amplitude, it is of significant interest to
reconstruct and describe the past secular minima on the basis of actual
observations at the time. The Dalton Minimum is often considered
one of the secular minima captured in the coverage of telescopic
observations. Nevertheless, the reconstructions of the sunspot group
number vary significantly, and the existing butterfly diagrams have
a large data gap during the period. This is partially because most
long-term observations at that time have remained unexplored in
historical archives. Therefore, to improve our understanding on the
Dalton Minimum, we have located two series of Thaddäus Derfflinger's
observational records spanning 1802-1824 (a summary manuscript
and logbooks), as well as his Brander's 5.5 feet azimuthal quadrant
preserved in the Kremsmünster Observatory. We have revised the existing
Derfflinger's sunspot group number with Waldmeier classification, and
eliminated all the existing "spotless days" to remove contaminations
from solar elevation observations. We have reconstructed the butterfly
diagram on the basis of his observations and illustrated sunspot
distributions in both solar hemispheres. Our article aims to revise
the trend of Derfflinger's sunspot group number and to bridge a data
gap of the existing butterfly diagrams around the Dalton Minimum. Our
results confirm that the Dalton Minimum is significantly different
from the Maunder Minimum, both in terms of cycle amplitudes and sunspot
distributions. Therefore, the Dalton Minimum is more likely a secular
minimum in the long-term solar activity, while further investigations
for the observations at that time are required.
Title: Orbital stability of ensembles of particles in regions of
magnetic reconnection in Earth's magneto-tail
Authors: Lhotka, Christoph; Bourdin, Philippe; Pilat-Lohinger, Elke
Bibcode: 2019PhPl...26g2903L
Altcode: 2019arXiv190713478L
We investigate the collective behavior of particle orbits in the
vicinity of magnetic reconnection in Earth's magneto-tail. Various
regions of different kinds of orbital stability of particle motions
are found. We locate regimes of temporary capture of particle orbits
in configuration space as well as locations, where strong particle
accelerations take place. With this study, we are able to provide a
detailed map, i.e., the topology, of high and low acceleration centers
close to the reconnection site. Quasiregular and chaotic kinds of
motions of elementary particles can be determined as well. The orbital
stability of particle orbits is obtained by a statistical analysis of
the outcome of the system of variational equations of particle orbits
within the framework of particle-in-cell simulations. Using the concept
of Lyapunov characteristic numbers to ensembles of particle orbits,
we introduce Lyapunov ensemble averages to describe the response of
particle orbits to local perturbations induced by the electromagnetic
field.
Title: Application of the Electromotive Force as a Shock Front
Indicator in the Inner Heliosphere
Authors: Hofer, Bernhard; Bourdin, Philippe-A.
Bibcode: 2019ApJ...878...30H
Altcode: 2019arXiv190502596H
The electromotive force (EMF) describes how the evolution and
generation of a large-scale magnetic field is influenced by small-scale
turbulence. Recent studies of in situ measurements have shown a
significant peak in the EMF while a coronal mass ejection (CME) shock
front passes by the spacecraft. The goal of this study is to use the
EMF as an indicator for the arrival of CME shock fronts. With Helios
spacecraft measurements we carry out a statistical study on the EMF
during CMEs in the inner heliosphere. We develop an automated shock
front detection algorithm using the EMF as the main detection criterion
and compare the results to an existing CME database. The properties
of the EMF during the recorded events are discussed as a function of
the heliocentric distance. Our algorithm reproduces most of the events
from Kilpua et al. and finds many additional CME-like events, which
proves that the EMF is a good shock front indicator. The largest peaks
in the EMF are found from 0 to 50 minutes after the initial shock. We
find a power law of -1.54 and -2.18 for two different formulations of
the EMF with the heliocentric distance.
Title: Magnetic Helicity from Multipolar Regions on the Solar Surface
Authors: Bourdin, Philippe-A.; Brandenburg, Axel
Bibcode: 2018ApJ...869....3B
Altcode: 2018arXiv180404160B
The emergence of dipolar magnetic features on the solar surface
is an idealization. Most of the magnetic flux emergence occurs in
complex multipolar regions. Here, we show that the surface pattern of
magnetic structures alone can reveal the sign of the underlying magnetic
helicity in the nearly force-free coronal regions above. The sign of
the magnetic helicity can be predicted to good accuracy by considering
the three-dimensional position vectors of three spots on the sphere
ordered by their relative strengths at the surface and compute from
them the skew product. This product, which is a pseudoscalar, is shown
to be a good proxy for the sign of the coronal magnetic helicity.
Title: Magnetic Helicity Reversal in the Corona at Small Plasma Beta
Authors: Bourdin, Philippe; Singh, Nishant K.; Brandenburg, Axel
Bibcode: 2018ApJ...869....2B
Altcode: 2018arXiv180404153B
Solar and stellar dynamos shed small-scale and large-scale magnetic
helicity of opposite signs. However, solar wind observations and
simulations have shown that some distance above the dynamo both
the small-scale and large-scale magnetic helicities have reversed
signs. With realistic simulations of the solar corona above an active
region now being available, we have access to the magnetic field and
current density along coronal loops. We show that a sign reversal in
the horizontal averages of the magnetic helicity occurs when the local
maximum of the plasma beta drops below unity and the field becomes
nearly fully force free. Hence, this reversal is expected to occur well
within the solar corona and would not directly be accessible to in situ
measurements with the Parker Solar Probe or SolarOrbiter. We also show
that the reversal is associated with subtle changes in the relative
dominance of structures with positive and negative magnetic helicity.
Title: Electromotive force in the vincinity of an ICME shock front
Authors: Bourdin, Philippe A.
Bibcode: 2018shin.confE.202B
Altcode:
The electromotive force is a key quantity in magneto-hydrodynamic
turbulence and dynamo research that couples magnetic field with
plasma bulk flow fluctuations. From Helios observations it was thought
that the electromotive force is negligible in the solar wind within
the inner heliosphere between 0.3 and 1 AU. We revisit those data
sets particularly around ICME and magnetic transient events. We
compute the spatial derivatives along the solar-wind stream from
in-situ measurements, which allows to determine quantities like the
flow vorticity, the cross-helicity, and turbulent diffusion. With
different formulations of the electromotive force from mean-field
electrodynamics and turbulence research, we may compare the in-situ
electromotive force with a simple ICME model of the magnetic field
and the plasma bulk flow. We find the electromotive force becomes
significantly enhanced and is no longer negligible during such magnetic
transient events. Our toy-model fits well to the observed data and
we may read several parameters, like the magnetic helicity and flow
vorticity during this event. Hence, the electromotive force is not
only a good in-situ indicator of ICME-like events, but also our method
allows to draw conclusions on the actual internal magnetic structure
of ICMEs. For future inner-heliospheric missions, like Parker Solar
Probe and SolarOrbiter, this method may be applied to automatically
detect and analyze ICMEs in at least a statistical sense.
Title: Chaotic motions of plasma and dust particles in magnetic
reconnection regimes in Earth's magnetotail
Authors: Lhotka, Christoph; Pilat-Lohinger, Elke; Bourdin, Philippe
Bibcode: 2018cosp...42E1985L
Altcode:
We investigate the role of regular and chaotic motions of plasma and
dust particles in the regime of magnetic reconnection of the Earth
magnetotail on plasma processes. Our study is based on numerical
simulations of particle orbits in plasma simulations. We analyze
the variational system of equations together with the evolution and
characteristics of the short time Local Lyapunov Indicators. We find
regular and chaotic motions of (dust) particle orbits in phase space
and link our results to open problems of plasma physics.
Title: Ensemble Prediction of a Halo Coronal Mass Ejection Using
Heliospheric Imagers
Authors: Amerstorfer, T.; Möstl, C.; Hess, P.; Temmer, M.; Mays,
M. L.; Reiss, M. A.; Lowrance, P.; Bourdin, P. -A.
Bibcode: 2018SpWea..16..784A
Altcode: 2017arXiv171200218A
The Solar TErrestrial RElations Observatory (STEREO) and its
heliospheric imagers (HIs) have provided us the possibility to enhance
our understanding of the interplanetary propagation of coronal mass
ejections (CMEs). HI-based methods are able to forecast arrival times
and speeds at any target and use the advantage of tracing a CME's path
of propagation up to 1 AU and beyond. In our study, we use the ELEvoHI
model for CME arrival prediction together with an ensemble approach to
derive uncertainties in the modeled arrival time and impact speed. The
CME from 3 November 2010 is analyzed by performing 339 model runs
that are compared to in situ measurements from lined-up spacecraft
MErcury Surface, Space ENvironment, GEochemistry, and Ranging and
STEREO-B. Remote data from STEREO-B showed the CME as halo event,
which is comparable to an HI observer situated at L1 and observing an
Earth-directed CME. A promising and easy approach is found by using
the frequency distributions of four ELEvoHI output parameters, drag
parameter, background solar wind speed, initial distance, and speed. In
this case study, the most frequent values of these outputs lead to
the predictions with the smallest errors. Restricting the ensemble
to those runs, we are able to reduce the mean absolute arrival time
error from 3.5 ± 2.6 to 1.6 ± 1.1 hr at 1 AU. Our study suggests that
L1 may provide a sufficient vantage point for an Earth-directed CME,
when observed by HI, and that ensemble modeling could be a feasible
approach to use ELEvoHI operationally.
Title: Inner Structure of CME Shock Fronts Revealed by the
Electromotive Force and Turbulent Transport Coefficients in Helios-2
Observations
Authors: Bourdin, Philippe-A.; Hofer, Bernhard; Narita, Yasuhito
Bibcode: 2018ApJ...855..111B
Altcode: 2018arXiv180210111B
Electromotive force is an essential quantity in dynamo theory. During a
coronal mass ejection (CME), magnetic helicity gets decoupled from the
Sun and advected into the heliosphere with the solar wind. Eventually,
a heliospheric magnetic transient event might pass by a spacecraft,
such as the Helios space observatories. Our aim is to investigate
the electromotive force, the kinetic helicity effect (α term),
the turbulent diffusion (β term), and the cross-helicity effect (γ
term) in the inner heliosphere below 1 au. We set up a one-dimensional
model of the solar wind velocity and magnetic field for a hypothetic
interplanetary CME. Because turbulent structures within the solar wind
evolve much slower than this structure needs to pass by the spacecraft,
we use a reduced curl operator to compute the current density and
vorticity. We test our CME shock-front model against an observed
magnetic transient that passes by the Helios-2 spacecraft. At the
peak of the fluctuations in this event we find strongly enhanced α,
β, and γ terms, as well as a strong peak in the total electromotive
force. Our method allows us to automatically identify magnetic transient
events from any in situ spacecraft observations that contain magnetic
field and plasma velocity data of the solar wind.
Title: Catalog of fine-structured electron velocity distribution
functions - Part 1: Antiparallel magnetic-field reconnection (Geospace
Environmental Modeling case)
Authors: Bourdin, Philippe-A.
Bibcode: 2017AnGeo..35.1051B
Altcode: 2017arXiv170905564B
To understand the essential physics needed to reproduce magnetic
reconnection events in 2.5-D particle-in-cell (PIC) simulations, we
revisit the Geospace Environmental Modeling (GEM) setup. We set up a 2-D
Harris current sheet (that also specifies the initial conditions) to
evolve the reconnection of antiparallel magnetic fields. In contrast
to the GEM setup, we use a much smaller initial perturbation to
trigger the reconnection and evolve it more self-consistently. From
PIC simulation data with high-quality particle statistics, we study
a symmetric reconnection site, including separatrix layers, as well
as the inflow and the outflow regions. The velocity distribution
functions (VDFs) of electrons have a fine structure and vary strongly
depending on their location within the reconnection setup. The goal
is to start cataloging multidimensional fine-structured electron
velocity distributions showing different reconnection processes in
the Earth's magnetotail under various conditions. This will enable a
direct comparison with observations from, e.g., the NASA Magnetospheric
MultiScale (MMS) mission, to identify reconnection-related events. We
find regions with strong non-gyrotropy also near the separatrix layer
and provide a refined criterion to identify an electron diffusion region
in the magnetotail. The good statistical significance of this work
for relatively small analysis areas reveals the gradual changes within
the fine structure of electron VDFs depending on their sampling site.
Title: Solar wind driven instability with non-Maxwellian distribution
functions
Authors: Ehsan, Z.; Poedts, S.; Vranjes, J.; Arshad, K.; Shah, H. A.;
Bourdin, P. A.
Bibcode: 2016AGUFMSH21D2558E
Altcode:
In plasmas with an electron drift current relative to static ions, ion
acoustic waves are subject to the kinetic instability. The instability
threshold however, when one quasi-neutral electron-ion plasma propagates
through another static target plasma, may be well below the ion
acoustic speed of the static plasma. Such a currentless instability
may frequently be driven by the solar wind when it permeates through
another plasma in space. Such kinetic instabilities were previously
studied in the framework of thermodynamically stable plasmas obeying
a Maxwellian behavior. Recently, it has become possible to construct
the distribution function from the empirical data, which is found to
deviate from the Maxwellian due to the presence of high energy tails
and shoulders in the profile of the distribution functions. Here we
study a situation where non-Maxwellian (Lorentzian or kappa) solar
wind plasma interacts with another relatively slow plasma, and then
excites a kinetic instability in the acoustic mode. As a special case,
we also discuss the presence of interstellar dust and discuss dispersion
properties and growth rates of ion/dust acoustic modes quantitatively.
Title: Firedrakeproject/Petsc: Portable, Extensible Toolkit For
Scientific Computation
Authors: Smith, Barry; Balay, Satish; Knepley, Matthew; Brown, Jed;
Curfman McInnes, Lois; Zhang, Hong; Brune, Peter; Sarich, Jason;
tisaac; stefanozampini; Dalcin, Lisandro; Karpeyev, Dmitry; markadams;
Minden, Victor; VictorEijkhout; vijaysm; Rupp, Karl; dmay23; Kong,
Fande; SurtaiHan; Lange, Michael; tmunson; Meiser, Dominic; Sanan,
Patrick; emconsta; Zhou, Xuan; baagaard-usgs; Mitchell, Lawrence;
bourdin; sozmen
Bibcode: 2016zndo....161513S
Altcode:
Version of Firedrake used in 'Vertical slice modelling of nonlinear
Eady waves using a compatible finite element method'. This release is
specifically created to document the version of Firedrake used in a
particular set of experiments. Please do not cite this as a general
source for Firedrake or any of its dependencies. Instead, refer to
http://www.firedrakeproject.org/publications.html
Title: Stable motions of charged dust grains subject to solar wind,
Poynting-Robertson drag, and the mean interplanetary magnetic field
Authors: Lhotka, Christoph; Bourdin, Philippe; Narita, Yasuhito
Bibcode: 2016DPS....4852101L
Altcode:
We investigate the combined effect of solar wind, Poynting-Robertson
drag, and the frozen-in interplanetary magnetic field on the motion
of charged dust grains in our solar system. It is generally accepted
that the combined effects of solar wind and photon absorption and
re-emmision (Poynting-Robertson drag) lead to a decrease in semi-major
axis on secular time scales. On the contrary, we demonstrate that
the interplanetary magnetic field may counteract these drag forces
under certain circumstances. We derive a simple relation between the
parameters of the magnetic field, the physical properties of the dust
grain as well as the shape and orientation of the orbital ellipse of
the particle, which is a necessary conditions for the stabilization
in semi-major axis.
Title: Firedrakeproject/Petsc: Portable, Extensible Toolkit For
Scientific Computation
Authors: Smith, Barry; Balay, Satish; Knepley, Matthew; Brown, Jed;
Curfman McInnes, Lois; Zhang, Hong; Brune, Peter; sarich; tisaac;
stefanozampini; Dalcin, Lisandro; Karpeyev, Dmitry; markadams; Minden,
Victor; VictorEijkhout; vijaysm; Rupp, Karl; dmay23; Kong, Fande;
SurtaiHan; Lange, Michael; Meiser, Dominic; emconsta; Sanan, Patrick;
Zhou, Xuan; baagaard; Mitchell, Lawrence; tmunson; sozmen; bourdin
Bibcode: 2016zndo....153972S
Altcode:
Version of Firedrake used in 'High level implementation of geometric
multigrid solvers for finite element problems: applications
in atmospheric modelling' This release is specifically created
to document the version of Firedrake used in a particular set
of experiments. Please do not cite this as a general source
for Firedrake or any of its dependencies. Instead, refer to
http://www.firedrakeproject.org/publications.html
Title: Charged Dust Grain Dynamics Subject to Solar Wind,
Poynting-Robertson Drag, and the Interplanetary Magnetic Field
Authors: Lhotka, Christoph; Bourdin, Philippe; Narita, Yasuhito
Bibcode: 2016ApJ...828...10L
Altcode: 2016arXiv160807040L
We investigate the combined effect of solar wind, Poynting-Robertson
drag, and the frozen-in interplanetary magnetic field on the motion of
charged dust grains in our solar system. For this reason, we derive
a secular theory of motion by the means of an averaging method and
validate it with numerical simulations of the unaveraged equations
of motions. The theory predicts that the secular motion of charged
particles is mainly affected by the z-component of the solar magnetic
axis, or the normal component of the interplanetary magnetic field. The
normal component of the interplanetary magnetic field leads to an
increase or decrease of semimajor axis depending on its functional
form and sign of charge of the dust grain. It is generally accepted
that the combined effects of solar wind and photon absorption and
re-emmision (Poynting-Robertson drag) lead to a decrease in semimajor
axis on secular timescales. On the contrary, we demonstrate that
the interplanetary magnetic field may counteract these drag forces
under certain circumstances. We derive a simple relation between the
parameters of the magnetic field, the physical properties of the dust
grain, as well as the shape and orientation of the orbital ellipse of
the particle, which is a necessary conditions for the stabilization
in semimajor axis.
Title: Effects from switching on PIC simulations: Geospace
Environmental Modeling (GEM) reconnection setup revisited
Authors: Bourdin, P. A.; Nakamura, T.; Narita, Y.
Bibcode: 2015AGUFMSH43A2438B
Altcode:
Electromagnetic Parcile-In-Cell (PIC) simulations are widely used
to study plasma phenomena where kinetic scales are coupled to
fluid scales. One of these phenomena is the evolution of magnetic
reconnection. Switch-on effects have been described earlier for
magneto-/hydrodynamic (MHD and HD) simulations, where oscillations
are ignited by the initial condition and the usual instantaneous
way of starting a simulation run. Here we revisit the GEM setup (a
Harris current sheet) and demonstrate the immediate generation of
oscillations propagating perpendicular to the magnetic shear layer
(in Bz). Also we show how these oscillations do not dissipate quickly
and will later be mode-converted to generate wave power, first in By,
much later also in Bx (pointing along the shear direction). One needs
to take care not to interpret these oscillations as physical wave
modes associated with the nature of reconnection. We propose a method
to prevent such switch-on effects from the beginning, that should be
considered for implementation in other PIC simulation codes as well.
Title: Rising coronal loops in a 3D-MHD model and the time evolution
of the magnetic topology of a solar active region
Authors: Bourdin, Philippe A.
Bibcode: 2015IAUGA..2257253B
Altcode:
Magnetic flux emergence from the photosphere into the solar atmosphere
has been observed to drive a magnetic field reconfiguration in the
corona, eventually resulting in plasma outbreaks. Currently it is under
discussion, at which rate this reconnection may happen and how the
magnetic energy is released, e.g. in short-lived intermittent heating
events (nanoflares) or in a more quasi-static diffusive manner leading
to persistent electric currents to be dissipated in the corona. To
address this question, we use the results of an observationally driven
3D-MHD model in order to study the time-evolution of the magnetic field,
that is otherwise inaccessible to observations. The model features
some EUV-bright coronal loops system that was observed to have similar
plasma flow dynamics along these loops. We find that typically such
loops are rising with a speed of about 2 km/s, which is consistent
with earlier studies of loops just entering the corona at its base. We
will demonstrate the influence on plasma flows along the loops due to
their rise. A statistical Doppler-shift analysis reveals that in the
typical case, such loops not only rise through the atmosphere, but also
often are asymmetrically heated. Due to the match to observations,
we conclude that the magnetic energy dissipation process we model,
which is Ohmic dissipation of currents that are induced by a field-line
braiding process in the photosphere, is sufficient to explain the
magnetic reconfiguration process in the corona and yields to realistic
reconnection rates on scales of about 250 km.
Title: Signal-noise separation based on self-similarity testing in
1D-timeseries data
Authors: Bourdin, Philippe A.
Bibcode: 2015IAUGA..2257225B
Altcode:
The continuous improvement of the resolution delivered by modern
instrumentation is a cost-intensive part of any new space- or
ground-based observatory. Typically, scientists later reduce the
resolution of the obtained raw-data, for example in the spatial,
spectral, or temporal domain, in order to suppress the effects of
noise in the measurements. In practice, only simple methods are used
that just smear out the noise, instead of trying to remove it, so that
the noise can nomore be seen. In high-precision 1D-timeseries data,
this usually results in an unwanted quality-loss and corruption of
power spectra at selected frequency ranges. Novel methods exist that
are based on non-local averaging, which would conserve much of the
initial resolution, but these methods are so far focusing on 2D or 3D
data. We present here a method specialized for 1D-timeseries, e.g. as
obtained by magnetic field measurements from the recently launched MMS
satellites. To identify the noise, we use a self-similarity testing and
non-local averaging method in order to separate different types of noise
and signals, like the instrument noise, non-correlated fluctuations in
the signal from heliospheric sources, and correlated fluctuations such
as harmonic waves or shock fronts. In power spectra of test data, we
are able to restore significant parts of a previously know signal from
a noisy measurement. This method also works for high frequencies, where
the background noise may have a larger contribution to the spectral
power than the signal itself. We offer an easy-to-use software tools
set, which enables scientists to use this novel technique on their
own noisy data. This allows to use the maximum possible capacity of
the instrumental hardware and helps to enhance the quality of the
obtained scientific results.
Title: Coronal and transition-region Doppler shifts of an active
region 3D-MHD model as indicator for the magnetic activity cycle of
solar-like stars
Authors: Bourdin, Philippe A.
Bibcode: 2015IAUGA..2257021B
Altcode:
For the Sun and solar-like stars, Doppler blueshifts are observed in the
hot corona, while in average redshifts are seen in the cooler transition
region layer below the corona. This clearly contradicts the idea of
a continuous flow-equilibrium starting from a star's atmosphere and
forming the stellar wind. To explain this, we implement a 3D-MHD model
of the solar corona above an observed active region and use an atomic
database to obtain the emission from the million Kelvin hot plasma. The
generated EUV-bright loops system from the model compares well to
the observed coronal loops. Therefore, we have access to realistic
plasma parameters, including the flow dynamics within the active region
core, and can derive total spectra as if we look the Sun as a star. We
compare the model spectra to actual statistical observations of the Sun
taken at different magnetic activity levels. We find characteristic
Doppler-shift statistics that can be used to identify the magnetic
activity state of the Sun and solar-like stars. This should help to
model the variability of such stars by inferring their activity level
from total spectra of coronal and transition-region emission lines.
Title: Coronal loops above an active region: Observation versus model
Authors: Bourdin, Philippe-A.; Bingert, Sven; Peter, Hardi
Bibcode: 2014PASJ...66S...7B
Altcode: 2014PASJ..tmp..113B; 2014arXiv1410.1216B
We conducted a high-resolution numerical simulation of the solar corona
above a stable active region. The aim is to test the field line braiding
mechanism for a sufficient coronal energy input. We also check the
applicability of scaling laws for coronal loop properties like the
temperature and density. Our 3D MHD model is driven from below by
Hinode observations of the photosphere, in particular a high-cadence
time series of line-of-sight magnetograms and horizontal velocities
derived from the magnetograms. This driving applies stress to the
magnetic field and thereby delivers magnetic energy into the corona,
where currents are induced that heat the coronal plasma by Ohmic
dissipation. We compute synthetic coronal emission that we directly
compare to coronal observations of the same active region taken by
Hinode. In the model, coronal loops form at the same places as they
are found in coronal observations. Even the shapes of the synthetic
loops in 3D space match those found from a stereoscopic reconstruction
based on STEREO spacecraft data. Some loops turn out to be slightly
over-dense in the model, as expected from observations. This shows that
the spatial and temporal distribution of the Ohmic heating produces
the structure and dynamics of a coronal loops system close to what is
found in observations.
Title: Standard 1D solar atmosphere as initial condition for MHD
simulations and switch-on effects
Authors: Bourdin, P. -A.
Bibcode: 2014CEAB...38....1B
Altcode: 2015arXiv150701218B
Many applications in Solar physics need a 1D atmospheric model as
initial condition or as reference for inversions of observational
data. The VAL atmospheric models are based on observations and are
widely used since decades. Complementary to that, the FAL models
implement radiative hydrodynamics and showed the shortcomings of the
VAL models since almost equally long time. In this work, we present a
new 1D layered atmosphere that spans not only from the photosphere to
the transition region, but from the solar interior up to far in the
corona. We also discuss typical mistakes that are done when switching
on simulations based on such an initial condition and show how the
initial condition can be equilibrated so that a simulation can start
smoothly. The 1D atmosphere we present here served well as initial
condition for HD and MHD simulations and should also be considered as
reference data for solving inverse problems.
Title: VizieR Online Data Catalog: 3D-MHD model of a solar active
region corona (Bourdin+, 2013)
Authors: Bourdin, P. -A.; Bingert, S.; Peter, H.
Bibcode: 2013yCat..35550123B
Altcode: 2013yCat..35559123B
Parameter and setup files used for a 3D-MHD simulation with the
Pencil Code. The parameters are needed to reproduce the simulation,
while the setup files show which modules of the Pencil Code were
used to conduct the simulation. The parameters file are in the
state as used at the end of the simulation, when the analysis was
performed. With the logfile, one can reconstruct the state at any
time during the simulation run (this applies to "run.in"). The
code revision logfile indicates which code revision was used when,
where only changes in the configuration are listed together with the
full initial and final configuration. All *.in files are in
Fortran Namelist format. The *.in and *.local files are all ready
to be used with Pencil Code. The Pencil Code can be obtained at:
http://pencil-code.nordita.org/ (7 data files).
Title: Coronal structure and dynamics above an active region -
MHD model versus observation
Authors: Bourdin, Philippe-A.; Bingert, Sven; Peter, Hardi
Bibcode: 2013enss.confE..56B
Altcode:
We present a one-to-one comparison between an observed active region
and a 3D MHD model including spectral synthesis. We set up the 3D MHD
model from the photosphere to the corona and use the actually observed
photospheric magnetograms and horizontal motions as a lower boundary
condition to drive the 3D coronal model. Following Parker's model for
field-line braiding this induces currents that are dissipated and heat
the corona. From the 3D MHD model we synthesize emission spectra in
EUV and X-rays that can be compared directly to the Hinode/EIS and XRT
observation of the active region we model. We find that the hot coronal
loops that form in the model occur at just the same places as they are
found in the actual observations. Moreover, their spatial structure
and the flows along the loops as seen in the synthesized intensity
and Doppler maps compare well to the actual observations. By this we
present the first coronal model driven by photospheric observations
that provides a one-to-one match to the coronal structure and dynamics
observed for that same active region. This shows that the distribution
of the energy input in time and space through the field-line braiding
is close to the real solar coronal energy deposition.
Title: Observationally driven 3D MHD model of the solar corona above
a magnetically active region
Authors: Bourdin, Philippe-André
Bibcode: 2013PhDT.......560B
Altcode:
No abstract at ADS