Author name code: opher
ADS astronomy entries on 2022-09-14
author:"Opher, Merav,"
------------------------------------------------------------------------
Title: Near-Earth Supernovae in the Past 10 Myr: Implications for
the Heliosphere
Authors: Miller, Jesse A.; Fields, Brian D.; Chen, Thomas Y.;
Ellis, John; Ertel, Adrienne F.; Manweiler, Jerry W.; Opher, Merav;
Provornikova, Elena; Slavin, Jonathan D.; Sokół, Justyna; Sterken,
Veerle; Surman, Rebecca; Wang, Xilu
Bibcode: 2022arXiv220903497M
Altcode:
We summarize evidence that multiple supernovae exploded within 100
pc of Earth in the past few Myr. These events had dramatic effects
on the heliosphere, compressing it to within ~20 au. We advocate
for cross-disciplinary research of nearby supernovae, including on
interstellar dust and cosmic rays. We urge for support of theory work,
direct exploration, and study of extrasolar astrospheres.
Title: To Boldly Go, Where No One Has Gone Before: Overview of the
Science Discoveries Enabled by an Interstellar Probe in the 2030's
Authors: Brandt, Pontus; Roelof, Edmond; Kurth, William; Provornikova,
Elena; Opher, Merav; McNutt, Ralph; Galli, Andre; Hill, Matthew; Wurz,
Peter; Bale, Stuart; Lisse, Carey; Kollmann, Peter; Demajistre, Robert;
Zemcov, Michael; Mandt, Kathleen; Rymer, Abi; Beichman, Charles;
Linsky, Jeffrey; Runyon, Kirby; Mostafavi, Parisa; Redfield, Seth;
Turner, Drew
Bibcode: 2022cosp...44.3194B
Altcode:
For the past 60, 000 years our Sun and its protective heliosphere
have been plowing through the Local Interstellar Cloud (LIC), but is
now in a historic transition region towards the G-cloud that could
have dramatic consequences for the global heliospheric structure. An
Interstellar Probe mission to the Very Local Interstellar Medium (VLISM)
would bring new scientific discoveries of the mechanisms upholding our
vast heliosphere and directly sample the Local Interstellar Clouds to
allow us, not only to understand the current dynamics and shielding,
but also how the heliosphere responded in the past and how it will
respond in the new interstellar environment. An international team
of scientists and experts have now completed a NASA-funded study led
by The Johns Hopkins University Applied Physics Laboratory (APL) to
develop pragmatic example mission concepts for an Interstellar Probe
with a nominal design lifetime of 50 years. The team has analyzed dozens
of launch configurations and demonstrated that asymptotic speeds in
excess of 7.5 Astronomical Units (AU) per year can be achieved using
existing or near-term propulsion stages with a powered or passive
Jupiter Gravity Assist (JGA). These speeds are more than twice that
of the fastest escaping man-made spacecraft to date, which is Voyager
1 currently at 3.59 AU/year. An Interstellar Probe would therefore
reach the Termination Shock (TS) in less than 12 years and cross
the Heliopause into the VLISM after about 16 years from launch. In
this presentation we provide an overview of the study, the science
mission concept, discuss the compelling discoveries that await, and
the associated example science payload, measurements and operations
ensuring a historic data return that would push the boundaries of
space exploration by going where no one has gone before.
Title: On the energization of pickup ions downstream of the
heliosheric termination shock, by comparing 0.52-55 keV observed
ENA spectra to simulated ENAs inferred by proton hybrid simulations.
Authors: Gkioulidou, Matina; Richardson, John; Mitchell, Donald; Opher,
Merav; Krimigis, Stamatios; Zank, Gary; Giacalone, Joe; Fuselier,
Stephen; Dialynas, Konstantinos; Baliukin, Igor; Kornbleuth, Marc;
Roussos, Elias; Gkioulidou, Matina
Bibcode: 2022cosp...44.1315G
Altcode:
As the solar system and its surrounding heliosphere move through the
local interstellar medium, interstellar neutral atoms, mostly atomic
Hydrogen, enter the heliosphere and undergo charge-exchange collisions
with the continuously flowing solar wind protons. Newly created
ions from the interstellar neutral population are advected outward
with the solar wind, forming a population that is commonly known as
pickup ions (PUIs). When PUIs reach the termination shock, they are
heated, with a fraction of their distribution being reflected off the
shock surface and undergoing additional heating. The heated PUIs that
populate the heliosheath (HS), charge-exchange with the interstellar
neutrals, creating Energetic Neutral Atoms (ENAs) that are measured
remotely by the Interstellar Boundary Explorer (IBEX; 0.01-6 keV)
and Cassini/Ion and Neutral Camera (INCA; 5.2-55 keV). Understanding
the PUI distribution in the heliosheath is essential in order to i)
study the pressure balance and acceleration mechanisms inside the
heliosheath, and ii) to determine the ENA emission from the heliosheath,
since these ENAs are used to remotely sense the boundaries of our
heliosphere and its interaction with the very local interstellar
medium. In this study, we present an unprecedented comparison of ~
0.52 - 55 keV Energetic Neutral Atom (ENA) heliosheath measurements,
remotely sensed by the Interstellar Boundary Explorer (IBEX) mission
and the Ion and Neutral Camera (INCA) on the Cassini mission, with
modeled ENA inferred from interstellar pickup protons that have been
accelerated at the termination shock using hybrid simulations, towards
assessing the PUI energetics within the heliosheath. This is the first
study to use hybrid simulations that are able to accurately model the
acceleration of ions to 10s of keV energies, which is essential in
order to model ENA fluxes in the heliosheath, covering the full energy
range observed by IBEX and CASSINI/INCA. The observed ENA intensities
are an average value over the time period from 2009 to the end of
2012, along the Voyager 2 trajectory. The hybrid simulations upstream
of the termination shock, where Voyager 2 crossed, are constrained
by observations. We report an energy dependent discrepancy between
observed and simulated ENA fluxes, with the observed ENA fluxes, being
persistently higher than the simulated ones. Our analysis reveals that
the termination shock may not accelerate pick up ions to sufficient
energies to account for the observed ENA fluxes. We, thus, suggest
that the further acceleration of these pick up ions is most likely
occurring within the heliosheath, via additional physical processes
like turbulence or magnetic reconnection. Yet, the redistribution of
energy inside the heliosheath remains an open question.
Title: Climate Change and Human Evolution from the Passage of the
Solar System through a Cold Cloud 2-3Myrs ago
Authors: Opher, Merav; Loeb, Abraham
Bibcode: 2022cosp...44.3203O
Altcode:
There is overwhelming geological evidence from 60Fe and 244Pu isotopes
that Earth was in direct contact with the interstellar medium (ISM)
2-3 Myr ago. The local interstellar medium is home to several nearby
cold clouds. Here we show that if the solar system passed through
a cloud such as Local Leo Cold Cloud, then the heliosphere which
protects the solar system from interstellar particles, had shrunk to
a scale smaller than the Earth's orbit around the Sun (0.22AU). Using
a magnetohydrodynamic simulation that includes charge exchange between
neutral atoms and ions, we show that during the heliosphere shrinkage,
Earth was exposed to a neutral hydrogen density of up to 3000cm-3. This
could have had drastic effects on Earth's climate and potentially of
human evolution at that time, as suggested by previous data.
Title: Considerations of the Global Heliopause Boundary Using
Macroscopic, Multipoint Voyager Observations in the Context of
Microscopic, Multipoint MMS Observations at Earth's Magnetopause
Authors: Turner, Drew; Provornikova, Elena; Opher, Merav; Hill,
Matthew; Brandt, Pontus; Lavraud, Benoit; Schwadron, Nathan; Eriksson,
Stefan; Kornbleuth, Marc; Cohen, Ian; Westlake, Joseph; Clark, George;
McComas, David; Mostafavi, Parisa; Michael, Adam
Bibcode: 2022cosp...44.1314T
Altcode:
Voyager-1 and -2 encountered a clear plasma boundary between the
solar-dominated heliosheath and the apparent very local interstellar
medium (VLISM) at heliocentric distances of 121.7 AU in August 2012 and
118.0 AU in November 2018, respectively. One intriguing mystery of the
Voyagers' crossings of the heliopause was that both spacecraft found
that the magnetic fields on either side of the boundary were generally
parallel to each other; that is, at both Voyager-1 and Voyager-2 in
their divergent crossing locations along the heliopause, the solar
magnetic field on the inside of the heliopause was essentially parallel
to the interstellar magnetic field on the outside of the heliopause. In
this study, we revisit these confounding and intriguing results
by putting observations of magnetic fields and energetic particles
at both Voyagers plus plasma data from Voyager-2 into context with
magnetic field, plasma, and energetic particle data from Magnetospheric
Multiscale (MMS) observations of crossings of Earth's magnetopause, an
analogous boundary between two distinct plasma environments. With this
combination of the two Voyagers as an enormous macroscope, providing
details of the plasma conditions at two disparate locations around the
upstream heliopause, alongside MMS observations as a precision "electron
microscope" at a different yet analogous boundary, we offer new insight
on interpretation of the Voyager observations. In particular, we address
the possibility of active magnetic reconnection along the heliopause and
implications considering IBEX results, NASA's upcoming IMAP mission, and
a future Interstellar Probe. Our results indicate that both Voyagers may
have crossed into an extended heliopause boundary layer resulting from
active reconnection between interstellar magnetic fields and the Sun's
interplanetary magnetic fields along the flanks of the heliopause. We
estimate that - because of a combination of long-temporal stability
of the interstellar magnetic field direction plus the extreme spatial
distances (100s of AU along the nose-side heliopause) and relatively
slow plasma speeds (advective flows and Alfvén speeds on the order
of ~20 to 40 km/s) - the reconnected boundary layer may extend as far
as several 10s of AU radially outward from the Voyagers' respective
crossing points. Furthermore, because of the steady, solar-westward
orientation of the magnetic field observed by the Voyagers in this
boundary layer, we offer a prediction about which quadrant of the
flank heliopause the reconnection occurred at for field lines mapping
to both Voyager spacecraft. In future work, these predictions should
be tested with state-of-the-art, global heliospheric models.
Title: Lys/STELLA: H Lyman Alpha Spectrograph for the Interstellar
Probe
Authors: Quemerais, Eric; Matta, Majd; Provornikova, Elena; Opher,
Merav; Clarke, John; Koutroumpa, Dimitra
Bibcode: 2022cosp...44.3207Q
Altcode:
The Interstellar Probe project gives an unprecedented opportunity
to study the hydrogen atom distribution from the interstellar medium
to the inner heliosphere. The solar H Lyman alpha emission (121.6nm)
is the brightest line in the UV range. Solar Lyman alpha photons are
backscattered by hydrogen atoms in the interplanetary medium producing
the interplanetary glow that extends far beyond the heliopause into
the interstellar medium. A Lyman alpha spectrograph will measure the
LISM H number density giving the first direct measurement of this
quantity just outside of the heliospheric interface. This value is
one of the critical parameters defining the size and behavior of the
heliospheric interace. With a high resolution spectrograph, it will
be possible to differentiate between the Lyman alpha galactic emission
derived from the UVS-Voyager data and the LISM H Lyman alpha emission
from the line of sight velocity of the atoms. Because of resonant
charge exchange between the hydrogen atoms and the protons, the H
atom distribution is strongly affected when the neutrals cross the
heliospheric interface region. H atoms created after charge exchange
keep the velocity distribution of the protons that they were created
from. Therefore, the backscattered Lyman alpha line profile will change
as the interstellar probe crosses through the inner heliosheath to
the outer heliosheath and then moves into the LISM, providing a test
on the proton distribution in the heliosphere regions crossed by the
interstellar probe. Here, we will present an instrumental design that
will allow for this study bringing new information on the heliospheric
interface and the very local interstellar medium.
Title: On the Energy Dependence of Galactic Cosmic Ray Anisotropies
in the Very Local Interstellar Medium
Authors: Nikoukar, Romina; Hill, Matthew E.; Brown, Lawrence; Kota,
Jozsef; Decker, Robert B.; Dialynas, Konstantinos; Hamilton, Douglas
C.; Krimigis, Stamatios M.; Lasley, Scott; Roelof, Edmond C.; Mitchell,
J. Grant; Florinski, Vladimir.; Giacalone, Joe.; Richardson, John;
Opher, Merav
Bibcode: 2022ApJ...934...41N
Altcode: 2022arXiv220107844N
We report on the energy dependence of Galactic cosmic rays (GCRs)
in the very local interstellar medium (VLISM) as measured by the
Low Energy Charged Particle (LECP) instrument on the Voyager 1
spacecraft. The LECP instrument includes a dual-ended solid-state
detector particle telescope mechanically scanning through 360° across
eight equally spaced angular sectors. As reported previously, LECP
measurements showed a dramatic increase in GCR intensities for all
sectors of the ≥211 MeV count rate (CH31) at the Voyager 1 heliopause
(HP) crossing in 2012; however, since then the count rate data have
demonstrated systematic episodes of intensity decrease for particles
around 90° pitch angle. To shed light on the energy dependence of
these GCR anisotropies over a wide range of energies, we use Voyager
1 LECP count rate and pulse height analyzer (PHA) data from ≥211
MeV channel together with lower-energy LECP channels. Our analysis
shows that, while GCR anisotropies are present over a wide range of
energies, there is a decreasing trend in the amplitude of second-order
anisotropy with increasing energy during anisotropy episodes. A stronger
pitch angle scattering at higher velocities is argued as a potential
cause for this energy dependence. A possible cause for this velocity
dependence arising from weak rigidity dependence of the scattering
mean free path and resulting velocity-dominated scattering rate is
discussed. This interpretation is consistent with a recently reported
lack of corresponding GCR electron anisotropies.
Title: Societal and Science Case For Inner Heliospheric Solar Wind
Constellation
Authors: Nykyri, Katariina; Balikhin, Michael A.; Wing, Simon; Opher,
Merav; Sibeck, David; Hesse, Michael; Ebert, Robert; Fuselier, Stephen;
Ma, Xuanye; Burkholder, Brandon; Parker, Jeffrey; Cuellar Rangel,
Roberto; Liou, Yu-Lun; Broll, Jeffrey; Wilder, Rick; Holland, Katherine
Bibcode: 2022cosp...44.1607N
Altcode:
The solar wind exhibits large-scale and mesoscale structures whose
presence and evolution directly affect Earth's space environment and
can impact key assets on and orbiting Earth. Phenomena such as coronal
mass ejections, co-rotating interaction regions, and interplanetary
shocks can have rapid and dramatic geospace effects via large-scale
fluctuations in the interplanetary magnetic field, plasma pressure
and density, and solar energetic particle (SEP) energization and
propagation. Satellite constellations at the Earth-Sun Lagrange 1
(L1) point can only provide solar wind plasma and magnetic field
measurements ~ 1 hr in advance of their arrival at Earth, limiting
our ability to forecast significant events and avoid technological
and societal disaster; the recent loss of 40 Starlink satellites due
to geomagnetic storm activity, for example, highlights the need for
1-2 day advanced space weather forecasts. To prepare our technological
society for the next decade and beyond, we need to have a network of
upstream spacecraft at various radial distances from Sun whose data
could be assimilated near real-time into space weather modeling. This
could be achieved by placing constellations at the Mercury, Venus and
Earth Lagrange points, which - with international collaboration is
possible over - the coming decades. As a first step, we propose the
first of its kind Pathfinder mission, placing spacecraft into Venus-Sun
Lagrange points to enable study of the physical processes responsible
for the large- to meso-scale plasma and magnetic structures in the
inner heliosphere and energetic particle dynamics. This mission will
provide the first in-situ, synchronized, multi-point magnetic field
and energetic particle measurements in a region only sparsely covered
by single-point measurements from flybys of sun- and Mercury-bound
missions since the end of Venus Express in 2014. When one or more
of the Venus-Sun Lagrange points lies sunward from the Earth and/or
further towards the west limb of the Sun, a coverage period of ~50
Days/Earth year, these observations would allow us to develop and
test space weather warning algorithms based on coronagraphs and
in-situ observations of the solar wind at L1; even when not in the
flight path of Earthward-bound solar wind, the multiscale nature of
the observations would provide key insight into the propagation and
evolution of solar wind structures.
Title: Correction to: Interstellar Neutrals, Pickup Ions, and
Energetic Neutral Atoms Throughout the Heliosphere: Present Theory
and Modeling Overview
Authors: Sokół, Justyna M.; Kucharek, Harald; Baliukin, Igor I.;
Fahr, Hans; Izmodenov, Vladislav V.; Kornbleuth, Marc; Mostafavi,
Parisa; Opher, Merav; Park, Jeewoo; Pogorelov, Nikolai V.; Quinn,
Philip R.; Smith, Charles W.; Zank, Gary P.; Zhang, Ming
Bibcode: 2022SSRv..218...25S
Altcode:
No abstract at ADS
Title: Terrestrial Impact from the Passage of the Solar System
through a Cold Cloud a Few Million Years Ago
Authors: Opher, Merav; Loeb, Abraham
Bibcode: 2022AAS...24022706O
Altcode:
It is expected that as the Sun travels through the interstellar medium
(ISM), there will be different filtration of Galactic Cosmic Rays
(GCR) that affect Earth. The effect of GCR on Earth's atmosphere and
climate is still uncertain. Although the interaction with molecular
clouds was previously considered, the terrestrial impact of compact
cold clouds was neglected. There is overwhelming geological evidence
from 60Fe and 244Pu isotopes that Earth was in
direct contact with the ISM 2-3 million years ago, and the local ISM
is home to several nearby cold clouds. Here we show, with a state-of
the art simulation that incorporate all the current knowledge about
the heliosphere that if the solar system passed through a cloud
such as Local Leo Cold Cloud, then the heliosphere which protects
the solar system from interstellar particles, must have shrunk to a
scale smaller than the Earth's orbit around the Sun (0.22 AU). Using
a magnetohydrodynamic simulation that includes charge exchange
between neutral atoms and ions, we show that during the heliosphere
shrinkage, Earth was exposed to a neutral hydrogen density of up to
3000 cm-3. This could have had drastic effects on Earth's
climate and potentially on human evolution at that time, as suggested
by existing data.
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: The Heliosphere and Local Interstellar Medium from Neutral
Atom Observations at Energies Below 10 keV
Authors: Galli, André; Baliukin, Igor I.; Bzowski, Maciej; Izmodenov,
Vladislav V.; Kornbleuth, Marc; Kucharek, Harald; Möbius, Eberhard;
Opher, Merav; Reisenfeld, Dan; Schwadron, Nathan A.; Swaczyna, Paweł
Bibcode: 2022SSRv..218...31G
Altcode:
As the heliosphere moves through the surrounding interstellar medium,
a fraction of the interstellar neutral helium, hydrogen, and heavier
species crossing the heliopause make it to the inner heliosphere as
neutral atoms with energies ranging from few eV to several hundred
eV. In addition, energetic neutral hydrogen atoms originating from solar
wind protons and from pick-up ions are created through charge-exchange
with interstellar atoms.
Title: On the Energization of Pickup Ions Downstream of the
Heliospheric Termination Shock by Comparing 0.52-55 keV Observed
Energetic Neutral Atom Spectra to Ones Inferred from Proton Hybrid
Simulations
Authors: Gkioulidou, Matina; Opher, M.; Kornbleuth, M.; Dialynas,
K.; Giacalone, J.; Richardson, J. D.; Zank, G. P.; Fuselier, S. A.;
Mitchell, D. G.; Krimigis, S. M.; Roussos, E.; Baliukin, I.
Bibcode: 2022ApJ...931L..21G
Altcode:
We present an unprecedented comparison of ~0.52-55 keV energetic neutral
atom (ENA) heliosheath measurements, remotely sensed by the Interstellar
Boundary Explorer (IBEX) mission and the Ion and Neutral Camera (INCA)
on the Cassini mission, with modeled ENAs inferred from interstellar
pickup protons that have been accelerated at the termination shock,
using hybrid simulations, to assess the pickup ion energetics within
the heliosheath. This is the first study to use hybrid simulations
that are able to accurately model the acceleration of ions to tens
of keV energies, which is essential in order to model ENA fluxes in
the heliosheath, covering the full energy range observed by IBEX and
CASSINI/INCA. The observed ENA intensities are an average value over
the time period from 2009 to the end of 2012, along the Voyager 2
(V2) trajectory. The hybrid simulations upstream of the termination
shock, where V2 crossed, are constrained by observations. We report
an energy-dependent discrepancy between observed and simulated ENA
fluxes, with the observed ENA fluxes being persistently higher than
the simulated ones. Our analysis reveals that the termination shock
may not accelerate pickup ions to sufficient energies to account
for the observed ENA fluxes. We, thus, suggest that the further
acceleration of these pickup ions is most likely occurring within
the heliosheath, via additional physical processes like turbulence or
magnetic reconnection. However, the redistribution of energy inside
the heliosheath remains an open question.
Title: The Structure of the Large-Scale Heliosphere as Seen by
Current Models
Authors: Kleimann, Jens; Dialynas, Konstantinos; Fraternale, Federico;
Galli, André; Heerikhuisen, Jacob; Izmodenov, Vladislav; Kornbleuth,
Marc; Opher, Merav; Pogorelov, Nikolai
Bibcode: 2022SSRv..218...36K
Altcode:
This review summarizes the current state of research aiming at a
description of the global heliosphere using both analytical and
numerical modeling efforts, particularly in view of the overall
plasma/neutral flow and magnetic field structure, and its relation
to energetic neutral atoms. Being part of a larger volume on current
heliospheric research, it also lays out a number of key concepts
and describes several classic, though still relevant early works
on the topic. Regarding numerical simulations, emphasis is put on
magnetohydrodynamic (MHD), multi-fluid, kinetic-MHD, and hybrid modeling
frameworks. Finally, open issues relating to the physical relevance of
so-called "croissant" models of the heliosphere, as well as the general
(dis)agreement of model predictions with observations are highlighted
and critically discussed.
Title: Thank You to Our 2021 Peer Reviewers
Authors: Rajaram, Harihar; Camargo, Suzana; Cappa, Christopher D.;
Carey, Rebecca; Cory, Rose M.; Dombard, Andrew J.; Donohue, Kathleen
A.; Flesch, Lucy; Giannini, Alessandra; Gu, Yu; Huber, Christian;
Ivanov, Valeriy; Korte, Monika; Lu, Gang; Morlighem, Mathieu;
Magnusdottir, Gudrun; Opher, Merav; Patricola, Christina M.; Prieto,
Germán. A.; Qiu, Bo; Su, Hui; Sun, Daoyuan; Thornton, Joel A.; Wang,
Kaicun; Whalen, Caitlin; White, Angelicque E.; Williams, Quentin;
Yau, Andrew
Bibcode: 2022GeoRL..4998947R
Altcode:
No abstract at ADS
Title: Interstellar Neutrals, Pickup Ions, and Energetic Neutral
Atoms Throughout the Heliosphere: Present Theory and Modeling Overview
Authors: Sokół, Justyna M.; Kucharek, Harald; Baliukin, Igor I.;
Fahr, Hans; Izmodenov, Vladislav V.; Kornbleuth, Marc; Mostafavi,
Parisa; Opher, Merav; Park, Jeewoo; Pogorelov, Nikolai V.; Quinn,
Philip R.; Smith, Charles W.; Zank, Gary P.; Zhang, Ming
Bibcode: 2022SSRv..218...18S
Altcode:
Interstellar neutrals (ISNs), pick-up ions (PUIs), and energetic
neutral atoms (ENAs) are fundamental constituents of the heliosphere
and its interaction with the neighboring interstellar medium. Here, we
focus on selected aspects of present-day theory and modeling of these
particles. In the last decades, progress in the understanding of the
role of PUIs and ENAs for the global heliosphere and its interaction
with very local interstellar medium is impressive and still growing. The
increasing number of measurements allows for verification and continuing
development of the theories and model attempts. We present an overview
of various model descriptions of the heliosphere and the processes
throughout it including the kinetic, fluid, and hybrid solutions. We
also discuss topics in which interplay between theory, models, and
interpretation of measurements reveals the complexity of the heliosphere
and its understanding. They include model-based interpretation of the
ISN, PUI, and ENA measurements conducted from the Earth's vicinity. In
addition, we describe selected processes beyond the Earth's orbit up to
the heliosphere boundary regions, where PUIs significantly contribute
to the complex system of the global heliosphere and its interaction
with the VLISM.
Title: Terrestrial Impact from the Passage of the Solar System
through a Cold Cloud a Few Million Years Ago
Authors: Opher, Merav; Loeb, Abraham
Bibcode: 2022arXiv220201813O
Altcode:
It is expected that as the Sun travels through the interstellar medium
(ISM), there will be different filtration of Galactic Cosmic Rays (GCR)
that affect Earth. The effect of GCR on Earth's atmosphere and climate
is still uncertain. Although the interaction with molecular clouds was
previously considered, the terrestrial impact of compact cold clouds
was neglected. There is overwhelming geological evidence from 60Fe and
244Pu isotopes that Earth was in direct contact with the ISM 2 million
years ago, and the local ISM is home to several nearby cold clouds. Here
we show, with a state-of the art simulation that incorporate all the
current knowledge about the heliosphere that if the solar system passed
through a cloud such as Local Leo Cold Cloud, then the heliosphere which
protects the solar system from interstellar particles, must have shrunk
to a scale smaller than the Earth's orbit around the Sun (0.22). Using
a magnetohydrodynamic simulation that includes charge exchange between
neutral atoms and ions, we show that during the heliosphere shrinkage,
Earth was exposed to a neutral hydrogen density of up to 3000cm-3. This
could have had drastic effects on Earth's climate and potentially on
human evolution at that time, as suggested by existing data.
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: Using Magnetic Flux Conservation to Determine Heliosheath
Speeds
Authors: Richardson, John; Cummings, Alan; Burlaga, Leonard; Giacalone,
Joe; Opher, Merav; Stone, Edward
Bibcode: 2021AGUFMSH25C2104R
Altcode:
The heliosheath (HSH) speeds at Voyager 2 (V2) derived from the plasma
instrument (PLS) and from particle instruments using the Compton-Getting
(CG) effect are very different. At V2 the CG speeds are more variable
than the plasma speeds and decrease about two years before the
heliopause. We use magnetic flux conservation to differentiate between
these two speed profiles at V2, comparing the magnetic flux observed
at 1 AU and in the HSH. For V2 the PLS speed profile is significantly
more consistent with magnetic flux conservation than the CG speeds. For
Voyager 1 (V1), we present new VR derivations from the cosmic ray
subsystem (CRS) using the CG method that agree reasonably well with
those previously obtained from the low energy charged particle (LECP)
instrument. If we use the V2 PLS speed profile to calculate the magnetic
flux at V1, we again find much better agreement than if we use the V1
CG speeds. These results suggest that the radial speeds derived from
particle anisotropy observations in the HSH may not be reliable.
Title: A Turbulent Heliosheath Driven by the Rayleigh-Taylor
Instability
Authors: Opher, M.; Drake, J. F.; Zank, G.; Powell, E.; Shelley, W.;
Kornbleuth, M.; Florinski, V.; Izmodenov, V.; Giacalone, J.; Fuselier,
S.; Dialynas, K.; Loeb, A.; Richardson, J.
Bibcode: 2021ApJ...922..181O
Altcode:
The heliosphere is the bubble formed by the solar wind as it interacts
with the interstellar medium (ISM). The collimation of the heliosheath
(HS) flows by the solar magnetic field in the heliotail into distinct
north and south columns (jets) is seen in recent global simulations
of the heliosphere. However, there is disagreement between the
models about how far downtail the two-lobe feature persists and
whether the ambient ISM penetrates into the region between the two
lobes. Magnetohydrodynamic simulations show that these heliospheric jets
become unstable as they move down the heliotail and drive large-scale
turbulence. However, the mechanism that produces this turbulence had
not been identified. Here we show that the driver of the turbulence
is the Rayleigh-Taylor (RT) instability produced by the interaction
of neutral H atoms streaming from the ISM with the ionized matter in
the HS. The drag between the neutral and ionized matter acts as an
effective gravity, which causes an 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 timescale 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 maps from
future missions such as the Interstellar Mapping and Acceleration Probe
(IMAP). The turbulence driven by the instability is macroscopic and
potentially has important implications for particle acceleration.
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: 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: 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: Modeling Galactic Cosmic Rays in the Very Local Interstellar
Medium
Authors: Florinski, Vladimir; le Roux, Jakobus; Opher, Merav; Kleimann,
Jens; Ghanbari, Keyvan
Bibcode: 2021AGUFMSH31B..04F
Altcode:
The very local interstellar medium (VLISM) presents significant
challenges for energetic particle modeling because of the presence of
both incompressible and compressive turbulent magnetic fluctuations (in
the sense of the presence of the magnetic fluctuation component parallel
to the mean field) that makes it a very distinct transport environment
compared with the more familiar solar wind. This paper presents a
pitch-angle dependent diffusive transport model in two-dimensional,
compressive turbulence, and a framework for computer modeling of charged
particles with high velocities applicable to galactic cosmic rays
(GCRs). The model elaborates on existing weakly nonlinear theories of
perpendicular diffusion in the limit of weak pitch-angle scattering
combined with possibly rapid diffusive motion of the guiding center
normal to the magnetic field. The numerical framework is based in the
SPECTRUM (Space Plasma and Energetic Charged particle TRansport on
Unstructured Meshes) suite of simulation codes. Two representative
simulations are presented. The first is a high-resolution study of
GCR transport in the VLISM region with a particular emphasis on the
distribution of the heliopause crossing points. This model uses an
analytic formalism for the magnetic field draping around the hsurface of
the heliopause. The second case is a simulation of GCRs in a mesh-based
representation of the heliosphere derived from MHD simulations converged
to a steady state, developed for the SHIELD project. The results are
discussed in the context of the earlier model based on the nearly
isotropic (Parker) formalism.
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: Interplanetary Hydrogen Properties as Probes into the
Heliospheric Interface
Authors: Mayyasi, Majd; Clarke, John; Quemerais, Eric; Katushkina,
Olga; Izmodenov, Vladislav; Provornikova, Elena; Sokol, Justyna;
Brandt, Pontus; Galli, Andre; Opher, Merav; Kornbleuth, Marc; Linsky,
Jeffrey; Wood, Brian
Bibcode: 2021AGUFMSH15F2069M
Altcode:
A NASA sponsored study conducted at John Hopkins University Applied
Physics Lab culminated in a community-inspired heliospheric mission
concept called the Interstellar Probe (ISP). The ISP's science goals
include understanding our habitable astrosphere by investigating
its interactions with the interstellar medium, and determining the
structure, composition, and variability of its constituents. A suite
of instruments were proposed to achieve these and other science
objectives. The instruments include a Lyman-a spectrograph for
velocity-resolved measurements of neutral H atoms. The capability to
address key components of the ISP's science objectives by utilizing
high spectral resolution Lyman-a measurements are described in this
presentation. These findings have been submitted as a community White
Paper to the recent Heliophysics decadal survey.
Title: Signature of a Heliotail Organized by the Solar Magnetic
Field and the Role of Nonideal Processes in Modeled IBEX ENA Maps:
A Comparison of the BU and Moscow MHD Models
Authors: Kornbleuth, M.; Opher, M.; Baliukin, I.; Dayeh, M. A.;
Zirnstein, E.; Gkioulidou, M.; Dialynas, K.; Galli, A.; Richardson,
J. D.; Izmodenov, V.; Zank, G. P.; Fuselier, S.
Bibcode: 2021ApJ...921..164K
Altcode: 2021arXiv211013965K
Energetic neutral atom (ENA) models typically require post-processing
routines to convert the distributions of plasma and H atoms into ENA
maps. Here we investigate how two kinetic-MHD models of the heliosphere
(the BU and Moscow models) manifest in modeled ENA maps using the
same prescription and how they compare with Interstellar Boundary
Explorer (IBEX) observations. Both MHD models treat the solar wind as
a single-ion plasma for protons, which include thermal solar wind ions,
pick-up ions (PUIs), and electrons. Our ENA prescription partitions the
plasma into three distinct ion populations (thermal solar wind, PUIs
transmitted and ones energized at the termination shock) and models the
populations with Maxwellian distributions. Both kinetic-MHD heliospheric
models produce a heliotail with heliosheath plasma that is organized by
the solar magnetic field into two distinct north and south columns that
become lobes of high mass flux flowing down the heliotail; however,
in the BU model, the ISM flows between the two lobes at distances
in the heliotail larger than 300 au. While our prescription produces
similar ENA maps for the two different plasma and H atom solutions at
the IBEX-Hi energy range (0.5-6 keV), the modeled ENA maps require a
scaling factor of ~2 to be in agreement with the data. This problem
is present in other ENA models with the Maxwellian approximation of
multiple ion species and indicates that either a higher neutral density
or some acceleration of PUIs in the heliosheath is required.
Title: Using Magnetic Flux Conservation to Determine Heliosheath
Speeds
Authors: Richardson, J. D.; Cummings, A. C.; Burlaga, L. F.; Giacalone,
J.; Opher, M.; Stone, E. C.
Bibcode: 2021ApJ...919L..28R
Altcode:
The heliosheath (HSH) radial speeds at Voyager 2 (V2) derived from
the plasma instrument (PLS) and from particle instruments using the
Compton-Getting (CG) effect are different. At V2 the CG speeds are
more variable than the plasma speeds and decrease about 2 yr before the
heliopause. We use magnetic flux conservation to differentiate between
these two speed profiles at V2, comparing the magnetic flux observed
at 1 au and in the HSH. For V2 the PLS speed profile is significantly
more consistent with magnetic flux conservation than the CG speeds. For
Voyager 1 (V1), we present new VR derivations from the
Cosmic Ray Subsystem (CRS) using the CG method that agree reasonably
well with those previously obtained from the low energy charged particle
(LECP) instrument. If we use the V2 PLS speed profile to calculate the
magnetic flux at V1, we again find much better agreement than if we use
the V1 CG speeds. These results suggest that the radial speeds derived
from particle anisotropy observations in the HSH are not reliable.
Title: Energetic Neutral Atom Fluxes from the Heliosheath: Constraints
from in situ Measurements and Models
Authors: Fuselier, S. A.; Galli, A.; Richardson, J. D.; Reisenfeld,
D. B.; Zirnstein, E. J.; Heerikhuisen, J.; Dayeh, M. A.; Schwadron,
N. A.; McComas, D. J.; Elliott, H. A.; Gomez, R. G.; Starkey, M. J.;
Kornbleuth, M. Z.; Opher, M.; Dialynas, K.
Bibcode: 2021ApJ...915L..26F
Altcode:
Voyager 2 observations throughout the heliosheath from the termination
shock to the heliopause are used to normalize and constrain model pickup
ion (PUI) fluxes. Integrating normalized PUI fluxes along the Voyager
2 trajectory through the heliosheath, and combining these integral
fluxes with the energy-dependent charge-exchange cross section and
the neutral hydrogen density, produces semi-empirical estimates of
the energetic neutral atom (ENA) fluxes from the heliosheath. These
estimated ENA fluxes are compared with observed ENA fluxes from the
Interstellar Boundary Explorer (IBEX) to determine what percentage of
the observed fluxes at each IBEX energy are from the heliosheath. These
percentages are a maximum of ~10% for most energies and depend strongly
on termination shock properties, plasma density, bulk plasma flow
characteristics, the shape of the heliopause, and turbulent energy
diffusion in the heliosheath.
Title: Thank You to Our 2020 Peer Reviewers
Authors: Rajaram, Harihar; Camargo, Suzana; Cappa, Christopher; Carey,
Rebecca; Cory, Rose; Dombard, Andrew; Donohue, Kathleen; Flesch,
Lucy; Giannini, Alessandra; Gu, Yu; Hayes, Gavin; Hogg, Andrew; Huber,
Christian; Ivanov, Valeriy; Jacobsen, Steven; Korte, Monika; Lu, Gang;
Morlighem, Mathieu; Magnusdottir, Gudrun; Opher, Merav; Patricola,
Christina; Prieto, Germán.; Qiu, Bo; Ritsema, Jeroen; Sprintall,
Janet; Su, Hui; Sun, Daoyuan; Thornton, Joel; Trouet, Valerie; Wang,
Kaicun; Whalen, Caitlin; White, Angelicque; Yau, Andrew
Bibcode: 2021GeoRL..4893126R
Altcode:
No abstract at ADS
Title: Hybrid Simulations of Interstellar Pickup Protons Accelerated
at the Solar-wind Termination Shock at Multiple Locations
Authors: Giacalone, J.; Nakanotani, M.; Zank, G. P.; Kòta, J.; Opher,
M.; Richardson, J. D.
Bibcode: 2021ApJ...911...27G
Altcode:
We estimate the intensity of interstellar pickup protons accelerated
to ∼50 keV at various locations along the solar-wind termination
shock, using two-dimensional hybrid simulations. Parameters for the
solar wind, interstellar pickup ions (PUIs), and magnetic field just
upstream of the termination shock at one flank of the heliosphere,
and at the location in the downwind (or tail-ward) direction are based
on a solar-wind/pickup-ion/turbulence model. The parameters upstream
of the shock where Voyager 2 crossed are based on observations. The
simulation is limited in size, and therefore cannot accurately model
the distribution to energies much beyond ∼50 keV. This is sufficient
to study the origin of the high-energy tail of the distribution, which
is the low-energy portion of the anomalous cosmic-ray spectrum. We
also extrapolate our results to other locations along the termination
shock, such as the other flank, and the poles of the heliosphere. We
find that the intensity of ∼10-50 keV accelerated pickup protons is
remarkably similar at all three locations we simulated, suggesting that
particles in this energy range are relatively uniformly distributed
along the termination shock, and are likely quite uniform throughout
the entire heliosheath. In addition, we find significant differences in
the distribution in the 0.5-1 keV energy range for energetic neutral
atoms coming from the tail region of the heliosphere compared to that
at the nose or flank look directions. This is because the peak in the
PUI distribution is at a higher energy there.
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: Energy Dependence of GCR Anisotropies in the VLISM
Authors: Nikoukar, Romina; Richardson, John; Roelof, Edmond; Opher,
Merav; Krimigis, Stamatios; Hamilton, Doug C.; Hill, Matthew;
Florinski, Vladimir; Decker, Robert; Kota, Jozsef; Giacalone, Joe;
Dialynas, Konstantinos; Brown, Lawrence
Bibcode: 2021cosp...43E.865N
Altcode:
As part of the SHIELD center, in this work we report on the energy
dependence of galactic cosmic rays (GCRs) in the very local interstellar
medium (VLISM) as measured by the Low Energy Charged Particle (LECP)
instruments on the Voyager 1 and 2 spacecraft (V1 and V2). The LECP
instruments include a dual-ended telescope mechanically scanning through
360° over eight equally-spaced angular sectors. The LECP telescope
detects charged particles having energies from a few MeV up to GCR
energies (>= ~100 MeV). As expected, LECP measurements showed a
dramatic increase in GCR intensities for all sectors of the >=210 MeV
LECP count rate (CH31) at the V1 heliopause crossing in 2012, however,
since then the count rate data have demonstrated systematic episodes
of intensity decrease for particles around 90° pitch angle. To shed
light on the energy dependence of GCR anisotropies over a wide range
of energies we use V1 and V2 CH31 pulse height analyzer (PHA) data,
which allows us to divide the overall CH31 data into multiple smaller
energy ranges, together with lower energy LECP channels. Our preliminary
analysis shows that GCR anisotropies are present over a wide range of
energies, and the magnitude of the anisotropies vary as a function of
energies. The results of our analysis are used to place observational
constraints that test existing theories or help develop new theories.
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: 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: Combined ∼10 eV to ∼344 MeV Particle Spectra and Pressures
in the Heliosheath along the Voyager 2 Trajectory
Authors: Dialynas, Konstantinos; Galli, Andre; Dayeh, Maher A.;
Cummings, Alan C.; Decker, Robert B.; Fuselier, Stephen A.; Gkioulidou,
Matina; Roussos, Elias; Krimigis, Stamatios M.; Mitchell, Donald G.;
Richardson, John D.; Opher, Merav
Bibcode: 2020ApJ...905L..24D
Altcode:
We report a unique combination of ∼10 eV to ∼344 MeV in situ
ion measurements from the Plasma Science (PLS), Low Energy Charged
Particle (LECP), and Cosmic Ray Subsystem (CRS) experiments on the
Voyager 2 (V2) spacecraft, and remotely sensed ∼110 eV to ∼55
keV energetic neutral atom (ENA) measurements from the Interstellar
Boundary Explorer (IBEX) mission and Ion and Neutral Camera (INCA)
on the Cassini mission. This combination is done over the time period
from 2009 to the end of 2016, along the V2 trajectory, toward assessing
the properties of the ion energy spectra inside the heliosheath. The
combined energy spectra exhibit a series of softening and hardening
breaks, providing important insights on the various ion acceleration
processes inside the heliosheath. Ions in the <6 keV energy range
dominate the total pressure distribution inside the heliosheath but
the ion distributions at higher energies (>5.2 keV) provide a
significant contribution to the total pressure. With the assumption
that all ENAs (∼110 eV to 55 keV) are created by charge-exchange
interactions inside the heliosheath, we estimate that the magnetic
field upstream at the heliopause required to balance the pressure from
the heliosheath in the direction of V2 is ∼0.67 nT. This number is
consistent with the measured magnetic field at V2 from 2018 November,
when the spacecraft entered interstellar space.
Title: SIHLA , a Mission of Opportunity to L1 to Map H Lyman Alpha
Emissions from the Heliopause, the Interplanetary Medium, the Earth's
Geocorona and Comets
Authors: Paxton, L. J.; Provornikova, E.; Roelof, E. C.; Quemerais,
E.; Izmodenov, V.; Katushkina, O. A.; Mierkiewicz, E. J.; Baliukin, I.;
Gruntman, M.; Taguchi, M.; Pryor, W. R.; Mayyasi, M.; Koutroumpa, D.;
Opher, M.; Lallement, R.; Barjatya, A.; Vervack, R. J., Jr.; Lisse,
C. M.; Schaefer, R. K.; Barnes, R. J.; Wood, B. E.
Bibcode: 2020AGUFMSH040..03P
Altcode:
SIHLA (Spatial/Spectral Imaging of Heliospheric Lyman Alpha pronounced
as `Scylla' [e.g. Homer, Odyssey, ~675-725 BCE] investigates fundamental
physical processes that determine the interaction of the Sun with the
interstellar medium (ISM); the Sun with the Earth; and the Sun with
comets and their subsequent evolution. To accomplish these goals,
SIHLA studies the shape of the heliosphere and maps the solar wind in
3D; characterizes changes in Earth's extended upper atmosphere (the
hydrogen `geocorona'); discovers new comets and tracks the composition
changes of new and known ones as they pass near the Sun. SIHLA
is a NASA Mission of Opportunity that has just completed its Phase A
study (the Concept Study Report or CSR). At the time of the writing of
this abstract NASA has not decided whether to fly this small satellite
mission or its competitor (GLIDE: PI Prof. Lara Waldrop). SIHLA observes
the ion-neutral interactions of hydrogen, the universe's most abundant
element, from the edge of the solar system to the Earth, to understand
the fundamental properties that shaped our own home planet Earth and
the heliosphere. From its L1 vantage point, well outside the Earth's
obscuring geocoronal hydrogen cloud, SIHLA maps the entire sky using
a flight-proven, compact, far ultraviolet (FUV) hyperspectral imager
with a Hydrogen Absorption Cell (HAC). The hyperspectral scanning
imaging spectrograph (SIS) in combination with the spacecraft roll,
creates 4 maps >87% of the sky each day, at essentially monochromatic
lines over the entire FUV band (115 to 180nm) at every point in the
scan. During half of these daily sky maps, the hydrogen absorption
cell (HAC) provides a 0.001nm notch rejection filter for the H Lyman a
. Using the HAC, SIHLA builds up the lineshape profile of the H Lyman
a emissions over the course of a year. SIHLA's SIS/HAC combination
enables us to image the result of the ion-neutral interactions in the
heliosheath, 100 AU away, in the lowest energy, highest density, part
of the neutral atom spectrum - H atoms with energies below 10eV. The novel aspects of SIHLA are the scope of the science done within
a MoO budget. The SIHLA projected costs were below the $75M cap with a
31.3% reserve for Phase B-D. The re-purposing of a spectrographic that
was part of the DMSP SSUSI line (a copy was flown and NASA TIMED/GUVI
and as NASA NEAR/NIS). Risk is extremely low in this Class-D mission
with all major elements at least at TRL6 at this time. SIHLA
has a high potential for discovery. We expect that we will 1) First
detection of the hot H atoms produced directly from the ion-neutral
interactions at the heliopause; 2) First detection of structures in
Interplanetary Medium H emission, 3) First detection of response of the
Earth's extended (out to lunar orbit) geocorona to solar/geomagnetic
drivers, 4) New UV-bright comets as they enter the inner solar system.
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: 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: Structure of the Heliosphere and Heliotail from different
MHD models as Probed by ENA maps
Authors: Opher, M.
Bibcode: 2020AGUFMSH027..04O
Altcode:
The canonical view of the shape of the heliosphere until recently was
that it has a long comet-like tail. This view is being challenged and
it is now debated whether the heliosphere has a long comet-like shape,
has a bubble shape, or has a "croissant"-like shape and these options
are being investigated prompted through observations and modeling. One direct way to probe the structure of the heliotail is through
energetic neutral atom (ENA) maps. These ENAs have been observed by
the Interstellar Boundary Explorer (IBEX) at energies of 0.5-6 keV
by the IBEX-Hi instrument and show a multi-lobe structure. These
lobes were interpreted as signatures of slow and fast wind within a
long heliospheric tail as part of the 11-year solar cycle (McComas
et al. 2013; Zirnstein et al. 2017). In contrast, higher energy ENAs
observed by CASSINI suggest that the heliosphere is round (Dialynas
et al. 2017). Opher et al. (2015) suggest that the heliosphere
has two lobes (is "croissant"-like). They extend their global 3D
MHD model to treat thermal plasma and pickup ions as separate fluids
and show that this treatment deflates the heliosphere leading to a
smaller and rounder shape (Opher et al. 2020). Izmodenov et al. 2020
argue for confinement but in a long extended tail. Regardless of
the shape of the heliotail, the models agree that the solar magnetic
field in the inner heliosheath has a "slinky" structure (Opher et
al. 2015; Pogorelov et al. 2015; Izmodenov et al. 2015) that confines
the heliosphere plasma. In this work, as part of the recently
funded SHIELD (Solar-wind with Hydrogen Ion Exchange and Large-scale
Dynamics ) center which is now in Phase I, we revisit two different
MHD models (Izmodenov et al. 2018; Opher et al. 2020) and explore how
the different physical assumptions manifest in ENA maps. We comment
as well on how the conditions ahead of the heliosphere in the VLISM
are different in the two models.
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: The Downwind Solar Wind: Model Comparison with Pioneer 10
Observations
Authors: Nakanotani, M.; Zank, G. P.; Adhikari, L.; Zhao, L. -L.;
Giacalone, J.; Opher, M.; Richardson, J. D.
Bibcode: 2020ApJ...901L..23N
Altcode:
The solar wind in the upwind region has been well modeled using a
pickup ion (PUI) mediated MHD model (Zank et al.). It suggests that
PUIs have an important role in heating the solar wind in the outer
heliosphere. However, the solar wind in the downwind region is not as
well understood. Here, we compare the Zank et al. model with Pioneer
10 observations, which allows us to investigate the downwind solar
wind out to 60 au. We use a model in which the hydrogen temperature
is finite to obtain a proper hydrogen number density distribution in
the downwind region and incorporate it into the model. Our results
explain Pioneer 10 observations well and indicate that the heating
due to PUIs is less effective than in the upwind region since the
density of PUIs in the downwind region is less than the upwind PUIs
density. We also derive parameters at several possible locations of
the downwind termination shock.
Title: Thank You to Our 2019 Peer Reviewers
Authors: Rajaram, Harihar; Camargo, Suzana; Carey, Rebecca; Corey, Rose
M.; Dombard, Andrew J.; Donohue, Kathleen A.; Flesch, Lucy; Giannini,
Alessandra; Hayes, Gavin; Huber, Christian; Hogg, Andy M.; Ivanov,
Valeriy; Jacobsen, Steven D.; Korte, Monika; Lu, Gang; Morlighem,
Mathieu; Magnusdottir, Gudrun; Opher, Merav; Patricola, Christina M.;
Ritsema, Jeroen; Sprintall, Janet; Su, Hui; Thornton, Joel A.; Trouet,
Valerie; Wang, Kaicun; White, Angelicque E.; Yau, Andrew
Bibcode: 2020GeoRL..4788048R
Altcode:
On behalf of the journal, AGU, and the scientific community, the editors
would like to sincerely thank those who reviewed the manuscripts for
Geophysical Research Letters in 2019. The hours reading and commenting
on manuscripts not only improve the manuscripts but also increase
the scientific rigor of future research in the field. We particularly
appreciate the timely reviews in light of the demands imposed by the
rapid review process at Geophysical Research Letters. With the revival
of the "major revisions" decisions, we appreciate the reviewers'
efforts on multiple versions of some manuscripts. With the advent of
AGU's data policy, many reviewers have helped immensely to evaluate the
accessibility and availability of data associated with the papers they
have reviewed, and many have provided insightful comments that helped
to improve the data presentation and quality. We greatly appreciate
the assistance of the reviewers in advancing open science, which
is a key objective of AGU's data policy. Many of those listed below
went beyond and reviewed three or more manuscripts for our journal,
and those are indicated in italics.
Title: Major Scientific Challenges and Opportunities in Understanding
Magnetic Reconnection and Related Explosive Phenomena in Solar and
Heliospheric Plasmas
Authors: Ji, H.; Karpen, J.; Alt, A.; Antiochos, S.; Baalrud, S.;
Bale, S.; Bellan, P. M.; Begelman, M.; Beresnyak, A.; Bhattacharjee,
A.; Blackman, E. G.; Brennan, D.; Brown, M.; Buechner, J.; Burch, J.;
Cassak, P.; Chen, B.; Chen, L. -J.; Chen, Y.; Chien, A.; Comisso,
L.; Craig, D.; Dahlin, J.; Daughton, W.; DeLuca, E.; Dong, C. F.;
Dorfman, S.; Drake, J.; Ebrahimi, F.; Egedal, J.; Ergun, R.; Eyink,
G.; Fan, Y.; Fiksel, G.; Forest, C.; Fox, W.; Froula, D.; Fujimoto,
K.; Gao, L.; Genestreti, K.; Gibson, S.; Goldstein, M.; Guo, F.; Hare,
J.; Hesse, M.; Hoshino, M.; Hu, Q.; Huang, Y. -M.; Jara-Almonte, J.;
Karimabadi, H.; Klimchuk, J.; Kunz, M.; Kusano, K.; Lazarian, A.; Le,
A.; Lebedev, S.; Li, H.; Li, X.; Lin, Y.; Linton, M.; Liu, Y. -H.;
Liu, W.; Longcope, D.; Loureiro, N.; Lu, Q. -M.; Ma, Z-W.; Matthaeus,
W. H.; Meyerhofer, D.; Mozer, F.; Munsat, T.; Murphy, N. A.; Nilson,
P.; Ono, Y.; Opher, M.; Park, H.; Parker, S.; Petropoulou, M.; Phan,
T.; Prager, S.; Rempel, M.; Ren, C.; Ren, Y.; Rosner, R.; Roytershteyn,
V.; Sarff, J.; Savcheva, A.; Schaffner, D.; Schoeffier, K.; Scime, E.;
Shay, M.; Sironi, L.; Sitnov, M.; Stanier, A.; Swisdak, M.; TenBarge,
J.; Tharp, T.; Uzdensky, D.; Vaivads, A.; Velli, M.; Vishniac, E.;
Wang, H.; Werner, G.; Xiao, C.; Yamada, M.; Yokoyama, T.; Yoo, J.;
Zenitani, S.; Zweibel, E.
Bibcode: 2020arXiv200908779J
Altcode:
Magnetic reconnection underlies many explosive phenomena in the
heliosphere and in laboratory plasmas. The new research capabilities in
theory/simulations, observations, and laboratory experiments provide the
opportunity to solve the grand scientific challenges summarized in this
whitepaper. Success will require enhanced and sustained investments
from relevant funding agencies, increased interagency/international
partnerships, and close collaborations of the solar, heliospheric,
and laboratory plasma communities. These investments will deliver
transformative progress in understanding magnetic reconnection and
related explosive phenomena including space weather events.
Title: Voyager 2 Observations Near the Heliopause
Authors: Richardson, John D.; Belcher, John W.; Burlaga, Leonard F.;
Cummings, Alan C.; Decker, Robert B.; Opher, Merav; Stone, Edward C.
Bibcode: 2020JPhCS1620a2016R
Altcode:
This paper discusses plasma characteristics in the heliosheath
region before the heliopause (HP), at the HP, and in the very local
interstellar medium (VLISM). The Voyager 2 (V2) HP was a sharp boundary
where the radial plasma currents went to background levels. The radial
flow speeds derived from 53-85 keV (V1) and 28-43 keV (V2) ion data
decreased about 2 years (8 AU) before the HP at V1 and V2. A speed
decrease was not observed by the V2 plasma instrument until 160 days
(1.5 AU) before the HP crossing when V2 entered the plasma boundary
layer where the plasma density and 28-43 keV ion intensity increased. We
determine the HP orientation based on the plasma flow and magnetic field
data and show these observations are consistent with models predicting
a blunt HP. Variations are observed in the currents observed in the
VLISM; roll data from this region clearly show the plasma instrument
observes the interstellar plasma and may be consistent with larger
than expected VLISM temperatures near the HP.
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: 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: 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: Major Scientific Challenges and Opportunities in Understanding
Magnetic Reconnection and Related Explosive Phenomena throughout
the Universe
Authors: Ji, H.; Alt, A.; Antiochos, S.; Baalrud, S.; Bale, S.;
Bellan, P. M.; Begelman, M.; Beresnyak, A.; Blackman, E. G.; Brennan,
D.; Brown, M.; Buechner, J.; Burch, J.; Cassak, P.; Chen, L. -J.;
Chen, Y.; Chien, A.; Craig, D.; Dahlin, J.; Daughton, W.; DeLuca, E.;
Dong, C. F.; Dorfman, S.; Drake, J.; Ebrahimi, F.; Egedal, J.; Ergun,
R.; Eyink, G.; Fan, Y.; Fiksel, G.; Forest, C.; Fox, W.; Froula, D.;
Fujimoto, K.; Gao, L.; Genestreti, K.; Gibson, S.; Goldstein, M.; Guo,
F.; Hesse, M.; Hoshino, M.; Hu, Q.; Huang, Y. -M.; Jara-Almonte, J.;
Karimabadi, H.; Klimchuk, J.; Kunz, M.; Kusano, K.; Lazarian, A.;
Le, A.; Li, H.; Li, X.; Lin, Y.; Linton, M.; Liu, Y. -H.; Liu, W.;
Longcope, D.; Loureiro, N.; Lu, Q. -M.; Ma, Z-W.; Matthaeus, W. H.;
Meyerhofer, D.; Mozer, F.; Munsat, T.; Murphy, N. A.; Nilson, P.;
Ono, Y.; Opher, M.; Park, H.; Parker, S.; Petropoulou, M.; Phan, T.;
Prager, S.; Rempel, M.; Ren, C.; Ren, Y.; Rosner, R.; Roytershteyn,
V.; Sarff, J.; Savcheva, A.; Schaffner, D.; Schoeffier, K.; Scime, E.;
Shay, M.; Sitnov, M.; Stanier, A.; TenBarge, J.; Tharp, T.; Uzdensky,
D.; Vaivads, A.; Velli, M.; Vishniac, E.; Wang, H.; Werner, G.; Xiao,
C.; Yamada, M.; Yokoyama, T.; Yoo, J.; Zenitani, S.; Zweibel, E.
Bibcode: 2020arXiv200400079J
Altcode:
This white paper summarizes major scientific challenges and
opportunities in understanding magnetic reconnection and related
explosive phenomena as a fundamental plasma process.
Title: CME deflections due to magnetic forces from the Sun and
Kepler-63
Authors: Menezes, F.; Netto, Y.; Kay, C.; Opher, M.; Valio, A.
Bibcode: 2020IAUS..354..421M
Altcode:
The stellar magnetic field is the driver of activity in the star and
can trigger energetic flares, CMEs and ionized wind. These phenomena,
specially CMEs, may have an important impact on the magnetosphere and
atmosphere of the orbiting planets. To predict whether a CME will impact
a planet, the effects of the background on the CME's trajectory must
be taken into account. We used the MHD code ForeCAT - a model for CME
deflection due to magnetic forces - to perform numerical simulations of
CMEs being launched from both the Sun and Kepler-63, which is a young,
solar-like star with high activity. Comparing results from Kepler-63
and the Sun gives us a panorama of the distinct activity level and
star-planet interactions of these systems due to the difference of
stellar ages and star-planet distances.
Title: Energetic Neutral Atom Maps from a Kinetic-MHD Description
of the "Croissant-like" Heliosphere
Authors: Kornbleuth, M. Z.; Opher, M.; Michael, A.; Sokol, J. M.
Bibcode: 2019AGUFMSH51C3335K
Altcode:
Opher et al. (2015) suggested that due to the collimation of the solar
wind plasma by the solar magnetic field, two high latitude lobes would
emerge, resulting in a shortened heliotail with a "croissant-like"
shape. Other works hypothesized that using a kinetic treatment of
neutrals in modeling the heliosphere would lead to the disappearance
of this "croissant-like" shape. Recently, Michael et al. (2019) showed
that using the Solar-wind with Hydrogen Ion Exchange and Large-scale
Dynamics (SHIELD) model, which is a 3D MHD model coupled with a
kinetic description of neutrals, the "croissant-like" structure
of the heliosphere persists. The Interstellar Boundary Explorer
(IBEX) is probing the heliosphere by using energetic neutral atoms
(ENAs). McComas et al. (2013) and Schwadron et al. (2014) showed two
high latitude lobes of increased ENA flux at the highest IBEX energies,
with a deficit of ENA flux in the low latitude tail. This observed
structure was suggested to be the result of the latitudinal variation
of the solar wind. Zirnstein et al. (2017) showed that using a time
dependent model of the heliosphere, the ENA structure observed by IBEX
could be reasonably replicated. Kornbleuth et al. (2018) showed that
the collimation of the solar wind plasma seen by Opher et al. (2015)
could also lead to the emergence of high latitude lobes of increased
ENA flux in the absence of a varying solar wind structure. In this
work, we use the SHIELD model of the heliosphere to investigate the
underlying effect of solar wind collimation on ENA maps. We present
maps from a case where no collimation is present (by neglecting solar
magnetic field) and compare with a case where collimation is present. In
both cases we include the solar wind latitudinal variations as in
solar minimum in 2008 using a model developed by Sokol et al (2015),
which is based on the interplanetary scintillation observations of
the solar wind structure (Tokumaru et al 2012). We find that while
a latitudinally-varying solar wind structure can replicate IBEX
observations in the absence of solar wind collimation, the inclusion
of collimation causes an enhancement of the high latitude lobes at
the highest IBEX energies. As the solar magnetic field strengthens or
weakens over the course of a solar cycle, the varying strength of the
collimation should be observable in IBEX ENA observations.
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: 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: 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: Thank You to Our 2018 Peer Reviewers
Authors: Rajaram, Harihar; Diffenbaugh, Noah; Camargo, Suzana;
Cardenas, M. Bayani; Carey, Rebecca; Cobb, Kim; Cory, Rose; Cronin,
Meghan; Dombard, Andrew; Donohue, Kathleen; Flesch, Lucy; Giannini,
Alessandra; Hayes, Gavin; Hogg, Andrew; Ilyina, Tatiana; Ivanov,
Valeriy; Jacobsen, Steven; Korte, Monika; Lu, Gang; Morlighem, Mathieu;
Magnusdottir, Gudrun; Newman, Andrew; Opher, Merav; Passalacqua,
Paola; Patricola, Christina; Ritsema, Jeroen; Sprintall, Janet; Su,
Hui; Thornton, Joel; Williams, Paul; Yau, Andrew
Bibcode: 2019GeoRL..4612608R
Altcode:
On behalf of the journal, AGU, and the scientific community, the
Editors would like to sincerely thank those who reviewed manuscripts for
Geophysical Research Letters in 2018. The hours reading and commenting
on manuscripts not only improves the manuscripts but also increases
the scientific rigor of future research in the field. We particularly
appreciate the timely reviews, in light of the demands imposed by the
rapid review process at Geophysical Research Letters. With the revival
of the "major revisions" decisions, we appreciate the reviewers' efforts
on multiple versions of some manuscripts. Many of those listed below
went beyond and reviewed three or more manuscripts for our journal, and
those are indicated in italics. In total, 4,484 referees contributed to
7,557 individual reviews in journal. Thank you again. We look forward
to the coming year of exciting advances in the field and communicating
those advances to our community and to the broader public.
Title: Principles Of Heliophysics: a textbook on the universal
processes behind planetary habitability
Authors: Schrijver, Karel; Bagenal, Fran; Bastian, Tim; Beer,
Juerg; Bisi, Mario; Bogdan, Tom; Bougher, Steve; Boteler, David;
Brain, Dave; Brasseur, Guy; Brownlee, Don; Charbonneau, Paul; Cohen,
Ofer; Christensen, Uli; Crowley, Tom; Fischer, Debrah; Forbes, Terry;
Fuller-Rowell, Tim; Galand, Marina; Giacalone, Joe; Gloeckler, George;
Gosling, Jack; Green, Janet; Guetersloh, Steve; Hansteen, Viggo;
Hartmann, Lee; Horanyi, Mihaly; Hudson, Hugh; Jakowski, Norbert;
Jokipii, Randy; Kivelson, Margaret; Krauss-Varban, Dietmar; Krupp,
Norbert; Lean, Judith; Linsky, Jeff; Longcope, Dana; Marsh, Daniel;
Miesch, Mark; Moldwin, Mark; Moore, Luke; Odenwald, Sten; Opher, Merav;
Osten, Rachel; Rempel, Matthias; Schmidt, Hauke; Siscoe, George;
Siskind, Dave; Smith, Chuck; Solomon, Stan; Stallard, Tom; Stanley,
Sabine; Sojka, Jan; Tobiska, Kent; Toffoletto, Frank; Tribble, Alan;
Vasyliunas, Vytenis; Walterscheid, Richard; Wang, Ji; Wood, Brian;
Woods, Tom; Zapp, Neal
Bibcode: 2019arXiv191014022S
Altcode:
This textbook gives a perspective of heliophysics in a way that
emphasizes universal processes from a perspective that draws attention
to what provides Earth (and similar (exo-)planets) with a relatively
stable setting in which life as we know it can thrive. The book is
intended for students in physical sciences in later years of their
university training and for beginning graduate students in fields of
solar, stellar, (exo-)planetary, and planetary-system sciences.
Title: Coronal disturbances and their effects on the dynamics of
the heliosphere
Authors: Provornikova, Elena; Merkin, Vyacheslav; Opher, Merav;
Richardson, John; Izmodenov, Vladislav; Brandt, Pontus; McNutt, Ralph
Bibcode: 2019EPSC...13.1229P
Altcode:
The Sun blows out the solar wind which propagates into the
interplanetary medium and forms the heliosphere about 100 AU across. The
solar activity causes various types of time-dependent phenomena in the
solar wind from long-lived corotating interaction regions to shorter
on duration but more extreme events like coronal mass ejections. As
these structures propagate outward from the Sun, they evolve and
interact with each other and the ambient solar wind. Voyager 1 and
2 provided first unique in-situ measurements of these structures in
the outer heliosphere. In particular, Voyager observations in the
heliosheath, the outermost region of the heliosphere, showed highly
variable plasma flows indicating effects of solar variations extending
from the Sun to the heliosphere boundaries. Most surprisingly, Voyager
1 data shows shocks and pressure waves beyond the heliosphere in the
interstellar medium. Important questions for the future Interstellar
Probe mission are (1) how do the heliosphere boundaries respond to solar
variations? (2) how do disturbances evolve in the heliosheath? and (3)
how far does the Sun influence extend into the interstellar medium? This
talk will review observations and recent modeling efforts demonstrating
highly variable and dynamic nature of the global heliosphere in response
to disturbances originated in the Sun's atmosphere.
Title: Corrugated Features in Coronal-mass-ejection-driven Shocks:
A Discussion on the Predisposition to Particle Acceleration
Authors: Páez, A.; Jatenco-Pereira, V.; Falceta-Gonçalves, D.;
Opher, M.
Bibcode: 2019ApJ...879..122P
Altcode: 2019arXiv190707884P
The study of the acceleration of particles is an essential element of
research in heliospheric science. Here, we discuss the predisposition to
the particle acceleration around shocks driven by coronal mass ejections
(CMEs) with corrugated wave-like features. We adopt these attributes
on shocks formed from disturbances due to the bimodal solar wind, CME
deflection, irregular CME expansion, and the ubiquitous fluctuations
in the solar corona. In order to understand the role of a wavy shock in
particle acceleration, we define three initial smooth shock morphologies
each associated with a fast CME. Using polar Gaussian profiles we
model these shocks in the low corona. We establish the corrugated
appearance on smooth shock by using combinations of wave-like functions
that represent the disturbances from the medium and CME piston. For
both shock types, smooth and corrugated, we calculate the shock normal
angles between the shock normal and the radial upstream coronal magnetic
field in order to classify the quasi-parallel and quasi-perpendicular
regions. We consider that corrugated shocks are predisposed to different
processes of particle acceleration due to irregular distributions of
shock normal angles around the shock. We suggest that disturbances
due to CME irregular expansion may be a decisive factor in origin of
particle acceleration. Finally, we regard that accepting these features
on shocks may be the starting point for investigating some questions
regarding the sheath and shock, like downstream jets, instabilities,
shock thermalization, shock stability, and injection particle processes.
Title: Community Input Solicited for Heliophysics Decadal Survey
Midterm Assessment Committee
Authors: Woods, Thomas; Millan, Robyn; Charo, Art; Bastian, Tim;
Bobra, Monica; Coster, Anthea; DeLuca, Ed; England, Scott; Fuselier,
Stephen; Lopez, Ramon; Luhmann, Janet; Nykyri, Katariina; Oberheide,
Jens; Opher, Merav; Schrijver, Karel; Semeter, Josh; Thayer, Jeff;
Title, Alan
Bibcode: 2019shin.confE...6W
Altcode:
The National Academies of Sciences, Engineering, and Medicine has
convened a committee to review the progress towards implementing the
2013 Heliophysics Decadal Survey, titled Solar and Space Physics: a
Science for a Technological Society. This review serves as a midterm
assessment before the next Heliophysics Decadal Survey committee would
begin its formulation. This committee is interested to receive input
from the heliophysics and space weather communities about the 2013-2018
progress realizing the 15 recommendations and applications specified in
the 2013 Heliophysics Decadal Survey, about any suggested actions to
optimize the science value during 2019-2023, about any suggestions to
improve the process for the next Heliophysics Decadal Survey, and about
any suggested actions to enhance all stages of careers for scientists
and engineers in the solar and space physics community. This poster
outlines the Heliophysics Decadal Survey recommendations and recent
progress, and it also summarizes the tasks for this midterm assessment
committee. There will be an opportunity to discuss your inputs with
a couple of the Committee members during the SHINE meeting.
Title: Major Scientific Challenges and Opportunities in Understanding
Magnetic Reconnection and Related Explosive Phenomena throughout
the Universe
Authors: Ji, Hantao; Alt, A.; Antiochos, S.; Baalrud, S.; Bale, S.;
Bellan, P. M.; Begelman, M.; Beresnyak, A.; Blackman, E. G.; Brennan,
D.; Brown, M.; Buechner, J.; Burch, J.; Cassak, P.; Chen, L. -J.;
Chen, Y.; Chien, A.; Craig, D.; Dahlin, J.; Daughton, W.; DeLuca, E.;
Dong, C. F.; Dorfman, S.; Drake, J.; Ebrahimi, F.; Egedal, J.; Ergun,
R.; Eyink, G.; Fan, Y.; Fiksel, G.; Forest, C.; Fox, W.; Froula, D.;
Fujimoto, K.; Gao, L.; Genestreti, K.; Gibson, S.; Goldstein, M.;
Guo, F.; Hesse, M.; Hoshino, M.; Hu, Q.; Huang, Y. -M.; Jara-Almonte,
J.; Karimabadi, H.; Klimchuk, J.; Kunz, M.; Kusano, K.; Lazarian,
A.; Le, A.; Li, H.; Li, X.; Lin, Y.; Linton, M.; Liu, Y. -H.; Liu,
W.; Longcope, D.; Louriero, N.; Lu, Q. -M.; Ma, Z. -W.; Matthaeus,
W. H.; Meyerhofer, D.; Mozer, F.; Munsat, T.; Murphy, N. A.; Nilson,
P.; Ono, Y.; Opher, M.; Park, H.; Parker, S.; Petropoulou, M.; Phan,
T.; Prager, S.; Rempel, M.; Ren, C.; Ren, Y.; Rosner, R.; Roytershteyn,
V.; Sarff, J.; Savcheva, A.; Schaffner, D.; Schoeffier, K.; Scime, E.;
Shay, M.; Sitnov, M.; Stanier, A.; TenBarge, J.; Tharp, T.; Uzdensky,
D.; Vaivads, A.; Velli, M.; Vishniac, E.; Wang, H.; Werner, G.; Xiao,
C.; Yamada, M.; Yokoyama, T.; Yoo, J.; Zenitani, S.; Zweibel, E.
Bibcode: 2019BAAS...51c...5J
Altcode: 2019astro2020T...5J
This is a group white paper of 100 authors (each with explicit
permission via email) from 51 institutions on the topic of magnetic
reconnection which is relevant to 6 thematic areas. Grand challenges
and research opportunities are described in observations, numerical
modeling and laboratory experiments in the upcoming decade.
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: Globally Distributed Energetic Neutral Atom Maps for the
“Croissant” Heliosphere
Authors: Kornbleuth, M.; Opher, M.; Michael, A. T.; Drake, J. F.
Bibcode: 2018ApJ...865...84K
Altcode: 2018arXiv180805997K
A recent study by Opher et al. suggested the heliosphere has a
“croissant” shape, where the heliosheath plasma is confined by the
toroidal solar magnetic field. The “croissant” heliosphere is in
contrast to the classically accepted view of a comet-like tail. We
investigate the effect of the “croissant” heliosphere model on
energetic neutral atom (ENA) maps. Regardless of the existence of a
split tail, the confinement of the heliosheath plasma should appear in
ENA maps. ENA maps from the Interstellar Boundary Explorer (IBEX) have
shown two high latitude lobes with excess ENA flux at higher energies
in the tail of the heliosphere. These lobes could be a signature of
the confinement of the heliosheath plasma, while some have argued
they are caused by the fast/slow solar wind profile. Here we present
ENA maps of the “croissant” heliosphere, focusing on understanding
the effect of the heliosheath plasma collimation by the solar magnetic
field while using a uniform solar wind. We incorporate pick-up ions
(PUIs) into our model based on Malama et al. and Zank et al. We use the
neutral solution from our MHD model to determine the angular variation
of the PUIs, and include the extinction of PUIs in the heliosheath. In
the presence of a uniform solar wind, we find that the collimation
in the “croissant” heliosphere does manifest itself into two high
latitude lobes of increased ENA flux in the downwind direction.
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 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: 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: 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: Effects of Neutrals in the Outer Heliosphere- lessons learned
from Voyager, Cassini, IBEX, about our home in the galaxy
Authors: Opher, Merav
Bibcode: 2018tess.conf40003O
Altcode:
In this talk, I will discuss what we recently learned from
the in-situ measurements from Voyager spacecraft as well as the
remote sensing of energetic neutral atoms from CASSINI, IBEX about
the heliosphere. Interstellar Boundary Explorer (IBEX) is being
observing the heliosphere with maps of energetic neutral atoms (ENAs)
from 1-6keV. INCA on board of CASSINI is taking ENA images of the
heliosphere in energies 5-55keV. Voyager 2 is still exploring the
heliosheath while of Voyager 1 spacecraft is measuring the local
interstellar medium since 2012. In particular I will review the
effects of neutral H atoms streaming from the Interstellar Medium
have on the heliosphere. The heliosphere is the only local example
of astrosphere that can be probed in such details. 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. From the Energetic
Neutral Atoms images of IBEX and CASSINI our knowledge was transformed
about the shape of the heliosphere, as well as processes occurring in
the very local interstellar medium ahead of the heliosphere. I will
review these different different measurements and comment in particular
about the recent debate where the shape of the Heliosphere is being
challenged by theoretical and observation work (Opher et al. 2015;
Diyalinas et al. 2017) and what we can learn from future missions such
as IMAP.
Title: Appreciation of 2017 GRL Peer Reviewers
Authors: Diffenbaugh, Noah; Beal, Lisa; Bayani Cardenas, M.; Cobb,
Kim; Cory, Rose; Cronin, Meghan; Dombard, Andrew J.; Hogg, Andrew;
Ilyina, Tatiana; Korte, Monika; Lu, Gang; Magnusdottir, Gudrun; Newman,
Andrew V.; Opher, Merav; Ritsema, Jeroen; Sprintall, Janet; Stroeve,
Julienne; Thornton, Joel A.; Williams, Paul D.; Yau, Andrew
Bibcode: 2018GeoRL..45.4494D
Altcode:
Thank you to those who reviewed in 2017 for Geophysical Research
Letters.
Title: A Science-Driven Mission to an Exoplanet
Authors: Weinstein-Weiss, S.; Rayman, Marc; Turyshev, Slava; Biswass,
Abhijit; Jun, Insoo; Price, Hoppy; Mamajek, Eric; Callas, John;
McElrath, Tim; Woerner, Dave; Brophy, John; Shao, Mike; Alkalai, Leon;
Arora, Nitin; Johnson, Les; Opher, Merav; Redfield, Seth; McNutt,
Ralph; Sotker, Carol; Blank, Jennifer; Caldwell, Douglas; Friedman,
Louis; Frisbee, Robert; Bennett, Gary
Bibcode: 2018JBIS...71..140W
Altcode:
A concept for a science-driven robotic mission to an exoplanet was
developed based on key mission and science requirements designed to
address the question: "What makes a flight mission to an exoplanet
compelling, in terms of science return, compared to what will be
learned in the next few decades with large near-Earth telescopes
or other remote sensing techniques such as a telescope at the Solar
Gravity Lens Focus?" By thinking systematically through mission and
science goals as well as objectives, key requirements were developed
that would drive technology developments in all necessary aspects,
not just on propulsion. One of the key mission science objectives
was to confirm and characterize life. The team concluded that a direct
confirmation of life would require in situ observations and measurements
that cannot be performed on a fast (0.1c) flyby; thus, the mission would
require a method to slow down, orbit or send a probe to the exoplanet's
surface. This capability drives a trade between interstellar travel
velocity, trip duration and propulsion architecture as well as a high
level of onboard autonomy, including adaptive science data collection,
on-board data processing and analysis. This paper describes the mission
concept, the key requirements and open trades.
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: The Energetic Neutral Atoms of the "Croissant" Heliosphere
with Jets
Authors: Kornbleuth, M. Z.; Opher, M.; Michael, A.
Bibcode: 2017AGUFMSH51D2535K
Altcode:
Opher et al. (2015) suggests the heliosphere may have two jets in the
tail-ward direction driven to the north and south. This new model, the
"Croissant Heliosphere", is in contrast to the classically accepted
view of a comet-like tail. We investigate the effect of the heliosphere
with jets model on energetic neutral atom (ENA) maps. Regardless of
the existence of a split tail, other models show heliosheath plasma
confined by the toroidal magnetic field in a "slinky" structure, similar
to astrophysical jets bent by the interstellar medium. Therefore,
the confinement of the plasma should appear in the ENA maps. ENA maps
from the Interstellar Boundary Explorer (IBEX) have recently shown
two high latitude lobes with excess ENA flux at higher energies in
the tail of the heliosphere. These lobes could be a signature of the
two jet structure of the heliosphere, while some have argued they are
cause by the fast/slow solar wind profile. Here we present the ENA
maps of the "Croissant Heliosphere" using initially a uniform solar
wind. We incorporate pick-up ions (PUIs) into our model based on the
kinetic modeling of Malama et al. (2006). We include the extinction of
PUIs in the heliosheath and describe a locally created PUI population
resulting from this extinction process. Additionally, we include the
angular dependence of the PUIs based on the work of Vasyliunas &
Siscoe (1976). With our model, we find that, in the presence of a
uniform solar wind, the "heliosphere with jets" model is able to
qualitatively reproduce the lobe structure of the tail seen in IBEX
measurements. Turbulence also manifests itself within the lobes of the
simulated ENA maps on the order of years. Finally we will present ENA
maps using a time-dependent model of the heliosphere with the inclusion
of solar cycle.
Title: From the Outside Looking In - Looking Back at Our Heliosphere
in Energetic Neutral Atoms
Authors: Demajistre, R.; Brandt, P. C.; Gruntman, M.; McNutt, R. L.,
Jr.; Opher, M.; Roelof, E. C.; Wood, B. E.
Bibcode: 2017AGUFMSH23B2655D
Altcode:
Energetic Neutral Atoms (ENAs) have been used over the past two
decades to image space plasmas in planetary magnetospheres as well
as the structure of the heliosheath. Any energetic plasma containing
singly charged ions embedded in a cold neutral gas will 'glow' in ENAs,
and this glow can be analyzed to infer the properties of the source
plasma, giving us insight into processes that are difficult to study
with the more traditional sensors that use photons/electromagnetic
waves as an information carrier. ENA measurements of the heliosphere
have (obviously) all been taken from vantage points in the inner
heliosphere. ENAs created in the inner heliosphere from the solar wind
and Pick Up Ions (PUIs) generally have large outward velocity, and
thus do not reach sensors closer to the sun. Thus, the plasma is only
'visible' in ENAs to an inner heliosphere observer after it reaches
the termination shock, where its outward motion is slowed and it is
heated. This perspective from the inside looking out is convenient to
study the outer boundary of the heliophere, but contains no direct
information about the plasma and processes occurring in the inner
heliosphere. ENA sensors placed outside the heliosphere, conversely
would allow us to remotely sense both the inner and outer heliosphere,
allowing us full access to the evolution of the solar wind and PUIs as
they travel from the sun outward. Further, such a perspective would
allow us to more directly measure the boundaries of the heliosphere
with the LISM without the obscuration of the inner heliosheath. In this
paper, we present modeled views of ENA images from the outside looking
in at energies between 0.5 and 100 keV. It is important to note that
while measurements of the outer heliosphere have been made by IBEX,
Cassini/INCA, SoHO/HSTOF and the Voyagers, there are still important
outstanding questions about the global structure and plasma flow
patterns in the heliosphere. We will show here how new observations
from the outside looking in can be used to address these questions.
Title: Kelvin-Helmholtz Instability at the CME-Sheath and
Sheath-Solar-wind Interfaces
Authors: Páez, A.; Jatenco-Pereira, V.; Falceta-Gonçalves, D.;
Opher, M.
Bibcode: 2017ApJ...851..112P
Altcode:
Wave-like features recently observed in some coronal mass ejections
(CMEs) have been associated with the presence of Kelvin-Helmholtz
instability (KHI) in the low corona. Previous works found observational
evidence of KHI in a CME; this was followed by numerical simulations
in order to determine the magnetic field strength allowing for its
existence. Here, we present the first discussion of KHI formation in
the outer corona at heliocentric distances from 4 {R}⊙
to 30 {R}⊙ . We study separately the CME-sheath and
sheath-solar-wind (Sh-SW) interfaces of two CMEs that propagated in
the slow and fast SWs. Mapping the velocities, densities, and magnetic
field strengths of the CMEs, sheaths, and SWs in the CME’s flanks,
we solve the Chandrasekhar condition for KHI formation. Calculations
show that KHI formation is more likely in a CME propagating in a slow
SW (CME 1) than that propagating in a fast SW due to the large shear
flow between the CME and the slow SW. Comparing the interfaces for
both CME cases, we note that the Sh-SW interface of CME 1 is more
conducive to the instability because of the similar strengths of the
magnetic field necessary for KHI formation and of the SW magnetic field.
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: Understanding the Heliosphere with Jets Using Energetic
Neutral Atoms
Authors: Kornbleuth, Marc Zachary; Opher, Merav; Michael, Adam
Bibcode: 2017shin.confE.167K
Altcode:
The Interstellar Boundary Explorer (IBEX) has been probing the
global structure of the heliosphere using energetic neutral atoms
(ENAs). McComas et al. (2013) showed the presence of two high latitude
lobes of increased ENA flux at higher energies in IBEX measurements. It
was suggested that these measurements could be the result of slow/fast
wind in the heliosphere affecting the measured ENA flux. Recently, Opher
et al. (2015) proposed the heliosphere might have two turbulent jets
in the tail region, as opposed to the classically view of a quiescent,
comet-like structure in the tail. If confirmed, this heliosphere with
jets model would significantly change our understanding of how the
interstellar medium interacts with the solar wind. We use the Opher et
al. (2015) model to create simulated ENA maps of the heliosphere. Our
ENA code is based on a previously created code from Prested et
al. (2008) and Opher et al. (2013). We incorporate multiple pick-up ion
populations, extinction along streamlines, and a pick-up ion profile
based on Vasyliunas & Siscoe (1976) that depends on the latitude
and longitude with respect to the neutral streaking direction. Using
our MHD model with a uniform solar wind, we find two high latitude
lobes present in our simulated maps which are consistent with IBEX
measurements. We also find small-scale changes in the lobes resulting
from turbulence in the jets, which should be observable by IBEX or IMAP.
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: 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: 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: The Deflection of the Cartwheel CME: ForeCAT Results
Authors: Capannolo, Luisa; Opher, Merav; Kay, Christina; Landi, Enrico
Bibcode: 2017ApJ...839...37C
Altcode:
We analyze the Cartwheel coronal mass ejection's (CME; 2008 April 9)
trajectory in the low corona with the ForeCAT model. This complex event
presented a significant rotation in the low corona and a reversal
in its original latitude direction. We successfully reproduce the
observed CME’s trajectory (latitude and longitude deflection) and
speed. Through a {χ }2 test, we are able to constrain the
CME’s mass to (2.3-3.0) × 1014 g and the CME’s initial
shape. We are able to constrain the expansion of the CME as well: the
angular width linearly increases until 2.1 {R}⊙ , and is
constant afterward. In order to match the observed latitude, we include
a non-radial initial speed of -42 km s-1. Despite allowing
the CME to rotate in the model, the magnetic forces of the solar
background are not able to reproduce the observed rotation. We suggest
that the complex reversal in latitude and the significant rotation of
the Cartwheel CME can be justified with an asymmetrical reconnection
event that ejected the CME non-radially and also initiated its rotation.
Title: The Formation of Magnetic Depletions and Flux Annihilation
Due to Reconnection in the Heliosheath
Authors: Drake, J. F.; Swisdak, M.; Opher, M.; Richardson, J. D.
Bibcode: 2017ApJ...837..159D
Altcode: 2017arXiv170201697D
The misalignment of the solar rotation axis and the magnetic axis of
the Sun produces a periodic reversal of the Parker spiral magnetic
field and the sectored solar wind. The compression of the sectors is
expected to lead to reconnection in the heliosheath (HS). We present
particle-in-cell simulations of the sectored HS that reflect the plasma
environment along the Voyager 1 and 2 trajectories, specifically
including unequal positive and negative azimuthal magnetic flux as
seen in the Voyager data. Reconnection proceeds on individual current
sheets until islands on adjacent current layers merge. At late time,
bands of the dominant flux survive, separated by bands of deep magnetic
field depletion. The ambient plasma pressure supports the strong
magnetic pressure variation so that pressure is anticorrelated with
magnetic field strength. There is little variation in the magnetic
field direction across the boundaries of the magnetic depressions. At
irregular intervals within the magnetic depressions are long-lived pairs
of magnetic islands where the magnetic field direction reverses so that
spacecraft data would reveal sharp magnetic field depressions with only
occasional crossings with jumps in magnetic field direction. This is
typical of the magnetic field data from the Voyager spacecraft. Voyager
2 data reveal that fluctuations in the density and magnetic field
strength are anticorrelated in the sector zone, as expected from
reconnection, but not in unipolar regions. The consequence of the
annihilation of subdominant flux is a sharp reduction in the number
of sectors and a loss in magnetic flux, as documented from the Voyager
1 magnetic field and flow data.
Title: The Interstellar Probe Mission: Humanity's First Explicit
Step in Reaching Another Star
Authors: Brandt, P. C.; McNutt, R.; Hallinan, G.; Shao, M.; Mewaldt,
R.; Brown, M.; Alkalai, L.; Arora, N.; McGuire, J.; Turyshev, S.;
Biswas, A.; Liewer, P.; Murphy, N.; Desai, M.; McComas, D.; Opher,
M.; Stone, E.; Zank, G.; Friedman, L.
Bibcode: 2017LPICo1989.8173B
Altcode:
An Interstellar Probe Mission concept to the Interstellar Medium
is discussed that would represent humanity's first explicit step
scientifically, technologically, and programmatically to reach
another star.
Title: Predicting the Magnetic Field of Earth-impacting CMEs
Authors: Kay, C.; Gopalswamy, N.; Reinard, A.; Opher, M.
Bibcode: 2017ApJ...835..117K
Altcode:
Predicting the impact of coronal mass ejections (CMEs) and the southward
component of their magnetic field is one of the key goals of space
weather forecasting. We present a new model, the ForeCAT In situ Data
Observer (FIDO), for predicting the in situ magnetic field of CMEs. We
first simulate a CME using ForeCAT, a model for CME deflection and
rotation resulting from the background solar magnetic forces. Using
the CME position and orientation from ForeCAT, we then determine the
passage of the CME over a simulated spacecraft. We model the CME’s
magnetic field using a force-free flux rope and we determine the in
situ magnetic profile at the synthetic spacecraft. We show that FIDO
can reproduce the general behavior of four observed CMEs. FIDO results
are very sensitive to the CME’s position and orientation, and we
show that the uncertainty in a CME’s position and orientation from
coronagraph images corresponds to a wide range of in situ magnitudes
and even polarities. This small range of positions and orientations
also includes CMEs that entirely miss the satellite. We show that two
derived parameters (the normalized angular distance between the CME
nose and satellite position and the angular difference between the
CME tilt and the position angle of the satellite with respect to the
CME nose) can be used to reliably determine whether an impact or miss
occurs. We find that the same criteria separate the impacts and misses
for cases representing all four observed CMEs.
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: 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: Investigating the Effect of the Heliosphere with Jets on ENAs
as a Function of Solar Cycle
Authors: Kornbleuth, M. Z.; Opher, M.; Michael, A.; Zieger, B.
Bibcode: 2016AGUFMSH31A2535K
Altcode:
The Interstellar Boundary Explorer (IBEX) and INCA, on board the Cassini
spacecraft, have been probing the global structure of the heliosphere
using energetic neutral atoms (ENAs). IBEX tail measurements show
a latitudinal dependence in the ENA flux, where two lobes appear at
high latitudes in higher energies (4 keV). These measurements were
explained as being representative of the presence of the slow and fast
wind (McComas et al. 2013). Recently, Opher et al. (2015) proposed
that the heliosphere might have turbulent jets in its tail region,
as opposed to the classically accepted quiescent, extended comet-like
tail. This proposed model of the heliosphere has a "croissant-like"
shape, suggesting the lobes seen by IBEX are a structural feature. Over
a given solar cycle, the lobes seen by IBEX should evolve differently
based on whether they are a result of the presence of slow/fast wind
or if they are a structural feature of the heliosphere. If confirmed,
the "croissant-like" heliosphere would significantly change our
understanding of how the interstellar medium interacts with the
solar wind. We investigate the effect of the solar cycle on the lobe
structure of the heliosphere with jets model, and the resulting ENA
maps using a multi-ion, multi-fluid model. We compare our results with
observations from IBEX to assess the validity of the "croissant-like"
model. We find that the jets produce ENA signatures consistent with
IBEX measurements of the heliotail, where two lobes are visible in
the northern and southern hemispheres (McComas et al. 2013; Schwadron
et al. 2014). The jets are associated with a strong ENA flux around 4
keV, while the interstellar medium flowing between the jets generates
a lower ENA flux at this IBEX energy band.
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: 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: Turbulence in the Heliospheric Jets
Authors: Drake, J. F.; Swisdak, M.; Opher, M.; Hassam, A.; Ohia, O.
Bibcode: 2016AGUFMSH31A2536D
Altcode:
The conventional picture of the heliosphere is that of a comet-shaped
structure with an extended tail produced by the relative motion
of the sun through the local interstellar medium (LISM). Recent MHD
simulations of the global heliosphere have revealed, however, that the
heliosphere drives magnetized jets to the North and South similar to
those driven by the Crab Nebula and other astrophysical objects. These
simulations reveal that the jets become turbulent with scale lengths
as large as 100AU [1,2]. An important question is what drives this
large-scale turbulence, what are the implications for mixing of
interstellar and heliospheric plasma and does this turbulence drive
energetic particles? An analytic model of the heliospheric jets in
the simple limit in which the interstellar flow and magnetic field
are neglected yields an equilibrium state that can be analyzed
to explore potential instabilities [3]. Calculations suggest that
because the axial magnetic field within the jets is small, the dominant
instability is the sausage mode, driven by the azimuthal solar magnetic
field. Other drive mechanisms, including Kelvin Helmholtz, are also
being explored. 3D MHD and Hall MHD simulations are being carried out
to explore the development of this turbulence, its impact on the mixing
of interstellar and heliosheath plasma and the production of energetic
particles. [1] Opher et al ApJ Lett. 800, L28, 2015[2] Pogorelov et
al ApJ Lett. 812,L6, 2015[3] Drake et al ApJ Lett. 808, L44, 2015
Title: The ForeCAT In Situ Data Observer and the Effects of Deflection
and Rotation on CME Geoeffectiveness
Authors: Kay, C.; Gopalswamy, N.; Reinard, A.; Opher, M.;
Nieves-Chinchilla, T.
Bibcode: 2016AGUFMSH13B2298K
Altcode:
CMEs drive the strongest space weather events at Earth and throughout
the solar system. At Earth, the amount of southward magnetic field in a
CME is a major component in determining the severity of an impact. We
present results from ForeCAT (Forecasting a CME's Altered Trajectory,
Kay et al. 2015), which predicts the deflection and rotation of
CMEs based on magnetic forces determined by the background magnetic
field. Understanding these deflections and rotations is essential to
understanding the geoeffectiveness of CMEs as it determines whether a
CME will hit Earth and the orientation of the flux rope magnetic field
upon impact. Using the CME location and orientation from ForeCAT and
simple flux rope models we show that we can reproduce the in situ
magnetic profiles of Earth-impacting CMEs with the new ForeCAT In
situ Data Observer (FIDO). We compare these results with the in situ
profiles obtained assuming that no deflection or rotation occurs, and
find that including these nonradial effects is essential for accurate
space weather forecasting. For several observed cases we comment on
how the deflection and rotation affects the southward component of
the CME's magnetic field, and therefore the CME's geoeffectiveness.
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: Voyager Observations of Magnetic Sectors and Heliospheric
Current Sheet Crossings in the Outer Heliosphere
Authors: Richardson, J. D.; Burlaga, L. F.; Drake, J. F.; Hill, M. E.;
Opher, M.
Bibcode: 2016ApJ...831..115R
Altcode:
Voyager 1 (V1) has passed through the heliosheath and is in the local
interstellar medium. Voyager 2 (V2) has been in the heliosheath since
2007. The role of reconnection in the heliosheath is under debate;
compression of the heliospheric current sheets (HCS) in the heliosheath
could lead to rapid reconnection and a reconfiguration of the magnetic
field topology. This paper compares the expected and actual amounts
of time the Voyager spacecraft observe each magnetic sector and the
number of HCS crossings. The predicted and observed values generally
agree well. One exception is at Voyager 1 in 2008 and 2009, where the
distribution of sectors is more equal than expected and the number of
HCS crossings is small. Two other exceptions are at V1 in 2011-2012 and
at V2 in 2012, when the spacecraft are in the opposite magnetic sector
less than expected and see fewer HCS crossings than expected. These
features are consistent with those predicted for reconnection, and
consequently searches for other reconnection signatures should focus
on these times.
Title: Determining ICME Magnetic Field Orientation with the ForeCAT
In Situ Data Observer
Authors: Kay, Christina; Gopalswamy, N.; Reinard, A.; Opher, M.
Bibcode: 2016usc..confE..20K
Altcode:
CMEs drive the strongest space weather events at Earth and throughout
the solar system. At Earth, the amount of southward magnetic field in a
CME is a major component in determining the severity of an impact. We
present results from ForeCAT (Forecasting a CME's Altered Trajectory,
Kay et al. 2015), which predicts the deflection and rotation of
CMEs based on magnetic forces determined by the background magnetic
field. Using HMI magnetograms to reconstruct the background magnetic
field and AIA images to constrain the early evolution of CMEs, we show
that we can reproduce the deflection and rotation of CMEs observed
in the corona. Using this CME location and orientation from ForeCAT
results and a simple force-free flux rope model we show that we can
reproduce the in situ magnetic profiles of Earth-impacting CMEs. We
compare these results with the in situ profiles obtained assuming
that no deflection or rotation occurs, and find that including these
nonradial effects is essential for accurate space weather forecasting.
Title: Using ForeCAT Deflections and Rotations to Constrain the
Early Evolution of CMEs
Authors: Kay, C.; Opher, M.; Colaninno, R. C.; Vourlidas, A.
Bibcode: 2016ApJ...827...70K
Altcode: 2016arXiv160603460K
To accurately predict the space weather effects of the impacts of
coronal mass ejection (CME) at Earth one must know if and when a CME
will impact Earth and the CME parameters upon impact. In 2015 Kay et
al. presented Forecasting a CME’s Altered Trajectory (ForeCAT),
a model for CME deflections based on the magnetic forces from the
background solar magnetic field. Knowing the deflection and rotation of
a CME enables prediction of Earth impacts and the orientation of the
CME upon impact. We first reconstruct the positions of the 2010 April
8 and the 2012 July 12 CMEs from the observations. The first of these
CMEs exhibits significant deflection and rotation (34° deflection
and 58° rotation), while the second shows almost no deflection or
rotation (<3° each). Using ForeCAT, we explore a range of initial
parameters, such as the CME’s location and size, and find parameters
that can successfully reproduce the behavior for each CME. Additionally,
since the deflection depends strongly on the behavior of a CME in the
low corona, we are able to constrain the expansion and propagation of
these CMEs in the low corona.
Title: Probability of CME Impact on Exoplanets Orbiting M Dwarfs
and Solar-like Stars
Authors: Kay, C.; Opher, M.; Kornbleuth, M.
Bibcode: 2016ApJ...826..195K
Altcode: 2016arXiv160502683K
Solar coronal mass ejections (CMEs) produce adverse space weather
effects at Earth. Planets in the close habitable zone of magnetically
active M dwarfs may experience more extreme space weather than at
Earth, including frequent CME impacts leading to atmospheric erosion
and leaving the surface exposed to extreme flare activity. Similar
erosion may occur for hot Jupiters with close orbits around solar-like
stars. We have developed a model, Forecasting a CME's Altered Trajectory
(ForeCAT), which predicts a CME's deflection. We adapt ForeCAT to
simulate CME deflections for the mid-type M dwarf V374 Peg and hot
Jupiters with solar-type hosts. V374 Peg's strong magnetic fields can
trap CMEs at the M dwarfs's Astrospheric Current Sheet, that is, the
location of the minimum in the background magnetic field. Solar-type
CMEs behave similarly, but have much smaller deflections and do not
become trapped at the Astrospheric Current Sheet. The probability
of planetary impact decreases with increasing inclination of the
planetary orbit with respect to the Astrospheric Current Sheet: 0.5-5
CME impacts per day for M dwarf exoplanets, 0.05-0.5 CME impacts per
day for solar-type hot Jupiters. We determine the minimum planetary
magnetic field necessary to shield a planet's atmosphere from CME
impacts. M dwarf exoplanets require values between tens and hundreds
of Gauss. Hot Jupiters around a solar-type star, however, require a
more reasonable <30 G. These values exceed the magnitude required
to shield a planet from the stellar wind, suggesting that CMEs may be
the key driver of atmospheric losses.
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: Investigating the Effect of the 'Croissant-like' Heliosphere
on ENAs
Authors: Kornbleuth, Marc Zachary; Opher, Merav; Zieger, Bertalan
Bibcode: 2016shin.confE.124K
Altcode:
The Interstellar Boundary Explorer (IBEX) and Cassini spacecraft
have been probing the global structure of the heliosphere using
energetic neutral atoms (ENAs). Recently, Opher et al. (2015)
proposed that the heliosphere may have turbulent jets in its
tail region, as opposed to the classically accepted quiescent,
extended comet-like tail. This proposed model of the heliosphere
is considered to have a 'croissant-like' shape. We investigate the
effect of the 'croissant-like' heliosphere on ENA maps. Here we
present preliminary results of the globally distributed ENA flux and
compare with observations (Schwadron et al. 2014). We assume a kappa
distribution for the plasma in the heliosheath (Prested et al. 2008)
and a Maxwellian distribution for the plasma in the interstellar
medium. We find that the jets produce an ENA signature consistent with
IBEX measurements of the heliotail (McComas et al. 2013; Schwadron et
al. 2014). Future studies will investigate the evolution of the jets
with solar cycle and their signature in ENAs.
Title: The deflection of the 'Cartwheel' CME: ForeCAT results
Authors: Capannolo, Luisa; Opher, M.; Kay, C. C.; Landi, E.
Bibcode: 2016shin.confE..48C
Altcode:
Coronal Mass Ejections (CMEs) are of high scientific interest as
they represent the major cause of geomagnetic activity at Earth. In
this work, we examine the CME that occurred on April 9th, 2008,
during the solar minimum of solar cycle 24. This CME is referred to
as the 'Cartwheel CME' due to its unusual motion in the coronagraph
observations: the CME clearly rotates as it propagates outward. The CME
also shows a reversal in its latitudinal direction: the CME is ejected
at -20 degrees and moves southward to -30 degrees, then turns and
deflects northward to -20 degrees until it begins propagating radially
at 5-6 solar radii. Longitudinally, the CME is essentially stable. We
model the trajectory of the CME in the low corona with the ForeCAT model
(Kay et al., 2013; Kay et al., 2015). ForeCAT is based on magnetic
forces that act on CMEs as they propagate in the solar wind. Given a
magnetic background and initial parameters, ForeCAT provides the CME
trajectory, including any deflection or rotation, as a function of
time and distance from the Sun. We compare the results of the model
to available data of latitude and longitude of the CME (Landi et al.,
2010). ForeCAT successfully predicts the reversal in the latitudinal
deflection of the Cartwheel CME. To match the data, we constrain the
initial mass of the CME to 3.5 10^14 g in the low corona, the initial
CME size and the angular width expansion law of the CME (linear as a
function of distance until 2.10 solar radii and constant onwards).
Title: Voyager 2 solar plasma and magnetic field spectral analysis
for intermediate data sparsity
Authors: Gallana, Luca; Fraternale, Federico; Iovieno, Michele;
Fosson, Sophie M.; Magli, Enrico; Opher, Merav; Richardson, John D.;
Tordella, Daniela
Bibcode: 2016JGRA..121.3905G
Altcode: 2015arXiv151004304G
The Voyager probes are the furthest, still active, spacecraft ever
launched from Earth. During their 38 year trip, they have collected
data regarding solar wind properties (such as the plasma velocity and
magnetic field intensity). Unfortunately, a complete time evolution
of the measured physical quantities is not available. The time series
contains many gaps which increase in frequency and duration at larger
distances. The aim of this work is to perform a spectral and statistical
analysis of the solar wind plasma velocity and magnetic field using
Voyager 2 data measured in 1979, when the gap density is between the
30% and 50%. For these gap densities, we show the spectra of gapped
signals inherit the characteristics of the data gaps. In particular, the
algebraic decay of the intermediate frequency range is underestimated
and discrete peaks result not from the underlaying data but from the gap
sequence. This analysis is achieved using five different data treatment
techniques coming from the multidisciplinary context: averages on
linearly interpolated subsets, correlation without data interpolation,
correlation of linearly interpolated data, maximum likelihood data
reconstruction, and compressed sensing spectral estimation. With five
frequency decades, the spectra we obtained have the largest frequency
range ever computed at five astronomical units from the Sun; spectral
exponents have been determined for all the components of the velocity
and magnetic field fluctuations. Void analysis is also useful in
recovering other spectral properties such as micro and integral scales.
Title: ForeCAT - A Model for Magnetic Deflections of Coronal Mass
Ejections
Authors: Kay, Christina; Opher, Merav
Bibcode: 2016SPD....4710303K
Altcode:
Accurate space weather forecasting requires knowledge of the trajectory
of CMEs. Decades of observations show that CMEs can deflect from a
purely radial trajectory, however, no consensus exists as to the cause
of these deflections. We developed a model for CME deflection and
rotation from magnetic forces, called Forecasting a CME’s Altered
Trajectory (ForeCAT). ForeCAT has been designed to run fast enough
for large parameter phase space studies, and potentially real-time
predictions.ForeCAT reproduces the general trends seen in observed
CME deflections. In particular, CMEs deflect toward regions of minimum
magnetic energy - frequently the Heliospheric Current Sheet (HCS) on
global scales. The background magnetic forces decrease rapidly with
distance and quickly become negligible. Most deflections and rotations
can be well-described by assuming constant angular momentum beyond
10 Rs.ForeCAT also reproduces individual observed CME deflections
- the 2008 December 12, 2008 April 08, and 2010 July 12 CMEs. By
determining the reduced chi-squared best fit between the ForeCAT
results and the observations we constrain parameters related to the
CME and the background solar wind. Additionally, we constrain whether
different models for the low corona magnetic backgrounds can produce
the observed CME deflection.
Title: The Heliosphere: What Did We Learn in Recent Years and the
Current Challenges
Authors: Opher, M.
Bibcode: 2016SSRv..200..475O
Altcode: 2015SSRv..tmp...80O
No abstract at ADS
Title: Turbulence in the solar wind: spectra from Voyager 2 data at
5 AU
Authors: Fraternale, F.; Gallana, L.; Iovieno, M.; Opher, M.;
Richardson, J. D.; Tordella, D.
Bibcode: 2016PhyS...91b3011F
Altcode: 2015arXiv150207114F
Fluctuations in the flow velocity and magnetic fields are ubiquitous
in the Solar System. These fluctuations are turbulent, in the sense
that they are disordered and span a broad range of scales in both space
and time. The study of solar wind turbulence is motivated by a number
of factors all keys to the understanding of the Solar Wind origin
and thermodynamics. The solar wind spectral properties are far from
uniformity and evolve with the increasing distance from the sun. Most
of the available spectra of solar wind turbulence were computed at 1
astronomical unit, while accurate spectra on wide frequency ranges at
larger distances are still few. In this paper we consider solar wind
spectra derived from the data recorded by the Voyager 2 mission during
1979 at about 5 AU from the sun. Voyager 2 data are an incomplete
time series with a voids/signal ratio that typically increases as the
spacecraft moves away from the sun (45% missing data in 1979), making
the analysis challenging. In order to estimate the uncertainty of the
spectral slopes, different methods are tested on synthetic turbulence
signals with the same gap distribution as V2 data. Spectra of all
variables show a power law scaling with exponents between -2.1 and -1.1,
depending on frequency subranges. Probability density functions (PDFs)
and correlations indicate that the flow has a significant intermittency.
Title: Conditions for the existence of Kelvin-Helmholtz instability
in a CME
Authors: Páez, Andrés; Jatenco-Pereira, Vera; Falceta-Gonçcalves,
Diego; Opher, Merav
Bibcode: 2016IAUS..320..218P
Altcode:
The presence of Kelvin-Helmholtz instability (KHI) in the sheaths
of Coronal Mass Ejections (CMEs) has been proposed and observed by
several authors in the literature. In the present work, we assume
their existence and propose a method to constrain the local properties,
like the CME magnetic field intensity for the development of KHI. We
study a CME in the initiation phase interacting with the slow solar
wind (Zone I) and with the fast solar wind (Zone II). Based on the
theory of magnetic KHI proposed by Chandrasekhar (1961) we found the
radial heliocentric interval for the KHI existence, in particular we
constrain it with the CME magnetic field intensity. We conclude that
KHI may exist in both CME Zones but it is perceived that Zone I is
more appropriated for the KHI formation.
Title: Cross and magnetic helicity in the outer heliosphere from
Voyager 2 observations
Authors: Iovieno, M.; Gallana, L.; Fraternale, F.; Richardson, J. D.;
Opher, M.; Tordella, D.
Bibcode: 2016EJMF...55..394I
Altcode: 2015arXiv150408154I
Plasma velocity and magnetic field measurements from the Voyager 2
mission are used to study solar wind turbulence in the slow solar wind
at two different heliocentric distances, 5 and 29 astronomical units,
sufficiently far apart to provide information on the radial evolution
of this turbulence. The magnetic helicity and the cross-helicity,
which express the correlation between the plasma velocity and the
magnetic field, are used to characterize the turbulence. Wave number
spectra are computed by means of the Taylor hypothesis applied to time
resolved single point Voyager 2 measurements. The overall picture we get
is complex and difficult to interpret. A substantial decrease of the
cross-helicity at smaller scales (over 1-3 hours of observation) with
increasing heliocentric distance is observed. At 5 AU the only peak in
the probability density of the normalized residual energy is negative,
near -0.5. At 29 AU the probability density becomes doubly peaked,
with a negative peak at -0.5 and a smaller peak at a positive values of
about 0.7. A decrease of the cross-helicity for increasing heliocentric
distance is observed, together with a reduction of the unbalance toward
the magnetic energy of the energy of the fluctuations. For the smaller
scales, we found that at 29 AU the normalized polarization is small and
positive on average (about 0.1), it is instead zero at 5 AU. For the
larger scales, the polarization is low and positive at 5 AU (average
around 0.1) while it is negative (around - 0.15) at 29 AU.
Title: The Heliosphere: What Did We Learn in Recent Years and the
Current Challenges
Authors: Opher, M.
Bibcode: 2016mssf.book..211O
Altcode:
No abstract at ADS
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: 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: A Model of the Heliosphere with Jets
Authors: Drake, J. F.; Swisdak, M.; Opher, M.
Bibcode: 2015AGUFMSH53C..02D
Altcode:
The conventional picture of the heliosphere is that of a comet-shaped
structure with an extended tail produced by the relative motion of the
sun through the local interstellar medium (LISM). On the other hand,
the measurements of energetic neutral atoms (ENAs) by IBEX and CASSINI
produced some surprises. The CASSINI ENA fluxes from the direction of
the nose and the tail were comparable, leading the CASSINI observers to
conclude that the heliosphere was ``tailless''. The IBEX observations
from the tail revealed that the hardest spectrum of ENAs were localized
in two lobes at high latitude while the softest spectra were at low
latitudes. Recent MHD simulations of the global heliosphere have
revealed that the heliosphere drives magnetized jets to the north and
south similar to those driven by the Crab Nebula and other astrophysical
objects [1]. That the sun's magnetic field can drive such jets when the
magnetic pressure in the outer heliosphere is small compared with the
local plasma pressure (β=8∏ P/B2 >> 1) is a major surprise. An
analytic model of the heliosheath (HS) between the termination shock
(TS) and the heliopause (HP) is developed in the limit in which the
interstellar flow and magnetic field are neglected [2]. The heliosphere
in this limit is axisymmetric. The overall structure of the HS and
HP are controlled by the solar magnetic field even in the limit of
very high β because the large pressure in the HS is to lowest order
balanced by the pressure of the LISM. The tension of the solar magnetic
field produces a drop in the total pressure between the TS and the
HP. This same pressure drop accelerates the plasma flow downstream
of the TS into the north and south directions to form two collimated
jets. The radii of these jets are controlled by the flow through the TS
and the acceleration of this flow by the magnetic field -- a stronger
solar magnetic field boosts the velocity of the jets and reduces the
radii of the jets and the HP. Magnetohydrodynamic (MHD) simulations
of the global helioshere embedded in a stationary interstellar medium
match well with the analytic model. The possbility of testing the jet
model of the heliosphere using energetic neutral atoms from the outer
heliosphere from IBEX and CASSINI is discussed. [1] Opher et al ApJ
Lett. 800, L28, 2015.[2] Drake et al ApJ Lett., in press, 2015.
Title: At What Distance are CME Deflections Determined?
Authors: Opher, M.; Kay, C.
Bibcode: 2015AGUFMSH53A2461O
Altcode:
Understanding the trajectory of a coronal mass ejection (CME), including
any deflection from a radial path, is essential for space weather
predictions. Kay et al. (2015a) developed a model, Forecasting a CME's
Altered Trajectory (ForeCAT), of CME deflections due to magnetic forces,
not including the effects of reconnection. ForeCAT is able to reproduce
the deflection of observed CMEs (Kay et al. 2015b). The deflecting
CMEs tend to show a rapid increase of their angular momentum close to
the Sun, followed by little to no increase at farther distances. Here
we quantify the distance at which the CME deflection is "determined,"
which we define as the distance after which the background solar wind
has negligible influence on the total deflection. We consider a wide
range in CME masses and radial speeds and determine that the majority
of simulated CMEs obtain 90% of their total angular momentum at 1
AU below 2 Rs. The deflection of these CMEs can be well-described
by assuming they propagate with constant angular momentum beyond 10
Rs. The assumption of constant angular momentum beyond 10 Rs yields
underestimates of the total deflection at 1 AU of only 5% to 10%. Since
the deflection from magnetic forces is determined by 10 Rs, non-magnetic
forces must be responsible for any observed interplanetary deflections
where the CME has increasing angular momentum.
Title: Magnetic flux annihilation and the development of magnetic
field depletions in the sectored heliosheath
Authors: Drake, J. F.; Swisdak, M.; Opher, M.
Bibcode: 2015AGUFMSH41C2391D
Altcode:
The dynamics of magnetic reconnection in the sectored heliosheath
isexplored with the goal of identifying signatures that can be
comparedwith Voyager observations. Simulations now include much
more realisticinitial conditions, including unequal magnetic
fluxes in adjacentsectors and very high β. Large numbers of small
magnetic islandsform early but rapidly coalesce to sector-size
structures. Thelate-time magnetic structure of the sector zone
differs greatly fromthat obtained in earlier simulations. Bands of
unreconnected azimuthalmagnetic flux thread through the simulation
domain separating regionsof depleted magnetic field strength. The
depletion regions have radialscale sizes somewhat greater than the
initial sector width. Theboundaries of the magnetic depletions are
sharp and reveal littlechange in the direction of B. The characteristic
minima of thedepletions are one third of the initial magnetic field
strength. Atlate time surviving magnetic islands are widely spaced
and occur inpairs. Cuts across the domain in the radial direction
reveal mostlyunipolar flux except when a cut crosses one of the
remnant magneticislands. This unusual late time magnetic structure
is generic resultof reconnection in a high β system. The magnetic
depletionsexhibit many of the properties of ``proton boundary layers''
seen inthe Voyager 1 magnetic field data. The simulations suggest
that significant flux loss should take place in the heliosheath,
which is consistent with Voyager measurements. The long periods of
unipolar fluxseen by Voyager 1 prior to crossing the heliopause likely
results fromthe annihilation of the sectors rather than an exit from
the sectorzone.
Title: Using ForeCAT to constrain the initial parameters of the 2010
August 14 CME in the low corona.
Authors: Opher, M.; Pisharody, V. A.; Kay, C.
Bibcode: 2015AGUFMSH53A2462O
Altcode:
Forecasting a CME's Altered Trajectory (ForeCAT) is a model of the
trajectory of coronal mass ejections (CMEs) (Kay et al. (2013,
2015)). ForeCAT models a CME as a torus, calculates magnetic
pressure and tension forces and drag at grid points along the CME,
and integrates these forces to calculate a complete trajectory. To do
so, ForeCAT must assume models of CME mass and size evolution. Kay
et al. (2015b) demonstrated that when approximating CME mass as
constant and using observed angular widths to determine CME size
evolution, ForeCAT successfully replicates the observed trajectory
of the 2008 December 12 CME. Here, we use ForeCAT to replicate the
observed trajectory of the 2010 August 14 CME assuming constant mass
and constant angular width. We also find that ForeCAT can reproduce the
observed trajectory when we assume an increasing mass with distance as
the CME propagates, and when assuming a changing angular width. Under
each of these assumptions, we calculate the reduced chi-squared between
simulated and observed latitudes to constrain CME parameters such as
drag coefficient, initial latitude and longitude, and initial speed
of the CME. With this exploration we show that ForeCAT can constrain
tightly the initial parameters of the CME in the low corona.
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: The Heliocentric Distance where the Deflections and Rotations
of Solar Coronal Mass Ejections Occur
Authors: Kay, C.; Opher, M.
Bibcode: 2015ApJ...811L..36K
Altcode: 2015arXiv150904948K
Understanding the trajectory of a coronal mass ejection (CME), including
any deflection from a radial path, and the orientation of its magnetic
field is essential for space weather predictions. Kay et al. developed
a model, Forecasting a CME’s Altered Trajectory (ForeCAT), of CME
deflections and rotation due to magnetic forces, not including the
effects of reconnection. ForeCAT is able to reproduce the deflection
of observed CMEs. The deflecting CMEs tend to show a rapid increase
of their angular momentum close to the Sun, followed by little to no
increase at farther distances. Here we quantify the distance at which
the CME deflection is “determined,” which we define as the distance
after which the background solar wind has negligible influence on the
total deflection. We consider a wide range in CME masses and radial
speeds and determine that the deflection and rotation of these CMEs
can be well-described by assuming they propagate with constant angular
momentum beyond 10 R⊙. The assumption of constant angular
momentum beyond 10 R⊙ yields underestimates of the total
deflection at 1 AU of only 1%-5% and underestimates of the rotation
of 10%. Since the deflection from magnetic forces is determined by
10 R⊙, non-magnetic forces must be responsible for any
observed interplanetary deflections or rotations where the CME has
increasing angular momentum.
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: Conditions for the existence of Kelvin-Helmholtz instability
in a CME
Authors: Jatenco-Pereira, Vera; Páez, Andrés; Falceta-Gonçalves,
Diego; Opher, Merav
Bibcode: 2015IAUGA..2226591J
Altcode:
The presence of Kelvin-Helmholtz instability (KHI) in the sheaths of
the Coronal Mass Ejection (CME) has motivated several analysis and
simulations to test their existence. In the present work we assume the
existence of the KHI and propose a method to identify the regions where
it is possible the development of KHI for a CME propagating in a fast
and slow solar wind. We build functions for the velocities, densities
and magnetic fields for two different zones of interaction between the
solar wind and a CME. Based on the theory of magnetic KHI proposed by
Chandrasekhar (1961) and we found conditions for the existence of KHI
in the CME sheaths. Using this method it is possible to determine the
range of parameters, in particular CME magnetic fields in which the
KHI could exist. We conclude that KHI may exist in the two CME flanks
and it is perceived that the zone with boundaries with the slow solar
wind is more appropriated for the formation of the KHI.
Title: A Model of the Heliosphere with Jets
Authors: Drake, J. F.; Swisdak, M.; Opher, M.
Bibcode: 2015ApJ...808L..44D
Altcode: 2015arXiv150501451D
An analytic model of the heliosheath (HS) between the termination shock
(TS) and the heliopause (HP) is developed in the limit in which the
interstellar flow and magnetic field are neglected. The heliosphere
in this limit is axisymmetric and the overall structure of the HS
and HP is controlled by the solar magnetic field even in the limit
in which the ratio of the plasma to magnetic field pressure, β =
8πP/B2, in the HS is large. The tension of the solar
magnetic field produces a drop in the total pressure between the
TS and the HP. This same pressure drop accelerates the plasma flow
downstream of the TS into the north and south directions to form
two collimated jets. The radii of these jets are controlled by the
flow through the TS and the acceleration of this flow by the magnetic
field—a stronger solar magnetic field boosts the velocity of the jets
and reduces the radii of the jets and the HP. MHD simulations of the
global heliosphere embedded in a stationary interstellar medium match
well with the analytic model. The results suggest that mechanisms that
reduce the HS plasma pressure downstream of the TS can enhance the jet
outflow velocity and reduce the HP radius to values more consistent
with the Voyager 1 observations than in current global models.
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 Effect of the Heating and Acceleration of Winds on
Conditions Ahead of Hot Jupiters: Solar and V374 Peg Cases
Authors: Kornbleuth, Marc Zachary; Opher, Merav; Evans, Rebekah M.
Bibcode: 2015shin.confE..88K
Altcode:
We study how different heating and acceleration processes of stellar
winds affect their mass-loss rates and the conditions near exo-planets
at close distances of 10 stellar radii. The exact mechanisms responsible
for the heating and acceleration of the solar wind are still being
debated. We explore thermal heating (Cohen et al. 2007) (TER) and
an Alfvén wave driven wind with Alfvén wave damping by turbulence
and surface Alfvén waves (Evans et al. 2012) (ALF). For different
solar wind models, we find a difference of orders of magnitude in
mass-loss rates for the same lower corona density and temperature. For
the M dwarf star V374 Peg, the two heating processes yield mass-loss
rates differing by a factor of 80%. For this star, an isothermal model
(Vidotto et al. 2011) (ISO) yields a different mass-loss rate from TER
by a factor of 80% and from ALF by a factor of 230%. The difference
between the mass-loss rates stems from constant, extended heating of
ISO, whereas TER and ALF have a strong variance in heating until two
stellar radii. When comparing the heating rates of ALF and TER, the
rates differ by an order of magnitude. These large differences indicate
the importance of the heating and acceleration of winds. These different
heating mechanisms also predict different conditions ahead of Hot
Jupiters for distances near 10 stellar radii. Perpendicular diffusion
has been particularly challenging for physicists. One of the relatively
unexplored topic has been the effect of turbulent structures in a
realistic physical scenario. Previous works have utilized the synthetic
realization of data that have Gaussian Probability Density Functions
(PDFs) of magnetic field differences and currents. The fields generated
this way does not take into account the effects of intermittency and
coherent structures on the diffusion coefficient. In this study we
use the results of fields generated from reduced magnetohydrodynamic
(RMHD) turbulence with and without phase randomization to examine the
effects of spatial structures and intermittency on the perpendicular
diffusion of charged particles.
Title: Radial Evolution of CME Deflection and Angular Momentum
Authors: Kay, Christina Danielle; Opher, Merav
Bibcode: 2015shin.confE.167K
Altcode:
Understanding the trajectory of a coronal mass ejection (CME), including
any deflection from a radial path, is essential for space weather
predictions. Kay et al. (2015a) developed a model, Forecasting a CME's
Altered Trajectory (ForeCAT), of CME deflection due to magnetic forces
that reproduces the general trends in the magnitude and direction of
observed CME deflections. ForeCAT can also reproduce the deflection
of individual observed CMEs (Kay et al. 2015b). The deflecting CMEs
tend to show a rapid increase in the angular momentum close to the
Sun, followed by little to no increase at farther distances. Here we
quantify the distance at which the CME deflection is 'determined,'
which we define as the distance after which the background solar
wind has negligible influence on the total deflection. We determine
this distance by calculating the radial distance at which the CME
reaches either 90% of its total deflection or angular momentum at 1
AU. We consider a wide range in CME mass and velocity parameter space
and find that the deflection is typically determined by 2 Rs. This
implies that non-magnetic forces must be responsible for any observed
interplanetary deflections where the CME actually accelerates and that
it is absolutely essential to accurately describe the solar environment
below 2 Rs to obtain accurate predictions of CME deflections.
Title: Global Trends of CME Deflections Based on CME and Solar
Parameters
Authors: Kay, C.; Opher, M.; Evans, R. M.
Bibcode: 2015ApJ...805..168K
Altcode: 2014arXiv1410.4496K
Accurate space weather forecasting requires knowledge of the trajectory
of coronal mass ejections (CMEs), including any deflections close
to the Sun or through interplanetary space. Kay et al. introduced
ForeCAT, a model of CME deflection resulting from the background
solar magnetic field. For a magnetic field solution corresponding to
Carrington Rotation (CR) 2029 (declining phase, 2005 April-May), the
majority of the CMEs deflected to the Heliospheric Current Sheet, the
minimum in magnetic pressure on global scales. Most of the deflection
occurred below 4 {{R}⊙ }. Here we extend ForeCAT to
include a three-dimensional description of the deflecting CME. We
attempt to answer the following questions: (1) do all CMEs deflect
to the magnetic minimum? and (2) does most deflection occur within
the first few solar radii (4 {{R}⊙ })? Results for solar
minimum and declining-phase CMEs show that not every CME deflects to
the magnetic minimum and that typically the majority of the deflection
occurs below 10 {{R}⊙ }. Slow, wide, low-mass CMEs in
declining-phase solar backgrounds with strong magnetic field and
magnetic gradients exhibit the largest deflections. Local gradients
related to active regions tend to cause the largest deviations from the
deflection predicted by global magnetic gradients, but variations can
also be seen for CMEs in the quiet-Sun regions of the declining-phase
CR. We show the torques due to differential forces along the CME can
cause rotation about the CME’s toroidal axis.
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: Constraining the Masses and the Non-radial Drag Coefficient
of a Solar Coronal Mass Ejection
Authors: Kay, C.; dos Santos, L. F. G.; Opher, M.
Bibcode: 2015ApJ...801L..21K
Altcode: 2015arXiv150300664K
Decades of observations show that coronal mass ejections (CMEs)
can deflect from a purely radial trajectory, however, no consensus
exists as to the cause of these deflections. Many theories attribute
CME deflection to magnetic forces. We developed Forecasting a CMEs
Altered Trajectory (ForeCAT), a model for CME deflections based
solely on magnetic forces, neglecting any reconnection effects. Here,
we compare ForeCAT predictions to the observed deflection of the
2008 December 12 CME and find that ForeCAT can accurately reproduce
the observations. Multiple observations show that this CME deflected
nearly 30° in latitude and 4.°4 in longitude. From the observations,
we are able to constrain all of the ForeCAT input parameters (initial
position, radial propagation speed, and expansion) except the CME mass
and the drag coefficient that affects the CME motion. By minimizing the
reduced chi-squared, χ ν 2, between the ForeCAT
results and the observations, we determine an acceptable mass range
between 4.5 × 1014 and 1 × 1015 g and a drag
coefficient less than 1.4 with a best fit at 7.5 × 1014
g and 0 for the mass and drag coefficient. ForeCAT is sensitive to
the magnetic background and we are also able to constrain the rate
at which the quiet Sun magnetic field falls to be similar or slightly
slower than the Potential Field Source Surface model.
Title: Magnetized Jets Driven By the Sun: the Structure of the
Heliosphere Revisited
Authors: Opher, M.; Drake, J. F.; Zieger, B.; Gombosi, T. I.
Bibcode: 2015ApJ...800L..28O
Altcode: 2014arXiv1412.7687O
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
(AUs). Here, we show, based on magnetohydrodynamic (MHD) simulations,
that the tension (hoop) 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
jets are deflected into the tail region by the motion of the Sun through
the ISM similar to bent galactic jets moving through the intergalactic
medium. 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,
as happens to some astrophysical jets. Instead, the interstellar wind
flows around the heliosphere and into the equatorial region between the
two jets. As in some astrophysical jets that are kink unstable, we show
here that the heliospheric jets are turbulent (due to large-scale MHD
instabilities and reconnection) and strongly mix the solar wind with the
ISM beyond 400 AU. 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.”
Title: Interstellar Mapping and Acceleration Probe (IMAP) - Its Time
Has Come!
Authors: Schwadron, N.; Kasper, J. C.; Mewaldt, R. A.; Moebius, E.;
Opher, M.; Spence, H. E.; Zurbuchen, T.
Bibcode: 2014AGUFMSH21D..01S
Altcode:
Our piece of cosmic real-estate, the heliosphere, is the domain
of all human existence -- an astrophysical case-history of the
successful evolution of life in a habitable system. By exploring
our global heliosphere and its myriad interactions, we develop key
physical knowledge of the interstellar interactions that influence
exoplanetary habitability as well as the distant history and destiny
of our solar system and world. IBEX was the first mission to explore
the global heliosphere and in concert with Voyager 1 and Voyager 2
is discovering a fundamentally new and uncharted physical domain of
the outer heliosphere. The enigmatic IBEX ribbon is an unanticipated
discovery demonstrating that much of what we know or think we understand
about the outer heliosphere needs to be revised. The next quantum leap
enabled by IMAP will open new windows on the frontier of Heliophysics
at a time when the space environment is rapidly evolving. IMAP with 100
times the combined resolution and sensitivity of IBEX will discover
the substructure of the IBEX ribbon and will reveal in unprecedented
resolution global maps of our heliosphere. The remarkable synergy
between IMAP, Voyager 1 and Voyager 2 will remain for at least the
next decade as Voyager 1 pushes further into the interstellar domain
and Voyager 2 moves through the heliosheath. Voyager 2 moves outward
in the vicinity of the IBEX ribbon and its plasma measurements will
create singular opportunities for discovery in the context of IMAP's
global measurements. IMAP, like ACE before it, will be a keystone of
the Heliophysics System Observatory by providing comprehensive cosmic
ray, energetic particle, pickup ion, suprathermal ion, neutral atom,
solar wind, solar wind heavy ion, and magnetic field observations to
diagnose the changing space environment and understand the fundamental
origins of particle acceleration. Thus, IMAP is a mission whose time
has come. IMAP is the highest ranked next Solar Terrestrial Probe in
the Decadal Survey, is ready to be implemented and explores fundamental
outstanding problems in Heliophysics concerning the outer boundaries
of our solar system, the physics of interstellar interactions with
the solar wind, the origin and physics of the IBEX ribbon, and the
fundamental origins particle acceleration throughout the heliosphere.
Title: The Interaction of Solar Eruptions and Large-Scale Coronal
Structures Revealed Through Modeling and Observational Analysis
Authors: Evans, R. M.; Savcheva, A. S.; Zink, J. L.; Muglach, K.;
Kozarev, K. A.; Opher, M.; van der Holst, B.
Bibcode: 2014AGUFMSH11D..05E
Altcode:
We use numerical and observational approaches to explore how
the interaction of a coronal mass ejection (CME) with preexisting
structures in the solar atmosphere influences its evolution and space
weather effects. We study two aspects of CME evolution: deflection of
the CME's propagation direction, and expansion. First, we perform a
statistical study of the influence of coronal holes on CME trajectories
for more than 50 events during years 2010-2014. Second, we use the Space
Weather Modeling Framework (SWMF) to model CME propagation in the Alfven
Wave Solar Model (AWSoM), which includes a sophisticated treatment
of the physics of coronal heating and solar wind acceleration. The
major progress in these simulations is that the initial conditions
of the eruptions are highly data-constrained. From the simulations,
we determine the CME's trajectory and expansion. We calculate the
pile-up of material along the front and sides of a CME due to its
expansion, and constrain the properties of the pile-up under a range
of conditions. Finally, we will discuss the connection between these
plasma density structures and the acceleration of protons to energies
relevant to space weather.
Title: Magnetic Reconnection in the Heliospheric Current Sheet:
The Implications of the Different Environments Seen by the
VoyagerSpacecraft
Authors: Swisdak, M. M.; Drake, J. F.; Opher, M.
Bibcode: 2014AGUFMSH11B4048S
Altcode:
The magnetic field abutting the heliospheric current sheet (HCS)
is primarily in the azimuthal direction, either east-to-west or
west-to-east. Mis-alignment of the solar rotational and magnetic
axesleads to the characteristic ballerina-skirt shape of the HCS
and during the solar cycle there can be large excursions in the
sheet's latitudinal extent. Voyager 2's observations of energetic
electrondropouts are related to its crossing of this boundary. Magnetic
reconnection is also thought to occur as the HCS compresses and narrows
between the termination shock and the heliopause. Near theequator the
two HCS field alignments are present in roughly equal amounts, while
near the edges the distribution can be considerably skewed. This will
lead to substantial differences in the environmentsof the two Voyager
spacecraft since Voyager 1 is north of the equator, but firmly in the
sector region, while Voyager 2 is south of the equator and skirting
the edges of the sector region. We presentparticle-in-cell simulations
demonstrating the consequences of the reconnection of asymmetric amounts
of flux. In particular, we will discuss Voyager 2's remaining time
in the heliosphere -- including theimplications for the solar wind
velocity, energetic particle transport, and the expected structure
of Voyager 2's heliopause crossing -- and compare it with the data
collected from Voyager 1.
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 Field Orientation Across the Heliopause As a Result
of Regions of Reconnection
Authors: Opher, M.; Drake, J. F.; Zieger, B.; Gombosi, T. I.
Bibcode: 2014AGUFMSH11B4043O
Altcode:
Based on the difference between the orientation of the interstellar and
the solar magnetic fields, there was an expectation by the community
that the magnetic field direction will rotate dramatically across the
heliopause (HP). Based on the radio emission, the Voyager team concluded
that Voyager 1 (V1) crossed into interstellar space at the end of August
2013. The question is then why there was no significant rotation in
the direction of the magnetic field across the HP. Our recent global
simulations (Opher & Drake 2013) revealed that strong rotations
in the direction of the magnetic field at the HP at the location of
V1 (and Voyager 2) are not expected. We showed that for a wide range
of orientations of BISM the angle δ = a sin(BN /B) is small (around
10◦-20◦) ahead of V1 as seen in the observations. Only after some
significant distance outside the HP (~ 20AU) is the direction of the
interstellar field distinguishably different from that of the Parker
spiral. The field outside the HP slowly rotates with a small change
(around 2 degree/AU); as seen by observations (Burlaga & Ness
2014). Here we show that the reason for the twist of the BISM to the
solar direction is due to favorable locations for global reconnection
on the HP. We explore of the effect of the location of the reconnection
on the draping of the magnetic field and flows just outside the HP. We
further explore the consequences for what Voyager 2 will encounter.
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: Magnetic Reconnection in Interplanetary Coronal Mass Ejections
Authors: Fermo, R. L.; Opher, M.; Drake, J. F.
Bibcode: 2014AGUFMSH22A..02F
Altcode:
Magnetic reconnection is a ubiquitous phenomenon in many varied space
and astrophysical plasmas, and as such plays an important role in
the dynamics of interplanetary coronal mass ejections (ICMEs). It is
widely regarded that reconnection is instrumental in the formation and
ejection of the initial CME flux rope, but reconnection also continues
to affect the dynamics as it propagates through the interplanetary
medium. For example, reconnection on the leading edge of the ICME,
by which it interacts with the interplanetary medium, leads to
flux erosion. However, recent in situ observations by Gosling et
al. found signatures of reconnection exhausts in the interior. In
light of this data, we consider the stability properties of systems
with this flux rope geometry with regard to their minimum energy
Taylor state. Variations from this state will result in the magnetic
field relaxing back towards the minimum energy state, subject to
the constraints that the toroidal flux and magnetic helicity remain
invariant. In reversed field pinches, this relaxation is mediated
by reconnection in the interior of the system, as has been shown
theoretically and experimentally. By treating the ICME flux rope in
a similar fashion, we show analytically that the the elongation of
the flux tube cross section in the latitudinal direction will result
in a departure from the Taylor state. The resulting relaxation of the
magnetic field causes reconnection to commence in the interior of the
ICME, in agreement with the observations of Gosling et al. We present
MHD simulations in which reconnection initiates at a number of rational
surfaces, and ultimately produces a stochastic magnetic field. If the
time scales for this process are shorter than the propagation time to
1 AU, this result explains why many ICME flux ropes no longer exhibit
the smooth, helical flux structure characteristic of a magnetic cloud.
Title: ForeCAT: Using CME Deflections to Constrain their Mass and
the Drag
Authors: Kay, C.; dos Santos, L. F. G.; Opher, M.
Bibcode: 2014AGUFMSH43B4210K
Altcode:
Observations show that CMEs can deflect from a purely radial trajectory
yet no consensus exists as to the cause of these deflections. The
majority of the deflection motion occurs in the corona at distances
where the magnetic energy dominates. Accordingly, many theories
attribute the CME deflection to magnetic forces. In Kay et al. (2013)
we presented ForeCAT, a model for CME deflections based on the magnetic
forces (magnetic tension and magnetic pressure gradients). Kay
et al. (2014) introduced an improved three-dimensional version of
ForeCAT. Here we study the 2008 December 12 CME which occurred during
solar minimum of Solar Cycle 24 (Byrne et al 2010, Gui et al. 2011,
Liu et al 2010a,b). This CME erupted from high latitudes, and,
despite the weak background magnetic field, deflected to the ecliptic,
impacting Earth. From the observations, we are able to constrain all
of the ForeCAT input parameters except for the CME mass and the drag
coefficient that affects the CME motion. The reduced chi-square best
fit to the observations constrains the CME mass range to 3e14 to 7e14
g and the drag coefficient range to 1.9 to 2.4. We explore the effects
of a different magnetic background which decreases less rapidly than
our standard Potential Field Source Surface (PFSS) model, as type II
radio bursts suggest that the PFSS magnetic field decays too rapidly
above active regions. For the case of the filament eruption of 2008
December 12 we find that the quiet sun coronal magnetic field should
behave similar to the PFSS model. Finally, we present our current work
exploring the case of the 2008 April 9 CME.
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: Magnetic Reconnection in the Interior of Interplanetary
Coronal Mass Ejections
Authors: Fermo, R. L.; Opher, M.; Drake, J. F.
Bibcode: 2014PhRvL.113c1101F
Altcode:
Recent in situ observations of interplanetary coronal mass ejections
(ICMEs) found signatures of reconnection exhausts in their interior or
trailing edge. Whereas reconnection on the leading edge of an ICME would
indicate an interaction with the coronal or interplanetary environment,
this result suggests that the internal magnetic field reconnects with
itself. In light of this data, we consider the stability properties of
flux ropes first developed in the context of astrophysics, then further
elaborated upon in the context of reversed field pinches (RFPs). It
was shown that the lowest energy state of a flux rope corresponds to
∇×B=λB with λ a constant, the so-called Taylor state. Variations
from this state will result in the magnetic field trying to reorient
itself into the Taylor state solution, subject to the constraints that
the toroidal flux and magnetic helicity are invariant. In reversed
field pinches, this relaxation is mediated by the reconnection of
the magnetic field, resulting in a sawtooth crash. If we likewise
treat the ICME as a flux rope, any deviation from the Taylor state
will result in reconnection within the interior of the flux tube, in
agreement with the observations by Gosling et al. Such a departure
from the Taylor state takes place as the flux tube cross section
expands in the latitudinal direction, as seen in magnetohydrodynamic
(MHD) simulations of flux tubes propagating through the interplanetary
medium. We show analytically that this elongation results in a state
which is no longer in the minimum energy Taylor state. We then present
magnetohydrodynamic simulations of an elongated flux tube which has
evolved away from the Taylor state and show that reconnection at many
surfaces produces a complex stochastic magnetic field as the system
evolves back to a minimum energy state configuration.
Title: Do All CMEs Deflect to the Magnetic Minimum by 4 Rs?
Authors: Kay, Christina Danielle; Opher, Merav
Bibcode: 2014shin.confE..11K
Altcode:
Accurate space weather forecasting requires knowledge of the trajectory
of coronal mass ejections (CMEs), including any CME deflection close to
the Sun or through interplanetary space. Kay et al. (2013) introduced
ForeCAT, a model of CME deflection resulting from the background solar
magnetic field. For a magnetic background corresponding to Carrington
Rotation (CR) 2029, the majority of CMEs deflected to the streamer
belt, the minimum in magnetic pressure, below 4 Rs. We have eliminated
many of the underlying simplifications of ForeCAT presented in Kay et
al. (2013) with a more detailed three dimensional description of the
deflecting flux rope. We answer two questions: Do all CMEs deflect to
the magnetic minimum? Does all deflection occur within 4 Rs?
Title: Flux rope degradation of ICMEs by interior reconnection
Authors: Fermo, Raymond Luis; Opher, M.; Drake, J. F.
Bibcode: 2014shin.confE..35F
Altcode:
The magnetic structure of interplanetary coronal mass ejections
(ICMEs) is often considered to be a magnetic cloud, characterized by a
smooth rotation of the magnetic field. However, perhaps as few as 30%
of observed ICMEs display such a coherent helical flux rope geometry
(Gosling et al., 1990). We propose that reconnection in the interior
of the ICME could result in a complex stochastic magnetic field and
the destruction of the magnetic cloud structure. Such reconnection
events within the core of ICMEs have been seen in recent in situ
observations (Gosling et al., 2007). We show that reconnection can be
initiated as the ICME flux rope becomes elongated in the latitudinal
direction as it propagates through the interplanetary medium. This
elongation forces the ICME flux rope from its force-free Taylor state,
and as a consequence, the flux rope will attempt to relax back to that
minimum energy state. Subject to the constraints that the toroidal
flux and magnetic helicity are invariant, this relaxation must be
mediated by reconnection of the interior magnetic field. We present
MHD simulations of an elongated flux rope which has evolved away from
the Taylor state and show that reconnection at many surfaces produces
a stochastic magnetic field as the system evolves back to a minimum
energy state configuration.
Title: Implications of CME Deflections on the Habitability of Planets
Around M Dwarfs
Authors: Kay, Christina; Opher, Merav
Bibcode: 2014AAS...22412024K
Altcode:
Solar coronal mass ejections (CMEs) are known to produce adverse
space weather effects at Earth. These effects include geomagnetically
induced currents and energetic particles accelerated by CME-driven
shocks. Significant non-radial motions are observed for solar CMEs with
the CME path deviating as much as 30 degrees within 20 solar radii. We
have developed a model, Forecasting a CME's Altered Trajectory
(ForeCAT), which predicts the deflected path of a CME according
to the magnetic forces of the background solar wind. In Kay et al
(2013), we show that these magnetic forces cause CMEs to deflect
towards the region of minimum magnetic field strength. For the Sun,
this magnetic minimum corresponds to the Heliospheric Current Sheet
(HCS). We predict that the Earth is most likely to be impacted by a
deflected CME when its orbit brings it near the HCS. M dwarfs can have
magnetic field strengths several orders of magnitude larger than the
Sun which will strongly affect CME deflections. We explore stellar CME
deflections with ForeCAT. We present results for M4V star V374 Peg. We
determine potential impacts caused by CME deflections for a planet
located within the habitable zone of V374 Peg 20-40 solar radii). We
discuss future extensions as including variations in solar cycle,
capturing small structures such as active regions, and extensions for
other M dwarf stars.
Title: Do all CMEs deflect to the background magnetic minimum by 4Rs?
Authors: Kay, Christina; Opher, Merav
Bibcode: 2014AAS...22430305K
Altcode:
Accurate space weather forecasting requires knowledge of the trajectory
of coronal mass ejections (CMEs), including any CME deflection close to
the Sun or through interplanetary space. Kay et al. (2013) introduced
ForeCAT, a model of CME deflection resulting from the background solar
magnetic field. For a magnetic background corresponding to Carrington
Rotation (CR) 2029 (declining phase, April-May 2005), the majority
of the CMEs deflected to the streamer belt, the minimum in magnetic
pressure. Most of the deflection occurred below 4 Rs. Here we explore
the questions: a) Do all CMEs deflect to the magnetic minimum? and b)
Does most deflection occur within 4 Rs? We have eliminated many of the
underlying simplifications of ForeCAT presented in Kay et al. (2013)
with a more detailed three dimensional description of the deflecting
flux rope. The locations of coronal magnetic structures that determine
the background magnetic minima vary throughout the solar cycle. We
show that these variations reproduce observed trends in the direction
of CME deflections throughout the solar cycle.
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: M-dwarf stellar winds: the effects of realistic magnetic
geometry on rotational evolution and planets
Authors: Vidotto, A. A.; Jardine, M.; Morin, J.; Donati, J. F.; Opher,
M.; Gombosi, T. I.
Bibcode: 2014MNRAS.438.1162V
Altcode: 2013MNRAS.tmp.2947V; 2013arXiv1311.5063V
We perform three-dimensional numerical simulations of stellar winds
of early-M-dwarf stars. Our simulations incorporate observationally
reconstructed large-scale surface magnetic maps, suggesting that the
complexity of the magnetic field can play an important role in the
angular momentum evolution of the star, possibly explaining the large
distribution of periods in field dM stars, as reported in recent
works. In spite of the diversity of the magnetic field topologies
among the stars in our sample, we find that stellar wind flowing
near the (rotational) equatorial plane carries most of the stellar
angular momentum, but there is no preferred colatitude contributing
to mass-loss, as the mass flux is maximum at different colatitudes
for different stars. We find that more non-axisymmetric magnetic
fields result in more asymmetric mass fluxes and wind total pressures
ptot (defined as the sum of thermal, magnetic and ram
pressures). Because planetary magnetospheric sizes are set by pressure
equilibrium between the planet's magnetic field and ptot,
variations of up to a factor of 3 in ptot (as found in the
case of a planet orbiting at several stellar radii away from the star)
lead to variations in magnetospheric radii of about 20 per cent along
the planetary orbital path. In analogy to the flux of cosmic rays that
impact the Earth, which is inversely modulated with the non-axisymmetric
component of the total open solar magnetic flux, we conclude that
planets orbiting M-dwarf stars like DT Vir, DS Leo and GJ 182, which
have significant non-axisymmetric field components, should be the more
efficiently shielded from galactic cosmic rays, even if the planets
lack a protective thick atmosphere/large magnetosphere of their own.
Title: Dependence of Energetic Ion and Electron Intensities on
Proximity to the Magnetically Sectored Heliosheath: Voyager 1 and
2 Observations
Authors: Hill, M. E.; Decker, R. B.; Brown, L. E.; Drake, J. F.;
Hamilton, D. C.; Krimigis, S. M.; Opher, M.
Bibcode: 2014ApJ...781...94H
Altcode:
Taken together, the Voyager 1 and 2 (V1 and V2) spacecraft have
collected over 11 yr of data in the heliosheath. Despite extensive
study, energetic particles and magnetic fields measured in the
heliosheath have not been reconciled by existing models. In particular,
the differences between the energetic particle intensity variations at
V1 and V2 are unexplained. While energetic particle intensities at V1
change gradually over 7 yr in the heliosheath, those at V2 vary by a
factor ~10 in 1 yr. Energetic particle intensities at V2 show temporally
coherent variations over a broad range of species and energies: from
suprathermal ions (10s of keV) to galactic cosmic rays (>1 GeV),
as well as electrons from 10s of keV to >100 MeV, corresponding to
a range ~104 in particle gyroradii. Here we suggest that
many of the intensity variations of energetic particle populations in
the heliosheath are organized by their proximity to two fundamentally
different regions—the unipolar heliosheath (UHS) and the sectored
heliosheath (SHS). The SHS is a region of enhanced particle intensities,
wherein particle transport, acceleration, and magnetic connectivity
differ from those in the UHS. The SHS may serve as either a reservoir
of energetic particles or as a region of enhanced transport, depending
on the particle species and energy. Comparatively, particle intensities
in the UHS are greatly reduced. We propose that the boundary between
the SHS and UHS plays as important a role in the physics of heliosheath
particles and fields as do the termination shock and heliopause.
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: On the Rotation the Interstellar Magnetic Field Ahead of
the Heliopause
Authors: Opher, Merav; Drake, James
Bibcode: 2014cosp...40E2381O
Altcode:
Based on the difference between the orientation of the interstellar and
the solar magnetic fields, there was an expectation by the community
that the magnetic field direction will rotate dramatically across the
heliopause (HP). Recently, the Voyager team concluded that Voyager 1
(V1) crossed into interstellar space last year. The question is then
why there was no significant rotation in the direction of the magnetic
field across the HP. Here we present simulations that reveal that
strong rotations in the direction of the magnetic field at the HP at
the location of V1 (and Voyager 2) are not expected. The solar magnetic
field strongly affects the draping of the interstellar magnetic field
(BISM) around the HP. BISM twists as it approaches the HP and acquires
a strong T component (East-West). The strong increase in the T component
occurs where the interstellar flow stagnates in front of the HP. At this
same location the N component BN is significantly reduced. Above and
below, the neighboring BISM lines also twist into the T direction. This
behavior occurs for a wide range of orientations of BISM. The angle
delta = a sin(BN /B) is small (around 10(°) -20(°) ), as seen in the
observations. Only after some significant distance outside the HP is the
direction of the interstellar field distinguishably different from that
of the Parker spiral. In the twist region (after the HP) there is a fast
variation of the angle delta/AU and then a slower one farther away as
seen in the observations (Burlaga & Ness 2014). We will discuss,
as well in this talk, the mechanism responsible for the twist. The
same twist is seen ahead of the magnetopause, where the field in the
magnetosheath (equivalent to BISM) (in cases where reconnection is
small) rotates toward the direction of the magnetospheric magnetic field
(equivalent to the HS magnetic field) well upstream of the magnetopause
(Phan et al. 1994). The IBEX ribbon, the band of increased intensity
of energetic neutral atoms at 1 keV in the outer heliosphere, was
originally believed to be aligned with the BISM · r = 0 just outside
the HP. These results indicate that the draping of BISM is strongly
influenced by the solar magnetic field. Only beyond ≈10 AU outside
the HP is the centroid of the band of BISM · r = 0 is aligned with
the original BISM direction.
Title: Interactions between exoplanets and the winds of young stars
Authors: Vidotto, A. A.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2014EPJWC..6404006V
Altcode:
The topology of the magnetic field of young stars is important
not only for the investigation of magnetospheric accretion, but
also responsible in shaping the large-scale structure of stellar
winds, which are crucial for regulating the rotation evolution of
stars. Because winds of young stars are believed to have enhanced
mass-loss rates compared to those of cool, main-sequence stars, the
interaction of winds with newborn exoplanets might affect the early
evolution of planetary systems. This interaction can also give rise
to observational signatures which could be used as a way to detect
young planets, while simultaneously probing for the presence of their
still elusive magnetic fields. Here, we investigate the interaction
between winds of young stars and hypothetical planets. For that, we
model the stellar winds by means of 3D numerical magnetohydrodynamic
simulations. Although these models adopt simplified topologies of the
stellar magnetic field (dipolar fields that are misaligned with the
rotation axis of the star), we show that asymmetric field topologies can
lead to an enhancement of the stellar wind power, resulting not only
in an enhancement of angular momentum losses, but also intensifying
and rotationally modulating the wind interactions with exoplanets.
Title: Do all CMEs deflect to the background magnetic minimum by 4Rs?
Authors: Kay, Christina; Opher, Merav
Bibcode: 2014cosp...40E1437K
Altcode:
Accurate space weather forecasting requires knowledge of the trajectory
of coronal mass ejections (CMEs), including any CME deflection close to
the Sun or through interplanetary space. Kay et al. (2013) introduced
ForeCAT, a model of CME deflection resulting from the background solar
magnetic field. For a magnetic background corresponding to Carrington
Rotation (CR) 2029 (declining phase, April-May 2005), the majority
of the CMEs deflected to the streamer belt, the minimum in magnetic
pressure. Most of the deflection occurred below 4 Rs. Here we explore
the questions: a) Do all CMEs deflect to the magnetic minimum? and b)
Does most deflection occur within 4 Rs? We have eliminated many of the
underlying simplifications of ForeCAT presented in Kay et al. (2013)
with a more detailed three dimensional description of the deflecting
flux rope. The locations of coronal magnetic structures that determine
the background magnetic minima vary throughout the solar cycle. We
show that these variations reproduce observed trends in the direction
of CME deflections throughout the solar cycle. We further explore the
sensitivity of deflections to changes in the background magnetic minima
at distances 1-2Rs guided by polarizations measures by instruments such
ComP. Such deflections could be a probe of the lower corona background
at these small distances.
Title: On the Rotation of the Magnetic Field Across the Heliopause
Authors: Opher, M.; Drake, J. F.
Bibcode: 2013ApJ...778L..26O
Altcode: 2013arXiv1310.0808O
Based on the difference between the orientation of the interstellar and
the solar magnetic fields, there was an expectation by the community
that the magnetic field direction will rotate dramatically across the
heliopause (HP). Recently, the Voyager team concluded that Voyager 1
(V1) crossed into interstellar space last year. The question is then
why there was no significant rotation in the direction of the magnetic
field across the HP. Here we present simulations that reveal that
strong rotations in the direction of the magnetic field at the HP
at the location of V1 (and Voyager 2) are not expected. The solar
magnetic field strongly affects the drapping of the interstellar
magnetic field (B ISM) around the HP. B ISM
twists as it approaches the HP and acquires a strong T component
(East-West). The strong increase in the T component occurs where the
interstellar flow stagnates in front of the HP. At this same location
the N component BN is significantly reduced. Above and
below, the neighboring B ISM lines also twist into the T
direction. This behavior occurs for a wide range of orientations of B
ISM. The angle δ = asin (BN /B) is small (around
10°-20°), as seen in the observations. Only after some significant
distance outside the HP is the direction of the interstellar field
distinguishably different from that of the Parker spiral.
Title: Global Numerical Modeling of Energetic Proton Acceleration
in a Coronal Mass Ejection Traveling through the Solar Corona
Authors: Kozarev, Kamen A.; Evans, Rebekah M.; Schwadron, Nathan A.;
Dayeh, Maher A.; Opher, Merav; Korreck, Kelly E.; van der Holst, Bart
Bibcode: 2013ApJ...778...43K
Altcode: 2014arXiv1406.2377K
The acceleration of protons and electrons to high (sometimes
GeV/nucleon) energies by solar phenomena is a key component of
space weather. These solar energetic particle (SEP) events can damage
spacecraft and communications, as well as present radiation hazards to
humans. In-depth particle acceleration simulations have been performed
for idealized magnetic fields for diffusive acceleration and particle
propagation, and at the same time the quality of MHD simulations of
coronal mass ejections (CMEs) has improved significantly. However,
to date these two pieces of the same puzzle have remained largely
decoupled. Such structures may contain not just a shock but also
sizable sheath and pileup compression regions behind it, and may vary
considerably with longitude and latitude based on the underlying
coronal conditions. In this work, we have coupled results from a
detailed global three-dimensional MHD time-dependent CME simulation to
a global proton acceleration and transport model, in order to study
time-dependent effects of SEP acceleration between 1.8 and 8 solar
radii in the 2005 May 13 CME. We find that the source population is
accelerated to at least 100 MeV, with distributions enhanced up to
six orders of magnitude. Acceleration efficiency varies strongly along
field lines probing different regions of the dynamically evolving CME,
whose dynamics is influenced by the large-scale coronal magnetic field
structure. We observe strong acceleration in sheath regions immediately
behind the shock.
Title: Probing the Nature of the Heliosheath with the Neutral Atom
Spectra Measured by IBEX in the Voyager 1 Direction
Authors: Opher, M.; Prested, C.; McComas, D. J.; Schwadron, N. A.;
Drake, J. F.
Bibcode: 2013ApJ...776L..32O
Altcode:
We are able to show by comparing modeled energetic neutral atoms (ENAs)
spectra to those measured by Interstellar Boundary Explorer (IBEX) that
the models along the Voyager 1 (V1) trajectory that best agree with
the low energy IBEX data include extra heating due to ram and magnetic
energy in the quasi-stagnation region or a kappa ion distribution
(with κ = 2.0) in the outer heliosheath. The model explored is the
multi-ion, multi-fluid (MI-MF) which treats the pick-up ions and the
thermal ion fluids with separate Maxwellian distributions. These effects
are included ad hoc in the modeled ENA since they are not present
in the model. These results indicate that the low energy spectra of
ENAs as measured by IBEX is sensitive to the physical nature of the
heliosheath and to effects not traditionally present in current global
models. Therefore, by comparing the low energy ENA spectra to models,
we can potentially probe the heliosheath in locations beyond those
probed by V1 and Voyager 2 (V2).
Title: A Porous, Layered Heliopause
Authors: Swisdak, M.; Drake, J. F.; Opher, M.
Bibcode: 2013ApJ...774L...8S
Altcode: 2013arXiv1307.0850S
The picture of the heliopause (HP)—the boundary between the domains
of the Sun and the local interstellar medium (LISM)—as a pristine
interface with a large rotation in the magnetic field fails to describe
recent Voyager 1 (V1) data. Magnetohydrodynamic (MHD) simulations of
the global heliosphere reveal that the rotation angle of the magnetic
field across the HP at V1 is small. Particle-in-cell simulations,
based on cuts through the MHD model at V1's location, suggest that
the sectored region of the heliosheath (HS) produces large-scale
magnetic islands that reconnect with the interstellar magnetic field
while mixing LISM and HS plasma. Cuts across the simulation reveal
multiple, anti-correlated jumps in the number densities of LISM and HS
particles, similar to those observed, at the magnetic separatrices. A
model is presented, based on both the observations and simulations,
of the HP as a porous, multi-layered structure threaded by magnetic
fields. This model further suggests that contrary to the conclusions
of recent papers, V1 has already crossed the HP.
Title: Forecasting a Coronal Mass Ejection's Altered Trajectory:
ForeCAT
Authors: Kay, C.; Opher, M.; Evans, R. M.
Bibcode: 2013ApJ...775....5K
Altcode: 2013arXiv1307.7603K
To predict whether a coronal mass ejection (CME) will impact Earth,
the effects of the background on the CME's trajectory must be taken
into account. We develop a model, ForeCAT (Forecasting a CME's Altered
Trajectory), of CME deflection due to magnetic forces. ForeCAT includes
CME expansion, a three-part propagation model, and the effects of drag
on the CME's deflection. Given the background solar wind conditions,
the launch site of the CME, and the properties of the CME (mass, final
propagation speed, initial radius, and initial magnetic strength),
ForeCAT predicts the deflection of the CME. Two different magnetic
backgrounds are considered: a scaled background based on type II
radio burst profiles and a potential field source surface (PFSS)
background. For a scaled background where the CME is launched from
an active region located between a coronal hole and streamer region,
the strong magnetic gradients cause a deflection of 8.°1 in latitude
and 26.°4 in longitude for a 1015 g CME propagating out to
1 AU. Using the PFSS background, which captures the variation of the
streamer belt (SB) position with height, leads to a deflection of 1.°6
in latitude and 4.°1 in longitude for the control case. Varying the
CME's input parameters within observed ranges leads to the majority
of CMEs reaching the SB within the first few solar radii. For these
specific backgrounds, the SB acts like a potential well that forces
the CME into an equilibrium angular position.
Title: Coronal Mass Ejection Plasma Heating by Alfven Wave Dissipation
Authors: Evans, Rebekah M.; Opher, M.; Van Der Holst, B.
Bibcode: 2013SPD....4410401E
Altcode:
Recent studies suggest that the thermal energy input into a coronal
mass ejection is comparable to the kinetic energy. The dissipation
of magnetic energy is thought to be the source of this heating. One
possible mechanism, the dissipation of Alfven waves, has generally
been neglected because heating rates calculated from models of the fast
solar wind are orders of magnitude less than what is required to match
CME plasma observations. Using new a three-dimensional solar wind model
driven by Alfven waves within the Space Weather Modeling Framework, we
simulate eruptions in the low to middle corona. The goal is to explore
the self-consistent heating of CME plasma by wave dissipation. We find
that the expansion of a flux rope can create regions of enhanced plasma
density at the back of the sheath, which we call piled-up compression
(PUC) regions. The Alfven wave energy is also enhanced in the sheath,
where surface Alfven wave damping due to the density gradients
dissipates the wave energy. This heating rate is orders of magnitude
larger than the heating rate in the fast solar wind, which suggests
that Alfven wave dissipation may play a role in CME plasma heating.
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: Predicting CME Deflections Using ForeCAT
Authors: Kay, Christina Danielle; Opher, M.; Evans, R. M.
Bibcode: 2013shin.confE..73K
Altcode:
To predict whether a coronal mass ejection (CME) will impact Earth,
the effects of the background on the CME's trajectory must be taken
into account. We developed a model, ForeCAT (Forecasting a CME's Altered
Trajectory), of CME deflection due to magnetic forces. ForeCAT includes
CME expansion, a three-part propagation model, and the effects of drag
on the CME's deflection. Given the background solar wind conditions,
the launch site of the CME, and the properties of the CME (mass, final
propagation speed, initial radius, and initial magnetic strength),
ForeCAT predicts the deflection of the CME. Two different magnetic
backgrounds are considered: a scaled magnetic background and a
Potential Field Source Surface (PFSS) background. The scaled magnetic
background scales with distance as R^-2 (for quiet sun) and R^-3 (for
active regions). The magnetic field in the PFSS description falls much
quicker but captures the variation of features with height, such as
the streamer belt position. The CME is launched from an active region
located between a CH and streamer region and the magnetic gradients
deflect the CME towards the minimum in magnetic intensity. For this
background with strong magnetic gradients, the streamer belt acts
as a potential well that forces the CME into an equilibrium angular
position when only magnetic forces are considered. For the scaled
magnetic background this leads to deflection of 8.1° in latitude and
26.4° in longitude for a CME with initial mass 10^15 g. For the PFSS
background, in turn the deflection is much smaller, 1.6° in latitude
and 4.1° in longitude. ForeCAT shows that magnetic forces alone can
reproduce deflections of comparable magnitude to those observed in
coronagraph images. Future work will explore further the effects of
different magnetic backgrounds and many of the underlying assumptions
in ForeCAT and provide comparisons with observed deflections.
Title: Features of coronal SEP acceleration in a globally modeled
realistic CME
Authors: Kozarev, Kamen Asenov; Evans, Rebekah; Schwadron, Nathan;
Opher, Merav; Korreck, Kelly
Bibcode: 2013shin.confE.133K
Altcode:
The next generation of solar exploratory missions (Solar Probe Plus
and Solar Orbiter) will probe the plasma and particle conditions
near the Sun directly. Recent studies suggest that solar energetic
particles (SEP) may gain most of their energy at coronal mass ejection
(CME)-driven shocks relatively close to the Sun, and therefore a
better understanding of these acceleration processes in the corona is
necessary. The rapidly varying conditions in the corona during CMEs,
and the highly compressed sheaths that may form in front of ejecta,
likely enable rapid particle acceleration to high energies. By combining
a realistic time-dependent MHD model of a CME in the low and middle
corona (SWMF) with a global kinetic acceleration and transport model
(EPREM), we address two important questions concerning coronal SEP
acceleration: 1) How do changes in the CME plasma environment influence
local adiabatic acceleration on open field lines? 2) What role does
stochastic acceleration play in coronal SEP creation?
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: Global Modeling of the July 23, 2012 Coronal Mass Ejection
and Solar Energetic Particle Event
Authors: Evans, Rebekah Minnel; Kozarev, Kamen A.; Schwadron, Nathan
A.; Opher, Merav; Manchester, Ward; Sokolov, Igor; van der Holst, Bart
Bibcode: 2013shin.confE...7E
Altcode:
The CME and SEP event of July 23, 2012 was extreme in many ways - the
speed of a CME as imaged in coronagraphs, the speed and magnetic field
strength measured in-situ, and the level of energetic particles. Another
special feature of this event is that it caused SEP events at Earth,
STEREO A and STEREO B, which were very separated at the time. The
extreme and whole-heliosphere nature of this event makes it an
excellent candidate to study with two recently coupled models: the
Space Weather Modeling Framework (SWMF) and the Energetic Particle
Radiation Environment Module (EPREM). The SWMF, which itself couples
three-dimensional magnetohydrodynamic (MHD) models describing the solar
corona and heliosphere, is used to simulate the eruption starting
from the low corona. The MHD output describing the fast CME event
is coupled to a global kinetic simulation of particle acceleration
and transport within EPREM. The output of the particle simulation is
synthetic time-dependent spectra influenced by the dynamics of CME
structures that form self-consistently during propagation. With these
simulations, we can probe how the properties of the CME sheath and shock
vary as the CME interacts with the ambient corona and heliosphere. These
simulations can test current theories of SEP production, including
how SEP properties relate to the properties of the associated CME,
CME-driven shock and coronal environment. Finally, we can trace how
particles that interacted with the CME near the Sun propagate throughout
the heliosphere.
Title: Magnetic reconnection in the interior of interplanetary
coronal mass ejections
Authors: Fermo, Raymond Luis; Opher, Merav; Drake, James F.
Bibcode: 2013shin.confE..69F
Altcode:
Recent in situ observations of interplanetary coronal mass ejections
(ICMEs) found signatures of reconnection exhausts in their interior
or trailing edge. Whereas reconnection on the leading edge of an ICME
would indicate an interaction with the coronal or interplanetary
environment, this result suggests that the internal magnetic field
reconnects with itself. In light of this data, we consider some of the
physics developed by the fusion plasma community. In the context of a
tokamak, Taylor showed that the lowest energy state corresponds to one
in which curl B = lambda B with constant lambda, the so-called Taylor
state. Variations from this state will result in the magnetic field
trying to re-orient itself into the Taylor state solution, subject
to the constraints that the toroidal flux and magnetic helicity are
invariant. This relaxation is mediated by the reconnection of magnetic
field lines along rational surfaces, that is, flux surfaces where the
safety factor q = m/n for integer m and n. In tokamaks, the result is
a "sawtooth crash" te{Kadomtsev75b}. In an ICME, if we likewise treat
the flux rope as a toroidal flux tube, any variation from the Taylor
state will result in reconnection within the interior of the flux tube,
in agreement with the observation by Gosling et al (2007). One such
way in which the Taylor state might be violated is by the elongation
of the flux tube cross section in the non-radial direction, as seen
in magnetohydrodynamic (MHD) simulations of flux tubes propagating
through the interplanetary medium. We show analytically that this this
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: The Slow Bow Shock Model of the Heliospheric Interface
Authors: Zieger, B.; Opher, M.
Bibcode: 2013AGUSMSH24A..04Z
Altcode:
Recent IBEX observations indicate that the pristine interstellar
wind is most likely subfast and sub-Alfvenic, which means that
no regular fast magnetosonic bow shock can form upstream of the
heliosphere. Nevertheless, a slow magnetosonic bow shock can still exist
in the local interstellar medium, provided that the angle between the
interstellar magnetic field and the interstellar plasma flow velocity
(alpha_Bv) is sufficiently small. The latter is supported by a number
of kinetic-gasdynamic and multi-fluid MHD simulations that used the
Voyager termination shock crossings to constrain the magnitude (3 to 4
microG) and direction (alpha_Bv= 15 to 30 degrees) of the interstellar
magnetic field. We propose a quasi-parallel slow bow shock model as a
likely alternative of the currently prevailing no bow shock model. The
theoretically expected slow bow shock is self-consistently reproduced
in our multi-fluid MHD simulations. Since slow-mode information
can propagate mainly along the magnetic field, the slow bow shock is
significantly shifted from the nose of the heliosphere toward the flank
in the direction of the interstellar magnetic field. Such a displaced
slow bow shock results in a dense and highly asymmetric hydrogen wall
that is expected to produce detectable extra Lyman alpha absorption not
only around the nose direction but also in some preferential tailward
directions. This could explain among others the puzzling blue shift
observed in the Lyman alpha absorption profile of Sirius. The slow
bow shock model could easily explain the hotter and slower secondary
interstellar hydrogen population observed by IBEX, which is thought to
originate from the outer heliosheath. Thus both Lyman alpha and IBEX
observations seem to be more consistent with a slow bow shock rather
than a shock-free fast bow wave. Voyager 1 is most likely heading
towards the slow bow shock, while Voyager 2 is not, which means that
the two spacecraft are expected to encounter fundamentally different
interstellar plasma populations beyond the heliopause.
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: Update from the BU-CME Group: Accurate Prediction of CME
Deflection and Magnetic reconnection in the interior of interplanetary
CMEs
Authors: Opher, M.; Kay, C.; Fermo, R. L.; Drake, J. F.; Evans, R. M.
Bibcode: 2013AGUSMSH23B..02O
Altcode:
The accurate prediction of the path of coronal mass ejections (CMEs)
plays an important role in space weather forecasting, and knowing
the source location of the CME does not always suffice. During
solar minimum, for example, polar coronal holes (CHs) can deflect
high latitude CMEs toward the ecliptic plane and when CHs extend to
lower latitudes deflections in other directions can occur. To predict
whether a CME will impact Earth the effects of the solar background
on the CME's trajectory must be taken into account. Here we develop a
model (Kay et al. 2013), called ForeCAT (Forecasting a CME's Altered
Trajectory), of CME deflection close to the Sun where magnetic forces
dominate. Given the background solar wind conditions, the launch
site of the CME, and the properties of the CME (such as its mass and
size), ForeCAT predicts the deflection of the CME as well as the full
trajectory as the CME propagates away from the Sun. For a magnetic
background where the CME is launched from an active region located in
between a CH and streamer region the strong magnetic gradients cause
a deflection of 39.0o in latitude and 21.9o
in longitude. Varying the CME's input parameters within observed
ranges leads to deflections predominantly between 36.2o
and 44.5o in latitude and between 19.5o and 27.9
in longitude. For all cases, the majority of the deflection occurs
before the CME reaches a radial distance of 3 R⊙. Recent in situ
observations of interplanetary mass ejections (ICMEs) found signatures
of reconnection exhausts in their interior or trailing edge. This result
suggests that the internal magnetic field reconnects with itself. To
this end, we propose an approach (Fermo et al. 2013) borrowed from
the fusion plasma community. Taylor (1974) showed that the lowest
energy state corresponds to one in which \grad × B = λ B. Variations
from this state will result in the magnetic field trying to re-orient
itself into the Taylor state solution, subject to the constraints that
the toroidal flux and magnetic helicity are invariant. In tokamaks,
the result is a sawtooth crash. In an ICME, if we likewise treat the
flux rope as a toroidal flux tube, any variation from the Taylor state
will result in reconnection within the interior of the flux tube,
in accord with the observations by Gosling et al. (2007). We present
MHD and PIC simulations that shows that indeed this is the case and
discuss the implications for ICMEs.
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: Magnetic Flux Conservation in the Heliosheath
Authors: Richardson, J. D.; Burlaga, L. F.; Decker, R. B.; Drake,
J. F.; Ness, N. F.; Opher, M.
Bibcode: 2013ApJ...762L..14R
Altcode:
Voyager 1(V1) and Voyager 2(V2) have observed heliosheath plasma since
2005 December and 2007 August, respectively. The observed speed profiles
are very different at the two spacecrafts. Speeds at V1 decreased
to zero in 2010 while the average speed at V2 is a constant 150 km
s-1 with the direction rotating tailward. The magnetic flux
is expected to be constant in these heliosheath flows. We show that
the flux is constant at V2 but decreases by an order of magnitude at
V1, even after accounting for divergence of the flows and changes in
the solar field. If reconnection were responsible for this decrease,
the magnetic field would lose 70% of its free energy to reconnection
and the energy density released would be 0.6 eV cm-3.
Title: Intensities and spectral properties of 0.03-6 keV Energetic
Neutral Atoms Measured by the Interstellar Boundary Explorer (IBEX)
Along the Lines-of-Sight of Voyager
Authors: Desai, M. I.; Allegrini, F.; Dayeh, M. A.; DeMajistre, B.;
Funsten, H. O.; Heerikhuisen, J.; McComas, D. J.; Pogorelov, N. V.;
Prested, C. L.; Opher, M.; Schwadron, N. A.; Zank, G. P.; Fuselier,
S. A.
Bibcode: 2012AGUFMSH13D..08D
Altcode:
Energetic Neutral Atoms (ENAs) observed by the Interstellar Boundary
Explorer (IBEX) provide powerful diagnostics about the origin of the
progenitor ion populations and the physical mechanisms responsible
for their production. Here we survey the fluxes, energy spectra,
and energy-dependence of the spectral indices of ~0.03-6 keV ENAs
measured by IBEX-Hi and IBEX-Lo along the lines-of-sight of Voyager 1
and 2. We compare the ENA spectra observed at IBEX with predictions of
models that simulate the microphysics of the heliospheric termination
shock to predict the shape and relative contributions of a variety
of heliosheath ion populations. We show: (1) The ENA spectra between
~0.7-6 keV do not exhibit sharp cut-offs at ~twice the solar wind
speed as is typically observed for shell-like PUI distributions in
the heliosphere and are reasonably well accounted for by most of the
models. (2) The 0.03-0.7 keV ENA intensities are larger by more than
an order of magnitude compared with most existing models. We conclude
that the 0.7-5 keV ENAs at IBEX are generated by transmitted PUIs
in the ~0.5-5 keV energy range, the PUI distribution likely being
a smoothed superposition of Maxwellian or kappa distributions and
partially filled shell distributions in velocity space. In contrast,
the origin of the heliosheath parent ion population for the <0.7
keV ENAs remains poorly understood and here we discuss possible causes
of the discrepancy between IBEX observations and model predictions.
Title: Global Numerical Modeling of SEP Acceleration by a CME Shock
in the Solar Corona and Subsequent Transport to 1 AU
Authors: Kozarev, K. A.; Evans, R. M.; Schwadron, N. A.; Dayeh, M. A.;
Opher, M.; van der Holst, B.
Bibcode: 2012AGUFMSH23B..04K
Altcode:
It has been suggested that solar energetic particles (SEP) may gain most
of their energy at coronal mass ejection (CME)-driven shocks relatively
close to the Sun. The observed and modeled Alfven speed profiles in the
solar corona allow for fast shocks to develop within 10 solar radii. In
addition, rapid changes occur in the ejected plasma structures and there
is a great abundance of charged seed particles close to the Sun relative
to the interplanetary populations. The combination of these conditions
is favorable for the acceleration of large SEP fluxes, especially
protons. However, the details of the acceleration process remain hidden
due to the lack of in situ observations in the corona. As the next
generation of solar exploratory missions (Solar Probe Plus and Solar
Orbiter) gets ready to probe the plasma and particle conditions near
the Sun directly, a better understanding of SEP acceleration processes
in the corona is necessary. We have developed a comprehensive model for
studying proton acceleration and global interplanetary transport. It
consists of two parts: a three-dimensional magnetohydrodynamics (MHD)
model of the solar corona and interplanetary space (part of the Space
Weather Modeling Framework), which we use to simulate the corona,
solar wind, and a CME; and a global energetic particle acceleration and
transport kinetic model (the Energetic Particle Radiation Environment
Module), which uses the results from the MHD simulation to model the
time-dependent behavior of protons from the corona to 1 AU. We show that
the shock and plasma structures may efficiently accelerate suprathermal
protons to hundreds of MeV energies during their transit. We find that
the resulting SEP spectra vary greatly depending on the location of
their guiding field lines relative to the shock and CME.
Title: How Structures of the Solar Corona and Eruptions Interact to
Create Extreme Energetic Particle Events
Authors: Evans, R. M.; Kozarev, K. A.; Zheng, Y.; Pulkkinen, A.;
Taktakishvili, A.; Kuznetsova, M. M.; Opher, M.; Dayeh, M. A.;
Schwadron, N. A.; van der Holst, B.
Bibcode: 2012AGUFMSH14A..06E
Altcode:
As the Sun approaches maximum activity, the number of solar energetic
particle (SEP) events is rapidly increasing. These strong events
have the potential to damage technical systems, so it is essential to
understand what causes them. Although relationships exist between the
characteristics of SEP events and the associated flares and coronal mass
ejections (CMEs), the strongest solar events may not lead to the most
intense particle events. For example, the first Ground Level Enhancement
event of Solar Cycle 24 was associated with only a moderately strong
flare and CME. Presumably, there must be other factors that determine
the acceleration of the highest energy particles. To address this
question, we combine observations and innovative theoretical modeling
of recent SEP events. We use a three-dimensional magnetohydrodynamics
(MHD) model of the solar corona (within the Space Weather Modeling
Framework) to simulate eruptions in the low to middle corona. The
MHD output is coupled to a global kinetic simulation of particle
acceleration and transport (within the Energetic Particle Radiation
Environment Module). The output of the simulation is a synthetic
spectral profile response to realistic solar corona conditions during
the propagation of a CME. We study the evolution of the CME structures
(shock and compression regions within the sheath) and the relation of
these features to the preexisting coronal magnetic field geometry and
solar wind distribution. Then we determine which factors affect the
efficiency of particle acceleration and transport. For the first time,
we can probe how particle acceleration varies in different regions of
the CME as it interacts with the solar wind. R. M. E. is supported
through an appointment to the NASA Postdoctoral Program at GSFC,
administered by Oak Ridge Associated Universities through a contract
with NASA.
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: Reconnection at the Heliopause and Its Effects on the Transport
of Energetic Particles
Authors: Swisdak, M. M.; Drake, J. F.; Opher, M.
Bibcode: 2012AGUFMSH11A2195S
Altcode:
At the heliopause the interstellar magnetic field abuts the sectored
field of the heliosheath wherein, upstream of the heliopause, magnetic
reconnection generates a bath of magnetic islands. Further reconnection
can occur at the heliopause itself and provide a natural pathway
for energetic particles (e.g., anomalous cosmic rays, ACRs, from
within the heliosphere and galactic cosmic rays, GCRs, from without)
to penetrate the boundary. Once within the heliosheath, interactions
with magnetic islands strongly influence the motion of energetic
particles. In order to investigate this scenario we have carried out
kinetic particle-in-cell simulations (with initial conditions taken
from a global heliospheric model) that self-consistently include a
small number of energetic particles. We find that, after reconnection
begins, particles diffuse across the heliopause --- ACRs are found
in interstellar space and GCRs are found within the heliosheath. We
trace the trajectories of representative energetic particles through
this bath. We show that their propagation parallel to the magnetic
field in the island-filled heliosheath is slower than through the more
laminar interstellar field, while motions perpendicular to the field
have the opposite tendencies. By the simulation's end the initially
flat heliopause has been strongly distorted by the magnetic islands
that have grown during reconnection and become porous, allowing the
interstellar medium to access the heliosheath. We will discuss the
implications of these findings for the Voyager 1 spacecraft, which is
quickly approaching, and may soon pass, the heliopause.
Title: Heavy Ion Heating from the Sun to 1AU
Authors: Korreck, K. E.; Lepri, S. T.; Kasper, J. C.; Case, A. W.;
Kozarev, K. A.; Opher, M.; Evans, R. M.; Stevens, M. L.; Schwadron,
N. A.
Bibcode: 2012AGUFMSH51A2217K
Altcode:
The heating of heavy ions at the Sun and as they travel through the
interplanetary space is relevant to both identifying the solar wind
source region as well as the overall heating mechanisms and kinetics
of the solar wind. Using ACE SWICS data on heavy ions from the shock
associated with a CME on May 13, 2005, we examine the heavy ion heating
and non-thermal nature of the helium distributions at 1AU as well as
bulk solar wind parameters around the time of the CME. We utilize
current work on high resolution 3D MHD models to compare the bulk
solar wind parameters from the Sun to the inner heliosphere with a
CME input. The relationship between the model's parameters and the
observations at different regions of interest i.e the Solar Probe
and Solar Orbiter orbits will be extrapolated. This model will in the
future be extended to quiescent times of the solar wind.
Title: Reconnection in ICMEs by Relaxation into the Taylor State
Authors: Fermo, R. L.; Opher, M.; Drake, J. F.
Bibcode: 2012AGUFMSH31A2199F
Altcode:
Recent in situ observations of interplanetary mass ejections (ICMEs)
found signatures of reconnection exhausts in their interior or trailing
edge [Gosling et al., 2007]. Whereas reconnection on the leading
edge of an ICME would indicate an interaction with the coronal or
interplanetary environment, this result suggests that the internal
magnetic field reconnects with itself. To this end, we propose an
approach borrowed from the fusion plasma community. In the context of a
tokamak, Taylor [1974] showed that the lowest energy state corresponds
to one in which curl B = λB. Variations from this state will result
in the magnetic field trying to re-orient itself into the Taylor state
solution, subject to the constraints that the toroidal flux and magnetic
helicity are invariant. This relaxation is mediated by the reconnection
of magnetic field lines in the m=1 mode. In tokamaks, the result is a
"sawtooth crash" [Kadomtsev, 1975]. In an ICME, if we likewise treat
the flux rope as a toroidal flux tube, any variation from the Taylor
state will result in reconnection within the interior of the flux tube,
in accord with the observation by Gosling et al. [2007]. One such way
in which the Taylor state might be violated is by the elongation of
the flux tube cross section in the non-radial direction, as seen in
MHD simulations of flux tubes propagating through the interplanetary
medium. We show analytically that this this elongation results in a
violation of the Taylor state criterion curl B = λB. Lastly, we shall
present PIC simulations of an elongated flux tube which has deviated
from the Taylor state.
Title: CME Deflection Predictions Using ForeCAT (Forecasting a CME's
Altered Trajectory)
Authors: Kay, C.; Opher, M.; Evans, R. M.; van der Holst, B.
Bibcode: 2012AGUFMSH14A..02K
Altcode:
The accurate prediction of the path of coronal mass ejections (CMEs)
plays an important role in space weather forecasting, and knowing
the source location of the CME does not always suffice. During solar
minimum polar coronal holes (CHs) deflect high latitude CMEs toward
the ecliptic and when CHs extend to lower latitudes other deflections
can occur. To predict whether a CME will impact Earth, these nonideal
effects must be taken into account. Our previous simulations of an
erupting flux rope placed near a CH in the low corona indicate magnetic
forces as the key driver behind these nonradial motions close to the
Sun's surface. Here, we present a newly developed IDL routine ForeCAT
(Forecasting a CME's Altered Trajectory) to predict the path of a
CME. Given the background solar wind conditions, the launch site of the
CME, and the properties of the CME (such as its magnetic energy), we
forecast the deflection of the CME. Our model incorporates the effects
of magnetic tension and magnetic pressure gradient forces acting on
opposite edges of the CME as the primary drivers of the deflection,
and the CME expands according to its magnetic energy. The strength of
the magnetic pressure and tension forces results from the CME size
and location with respect to various solar features such as CHs,
active regions, or streamer regions. We also include the effects of
drag as the edges propagate outward against the solar wind. For each
edge, we numerically integrate the forces leading to a change in edge
position. We present comparisons with previously observed deflection
events and studies of the model's sensitivity to input parameters.
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: Dependence of Energetic Ion and Electron Intensities on
Proximity to the Magnetically Sectored Heliosheath: Voyager 1 and
2 Observations
Authors: Hill, M. E.; Decker, R. B.; Brown, L. E.; Drake, J. F.;
Hamilton, D. C.; Krimigis, S. M.; Opher, M.
Bibcode: 2012AGUFMSH13D..02H
Altcode:
Taken together, the Voyager 1 and 2 (V1 and V2) spacecraft have
collected over eleven years of data in the heliosheath. Despite
extensive study, energetic particles and magnetic fields measured
in the heliosheath have not been reconciled by existing models. In
particular the differences between the energetic particle intensity
variations at V1 and V2 are unexplained. While energetic particle
intensities at V1 change gradually over seven years in the heliosheath,
those at V2 vary by a factor ~10 in one year. Energetic particle
intensities at V2 show temporally coherent variations over a broad
range of species and energies: from suprathermal ions (10s of keV)
to galactic cosmic rays (>1 GeV), as well as electrons from 10s of
keV to >100 MeV, corresponding to a ~4-order-of-magnitude range in
particle gyroradii. Here we show that many of the intensity variations
of energetic particle populations in the heliosheath are organized by
their proximity to two fundamentally different regions—the unipolar
heliosheath (UHS) and the sectored heliosheath (SHS). The SHS is a
region of enhanced particle intensities, wherein particle transport,
acceleration, and magnetic connectivity differ from those in the
UHS. The SHS may serve as either a reservoir of energetic particles or
as a region of enhanced transport, depending on the particle species
and energy. Comparatively, particle intensities in the UHS are greatly
reduced. We propose that the boundary between the SHS and UHS plays
as important a role in the physics of heliosheath particles and fields
as do the termination shock and heliopause.
Title: Magnetic reconnection in the heliosheath and the generation
of anomalous cosmic rays
Authors: Drake, J. F.; Opher, M.; Schoeffler, K. M.; Swisdak, M. M.;
Dahlin, J.; Fermo, R. L.
Bibcode: 2012AGUFMSH13D..03D
Altcode:
The recent observations of the anomalous cosmic ray (ACR) energy
spectrum as Voyagers 1 and 2 crossed the heliospheric termination
shock have called into question the conventional shock source of these
energetic particles. We suggest that the sectored heliospheric magnetic
field, which results from the flapping of the heliospheric current
sheet, compresses across the termination shock and reconnects in the
subsonic flow of the heliosheath. A number of Voyager observations
support the hypothesis that the heliosheath sectored field has
reconnected. Particle-in-cell (PIC) simulations in 2-D suggest that the
sectors break up into a bath of elongated magnetic islands and that
most of the magnetic energy released goes into the pickup ions. The
most energetic ions gain energy as they circulate in contracting and
merging magnetic islands, a first order Fermi process. The firehose
condition plays an essential role in the reconnection dynamics and
particle acceleration. The simulations are being extended to 3-D where
ions circulating within islands have a finite lifetime. Measured energy
spectra are similar to those in 2-D. We present a new analytic model
of particle acceleration in a multi-island reconnecting system that
describes the energy spectrum of ions parallel and perpendicular to the
local magnetic field. Including anisotropy is essential to describe
reconnection driven particle acceleration since Fermi acceleration
during reconnection drives anisotropy, which is self-consistently
limited by scattering and the approach to firehose marginal stability,
which is now explicitly evaluated from the anisotropic spectrum. The
limiting ACR differential energy spectrum takes the form of a power law
with a spectral index of 1.5, a result which was obtained earlier in a
much more primitive model. The new transport equation for the particle
energy spectrum is suitable for calculating the global distribution
of reconnection driven energetic particles in the heliosphere.
Title: Thermal Pressure of the Proton Plasma in the Inner Heliosheath
Authors: Livadiotis, G.; McComas, D. J.; Schwadron, N. A.; Opher,
M.; Funsten, H. O.; Fuselier, S. A.; Dayeh, M. A.
Bibcode: 2012AGUFMSH11B2207L
Altcode:
We combine (i) data analysis of IBEX sky maps of ENA fluxes, and
(ii) modeling of the proton distributions [1] and the plasma flow
in the inner heliosheath [2], to construct the sky maps of thermal
observables (e.g., temperature and thermal pressure), and determine
the thermodynamic processes in the inner heliosheath [3]. Normally,
multipoint in-situ measurements are needed to determine the
thermodynamic process of solar wind flow as this evolves in the
heliosphere. However, because solar wind flow bends within the
inner heliosheath, its evolution and thermodynamic process can be
determined using a snapshot map of the whole sky. The first year of
IBEX data reveal that both the Ribbon and the underlying globally
distributed flux [4] are characterized by quasi-isobaric processes,
corresponding to average thermal pressure ~1.1 and ~2.1 pdyn cm-2,
respectively. While the latter represents the pressure of the inner
heliosheath, we discuss the physical meaning of the Ribbon's source
pressure in relationship to a possible ENA secondary source from the
outer heliosheath. Under the assumptions of the model, we derive
the total thermal pressure characterizing the entire energy range
of the source proton distribution that is consistent with a kappa
distribution. This total thermal pressure is consistent with the
non-parametric partial pressure, derived directly from the observed ENA
flux over the finite IBEX energy range. Further application over 3-years
of IBEX data [5] allows us verify and refine the statistical method
and to detect temporal variations in derived thermodynamic properties
of the global heliosheath. (1) Livadiotis, G., et al. 2011, ApJ 734,
1. (2) Opher, M., et al. 2009, Nature 462, 1036. (3) Livadiotis, G.,
McComas, D. J. 2012, ApJ 749, 11. (4) Schwadron, N. A., et al. 2011,
ApJ, 731, 1. (5) McComas, D. J., et al. 2012, ApJSS, In Print.
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: 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: Coronal Heating by Surface Alfvén Wave Damping: Implementation
in a Global Magnetohydrodynamics Model of the Solar Wind
Authors: Evans, R. M.; Opher, M.; Oran, R.; van der Holst, B.; Sokolov,
I. V.; Frazin, R.; Gombosi, T. I.; Vásquez, A.
Bibcode: 2012ApJ...756..155E
Altcode:
The heating and acceleration of the solar wind is an active area of
research. Alfvén waves, because of their ability to accelerate and heat
the plasma, are a likely candidate in both processes. Many models have
explored wave dissipation mechanisms which act either in closed or open
magnetic field regions. In this work, we emphasize the boundary between
these regions, drawing on observations which indicate unique heating
is present there. We utilize a new solar corona component of the Space
Weather Modeling Framework, in which Alfvén wave energy transport is
self-consistently coupled to the magnetohydrodynamic equations. In
this solar wind model, the wave pressure gradient accelerates and
wave dissipation heats the plasma. Kolmogorov-like wave dissipation
as expressed by Hollweg along open magnetic field lines was presented
in van der Holst et al. Here, we introduce an additional dissipation
mechanism: surface Alfvén wave (SAW) damping, which occurs in regions
with transverse (with respect to the magnetic field) gradients in the
local Alfvén speed. For solar minimum conditions, we find that SAW
dissipation is weak in the polar regions (where Hollweg dissipation is
strong), and strong in subpolar latitudes and the boundaries of open
and closed magnetic fields (where Hollweg dissipation is weak). We
show that SAW damping reproduces regions of enhanced temperature at
the boundaries of open and closed magnetic fields seen in tomographic
reconstructions in the low corona. Also, we argue that Ulysses data in
the heliosphere show enhanced temperatures at the boundaries of fast
and slow solar wind, which is reproduced by SAW dissipation. Therefore,
the model's temperature distribution shows best agreement with these
observations when both dissipation mechanisms are considered. Lastly,
we use observational constraints of shock formation in the low corona to
assess the Alfvén speed profile in the model. We find that, compared
to a polytropic solar wind model, the wave-driven model with physical
dissipation mechanisms presented in this work is more aligned with an
empirical Alfvén speed profile. Therefore, a wave-driven model which
includes the effects of SAW damping is a better background to simulate
coronal-mass-ejection-driven shocks.
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: The stellar wind cycles and planetary radio emission of the
τ Boo system
Authors: Vidotto, A. A.; Fares, R.; Jardine, M.; Donati, J. -F.;
Opher, M.; Moutou, C.; Catala, C.; Gombosi, T. I.
Bibcode: 2012MNRAS.423.3285V
Altcode: 2012arXiv1204.3843V
τ Boo is an intriguing planet-host star that is believed to undergo
magnetic cycles similar to the Sun, but with a duration that is about
one order of magnitude smaller than that of the solar cycle. With the
use of observationally derived surface magnetic field maps, we simulate
the magnetic stellar wind of τ Boo by means of three-dimensional
magnetohydrodynamics numerical simulations. As the properties of
the stellar wind depend on the particular characteristics of the
stellar magnetic field, we show that the wind varies during the
observed epochs of the cycle. Although the mass-loss rates we find
(∼2.7 × 10-12 M⊙ yr-1) vary less
than 3 per cent during the observed epochs of the cycle, our derived
angular-momentum-loss rates vary from 1.1 to 2.2 × 1032
erg. The spin-down times associated with magnetic braking range between
39 and 78 Gyr. We also compute the emission measure from the (quiescent)
closed corona and show that it remains approximately constant through
these epochs at a value of ∼1050.6 cm-3. This
suggests that a magnetic cycle of τ Boo may not be detected by X-ray
observations. We further investigate the interaction between the
stellar wind and the planet by estimating radio emission from the hot
Jupiter that orbits at 0.0462 au from τ Boo. By adopting reasonable
hypotheses, we show that, for a planet with a magnetic field similar
to Jupiter (∼14 G at the pole), the radio flux is estimated to be
about 0.5-1 mJy, occurring at a frequency of 34 MHz. If the planet is
less magnetized (field strengths roughly smaller than 4 G), detection
of radio emission from the ground is unfeasible due to the Earth's
ionospheric cut-off. According to our estimates, if the planet is
more magnetized than that and provided the emission beam crosses the
observer line-of-sight, detection of radio emission from τ Boo b is
only possible by ground-based instruments with a noise level of ≲1
mJy, operating at low frequencies.
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: Magnetic reconnection in the heliosheath and its signatures
and consequences
Authors: Drake, James; Opher, Merav; Swisdak, Marc; Schoeffler, K.
Bibcode: 2012cosp...39..479D
Altcode: 2012cosp.meet..479D
The sectored magnetic field due to the flapping of the heliospheric
current sheet compresses across the termination shock and may reconnect
in the heliosheath, driving the anomalous cosmic rays and producing
a sea of elongated magnetic bubbles. A number of Voyager observations
are consistent with the bubble picture of the heliosheath, including
flow enhancements, magnetic field compressions and strongly-altered
transport properties. We are exploring large-scale structure of the
the 3-D heliosheath with MHD simulations and the dynamics of magnetic
reconnection and resultant magnetic bubbles with PIC simulations. The
goal is to understand particle acceleration and how the resulting
complex magnetic field will impact the transport of energetic particles,
including galactic cosmic rays. We find that magnetic bubbles form as
fully 3-D rather than 2-D objects. Because of the high beta conditions
of the helioosheath, the characteristic signatures of magnetic
reconnection differ greatly from that typical of 1AU. Reconnection is
largely quenched once bubbles reach characteristic widths of the order
of the sector spacing and the bubble cores bump against the marginal
firehose condition. The characteristic signatures of bubbles are being
identified for comparison with the magnetic field data from Voyager.
Title: A reconnection mechanism for the generation of anomalous
cosmic rays
Authors: Drake, James; Opher, Merav; Swisdak, Marc; Schoeffler, K.
Bibcode: 2012cosp...39..480D
Altcode: 2012cosp.meet..480D
The recent observations of the anomalous cosmic ray (ACR) energy
spectrum as Voyagers 1 and 2 crossed the heliospheric termination
shock have called into question the conventional shock source of
these energetic particles. We suggest that the sectored heliospheric
magnetic field, which results from the flapping of the heliospheric
current sheet, compresses across the termination shock and reconnects
in the subsonic flow of the heliosheath. Dropouts in the intensity of
energetic electrons and the most energetic ACR ions as Voyager 2 exits
the sector zone support the hypothesis that the heliosheath sectored
field has reconnected. The sector structure is examined with global MHD
simultions of the heliosphere. Particle-in-cell (PIC) simulations in
2-D and 3-D reveal that the sectors break up into a bath of elongated
magnetic islands and that most of the magnetic energy released goes
into energetic ions with significant but smaller amounts of energy
going into electrons. The most energetic particles gain energy as
they circulate in contracting magnetic islands, a first order Fermi
process. The simulations also reveal that the firehose condition
plays an essential role in the reconnection dynamics and particle
acceleration. An analytic model is constructed in which the Fermi
drive, modulated by the approach to firehose marginality, is balanced
by convective loss. The ACR differential energy spectrum takes the
form of a power law with a spectral index slightly above 1.5. The
model has the potential to explain several key ACR observations,
including the similarities in the spectra of different ion species.
Title: Reconnection in ICMEs caused by deviations from the Taylor
state
Authors: Fermo, Raymond Luis; Opher, Merav; Drake, James F.
Bibcode: 2012shin.confE..89F
Altcode:
Recent in situ observations of interplanetary mass ejections (ICMEs)
found signatures of reconnection exhausts in their interior or
trailing edge [Gosling et al., 2007]. Whereas reconnection on the
leading edge of an ICME would indicate an interaction with the
coronal or interplanetary environment, this result suggests that
the internal magnetic field reconnects with itself. To this end,
we propose an approach borrowed from the fusion plasma community. In
the context of a tokamak, Taylor [1974] showed that the lowest energy
state corresponds to one in which curl B = λB. Variations from this
state will result in the magnetic field trying to re-orient itself
into the Taylor state solution. Because the twist of the flux tube is
a topological constraint, the means by which this would occur must be
magnetic reconnection. In tokamaks, the result is a 'sawtooth crash'
[Kadomtsev, 1975]. In an ICME, if we likewise treat the flux rope as
a toroidal flux tube, any variation from the Taylor state will result
in reconnection within the interior of the flux tube, in accord with
the observation by Gosling et al. [2007]. One such way in which the
Taylor state might be violated is by the elongation of the flux tube
cross section in the non-radial direction, as seen in MHD simulations
of flux tubes propagating through the interplanetary medium. We show
that this this elongation results in a violation of the Taylor state
criterion curl B = λB. Lastly, we shall present PIC simulations of
an elongated flux tube which has deviated from the Taylor state.
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: A Goodbye Gift From AR1476: The First Ground Level Enhancement
Event of Solar Cycle 24
Authors: Evans, Rebekah Minnel; Zheng, Yihua; Pulkkinen, Antti;
Taktakishvili, Aleksandre; Mays, M. Leila; Kuznetsova, Maria M.;
Kozarev, Kamen; Opher, Merav; van der Holst, Bart; Hesse, Michael
Bibcode: 2012shin.confE..29E
Altcode:
We provide an overview of the M-class flare and O-type* coronal
mass ejection (CME) that occurred on May 17, 2012 as AR1476 was
passing behind the solar disk. This event is special because the long
duration flare and well-timed CME produced a solar energetic particle
(SEP) event that resulted in the first Ground Level Enhancement (GLE)
of Solar Cycle 24. At the Goddard Space Weather Center, we performed
real time analysis of the action, and gave a preliminary predicted ICME
arrival time at NASA"s STEREO-A spacecraft that was within one hour of
the actual arrival. The CME possibly facilitated the GLE in two ways:
1) the CME-driven shock could have contributed to the acceleration of
very high-energy protons required for a GLE, and 2) the CME could have
disturbed the coronal magnetic field, widening the longitudinal extent
of the SEP event. This event underscores the need for global modeling
of CME-driven shocks in the low corona. We discuss CME simulations
performed with the Space Weather Modeling Framework"s wave-driven
solar wind model, and emphasize the global structure of the eruption
as a key to understanding particle acceleration. Comparisons are made
between this event and the March 7, 2012 X-class flares and R-type*
CME.*O-type (Occasional), R-type (Rare) on the CME SCORE Scale (see
http://youtu.be/hN5bChbdky8 for more details). For an overview of the
event, see the Special Space Weather Report: http://youtu.be/8jutX8JgXIw
Title: Magnetic Reconnection and the Kinetic Structure of the
Heliopause
Authors: Swisdak, Marc; Drake, J. F.; Opher, M.; Schoeffler, K.
Bibcode: 2012shin.confE..57S
Altcode:
At the heliopause magnetic reconnection can potentially occur between
the heliospheric and interstellar magnetic fields. Complicating this
picture, however, is the possibility that reconnection has already
occurred within the heliosheath, between sectors of the heliospheric
field. We will discuss the implications of this view of heliosheath
plasma on the expected signatures of reconnection at the heliopause.
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: Magnetic Drivers of CME Deflection in the Low Corona
Authors: Kay, Christina Danielle; Opher, M.; Evans, R. M.; Gombosi, T.
Bibcode: 2012shin.confE..82K
Altcode:
Coronal mass ejection (CME) observations include cases where CMEs
follow a trajectory other than the radial path from the associated
launch site. The presence of a coronal hole can contribute to this
deflection. Using a 3D MHD model, the Space Weather Modeling Framework,
we simulate the propagation of a CME near a coronal hole. We establish
a steady state background solar wind starting with a magnetogram
of Carrington Rotation 2029 in which the solar wind is driven by
Alfven waves. Our model includes the effects of surface Alfven wave
and Kolmogorov-like dissipation. We launch the CME by inserting a
Titov-Demoulin flux rope in the region corresponding to active region
0758. Based on the orientation of the CH with respect to the CME, we
expect deflection to occur mostly in the longitudinal direction. By
tracking the position of the CME edges in the plane containing the
Sun's equator we measure a longitudinal deflection of 21 degrees. As
the deflection occurs low in the corona, a region of low plasma beta,
we expect magnetic forces to be responsible. We estimate the forces
from magnetic tension and magnetic pressure gradients and analyze the
magnitude of these forces over the CME's propagation. We see comparable
magnitudes between the coronal hole tension force and the difference
between pressure gradients on opposite sides of the CME. Both forces
act to push the CME away from the coronal hole. From this we conclude
both forces should be considered when looking at CME deflection near
a coronal hole.
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: Global Numerical Modeling of Energetic Proton Acceleration
in a CME and Shock in the Solar Corona
Authors: Kozarev, Kamen; Evans, Rebekah M.; Dayeh, Maher A.; Opher,
Merav; Schwadron, Nathan A.
Bibcode: 2012shin.confE..16K
Altcode:
A growing body of theoretical and observational evidence suggests that
solar energetic particles may gain most of their energy at traveling
shocks relatively close to the Sun. The observed and modeled Alfven
speed profiles in the corona allow for fast shocks to easily develop
within 20 solar radii. In addition, rapid changes occur in the ejected
plasma structures and there is a great abundance of charged particles
close to the Sun compared with interplanetary space. By combining global
MHD simulation results with a global energetic particle acceleration
and transport kinetic simulation, we can investigate the effect on a
seed suprathermal particle population of a coronal mass ejection and
related shock. We show that the shock and various plasma structures
may efficiently accelerate suprathermal protons to tens of MeV energies
between two and eight solar radii for a case study event. Furthermore,
we show that the resulting SEP flux spectra vary greatly depending on
the latitudes and longitudes of the guiding field lines. This result
may provide a single mechanism for the creation of energetic particles
in the vicinity of the Sun, and thus explain both the impulsive and
gradual phases of SEP events.
Title: Do shocks associated with merged interaction regions in the
supersonic solar wind survive in the heliosheath?
Authors: Provornikova, E. A.; Opher, M.; Izmodenov, V. V.
Bibcode: 2012EGUGA..14.5502P
Altcode:
Observations of the supersonic solar wind in the outer heliosphere by
Voyager 2 exhibit many examples of shocks. During the solar minimum,
shocks are usually associated with global structures in the solar
wind such as corotating interaction regions. Other transient events
in the solar wind such as interplanetary CMEs and merged interaction
regions usually occurred during the maximum of solar activity may
also drive shocks. As the shocks propagate from the inner to outer
heliosphere they evolve in the interaction with the ambient solar wind
and in collision and merging processes among each other. We explore the
effect of merging of shock pairs in the supersonic solar wind and study
the propagation of merged shock pairs in the heliosheath. We use a 3D
MHD model of the solar wind interaction with the interstellar medium
to generate a couple of shock pairs in the supersonic solar wind with
characteristics similar to those observed by Voyager 2 at 45 AU from the
Sun and analyze their propagation into the heliosheath. We show that
merging of shock pairs do not result in dissipation of shocks; on the
contrary, in some cases the shocks may become stronger. From modeling
a propagation of a pair of weak shocks from the region upstream the
termination shock into the heliosheath we found that several shocks
may form in the heliosheath. The absence of shocks in the Voyager 2
plasma data from the heliosheath could indicate that other dissipative
processes not included in our model are important in the heliosheath.
Title: The Heliosheath: The Ultimate Solar System Frontier
Authors: Opher, M.
Bibcode: 2012AstRv...7a..68O
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 lasted
decades are being revisited due to their puzzling measurements. In this
review, I will cover some of these puzzles and what we are learning
regarding the dynamic nature of the heliosheath.
Title: The Heliosheath: The Ultimate Solar System Frontier
Authors: Opher, M.
Bibcode: 2012AstRv...7d..68O
Altcode:
No abstract at ADS
Title: Understanding the Angular Momentum Loss of Low-Mass Stars:
The Case of V374 Peg
Authors: Vidotto, A. A.; Jardine, M.; Opher, M.; Donati, J. F.;
Gombosi, T. I.
Bibcode: 2011ASPC..448.1293V
Altcode: 2011arXiv1101.1233V; 2011csss...16.1293V
Recently, surface magnetic field maps had been acquired for a small
sample of active M dwarfs, showing that fully convective stars (spectral
types ∼ M4 and later) host intense (∼ kG), mainly axi-symmetrical
poloidal fields. In particular, the rapidly rotating M dwarf V374 Peg
(M4), believed to lie near the theoretical full convection threshold,
presents a stable magnetic topology on a time-scale of ∼ 1 yr. The
rapid rotation of V374 Peg (P = 0.44 days) along with its intense
magnetic field point toward a magneto-centrifugally acceleration of
a coronal wind. In this work, we aim at investigating the structure
of the coronal magnetic field in the M dwarf V374 Peg by means of
three-dimensional magnetohydrodynamical (MHD) numerical simulations
of the coronal wind. For the first time, an observationally derived
surface magnetic field map is implemented in MHD models of stellar winds
for a low-mass star. We self-consistently take into consideration the
interaction of the outflowing wind with the magnetic field and vice
versa. Hence, from the interplay between magnetic forces and wind
forces, we are able to determine the configuration of the magnetic
field and the structure of the coronal winds. Our results enable us
to evaluate the angular momentum loss of the rapidly rotating M dwarf
V374 Peg.
Title: The dynamics, structure and signatures of magnetic bubbles
in the outer heliosphere
Authors: Drake, J. F.; Opher, M.; Swisdak, M. M.; Schoeffler, K. M.
Bibcode: 2011AGUFMSH13C..07D
Altcode:
The sectored magnetic field due to the flapping of the heliospheric
current sheet compresses across the termination shock and may reconnect
in the heliosheath, driving the anomalous cosmic rays and producing
a sea of elongated magnetic bubbles. A number of Voyager observations
are consistent with the bubble picture of the heliosheath, including
flow enhancements, magnetic field compressions and strongly-altered
transport properties. We are exploring the 3-D structure and dynamics
of magnetic bubbles with PIC simulations to understand the associated
particle acceleration and how the resulting complex magnetic field
will impact the transport of energetic particles, including galactic
cosmic rays. We find that magnetic bubbles form as fully 3-D rather than
2-D objects. In spite of the 3-D nature of the reconnection process,
particle acceleration does not appear to be significantly changed from
earlier results in 2-D. The characteristic signatures of magnetic
bubbles are being identified for comparison with the magnetic field
data from Voyager. Intriguing Voyager 2 magnetic field observations
of brief negative polarity excursions during a nominally positive
unipolar period 2009.6-2010.3 are being studied as possible evidence
that magnetic bubbles from reconnection in the sector zone are being
ejected into the nominally unipolar region in a manner analogous to
spray from a water/air interface.
Title: Shocks in the Corona and Inner Heliosphere: Implications for
Solar Probe and Solar Orbiter
Authors: Korreck, K. E.; Kozarev, K. A.; Evans, R. M.; Opher, M.;
Schwadron, N. A.; Kasper, J. C.; Case, A. W.
Bibcode: 2011AGUFMSH44B..07K
Altcode:
Shocks in the solar corona and inner heliosphere are thought to be a
location of acceleration for Solar Energetic Particles (SEPs). Using
energetic particle transport code, 3-D MHD simulations, in-situ and
remote imaging data, links between the acceleration and propagation
of the particles from the Sun out to the Earth can be studied. These
types of multi-spacecraft and multi-method studies will be key
to understanding the data from Solar Probe and Solar Orbiter. The
required observations in terms of science payload of the mission will be
discussed. In addition, theoretical and modeling work that is necessary
to better understand the observations will also be highlighted.
Title: The Role of Coronal Holes in CME Deflection in the Lower Corona
Authors: Kay, C.; Opher, M.; Evans, R. M.; Gombosi, T. I.
Bibcode: 2011AGUFMSH23A1937K
Altcode:
Coronal mass ejections (CMEs) are known to be deflected when
ejected near a coronal hole (Gopalswamy et al. 2009). We present
results from simulations of CMEs near a coronal hole (CH) using a 3D
magnetohydrodymics model - the Space Weather Modeling Framework. We
propose magnetic tension and pressure as a cause of the CME deflection
from the disturbed magnetic field lines of the simulation coronal
hole. The solar wind is driven via Alfven waves and Kolmogorov-like
dissipation and surface Alfven wave damping are considered for the
dissipation of the waves (Evans et al. 2011). The magnetic field at
the inner boundary is specified with synoptic magnetogram data from
Carrington Rotation 2029, which corresponds to April 21 to May 18,
2005. CMEs are generated by inserting an out of equilibrium modified
Titov-Demoulin flux rope into active region (AR) 0758. Treating the
CME as a solid body we calculate the expected deflection from the
coronal hole field lines. We compare this value to the actual path
of the simulated CMEs for which we define a deflection angle as the
difference between the observed path and the radial vector connecting
the center of the Sun and the CME launch site. Finally, we generalize
the deflection by seeing how it scales with several physical parameters
such as CME mass, velocity and the separation of the AR and CH as well
as its intensity. We compare our simulated and estimated values with
observed deflections (Gopalswamy et. al 2009)
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: 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: Damping of Surface Alfvén Waves in a 3D Simulation of
Stellar Winds
Authors: Evans, R. M.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2011ASPC..448.1151E
Altcode: 2011csss...16.1151E
Surfave Alfvén wave damping has been used by many authors in order
to provide an heating and acceleration mechanism for driving winds
in many regions of HR diagram. Based on the 1D solar wind model
of Jatenco-Pereíra et al. (1994) we investigate the effect of
surface Alfvén wave damping, for solar minima conditions, using a
three-dimensional (3D) magnetohydrodynamics (MHD) model. The surface
Alfvén wave damping length LSW depends on the superradial expansion
factor S of magnetic field lines. We quantify S for Carrington Rotation
1912 with a steady state solar background generated with the Space
Weather Modeling Framework, and compare with estimates by Dobrzycka et
al. (1999) using SOHO observations. We estimate the surface Alfvén
wave damping for active regions, quiet sun, and the border between
open and closed magnetic field lines (Evans et al. 2009).
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: 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: CME-Sheath and Shock Heating by Surface Alfven Wave Dissipation
in the Lower Corona
Authors: Evans, R.; Opher, M.; van der Holst, B.
Bibcode: 2011AGUFMSH43A1933E
Altcode:
We use the new solar corona component of the Space Weather Modeling
Framework (van der Holst et al. 2010), in which the Alfven wave energy
evolution is coupled self-consistently to the magnetohydrodynamic
equations, to study the evolution of a coronal mass ejection (CME)
and the shock it drives in the lower corona (2-8Rs). In this solar
wind model, the wave pressure gradient accelerates the wind, and wave
dissipation heats the wind. Kolmogorov-like dissipation and surface
Alfven wave damping are considered for the dissipation of the waves
(Evans et al. 2011). We use a modified Titov-Demoulin flux rope to
initiate an eruption, and include magnetogram data from CR2029 (May
2005) as a boundary condition for the coronal magnetic field. Synthetic
white light images from the simulation are used to determine the
lateral expansion. We show that the expansion of the flux rope leads
to the concentration of wave energy at the shock and in the sheath
region. The expansion also creates a piled-up compression (PUC) region
of plasma density at the back of the sheath, strongest at the flanks
of the CME. The wave energy concentrated at the shock and sheath is
dissipated by surface Alfven wave damping due to the density gradients,
which heats the sheath. We present analysis of the momentum exchange
between the solar wind and the waves, and discuss the effect of wave
dissipation on the CME evolution.
Title: Reconnection at the Heliopause and the Motion of Energetic
Particles in the Outer Heliosphere
Authors: Swisdak, M. M.; Drake, J. F.; Opher, M.; Knizhnik, K.
Bibcode: 2011AGUFMSH11B1924S
Altcode:
At the heliopause the uni-directional interstellar magnetic field
abuts the piled-up sectored magnetic field and multiple current
sheets of the heliosheath. Reconnection of these fields provides a
natural pathway for energetic particles (e.g., anomalous cosmic rays
produced in the heliosphere and galactic cosmic rays produced outside)
to move across the heliopause. Here we report on 2D particle-in-cell
simulations of this system that self-consistently include a small
number of energetic particles designed to mimic these energetic
particles. Reconnection occurs at multiple current layers within the
heliosheath and leads to the formation of a bath of magnetic bubbles. By
tracing the trajectories of energetic particles through this bath we
show that their propagation acquires some characteristics of a random
walk. We discuss the implications for this behavior on the detection
and propagation of energetic particles throughout the outer heliosphere.
Title: Seemingly Incongruous Voyager 1 & 2 Energetic Particle
Observations in the Heliosheath Through 2011
Authors: Hill, M. E.; Decker, R. B.; Drake, J. F.; Hamilton, D. C.;
Krimigis, S. M.; Opher, M.; Roelof, E. C.
Bibcode: 2011AGUFMSH11A1906H
Altcode:
Conditions are changing in the heliosheath at the positions of Voyager
1 (V1) and Voyager 2 (V2) and are doing so in unexpected ways that
so far defy a single consistent interpretation. Some characteristic
intensity variations cut across a surprisingly broad range of energies
and species, from termination shock particles (TSPs), to energetic
electrons, to light and heavy anomalous cosmic rays (ACRs), and to
galactic cosmic rays (GCRs). The changes must be a mix of spatial
structure and temporal changes produced by the rise in activity of
Solar Cycle 24 in January 2010. Yet there are drastic differences
between some of the same species at V1 compared with V2. The puzzling
observations include V1 ACR intensities beginning to decline while at V2
they are exponentially increasing, finally reaching levels comparable
to or even exceeding those at V1. A distinct pattern of increases and
decreases is seen at V2 in TSPs, electrons, light ACRs, and GCRs, but
not in ACR heavy ions. However some things are happening similarly at
V1 and V2, like a recent increase in GCR protons. We will present an
overview of these observations, which also include spectral properties,
anisotropies, and solar wind speed. An essential interpretive element
is possible differences in the heliosheath configuration, in particular
the location of the sector region between V1 and V2 and the proximity
to the heliopause.
Title: 3D Simulations of Tilted Magnetospheres of Weak-Lined T
Tauri Stars
Authors: Vidotto, A. A.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2011RMxAC..40..133V
Altcode:
We perform 3D time-dependent numerical MHD simulations of the wind
and magnetospheric structures of weak-lined T Tauri stars, in the case
there is a misalignment between the axis of rotation of the star and
its magnetic dipole moment vector. The model allow us to study the
interaction of a magnetized wind with a magnetized exoplanet. Such
interaction gives rise to reconnection, generating electrons that
propagate along the planet's magnetic field lines and produce electron
cyclotron radiation at radio wavelengths. This radio emission could
be detectable by LOFAR in the near future.
Title: Ensemble-averaged heliosheath proton spectra
Authors: Prested, Christina Lee; Schwadron, N.; Fuselier,
H. O. Funsten. A.; Janzen, P. H.; McComas, D. J.; Opher, M.;
Reisenfeld, D. B.
Bibcode: 2011shin.confE..64P
Altcode:
New in situ observations by Voyager 2 and and remote observations
by the Interstellar Boundary Explorer (IBEX) have provided the first
measurements of the heliosheath plasma energy distribution. Contained
within this energy distribution is the physics of the termination
shock and the subsequent heating of the heliosheath plasma. The
Voyager measurements provide a time series of the plasma at a local
point, while the IBEX observations provide a global look at the
line-of-sight averaged plasma, an ensemble-average of the spatially and
temporally varying plasma in a given direction. To unravel the global
information contained in the IBEX energy spectra, we must understand
how ensemble-averaging effects the observed energy spectra. We take
advantage of overlap between the Voyager and IBEX data sets and
explore the average energy spectra produced by physically motivated
time and spatial distributions of heliosheath plasma. Other aspects
of the heliosheath energy distribution, particularly the pick-up ions,
are also considered.
Title: Interaction of a CME-driven Shock and Sheath with an Alfven
Wave-driven Solar Wind in the Lower Corona
Authors: Evans, Rebekah Minnel; Opher, Merav; Gombosi, Tamas I.
Bibcode: 2011shin.confE.141E
Altcode:
Coronal Mass Ejections (CMEs) are driven by a release of magnetic
energy, which dominates the interaction between the CME and the solar
wind in the very low corona (at heights less than 2 solar radii). At
distances larger than 10 solar radii, the interaction between the
solar wind and a CME is controlled by the drag force. In this work,
we study the interaction of a CME with a solar wind driven by Alfven
waves in the lower corona (2-7 solar radii). We use the new solar
corona component of the Space Weather Modeling Framework (van der Holst
et al. 2010), in which the Alfven wave energy evolution is coupled
self-consistently to the MHD equations. The wave stress accelerates the
wind, and wave dissipation heats the wind. The wave dissipation is due
to turbulence and to surface Alfven wave damping. We use a modified
Titov-Demoulin flux rope to initiate the eruption, and include MDI
magnetogram data from CR2029 (May 2005) as a boundary condition for
the coronal magnetic field. Synthetic white light images from the
simulation are used to determine the lateral expansion from both halo
and limb event vantage points. We show that the expansion of the flux
rope leads to the concentration of wave energy at the shock and in
the sheath region. The expansion also creates a piled-up compression
(PUC) region of plasma density at the back of the sheath, strongest
at the flanks of the CME. The wave energy concentrated at the shock
and sheath is dissipated by surface Alfven wave damping due to the
density gradients, which heats the sheath. We present analysis of the
momentum exchange between the solar wind and the waves, and the effect
of wave dissipation on the CME evolution.
Title: 3D MHD modeling of the CMIR propagation in the heliosheath
Authors: Provornikova, Elena; Opher, M.; Izmodenov, V.; Gabor, T.
Bibcode: 2011shin.confE..69P
Altcode:
One of the dominating large-scale structures in the solar wind is
an interaction region (or corotating interaction region CIR). As the
CIRs propagate outward they merge each other and form CMIRs. CMIRs were
clearly observed by Voyager 1 and 2 at large heliospheric distances. We
use global 3D time-dependent MHD multi-fluid model (Opher et al. 2009)
of the interaction of the solar wind with the local interstellar medium
to study the evolution of the CMIR from 30 AU to the heliospheric
boundaries. We show the change in CMIR structure caused by the
interaction with the heliospheric termination shock and study the
propagation of the modified CMIR in the heliosheath. We discuss the
response of the heliopause to the CMIR structure and the following
flow in the heliosheath.
Title: Simulation of a CME Near a Coronal Hole
Authors: Kay, Christina Danielle; Opher, M.; Evans, R.; Gombosi, T.
Bibcode: 2011shin.confE.132K
Altcode:
We present results from the simulation of a coronal mass ejection
(CME) near a large coronal hole. Observational evidence suggests that
the open field lines from a coronal hole can deflect a CME from its
initial trajectory. Using the Space Weather Modeling Framework with a
background solar wind driven by Alfven waves that includes the effects
of surface Alfven wave dissipation, a CME is launched from active
region 0758 in Carrington rotation 2029. We follow the propagation
from the lower corona out to approximately 4.5 solar radii. We find
that the presence of the CME induces curvature in the open field lines
of the coronal hole and investigate the resulting magnetic tension as
a possible cause of CME deflection. We also explore the effect of the
open field lines on the shape of the CME.
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: Signatures of two distinct driving mechanisms in the evolution
of coronal mass ejections in the lower corona
Authors: Loesch, C.; Opher, M.; Alves, M. V.; Evans, R. M.; Manchester,
W. B.
Bibcode: 2011JGRA..116.4106L
Altcode:
We present a comparison between two simulations of coronal mass
ejections (CMEs), in the lower corona, driven by different flux rope
mechanisms presented in the literature. Both mechanisms represent
different magnetic field configurations regarding the amount of twist
of the magnetic field lines and different initial energies. They are
used as a “proof of concept” to explore how different initialization
mechanisms can be distinguished from each other in the lower corona. The
simulations are performed using the Space Weather Modeling Framework
(SWMF) during solar minimum conditions with a steady state solar
wind obtained through an empirical approach to mimic the physical
processes driving the solar wind. Although the two CMEs possess
different initial energies (differing by an order of magnitude) and
magnetic configurations, the main observables such as acceleration,
shock speed, Mach number, and $\theta$Bn (the angle between
the shock normal and the upstream magnetic field) present very similar
behavior between 2 and 6 R$\odot$. We believe that through
the analysis of other quantities, such as sheath width and postshock
compression (pileup and shock indentation compressions), the effect
of different magnetic configurations and initializations can be
distinguished. We discuss that coronal models that employ a reduced
value of polytropic index (γ) may significantly change the energetics
of the CME and that the background solar wind plays an important role
in the CMEs' shock and sheath evolution.
Title: Downstream structure and evolution of a simulated CME-driven
sheath in the solar corona
Authors: Liu, Y. C. -M.; Opher, M.; Wang, Y.; Gombosi, T. I.
Bibcode: 2011A&A...527A..46L
Altcode:
Context. The transition of the magnetic field from the ambient magnetic
field to the ejecta in the sheath downstream of a coronal mass ejection
(CME) driven shock is analyzed in detail. The field rotation in the
sheath occurs in a two-layer structure. In the first layer, layer 1,
the magnetic field rotates in the coplanarity plane (plane of shock
normal and the upstream magnetic field), and in layer 2 rotates off
this plane. We investigate the evolution of the two layers as the
sheath evolves away from the Sun.
Aims: In situ observations
have shown that the magnetic field in the sheath region in front of
an interplanetary coronal mass ejection (ICME) form a planar magnetic
structure, and the magnetic field lines drape around the flux tube. Our
objective is to investigate the magnetic configuration of the CME near
the sun.
Methods: We used the space weather modeling framework
(SWMF), a 3D magnetohydrodynamics (MHD) simulation code, to simulate
the propagation of CMEs and the shock driven by it.
Results: We
find that close to the Sun, layer 2 dominates the width of the sheath,
diminishing its importance as the sheath evolves away from the Sun,
in agreement with observations at 1 AU.
Title: Evolution of Piled-up Compressions in Modeled Coronal Mass
Ejection Sheaths and the Resulting Sheath Structures
Authors: Das, Indrajit; Opher, Merav; Evans, Rebekah; Loesch,
Cristiane; Gombosi, Tamas I.
Bibcode: 2011ApJ...729..112D
Altcode:
We study coronal mass ejection (CME)-driven shocks and the resulting
post-shock structures in the lower corona (2-7 R sun). Two
CMEs are erupted by modified Titov-Démoulin (TD) and Gibson-Low (GL)
type flux ropes (FRs) with the Space Weather Modeling Framework. We
observe a substantial pile-up of density compression and a narrow region
of plasma depletion layer (PDL) in the simulations. As the CME/FR
moves and expands in the solar wind medium, it pushes the magnetized
material lying ahead of it. Hence, the magnetic field lines draping
around the CME front are compressed in the sheath just ahead of the
CME. These compressed field lines squeeze out the plasma sideways,
forming PDL in the region. Solar plasma being pushed and displaced from
behind forms a strong piled-up compression (PUC) of density downstream
of the PDL. Both CMEs have comparable propagation speeds, while GL
has larger expansion speed than TD due to its higher initial magnetic
pressure. We argue that high CME expansion speed along with high solar
wind density in the region is responsible for the large PUC found in
the lower corona. In case of GL, the PUC is much wider, although the
density compression ratio for both the cases is comparable. Although
these simulations artificially initiate out-of-equilibrium CMEs and
drive them in an artificial solar wind solution, we predict that PUCs,
in general, will be large in the lower corona. This should affect the
ion profiles of the accelerated solar energetic particles.
Title: Powerful winds from low-mass stars: V374 Peg
Authors: Vidotto, A. A.; Jardine, M.; Opher, M.; Donati, J. F.;
Gombosi, T. I.
Bibcode: 2011MNRAS.412..351V
Altcode: 2010MNRAS.tmp.1873V; 2010arXiv1010.4762V
The M dwarf V374 Peg (M4) is believed to lie near the theoretical
mass threshold for fully convective interiors. Its rapid rotation
(P= 0.44 d) along with its intense magnetic field point towards
magnetocentrifugal acceleration of a coronal wind. In this work, we
investigate the structure of the coronal wind of V374 Peg by means of
three-dimensional magnetohydrodynamical (MHD) numerical simulations. For
the first time, an observationally derived surface magnetic field
map is implemented in MHD models of stellar winds for a low-mass
star. By self-consistently taking into consideration the interaction
of the outflowing wind with the magnetic field and vice versa, we
show that the wind of V374 Peg deviates greatly from a low-velocity,
low-mass-loss rate solar-type wind. We have found general scaling
relations for the terminal velocities, mass-loss rates and spin-down
times of highly magnetized M dwarfs. In particular, for V374 Peg, our
models show that terminal velocities across a range of stellar latitudes
reach u∞≃ (1500-2300) n-1/212
km s-1, where n12 is the coronal wind base
density in units of 1012 cm-3, while the
mass-loss rates are about ?. We also evaluate the angular momentum
loss of V374 Peg, which presents a rotational braking time-scale τ≃
28 n-1/212 Myr. Compared to observationally
derived values from period distributions of stars in open clusters,
this suggests that V374 Peg may have low coronal base densities
(≲1011 cm-3). We show that the wind ram pressure
of V374 Peg is about 5 orders of magnitude larger than for the solar
wind. Nevertheless, a small planetary magnetic field intensity (∼0.1
G) is able to shield a planet orbiting at 1 au against the erosive
effects of the stellar wind. However, planets orbiting inside the
habitable zone of V374 Peg, where the wind ram pressure is higher, might
be facing a more significant atmospheric erosion. In that case, higher
planetary magnetic fields of, at least, about half the magnetic field
intensity of Jupiter are required to protect the planet's atmosphere.
Title: Learning from the Outer Heliosphere: Interplanetary Coronal
Mass Ejection Sheath Flows and the Ejecta Orientation in the Lower
Corona
Authors: Evans, R. M.; Opher, M.; Gombosi, T. I.
Bibcode: 2011ApJ...728...41E
Altcode:
The magnetic field structure of the ejecta of a coronal mass ejection
(CME) is not known well near the Sun. Here we demonstrate, with a
numerical simulation, a relationship between the subsonic plasma flows
in the CME-sheath and the ejecta magnetic field direction. We draw an
analogy to the outer heliosphere, where Opher et al. used Voyager 2
measurements of the solar wind in the heliosheath to constrain the
strength and direction of the local interstellar magnetic field. We
simulate three ejections with the same initial free energy,
but different ejecta magnetic field orientations in relation to
the global coronal field. Each ejection is launched into the same
background solar wind using the Space Weather Modeling Framework. The
different ejecta magnetic field orientations cause the CME-pause (the
location of pressure balance between solar wind and ejecta material)
to evolve differently in the lower corona. As a result, the CME-sheath
flow deflections around the CME-pauses are different. To characterize
this non-radial deflection, we use θ_F=tan ^{-1}{V_N}/{V_T}, where
VN and VT are the normal and tangential plasma
flow as measured in a spacecraft-centered coordinate system. Near the
CME-pause, we found that θ F is very sensitive to the
ejecta magnetic field, varying from 45° to 98° between the cases when
the CME-driven shock is located at 4.5 R sun. The deflection
angle for each case is found to evolve due to rotation of the ejecta
magnetic field. We find that this rotation should slow or stop by 10 R
sun (also suggested by observational studies). These results
indicate that an observational study of CME-sheath flow deflection
angles from several events (to account for the interaction with the
solar wind), combined with numerical simulations (to estimate the
ejecta magnetic field rotation between eruption and 10 R sun)
can be used to constrain the ejecta magnetic field in the lower corona.
Title: Energetic protons accelerated by a model Coronal Mass Ejection
and associated shock in the solar corona
Authors: Kozarev, K. A.; Evans, R. M.; Dayeh, M. A.; Schwadron, N. A.;
Opher, M.; Korreck, K. E.; Gombosi, T. I.
Bibcode: 2010AGUFMSH33A1832K
Altcode:
Modeling and observational studies of coronal and interplanetary
shocks suggest that they are most effective in accelerating Solar
Energetic Particles (SEP) relatively close to the Sun. Interplanetary
shocks have been quite well studied, thanks to in situ measurements
of energetic articles near Earth and throughout the solar system. Many
bursts of energetic charged particles observed close to Earth are not
directly associated with shocks that pass by Earth. This suggests
that energetic particles could be accelerated much lower, in the
solar corona, possibly by shocks that form near the Sun or through
magnetic reconnection. For the first time, we have used results
from a three-dimensional time-dependent magnetohydrodynamic (MHD)
simulation of a coronal mass ejection (CME) in the solar corona,
coupled with a three-dimensional energetic particle propagation
and acceleration model, in order to investigate how suprathermal
protons respond to an enhanced traveling plasma structure and shock
in the corona. The detailed MHD simulation reveals multiple density
and magnetic field enhancements behind the traveling shock, which
cause rapid acceleration of suprathermal protons via diffusive shock
acceleration in the kinetic simulation. The resulting spectra and time
profiles of energetic protons at different radial distances from the
Sun are presented. This work will help address the question of whether
and how efficient CMEs and shocks close to the Sun are in accelerating
suprathermal particle populations to high energies.
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: 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: 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: 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: Coronal Heating by Surface Alfven Wave Damping: Implementation
in MHD Modeling and Connection to Observations
Authors: Evans, R. M.; Opher, M.; Oran, R.; van der Holst, B.; Sokolov,
I.; Frazin, R. A.; Gombosi, T. I.
Bibcode: 2010AGUFMSH42A..07E
Altcode:
We present results from the development of a solar wind model
driven by Alfven waves with realistic damping mechanisms. We
self-consistently introduce surface Alfven wave damping, which is
characterized by transverse gradients in density. The plasma gradients
set up a resonant layer, in which the waves dissipate energy to the
wind. First, we applied surface Alfven wave damping in a solar wind
model driven by a flat wave spectrum (van der Holst et al. 2010), and
demonstrated its effect at the boundary of open and closed magnetic
fields (Evans et al. 2010). Here we apply surface wave damping to
a model which allows a Kolmogorov-type spectrum of Alfven waves to
evolve in frequency space (Oran et al. 2010). We consider waves with
frequencies lower than those damped in the chromosphere, and on the
order of those dominating the heliosphere (0.0001 to 100 Hz). We
provide wave dissipation as a function of frequency. We connect our
modeling results to recent observations, including an estimation of
resonant absorption damping by Verth, Terradas & Goossens (2010)
and density and temperature distributions using differential emission
measure tomography by Vasquez, Frazin & Manchester (2010), which
we present as both direct and indirect evidence that this dissipation
mechanism occurs and is important in the lower corona.
Title: Evolution of Piled Up Compressions in Modeled CME Sheaths
and the Resulting Sheath Structures
Authors: Das, I.; Opher, M.; Evans, R. M.; Gombosi, T. I.
Bibcode: 2010AGUFMSH51E1732D
Altcode:
We study Coronal Mass Ejection (CME) driven shocks and the resulting
post shock structures in the lower corona (~ 2-7 Rsun). Two CMEs are
erupted by modified Titov-Demoulin (TD) and Gibson-Low (GL) type flux
ropes with Space Weather Modeling Framework. We observe a substantial
pile up of density compression and a narrow region of plasma depletion
layer (PDL) in the simulations. As the CME/flux rope moves and expands
in solar wind medium, it pushes the magnetized material laying ahead
of it. Hence, the magnetic field lines draping around the CME front are
compressed in the sheath just ahead of the CME. These compressed field
lines squeeze out the plasma sideways forming PDL in the region. Solar
plasma being pushed and displaced from behind, forms a strong piled
up compression (PUC) of density downstream of the PDL. Both CMEs have
comparable propagation speeds while GL has larger expansion speed than
TD due to its higher initial magnetic pressure. We argue that high
CME expansion speed along with high solar wind density in the region
are responsible for the large PUC found in the lower corona. In case
of GL the PUC is much wider although the density compression ratio for
both the cases are comparable. Although these simulations artificially
initiate out-of-equilibrium CMEs and drive them in an artificial solar
wind solution, we predict that PUCs, in general, will be large in the
lower corona. This should affect the ion profiles of the accelerated
solar energetic particles.
Title: Simulations of Winds of Weak-lined T Tauri Stars. II. The
Effects of a Tilted Magnetosphere and Planetary Interactions
Authors: Vidotto, A. A.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2010ApJ...720.1262V
Altcode: 2010arXiv1007.3874V
Based on our previous work, we investigate here the effects on the
wind and magnetospheric structures of weak-lined T Tauri stars
due to a misalignment between the axis of rotation of the star
and its magnetic dipole moment vector. In such a configuration,
the system loses the axisymmetry presented in the aligned case,
requiring a fully three-dimensional (3D) approach. We perform 3D
numerical magnetohydrodynamic simulations of stellar winds and
study the effects caused by different model parameters, namely the
misalignment angle θ t , the stellar period of rotation,
the plasma-β, and the heating index γ. Our simulations take into
account the interplay between the wind and the stellar magnetic field
during the time evolution. The system reaches a periodic behavior with
the same rotational period of the star. We show that the magnetic
field lines present an oscillatory pattern. Furthermore, we obtain
that by increasing θ t , the wind velocity increases,
especially in the case of strong magnetic field and relatively rapid
stellar rotation. Our 3D, time-dependent wind models allow us to study
the interaction of a magnetized wind with a magnetized extrasolar
planet. Such interaction gives rise to reconnection, generating
electrons that propagate along the planet's magnetic field lines
and produce electron cyclotron radiation at radio wavelengths. The
power released in the interaction depends on the planet's magnetic
field intensity, its orbital radius, and on the stellar wind local
characteristics. We find that a close-in Jupiter-like planet orbiting
at 0.05 AU presents a radio power that is ~5 orders of magnitude larger
than the one observed in Jupiter, which suggests that the stellar wind
from a young star has the potential to generate strong planetary radio
emission that could be detected in the near future with LOFAR. This
radio power varies according to the phase of rotation of the star. For
three selected simulations, we find a variation of the radio power of a
factor 1.3-3.7, depending on θ t . Moreover, we extend the
investigation done in Vidotto et al. and analyze whether winds from
misaligned stellar magnetospheres could cause a significant effect
on planetary migration. Compared to the aligned case, we show that
the timescale τ w for an appreciable radial motion of
the planet is shorter for larger misalignment angles. While for the
aligned case τ w ~= 100 Myr, for a stellar magnetosphere
tilted by θ t = 30°, τ w ranges from ~40 to
70 Myr for a planet located at a radius of 0.05 AU. Further reduction
on τ w might occur for even larger misalignment angles
and/or different wind parameters.
Title: Radio emission from close-in giant planets around young stars
Authors: Vidotto, A. A.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2010epsc.conf..233V
Altcode:
No abstract at ADS
Title: Energetic protons accelerated by a Coronal Mass Ejection
(CME)-driven traveling plasma structures in the solar corona
Authors: Kozarev, Kamen Asenov; Das, Indrajit; Schwadron, Nathan;
Opher, Merav; Desai, Mihir; Gombosi, Tamas
Bibcode: 2010shin.confE..92K
Altcode:
A growing body of theoretical and observational research suggests that
Solar Energetic Particles (SEP) gain most of their energy at shocks
relatively close to the Sun. Interplanetary shocks have been quite well
studied, thanks to in situ measurements of energetic particles near
Earth and throughout the solar system. Many bursts of energetic charged
particles observed close to Earth are not directly associated with
shocks that pass by Earth. This suggests that energetic particles could
be formed much lower, in the solar corona, possibly by shocks that form
near the Sun or through magnetic reconnection. We have used results from
a magnetohydrodynamic (MHD) simulation of a coronal mass ejection (CME)
in the solar corona, combined with an energetic particle propagation
and acceleration model, in order to investigate how energetic protons
respond to an enhanced traveling plasma structure and shock in the
corona. This work will help address the question of whether and how
efficient CME-driven plasma structures and shocks close to the Sun
are in accelerating suprathermal particle populations to high energies.
Title: Surface Alfven Wave Contribution to Coronal Heating in a
Wave-Driven Solar Wind Model
Authors: Evans, Rebekah Minnel; Opher, Merav; Oran, Rona; Sokolov,
Igor V.; van der Holst, Bart; Gombosi, Tamas I.
Bibcode: 2010shin.confE.119E
Altcode:
We present results from the development of a solar wind model driven
by a spectrum of Alfven waves with realistic damping mechanisms in the
Space Weather Modeling Framework. Whereas other works have focused on
the dissipation of wave energy in closed magnetic field regions or along
open polar field lines, we emphasize here the boundary between these
two regions as a source for coronal heating and wind acceleration. This
region is characterized by gradients in density and magnetic field,
that set up a resonant layer in which surface Alfven waves arise and
dissipate their energy to the solar wind. Observations of latitudinal
density distributions at 1.035-1.225 solar radii from differential
emission measure tomography (Vasquez, Frazin & Manchester 2009)
show density enhancements at the boundary of open and closed magnetic
fields, which supports the presence of surface Alfven wave damping in
this region. We utilize a first principle solar wind model within the
Space Weather Modeling Framework. The wave transport equation, including
wave advection and dissipation, is coupled to the magnetohydrodynamics
equations for the plasma. We extend this model to include surface
Alfven wave damping. We provide the first global damping length map for
surface Alfven waves in a realistic background solar wind. We quantify
the contribution of the damping to coronal heating and acceleration of
the wind. The boundary conditions for this solar wind model are
obtained from observations and a semi-empirical model. The velocities
at 1AU obtained from the semi-empirical Wang-Sheeley-Arge model in
combination with conservation of the total energy density along the
magnetic field lines determines the Alfven wave pressure at the lower
coronal boundary. The electron density and temperature at the lower
solar 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 with ACE
data for Carrington rotation 2077 (2008, November 20 through December
17). Overall, the simulated results at 1AU match the ACE observations
rather well.
Title: Is the Magnetic Field in the Heliosheath Sector Region and
in the Outer Heliosheath Laminar?
Authors: Opher, Merav; Drake, J. F.; Swisdak, M.
Bibcode: 2010shin.confE..65O
Altcode:
All the current global models are based on our understanding that
the magnetic field in the outer heliosheath close to the heliopause
is laminar. We argue that in the outer heliosheath, close to the
heliopause, the heliospheric magnetic field is in fact not laminar but
instead filled with 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. In this process energetic
electrons are also produced. As a product of the annihilation of the
sectored magnetic field, magnetic islands are produced. These magnetic
islands will be convected with the flows as the sector boundary
is carried to higher latitudes filling the outer heliosheath. We
further argue that the magnetic islands will propagate upstream and
affect the structure of the magnetic field in the heliosheath sector
region making it disorganized. Due to the increased pressure of the
interstellar magnetic field the sector boundary is carried mostly to
the northern hemisphere (Opher et al. 2006, 2007). We argue that the
sector boundary fills a large portion of the northern part of the
heliosphere with a smaller extension in the southern hemisphere. We
therefore predict an asymmetry of the magnetic structure between the
northern and southern hemispheres and between the heliosheath sector
region and the field outside of it. Within this scenario we are able
to explain the the sudden decrease seen in mid 2008 in Voyager 2 in
the low energy electrons (0.02-1.5MeV) from the LECP instrument; in the
low energy Galactic Cosmic Ray Electrons (2-14MeV) and the north-south
asymmetry seen in the Galactic Cosmic Ray Electrons between Voyager 1
and 2 intensities. We argue that these observations are a consequence
of Voyager 2 leaving the sector region of disorganized field in mid
2008 and crossing into a region of unipolar organized laminar field.
Title: The effects of the solar cycle variations on the solar wind
properties at the heliospheric boundaries
Authors: Provornikova, Elena Aleksandrovna; Izmodenov, V. V.; Opher,
M.; Malama Y., G.
Bibcode: 2010shin.confE...7P
Altcode:
The propagation and evolution of fluctuations of the solar wind
are studied in the frame of the two-dimensional non-stationary
kinetic-gasdynamic model of the interaction of solar wind with the
local interstellar medium (Izmodenov et al., 2005, 2008). For this
purpose we analyzed how various types of waves in the solar wind pass
through the termination shock and heliopause. Results show that solar
wind fluctuations strongly influence the location of heliospheric
boundaries. Using OMNI data for solar wind parameters at 1 a.u. for
the last 3 solar cycles we investigate the variation of the distances
to the termination shock and heliopause. Particularly we focus on
the questions how the anomalously low solar wind dynamic pressure
during 2008-2009 affects the locations of the termination shock and
the heliopause at the present time and in the future.Voyager 2 has
crossed the termination shock in August 2007 and now measures the
plasma parameters in the inner heliosheath. In this work we estimate
the time when Voyager 2 might cross the heliopause. Also the solar
wind parameters along the trajectory of Voyager 2 obtained in the model
are compared with experimental data obtained on the board of Voyager 2.
Title: The Imprint of the Very Local Interstellar Magnetic Field in
Simulated Energetic Neutral Atom Maps
Authors: Prested, C.; Opher, M.; Schwadron, N.
Bibcode: 2010ApJ...716..550P
Altcode:
The interaction of the solar wind with the very local interstellar
medium (VLISM) forms the boundaries of the heliosphere. A strong
asymmetry of the heliosphere was found both directly by the Voyager
probes and indirectly from measurements of the deflection of neutral
hydrogen. The most likely source of this asymmetry is from the
interstellar magnetic field, the properties of which are highly
unconstrained. Energetic neutral atom (ENA) images will provide an
additional method to view the heliosphere and infer the interstellar
magnetic field. This paper investigates the imprint of the interstellar
magnetic field on simulated energetic neutral atom all-sky maps. We
show that a significant source of 0.5-1 keV ENAs may originate from the
outside of the heliopause, if a strong suprathermal population exists
in the VLISM. In simulations, a strong outer heliosheath ENA feature
appears near the nose of the heliosphere. A weaker, complementary
feature is also present consisting entirely of inner heliosheath
ENAs. From this feature the direction of the interstellar magnetic
field can be easily inferred.
Title: Shocks in heliophysics
Authors: Opher, Merav
Bibcode: 2010hssr.book..193O
Altcode:
No abstract at ADS
Title: Surface Alfven Wave Contribution to Coronal Heating in a
Wave-Driven Solar Wind Model
Authors: Evans, Rebekah M.; Opher, M.; Oran, R.; Sokolov, I. V.
Bibcode: 2010AAS...21640719E
Altcode: 2010BAAS...41..862E
We present results from the development of a solar wind model driven
by Alfven waves with realistic damping mechanisms. We investigate the
contribution of surface Alfven wave damping to the heating of the
corona and acceleration of the solar wind. These waves are present
and damp in regions of strong gradients in density or magnetic field
(e.g., the border between open and closed magnetic fields). Recently
Oran et al. (2009) implemented a first principle solar wind model
driven by a spectrum of Alfven waves into the Space Weather Modeling
Framework. The wave transport equation, including wave advection
and dissipation, is coupled to the MHD equations for the wind. The
waves contribute to the momentum and energy of the wind through the
action of wave pressure. Here we extend this model to include surface
Alfven wave damping as a dissipation mechanism, considering waves with
frequencies lower than those damped in the chromosphere and on the order
of those dominating the heliosphere (0.0001 to 100 Hz.) We demonstrate
the influence of the damping by quantifying the differences between
a solution that includes surface Alfven wave damping and one driven
solely by Alfven wave pressure. We relate to possible observational
signatures of heat transfer by surface Alfven wave damping. This work is
the first to study surface Alfven waves self-consistently as an energy
driven for the solar wind in a 4D (three in space and one in frequency)
environment. This work is supported by the NSF CAREER Grant.
Title: Sheath Flows and Reconnection in the Lower Corona: New
Diagnostics for the Initial Orientation of the Ejecta of Coronal
Mass Ejections
Authors: Opher, Merav; Evans, R. M.
Bibcode: 2010AAS...21640603O
Altcode: 2010BAAS...41..880O
The structure of the magnetic field of the ejecta of a coronal mass
ejection (CME) is not well known near the Sun. We propose using
the subsonic plasma flows in the CME-sheath to constrain the CME
field direction. We draw an analogy to the outer heliosphere, where
Opher et al. (2009) used Voyager 2 measurements of the solar wind in
the heliosheath to constrain the strength and direction of the local
interstellar magnetic field. We simulate three ejections in a realistic
background in the solar minimum conditions of 1997 May with the Space
Weather Modeling Framework. Each ejection has the same initial energy,
but a different magnetic field orientation in relation to the overall
orientation of the active region field. We show that the sheath flows
are sensitive to the direction of the initial magnetic field, and
differ by more than 60 degrees when the CME-driven shock is located
at 4.5 solar radii. Unlike the heliosheath flows, the CME-sheath
flows are affected not only by the initial ejecta orientation but
by the CME's evolution in the lower corona as well. We show that
the evolutions differ because of the locations and intensities of
reconnection events. We distinguish between the initial reconnection
between the ejecta and the overlying field of the active region, and
further reconnection events with the global solar coronal field (which
occur beyond 2 solar radii). This late reconnection causes bulk motion
and heating in the ejecta and sheaths, which affects the size of the
CME-pause and the velocity profile of the CME. We suggest identifying
the orientation of the magnetic field ejecta through velocity profiles
in the lower corona and in situ CME-sheath flow measurements. These
results provide new diagnostics to identify different initial CME
magnetic field orientations without need for direct measurement.
Title: Magnetic fields in the Local ISM and the Local Bubble
Authors: Opher, Merav
Bibcode: 2010AAS...21620103O
Altcode:
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), but 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 μG 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 μG. 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 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. We will discuss the
possible implications of a strong magnetic field for the environment
in the Local ISM and the Local Bubble.
Title: The Vector Direction of the Interstellar Magnetic Field
Outside the Heliosphere
Authors: Swisdak, M.; Opher, M.; Drake, J. F.; Alouani Bibi, F.
Bibcode: 2010ApJ...710.1769S
Altcode: 2010arXiv1001.0589S
We propose that magnetic reconnection at the heliopause (HP) only occurs
where the interstellar magnetic field points nearly anti-parallel to
the heliospheric field. By using large-scale magnetohydrodynamic (MHD)
simulations of the heliosphere to provide the initial conditions for
kinetic simulations of HP reconnection, we show that the energetic
pickup ions downstream from the solar wind termination shock induce
large diamagnetic drifts in the reconnecting plasma and stabilize
non-anti-parallel reconnection. With this constraint, the MHD
simulations can show where HP reconnection most likely occurs. We
also suggest that reconnection triggers the 2-3 kHz radio bursts that
emanate from near the HP. Requiring the burst locations to coincide
with the loci of anti-parallel reconnection allows us to determine,
for the first time, the vector direction of the local interstellar
magnetic field. We find it to be oriented toward the southern solar
magnetic pole.
Title: A Magnetic Reconnection Mechanism for the Generation of
Anomalous Cosmic Rays
Authors: Drake, J. F.; Opher, M.; Swisdak, M.; Chamoun, J. N.
Bibcode: 2010ApJ...709..963D
Altcode: 2009arXiv0911.3098D
The recent observations of the anomalous cosmic ray (ACR) energy
spectrum as Voyager 1 and Voyager 2 crossed the heliospheric termination
shock have called into question the conventional shock source of
these energetic particles. We suggest that the sectored heliospheric
magnetic field, which results from the flapping of the heliospheric
current sheet, piles up as it approaches the heliopause, narrowing the
current sheets that separate the sectors and triggering the onset of
collisionless magnetic reconnection. Particle-in-cell simulations reveal
that most of the magnetic energy is released and most of this energy
goes into energetic ions with significant but smaller amounts of energy
going into electrons. The energy gain of the most energetic ions results
from their reflection from the ends of contracting magnetic islands,
a first-order Fermi process. The energy gain of the ions in contracting
islands increases their parallel (to the magnetic field B) pressure
p par until the marginal fire-hose condition is reached,
causing magnetic reconnection and associated particle acceleration to
shut down. Thus, the feedback of the self-consistent development of
the energetic ion pressure on reconnection is a crucial element of any
reconnection-based, particle-acceleration model. The model calls into
question the strong scattering assumption used to derive the Parker
transport equation and therefore the absence of first-order Fermi
acceleration in incompressible flows. A simple one-dimensional model
for particle energy gain and loss is presented in which the feedback
of the energetic particles on the reconnection drive is included. The
ACR differential energy spectrum takes the form of a power law with
a spectral index slightly above 1.5. The model has the potential to
explain several key Voyager observations, including the similarities
in the spectra of different ion species.
Title: Preferential Low-Latitude Acceleration and Transport of
Low-Energy Anomalous Cosmic Rays
Authors: Hill, Matthew; Drake, James; Opher, Merav
Bibcode: 2010cosp...38.1666H
Altcode: 2010cosp.meet.1666H
During the last decade the encounters by the Voyager 1 and 2
spacecraft with the termination shock and continuing cruise through
the heliosheath have upset the classical anomalous cosmic ray (ACR)
paradigm, which has interstellar neutral atoms being ionized, picked up
by the solar wind, and accelerated at essentially all regions of the
termination shock. Observations show that ACRs are not accelerated
at the termination shock, at least not at the locations of the
Voyager encounters. ACR transport is also supposed to be dominated
by drift motion arising from the curvature and gradients of the
global heliospheric magnetic field; the well-known drift pattern
of cosmic rays down along the poles and out along the heliospheric
current sheet during the so called A > 0 solar cycles (and reverse
pattern during A < 0) is considered a hallmark of the classic
theory. Additionally the observed striking similarity of the spectral
slope of suprathermal ions across wide regions and conditions in the
heliosphere has forced a general rethinking of the role of diffusive
shock acceleration. We present the results of two independent
lines of inquiry. First, recent theoretical and particle-in-cell
simulation work has combined determination of the physical cause for
the special spectral form with a proposed mechanism for the source
of ACRs—explained by the conversion of magnetic energy into kinetic
energy due to the annihilation of magnetic flux near the heliopause,
at low latitudes. Second, observational study of ACR transport during
the A > 0 cycle shows—for low-energy ions of a given species
(actually for low rigidities, less than 2 GV, when all species are
considered)—no evidence for a strong positive latitudinal intensity
gradient, as predicted. Quite the opposite is true. For the lowest
rigidities these gradients are negative, as large as -15%/degree. This
and other work suggests that the low-latitude region is the region where
ACR activity is most significant. We will compare the theoretical and
observational results and discuss the implications for the surprising
dearth of ACRs observed during the termination shock encounters,
and the subsequent variations in the heliosheath.
Title: Simulations of Winds of Weak-Lined T Tauri Stars: The Magnetic
Field Geometry and The Influence of the Wind on Giant Planet Migration
Authors: Opher, Merav; Vidotto, A.; Jatenco-Pereira, V.; Gombosi, T.
Bibcode: 2010AAS...21534902O
Altcode: 2010BAAS...42..531O
By means of numerical simulations, we investigate magnetized stellar
winds of pre-main sequence stars. In particular we analyze under which
circumstances these stars will present elongated magnetic features
(e.g., helmet streamers, slingshot prominences, etc). We focus on
weak-lined T Tauri stars, as the presence of the tenuous accretion
disk is not expected to have strong influence on the structure of
the stellar wind. We show that the plasma-beta parameter (the ratio
of thermal to magnetic energy densities) is a decisive factor in
defining the magnetic configuration of the stellar wind. Using initial
parameters within the observed range for these stars, we show that the
coronal magnetic field configuration can vary between a dipole-like
configuration and a configuration with strong collimated polar lines
and closed streamers at the equator (multi component configuration for
the magnetic field). We show that elongated magnetic features will
only be present if the plasma-beta parameter at the coronal base is
beta0 << 1. Using our self-consistent 3D MHD model, we estimate
for these stellar winds the time scale of planet migration due to drag
forces exerted by the stellar wind on a hot-Jupiter. In contrast to the
findings of Lovelace et al. (2008), who estimated such time-scales using
the Weber \& Davis model, our model suggests that the stellar wind
of these multi component coronae are not expected to have significant
influence on hot-Jupiters migration. Further simulations are necessary
to investigate this result under more intense surface magnetic field
strengths ( 2-3kG) and higher coronal base densities, as well as in
a tilted stellar magnetosphere.
Title: A magnetic reconnection mechanism for the generation of
anomalous cosmic rays
Authors: Drake, James; Opher, Merav; Swisdak, Marc; Chamoun, Jacob
Bibcode: 2010cosp...38.1608D
Altcode: 2010cosp.meet.1608D
The recent observations of the anomalous cosmic ray (ACR) energy
spectrum as Voyagers 1 and 2 crossed the heliospheric termination
shock have called into question the conventional shock source of
these energetic particles. We suggest that the sectored heliospheric
magnetic field, which results from the flapping of the heliospheric
current sheet, piles up as it approaches the heliopause, narrowing
the current sheets that separate the sectors and triggering the onset
of collisionless magnetic reconnection. Particle-in-cell simulations
reveal that the current layers break up into a turbulent bath of
magnetic islands that merge to release a large fraction of the energy
in the sectored magnetic field. Most of the magnetic energy goes into
energetic ions with significant but smaller amounts of energy going into
electrons. The dominant acceleration mechanism is through reflection in
contracting islands, a first-order Fermi mechanism. Particle energy gain
is regulated by the approach to the marginal firehose condition. The
ACR differ-ential energy spectrum for all of the ion species takes
the form of a power law with a spectral index slightly above 1.5,
which is consistent with observations.
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: Relationship between Flow and Magnetic Field in Coronal
Mass Ejections
Authors: Evans, Rebekah M.; Opher, M.
Bibcode: 2010AAS...21532205E
Altcode: 2010BAAS...42..324E
Magnetic fields impact the dynamics of astrophysical plasmas in
many regimes, from galaxies to stars to planets. This universal
process suggests that knowledge can be gained by doing comparative
analysis in different regimes. Recently, Opher et al. 2009 used a 3D
magnetohydrodynamics (MHD) simulation of the heliosphere to show that
the flow inside the heliosheath is sensitive to the direction of the
magnetic field in the interstellar medium. Direct measurements of the
flows in this region by Voyager 2 allowed for the best estimates to
date of the strength and direction of the local interstellar magnetic
field. Here we draw an analogy between the heliosphere and
Coronal Mass Ejections (CMEs). Like the interstellar magnetic field,
the structure of the magnetic field in a CME eruption is not well known
near the Sun, and several initiation models exist. We characterize
plasma flows in the CME-sheath - the subsonic flow region between the
CME-driven shock and the location of pressure balance between the solar
wind and the ejected material (analogous to the heliosheath). Using a
3D MHD simulation, we investigate the relationship between these flows
and the orientation of the CME's magnetic field. This result provides
a new diagnostic to probe the 3D magnetic field structure of CMEs,
without need for direct measurement. This research is supported
by the NSF CAREER Grant and LWS.
Title: The possibility of magnetic reconnection at the heliopause
Authors: Swisdak, Marc; Drake, James; Opher, Merav
Bibcode: 2010cosp...38.1606S
Altcode: 2010cosp.meet.1606S
We propose that magnetic reconnection at the heliopause only occurs
where the interstellar magnetic field points nearly anti-parallel to
the heliospheric field. By using large-scale mag-netohydrodynamic
simulations of the heliosphere to provide the initial conditions
for kinetic simulations of heliopause reconnection we show that the
energetic pickup ions downstream from the solar wind termination shock
induce large diamagnetic drifts in the reconnecting plasma and stabilize
non-anti-parallel reconnection. With this constraint the MHD simulations
can show where heliopause reconnection most likely occurs. We also
suggest that reconnection triggers the 2-3 kHz radio bursts that emanate
from near the heliopause. Requiring the burst locations to coincide
with the loci of anti-parallel reconnection allows us to determine,
for the first time, the vector direction of the local interstellar
magnetic field. We find it to be oriented towards the southern solar
magnetic pole.
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: Surface Alfven Wave Damping in a Solar Wind Simulation Driven
by Alfven Waves
Authors: Evans, R. M.; Opher, M.; Oran, R.; Sokolov, I.
Bibcode: 2009AGUFMSH53A1309E
Altcode:
We present results in an effort to develop a solar wind model driven
by Alfven waves with realistic damping mechanisms. Here we investigate
the contribution of surface Alfven wave damping to the heating of the
solar wind in minima conditions. These waves are present and damp in
regions of strong gradients in density or magnetic field (e.g., the
border between open and closed magnetic field lines). By considering
the geometry of open field lines and the background solar wind in
these regions, we showed that surface Alfven wave contribution to
heating is on the order of the heating by a variable polytropic index
in the semiempirical thermodynamics model of Cohen et al. (Evans et
al. 2009). Recently Oran et al. implemented a first principle steady
state solar wind driven by a spectrum of Alfven waves in the SWMF. The
waves contribute to the momentum and the energy of the wind. The
wave transport equation, including wave advection and dissipation,
is coupled to the MHD equations for the wind. In this work we extend
this model to include surface Alfven wave damping, considering waves
with frequencies lower than those that are damped in the chromosphere
and on the order of those dominating the heliosphere (0.0001 to 100
Hz.) We compare to results of the variable polytropic index model, and
a wind driven solely by Alfven wave pressure. This work is the first to
study surface Alfven waves self-consistently as an energy driven for the
solar wind in a 4D (three in space and one in frequency) environment.
Title: Comparison of Model ENAs Produced from Heliospheric Multi-fluid
MHD with the First All-Sky ENA Maps
Authors: Prested, C. L.; Schwadron, N. A.; Opher, M.; McComas, D. J.;
Funsten, H. O.; Fuselier, S. A.
Bibcode: 2009AGUFMSH21B1509P
Altcode:
Using a multi-fluid MHD plus neutrals model of the heliosphere,
we produce and compare model energetic neutral atom (ENA) maps to the
first observations of the Interstellar Boundary Explorer (IBEX) mission,
specifically comparing to data from the IBEX - Hi sensor at energies
of 0.5 keV to 6 keV. We explore how model ENA maps are affected by
varying several parameters including the Very Local Interstellar Medium
(VLISM) magnetic field strength and orientation, the assumed plasma
distribution of the inner heliosheath, and the plasma distribution
of the outer heliosheath. If a suprathermal population exists in the
outer heliosheath, then at energies < 2 keV the high density region
of VLISM plasma and neutrals along the nose of the heliopause produces
as many, or more, ENAs as the inner heliosheath. We provide a system
of metrics for comparison with the IBEX data and discuss the extent to
which our model agrees or disagrees with the first complete ENA sky
maps. Based on the metric results, we suggest future improvements on
our model.
Title: A reconnection mechanism for the generation of anomalous
cosmic rays
Authors: Drake, J. F.; Swisdak, M. M.; Opher, M.; Schoeffler, K. M.
Bibcode: 2009AGUFMSH24A..06D
Altcode:
The recent observations of the anomalous cosmic ray (ACR) energy
spectrum as Voyagers 1 and 2 crossed the heliospheric termination
shock have called into question the conventional shock source of
these energetic particles. We suggest that the sectored heliospheric
magnetic field, which results from the flapping of the heliospheric
current sheet, piles up as it approaches the heliopause, narrowing
the current sheets that separate the sectors and triggering the onset
of collisionless magnetic reconnection. Particle-in-cell simulations
reveal that most of the magnetic energy goes into energetic ions with
significant but smaller amounts of energy going into electrons. The
most energetic ions gain energy as they reflect from contracting
magnetic islands, a first order Fermi process. The simulations also
reveal that the mirror and firehose conditions play an essential role
in the reconnection dynamics and particle acceleration. An analytic
model is constructed in which the Fermi drive, modulated by the
approach to firehose marginality, is balanced by convective loss. The
ACR differential energy spectrum takes the form of a power law with
a spectral index slightly above 1.5. The model has the potential to
explain several key ACR observations, including the similarities in
the spectra of different ion species.
Title: Acceleration of Anomalous Cosmic Rays via Reconnection in
the Heliosheath
Authors: Lazarian, A.; Opher, M.
Bibcode: 2009AGUFMSH21A1498L
Altcode:
We discuss a model of cosmic ray acceleration that accounts for the
observations of anomalous cosmic rays (ACRs) by Voyager 1 and 2. The
model appeals to fast magnetic reconnection rather than shocks as the
driver of acceleration. The ultimate source of energy is associated
with magnetic field reversals that occur in the heliosheath. It is
expected that the magnetic field reversals will occur throughout
the heliosheath, but especially near the heliopause where the flows
slow down and diverge with respect to the interstellar wind and also
in the boundary sector in the heliospheric current sheet. While the
first-order Fermi acceleration theory within reconnection layers is
in its infancy, the predictions do not contradict the available data
on ACR spectra measured by the spacecraft. We argue that the Voyager
data are one of the first pieces of evidence favoring the acceleration
within regions of fast magnetic reconnection, which we believe to be a
widely spread astrophysical process. Meridional iew of the boundary of
the heliospheric current sheet and how the opposite sectors get tighter
closer to the heliopause. There in the presence of turbulence fast
reconnection produces first order Fermi acceleration of the anomalous
cosmic rays.
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: 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: The Heliopause Reconnection X-line
Authors: Olson, D. K.; Moore, T. E.; Bibi, F. A.; Opher, M.; Coplan,
M. A.
Bibcode: 2009AGUFMSH21B1507O
Altcode:
The behavior of the interaction between the magnetosphere and the
interplanetary magnetic field and the formation of reconnection
X-lines have previously been modeled (Moore et al., JGR 2002) and
observed (Pu et al., JGR 2007). We apply a similar method to examining
the interaction of the heliosphere with the interstellar magnetic
field. While today it is difficult to make direct measurements of the
heliopause, an understanding of the characteristics of this interaction
can help us compare models of the heliosphere to new observations of
the interstellar boundary. Using a 3D magnetohydrodynamic simulation
(Opher et al., Science 2007), a solution is obtained for a specified
interstellar field. From this solution, we can identify the heliopause
by selecting an appropriate isothermal surface. The change in magnetic
field across this boundary reveals the likely locations for magnetic
reconnection, defining the reconnection X-line at the heliosphere. The
shape of the heliospheric X-line is presented as a function of the
orientation of the interstellar magnetic field.
Title: The Spatial Distribution of Magnetic Reconnection at the
Heliopause
Authors: Swisdak, M. M.; Opher, M.; Drake, J. F.; Bibi, F. A.
Bibcode: 2009AGUFMSH21A1491S
Altcode:
We propose that magnetic reconnection at the heliopause only occurs
where the interstellar magnetic field points nearly anti-parallel to
the heliospheric field. By using large-scale magnetohydrodynamic (MHD)
simulations of the heliosphere to provide the initial conditions for
kinetic simulations of heliopause (HP) reconnection we show that the
energetic pickup ions downstream from the solar wind termination shock
induce large diamagnetic drifts in the reconnecting plasma and stabilize
non-anti-parallel reconnection. With this constraint the MHD simulations
can then show where HP reconnection most likely occurs. We also suggest
that reconnection triggers the 2-3 kHz radio bursts observed to emanate
from near the HP. The source locations can then be used to constrain
the direction and magnitude of the local interstellar magnetic field.
Title: Temporal & Spatial Evolution of a Modeled CME Shock and
Post-shock Compression
Authors: Das, I.; Opher, M.; Evans, R. M.; Gombosi, T. I.
Bibcode: 2009AGUFMSH31A1450D
Altcode:
We studied the temporal and spatial evolution of a modeled Coronal Mass
Ejection (CME) driven shock and it's post-shock compression. Our goal
has been to understand how the shock and the post-shock compression, as
a whole with it's typical geometrical features, evolve over real time
in different directions. We investigated how θ_Bn (the angle between
the shock normal and the upstream magnetic field), Vs (shock velocity),
Ms (Sonic Mach number), Ma (Alfven Mach number) evolve in real time at
different locations on the shock and the post-shock surface. To do this,
we used Rankine-Hugoniot (R-H) shock conditions of a 3D MHD shock and
compared it with the other popular shock defining parameters. We also
comment on the discrepancies and consequences on our observations. The
CME has been initiated and then evolved in the lower solar corona with
the help of Space Weather modeling Framework with a Titov- Demoulin
(TD) type flux rope.
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: Simulations of Winds of Weak-Lined T Tauri Stars: The Magnetic
Field Geometry and the Influence of the Wind on Giant Planet Migration
Authors: Vidotto, A. A.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2009ApJ...703.1734V
Altcode: 2009arXiv0908.2573V
By means of numerical simulations, we investigate magnetized stellar
winds of pre-main-sequence stars. In particular, we analyze under which
circumstances these stars will present elongated magnetic features
(e.g., helmet streamers, slingshot prominences, etc). We focus on
weak-lined T Tauri stars, as the presence of the tenuous accretion
disk is not expected to have strong influence on the structure of
the stellar wind. We show that the plasma-β parameter (the ratio
of thermal to magnetic energy densities) is a decisive factor in
defining the magnetic configuration of the stellar wind. Using initial
parameters within the observed range for these stars, we show that the
coronal magnetic field configuration can vary between a dipole-like
configuration and a configuration with strong collimated polar lines
and closed streamers at the equator (multicomponent configuration
for the magnetic field). We show that elongated magnetic features
will only be present if the plasma-β parameter at the coronal base
is β0 Lt 1. Using our self-consistent three-dimensional
magnetohydrodynamics model, we estimate for these stellar winds the
timescale of planet migration due to drag forces exerted by the stellar
wind on a hot-Jupiter. In contrast to the findings of Lovelace et
al., who estimated such timescales using the Weber and Davis model,
our model suggests that the stellar wind of these multicomponent
coronae are not expected to have significant influence on hot-Jupiters
migration. Further simulations are necessary to investigate this result
under more intense surface magnetic field strengths (~2-3 kG) and higher
coronal base densities, as well as in a tilted stellar magnetosphere.
Title: A Model of Acceleration of Anomalous Cosmic Rays by
Reconnection in the Heliosheath
Authors: Lazarian, A.; Opher, M.
Bibcode: 2009ApJ...703....8L
Altcode: 2009arXiv0905.1120L
We discuss a model of cosmic ray acceleration that accounts for the
observations of anomalous cosmic rays (ACRs) by Voyager 1 and 2. The
model appeals to fast magnetic reconnection rather than shocks as the
driver of acceleration. The ultimate source of energy is associated
with magnetic field reversals that occur in the heliosheath. It is
expected that the magnetic field reversals will occur throughout the
heliosheath, but especially near the heliopause where the flows slow
down and diverge with respect to the interstellar wind and also in the
boundary sector in the heliospheric current sheet. While the first-order
Fermi acceleration theory within reconnection layers is in its infancy,
the predictions do not contradict the available data on ACR spectra
measured by the spacecraft. We argue that the Voyager data are one of
the first pieces of evidence favoring the acceleration within regions
of fast magnetic reconnection, which we believe to be a widely spread
astrophysical process.
Title: Surface Alfvén Wave Damping in a Three-Dimensional Simulation
of the Solar Wind
Authors: Evans, R. M.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2009ApJ...703..179E
Altcode: 2009arXiv0908.3146E
Here we investigate the contribution of surface Alfvén wave damping
to the heating of the solar wind in minima conditions. These waves
are present in the regions of strong inhomogeneities in density or
magnetic field (e.g., the border between open and closed magnetic field
lines). Using a three-dimensional (3D) magnetohydrodynamics (MHD) model,
we calculate the surface Alfvén wave damping contribution between 1
and 4 R sun (solar radii), the region of interest for both
acceleration and coronal heating. We consider waves with frequencies
lower than those that are damped in the chromosphere and on the
order of those dominating the heliosphere: 3 × 10-6 to
10-1 Hz. In the region between open and closed field lines,
within a few R sun of the surface, no other major source
of damping has been suggested for the low frequency waves we consider
here. This work is the first to study surface Alfvén waves in a 3D
environment without assuming a priori a geometry of field lines or
magnetic and density profiles. We demonstrate that projection effects
from the plane of the sky to 3D are significant in the calculation of
field line expansion. We determine that waves with frequencies >2.8
×10-4 Hz are damped between 1 and 4 R sun. In
quiet-Sun regions, surface Alfvén waves are damped at further distances
compared to active regions, thus carrying additional wave energy
into the corona. We compare the surface Alfvén wave contribution to
the heating by a variable polytropic index and find it as an order
of magnitude larger than needed for quiet-Sun regions. For active
regions, the contribution to the heating is 20%. As it has been argued
that a variable gamma acts as turbulence, our results indicate that
surface Alfvén wave damping is comparable to turbulence in the lower
corona. This damping mechanism should be included self-consistently
as an energy driver for the wind in global MHD models.
Title: Shocks and Magnetized Winds: Learning from the Interaction
of the Solar System with the Interstellar Medium
Authors: Opher, M.
Bibcode: 2009RMxAC..36...60O
Altcode:
Through the interaction of the solar system with the interstellar medium
we can learn about shocks and magnetized winds. 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 in-situ measurements of the subsonic solar wind in
the heliosheath. 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. As a result of
the interstellar magnetic field the solar system is asymmetric being
pushed in the southern direction.
Title: Flows in Inner and Outer Heliosphere
Authors: Opher, Merav
Bibcode: 2009shin.confE.124O
Altcode:
In this work we will summarize our group effort on analyzing flows being
deflected in the CME-sheats and in the Heliosheath. The subsonic flows
are immediately sensitive to the magnetic structures ahead. We will
compare the flows in both the lower corona and the outer heliosphere. We
will show how they are sensitive to both the magnetic filament in CMEs
and the interstellar magnetic field in the outer heliosphere case.
Title: The Effect of the Very Local Interstellar Magnetic Field and
Pick-Up Ions on Energetic Neutral Atom Maps
Authors: Prested, Christina Lee; Opher, M.; Alouani Bibi, F.;
Schwadron, N.
Bibcode: 2009shin.confE..26P
Altcode:
The Interstellar Boundary Explorer (IBEX) recently completed its first
all-sky energetic neutral atom (ENA) map. This map details the intensity
of 0.01-6 keV ENAs, which carry with them the signature of the plasma
from the edge of the solar system, where the solar wind and the very
local interstellar medium (VLISM) collide. While both the parameters
of the solar wind and VLISM control this boundary region, it has been
proposed the interstellar magnetic field may be responsible for the
N-S asymmetry as observed by the Voyager probes. For comparison with
IBEX's results, we simulate ENA maps for a variety of magnetic field
orientations at 0.1 keV and find a compass like effect from which
the VLISM magnetic field direction can be read. We also provide
an update on the Opher et al. multi-fluid MHD plus neutrals model
of the heliopshere and the ongoing effort to incorporate a separate
pick-up ion plasma. Pick-up ions are known to carry upwards of 80%
of the pressure at the termination shock, but their full effect on ENA
maps is not yet determined. We offer initial maps from this study and
suggest further modifications on the assumed pick-up ion distribution
to explore in the future.
Title: Pinning Down the Intensity and Direction of the Local
Interstellar Magnetic Field
Authors: Opher, M.
Bibcode: 2009AIPC.1156..153O
Altcode:
Through the interaction of the solar system with the interstellar medium
we can learn about shocks and magnetized winds. 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 in situ measurements of the subsonic solar wind in
the heliosheath. 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. As a result of the interstellar
magnetic field the solar system is asymmetric, being pushed in the
southern direction.
Title: Reconnection of the sectored heliospheric magnetic field
near the heliopause: a mechanism for the generation of anomalous
cosmic rays
Authors: Drake, James F.; Opher, M.; Swisdak, M.
Bibcode: 2009shin.confE..22D
Altcode:
The recent observations of the anomalous cosmic ray (ACR) energy
spectrum as Voyagers 1 and 2 crossed the heliospheric termination
shock have called into question the conventional shock source of
these energetic particles. We suggest that the sectored heliospheric
magnetic field, which results from the flapping of the heliospheric
current sheet, piles up as it approaches the heliopause, narrowing
the current sheets that separate the sectors and triggering the onset
of collisionless magnetic reconnection. Particle-in-cell simulations
reveal that most of the magnetic energy goes into energetic ions with
significant but smaller amounts of energy going into electrons. The
ACR differential energy spectrum takes the form of a power law with
a spectral index slightly above 1.5. The model has the potential to
explain several key observations, including the similarities in the
spectra of different ion species.
Title: Surface Alfven Wave Damping in a 3D Simulation of the
Solar Wind
Authors: Evans, Rebekah Minnel; Opher, Merav; Jatenco-Pereira, Vera;
Gombosi, Tamas I.
Bibcode: 2009shin.confE.131E
Altcode:
Here we investigate the contribution of surface Alfven wave damping to
the heating of the solar wind in minima conditions. These waves are
present in regions of strong inhomogenities in density or magnetic
field (e. g., the border between open and closed magnetic field
lines). Using a 3D MHD model, we calculate the surface Alfven wave
damping contribution between 1-4 Rs (solar radii), the region of
interest for both acceleration and coronal heating. We consider waves
with frequencies lower than those that are damped in the chromosphere
and on the order of those dominating the heliosphere. This work is
the first to study surface Alfven wave damping in a 3D environment
without assuming a priori a geometry of field lines or magnetic and
density profiles. We demonstrate that projection effects from the
plane of the sky to 3D are significant in the calculation of field
line expansion. We determine that waves with frequencies >2.8 -
10^;ˆ’4 Hz are damped between 1-4 Rs. In quiet sun regions, surface
Alfven waves are damped at further distances compared to active regions,
thus carrying additional wave energy into the corona. We compare the
wave contribution to the heating by a variable polytropic index and
find that it is the same order. As it has been argued that a variable
gamma acts as turbulence, our results indicate that surface Alfven
wave damping is comparable to turbulence in the lower corona. This
damping mechanism should be included self consistently as an energy
driver for the wind in global MHD models.
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: Three-dimensional Numerical Simulations of Magnetized Winds
of Solar-like Stars
Authors: Vidotto, A. A.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2009ApJ...699..441V
Altcode: 2009arXiv0904.4398V
By means of self-consistent three-dimensional magnetohydrodynamics (MHD)
numerical simulations, we analyze magnetized solar-like stellar winds
and their dependence on the plasma-β parameter (the ratio between
thermal and magnetic energy densities). This is the first study to
perform such analysis solving the fully ideal three-dimensional MHD
equations. We adopt in our simulations a heating parameter described by
γ, which is responsible for the thermal acceleration of the wind. We
analyze winds with polar magnetic field intensities ranging from 1
to 20 G. We show that the wind structure presents characteristics
that are similar to the solar coronal wind. The steady-state magnetic
field topology for all cases is similar, presenting a configuration of
helmet streamer-type, with zones of closed field lines and open field
lines coexisting. Higher magnetic field intensities lead to faster and
hotter winds. For the maximum magnetic intensity simulated of 20 G and
solar coronal base density, the wind velocity reaches values of ~1000
km s-1 at r ~ 20r 0 and a maximum temperature
of ~6 × 106 K at r ~ 6r 0. The increase of
the field intensity generates a larger "dead zone" in the wind, i.e.,
the closed loops that inhibit matter to escape from latitudes lower
than ~45° extend farther away from the star. The Lorentz force leads
naturally to a latitude-dependent wind. We show that by increasing
the density and maintaining B 0 = 20 G the system recover
back to slower and cooler winds. For a fixed γ, we show that the key
parameter in determining the wind velocity profile is the β-parameter
at the coronal base. Therefore, there is a group of magnetized flows
that would present the same terminal velocity despite its thermal
and magnetic energy densities, as long as the plasma-β parameter
is the same. This degeneracy, however, can be removed if we compare
other physical parameters of the wind, such as the mass-loss rate. We
analyze the influence of γ in our results and we show that it is also
important in determining the wind structure.
Title: Numerical simulations of magnetized winds of solar-like stars
Authors: Vidotto, Aline A.; Opher, M.; Jatenco-Pereira, V.; Gombosi,
T. I.
Bibcode: 2009IAUS..259..415V
Altcode: 2009arXiv0901.1118V
We investigate magnetized solar-like stellar winds by means of
self-consistent three-dimensional (3D) magnetohydrodynamics (MHD)
numerical simulations. We analyze winds with different magnetic
field intensities and densities as to explore the dependence on the
plasma-β parameter. By solving the fully ideal 3D MHD equations,
we show that the plasma-β parameter is the crucial parameter in the
configuration of the steady-state wind. Therefore, there is a group of
magnetized flows that would present the same terminal velocity despite
of its thermal and magnetic energy densities, as long as the plasma-β
parameter is the same.
Title: Properties and Selected Implications of Magnetic Turbulence
for Interstellar Medium, Local Bubble and Solar Wind
Authors: Lazarian, A.; Beresnyak, A.; Yan, H.; Opher, M.; Liu, Y.
Bibcode: 2009SSRv..143..387L
Altcode: 2008SSRv..tmp..172L; 2008arXiv0811.0826L
Astrophysical fluids, including interstellar and interplanetary
medium, are magnetized and turbulent. Their appearance, evolution,
and overall properties are determined by the magnetic turbulence
that stirs it. We argue that examining magnetic turbulence at a
fundamental level is vital to understanding many processes. A point
that frequently escapes the attention of researchers is that magnetic
turbulence cannot be confidently understood only using “brute
force” numerical approaches. In this review we illustrate this point
on a number of examples, including intermittent heating of plasma by
turbulence, interactions of turbulence with cosmic rays and effects
of turbulence on the rate of magnetic reconnection. We show that the
properties of magnetic turbulence may vary considerably in various
environments, e.g. imbalanced (or cross-helical) turbulence in solar
wind differs from balanced turbulence and both of these differ from
turbulence in partially ionized gas. Appealing for the necessity of
more observational data on magnetic fields, we discuss a possibility
of studying interplanetary turbulence using alignment of Sodium atoms
in the tail of comets.
Title: The Dynamic Heliosphere: Outstanding Issues. Report of Working
Groups 4 and 6
Authors: Florinski, V.; Balogh, A.; Jokipii, J. R.; McComas, D. J.;
Opher, M.; Pogorelov, N. V.; Richardson, J. D.; Stone, E. C.; Wood,
B. E.
Bibcode: 2009SSRv..143...57F
Altcode:
Properties of the heliospheric interface, a complex product of an
interaction between charged and neutral particles and magnetic fields
in the heliosphere and surrounding Circumheliospheric Medium, are
far from being fully understood. Recent Voyager spacecraft encounters
with the termination shock and their observations in the heliosheath
revealed multiple energetic particle populations and noticeable
spatial asymmetries not accounted for by the classic theories. Some
of the challenges still facing space physicists include the origin
of anomalous cosmic rays, particle acceleration downstream of the
termination shock, the role of interstellar magnetic fields in producing
the global asymmetry of the interface, the influence of charge exchange
and interstellar neutral atoms on heliospheric plasma flows, and the
signatures of solar magnetic cycle in the heliosheath. These and other
outstanding issues are reviewed in this joint report of working groups
4 and 6.
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: The Dynamic Heliosphere: Outstanding Issues
Authors: Florinski, V.; Balogh, A.; Jokipii, J. R.; McComas, D. J.;
Opher, M.; Pogorelov, N. V.; Richardson, J. D.; Stone, E. C.; Wood,
B. E.
Bibcode: 2009fohl.book...57F
Altcode:
Properties of the heliospheric interface, a complex product of an
interaction between charged and neutral particles and magnetic fields
in the heliosphere and surrounding Circumheliospheric Medium, are
far from being fully understood. Recent Voyager spacecraft encounters
with the termination shock and their observations in the heliosheath
revealed multiple energetic particle populations and noticeable
spatial asymmetries not accounted for by the classic theories. Some
of the challenges still facing space physicists include the origin
of anomalous cosmic rays, particle acceleration downstream of the
termination shock, the role of interstellar magnetic fields in producing
the global asymmetry of the interface, the influence of charge exchange
and interstellar neutral atoms on heliospheric plasma flows, and the
signatures of solar magnetic cycle in the heliosheath. These and other
outstanding issues are reviewed in this joint report of working groups
4 and 6.
Title: Properties and Selected Implications of Magnetic Turbulence
for Interstellar Medium, Local Bubble and Solar Wind
Authors: Lazarian, A.; Beresnyak, A.; Yan, H.; Opher, M.; Liu, Y.
Bibcode: 2009fohl.book..387L
Altcode:
Astrophysical fluids, including interstellar and interplanetary
medium, are magnetized and turbulent. Their appearance, evolution,
and overall properties are determined by the magnetic turbulence
that stirs it. We argue that examining magnetic turbulence at a
fundamental level is vital to understanding many processes. A point
that frequently escapes the attention of researchers is that magnetic
turbulence cannot be confidently understood only using "brute force"
numerical approaches. In this review we illustrate this point on
a number of examples, including intermittent heating of plasma by
turbulence, interactions of turbulence with cosmic rays and effects
of turbulence on the rate of magnetic reconnection. We show that the
properties of magnetic turbulence may vary considerably in various
environments, e.g. imbalanced (or cross-helical) turbulence in solar
wind differs from balanced turbulence and both of these differ from
turbulence in partially ionized gas. Appealing for the necessity of
more observational data on magnetic fields, we discuss a possibility
of studying interplanetary turbulence using alignment of Sodium atoms
in the tail of comets.
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: 3D Numerical Simulations Of Magnetized Winds Of Solar-Like
Stars
Authors: Vidotto, A. A.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2008AGUFMSH21A1590V
Altcode:
By means of self-consistent three-dimensional (3D) magnetohydrodynamics
(MHD) numerical simulations, we analyze magnetized solar-like stellar
winds and their dependence on the plasma-β parameter (the ratio between
thermal and magnetic energy densities). This is the first study to
perform such analysis solving the fully ideal 3D MHD equations. We
analyze winds with polar magnetic field intensities ranging from 1
to 20~G. We show that the wind structure presents characteristics
that are similar to the solar coronal wind. The steady-state magnetic
field topology for all cases is similar, presenting a configuration of
helmet streamer-type, with zones of closed field lines and open field
lines coexisting. Higher magnetic field intensities lead to faster
and hotter winds. For the maximum magnetic intensity simulated of
20~G, the wind velocity reaches values of ~ 1000 km~s-1 at r ~ 20~r0
and a maximum temperature of ~ 6 × 106~K at r~ 6~r0. The increase
of the field intensity generates a larger "dead zone" in the wind,
i. e., the closed loops that inhibit matter to escape from latitudes
lower than ~ 45° extend farther away from the star. The Lorentz
force leads naturally to a latitude-dependent wind. We show that by
increasing the density, the system recover back to slower and cooler
winds. The key parameter in determining the wind velocity profile is
the β-parameter. Therefore, there is a group of magnetized flows that
would present the same terminal velocity despite of its thermal and
magnetic energy densities, as long as the plasma-β parameter is the
same. This degeneracy, however, can be removed if we compare other
physical parameters of the wind, such as the mass-loss rate.
Title: Presence Of A Reverse Shock In The Evolution Of A CME In The
Lower Solar Corona
Authors: Das, I.; Opher, M.
Bibcode: 2008AGUFMSH13B1546D
Altcode:
We study the birth and the evolution of a reverse shock in the evolution
of a CME in the lower solar corona. We study the evolution of the CME
with Space Weather Modeling Framework (SWMF). To initiate the CME, we
inserted a Titov-Demoulin (TD) flux rope in an active region of the
Sun with magnetic field based on the MDI data for the solar surface
during Carrington rotation 1922. The CME advances on the top of a
background solar wind created with the help of Wang-Sheeley-Arge (WSA)
model. We'd explore the signature and characteristics of the reverse
shock as the CME evolves through the lower corona. We also discuss
it's implications on the acceleration of particles.
Title: Comparison of MHD Simulations of CME Evolution and Structure
with Coronagraph Observations
Authors: Manchester, W. B.; Vourlidas, A.; Jai, Y.; Lugaz, N.; Roussev,
I.; Gombosi, T.; Opher, M.
Bibcode: 2008AGUFMSH11A..07M
Altcode:
Coronal mass ejections (CMEs) expel significant amounts of plasma into
interplanetary space producing large-scale variations in density that
are manifest in coronagraph images. A limitation of these images is
that they present two-dimensional projections of three-dimensional
structures that are challenging to interpret. The circumstances are
even more complex when CMEs are observed at large elongation and
the location of preferential scattering is significantly curved. To
address the interpretation of such coronagraph images, we examine
the Thomson-scattered white-light appearance of 3D MHD simulations
of CMEs to identify and reproduce features observed by LASCO and
SECCHI coronagraphs. We find close quantitative comparison with
LASCO observations and produce shapes at large elongations as seen
by SECCHI. We find 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
3-D structure of CMEs is affected by propagation through a structured
solar wind.
Title: Signatures of Two Distinct Initiation Mechanisms in the
Evolution of CMEs in the Lower Corona.
Authors: de Souza Costa, C. L.; Opher, M.; Alves, M. V.; Liu, Y. C.;
Manchester, W. B.; Gombosi, T. I.
Bibcode: 2008AGUFMSH23B1636D
Altcode:
We present a comparison of a three-dimensional (3D) simulation of
coronal mass ejections (CMEs), in the lower corona, generated with two
different initiation mechanisms presented in the literature: Gibson
& Low (1998) (as GL98 hereafter) and Titov & Démoulin (1999)
(as TD99 hereafter). The simulations are performed using the Space
Weather Modeling Framework (SWMF) during the solar minimum (CR1922). Our
goal is to understand how the initial magnetic configuration of a CME
affects its evolution through the lower corona, until 6R⊙. We found
that both CME-driven shocks are quasi-parallel at the nose and that
GL98 presents a higher shock acceleration (~150 m/ s2 versus ~100 m/
s2) and a higher Mach number, indicating it would accelerate particles
more efficiently. Both CMEs also presented a post-shock compression for
R>3R⊙, being slightly larger in the case of TD99. They presented
also a similar sheath width that increases while propagating away
from the Sun (larger in GL98 case). We also found that in GL98 case
the CME is driven by a combination of magnetic and thermal pressure,
while in TD99 case the thermal pressure dominates its evolution. One of
the reasons why GL98 presents higher force values, is probably related
to the fact that its sheath mass is ~20% larger than for TD99. This
paper intends to serve as a prototype for future comparisons of CME
evolution, in the lower corona.
Title: The Effects of Pickup Ions on Magnetic Reconnection at the
Heliopause
Authors: Swisdak, M.; Opher, M.; Drake, J. F.
Bibcode: 2008AGUFMSH21B1610S
Altcode:
Recent observations by the Voyager 2 spacecraft after crossing the
termination shock suggest that interstellar pickup ions account for
most of the plasma energy downstream from the heliopause. This implies
that the plasma beta (the ratio of the thermal to magnetic pressure)
is significantly larger than unity and that strong gradients in the
temperature exist at the heliopause. Previous work has shown that for
similar conditions at the Earth's magnetopause the diamagnetic drift
of X-lines stabilizes magnetic reconnection unless the reconnecting
fields are nearly anti-parallel. We explore the heliospheric case with
a combination of MHD simulations of the heliosphere and PIC simulations
of the region near the X-line and make predictions for the Voyager
crossings of the heliopause.
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: Surface Alfven Wave Damping in a 3D Simulation of the
Solar Wind
Authors: Evans, R. M.; Opher, M.; Jatenco-Pereira, V.; Gombosi, T. I.
Bibcode: 2008AGUFMSH51B1600E
Altcode:
It is known that a source of additional momentum is needed to drive
the solar wind. Here we investigate the effect of surface Alfvén wave
damping in solar minima and solar maxima conditions. The surface Alfvén
wave damping length L depends on the superradial expansion factor S
of magnetic field lines. We calculate S for Carrington Rotation 1912
with a steady state solar background generated with the Space Weather
Modeling Framework, and compare with estimates by Dobrzycka et al. 1999
using SOHO observations. We estimate the surface Alfvén wave damping
for active regions, quiet sun, and the border between open and closed
magnetic field lines. We address how our results can be incorporated
in a MHD thermally driven-wind model.
Title: Effects Non-uniform Flux Transfer and Empirically Based
Heliosheath Plasma Distributions on Global Maps of Heliospheric
Energetic Neutral Atoms
Authors: Prested, C.; Schwadron, N.; McComas, D.; Opher, M.; Crew,
G.; Vanderspek, R.; Maynard, K.; Goodrich, K.; Fuselier, S.; Funsten,
H.; Janzen, P.; Kucharek, H.; Moebius, E.; Reisenfeld, D.; Peterson,
L.; Saul, L.
Bibcode: 2008AGUFMSH21B1598P
Altcode:
The launch of the Interstellar Boundary Explorer (IBEX) begins a
new generation of outer heliospheric science. From its high-altitude
orbit, the IBEX mission will produce the first all-sky maps of energetic
neutral atoms (ENAs) created directly from the heliosheath plasma, which
carries the imprint of the global boundaries of the solar system. Here,
we explore the importance of key interstellar and solar wind parameters
to global maps of ENA flux at 1 AU, generated by a combination of
physical models: a magnetohydrodynamic heliosheath plasma simulation,
flux-transfer through the heliosphere including non-uniform loss,
and a full IBEX instrument model. We also discuss the impact of the
pick-up ion and thermal solar wind distributions as implied by recent
STEREO and Voyager measurements.
Title: Alfvén Profile in the Lower Corona: Implications for Shock
Formation
Authors: Evans, R. M.; Opher, M.; Manchester, W. B., IV; Gombosi, T. I.
Bibcode: 2008ApJ...687.1355E
Altcode:
Observations of type II radio bursts and energetic electron events
indicate that shocks can form at 1-3 solar radii and are responsible
for the GeV nucleon-1 energies observed in ground level
solar energetic particle (SEP) events. Here we provide the first study
of the lower corona produced from 10 state-of-the-art models. In
particular, we look to the Alfvén speed profiles as the criterion
for shock formation, independent of exciting agent (e.g., flares
and CMEs). Global magnetohydrodynamic models produce Alfvén speed
profiles that are in conflict with observations: (1) multiple SEP
events are observed with a single exciting agent, but most profiles
are missing the "hump" required to form multiple shocks; and (2) few
slow CMEs cause large SEP events, but most profiles drop very quickly,
allowing all slow CMEs to drive strong shocks to form between 1 and
3 R⊙. Simplified Alfvén wave-driven wind models have
steeper profiles, but are still in disagreement with multiple shock
formation. Only studies that include Alfvén waves with physically
based damping are in agreement with observations. This implies the
results of these one-dimensional local studies must be included in
global models before we can study shock formation in the lower corona.
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: A Simulation of a Coronal Mass Ejection Propagation and Shock
Evolution in the Lower Solar Corona
Authors: Liu, Y. C. -M.; Opher, M.; Cohen, O.; Liewer, P. C.; Gombosi,
T. I.
Bibcode: 2008ApJ...680..757L
Altcode:
We present a detailed simulation of the evolution of a moderately slow
coronal mass ejection (CME; 800 km s-1 at 5 R⊙,
where R⊙ is solar radii) in the lower solar corona
(2-5 R⊙). The configuration of the Sun's magnetic field
is based on the MDI data for the solar surface during Carrington
rotation 1922. The pre-CME background solar wind is generated using
the Wang-Sheeley-Arge (WSA) model. To initiate a CME, we inserted a
modified Titov-Demoulin flux rope in an active region near the solar
equator using the Space Weather Modeling Framework (SWMF). After
the initiation stage (within 2.5 R⊙), the CME evolves
at a nearly constant and slow acceleration of the order of 100 m
s-2, which corresponds to an intermediate-acceleration
CME. Detailed analysis of the pressures shows that the thermal pressure
accounts for most of the acceleration of the CME. The magnetic pressure
contributes to the acceleration early in the evolution and becomes
negligible when the CME moves beyond ~3 R⊙. We also
present the evolution of the shock geometry near the nose of the CME,
which shows that the shock is quasi parallel most of the time.
Title: Implications of solar wind suprathermal tails for IBEX ENA
images of the heliosheath
Authors: Prested, C.; Schwadron, N.; Passuite, J.; Randol, B.; Stuart,
B.; Crew, G.; Heerikhuisen, J.; Pogorelov, N.; Zank, G.; Opher, M.;
Allegrini, F.; McComas, D. J.; Reno, M.; Roelof, E.; Fuselier, S.;
Funsten, H.; Moebius, E.; Saul, L.
Bibcode: 2008JGRA..113.6102P
Altcode:
Decades of interplanetary measurements of the solar wind and other
space plasmas have established that the suprathermal ion intensity
distributions (j) are non-Maxwellian and are characterized by
high-energy power law tails (j ∼ E-κ). Recent analysis
by Fisk and Gloeckler of suprathermal ion observations between 1-5 AU
demonstrates that a particular differential intensity distribution
function emerges universally between ∼2-10 times the solar wind
speed with κ ∼ 1.5. This power law tail is particularly apparent
in downstream distributions beyond reverse shocks associated with
corotating interaction regions. Similar power law tails have been
observed in the downstream flow beyond the termination shock by
the Low Energy Charged Particle instrument on both Voyager 1 and
Voyager 2. Using kappa distributions with internal energy, density,
and bulk flow derived from large-scale magnetohydrodynamic models,
we calculate the simulated flux of energetic neutral atoms (ENAs)
produced in the heliosheath by charge exchange between solar wind
protons and interstellar hydrogen. We then produce simulated ENA
maps of the heliosheath, such as will be measured by the Interstellar
Boundary Explorer Mission (IBEX). We also estimate the expected signal
to noise and background ratio for IBEX. The solar wind suprathermal
tail significantly increases the ENA flux within the IBEX energy
range, ∼0.01-6 keV, by more than an order of magnitude at the
highest energies over the estimates using a Maxwellian. It is therefore
essential to consider suprathermal tails in the interpretation of IBEX
ENA images and theoretical modeling of the heliospheric termination
shock.
Title: Role of the Interstellar Magnetic Field in the Flows in
the Heliosheath
Authors: Opher, M.; Stone, E. C.; Richardson, J. C.; Gombosi, T. I.
Bibcode: 2008AGUSMSH24A..08O
Altcode:
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.
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: Effects of the helisopheric and interstellar magnetic field
on the heliospheric interface
Authors: Alexashov, Dmitry; Izmodenov, Vladislav; Malama, Yury;
Opher, Merav
Bibcode: 2008cosp...37...56A
Altcode: 2008cosp.meet...56A
First results of the numerical simulations of the heliospheric interface
that take into account both the interstellar hydrogen atoms and the
heliospheric and interstellar magnetic fields are presented. The
calculations are based on the newly created stationary 3D kinetic-MHD
model that treates the H atoms kinetically. The effects of the magnetic
fields on the shapes and positions of the strong plasma discontinuties
are clearly shown. The influence of the interstellar magnetic field
direction and amplitude is studied. The imprints of the interstellar
and heliospheric magnetic field on distribution of interstellar H
atoms inside the heliosphere are explored.
Title: The Interstellar Boundary Explorer Instrument Models and
Predicted ENA Count Rates
Authors: Prested, C.; Schwadron, N.; Passuite, J.; Randol, B.; Stuart,
B.; Heerikhuisen, J.; Opher, M.; Allegrini, F.; Steve, F.; Funsten,
H.; Moebius, E.
Bibcode: 2007AGUFMSH14A1688P
Altcode:
The upcoming launch of the Interstellar Boundary Explorer (IBEX)
promises a unique data set of heliospheric energetic neutral atoms
(ENAs), rich with information about the global dynamics of the
termination shock and heliosheath. We have developed a suite of tools
to predict synthetic ENA flux from the internal energy, density, and
bulk flow derived from large-scale magnetohydrodynamic simulations of
the heliosheath, creating a visualization framework for ENA flux maps
as well as making predictions for the IBEX mission. In the future
these tools will be critical for interpreting the implications of
IBEX observations. The impact of the ion distribution function is
also explored in the context of ENA flux maps. Studies from ACE,
WIND, and Ulysses have shown the solar wind ion population has a power
law tail in suprathermal velocities between 2-10 times the solar wind
speed. This solar wind characteristic is found to increase the predicted
flux by more than an order of magnitude at the highest IBEX energies,
with less but considerable impact at lower energies.
Title: Numerical Simulation of a Coronal Mass Ejection in the Lower
Corona: Comparison of Two Initiation Models
Authors: Loesch, C.; Opher, M.; Liu, Y.; Manchester, W. B., IV;
Gombosi, T. I.; Alves, M. V.
Bibcode: 2007AGUFMSH32A0783L
Altcode:
Coronal mass ejections (CME), eruptions of plasma and embedded magnetic
field from the Sun's corona into interplanetary space, are the most
energetic events on the Sun. The exact processes involved in the release
of CMEs are not known. In order to understand them and how they affect
the environment around Earth we need to comprehend their eruption,
development and propagation through the interplanetary space. In this
work, we present a simulation of a CME event occurred during the solar
minimum. This simulation was performed using the Space Weather Modeling
Framework (SWMF). Within this model, after generating a global steady
state of the solar corona, for CR1922, we drive a CME to erupt using
two different initiation models presented in the literature; Gibson
and Low (1998) and Titov and Démoulin (1999). The ejections, that
were followed up to distances of 10 R\sun, reached maximum speeds of
800-1000 km s-1. We discuss these two CME initiation models establishing
a comparative analysis of their characteristics and how the initiation
process changes the evolution of a simulated CME.
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: A simulation of a CME propagation and shock evolution in the
lower solar corona
Authors: Liu, Y. C.; Opher, M.; Cohen, O.; Gombosi, T. I.
Bibcode: 2007AGUFMSH32A0777L
Altcode:
We present a simulation of the evolution of a CME (~800km/s at 5
solar radii) in the lower solar corona (until 5 solar radii) using
Space Weather Modeling Framework (SWMF). The configuration of the
sun's magnetic field is based on the MDI data on the solar surface
during Carrington Rotation 1922. The pre-CME background solar wind is
generated under this boundary condition and Wang-Sheeley-Arge (WSA)
model. To initiate a CME, we inserted a Titov-Demoulin flux rope in an
active region near the solar equator. The zone along nose of the CME
is refined to resolve the CME-driven-shock. Our results show that a
higher density region is followed by a dark cavity behind the shock and
the higher density region is expanding while propagating away from the
sun. These features are consistent with the CME observations which shows
that a bright front followed by a dark area after the shock. After the
initiation stage, in which the CME has a large acceleration followed
by a deceleration, the CME demonstrates a nearly constant and slow
acceleration of the order of 100m/s 2. At 5 solar radii, the CME has a
speed of 800km/s. Although CME is accelerating, the Mach number of the
shock is decreasing because the Alfven speed upstream of the shock is
increasing. Detailed analysis of the pressures on the CME shows that
the thermal pressure account for most of the acceleration of the CME
and the magnetic pressure contribute to the acceleration at an early
time but it becomes negligible when the CME moves further away from
the sun. We also present the evolution of shock geometry near the nose
of the CME and find that the shock is nearly perpendicular. Further
investigation of the dependency in latitude of the shock and their
effects on particle acceleration are required in a future work.
Title: Alfven Profile in the Lower Corona: Implications for Shock
Formation
Authors: Evans, R. M.; Opher, M.; Manchester, W. B.; Velli, M.;
Gombosi, T. I.
Bibcode: 2007AGUFMSH21A0286E
Altcode:
Recent events (e.g. Tylka et al. 2005) indicate that CME-driven shocks
can form at 1-3 solar radii and are responsible for the GeV/nucleon
energies observed in some ground level solar energetic particle
events. The formation of shocks depends crucially on the background
solar wind environment, in particular on the profile of the background
Alfvén speed in the corona. Significant strides have been made in
the effort to develop realistic models of CME events; however, there
is no consensus as to the profile of the Alfvén speed in the lower
corona. Here we provide an overview of ten state-of-the-art models,
which includes various methods to model magnetic field and density,
as well as different strategies for accelerating the solar wind. We
present the Alfvén speed profile for each model in the lower corona. We
find that the "valley" and "hump" structures anticipated by Mann et
al. (2003) are sometimes present, but in some models the Alfvén
profiles drop off quickly. We discuss the implications of these
profiles, such as whether it will allow a shock to form, dissipate,
and form again (i.e. multiple shocks). Our study indicates that it is
crucial to establish the Alfvén speed as a function of height before
determining if shocks can form in the lower corona.
Title: The Orientation of the Local Interstellar Magnetic Field and
Induced Asymmetries on the Heliosphere
Authors: Opher, M.; Stone, E. C.; Gombosi, T.
Bibcode: 2007AGUSMSH43A..07O
Altcode:
We combine radio emission and energetic particle streaming measurements
with extensive 3D MHD computer simulations of magnetic field draping
over the heliopause to obtain information on the inclination angle of
the local interstellar magnetic field. The orientation of the local
interstellar magnetic field introduces asymmetries in the heliosphere
that affect the location of radio emission and the streaming direction
of ions from the termination shock of the solar wind. In this talk
we discuss the orientation of the plane of the local interstellar
field and the global asymmetries induced in the heliosphere and in
the heliosheath.
Title: Test-particle Orbit Simulations in Fields from a Realistic
3D MHD Simulation
Authors: Decker, R. B.; Opher, M.; Hill, M. E.
Bibcode: 2007AGUSMSH51A..02D
Altcode:
Models designed to explore the global structure of the heliosphere have
become increasing sophisticated. Incentives to increase and to further
explore the predictive capabilities of such models include the entry
of the Voyager spacecraft into the foreshock region of the termination
shock (TS), Voyager 1 in mid-2002 and Voyager 2 in late 2004, and the
crossing of the TS and passage into the heliosheath (HSH) of Voyager
1 in 2004 day 351. Using the electric and magnetic fields generated by
a MHD model of a 3D, asymmetric heliosphere [Opher et al., Ap. J. L.,
640, 2006], we have developed full-particle and adiabatic-orbit codes
to simulate the motion of test particles in the solar wind, TS, and
HSH environments. The full-particle orbits are necessary to investigate
energetic ion (e.g., anomalous and galactic cosmic ray) motion at the TS
and within the heliospheric current sheet that is included in the MHD
model. Adiabatic orbits are used to study particle motion in the much
larger volume of the HSH where the non-homogeneous model fields produce
complex guiding center motions, including mirroring in local field
compressions. We will present results from these orbit computations,
which are intended to provide an initial, albeit simplified, look at
the propagation of high-energy charged particles, in the scatter-free
limit, in the best model of the TS/HSH field configurations currently
available. We will also display drift paths of high-energy ions in the
HSH fields using the guiding center drift equations that are applicable
in the limit of diffusive propagation.
Title: The Orientation of the Local Interstellar Magnetic Field
Authors: Opher, M.; Stone, E. C.; Gombosi, T. I.
Bibcode: 2007Sci...316..875O
Altcode: 2007arXiv0705.1841O
The orientation of the local interstellar magnetic field introduces
asymmetries in the heliosphere that affect the location of heliospheric
radio emissions and the streaming direction of ions from the termination
shock of the solar wind. We combined observations of radio emissions
and energetic particle streaming with extensive three-dimensional
magnetohydrodynamic computer simulations of magnetic field draping
over the heliopause to show that the plane of the local interstellar
field is ~60° to 90° from the galactic plane. This finding suggests
that the field orientation in the Local Interstellar Cloud differs
from that of a larger-scale interstellar magnetic field thought to
parallel the galactic plane.
Title: Constraining the Local Interstellar Magnetic Field Direction
from Source Location of the Heliospheric 2-3kHz Radio Emissions
Authors: Opher, M.; Stone, E. C.; Gombosi, T. I.
Bibcode: 2006AGUFMSH53B1488O
Altcode:
Using an MHD model, we have investigated the recent suggestion by
Gurnett et al. (2006) that the sources of the heliospheric 2-3~kHz radio
detected by Voyager 1 and 2 should be located where the interstellar
magnetic field is tangential to the surface of the shock that excites
the plasma. Because the field is draped over the heliopause surface that
is distorted by the field, we ran models with different interstellar
field directions. The best agreement is obtained for an interstellar
magnetic field parallel to the plane perpendicular to the galactic
plane (PPG) as suggested by Gurnett et al. and having a small angle
with respect to the velocity of the interstellar wind. The PPG plane
is similar to the plane suggested by Lallement et al. 2005 (differing
by 16°) that Opher et al. (2006) showed to be consistent with the
streaming directions of energetic particles from the termination shock
as observed by Voyager 1 and 2. We suggest the radio source locations
can be used to further constraint a more complete model.
Title: Global asymmetry of the heliosphere
Authors: Opher, Merav; Stone, Edward C.; Liewer, Paulett C.; Gombosi,
Tamas
Bibcode: 2006AIPC..858...45O
Altcode: 2006astro.ph..6324O
Opher et al. showed that an interstellar magnetic field parallel to
the plane defined by the deflection of interstellar hydrogen atoms can
produce a north/south asymmetry in the distortion of the solar wind
termination shock. This distortion is consistent with Voyager 1 and
Voyager 2 observations of the direction of field-aligned streaming
of the termination shock particles upstream the shock. The model
also indicates that such a distortion will result in a significant
north/south asymmetry in the distance to the shock and the thickness
of heliosheath. The two Voyager spacecraft should reveal the nature
and degree of the asymmetry in the termination shock and heliosheath.
Title: Tearing and Kelvin-Helmholtz instabilities in the heliospheric
plasma
Authors: Bettarini, L.; Landi, S.; Rappazzo, F. A.; Velli, M.;
Opher, M.
Bibcode: 2006A&A...452..321B
Altcode:
We used 2.5D simulations to analyze the magnetohydrodynamic
instabilities arising from an initial equilibrium configuration
consisting of a plasma jet or wake in the presence of a magnetic
field with strong transverse gradients, such as those arising in the
solar wind. Our analysis extends previous results by considering both
a force-free equilibrium and a pressure-balance condition for a jet
in a plasma sheet, along with arbitrary angles between the magnetic
field and velocity field. In the force-free case, the jet/wake does
not contain a neutral sheet but the field rotates through the flow to
invert its polarity. The presence of a magnetic field component aligned
with the jet/wake destroys the symmetric nature of the fastest growing
modes, leading to asymmetrical wake acceleration (or, equivalently,
jet deceleration). In the case of a jet, the instability properties
depend both on the magnetic field and flow gradients, as well as on
the length of the jet. The results are applied to the post-termination
shock jet recently found in 3D global heliospheric simulations, where
our analysis confirms and explains the stability properties found in
such simulations.
Title: Surprises From The Edge Of The Solar System: Voyager At The
Final Frontier
Authors: Opher, Merav
Bibcode: 2006SPD....37.2301O
Altcode: 2006BAAS...38..250O
Our solar system presents a unique local example of the interaction
of a stellar wind and the interstellar medium. As the Sun travels
through the interstellar medium, it is subject to an interstellar
wind. The heliosphere is created by the supersonic solar wind that
abruptly slows, forming a termination shock as it approaches contact
with the interstellar medium at the heliopause. After 27 years of
anticipation, in 2004 December 16, Voyager 1, crossed the termination
shock, at 94AU, and began exploring the heliosheath. The twin Voyager
spacecraft are probing the northern and southern hemispheres of the
heliosphere. Voyager 1 is now beyond 98AU, while Voyager 2 is beyond 78
AU. As Voyager 1 crossed the termination shock, and began exploring the
heliosheath it became increasingly clear that this previously unexplored
region is full of surprises. These include the startling absence of
the anomalous cosmic ray source that had been widely anticipated,
the unusually slow and even sunward flow of the solar wind in the
heliosheath, and the unexpected direction of the magnetic field downwind
of the shock. In mid 2002, Voyager 1 began observing strong energetic
beams of termination shock particles, streaming outward along the spiral
magnetic field upstream the shock. This led to the suggestion that
the termination shock is a blunt structure. Recently we showed that
an interstellar magnetic field can produce a north/south asymmetry in
the solar wind termination shock, consistent with Voyager 1 observation
of the direction of streaming of the particles. These recent surprises
indicate that a global understanding of the heliosphere is crucial. In
this talk, I will review the current understanding of the edge the
solar system, indicate predictions of what Voyager 2 will encounter,
and describe the directions that research should take to understand
the global structure of the heliosphere.
Title: Effects of a Local Interstellar and Interplanetary Magnetic
Field on the Heliosheath
Authors: Opher, M.; Stone, E. C.; Liewer, P. C.; Gombosi, T. I.
Bibcode: 2006AGUSMSH22A..04O
Altcode:
In this talk we review some of our recent results showing that that
an interstellar magnetic field can produce a north/south asymmetry in
solar wind termination shock. Using Voyager 1 and 2 measurements, we
suggest that the angle α between the interstellar wind velocity and
magnetic field is 30 < α < 60°. The distortion of the shock
is such that termination shock particles could stream outward along
the spiral interplanetary magnetic field connecting Voyager 1 to the
shock when the spacecraft was within ~ 2~AU of the shock. The shock
distortion is larger in the southern hemisphere, and Voyager 2 could
be connected to the shock when it is within ~ 5~AU of the shock, but
with particles from the shock streaming inward along the field. Tighter
constraints on the interstellar magnetic field should be possible when
Voyager 2 crosses the shock in the next several years. We comment
additionally on previous work (Opher et al. 2003, 2004) that show
that the magnetic field shape dramatically the heliosheath flows. We
indicate future directions of research to probe these effects.
Title: The Effects of a Local Interstellar Magnetic Field on Voyager
1 and 2 Observations
Authors: Opher, Merav; Stone, Edward C.; Liewer, Paulett C.
Bibcode: 2006ApJ...640L..71O
Altcode: 2006astro.ph..3318O
We show that an interstellar magnetic field can produce a
north-south asymmetry in the solar wind termination shock. Using
Voyager 1 and 2 measurements, we suggest that the angle α
between the interstellar wind velocity and the magnetic field is
30deg<α<60deg. The distortion of the shock
is such that termination shock particles could have streamed outward
along the spiral interplanetary magnetic field connecting Voyager 1
to the shock when the spacecraft was within ~2 AU of the shock. The
shock distortion is larger in the southern hemisphere, and Voyager
2 could be connected to the shock when it is within ~5 AU of the
shock, but with particles from the shock streaming inward along the
field. Tighter constraints on the interstellar magnetic field should
be possible when Voyager 2 crosses the shock in the next several years.
Title: Nonlinear analysis of jet/wake and current sheet interactions
in the heliospheric plasma
Authors: Bettarini, L.; Landi, S.; Rappazzo, F.; Velli, M.; Opher, M.
Bibcode: 2006cosp...36.2383B
Altcode: 2006cosp.meet.2383B
The interactions between a stream and a current sheet is the starting
point to understand the dynamics and evolution of complex structures
in the Heliospheric region We used 2 5D simulations to analyze the
magnetohydrodynamic instabilities arising from an initial equilibrium
configuration consisting of a plasma jet or wake in the presence of a
magnetic field with strong transverse gradients such as those arising
in the solar wind both close to the Sun and far from it Our analysis
extends previous results by considering both a force-free equilibrium
and a pressure-balance condition for a jet in a plasma sheet along with
arbitrary angles between the magnetic field and velocity field In the
force-free case the jet wake does not contain a neutral sheet but the
field rotates through the flow to invert its polarity The presence
of a magnetic field component aligned with the jet wake destroys the
symmetric nature of the fastest growing modes leading to asymmetrical
wake acceleration or equivalently jet deceleration In the case of a jet
the instability properties depend both on the magnetic field and flow
gradients as well as on the length of the jet We applied our results to
the wake model of the solar wind on the solar equatorial plane above the
helmet streamer cusp considering arbitrary angles between the magnetic
field and the velocity field and to the post-termination shock jet
recently found in 3D global heliospheric simulations where our analysis
confirms and explains the stability properties found in such simulations
Title: Modeling the Non-Relativistic Jets in R Aquarii
Authors: Korreck, K. E.; Sokoloski, J. L.; Opher, M.
Bibcode: 2005AAS...207.1306K
Altcode: 2005BAAS...37.1173K
R Aqr is a binary star system containing a Mira variable transferring
material to a hot, compact object that is presumably a white dwarf. The
accreting white dwarf produces non-relativistic jets, which have been
observed at radio, optical, UV, and X-ray wavelengths. We are developing
an MHD model to investigate the interaction of the jet with the ISM,
and more broadly, the formation of the jet in this binary system. We
are utilizing a block adaptive mesh refinement (AMR) MHD code that
has been used to model various space physics plasmas to simulate the
jets. We present X-ray spectral models based on our simulations and a
comparison of these models with existing X-ray data for the northeast
jet in the R Aqr binary system. We greatfully acknowledge funding from
the National Science Foundation.
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: Effect of the Interstellar Magnetic Field on the Termination
Shock: Explaining the Voyager Results
Authors: Opher, M.; Stone, E. C.; Liewer, P. C.
Bibcode: 2005AGUFMSH43B..02O
Altcode:
After a twenty-seven year journey, Voyager 1 crossed the termination
shock, the first boundary separating the solar system from the
rest of the galaxy, and is now on the other side exploring the
heliosheath. Since mid-2002 Voyager 1 has been observing strong beams
of energetic particles coming outward along the spiral magnetic field,
the opposite of the direction expected for particles accelerated
at the shock. This can be explained if the shock is non-spherical
so that the interplanetary magnetic field lines cross the shock and
reenters the solar wind before reaching Voyager 1. This configuration
has been invoked recently (Jokipii et al. 2004; Stone et al. 2005)
to reconcile the data recently collected and explain how Voyager 1
can detect energetic particles accelerated at the shock several years
before crossing it. We show that the termination shock is, in fact,
non-spherical due the distortion caused by an inclined interstellar
magnetic field. We use the best values for the direction of the
interstellar magnetic field (derived by Frisch 2003; and Lallement
et al. 2005) showing that the shape of the termination shock depends
strongly on the direction of the interstellar magnetic field. We also
make predictions for Voyager 2 that will encounter the shock in the
next couple of years.
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: 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: 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: 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: 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: 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: 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.; Gombosi, T.; Manchester,
W.; DeZeeuw, D.
Bibcode: 2003AAS...20313403O
Altcode: 2003BAAS...35.1421O
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 × 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: 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: 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: Probing the Edge of the Solar System: Formation of an Unstable
Jet-Sheet
Authors: Opher, Merav
Bibcode: 2003kas..confE..42O
Altcode:
No abstract at ADS
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: 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: 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: Magnetic Field Generation in Galactic Plasmas
Authors: Opher, M.; Cowley, S.; Schekochihin, A.; Kinney, R. M.;
Chandran, B.; Maron, J.; McWilliams, J. C.
Bibcode: 2001AAS...198.5411O
Altcode: 2001BAAS...33..866O
The origin of the magnetic field in the universe is one of the great
problems in astrophysics. The observed magnetic fields in spiral
galaxies, for example, are of the order of microgauss and are coherent
over galactic scales. Its is usually assumed that turbulent fluid
motions will enhance a seed field. In the present work we invetigate
the growth of the magnetic field in plasmas with high magnetic Prandtl
number (the ratio of viscosity to resistivity). This growth occur
initially at scales below the viscous scale [1]. Kinney et al. [2]
showed that in 2D the field saturates at an amplitude independent of
the mean scale of the field. We discuss the initial growth in the three
dimensional case where the dynamics of the field on scales less than
the viscosity scale [3]. At low initial field, the field grows and
the scale decreases until the resistive scale is reached. The field
then grows at a reduced rate until it reaches an equilibrium with
the mean scale at a resistive scale. At higher initial amplitude,
the field saturates before the mean scale has decreased to the
resistive scale. The subsequent evolution is a slow decrease of the
scale to the resistive scale, at which point it reaches equilibrium
and stops evolving. To explain the large scale coherence of galactic
fields, an inverse cascade is necessary. There is no evidence of an
inverse cascade. We will present results for extended physics models
including tensor viscosity and ambipular diffusion. [1] R. Kulsrud, and
S. Anderson, Astrophys. J., 396, 606 (1992); A. Gruzinov, S. Cowley,
and R. Sudan, Phys.Rev.Lett., 77, 4342 (1996). [2] R. M. Kinney,
B. Chandran, S. Cowley, J. C. McWilliams, Astrophys. J., accepted
to publication (2000). [3] M. Opher, S. Cowley, A. Schekochihin,
R. M. Kinney, B. Chandran, J. Maron and J.C. McWilliams, in preparation
(2001).
Title: Magnetic-Field Structure and Saturation in the Small-Scale
Dynamo Theory
Authors: Schekochihin, A.; Maron, J.; Opher, M.; Cowley, S.
Bibcode: 2001AAS...198.9001S
Altcode: 2001BAAS...33..918S
A weak magnetic field passively advected by a turbulent velocity
field grows exponentially while its characteristic scale decays. In
the interstellar medium and protogalactic plasmas, the magnetic
Prandtl number is very large. and the kinematic stage of magnetic
dynamo therefore produces a broad spectrum of magnetic fluctuations
on small (subviscous) scales. The distribution of the field stregth
in the kinematic regime is lognormal (highly intermittent). A study
of statistical correlations that are set up in the field pattern shows
that the magnetic field lines possess a folding structure, where most
of the characteristic-scale decrease is due to the field variation
across itself (rapid transverse direction reversals), while the scale
of the field variation along itself stays approximately constant. The
field structure determines the conditions under which the nonlinear
effects set in. We find that the advent of Lorentz back reaction leads
to saturation of the magnetic energy and a substatial suppression of the
intermittency of the field distribution. The folding pattern persists
into the nonlinear stage, but the decrease of the magnetic-field scales
is arrested. Our findings derive from the statistical theory of the
small-scale magnetic fluctuations in the viscosity-dominated regime
and are corroborated by an array of numerical simulations. This work
was supported by the NSF Grant No. AST 97-13241 and the DOE Grant
No. DE-FG03-93ER54 224.
Title: Nuclear reaction rates and energy in stellar plasmas: The
effect of highly damped modes
Authors: Opher, Merav; Silva, Luis O.; Dauger, Dean E.; Decyk, Viktor
K.; Dawson, John M.
Bibcode: 2001PhPl....8.2454O
Altcode: 2001astro.ph..5153O
The effects of the highly damped modes in the energy and reaction rates
in a plasma are discussed. These modes, with wave numbers k>>kD,
even being only weakly excited, with less than kBT per mode, make a
significant contribution to the energy and screening in a plasma. When
the de Broglie wavelength is much less than the distance of closest
approach of thermal electrons, a classical analysis of the plasma can
be made. It is assumed, in the classical analysis, with ℏ-->0,
that the energy of the fluctuations ℏω<<kBT. Using the
fluctuation-dissipation theorem, the spectra of fluctuations with
ℏ≠0 is appreciably decreased. The decrease is mainly for the
highly damped modes at high frequencies (~0.5-3kBT). Reaction rates are
enhanced in a plasma due to the screening of the reacting ions. This
is taken into account by the Salpeter factor, which assumes slow
motion for the ions. The implication of including the highly damped
modes (with ℏ≠0) in the nuclear reaction rates in a plasma is
discussed. Finally, the investigations presently done on these effects
in particle simulations with the sheet model and the multiparticle
quantum simulation code are described.
Title: Magnetic Field Generation in Galactic Plasmas
Authors: Opher, Merav; Cowley, Steve; Maron, Jason; McWilliams, James
Bibcode: 2000APS..DPPBP1057O
Altcode:
The origin of the magnetic field in the universe is one of the great
problems in astrophysics. The observed magnetic fields in spiral
galaxies, for example, are of the order of microgauss and are coherent
over galactic scales. It is usually assumed that turbulent fluid motions
will enhance a seed field. In the present work we investigate the growth
of the magnetic field in plasmas with high magnetic Prandtl number
(the ratio of viscosity to resistivity). This growth occurs initially
at scales below the viscous scale [1]. Kinney et al. [2] showed that in
2D the field saturates at an amplitude independent of the mean scale of
the field. We discuss the initial growth in the three dimensional case
where the dynamics of the field are on scales less than the viscosity
scale [3]. At low initial field, the field grows and the scale decreases
until the resistive scale is reached. The field then grows at a reduced
rate until it reaches an equilibrium with the mean scale at a resistive
scale. At higher initial amplitude, the field saturates before the mean
scale has decreased to the resistive scale. The subsequent evolution
is a slow decrease of the scale to the resistive scale, at which point
it reaches equilibrium and stops evolving. To explain the large scale
coherence of galactic fields, an inverse cascade is necessary. There
is no evidence of an inverse cascade. We will present results for
extended physics models including tensor viscosity and ambipular
diffusion. [1] R. Kulsrud, and S. Anderson, Astrophys. J., 396, 606
(1992); A. Gruzinov, S. Cowley, and R. Sudan, Phys.Rev.Lett., 77, 4342
(1996). [2] R. M. Kinney, B. Chandran, S. Cowley, J. C. McWilliams,
Astrophys. J., accepted to publication (2000). [3] M. Opher, S. Cowley,
R. M. Kinney, B. Chandran, J. Maron and J.C. McWilliams, in preparation
(2000).
Title: Nuclear Reaction Rates in a Plasma: The Effect of Highly
Damped Modes
Authors: Opher, Merav; Opher, Reuven
Bibcode: 2000astro.ph..6326O
Altcode:
The fluctuation-dissipation theorem is used to evaluate the screening
factor of nuclear reactions due to the electromagnetic fluctuations in
a plasma. We show that the commonly used Saltpeter factor is obtained
if only fluctuations near the plasma eigenfrequency are assumed to be
important (\omega \sim \omega_{pe}\ll T (\hbar=k_{B}=1)). By taking
into account all the fluctuations, the highly damped ones, with \omega
>\omega_{pe}, as well as those with \omega\leq\omega_{pe}, we find
that nuclear reaction rates are higher than those obtained using the
Saltpeter factor, for many interesting plasmas.
Title: Dynamic Screening in Thermonuclear Reactions
Authors: Opher, Merav; Opher, Reuven
Bibcode: 2000ApJ...535..473O
Altcode: 1999astro.ph..8218O
It has recently been argued that there are no dynamic screening
corrections to Salpeter's enhancement factor in thermonuclear reactions,
in the weak-screening limit. Two arguments were used: (1) the Gibbs
probability distribution is factorable into two parts, one of which,
exp(-βeiej/rij) (β=1/kBT),
is independent of velocity space, and (2) the enhancement factor is
w=1+β2e2Z1Z2<φ2>
with
<φ2>k=<E2>k/k2
and <E2>k/(8π)=(T/2)[1-ɛ-
1(0,k)]. We show that both of these arguments are incorrect.
Title: Change in Primordial Abundances Due to a Change in the
Primordial Plasma Energy Density
Authors: Opher, M.; Opher, R.
Bibcode: 2000IAUS..198..116O
Altcode:
No abstract at ADS
Title: The energy of the primordial plasma
Authors: Opher, M.; Opher, R.
Bibcode: 2000NuPhS..80C0416O
Altcode:
No abstract at ADS
Title: Energy of a Plasma in the Classical Limit
Authors: Opher, Merav; Opher, Reuven
Bibcode: 1999PhRvL..82.4835O
Altcode: 1999astro.ph..6018O
When λT<<dT, where λT is the
de Broglie wavelength and dT is the distance of closest
approach of thermal electrons, a classical analysis of the energy of
a plasma can be made. In all the classical analysis made until now,
it was assumed that the frequency of the fluctuations ω<<T,
( kB = ħ = 1). Using the fluctuation-dissipation theorem,
we evaluate the energy of a plasma, allowing the frequency of the
fluctuations to be arbitrary. We find that the energy density is
appreciably larger than previously thought for many interesting plasmas,
such as the plasma of the Universe before the recombination era.
Title: Energy in the Primordial Plasma
Authors: Opher, Merav; Opher, Reuven
Bibcode: 1999magr.meet.1339O
Altcode:
No abstract at ADS
Title: Seed magnetic Fields Generated by Primordial Supernova
Explosions
Authors: Miranda, Oswaldo D.; Opher, Merav; Opher, Reuven
Bibcode: 1998MNRAS.301..547M
Altcode: 1998astro.ph..8161M
The origin of the magnetic field in galaxies is an open question
in astrophysics. Several mechanisms have been proposed related,
in general, to the generation of small seed fields amplified by a
dynamo mechanism. In general, these mechanisms have difficulty in
satisfying both the requirements of a sufficiently high strength for
the magnetic field and the necessary large coherent scales. We show
that the formation of dense and turbulent shells of matter, in the
multiple explosion scenario of Miranda & Opher for the formation
of the large-scale structures of the Universe, can naturally act as a
seed for the generation of a magnetic field. During the collapse and
explosion of Population III objects, a temperature gradient not parallel
to a density gradient can naturally be established, producing a seed
magnetic field through the Biermann battery mechanism. We show that
seed magnetic fields ~10^-12-10^-14G can be produced in this multiple
explosion scenario on scales of the order of clusters of galaxies
(with coherence length L~1.8Mpc) and up to ~4.5x10^-10G on scales of
galaxies (L~100kpc).
Title: Less Energy in the Early Universe
Authors: Opher, M.; Opher, R.
Bibcode: 1998tx19.confE.189O
Altcode:
The standard energy calculation of the primordial plasma assumes ideal
gas particles and that the electromagnetic spectrum is a blackbody
spectrum in vacuum. Through the fluctuation-dissipation theorem (FDT),
used in the studies of Opher and Opher (Phys.Rev.Lett. 79, 2628 (1997)
and Phys.Rev.D 56, 3296 (1997)), we estimate the energy contained in
the electromagnetic fluctuations. We show that the energy density of the
plasma is appreciably less than the standard calculation, approximately
-10% rhogamma for temperatures ~1010 K, where
rhogamma is the blackbody energy density in vacuum. This
correction is appreciably different from the usual one using a finite
temperature QED calculation. The reason is that FDT takes into account
all the fluctuations in the plasma (not only the photon and plasmons),
and includes dynamic screening, as well. We discuss the differences
between the two approaches.
Title: Additional Energy at the Epoch of Primordial Nucleosynthesis
Authors: Opher, M.
Bibcode: 1998tsra.conf..248O
Altcode:
No abstract at ADS
Title: Was The Electromagnetic Spectrum A Blackbody Spectrum In The
Early Universe?
Authors: Opher, Merav; Opher, Reuven
Bibcode: 1997PhRvL..79.2628O
Altcode: 1997astro.ph..8246O
It is generally assumed that the electromagnetic spectrum in the
primordial universe was a blackbody spectrum in vacuum. We derive the
electromagnetic spectrum based on the fluctuation-dissipation theorem
that describes the electromagnetic fluctuations in a plasma. Our
description includes thermal and collisional effects in a plasma. The
electromagnetic spectrum obtained differs from a blackbody spectrum
in vacuum at low frequencies. In particular, concentrating on the
primordial nucleosynthesis era, it has more energy than the blackbody
spectrum for frequencies less than 3ωpe to 6ωpe,
where ωpe is the electron plasma frequency.
Title: Magnetic field spectrum in a plasma in thermal equilibrium
in the epoch of primordial nucleosynthesis
Authors: Opher, Merav; Opher, Reuven
Bibcode: 1997PhRvD..56.3296O
Altcode: 1997astro.ph..8251O
The low-frequency magnetic field spectrum in the primordial plasma is
of particular interest as a possible origin of magnetic fields in the
universe (e.g., Tajima and co-workers and Cable and Tajima). We derive
the magnetic field spectrum in the primordial plasma, in particular,
at the epoch of primordial nucleosynthesis. The pioneering study of
Cable and Tajima of the electromagnetic fluctuations, based on the
fluctuation-dissipation theorem, is extended. Our model describes
both the thermal and collisional effects in a plasma. It is based
on a kinetic description with the Bhatnagar, Gross, and Krook (BGK)
collision term. It is shown that the zero-frequency peak found by Cable
and Tajima decreases. At high frequencies, the blackbody spectrum is
obtained naturally without the necessity of the link procedure used by
them. At low frequencies (ω<=4ωpe, where ωpe
is the electron plasma frequency), it is shown that the magnetic field
spectrum has more energy than the blackbody spectrum in vacuum.
Title: Origin of the Magnetic Field in Young Galaxies
Authors: Opher, M.; Opher, R.; Miranda, O. D.
Bibcode: 1997ASPC..114..129O
Altcode: 1997ygqa.conf..129O
No abstract at ADS
Title: Primordial Magnetic Fields and the Formation of the First
Objects in the Universe
Authors: Opher, Reuven; Miranda, Oswaldo D.; Oliveira, Sandra R.;
Pires, Nilza; Opher, Merav
Bibcode: 1996plas.work..162O
Altcode:
We evaluate the effects of the various physical mechanisms that were
present during and after the recombination era (photon drag, photon
cooling, recombination, photoionization, collisional ionization,
and hydrogen molecule production, destruction and cooling - see de
Araujo & Opher 1988, 1989, 1994) and a cosmological constant upon
perturbation evolution for different initial perturbations. We rewrote
the equations of de Araujo & Opher in the Lagrangian formulation
and calculate the internal structure of the primordial clouds. We
show that the collapse and explosion of these objects can create a
primordial magnetic field by the Biermann mechanism in the shocks
created by the explosion of these objects.
Title: Plasma effects on primordial nucleosynthesis
Authors: Opher, M.; Opher, R.
Bibcode: 1994STIN...9622817O
Altcode:
We modify the standard code of primordial nucleosynthesis to include
plasma effects: (1) Plasmons (oscillations near the Langmuir frequency);
and (2) The zero frequency fluctuations predicted by the Fluctuation
Dissipation Theorem (FDT). We found a change in the He-4 yield,
delta Y/Y approximately 10-3 for the plasmons and delta
Y/Y approximately 10-4 for FDT. The result for the case of
plasmons, for example, is an order of magnitude higher than the most
recent correction to the He-4 abundance.
Title: The formation of the large-scale structures of the universe
and primordial magnetic field by supernovae explosions
Authors: Miranda, O. D.; Opher, M.; Opher, R.
Bibcode: 1994spub.reptS....M
Altcode:
The theory of galactic formation and of large-scale structure generally
assumes that all existing structures of the universe were formed
from perturbations present initially in a homogeneous and isotropic
universe. We study here the formation of the large-scale structures
beginning from the collapse of a Population III object which created a
shock wave at high redshift. The influence of various physical processes
in the evolution of the shock wave such as Compton cooling by the
radiation background, is analyzed in detail. Our results demonstrate
that it is possible to obtain large voids of matter of dimensions
approximately 55-69 Mpc, and masses of the shells on the order of
superclusters of galaxies. We suggest the creation of a primordial
magnetic field by a Biermann type mechanism in the shocks of primordial
supernovae. We estimate the magnetic field created in the shock as B
approximately 10-9G. This field is subsequently amplified
by an alpha2 - dynamo mechanism in the turbulent region
behind the shock.