ofman

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Author name code: ofman
ADS astronomy entries on 2022-09-14
author:"Ofman, Leon"

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Title: Observations of Ion-Scale Cyclotron Waves and Their
Relationship with Non-thermal Ion Distributions in the Solar Wind
Authors: Jian, Lan; Ofman, Leon; Wei, Hanying; Stevens, Michael;
Alterman, Benjamin L.; Larson, Davin; Boardsen, Scott; Verniero, Jaye
2022cosp...44.1656J Altcode:
Among contemporary heliospheric missions, Parker Solar Probe (PSP)
and Wind spacecraft have been observing non-thermal distributions
of solar wind ions from about 0.08 AU (about 17 solar radii) to 1
AU. There are sometimes secondary populations of protons and/or alpha
particles as well as anisotropic ion distributions with respect to
the interplanetary magnetic field (IMF). On the other hand, using
the high-cadence magnetic field data from PSP and Wind missions, we
have detected the near-circularly-polarized electromagnetic waves
in the solar wind, in the frequency range near the local proton
and alpha-particle cyclotron frequencies. They are preferentially
observed when the IMF is radial. Based on our long-term (covering
more than two years) surveys of these waves using PSP and Wind data,
we investigate the relationship between the non-thermal solar wind
ion distributions and the properties of these ion-scale waves. We
also statistically study the radial variations of these solar wind
ion parameters and wave properties (occurrence rate, wave frequency,
wave power, etc.) in the inner heliosphere. Such an investigation using
the solar wind plasma as a natural laboratory would deepen our general
understanding of wave-particle interactions at ion kinetic scales.

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Title: Observations and Models of Proton and Alpha Particle Beams
at PSP Perihelia with Implications for Solar Wind Heating
Authors: Ofman, Leon; Jian, Lan; Larson, Davin; Boardsen, Scott;
Verniero, Jaye
2022cosp...44.1087O Altcode:
The Parker Solar Probe (PSP) Solar Wind Electrons Alphas &amp; Protons
(SWEAP)/Solar Probe Analyzers-Ions (SPAN-I) provide details of proton
and alpha particle velocity distributions (VDFs), and associated kinetic
wave activity detected with the FIELDS instrument. In particular the
PSP observations at perihelia show that beam-core relative speed often
exceeds the local Alfven speed, and that the ions temperatures are
anisotropic with T$ _{\perp}/T_\parallel&gt;1$. The origin of these ion
beams and the implications for solar wind plasma kinetic heating are not
well known. Recent hybrid modeling results show that large amplitude
Alfven waves may drive the ion beams. Motivated by PSP observations
we develop 2.5D and 3D hybrid-particle-in-cell (hybrid-PIC) models
of proton and alpha particle super-Alfvenic beams in the solar wind
plasma. We model for the first time the combined proton and alpha
ion populations with beams and drifts, for a range of parameters
relevant to PSP perihelia conditions. We find that beams and drifts
drive nonlinearly coupled ion kinetic instabilities with associated
ion-scale wave spectra in the inner-heliospheric solar wind. The
results of the hybrid models provide the nonlinear evolution of the
anisotropic core-beam ion VDFs, ion relative drifts, ion temperature
anisotropies, and the wave k-spectra. We model the partition of the
energies of the ions (thermal and kinetic), and waves (magnetic)
due to the ion-kinetic instabilities. We conclude that the unstable
ion beams can provide a mechanism for dissipating kinetic and waves
energy resulting solar wind plasma heating.

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Title: Excitation and Damping of Slow Magnetosonic Waves in Flaring
Hot Coronal Loops: Effects of Compressive Viscosity
Authors: Ofman, Leon; Wang, Tongjiang
2022ApJ...926...64O Altcode: 2021arXiv211110696O
Slow magnetosonic waves associated with flares were observed
in coronal loops by Solar and Heliospheric Observatory/Solar
Ultraviolet Measurements of Emitted Radiation, Solar Dynamics
Observatory/Atmospheric Imaging Assembly in various EUV bandpasses,
and other instruments. The excitation and damping of slow magnetosonic
waves provides information on the magnetic, temperature, and density
structure of the loops. Recently, it was found using 1.5D models
that the thermal conduction is suppressed and compressive viscosity
is enhanced in hot (T &gt; 6 MK) flaring coronal loops. We model
the excitation and dissipation of slow magnetosonic waves in hot
coronal loops with realistic magnetic geometry, enhanced density, and
temperature (compared to background corona) guided by EUV observations
using a 3D magnetohydrodynamic (MHD) visco-resistive model. The effects
of the compressive viscosity tensor component along the magnetic field
are included with classical and enhanced viscosity coefficient values
for the first time in a 3D MHD coronal loop model. The waves are excited
by a velocity pulse at the footpoint of the loop at the coronal lower
boundary. The modeling results demonstrate the excitation of the slow
magnetosonic waves and nonlinear coupling to other wave modes, such
as the kink and fast magnetosonic. We find significant leakage of
the waves from the hot coronal loops with a small effect of viscous
dissipation in cooler (6 MK) loops, and more significant effects of
viscous dissipation in hotter (10.5 MK) coronal loops. Our results
demonstrate that nonlinear 3D MHD models are required to fully account
for the various wave couplings, damping, standing wave formation,
and viscous dissipation in hot flaring coronal loops. Our viscous 3D
MHD code provides a new tool for improved coronal seismology.

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Title: Modeling Ion Beams, Kinetic Instabilities, and Waves Observed
by the Parker Solar Probe near Perihelia
Authors: Ofman, Leon; Boardsen, Scott A.; Jian, Lan K.; Verniero,
Jaye L.; Larson, Davin
2022ApJ...926..185O Altcode: 2021arXiv211202357O
Recent in situ observations from the Parker Solar Probe (PSP) mission
in the inner heliosphere near perihelia show evidence of ion beams,
temperature anisotropies, and kinetic wave activity, which are
likely associated with kinetic heating and acceleration processes
of the solar wind. In particular, the proton beams were detected by
PSP/Solar Probe Analyzers-Ion (SPAN-I) and related magnetic fluctuation
spectra associated with ion-scale waves were observed by the FIELDS
instrument. We present the ion velocity distribution functions (VDFs)
from SPAN-I and the results of 2.5D and 3D hybrid-particle-in-cell
models of proton and α particle super-Alfvénic beams that drive
ion kinetic instabilities and waves in the inner heliospheric solar
wind. We model the evolution of the ion VDFs with beams, and obtain
the ion relative drifts speeds, and ion temperature anisotropies for
solar wind conditions near PSP perihelia. We calculate the partition
of energies between the particles (ions) along and perpendicular and
parallel to the magnetic field, as well as the evolution of magnetic
energy, and compare to observationally deduced values. We conclude that
the ion beam driven kinetic instabilities in the solar wind plasma near
perihelia are important components in the cascade of energy from fluid
to kinetic scales, an important component in the solar wind plasma
heating process.

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Title: Automated identification of transiting exoplanet candidates
in NASA Transiting Exoplanets Survey Satellite (TESS) data with
machine learning methods
Authors: Ofman, Leon; Averbuch, Amir; Shliselberg, Adi; Benaun, Idan;
Segev, David; Rissman, Aron
2022NewA...9101693O Altcode: 2021arXiv210210326O
A novel artificial intelligence (AI) technique that uses machine
learning (ML) methodologies combines several algorithms, which
were developed by ThetaRay, Inc., is applied to NASA's Transiting
Exoplanets Survey Satellite (TESS) dataset to identify exoplanetary
candidates. The AI/ML ThetaRay system is trained initially with Kepler
exoplanetary data and validated with confirmed exoplanets before its
application to TESS data. Existing and new features of the data, based
on various observational parameters, are constructed and used in the
AI/ML analysis by employing semi-supervised and unsupervised machine
learning techniques. By the application of ThetaRay system to 10,803
light curves of threshold crossing events (TCEs) produced by the TESS
mission, obtained from the Mikulski Archive for Space Telescopes, the
algorithm yields about 50 targets for further analysis, and we uncover
three new exoplanetary candidates by further manual vetting. This
study demonstrates for the first time the successful application of
the particular combined multiple AI/ML-based methodologies to a large
astrophysical dataset for rapid automated classification of TCEs.

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Title: Modeling the proton and particle beam and drift instabilities
and the related ion-scale waves observed by the Parker Solar Probe
in the solar wind
Authors: Ofman, Leon; Jian, Lan; Boardsen, Scott; Verniero, Jaye;
Larson, Davin
2021AGUFMSH11A..04O Altcode:
Parker Solar Probe SPAN-I data near perihelia encounters (for example,
E4-E8) find ion beams in protons and in alpha particle data, in
addition to the proton-alpha drift velocity, and ion temperature
anisotropies. The FIELDS instrument provides measurements of ion-scale
waves with increased wave activity periods associated with enhanced ion
beam magnitudes. It is well known from Vlasovs linear theory that ion
velocity distributions (VDFs) with super-Alfvenic beams are subject
to the ion-cyclotron instability and increase of ion temperature
anisotropy with perpendicular and parallel (to the magnetic field)
ion heating. Magnetosonic instability due to super-Alfvenic proton
alpha drift can also contribute to the kinetic wave activity, produce
anisotropic heating and ion scale waves. However, PSP data shows
complex VDFs with multiple ion populations that require considering
nonlinear interactions, growth, and nonlinear saturation of the ion
instabilities. Motivated by the PSP observations we carry out 2.5D
and 3D hybrid modeling of the expanding proton-alpha streaming solar
wind plasma and study the excitation and relaxation of the ion kinetic
instabilities, and their effects on ion-scale wave spectra. The models
produce self-consistent proton and alpha particle VDFs, ion temperature
anisotropies, and magnetic fluctuations spectra that can help understand
the PSP ion and waves data and evaluate the impact of the ion kinetic
instabilities on the heating of the SW plasma.

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Title: Are the properties of the ion cyclotron wave in the solar
wind indicative for their sources?
Authors: Wei, Hanying; Jian, Lan; Boardsen, Scott; Gershman, Daniel;
Russell, Christopher; Ofman, Leon
2021AGUFMSH35C2068W Altcode:
Electromagnetic waves near the ion cyclotron frequency have been
frequently observed in the solar wind from a wide range of heliocentric
distances. These waves could play important roles in energy transferring
or mediating the temperature anisotropy between ion species. The recent
studies of Parker Solar Probe data and the Magnetospheric Multiscale
data suggest ion beams appear to be a major source for generating these
circularly polarized and field-aligned propagating waves. STEREO and
WIND observations, both far away from the Earth bow shock to exclude
it from being the source, provide a large sample set to investigate
the wave properties statistically. We use these observations to infer
the properties of the source ions by assuming they are generated
from ion beam or ion with temperature anisotropies. We suggest that
super-Alfvenic relative drift of or unstable ion temperature anisotropy
could be the possible source of these widely observed waves (from 0.1
to 1AU) in the heliosphere.

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Title: Radial Evolution of the Ion-Scale Cyclotron Waves from 0.1
to 1 AU Based on PSP, Wind, and STEREO Observations
Authors: Jian, Lan; Boardsen, Scott; Wei, Hanying; Ofman, Leon;
Stevens, Michael; Verniero, Jaye; Larson, Davin; Russell, Christopher
2021AGUFMSH45A2348J Altcode:
Using the high-cadence magnetic field data from PSP (Parker
Solar Probe), Wind, and STEREO (Solar Terrestrial Relations
Observatory) missions, we have conducted long-term surveys of the
circularly-polarized electromagnetic waves in the inner heliosphere
and at 1 AU, in the frequency range near the local proton and
alpha-particle cyclotron frequencies. Based on the large wave event
lists from the three missions covering October 2018 March 2021, we
investigate the radial evolution of the wave properties from 0.1 to
1 AU statistically, including the occurrence rate, wave frequency,
wave power, etc. These waves are left-hand (LH) or right-hand (RH)
polarized in the spacecraft frame, and they often propagate in the
direction near the local magnetic field. We first select the events
in which LH and RH waves occur closely in time or simultaneously,
and then analyze their intrinsic frequencies in the plasma frame and
how the wave parameters vary with plasma conditions such as the solar
wind ion temperature anisotropy and relative drift. The implication
of the radial evolution of the LH and RH waves on models of solar wind
heating and acceleration is discussed.

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Title: Magnetohydrodynamic Waves in Open Coronal Structures
Authors: Banerjee, D.; Krishna Prasad, S.; Pant, V.; McLaughlin, J. A.;
Antolin, P.; Magyar, N.; Ofman, L.; Tian, H.; Van Doorsselaere, T.;
De Moortel, I.; Wang, T. J.
2021SSRv..217...76B Altcode: 2020arXiv201208802B
Modern observatories have revealed the ubiquitous presence of
magnetohydrodynamic waves in the solar corona. The propagating waves
(in contrast to the standing waves) are usually originated in the lower
solar atmosphere which makes them particularly relevant to coronal
heating. Furthermore, open coronal structures are believed to be the
source regions of solar wind, therefore, the detection of MHD waves
in these structures is also pertinent to the acceleration of solar
wind. Besides, the advanced capabilities of the current generation
telescopes have allowed us to extract important coronal properties
through MHD seismology. The recent progress made in the detection,
origin, and damping of both propagating slow magnetoacoustic waves and
kink (Alfvénic) waves is presented in this review article especially
in the context of open coronal structures. Where appropriate, we give
an overview on associated theoretical modelling studies. A few of the
important seismological applications of these waves are discussed. The
possible role of Alfvénic waves in the acceleration of solar wind is
also touched upon.

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Title: Large-scale EUV Waves and Their Implications for Global
Coronal Seismology
Authors: Liu, W.; Jin, M.; Wang, T.; Ofman, L.; Sun, X.
2021AAS...23832817L Altcode:
Large-scale extreme ultraviolet (EUV) waves associated with coronal mass
ejections (CMEs) and solar flares can provide novel diagnostics of the
solar corona on global scales, an area yet to be fully exploited. We
perform detailed analysis of various behaviors, such as reflection,
refraction, and diffraction of several well-observed EUV waves,
including those associated with the SOL2017-09-10 X8.2 flare and
the SOL2011-02-15 X2 flare. We also performed data-constrained MHD
simulations of these events using the University of Michigan Alfven Wave
Solar Model (AWSoM). By comparing the observations and simulations,
we benchmark diagnostics of the magnetic field strengths and thermal
properties of the solar corona. This opens the door to the full
applications to global coronal seismology using large-scale EUV waves.

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Title: Observations and 3D MHD Modeling of Small-scale Solar
Prominence Oscillations
Authors: Ofman, L.; Kucera, T.; DeVore, C. R.
2021AAS...23810607O Altcode:
Small scale oscillations were recently observed in prominences with
high resolution Hinode/SOT and IRIS SJI in unprecedented detail and
identified as fast magnetosonic waves. The high-resolution observations
provide evidence of flows of cool material, fluid instabilities
such as Kelvin-Helmholtz and Rayleigh-Taylor, and the spectroscopic
information provides evidence of Doppler shifts, heating, and cooling
of the prominence material. Recently nonlinear fast magnetosonic
waves were observed with periods in the range of 5-11 minutes and
wavelengths in the plane of the sky (POS) of ~ 2000 km and flows,
and the flows in narrow threads with POS speed ∼16-46 km/s. The
nonlinear fast magnetosonic waves and flows were modeled using 2.5D MHD
(Ofman &amp; Kucera 2020). Here, we extend the study of the nonlinear
fast magnetosonic waves using more realistic 3D MHD model. The model
includes the 3D structure of the density and the magnetic field as well
as mode coupling and demonstrate the propagating density compressions
associated with the nonlinear fast magnetosonic waves, as well as the
guided modes in the pillar. The 3D MHD modeling improve understanding
of the POS effects in limb prominence oscillations observations. The
results of the modeling are useful for coronal seismology of the
prominence structure.

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Title: Oblique High Mach Number Heliospheric Shocks: The Role of
α Particles
Authors: Ofman, L.; Wilson, L. B.; Koval, A.; Szabo, A.
2021JGRA..12628962O Altcode:
Spacecraft observations of heliospheric shocks often find oscillations
in the magnetic field and density both, upstream and downstream. The
downstream magnetic oscillations of oblique collisionless shocks were
detected by Wind with 10.9 samples s-1 and DSCOVR spacecraft
with high temporal resolution of 50 samples s-1. The
density oscillations associated with the shocks are also evident in
proton and α particle density by Wind (with much lower temporal
resolution). Recently, we have investigated low Mach number low
β oblique shock oscillations using satellite data and 2.5D hybrid
modeling with electrons modeled as fluid and ions modeled as particles
and found that α particles—an important component of heliospheric
plasma—may affect considerably the downstream oscillations and the
shock structure. The objective of the present study is to investigate
the effects of α particles on high Mach number heliospheric shocks
dynamics, oscillations, nonstationarity, and shock front rippling. We
extend the study to high Mach number shocks (M &gt; 3), investigate
several α particle typical densities, and compare the results for the
various shock parameters. We model the effects of α particles on the
shock ramp, wake, and downstream oscillation structure and the kinetic
properties of proton and α particle velocity distributions at various
locations downstream of the shocks. Using the 2.5D hybrid model we found
that the modeled high Mach number quasi perpendicular shock magnetic
and density structures are significantly affected by α particles with
typical solar wind relative abundances, suggesting that the observed
high Mach number shocks are similarly affected by α particles.

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Title: Simulating the Solar Minimum Corona in UV Wavelengths with
Forward Modeling II. Doppler Dimming and Microscopic Anisotropy Effect
Authors: Zhao, Jie; Gibson, Sarah E.; Fineschi, Silvano; Susino,
Roberto; Casini, Roberto; Cranmer, Steven R.; Ofman, Leon; Li, Hui
2021ApJ...912..141Z Altcode:
In ultraviolet (UV) spectropolarimetric observations of the solar
corona, the existence of a magnetic field, solar wind velocity, and
temperature anisotropies modify the linear polarization associated with
resonant scattering. Unlike previous empirical models or global models,
which present blended results of the above physical effects, in this
work, we forward-model expected signals in the H I Lyα line (121.6 nm)
by adopting an analytic model that can be adjusted to test the roles
of different effects separately. We find that the impact of all three
effects is most evident in the rotation of the linear polarization
direction. In particular, (1) for magnetic fields between ∼10 and
∼100 G, the Hanle effect modifies the linear polarization at low
coronal heights, rotating the linear polarization direction clockwise
(counterclockwise) when the angle between the magnetic field and the
local vertical is greater (less) than the van Vleck angle, which is
consistent with the result of Zhao et al.; (2) solar wind velocity,
which increases with height, has a significant effect through the
Doppler dimming effect at higher coronal heights, rotating the linear
polarization direction in an opposite fashion to the Hanle effect;
and (3) kinetic temperature anisotropies are most significant at
lower heights in open nonradial magnetic field regions, producing
tilt opposite to isotropic Doppler dimming. The fact that the three
effects operate differently in distinct spatial regimes opens up the
possibility for using linear polarization measurements in UV lines to
diagnose these important physical characteristics of the solar corona.

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Title: Slow-Mode Magnetoacoustic Waves in Coronal Loops
Authors: Wang, Tongjiang; Ofman, Leon; Yuan, Ding; Reale, Fabio;
Kolotkov, Dmitrii Y.; Srivastava, Abhishek K.
2021SSRv..217...34W Altcode: 2021arXiv210211376W
Rapidly decaying long-period oscillations often occur in hot
coronal loops of active regions associated with small (or micro-)
flares. This kind of wave activity was first discovered with the
SOHO/SUMER spectrometer from Doppler velocity measurements of hot
emission lines, thus also often called "SUMER" oscillations. They
were mainly interpreted as global (or fundamental mode) standing slow
magnetoacoustic waves. In addition, increasing evidence has suggested
that the decaying harmonic type of pulsations detected in light curves
of solar and stellar flares are likely caused by standing slow-mode
waves. The study of slow magnetoacoustic waves in coronal loops has
become a topic of particular interest in connection with coronal
seismology. We review recent results from SDO/AIA and Hinode/XRT
observations that have detected both standing and reflected intensity
oscillations in hot flaring loops showing the physical properties (e.g.,
oscillation periods, decay times, and triggers) in accord with the SUMER
oscillations. We also review recent advances in theory and numerical
modeling of slow-mode waves focusing on the wave excitation and damping
mechanisms. MHD simulations in 1D, 2D and 3D have been dedicated to
understanding the physical conditions for the generation of a reflected
propagating or a standing wave by impulsive heating. Various damping
mechanisms and their analysis methods are summarized. Calculations
based on linear theory suggest that the non-ideal MHD effects such
as thermal conduction, compressive viscosity, and optically thin
radiation may dominate in damping of slow-mode waves in coronal loops
of different physical conditions. Finally, an overview is given of
several important seismological applications such as determination of
transport coefficients and heating function.

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Title: Rossby Waves in Astrophysics
Authors: Zaqarashvili, T. V.; Albekioni, M.; Ballester, J. L.;
Bekki, Y.; Biancofiore, L.; Birch, A. C.; Dikpati, M.; Gizon, L.;
Gurgenashvili, E.; Heifetz, E.; Lanza, A. F.; McIntosh, S. W.; Ofman,
L.; Oliver, R.; Proxauf, B.; Umurhan, O. M.; Yellin-Bergovoy, R.
2021SSRv..217...15Z Altcode:
Rossby waves are a pervasive feature of the large-scale motions of the
Earth's atmosphere and oceans. These waves (also known as planetary
waves and r-modes) also play an important role in the large-scale
dynamics of different astrophysical objects such as the solar
atmosphere and interior, astrophysical discs, rapidly rotating stars,
planetary and exoplanetary atmospheres. This paper provides a review
of theoretical and observational aspects of Rossby waves on different
spatial and temporal scales in various astrophysical settings. The
physical role played by Rossby-type waves and associated instabilities
is discussed in the context of solar and stellar magnetic activity,
angular momentum transport in astrophysical discs, planet formation,
and other astrophysical processes. Possible directions of future
research in theoretical and observational aspects of astrophysical
Rossby waves are outlined.

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Title: The effects of the multi-ion kinetic instabilities on
electromagnetic cyclotron wave spectra in the solar wind
Authors: Ofman, Leon; Jian, Lan
2021cosp...43E.942O Altcode:
Electromagnetic ion cyclotron (EMIC) waves were identified in the solar
wind (SW) in the past using in-situ data from STEREO (Jian et al. 2009),
Wind, and other spacecraft data. In-situ data in the inner heliosphere
form Helios 1 &amp; 2 show strong evidence of non-equilibrium
(non-Maxwellian) ion velocity distribution functions (VDFs),
differential alpha-proton streaming, ion temperature anisotropies, and
various forms of magnetic fluctuation spectra with distinct ion kinetic
scales effects. Parker Solar Probe perihelion measurements provide SW
plasma data and are expected to provide VDFs of protons and alphas,
with additional ion data expected from the Solar Orbiter. Motivated
by these observations we carry out 2.5D and 3D hybrid modeling of
the expanding proton-alpha streaming solar wind plasma and study the
excitation and relaxation of the ion kinetic instabilities, and their
effects on EMIC wave spectra. The models produce self-consistent ion
VDFs, temperature anisotropies, and magnetic fluctuations spectra
that can test and improve the predictions of linear Vlasov theory
and compared to in-situ spacecraft measurements. The results help
understanding the multi-ion SW plasma expansion and heating in the
acceleration region close to the Sun.

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Title: Modeling the effects of α particles on collisionless oblique
heliospheric shocks
Authors: Ofman, Leon; Wilson, Lynn; Szabo, Adam; Koval, Andriy
2021APS..DPPBM0006O Altcode:
The α particles in the solar wind are the second most abundant ion,
and can carry significant energy, momentum and mass flux. We investigate
the effects of α particles on the dynamics and the oscillations in
high-Mach number (M &gt;3) oblique heliospheric shocks. However,
detailed in-situ observations of α particle properties in these
shocks are rare, in particular at high cadence on-par with the
magnetic field measurements. The downstream magnetic oscillations in
oblique collisionless heliospheric shocks were detected by Wind with
10.9 samples/s and recently by DSCOVR spacecraft with high temporal
resolution of 50 samples/s. The ions were also detected by Wind, albeit
with lower temporal resolution then the magnetic oscillation. It is
expected that Parker Solar Probe and Solar Orbiter will observe shocks
in the inner heliosphere with detailed proton and α particle data
with the expected increase of solar activity. Meanwhile, we report
the results of 2.5D and 3D hybrid models of high Mach number shocks,
where we investigate several α particle typical relative abundances,
Mach numbers, and shock normal directions, and compare the results
for the various shock parameters. In particular we model the effects
of α particles on the shock ramp, wake, and downstream oscillations
and study the kinetic properties of proton and α particle velocity
distributions function (VDFs) downstream of the shocks. The modeling
results demonstrate that with typical α particle solar wind abundances
of 5% the dynamics and the oscillations of high-Mach number shocks
is significantly affected, evident from comparison to proton only
shock models. We discussed the implication of our modeling results to
the interpretation of spacecraft observations. LO acknowledges
support by NASA Cooperative agreement NNG11PLA10A to CUA. Resources
supporting this work were provided by the NASA High-End Computing(HEC)
Program through the NASA Advanced Supercomputing (NAS) Division at
Ames Research Center.

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Title: Comprehensive modeling of EMIC wave generation and their
impact on different plasma populations using a kinetic convection
diffusion model
Authors: Kang, S. B.; Fok, M. C. H.; Glocer, A.; Ofman, L.; Denton,
R. E.; Buzulukova, N.
2020AGUFMSM037..14K Altcode:
Electromagnetic ion cyclotron (EMIC) waves play important roles in
charged particle dynamics in the inner magnetosphere, heating both
thermal ions and cold electrons and causing loss of both ring current
ions and radiation belt electrons. EMIC waves are one of the key
phenomena connecting ring current, cold plasma, and radiation belt
populations through wave-particle interaction. Ring current ions with
anisotropic pressure provides a free energy source to excite EMIC waves,
whereas cold plasma population provides a reservoir taking energy from
EMIC waves and medium for EMIC waves to be able to propagate. Therefore,
modeling of EMIC waves (in particular their wave spectra and amplitudes)
and their impact on different plasma populations are also very
important in order to understand the dynamics between ring current,
plasmasphere, and radiation belts. Hybrid or full particle codes can
self-consistently calculate EMIC wave growth, wave amplitude, and
their interaction with particle populations conserving all the basic
physics, but it is difficult to simulate this on global scale because
of their high computational cost. As a compromise, we use Comprehensive
Inner Magnetosphere and Ionosphere (CIMI) model, which is a kinetic
convection-diffusion model including ring current, plasmasphere,
and radiation belt and parameterization of EMIC wave saturation
amplitude, which estimates EMIC waves from a linear growth rate and
plasma parameters such as densities and plasma pressure. We calculate
event-specific linear growth rate and estimate global power spectral
densities from the plasma parameters simultaneously calculated in
CIMI. Furthermore, we calculate quasi-linear diffusion coefficients in
momentum space and evaluate how EMIC waves heat or scatter ring current
ions and radiation belt electrons. We also calculate the dependence of
saturated EMIC wave amplitudes on various plasma parameters using the
empirical formulas obtained from by 2.5D hybrid models. To validate,
we compare RBSP observation to our simulation. This investigation
represents a state-of-the-art comprehensive study of EMIC wave growth
and their effects on ring current ions and radiation belt electrons.

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Title: Simulations of longitudinal oscillations in flaring coronal
loops observed with SDO/AIA
Authors: Wang, T.; Ofman, L.; Bradshaw, S. J.
2020AGUFMSH0430014W Altcode:
Longitudinal intensity oscillations generated in flare-heated
coronal loops were recently observed with SDO/AIA in 94 Å and 131
Å channels. These oscillations have been interpreted as standing
or reflected propagating slow magnetoacoustic waves. They are mostly
triggered by a circular-ribbon flare located at one footpoint of the
loop, which may be associated with a fan-spine magnetic topology. The
propagation, damping, and excitation mechanisms of such slow-mode
waves in flaring loops are still poorly understood. Recent studies
based on linear theory and 1D MHD simulations have demonstrated
the determination of effective transport coefficients from observed
oscillations by coronal seismology techniques (Wang et al 2015, 2018,
2019). Evidence for thermal conduction suppression and compressive
viscosity enhancement has been found with this technique. The presence
of anomalous transport processes in hot flaring plasma may help shed
light on the wave excitation mechanism and long-standing puzzles such
as long-duration EUV/X-ray flares. In this presentation, we report on
the analyzed results for seven new oscillation events observed with
SDO/AIA. By simulating the propagation of slow waves in a 2D and 3D
MHD model of hot AR loop constrained by observations, we explore the
effect of modified transport coefficients on the wave excitation and
damping. We also study the effect of modified transport coefficients on
the thermal evolution of a heated loop using a field-aligned HD model.

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Title: Oblique High Mach Number Heliospheric Shocks: the Role of
Alpha Particles
Authors: Ofman, L.; Koval, A.; Wilson, L. B., III; Szabo, A.
2020AGUFMSH0420012O Altcode:
Spacecraft observations of heliospheric shocks often show oscillations
in the magnetic field and density, both upstream and downstream. The
magnetic oscillations of oblique collisionless shocks were detected by
Wind and DSCOVR with high temporal resolution of up to 50 samples/s. The
density oscillations associated with the shocks are also evident in
density by Wind (with lower temporal resolution). Recently, we have
investigated low Mach number low-beta oblique shock oscillations using
satellite data and 2.5D hybrid modeling with electrons modeled as
fluid and ions modeled as particles and found that alpha particles
may affect considerably the downstream oscillations and the shock
structure. Here, we extend the study to high Mach number shocks
(M&gt;3), investigate several alpha particle typical densities, and
compare the results. Using the 2.5D hybrid model we found that high
Mach number quasi-perpendicular shock magnetic and density structures
are significantly affected by alpha particles typical densities,
manifesting in effect on rippling, nonstationarity, and reformation
of the shocks. Multiple point spacecraft observations are needed to
properly account for these shock features. We investigate the effects
of alpha particles relative abundance on the shock ramp, wake, and
downstream oscillation structure as well as kinetic properties of
proton and alpha particle velocity distributions.

---------------------------------------------------------
Title: Coronal Heating by MHD Waves
Authors: Van Doorsselaere, Tom; Srivastava, Abhishek K.; Antolin,
Patrick; Magyar, Norbert; Vasheghani Farahani, Soheil; Tian, Hui;
Kolotkov, Dmitrii; Ofman, Leon; Guo, Mingzhe; Arregui, Iñigo; De
Moortel, Ineke; Pascoe, David
2020SSRv..216..140V Altcode: 2020arXiv201201371V
The heating of the solar chromosphere and corona to the observed high
temperatures, imply the presence of ongoing heating that balances
the strong radiative and thermal conduction losses expected in the
solar atmosphere. It has been theorized for decades that the required
heating mechanisms of the chromospheric and coronal parts of the active
regions, quiet-Sun, and coronal holes are associated with the solar
magnetic fields. However, the exact physical process that transport
and dissipate the magnetic energy which ultimately leads to the solar
plasma heating are not yet fully understood. The current understanding
of coronal heating relies on two main mechanism: reconnection and MHD
waves that may have various degrees of importance in different coronal
regions. In this review we focus on recent advances in our understanding
of MHD wave heating mechanisms. First, we focus on giving an overview
of observational results, where we show that different wave modes have
been discovered in the corona in the last decade, many of which are
associated with a significant energy flux, either generated in situ
or pumped from the lower solar atmosphere. Afterwards, we summarise
the recent findings of numerical modelling of waves, motivated by the
observational results. Despite the advances, only 3D MHD models with
Alfvén wave heating in an unstructured corona can explain the observed
coronal temperatures compatible with the quiet Sun, while 3D MHD wave
heating models including cross-field density structuring are not yet
able to account for the heating of coronal loops in active regions to
their observed temperature.

---------------------------------------------------------
Title: Parker Solar Probe Proton Beams and Waves: Observations
and Modeling
Authors: Ofman, L.; Jian, L.; Boardsen, S. A.
2020AGUFMSH0490014O Altcode:
Parker Solar Probe (PSP) observations with Solar Probe Analyzer for
Ions (SPAN-I) detects the 3D velocity distribution function (VDF) of
protons and a particles with evidence of super-Alfvénic beams. The
data is supplemented with FIELDS instrument that shows evidence of
accompanying ion-scale wave storms, such as reported in Verniero et
al. (2020). We report new coordinated wave-particle investigations
focusing on the periods with the extensive existence of proton beams
near PSP perihelion. We use the observed plasma parameters of the proton
beam events to setup 2.5D hybrid model (2 spatial dimensions with 3D
velocity and magnetic field components). In the model the protons and
alpha particles are modeled kinetically with Particle In Cell (PIC)
method, while electrons are treated as fluid. We investigate the
relaxation of the drift instability due to the proton beam events,
the generation of non-thermal VDFs and temperature anisotropy of
protons, the effects of alpha particles, and the associated spectrum
of magnetic fluctuations. The modeling results are in good agreement
with PSP observations, and allow investigating the onset and the kinetic
evolution of proton beam events for a range of observationally motivated
solar wind plasma parameters.

---------------------------------------------------------
Title: Fast Magnetosonic Waves and Flows in a Solar Prominence Foot:
Observations and Modeling
Authors: Ofman, Leon; Kucera, Therese A.
2020ApJ...899...99O Altcode: 2020arXiv200605885O
We study recent observations of propagating fluctuations in a prominence
foot with Hinode Solar Optical Telescope (SOT) high-resolution
observations in Ca II and Hα emission, which we identify as nonlinear
fast magnetosonic waves. Here we analyze further the observations of
propagating waves and flows with Interface Region Imaging Spectrograph
Mg II slit jaw images, in addition to Hinode/SOT Ca II images. We find
that the waves have typical periods in the range of 5-11 minutes and
wavelengths in the plane of the sky (POS) of about 2000 km, while the
flows in narrow threads have a typical speed in the POS of ∼16-46
km s-1. We also detect apparent kink oscillations in the
threads with flowing material, and apply coronal seismology to estimate
the magnetic field strength in the range of 5-17 G. Using 2.5D MHD we
model the combined effects of nonlinear waves and flows on the observed
dynamics of the prominence material, and reproduce the propagating and
refracting fast magnetosonic waves, as well as standing kink-mode waves
in flowing material along the magnetic field. The modeling results are
in good qualitative agreement with the observations of the various
waves and flows in the prominence foot, further confirming coronal
seismology analysis and improving the understanding of the fine-scale
dynamics of the prominence material.

---------------------------------------------------------
Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks
from the X8.2 Eruptive Flare on 2017 September 10
Authors: Jin, M.; Liu, W.; Cheung, C. M. M.; Nitta, N.; DeRosa,
M. L.; Manchester, W.; Ofman, L.; Downs, C.; Petrosian, V.; Omodei,
N.; Moschou, S. P.; Sokolov, I.
2019AGUFMSH32A..01J Altcode:
As one of the largest flare-CME eruptions during solar cycle 24, the
2017 September 10 X8.2 flare event is associated with spectacular
global EUV waves that transverse almost the entire visible solar
disk, a CME with speed &gt; 3000 km/s, which is one of the fastest
CMEs ever recorded, and &gt;100 MeV Gamma-ray emission lasting for
more than 12 hours. All these unique observational features pose new
challenge on current numerical models to reproduce the multi-wavelength
observations. To take this challenge, we simulate the September 10
event using a global MHD model (AWSoM: Alfven Wave Solar Model) within
the Space Weather Modeling Framework and initiate CMEs by Gibson-Low
flux rope. We assess several important observed and physical inputs
(e.g., flux rope properties, polar magnetic field) in the model to
better reproduce the multi-wavelength observations. We find that the
simulated EUV wave morphology and kinematics are sensitive to the
orientation of the initial flux rope introduced to the source active
region. An orientation with the flux-rope axis in the north-south
direction produces the best match to the observations, which suggests
that EUV waves may potentially be used to constrain the flux-rope
geometry for such limb or behind-the-limb eruptions that lack good
magnetic field observations. By further combining with the white
light and radio observations, we demonstrate the flux rope-corona
interaction can greatly impact the early phase shock evolution (e.g.,
geometry and shock parameters) therefore plays a significant role
for particle acceleration near the Sun in this event. By propagating
the CMEs into the heliosphere and beyond the Earth and Mars orbits, we
compare the model results with the in-situ measurements and demonstrate
the importance of input polar magnetic field on the realistic CME
modeling therefore space weather forecasting.

---------------------------------------------------------
Title: The effects of Alpha Particles on Oblique High Mach Number
Heliospheric Shocks
Authors: Ofman, L.; Wilson, L. B., III; Koval, A.; Szabo, A.
2019AGUFMSH23B3401O Altcode:
Spacecraft observations of shocks often show oscillations in the
magnetic field and density both, upstream and downstream. The magnetic
oscillations of oblique collisionless shocks were detected by DSCOVR/MAG
with high temporal resolution of 50 samples/s. The density oscillations
associated with the shocks are seen by DSCOVR and Wind in protons and
in α particle by Wind (with lower temporal resolution). Recently,
we have investigated low Mach number low-β oblique shock oscillations
using satellite data and 2.5D hybrid modeling with electrons modeled
as fluid and ions modeled as particles. In particular we found that
α particles may affect considerably the downstream oscillations and
the shock structure. Here, we extend our previous study to high Mach
number shocks (M&gt;3) and investigate a range of plasma β values in
the β&lt;~1 range and compare the results to available observations
of similar shocks. Using the 2.5D hybrid model we find that high Mach
number shocks exhibit time-dependent corrugation (rippling) of the
shock front. We investigate the effects of α particle abundances and
other kinetic properties on the rippling and the non-stationarity of
the oblique high Mach number shocks. We model the structure and the
evolution of the proton and α particle velocity distributions in
various locations in the downstream region of the shocks and discuss
the observational implications.

---------------------------------------------------------
Title: Determination of transport coefficients from flare-induced
slow magnetoacoustic waves by parametric study
Authors: Wang, T.; Ofman, L.; Bradshaw, S. J.
2019AGUFMSH33D3408W Altcode:
Recent studies of slow-mode waves in a flaring coronal loop observed
by SDO/AIA have revealed the suppression of thermal conduction and
significant enhancement of compressive viscosity in hot (~ 10 MK)
plasma (Wang et al. 2015, 2018). The strong suppression of thermal
conduction may provide an explanation for the slower-than-expected
cooling of flare plasma in the decay phase, while the anomalously
enhanced viscosity can explain the quick formation of standing slow
magnetosonic waves seen in observations. In this study we aim at
developing a new coronal seismology tool for determining the transport
coefficients in flaring loop plasma based on a parametrical study of
wave properties. For this purpose we are using a 1D nonlinear MHD
loop model in combination with the linear theory. We find that the
classical thermal conductivity is suppressed by a factor of about 3
derived from the observed phase shift between temperature and density
perturbations, and the classical viscosity coefficient is enhanced by
a factor of 10 from the observed decay time. Using the 1D loop model
with these refined transport coefficients, we study the excitation
of slow-mode waves by launching a flow pulse from one footpoint. The
simulation can self-consistently produce the fundamental standing
wave on a timescale in agreement with the observation. We extend
the model to more realistic 2.5D MHD and study the effects of the
seismology-determined transport coefficients on the wave excitation
and damping times using simulations of a field-aligned hydrodynamic
loop model with impulsive heating. We model the impulsive excitation
of slow magnetosonic waves in a bipolar coronal active region (AR)
using 2.5D MHD model that includes a hot and dense loop initially in
hydrostatic equilibrium. We discuss the effect of the loop's transverse
and longitudinal inhomogeneity on the resulting wave dynamics.

---------------------------------------------------------
Title: Determination of Transport Coefficients by Coronal Seismology
of Flare-induced Slow-mode Waves: Numerical Parametric Study of a
1D Loop Model
Authors: Wang, Tongjiang; Ofman, Leon
2019ApJ...886....2W Altcode: 2019arXiv190910910W
Recent studies of a flaring loop oscillation event on 2013 December
28 observed by the Atmospheric Imaging Assembly of the Solar Dynamics
Observatory have revealed the suppression of thermal conduction and
significant enhancement of compressive viscosity in hot (∼10 MK)
plasma. In this study we aim at developing a new coronal seismology
method for determining the transport coefficients based on a parametric
study of wave properties using a 1D nonlinear magnetohydrodynamics
(MHD) loop model in combination with the linear theory. The simulations
suggest a two-step scheme: we first determine the effective thermal
conduction coefficient from the observed phase shift between
temperature and density perturbations as this physical parameter
is insensitive to the unknown viscosity; then from the loop model
with the obtained thermal conduction coefficient, we determine the
effective viscosity coefficient from the observed decay time using
the parametric modeling. With this new seismology technique we are
able to quantify the suppression of thermal conductivity by a factor
of about 3 and the enhancement of viscosity coefficient by a factor of
10 in the studied flaring loop. Using the loop model with these refined
transport coefficients, we study the excitation of slow magnetoacoustic
waves by launching a flow pulse from one footpoint. The simulation can
self-consistently produce the fundamental standing wave on a timescale
in agreement with the observation.

---------------------------------------------------------
Title: Hybrid Simulation of Solar-Wind-Like Turbulence
Authors: Roberts, D. Aaron; Ofman, Leon
2019SoPh..294..153R Altcode:
We present 2.5D hybrid simulations of the spectral and thermodynamic
evolution of an initial state of magnetic field and plasma
variables that in many ways represents solar wind fluctuations. In
accordance with Helios near-Sun high-speed stream observations,
we start with Alfvénic fluctuations along a mean magnetic field
in which the fluctuations in the magnitude of the magnetic field are
minimized. Since fluctuations in the radial flow speed are the dominant
free energy in the observed fluctuations, we include a field-aligned
v∥(k⊥) with an k−1 spectrum
of velocity fluctuations to drive the turbulent evolution. The
flow rapidly distorts the Alfvénic fluctuations, yielding spectra
(determined by spacecraft-like cuts) transverse to the field that
become comparable to the k∥ fluctuations, as in spacecraft
observations. The initial near constancy of the magnetic field is lost
during the evolution; we show this also takes place observationally. We
find some evolution in the anisotropy of the thermal fluctuations,
consistent with expectations based on Helios data. We present 2D spectra
of the fluctuations, showing the evolution of the power spectrum
and cross-helicity. Despite simplifying assumptions, many aspects
of simulations and observations agree. The greatly faster evolution
in the simulations is at least in part due to the small scales being
simulated, but also to the non-equilibrium initial conditions and the
relatively low overall Alfvénicity of the initial fluctuations.

---------------------------------------------------------
Title: Pitch Angle Scattering of Sub-MeV Relativistic Electrons by
Electromagnetic Ion Cyclotron Waves
Authors: Denton, R. E.; Ofman, L.; Shprits, Y. Y.; Bortnik, J.; Millan,
R. M.; Rodger, C. J.; da Silva, C. L.; Rogers, B. N.; Hudson, M. K.;
Liu, K.; Min, K.; Glocer, A.; Komar, C.
2019JGRA..124.5610D Altcode:
Electromagnetic ion cyclotron (EMIC) waves have long been considered to
be a significant loss mechanism for relativistic electrons. This has
most often been attributed to resonant interactions with the highest
amplitude waves. But recent observations have suggested that the
dominant energy of electrons precipitated to the atmosphere may often
be relatively low, less than 1 MeV, whereas the minimum resonant energy
of the highest amplitude waves is often greater than 2 MeV. Here we use
relativistic electron test particle simulations in the wavefields of
a hybrid code simulation of EMIC waves in dipole geometry in order
to show that significant pitch angle scattering can occur due to
interaction with low-amplitude short-wavelength EMIC waves. In the
case we examined, these waves are in the H band (at frequencies above
the He+ gyrofrequency), even though the highest amplitude
waves were in the He band frequency range (below the He+
gyrofrequency). We also present wave power distributions for 29 EMIC
simulations in straight magnetic field line geometry that show that the
high wave number portion of the spectrum is in every case mostly due
to the H band waves. Though He band waves are often associated with
relativistic electron precipitation, it is possible that the He band
waves do not directly scatter the sub-megaelectron volts (sub-MeV)
electrons, but that the presence of He band waves is associated with
high plasma density which lowers the minimum resonant energy so that
these electrons can more easily resonate with the H band waves.

---------------------------------------------------------
Title: On the Origin of Quasi-periodic Fast-mode Propagating Wave
Trains (QFPs): A Statistical Survey
Authors: Silver, Jay; Liu, Wei; Ofman, Leon
2019AAS...23421001S Altcode:
The magnetized solar corona hosts a variety of waves that are physically
important and can serve as useful diagnostic tools. One type of such
coronal waves are Quasi-periodic Fast-mode Propagating wave trains
(QFPs), which were first detected in extreme ultraviolet (EUV) by
the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
Observatory (SDO). QFPs are not uncommon and are generally associated
with some, but not all solar flares and/or coronal mass ejections
(CMEs). To search for physical conditions that can contribute to QFP
production, we carried out a systematic survey of QFPs from the full
SDO mission. We found that about 1/5 of global EUV waves were associated
with QFPs. We also conducted a comparative study of two active regions
(ARs) visible between October and November 2014, AR12192 and AR12205,
with very different levels of QFP activity. AR12205 produced less
flares but more QFPs, which were all associated with blow-out,
eruptive flares and global EUV waves. In contrast, AR12192 produced
more (mostly confined) flares, but with virtually no QFPs and less
CMEs. This suggests that blow-out eruptions could be a necessary,
but not sufficient condition for QFP production and/or detectability.

---------------------------------------------------------
Title: The Global EUV Wave Associated with the SOL2017-09-10 X8.2
Flare: SDO/AIA Observations and Data-constrained MHD Simulations
Authors: Liu, Wei; Jin, Meng; Ofman, Leon; DeRosa, Marc L.
2019AAS...23430701L Altcode:
While large-scale extreme ultraviolet (EUV) waves associated with
coronal mass ejections (CMEs) and solar flares are common, the EUV
wave triggered by the X8 flare-CME eruption on 2017 September 10
was an extreme. This was, to the best of our knowledge, the first
detection of an EUV wave traversing the full-Sun corona over the entire
visible disk and off-limb circumference, manifesting a truly global
nature. In addition to commonly observed reflections, it had strong
transmissions in and out of both polar coronal holes, at elevated
wave speeds of &gt;2000 km/s within them. With an exceptionally large
wave amplitude, it produced significant compressional heating to local
coronal plasma. We present detailed analysis of SDO/AIA observations,
global magnetic field extrapolations with the potential-field source
surface (PFSS) model, and data-constrained MHD simulations of this
event using the University of Michigan Alfven Wave Solar Model
(AWSoM). By comparing the observations and simulations, we benchmark
diagnostics of the magnetic field strengths and thermal properties of
the solar corona on global scales. We discuss the future prospects of
using such extreme EUV waves as probes for global coronal seismology,
an area yet to be fully exploited.

---------------------------------------------------------
Title: Reconstructing Extreme Space Weather From Planet Hosting Stars
Authors: Airapetian, Vladimir; Adibekyan, V.; Ansdell, M.; Alexander,
D.; Barklay, T.; Bastian, T.; Boro Saikia, S.; Cohen, O.; Cuntz,
M.; Danchi, W.; Davenport, J.; DeNolfo, G.; DeVore, R.; Dong, C. F.;
Drake, J. J.; France, K.; Fraschetti, F.; Herbst, K.; Garcia-Sage,
K.; Gillon, M.; Glocer, A.; Grenfell, J. L.; Gronoff, G.; Gopalswamy,
N.; Guedel, M.; Hartnett, H.; Harutyunyan, H.; Hinkel, N. R.; Jensen,
A. G.; Jin, M.; Johnstone, C.; Kahler, S.; Kalas, P.; Kane, S. R.;
Kay, C.; Kitiashvili, I. N.; Kochukhov, O.; Kondrashov, D.; Lazio, J.;
Leake, J.; Li, G.; Linsky, J.; Lueftinger, T.; Lynch, B.; Lyra, W.;
Mandell, A. M.; Mandt, K. E.; Maehara, H.; Miesch, M. S.; Mickaelian,
A. M.; Mouschou, S.; Notsu, Y.; Ofman, L.; Oman, L. D.; Osten, R. A.;
Oran, R.; Petre, R.; Ramirez, R. M.; Rau, G.; Redfield, S.; Réville,
V.; Rugheimer, S.; Scheucher, M.; Schlieder, J. E.; Shibata, K.;
Schnittman, J. D.; Soderblom, David; Strugarek, A.; Turner, J. D.;
Usmanov, A.; Van Der Holst, B.; Vidotto, A.; Vourlidas, A.; Way, M. J.;
Wolk, Scott J.; Zank, G. P.; Zarka, P.; Kopparapu, R.; Babakhanova,
S.; Pevtsov, A. A.; Lee, Y.; Henning, W.; Colón, K. D.; Wolf, E. T.
2019BAAS...51c.564A Altcode: 2019astro2020T.564A; 2019arXiv190306853A
The goal of this white paper is to identify and describe promising key
research goals to aid the theoretical characterization and observational
detection of ionizing radiation from quiescent and flaring upper
atmospheres of planet hosts as well as properties of stellar coronal
mass ejections (CMEs) and stellar energetic particle (SEP) events.

---------------------------------------------------------
Title: Multi-fluid models and UV observations of coronal streamers
Authors: Ofman, Leon; Abbo, Lucia; Giordano, Silvio
2019shin.confE.197O Altcode:
The sources of the slow solar wind were long associated with coronal
streamers through empirical connections from remote sensing and in-situ
observations, and modeling. Near solar activity minimum the solar
magnetic field is dominated by a tilted dipole and forms a streamer
belt due to the outflow of the slow solar wind. Parker Solar Probe
(PSP) will likely provide for the first time in-situ measurements in the
stalks of streamers at perihelia. It has been found from Ulysses/SWICS
observation that the signatures of the slow and fast solar wind could
be identified by heavy ion abundances ratio. UV observations close to
the Sun by the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO
during the 1996 minimum activity has demonstrated that the streamer
belt structure depends strongly on the observed emission lines, such
as H I Ly alpha or O VI ions. Subsequent analysis and 2D multi-fluid
modeling have shown that the variability of the heavy ion intensity
in various parts of the streamers is associated with regions of slow
solar wind outflow. We report the results of 3D multi-fluid models of
coronal streamer belt and the associated emissivities of H I Ly alpha,
O VI, and other heavy ions computed from the model results. We compare
the results of the models with solar minimum observations and find good
qualitative agreement. The 3D multi-fluid model allows computing the
important line-of-sight integration effects on the observed streamer
structure in the plane of the sky in the UV ion emission lines. The
model shows the associations between the heavy ion properties in the
cores and legs of streamers, and the slow solar wind outflow regions
in realistic streamer belt structure, as well as in more realistic
magnetic structure based on solar magnetogram boundary conditions. The
results could be useful for understanding future PSP data.

---------------------------------------------------------
Title: Nonlinear Evolution of Ion Kinetic Instabilities in the
Solar Wind
Authors: Ofman, Leon
2019SoPh..294...51O Altcode: 2019arXiv190311343O
In-situ observations of the solar wind (SW) plasma from 0.29 to 1
AU show that the protons and α particles are often non-Maxwellian,
with evidence of kinetic instabilities, temperature anisotropies,
differential ion streaming, and associated magnetic fluctuations
spectra. The kinetic instabilities in the SW multi-ion plasma can lead
to preferential heating of α particles and the dissipation of magnetic
fluctuation energy, affecting the kinetic and global properties of
the SW. Using for the first time a three-dimensional hybrid model,
where ions are modeled as particles using the Particle-In-Cell
(PIC) method and electrons are treated as fluid, we study the onset,
nonlinear evolution and dissipation of ion kinetic instabilities. The
Alfvén/ion cyclotron, and the ion drift instabilities are modeled in
the region close to the Sun (∼10 Rs). Solar wind expansion
is incorporated in the model. The model produces self-consistent
non-Maxwellian velocity distribution functions (VDFs) of unstable ion
populations, the associated temperature anisotropies, and wave spectra
for several typical SW instability cases in the nonlinear growth
and saturation stage of the instabilities. The 3D hybrid modeling of
the multi-ion SW plasma could be used to study the SW acceleration
region close to the Sun, which will be explored by the Parker Solar
Probe mission.

---------------------------------------------------------
Title: Understanding the Role of α Particles in Oblique Heliospheric
Shock Oscillations
Authors: Ofman, L.; Koval, A.; Wilson, L. B.; Szabo, A.
2019JGRA..124.2393O Altcode:
Recent observations by DSCOVR provide high temporal resolution (50
samples per second) magnetic vector field data that allows investigating
the details of oblique heliospheric shock oscillations. It was found
that some of these shocks exhibit magnetic oscillations, both downstream
and upstream of the shock front. The DSCOVR/MAG magnetic field data
are supplemented by an extensive database of low Mach number (M &lt; 3)
low-β (&lt;1) shock data observed by Wind albeit with lower temporal
resolution. Motivated by the observations, we use the 2.5D hybrid
model of the oblique shocks with α particles in addition to kinetic
protons and electron fluid. We model the properties of the oblique
shocks for a number of typical parameters found in observations and
study the effects of the shock parameters and the relative α particle
abundances on the properties of the shock magnetic field, density,
and velocity oscillations. We find the α particles "surf" on the
shock front and produce a wake of density oscillations. We examine
the details of the phase space of the ions as well as the ion velocity
distribution functions in various parts of the shock and study their
nonthermal properties. We determine the effects of the α particle
kinetic properties and abundances on the structure and dynamics of
the shock downstream oscillations for a range of parameters relevant
to low Mach number low-β heliospheric shocks.

---------------------------------------------------------
Title: UV core dimming in coronal streamer belt and the projection
effects
Authors: Abbo, L.; Giordano, S.; Ofman, L.
2019A&A...623A..95A Altcode:
During solar minimum activity, the coronal structure is dominated
by a tilted streamer belt, associated with the sources of the slow
solar wind. It is known that some UV coronal spectral observations
show a quite evident core dimming in heavy ions emission in quiescent
streamers. In this paper, our purpose is to investigate this phenomenon
by comparing observed and simulated UV coronal ion spectral line
intensities. First, we computed the emissivities and the intensities of
HI Lyα and OVI spectral lines starting from the physical parameters
of a time-dependent 3D three-fluid MHD model of the coronal streamer
belt. The model is applied to a tilted dipole (10°) solar minimum
magnetic structure. Next, we compared the results obtained from the
model in the extended corona (from 1.5 to 4 R⊙) to the
UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer
(UVCS) onboard SOHO during the minimum of solar activity (1996). We
investigate the line-of-sight integration and projection effects in
the UV spectroscopic observations, disentangled by the 3D multifluid
model. The results demonstrate that the core dimming in heavy ions
is produced by the physical processes included in the model (i.e.,
combination of the effects of heavy ion gravitational settling,
and energy exchange of the preferentially heated heavy ions through
the interaction with electrons and protons) but it is visible only
in some cases where the magnetic structure is simple, such as a
(tilted) dipole. Movie associated to Fig. 3 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201834299/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Collisionless relaxation of the ion ring distribution in
space plasma
Authors: Ofman, L.; Moore, T. E.; Glocer, A.
2019P&SS..165...75O Altcode:
Energetic processes often produce transversely-heated angular
distributions of the magnetized core (lowest energy) plasma. This
characteristic is found in solar wind ion pickup, resulting from
cometary or interstellar gas ionization, in Earths' ionosphere, and
with hot ions formed around the Space Transportation System during
gas releases. We investigate the thermalization of O+ ion
pickup using the 2.5D hybrid simulation method (with fluid electrons
and kinetic ions) of the ion pickup (ring) distributions, formed in
the auroral ionosphere, with a range of ring velocities and thermal to
magnetic pressure ratios. We find that in the unstable collisonless
regime the anisotropy of the non-thermal distribution produces the
ion-cyclotron instability, and the nonlinear relaxation is accompanied
by wave-particle scattering that results in an emitted power of EMIC
waves. We conclude that ionospheric pickup thermalization is slow due
to the small ring speed compared to the thermal and Alfvén speeds,
while in the solar wind and other space plasmas regions with larger
ion-ring velocity the collisionless relaxation and thermalization is
rapid in terms of O+ ion gyro-period.

---------------------------------------------------------
Title: Observed and simulated coronal UV lines at solar minimum
activity: The impact of the 3D tilted coronal streamer belt
Authors: Abbo, L.; Giordano, S.; Ofman, L.
2019NCimC..42...24A Altcode:
The aim of this study is to improve the knowledge of the slow solar
wind origin. In particular, we compute the emissivities and the
intensities of UV spectral lines starting from the physical parameters
of a time-dependent 3D three-fluid MHD model of the tilted coronal
streamer belt. The results obtained from the model are compared in
the extended corona (at 1.5 and 1.9 R _{⊙} to the UV spectroscopic
data from the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO
in the streamer belt during the minimum of solar activity (1996). The
discussion is focused on the importance of the projection effects due
to the integration along the line of sight in the coronal ultraviolet
observations of streamer core dimming.

---------------------------------------------------------
Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks
from the X8.2 Eruptive Flare on 2017 September 10
Authors: Jin, Meng; Liu, Wei; Cheung, Mark; Nitta, Nariaki; Manchester,
Ward; Ofman, Leon; Downs, Cooper; Petrosian, Vahe; Omodei, Nicola
2018csc..confE..66J Altcode:
As one of the largest flare-CME eruptions during solar cycle 24, the
2017 September 10 X8.2 flare event is associated with spectacular
global EUV waves that transverse almost the entire visible solar
disk, a CME with speed &gt; 3000 km/s, which is one of the fastest
CMEs ever recorded, and &gt;100 MeV Gamma-ray emission lasting for
more than 12 hours. All these unique observational features pose new
challenge on current numerical models to reproduce the multi-wavelength
observations. To take this challenge, we simulate the September 10 event
using a global MHD model (AWSoM: Alfven Wave Solar Model) within the
Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux
rope. We conduct detailed comparisons of the synthesized EUV images with
SDO/AIA observations of global EUV waves. We find that the simulated
EUV wave morphology and kinematics are sensitive to the orientation
of the initial flux rope introduced to the source active region. An
orientation with the flux-rope axis in the north-south direction
produces the best match to the observations, which suggests that EUV
waves may potentially be used to constrain the flux-rope geometry for
such limb or behind-the-limb eruptions that lack good magnetic field
observations. We also compare observed and simulated EUV intensities
in multiple AIA channels to perform thermal seismology of the global
corona. Furthermore, we track the 3D CME-driven shock surface in the
simulation and derive the time-varying shock parameters together with
the dynamic magnetic connectivity between the shock and the surface
of the Sun, with which we discuss the role of CME-driven shocks in
the long-duration Gamma-ray events.

---------------------------------------------------------
Title: A Truly Global Extreme Ultraviolet Wave from the SOL2017-09-10
X8.2+ Solar Flare-Coronal Mass Ejection
Authors: Liu, Wei; Jin, Meng; Downs, Cooper; Ofman, Leon; Cheung,
Mark C. M.; Nitta, Nariaki V.
2018csc..confE..40L Altcode:
We report SDO/AIA observations of an extraordinary global extreme
ultraviolet (EUV) wave triggered by the X8.2+ flare-CME eruption on 2017
September 10. This was one of the best EUV waves ever observed with
modern instruments, yet it was likely the last one of such magnitudes
of Solar Cycle 24 as the Sun heads toward the minimum. Its remarkable
characteristics include the following. (1) The wave was observed,
for the first time, to traverse the full-Sun corona over the entire
visible solar disk and off-limb circumference, manifesting a truly
global nature, owing to its exceptionally large amplitude, e.g., with
EUV enhancements by up to 300% at 1.1 Rsun from the eruption. (2)
This leads to strong transmissions (in addition to commonly observed
reflections) in and out of both polar coronal holes, which are usually
devoid of EUV waves. It has elevated wave speeds &gt;2000 km/s within
them, consistent with the expected higher fast-mode magnetosonic wave
speeds. The coronal holes essentially serve as new "radiation centers"
for the waves being refracted out of them, which then travel toward the
equator and collide head-on, causing additional EUV enhancements. (3)
The wave produces significant compressional heating to local plasma
upon its impact, indicated by long-lasting EUV intensity changes and
differential emission measure increases at higher temperatures (e.g.,
log T=6.2) accompanied by decreases at lower temperatures (e.g.,
log T=6.0). These characteristics signify the potential of such EUV
waves for novel magnetic and thermal diagnostics of the solar corona
on global scales.

---------------------------------------------------------
Title: A Truly Global Extreme Ultraviolet Wave from the SOL2017-09-10
X8.2+ Solar Flare-Coronal Mass Ejection
Authors: Liu, Wei; Jin, Meng; Downs, Cooper; Ofman, Leon; Cheung,
Mark C. M.; Nitta, Nariaki V.
2018ApJ...864L..24L Altcode: 2018arXiv180709847L
We report Solar Dynamics Observatory/Atmospheric Imaging Assembly
(SDO/AIA) observations of an extraordinary global extreme ultraviolet
(EUV) wave triggered by the X8.2+ flare-CME eruption on 2017 September
10. This was one of the best EUV waves ever observed with modern
instruments, yet it was likely the last one of such magnitudes of
Solar Cycle 24 as the Sun heads toward the minimum. Its remarkable
characteristics include the following. (1) The wave was observed,
for the first time, to traverse the full-Sun corona over the entire
visible solar disk and off-limb circumference, manifesting a truly
global nature, owing to its exceptionally large amplitude, e.g.,
with EUV enhancements by up to 300% at 1.1 {R}⊙ from
the eruption. (2) This leads to strong transmissions (in addition to
commonly observed reflections) in and out of both polar coronal holes
(CHs), which are usually devoid of EUV waves. It has elevated wave
speeds &gt;2000 {km} {{{s}}}-1 within the CHs, consistent
with the expected higher fast-mode magnetosonic wave speeds. The CHs
essentially serve as new “radiation centers” for the waves being
refracted out of them, which then travel toward the equator and collide
head-on, causing additional EUV enhancements. (3) The wave produces
significant compressional heating to local plasma upon its impact,
indicated by long-lasting EUV intensity changes and differential
emission measure increases at higher temperatures (e.g., {log}T=6.2)
accompanied by decreases at lower temperatures (e.g., {log}T=6.0). These
characteristics signify the potential of such EUV waves for novel
magnetic and thermal diagnostics of the solar corona on global scales.

---------------------------------------------------------
Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks
from the X8.2 Eruptive Flare on 2017 September 10
Authors: Jin, Meng; Liu, Wei; Cheung, Mark; Nitta, Nariaki; Manchester,
Ward; Ofman, Leon; Downs, Cooper; Petrosian, Vahe; Omodei, Nicola
2018shin.confE.207J Altcode:
As one of the largest flare-CME eruptions during solar cycle 24, the
2017 September 10 X8.2 flare event is associated with spectacular
global EUV waves that transverse almost the entire visible solar
disk, a CME with speed &gt; 3000 km/s, which is one of the fastest
CMEs ever recorded, and &gt;100 MeV Gamma-ray emission lasting for
more than 12 hours. All these unique observational features pose new
challenge on current numerical models to reproduce the multi-wavelength
observations. To take this challenge, we simulate the September 10 event
using a global MHD model (AWSoM: Alfven Wave Solar Model) within the
Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux
rope. We conduct detailed comparisons of the synthesized EUV images with
SDO/AIA observations of global EUV waves. We find that the simulated
EUV wave morphology and kinematics are sensitive to the orientation
of the initial flux rope introduced to the source active region. An
orientation with the flux-rope axis in the north-south direction
produces the best match to the observations, which suggests that EUV
waves may potentially be used to constrain the flux-rope geometry for
such limb or behind-the-limb eruptions that lack good magnetic field
observations. We also compare observed and simulated EUV intensities
in multiple AIA channels to perform thermal seismology of the global
corona. Furthermore, we track the 3D CME-driven shock surface in the
simulation and derive the time-varying shock parameters together with
the dynamic magnetic connectivity between the shock and the surface
of the Sun, with which we discuss the role of CME-driven shocks in
the long-duration Gamma-ray events.

---------------------------------------------------------
Title: Modeling Flare-Generated Quasi-Periodic Propagating Fast
Magnetosonic Waves Observed by SDO/AIA
Authors: Ofman, Leon; Liu, Wei
2018cosp...42E2492O Altcode:
Fast-propagating (phase speeds of ∼1000 km/s) quasi-periodic,
fast-mode wave (QFPs) accompanying many solar flares have been
discovered by SDO/AIA (Liu et al. 2011). They typically propagate in
funnel-like structures associated with the expanding magnetic field
topology of the active regions (ARs), driven by flare-pulsations
duration of impulsive phase. The fast magnetosonic waves provide
information on the magnetic, density, and temperature structure
through coronal seismology. While all previously reported QFP waves
originate from a single localized flaring source, we report the first
AIA observation and 3D MHD modeling of counter-QFPs originating from
two 'sympathetic' flares. The waves are excited at the two sources
associated with flare locations and connected by magnetic loops,
by time-depended forcing, constrained by the spatial (localized) and
quasi-periodic temporal evolution of the flare pulsations. With the
aid of 3D MHD modeling we investigate the excitation, propagation,
nonlinearity, and interaction of the counter-propagating waves for
a range of key parameters, such as the properties of the flaring
sources and the background magnetic topology. In addition to QFPs,
we find evidence of associated waves, such as trapped fast (kink)
modes in coronal loops, and slow mode waves propagating along the
AR loops. Our model results are in qualitative agreement with the
AIA-observed counter propagating waves providing the first direct
evidence of counter-propagating fast magnetosonic waves that carry
significant energy flux in low-corona magnetic structures.

---------------------------------------------------------
Title: The Best and Last of Solar Cycle 24 - The Global EUV Wave from
the X8 Flare-CME Eruption on 2017-Sept-10: SDO/AIA Observations and
Data-constrained Simulations
Authors: Liu, Wei; Ofman, Leon; Nitta, Nariaki; Cheung, Mark; Downs,
Cooper; Jin, Meng
2018cosp...42E2051L Altcode:
Global extreme ultraviolet (EUV) waves are commonly associated with
coronal mass ejections (CMEs) and flares. One particular EUV wave
that was triggered by the X8 flare-CME eruption on 2017 September
10 was extraordinary - one of the best EUV waves ever observed with
modern instruments (e.g., SDO/AIA and GOES/SUVI), yet likely the last
one of such magnitudes in Cycle 24 as the Sun heads toward the solar
minimum. We present here detailed analysis of SDO/AIA observations
of this event and comparison with high-fidelity, data-constrained MHD
simulations using the University of Michigan Alfven Wave Solar Model
(AWSoM). Observational highlights include: (1) The EUV wave traverses
almost the entire visible solar disk and circumference, manifesting its
truly global nature. This vast range is mainly due to the exceptionally
large wave amplitude, with EUV intensity changes by up to a factor of
3 (as opposed to, e.g., 30% for moderate events). (2) The large wave
amplitude also leads to the novel detection of strong transmission
components (in addition to commonly observed reflections) into and
through both polar coronal holes, at elevated apparent wave speeds up
to 2600 km/s. (3) The wave also produces significant heating, indicated
by long-lasting EUV intensity changes. As such, this EUV wave offers
unique magnetic and thermal diagnostics of the global, CME-spawning
corona. Our MHD simulations have largely reproduced the observed
features. We find that the simulated EUV wave morphology and kinematics
are sensitive to the orientation of the initial flux rope introduced to
the host active region. An orientation with the flux-rope axis in the
north-south direction produces the best match to the observations. This
suggests that EUV waves may potentially be used to constrain the
flux-rope geometry for such limb or behind-the-limb eruptions, whose
source-region magnetic fields cannot be directly observed, and thus
offer useful implications for space-weather predictions.

---------------------------------------------------------
Title: Motions in Prominence Barbs Observed on the Solar Limb
Authors: Kucera, T. A.; Ofman, L.; Tarbell, T. D.
2018ApJ...859..121K Altcode:
We analyze and discuss an example of prominence barbs observed on the
limb on 2016 January 7 by the Hinode/Solar Optical Telescope in Ca
II and Hα, the Interface Region Imaging Spectrograph, with slit jaw
images and Mg II spectral data, and the Solar Dynamics Observatory’s
Atmospheric Imaging Assembly. In the recent literature there has
been a debate concerning whether these features, sometimes referred
to as “tornadoes,” are rotating. Our data analysis provides no
evidence for systematic rotation in the barbs. We do find line-of-sight
motions in the barbs that vary with location and time. We also discuss
observations of features moving along the barbs. These moving features
are elongated parallel to the solar limb and tend to come in clusters
of features moving along the same or similar paths in the plane of
the sky during a period of 10 minutes to an hour, moving toward or
away from the limb. The motion may have a component along the line
of sight as well. The spectral data indicate that the features are
Doppler shifted. We discuss possible explanations for these features.

---------------------------------------------------------
Title: Effect of Transport Coefficients on Excitation of Flare-induced
Standing Slow-mode Waves in Coronal Loops
Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Solanki, Sami K.;
Davila, Joseph M.
2018ApJ...860..107W Altcode: 2018arXiv180503282W
Standing slow-mode waves have been recently observed in flaring loops by
the Atmospheric Imaging Assembly of the Solar Dynamics Observatory. By
means of the coronal seismology technique, transport coefficients in
hot (∼10 MK) plasma were determined by Wang et al., revealing that
thermal conductivity is nearly suppressed and compressive viscosity is
enhanced by more than an order of magnitude. In this study, we use 1D
nonlinear MHD simulations to validate the predicted results from the
linear theory and investigate the standing slow-mode wave excitation
mechanism. We first explore the wave trigger based on the magnetic
field extrapolation and flare emission features. Using a flow pulse
driven at one footpoint, we simulate the wave excitation in two types
of loop models: Model 1 with the classical transport coefficients and
Model 2 with the seismology-determined transport coefficients. We
find that Model 2 can form the standing wave pattern (within about
one period) from initial propagating disturbances much faster than
Model 1, in better agreement with the observations. Simulations of
the harmonic waves and the Fourier decomposition analysis show that
the scaling law between damping time (τ) and wave period (P) follows
τ ∝ P 2 in Model 2, while τ ∝ P in Model 1. This
indicates that the largely enhanced viscosity efficiently increases
the dissipation of higher harmonic components, favoring the quick
formation of the fundamental standing mode. Our study suggests that
observational constraints on the transport coefficients are important
in understanding both the wave excitation and damping mechanisms.

---------------------------------------------------------
Title: Quasi-periodic Counter-propagating Fast Magnetosonic Wave
Trains from Neighboring Flares: SDO/AIA Observations and 3D MHD
Modeling
Authors: Ofman, Leon; Liu, Wei
2018ApJ...860...54O Altcode: 2018arXiv180500365O
Since their discovery by the Solar Dynamics Observatory/Atmospheric
Imaging Assembly (AIA) in the extreme ultraviolet, rapid (phase
speeds of ∼1000 km s-1), quasi-periodic, fast-mode
propagating (QFP) wave trains have been observed accompanying many solar
flares. They typically propagate in funnel-like structures associated
with the expanding magnetic field topology of the active regions
(ARs). The waves provide information on the associated flare pulsations
and the magnetic structure through coronal seismology (CS). The reported
waves usually originate from a single localized source associated with
the flare. Here we report the first detection of counter-propagating
QFPs associated with two neighboring flares on 2013 May 22, apparently
connected by large-scale, trans-equatorial coronal loops. We present
the first results of a 3D MHD model of counter-propagating QFPs in
an idealized bipolar AR. We investigate the excitation, propagation,
nonlinearity, and interaction of the counter-propagating waves for a
range of key model parameters, such as the properties of the sources
and the background magnetic structure. In addition to QFPs, we also
find evidence of trapped fast- (kink) and slow-mode waves associated
with the event. We apply CS to determine the magnetic field strength
in an oscillating loop during the event. Our model results are in
qualitative agreement with the AIA-observed counter-propagating waves
and used to identify the various MHD wave modes associated with the
observed event, providing insights into their linear and nonlinear
interactions. Our observations provide the first direct evidence of
counter-propagating fast magnetosonic waves that can potentially lead
to turbulent cascade and carry significant energy flux for coronal
heating in low-corona magnetic structures.

---------------------------------------------------------
Title: Understanding the Role of Alpha Particles in Oblique
Heliospheric Shock Oscillations
Authors: Ofman, Leon; Koval, Andriy; Wilson, Lynn B., III; Szabo, Adam
2018tess.conf22302O Altcode:
Recent observations by DSCOVR provide high temporal resolution (50Hz)
magnetic vector field data that allows investigating the details
of oblique heliospheric shock oscillations. It was found that the
shocks exhibits oscillations, both, downstream and upstream of the
shock front. The DSCOVR/MAG magnetic field data is supplemented by
extensive database of low-Mach number (M&lt;3) low-β (β&lt;1) shock
data observed by WIND (Wilson et al. 2017) albeit with lower temporal
resolution. Motivated by the observations we develop 1D and 2D hybrid
models of the oblique shocks with alpha particles in addition to kinetic
protons and electron fluid. We model the properties of the oblique
shocks for a range of parameters found in observations and study the
effects of the shock parameters, such as the Mach number, electron
and ion beta, oblique angle, and the relative alpha abundances on the
properties of the shock oscillations. We find that the alphas surf on
the shock front and produce a wake. We examine the detail of the phase
space of the ions as well as the ion velocity distribution functions in
various parts of the shock and study their non-thermal properties. We
determine the effects of the alpha kinetic properties, and abundances
on the structure and dynamics of the shock oscillations for a range of
parameters relevant to low Mach number low-beta shocks. The results help
quantify the relation between the alpha particle physical parameters
and the magnetic properties of oblique shocks in the heliosphere.

---------------------------------------------------------
Title: Motions in Prominence Barbs Observed on the Solar Limb
Authors: Kucera, Therese Ann; Ofman, Leon; Tarbell, Theodore D.
2018tess.conf21059K Altcode:
We analyze and discuss an example of prominence barbs observed on the

---------------------------------------------------------
Title: Excitation and Damping of Standing Slow-Mode Waves in Flaring
Coronal Loops
Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Solanki, Sami K.;
Davila, Joseph M.
2018tess.conf22204W Altcode:
We analyze and model a flare-induced longitudinal oscillation event
detected by SDO/AIA. The magnetic field extrapolation and flare emission
features suggest that the wave event is generated by slipping and
null-point-type reconnections in a closed fan-spine magnetic topology,
and the large spine loop appears to be heated impulsively to the flare
temperature before the wave disturbances travel along it. By means of
the seismology technique, we determined the transport coefficients
in hot (about 10 MK) plasma, and found that thermal conductivity is
nearly suppressed and compressive viscosity is enhanced by more than
an order of magnitude from the observed wave properties. Using a flow
pulse injected at the loop's footpoint constrained by the observation,
we simulate the excitation of slow-mode waves in two types of 1D loop
models. We find that the models with the seismology-determined transport
coefficients can excite the standing waves quickly as observed, while
the models with the classical transport coefficients excites basically
the reflecting propagating waves. Simulations of harmonic waves and
the Fourier decomposition analysis reveal a scaling between damping
time and wave period as Td ~ P in the former type of models,
while Td ~ P2 in the latter type. This suggests
that anomalously large viscosity can efficiently enhance the dissipation
of higher harmonic components, favoring quick setup of the fundamental
standing mode. Our study indicates that observational constraints on
the transport coefficients are crucial in understanding both the wave
excitation and damping mechanisms.

---------------------------------------------------------
Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks
from the X8.2 Eruptive Flare on 2017 September 10
Authors: Jin, Meng; Liu, Wei; Cheung, Chun Ming Mark; Nitta, Nariaki;
Manchester, Ward; Ofman, Leon; Downs, Cooper; Petrosian, Vahe;
Omodei, Nicola
2018tess.conf31905J Altcode:
As one of the largest flare-CME eruptions during solar cycle 24, the
2017 September 10 X8.2 flare event is associated with spectacular
global EUV waves that transverse almost the entire visible solar
disk, a CME with speed &gt; 3000 km/s, which is one of the fastest
CMEs ever recorded, and &gt;100 MeV Gamma-ray emission lasting for
more than 12 hours. All these unique observational features pose new
challenge on current numerical models to reproduce the multi-wavelength
observations. To take this challenge, we simulate the September 10 event
using a global MHD model (AWSoM: Alfven Wave Solar Model) within the
Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux
rope. We conduct detailed comparisons of the synthesized EUV images with
SDO/AIA observations of global EUV waves. We find that the simulated
EUV wave morphology and kinematics are sensitive to the orientation
of the initial flux rope introduced to the source active region. An
orientation with the flux-rope axis in the north-south direction
produces the best match to the observations, which suggests that EUV
waves may potentially be used to constrain the flux-rope geometry for
such limb or behind-the-limb eruptions that lack good magnetic field
observations. We also compare observed and simulated EUV intensities
in multiple AIA channels to perform thermal seismology of the global
corona. Furthermore, we track the 3D CME-driven shock surface in the
simulation and derive the time-varying shock parameters together with
the dynamic magnetic connectivity between the shock and the surface
of the Sun, with which we discuss the role of CME-driven shocks in
the long-duration Gamma-ray events.

---------------------------------------------------------
Title: Kelvin-Helmholtz instability in a twisting solar polar coronal
hole jet observed by SDO/AIA
Authors: Zhelyazkov, I.; Zaqarashvili, T. V.; Ofman, L.; Chandra, R.
2018AdSpR..61..628Z Altcode: 2017arXiv170603703Z
We investigate the conditions under which the fluting (m = 2), m =
3 , and m = 12 magnetohydrodynamic (MHD) modes in a uniformly twisted
flux tube moving along its axis become unstable in order to model the
Kelvin-Helmholtz (KH) instability in a twisting solar coronal hole
jet near the northern pole of the Sun. We employed the dispersion
relations of MHD modes derived from the linearized MHD equations. We
assumed real wavenumbers and complex angular wave frequencies, namely
complex wave phse velocities. The dispersion relations were solved
numerically at fixed input parameters (taken from observational data)
and varying degrees of torsion of the internal magnetic field. It is
shown that the stability of the modes depends upon five parameters:
the density contrast between the flux tube and its environment, the
ratio of the external and internal axial magnetic fields, the twist
of the magnetic field lines inside the tube, the ratio of transverse
and axial jet's velocities, and the value of the Alfvén Mach number
(the ratio of the tube axial velocity to Alfvén speed inside the flux
tube). Using a twisting jet of 2010 August 21 by SDO/AIA and other
observations of coronal jets we set the parameters of our theoretical
model and have obtained that in a twisted magnetic flux tube of radius
of 9.8 Mm, at a density contrast of 0.474 and fixed Alfvén Mach
number of ≅ 0.76 , for the three MHD modes there exist instability
windows whose width crucially depends upon the internal magnetic field
twist. It is found that for the considered modes an azimuthal magnetic
field of 1.3 - 1.4 G (computed at the tube boundary) makes the width
of the instability windows equal to zero, that is, it suppress the
KH instability onset. On the other hand, the times for developing KH
instability of the m = 12 MHD mode at instability wavelengths between
15 and 12 Mm turn out to be in the range of 1.9 - 4.7 min that is in
agreement with the growth rates estimated from the temporal evolution
of the observed unstable jet's blobs in their initial stage.

---------------------------------------------------------
Title: Excitation of flare-induced waves in coronal loops and the
effects of radiative cooling
Authors: Provornikova, Elena; Ofman, Leon; Wang, Tongjiang
2018AdSpR..61..645P Altcode: 2017arXiv170604219P
EUV imaging observations from several space missions (SOHO/EIT,
TRACE, and SDO/AIA) have revealed a presence of propagating
intensity disturbances in solar coronal loops. These disturbances are
typically interpreted as slow magnetoacoustic waves. However, recent
spectroscopic observations with Hinode/EIS of active region loops
revealed that the propagating intensity disturbances are associated
with intermittent plasma upflows (or jets) at the footpoints which
are presumably generated by magnetic reconnection. For this reason,
whether these disturbances are waves or periodic flows is still being
studied. This study is aimed at understanding the physical properties
of observed disturbances by investigating the excitation of waves
by hot plasma injections from below and the evolution of flows and
wave propagation along the loop. We expand our previous studies based
on isothermal 3D MHD models of an active region to a more realistic
model that includes full energy equation accounting for the effects
of radiative losses. Computations are initialized with an equilibrium
state of a model active region using potential (dipole) magnetic field,
gravitationally stratified density and temperature obtained from the
polytropic equation of state. We model an impulsive injection of hot
plasma into the steady plasma outflow along the loops of different
temperatures, warm (∼1 MK) and hot (∼6 MK). The simulations show
that hot jets launched at the coronal base excite slow magnetoacoustic
waves that propagate to high altitudes along the loops, while the
injected hot flows decelerate rapidly with heights. Our results
support that propagating disturbances observed in EUV are mainly
the wave features. We also find that the effect of radiative cooling
on the damping of slow-mode waves in 1-6 MK coronal loops is small,
in agreement with the previous conclusion based on 1D MHD models.

---------------------------------------------------------
Title: Energy release from a stream of infalling prominence debris
on 2011 September 7-8
Authors: Inglis, A. R.; Gilbert, H. R.; Ofman, L.
2017AGUFMSH43A2805I Altcode:
In recent years high-resolution and high-cadence EUV imaging
has revealed a new phenomenon, impacting prominence debris, where
prominence material from failed or partial eruptions can impact the
lower atmosphere and release energy. We present a clear example of
this phenomenon occurring on 2011 September 7-8. The initial eruption
of prominence material was associated with an X1.8-class flare from
AR11283, occurring at 22:30 UT on 2011 September 7, resulting in a
semi-continuous stream of this material returning to the solar surface
between 00:20 - 00:40 UT on 2011 September 8. A substantial area remote
from the original active region experienced brightening in multiple EUV
channels observed by SDO/AIA. Using the differential emission measure,
we estimated the energetic properties of this event. We found that
the radiated energy of the impacted plasma was of order 10^27 ergs,
while the upper limit on the thermal energy peaked at 10^28 ergs. Based
on these estimates we were able to determine the mass content of the
debris to be in the range 2x10^14 &lt; m &lt; 2x10^15 g. Given typical
promimence masses, the likely debris mass is towards the lower end of
this range. This clear example of a prominence debris event shows that
significant energy release takes place during these events, and that
such impacts may be used as a novel diagnostic tool for investigating
prominence material properties.

---------------------------------------------------------
Title: Three-dimensional hybrid modeling of ion kinetic instabilities
in space plasma
Authors: Ofman, L.
2017AGUFMSH33A2759O Altcode:
Ion kinetic instabilities in space plasma are believed to play an
imprortant role in energy transport, heating, dissipation of turbulence,
as well as in generating of spectrum of magnetic fluctuations in
the kinetic frequency range. The velocity distribution functions
(VDFs) of unstable ion populations are generally non-Maxwellian
and provide the free energy source that drives the waves. The
VDFs were measured in-situ by satellites such as Helios, WIND, and
would be obtained in the future Parkers' Solar Probe close to the
Sun. In particular, temperature anisotropy provides a measure of VDF
non-equilibroum structure, that together with parallel-beta determine
the threshold of kinetic instabilities, such as mirror, ion-cyclotron,
and firehose. Drifting population of alphas with respect to protons
lead to the magnetosonic instability. So far, these isntabilities
were studied primaraly using 1.5D or 2.5D particle-in-cell (PIC)
or hybrid models (where electrons are modeled as a fluid), i.e., in
1 or 2 spatial dimensions with 3 components of velocity and magnetic
field. I will present the results of recent full 3D hybrid models that
studies these instabilities for heliospheric conditions and compare
to previous modeling results. I will discuss the agreement and the
differences between the 3D and more approximate models of the VDFs,
the magnetic fluctuations spectra, and the temporal evolution of the
anisotropy for typical instabilities relevant for space plasma. I will
duscuss the use of the modeled VDFs for diagnostic of the physical
processes that lead to space plasma energization from the observed
VDFs in the heliospheric and magnetospheric plasma.

---------------------------------------------------------
Title: Energy Release in the Solar Atmosphere from a Stream of
Infalling Prominence Debris
Authors: Inglis, A. R.; Gilbert, H. R.; Ofman, L.
2017ApJ...847L..17I Altcode: 2017arXiv170801555I
Recent high-resolution and high-cadence extreme-ultraviolet (EUV)
imaging has revealed a new phenomenon, impacting prominence debris,
where prominence material from failed or partial eruptions can impact
the lower atmosphere, releasing energy. We report a clear example of
energy release and EUV brightening due to infalling prominence debris
that occurred on 2011 September 7-8. The initial eruption of material
was associated with an X1.8-class flare from AR 11283, occurring at
22:30 UT on 2011 September 7. Subsequently, a semicontinuous stream
of this material returned to the solar surface with a velocity v &gt;
150 km s-1, impacting a region remote from the original
active region between 00:20 and 00:40 UT on 2011 September 8. Using
the Solar Dynamics Observatory/Atmospheric Imaging Assembly, the
differential emission measure of the plasma was estimated throughout
this brightening event. We found that the radiated energy of the
impacted plasma was {L}{rad}∼ {10}27 erg,
while the thermal energy peaked at ∼1028 erg. From
this we were able to determine the mass content of the debris to be
in the range 2× {10}14&lt; m&lt; 2× {10}15
g. Given typical prominence masses, the likely debris mass is toward
the lower end of this range. This clear example of a prominence debris
event shows that significant energy release takes place during these
events and that such impacts may be used as a novel diagnostic tool
for investigating prominence material properties.

---------------------------------------------------------
Title: Effects of transport coefficients on excitation of
flare-induced standing slow-mode waves
Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph
2017SPD....48.0202W Altcode:
The flare-excited longitudinal intensity oscillations in hot flaring
loops have been recently detected by SDO/AIA, and interpreted as the
slow-mode standing waves. By means of the seismology technique we
have, for the first time, determined the transport coefficients in the
hot (&gt;9 MK) flare plasma, and found that thermal conductivity is
suppressed by at least 3 times and viscosity coefficient is enhanced
by a factor of 15 as the upper limit (Wang et al. 2015, ApJL, 811,
L13). In this presentation, we first discuss possible causes for
conduction suppression and viscosity enhancements. Then we use the
nonlinear MHD simulations to validate the seismology method that is
based on linear analytical analysis, and demonstrate the inversion
scheme for determining transport coefficients using numerical parametric
study. Finally, we show how the seismologically-determined transport
coefficients are crucial for understanding the excitation of the
observed standing slow-mode waves in coronal loops and the heating of
the loop plasma by a footpoint flare.

---------------------------------------------------------
Title: Realistic Modeling of Fast MHD Wave Trains in Coronal Active
Regions
Authors: Ofman, Leon; Sun, Xudong
2017SPD....4840503O Altcode:
Motivated by recent SDO/AIA observations we have developed realistic
modeling of quasi-periodic, fast-mode propagating MHD wave trains (QFPs)
using 3D MHD model initiated with potential magnetic field extrapolated
from the solar coronal boundary. Localized quasi-periodic pulsations
associated with C-class flares that drive the waves (as deduced from
observations) are modeled with transverse periodic displacement of
magnetic field at the lower coronal boundary. The modeled propagating
speed and the form of the wave expansions matches the observed fast
MHD waves speed &gt;1000 km/s and topology. We study the parametric
dependence of the amplitude, propagation, and damping of the waves for
a range of key model parameters, such as the background temperature,
density, and the location of the flaring site within the active
region. We investigate the interaction of multiple QFP wave trains
excited by adjacent flaring sources. We use the model results to
synthesize EUV intensities in multiple AIA channels and obtain the
model parameters that best reproduce the properties of observed QFPs,
such as the recent DEM analysis. We discuss the implications of our
modeling results for the seismological application of QFPs for the
diagnostic of the active region field, flare pulsations, end estimate
the energy flux carried by the waves.

---------------------------------------------------------
Title: Fast-mode Coronal EUV Wave Trains Associated with Solar Flares
and CMEs
Authors: Liu, Wei; Ofman, Leon; Downs, Cooper; Karlicky, Marian;
Chen, Bin
2017SPD....48.0401L Altcode:
As a new observational phenomenon, Quasi-periodic, Fast Propagating EUV
wave trains (QFPs) are fast-mode magnetosonic waves closely related
to quasi-periodic pulsations commonly detected in solar flares
(traditionally with non-imaging observations). They can provide
critical clues to flare energy release and serve as new tools for
coronal seismology. We report recent advances in observing and modeling
QFPs, including evidence of heating and cooling cycles revealed with
differential emission measure (DEM) analysis that are consistent
with alternating compression and rarefaction expected for magnetosonic
waves. Through a statistical survey, we found a preferential association
of QFPs with eruptive flares (with CMEs) rather than confined flares
(without CMEs). We also identified some correlation with quasi-periodic
radio bursts observed at JVLA and Ondrejov observatories. We will
discuss the implications of these results and the potential roles of
QFPs in coronal heating and energy transport.

---------------------------------------------------------
Title: Dissipation of kinetic instabilities in proton-alpha solar
wind plasma
Authors: Ofman, Leon; Roberts, D. A.; Vinas, A. -F.
2017shin.confE.114O Altcode:
Collisionless dissipation of kinetic instabilities plays an important
role in shaping the properties of the solar wind plasma, as evident from
WIND, Helios, ACE, and other satellite data. We present the results
of 2.5D and 3D hybrid modeling or the proton-alpha solar wind plasma
(with fluid electrons) and study parametrically the dissipation of
magnetosonic drift and temperature anisotropy driven instabilities. We
demonstrate the role of the background solar wind density and velocity
inhomogeneities on the collisionless anisotropic heating and cooling of
the plasma ion components. We find that the anisotropic plasma heating
and the associated non-Maxwellian velocity distribution functions
(VDFs) are affected by the background inhomogenities. We demonstrate
the generation and evolution of the parallel and obliquely propagating
kinetic wave spectra by the instabilities, and the associated dispersion
relations. We discuss the relation of our modeling results to the
kinetic dissipation processes observed in the solar wind.

---------------------------------------------------------
Title: The effects of inhomogeneous proton-α drifts on the heating
of the solar wind
Authors: Ofman, L.; Viñas, A. F.; Roberts, D. A.
2017JGRA..122.5839O Altcode:
Previous modeling studies have demonstrated that waves and
super-Alfvénic drift can lead to perpendicular preferential heating of
the α particles with respect to protons. Using 2.5-D hybrid model of
the solar wind α-proton plasma, we study the effects of inhomogeneous
(across the magnetic field) background streaming focusing on the fast
solar wind. We explore the effects of an initial relative, inhomogeneous
ion drift on the perpendicular ion heating and cooling and consider
the effects of solar wind expansion. We study the spectrum of the
magnetic fluctuations in the inhomogeneous background solar wind
and demonstrate the generation of oblique waves and their effects on
enhanced resonant anisotropic ion heating. The model reproduces the
typical ion temperature anisotropy values seen in observations. Using
our model, we find that inhomogeneous super-Alfvénic ion drift in the
plasma generates significant power of oblique waves in the solar wind
plasma, in addition to enhanced heating compared to the nondrifting
populations. We demonstrate the effects of various inhomogeneity
profiles and regions of the drift on the ion anisotropic heating in
super-Alfvénic and near-Alfvénic drifts. We find that the cooling
effect due to the solar wind expansion is not significant when
super-Alfvénic drifts are considered.

---------------------------------------------------------
Title: Growth and nonlinear saturation of electromagnetic ion
cyclotron waves in multi-ion species magnetospheric plasma
Authors: Ofman, L.; Denton, R. E.; Bortnik, J.; An, X.; Glocer, A.;
Komar, C.
2017JGRA..122.6469O Altcode:
The growth and saturation of electromagnetic ion cyclotron (EMIC)
waves is essential to the magnetospheric dynamics. Determining and
isolating the effects of multiple ion parameters such as temperatures,
anisotropies, and relative abundances is important for quantifying
these processes in the magnetospheric plasma. In order to study these
process, we utilize a 2.5-D hybrid model (where ions are modeled
with the particle-in-cell (PIC) method, and electrons are modeled as
background neutralizing fluid) to study the nonlinear electromagnetic
wave-particle interactions of hot H+, cold H+,
cold He+, and cold or hot O+ ions for a broad
range of typical magnetospheric parameters. The excitation of EMIC
waves is driven by the temperature anisotropy of hot H+
in our model. As a result, we quantify the parametric dependence of
the linear growth, the nonlinear saturation level of perpendicular
magnetic fluctuations, and the temporal evolution of the ion temperature
anisotropies. We establish the relation between key plasma parameters
and the saturated EMIC wave power, using either power law fits or a
nonlinear regression method. We construct the dispersion relation of
the waves using the results of the model and investigate the energy
content in the various branches of the dispersion (k∥-ω
space), showing that the different modes can generate wave power
in different regions of k space. We find that large O+
concentration reduces the growth and saturated amplitude of the waves;
but the waves are less sensitive to the temperature of the O+
in the temperature range relevant to the magnetosphere.

---------------------------------------------------------
Title: Hα Doppler shifts in a tornado in the solar corona
Authors: Schmieder, B.; Mein, P.; Mein, N.; Levens, P. J.; Labrosse,
N.; Ofman, L.
2017A&A...597A.109S Altcode: 2016arXiv161202232S
Context. High resolution movies in 193 Å from the Atmospheric
Imaging Assembly (AIA) on the Solar Dynamic Observatory (SDO)
show apparent rotation in the leg of a prominence observed during
a coordinated campaign. Such structures are commonly referred to as
tornadoes. Time-distance intensity diagrams of the AIA data show the
existence of oscillations suggesting that the structure is rotating. Aims: The aim of this paper is to understand if the cool plasma
at chromospheric temperatures inside the tornado is rotating around
its central axis. Methods: The tornado was also observed in Hα
with a cadence of 30 s by the MSDP spectrograph, operating at the Solar
Tower in Meudon. The MSDP provides sequences of simultaneous spectra
in a 2D field of view from which a cube of Doppler velocity maps is
retrieved. Results: The Hα Doppler maps show a pattern with
alternatively blueshifted and redshifted areas of 5 to 10” wide. Over
time the blueshifted areas become redshifted and vice versa, with
a quasi-periodicity of 40 to 60 min. Weaker amplitude oscillations
with periods of 4 to 6 min are superimposed onto these large period
oscillations. Conclusions: The Doppler pattern observed in
Hα cannot be interpreted as rotation of the cool plasma inside the
tornado. The Hα velocity observations give strong constraints on the
possible interpretations of the AIA tornado.

---------------------------------------------------------
Title: Inference of magnetic field in the coronal streamer invoking
kink wave motions generated by multiple EUV waves
Authors: Srivastava, A. K.; Singh, Talwinder; Ofman, Leon; Dwivedi,
Bhola N.
2016MNRAS.463.1409S Altcode: 2016arXiv160600337S; 2016MNRAS.tmp.1136S
We analyse the observations from Solar TErrestrial RElations
Observatory (STEREO) of an oscillating coronal streamer. STEREO-B
Extreme Ultraviolet Imaging (EUVI) temporal data on 2012 March 7 show
an evolution of two consecutive EUV waves that interact with footpoint
of a coronal streamer clearly evident in the co-spatial and co-temporal
STEREO-B/COR-1 observations. The waves are observed in the STEREO-B/EUVI
too, and its apparent energy exchange with coronal streamer generates
kink oscillations. We apply the methodology of magnetohydrodynamic
(MHD) seismology of the observed waves and determine the magnetic
field profile of the coronal streamer. In particular, we estimate
the phase velocities of the kink wave perturbations by tracking them
at different heights. We also estimate electron densities inside and
outside the streamer using spherically symmetric inversion of polarized
brightness images in STEREO-B/COR-1. We detect two large-scale kink
wave oscillations that diagnose exponentially decaying radial profiles
of magnetic field in streamer up to 3 solar radii. Within the limit
of observational and systematic uncertainties, we find that magnetic
field of streamer varies slowly at various heights, although its
nature always remains exponentially decaying with height. It is seen
that during evolution of second kink motion in streamer, it increases
in brightness (thus mass density), and also in areal extent slightly,
which may be associated with decreased photospheric magnetic flux at
footpoint of streamer. As a result, magnetic field profile produced
by second kink wave is reduced within streamer compared to the one
diagnosed by the first one.

---------------------------------------------------------
Title: Observations and Modeling of Plasma Waves in the Solar
Atmosphere
Authors: Liu, W.; Ofman, L.; Downs, C.
2016AGUFMSH14B..01L Altcode:
The solar atmosphere, especially the extended corona, provides rich
observations of magnetohydrodynamic (MHD) waves and plasma waves in
general. Such waves can be used as seismological tools to probe the
physical conditions of the medium in which they travel, such as the
coronal magnetic field and plasma parameters. Recent high-resolution
imaging and spectroscopic observations in extreme ultraviolet (EUV)
by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
Observatory (SDO) and in UV by the Interface Region Imaging Spectrograph
(IRIS) have opened a new chapter in understanding these waves and
in utilizing them for coronal seismology. We will review such new
observations of two intimately related phenomena - global EUV waves
(so-called "EIT waves") associated with coronal mass ejections (CMEs)
and quasi-periodic, fast-mode magnetosonic wave trains associated with
flares. We will focus on the generation and propagation of global
EUV waves and their interaction with coronal structures, as well
as the correlation of AIA-detected fast-mode wave trains with flare
pulsations seen from radio to hard X-ray wavelengths. We will also
present recent MHD modeling efforts in reproducing these waves using
realistic, observationally-driven simulations. We will discuss the
roles of such waves in energy transport within the solar atmosphere
and in their associated CME/flare eruptions.

---------------------------------------------------------
Title: Fundamental Physics of the Slow Solar Wind - What do we Know?
Authors: Ofman, L.; Abbo, L.; Antiochos, S. K.; Hansteen, V. H.;
Harra, L.; Ko, Y. K.; Lapenta, G.; Li, B.; Riley, P.; Strachan, L.;
von Steiger, R.; Wang, Y. M.
2016AGUFMSH42A..01O Altcode:
Fundamental physical properties of the slow solar wind (SSW), such
as density, temperature, outflow speed, heavy ion abundances and
charges states were obtained from in-situ measurements at 1AU in
the past from WIND, ACE, and other spacecraft. Plasma and magnetic
field measurement are available as close as 0.3 AU from Helios data,
Spektr-R, and MESSENGER spacecraft. Remote sensing spectroscopic
measurements are available in the corona and below from SOHO/UVCS,
Hinode, and other missions. One of the major objectives of the Solar
Orbiter and Solar Probe Plus missions is to study the sources of the
SSW close to the Sun. The present state of understanding of the physics
of the SSW is based on the combination of the existing observations,
theoretical and numerical 3D MHD and multi-fluid models, that connect
between the SSW sources in the corona and the heliosphere. Recently,
hybrid models that combine fluid electrons and kinetic ions of the
expanding solar wind were developed, and provide further insights of the
local SSW plasma heating processes that related to turbulent magnetic
fluctuations spectra and kinetic ion instabilities observed in the
SSW plasma. These models produce the velocity distribution functions
(VDFs) of the protons and heavier ions as well as the ion anisotropic
temperatures. I will discuss the results of the above observations
and models, and review the current status of our understanding of
the fundamental physics of the SSW. I will review the open questions,
and discuss how they could be addressed with near future observations
and models.

---------------------------------------------------------
Title: Growth and Nonlinear Saturation of Electromagnetic Ion
Cyclotron Waves In Multi-Ion Species Magnetospheric Plasma: 2.5D
Hybrid Modeling
Authors: Ofman, L.; Denton, R. E.; Bortnik, J.; Glocer, A.; Roman,
N. M.
2016AGUFMSM31A2458O Altcode:
We investigate the collisionless interactions of a multiple ion
species magnetospheric plasma and study the parametric dependence of
electromagnetic ion cyclotron (EMIC) wave growth and saturation. We
utilize a 2.5D hybrid model (where ions are treated as particles
using the PIC method, and electrons are modeled as a background
neutralizing fluid) to study the nonlinear electromagnetic wave-particle
interactions of cold H+, hot H+, He+, and O+ ions for a broad range
of typical magnetospheric parameters. The excitation of EMIC waves
is driven primarily by the temperature anisotropy of hot H+. We vary
(independently) the initial parallel beta, temperature anisotropy,
and concentrations of the hot H+ component, He+, and O+ ions in five
sweeps of these parameters. The effects of O+ density and temperature
are considered in two additional parameters sweeps. We investigate
the parametric dependence of the initial brief linear growth, the
nonlinear saturation level of perpendicular magnetic fluctuations, and
the temporal evolution of the ion temperature anisotropies. We construct
the dispersion relation of the waves using the results of the model
at several times during the evolution at the initial growth stage and
at the nonlinear saturated state and investigate the energy content in
the various branches of the dispersion (in k||-ω space). We determine
the distribution of energy in the left-hand polarized ion-resonant and
the right-hand modes. The results are compared and contrasted with the
predictions of linear Vlasov theory. We discuss the implications of our
results for the physics of the inner magnetosphere and radiation belts.

---------------------------------------------------------
Title: Power law "thermalization" of ion pickup and ionospheric
outflows
Authors: Moore, T. E.; Ofman, L.; Glocer, A.; Gershman, D. J.;
Khazanov, G. V.; Paterson, W. R.
2016AGUFMSM51F2564M Altcode:
One observed feature of ionospheric outflows is that the active
ion heating processes produce power law tails of the core plasma
velocity distribution, as well as transverse or conic peaks in the
angular distributions. This characteristic is shared with hot ion
distributions produced by ion pickup in the solar wind, resulting from
cometary or interstellar gas ionization, and with hot ions observed
around the Space Transportation System during gas releases. We
revisit relevant observations and consider the hypothesis that the
ion pickup thermalization process tends to produce power law (𝛋)
energy distributions, using a simulation of the instability of a simple
pickup (ring) distribution. Simulation results are derived for cases
representative of both solar wind pickup, where ion velocities exceed
the local Alfvén speed, and ionospheric pickup, where the local
Alfvén speed exceeds ion velocities. The sub-Alfvenic pickup ring
distribution appears to have a slow growth rate (per ion gyro period),
that is, the instability evolves more slowly in the latter case than
in the former. Implications for ionospheric outflow are discussed.

---------------------------------------------------------
Title: Slow Solar Wind: Observations and Modeling
Authors: Abbo, L.; Ofman, L.; Antiochos, S. K.; Hansteen, V. H.;
Harra, L.; Ko, Y. -K.; Lapenta, G.; Li, B.; Riley, P.; Strachan, L.;
von Steiger, R.; Wang, Y. -M.
2016SSRv..201...55A Altcode: 2016SSRv..tmp...34A
While it is certain that the fast solar wind originates from coronal
holes, where and how the slow solar wind (SSW) is formed remains an
outstanding question in solar physics even in the post-SOHO era. The
quest for the SSW origin forms a major objective for the planned future
missions such as the Solar Orbiter and Solar Probe Plus. Nonetheless,
results from spacecraft data, combined with theoretical modeling, have
helped to investigate many aspects of the SSW. Fundamental physical
properties of the coronal plasma have been derived from spectroscopic
and imaging remote-sensing data and in situ data, and these results
have provided crucial insights for a deeper understanding of the origin
and acceleration of the SSW. Advanced models of the SSW in coronal
streamers and other structures have been developed using 3D MHD and
multi-fluid equations.

---------------------------------------------------------
Title: Dynamic Mapping of Prominence Activity
Authors: Thompson, Barbara J.; Gilbert, Holly R.; Kirk, Michael
S.; Mays, M. Leila.; Ofman, Leon; Uritsky, Vadim; Wyper, Peter;
Hovis-Afflerbach, Beryl
2016usc..confE..82T Altcode:
We present the results of a prominence mapping effort designed to
extract the dynamics of erupting prominences. The material from
partially erupting prominences can fall back to the sun, tracing
out the topology of the mid- and post-eruptive corona. One question
involving the range of observed behavior is the role of magnetic
field topology and evolution in determining the motion of the erupting
prominence material. A variable-g ballistic approximation is applied
to study the motion of the material, using the deviations from constant
angular momentum as a means of quantifying the local Lorentz (and other)
forces on each piece of material. Variations in dynamic behavior can be
traced back to changes in the local magnetic field and the formation
of instabilities such as Rayleigh-Taylor. We discuss the use of the
prominence trajectories as a means of diagnosing eruptive topologies.

---------------------------------------------------------
Title: Flare-associated Fast-mode Coronal Wave Trains Detected by
SDO/AIA: Recent Observational Advances
Authors: Liu, Wei; Ofman, Leon; Downs, Cooper; Cheung, Mark; De
Pontieu, Bart
2016usc..confE.107L Altcode:
Quasi-periodic Fast Propagating wave trains (QFPs) are new observational
phenomena discovered by SDO/AIA in extreme ultraviolet (EUV). They
were interpreted as fast-mode magnetosonic waves using MHD modeling,
and also found to be closely related to quasi-periodic pulsations
in solar flare emission ranging from radio to X-ray wavelengths. The
significance of QFPs lies in their diagnostic potential (and possibly
in flare energy transport), because they can provide critical clues to
flare energy release and serve as new tools for coronal seismology. In
this presentation, we report recent advances in observing QFPs. In
particular, using differential emission measure (DEM) inversion,
we found clear evidence of heating and cooling cycles that are
consistent with alternating compression and rarefaction expected for
magnetosonic wave pulses. We also found that different local magnetic
and plasma environments can lead to two distinct types of QFPs located
in different spatial domains with respect to their accompanying coronal
mass ejections (CMEs). More interestingly, from a statistical survey of
over 100 QFP events, we found a preferential association with eruptive
flares rather than confined flares. We will discuss the implications
of these results and the potential roles of QFPs in coronal heating,
energy transport, and solar eruptions.

---------------------------------------------------------
Title: Determination of transport coefficients from flare-excited
standing slow-mode waves observed by SDO/AIA
Authors: Wang; Tongjiang; Ofman, Leon; Davila, Joseph M.
2016usc..confE..36W Altcode:
The flare-excited longitudinal intensity oscillations in hot flaring
loops have been recently detected by SDO/AIA in 94 and 131 Angstrom
bandpasses. These oscillations show similar physical properties (such
as period, decay time, and trigger) as the Doppler shift oscillations
previously detected by the SOHO/SUMER spectrometer in flare lines formed
above 6 MK, which were mostly interpreted as the slow-mode standing
waves. By applying the coronal seismology method we have, for the first
time, found quantitative evidence of thermal conduction suppression in
a hot (&gt;9 MK) flare-heated loop with SDO/AIA (Wang et al. 2015, ApJL,
811, L13). This result has significant implications in two aspects. The
first aspect is that the conduction suppression suggests the need of
greatly enhanced compressive viscosity to interpret the observed strong
wave damping. The second aspect is that the conduction suppression
provides a reasonable mechanism for explaining the long-duration events
where the hot plasma detected in X-rays or EUV in many flares cools much
slower than expected from the classical Spitzer conductive cooling. In
this presentation, we first review the observational results of the
event, and then discuss possible causes for conduction suppression
and viscosity enhancements. In addition, we will use the nonlinear
MHD simulations to validate the seismology method that is based on
linear analytical analysis, and demonstrate the inversion scheme
for determining transport coefficients using numerical parametric
study. Finally, as an application of our analysis, we will demonstrate
how the observationally-constrained transport coefficients are crucial
in providing a self-consistent explanation for the rapid excitation
of standing slow-mode waves in a coronal loop by a footpoint flare.

---------------------------------------------------------
Title: Coronal and Flare Diagnostic with SDO/AIA-discovered Fast
MHD Wave Trains in Active Regions
Authors: Ofman, Leon; Liu, Wei
2016usc..confE.106O Altcode:
Recently, SDO/AIA discovered quasi-periodic, fast-mode propagating
MHD wave trains (QFPs) that propagate at high speeds of more than 1000
km/s. The waves provide a new diagnostic tool for coronal seismology
that includes information on the flare energy release and the magnetic
structure of the active regions. Many events are now available in a
statistical study. However, for improved accuracy of coronal seismology,
3D MHD modeling is required and simple wave-mode analysis may be
insufficient. We present new results of observationally constrained
models of QFPs using our recently upgraded radiative, thermally
conductive, visco-resistive 3D MHD code. The waves are excited by
time-depended boundary conditions constrained by the spatial (localized)
and quasi-periodic temporal evolution of a C-class flare typically
associated with QFPs, and produce observable density and temperature
fluctuations. We investigate parametrically the excitation, propagation,
and damping of the waves for a range of key model parameters, such
as the background temperature, density, magnetic field structure,
and the location of the flaring site within the active region. We
synthesize EUV intensities in multiple AIA channels and then obtain the
model parameters that best reproduce the properties of observed QFPs,
such as the recent DEM analysis. We discuss the implications of our
modeling results for the seismological application of QFPs for the
diagnostic of the active region field and flare pulsations.

---------------------------------------------------------
Title: Dynamic Mapping of Prominence Activity
Authors: Thompson, Barbara J.; Uritsky, Vadim; Ofman, Leon
2016shin.confE.141T Altcode:
We present the results of a prominence mapping effort designed to
extract the dynamics of both erupting and quiescent prominences. The
material from partially erupting prominences can fall back to the sun,
tracing out the topology of the post-eruptive corona. A variable-g
ballistic approximation is applied to study the motion of the material,
using the deviations from constant angular momentum as a means of
quantifying the local Lorentz (and other) forces on each piece of
material. Variations in dynamic behavior can be traced back to changes
in the local magnetic field and the formation of instabilities such
as Rayleigh-Taylor.

---------------------------------------------------------
Title: Brightenings Caused by Falling Filament Material on 2011
September 7
Authors: Gilbert, Holly; Inglis, Andrew; Mays, M. Leila; Ofman, Leon;
Provornikova, Elena
2016shin.confE.138G Altcode:
Solar filaments exhibit a range of eruptive-like dynamic activity from
the full, or partial, eruption of the filament mass and surrounding
magnetic structure, as a CME, to a fully confined dynamic evolution or
"failed" eruption. On 2011 September 7, a partial eruption of a filament
was observed by SDO and STEREO, generating a substantial stream of
returning filament material that exhibited a strong interaction with
the solar surface. Similarly to the recently studied 2011 June 7 event,
the impact sites show clear evidence of brightening in the observed
EUV wavelengths due to energy release by the impact. We explore two
plausible physical mechanisms that would cause such brightening:
heating of the plasma due to the kinetic energy of the impacting
material - compression of the plasma, or reconnection between the
magnetic field of the low-laying loops with the field carried by the
impacting material, or combination thereof. By analyzing the emission
of the brightenings in several SDO/AIA wavelengths, and comparing the
kinetic energy of the impacting material to the radiative energy we
provide clues for the dominant mechanism of energy release involved in
the observed brightenings. We compare this event to another in which
we performed the same analysis (2011 June 7) where we determined that
compression was the dominant mechanism.

---------------------------------------------------------
Title: Motions in Prominence Barbs as observed by Hinode/SOT and IRIS
Authors: Kucera, Therese A.; Ofman, Leon; Tarbell, Theodore D.
2016SPD....47.0316K Altcode:
We discuss observations of prominence barb dynamics as observed by
Hinode/SOT and IRIS. Prominence barbs extend outwards to the side of the
main prominence spine and downwards towards the chromosphere. Their
properties, including the structure of their magnetic field and
the nature of the motions observed in them are a subject of current
debate. We use a combination of high cadence, high resolution imaging,
H-alpha Doppler, and Mg II line profile data to analyze and understand
waves and flows in barbs and discuss their ramifications in terms of
a model of the barb magnetic field as collection of dipped field lines.

---------------------------------------------------------
Title: Fast-mode Coronal Wave Trains Detected by SDO/AIA: Recent
Observational Progress
Authors: Liu, Wei; Downs, Cooper; Ofman, Leon
2016SPD....4730802L Altcode:
Quasi-periodic Fast Propagating wave trains (QFPs) are a new
observational phenomenon discovered by SDO/AIA in extreme ultraviolet
(EUV). They are fast-mode magnetosonic waves, closely related to
quasi-periodic pulsations in solar flare emission ranging from
radio to X-ray wavelengths. The significance of QFPs lies in their
diagnostic potential, because they can provide critical clues to flare
energy release and serve as new tools for coronal seismology. In
this presentation, we report recent advances in observing QFPs. In
particular, using differential emission measure (DEM) inversion,
we found clear evidence of heating and cooling cycles that are
consistent with alternating compression and rarefaction expected for
magnetosonic wave pulses. We also found that different local magnetic
and plasma environments can lead to two distinct types of QFPs located
in different spatial domains with respect to their accompanying
coronal mass ejections (CMEs). Moreover, recent IRIS observations
of QFP source regions revealed sawtooth-like flare ribbon motions,
indicative of pulsed magnetic reconnection, that are correlated with
QFP excitation. More interestingly, from a statistical survey of over
100 QFP events, we found a preferential association with eruptive
flares rather than confined flares. We will discuss the implications
of these results and the potential roles of QFPs in coronal heating,
energy transport, and solar eruptions.

---------------------------------------------------------
Title: Realistic Modeling of SDO/AIA-discovered Coronal Fast MHD
Wave Trains in Active Regions
Authors: Ofman, Leon; Liu, Wei
2016SPD....47.0621O Altcode:
High-resolution EUV observations by space telescopes have provided
plenty of evidence for coronal MHD waves in active regions. In
particular, SDO/AIA discovered quasi-periodic, fast-mode propagating
MHD wave trains (QFPs), which can propagate at speeds of ~1000 km/s
perpendicular to the magnetic field. Such waves can provide information
on the energy release of their associated flares and the magnetized
plasma structure of the active regions. Before we can use these waves
as tools for coronal seismology, 3D MHD modeling is required for
disentangling observational ambiguities and improving the diagnostic
accuracy. We present new results of observationally contained models
of QFPs using our recently upgraded radiative, thermally conductive,
visco-resistive 3D MHD code. The waves are excited by time-depended
boundary conditions constrained by the spatial (localized) and
quasi-periodic temporal evolution of a C-class flare typically
associated with QFPs. We investigate the excitation, propagation,
and damping of the waves for a range of key model parameters, such as
the background temperature, density, magnetic field structure, and the
location of the flaring site within the active region. We synthesize
EUV intensities in multiple AIA channels and then obtain the model
parameters that best reproduce the properties of observed QFPs. We
discuss the implications of our model results for the seismological
application of QFPs and for understanding the dynamics of their
associated flares.

---------------------------------------------------------
Title: Coronal Seismology of Flare-Excited Standing Slow-Mode Waves
Observed by SDO/AIA
Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.
2016SPD....47.0632W Altcode:
Flare-excited longitudinal intensity oscillations in hot flaring
loops have been recently detected by SDO/AIA in 94 and 131 Å
bandpasses. Based on the interpretation in terms of a slow-mode wave,
quantitative evidence of thermal conduction suppression in hot (&gt;9
MK) loops has been obtained for the first time from measurements
of the polytropic index and phase shift between the temperature and
density perturbations (Wang et al. 2015, ApJL, 811, L13). This result
has significant implications in two aspects. One is that the thermal
conduction suppression suggests the need of greatly enhanced compressive
viscosity to interpret the observed strong wave damping. The other
is that the conduction suppression provides a reasonable mechanism
for explaining the long-duration events where the thermal plasma is
sustained well beyond the duration of impulsive hard X-ray bursts in
many flares, for a time much longer than expected by the classical
Spitzer conductive cooling. In this study, we model the observed
standing slow-mode wave in Wang et al. (2015) using a 1D nonlinear MHD
code. With the seismology-derived transport coefficients for thermal
conduction and compressive viscosity, we successfully simulate the
oscillation period and damping time of the observed waves. Based on
the parametric study of the effect of thermal conduction suppression
and viscosity enhancement on the observables, we discuss the inversion
scheme for determining the energy transport coefficients by coronal
seismology.

---------------------------------------------------------
Title: Quasi-periodic fast-mode magnetosonic wave trains within
coronal waveguides associated with flares and CMEs
Authors: Liu, Wei; Ofman, Leon; Broder, Brittany; Karlický, Marian;
Downs, Cooper
2016AIPC.1720d0010L Altcode: 2015arXiv151207930L
Quasi-periodic, fast-mode, propagating wave trains (QFPs) are a new
observational phenomenon recently discovered in the solar corona by
the Solar Dynamics Observatory with extreme ultraviolet (EUV) imaging
observations. They originate from flares and propagate at speeds up to
∼2000 km s-1 within funnel-shaped waveguides in the wakes
of coronal mass ejections (CMEs). QFPs can carry suffcient energy fluxes
required for coronal heating during their occurr ences. They can provide
new diagnostics for the solar corona and their associated flares. We
present recent observations of QFPs focusing on their spatio-temporal
properties, temperature dependence, and statistical correlation
with flares and CMEs. Of particular interest is the 2010-Aug-01 C3.2
flare with correlated QFPs and drifting zebra and fiber radio bursts,
which might be different manifestations of the same fast-mode wave
trains. We also discuss the potential roles of QFPs in accelerating
and/or modulating the solar wind.

---------------------------------------------------------
Title: MHD Waves in the Solar Wind
Authors: Ofman, L.
2016GMS...216..241O Altcode:
This chapter focuses on reviewing several observational aspects of
magnetohydrodynamic (MHD) waves in the solar wind, in particular on
Alfvén waves, Alfvénic turbulent spectrum, and their role in heating
and accelerating the solar wind. It also reviews computational models
that incorporate Alfvén waves as the driving source of the wind
in the lower corona (coronal holes) and in the inner heliosphere,
with emphasis on multi-dimensional models. Evidence for MHD waves in
the solar wind is obtained from interplanetary scintillation (IPS)
observations using Earth-based radio telescope observations of distant
(galactic) radio sources. The solar wind electron density variability
in the line of sight affects the received radio signal. The propagating
fluctuations and their correlations are used to estimate the solar wind
velocity and the wave amplitude in the parallel and the perpendicular
directions in line of sight.

---------------------------------------------------------
Title: Evidence of thermal conduction suppression in hot coronal
loops: supplementary results
Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Provornikova,
Elena; Davila, Joseph M.
2016IAUS..320..202W Altcode: 2015arXiv151002750W
Slow magnetoacoustic waves were first detected in hot (&gt;6 MK) flare
loops by the SOHO/SUMER spectrometer as Doppler shift oscillations in Fe
xix and Fe xxi lines. Recently, such longitudinal waves have been found
by SDO/AIA in the 94 and 131 Å channels. Wang et al. (2015) reported
the first AIA event revealing signatures in agreement with a fundamental
standing slow-mode wave, and found quantitative evidence for thermal
conduction suppression from the temperature and density perturbations in
the hot loop plasma of &gt;~ 9 MK. The present study extends the work of
Wang et al. (2015) by using an alternative approach. We determine the
polytropic index directly based on the polytropic assumption instead
of invoking the linear approximation. The same results are obtained as
in the linear approximation, indicating that the nonlinearity effect
is negligible. We find that the flare loop cools slower (by a factor
of 2-4) than expected from the classical Spitzer conductive cooling,
approximately consistent with the result of conduction suppression
obtained from the wave analysis. The modified Spitzer cooling timescales
based on the nonlocal conduction approximation are consistent with
the observed, suggesting that nonlocal conduction may account for
the observed conduction suppression in this event. In addition, the
conduction suppression mechanism predicts that larger flares may tend
to be hotter than expected by the EM-T relation derived by Shibata &amp;
Yokoyama (2002).

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Title: Flare-associated Fast-mode Coronal Wave Trains Discovered by
SDO/AIA: Physical Properties and Implications
Authors: Liu, W.; Ofman, L.; Downs, C.; Cheung, C. M. M.; Broder,
B.; De Pontieu, B.
2015AGUFMSH54B..02L Altcode:
Quasi-periodic Fast Propagating wave trains (QFPs) are a new
observational phenomenon discovered in extreme ultraviolet (EUV) by
the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
Observatory (SDO). They are fast-mode magnetosonic waves, closely
related to quasi-periodic pulsations in solar flare emission ranging
from radio to X-ray wavelengths. The significance of QFPs lies in their
diagnostic potential, because they can provide critical clues to flare
energy release and serve as new tools for coronal seismology. In
this presentation, we report recent advances in observing and
modeling QFPs. For example, using differential emission measure (DEM)
inversion, we found clear evidence of heating and cooling cycles that
are consistent with alternating compression and rarefaction expected
for magnetosonic wave pulses. Moreover, recent IRIS observations
of QFP source regions revealed sawtooth-like flare ribbon motions,
indicative of pulsed magnetic reconnection, that are correlated with QFP
excitation. More interestingly, from a survey of over 100 QFP events,
we found a preferential association with eruptive flares rather than
confined flares. We will discuss the implications of these results
and the potential roles of QFPs in coronal heating, energy transport,
and solar eruptions.

---------------------------------------------------------
Title: Fast Wave Trains Associated with Solar Eruptions: Insights
from 3D Thermodynamic MHD Simulations
Authors: Downs, C.; Liu, W.; Torok, T.; Linker, J.; Mikic, Z.;
Ofman, L.
2015AGUFMSH22A..06D Altcode:
EUV imaging observations during the SDO/AIA era have provided new
insights into a variety of wave phenomena occurring in the low
solar corona. One example is the observation of quasi-periodic,
fast-propagating wave trains that are associated with solar eruptions,
including flares and CMEs. While there has been considerable
progress in understanding such waves from both an observational
and theoretical perspective, it remains a challenge to pin down
their physical origin. In this work, we detail our results from
a case-study 3D thermodynamic MHD simulation of a coronal mass
ejection where quasi-periodic wave trains are generated during the
simulated eruption. We find a direct correlation between the onset of
non-steady reconnection in the flare current sheet and the generation
of quasi-periodic wave train signatures when patchy, collimated
downflows interact with the flare arcade. Via forward modeling of
SDO/AIA observables, we explore how the appearance of the wave trains
is affected by line-of-sight integration and the multi-thermal nature
of the coronal medium. We also examine how the wave trains themselves
are channeled by natural waveguides formed in 3D by the non-uniform
background magnetic field. While the physical association of the
reconnection dynamics to the generation of quasi-periodic wave trains
appears to be a compelling result, unanswered questions posed from
recent observations as well as future prospects will be discussed.

---------------------------------------------------------
Title: Transition From Turbulence to Dissipation in the Solar Wind
Plasma: Results From Hybrid Simulations
Authors: Ofman, L.; Roberts, D. A.
2015AGUFMSH11E2419O Altcode:
Spacecraft observations such as WIND, and ACE show ample evidence of
turbulent spectra of magnetic and velocity fluctuations, and kinetic
dissipation in the solar wind plasma at ~1AU. Helios and MESSENGER
confirm these properties close to the Sun at ~0.3AU, and future Solar
Probe+ mission will provide information on turbulent spectra closer
to the Sun in the outer corona. The transition between turbulence and
dissipation occurs at scales that have clear dependence on heliocentric
distance, as expected from solar wind expansion. We perform 2.5 hybrid
modeling studies (where ions are described as particles, and electrons
as background fluid) of the evolution of the turbulent spectra of
fluctuations in electron-proton-He++ solar wind plasma at 1AU and closer
to the Sun by varying the model plasma parameters. We investigate the
dependence of the turbulence cascade and the transition to kinetic
dissipation on the plasma parameters. We consider the effects of the
solar wind expansion on the evolution of the turbulence and on the ion
heating. We find important differences between the magnetic fluctuations
spectrum, and the velocity fluctuations parallel and perpendicular to
the field affected by ion-cyclotron, and mirror instabilities, as well
as proton and alpha density fluctuations due to coupling to magnetosonic
instability. We investigate the effects of the alpha-proton drift,
and an injected spectrum on the turbulent magnetic fluctuations on
the evolution of the solar wind plasma and the ion heating.

---------------------------------------------------------
Title: Slow Solar Wind: Observable Characteristics for Constraining
Modelling
Authors: Ofman, L.; Abbo, L.; Antiochos, S. K.; Hansteen, V. H.;
Harra, L.; Ko, Y. K.; Lapenta, G.; Li, B.; Riley, P.; Strachan, L.;
von Steiger, R.; Wang, Y. M.
2015AGUFMSH11F..03O Altcode:
The Slow Solar Wind (SSW) origin is an open issue in the post SOHO
era and forms a major objective for planned future missions such as
the Solar Orbiter and Solar Probe Plus.Results from spacecraft data,
combined with theoretical modeling, have helped to investigate many
aspects of the SSW. Fundamental physical properties of the coronal
plasma have been derived from spectroscopic and imaging remote-sensing
data and in-situ data, and these results have provided crucial insights
for a deeper understanding of the origin and acceleration of the
SSW.Advances models of the SSW in coronal streamers and other structures
have been developed using 3D MHD and multi-fluid equations.Nevertheless,
there are still debated questions such as:What are the source regions
of SSW? What are their contributions to the SSW?Which is the role
of the magnetic topology in corona for the origin, acceleration and
energy deposition of SSW?Which are the possible acceleration and heating
mechanisms for the SSW?The aim of this study is to present the insights
on the SSW origin and formationarisen during the discussions at the
International Space Science Institute (ISSI) by the Team entitled
”Slowsolar wind sources and acceleration mechanisms in the corona”
held in Bern (Switzerland) in March2014--2015. The attached figure will
be presented to summarize the different hypotheses of the SSW formation.

---------------------------------------------------------
Title: Deriving Kinematic Properties of Non-Radial, Asymmetric and
Deflecting CMEs: Methods and Implications
Authors: Thompson, B. J.; Liewer, P. C.; Mays, M. L.; Richardson,
I. G.; Kwon, R.; Ofman, L.; Makela, P. A.; Ireland, J.; Hess, P.;
Waldron, Z.
2015AGUFMSH33B2467T Altcode:
An improved understanding of the kinematic properties of CMEs and
CME-associated phenomena has several impacts: 1) a less ambiguous
method of mapping propagating structures into their inner coronal
manifestations, 2) a clearer view of the relationship between the
"main" CME and CME-associated brightenings, and 3) an improved
identification of the heliospheric sources of shocks, Type II bursts,
and SEPs. However, there are several challenges in characterizing
the kinematic properties of CMEs. Most rapidly-evolving eruptions are
accompanied by changes in the surrounding corona. The larger the impact
on the surrounding corona, the more difficult it is to separate the
"main" CME from the CME-associated brightenings. Complicating the
issue is the range of observed propagation properties: super-radial
expansion, asymmetric expansion, non-radial propagation, and alterations
in the direction of propagation. These properties can be a function
of both the internal magnetic structure of the CME and the structure
of the corona through which the CME is propagating. While the relative
contribution of internal/external factors can be difficult to assess,
it is of fundamental importance because it not only reveals the nature
of CMEs but also CME-associated phenomena such as EUV waves, Type
II radio bursts, shocks, and SEPs. Most halo CMEs are a combination
of both the "main" CME and the CME-associated brightenings, but
new diagnostic methods such as time convolution mapping can help
separate the CME mass from the impacted corona. Additionally, while
most CME-fitting methods assume symmetry about the radial direction,
adaptive methods allow us to study highly asymmetric CME expansion
and take into account the fundamentally different natures of the CME
and the shocked/deflected corona. Several methods will be examined,
and each has their respective strengths and weaknesses; for example,
the difference between the direction of a highly non-radial CME and a
sun-centered model's orientation can exceed 45 degrees, which impacts
our ability to correctly assess changes in propagation direction and
the causes of these changes. We examine the assumptions inherent in
these methods and how they may produce artifacts that can influence
conclusions about CME kinematics.

---------------------------------------------------------
Title: Coronal seismology of flare-excited longitudinal slow
magnetoacoustic waves in hot coronal loops
Authors: Wang, T.; Ofman, L.; Sun, X.; Provornikova, E. A.; Davila,
J. M.
2015AGUFMSH13B2435W Altcode:
The flare-excited longitudinal intensity oscillations in hot
flaring loops have been recently detected by SDO/AIA in 94 and 131
bandpasses. These oscillations show similar physical properties (such
as period, decay time, and trigger) as those slow-mode standing waves
previously detected by the SOHO/SUMER spectrometer in Doppler shift of
flare lines formed above 6 MK. The multi-wavelength AIA observations
with high spatio-temporal resolution and wide temperature coverage
enable us to measure both thermal and wave properties of the oscillating
hot plasma with unprecedented accuracy. These new measurements can
be used to diagnose the complicated energy transport processes in
flare plasma by a technique called coronal seismology based on the
combination of observations and MHD wave theory. From a detailed case
study we have found evidence for thermal conduction suppression in
hot loops by measuring the polytropic index and analyzing the phase
relationship between the temperature and density wave signals. This
result is not only crucial for better understanding the wave dissipation
mechanism but also provides an alternative mechanism to explain the
puzzles of long-duration events and X-ray loop-top sources which show
much slower cooling than expected by the classical Spitzer conductive
cooling. This finding may also shed a light on the coronal heating
problem because weak thermal conductivity implies slower cooling of hot
plasma in nanoflares, so increasing the average coronal temperature
for the same heating rate. We will discuss the effects of thermal
conduction suppression on the wave damping and loop cooling based on
MHD simulations.

---------------------------------------------------------
Title: Nonlinear MHD Waves in a Prominence Foot
Authors: Ofman, L.; Knizhnik, K.; Kucera, T.; Schmieder, B.
2015ApJ...813..124O Altcode: 2015arXiv150907911O
We study nonlinear waves in a prominence foot using a 2.5D MHD model
motivated by recent high-resolution observations with Hinode/Solar
Optical Telescope in Ca ii emission of a prominence on 2012 October
10 showing highly dynamic small-scale motions in the prominence
material. Observations of Hα intensities and of Doppler shifts show
similar propagating fluctuations. However, the optically thick nature
of the emission lines inhibits a unique quantitative interpretation
in terms of density. Nevertheless, we find evidence of nonlinear wave
activity in the prominence foot by examining the relative magnitude of
the fluctuation intensity (δI/I ∼ δn/n). The waves are evident as
significant density fluctuations that vary with height and apparently
travel upward from the chromosphere into the prominence material
with quasi-periodic fluctuations with a typical period in the range
of 5-11 minutes and wavelengths &lt;2000 km. Recent Doppler shift
observations show the transverse displacement of the propagating
waves. The magnetic field was measured with the THEMIS instrument
and was found to be 5-14 G. For the typical prominence density the
corresponding fast magnetosonic speed is ∼20 km s-1,
in qualitative agreement with the propagation speed of the detected
waves. The 2.5D MHD numerical model is constrained with the typical
parameters of the prominence waves seen in observations. Our numerical
results reproduce the nonlinear fast magnetosonic waves and provide
strong support for the presence of these waves in the prominence
foot. We also explore gravitational MHD oscillations of the heavy
prominence foot material supported by dipped magnetic field structure.

---------------------------------------------------------
Title: Stability of Rotating Magnetized Jets in the Solar
Atmosphere. I. Kelvin-Helmholtz Instability
Authors: Zaqarashvili, Teimuraz V.; Zhelyazkov, Ivan; Ofman, Leon
2015ApJ...813..123Z Altcode: 2015arXiv151001108Z
Observations show various jets in the solar atmosphere with significant
rotational motions, which may undergo instabilities leading to heat
ambient plasma. We study the Kelvin-Helmholtz instability (KHI) of
twisted and rotating jets caused by the velocity jumps near the jet
surface. We derive a dispersion equation with appropriate boundary
conditions for total pressure (including centrifugal force of tube
rotation), which governs the dynamics of incompressible jets. Then, we
obtain analytical instability criteria of KHI in various cases, which
were verified by numerical solutions to the dispersion equation. We
find that twisted and rotating jets are unstable to KHI when the
kinetic energy of rotation is more than the magnetic energy of the
twist. Our analysis shows that the azimuthal magnetic field of 1-5
G can stabilize observed rotations in spicule/macrospicules and
X-ray/extreme-ultraviolet (EUV) jets. On the other hand, nontwisted
jets are always unstable to KHI. In this case, the instability growth
time is several seconds for spicule/macrospicules and a few minutes (or
less) for EUV/X-ray jets. We also find that standing kink and torsional
Alfvén waves are always unstable near the antinodes, owing to the jump
of azimuthal velocity at the surface, while the propagating waves are
generally stable. Kelvin-Helmholtz (KH) vortices may lead to enhanced
turbulence development and heating of surrounding plasma therefore,
rotating jets may provide energy for chromospheric and coronal heating.

---------------------------------------------------------
Title: Three-dimensional MHD modeling of vertical kink oscillations
in an active region plasma curtain
Authors: Ofman, L.; Parisi, M.; Srivastava, A. K.
2015A&A...582A..75O Altcode: 2015arXiv150505427O
Context. Observations on 2011 August 9 of an X 6.9-class flare in
active region (AR) 11263 by the Atmospheric Imaging Assembly (AIA)
on board the Solar Dynamics Observatory (SDO), were followed by
a rare detection of vertical kink oscillations in a large-scale
coronal active region plasma curtain in extreme UV coronal lines
with periods in the range 8.8-14.9 min. Aims: Our aim is to
study the generation and propagation of the magnetohydrodynamic (MHD)
oscillations in the plasma curtain taking the realistic 3D magnetic
and the density structure of the curtain into account. We also aim to
test and improve coronal seismology for a more accurate determination
of the magnetic field than with the standard method. Methods:
We use the observed morphological and dynamical conditions, as well
as plasma properties of the coronal curtain, to initialize a 3D
MHD model of the observed vertical and transverse oscillations. To
accomplish this, we implemented the impulsively excited velocity pulse
mimicking the flare-generated nonlinear fast magnetosonic propagating
disturbance interacting obliquely with the curtain. The model is
simplified by utilizing an initial dipole magnetic field, isothermal
energy equation, and gravitationally stratified density guided by
observational parameters. Results: Using the 3D MHD model, we
are able to reproduce the details of the vertical oscillations and study
the process of their excitation by a nonlinear fast magnetosonic pulse,
propagation, and damping, finding agreement with the observations. Conclusions: We estimate the accuracy of simplified slab-based
coronal seismology by comparing the determined magnetic field
strength to actual values from the 3D MHD modeling results, and
demonstrate the importance of taking more realistic magnetic geometry
and density for improving coronal seismology into account. A
movie associated to Fig. 1 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201425054/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Evidence of Thermal Conduction Suppression in a Solar Flaring
Loop by Coronal Seismology of Slow-mode Waves
Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Provornikova,
Elena; Davila, Joseph M.
2015ApJ...811L..13W Altcode: 2015arXiv150900920W
Analysis of a longitudinal wave event observed by the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory is
presented. A time sequence of 131 Å images reveals that a C-class flare
occurred at one footpoint of a large loop and triggered an intensity
disturbance (enhancement) propagating along it. The spatial features
and temporal evolution suggest that a fundamental standing slow-mode
wave could be set up quickly after meeting of two initial disturbances
from the opposite footpoints. The oscillations have a period of ∼12
minutes and a decay time of ∼9 minutes. The measured phase speed of
500 ± 50 km s-1 matches the sound speed in the heated loop
of ∼10 MK, confirming that the observed waves are of slow mode. We
derive the time-dependent temperature and electron density wave signals
from six AIA extreme-ultraviolet channels, and find that they are nearly
in phase. The measured polytropic index from the temperature and density
perturbations is 1.64 ± 0.08 close to the adiabatic index of 5/3 for
an ideal monatomic gas. The interpretation based on a 1D linear MHD
model suggests that the thermal conductivity is suppressed by at least
a factor of 3 in the hot flare loop at 9 MK and above. The viscosity
coefficient is determined by coronal seismology from the observed wave
when only considering the compressive viscosity dissipation. We find
that to interpret the rapid wave damping, the classical compressive
viscosity coefficient needs to be enhanced by a factor of 15 as the
upper limit.

---------------------------------------------------------
Title: Evidence of thermal conduction depression in hot coronal loops
Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Provornikova,
Elena; Davila, Joseph
2015IAUGA..2257766W Altcode:
Slow magnetoacoustic waves were first detected in hot (&gt;6 MK) flare
loops by the SOHO/SUMER spectrometer as Doppler shift oscillations in
Fe XIX and Fe XXI lines. These oscillations are identified as standing
slow-mode waves because the estimated phase speeds are close to the
sound speed in the loop and some cases show a quarter period phase
shift between velocity and intensity oscillations. The observed very
rapid excitation and damping of standing slow mode waves have been
studied by many authors using theories and numerical simulations,
however, the exact mechanisms remain not well understood. Recently,
flare-induced longitudinal intensity oscillations in hot post-flare
loops have been detected by SDO/AIA. These oscillations have the
similar physical properties as SUMER loop oscillations, and have
been interpreted as the slow-mode waves. The multi-wavelength AIA
observations with high spatio-temporal resolution and wide temperature
coverage allow us to explore the wave excitation and damping mechanisms
with an unprecedented detail to develope new coronal seismology. In this
paper, we present accurate measurements of the effective adiabatic index
(γeff) in the hot plasma from the electron temperature and
density wave signals of a flare-induced longitudinal wave event using
SDO/AIA data. Our results strikingly and clearly reveal that thermal
conduction is highly depressed in hot (∼10 MK) post-flare loops and
suggest that the compressive viscosity is the dominant wave damping
mechanism which allows determination of the viscosity coefficient from
the observables by coronal seismology. This new finding challenges our
current understanding of thermal energy transport in solar and stellar
flares, and may provide an alternative explanation of long-duration
events and enhance our understand of coronal heating mechanism. We will
discuss our results based on non-ideal MHD theory and simulations. We
will also discuss the flare trigger mechanism based on magnetic topology
derived from SDO/HMI vector magnetic fields using nonlinear force-free
field extrapolations and discuss the wave excitation mechanism based
on 3D MHD modeling of the active region.

---------------------------------------------------------
Title: Relative drifts and temperature anisotropies of protons and
α particles in the expanding solar wind: 2.5D hybrid simulations
Authors: Maneva, Y. G.; Ofman, L.; Viñas, A.
2015A&A...578A..85M Altcode: 2014arXiv1410.3358M
Context. We perform 2.5D hybrid simulations to investigate the origin
and evolution of relative drift speeds between protons and α particles
in the collisionless turbulent low- tildeβ solar wind plasma. 
Aims: We study the generation of differential streaming by wave-particle
interactions and absorption of turbulent wave spectra. Next we focus
on the role of the relative drifts for the turbulent heating and
acceleration of ions in the collisionless fast solar wind streams. Methods: The energy source is given by an initial broad-band spectrum
of parallel propagating Alfvén-cyclotron waves, which co-exists with
the plasma and is self-consistently coupled to the perpendicular
ion bulk velocities. We include the effect of a gradual solar wind
expansion, which cools and decelerates the minor ions. We here consider
for the first time the combined effect of self-consistently initialized
dispersive turbulent Alfvénic spectra with differentially streaming
protons and α particles in the expanding solar wind outflows within
a 2.5D hybrid simulation study. Results: For differential
streaming of Vαp &lt; 0.5VA, the selected
initial wave spectrum accelerates the minor ions in the non-expanding
wind. At Vαp = 0.5VA the relative drift speed
remains nearly steady. For ions that stream below this threshold
value, the waves act to increase the magnitude of the relative drift
speed. Ions that stream faster than the threshold value become subject
to a nonlinear streaming instability, and as the system evolves,
their bulk velocities decrease. We find that the solar wind expansion
strongly affects the relative drift speed and significantly slows down
both ion species for all values of the relative drift speeds considered
in this study. The initial nonresonant wave spectra interact with the
particles, resulting in preferential and anisotropic heating for the
minor ions with a prominent increase of their perpendicular temperature,
which overcomes the effect of the double-adiabatic cooling that is
due to the solar wind expansion. Finally, the initial parallel spectra
undergo a micro-turbulent nonlinear cascade during which oblique waves
are generated, whose intensity depends on the value of the relative
drift speed.

---------------------------------------------------------
Title: Turbulent photospheric drivers of multiscale solar corona
Authors: Uritsky, Vadim M.; Ofman, Leon; Davila, Joseph M.
2015TESS....121305U Altcode:
We investigate the collective dynamics of transient photospheric and
coronal events detected using high-resolution solar magnetograms and
coronal emission images. We focus on statistical, ensemble-averaged
properties of the interacting solar regions [Uritsky et al., 2011,
2013, 2014; Uritsky and Davila, 2012], as opposed to case-oriented
methodologies recruited in some previous studies. The behavior
of solar events is studied in the three-dimensional space-time
enabling accurate representation of the event evolution. By applying
advanced data analysis methods including feature tracking algorithms,
multiscale correlation analysis and scaling analysis techniques,
we identify leading physical scenarios of the photosphere - corona
coupling in quiet and active solar regions, and strive to identify
new statistical precursors of coronal eruptions. We also discuss the
possibility of modeling multiscale photosphere - corona interactions
using idealized three-dimensional MHD models. The obtained results
shed a new light on the origin of multiscale dissipation in the
solar corona by enabling quantitative validation of several popular
statistical physical scenarios, such as e.g. intermittent turbulence,
self-organized criticality, and topological complexity.

---------------------------------------------------------
Title: Ion Heating in Inhomogeneous Expanding Solar Wind Plasma:
The Role of Parallel and Oblique Ion-cyclotron Waves
Authors: Ozak, N.; Ofman, L.; Viñas, A. -F.
2015ApJ...799...77O Altcode: 2014arXiv1407.4622O
Remote sensing observations of coronal holes show that heavy ions
are hotter than protons and their temperature is anisotropic. In-situ
observations of fast solar wind streams provide direct evidence for
turbulent Alfvén wave spectrum, left-hand polarized ion-cyclotron
waves, and He++ - proton drift in the solar wind plasma,
which can produce temperature anisotropies by resonant absorption
and perpendicular heating of the ions. Furthermore, the solar wind
is expected to be inhomogeneous on decreasing scales approaching the
Sun. We study the heating of solar wind ions in inhomogeneous plasma
with a 2.5D hybrid code. We include the expansion of the solar wind
in an inhomogeneous plasma background, combined with the effects of a
turbulent wave spectrum of Alfvénic fluctuations and initial ion-proton
drifts. We study the influence of these effects on the perpendicular ion
heating and cooling and on the spectrum of the magnetic fluctuations
in the inhomogeneous background wind. We find that inhomogeneities
in the plasma lead to enhanced heating compared to the homogenous
solar wind, and the generation of significant power of oblique waves
in the solar wind plasma. The cooling effect due to the expansion is
not significant for super-Alfvénic drifts, and is diminished further
when we include an inhomogeneous background density. We reproduce the
ion temperature anisotropy seen in observations and previous models,
which is present regardless of the perpendicular cooling due to solar
wind expansion. We conclude that small scale inhomogeneities in the
inner heliosphere can significantly affect resonant wave ion heating.

---------------------------------------------------------
Title: Spectroscopic Diagnosis of Propagating disturbances in coronal
loops: Waves or flows?
Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.
2015arXiv150104082W Altcode:
The analysis of multiwavelength properties of propagating disturbances
(PDs) using Hinode/EIS observations is presented. Quasi-periodic
PDs were mostly interpreted as slow magnetoacoustic waves in early
studies, but recently suggested to be intermittent upflows of the
order of 50-150 km/s based on the Red-Blue (RB) asymmetry analysis of
spectral line profiles. Using the forward models, velocities of the
secondary component derived from the RB analysis are found significantly
overestimated due to the saturation effect when its offset velocities
are smaller than the Gaussian width. We developed a different method
to examine spectral features of the PDs. This method is assuming that
the excessive emission of the PD profile against the background (taken
as that prior to the PD) is caused by a hypothetic upflow. The derived
LOS velocities of the flow are on the order of 10-30 km/s from the warm
(1-1.5 MK) coronal lines, much smaller than those inferred from the
RB analysis. This result does not support the flow interpretation but
favors of the early wave interpretation.

---------------------------------------------------------
Title: Role of Parallel and Oblique Ion-Cyclotron Waves in Heating
Ions in an Inhomogeneous Expanding Solar Wind Plasma
Authors: Ofman, L.; Ozak, N. O.; Vinas, A. F.
2014AGUFMSH33A4147O Altcode:
In-situ observations of fast solar wind streams at distances of
0.29 AU and beyond by Helios and recently by MESSENGER, and at ~1
AU by STEREO, ACE, and Wind spacecraft provide direct evidence for
the presence of turbulent Alfvén wave spectrum and of left-hand
polarized ion-cyclotron waves as well as He++ - proton drift in the
solar wind plasma. The waves and the super-Alfvénic drift can produce
temperature anisotropies by resonant absorption and perpendicular
heating of the ions. Measurements indicate that proton velocity
distributions are generally non-Maxwellian with evidence for beams,
while remote sensing observations of coronal holes have shown that
heavy ions are hotter than protons with a temperature anisotropy
greater than one (Ti,perp&gt; Ti,||). In addition to the anisotropy,
it is expected that the solar wind will be inhomogeneous on decreasing
scales approaching the Sun. Here we use a 2.5 D hybrid code and extend
previous work to study the heating of solar wind ions (H+, He+) in an
inhomogeneous plasma background. We explore the effects of an initial
ion drift and of a turbulent wave spectrum on the perpendicular ion
heating and cooling and on the spectrum of the magnetic fluctuations
in the inhomogeneous background solar wind. Using the 2D hybrid model
we find that inhomogeneities in the plasma generate significant power
of oblique waves in the solar wind plasma, in addition to enhanced
heating compared to the homogenous solar wind case. We find that the
cooling effect due to the solar wind expansion is only significant
when sub-Alfvénic drifts are explored. On the other hand, the cooling
is not significant in the presence of a super-Alfvénic drift, and it
is even less significant when we include an inhomogeneous background
density. We are able to reproduce the ion temperature anisotropy
seen in observations and previous models and find that small-scale
inhomogeneities in the inner heliosphere can have a significant impact
on resonant wave ion heating.

---------------------------------------------------------
Title: Modeling the heating and the acceleration of the fast solar
wind ion
Authors: Ofman, L.; Vinas, A. F.
2014AGUFMSH33A4119O Altcode:
The solar wind is the major component of solar activity and
is the variable background state for the propagating solar
disturbances that affect the heliosphere and interact with planetary
magnetospheres. However, the physical mechanisms of solar wind
acceleration and heating are not fully understood. During periods of
solar maxima streamers dominate the solar corona and the slow solar
wind streams are ubiquitous in the heliosphere. The ion composition and
the charge states of the solar wind streams measured in situ and are
used to determine their coronal origin. The physical properties of the
multi-ion solar wind plasma and turbulent wave spectra are modeled with
multifluid models, while the kinetic processes that lead to solar wind
ion heating by resonant waves and instabilities are modeled with 2.5
hybrid models that include the kinetic ion wave-particle interactions
and ion-cyclotron wave heating processes. We will show recent results of
multi-fluid and hybrid models constrained by remote sensing and in situ
observations of the solar wind and discuss how this modeling approach
improves understanding of the heating and acceleration processes of
the solar wind.

---------------------------------------------------------
Title: Coronal Extreme Ultraviolet (EUV) Waves and Their Seismological
Applications
Authors: Liu, W.; Ofman, L.
2014AGUFMSH23C..01L Altcode:
Magnetohydrodynamic (MHD) waves can be used as seismological tools
to probe the physical conditions of the solar corona, including its
magnetic field and plasma parameters. Recent high cadence and full-disk
imaging observations in extreme ultraviolet (EUV) by the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO)
have opened a new chapter in understanding these waves and utilizing
them for coronal seismology. We will review such new observations,
focusing on two intimately related phenomena - global EUV waves
(so-called "EIT waves") associated with coronal mass ejections (CMEs)
and quasi-periodic, fast-mode magnetosonic wave trains associated
with flares: (1) The generation and propagation of global EUV waves
and their interaction with coronal structures, e.g., reflection and
refraction, can provide diagnostics for the global corona in which they
propagate, such as mapping the spatial distribution of the wave phase
speed and thus the magnetic field strength. (2) AIA-detected fast-mode
wave trains are closely correlated with flare pulsations seen from
radio to hard X-rays and propagate at typically 500-2000 km/s along
funnel-shaped waveguides often located within CME bubbles. They can
provide diagnostics for flare energy release mechanisms and the local
corona around the flaring active region. We will discuss the roles
of such waves in energy transport within the solar atmosphere and in
their associated CME/flare eruptions.

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Title: Brightenings Associated with Falling Filament Material
Authors: Gilbert, H. R.; Inglis, A. R.; Mays, M. L.; Ofman, L.;
Provornikova, E.; Thompson, B. J.; Young, C. A.
2014AGUFMSH13B4101G Altcode:
Solar filaments exhibit a range of eruptive-like dynamic activity,
including in some cases the confined or 'failed' ejection of prominence
material from the solar atmosphere. In rare cases material that
fails to erupt exhibits a strong interaction with the lower corona as
the material returns to the solar surface, observed as substantial
broadband brightening of EUV emission. We investigate a selection
of recent partial prominence eruptions in order to understand the
apparent rarity of the brightening phenomenon. Using combined data
from SDO/AIA and STEREO, we explore the energetics and kinematics of
these events, assessing the likely conditions of both the corona and
the prominence material that are required in order to explain these EUV
brightenings. We further demonstrate the potential of this phenomenon
as diagnostic tool for both prominence material conditions and the
coronal magnetic field.

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Title: SDO/AIA Observation and Modeling of Flare-excited Slow Waves
in Hot Coronal Loops
Authors: Wang, T.; Ofman, L.; Provornikova, E.; Sun, X.; Davila, J. M.
2014AGUFMSH13A4074W Altcode:
The flare-excited standing slow waves were first detected by SOHO/SUMER
as Doppler shift oscillations in hot (&gt;6 MK) coronal loops. It has
been suggested that they are excited by small or micro- flares at one
loop's footpoint. However, the detailed excitation mechanism remains
unclear. In this study, we report an oscillation event observed by
SDO/AIA in the 131 channel. The intensity disturbances excited by a
C-class flare propagated back and forth along a hot loop for about two
period with a strong damping. From the measured oscillation period
and loop length, we estimate the wave phase speed to be about 410
km/s. Using a regularized DEM analysis we determine the loop temperature
and electron density evolution and find that the loop plasma is heated
to a temperature of 8-12 MK with a mean about 9 MK. These measurements
support the interpretation as slow magnetoacousic waves. Magnetic
field extrapolation suggests that the flare is triggered by slipping
and null-point-type reconnections in a fan-spine magnetic topology, and
the injected (or impulsively evaporated) hot plasmas flowing along the
large spine field lines form the oscillating hot loops. To understand
why the propagating waves but not the standing waves as observed
previously are excited in this event, we preform simulations using a
3D MHD model based on the observed magnetic configuration including
full energy equation. Our simulations indicate that the nature of
loop temperature structure is critical for the excitation of whether
propagating or standing waves in a hot loop. Our result demonstrates
that the slow waves may be used for heating diagnostics of coronal
loops with coronal seismology. We also discuss the application of
coronal seismology for estimating the average magnetic field strength
in the hot loop based on the observed slow waves.

---------------------------------------------------------
Title: Advances in Observing Various Coronal EUV Waves in the SDO
Era and Their Seismological Applications (Invited Review)
Authors: Liu, Wei; Ofman, Leon
2014SoPh..289.3233L Altcode: 2014SoPh..tmp...67L; 2014arXiv1404.0670L
Global extreme-ultraviolet (EUV) waves are spectacular traveling
disturbances in the solar corona associated with energetic eruptions
such as coronal mass ejections (CMEs) and flares. Over the past
15 years, observations from three generations of space-borne EUV
telescopes have shaped our understanding of this phenomenon and at
the same time led to controversy about its physical nature. Since its
launch in 2010, the Atmospheric Imaging Assembly (AIA) onboard the
Solar Dynamics Observatory (SDO) has observed more than 210 global
EUV waves in exquisite detail, thanks to its high spatio-temporal
resolution and full-disk, wide-temperature coverage. A combination of
statistical analysis of this large sample, more than 30 detailed case
studies, and data-driven MHD modeling, has been leading their physical
interpretations to a convergence, favoring a bimodal composition
of an outer, fast-mode magnetosonic wave component and an inner,
non-wave CME component. Adding to this multifaceted picture, AIA has
also discovered new EUV wave and wave-like phenomena associated with
various eruptions, including quasi-periodic fast propagating (QFP)
wave trains, magnetic Kelvin-Helmholtz instabilities (KHI) in the
corona and associated nonlinear waves, and a variety of mini-EUV
waves. Seismological applications using such waves are now being
actively pursued, especially for the global corona. We review such
advances in EUV wave research focusing on recent SDO/AIA observations,
their seismological applications, related data-analysis techniques,
and numerical and analytical models.

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Title: Brightenings Caused by Falling Filament Material on 2011
September 7
Authors: Gilbert, Holly; Inglis, Andrew; Mays, Leila; Ofman, Leon;
Provornikova, Elena
2014AAS...22432313G Altcode:
Solar filaments exhibit a range of eruptive-like dynamic activity from
the full, or partial, eruption of the filament mass and surrounding
magnetic structure, as a CME, to a fully confined dynamic evolution
or ‘failed’ eruption. On 2011 September 7, a partial eruption of a
filament was observed by SDO and STEREO, generating a substantial stream
of returning filament material that exhibited a strong interaction with
the solar surface. Similarly to the recently studied 2011 June 7 event,
the impact sites show clear evidence of brightening in the observed
EUV wavelengths due to energy release by the impact. We explore two
plausible physical mechanisms that would cause such brightening:
heating of the plasma due to the kinetic energy of the impacting
material - compression of the plasma, or reconnection between the
magnetic field of the low-laying loops with the field carried by the
impacting material, or combination thereof. By analyzing the emission
of the brightenings in several SDO/AIA wavelengths, and comparing the
kinetic energy of the impacting material to the radiative energy we
provide clues for the dominant mechanism of energy release involved in
the observed brightenings. We compare this event to another in which
we performed the same analysis (2011 June 7) where we determined that
compression was the dominant mechanism.

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Title: Two-dimensional hybrid models of H+-He++
expanding solar wind plasma heating
Authors: Ofman, L.; Viñas, A. F.; Maneva, Y.
2014JGRA..119.4223O Altcode:
Preferential heating and acceleration of the solar wind He++
ions compared to protons in fast solar wind streams have been known
for decades, thanks to in situ spacecraft measurements at 0.29-5
AU. Turbulent magnetic field fluctuations with approximate power
law spectra have been observed as well. However, the exact causes
of these processes are still not known due to the lack of detailed
information on the magnetic field fluctuations and ion velocity
distributions in the acceleration region of the solar wind. Here the
collisionless heating processes in expanding solar wind plasma are
investigated using 2-D hybrid modeling with parameters appropriate
to the heliocentric distance of 10 RS. In this study the
ion dynamics is described kinetically, while electrons are treated
as a background massless fluid in an expanding solar wind model. The
source of free energy for the heating is introduced through an initial
nonequilibrium state of the plasma with large He++ ion
temperature anisotropy or with super-Alfvénic relative ion drift. We
also employ an externally imposed spectrum of magnetic fluctuations in
the frequency range below the proton gyroresonant frequency to heat
the He++ ions. We investigate the effects of solar wind
radial expansion by modeling several values of the expansion rate
in a parametric study. We find that the preferential ion heating is
attained in both nonexpanding and expanding solar wind models. Thus,
the expansion has little effect on the preferential He++ ion
heating by the processes considered here. Moreover, the expansion leads
to faster evolution of the magnetosonic drift instability, reducing the
drift velocity to lower values sooner, and the corresponding generation
of the magnetic fluctuations that heat the ions, compared to the
nonexpanding case. This is due to the reduction of the perpendicular
particle velocities in the expanding (inflated) frame. For cases with
little proton perpendicular heating, the solar wind expansion leads
to the reduction of the proton temperature anisotropy to values less
than one in the low-βp∥ solar wind acceleration region
consistent with some observed values. However, this effect must be
offset by perpendicular proton heating—likely by the same process
that heats the He++ ions to be consistent with the full
range of observed proton perpendicular temperature values.

---------------------------------------------------------
Title: Modeling the multi-ion structure of the solar corona
Authors: Ofman, Leon; Provornikova, Elena; Wang, Tongjiang
2014AAS...22440805O Altcode:
The solar corona is typically observed in EUV by SDO/AIA and other
instruments using the heavy ion emission lines such as Fe IX, Fe
XII, and other ion emission lines. However, the relative (to protons)
abundance of the emitting ions is very low and the collisional coupling
between the Fe ions and electrons decreases rapidly with height in
the low corona, while gravitational settling may become significant in
quiescent long-lived magnetic structures, such as streamers. Thus, the
structure of the weakly collisional solar corona imaged in Fe IX (and
other heavy ions) may differ significantly from the structure of the
main electron-proton constituents of the corona. The electron structure
is observed by white light coronagraphs, and during solar eclipses in
the low corona. I present the results of multi-fluid modeling of coronal
streamers and other magnetic structures that demonstrate the effects of
weak coupling between the heavy ions and the coronal electron-proton
components, and show that the multi-ion coronal structure must be
taken into account in interpretation of EUV observations.

---------------------------------------------------------
Title: Height-dependent Refraction of A Global EUV Wave and Its
Associated Sympathetic Eruptions
Authors: Liu, Wei; Ofman, Leon; Downs, Cooper; Schrijver, Karel
2014AAS...22421814L Altcode:
The height dependence of global extreme-ultraviolet (EUV) waves in
the solar corona, especially of their wave-like behaviors such as
transmission and reflection, is critical to understanding their physical
nature. Prior observations of such behaviors, when detected on the solar
disk, were compromised because height-dependent information is lost
due to the line-of-sight projection from a top-down view. We report a
global EUV wave on the limb observed by SDO/AIA from a side-view that
evidently shows height-dependent transmission and refraction. As the
wave travels through an active region, the orientation of the low-corona
wave front changes from a forward inclination toward the solar surface
to a backward inclination. This indicates that the EUV wave speed
is lower at higher altitudes, which is expected because of the rapid
drop with height of the Alfven and fast-mode speeds in active regions,
as predicted by MHD models. When traveling into the active region,
the EUV wave speed in the low corona increases from ~600 km/s to ~900
km/s. In addition, in the neighborhood of the active region, sympathetic
eruptions of local coronal structures take place sequentially upon
the wave impact and may appear as wave reflection. Understanding
propagation behaviors of global EUV waves brings us one step closer
to fully utilizing them for seismological diagnostics of the global
corona, such as mapping the spatial distribution of the Alfven speed
and magnetic field strength.

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Title: SDO/AIA observations and model of standing waves in hot
coronal loops excited by a flare
Authors: Wang, Tongjiang; Ofman, Leon; Provornikova, Elena; Davila,
Joseph M.
2014AAS...22432354W Altcode:
The strongly damped Doppler shift oscillations in hot coronal loops
were first observed by SOHO/SUMER in flare lines formed at plasma
temperature more than 6 MK. They were mainly interpreted as the
standing slow magnetosonic waves excited by impulsive energy release
at the loop’s footpoint based on the measured properties and on MHD
modeling results. Longitudinal waves with similar properties have been
recently observed by SDO/AIA in active region loops. In this study,
we report a new event that exhibited the flare-excited intensity
disturbances propagating back and forth in a hot coronal loop imaged by
AIA in 131 bandpass. We measure the physical parameters of the wave and
loop plasma, determine the loop geometry, and explore the triggering
mechanism. We identify the wave modes (propagating or standing waves)
based on these measurements and on 3D MHD modeling. A loop model
is constructed with enhanced density in a hydrostatic equilibrium
following potential or force-free magnetic field lines extrapolated
from the photospheric magnetic field data observed by SDO/HMI. We also
discuss the applications of coronal seismology to this event.

---------------------------------------------------------
Title: Waves and jets in coronal loops: the effects of radiative
cooling
Authors: Provornikova, Elena; Ofman, Leon; Wang, Tongjiang
2014AAS...22432348P Altcode:
Observations with Hinode/EIS of coronal loops in solar active regions
revealed that propagating disturbances of EUV intensity are associated
with plasma upflows or jets at loops footpoints. To investigate the
excitation and evolution of waves due to plasma jets, we expand recent
studies with more realistic 3D MHD model that includes full energy
equation with empirical heating and radiative cooling terms. We perform
3D MHD simulations of loops by applying different flow drivers at the
loops footpoints, a single upflow pulse and a broadband excitation of
small amplitude (subsonic) velocity pulses. Parameters of the pulses
are chosen according to the observed properties. We initialize the
computations with an equilibrium state of a model active region using
potential (dipole) magnetic field, gravitationally stratified density
and temperature obtained from polytropic equation of state of the
background coronal plasma. We study the initiation and the dynamics
of plasma flows, excitation and damping of waves, and flow-wave
interactions in the loops for various forms of heating. We investigate
the effects of radiation losses on the damping of MHD waves on the
jets in coronal loops.

---------------------------------------------------------
Title: 3D MHD modeling of waves excited by hot plasma jets in active
regions loops
Authors: Provornikova, Elena; Ofman, Leon; Wang, Tongjiang
2014shin.confE.158P Altcode:
EUV imaging and spectroscopic observations from several space
missions (SOHO, TRACE, Hinode/EIS, SDO/AIA) have revealed a presence
of propagating disturbances in solar coronal loops interpreted as
MHD waves. Recent observations with Hinode/EIS of active region
loops showed that propagating disturbances of EUV intensity are
associated with plasma upflows (or jets) at loops footpoints. In our
study we aim to investigate the excitation and evolution of waves
in the loops due to hot plasma jets at their footpoints. We expand
previous isothermal studies with more realistic 3D MHD model of active
region that includes full energy equation accounting for effects of
radiative losses. Computations are initialized with an equilibrium
state of a model active region using potential (dipole) magnetic
field, gravitationally stratified density and temperature obtained
from polytropic equation of state of the background coronal plasma. We
model two scenarios of wave excitation in both warm ( 1 MK) and hot (
6 MK) loops: impulsive injection of hot plasma into the steady plasma
outflow and repetitive small-scale hot plasma jets. Parameters of the
jets are chosen according to the observed properties. We study the
initiation and the dynamics of plasma flows, excitation and damping
of waves, and flow-wave interactions in the loops. We investigate the
effects of radiation losses on the damping of MHD waves on the jets
in coronal loops.

---------------------------------------------------------
Title: Modeling quasi-perpendicular shock front ion dynamics and
magnetic evolution
Authors: Ofman, Leon; Gedalin, Michael; Provornikova, Elena
2014shin.confE..14O Altcode:
Collisionless shocks result from CMEs propagating in the heliosphere,
and in regions of interaction between the solar wind and solar system
bodies. The shocks are responsible for energetic processes and particle
acceleration in the heliosphere. The magnetized shocks efficiently
convert the energy of the directed ion flow into gyration energy of
particles behind the shock front. Downstream ions play the key role
in the postshock dynamics, including development of instabilities and
eventual thermalization of the plasma. We use 2D hybrid model to study
the magnetic evolution and the dynamics of ions in a quasi-perpendicular
shock. The 2D hybrid modeling approach allows full kinetic nonlinear
description of the proton and other ion motions, wave-particle
interactions for parallel propagating and oblique waves, and velocity
distribution functions (VDFs) in the magnetized plasma of the shocks,
while the electrons are treated as background neutralizing fluid. The
magnetic and VDFs structure of the shock can be directly compared to
in-situ spacecraft measurements. The boundary conditions appropriate
for shocks are non-periodic and finite difference solver is implemented
for the fields. We investigate a broad range of shock parameters such
as the Mach number and find the conditions where laminar, as well
as corrugated shock-fronts are produced. The structure of the shock
fronts affects the energy transfer between the shock and the particle
populations, as well as the diagnostic of spacecraft measurements.

---------------------------------------------------------
Title: Quasi-periodic Fast-mode Magnetosonic Wave Trains Detected
by SDO/AIA and Their Correlation with Quasi-period Flare Pulsations
Authors: Liu, Wei; Ofman, Leon; Fleishman, Gregory; Downs, Cooper
2014shin.confE.157L Altcode:
Quasi-periodic fast propagating wave trains (QFPs; Liu et al. 2011,
2012) are a new phenomenon recently discovered in extreme ultraviolet
(EUV) by the Atmospheric Imaging Assembly (AIA) onboard the Solar
Dynamics Observatory (SDO). They are fast-mode magnetosonic waves,
closely related to quasi-periodic pulsations of solar flares observed
from radio to hard X-rays. QFPs usually originate from a flare and
propagate at typically 500-2000 km/s within a funnel-shaped waveguide
located inside a CME bubble. QFPs can potentially be used for coronal
seismological diagnostics and provide critical clues to flare energy
release and particle acceleration processes. We will present recent
observational and numerical results of QFPs and compare them with
quasi-periodic flare pulsations.

---------------------------------------------------------
Title: Nonlinear MHD waves in a Prominence Foot: Observations
and Models
Authors: Ofman, Leon; Schmieder, Brigitte; Kucera, Therese; Knizhnik,
Kalman
2014cosp...40E2338O Altcode:
Recent high-resolution observations with Hinode/SOT in Ca II emission
of a prominence on October 12, 2012 show highly dynamic small-scale
motions in the prominence material. Observations in Hα and of Doppler
shifts show similar propagating fluctuations. However the optically
thick nature of the emission lines inhibits unique quantitative
interpretation in terms of density. Nevertheless, we find evidence of
nonlinear wave activity in the prominence foot by examining the relative
magnitude of the fluctuation intensity (dI/I~ dn/n). The waves are
evident as significant density fluctuations (dn/n~O(1)) with weak height
dependence, and apparently travel upward from the chromosphere into the
prominence material with quasi-periodic fluctuations on the order of 5
minutes, and wavelengths ~&lt;2000 km. Doppler shift observations show
the transverse displacement of the propagating waves. The magnetic
field is measured with THEMIS and is found to be 5-14 G. For the
typical prominence density the corresponding fast magnetosonic speed
is ~20 km/s in qualitative agreement with the propagation speed of
the detected wave. We use 2D and 3D MHD numerical models to reproduce
the nonlinear magnetosonic waves with the typical parameters of the
prominence guided by observations. We investigate the parameter range
of the model that fits the observed properties of the waves in order
confirm the identification of the wave nature of these observations.

---------------------------------------------------------
Title: Three-dimensional MHD modeling of flare-induced waves in
coronal loops: thermal effects
Authors: Provornikova, Elena; Ofman, Leon; Wang, Tongjiang
2014cosp...40E2635P Altcode:
EUV imaging and spectroscopic observations from several space missions
(SOHO, TRACE, Hinode/EIS, SDO/AIA) have revealed the presence of
MHD waves in solar coronal loops. Past analysis of SOHO/SUMER data
suggested that slow magnetosonic waves in hot coronal loops are
excited by flares at the loop`s footpoint. Recent Hinode/EIS observed
propagating disturbances in active region loops were interpreted as
flows as well as waves most likely generated by plasma outflows or
jets. In order to understand dynamics of plasma in coronal loops due
to flares or jets at the lower corona boundary, we perform full 3D
MHD modeling of an active region and consider different mechanisms of
wave excitation. We assume an initial equilibrium of the model active
region with dipole magnetic field structure, gravitationally stratified
density and temperature obtained from polytropic equation of state of
the background coronal plasma. We extend previous isothermal studies
by including full energy equation with empirical heating and radiative
losses terms in the model. We study waves in both, short and long loops,
and consider two excitation mechanisms in the model: impulsive plasma
injection into the steady plasma upflow along the magnetic field lines,
and impulsive heating at the footpoint of the loop. We show initiation
and evolution of flows, excitation and damping of waves and flow-wave
interaction in the loops. We compare our new results with previous
models and observations.

---------------------------------------------------------
Title: Measuring Temperature-dependent Propagating Disturbances in
Coronal Fan Loops Using Multiple SDO/AIA Channels and the Surfing
Transform Technique
Authors: Uritsky, Vadim M.; Davila, Joseph M.; Viall, Nicholeen M.;
Ofman, Leon
2013ApJ...778...26U Altcode: 2013arXiv1308.6195U
A set of co-aligned high-resolution images from the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory is
used to investigate propagating disturbances (PDs) in warm fan loops
at the periphery of a non-flaring active region NOAA AR 11082. To
measure PD speeds at multiple coronal temperatures, a new data
analysis methodology is proposed enabling a quantitative description
of subvisual coronal motions with low signal-to-noise ratios of the
order of 0.1%. The technique operates with a set of one-dimensional
"surfing" signals extracted from position-time plots of several AIA
channels through a modified version of Radon transform. The signals are
used to evaluate a two-dimensional power spectral density distribution
in the frequency-velocity space that exhibits a resonance in the
presence of quasi-periodic PDs. By applying this analysis to the same
fan loop structures observed in several AIA channels, we found that
the traveling velocity of PDs increases with the temperature of the
coronal plasma following the square-root dependence predicted for slow
mode magneto-acoustic waves which seem to be the dominating wave mode in
the loop structures studied. This result extends recent observations by
Kiddie et al. to a more general class of fan loop system not associated
with sunspots and demonstrating consistent slow mode activity in up
to four AIA channels.

---------------------------------------------------------
Title: Global Coronal Seismology in the Extended Solar Corona through
Fast Magnetosonic Waves Observed by STEREO SECCHI COR1
Authors: Kwon, Ryun-Young; Kramar, Maxim; Wang, Tongjiang; Ofman,
Leon; Davila, Joseph M.; Chae, Jongchul; Zhang, Jie
2013ApJ...776...55K Altcode:
We present global coronal seismology for the first time, which allows
us to determine inhomogeneous magnetic field strength in the extended
corona. From the measurements of the propagation speed of a fast
magnetosonic wave associated with a coronal mass ejection (CME)
and the coronal background density distribution derived from the
polarized radiances observed by the STEREO SECCHI COR1, we determined
the magnetic field strengths along the trajectories of the wave at
different heliocentric distances. We found that the results have an
uncertainty less than 40%, and are consistent with values determined
with a potential field model and reported in previous works. The
characteristics of the coronal medium we found are that (1) the density,
magnetic field strength, and plasma β are lower in the coronal hole
region than in streamers; (2) the magnetic field strength decreases
slowly with height but the electron density decreases rapidly so that
the local fast magnetosonic speed increases while plasma β falls off
with height; and (3) the variations of the local fast magnetosonic
speed and plasma β are dominated by variations in the electron
density rather than the magnetic field strength. These results imply
that Moreton and EIT waves are downward-reflected fast magnetosonic
waves from the upper solar corona, rather than freely propagating
fast magnetosonic waves in a certain atmospheric layer. In addition,
the azimuthal components of CMEs and the driven waves may play an
important role in various manifestations of shocks, such as type II
radio bursts and solar energetic particle events.

---------------------------------------------------------
Title: Rippled quasi-perpendicular collisionless shocks: Local and
global normals
Authors: Ofman, L.; Gedalin, M.
2013JGRA..118.5999O Altcode:
Proper determination of the shock normal is necessary for reliable
determination of observed heliospheric shock parameters and comparison
of observations with theory. The existing methods work sufficiently
well for low and moderate Mach numbers one-dimensional stationary
shocks. Higher-Mach-number shocks are no longer planar at the scales
of the ion convective gyroradius or smaller. In rippled shock fronts,
the local shock normal may differ substantially from the global
normal. The former is determined by the local direction of the fastest
variation of the magnetic field, while the latter is determined by
the far upstream and far downstream plasma conditions. Here we use
2-D hybrid modeling of quasi-perpendicular collisionless shocks with
moderate and high Mach numbers to quantify the difference between
the directions of the two normals. We find that the angle between the
local normal and the global normal may be as large as 40° within the
front of a rippled heliospheric shock. The coplanarity method of the
shock normal determination is sensitive to the choice of the region
for the magnetic field averaging. We also find that the usage of the
sliding averaging region in the close vicinity of the shock transition
provides satisfactory estimates of the global normal.

---------------------------------------------------------
Title: Energy Release from Impacting Prominence Material Following
the 2011 June 7 Eruption
Authors: Gilbert, H. R.; Inglis, A. R.; Mays, M. L.; Ofman, L.;
Thompson, B. J.; Young, C. A.
2013ApJ...776L..12G Altcode: 2013arXiv1309.1769G
Solar filaments exhibit a range of eruptive-like dynamic activity,
ranging from the full or partial eruption of the filament mass
and surrounding magnetic structure as a coronal mass ejection to
a fully confined or failed eruption. On 2011 June 7, a dramatic
partial eruption of a filament was observed by multiple instruments
on board the Solar Dynamics Observatory (SDO) and Solar-Terrestrial
Relations Observatory. One of the interesting aspects of this event
is the response of the solar atmosphere as non-escaping material
falls inward under the influence of gravity. The impact sites show
clear evidence of brightening in the observed extreme ultraviolet
wavelengths due to energy release. Two plausible physical mechanisms
for explaining the brightening are considered: heating of the plasma due
to the kinetic energy of impacting material compressing the plasma, or
reconnection between the magnetic field of low-lying loops and the field
carried by the impacting material. By analyzing the emission of the
brightenings in several SDO/Atmospheric Imaging Assembly wavelengths,
and comparing the kinetic energy of the impacting material (7.6 ×
1026-5.8 × 1027 erg) to the radiative energy
(≈1.9 × 1025-2.5 × 1026 erg), we find
the dominant mechanism of energy release involved in the observed
brightening is plasma compression.

---------------------------------------------------------
Title: Three-dimensional Magnetohydrodynamic Modeling of Propagating
Disturbances in Fan-like Coronal Loops
Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.
2013ApJ...775L..23W Altcode: 2013arXiv1308.0282W
Quasi-periodic propagating intensity disturbances (PDs) have been
observed in large coronal loops in EUV images over a decade, and are
widely accepted to be slow magnetosonic waves. However, spectroscopic
observations from Hinode/EIS revealed their association with persistent
coronal upflows, making this interpretation debatable. Motivated by the
scenario that the coronal upflows could be the cumulative result of
numerous individual flow pulses generated by sporadic heating events
(nanoflares) at the loop base, we construct a velocity driver with
repetitive tiny pulses, whose energy frequency distribution follows
the flare power-law scaling. We then perform three-dimensional MHD
modeling of an idealized bipolar active region by applying this
broadband velocity driver at the footpoints of large coronal loops
which appear open in the computational domain. Our model successfully
reproduces the PDs with similar features as the observed, and shows
that any upflow pulses inevitably excite slow magnetosonic wave
disturbances propagating along the loop. We find that the generated
PDs are dominated by the wave signature as their propagation speeds
are consistent with the wave speed in the presence of flows, and the
injected flows rapidly decelerate with height. Our simulation results
suggest that the observed PDs and associated persistent upflows may
be produced by small-scale impulsive heating events (nanoflares) at
the loop base in the corona, and that the flows and waves may both
contribute to the PDs at lower heights.

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Title: Fast Magnetosonic Waves and Global Coronal Seismology in the
Extended Solar Corona
Authors: Kwon, Ryun Young; Zhang, J.; Kramar, M.; Wang, T.; Ofman,
L.; Davila, J. M.
2013SPD....4410303K Altcode:
We present global coronal seismology, for the first time, that
allows us to determine inhomogeneous magnetic field strengths in
a wide range of the extended solar corona. We use observations of
propagating disturbance associated with a coronal mass ejection
observed on 2011 August 4 by the COR1 inner coronagraphs on board
the STEREO spacecraft. We establish that the disturbance is in fact
a fast magnetosonic wave as the upper coronal counterpart of the EIT
wave observed by STEREO EUVI and travels across magnetic field lines
with inhomogeneous speeds, passing through various coronal regions
such as quiet/active corona, coronal holes, and streamers. We derive
magnetic field strengths along the azimuthal trajectories of the fronts
at heliocentric distances 2.0, 2.5, and 3.0 Rs, using the varying
speeds and electron densities. The derived magnetic field strengths are
consistent with values determined with a potential field source surface
model and reported in previous works. The ranges of the magnetic field
strengths at these heliocentric distances are 0.44 ± 0.29, 0.23 ±
0.15, and 0.26 ± 0.14 G, respectively. The uncertainty in determining
magnetic field strengths is about 40 %. This work demonstrates that
observations of fast magnetosonic waves by white-light coronagraphs
can provide us with a unique way to diagnose magnetic field strength
of an inhomogeneous medium in a wide spatial range of the extended
solar corona.

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Title: Quasi-periodic Fast-mode Magnetosonic Wave Trains Inside and
Outside CME Bubbles Detected by SDO/AIA
Authors: Liu, Wei; Ofman, L.; Downs, C.; Title, A. M.
2013SPD....44...50L Altcode:
Quasi-periodic fast-mode magnetosonic wave trains both inside and
outside expanding CME bubbles have recently been discovered by
SDO/AIA (Liu et al. 2011, 2012; Shen &amp; Liu 2012). In general,
a wave train inside a CME bubble originates from a flare site and
propagates along a funnel of coronal loops at typically 1000-2000 km/s
(Ofman et al. 2011). A wave train outside a CME usually originates
from a CME flank and propagates in the low corona along the solar
surface following the leading front of a global EUV wave at typically
500-1000 km/s. The former is primarily seen in the cooler 171 Angstrom
channel with a characteristic temperature of 0.8 MK, while the latter
is pronounced in the hotter 193 and 211 Angstrom channels of typically
1.6-2.0 MK. What is the relationship between the two types of wave
trains? Why do they appear differently in location and wavelength
(temperature)? To answer these questions, we report here for the
first time the evidence that the wave train beyond the CME bubble is
the continuation of the same wave train along the funnel within the
CME. The continuous deceleration of the waves is consistent with the
expected decrease of the local fast-mode speed with distance from the
active region (e.g., Ofman et al. 2011; Downs et al. 2012). There is
an abrupt change of the wave speed at the topological interface where
the expanding CME flank is located, indicative of contrasting magnetic
and plasma conditions, which can give rise to different (fast-mode)
speeds and wavelength (temperature) dependent appearances of these wave
trains.Abstract (2,250 Maximum Characters): Quasi-periodic fast-mode
magnetosonic wave trains both inside and outside expanding CME bubbles
have recently been discovered by SDO/AIA (Liu et al. 2011, 2012;
Shen &amp; Liu 2012). In general, a wave train inside a CME bubble
originates from a flare site and propagates along a funnel of coronal
loops at typically 1000-2000 km/s (Ofman et al. 2011). A wave train
outside a CME usually originates from a CME flank and propagates in
the low corona along the solar surface following the leading front of a
global EUV wave at typically 500-1000 km/s. The former is primarily seen
in the cooler 171 Angstrom channel with a characteristic temperature
of 0.8 MK, while the latter is pronounced in the hotter 193 and 211
Angstrom channels of typically 1.6-2.0 MK. What is the relationship
between the two types of wave trains? Why do they appear differently
in location and wavelength (temperature)? To answer these questions,
we report here for the first time the evidence that the wave train
beyond the CME bubble is the continuation of the same wave train
along the funnel within the CME. The continuous deceleration of the
waves is consistent with the expected decrease of the local fast-mode
speed with distance from the active region (e.g., Ofman et al. 2011;
Downs et al. 2012). There is an abrupt change of the wave speed at
the topological interface where the expanding CME flank is located,
indicative of contrasting magnetic and plasma conditions, which can
give rise to different (fast-mode) speeds and wavelength (temperature)
dependent appearances of these wave trains.

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Title: Modeling coronal loop oscillations in realistic magnetic and
density structures
Authors: Ofman, Leon; Wang, T.; Malanushenko, A.; Davila, J. M.
2013SPD....4410404O Altcode:
Recently, ubiquitous coronal loop oscillations were detected in
active region loops by SDO/AIA. Hinode/EIS observations indicate that
quasi-periodic flows are present at footpoints of loops in active
regions, and related propagating disturbances (PD's) were detected in
open and closed loop structures. Recent 3D MHD models in idealized
(bipolar) active regions (Ofman et al. 2012; Wang et al. 2013,
this meeting) have demonstrated that the flows can produce slow
magnetosonic waves in loops, as well as transverse oscillations. We
extend the idealized studies by considering more realistic magnetic
field structures modeled by including photospheric magnetic field
extrapolated to the corona as boundary and initial conditions for
the 3D MHD modeling. We use potential and nonlinear magnetic field
extrapolations combined with gravitationally stratified density and
introduce flows at the corona-transition region boundary in our 3D MHD
model. We apply coronal seismology to the resulting loop oscillations
and compare to oscillation events detected by SDO/AIA. We aim to
improve the accuracy of coronal seismology by modeling coronal loop
oscillations in realistic magnetic geometry and density structures.

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Title: Three-Dimensional MHD Modeling of Propagating Disturbances
in Fanlike AR Coronal Loops
Authors: Wang, Tongjiang; Ofman, L.; Davila, J. M.
2013SPD....44...36W Altcode:
Quasi-periodic propagating intensity disturbances (PDs) have been
observed in cool (about 1 MK) coronal loops in EUV images over a
decade. They are widely accepted to be slow magnetosonic waves
since their propagation velocity is close to the coronal sound
speed. However, recent spectroscopic observations from Hinode/EIS
revealed their association with persistent coronal upflows, making this
interpretation debatable. Motivated by the scenario that the observed
persistent upflows could be cumulative result of numerous individual
flow pulses generated by sporadic heating events (nanoflares) at the
loop base, we constructed a broadband velocity driver with repetative
tiny pulses, whose energy frequency distribution follows the flare
power-law scaling distribution. We then performed 3D MHD modeling
of an idealized bipolar active region by applying this broadband
velocity driver at the footpoints of coronal loops which appear open
in the computational domain. Our model successfully reproduced the
propagating disturbances with similar features as the observed. We
find, based on our simulations, that upflow pulses unavoidably excites
a slow magnetosonic wave fronts propagating along the loop with the
phase speed which is much larger than the local flow speed as the flow
velocity decreases with height. Our modeling results support that the
observed PDs are mainly the signature of waves above the footpoints of
the loops, and suggest that the observed PDs and associated persistent
upflows may be driven by the same mechanism such as impulsive heating
at the loop base.

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Title: Slow mode waves and quasi-periodic upflows in the
multi-temperature solar corona as seen by the SDO
Authors: Uritsky, Vadim; Davila, J. M.; Viall, N.; Ofman, L.
2013SPD....4410405U Altcode:
We report results the analysis of coronal fan loops in a non-flaring
solar active region exhibiting temperature-dependent propagating optical
disturbances. A 6-hour set of high resolution coronal observations
provided by the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamics Observatory (SDO) has been used for characterizing apparent
propagating patterns at multiple coronal temperatures (131A, 171A,
193A and 211A). A new data analysis methodology has been developed
enabling an identification of subvisual motions with low signal-to-noise
ratios not previously examined in this context. The technique involves
spatiotemporal tracking of fan loop filaments containing propagating
disturbances, construction of position - time plots for different
temperature channels, obtaining the waveforms of the propagating optical
features, and evaluation of Fourier spectral power of the waveforms
as a function of phase speed and frequency. Using this methodology,
we identified the parameters of propagating optical disturbances in
different magnetic geometries, and classified these events as waves
and/or plasma jets. We explored coronal conditions favoring wave-like
and jet-like traveling plasma density enhancements in fan loops and
the mechanisms of their generation, damping and interaction. The
results obtained are compared with the behavior of a resistive MHD
model exhibiting both types of propagating disturbances.

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Title: Brightenings Caused by Falling Filament Material in the 2011
June 7 Event
Authors: Gilbert, Holly; Inglis, A.; Ofman, L.; Mays, L. M.; Thompson,
B. J.; Young, A.
2013SPD....44...30G Altcode:
Solar filaments exhibit a range of eruptive-like dynamic activity from
the full, or partial, eruption of the filament mass and surrounding
magnetic structure, as a CME, to a fully confined dynamic evolution or
‘failed’ eruption. On 2011 June 7, a dramatic partial eruption of a
filament was observed by multiple instruments and SDO and STEREO. One
of the interesting aspects of this partial eruption was the response
of the surface as non-erupting material fell back under the influence
of gravity. The impact sites show clear evidence of brightening in the
observed EUV wavelengths due to energy release by the impact. There
are two plausible physical mechanisms of the brightening: heating
of the plasma due to the kinetic energy of the impacting material -
compression of the plasma, or reconnection between the magnetic field of
the low-laying loops with the field carried by the impacting material,
or combination thereof. By analyzing the emission of the brightenings
in several SDO/AIA wavelength, and comparing the kinetic energy of the
impacting material (with true velocity determined from triangulation
of the two STEREO spacecraft) to the radiative energy we provide clues
for the dominant mechanism of energy release involved in the observed
brightenings.

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Title: The effect of broad-band Alfvén-cyclotron waves spectra on the
preferential heating and differential acceleration of He++
ions in the solar wind
Authors: Maneva, Y. G.; Ofman, L.; Viñas, A. F.
2013AIPC.1539...34M Altcode:
In anticipation of results from inner heliospheric missions such as
the Solar Orbiter and the Solar Probe we present the results from
1.5D hybrid simulations to study the role of magnetic fluctuations
for the heating and differential acceleration of He++
ions in the solar wind. We consider the effects of nonlinear
Alfvén-cyclotron waves at different frequency regimes. Monochromatic
nonlinear Alfvén-alpha-cyclotron waves are known to preferentially
heat and accelerate He++ ions in collisionless low
beta plasma. In this study we demonstrate that these effects are
preserved when higherfrequency monochromatic and broad-band spectra
of Alfvén-proton-cyclotron waves are considered. Comparison between
several nonlinear monochromatic waves shows that the ion temperatures,
anisotropies and relative drift are quantitatively affected by the
shift in frequency. Including a broad-band wave-spectrum results in
a significant reduction of both the parallel and the perpendicular
temperature components for the He++ ions, whereas the proton
heating is barely influenced, with the parallel proton temperature only
slightly enhanced. The differential streaming is strongly affected
by the available wave power in the resonant daughter ion-acoustic
waves. Therefore for the same initial wave energy, the relative drift is
significantly reduced in the case of initial wave-spectra in comparison
to the simulations with monochromatic waves.

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Title: Global Coronal Seismology in the Extended Solar Corona through
Fast Magnetosonic Waves Observed by STEREO SECCHI COR1
Authors: Kwon, Ryun Young; Zhang, Jie; Kramar, Maxim; Wang, Tongjiang;
Ofman, Leon; Davila, Joseph M.
2013shin.confE..75K Altcode:
We present global coronal seismology, for the first time, that allows us
to determine inhomogeneous magnetic field strengths in a wide range of
the extended solar corona. We use observations of a fast magnetosonic
wave associated with a coronal mass ejection observed on 2011 August
4 by the COR1 inner coronagraphs on board the STEREO spacecraft. In
order to estimate inhomogeneous magnetic field strength, we choose the
azimuthal trajectories of the wave front at heliocentric distances
2.0, 2.5, and 3.0 solar radii and determine the speeds of the wave
front and electron densities using polarized brightness images along
the trajectories. The magnetic field strengths are derived with an
uncertainty less than 40 % and consistent with values determined with a
potential field source surface model and reported in previous works. The
characteristics of the coronal medium revealed with our global coronal
seismology are that: (1) density, magnetic field strength, plasma beta
are lower in the coronal hole than in the streamers, (2) magnetic field
strength decreases slowly with height but electron density decreases
rapidly so that local fast magnetosonic speed increases while plasma
beta falls off with height, and (3) the variations of local fast
magnetosonic speed and plasma beta are in accordance with the electron
density rather than magnetic field strength. These characteristics of
the coronal medium imply that Moreton and EIT waves are downward shock
fronts of fast magnetosonic waves refracted from the upper solar corona,
rather than freely propagating fast magnetosonic waves in a certain
solar atmospheric layer. In addition, the azimuthal components of
CMEs may play an important role in various manifestations of shocks,
such as type II radio bursts and solar energetic particle events.

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Title: Turbulent heating and acceleration of He++ ions
by spectra of Alfvén-cyclotron waves in the expanding solar wind:
1.5-D hybrid simulations
Authors: Maneva, Y. G.; ViñAs, A. F.; Ofman, L.
2013JGRA..118.2842M Altcode:
Both remote sensing and in situ measurements show that the fast solar
wind plasma significantly deviates from thermal equilibrium and is
strongly permeated by turbulent electromagnetic waves, which regulate
the ion temperature anisotropies and relative drifts. Thus, the ion
kinetics is governed by heating and cooling related to absorption and
emission of ion-acoustic and ion-cyclotron waves, as well as nonresonant
pitch angle scattering and diffusion in phase space. Additionally,
the solar wind properties are affected by its nonadiabatic expansion
as the wind travels away from the Sun. In this study we present
results from 1.5-D hybrid simulations to investigate the effects of
a nonlinear turbulent spectrum of Alfvén-cyclotron waves and the
solar wind expansion on the anisotropic heating and differential
acceleration of protons and He++ ions. We compare the
different heating and acceleration by turbulent Alfvén-cyclotron
wave spectra and by pure monochromatic waves. For the waves and the
wave spectra used in our model, we find that the He++
ions are preferentially heated and by the end of the simulations
acquire much more than mass-proportional temperature ratios,
Tα/Tp&gt;mα/mp. The
differential acceleration between the two species strongly depends on
the initial wave amplitude and the related spectral index and is often
suppressed by the solar wind expansion. We also find that the expansion
leads to perpendicular cooling for both species, and depending on the
initial wave spectra, it can either heat or cool the ions in parallel
direction. Despite the cooling effect of the expansion in perpendicular
direction, the wave-particle interactions provide an additional heating
source, and the perpendicular temperature components remain higher
than the adiabatic predictions.

---------------------------------------------------------
Title: Brightenings Caused by Falling Filament Material in the 2011
June 7 Event
Authors: Gilbert, Holly; Inglis, Andrew; Mays, Leila; Ofman, Leon;
Thompson, Barbara; Young, Alex
2013shin.confE..74G Altcode:
Solar filaments exhibit a range of eruptive-like dynamic activity,
ranging from the full or partial eruption of the filament mass and
surrounding magnetic structure as a coronal mass ejection (CME), to
a fully confined dynamic evolution or 'failed' eruption. On 2011 June
7, a dramatic partial eruption of a filament was observed by multiple
instruments on SDO and STEREO. One of the interesting aspects of this
partial eruption is the response of the solar atmosphere as non-escaping
material falls inward under the influence of gravity. The impact sites
show clear evidence of brightening in the observed EUV wavelengths due
to energy release. Two plausible physical mechanisms explaining the
brightening are considered: heating of the plasma due to the kinetic
energy of impacting material compressing the plasma, or reconnection
between the magnetic field of the low-lying loops and the field carried
by the impacting material. By analyzing the emission of the brightenings
in several SDO/AIA wavelengths, and comparing the kinetic energy of the
impacting material ((2.12-60.4) - 10^26 ergs) to the radiative energy
( 10^25 ergs) we find the dominant mechanism of energy release involved
in the observed brightening is plasma compression.

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Title: Two-dimensional hybrid simulations of quasi-perpendicular
collisionless shock dynamics: Gyrating downstream ion distributions
Authors: Ofman, L.; Gedalin, M.
2013JGRA..118.1828O Altcode:
collisionless shocks undergo structural changes with the increase
of the Mach number. These changes are related to the increasing
role of the reflected ions, which have a highly nongyrotropic
distribution. Eventually, it is expected that the shock front becomes
nonstationary. At low and moderate Mach numbers, the fraction of
reflected ions is small, yet recent observations show the existence
of a well-pronounced structure of the postshock magnetic field in the
close vicinity of the transition layer. Large amplitude oscillations
were earlier interpreted as waves generated by the shock front or
passing through the shock in the downstream direction. Here we show,
using two-dimensional hybrid simulations of quasi-perpendicular
shocks, that the gyration of the directly transmitted ions
downstream of the ramp produces the spatial pressure variations,
which are accompanied with the observed magnetic oscillations due
to the momentum conservation. In a wide range of the upstream ion
temperatures, the low and moderate-Mach-number shocks remain stationary
and one-dimensional, so that the magnetic and electric field depend
only on the coordinate along the shock normal. The downstream ion
distributions gradually gyrotropize due to the collisionless mixing
of gyrophases. Nonstationary effects in these shocks do not affect
noticeably the ion dynamics. However, we find that with the increase
of the Mach number, shocks form rippled fronts in the low-β and
moderate-β regimes.

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Title: Stochastic Coupling of Solar Photosphere and Corona
Authors: Uritsky, Vadim M.; Davila, Joseph M.; Ofman, Leon; Coyner,
Aaron J.
2013ApJ...769...62U Altcode: 2012arXiv1212.5610U
The observed solar activity is believed to be driven by the dissipation
of nonpotential magnetic energy injected into the corona by dynamic
processes in the photosphere. The enormous range of scales involved
in the interaction makes it difficult to track down the photospheric
origin of each coronal dissipation event, especially in the presence of
complex magnetic topologies. In this paper, we propose an ensemble-based
approach for testing the photosphere-corona coupling in a quiet solar
region as represented by intermittent activity in Solar and Heliospheric
Observatory Michelson Doppler Imager and Solar TErrestrial RElations
Observatory Extreme Ultraviolet Imager image sets. For properly adjusted
detection thresholds corresponding to the same degree of intermittency
in the photosphere and corona, the dynamics of the two solar regions is
described by the same occurrence probability distributions of energy
release events but significantly different geometric properties. We
derive a set of scaling relations reconciling the two groups of
results and enabling statistical description of coronal dynamics based
on photospheric observations. Our analysis suggests that multiscale
intermittent dissipation in the corona at spatial scales &gt;3 Mm is
controlled by turbulent photospheric convection. Complex topology of
the photospheric network makes this coupling essentially nonlocal and
non-deterministic. Our results are in an agreement with the Parker's
coupling scenario in which random photospheric shuffling generates
marginally stable magnetic discontinuities at the coronal level,
but they are also consistent with an impulsive wave heating involving
multiscale Alfvénic wave packets and/or magnetohydrodynamic turbulent
cascade. A back-reaction on the photosphere due to coronal magnetic
reconfiguration can be a contributing factor.

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Title: Observations and models of the slow solar wind in coronal
streamers during solar minimum
Authors: Ofman, L.
2013AGUSMSH31B..05O Altcode:
A quiescent dipolar streamer belt often dominated the coronal streamer
structures during past solar minima. Past UV observations with SOHO/UVCS
show that the intensity of heavy ion emission lines (such as O VI and
Mg X) is dimmer at the cores than at the streamer edges. Three-fluid
2.5D models indicated that the observed emission variability is the
signature of slow solar wind outflow regions, where Coulomb coupling
between the electron, protons, and heavy ions leads to enhanced
emission of heavy ions at the edges of streamers. Recently, Ofman et al
(2011, 2012) have modeled in detail the three-fluid interactions and
the emission in a quiescent streamer due to Ly α, O 5+, and Mg 9+
ions at solar minimum, and used the model results to synthesize the
corresponding line emissions. They found that the model results are
in good agreement with observations, provided that the heavy ions
experience preferential heating compared to protons. Similar results
were found to hold for He++ ions in quiescent streamers. Recently, the
2.5D three-fluid model was extended to full 3D, allowing modeling the
ion abundance variations in tilted dipole streamer belt, and eventually
in solar maximum streamers. I will discuss the implication of heavy
ion emission structure in streamers and the corresponding three-fluid
models on the understanding of the slow solar wind sources.

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Title: Global oscillations and small scale dynamics of a filament
Authors: Tian, Hui; Ofman, Leon; Wang, Tongjiang
2013enss.confE.104T Altcode:
Using AIA data, we observed global oscillatory motions along the axis
of a filament with detailed small scale dynamics. The global oscillation
lasted for more than two days before the eruption of the filament. Both
magnetic tension and gravity are likely to be involved in the global
oscillation, as predicted by theoretical models. A closer look of the
detailed dynamics within the filament suggests that torsional motions
around the prominence axis are also present. Torsional motions around
the two legs of the filament resemble the so-called "solar tornadoes"
observed at limb by AIA. Variable counter-streaming flows in the
prominence body were detected as well before the filament eruption. The
HMI magnetic field data and multi-line diagnostics are used to
investigate possible mechanisms responsible for the different types
of oscillations and flows before the eventual eruption of the filament.

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Title: Vertical kink oscillations of coronal loops triggered by
recurrent jets
Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.
2013enss.confE..99W Altcode:
Transverse coronal loop oscillations were first observed by TRACE
in EUV images, and have been interpreted as global standing kink
modes. These loop oscillations are thought to be excited by a blast
wave in the form of a shock or a fast-mode wave produced by a flare
or CME. In this presentation, we report simultaneous imaging and
spectroscopic observations with SDO/AIA and Hinode/EIS of a vertical
loop oscillations triggered by recurrent jets at the footpoints. These
oscillations start with a fast disturbance traveling along the loop
with the propagating speed more than 500 km/s, much faster than the
apparent EUV jets. The vertical loop oscillations are associated with
quasi-periodic outwardly propagating features with the speeds 30-300
km/s, suggestive of loop expansions. In addition, we perform 3D MHD
modeling of a typical such event to understand the excitation of kink
oscillations by impulsive flows.

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Title: Recent Advances in Observations of Coronal EUV Waves
Authors: Liu, Wei; Ofman, Leon; Aschwanden, Markus J.; Nitta, Nariaki;
Zhao, Junwei; Title, Alan M.
2013enss.confE..67L Altcode:
MHD waves can be used as seismological tools to decipher otherwise
elusive physical parameters of the solar corona, such as the magnetic
field strength and plasma density. Recent high cadence, high resolution,
full-disk imaging observations from SDO/AIA have opened a new chapter
in understanding these waves. Various types of EUV waves associated with
flares/CMEs have been discovered or observed in unprecedented detail. In
this talk, we will review such new observations, focusing on the
following topics and their interrelationships: (1) quasi-periodic fast
waves traveling along coronal funnels within CME bubbles at speeds up
to 2000 km/s, associated with flare pulsations at similar frequencies;
(2) quasi-periodic wave trains within broad, diffuse pulses of global
EUV waves (so-called "EIT waves") running ahead of CME fronts; (3)
interactions of global EUV waves with local coronal structures on
their paths, such as flux-rope coronal cavities and their embedded
filaments (kink oscillations) and coronal holes or active regions
(deflections). We will discuss the implications of these observations
on coronal seismology, on their roles in transporting energy through
different parts of the solar atmosphere, and on understanding their
associated eruptive flares/CMEs.

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Title: STEREO Observations of Fast Magnetosonic Waves in the Extended
Solar Corona Associated with EIT/EUV Waves
Authors: Kwon, Ryun-Young; Ofman, Leon; Olmedo, Oscar; Kramar, Maxim;
Davila, Joseph M.; Thompson, Barbara J.; Cho, Kyung-Suk
2013ApJ...766...55K Altcode:
We report white-light observations of a fast magnetosonic wave
associated with a coronal mass ejection observed by STEREO/SECCHI/COR1
inner coronagraphs on 2011 August 4. The wave front is observed in the
form of density compression passing through various coronal regions such
as quiet/active corona, coronal holes, and streamers. Together with
measured electron densities determined with STEREO COR1 and Extreme
UltraViolet Imager (EUVI) data, we use our kinematic measurements of
the wave front to calculate coronal magnetic fields and find that the
measured speeds are consistent with characteristic fast magnetosonic
speeds in the corona. In addition, the wave front turns out to be
the upper coronal counterpart of the EIT wave observed by STEREO
EUVI traveling against the solar coronal disk; moreover, stationary
fronts of the EIT wave are found to be located at the footpoints of
deflected streamers and boundaries of coronal holes, after the wave
front in the upper solar corona passes through open magnetic field
lines in the streamers. Our findings suggest that the observed EIT
wave should be in fact a fast magnetosonic shock/wave traveling in
the inhomogeneous solar corona, as part of the fast magnetosonic wave
propagating in the extended solar corona.

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Title: New frontiers in wave studies and coronal seismology
Authors: Ofman, Leon
2013enss.confE..72O Altcode:
The launch of the SDO and the unprecedented high resolution, high
cadence observations with AIA provide new details on wave activity in
the solar corona. These observations, supplemented by spectroscopic
data from Hinode/EIS, theory, and numerical modeling open new frontiers
in wave studies and in coronal seismology - the use of waves for the
determination of the physical parameters (such as the magnetic field
and density) in the corona. The idealized theoretical wave studies
were recently expanded by sophisticated there-dimensional MHD models
that include additional phenomena, such as more realistic coronal loop
magnetic and density structure, broad band waves, and quasi-periodic
flows, enabling further expansion of coronal seismology as a tool
for coronal plasma diagnostics. I will review the recent progress in
observational and theoretical studied of waves and the development of
coronal seismology.

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Title: Coronal and Solar Wind Ion heating by dispersive Alfven waves -
2.5D hybrid simulations
Authors: Maneva, Y.; Ofman, L.; Vinas, A.
2013enss.confE..65M Altcode:
We perform 2.5D hybrid simulations to model the preferential heating
and differential acceleration of minor ions as observed by remote
sensing in coronal holes and measured in situ in the fast solar wind
at various heliospheric distances. We consider a low-beta plasma
consisting of fluid electrons, particle-in-cell protons and He++ ions
and different spectra of parallel propagating Alfven-cyclotron waves
as initial energy source for the ion heating and acceleration. For
fixed low wave-numbers the generated wave spectrum generally shifts
towards higher frequencies in multi-species plasma. This effect is
further enhanced when differential streaming is present due to the
expected preferential acceleration of heavy ions in coronal holes. We
use the results from the cold plasma linear theory to initialize the
nonlinear 2.5D hybrid simulations and compare the resulting ion heating,
temperature anisotropies and differential streaming when the initial
wave spectra belongs to the alpha-cyclotron and the proton-cyclotron
dispersion branches, with and without initial relative drifts, and
study the nonlinear 2D effects, extending our previous 1D hybrid
studies. Finally, we investigate the effect of a gradual solar wind
expansion, consider its influence on the wave-particle interactions
and discuss its implications for non-adiabatic perpendicular cooling
for both ion species.

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Title: Observations and Models of Slow Solar Wind with Mg9
+ Ions in Quiescent Streamers
Authors: Ofman, L.; Abbo, L.; Giordano, S.
2013ApJ...762...18O Altcode: 2012arXiv1211.1524O
Quiescent streamers are characterized by a peculiar UV signature as
pointed out by the results from the observations of the Ultraviolet
and Coronograph Spectrometer (UVCS) on board SOHO: the intensity of
heavy-ion emission lines (such as O VI) shows dimmer core relative to
the edges. Previous models show that the structure of the heavy-ion
streamer emission relates to the acceleration regions of the slow solar
wind at streamer legs and to gravitational settling processes in the
streamer core. Observations of Mg9 + ion EUV emission in
coronal streamers at solar minimum were first reported by the UVCS
instrument. The Mg X 625 Å emission is an order of magnitude smaller
than the O VI 1032 Å emission, requiring longer exposures to obtain
statistically significant results. Here, Mg X coronal observations
are analyzed and compared, for the first time, with the solar minimum
streamer structure in hydrogen and O VI emissions. We employ the 2.5D
three-fluid model, developed previously to study the properties of
O5 + ions in streamers, and calculate for the first time the
density, temperature, and outflow structure of Mg9 + ions
in the solar minimum streamer. The Mg9 + ions are heated by
an empirical radial heating function constrained by observations of the
kinetic ion temperature obtained from Mg X emission line profiles. The
detailed structure of Mg9 + density, temperature, and outflow
speed is determined by the Coulomb momentum and energy exchange as
well as electromagnetic interactions with electrons and protons in
the three-fluid model of the streamer. The results of the model are
in good qualitative agreement with observations, and provide insights
on the possible link between the magnetic structure of the streamer,
slow solar wind sources, and relative abundances of heavy ions.

---------------------------------------------------------
Title: Ion heating and acceleration by Alfvén-cyclotron and kinetic
Alfvén waves - 2.5D hybrid simulations
Authors: Maneva, Y. G.; Ofman, L.; Vinas, A.
2012AGUFMSH51B2251M Altcode:
We perform 2.5D hybrid simulations to investigate the anisotropic
preferential heating and differential acceleration of heavy ions
in the collisionless fast solar wind. We consider low plasma β
conditions in the extended solar corona to study the turbulent ion
heating and differential acceleration of He++ ions by
initial wave-spectra of parallel finite amplitude Alfvén-cyclotron
waves and investigate their anisotropic cascade and energy transfer
towards perpendicular wave numbers. We investigate the generation
of oblique modes and compare the differential streaming, the ion
heating and acceleration rates, when the initial wave-spectra consists
of kinetic Alfvén waves and when initially parallel, and oblique
Alfvén-cyclotron wave are considered. The results are applied to
better understanding the anisotropic turbulent cascade in the solar
wind, the origin of ion differential streaming and the regulation
of ion temperature anisotropies via plasma micro-instabilities and
wave-particle interactions.

---------------------------------------------------------
Title: Two-dimensional hybrid models of ion dynamics in collisionless
quasi-perpendicular shocks
Authors: Gedalin, M.; Ofman, L.
2012AGUFMSH32B..06G Altcode:
Spacecraft observations show that collisionless shocks are ubiquitous in
the heliosphere from CME shock fronts to the heliospheric termination
shock with broad range of Mach numbers. Evidently, quasi-perpendicular
collisionless shocks undergo structural changes with the increase
of the Mach number. These changes are related to the increasing
role of the reflected ions, which have a highly non-gyrotropic
distribution. Eventually, it is expected that the shock front becomes
non-stationary and rippled. At low and moderate Mach numbers the
fraction of reflected ions is small, yet recent observations show
existence of a well-pronounced structure of the post-shock magnetic
field in the close vicinity of the transition layer. Here we show, using
2D hybrid simulations, that the gyration of the directly transmitted
ions downstream of the ramp produces spatial pressure variations,
accompanied with the observed magnetic oscillations due to the momentum
conservation. In a wide range of the upstream ion temperatures the low
and moderate Mach number shocks remain stationary and one-dimensional
(on smaller scale than the variation of the global magnetic field),
so that the magnetic and electric field depend only on the coordinate
along the shock normal. The downstream ion distributions gradually
gyrotropize due to the collisionless mixing of gyrophases of the ion
velocity distributions. Non-stationary effects in these shocks do not
affect noticeably the ion dynamics. However, we find that with the
increase of the Mach number rippled fronts are formed in the low-beta
and moderate-beta regimes.

---------------------------------------------------------
Title: Three-fluid model of the slow solar wind with Mg9+ ions in
quiescent steamers and comparison to observations
Authors: Ofman, L.; Abbo, L.; Giordano, S.
2012AGUFMSH53A2256O Altcode:
Quiescent streamers are characterized by a peculiar UV signature as
pointed out by the results from the observations of the Ultraviolet and
Coronograph Spectrometer (UVCS) on board SOHO: the intensity of heavy
ion emission lines (such as OVI and Mg X) show dimmer core relative
to the edges. Previous models have shown that the structure of the
heavy ion streamer emission relates to the acceleration regions of the
slow solar wind in open field regions and to gravitational settling
processes in the streamers close field core. The UVCS instrument first
produced observations of Mg X 625 A emission in coronal streamers at
solar minimum, which is an order of magnitude smaller than the O VI
1032A emission, requiring longer exposures for statistically significant
results. We analyze and compare coronal Mg X observations for the first
time with the solar minimum streamer structure in hydrogen and O VI
emissions. We employ the 2.5D three-fluid model, developed previously
to study the properties of O VI emission streamers, and calculate
for the first time the density, temperature, and outflow structure of
preferentially heated Mg 9+ ions in the solar minimum streamer. The
structure of empirically heated Mg9+ ion density, temperature, and
outflow speed in the streamer are determined by the Coulomb momentum and
energy exchange as well as electromagnetic interactions with electrons
and protons in the three-fluid model. The results of the model are
in good qualitative agreement with observations, and provide insights
on the possible link between the magnetic structure of the streamer,
slow solar wind sources, and relative abundance variation of heavy ions.

---------------------------------------------------------
Title: Erratum: "SDO/AIA Observation of Kelvin-Helmholtz Instability
in the Solar Corona" <A href="/abs/2011ApJ...734L..11O">(2011, ApJ,
734, L11)</A>
Authors: Ofman, L.; Thompson, B. J.
2012ApJ...760L..19O Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Persistent Doppler Shift Oscillations Observed with Hinode/EIS
in the Solar Corona: Spectroscopic Signatures of Alfvénic Waves
and Recurring Upflows
Authors: Tian, Hui; McIntosh, Scott W.; Wang, Tongjiang; Ofman, Leon;
De Pontieu, Bart; Innes, Davina E.; Peter, Hardi
2012ApJ...759..144T Altcode: 2012arXiv1209.5286T
Using data obtained by the EUV Imaging Spectrometer on board Hinode,
we have performed a survey of obvious and persistent (without
significant damping) Doppler shift oscillations in the corona. We
have found mainly two types of oscillations from February to April
in 2007. One type is found at loop footpoint regions, with a dominant
period around 10 minutes. They are characterized by coherent behavior
of all line parameters (line intensity, Doppler shift, line width,
and profile asymmetry), and apparent blueshift and blueward asymmetry
throughout almost the entire duration. Such oscillations are likely to
be signatures of quasi-periodic upflows (small-scale jets, or coronal
counterpart of type-II spicules), which may play an important role
in the supply of mass and energy to the hot corona. The other type of
oscillation is usually associated with the upper part of loops. They are
most clearly seen in the Doppler shift of coronal lines with formation
temperatures between one and two million degrees. The global wavelets
of these oscillations usually peak sharply around a period in the range
of three to six minutes. No obvious profile asymmetry is found and
the variation of the line width is typically very small. The intensity
variation is often less than 2%. These oscillations are more likely to
be signatures of kink/Alfvén waves rather than flows. In a few cases,
there seems to be a π/2 phase shift between the intensity and Doppler
shift oscillations, which may suggest the presence of slow-mode standing
waves according to wave theories. However, we demonstrate that such a
phase shift could also be produced by loops moving into and out of a
spatial pixel as a result of Alfvénic oscillations. In this scenario,
the intensity oscillations associated with Alfvénic waves are caused by
loop displacement rather than density change. These coronal waves may be
used to investigate properties of the coronal plasma and magnetic field.

---------------------------------------------------------
Title: Hybrid simulation of the shock wave formation behind the Moon
Authors: Israelevich, P.; Ofman, L.
2012epsc.conf...39I Altcode: 2012espc.conf...39I
A standing shock wave behind the Moon was predicted by Michel (1967)
but never observed nor simulated. We use 1D hybrid code in order to
simulate the collapse of the plasma-free cavity behind the Moon and
for the first time to model the formation of this shock. Starting
immediately downstream of the obstacle we consider the evolution of
plasma expansion into the cavity in the frame of reference moving
along with the solar wind. Wellknown effects as electric charging of
the cavity affecting the plasma flow and counter streaming ion beams
in the wake are reproduced. Near the apex of the inner Mach cone where
the plasma flows from the opposite sides of the obstacle meet, a shock
wave arises. The shock is produced by the interaction of oppositely
directed proton beams in the plane containing solar wind velocity and
interplanetary magnetic field vectors. In the direction across the
magnetic field and the solar wind velocity, the shock results from
the interaction of the plasma flow with the region of the enhanced
magnetic field inside the cavity that plays the role of the magnetic
barrier. Simulations with lower electron temperatures (Te~20eV) show
weakened shock formation behind the moon at much greater distances. The
shock disappears for typical solar wind conditions (Ti ~ Te) Therefore,
in order to observe the trailing shock, a satellite should have a
trajectory passing very close to the wake axis during the period of hot
solar wind streams. We expect the shock to be produced at periods of
high electron temperature solar wind streams (Ti&lt;&lt;Te~100eV). The
appearance of the standing shock wave is expected at the distance of ~
7RM downstream of the Moon.

---------------------------------------------------------
Title: Hybrid simulation of the shock wave trailing the Moon
Authors: Israelevich, P.; Ofman, L.
2012JGRA..117.8223I Altcode: 2012JGRA..11708223I
A standing shock wave behind the Moon was predicted by Michel (1967)
but never observed nor simulated. We use 1D hybrid code in order to
simulate the collapse of the plasma-free cavity behind the Moon and
for the first time to model the formation of this shock. Starting
immediately downstream of the obstacle we consider the evolution of
plasma expansion into the cavity in the frame of reference moving along
with the solar wind. Well-known effects as electric charging of the
cavity affecting the plasma flow and counterstreaming ion beams in the
wake are reproduced. Near the apex of the inner Mach cone where the
plasma flows from the opposite sides of the obstacle meet, a shock
wave arises. We expect the shock to be produced at periods of high
electron temperature solar wind streams (Ti ≪ Te
∼ 100 eV). The shock is produced by the interaction of oppositely
directed proton beams in the plane containing solar wind velocity and
interplanetary magnetic field vectors. In the direction across the
magnetic field and the solar wind velocity, the shock results from
the interaction of the plasma flow with the region of the enhanced
magnetic field inside the cavity that plays the role of the magnetic
barrier. The appearance of the standing shock wave is expected at the
distance of ∼7RM downstream of the Moon.

---------------------------------------------------------
Title: Slow Magnetosonic Waves and Fast Flows in Active Region Loops
Authors: Ofman, L.; Wang, T. J.; Davila, J. M.
2012ApJ...754..111O Altcode: 2012arXiv1205.5732O
Recent extreme ultraviolet spectroscopic observations indicate
that slow magnetosonic waves are present in active region (AR)
loops. Some of the spectral data were also interpreted as evidence
of fast (~100-300 km s-1) quasi-periodic flows. We have
performed three-dimensional magnetohydrodynamic (3D MHD) modeling of
a bipolar AR that contains impulsively generated waves and flows in
coronal loops. The model AR is initiated with a dipole magnetic field
and gravitationally stratified density, with an upflow-driven steadily
or periodically in localized regions at the footpoints of magnetic
loops. The resulting flows along the magnetic field lines of the AR
produce higher density loops compared to the surrounding plasma by
injection of material into the flux tubes and the establishment of
siphon flow. We find that the impulsive onset of flows with subsonic
speeds result in the excitation of damped slow magnetosonic waves that
propagate along the loops and coupled nonlinearly driven fast-mode
waves. The phase speed of the slow magnetosonic waves is close to
the coronal sound speed. When the amplitude of the driving pulses is
increased we find that slow shock-like wave trains are produced. When
the upflows are driven periodically, undamped oscillations are produced
with periods determined by the periodicity of the upflows. Based on
the results of the 3D MHD model we suggest that the observed slow
magnetosonic waves and persistent upflows may be produced by the same
impulsive events at the bases of ARs.

---------------------------------------------------------
Title: Quasi-periodic Fast-mode Wave Trains within a Global EUV Wave
and Sequential Transverse Oscillations Detected by SDO/AIA
Authors: Liu, Wei; Ofman, Leon; Nitta, Nariaki V.; Aschwanden, Markus
J.; Schrijver, Carolus J.; Title, Alan M.; Tarbell, Theodore D.
2012ApJ...753...52L Altcode: 2012arXiv1204.5470L
We present the first unambiguous detection of quasi-periodic wave
trains within the broad pulse of a global EUV wave (so-called EIT wave)
occurring on the limb. These wave trains, running ahead of the lateral
coronal mass ejection (CME) front of 2-4 times slower, coherently
travel to distances &gt;~ R ⊙/2 along the solar surface,
with initial velocities up to 1400 km s-1 decelerating to
~650 km s-1. The rapid expansion of the CME initiated at
an elevated height of 110 Mm produces a strong downward and lateral
compression, which may play an important role in driving the primary
EUV wave and shaping its front forwardly inclined toward the solar
surface. The wave trains have a dominant 2 minute periodicity that
matches the X-ray flare pulsations, suggesting a causal connection. The
arrival of the leading EUV wave front at increasing distances produces
an uninterrupted chain sequence of deflections and/or transverse (likely
fast kink mode) oscillations of local structures, including a flux-rope
coronal cavity and its embedded filament with delayed onsets consistent
with the wave travel time at an elevated (by ~50%) velocity within
it. This suggests that the EUV wave penetrates through a topological
separatrix surface into the cavity, unexpected from CME-caused magnetic
reconfiguration. These observations, when taken together, provide
compelling evidence of the fast-mode MHD wave nature of the primary
(outer) fast component of a global EUV wave, running ahead of the
secondary (inner) slow component of CME-caused restructuring.

---------------------------------------------------------
Title: Ion heating by dissipation of nonlinear Alfven-cyclotron waves
Authors: Maneva, Yana G.; Ofman, L.; Vinas, A.
2012shin.confE.196M Altcode:
We present the results from hybrid simulations to investigate the
ion heating and acceleration by dissipation of large-amplitude
Alfven-cyclotron waves. We compare the resulting heating and
acceleration by a monochromatic wave and a broad band wave spectra
and find that for the same total wave energy input the broad band
leads to similar heating but to a lower rate for the ion differential
acceleration. We investigate the influence of solar wind expansion and
show that its effect on the ion kinetics highly depends on the initial
wave spectra and the relative drifts. In general the slow expansion
considered in the model leads to perpendicular cooling and changes
the energy input required for heating of the corona and acceleration
of the solar wind.

---------------------------------------------------------
Title: Growing Transverse Oscillations of a Multistranded Loop
Observed by SDO/AIA
Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.; Su, Yang
2012ApJ...751L..27W Altcode: 2012arXiv1204.1376W
The first evidence of transverse oscillations of a multistranded
loop with growing amplitudes and internal coupling observed by the
Atmospheric Imaging Assembly on board the Solar Dynamics Observatory
is presented. The loop oscillation event occurred on 2011 March 8,
triggered by a coronal mass ejection (CME). The multiwavelength analysis
reveals the presence of multithermal strands in the oscillating loop,
whose dynamic behaviors are temperature-dependent, showing differences
in their oscillation amplitudes, phases, and emission evolution. The
physical parameters of growing oscillations of two strands in 171 Å
are measured and the three-dimensional loop geometry is determined
using STEREO-A/EUVI data. These strands have very similar frequencies,
and between two 193 Å strands a quarter-period phase delay sets
up. These features suggest the coupling between kink oscillations of
neighboring strands and the interpretation by the collective kink mode
as predicted by some models. However, the temperature dependence of
the multistranded loop oscillations was not studied previously and
needs further investigation. The transverse loop oscillations are
associated with intensity and loop width variations. We suggest that
the amplitude-growing kink oscillations may be a result of continuous
non-periodic driving by magnetic deformation of the CME, which deposits
energy into the loop system at a rate faster than its loss.

---------------------------------------------------------
Title: Slow-Mode Oscillations of Hot Loops Excited at Flaring
Footpoints
Authors: Wang, T.; Liu, W.; Ofman, L.; Davila, J.
2012ASPC..456..127W Altcode: 2017arXiv170605427W
The analysis of a hot loop oscillation event using SOHO/SUMER,
GOES SXI, and RHESSI observations is presented. Damped Doppler shift
oscillations were detected in the Fe xix line by SUMER, and interpreted
as a fundamental standing slow mode. The evolution of soft X-ray
emission from GOES/SXI and hard X-ray sources from RHESSI suggests
that the oscillations of a large loop are triggered by a small flare,
which may be produced by interaction (local reconnection) of this
large loop with a small loop at its footpoint. This study provides
clear evidence supporting our early conjecture that the slow-mode
standing waves in hot coronal loops are excited by impulsive heating
(small or microflares) at the loop's footpoint.

---------------------------------------------------------
Title: Propagating Intensity Disturbances in Fan-like Coronal Loops:
Flows or Waves?
Authors: Wang, T.; Ofman, L.; Davila, J. M.
2012ASPC..455..227W Altcode: 2011arXiv1101.6017W
Quasi-periodic intensity disturbances propagating upward along the
coronal structure have been extensively studied using EUV imaging
observations from SOHO/EIT and TRACE. They were interpreted as either
slow mode magnetoacoustic waves or intermittent upflows. In this study
we aim at demonstrating that time series of spectroscopic observations
are critical to solve this puzzle. Propagating intensity and Doppler
shift disturbances in fanlike coronal loops are analyzed in multiple
wavelengths using sit-and-stare observations from Hinode/EIS. We find
that the disturbances did not cause the blue-wing asymmetry of spectral
profiles in the warm (∼1.5 MK) coronal lines. The estimated small
line-of-sight velocities also did not support the intermittent upflow
interpretation. In the hot (∼2 MK) coronal lines the disturbances
did cause the blue-wing asymmetry, but the double fits revealed that
a high-velocity minor component is steady and persistent, while the
propagating intensity and Doppler shift disturbances are mainly due
to variations of the core component, therefore, supporting the slow
wave interpretation. However, the cause for blueward line asymmetries
remains unclear.

---------------------------------------------------------
Title: SDO/AIA Detection of Quasi-periodic Wave Trains Within Global
EUV ("EIT") Waves and Their Coronal Seismology Implications
Authors: Liu, Wei; Ofman, L.; Aschwanden, M. J.; Nitta, N.; Schrijver,
C. J.; Title, A. M.; Tarbell, T. D.
2012AAS...22051501L Altcode:
The nature of global EUV waves (so-called "EIT waves") has long
been under debate because of instrumental limitations and projection
effects when viewed on the solar disk. We present here high cadence
SDO/AIA observations of global EUV waves occurring on the limb. We
report newly discovered quasi-periodic wave trains located in the low
corona within a broad, diffuse pulse of the global EUV wave ahead of
the lateral CME front/flank. These waves coherently travel to large
distances on the order of 1 solar radii with initial velocities up
to 1400 km/s. They have dominant 1-3 minute periodicities that often
match the X-ray pulsations of the accompanying flare, suggestive of
a causal connection. In addition, recently discovered quasi-periodic
fast propagating (QFP) waves of 1000-2000 km/s (Liu, Title, Zhao et
al. 2011 ApJL) are found in the funnel of coronal loops rooted at the
flare kernel. These waves are spatially confined within the CME bubble
and rapidly disappear while approaching the CME front, suggestive
of strong damping and/or dispersion. These observations provide new
evidence of the fast-mode wave nature of the primary, fast component
of a global EUV wave, running ahead of a secondary, slow component
of CME-caused restructuring of the coronal magnetic field. We suggest
that the two types of quasi-periodic waves are both integral parts of
global coronal dynamics manifested as a CME/flare eruption, and they
have important implications for global and local coronal seismology.

---------------------------------------------------------
Title: Stereo Observations Of Fast Magnetosonic Waves In The
Extended Corona
Authors: Kwon, Ryun Young; Davila, J. M.; Ofman, L.
2012AAS...22052106K Altcode:
Here, we present fast magnetosonic waves propagating across solar
radial magnetic fields. STEREO COR1 and EUVI observations showed
coronal disturbances associated with flares/CMEs and they propagate
in the low solar corona in the form of EIT waves and in the high
solar corona (above 1.5 Rs) in the form of density compressions
along radial magnetic field lines above EIT wave fronts. It turns out
that the coronal disturbances pass through streamers which contain
a magnetic separatrix. The wave energy appears to be trapped by the
streamers and this leads to stationary fronts at the footpoints of the
streamers. Our results suggest that the coronal disturbances associated
with flares/CMEs are fast magnetosonic waves propagating with local fast
magnetosonic speeds and passing through magnetic separatrices. Moreover,
we conclude that EIT waves are ‘real’ fast magnetosonic waves. The
speeds of the coronal disturbances are 475 ± 14, 926 ± 19, 1217 ±
24, 1734 ± 48, and 1928 ± 42 km/s at 1.0, 1.6, 2.0, 2.5, and 3.0 Rs,
respectively. Using coronal seismology, we estimated magnetic field
strengths corresponding to these speeds at the heights and they are
1.81 ± 0.06, 0.98 ± 0.02, 0.70 ± 0.01, 0.55 ± 0.02, and 0.39 ±
0.01 G, respectively.

---------------------------------------------------------
Title: Growing Transverse Oscillations of a Multistranded Loop
Observed by SDO/AIA
Authors: Wang, Tongjiang; Ofman, L.; Davila, J. M.; Su, Y.
2012AAS...22020717W Altcode:
The flare-excited transverse loop oscillations previously observed by
TRACE have been mainly interpreted as the global fast kink modes. These
oscillations typically have a rapid decay, and their damping mechanism
has been a major topic of theoretical studies. In this presentation,
we report an unusual case of transverse loop oscillations with growing
amplitudes observed by SDO/AIA for the first time. This oscillation
event was triggered by a flare associated with a CME above the limb. The
multiwavelength analysis reveals that the loop consists of multithermal
strands and their dynamical behaviors are temperature-dependent. These
strands have very similar oscillation frequencies and appear to
oscillate in-phase or in a quarter-period phase delay. These features
suggest the coupling between kink oscillations of neighboring strands
and the interpretation by the collective kink mode as predicted by
some models. The transverse loop oscillations are also associated with
intensity and loop width variations. We determine the trigger of the
oscillation and measure the 3-D loop geometry using STEREO/EUVI-A
data. The possible mechanisms that can excite the growing kink
oscillations will be discussed.

---------------------------------------------------------
Title: Impulsively Driven Waves And Flows In Coronal Active Regions
Authors: Ofman, Leon; Wang, T.; Davila, J. M.; Liu, W.
2012AAS...22032204O Altcode:
Recent SDO/AIA and Hinode EIS observations indicate that both (super)
fast and slow magnetosonic waves are present in active region (AR)
magnetic structures. Evidence for fast (100-300 km/s) impulsive flows
is found in spectroscopic and imaging observations of AR loops. The
super-fast waves were observed in magnetic funnels of ARs. The
observations suggest that waves and flow are produced by impulsive
events, such as (micro) flares. We have performed three-dimensional
magnetohydrodynamic (3D MHD) simulations of impulsively generated
flows and waves in coronal loops of a model bi-polar active region
(AR). The model AR is initiated with a dipole magnetic field and
gravitationally stratified density, with impulsively driven flow at
the coronal base of the AR in localized magnetic field structures. We
model the excitation of the flows in hot (6MK) and cold (1MK) active
region plasma, and find slow and fast magnetosonic waves produced by
these events. We also find that high-density (compared to surrounding
corona) loops are produced as a result of the upflows. We investigate
the parametric dependence between the properties of the impulsive
flows and the waves. The results of the 3D MHD modeling study supports
the conjecture that slow magnetosonic waves are often produced by
impulsive upflows along the magnetic field, and fast magnetosonic
waves can result from impulsive transverse field line perturbations
associated with reconnection events. The waves and flows can be used
for diagnostic of AR structure and dynamics.

---------------------------------------------------------
Title: Spectroscopic Diagnosis of Propagating Disturbances in Coronal
Loops: Waves or flows?
Authors: Wang, T.; Ofman, L.; Davila, J. M.
2012ASPC..456...91W Altcode:
The analysis of multiwavelength properties of propagating disturbances
(PDs) using Hinode/EIS observations is presented. Quasi-periodic PDs
were mostly interpreted as slow magnetoacoustic waves in early studies,
but recently suggested to be intermittent upflows of the order of
50-150 km s-1 based on the Red-Blue (RB) asymmetry analysis
of spectral line profiles. Using the forward models, velocities of the
secondary component derived from the RB analysis are found significantly
overestimated due to the saturation effect when its offset velocities
are smaller than the Gaussian width. We developed a different method
to examine spectral features of the PDs. This method is assuming that
the excessive emission of the PD profile against the background (taken
as that prior to the PD) is caused by a hypothetic upflow. The derived
LOS velocities of the flow are on the order of 10-30 km s-1
from the warm (1-1.5 MK) coronal lines, much smaller than those
inferred from the RB analysis. This result does not support the flow
interpretation but favors of the early wave interpretation.

---------------------------------------------------------
Title: Hybrid simulation of the shock wave trailing the Moon
Authors: Israelevich, P.; Ofman, L.
2012EGUGA..14.2121I Altcode:
Standing shock wave behind the Moon was predicted be Michel (1967)
but never observed nor simulated. We use 1D hybrid code in order to
simulate the collapse of the plasma-free cavity behind the Moon and
for the first time to model the formation of this shock. Starting
immediately downstream of the obstacle we consider the evolution of
plasma expansion into the cavity in the frame of reference moving
along with the solar wind. Well-known effects as electric charging of
the cavity affecting the plasma flow and counter streaming ion beams
in the wake are reproduced. Near the apex of the inner Mach cone where
the plasma flows from the opposite sides of the obstacle meet, a shock
wave arises. The shock is produced by the interaction of oppositely
directed proton beams in the plane containing solar wind velocity and
interplanetary magnetic field vectors. In the direction across the
magnetic field and the solar wind velocity, the shock results from the
interaction of the plasma flow with the region of the enhanced magnetic
field inside the cavity that plays the role of magnetic barrier. The
appearance of the standing shock wave is expected at the distance of ~
7RM downstream of the Moon.

---------------------------------------------------------
Title: Growing and coupled transverse oscillations of a multistranded
loop observed by SDO/AIA
Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.; Su, Yang
2012decs.confE..51W Altcode:
We report the first evidence of transverse oscillations of a
multistranded loop with growing amplitudes and internal coupling
observed by SDO/AIA. The loop oscillations were triggered by a
flare-CME event occurring in an active region visible at the limb. The
multiwavelength analysis reveals the temperature dependence of multiple
strands, which show differences in their oscillation amplitudes,
phases and emission evolution. The physical parameters of growing
transverse oscillations in 171A band are measured and the 3-D loop
geometry is determined using STEREO/EUVI-A data. The strands have very
similar oscillation frequencies and appear to oscillate in-phase or in
a quarter-period phase delay. The observed oscillation properties of
the loop strands agree with theoretically expected coupling between
neighboring strands of a loop that undergoes a global kink mode
oscillation. The transverse loop oscillations are also associated with
intensity and loop width variations. We discuss the possible mechanisms
that can excite the kink oscillations with growing amplitudes, and
their associations with intensity and loop width variations.

---------------------------------------------------------
Title: Modeling waves, flows, and instabilities produced by impulsive
events in coronal active regions
Authors: Ofman, L.; Liu, W.; Wang, T. J.; Davila, J. M.; Thompson,
B. J.
2012decs.confE..73O Altcode:
Recent high-resolution observations by SDO/AIA combined with spectral
data from Hinode provide insights into the properties of MHD waves,
flows, and instabilities in coronal active region plasma and
their connection with impulsive energy release. Shear flow driven
instabilities, such as the Kelvin-Helmholtz (KH) instability were
only recently detected in detail in the corona. I will present recent
results of 3D MHD models of slow and fast magnetosonic waves in active
regions excited by jets and quasi-periodic flows driven by micro-flares
at loops' footpoints. I will discuss models of super-fast magnetosonic
waves detected recently by SDO/AIA. I will also discuss models of global
(EIT) waves, and KH instabilities driven by CMEs. The relations between
waves, flows, instabilities, and impulsive events such as flares and
CMEs are becoming apparent thanks to the combination of observational
data analysis and the 3D MHD modeling. Understanding these relations
is useful for coronal seismology and for tracing the flow of energy
from the transition region to the corona.

---------------------------------------------------------
Title: SDO/AIA Observations of Various Coronal EUV Waves Associated
with Flares/CMEs and Their Coronal Seismology Implications
Authors: Liu, Wei; Ofman, Leon; Aschwanden, Markus J.; Nitta, Nariaki;
Zhao, Junwei; Title, Alan M.
2012decs.confE..87L Altcode:
MHD waves can be used as diagnostic tools of coronal seismology to
decipher otherwise elusive critical physical parameters of the solar
corona, such as the magnetic field strength and plasma density. They
are analogous to acoustic waves used in helioseismology, but with
complexities arising from the magnetic field and nonlinearity. Recent
high cadence, high resolution, full-disk imaging observations from
SDO/AIA have opened a new chapter in understanding these waves. Various
types of EUV waves associated with flares/CMEs have been discovered
or observed in unprecedented detail. In this presentation, we will
review such new AIA observations, focusing on the following topics and
their interrelationships: (1) quasi-periodic fast waves traveling along
coronal funnels within CME bubbles at speeds up to 2000 km/s, associated
with flare pulsations at similar frequencies; (2) quasi-periodic wave
trains within broad, diffuse pulses of global EUV waves (so-called
EIT waves) running ahead of CME fronts; (3) interactions of global EUV
waves with local coronal structures on their paths, such as flux-rope
coronal cavities and their embedded filaments (kink oscillations)
and coronal holes/active regions (deflections). We will discuss the
implications of these observations on coronal seismology, on their roles
in transporting energy through different parts of the solar atmosphere,
and on understanding their associated eruptive flares/CMEs.

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Title: SDO/AIA Observations of Quasi-periodic Fast (~1000 km/s)
Propagating (QFP) Waves as Evidence of Fast-mode Magnetosonic Waves
in the Low Corona: Statistics and Implications
Authors: Liu, W.; Ofman, L.; Title, A. M.; Zhao, J.; Aschwanden, M. J.
2011AGUFMSH33A2043L Altcode:
Recent EUV imaging observations from SDO/AIA led to the discovery of
quasi-periodic fast (~2000 km/s) propagating (QFP) waves in active
regions (Liu et al. 2011). They were interpreted as fast-mode
magnetosonic waves and reproduced in 3D MHD simulations (Ofman
et al. 2011). Since then, we have extended our study to a sample
of more than a dozen such waves observed during the SDO mission
(2010/04-now). We will present the statistical properties of these waves
including: (1) Their projected speeds measured in the plane of the sky
are about 400-2200 km/s, which, as the lower limits of their true speeds
in 3D space, fall in the expected range of coronal Alfven or fast-mode
speeds. (2) They usually originate near flare kernels, often in the wake
of a coronal mass ejection, and propagate in narrow funnels of coronal
loops that serve as waveguides. (3) These waves are launched repeatedly
with quasi-periodicities in the 30-200 seconds range, often lasting
for more than one hour; some frequencies coincide with those of the
quasi-periodic pulsations (QPPs) in the accompanying flare, suggestive
a common excitation mechanism. We obtained the k-omega diagrams and
dispersion relations of these waves using Fourier analysis. We estimate
their energy fluxes and discuss their contribution to coronal heating
as well as their diagnostic potential for coronal seismology.

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Title: Three-Dimensional MHD Models of Waves and Flows in Coronal
Active Region Loops
Authors: Ofman, L.; Wang, T.; Davila, J. M.
2011AGUFMSH34B..02O Altcode:
Recent observations show that slow magnetosonic waves are present in
active region loops, and are often associated with subsonic up-flows
of coronal material. In order to study the relation between up-flows
and waves we develop a 3D MHD model of an idealized bi-polar active
region with flows in coronal loops. The model is initiated with a
dipole magnetic field and gravitationally stratified isothermal
atmosphere. To model the effects of flares, coronal material is
injected in small-scale regions at the base of the model active
region. The up-flows have sub-sonic speeds of ∼100 km/s and are
steady or periodic, producing higher density loops by filling magnetic
flux-tubes with injected material. We find that the up-flows produce
fast and slow magnetosonic waves that propagate in the coronal loops. We
perform a parametric study of up-flow magnitude and periodicity, and the
relation with the resulting waves. As expected, we find that the up-flow
speed decreases with loop height due to the diverge of the flux tubes,
while the slow magnetosonic speed is independent of height. When the
amplitude of the driving pulses is increased above the sound speed,
we find that slow shocks are produced in the loops. Using the results
of the 3D MHD model we show that observed slow magnetosonic waves in
active region loops can be driven by impulsive flare-produced up-flows
at the transition region/corona interface of active regions.

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Title: Propagating low-frequency waves in coronal streamers observed
by STEREO COR1
Authors: Kwon, R.; Davila, J. M.; Ofman, L.
2011AGUFMSH43C1981K Altcode:
Compressional and transverse propagating waves high above the solar
surface may play an important role in heating and accelerating the solar
wind. Waves with periods of about an hour were detected in streamers
in the past using SOHO/LASCO observations. STEREO COR1 provides us
with the coronagraph (~4 solar radius) with high temporal resolution
(5 min time cadence) so that it allows us to study low frequency waves
systematically and address line-of-sight ambiguity. We present a method
to detect the periodic oscillations along coronal streamers observed
by STEREO COR1 and to determine the wavelength, period and phase speed
with wavelet analysis. Further, we discuss physical implications of
our results and the possible origin of the waves we found.

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Title: Hybrid Modeling of Solar Wind Ion Heating
Authors: Maneva, Y. G.; Ofman, L.; Vinas, A. -
2011AGUFMSH53B2038M Altcode:
Hybrid simulations are performed to describe the anisotropic and
preferential heating of protons and minor ions in a hot multi-species
solar wind plasma. The electrons are considered as a massless fluid
to ensure that the total charge and current are conserved, whereas the
ions are treated fully kinetically. The energy source is a spectrum of
Alfvén-cyclotron waves. The minor ions are differentially accelerated
depending the wave spectra, the values of their plasma β and their
relative number densities. We discuss the effects of the heating by
Alfvén-cyclotron wave spectra on the ions and compare them with the
ion heating by pure monochromatic large-amplitude Alfvén-cyclotron
waves. We consider the effects of solar wind expansion and compare
the results for various forms of Alfvénic wave spectra on the ion
heating and acceleration in expanding solar wind plasma. The heating
by Alfvén-cyclotron waves in both homogeneous and inhomogeneous
plasma is considered in 2.5D study. We find that inhomogeneity leads to
preferential heating of minor and heavy ions, whereas their differential
acceleration is strongly dependent on the input wave spectra considered.

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Title: Modeling Super-fast Magnetosonic Waves Observed by SDO in
Active Region Funnels
Authors: Ofman, L.; Liu, W.; Title, A.; Aschwanden, M.
2011ApJ...740L..33O Altcode:
Recently, quasi-periodic, rapidly propagating waves have been observed
in extreme ultraviolet by the Solar Dynamics Observatory/Atmospheric
Imaging Assembly (AIA) instrument in about 10 flare/coronal mass
ejection (CME) events thus far. A typical example is the 2010 August 1
C3.2 flare/CME event that exhibited arc-shaped wave trains propagating
in an active region (AR) magnetic funnel with ~5% intensity variations
at speeds in the range of 1000-2000 km s-1. The fast
temporal cadence and high sensitivity of AIA enabled the detection
of these waves. We identify them as fast magnetosonic waves driven
quasi-periodically at the base of the flaring region and develop
a three-dimensional MHD model of the event. For the initial state
we utilize the dipole magnetic field to model the AR and include
gravitationally stratified density at coronal temperature. At the
coronal base of the AR, we excite the fast magnetosonic wave by
periodic velocity pulsations in the photospheric plane confined to a
funnel of magnetic field lines. The excited fast magnetosonic waves
have similar amplitude, wavelength, and propagation speeds as the
observed wave trains. Based on the simulation results, we discuss the
possible excitation mechanism of the waves, their dynamical properties,
and the use of the observations for coronal MHD seismology.

---------------------------------------------------------
Title: Coronal Seismology in the SDO Era: AIA Observations of Various
Coronal Waves Associated with CMEs/Flares
Authors: Liu, Wei; Ofman, Leon; Aschwanden, Markus J.; Nitta, Nariaki;
Zhao, Junwei; Title, Alan M.
2011sdmi.confE..49L Altcode:
MHD waves, as critical diagnostic tools of coronal seismology, can be
used to decipher otherwise elusive physical parameters of the solar
corona, such as the magnetic field strength and plasma density. They
are analogous to acoustic waves used in helioseismology. Recent high
cadence, high resolution, full-disk imaging observations from SDO/AIA
have opened a new chapter in understanding these waves. Various types
of waves associated with flares and/or CMEs have been discovered. In
this presentation, we will review such new AIA observations, focusing
on the following topics: (1) fine structures in CME-related global EUV
waves (so-called EIT waves), including a diffuse pulse superimposed
with multiple sharp fronts or "ripples" (Liu et al. 2010, ApJL); (2)
quasi-periodic fast waves traveling in coronal funnels at speeds up to
2000 km/s and associated with flares pulsating at similar frequencies
(Liu et al. 2011, ApJL); (3) interaction of global EUV waves with local
coronal structures on their paths, such as flux-rope coronal cavities
(triggered kink oscillations, Liu et al. in preparation) and coronal
holes/active regions (deflection). We will discuss the implications
of these observations on coronal seismology and on understanding their
associated flares and CMEs. We also anticipate to exchange ideas with
helioseismologists at this workshop, in a hope to bring together coronal
seismology and helioseismology techniques to advance our understanding
of solar oscillations from the interior to the upper atmosphere.

---------------------------------------------------------
Title: Slow Magnetoacoustic Wave Oscillation of an Expanding
Coronal Loop
Authors: Schmidt, J. M.; Ofman, L.
2011ApJ...739...75S Altcode:
We simulated an expanding loop or slow coronal mass ejection (CME)
in the solar corona dimensioned with size parameters taken from real
coronal expanding loops observed with the STEREO spacecraft. We find
that the loop expands to Sun's size within about one hour, consistent
with slow CME observations. At the top of the loop, plasma is being
blown off the loop, enabled with the reconnection between the loop's
flux rope magnetic field and the radial magnetic field of the Sun,
thus yielding feeding material for the formation of the slow solar
wind. This mechanism is in accordance with the observed blob formation
of the slow solar wind. We find wave packets traveling with local
sound speed downward toward the footpoints of the loop, already seen
in coronal seismology observations and simulations of stationary
coronal loops. Here, we generalize these results for an expanding
medium. We also find a reflection of the wave packets, identified
as slow magnetoacoustic waves, at the footpoints of the loop. This
confirms the formation of standing waves within the coronal loop. In
particular, the reflected waves can partly escape the loop top and
contribute to the heating of the solar wind. The present study improves
our understanding on how loop material can emerge to form blobs, major
ingredients of slow CMEs, and how the release of the wave energy stored
in slow magnetoacoustic waves, and transported away from the Sun within
expanding loops, contributes to the acceleration and formation of the
slow solar wind.

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Title: Hybrid simulation of ion-acoustic waves excitation by
non-linear Alfvén wave
Authors: Israelevich, P. L.; Ofman, L.
2011AdSpR..48...25I Altcode:
The results of one dimensional hybrid simulation of standing Alfvén
wave in low beta plasma are presented. Plasma is accelerated from the
anti-nodes toward the nodes of the standing waves with finite amplitude
under the action of the variable magnetic field pressure. As a result,
a sharp maximum of the number density (and electron pressure) arises
near the nodes of the standing wave. The plasma flow is spatially
modulated with half wavelength of the driving Alfvén wave. Standing
ion-acoustic waves produced by spatial modulation of the flow are
observed in hybrid simulation. The effective parallel electric field
E∗=E+{1}/{ne}∇pe appears due to both electron
pressure gradient near the nodes and electron pressure variations in
the acoustic waves.

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Title: Direct Imaging of Quasi-periodic Fast Propagating Waves of
~2000 km s-1 in the Low Solar Corona by the Solar Dynamics
Observatory Atmospheric Imaging Assembly
Authors: Liu, Wei; Title, Alan M.; Zhao, Junwei; Ofman, Leon;
Schrijver, Carolus J.; Aschwanden, Markus J.; De Pontieu, Bart;
Tarbell, Theodore D.
2011ApJ...736L..13L Altcode: 2011arXiv1106.3150L
Quasi-periodic propagating fast mode magnetosonic waves in the solar
corona were difficult to observe in the past due to relatively low
instrument cadences. We report here evidence of such waves directly
imaged in EUV by the new Atmospheric Imaging Assembly instrument
on board the Solar Dynamics Observatory. In the 2010 August 1 C3.2
flare/coronal mass ejection event, we find arc-shaped wave trains of
1%-5% intensity variations (lifetime ~200 s) that emanate near the
flare kernel and propagate outward up to ~400 Mm along a funnel of
coronal loops. Sinusoidal fits to a typical wave train indicate a phase
velocity of 2200 ± 130 km s-1. Similar waves propagating
in opposite directions are observed in closed loops between two flare
ribbons. In the k-ω diagram of the Fourier wave power, we find a
bright ridge that represents the dispersion relation and can be well
fitted with a straight line passing through the origin. This k-ω
ridge shows a broad frequency distribution with power peaks at 5.5,
14.5, and 25.1 mHz. The strongest signal at 5.5 mHz (period 181 s)
temporally coincides with quasi-periodic pulsations of the flare,
suggesting a common origin. The instantaneous wave energy flux
of (0.1-2.6) × 107 erg cm-2 s-1
estimated at the coronal base is comparable to the steady-state heating
requirement of active region loops.

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Title: Multi-fluid Model of a Streamer at Solar Minimum and Comparison
with Observations
Authors: Ofman, Leon; Abbo, Lucia; Giordano, Silvio
2011ApJ...734...30O Altcode:
We present the results of a time-dependent 2.5-dimensional three-fluid
magnetohydrodynamic model of the coronal streamer belt, which is
compared with the slow solar wind plasma parameters obtained in the
extended corona by the UV spectroscopic data from the Ultraviolet
Coronagraph Spectrometer (UVCS) on board SOHO during the past
minimum of solar activity (Carrington Rotation 1913). Our previous
three-fluid streamer model has been improved by considering the solar
magnetic field configuration relevant for solar minimum conditions,
and preferential heating for O5 + ions. The model was run
until a fully self-consistent streamer solution was obtained in the
quasi-steady state. The plasma parameters from the multi-fluid model
were used to compute the expected UV observables from H I Lyα 1216
Å and O VI 1032 Å spectral lines, and the results were compared in
detail with the UVCS measurements. A good agreement between the model
and the data was found. The results of the study provide insight into
the acceleration and heating of the multi-ion slow solar wind.

---------------------------------------------------------
Title: SDO/AIA Observation of Kelvin-Helmholtz Instability in the
Solar Corona
Authors: Ofman, L.; Thompson, B. J.
2011ApJ...734L..11O Altcode: 2011arXiv1101.4249O
We present observations of the formation, propagation, and decay of
vortex-shaped features in coronal images from the Solar Dynamics
Observatory associated with an eruption starting at about 2:30
UT on 2010 April 8. The series of vortices were formed along the
interface between an erupting (dimming) region and the surrounding
corona. They ranged in size from several to 10 arcsec and traveled
along the interface at 6-14 km s-1. The features were
clearly visible in six out of the seven different EUV wave bands of
the Atmospheric Imaging Assembly. Based on the structure, formation,
propagation, and decay of these features, we identified the event as
the first observation of the Kelvin-Helmholtz instability (KHI) in the
corona in EUV. The interpretation is supported by linear analysis and
by a nonlinear 2.5-dimensional magnetohydrodynamic model of KHI. We
conclude that the instability is driven by the velocity shear between
the erupting and closed magnetic field of the coronal mass ejection. The
shear-flow-driven instability can play an important role in energy
transfer processes in coronal plasma.

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Title: SDO/AIA Observations of a Global EUV Disturbance Traveling
into a Coronal Cavity and Its Subsequent Oscillations: New Evidence
of Fast Mode MHD Waves
Authors: Liu, Wei; Aschwanden, M. J.; Ofman, L.; Nitta, N. V.; Tarbell,
T. D.
2011SPD....42.0906L Altcode: 2011BAAS..43S.0906L
We report new SDO/AIA observations of a global EUV disturbance
that propagates at 600 km/s and sweeps through a coronal cavity,
instigating its bodily transverse oscillations. The high temporal
resolution and large FOV of AIA allow us to clearly see, for the first
time, the timing coincidence between the onsets of the oscillations
and the arrival of the disturbance at increasing distances covering
300 Mm in the neighborhood of the cavity. There is a time delay of
the oscillations from the near side to the far side of the cavity,
which is consistent with the travel time of the global perturbation. In
addition, we find a fine structure consisting of evenly spaced pulses
of periods 100-120 s within the global disturbance. In contrast, the
CME loop expansion falls behind the global disturbance at a smaller
velocity of 200 km/s. These observations suggests that this global
disturbance is a real fast mode MHD wave that continues propagating
into the cavity, rather than an apparent wave caused by CME expulsion
that is not expected to penetrate through a topological separatrix,
including the flux rope cavity boundary here. The cavity and its
hosted prominence have oscillation amplitudes of 20 km/s and periods
of 20-30 minutes. Such unusually long periods, compared with a few
minutes commonly observed in coronal loops, likely reflect kink mode
oscillations of the long cavity flux rope of a large length (a fraction
of the solar radius).

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Title: Evidence For Forced Kink-mode Loop Oscillations Observed
By Sdo/aia
Authors: Wang, Tongjiang; Ofman, L.; Davila, J. M.; Su, Y.
2011SPD....42.2113W Altcode: 2011BAAS..43S.2113W
Transverse loop oscillations were first discovered by TRACE in EUV
wavelength and interpreted as global fast kink modes. These oscillations
are impulsively excited by flares or filament eruptions and often show
a strong damping within few oscillation periods. The oscillations and
the damping mechanism have been intensively studied in observation
and theory, leading to great advance in coronal seismology. However,
measurements of the damping rate remains difficult, often limited
by the short length of the detectable oscillation sequence in one
single filter. SDO/AIA with multiple wavebands of unprecedentedly high
sensitivity and wide temperature coverage provides a good opportunity
in improving the accuracy of these measurements. Here we present an
example of long-lasting oscillation events observed using SDO/AIA. In
this event, kink oscillations of a slowly evolving coronal loop seen
in 171, 193 and 211 A bands are excited by several flow ejections. The
oscillations last over one and a half hours with periods of 3-4 min
and no evident decay. In particular, the amplitudes of the oscillations
show increase during the period of a large flow ejection with speeds of
200-300 km/s which lasts for about a half hour, and then falls down at
speeds of 60-70 km/s measured in 304 A band. We interpret the growing
oscillations as driven fast magnetosonic waves by impacting flows. We
perform preliminary 3D MHD study of the event using an idealized
bipolar active region model.

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Title: 3D Structure and the Evolution of EUV Bright Points Observed
by STEREO/SECCHI/EUVI: Evidence for Coronal Magnetic Reconnection
Driven by Emerging Magnetic Flux?
Authors: Kwon, Ryun Young; Davila, J. M.; Ofman, L.
2011SPD....42.1808K Altcode: 2011BAAS..43S.1808K
The 3D structure of EUV bright points and its physical relation
with the underlying magnetic flux concentrations are unveiled here
observationally for the first time. The heights of EUV bright points
have been measured within their lifetimes by 3D reconstruction method
developed by Kwon, Chae, &amp; Zhang (2010) using data sets taken from
STEREO/SECCHI/EUVI. We found three distinct changes in the heights which
were decreasing, increasing, and constant. In general, EUV bright points
are multi-temperature loop system whose hot loops (T 106.2K)
with an average height of 8.9Mm are overlying cooler loops (T &lt;
106.0K) with an average height of 6.7Mm. This loop system has
cool legs which have the peak temperature of T 104.9K and
an average height of 5.2Mm. The heights were found to have remarkable
correlations with lengths and distances of two opposite magnetic
flux concentrations, indicating that the 3D structures of bright
points were determined by the geometry of associated photospheric
magnetic fluxes. Accordingly, the three types of bright points we
found were associated with three distinct types of their underlying
magnetic fragments: converging, diverging, and shearing. In all cases,
both flux emergences and flux cancellations were observed during the
lifetimes of the bright points. The flux emergences were dominant in
the initial phase and the flux cancellations were significant after
the intensities reached their maxima. Our results suggest that EUV
bright points may be the flaring loop systems (Masuda et al. 1994)
formed by coroanl magnetic reconnection and the flux emergence appears
to be important to driving the coronal magnetic reconnection.

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Title: Pulsed Flows Along a Cusp Structure Observed with SDO/AIA
Authors: Thompson, Barbara; Démoulin, P.; Mandrini, C.; Mays, M.;
Ofman, L.; Van Driel-Gesztelyi, L.; Viall, N.
2011SPD....42.2117T Altcode: 2011BAAS..43S.2117T
We present observations of a cusp-shaped structure that formed after
a flare and coronal mass ejection on 14 February 2011. Throughout
the evolution of the cusp structure, blob features up to a few Mm in
size were observed flowing along the legs and stalk of the cusp at
projected speeds ranging from 50 to 150 km/sec. Around two dozen blob
features, on order of 1 - 3 minutes apart, were tracked in multiple
AIA EUV wavelengths. The blobs flowed outward (away from the Sun)
along the cusp stalk, and most of the observed speeds were either
constant or decelerating. We attempt to reconstruct the 3-D magnetic
field of the evolving structure, discuss the possible drivers of the
flows (including pulsed reconnection and tearing mode instability),
and compare the observations to studies of pulsed reconnection and
blob flows in the solar wind and the Earth's magnetosphere.

---------------------------------------------------------
Title: Direct Imaging by SDO/AIA of Quasi-periodic Propagating Fast
Mode Magnetosonic Waves of 2000 km/s in the Solar Corona
Authors: Liu, Wei; Title, A. M.; Zhao, J.; Ofman, L.; Schrijver,
C. J.; Aschwanden, M. J.; De Pontieu, B.; Tarbell, T. D.
2011SPD....42.2114L Altcode: 2011BAAS..43S.2114L
Quasi-periodic, propagating fast mode magnetosonic waves in the
corona were difficult to observe in the past due to relatively low
instrument cadences. We report here unprecedented evidence of such
waves directly imaged in EUV by the new SDO/AIA instrument. In the 2010
August 1 C3.2 flare/CME event, we find arc-shaped wave trains of 1-5%
intensity variations emanating near the flare kernel and propagating
outward along a funnel of coronal loops. Sinusoidal fits to a typical
wave train indicate a phase velocity of 2350 +/- 210 km/s. Similar
waves propagating in opposite directions are observed in closed loops
between two flare ribbons. In the k-omega diagram of the Fourier wave
power, we find a bright ridge that represents the dispersion relation
and can be well fitted with a straight line passing through the
origin, giving an equal phase and group velocity of 1630 +/- 760 km/s
averaged over the event. This k-omega ridge shows a broad frequency
distribution with prominent power at four non-harmonic frequencies,
5.5, 14.5, 25.1, and 37.9 mHz, among which the 14.5 mHz (period:
69 s) signal is the strongest. The signal at 5.5 mHz (period: 181 s,
same as chromospheric 3-minute oscillations) temporally coincides with
flare pulsations, suggesting a common origin of possibly quasi-periodic
magnetic reconnection. The instantaneous wave energy flux of (0.1-2.6)e7
ergs/cm2/s estimated at the coronal base is comparable to
the steady-state heating requirement of active region loops.

---------------------------------------------------------
Title: Modeling Waves And Flows In Active Region Loops
Authors: Ofman, Leon; Wang, T.; Davila, J. M.
2011SPD....42.1815O Altcode: 2011BAAS..43S.1815O
Recent Hinode/EIS observations indicated that slow magnetosonic
waves are present in active region loops. Some of the spectral data
were also interpreted as evidence of quasi-periodic flows. We perform
three dimensional MHD model of an active region with waves and flows in
coronal loops. The model is initiated with a dipole magnetic field and
gravitationally stratified density, and velocity pulses are driven
periodically in localized regions at the footpoints of magnetic
loops. The resulting flows produce higher density loops compared to
the surrounding plasma by injecting material along the field. We find
that the excitation of periodic flows with subsonic speeds result in
the excitation of slow magnetosonic waves that propagate along the
loops. The phase speed of the waves is 100 km/s, close to coronal sound
speed. When the amplitude of the driving pulses is increased we find
that slow shock trains are produced. Using the results of the 3D MHD
model we suggest that the observed slow magnetosonic waves and quasi
periodic-flows are driven by the same quasi-periodic impulsive events
at the bases of active regions.

---------------------------------------------------------
Title: Modeling Fast Magnetosonic Waves Observed by SDO in Active
region Funnels
Authors: Ofman, Leon; Liu, W.; Title, A.; Aschwanden, M.
2011SPD....42.2104O Altcode: 2011BAAS..43S.2104O
Recently, quasi-periodic, propagating waves have been observed in EUV by
the SDO/AIA instrument in about 10 flare/CME events thus far. A typical
example is the waves associated with the 2010 August 1 C3.2 flare/CME
that exhibited arc-shaped wave trains propagating in an active region
magnetic funnel with 5% intensity variations at speeds in the range
of 1000-2000 km/s. The fast temporal cadence and high sensitivity of
AIA enabled the detection of these waves. We identify them as fast
magnetosonic waves driven quasi-periodically at the base of the flaring
region, and develop a three-dimensional MHD model of the event. For
the initial state we utilize the dipole magnetic field to model the
active region, and include gravitationally stratified density at coronal
temperature. At the coronal base of the active region we excite the fast
magnetosonic wave by periodic velocity pulsations in the photospheric
plane confined to the funnel of magnetic field line. The excited fast
magnetosonic waves have similar amplitude, wavelength and propagation
speeds as the observed wave trains. Based on the simulation results, we
discuss the possible excitation mechanism of the waves, their dynamical
properties, and the use of the event for coronal MHD seismology.

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Title: Slow-Mode Oscillations of Hot Coronal Loops Excited at
Flaring Footpoints
Authors: Wang, Tongjiang; Liu, W.; Ofman, L.; Davila, J. M.
2011SPD....42.2214W Altcode: 2011BAAS..43S.2214W
A large number of strongly damped oscillations in hot coronal loops
have been observed by SOHO/SUMER in the past decade in Doppler shifts
of flaring (&gt;6 MK) lines (Fe XIX and Fe XXI). These oscillations
with periods on the order of 10-30 min were interpreted as fundamental
standing slow modes. They often manifest features such as recurrence
and association with a flow (100-300 km/s) pulse preceding to the
oscillation, which suggests that they are likely driven by microflares
at the footpoints. With coordinated RHESSI observations, we have found
a dozen such events supporting this conjecture. A typical event is
presetned here. By analyzing RHESSI hard X-ray and GOES/SXI soft
X-ray emissions as well as SUMER Doppler shifts, we identify the
flare that triggers the loop oscillations. From RHESSI spectra, we
measure physical parameters such as temperature, emission measure,
and thermal/non-thermal energy contents as functions of time. We
discuss the wave excitation mechanism based on these observations. Our
results provide important observational constraints that can be used
for improving theoretical models of magnetosonic wave excitation,
and for coronal seismology.

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Title: The Role of Active Region Loop Geometry. II. Symmetry Breaking
in Three-dimensional Active Region: Why are Vertical Kink Oscillations
Observed so Rarely?
Authors: Selwa, M.; Solanki, S. K.; Ofman, L.
2011ApJ...728...87S Altcode:
We present numerical results of simulations of kink oscillations of
coronal loops in an idealized active region (AR) that is initialized
as a potential dipole magnetic configuration with gravitationally
stratified density. We consider loops, with density higher than
the surrounding plasma, embedded into the dipolar AR. We study the
excitation of kink oscillations of such loops by velocity pulses at
different positions, of a given duration and amplitude. The position of
the pulse varies in the parametric studies. For a central (symmetric)
loop within the AR, we find that the amplitude of vertical kink
oscillations is significantly amplified in comparison to horizontal
kink oscillations for exciters located centrally (symmetrically) below
the loop. For pulses initiated further from such a symmetric loop a
combination of vertical and horizontal oscillations is excited. The
scenario changes significantly when we study an inclined loop
(non-symmetric within a dipole field). In this case, we do not
see vertical kink oscillations of any significant amplitude being
excited, while horizontal ones can be easily detected. These results
indicate that the reason why vertical kink oscillations are observed so
rarely is that their excitation requires a set of conditions to occur
simultaneously: the exciting pulse must be located roughly below the
loop apex and the loop itself must be located symmetrically within
the group of loops. The new findings of the present study show the
importance of not only the position of the pulse, but mainly of the
location of the loop within the set of field lines having the same
magnetic connectivity. We find that the slow propagating wave is excited
in all the studied loops and its excitation does not depend either on
the geometry of the loop or the pulse. We discuss TRACE observations
of coronal loop oscillations in view of our findings and find that
our results can be used for identifying the polarization of the kink
mode based on the location of the loop within the set of field lines
of the same connectivity and the position of the flare.

---------------------------------------------------------
Title: Probing the Thermodynamics and Kinematics of Solar Coronal
Streamers
Authors: Airapetian, V.; Ofman, L.; Sittler, E. C.; Kramar, M.
2011ApJ...728...67A Altcode:
We present the results of a resistive magnetohydrodynamic (MHD) model of
an equatorially confined streamer belt using observational constraints
for the heating and acceleration of the solar wind. To initiate the
2.5 dimensional MHD calculations, we used the Potential Field Source
Surface model of the coronal magnetic field configuration with the
boundary conditions at the photosphere specified by the National Solar
Observatory/GONG magnetogram data. Calculations were performed for the
fully thermal conductive model with observationally constrained heat
flux, q eff, and the effective temperature, T eff,
derived from the semi-empirical steady-state two-dimensional model of
the solar corona. We compared the results of the model to a polytropic
solution (polytropic index γ = 1.05), and demonstrate that our MHD
model is in better agreement with reconstructed density and observed
flow velocity than the polytropic model for the coronal streamer
structure observed during 2008 February 1-13 by the COR1 coronagraph
on board the STEREO spacecraft.

---------------------------------------------------------
Title: The Role of Active Region Loop Geometry. I. How Can it Affect
Coronal Seismology?
Authors: Selwa, M.; Ofman, L.; Solanki, S. K.
2011ApJ...726...42S Altcode:
We present numerical results of coronal loop oscillation excitation
using a three-dimensional (3D) MHD model of an idealized active region
(AR) field. The AR is initialized as a potential dipole magnetic
configuration with gravitationally stratified density and contains a
loop with a higher density than its surroundings. We study different
ways of excitation of vertical kink oscillations of this loop by
velocity: as an initial condition, and as an impulsive excitation
with a pulse of a given position, duration, and amplitude. We vary the
geometry of the loop in the 3D MHD model and find that it affects both
the period of oscillations and the synthetic observations (difference
images) that we get from oscillations. Due to the overestimated
effective length of the loop in the case of loops which have maximum
separation between their legs above the footpoints (&gt;50% of observed
loops), the magnetic field obtained from coronal seismology can also
be overestimated. The 3D MHD model shows how the accuracy of magnetic
field strength determined from coronal seismology can be improved. We
study the damping mechanism of the oscillations and find that vertical
kink waves in 3D stratified geometry are damped mainly due to wave
leakage in the horizontal direction.

---------------------------------------------------------
Title: SDO/AIA Observation of Kelvin-Helmholtz Instability in the
Solar Corona associated with CME
Authors: Ofman, L.; Thompson, B. J.
2010AGUFMSH14A..02O Altcode:
We present observations of the formation, propagation and decay
of vortex-shaped features in coronal images from the Solar Dynamics
Observatory (SDO) associated with Coronal Mass Ejection (CME) at about
2:34UT on Apr 8, 2010. The series of vortices are seen at 3:20UT
to 3:37UT formed along the interface between erupting (dimming)
region and the surrounding corona and ranged in size from several
to ten arcseconds, traveling along the interface at approximately
5 km/sec. The features are clearly visible in five out of the six
different EUV wavebands of the Atmospheric Imaging Assembly (AIA). Based
on the structure, formation, propagation and decay of these features, we
conclude that these are the first observations of the Kelvin-Helmholtz
(KH) instability in the corona. The KH instability is likely driven
by the velocity shear between the erupting and closed magnetic field
regions. We compare the dynamics and structure of SDO/AIA observation
to an MHD model of KH instability in the nonlinear stage in magnetized
plasma, and find good agreement.

---------------------------------------------------------
Title: Winds from Luminous Late-type Stars. II. Broadband Frequency
Distribution of Alfvén Waves
Authors: Airapetian, V.; Carpenter, K. G.; Ofman, L.
2010ApJ...723.1210A Altcode: 2010arXiv1008.3955A
We present the numerical simulations of winds from evolved giant
stars using a fully nonlinear, time-dependent 2.5-dimensional
magnetohydrodynamic (MHD) code. This study extends our previous fully
nonlinear MHD wind simulations to include a broadband frequency spectrum
of Alfvén waves that drive winds from red giant stars. We calculated
four Alfvén wind models that cover the whole range of the Alfvén wave
frequency spectrum to characterize the role of freely propagated and
reflected Alfvén waves in the gravitationally stratified atmosphere
of a late-type giant star. Our simulations demonstrate that, unlike
linear Alfvén wave-driven wind models, a stellar wind model based
on plasma acceleration due to broadband nonlinear Alfvén waves can
consistently reproduce the wide range of observed radial velocity
profiles of the winds, their terminal velocities, and the observed
mass-loss rates. Comparison of the calculated mass-loss rates with the
empirically determined mass-loss rate for α Tau suggests an anisotropic
and time-dependent nature of stellar winds from evolved giants.

---------------------------------------------------------
Title: Web-Based Data Processing System for Automated Detection of
Oscillations with Applications to the Solar Atmosphere
Authors: Sych, R. A.; Nakariakov, V. M.; Anfinogentov, S. A.; Ofman, L.
2010SoPh..266..349S Altcode: 2010SoPh..tmp..154S; 2010arXiv1005.3591S
A web-based, interactive system for the remote processing of imaging
data sets (i.e., EUV, X-ray, and microwave) and the automated
interactive detection of wave and oscillatory phenomena in the solar
atmosphere is presented. The system targets localized, but spatially
resolved, phenomena such as kink, sausage, and longitudinal propagating
and standing waves. The system implements the methods of Periodmapping
for pre-analysis, and Pixelized Wavelet Filtering for detailed analysis
of the imaging data cubes. The system is implemented on the dedicated
data-processing server http://pwf.iszf.irk.ru, which is situated at
the Institute of Solar-Terrestrial Physics, Irkutsk, Russia. Input
data in the .sav, .fits, or .txt formats can be submitted via the
local and/or global network (the Internet). The output data can be in
the png, jpeg, and binary formats, on the user's request. The output
data are periodmaps; narrowband amplitude, power, phase and correlation
maps of the wave's sources at significant harmonics and in the chosen
spectral intervals, and mpeg movies of their evolution. The system
was tested by the analysis of the EUV and microwave emission from the
active region NOAA 10756 on 4 May 2005 observed with TRACE and the
Nobeyama Radioheliograph. The similarity of the spatial localization
of three-minute propagating waves, near the footpoint of locally open
magnetic-field lines determined by the potential-field extrapolation,
in both the transition region and the corona was established. In the
transition region the growth of the three-minute amplitude was found
to be accompanied by the decrease in the line-of-sight angle to the
wave-propagation direction.

---------------------------------------------------------
Title: Wave Modeling of the Solar Wind
Authors: Ofman, Leon
2010LRSP....7....4O Altcode:
The acceleration and heating of the solar wind have been studied
for decades using satellite observations and models. However, the
exact mechanism that leads to solar wind heating and acceleration
is poorly understood. In order to improve the understanding of the
physical mechanisms that are involved in these processes a combination
of modeling and observational analysis is required. Recent models
constrained by satellite observations show that wave heating in
the low-frequency (MHD), and high-frequency (ion-cyclotron) range
may provide the necessary momentum and heat input to coronal plasma
and produce the solar wind. This review is focused on the results of
several recent solar modeling studies that include waves explicitly in
the MHD and the kinetic regime. The current status of the understanding
of the solar wind acceleration and heating by waves is reviewed.

---------------------------------------------------------
Title: Modeling the Slow Solar Wind during the Solar Minimum
Authors: Ofman, L.; Kramar, M.
2010ASPC..428..321O Altcode: 2010arXiv1004.4847O
During the solar minimum, STEREO observations show that the
three-dimensional structure of the solar corona can be described
well by a tilted bipolar magnetic configuration. The slow solar wind
is modeled using a three-fluid model that includes heavy ions such
as He II and O VI. The model is initialized with a dipole magnetic
field and spherically symmetric density. The resulting steady state,
non-potential, and non-uniform streamer configuration calculated with
this model is compared to STEREO observations of the streamer density
structure. SOHO/UVCS observations are used to compare the O VI emission
to model results. We discuss the unique properties of the solar wind
produced in this configuration.

---------------------------------------------------------
Title: Three-dimensional MHD Model Of Active Region Loop Oscillations
With Background Flow
Authors: Ofman, Leon; Schmidt, J.; Wang, T.
2010AAS...21630204O Altcode:
Recent observations by Hinode satellite show that oscillating coronal
loops with periods of several minutes contain cool flowing material
at 100 km/s. The flow may affects significantly the oscillations and
the damping of the wave energy. We model the oscillating loops with
background flow in 3D MHD model of a bi-polar active region, that
includes the effects of loop curvature and chromospheric boundary
conditions. The oscillations are excited impulsively by a velocity
pulse. We study the effects of flow magnitude, and loop parameters
on the excitation and damping of the oscillations. The results of the
parametric study have implication for coronal seismology, and for wave
heating of active region coronal loops.

---------------------------------------------------------
Title: Three-dimensional MHD Modeling Of Waves In Active Regions:
Comparison To Observations
Authors: Schmidt, Joachim; Ofman, L.
2010AAS...21640717S Altcode: 2010BAAS...41..862S
We present the results of 3D MHD models of waves in active regions
generated by a CME. We study the propagation and reflection of the
waves in the solar corona and compare to recent STEREO observations. We
also investigate the excitation of oscillations in individual coronal
loops in realistic active region magnetic field initialized with
extrapolated WSO magnetogram data. We compare the results of the model
to EUV observations and demonstrate the development and application
of coronal seismology.

---------------------------------------------------------
Title: What Do High-resolution EIT Waves Tell Us About CMEs?
Authors: Thompson, Barbara; Biesecker, D. A.; Nitta, N.; Ofman, L.;
West, M. J.
2010AAS...21640229T Altcode:
Although many studies have demonstrated that some coronal waves are
not generated by coronal mass ejections, we have learned a great
deal about the ability of coronal mass ejections to drive large-scale
coronal waves, also called "EIT waves." We present new results based
on EIT wave amplitude, timing, speed, and direction of propagation,
with respect to their correlation with CME-related dimmings, speeds,
locations and widths. Furthermore, we demonstrate the ability to
correlate different aspects of EIT waves with some of the observed
structure of CMEs observed in coronagraph data. Finally, we expand
on the discussion of the types of wave modes that can be generated
by a coronal mass ejection, and how these observations can serve as a
diagnostic of the type of impulse a CME can deliver to the surrounding
corona. These diagnostics are obtained by examining the motion of
individual field lines, requiring high-resolution observations like
those provided by TRACE and SDO/AIA.

---------------------------------------------------------
Title: The Role of Active Region Topology in Excitation, Trapping,
and Damping of Coronal Loop Oscillations
Authors: Selwa, M.; Ofman, L.
2010ApJ...714..170S Altcode:
We investigate the role of magnetic field topology in dense coronal
loop oscillation by the means of three-dimensional magnetohydrodynamic
numerical simulations of two models of idealized active regions
(ARs). The first AR model is initialized as a straight cylinder
surrounded by the field lines of the same length and orientation. The
second model consists of a potential dipole magnetic configuration and
contains a loop with a higher density than its surroundings. Dipole
field lines have position-dependent length and orientation in contrary
to straight ones. We study different ways of excitation of transverse
loop oscillations by an external pulse and a nearly eigenmode excitation
implemented inside the loop. We find that perturbation acting directly
on a single loop excites oscillations both in cylindrical and dipole
loops. However, the leakage of the wave energy is larger in a curved
loop compared to a straight loop. External excitation of the whole AR
is efficient in the excitation of oscillation in the straight field
configuration, but results in less efficient excitation in the case of
dipole field. We show that excitation of collective motion of straight
field lines having the same wave periods and planes of the oscillations
requires much less energy than excitation of dipole field lines having
position-dependent orientation and wave periods and being excited
individually, not having a collective mode of oscillation. We conclude
that coherent motion of straight field lines is one of the factors that
decrease the energy leakage from an oscillating loop, while individual
motions of dipole field lines require more energy from the source to
produce the loop oscillations, and also lead to higher damping rate
compared to the straight field case. We discuss Transition Region and
Coronal Explorer (TRACE) observations of coronal loop oscillations in
view of our theoretical findings. We show several examples of time
signatures of transversal loop oscillations observed by TRACE that
agree with numerical simulations of externally excited oscillations.

---------------------------------------------------------
Title: Acceleration and Heating of Solar Wind Ions by Nonlinear Waves
Authors: Ofman, L.
2010aogs...21....1O Altcode:
Recent advances in observations and modeling provide better
understanding of the possible role of waves in the acceleration and
heating of the solar wind. Ulysses, ACE, Helios, SOHO, TRACE, and other
satellite observations found ample evidence for waves in the corona and
in the solar wind. Numerical models show that nonlinear interaction
between MHD waves and the plasma can provide the necessary momentum
and heat input to produce the fast solar wind in coronal holes. It
was also found that the heating of solar wind protons and heavy ions
is more significant than of electrons. Temperature anisotropy suggests
that ion-cyclotron wave heating is taking place in heavy ions. In this
review article, several recent observations and numerical models of
nonlinear wave driven wind are discussed.

---------------------------------------------------------
Title: Propagating Intensity Disturbances In Coronal Loops: Waves
Or Flows?
Authors: Wang, Tongjiang; Ofman, L.; Davila, J. M.
2010AAS...21640715W Altcode: 2010BAAS...41..862W
Quasi-periodic propagating intensity disturbances were found by
SOHO/EIT and TRACE imaging observations in fanlike coronal loops
10 year ago. The 3 min and 5 min oscillations have been interpreted
as propagating slow magnetoacoustic waves which originate from the
photospheric p-mode oscillations due to the wave leakage. However,
some cases show oscillations with periodicities of more than 10 min,
which are hard to explain by wave leakage, and so were argued in some
studies that they may be periodic flows. In this presentation, we report
the first observation of multiple-periodic (12 and 25 min) propagating
disturbances along a fan-like coronal structure simultaneously
detected in both intensity and Doppler shift in the Fe XII line with
EIS onboard Hinode. We measured Doppler shift amplitude of 1-2 km/s,
relative intensity amplitude of (3-5)% and the apparent propagation
speed of 100-120 km/s. The amplitude relationship between intensity
and Doppler shift oscillations provides convincing evidence that these
propagating features are a manifestation of slow magnetoacoustic waves
but not flows. The feature of symmetric line profiles also confirms
that the measured small Doppler-shift amplitudes are not due to the
line wing enhancement caused by high-speed flows. A new application
of coronal seismology is provided based on these observations, with
which we determine the inclination angle of the magnetic field and
the temperature of a coronal loop. We will also show the result of
multi-temperature line analysis to explore the temperature-dependent
behavior of this phenomenon.

---------------------------------------------------------
Title: Hybrid model of inhomogeneous solar wind plasma heating by
Alfvén wave spectrum: Parametric studies
Authors: Ofman, L.
2010JGRA..115.4108O Altcode: 2010JGRA..11504108O
Observations of the solar wind plasma at 0.3 AU and beyond show that
a turbulent spectrum of magnetic fluctuations is present. Remote
sensing observations of the corona indicate that heavy ions
are hotter than protons and their temperature is anisotropic
(T$\perp$/T$\parallel$ $\gg$ 1). We study
the heating and the acceleration of multi-ion plasma in the solar
wind by a turbulent spectrum of Alfvénic fluctuations using a 2-D
hybrid numerical model. In the hybrid model the protons and heavy
ions are treated kinetically as particles, while the electrons
are included as neutralizing background fluid. This is the first
two-dimensional hybrid parametric study of the solar wind plasma that
includes an input turbulent wave spectrum guided by observation with
inhomogeneous background density. We also investigate the effects of
He++ ion beams in the inhomogeneous background plasma density
on the heating of the solar wind plasma. The 2-D hybrid model treats
parallel and oblique waves, together with cross-field inhomogeneity,
self-consistently. We investigate the parametric dependence of
the perpendicular heating, and the temperature anisotropy in the
H+-He++ solar wind plasma. It was found that the
scaling of the magnetic fluctuations power spectrum steepens in the
higher-density regions, and the heating is channeled to these regions
from the surrounding lower-density plasma due to wave refraction. The
model parameters are applicable to the expected solar wind conditions
at about 10 solar radii.

---------------------------------------------------------
Title: Global Simulation of an Extreme Ultraviolet Imaging Telescope
Wave
Authors: Schmidt, J. M.; Ofman, L.
2010ApJ...713.1008S Altcode:
We use the observation of an Extreme Ultraviolet Imaging Telescope (EIT)
wave in the lower solar corona, seen with the two Solar Terrestrial
Relations Observatory (STEREO) spacecraft in extreme ultraviolet light
on 2007 May 19, to model the same event with a three-dimensional
(3D) time-depending magnetohydrodynamic (MHD) code that includes
solar coronal magnetic fields derived with Wilcox Solar Observatory
magnetogram data, and a solar wind outflow accelerated with empirical
heating functions. The model includes a coronal mass ejection (CME)
of Gibson and Low flux rope type above the reconstructed active region
with parameters adapted from observations to excite the EIT wave. We
trace the EIT wave running as circular velocity enhancement around the
launching site of the CME in the direction tangential to the sphere
produced by the wave front, and compute the phase velocities of the
wave front. We find that the phase velocities are in good agreement
with theoretical values for a fast magnetosonic wave, derived with
the physical parameters of the model, and with observed phase speeds
of an incident EIT wave reflected by a coronal hole and running at
about the same location. We also produce in our 3D MHD model the
observed reflection of the EIT wave at the coronal hole boundary,
triggered by the magnetic pressure difference between the wave front
hitting the hole and the boundary magnetic fields of the coronal hole,
and the response of the coronal hole, which leads to the generation of
secondary reflected EIT waves radiating away in different directions
than the incident EIT wave. This is the first 3D MHD model of an EIT
wave triggered by a CME that includes realistic solar magnetic field,
with results comparing favorably to STEREO Extreme Ultraviolet Imager
observations.

---------------------------------------------------------
Title: Streamers study at solar minimum: combination of UV
observations and numerical modeling
Authors: Abbo, Lucia; Ofman, Leon; Giordano, Silvio
2010AIPC.1216..387A Altcode:
The present study concerns a comparison between the slow solar
wind plasma parameters obtained in the extended corona by the UV
spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS)
onboard SOHO during the minimum of solar activity (1996) and the results
of a time-dependent 2.5 D three-fluid MHD model of coronal streamer
belt. The aim of the study is to improve the knowledge of the slow
solar wind acceleration mechanism and the origin of its variability.

---------------------------------------------------------
Title: Excitation of vertical kink waves in a solar coronal arcade
loop by a periodic driver
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Ofman, L.
2010A&A...512A..76S Altcode:
 Aims: We study an oscillatory driver as a possible excitation
mechanism of vertical kink loop oscillations in the ideal MHD
regime. Methods: We consider a solar coronal magnetic arcade
with a dense photospheric layer. The two-dimensional numerical model
that we implement includes the effects of nonlinearity and line
curvature on the excitation and attenuation of fast magnetosonic kink
waves. We investigate the effects of a driven sinusoidal pressure
pulse and compare it with the impulsive excitation by a pressure
pulse that impacts the overlying loop. Results: Our numerical
simulations reveal wave signatures that are reminiscent of vertical
loop oscillations seen in TRACE observational data. Conclusions:
We conclude that attenuation of vertical kink oscillations can be
reduced to the value observed by adopting an oscillatory instead of an
impulsive excitation. An oscillatory driver also naturally explains why
only a small subset of all loops is excited to oscillate transversally
in an active region.

---------------------------------------------------------
Title: 2.5d Mhd Simulations Of Winds From Red Giants Stars: Broadband
Alfvén Waves
Authors: Airapetian, Vladimir; Carpenter, K.; Ofman, L.
2010AAS...21542703A Altcode: 2010BAAS...42..342A
We present the numerical simulations of winds from evolved giant
stars using a fully non-linear, time dependent, 2.5-dimensional
magnetohydrodynamic (MHD) code. This study extends our previous
fully non-linear MHD wind simulations to the parameter space that
describes winds from red giant stars. In the current version of this
Alfvén wave driven model, a wind is driven by randomly generated
low-frequency non-linear Alfvén waves in a broadband frequency
range at the base of the wind. We simulate freely propagated and
partially reflected Alfvén waves in the gravitationally stratified
atmosphere of a late-type giant star, in a self-consistent manner,
until a steady-state wind is formed. Our simulations demonstrate
that, unlike linear Alfven wave-driven wind models, a stellar wind
model based on plasma acceleration due to low frequency broad-band
non-linear Alfvén waves, can consistently reproduce the observed radial
velocity profiles of the winds, their terminal velocities, the turbulent
broadening of UV lines emitted from those winds and the observed mass
loss rates. We find that conversion of non-linear transverse Alfvén
waves into longitudinal magnetosonic waves plays the major role in
depositing momentum and energy into the stellar wind. The fitting of
mass-loss rates from α Tau with the predicted rate suggests a highly
anisotropic stellar wind in this evolved giant. The model also predicts
a variation of the wind mass-loss rates on time scales of 1 month.

---------------------------------------------------------
Title: Propagating intensity disturbances in coronal loops: Waves
or flows?
Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph
2010cosp...38.2924W Altcode: 2010cosp.meet.2924W
Quasi-periodic propagating intensity disturbances were found by
SOHO/EIT and TRACE imaging observations in fanlike coronal loops
10 year ago. The 3 min and 5 min oscillations have been interpreted
as propagating slow magnetoacoustic waves which originate from the
photospheric p-mode oscillations due to the wave leakage. However,
some cases show oscil-lations with periodicities of more than 10 min,
which are hard to explain by wave leakage, and so were argued in
some studies that they may be periodic flows. In this presentation,
we report the first observation of multiple-periodic (12 and 25
min) propagating disturbances along a fan-like coronal structure
simultaneously detected in both intensity and Doppler shift in
the Fe xii line with EIS onboard Hinode. We measured Doppler shift
amplitude of 1-2 km/s, relative intensity amplitude of (3-5)% and the
apparent propagation speed of 100-120 km/s. The amplitude relationship
between intensity and Doppler shift oscillations provides convinc-ing
evidence that these propagating features are a manifestation of slow
magnetoacoustic waves but not flows. The feature of symmetric line
profiles also confirms that the measured small Doppler-shift amplitudes
are not due to the line wing enhancement caused by high-speed flows. A
new application of coronal seismology is provided based on these
observations, with which we determine the inclination angle of the
magnetic field and the temperature of a coronal loop. We will also show
the result of multi-temperature spectral line analysis to explore the
temperature-dependent behavior of this phenomenon.

---------------------------------------------------------
Title: Ion-acoustic Waves Excitation by a standing Alfvén wave
Authors: Israelevich, Peter; Ofman, Leon
2010cosp...38.2039I Altcode: 2010cosp.meet.2039I
The results of hybrid simulation of standing Alfvén wave in low
beta plasma are presented. Plasma is accelerated from the anti-nodes
toward the nodes of the standing waves with finite amplitude under
the action of the magnetic field pressure. As a result, a sharp
maximum of the number density (and electron pressure) arises near
the nodes. The plasma flow is modulated by the doubled frequency of
the driving Alfvén wave thus giving rise to ion-acoustic waves. The
effective parallel electric field appears due to both electron pressure
gradient near the nodes and electron pressure variations in the acoustic
waves. Landau damping limits the amplitude of the exited ion-acoustic
waves. In the 1D case, Landau damping can be avoided only if Te is
much larger than Ti, since the electric current is perpendicular to the
background magnetic field. However, if ion-acoustic waves are excited
by alternating field-aligned current (i.e. by oblique Alfvén wave),
the ion-acoustic instability occurs for strong currents with carriers
velocity larger than cs, and the excitation becomes more effective. This
process may account for the observations of parallel electric field
in the auroral ionosphere.

---------------------------------------------------------
Title: Comparison of observations and multi-fluid models of streamers
at solar minimum
Authors: Ofman, Leon; Abbo, Lucia; Giordano, Silvio; Kramar, Maxim
2010cosp...38.2940O Altcode: 2010cosp.meet.2940O
We present the results comparison between the slow solar wind plasma
parameters obtained in the extended corona by the UV spectroscopic data
from the Ultraviolet Coronagraph Spectrom-eter (UVCS) on-board SOHO and
STEREO during the past minima of solar activity (CR1913; and CR2066)
and the results of a time-dependent 2.5D three-fluid MHD model of the
coronal streamer belt. The previous three-fluid (e, p, and O5+ or He++
) streamer model has been improved by considering real solar magnetic
field obtained by Wilcox Solar Observatory as boundary condition, and
PFSS model as initial state of the magnetic configuration. This is the
first study that incorporates real magnetic field in the three-fluid
model. The model was run until fully self consistent streamer was
formed in the quasi-steady state. The electron density reconstructed
from STEREO Cor1 observations was compared to the results of the
three-fluid model to validate the model. The plasma parameters from
the multi-fluid model were used to compute the expected UV observables
from HI Ly-α and OVI 1032 spectral lines and the results were compared
in details with the UVCS measurements.

---------------------------------------------------------
Title: Hinode/EIS Observations of Propagating Slow Magnetoacoustic
Waves in a Coronal Loop
Authors: Wang, T. J.; Ofman, L.; Davila, J. M.
2009ASPC..415...28W Altcode:
We present the first Hinode/EIS observations of 5 min quasi-periodic
oscillations detected in the transition region and corona at the
footpoint of a coronal loop. The oscillations are characterized by a
series of wave packets with nearly constant period, typically persisting
for 4--6 cycles. There is an in-phase relation between Doppler shift
and intensity oscillations, indicating upwardly propagating slow
magnetoacoustic waves in the loop. We find that the oscillations
detected in the five coronal lines are highly correlated, and the
amplitude decreases with increasing temperature. These oscillations
may be caused by the leakage of the photospheric p-modes through the
chromosphere and transition region into the corona, which has been
suggested as the source for intensity oscillations previously observed
by TRACE. The temperature dependence of the oscillation amplitudes
can be explained by damping of the waves traveling along the loop with
multithread structure near the footpoint.

---------------------------------------------------------
Title: Two-dimensional Hybrid model of Collisionless Relaxation of
Ion Distributions downstream of Quasi-perpendicular Shocks
Authors: Ofman, L.; Gedalin, M.
2009AGUFMSH42A..05O Altcode:
Recent STEREO observations reveal that large scale downstream
magnetic oscillations are quite typical for quasi-perpendicular
low-Mach number shock. It has been shown recently, both in theory and
1D hybrid simulations, that these oscillations are, most plausibly,
related to the collisionless relaxation of the downstream gyrating ion
distributions. A number of observed shocks exhibit clear deviations from
one-dimensionality. We extend our previous analysis to two-spatial
dimensions by using 2D hybrid code, which allows studying the
inhomogeneity along the shock front. We investigate in detail the
formation of gyrating distributions in this 2D geometry and further
relaxation of these distributions accompanying with generation of
magnetic oscillations.

---------------------------------------------------------
Title: Global simulation of an EIT wave
Authors: Schmidt, J. M.; Ofman, L.
2009AGUFMSH41B1658S Altcode:
We use the observation of an EIT wave in the lower solar corona, seen
with the two STEREO s/c in extreme ultraviolet light on 19 May 2007,
to model the same event with a three-dimensional (3D) time-depending
magneto hydrodynamic (MHD) code that includes solar coronal magnetic
fields derived with Wilcox Solar Observatory magnetogram data, a solar
wind outflow accelerated with empirical heating functions. The model
includes a coronal mass ejection (CME) of Gibson and Low flux rope
type above the reconstructed active region with parameters adapted from
observations to excite the EIT wave. We trace the EIT wave running as
circular velocity enhancement around the launching site of the CME in
the direction tangential to the sphere produced by the wavefront, and
compute the phase velocities of the wavefront. We find that the phase
velocities are in good agreement with theoretical values for a fast
magnetosonic wave, derived with the physical parameters of the model,
and with observed phase speeds of an EIT wave reflected by a coronal
hole and running at about the same location. We also produce in our
3D MHD model the observed reflection of the EIT wave at the coronal
hole boundary, triggered by the magnetic pressure difference between
the wave front hitting the hole and the boundary magnetic fields of
the coronal hole, and the response of the coronal hole, which leads
to the generation of secondary reflected EIT waves radiating away in
different direction than the incident EIT wave.

---------------------------------------------------------
Title: Dynamics of Coronal Streamers: 2.5D MHD simulations with
semi-empirical heating and momentum terms
Authors: Airapetian, V.; Ofman, L.; Sittler, E. C.; Kramar, M.
2009AGUFMSH41B1657A Altcode:
We present the results of fully non-linear resistive magnetohydrodynamic
(MHD) simulations of an equatorially confined streamer belt
using observational constrains in a two-fluid 2.5D MHD modeling
in spherical geometry . Specifically, we used the PFSS model of
the initial coronal magnetic field configuration with the boundary
conditions at the photosphere specified by the NSO/GONG magnetogram
data. Calculations were performed for the fully thermally conductive
case with the two-component (electrons and protons) heat flux, qeff ,
and the effective temperature, Teff, derived from the semi-empirical
steady-state model (SG model). Our simulations were performed between
the coronal base at 1.02 to 5 solar radii. We show that our MHD
simulations are more realistic than polytropic models, and capable
of reproducing basic thermodynamic and kinematic properties of the
coronal streamer structure observed in July 3-17, 2007 by COR1 STEREO.

---------------------------------------------------------
Title: Progress, Challenges, and Perspectives of the 3D MHD Numerical
Modeling of Oscillations in the Solar Corona
Authors: Ofman, Leon
2009SSRv..149..153O Altcode:
Recent high temporal and spatial resolution satellite observations of
the solar corona provide ample evidence of oscillations in coronal
structures. The observed waves and oscillations can be used as
a diagnostic tool of the poorly known coronal parameters, such
as magnetic field, density, and temperature. The emerging field
of coronal seismology relies on the interpretation of the various
coronal oscillations in terms of theoretically known wave modes, and
the comparison of observed and theoretical wave mode properties for the
determination of the coronal parameters. However, due to complexity of
coronal structures the various modes are coupled, and the application
of linear theory of idealized structures to coronal loops and active
regions limits the usefulness of such methods. Improved coronal
seismology can be achieved by the development of full 3D MHD dynamical
model of relevant coronal structures and the oscillation phenomena. In
addition to improved accuracy compared to linear analysis, 3D MHD models
allow the diagnostic method to include nonlinearity, compressibility,
and dissipation. The current progress made with 3D MHD models of waves
in the corona is reviewed, and the challenges facing further development
of this method are discussed in the perspective of future improvement
that will be driven by new high resolution and high cadence satellite
data, such as received from Hinode and STEREO, and expected from SDO.

---------------------------------------------------------
Title: Collisionless relaxation of ion distributions downstream of
laminar quasi-perpendicular shocks
Authors: Ofman, L.; Balikhin, M.; Russell, C. T.; Gedalin, M.
2009JGRA..114.9106O Altcode: 2009JGRA..11409106O
Directed flow of incident ions provides the free energy which is
redistributed in a shock among heated ions and electrons, accelerated
particles, and magnetic compression. In low Mach number laminar shock
the main channel of conversion is into downstream gyrating ions. Just
behind the shock transition the ion distribution is substantially
nongyrotropic, which results in spatially periodic variations of
the ion pressure and, consequently, in time stationary downstream
oscillations of the magnetic field. In the absence of significant level
of nonstationarity, gyrotropization is due to the gyrophase mixing and
slow. Theoretical analysis of the phenomenon and supporting hybrid
simulations are presented. It is shown that these oscillations are
more likely to be observed at low Mach number low β shocks, while at
higher Mach numbers or higher β they may be obscured by waves crossing
the shocks.

---------------------------------------------------------
Title: Hinode/EIS observations of propagating low-frequency slow
magnetoacoustic waves in fan-like coronal loops
Authors: Wang, T. J.; Ofman, L.; Davila, J. M.; Mariska, J. T.
2009A&A...503L..25W Altcode: 2009arXiv0908.0310W
Aims: We report the first observation of multiple-periodic propagating
disturbances along a fan-like coronal structure simultaneously detected
in both intensity and Doppler shift in the Fe xii 195 Å line with the
EUV Imaging Spectrometer (EIS) onboard Hinode. A new application of
coronal seismology is provided based on this observation. Methods:
We analyzed the EIS sit-and-stare mode observation of oscillations
using the running difference and wavelet techniques. Results:
Two harmonics with periods of 12 and 25 min are detected. We measured
the Doppler shift amplitude of 1-2 km s-1, the relative
intensity amplitude of 3%-5% and the apparent propagation speed of
100-120 km s-1. Conclusions: The amplitude relationship
between intensity and Doppler shift oscillations provides convincing
evidence that these propagating features are a manifestation of slow
magnetoacoustic waves. Detection lengths (over which the waves are
visible) of the 25 min wave are about 70-90 Mm, much longer than those
of the 5 min wave previously detected by TRACE. This difference may
be explained by the dependence of damping length on the wave period
for thermal conduction. Based on a linear wave theory, we derive an
inclination of the magnetic field to the line-of-sight about 59 ±
8°, a true propagation speed of 128 ± 25 km s-1 and
a temperature of 0.7 ± 0.3 MK near the loop's footpoint from our
measurements. Appendix is only available in electronic form at
http://www.aanda.org

---------------------------------------------------------
Title: Analysis of Active Region and Quiet Sun Spectra from SERTS-99
Observations
Authors: Coyner, Aaron J.; Davila, J. M.; Brosius, J. W.; Ofman, L.
2009SPD....40.1216C Altcode:
The Solar EUV Research Telescope and Spectrograph is a rocket-based
instrument that uses high resolution extreme ultraviolet spectra to
investigate features in the solar corona and transition region. The 1999
flight occurred on 24 June 1999 and obtained spectra from both active
regions and quiet sun regions on the solar disk covering a spectral
bandpass 300-355 angstroms We report here the calibrated intensities
and measured linewidths determined from the spatially-averaged spectra
of both active regions and quiet sun regions respectively. In addition,
we determine a distribution of non-thermal velocity components from the
measured linewidths of the identified lines. This distribution provides
a quantitative constraint on the available energy of non-thermal origin
in the observed regions which is available for coronal heating.

---------------------------------------------------------
Title: Propagating Slow Magnetoacoustic Waves in Coronal Loops
Observed by Hinode/EIS
Authors: Wang, T. J.; Ofman, L.; Davila, J. M.
2009ApJ...696.1448W Altcode: 2009arXiv0902.4480W
We present the first Hinode/EUV Imaging Spectrometer observations of
5 minute quasi-periodic oscillations detected in a transition-region
line (He II) and five coronal lines (Fe X, Fe XII, Fe XIII, Fe XIV,
and Fe XV) at the footpoint of a coronal loop. The oscillations
exist throughout the whole observation, characterized by a series of
wave packets with nearly constant period, typically persisting for
4-6 cycles with a lifetime of 20-30 minutes. There is an approximate
in-phase relation between Doppler shift and intensity oscillations. This
provides evidence for slow magnetoacoustic waves propagating upward from
the transition region into the corona. We find that the oscillations
detected in the five coronal lines are highly correlated, and the
amplitude decreases with increasing temperature. The amplitude of
Doppler shift oscillations decrease by a factor of about 3, while
that of relative intensity decreases by a factor of about 4 from Fe
X to Fe XV. These oscillations may be caused by the leakage of the
photospheric p-modes through the chromosphere and transition region
into the corona, which has been suggested as the source for intensity
oscillations previously observed by Transition Region and Coronal
Explorer. The temperature dependence of the oscillation amplitudes
can be explained by damping of the waves traveling along the loop with
multithread structure near the footpoint. Thus, this property may have
potential value for coronal seismology in diagnostic of temperature
structure in a coronal loop.

---------------------------------------------------------
Title: Propagating Slow Magnetoacoustic Waves in Coronal Loops
Observed by Hinode/EIS
Authors: Wang, Tongjiang; Ofman, L.; Davila, J.
2009SPD....40.3003W Altcode:
We present two cases of propagating slow magnetoacoustic waves in
coronal loops observed by Hinode/EIS. In the first case, the 5-min
waves were detected in a transition-region line (He II) and five coronal
lines (Fe X - Fe XV) at a plage region. We find that the oscillations
detected in coronal lines are highly correlated, and the amplitude
decreases with increasing temperature. These waves may be caused by
the leakage of the p-modes through the chromosphere and transition
region into the corona. The temperature dependence of the oscillation
amplitudes can be explained by damping of the waves traveling along
the loop with multithermal fine structure near the footpoint. In
the second case, outwardly propagating (on the order of 100 km/s)
quasi-periodic disturbances along a fan-like coronal structure were
for the first time detected simultaneously in intensity and Doppler
shift. The measured amplitudes for the oscillations are consistent
with the interpretation in terms of slow magnetoacoustic waves rather
than high-speed outflows. The waves contain multiple harmonics of the
periods of 12 min and 25 min. Their origin is not clear. The damping
length of these low-frequency waves is distinctly longer than that of 5
min waves previously detected by TRACE in the similar structure. A new
application of coronal seismology is given based on this observation,
with which the true sound speed and temperature near the loop's
footpoint are estimated. The work of LO and TJW was supported by NRL
grant N00173-06-1-G033. LO was also supported by NASA grant NNG06GI55G.

---------------------------------------------------------
Title: Probing Thermodynamic and Kinematic Properties of a Coronal
Streamer Event Formed During the Solar Minimum
Authors: Airapetian, Vladimir; Ofman, L.; Sitter, E., Jr.; Kramar, M.
2009SPD....40.1409A Altcode:
We present the results of semi-empirical time-dependent fully non-linear
magnetohydrodynamic (MHD) simulations of an equatorially confined
streamer belt using observational constrains in a two-fluid 2.5D MHD
modeling. Specifically, we reproduced the COR1 STEREO observations of
an equatorially confined streamer obtained in July 3-17, 2007. For
this streamer event we used the PFSS model of the initial coronal
magnetic field configuration with the boundary conditions at the
photosphere specified by the NSO/GONG magnetogram data. Calculations
were performed for nearly isothermal polytropic flow and for the fully
thermally conductive case with the two-component (electrons and protons)
heat flux, qeff, and the effective temperature, Teff
, derived from a semi-empirical state-state model (SG model). We
show that our realistic MHD simulations are capable of reproducing
basic thermodynamic and kinematic properties of the observed coronal
streamer structure at distances between 1.5 to 4 solar radii.

---------------------------------------------------------
Title: Constraints On Coronal Non-thermal Velocities From SERTS
1991-1997 Observations
Authors: Coyner, Aaron J.; Davila, J. M.; Ofman, L.
2009SPD....40.1302C Altcode:
The determination of non-thermal velocities from spectral line
observations provide insight into the availability of additional energy
sources within the observed regions of the corona. These non-thermal
velocities can be attributed to waves, electron beams, turbulent
motions among other potential sources. Observationally constraining
these velocities directly limits the available energy for heating
within the observed coronal regions. We present the determination
of non-thermal velocity distributions from the 397 identified lines
from the SERTS 1991-1997 flights covering the spectral range 171-355
angstroms along with the distributions for the 253 lines identified
in active regions, the 102 lines from quiet sun regions, and 42 lines
from off limb observations respectively. We find that for all four
the velocity distributions peak at non-thermal velocities between
23-30 km/s independent of activity level suggesting that many of these
non-thermal velocities are likely the result of non-thermal motions
of cooling plasma visible in both active and quiet regions; however
the active region distribution does exhibit a more pronounced high
velocity tail with a secondary bump which could .be the result of a
component resulting from heating of the coronal plasma.

---------------------------------------------------------
Title: Three-Dimensional Magnetohydrodynamic Models of Twisted
Multithreaded Coronal Loop Oscillations
Authors: Ofman, L.
2009ApJ...694..502O Altcode:
The multithreaded structure of active region coronal loops was
deduced from past spectroscopic observations. Recent high-resolution
observations by Transition Region and Coronal Explorer and Hinode
satellites provided direct evidence that active region loops consist
of multiple magnetic threads filled with plasma with higher density
than neighboring loop material. High-resolution observations of loops
near a flare site suggest that the threads are twisted or tangled,
the magnetic field is not force free, and flows are present. To better
understand these observations, we developed for the first time a
three-dimensional magnetohydrodynamic model of twisted multithreaded
loops that oscillate as a result of an impulsive event. The twist is
induced by applying a rotating velocity field at the footpoint of the
initially parallel set of threads, and parallel flow is included. The
oscillations of the twisted loops are excited by a fast magnetosonic
pulse. The evolution and the damping of the fast magnetosonic wave
excited in the twisted multithreaded loop are compared to oscillations
of a four-parallel-threaded loop. It was found that twisted loop
oscillations result in filamented current and velocity structure that
cannot be described by the fundamental kink mode. When parallel flow
is present, the oscillation induces nonlinear compressive modulation
of the flow and density in the threads. The twisted loop oscillates
and damps faster than the parallel-threaded loop. The results of the
study demonstrate the effects of the twist, internal loop structure,
and flow on the evolution of the waves in coronal active region loops.

---------------------------------------------------------
Title: Three-dimensional MHD modeling of waves in active region loops
Authors: Ofman, Leon; Selwa, Małgorzata
2009IAUS..257..151O Altcode:
Observations show that MHD waves are one of the most important
universal processes in the heliosphere. These waves are likely to
play an important role in energy transfer in the heliosphere, and
they can be used as a diagnostic tool of the properties of the local
magneto-fluid environment. Recent observations by TRACE and Hinode
satellites provide ample evidence of oscillations in coronal active
region loops. The oscillations were interpreted as fast (kink), slow,
and Alfvén modes, and the properties of the waves were used for
coronal seismology. However, due to the complex interactions of the
various modes in the inhomogeneous active region plasma, and due to
nonlinearity, idealized linear theory is inadequate to properly describe
the waves. To overcome this theoretical shortcoming we developed 3D MHD
models of waves in active region loops. We investigated the effects of
3D active region magnetic and density structure on the oscillations and
the wave dissipation, and we investigated the oscillation of individual
loops. Some loops were constructed to contain several threads and
twist. Here, we present the results of our models, and show how they
can be used to understand better the properties of the waves, and of
the active regions.

---------------------------------------------------------
Title: Development of Solar Wind Model Driven by Empirical Heat Flux
and Pressure Terms
Authors: Sittler, E. C.; Ofman, L.; Selwa, M. A.; Kramar, M.
2008AGUFMSH13B1537S Altcode:
We are developing a time stationary self-consistent 2D MHD model
of the solar corona and solar wind as suggested by Sittler
et al. (2003). Sittler &amp; Guhathakurta (1999) developed a
semi-empirical steady state model (SG model) of the solar wind in a
multipole 3-streamer structure, with the model constrained by Skylab
observations. Guhathakurta et al. (2006) presented a more recent
version of their initial work. Sittler et al. (2003) modified the
SG model by investigating time dependent MHD, ad hoc heating term
with heat conduction and empirical heating solutions. Next step of
development of 2D MHD models was performed by Sittler &amp; Ofman
(2006). They derived effective temperature and effective heat flux
from the data-driven SG model and fit smooth analytical functions to
be used in MHD calculations. Improvements of the Sittler &amp; Ofman
(2006) results now show a convergence of the 3-streamer topology
into a single equatorial streamer at altitudes &gt; 2 RS. This is a
new result and shows we are now able to reproduce observations of an
equatorially confined streamer belt. In order to allow our solutions
to be applied to more general applications, we extend that model by
using magnetogram data and PFSS model as a boundary condition. Initial
results were presented by Selwa et al. [2008]. We choose solar minimum
magnetogram data since during solar maximum the boundary conditions
are more complex and the coronal magnetic field may not be described
correctly by PFSS model. As the first step we studied the simplest
2D MHD case with variable heat conduction, and with empirical heat
input combined with empirical momentum addition for the fast solar
wind. We use realistic magnetic field data based on NSO/GONG data,
and plan to extend the study to 3D. This study represents the first
attempt of fully self-consistent realistic model based on real data and
including semi-empirical heat flux and semi-empirical effective pressure
terms. References: Sittler E. C. Jr. and Guhathakurta M., 1999, ApJ,
523, 812-826 Sittler E. C. Jr., Ofman L., Gibson S., Guhathakurta M.,
Davila J., Skoug R., Fludra A., Holzer T., 2003, Solar Wind 10, 113
Sittler, E. C. Jr. and Ofman L., 2006, ILWS, GOA, India Guhathakurta,
M., E. C. Sittler Jr. and L. Ofman, JGR, Vol 111, A11215, 2006. Selwa,
M., L. Ofman, E. C. Sittler Jr. and M. Kramar, Development of solar
wind model driven by empirical heat flux, SHINE Meeting, 2008.

---------------------------------------------------------
Title: The role of AR topology on excitation, trapping and damping
of individual loop oscillations
Authors: Selwa, M. A.; Ofman, L.
2008AGUFMSH13A1517S Altcode:
We investigate the role of magnetic field topology on individual
dense loop oscillation by the means of 3D MHD numerical simulations of
two models of idealized active regions (AR's). The first model of AR
is initialized as a straight cylinder surrounded by the fieldlines
of the same length and orientation. The second model consists of
a force-free dipole magnetic configuration and contains a loop
with a higher density than its surroundings. Dipole fieldlines
have position dependent length and orientation. We study different
ways of excitation of transverse loop oscillations by an external
pulse and by a nearly eigenmode excitation implemented inside the
loop. We find that perturbation acting directly on a single loop
excites oscillations both in cylindrical and dipole loop. However,
the leakage of the wave energy is larger in a curved loop compared to
straight loop. External excitation of the whole AR is efficient in the
excitation of oscillation in the straight cylindrical AR, but results
in less efficient excitation in the case of dipole AR loop. We claim
that excitation of collective motion of straight fieldlines having the
same wave-periods and planes of the oscillations requires much less
energy than excitation of dipole fieldlines having position-dependent
orientation and wave-periods and being excited individually, not having
a collective mode of oscillation. We conclude that coherent motion of
straight fieldlines is one of the factors that decreases the energy
leakage from an oscillating loop, while individual motions of dipole
fieldlines require more energy from the source to produce the loop
oscillations, and also lead to higher damping rate compared to the
straight field case.

---------------------------------------------------------
Title: Acceleration and heating of solar wind ions by turbulent
wave spectrum
Authors: Ofman, L.
2008AGUFMSH43A1648O Altcode:
We model the heating and the acceleration of multi-ion plasma of
the solar wind by turbulent spectrum of Alfvénic fluctuations in the
resonant and nonresonant frequency range. The modeling effort is guided
by the observed properties of the spectrum and the measured physical
parameters of the solar wind plasma in the heliosphere in-situ, as well
as close to the sun from remote sensing observations. We start with
2.5D multifluid model that includes ion-cyclotron terms to study the
nonresonant wave heating and acceleration, and proceed with 2D hybrid
model that extends into the resonant frequency range. In addition
to protons the model includes helium ions, and other heavy ions,
and the results of the turbulent Alfvénic wave spectrum is compared
to observation. In the hybrid model the protons and heavy ions are
treated kinetically, while the electrons are included as neutralizing
background fluid. This model allows to extend the study to resonant
frequency range, and explore the nonlinear saturation of the heating
for resonant and nonresonant waves. The models are used to explore the
effect of non-homogeneous background density across the magnetic field,
and of ion beams on the heating by turbulent wave spectrum.

---------------------------------------------------------
Title: 3D MHD Simulations of Excitation and Damping of Vertical Kink
Waves in Coronal Active Region Loops
Authors: Selwa, M.; Ofman, L.
2008ASPC..397..189S Altcode:
We present numerical results of a three dimensional MHD model of
an idealized active region field. The active region is initialized
as a force-free dipole magnetic configuration with gravitationally
stratified density and contains a loop with a higher density than
its surroundings. We study different ways of exciting vertical
kink oscillations by velocity: as an initial condition, and as an
impulsive excitation with a pulse of a given position, duration, and
amplitude. These properties are varied in the parametric studies. We
find that vertical kink oscillations amplitude is significantly
amplified in comparison to horizontal kink oscillations amplitude
for exciters located centrally (symmetrically) below the loop, which
explains why the pure vertical kink mode is so rarely observed in
comparison to the horizontally polarized one. We observe that vertical
kink waves in 3D stratified geometry are damped mainly due to wave
leakage. We compare our simulation with TRACE observational data and
find qualitative agreement. We plan to search for vertical kink modes
in Hinode data, and compare to our models.

---------------------------------------------------------
Title: Standing fast magnetoacoustic kink waves of solar coronal
loops with field-aligned flow
Authors: Gruszecki, M.; Murawski, K.; Ofman, L.
2008A&A...488..757G Altcode:
Aims: We refer to the recent observational data of Hinode, which
detected weakly-attenuated coronal loop oscillations in the presence
of background flow (Ofman &amp; Wang 2008, A&amp;A, 482, L9). Vertical
loop oscillations that lasted for three wave periods were reported
with a wave period P = 113 ± 2 s, attenuation time τ = 560 ± 260 s,
and wave amplitude A{max} = 0.67 ± 0.12 Mm. Ofman &amp;
Wang (2008) estimated the flow speed within the range of 74-123 km
s-1. We consider impulsively generated standing fast
magnetoacoustic kink waves of a straight solar coronal slab with
field-aligned internal flow. We aim to determine the influence of
such flow on the spatial and temporal signatures of these waves. Methods: The time-dependent, ideal magnetohydrodynamic equations are
solved numerically. Results: The numerical results show that as a
result of wave scattering on inhomogeneous flow kink waves experience
stronger attenuation than for a still plasma, while P remains weakly
altered by this flow. Numerically evaluated values of A{max}
and P are close to the observational data. A value of τ is about two
times smaller than observed.

---------------------------------------------------------
Title: Three-dimensional Magnetohydrodynamic Wave Behavior in Active
Regions: Individual Loop Density Structure
Authors: McLaughlin, J. A.; Ofman, L.
2008ApJ...682.1338M Altcode:
We present the numerical results from a three-dimensional (3D) nonlinear
MHD simulation of wave activity in an idealized active region in
which individual, realistic loop density structure is included. The
active region is modeled by an initially force-free, dipole magnetic
configuration with gravitationally stratified density and contains a
loop with a higher density than its surroundings. This study represents
an extension to the model of Ofman &amp; Thompson. As found in their
work, we see that fast wave propagation is distorted by the Alfvén
speed profile and that the wave propagation generates field line
oscillations, which are rapidly damped. We find that the addition of
a high-density loop significantly changes the behavior inside that
loop, specifically in that the loop can support trapped waves. We
also find that the impact of the fast wave impulsively excites both
horizontal and vertical loop oscillations. From a parametric study
of the oscillations, we find that the amplitude of the oscillations
decreases with increasing density contrast, whereas the period and
damping time increase. This is one of the key results presented here:
that individual loop density structure can influence the damping rate,
and specifically that the damping time increases with increasing density
contrast. All these results were compared with an additional study
performed on a straight coronal loop with similar parameters. Through
comparison with the straight loop, we find that the damping mechanism
in our curved loop is wave leakage due to curvature. The work performed
here highlights the importance of including individual loop density
structure in the modeling of active regions and illustrates the need
for obtaining accurate density measurements for coronal seismology.

---------------------------------------------------------
Title: Hinode observations of transverse waves with flows in
coronal loops
Authors: Ofman, L.; Wang, T. J.
2008A&A...482L...9O Altcode:
Aims: We report the first evidence for transverse waves in coronal
multithreaded loops with cool plasma ejected from the chromosphere
flowing along the threads. These observations are good candidates for
coronal seismology. Methods: We analyzed observations made with
Solar Optical Telescope (SOT) on board the Hinode satellite in the Ca
II H line filter. Results: The oscillations are visible for about
3 periods, with a period lasting about 2 min, with weak damping. We see
the oscillations in thin threads (~0.5 arcsec) of cool plasma flowing in
the coronal loops with speeds in the range 74-123 km s-1. Conclusions: Observations indicate that the waves exhibit different
properties in the various threads. In some threads, the waves are nearly
standing fundamental kink modes with a phase speed of about 1250 km
s-1, whereas the dynamics of other threads is consistent
with propagating fast magnetosonic waves. Based on the observed wave
and loop properties and the assumed active region loop density in the
range (1-5) × 109 cm-3, the estimated energy
flux is sufficient to heat the loops to coronal temperatures, and the
average magnetic field in the threads is estimated as 20 ± 7 G.

---------------------------------------------------------
Title: Identification of types of kink modes in coronal loops:
principles and application to TRACE results
Authors: Wang, T.; Solanki, S.; Selwa, M.; Ofman, L.
2008AGUSMSP31C..08W Altcode:
We explore the possible signatures of different types of kink modes
(horizontal and vertical oscillations in their fundamental mode and
second harmonic) which may arise in coronal loops. Based on the 3D
geometrical parameters of 14 TRACE loops of transverse oscillations,
we simulate qualitatively the loop displacements due to these types
of kink mode oscillations. We find that for many combinations of
viewing and loop geometry it is not straightforward to distinguish
between the two types of kink modes. We have also considered Doppler
signatures and found that these can in principle help to obtain
unique identifications of the oscillation modes. We then compared
the simulated spatial signatures with the observations for 14
TRACE loops. We find that two cases of loop oscillations previously
identified as a fundamental horizontal mode appear to be a fundamental
vertical mode, while in two other cases it is not possible to clearly
distinguish between a horizontal oscillation of the fundamental
mode and the second-harmonic, and in six cases it is not possible
to clearly distinguish between a fundamental horizontal mode and a
second-harmonic vertical mode. In addition, for the particular case
that the oscillating loop has a S-shape, we find that the fundamental
vertical oscillation can take on the appearance of the horizontal second
harmonic due to projection effects. We also present numerical results
of three dimensional MHD model of an idealized active region field with
S-shaped field-lines. The active region is initialized as a force-free
dipole magnetic configuration with uniform density and contains a loop
with a higher density than its surroundings. We introduce a velocity
pulse which models the impact of a flare on surrounding fields. Both
the qualitative study and the MHD simulation support the conclusion
of the presence of fundamental mode of vertical kink oscillations in
an S-shaped loop. Our interpretation can naturally solve the puzzle of
the absence of the fundamental mode and the apparent presence of second
harmonic oscillations observed in a TRACE loop by De Moortel and Brady
(2007).

---------------------------------------------------------
Title: Three dimensional MHD models of twisted multi-threaded loop
oscillations
Authors: Ofman, L.
2008AGUSMSP41C..07O Altcode:
The multi-threaded structure of active region coronal loops was
deduced from past spectroscopic observations. Recent high resolution
observations by TRACE and Hinode provide direct evidence that active
region loops consist of multiple magnetic threads filled with plasma
with higher density than neighboring loop material. High resolution
observations of loops near a flare site suggest that the threads are
twisted, and the magnetic field is not force-free. To better understand
these observations I developed 3D MHD model of twisted multi-threaded
loop oscillations. The twist is induced by applying rotating velocity
field at the foot-point of the initially parallel set of threads. The
oscillations of the twisted loops are excited by a fast magnetosonic
pulse. The evolution and the damping of the fast magnetosonic wave
excited in the twisted multi-threaded loop is compared to the wave in
single threaded loop, and to parallel threaded loop. The results of the
study show the effect of the twist and internal loop structure on the
damping of the waves. *Visiting Associate Professor, Tel Aviv University

---------------------------------------------------------
Title: 3D MHD model of kink waves in a loop anchored in a realistic
active region
Authors: Selwa, Malgorzata; Ofman, Leon; Wang, Tongjiang; Solanki, Sami
2008cosp...37.2804S Altcode: 2008cosp.meet.2804S
We present numerical results of three dimensional MHD model of the
active region field. The active region is initialized using MDI data
of 15 May 2001, 02:57 UT and potential extrapolation of the magnetic
field with gravitationally stratified density and contains a loop
with a higher density than its surroundings. The potential model
imitates the original TRACE AR quite well, however, the choice of
particular loop within AR is inaccurate due to limitation of the
plane-of-the-sky view. This study represents an extension to the
model of Ofman (2007). We introduce a velocity pulse based on TRACE
observations to model the impact of a flare on surrounding fields, and
study the resulting loop oscillations. The flare is initialized as a
semispherical velocity pulse at the bottom of AR and corresponds to the
event between loop's footpoints captured by TRACE. We investigate the
influence of a realistic dense loop on the excitation and damping of
the oscillations and compare our results with TRACE observations. By
the means of 3D computer simulation we confirm that considering
combination of viewing and loop geometry and Doppler signatures it
is straightforward to distinguish between at least two types of kink
modes: horizontal and vertical in the real loop observed by Aschwanden
et al. (2002). We find that oscillation previously identified as a
fundamental horizontal mode (Aschwanden et al. 2002) appears to be a
fundamental vertical mode. As such vertical kink oscillations are not
as rare compared to horizontal ones as previously thought.

---------------------------------------------------------
Title: Oscillation of twisted multi-threaded loops in coronal
active regions
Authors: Ofman, Leon
2008cosp...37.2274O Altcode: 2008cosp.meet.2274O
Recent high resolution observations by Hinode satellite shows that
coronal active region loops near the site of a flare are multi-threaded
structures that are oscillating, and may be twisted non-force-free
structures. The physical properties of the threads are not identical,
and the oscillations can vary in each thread. I report the results
of three-dimensional MHD simulation of a twisted non-force-free
multi-threaded loop, that exhibits damped oscillations. The loop was
initialized with four threads of high density plasma (compared to
surrounding corona), and the twist was obtained by inducing rotation
velocity field centered at one footpoint. The resulting twisted
structure was impacted by a fast magnetosonic pulse that produced
damped oscillations in the structure. I compare the results of the
twisted multi-threaded loop model to oscillations of a straight
(untwisted) multi-threaded loop, and to Hinode observations of
oscillating coronal loop structures. I find that the twist affects the
oscillations considerably, which suggest a new method for diagnostic
of the non-force-free field.

---------------------------------------------------------
Title: 3D simulations of damping of waves in a loop anchored in
a dipole active region: does resonant absorption take place in
realistic loops?
Authors: Selwa, M. A.; Ofman, L.
2007AGUFMSH53A1056S Altcode:
We present numerical results of three dimensional MHD model of an
idealized active region field. The active region is initialized
as a force-free dipole magnetic configuration with gravitationally
stratified density and contains a loop with a higher density than
its surroundings. This study represents an extension to the model
of McLaughlin &amp; Ofman (2007). We examine the impact of different
density profiles of the loop on damping of kink waves by introducing
a velocity pulse which models the impact of a flare on surrounding
fields. We compare our results with a straight cylinder model of the
loop which can be solved analytically. We study the resulting loop
oscillations and compare our results with TRACE observations.

---------------------------------------------------------
Title: Propagating Alfven waves in Coronal Loops Observed by Hinode
Authors: Ofman, L.; Wang, T.
2007AGUFMSH52C..02O Altcode:
Observations made with Solar Optical Telescope (SOT) on board the Hinode
satellite reveal that coronal loop with flowing cool chromospheric
material exhibit periodic oscillation. Additional related observations
were obtained by EIS imaging spectrometer. The oscillations are visible
for about 3 periods in multiple strands of the loops in transverse
direction to the loop axis, suggesting that these are Alfvén
waves propagating along the strands of the loop. The period of the
oscillations is about 2 minutes and the damping time is on the order
of 1000 seconds. The flow velocity of the cool material and the phase
speed of the waves were determined directly, by comparing frames of
the observed time sequence. The phase speed agrees with the expected
speed of standing waves for the observed loop length and period. We
find that MHD model of the waves in a coronal loop is in good agreement
with observations. We also find that the energy flux in the observed
waves appears to be sufficient to heat the loop to coronal temperatures.

---------------------------------------------------------
Title: Numerical Simulations of Slow Standing Waves in a Curved
Solar Coronal Loop
Authors: Selwa, M.; Ofman, L.; Murawski, K.
2007ApJ...668L..83S Altcode:
We consider slow standing waves that are impulsively excited in a
curved solar coronal loop. The numerical model we implement includes
the effect of nonlinearity in the frame of two-dimensional ideal
magnetohydrodynamics. We discuss the role of curved magnetic field
lines and of the slow and fast pulses overlapping at one of the loop's
footpoints in the excitation and attenuation of slow standing waves. We
find that slow waves can be excited faster in curved loops than in slabs
due to the combined effect of the pulse inside and outside the loop.

---------------------------------------------------------
Title: The Energetics of the Slow Solar Wind
Authors: Ofman, L.
2007ASPC..369..569O Altcode:
Observations and numerical models show that the slow solar wind is
associated with coronal streamers. However, the exact heating and
acceleration mechanism of the slow wind is unknown. Moreover, the
energization mechanism is likely to be different for electrons, protons,
and heavy ions. Some of the main objectives of Solar-B is to understand
the opening of magnetic field and heating of the coronal plasma that
forms the solar wind. Recent results of three-fluid numerical models
of the slow solar wind heating and acceleration in coronal streamers
are shown. The possible heating mechanisms of electrons, protons,
and heavy ions in the slow wind, and the formation of open flux in
streamers is discussed. The relation of the numerical results to past
observations by SOHO, and Ulysses spacecraft, and future observations
with Solar-B is discussed.

---------------------------------------------------------
Title: Attenuation of Alfvén waves in straight and curved coronal
slabs
Authors: Gruszecki, M.; Murawski, K.; Solanki, S. K.; Ofman, L.
2007A&A...469.1117G Altcode:
Aims:We consider impulsively generated Alfvén waves in coronal loops
to investigate the role of energy leakage on wave attenuation, which
includes lateral leakage, leakage into dense photospheric regions and
nonlinear driving of magnetosonic waves. Methods: A coronal loop
is modelled either as a straight magnetic slab or as a curved slab
of smooth mass density profiles. We perform numerical simulations of
2.5D ideal magnetohydrodynamic equations to determine the signatures of
Alfvén waves. Results: The numerical results show that lateral
leakage of Alfvén waves is significant in comparison to leakage into
the photospheric regions for realistic corona to photospheric density
ratios. Energy leakage is enhanced by curvature of magnetic field lines
and for large amplitude Alfvén waves for which nonlinear driving of
magnetosonic waves is more significant than in the linear regime.

---------------------------------------------------------
Title: Two-dimensional hybrid model of wave and beam heating of
multi-ion solar wind plasma
Authors: Ofman, L.; ViñAs, A. F.
2007JGRA..112.6104O Altcode: 2007JGRA..11206104O
We study the heating and the acceleration of protons and heavy ions
by waves in the solar wind, as well as the nonlinear influence of
heavy ions on the wave structure, using a two-dimensional (2-D) hybrid
model. Protons and heavy ions are treated kinetically by solving their
equations of motion in the self-consistent electric and magnetic fields
of the waves, while electrons are treated as a neutralizing background
fluid. We use the 2-D hybrid code to investigate more realistic 2-D
plasma model than previous 1-D simulation and analytical studies,
which allows parallel as well as obliquely propagating waves and
localized driver. Using the hybrid code, we consider for the first
time the heating and acceleration of protons and heavy ions by a
driven-input spectrum of Alfvén/cyclotron waves and by heavy ion
beam in the multispecies coronal plasma in two spatial dimensions. We
find that the ion beam is more efficient in generating temperature
anisotropy than the driven wave spectrum in our model. We discuss the
observational implication of the results to the solar wind.

---------------------------------------------------------
Title: The Influence Of Helium Ions And Heating On Coronal Streamer
Structure
Authors: Ofman, Leon
2007AAS...210.3001O Altcode: 2007BAAS...39..142O
The magnetic and compositional structure and dynamics of a coronal
streamer is investigated using thermally conductive multi-fluid
model. The variation of proton density, and He I/He II abundances
is studied as a function of latitude and height. The effects of
various heating rates, and heating profiles on the formation, and
the compositional structure of streamers are studied. The dependence
of the acceleration profile of the multi-component slow solar wind,
as well as the properties of the differential ion outflow on the heat
input is investigated numerically and compared to observations.

---------------------------------------------------------
Title: Coronal Heating and Acceleration of the Solar Wind
Authors: Ofman, L.
2007ASPC..370...82O Altcode:
The heating of the solar corona to millions of degrees have puzzled
solar physicist for decades. The related process of solar wind
acceleration is also not well understood. Although, the exact physical
mechanisms of these processes are being debated, current spectroscopic,
and white light observations of the corona provide important constrains
on the possible models. I provide a brief overview of the relevant
observations by Ulysses, SOHO, and RHESSI spacecrafts, and discuss
the theoretical models of the possible heating and acceleration
mechanisms. I show the results of computations that lead towards the
understanding of these processes.

---------------------------------------------------------
Title: 2d Simulations Of Excitation And Damping Of Vertical Kink Waves
Authors: Selwa, Malgorzata; Murawski, K.; Solanki, S. K.; Ofman, L.
2007AAS...210.9115S Altcode: 2007BAAS...39S.206S
We consider different kinds of excitation of fast vertical kink
standing waves in a solar coronal loop that is embedded in a potential
arcade. The two dimensional numerical model we implement includes the
effects of field line curvature and nonlinearity on the excitation
and damping of standing fast magnetosonic waves. We investigate the
effects of a driven sinusodial pressure pulse and compare it with an
impulsive excitation by a pressure pulse that impacts the overlaying
loop. The results of the numerical simulations reveal wave signatures
which are characteristic of vertical loop oscillations seen in recent
TRACE observational data.

---------------------------------------------------------
Title: 3d Simulations Of Excitation And Damping Of Waves In A Dipole
Active Region
Authors: Selwa, Malgorzata; Ofman, L.; McLaughlin, J.
2007AAS...210.9114S Altcode: 2007BAAS...39R.206S
We present numerical results of three dimensional MHD model of an
idealized active region field. The active region is initialized
as a force-free dipole magnetic configuration with gravitationally
stratified density and contains a loop with a higher density than
its surroundings. This study represents an extension to the model of
McLaughlin &amp; Ofman (2007). We examine the impact of a different
density profiles of the loop on excitation and damping of kink waves by
introducing a velocity or pressure pulse which models the impact of a
flare on surrounding fields. We study the resulting loop oscillations
and compare our results with TRACE observations.

---------------------------------------------------------
Title: Understanding coronal heating and solar wind acceleration:
Case for in situ near-Sun measurements
Authors: McComas, D. J.; Velli, M.; Lewis, W. S.; Acton, L. W.;
Balat-Pichelin, M.; Bothmer, V.; Dirling, R. B.; Feldman, W. C.;
Gloeckler, G.; Habbal, S. R.; Hassler, D. M.; Mann, I.; Matthaeus,
W. H.; McNutt, R. L.; Mewaldt, R. A.; Murphy, N.; Ofman, L.; Sittler,
E. C.; Smith, C. W.; Zurbuchen, T. H.
2007RvGeo..45.1004M Altcode:
The solar wind has been measured directly from 0.3 AU outward,
and the Sun's atmosphere has been imaged from the photosphere out
through the corona. These observations have significantly advanced our
understanding of the influence of the Sun's varying magnetic field on
the structure and dynamics of the corona and the solar wind. However,
how the corona is heated and accelerated to produce the solar wind
remains a mystery. Answering these fundamental questions requires
in situ observations near the Sun, from a few solar radii (R S
) out to ~20 R S , where the internal, magnetic, and
turbulent energy in the coronal plasma is channeled into the bulk energy
of the supersonic solar wind. A mission to make such observations has
long been a top priority of the solar and space physics community. The
recent Solar Probe study has proven that such a mission is technically
feasible and can be accomplished within reasonable resources.

---------------------------------------------------------
Title: Three-dimensional MHD Model of Wave Activity in a Coronal
Active Region
Authors: Ofman, L.
2007ApJ...655.1134O Altcode:
MHD wave activity associated with a flare was observed in coronal active
region AR 8270 in the extreme ultraviolet (EUV) by the Transition
Region and Coronal Explorer (TRACE) satellite on 1998 July 14. In
this study, a three-dimensional MHD model of the active region field
was initialized using a National Solar Observatory (NSO) Kitt Peak
magnetogram and potential extrapolation of the magnetic field, together
with gravitationally stratified density. To model the observed wave
activity following the flare, a velocity pulse was launched into a model
active region from below. It was found that the global oscillations
in the model active region are in good qualitative agreement with
observations. The main difference between the observations and the
model is in the oscillation of several individual loops that damp on
longer timescales compared to the corresponding magnetic field line
oscillation damping in the model.

---------------------------------------------------------
Title: Observing The He II Off-Limb Corona From Solar Orbiter
Authors: Giordano, S.; Fineschi, S.; Ofman, L.; Mancuso, S.; Abbo, L.
2007ESASP.641E..31G Altcode:
The SOLar Orbiter, SOLO, represents a unique platform for off-limb
solar corona observations, because of the near-Sun, helio-synchronous
and out-of-ecliptic perspective. We discuss as the simultaneous
monochromatic imaging of the UltraViolet spectral lines emitted by
the neutral hydrogen (HI) and singly ionized helium ions (HeII) in
solar corona in addition to the visible light imaging allows to use
the Doppler dimming diagnostics to derive velocity maps of the full
corona and the maps of the abundance of helium relative to hydrogen. We
compute the expected HeII 303. 78 A, HI Lyα 1215. 56 A and Visible
Light emissivity for a coronal model derived from a MHD computation of
the coronal physical parameters, such as electron and ions density,
kinetic temperatures and outflow velocity in the region from 1. 2
to 5. 0 solar radii. The UV lines are Doppler dimmed in presence of
outflows, moreover we take into account the possibility of pumping
effect on the He II line due to nearby Si XI 303. 32 A spectral line
which can excited the He II line for plasma speeds around 450 km/s. We
study as the helium coronal diagnostics from the out-of-ecliptic and
helio-synchronous observations can moreover address the understanding
of the processes leading to the elemental composition of the coronal
streamers and hole boundaries, as example to establish roles of
gravitational settling and Coulomb drag.

---------------------------------------------------------
Title: 3D MHD Model of Waves in an Active Region
Authors: Ofman, L.; McLaughlin, J.
2006AGUFMSH33B0416O Altcode:
Wave activity associated with flares and CME's have been observed with
SOHO, TRACE, and other satellites. The propagation and dissipation of
the waves provide information on the coronal magnetic structures. In
particular, MHD waves were observed in coronal active region AR8270
following a flare with TRACE on July 14, 1998. In this study, three
dimensional MHD model of the active region field was constructed using
National Solar Observatory (NSO) Kitt Peak magnetogram and potential
extrapolation of the magnetic field, together with gravitationally
stratified density as the initial state. The model was evolved to steady
state, and a velocity pulse with amplitude of ~100 km/sec was launched
into the active region from below to mimic the observed effect of the
flare. It was found that the global oscillations in the model active
region are in good qualitative agreement with observations. The main
difference between the observations and the model is in the oscillation
of several individual loops that damp on longer time scale, compared
to the corresponding magnetic field line oscillation damping in the
model. We investigate the effects of global active region magnetic
structure, as well as local loop structure on the trapping and damping
of waves in the active region.

---------------------------------------------------------
Title: Numerical simulations of vertical oscillations of a
multi-stranded coronal loop
Authors: Gruszecki, M.; Murawski, K.; Selwa, M.; Ofman, L.
2006A&A...460..887G Altcode:
Aims. We consider impulsively generated oscillations in a 2D model of
a curved solar coronal arcade loop that consists of up to 5 strands
of dense plasma. Methods: . First we do a simulation for a loop
which consists of two curved strands. We evaluate by means of numerical
simulations the influence of the distance between the strands and their
number on wave period, attenuation time, and amplitudes of standing
kink waves. Results: . The results of the numerical simulations
reveal that only strands which are very close to each other (distance
comparable to the strand width) considerably change the collective
behavior of kink oscillations. More distant strands also exhibit weak
coupling of the oscillations. However, their behavior can essentially
be explained in terms of separate oscillating loops. We compare the
numerical results with recent TRACE observational findings, and find
qualitative agreement.

---------------------------------------------------------
Title: 3D MHD Wave Behavior in Active Regions: Trapped Modes
Authors: McLaughlin, J. A.; Ofman, L.
2006AGUFMSH33B0413M Altcode:
We present the numerical results of a fast magnetoacoustic wave
propagating within an idealized active region. The active region is
modeled by an initially force-free, dipole magnetic configuration with
gravitationally stratified density and contains a loop with a higher
density than its surroundings. This study represents an extension to
the model of Ofman &amp;Thompson (2002). As found in their work, we see
that fast wave propagation is distorted by the Alfvén speed profile
and that the wave propagation generates fieldline oscillations and
these oscillations are rapidly damped. Inside the high density loop,
we find that the amplitude of these oscillations decreases as the
density contrast, ξ, increases. We also find that the high density
loop undergoes both vertical and horizontal oscillations. We calculate
how the rate of wave damping in our loop varies with ξ and find a
local minimum at about ξ=2.5, and we argue that this is evidence of
wave trapping. Thus, this work illustrates the importance of obtaining
accurate loop density measurements for coronal seismology.

---------------------------------------------------------
Title: Semi-Empirically Derived Heating Function of the
Corona-Heliopshere During the Whole- Sun Month
Authors: Guhathakurta, M.; Sittler, E.; Ofman, L.
2006AGUFMSH23B0354G Altcode:
In spite of many recent developments in observations and models of the
solar corona, the exact form of the heating function of the solar wind
plasma is unknown. Here we attempt to make some progress on that problem
by applying a previously developed simplified magnetohydrodynamic
model to a unique synthesis of remote sensing coronal observations
from SOHO and Spartan 201 and in-situ data from Ulysses during the
quiescent phase of solar cycle 23 (1995-1997) which also included the
Whole Sun Month (August/September, 1996) study period. Our analysis
provides for the first time an empirically derived estimate of the
heat flux and temperature profile of the corona and interplanetary
medium as a function of latitude and radial distance for this data
set. Our results suggest that the effective heat flux and temperature
may include thermal and non-thermal components possibly providing as
much as half of the total heat input. The primary contribution of our
analysis is that parameters calculated from our model provide insight
into the energy deposition profile and the model results can be used as
a test of observations of flow speed and temperature using different
observational techniques for this period. The main limitations of the
model are calculations of the magnetic field in equatorial regions,
and the neglect of force balance across field lines.

---------------------------------------------------------
Title: Semiempirically derived heating function of the corona
heliosphere during the Whole Sun Month
Authors: Guhathakurta, M.; Sittler, E. C.; Ofman, L.
2006JGRA..11111215G Altcode:
In spite of many recent developments in observations and models of the
solar corona, the exact form of the heating function of the solar wind
plasma is unknown. Here we attempt to make some progress on that problem
by applying a previously developed simplified magnetohydrodynamic
model to a unique synthesis of remote sensing coronal observations from
SOHO and Spartan 201, and in-situ data from Ulysses spacecraft during
the quiescent phase of solar cycle 23 (1995-1997) which also included
the Whole Sun Month (August/September 1996) study period. Our analysis
provides for the first time an empirically derived estimate of the heat
flux and temperature profile of the corona and interplanetary medium
over the solar polar regions as a function of latitude and radial
distance for this data set. The latitudinal and radial variation is
extended to include the equatorial regions but with less fidelity given
the significant structure associated with the streamer belt. Our results
suggest that both thermal and nonthermal heating terms contribute to
the temperature and heat flux in the low corona, particularly above
the poles, with the non-thermal component possibly providing as much
as half of the total heat input.

---------------------------------------------------------
Title: Improved input to the empirical coronal mass ejection (CME)
driven shock arrival model from CME cone models
Authors: Xie, H.; Gopalswamy, N.; Ofman, L.; St. Cyr, O. C.; Michalek,
G.; Lara, A.; Yashiro, S.
2006SpWea...410002X Altcode:
We study the Sun-Earth travel time of interplanetary shocks driven
by coronal mass ejections (CMEs) using empirical cone models. Three
different cone models have been used to obtain the radial speeds of
the CMEs, which are then used as input to the empirical shock arrival
(ESA) model to obtain the Sun to Earth travel time of the shocks. We
compare the predicted and observed shock transit times and find that
the accuracy of the ESA model is improved by applying CME radial speeds
from the cone models. There are two ways of calculating the shock travel
time: using the ESA model or using the simplified ESA formula obtained
by an exponential fit to the ESA model. The average mean error in the
travel time with the cone model speeds is 7.8 hours compared to 14.6
hours with the sky plane speed, which amounts to an improvement of
46%. With the ESA formula, the corresponding mean errors are 9.5 and
11.7 hours, respectively, representing an improvement of 19%. The cone
models minimize projection effects and hence can be used to obtain
CME radial speeds. When input to the ESA model, the large scatter in
the shock travel time is reduced, thus improving CME-related space
weather predictions.

---------------------------------------------------------
Title: Three-Dimensional MHD Models of Waves in Active Regions:
Application to Coronal Seismology
Authors: McLaughlin, J. A.; Ofman, L.
2006ESASP.617E.102M Altcode: 2006soho...17E.102M
We present results from three-dimensional MHD simulations of the
behaviour of MHD waves in 3D models of coronal active regions and
loops. The models of the active regions are constructed by using a
dipole magnetic field and gravitationally stratified coronal density
structure. We compare the main features of the model with those
seen recently by the SOHO and TRACE satellites and investigate the
application of the results to coronal seismology. We discuss the
possible applications of STEREO data to the improvement of our model.

---------------------------------------------------------
Title: Waves In Active Regions: Comparing Observations And 3D
MHD Models
Authors: Ofman, Leon; McLaughlin, J.
2006SPD....37.1802O Altcode: 2006BAAS...38..246O
Recent TRACE observations of active regions in EUV shows waveactivity
in coronal active regions following impulsive events.Motivated by
these observations we construct 3D MHD models of theactive regions
using photospheric magnetic field as boundarycondition from SOHO
MDI or Kitt Peak data, and nonuniform densitystructure to model
individual loops. We introduce several forms ofvelocity and density
pulses to model the effects of impulsiveevents, such as flares,
and follow the evolution of the modelactive region. We find good
agreement between the observedevolution of active regions, and the 3D
MHD models. Thus, wedemonstrate that the 3D MHD models can be used
for coronalseismology. In the near future STEREO data may provide
improvedinput for these models.

---------------------------------------------------------
Title: Oscillations of Hard X-Ray Flare Emission Observed by RHESSI:
Effects of Super-Alfvénic Beams?
Authors: Ofman, L.; Sui, L.
2006ApJ...644L.149O Altcode:
Recent Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI)
observations of hard X-ray (&gt;25 keV) emission from several flares
show damped oscillations with periods of 2-4 minutes and damping times
of several tens of minutes. We analyze the observations of the 2005
January 19 flare that show the quasi-periodic, damped oscillations,
and we propose a physical mechanism for this phenomenon. Namely,
we suggest that super-Alfvénic beams in the vicinity of the
reconnection region lead to the excitation of the oscillations. The
oscillations damp as the flows and the reconnecting magnetic fields
dissipate during the decay phase of the flare. We show the results of
2.5-dimensional viscoresistive MHD simulations of this mechanism, and we
find qualitative agreement with the RHESSI observations. In addition,
we find that the flows destabilize the current sheet, which leads to
an increased reconnection rate compared to the case without the beams.

---------------------------------------------------------
Title: 3d Mhd Wave Behavior In Active Regions: Modeling Techniques
Authors: McLaughlin, James A.; Ofman, L.
2006SPD....37.0116M Altcode: 2006BAAS...38..218M
We have performed simulations of three-dimensional MHD wave propagation
in models of coronal active regions. Here, we present descriptions of
the methodology and techniques that are used in the construction of such
simulations. These include:1) The MHD equations solved and the velocity
perturbations used to simulate, for example, incoming EIT waves.2)
The construction of the active region model using extrapolations of the
observed photospheric magnetic field and gravitational stratification of
the coronal density structure.3) The inclusion of the density structure
of individual, realistic coronal loops using a new technique.We also
discuss the application of the model to coronal seismology and the
possibility of using STEREO data to the improvement of the simulations.

---------------------------------------------------------
Title: 3D MHD models of waves in active regions: application to
coronal seismology
Authors: McLaughlin, J. A.; Ofman, L.
2006AGUSMSH52A..06M Altcode:
We present results from three-dimensional MHD simulations of the
behavior of MHD waves in realistic models of coronal active regions. The
models of the active regions are constructed by using the observed
photospheric magnetic field and gravitationally stratified coronal
density structure with individual loops. We compare the main features
of the model with those seen recently by the SOHO and TRACE satellites,
and investigate the application of the results to coronal seismology. We
discuss the possible application of STEREO data to the improvement of
our model.

---------------------------------------------------------
Title: 2D MHD model of the solar corona and solar wind: Recent results
Authors: Sittler, E. C., Jr.; Ofman, L.
2006ilws.conf..128S Altcode:
We have been developing a self-consistent 2D MHD steady-state model of
the solar corona and solar wind. This model is empirically constrained
by 2D maps of the effective temperature, Teff , and heat flux, qeff ,
as originally derived by Sittler and Guhathakurta or SG model. The
SG model has been applied to Mark II K-coronameter data, Skylab,
Spartan and SOHO/LASCO white light coronagraph data, plus plasma
and magnetic field Ulysses data. Our model uses the MHD conservation
equations of mass, momentum and energy with a multipole expansion of
the coronal magnetic field up to octupole term as the initial state
for the MHD solutions. At present our MHD solutions are confined
between the coronal base at 1.03 RS and 5 RS and will be expanded to
larger heliocentric distances in the future. In order to make our MHD
solutions more tractable, we have fit smooth analytical functions to
Teff and qeff derived from the data-driven SG model. We will present
solutions under these conditions, some of the difficulties we have
had to deal with and show the future direction of our research.

---------------------------------------------------------
Title: Magnetohydrodynamic waves throughout the heliosphere
Authors: Ofman, L.
2006cosp...36.2675O Altcode: 2006cosp.meet.2675O
Magnetohydrodynamic waves are observed in the solar corona the solar
wind and in planetary magnetospheres and play an important role in
energy transport in heliospheric plasma Observations of the MHD waves
serve as a diagnostic tool of heliospheric dynamical processes and of
the magnetized plasma structures throughout the heliosphere Thus the
observations and the theoretical studies of MHD waves advances our
understanding of important heliospherical processes which governs
the sun s influence on earth I will present an overview of current
observations of MHD waves throughout the heliosphere and of recent
theoretical and computational models of MHD waves in heliospheric plasma
I will discuss how cross-disciplinary international collaborative
study of the universal MHD wave processes in the heliosphere can be
carried out during IHY 2007

---------------------------------------------------------
Title: Wave acceleration of the fast solar wind
Authors: Ofman, Leon
2006AdSpR..38...64O Altcode:
Observations show that the solar wind exhibits two modes of outflow:
the slow (∼400 km s -1), high density, highly variable
wind that emerges from equatorial solar regions, and the high latitude,
fast (∼800 km s -1), low density, steady solar wind. The
bi-modal solar wind outflow is most evident near minima of solar
activity. Theoretical studies of the fast solar wind in open magnetic
structures motivated by SOHO, Ulysses, and Helios observations indicate
that both, high frequency kinetic waves, and low frequency MHD waves
play a role in its acceleration and heating. Ion-cyclotron waves have
been suggested as the main energy source of the solar wind. However,
there are theoretical difficulties with the ion-cyclotron wave heating
of the protons, and these waves do not heat electrons. Low frequency
MHD waves are still the best candidates to transport momentum and
energy far from the Sun, to accelerate the solar wind on large spatial
scales. I will present recently developed two-dimensional three-fluid
model that includes explicit wave acceleration, and visco-resistive
dissipation. The model describes electrons, protons, and minor ions as
three coupled fluids that are heated by different heating processes
with the parameters constrained by observations. I will present
the results of 2.5D three-fluid simulations of the fast solar wind
plasma that combine the effects of MHD waves self-consistently, and
ion-cyclotron waves parametrically on the acceleration and heating
processes. I will present the results of hybrid kinetic models of
ion-cyclotron wave heating of the heavy ions in the solar wind plasma.

---------------------------------------------------------
Title: A 3D Numerical Toolkit for Modeling the Heliosphere
Authors: Spicer, D. S.; Davila, J. M.; Ofman, L.
2005AGUFMSH11A0258S Altcode:
We present results from a numerical toolkit that can be used by
observers, analysts, and modelers to study solar activity and its effect
on the heliosphere. The core of the toolkit is a 3D AMR unstructured
mesh high order Godunov code that was orginally designed to model the
magnetospheric-ionospheric system. We plan to make the code available
in portable code form through the CCMC.

---------------------------------------------------------
Title: Two-dimensional hybrid modeling of wave heating in the solar
wind plasma
Authors: Ofman, L.; Vinas, A.
2005AGUFMSH53A1253O Altcode:
We study the heating and the acceleration of protons, and heavy ions by
waves in the solar wind, as well as the nonlinear influence of heavy
ions on the wave structure using a 2D hybrid model. Protons and heavy
ions are treated kinetically by solving their equations of motion in
the self-consistent electric and magnetic fields of the waves, while
electrons are treated as a neutralizing background MHD fluid. We use
the 2D hybrid code to investigate more realistic obliquely propagating
waves, boundary conditions, and background field structures, than
previous 1D-simulation and analytical studies. Using the 2D hybrid
code we consider for the first time the heating and acceleration of
protons and heavy ions by a driven-input spectrum of Alfvén/cyclotron
waves in the multi-species coronal plasma. We discuss the observational
implication of the results to the solar wind, as well as the relation
to the acceleration of stellar winds with hot magnetized coronae.

---------------------------------------------------------
Title: Solar Probe: Humanity's First Visit to a Star (Invited)
Authors: McComas, D. J.; Velli, M.; Lewis, W. S.; Acton, L. W.;
Balat-Pichelin, M.; Bothmer, V.; Dirling, R. B.; Eng, D. A.; Feldman,
W. C.; Gloeckler, G.; Guhathakurtha, M.; Habbal, S. R.; Hassler, D. M.;
Mann, I.; Maldonado, H. M.; Matthaeus, W. H.; McNutt, R. L.; Mewaldt,
R. A.; Murphy, N.; Ofman, L.; Potocki, K. A.; Sittler, E. C.; Smith,
C. W.; Zurbuchen, T. H.
2005ESASP.592..279M Altcode: 2005ESASP.592E..42M; 2005soho...16E..42M
No abstract at ADS

---------------------------------------------------------
Title: Multifluid Models of the Solar Wind
Authors: Ofman, L.
2005ESASP.592..205O Altcode: 2005ESASP.592E..32O; 2005soho...16E..32O
No abstract at ADS

---------------------------------------------------------
Title: High-frequency Alfvén waves in multi-ion coronal plasma:
Observational implications
Authors: Ofman, L.; Davila, J. M.; Nakariakov, V. M.; ViñAs, A. -F.
2005JGRA..110.9102O Altcode: 2005JGRA..11009102O
We investigate the effects of high-frequency (of order ion
gyrofrequency) Alfvén and ion-cyclotron waves on ion emission lines
by studying the dispersion of these waves in a multi-ion coronal
plasma. For this purpose we solve the dispersion relation of the
linearized multifluid and Vlasov equations in a magnetized multi-ion
plasma with coronal abundances of heavy ions. We also calculate the
dispersion relation using nonlinear one-dimensional hybrid kinetic
simulations of the multi-ion plasma. When heavy ions are present the
dispersion relation of parallel propagating Alfvén cyclotron waves
exhibits the following branches (in the positive Ω - k quadrant):
right-hand polarized nonresonant and left-hand polarized resonant
branch for protons and each ion. We calculate the ratio of ion to
proton velocities perpendicular to the direction of the magnetic field
for each wave modes for typical coronal parameters and find strong
enhancement of the heavy ion perpendicular fluid velocity compared
with proton perpendicular fluid velocity. The linear multifluid cold
plasma results agree with linear warm plasma Vlasov results and with
the nonlinear hybrid simulation model results. In view of our findings
we discuss how the observed nonthermal line broadening of minor ions
in coronal holes may relate to the high-frequency wave motions.

---------------------------------------------------------
Title: Semi-Empirical Model of Electron Heat Flux: Soho and Ulysses
Observations
Authors: Sittler, E. C., Jr.; Skoug, Ruth; Ofman, Leon; Fludra,
Andrezej
2005ESASP.592..445S Altcode: 2005soho...16E..78S; 2005ESASP.592E..78S
No abstract at ADS

---------------------------------------------------------
Title: MHD Waves and Heating in Coronal Holes
Authors: Ofman, Leon
2005SSRv..120...67O Altcode:
Coronal holes have been identified as source regions of the fast solar
wind, and MHD wave activity has been detected in coronal holes by
remote sensing, and in situ in fast solar wind streams. I review some
of the most suggestive wave observations, and discuss the theoretical
aspects of MHD wave heating and solar wind acceleration in coronal
holes. I review the results of single fluid 2.5D MHD, as well as
multi-fluid 2.5D MHD models of waves in coronal holes, the heating,
and the acceleration of the solar wind be these waves.

---------------------------------------------------------
Title: Modeling Wave Activity in Coronal Active Regions
Authors: Ofman, L.
2005AGUSMSH13B..02O Altcode:
Wave activity in coronal active regions has been detected recently
in EUV and as Doppler velocity oscillations by SOHO, and in EUV by
TRACE. The properties of the waves are determined by the excitation
mechanism, and by the local physical conditions, such as magnetic
field strength and geometry, temperature, and density. It has been
demonstrated that the phase speeds of the various wave modes can
be determined from observations. Using 3D MHD model I investigate
the generation, propagation, and damping of MHD waves in active
regions, with the goal of developing a diagnostic tool of active
region physical properties. Photospheric magnetograms were used as the
boundary conditions for the magnetic field model, and the initial state
was constructed using force-free extrapolation, and gravitationally
stratified density. Here I expand previous studies, and investigate
possible excitation mechanism, as well as the damping of the transverse
oscillations due to resistivity, and leakage. I also investigate the
generation, propagation, and damping of longitudinal oscillations in
the active region loops. In the present study improved boundary and
initial conditions are developed, and the effects of chromospheric
coupling on the excitation and damping of the waves are investigated.

---------------------------------------------------------
Title: Improved Empirical CME Arrival Time Model Via Cone Model
Authors: Xie, H.; Gopalswamy, N.; Ofman, L.; Michalek, G.; Lara, A.;
Yashiro, S.
2005AGUSMSH53A..09X Altcode:
In this study, we compare the results obtained from two cone models
and carry out the statistical study of the distribution of the actual
size and space speed of Coronal Mass Ejections (CMEs). We improved
the existing empirical CME arrival (ECA) model, based on previously
developed empirical models and provided the prediction of CME transit
time from the Sun to the Earth. The previous ECA model was in good
agreement with the observations for high-speed CMEs. However, the
agreement was not as good for low-speed events. One of possible reasons
may be due to errors caused by the significant scatter of CME projection
speeds in low projected-speed events. Using the cone models we reduced
the errors and improved the accuracy of the ECA model by applying the
cone models to halo CMEs erupted from near disk center of the Sun
(within &lt; 30 deg.) to determine the actual speed. We found that
both cone models provide similar improved accuracy for the arrival time.

---------------------------------------------------------
Title: Three dimensional MHD models of active region loops
Authors: Ofman, Leon
2005AdSpR..36.1572O Altcode:
Present imaging and spectroscopic observations of active region
loops allow to determine many physical parameters of the coronal
loops, such as the density, temperature, velocity of flows in loops,
and the magnetic field. However, due to projection effects many of
these parameters remain ambiguous. Three dimensional (3D) imaging
in EUV by the STEREO spacecraft will help to resolve the projection
ambiguities, and the observations could be used to setup 3D MHD models
of active region loops to study the dynamics and stability of active
regions. Here the results of 3D MHD models of active region loops, and
the progress towards more realistic 3D MHD models of active regions
are presented. In particular the effects of impulsive events on the
excitation of active region loop oscillations, and the generation,
propagations and reflection of EIT waves are shown. It is demonstrated
how 3D MHD models together with 3D EUV observations can be used as
a diagnostic tool for active region loop physical parameters, and to
advance the science of the sources of solar coronal activity.

---------------------------------------------------------
Title: Coronal Heating in Open vs. Closed Field
Authors: Ofman, L.
2004ESASP.575...41O Altcode: 2004soho...15...41O
No abstract at ADS

---------------------------------------------------------
Title: Transverse Oscillations in a Coronal Loop Arcade
Authors: Verwichte, E.; Nakariakov, V. M.; Ofman, L.; Deluca, E. E.
2004ESASP.575..460V Altcode: 2004soho...15..460V
No abstract at ADS

---------------------------------------------------------
Title: Alfvén waves in the solar corona, the solar wind, and the
magnetosphere
Authors: Ofman, L.
2004AGUFMSM44A..02O Altcode:
Observations and theoretical models show that Alfvén waves play an
important role in many physical processes taking place in the plasma
of the "local cosmos." For example, Alfvén waves are still the major
candidates for the acceleration and heating of the fast solar wind,
since they were proposed nearly 4 decades ago. Recently, MHD waves were
observed in coronal loops in the EUV with the TRACE satellite. The
SOHO, and TRACE instrument provide evidence for slow magnetosonic
waves in coronal plumes. In-situ Helios and Ulysses spacecraft find
ample evidence for the presence of propagating Alfvén waves in the
solar wind. The CLUSTER mission provides for the first time multi-point
view of the magnetospheric and solar wind plasma environment, and in
particular high cadence magnetic field measurements with the Fluxgate
Magnetometer (FGM), that enables to study the properties of Alfvén
waves in various parts of the magnetosphere simultaneously. I will
discuss the observations and modeling of Alfvén waves starting from the
low corona (loops), continuing into the solar wind, the magnetosphere,
and to the auroral ionosphere. I will present the results of MHD,
multifluid, and hybrid models of low-frequency (MHD), as well as kinetic
Alfvén waves in the plasma in various parts of the "local cosmos",
and I will discuss the role Alfvén waves play in the energization of
the plasma, and as a diagnostic tool of the plasma physical processes.

---------------------------------------------------------
Title: Characteristics of transverse oscillations in a coronal
loop arcade
Authors: Verwichte, E.; Nakariakov, V. M.; Ofman, L.; Deluca, E. E.
2004SoPh..223...77V Altcode:
TRACE observations from 15 April 2001 of transverse oscillations in
coronal loops of a post-flare loop arcade are investigated. They
are considered to be standing fast kink oscillations. Oscillation
signatures such as displacement amplitude, period, phase and damping
time are deduced from 9 loops as a function of distance along the loop
length. Multiple oscillation modes are found with different amplitude
profile along the loop length, suggesting the presence of a second
harmonic. The damping times are consistent with the hypothesis of
phase mixing and resonant absorption, although there is a clear bias
towards longer damping times compared with previous studies. The
coronal magnetic field strength and coronal shear viscosity in the
loop arcade are derived.

---------------------------------------------------------
Title: Parallel electric field in the auroral ionosphere: excitation
of acoustic waves by Alfvén waves
Authors: Israelevich, P.; Ofman, L.
2004AnGeo..22.2797I Altcode:
Available from <A
href="http://www.copernicus.org/site/EGU/annales/22/8/2797.htm?FrameEngine=false;">http://www.copernicus.org/site/EGU/annales/22/8/2797.htm?FrameEngine=false;</A>

---------------------------------------------------------
Title: Multiple ions resonant heating and acceleration by
Alfvén/cyclotron fluctuations in the corona and the solar wind
Authors: Xie, Hong; Ofman, Leon; ViñAs, Adolfo
2004JGRA..109.8103X Altcode:
We study the interaction between protons, multiple minor ions
(O5+, He++), and a given Alfvén/cyclotron
fluctuation spectra in the corona and the solar wind. One-dimensional
hybrid simulations are performed in initially homogeneous,
collisionless, magnetized plasma with waves propagating parallel to
the background magnetic field. The self-consistent hybrid simulations
and linear Vlasov theory are used to study the effect of the driving
spectrum, ion drift velocity, and microinstabilities on the coronal
plasma and solar wind heating. The simulation results provide a clear
picture of wave-particle interaction and successfully explain (1) how
the driving spectrum frequency range and the power law index affect
the resonant heating, (2) how ion double-peak distribution is formed
and how differential flows affect the resonant interaction via the
change of the resonant wave dispersion relation, and (3) how local
microinstabilities affect minor ion heating and constraint the values
of plasma parameters observed in the solar wind.

---------------------------------------------------------
Title: Three-fluid model of the heating and acceleration of the fast
solar wind
Authors: Ofman, L.
2004JGRA..109.7102O Altcode:
A new three-fluid, two-dimensional, wave-driven model that includes, for
the first time, heat conduction, viscous, and resistive dissipation for
protons and electrons in two-dimensional coronal hole is presented. The
fast solar wind model includes electron, proton, and He++ or
O5+ ion fluids. The heating of the solar wind plasma due to
MHD waves is modeled as follows: A broadband spectrum of low-frequency
Alfvén waves is launched from the base of the corona. The waves deposit
momentum and heat into the plasma to produce the fast solar wind. The
values of the resistivity and shear viscosity coefficients required
to produce the hot and fast solar wind consistent with observations
are orders of magnitude larger than classical values. An empirical
heating term that represents the contribution of additional heating
processes, such as resonant heating by ion cyclotron waves, is included
for the heavy ions and for protons in three out of four cases in the
present study.

---------------------------------------------------------
Title: Loop Density Enhancement by Nonlinear Magnetohydrodynamic Waves
Authors: Terradas, J.; Ofman, L.
2004ApJ...610..523T Altcode:
We study the possibility that waves in coronal loops can produce
density enhancements at loop tops. The mechanism involved is the
ponderomotive force of standing magnetohydrodynamic (MHD) waves. We
study the effect of large-amplitude waves in loops by first using a
simple second-order one-dimensional MHD model for which analytical
expressions are available. This simple model shows how Alfvén waves
can excite density fluctuations on slow timescales. Next, we solve the
time-dependent nonlinear 2.5-dimensional MHD equations in an arcade
model, in order to study the effect of nonuniform Alfvén speed along
the loop on large-amplitude waves. Finally, we solve the nonlinear
three-dimensional MHD equations in a flux-tube configuration. Waves
are launched by an initial transverse velocity profile in the loop,
with footpoints fixed in the photosphere. We find that large initial
disturbances produce a pressure imbalance along the loop, which results
in an upflow from its legs. The accumulation of mass at the top of
the oscillating loop can produce significant density enhancements for
typical coronal conditions. In a later stage, the pressure gradient
becomes dominant and inhibits the concentration of mass at the loop
top. We find that oscillating loops observed by the EUV telescope
on board TRACE on 1998 July 14 exhibit emission measure enhancements
consistent with this mechanism.

---------------------------------------------------------
Title: Development of MHD Wave Diagnostic and Models of Coronal
Active Regions
Authors: Ofman, L.; Thompson, B. J.; Davila, J. M.
2004AAS...204.9504O Altcode: 2004BAAS...36..826O
We investigate the generation, propagation, and damping of MHD waves in
active regions, with the goal to develop a diagnostic tool of active
region structure, dynamics, and stability. We used 3D MHD model to
study the generation and the propagation of EIT waves in a simple
model of an active regions, and the interaction of EIT waves with
the active region magnetic field. We model the oscillation of active
region loops numerically using the 3D MHD model active regions. Such
oscillations have been recently observed by TRACE. We use photospheric
magnetograms as the boundary conditions for the magnetic field model,
and construct an initial field using force-free extrapolation. Finite
plasma temperature, density, and gravity are included in the model. We
construct loop density structures in the model, guided by TRACE and EIT
observations in the EUV. We demonstrate that by comparing the results
of the MHD models of waves in an active region to observations we will
be able to construct a diagnostic tool for the physical properties of
the active regions, such as magnetic field and density structure.

---------------------------------------------------------
Title: Multiple Ions Resonant Heating and acceleration by
Alfvén/cyclotron Fluctuations in the corona and the solar Wind
Authors: Hong, X.; Ofman, L.
2004AAS...204.7201H Altcode: 2004BAAS...36R.798H
We study the interaction between protons, multiple minor ions
(O5+, He++) and a given Alfvén/cyclotron
fluctuations spectra in the corona and the solar wind. One-dimensional
hybrid simulations are performed in initially homogeneous,
collisionless, magnetized plasma with waves propagating parallel to the
background magnetic field. The self-consistent hybrid simulations and
linear Vlasov theory are used to study how multiple minor species and
the differential drift velocity may affect the resonance interaction
between cyclotron waves and the solar wind protons. The results of
the simulations provide a clear picture of wave-particle interaction
under various plasma conditions, which can explain 1) how multiple
minor ions affect the resonant heating of the coronal plasma and
the solar wind by a given wave spectrum, relative drift velocity,
and micro-instability; 2) how energy is distributed and transferred
among waves and different ion species; 3) the growth and damping of
different beam micro-instability modes, including both, right-hand and
left-hand waves; 4) the formation of ion double-peak distribution and
He++ anisotropy in the solar wind.

---------------------------------------------------------
Title: Cone model for halo CMEs: Application to space weather
forecasting
Authors: Xie, Hong; Ofman, Leon; Lawrence, Gareth
2004JGRA..109.3109X Altcode:
In this study, we present an innovative analytical method to determine
the angular width and propagation orientation of halo Coronal Mass
Ejections (CMEs). The relation of CME actual speed with apparent
speed and its components measured at different position angle has been
investigated. The present work is based on the cone model proposed by
[2002]. We have improved this model by (1) eliminating the ambiguity via
a new analytical approach, (2) using direct measurements of projection
onto the plane of the sky (POS), (3) determining the actual radial
speeds from projection speeds at different position angles to clarify
the uncertainty of projection speeds in previous empirical models. Our
analytical approach allows us to use coronagraph data to determine
accurately the geometrical features of POS projections, such as major
axis, minor axis, and the displacement of the center of its projection,
and to determine the angular width and orientation of a given halo
CME. Our approach allows for the first time the determination of the
actual CME speed, width, and source location by using coronagraph
data quantitatively and consistently. The method greatly enhances the
accuracy of the derived geometrical and kinematical properties of halo
CMEs, and can be used to optimize Space Weather forecasts. The applied
model predications are in good agreement with observations.

---------------------------------------------------------
Title: Theoretical Aspects of Wave Acceleration in Open Magnetic
Structures
Authors: Ofman, L.
2004ESASP.547..345O Altcode: 2004soho...13..345O
Theoretical studies of the solar wind outflow in open magnetic
structures motivated by SOHO observations indicate that both, high
frequency ion-cyclotron waves and low frequency MHD waves play a role in
the acceleration and heating of the solar wind plasma. In particular,
the high temperature anisotropy of O5+ ions deduced from SOHO UVCS
observations suggests that resonant heating due to ion cyclotron waves
is important in minor ions. However, there are theoretical difficulties
with the ion-cyclotron wave heating model of protons. It appears that
low-frequency waves are still required to transport energy and to
accelerate the solar wind on large scales. In addition, the source of
electron heating is still an open question. I will review some of the
recent wave heating models of the fast solar wind. I will discuss the
threefluid model, that describes electrons, protons, and heavy ions as
coupled fluids. This description allows to model different properties
and heating processes for each particle species and to model the
high temperature of the heavy ions in accordance with observations. I
will show the results of 2.5D three-fluid, simulations of the solar
wind plasma that combine the effects of MHD waves selfconsistently,
and ion-cyclotron waves empirically as the sources of energy. I will
review several results of hybrid kinetic models of ion-cyclotron wave
heating and relaxation of heavy ion anisotropy.

---------------------------------------------------------
Title: The origin of the slow solar wind in coronal streamers
Authors: Ofman, L.
2004AdSpR..33..681O Altcode:
The highly variable slow solar wind has been associated with
low-latitude regions of the heliosphere most clearly by the Ulysses
spacecraft. Although, it is evident today that the slow solar wind
originates in coronal helmet streamers, the mechanism of the slow solar
wind acceleration, and the origin of the variability are still being
debated. The combination of new observations and numerical modeling
are beginning to address these questions. I will discuss how recent
in-situ observations by Ulysses, white light and EUV observations by
the LASCO and UVCS instruments on SOHO advanced our understanding
of the streamer structure, dynamics, and stability. I will briefly
review the current state of numerical MHD modeling of streamers,
and the possible mechanisms that may produce the highly variable slow
wind. I will present the results of recent heat-conductive MHD modeling
of multiple streamer slow solar wind with heating function constrained
by observations. I will show how multi-fluid numerical modeling of the
slow solar wind in streamers helps to identify the regions of the slow
solar wind outflow.

---------------------------------------------------------
Title: 3D MHD Simulation of the Interaction of Fast Magnetosonic
Waves and a Coronal Active Region
Authors: Terradas, J.; Ofman, L.
2004ESASP.547..469T Altcode: 2004soho...13..469T
We present a three-dimensional MHD simulation of the local interaction
between fast magnetoacoustic waves and a coronal active region
observed with the Transition Region and Coronal Explorer (TRACE) on
June 13, 1998. The 3D MHD model is initiated with the active region
magnetic field calculated from the extrapolation of photospheric
magnetograms. The corona is assumed to be isothermal and resistive
dissipation is included in the model. We compare the main features
of the simulated wave with the wave observed with TRACE. We find that
many aspects of the simulation match the observations. In particular,
we show how the wave's trajectory is modified, undergoing strong
reflection and refraction away from the active region.

---------------------------------------------------------
Title: 3D MHD Models of Active Region Loops
Authors: Ofman, L.
2004cosp...35.4568O Altcode: 2004cosp.meet.4568O
Present imaging and spectroscopic observations of active region loops
allow to determine many physical parameters of the coronal loops, such
as the density, temperature, velocity of flows in loops, and possibly
the magnetic field. However, due to projection effects many of these
parameters remain ambiguous. Three dimensional imaging in EUV by the
STEREO spacecraft will help to resolve the projection ambiguities, and
the observations could be used to setup 3D MHD models of active region
loops to study the dynamics and stability. Here I present the results
of 3D MHD models of active region loops, and the progress toward more
realistic 3D MHD models of active regions. In particular I show the
effects of impulsive events on the excitation of active region loop
oscillations, and the generation, propagations and reflection of EIT
waves. I show how 3D MHD models together with 3D EUV observations can
be used as a diagnostic tool for active region loop physical parameters,
and to advance the science of the sources of solar coronal activity.

---------------------------------------------------------
Title: Looptop Density Enhancement By Nonlinear Magnetohydrodynamic
Waves
Authors: Terradas, J.; Ofman, L.
2003AGUFMSH42B0539T Altcode:
We discuss the possibility that disturbances generated in flares can
produce the emission measure enhancement at the top of coronal loops
observed by the Transition Region and Coronal Explorer ({TRACE}). The
mechanism involved is the ponderomotive force of standing waves in
the loops. We study the effect of large amplitude waves in loops
using first a simple one-dimensional model for which analytical
expressions are available, and second by solving the time dependent
nonlinear magnetohydrodynamic (MHD) equations in a more realistic
three-dimensional configuration. Waves are launched by an initial
transverse velocity profile in the loop with footpoints fixed in the
photosphere. We find that large initial disturbances can provide an
imbalance along the loop, which results in an upflow from the legs of
the loop. The accumulation of mass at the top of the loop produces a
strong density enhancement. In a later stage, the pressure gradient
becomes dominant and inhibits the concentration of mass at the loop
apex.

---------------------------------------------------------
Title: Alfvén Waves in Multi-ion Coronal Plasma: Observational
Implications
Authors: Ofman, L.; Nakariakov, V. M.; Davila, J. M.
2003AGUFMSH11D1129O Altcode:
We investigate low-frequency Alfvén waves in a multi-ion coronal plasma
by deriving the dispersion relation of the linearized three-fluid
equations in magnetized plasma with coronal parameters. We study
the effect of collisions on the velocity amplitude of minor ions due
to the Alfvén waves compared to the proton wave amplitude. We find
that in the collisionless plasma the minor ion velocity is reduced
by the factor Z/A compared to protons, where Z is the ion charge,
and A is mass in units of proton mass. When the collision frequency
is much larger then the Alfvén wave frequency the velocity amplitude
of the minor ions is equal to the proton velocity amplitude. We show
the effects of minor ions and collisions on the dispersion relation
of Alfvén waves in the three fluid plasma. In view of our results we
show how the observed nonthermal line broadening of minor ions relates
to the wave motions of protons as a function of heliocentric distance,
and the plasma physical parameters.

---------------------------------------------------------
Title: Development of 2D MHD Self-Consistent Empirical Model of the
Corona and Solar Wind
Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Holzer, T.; Davila,
J.; Guhathakurta, M.
2003AGUFMSH42D..07S Altcode:
We are developing a 2D MHD self-consistent empirical model of
the solar corona and solar wind. We constrain the solution using
empirically determined estimates of the effective pressure for the
momentum equation and effective heat flux for the energy equation
provided from coronagraph data and Ulysses plasma and magnetic field
data. Our solutions are steady state and do not use a polytrope which
we know is not valid in the solar corona. We have been able to achieve
preliminary convergence. We will present the results of an error
analysis. Our results are presently only valid during solar minimum,
but are generalizing so it can be used during the transition toward
solar maximum (i.e., three current sheets). We will also present some
preliminary results which will allow us to apply our solutions to
solar maximum conditions.

---------------------------------------------------------
Title: Multiple Ions Resonant Heating and Acceleration by
Alfven/cyclotron Fluctuations in the Solar Wind
Authors: Xie, H.; Ofman, L.
2003AGUFMSH11D1133X Altcode:
We study the interaction between protons, and multiple minor ions
(O5+, He++) and a given cyclotron resonant spectra in coronal hole
plasma. One-dimensional hybrid simulations are performed in initially
homogeneous, collisionless, magnetized plasma with waves propagating
parallel to the background magnetic field. The self-consistent hybrid
simulations are used to study how multiple minor species may affect
the resonance interaction between a spectrum of waves and the solar
wind protons. The results of the simulations provide a clear picture
of wave-particle interaction under various coronal conditions, which
can explain 1) how multiple minor ions affect the resonant heating and
the temperature anisotropy of the solar wind protons by a given wave
spectrum; 2) how energy is distributed and transferred among waves and
different ion species; 3) the growth and damping of different beam
microinstability modes, including both inward and outward waves; 4)
the formation of proton double-peak distribution in the solar wind.

---------------------------------------------------------
Title: Flows in coronal loops driven by Alfvén waves: 1.5 MHD
simulations with transparent boundary conditions
Authors: Grappin, R.; Léorat, J.; Ofman, L.
2003AIPC..679..750G Altcode:
We investigate time-dependent siphon flows in coronal loops driven
by Alfvén waves. We consider a 1.5 D isothermal, MHD model in which
the coordinate is the abscissa along the loop, with an external
gravity field reversing sign in the middle, and a uniform magnetic
field parallel to the x-axis. We use transparent boundary conditions,
meant to describe the upper part of the loop. The reaction of the loop
to Alfvén waves depends entirely on whether we allow or not incoming
parallel velocity fluctuations: only in the latter case do transonic
flows arise, but the flow is in that case generated by a nonlinear
coupling of the waves with the boundaries.

---------------------------------------------------------
Title: Development of Multidimensional MHD Model for the Solar Corona
and Solar Wind
Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Guhathakurta, M.;
Davila, J.; Skoug, R.; Fludra, A.; Holzer, T.
2003AIPC..679..113S Altcode:
We are developing a time stationary self-consistent 2D MHD model of
the solar corona and solar wind that explicitly solves the energy
equation, using a semi-empirical 2D MHD model of the corona to provide
an empirically determined effective heat flux qeff (i.e., the term
effective means the possible presence of wave contributions). But,
as our preliminary results indicate, in order to achieve high
speed winds over the poles we also need to include the empirically
determined effective pressure Peff as a constraint in the momentum
equation, which means that momentum addition by waves above 2 RS are
required to produce high speed winds. At present our calculations do
not include the Peff constraint. The estimates of Peff and qeff come
from the semi-empirical 2D MHD model of the solar corona by Sittler
and Guhathakurta (1999a,2002) which is based on Mk-III, Skylab and
Ulysses observations. For future model development we plan to use SOHO
LASCO, CDS, EIT, UVCS and Ulysses data as constraints for our model
calculations. The model by Sittler and Guhathakurta (1999a, 2002) is
not a self-consistent calculation. The calculations presented here is
the first attempt at providing a self-consistent calculation based on
empirical constraints.

---------------------------------------------------------
Title: Damped Oscillations of Multithreaded Coronal Loops: results
of 3D MHD Simulations
Authors: Ofman, L.; Terradas, J.
2003SPD....34.0108O Altcode: 2003BAAS...35..806O
Recently, scaling laws of the damping time of coronal loop oscillations
were constructed from TRACE observations in the EUV of damped coronal
loop oscillations (Ofman and Aschwanden 2002). The scaling laws suggest
that the damping of the oscillations is due to phase mixing with
anomalously high viscosity or resistivity. The phase mixing dissipation
scenario is most likely realized due to the multithread structure of
the coronal loops as suggested by observations. We develop a resistive
3D MHD model of an active region coronal loop in low-beta plasma. We
model the damping of an active region coronal loop oscillations using
the resistive 3D MHD equations. The oscillations are excited by a model
"EIT wave" that hits the loop. We investigate the evolution and the
damping of the oscillations in a multithreaded loop and compare the
results with a cylindrical loop. We find that the damping time is
strongly dependent on the resistivity for the multithreaded loop,
while for the cylindrical loop the damping time is weakly dependent
on resistivity, in agreement with previous analytical results. We
investigate the effects of boundary conditions, resistivity, and loop
parameters on the damping rate in the multithreaded loop.

---------------------------------------------------------
Title: Winds from “Non-Coronal” and “Hybrid” Stars Driven by
MHD Waves
Authors: Airapetian, V. S.; Carpenter, K.; Ofman, L.
2003AAS...202.3214A Altcode: 2003BAAS...35..745A
Observations obtained with IUE, HST and FUSE provide extensive data
on atmospheric heating and wind dynamics for late-type luminous
stars. The physical processes which drive winds in these stars are
poorly understood, despite decades of study. In our previous study we
have shown that observational signatures of winds can be interpreted
by our model of winds driven by propagated Alfvén waves in stellar
atmospheres and launched at a single frequency at the wind base
(Airapetian et al. 2000). We extend our MHD calculations of winds
from luminous late-type stars to include an Alfvén wave driver
with a broad-band frequency range. The calculations are applied to
“non-coronal” (α Tau) and “hybrid” (β Dra) giant stars to
consistently reproduce the observed velocity profiles of the winds,
its terminal velocity, the turbulent broadening of UV lines and mass
loss rates. The nature of wind variability in luminous late-type stars
is discussed. We also present the preliminary results of our first
MHD and LTE radiative transfer calculations to model the UV spectra
from the K5 giant, α Tau. This research is supported by the NASA
Research grant from GSFC No. NAG5-12869.

---------------------------------------------------------
Title: Observations of Slow Solar Wind Outflow in Coronal Streamers
and the Relation to Current Sheet Structure
Authors: Strachan, L.; Ofman, L.; Panasyuk, A. V.
2003SPD....34.0602S Altcode: 2003BAAS...35Q.817S
UVCS/SOHO observations have allowed measurements of the slow solar
wind outflow in streamers by using O VI emission at 1032 and 1037
Å (Strachan et al 2002). Here we analyze the UVCS data to obtain
more detailed outflow velocities of O 5+ in the legs and stalks of
streamers. According to MHD models current sheets are believed to
exist in the stalks and legs of coronal streamers, and the slow solar
wind outflow speed peaks at same locations. In this work we compare
the observations of outflow velocities to the velocities predicted
by three-fluid model that includes O 5+. We present some preliminary
data and discuss constraints on the observed and model values of the
streamer parameters.

---------------------------------------------------------
Title: Nanoflare Frequency Distribution Scaling from Wave Heating:
Results of Nonlinear Loop Modeling
Authors: Davila, J. M.; Ofman, L.; Davila, J. M.; Ofman, L.
2003SPD....34.1601D Altcode: 2003BAAS...35..832D
The statistics of nanoflare events observed by TRACE in the EUV and
Yohkoh in soft X-rays exhibits a power law relation between the peak
thermal energy and the number of events per energy interval. Using
1D coronal loop model with nonlinear coupling to the chromosphere
(Ofman, Klimchuk, and Davila 1998) we calculate the distribution of
heating events due to the dissipation of waves driven by a random
Alfven wave source. Initial results show that the number of heating
events per energy bin scale with energy with the power of 2+/-
0.4. The scaling is consistent with the observed value of 1.86+/-0.07
at 171Å and 1.81+/-0.10 at 195Å found with TRACE (Aschwanden and
Parnell 2002). Thus, we conclude that in the nanonflare energy range
(E&lt;1028 erg) the observed frequency distribution of peak
energy is consistent with wave heating.

---------------------------------------------------------
Title: 3D MHD Simulation of the Interaction of Fast Magnetoacoustic
Waves and Coronal Active Regions
Authors: Terradas, J.; Ofman, L.
2003SPD....34.0109T Altcode: 2003BAAS...35..806T
Following the work of Ofman and Thompson (2002), we present a
three-dimensional MHD simulation of the local interaction between
fast magnetosonic waves and coronal active regions. In order to
have a realistic simulation, in the present work the active region
is modeled by an initially potential magnetic field configuration
calculated from the extrapolation of photospheric magnetograms. The
density is gravitationally stratified and we also include resistive
dissipation in the model. We compare the main features of the simulated
wave with a wave observed with the Transition Region and Coronal
Explorer (TRACE). We find that many aspects of the simulation match
the observations. In particular, we show how the wave's trajectory
is modified, undergoing strong reflection and refraction away from
the active region. We also discuss how we can use the simulations as
a tool to understand the three-dimensional topology and stability of
active regions, in anticipation of the STEREO mission.

---------------------------------------------------------
Title: Consequences of proton and alpha anisotropies in the solar
wind: Hybrid simulations
Authors: Gary, S. Peter; Yin, Lin; Winske, Dan; Ofman, Leon; Goldstein,
Bruce E.; Neugebauer, Marcia
2003JGRA..108.1068G Altcode:
Alfvén fluctuations propagating away from the Sun in the solar
corona and solar wind transfer energy via cyclotron resonances to
ions of successively larger charge-to-mass ratios. This can yield
T⟂/T∥ &gt; 1 for each ion species, where the
subscripts refer to directions relative to the background magnetic
field. If these anisotropies become sufficiently large, they drive
electromagnetic ion cyclotron instabilities. This paper describes
two-dimensional hybrid simulations of a collisionless, homogeneous,
magnetized plasma to study the consequences of scattering by enhanced
field fluctuations from such instabilities. The ions in the simulations
consist of majority protons and minority alpha particles with initial
bi-Maxwellian velocity distributions and representative solar wind
parameters including a nonzero alpha/proton relative speed. The
simulations show that both helium and proton cyclotron instabilities
reduce the driving anisotropy, reduce initial differences between
the proton and alpha particle anisotropies, and, as a new result,
usually reduce initial alpha/proton speeds. These results are somewhat
different from theoretical predictions of ion scattering by interaction
with outward propagating Alfvén-cyclotron waves but are consistent
with observations from Ulysses.

---------------------------------------------------------
Title: Empirically Constrained Multidimensional MHD Model for the
Solar Corona and Solar Wind
Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Guthathakurta, M.;
Skoug, R.; Fludra, A.; Davila, J.; Holzer, T.
2002AGUFMSH21A0502S Altcode:
We are developing a time stationary self-consistent 2D MHD model of
the solar corona and solar wind that explicitly solves the energy
equation, using a semi-empirical 2D MHD model of the corona to provide
an empirically determined effective heat flux qeff (i.e.,
the term effective means the possible presence of wave contributions)
for the energy equation and effective pressure Peff
for the momentum equation. Preliminary results indicated that in
order to achieve high speed winds over the poles we not only needed
to use qeff in the energy equation, but also needed to
include the empirically determined effective pressure Peff
as a constraint in the momentum equation, which means that momentum
addition by waves above 2 RS are required to produce high
speed winds. A solution which only included qeff showed high
acceleration over the poles below 2 RS, but then drooped
above that radial distance indicating we needed momentum addition above
that height to get high speed flows over the poles. We will show new
results which include the added constraint of Peff in the
momentum equation. This method will allows us to estimate the momentum
addition term due to waves as a function of height and latitude within
the corona. The estimates of Peff and qeff come
from the semi-empirical 2D MHD model of the solar corona by Sittler and
Guhathakurta (1999, 2002) which is based on Mk-III, Skylab and Ulysses
observations. For future model development we plan to use SOHO LASCO,
CDS, EIT, UVCS, Spartan 201-05 and Ulysses data as constraints for
our model calculations. The model by Sittler and Guhathakurta (1999,
2002) is not a self-consistent calculation. The calculations presented
here are a continuing effort to provide a self-consistent calculation
based on empirical constraints.

---------------------------------------------------------
Title: Doppler oscillations in hot coronal loops
Authors: Curdt, W.; Wang, T. J.; Innes, D. E.; Solanki, S. K.;
Dammasch, I. E.; Kliem, B.; Ofman, L.
2002ESASP.506..581C Altcode: 2002ESPM...10..581C; 2002svco.conf..581C
Recently, a new kind of damped oscillations of hot coronal loops was
revealed by the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on SOHO. Such events seem to be a common feature
observed in active region loops, seen very often when these lines
brighten. The oscillations always have an impulsive trigger and
are strongly damped while they cool down. However, in lines formed
at coronal temperatures of ≍2 MK never any signature of these
oscillations has been observed. In this study, we present the main
properties of Doppler oscillations derived from a statistical study
of 17 flare-like events, and a comparison with TRACE transverse loop
oscillations. We also discuss the oscillation modes and their damping
mechanism.

---------------------------------------------------------
Title: Kink oscillations of coronal loops as a tool for the
determination of coronal magnetic field
Authors: Nakariakov, Valery; Ofman, Leon
2002ESASP.506..461N Altcode: 2002svco.conf..461N; 2002ESPM...10..461N
We develop a new method for the determination of the absolute value
of the magnetic field strength in coronal closed magnetic structures,
based on the analysis of flare-generated oscillations of coronal
loops. Interpretation of the quasi-harmonic oscillations observed in
terms of global standing kink waves allows to connect the period of
the oscillations and the loops length with the magnetic field strength
in the loops. Improved diagnostic of the loop length, the oscillation
period, and the plasma density in the loop will significantly improve
the method's precision.

---------------------------------------------------------
Title: Consequences of proton and alpha anisotropies in the solar
wind: Hybrid simulations
Authors: Gary, S. P.; Yin, L.; Winske, D.; Ofman, L.; Goldstein,
B. E.; Neugebauer, M.
2002AGUFMSH12A0390G Altcode:
Alfvén-like fluctuations in the solar corona and solar
wind may cascade from lower to higher frequencies where they
transfer energy via cyclotron resonances to ions of successively
higher charge-to-mass-ratios. This yields Tperpendicular to
}/T{∥ &gt; 1 for each ion species, where the
subscripts refer to directions relative to the background magnetic
field. If sufficiently large, these anisotropies drive electromagnetic
ion cyclotron instabilities. This manuscript describes the use of
two-dimensional hybrid simulations of a collisionless, homogeneous,
magnetized plasma with both protons and alpha particles to study
the consequences of scattering by enhanced field fluctuations from
such instabilities. The most important new results are that both
helium and proton cyclotron instabilities reduce initial differences
between the proton and alpha particle anisotropies, and also reduce
initial alpha/proton relative speeds. These simulation results are
different from theoretical predictions of ion responses to their direct
interaction with cascading Alfvén/cyclotron waves, but are consistent
with observations from the Ulysses spacecraft.

---------------------------------------------------------
Title: EUV Dimmings: Simple or Enigmatic?
Authors: Thompson, B.; Biesecker, D. A.; Ofman, L.; St. Cyr, O. C.;
Wills-Davey, M. J.
2002AGUFMSH52A0488T Altcode:
EUV dimmings are large-scale depletions in coronal EUV emission
associated with coronal mass ejections. Their occurrence is nearly
perfect in correlation with fast CMEs. Many of the EUV dimming
observations appear to correspond well in appearance and behavior to
SXR dimmings. It has been assumed that the dimmings are merely the
location of the CME mass removal in the corona, and that their similar
appearance to coronal holes is because they are transient coronal
holes with fieldlines opened by the coronal mass ejection. However,
not all CMEs have dimmings, and large-scale EUV dimmings have also
been caused by heating of local plasma, and due to absorption by cool
material "clouds" evolving in the wake of an eruption. Additionally,
there are several ways in which these regions "heal," presumably due to
the closing down of the open field lines. The presentation will include
a range of EUV dimming observations, a discussion of their origin,
and what they might imply about the nature of the associated CMEs.

---------------------------------------------------------
Title: Resonant heating and acceleration of ions in coronal holes
driven by cyclotron resonant spectra
Authors: Ofman, L.; Gary, S. P.; ViñAs, A.
2002JGRA..107.1461O Altcode:
Recent observations and models suggest that the resonant absorption
of ion cyclotron waves heats and accelerates the ions in the
solar wind. Velocity distributions of minor ions derived from
SOHO Ultraviolet Cronagraph Spectrometer (UVCS) observations in
coronal holes indicate that the minor ion temperature anisotropy is
T⟂/T∣∣ &gt; 10 and that outflow speeds
are higher than those of the solar wind protons. Here one-dimensional
hybrid simulations of initially homogeneous, collisionless plasmas are
used to study a model of coronal plasmas including kinetic protons, a
tenuous component of oxygen ions, and massless fluid electrons. Spectra
of ion cyclotron resonant Alfvén waves are imposed on the system
to study the resultant heating of both ion species. We investigate
the effects of various power spectra of the form f-1 or
f-5/3 and vary the input frequency range. We find that the
ion heating strongly depends on the power contained in the frequency
range of the input spectrum that can resonate with the ions. The minor
O5+ ions are easily heated and become anisotropic due to
various forms of the spectra. The protons remain nearly isotropic
and are weakly heated in most cases in this study. We investigate the
self-consistent fluctuation spectrum generated by the response of the
ions and the non-Maxwellian features in the velocity distribution.

---------------------------------------------------------
Title: Acceleration and Heating of the Fast Solar Wind by
Ion-Cyclotron and MHD Waves
Authors: Ofman, L.
2002AGUFMSH12A0417O Altcode:
The basic plasma properties of the fast solar wind as deduced from
observations suggest that both, high frequency ion-cyclotron waves,
and low frequency MHD waves play a role in the acceleration and heating
of the coronal hole plasma. The heating due to high-frequency waves
is particularly important in minor ions, such as O5+. I
will present the results of 3-fluid, simulations of the solar wind
plasma that combine the effects of ion-cyclotron, and MHD waves. The
low frequency waves are included self-consistently as the source
of momentum and heating of protons and electrons. Additional heat
and momentum input terms due to ion-cyclotron waves are included
in protons and minor ions. The 3-fluid gyrotropic model allows for
Tperpendicular to &gt;T_∥ of the ions in accordance
with observations. The heating term that contributes mostly to the
perpendicular temperature of minor ions is constructed using the
saturated state of the hybrid kinetic model of the solar wind plasma
at several locations in the coronal hole, with the plasma β and other
parameters varying with radial distance. Iterative update of these
parameters is planed in a future study. The temperature anisotropy
estimated from SOHO UVCS spectral observations is used to constrain
the hybrid kinetic modeling. Ulysses and Helios observations are used
to constrain the asymptotic solar wind speed and mass flux.

---------------------------------------------------------
Title: Hot Coronal Loop Oscillations Observed by SUMER: Slow
Magnetosonic Wave Damping by Thermal Conduction
Authors: Ofman, L.; Wang, Tongjiang
2002ApJ...580L..85O Altcode:
Recently, strongly damped Doppler shift oscillations of hot (T&gt;6 MK)
coronal loops were observed with the Solar Ultraviolet Measurement
of Emitted Radiation (SUMER) spectrometer on board the Solar and
Heliospheric Observatory. The oscillations are interpreted as signatures
of slow-mode magnetosonic waves excited impulsively in the loops. Using
a one-dimensional MHD code, we model the oscillations and the damping of
slow magnetosonic waves in a model coronal loop. We find that because
of the high temperature of the loops, the large thermal conduction,
which depends on temperature as T2.5, leads to rapid damping
of the slow waves on a timescale comparable to observations (5.5-29
minutes). The scaling of the dissipation time with period agrees well
with SUMER observations of 35 cases in 17 events. We also find that the
decay time due to compressive viscosity alone is an order of magnitude
longer than the observed decay times.

---------------------------------------------------------
Title: Estimating random transverse velocities in the fast solar
wind from EISCAT Interplanetary Scintillation measurements
Authors: Canals, A.; Breen, A. R.; Ofman, L.; Moran, P. J.; Fallows,
R. A.
2002AnGeo..20.1265C Altcode:
Interplanetary scintillation measurements can yield estimates of a
large number of solar wind parameters, including bulk flow speed,
variation in bulk velocity along the observing path through the solar
wind and random variation in transverse velocity. This last parameter
is of particular interest, as it can indicate the flux of low-frequency
Alfvén waves, and the dissipation of these waves has been proposed
as an acceleration mechanism for the fast solar wind. Analysis of IPS
data is, however, a significantly unresolved problem and a variety of a
priori assumptions must be made in interpreting the data. Furthermore,
the results may be affected by the physical structure of the radio
source and by variations in the solar wind along the scintillation
ray path. We have used observations of simple point-like radio
sources made with EISCAT between 1994 and 1998 to obtain estimates
of random transverse velocity in the fast solar wind. The results
obtained with various a priori assumptions made in the analysis are
compared, and we hope thereby to be able to provide some indication
of the reliability of our estimates of random transverse velocity
and the variation of this parameter with distance from the Sun. Key words. Interplanetary physics (MHD waves and turbulence;
solar wind plasma; instruments and techniques)

---------------------------------------------------------
Title: Damping Time Scaling of Coronal Loop Oscillations Deduced
from Transition Region and Coronal Explorer Observations
Authors: Ofman, L.; Aschwanden, M. J.
2002ApJ...576L.153O Altcode:
The damping mechanism of recently discovered coronal loop transverse
oscillations provides clues to the mechanism of coronal heating. We
determine the scaling of the damping time with the parameters of the
loops observed in extreme ultraviolet by the Transition Region and
Coronal Explorer. We find excellent agreement of the scaling power
to the power predicted by phase mixing and poor agreement with the
power predicted by the wave leakage or ideal decay of the cylindrical
kink mode mechanisms. Phase mixing leads to rapid dissipation of the
Alfvén waves due to the variation of the Alfvén speed across the
wave front and formation of small scales. Our results suggest that
the loop oscillations are dissipated by phase mixing with anomalously
high viscosity.

---------------------------------------------------------
Title: Interaction of EIT Waves with Coronal Active Regions
Authors: Ofman, L.; Thompson, B. J.
2002ApJ...574..440O Altcode:
Large-scale coronal waves associated with flares were first observed
by the Solar and Heliospheric Observatory (SOHO) Extreme ultraviolet
Imaging Telescope (EIT). We present the first three-dimensional MHD
modeling of the interaction of the EIT waves with active regions and the
possibility of destabilization of an active region by these waves. The
active region is modeled by an initially force-free, bipolar magnetic
configuration with gravitationally stratified density. We include
finite thermal pressure and resistive dissipation in our model. The
EIT wave is launched at the boundary of the region, as a short time
velocity pulse that travels with the local fast magnetosonic speed
toward the active region. We find that the EIT wave undergoes strong
reflection and refraction, in agreement with observations, and induces
transient currents in the active region. The resulting Lorentz force
leads to the dynamic distortion of the magnetic field and to the
generation of secondary waves. The resulting magnetic compression
of the plasma induces flows, which are particularly strong in the
current-carrying active region. We investigate the effect of the
magnetic field configuration and find that the current-carrying active
region is destabilized by the impact of the wave. Analysis of the
three-dimensional interaction between EIT waves and active regions can
serve as a diagnostic of the active region coronal magnetic structure
and stability.

---------------------------------------------------------
Title: Self-consistent 2D MHD modeling of multi-streamer coronal
structures
Authors: Ofman, L.; Sittler, E. C.; Gibson, S.; Holzer, T. E.;
Guhathakurta, M.
2002AGUSMSH21B..02O Altcode:
Recently, a semi-empirical 2D MHD model of the solar corona was
constructed by Sittler and Guhathakurta [1999]. The model uses an
empirical electron density and empirical magnetic field during solar
minimum as input to the conservation equations of mass, momentum,
and energy to derive an empirical effective heat flux, or empirical
heating function. This semi-empirical model is not a self-consistent
calculation. We explore the possibility of developing a self-consistent
model that uses the empirical heating function as a constraint for the
calculations. This allows us to solve the energy equation without use of
a polytrope which we know does not apply near the Sun. For our initial
attempt we use the empirically derived magnetic field model obtained
from observed streamer topologies and Ulysses boundary conditions to
initialize our self-consistent 2D MHD model of the solar corona. We
solve the thermally conductive energy equations with an empirical
heating function, and obtain 3-streamer structure with self-consistent
magnetic field, current-sheets, solar wind outflow, density, and
temperature. We compare the results of the thermally conductive model
to the polytropic model, and to the empirical model. We find that
the self-consistent magnetic field structure is more realistic then
the empirical model. We find that the thermally conductive streamers
result in more diffuse current-sheets than in the polytropic model. We
also find that the heating function reduces the heliocentric distance
of the streamers' cusp, and produces more rapid acceleration of the
solar wind in the thermally conductive model then in the polytropic
model, consistent with observations. We investigate the effect of
various forms of the heating function, and of an empirically derived
heat flux on the solutions.

---------------------------------------------------------
Title: Chromospheric Leakage of Alfvén Waves in Coronal Loops
Authors: Ofman, L.
2002ApJ...568L.135O Altcode:
The recently observed rapid damping of coronal loop oscillations
generated discussion regarding the physical mechanism responsible for
the damping, with the leakage into the chromosphere suggested as one
of the possible mechanisms. I study the leakage of Alfvén waves into
the chromospheric footpoints of a coronal loop using the nonlinear
viscoresistive 1.5-dimensional MHD model. The waves were launched by
an initial transverse velocity profile in the loop. I find that the
leakage time of long-wavelength transverse oscillations, such as the
ones observed recently by the Transition Region and Coronal Explorer
(TRACE), is 5 times longer than the observed damping time of the
oscillations. For the loop recently observed by TRACE, I conclude that
the observed damping of the long-wavelength oscillations is not due
to leakage into the chromosphere. However, depending on particular
chromospheric and coronal properties, chromospheric leakage may be
significant in some events of coronal loop oscillations.

---------------------------------------------------------
Title: The Origin of the Slow Solar Wind in Coronal Streamers
Authors: Ofman, L.
2002cosp...34E.825O Altcode: 2002cosp.meetE.825O
The highly variable slow solar wind has been associated with
low-latitude regions of the heliosphere most clearly by the Ulysses
spacecraft. Although, it is clear today that the slow solar wind
is associated with coronal helmet streamers, the mechanism of the
slow solar wind acceleration, and the origin of its variability
are still being debated. The combination of new observations and
numerical modeling began to address these questions. I will discuss
how recent white light and EUV observations of streamers by the
LASCO and UVCS instruments on SOHO advanced our understanding of the
streamer structure, dynamics, and stability. I will briefly review the
current state of numerical MHD modeling of streamers, and the possible
mechanisms that may produce the highly variable slow wind. I will show
how multifluid numerical modeling of the slow solar wind in streamers
helps to identify the regions of the slow solar wind outflow. I will
present the results of recent attempts of self-consistent MHD modeling
of multiple streamer slow solar wind with empirical heating function
constrained by observations.

---------------------------------------------------------
Title: Resonant Heating and Acceleration of Ions in Coronal Holes
by High-Frequency Wave Spectrum
Authors: Ofman, L.; Gary, S. P.; Vinas, A.
2001AGUFMSH11A0696O Altcode:
Recent observations and models suggest that the resonant absorption
of ion cyclotron waves heats and accelerates the ions in the solar
wind. Velocity distributions of minor ions derived from SOHO UVCS
observations in coronal holes indicate that the minor ion temperature
anisotropy &gt;10 and outflow speeds is higher then the solar wind
protons. Using 1D hybrid code we investigate the effects of differential
flow and anisotropy on the stability of the solar wind plasma. We
investigate the heating and the acceleration of the solar wind plasma
ions by including an input spectrum of the form f-1 and
f-5/3. We find that the ion heating strongly depends on the
power contained in the frequency range of the power-law spectrum that
can resonate with the ions. The heating also depends on the plasma β ,
and the abundance of the minor ions. We investigate the self-consistent
fluctuations spectrum generated by the response of the ions. We have
used second-order theory (Gary and Tokar 1985) to evaluate the rates
of proton heating, anisotropy formation, and acceleration, and have
compared these predictions against the simulation results.

---------------------------------------------------------
Title: New Observations of Oscillating Coronal Loops
Authors: Reeves, K. K.; Shoer, J.; Deluca, E. E.; Winebarger, A. R.;
Ofman, L.; Davila, J. M.
2001AGUFMSH11A0704R Altcode:
One of the most promising discoveries of the TRACE mission is the first
observations of transverse oscillations in coronal loops (Aschwanden
et al 1999, Nakariakov et al 1999). Loops are set into motion from
nearby flares, oscillate with a well defined frequency and decay
on a time scale of 10 minutes. While the theoretical study of MHD
waves in the corona has a long history, observational support has
dramatically increased over the past 10 years as coronal instruments
have improved. The transverse oscillations have been identified as
standing kink modes for the 14-July-1998 observations cited above. In
this paper we present clear evidence for a decaying global kink modes
observed by TRACE on 15-Apr-2001. Six different loops have been observed
to oscillate with a frequency in the range: 15-20 mHz (compared with
4 mHz for 14-July-1998) and a decay time in the range: 8-23 minutes
(compared with 11 minutes for the earlier event). The implications
for these results for coronal diagnostics and solar coronal seismology
will be discussed.

---------------------------------------------------------
Title: Publicly Available Numerical Codes for Modeling the X-ray
and Microwave Emissions from Solar and Stellar Activity
Authors: Holman, G. D.; Mariska, J. T.; McTiernan, J. M.; Ofman, L.;
Petrosian, V.; Ramaty, R.
2001AAS...199.9302H Altcode: 2001BAAS...33.1444H
We have posted numerical codes on the Web for modeling the
bremsstrahlung x-ray emission and the gyrosynchrotron radio emission
from solar and stellar activity. In addition to radiation codes,
steady-state and time-dependent Fokker-Planck codes are provided for
computing the distribution and evolution of accelerated electrons. A
1-D hydrodynamics code computes the response of the stellar atmosphere
(chromospheric evaporation). A code for modeling gamma-ray line
spectra is also available. On-line documentation is provided for each
code. These codes have been developed for modeling results from the
High Energy Solar Spectroscopic Imager (HESSI) along with related
microwave observations of solar flares. Comprehensive codes for
modeling images and spectra of solar flares are under development. The
posted codes can be obtained on NASA/Goddard's HESSI Web Site at
http://hesperia.gsfc.nasa.gov/hessi/modelware.htm This work is supported
in part by the NASA Sun-Earth Connection Program.

---------------------------------------------------------
Title: Reconnection remnants in the magnetic cloud of October 18-19,
1995: A shock, monochromatic wave, heat flux dropout, and energetic
ion beam
Authors: Collier, Michael R.; Szabo, A.; Farrell, W. M.; Slavin,
J. A.; Lepping, R. P.; Fitzenreiter, R.; Thompson, B.; Hamilton,
D. C.; Gloeckler, G.; Ho, G. C.; Bochsler, P.; Larson, D.; Ofman, L.
2001JGR...10615985C Altcode:
Evidence is presented that the Wind spacecraft observed particle and
field signatures on October 18-19, 1995, due to reconnection near
the foot points of a magnetic cloud (i.e., between 1 and 5 solar
radii). These signatures include (1) an internal shock traveling
approximately along the axis of the magnetic cloud, (2) a simple
compression of the magnetic field consistent with the foot point
magnetic fields being thrust outward at speeds much greater than the
solar wind speed, (3) an electron heat flux dropout occurring within
minutes of the shock, indicating a topological change resulting from
disconnection from the solar surface, (4) a very cold 5 keV proton
beam, and (5) an associated monochromatic wave. We expect that given
observations of enough magnetic clouds, Wind and other spacecraft
will see signatures similar to the ones reported here indicating
reconnection. However, these observations require the spacecraft to
be fortuitously positioned to observe the passing shock and other
signatures and will therefore be associated with only a small fraction
of magnetic clouds. Consistent with this, a few magnetic clouds observed
by Wind have been found to possess internal shock waves.

---------------------------------------------------------
Title: Electromagnetic heavy ion cyclotron instability: Anisotropy
constraint in the solar corona
Authors: Gary, S. Peter; Yin, Lin; Winske, Dan; Ofman, Leon
2001JGR...10610715G Altcode:
The electromagnetic proton cyclotron anisotropy instability
is driven by T⊥p/T∥p&gt;1 where
p represents protons and the directional subscripts
denote directions relative to the background magnetic
field. Fluctuating field growth leads to wave-particle scattering,
which in turn imposes an upper bound on the anisotropy of the form
T⊥p/T∥p-1=Sp/β∥pαp,
where
β∥p≡8πnpkBT∥p/Bo2,
and the fitting parameters Sp&lt;~1 and
αp~=0.4. Recent SOHO observations indicate that minority
heavy ions are substantially hotter and more anisotropic than protons
in the solar corona. Here linear theory and hybrid simulations
have been carried out in a model of a homogeneous, magnetized,
collisionless plasma with anisotropic minority oxygen ions (denoted
by subscript O). These calculations show that the electromagnetic
oxygen ion cyclotron anisotropy instability also leads to
wave-particle scattering, which constrains that anisotropy by the form
T⊥O/T∥O-1=SO/[(mp/mO)β~∥O]αo,
where
β~∥O≡8πnekBT∥O/Bo2,
So~10 and αO~0.4. This constraint should be
observable in the solar corona.

---------------------------------------------------------
Title: Three-Fluid 2.5-dimensional Magnetohydrodynamic Model of the
Effective Temperature in Coronal Holes
Authors: Ofman, L.; Davila, J. M.
2001ApJ...553..935O Altcode:
Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS)
observations show that protons and minor ions are hot
(Tp&gt;106 K, Ti&gt;107
K) and anisotropic in coronal holes. A possible cause of the large
perpendicular motions is unresolved Alfvénic fluctuations in
the solar wind. Using the three-fluid 2.5-dimensional MHD model,
we have shown that the unresolved Alfvénic fluctuations lead to
apparent proton temperature and anisotropy consistent with UVCS
observations. However, Alfvén waves with realistic amplitudes cannot
reproduce the O5+ perpendicular temperature and anisotropy
deduced from UVCS observations. This suggests that the minor ions are
heated by a different mechanism than protons.

---------------------------------------------------------
Title: Determination of the coronal magnetic field by coronal loop
oscillations
Authors: Nakariakov, V. M.; Ofman, L.
2001A&A...372L..53N Altcode:
We develop a new method for the determination of the absolute value
of the magnetic field strength in coronal closed magnetic structures,
based on the analysis of flare-generated oscillations of coronal
loops. Interpretation of the oscillations observed in terms of global
standing kink waves allows to connect the period of the oscillations and
the loops length with the magnetic field strength in the loops. For loop
oscillations observed with TRACE on 14th July 1998 and 4th July 1999,
we estimate the magnetic field strength as 4-30 G. Using TRACE 171 Å
and 195 Å images of the loop, taken on 4th July 1999 to determine the
plasma density, we estimate the magnetic field in the loop as 13+/-
9 G. Improved diagnostic of the loop length, the oscillation period,
and the plasma density in the loop will significantly improve the
method's precision.

---------------------------------------------------------
Title: Multifluid and Hybrid Modeling of Waves in Coronal Holes:
Implications for Heating Theories
Authors: Ofman, L.; Davila, J. M.
2001AGUSM..SH22E01O Altcode:
Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS)
observations show that protons and minor ions are hot
(Tp&gt;106 K, Ti&gt;107
K) and anisotropic in coronal holes. A possible cause of the large
perpendicular motions is unresolved Alfvénic fluctuations in the
solar wind. Using the three-fluid 2.5D MHD model we have shown
that the unresolved Alfvénic fluctuations lead to apparent proton
temperature and anisotropy consistent with UVCS observations. However,
\Alfven waves with realistic amplitudes can not reproduce the
O5+ perpendicular temperature and anisotropy deduced from
UVCS observations. We use the hybrid model to investigate constrains
on the anisotropy of the minor ions. Our results suggests that
the minor ions are heated and accelerated by high-frequency waves (
~103 Hz), while proton heating occurs by low frequency waves
( ~10-3 Hz).

---------------------------------------------------------
Title: Interaction of EIT Waves with Coronal Active Regions
Authors: Ofman, L.
2001AGUSM..SH31D11O Altcode:
We use 3D MHD modeling to investigate the interaction of the EIT waves
with active regions. The active region is modeled by an initially
force-free, bipolar, magnetic configuration. We include gravity,
finite thermal pressure, and resistive dissipation in our model. The
EIT wave is launched at the boundary of the region, as short time
velocity pulse that travels with the local fast magnetosonic speed
( ~ 250 km/s) towards the active region. We investigate the effect
of the pulse amplitude and direction relative to the active region
magnetic field orientation. We find that the EIT wave reconnects with
the active region magnetic field, and induces transient currents. The
currents and the resulting Lorenz force lead to the dynamic distortion
of the active region magnetic field, and the generation of secondary
waves that propagate away from the active regions. The Lorenz force
compresses the plasma and induces flow along the magnetic flux tubes
producing active region loops. Analysis of the interaction between
the EIT wave and the active region can serve as a diagnostic of the
active region coronal magnetic structure. We show animations of the
interaction of the EIT waves with the active regions.

---------------------------------------------------------
Title: Constraints on the O+5 Anisotropy in the Solar
Corona
Authors: Ofman, L.; Viñas, A.; Gary, S. P.
2001ApJ...547L.175O Altcode:
Velocity distributions of O+5 ions derived from
Ultraviolet Coronagraph Spectrometer (UVCS) observations in coronal
holes indicate that the O+5 ions are highly anisotropic
(T⊥i/T∥i~30-300 at 3.5 Rsolar). The
observations provide empirical values for the electron density and
the ion temperatures. It is well known that the electromagnetic
ion cyclotron instability is driven by temperature anisotropy. The
instability leads to the rapid decrease of anisotropy and transfer of
part of the kinetic energy of the particles into the magnetic field
fluctuations. Here we use linear theory and hybrid simulations combined
with the empirical values of the densities and the temperatures to
investigate the ion cyclotron instability of the anisotropic minor ions
in the coronal hole plasma. We find that an initial O+5
anisotropy of 50 decreases by an order of magnitude within ~300-900
proton cyclotron periods. Thus, the ion cyclotron instability constrains
the anisotropy of O+5 ions that can be sustained in the
solar corona without continuous perpendicular heating.

---------------------------------------------------------
Title: Acceleration of the Fast Solar Wind by Solitary Waves in
Coronal Holes
Authors: Ofman, Leon
2001STIN...0132396O Altcode:
The purpose of this investigation is to develop a new model for the
acceleration of the fast solar wind by nonlinear. time-dependent
multidimensional MHD simulations of waves in solar coronal
holes. Preliminary computational studies indicate that nonlinear waves
are generated in coronal holes by torsional Alfvén waves. These waves
in addition to thermal conduction may contribute considerably to the
accelerate the solar wind. Specific goals of this proposal are to
investigate the generation of nonlinear solitary-like waves and their
effect on solar wind acceleration by numerical 2.5D MHD simulation
of coronal holes with a broad range of plasma and wave parameters; to
study the effect of random disturbances at the base of a solar coronal
hole on the fast solar wind acceleration with a more advanced 2.5D
MHD model and to compare the results with the available observations;
to extend the study to a full 3D MHD simulation of fast solar wind
acceleration with a more realistic model of a coronal hole and solar
boundary conditions. The ultimate goal of the three year study is
to model the, fast solar wind in a coronal hole, based on realistic
boundary conditions in a coronal hole near the Sun, and the coronal hole
structure (i.e., density, temperature. and magnetic field geometry,)
that will become available from the recently launched SOHO spacecraft.

---------------------------------------------------------
Title: Three-fluid 2.5D MHD models of waves in solar coronal holes
and the relation to SOHO/UVCS observations
Authors: Ofman, L.
2000AIPC..537..119O Altcode: 2000wdss.conf..119O
The physical properties of the minor ions in the corona
provide clues on the coronal heating and solar wind acceleration
mechanism. Recent observations show that protons and minor ions are hot
(Tp&gt;106 K, Ti&gt;108
K) and anisotropic in coronal holes. A possible cause of the large
perpendicular motions is unresolved Alfvénic fluctuations in
the solar wind. Using the three-fluid 2.5D MHD model I have shown
that the unresolved Alfvénic fluctuations lead to apparent proton
temperature and anisotropy consistent with UVCS observations. I show
the calculated dependence of the apparent kinetic temperatures of
protons and O5+ ions with heliocentric distance and compare
the results to the UVCS observations. .

---------------------------------------------------------
Title: Imaging the Sun in extreme ultraviolet and in X-rays with
spaceborne instruments
Authors: Ofman, Leon
2000OptPN..11...54O Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Source regions of the slow solar wind in coronal streamers
Authors: Ofman, L.
2000GeoRL..27.2885O Altcode:
Recent SOHO/UVCS observations of the O5+ ion line emission
at 1032Å in coronal streamers indicate that the emission is stronger
by an order of magnitude at the edges (legs) of streamers than in the
central core of streamers. In contrast, the brightness of the Ly-α
emission peaks in the core of streamers. I have developed the first
2.5D, three-fluid numerical MHD model of the slow solar wind flow
in a coronal streamer. Using the model I find that the enhancement
of the oxygen line emission occurs due to the enhanced abundances
of O5+ ions in the legs of streamer caused by the Coulomb
friction with the outflowing protons. Thus, the enhanced O5+
emission traces the source regions of the slow solar wind in coronal
streamers. The identification of these regions helps to understand
the origins and the composition of the slow solar wind.

---------------------------------------------------------
Title: Three-dimensional MHD modeling of an impulsive excitation of
a coronal loop motivated by TRACE observations
Authors: Ofman, L.; Davila, J. M.
2000SPD....31.0604O Altcode: 2000BAAS...32..838O
Recently, decaying transversal oscillations of bright coronal loops
in the 171 Angstroms and 195 Angstroms emission lines were observed
with the imaging telescope on-board the TRACE satellite. The loop
oscillations were excited impulsively by a solar flare in the adjacent
active region. Using 3D MHD model of the loop the period and the decay
rate of the oscillations, together with the loop geometry, density,
and temperature can be used to determine the average magnetic field of
the loop, and the magnetic or viscous Reynolds number (R). Recently,
Nakariakov et al. (1999) used the R1/5 heating time scaling
to determine the range of the dissipation coefficients in the loop
observed with TRACE. Using the linearized 3D MHD model we investigate
the coupling of the decaying transverse mode and the internal Alfvén
mode, and examine the relation between the decay time of the transverse
oscillations and the heating time of the loop for a range of Reynolds
numbers, and wavenumbers. We use the nonlinear 3D MHD model with more
realistic loop geometry, boundary conditions, and mode coupling to study
the relaxation of the impulsively excited coronal loop oscillation. We
find that when the Reynolds number is large (R=104) the
nonlinear effects become important at the resonant dissipation layer,
and the heating time decreases compared to the linear case. We plan
to expand the nonlinear 3D model to include the effects of gravity,
and loop curvature to better model the loop oscillations observed
by TRACE. LO would like to acknowledge support by the NASA SR&amp;T,
and the HPCC programs.

---------------------------------------------------------
Title: Dissipation of Slow Magnetosonic Waves in Coronal Plumes
Authors: Ofman, L.; Nakariakov, V. M.; Sehgal, N.
2000ApJ...533.1071O Altcode:
Recently, slow magnetosonic waves were identified in polar plumes,
at heights up to about 1.2 Rsolar using the Extreme
Ultraviolet Imaging Telescope (EIT) observations of quasi-periodic EUV
intensity fluctuations, and higher in the corona using the Ultraviolet
Coronagraph Spectrometer (UVCS) white-light channel. First, we derive
the linear dispersion relation for the slow waves in the viscous
plasma. Next, we derive and solve an evolutionary equation of the
Burgers type for the slow waves, incorporating the effects of radial
stratification, quadratic nonlinearity, and viscosity. Finally, we
model the propagation and dissipation of slow magnetosonic waves in
polar plumes using one-dimensional and two-dimensional MHD codes in
spherical geometry. The waves are launched at the base of the corona
with a monochromatic source. We find that the slow waves nonlinearly
steepen as they propagate away from the Sun into the solar wind. The
nonlinear steepening of the waves leads to enhanced dissipation owing to
compressive viscosity at the wave fronts. The efficient dissipation of
the slow wave by compressive viscosity leads to damping of the waves
within the first solar radii above the surface. We investigate the
parametric dependence of the wave properties.

---------------------------------------------------------
Title: Propagation and Dissipation of Slow Magnetosonic Waves in
Coronal Plumes
Authors: Ofman, L.
2000ASPC..205..147O Altcode: 2000ltse.conf..147O
Recently, slow magnetosonic waves were identified in polar plumes at
heights of up to ~1.2Rodot using the Extreme Ultraviolet
Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory
(SOHO) spacecraft. We model the propagation of these waves in solar
polar coronal plumes, and the dissipation of the waves by compressive
viscosity. First, we estimate the damping rate of the waves using
linear theory. Next, we model the slow magnetosonic wave with a 2D
MHD code in spherical geometry and assume azimuthal symmetry of the
plumes. We find that the slow magnetosonic waves generated at the base
of the plumes by periodic compressions propagate outward and dissipate
in the plumes. The background atmosphere includes Parker's flow and
the corresponding density stratified by gravity close to the Sun. The
stratification leads to the nonlinear steepening, and to enhanced
dissipation over the linear rate of the waves. The dissipation may
contribute to the heating and the acceleration of the solar wind. By
observing the density structure of the plumes during an eclipse it
may be possible to learn more about these waves.

---------------------------------------------------------
Title: UVCS WLC Observations of Compressional Waves in the South
Polar Coronal Hole
Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.
2000ApJ...529..592O Altcode:
Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) white light
channel (WLC) observations of the south polar coronal hole plumes and
interplume regions produce signatures of quasi-periodic variations in
the polarized brightness (pB) at a heliocentric distance of 1.9 solar
radii (Rsolar). The Fourier power spectrum of the pB time
series shows significant peaks at about 1.6-2.5 mHz and additional
smaller peaks at longer and shorter timescales. Wavelet analysis of
the pB time series shows that the coherence time of the fluctuations
is about 30 minutes. The new observations strongly suggest that the
fluctuations are compressional wave packets propagating in the coronal
hole high above the limb. The presence of compressional waves may have
important implications that help to explain the heating of coronal
holes and the fast solar wind acceleration.

---------------------------------------------------------
Title: Nonlinear dissipative spherical Alfvén waves in solar
coronal holes
Authors: Nakariakov, V. M.; Ofman, L.; Arber, T. D.
2000A&A...353..741N Altcode:
The weakly nonlinear dynamics of linearly polarized, spherical Alfvén
waves in coronal holes is investigated. An evolutionary equation,
combining the effects of spherical stratification, nonlinear steepening
and dissipation due to shear viscosity is derived. The equation is a
spherical analog of the scalar Cohen-Kulsrud-Burgers equation. Three
main stages of the wave evolution are distinguished: geometrical
amplification, wave breaking and enhanced dissipation. The wave
dissipation is dramatically increased by the nonlinear transfer of
energy to smaller scales. The scenario of the nonlinear dissipation is
practically independent of viscosity. The dissipation rate is stronger
for highest amplitudes, and depends weakly on the wave period and the
temperature of the atmosphere. Waves with periods less than 300 s and
initial amplitudes about 2-3% of the Alfvén speed at the base of the
corona are subject to the nonlinear steepening and dissipation in less
than 10 solar radii. For the Alfvén waves with amplitudes less than
25 km s-1 at the base of the corona, the maximum amplitude
of up to 200 km s-1 is reached at several solar radii. The
nonlinear distortion of the wave shape is accompanied by the generation
of longitudinal motions and density perturbations.

---------------------------------------------------------
Title: Acceleration of the Fast Solar Wind by Solitary Waves in
Coronal Holes
Authors: Ofman, Leon
2000STIN...0021484O Altcode:
The purpose of this investigation is to develop a new model for the
acceleration of the fast solar wind by nonlinear, time-dependent
multidimensional MHD simulations of waves in solar coronal
holes. Preliminary computational studies indicate that solitary-like
waves are generated in coronal holes nonlinearly by torsional Alfven
waves. These waves in addition to thermal conduction may contribute
considerably to the accelerate the solar wind. Specific goals of this
proposal are to investigate the generation of nonlinear solitary-like
waves and their effect on solar wind acceleration by numerical 2.5D
MHD simulation of coronal holes with a broad range of plasma and wave
parameters; to study the effect of random disturbances at the base of
a solar coronal hole on the fast solar wind acceleration with a more
advanced 2.5D MHD model and to compare the results with the available
observations; to extend the study to a full 3D MHD simulation of fast
solar wind acceleration with a more realistic model of a coronal hole
and solar boundary conditions. The ultimate goal of the three year study
is to model the fast solar wind in a coronal hole, based on realistic
boundary conditions in a coronal hole near the Sun, and the coronal
hole structure (i.e., density, temperature, and magnetic field geometry)
that will become available from the recently launched SOHO spacecraft.

---------------------------------------------------------
Title: Winds from Luminous Late-Type Stars. I. The Effects of
Nonlinear Alfvén Waves
Authors: Airapetian, V. S.; Ofman, L.; Robinson, R. D.; Carpenter,
K.; Davila, J.
2000ApJ...528..965A Altcode:
We present the results of magnetohydrodynamic (MHD) modeling of winds
from luminous late-type stars using a 2.5-dimensional, nonlinear MHD
computer code. We assume that the wind is generated within an initially
hydrostatic atmosphere and is driven by torsional Alfvén waves
generated at the stellar surface. Two cases of atmospheric topology
are considered: case I has longitudinally uniform density distribution
and isotropic radial magnetic field over the stellar surface, and case
II has an isotropic, radial magnetic field with a transverse density
gradient, which we refer to as an “atmospheric hole.” We use the
same set of boundary conditions for both models.The calculations
are designed to model a cool luminous star, for which we assume an
initial hydrostatic pressure scale height of 0.072 R*,
an Alfvén wave speed of 92 km s-1 at the surface, and a
wave period of 76 days, which roughly corresponds with the convective
turnover time. For case I the calculations produce a wind with terminal
velocity of ~22 km s-1 and a mass loss rate comparable to the
expected value of 10-6 Msolar yr-1. For
case II we predict a two-component wind: a fast (25 km s-1)
and relatively dense wind outside of the atmospheric hole and a slow
(15 km s-1), rarefied wind inside of the hole.

---------------------------------------------------------
Title: Numerical Simulations of Trapped Slow Magnetosonic Waves in
Solar Coronal Plumes
Authors: Ofman, L.; Deforest, C. E.
2000AdSpR..25.1909O Altcode:
Recent observations of polar plumes in the southern solar coronal
hole by the Extreme ultraviolet Imaging Telescope (EIT) on board
the SOHO spacecraft show signatures of quasi-periodic compressional
waves. Here, we present the results of a nonlinear, 2D MHD simulation
of the slow magnetosonic waves in plumes for typical coronal conditions
consistent with observations. Our numerical simulations confirm the
interpretation of the observed intensity fluctuations as propagating
slow magnetosonic waves. On March 7 1996 DeForest and Gurman (1998)
detected quasi-periodic intensity variations of 10-20% in the EIT
Fe IX and X line emission at 171A&amp;ring that propagate outward
in several polar plumes at 75-150 km s-1 with a period of
10-15 minutes. The observed propagation velocity agrees well with the
expected sound velocity inside the plumes. The lower phase speed in
the plumes than in the ambient plasma leads to partial trapping of the
slow magnetosonic waves in the plumes. The slow magnetosonic waves may
contribute to the heating of the lower corona by compressive dissipation

---------------------------------------------------------
Title: Dissipation and Steepening of Slow Magnetosonic Waves in
Polar Plumes and the Effect on the Solar Wind Close to the Sun
Authors: Ofman, L.
1999ESASP.446..515O Altcode: 1999soho....8..515O
Recently, slow magnetosonic waves were identified in polar plumes at
heights up to about 1.2Rs, using Extreme ultraviolet Imaging Telescope
(EIT) observations of quasi-periodic EUV intensity fluctuations (Ofman,
Nakariakov, DeForest 1999). We model the propagation and dissipation of
slow magnetosonic waves in polar plumes using 2D MHD code in spherical
geometry. We find that outward propagating slow magnetosonic waves may
become trapped due to transverse density and temperature structure of
the plumes. The slow waves nonlinearly steepen in the gravitationally
stratified plumes. The nonlinear steepening of the waves leads to
enhanced acceleration of the subsonic solar wind due to momentum
transfer, and to the enhances dissipation due to compressive viscosity
at the wave-fronts. The slow waves can contribute to the heating of
coronal holes close to the Sun (r&lt;2Rs), a region where the shear
Alfven wave heating is inefficient.

---------------------------------------------------------
Title: Alfvén wave phase mixing driven by velocity shear in
two-dimensional open magnetic configurations
Authors: Ruderman, M. S.; Goldstein, M. L.; Roberts, D. A.; Deane,
A.; Ofman, L.
1999JGR...10417057R Altcode:
Phase mixing of torsional Alfvén waves in axisymmetric equilibrium
magnetic configurations with purely poloidal magnetic field and
stationary flow along the field lines in resistive viscous plasmas
is studied. The characteristic wavelength along the magnetic field
lines is assumed to be much smaller than the characteristic scale
of inhomogeneity in the magnetic field direction, and the WKB method
is used to obtain an analytic solution describing phase mixing. The
general solution is applied to a particular configuration with
the radial magnetic field and flow under the assumptions that the
magnetic field and density are independent of the polar angle in the
spherical coordinates and the flow velocity is independent of the radial
coordinate. The only source of phase mixing in this configuration is
velocity shear. The analytical solution is compared with a numerical
simulation of the fully nonlinear resistive MHD equations. The numerical
and analytical results are in good agreement. Consequences for wave
energy deposition into the solar corona and solar wind and for the
evolution of the Alfvén wave energy spectrum are discussed.

---------------------------------------------------------
Title: TRACE observation of damped coronal loop oscillations:
Implications for coronal heating
Authors: Nakariakov, V. M.; Ofman, L.; Deluca, E. E.; Roberts, B.;
Davila, J. M.
1999Sci...285..862N Altcode:
The imaging telescope on board the Transition Region and Coronal
Explorer (TRACE) spacecraft observed the decaying transversal
oscillations of a long [(130 ± 6) × 106 meters], thin
[diameter (2.0 ± 0.36) × 106 meters], bright coronal
loop in the 171 angstrom FeIX emission line. The oscillations were
excited by a solar flare in the adjacent active region. The decay
time of the oscillations is 14.5 ± 2.7 minutes for an oscillation
with a frequency 3.90 ± 0.13 millihertz. The coronal dissipation
coefficient is estimated to be eight to nine orders of magnitude
larger than the theoretically predicted classical value. The larger
dissipation coefficient may solve existing difficulties with wave
heating and reconnection theories.

---------------------------------------------------------
Title: Alfvén wave phase mixing driven by velocity shear in two
dimensions
Authors: Ruderman, M. S.; Goldstein, M. L.; Roberts, D. A.; Deane,
A.; Ofman, L.
1999AIPC..471..337R Altcode: 1999sowi.conf..337R
We investigate the role of velocity shears in producing strong phase
mixing and damping of Alfvén waves. We show that phase mixing damps
waves in regions of strong velocity shear, thus providing a possible
source of heat to the solar corona and solar wind. We compare the linear
solutions with direct numerical solution of the three-dimensional
equations of compressible (resistive) magnetohydrodynamics (MHD). In
regions far removed from the velocity shear, the simulations show
that the radial evolution of the wave amplitudes follows closely WKB
theory. In the shear layer, strong damping occurs in the numerical
simulations, quantitatively close to that computed from the linearized
analysis.

---------------------------------------------------------
Title: Two-fluid 2.5D MHD model of the fast solar wind and the
effective proton temperature
Authors: Ofman, L.; Davila, J. M.
1999AIPC..471..405O Altcode: 1999sowi.conf..405O
Recent SOHO/UVCS observations indicate that the perpendicular proton
and ion temperatures are much larger than electron temperatures (Kohl et
al. 1997). In the present study we simulate numerically the solar wind
flow in a coronal hole with the two-fluid approach. For simplicity,
we neglect electron inertia. We investigate the effects of electron
and proton temperatures on the solar wind acceleration by nonlinear
waves. In the model the nonlinear waves are generated by Alfvén waves
with frequencies in the 10-3 Hz range, driven at the base
of the coronal hole. The resulting electron and proton flow profile
exhibits density and velocity fluctuations. The fluctuations may steepen
into shocks as they propagate away from the sun. We construct the proton
velocity distribution and a synthetic Ly-α line profile by including
the combined effects of temperature and velocity fluctuations in the
model, and compare them to the UVCS observations.

---------------------------------------------------------
Title: Temporal Evolution and Physical Properties of North Polar
Coronal Hole from SPARTAN 201-05, SOHO, TRACE and Mk3
Authors: Guhathakurta, M.; Deforest, C.; Fisher, R. R.; Ofman, L.;
Kucera, T.; Gibson, S.; Spartan201 Team
1999AAS...194.3203G Altcode: 1999BAAS...31..870G
Polar coronal rays/plumes as long lived structures that extend out
to 6 R_sun were first observed during the first flight of SPARTAN 201
spacecraft during April 11-12 of 1993. In this paper we will present
detail observations from the WLC aboard Spartan 201 spacecraft (31
Oct.- 2 Nov.,1998) of the north polar coronal hole and comapre its
physical properties to the past three Spartan missions. We will present
comparisons of the Spartan WL observations with the Mk3 pB observations,
SOHO LASCO and EIT observations, and finally the high resolution TRACE
171 Angstroms observations, to characterize the north polar coronal
hole all the way from the base of the corona out to 30 R_sun. We will
also look for signatures of waves (quasi-period variations) in the
coronal hole plumes and interplume regions in the high cadence Spartan
pB observations obtained during this mission.

---------------------------------------------------------
Title: A Numerical Package for Modeling Solar Flares and Interpreting
HESSI Data
Authors: Holman, G. D.; Mariska, J. T.; McTiernan, J. M.; Ofman, L.;
Petrosian, V.; Ramaty, R. R.
1999AAS...194.8008H Altcode: 1999BAAS...31..966H
HESSI, the High Energy Solar Spectroscopic Imager, will observe the
x-ray and gamma-ray emission from solar flares with an unprecedented
combination of spectral, spatial, and temporal resolution. The
quantitative interpretation of the HESSI data will require a level of
numerical modeling not generally demanded by previous observations. In
view of this, we are developing an integrated package of modular
numeric codes and models for the analysis and interpretation
of these data. The package will focus on the energetic electrons
produced during the impulsive phase of flares. It will compute both
the bremsstrahlung x-ray/gamma-ray emission and the gyrosynchrotron
radio emission from model flare configurations and initial electron
distributions. Steady-state and time-dependent Fokker-Planck codes
will compute the transport of suprathermal electrons. A hydrodynamic
code will compute the response of the flare plasma in the model
configurations. The proposed computational package will allow for
comprehensive modeling of energized electrons in different flare
scenarios. The predicted emissions can be compared directly with
HESSI and radio images and spectra. The package will provide the
necessary framework for comparing electron acceleration models with
HESSI data. This work is supported in part by the NASA Sun-Earth
Connection Program.

---------------------------------------------------------
Title: Determination of the Reynolds number from TRACE Observation
of Damped Coronal Loop Oscillations Induced by a Flare
Authors: Ofman, L.; Nakariakov, V. M.; Deluca, E.; Roberts, B.;
Davila, J. M.
1999AAS...194.7909O Altcode: 1999BAAS...31..964O
The Transition Region and Coronal Expolorer (TRACE) observes the solar
corona with unprecedented spatial and temporal resolution. We analyzed
active region loop observation in the 171 Angstroms Fe IX emission line,
and report the direct observations of damped transverse oscillations
of a long (130+/-6 Mm) thin (diameter 2+/-0.36 Mm) bright active region
loop. The oscillations were detected following a flare in the adjacent
active region. We determined the oscillation frequency and the decay
time by the least-square fit of an exponentially decaying sinusoidal
function. Using the dispersion relation for the transverse oscillations,
and the observed loop geometry we estimated the Alfven crossing time
in the loop. The Alfven time can be used to determine the magnetic
field strength in the loop if the density is known. All parts of the
loop were observed to oscillate transversly in-phase, implying that the
ocillation is a global mode of the loop. Using dissipative MHD model for
resonant absorption of global mode oscillations for the coronal loop
we determined the Reynolds number that produces the observed damping
rate of the observed global mode. The value of the Reynolds number is
in the 10(5-10^6) range, which is eight to nine orders of magnitude
smaller than the classical coronal value. We discuss the important
implication of the small Reynolds number on coronal heating theories.

---------------------------------------------------------
Title: Slow Magnetosonic Waves in Coronal Plumes
Authors: Ofman, L.; Nakariakov, V. M.; DeForest, C. E.
1999ApJ...514..441O Altcode:
Recent observations of polar plumes in the southern solar coronal
hole by the Extreme-Ultraviolet Imaging Telescope (EIT) on board
the SOHO spacecraft show signatures of quasi-periodic compressional
waves with periods of 10-15 minutes. The relative wave amplitude
was found to increase with height in the plumes up to about 1.2
Rsolar. Using a one-dimensional linear wave equation for
the magnetosonic wave, we show that the waves are propagating and
that their amplitude increases with height. The observed propagation
velocity agrees well with the expected sound velocity inside the
plumes. We present the results of the first nonlinear, two-dimensional,
magnetohydrodynamic (MHD) simulation of the magnetosonic waves in
plumes for typical coronal conditions consistent with observations
and gravitationally stratified solar corona. We find numerically
that outward-propagating slow magnetosonic waves are trapped, and
nonlinearly steepen in the polar plumes. The nonlinear steepening of
the magnetosonic waves may contribute significantly to the heating of
the lower corona by compressive dissipation.

---------------------------------------------------------
Title: Signatures of Nonlinear Waves in Coronal Plumes and Holes
Authors: Ofman, Leon
1999STIN...0119003O Altcode:
In recent Ultraviolet Coronagraph Spectrometer/Solar and Heliospheric
Observatory (UVCS/SOHO) White Light Channel (WLC) observations we found
quasi-periodic variations in the polarized brightness (pB) in the polar
coronal holes at heliocentric distances of 1.9-2.45 solar radii. The
motivation for the observation is the 2.5D Magnetohydrodynamics (MHD)
model of solar wind acceleration by nonlinear waves, that predicts
compressive fluctuations in coronal holes. To help identify the waves
observed with the UVCS/WLC we model the propagation and dissipation
of slow magnetosonic waves in polar plumes using 1D MHD code in
spherical geometry, We find that the slow waves nonlinearly steepen
in the gravitationally stratified plumes. The nonlinear steepening of
the waves leads to enhanced dissipation due to compressive viscosity
at the wave-fronts.

---------------------------------------------------------
Title: Two-fluid 2.5D MHD Simulations of the Fast Solar Wind in
Coronal Holes and the Relation to UVCS Observations
Authors: Davila, J. M.; Ofman, L.
1999SSRv...87..165D Altcode:
Recent SOHO/UVCS observations indicate that the perpendicular proton
and ion temperatures are much larger than electron temperatures. In
the present study we simulate numerically the solar wind flow in a
coronal hole with the two-fluid approach. We investigate the effects
of electron and proton temperatures on the solar wind acceleration
by nonlinear waves. In the model the nonlinear waves are generated
by Alfvén waves with frequencies in the 10-3 Hz range,
driven at the base of the coronal hole. The resulting electron and
proton flow profile exhibits density and velocity fluctuations. The
fluctuations may steepen into shocks as they propagate away from
the sun. We calculate the effective proton temperature by combining
the thermal and wave velocity of the protons, and find qualitative
agreement with the proton kinetic temperature increase with height
deduced from the UVCS Ly-α observations by Kohl et al. (1998).

---------------------------------------------------------
Title: SOHO Observations of Density Fluctuations in Coronal Holes
Authors: Ofman, L.; Romoli, M.; Noci, G.; Poletto, G.; Kohl, J. L.;
Howard, R. A.; Cyr, C. St.; Deforest, C. E.
1999SSRv...87..287O Altcode:
In recent UVCS/SOHO White Light Channel (WLC) observations we found
quasi-periodic variations in the polarized brightness (pB) in the
polar coronal holes at heliocentric distances of 1.9 to 2.45 solar
radii. The motivation for the observation is the 2.5D MHD model of
solar wind acceleration by nonlinear waves, that predicts compressive
fluctuations in coronal holes. In February 1998 we performed new
observations using the UVCS/WLC in the coronal hole and obtained
additional data. The new data corroborate our earlier findings with
higher statistical significance. The new longer observations show that
the power spectrum peaks in the 10 12 minute range. These timescales
agree with EIT observations of brightness fluctuations in polar
plumes. We performed preliminary LASCO/C2 observations in an effort
to further establish the coronal origin of the fluctuations.

---------------------------------------------------------
Title: Ultraviolet Coronagraph Spectrometer Observations of Density
Fluctuations in the Solar Wind
Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.
1998ApJ...507L.189O Altcode:
In the Letter “Ultraviolet Coronagraph Spectrometer
Observations of Density Fluctuations in the Solar Wind” by
L. Ofman, M. Romoli, G. Poletto, G. Noci, and J. L. Kohl (<A
href="/abs/1997ApJ...491L.111">ApJ, 491, L111 [1997]</A>), there was
an error in the data reduction of the polarized brightness (pB). It
was assumed that the cadence of the data and the exposure time are
equal. However, the correct cadence is30 s longer than the exposure
time because of the time it takes the polarizer to change orientation
between exposures. This error does not affect the main result of the
Letter, i.e., the detection of quasi-periodic density fluctuations in
the solar wind. However, the correct cadences of the data in Table 1
are 30 s longer. This correction can be taken into account in Figure
1 by multiplying the times by 1.5 and dividing the frequencies by
the same factor. Thus, the highest peak in the power spectrum is at
1.8+/-0.07 mHz (the corresponding period is 9.3+/-0.4 minutes). The
correction factor is 1.1 in Figure 2 because of the longer exposure
time in this observation.

---------------------------------------------------------
Title: SUMER Observations of the Evolution and the Disappearance of
a Solar Prominence
Authors: Ofman, L.; Kucera, T. A.; Mouradian, Z.; Poland, A. I.
1998SoPh..183...97O Altcode:
The mechanisms that lead to the formation and the disappearance of
prominences are poorly understood, at present. An arch-shaped prominence
was observed with the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) spectrometer on board the Solar and Heliospheric
Observatory (SOHO) on 31 March-1 April 1996. The observations were
performed at three wave-bands in the Lyman continuum. Ten successive
images were obtained at 41-minute time intervals. Based on computed
models of Gouttebroze, Heinzel, and Vial (1993), we have determined the
temperature distribution of the prominence using the intensity ratio of
876 Å and 907 Å. The observed time sequence shows that parts of the
prominence disappear possibly by heating, while other parts exhibit
heating and cooling with apparent outward motion. We model the heat
input with the linearized MHD equations using a prescribed initial
density and a broad-band spectrum of Alfvén waves. We find a good
qualitative agreement with observations. In the model the prominence
is heated by the resonant absorption of Alfvén waves with frequencies
that match the resonant condition for a particular flux tube structure
that is determined by the magnetic field topology and plasma density.

---------------------------------------------------------
Title: Solar wind acceleration by large-amplitude nonlinear waves:
Parametric study
Authors: Ofman, L.; Davila, J. M.
1998JGR...10323677O Altcode:
We investigate the parametric dependence of the solar wind acceleration
by large-amplitude nonlinear (LAN) magnetohydrodynamic waves. For
this purpose we model numerically the self-consistent problem of
the solar wind with waves by solving time-dependent, nonlinear,
resistive 2.5-dimensional (three-dimensional with azimuthal symmetry)
MHD equations driven by Alfvén waves. We find that when the Alfvén
wave amplitude is above a parameter-dependent threshold, LAN waves are
generated in the model coronal hole. For typical coronal parameters the
solar wind speed and density fluctuate considerably on a timescale of
~10-40 min and with an amplitude of up to several hundred kmilometers
per second near the Sun (r&lt;~10RS) in agreement with
recent interplanetary scintillation observations. The solar wind speed
is inversely dependent on the driving frequency in the range 0.35-3
mHz. The amplitude of the velocity fluctuations increases with the
amplitude of the magnetic field and the driving Alfvén waves at the
base of the corona and decreases with the coronal temperature. We found
that for the same typical solar wind and Alfvén wave parameters and an
isothermal initial atmosphere, the WKB model predicts 30% higher flow
velocities far from the Sun (32RS) than our self-consistent
wave model with high-frequency Alfvén waves (f=2.78mHz), conforming
to the WKB approximation. However, our model predicts significantly
higher average flow speed near the Sun. When low-frequency non-WKB
waves drive the wind, our model predicts 25% higher solar wind speed
than the WKB model far from the Sun. This result of our model is in
agreement with linear studies of solar wind acceleration by Alfvén
waves that take into account Alfvén wave reflection.

---------------------------------------------------------
Title: Observation of Prominence Heating and the Heating Mechanism
Authors: Ofman, L.; Mouradian, Z.; Kucera, T. A.; Poland, A. I.
1998ASPC..150..159O Altcode: 1998IAUCo.167..159O; 1998npsp.conf..159O
No abstract at ADS

---------------------------------------------------------
Title: A Self-consistent Model for the Resonant Heating of Coronal
Loops: The Effects of Coupling with the Chromosphere
Authors: Ofman, L.; Klimchuk, J. A.; Davila, J. M.
1998ApJ...493..474O Altcode:
We present the first model of resonant heating of coronal loops that
incorporates the dependence of the loop density on the heating rate. By
adopting the quasi-static equilibrium scaling law ρ ~ Q5/7,
where ρ is the density and Q is the volumetric heating rate, we
are able to approximate the well-known phenomena of chromospheric
evaporation and chromospheric condensation, which regulate the coronal
density. We combine this scaling law with a quasi-nonlinear MHD model
for the resonant absorption of Alfvén waves in order to study the
spatial and temporal dependence of the heating. We find that the heating
is concentrated in multiple resonance layers, rather than in the single
layer of previous models, and that these layers drift throughout the
loop to heat the entire volume. These newfound properties are in much
better agreement with coronal observations.

---------------------------------------------------------
Title: Atmospheric Dynamics of Luminous Late-Type Stars
Authors: Airapetian, V. S.; Ofman, L.; Robinson, R. D.; Carpenter,
K.; Davila, J.
1998ASPC..154.1569A Altcode: 1998csss...10.1569A
We present first results of magnetohydrodynamic (MHD) calculations of
winds from luminous late-type stars using an existing, 2.5D, non-linear
MHD code recently developed by Ofman &amp; Davila (e.g., Ofman &amp;
Davila 1997). We assume that the wind is initiated in a hydrostatic
atmosphere with an isothermal pressure scale height of 0.072 R* and a
“chromospheric hole” modeled by a transverse density structure and
a radial magnetic field. To ensure that we are accurately assessing
the terminal velocity of the wind, we carried out the calculations
to a height of 20 stellar radii. We find that in the higher density
(low Alfven velocity) regions outside of the “chromospheric hole” the
Alfven waves are freely propagating. Ponderomotive forces associated
with these waves drive radial, compressive motions and contribute to
stellar wind acceleration. The compressive motions then excite slow
magnetosonic waves which non-linearly steepen into solitary waves that
propagate on top of a background flow. This situation is similar to
solar coronal hole models. In the lower density “chromospheric hole”
region the Alfven wave are strongly reflected, and produce a substantial
outflow, with both radial and azimuthal velocities approaching the
local Alfven speed. Our results are in qualitative agreement with
observational signatures of winds in cool, luminous late-type stars.

---------------------------------------------------------
Title: Ultraviolet Coronagraph Spectrometer Observations of Density
Fluctuations in the Solar Wind
Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.
1997ApJ...491L.111O Altcode:
Recent Ultraviolet Coronagraph Spectrometer (UVCS) white-light
channel (WLC) observations on board the Solar and Heliospheric
Observatory (SOHO) indicate quasi-periodic variations in the
polarized brightness (pB) in the polar coronal holes. This is
the first observation of possible signatures of compressional
waves high above the limb (at heliocentric distances in the range
1.9-2.45 Rsolar). The Fourier power spectrum of the
pB time series at 1.9 Rsolar shows significant peak
at about 6 minutes and possible fluctuations on longer timescales
(20-50 minutes). The observation at 1.9 Rsolar is the only
currently available WLC data set with sufficient cadence to resolve
the 6 minute period. These preliminary observations may result from
density fluctuations caused by compressional waves propagating in
polar coronal holes. We stress that our results are preliminary, and
we plan future high-cadence observations in both plume and interplume
regions of coronal holes. Recently, Ofman &amp; Davila used a 2.5 D
MHD model and found that Alfvén waves with an amplitude of 20-70 km
s-1 at the base of the coronal hole can generate nonlinear,
high-amplitude compressional waves that can contribute significantly to
the acceleration of the fast solar wind. The nonlinear solitary-like
waves appear as fluctuations in the density and the radial outflow
velocity and contribute significantly to solar wind acceleration
in open magnetic field structures. The motivation for the reported
observations is the MHD model prediction.

---------------------------------------------------------
Title: IPS Observations of the Solar Wind Velocity and the
Acceleration Mechanism
Authors: Ofman, L.; Davila, J. M.; Coles, W. A.; Grall, R. R.;
Klinglesmith, M. T.
1997ESASP.415..361O Altcode: 1997cpsh.conf..361O
No abstract at ADS

---------------------------------------------------------
Title: Fast Solar Wind Acceleration by Nonlinear Waves in Coronal
Holes
Authors: Ofman, L.; Davila, J. M.
1997AAS...191.7414O Altcode: 1997BAAS...29.1326O
We use the 2.5D (3D with azimuthal symmetry) MHD equations to model
numerically the solar wind acceleration in a nonhomogeneous coronal
hole. We investigate the parametric dependence of the solar wind
acceleration by nonlinear MHD waves with a monochromatic and a broad
band driving source. We find that when the Alfven wave amplitude is
above a parameter dependent threshold , large amplitude nonlinear
longitudinal waves are generated and contribute to the radial
acceleration. The calculated solar wind speed and density fluctuates
considerably on a time scale of tens of minutes with an amplitude of
up to several hundred km/s near the sun (4R_sun&lt;r&lt;10R_sun). The
amplitude of the fluctuations decreases with the distance from the
sun. Using the monochromatic driver we find that the solar wind speed
and the amplitude of the nonlinear waves is inversely dependent on
the driving frequency in the range 0.3-3 mHz. The acceleration due to
the broad band driver depends on the power spectrum of the driver. The
amplitude of the nonlinear waves and the acceleration increases with
the magnitude of the magnetic field and decreases with the temperature
of the coronal hole.

---------------------------------------------------------
Title: A Self-Consistent Model for the Resonant Heating of Coronal
Loops: the Effects of Coupling with the Chromosphere
Authors: Klimchuk, J. A.; Ofman, L.; Davila, J. M.
1997SPD....28.0504K Altcode: 1997BAAS...29..909K
The physical nature of coronal heating remains one of the great problems
of solar physics. One of the several theories that are being pursued
is the resonant absorption of MHD waves. While promising in several
respects, this theory has suffered from a glaring deficiency: the
computed heating is incompatible with both the assumed density and
the observed structure of coronal loops. We present the first model
of resonant heating of coronal loops that incorporates the dependence
of the loop density on the heating rate. By adopting the quasi-static
equilibrium scaling law rho ~ Q(5/7) , where rho is the density and Q is
the volumetric heating rate, we are able to approximate the well-known
phenomena of chromospheric evaporation and chromospheric condensation,
which regulate the coronal density. We combine this scaling law with
a linearized MHD model for the resonant absorption of Alfven waves
to study the spatial and temporal dependence of the heating. We find
that the heating is concentrated in multiple resonance layers, rather
than the single layer of previous models, and that these layers drift
throughout the loop to heat the entire volume. These new properties
are in much better agreement with coronal observations, including
recent observations from the CDS and EIT instruments on SOHO, as well
as earlier observations from the SXT instrument on Yohkoh.

---------------------------------------------------------
Title: Do First Results from SOHO UVCS Indicate That the Solar Wind
Is Accelerated by Solitary Waves?
Authors: Ofman, L.; Davila, J. M.
1997ApJ...476L..51O Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on board the recently
launched US-European Solar and Heliospheric Observatory (SOHO) satellite
has found O VI and H I emission lines with a broad component that
corresponds to ~300 km s-1 unresolved motions at about
0.7 solar radii above the photosphere. These motions appear to be
independent of ion mass. We suggest that the large Doppler broadening of
the ion emission lines observed by the UVCS are signatures of solitary
waves in the solar wind plasma. According to our recent 2.5-dimensional
(i.e., three-dimensional with azimuthal symmetry) MHD simulations,
these waves may contribute significantly to the solar wind acceleration
and may generate velocity fluctuations with a magnitude that agrees
with the above observations.

---------------------------------------------------------
Title: Solar Wind Acceleration by Solitary Waves in Coronal Holes
Authors: Ofman, L.; Davila, J. M.
1997ApJ...476..357O Altcode:
Coronal holes are well-known sources of the high-speed solar wind;
however, the exact acceleration mechanism of the fast wind is still
unknown. We solve numerically the time-dependent, nonlinear, resistive
2.5-dimensional MHD equations and find that solitary waves are generated
in coronal holes nonlinearly by torsional Alfvén waves. The solitary
wave phase velocity was found to be slightly above the sound speed
in the coronal hole; for example, with the driving Alfvén wave
amplitude vd ~ 36 km s-1 and plasma β = 5%,
the solitary wave phase speed is ~185 km s-1. We show with a
more simplified analytical model of the coronal hole that sound waves
are generated nonlinearly by Alfvén waves. We find numerically that
these waves steepen nonlinearly into solitary waves. In addition,
ohmic heating takes place in the coronal hole inhomogeneities owing
to phase-mixing of the torsional Alfvén waves. When solitary
waves are present, the solar wind speed and density fluctuate
considerably on timescales of ~20-40 minutes in addition to the
Alfvénic fluctuations. The solitary wave-driven wind might be in
better qualitative agreement with observations than the thermally
driven and WKB Alfvén wave solar wind models.

---------------------------------------------------------
Title: Possible Signatures of Nonlinear MHD Waves in the Solar Wind:
UVCS Observatio ns and Models
Authors: Ofman, L.; Romoli, M.; Davila, J. M.; Poletto, G.; Kohl,
J.; Noci, G.
1997ESASP.404..571O Altcode: 1997cswn.conf..571O
No abstract at ADS

---------------------------------------------------------
Title: Solitary waves in coronal holes-predicted signatures close
to the sun
Authors: Ofman, L.; Davila, J. M.
1997AIPC..385..227O Altcode: 1997recs.conf..227O
Coronal holes are well known sources of the high speed solar wind,
however, the exact acceleration mechanism of the wind is still
unknown. We find that solitary waves may be generated in coronal
holes nonlinearly by Alfvén waves. The solitary waves may efficiently
accelerate the fast solar wind in addition to thermal conduction. We
solve numerically the time-dependent, nonlinear, resistive 2.5-D MHD
equations in spherical geometry with azimuthal symmetry to model solar
wind acceleration by waves in coronal holes. Torsional Alfvén waves
are driven at the base of the model coronal hole and propagate into the
corona. Ohmic heating layers are found to occur at the coronal hole
boundaries due to phase-mixing of the torsional Alfvén waves. The
nonlinear coupling of the perpendicular (to the background magnetic
field) components of the velocity and the magnetic field to the radial
component of the momentum equation leads to the acceleration of the
solar wind in the radial direction and to the generation of solitary
waves. The solitary wave phase velocity was found to be above the sound
speed in the coronal hole, with the driving Alfvén wave amplitude
vd~25 km s-1, and plasma β=2.5%. We discuss
the implication of our results to the proposed in-situ observations
in the region r&lt;10Rs with the future solar probe mission.

---------------------------------------------------------
Title: A New Mechanism for Solar Wind Acceleration
Authors: Ofman, L.; Davila, J. M.
1997IAUJD..19E..34O Altcode:
We investigate the parametric dependence of a new solar wind
acceleration mechanism by nonlinear magneto-hydrodynamic waves, by
solving numerically the time-dependent, nonlinear, resistive 2.5-D
MHD equations. We find that large amplitude nonlinear longitudinal
waves are generated in coronal holes by torsional Alfven waves for
a broad range of parameters in the 10^6 K magnetized plasma. The
structure and the dependence of the phase speed on the amplitude of
these waves are similar to solitary waves. We find that the solar wind
speed and density fluctuate considerably on a time scales of ~20-40
min with an amplitude of several hundred km s^{-1}. The amplitude
of the radial velocity fluctuations increases with the amplitude of
the driving torsional Alfven waves at the base of the corona and the
magnetic field strength, decreases with the temperature, and nearly
independent of the driving frequency. The typical driving frequency
of the Alfven waves is in the mHz range, determined by wave reflection
in the radially stratified coronal hole, with an amplitude of 30-60 km
s^{-1}. For typical coronal hole parameters the nonlinear wave driven
wind accelerates to more than twice the Parker's solar wind speed and
is in qualitative agreement with recent SOHO observations.

---------------------------------------------------------
Title: Heating of coronal holes by the resonant absorption and
dissipation of Alfvén waves
Authors: Ofman, L.; Davila, J. M.
1996AIPC..382..149O Altcode:
Coronal hole regions are well known sources of high-speed solar
wind, however to account for the observed properties of the solar
wind a source of energy must be included in addition to heat
conduction. Alfvén waves were suggested as the possible source
of heating that accelerates the solar wind. We investigate the
heating and propagation of Alfvén waves in coronal holes via 2-D
MHD simulation in slab geometry. Resonance heating layers are found
to occur when shear Alfvén waves are driven at the coronal boundary
and a continuous density profile is assumed for the coronal hole. The
heating is enhanced by phase mixing when coronal hole inhomogeneities
(i.e., plumes) are included. We investigate the dependence of the
heating rate on the driver frequency and the Lundquist number S and
find a good agreement with the analytical S1/3 scaling
of the dissipation length for uniform background magnetic field. We
find that when S=104 the low frequency Alfvén waves
can be a significant source of heating of coronal holes at several
solar radii. At larger values of S nonlinear effects may reduce the
effective dissipation length. We also find that the radial dependence
of the heating rate has the same form as the observed scale height
temperature radial profiles observed by SPARTAN 201-01.

---------------------------------------------------------
Title: Acceleration of the Solar Wind by Solitary Waves in Coronal
Holes
Authors: Ofman, L.; Davila, J. M.
1996AAS...188.8602O Altcode: 1996BAAS...28..963O
Coronal holes are well known sources of the high speed solar wind,
however, the exact acceleration mechanism of the wind is still
unknown. We solve numerically the time-dependent, nonlinear, resistive
2(1)/(2)-D MHD equations and find that solitons are generated in
coronal holes nonlinearly by torsional Alfven waves. Initially,
the ponderomotive force due to Alfven waves excites longitudinal
magnetosonic waves by coupling to the radial component of the momentum
equation. Next, these waves steepen into solitons that accelerate
the solar wind to supersonic speed in the radial direction even in
a low-beta plasma. The solitary wave phase velocity was found to be
slightly above the sound speed in the coronal hole; for example, with
the driving Alfven wave amplitude v_d~40 km s(-1) , and plasma beta =5%
the soliton phase speed ~ 200 km s(-1) . We investigate the parametric
dependence of the soliton wavelength and frequency on the plasma beta ,
and on the driving Alfven wave amplitude and frequency. More simplified
analytical model of the coronal hole leads to the Benjamin-Ono equation
that predicts the generation of solitons analytically. The compressive
dissipation of solitary waves may contribute significantly to coronal
hole heating. In addition, Ohmic heating takes place near the coronal
hole boundaries due to phase-mixing of the torsional Alfven waves in
the inhomogeneous regions. When solitary waves are present the solar
wind fluctuates considerably on long time scales and on small spatial
scales in addition to the Alfvenic fluctuations. This is in better
qualitative agreement with observations than the thermally driven and
WKB Alfven wave solar wind models.

---------------------------------------------------------
Title: Are thermal sudden disappearances of prominences driven by
resonant absorption of Alfven waves?
Authors: Ofman, L.; Mouradian, Z.
1996A&A...308..631O Altcode:
In the present study we propose the resonant absorption of Alfven waves
as the heating mechanism that leads to thermal sudden disappearances
(DBt) of prominences. The physical parameters of prominence flux tubes
are used with the low-{be}, linearized, resistive magnetohydrodynamic
(MHD) model to calculate the heating times of prominences for a range of
wavenumbers. The heating time dependence on the wavenumbers is compared
to the measured times for DBt of quiescent prominences and a qualitative
agreement is found. We find that present observational evidence is in
qualitative agreement with the predictions of the resonant absorption
heating mechanism for DBt of prominences. However, more observations
of DBt are required to establish the heating mechanism with a higher
degree of certainty.

---------------------------------------------------------
Title: Signatures of Global Mode Alfven Resonance Heating in
Coronal Loops
Authors: Ofman, L.; Davila, J. M.; Shimizu, T.
1996ApJ...459L..39O Altcode:
The Yohkoh Soft X-Ray Telescope (SXT) observations of active region
coronal loops transient brightening is analyzed, and the scaling of
the thermal energy release with loop lengths is found to be Eth ~
L1.60+/-0.09. The numerically determined scaling of the global
mode heating rate for the resonant absorption of Alfven waves,
H ~ L, is found to agree with the heating rate deduced from the
observed thermal energy scaling, provided that the magnetic field
scales as B ~ L-0.70+/-0.05 and the waves are driven with a omega -1
spectrum. Previous analytical and numerical studies have shown that the
heating due to resonant absorption of Alfven waves is most efficient at
the global mode frequency. In agreement with these studies, we suggest
that coronal loop transient X-ray brightenings occur when a given
length coronal loop is perturbed at its global mode frequency by random
footpoint motions, which results in more efficient heating of the loop.

---------------------------------------------------------
Title: Nonlinear Excitation of Global Modes and Heating in Randomly
Driven Coronal Loops
Authors: Ofman, L.; Davila, J. M.
1996ApJ...456L.123O Altcode:
We solve the nonlinear three-dimensional MHD equations for fully
compressible, low- beta , resistive plasma to model resonant Alfven
wave heating of a coronal loop. Alfven waves are driven in the loop by
a (pseudo)random time-dependent forcing with a bounded amplitude. We
find that global modes are excited and resonantly heat the loop in
the nonlinear regime in three dimensions. Resonant heating occurs in
several narrow layers accompanied by high velocity and magnetic field
shear. The narrow dissipation layers are affected by the self-consistent
velocity shear and are carried around by the flow. Consequently, the
topology of the perpendicular magnetic field and the ohmic heating
regions differs significantly from the linear or single-frequency
driver regimes, and the heating is spread more uniformly inside the
loop. The heating rate varies significantly on a timescale of one to
several global mode periods. We conclude that, in solar active regions,
random field-line motions can excite global mode oscillations and
resonantly heat the loops with a time-varying heating rate.

---------------------------------------------------------
Title: Alfvén wave heating of coronal holes and the relation to
the high-speed solar wind
Authors: Ofman, L.; Davila, J. M.
1995JGR...10023413O Altcode:
Coronal hole regions are well-known sources of high-speed solar
wind; however, to account for the observed properties of the solar
wind, a source of energy must be included in addition to heat
conduction. Alfvén waves were suggested as the possible source of
heating that accelerates the solar wind. We investigate the heating
and propagation of the fast and shear Alfvén waves in coronal holes
via numerical solution of the time-dependent, linearized, resistive,
low-β, two-dimensional MHD equations in slab geometry. The waves are
driven at the lower boundary of the coronal hole and propagate into the
corona. We find that fast waves are partially reflected at the coronal
hole boundary and significant part of the wave energy leaks out of the
coronal hole. We compare the calculated wavelengths and the attenuation
rate of the fast waves in the leaky waveguide formed by the coronal
hole with the analytical ideal MHD solutions for ky=0, where
ky is the perpendicular wavenumber, and find an excellent
agreement. When ky≠0 the fast waves couple to the shear
Alfvén waves and transfer energy across field lines. Resonance
heating layers are found to occur when shear Alfvén waves are driven
and a continuous density profile is assumed for the coronal hole. When
resonance absorption is considered, the leakage is small compared to
the heating rate. The heating is enhanced by phase mixing when coronal
hole inhomogeneities (i.e., plumes) are included. We investigate the
dependence of the heating rate on the driver frequency and the Lundquist
number S and find a good agreement with the analytical S1/3
scaling of the dissipation length. We find that when S=104
the low-frequency Alfvén waves can be a significant source of heating
of coronal holes at several solar radii. At larger values of S,
nonlinear effects might reduce the effective dissipation length. We
discuss the relation of our results to the observed properties of
high-speed solar wind and coronal holes.

---------------------------------------------------------
Title: Nonlinear resonant absorption of Alfvén waves in three
dimensions, scaling laws, and coronal heating
Authors: Ofman, L.; Davila, J. M.
1995JGR...10023427O Altcode:
The nonlinear evolution of the resonant absorption of standing and
propagating Alfvén waves in an inhomogeneous plasma is studied via
solution of the time-dependent, three-dimensional, low-β, resistive
MHD equations over a wide parameter range. When the nonlinear effects
become important, the velocities at the dissipation layer were found to
be lower than the linear scaling of S1/3 would predict, where
S is the Lundquist number. Highly sheared velocities that are subject
to the Kelvin-Helmholtz-like instability were found at the narrow
dissipation layers. Three-dimensional Kelvin-Helmholtz-like vortices
appear at and near the dissipation layers and propagate along the slab
of plasma when traveling Alfvén wave solution are considered. The
narrow resonant heating layers are deformed by the self-consistent
shear flow. In the solar active regions where the resonant absorption
of Alfvén waves is believed to occur, the instability may lead to
turbulent enhancement of the dissipation parameters and account for the
observed turbulent velocities inferred from the nonthermal broadening
of x-ray and EUV emission lines. The self consistent J×B force changes
significantly the density structure of the loop that leads to a shift
in the global mode frequency response of the loop and a subsequent
drop in the heating rate. In the solar corona the density evolution
of the loop is likely to be dominated by evaporation of material from
the transition region.

---------------------------------------------------------
Title: Reply to “Comment on nonlinear studies of coronal heating
by the resonant absorption of Alfvén waves” by J. V. Hollweg
Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S.
1995GeoRL..22.2679O Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations and physical interpretations of the solar wind
flow properties as obtained from white light coronagraph aboard
SPARTAN 201-01
Authors: Guhathakurta, Madhulika; Fisher, Richard; Ofman, Leon
1995sowi.conf...64G Altcode:
The solar corona was observed with an externally occulted White Light
Coronagraph (WLC) carried on the SPARTAN 201-1 spacecraft on 11-12
Apr. 1993. With observations from WLC and the ground based Mauna Loa
White Light Coronagraph, a large number of polar plumes both in the
north and south polar holes were traced from 1.16 to 5.5 Rs. Flow
properties of the solar wind in coronal holes have been determined
(Habbal et al., 1995) by using a two fluid model constrained by
density profiles and scale height temperatures from the white light
observations, and interplanetary measurements of the flow speed and
proton mass flux from Ulysses' south polar passage. Provisions for
acceleration by Alfven waves, as well as electron and proton heating,
are included in the momentum and the energy equations respectively. The
model computations fit remarkably well the empirical constraints of
the two different density structures (plumes and coronal holes) for a
range of input parameters. In this study we investigate the physical
nature of the heating function used in the two-fluid model. Alfven
waves have been suggested as the possible source of heating that
accelerates the solar wind (Ofman and Davila, 1995). We utilize the
density contrast observed in WLC data in the plume and ambient coronal
hole region to estimate the Alfven wave frequencies responsible for
heating these structures. The source heating function utilized in the
two fluid model of the solar wind acceleration will be compared with
the resonant Alfven wave heating function.

---------------------------------------------------------
Title: Heating of coronal holes by the resonant absorption
and dissipation of Alfven waves and its relation to solar wind
acceleration
Authors: Ofman, L.; Davila, J. M.
1995sowi.confQ..66O Altcode:
Coronal hole regions are well known sources of high-speed solar wind,
however to account for the observed properties of the solar wind
a source of momentum and heat must be included. Alfven waves were
suggested as the possible source of heating that accelerates the solar
wind. We investigate the propagation of the Alfven waves in coronal
holes via numerical solution of the linearized 2-D resistive MHD
equations in slab geometry. The Alfven waves are driven at the lower
boundary of the coronal hole and propagate into the corona. The waves
are reflected at the coronal hole boundary and part of the wave energy
leaks out of the coronal hole. We compare the calculated wavelengths
and the attenuation rate of the fast mode Alfven waves in the leaky
waveguide formed by the coronal hole with the analytical ideal MHD
solutions. The formation of resonance heating layers is found to occur
when shear Alfven waves propagate in an inhomogeneous coronal hole. The
heating is enhanced when fast mode waves couple to the shear Alfven
waves. The narrow heating layers are formed near the location of the
ideal resonance, which might occur near the coronal hole boundary for
a nearly constant density coronal hole, surrounded by a higher density
plasma. We investigate the dependence of the heating on the driver
frequency, the Lundquist number, and on the heliocentric distance. and
find that the low frequency Alfven waves can be an efficient source
of heating at large distances from the Sun. We discuss the relation
of our results to the observed properties of high-speed solar wind
and coronal holes.

---------------------------------------------------------
Title: Coronal Heating by the Resonant Absorption of Alfven Waves:
Wavenumber Scaling Laws
Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S.
1995ApJ...444..471O Altcode:
The importance of global modes in coronal loop heating is well
established. In the present work the scaling of the global-mode resonant
heating rate with the perturbation wavenumbers is studied with the
numerical solution of the linearized time-dependent MHD equations for
a full compressible, low-beta, resistive plasma using an implicit
integration scheme. The numerical simulations demonstrate that the
dissipation on inhomogeneities in the background Alfven speed occurs in
narrow resonant layer with the highest heating rate at the global-mode
frequency. The global-mode heating rate H r was found to
scale as H (Sub r) approximately k y 1.03 when k
z = 0.1, and as H r approximately k y
-1.93 when k z = 0.75, where k y and
k z are the wavenumbers in the perpendicular and parallel to
the magnetic field directions, respectively, while the dependence of H
r on k z is more complex. The quality factor Q
of the MHD resonance cavity scales as Q approximately k y
-1.8 for k z = 0.75 and as Q approximately k
y -1.46 for k z = 0.1. The numerically
determined heating rate scaling, the global-mode fequency, and the
quality factor are in good agreement with the analytical linear
theory. The magnitude of the perturbed velocities was found to
decrease with k y. Assuming typical coronal loop parameters
(B 0 = 100-200 G, upsilon A = 2000-4000 km/s),
the Alfven waves can supply the required heating to a low-Q loops.

---------------------------------------------------------
Title: Heating of Coronal Holes by the Resonant Absorption and
Dissipation of Alfvén Waves
Authors: Ofman, L.; Davila, J. M.
1995SPD....26..907O Altcode: 1995BAAS...27..974O
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Reconnection and Current-Sheet Formation at X-type
Neutral Points
Authors: Steinolfson, R. S.; Ofman, L.; Morrison, P. J.
1995GMS....86..189S Altcode: 1995spcb.book..189S
Numerical solutions of the nonlinear, resistive magnetohydrodynamic
(MHD) equations are used to study the evolution of a perturbed or
stressed x-type neutral point. By performing individual simulations
for both compressible and incompressible plasmas, we are able to
demonstrate that the important physics for this problem involves just
the interaction between the plasma flow velocity and the magnetic
field and that the thermodynamics has a relatively passive effect. We
have also done separate simulations for both solid, conducting wall
boundary conditions at a fixed distance from the x-point and for
open boundary conditions that adjust as required by the evolving
solution within the boundaries. With solid, conducting wall boundary
conditions, our solutions for azimuthally symmetric disturbances agree
(for essentially linear perturbations) with those obtained in previous
analytic linear studies. In this case the stressed x-point relaxes back
to the unstressed state on a time scale somewhat shorter than the time
scale for the linear resistive tearing mode. Perturbations that are
not azimuthally symmetric can relax even faster than the symmetric
modes. When the conditions at the boundary are free to adjust, the
disturbances grow in amplitude on an Alfvén time scale with the
eventual formation of a current sheet separating two y-points. This
rapid growing behavior is, of course, in sharp contrast to the
relatively slow decaying solutions obtained with closed boundaries. The
growing solutions qualitatively agree with previous analytic x-point
solutions that have been suggested as an explanation for the rapid
energy conversion in flares and substorms.

---------------------------------------------------------
Title: Nonlinear studies of coronal heating by the resonant absorption
of Alfvén waves
Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S.
1994GeoRL..21.2259O Altcode:
The first nonlinear study of the instability of the resonant
absorption is presented in this paper. The nonlinear evolution of the
resonant absorption of Alfvén waves in an inhomogeneous plasma is
studied via solution of the time-dependent 3-D, low-β, resistive
MHD equations. Highly sheared velocities that are subject to the
Kelvin-Helmholtz like instability are found at the narrow dissipation
layers. Three dimensional Kelvin-Helmholtz like vortices appear at and
near the dissipation layers and propagate along the slab of plasma. The
narrow resonant heating layers are deformed by the self-consistent
shear flow. In the solar active regions where the resonant absorption of
Alfvén waves is believed to occur the instability may lead to turbulent
enhancement of the dissipation parameters and account for the observed
turbulent velocities inferred from the non-thermal broadening of x-ray
and EUV emission lines.

---------------------------------------------------------
Title: Coronal Heating by the Resonant Absorption of Alfven Waves
Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S.
1994scs..conf..473O Altcode: 1994IAUCo.144..473O
Nonlinear evolution and stability of the resonant absorption layer
is considered by solving the time-dependent 3D, low-β, resistive MHD
equations with the Lax-Wendroff explicit method. The narrow resonant
heating layers are deformed by the self-consistent shear flow. When
the driver amplitude is small compared to the average Alfvén speed the
dissipation layer appears to be stable and the driver-period-averaged
ohmic heating rate saturates at a slightly higher than the linear
rate. When the driver amplitude is large (Fd ≍ 1) the
resonant heating may become unstable.

---------------------------------------------------------
Title: Coronal Heating by the Resonant Absorption of Alfven Waves:
The Effect of Viscous Stress Tensor
Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S.
1994ApJ...421..360O Altcode:
The time-dependent linearized magnetohydrodynamics (MHD) equations
for a fully compressible, low-beta, viscoresistive plasma are
solved numerically using an implicit integration scheme. The full
viscosity stress tensor (Braginskii 1965) is included with the five
parameters etai i = 0 to 4. In agreement with previous
studies, the numerical simulations demonstrate that the dissipation
on inhomogeneities in the background Alfven speed occurs in a
narrow resonant layer. For an active region in the solar corona
the values of etai are etao = 0.65 g/cm/s,
eta1 = 3.7 x 10-12 g/cm/s, eta2 =
4 eta1, eta3 = 1.4 x 10-6 g/cm/s,
eta4 = 2 eta3, with n = 1010/cu
cm, T = 2 x 106 K, and B = 100 G. When the Lundquist
number S = 104 and R1 much greater than S
(where R1 is the dimensionless shear viscous number)
the width of the resistive dissipation layer dr is 0.22a
(where a is the density gradient length scale) and dr
approximately S-1/3. When S much greater than R1
the shear viscous dissipation layer width dr scales as
R1-1/3. The shear viscous and the resistive
dissipation occurs in an overlapping narrow region, and the total
heating rate is independent of the value of the dissipation parameters
in agreement with previous studies. Consequently, the maximum values
of the perpendicular velocity and perpendicular magnetic field scale
as R1-1/3. It is evident from the simulations
that for solar parameters the heating due to the compressive viscosity
(R0 = 560) is negligible compared to the resistive and the
shear viscous (R1) dissipation and it occurs in a broad layer
of order a in width. In the solar corona with S approximately equals
104 and R1 approximately equals 1014
(as calculated from the Braginskii expressions), the shear viscous
resonant heating is of comparable magnitude to the resistive resonant
heating.

---------------------------------------------------------
Title: Nonlinear Evolution of Coronal Heating by the Resonant
Absorption of Alfven Waves
Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S.
1993AAS...183.5904O Altcode: 1993BAAS...25.1386O
The nonlinear 3-D MHD equations for a fully compressible, low-beta,
visco-resistive plasma are solved numerically using the Lax-Wendroff
integration scheme (the explicit integration scheme was found to
converge considerably faster in terms of physical time per CPU time
than the Alternating Direction Implicit method). The calculations
are initiated with the solutions of the linearized version of the MHD
equations (Ofman, Davila, and Steinolfson 1994, Ap.J., in press), with
inhomogeneous background density, and a constant magnetic field. The
numerical simulations demonstrate that the narrow dissipation layer
is affected by the self-consistent velocity shear: i.e., the regions
of high ohmic heating are carried around by the flow. Consequently,
the topology of the perpendicular magnetic field and the ohmic heating
regions differs significantly from the linear case. Additional harmonics
of the driver frequency appear in the temporal oscillations with the
dominant frequency of double the driver frequency. When the Lundquist
number is S=10(3) the average width of the resistive dissipation layer
is 0.4a (where a is the density gradient length scale) and consistent
with the linear results. When the driver amplitude is small compared
to the average Alfven speed the dissipation layer appears to be
stable and the ohmic heating rate is enhanced by about 15% over the
linear heating rate. When the driver amplitude is comparable to the
average Alfven speed the nonlinear effects dominate the evolution and
the resonant heating layer may become unstable. A parametric study
of the instability is presented. The effect of the self-consistent
velocity on the instability is considered by generalizing the linear
theory (Davila 1987) to include shear flow and solving the linearized
dispersion relation of the resonant absorption with the background
shear flow. (*) NRC-NAS Resident Research Associate.

---------------------------------------------------------
Title: Magnetic Reconnection at Stressed X-Type Neutral Points
Authors: Ofman, L.; Morrison, P. J.; Steinolfson, R. S.
1993ApJ...417..748O Altcode:
The reconnection and relaxation of two-dimensional stressed
(nonpotential) X-type neutral point magnetic fields are studied via
solution of the nonlinear resistive two-dimensional MHD equations
and by analytical solution of the linear eigenvalue problem. Previous
linear studies (Craig &amp; McClymont 1991; Hassam 1992; Craig &amp;
Watson 1992), have shown that such stressed fields may relax on a time
substantially shorter (i.e., ∼ |log η|2, where η is the
resistivity) than the usual time scale for linear reconnection (i.e.,
η3/5. We have generalized the linear dispersion relation for
azimuthally nonsymmetric perturbations and have found that for modes
with azimuthal mode numbers m &gt; 0, the relaxation can occur at a
rate faster than that for n = m = 0, where n is the radial "quantum"
number. All of the results presented are for frozen-in (line-tied)
boundary conditions at some distance from the X-point, and we emphasize
that these boundary conditions are essential in order to obtain our
solutions. We find that for nearly azimuthally symmetric magnetic
perturbations the fields relax incompressibly and nonlinearly to the
unstressed X-type neutral point at a rate close to that predicted by
linear theory. Also, fully compressible nonlinear MHD simulations have
been performed, which show that the interaction between the plasma
flow velocity and the magnetic field is the important physical effect,
while the inclusion of thermodynamics does not affect the evolution
considerably. A Liapunov functional for the nonlinear incompressible
two-dimensional resistive MHD equations is derived to show that the
current-free X-point configuration is a global equilibrium to which
general initial conditions relax.

---------------------------------------------------------
Title: Coronal Heating by the Resonant Absorption of Alfven Waves:
The Effects of Viscous Stress Tensor
Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S.
1993BAAS...25.1202O Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Reconnection of Magnetic Fields with Stressed X-type Neutral
Points
Authors: Ofman, L.; Steinolfson, R. S.; Morrison, P. J.
1992AAS...180.5503O Altcode: 1992BAAS...24..819O
The reconnection of two-dimensional stressed X-type neutral point
magnetic fields is studied via solution of the nonlinear resistive
MHD equations and by analytical solution of the linear eigenvalue
problem. Previous linear studies [I. Craig and A. McClymont, Ap. J. 371,
L41 (1991); A. Hassam, Ap. J. submitted (1991)] have shown that such
stressed fields may relax on a time substantially shorter than the usual
time scale for liner reconnection (i.e. eta (3/5) ). We find that for
azimuthally symmetric (m=0) and nonsymmetric (m&gt;0) perturbations,
the fields relax to the unstressed X-type neutral point at a rate
close to that predicted by linear theory, provided the fields at the
boundaries are fixed, and there is no flow through the boundaries. If
outflowing boundary conditions are imposed, we find that the perturbed
X-point evolves into a sheet current within several Alfven times. This
process is of the type proposed to explain solar flare discharges
[J. Dungey, Phil. Mag. 44 354 (1953)].

---------------------------------------------------------
Title: Nonlinear Evolution of the Resistive Tearing Mode Instability
with Shear Flow and Viscosity
Authors: Ofman, L.; Morrison, P. J.; Steinolfson, R. S.
1991BAAS...23.1042O Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Determination of force-free magnetic fields above the
photosphere using three-component boundary conditions - Moderately
non-linear case
Authors: Cuperman, S.; Ofman, L.; Semel, M.
1990A&A...230..193C Altcode:
The calculation of the magnetic field components and the tracing
of the magnetic field lines above the photosphere are considered
within the framework of the nonlinear force-free field model, upon
using three-component magnetic fields as boundary conditions. This
vertical integration represents an extrapolation in the small and is
free of any implicit or explicit assumption in the large. As a study
case, an analytical model providing magnetic field components at a
surface (representing the photosphere) and above it is used. Magnetic
field components and magnetic field lines at z greater than 0 are
obtained. Their comparison with the analytical ones provides a measure
of the calculational accuracy. The method is demonstrated for the case
of moderately nonlinear force-free forces.

---------------------------------------------------------
Title: Resistive Tearing Mode Instability with Shear Flow and
Viscosity
Authors: Ofman, L.; Steinolfson, R. S.; Chen, X. L.; Morrison, P. J.
1990BAAS...22..853O Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Thermally Conductive Magnetohydrodynamic Flows in
Helmet-Streamer Coronal Structures
Authors: Cuperman, S.; Ofman, L.; Dryer, M.
1990ApJ...350..846C Altcode:
The behavior of thermally conductive plasma flows in helmet-streamer
coronal structures is investigated within the framework of
the axisymmetric nonrotating one-fluid MHD model. Continuous
subsonic-supersonic solutions satisfying observed boundary conditions
at the sun as well as the vanishing of the temperature at infinity
are obtained and presented. Special attention is paid to the combined
effects of conductive flow (and corresponding thermal force) and
rapidly diverging magnetic field on the critical points. In this,
the heliocentric distance of the neutral point determining the
separation between closed and open field lines (cusp) is treated as
a free parameter. These thermally conductive solutions are contrasted
with those provided by corresponding isothermal models.

---------------------------------------------------------
Title: The absolute value and sign of the function alpha(r) in the
force-free magnetic field modelling of photospheric observations
Authors: Cuperman, S.; Ofman, L.; Semel, M.
1990A&A...227..227C Altcode:
A relatively simple method for the determination of the quantity α =
J/B characterizing the force-free magnetic fields based on photospheric
vector magnetic fields is presented. Magnetic configurations
for which the sign of α does not change are considered. The method consists of two steps, namely: (a) Expression of
force-free field equations in terms of the observed quantities
Bz, B2x, B2y
and BxBy and determination of |α|; (b) Selection
of the proper sign of α (corresponding to the magnetic configuration
under consideration) by (i) solving the FFF equations under the
assumptions α = - |α| and α = +|α|, (ii) using the two types of
solutions to calculate the surface energy integral ES(z)
= ∫ (B2x + B2y
+ B2x)ds, and (iii) retaining the sign that
leads to a decrease with height (z) of Es(z). The
proposed method is tested by considering three different FFF magnetic
configurations for which analytical solutions exist.

---------------------------------------------------------
Title: Extrapolation of photospheric potential magnetic fields using
oblique boundary values - A simplified approach
Authors: Cuperman, S.; Ofman, L.; Semel, M.
1990A&A...227..583C Altcode:
The problem of extrapolating photospheric potential magnetic fields
is addressed using the oblique line-of-sight component B1(rs) as a
boundary condition and reducing it to that for the normal line-of-sight
component Bz(rs). The observed B1(rs) component is used along with
the direction cosines of the line-of-sight alpha, beta, and gamma
to calculate semianalytically the photospheric components Bx(rs)
and By(rs). All these values are used to find the normal photospheric
component Bx(rs). Finally, using the distribution Bz(rs) as boundary
values, the relatively simpler problem corresponding to the case
in which the normal components are known is solved. The method is
tested on the case of an analytical model configuration for which
exact solutions in the half-space above the photosphere exist.

---------------------------------------------------------
Title: Reply
Authors: Cuperman, S.; Ofman, L.; Dryer, M.
1989JGR....9410153C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Determination of constant-alpha force-free magnetic fields
above the photosphere using three-component boundary conditions
Authors: Cuperman, S.; Ofman, L.; Semel, M.
1989A&A...216..265C Altcode:
The constant-α, force-free magnetic field equations are
numerically integrated for the case in which all three field
components are specified at the photo sphere and used as boundary
conditions. Test-cases successfully compare the numerical results with
exact analytical values.

---------------------------------------------------------
Title: On the dispersion of ion cyclotron waves in
H+-He++ solar wind-like magnetized
plasmas
Authors: Cuperman, S.; Ofman, L.; Dryer, M.
1988JGR....93.2533C Altcode:
We investigate by computer simulation experiments the nonlinear behavior
of mixed H+-He++ plasma systems under
the particular physical conditions found by the linear theory to allow
the parallel propagation of only weakly damped electromagnetic ion
cyclotron waves at the alpha particle cyclotron frequency. Here the
waves are generated by anisotropic proton populations. The essentially
nonlinear results of our computer simulations indicate a strong damping
of the parallel propagating electromagnetic ion cyclotron waves and a
significant dip in the energy spectrum, both centered cyclotron waves
and a significant dip in the energy spectrum, both centered at about
ω=Ωα.

---------------------------------------------------------
Title: On the Dispersion of Ion Cyclotron Waves in Magnetized
H+ -He++ Solar Wind-Like Plasmas
Authors: Cuperman, S.; Ofman, L.; Dryer, M.
1987sowi.conf..346C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Nonlinear aspects of collective, electromagnetic interactions
in magnetized plasmas with anisotropic protons and isotropic alpha
particles
Authors: Cuperman, S.; Ofman, L.; Dryer, M.
1986JPlPh..36..387C Altcode:
We use computer simulation experiments to investigate the nonlinear
behaviour of plasmas with a mixture of anisotropic protons and isotropie
alpha particles, embedded in a static magnetic field. Specifically,
we study the linearly predicted ‘stop-band’ for the propagation of
the proton-produced electromagnetic ion cyclotron waves in conjunction
with the energization of the heavier ions by the same waves. For this,
three cases are considered: (1) proton + electron plasma; (2) proton +
electron + cold alpha particle plasma, and (3) proton + electron + warm
alpha particle plasma. Among the main results obtained we mention the
following, (a) In the presence of significant relative He2+
concentrations (either cold or warm) all proton-produced left-polarized
waves having frequencies above the alpha-particle gyrofrequency are
practically suppressed, during the entire nonlinear evolution of
the system, indicating that particle-wave-particle interactions
are confined to the low-frequency branch of the waves, (b) The
‘remnant’ wave energy, i.e. that part of the wave energy not
transferred to the particles, decreases significantly when going from
case 1 to case 3. (c) Nevertheless, in all three cases, the initial
proton thermal anisotropy relaxes to the same quasi-equilibrium value
( 1·5). (d) The cold alpha particles in case 2 are strongly heated by
their non-resonant interaction with the proton-produced ion cyclotron
electromagnetic waves, (e) In contrast, the initially warm isotropic
alpha particles in case 3 are heated by resonant interaction with the
proton-produced waves, resulting in an increase in the perpendicular
energy and a decrease in the parallel energy. The physical processes
involved in the collisionless interaction of these mixed protons and
heavier ions (alpha particles) are discussed.