Author name code: marsch
ADS astronomy entries on 2022-09-14
author:"Marsch, Eckart"
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Title: Evaluating Electrostatic Analyser measurements of 3D Solar
Wind Velocity Distributions: The SIRTH Method
Authors: Steinhagen, J.; Berger, L.; Heidrich-Meisner, V.; Marsch,
E.; Wimmer-Schweingruber, R. F.
Bibcode: 2020AGUFMSH013..01S
Altcode:
The solar wind is often characterised by few key parameters,
such as density, velocity, and temperature. These parameters only
describe the underlying 3D velocity distribution well for a Maxwellian
distribution. Since the solar wind often deviates from a Maxwellian, it
is desirable to characterise distributions in more detail. We analyse
data from Helios E1 instrument 1a, an electrostatic analyser that
separates ions with respect to their E/q ratio. A typical problem with
instrument 1a data is the overlap of protons and alphas in the proton
velocity frame. The magnetic field represents a prominent direction
for the gyromotion of ions, but typically does not align with the
instrumental frame of reference. We therefore rotate the experimental
data accordingly before we translate the coordinate system into the
proton maximum. We further refine our coordinate system such that the
magnetic field axis, alphas and protons lie in one coordinate plane. The
assumption of gyrotropy is then sufficient to separate protons and
alphas in most cases. Density and temperature changes along the magnetic
field direction can now be derived without contamination by alphas and
protons, respectively. We call it Subgrid, Interpolation, Rotation,
Translation and Histogramming (SIRTH) method, closely following the
individual implementation steps. We present first results for proton
plasma properties in 40s time resolution. The concept of this method
can also be applied to other electrostatic analysers like 3DP-PESA on
Wind, SWEAP-SPAN on Parker Solar Probe and SWA-PAS on Solar Orbiter.
Title: The Solar Orbiter magnetometer
Authors: Horbury, T. S.; O'Brien, H.; Carrasco Blazquez, I.; Bendyk,
M.; Brown, P.; Hudson, R.; Evans, V.; Oddy, T. M.; Carr, C. M.; Beek,
T. J.; Cupido, E.; Bhattacharya, S.; Dominguez, J. -A.; Matthews, L.;
Myklebust, V. R.; Whiteside, B.; Bale, S. D.; Baumjohann, W.; Burgess,
D.; Carbone, V.; Cargill, P.; Eastwood, J.; Erdös, G.; Fletcher,
L.; Forsyth, R.; Giacalone, J.; Glassmeier, K. -H.; Goldstein, M. L.;
Hoeksema, T.; Lockwood, M.; Magnes, W.; Maksimovic, M.; Marsch, E.;
Matthaeus, W. H.; Murphy, N.; Nakariakov, V. M.; Owen, C. J.; Owens,
M.; Rodriguez-Pacheco, J.; Richter, I.; Riley, P.; Russell, C. T.;
Schwartz, S.; Vainio, R.; Velli, M.; Vennerstrom, S.; Walsh, R.;
Wimmer-Schweingruber, R. F.; Zank, G.; Müller, D.; Zouganelis, I.;
Walsh, A. P.
Bibcode: 2020A&A...642A...9H
Altcode:
The magnetometer instrument on the Solar Orbiter mission is designed
to measure the magnetic field local to the spacecraft continuously
for the entire mission duration. The need to characterise not only
the background magnetic field but also its variations on scales from
far above to well below the proton gyroscale result in challenging
requirements on stability, precision, and noise, as well as magnetic
and operational limitations on both the spacecraft and other
instruments. The challenging vibration and thermal environment has
led to significant development of the mechanical sensor design. The
overall instrument design, performance, data products, and operational
strategy are described.
Title: The Solar Orbiter SPICE instrument. An extreme UV imaging
spectrometer
Authors: SPICE Consortium; Anderson, M.; Appourchaux, T.; Auchère, F.;
Aznar Cuadrado, R.; Barbay, J.; Baudin, F.; Beardsley, S.; Bocchialini,
K.; Borgo, B.; Bruzzi, D.; Buchlin, E.; Burton, G.; Büchel, V.;
Caldwell, M.; Caminade, S.; Carlsson, M.; Curdt, W.; Davenne, J.;
Davila, J.; Deforest, C. E.; Del Zanna, G.; Drummond, D.; Dubau,
J.; Dumesnil, C.; Dunn, G.; Eccleston, P.; Fludra, A.; Fredvik, T.;
Gabriel, A.; Giunta, A.; Gottwald, A.; Griffin, D.; Grundy, T.; Guest,
S.; Gyo, M.; Haberreiter, M.; Hansteen, V.; Harrison, R.; Hassler,
D. M.; Haugan, S. V. H.; Howe, C.; Janvier, M.; Klein, R.; Koller,
S.; Kucera, T. A.; Kouliche, D.; Marsch, E.; Marshall, A.; Marshall,
G.; Matthews, S. A.; McQuirk, C.; Meining, S.; Mercier, C.; Morris,
N.; Morse, T.; Munro, G.; Parenti, S.; Pastor-Santos, C.; Peter, H.;
Pfiffner, D.; Phelan, P.; Philippon, A.; Richards, A.; Rogers, K.;
Sawyer, C.; Schlatter, P.; Schmutz, W.; Schühle, U.; Shaughnessy,
B.; Sidher, S.; Solanki, S. K.; Speight, R.; Spescha, M.; Szwec, N.;
Tamiatto, C.; Teriaca, L.; Thompson, W.; Tosh, I.; Tustain, S.; Vial,
J. -C.; Walls, B.; Waltham, N.; Wimmer-Schweingruber, R.; Woodward,
S.; Young, P.; de Groof, A.; Pacros, A.; Williams, D.; Müller, D.
Bibcode: 2020A&A...642A..14S
Altcode: 2019arXiv190901183A; 2019arXiv190901183S
Aims: The Spectral Imaging of the Coronal Environment (SPICE)
instrument is a high-resolution imaging spectrometer operating at
extreme ultraviolet wavelengths. In this paper, we present the concept,
design, and pre-launch performance of this facility instrument on the
ESA/NASA Solar Orbiter mission.
Methods: The goal of this paper
is to give prospective users a better understanding of the possible
types of observations, the data acquisition, and the sources that
contribute to the instrument's signal.
Results: The paper
discusses the science objectives, with a focus on the SPICE-specific
aspects, before presenting the instrument's design, including optical,
mechanical, thermal, and electronics aspects. This is followed by a
characterisation and calibration of the instrument's performance. The
paper concludes with descriptions of the operations concept and data
processing.
Conclusions: The performance measurements of the
various instrument parameters meet the requirements derived from the
mission's science objectives. The SPICE instrument is ready to perform
measurements that will provide vital contributions to the scientific
success of the Solar Orbiter mission.
Title: The Solar Orbiter mission. Science overview
Authors: Müller, D.; St. Cyr, O. C.; Zouganelis, I.; Gilbert, H. R.;
Marsden, R.; Nieves-Chinchilla, T.; Antonucci, E.; Auchère, F.;
Berghmans, D.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic,
M.; Owen, C. J.; Rochus, P.; Rodriguez-Pacheco, J.; Romoli, M.;
Solanki, S. K.; Bruno, R.; Carlsson, M.; Fludra, A.; Harra, L.;
Hassler, D. M.; Livi, S.; Louarn, P.; Peter, H.; Schühle, U.;
Teriaca, L.; del Toro Iniesta, J. C.; Wimmer-Schweingruber, R. F.;
Marsch, E.; Velli, M.; De Groof, A.; Walsh, A.; Williams, D.
Bibcode: 2020A&A...642A...1M
Altcode: 2020arXiv200900861M
Aims: Solar Orbiter, the first mission of ESA's Cosmic Vision
2015-2025 programme and a mission of international collaboration between
ESA and NASA, will explore the Sun and heliosphere from close up and
out of the ecliptic plane. It was launched on 10 February 2020 04:03
UTC from Cape Canaveral and aims to address key questions of solar and
heliospheric physics pertaining to how the Sun creates and controls
the Heliosphere, and why solar activity changes with time. To answer
these, the mission carries six remote-sensing instruments to observe
the Sun and the solar corona, and four in-situ instruments to measure
the solar wind, energetic particles, and electromagnetic fields. In
this paper, we describe the science objectives of the mission, and how
these will be addressed by the joint observations of the instruments
onboard.
Methods: The paper first summarises the mission-level
science objectives, followed by an overview of the spacecraft and
payload. We report the observables and performance figures of each
instrument, as well as the trajectory design. This is followed by a
summary of the science operations concept. The paper concludes with a
more detailed description of the science objectives.
Results:
Solar Orbiter will combine in-situ measurements in the heliosphere
with high-resolution remote-sensing observations of the Sun to address
fundamental questions of solar and heliospheric physics. The performance
of the Solar Orbiter payload meets the requirements derived from the
mission's science objectives. Its science return will be augmented
further by coordinated observations with other space missions and
ground-based observatories. ARRAY(0x207ce98)
Title: The Solar Orbiter EUI instrument: The Extreme Ultraviolet
Imager
Authors: Rochus, P.; Auchère, F.; Berghmans, D.; Harra, L.; Schmutz,
W.; Schühle, U.; Addison, P.; Appourchaux, T.; Aznar Cuadrado,
R.; Baker, D.; Barbay, J.; Bates, D.; BenMoussa, A.; Bergmann, M.;
Beurthe, C.; Borgo, B.; Bonte, K.; Bouzit, M.; Bradley, L.; Büchel,
V.; Buchlin, E.; Büchner, J.; Cabé, F.; Cadiergues, L.; Chaigneau,
M.; Chares, B.; Choque Cortez, C.; Coker, P.; Condamin, M.; Coumar,
S.; Curdt, W.; Cutler, J.; Davies, D.; Davison, G.; Defise, J. -M.;
Del Zanna, G.; Delmotte, F.; Delouille, V.; Dolla, L.; Dumesnil, C.;
Dürig, F.; Enge, R.; François, S.; Fourmond, J. -J.; Gillis, J. -M.;
Giordanengo, B.; Gissot, S.; Green, L. M.; Guerreiro, N.; Guilbaud,
A.; Gyo, M.; Haberreiter, M.; Hafiz, A.; Hailey, M.; Halain, J. -P.;
Hansotte, J.; Hecquet, C.; Heerlein, K.; Hellin, M. -L.; Hemsley, S.;
Hermans, A.; Hervier, V.; Hochedez, J. -F.; Houbrechts, Y.; Ihsan,
K.; Jacques, L.; Jérôme, A.; Jones, J.; Kahle, M.; Kennedy, T.;
Klaproth, M.; Kolleck, M.; Koller, S.; Kotsialos, E.; Kraaikamp, E.;
Langer, P.; Lawrenson, A.; Le Clech', J. -C.; Lenaerts, C.; Liebecq,
S.; Linder, D.; Long, D. M.; Mampaey, B.; Markiewicz-Innes, D.;
Marquet, B.; Marsch, E.; Matthews, S.; Mazy, E.; Mazzoli, A.; Meining,
S.; Meltchakov, E.; Mercier, R.; Meyer, S.; Monecke, M.; Monfort,
F.; Morinaud, G.; Moron, F.; Mountney, L.; Müller, R.; Nicula, B.;
Parenti, S.; Peter, H.; Pfiffner, D.; Philippon, A.; Phillips, I.;
Plesseria, J. -Y.; Pylyser, E.; Rabecki, F.; Ravet-Krill, M. -F.;
Rebellato, J.; Renotte, E.; Rodriguez, L.; Roose, S.; Rosin, J.;
Rossi, L.; Roth, P.; Rouesnel, F.; Roulliay, M.; Rousseau, A.; Ruane,
K.; Scanlan, J.; Schlatter, P.; Seaton, D. B.; Silliman, K.; Smit,
S.; Smith, P. J.; Solanki, S. K.; Spescha, M.; Spencer, A.; Stegen,
K.; Stockman, Y.; Szwec, N.; Tamiatto, C.; Tandy, J.; Teriaca, L.;
Theobald, C.; Tychon, I.; van Driel-Gesztelyi, L.; Verbeeck, C.;
Vial, J. -C.; Werner, S.; West, M. J.; Westwood, D.; Wiegelmann, T.;
Willis, G.; Winter, B.; Zerr, A.; Zhang, X.; Zhukov, A. N.
Bibcode: 2020A&A...642A...8R
Altcode:
Context. The Extreme Ultraviolet Imager (EUI) is part of the remote
sensing instrument package of the ESA/NASA Solar Orbiter mission
that will explore the inner heliosphere and observe the Sun from
vantage points close to the Sun and out of the ecliptic. Solar Orbiter
will advance the "connection science" between solar activity and the
heliosphere.
Aims: With EUI we aim to improve our understanding
of the structure and dynamics of the solar atmosphere, globally as well
as at high resolution, and from high solar latitude perspectives.
Methods: The EUI consists of three telescopes, the Full Sun Imager and
two High Resolution Imagers, which are optimised to image in Lyman-α
and EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere
up to corona. The EUI is designed to cope with the strong constraints
imposed by the Solar Orbiter mission characteristics. Limited telemetry
availability is compensated by state-of-the-art image compression,
onboard image processing, and event selection. The imposed power
limitations and potentially harsh radiation environment necessitate
the use of novel CMOS sensors. As the unobstructed field of view of
the telescopes needs to protrude through the spacecraft's heat shield,
the apertures have been kept as small as possible, without compromising
optical performance. This led to a systematic effort to optimise the
throughput of every optical element and the reduction of noise levels
in the sensor.
Results: In this paper we review the design
of the two elements of the EUI instrument: the Optical Bench System
and the Common Electronic Box. Particular attention is also given to
the onboard software, the intended operations, the ground software,
and the foreseen data products.
Conclusions: The EUI will
bring unique science opportunities thanks to its specific design,
its viewpoint, and to the planned synergies with the other Solar
Orbiter instruments. In particular, we highlight science opportunities
brought by the out-of-ecliptic vantage point of the solar poles,
the high-resolution imaging of the high chromosphere and corona,
and the connection to the outer corona as observed by coronagraphs.
Title: Kinetic Simulation of Slow Magnetosonic Waves and
Quasi-Periodic Upflows in the Solar Corona
Authors: He, Jiansen; Peter, Hardi; Vocks, Christian; Marsch, Eckart;
Wang, Linghua; Zhang, Lei; Ruan, Wenzhi
Bibcode: 2018cosp...42E1405H
Altcode:
Quasi-periodic disturbances of emission-line parameters are frequently
observed in the corona. These disturbances propagate upward along
the magnetic field with speeds of _100 km/s. This phenomenon has been
interpreted as evidence of the propagation of slow magnetosonic waves or
has been argued to be a signature of intermittent outflows superposed on
the background plasmas. Here we aim to present a new "wave + flow" model
to interpret these observations. In our scenario, the oscillatory motion
is a slow-mode wave, and the flow is associated with a beam created by
the wave-particle interaction owing to Landau resonance. With the help
of a kinetic model, we simulate the propagation of slow-mode waves and
the generation of beam flows. We find that weak periodic beam flows
can be generated by to Landau resonance in the solar corona, and the
phase with the strongest blueward asymmetry is ahead of that with the
strongest blueshift by about 1/4 period. We also find that the slow wave
dampsto the level of 1/e after the transit time of two wave periods,
owing to Landau damping and Coulomb collisions in our simulation. This
damping timescale is similar to that resulting from thermal conduction
in the MHD regime.The beam flow is weakened/attenuated with increasing
wave period and decreasing wave amplitude since Coulomb collisions
become more and more dominant over the wave action. We suggest that
this "wave + flow"kinetic model provides an alternative explanation
for the observed quasi-periodic propagating perturbations in various
parameters in the solar corona.
Title: Solar Wind and Kinetic Heliophysics - Hannes Alfven Medal
Lecture at the EGU General Assembly 2018
Authors: Marsch, Eckart
Bibcode: 2018EGUGA..20.1790M
Altcode:
This lecture reviews recent aspects of solar wind physics and
elucidates the role Alfven waves play in solar wind acceleration and
turbulence, which prevail in the low corona and inner heliosphere. Our
understanding of the solar wind has made considerable progress based
on remote sensing, in-situ measurements, kinetic simulation and fluid
modelling. Further insights are expected from such missions as the
Parker Solar Probe and Solar Orbiter. The sources of the solar wind
have been identified in the chromospheric network, transition region
and corona of the sun. Alfven waves excited by reconnection in the
network contribute to the driving of turbulence and plasma flows
in funnels and coronal holes. The dynamic solar magnectic field
causes solar wind variations over the solar cycle. Fast and slow
solar wind streams, as well as transient coronal mass ejections
are generated by the sun's magnetic activity. Magnetohydrodynamic
turbulence originates at the sun and evolves into interplanetary
space. The major Alfven waves and minor magnetosonic waves, with
an admixture of pressure-balanced structures at various scales,
constitute heliophysical turbulence. Its spectra evolve radially and
develope anisotropies. Numerical simulations of turbulence spectra
have reproduced key observational features. Collisionless dissipation
of fluctuations remains a subject of intense research. Detailed
measurements of particle velocity distributions have revealed
non-maxwellian electrons, strongly anisotropic protons and heavy ion
beams. Besides macroscopic forces in the heliosphere local wave-particle
interactions shape the distribution functions. They can be described by
the Boltzmann-Vlasov equation including collisions and waves. Kinetic
simulations permit us to better understand the combined evolution of
particles and waves in the heliosphere.
Title: Qualitative numerical studies of the modification of the
pitch angle distribution of test particles by alfvènic wave activity
Authors: Keilbach, D.; Drews, C.; Berger, L.; Marsch, E.;
Wimmer-Schweingruber, R. F.
Bibcode: 2017AGUFMSH33B2768K
Altcode:
Using a test particle approach we have investigated, how an oxygen
pickup ion torus velocity distribution is modified by continuous and
intermittent alfvènic waves on timescales, where the gyro trajectory
of each particle can be traced.We have therefore exposed the test
particles to mono frequent waves, which expanded through the whole
simulation in time and space. The general behavior of the pitch angle
distribution is found to be stationary and a nonlinear function of the
wave frequency, amplitude and the initial angle between wave elongation
and field-perpendicular particle velocity vector. The figure shows the
time-averaged pitch angle distributions as a function of the Doppler
shifted wave frequency (where the Doppler shift was calculated with
respect to the particles initial velocity) for three different wave
amplitudes (labeled in each panel). The background field is chosen
to be 5 nT and the 500 test particles were initially distributed
on a torus with 120° pitch angle at a solar wind velocity of 450
km/s. Each y-slice of the histogram (which has been normalized to it's
respective maximum) represents an individual run of the simulation.The
frequency-dependent behavior of the test particles is found to
be classifiable into the regimes of very low/high frequencies and
frequencies close to first order resonance. We have found, that only
in the latter regime the particles interact strongly with the wave,
where in the time averaged histograms a branch structure is found,
which was identified as a trace of particles co-moving with the wave
phase. The magnitude of pitch angle change of these particles is as
well as the frequency margin, where the branch structure is found, an
increasing function with the wave amplitude.We have also investigated
the interaction with mono frequent intermittent waves. Exposed to
such waves a torus distribution is scattered in pitch angle space,
whereas the pitch angle distribution is broadened systematically over
time similar to pitch angle diffusion.The framework of our simulations
is a first step toward understanding wave particle interactions at the
most basic level and is readily expandable to e.g. the inclusion of
multiple wave frequencies, intermittent wave activity, gradients in
the background magnetic field or collisions with solar wind particles.
Title: Numerical study of alfvénic wave activity in the solar wind
as a cause for pitch angle scattering with focus on kinetic processes
Authors: Keilbach, D.; Berger, L.; Drews, C.; Marsch, E.;
Wimmer-Schweingruber, R. F.
Bibcode: 2017AGUFMSH33B2785K
Altcode:
Recent studies, that determined the inflow longitude of the local
interstellar medium from the anisotropy of interstellar pickup ion (PUI)
radial velocity, have once again raised the question, how transport
effects and especially wave activity in the solar wind modifies the
velocity distribution function of PUIs.This study investigates the
modification of an oxygen PUI torus distribution by alfvénic waves
qualitatively with a numerical approach. The focus of this study
is to understand this modification kinetically, which means, that
instead of describing the PUI transport through diffusion approaches,
we trace the trajectories of test particles in pitch angle space with
a time resolution of at least 100 time steps per gyro orbit in order
to find first principles of wave particle interactions on the most
basic scale.Therefore we have implemented a Leapfrog solver of the
Lorentz-Newton equations of motion for a charged test particle in a
electro-magnetic field. The alfvénic waves were represented through
a continuous circularly polarized wave superimposed to a constant 5 nT
background magnetic field. In addition an electric field arising from
induction has been added to the simulation's boundary conditions. The
simulation code computes the particles' trajectories in the solar wind
bulk system.Upon interaction with mono frequent single-frequency waves,
the particles are found to perform stationary trajectories in pitch
angle space, so that the pitch angle distribution of a conglomerate
of test particles does not experience a systematic broadening over
time. Also the particles do not react most strongly with waves at
resonant frequencies, since the pitch angle modification by the waves
sweeps their parallel velocity out of resonance quickly. However,
within frequencies close to first order resonance, strong interactions
between waves and particles are observed.Altogether the framework of
our simulation is readily expandable to simulate additional effects,
which may modify the test particles' pitch angle distribution strongly
(e.g. collisions with solar wind particles or gradient drifts). So
far we have expanded the simulation to support intermittent waves,
where we have observed, that the pitch angle distribution of the test
particles broadens systematically over time.
Title: Influence of Intermittency on the Quasi-perpendicular Scaling
in Three-dimensional Magnetohydrodynamic Turbulence
Authors: Yang, Liping; He, Jiansen; Tu, Chuanyi; Li, Shengtai; Zhang,
Lei; Wang, Xin; Marsch, Eckart; Wang, Linghua
Bibcode: 2017ApJ...846...49Y
Altcode:
Solar wind fluctuations reveal the ubiquity of intermittency, which
is believed to affect the spectral signatures of turbulence. In this
work, based on simulation of driven compressible MHD turbulence,
we apply the wavelet technique to the magnetic field and velocity
to identify intermittency, and we analyze the influence of the
intermittency on the quasi-perpendicular scaling in the inertial
range. The numerical results show that the original magnetic and
velocity fluctuations are anisotropic, and have a power anisotropy
with a spectral index approaching the Iroshnikov-Kraichnan -3/2
scaling in the direction quasi-perpendicular to the local mean magnetic
field. As in observations of the solar wind fluctuations, as the scale
decreases in the simulation, the calculated probability distribution
functions (pdfs) of the wavelet coefficients become extended on
both tails of the non-Gaussian distribution, with a rapid increase
in flatness. After intermittency has been removed from the driven
turbulence, at each scale, the pdfs approach a Gaussian distribution,
with the flatness being ∼3. Meanwhile, the quasi-perpendicular scaling
for both fluctuations becomes steeper and close to a Kolmogorov -5/3
scaling, which may be a result of the stronger intermittency in the
quasi-perpendicular direction and at the smaller scales. These results
suggest that there is intermittency superposed on the “background”
turbulence that seems to have the Kolmogorov scaling, whereby the
overall slope is getting flatter with the involvement of intermittency.
Title: Multiscale Pressure-Balanced Structures in Three-Dimensional
Magnetohydrodynamic Turbulence
Authors: Yang, Liping; He, Jiansen; Tu, Chuanyi; Li, Shengtai; Zhang,
Lei; Marsch, Eckart; Wang, Linghua; Wang, Xin; Feng, Xueshang
Bibcode: 2017ApJ...836...69Y
Altcode: 2016arXiv161201496Y
Observations of solar wind turbulence indicate the existence
of multiscale pressure-balanced structures (PBSs) in the solar
wind. In this work, we conduct a numerical simulation to investigate
multiscale PBSs and in particular their formation in compressive
magnetohydrodynamic turbulence. By the use of the higher-order Godunov
code Athena, a driven compressible turbulence with an imposed uniform
guide field is simulated. The simulation results show that both
the magnetic pressure and the thermal pressure exhibit a turbulent
spectrum with a Kolmogorov-like power law, and that in many regions of
the simulation domain they are anticorrelated. The computed wavelet
cross-coherence spectra of the magnetic pressure and the thermal
pressure, as well as their space series, indicate the existence of
multiscale PBSs, with the small PBSs being embedded in the large
ones. These multiscale PBSs are likely to be related to the highly
oblique-propagating slow-mode waves, as the traced multiscale PBS is
found to be traveling in a certain direction at a speed consistent
with that predicted theoretically for a slow-mode wave propagating in
the same direction.
Title: Multi-scale Pressure-balanced Structures and Influence of
Intermittency on the Perpendicular Spectrum in Three-dimensional
Magnetohydrodynamic Turbulence
Authors: Liping, Y.; He, J.; Li, S.; Marsch, E.; Tu, C. Y.; Wang,
L.; Zhang, L.; Wang, X.; Feng, X. S.
Bibcode: 2016AGUFMSH41A2524L
Altcode:
Observations of solar wind turbulence indicate the existence of
multi-scale pressure-balanced structures (PBSs) in the solar wind. In
this work, we conduct a numerical simulation to investigate multi-scale
PBSs and Influence of Intermittency on the Perpendicular Spectrum in
3D MHD turbulence. By the use of a higher order Godunov code Athena,
a driven compressible turbulence with an imposed uniform guide field
is simulated. The simulation results show that both the magnetic
pressure and the thermal pressure exhibit a turbulent spectrum with a
Kolmogorov-like power law, and that in many regions of the simulation
domain they are anti-correlated. The computed wavelet cross-coherence
spectrum of the magnetic pressure and the thermal pressure, as well as
their space series, indicate the existence of multi-scale PBSs, with
the small PBSs being embedded in the large ones. These multi-scale
PBSs are likely to be related with the highly oblique-propagating
slow-mode waves, as the traced multi-scale PBS is found to be traveling
in a certain direction at a speed consistent with that predicted
theoretically for a slow-mode wave propagating in the same direction. By
applying the wavelet technique to the magnetic field and flow velocity
in MHD turbulence, the relation between the intermittency and the
perpendicular power spectrum is also investigated. It is found that
when the intermittency is removed from the turbulence, the spectral
indices of the perpendicular power spectra of the field and velocity
change from about -1.5 to about -1.67.
Title: Spectral Anisotropy of Magnetic Field Fluctuations around
Ion Scales in the Fast Solar Wind
Authors: Wang, X.; Tu, C.; He, J.; Marsch, E.; Wang, L.
Bibcode: 2016AGUFMSH41A2520W
Altcode:
The power spectra of magnetic field at ion scales are significantly
influenced by waves and structures. In this work, we study the ΘRB
angle dependence of the contribution of waves on the spectral index
of the magnetic field. Wavelet technique is applied to the high
time-resolution magnetic field data from WIND spacecraft measurements
in the fast solar wind. It is found that around ion scales, the parallel
spectrum has a slope of -4.6±0.1 originally. When we remove the waves,
which correspond to the data points with relatively larger value of
magnetic helicity, the parallel spectrum gets shallower gradually
to -3.2±0.2. However, the perpendicular spectrum does not change
significantly during the wave-removal process, and its slope remains
-3.1±0.1. It means that when the waves are removed from the original
data, the spectral anisotropy gets weaker. This result may help us
understand the physical nature of the spectral anisotropy around the
ion scales.
Title: A Form of Nascent Solar Wind Outflow: Beam flow Generated by
Slow-Mode Waves Through Landau Resonance in the Weakly Collisional
Solar Atmosphere
Authors: He, J.; Ruan, W.; Zhang, L.; Vocks, C.; Marsch, E.; Tu, C.;
Peter, H.; Wang, L.
Bibcode: 2016AGUFMSH51B2589H
Altcode:
Quasi-periodic disturbances of emission-line parameters are frequently
observed in the corona. These disturbances propagate upward along
the magnetic field with speeds 100 km s-1. This phenomenon has been
interpreted as an evidence of the propagation of slow magnetosonic waves
or argued to be a signature of the intermittent outflows superposed
on the background plasmas. Here we aim to present a new "wave + flow"
model to interpret these observations. In our scenario, the oscillatory
motion is a slow mode wave, and the flow is associated with a beam
created by the wave-particle interaction owing to Landau resonance. With
the help of a kinetic model, we simulate the propagation of slow mode
waves and the generation of beam flows. We find that weak periodic beam
flows can be generated owing to Landau resonance in the solar corona,
and the phase with strongest blueward asymmetry is ahead of that with
strongest blueshift by about 1/4 period. We also find that the slow wave
damps to the level of 1/e after the transit time of two wave periods,
owing to Landau damping and Coulomb collisions in our simulation. This
damping time scale is similar to that resulting from thermal-conduction
in the MHD regime. The beam flow is weakened/attenuated with increasing
wave period and decreasing wave amplitude since Coulomb collision
becomes more and more dominant over the wave action. We suggest that
this "wave + flow" kinetic model provides an alternative explanation
for the observed quasi-periodic propagating perturbations in various
parameters in the solar corona. Therefore, the compressible slow-mode
waves, which can be driven and launched by magnetic reconnection,
vertical piston oscillation, or periodic horizontal squeezing, is
believed to play an important role in accelerating the plasmas into
a form of the solar wind nascent outflows.
Title: The anisotropy of sunward-propagating Alfvénic fluctuations
with power-law spectra observed by Wind spacecraft
Authors: Wu, H.; Wang, X.; Tu, C.; Wang, L.; He, J.; Tian, H.;
Marsch, E.
Bibcode: 2016AGUFMSH41A2515W
Altcode:
Sunward-propagating Alfvén fluctuations with power-law spectra
(UPAFs) were reported to be the clue on understanding nonlinear inverse
cascade. Here we present for the first time the spectral anisotropy of
UPAFs with respect to the global mean magnetic field direction using
Wind spacecraft measurements within 20 years from 1995 to 2005. It is
found that the spectral anisotropy of UPAFs is different from that
of the anti-sunward-propagating Alfvén fluctuations (DPAFs). By
determining the propagation direction of the fluctuations straightly
by strahl electron outflow rather than the measured magnetic field
data, we find 1190 UPAFs and 37663 DPAFs. UPAFs spectrum has an
average spectral index of -2.14 when θRB is close to 0° and -1.77
when θRB is close to 90°, while for DPAFs they are -2.00 and -1.64,
respectively. The power of UPAFs shows no obvious anisotropy, although
DPAFs do have larger power at larger θRB. Here we also present the
first probable picture for illustrating inverse cascade in the solar
wind. Those results reveal that UPAFs could help us interpret the
physical process as a new objective.
Title: Kinetic Simulation of Slow Magnetosonic Waves and
Quasi-Periodic Upflows in the Solar Corona
Authors: Ruan, Wenzhi; He, Jiansen; Zhang, Lei; Vocks, Christian;
Marsch, Eckart; Tu, Chuanyi; Peter, Hardi; Wang, Linghua
Bibcode: 2016ApJ...825...58R
Altcode: 2016arXiv160101823R
Quasi-periodic disturbances of emission-line parameters are frequently
observed in the corona. These disturbances propagate upward along
the magnetic field with speeds of ∼100 km s-1. This
phenomenon has been interpreted as evidence of the propagation of slow
magnetosonic waves or has been argued to be a signature of intermittent
outflows superposed on the background plasmas. Here we aim to present
a new “wave + flow” model to interpret these observations. In our
scenario, the oscillatory motion is a slow-mode wave, and the flow is
associated with a beam created by the wave-particle interaction owing
to Landau resonance. With the help of a kinetic model, we simulate the
propagation of slow-mode waves and the generation of beam flows. We find
that weak periodic beam flows can be generated by to Landau resonance in
the solar corona, and the phase with the strongest blueward asymmetry
is ahead of that with the strongest blueshift by about 1/4 period. We
also find that the slow wave damps to the level of 1/e after the
transit time of two wave periods, owing to Landau damping and Coulomb
collisions in our simulation. This damping timescale is similar to that
resulting from thermal conduction in the MHD regime. The beam flow is
weakened/attenuated with increasing wave period and decreasing wave
amplitude since Coulomb collisions become more and more dominant over
the wave action. We suggest that this “wave + flow” kinetic model
provides an alternative explanation for the observed quasi-periodic
propagating perturbations in various parameters in the solar corona.
Title: Influence of intermittency on the anisotropy of magnetic
structure functions of solar wind turbulence
Authors: Pei, Zhongtian; He, Jiansen; Wang, Xin; Tu, Chuanyi; Marsch,
Eckart; Wang, Linghua; Yan, Limei
Bibcode: 2016JGRA..121..911P
Altcode:
Intermittency appears to be connected with the spectral anisotropy
of solar wind turbulence. We use the Local Intermittency Measure
to identify and remove intermittency from the magnetic field data
measured by the Ulysses spacecraft in fast solar wind. Structure
functions are calculated based on the time sequences as obtained
before and after removing intermittency and arranged by time scale
(τ) and ΘRB (the angle between local mean magnetic field
B0 and radial direction R). Thus, the scaling exponent
(ξ(p, ΘRB)) of every structure function of order (p) is
obtained for different angles. Before removing intermittency, ξ(p,
ΘRB) shows a distinctive dependence on ΘRB:
from monofractal scaling law at ΘRB ~0° to multifractal
scaling law at ΘRB ~90°. In contrast after eliminating
the intermittency, ξ(p, ΘRB) is found to be more
monofractal for all ΘRB. The extended structure-function
model is applied to ξ(p, ΘRB), revealing differences of
its fitting parameters α (a proxy of the power spectral index) and
P1 (fragmentation fraction) for the cases with and without
intermittency. Parameter α shows an evident angular trend falling
from 1.9 to 1.6 for the case with intermittency but has a relatively
flat profile around 1.8 for the case without intermittency. Parameter
P1 rises from around 0.5 to above 0.8 with increasing
ΘRB for the intermittency case and is located between 0.5
and 0.8 for the case lacking intermittency. Therefore, we may infer that
it is the anisotropy of intermittency that causes the scaling anisotropy
of energy spectra and the unequal fragmentation of energy cascading.
Title: Scale-dependent Normalized Amplitude and Weak Spectral
Anisotropy of Magnetic Field Fluctuations in the Solar Wind Turbulence
Authors: Wang, Xin; Tu, Chuanyi; Marsch, Eckart; He, Jiansen; Wang,
Linghua
Bibcode: 2016ApJ...816...15W
Altcode:
Turbulence in the solar wind was recently reported to be anisotropic,
with the average power spectral index close to -2 when sampling parallel
to the local mean magnetic field B0 and close to -5/3
when sampling perpendicular to the local B0. This result
was widely considered to be observational evidence for the critical
balance theory (CBT), which is derived by making the assumption that the
turbulence strength is close to one. However, this basic assumption
has not yet been checked carefully with observational data. Here
we present for the first time the scale-dependent magnetic-field
fluctuation amplitude, which is normalized by the local B0
and evaluated for both parallel and perpendicular sampling directions,
using two 30-day intervals of Ulysses data. From our results, the
turbulence strength is evaluated as much less than one at small scales
in the parallel direction. An even stricter criterion is imposed when
selecting the wavelet coefficients for a given sampling direction, so
that the time stationarity of the local B0 is better ensured
during the local sampling interval. The spectral index for the parallel
direction is then found to be -1.75, whereas the spectral index in the
perpendicular direction remains close to -1.65. These two new results,
namely that the value of the turbulence strength is much less than one
in the parallel direction and that the angle dependence of the spectral
index is weak, cannot be explained by existing turbulence theories,
like CBT, and thus will require new theoretical considerations and
promote further observations of solar-wind turbulence.
Title: Spectral Anisotropy of Elsässer Variables in Two-dimensional
Wave-vector Space as Observed in the Fast Solar Wind Turbulence
Authors: Yan, Limei; He, Jiansen; Zhang, Lei; Tu, Chuanyi; Marsch,
Eckart; Chen, Christopher H. K.; Wang, Xin; Wang, Linghua; Wicks,
Robert T.
Bibcode: 2016ApJ...816L..24Y
Altcode: 2016arXiv160407760Y
Intensive studies have been conducted to understand the anisotropy
of solar wind turbulence. However, the anisotropy of Elsässer
variables (Z+/- ) in 2D wave-vector space has yet to
be investigated. Here we first verify the transformation based on
the projection-slice theorem between the power spectral density
PSD2(k\parallel ,k\perp ) and
the spatial correlation function CF2D(r\parallel
,r\perp ). Based on the application of the
transformation to the magnetic field and the particle measurements
from the WIND spacecraft, we investigate the spectral anisotropy of
Elsässer variables (Z+/- ), and the distribution of residual
energy ER, Alfvén ratio RA, and Elsässer
ratio RE in the (k\parallel ,k\perp
) space. The spectra PSD2D(k\parallel
,k\perp ) of B, V, and Zmajor
(the larger of Z+/- ) show a similar pattern that
PSD2D(k\parallel,k\perp) is mainly
distributed along a ridge inclined toward the k⊥ axis. This
is probably the signature of the oblique Alfvénic fluctuations
propagating outwardly. Unlike those of B, V, and Zmajor, the
spectrum PSD2D(k\parallel, k\perp )
of Zminor is distributed mainly along the k⊥
axis. Close to the k⊥ axis, | ER| becomes larger
while RA becomes smaller, suggesting that the dominance of
magnetic energy over kinetic energy becomes more significant at small
k∥. RE is larger at small k∥,
implying that PSD2D(k\parallel ,k\perp
) of Zminor is more concentrated along the
k⊥ direction as compared to that of Zmajor. The
residual energy condensate at small k∥ is consistent with
simulation results in which ER is spontaneously generated
by Alfvén wave interaction.
Title: Low-Amplitude Solar Wind Turbulence: Spectral Features
Authors: Wang, X.; Tu, C. Y.; He, J.; Marsch, E.; Wang, L.; Salem,
C. S.
Bibcode: 2015AGUFMSH33A2447W
Altcode:
Most previous turbulence observations in the solar wind were made for
large- and moderate-amplitude fluctuations, which include current sheets
and intermittent structures. Here we first present the spectral analysis
on the low-amplitude fluctuations that may be considered as nearly
stationary, and compare the results with those of moderate-amplitude
fluctuations which show intermittency. By using measurements from the
WIND spacecraft, we present spectral features as derived by the FFT
method from 6-minute time series of magnetic fluctuations with low
relative amplitudes of only 0.05 to 0.11. When comparing their spectra
with those of moderate-amplitude fluctuations (relative amplitude
of about 0.4), we find that for the low-amplitude fluctuations the
averaged spectral indices are -1.67 and -1.46, respectively for small
and large sampling angles, i.e. the angle between the Sun-to-Earth
radial direction and the mean magnetic field direction. However, for the
moderate-amplitude fluctuations, these two indices are -1.89 and -1.70,
respectively. This result of the moderate-amplitude fluctuations is
consistent with that of previous analyses, which by using the wavelet
technique revealed spectral anisotropy and yielded an index of -2 in
the parallel direction and -5/3 in the perpendicular direction. But the
result found here for the low-amplitude fluctuations was not reported
before, and thus will probably initiate new studies aiming to understand
better the turbulence nature of such low-amplitude fluctuations. Future
studies will help us to understand why the spectral anisotropy differs
for fluctuations of different amplitudes.
Title: A Numerical Investigation of the Recurrent High-speed Jets
as a Possibility of Solar Wind Origin
Authors: Yang, Liping; He, Jiansen; Peter, Hardi; Tu, Chuanyi; Zhang,
Lei; Marsch, Eckart; Wang, Linghua; Feng, Xueshang
Bibcode: 2015arXiv151201868Y
Altcode:
In the solar atmosphere, jets are prevalent and they are significant for
the mass and energy transport. Here we conduct numerical simulations to
investigate the mass and energy contributions of the recently observed
high-speed jets to the solar wind. With a one-dimensional hydrodynamic
solar wind model, the time-dependent pulses are imposed at the bottom
to simulate the jets. The simulation results show that without other
energy source, the injected plasmas are accelerated effectively to be
a transonic wind with a substantial mass flux. The rapid acceleration
occurs close to the Sun, and the resulting asymptotic speed, number
density at 0.3 AU, as well as mass flux normalized to 1 AU are
compatible with in situ observations. As a result of the high speed,
the imposed pulses generate a train of shocks traveling upward. By
tracing the motions of the injected plasma, it is found that these
shocks heat and accelerate the injected plasmas successively step by
step to push them upward and eventually allow them to escape. The
parametric studies show that increasing the speed of the imposed
pulses or their temperature gives a considerably faster, and hotter
solar wind, while increasing their number density or decreasing their
recurring period only bring a denser solar wind. These studies provide
a possibility that the ubiquitous high-speed jets are a substantial
mass and energy contributions to the solar wind.
Title: No evidence that solar wind turbulence can be described by
the critical balance theory
Authors: Wang, X.; Tu, C. Y.; Marsch, E.
Bibcode: 2015AGUFMSH33A2448W
Altcode:
The critical balance theory (GS, Goldreich and Sridhar, 1995)
in MHD turbulence seems now to be well accepted in the turbulence
community. During recent years, quite a few papers claimed to have
provided evidence in support of this theory by solar wind turbulence
observations. Here we present new data that result in a different
conclusion, namely that the previous observations cannot be considered
as evidence for the GS theory. It is based on the critical balance
assumption that the parallel Alfven wave propagation time equals
the perpendicular cascade time, k⊥v⊥=k//VA. Assuming that the
cascading energy flux does not change with scale, a spectral index
of -2 is obtained for the parallel power spectrum P(k//). To check
this theoretical prediction, small sampling angle (θRB) with the
mean magnetic field averaged at the local time and the local scale
is used for selecting the local power spectral densities (PSDs). We
recovered that the so averaged PSDs at different scales have a nearly
-2 slope. However, using 30 days of Ulysses data we discovered that
the critical balance assumption was invalid in the corresponding
data analysis. The values of δB/B0 corresponding to the selected
local PSDs are all found to be much smaller than the required value of
tan(θRB). Most of the observations with a small sampling angle may be
considered to be rather more perpendicular from the theoretical point
of view. We also found that the spectral index of the selected PSDs
depends on the selection criterion. If one guarantees constantly small
sampling angles in a local time period, the slope of the selected PSD
changes to -1.7. Thus our conclusion is that no evidence exists that
solar wind turbulence can be described by the GS theory. What is the
true origin of the spectral anisotropy of the solar wind turbulence
remains an important open question.
Title: Alfvénic fluctuations with power-law spectra propagating
sunward within the region from L1 to the Earth's bow shock
Authors: Wu, H.; Wang, X.; Wang, L.; Tu, C.; He, J.; Marsch, E.
Bibcode: 2015AGUFMSH33A2449W
Altcode:
According to several theories, the beam instability induced by
shock-accelerated ions can generate upstream-propagating Alfvén waves
(UPAWs) with a bump near 0.03 Hz in the power spectrum, while the
nonlinear wave-wave interaction favors an inverse cascade to create a
power-law spectrum. Here we present the first observational evidence for
the upstream-propagating Alfvénic fluctuations (UPAFs) with power-law
spectra by using measurements from the WIND spacecraft in year 1995. We
utilize a new criterion to identify the upstream-propagating Alfvénic
intervals: the propagation direction is opposite to that of solar
wind strahl electron outflow. Besides 35 UPAWs, we find 47 UPAFs with
power-law spectra, and ~47% of these UPAFs are associated with energetic
ion events (>30 keV). These UPAWs and UPAFs are mostly observed in
the slow solar wind. However, their occurrence rate and power behave
differently in dependence on the radial distance from the Earth. The
spectral indices of UPAFs are between -3 and -2. These power-law spectra
cannot be explained by the linear ion-beam instability. The results
provide new clues on understanding the dynamic equilibrium between
the non-linear inverse cascade and the linear ion-beam instability.
Title: Proton Heating in Solar Wind Compressible Turbulence with
Collisions between Counter-propagating Waves
Authors: He, Jiansen; Tu, Chuanyi; Marsch, Eckart; Chen, Christopher
H. K.; Wang, Linghua; Pei, Zhongtian; Zhang, Lei; Salem, Chadi S.;
Bale, Stuart D.
Bibcode: 2015ApJ...813L..30H
Altcode: 2015arXiv150904077H
Magnetohydronamic turbulence is believed to play a crucial role
in heating laboratory, space, and astrophysical plasmas. However,
the precise connection between the turbulent fluctuations and the
particle kinetics has not yet been established. Here we present
clear evidence of plasma turbulence heating based on diagnosed
wave features and proton velocity distributions from solar
wind measurements by the Wind spacecraft. For the first time,
we can report the simultaneous observation of counter-propagating
magnetohydrodynamic waves in the solar wind turbulence. As opposed to
the traditional paradigm with counter-propagating Alfvén waves (AWs),
anti-sunward AWs are encountered by sunward slow magnetosonic waves
(SMWs) in this new type of solar wind compressible turbulence. The
counter-propagating AWs and SWs correspond, respectively, to the
dominant and sub-dominant populations of the imbalanced Elsässer
variables. Nonlinear interactions between the AWs and SMWs are inferred
from the non-orthogonality between the possible oscillation direction
of one wave and the possible propagation direction of the other. The
associated protons are revealed to exhibit bi-directional asymmetric
beams in their velocity distributions: sunward beams appear in short,
narrow patterns and anti-sunward in broad extended tails. It is
suggested that multiple types of wave-particle interactions, i.e.,
cyclotron and Landau resonances with AWs and SMWs at kinetic scales, are
taking place to jointly heat the protons perpendicular and in parallel.
Title: The Spectral Features of Low-amplitude Magnetic Fluctuations
in the Solar Wind and Their Comparison with Moderate-amplitude
Fluctuations
Authors: Wang, Xin; Tu, Chuanyi; He, Jiansen; Marsch, Eckart; Wang,
Linghua; Salem, Chadi
Bibcode: 2015ApJ...810L..21W
Altcode:
The power-spectrum index of magnetic fluctuations is a crucial parameter
for the characterization of nonlinear interactions affecting the
solar wind turbulence. Most previous observations were made for large-
and moderate-amplitude magnetic fluctuations, which include current
sheets and intermittent structures. Here, by using measurements
from the WIND spacecraft, we present magnetic spectral features as
derived by the fast Fourier transform method from six-minute time
series of magnetic fluctuations with low relative amplitudes (δ
B/{B}0) of only 0.05-0.11. When comparing their spectra
with those of moderate-amplitude fluctuations (δ B/{B}0≈
0.4), we find that for the low-amplitude fluctuations the averaged
magnetic spectral indices are -1.67 and -1.46, respectively, for small
and large sampling angles, i.e., the angle between the Sun-to-Earth
radial direction and the mean magnetic field direction. However,
for the moderate-amplitude fluctuations, these two indices are
-1.89 and -1.70, respectively. This result of the moderate-amplitude
fluctuations is consistent with that of previous analyses, which, by
using the wavelet technique, revealed spectral anisotropy of magnetic
fluctuations and yielded an index of -2 in the parallel direction and
-5/3 in the perpendicular direction. However, the result found here for
the low-amplitude fluctuations has not been reported before, and thus
will probably initiate new studies aiming to better understand the
turbulent nature of such low-amplitude fluctuations. Future studies
will help us to understand why the spectral anisotropy differs for
fluctuations of different amplitudes.
Title: The Formation of Rotational Discontinuities in Compressive
Three-dimensional MHD Turbulence
Authors: Yang, Liping; Zhang, Lei; He, Jiansen; Tu, Chuanyi; Wang,
Linghua; Marsch, Eckart; Wang, Xin; Zhang, Shaohua; Feng, Xueshang
Bibcode: 2015ApJ...809..155Y
Altcode: 2015arXiv150405348Y
Measurements of solar wind turbulence reveal the ubiquity
of discontinuities. In this study we investigate how the
discontinuities, especially rotational discontinuities (RDs), are
formed in MHD turbulence. In a simulation of the decaying compressive
three-dimensional (3D) MHD turbulence with an imposed uniform background
magnetic field, we detect RDs with sharp field rotations and little
variations of magnetic field intensity, as well as mass density. At
the same time, in the de Hoffman-Teller frame, the plasma velocity
is nearly in agreement with the Alfvén speed, and is field-aligned
on both sides of the discontinuity. We take one of the identified
RDs to analyze its 3D structure and temporal evolution in detail. By
checking the magnetic field and plasma parameters, we find that the
identified RD evolves from the steepening of the Alfvén wave with
moderate amplitude, and that steepening is caused by the nonuniformity
of the Alfvén speed in the ambient turbulence.
Title: Parallel and perpendicular heating of solar wind protons by
kinetic waves as observed from the WIND spacecraft
Authors: He, Jiansen; Wang, Linghua; Tu, Chuanyi; Marsch, Eckart;
Zong, Qiugang
Bibcode: 2015shin.confE.133H
Altcode:
The magnetic fluctuations of fast solar wind streams in the transition
region between the inertial range and the sub-ion range are revealed
to probably consist of both quasi-parallel ion-cyclotron waves
and quasi-perpendicular kinetic Alfven waves. The proton kinetics
corresponding to the two-component fluctuations has not yet been
analyzed observationally. Here we show new evidence of wave-particle
interactions by combining the diagnosis of wave modes with the
analysis of particle kinetics on the basis of measurements from the
WIND spacecraft with a high cadence of about 3 s. Solar wind protons
appear to be highly dynamic in their velocity distribution consisting
of varying anisotropic core and beam components. The basic scenario
of solar wind proton heating through wave-particle interaction is
suggested to be the following. Left-handed cyclotron resonance occurs
continuously, and is evident from the observed proton core velocity
distribution and the concurrent quasi-parallel left-handed Alfvén
cyclotron waves. Landau and right-handed cyclotron resonances are
persistent and indicated by the observed drifting anisotropic beam
and the simultaneous quasi-perpendicular right-handed kinetic Alfvén
waves in a general sense. The persistence of non-gyrotropic proton
distributions may be the result of interaction between particles
and waves near and beyond the proton gyro-frequency, e.g., oblique
whistler waves.
Title: Observations of counter-propagating waves and associated
proton kinetics in the solar wind turbulence
Authors: He, Jiansen; Tu, Chuanyi; Marsch, Eckart; Wang, Linghua;
Chen, C. H. K.; Pei, Zhongtian; Zhang, Lei; Salem, Chadi; Bale, Stuart
Bibcode: 2015shin.confE.111H
Altcode:
Magnetohydronamic turbulence is believed to play a crucial role
in heating plasma in various contexts, like laboratory, space,
and astrophysics. However, the definite connection between the
turbulent fluctuations and the plasma thermo-kinetics has not yet
been established observationally. Here we present an evidence of
plasma turbulence heating based on the diagnosed wave features and
reconstructed proton velocity distributions from the solar wind
measurements by the WIND spacecraft. We report an observation
of counter-propagating magnetohydrodynamic waves, anti-sunward
Alfven waves and sunward slow magnetosonic waves, in the solar wind
turbulence. The associated proton kinetics is revealed to behave in
response to the counter-propagating waves, exhibiting bi-directional
asymmetric beams in the velocity distributions: sunward beams appearing
in short and narrow shapes and anti-sunward broad extended tails. It is
suggested that wave-particle interactions, e.g., Landau and cyclotron
resonances with slow magnetosonic wave and Alfven waves at kinetic
scales, are invoked in the turbulence to heat the plasma parallel and
perpendicularly. The scenario of collisions between counter-propagating
Alfven waves and slow magnetosonic waves is helpful to understand the
wave coupling, energy cascading and dissipation in the compressible
magnetohydrodynamic turbulence.
Title: Sunward Propagating Alfvén Waves in Association with Sunward
Drifting Proton Beams in the Solar Wind
Authors: He, Jiansen; Pei, Zhongtian; Wang, Linghua; Tu, Chuanyi;
Marsch, Eckart; Zhang, Lei; Salem, Chadi
Bibcode: 2015ApJ...805..176H
Altcode:
Using measurements from the WIND spacecraft, here we report the
observation of sunward propagating Alfvén waves (AWs) in solar wind
that is magnetically disconnected from the Earth's bow shock. In
the sunward magnetic field sector, we find a period lasting for more
than three days in which there existed (during most time intervals)
a negative correlation between the flow velocity and magnetic
field fluctuations, thus indicating that the related AWs are mainly
propagating sunward. Simultaneous observations of counter-streaming
suprathermal electrons suggest that these sunward AWs may not simply
be due to the deflection of an open magnetic field line. Moreover,
no interplanetary coronal mass ejection appears to be associated with
the counter-streaming suprathermal electrons. As the scale goes from
the magnetohydrodynamic down to the ion kinetic regime, the wave
vector of magnetic fluctuations usually becomes more orthogonal
to the mean magnetic field direction, and the fluctuations become
increasingly compressible, which are both features consistent with
quasi-perpendicular kinetic AWs. However, in the case studied here,
we find clear signatures of quasi-parallel sunward propagating
ion-cyclotron waves. Concurrently, the solar wind proton velocity
distribution reveals a sunward field-aligned beam that drifts at about
the local Alfvén speed. This beam is found to run in the opposite
direction of the normally observed (anti-sunward) proton beam, and is
apparently associated with sunward propagating Alfvén/ion-cyclotron
waves. The results and conclusions of this study enrich our knowledge
of solar wind turbulence and foster our understanding of proton heating
and acceleration within a complex magnetic field geometry.
Title: The upstream-propagating Alfvénic fluctuations with power
law spectra in the upstream region of the Earth's bow shock
Authors: Wang, Xin; Tu, Chuanyi; Wang, Linghua; He, Jiansen; Marsch,
Eckart
Bibcode: 2015GeoRL..42.3654W
Altcode:
Based on theories, the beam instability induced by shock-accelerated
ions can generate upstream-propagating Alfvén waves (UPAWs)
with a power spectral bump near 0.03 Hz, while the nonlinear
wave-wave interaction favors an inverse cascade to create a power
law spectrum. Here we present the first observational evidence for
the upstream-propagating Alfvénic fluctuations (UPAFs) with power law
spectra. We utilize a new criterion to identify the upstream-propagating
Alfvénic intervals: the propagation direction is opposite to that of
solar wind strahl electron outflow. Besides 35 UPAWs, we find 47 UPAFs
with power law spectra, and ∼47% of these UPAFs are associated with
energetic ion events (>30 keV). These UPAWs and UPAFs are mostly
observed in the slow solar wind. However, their occurrence rate and
power behave differently in dependence on the radial distance from the
Earth. These results provide new clues on understanding the dynamic
equilibrium between the nonlinear inverse cascade and the linear ion
beam instability.
Title: Kinetic Slow Mode in the Solar Wind and Its Possible Role in
Turbulence Dissipation and Ion Heating
Authors: Narita, Yasuhito; Marsch, Eckart
Bibcode: 2015ApJ...805...24N
Altcode:
The solar wind is permeated by various kinds of fluctuations ranging
broadly in scales from those of the solar corona and inner heliosphere
down to the local ion and electron plasma kinetic scales. The
question of what rules the dissipation of magnetohydrodynamic (MHD)
turbulence in the solar wind has not conclusively been answered,
but remains a key research topic of space plasma physics. Here we
propose a new dissipation mechanism, the proton Landau damping of
the quasi-perpendicular kinetic slow mode. This mode is linked to
the oblique MHD slow mode, yet has shorter wavelengths going down to
the proton inertial length. The kinetic slow mode can be separated
from the kinetic Alfvén mode by the Alfvén resonance parameter,
the proton Landau resonance parameter, the magnetic compressibility,
and the electric field polarization. Numerical simulations and in
situ observations indicate that the MHD turbulent cascade preferably
transfers energy in the direction perpendicular to the background
magnetic field. If the kinetic slow mode is also generated and
replenished by the energy cascade, this mode can lead to both
perpendicular and parallel heating of the protons.
Title: Occurrence Rates and Heating Effects of Tangential and
Rotational Discontinuities as Obtained from Three-dimensional
Simulation of Magnetohydrodynamic Turbulence
Authors: Zhang, Lei; He, Jiansen; Tu, Chuanyi; Yang, Liping; Wang,
Xin; Marsch, Eckart; Wang, Linghua
Bibcode: 2015ApJ...804L..43Z
Altcode: 2015arXiv150305410Z
MHD discontinuities are ubiquitous in the solar wind and are often found
at the origin of turbulence intermittency. They may also play a key
role in the turbulence dissipation and heating of the solar wind. The
tangential discontinuities (TDs) and rotational discontinuities (RDs)
are the two most important types of discontinuities. Recently, the
connection between turbulence intermittency and proton thermodynamics
has been observationally investigated. Here, we present numerical
results from a three-dimensional MHD simulation with pressure anisotropy
and we define new methods for identifying and distinguishing TDs and
RDs. Three statistical results obtained for the relative occurrence
rates and heating effects are highlighted: (1) RDs tend to take up the
majority of the discontinuities along with time; (2) the thermal states
embedding TDs tend to be associated with extreme plasma parameters
or instabilities while RDs do not; (3) TDs have a higher average
T as well as perpendicular temperature {{T}\bot }. The
simulation shows that TDs and RDs evolve and contribute to solar wind
heating differently. These results will improve our understanding of
the mechanisms that generate discontinuities and cause plasma heating.
Title: Evidence of Landau and Cyclotron Resonance between Protons
and Kinetic Waves in Solar Wind Turbulence
Authors: He, Jiansen; Wang, Linghua; Tu, Chuanyi; Marsch, Eckart;
Zong, Qiugang
Bibcode: 2015ApJ...800L..31H
Altcode:
The wave-particle interaction processes occurring in the solar wind
provide crucial information to understand the wave dissipation and
simultaneous particle heating in plasma turbulence. One requires
observations of both wave fluctuations and particle kinetics near
the dissipation range, which have, however, not yet been analyzed
simultaneously. Here we show new evidence of wave-particle interactions
by combining the diagnosis of wave modes with the analysis of particle
kinetics on the basis of measurements from the WIND spacecraft
with a high cadence of about 3 s. Solar wind protons appear to be
highly dynamic in their velocity distribution consisting of varying
anisotropic core and beam components. The basic scenario of solar wind
proton heating through wave-particle interaction is suggested to be
the following. Left-handed cyclotron resonance occurs continuously,
and is evident from the observed proton core velocity distribution
and the concurrent quasi-parallel left-handed Alfvén cyclotron
waves. Landau and right-handed cyclotron resonances are persistent and
indicated by the observed drifting anisotropic beam and the simultaneous
quasi-perpendicular right-handed kinetic Alfvén waves in a general
sense. The persistence of non-gyrotropic proton distributions may cast
new light on the nature of the interaction between particles and waves
near and beyond the proton gyro-frequency.
Title: The anisotropic nature of the intermittent turbulence spectra
in the solar wind
Authors: Wang, X.; Tu, C. Y.; He, J.; Marsch, E.; Wang, L.
Bibcode: 2014AGUFMSH51A4139W
Altcode:
Intermittent structures in the solar wind turbulence carry important
information on the turbulent non-linear dynamics and the heating
effect of solar wind. However, the intermittency on small scales was
rarely studied. Here we present a study of intermittent structures
in the small timescale from 5 seconds to 100 seconds using the data
from WIND observations in the high-speed solar wind. We find that the
intermittent structures dominate the magnetic field turbulence in the
scale. In this scale, the power spectrum of the intermittent structures
with PVI >1 appears to be anisotropic with regards to the angle
θRB between the direction of the local background magnetic field
and the radial direction. The anisotropic nature in this sub-range
is presented as follows: 1. At the scale τ=12s, the power spectral
density of the intermittency withθRB = 84o-90o is one time larger
than that of the intermittency with θRB =0o-6o; 2. The power spectrum
becomes flatter as θRB increases, with an index of -2 at θRB =0o-6o
and index of -1.6 at θRB =84o-90o; 3. The most probable value of
the proton temperature distribution of the intermittent structures
is 2.1×105K, higher than the most probable proton temperature for
the general solar wind (1.9×105K); 4. The most probable value of the
proton temperature of the intermittency with θRB =70o-90o is 2.2×105K,
clearly higher than that with θRB =0o-20o, which is 2.0×105K. We
think that the intermittent structures in the scale from 5s to 100s and
their anisotropic spectral nature could be related to the non-linear
interactions in the MHD turbulence, and they may have some influence
on the dissipation processes in the solar wind turbulence.
Title: Observation of Counter Propagating Alfven Waves with
Perpendicular Polarizations and the Associated Proton Kinetics
Authors: He, J.; Pei, Z. T.; Wang, L.; Tu, C. Y.; Marsch, E.; Yao, S.
Bibcode: 2014AGUFMSH53C..07H
Altcode:
It is believed that MHD turbulence cascading is mainly caused by
the collisions between Alfven waves, which propagate oppositely and
are polarized perpendicularly to each other. Nonlinear interaction
will vanish if the counter-propagating Alfven waves have their
polarization aligned with each other. However, the Alfven waves
satisfying these collision criteria have not yet been found in the
solar wind observations. Here we report the existence of Alfven
waves with opposite propagation and non-aligned polarization in the
solar wind. In one case of anti-sunward magnetic sector, with RTN as
the coordinates, the magnetic fluctuations in T-component (BT) are
anti-correlated with the velocity fluctuations in T-component (VT),
while BR and BN fluctuations are in positive correlation with VR and VN
fluctuations, respectively. These features suggest a possible nonlinear
interaction between outward propagating Alfven wave with polarization
in T-direction and inward propagating Alfven wave with polarization in
R&N-directions. Moreover, the associated proton kinetics shows the
existence of field-aligned sunward beam rather than anti-sunward beam,
which may indicate a parallel Landau heating by sunward kinetic Alfven
waves. A statistical study including more cases is also conducted.
Title: The isotropic nature of the background turbulence spectra in
the solar wind
Authors: Wang, X.; Tu, C. Y.; He, J.; Marsch, E.; Wang, L.
Bibcode: 2014AGUFMSH51A4149W
Altcode:
At the high-frequency end of the inertial range, the solar wind
turbulence power spectrum was recently found to be anisotropic with
respect to the direction of local magnetic field, as an evidence for
the presence of a "critical balance" style turbulence cascade. However,
we find that the spectral anisotropy seems to result from intermittent
structures. The following two independent studies corroborate
this statement by showing that the power spectra of the background
turbulence, in which there are no intermittent structures, have an
isotropic nature. In Study 1, we remove the wavelet coefficients of
the local intermittency with large partial variance increment (PVI),
and find the spectral indices of the magnetic field are 1.63±0.02,
independent of the angle θRB between the direction of the local
background magnetic field and the radial direction. In Study 2,
we make a statistical study on the magnetic field spectral indices
obtained by using Fast Fourier Transform on 40 time series, in which
no intermittent structures appear. We find that for the time series
with 0o<θRB <6o, the probability distribution of the observed
spectral indices peaks at -1.7, while the -2 index predicted by the
"critical balance" theory rarely appears. For the time series with 84
o <θRB <90 o, the probability distribution of the indices peaks
at -1.5. Considering the uncertainty of the statistics, these results
show that the background-turbulence spectra are nearly isotropic with
respect to θRB, which may be consistent with some explanations based
on hydrodynamic turbulence theory.
Title: A Survey of Velocity Distributions of Solar Wind Ions :
ACE/SWICS observations
Authors: Berger, L.; Marsch, E.; Wimmer-Schweingruber, R. F.
Bibcode: 2014AGUFMSH33A4135B
Altcode:
The state of solar wind ions is generally described by a small set
of state variables. In detail these aretotal density (or flux),
center of mass (or bulk) velocity, and temperature. These variables
are obtainedfrom measured velocity distributions either by fitting a
Maxwell-Boltzmann distribution or by calculatingthe zeroth, first,
and second order moments of the distribution. Obviously the first
approach requires athermalized distribution to yield meaningful results,
while the second approach is universally valid.However, in both cases
the shape of the distribution can not be reproduced by the derived
parameters.From observations of solar wind protons and alpha particles
it is known that the assumption of a thermalized distribution is not
valid, at least for the majority of observations. For heavy solar
wind ions most observationsare severely limited by statistics and do
not even allow to distinguish whether the distribution is thermal
or not.This often insufficient characterization of the solar wind
VDF severely limits the information which can beobtained for more
detailed studies, especially about microscopic kinetic physics and
the associatedwave-particle interactions. These naturally yield
deviations from Maxwell-Boltzmann distributions.To address this
problem we have analyzed ten years worth of data from the Solar Wind
Ion Composition Spectrometer (SWICS)and the Magnetometer (MAG) on the
Advanced Composition Explorer (ACE). From our analysis we obtained
reduced 1D velocity spectra in 12 minute cadence for some 40 solar
wind ions, from protons and alpha particles up to iron.Using the
magnetic field vector information we were able to study periods where
the reduced 1D spectra representthe parallel and perpendicular shape
of the velocity distributions. We present our results and discussthem
in the aforementioned context.
Title: Generation of temperature anisotropy for alpha particle
velocity distributions in solar wind at 0.3 AU: Vlasov simulations
and Helios observations
Authors: Perrone, D.; Bourouaine, S.; Valentini, F.; Marsch, E.;
Veltri, P.
Bibcode: 2014JGRA..119.2400P
Altcode:
Solar wind "in situ" measurements from the Helios spacecraft in regions
of the Heliosphere close to the Sun (∼0.3 AU), at which typical
values of the proton plasma beta are observed to be lower than unity,
show that the alpha particle distribution functions depart from the
equilibrium Maxwellian configuration, displaying significant elongations
in the direction perpendicular to the background magnetic field. In
the present work, we made use of multi-ion hybrid Vlasov-Maxwell
simulations to provide theoretical support and interpretation to the
empirical evidences above. Our numerical results show that, at variance
with the case of βp≃1 discussed in Perrone et al. (2011),
for βp=0.1 the turbulent cascade in the direction parallel
to the ambient magnetic field is not efficient in transferring energy
toward scales shorter than the proton inertial length. Moreover,
our numerical analysis provides new insights for the theoretical
interpretation of the empirical evidences obtained from the Helios
spacecraft, concerning the generation of temperature anisotropy in
the particle velocity distributions.
Title: The Influence of Intermittency on the Spectral Anisotropy of
Solar Wind Turbulence
Authors: Wang, Xin; Tu, Chuanyi; He, Jiansen; Marsch, Eckart; Wang,
Linghua
Bibcode: 2014ApJ...783L...9W
Altcode:
The relation between the intermittency and the anisotropy of the power
spectrum in the solar wind turbulence is studied by applying the wavelet
technique to the magnetic field and flow velocity data measured by the
WIND spacecraft. It is found that when the intermittency is removed from
the turbulence, the spectral indices of the power spectra of the field
and velocity turn out to be independent of the angle θRB
between the direction of the local scale-dependent background magnetic
field and the heliocentric direction. The spectral index becomes -1.63
± 0.02 for magnetic field fluctuations and -1.56 ± 0.02 for velocity
fluctuations. These results may suggest that the recently found spectral
anisotropy of solar wind power spectra in the inertial range could
result from turbulence intermittency. As a consequence, a new concept is
here proposed of an intermittency-associated sub-range of the inertial
domain adjacent to the dissipation range. Since spectral anisotropy
was previously explained as evidence for the presence of a "critical
balance" type turbulent cascade, and also for the existence of kinetic
Alfvén waves, this new finding may stimulate fresh thoughts on how to
analyze and interpret solar wind turbulence and the associated heating.
Title: Regulation of Ion Drifts and Anisotropies by Parametrically
Unstable Finite-amplitude Alfvén-cyclotron Waves in the Fast
Solar Wind
Authors: Maneva, Y. G.; Araneda, J. A.; Marsch, E.
Bibcode: 2014ApJ...783..139M
Altcode:
We study the preferential heating and differential acceleration of
minor ions by dissipation of ion-acoustic waves (IAWs) generated
by parametric instabilities of a finite-amplitude monochromatic
Alfvén-cyclotron pump wave. We consider the associated kinetic
effects of Landau damping and nonlinear pitch-angle scattering of
protons and α particles in the tenuous plasma of coronal holes
and the fast solar wind. Various data collected by Wind spacecraft
show signatures for a local transverse heating of the minor ions,
presumably by Alfvén-cyclotron wave dissipation, and an unexpected
parallel heating by a so far unknown mechanism. Here, we present the
results from a set of 1.5 dimensional hybrid simulations in search for a
plausible explanation for the observed field-aligned kinetic features in
the fast solar wind minor ions. We investigate the origin and regulation
of ion relative drifts and temperature anisotropies in low plasma β,
fast solar wind conditions. Depending on their initial drifts, both ion
species can heat up not only transversely through cyclotron resonance
and non-resonant wave-particle interactions, but also strongly in the
parallel direction by Landau damping of the daughter IAWs. We discuss
the dependence of the relative ion drifts and temperature anisotropies
on the plasma β of the individual species and we describe the effect
of the pump wave amplitude on the ion heating and acceleration.
Title: Small-scale Pressure-balanced Structures Driven by Mirror-mode
Waves in the Solar Wind
Authors: Yao, Shuo; He, J. -S.; Tu, C. -Y.; Wang, L. -H.; Marsch, E.
Bibcode: 2013ApJ...776...94Y
Altcode:
Recently, small-scale pressure-balanced structures (PBSs) have been
studied with regard to their dependence on the direction of the local
mean magnetic field B0 . The present work continues these
studies by investigating the compressive wave mode forming small PBSs,
here for B0 quasi-perpendicular to the x-axis of Geocentric
Solar Ecliptic coordinates (GSE-x). All the data used were measured
by WIND in the quiet solar wind. From the distribution of PBSs on
the plane determined by the temporal scale and angle θxB
between the GSE-x and B0 , we notice that at θxB
= 115° the PBSs appear at temporal scales ranging from 700 s to 60
s. In the corresponding temporal segment, the correlations between the
plasma thermal pressure P th and the magnetic pressure P
B, as well as that between the proton density N p
and the magnetic field strength B, are investigated. In addition,
we use the proton velocity distribution functions to calculate the
proton temperatures T and T ∥. Minimum
Variance Analysis is applied to find the magnetic field minimum
variance vector BN . We also study the time variation of the
cross-helicity σc and the compressibility C p
and compare these with values from numerical predictions for the
mirror mode. In this way, we finally identify a short segment that
has T > T ∥, proton β ~= 1, both pairs
of P th-P B and N p-B showing
anti-correlation, and σc ≈ 0 with C p >
0. Although the examination of σc and C p
is not conclusive, it provides helpful additional information for
the wave mode identification. Additionally, BN is found to
be highly oblique to B0 . Thus, this work suggests that a
candidate mechanism for forming small-scale PBSs in the quiet solar
wind is due to mirror-mode waves.
Title: Small-scale Pressure-balanced Structures Driven by Oblique
Slow Mode Waves Measured in the Solar Wind
Authors: Yao, Shuo; He, J. -S.; Tu, C. -Y.; Wang, L. -H.; Marsch, E.
Bibcode: 2013ApJ...774...59Y
Altcode:
Recently, small-scale pressure-balanced structures (PBSs) were
identified in the solar wind, but their formation mechanism remains
unclear. This work aims to reveal the dependence of the properties of
small-scale PBSs on the background magnetic field (B 0)
direction and thus to corroborate the in situ mechanism that forms
them. We analyze the plasma and magnetic field data obtained by WIND in
the quiet solar wind at 1 AU. First, we use a developed moving-average
method to obtain B 0(s, t) for every temporal scale (s) at
each time moment (t). By wavelet cross-coherence analysis, we obtain the
correlation coefficients between the thermal pressure P th
and the magnetic pressure P B, distributing against the
temporal scale and the angle θxB between B 0(s,
t) and Geocentric Solar Ecliptic coordinates (GSE)-x. We note that the
angle coverage of a PBS decreases with shorter temporal scale, but the
occurrence of the PBSs is independent of θxB. Suspecting
that the isolated small PBSs are formed by compressive waves in situ,
we continue this study by testing the wave modes forming a small-scale
PBS with B 0(s, t) quasi-parallel to GSE-x. As a result,
we identify that the cross-helicity and the compressibility attain
values for a slow mode from theoretical calculations. The wave vector is
derived from minimum variance analysis. Besides, the proton temperatures
obey T < T ∥ derived from the velocity
distribution functions, excluding a mirror mode, which is the other
candidate for the formation of PBSs in situ. Thus, a small-scale PBS
is shown to be driven by oblique, slow-mode waves in the solar wind.
Title: On Intermittent Turbulence Heating of the Solar Wind:
Differences between Tangential and Rotational Discontinuities
Authors: Wang, Xin; Tu, Chuanyi; He, Jiansen; Marsch, Eckart; Wang,
Linghua
Bibcode: 2013ApJ...772L..14W
Altcode:
The intermittent structures in solar wind turbulence, studied by using
measurements from the WIND spacecraft, are identified as being mostly
rotational discontinuities (RDs) and rarely tangential discontinuities
(TDs) based on the technique described by Smith. Only TD-associated
current sheets (TCSs) are found to be accompanied with strong local
heating of the solar wind plasma. Statistical results show that the TCSs
have a distinct tendency to be associated with local enhancements of the
proton temperature, density, and plasma beta, and a local decrease of
magnetic field magnitude. Conversely, for RDs, our statistical results
do not reveal convincing heating effects. These results confirm the
notion that dissipation of solar wind turbulence can take place in
intermittent or locally isolated small-scale regions which correspond
to TCSs. The possibility of heating associated with RDs is discussed.
Title: Radial Evolution of the Wavevector Anisotropy of Solar Wind
Turbulence between 0.3 and 1 AU
Authors: He, Jiansen; Tu, Chuanyi; Marsch, Eckart; Bourouaine, Sofiane;
Pei, Zhongtian
Bibcode: 2013ApJ...773...72H
Altcode: 2013arXiv1302.0699H
We present observations of the power spectral anisotropy in the
wavevector space of solar wind turbulence and study how it evolves
in interplanetary space with increasing heliocentric distance. We use
magnetic field measurements from the Helios 2 spacecraft within 1 AU. To
derive the power spectral density (PSD) in the (k ∥,
k ) space based on single-satellite measurements is a
challenging task that had not been accomplished previously. Here, we
derive the spectrum PSD2D(k ∥, k_\bot) from
the spatial correlation function CF2D(r ∥,
r ) by a transformation according to the projection-slice
theorem. We find the so-constructed PSDs to be distributed in k space
mainly along a ridge that is more inclined toward the k_\bot axis than
the k_\parallel axis. Furthermore, this ridge of the distribution
is found to gradually get closer to the k_\bot axis as the outer
scale length of the turbulence becomes larger with increasing radial
distance. In the vicinity of the k_\parallel axis, a minor spectral
component appears that probably corresponds to quasi-parallel Alfvénic
fluctuations. Their relative contribution to the total spectral density
tends to decrease with radial distance. These findings suggest that
solar wind turbulence undergoes an anisotropic cascade transporting most
of its magnetic energy toward larger k_\bot and that the anisotropy in
the inertial range is radially developing further at scales that are
relatively far from the ever increasing outer scale. For the ion-scale
fluctuations, we speculate, from the radial evolution of the extended
oblique major component, a transition tendency from dominance by oblique
Alfvén/ion-cyclotron waves (<1 AU) to dominance by kinetic Alfvén
waves (>1 AU).
Title: SOLAR WIND 13: Proceedings of the Thirteenth International
Solar Wind Conference
Authors: Zank, Gary P.; Borovsky, Joe; Bruno, Roberto; Cirtain,
Jonathan; Cranmer, Steve; Elliott, Heather; Giacalone, Joe; Gonzalez,
Walter; Li, Gang; Marsch, Eckart; Moebius, Ebehard; Pogorelov, Nick;
Spann, Jim; Verkhoglyadova, Olga
Bibcode: 2013AIPC.1539.....Z
Altcode:
No abstract at ADS
Title: Injection of Plasma into the Nascent Solar Wind via
Reconnection Driven by Supergranular Advection
Authors: Yang, Liping; He, Jiansen; Peter, Hardi; Tu, Chuanyi; Chen,
Wenlei; Zhang, Lei; Marsch, Eckart; Wang, Linghua; Feng, Xueshang;
Yan, Limei
Bibcode: 2013ApJ...770....6Y
Altcode:
To understand the origin of the solar wind is one of the key research
topics in modern solar and heliospheric physics. Previous solar wind
models assumed that plasma flows outward along a steady magnetic
flux tube that reaches continuously from the photosphere through the
chromosphere into the corona. Inspired by more recent comprehensive
observations, Tu et al. suggested a new scenario for the origin
of the solar wind, in which it flows out in a magnetically open
coronal funnel and mass is provided to the funnel by small-scale side
loops. Thus mass is supplied by means of magnetic reconnection that
is driven by supergranular convection. To validate this scenario and
simulate the processes involved, a 2.5 dimensional (2.5D) numerical
MHD model is established in the present paper. In our simulation a
closed loop moves toward an open funnel, which has opposite polarity
and is located at the edge of a supergranulation cell, and magnetic
reconnection is triggered and continues while gradually opening up
one half of the closed loop. Its other half connects with the root
of the open funnel and forms a new closed loop which is submerged by
a reconnection plasma stream flowing downward. Thus we find that the
outflowing plasma in the newly reconnected funnel originates not only
from the upward reconnection flow but also from the high-pressure leg
of the originally closed loop. This implies an efficient supply of mass
from the dense loop to the dilute funnel. The mass flux of the outflow
released from the funnel considered in our study is calculated to be
appropriate for providing the mass flux at the coronal base of the
solar wind, though additional heating and acceleration mechanisms are
necessary to keep the velocity at the higher location. Our numerical
model demonstrates that in the funnel the mass for the solar wind may
be supplied from adjacent closed loops via magnetic reconnection as
well as directly from the footpoints of open funnels.
Title: Diffusion in velocity space of solar wind protons exposed to
parallel and oblique plasma waves
Authors: Marsch, Eckart; Tu, Chuanyi
Bibcode: 2013AIPC.1539..243M
Altcode:
The solar wind plasma is permeated by all kinds of waves with a broad
range of wavelengths and frequencies. Kinetic plasma waves in particular
can resonantly interact with the ions, a process that is described
within quasilinear theory as diffusion. The resulting effects on the
proton velocity distribution function (VDF) are discussed. Theoretical
predictions are compared with detailed measurements made in-situ by
Helios, and found to comply favourably with resonant diffusion of
the protons in the wave field. The shape of the proton VDF, showing
an anisotropic core and a beam at positive velocities in the solar
wind frame, can well be explained by scattering of the protons in
weakly compressive and obliquely propagating Alfvén/ion-cyclotron
and fast/slow-magnetoacoustic waves.
Title: Helios: Evolution of Distribution Functions 0.3–1 AU
Authors: Marsch, Eckart
Bibcode: 2013mspc.book...23M
Altcode:
No abstract at ADS
Title: Foreword
Authors: Burgess, David; Drake, James; Marsch, Eckart; Velli, Marco;
von Steiger, Rudolf; Zurbuchen, Thomas H.
Bibcode: 2013mspc.book....1B
Altcode:
No abstract at ADS
Title: Interactions of Alfvén-Cyclotron Waves with Ions in the
Solar Wind
Authors: Araneda, J. A.; Astudillo, H.; Marsch, E.
Bibcode: 2013mspc.book..361A
Altcode:
No abstract at ADS
Title: Multi-scale Physics in Coronal Heating and Solar Wind
Acceleration
Authors: Burgess, David; Drake, James; Marsch, Eckart; von Steiger,
Rudolf; Velli, Marco; Zurbuchen, Thomas
Bibcode: 2013mspc.book.....B
Altcode:
No abstract at ADS
Title: Magnetic Correlation Lengths in the Turbulent Solar Wind
Authors: Ruiz, M. E.; Dasso, S.; Matthaeus, W. H.; Weygand, J. M.;
Marsch, E.
Bibcode: 2012AGUFMSH51B2233R
Altcode:
We analyze the evolution of the interplanetary magnetic field spatial
structure by examining the heliospheric autocorrelation functions (R)
based on "in situ" observations and using classical single-spacecraft
techniques. Correlation lengths (λ) derived from R can be viewed
as a measured of the integral scale of the turbulence. We focus on
how evolves the anisotropy of λ with respect to the aging of fluid
parcels traveling away from the Sun, and according to the anisotropy
of the measured λ, distinguishing mainly the values parallel (λ∥)
or perpendicular (λ⊥) to the direction of the local average magnetic
field B0. We find that close to the Sun, λ∥ < λ⊥, supporting a
slab-like spectral model, and a progressive isotropization of λ with
a trend to reach an inverted relation, while moving towards higher
heliodistances, supporting dynamical spectral transfer of energy. We
also present preliminary results on the probability distribution
functions (PDFs) of λ from an analysis at different heliodistances
from the Sun using observations from Helios, ACE and Ulysses. Advances
made to better characterize the nature of interplanetary fluctuations,
as those presented here, has significant implications in space and
astrophysical plasmas, including scattering and transport of charged
energetic particles, and theories of MHD turbulence.
Title: The angle distribution of the small scale pressure-balanced
structures in the solar wind
Authors: Yao, S.; Tu, C.; He, J.; Marsch, E.
Bibcode: 2012AGUFMSH51B2234Y
Altcode:
This work is aimed to reveal the features of the previously detected
small scale pressure-balanced structures (PBSs) in the solar wind. In
detail, the distribution of the small scale PBSs on the local magnetic
field directions is studied for both the fast solar wind and the
slow solar wind in this work. First the wavelet coherence spectrum
analysis is applied to show the correlation between the electron
density (Ne) and the magnetic field strength (B) measurements. Second,
the angle Theta_vB, which is between the local mean magnetic field
vector of the studied temporal scale and the sun-earth direction,
is calculated for each time point. Finally, the wavelet coherence
spectrum is reconstructed according to the angle Theta_vB rather
than the time. From the reconstructed wavelet coherence spectrum, the
distribution of the anti-correlation between Ne and B on Theta_vB is
identified, and thus the distribution of the possible small scale PBSs
on local B direction could be obtained, as the anti-correlation between
Ne and B indicates the existence of PBSs. This work analyzed 12 quiet
solar wind periods measured by the WIND satellite at 1 AU, in which 7 of
them are fast solar wind periods and 5 are slow solar wind periods. It
is identified that the anti-correlation between Ne and B covers a wide
range of angles in the single temporal period of the slow solar wind,
while it concentrates on a distinct angle for each temporal period in
the fast solar wind. Moreover, the PBSs identified in the slow solar
wind are of larger scale than their counterparts in the fast solar
wind. Besides, the positive correlation between Ne and B is observed
in the fast solar wind periods in this work. This means that the fast
magnetosonic waves appear in the studied fast solar wind. Above all,
we would summarize our work as below. First the small scale PBSs exist
in both the fast and slow solar wind, but the PBSs in the slow solar
wind are larger and more than that in the fast solar wind. Second,
the angle distributions of the small scale PBSs counted for all the
periods of either the fast or the slow solar wind indicate that the
PBSs are isotropic on the Theta_vB. Third, the PBSs in the fast solar
wind stay simultaneously with the fast magnetosonic waves. To explain
these results, we tend to suggest that they may be formed from the
different origin of the fast and slow solar wind.
Title: Helios: Evolution of Distribution Functions 0.3-1 AU
Authors: Marsch, Eckart
Bibcode: 2012SSRv..172...23M
Altcode: 2010SSRv..tmp..196M; 2010SSRv..tmp..188M
The radial evolution of the velocity distribution functions of the
protons, electrons and ions, as they were measured during the Helios
mission in the solar wind between 0.3 and 1.0 AU, is discussed and
analysed. Emphasis is placed on the detailed plasma measurements,
and on the non-thermal features of the particles and the kinetic
processes they undergo in the expanding solar wind. As the plasma
is multi-component and nonuniform, complexity prevails and the
observed distributions exhibit, owing to their low number densities,
significant deviations from local thermal equilibrium, and reveal
such suprathermal particles as the strahl electrons, as well as ion
beams and temperature anisotropies. The distribution functions still
carry imprints of their solar boundaries that are reflected locally,
but also have ample free energy driving in situ plasma instabilities
which are triggered and modulated by wave-particle interactions. The
ion temperatures and their anisotropies and the non-adiabatic radial
evolution of the solar wind internal energy are discussed in detail.
Title: Interactions of Alfvén-Cyclotron Waves with Ions in the
Solar Wind
Authors: Araneda, J. A.; Astudillo, H.; Marsch, E.
Bibcode: 2012SSRv..172..361A
Altcode: 2011SSRv..tmp..203A; 2011SSRv..tmp...44A; 2011SSRv..tmp...59A;
2011SSRv..tmp..362A; 2011SSRv..tmp..127A
The results of a study of linear and nonlinear properties of
Alfvén-cyclotron waves propagating along a background magnetic
field in collisionless plasmas are presented. Kinetic theory and
one-dimensional hybrid simulations are used to identify the complete
family of growing and damped wave modes and the connection with the
spontaneous fluctuations in plasmas. The self-consistent reshaping of
initially cold ion velocity distributions, the simultaneous generation
of beam protons, and the preferential heating and acceleration of alpha
particles are shown to occur by the same mechanism: ion trapping and
induced pitch-angle scattering by parametrically driven ion acoustic
waves.
Title: Foreword
Authors: Burgess, David; Drake, James; Marsch, Eckart; Velli, Marco;
von Steiger, Rudolf; Zurbuchen, Thomas H.
Bibcode: 2012SSRv..172....1B
Altcode: 2012SSRv..tmp...85B
No abstract at ADS
Title: Spectroscopic observations of propagating disturbances in a
polar coronal hole: evidence of slow magneto-acoustic waves
Authors: Gupta, G. R.; Teriaca, L.; Marsch, E.; Solanki, S. K.;
Banerjee, D.
Bibcode: 2012A&A...546A..93G
Altcode: 2012arXiv1209.3524G
Aims: We focus on detecting and studying quasi-periodic
propagating features that have been interpreted in terms of both slow
magneto-acoustic waves and of high-speed upflows.
Methods:
We analyzed long-duration spectroscopic observations of the on-disk
part of the south polar coronal hole taken on 1997 February 25 by
the SUMER spectrometer onboard SOHO. We calibrated the velocity
with respect to the off-limb region and obtained time-distance maps
in intensity, Doppler velocity, and line width. We also performed a
cross-correlation analysis on different time series curves at different
latitudes. We studied average spectral line profiles at the roots
of propagating disturbances and along the propagating ridges, and
performed a red-blue asymmetry analysis.
Results: We clearly
find propagating disturbances in intensity and Doppler velocity with
a projected propagation speed of about 60 ± 4.8 km s-1
and a periodicity of ≈14.5 min. To our knowledge, this is the first
simultaneous detection of propagating disturbances in intensity as
well as in Doppler velocity in a coronal hole. During the propagation,
an intensity enhancement is associated with a blueshifted Doppler
velocity. These disturbances are clearly seen in intensity also
at higher latitudes (i.e., closer to the limb), while disturbances
in Doppler velocity become faint there. The spectral line profiles
averaged along the propagating ridges are found to be symmetric, to
be well fitted by a single Gaussian, and have no noticeable red-blue
asymmetry.
Conclusions: Based on our analysis, we interpret
these disturbances in terms of propagating slow magneto-acoustic waves.
Title: Parametric decay of oblique Alfvén waves in two-dimensional
hybrid simulations
Authors: Verscharen, D.; Marsch, E.; Motschmann, U.; Müller, J.
Bibcode: 2012PhRvE..86b7401V
Altcode: 2012arXiv1207.6144V
Certain types of plasma waves are known to become parametrically
unstable under specific plasma conditions, in which the pump wave
will decay into several daughter waves with different wavenumbers
and frequencies. In the past, the related plasma instabilities have
been treated analytically for various parameter regimes and by use of
various numerical methods, yet the oblique propagation with respect
to the background magnetic field has rarely been dealt with in two
dimensions, mainly because of the high computational demand. Here
we present a hybrid-simulation study of the parametric decay of a
moderately oblique Alfvén wave having elliptical polarization. It is
found that such a compressive wave can decay into waves with higher
and lower wavenumbers than the pump.
Title: Dynamical evolution of anisotropies of the solar wind magnetic
turbulent outer scale
Authors: Ruiz, M. E.; Dasso, S.; Matthaeus, W. H.; Marsch, E.; Weygand,
J. M.
Bibcode: 2012IAUS..286..164R
Altcode:
The evolution of the turbulent properties in the solar wind,
during the travel of the parcels of fluid from the Sun to the outer
heliosphere still has several unanswered questions. In this work,
we will present results of an study on the dynamical evolution of
turbulent magnetic fluctuations in the inner heliosphere. We focused
on the anisotropy of the turbulence integral scale, measured parallel
and perpendicular to the direction of the local mean magnetic field,
and study its evolution according to the aging of the plasma parcels
observed at different heliodistances. As diagnostic tool we employed
single-spacecraft correlation functions computed with observations
collected by Helios 1 & 2 probes over nearly one solar cycle. Our
results are consistent with driving modes with wave-vectors parallel
to the direction of the local mean magnetic field near the Sun, and a
progressive spectral transfer of energy to modes with perpendicular
wave-vectors. Advances made in this direction, as those presented
here, will contribute to our understanding of the magnetohydrodynamical
turbulence and Alfvénic-wave activity for this system, and will provide
a quantitative input for models of charged solar and galactic energetic
particles propagation and diffusion throughout the inner heliosphere.
Title: Spectroscopic Observations of Propagating Disturbances in
Polar Coronal Hole
Authors: Gupta, Girjesh R.; Marsch, Eckart; Solanki, Sami K.; Banerjee,
Dipankar; Teriaca, Luca
Bibcode: 2012cosp...39..689G
Altcode: 2012cosp.meet..689G
We focus on long duration spectroscopic observations of the south
polar coronal hole taken on 1997 February 25 by the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer aboard SOHO. We
analyze the data in the on-disk part of the coronal hole to find any
signature of propagating waves or high speed up-flows. We find the
clear presence of propagating disturbances in intensity and Doppler
velocity with a projected propagation speed of about 60~km~s^{-1} and
a periodicity of ≈14.5~min. During the propagation, the intensity
enhancement is associated with a blue-shifted Doppler velocity. These
disturbances are clearly seen in intensity at higher latitudes
(i.e. closer to the limb), whereas disturbances in Doppler velocity
becomes faint there. We study average spectral line profiles at the
roots of these disturbances and along the propagating ridge. Based on
our analysis, we interpret these disturbances in terms of propagating
slow magneto-acoustic waves.
Title: Electron Transport in the Fast Solar Wind
Authors: Smith, H. M.; Marsch, E.; Helander, P.
Bibcode: 2012ApJ...753...31S
Altcode:
The electron velocity distribution function is studied in the extended
solar corona above coronal holes (i.e., the inner part of the fast
solar wind) from the highly collisional corona close to the Sun to the
weakly collisional regions farther out. The electron kinetic equation
is solved with a finite-element method in velocity space using a
linearized Fokker-Planck collision operator. The ion density and
temperature profiles are assumed to be known and the electric field and
electron temperature are determined self-consistently. The results show
quantitatively how much lower the electron heat flux and the thermal
force are than predicted by high-collisionality theory. The sensitivity
of the particle and heat fluxes to the assumed ion temperature profile
and the applied boundary condition at the boundary far from the Sun
is also studied.
Title: Proton energetics in the solar wind between 0.3 and 1 AU:
Helios reloaded
Authors: Hellinger, P.; Matteini, L.; Travnicek, P. M.; Stverak, S.;
Marsch, E.
Bibcode: 2012EGUGA..14.2879H
Altcode:
The proton thermal energetics in the solar wind between 0.3 and 1 AU
is re-investigated using the Helios 1 and 2 data. Heating and cooling
rates are evaluated for the slow and fast solar wind and compared
with estimates of the turbulent cascading energy. Possible influence
of the interaction between fast and slow solar wind streams on the
proton energetics is discussed.
Title: On Spectral Breaks in the Power Spectra of Magnetic
Fluctuations in Fast Solar Wind between 0.3 and 0.9 AU
Authors: Bourouaine, S.; Alexandrova, O.; Marsch, E.; Maksimovic, M.
Bibcode: 2012ApJ...749..102B
Altcode:
We analyze the radial variation of the power spectra of the magnetic
field from 0.3 to about 0.9 AU, using Helios 2 spacecraft measurements
in the fast solar wind. The time resolution of the magnetic field
data allows us to study the power spectra up to 2 Hz. Generally,
the corresponding spectral break frequency fb and the
Doppler-shifted frequencies, which are related to the proton gyroradius
and inertial scales, are close to a frequency f of about 0.5 Hz at a
distance of 1 AU from the Sun. However, studying the radial evolution
of the power spectra offers us the possibility to distinguish between
those scales. Recent Ulysses observations show that, while the proton
scales vary, fb stays nearly constant with the heliocentric
distance R. In our study we confirm that fb varies within
a small interval of [0.2, 0.4] Hz only, as R varies from 0.3 to 0.9
AU. Moreover, if we assume parallel propagating fluctuations (with
respect to the solar wind flow or background magnetic field), we can
show that none of the proton scales are coincident with the break
scale. If, however, we take into account the two-dimensional nature of
the turbulent fluctuations, then we can show that the spatial scale
corresponding to fb (R) does follow the proton inertial
scale, λ p (R), but not the proton gyroradius scale,
ρ p (R), as a function of heliocentric distance. These
observations indicate that the spectral break at the proton inertial
scale might be related to the Hall effect, or be controlled by the
ion-cyclotron damping of obliquely propagating fluctuations or the
formation of current sheets scaling like λ p , which could
be responsible for ion heating through magnetic reconnection.
Title: Reproduction of the Observed Two-component Magnetic Helicity
in Solar Wind Turbulence by a Superposition of Parallel and Oblique
Alfvén Waves
Authors: He, Jiansen; Tu, Chuanyi; Marsch, Eckart; Yao, Shuo
Bibcode: 2012ApJ...749...86H
Altcode:
The angular distribution of the normalized reduced magnetic helicity
density (σ r m ) in solar wind turbulence
reveals two components of distinct polarity in different angle
ranges. This kind of two-component σ r m may
indicate the possible wave modes and power spectral densities (PSDs)
of the turbulent fluctuations. Here we model the measured angular
distribution of σ r m by assuming a PSD
distribution for Alfvén fluctuations in wavevector space, and then
fit the model results to the observations by adjusting the pattern of
the PSD distribution. It is found that the two-component form of the
PSD, which has a major and minor component close to k and
kpar, respectively, seems to be responsible for the observed
two-component σ r m . On the other hand,
both an isotropic PSD and a PSD with only a single component bending
toward k fail to reproduce the observations. Moreover,
it is shown that the effect of gradual balance between outward and
inward wave-energy fluxes with decreasing spatial scale needs to be
considered in order to reproduce the observed diminishing of |σ
r m | at shorter scales. Therefore, we suggest
that the observed two-component σ r m in
the solar wind turbulence may be due to a superposition of Alfvén
waves with quasi-perpendicular (major part) and quasi-parallel (minor
part) propagation. The waves seem to become gradually balanced toward
shorter scales.
Title: Large-amplitude Alfvén Wave in Interplanetary Space: The
Wind Spacecraft Observations
Authors: Wang, Xin; He, Jiansen; Tu, Chuanyi; Marsch, Eckart; Zhang,
Lei; Chao, Jih-Kwin
Bibcode: 2012ApJ...746..147W
Altcode:
We present, for the first time, measurements of arc-polarized velocity
variations together with magnetic field variations associated with a
large-amplitude Alfvén wave as observed by the Wind satellite. The
module of the magnetic field variance is larger than the magnitude of
the average magnetic field, indicating the large amplitude of these
fluctuations. When converting to the deHoffman-Teller frame, we find
that the magnetic field and velocity vector components, in the plane
perpendicular to the minimum-variance direction of the magnetic field,
are arc-polarized, and their tips almost lie on the same circle. We also
find that the normalized cross helicity and Alfvén ratio of the wave
are both nearly equal to unity, a result which has not been reported in
previous studies at 1 AU. It is worthy to stress here that pure Alfvén
waves can also exist in the solar wind even near the Earth at 1 AU,
but not only near 0.3 AU. Further study could be done to help us know
more about the properties of pure Alfvén wave at 1 AU that could not be
figured out easily before because of the contaminations (e.g., Alfvén
waves propagating in different directions, magnetic structures, and
other compressional waves) on previously reported Alfvén wave cases.
Title: Kinetic cascade beyond magnetohydrodynamics of solar wind
turbulence in two-dimensional hybrid simulations
Authors: Verscharen, D.; Marsch, E.; Motschmann, U.; Müller, J.
Bibcode: 2012PhPl...19b2305V
Altcode: 2012arXiv1201.2784V
The nature of solar wind turbulence in the dissipation range at scales
much smaller than the large magnetohydrodynamic (MHD) scales remains
under debate. Here, a two-dimensional model based on the hybrid code
abbreviated as A.I.K.E.F. is presented, which treats massive ions as
particles obeying the kinetic Vlasov equation and massless electrons
as a neutralizing fluid. Up to a certain wavenumber in the MHD regime,
the numerical system is initialized by assuming a superposition of
isotropic Alfvén waves with amplitudes that follow the empirically
confirmed spectral law of Kolmogorov. Then, turbulence develops
and energy cascades into the dispersive spectral range, where also
dissipative effects occur. Under typical solar wind conditions, weak
turbulence develops as a superposition of normal modes in the kinetic
regime. Spectral analysis in the direction parallel to the background
magnetic field reveals a cascade of left-handed Alfvén/ion-cyclotron
waves up to wave vectors where their resonant absorption sets in,
as well as a continuing cascade of right-handed fast-mode and whistler
waves. Perpendicular to the background field, a broad turbulent spectrum
is found to be built up of fluctuations having a strong compressive
component. Ion-Bernstein waves seem to be possible normal modes in this
propagation direction for lower driving amplitudes. Also, signatures
of short-scale pressure-balanced structures (very oblique slow-mode
waves) are found.
Title: Do Oblique Alfvén/Ion-cyclotron or Fast-mode/Whistler Waves
Dominate the Dissipation of Solar Wind Turbulence near the Proton
Inertial Length?
Authors: He, Jiansen; Tu, Chuanyi; Marsch, Eckart; Yao, Shuo
Bibcode: 2012ApJ...745L...8H
Altcode:
To determine the wave modes prevailing in solar wind turbulence at
kinetic scales, we study the magnetic polarization of small-scale
fluctuations in the plane perpendicular to the data sampling direction
(namely, the solar wind flow direction, {V}_{SW}) and analyze its
orientation with respect to the local background magnetic field
{B}_{0,local}. As an example, we take only measurements made in an
outward magnetic sector. When {B}_{0,local} is quasi-perpendicular to
{V}_{SW}, we find that the small-scale magnetic-field fluctuations,
which have periods from about 1 to 3 s and are extracted from a
wavelet decomposition of the original time series, show a polarization
ellipse with right-handed orientation. This is consistent with a
positive reduced magnetic helicity, as previously reported. Moreover,
for the first time we find that the major axis of the ellipse is
perpendicular to {B}_{0,local}, a property that is characteristic
of an oblique Alfvén wave rather than oblique whistler wave. For
an oblique whistler wave, the major axis of the magnetic ellipse is
expected to be aligned with {B}_{0,local}, thus indicating significant
magnetic compressibility, and the polarization turns from right
to left handedness as the wave propagation angle (θkB)
increases toward 90°. Therefore, we conclude that the observation of
a right-handed polarization ellipse with orientation perpendicular to
{B}_{0,local} seems to indicate that oblique Alfvén/ion-cyclotron
waves rather than oblique fast-mode/whistler waves dominate in the
"dissipation" range near the break of solar wind turbulence spectra
occurring around the proton inertial length.
Title: Does the Kinetic Alfven Wave or Oblique Whistler Wave dominate
the Dissipation Range of Solar Wind Turbulence?
Authors: He, J.; Marsch, E.; Tu, C.; Wang, X.; Yao, S.; Tian, H.
Bibcode: 2011AGUFMSH42B..04H
Altcode:
Presently, there is an intense debate on which oblique wave mode is,
besides the parallel Alfven-cyclotron wave, responsible for further
energy cascading or damping in the dissipation range of solar wind
turbulence. From numerical simulation and dimensional analysis, the
power spectra in the dissipation range with a power law like k^(-7/3)
can be reproduced based on either the kinetic Alfven wave or whistler
wave. Here, we aim to show which one may be dominant in reality on
the basis of solar wind measurements by STEREO satellite. We extract
small-scale magnetic fluctuations in the dissipation range from
the time series by employing the wavelet decomposition method. We
then study two parameters (magnetic compressibility and magnetic
polarization) of the small-scale magnetic fluctuations in such time
intervals where the direction of the local mean magnetic field is nearly
orthogonal to the direction of the solar wind velocity. We find that
the magnetic compressibility in the dissipation range is less than
0.25, which is much smaller than the magnetic compressibility (~1.0)
of quasi-perpendicular whistler waves, but closer to the value of
kinetic Alfven waves. Moreover, we find that the small-scale magnetic
fluctuations seems to be elliptically polarized in the plane normal
to the solar wind velocity direction, and the major axis of the
polarization ellipse is perpendicular to local mean magnetic field
direction. This kind of observed magnetic polarization is consistent
with the characteristics of kinetic Alfven waves. Therefore, we may
conclude that, in the fast solar wind streams we have looked at,
oblique kinetic Alfven waves do exist and may play a role in the
dissipation range and for turbulence cascading and damping.
Title: Hybrid simulations of the two-dimensional cascade of weak
solar wind turbulence beyond MHD scales
Authors: Verscharen, D.; Marsch, E.; Motschmann, U. M.; Müller, J.
Bibcode: 2011AGUFMSH52A..01V
Altcode:
The nature of solar wind turbulence in the dissipation range beyond
the typical large MHD scales is still under debate. A two-dimensional
model is presented based on the hybrid code A.I.K.E.F., which treats
ions as particles following the Vlasov equation and electrons as a
massless neutralizing fluid. Up to a certain wavenumber in the MHD
regime, the system is initialized with a superposition of isotropic
Alfvén waves with amplitudes following the empirically confirmed
spectral power law of Kolmogorov. The turbulence then evolves and
cascades into the dispersive spectral range, where also dissipative
effects emerge. Under typical solar wind conditions, weak turbulence
develops as a superposition of normal modes in the kinetic regime. The
spectral analysis in the direction parallel to the background magnetic
field reveals a cascade of left-handed Alfvén/ion-cyclotron waves
until the resonant absorption sets in and a right-handed fast/whistler
component. Perpendicular to the background field, a broad turbulent
spectrum is found built up of fluctuations with a strong compressive
component. Ion-Bernstein waves are possible normal modes in this
direction of propagation.
Title: Heating and Cooling of Protons in the Fast Solar Wind Between
0.3 and 1 AU: Helios Reloaded
Authors: Hellinger, P.; Matteini, L.; Stverak, S.; Travnicek, P. M.;
Marsch, E.
Bibcode: 2011AGUFMSH44B..01H
Altcode:
The proton thermal energetics in the fast solar wind between 0.3 and 1
AU is re-investigated using the Helios 1 and 2 data. Closer to the Sun,
it is estimated that, to account for the observed radial profiles of the
proton parallel and perpendicular temperature, non-negligible parallel
cooling and perpendicular heating are necessary. Around 1 AU heating
is needed in both directions. We also calculate the corresponding
rates and find that in total significant interplanetary heating is
necessary, in agreement with previous results. The possible influence
that deceleration of fast solar wind streams due to interaction with
slow ones has on the proton thermodynamics is evaluated.
Title: Energetics of solar wind electrons from Helios observations
Authors: Stverak, S.; Hellinger, P.; Travnicek, P. M.; Marsch, E.
Bibcode: 2011AGUFMSH33B2056S
Altcode:
The electron heat flux properties in the solar wind have been examined
based on Helios 1 and 2 in situ observations. The data set covers
the heliocentric radial range between 0.3 and 1.0 AU in the ecliptic
plane only. Understanding the fundamental heat transport and energy
dissipation in the expanding solar wind plasmas requires a detail
analysis of electron velocity distribution functions (eVDF) and
particularly their non-thermal features. Our study is based on a full
three component (core-halo-strahl) analytical modelling of measured 2D
eVDF and consequent analysis of derived eVDF moments. First we provide
radial profiles of observed characteristics (densities, temperature,
heat flux) for each of the eVDF component. These profiles are further
used to analyse corresponding heating/cooling rates in the expanding
solar wind, separately for the slow and fast solar wind streams.
Title: Radial evolution of the power spectral density of the magnetic
field from 0.3 to 0.9 AU
Authors: Bourouaine, S.; Alexandrova, O.; Marsch, E.; Maksimovic, M.
Bibcode: 2011AGUFMSH43C1958B
Altcode:
The power spectra of the magnetic field from 0.29 to about 0.9 AU
using Helios 2 spacecraft measurements is analyzed. It is known that,
at distance of 1 AU from the Sun, the scale corresponding to the break
frequency fb and the Doppler- shifted proton scales are
all close to f ∼ 0.5Hz. However, the radial evolution of the power
spectra studied here gives the possibility to distinguish between
those scales. In this study we show that fb varies in a tiny
interval [0.2,0.4] along the distance R. Also, when we assume parallel
propagating (with respect to the solar wind flow or to the background
magnetic field) fluctuations we find that none of the proton scales
is following the spectral break scale. However, taking into account
the 2-dimensional nature of turbulent fluctuations, we show that scale
corresponding to fb(R) follows λ p(R) and not
the fcp(R) or ρ p(R) along the heliocentric
distance. These observations may indicate that the spectral break at
the high frequency range might be controlled by the Hall effect or by
the onset of the ion dissipation due to 2D magnetic reconnection near
the ion skin depth scale.
Title: On the Nature of a Large-Amplitude Alfven Wave Measured by
the WIND Spacecraft
Authors: Wang, X.; Chao, J. K.; He, J.; Tu, C.; Marsch, E.; Zhang, L.
Bibcode: 2011AGUFMSH43C1957W
Altcode:
We present, for the first time, measurements of arc-polarized velocity
variations associated with a large-amplitude Alfven wave that was
observed by the WIND satellite. The trace of the magnetic field
variance within a period of 35 minutes is larger than the variance of
the average magnetic field. When moving into the deHoffman-Teller frame
(which was hardly ever used before in solar wind wave studies), we find
that the magnetic-field and velocity vector components in the plane
perpendicular to the minimum-variance direction of the magnetic field
are arc-polarized, and their tips lie on the same circle. We also find
that the normalized cross-helicity and Alfven ratio of the wave are both
nearly equal to unity, a result which has not been reported in previous
studies at 1 AU. The power spectrum for this pure large-amplitude
Alfven wave exhibits Kolmogorov's 5/3-law. To explain these results
requires new theoretical efforts and is worth further data analysis,
using the present methods in future studies of solar wind turbulence.
Title: Temperature anisotropy and differential streaming of solar
wind ions. Correlations with transverse fluctuations
Authors: Bourouaine, S.; Marsch, E.; Neubauer, F. M.
Bibcode: 2011A&A...536A..39B
Altcode: 2011arXiv1111.2724B
We study correlations of the temperature ratio (which is an indicator
for perpendicular ion heating) and the differential flow of the
alpha particles with the power of transverse fluctuations that have
wave numbers between 0.01 and 0.1 (normalized to kp
= 1/lp, where lp is the proton inertial
length). We found that both the normalized differential ion
speed, Vαp/VA (where VA
is the Alfvén speed) and the proton temperature anisotropy,
T⊥p/T∥p, increase when the relative wave
power is growing. Furthermore, if the normalized differential ion
speed stays below 0.5, the alpha-particle temperature anisotropy,
T⊥α/T∥α, correlates positively with
the relative power of the transverse fluctuations. However,
if Vαp/VA is higher than 0.6, then the
alpha-particle temperature anisotropy tends to become lower and attain
even values below unity despite the presence of transverse fluctuations
of relatively high amplitudes. Our findings appear to be consistent
with the expectations from kinetic theory for the resonant interaction
of the ions with Alfvén/ion-cyclotron waves and the resulting wave
dissipation.
Title: Velocity-space diffusion of solar wind protons in oblique
waves and weak turbulence
Authors: Marsch, E.; Bourouaine, S.
Bibcode: 2011AnGeo..29.2089M
Altcode:
The fast solar wind is permeated by all kinds of plasma waves
which have a broad range of wavelengths and occur on many different
scales. Kinetically, a plasma wave induces ion-wave interactions
which can within the quasi-linear theory be described as a diffusion
process. The impact this diffusion may have on the shape of the proton
velocity distribution function (VDF) is studied. We first analyse
theoretically some of the possible kinetic effects of the waves on the
ions. Then the model predictions are compared with the detailed in-situ
plasma measurements made by the Helios spacecraft on 14 April 1976 at
0.3 AU and found to comply favourably with resonant diffusion of protons
in obliquely propagating magnetohydrodynamic waves. In particular,
the shape at the edges of the VDFs at positive proton velocities in the
wind frame can be well explained by cyclotron-resonant diffusion of the
protons in oblique fast magnetoacoustic and Alfvén waves propagating
away from the Sun.
Title: Aging of anisotropy of solar wind magnetic fluctuations in
the inner heliosphere
Authors: Ruiz, M. E.; Dasso, S.; Matthaeus, W. H.; Marsch, E.; Weygand,
J. M.
Bibcode: 2011JGRA..11610102R
Altcode: 2011arXiv1110.4012R
We analyze the evolution of the interplanetary magnetic field spatial
structure by examining the inner heliospheric autocorrelation function,
using Helios 1 and Helios 2 in situ observations. We focus on the
evolution of the integral length scale (λ) anisotropy associated
with the turbulent magnetic fluctuations, with respect to the aging
of fluid parcels traveling away from the Sun, and according to
whether the measured λ is principally parallel (λ∥)
or perpendicular (λ⊥) to the direction of a suitably
defined local ensemble average magnetic field B0. We analyze
a set of 1065 24-hour long intervals (covering full missions). For
each interval, we compute the magnetic autocorrelation function, using
classical single-spacecraft techniques, and estimate λ with help of
two different proxies for both Helios data sets. We find that close
to the Sun, λ∥ < λ⊥. This supports a
slab-like spectral model, where the population of fluctuations having
wave vector k parallel to B0 is much larger than the one with
k-vector perpendicular. A population favoring perpendicular k-vectors
would be considered quasi-two dimensional (2D). Moving toward 1 AU,
we find a progressive isotropization of λ and a trend to reach an
inverted abundance, consistent with the well-known result at 1 AU
that λ∥ > λ⊥, usually interpreted as
a dominant quasi-2D picture over the slab picture. Thus, our results
are consistent with driving modes having wave vectors parallel to
B0 near Sun, and a progressive dynamical spectral transfer
of energy to modes with perpendicular wave vectors as the solar wind
parcels age while moving from the Sun to 1 AU.
Title: Compressive high-frequency waves riding on an
Alfvén/ion-cyclotron wave in a multi-fluid plasma
Authors: Verscharen, Daniel; Marsch, Eckart
Bibcode: 2011JPlPh..77..693V
Altcode: 2011arXiv1103.2029V
In this paper, we study the weakly-compressive high-frequency
plasma waves which are superposed on a large-amplitude Alfvén
wave in a multi-fluid plasma consisting of protons, electrons,
and alpha particles. For these waves, the plasma environment is
inhomogenous due to the presence of the low-frequency Alfvén wave
with a large amplitude, a situation that may apply to space plasmas
such as the solar corona and solar wind. The dispersion relation
of the plasma waves is determined from a linear stability analysis
using a new eigenvalue method that is employed to solve the set of
differential wave equations which describe the propagation of plasma
waves along the direction of the constant component of the Alfvén
wave magnetic field. This approach also allows one to consider weak
compressive effects. In the presence of the background Alfvén wave,
the dispersion branches obtained differ significantly from the situation
of a uniform plasma. Due to compressibility, acoustic waves are excited
and couplings between various modes occur, and even an instability of
the compressive mode. In a kinetic treatment, these plasma waves would
be natural candidates for Landau-resonant wave-particle interactions,
and may thus via their damping lead to particle heating.
Title: Heating and cooling of protons in the fast solar wind between
0.3 and 1 AU: Helios revisited
Authors: Hellinger, Petr; Matteini, Lorenzo; Štverák, Štěpán;
Trávníček, Pavel M.; Marsch, Eckart
Bibcode: 2011JGRA..116.9105H
Altcode:
The proton thermal energetics in the fast solar wind between 0.3 and 1
AU is reinvestigated using the Helios 1 and 2 data. Closer to the Sun,
it is estimated that, to account for the observed radial profiles of the
proton parallel and perpendicular temperature, nonnegligible parallel
cooling and perpendicular heating are necessary. Around 1 AU heating
is needed in both directions. We also calculate the corresponding
rates and find that in total significant interplanetary heating is
necessary, in agreement with previous results. The possible influence
that deceleration of fast solar wind streams due to interaction with
slow ones has on the proton thermodynamics is evaluated.
Title: Interplanetary shock wave extent in the inner heliosphere as
observed by multiple spacecraft
Authors: de Lucas, A.; Schwenn, R.; dal Lago, A.; Marsch, E.; Clúa
de Gonzalez, A. L.
Bibcode: 2011JASTP..73.1281D
Altcode:
For over an entire solar cycle, from the end of 1974 until the
beginning of 1986, the twin Helios spacecraft explored the inner
heliosphere. These in situ, high-resolution plasma and magnetic
field measurements covered heliocentric distances between 0.3 and 1
AU from the Sun and are of particular interest to studies of space
weather phenomena. During this period the two spacecraft detected
395 ICME-driven shocks and these waves were found to be driven
by interplanetary coronal mass ejections (ICMEs). Based on these
multi-spacecraft measurements, which include a third vantage point
with the observations from ISEE-3/IMP-8, the longitudinal extent of the
shock waves were measured in the inner heliosphere. It was found that
shock waves have about a 50% chance to be observed by two different
locations separated by 90°. In practice, one can expect with about a
50% chance that the shock driven by a limb coronal mass ejections (CMEs)
will hit the Earth, considering the expansion in longitude of shock
waves driven by their associated ICMEs. For a larger separation the
uncertainty increases, as only a few cases could be observed. With the
absence of simultaneous solar disk observations one can then no longer
unequivocally identify the shock waves observed at each spacecraft.
Title: On nonlinear Alfvén-cyclotron waves in multi-species plasma
Authors: Marsch, Eckart; Verscharen, Daniel
Bibcode: 2011JPlPh..77..385M
Altcode: 2011arXiv1101.1060M
Large-amplitude Alfvén waves are ubiquitous in space plasmas and
a main component of magnetohydrodynamic (MHD) turbulence in the
heliosphere. As pump waves, they are prone to parametric instability by
which they can generate cyclotron and acoustic daughter waves. Here,
we revisit a related process within the framework of the multi-fluid
equations for a plasma consisting of many species. The nonlinear
coupling of the Alfvén wave to acoustic waves is studied, and a set
of compressive and coupled-wave equations for the transverse magnetic
field and longitudinal electric field is derived for waves propagating
along the mean-field direction. It turns out that slightly compressive
Alfvén waves exert, through induced gyro-radius and kinetic-energy
modulations, an electromotive force on the particles in association
with a longitudinal electric field, which has a potential that is
given by the gradient of the transverse kinetic energy of the particles
gyrating about the mean field. This in turn drives electric fluctuations
(sound and ion-acoustic waves) along the mean magnetic field, which
can nonlinearly react back on the transverse magnetic field. Mutually
coupled Alfvén-cyclotron-acoustic waves are thus excited, a nonlinear
process that can drive a cascade of wave energy in the plasma, and may
generate compressive microturbulence. These driven electric fluctuations
might have consequences for the dissipation of an MHD turbulence and,
thus, for the heating and acceleration of particles in the solar wind.
Title: Two-dimensional correlation functions for density and magnetic
field fluctuations in magnetosheath turbulence measured by the
Cluster spacecraft
Authors: He, J. -S.; Marsch, E.; Tu, C. -Y.; Zong, Q. -G.; Yao, S.;
Tian, H.
Bibcode: 2011JGRA..116.6207H
Altcode:
Knowledge of multidimensional correlation functions is crucial for
understanding the anisotropy of turbulence. The two-dimensional (2-D)
spatial correlation functions (SCFs) obtained in previous studies
of space plasma turbulence were restricted to large-length scales
and covered a limited angular domain of the two-point separation
vector with respect to the mean magnetic field. Here we aim to
derive 2-D SCFs with smaller-length scale and nearly full angular
distribution for the fluctuations of the number density and magnetic
field in magnetosheath turbulence. We use the Cluster four-spacecraft
measurements of the fluctuations with respect to a temporally and
spatially varying background magnetic field to construct the 2-D
SCFs. We find that the correlation function of the density fluctuations
shows a pattern similar to that of the magnetic field fluctuations,
both of which appear to be composed of two populations, whereby the
major population extends along the coordinate parallel to mean magnetic
field (S$\parallel$) and the minor one deviates toward the
perpendicular coordinate (S$\perp$). This pattern of 2-D SCFs
implies that the energy of magnetosheath turbulence seems to cascade,
in the inertial range close to the ion scale, mostly transverse to the
background magnetic field and meanwhile partly along the field (i.e.,
k$\perp$ $\gg$ k$\parallel$).
Title: Apparent temperature anisotropies due to wave activity in
the solar wind
Authors: Verscharen, D.; Marsch, E.
Bibcode: 2011AnGeo..29..909V
Altcode: 2011arXiv1106.5878V
The fast solar wind is a collisionless plasma permeated by plasma
waves on many different scales. A plasma wave represents the natural
interplay between the periodic changes of the electromagnetic field and
the associated coherent motions of the plasma particles. In this paper,
a model velocity distribution function is derived for a plasma in a
single, coherent, large-amplitude wave. This model allows one to study
the kinetic effects of wave motions on particle distributions. They
are by in-situ spacecraft measured by counting, over a certain sampling
time, the particles coming from various directions and having different
energies. We compare our results with the measurements by the Helios
spacecraft, and thus find that by assuming high wave activity we are
able to explain key observed features of the measured distributions
within the framework of our model. We also address the recent
discussions on nonresonant wave-particle interactions and apparent
heating. The applied time-averaging procedure leads to an apparent
ion temperature anisotropy which is connected but not identical to
the intrinsic temperature of the underlying distribution function.
Title: Possible Evidence of Alfvén-cyclotron Waves in the Angle
Distribution of Magnetic Helicity of Solar Wind Turbulence
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Yao, Shuo; Tian, Hui
Bibcode: 2011ApJ...731...85H
Altcode:
The fluctuating magnetic helicity is considered an important parameter
in diagnosing the characteristic modes of solar wind turbulence. Among
them is the Alfvén-cyclotron wave, which is probably responsible for
the solar wind plasma heating, but has not yet been identified from
the magnetic helicity of solar wind turbulence. Here, we present the
possible signatures of Alfvén-cyclotron waves in the distribution
of magnetic helicity as a function of θVB, which is
the angle between the solar wind velocity and local mean magnetic
field. We use magnetic field data from the STEREO spacecraft to
calculate the θVB distribution of the normalized reduced
fluctuating magnetic helicity σm. We find a dominant
negative σm for 1 s < p < 4 s (p is time period)
and for θVB < 30° in the solar wind outward magnetic
sector, and a dominant positive σm for 0.4 s < p
< 4 s and for θVB>150° in the solar wind inward
magnetic sector. These features of σm appearing around the
Doppler-shifted ion-cyclotron frequencies may be consistent with the
existence of Alfvén-cyclotron waves among the outward propagating
fluctuations. Moreover, right-handed polarized waves at larger
propagation angles, which might be kinetic Alfvén waves or whistler
waves, have also been identified on the basis of the σm
features in the angular range 40° < θVB < 140°. Our
findings suggest that Alfvén-cyclotron waves (together with other
wave modes) play a prominent role in turbulence cascading and plasma
heating of the solar wind.
Title: Multi-scale Anti-correlation Between Electron Density and
Magnetic Field Strength in the Solar Wind
Authors: Yao, Shuo; He, J. -S.; Marsch, E.; Tu, C. -Y.; Pedersen,
A.; Rème, H.; Trotignon, J. G.
Bibcode: 2011ApJ...728..146Y
Altcode:
This work focuses on the relation between the electron density and
the magnetic field strength in the solar wind, and aims to reveal its
compressive nature and to determine the level of compressibility. For
this purpose, we choose a period of quiet solar wind data obtained
at 1 AU by the Cluster C1 satellite. The electron density is derived
with a sampling time as high as 0.2 s from the spacecraft-potential
measurements made by the Electric Field and Waves instrument. We use the
wavelet cross-coherence method to analyze the correlation between the
electron density and the magnetic field strength on various scales. We
find a dominant anti-correlation between them at different timescales
ranging from 1000 s down to 10 s, a result which has never been
reported before. This may indicate the existence of pressure-balanced
structures (PBSs) with different sizes in the solar wind. The small
(mini) PBSs appear to be embedded in the large PBSs, without affecting
the pressure balance between the large structures. Thus, a nesting of
these possible multi-scale PBSs is found. Moreover, we find for the
first time that the relative fluctuation spectra of both the electron
number density and the magnetic field strength look almost the same
in the range from 0.01 Hz to 2.5 Hz, implying a similar cascading for
these two types of fluctuations. Probable formation mechanisms for
the multi-scale possible PBSs are discussed. The results of our work
are believed to be helpful for understanding the compressive nature
of solar wind turbulence as well as the connections between the solar
wind streams and their coronal sources.
Title: A novel technique to measure intensity fluctuations in EUV
images and to detect coronal sound waves nearby active regions
Authors: Stenborg, G.; Marsch, E.; Vourlidas, A.; Howard, R.;
Baldwin, K.
Bibcode: 2011A&A...526A..58S
Altcode:
Context. In the past years, evidence for the existence of outward-moving
(Doppler blue-shifted) plasma and slow-mode magneto-acoustic propagating
waves in various magnetic field structures (loops in particular) in
the solar corona has been found in ultraviolet images and spectra. Yet
their origin and possible connection to and importance for the mass and
energy supply to the corona and solar wind is still unclear. There has
been increasing interest in this problem thanks to the high-resolution
observations available from the extreme ultraviolet (EUV) imagers on
the Solar TErrestrial RElationships Observatory (STEREO) and the EUV
spectrometer on the Hinode mission.
Aims: Flows and waves exist
in the corona, and their signatures appear in EUV imaging observations
but are extremely difficult to analyse quantitatively because of their
weak intensity. Hence, such information is currently available mostly
from spectroscopic observations that are restricted in their spatial
and temporal coverage. To understand the nature and origin of these
fluctuations, imaging observations are essential. Here, we present
measurements of the speed of intensity fluctuations observed along
apparently open field lines with the Extreme UltraViolet Imagers (EUVI)
onboard the STEREO mission. One aim of our paper is to demonstrate that
we can make reliable kinematic measurements from these EUV images,
thereby complementing and extending the spectroscopic measurements
and opening up the full corona for such an analysis. Another aim is to
examine the assumptions that lead to flow versus wave interpretation
for these fluctuations.
Methods: We have developed a novel
image-processing method by fusing well established techniques for
the kinematic analysis of coronal mass ejections (CME) with standard
wavelet analysis. The power of our method lies with its ability
to recover weak intensity fluctuations along individual magnetic
structures at any orientation , anywhere within the full solar disk ,
and using standard synoptic observing sequences (cadence <3 min)
without the need for special observation plans.
Results: Using
information from both EUVI imagers, we obtained wave phase speeds
with values on the order of 60-90 km s-1, compatible with
those obtained by other previous measurements. Moreover, we studied the
periodicity of the observed fluctuations and established a predominance
of a 16-min period, and other periods that seem to be multiples of
an underlying 8-min period.
Conclusions: The validation of our
analysis technique opens up new possibilities for the study of coronal
flows and waves, by extending it to the full disk and to a larger
number of coronal structures than has been possible previously. It
opens up a new scientific capability for the EUV observations from
the recently launched Solar Dynamics Observatory. Here we clearly
establish the ubiquitous existence of sound waves which continuously
propagate along apparently open magnetic field lines. Movies 1
and 2 (Figs. 12 and 13) are only available in electronic form at http://www.aanda.org
Title: On the Relative Speed and Temperature Ratio of Solar Wind
Alpha Particles and Protons: Collisions Versus Wave Effects
Authors: Bourouaine, Sofiane; Marsch, Eckart; Neubauer, Fritz M.
Bibcode: 2011ApJ...728L...3B
Altcode:
We study the relative flow speed and the temperature ratio of alpha
particles and protons and their connections to the helium ion abundance,
the collisional age, and the power of transverse fluctuations within
the inertial range. It is found that the alpha-to-proton temperature
ratio, T α/Tp , anti-correlates with the helium
ion abundance. Despite a relatively high collisional age and small wave
power, the ratio T α/Tp can reach comparatively
high values (even above 2) whenever the helium ion abundance is below
about 0.02. In contrast, the differential speed of alpha particles
with respect to protons is correlated with the total wave power and
anti-correlated with the collisional age. Ultimately, the individual
heating of each ion species is positively correlated with the total
wave power. Our findings suggest that a high-friction collision could
be efficient in reducing the differential speed between alpha particles
and protons, but appears not to be sufficient to equalize the alpha and
proton temperatures, i.e., to make T α ~= Tp
. This is a hint that the local wave heating process is acting on a
timescale shorter than the collision time.
Title: The coronal convection
Authors: Curdt, W.; Tian, H.; Marsch, E.
Bibcode: 2011CEAB...35..187C
Altcode: 2011arXiv1101.2365C
We study the hydrogen Lyman emission in various solar features -- now
including Ly-α observations free from geocoronal absorption -- and
investigate statistically the imprint of flows and of the magnetic field
on the line profile and radiance distribution. As a new result, we found
that in Ly-α rasters locations with higher opacity cluster in the cell
interior, while the network has a trend to flatter profiles. Even deeper
self reversals and larger peak distances were found in coronal hole
spectra. We also compare simultaneous Ly-α and Ly-β profiles. There
is an obvious correspondence between asymmetry and redshift for both
lines, but, most surprisingly, the asymmetries of Ly-α and Ly-β
are opposite. We conclude that in both cases downflows determine
the line profile, in case of Ly-α by absorption and in the case of
Ly-β by emission. Our results show that the magnetically structured
atmosphere plays a dominating role in the line formation and indicate
the presence of a persisting downflow at both footpoints of closed
loops. We claim that this is the manifestation of a fundamental mass
transportation process, which Foukal back in 1978 introduced as the
'coronal convection'.
Title: On the interactions of transverse ion-cyclotron waves with
ions in solar wind plasma
Authors: Bourouaine, S.; Marsch, E.; Neubauer, F. M.
Bibcode: 2010AGUFMSH43D..05B
Altcode:
We show the evidence of the ion-cyclotron dissipation mechanism in
solar wind plasma using Helios data. From our statistical analysis
we found that the wave power of high-frequency transverse waves
(having frequencies between 0.01 and 1 normalized to the proton
gyrofrequency in the plasma frame) correlates with both, the proton
temperature anisotropy, T⊥}/T{∥ , and the
normalized differential speed, V{α p}/VA,
between alpha particles and protons. Furthermore, when this speed stays
below 0.5, then the alpha-particle temperature anisotropy correlates
positively with the relative power of the transverse waves. However,
if V{α p}/VA is larger than 0.6, then the
alpha-particle temperature anisotropy tends to decrease towards values
below unity, despite the presence of transverse waves with relatively
large amplitudes. For small relative wave amplitude, it is found
that alpha particles can even be heated more strongly than protons
when the alpha-to-electron density ratio nearly or below 0.01. Our
findings are in good agreement with predictions of kinetic theory for
the resonant interaction of ions with Alfvén-cyclotron waves and for
the resulting wave dissipation. Therefore, the solar wind turbulence
may lead to the presence of parallel (or quasi-parallel) transverse
high-frequency waves, e.g, Alfvén-cylcotron waves.
Title: Evolution of the electron heat flux in the expanding solar
wind: Helios observations
Authors: Stverak, S.; Travnicek, P. M.; Hellinger, P.; Marsch, E.
Bibcode: 2010AGUFMSH11B1665S
Altcode:
Electron velocity distribution functions (eVDFs) observed in the solar
wind exhibit significant deviations from Maxwellian properties. In
particular, a considerable skewness, the so-called strahl population,
is typically present along the local magnetic field at supra-thermal
energies. Supra-thermal electrons, building up the non-thermal strahl
tail of the eVDF, carry a substantial part of the heat flux in the solar
wind. Understanding the fundamental heat transport and dissipation in
the expanding solar wind plasmas therefore requires a detail analysis
of eVDF properties and kinetic treatment of observed phenomena. Here
we present a large survey of electron heat flux properties as observed
between 0.3 and 1 AU by the Helios I&II spacecraft. The study is
based on a full analytical modeling of measured 2D eVDFs and consequent
analysis of derived eVDF moments. Particularly we examine electron heat
flux properties and their evolution along the solar wind expansion with
respect to local electron temperature and temperature gradient. In
addition we compare our findings with theoretical approaches of heat
transport in plasma environments and related mechanisms.
Title: Aging of solar wind magnetic and velocity fluctuations from
observations in the inner heliosphere
Authors: Ruiz, M. E.; Dasso, S.; Matthaeus, W. H.; Weygand, J. M.;
Marsch, E.
Bibcode: 2010AGUFMSH41B1783R
Altcode:
The heliosphere is a natural laboratory to study several aspects of
Magnetohydrodynamic (MHD) turbulence. MHD fluctuations are ubiquitous
in the solar wind (SW) and 'in situ' observations of plasma properties
and magnetic field are one of the keys to unveil the secrets of MHD
turbulence. In the interplanetary medium, MHD scale fluctuations
are usually anisotropic, and these fluctuations frequently present
different properties in regions of quasi-stationary SW with different
bulk plasma parameters, or in regions associated with the presence
of transients (e.g., magnetic clouds). It is known that the spatial
structure of magnetic and velocity correlation functions evolves in
the inner heliosphere. This evolution in terms of the aging of plasma
parcels, as observed by the spacecrafts Helios 1-2, is the subject of
the work presented here. Particular interest is put on the evolution
of anisotropies in the integral length scale. Results are consistent
with driving modes with wavevectors parallel to the direction of the
local mean magnetic field near Sun, and a progressive spectral transfer
of energy to modes with perpendicular wavevectors. Advances made in
this direction, as those presented here, will be usefull to refine
models used to describe the propagation and diffusion of charged solar
and galactic energetic particles in the inner heliosphere, and will
contribute to understand the MHD Alfvenic wave activity for this system.
Title: Existence of Alfvén-cyclotron waves in solar wind turbulence
as identified from the angular distribution of magnetic helicity
Authors: He, J.; Marsch, E.; Tu, C.; Yao, S.; Tian, H.
Bibcode: 2010AGUFMSH43D..07H
Altcode:
The fluctuating magnetic helicity is a helpful mean for diagnosing
the wave characteristics in solar wind turbulence. However, the
signature of the Alfvén-cyclotron wave has not yet been revealed
from magnetic helicity, due to the limitations of the methods used
previously. We propose a new method to study the magnetic helicity,
σ_m, which is now considered as a function not only of the frequency
(f) but also the angle (Θ_VB) between the solar wind velocity
and local mean magnetic field B_0. We apply this method to STEREO
measurements of solar wind turbulence in both the magnetic-field
outward sectors and inward sectors. As a result, we find the following
remarkable features of the σ_m distributions. In outward sectors,
σ_m<0 for f∈[0.1,1.0]Hz and Θ_VB<30, and σ_m>0 for
f∈[0.1,1.0]Hz and 30<Θ_VB<150. In inward sectors, σ_m>0
for f∈[0.1,1.0]Hz and Θ_VB>150, and σ_m<0 for f∈[0.1,1.0]Hz
and 30<Θ_VB<150. These new findings indicate the existence of
Alfvén-cyclotron waves propagating quasi-parallel or anti-parallel
to B_0, besides the possible existence of kinetic-Alfvén or whistler
waves propagating obliquely to B_0. Therefore, we suggest that the
Alfvén-cyclotron wave, together with other wave modes, plays a crucial
role in turbulence cascading and heating of the solar wind.
Title: Turbulence in the Solar Atmosphere and Solar Wind
Authors: Petrosyan, A.; Balogh, A.; Goldstein, M. L.; Léorat, J.;
Marsch, E.; Petrovay, K.; Roberts, B.; von Steiger, R.; Vial, J. C.
Bibcode: 2010SSRv..156..135P
Altcode: 2010SSRv..tmp..117P
The objective of this review article is to critically analyze turbulence
and its role in the solar atmosphere and solar wind, as well as to
provide a tutorial overview of topics worth clarification. Although
turbulence is a ubiquitous phenomenon in the sun and its heliosphere,
many open questions exist concerning the physical mechanisms of
turbulence generation in solar environment. Also, the spatial and
temporal evolution of the turbulence in the solar atmosphere and solar
wind are still poorly understood. We limit the scope of this paper
(leaving out the solar interior and convection zone) to the magnetized
plasma that reaches from the photosphere and chromosphere upwards to
the corona and inner heliosphere, and place particular emphasis on
the magnetic field structures and fluctuations and their role in the
dynamics and radiation of the coronal plasma. To attract the attention
of scientists from both the fluid-dynamics and space-science communities
we give in the first two sections a phenomenological overview of
turbulence-related processes, in the context of solar and heliospheric
physics and with emphasis on the photosphere-corona connection and
the coupling between the solar corona and solar wind. We also discuss
the basic tools and standard concepts for the empirical analysis and
theoretical description of turbulence. The last two sections of this
paper give a concise review of selected aspects of oscillations and
waves in the solar atmosphere and related fluctuations in the solar
wind. We conclude with some recommendations and suggest topics for
future research.
Title: Horizontal supergranule-scale motions inferred from TRACE
ultraviolet observations of the chromosphere
Authors: Tian, H.; Potts, H. E.; Marsch, E.; Attie, R.; He, J. -S.
Bibcode: 2010A&A...519A..58T
Altcode: 2010arXiv1006.0321T
Aims: We study horizontal supergranule-scale motions
revealed by TRACE observation of the chromospheric emission, and
investigate the coupling between the chromosphere and the underlying
photosphere.
Methods: A highly efficient feature-tracking
technique called balltracking has been applied for the first time to
the image sequences obtained by TRACE (transition region and coronal
explorer) in the passband of white light and the three ultraviolet
passbands centered at 1700 Å, 1600 Å, and 1550 Å. The resulting
velocity fields have been spatially smoothed and temporally averaged
in order to reveal horizontal supergranule-scale motions that may
exist at the emission heights of these passbands.
Results:
We find indeed a high correlation between the horizontal velocities
derived in the white-light and ultraviolet passbands. The horizontal
velocities derived from the chromospheric and photospheric emission
are comparable in magnitude.
Conclusions: The horizontal
motions derived in the UV passbands might indicate the existence of
a supergranule-scale magneto-convection in the chromosphere, which
may shed new light on the study of mass and energy supply to the
corona and solar wind at the height of the chromosphere. However, it
is also possible that the apparent motions reflect the chromospheric
brightness evolution as produced by acoustic shocks which might be
modulated by the photospheric granular motions in their excitation
process, or advected partly by the supergranule-scale flow towards
the network while propagating upward from the photosphere. To reach a
firm conclusion, it is necessary to investigate the role of granular
motions in the excitation of shocks through numerical modeling, and
future high-cadence chromospheric magnetograms must be scrutinized.
Title: Magnetic and spectroscopic properties of supergranular-scale
coronal jets and erupting loops in a polar coronal hole
Authors: He, J. -S.; Marsch, E.; Curdt, W.; Tian, H.; Tu, C. -Y.;
Xia, L. -D.; Kamio, S.
Bibcode: 2010A&A...519A..49H
Altcode:
Context. Coronal jets and mass ejections associated with erupting loops
are two distinct and frequently observed types of transient upflows
of plasma in coronal holes (CHs). But the magnetic and spectroscopic
properties of these events at the supergranular scale are not well
known.
Aims: Here we aim at studying in a polar hole the plasma
and field characteristics of coronal jets and erupting loops of a
supergranular size, for which we use observations from XRT, EIS and SOT
on Hinode as well as EUVI on STEREO.
Methods: The open magnetic
field structures related to the coronal jets are obtained by magnetic
field extrapolation into the corona from SOT magnetograms. Furthermore,
we use the EIS observations to analyze ultraviolet line intensities
and Doppler shifts in association with the erupting loops.
Results: We find that the coronal jet plasma is indeed ejected along
open field lines, thus confirming the conjecture of jet formation in
an open magnetic environment. The magnetic evolution at the jet base
is investigated, and the results indicate that the interaction between
two flux tubes of opposite magnetic polarities as well as the squeezing
of several tubes with identical polarities might be responsible for
the jet initiation. We reveal for the first time the spectroscopic
signatures of a supergranular-size erupting loop at its early stage,
which consists of three steps. The first step is the onset, which is
featured by a sudden brightening of one footpoint, as well as by the
occurrence of blueshifts along almost its entire path. The second step
is the initial expansion of the closed loop, which is estimated to move
upward at a speed of about 20 km s-1, as derived from the
line-of-sight (LOS) blueshift and the loop enlargement projected onto
the plane of the sky. In the third step, the loop's bright footpoint
is apparently diminishing its intensity and enhancing its blueshift,
which indicates that plasma upflow from the leg is filling the expanding
loop volume.
Conclusions: From our results we conclude that
in polar CHs, where the steady fast solar wind is known to emanate,
there are also at least two possible ways of causing transient plasma
outflows at supergranular scale. One is related to coronal jets
guided by open field lines, the other to the eruption of closed loops,
which is triggered by magnetic reconnection at their footpoints. 3 movies (for Figs. 2-4) are only available in electronic form at
http://www.aanda.org
Title: On the interactions of transverse ion-cyclotron waves with
ions in solar wind plasma
Authors: Bourouaine, Sofiane; Marsch, Eckart; Neubauer, Fritz M.
Bibcode: 2010arXiv1008.2893B
Altcode:
We show the evidence of ion-cyclotron dissipation mechanism in
solar wind plasma using Helios data. From our statistical analysis
we found that the wave power of high-frequency transverse waves
(having frequencies between 0.01 and 1 normalized to the proton
gyrofrequency in the plasma frame) correlates with both, the proton
temperature anisotropy, $T_{\perp}/T_{\parallel}$, and the normalized
differential speed, $V_{\alpha p}/V_A$, between alpha particles
and protons. Furthermore, when this speed stays below 0.5, then the
alpha-particle temperature anisotropy correlate positively with the
relative power of the transverse waves. However, if $V_{\alpha p}/V_A$
is larger than 0.6, then the alpha-particle temperature anisotropy
tends to decrease towards values below unity, despite the presence
of transverse waves with relatively large amplitudes. For small
relative wave amplitude, it is found that alpha particles can even be
heated more strongly than protons when the alpha-to-electron density
ratio nearly or below 0.01. Our findings are in good agreement with
predictions of kinetic theory for the resonant interaction of ions with
Alfvén-cyclotron waves and for the resulting wave dissipation. Also,
the study suggests that the turbulence could lead to the generation
of parallel Alfven cyclotron waves.
Title: Correlations between the proton temperature anisotropy and
transverse high-frequency waves in the solar wind
Authors: Bourouaine, Sofiane; Marsch, Eckart; Neubauer, Fritz M.
Bibcode: 2010GeoRL..3714104B
Altcode: 2010arXiv1003.2299B
Correlations are studied between the power density of transverse
waves having frequencies between 0.01 and 1 normalized to the proton
gyrofrequency in the plasma frame and the ratio of the perpendicular
and parallel temperature of the protons. The wave power spectrum is
evaluated from high-resolution 3D magnetic field vector components,
and the ion temperatures are derived from the velocity distribution
functions as measured in fast solar wind during the Helios-2 primary
mission at radial distances from the Sun between 0.3 AU and 0.9 AU. From
our statistical analysis, we obtain a striking correlation between
the increases in the proton temperature ratio and enhancements in
the wave power spectrum. Near the Sun the transverse part of the wave
power is often found to be by more than an order of magnitude higher
than its longitudinal counterpart. Also the measured ion temperature
anisotropy appears to be limited by the theoretical threshold value
for the ion-cyclotron instability. This suggests that high-frequency
Alfvén-cyclotron waves regulate the proton temperature anisotropy.
Title: Intermittent outflows at the edge of an active region -
a possible source of the solar wind?
Authors: He, J. -S.; Marsch, E.; Tu, C. -Y.; Guo, L. -J.; Tian, H.
Bibcode: 2010A&A...516A..14H
Altcode:
Context. It has already been established that the solar wind may
originate at the edges of active regions (ARs), but the key questions
of how frequently these outflows occur, and at which height the
nascent solar wind originates have not yet been addressed.
Aims: We study the occurrence rate of these intermittent outflows,
the related plasma activities beneath in the low solar atmosphere,
and the interplanetary counterparts of the nascent solar wind
outflow.
Methods: We use the observations from XRT/Hinode
and TRACE to study the outflow patterns. The occurrence frequency of
the intermittent outflow is estimated by counting the occurrences of
propagating intensity enhancements in height-time diagrams. We adopt
observations of SOT/Hinode and EIS/Hinode to investigate the phenomena
in the chromosphere associated with the coronal outflows. The ACE
plasma and field in-situ measurements near Earth are used to study
the interplanetary manifestations.
Results: We find that in
one elongated coronal emission structure, referred to as strand,
the plasma flows outward intermittently, about every 20 min. The flow
speed sometimes exceeds 200 km s-1, which is indicative of
rapid acceleration, and thus exceeds the coronal sound speed at low
altitudes. The inferred flow speed of the soft-X-ray-emitting plasma
component seems a little higher than that of the Fe ix/x-emitting plasma
component. Chromospheric jets are found to occur at the root of the
strand. Upflows in the chromosphere are also confirmed by blue-shifts of
the He ii line. The heliospheric plasma counterpart close to the Earth
is found to be an intermediate-speed solar wind stream. The AR edge may
also deliver some plasmas to a fraction of the fast solar wind stream,
most of which emanate from the neighboring CH.
Conclusions:
The possible origin of the nascent solar wind in the chromosphere,
the observed excessive outflow speed of over 200 km s-1 in
the lower corona, and the corresponding intermediate-speed solar wind
stream in interplanetary space are all linked in our case study. These
phenomena from the low solar atmosphere to the heliosphere near Earth in
combination shed new light on the solar wind formation process. These
observational results will constrain future modeling of the solar
winds originating close to an AR.
Title: Identification of prominence ejecta by the proton distribution
function and magnetic fine structure in interplanetary coronal mass
ejections in the inner heliosphere
Authors: Yao, Shuo; Marsch, Eckart; Tu, Chuan-Yi; Schwenn, Rainer
Bibcode: 2010JGRA..115.5103Y
Altcode: 2010JGRA..11505103Y
This work presents in situ solar wind observations of three magnetic
clouds (MCs) that contain cold high-density material when Helios 2
was located at 0.3 AU on 9 May 1979, 0.5 AU on 30 March 1976, and 0.7
AU on 24 December 1978. In the cold high-density regions embedded
in the interplanetary coronal mass ejections we find (1) that the
number density of protons is higher than in other regions inside the
magnetic cloud, (2) the possible existence of He+, (3)
that the thermal velocity distribution functions are more isotropic
and appear to be colder than in the other regions of the MC, and the
proton temperature is lower than that of the ambient plasma, and (4)
that the associated magnetic field configuration can for all three MC
events be identified as a flux rope. This cold high-density region is
located at the polarity inversion line in the center of the bipolar
structure of the MC magnetic field (consistent with previous solar
observation work that found that a prominence lies over the neutral
line of the related bipolar solar magnetic field). Specifically, for
the first magnetic cloud event on 8 May 1979, a coronal mass ejection
(CME) was related to an eruptive prominence previously reported as a
result of the observation of Solwind (P78-1). Therefore, we identify
the cold and dense region in the MC as the prominence material. It
is the first time that prominence ejecta were identified by both the
plasma and magnetic field features inside 1 AU, and it is also the first
time that the thermal ion velocity distribution functions were used to
investigate the microstate of the prominence material. Moreover, from
our three cases, we also found that this material tended to fall behind
the magnetic cloud and become smaller as it propagated farther away
from the Sun, which confirms speculations in previous work. Overall,
our in situ observations are consistent with three-part CME models.
Title: New views on the emission and structure of the solar transition
region
Authors: Tian, Hui; Marsch, Eckart; Tu, Chuanyi; Curdt, Werner;
He, Jiansen
Bibcode: 2010PhDT.......178T
Altcode: 2010arXiv1004.3017T
The Sun is the only star that we can spatially resolve and it can
be regarded as a fundamental plasma laboratory of astrophysics. The
solar transition region (TR), the layer between the solar chromosphere
and corona, plays an important role in solar wind origin and coronal
heating. Recent high-resolution observations made by SOHO, TRACE,
and Hinode indicate that the TR is highly nonuniform and magnetically
structured. Through a combination of spectroscopic observations and
magnetic field extrapolations, the TR magnetic structures and plasma
properties have been found to be different in coronal holes and in the
quiet Sun. In active regions, the TR density and temperature structures
also differ in sunspots and the surrounding plage regions. Although
the TR is believed to be a dynamic layer, quasi-steady flows lasting
from several hours to several days are often present in the quiet
Sun, coronal holes, and active regions, indicating some kind of
plasma circulation/convection in the TR and corona. The emission of
hydrogen Lyman lines, which originates from the lower TR, has also
been intensively investigated in the recent past. Observations show
clearly that the flows and dynamics in the middle and upper TR can
greatly modify the Lyman line profiles.
Title: Is the 3-D magnetic null point with a convective electric
field an efficient particle accelerator?
Authors: Guo, J. -N.; Büchner, J.; Otto, A.; Santos, J.; Marsch,
E.; Gan, W. -Q.
Bibcode: 2010A&A...513A..73G
Altcode:
Aims: We study the particle acceleration at a magnetic null point
in the solar corona, considering self-consistent magnetic fields, plasma
flows and the corresponding convective electric fields.
Methods:
We calculate the electromagnetic fields by 3-D magnetohydrodynamic
(MHD) simulations and expose charged particles to these fields within
a full-orbit relativistic test-particle approach. In the 3-D MHD
simulation part, the initial magnetic field configuration is set to be a
potential field obtained by extrapolation from an analytic quadrupolar
photospheric magnetic field with a typically observed magnitude. The
configuration is chosen so that the resulting coronal magnetic
field contains a null. Driven by photospheric plasma motion, the MHD
simulation reveals the coronal plasma motion and the self-consistent
electric and magnetic fields. In a subsequent test particle experiment
the particle energies and orbits (determined by the forces exerted by
the convective electric field and the magnetic field around the null)
are calculated in time.
Results: Test particle calculations
show that protons can be accelerated up to 30 keV near the null if the
local plasma flow velocity is of the order of 1000 km s-1 (in
solar active regions). The final parallel velocity is much higher than
the perpendicular velocity so that accelerated particles escape from
the null along the magnetic field lines. Stronger convection electric
field during big flare explosions can accelerate protons up to 2 MeV
and electrons to 3 keV. Higher initial velocities can help most protons
to be strongly accelerated, but a few protons also run the risk to be
decelerated.
Conclusions: Through its convective electric field
and due to magnetic nonuniform drifts and de-magnetization process, the
3-D null can act as an effective accelerator for protons but not for
electrons. Protons are more easily de-magnetized and accelerated than
electrons because of their larger Larmor radii. Notice that macroscopic
MHD simulations are blind to microscopic magnetic structures where more
non-adiabatic processes might be taking place. In the real solar corona,
we expect that particles could have a higher probability to experience a
de-magnetization process and get accelerated. To trigger a significant
acceleration of electrons and even higher energetic protons, however,
the existence of a resistive electric field mainly parallel to the
magnetic field is required. A physically reasonable resistivity model
included in resistive MHD simulations is direly needed for the further
investigations of electron acceleration by parallel electric fields.
Title: Evolution of magnetic clouds in the inner heliosphere
Authors: Gulisano, Adriana Maria; Démoulin, Pascal; Dasso, Sergio;
Ruiz, Maria Emilia; Marsch, Eckart
Bibcode: 2010AIPC.1216..391G
Altcode:
Magnetic clouds (MCs) are objects in expansion during their travel
through the heliosphere. In situ observations indicate that their front
travel faster than their back, showing a clear empirical signature
of expansion. With the aim of quantifying the expansion rate of MCs
in the inner heliosphere (0.3 to 1 AU), we present here a statistical
study of events observed by the spacecraft Helios 1 and 2, during their
complete period of operations. From the analysis of the profile of the
MC magnetic field components in its local frame, which is obtained
from a rotation of the observed magnetic field vectors to a system
of reference oriented as the main axis of the flux rope, we revise a
list of events identified in previous works and redefine improved MC
boundaries/orientation for each event. We then split the sample into two
subsets according to the characteristics of their velocity profiles,
(a) those MCs with a significantly perturbed velocity profile due to
the interaction with their surrounding solar wind (i.e. overtaken
by streams) and (b) those that are not perturbed. We compute the
dimensionless local expansion rate (ζ) for MCs defined by several
works [e.g. Démoulin et al., Solar Phys, 250, 347-374 (2008)]. We find
significantly different distribution of values for ζ when perturbed
and non perturbed events are considered. Non perturbed MCs expand at
rates ζ consistent with the expected value from the global pressure
decay in the surrounding solar wind for increasing helio-distances,
while perturbed ones may present strong departures from that global
rule. We interpret these departures of ζ for perturbed MCs as a
consequence of interaction with streams on their expansion.
Title: Upward and downward propagation of transverse waves due to
small-scale magnetic reconnection in the chromosphere
Authors: He, J. -S.; Marsch, E.; Tu, C. -Y.; Tian, H.
Bibcode: 2010AIPC.1216...32H
Altcode:
We aim at studying the connections between the propagation
of transverse waves on spicules and the small-scale magnetic
reconnections at the feet of the spicules. The observed transverse
wave may be interpreted as an Alfvén wave or a kink wave. We use the
observations from SOT/Hinode in the Ca II H line to study the spicule
dynamics above the reconnection sites. We found in three cases that
the transverse oscillations were excited by magnetic reconnection,
and steepened while propagating upwardly. In case-1, the steepening
oscillations were attenuated at greater heights in association with
the extension of the spicule plasma. In case-2, the transverse wave
seems to be initiated by a footpoint jump of the spicule trace in the
photosphere. The transverse wave in case-3 was found to be reflected,
and then to propagate downward. These results reveal the wave dynamics
in the low solar atmosphere, and provide observational evidence that is
useful for the modeling of coronal heating and solar wind acceleration,
involving wave generation by magnetic reconnection in the chromosphere.
Title: Upflows in the upper transition region of the quiet Sun
Authors: Tian, H.; Tu, C. -Y.; Marsch, E.; He, J. -S.; Zhou, C.;
Zhao, L.
Bibcode: 2010AIPC.1216...36T
Altcode: 2009arXiv0911.1833T
We investigate the physical meaning of the prominent blue shifts of
Ne VIII, which is observed to be associated with quiet-Sun network
junctions (boundary intersections), through data analyses combining
force-free-field extrapolations with EUV spectroscopic observations. For
a middle-latitude region, we reconstruct the magnetic funnel structure
in a sub-region showing faint emission in EIT-Fe 195. This funnel
appears to consist of several smaller funnels that originate from
network lanes, expand with height and finally merge into a single
wide open-field region. However, the large blue shifts of Ne VIII are
generally not associated with open fields, but seem to be associated
with the legs of closed magnetic loops. Moreover, in most cases
significant upflows are found in both of the funnel-shaped loop
legs. These quasi-steady upflows are regarded as signatures of
mass supply to the coronal loops rather than the solar wind. Our
observational result also reveals that in many cases the upflows in
the upper transition region (TR) and the downflows in the middle TR
are not fully cospatial. Based on these new observational results, we
suggest different TR structures in coronal holes and in the quiet Sun.
Title: Anisotropy of the magnetic correlation function in the inner
heliosphere
Authors: Ruiz, M. E.; Dasso, S.; Matthaeus, W. H.; Marsch, E.; Weygand,
J. M.
Bibcode: 2010AIPC.1216..160R
Altcode:
For over four decades, low frequency plasma and electromagnetic
fluctuations have been observed in the solar wind (SW), making it
the most completely studied case of magnetohydrodynamic turbulence
in astrophysics, and the only one extensively and directly studied
using in situ observations. Magnetohydrodynamic scale fluctuations
in the SW are usually anisotropic with respect to the local mean
magnetic field (B0). In this work, we present a study of
turbulent properties in the inner heliosphere (solar wind between 0.3
and 1 AU) based on modeling in situ plasma and magnetic observations
collected by Helios 1 and Helios 2 spacecraft throughout a solar
minimum. We present preliminary results on the evolution of the spatial
structure of the magnetic self-correlation function in the inner
heliosphere. In particular we focus on the evolution of the integral
length scale (λ) for magnetic fluctuations and on its anisotropy
in the inertial range. As previously known from different studies,
we confirm that near Earth λ||>λ⊥ (with
λ|| and λ⊥ representing the integral length
in the parallel and perpendicular directions respect to B0,
respectively). However, for lower distances to the Sun we found that
λ||<λ⊥. Results presented here will help
us to refine models used to describe the turbulence and waves activity
in the inner heliosphere.
Title: Prominence material identified in magnetic cloud
Authors: Yao, Shuo; Marsch, E.; Tu, C. -Y.
Bibcode: 2010AIPC.1216..235Y
Altcode:
Coronal mass ejections (CMEs) often appear in coronagraph images as
three-part structures composed of a leading bright front, a dark cavity
and a bright core, which are believed to be associated with the sheath
of compressed solar wind, the erupting magnetic flux rope and the
cool and dense prominence plasma, respectively. However, a convincing
identification of this three-part structure in the in-situ solar wind
is extremely rare. Therefore, there still remains an open question as
to what kind of signatures these three CME parts will reveal in the in
situ data ([5]). Our work presents a clear identification of prominence
material from in situ observations of the solar wind magnetic field
and plasma parameters. The Helios 2 solar probe detected a magnetic
cloud at 0.5 AU on 30 March 1976. In this event, we found a region
with lower proton temperature and higher proton number density than
outside, which is consistent with key features of a prominence as
cold and dense solar material. During the same time we also found the
occurrence of what possibly is He+, which is a special ion
expected to occur only in prominence ejecta. Furthermore, the above
observations were all made at a location related to the turning point
of a bipolar structure of the interplanetary magnetic field, which
is coincident with the notion that a solar prominence lies under the
magnetic field lines of a bipolar region and is oriented along the
neutral line. Furthermore, from our analysis of solar wind velocity
distribution functions (VDFs) we can confirm by kinetic evidence that
the plasma inside this special region is colder and more isotropic
than outside. Above all, our observations circumstantially confirm
the 3-part CME model as described in references [10] and [7].
Title: Longitudinal oscillation of intensity fronts in a strand at
the edge of an active region
Authors: Guo, L. -J.; He, J. -S.; Tu, C. -Y.; Marsch, E.
Bibcode: 2010AIPC.1216...76G
Altcode:
The edge of a solar active region (AR) is considered as a possible
source region of the slow solar wind. Winebarger et al. (2001) observed
outflows from an AR with velocities between 5 and 20 km/s. Recently,
Sakao et al. (2007) reported the outflow of X-ray-emitting plasma from
the edge of an AR. This outflow was inferred from the observation of
outward traveling intensity enhancements. However, in Robbrecht et
al. (2001), propagation of slow magnetoacoustic waves along the strand
was considered as the possible cause for the longitudinal extension
of the strand. Whether this phenomenon relates to a slow-mode wave or
the outflow of plasma or a heating process of different parts of the
strand is still an open question. Here we try to identify the nature
of such a traveling event through studying the longitudinal motions of
certain intensity level fronts in the strand. We find that the intensity
front is oscillating like a sinusoidal signal along the strand with
a period of 11 minutes. This result suggests that the oscillation
might be partly related with the 5-minute p-mode oscillation in the
photosphere. Moreover, we find that such oscillation of intensity-level
fronts can be described by a model in which the strand has periodic
extension. Yet, the relation between the extending strand and slow
solar wind needs to be further studied.
Title: Ion distributions in coronal holes and fast solar wind
Authors: Maneva, Y. G.; Araneda, J. A.; Marsch, E.
Bibcode: 2010AIPC.1216..227M
Altcode:
We perform 1 D hybrid simulations to investigate the nonlinear kinetic
behavior of the tenuous collisionless magnetized plasma in coronal holes
and fast solar wind. Initially isotropic ion distributions are reshaped
via wave-particle interactions with resonant daughter waves that are
born by parametrically unstable large-amplitude Alfvén-cyclotron
waves. Decay processes lead to the formation of both acoustic and
electromagnetic micro-turbulence, which further influence the motion
of the ions via Landau damping and pitch-angle scattering. This leads
to a depletion of the pump and destroys the fluid coherence of the
medium. Parametric instabilities act to randomize the ion distributions,
causing anisotropic heating and resulting in differential streaming
and formation of ion beams. Due to their low mass densities and
charge-to-mass ratios heavy ions are preferentially heated and obtain
higher anisotropies than protons.
Title: Reconfiguration of the coronal magnetic field by means of
reconnection driven by photospheric magnetic flux convergence
Authors: He, J. -S.; Marsch, E.; Tu, C. -Y.; Tian, H.; Guo, L. -J.
Bibcode: 2010A&A...510A..40H
Altcode:
Context. Magnetic reconnection is commonly believed to be responsible
for flare-like events and plasma ejections in the solar atmosphere,
but the field-line reconfiguration observed in association with magnetic
reconnection has rarely been observed before.
Aims: We attempt to
reconstruct the configuration of the magnetic field during a magnetic
reconnection event, estimate the reconnection rate, and analyze the
resulting X-ray burst and plasma ejection.
Methods: We use the
local-correlation-tracking (LCT) method to track the convergence of
magnetic fields with opposite polarities using photospheric observations
from SOT/Hinode. The magnetic field lines are then extrapolated from
the tracked footpoint positions into the corona, and the changes in
field-line connections are marked. We estimate the reconnection rate
by calculating the convective electric field in the photosphere, which
is normalized to the product of the plasma jet speed and the coronal
magnetic field strength inside the inflow region. The observed X-ray
burst and plasma ejection are analysed with data from XRT/Hinode and
TRACE, respectively.
Results: We find that in this reconnection
event the two sets of approaching closed loops were reconfigured to
a set of superimposed large-scale closed loops and another set of
small-scale closed loops. Enhanced soft X-ray emission was seen to
rapidly fill the reconnected loop after the micro-flare occurred at
the reconnection site. Plasma was ejected from that site with a speed
between 27 and 40 km s-1. The reconnection rate is estimated
to range between 0.03 and 0.09.
Conclusions: Our work presents
a study of the magnetic field reconfiguration owing to magnetic
reconnection driven by flux convergence in the photosphere. This
observation of the magnetic structure change is helpful for future
diagnosis of magnetic reconnection. The results obtained for the
reconnection rate, the X-ray emission burst, and the plasma ejection
provides new observational evidence, and places constraints on future
theoretical study of magnetic reconnection in the Sun.
Title: Identification of prominence ejecta by the proton distribution
function and magnetic fine structure in ICMEs in the inner heliosphere
Authors: Marsch, Eckart; Yao, Shuo; Tu, Chuanyi; Schwenn, Rainer
Bibcode: 2010cosp...38.1876M
Altcode: 2010cosp.meet.1876M
This work presents in-situ solar wind observations of three magnetic
clouds that contain certain cold high-density material, when Helios
2 was located at 0.3 AU, on 9 May 1979, 0.5 AU on 30 March 1976, and
0.7 AU on 24 December 1978, respectively. In the cold high-density
regions embedded in the ICMEs we find that (1) the number density of
protons is higher than in other regions inside the magnetic cloud (MC),
(2)the possible existence of He+, (3) the thermal velocity distribution
functions (VDFs) are more isotropic and appear to be colder than in the
other regions of the MC, and the proton temperature is lower than that
of the ambient plasma, (4) the associated magnetic field configuration
can for all three MC events be identified as a flux rope. This cold
high-density region is located at the polarity inversion line in the
center of the bipolar structure of the MC magnetic field (consistent
with previous work of solar observation that a prominence lies over
the neutral line of the related bipolar solar magnetic field ). It is
the first time that prominence ejecta are identified by both the plasma
and magnetic field features inside 1 AU, and that thermal ion velocity
distribution functions are used to investigate the microstate of the
prominence material. Overall, our in situ observations are consistent
with the three-part CME models.
Title: The coronal convection
Authors: Curdt, Werner; Tian, Hui; Marsch, Eckart
Bibcode: 2010cosp...38.2927C
Altcode: 2010cosp.meet.2927C
We studied with SUMER the hydrogen Lyman emission in various solar
features -now including Ly-α observations -and investigated the
imprints that coronal flows and the solar magnetic field have on the
line profile and radiance distribution. As a new result, we found
that in Ly-α raster maps the locations with higher line opacity
(evident by strong self-absorption dips) cluster in the cell interior
of the magnetic network, while the lines from the network lanes tend
to reveal flatter profiles. Even deeper self reversals and larger
peak separations were found in coronal hole spectra. We also compared
the quasi-simultaneously obtained Ly-α and Ly-β profiles and found
an obvious correspondence between asymmetry and redshift for both
lines, but, most surprisingly, the asymmetries of Ly-α and Ly-β are
opposite. We conclude that in both cases downflows determine the line
profile, in the case of Ly-α by absorption and in the case of Ly-β
by emission. Our results, which are further supported by recent Hinode
data, show that the magnetic structure of the solar atmosphere plays
a dominant role in the line formation, and indicate the prevalence of
persistent downflows at both footpoints of closed loops. We suggest
all this to be the manifestation of a continuous mass-transportation
process, which Foukal back in 1978 introduced as 'coronal convection'.
Title: Upward propagation and subsequent steepening of transverse
waves launched by small-scale magnetic reconnection in the
chromosphere
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Tian, Hui
Bibcode: 2010cosp...38.1805H
Altcode: 2010cosp.meet.1805H
SOT observations of chromospheric spicules have revealed that
Alfven-like transverse oscilla-tions on the spicules are prevalent
in the chromosphere. But the propagation features, e.g., the phase
speed and the propagation direction, have not been derived directly
from observations. It is still not clear how these transverse waves
are generated. Here we aim at identifying the propagation feature of
the transverse wave, studying its ampli-tude evolution as well as its
generation by magnetic reconnection underneath. The phase speed is
estimated to range between 20 and 150 km/s, based on time lags between
different transverse oscillation profiles at various heights along the
dynamic spicule. The transverse fluctuation is found to originate at
the cusp of an inverted Y-shaped emission structure, where apparently
magnetic reconnection occurred. The transverse wave steepened with
height probably due to density rarefaction in the stratified atmosphere,
and evolved into a nonlinear state with a large relative disturbance,
yielding a relative velocity-amplitude (dV/Vph) of 0.21 at 5.5 Mm. The
nonlinear transverse wave seems to be damped in velocity amplitude
beyond 5.5 Mm, with the transverse-fluctuation energy possibly being
converted to the longitudinal-motion energy. We also estimate the
energy flux density carried by the transverse wave, and find it is
still sufficient, in spite of possible attenuation in the transition
region, for heating the quiet corona or driving the solar wind. In
another case, we find that upward propagation (launched by magnetic
recon-nection) is subsequently followed by clear downward propagation,
which may indicate possible wave reflection at some height in the
transition region. Our findings shed new light on future modelling
of coronal heating and solar wind acceleration, involving magnetic
reconnection in the chromosphere. References: [1]. He, J.-S., Marsch,
E., Tu, C.-Y., Tian, H., Excitation of kink waves due to small-scale
magnetic reconnection in the chromosphere? ApJL, 705, L217-L222,
2009. [2]. He, J.-S., Marsch, E., Tu, C.-Y., Tian, H., Upward and
downward propagation of transverse waves due to small-scale magnetic
reconnection in the chromospehre, SolarWind-12, in press.
Title: Non-thermal features in ion distributions caused by
large-amplitude Alfven-cyclotron waves
Authors: Maneva, Yana; Araneda, Jaime; Marsch, Eckart
Bibcode: 2010cosp...38.1817M
Altcode: 2010cosp.meet.1817M
We perform 1D hybrid simulations to investigate the non-thermal
features of the ion distri-butions in the fast solar wind. We explore
the the origin and evolution of ion anisotropies, differential
streaming and formation of ion beams. Simulation results show
preferential heating and acceleration for the minor ions under
low plasma β conditions. The energy source is the dissipation of
a large-amplitude parallel propagating Alfven-cyclotron pump wave,
that under-goes parametric instabilities, leading to energy transfer
and generation of spectra of daughter ion-acoustic and (both lower
and higher frequency) Alfven-cyclotron waves. In the presence of the
nonlinear pump all particles are forced to follow certain orbits in
perpendicular direction, depending on the amplitude, frequency and
the phase speed of the pump. As the pump decays, the ions are free
to move in velocity space and a diffusion process sets on. Further
on, wave-particle interactions, like Landau damping and nonlinear
pitch-angle scattering take place, that additionally deform the
ion distribution functions and deviations from thermal-equilibrium
oc-cur. Finally we compare the simulation results with real solar wind
data, where non-thermal features are ubiquitous.
Title: Reconstruction of reconnecting magnetic field in both solar
corona and geo-magnetosphere and its application to reconnection
diagnosis
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Zong, Qiugang;
Tian, Hui; Guo, Lijia
Bibcode: 2010cosp...38.1942H
Altcode: 2010cosp.meet.1942H
Magnetic reconnection is a critical process of energy transfer in the
solar-terrestrial plasma. The related 3-D magnetic field geometry
and its temporal reconfiguration are important for reconnection
diagnosis. For example, we can estimate how fast the coronal
magnetic field is reconnected, based on temporal variation of the
reconnecting field lines, and we can learn about the micro-physics
in the reconnection region with the help of 3-D reconstruction of the
magnetic field in geo-space. For a solar micro-flare event, we study
the evolution of magnetic field lines, which are ex-trapolated from
dynamic footpoints showing convergence motions. We find that the two
sets of approaching closed loops were reconfigured to form a joint set
of superimposed large-scale closed loops and another set of small-scale
closed loops. We estimate the reconnection rate in two ways. One way
is to calculate the convective electric field in the photosphere,
which is normalized to the product of the plasma jet speed and the
coronal magnetic field strength inside the inflow region. Another
way is to directly calculate the reconnection rate based on Vin/VA,
where Vin is the motion of the convex segments on the reconnecting
field lines. The reconnection rate is estimated to range between 0.03
and 0.09. This is the first work illustrat-ing the reconfiguration
of the magnetic field geometry, owing to reconnection driven by flux
convergence in the photosphere. For a magnetic reconnection event in
the geo-magnetotail, we reconstruct the 3D magnetic field structure
containing a pair of nulls with a novel method based on Cluster
4-spacecraft measurements. We study the electron dynamics near one
null of the pair, and propose a new scenario of micro-physics in the
null region. In this scenario, electrons are temporarily trapped in the
central reconnection region, accelerated possibly by parallel electric
field and electron pressure gradient, and reflected from the magnetic
cusp mirrors leading to the bi-directional energetic electron beams,
which may excite the high-frequency electrostatic waves. Here, we
have demonstrated that reconstruction of the real-time magnetic field
structure is quite helpful for magnetic reconnection diagnosis, e.g.,
estimation of the reconnection rate and analysis of the micro-physics in
the inner reconnection region. References: [1]. He, J.-S., Marsch, E.,
Tu, C.-Y., Tian, H., Guo, L.-J., Reconfiguration of the coronal magnetic
field by means of reconnection driven by photospheric magnetic flux
convergence, AA, 510, A40, 2010. [2]. He, J.-S., Zong, Q.-G., Deng,
X.-H., Tu, C.-Y., et al., Electron trapping around a magnetic null,
Geophys. Res. Lett., 35, L14104, 2008.
Title: Solar wind origins in coronal holes and in the quiet Sun
Authors: He, J. -S.; Tu, C. -Y.; Tian, H.; Marsch, E.
Bibcode: 2010AdSpR..45..303H
Altcode:
Coronal hole (CH) and the quiet Sun (QS) are considered to account
for sources of fast and slow solar wind streams, respectively. The
differences between the solar wind streams flowing out from the CH
and the QS are thought to be related with different plasma generation
and acceleration mechanisms in the respective source regions. Here we
review recent studies on the solar wind origin in the CH and the QS,
compare the possible flow geometries and magnetic structures in these
two kinds of solar regions, and summarize the physics associated with
two different origin scenarios.
Title: Coronal sound waves on open magnetic field lines originating
near solar active regions
Authors: Stenborg, Guillermo; Marsch, Eckart; Vourlidas, Angelos;
Howard, Russell; Baldwin, Katherine
Bibcode: 2010cosp...38.1814S
Altcode: 2010cosp.meet.1814S
In the past years, evidence for the existence of outward-moving plasma
and slow-mode magne-toacoustic waves propagating in various magnetic
field structures (loops in particular) in the solar corona has been
found, yet their origin and possible connection with the mass and energy
supply to the corona and solar wind is still unclear. These results
were obtained by the high-resolution observations available from the
extreme ultraviolet (EUV) imagers on the STEREO and Hinode missions,
and from data obtained by the ultraviolet spectrometer on Hinode. Here,
we present the first measurements of intensity fluctuations observed by
the Extreme Ultra-Violet Imagers (EUVI) onboard the Solar TErrestrial
RElationships Observatory (STEREO) mission along apparently open
field lines near solar active regions. We demonstrate that one can
make reliable kinematic measurements (speed, acceleration) from these
EUV images, thereby complementing and extending the spectroscopic
measurements. We have developed a series of image-processing steps
to recover the weak intensity fluctuations along individual magnetic
structures, de-projected them and produced distance-time maps. They
can be analysed by use of well established techniques adapted from the
kinematic analysis of Coronal Mass Ejection (CME), and by standard
methods of wavelet analysis. We obtained wave phase speeds with
values on the order of 100 km/s. We also studied the periodicity
of the observed fluctuations and established a predominance of a
16-minutes period, as well as other periods being multi-ples of the
8-minutes period that appears to be the basic value. Thus we clearly
established the ubiquitous existence of sound waves which seem to
emanate continuously on open coronal fields.
Title: Global and local expansion of magnetic clouds in the inner
heliosphere
Authors: Gulisano, A. M.; Démoulin, P.; Dasso, S.; Ruiz, M. E.;
Marsch, E.
Bibcode: 2010A&A...509A..39G
Altcode: 2012arXiv1206.1112G
Context. Observations of magnetic clouds (MCs) are consistent with the
presence of flux ropes detected in the solar wind (SW) a few days after
their expulsion from the Sun as coronal mass ejections (CMEs).
Aims: Both the in situ observations of plasma velocity profiles and the
increase of their size with solar distance show that MCs are typically
expanding structures. The aim of this work is to derive the expansion
properties of MCs in the inner heliosphere from 0.3 to 1 AU.
Methods: We analyze MCs observed by the two Helios spacecraft using in
situ magnetic field and velocity measurements. We split the sample in
two subsets: those MCs with a velocity profile that is significantly
perturbed from the expected linear profile and those that are not. From
the slope of the in situ measured bulk velocity along the Sun-Earth
direction, we compute an expansion speed with respect to the cloud
center for each of the analyzed MCs.
Results: We analyze how
the expansion speed depends on the MC size, the translation velocity,
and the heliocentric distance, finding that all MCs in the subset of
non-perturbed MCs expand with almost the same non-dimensional expansion
rate (ζ). We find departures from this general rule for ζ only for
perturbed MCs, and we interpret the departures as the consequence of
a local and strong SW perturbation by SW fast streams, affecting the
MC even inside its interior, in addition to the direct interaction
region between the SW and the MC. We also compute the dependence of
the mean total SW pressure on the solar distance and we confirm that
the decrease of the total SW pressure with distance is the main origin
of the observed MC expansion rate. We found that ζ was 0.91 ± 0.23
for non-perturbed MCs while ζ was 0.48 ± 0.79 for perturbed MCs,
the larger spread in the last ones being due to the influence of the
solar wind local environment conditions on the expansion.
Title: Multi-strand Coronal Loop Model
Authors: Bourouaine, Sofiane; Marsch, Eckart
Bibcode: 2010cosp...38.2846B
Altcode: 2010cosp.meet.2846B
We model a coronal loop as a bundle of seven separate strands or
filaments. Each of the loop strands used in this model can independently
be heated (near their left footpoints) by Alfvén/ion-cyclotron waves
via wave-particle interactions. The Alfvén waves are assumed to
penetrate the strands from their footpoints, at which we consider
different wave energy inputs. As a result, the loop strands can
have different heating profiles, and the differential heating can
lead to a varying cross-field temperature in the total coronal
loop. The simulation of Transition Region and Coronal Explorer
(TRACE) observations by means of this loop model implies two uniform
temperatures along the loop length, one inferred from the 171:195
filter ratio and the other from the 171:284 ratio. The reproduced
flat temperature profiles are consistent with those inferred from the
observed extreme-ultraviolet coronal loops. According to our model,
the flat temperature profile is a consequence of the coronal loop
consisting of filaments, which have different temperatures but almost
similar emission measures in the cross-field direction. Furthermore,
when we assume certain errors in the simulated loop emissions (e.g.,
due to photometric uncertainties in the TRACE filters) and use the
triple-filter analysis, our simulated loop conditions become consistent
with those of an isothermal plasma. This implies that the use of
TRACE or EUV Imaging Telescope triple filters for observation of a
warm coronal loop may not help in determining whether the cross-field
isothermal assumption is satisfied or not.
Title: Multi-spacecraft observation of a magnetic cloud
Authors: de Lucas, Aline; Dal Lago, Alisson; Schwenn, Rainer; Clúa de
Gonzalez, Alicia L.; Marsch, Eckart; Lamy, Philippe; Damé, Luc; Curdt,
W.; Davila, J.; Defise, J. M.; Fineschi, S.; Heinzel, P.; Howard, R.;
Kuzin, S.; Schmutz, W.; Tsinganos, K.; Turck-Chièze, S.; Zhukov, A.
Bibcode: 2010cosp...38.1921D
Altcode: 2010cosp.meet.1921D
Classical externally-occulted coronagraphs are presently limited in
their performances by the distance between the external occulter and
the front objective. The diffraction fringe from the occulter and
the vignetted pupil which degrades the spatial resolution prevent
useful observa-tions of the white light corona inside typically 2-2.5
Rsun. Formation flying offers an elegant solution to these limitations
and allows conceiving giant, externally-occulted coronagraphs
us-ing a two-component space system with the external occulter on
one spacecraft and the optical instrument on the other spacecraft
at distances of hundred meters. Such an instrument has just been
selected by ESA to fly (by the end of 2013) on its PROBA-3 mission,
presently in phase B, to demonstrate formation flying. It will perform
both high spatial resolution imaging of the solar corona as well as
2-dimensional spectroscopy of several emission lines (in partic-ular
the forbidden line of FeXIV at 530.285 nm) from the coronal base out
to 3 Rsun using a Fabry-Perot interferometer. The classical design of
an externally-occulted coronagraph is adapted to the formation flying
configuration allowing the detection of the very inner corona as close
as 0.05 Rsun from the solar limb. By tuning the position of the occulter
spacecraft, it may even be possible to try reaching the chromosphere
and the upper part of the spicules. ASPIICS/PROBA-3 mission, payload
and scientific objectives are presented.
Title: Ion heating and acceleration by trapping in parametrically
unstable Alfven-cyclotron waves in the solar wind
Authors: Araneda, Jaime; Maneva, Yana; Marsch, Eckart
Bibcode: 2010cosp...38.1893A
Altcode: 2010cosp.meet.1893A
We study fluctuations driven by the parametric instabilities of an
Alfven-cyclotron pump wave, which have an influence on the shape of the
ion velocity distributions in the solar wind. Longi-tudinal ion-acoustic
waves (IAW) and transverse ion-cyclotron (ICW) daughter waves, resulting
from the parametric decay, can destroy the coherent fluid motion of the
ions and by trapping lead to differential heating and acceleration. We
identify key instabilities and find that, even in the parameter regime
where fluid theory seems appropriate, kinetic effects prevail.
Title: New views on the emission and structure of the solar transition
region
Authors: Tian, Hui; Marsch, Eckart; Tu, Chuanyi; Curdt, Werner;
He, Jiansen
Bibcode: 2010NewAR..54...13T
Altcode:
The Sun is the only star that we can spatially resolve and it can
be regarded as a fundamental plasma laboratory of astrophysics. The
solar transition region (TR), the layer between the solar chromosphere
and corona, plays an important role in solar wind origin and coronal
heating. Recent high-resolution observations made by SOHO, TRACE,
and Hinode indicate that the TR is highly nonuniform and magnetically
structured. Through a combination of spectroscopic observations and
magnetic field extrapolations, the TR magnetic structures and plasma
properties have been found to be different in coronal holes and in the
quiet Sun. In active regions, the TR density and temperature structures
also differ in sunspots and the surrounding plage regions. Although
the TR is believed to be a dynamic layer, quasi-steady flows lasting
from several hours to several days are often present in the quiet
Sun, coronal holes, and active regions, indicating some kind of
plasma circulation/convection in the TR and corona. The emission of
hydrogen Lyman lines, which originates from the lower TR, has also
been intensively investigated in the recent past. Observations show
clearly that the flows and dynamics in the middle and upper TR can
greatly modify the Lyman line profiles.
Title: Electron transport in the solar wind -results from numerical
simulations
Authors: Smith, Håkan; Marsch, Eckart; Helander, Per
Bibcode: 2010cosp...38.1889S
Altcode: 2010cosp.meet.1889S
A conventional fluid approach is in general insufficient for a
correct description of electron trans-port in weakly collisional
plasmas such as the solar wind. The classical Spitzer-Hürm theory
is a not valid when the Knudsen number (the mean free path divided
by the length scale of tem-perature variation) is greater than ∼
10-2 . Despite this, the heat transport from Spitzer-Hürm a theory
is widely used in situations with relatively long mean free paths. For
realistic Knud-sen numbers in the solar wind, the electron distribution
function develops suprathermal tails, and the departure from a local
Maxwellian can be significant at the energies which contribute the
most to the heat flux moment. To accurately model heat transport a
kinetic approach is therefore more adequate. Different techniques
have been used previously, e.g. particle sim-ulations [Landi, 2003],
spectral methods [Pierrard, 2001], the so-called 16 moment method
[Lie-Svendsen, 2001], and approximation by kappa functions [Dorelli,
2003]. In the present study we solve the Fokker-Planck equation for
electrons in one spatial dimension and two velocity dimensions. The
distribution function is expanded in Laguerre polynomials in energy,
and a finite difference scheme is used to solve the equation in the
spatial dimension and the velocity pitch angle. The ion temperature
and density profiles are assumed to be known, but the electric field is
calculated self-consistently to guarantee quasi-neutrality. The kinetic
equation is of a two-way diffusion type, for which the distribution of
particles entering the computational domain in both ends of the spatial
dimension must be specified, leaving the outgoing distributions to be
calculated. The long mean free path of the suprathermal electrons has
the effect that the details of the boundary conditions play an important
role in determining the particle and heat fluxes as well as the electric
potential drop across the domain. Dorelli, J. C., and J. D. Scudder,
J. D. 2003, J. Geophys. Res. 108, 1294. Landi, S., and Pantellini,
F. G. E. 2003, Astron. Astrophys., 400, 769. Lie-Svendsen, Ø., Leer,
E., and Hansteen, V. H. 2001, J. Geophys. Res., 106, 8217. Pierrard,
V., Maksimovic, M., and Lemaire, J. 2001, J. Geophys. Res., 106, 29305.
Title: The Nascent Fast Solar Wind Observed by the EUV Imaging
Spectrometer on Board Hinode
Authors: Tian, Hui; Tu, Chuanyi; Marsch, Eckart; He, Jiansen; Kamio,
Suguru
Bibcode: 2010ApJ...709L..88T
Altcode: 2009arXiv0912.4316T
The origin of the solar wind is one of the most important unresolved
problems in space and solar physics. We report here the first
spectroscopic signatures of the nascent fast solar wind on the basis
of observations made by the EUV Imaging Spectrometer on Hinode in a
polar coronal hole in which patches of blueshift are clearly present on
Dopplergrams of coronal emission lines with a formation temperature of
lg(T/K)>5.8. The corresponding upflow is associated with open field
lines in the coronal hole and seems to start in the solar transition
region and becomes more prominent with increasing temperature. This
temperature-dependent plasma outflow is interpreted as evidence of the
nascent fast solar wind in the polar coronal hole. The patches with
significant upflows are still isolated in the upper transition region
but merge in the corona, in agreement with the scenario of solar wind
outflow being guided by expanding magnetic funnels.
Title: A new view of solar wind origin near active regions and in
polar coronal holes on the basis of Hinode observations
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Tian, Hui; Guo,
Lijia; Curdt, Werner; Xia, Lidong; Kamio, Suguru
Bibcode: 2010cosp...38.2938H
Altcode: 2010cosp.meet.2938H
The possibility of full-range solar observations from Hinode with high
temporal and spatial resolution motivated us to revisit the solar wind
origin in the solar atmosphere. For the solar wind origin near active
regions, we reveal activity in the chromosphere to be responsible for
the coronal outflow at the AR edge; meanwhile we also succeeded in
finding the related solar wind stream in the heliosphere. Chromospheric
spicule-like jets are found to occur intermittently, and to flow
in similar direction than the intermittent coronal outflows. EIS
observations reveal that there are blue-shifts at the edge of AR
in both chromosphere and corona, and that the blue-shift increases
with temperature. Therefore, we suggest that the nascent solar wind
may probably originate in the chromosphere at the edge of ARs. The
connection between the source regions and their respective solar
wind streams is established through magnetic field lines, which are
extrapolated to reach the solar ecliptic plane at 2.5 Rs. We find that
the AR edge may be the source region of an intermediate-speed (400 km/s)
solar wind stream. For the solar wind origin in polar coronal holes
(CHs), we extend the blue-shift observations from the transition
region up to the corona, investigate the magnetic characteristics
in association with the polar coronal jets, and study in details the
initial phase of meso-scale loop eruption in polar CHs. We find that the
blue-shift becomes more and more dominant with increasing temperature
from the transition region to the corona. The polar coronal jets are
found to be elongated along the extrapolated open field lines, which
appear in fanning-out shape. The cancellation between bipolar magnetic
fields, or squeezing of monopolar magnetic fields, may be the driver for
a jet launch. The meso-scale loop started its eruption with a sudden
brightening at one footpoint, then expanded and moved upwardly with a
speed of 20 km/s, causing the mass at the footpoint to flow outwardly
and to fill in the expanded volume. We suggest that mass confined in
the coronal loops may be dynamically released into the outer corona
and even heliosphere via magnetic reconnection. References: [1]. He,
J.-S., Marsch, E., Tu, C.-Y., Guo, L.-J., Tian, H., Intermittent
outflows at the edge of an active region -a possible source of the
solar wind. Submitted to AA. [2]. Tian, H., Tu, C.-Y., Marsch, E.,
He, J.-S., Kamio, S., The nascent fast solar wind observed by the EUV
imaging spectrometer on board Hinode, ApJ, 709, L88-L93, 2010. [3]. He,
J.-S., Marsch, E., Curdt, W., Tu, C.-Y., Xia, L.-D., Tian, H., Kamio,
S., Meso-scale coronal jets and erupting loops guided by magnetic
fields in a polar coronal hole region, in preparation.
Title: Analysis of Magnetic Clouds Evolution from 0.3 to 5
Astronomical Units
Authors: Dasso, Sergio; Gulisano, Adriana Maria; Demoulin, Pascal;
Marsch, Eckart
Bibcode: 2010cosp...38.1922D
Altcode: 2010cosp.meet.1922D
Magnetic clouds (MCs) are transient structures in the solar wind,
formed by large scale magnetic flux ropes as deduced from in situ
observations of magnetic field. Moreover, in situ observations of
the plasma velocity frequently show a clear evidence of an expansion
in the radial direction from the Sun, unlike in the solar wind. This
expansion has important consequences on the MC evolution, such as on
the rates of decrease of mass density or magnetic field intensity. The
aim of this work is to show properties of the evolution of MCs in
the inner and outer heliosphere from 0.3 to 5 AUs. We present here an
analysis of MCs observed by the Helios and Ulysses spacecraft, using
in situ magnetic field and bulk plasma measurements. We analyze the
dependence of several properties of MCs with the distance to the Sun,
and in particular we analyze the dimensionless local expansion rate
(ζ) [e.g. Démoulin et al., 2008]. We explore the dependence of
the expansion speed on the MC size, the translation velocity, and
the heliocentric distance, finding that there is a subset of MCs with
almost the same non-dimensional expansion rate (ζ). The time velocity
profile observed in this subset of MCs is almost linear, then we call
them non perturbed MCs. These MCs expand at rates ζ consistent with
the expected value from the global pressure decay in the surrounding
solar wind for increasing helio-distances, while perturbed ones may
present strong departures from that global rule. We interpret these
departures of ζ for perturbed MCs as a consequence of the interaction
of MCs with fast streams on their expansion.
Title: Multi-strand Coronal Loop Model and Filter-ratio Analysis
Authors: Bourouaine, Sofiane; Marsch, Eckart
Bibcode: 2010ApJ...708.1281B
Altcode: 2009arXiv0911.3506B
We model a coronal loop as a bundle of seven separate strands or
filaments. Each of the loop strands used in this model can independently
be heated (near their left footpoints) by Alfvén/ion-cyclotron waves
via wave-particle interactions. The Alfvén waves are assumed to
penetrate the strands from their footpoints, at which we consider
different wave energy inputs. As a result, the loop strands can
have different heating profiles, and the differential heating can
lead to a varying cross-field temperature in the total coronal
loop. The simulation of Transition Region and Coronal Explorer
(TRACE) observations by means of this loop model implies two uniform
temperatures along the loop length, one inferred from the 171:195
filter ratio and the other from the 171:284 ratio. The reproduced
flat temperature profiles are consistent with those inferred from the
observed extreme-ultraviolet coronal loops. According to our model,
the flat temperature profile is a consequence of the coronal loop
consisting of filaments, which have different temperatures but almost
similar emission measures in the cross-field direction. Furthermore,
when we assume certain errors in the simulated loop emissions (e.g.,
due to photometric uncertainties in the TRACE filters) and use the
triple-filter analysis, our simulated loop conditions become consistent
with those of an isothermal plasma. This implies that the use of
TRACE or EUV Imaging Telescope triple filters for observation of a
warm coronal loop may not help in determining whether the cross-field
isothermal assumption is satisfied or not.
Title: Decay of Alfven-cyclotron waves and kinetic effects on ions
in the solar wind
Authors: Marsch, E.; Araneda, J. A.; Maneva, Y.
Bibcode: 2009AGUFMSH51C..04M
Altcode:
Vlasov theory and one-dimensional hybrid simulations are used to study
the effects that compressive fluctuations, driven by the parametric
instabilities of an Alfven-cyclotron pump wave, have on ion velocity
distributions in the solar wind. The resulting longitudinal ion-acoustic
waves (IAW) and transverse ion-cyclotron (ICW) waves can selectively
destroy the coherent fluid motion of the ions in the pump wave and lead
to differential effects. Trapping of the more abundant protons by fast
IAWs generates a proton beam with a drift at about the Alfven speed. The
major core part of the proton distribution becomes due to phase mixing
anisotropic. Because of their larger mass, the alpha particles do
not become significantly trapped, but start by conservation of total
ion momentum drifting relative to the receding bulk protons. The core
protons and alpha particles are differentially heated and accelerated
via ICW pitch-angle scattering. We identify key instabilities and find
that, even in the parameter regime where fluid theory seems appropriate,
kinetic effects prevail.
Title: Multi-spacecraft observation of a magnetic cloud
Authors: de Lucas, A.; Dal Lago, A.; Schwenn, R.; Clua de Gonzalez,
A. L.; Marsch, E.; Gonzalez, W. D.
Bibcode: 2009AGUFMSH13B1515D
Altcode:
During the time operation of the Helios mission, from 1974 to 1986,
a large number of magnetic clouds was identified by the magnetic
field and solar wind sensors onboard the probes. Among these magnetic
clouds, some of them were identified by at least two probes, provided
that IMP-8 and ISEE-3 were monitoring the dayside magnetosphere. The
magnetic cloud observed on from DOY 029 to DOY 030/1977 by Helios 1,
Helios 2, and IMP-8 represents a potential multi-spacecraft observed
magnetic cloud. Despite the interaction with the high-speed stream
that compressed the magnetic cloud, the minimum variance analysis
technique showed the same direction of rotation of the magnetic field
inside the magnetic cloud. This helped to associate the observation
of the magnetic cloud at multi-spacecraft.
Title: Excitation of Kink Waves Due to Small-Scale Magnetic
Reconnection in the Chromosphere?
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Tian, Hui
Bibcode: 2009ApJ...705L.217H
Altcode:
The kink wave, which has often been observed in coronal loops, is
considered as a possibly important energy source contributing to coronal
heating. However, its generation has not yet been observed. Here, we
report the first observation of kink-wave excitation caused by magnetic
reconnection as inferred from Solar Optical Telescope measurements made
in the Ca II line. We observed transverse-displacement oscillations
on a spicule which propagated upwardly along the spicule trace and
originated from the cusp of an inverted Y-shaped structure, where
apparently magnetic reconnection occurred. Such transverse oscillation
of an individual spicule is interpreted by us to be the signature
of a kink wave that was excited by magnetic reconnection. We present
the height variations of the velocity amplitude, δv, and the phase
speed, C k, of the kink wave, starting from its source
region. The kink wave is found to steepen with height and to evolve
into a nonlinear state with a large relative disturbance, yielding a
(δv/C k) of 0.21 at 5.5 Mm. This nonlinear kink wave seems
to be damped in velocity amplitude beyond 5.5 Mm, which may result from
the conversion of transverse-fluctuation energy to longitudinal-motion
energy required to sustain the spicule. We also estimate the energy
flux density carried by the kink wave, and in spite of its attenuation
in the transition region conclude it to be sufficient for heating the
quiet corona. Our findings shed new light on future modeling of coronal
heating and solar wind acceleration involving magnetic reconnection
in the chromosphere.
Title: Upflows in Funnel-like Legs of Coronal Magnetic Loops
Authors: Tian, Hui; Marsch, Eckart; Curdt, Werner; He, Jiansen
Bibcode: 2009ApJ...704..883T
Altcode: 2009arXiv0909.0739T
The prominent blueshifts of Ne VIII associated with the junctions of the
magnetic network in the quiet Sun are still not well understood. By
comparing the coronal magnetic-field structures as obtained by a
potential-field reconstruction with the conspicuous blueshift patches
on the Dopplergram of Ne VIII as observed in an equatorial quiet-Sun
region, we find that most of the regions with significant upflow are
associated with the funnel-like legs of magnetic loops and cospatial
with increments of the line width. These quasi-steady upflows can be
regarded as the signatures of mass supply to coronal loops. By using the
square root of the line intensity as a proxy for the plasma density,
the mass flux of the upflow in each funnel can be estimated. We find
that the mass flux is anti-correlated with the funnel's expansion factor
as determined from the extrapolated magnetic field. One of the loop
systems is associated with a coronal bright point, which was observed
by several instruments and exhibited various morphologies in different
wavelengths and viewing directions. A remarkable agreement between its
magnetic structure and the associated EUV emission pattern was found,
suggesting an almost potential-field nature of the coronal magnetic
field. We also report the direct detection of a small-scale siphon flow
by both STEREO satellites. However, this transient siphon flow occurred
in a weak mixed-polarity-field region, which was outside the adjacent
magnetic funnel, and thus it is perhaps not related to plasma upflow
in the funnel. Based on these observations, we suggest that at upper
transition region (TR) temperatures the dominant flows in quiet-Sun
coronal loops are long-lasting upflows rather than siphon flows. We
also discuss the implications of our results for coronal heating and
unresolved magnetic structures.
Title: Solar transition region above sunspots
Authors: Tian, H.; Curdt, W.; Teriaca, L.; Landi, E.; Marsch, E.
Bibcode: 2009A&A...505..307T
Altcode: 2009arXiv0906.2211T
Aims: We study the transition region (TR) properties above sunspots and
the surrounding plage regions, by analyzing several sunspot reference
spectra obtained by the SUMER (Solar Ultraviolet Measurements of Emitted
Radiation) instrument in March 1999 and November 2006.
Methods:
We compare the SUMER spectra observed in the umbra, penumbra, plage,
and sunspot plume regions. The hydrogen Lyman line profiles averaged
in each of the four regions are presented. For the sunspot observed
in 2006, the electron densities, differential emission measure (DEM),
and filling factors of the TR plasma in the four regions are also
investigated.
Results: The self-reversals of the hydrogen Lyman
line profiles are almost absent in sunspots at different locations (at
heliocentric angles of up to 49°) on the solar disk. In the sunspot
plume, the Lyman lines are also not reversed, whilst the lower Lyman
line profiles observed in the plage region are obviously reversed, a
phenomenon found also in the normal quiet Sun. The TR densities of the
umbra and plume are similar and one order of magnitude lower than those
of the plage and penumbra. The DEM curve of the sunspot plume exhibits
a peak centered at log(T / K) ~ 5.45, which exceeds the DEM of other
regions by one to two orders of magnitude at these temperatures. We
also find that more than 100 lines, which are very weak or not observed
anywhere else on the Sun, are well observed by SUMER in the sunspot,
especially in the sunspot plume.
Conclusions: We suggest that the
TR above sunspots is higher and probably more extended, and that the
opacity of the hydrogen lines is much lower above sunspots, compared to
the TR above plage regions. Our result indicates that the enhanced TR
emission of the sunspot plume is probably caused by a large filling
factor. The strongly enhanced emission at TR temperatures and the
reduced continuum ensure that many normally weak TR lines are clearly
distinctive in the spectra of sunspot plumes. Tables 5 and 6 are
only available in electronic form at http://www.aanda.org
Title: Hydrogen Lyman-α and Lyman-β spectral radiance profiles in
the quiet Sun
Authors: Tian, H.; Curdt, W.; Marsch, E.; Schühle, U.
Bibcode: 2009A&A...504..239T
Altcode: 2009arXiv0907.1069T
Aims: We extend earlier work by studying the line profiles of the
hydrogen Lyman-α and Lyman-β lines in the quiet Sun. They were
obtained quasi-simultaneously in a raster scan with a size of about
150'' × 120'' near disk center.
Methods: The self-reversal depths
of the Ly-α and Ly-β profiles. we are quantified by measuring the
maximum spectral radiances of the two horns and the minimum spectral
radiance of the central reversal. The information on the asymmetries
of the Ly-α and Ly-β profiles is obtained through calculating
the 1st and 3rd-order moments of the line profiles. By comparing
maps of self-reversal depths and the moments with radiance images
of the Lyman lines, photospheric magnetograms, and Dopplergrams of
two other optically thin lines, we studied the spatial distribution
of the Ly-α and Ly-β profiles with different self-reversal depths,
and investigated the relationship between profile asymmetries and flows
in the solar atmosphere.
Results: We find that the emissions of
the Lyman lines tend to be more strongly absorbed in the internetwork,
as compared to those in the network region. Almost all of the Ly-α
profiles are self-reversed, while about 17% of the Ly-β profiles are
not reversed. The ratio of Ly-α and Ly-β intensities seems to be
independent of the magnetic field strength. Most Ly-α profiles are
stronger in the blue horn, whereas most Ly-β profiles are stronger
in the red horn. However, the opposite asymmetries of Ly-α and
Ly-β are not correlated pixel-to-pixel. We also confirm that when
larger transition-region downflows are present, the Ly-α and Ly-β
profiles are more enhanced in the blue and red horns, respectively. The
first-order moment of Ly-β, which reflects the combined effects of
the profile asymmetry and motion of the emitting material, strongly
correlates with the Doppler shifts of the Si iii and O vi lines, while
this correlation is much weaker for Ly-α. Our analysis shows that both
Ly-α and Ly-β might be more redshifted if stronger transition-region
downflows are present. We also find that the observed average Ly-β
profile is redshifted with respect to its rest position.
Title: Drift instabilities in the solar corona within the multi-fluid
description
Authors: Mecheri, R.; Marsch, E.
Bibcode: 2009A&A...503..589M
Altcode:
No abstract at ADS
Title: Radial evolution of nonthermal electron populations in the
low-latitude solar wind: Helios, Cluster, and Ulysses Observations
Authors: Štverák, Štěpán; Maksimovic, Milan; Trávníček,
Pavel M.; Marsch, Eckart; Fazakerley, Andrew N.; Scime, Earl E.
Bibcode: 2009JGRA..114.5104S
Altcode: 2009JGRA..11405104S
We have performed a statistical study of a substantial amount of solar
wind electron velocity distribution functions (eVDFs). In our data set,
we combine measurements acquired onboard three spacecrafts (Helios,
Cluster II, and Ulysses) in the low ecliptic latitudes covering the
heliocentric distance from 0.3 up to 4 AU. In this study, we focus
on the nonthermal properties of the measured eVDFs in both the slow
and the fast solar wind regimes. The aim of the present study is (1)
to provide, for the first time, an analytical model to fit separately
all three components of the solar wind eVDFs (i.e., the core, the
halo, and the strahl) and (2) to study the fractional densities of
the three electron components and also the non-Maxwellian character of
the high-energy eVDF tails as a function of the radial distance from
the sun. Basically, our study is incremental to the previous studies
of the fast solar wind and primarily extends their conclusions on
a large number of slow wind observations in the ecliptic plane. We
confirm that the halo and the strahl relative densities vary in an
opposite way. The relative number of strahl electrons is decreasing
with radial distance, whereas the relative number of halo electrons
is increasing. The fractional density of the core population remains
roughly constant. These findings suggest that there are mechanisms in
the solar wind that scatter the strahl electrons into the halo. Also,
we find that the relative importance of the nonthermal electrons in
the fast solar wind is slightly higher compared to the slow wind.
Title: Preferential Heating and Acceleration of α Particles by
Alfvén-Cyclotron Waves
Authors: Araneda, J. A.; Maneva, Y.; Marsch, E.
Bibcode: 2009PhRvL.102q5001A
Altcode:
Preferential heating and acceleration of heavy ions in the solar
wind and corona represent a long-standing theoretical problem in
space physics, and are distinct experimental signatures of kinetic
processes occurring in collisionless plasmas. We show that fast
and slow ion-acoustic waves (IAW) and transverse waves, driven by
Alfvén-cyclotron wave parametric instabilities can selectively
destroy the coherent fluid motion of different ion species and, in
this way lead to their differential heating and acceleration. Trapping
of the more abundant protons by the fast IAW generates a proton beam
with drift speed of about the Alfvén speed. Because of their larger
mass, α particles do not become significantly trapped and start, by
conservation of total ion momentum, drifting relative to the receding
bulk protons. Thus the resulting core protons and the α particles
are differentially heated via pitch-angle scattering.
Title: Upward Propagating Alfvén Wave and its Connection With
Magnetic Reconnection in the Chromosphere as Observed by SOT
Authors: Tu, C.; He, J.; Marsch, E.; Tian, H.; Guo, L.; Yao, S.
Bibcode: 2009AGUSMSH31B..02T
Altcode:
We identify high-frequency Alfvén waves propagating upward in the solar
chromosphere and transition region from observational data obtained
by the Solar Optical Telescope (SOT) onboard Hinode. We find that in
four cases the spicules are modulated by high-frequency (>0.02~Hz)
transverse fluctuations, which are inferred to be associated with
Alfvén waves. They apparently propagate upward along the spicules with
phase speeds ranging from 50 to 150~km/s. Three of these modulated
spicules show clear wave-like shapes, with short wavelengths being
less than 8~Mm. In our analysis we thus identified directly upward
propagation of Alfvén waves in the solar chromosphere and transition
region. In addition to the recently reported Alfvén waves with
very long wavelengths and wave periods, we find here four examples
of Alfvén waves with shorter wavelengths and periods. Moreover,
we report observational evidence for Alfvén-wave excitation due to
magnetic reconnection. These findings shed new light on the wave origin
and on the coronal and solar-wind heating by waves.
Title: Radial Evolution of Non-thermal Electron populations in the
Low-latitude Solar Wind: Helios, Cluster and Ulysses observations
Authors: Stverak, S.; Travnicek, P. M.; Maksimovic, M.; Marsch, E.;
Fazakerley, A. N.; Scime, E. E.
Bibcode: 2009EGUGA..1111960S
Altcode:
We have performed a statistical study of a substantial amount of solar
wind electron velocity distribution functions (eVDFs). In our data set
we combine measurements acquired on-board three spacecraft (HELIOS,
CLUSTER II and ULYSSES) in the low ecliptic latitudes covering the
heliocentric distance from 0.3 up to 4 AU. In this study we focus on the
non-thermal properties of the measured eVDFs in both the slow and the
fast solar wind regimes. All three eVDF components typically observed
in the solar wind, i.e. the core, the halo and the strahl, are modeled
analytically. We study the radial evolution of the basic eVDF moments,
i.e. density, temperature and heatflux, of the three electron components
and also the non-Maxwellian character of the high energy eVDF tails as
a function of the radial distance from the Sun. In addition, we provide
results on break-point energy between thermal and nonthermal part of
the eVDF and verify also the zero-current condition. We then summarize
all mean electron properties in the radial evolution of the model eVDF.
Title: Upward propagating high-frequency Alfvén waves as identified
from dynamic wave-like spicules observed by SOT on Hinode
Authors: He, J. -S.; Tu, C. -Y.; Marsch, E.; Guo, L. -J.; Yao, S.;
Tian, H.
Bibcode: 2009A&A...497..525H
Altcode:
Aims: We identify high-frequency Alfvén waves propagating upward in
the solar chromosphere and transition region from observation by Solar
Optical Telescope (SOT) onboard Hinode.
Methods: The spicule shape
is enhanced through application of a normal radial gradient filter and
an un-sharp mask on the images taken by SOT. The displaced position
of the spicule is at each height obtained by tracing the maximum
intensity after image processing. The dominant wave period is obtained
by the FFT method applied to the time variations of the displaced
position at a certain height. The phase speed is estimated with the
help of a cross-correlation analysis of two temporal sequences of the
displaced positions at two heights along the spicule.
Results:
We find in four cases that the spicules are modulated by high-frequency
(≥0.02 Hz) transverse fluctuations. Such fluctuations are suggested
to be Alfvén waves that propagate upward along the spicules with
phase speed ranges from 50 to 150 km s-1. Three of the
modulated spicules show clear wave-like shapes with short wavelengths
less than 8 Mm.
Conclusions: Our work identified directly upward
propagation of Alfvén waves in the solar chromosphere and transition
region. In addition to the recently reported Alfvén waves with very
long wavelength and wave period, we find here four examples of Alfvén
waves with shorter wavelengths and periods. These findings shed new
light on the wave origin and on coronal and solar-wind heating.
Title: Parametrically Unstable Alfvén-cyclotron Waves and
Wave-Particle Interactions in the Solar Corona and Solar Wind
Authors: Maneva, Y. G.; Araneda, J. A.; Marsch, E.
Bibcode: 2009AIPC.1121..122M
Altcode:
We consider the parametric instabilities of large-amplitude
Alfvén/ion-cyclotron waves and the consequent wave-particle
interactions, and discuss their importance for modelling the
evolution of ion velocity distribution functions in the tenuous and
collisionless plasma of a coronal hole and the fast solar wind. We
perform 1D hybrid simulations to study the nonlinear evolution of the
parametric instabilities by analyzing the simulation results in terms
of microinstabilities and discussing the influence of both Landau and
cyclotron resonances on the evolution of the ion distributions. We
demonstrate the origin of a relative drift between the protons
and alpha particles, show the related anisotropic ion heating and
follow the simultaneous proton beam formation. Finally, we focus on
the development and evolution of both electromagnetic and acoustic
micro-turbulence and present indications for an inverse energy cascade
from shorter to longer wavelengths.
Title: Proton beam velocity distributions and prominence material
in ICME
Authors: Marsch, E.; Yao, S.; Tu, C. Y.
Bibcode: 2009EGUGA..11.1465M
Altcode:
This work discusses two phenomena in Interplanetary Coronal
Mass Ejection (ICME)(1)proton beam velocity distribution (2) cold
high-density material. The plasma and magnetic-field instruments on the
Helios 2 spacecraft detected three events of interplanetary coronal
mass ejections, which occurred on 3 April 1979 at the location of
0.68 AU, on 9 May 1979 at 0.29 AU and on 30 March 1976 at 0.48 AU,
named as case 1, case 2 and case 3, respectively. All three cases
were revealed by the typical signature of magnetic field rotation,
indicating a force-free magnetic flux tube. We present here, to our
knowledge for the first time, the detailed proton velocity distributions
measured within an ICME. In case 1, a beam velocity distribution was
observed which lasted for almost an hour. These cold distributions
were characterized by an isotropic core part with a low temperature,
T ≤ 105 K, and by a broad and extended hot proton beam propagating
along the local magnetic field direction with a speed of a sizable
fraction of the local Alfv
Title: Multi-spacecraft observations to study the shock extension
in the inner heliosphere
Authors: de Lucas, Aline; Schwenn, Rainer; Marsch, Eckart; Lago,
Alisson Dal; de Gonzalez, Alicia L. Clúa; Echer, Ezequiel; Gonzalez,
Walter D.; da Silva, Marlos R.
Bibcode: 2009IAUS..257..481D
Altcode:
The two Helios probes traveled at variable longitudinal and radial
separations through the inner heliosphere. They collected most valuable
high resolution plasma and magnetic field data for an entire solar
cycle. The mission is still so successful that no other missions
will collect the same kind of data in the next 20 years. One of the
subjects studied after the success of the Helios mission was the
identification of more than 390 shock waves driven by Interplanetary
Coronal Mass Ejections (ICMEs). Combining the data from both probes,
we make a statistical study for the extension of the shock waves in
the interplanetary medium. For longitudinal separations of 90° we
found a cutoff value at this angular separation. A shock has 50%
of chance to be observed by both probes and the same probability
for not being observed by two spacecrafts at the same time, when the
angle between them is around 90°. We describe the dependence of the
probability for shocks to be observed by both probes with decreasing
spacecraft separation. Including plasma data from the ISEE-3 and IMP-8
spacecrafts improves our statistical evaluation substantially.
Title: Multiple-spacecraft study of an extended magnetic structure
in the solar wind
Authors: Ruan, P.; Korth, A.; Marsch, E.; Inhester, B.; Solanki, S.;
Wiegelmann, T.; Zong, Q. -G.; Bucik, R.; Fornacon, K. -H.
Bibcode: 2009JGRA..114.2108R
Altcode: 2009JGRA..11402108R
An extended magnetic structure was observed consecutively by five
spacecraft (ACE, WIND, STEREO A and B, and CLUSTER) in the solar wind on
15 January 2007. The similar bipolar magnetic field variations from five
spacecraft suggest that the magnetic structure is two-dimensional. The
abrupt disappearance of the beam electrons in the core of the structure
suggests that the core of the structure is magnetically isolated from
the surrounding environment. Our analysis shows that this magnetic
structure is a magnetic flux rope, which extends over at least 180 R
E in space. The length and orientation of the flux rope were
determined by a local minimum variance analysis (MVA) from individual
spacecraft observations of the magnetic field and a timing analysis
based on the joint observations by all five spacecraft. The results
show that the orientation of the flux rope stays constant in space
and time. The flux rope is embedded in a corotating interaction region
(CIR), which followed a magnetic cloud.
Title: Proton beam velocity distributions in an interplanetary
coronal mass ejection
Authors: Marsch, E.; Yao, S.; Tu, C. -Y.
Bibcode: 2009AnGeo..27..869M
Altcode:
The plasma and magnetic-field instruments on the Helios 2 spacecraft,
which was on 3 April 1979 located at 0.68 AU, detected an interplanetary
coronal mass ejection (ICME) that revealed itself by the typical
signature of magnetic field rotation. The solar wind flow speed
ranged between 400 and 500 km/s. We present here some detailed
proton velocity distributions measured within the ICME. These cold
distributions are characterized by an isotropic core part with a low
temperature, T≤105 K, but sometimes reveal a broad and
extended hot proton tail or beam propagating along the local magnetic
field direction. These beams lasted only for about an hour and were
unusual as compared with the normal ICME protons distribution which
were comparatively isotropic. Furthermore, we looked into the velocity
and field fluctuations in this ICME and found signatures of Alfvén
waves, which might be related to the occurrence of the hot proton
beams. However, it cannot be excluded that the beam originated from
the Sun.
Title: Solar Space Missions: present and future
Authors: Solanki, Sami K.; Marsch, Eckart
Bibcode: 2009RvMA...21..229S
Altcode:
No abstract at ADS
Title: Future high-latitude observations anticipated from the Solar
Orbiter mission
Authors: Woch, J.; Solanki, S. K.; Marsch, E.
Bibcode: 2008AGUFMSH44A..08W
Altcode:
As one of the cornerstones of the HELEX programme, the Solar Orbiter
mission is currently scheduled for launch in 2015. After an initial
cruise phase, Solar Orbiter will reach its science orbit in 2018. This
orbit comprises initially a nearly Sun-synchronous phase at a distance
of only 0.22 AU from Sun center. In a later stage, the orbital
inclination will be raised, thus allowing Solar Orbiter to reach
solar latitudes of about 35 degrees, and making it the first mission
after Ulysses to study the Sun from a high-latitude vantage point. In
contrast to Ulysses, however, Solar Orbiter will carry a complementary
suite of both, in-situ and remote- sensing instruments, which will
allow the study of the solar atmosphere to be extended to the largely
unexplored polar regions of the Sun. The polar magnetic fields are
responsible for the polar coronal holes driving the fast solar wind,
but are poorly known. From its vantage point outside the ecliptic,
Solar Orbiter will uncover the surface and sub-surface flows at the
poles, the polar magnetic field structure and its evolution. It will
provide new insights into the formation of the polar coronal holes,
the nature of their boundaries and the acceleration of the fast
solar wind emanating from the holes. The potential of Solar Orbiter
for investigating the acceleration mechanism of the fast wind, the
plumes and X-ray jets at the poles, and the high-latitude meridional
circulation will be discussed.
Title: Solar Wind Measurements on Solar Orbiter: Discovering the
Links Between the Solar Wind and the Atmosphere of our Sun
Authors: Livi, S. A.; Allegrini, F.; Collier, M.; Desai, M.; Galvin,
A.; Kasper, J.; Kistler, L.; Korreck, K.; Lepri, S.; McComas, D.;
Schwadron, N.; Zurbuchen, T.; Owen, C.; Louarn, P.; Bruno, R.;
Marsch, E.
Bibcode: 2008AGUFMSH51A1597L
Altcode:
The Solar Orbiter spacecraft will be launched in 2015 and will include
the Solar Wind Analyzer instrumentation suite. This space mission will
allow for unprecedented data collection of particle characteristics
near the Sun at various heliolatitudes during both the quiet and
active phases of the solar cycle. The close proximity will allow
for determination of the source regions on the sun for the observed
events. Of particular interest will be the study of the origins of
and processes related to solar energetic particles. This mission will
lead to a better understanding of the Sun and the interstellar medium
in our solar system.
Title: Radial Evolution of Non-thermal Electrons in the Low-latitude
Solar Wind: Helios, Cluster and Ulysses Observations
Authors: Stverak, S.; Travnicek, P.; Maksimovic, M.; Marsch, E.;
Fazakerley, A. N.; Scime, E. E.
Bibcode: 2008AGUFMSH21A1581S
Altcode:
We have performed a statistical study of a substantial amount of solar
wind electron velocity distribution functions (eVDFs). In our data set
we combine measurements acquired on-board three spacecraft (HELIOS,
CLUSTER II and ULYSSES) in the low ecliptic latitudes covering the
heliocentric distance from 0.3 up to 4 AU. In this study we focus
on the non-thermal properties of the measured eVDFs in both the slow
and the fast solar wind regimes. All three eVDF components typically
observed in the solar wind, i.e. the core, the halo and the strahl,
are modeled analytically. We mainly study the fractional densities of
the three electron components and also the non-Maxwellian character of
the high energy eVDF tails as a function of the radial distance from
the Sun. Furthermore, we provide some preliminary results concerning
the higher eVDF moments, i.e. the temperature of the eVDF components
and their contribution to the overall electron heat flux. In addition,
we summarize all mean electron properties in the radial evolution of
the model eVDF.
Title: The redshifted network contrast of transition region emission
Authors: Curdt, W.; Tian, H.; Dwivedi, B. N.; Marsch, E.
Bibcode: 2008A&A...491L..13C
Altcode: 2009arXiv0901.0808C
Aims: We study the VUV emission of the quiet Sun and the net redshift
of transition region lines in the SUMER spectral range. We aim at
establishing a link with atmospheric processes and interpreting the
observed downflow as the most evident part of the prevailing global
coronal mass transport.
Methods: We rank and arrange all pixels
of a monochromatic raster scan by radiance and define equally-sized
bins of bright, faint, and medium-bright pixels. Comparing the bright
pixels with the faint pixels, we determine the spectrally-resolved
network contrast for 19 emission lines. We then compare the contrast
centroids of these lines with the position of the line itself. We
establish a relationship between the observed redshift of the network
contrast with the line formation temperature.
Results: We find
that the network contrast is offset in wavelength compared to the
emission line itself. This offset, if interpreted as redshift, peaks
at middle transition region temperatures and is 10 times higher than
the previously reported net redshift of transition region emission
lines. We demonstrate that the brighter pixels are more redshifted,
causing both a significant shift of the network contrast profile and the
well-known net redshift. We show that this effect can be reconstructed
from the radiance distribution. This result is compatible with loop
models, which assume downflows near both footpoints.
Title: Plasma Flows Guided by Strong Magnetic Fields in the Solar
Corona
Authors: Marsch, Eckart; Tian, Hui; Sun, Jian; Curdt, Werner;
Wiegelmann, Thomas
Bibcode: 2008ApJ...685.1262M
Altcode:
In this study new results are presented regarding the relationships
between the coronal magnetic field and the intensities and Doppler
shifts of ultraviolet emission lines. This combination of magnetic
field and spectroscopic data is used here to study material flows in
association with the coronal field. We introduce the term "coronal
circulation" to describe this flow, and to indicate that the plasma is
not static but flows everywhere in the extended solar atmosphere. The
blueshifts and redshifts often seen in transition region and coronal
ultraviolet emission lines are interpreted as corresponding to upflows
and downflows of the plasma on open (funnels) and closed (loops) coronal
magnetic field lines, which tightly confine and strongly lead the flows
in the low-beta plasma. Evidence for these processes exists in the
ubiquitous redshifts mostly seen at both legs of loops on all scales,
and the sporadic blueshifts occurring in strong funnels. Therefore,
there is no static magnetically stratified plasma in the corona, since
panta rhei, but rather a continuous global plasma circulation, being
the natural perpetuation of photospheric convection which ultimately
is the driver.
Title: Cool and Hot Components of a Coronal Bright Point
Authors: Tian, H.; Curdt, W.; Marsch, E.; He, J. -S.
Bibcode: 2008ESPM...122.113T
Altcode:
We performed a systematic study of the Doppler shifts and electron
densities measured in an EUV bright point (hereafter BP) observed in
more than 10 EUV lines with formation temperatures from log(T=K) =
4.5 to 6.3. Those parts of a BP seen in transition region and coronal
lines are defined as its cool and hot components, respectively. We find
that the transition from cool to hot occurs at a temperature around
log(T=K) = 5.7. The two components of the BP reveal a totally different
orientation and Doppler-shift pattern, which might result from a twist
of the associated magnetic loop system. The analysis of magnetic-field
evolution and topology seems to favour a two-stage heating process,
in which magnetic cancelation and separator reconnection are powering,
respectively, the cool and hot components of the BP. We also found
that the electron densities of both components of the BP are higher
than those of the surrounding quiet Sun, and comparable to or smaller
than active-region densities.
Title: On the Efficiency of Nonresonant Ion Heating by Coronal
Alfvén Waves
Authors: Bourouaine, Sofiane; Marsch, Eckart; Vocks, Christian
Bibcode: 2008ApJ...684L.119B
Altcode:
Nonresonant wave-particle interactions are studied within the framework
of quasi-linear theory for the reduced velocity distribution functions
of coronal ions. Our parametric study shows that in collisionless low-β
plasma, Alfvén waves at low-frequencies (with ω ll Ωi,
where Ωi is ion gyrofrequency) can heat ions perpendicularly
to the direction of the mean magnetic field. Consequently, a temperature
anisotropy can be achieved by the ions, whereby the heavy species
are heated more strongly, by a factor of the mass ratio, than the
protons. Yet in the lower corona, such wave-induced features will
be destroyed by collisions that are still strong there. Although
the coronal plasma β is small, Alfvén waves may efficiently heat
the nonresonant ions only if their energy is relatively large. The
heuristic values of wave energy needed for strong heating are, however,
much larger than the ones assumed in previous models and obtained from
recent observations. Nevertheless, heating of the ions by low-frequency
Alfvén waves can contribute to raising the temperature of the lower
solar transition region.
Title: The Redshifted Network Contrast - Signature of Coronal
Convectio
Authors: Curdt, W.; Tian, H.; Dwivedi, B. N.; Marsch, E.
Bibcode: 2008ESPM...12.2.92C
Altcode:
Observations and interpretations of red- and/or blueshifted emission
lines from cosmic objects are crucial to understanding the physical
processes at work there. The ubiquituous net redshifts of solar
transition region (TR) emission lines are known since the Skylab
era. Brekke et al. and Chae et al. independently verified this result
by analyzing the high spectral resolution observations from the
SUMER/SoHO instrument. Both these groups found similar results for
the quantitative dependence of the net redshift on line formation
temperatures from 30 000 K to 1 MK. To our knowledge, however, a
satisfactory physical explanation of the redshift is still a matter
of debate. We present a new method to explain the TR red shift, which
is based on the radiance-redshift relationship, and which employs the
redshift of the network contrast as compared to the position of the
emission line itself. In contrast to the earlier work, our indirect
method is unique in several ways namely, (i) it does not require
a good wavelength calibration and thus avoids related problems, (ii) it is independent of the knowledge of the exact rest wavelength,
and (iii) it intimately relies on the physical processes in the
solar atmosphere.
Title: Modeling of Solar Wind in the Coronal Funnel with Mass and
Energy Supplied at 5 Mm
Authors: He, J. -S.; Tu, C. -Y.; Marsch, E.
Bibcode: 2008SoPh..250..147H
Altcode: 2008SoPh..tmp..114H
The origin of the solar wind is a long-standing issue in both
observational and theoretical studies. To understand how and where in
the solar atmosphere the mass and energy of the solar wind are supplied
is very important. Previous observation suggests a scenario in which
the fast solar wind originates at heights above 5 Mm in the magnetically
open funnel, a process that is accompanied by downward flow below 5 Mm,
whereby the mass and energy are supplied through reconnection between
the open funnel and adjacent closed loops. Based on this scenario,
we develop a fluid model to study the solar wind generation under the
assumption that mass and energy are deposited in the open funnel at
5 Mm. The mass supply rate is estimated from the mass loss rate as
given by the emptying of the side loops as a result of their assumed
reconnection with the open funnel. Similarly, the energy input rate is
consistent with the energy release rate as estimated from the energy
flux associated with the reconnection between the open magnetic funnel
and the closed magnetic loops. Following the observations, we not
only simulate the plasma flowing upward to form the solar wind but
also calculate the downward flow back to the lower atmosphere. This
model is a first attempt to study physically the proposed scenario of
solar wind origin and gives a new physical illustration of the possible
initial deposition and consequent transportation of mass and energy
in the coronal funnel.
Title: Cool and Hot Components of a Coronal Bright Point
Authors: Tian, Hui; Curdt, Werner; Marsch, Eckart; He, Jiansen
Bibcode: 2008ApJ...681L.121T
Altcode: 2009arXiv0906.3005T
We performed a systematic study of the Doppler shifts and electron
densities measured in an EUV bright point (hereafter BP) observed in
more than 10 EUV lines with formation temperatures from log (T/K) =
4.5 to 6.3. Those parts of a BP seen in transition region and coronal
lines are defined as its cool and hot components, respectively. We find
that the transition from cool to hot occurs at a temperature around log
(T/K) = 5.7. The two components of the BP reveal a totally different
orientation and Doppler-shift pattern, which might result from a twist
of the associated magnetic loop system. The analysis of magnetic field
evolution and topology seems to favor a two-stage heating process, in
which magnetic cancellation and separator reconnection are powering,
respectively, the cool and hot components of the BP. We also found
that the electron densities of both components of the BP are higher
than those of the surrounding quiet Sun, and comparable to or smaller
than active region densities.
Title: Multi-Ion Kinetic Model for Coronal Loop
Authors: Bourouaine, Sofiane; Vocks, Christian; Marsch, Eckart
Bibcode: 2008ApJ...680L..77B
Altcode:
A multi-ion kinetic model for a coronal loop is presented, whereby ion
heating in the magnetically confined plasma is achieved by absorption
of ion-cyclotron waves. We assume that linear Alfvén/cyclotron
waves penetrate the loop from its footpoint and directly heat the
ions. Then due to electron-ion collisions the electrons can also
be heated. Depending on the spatial variation of the mean magnetic
field, the model is able to produce warm and hot model loops having
features similar to the ones observed in extreme-ultraviolet and
soft X-ray emissions in real coronal loops. Furthermore, it is found
that a loop with high expansion factor is far from local thermal
equilibrium (LTE) and shows remarkable temperature differences between
electrons and ions. Also in such a case, the heavy ions (minor ions)
are via resonant wave absorption heated more than the protons and
helium ions (major background ions), whereby the cyclotron-resonance
effect leads to a temperature anisotropy with T⊥ >
T∥. However, if the flux tube cross section is nearly
homogeneous, temperature isotropy of the ions is maintained in most
parts of the loop, and the plasma is nearly in LTE.
Title: Coronal Loop Model Including Ion Kinetics
Authors: Bourouaine, Sofiane; Vocks, Christian; Marsch, Eckart
Bibcode: 2008ApJ...676.1346B
Altcode:
We present a kinetic coronal loop model including collisions and
wave-particle interactions to study the mechanisms of loop heating. The
model is based on a quasi-linear treatment of the Vlasov equation for
the reduced velocity distribution functions of the protons, which are
the only ions considered in the loop plasma. For the energy input into
the loop, we assume that linear Alfvén waves penetrate the loop from
its footpoints and heat the protons via wave-particle interactions
and wave absorption. Through Coulomb collisions between protons and
electrons some thermal energy can be transferred to the electrons. It
turns out that in such a model protons are hotter than electrons,
and the scale length for proton heating along the loop is determined
by the dissipation scale of the ion-cyclotron waves. Through the
gyrofrequency this scale is connected to the cross section area of
the loop and, thus, to the spatial variation of the magnetic field
shaping the coronal loop. Furthermore, it is shown that in the case of a
nearly homogeneous flux tube cross section, an almost flat temperature
profile occurs along the major part of the loop with an enhanced
plasma density. These plasma parameter profiles are consistent with
those of loops having temperatures between 1 and 1.5 MK as observed in
extreme-ultraviolet emission. However, if the magnetic field lines are
more strongly diverging from the footpoints to the loop apex, the proton
heating is found to be more uniform, resulting in a higher temperature
and lower density along the loop. These profiles are similar to those
observed in X-ray loops.
Title: Drift instabilities in the solar corona within the multi-fluid
description
Authors: Mecheri, R.; Marsch, E.
Bibcode: 2008A&A...481..853M
Altcode: 2008arXiv0802.0340M
Context: Recent observations have revealed that the solar atmosphere
is highly structured in density, temperature, and magnetic field. The
presence of these gradients may lead to the appearance of currents in
the plasma, which in the weakly collisional corona can constitute
sources of free energy for driving micro-instabilities. Such
instabilities are very important since they represent a possible
source of ion-cyclotron waves that have been conjectured as playing
a prominent role in coronal heating, but whose solar origin remains
unclear.
Aims: Considering a density stratification transverse
to the magnetic field, this paper aims at studying the possible
occurrence of gradient-induced plasma micro-instabilities under the
conditions typical of coronal holes.
Methods: Taking the WKB
(Wentzel-Kramers-Brillouin) approximation into account, we performed
the Fourier plane wave analysis using the collisionless multi-fluid
model. By neglecting the electron inertia, this model allowed us to
take into account ion-cyclotron wave effects that are absent from
the one-fluid model of magnetohydrodynamics (MHD). Realistic models
of density and temperature, as well as a 2D analytical magnetic-field
model, have been used to define the background plasma in the open-field
funnel in a polar coronal hole. The ray-tracing theory has been used to
compute the ray path of the unstable waves, as well as the evolution of
their growth rates during the propagation.
Results: We demonstrate
that in typical coronal hole conditions, and when assuming typical
transverse density length scales taken from radio observations,
the current generated by a relative electron-ion drift provides
enough free energy for driving the mode unstable. This instability
results from coupling between slow-mode waves propagating in opposite
directions. However, the ray-tracing computation shows that the unstable
waves propagate upward to only a short distance but then are reflected
backward. The corresponding growth rate increases and decreases
intermittently in the upward propagating phase, and the instability
ceases while the wave is propagating downward.
Conclusions:
Drift currents caused by fine structures in the density distribution
in the magnetically-open coronal funnels can provide enough energy to
drive plasma micro-instabilities, which constitute a possible source
of the ion-cyclotron waves that have been invoked for coronal heating.
Title: Sizes of transition-region structures in coronal holes and
in the quiet Sun
Authors: Tian, H.; Marsch, E.; Tu, C. -Y.; Xia, L. -D.; He, J. -S.
Bibcode: 2008A&A...482..267T
Altcode: 2009arXiv0906.3028T
Aims: We study the height variations of the sizes of chromospheric and
transition-region features in a small coronal hole and the adjacent
quiet Sun, considering images of the intensity, Doppler shift, and
non-thermal motion of ultraviolet emission lines as measured by SUMER
(Solar Ultraviolet Measurements by Emitted Radiation), together with
the magnetic field as obtained by extrapolation from photospheric
magnetograms.
Methods: In order to estimate the characteristic
sizes of the different features present in the chromosphere and
transition region, we have calculated the autocorrelation function
for the images as well as the corresponding extrapolated magnetic
field at different heights. The Half Width at Half Maximum (HWHM) of
the autocorrelation function is considered to be the characteristic
size of the feature shown in the corresponding image.
Results:
Our results indicate that, in both the coronal hole and quiet Sun,
the HWHM of the intensity image is larger than that of the images of
Doppler-shift and non-thermal width at any given altitude. The HWHM
of the intensity image is smaller in the chromosphere than in the
transition region, where the sizes of intensity features of lines at
different temperatures are almost the same. But in the upper part of
the transition region, the intensity size increases more strongly with
temperature in the coronal hole than in the quiet Sun. We also studied
the height variations of the HWHM of the magnetic field magnitude B
and its component \vert Bz \vert, and found they are equal
to each other at a certain height below 40 Mm in the coronal hole. The
height variations of the HWHM of \vert Bz/B \vert seem to be
consistent with the temperature variations of the intensity size.
Conclusions: Our results suggest that coronal loops are much lower,
and magnetic structures expand through the upper transition region
and lower corona much more strongly with height in the coronal hole
than in the quiet Sun.
Title: Electron temperature anisotropy constraints in the solar wind
Authors: ŠtveráK, Štěpán; Trávníček, Pavel; Maksimovic, Milan;
Marsch, Eckart; Fazakerley, Andrew N.; Scime, Earl E.
Bibcode: 2008JGRA..113.3103S
Altcode:
We have performed a statistical study of a substantial amount of
electron data acquired in the solar wind to understand the constraints
on electron temperature anisotropy by plasma instabilities and Coulomb
collisions. We use a large data set of electron measurements from three
different spacecraft (Helios I, Cluster II, and Ulysses) collected in
the low ecliptic latitudes covering the radial distance from the Sun
from 0.3 up to 4 AU. We estimate the electron temperature anisotropy
using fits of the measured electron velocity distribution functions
acquired in situ. We use a two population (core and halo) analytical
model and properties of both populations are studied separately. We
examine all the acquired data in terms of temperature anisotropy versus
parallel electron plasma beta, and we relate the measurements to the
growth rates of unstable modes. The effect of Coulomb collisions is
expressed by the electron collisional age Ae defined as the
number of collisions suffered by an electron during the expansion of
the solar wind. We show that both instabilities and collisions are
strongly related to the isotropisation process of the electron core
population. In addition we examine the radial evolution of these effects
during the expansion of the solar wind. We show that the bulk of the
solar wind electrons are constrained by Coulomb collisions, while the
large departures from isotropy are constrained by instabilities.
Title: Proton Core Heating and Beam Formation via Parametrically
Unstable Alfvén-Cyclotron Waves
Authors: Araneda, Jaime A.; Marsch, Eckart; F. -Viñas, Adolfo
Bibcode: 2008PhRvL.100l5003A
Altcode:
Vlasov theory and one-dimensional hybrid simulations are used
to study the effects that compressible fluctuations driven by
parametric instabilities Alfvén-cyclotron waves have on proton
velocity distributions. Field-aligned proton beams are generated
during the saturation phase of the wave-particle interaction, with
a drift speed which is slightly greater than the Alfvén speed and
is maintained until the end of the simulation. The main part of the
distribution becomes anisotropic due to phase mixing as is typically
observed in the velocity distributions measured in the fast solar
wind. We identify the key instabilities and also find that, even in
the parameter regime where fluid theory appears to be appropriate,
strong kinetic effects still prevail.
Title: Signature of mass supply to quiet coronal loops
Authors: Tian, H.; Tu, C. -Y.; Marsch, E.; He, J. -S.; Zhou, G. -Q.
Bibcode: 2008A&A...478..915T
Altcode: 2009arXiv0906.3007T
Aims:The physical implication of large blue shift of Ne viii in the
quiet Sun region is investigated in this paper.
Methods: We
compare the significant Ne viii blue shifts, which are visible as large
blue patches on the Doppler-shift map of a middle-latitude quiet-Sun
region observed by SUMER, with the coronal magnetic-field structures
as reconstructed from a simultaneous photospheric magnetogram by means
of a force-free-field extrapolation.
Results: We show for the
first time that coronal funnels also exist in the quiet Sun. The
region studied contains several small funnels that originate from
network lanes, expand with height and finally merge into a single wide
open-field region. However, the large blue shifts of the Ne viii line
are not generally associated with funnels. A comparison between the
projections of coronal loops onto the solar x{-}y-plane and the Ne
viii dopplergram indicates that there are some loops that reveal large
Ne viii blue shifts in both legs, and some loops with upflow in one
and downflow in the other leg.
Conclusions: Our results suggest
that strong plasma outflow, which can be traced by large Ne viii blue
shift, is not necessarily associated with the solar wind originating
in coronal funnels but appears to be a signature of mass supply to
coronal loops. Under the assumption that the measured Doppler shift
of the Ne viii line represents the real outflow velocity of the neon
ions being markers of the proton flow, we estimate the mass supply
rate to coronal loops to be about 1034 s-1.
Title: Space weather explorer The KuaFu mission
Authors: Schwenn, R.; Donovan, E.; Marsch, E.; Wang, J. -S.; Xia,
L. -D.; Zhang, Y. -W.; KuaFu Working Team
Bibcode: 2008AdSpR..41..190S
Altcode:
The KuaFu mission is designed to explore the physical processes
that are responsible for space weather, complementing planned
in situ and ground-based programs, and also to make an essential
contribution to the space weather application. KuaFu encompasses
three spacecraft. KuaFu-A will be located at the L1 libration point
and have instruments to observe solar extreme ultraviolet (EUV) and
far ultraviolet (FUV) emissions and white-light coronal mass ejections
(CMEs), and to measure radio waves, the local plasma and magnetic field,
and high-energy particles. KuaFu-B1 and KuaFu-B2 will be in elliptical
polar orbits chosen to facilitate continuous (24 h per day 7 days
per week) observation of the northern polar aurora oval and the inner
magnetosphere. The KuaFu mission is designed to observe globally the
complete chain of disturbances from the solar atmosphere to geospace,
including solar flares, CMEs, interplanetary clouds, shock waves, and
their geo-effects, with a particular focus on dramatic space weather
events such as magnetospheric substorms and magnetic storms. The mission
start is targeted for the next solar maximum with launch hoped for
in 2012. The initial mission lifetime will be 3 years. The overall
mission design, instrument complement, and incorporation of recent
technologies will advance our understanding of the physical processes
underlying space weather, solve several key outstanding questions
including solar CME initiation, Earth magnetic storm and substorm
mechanisms, and advance our understanding of multi-scale interactions
in and system-level behavior of our Sun Earth space plasma system.
Title: Propiedades turbulentas de la heliosfera interna
Authors: Ruiz, M. E.; Dasso, S.; Matthaeus, W. H.; Marsch, E.; Weygand,
J. M.
Bibcode: 2008BAAA...51...35R
Altcode:
The dynamical evolution of solar and galactic cosmic rays in the
heliosphere is significantly affected by the magnetic conditions
of the medium. These effects arise mainly from a combination of (i)
the large-scale magnetic field configuration (which just acts as a
guide for charged particles) and (ii) the small-scale fluctuations
(which cause abrupt changes in their energy and/or momentum, known
as wave-particle interaction). Magnetic fluctuations developed in
the system in a spatial range larger than the ion skin depth can
be modeled using the framework of MHD turbulence. In this work, we
present a study of the turbulent properties in the inner heliosphere
(solar wind between 0.3 and 1 astronomical unit) based on modeling
in situ plasma and magnetic observations collected by Helios 1 and
Helios 2 spacecraft throughout one full eleven-year solar cycle. In
particular we study the magnetic anisotropy properties in the inertial
range. FULL TEXT IN SPANISH
Title: Sizes and heights of magnetic structures in the solar
transition region as observed in ultraviolet emission lines at
different temperatures
Authors: Marsch, Eckart; Tian, Hui; Tu, Chuanyi; He, Jiansen; Zhou,
G. -Q.; Xia, Lidong
Bibcode: 2008cosp...37.1922M
Altcode: 2008cosp.meet.1922M
We investigate the height variations of the sizes of transition-region
(TR) features in a small coronal hole and the adjacent quiet Sun,
thereby considering images of the intensity, Doppler shift, and
non-thermal motion of ultraviolet emission lines as measured by SUMER
(Solar Ultraviolet Measurements by Emitted Radiation), together with
the magnetic field as obtained by extrapolation from photospheric
magnetograms. In order to estimate the sizes of different features
present in the upper chromosphere and TR, we have calculated the
autocorrelation function for the images as well as the corresponding
extrapolated magnetic field at different heights. The half width at
half maximum of the autocorrelation function is considered as the
characteristic size of a feature shown in the corresponding image, and
found in the intensity image to be smaller in the upper chromosphere
than the TR. Through a correlation analysis of the emission pattern
with the magnetic field (network and carpet of loops), the so-called
correlation height of the emission can be determined. A detailed
comparison is made of the coronal magnetic field obtained by
extrapolation with the radiances of many ultraviolet lines, which
are emitted by ions of various elements in different ionization
stages, corresponding to different local coronal temperatures. At
mesoscopic scales of several megameters the regions with strong emission
(originating from multiple small closed loops) are found to be located
at low heights, whereas weak emissions (coming from locally open,
i.e. far reaching fields) appear to originate at greater heights. Our
analysis confirms the notion that plasma at different temperature can
coexist at the same height, and that the TR is not thermally stratified
but strongly nonuniform and magnetically structured.
Title: Proton heating and beam formation via parametrically unstable
Alfven-cyclotron waves
Authors: Marsch, Eckart; Araneda, Jaime; -Vinas, Adolfo F.
Bibcode: 2008cosp...37.1923M
Altcode: 2008cosp.meet.1923M
Vlasov theory and one-dimensional hybrid simulations are used to
study the effects that compressible fluctuations driven by parametric
instabilities of Alfvén/cyclotron waves have on proe ton velocity
distributions. Field-aligned proton beams are generated during the
saturation phase of the wave-particle interaction, with a drift speed
which is slightly greater than the Alfvén speed and is maintained
until the end of the simulation. The main part of the dise tribution
becomes anisotropic due to phase mixing as is typically observed in
the velocity distributions measured in the fast solar wind. We identify
the key instabilities and also find that even in the parameter regime,
where fluid theory appears to be appropriate, strong kinetic effects
still prevail.
Title: A model of the solar wind driven by supergranular circulation
Authors: Tu, Chuanyi; Tian, Hui; He, Jiansen; Marsch, Eckart
Bibcode: 2008cosp...37.3238T
Altcode: 2008cosp.meet.3238T
The scenario for the origin of the solar wind driven by the
supergranular circulation as suggested by Tu et al. (2005) is tested
with model calculation and data analysis. This scenario assumes that the
fast solar wind originates at heights above 5 Mm in magnetically open
funnels in corona holes. Mass and energy are supplied to the solar wind
through reconnection of open field lines in the funnels with closed
loops advected by the supergranular circulation to the reconnection
sites. To test this scenario, we developed a one-dimensional one-fluid
model with mass flux and energy flux supplied at 5 Mm to mimic the
result expected from field-line reconnections. The upward flow and
the downward flow resulting from this model are shown to be consistent
with the blueshift of Ne VIII and redshift of Si II observed by SUMMER
on SOHO. The mass and energy supply rates required by the model are
shown to be consistent with the mass and energy delivery rates due to
reconnection between magnetic loops in the intra-network region and open
magnetic funnel at the network intersections. The model calculations
support the scenario of the solar wind being driven by supergranular
circulation. A discussion of a possible mechanism for the solar wind
origin in the quiet sun is also given, where the solar wind is suggested
to start flowing outward at a height of 20 Mm, which is higher than the
emission height of Ne VIII ( 5 Mm). We found that Ne VIII blueshifts
can occur at both legs of some closed loops, which suggests that mass
can be supplied upward to the corona from both footpoints. Tu, C.-Y.,
Zhou, C., Marsch, E., Xia, L.-D., Zhao, L., Wang, J.-X., and Wilhelm,
K., Solar wind origin in coronal funnels, Science, 308, 519, 2005.
Title: A Statistical Analysis of Shock Wave Extension in the Inner
Heliosphere as observed by the two Helios probes
Authors: de Lucas, Aline; Schwenn, Rainer; Marsch, Eckart; Dal Lago,
Alisson; Clúa de Gonzalez, Alicia L.; Gonzalez Alarcon, Walter
Demétrio
Bibcode: 2008cosp...37..661D
Altcode: 2008cosp.meet..661D
The two Helios probes traveled at variable longitudinal and radial
separations through the inner heliosphere. They collected most valuable
high resolution plasma data for an entire solar cycle. The mission
is still so successful that no other missions will collect the same
kind of data in the next 20 years. One of the subjects studied after
the success of the Helios mission was the identification of more
than 390 shock waves driven by Interplanetary Coronal Mass Ejections
(ICMEs). Combining the data from both probes, we make a statistical
study for the extension of the shock waves in the interplanetary
medium. For longitudinal separations of 90° we found a cutoff value
at this angular separation. A shock has 50
Title: Strahl properties in the solar wind: Observations
Authors: Stverak, S.; Maksimovic, M.; Travnicek, P.; Marsch, E.;
Fazakerley, A. N.; Scime, E. E.
Bibcode: 2007AGUFMSH21A0293S
Altcode:
We have performed a statistical study of a substantial amount of
electron data acquired in the solar wind to describe the properties
of the strahl electron population. We use a large data set of electron
measurements from three different spacecraft (HELIOS I, CLUSTER II and
ULYSSES) collected in the low ecliptic latitudes covering the radial
distance from the Sun from 0.3 up to 4 AU. Beside the thermal core, the
electron velocity distribution functions in the solar wind typically
exhibit two non-thermal features: supra thermal tails known as the
halo population and the strahl. This last component is highly aligned
in the direction parallel to the interplanetary magnetic field and is
largely moving away from the Sun. Even thought it comprises less than
a few percents of the total number density, it is important to study
some important solar wind plasma properties. Thanks its attributes,
the strahl is responsible for the main part of the electron heat
flux and it can also provide a possible source of electron kinetic
plasma instabilities. We fit the observed distribution functions with
analytical models. The resulting characteristics are compared with other
electron properties in order to study their possible correlations. In
addition we examine the radial evolution of these characteristics
during the expansion of the solar wind.
Title: The evolution of the solar wind proton temperature anisotropy
from 0.3 to 2.5 AU
Authors: Matteini, L.; Hellinger, P.; Landi, S.; Pantellini, F.;
Maksimovic, M.; Velli, M.; Goldstein, B. E.; Marsch, E.
Bibcode: 2007AGUFMSH21A0287M
Altcode:
We report an analysis of the proton temperature anisotropy evolution
from 0.3 to 2.5 AU based on the Helios and Ulysses observations. With
increasing distance, the fast wind data show a path in the parameter
space (βallel p,T\perp p/Tallel p), and the first part of the
trajectory is well described by an anticorrelation between the
temperature anisotropy T\perp p/Tallel p and the proton parallel
beta, while after 1 AU the evolution with distance in the parameter
space changes and the data result in agreement with the constraints
derived by a fire hose instability. The slow wind data show a more
irregular behavior, and in general it is not possible to recover a
single evolution path. However, on small temporal scale we find that
different slow streams populate different regions of the parameter
space, and this suggests that when considering single streams also
the slow wind follows some possible evolution path.
Title: Observations of the Sun at Vacuum-Ultraviolet Wavelengths
from Space. Part II: Results and Interpretations
Authors: Wilhelm, Klaus; Marsch, Eckart; Dwivedi, Bhola N.; Feldman,
Uri
Bibcode: 2007SSRv..133..103W
Altcode:
In Part I of this review, the concepts of solar vacuum-ultraviolet
(VUV) observations were outlined together with a discussion of
the space instrumentation used for the investigations. A section on
spectroradiometry provided some quantitative results on the solar VUV
radiation without considering any details of the solar phenomena leading
to the radiation. Here, in Part II, we present solar VUV observations
over the last decades and their interpretations in terms of the plasma
processes and the parameters of the solar atmosphere, with emphasis
on the spatial and thermal structures of the chromosphere, transition
region and corona of the quiet Sun. In addition, observations of
active regions, solar flares and prominences are included as well as
of small-scale events. Special sections are devoted to the elemental
composition of the solar atmosphere and theoretical considerations on
the heating of the corona and the generation of the solar wind.
Title: Coronal ion-cyclotron beam instabilities within the multi-fluid
description
Authors: Mecheri, R.; Marsch, E.
Bibcode: 2007A&A...474..609M
Altcode: 2007arXiv0706.0752M
Context: Spectroscopic observations and theoretical models suggest
resonant wave-particle interactions, involving high-frequency
ion-cyclotron waves, as the principal mechanism for heating and
accelerating ions in the open coronal holes. However, the mechanism
responsible for the generation of the ion-cyclotron waves remains
unclear. One possible scenario is that ion beams originating from
small-scale reconnection events can drive micro-instabilities that
constitute a possible source for the excitation of ion-cyclotron
waves.
Aims: We use the multi-fluid model in the low-β coronal
plasma to study ion beam-driven electromagnetic instabilities. By
neglecting the electron inertia this model allows one to take into
account ion-cyclotron wave effects that are absent from the one-fluid
magnetohydrodynamics (MHD) model. Realistic models of density and
temperature as well as a 2-D analytical magnetic field model are
used to define the background plasma in the open-field funnel region
of a polar coronal hole.
Methods: Taking into account the WKB
(Wentzel-Kramers-Brillouin) approximation, a Fourier plane-wave linear
mode analysis is employed to derive the dispersion relation. The
ray-tracing theory is used to compute the ray path of the unstable
wave as well as the evolution of the growth rate of the wave while
propagating in the coronal funnel.
Results: We demonstrate that
in typical coronal hole conditions and assuming realistic values of the
beam velocity, the free energy provided by the ion beam propagating
parallel to the ambient field can drive micro-instabilities through
resonant ion-cyclotron excitation.
Title: Evolution of the solar wind proton temperature anisotropy
from 0.3 to 2.5 AU
Authors: Matteini, Lorenzo; Landi, Simone; Hellinger, Petr; Pantellini,
Filippo; Maksimovic, Milan; Velli, Marco; Goldstein, Bruce E.;
Marsch, Eckart
Bibcode: 2007GeoRL..3420105M
Altcode:
We report an analysis of the proton temperature anisotropy evolution
from 0.3 to 2.5 AU based on the Helios and Ulysses observations. With
increasing distance the fast wind data show a path in the parameter
space (β $\parallel$ p , T $\perp$ p /T
$\parallel$ p ). The first part of the trajectory is well
described by an anticorrelation between the temperature anisotropy T
$\perp$ p /T $\parallel$ p and the proton
parallel beta, while after 1 AU the evolution with distance in the
parameter space changes and the data result in agreement with the
constraints derived by a fire hose instability. The slow wind data
show a more irregular behavior, and in general it is not possible to
recover a single evolution path. However, on small temporal scale
we find that different slow streams populate different regions of
the parameter space, and this suggests that when considering single
streams also the slow wind follows some possible evolution path.
Title: Can the solar wind originate from a quiet Sun region?
Authors: He, J. -S.; Tu, C. -Y.; Marsch, E.
Bibcode: 2007A&A...468..307H
Altcode:
Context: It is well known that the fast solar wind originates
from coronal holes (CHs). However, the question whether it can also
originate from quiet Sun regions has not yet been answered.
Aims:
To study this problem we analyze SOHO data obtained from observations
made in a quiet Sun area. The data set includes far-ultraviolet data
from SUMER, magnetic field data from MDI, and extreme-ultraviolet
data from EIT.
Methods: We make a potential-field extrapolation
of the coronal magnetic field and calculate the field lines from the
photosphere up to 80 Mm height. Those field lines which can be traced
from the bottom to the top of the extrapolation box are called (locally)
open field lines. By a combined analysis of the coronal magnetic field
structures inferred from MDI data, the flows indicated by the Ne viii
Doppler shifts in the SUMER data, and the Fe xii radiance images from
EIT, it is possible to study this problem in depth.
Results:
We find that most of the sites with plasma outflow, which can be
recognized by the Ne viii blue shift, are not located in regions with
an open magnetic field. Most likely, these outflows just correspond to
plasma being delivered to magnetic loops. It is further found that, in
a cross-section plane located at a height of 25 Mm, the pattern of open
field lines intersecting that plane is consistent with the dark pattern
of low radiance in the image of the Fe xii 19.5 nm line. Usually,
small dark regions are considered to represent small CHs, and thus
are assumed to be sources of the solar wind. However, since here
the source of the low emission appears to be located at a height of
only 25 Mm, it seems more likely that this radiation originates near
the foot points of large coronal loops.
Conclusions: Previous
results obtained at middle latitudes on the quiet Sun indicated that
sizable outflow velocities occur at the intersections of the network
boundaries. This finding is also confirmed here. However, we could not
identify most of these intersections as sources of the solar wind. Only
a few small outflow regions might be sources. Yet, one dark area that
we found on the EIT map seems to be connected with open field lines,
and therefore it could be a source of the solar wind.
Title: Collisionless damping of parametrically unstable Alfvén waves
Authors: Araneda, J. A.; Marsch, E.; ViñAs, A. F.
Bibcode: 2007JGRA..112.4104A
Altcode: 2007JGRA..11204104A
Linear Vlasov theory and one-dimensional hybrid simulations are used to
study the parametric instabilities of a circularly polarized parallel
propagating Alfvén wave in a homogeneous, magnetized, and collisionless
plasma. We discuss the linear and the weakly nonlinear development of
the instabilities of the Alfvén waves, including kinetic effects, and
investigate the structure, the growth, and the damping of the driven
ion acoustic-like waves. The dispersion relation reproduces the fluid
characteristics of the instabilities in the case that protons are cold
but contains an infinite number of roots in the general case. We show
that at low proton plasma βp (βp ≈ 0.1),
kinetic effects break the degeneracy of the mode-coupling solutions of
the fluid theory, and we unambiguously identify the growing and the
damped modes. We find that contrary to traditional thought, kinetic
effects are important even for very low-βp in the late
stages of the linear evolution, leading to a dephasing effect between
the plasma pressure and the density fluctuations. The relevance of
the results to the experimental identification of the instabilities,
to the generation of local turbulence, and to the reduction of cross
helicity in the solar wind are pointed out.
Title: Correlation Height of the Source Region of Si II Emission
Lines in Coronal Hole Regions
Authors: Zhou, Gui-qing; He, Jian-sen; Tu, Chuan-yi; Marsch, E.
Bibcode: 2007ChA&A..31..137Z
Altcode:
The height of the source region of Si II emission lines characterizes
the height of the bottom layer of solar atmosphere's transition
region. The correlation analysis of the intensities of ultraviolet
spectral lines and the threedimensional structure of magnetic field
yielded by force-free extrapolation is a new method for determining the
height of ultraviolet emission lines' source region. It has been found
that the height thus obtained is larger than that given by traditional
viewpoint. Because the existing numerical analyses with this method are
scarce, this result has to be further verified with more observational
materials. In this work, this method is applied to the Si II emission
lines observed by SOHO/SUMER for the solar surface region beneath
the solar coronal hole at southern pole and to the magnetic fields
measured by National Solar Observatory/Kitt Peak (NSO/KP) in U.S.A. The
correlation height of the source region of Si II emission lines in
coronal hole region is approximately 5.0 Mm. This result supports the
conclusion that the height of the bottom layer of transition region
in coronal hole region is larger than that in quiet regions. Moreover,
some new phenomena have been discovered and their causes are probed.
Title: Diffusion plateaus in the velocity distributions of fast
solar wind protons
Authors: Heuer, M.; Marsch, E.
Bibcode: 2007JGRA..112.3102H
Altcode: 2007JGRA..11203102H
In a collisionless plasma, such as the fast solar wind, wave-particle
interactions play the decisive role in determining the shape of
particle velocity distribution functions (VDFs). In this paper we
provide observational evidence for cyclotron-resonant interaction of ion
cyclotron Alfvén waves, which propagate outward from the Sun along the
interplanetary magnetic field, with fast solar wind protons. According
to quasi-linear theory, the protons thereby diffuse in velocity space, a
process leading to the formation of plateaus in the VDF. This diffusion
plateau formation naturally explains the observed thermal anisotropies
in the core of the proton VDFs. In this respect, we investigated a
large number of data from several distinct fast solar wind streams
between 0.3 and 1 AU. All measurements were made on Helios 2 during
the solar minimum in 1976 and 1977. The proton VDFs as provided by the
plasma instrument are modeled by a superposition of multiple Gaussians,
such that the plasma dispersion relation for parallel propagating
cyclotron waves can readily be solved numerically. Thus the details
of the proton VDFs are well represented and are reflected in the
dispersion relation, which makes our analysis as self-consistent as
possible. Proton thermal effects on the wave dispersion relation are
naturally taken into account.
Title: T he Lower Transition Region As Seen In The H I Lyman-α Line
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
Bibcode: 2007ESASP.641E..84T
Altcode:
The SUMER spectrometer aboard SOHO has been used to acquire several
raster images and temporal series of quiet-Sun targets at both disk
centre and the limb. Spectra have been recorded simultaneously in the
H I Lyman α and the Si III 120.6 nm line. Both spatial and temporal
maps of the integrated radiances appear very similar in the two lines,
despite the huge difference in optical thickness, a result showing the
H I Lyman α to be a good diagnostic of the dynamics and morphology of
the lower transition region. Oscillations can be detected and studied
at all observed locations. At disk centre, the 3 minute oscillations are
sporadically observed in the inter-network but also at locations at the
edges of network lanes, while 5 minute oscillations clearly dominate
the network. At the limb, evidence of 3 to 5 minute oscillations is
found at the base of spicules. Moreover, H I Lyman α spectra shows a
high degree of variability, revealing also the signature of explosive
events. The combination of high spectral purity images and slit spectra
in the H I Lyman α line would therefore be an exceptional new tool
to investigate the nature of the solar transition region. This line
is therefore of interest for both, a high resolution channel in the
EUI instrument and for the EUS spectrometer.
Title: T he Lower Transitio n Region As Seen In The H I Lyman-α Line.
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
Bibcode: 2007ESASP.641E..36T
Altcode:
The SUMER spectrometer aboard SOHO has been used to acquire several
raster images and temporal series of quiet-Sun targets at both disk
centre and the limb. Spectra have been recorded simultaneously in the
H I Lyman α and the Si III 120.6 nm line. Both spatial and temporal
maps of the integrated radiances appear very similar in the two lines,
despite the huge difference in optical thickness, a result showing the
H I Lyman α to be a good diagnostic of the dynamics and morphology of
the lower transition region. Oscillations can be detected and studied
at all observed locations. At disk centre, the 3 minute oscillations are
sporadically observed in the inter-network but also at locations at the
edges of network lanes, while 5 minute oscillations clearly dominate
the network. At the limb, evidence of 3 to 5 minute oscillations is
found at the base of spicules. Moreover, H I Lyman α spectra shows a
high degree of variability, revealing also the signature of explosive
events. The combination of high spectral purity images and slit spectra
in the H I Lyman α line would therefore be an exceptional new tool
to investigate the nature of the solar transition region. This line
is therefore of interest for both, a high resolution channel in the
EUI instrument and for the EUS spectrometer.
Title: EUI, The Ultraviolet Imaging Telescopes Of Solar Orbiter
Authors: Hochedez, J. -F.; Appourchaux, T.; Defise, J. -M.; Harra,
L. K.; Schühle, U.; Auchère, F.; Curdt, W.; Hancock, B.; Kretzschmar,
M.; Lawrence, G.; Leclec'h, J. -C.; Marsch, E.; Mercier, R.; Parenti,
S.; Podladchikova, E.; Ravet, M. -F.; Rochus, P.; Rodriguez, L.;
Rouesnel, F.; Solanki, S.; Teriaca, L.; Van Driel, L.; Vial, J. -C.;
Winter, B.; Zhukov, A.
Bibcode: 2007ESASP.641E..33H
Altcode:
The scientific objectives of Solar Orbiter rely ubiquitously on EUI,
its suite of solar atmosphere imaging telescopes. In the configuration
discussed here, EUI includes three co-aligned High Resolution Imagers
(HRI) and one Full Sun Imager (FSI). FSI and two HRIs observe in extreme
ultraviolet passbands, dominated by coronal emission. Another HRI is
designed for the hydrogen Lyman α radiation in the far UV, imaging the
Chromosphere and the lower Transition Region. The current EUI design
and some of its development challenges are highlighted. EUI profits from
co-rotation phases, solar proximity and departure from the ecliptic. In
synergy with the other S.O. payload, EUI probes the dynamics of the
solar atmosphere, provides context data for all investigations and helps
to link in-situ and remote-sensing observations. In short, it serves all
four top-level goals of the mission. For these reasons, the EUI suite
is keenly anticipated in the European scientific community and beyond.
Title: S olar Orbiter Neutral Solar Wind Detector
Authors: Hilchenbach, M.; Orsini, S.; Hsieh, K. C.; Antonucci, E.;
Barabash, S.; Bamert, K.; Bruno, R.; Collier, M. R.; Czechowski,
A.; D'Amicis, R.; De Angelis, E.; Dandouras, I.; Di Lellis, A. M.;
Esser, R.; Giacalone, J.; Gruntman, M.; Habbal, S. R.; Jokipii, J. R.;
Kallio, E.; Kota, J.; Kucharek, H.; Leoni, R.; Livi, S.; Mann, I.;
Marsch, E.; Massetti, S.; Milillo, A.; Möbius, E.; Mura, A.; Sheldon,
R. B.; Schmidt, W.; Selci, S.; Szego, K.; Woch, J.; Wurz, P.; Zanza,
V.; Zurbuchen, T. H.
Bibcode: 2007ESASP.641E..46H
Altcode:
Neutral hydrogen atoms, which give rise to the prominent so lar Ly-α
corona, are closely coup led to the emerging solar-wind plasma. The
density ratio of neutral hydrogen to protons is minute, ~10-6;
therefore, the neutral atoms are tracers in the solar wind. In-situ
observations of the neutral atoms, their flight paths (imag ing),
density, and velocity distribu tions are a new tool to the understanding
of the Ly-α corona, i.e. setting limits on the plasma velocity
distribution along the solar magnetic field lines. The other goal of
the neutral solar- wind instrumentation is the in-situ observation
of the interactions between solar wind plasma and dust grains near
the Sun. We will discuss the science objectives and the potential
"zero charge" solar-wind instrument envelope onboard Solar Orbiter .
Title: Ray tracing of ion-cyclotron waves in a coronal funnel
Authors: Mecheri, R.; Marsch, E.
Bibcode: 2007msfa.conf..355M
Altcode: 2007arXiv0706.0936M
Remote observations of coronal holes have strongly implicated the
kinetic interactions of ion-cyclotron waves with ions as a principal
mechanism for plasma heating and acceleration of the fast solar wind. In
order to study these waves, a linear perturbation analysis is used in
the work frame of the collisionless multi-fluid model. We consider a
non-uniform background plasma describing a funnel region and use the
ray tracing equations to compute the ray path of the waves as well as
the spatial variation of their properties.
Title: Status Of Knowledge After Helios, Ulysses And SOHO Of The
Microstate Of The Coronal And Solar-Wind Plasma
Authors: Marsch, E.
Bibcode: 2007ESASP.641E...4M
Altcode:
One main goal of Solar Orbiter is to determine the properties,
dynamics and interactions of plasma, fields and particles in the
near-Sun heliosphere. In this review we will address the kinetic
plasma physics of the solar wind, with emphasis on the present state
of empirical knowledge and theoretical understanding. The in-situ
measurements of solar-wind particles and plasma waves are discussed,
as well as the results obtained by remote- sensing of the solar corona
by means of ultraviolet spectroscopy and imaging. To explain coronal
and interplanetary heating, and generally transport phenomena, the
dissipation at small scales of various forms of mechanical, electric
and magnetic energy (contained in nonthermal particles, waves and
turbulence) must be addressed. We discuss, besides the effects of
Coulomb collisions, important kinetic processes such as wave-particle
interactions through Landau or cyclotron-resonant absorption and
emission of plasma waves and some related microinstabilities. Promising
areas and future perspectives for research to be done with Solar
Orbiter are identified.
Title: Emission heights of coronal bright points on Fe XII radiance
map
Authors: Tian, H.; Tu, C. -Y.; He, J. -S.; Marsch, E.
Bibcode: 2007AdSpR..39.1853T
Altcode: 2009arXiv0907.4954T
The study of coronal bright points (BPs) is important for understanding
coronal heating and the origin of the solar wind. Previous studies
indicated that coronal BPs have a highly significant tendency to
coincide with magnetic neutral lines in the photosphere. Here we further
studied the emission heights of the BPs above the photosphere in the
bipolar magnetic loops that are apparently associated with them. As BPs
are seen in projection against the disk their true emission heights are
unknown. The correlation of the BP locations on the Fe XII radiance
map from EIT with the magnetic field features (in particular neutral
lines) was investigated in detail. The coronal magnetic field was
determined by an extrapolation of the photospheric field (derived from
2-D magnetograms obtained from the Kitt Peak observatory) to different
altitudes above the disk. It was found that most BPs sit on or near a
photospheric neutral line, but that the emission occurs at a height
of about 5 Mm. Some BPs, while being seen in projection, still seem
to coincide with neutral lines, although their emission takes place
at heights of more than 10 Mm. Such coincidences almost disappear
for emissions above 20 Mm. We also projected the upper segments of
the 3-D magnetic field lines above different heights, respectively,
on to the tangent x- y plane, where x is in the east-west and y in
the south-north direction. The shape of each BP was compared with the
respective field-line segment nearby. This comparison suggests that
most coronal BPs are actually located on the top of their associated
magnetic loops. Finally, we calculated for each selected BP region the
correlation coefficient between the Fe XII intensity enhancement and
the horizontal component of the extrapolated magnetic field vector at
the same x- y position in planes of different heights, respectively. We
found that for almost all the BP regions we studied the correlation
coefficient, with increasing height, increases to a maximal value and
then decreases again. The height corresponding to this maximum was
defined as the correlation height, which for most bright points was
found to range below 20 Mm.
Title: Proceedings of The Second Solar Orbiter Workshop
Authors: Marsch, E.; Tsinganos, K.; Marsden, R.; Conroy, L.
Bibcode: 2007ESASP.641E....M
Altcode:
No abstract at ADS
Title: T he Solar Wind Proton And Alpha Sensor For The Solar Orbiter
Authors: McComas, D. J.; Desai, M. I.; Allegrini, F.; Berthomier,
M.; Bruno, R.; Louarn, P.; Marsch, E.; Owen, C. J.; Schwadron, N. A.;
Zurbuchen, T. H.
Bibcode: 2007ESASP.641E..40M
Altcode:
The primary scientific objective of the Solar Wind- Proton and
Alpha Sensor (SW-PAS) for the Solar Orbiter (SO) mission is to
provide observations of kinetic and fluid properties of the bulk
solar wind plasma that will ultimately lead to new discoveries
and improved understanding of coronal heating, the origin and
acceleration of the solar wind, and the seed population of solar
proton events. Specifically, the SW- PAS will measure the 3-D velocity
distribution functions of solar wind and suprathermal protons and -
particles between 200 eV/q-20 keV/q energy range at high temporal
resolution. In this paper, we outline the main scientific goals,
instrument concept, and critical issues required for the design and
development of the SW-PAS sensor.
Title: Electron Anisotropy Constraint in the Solar Wind
Authors: Stverak, S.; Travnicek, P.; Maksimovic, M.; Marsch, E.;
Fazakerley, A. N.; Scime, E. E.
Bibcode: 2006AGUFMSH53A1482S
Altcode:
We present a statistical study of solar wind electrons using data
from several spacecrafts missions (HELIOS-I, CLUSTER-II and ULYSSES)
collected in the ecliptic plane covering the radial distance from
the Sun from 0.3 up to 4 AU. We focused on the electron temperature
anisotropy which control mechanisms are still not well understood. For
this purpose we looked at the temperature anisotropy as a function
of two important parameters, namely the electron collisional age A_e
defined as a number of collision suffered by an electron during the
expansion of the solar wind and the electron parallel plasma beta β||,
to see whether the electrons are constrained by some instabilities or
driven by collisions. The radial evolution of these relations were
also examined. The temperature anisotropy was computed by fitting
the measured electron velocity distribution functions (eVDF) with a
core-halo model defined as a sum of a bi-Maxwellian and a bi-Kappa
function representing the core and halo population respectively.
Title: Magnetic structure of the solar transition region as observed
in various ultraviolet lines emitted at different temperatures
Authors: Marsch, E.; Zhou, G. -Q.; He, J. -S.; Tu, C. -Y.
Bibcode: 2006A&A...457..699M
Altcode:
Aims.The structure of the solar transition region (TR) in a polar
coronal hole of the Sun is studied. In particular, the detailed
association of the coronal magnetic field (carpet) with the radiance
patterns of the TR, when seen in various far ultraviolet (FUV)
emission lines, is investigated.
Methods: .A detailed comparison
is made of the coronal magnetic field, as obtained by extrapolation
of the NSO/Kitt-Peak photospheric field to heights of several tens of
megameters, with the radiances of many FUV lines, which are emitted by
ions of various elements at different ionization stages, corresponding
to different local coronal temperatures. By a correlation analysis
of the emission pattern with the magnetic field (network and carpet
of loops), the so-called correlation height of the emission can be
determined. By its help and through a correlation analysis the magnetic
nature of the emission regions and the temperature structure of the TR
can be better revealed and understood.
Results: .In particular,
at mesoscopic scales of several megameters the regions with strong
emission (originating from multiple small closed loops) are found
to be located at low heights, whereas weak emissions (coming from
locally open, i.e. far reaching fields) appear to originate at greater
heights. These findings are consistent with similar results obtained
at large scales for large-size loops and big coronal holes.
Conclusions: .Our correlation-height analysis of the emission lines
confirms the notion that plasma at different temperature can coexist
at the same height. The TR is not thermally stratified but strongly
nonuniform and magnetically structured.
Title: On the Structure of the Solar Transition Region
Authors: Marsch, E.; Zhou, G. -Q.; He, J. -S.; Tu, C. -Y.
Bibcode: 2006ESASP.617E.100M
Altcode: 2006soho...17E.100M
No abstract at ADS
Title: Plasma Outflows and Open Magnetic Fields in a Quiet-Sun Region
Authors: Tu, C. -Y.; He, J. -S.; Marsch, E.
Bibcode: 2006ESASP.617E..99T
Altcode: 2006soho...17E..99T
No abstract at ADS
Title: Drift-Instabilities in a Coronal Funnel Within the Multi-Fluid
Description
Authors: Mecheri, R.; Marsch, E.
Bibcode: 2006ESASP.617E.103M
Altcode: 2006soho...17E.103M
No abstract at ADS
Title: Solar Microscopy: Unveiling the Sun's Basic Physical Processes
at their Intrinsic Scales
Authors: Solanki, S. K.; Marsch, E.
Bibcode: 2006ESASP.617E..34S
Altcode: 2006soho...17E..34S
No abstract at ADS
Title: On the Role of the Parallel Proton Fire Hose Instability in
the Expanding Solar Wind: Simulations and Observations
Authors: Matteini, L.; Landi, S.; Hellinger, P.; Velli, M.; Maksimovic,
M.; Pantellini, F.; Marsch, E.
Bibcode: 2006ESASP.617E.101M
Altcode: 2006soho...17E.101M
No abstract at ADS
Title: The Dynamic Nature of the Lower Transition Region as Revealed
by Spectroscopy of the Hydrogen Lyman-α Line
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
Bibcode: 2006ESASP.617E..77T
Altcode: 2006soho...17E..77T
No abstract at ADS
Title: Kinetic Physics of the Solar Corona and Solar Wind
Authors: Marsch, Eckart
Bibcode: 2006LRSP....3....1M
Altcode:
Kinetic plasma physics of the solar corona and solar wind are
reviewed with emphasis on the theoretical understanding of the in
situ measurements of solar wind particles and waves, as well as on
the remote-sensing observations of the solar corona made by means of
ultraviolet spectroscopy and imaging. In order to explain coronal and
interplanetary heating, the micro-physics of the dissipation of various
forms of mechanical, electric and magnetic energy at small scales (e.g.,
contained in plasma waves, turbulences or non-uniform flows) must be
addressed. We therefore scrutinise the basic assumptions underlying
the classical transport theory and the related collisional heating
rates, and also describe alternatives associated with wave-particle
interactions. We elucidate the kinetic aspects of heating the solar
corona and interplanetary plasma through Landau- and cyclotron-resonant
damping of plasma waves, and analyse in detail wave absorption and micro
instabilities. Important aspects (virtues and limitations) of fluid
models, either single- and multi-species or magnetohydrodynamic and
multi-moment models, for coronal heating and solar wind acceleration are
critically discussed. Also, kinetic model results which were recently
obtained by numerically solving the Vlasov-Boltzmann equation in a
coronal funnel and hole are presented. Promising areas and perspectives
for future research are outlined finally.
Title: The Current-Free Electric Double Layer in a Coronal Magnetic
Funnel
Authors: Boswell, Roderick W.; Marsch, Eckart; Charles, Christine
Bibcode: 2006ApJ...640L.199B
Altcode:
Current-free double layers (CFDLs) have been recently discovered
in a number of laboratory devices, when a low collisional plasma
is forced to expand from a high magnetic field source region to a
low magnetic field diffusion region. This experimental setup bears
a striking resemblance to the natural conditions prevailing in the
magnetic funnels of the solar corona. It was commonly thought that
magnetic-field-aligned potential disruptions were driven by electron
currents, although the theoretical possibility of a CDFL has been
known of for some time. Given its recent experimental verification,
we make here a contribution to solar plasma physics by investigating
the possibility of CFDLs in coronal funnels, which have much in common
with the laboratory experiments. Therefore, CFDLs may play an important
role in supplying and accelerating plasma in coronal funnels.
Title: Coronal waves: propagation in the multi-fluid description
Authors: Mecheri, Redouane; Marsch, Eckart
Bibcode: 2006RSPTA.364..537M
Altcode:
No abstract at ADS
Title: Limits on the proton temperature anisotropy in the solar wind
Authors: Marsch, E.; Zhao, L.; Tu, C. -Y.
Bibcode: 2006cosp...36..930M
Altcode: 2006cosp.meet..930M
We analyse the temperature anisotropy of the protons in the solar wind
and thereby concentrate on plasma data obtained in the year 1976 of
the Helios 1 and Helios 2 missions We derive the proton temperatures
in the directions perpendicular and parallel to the magnetic field
as well as the parallel proton plasma beta The data are separately
analysed for two distance ranges R 0 4 AU and R 0 4 AU and divided
into 48 bins for the core plasma beta in the range from 0 03 to 10
and into many bins for the total temperature anisotropy which is here
only considered in the range from 0 0 to 0 9 The number of spectra
in each bin is then determined to obtain frequency distributions Our
statistical results are presented in two-dimensional histograms The
empirical anisotropy values are compared with the known theoretical
thresholds for the non-resonant firehose fluid instability as well
as the resonant temperature anisotropy driven kinetic instability
Apparently solar wind protons are not prone to these instabilities
Title: Origin and evolution of the solar wind
Authors: Marsch, E.
Bibcode: 2006IAUS..233..259M
Altcode:
The magnetic field of the Sun and the plasma properties of its
atmosphere, such as temperature, density and waves in the solar corona,
determine the origin, energetics and evolution of the solar wind. The
solar wind comes in three main kinds, as steady fast streams, variable
slow flows and transient fast coronal mass ejections, with all being
closely associated with the structure and activity of the coronal
magnetic field that evolves on a multitude scales. This tutorial paper
places emphasis on the observed and measured characteristics of the
solar wind sources and their magnetic structure. The boundary conditions
in the magnetically closed corona, in the transiently opening corona,
and in the lastingly open corona (funnels and holes) will be discussed,
and their influences on and consequences for the interplanetary solar
wind be addressed. The resulting three-dimensional structure of the
solar wind and its evolution over the solar cycle are also briefly
discussed.
Title: Solar wind responses to the solar activity cycle
Authors: Marsch, Eckart
Bibcode: 2006AdSpR..38..921M
Altcode:
The solar magnetic field and the plasma properties, such as the
temperature and density distributions in the solar corona, determine
the solar wind stream structure and the extent and dynamics of the
entire heliosphere, including its global magnetic field. The variation
of the solar wind (coming in the form of steady fast streams, variable
slow flows and transient fast mass ejections) in response to solar
activity over the whole cycle is reviewed in detail. Emphasis is
placed on the observed and inferred changes of the plasma states in
the closed corona (streamers, loops) and open corona (funnels, holes),
and on the evolution of the coronal and interplanetary magnetic field
on all scales. The resulting three-dimensional structure of the solar
wind and the evolution of the inner heliosphere over the solar cycle
are discussed. The variations of the solar wind ram pressure and
consequent variations of the global heliosphere are briefly addressed.
Title: Coronal origins of the solar wind - sources of steady streams
and transient flows caused by solar magnetic eruptions
Authors: Marsch, E.
Bibcode: 2006ilws.conf..111M
Altcode:
The magnetic field of the Sun and the plasma properties of its
atmosphere, such as temperature distribution, density stratification,
photospheric convection and waves in the corona, determine the origin,
energetics and evolution of the solar wind. The solar wind comes in
three main kinds, as steady fast streams, variable slow flows and
transient slow and fast coronal mass ejections. The three types of
solar wind are closely associated with the structure and activity of
the coronal magnetic field. The plasma characteristics and magnetic
features of the solar wind source regions are reviewed. The boundary
conditions in the mostly closed corona (streamers and loops), in the
transiently opening corona (eruptive prominences and loops) and in
the lastingly open corona (funnels and holes) will be analyzed. The
resulting properties of the solar wind are discussed.
Title: KuaFu A observations of mass supply to and loss from the
solar corona
Authors: Marsch, E.
Bibcode: 2006cosp...36..939M
Altcode: 2006cosp.meet..939M
One of the new solar science objectives of Kuafu is the continuous
imaging of the source regions of solar eruptive events in ultraviolet
lines Studies are intended of dynamic features in the lower solar
atmosphere such as the network spicules cold loops quiescent and
eruptive filaments With its Lyman-alpha imager Kuafu will observe
the line-of-sight velocity of the initial expansion of an erupting
prominence and the associated CME by spectral measurements made in the
Lyman-alpha line Kuafu will thus permit us to study the characteristic
evolution of magnetic flux and filament eruptions to address such
questions as what are the physical mechanisms and causal links between
filament eruptions and coronal mass ejections what triggers and drives
solar coronal magnetic flux eruptions or what are the mechanisms
of flux emergence storage and release of magnetic field energy
leading to CMEs In this way Kuafu will determine the solar magnetic
preconditions indicative for a CME Another major goal is to study
what the mechanisms of mass loss from the corona are Jets eruptions
chromospheric evaporation spicules what do they all contribute to the
supply of coronal mass and what is the link between spicules and the
solar wind In this talk we will generally address the mechanisms of
mass supply to and loss from the solar corona
Title: Magnetic structure of the solar transition region as observed
in various ultraviolet lines emitted at different temperatures
Authors: Marsch, E.; Zhou, G. -Q.; He, J. -S.; Tu, C. -Y.
Bibcode: 2006cosp...36..936M
Altcode: 2006cosp.meet..936M
The structure of the solar transition region TR in a polar coronal
hole of the Sun is studied In particular the detailed assocation
of the coronal magnetic field carpet with the radiance patterns of
the TR when seen in various far ultraviolet FUV emission lines is
investigated A detailed comparison is made of the coronal magnetic
field as obtained by extrapolation of the NSO Kitt-Peak photospheric
field to heights of several tens of megameters with the radiances
of many FUV lines which are emitted by ions of various elements at
different ionization stages corresponding to different local coronal
temperatures By a correlation analysis of the emission pattern with the
magnetic field network and carpet of loops the so-called correlation
height of the emission can be determined By its help and through
a correlation analysis the magnetic nature of the emission regions
and the temperature structure of the TR can be better revealed and
understood In particular at mesocopic scales of several megameters the
regions with strong emission originating from multiple small closed
loops are found to be located at low heights whereas weak emissions
coming from locally open i e far reaching fields appear to originate
at greater heights These findings are qualitatively consistent with
similar results obtained at large scales for large-sacle loops and
coronal holes Our correlation-height analysis of the emission lines
confirms the notion that plasma at different temperature can coexist
at the same height The TR is not thermally stratified but strongly
Title: Diffusion plateaus in the velocity distributions of fast
solar wind protons
Authors: Heuer, M.; Marsch, E.
Bibcode: 2006cosp...36..926H
Altcode: 2006cosp.meet..926H
In a collisionless plasma such as the fast solar wind wave-particle
interaction plays the decisive role in determining the shape of
particle velocity distribution functions In this paper we provide
observational evidence for cyclotron-resonant absorption of Alfven waves
which propagate outward from the sun along the interplanetary magnetic
field by fast solar wind protons According to quasi-linear theory the
protons diffuse in velocity space a process leading to the formation of
diffusion plateaus in the velocity distribution function In this respect
we investigated a large number of observed data from several distinct
fast solar wind streams between 0 3 and 1 AU The measurements were
made on Helios 2 during solar minimum in 1976 The cyclotron-resonant
absorption of Alfven waves naturally explains the observed thermal
anisotropy in the core of the proton velocity distribution
Title: Can the solar wind originate in the quiet-Sun region?
Authors: Tu, C. -Y.; He, J. -S.; Marsch, E.
Bibcode: 2006cosp...36..594T
Altcode: 2006cosp.meet..594T
It is well known that the fast solar wind streams are mainly created
in solar coronal holes CHs However if the quiet-Sun regions also
generate solar wind is still an unsolved problem For studying this
question we will analyze the magnetic field in the solar transition
region TR and low corona in a quiet-Sun area We will also analyze
the far ultraviolet data from SUMER magnetic field data from MDI the
extreme ultraviolet data from EIT with all being obtained on SOHO We
make a force-free extrapolation of the observed magnetic field and
trace the field lines from the photosphere up to 80 Mm height Through
our correlation analysis the magnetic nature of the emission regions
and the plasma flow in the TR can be better revealed and understood It
is found that most of the intersections of network boundaries related
with outflows are not located in an open-file-line region Most likely
the outflows from intersections just feed plasma to the the loops of
the magnetic carpet It is further found that in a cross-section plane
at 40 Mm height the intersection pattern of the open field lines is
consistent with the pattern of a dark region seen in the Fe XII 19
5 nm image Usually small dark regions are considered to be small CHs
and thus assumed to be possible sources of the solar win However since
the source of the low emission is at the height of only 40 Mm it is
also possible that this radiation originate near the foot points of
large coronal loops The previous findings of relatively large outflow
velocities at the intersections of the network boundaries at
Title: a Study on the Height of the Corona Bright Points on FeXII
Radiance Map
Authors: Tian, H.; Tu, C. -Y.; He, J. -S.; Marsch, E.
Bibcode: 2006cosp...36.1952T
Altcode: 2006cosp.meet.1952T
By registering SOHO EIT FeXII -19 5 nm coronal images with Kitt Peak
magnetograms D A Falconer et al 1998 found that the brightest features
in the network lanes which they called network coronal bright points
had a highly significant coincidence with magnetic network neutral lines
They found that most bright points sit on neutral lines in the network
magnetic flux We further studied the height information of the bright
points on the FeXII radiance map by comparing the individual pattern
of the coronal bright points with the distribution of the top segments
of the loops from the 3-D magnetic field force-free extrapolated from
the photospheric magnetogram If we assume the source regions of the
bright points are all on the top of the loops then the height of bright
points of FeXII radiance is between 5Mm-10Mm
Title: Emission height of a dark region in the radiance map of the
Fe XII 19.5 nm line as observed in a quiet-Sun region
Authors: He, J. -S.; Tu, C. -Y.; Marsch, E.
Bibcode: 2006cosp...36.1930H
Altcode: 2006cosp.meet.1930H
We studied the emission height of the source region of the Fe XII 19 5
nm line radiation where it appears as a dark pattern on the radiance map
We derived the coronal magnetic field from a force-free extrapolation
of the photospheric magnetogramm related to that region If the field
reaches the top of the extrapolation box we consider the field lines to
be open We then used the vertical magnetic field strength normalized
to its average over the entire area considered at any given height as
a weight function in order to define by its multiplication with the
measured radiance a new weighted radiance for each of the original
pixels in the map The weighted radiance is then summed up over all
pixels in the dark region The resulting weighted radiance still is
a function of the height and by varying this reference height we
can obtain its minimum value The corresponding height is suggested
to indicate the height of the source of the dark region We apply
this technique to a quiet-sun region where the original SOHO SUMER
observation was made on 22 September 1996 The minimum height of the
weighted radiance is 20 Mm
Title: Beam-Instabilities in a Coronal Funnel Within the Multi-Fluid
Description
Authors: Mecheri, R.; Marsch, E.
Bibcode: 2005ESASP.600E..90M
Altcode: 2005dysu.confE..90M; 2005ESPM...11...90M
No abstract at ADS
Title: The Dynamics of the Lower Transition Region as Inferred from
Spectroscopy of the Hydrogen LYMAN-α Line
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
Bibcode: 2005ESASP.600E.100T
Altcode: 2005ESPM...11..100T; 2005dysu.confE.100T
No abstract at ADS
Title: The Structure of the Lower Transition Region as Inferred from
the Hydrogen LYMAN-α Line Radiance
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
Bibcode: 2005ESASP.596E..66T
Altcode: 2005ccmf.confE..66T
No abstract at ADS
Title: The Height of Solar Wind Origin in Coronal Funnels and a 3-D
Scenario for Solar Wind Formation
Authors: Tu, C. -Y.; Zhou, C.; Marsch, E.; Wilhelm, Klaus; Xia,
Li-Dong; Zhao, Liang; Wang, Jing-Xia
Bibcode: 2005ESASP.592..131T
Altcode: 2005ESASP.592E..19T; 2005soho...16E..19T
No abstract at ADS
Title: Importance of Kinetic Effects in Heating the Open and Closed
Corona (Invited)
Authors: Marsch, E.
Bibcode: 2005ESASP.592..191M
Altcode: 2005ESASP.592E..30M; 2005soho...16E..30M
No abstract at ADS
Title: Radial evolution of the electron distribution functions in
the fast solar wind between 0.3 and 1.5 AU
Authors: Maksimovic, M.; Zouganelis, I.; Chaufray, J. -Y.; Issautier,
K.; Scime, E. E.; Littleton, J. E.; Marsch, E.; McComas, D. J.; Salem,
C.; Lin, R. P.; Elliott, H.
Bibcode: 2005JGRA..110.9104M
Altcode: 2005JGRA..11009104M
Observed electron distribution functions of the solar wind permanently
exhibit three different components: a thermal core and a suprathermal
halo, which are always present at all pitch angles, and a sharply
magnetic field aligned "strahl" which is usually anti-sunward
moving. Whereas Coulomb collisions can explain the relative isotropy
of the core population, the origin of the halo population, and
more specifically the origin of its sunward directed part, remains
unknown. In this study we present the radial evolution of the electron
velocity distribution functions in the fast solar wind between 0.3 and
1.5 AU. For this purpose we combine data measured separately by the
Helios, Wind, and Ulysses spacecraft. We compute average distributions
over distance and normalize them to 1 AU to remove the effects of
the solar wind expansion. Then we model separately the core, halo,
and strahl components to compute their relative number density or
fraction of the total electron density. We observe that, while the
core fractional density remains roughly constant with radial distance,
the halo and strahl fractional densities vary in an opposite way. The
relative number of halo electrons is increasing, while the relative
number of strahl electrons is decreasing with distance. Therefore we
provide, for the first time, strong evidences for a scenario that is
commonly assumed: the heliospheric electron halo population consists
partly of electrons that have been scattered out of the strahl.
Title: On the nature of the unidentified solar emission near 117 nm
Authors: Wilhelm, K.; Schühle, U.; Curdt, W.; Hilchenbach, M.;
Marsch, E.; Lemaire, P.; Bertaux, J. -L.; Jordan, S. D.; Feldman, U.
Bibcode: 2005A&A...439..701W
Altcode:
Spectral observations of the Sun in the vacuum-ultraviolet wavelength
range by SUMER on SOHO led to the discovery of unusual emission
features - called humps here - at 116.70 nm and 117.05 nm on either
side of the He i 58.43 nm line. This resonance line is seen in the
second order of diffraction, whereas the humps are recorded in the
first order with the SUMER spectrometer. In its spectra both orders
are superimposed. Two less pronounced humps can be detected at 117.27
nm and near 117.85 nm. After rejecting various possibilities of an
instrumental cause of the humps, they are studied in different solar
regions. Most of the measurements, in particular those related to the
limb-brightening characteristics, indicate that the humps are not part
of the background continuum. An assembly of spectrally-unresolved atomic
or ionic emission lines might be contributing to the hump at 117.05
nm, but no such lines are known near 116.7 nm. It is concluded that we
detect genuine radiation, the generation of which is not understood. A
two-photon emission process, parametric frequency down conversion,
and molecular emissions are briefly considered as causes of the humps,
but a final conclusion could not be reached.
Title: Correlation Heights of the Sources of Solar Ultraviolet
Emission Lines in a Quiet-Sun Region
Authors: Tu, Chuan-Yi; Zhou, Cheng; Marsch, Eckart; Wilhelm, Klaus;
Zhao, Liang; Xia, Li-Dong; Wang, Jing-Xiu
Bibcode: 2005ApJ...624L.133T
Altcode:
The radiance and Doppler-velocity maps of the emission lines of Si
II, C IV, and Ne VIII obtained in a quiet region of the Sun by SUMER
(Solar Ultraviolet Measurements of Emitted Radiation) are correlated
with the vertical component, Bz, of the magnetic field
vector as extrapolated, by means of a force-free field model, from
the photospheric magnetic field measured by MDI (Michelson Doppler
Imager). It is found that, with increasing vertical height, each of the
correlation coefficients initially increases to a maximum value before
it decreases again. The height corresponding to this maximum is called
the correlation height. For the data sets selected from a quiet-Sun
region, the correlation heights of Si II and C IV are near 2 Mm,
and for Ne VIII near 4 Mm. At their correlation heights, the averaged
square root of the radiance of the emission lines of Si II and C IV,
considered as a proxy of the plasma density, has a linear relationship
with Bz. This result supports the empirical concept that the
solar transition region is very thin and still affected by frozen-in
convection. A way for improvement of such studies is also outlined.
Title: Solar Wind Origin in Coronal Funnels
Authors: Tu, Chuan-Yi; Zhou, Cheng; Marsch, Eckart; Xia, Li-Dong;
Zhao, Liang; Wang, Jing-Xiu; Wilhelm, Klaus
Bibcode: 2005Sci...308..519T
Altcode:
The origin of the solar wind in solar coronal holes has long been
unclear. We establish that the solar wind starts flowing out of the
corona at heights above the photosphere between 5 megameters and 20
megameters in magnetic funnels. This result is obtained by a correlation
of the Doppler-velocity and radiance maps of spectral lines emitted
by various ions with the force-free magnetic field as extrapolated
from photospheric magnetograms to different altitudes. Specifically,
we find that Ne7+ ions mostly radiate around 20 megameters,
where they have outflow speeds of about 10 kilometers per second,
whereas C3+ ions with no average flow speed mainly radiate
around 5 megameters. Based on these results, a model for understanding
the solar wind origin is suggested.
Title: Links between magnetic fields and plasma flows in a coronal
hole
Authors: Wiegelmann, T.; Xia, L. D.; Marsch, E.
Bibcode: 2005A&A...432L...1W
Altcode: 2008arXiv0801.4724W
We compare the small-scale features visible in the Ne viii Doppler-shift
map of an equatorial coronal hole (CH) as observed by SUMER with the
small-scale structures of the magnetic field as constructed from a
simultaneous photospheric magnetogram by a potential magnetic-field
extrapolation. The combined data set is analysed with respect to
the small-scale flows of coronal matter, which means that the Ne viii
Doppler-shift used as tracer of the plasma flow is investigated in close
connection with the ambient magnetic field. Some small closed-field
regions in this largely open CH are also found in the coronal volume
considered. The Doppler-shift patterns are found to be clearly linked
with the field topology.
Title: Solar Orbiter—mission profile, main goals and present status
Authors: Marsch, Eckart; Marsden, Richard; Harrison, Richard;
Wimmer-Schweingruber, Robert; Fleck, Bernhard
Bibcode: 2005AdSpR..36.1360M
Altcode:
The main goals and present status of the Solar Orbiter mission are
briefly described. solar orbiter will determine in situ the properties
of fields and particles in the unexplored near-Sun heliosphere in
three dimensions, investigate remotely the fine-scale structures and
events in the magnetically coupled layers of the Sun’s atmosphere,
identify through near corotation the links between activity on the
solar surface and the resulting evolution of the inner heliosphere, and
observe from relatively high latitudes the polar regions and equatorial
corona. Some results from recent activities, such as industrial studies,
payload working group meetings, science definition team meetings and
ESA internal studies are briefly reviewed. Solar Orbiter is currently
planned for launch in October 2013.
Title: Kinetic Aspects of Coronal Heating
Authors: Marsch, E.
Bibcode: 2004ESASP.575..186M
Altcode: 2004soho...15..186M
No abstract at ADS
Title: Coronal plasma flows and magnetic fields in solar active
regions. Combined observations from SOHO and NSO/Kitt Peak
Authors: Marsch, E.; Wiegelmann, T.; Xia, L. D.
Bibcode: 2004A&A...428..629M
Altcode:
During the early days of the SOHO mission, SUMER observed a few
active regions (ARs) connected with sunspots on the Sun and took their
images and spectra in various EUV emission lines. In addition to these
spectroscopic data magnetograms of the photospheric footpoint regions
of the AR loops were available from the MDI on SOHO and the National
Solar Observatory/Kitt Peak (NSO/KP), data which here are used to
construct the coronal magnetic field of the ARs by force-free-field
extrapolation. The combined data set is analysed with respect to
the large-scale circulation of coronal matter, which means that the
Dopplershifts of various lines used as tracers of the plasma flow are
investigated in close connection with the ambient magnetic field,
which is found to be either closed or open in the coronal volume
considered. The Dopplershift pattern is found to be clearly linked
with the field topology, and several regions of strong velocity shear
are identified. We also estimate the coronal currents. We discuss
the results of this mainly phenomenological correlative study with
the perspective to understand coronal heating and mass supply to the
extended corona, and with respect to the role played by the field in
guiding and constraining plasma flows.
Title: Waves and Turbulence in the Solar Corona
Authors: Marsch, Eckart
Bibcode: 2004ASSL..317..283M
Altcode: 2004shis.conf..283M
No abstract at ADS
Title: On the network structures in solar equatorial coronal
holes. Observations of SUMER and MDI on SOHO
Authors: Xia, L. D.; Marsch, E.; Wilhelm, K.
Bibcode: 2004A&A...424.1025X
Altcode:
By combining observations of the Sun made by SUMER and MDI aboard
SOHO, the network structures in equatorial coronal holes have been
studied, in particular the relationship between the ultraviolet
emission-line parameters (line radiance, Doppler shift and line width)
and the underlying magnetic field. The bases of coronal holes seen in
chromospheric spectral lines with relatively low formation temperatures
generally have similar properties as normal quiet-Sun regions, i.e.,
small bright patches with a size of about 2 arcsec to 10 arcsec are
the dominant features in the network as well as in cell interiors. With
the increase of the formation temperature, these features become more
diffuse, and have an enlarged size. Loop-like structures are the most
prominent features in the transition region. In coronal holes, we
found that many of such structures seem to have one footpoint rooted
in the intra-network and to extend into the cell interiors. Some of
them appear as star-shape clusters. In Dopplergrams of the O VI line
at 1032 Å, there are also fine structures with apparent blue shifts,
although, on average, they are red shifted. Structures with blue shifts
have usually also broader line widths. They seem to represent plasma
above large concentrations of unipolar magnetic field, without obvious
bipolar photospheric magnetic features nearby. Table 1 is only
available in electronic form at http://www.edpsciences.org
Title: Radial Evolution of the Electron Distribution Functions of
the Fast Solar Wind Combining Measurements From the HELIOS, WIND
and ULYSSES Spacecraft
Authors: Zouganelis, I.; Maksimovic, M.; Issautier, K.; Chaufray,
J.; Scime, E.; Littleton, J.; Salem, C.; Marsch, E.; Elliott, H.;
McComas, D.
Bibcode: 2004AGUSMSH21A..08Z
Altcode:
Observed electron distribution functions of the solar wind permanently
exhibit three different components: a thermal core and a supra-thermal
halo, which are always present at all pitch angles, and a sharply
magnetic field aligned "strahl" which is usually antisunward-moving. If
the Coulomb collisions could explain the relative isotropy of the core
population, the origin of the halo population and more specifically the
origin of its sunward-directed part remains unknown. Various processes
like scattering of strahl electrons by shocks, corotating interaction
regions or other wave/particle interactions have been invoked. We
look for possible observational constraints on these processes by
examining the radial evolution of the different populations of the
electron distribution functions in the solar wind. For this purpose
we combine HELIOS (0.3 to 0.7 AU), WIND (1 AU) and ULYSSES (1.3 to 3
AU) observations performed during fast solar wind periods at minimum
of activity.
Title: Dependence of the proton beam drift velocity on the proton
core plasma beta in the solar wind
Authors: Tu, C. -Y.; Marsch, E.; Qin, Z. -R.
Bibcode: 2004JGRA..109.5101T
Altcode:
A correlation between the proton core plasma beta and the proton
beam drift speed in units of the local Alfvén speed has been found
in high-speed solar wind with the Helios 2 spacecraft plasma data
obtained in 1976. This relation reads vd/vA =
(2.16 ± 0.03) β∥c(0.281±0.008) for the
range β∥c = 0.1 to 0.6, where β∥c is
the proton core plasma beta determined from the proton core thermal
velocity component parallel to the magnetic field, vd is
the proton beam drift speed relative to the core, and vA
is the local Alfvén speed. This relation places a tight constraint on
theoretical models which describe the formation of the proton beam in
the fast solar wind. It is also found that most of the observed proton
beam distributions are stable with respect to the electromagnetic
proton instability.
Title: On the temperature anisotropy of the core part of the proton
velocity distribution function in the solar wind
Authors: Marsch, E.; Ao, X. -Z.; Tu, C. -Y.
Bibcode: 2004JGRA..109.4102M
Altcode:
In this paper we analyze the temperature anisotropy of velocity
distribution functions (VDFs) of protons measured by the Helios
spacecraft in fast solar wind. We concentrate on data obtained during
the primary mission, including the first perihelion passage, of Helios 2
in a distance range between 0.98 and 0.29 AU for the days 23 through 114
of the year 1976. The main goal is to provide solid statistical evidence
on the relation between the anisotropy and the proton plasma beta,
parameters that play a key role in the regulation of the shape of the
core. It is believed to be formed by resonant interactions between ion
cyclotron waves and protons, as described by the quasi-linear theory of
pitch angle diffusion. In the analysis of the VDF, particular attention
is paid to the symmetry axis, which can be determined by the directions
of either the magnetic field, the proton heat flux, or the alpha-proton
relative drift. We analyze in detail the core part of the proton VDF,
carefully avoiding a possible influence of the proton beam component.
Title: Observations of the Sun at Vacuum- Ultraviolet Wavelengths
from Space. Part I: Concepts and Instrumentation
Authors: Wilhelm, Klaus; Dwivedi, Bhola N.; Marsch, Eckart; Feldman,
Uri
Bibcode: 2004SSRv..111..415W
Altcode:
Studies of the high-temperature solar atmosphere are to a large extent
based on spectroscopic observations of emission lines and continuum
radiation in the vacuum-ultraviolet (VUV) wavelength range of the
electromagnetic spectrum. In addition, important contributions stem
from soft X-ray measurements. Most of the VUV radiation is produced
by transitions of atoms and ions. The resulting atomic and ionic
spectral lines have formation temperatures between 10 000 K and 20 MK,
representative of the chromosphere, transition region, corona, and
solar flares. Some molecular lines and the continua originate in cooler
regions of the Sun, around and below the temperature minimum between
the photosphere and the chromosphere. Radiation at VUV wavelengths
is strongly absorbed by the Earth's atmosphere. Consequently, it can
only be detected with instruments on sounding rockets and spacecraft
operating above the atmosphere. The progress in this field of research,
in particular over the last 25 years, will be presented in the first
part of this review by describing the concepts and instrumentation
of modern spectrographs and imaging telescopes. This presentation
is accompanied by some examples of high-resolution solar images
and a discussion of radiometric-calibration aspects and wavelength
measurements. A second part will follow in the near future, summarizing
important results obtained on the plasma conditions in the solar
atmosphere.
Title: Observational Constraints on Ion Acceleration by Waves in
Coronal Holes
Authors: Xia, L.; Marsch, E.
Bibcode: 2004ESASP.547..387X
Altcode: 2004soho...13..387X
The relationships between the deduced parameters of the coronal emission
line of Mg X at 625 Å (with a formation temperature of about 1 MK)
as observed by SUMER and the photospheric magnetic field as measured
by NSO/Kitt Peak have been investigated. It has been found that the
line width deduced from the Mg X line (in different equatorial coronal
holes) shows a clear trend to increase with increasing magnetic field
strength. Evidence for preferential heating and acceleration of heavy
ions very near the Sun had previously been found in observations
with UVCS and SUMER aboard SOHO. This suggests that dissipation
of high-frequency Alfvén waves in coronal funnels may be a prime
candidate for the heating of the magnetically open corona. Following
this reasoning, our result seem to indicate that the wave-mechanical
energy flux correlates with the strength of the magnetic field in
coronal holes. Moreover, the spectroscopically obtainable quantity v I
(with the intensity scaling like I n2 e), which can be used as a proxy
for the coronal mass flux of the nascent fast solar wind, also reveals
a clear positive correlation with the magnetic field strength. If this
estimation of the mass flux (and its ratio between different holes)
can be trusted, we could interpret our results as evidence that the
mass flux is directly associated with the net magnetic flux density
in a coronal hole.
Title: Solar wind responses to the solar activity cycle
Authors: Marsch, E.
Bibcode: 2004cosp...35..381M
Altcode: 2004cosp.meet..381M
The solar magnetic field and the plasma properties, such as temperature
and density, in the solar corona determine the solar wind stream
structure and the extent and dynamics of the entire heliosphere,
including its global magnetic field. The variation of the solar wind
(coming in the form of steady fast streams, variable slow flows
and transient fast mass ejections) in response to solar activity
over the whole cycle is reviewed in detail. Emphasis is placed on
the observed and inferred changes of the plasma states in the closed
corona (streamers, loops) and open corona (funnels, holes), and on the
evolution of the coronal magnetic field on all scales. The consequent
three-dimensonal structure and evolution of the inner heliosphere and
the resulting observed and assumed variations of the outer heliosphere
and its boundary layers to the local interstellar medium are also
discussed.
Title: Topological Changes of the Magnetic Network as Seen in
Different UV/EUV Emission Lines
Authors: Xia, L. D.; Marsch, E.; Wilhelm, K.
Bibcode: 2004ESASP.547..169X
Altcode: 2004soho...13..169X
By combining observations made by SUMER and MDI aboard SOHO, fine
structures in equatorial coronal holes have been studied, in particular
the relationship between the ultraviolet emission line parameters (line
radiance, Doppler shift and line width) and the underlying magnetic
field. The bases of coronal holes seen in chromospheric lines generally
have similar properties as normal QS regions, i.e., small bright points
are the predominant features. An obvious difference has been found in
the shape of the H I L line, which has very asymmetric profiles (skewed
towards the blue side) in coronal holes. Loop-like structures are the
most prominent features in the transition region. In coronal holes, we
found that many of such structures seem to have one footpoint rooted
in the intra-network and to extend into the cell interiors. Some of
them appear as star-shape clusters. In Dopplergrams of the O VI line,
there are also fine structures with apparent blue shifts, although on
average they are red shifted. Structures with blue shifts have usually
also broader line widths. They seem to represent plasma above large
concentrations of unipolar magnetic field, without obvious bipolar
photospheric magnetic features nearby.
Title: Solar Orbiter - main goals and present status
Authors: Marsch, E.
Bibcode: 2004cosp...35.1681M
Altcode: 2004cosp.meet.1681M
ESA's Solar Orbiter will be launched in 2014. Its main goals and present
status are briefly described. Solar Orbiter will determine in-situ
the properties of fields and particles in the unexplored near-Sun
heliosphere in three dimensions, investigate remotely the fine-scale
structures and events in the magnetically coupled layers of the Sun's
atmosphere, identify through corotation the links between activity on
the Sun's surface and the resulting evolution of the inner heliosphere,
and observe from high latitudes the Sun's polar regions and equatorial
corona. Some results from recent activities, such as industrial studies,
payload working group meetings, science definition team meetings and
ESA internal studies are shortly reviewed.
Title: Waves in the Solar Corona
Authors: Marsch, E.
Bibcode: 2004IAUS..219..449M
Altcode: 2003IAUS..219E..33M
Waves at all scales ranging in wavelength from the size of a loop
(fraction of a solar radius) down to the gyroradii (a few meters)
of coronal ions are believed to play a key role in the transport of
mechanical energy from the chromosphere to the Sun's corona and wind
and through the dissipation of wave energy in the heating and sustaining
of the solar corona. A concise review of new observations and theories
of waves in the magnetically confined (loops) as well as open (holes)
corona is given with emphasis on energetics and dynamics. Recent
remote-sensing solar observations have revealed loop oscillations as
expected from MHD theory. These low-frequency oscillations are excited
in connection with flares and appear to be strongly damped. Recent
analysis of in-situ measurements of ions in fast solar wind and related
theory have indicated the importance of pitch-angle scattering of ions
in the wave frame as predicted from kinetic plasma theory a microprocess
that may hold the key to understand plasma acceleration and heating by
damping of high-frequency waves. Evidence obtained from spectroscopy
of coronal ions points to cyclotron resonance absorption as a possible
cause of the observed emission-line broadenings.
Title: Turbulence and waves in the solar wind
Authors: Marsch, E.
Bibcode: 2004cosp...35..383M
Altcode: 2004cosp.meet..383M
A short review of waves and turbulence in the solar wind is given with
respect to those properties of plasma and field fluctuations that are
relevant for the diffusion and propagation of energetic particles
and cosmic rays in the heliosphere. In particular, the typical
turbulence spectra and their variations with heliocentric distance
and heliographic latitude over the solar cycle are discussed. Also,
such important features as amplitude, anisotropy, cross-helicity,
intermittency and compressibility of the fluctuations in various types
of solar wind are briefly adressed.
Title: Radial Evolution of the Non-thermal Character of Electron
Distribution Functions in the Solar Wind
Authors: Maksimovic, M.; Zouganelis, I.; Chaufray, J.; Issautier,
K.; Scime, E.; Littleton, J.; Salem, C. S.; Marsch, E.; Elliott, H.;
McComas, D. J.; Lin, R. P.
Bibcode: 2003AGUFMSH21B0159M
Altcode:
Observed electron distribution functions of the solar wind permanently
exhibit three different components : a thermal core and a supra-thermal
halo, which are always present at all pitch angles, and a sharply
magnetic field aligned "strahl" which is usually antisunward-moving. If
the Coulomb collisions could explain the relative isotropy of the core
population, the origin of the halo population and more specifically the
origin of its sunward-directed part remains unknown. Processes invoking
scattering of strahl electrons by shocks, corotating interaction regions
or other wave/particle interactions have been invoked. We look for
possible observationnal constraints on these processes by examining the
radial evolution of the various populations of the electron distribution
functions in the solar wind. For this purpose we combine HELIOS (0.3 to
0.7 AU), WIND (1 AU) and ULYSSES (1.3 to 3 AU) observations performed
during fast solar wind periods at minimum of activity.
Title: The Microscopic State of the Solar Wind
Authors: Marsch, Eckart
Bibcode: 2003AIPC..679..399M
Altcode:
The microscopic state of the solar wind is reviewed, in particular the
measurements and models of proton and electron velocity distributions
and kinetic features of heavy ions in the fast solar wind and coronal
holes. Apparently, electron distributions are largely determined by
Coulomb collisions. Concerning the ions, there is mounting evidence that
pitch-angle diffusion in resonance with ion-cyclotron waves is the main
process forming the shape of ion velocity distributions. Moreover,
the absorption of high-frequency waves seems to play a major role
in the heating of the corona and solar wind. Dispersive plasma
waves and associated wave-particle interactions are the key to this
problem. Plasma stability analyses and model calculations, as well
as observations adressing these subjects are briefly reviewed, while
focussing on the critical issues.
Title: Cyclotron-resonant diffusion regulating the core and beam of
solar wind proton distributions
Authors: Tu, C. -Y.; Marsch, E.; Wang, L. -H.
Bibcode: 2003AIPC..679..389T
Altcode:
Ion diffusion as predicted by quasi-linear theory has been compared with
in-situ solar wind proton measurements. It is found that the observed
phase-space-density contours match very well those corresponding to the
time-asymptotic plateau generated by proton diffusion in cyclotron-wave
resonance. Observations show that the perpendicular temperature of
the beam distribution is of the same order as its parallel one. A
perpendicular heating mechanism is needed to balance the radial tendency
for adiabatic cooling. Outward and inward propagating cyclotron waves
may together be able to control the thermal anisotropy of the core
distribution. However, there are hardly any cyclotron waves, which
could resonate with a proton beam having a drift velocity equal
to or greater than the Alfvén speed. Therefore, we consider also
outward-propagating waves, with both left and right hand polarization,
on a second dispersion branch existing in a cold plasma with electrons,
protons and alpha particles. These waves can resonate with the beam
protons. The resulting diffusion can indeed explain the shape of the
beam distribution. A time-dependent kinetic code, in two-dimensional
velocity space, has been developed to integrate the quasi-linear
diffusion equation. An initial shuttle-like distribution function is
shown to develop into a distribution having a core and a beam. The
beam is found to drift at the Alfvén speed and be less anisotropic
than the core. The radial evolution of the beam density in the model
is found to be consistent with the observations.
Title: Equatorial Coronal Holes and Their Relation to High-Speed
Solar Wind Streams
Authors: Xia, Lidong; Marsch, Eckart
Bibcode: 2003AIPC..679..319X
Altcode:
Using together SUMER, EIT and MDI onboard SOHO, we examine plasma
properties and magnetic fields at the base of three equatorial
coronal holes (ECHs) occurring during August and October 1996
near solar minimum. We estimate the electron density, flow speed
deduced from UV/EUV lines as well as the average magnetic field of
the photosphere. These ECHs produced distinct high-speed streams
in the ecliptic plane with average flow speeds of larger than 500
kms-1. With SWE and MFI both onboard the WIND satellite, we
also determine the parameter values of the plasma and magnetic field
of these high-speed streams at 1 AU in the Earth's orbit. We discuss
the relationships between observations of high-speed streams at 1 AU
and coronal holes at the coronal base.
Title: Topological Changes of the Magnetic Network as Seen in
different UV/EUV Emission Lines
Authors: Xia, Lidong D.; Marsch, Eckart; Wilhelm, K.
Bibcode: 2003ANS...324Q.100X
Altcode: 2003ANS...324..P04X
No abstract at ADS
Title: Wave-particle Interactions and Ion Kinetics in the Solar
Corona and Solar Wind
Authors: Marsch, Eckart
Bibcode: 2003ANS...324R..12M
Altcode: 2003ANS...324..B08M
No abstract at ADS
Title: Observational Constraints on Ion Acceleration by Waves in
Coronal Holes
Authors: Xia, Lidong D.; Marsch, Eckart
Bibcode: 2003ANS...324R.100X
Altcode: 2003ANS...324..P05X
No abstract at ADS
Title: Slow-mode standing waves observed by SUMER in hot coronal
loops
Authors: Wang, T. J.; Solanki, S. K.; Innes, D. E.; Curdt, W.;
Marsch, E.
Bibcode: 2003A&A...402L..17W
Altcode:
We report the first detection of postflare loop oscillations seen in
both Doppler shift and intensity. The observations were recorded in
an Fe Xix line by the SUMER spectrometer on SOHO in the corona about
70 min after an M-class flare on the solar limb. The oscillation has a
period of about 17 min in both the Doppler velocity and the intensity,
but their decay times are different (i.e., 37 min for the velocity and
21 min for the intensity). The fact that the velocity and the intensity
oscillations have exactly a 1/4-period phase difference points to the
existence of slow-mode standing waves in the oscillating loop. This
interpretation is also supported by two other pieces of evidence:
(1) the wave period and (2) the amplitude relationship between the
intensity and velocity are as expected for a slow-mode standing wave.
Title: A possible way of understanding the differential motion of
minor ions in the solar wind
Authors: Tu, C. -Y.; Wang, L. -H.; Marsch, E.
Bibcode: 2003JGRA..108.1161T
Altcode:
Measurements with Solar and Heliospheric Observatory (SOHO)/Charge,
Element, and Isotope Analysis System (CELIAS) in high-speed solar wind
show that some minor ions such as O6+ have a relatively high
drift velocity; however, other ions such as Fe9+ tend to lag
behind oxygen by a few tens of km/s [, 1998]. This subtle observational
feature has not yet been understood. A possible way, based on the
quasi-linear theory of cyclotron resonance, of understanding this
phenomenon is presented in this paper. The charge per mass of the ion
O6+ and Fe9+ are different, a fact which results
in different features of the ion-cyclotron resonance with waves. In
plasma with protons, drifting alpha particles, and electrons, the
dispersion relation of cyclotron waves has two branches. The oxygen
ions tend to resonate with the inward propagating waves of the
left-hand-polarized (LHP) first branch and the outward propagating
waves of the LHP second branch. These resonances may together lead to
a velocity distribution with a central velocity higher than the proton
(solar wind) bulk velocity by about 50 km/s at 1 AU. The Fe9+
ions tend to resonate with both the inward and outward propagating
waves of the first branch and may thus form a velocity distribution
with a central velocity very near the proton bulk velocity. These
analytical results are shown to be supported by numerical results
from a two-dimensional simulation based on the quasi-linear diffusion
equation. The limitations of the present analysis and further work,
which should be done to support the ideas proposed here, are also
discussed.
Title: On the outflow in an equatorial coronal hole
Authors: Xia, L. D.; Marsch, E.; Curdt, W.
Bibcode: 2003A&A...399L...5X
Altcode:
We report new observations concerning the source of the fast solar
wind by directly comparing Doppler-shift maps of Ne7+ with
charts of the photospheric magnetic field in an equatorial coronal
hole, which was observed by SUMER/SOHO and NSO/Kitt Peak on November 5,
1999. The relationship between the velocity field, line intensity and
magnetic network is discussed. Our data show that there are both dark
and bright regions in this coronal hole as seen in the Ne Viii line. The
larger blue shifts of the Ne Viii line are associated mainly with the
darker region, where the strong magnetic flux with a single polarity is
concentrated. Conversely, the smaller blue shifts are measured mainly
in the brighter region, with an underlying mixed-polarity magnetic
structure. These observational results are in agreement with the model
prediction that the fast solar wind is initially accelerated in the
coronal funnels, which are regions with globally open coronal fields
rooted in the magnetic network.
Title: Novel Solar and Heliospheric Research with Solar Orbiter
Authors: Marsch, Eckart
Bibcode: 2003IAUJD...7E...8M
Altcode:
ESA's Solar Orbiter is going to be launched in 2011. It will determine
in-situ the properties of fields and particles in the unexplored
near-Sun heliosphere in three dimensions investigate remotely the
fine-scale structures and events in the magnetically coupled layers
of the Sun's atmosphere identify through corotation the links between
activity on the Sun's surface and the resulting evolution of the inner
heliosphere and observe from high latitudes the Sun
Title: Solar wind
Authors: Marsch, E.; Axford, W. I.; McKenzie, J. F.
Bibcode: 2003dysu.book..374M
Altcode:
There are three major types of solar wind - the steady fast wind,
the unsteady slow wind, and the variable transient wind. The fast
streams are the normal modes of the solar wind. Their basic properties
can be reproduced by multi-fluid models involving waves. After
briefly reviewing the history of the subject and describing some of
the modern theories of the fast wind, the boundary conditions and
in-situ constraints are discussed which are imposed on the models,
in particular by Ulysses at high latitudes. Some of the results are
then presented from SOHO observations that have brought a wealth of
new information on the state of the wind in the inner corona as well
as the plasma source conditions prevailing in the transition region
and solar chromosphere. Finally, problem areas are identified and
future research perspectives are outlined.
Title: Mechanism for Generating Differential Motion of Minor Ions
in the Solar Wind
Authors: Tu, C.; Wang, L.; Marsch, E.
Bibcode: 2002AGUFMSH12A0389T
Altcode:
Measurements with SOHO/CELLAS in high-speed solar wind show that some
minor ions such as O6+ have a relatively high drift velocity,
however others such as Fe9+ tend to lag behind oxygen by
a few tens of km/s (Hefti et al. 1998). This subtle observational
feature has not yet been understood. A possible mechanism, based on
quasi-linear theory of cyclotron resonance, for an understanding of this
phenomenon is presented in this paper . The mass per charge of the ion
O6+ and Fe9+ are different, a fact which results
in different features of the resonance with ion-cyclotron waves. In
a plasma with protons, alpha particles and electrons, the dispersion
relation of cyclotron waves has two branches. The oxygen ions tend to
resonate with the inward-propagating waves of the left-hand polarised
(LHP) first branch and the outward-propagating waves of the LHP second
branch. These resonances together may lead to a velocity distribution
having a central velocity higher than the proton (solar wind bulk)
velocity by about 50~km/s at 1~AU. The Fe9+ ions tend
to resonate with both the inward and outward propagating waves of
the first branch and may thus form a velocity distribution with
the central velocity being very near the proton bulk velocity. These
analytical results are shown to be supported by numerical results from
a 2-dimensional simulation based on the quasi-linear diffusion equation.
Title: Formation of the proton beam distribution in high-speed
solar wind
Authors: Tu, C. -Y.; Wang, L. -H.; Marsch, E.
Bibcode: 2002JGRA..107.1291T
Altcode:
A new mechanism is suggested to explain the formation of proton beam
velocity distributions in high-speed streams of the solar wind. The
proton beam is a well-known kinetic phenomenon, which was already found
in the early days of solar wind in situ measurements [, 1973; , 1982a;
, 1981]. Observationally, proton beams move faster than the core part
of the proton distribution by more than the Alfvén speed. The beam
has a higher temperature than the core, but the thermal anisotropy
is usually smaller. Until today none of the major properties of the
observed beams have been adequately explained. The basic difficulty
faced by previous investigations is that in a proton-electron plasma,
hardly any cyclotron waves are found to be in resonance with the beam
protons. However, when considering a proton-alpha-electron plasma,
we find a second dispersion branch of outward propagating RHP and
LHP waves. This branch is mainly determined by the alpha particles
drifting at the Alfvén speed. The associated waves can resonate
with the beam protons, and the resulting cyclotron-resonance-induced
diffusion produces a beam velocity distribution. The time-dependent
two-dimensional diffusion equation, as determined from the quasi-linear
theory of ion cyclotron-wave resonance, is solved numerically. A
proton beam distribution is shown to form, by diffusion in the
wave field, out of an initial shuttle-like bi-Maxwellian velocity
distribution function. The drift velocity of the model beam is about
the Alfvén speed. The perpendicular thermal speed is about 44 km/s,
and the thermal anisotropy of the beam is much less than the core
anisotropy. Limitations of the present model and work to be done in
the future are also discussed.
Title: Anisotropy regulation and plateau formation through pitch angle
diffusion of solar wind protons in resonance with cyclotron waves
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 2002JGRA..107.1249T
Altcode:
In this paper the velocity distribution functions (VDFs) of protons
measured by Helios in fast solar wind are analyzed in the framework
of quasilinear theory (QLT). Evidence is presented that the shape of
the central isodensity contours in velocity space and the temperature
anisotropy of the core part of the VDFs can be explained by wave-induced
plateau formation according to QLT. The plateau is formed by protons
that are in resonance with cyclotron waves, which are assumed to
propagate both outwardly and inwardly at phase speeds following from
the plasma dispersion relation. For the proton VDFs measured near 0.3
AU in fast low-beta solar wind, the theoretical predictions of QLT,
using the cold plasma dispersion relation, agree well with the in situ
observations. For the proton VDFs measured near 1 AU in fast high-beta
wind, the predictions of QLT, using again the cold plasma dispersion
relation, only give an upper limit for the anisotropy. Yet, considering
thermal effects in the dispersion relation, a better agreement between
the theory based on resonant ion diffusion and the observations is
obtained. For nondispersive waves a simple relation between the ion
thermal speed parallel to the magnetic field and the ion-temperature
anisotropy is derived, which is shown to be consistent with the
anisotropy of the heavy O+5 ion as observed on the Solar
and Heliospheric Observatory (SOHO), as well as with the anisotropy
predicted numerically by a hybrid simulation of the ion-temperature
regulation by waves.
Title: Kinetic Results for Ions in the Solar Corona with Wave-Particle
Interactions and Coulomb Collisions
Authors: Vocks, C.; Marsch, E.
Bibcode: 2002ApJ...568.1030V
Altcode:
In a companion paper, a kinetic model for ions in the solar corona has
been described. The model is based on reduced velocity distribution
functions (VDFs) that depend only on one spatial coordinate s and one
velocity component v∥ along the background magnetic field,
and includes wave-particle interactions and Coulomb collisions. In
this paper, numerical solutions of the kinetic equations for various
ions in a coronal funnel and a coronal hole are presented. It is
found that heavy ions are heated preferentially and that sizable
temperature anisotropies form, results that are in accord with Solar and
Heliospheric Observatory observations. The reduced VDFs of the heavy
ions are found to develop pronounced deviations from a Maxwellian,
which increase with height because of the decrease of the density,
and thus of the efficiency of Coulomb collisions. Calculations of the
wave damping/growth rate γ show that the VDFs can reach the limit of
marginal stability over a wide range of resonance speeds, at which
wave absorption ceases. The consequences for the spectral evolution
of the waves in the corona are discussed. The way in which the heavy
ion mass and charge influence the kinetic model results is also studied.
Title: Solar Orbiter - A high-resolution mission to the Sun and
inner heliosphere
Authors: Marsch, E.
Bibcode: 2002cosp...34E1453M
Altcode: 2002cosp.meetE1453M
The scientific rationale of the Solar Orbiter is to provide
multi-wavelengths observations of the solar atmosphere (at high spatial,
35 km pixel size, and temporal resolution) together with comprehensive
in-situ measurements of the unexplored inner heliosphere. Novel
observations will be made in the almost heliosynchronous segments of
the orbits at heliocentric distances near 45 solar radii and out of the
ecliptic plane, with highest heliographic latitudes ranging from of 30
to 38 degrees. The Solar Orbiter will achieve its wide-ranging aims
with a suite of sophisticated instruments and through an innovative
design of the orbit. The first near - Sun interplanetary measurements
together with concurrent remote observations of the Sun will permit
us to determine and understand, through correlative studies, the
characteristics of the solar wind and energetic particles in close
linkage with the plasma and radiation conditions in the source regions
on the Sun. Over extended periods the Solar Orbiter will deliver
images of the polar regions and the side of the Sun invisible from
the Earth. The possible role of Solar Orbiter in the ILWS programme
is described
Title: Preface
Authors: Damé, Luc; Marsch, Eckart
Bibcode: 2002AdSpR..29.1997D
Altcode:
No abstract at ADS
Title: Pitch-angle diffusion of solar wind protons in resonance with
waves - beam formation and anisotropy regulation
Authors: Marsch, E.; Tu, C.; Whang, L.
Bibcode: 2002cosp...34E1682M
Altcode: 2002cosp.meetE1682M
The velocity distribution functions (VDFs) of protons measured by
Helios in fast solar wind are analysed in the framework of quasilinear
theory (QLT). New mechanisms are suggested to explain the formation
of the proton beam and temperature anisotropy appearing in the
VDFs. Observationally, the beam moves faster than the core part of
the VDF by more than the Alfven speed and has a higher temperature
than the core, but its thermal anisotropy is usually smaller. When
considering a proton-alpha-electron plasma, we find in addition to the
LHP core- proton cyclotron waves a second dispersion branch of outward
propagating RHP and LHP waves. These branches are mainly determined
by alpha particles drifting nearly at the Alfven speed. The associated
waves can resonantly interact with the beam protons. The time-dependent
two-dimensional diffusion equation of QLT is solved numerically. A
proton beam is shown to form by diffusion in the wave fields. M
oreover, evidence is presented that the shape of the central isodensity
contours of the VDFs as well as the core temperature anisotropy can
be explained by wave- induced plateau formation according to QLT. The
plateau is formed by protons being in resonance with cyclotron waves
that propagate both outwardly and inwardly at phase speeds obtained
from the warm plasma dispersion relation.
Title: Solar orbiter, a high-resolution mission to the sun and
inner heliosphere
Authors: Marsch, E.; Antonucci, E.; Bochsler, P.; Bougeret, J. -L.;
Fleck, B.; Harrison, R.; Langevin, Y.; Marsden, R.; Pace, O.; Schwenn,
R.; Vial, J. -C.
Bibcode: 2002AdSpR..29.2027M
Altcode:
The scientific rationale of the Solar Orbiter is to provide, at high
spatial (35 km pixel size) and temporal resolution, observations of the
solar atmosphere and unexplored inner heliosphere. Novel observations
will be made in the almost heliosynchronous segments of the orbits at
heliocentric distances near 45 R⊙ and out of the ecliptic plane at
the highest heliographic latitudes of 30° - 38°. The Solar Orbiter
will achieve its wide-ranging aims with a suite of sophisticated
instruments through an innovative design of the orbit. The first
near-Sun interplanetary measurements together with concurrent remote
observations of the Sun will permit us to determine and understand,
through correlative studies, the characteristics of the solar wind
and energetic particles in close linkage with the plasma and radiation
conditions in their source regions on the Sun. Over extended periods
the Solar Orbiter will deliver the first images of the polar regions
and the side of the Sun invisible from the Earth.
Title: Solar Orbiter: a high-resolution mission to the sun and
inner heliosphere
Authors: Fleck, Bernhard; Marsch, E.; Antonucci, Ester; Bochsler,
Peter A.; Bougeret, J. L.; Harrison, R.; Marsden, R. P.; Coradini,
M.; Pace, Oscar; Schwenn, Rainer; Vial, Jean-Claude
Bibcode: 2001SPIE.4498....1F
Altcode:
The key mission objective of the Solar Orbiter is to study the Sun
from close-up (45 solar radii, or 0.21 AU) in an orbit tuned to solar
rotation in order to examine the solar surface and the space above from
a co-rotating vantage point at high spatial resolution. Solar Orbiter
will also provide images of the Sun's polar regions from heliographic
latitudes as high as 38 degrees. The strawman payload encompasses
two instrument packages: Solar remote-sensing instruments: EUV
full-sun and high resolution imager, high-resolution EUV spectrometer,
high-resolution and full-sun visible light telescope and magnetograph,
EUV and visible-light coronagraphs, radiometers. Heliospheric
instruments: solar wind analyzer, radio and plasma wave analyzer,
magnetometer, energetic particle detectors, interplanetary dust
detector, neutral particle detector, solar neutron detector. To
reach its novel orbit, Solar Orbiter will make use of low-thrust
solar electric propulsion (SEP) interleaved by Earth and Venus gravity
assists. Solar Orbiter was selected by ESA's Science Programme Committee
(SPC) in October 2000 as a Flexi-mission, to be implemented after the
BepiColombo cornerstone mission to Mercury before 2013. This paper
summarizes the science to be addressed with the Solar Orbiter, followed
by brief descriptions of the strawman payload, the mission profile,
and the spacecraft and ground segment designs.
Title: Formation of Proton Beams in High-Speed Solar Wind
Authors: Tu, C.; Marsch, E.
Bibcode: 2001AGUFMSH32A0734T
Altcode:
A new mechanism is suggested to explain the formation of proton beams
in high-speed solar wind streams. Proton beams were already observed
in the early days of solar wind in-situ measurements ( Feldman et al.,
1973, Marsch et al., 1982). The proton beam is found to move faster than
the core part of the distribution by about the Alfven speed. The density
ratio between beam and core is observed to increase radially from 0.3 AU
to 1 AU. Several papers tried to explain this phenomenon. However, till
today none of these two major properties has been explained properly. We
suggest here that outward propagating RHP waves and LHP waves, for which
the second branch of the dispersion relation is determined by including
also the drifting alpha particles, may together play an important role
in the formation of proton beams. The time-dependent two-dimensional
diffusion equation, as determined from the quasi-linear theory of
ion-cyclotron-wave resonance, is solved numerically to illustrate the
evolution of the proton velocity distribution. Assuming the wave spectra
to be given, a proton beam is shown to evolve by diffusion in the wave
field from an initial bi-Maxwellian velocity distribution function. The
drift velocity of the model beam is about the Alfven speed, and its
density is found to increase with decreasing Alfven speed, in accord
with the in-situ observations. Limitations of the present model and
work that should be done in the future are also discussed. Feldman,
W.C., et al., J. Geophys. Res., 78, 2017, 1973. Marsch, E., et.al.,
J. Geophys. Res., 87, 52, 1982.
Title: Kinetics of Ions in the Solar Corona With Wave-Particle
Interaction and Coulomb Collisions
Authors: Vocks, C.; Marsch, E.
Bibcode: 2001AGUFMSH42B..04V
Altcode:
A kinetic model for the ions in the solar corona is presented. The
model describes the wave-particle interaction within the framework
of quasilinear theory and guarantees conservation of energy between
waves and ions. The Coulomb collisions are evaluated using the Landau
collision integral. Integration of the ion velocity distribution
functions (VDFs) over the velocity components perpendicular to the
background magnetic field introduces "reduced VDFs". Since the coupled
Vlasov equations for these reduced VDFs depend only on the spatial
coordinate, s, and speed component, v&|slash, parallel
to the background magnetic field, they can be solved with reasonable
numerical effort. Results for ions in a coronal funnel are presented. It
is found that the heavy ions are heated preferredly and form strong
temperature anisotropies, consistent with observations of the solar
coronal plasma. The anisotropies increase with height, as the density
and thus the efficiency of the Coulomb collisions decreases. The reduced
VDFs develop pronounced deviations from a Maxwellian. Calculating the
wave growth rate γ shows that the VDFs can reach the limit of marginal
stability over a wide range of resonance speeds. The effects of the
choice of the heavy ion species in the model plasma on the simulation
results are also studied.
Title: Foreward
Authors: Marsch, E.
Bibcode: 2001ESASP.493D...9M
Altcode: 2001sefs.workD...9M
The Solar Orbiter was selected three months ago as an ESA
F-mission for the time frame 2008-2013 (for information see
http://solarsystem.estec.esa.nl/projects/solar_orbiter.htm). It is
now up to the solar/heliospheric community to exploit this excellent
opportunity to the full. To that effect, the first Solar Orbiter
workshop is now being organised. The prime objectives of the Solar
Orbiter workshop are to inform the community about the science
opportunities of the Solar Orbiter mission, provide a forum for
sharpening and focusing the science goals, allow the hardware groups and
future instrument proposers to review critically the strawman payload,
establish international contacts and collaborations.
Title: Solar Orbiter, a high-resolution mission to the Sun and
inner heliosphere
Authors: Marsch, E.; Harrison, R.; Pace, O.; Antonucci, E.; Bochsler,
P.; Bougeret, J. -L.; Fleck, B.; Langevin, Y.; Marsden, R.; Schwenn,
R.; Vial, J. -C.
Bibcode: 2001ESASP.493D..11M
Altcode: 2001sefs.workD..11M
Solar Orbiter will provide, at very high spatial (35 km pixel size)
and temporal resolution, novel observations of the solar atmosphere
and unexplored inner heliosphere. It will achieve its wide-ranging
scientific aims with a suite of sophisticated instruments through an
innovative orbit design. Unprecedented observations will be made in
the heliosynchronous segments of the orbits at heliocentric distances
near 45 Rsolar and out of the ecliptic plane at the highest
heliographic latitudes of 30° - 38°. The first near-Sun interplanetary
measurements together with concurrent remote-sensing observations of
the Sun and its corona will permit us to determine and understand,
through correlative studies, the characteristics of the solar wind
and energetic particles in close linkage with the plasma and radiation
conditions in the source regions on the Sun. Solar Orbiter will deliver
the first images of the polar regions and the far side of the Sun
invisible from the Earth.
Title: On the role of ion-cyclotron kinetic Alfvén waves in the
solar wind: results from HELIOS and expectations for Solar Orbiter
Authors: Voitenko, Yu.; Goossens, M.; Marsch, E.
Bibcode: 2001ESASP.493..411V
Altcode: 2001sefs.work..411V
No abstract at ADS
Title: Solar encounter
Authors: Battrick, Bruce; Sawaya-Lacoste, H.; Marsch, E.; Martinez
Pillet, V.; Fleck, B.; Marsden, R.
Bibcode: 2001ESASP.493.....B
Altcode: 2001sefs.work.....B
The prime objectives of the workshop were to: inform the community
about the science opportunities of the Solar Orbiter mission; to
provide a forum for sharpening and focussing the science goals; allow
the hardware groups and instrument proposers to critically review the
payload; establish international contacts and collaborations.
Title: Evidence for the Resonance Between Solar Wind Protons and
Parallel Propagating Cyclotron Waves
Authors: Tu, C.; Marsch, E.
Bibcode: 2001AGUSM..SH22E03T
Altcode:
Direct evidence from Helios observation is, for the first time,
provided for the occurrence of pitch-angle diffusion of solar wind
protons, induced by resonance with ion-cyclotron waves propagating
away from the Sun. The iso-density contours of the sunward halo
part of the proton velocity distribution function (VDF) are shown
to be well outlined by a sequence of segments of circles centered at
the wave phase speed, which is only slightly smaller than the local
Alfven speed. These circular segments correspond to the plateaus as
predicted by quasi-linear theory. A plateau is defined by a vanishing
pitch-angle gradient of the VDF in the resonant regime, whereby the
proton conserves during pitch-angle diffusion its total kinetic energy
in the frame moving with the wave phase speed. The influence of the wave
dispersion relation is studied by comparing the measured iso-density
contours and the theoretical plateaus, as defined by the dispersion
relation of either a cold or a warm plasma. When defined by the phase
speed based on the cold-plasma dispersion, the plateau is shown to
match the observed contours better than when defined by either the
Alfven speed or the dispersive phase speed of the warm-plasma. The
contours of the anti-sunward halo part of the proton VDF are also
found to match the diffusion plateau as formed by the resonance with
inward-propagating cyclotron waves. The implication of these results
for the heating and kinetic transport of solar wind ions are discussed.
Title: Evidence for pitch angle diffusion of solar wind protons in
resonance with cyclotron waves
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 2001JGR...106.8357M
Altcode:
Quasi-linear theory predicts that ions in resonance with transverse
ion cyclotron waves suffer merely pitch angle diffusion while
conserving their total kinetic energy in the frame moving with the
wave phase speed. For the first time, direct observational evidence
from Helios plasma data is shown for the occurrence of this pitch
angle diffusion of solar wind protons, induced by resonance with
parallel ion cyclotron waves propagating away from the Sun. Parts
of the isodensity contours in velocity space are well outlined by a
sequence of segments of circles centered at the adapted wave phase
speed, which is assumed to vary slightly and to be due to dispersion
smaller than the local Alfvén speed. This observation confirms the
validity of basic concepts of resonant wave-particle interactions
as described by quasi-linear theory. The solar wind proton velocity
distributions show a ``plateau'' defined by a vanishing pitch angle
gradient in the resonant regime, implying marginal stability of the
distribution function. The implications of these results for solar
wind ion heating and kinetic transport are discussed.
Title: A semi-kinetic model of wave-ion interaction in the solar
corona
Authors: Vocks, C.; Marsch, E.
Bibcode: 2001GeoRL..28.1917V
Altcode:
A semi-kinetic model of the ions in the solar corona is presented,
which includes the effects of wave-particle interactions and Coulomb
collisions. At the coronal base a spectrum of Alfvén waves is
assumed. The spatiotemporal evolution of the spectrum in a 2-D
computational domain is determined, taking the absorption of the
waves by the particles into account. Integration over the velocity
components perpendicular to the magnetic field yields “reduced”
velocity distribution functions, for which a Vlasov equation is derived
and solved numerically. The results obtained for a model of the heating
process in a coronal funnel and in the lower corona are presented. The
calculated velocity distribution functions show distinct kinetic
effects and reflect key properties of the corona as observed by SOHO.
Title: On cyclotron wave heating and acceleration of solar wind ions
in the outer corona
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 2001JGR...106.8233T
Altcode:
The preferential heating and acceleration of O+5 ions, as
observed by Ultraviolet Coronagraph Spectrometer (UVCS) on Solar and
Heliospheric Observatory (SOHO) [Kohl et al., 1998] in the solar coronal
holes have been interpreted and modeled by invoking wave-particle
cyclotron resonance [Cranmer et al., 1999a, 1999b]. However, in
the model of Cranmer et al. [1999a, 1999b] and in other subsequent
models the assumption of a rigid slope of the wave spectrum was
made in calculating the wave energy absortion by the different ion
species. In the present paper it is shown that a self-consistent
treatment of the wave damping and absorption is necessary and leads to
substantially different results. On the basis of quasi-linear theory,
the interaction between the ions and the ion-cyclotron waves [Marsch
et al., 1982a; Marsch, 1998] is studied. The total energy conservation
equation, including the kinetic energy of the resonant particles and
the wave energy, is derived and discussed in detail. The spectral
evolution equation for cyclotron waves, when being controlled by the
wave growth/damping rate and WKB effects, is solved self-consistently
together with the full set of anisotropic multifluid equations for the
ions including the cyclotron-resonance wave heating and acceleration
rates. From the numerical results we reach the following conclusions:
(1) It is physically questionable to use a spectrum with a fixed
spectral slope near the cyclotron resonance when one calculates the
partition of wave energy among the different ionic species and the
kinetic degrees of freedom parallel and perpendicular to the magnetic
field. This assumption neglects the important effects of wave absorption
and the concurrent reshaping of the wave spectrum, and thus leads
in the dissipation domain to extremely low amplitudes of the waves
and to difficulties in supplying enough energy to balance the wave
absorption at the cyclotron resonances. (2) If the spectrum is allowed
to evolve self-consistently and concurrently with the particles' heating
and acceleration through wave absorption, such a high perpendicular
temperature and corresponding large temperature anisotropy as observed
by UVCS do not occur or cannot be maintained. We conclude that the UVCS
oxygen ion observations have not yet been explained satisfactorily by
the cyclotron-resonance theory.
Title: Wave dissipation by ion cyclotron resonance in the solar corona
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 2001A&A...368.1071T
Altcode:
It has recently been suggested that small-scale reconnection occurring
in the chromospheric network creates high-frequency Alfvén waves,
and that these waves may represent the main energy source for the
heating of the solar corona and generation of the solar wind. However,
if these waves exist, they will be absorbed preferentially by the minor
heavy ions with low gyrofrequencies, and thus it is unclear whether
there is actually enough wave energy left over for the heating and
acceleration of the major solar wind ions, namely protons and alpha
particles, in the extended corona after the absorption by heavy ions
(Cranmer \cite{Cranmer00}). We have studied this problem with the
multi-fluid model presented by Tu & Marsch (2001), which includes
the self-consistent treatment of the damping of the waves as well
as the associated acceleration and heating of the ions. We found
that if the wave power density is sufficiently large, say about 1000
nT2 Hz-1 at 160 Hz and 2.5 Rsun, then
the wave absorption by a prominent minor ion such as O+5
is small, and most of the wave energy is left for absorption by
protons. This occurs because the minor ions are quickly (within several
gyroperiods) accelerated and then are induced to partially surfing
the waves. However, if the wave power is too low, say lower than 10
nT2 Hz-1 at 160 Hz and 2.5 Rsun, then
the damping of the wave power by the O+5 ions is severe,
and little wave energy is left for protons.
Title: Heating and acceleration of ions by cyclotron- and
Landau-resonances (Oral papers and posters which were given at the
conference, but for which no manuscripts were submitted)
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 2001ohnf.conf..394M
Altcode:
No abstract at ADS
Title: Solar Orbiter - A high resolution mission to the Sun and the
inner heliosphere (Oral papers and posters which were given at the
conference, but for which no manuscripts were submitted)
Authors: Marsch, E.; Fleck, B.; Schwenn, R.
Bibcode: 2001ohnf.conf..445M
Altcode:
No abstract at ADS
Title: Solar Orbiter, a High-Resolution Mission to the Sun and
Inner Heliosphere
Authors: Marsch, E.; Antonucci, E.; Bochsler, P.; Bougeret, J. -L.;
Fleck, B.; Harrison, R.; Marsden, R.; Schwenn, R.; Vial, J. -C.
Bibcode: 2001IAUS..203..565M
Altcode:
The scientific rationale of the Solar Orbiter (SO) is to provide,
at high spatial and temporal resolution, observations of the solar
atmosphere and unexplored inner heliosphere. The most interesting and
novel observations will be made in the almost heliosynchronous segments
of the orbits at heliocentric distances near 45 Rodot and
out-of-ecliptic at the highest heliographic latitudes of 38 degrees. The
SO will achieve its many and varied aims with a suite of small and
innovative instruments through a clever choice of orbits. The first
near-Sun interplanetary measurements together with concurrent remote
observations of the Sun will permit us to determine and understand,
through correlative studies, the characteristics of the solar wind and
energetic particles in close linkage with the plasma and radiation
conditions in their source regions on the Sun. The SO will, during
the high-latitude orbital passes, provide the first observations of
the Sun's polar regions as seen from outside the ecliptic and also
measure the magnetic field at the poles.
Title: Velocity Fields in an Active Region Loop System Observed on
the Solar Disc with SUMER/SOHO (CD-ROM Directory: contribs/lanzafam)
Authors: Lanzafame, A. C.; Spadaro, D.; Consoli, L.; Marsch, E.;
Brooks, D. H.
Bibcode: 2001ASPC..223..691L
Altcode: 2001csss...11..691L
No abstract at ADS
Title: The Outer Heliosphere: The Next Frontiers
Authors: Scherer, K.; Fichtner, Horst; Fahr, Hans Jörg; Marsch, Eckart
Bibcode: 2001ohnf.conf.....S
Altcode:
The 11th COSPAR Colloquium "The Outer Heliosphere: The Next Frontiers"
was held in Potsdam, Germany, from July 24 to 28, 2000, and is the
second dedicated to this subject after the first one held in Warsaw,
Poland in 1989. Roughly a century has passed after the first ideas by
Oliver Lodge, George Francis Fitzgerald and Kristan Birkeland about
particle clouds emanating from the Sun and interacting with the Earth
environment. Only a few decades after the formulation of the concepts
of a continuous solar corpuscular radiation by Ludwig Bierman and a
solar wind by Eugene Parker, heliospheric physics has evolved into an
important branch of astrophysical research. Numerous spacecraft missions
have increased the knowledge about the heliosphere tremendously. Now, at
the beginning of a new millenium it seems possible, by newly developed
propulasion technologies to send a spacecraft beyond the boundaries
of the heliosphere. Such an Interstellar Proce will start the in-situ
exploration of interstellar space and, thus, can be considered as the
first true astrophysical spacecraft. The year 2000 appeared to be a
highly welcome occassion to review the achievements since the last
COSPAR Colloquia 11 years ago, to summarize the present developments
and to give new impulse for future activities in heliospheric research.
Title: Long-term variations of the flow direction and angular momentum
of the solar wind observed by Helios
Authors: Scherer, K.; Marsch, E.; Schwenn, R.; Rosenbauer, H.
Bibcode: 2001A&A...366..331S
Altcode:
The flow directions of solar wind protons were measured in situ by
the Helios spacecraft. A long-term average of the velocity shows a
systematic drift in the latitudinal flow angle of about +1o
north observed with Helios 1 and -1o south observed onboard
of Helios 2. The longitudinal flow angle migrates about +1o
west over a period of almost 10 years for Helios 1 and 6 years for
Helios 2. This systematic change with time of the plasma flow direction
may be caused by solar-cycle variations of the orientation of the Sun's
magnetic field which partially corotates with the Sun inside the Alfvén
surface (varying in distance between 10 Rsun over the poles
and 30 Rsun near the equator). These variations must have
been imprinted on the solar wind flow when it detached from corotation
with the Sun near the Alfvén point. The angular momentum of the wind
is intimately connected with the flow and field directions. The gain of
total angular momentum of the wind equals the loss of angular momentum
of the Sun, which is caused by the torque exerted on the rotating
Sun through the magnetic field of the expanding corona. Implications
of the Helios observations for models of the magnetic fields of the
Sun as well as the solar wind are discussed. We show evidence, that
changes of the solar magnetic field inside the Alfvén surface are
responsible for systematic drifts in the solar wind flow direction.
Title: Heating and acceleration of coronal ions interacting with
plasma waves through cyclotron and Landau resonance
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 2001JGR...106..227M
Altcode:
On the basis of quasi-linear theory, the parallel and perpendicular
wave heating and acceleration rates for gyrotropic particle velocity
distribution functions are derived. These rates can be used in
anisotropic multicomponent fluid equations, in order to describe the
wave-particle interactions of ions with, for examples, kinetic Alfvén
and electromagnetic or electrostatic ion cyclotron, respectively,
magnetosonic waves propagating along or obliquely to the mean magnetic
field. The waves of coronal origin propagating away from the Sun into
the interplanetary medium can resonantly heat the solar wind ions and
accelerate minor ions preferentially with respect to the protons. Such
processes are required in order to explain and understand the measured
characteristics of ion velocity distributions in the solar wind and to
interpret the recent spectroscopic evidence obtained from EUV emission
line measurements made by the Solar and Heliospheric Observatory (SOHO)
spacecraft, which indicate cyclotron-resonance-related line broadenings
and shifts.
Title: Observations and Models of the Fast and Slow Solar Wind
Authors: Marsch, E.
Bibcode: 2001IAUS..203..447M
Altcode:
There are two major types of solar wind. The steady fast wind
originates on open magnetic field lines in coronal holes, which may
last for many solar rotations. In contrast, the unsteady slow wind is
coming from the bulk or boundary layer of streamers, which are mostly
magnetically closed and open up only temporarily. Many observations
of the solar wind have in the past been made, e.g., in situ by Helios
and Ulysses and remotely by SOHO. Correspondingly, many models for
the fast and slow wind have been developed to different levels of
sophistication. The majority of the models is concerned with the fast
wind. Essential properties of fast streams can be reproduced by 1-D
multi-fluid models involving broad-band waves. Yet, the integration of
the fluid equations must start low in the corona in the magnetic funnels
at transition region level. Also, 3-D MHD models have recently been
developed. Owing to its time-variable nature, no robust understanding
of the slow wind exist. Apparently, its acceleration starts only beyond
two solar radii. Key empirical constraints, which are imposed on the
models by the Helios (near-Sun, in-ecliptic) and Ulysses (high-latitude)
interplanetary measurements and by the SOHO plasma-spectroscopy results,
are discussed with respect to the fluid as well as kinetic properties
of the wind. Selected results from modelling and observations are
presented and discussed.
Title: Solar Wind: Kinetic Properties
Authors: Marsch, E.
Bibcode: 2000eaa..bookE2304M
Altcode:
The SOLAR WIND consists of electrons, protons, alpha particles and heavy
ions. Its kinetic physics deals with the collective behavior of these
particles in a statistical ensemble. Space-borne particle spectrometers
enable us to measure the composition and three-dimensional velocity
distribution functions (VDFs) of the particles. Vlasov kinetic plasma
theory provides the adequate means for their t...
Title: On the origin of the fast solar wind in polar coronal funnels
Authors: Hackenberg, P.; Marsch, E.; Mann, G.
Bibcode: 2000A&A...360.1139H
Altcode:
Funnels are open magnetic structures connecting the chromosphere with
the solar corona ( \cite{Axf97,Mar97,Hac99}). We investigate the
stationary plasma flow out of funnels with a flux-tube model. The
funnel area function is derived from an analytical 2-D magnetic
field model. Since the funnel height is only approximately 15 Mm,
the area function for greater heights is taken from the Banaszkiewicz
et al. (\cite*{Ban98}) coronal magnetic field model. Thus we obtain
a realistic area function being valid into the upper corona. The
plasma in the funnel is treated with two-fluid equations including
radiative losses, thermal conduction, electron-proton heat exchange,
proton heating by cyclotron-damped Alfvén waves and Alfvén wave
pressure. We adjust the free parameters to the quantities measured in
the lower solar corona (≈ 100 000 km above the photosphere) by SUMER
aboard SOHO ( te{Wil98b}). The thereby obtained height profiles of
the plasma properties (e.g. density, electron and proton temperatures,
flow speed) within the funnel are presented and compared with recent
SUMER measurements.
Title: Hydrogen temperature gradient in the transition region of a
solar coronal hole
Authors: Marsch, E.; Tu, C. -Y.; Wilhelm, K.
Bibcode: 2000A&A...359..381M
Altcode:
The Lyman series of hydrogen was observed by SUMER on SOHO on the
north polar limb of the Sun with a total exposure time of more than
ten hours. The resulting line profiles have been analysed using
the technique described by Marsch et al. (1999). The data analysis
corroborates earlier findings on the Lyman lines, but also yields
phenomena which cannot be fully understood at the present time. Firstly,
the line width of the Lyman lines increases with decreasing series or
quantum number. Secondly, the hydrogen temperature gradient in the
height range from 12 000 km to 18 000 km is unexpectedly small and
does not reveal a steep jump as might be expected from modelling of
the transition region. The average temperature increases only slightly
from 1;105 K to 2;105 K. Possible explanations
of these observations are given and models are briefly discussed.
Title: Structure and dynamics of an active region loop system observed
on the solar disc with SUMER on SOHO
Authors: Spadaro, D.; Lanzafame, A. C.; Consoli, L.; Marsch, E.;
Brooks, D. H.; Lang, J.
Bibcode: 2000A&A...359..716S
Altcode:
In this paper we present and discuss spectra obtained by SUMER on SOHO
from an active region loop system observed on the solar disc, close to
the central meridian, on July 26th, 1996. The region was observed with a
spatial resolution of about 2arcsec by 2arcsec in emission lines forming
in the transition region and inner corona, with the aim of investigating
the physical structure and dynamical behaviour of the plasma in active
region magnetic loops. To this purpose we have reduced and analysed the
spectral observations in order to determine the values of intensity,
Doppler shift and line profile width for the selected emission lines
in all the spatially resolved elements of the examined area of the
solar disc. By comparing intensity, velocity maps and photospheric
magnetic fields obtained by MDI on SOHO, several magnetic loops have
been identified, some of which contemporarily appear over a range of
temperatures, while others are compact and only visible in a limited
temperature range. A few loops exhibit velocity fields typical of siphon
flows, the siphon-like velocities being higher in compact loops. Two
compact loops seen in the transition region lines show asymmetric
siphon-like velocity fields and high non-thermal velocities at the
upflowing footpoint. High non-thermal velocities are also associated
with the falling footpoint of a larger loop. Besides such loops, other
bright features are observed in the transition region lines, whose
morphology cannot be identified as arch-like. They have no coronal
counterpart, are red-shifted with respect to the median line centroid
position and exhibit high non-thermal velocities.
Title: Preface (The outer heliosphere: beyond the planets)
Authors: Scherer, Klaus; Fichtner, Horst; Marsch, Eckart
Bibcode: 2000ohbp.confD...5S
Altcode:
No abstract at ADS
Title: Solar Orbiter --- A High Resolution Mission to the Sun and
Inner Heliosphere
Authors: Fleck, B.; Marsch, E.; Schwenn, R.; Antonucci, E.; Bochsler,
P.; Bougeret, J. -L.; Harrison, R. A.; Marsden, R.; Vial, J. -C.
Bibcode: 2000SPD....31.0296F
Altcode: 2000BAAS...32..828F
The scientific rationale of the Solar Orbiter (SO) is to provide,
at high spatial and temporal resolution, observations of the solar
atmosphere and unexplored inner heliosphere. The most interesting and
novel observations will be made in the almost heliosynchronous segments
of the orbits at heliocentric distances near 45 Rsun and
out-of-ecliptic at heliographic latitudes of up to 38o. By
going to 45 Rsun the SO will allow remote sensing of the
solar atmosphere with unprecedented spatial resolution, and the almost
heliosynchronous orbit segments will permit us to disentangle spatial
and temporal variations in the solar wind in close linkage with the
plasma and radiation conditions in the source regions of the Sun. The
strawman payload encompasses two instrument packages: Heliospheric
Instruments --- high-res visible light telescope and magnetograph
(<40 km), high-res X-ray/EUV imager (<30 km), high-res EUV
spectrometer (<100 km), EUV and visible-light coronagraphs, solar
neutron and γ -ray detectors, radiometers. Heliospheric Instruments
--- solar wind analyzer, magnetometer, energetic particle detectors, IP
dust detector, plasma wave analyser, radio experiment, neutral particle
detector. Using solar electric propulsion (SEP) in conjunction with
multiple planet swing-by manoeuvres, it will take SO two years to reach
a perihelion of 45 Rsun at an orbital period of 149 days,
with an inclination ranging from 6.7o to 23.4o
w.r.t. the ecliptic. During an extended mission phase of about 2
years the inclination will increase to 31.7o, leading to
a maximum heliographic latitude of 38.3o. The SO was one
of the about 40 responses to the Call for Proposals for the next two
"flexi-missions" (F2 and F3) within ESA's Scientific Programme. At
its meeting on 1 March 2000, ESA's Space Science Advisory Committee
recommended the Solar Orbiter among 5 other proposals for an assessment
study. Launch is expected by the end of the decade.
Title: Dynamical processes in interplanetary space
Authors: Marsch, Eckart
Bibcode: 2000ohbp.conf...41M
Altcode:
A concise introduction is given into dynamical processes occurring in
interplanetary space. The coronal magnetic field and the heliospheric
current sheet are described. Following the Parker model, the concept of
the solar wind is outlined and observations of the three-dimensional
solar wind are presented. The heliospheric magnetic (spiral) field
is explained. Then structures and flux ropes in the wind, and waves
and turbulence are discussed, in particular Alfvénic fluctuations,
magnetosonic waves and shocks. Shocks and corotating interaction regions
are illustrated. Then we concentrate on large-scale stream dynamics,
leading to collisions and merging of different flows, which may form
compound streams and corotating shells of high pressure. The basic
elements of solar-wind and MHD theory are developed. Ample references
are provided to the reader for further in-depth study of the subjects
discussed.
Title: The outer heliosphere: beyond the planets
Authors: Scherer, Klaus; Fichtner, Horst; Marsch, Eckart
Bibcode: 2000ohbp.conf.....S
Altcode:
No abstract at ADS
Title: On the source regions of the fast solar wind in polar
coronal holes
Authors: Wilhelm, K.; Dammasch, I. E.; Marsch, E.; Hassler, D. M.
Bibcode: 2000A&A...353..749W
Altcode:
Fast streams of the solar wind with speeds of up to ~ 800 km
s-1 at a distance of 1 AU (astronomical unit) from the Sun
are known to originate in solar coronal holes. With the Solar and
Heliospheric Observatory (SOHO) detailed studies of the solar wind
source regions have been made possible for the first time. We show
images of solar polar coronal holes in the extreme ultraviolet (EUV),
which were obtained by the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) spectrograph on the SOHO spacecraft. The light is
emitted in spectral lines of helium atoms and Ne7+ ions
formed at temperatures of about 20 000 K and 630 000 K, respectively,
in ionization equilibrium. The sources of the fast solar wind in polar
coronal holes can clearly be seen in the chromospheric He i line and
in the Ne viii line of the low corona, either as dark polar caps
in radiance diagrams or as regions of predominant blue shift. The
average blue shifts along the line of sight in coronal holes amount
to speeds of ~ 3 km s-1 for both He and Ne7+,
if the Doppler shift can be interpreted as an indication of bulk
motions. Bright points and polar plumes seen in Ne viii (lambda 770)
do, however, not show signatures of outflow.
Title: On the origin of the fast solar wind in coronal funnels
Authors: Hackenberg, P.; Mann, G.; Marsch, E.
Bibcode: 1999ESASP.446..341H
Altcode: 1999soho....8..341H
"Funnels" are open structures connecting the lower transition region
with the solar corona. We investigate the stationary plasma flow out
of funnels with a flux tube model. The area-function is derived from
an analytical 2-D magnetic field funnel model. Since the funnel height
is only approximately 15 Mm, the area-function for greater heights is
taken from the Banaszkiewicz et al. (1998) magnetic field model. Thus
we obtain a realistic area-function up to the upper corona. The
plasma within the funnel is treated with two-fluid equations including
thermal conduction, electron-proton heat exchange, proton heating by
cyclotron-damped Alfvén waves and Alfvén wave-pressure. We adjust
the free parameters with quantities measured at the lower solar corona
~100 Mm above the photosphere) by SUMER aboard SOHO (Wilhelm et al.,
1998). The thereby found height profiles of the plasma properties
(e.g. density, electron and proton temperatures, flow speed) within the
funnel are presented and partly compared with recent SUMER measurements.
Title: Dynamical Properties Of An Active Region Loop System Observed
On The Solar Disc With SUMER/SOHO
Authors: Lanzafame, A. C.; Spadaro, D.; Consoli, L.; Marsch, E.;
Brooks, D. H.
Bibcode: 1999ESASP.446..429L
Altcode: 1999soho....8..429L
In this paper we present and discuss spectra obtained by SUMER from
an active region loop system observed on the solar disc, close to
the central meridian. This region has been observed with a spatial
resolution of about 2'' by 2'' in emission lines formed in the
transition region and inner corona. Our aim is to investigate the
physical structure and dynamical behaviour of the plasma in the
transition region portion of the magnetic loops. To this purpose,
we have reduced and analysed the spectral observations in order to
determine the values of intensity, Doppler shift and line profile
width for the selected emission lines in all the spatially resolved
elements of the examined area of the solar disc. These data have
been used to locate the coronal structures within the observed active
region and to identify their morphology. They have also been used to
include a study of the spatial relationship between loops as seen in
spectral lines formed at different temperatures. As far as the data
relating to the line profiles are concerned, they have been analysed
with the purpose of examining indications of the presence of resolved
mass motions inside the active region and also for investigating the
non-thermal broadening of the lines, which is usually attributed to
microturbulence and probably related to the heating mechanisms working
in these layers of the solar atmosphere. We have also explored the
possibility of correlations amongst the line intensities, Doppler
shifts and microturbulence velocities, which might help us to gain
insight into the physical processes occurring in active regions,
particularly in the transition region portion of magnetic loops.
Title: Proton and hydrogen temperatures at the base of the solar
polar corona
Authors: Marsch, E.; Tu, C. -Y.; Heinzel, P.; Wilhelm, K.; Curdt, W.
Bibcode: 1999A&A...347..676M
Altcode:
The SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
Spectrometer on SOHO (Solar and Heliospheric Observatory) has been
used to observe the lines of the Lyman series (up to quantum numbers
larger than 20) of hydrogen emitted in the solar atmosphere. The
line shapes and intensities versus height are obtained near the limb
from about -10\arcsec to 70\arcsec. The lines are broad and show the
typical self-absorption reversal near the limb, where the emission
comes from optically thick material, and change systematically with
increasing height. The H i Ly6, Ly7 and Ly9 lines attain a Gaussian
shape at heights above the visible limb between about 19\arcsec and
22\arcsec, where the emission comes from an optically thin plasma. The
line shapes and intensities can be fitted well by model profiles
obtained from multilevel NLTE (Non Local-Thermodynamic-Equilibrium)
radiative transfer calculations which allow us, assuming excitation
and ionization equilibrium, to derive consistently the temperatures and
densities of the hydrogen atoms and, with additional assumptions, of the
protons. Temperature values range between 1 10(5) K to 2 10(5) K. We
present the systematics of the line shapes as observed in different
emission regions and discuss briefly the relevance of these results
for the solar wind acceleration and coronal heating.
Title: Solar Origin and Interplanetary Evolution of Stream Interfaces
Authors: Forsyth, R. J.; Marsch, E.
Bibcode: 1999SSRv...89....7F
Altcode:
In a Corotating Interaction Region (CIR) the stream interface is
identified as a relatively sharp density drop, temperature rise,
and flow shear in the solar wind, and is now generally believed to
mark the boundary between solar wind which was originally slow when
it left the Sun and solar wind which was originally fast. This paper
summarises some important facts and open questions about the origin and
nature of the boundary between fast and slow solar wind near the Sun,
the evolution of stream interfaces with heliocentric distance in the
inner heliosphere, and their relationship.
Title: CIR Morphology, Turbulence, Discontinuities, and Energetic
Particles
Authors: Crooker, N. U.; Gosling, J. T.; Bothmer, V.; Forsyth, R. J.;
Gazis, P. R.; Hewish, A.; Horbury, T. S.; Intriligator, D. S.; Jokipii,
J. R.; Kóta, J.; Lazarus, A. J.; Lee, M. A.; Lucek, E.; Marsch, E.;
Posner, A.; Richardson, I. G.; Roelof, E. C.; Schmidt, J. M.; Siscoe,
G. L.; Tsurutani, B. T.; Wimmer-Schweingruber, R. F.
Bibcode: 1999SSRv...89..179C
Altcode:
Corotating interaction regions (CIRs) in the middle heliosphere have
distinct morphological features and associated patterns of turbulence
and energetic particles. This report summarizes current understanding
of those features and patterns, discusses how they can vary from
case to case and with distance from the Sun and possible causes of
those variations, presents an analytical model of the morphological
features found in earlier qualitative models and numerical simulations,
and identifies aspects of the features and patterns that have yet to
be resolved.
Title: The Solar Origin of Corotating Interaction Regions and Their
Formation in the Inner Heliosphere
Authors: Balogh, A.; Bothmer, V.; Crooker, N. U.; Forsyth, R. J.;
Gloeckler, G.; Hewish, A.; Hilchenbach, M.; Kallenbach, R.; Klecker,
B.; Linker, J. A.; Lucek, E.; Mann, G.; Marsch, E.; Posner, A.;
Richardson, I. G.; Schmidt, J. M.; Scholer, M.; Wang, Y. -M.;
Wimmer-Schweingruber, R. F.; Aellig, M. R.; Bochsler, P.; Hefti, S.;
Mikić, Z.
Bibcode: 1999SSRv...89..141B
Altcode:
Corotating Interaction Regions (CIRs) form as a consequence of the
compression of the solar wind at the interface between fast speed
streams and slow streams. Dynamic interaction of solar wind streams
is a general feature of the heliospheric medium; when the sources of
the solar wind streams are relatively stable, the interaction regions
form a pattern which corotates with the Sun. The regions of origin
of the high speed solar wind streams have been clearly identified
as the coronal holes with their open magnetic field structures. The
origin of the slow speed solar wind is less clear; slow streams may
well originate from a range of coronal configurations adjacent to,
or above magnetically closed structures. This article addresses
the coronal origin of the stable pattern of solar wind streams
which leads to the formation of CIRs. In particular, coronal models
based on photospheric measurements are reviewed; we also examine
the observations of kinematic and compositional solar wind features
at 1 AU, their appearance in the stream interfaces (SIs) of CIRs,
and their relationship to the structure of the solar surface and the
inner corona; finally we summarise the Helios observations in the
inner heliosphere of CIRs and their precursors to give a link between
the optical observations on their solar origin and the in-situ plasma
observations at 1 AU after their formation. The most important question
that remains to be answered concerning the solar origin of CIRs is
related to the origin and morphology of the slow solar wind.
Title: Study of the heating mechanism of solar wind ions in coronal
holes
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1999AIPC..471..373T
Altcode: 1999sowi.conf..373T
Observational results obtained by UVCS and SUMER on SOHO provide an
excellent opportunity to study the heating and acceleration mechanism
of solar wind ions in the solar corona. The heating rate per unit mass
for neutral hydrogen is derived from the observed height profiles of the
microscopic velocity (derived from EUV line widths) and is found to be
about 14 (km/s)2/s at 2-3 Rsolar. For Oxygen O+5
the rate is about 120 (km/s)2/s. Since the observed microscopic velocity
includes thermal motions and wave-related fluid motions, these values
may be considered as upper-limit estimates. The heating rate of neutral
hydrogen may also be representative for the heating rate of solar
wind protons. Although it is now widely believed that the observed
heating of O+5 provides evidence for cyclotron-resonance
wave heating, no consistent common explanation for the heating rates of
both Oxygen and Hydrogen has been proposed. We suggest here a two-step
model describing systematically both the heating of the protons and
Oxygen ions based on the quasi-linear theory. First, the heavy ions
absorb almost all the energy of the waves and are preferentially
accelerated. Then, because of the Doppler shift and dependence of
the resonant frequency of the heavy ions upon their drift speed,
these heavy ions become resonant with cyclotron waves at higher wave
numbers, at which a considerable number of the protons are also resonant
with the waves. This resonance is possible because the protons have a
finite plasma beta. The shape of the spectrum at the high wave numbers
determines finally how much energy is absorbed by each of the species.
Title: Closure of multi-fluid equations for cyclotron-resonant
interactions of ions with Alfvén waves in the solar corona
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 1999AIPC..471..393M
Altcode: 1999sowi.conf..393M
Based on quasilinear theory, a set of anisotropic, multi-component
fluid equations is derived. These equations describe the wave-particle
interactions of ions with electromagnetic Alfvén and ion-cyclotron
waves propagating along the mean magnetic field. The ion acceleration
and heating rates are calculated. They may be used in the multifluid
momentum and energy equations as anomalous transport terms. The
associated evolution equation for the average wave spectrum is also
established, and the effective growth/damping rate for the wave energy
spectrum is calculated. The wave-particle-interaction terms attain forms
resembling the ones for collisional friction and temperature-anisotropy
relaxation (due to pitch angle scattering), but with collision
rates that are proportional to the gyrofrequency times the relative
wave-fluctuation level with respect to the background field. A
simple closure scheme is suggested, which connects the dissipation of
turbulence and waves with the individual heating rates of the minor
ions in the corona. The heavy-ion emission-line widths observed by SOHO
and the derived ion temperatures provide new empirical evidence that
the heating may be related with cyclotron-resonance wave dissipation.
Title: CIR Morphology, Turbulence, Discontinuities, and Energetic
Particles
Authors: Crooker, N. U.; Gosling, J. T.; Bothmer, V.; Forsyth, R. J.;
Gazis, P. R.; Hewish, A.; Horbury, T. S.; Intriligator, D. S.; Jokipii,
J. R.; Kóta, J.; Lazarus, A. J.; Lee, M. A.; Lucek, E.; Marsch, E.;
Posner, A.; Richardson, I. G.; Roelof, E. C.; Schmidt, J. M.; Siscoe,
G. L.; Tsurutani, B. T.; Wimmer-Schweingruber, R. F.
Bibcode: 1999cir..book..179C
Altcode:
No abstract at ADS
Title: Solar Origin and Interplanetary Evolution of Stream Interfaces
Authors: Forsyth, R. J.; Marsch, E.
Bibcode: 1999cir..book....7F
Altcode:
No abstract at ADS
Title: Working Group 1 Report: Solar Wind Models from the Sun to 1
AU: Constraints by "in situ" and Remote Sensing Measurements
Authors: Leer, E.; Marsch, E.
Bibcode: 1999SSRv...87...67L
Altcode:
The goal of Working Group 1 was to discuss constraints on solar wind
models. The topics for discussion, outlined by Eckart Marsch in his
introduction, were: (1) what heats the corona, (2) what is the role of
waves, (3) what determines the solar wind mass flux, (4) can stationary,
multi-fluid models describe the fast and slow solar wind, or (5) do we
need time dependent fluid models, kinetic models, and/or MHD models to
describe solar wind acceleration. The discussion in the working group
focused on observations of "temperatures" in the corona, mainly in
coronal holes, and whether the observations of line broadening should
be interpreted as thermal broadening or wave broadening. Observations
of the coronal electron density and the flow speed in coronal holes
were also discussed. There was only one contribution on observations of
the distant solar wind, but we can place firm constraints on the solar
wind particle fluxes and asymptotic flow speeds from observations with
Ulysses and other spacecraft. Theoretical work on multi-fluid models,
higher-order moment fluid models, and MHD models of the solar wind
were also presented.
Title: The Solar Origin of Corotating Interaction Regions and their
Formation in the Inner Heliosphere
Authors: Balogh, A.; Bothmer, V.; Crooker, N. U.; Forsyth, R. J.;
Gloeckler, G.; Hewish, A.; Hilchenbach, M.; Kallenbach, R.; Klecker,
B.; Linker, J. A.; Lucek, E.; Mann, G.; Marsch, E.; Posner, A.;
Richardson, I. G.; Schmidt, J. M.; Scholer, M.; Wang, Y. -M.;
Wimmer-Schweingruber, R. F.; Aellig, M. R.; Bochsler, P.; Hefti, S.;
Mikić, Z.
Bibcode: 1999cir..book..141B
Altcode:
No abstract at ADS
Title: Cyclotron Heating of the Solar Corona
Authors: Marsch, Eckart
Bibcode: 1999Ap&SS.264...63M
Altcode: 1998Ap&SS.264...63M
A physical model of the solar transition region and corona is presented,
in which plasma flows in rapidly-diverging coronal funnels and holes
are described within the framework of a two-fluid model including
wave-particle interactions. The ions are heated by wave dissipation
and accelerated by the pressure gradient of high-frequency Alfvén
waves, which are assumed to originate at the bottom of the magnetic
network by small-scale reconnection. The heating is assumed to
be due to cyclotron-resonant damping of the waves near the local
ion gyrofrequency. The EUV emission lines observed by the SUMER
spectrometer on SOHO show very strong broadenings, which seem to be
ordered according to the ion charge-per-mass ratio and thus to indicate
cyclotron-resonant heating by waves. Based on quasilinear theory,
a closure scheme for anisotropic multi-component fluid equations is
developed for the wave-particle interactions of the ions with Alfvén
waves. The acceleration and heating rates are calculated.
Title: The ESA Solar Orbiter Mission
Authors: Marsch, E.
Bibcode: 1999AGAb...15...13M
Altcode: 1999AGM....15..A16M
Presently, a group of solar and space-plasma physicists is studying a
high-resolution ESA mission called Solar Orbiter. This mission will be
proposed to ESA in response to a call, expected in late fall this year,
for ideas for a F 2/3 (flexible) mission and will concentrate on solar
and heliospheric physics. The science objectives, the S/C and orbital
design, and some key instruments of the strawman payload currently
envisioned for the Solar Orbiter will be described and presented. The
agreed baseline of the mission is to fly a set of in-situ particles
and fields experiments, together with a set of optical instruments
(white light imager and coronagraph, EUV imager and spectrometer) into
a near-Sun orbit with a perihelion of about 40 Rodot. This
is achieved by means of an electric propulsion system powered by
large solar-cell arrays. In a possible extended mission the S/C
will climb to about 33circ in heliographic latitude,
thus enabling optical observations to be carried out for the first
time over the Sun's polar regions. One main goal of the mission is
to correlate these remote-sensing observations, to be made with high
spatial resolution at the 100 km scale on the Sun, of the sources
of the solar wind and energetic particles with simultaneous in-situ
measurements of the particles and their associated fields. The plasma
measurements will be made with high-resolution in time and phase-space
at the S/C location, while the S/C corotates partly with the Sun during
the perihelion passage.
Title: Plasma Properties in Coronal Funnels
Authors: Hackenberg, P.; Mann, G.; Marsch, E.
Bibcode: 1999SSRv...87..207H
Altcode:
A two dimensional model of the transition region and the lower corona,
based on the idea that the magnetic flux is strongly concentrated at the
boundaries of the supergranular convection cells, has been proposed by
Gabriel in 1976. The plasma moves along the open magnetic field lines,
which define the the so-called "funnel," and eventually builds up the
solar wind.
Title: Solar Wind Models from the Sun to 1 AU: Constraints by in
Situ and Remote Sensing Measurements
Authors: Marsch, E.
Bibcode: 1999SSRv...87....1M
Altcode:
There are three major types of solar wind: The steady fast wind
originating on open magnetic field lines in coronal holes, the unsteady
slow wind coming probably from the temporarily open streamer belt and
the transient wind in the form of large coronal mass ejections. The
majority of the models is concerned with the fast wind, which is,
at least during solar minimum, the normal mode of the wind and most
easily modeled by multi-fluid equations involving waves. The in-situ
constraints imposed on the models, mainly by the Helios (in ecliptic)
and Ulysses (high-latitude) interplanetary measurements, are extensively
discussed with respect to fluid and kinetic properties of the wind. The
recent SOHO observations have brought a wealth of new information
about the boundary conditions for the wind in the inner solar corona
and about the plasma conditions prevailing in the transition region and
chromospheric sources of the wind plasma. These results are presented,
and then some key questions and scientific issues are identified.
Title: Plasma astrophysics and space physics. Proceedings. 7th
International Conference on Plasma Astrophysics, Katlenburg-Lindau
(Germany), 4 - 8 May 1998.
Authors: Büchner, J.; Axford, I.; Marsch, E.; Vasyliunas, V.
Bibcode: 1999Ap&SS.264.....B
Altcode: 1998Ap&SS.264.....B
The following topics were dealt with: magnetic reconnection, coronal
heating and solar wind acceleration, jets and winds, multi-ion
and dusty plasmas, nonlinear dynamics, dynamo, plasma turbulence,
nonthermal radiation, cosmic ray and particle acceleration.
Title: Ion Temperatures as Observed in a Solar Coronal Hole
Authors: Tu, C. -Y.; Marsch, E.; Wilhelm, K.
Bibcode: 1999SSRv...87..331T
Altcode:
From the widths of the extreme ultraviolet (EUV) lines measured by
the SUMER instrument on SOHO, it was found previously (Tu et al. 1998)
that the average temperature of Ne+7, at heights (relative
to h0) above the southern solar limb from 17″ to 64″,
ranges between 1.3 and 5 × 106 K and of Ne+6
between 1 and 4 × 106 K. For mass-per-charge numbers
greater than 4 the temperatures of the ions increase slightly with
increasing mass-per-charge, while the thermal speed reveals no clear
trend. We present a new data set with exposure times much longer than
the ones in the previous study. The results obtained from line width
analysis of Fe XII (1242 Å), Mg X (1249 Å), Mg VIII (772 Å) Ne VIII
(770 Å), and Si VIII (1445 Å) support our previous study. In this
case, the trend of increasing temperature begins at a mass-per-charge
number of 3. A qualitative explanation based on ion-cyclotron-resonance
heating within linear kinetic theory is suggested.
Title: Kinetic properties of solar wind minor ions and protons
measured with SOHO/CELIAS
Authors: Hefti, S.; Grünwaldt, H.; Ipavich, F. M.; Bochsler, P.;
Hovestadt, D.; Aellig, M. R.; Hilchenbach, M.; Kallenbach, R.; Galvin,
A. B.; Geiss, J.; Gliem, F.; Gloeckler, G.; Klecker, B.; Marsch, E.;
Möbius, E.; Neugebauer, M.; Wurz, P.
Bibcode: 1998JGR...10329697H
Altcode:
Using observations of the Charge Time-of-Flight (CTOF) charge
and mass spectrometer of the Charge, Element and Isotope Analysis
System (CELIAS), and of CELIAS/proton monitor on board the Solar and
Heliospheric Observatory (SOHO), we present an overview of speeds
and kinetic temperatures of minor ions and protons in the solar wind
near solar minimum, covering the Carrington Rotations 1908 to 1912. In
the case of a collision-dominated solar wind the speed of minor ions
is expected to be lower or equal to the speed of the protons, and
all species are expected to have equal temperatures. On the other
hand, minor ions can be accelerated and heated by wave-particle
interaction. In this case, equal thermal speeds of all species are
expected. CTOF data allow the determination of the kinetic parameters of
various ions with high accuracy and with high time resolution. The mean
O6+ speed of the observed period is 390 kms-1. The
speeds of Si7+ and Fe9+ correlate well with
O6+, the linear correlation coefficient being 0.96 or
higher. Our results also indicate that silicon and iron tend to lag
behind oxygen with a speed difference of ~20 kms-1 at 500
kms-1. At the same time, the kinetic temperature of the
ions under investigation exhibit the well-known mass proportionality,
which is attributed to wave-particle interactions. During the period
of low solar activity in consideration, many cases are observed where
the kinetic temperature is extraordinarily low (104K for
O6+).
Title: Solitons in multi-ion plasmas
Authors: Hackenberg, Peter; Mann, Gottfried; Marsch, Eckart
Bibcode: 1998JPlPh..60..845H
Altcode:
Available from http://journals.cambridge.org/bin/bladerunner?REQUNIQ=1105385229&REQSESS=958582&118000REQEVENT=&REQINT1=18465&REQAUTH=0
Title: Magnesium isotopic composition as observed with the CELIAS/MTOF
experiment on the SOHO spacecraft
Authors: Kucharek, H.; Ipavich, F. M.; Kallenbach, R.; Bochsler,
P.; Hovestadt, D.; Grünwaldt, H.; Hilchenbach, M.; Axford, W. I.;
Balsiger, H.; Bürgi, A.; Coplan, M. A.; Galvin, A. B.; Geiss, J.;
Gliem, F.; Gloeckler, G.; Hsieh, K. C.; Judge, D. J.; Klecker, B.;
Lee, M. A.; Livi, S.; Managadze, G. G.; Marsch, E.; Möbius, E.;
Neugebauer, M.; Ogawa, H. S.; Reiche, K. -U.; Scholer, M.; Verigin,
M. I.; Wilken, B.; Wurz, P.
Bibcode: 1998JGR...10326805K
Altcode:
Solar wind abundance ratios of magnesium isotopes measured with the
high resolution Mass Time-of-Flight spectrometer (MTOF) of the Charge,
Element, and Isotope Analysis System (CELIAS) experiment on board
the Solar and Heliospheric Observatory (SOHO) are presented. MTOF,
as part of CELIAS, is, because of its high time and mass resolution,
an excellent tool for isotope abundance measurements in the
solar wind. From the data analysis we have found that the isotopic
composition of magnesium in the solar wind agrees with the terrestrial
composition within the experimental uncertainty. We have obtained
isotopic ratios of 24Mg/25Mg=7.7+/-0.4
and 24Mg/26Mg=7.0+/-0.5. These
values are consistent with the terrestrial values
of 24Mg/25Mg=7.90+/-0.01 and
24Mg/26Mg=7.17+/-0.03. Furthermore, these
investigations also show that with the given uncertainties the abundance
ratios do not vary significantly within a solar wind velocity range
from 375 km/s to 530 km/s.
Title: Detection of 55-80 keV Hydrogen Atoms of Heliospheric Origin
by CELIAS/HSTOF on SOHO
Authors: Hilchenbach, M.; Hsieh, K. C.; Hovestadt, D.; Klecker, B.;
Grünwaldt, H.; Bochsler, P.; Ipavich, F. M.; Bürgi, A.; Möbius,
E.; Gliem, F.; Axford, W. I.; Balsiger, H.; Bornemann, W.; Coplan,
M. A.; Galvin, A. B.; Geiss, J.; Gloeckler, G.; Hefti, S.; Judge,
D. L.; Kallenbach, R.; Laeverenz, P.; Lee, M. A.; Livi, S.; Managadze,
G. G.; Marsch, E.; Neugebauer, M.; Ogawa, H. S.; Reiche, K. -U.;
Scholer, M.; Verigin, M. I.; Wilken, B.; Wurz, P.
Bibcode: 1998ApJ...503..916H
Altcode:
The High-Energy Suprathermal Time-of-Flight sensor (HSTOF) of the
Charge, Element, and Isotope Analysis System (CELIAS) on the Solar
and Heliospheric Observatory (SOHO) near the Lagrangian point L1 is
capable of identifying energetic hydrogen atoms (EHAs) between 55 and 80
keV. Between 1996 February 13 and 1997 August 31, near solar minimum,
there were 285 ``quiet'' days when the interplanetary charged-particle
flux was low. During these quiet times, HSTOF scanned the apex of
the heliosphere once and the antiapex twice. The flux level and time
profile, and hence the arrival direction, of the EHAs accumulated during
these quiet times are best interpreted as fluxes of EHAs coming from
the heliosheath.
Title: Iron freeze-in temperatures measured by SOHO/CELIAS/CTOF
Authors: Aellig, M. R.; Grünwaldt, H.; Bochsler, P.; Wurz, P.;
Hefti, S.; Kallenbach, R.; Ipavich, F. M.; Axford, W. I.; Balsiger,
H.; Bürgi, A.; Coplan, M. A.; Galvin, A. B.; Geiss, J.; Gliem, F.;
Gloeckler, G.; Hilchenbach, M.; Hovestadt, D.; Hsieh, K. C.; Klecker,
B.; Lee, M. A.; Livi, S.; Managadze, G. G.; Marsch, E.; Möbius, E.;
Neugebauer, M.; Reiche, K. -U.; Scholer, M.; Verigin, M. I.; Wilken, B.
Bibcode: 1998JGR...10317215A
Altcode:
The CELIAS particle experiment on SOHO contains the Charge Time
Of Flight (CTOF) mass spectrometer which measures the ionic and
elemental composition of minor ions in the solar wind. In this paper
we present iron freeze-in temperatures derived with a time resolution
of 5 min. They indicate that some of the filamentary structures of the
inner corona observed in Hα survive in the interplanetary medium as
far as 1 AU.
Title: Solar wind measurements with SOHO: The CELIAS/MTOF proton
monitor
Authors: Ipavich, F. M.; Galvin, A. B.; Lasley, S. E.; Paquette, J. A.;
Hefti, S.; Reiche, K. -U.; Coplan, M. A.; Gloeckler, G.; Bochsler,
P.; Hovestadt, D.; Grünwaldt, H.; Hilchenbach, M.; Gliem, F.; Axford,
W. I.; Balsiger, H.; Bürgi, A.; Geiss, J.; Hsieh, K. C.; Kallenbach,
R.; Klecker, B.; Lee, M. A.; Managadze, G. G.; Marsch, E.; Möbius,
E.; Neugebauer, M.; Scholer, M.; Verigin, M. I.; Wilken, B.; Wurz, P.
Bibcode: 1998JGR...10317205I
Altcode:
The proton monitor, a small subsensor in the Charge, Element, and
Isotope Analysis System/Mass Time-of-Flight (CELIAS/MTOF) experiment
on the SOHO spacecraft, was designed to assist in the interpretation
of measurements from the high mass resolution main MTOF sensor. In
this paper we demonstrate that the proton monitor data may be used to
generate reasonably accurate values of the solar wind proton bulk speed,
density, thermal speed, and north/south flow direction. Correlation
coefficients based on comparison with the solar wind measurements from
the SWE instrument on the Wind spacecraft range from 0.87 to 0.99. On
the basis of the initial 12 months of observations, we find that the
proton momentum flux is almost invariant with respect to the bulk speed,
confirming a previously published result. We present observations of
two interplanetary shock events, and of an unusual solar wind density
depletion. This large density depletion, and the correspondingly
large drop in the solar wind ram pressure, may have been the cause
of a nearly simultaneous large increase in the flux of relativistic
magnetospheric electrons observed at geosynchronous altitudes by the
GOES 9 spacecraft. Extending our data set with a 10-year time span from
the OMNIWeb data set, we find an average frequency of about one large
density depletion per year. The origin of these events is unclear;
of the 10 events identified, 3 appear to be corotating and at least
2 are probably CME related. The rapidly available, comprehensive data
coverage from SOHO allows the production of near-real time solar wind
parameters that are now accessible on the World Wide Web.
Title: Ion Temperatures in a Solar Polar Coronal Hole Observed by
SUMER on SOHO
Authors: Tu, C. -Y.; Marsch, E.; Wilhelm, K.; Curdt, W.
Bibcode: 1998ApJ...503..475T
Altcode:
The temperatures of some highly charged ions in the southern solar polar
coronal hole are determined from the widths of the extreme ultraviolet
(EUV) lines measured by the SUMER (Solar Ultraviolet Measurements
of Emitted Radiation) instrument on SOHO (Solar and Heliospheric
Observatory). Radiation from both light ions, such as Ne6+,
Ne7+, Mg7+, Mg9+, Si6+,
and Si7+, and heavy ions, such as Fe9+,
Fe10+, and Fe11+, are recorded in off-limb
observations. We refer here to the limb as the height, h0,
where the limb brightening of the N IV 765 Å line maximizes. After
correction of the measured line widths for instrument contributions,
the intrinsic widths of these emission lines are derived. These are
produced by thermal motions of the ions and turbulent wave motions of
the background plasma. Since the turbulent line broadening should be the
same for all the different ions, its upper limit can be determined from
the widths of the iron lines, assuming zero iron temperatures. Thus,
the range of kinetic temperatures permitted for the light species can
be delimited. For example, the average temperature of Ne7+,
at heights above the southern limb relative to h0 from 17"
to 64", ranges between 1.3 and 5 × 106 K, and the average
temperature of Ne6+ ranges between 1 and 4 × 106
K. The interpretation of these measurements does not require knowledge
of the ion formation (or electron) temperature. It is also found that
the ion thermal speed decreases with increasing mass per charge, while
the ion temperature remains roughly constant. In another observation
at heights from 167" to 183" above h0, the temperature of
the ions increases slightly with increasing mass per charge, while
the thermal speed reveals no clear trend. The upper limits of the
turbulence amplitude, <δv2>1/2, derived
for these two altitude ranges are 33-37 and 44 km s-1,
respectively. The implications of these results for the heating of
the solar corona and the acceleration of the solar wind are discussed.
Title: Elemental composition of the January 6, 1997, CME
Authors: Wurz, P.; Ipavich, F. M.; Galvin, A. B.; Bochsler, P.; Aellig,
M. R.; Kallenbach, R.; Hovestadt, D.; Grünwaldt, H.; Hilchenbach,
M.; Axford, W. I.; Balsiger, H.; Bürgi, A.; Coplan, M. A.; Geiss,
J.; Gliem, F.; Gloeckler, G.; Hefti, S.; Hsieh, K. C.; Klecker, B.;
Lee, M. A.; Managadze, G. G.; Marsch, E.; Möbius, E.; Neugebauer,
M.; Reiche, K. -U.; Scholer, M.; Verigin, M. I.; Wilken, B.
Bibcode: 1998GeoRL..25.2557W
Altcode:
Using solar wind particle data from the CELIAS/MTOF sensor on the SOHO
mission, we studied the abundance of the elements O, Ne, Mg, Si, S,
Ca, and Fe for the time period around the January 6, 1997, coronal mass
ejection event (CME). In the interstream and coronal hole regions before
and after this event we found elemental abundances consistent with the
expected abundance patterns of the respective flow regimes. However,
during the passage of the CME and during the passage of the erupted
filament, which followed the CME, we found that the elemental
composition differed markedly from the interstream and coronal hole
regions before and after this event. During the passage of the CME and
the passage of the erupted filament we found a mass-dependent element
fractionation, with a monotonic increase toward heavier elements. We
observed Si/O and Fe/O abundance ratios of about one half during these
time periods, which is significantly higher than for typical solar wind.
Title: The Solar Corona Above Polar Coronal Holes as Seen by SUMER
on SOHO
Authors: Wilhelm, Klaus; Marsch, Eckart; Dwivedi, Bhola N.; Hassler,
Donald M.; Lemaire, Philippe; Gabriel, Alan H.; Huber, Martin C. E.
Bibcode: 1998ApJ...500.1023W
Altcode:
In order to address two of the principal scientific objectives of the
Solar and Heliospheric Observatory (SOHO), studies of the heating
mechanisms of the solar corona and the acceleration processes of
the solar wind, we deduce electron temperatures, densities, and
ion velocities in plumes and interplume regions of polar coronal
holes using ultraviolet observations from SUMER (Solar Ultraviolet
Measurements of Emitted Radiation) on SOHO. SUMER allows us to study
the inner corona up to a distance of about 430,000 km above the
limb, or r = 1.6 R⊙ (solar radius) from the center
of the disk. We find the electron temperatures, Te,
to be less than 800,000 K in a plume in the range from r = 1.03 to
1.60 R⊙, decreasing with height to ~330,000 K. Near
an interplume lane, the electron temperature is also low, but stays
between 750,000 and 880,000 K in the same height interval. Doppler
widths of O VI lines in plumes are narrower (ΔλD ~
150 mÅ, v1/E ~ 43 km s-1) than in interplume
lanes (~190 mÅ, ~55 km s-1). The thermal and turbulent
ion speeds, v1/E, of Si7+ reach values up to
~80 km s-1 in the darkest regions outside plumes above the
coronal hole. This corresponds to a kinetic ion temperature of 1 ×
107 K. A limit of ~18 km s-1 for the bulk speed
in plumes below r = 1.2 R⊙ is deduced from O VI line shift
measurements and consideration of the three-dimensional plume geometry
(differential line-of-sight velocities <=3 km s-1),
whereas differential line-of-sight velocities of Mg8+
ions up to 34 km s-1 can be seen in dark regions.
Title: Hydrogen and helium in the solar chromosphere: a background
model for fractionation
Authors: Peter, Hardi; Marsch, Eckart
Bibcode: 1998A&A...333.1069P
Altcode:
A multi-fluid model for a hydrogen-helium mixture in an
ionization-diffusion layer in the (solar) chromosphere is presented. The
purpose of this model is to serve as a background for fractionation
models calculating the abundance variations of minor species from the
photosphere to the solar wind. The emphasis will be on the determination
of the (mean) flow velocity in that ionization layer. The equations
of continuity and momentum of every component, neutral and (singly)
ionized for both elements, will be solved together with an energy
equation including heating and radiative losses. Special attention
will be paid to the ionization and the elastic collisions as well as
to resonant charge exchange. One of the main results is the connection
of the particle flux through the chromosphere with the ionization rate,
i. with the photon flux in the UV. Furthermore the abundance variations
of helium are discussed with the result, that the ion-neutral separation
processes leading to the fractionation of the minor elements cannot
explain the fractionation of helium as measured in the solar wind.
Title: The Magnetic Reconnection Explorer (MAGREX)
Authors: Schühle, U.; Antionchos, S. K.; Barbee, T. W., Jr.; Bixler,
J. V.; Brown, C. M.; Carter, P. H., II; Curdt, W.; Davila, J. M.;
Doschek, G.; Feldman, U.; Goldstein, W. H.; Kordas, J.; Lemaire, P.;
Mariska, J. T.; Marsch, E.; Moses, J. D.; Seely, J. F.; Wilhelm, K.;
Woods, T. N.
Bibcode: 1998ESASP.417..289S
Altcode: 1998cesh.conf..289S
No abstract at ADS
Title: Solar Wind
Authors: Marsch, Eckart
Bibcode: 1998LNP...507..107M
Altcode: 1998sspt.conf..107M
A concise tutorial review is given of solar wind observations and theory
with emphasis on the more recent findings from the Ulysses and SOHO
missions, in particular about the plasma state and structure of the
polar coronal holes, and on theoretical efforts to model the coronal
hole flows and the fast solar wind emanating therefrom. The structure of
the large-scale corona is discussed and the microstate of the solar wind
in terms of particle and wave observations is analysed. Observational
evidence is mounting that the magnetically open coronal holes are
far away from a state of local thermodynamic equilibrium, as is the
associated interplanetary solar wind, and that they differ substantially
in their plasma parameters from the low-latitude streamers with
closed magnetic fields, which only open intermittently to release
the slow solar wind. The coronal sources and their plasma boundary
conditions as well as the interplanetary constraints on the wind
models are presented and discussed. Modern theories and models of the
solar wind are reviewed. First the basic concept of the single-fluid
Parker-type model is outlined, and then two-fluid models are described,
in particular those incorporating strong heating of protons close to
the Sun, which yields fast acceleration with the terminal wind speed
being attained within 10 R ⊙. Finally, the most recent
modelling efforts to generate the wind plasma through ionization in
the chromospheric network are presented.
Title: Plasma Properties in Coronal Funnels
Authors: Hackenberg, P.; Mann, G.; Marsch, E.
Bibcode: 1998cee..workE..41H
Altcode:
A two dimensional model for the chromosphere and the corona based
on the idea that the magnetic flux is strongly concentrated at
the boundaries of supergranule convection cells has been proposed
by Gabriel in 1976. Thus he introduced a non-trivial geometry,
the so-called ``funnel'', which is defined by the magnetic field
lines. Dowdy et al. (1987) investigated the influence of the shape
of the funnel on the temperature profile, i.e. on the ability to
heat the corona. Since the magnetic field lines of the funnel are
open field lines, the plasma is free to move along this field lines
and eventually builds up the solar wind. In both of the aforementioned
models this effect has been neglected. Based on a two dimensional funnel
model we investigate the plasma flow. Also heat conduction, radiative
losses and a heating function are considered. We linked our model to
the observed quantities at the transition region and the lower solar
corona at ~15000 km above the photosphere. The thereby found height
profiles of the plasma properties within the funnel are presented.
Title: Space mission for exploration of the sun, mercury and inner
heliosphere (``InterHelios'')
Authors: Axford, W. I.; Marsch, E.; Oraevsky, V. N.; Kuznetsov, V. D.;
Breus, T. K.; Scwenn, R.; Ip, W. -H.; Ksanfomality, L. V.; Thomas,
N.; Kogan, A.; Utkin, V. F.; Uspensky, G. R.
Bibcode: 1998AdSpR..21..275A
Altcode:
The scientific objectives for a new mission for exploration of the
Sun, Mercury and inner Heliosphere (InterHelios), its ballistic design
and orbital characteristics are presented. This mission will provide
observations of the Sun and solar wind from almost heliosynchronous
orbits within heliocentric distances from about 30 to 40 R_s. The
mission is designed for multiple encounters with Mercury and
observations of its surface and its gas and plasma environment. The
in-situ-wind and remote-solar measurements will permit us to determine
the characteristics of the wind and associated plasma and magnetic
fields in the regions of the heliosphere that are related with the
magnetically active streamer belt and coronal holes extending to
near-ecliptic latitudes.
Title: INTERHELIOS - Sun and Heliosphere Observer
Authors: Marsch, E.; Kogan, A.; Axford, W. I.; Breus, T.; Kuznetsov,
V. D.; Oraevsky, V. N.
Bibcode: 1998ESASP.417...91M
Altcode: 1998cesh.conf...91M
No abstract at ADS
Title: Elemental Composition Before, During, and After the January 6,
1997 CME Event Measured by CELIAS/SOHO
Authors: Wurz, P.; Ipavich, F. M.; Galvin, A. B.; Bochsler, P.; Aellig,
M. R.; Kallenbach, R.; Hovestadt, D.; Grünwaldt, H.; Hilchenbach,
M.; Axford, W. I.; Balsinger, H.; Bürgi, A.; Coplan, M. A.; Geiss,
J.; Gliem, F.; Gloeckler, G.; Hefti, S.; Hsieh, K. C.; Klecker, B.;
Lee, M. A.; Livi, S.; Managadze, G. G.; Marsch, E.; Möbius, E.;
Neugebauer, M.; Reiche, K. U.; Scholer, M.; Verigin, M. I.; Wilken, B.
Bibcode: 1997ESASP.415..395W
Altcode: 1997cpsh.conf..395W
No abstract at ADS
Title: Isotopic composition of solar wind neon measured by CELIAS/MTOF
on board SOHO
Authors: Kallenbach, R.; Ipavich, F. M.; Bochsler, P.; Hefti, S.;
Hovestadt, D.; Grünwaldt, H.; Hilchenbach, M.; Axford, W. I.;
Balsiger, H.; Bürgi, A.; Coplan, M. A.; Galvin, A. B.; Geiss, J.;
Gliem, F.; Gloeckler, G.; Hsieh, K. C.; Klecker, B.; Lee, M. A.;
Livi, S.; Managadze, G. G.; Marsch, E.; Möbius, E.; Neugebauer, M.;
Reiche, K. -U.; Scholer, M.; Verigin, M. I.; Wilken, B.; Wurz, P.
Bibcode: 1997JGR...10226895K
Altcode:
We present first results taken from the high-resolution mass
time-of-flight spectrometer (MTOF) of the charge, element, and
isotope analysis system (CELIAS) experiment on board the Solar and
Heliospheric Observatory (SOHO) spacecraft launched in December 1995,
concerning the abundance ratios of neon isotopes in the solar wind. We
obtain the isotopic ratios 20Ne/22Ne=(13.8+/-0.7)
and 20Ne/21Ne=(440+/-110), which agree with the
values obtained from the Apollo foil solar wind experiments and which
have been derived from measurements of solar particles implanted in
lunar and meteoritic samples.
Title: Observations and Models of the Fast and Slow Solar Wind
Authors: Marsch, E.
Bibcode: 1997ESASP.415....7M
Altcode: 1997cpsh.conf....7M
No abstract at ADS
Title: Solar Wind and Chromospheric Network
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 1997SoPh..176...87M
Altcode:
A physical model of the transition region, including upflow of the
plasma in magnetic field funnels that are open to the overlying corona,
is presented. A numerical study of the effects of Alfvén waves on the
heating and acceleration of the nascent solar wind originating in the
chromospheric network is carried out within the framework of a two-fluid
model for the plasma. It is shown that waves with reasonable amplitudes
can, through their pressure gradient together with the thermal pressure
gradient, cause a substantial initial acceleration of the wind (on
scales of a few Mm) to locally supersonic flows in the rapidly expanding
magnetic field `trunks' of the transition region network. The concurrent
proton heating is due to the energy supplied by cyclotron damping of the
high-frequency Alfvén waves, which are assumed to be created through
small-scale magnetic activity. The wave energy flux of the model is
given as a condition at the upper chromosphere boundary, located above
the thin layer where the first ionization of hydrogen takes place.
Title: Linear mode analysis in multi-ion plasmas
Authors: Mann, G.; Hackenberg, P.; Marsch, E.
Bibcode: 1997JPlPh..58..205M
Altcode:
Available from http://journals.cambridge.org/bin/bladerunner?REQUNIQ=1105385056&REQSESS=958582&118000REQEVENT=&REQINT1=18157&REQAUTH=0
Title: Venus tail ray observation near Earth
Authors: Grünwaldt, H.; Neugebauer, M.; Hilchenbach, M.; Bochsler,
P.; Hovestadt, D.; Bürgi, A.; Ipavich, F. M.; Reiche, K. -U.; Axford,
W. I.; Balsiger, H.; Galvin, A. B.; Geiss, J.; Gliem, F.; Gloeckler,
G.; Hsieh, K. C.; Kallenbach, R.; Klecker, B.; Livi, S.; Lee, M. A.;
Managadze, G. G.; Marsch, E.; Möbius, E.; Scholer, M.; Verigin,
M. I.; Wilken, B.; Wurz, P.
Bibcode: 1997GeoRL..24.1163G
Altcode:
In June, 1996, Venus passed through a very close inferior conjunction
with the Sun. At that time the CTOF detector of the CELIAS mass
spectrometer experiment on the SOHO spacecraft near Earth's L1
Lagrangian point was measuring heavy ions in the solar wind ∼4.5 ×
107 km downstream of Venus. Close to the time predicted
by simple geometric arguments for passage of SOHO through the Venus
wake, CTOF made three encounters with unusual fluxes of O+
and C+ ions. Their energy distributions resembled those
of tail rays originating in the Venus ionosphere or ionopause region
rather than of ions produced in the corona of neutral atoms that
surrounds the planet. The C+ abundance was ≈ 10% of
O+. The observed O+ speed was very close to
the simultaneous solar wind speed and the O+ temperature
was a cool 5600 K/amu. The flux densities for the three events were
(2.4-4.4) × 10³ cm-2s-1.
Title: Two-Fluid Model for Heating of the Solar Corona and
Acceleration of the Solar Wind by High-Frequency ALFVÉN Waves
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1997SoPh..171..363T
Altcode:
A model of the solar corona and wind is developed which includes for
the first time the heating and acceleration effects of high-frequency
Alfvén waves in the frequency range between 1 Hz and 1 kHz. The
waves are assumed to be generated by the small-scale magnetic
activity in the chromospheric network. The wave dissipation near
the gyro-frequency, which decreases with increasing solar distance,
leads to strong coronal heating. The resulting heating function is
different from other artificial heating functions used in previous
model calculations. The associated thermal pressure-gradient force and
wave pressure-gradient force together can accelerate the wind to high
velocities, such as those observed by Helios and Ulysses. Classical
Coulomb heat conduction is also considered and turns out to play a
role in shaping the temperature profiles of the heated protons. The
time-dependent two-fluid (electrons and protons) model equations and
the time-dependent wave-spectrum equation are numerically integrated
versus solar distance out to about 0.3 AU. The solutions finally
converge and settle on time-stationary profiles which are discussed
in detail. The model computations can be made to fit the observed
density profiles of a polar coronal hole and polar plume with the
sonic point occurring at 2.4 R⊙ and 3.2 R⊙,
respectively. The solar wind speeds obtained at 63 R⊙ are
740 km s-1 and 540 km s-1; the mass flux is 2.1
and 2.2 × 108 cm-2 s-1 (normalized
to 1 AU), respectively. The proton temperature increases from a value
of 4 × 105 K at the lower boundary to 2 × 106
K in the corona near 2 R⊙.
Title: The effects of high-frequency Alfven waves on coronal heating
and solar wind acceleration.
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 1997A&A...319L..17M
Altcode:
Wave effects in a two-fluid model for the solar corona and wind are
studied. Heating and acceleration are achieved by high-frequency
Alfven waves, which are assumed to be created through small-scale
reconnections in the chromospheric network. The wave energy flux F_w_
is given in the model as a lower boundary condition. Waves with a
power spectrum of the form P_0_(f/f_0_)^-1^ in the frequency range
from 1 to 800Hz and with P_0_=40x10^11^nT^2^/Hz and f_0_=10^-5^Hz,
corresponding to an integrated amplitude of 35km/s, can heat the corona
to a temperature of 10^6^K at r=1.2Rsun_, and 2.6x10^6^K
(the maximum) at r=2Rsun_, starting from 4x10^5^K at
r=1Rsun_. Thermal and wave pressure gradients accelerate
the wind to speeds of 100km/s at r=1.2Rsun_, and 212km/s
at r=2Rsun_, starting from 2km/s at r=1Rsun_
in a rapidly diverging stream tube. Asymptotic wind speeds in the
observed range of 700 to 800km/s at 0.3AU are obtained with wave
amplitudes of 30 to 37km/s in the frequency range from 1 to 30Hz,
corresponding to P_0_=90x10^11^nT^2^/Hz.
Title: Pressure enhancement associated with meridional flow in
high-speed solar wind: possible evidence for an interplanetary
magnetic flux rope
Authors: Tu, C. -Y.; Marsch, E.; Ivory, K.; Schwenn, R.
Bibcode: 1997AnGeo..15..137T
Altcode: 1997AnG....15..137T
A sizable total-pressure (magnetic pressure plus kinetic pressure)
enhancement was found within the high-speed wind stream observed by
Helios 2 in 1976 near 0.3 AU. The proton density and temperature and
the magnetic magnitude simultaneously increased for about 6 h. This
pressure rise was associated with a comparatively large southward
flow velocity component (with Vz <>~<> -100 km · s-1)
and magnetic-field rotation. The pressure enhancement was associated
with unusual features in the electron distribution function. It shows a
wide angular distribution of electron counting rates in the low-energy
(57.8 eV) channel, while previous to the enhancement it exhibits a
wide angular distribution of electron count rate in the high-energy
(112, 221 and 309 eV) channels, perhaps indicating the mirroring of
electrons in the converging field lines of the background magnetic
field. These fluid and kinetic phenomena may be explained as resulting
from an interplanetary magnetic flux rope which is not fully convected
by the flow but moves against the background wind towards the Sun.
Title: The Sun at Minimum Activity: Results from the CELIAS Experiment
on SOHO
Authors: Boschler, P.; Hovestadt, D.; Grünwaldt, H.; Hilchenbach, M.;
Ipavich, F. M.; Aelling, M. R.; Axford, W. I.; Balsiger, H.; Bogdanov,
A.; Bürgi, A.; Coplan, M. A.; Galvin, A. B.; Geiss, J.; Gloeckler,
G.; Hefti, S.; Hsieh, K. C.; Judge, D. L.; Kallenbach, R.; Klecker,
B.; Kucharek, H.; Lasley, S. E.; Lee, M. A.; Litvinenko, Yu.; Livi,
S.; Managadze, G. G.; Marsch, E.; Möbius, E.; Neugebauer, M.; Ogawa,
H. S.; Paquette, J. A.; Reiche, K. -U.; Scholer, M.; Verigin, M. I.;
Wilken, B.; Wurz, P.
Bibcode: 1997ESASP.404...37B
Altcode: 1997cswn.conf...37B; 1997soho....5...37B
No abstract at ADS
Title: Magnesium Isotope Composition in the Solar Wind as Observed
with the MTOF Sensor on the CELIAS Experiment On Board the SOHO
Spacecraft
Authors: Kucharek, H.; Ipavich, F. M.; Kallenbach, R.; Bochsler,
P.; Hovestadt, D.; Grünwaldt, H.; Hilchenbach, M.; Axford, W. I.;
Balsiger, H.; Bürgi, A.; Coplan, M. A.; Galvin, A. B.; Geiss, J.;
Gloeckler, G.; Hsieh, K. C.; Klecker, B.; Lee, M. A.; Livi, S.;
Managadzem G. G.; Marsch, E.; Möbius, E.; Neugebauer, M.; Reiche,
K. U.; Scholer, M.; Verigin, M. I.; Wilkin, B.; Wurz, P.
Bibcode: 1997ESASP.404..473K
Altcode: 1997cswn.conf..473K
No abstract at ADS
Title: Bright Plumes and Dark Lanes as Observed in MgX 625 Å and
NV 1239 Å in the Solar Polar Corona
Authors: Marsch, E.; Tu, C. -Y.; Wilhelm, K.; Curdt, W.; Schühle,
U.; Dammasch, I. E.
Bibcode: 1997ESASP.404..555M
Altcode: 1997cswn.conf..555M
No abstract at ADS
Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
I. Spectra and Spectroradiometry
Authors: Wilhelm, K.; Lemaire, P.; Curdt, W.; Schühle, U.; Marsch, E.;
Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Huber,
M. C. E.; Vial, J. -C.; Kühne, M.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.; Feldman, U.; Hollandt, J.; Brekke, P.
Bibcode: 1997SoPh..170...75W
Altcode:
SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation
instrument on the Solar and Heliospheric Observatory (SOHO) - observed
its first light on January 24, 1996, and subsequently obtained a
detailed spectrum with detector B in the wavelength range from 660
to 1490 Å (in first order) inside and above the limb in the north
polar coronal hole. Using detector A of the instrument, this range
was later extended to 1610 Å. The second-order spectra of detectors
A and B cover 330 to 805 Å and are superimposed on the first-order
spectra. Many more features and areas of the Sun and their spectra
have been observed since, including coronal holes, polar plumes and
active regions. The atoms and ions emitting this radiation exist at
temperatures below 2 × 106 K and are thus ideally suited
to investigate the solar transition region where the temperature
increases from chromospheric to coronal values. SUMER can also be
operated in a manner such that it makes images or spectroheliograms
of different sizes in selected spectral lines. A detailed line profile
with spectral resolution elements between 22 and 45 mÅ is produced for
each line at each spatial location along the slit. From the line width,
intensity and wavelength position we are able to deduce temperature,
density, and velocity of the emitting atoms and ions for each emission
line and spatial element in the spectroheliogram. Because of the high
spectral resolution and low noise of SUMER, we have been able to detect
faint lines not previously observed and, in addition, to determine
their spectral profiles. SUMER has already recorded over 2000 extreme
ultraviolet emission lines and many identifications have been made on
the disk and in the corona.
Title: Working Group 3: Coronal Hole Structure and High Speed
Solar Wind
Authors: Marsch, E.
Bibcode: 1997ESASP.404..135M
Altcode: 1997cswn.conf..135M
No abstract at ADS
Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
II. Imagery and Data Management
Authors: Lemaire, P.; Wilhelm, K.; Curdt, W.; SchÜle, U.; Marsch,
E.; Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Vial,
J. C.; KÜhne, M.; Huber, M. C. E.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.
Bibcode: 1997SoPh..170..105L
Altcode:
SUMER - Solar Ultraviolet Measurements of Emitted Radiation - is not
only an extreme ultraviolet (EUV) spectrometer capable of obtaining
detailed spectra in the range from 500 to 1610 Å, but, using the
telescope mechanisms, it also provides monochromatic images over
the full solar disk and beyond, into the corona, with high spatial
resolution. We report on some aspects of the observation programmes
that have already led us to a new view of many aspects of the Sun,
including quiet Sun, chromospheric and transition region network,
coronal hole, polar plume, prominence and active region studies. After
an introduction, where we compare the SUMER imaging capabilities to
previous experiments in our wavelength range, we describe the results
of tests performed in order to characterize and optimize the telescope
under operational conditions. We find the spatial resolution to be
1.2 arc sec across the slit and 2 arc sec (2 detector pixels) along
the slit. Resolution and sensitivity are adequate to provide details
on the structure, physical properties, and evolution of several solar
features which we then present. Finally some information is given on
the data availability and the data management system.
Title: Ionization Layer of Hydrogen in the Solar Chromosphere and
the Solar Wind Mass Flux
Authors: Peter, H.; Marsch, E.
Bibcode: 1997ESASP.404..591P
Altcode: 1997cswn.conf..591P
No abstract at ADS
Title: Kinetic Phenomena in the Solar Wind
Authors: Feldman, W. C.; Marsch, E.
Bibcode: 1997cwh..conf..617F
Altcode: 2006mslp.conf..617F
No abstract at ADS
Title: Evidence for nongyrotropic alpha particle and proton
distribution functions: TAUS solar wind measurements
Authors: Astudillo, H. F.; Livi, S.; Marsch, E.; Rosenbauer, H.
Bibcode: 1996JGR...10124423A
Altcode:
The goal of this paper is to present convincing evidence for the
occurrence of nongyrotropic alpha particle and proton velocity
distribution functions in the solar wind plasma. We analyze the
three-dimensional velocity distribution functions obtained by
measurements with high time resolution (8 s for alpha particles and 2
s for protons) of the plasma experiment TAUS on the PHOBOS II mission
to planet Mars. The measurements were made at heliocentric distances
near 1.3 AU during an event which occurred after a discontinuity in
the interplanetary magnetic field. It was characterized by a spike in
the density and temperature ratios, with nα/np
and Tα/Tp reaching values of about 0.3 and
12, respectively. In a detailed analysis of the distributions, we
show that the nongyrotropic features are associated with sizable
fractions of the alpha particle distribution functions. Furthermore,
it is also shown that similar nongyrotropic features are present in
solar wind proton distributions. The nongyrotropic particles of both
species in the distributions can be characterized as particles being
gyro-phase-bunched in velocity space. We indicate that there might be
a close relation between the nongyrotropy of the distribution and the
large temperature anisotropies (with T⊥>T∥)
observed in these events. We also point out some differences in the
symmetry properties with respect to the local magnetic field direction
between the nongyrotropic proton distribution functions found in the
undisturbed solar wind and the nongyrotropic distributions originating
at interplanetary shocks.
Title: TAUS measurements of non-gyrotropic distribution functions
of solar wind alpha particles
Authors: Astudillo, H. F.; Marsch, E.; Livi, S.; Rosenbauer, H.
Bibcode: 1996AIPC..382..289A
Altcode:
We analyse three-dimensional distribution functions of solar wind
alpha particles in velocity space and study their symmetry properties
relative to the interplanetary magnetic field. We present convincing
evidence for the occurrence of non-gyrotropic alpha-particle velocity
distribution functions in the solar wind plasma. The three-dimensional
distributions are obtained by measurements with high resolution (8
s for alpha particles and 2 s for protons) of the plasma experiment
TAUS on the PHOBOS II mission to planet Mars. The measurements were
made at heliocentric distances near 1.3 AU. In a detailed analysis of
the distributions we show that non-gyrotropic features are related
to a sizable fraction of phase space density in the alpha-particle
distributions. These non-gyrotropic particles can be characterised
as being gyro-phase bunched in velocity space. There are indications
of a close relation between the non-gyrotropy of the core particles
of a distribution and the large core temperature anisotropies (with
T⊥>T∥), which are observed in these events.
Title: Energy spectrum transfer equations of solar wind turbulence
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1996AIPC..382..233T
Altcode:
Recent studies of transfer equations for solar wind MHD turbulence
are reviewed. Emphasis is placed on the comparison of theoretical with
observational results. The Helios, Voyager and Ulysses missions provide
opportunities to study the radial evolution of the power spectra,
cross-helicity, Alfvén ratio and minimum variance direction. Spectrum
tranfer equations are a tool to explore theoretically the radial
evolution of the fluctuations. The transfer equations are derived
from the incompressible MHD equations. Generally, one needs to make
assumptions about the nature of the fluctuations and their turbulent
interactions, in order to derive models from which numerical results
that can be compared with the observations are obtained. Results for
special simple models, which involve only structures and assume strong
mixing, or consider Alfvén waves with weak turbulent interactions,
or a superposition of outward Alfvén waves with convected structures,
are briefly discussed. The differences between various approaches
for deriving and approximating the general transfer equations are
elucidated. The references in this short review are not complete. An
exhaustive list of papers can be found in the recent review of Tu and
Marsch [1995a]. A related discussion may be also found in a detailed
review by Goldstein et al. [1995a].
Title: The microscopic state of the solar wind-links between
composition, velocity distributions and waves
Authors: Marsch, E.
Bibcode: 1996AIPC..382..187M
Altcode:
An overview is given of the microscopic state of the solar wind with
emphasis on recent Ulysses high-latitude observations and previous
Helios in-ecliptic observations. Emphasis is placed on the connection of
interplanetary kinetic-scale phenomena with their generating microscopic
processes in the corona. The fast streams seem to consist of mesoscale
pressure-balanced magnetic flux tubes, reminiscent of the supergranular
or smaller structures building the open corona, from which copious
Alfvén waves emanate. The wind from the magnetically structured
and active corona shows considerable abundance and ionization state
variations. Some modelling attempts to explain the observed element
fractionation are mentioned. The nonthermal particle features, such as
proton-ion differential streaming, ion beams, temperature anisotropies,
and skewed electron distributions associated with collisionless heat
conduction, and the related wave-particle interactions are discussed.
Title: A method for shock determination and classification
Authors: Liu, Shuhui; Marsch, E.; Schwenn, R.; Rosenbauer, H.
Bibcode: 1996AIPC..382..376L
Altcode:
A new method to present, to determine and to classify shocks from in
situ measurements is developed, using normalized velocities up- and
down-stream in a velocity V1-V2 diagram. With
this method one can show how the observed shock solutions vary with
different time averages over the data from the up- and down-stream
region. Some shock events have been analyzed. The Helios measurements
show, that the solutions for the fast forward shock are confined well
in the 1-->2 region. The different solutions, obtained by means of
straightforward averages with different time intervals, are somewhat
distributed in the normalized V1-V2 diagram. But
only the shock solutions which are consistent with the Rankine-Hugoniot
relations and an entropy increase really define a particular shock.
Title: Spatial evolution of the magnetic field spectral exponent in
the solar wind: Helios and Ulysses comparison
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 1996JGR...10111149M
Altcode:
The spatial evolution of the spectral exponent of magnetic field
fluctuations in the solar wind is investigated by a comparison of
spectra and length functions obtained from Helios for in-ecliptic
and from Ulysses for high-latitude observations. A similar radial
evolution trend is found in both data sets for the Bz
component of the magnetic field, which is least affected by compressive
interactions. Yet the fluctuations seem to evolve more slowly in the
polar flows as compared with the Alfvénic fluctuations found by the
Helios experiments in coronal-hole-related flows near the Sun in the
ecliptic plane.
Title: Solar Wind Composition: First Results from SOHO and Future
Expectations
Authors: Galvin, A. B.; Ipavich, F. M.; Gloeckler, G.; Coplan, M.;
Hovestadt, D.; Hilchenbach, M.; Buergi, A.; Klecker, B.; Scholer,
M.; Bochsler, P.; Balsiger, H.; Geiss, J.; Kallenbach, R.; Wurz, P.;
Gruenwaldt, H.; Axford, W. I.; Livi, S.; Marsch, E.; Wilken, B.;
Gliem, F.; Reiche, K. -U.; Lee, M. A.; Moebius, E.; Hsieh, K. C.;
Neugebauer, M.; Managadze, G. G.; Verigin, M. I.
Bibcode: 1996AAS...188.4905G
Altcode: 1996BAAS...28..897G
The SOHO payload includes three experiments designed to make "in situ"
particle measurements of the solar wind and solar energetic particles
(CELIAS, D. Hovestadt PI; COSTEP, H. Kunow PI; ERNE, J. Torsti
PI). The solar wind measurements that are the focus of this talk are
primarily provided by the CELIAS CTOF and MTOF sensors. (CELIAS/STOF
and COSTEP-ERNE measure solar and interplanetary suprathermal and
energetic particle populations.) CELIAS/CTOF measures solar wind
heavy ion elemental and charge state abundances, information which
is used (for example) in identifying the type of solar wind flow and
the ionization processes in the corona where the solar wind charge
states become "frozen-in". CELIAS/MTOF provides heavy ion elemental
and isotopic abundances that are important (for example) in the study
of fractionation factors in coronal abundances (as in the so-called
"FIP-effect") for the rarer elements not resolvable in conventional
solar wind composition instruments, and in determining the isotopic
make-up of the solar corona. MTOF is, by far, the most powerful solar
wind mass spectrometer flown to date, and already has new science
to report at the time of this writing. This happenstance is due to a
combination of (1) advanced technology in obtaining high mass resolution
for ions at solar wind energies, and (2) increased statistics. The
excellent counting statistics are largely due to continuous solar wind
monitoring (with its position at L1, ``the Sun never sets on SOHO''),
and the continuous sampling of the solar wind by the 3-axis stabilized
spacecraft further enhanced by MTOF's novel, never previously flown
deflection system that encompasses a very large dynamic range. As might
be expected, this unique opportunity has allowed MTOF to identify
a number of elements for the first time in the solar wind (e.g., P,
Ti, Cr and Ni). A rich assortment of solar wind isotopes have been
identified for the first time, many of which (e.g., Fe 54 and 56; Ni
58,60,62) have not been detected previously even in solar energetic
particle populations nor remotely using spectroscopic techniques.
Title: Multifractal scaling of the kinetic energy flux in solar
wind turbulence
Authors: Marsch, E.; Tu, C. -Y.; Rosenbauer, H.
Bibcode: 1996AnGeo..14..259M
Altcode: 1996AnG....14..259M
The geometrical and scaling properties of the energy flux of the
turbulent kinetic energy in the solar wind have been studied. Using
present experimental technology in solar wind measurements we
cannot directly measure the real volumetric dissipation rate,
<varepsilon>(t), but are constrained to represent it by its
surrogate the energy flux near the dissipation range at the proton
gyro scale. There is evidence for the multifractal nature of the so
defined dissipation field <varepsilon>(t), a result derived from
the scaling exponents of its statistical moments. The generalized
dimension Dq has been determined and reveals that the dissipation
field has a multifractal structure, which is not compatible with
a scale-invariant cascade. The related multifractal spectrum f
(<alpha>) has been estimated for the first time for MHD
turbulence in the solar wind. Its features resemble those obtained
for turbulent fluids and other nonlinear multifractal systems. The
generalized dimension Dq can for turbulence in high-speed streams
be fitted well by the functional dependence of the p-model with a
comparatively large parameter p1=0.87, indicating a strongly
intermittent multifractal energy cascade. The experimental value for
Dp/3 used in the scaling exponent s(p) of the velocity
structure function gives an exponent that can describe some of the
observations. The scaling exponent <mu> of the autocorrelation
function of <varepsilon>(t) has also been directly evaluated,
being 0.37. Finally, the mean dissipation rate was determined, which
could be used in solar wind heating models.
Title: An extended structure-function model and its application to
the analysis of solar wind intermittency properties
Authors: Tu, Ac. -Y.; Marsch, E.; Rosenbauer, H.
Bibcode: 1996AnGeo..14..270T
Altcode: 1996AnG....14..270T
An extended structure-function model is developed by including the new
effect in the p-model of Meneveau and Sreenivasan which shows that the
averaged energy cascade rate changes with scale, a situation which has
been found to prevail in non-fully-developed turbulence in the inner
solar wind. This model is useful for the small-scale fluctuations in
the inner heliosphere, where the turbulence is not fully developed and
cannot be explained quantitatively by any of the previous intermittency
turbulence models. With two model parameters, the intrinsic index
of the energy spectrum <alpha>, and the fragmentation fraction
P1, the model can fit, for the first time, all the observed scaling
exponents of the structure functions, which are calculated for time
lags ranging from 81 s to 0.7 h from the Helios solar wind data. From
the cases we studied we cannot establish for P1 either a clear radial
evolution trend, or a solar-wind-speed or stream-structure dependence
or a systematic anisotropy for both the flow velocity and magnetic
field component fluctuations. Generally, P1 has values between 0.7
and 0.8. However, in some cases in low-speed wind P1 has somewhat
higher values for the magnetic components, especially for the radial
component. In high-speed wind, the inferred intrinsic spectral indices
(<alpha>) of the velocity and magnetic field components are
about equal, while the experimental spectral indices derived from the
observed power spectra differ. The magnetic index is somewhat larger
than the index of the velocity spectrum. For magnetic fluctuations in
both high- and low-speed winds, the intrinsic exponent <alpha>
has values which are near 1.5, while the observed spectral exponent
has much higher values. In the solar wind with considerable density
fluctuations near the interplanetary current sheet near 1 AU, it is
found that P1 has a comparatively high value of 0.89 for
Vx . The impact of these results on the understanding
of the nature of solar wind fluctuations is discussed, and the
limitations in using structure functions to study intermittency are
also described.<!--RID=""--> <!--ID="" Acknowledgements. The
research described in this publication was made possible in part by
Grant JDG100 from the International Science Foundation and Russia
Government. I would like to thank Dr. P. G. Richards and an anonymous
referee for critical reading of the manuscript as reviewers and for
helpful comments. Topical Editor, J.-C. Geŕard thanks P. G. Richards
and J. Kozyra for their help in evaluating this paper.-->
Title: First Steps to a Multi-fluid Model of the Solar Transition
Region
Authors: Peter, H.; Marsch, E.
Bibcode: 1996ApL&C..34...83P
Altcode:
No abstract at ADS
Title: Solar corona diagnostic with solar wind ion charge spectra.
Authors: Aellig, M. R.; Gruenwaldt, H.; Hefti, S.; Wurz, P.; Bochsler,
P.; Axford, W. I.; Balsiger, H.; Buergi, A.; Coplan, M. A.; Galvin,
A. B.; Geiss, J.; Gliem, F.; Gloeckler, G.; Hilchenbach, M.; Hovestadt,
D.; Hsieh, K. C.; Ipavich, F. M.; Judge, D. L.; Kallenbach, R.;
Klecker, B.; Lee, M. A.; Livi, S.; Managadze, G. G.; Marsch, E.;
Moebius, E.; Neugebauer, M.; Ogawa, H. S.; Reiche, K. U.; Scholer,
M.; Verigin, M. I.; Wilken, B.
Bibcode: 1996AcHPh..69...49A
Altcode:
Matter flowing away from the solar surface becomes highly ionized in the
corona (T ≍ 2·106K) by collisions with electrons. Due to
the decreasing electron density with increasing distance from the solar
surface, the charge state distributions freeze and remain unaltered
throughout the interplanetary medium. This is why charge spectra
measured at 1 AU are a valuable diagnostic tool for temperature and
density variations in the inner solar corona. Preliminary results
of ion charge spectra obtained from the SOHO CELIAS CTOF mass
spectrometer indicate a patchy structure of the corona at scales of
≍104km.
Title: Payload requirements for the Solar Probe
Authors: Marsch, E.; Roux, A.
Bibcode: 1996AdSpR..17c..31M
Altcode: 1996AdSpR..17...31M
The scientific goals and objectives for a Solar Probe determine the
requirements for a model payload and concepts for the instruments. To
accomplish the main aim, which is to make in-situ measurements of
particles and fields in the solar corona and wind, the strawman
payload must include a magnetometer and plasma wave instrument, fast
three-dimensional plasma anlyzers to measure ions and electrons,
and detectors for suprathermal and solar energetic particles. In
addition a light-weight dust detector is required to probe the dust
environment in the outer corona. Tight constraints are to be placed
on all instruments concerning mass, power and telemetry in order to
keep the expected costs and complexity to a bare minimum. This will
require further developments of existing instruments or innovative
concepts, allowing the objectives to be met with a payload of only
20 to 25 kg. All instruments have to be acommodated on a three-axis
stabilized probe and should be capable of measuring particle fluxes
that might vary by many orders of magnitude. The plasma experiments
are central to the mission and very demanding because of the wide
dynamic ranges required for the spatial, temporal, and particle-species
energy, mass and charge state measurements. Furthermore, ion velocity
distributions are expected to range from subsonic to supersonic in the
Sun's frame of reference and are to be measured from a spacecraft with
speed of about 300 km/s near perihelion at 4 R_solar. Also shapes and
heat flux tails of the distributions must be resolved, as they carry
information crucial to the determination of coronal heating and solar
wind acceleration mechanisms. The wave experiments must identify the
wave modes and spectral intensities, which are essential for quantifying
the wave effects on particles and their energization.
Title: CELIAS - Charge, Element and Isotope Analysis System for SOHO
Authors: Hovestadt, D.; Hilchenbach, M.; Bürgi, A.; Klecker, B.;
Laeverenz, P.; Scholer, M.; Grünwaldt, H.; Axford, W. I.; Livi, S.;
Marsch, E.; Wilken, B.; Winterhoff, H. P.; Ipavich, F. M.; Bedini, P.;
Coplan, M. A.; Galvin, A. B.; Gloeckler, G.; Bochsler, P.; Balsiger,
H.; Fischer, J.; Geiss, J.; Kallenbach, R.; Wurz, P.; Reiche, K. -U.;
Gliem, F.; Judge, D. L.; Ogawa, H. S.; Hsieh, K. C.; Möbius, E.;
Lee, M. A.; Managadze, G. G.; Verigin, M. I.; Neugebauer, M.
Bibcode: 1995SoPh..162..441H
Altcode:
The CELIAS experiment on SOHO is designed to measure the mass, ionic
charge and energy of the low and high speed solar wind, of suprathermal
ions, and of low energy flare particles. Through analysis of the
elemental and isotopic abundances, the ionic charge state, and the
velocity distributions of ions originating in the solar atmosphere,
the investigation focuses on the plasma processes on various temporal
and spatial scales in the solar chromosphere, transition zone,
and corona. CELIAS includes 3 mass- and charge-discriminating
sensors based on the time-of-flight technique: CTOF for the
elemental, charge and velocity distribution of the solar wind,
MTOF for the elemental and isotopic composition of the solar wind,
and STOF for the mass, charge and energy distribution of suprathermal
ions. The instrument will provide detailed in situ diagnostics of the
solar wind and of accelerated particles, which will complement the
optical and spectroscopic investigations of the solar atmosphere on
SOHO. CELIAS also contains a Solar Extreme Ultraviolet Monitor, SEM,
which continously measures the EUV flux in a wide band of 17 - 70 nm,
and a narrow band around the 30.4 nm He II line.
Title: SUMER - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Marsch, E.; Schühle, U.; Lemaire,
P.; Gabriel, A.; Vial, J. -C.; Grewing, M.; Huber, M. C. E.; Jordan,
S. D.; Poland, A. I.; Thomas, R. J.; Kühne, M.; Timothy, J. G.;
Hassler, D. M.; Siegmund, O. H. W.
Bibcode: 1995SoPh..162..189W
Altcode:
The instrument SUMER - Solar Ultraviolet Measurements of Emitted
Radiation is designed to investigate structures and associated dynamical
processes occurring in the solar atmosphere, from the chromosphere
through the transition region to the inner corona, over a temperature
range from 104 to 2 × 106K and above. These
observations will permit detailed spectroscopic diagnostics of plasma
densities and temperatures in many solar features, and will support
penetrating studies of underlying physical processes, including plasma
flows, turbulence and wave motions, diffusion transport processes,
events associated with solar magnetic activity, atmospheric heating,
and solar wind acceleration in the inner corona. Specifically, SUMER
will measure profiles and intensities of EUV lines; determine Doppler
shifts and line broadenings with high accuracy; provide stigmatic
images of the Sun in the EUV with high spatial, spectral, and temporal
resolution; and obtain monochromatic maps of the full Sun and the inner
corona or selected areas thereof. SUMER will be flown on the Solar
and Heliospheric Observatory (SOHO), scheduled for launch in November,
1995. This paper has been written to familiarize solar physicists with
SUMER and to demonstrate some command procedures for achieving certain
scientific observations.
Title: Element fractionation by diffusion in the solar chromosphere.
Authors: Marsch, E.; von Steiger, R.; Bochsler, P.
Bibcode: 1995A&A...301..261M
Altcode:
A new mechanism to explain the observed first ionization potential
(FIP) fractionation of coronal and solar wind element abundances
is proposed. By the FIP fractionation, low-FIP (<10eV) elements
are enriched in the solar corona and solar wind relative to the
photosphere. This effect has been located earlier to take place in the
chromosphere, at densities of N =~10^16^-10^18^m^-3^ and a temperature
of T=~10^4^K, where a large fraction of the gas is still neutral. We
discuss a new mechanism for the FIP fractionation in the form of
a stationary diffusion model. It is based on a weakly stratified
chromospheric layer of constant density of the element hydrogen and
constant temperature. This layer is permeated everywhere by ionizing
photons and contains a homogeneous vertical magnetic field. Otherwise,
our model does not invoke any particular geometry or special set up of
the system. It is thus founded solely on robust and well understood
atomic collisional physics. Technically, a boundary value problem
of four coupled differential equations is solved for each chemical
element, i.e. a continuity equation and a momentum equation for both
atoms and singly ionized particles. By splitting the system into a
main gas (hydrogen) and trace gases (16 elements from He to Xe), an
analytical solution for the former can be found. This then serves as
a background for the numerical integration of each trace gas system,
for which we consider collisions between its atoms and ions with the
main gas, i.e. protons and hydrogen. Boundary conditions are such that
the gas is neutral at the bottom of the slab and fully ionized at its
top, as a result of irradiation by the solar coronal EUV. Starting
with a uniform density at the bottom of the layer, we find that, after
a few hydrogen diffusion lengths, each minor species asymptotically
approaches a constant density. The ratios of these density values to
some reference trace element reproduce the observed FIP fractionation
pattern of heavy elements remarkably well. The step between low-FIP
and high-FIP element abundances is about a factor of 5, and He is
somewhat depleted relative to the high-FIP elements, in agreement
with the observations. The model fractionation pattern proves to be
remarkably stable against changes in the external parameters (within
reasonable chromospheric values), particularly N and T.
Title: Radial gradients of ion densities and temperatures derived
from SWICS/Ulysses observations
Authors: Liu, S.; Marsch, E.; Livi, S.; Woch, J.; Wilken, B.; von
Steiger, R.; Gloeckler, G.
Bibcode: 1995GeoRL..22.2445L
Altcode:
Mean density and temperature gradients of solar wind protons and α
particles are derived from SWICS/Ulysses observations between 1.2
and 5.4 AU in the ecliptic plane during declining solar activity. All
parameters are sorted in solar wind speed classes. The radial gradients
show a similar behavior for both ion species. In the slow solar wind
protons as well as α particles are found to expand adiabatically
all the way out to many AUs, while in the fast wind ions evolve
non-adiabatically and are heated by interplanetary sources. The
α particle to proton temperature and density ratios are also
determined. They do not show any clear radial dependence.
Title: Analysis of MHD Turbulence: Spectra of Ideal Invariants,
Structure Functions and Intermittency Scalings
Authors: Marsch, E.
Bibcode: 1995ESASP.371..107M
Altcode: 1995clus.work..107M
No abstract at ADS
Title: Book-Received - MHD Structures Waves and Turbulence in the
Solar Wind - Observations and Theories
Authors: Tu, C. Y.; Marsch, E.
Bibcode: 1995Sci...269.1124T
Altcode:
No abstract at ADS
Title: Comment on ``Evolution of energy-containing turbulent eddies
in the solar wind'' by W. H. Matthaeus, S. Oughton, D. H. Pontius,
Jr., and Y. Zhou
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1995JGR...10012323T
Altcode:
No abstract at ADS
Title: Magnetohydrodynamic Structures Waves and Turbulence in the
Solar Wind - Observations and Theories
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1995SSRv...73....1T
Altcode:
A comprehensive overview is presented of recent observational and
theoretical results on solar wind structures and fluctuations and
magnetohydrodynamic waves and turbulence, with preference given
to phenomena in the inner heliosphere. Emphasis is placed on the
progress made in the past decade in the understanding of the nature
and origin of especially small-scale, compressible and incompressible
fluctuations. Turbulence models to describe the spatial transport and
spectral transfer of the fluctuations in the inner heliosphere are
discussed, and results from direct numerical simulations are dealt
with. Intermittency of solar wind fluctuations and their statistical
distributions are briefly investigated. Studies of the heating and
acceleration effects of the turbulence on the background wind are
critically surveyed. Finally, open questions concerning the origin,
nature and evolution of the fluctuations are listed, and possible
avenues and perspectives for future research are outlined.
Title: Radial gradients of ion densities and temperatures observed
by SWICS/Ulysses
Authors: Liu, S.; Marsch, E.; Livi, S.; Woch, J.; Wilken, B.;
Gloeckler, G.; Geiss, J.
Bibcode: 1995sowi.conf...96L
Altcode:
Mean density and temperature gradients of solar wind protons
and alpha-particles between 1 and 5.4 AU are established from
SWICS/Ulysses observations. All parameters are classified in speed
intervals. au order scheme giving us a natural extension of the Helios
observations. which were usually classified according to speed of the
wind. The radial gradients show a similar behaviour of both particle
species, while the particles radially propagate and thereby cool off in
the heliosphere. The slow solar wind is found, for protons as well as
a particles. to expand adiabatically all the way out to 5.4 AU, while
the fast wind evolves non-adiabatically and is heated by interplanetary
sources. It, seems that the heating rate of the a-particles is larger
than the heating rate of the protons. The ion temperature ratio
and density ratio are determined. They do not indicate any radial
dependence. The temperature ratio Talpha/Tp is
on average about 4. It has a maximum of 4.5 in the velocity interval
where 400 km/s is less than vp is less than 500 km/s,
while in slow wind with vp is less than 400 km/s it has a
minimum value of 37. and for fast wind with vp is greater
than 500 km/s it is 3.9. The density gradients shows compression
effects resulting from fast wind overtaking the slow wind.
Title: Non-gyrotropic proton and alpha-particle velocity distributions
in the solar wind: TAUS observations and stability analysis
Authors: Astudillo, H. F.; Marsch, E.; Livi, S.; Rosenbauer, H.
Bibcode: 1995sowi.conf...74A
Altcode:
Ion velocity distribution functions have been measured with
high time resolution by the TAUS plasma instrument on the PHOBOS
mission to Mars in 1989. The unambiguous separation of protons and
alpha-particles by TAUS enabled us to study the nonthermal features
of their distributions separately and to analyze the stability of the
distributions against excitation of waves in the cyclotron-frequency
domain. Typical nonthermal features include temperature anisotropies,
with Tperpendicular larger than Tparallel,
and ion beam populations drifting along the local magnetic field
direction. Also, distinctly non-gyrotropic alpha-particle velocity
distributions were sometimes found. Non-gyrotropy strongly changes the
wave dispersion and gives rise to new growing modes, related to the
coupling of the standard wave modes existing in gyrotropic plasma. It
is found that for the measured non-gyrotropic ion distributions the
right-hand polarized wave can also be excited by a temperature anistropy
instead of the usual beam drift.
Title: An extended structure-function model and its application to
the analysis of solar wind intermittency
Authors: Tu, C. -Y.; Marsch, E.; Rosenbauer, H.
Bibcode: 1995sowi.conf...81T
Altcode:
An extended structure-function model is developed by including the new
effect in the p-model of Meneveau and Sreenivasan (1987a), i.e., that
the averaged energy cascade rate changes with scale, a situation which
has been found to prevail in non-fully-developed turbulence in the inner
solar wind. This model is useful for the small-scale fluctuations in
the inner heliosphere, where the turbulence is not fully developed and
cannot be explained quantitatively by any of the previous intermittency
turbulence models. With two model parameters, the intrinsic index of
the energy spectrum, alpha and the fragmentation fraction p, the model
can fit, for the first time, all the observed scaling exponents of the
structure functions, which are calculated for time lags ranging from 81
seconds to 0.7 hours from the Helios solar wind data. From the cases we
studied we can establish for p neither a clear radial evolution trend,
nor a solar-wind-speed, or stream-structure dependence, or a systematic
anisotropy for both the flow velocity and magnetic field component
fluctuations. Generally, p has values between 0. 7 and 0.8. However,
in some cases in low-speed wind p has somewhat higher values for the
magnetic components, especially for the radial component. In high-speed
wind, the inferred intrinsic spectral indices (alpha) of the velocity
and magnetic field components are about equal, while the experimental
spectral indices derived from the observed power spectra differ. The
magnetic index is somewhat larger than the index of the velocity
spectrum. For magnetic fluctuations in both high- and low-speed winds,
the intrinsic exponent alpha has values which are near 1.5, while the
observed spectral exponent has much higher values.
Title: Multifractal scaling of the kinetic energy flux in solar
wind turbulence
Authors: Marsch, E.; Rosenbauer, H.; Tu, C. -Y.
Bibcode: 1995sowi.conf...81M
Altcode:
The geometrical and scaling properties of the energy flux of the
turbulent kinetic energy in the solar wind have been studied. By
present experimental technology in solar wind measurements, we cannot
directly measure the real volumetric dissipation rate, epsilon(t), but
are constrained to represent it by surrogating the energy flux near the
dissipation range at the proton gyro scales. There is evidence for the
multifractal nature of the so defined dissipation field epsilon(t),
a result derived from the scaling exponents of its statistical
q-th order moments. The related generalized dimension D(q) has been
determined and reveals that the dissipation field has a multifractal
structure. which is not compatible with a scale-invariant cascade. The
associated multifractal spectrum f(alpha) has been estimated for
the first time for MHD turbulence in the solar wind. Its features
resemble those obtained for turbulent fluids and other nonlinear
multifractal systems. The generalized dimension D(q) can, for turbulence
in high-speed streams, be fitted well by the functional dependence of
the p-model with a comparatively large parameter, p = 0.87. indicating
a strongly intermittent multifractal energy cascade. The experimental
value for D(p)/3, if used in the scaling exponent s(p) of the velocity
structure function, gives an exponent that can describe some of the
observations. The scaling exponent mu of the auto correlation function
of epsilon(t) has also been directly evaluated. It has the value of
0.37. Finally. the mean dissipation rate was determined, which could
be used in solar wind heating models.
Title: The microscopic state of the solar wind: Links between
composition, velocity distributions, waves and turbulence
Authors: Marsch, E.
Bibcode: 1995sowi.conf...35M
Altcode:
An overview is given of the microscopic state of the solar wind
with emphasis on recent Ulysses high-latitude observations and
previous Helios in-ecliptic observations. The possible links between
composition, ionization state. velocity distribution functions of
electrons, protons and heavy ions. kinetic plasma waves and MHD-scale
turbulence are elaborated. Emphasis is placed on a connection of
interplanetary kinetic-scale phenomena with their generating microscopic
processes in the corona. The fast streams seem to consist of mesoscale
pressure-balanced plasma filaments and magnetic flux tubes, reminiscent
of the supergranular-size structures building the open corona, from
which copious Alfven waves emanate. The wind from the magnetically
structured and active corona shows developed compressive turbulence and
considerable abundance and ionization state variations. Some modelling
attempts to explain the observed element fractionation are briefly
reviewed. The causes of the nonthermal particle features. such as
proton-ion differential streaming, ion beams. temperature anisotropies,
and skewed distributions associated with collisionless heat conduction,
are ultimately to be searched in the fact, that the corona is never
quiescent but fundamentally variable in space and time. Consequently,
the radial evolution of the internal state of the wind resembles at
all latitudes a complicated relaxation process, in the course of which
the free (in comparison with LTE conditions) particle kinetic energy
is converted into plasma waves and MHD turbulence on a wide range
of scales. This leads to intermittent wave-particle interactions and
unsteady anomalous transport, mixed with the weak effects of the rare
Coulomb collisions. Spherical expansion and large-scale inhomogeneity
forces the wind to attain microscopically a complex internal state of
dynamic statistical equilibrium.
Title: Spatial transport and spectral transfer of solar wind
turbulence composed of Alfven waves and convective structures 1:
The theoretical model
Authors: Schmidt, J. M.; Marsch, E.
Bibcode: 1995AnGeo..13..459S
Altcode: 1995AnG....13..459S
In this paper we give a survey of detailed algebraic developments of
a solar wind turbulence model. The numerical solution of the coupled
system of spectral transfer equations for turbulence composed of
Alfvén waves and convective structures or two-dimensional turbulence
is prepared. The underlying theory of spectral transfer equations
was established by several authors in the early 1990s. The related
numerical turbulence model which is elaborated in detail in this paper
is based on a rotationally symmetric solar wind model for the background
magnetic and flow velocity fields with the full geometry of Parker's
spiral which has to be inserted into the transfer equations. Various
sources and sinks for turbulent energy are included and appropriately
modelled analytically. Spherical expansion terms related to radial
gradients of the background velocity fields are considered as far
as possible within a rotational symmetric solar wind model, which
excludes vorticity effects. Furthermore, nonlinear interaction terms
are considered, justified by phenomenological arguments and evaluated by
dimensional analysis. Moreover, parametric conversion terms for Alfvén
waves and wave-structure interactions are modelled and a generalized
spectral flux function for the residual energy eR is introduced. In
addition, we compensate the spectra for WKB trends and f -5/3-slopes
in order to prepare a convenient form of the equations for numerical
treatment. The modelling of source and sink terms includes a special
analytical treatment for correlation tensors. This first part presents
a summary of the main ideas and the special approximations used for all
these terms, together with details on the basic steps of the algebraic
calculations. The description of the numerical scheme and a survey
of the numerical results of our model, as well as a discussion of the
main physical results are contained in a companion paper.
Title: The Charge, Element, and Isotope Analysis System CELIAS on SOHO
Authors: Hovestadt, D.; Bochsler, P.; Grünwaldt, H.; Gliem, F.;
Hilchenbach, M.; Ipavich, F. M.; Judge, D. L.; Axford, W. I.; Balsiger,
H.; Bürgi, A.; Coplan, M.; Galvin, A. B.; Geiss, J.; Gloeckler,
G.; Hsieh, K. C.; Kallenbach, R.; Klecker, B.; Lee, M. A.; Livi, S.;
Managadze, G. G.; Marsch, E.; Möbius, E.; Neugebauer, M.; Reiche,
K. -U.; Scholer, M.; Verigin, M. I.; Wilken, D.; Wurz, P.
Bibcode: 1995LNP...444..271H
Altcode: 1995cmer.conf..271H
No abstract at ADS
Title: Linear mode analysis in multi-ion plasmas.
Authors: Hackenberg, P.; Mann, G.; Marsch, E.
Bibcode: 1995AGAb...11..315H
Altcode:
No abstract at ADS
Title: MHD structures, waves and turbulence in the solar wind:
observations and theories
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1995mswt.book.....T
Altcode:
No abstract at ADS
Title: MHD structures, waves and turbulence in the solar wind :
observations and theories
Authors: Tu, C. -Y.; Marsch, Eckart
Bibcode: 1995mhds.book.....T
Altcode:
No abstract at ADS
Title: Erratum: ``On the nature of compressive fluctuations in the
solar wind'' [Journal of Geophysical Research, 99, 21481-21510 (1994)]
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1994JGR....9923525T
Altcode:
No abstract at ADS
Title: Non-Gaussian probability distributions of solar wind
fluctuations
Authors: Marsch, E.; Tu, C. Y.
Bibcode: 1994AnGeo..12.1127M
Altcode:
The probability distributions of field differences
<Delta>x(<tau>)=x(t+<tau>)-x(t), where the variable
x(t) may denote any solar wind scalar field or vector field component
at time t, have been calculated from time series of Helios data
obtained in 1976 at heliocentric distances near 0.3 AU. It is found
that for comparatively long time lag <tau>, ranging from a few
hours to 1 day, the differences are normally distributed according
to a Gaussian. For shorter time lags, of less than ten minutes,
significant changes in shape are observed. The distributions are often
spikier and narrower than the equivalent Gaussian distribution with the
same standard deviation, and they are enhanced for large, reduced for
intermediate and enhanced for very small values of <Delta>x. This
result is in accordance with fluid observations and numerical
simulations. Hence statistical properties are dominated at small
scale <tau> by large fluctuation amplitudes that are sparsely
distributed, which is direct evidence for spatial intermittency of the
fluctuations. This is in agreement with results from earlier analyses
of the structure functions of <Delta>x. The non-Gaussian features
are differently developed for the various types of fluctuations. The
relevance of these observations to the interpretation and understanding
of the nature of solar wind magnetohydrodynamic (MHD) turbulence is
pointed out, and contact is made with existing theoretical concepts
of intermittency in fluid turbulence.
Title: On the nature of compressive fluctuations in the solar wind
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1994JGR....9921481T
Altcode:
A statistical analysis of the amplitudes of the thermal pressure
and total pressure of the solar wind and of several related cross
correlations between different compressive parameters has been
performed with the plamsa and magnetic field data obtained by Helios 1
and 2 in their primary missions. The statistical analysis is based on
small-band averages of the relevant spectra over the frequency range
(2-5) x 10-4 Hz, corresponding to hourly timescales. With
decreasing ratio between the fluctuation amplitudes of the total
pressure and the density, we found a systematical decrease of
the correlation coefficient between density and total pressure
and of the correlation coefficient between density and magnetic
field magnitide. Decreases of the correlation coefficients between
temperature and density and between thermal and magnetic pressure
are also found with decreasing ratio of the normalized amplitudes of
the fluctuations of the thermal pressure and the temperature. Most
of these results can be explained quantitatively by a model based on
a superposition of small-amplitude perpendicular fast magnetosonic
waves and small-amplitude pressure-balanced structures. We have found
a class of data points which seem to represent fluctuations dominated
by fast magnetosonic waves.
Title: Diffusive fractionation in the chromosphere
Authors: von Steiger, R.; Marsch, E.
Bibcode: 1994SSRv...70..341V
Altcode:
A new mechanism for the FIP fractionation in the solar wind in the form
of a stationary diffusion model is proposed. It is based on a weakly
stratified chromospheric layer of constant density and temperature,
permeated everywhere by ionizing photons and a homogeneous magnetic
field. Our model does not invoke any particular geometry or special set
up of the system and is founded solely on robust and well understood
atomic collisonal physics. Technically, a boundary value problem
of four coupled differential equations is solved for each chemical
element, i.e. a continuity equation and a momentum equation for both
atoms and singly ionized particles. For the main gas (hydrogen), an
analytical solution can be found. This then serves as a background for
the numerical integration of each trace gas system (several elements
from He to Fe). We find that, after a few hydrogen diffusion lengths,
each minor species asymptotically approaches a constant density. The
ratios of these density values to some reference element reproduce
the observed FIP fractionation pattern remarkably well.
Title: Theoretical models for the solar wind
Authors: Marsch, E.
Bibcode: 1994AdSpR..14d.103M
Altcode: 1994AdSpR..14..103M
Theoretical models for the solar wind are reviewed from the point
of view that a hot corona cannot be simply assumed as a given inner
boundary but rather as part of the overall problem and needs to be
explained in the first place. Models including the transition region
and the heating of the corona radiative and conductive losses are
discussed. The input at the sun of small-scale mechanical energy
and of waves and turbulence in the wind are addressed, as well as
interplanetary constraints placed on the coronal and wind expansion
by in situ measurements. Recent theoretical attempts to explain the
relative constancy of the observed mass flux in the framework of
multifluid models including Coulomb collisions are presented. Whether
or not the coronal temperature inversion can be modeled by exospheric
kinetic models, a currently debated issue, is briefly dealt with. More
exotic concepts of solar wind acceleration by means of plasmoids are
also discussed.
Title: 'SUMER' - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Gabriel, A. H.; Grewing, M.; Huber,
M. C. E.; Jordan, S. D.; Kuhne, M.; Lemaire, P.; Marsch, E.; Poland,
A. I.; Schuhle, U.; Thomas, R. J.; Timothy, J. G.; Vial, J. -C.
Bibcode: 1994scs..conf..619W
Altcode: 1994IAUCo.144..619W
SUMER is designed for the investigations of plasma flow characteristics,
turbulence and wave motions, plasma densities and temperatures,
structures and events associated with solar magnetic activity in the
chromosphere, the transition zone and the corona. The spatial and
spectral resolution capabilities of the instrument are considered in
some detail, and a new detector concept is introduced.
Title: Elsässer variable analysis of fluctuations in the ion
foreshock and undisturbed solar wind
Authors: Labelle, James; Treumann, Rudolf A.; Marsch, Eckart
Bibcode: 1994JGR....99...65L
Altcode:
MHD fluctuations in the solar wind have been investigated previously
by use of Elsässer variables. In this paper, we present a comparison
of the spectra of Elsässer variables in the undisturbed solar wind
at 1 AU and in the ion foreshock in the front of the Earth. Both
observations take place under relatively strong solar wind flow speed
conditions (~600 kms-1). In the undisturbed solar wind we
find that outward propagating Alfvén waves dominate, as reported by
other observers. In the ion foreshock the situation is more complex,
with neither outward nor inward propagation dominating over the entire
range investigated (1-10 mHz). Measurements of the Poynting vectors
associated with the fluctuations are consistent with the Elsässer
variable analysis. These results generally support interpretations of
the Elsässer variables which have been made based strictly on solar
wind data and provide additional insight into the nature of the ion
foreshock turbulence.
Title: Modeling results on spatial transport and spectral transfer
of solar wind Alfvénic turbulence
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 1993JGR....9821045M
Altcode:
In this paper a set of time stationary transport equations for
incompressible MHD fluctuations in the solar wind is derived from
previous general transport equations (Marsch and Tu, 1989; Zhou and
Matthaeus, 1990a), which have been found to give solutions with fast
time variations. The present derivation is based on the assumption
that the fluctuations are composed of small-scale convected structures
and short-wavelength Alfvén waves. The different contributions of
these two types of fluctuations to the total correlation functions
can be evaluated by means of temporal and spatial averaging of the
correlations over the small scales. Two linearly decoupled sets
of transport equations then result, which separately describe the
spatial evolution of the turbulent energies and cross correlations
of the structures and waves. For the propagating Alfvén waves a
multiple-scale analysis yields two WKB-type transfer equations for the
autocorrelation functions expressed in terms of Elsässer velocity
fields. For the structures a third additional equation is derived,
which determines the evolution of the residual energy, that is, the
difference between the kinetic and magnetic energy of the convected
fluctuations. The final set of equations is slowly varying in time and
thus satisfactory from the point of view of conventional statistical
turbulence theory. The nonlinearities are modeled by cascading flux
functions, which are determined by dimensional analysis following
the Kolmogorov phenomenology and based on the time stationarity
assumption. The new equations are consistent with this assumption
and equivalent to the equations obtained by Tu and Marsch (1993). The
present derivation aims at clarifying the relations between the general
and the time stationary set of transport equations. Consequently,
stationary equations governing the spatial and spectral evolution of
the power frequency spectra e+/- for Alfvénic fluctuations,
described in terms of the two Elsässer variables, are established and
integrated numerically. As a first step to study the effects of the
nonlinear terms, we neglect the coupling terms related to convected
structures. This approximation may apply to the fluctuations observed
in fast streams near 0.3 AU. We integrate the resulting two coupled
transport equations in frequency-distance-space by employing a new
technique based on the method of characteristics. Interplanetary
parametric decay instabilities are also included in the model. The
numerical results obtained show that (1) The cascade process which
is based on local nonlinear interactions in frequency space cannot
transport any initial value of the normalized cross-helicity from
the low-frequency boundary to the higher-frequency range. Cascade
processes alone invariably result in dynamic alignment and cause
the spectra of e+ as well as e- to steepen at
higher frequencies. (2) However, a parametric-decay-like source term
can enforce the normalized cross-helicity to decrease with increasing
heliocentric distance and can also produce and sustain a flatter part
in the spectrum of e- in the high-frequency range. These
results are in qualitative agreement with the observations. Research
topics which should be dealt with in the future to complete the present
preliminary numerical work are also pointed out.
Title: Book-Review - Physics of the Inner Heliosphere - V.2 -
Particles Waves and Turbulence
Authors: Schwenn, R.; Marsch, E.; Schwartz, S. J.
Bibcode: 1993SSRv...64..371S
Altcode:
No abstract at ADS
Title: Correlations between the fluctuations of pressure, density,
temperature and magnetic field in the solar wind.
Authors: Marsch, E.; Tu, C. Y.
Bibcode: 1993AnGeo..11..659M
Altcode: 1993AnG....11..659M
Compressive fluctuations and the pressure balance in the solar wind are
investigated with Helios data obtained in 1975 - 1976 from measurements
in the inner heliosphere between 0.3 and 1.0 AU. Broadband correlation
spectra and hourly correlation coefficients for any pair of solar wind
parameters like speed, density, temperature, magnetic field magnitude,
thermal and magnetic pressure, and the total pressure of the plasma
are calculated and analysed. The authors find that the nature and
intensity of the compressive fluctuations strongly depend on the flow
speed and systematically vary with the stream structure. A general
tendency is observed for the thermal and magnetic pressures to be
anti-correlated. Clear positive correlations between the solar wind
(proton) temperature and speed are found in the higher-frequency domain
for most of the cases considered. Significant positive correlations
between the relative fluctuations of the total pressure and the density
are obtained. The statistical studies carried out suggest the notion
that the compressive fluctuations are a complex superposition of
magnetoacoustic fluctuations and pressure-balanced structures, which
may be created by interplanetary stream interactions or be originally
related to plasma flow tubes of coronal origin.
Title: SUMER - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Marsch, E.; Schuehle, U.; Gabriel,
A. H.; Lemaire, P.; Vial, J. -C.; Grewing, M.; Huber, M. C. E.;
Jordan, S. D.; Poland, A. I.; Thomas, R. J.; Kuehne, M.; Timothy, J. G.
Bibcode: 1993BAAS...25.1192W
Altcode:
No abstract at ADS
Title: Book-Review - Solar Wind Seven
Authors: Marsch, E.; Schwenn, R.; Woan, G.
Bibcode: 1993Obs...113..151M
Altcode:
No abstract at ADS
Title: Book-Review - Physics of the Inner Heliosphere - Part Two -
Particles Waves and Turbulence
Authors: Schwenn, R.; Marsch, E.; Jackson, B. V.
Bibcode: 1993SoPh..145R.405S
Altcode:
No abstract at ADS
Title: Book-Review - Physics of the Inner Heliosphere - Part One -
Largescale Phenomena
Authors: Schwenn, R.; Marsch, E.; Jackson, B. V.
Bibcode: 1993SoPh..145Q.405S
Altcode:
No abstract at ADS
Title: Wave and stability properties of multi-ion plasmas with
applications to winds and flows
Authors: McKenzie, J. F.; Marsch, E.; Baumgaertel, K.; Sauer, K.
Bibcode: 1993AnGeo..11..341M
Altcode:
In many space plasma phenomena heavy ions are present in abundances
which are not negligible relative to protons so that the various
components of the plasma are mutually coupled through the Lorentz
force and the quasi-charge neutrality constraint. Some of the novel and
interesting effects which this coupling gives rise to are discussed here
within the context of wave and stability properties of the system. In
particular we show how differential streaming between the protons
and a heavier species (such as alpha particles in the solar wind) can
give rise to low frequency compressional instabilities. The effects of
Coulomb collisions, finite Debye length and kinetic effects are also
discussed and it is emphasized that collisionless Landau damping can
quench such instabilities except when the ions are sufficiently cold
relative to the electrons. In connection with steady flows (e.g. solar
and polar winds) it is shown how the idea of "critical points" must
be generalized and interpreted within the framework of the stationary
waves of the system ineluding differential streaming, and how these
"points" are intimately connected with nonlinear mutual regulation of
the ion fluxes.
Title: Structure functions and intermittency of velocity fluctuations
in the inner solar wind.
Authors: Marsch, E.; Liu, S.
Bibcode: 1993AnGeo..11..227M
Altcode: 1993AnG....11..227M
The authors provide evidence for the intermittent nature of the
fluctuations of the flow velocity and Alfvén velocity in the
inner solar wind between 0.3 and 1.0 AU. They analyse the p-th
order structure functions in the time domain between 40.5 seconds
(instrumental resolution period) and 24 hours, and investigate their
scaling properties in the Alvénic range from fractions of minutes to
several hours. Generally, the fast and slow wind regimes have to be
discriminated, because the scaling features of the velocity differences
with time lag τ vary systematically with the wind speed. Radial trends
are established by comparison of Helios data obtained near 0.3 AU and
1.0 AU.
Title: Books-Received - Solar Wind Seven
Authors: Marsch, E.; Schwenn, R.
Bibcode: 1993Sci...259.1634M
Altcode:
No abstract at ADS
Title: A model of solar wind fluctuations with two components:
Alfvén waves and convective structures
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1993JGR....98.1257T
Altcode:
A two-component incompressible fluctuations model is presented to
explain the radial evolution of the solar wind fluctuations. The basic
idea is to consider the small-scale fluctuations in the solar wind as
being composed of Alfvén waves and convective structures. The major
Alfvén waves are believed to be created near the coronal base and
to propagate outward along the magnetic field lines. The convective
structures are defined as the small-scale variations perpendicular to
the local magnetic field direction. They are either quasi-static or
turbulent and slowly evolving in the plasma frame of reference. The
small-scale perpendicular variations are connected, in the parallel
direction, with large-scale magnetic field variations, which are
convected by the solar wind as quasi-static structures during the wind
expansion time. The decomposition of the original fluctuations
can be done by using special space and time averages, which are defined
by space averaging along the directions parallel and perpendicular to
the local magnetic field vector and by time averaging in the plasma
frame of reference. The equations of motion of the fluctuations and
of the correlation functions for both Alfvén waves and convective
structures have been derived from the one-fluid MHD equations. A
combination of the correlation functions of these two components is
then used for a comparison with observational results. The influence
of the angle between the sampling direction and the magnetic field
vector on the final results has also been considered. As a first step
to apply these equations, a simple model has been suggested that is
based on the assumption that the fluctuations are only composed of
outward propagating Alfvén waves and static magnetic structures. For
comparison with the observations, new statistical results from data
obtained by Helios 1 during days 1-95, 1975, and Helios 2 during days
19-109, 1976, are presented. The numerical solutions are shown
to describe well the basic evolution trend of the fluctuation energy,
the normalized cross helicity, and the Alfvén ratio. It is also shown
that the basic physical process of the evolution of the convective
structures is the convection of the fluctuating velocity vortex lines
and the magnetic field lines by the expanding solar wind.
Title: MHD Turbulence in the Solar Wind and Interplanetary Dynamo
Effects
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 1993IAUS..157...51M
Altcode:
No abstract at ADS
Title: SUMER: temperatures, densities, and velocities in the outer
solar atmosphere.
Authors: Lemaire, P.; Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel,
A. H.; Grewing, M.; Huber, M. C. E.; Jordan, S. D.; Kuehne, M.;
Marsch, E.; Poland, A. I.; Richter, A. K.; Thomas, R. J.; Timothy,
J. G.; Vial, J. C.
Bibcode: 1992ESASP.348...13L
Altcode: 1992cscl.work...13L
The SUMER instrumentation, that will be mounted on the SOHO spacecraft,
is in development under MPAE leadership. It has some capability
to improve the solar angular resolution and the spectral resolution
already obtained in the far UV to the extreme UV, corresponding to the
temperature range between 104 and a few 106K. The
authors give some insights into the SUMER spectrometer that is developed
to study the dynamics and to infer temperatures and densities of the
low corona and the chromosphere-corona transition zone in using the
50 - 160 nm wavelength range. First, they recall the SUMER scientific
goals and the technics used. Then, after a brief description of the
instrumentation the expected performances are described. The way the
observations can be conducted is emphasized and it is shown how SUMER
is operated in coordination with other SOHO instrumentations and in
cooperation with ground-based observations.
Title: Spectra and structure functions of temperature fluctuations
in the inner solar wind.
Authors: Marsch, E.; Liu, S.; Rosenbauer, H.; Tu, C. Y.
Bibcode: 1992ESASP.346..315M
Altcode: 1992ssts.rept..315M
Proton temperature measurements from the Helios mission have been
analysed in order to derive spectral and scaling characteristics of
temperature fluctuations in the inner heliosphere near 0.3 AU. Special
attention is paid to their correlation with the large-scale stream
structure. Different scaling properties of the fluctuations are obtained
in fast and slow wind. The temperature spectra seem to indicate fully
developed Gaussian turbulence. However, the p-th order structure
functions of the temperature fluctuations considerably deviate from
Kolmogorov scaling. They indicate intermittency and variable scaling
behaviour of the temperature diffences as a function of the time lag
between subsequent measurements.
Title: CELIAS: charge, element and isotope analysis system for the
SOHO mission.
Authors: Hovestadt, D.; Geiss, J.; Gloeckler, G.; Axford, W. I.;
Balsiger, H.; Bochsler, P.; Bürgi, A.; Canfield, R.; Coplan, M.;
Dinse, H.; Galvin, A. B.; Gliem, F.; Gringauz, K. I.; Grünwaldt, H.;
Hilchenbach, M.; Hsieh, K. C.; Ipavich, F. M.; Judge, D.; Klecker,
B.; Kühne, M.; Lee, M. A.; Livi, S.; Managadze, G. G.; Marsch, E.;
Neugebauer, M.; Möbius, E.; Reiche, K. V.; Scholer, M.; Wilken, B.
Bibcode: 1992ESASP.346..343H
Altcode: 1992ssts.rept..343H
The status and further development as well as first calibration of the
CELIAS experiment on SOHO is presented. CELIAS is designed to measure
the mass, ionic charge, and energy of low and high speed solar wind of
suprathermal ions and of low energy flare particles. Through analysis
of the elemental and isotopic abundances (the ionic charge state and
velocity distributions of ions originating on the solar atmosphere),
the investigation focuses on studying the plasma processes in various
temporal and spatial scales in the solar chromosphere, transition zone,
and corona. Additionally, the CELIAS experiment includes the Solar EUV
Monitor (SEM). This unit, which consists of an EUV transmission grating
spectrometer and three isolated silicon photodiodes as detectors,
is described. The three mass and charge discriminating sensors based
on the time of flight technique are also described.
Title: "SUMER" - Solar Ultraviolet Measurements of Emitted Radiation.
Authors: Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel, A. H.;
Grewing, M.; Huber, M. C. E.; Jordan, S. D.; Kühne, M.; Lemaire, P.;
Marsch, E.; Poland, A. I.; Richter, A. K.; Thomas, R. J.; Timothy,
J. G.; Vial, J. C.
Bibcode: 1992eocm.rept..225W
Altcode:
The experiment Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) is designed for the investigations of plasma flow
characteristics, turbulence and wave motions, plasma densities
and temperatures, structures and events associated with solar
magnetic activity in the chromosphere, the transition zone and the
corona. Specifically, SUMER will measure profiles and intensities
of extreme ultraviolet (EUV) lines emitted in the solar atmosphere
ranging from the upper chromosphere to the lower corona; determine line
broadenings, spectral positions and Doppler shifts with high accuracy;
provide stigmatic images of selected areas of the Sun in the EUV with
high spatial, temporal and spectral resolution and obtain full images of
the Sun and the inner corona in selectable EUV lines, corresponding to a
temperature range from 104 to more than 1.8×106K.
Title: Planned observations at high resolution from space.
Authors: Lemaire, P.; Marsch, E.
Bibcode: 1992ESASP.344...15L
Altcode: 1992spai.rept...15L
The next generation of solar space experiments is under
development. SOHO with its set of coronal instruments has some
capability to improve the angular resolution already obtained in
the far UV to the extreme UV, corresponding to the temperature
range between 10 and a few 10K. The authors give some insights
into the two spectrometers SUMER and CDS, and the extreme UV imager
EIT. SUMER is developed to study the dynamics of the low corona and the
chromosphere-corona transition zone in using the 50 - 160 nm wavelength
range. CDS is a spectrometer built to observe the highest part of the
chromosphere-corona transition zone up to the high corona of several
millions of degrees in using the 15 - 80 nm wavelength range. EIT is
a multi-wavelength imager that will provide either full or partial
solar images in upper chromospheric and coronal lines.
Title: Design Rationale of the Solar Ultraviolet Network / Sun
Authors: Dame, L.; Acton, L.; Bruner, M. E.; Connes, P.; Cornwell,
T. J.; Curdt, W.; Foing, B. H.; Hammer, R.; Harrison, R.; Heyvaerts,
J.; Karabin, M.; Marsch, E.; Martic, M.; Mattic, W.; Muller, R.;
Patchett, B.; Roca-Cortes, T.; Rutten, R. J.; Schmidt, W.; Title,
A. M.; Tondello, G.; Vial, J. C.; Visser, H.
Bibcode: 1992ESOC...39..995D
Altcode: 1992hrii.conf..995D
No abstract at ADS
Title: Surface and body waves in solar wind flow tubes
Authors: Mann, G.; Marsch, E.; Roberts, B.
Bibcode: 1992sws..coll..495M
Altcode:
Parker (1963) already assumed that the solar wind might be
fine-structured in form of flow tubes. Such spatial structures can give
rise to surface and body waves with characteristic frequencies. These
waves are studied here by means of the ideal magnetohydrodynamic
equations. The resulting dispersion relations are discussed for
typical parameters of solar wind flow tubes observed by the two HELIOS
probes. These waves might be able to transport photospheric oscillations
into the interplanetary space.
Title: Introduction to kinetic physics, waves and turbulence in the
solar wind
Authors: Marsch, E.
Bibcode: 1992sws..coll..499M
Altcode:
This paper sets the stage for some of the following presentations on
kinetic physics, waves, and turbulence in the solar wind. Firstly,
a summary of some key observations is given, and the nature and
possible origin of the fluctuations are discussed. Emphasis is
placed on the kinetic aspects of the dissipation of turbulence and
the related heating of the protons. Relevant features of the velocity
distributions reflecting the wave-particle interactions are briefly
discussed. Some modern topics of turbulence such as intermittency,
multifractals, self-similar scaling and observations of the structure
function are examined. We address theoretical issues and problems
associated with models based on two-scale energy transfer equations
that have been proposed to describe the spatial and spectral evolution
of MHD turbulence in the inhomogeneous solar wind.
Title: On the possible role of plasma waves in the heating of
chromosphere and corona
Authors: Marsch, E.
Bibcode: 1992sws..coll...65M
Altcode:
The possible importance of kinetic plasma waves at frequencies near
and above the ion gyrofrequencies in the transport of energy through
the chromosphere and corona and the wave energy deposition in these
layers is hardly known and has little been investigated. This paper
intends to give a cursory review of some plasma waves that may perhaps
be relevant for anomalous transport. Some kinetic instabilities that
might arise due to spatial inhomogeneity and associated velocity
space anisotropies are briefly discussed. Atmospheric heating rates
are then estimated on the basis of quasilinear theory and compared
against radiative and conductive losses.
Title: The evolution of MHD turbulence in the solar wind
Authors: Tu, C. Y.; Marsch, E.
Bibcode: 1992sws..coll..549T
Altcode:
The radial evolution of solar-wind fluctuations is presently addressed
by an extended theoretical model which systematically combines the
observed Alfven wave, turbulence, and convective structures. Nonlinear
interactions that occur between inward and outward propagating Alfven
waves, as well as between the 2D turbulence cross-field variations
and between cross-field fluctuations and Alfven waves, render
the fluctuations turbulent in nature. In view of this, empirical
trends in the radial evolution of solar wind turbulence are easily
explained; an increase in the relative quantity of convective magnetic
fluctuations against propagating Alfven waves will lead to a decrease
in cross-helicity and Alfven ratio.
Title: Solar Wind Seven; Proceedings of the 3rd COSPAR Colloquium,
Goslar, Germany, Sept. 16-20, 1991
Authors: Marsch, E.; Schwenn, R.
Bibcode: 1992sws..coll.....M
Altcode:
The present conference discusses topics in coronal heating and solar
wind acceleration, the large-scale structure of the interplanetary
medium, minor ions and cosmic rays in the heliosphere, solar wind
kinetics and turbulence, and heliospheric dynamic phenomena. Attention
is given to the origin of high speed solar wind streams, density and
temperature structure of a coronal hole, a two-fluid model of the solar
wind, solar wind temperature observations in the outer heliosphere,
the solar wind transonic region, and the spectral structure evolution
of interplanetary medium parameters. Also discussed are MHD modeling
of the heliospheric interface, the magnetic field in the heliosheath,
radioastronomy of travelling interplanetary disturbances, Bernstein
waves in the solar wind, multifractals in the solar wind, solar
MHD turbulence, surface and body waves in solar wind flow tubes,
magnetospheric LF nonresonant ion-beam turbulence, nearly incompressible
fluid dynamics, and the interaction of intense magnetic clouds with
ambient solar wind streams.
Title: SUMER - Solar ultraviolet measurements of emitted radiation
Authors: Wilhelm, K.; Axford, W. I.; Gurdt, W.; Marsch, E.; Richter,
A. K.; Grewing, M.; Gabriel, A. H.; Lemaire, P.; Vial, J. -C.; Huber,
M. C. E.
Bibcode: 1992sws..coll..129W
Altcode:
The SUMER (solar ultraviolet measurements of emitted radiation)
experiment is described. It will study flows, turbulent motions, waves,
temperatures and densities of the plasma in the upper atmosphere of
the Sun. Structures and events associated with solar magnetic activity
will be observed on various spatial and temporal scales. This will
contribute to the understanding of coronal heating processes and the
solar wind expansion. The instrument will take images of the Sun in EUV
(extreme ultraviolet) light with high resolution in space, wavelength
and time. The spatial resolution and spectral resolving power of the
instrument are described. Spectral shifts can be determined with
subpixel accuracy. The wavelength range extends from 500 to 1600
angstroms. The integration time can be as short as one second. Line
profiles, shifts and broadenings are studied. Ratios of temperature
and density sensitive EUV emission lines are established.
Title: Correlations between the level of MHD fluctuations and the
bulk speed and mass flux in the solar wind
Authors: Tu, C. Y.; Marsch, E.; Rosenbauer, H.
Bibcode: 1992sws..coll..555T
Altcode:
A new type of solar wind speed and mass-flux diagram has been used
to study the correlations of the flow speed and mass flux with the
energy of outward propagating fluctuations e(+), their normalized
cross-helicity and the Alfven ratio. The data were obtained by
Helios 1 and 2 near 0.3 AU in solar activity maximum (1979-1980). The
results show that the variations of these correlations, as obtained by
changing the amplitude and Alfvenicity of the fluctuations, cannot be
described by using the single parameter Vp. But they can be described
satisfactorily by means of the velocity and mass flux diagram. The
statistical results also show that the well known correlations between
e(+) and proton velocity Vp and temperature do not exist in the solar
wind streams with a low energy flux (0.65-0.87 erg/sq cm s at 1 AU)
for the periods we studied. This low-energy-flux wind is a new kind of
solar wind that appears only near activity maximum. The correlations
of the fluctuations with the speed of this type of solar wind are more
complicated than the correlations found near the minimum (75-76).
Title: Electric field fluctuations and possible dynamo effects in
the solar wind
Authors: Marsch, E.; Tu, C. Y.
Bibcode: 1992sws..coll..505M
Altcode:
Magnetohydrodynamic fluctuations in different kinds of solar wind
have been investigated. Electric field fluctuation spectra, have been
obtained from the observed velocity and magnetic field fluctuations. The
mean electromotive force epsilon, generated by the turbulent motion of
the solar wind plasma and field, turns out to depend upon the nature
and Alfvenicity of the fluctuations. Dynamo theory predicts a linear
relationship between epsilon and the mean magnetic field. Correlation
studies carried out with the intention to establish this so-called
alpha effect have given negative results.
Title: Temperature fluctuation spectra in the inner solar wind.
Authors: Tu, C. Y.; Marsch, E.; Rosenbauer, H.
Bibcode: 1991AnGeo...9..748T
Altcode: 1991AnG.....9..748T
The proton temperature data from the Helios 1 and Helios 2 primary
missions (1975 - 1976) have been analyzed to establish spectral
characteristics of temperature fluctuations in the inner solar wind and
their relation to the large-scale morphology of the stream structure. It
is found that the temperature spectra in high- and low-speed winds are
very different. Possible mechanisms for the generation of temperature
fluctuations in the solar wind are discussed.
Title: A case study of very low cross-helicity fluctuations in the
solar wind.
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1991AnGeo...9..319T
Altcode: 1991AnG.....9..319T
Two periods of very low cross-helicity fluctuations observed by Helios 2
near 1 AU in 1976 have been studied in detail. It is shown that in both
cases a nearly zero cross-helicity occurs together with an extremely
low Alfvén ratio and a -5/3 power-law for the turbulent energy
spectra. The simultaneous occurrence of these features is apparently
not influenced by compressible fluctuations. Explaining the nature of
the zero cross-helicity fluctuations poses a new theoretical problem,
for which no satisfactory solution exists at the present time. However,
a possible scenario is suggested in which the observed fluctuations
mainly result from convecting static structures, not involving any
velocity variations but merely "Magnetic Field Directional Turnings"
(MFDTs). The associated evolutions of both the cross-helicity and the
Alfvén ratio in the inner solar system may qualitatively be explained
by including these structures in extended solar wind turbulence
models. The difficulties remaining with the scenario of MFDTs have
also been pointed out.
Title: Mercury Orbiter: report of the Science Working Team.
Authors: Belcher, J. W.; Slavin, J. A.; Armstrong, T. P.; Farquhar,
R. W.; Akasofu, S. -I.; Baker, D. N.; Cattell, C. A.; Cheng, A. F.;
Chupp, E. L.; Clark, P. E.; Davies, M. E.; Hones, E. W.; Kurth, W. S.;
Maezawa, J. K.; Mariani, F.; Marsch, E.; Parks, G. K.; Shelley, E. G.;
Siscoe, G. L.; Smith, E. J.; Strom, R. G.; Trombka, J. I.; Williams,
D. J.; Yen, C. -W.
Bibcode: 1991mors.book.....B
Altcode:
This report presents the results of the Mercury Orbiter Science Working
Team which held three workshops in 1988/1989. Spacecraft engineering and
mission design studies at the Jet Propulsion Laboratory were conducted
in parallel with this effort and are detailed elsewhere. The findings
of the engineering study, summarized in this report, indicate that
spin-stabilized spacecraft carrying comprehensive particles and fields
experiments and key planetology instruments in highly elliptical orbits
can survive and function in Mercury orbit without costly sun-shields
and active cooling systems.
Title: Book-Review - Physics of the Inner Heliosphere - Part One -
Largescale Phenomena
Authors: Schwenn, R.; Marsch, E.
Bibcode: 1991Sci...251..578S
Altcode:
No abstract at ADS
Title: Kinetic Physics of the Solar Wind Plasma
Authors: Marsch, Eckart
Bibcode: 1991pihp.book...45M
Altcode: 1991PCS....21...45M
No abstract at ADS
Title: Physics of the Inner Heliosphere II. Particles, Waves and
Turbulence
Authors: Schwenn, Rainer; Marsch, Eckart
Bibcode: 1991pihp.book.....S
Altcode: 1991PCS....21.....S
No abstract at ADS
Title: MHD Turbulence in the Solar Wind
Authors: Marsch, Eckart
Bibcode: 1991pihp.book..159M
Altcode: 1991PCS....21..159M
No abstract at ADS
Title: Signatures of Coronal Structures and Turbulence in the Solar
Wind (With 1 Figure)
Authors: Marsch, E.
Bibcode: 1991mcch.conf..162M
Altcode:
No abstract at ADS
Title: Turbulence in the Solar Wind.
Authors: Marsch, E.
Bibcode: 1991RvMA....4..145M
Altcode:
No abstract at ADS
Title: Spatial structures in high-speed streams as signatures of
fine structures in coronal holes.
Authors: Thieme, K. M.; Marsch, E.; Schwenn, R.
Bibcode: 1990AnGeo...8..713T
Altcode: 1990AnG.....8..713T
During solar eclipses one can observe fine ray-like structures in
coronal holes. In order to determine whether these structures might
be preserved in the evolving interplanetary high-speed solar wind the
authors used plasma and magnetic field data obtained by the two Helios
solar probes. For the time period from 1974 till 1977 they analysed
41 high-speed solar wind streams which were measured between 0.3 and 1
AU. They investigated the velocity of protons and α-particles as well
as the combined gas pressure of protons, α-particles, and electrons,
the magnetic pressure, and the total pressure. The authors found many
time periods with a strong anticorrelation between the variations in
the gas pressure and the magnetic pressure while the total pressure
was roughly constant. They interpret these features as structural
relics of coronal origin. To get an estimation of the mean angular
diameter of these structures they did a statistical analysis with the
entire set of 41 high-speed solar wind streams. The resulting data
show characteristic variations on an angular scale being of the same
order as the angular size of the structures in the coronal holes.
Title: Transfer equations for spectral densities of inhomogeneous
MHD turbulence
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1990JPlPh..44..103T
Altcode:
On the basis of the dynamic equations governing the evolution of
magneto-hydrodynamic fluctuations expressed in terms of Elsässer
variables and of their correlation functions derived by Marsch and Tu, a
new set of equations is presented here describing the evolutions of the
energy spectrum e± and of the residual energy spectra eR and
es of MHD turbulence in an inhomogeneous magnetofluid. The
nonlinearities associated with triple correlations in these equations
are analysed in detail and evaluated approximately. The resulting
energy-transfer functions across wavenumber space are discussed. For e±
they are shown to be approximately energy-conserving if the gradients
of the flow speed and density are weak. New cascading functions are
heuristically determined by an appropriate dimensional analysis and
plausible physical arguments, following the standard phenomenology of
fluid turbulence. However, for eR the triple correlations do
not correspond to an ‘energy’ conserving process, but also represent
a nonlinear source term for eR. If this source term can be
neglected, the spectrum equations are found to be closed. The problem
of dealing with the nonlinear source terms remains to be solved in
future investigations.
Title: Spectral and spatial evolution of compressible turbulence in
the inner solar wind
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 1990JGR....9511945M
Altcode:
Magnetic field and plasma data collected by the Helios spacecraft
between 0.3 and 1 AU near the activity minimum of solar cycle 21 have
been analyzed to establish spectral characteristics of compressive
fluctuations in the inner solar wind and their relation to the
morphology of the plasma flow and magnetic field. The compressive
turbulence level is found to be closely related to the stream
structure of latitudinal location with respect to the heliospheric
current sheet. Compressive turbulence in low-speed flows is more fully
developed and intense. The spectra are radially invariant and come close
to a -5/3 spectral law. In contrast, fast stream turbulence becomes
increasingly compressive, in terms of radially growing amplitudes of
δn/n and δB/B, with increasing heliocentric distance. The spectra
reveal a flatter high-frequency part, which gradually seems to get
straightened out at large solar distances. Single case studies, as
well as averaged spectra and their spectral features, are presented
and discussed in the context of the theoretical turbulence literature.
Title: On the radial evolution of MHD turbulence in the Inner
heliosphere
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 1990JGR....95.8211M
Altcode:
The radial evolution of MHD turbulence in the inner heliosphere,
as observed by the Helios probes between 0.3 and 1 AU, is reanalyzed
and new evaluated by means of Elsässer variable. It is found that
the spectra of the energy of the outward (e+) and inward
(e-) oriented fluctuations, of the cross helicity and cross
correlation and of related dimensionless ratios, like the ones named
after Alfvén or Elsässer, all undergo considerable radial evolution
with an overall trend for the spectra to steepen. These evolutionary
tendencies are established both by individual typical case studies
for a recurrent high-speed stream and neighboring low-speed flows as
well as by a statistical analysis of many sample spectra pertaining
to various heliocentric distances. In particular, the e+
spectrum considerably steepens in the low-frequency part. Whereas
the fluctuations in the Alfvénic domain are more transverse in the
perihelion, they radially evolve toward an equipartition of the energy
in the three spatial dimensions at larger heliocentric distances. The
e- spectrum does not change a lot at low frequencies but
strongly steepens beyond about 2×10-4 Hz. The spectral
results on e- suggest that isotropic turbulence with an
index of 5/3 is probably the ultimate state toward which solar wind
MHD fluctuations seem to evolve. The radial evolution of the cross
correlation eR is also analyzed.
Title: On the origin of solar wind MHD turbulence: Helios data
revisited
Authors: Grappin, Roland; Mangeney, Andre; Marsch, Eckart
Bibcode: 1990JGR....95.8197G
Altcode:
We study the fluctuations of density, magnetic and velocity fields in
the frequency range from (1 day)-1~1.2×10-5
Hz to (2.8 min)-1~6×10-3 Hz, as measured by
the primary Helios mission (118 days), at heliocentric distances
ranging from 0.3 to 1 AU. We address the question of the existence
of nonlinear cascades in the observed turbulence, possibly separate
for the two ``inward'' and ``outward'' components, corresponding to
opposite directions of propagation along the large-scale magnetic
field. We consider energies per unit volume, in order to work with
variables which are not very sensitive to the heliocentric distance
variations. We find that while the whole spectrum of total (kinetic plus
magnetic) turbulent energy undergoes very large daily variations both in
its amplitude and spectral shape the instantaneous spectrum follows a
power law in the frequency range 10-4 to 6×10-3
Hz. We show that both the amplitude and the spectral index m depend on
the proton temperature, in a monotonic way, so that a large temperature
(thermal speed about 60 km/s) leads to a low level of turbulence with
a steep, Kolmogorov-like spectrum (m~-1.8), while a low temperature
(thermal speed about 16 km/s) leads to a flatter spectrum (m~-1.2)
with a high level of turbulence. This relation is independent
from heliocentric distance, at least between 0.3 and 1 AU. Decomposing
the turbulent energy into two components, ``outward'' and ``inward,''
we find that the spectrum of the outward component also follows very
closely the daily proton temperature variations, while the inward
component's spectrum is less sensitive to the temperature but also
varies with the relative level of rms proton density fluctuations. As
a consequence, Alfvénic periods (in which energy is dominated by the
outgoing component) occur mainly when density fluctuations are low
and temperature is high, which does not contradict the classical view
that they are found in the ``trailing edges of high-speed streams''
(Belcher and Davis, 1971). The existence of inertial ranges controlled
by the level of density fluctuations is not completely new (see the
numerical simulations of purely hydrodynamic turbulence by Pouquet
and Passot (1987)), but the strong dependence of both turbulent energy
level and spectral slope on temperature is a new, unexpected property
of solar wind turbulence which remains to be explained.
Title: First results of measurements of ions of Martian origin and
the discovery of a plasma sheet in the Martian magnetosphere in the
TAUS experiment on Phobos-2
Authors: Rosenbauer, H.; Shutte, N.; Apathy, I.; Verigin, M.; Witte,
M.; Galeev, A.; Gringaus, K.; Grunwaldt, H.; Jockers, K.; Kiraly,
P.; Kotova, G.; Livi, S.; Marsch, E.; Remizov, A.; Richter, A.;
Riedler, W.; Szego, K.; Hemmerich, P.; Schwenn, R.; Schwingenschuh,
K.; Steller, M.
Bibcode: 1990PAZh...16..368R
Altcode:
TAUS measurements showed that the Martian magnetosphere is considerably
filled with fluxes of heavy ions originating from the planetary
atmosphere. A plasma sheet was found in the magnetotail, which also
consisted mainly of heavy ions. The flux of heavy ions leaving Mars
through the tail is tentatively estimated to be (0.5-2) x 10 to the
25th per sec.
Title: Evidence for a ``background'' spectrum of solar wind turbulence
in the inner heliosphere
Authors: Tu, C. -Y.; Marsch, E.
Bibcode: 1990JGR....95.4337T
Altcode:
This statistical analysis of power spectra of the fluctuating
Elsässer variables, δZ+/-=δV+/-δVA,
covers 3408 hours of interplanetary magnetic field and plasma
observations made by experiments on the Helios 1 and 2 spacecraft
during the years 1975, 1976, and 1980. The averaged spectra
of δZ- in the range 2×10-8
km-1<k*<4×10-7
km-1 (k*=k/2π, k is the wave number)
are found to show little variation with heliocentric distance,
solar wind velocity, and solar activity. The resulting averaged
power spectrum of δZ- obeys a power law with a slope of
-5/3. We suggest that it could be thought of a persistent ``background''
spectrum. The averaged spectrum of δZ+, however, is flatter
that of δZ-. The concurrent decrease of the normalized
cross-helicity with increasing heliocentric distance (e.g., Roberts
et al., 1987a, b) may therefore mainly result from a decrease of
δZ+ and not from an increase of δZ-. This
finding places an observational constraint on theoretical models for
the evolution of cross-helicity.
Title: First Measurements of Ions of Martian Origin and Observation
of a Plasma Layer in the Magnetosphere of Mars - the TAUS Experiment
on the Spacecraft PHOBOS-2
Authors: Rosenbauer, H.; Shutte, N.; Apathy, I.; Verigin, M.; Witte,
M.; Galeev, A.; Gringauz, K.; Grunwaldt, H.; Jockers, K.; Kiraly,
P.; Kotova, G.; Livi, S.; Marsch, E.; Remizov, A.; Richter, A.;
Riedler, W.; Szego, K.; Hemmerich, P.; Schwenn, R.; Schwingenschuh,
K.; Steller, M.
Bibcode: 1990SvAL...16..156R
Altcode:
No abstract at ADS
Title: The dependence of MHD turbulence spectra on the inner solar
wind stream structure near solar minimum
Authors: Tu, C. -Y.; Marsch, E.; Rosenbauer, H.
Bibcode: 1990GeoRL..17..283T
Altcode:
The variation of the power spectra (e±) of the fluctuating
Elsässer variables δZ± with the solar wind velocity has
been examined by either individual case study or statistical analysis
with Helios data obtained near solar minimum. It is found, when going
from high-speed to low-speed wind, that: 1.) The slopes of both energy
spectra systematically increase toward the value given by Kolmogorov's
law. 2.) The power density of δZ+ in the Alfvénic regime
above f ≈ 2 × 10-4 Hz strongly decreases while the power
density of δZ- does not change a lot. 3.) A somewhat higher
level of e- is found in the leading edges of high-speed
streams near the regions of large velocity shear. We also found that
density fluctuations might make some contributions to e-
in the low-frequency domain. The relevance of these findings with
respect to the evolution of the solar wind MHD turbulence is discussed.
Title: Introduction
Authors: Marsch, E.; Schwenn, R.
Bibcode: 1990pihl.book....1M
Altcode:
No abstract at ADS
Title: Physics of the Inner Heliosphere I. Large-Scale Phenomena.
Authors: Schwenn, Rainer; Marsch, Eckart
Bibcode: 1990pihl.book.....S
Altcode: 1990PCS....20.....S
Physics of the Inner Heliosphere gives for the first time a
comprehensive and complete summary of our knowledge of the inner solar
system. Using data collected over more than 11 years by the HELIOS
twin solar probes, one of the most successful ventures in unmanned
space exploration, the authors have compiled 10 extensive reviews of
the physical processes of the inner heliosphere and their connections
to the solar atmosphere. Researchers and advanced students in space and
plasma physics, astronomy, and solar physics will be surprised to see
just how closely the heliosphere is tied to the sun and how sensitively
it depends on our star. The four chapters of Volume I of the work deal
with large-scale phenomena: - observations of the solar corona - the
structure of the interplanetary medium - the interplanetary magnetic
field - interplanetary dust.
Title: Introduction to MHD turbulence.
Authors: Marsch, E.
Bibcode: 1990ppst.conf...93M
Altcode:
The author concentrates on magnetohydrodynamic (MHD) turbulence
concerned with the physics of irregular fluctuations of the flow
velocity and magnetic field vector in a magnetofluid (mostly assumed
to be imcompressible), i.e. a plasma considered on such scales in time
and space that it is accessible to a fluid-like description. One of the
most prominent examples of such a turbulent magnetofluid is the solar
wind for which a vast amount of empirical data has been collected by
means of in situ spacecraft observations.
Title: Ions of martian origin and plasma sheet in the martian
magnetosphere: initial results of the TAUS experiment
Authors: Rosenbauer, H.; Shutte, N.; Apáthy, I.; Galeev, A.; Gringauz,
K.; Grünwaldt, H.; Hemmerich, P.; Jockers, K.; Király, P.; Kotova,
G.; Livi, S.; Marsch, E.; Richter, A.; Riedler, W.; Remizov, T.;
Schwenn, R.; Schwingenschuh, K.; Steller, M.; Szegö, K.; Verigin,
M.; Witte, M.
Bibcode: 1989Natur.341..612R
Altcode:
UNLIKE plasma instruments used on previous space missions to Mars,
the TAUS instrument on Phobos 2 was designed so that the energy per
charge and angular spectra of three species of ions could be measured
separately. These species were H+ and He2+
characteristic of the solar wind, and 'heavy ions' collected in
one integral channel covering the mass per charge (M/q) range 3 to
infinite, which we anticipated to find predominantly in the near-martian
regime. In all spacecraft orbits around Mars we found a sharp boundary,
separating the shocked solar wind from the martian magnetosphere which
was characterized by the absence of solar-wind-like plasma. As the
plasma inside the magnetosphere, and particularly in the tail, was
dominated by heavy ions with number densities orders of magnitude
higher than found in the solar wind, we assumed it was mainly of
martian origin. Typically, heavy ions of low tailward flow velocity
were seen near the boundary of the magnetotail, whereas high-speed
tailward plasma flows of such ions were detected deeper inside the
tail, a region not investigated before. Near the centre of the martian
magnetotail a plasma regime, comparable to the terrestrial as well
as the venusian1 plasma sheet, was detected, characterized by highly
supersonic tailward streams of heavy ions. The flux of planetary ions
leaving Mars through its magnetotail is tentatively estimated to be
of the order of a few times 1025 s-1. Such loss
rates would be significant for the dissipation of the martian atmosphere
on cosmological timescales.
Title: Basic properties of solar wind MHD turbulence near 0.3 AU
analyzed by means of Elsässer variables
Authors: Tu, C. -Y.; Marsch, E.; Thieme, K. M.
Bibcode: 1989JGR....9411739T
Altcode:
Magnetic field and plasma data, obtained by the Helios 1 and 2
spacecraft in the solar wind near 0.3 AU during the years 1975 to
1976, have been analyzed by calculating 12 kinds of spectra related
to the Elsässer variables, δZ+=δV+δVA, and
δZ-=δV-δVA, where δV and δVA are
the bulk velocity and Alfvén velocity fluctuations, respectively. For
small amplitude alfvén waves the fluctuation variable δZ+
simply relates to outward propagation and δZ- to an inward
sense of propagation, if the ambient magnetic field B0
is directed inward. The frequency range analysed in this paper is
6×10-6 Hz to 6×10-3Hz. It
is found that (1) the autocorrelation length for δZ-
is much larger that for δZ+ in both the high-speed and
low-speed wind. (2) The power spectra of δZ-, especially
in high-wind speed, are steeper in the low-frequency range and
flatten in the high-frequency range. (3) In the low-frequency range,
the power spectra for the components of δZ+ tend to be
isotropic with respect to the three polarization directions, while the
spectra of δZ- are dominated by the radial component. In
the high-frequency domain, the spectra of both δXZ+ and
δZ- are dominated by the transverse component in high-speed
wind and are more isotropic in low-speed wind. (4) The spectra related
to the residual energy or the cross-correlation in low-speed flows have
a power law with the slope near to -5/3. However, in high-speed
flows the corresponding data are widely distributed in a cloud of points
with an upper envelope near to the spectrum of δZ-. The
origin of all these spectra and their importance for the solar wind
physics have also been discussed. Several generation mechanisms are
suggested as candidates. In the flat part of e- spectrum,
the fluctuations may be generated by non-local (in wave number
space) interactions with the low-frequency part of the e+
spectrum, or just by parametric decay of the high-frequency part of
the e+ spectrum. The steep part of e- (f) may
be related to small-scale stream tubes, or be influenced by pressure
waves, nonlinear cascading, and the interaction with the outgoing
Alfvén waves.
Title: Dynamics of correlation functions with Elsässer variables
for inhomogeneous MHD turbulence
Authors: Marsch, E.; Tu, C. -Y.
Bibcode: 1989JPlPh..41..479M
Altcode:
On the basis of the ideal MHD equations expressed in terms of Elsässer
variables, a new set of equations has been derived that governs the
dynamics of the inhomogeneous background plasma and the superimposed
incompressible fluctuations. From these equations the dynamic equation
for the two-point and two-time correlation tensor has been obtained,
and subsequently the equations of motion for the various spectral
densities related to energy, cross-helicity and residual energy or
the Alfvén ratio have been established. This set of equations offers
a new possibility of discussing and perhaps better understanding the
mostly incompressible fluctuations observed in the solar-wind plasma
and of analysing their radial evolution into interplanetary space and
their spectral development. The scope of the paper is limited to giving
mainly formal developments of the equations. A detailed evaluation of
the many terms in the light of interplanetary observations is intended
for the future, but is not presented in this paper.
Title: Cooling of solar wind electrons inside 0.3 AU
Authors: Marsch, E.; Pilipp, W. G.; Thieme, K. M.; Rosenbauer, H.
Bibcode: 1989JGR....94.6893M
Altcode:
Mean temperature gradients of solar wind electrons between 0.3 and I AU
are determined from Helios observations. Electrons are found to cool
more slowly than adiabatically, with flattest temperature profiles in
high-speed streams. These in situ observations are used to estimate the
radial gradients of Te inside 0.3 AU under the constraint
of matching coronal temperatures. Electrons in high-speed streams
are inferred to cool more strongly closer to the Sun than with the
Helios orbital range. For low-speed wind, no significant breaks in the
temperature profiles have been found, while for intermediate-speed
structures the results are somewhat ambiguous. These results are
discussed in the context of solar wind generation and modeling.
Title: Estimates of Alpha particle heating in the solar wind inside
0.3 AU
Authors: Thieme, K. M.; Marsch, E.; Rosenbauer, H.
Bibcode: 1989JGR....94.2673T
Altcode:
Helios observations are used to determine and compare the average
temperature gradients of protons and alpha particles in the solar
wind between 0.3 and 1 AU. The He2+ ions are found to cool
off more slowly than adiabatically. The radial profiles of their
temperature are somewhat steeper in fast than in slow solar wind,
a result which is in contrast to the proton results. These in situ
measurements are extrapolated to inside 0.3 AU in order to estimate
the radial gradients of Tz there and the required heating
rates. Thereby, the temperature profiles are adjusted to match coronal
boundary values. Clear evidence if found for continuous interplanetary
alpha particle heating, which supports theories invoking extended ion
heating by waves in the outer solar corona. © The American Geophysical
Union 1989
Title: SUMER - Solar ultraviolet measurements of emitted radiation.
Authors: Curdt, W.; Wilhelm, K.; Axford, W. I.; Marsch, E.; Richter,
A. K.; Gabriel, A. H.; Lemaire, P.; Vial, J. -C.; Grewing, M.; Huber,
M. C. E.; Jordan, S. D.; Poland, A. I.; Thomas, R. J.; Timothy, J. G.
Bibcode: 1989AGAb....2...14C
Altcode: 1989amt..conf...14C
No abstract at ADS
Title: Wave-Particle Interactions in the Solar Wind. (invited paper)
Authors: Marsch, E.
Bibcode: 1989npvp.conf..145M
Altcode:
No abstract at ADS
Title: Type II Interplanetary Radio Bursts and Electron Plasma
Oscillations Associated with Interplanetary Shocks, Superthermal
Electrons, and Low/Medium Energy Protons
Authors: Kikuchi, H.; Gurnett, D. A.; Anderson, R. R.; Keppler, E.;
Richter, A. K.; Schwenn, R.; Marsch, E.; Pilipp, W. G.; Richter, K.;
Rosenbauer, H.
Bibcode: 1989lsp..conf..415K
Altcode:
No abstract at ADS
Title: Are structures in high-speed streams signatures of coronal
fine structures?
Authors: Thieme, K. M.; Schwenn, R.; Marsch, E.
Bibcode: 1989AdSpR...9d.127T
Altcode: 1989AdSpR...9..127T
Interplanetary plasma and magnetic field data were measured by the
two Helios solar probes from 1974 until 1986 and from 1976 until 1980,
respectively, between 0.3 and 1 AU. We used these data to investigate
plasma parameters of high-speed streams, especially velocities,
densities, and temperatures of protons and α-particles. The possibility
is discussed that the variability in these parameters is due to spatial
structures which are remnants of the underlying coronal structures
(supergranulation cells) preserved in the outflowing solar wind.
Title: On the origin of solar wind turbulence. Helios data revisted.
Authors: Grappin, R.; Mangeney, A.; Marsch, E.
Bibcode: 1989tndm.conf...81G
Altcode:
No abstract at ADS
Title: SUMER: Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel, A. H.;
Grewing, M.; Huber, M. C. E.; Jordan, M. C. E.; Lemaire, P.; Marsch,
E.; Poland, A. I.
Bibcode: 1988sohi.rept...31W
Altcode:
The SUMER (solar ultraviolet measurements of emitted radiation)
experiment is described. It will study flows, turbulent motions, waves,
temperatures and densities of the plasma in the upper atmosphere of
the Sun. Structures and events associated with solar magnetic activity
will be observed on various spatial and temporal scales. This will
contribute to the understanding of coronal heating processes and the
solar wind expansion. The instrument will take images of the Sun in EUV
(extreme ultra violet) light with high resolution in space, wavelength
and time. The spatial resolution and spectral resolving power of the
instrument are described. Spectral shifts can be determined with
subpixel accuracy. The wavelength range extends from 500 to 1600
angstroms. The integration time can be as short as one second. Line
profiles, shifts and broadenings are studied. Ratios of temperature
and density sensitive EUV emission lines are established.
Title: HELIOS observational constraints on the development of
interplanetaryslow shocks.
Authors: Richter, A. K.; Marsch, E.
Bibcode: 1988AnGeo...6..319R
Altcode:
Helios plasma and magnetic field data between 0.3 and 1 AU have been
used to compute the average radial dependence of the sound-to-Alfven
speed ratio, of the ion-to-electron temperature ratio, and of the
total plasma kinetic-to-magnetic pressure ratio. The analysis takes
the stream structure of the solar wind and the parameters of protons,
alpha particles, and electrons into account. Although the probability
for the simultaneous fulfillment of the constraints for interplanetary
slow mode MHD waves to freely evolve, to withstand ion Landau damping,
and to steepen into slow shocks is extremely low, it is found to be
highest in the slow wind near and at cororotating interaction regions.
Title: Generation of solar wind proton tails and double beams by
Coulomb collisions
Authors: Livi, S.; Marsch, E.
Bibcode: 1987JGR....92.7255L
Altcode:
A kinetic model is presented for the generation of proton heat flux
tails and double beams by Coulomb collisions in the solar wind. The
combined action of the large-scale interplanetary magnetic field (mirror
effect) and of the collisional scattering (runaway) is shown to be able
to produce variously skewed velocity distributions. All intermediate
cases between the exospheric and isotropic adiabatic expansion can
be simulated as a function of the collisionality of the plasma. Good
qualitative agreement is achieved between in situ measurements and
model results in the collisional domains of the solar wind.
Title: Observational evidence for marginal stability of solar wind
ion beams
Authors: Marsch, E.; Livi, S.
Bibcode: 1987JGR....92.7263M
Altcode:
Solar wind proton double streams and proton-alpha differential
streaming may provide sufficient free energy to drive field-aligned
magnetosonic waves unstable. We carry out a statistical analysis of
this electromagnetic beam instability based on measured Helios ion
distributions. Observational evidence is indeed found for unstable
distributions, whereby the largest growth rates are obtained in the
collisionless high-speed wind. Alpha particles by themselves are not
able to excite these waves but mostly tend to stabilize an existing
proton double stream configuration by enhancing the cyclotron damping
of the main proton population.
Title: Ideal MHD equations in terms of compressible Elsässer
variables
Authors: Marsch, E.; Mangeney, A.
Bibcode: 1987JGR....92.7363M
Altcode:
By the help of the so-called Elsässer variables, if adopted to
the situation of a compressible plasma, the equations of ideal
magnetohydrodynamics can be rewritten in a new form. This appears to
be particularly suitable to describe the situation of compressive MHD
turbulence. After having derived the basic equations of motion, the
conservation equations for energy and cross-helicity are rephrased in
terms of Elsässer variables. The sinks and sources of cross-helicity
associated with the compressibility of the plasma are elucidated. A
standard normal mode analysis, performed in terms of Elsässer
variables, emphasizes their usefulness in treating hydrodynamic
waves. In the conclusions some possible future, more sophisticated
applications are outlined.
Title: On the He2+ to H+ temperature
ratio in slow solar wind
Authors: Hernandez, R.; Livi, S.; Marsch, E.
Bibcode: 1987JGR....92.7723H
Altcode:
On the basis of a three-fluid model with energy exchange by Colomb
collisions and heat flux degradation the ratio T of alpha to proton
temperatures is investigated. For various relative ion densities
and plasma parameters the collisional evolution of T is modeled and
compared with Helios in situ measurements. Good agreement between data
and theory is found. © American Geophysical Union
Title: On the equation of state and collision time for a
multicomponent, anisotropic solar wind.
Authors: Marsch, E.; Richter, A. K.
Bibcode: 1987AnGeo...5...71M
Altcode:
No abstract at ADS
Title: Relationship between Structures in the Solar Wind and Their
Source Regions in the Corona
Authors: Thieme, K. M.; Marsch, E.; Schwenn, R.
Bibcode: 1987sowi.conf..317T
Altcode:
No abstract at ADS
Title: On the collisional relaxation of solar wind velocity
distributions.
Authors: Livi, S.; Marsch, E.
Bibcode: 1986AnGeo...4..333L
Altcode:
The time-evolution of two non-Maxwellian distribution functions
under the effects of Coulomb self-collisions is investigated. The
full Fokker-Planck collision operator is employed, which describes
binary particle interactions resulting in small-angle deflections of
particle trajectories. Emphasis is placed on a detailed analysis of
the temporal evolution of an appropriate effective collision frequency,
which is formally defined by a relaxation-time version of the collision
operator. The time required for the distribution to become Maxwellian
is found to be nearly ten times the self-collision time. The collisional
evolution of the higher moments of the distributions is also discussed.
Title: Acceleration potential and angular momentum of undamped
MHD-waves in stellar winds
Authors: Marsch, E.
Bibcode: 1986A&A...164...77M
Altcode:
The effects of finite amplitude magnetohydrodynamic fluctuations on
the average background stellar wind are investigated. By a second
order perturbation scheme of the steady-state conservation equations
for mass, momentum and energy, the wave energy, pressure/stress
tensor, and energy flux density are evaluated. It is found that
MHD-waves exert an acceleration force on the ambient plasma and, if
compressible, may carry a sizable angular momentum, comparable to its
average value associated with the background plasma flow and magnetic
field stresses. In the Bernoulli equation the waves appear through an
acceleration potential which for Alfven, slow and fast magnetosonic
waves can concisely be expressed as a function of the Alfvenic Mach
vector, the plasma beta, and the wave propagation direction. A closed
set of integrated equations of motion for a spiral magnetic field
geometry is presented describing the stars overall loss of mass,
angular momentum, and energy as transported away by a stellar wind in
which undamped MHD-waves are embedded.
Title: Coulomb collisional domains in solar wind
Authors: Livi, S.; Marsch, E.; Rosenbauer, H.
Bibcode: 1986JGR....91.8045L
Altcode:
The role of Coulomb collisions in the solar wind, their number of
occurrence for protons, and the correlation between collisional effects
and the stream structure and large-scale interplanetary magnetic field
are investigated. Helios plasma data, displayed in Carrington rotation
plots, clearly show that the relative number of collisions (ratio of
expansion over collision time scale) maximizes near the heliospheric
current sheet, which is revealed as the main collisional domain of
the solar wind. Statistical results indicate that for about 20% of
the time the low-speed solar wind plasma is influenced strongly by
Coulomb collisions.
Title: Collisional transfer of energy and momentum between drifting
tri-Maxwellians
Authors: Hernandez, R.; Marsch, E.
Bibcode: 1986JPlPh..35..473H
Altcode:
The collisional transfer tensor for energy and transfer vector for
momentum exchange between drifting tri-Maxwellians for an arbitrary
central interaction force between neutral and/or ionized particles are
evaluated. We introduce the new concept of a generalized Rosenbluth
potential whereby the heat and momentum exchange rates can be written
in a concise form. We also discuss the associated time-scales which
depend on the masses, densities, temperatures, and drift velocities
of the two colliding species.
Title: Collisional time scales for temperature and velocity exchange
between drifting Maxwellians
Authors: Hernandez, R.; Marsch, E.
Bibcode: 1985JGR....9011062H
Altcode:
The Coulomb collision transfer rates for energy and momentum
exchange between drifting Maxwellians are evaluated. We discuss
the associated time scales which depend on the masses, densities,
temperatures, and velocities of the two colliding species. Inclusion
of finite mass density effects of the minor species generally leads
to shorter time scales, as compared to the test particle approach,
for any differential speed and temperature equalization. We find that
two particle species may, by collisions, attain a temperature ratio
which can range between 1 (thermodynamic equilibrium) an the inverse
ratio of their mass densities. This result suggests the possibility
of preferentially heating the species with the lower mass density
by Coulomb collisions, assuming that their differential speed can be
externally maintained against frictional deceleration.
Title: Coulomb self-collision frequencies for non-thermal velocity
distributions in the solar wind.
Authors: Marsch, E.; Livi, S.
Bibcode: 1985AnGeo...3..545M
Altcode:
Coulomb self-collision frequencies are evaluated for non-thermal
velocity distributions for solar wind ions and electrons. First,
the general Landau collision integral is revisited and rewritten in
a relaxation time form that involves the new concept of an effective
collision rate. This frequency and also the rates associated with
longitudinal and transverse diffusion and with collisional friction
are then calculated for model distributions composed of multiple
drifting Maxwellians. Second, numerical results for typical observed
double-humped and heat flux carrying particle distributions are
presented and discussed in terms of contour plot and one-dimensional
cuts parallel and perpendicular to the magnetic field. In this way
insight is provided into the collisional reshaping of realistic particle
distributions by velocity space diffusion and friction. Finally, some
conclusions are drawn with respect to Coulomb collision moderated
transport in the solar wind and in tenuous space plasmas.
Title: Beam-driven electron acoustic waves upstream of the earth's
bow shock
Authors: Marsch, E.
Bibcode: 1985JGR....90.6327M
Altcode:
Intense electrostatic waves of short wavelength are frequently observed
upstream of the earth's bow shock. These waves are very impulsive,
and their peak amplitudes correlate strongly with the temporal flux
profiles of simultaneously observed energetic ions and electrons
which are reflected from the shock. Our paper suggests an explanation
of this broadband electrostatic noise in terms of electron acoustic
waves driven unstable by the ion and/or electrom beams. These waves do
not exist in thermodynamic equilibrium plasma and therefore require
nonthermal distributions for their occurrence. A simple model is
developed for finite temperature beam and background particles with
Maxwellian or Lorentzian distributions. The beam-associated instability
can be classified as being due to Landau resonance or negative wave
energy. Depending on the plasma parameters the mode discussed here
naturally extends and links to the ion acoustic wave or electron plasma
oscillation. A numerical parameter study is provided for various beam
plasma situations. The frequency theoretically obtained ranges between
the ion and the electron plasma frequency, and the wavelength amounts
to several Debye lengths for maximum growth. Since the beam mode has
a linear dispersion relation, the Doppler-shifted frequency in the
spacecraft frame should depend linearly on the beam velocity and on
the wave vector as well. It is anticipated that these characteristics
may allow parts of the observed broadband high-frequency noise to be
identified as beam-driven electron acoustic waves.
Title: Energy Input Into the Solar Wind
Authors: Marsch, E.
Bibcode: 1985ESASP.235...11M
Altcode: 1985fmsh.work...11M; 1985shpp.rept...11M
The energy input into the solar wind is discussed, both in terms of
observations and fluid theory. Selected associated topics of solar wind
microphysics and transport are reviewed as well. Emphasis is placed on
the in situ observations beyond 0.3 AU and the consequent constraints
on solar wind expansion and energetics. Some experimental results on
the energy and mass flux obtained by indirect means and remote optical
sensing of the corona are also considered.
Title: Coulomb collision rates for self-similar and kappa
distributions
Authors: Marsch, E.; Livi, S.
Bibcode: 1985PhFl...28.1379M
Altcode:
The Coulomb collision operator for two nonthermal particle
distributions, the self-similar and kappa distributions, is investigated
theoretically. Associated friction and diffusion rates are evaluated
and calculated numerically as a function of velocity. It is shown that
the full collision term can be cast into a relaxation-time form with
an effective collision rate which differs drastically from the smooth
overall diffusion rates and is very sensitive to the shape of the
distribution. Numerical results for the effective rates are presented,
and the relevance of the present analysis to observed distributions
in space plasmas and to quasi-linear turbulence is discussed.
Title: Review of interplanetary shock phenomena near and within 1 AU
Authors: Richter, A. K.; Hsieh, K. C.; Luttrell, A. H.; Marsch, E.;
Schwenn, R.
Bibcode: 1985GMS....35...33R
Altcode:
A review of the more recent observations regarding interplanetary shock
waves and shock-related phenomena near and within 1 AU is presented. In
particular, the observations of interplanetary fast mode shocks are
summarized in terms of (1) their solar and interplanetary origin,
(2) their observed characteristics with respect to the solar cycle,
(3) the solar wind stream-structure, and (4) the heliocentric radial
distance; and in terms of (5) their three-dimensional propagation
properties in the inner part of the heliosphere. Postshock large-scale
flows and structures and some recent 'field and particle' observations
associated with interplanetary fast shocks are also reviewed.
Title: Velocity Distributions of Solar Wind Ions &ELECTRONS
Authors: Marsch, E.
Bibcode: 1984ESASP.207...33M
Altcode: 1984plap.rept...33M
Solar wind ion and electron three-dimensional velocity distributions
are presented emphasizing Helios measurements between 0.3 and 1 AU. The
observed distributions strongly deviate from Maxwellians. Their detailed
form distinctly correlates with the magnetic sector and solar wind
stream structure. Among the most prominent non-thermal features are
temperature anisotropies, heat fluxes, double ion streams, differential
motion between protons and alpha particles, and narrow field-aligned
electron strahl. Individual spectra are discussed and statistical
results are presented. Kinetic processes which may shape the particle
distributions, in particular the effects of Coulomb collisions,
are considered. A plasma stability analysis for magnetosonic waves
is mentioned.
Title: Helios observational constraints on solar wind expansion
Authors: Marsch, E.; Richter, A. K.
Bibcode: 1984JGR....89.6599M
Altcode:
Helios particle and magnetic field observations between 0.3 and 1 AU
are used to determine plasma parameters that characterize the bulk and
internal energy state of the solar-wind. Quantities expected to be
conserved in a time-satationary flow with local spherical symmetry
in the ecliptic plane are actually found to be invariant within
measurement uncertainties. These are the total mass, energy, and angular
momentum fluxes for the anisotropic solar wind plasma composited by
electrons, protons, and alphas. Although individual species have
nonthermal velocity distributions, the total plasma pressure is
almost isotropic (p⊥/p∥=0.9). The total
heat flux divided by the mass flux Or/ρur
is markedly smaller than thermal speeds squared
v∥.⊥2=ρ∥.⊥/ρ. By this
reason an appropriately defined polytropic index γ is found to be
almost 5/3 and rather insensitive to heliocentric distance and flow
speed. This index γ does not include terms due to wave turbulence or
external heat sources but is solely based on the total particle heat
flux. These observational findings indicate that the heat flux beyond
0.3 AU is observationally too small to cause a strong departure
from adiabaticity. The solar wind expansion may be conceived in
terms of a ``single particle'' moving in the binding gravitational
potential and in the accelerating thermal (enthalpy and heat fluxes)
and magnetorotational (aximuthal kinetic energy and Poynting flux)
potentials. The radial profiles of these potentials are derived from
observations.
Title: Distribution of solar wind angular momentum between particles
and magnetic field: Inferences about the Alfv'n critical point from
helios observations
Authors: Marsch, E.; Richter, A. K.
Bibcode: 1984JGR....89.5386M
Altcode:
We first discuss theoretically the relative importance and
the behavior of the two basic terms adding to the total angular
momentum flux, the angular momentum of the particles' (electrons,
protons and alpha particles) and of the magnetic field stresses,
respectively. Second, we analyze these two quantities with
respect to their dependence on heliocentric distance by using
the Helios 1 and 2 plasma and interplanetary magnetic field
observations between 0.3 and 1 AU classified according to
low-speed (<400 km s-1), intermediate
(400-600 km s-1), and high-speed (>600 km
s-1) solar wind for the 1975-1976 epoch. Applying
now these results as well as various combinations of the constants of
motion for the solar wind (such as the total angular momentum flux, the
mass flux, and the magnetic flux) and their observational constraints,
as deduced earlier by Marsch and Richter (1984), we finally present
various methods (1) to derive the values of several characteristic
solar wind plasma and magnetic field parameters at the Alfvén critical
points, (2) to estimate their locations above the solar surface,
(3) to obtain the radial slope of the associated solar wind velocity
profiles for the three solar wind classes separately.
Title: The effects of Coulomb collisions on solar wind ion velocity
distributions
Authors: Marsch, E.; Goldstein, H.
Bibcode: 1983JGR....88.9933M
Altcode:
The effects of coulomb collisions on solar wind ion velocity
distributions are investigated by using Helios data obtained between
0.3 and 1 AU. The mean free path of ions moving at thermal speed (in
the solar wind frame) varies by three orders of magnitude in dependence
on the plasma parameters. The number of collisions (roughly defined as
collision frequency times the solar wind expansion time) can easily
exceed one in low-speed wind near the heliospheric current sheet. In
these regions, almost Maxwellian distributions are observed. In solar
wind with intermediate speeds (ranging from 400-600 km/s) one usually
finds distributions with a nearly isotropic core which again can be
understood by the action of coulomb collisions. On the other hand,
the major part of high-speed solar wind ion distributions can by good
reason, be called collisionless on local scales.
Title: The radial evolution of a single solar wind plasma parcel
Authors: Schwartz, S. J.; Marsch, E.
Bibcode: 1983JGR....88.9919S
Altcode:
We have studied one of the rare occasions when the same piece of solar
wind plasma passed both Helios 1 (at 0.507 AU) and Helios 2 (at 0.72
AU). Our particular example occurred in the middle of a fairly smooth
and typical high-speed stream. We find clear indications that the ion
behavior during this transit did not conserve the partirlces adiabatic
vineriants and that some heating is required for the proton and
alpha perpendicular temperature. The situation regarding the parallel
temperature is less clear. The decreasing alpha-proton differential
speed does not appear to release very much free energy owing to a
natural ``adiabatic'' cooling process. A very strong radial dependence
of the electromagnetic energy flux, along with other factors, suggests
the possibility of strong dissipation of Alfvenic fluctuations. Our
conclusions are weakened somewhat by the many sources of inaccuracy
that we have found and that seem unavoidable in a study of this kind.
Title: Radial evolution of ion distribution functions.
Authors: Marsch, E.
Bibcode: 1983NASCP.2280.355M
Altcode: 1983sowi.conf..355M
A survey of solar wind ion velocity distributions and derived parameters
(temperature, ion differential speed, heat flux, adiabatic invariants)
is presented with emphasis on the heliocentric distance range between
0.3 and 1 AU traversed by the Helios solar probe. The radial evolution
of nonthermal features are discussed which are observed to be most
pronounced at perihelion. Within the framework of quasilinear plasma
theory, wave particle interactions that may shape the ion distributions
are considered. Some results of a self consistent model calculation
are presented accounting for ion acceleration and heating by resonant
momentum and energy exchange with ion cyclotron and magnetosonic
waves propagating away from the Sun along the interplanetary magnetic
field. Another tentative explanation for the occurrence of large
perpendicular proton temperatures is offered in terms of heating by
Landau damping of lower hybrid waves.
Title: Electromagnetic lower hybrid waves in the solar wind
Authors: Marsch, E.; Chang, T.
Bibcode: 1983JGR....88.6869M
Altcode:
An analysis of electromagnetic lower hybrid waves or hybrid whistlers
that propagate nearly perpendicular to the magnetic field lines in the
solar wind is described. Doppler-shifted, these waves have a broadband
nature when observed in the spacecraft frame depending on the direction
of propagation and the supersonic flow velocity of the wind. Lower
hybrid waves can energize ions normal to the interpletary magnetic
field. They may occasionally be responsible for the observed temperature
anisotropy in high speed streams and possibly for the acceleration
of heavier ions such as the oxygen ions, alpha particles, etc. These
modes are probably driven unstable by the anisotropic halos of the
solar wind electron distributions exhibiting `heat flux' profiles.
Title: Determination of the solar wind angular momentum flux from
the HELIOS data - an observational test of the Weber and Davis theory
Authors: Pizzo, V.; Schwenn, R.; Marsch, E.; Rosenbauer, H.;
Muehlhaeuser, K. -H.; Neubauer, F. M.
Bibcode: 1983ApJ...271..335P
Altcode:
In situ attempts to measure the sun's angular momentum loss in the
solar wind and thereby to test the Weber and Davis description of the
magnetic coupling between stellar rotation and winds have thus far
produced widely divergent and inconclusive results. A new estimate
for the solar loss rate in the ecliptic plane has been derived from
the Helios spacecraft data. By intercomparing measurements made by
the twin probes over the full 0.3-1.0 AU baseline of their orbits,
it is possible to eliminate the systematic instrumental offsets from
the true radial direction that have plagued previous efforts. The main
observational findings are that (1) the total angular momentum flux
loss rate (field + particles) near the solar equator is ∼0.2-0.3
× 1030 dyn cm sr-1, about one-quarter the
Weber and Davis prediction and much lower than previous spacecraft
estimates, and (2) the distribution of that flux between particles
and field stresses is very near the 1:3 ratio of the model, when
an important contribution from the heretofore neglected solar wind
α-particles is accounted for. Though few by number in the solar wind,
the α-particles' flow speed and direction in general differ from that
of the protons, largely offsetting the latters' angular momentum content
(+0.15-0.2 × 1030 for the protons, -0.1 × 1030
for the α-particles, plus being in the direction of corotation with
the Sun). As to the small value reported for the total flux, theory
and observation can be reconciled by moving the mean Alfvén radius,
rA, in to 12 Rsun, a figure that is consistent
with coronal models more realistic than the single polytrope formulation
used by Weber and Davis. There is a distinct tendency for slow solar
wind to carry positive total flux and for fast wind, negative; this
can probably be explained in terms of stream-interaction dynamics in
the super-Alfvénic region. It thus appears that the Weber and Davis
theory adequately describes angular momentum loss in solar-type winds,
insofar as simple magnetic stresses are taken as the dominant coupling
mechanism. However, in the general astrophysical application, it is
suggested that a more accurate treatment of coronal acceleration be
incorporated to properly locate rA (and hence fix the total
loss rate) and that some allowance for three-dimensional effects be
made. Also, should large speed differentials between α-particles and
protons occur well inside rA, a three-fluid version of the
Weber and Davis model may be in order.
Title: On the equaton of state of solar wind ions derived from
Helios measurements
Authors: Marsch, E.; Muehlhaeuser, K. H.; Rosenbauer, H.; Schwenn, R.
Bibcode: 1983JGR....88.2982M
Altcode:
Observations of solar wind ion velocity distributions made by the Helios
spacecraft between 0.3 and 1 AU are used to study the radial evolution
of the so-called adiabatic invariants, for example, the ion magnetic
moments. Significant differences between the parameters of protons and
α particles have been found in dependence on the wind velocity. On
the average, adiabaticity is observed to be violated. We interpret this
violation of adiabatic invariance as evidence that protons are heated
perpendicular to the field in fast streams and, with less statistical
significance, that α particles are cooled more strongly than for
adiabatic expansion parallel to the magnetic field. The contribution
of the differential streaming energy to the total internal energy of
the ions is briefly investigated. Also, average heliocentric radial
profiles for the ion heat fluxes are presented, and the possible
role of the ion heat flux in supplying thermal energy during the
radial expansion of the wind is examined. Our findings suggest that
wave-particle interactions and (or) Coulomb collisions (or other yet
unknown processes) have to be invoked in order to explain the thermal
energy state of solar wind ions and their radial temperature profiles.
Title: Lower hybrid waves in the solar wind
Authors: Marsch, E.; Chang, T.
Bibcode: 1982GeoRL...9.1155M
Altcode:
We demonstrate that the frequently observed broad band low frequency
electrostatic noise in the solar wind generally has a dominant lower
hybrid component. These modes are probably produced by the anisotropic
halos of the solar wind electron velocity distributions exhibiting "heat
flux" profiles and thus, are accompanied by broad band, "hybrid-like"
whistler waves. When the electron temperature is much larger than
the ion temperature, these modes can also co-exist with the ion
acoustic waves. Since lower hybrid modes propagate nearly normal to
the interplanetary magnetic field lines, the ions can be transversely
accelerated by these waves and attain the observed anisotropic and/or
loss-cone-like distributions.
Title: Wave heating and acceleration of solar wind ions by cyclotron
resonance
Authors: Marsch, E.; Goertz, C. K.; Richter, K.
Bibcode: 1982JGR....87.5030M
Altcode:
In order to explain the temperature anisotropies and differential
speeds, as observed in solar wind high-speed streams, a fluid
type model is presented that takes into ature anisotropies (like
Tp⊥>Tp∥) as predicted by the model agree
fairly well with the observations in fast streams. The results are
discussed with respect to the effects of various boundary conditions
and the inhomogeneity of the expanding solar wind plasma.
Title: Solar wind protons: Three-dimensional velocity distributions
and derived plasma parameters measured between 0.3 and 1 AU
Authors: Marsch, E.; Schwenn, R.; Rosenbauer, H.; Muehlhaeuser,
K. -H.; Pilipp, W.; Neubauer, F. M.
Bibcode: 1982JGR....87...52M
Altcode:
A survey of solar wind three-dimensional proton velocity
distributions as measured by the Helios solar probes between
0.3 and 1 AU is presented. A variety of nonthermal features like
temperature anisotropies, heat fluxes, or proton double streams has
been observed. The relative speed of the second proton component
increases on the average with increasing wind speed and decreasing
heliocentric radial distance and shows a correlation with the local
Alfvén speed. A marked anisotropy in the core of proton distributions
with a temperature larger perpendicular than parallel to the magnetic
field (T∥c<T⊥c) is a persistent feature
of high speed streams and becomes most pronounced in the perihelion
(~0.3 AU). Fairly isotropic distributions have only been measured
very close to and directly at magnetic sector boundaries. Low and
intermediate speed distributions usually show a total temperature
anisotropy T∥p/T⊥p>1 frequently caused by
'high-energy shoulders' or a resolved second proton component. No clear
radial gradient of the temperature anisotropy could be established
in these cases. The average dependence of the proton temperature on
heliocentric radial distance is given by a power law R-α,
where α~1 for T⊥p and 0.7<α<1 for T⊥p
are compatible neither with isothermal nor adiabatic expansion. Flattest
radial temperature profiles are obtained in high-speed streams. These
observations indicate that local heating or considerable proton heat
conduction occurs in the solar wind. Some consequences of nonthermal
features of proton distributions for plasma instabilities are discussed
as well as kinetic processes that may shape the observed distributions.
Title: Resonant Wave Acceleration of Minor Ions in the Solar Wind
Authors: McKenzie, J. F.; Marsch, E.
Bibcode: 1982Ap&SS..81..295M
Altcode:
This paper extends some previous work on the acceleration of minor
ions in the solar wind to include the effects of wave acceleration
and heating arising from minor ions interacting via the gyroresonance
with ion cyclotron waves. Resonant wave acceleration is made up of
two contributions, the first, and generally the more important, is a
‘local’ acceleration which is proportional to the wave power and
the number of resonant particles and is also sensitive to the details
of the distribution function; while the other contribution is basically
‘fluid dynamic’ in character, arises from the inhomogeneity of the
medium and is proportional to the radial gradient of the resonant wave
power. Under suitable cir-cumstances both contributions exhibit the
feature that heavier ions receive greater acceleration than lighter
ones. Also the kinematics of the resonance shows that the resonance
wave acceleration switches off above a maximum differential speed,
between ions and protons, which increases with increasing ratio of
mass to charge. We also examine briefly possible beam instabilities
driven by the streaming of minor ions relative to protons.
Title: Solar wind helium ions: obsevations of the Helios solar probes
between 0.3 and 1 AU
Authors: Marsch, E.; Rosenbauer, H.; Schwenn, R.; Muehlhaeuser,
K. -H.; Neubauer, F. M.
Bibcode: 1982JGR....87...35M
Altcode:
A survey of solar wind helium ion velocity distributions and
derived parameters as measured by the Helios solar probes between
0.3 and 1 AU is presented. Nonthermal features like heat flux or
He2+ double streams and temperature anisotropies have been
frequently observed. Fairly isotropic distributions have only been
measured close to sector boundaries of the interplanetary magnetic
field. At times in slow solar wind, persistent double-humped
helium ion distributions constituting a temperature anisotropy
T∥α/T⊥α> have been reliably
identified. Distributions in high-speed wind generally have small
total anisotropies (T∥α/T⊥α>1)
with a slight indication that in the core part the temperatures
are larger parallel than perpendicular to the magnetic field, in
contrast to simultaneous proton observations. The anisotropy tends to
increase with increasing heliocentric radial distance. The average
dependence of helium ion temperatures on radial distance from the
sun is described by a power law ~R-β with 0.7<~1.2 for
T∥α and 0.87<~β<~1.4 for T⊥α. In
fast solar wind the T⊥α profile is compatible with
nearly cooling. Pronounced differential ion speeds Δvαp
have been observed with values of more than 150 km/s near perihelion
(0.3 AU). In fast streams Δvαp tends to approach the local
Alfvén velocity vA, whereas in slow plasma values around
zero are obtained. Generally, the differential speed increases with
increasing proton bulk speed and (with the exception of slow plasma)
with increasing heliocentric radial distance. The role of Coulomb
collisions in limiting Δvαp and the ion temperature ratio
Tα/Tp is investigated. Collisions are shown to
play a negligible role in fast solar wind, possibly a minor role in
intermediate speed solar wind and a distinct role in low-speed wind
in limiting the differential ion velocity and temperature.
Title: Wave heating and acceleration of solar wind ions by cyclotron
resonance
Authors: Marsch, E.
Bibcode: 1981ESASP.161..405M
Altcode: 1981plas.work..405M
No abstract at ADS
Title: Wave heating and acceleration of solar wind ions by cyclotron
resonance
Authors: Marsch, E.
Bibcode: 1981plap.rept..405M
Altcode:
A model is presented which describes the radial evolution of solar
wind ion temperatures and speeds within a fluid framework. Resonant
wave-particle interactions are taken into account and the ion-wave
dynamic equilibrium is calculated self-consistenly. Numerical results
show that self-consistency in the calculations is of major importance
for a realistic description of energy and momentum balance between
waves and particles.
Title: Pronounced proton core temperature anisotropy, ion differential
speed, and simultaneous Alfvén wave activity in slow solar wind at
0.3 AU
Authors: Marsch, E.; Rosenbauer, H.; Schwenn, R.; Muehlhaeuser,
K. -H.; Denskat, K. U.
Bibcode: 1981JGR....86.9199M
Altcode:
In the Helios 2 perihelion (0.3 AU) im May 1978, pronounced ion
differential speeds Δvop>0 and large proton temperature
anisotropies T∥p/T⊥p<1 have been observed
in slow solar wind, in distinct contrast to earlier observations during
the phase of solar activity minimum. These features of ion distributions
occurred simultaneously with high Alfvénic wave activity. Coulomb
friction between the two ion species can be shown to play a minor role,
thus obviously favouring the establishment of a large differential ion
speed by preferentially accelerating wave forces. The observations
may also indicate that strong waves sometimes only heat the protons
without creating a fast solar wind.
Title: Some Characteristics of Proton Velocity Distributions in the
Solar Wind as Observed by the HELIOS Solar Probes
Authors: Marsch, E.; Pilipp, W. G.; Schwenn, R.; Mohlhauser, K. H.;
Rosenbauer, H.
Bibcode: 1981sowi.conf..273M
Altcode:
No abstract at ADS
Title: Ion Sound Turbulence in the Solar Wind
Authors: Dum, C. T.; Marsch, E.; Pilipp, W.; Gurnett, D. A.
Bibcode: 1981sowi.conf..299D
Altcode:
No abstract at ADS
Title: HELIOS - Indications of Resonant Wave-Particle Interaction
in Fast Stream Solar Wind Ion Distributions
Authors: Rosenbauer, H.; Marsch, E.; Mohlhauser, K. H.; Pilipp, W.;
Schwenn, R.
Bibcode: 1981sowi.conf..353R
Altcode:
No abstract at ADS
Title: Two States of the Solar Wind at the Time of Solar Activity
Minimum - Part Two - Radial Gradients of Plasma Parameters in Fast
and Slow Streams
Authors: Schwenn, R.; Mohlhauser, K. H.; Marsch, E.; Rosenbauer, H.
Bibcode: 1981sowi.conf..126S
Altcode:
No abstract at ADS
Title: Initial Results on Solar Wind Alpha Particle Distributions
as Measured by HELIOS Between 0.3AU and 1AU
Authors: Marsch, E.; Mohlhauser, K. H.; Pilipp, W.; Schwenn, R.;
Rosenbauer, H.
Bibcode: 1981sowi.conf..443M
Altcode:
No abstract at ADS
Title: Electron Characteristics in the Solar Wind as Deduced from
HELIOS Observations
Authors: Pilipp, W. G.; Schwenn, R.; Marsch, E.; Molhauser, K. H.;
Rosenbauer, H.
Bibcode: 1981sowi.conf..241P
Altcode:
No abstract at ADS
Title: Determination of wave growth from measured distribution
functions and transport theory
Authors: Dum, C. T.; Marsch, E.; Pilipp, W.
Bibcode: 1980JPlPh..23...91D
Altcode:
A stability analysis which directly uses particle distribution
functions determined from experiments or transport theory, rather
than model distributions, is carried out. The features of distribution
functions relevant to whistlers, ion cyclotron waves, including their
low-frequency extensions for propagation along the magnetic field,
and to ion-acoustic waves are analyzed in detail. The dependence of
wave growth on the precise shape of the distributions and the numerical
feasibility of the method is demonstrated by the use of measured solar
wind distributions.
Title: Ion acoustic waves and related plasma observations in the
solar wind
Authors: Gurnett, D. A.; Marsch, E.; Pilipp, W.; Schwenn, R.;
Rosenbauer, H.
Bibcode: 1979JGR....84.2029G
Altcode:
This paper presents an investigation of solar wind ion acoustic
waves and their relationship to the macroscopic and microscopic
characteristics of the solar wind plasma. Comparisons with the
overall solar wind corotational structure show that the most
intense ion acoustic waves usually occur in the low-velocity
regions ahead of high-speed solar wind streams. Of the detailed
plasma parameters investigated, the ion acoustic wave intensities
are found to be most closely correlated with the electron to
proton temperature ratio Te/Tp and with the
electron heat flux. Investigations of the detailed electron and
proton distribution functions also show that the ion acoustic waves
usually occur in regions with highly non-Maxwellian distributions
characteristic of double-proton streams. The distribution functions
for the double-proton streams are usually not resolved into two
clearly defined peaks, but rather they appear as a broad shoulder on
the main proton distribution. Two main mechanisms, an electron heat
flux instability and a double-ion beam instability, are considered
for generating the ion-acoustic-like waves observed in the solar
wind. Both mechanisms have favorable and unfavorable features. The
electron heat flux mechanism can account for the observed waves
at moderate to large ratios of Te/Tp but has
problems when Te/Tp is small, as sometimes
occurs. The ion beam instability appears to provide more flexibility on
the Te/Tp ratio; however detailed comparisons
using observed distribution functions indicate that the ion beam
mode is usually stable. Possible resolutions of these difficulties
are discussed.
Title: A survey on initial results of the HELIOS plasma experiment
Authors: Rosenbauer, H.; Schwenn, R.; Marsch, E.; Meyer, B.;
Miggenrieder, H.; Montgomery, M. D.; Muehlhaeuser, K. H.; Pilipp,
W.; Voges, W.; Zink, S. M.
Bibcode: 1977JGZG...42..561R
Altcode:
The reported results are mainly based on data obtained during the
first part of the Helios-1 mission. The sun was very quiet during
the considered period. The data are, therefore, representative
for comparatively stationary conditions in the solar corona. Data
obtained concerning the protons were evaluated by means of a special
computer routine. The significance of the data is discussed, taking
into account the status of the corona and the interplanetary plasma
during the considered part of the Helios-1 mission, fast stream
structures in the region between 0.3 and 1 AU, radial gradients
of fast and slow solar wind, and the separation of proton double
streams and alpha-particles. Attention is also given to the 'strahl'
in the electron distribution, differences between fast streams and
slow plasma on the basis of the observed electron distributions,
and radial gradients in the case of solar wind electron parameters.