Author name code: ryutova
ADS astronomy entries on 2022-09-14
author:"Ryutova, Margarita"
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Title: Physics of Magnetic Flux Tubes
Authors: Ryutova, Margarita
Bibcode: 2018ASSL..455.....R
Altcode:
No abstract at ADS
Title: Physics of Magnetic Flux Tubes
Authors: Ryutova, Margarita
Bibcode: 2015ASSL..417.....R
Altcode: 2015pmft.book.....R
No abstract at ADS
Title: Plasma Instabilities in Quiescent Prominences
Authors: Ryutova, M.; Berger, T.; Frank, Z.; Title, A.; Tarbell, T.
Bibcode: 2012ASPC..454..143R
Altcode:
We study dynamics of quiescent prominences using several data sets
taken with the SOT on Hinode. We find a number of processes occurring
at different stages of the prominence evolution that are common for
all the chosen cases, and having universal character, can be related
to a fundamental plasma instabilities. We combine the observational
evidence and theory to identify these instabilities. Here we discuss
only two examples: (1) Coronal cavity formation under a prominence
body and its evolution associated with screw pinch instability, and
(2) Development of a regular series of plumes and spikes typical to
the Rayleigh-Taylor instability modified by solenoidal magnetic field.
Title: Signatures of Moving Magnetic Features in and above the
Photosphere
Authors: Hagenaar, H.; Shine, R.; Ryutova, M.; Dalda, A. S.
Bibcode: 2012ASPC..454..181H
Altcode:
Hinode/SOT observations of NOAA AR 10933 from 2007 Jan 4 16:14 UT -
Jan 6 22:20 UT are used to study MMFs (moving magnetic features) in the
periphery of the region's large sunspot and the surrounding moat. The
data consist of a nearly continuous set of Fe 6302 Å Stokes V images
with sets of G band and Ca II H filtergrams at various cadences, FOV's,
and resolutions plus some SpectroPolarimeter (SP) scans. We also used
TRACE images in 171 Å to follow any possible signatures at higher
temperatures. We applied automatic object recognition and tracking
to the MMFs as seen in the Fe 6302 Å Stokes V images. An SP scan
was used to determine the line profiles for several paths. Reliable
inversions have not yet been done, but we find a few locations of
possible supersonic downflows from the Stokes IQUV line profiles. The
population of MMFs on the East side of the sunspot is much higher
than on the opposite side, mostly involving a large number of mixed
polarity MMFs. Consequently, the chromosphere shows strongly enhanced
brightenings with a clear pattern: enhanced brightenings in Ca H
outline the locations where opposite polarity MMFs meet. This activity
does not prevent formation of active low lying “closed” loops at
coronal temperatures seen in the TRACE 171 Å line. The other side,
with fewer MMFs, shows a pattern that we found earlier: regions with
an MMF deficiency show long living “open” coronal loops. This work
was supported by NASA contract NNM07AA01C.
Title: Flares Producing Well-organized Post-flare Arcades (Slinkies)
Have Early Precursors
Authors: Ryutova, M. P.; Frank, Z.; Hagenaar, H.; Berger, T.
Bibcode: 2011ApJ...733..125R
Altcode:
Exploding loop systems producing X-ray flares often, but not always,
bifurcate into a long-living, well-organized system of multi-threaded
loop arcades resembling solenoidal slinkies. The physical conditions
that cause or prevent this process are not known. To address this
problem, we examined most of the major (X-class) flares that occurred
during the last decade and found that the flares that bifurcate into
long-living slinky arcades have different signatures than those that
do not "produce" such structures. The most striking difference is that,
in all cases of slinky formation, GOES high energy proton flux becomes
significantly enhanced 10-24 hr before the flare occurs. No such effect
was found prior to the "non-slinky" flares. This fact may be associated
with the difference between energy production by a given active region
and the amount of energy required to bring the entire system into
the form of well-organized, self-similar loop arcades. As an example
illustrating the process of post-flare slinky formation, we present
observations taken with the Hinode satellite, in several wavelengths,
showing a time sequence of pre-flare and flare activity, followed by
the formation of dynamically stable, well-organized structures. One
of the important features revealed is that post-flare coronal slinky
formation is preceded by scale invariant structure formation in the
underlying chromosphere/transition region. We suggest that the observed
regularities can be understood within the framework of self-organized
critical dynamics characterized by scale invariant structure formation
with critical parameters largely determined by energy saturation
level. The observed regularities per se may serve as a long-term
precursor of strong flares and may help to study predictability of
system behavior.
Title: Greenhouse effect in quiescent prominences
Authors: Ryutova, M.; Berger, T. E.; Title, A. M.
Bibcode: 2010AGUFMSH51A1664R
Altcode:
Quiescent prominences, by definition, are huge ``clouds'' of cool,
dense plasma overlying rarefied hot corona and supported by a complex
magnetic field anchored in the photosphere along the magnetic polarity
inversion line. One of the most prominent features in their dynamics
is formation, growth and collapse of bubble/cavities filled by coronal
plasma and emerging, often repeatedly, under a prominence body. As
such, prominence/corona interface itself is subject of fundamental
plasma instabilities, which include development of a regular series
of plumes and spikes typical to the Rayleigh-Taylor instability, the
Kelvin-Helmholtz instability, often followed by a sudden collimated mass
upflow, which, in nonlinear stage having an explosive character may
be responsible for CMEs. These were only recently studied in detail
with high cadence, high resolution data obtained from the Hinode
satellite. Even more surprises are brought by the SDO/AIA instrument
showing the Sun's atmosphere in 12 visible and EUV wavelengths. AIA
multi-wavelength images in a temperature range from 105
~K to 2 × 106 ~K combined with the Hinode/SOT data show
that plasma inside the prominence cavity, being as expected, at
coronal temperatures, in fact exceeds the temperature of the ambient
corona. We suggest that an energetically open highly dynamic processes
releasing energy at the prominence/cavity interface accompanied by the
``radiative exchange'', may cause additional increase of temperature
and/or density inside cavity. Given pervasive character of prominences,
future studies will allow us to perform quantitative and statistical
analysis, and reveal relations between the size of cavity, its
temperature, and magnetic properties.
Title: Observation of Plasma Instabilities in Quiescent Prominences
Authors: Ryutova, M.; Berger, T.; Frank, Z.; Tarbell, T.; Title, A.
Bibcode: 2010SoPh..267...75R
Altcode: 2010SoPh..tmp..170R
We study dynamics of quiescent prominences using several data sets taken
with the Solar Optical Telescope (SOT) on Hinode. We find a number of
processes occurring at different stages of prominence evolution that
are common for all of our chosen cases and, having universal character,
can be related to fundamental plasma instabilities. We combine the
observational evidence and theory to identify these instabilities. Here
we discuss three examples: i) prominence cavity formation and its
evolution, associated with a screw-pinch instability; ii) development
of a regular series of plumes and spikes typical to the Rayleigh -
Taylor (RT) instability; and iii) the appearance of growing ripples at
the prominence/corona interface, often followed by a sudden collimated
mass upflow, attributed to the Kelvin - Helmholtz (KH) instability. The
conditions for transition from a linear (rippling mode) to nonlinear
stage of the KH instability, known to have an explosive character,
are specified. Given excellent Hinode data, all three aspects of
prominence dynamics allow quantitative analysis.
Title: Response of the Chromosphere to Penumbral Dynamics: Bow Shocks
and Microjets
Authors: Ryutova, M.; Berger, T.; Frank, Z.; Title, A.
Bibcode: 2009ASPC..415..373R
Altcode:
We have analyzed the data sets obtained with the SOT instrument
on Hinode during the disc passage of AR 10923 (November 10--20,
2006). Along with a limited number of jet-like features (Katsukawa
2007), we found other kinds of bright chromospheric transients
abundantly pervading the entire penumbra and drifting as a whole in
a direction perpendicular to their long axes. Quantitative analysis
based on our recent penumbral model (Ryutova et al. 2008a) shows that
they have all the signatures of bow shocks produced in the overlying
chromosphere by post-reconnection penumbral filaments.
Title: Formation and Dynamics of Multi-thread Arcades of Coronal Loops
Authors: Ryutova, M.; Frank, Z.; Berger, T.
Bibcode: 2009ASPC..415..291R
Altcode:
Coronal structures having various forms and dynamics, often bifurcate
into a long living, well organized multi-thread loop arcades. To
describe this process we use the model of energetically open system,
consisting of current carrying magnetic loops that interconnect a high
β energy production region with a low β dissipation region through
the resistive stresses. The model includes feedback managed by the
transition region. Such a system may be driven into various dynamic
forms including spontaneous process of self-organization.
Title: Sunspot Penumbrae: Formation and Fine Structure
Authors: Ryutova, M.; Berger, T.; Title, A.
Bibcode: 2009ASPC..415..361R
Altcode:
Sub-arcsecond observations revealing the fine sub-structure of
penumbral filaments and new properties of their dynamics, provide both
the basis and constraints for novel models of the penumbra. Even more
severe conditions are imposed on models by new data obtained with the
SOT instrument on Hinode, showing e.g. direct connection between the
dynamic changes in penumbra and appearance of bright transients in
the overlying chromosphere. We propose the mechanism that not only
explains the observed properties of individual filaments, but is part
of the physical process that determines formation of penumbra and its
impact on the overlying atmosphere.
Title: Helical Shape and Twisting Motion as Intrinsic Properties of
Penumbral Filaments
Authors: Shine, R. A.; Ryutova, M.; Berger, T. E.; Title, A. M.;
Tarbell, T. D.; Ichimoto, K.
Bibcode: 2009AGUFMSH23B1541S
Altcode:
A wealth of high resolution data obtained with advanced ground based
telescopes and the SOT instrument on HINODE have led to new findings
in the properties of penumbral filaments and controversies in their
interpretation. Here we address one such issue, namely the question of
whether the apparent twist of filaments is real or is just a viewing
effect. We show that the helical shape and twisting motions of penumbral
filaments follow from first principles and represent an integral part of
penumbra formation and dynamics. As such, these properties link together
other observed features of filaments including their magnetic and
thermal substructure and their impact on the overlying atmosphere. At
all stages of penumbral dynamics, qualitative agreement of theory and
observations is supported by quantitative analysis as well.
Title: Role of the Resistive and Thermal Instabilities in Dynamics
of Quiescent Prominences
Authors: Frank, Z.; Ryutova, M.; Berger, T. E.; Title, A. M.; Tarbell,
T. D.
Bibcode: 2009AGUFMSH41B1653F
Altcode:
We present the observations taken with the SOT instrument on Hinode in
G-band and Ca H lines. High cadence data compiled in movies show clear
evidence for several fundamental plasma instabilities. We combine
the observational evidence and theoretical estimates to identify
these instabilities. The following can be given as examples. (1)
An analogue of the Kelvin-Helmholtz instability develops at the
prominence/corona interface that manifests itself in growing ripples
during a linear growth phase and may be followed by a nonlinear stage
taking the form of an explosive instability corresponding to a CME
ejection. This instability also includes the regime of "smoke ring"
formation. (2) The appearence of "bubbles and spikes" typical to
the Rayleigh-Taylor instability are observed. Their evolution and
growth rates are found to be modified by both poloidal and toroidal
components of magnetic field. (3) A resistive interchange instability,
associated with an "unfavorable" magnetic field curvature relative to
the density/temperature gradients, may be responsible for a hot barb
formation, its evolution and collapse.
Title: Origin of Filamentary Structures and Flows in Quiescent
Prominences
Authors: Ryutova, M.; Berger, T. E.; Tarbell, T. D.; Frank, Z.; Title,
A. M.
Bibcode: 2009AGUFMSH23B1540R
Altcode:
The paradox of fine vertical structure has usually referred to an
apparent contradiction met when comparing vertical fine structures
of quiescent prominences observed on the limb with the necessary
horizontal magnetic field along their long axis. In addition to this
fundamental problem, the very formation of fine vertical structures
has been a long standing puzzle. Here we address these problems and
show that considering the global structure of a prominence as a large
scale skewed formation with toroidal and poloidal fields removes the
paradox and allows derivation of dynamic stability criteria. This also
includes the mechanism of the fine structure formation and peculiarities
of downward mass motions. Theoretical estimates of key parameters
are compared with the observations taken with the SOT instrument
on Hinode. We find results of comparison very encouraging. For the
approximate 3D reconstruction of the general shape of prominences,
the STEREO A and B images have been used.
Title: On the Penumbral Jetlike Features and Chromospheric Bow Shocks
Authors: Ryutova, M.; Berger, T.; Frank, Z.; Title, A.
Bibcode: 2008ApJ...686.1404R
Altcode:
We present observations of sunspot penumbrae obtained during the disk
passage of AR 10923 (2006 November 10-20) with the SOT instrument on
Hinode in 4305 Å G band and Ca II λ3968 H line. Along with recently
discovered jetlike features (Katsukawa et al. 2007), we find other
kinds of bright elongated transients abundantly pervading the entire
penumbra and drifting as a whole in a direction almost perpendicular
to their long axes. Their measured velocities strongly depend
on their orientation with respect to the line of sight and range
from simeq1 to simeq20 km s-1. We present quantitative
analysis of these features and interpret them relative to our recent
penumbral model (Ryutova et al. 2008) to show that they are produced
by shocks resulting from a slingshot effect associated with the ongoing
reconnection processes in neighboring penumbral filaments. Due to sharp
stratification of the low atmosphere, postreconnection flux tubes moving
upward quickly accelerate. At transonic velocities a bow (detached)
shock is formed in front of the flux tube, as usually occurs in cases
of blunt bodies moving with supersonic velocities. Observed parameters
of transients are in good agreement with calculated parameters of
bow shocks. On some, much more rare occasions compared to "drifting"
bow-shock-type transients, there appear compact bright transients
moving in the radial direction, along their long axis, and having
velocities of 20-50 km s-1. We relate these features to a
category of true microjets.
Title: Evershed Flows as an Integral Part of Penumbral Formation
and its Fine Structure
Authors: Ryutova, M.; Berger, T.; Lites, B.; Title, A.; Frank, Z.
Bibcode: 2008AGUSMSP41B..07R
Altcode:
Observations of Evershed flows with the Solar Optical Telescope (SOT)
on Hinode (Ichimito, Shine, Lites, et al. 2008, PASJ, 59, S593) showed
that penumbral flows have small scale structures and much more complex
properties than those of a simple outflow of material with unique
direction and appearence. We address this problem and show that the
flow properties are directly connected to the observed properties of
penumbral filaments and are an integral part of penumbral development
during sunspot formation. In our recent model (Ryutova, Berger, &
Title, 2008, ApJ, 676, April), based on the observations that sunspot
has a filamentary structure and consists of a dense conglomerate of
non-collinear interlaced flux tubes, the penumbra is formed due to
an on-going reconnection processes that leads to branching out of the
peripheral flux tubes from the "trunk". As flux tubes have different
parameters, branching occurs at different heights and with different
inclinations, thus forming an "uncombed" penumbra. Each elemental act
of reconnection generates an inevitable twist in the post-reconnection
filaments that acquire a screw pinch configuration. This explains
the remarkable dynamic stability of penumbral filaments and their
observed properties, such as presence of dark cores, wrapping and
spinning of filaments around each other, bright footpoints, etc. Here
we show that propagation of twist along current carrying helical flux
tubes is accompanied by plasma flows that may have diverse properties
depending on the location of interacting flux tubes, their inclination
and pitch. We apply the model to observations taken with the SOT
instrument, which includes spectro-polarimetric data, and perform
quantitative analysis.
Title: On the Fine Structure and Formation of Sunspot Penumbrae
Authors: Ryutova, M.; Berger, T.; Title, A.
Bibcode: 2008ApJ...676.1356R
Altcode:
Recent high-resolution observations with the 1 m Swedish Solar Telescope
(SST) on La Palma reveal the fine substructure of penumbral filaments
and new properties of their dynamics. These findings provide both the
basis and constraints for novel models of the penumbra. We present new
observations of a large isolated sunspot near Sun center obtained with
the SST in 2006. Our data, taken simultaneously in the 4305 Å G-band
and 4364 Å continuum bandpasses and compiled in high-cadence movies,
confirm the previous results and reveal new features of penumbral
filament dynamics. We find that individual filaments are cylindrical
helices with the apparent properties of vortex tubes exhibiting flow
patterns similar to kinked flux tubes. Measured pitch/radius ratios
of helical filaments indicate their dynamic stability. We propose a
mechanism that explains the fine structure of penumbral filaments,
their observed dynamics, and their formation process in association
with sunspot properties. The mechanism assumes that the umbra itself
is a dense conglomerate of twisted, interlaced flux tubes with
peripheral filaments branching out from the "trunk" at different
heights due to ongoing reconnection processes and arcing downward to
the photosphere. The twist of individual filaments, and the resulting
distribution of magnetic fields and temperature, is due to the onset
of the well-known screw pinch instability, the parameters of which
can be measured from our data.
Title: On the Chromospheric Micro-jets Associated with the Penumbral
Filaments
Authors: Ryutova, M.; Berger, T.; Tarbell, T.; Frank, Z.; Title, A.
Bibcode: 2007AGUFMSH22A0843R
Altcode:
We present observations of sunspot penumbrae obtained during the disk
passage of AR 10923 (November 10--20, 2006) with the Solar Optical
Telescope (SOT) on the Hinode satellite. Co-aligned multi-hour movies
taken simultaneously in several wavelengths show fine-scale dynamics
at the sub-arcsecond level. The dynamics include helical flows along
penumbral filaments, branching of filaments, and penumbral "micro-jets"
recently described by Katsukawa et al. (AAS 210, 94.13). We present
quantitative analyzes of the penumbral jets and interpret them relative
to our recent model of penumbral filaments (Ryutova, Berger and Title,
2007, in "Collective phenomena in macroscopic systems", Ed. G. Bertin,
et al., World Scientific) to show that the jets are the result of
magnetic reconnection of the helical field lines in neighboring
non-collinear filaments.
Title: Transient Phenomena in Multi-thread Arcades of Coronal Loops
Authors: Frank, Z.; Ryutova, M.
Bibcode: 2007AGUFMSH22A0842F
Altcode:
The post-flare coronal loops having well defined filamentary
structure, often appear as an arcades of thin magnetic threads
resembling winding in a curved solenoid or a funnel. Compared
to flare timescales, post-flare arcades are long living, well
organized structures. Elemental filaments in arcades are, however,
in highly dynamic state, showing oscillations, and harboring frequent
microflares. These microflares often appear simultaneously in different
places. Besides, many individual filaments produce homologous,
repetitive microflares. Microflares are often accompanied by short
living jets. We present the observations of these events using the
data taken with SOT and XRT instruments on Hinode combined with the
TRACE 195 ~Å coronal line. The object of the observation is AR 10930
which exhibited several flare events in December, 2006. After a major
flare on 13 December, a typical "solenoidal" system of coronal threads
was formed that lasted over 6 hours. The observed spatial and temporal
regularities in appearence of the EUV transients can be well understood
on basis of a spatio-temporal echoes resulted from nonlinear response of
a system ("coupled oscillators") to impulsive disturbences associated
with the changes in the photospheric magnetic fields. Observations in
the SOT chromospheric lines show appearence of precursors of coronal
jets and microflares.
Title: Penumbral Dynamics and its Manifestation in the Overlying
Chromosphere
Authors: Ryutova, Margarita; Berger, Thomas; Tarbell, Theodor; Frank,
Zoe; Title, Alan
Bibcode: 2007APS..DPPYP8056R
Altcode:
Mature sunspots are usually surrounded by penumbra - a dense
conglomerate of a random interlaced flux tubes with varying
inclinations. High resolution observations show a fine sub-structure
of penumbral filaments and new regularities in their dynamics. These
regularities fit well our recent model of penumbra based on cascading
reconnection events occurring in the system of non-collinear flux
tubes. Each act of reconnection generates twist in the reconnected
filaments and facilitates the onset of a screw pinch instability,
consistent with the observations showing that individual filaments
are cylindrical helices with a pitch/radius ratio providing their
stability. In addition, the post-reconnection products produce a
sling-shot effect that generates oblique shocks and leads to appearence
of a lateral jets. Here we report high resolution (120-180 km) high
cadence (15-30 sec) observations taken with the Solar Optical Telescope
(SOT) on the Hinode satellite. Co-aligned multi-hour movies taken
simultaneously in several wavelengths show detailed behavior of penumbra
filaments and their effect on the overlying chromosphere. We confirm
the ubiquitous nature of penumbral micro-jets recently discovered by
SOT instrument (Katsukawa et al. 2007, AAS 210, 94.13), and present
quantitative analysis of chromospheric jets based on our recent model
of penumbra.
Title: Magnetic Solitons: Unified Mechanism for Moving Magnetic
Features
Authors: Ryutova, M.; Hagenaar, H.
Bibcode: 2007SoPh..246..281R
Altcode:
In a highly dynamic environment with sources and sinks of energy,
flux tubes do not in general obey local conservation laws, nor do the
ensembles of flux tubes that exhibit collective phenomena. We use the
approach of energetically open dissipative systems to study nonlinear
waves in flux tubes and their role in the dynamics of the overlying
atmosphere. We present results of theoretical and observational studies
of the properties of moving magnetic features (MMFs) around sunspots and
the response of the overlying atmosphere to various types of MMFs. We
show that all types of MMFs, often having conflicting properties,
can be described on a unified basis by employing the model of shocks
and solitons propagating along the penumbral filaments co-aligned with
Evershed flows. The model is also consistent with the response of the
upper atmosphere to individual MMFs, which depends on their type. For
example, soliton-type bipolar MMFs mainly participate in the formation
of a moat and do not carry much energy into the upper atmosphere,
whereas shock-like MMFs, with the appearance of single-polarity
features, are often associated with chromospheric jets and microflares.
Title: Anticorrelation between Moving Magnetic Features and Coronal
Loop Formation
Authors: Ryutova, M. P.; Hagenaar, H.; Title, A.
Bibcode: 2007ApJ...656L..45R
Altcode:
We study a possible connection of moving magnetic features (MMFs)
and the overlying atmosphere using several sets of multiwavelength
observations of sunspot areas from the photosphere to the corona. We
find that as a collective phenomenon, very intense MMF formation
anticorrelates with the presence of large-scale ``stable'' coronal
loops: such loops are rooted at the side of sunspots with no or few
MMFs rather than at the side of the penumbra/moat highly populated by
MMFs. Conjectures to help understand the observed correlation between
the preferable site of coronal loops and the deficiency of MMFs are
discussed.
Title: Coupling effects throughout the solar atmosphere: 2. Model
of energetically open circuit
Authors: Ryutova, M.
Bibcode: 2006JGRA..111.9102R
Altcode: 2006JGRA..11109102R
EUV structures in the solar atmosphere are studied on the basis of
the energetically open equivalent circuits. The systems consist
of current carrying magnetic loops that interconnect a high β
energy-production region with a low β dissipation region and
include the transition region where the most efficient generation
of currents and transport of the accumulated energy through the
resistive stresses occurs. As nonconservative systems with a source
and sink of energy, they may be driven into various dynamic forms via
nonlinear processes with continuous flow of matter and energy. The
corresponding equivalent circuit equation has the form of the Van
der Pol oscillator. Depending on the coefficients determined by the
system parameters, this equation describes different behaviors of
the EUV structures including long-living steady loops with subtle
oscillations, loops in the relaxation regime, and the periodically
flaring and exploding loop systems. The model predicts that the EUV
loops must have a filamentary structure and allows us to estimate the
limiting currents and critical radii of elemental filaments associated
with the stability criteria. Simple relations between the parameters,
most of which are observables, may provide reliable diagnostic tools.
Title: Coupling effects throughout the solar atmosphere: Emerging
magnetic flux and structure formation
Authors: Ryutova, M.; Shine, R.
Bibcode: 2006JGRA..111.3101R
Altcode: 2006JGRA..11103101R
We report observations of the "birth," formation, and evolution
of compact coronal structures associated with strong localized
motions generated by emerging magnetic flux in the photosphere. We
use multiwavelength time series of data taken simultaneously with the
Swedish Vacuum Solar Telescope (SVST) on La Palma, the TRACE satellite,
and the MDI instrument on SOHO. We find that long before the magnetic
pore is formed, the chromosphere and transition region show a high
activity above the future site of pore formation: rising but not yet
visible magnetic flux exerts a strong pressure on the overlying plasma
generating highly collimated plasma flows seen in the Hα images. About
the time when the magnetic pores are formed and the Hα surges bifurcate
into the established arc-like flows, a system of compact coronal loops
is formed, showing direct connection between the motions associated with
the evolving magnetic fields and the coronal structure formation. We
propose a mechanism that may lead to the observed phenomena based on
the generation of currents by strong disturbances propagating upward
from a limited surface area.
Title: Tadpoles in Sunspot Penumbrae
Authors: Ryutova, M. P.; Hagenaar, M.
Bibcode: 2005AGUFMSH11A0239R
Altcode:
Observations of magnetic fields and flows in sunspot penumbrae at
a spatial resolution of 0.1"-0.2" revealed many earlier unavailable
details (see e.g. K. Langhans et al. 2005, A&A, 436, 1087). We
concentrate here on some properties of the fine structure of penumbrae
that briefly may be characterized as a dense ensemble of dark-cored
and bright magnetic filaments, highly dynamic at short time scales
and preserving their general properties for hours. Inclination of
dark and bright filaments, their magnetogram signals (having rapid
azimuthal variation), and plasma flows associated with them, are
significantly different. Topologically, dark-cored filaments surrounded
by bright threads, have a peculiar (and ubiquitous) shape of a tadpole
with a thick head ``diving'' into the umbra and a long tail reaching
sometimes the outer edge of the penumbra. The filaments have their own
sub-structure of various forms that continuously evolve from one to
another. We use the model of highly inhomogeneous ``magnetic fluid''
with the sheared mass flows to explain the observed regularities. We
show that differences in the inclination of magnetic fields and sheared
velocities result in the nonlinear instabilities associated with the
vortex motion and interaction of the poloidal and toroidal components
of magnetic fields. This, in turn, leads to a filamentation process, as
well as formation of the structures having the appearance of tadpoles.
Title: Self-focusing of Shocks and Hydrodynamic Cumulation in the
Solar Atmosphere
Authors: Tarbell, T.; Ryutova, M.
Bibcode: 2005AGUFMSH53A1251T
Altcode:
Network magnetic field in the solar atmosphere is concentrated
in isolated non-collinear thin flux tubes embedded in almost
non-magnetic environment with plasma beta β=8π pext/Bext2>>
1. Brought together by convective motions flux tubes collide and
reconnect. Post-reconnection dynamics of the photospheric magnetic flux
tubes is radically different from a low beta coronal plasma. Here
the reconnection does not give in situ heating, but it sets the
system in a highly unsteady state. After reconnection, the strongly
curved flux tubes behave as elastic bands: straightening they create
a sling-shot effect which generates complex 3D shock waves with the
curved surface. Self-focusing of these shocks occurs as they propagate
upward in the stratified atmosphere, producing a strong cumulative
effects. Depending on the geometry of the shock conversion, highly
concentrated energy may be either converted entirely into heat or into
strong jets, or be distributed between the two. These processes have
been observed in simultaneous observations of the solar atmosphere
from its surface to the corona obtained with the Solar and Heliospheric
Observatory (SOHO) and Transition Region and Coronal Explorer (TRACE)
showing a ubiquitous sequence of events that start from cancellation of
photospheric magnetic fields, pass through shock formation and result in
the transition region supersonic jets and microflares (Ryutova &
Tarbell, 2003, Physical Review Letters, 90, 191101). We also find
that lateral shocks produced by the reconnection of the same polarity
non-collinear magnetic flux tubes may cause the ubiquitous bright points
observed in sunspots and their environment. The mechanisms of energy
flow and release in the solar atmosphere involve fundamental physical
processes that are commonplace throughout astrophysics and laboratory
plasma physics. The advances in the coordinated observations with SOHO
and TRACE provide a unique opportunity to check the theoretical models,
and shed light on the general mechanisms of energy production, transfer
and release in stellar atmospheres and other astrophysical objects.
Title: Unified Mechanism for the Formation of Moving Magnetic Features
Authors: Ryutova, M. P.; Hagenaar, H. J.
Bibcode: 2005AGUSMSP31A..04R
Altcode:
In the highly dynamic environment around sunspots there are small
scale magnetic features, MMF's, that show clear regularities and may
be thus categorized according their observed properties. For now there
are at least 4 types of "MMF's" (Moving Magnetic Features). Type I
MMF's are compact pairs of opposite polarity elements that may emerge
anywhere in penumbra or moat region and move radially outward gradually
separating; their velocities exceed the velocities of ambient flows,
and their inner " foot" shares the sunspot's polarity. Type II MMF's
are seen as unipolar features of the same polarity as the sunspot,
moving outward from the sunspot with higher velocities than type
I. Type III MMF's are also seen as unipolar features but have the
polarity opposite to the sunspot's and travel with higher velocities
than the other two types of MMF's. Recently the "type IV" features
were observed in a sunspot formation region, that appear as compact
bipoles flowing into sunspots and with an inner foot of a polarity
opposite to the sunspot's. These were dubbed the MDF's (Moving Dipolar
Features). The observed properties of all types of MMF's clearly
violate the energy and momentum conservation laws, and thus require
the application of physical mechanisms adequate for energetically open
systems. Such mechanisms have been applied to type I and type II MMF's
(Ryutova, Shine, Title, and Sakai, 1998, ApJ, 492, 402) with a good
agreement between the theory and observations. Here we show that the
same approach not only explains the origin, structure and dynamics of
MDF's and type III MMF's, but consolidates all types of MMF's into one
scheme. Theoretical results are compared with the observed properties
of MMF's using time series of several data sets.
Title: Energy Transfer and the Acoustic Wave Packets in Randomly
Magnetized Solar Atmosphere
Authors: Ryutova, M. P.
Bibcode: 2005AGUSMSH13C..09R
Altcode:
Energy transfer from the acoustic waves and unsteady wave packets
to overlying atmosphere strongly depends on the 'magnetic status'
of the photosphere and chromosphere regions (Ryutova & Priest,
1993 ApJ, 419, 349; 419, 371 ). Here we concentrate on the magnetic
network outside sunspots and active regions, where we distinguish
several types of magnetic field topography, determined by the
distribution of flux tubes in space and over their physical parameters,
non-collinearity of flux tubes, predominance of one polarity elements
or balanced distribution of mixed polarities. Magnetic structures in
the chromosphere are as well very different and span from different
kinds of compact magnetic arcades to "tall" magnetic structures
typical to regions underlying the coronal holes. Interaction of
waves and wave packets with the ensembles of magnetic flux tubes is
accompanied by frequency shift and clear morphological effects in
the enhanced emission at chromosphere/transition region level that are
different for different regions. For example, over the regions with wide
distribution function of non-collinear flux tubes, variation of physical
parameters of flux tubes (radius, magnetic field strength, etc.) and
their inclinations lead to the spreading of the energy deposition
region and its dislocation from the expected site, i.e. site which
is directly above the studied magnetic region. The energy density,
frequency range, specific properties and location of the enhanced
emission ("magneto-acoustic halos") are given in terms of the observable
parameters for differently magnetized regions. Obtained results allow
quantitative analysis of magnetic effects in the seismology of upper
layers of atmosphere.
Title: Response of the Corona to Magnetic Activity in Underlying
Plage Regions
Authors: Ryutova, M.; Shine, R.
Bibcode: 2004ApJ...606..571R
Altcode:
We study the response of the solar corona to magnetic activity in the
underlying plage regions using high-resolution Michelson Doppler Imager
magnetograms co-aligned with multiwavelength images taken by TRACE at
chromospheric and coronal temperatures. We show that the EUV emission
above plage regions that are dominated by single-polarity magnetic
elements always has an amorphous shape that topologically mimics
the shape of the underlying plage. Spacetime slices of the amorphous
emission in the coronal lines show coherent braidlike structures with
almost constant period for a given area. Contrary to this, coronal
emission above mixed-polarity plages is highly discrete and consists
of sporadic localized radiative transients. As different regions of
strongly inhomogeneous corona evolve in different ways, separate
mechanisms for energy production, flow, and release are probably
required. We argue that in all cases the primary energy source lies
in continuous hydromagnetic activity among the photospheric magnetic
fields. The character of this activity determines the processes
of the extraction of energy and its transport throughout the solar
atmosphere. We propose a physical mechanism that may explain the diverse
properties of the UV/EUV emission in upper layers of atmosphere and
its relevance to the photospheric magnetic fields.
Title: Magnetic Coupling Between the Solar Surface and Corona:
Theory and Observations
Authors: Ryutova, Margarita; Shine, Richard
Bibcode: 2004AIPC..703..203R
Altcode:
Multi-wavelength observations taken simultaneously by several
instruments on the Solar and Heliospheric Observatory (SOHO)
and Transition Region and Coronal Explorer (TRACE) revealed a
clear connection between the photospheric magnetic fields and the
energetic events in the overlying atmosphere. We find that the EUV
coronal emission above the photosphere dominated by single polarity
magnetic elements is spongy in space and has coherent braid-like
structures in time. Contrary to these long living structures, corona
above the regions with mixed polarity magnetic elements is highly
discrete and consists of sporadic microflares, supersonic jets and
their combinations. We believe that in the unipolar magnetic regions
the energy flow from the surface to corona is associated with the
nonlinear collective phenomena in the ensemble of oscillating magnetic
flux tubes. These phenomena lead to formation of hot coronal ``clouds''
that have the properties of energetically open turbulence with tendency
to self-organization. Jets and microflares above the mixed polarity
regions are associated with shock waves produced by reconnecting
magnetic flux tubes in the photosphere and subsequent interaction of
shocks which leads to hydrodynamic cumulation of energy, which leads
to impulsive phenomena similar to shaped charges.
Title: MHD Shocks: The Origin of the Solar Transition Region and
Coronal Sporadic Events
Authors: Ryutova, M. P.; Tarbell, T. D.
Bibcode: 2004ESASP.547..239R
Altcode: 2004soho...13..239R
No abstract at ADS
Title: Coronal Loops as Van der Pol Oscillators: Theory and
Observations
Authors: Ryutova, M. P.
Bibcode: 2003SPD....34.0402R
Altcode: 2003BAAS...35..810R
We study formation and dynamics of coronal loops associated with various
magnetic fields in the underlying photosphere, from an isolated sunspot
penumbra to plage regions with newly emerged magnetic fluxes. We use
coordinated observations from Swedish Vacuum Solar Telescope (SVST)
on La Palma, the TRACE satellite and the MDI instrument on SOHO. High
resolution MDI magnetograms are assembled in a 6-hour movie and
co-aligned with TRACE Fe IX/X 171 Å images of the corona, H-alpha
filtergrams showing plasma motions at the chromospheric level. This
allowed us to follow the process of loop formation from its very
early stage and establish links between different stages of the
process and corresponding changes in underlying atmosphere. We found
that the dynamics of coronal loops, e.g. whether the loops exhibit a
``steady'', oscillatory or flaring behavior, strongly depends on the
underlying photospheric magnetic pattern. We propose a mechanism
to explain magneto-hydrodynamic coupling between the photospheric
magnetic fields and various types of coronal structures based on
the time-dependent electric circuit analogue. In nonlinear regime
the LRC equation acquires the form of Van der Pol oscillator with
dissipation and external driving force. Plasma conditions in the
overlying chromosphere and corona determine the main components of
the circuit. Depending on these components and the character of the
energy source (e.g. electro-mechanical driver in the photosphere) the
formed circuit may exhibit various regimes including the meta-stable
oscillatory behavior, explosive disruption and others. This work is
supported by NASA through the MDI project at Stanford & Lockheed
Martin (NAG510483).
Title: MHD Shocks and the Origin of the Solar Transition Region
Authors: Ryutova, Margarita; Tarbell, Theodore
Bibcode: 2003PhRvL..90s1101R
Altcode:
Simultaneous observations of the solar atmosphere from its surface to
the corona obtained with the Solar and Heliospheric Observatory (SOHO)
and Transition Region and Coronal Explorer (TRACE) show a ubiquitous
sequence of events that start from cancellation of photospheric magnetic
fields, pass through shock formation, and result in transition region
supersonic jets and microflares. These results support a novel view of
the energy buildup in the solar atmosphere associated with a cascade
of shock waves produced by interacting network magnetic elements
in the photosphere and provide insight into the origin of the solar
transition region. The findings account for the general mechanisms
of energy production, transfer, and release throughout the Sun's and
stellar atmospheres.
Title: Interaction and Dynamics of the Photospheric Network Magnetic
Elements
Authors: Ryutova, M.; Tarbell, T. D.; Shine, R.
Bibcode: 2003SoPh..213..231R
Altcode:
Small-scale magnetic elements in the quiet photospheric network are
believed to play a key role in the energy flow from the solar surface
to upper layers of atmosphere. Their intense hydro-magnetic activity
includes merging and fragmentation of same polarity fluxes, `total'
or partial cancellation of neighboring flux elements of opposite
polarity, dynamic appearance and disappearance of compact bipoles,
etc. We study the general features of these processes, and show
that non-collinearity of flux tubes, sharp stratification of low
atmosphere and finite plasma beta lead to several specific effects
in the interacting flux tubes that may explain the morphological
properties of network magnetic field and also provide a mechanism
for the energy build up and release in the nearby chromosphere and
transition region. We show that during the collision of flux tubes in
the photosphere reconnection occurs regardless of whether the flux
tubes are of opposite or of the same polarity. But the dynamics of
reconnection products are significantly different and lead to different
macroscopic effects that can be observed.
Title: Laboratory Simulation of Small-scale Coronal Plasmoids
Authors: Hwang, D.; Horton, R.; Ryutova, M.
Bibcode: 2002AGUSMSH32D..05H
Altcode:
The small scale ejection phenomena, plasmoids, are believed to play an
important role in the coronal dynamics and mass balance. First direct
observations of small (sub-arcsec) plasmoids propagating in the corona
(Koutchmy et al. 1994, Astron. AStrophys., 281, 249) revealed details
of dynamic behavior of plasmoid and lead authors to the plausible
model of plasmoid as a toroidal vortex. Many questions regarding
the interaction of the a cool magnetized plasmoid with surrounding
hot plasma remain unclear. These processes can be simulated in the
laboratory experiment using an accelerated spheromak-like compact toroid
(SCT) injected into a tokamak magnetized target region. The UC Davis
Compact Toroid accelerator (CTIX) is designed to study the formation
and acceleration of a compact toroid under repetitive operation, and
to diagnose the interaction and thermalization of the plasmoid as it
is injected into a target region. We present results of the experiment
with the parameters of the plasmoid and target plasma, scalable to
solar parameters. The different range of parameters and geometry of the
external magnetic field were used to simulate the various conditions
of the propagation of the compact toroid in the target chamber. We show
that in most cases the field reversal in the shell between the compact
toroid and ambient field occurs, suggesting a strong coupling between
the toroid and the ambient field that imay eventually leads to the
shock formation. We estimate the particle inventory balance depending
on the SCT injection rate and geometry. Using scalability criteria,
we present quantitative comparison between the dynamics of the compact
toroid and the observed properties of the coronal plasmoid. This work
is jointly supported by NSF and DOE.
Title: Large-scale Coronal Loop Formation: New Aspects
Authors: Ryutova, M.
Bibcode: 2002AGUSMSH32D..04R
Altcode:
We study formation of two different coronal loop structures typical
to regions overlying the sunspot penumbra: extremely ``quiet''
closed loops and ``open''- fan like - systems. We use coordinated
observations from Swedish Vacuum Solar Telescope (SVST) on La Palma,
the TRACE satellite and the MDI instrument on SOHO. High resolution
MDI magnetograms are assembled in a 6-hour movie and co-aligned with
TRACE Fe IX/X 171 Å images of the corona, Hα filtergrams showing
plasma motions at the ``chromospheric'' level. This allowed us to
follow the process of loop formation from its very early stage and
establish links between different stages of the process and dynamic
changes in underlying atmosphere. For quantitative analysis we propose
a model for the loop formation based on the current drive caused by
nonlinear magneto-hydrodynamic coupling between the sunspot magnetic
field and velocity field. Farther evolution of loop structures can
be described by electric circuit analogue. Plasma conditions in
the overlying chromosphere and corona determine the main components
of the circuit: resistance, ``inductance'' and capacitance of the
system. Depending on these components and the character of the energy
source (e.g. electro-mechanical driver in the photosphere) the formed
circuit may exhibit either meta-stable oscillatory behavior or be
explosively disrupted. We apply these results respectively to closed
(meta-stable) loop system and the open (disrupted) structures and find
good agreement with properties of the observed events.
Title: Self-organized Structures in the Solar Corona
Authors: Ryutova, M. P.
Bibcode: 2001AGUFMSH11A0701R
Altcode:
A regular pattern having a braided appearance was discovered (Shine,
1999) while sampling ``space-time'' slices in the TRACE Fe IX/X 171 Å
and Fe 195 Å data cubes corresponding to spongy EUV coronal emission
at temperatures of about 106 ~K. Such emission, associated
with some plages could be categorized as the ``moss'' - a low lying
(2-4 Mm above the photosphere) hot ``clouds'' with finite thickness
and short time-scale variation of brightness (Berger at al., 1999, ApJ,
519, L97). Here we use the time series of the EUV TRACE images (with ~=
40 ~s cadence) co-aligned with the high resolution MDI magnetograms of
270"x166" area containing three sunspots and several plages. We show
that spongy EUV emission always exists over and mimics the plage regions
that are dominated by one polarity magnetic elements. Space-time slices
show coherent braid-like structures with almost constant period for
a given area. The braid period varies slightly for different emission
regions ranging from 3 min to 10 min and depends mainly on the magnetic
filling of the underlying plage (the observation time is over 3 h). We
propose a mechanism to explain the observed properties of a ``meandering
moss'' based on the idea that a highly dynamic ensemble of magnetic
flux tubes is energetically open system with the source of the energy,
dispersion and dissipation. The unsteady wave packets generated here
are subject of modulation instabilities because of stratification and
transverse inhomogeneity of the medium (magnetic filling factor in pages
is f ~ 0.3). This leads to nonlinear self-organization of a system
in higher layers of atmosphere which manifest itself in periodically
spaced regions of enhanced brightening forming braid structures in
time. The solution for dynamic coherent structures in the enhanced
emission is similar to N-soliton solution of the modified KdV equation,
and contains the observable parameters that makes quantitative analysis
quite reliable. These structures, once formed, are known to exist as
long as the source and a sink of energy remain in place.
Title: On the Magnetic Energy Avalanche in the Solar Atmosphere
Authors: Ryutova, M. P.; Tarbell, T. D.
Bibcode: 2001Ap&SS.277..153R
Altcode:
We discuss a mechanism of energy production associated with the acoustic
and MHD shocks produced by colliding and reconnecting flux tubes and
present the observational results showing a connection between the
dynamic changes in the photosphere and the high velocity and heating
events in the transition region. We suggest that these processes may
provide a constant energy supply for the origin of the fast wind and
help to advance studies of coronal dynamics.
Title: Photospheric Network as the Energy Source for the quiet-Sun
corona
Authors: Ryutova, M.; Habbal, S.; Woo, R.; Tarbell, T.
Bibcode: 2001SoPh..200..213R
Altcode:
We propose a mechanism for the formation of a magnetic energy avalanche
based on highly dynamic phenomena within the ubiquitous small-scale
network magnetic elements in the quiet photosphere. We suggest that
this mechanism may provide constant mass and energy supply for the
corona and fast wind. Constantly emerging from sub-surface layers,
flux tubes collide and reconnect generating magneto-hydrodynamic shocks
that experience strong gradient acceleration in the sharply stratified
photosphere/chromosphere region. Acoustic and fast magnetosonic
branches of these waves lead to heating and/or jet formation due to
cumulative effects (Tarbell et al., 1999). The Alfvén waves generated
by post-reconnection processes have quite a restricted range of
parameters for shock formation, but their frequency, determined by the
reconnection rate, may be high enough (ω≃0.1-2.5 s−1)
to carry the energy into the corona. We also suggest that the primary
energy source for the fast wind lies far below the coronal heights, and
that the chromosphere and transition region flows and also radiative
transient form the base of the fast wind. The continuous supply of
emerging magnetic flux tubes provides a permanent energy production
process capable of explaining the steady character of the fast wind
and its energetics.
Title: Formation of Compact Coronal Structures Associated with the
Emerging Magnetic Flux
Authors: Ryutova, M. P.; Shine, R.; Tarbell, T. D.
Bibcode: 2001AGUSM..SH32C01R
Altcode:
We study the events associated with the emergence of magnetic flux
in the photosphere occurring throughout the solar atmosphere from
its surface up to the low corona using coordinated observations from
Swedish Vacuum Solar Telescope (SVST) on La Palma, the TRACE satellite
and the MDI instrument on SOHO. The object of the observations is a
plage dominated initially (UT 08:01:03, June 10, 1999) by positive
polarity elements with about 0.3 magnetic filling factor near the
same polarity sunspot. High resolution MDI magnetograms are assembled
in a 6-hour movie and co-aligned with TRACE Fe IX/X 171 Å images of
the corona, SVST Ca II K-line images showing the low chromosphere and
Hα filtergrams showing plasma motions higher in the chromosphere. To
study line of sight motions, we used filtergrams taken in the +/- 350
~mÅ (and +/- 700 ~mÅ) wings of Hα . During the first two hours,
there are almost no changes (at the MDI resolution) in the initial
magnetic field pattern of studied region, and the 171 Å emission
above this region shows stable amorphous structures. Then a series of
events lead to the formation of two opposite polarity pores in the
target region and compact coronal loops above it with the following
chronology. First, opposite polarity small-scale flux tubes emerge
and interact with the existing plage elements. This is followed almost
immediately by strong Hα surges, whose peak activity lasts about 10
minutes. After this lag, enhanced emission in 171 Å takes the form
of a short-lived transient. During the next one hour (long before
the pore and compact coronal loops form), there are several new Hα
surges and coronal plasma jets whose activity correlates well with
remarkable changes in the photospheric fluxes which eventually form
pores. For a quantitative analysis we apply a theoretical model of
energy transport from subsurface motions associated with the emerging
magnetic flux. Strong disturbances generated in a limited surface
area may propagate upward like blast waves along a cone. This in
turn may cause a sequence of phenomena associated with forward and
reflected shocks, whose signatures are similar to the observations. The
process may last as long as significant changes in the photospheric
magnetic field occur, until it is suppressed by the strong fields in
the pores. Under some condition the established pore structure may
be accompanied by a current drive which leads to formation of the
coronal loops.
Title: On the Transition Region Explosive Events
Authors: Ryutova, M. P.; Tarbell, T. D.
Bibcode: 2000ApJ...541L..29R
Altcode:
We describe the properties of high-velocity and explosive events in the
solar transition region determined from time series of data taken by
the Transition Region and Coronal Explorer and the SUMER instrument
on the Solar and Heliospheric Observatory (SOHO) simultaneously in
several chromospheric and transition region lines co-aligned with
high-resolution Michelson Doppler Imager (SOHO) magnetograms. We
outline what the various features of these events can tell us about
the heating mechanisms and formation of plasma flows. Our results
strongly support the mechanism of hydrodynamic cumulation of energy
associated with the cascade of shock waves produced by colliding
and reconnecting flux tubes in the photospheric network (as recently
discussed by T. D. Tarbell et al.). We find that the majority of the
explosive events are caused by the explosive instability occurring in
the presence of the behind-shock downflows, and less than 10% can be
explained by the direct collision of shock fronts.
Title: Observation of Shocks in the Chromosphere and Transition Region
Authors: Ryutova, M. P.; Tarbell, T. D.
Bibcode: 2000SPD....31.0141R
Altcode: 2000BAAS...32..808R
The spectra of CII and OVI lines corresponding to chromosphere and
transition region temperatures show significant broadening and complex
line profiles in regions overlying the sites of small scale magnetic
elements in the photopsheric network. Doppler shifted multiple peaks
in CII line are always seen soon after the reconnection of magnetic
flux tubes occurs and usually consist of supersonic and subsonic
components caused by shocks propagating upward. Multiple peaks in OVI
line have more diverse features: they are not as persistent as those
seen in CII line, and may have the configuration of maximum intensity
peaks corresponding either to forward or reflected shocks. We develop
a consistency analysis which allows to compare the shock relations
and their properties with the observed signatures and infer physical
parameters such as Mach number, direction of the shock propagation
and velocities. We use the uninterrupted time series of data to trace
particular events at the different stages of their evolution and deduce
some intrinsic features of the mechanism of the energy production and
its transport through the chromosphere/transition region.
Title: Electro-Mechanical Coupling Between the Photosphere and
Transition Region
Authors: Tarbell, T. D.; Ryutova, M.; Shine, R.
Bibcode: 2000SoPh..193..195T
Altcode:
We study the response of the chromosphere and transition region to
dynamic changes in the photospheric network magnetic fields. We present
results from simultaneous measurements taken by TRACE in chromospheric
and transition region (C iv) images, high-resolution magnetograms taken
by MDI, and spectra of chromospheric (C ii) and transition region
lines (O vi) obtained with the SUMER instrument on SOHO. Enhanced
emission in the C iv line is generally co-spatial with the magnetic
pattern in the photosphere. We propose a mechanism of electro-mechanical
coupling between the photosphere and upper layers of atmosphere based on
hydrodynamic cumulation of energy produced by reconnecting flux tubes in
the photosphere/chromosphere region (Tarbell et al., 1999). We believe
that a basic process causing energetic events is the cascade of shock
waves produced by colliding and reconnecting flux tubes. The continuous
supply of flux tubes in the `magnetic carpet' ensures the ubiquitous
nature of this process and its imprint on the upper atmosphere. The
appearance of bright transients often, but not always, correlates with
canceling mixed polarity magnetic elements in the photosphere. In
other cases, transients occur in regions of unipolar flux tubes,
suggesting reconnection of oblique components. Transients are also
seen in regions with no fields detected with the MDI sensitivity;
these may be reconnections of tiny features with diameters less than
100 km. Blinkers and other bright transients are often accompanied by
two directional plasma jets. These may be generated by cylindrical
self-focusing of shock fronts or by collision of shocks produced by
neighboring reconnection processes. The observations suggest that
stronger emissions correspond to lower velocity jets, and vice versa;
this property is a natural consequence of the proposed mechanism. Plasma
flows are always seen whenever the slit crosses strong magnetic flux
tubes or vertices of converging flows in the supergranular network. The
overall energy distribution between heating and plasma flows is an
intrinsic feature of our mechanism.
Title: Magnetic energy avalanche as the source of the fast wind
Authors: Ryutova, M. P.; Habbal, S. R.; Woo, R.; Tarbell, T.
Bibcode: 1999AIPC..471..227R
Altcode: 1999sowi.conf..227R
We propose a mechanism for the formation of a magnetic energy avalanche
based on highly dynamic phenomena within the ubiquitous small scale
network magnetic elements in the quiet photosphere. We suggest that
this mechanism may provide constant mass and energy supply for the
origin of the fast wind.
Title: Heating and jet formation by colliding shocks in solar
atmosphere
Authors: Tarbell, T.; Ryutova, M. P.; Covington, J.; Fludra, A.
Bibcode: 1999AIPC..471..419T
Altcode: 1999sowi.conf..419T
We show that ubiquitous small-scale magnetic flux ``tubes''
constantly emerging from subsurface layers, may cause the formation
of plasma jets and a sporadic excess of temperature near the solar
surface. Photospheric network magnetic elements collide and reconnect,
creating a sling-shot effect which generates complex 3D shock waves
with the curved surface. Self-focusing of these shocks occurs as they
propagate upward in the rarefied atmosphere. Depending on the geometry
of the shock collision, highly concentrated energy may be either
converted entirely into heat or into strong jets, or be distributed
between the two.
Title: Plasma Streaming and Explosive Events in the Solar Transition
Region: Theory and Observations
Authors: Ryutova, M.; Tarbell, T.
Bibcode: 1999AAS...194.7803R
Altcode: 1999BAAS...31..961R
As shown by Tarbell et al. (ApJ, 514, L47, 1999 ) a sporadic excess of
temperature and wide variety of plasma jets observed in the chromosphere
and transition region overlying quiet sun regions may be explained by
hydrodynamic cumulation resulted from the acoustic shocks generated by
the reconnecting small scale network magnetic elements in the solar
photosphere. Here we study magneto-hydrodynamic cumulation resulted
from post-reconnection MHD shocks generated in complex magnetic field
geometries typical to upper chromosphere and low corona. We present
the results for the observed regularities obtained from simultaneous
measurements taken by TRACE in chromospheric, transition region and
coronal images and MDI on SOHO showing time series of high resolution
magnetograms. We find that (1) All the essential features of the
hydrodynamic cumulation remain in place: the MHD shocks driven by the
post-reconnection sling-shot effect and self-focusing of these shocks
lead to several well observed signatures of the energy release. (2) The
evolution of generated flows depends on the geometry of intermittent
magnetic fields and the height of jet formation. In regions of open
magnetic structures plasma flows have tendency to accelerate and reach
supersonic and super-Alfvenic velocities. Due to linear KH instability
such flows may generate high frequency Alfven waves propagating along
the magnetic structures. (3) In those regions where cumulative effects
result in the predominant heating which is accompanied by generation of
"moderate" (sub-Alfvenic) velocity jets, there are conditions when high
velocity explosive events are driven. Our theoretical model shows that
the explosive events proceeded by appearance of the bright transients
are caused by the development of shear flow dissipative (nonlinear)
instabilities. We also suggest that "non-bright"explosive events may
be driven by rare effect of the cylindrical focusing of the MHD shocks
(the Guderley's effect).
Title: Heating and Jet Formation by Hydrodynamic Cumulation in the
Solar Atmosphere
Authors: Tarbell, T.; Ryutova, M.; Covington, J.; Fludra, A.
Bibcode: 1999ApJ...514L..47T
Altcode:
The solar transition region is the site of supersonic plasma jets and
sporadic radiative events, whose origin and physical nature have not
been understood. Here we show that ubiquitous small-scale magnetic flux
``tubes,'' constantly emerging from subsurface layers, may cause the
formation of plasma jets and a sporadic excess of temperature near
the solar surface. These flux tubes collide and reconnect, creating
a sling-shot effect that generates complex three-dimensional shock
waves with the curved surface. Self-focusing of these shocks occurs
as they propagate upward in the rarefied atmosphere. Depending on the
geometry of the shock collision, highly concentrated energy may be
converted entirely into either heat or strong jets, or distributed
between the two.
Title: A New Method for Diagnostics of Solar Magnetic Fields and
Flows from Time-Distance Analysis
Authors: Ryutova, Margarita; Scherrer, Philip
Bibcode: 1998ApJ...494..438R
Altcode:
We propose a new method to obtain information on plasma flows and
magnetic fields below the visible solar surface using time-distance
measurements. The method is based on sine and cosine transforms of
propagation times measured as a function of direction. The method allows
one to sort out various characteristics of the subsurface medium, the
flows, magnetic fields and their nonuniformities, and is less sensitive
to the measurement errors. We discuss the parity properties of various
contributions to the propagation times with respect to forward and
backward directions and show how these properties allow separation of
the effects of magnetic field and flows, as well as separation of the
horizontal components from the vertical. It is shown that the first
harmonics contain information on the direction and absolute value of the
velocity, while the second harmonics are sensitive to the orientation
and absolute value of horizontal magnetic fields and spatial gradients
of the flow velocity. We discuss the effects of discrete mesh on the
accuracy of measurements of the propagation time. An advantage of the
method is in its intrinsic invariance with respect to the choice of the
coordinate frame. The method provides an automatic rule of assigning
proper weights to every observation points. We give estimates of
the accuracy of the reconstruction of the flow field over distances
comparable with the scale of the convection. We also present the
``magnetic'' corrections to the propagation time in a vertically
stratified medium.
Title: A Possible Mechanism for the Origin of Emerging Flux in the
Sunspot Moat
Authors: Ryutova, M.; Shine, R.; Title, A.; Sakai, J. I.
Bibcode: 1998ApJ...492..402R
Altcode:
Mass and energy flow near sunspots are associated with the emergence
of magnetic flux, which then moves outward in the sunspot moat. We
present results of analytical and numerical studies of the interaction
of horizontal magnetic flux and plasma flows in three-dimensional
geometry. We show that nonlinear coupling of flux and plasma flows in
the presence of a gravitational field lead to nonlinear dissipative
instabilities that result in the formation of a solitary kink along
the magnetic flux. The stability of a kink and its further evolution
depend on the physical parameters of magnetic flux and the surrounding
medium. We discuss two major cases--magnetic soliton-like and shocklike
propagation along the magnetic flux--and specify the appropriate
physical conditions for their realization. In photospheric conditions,
the proposed mechanism may be a good candidate for understanding of
the dynamics of small-scale magnetic flux in the enhanced network at
the solar surface. We apply our results to the observed properties
of emerging flux in the sunspot region associated with moving magnetic
features and find reasonable qualitative and quantitative agreement.
Title: Raman spectroscopy of solar p-modes
Authors: Ryutova, M.
Bibcode: 1998IAUS..185..213R
Altcode:
In the present paper we propose a new application of time-distance
analysis. we show that time-distance measurements in helioseismic
tomography ( Duvall, Jr. et al, 1993; 1997) can be used for estimate
of the energy flux on the solar surface. Non-reciprocity of travel time
along the ray path and different parity properties of sound speed, flow
velocity and magnetic field, allow one to obtain the information on
large scale distribution of plasma flows and magnetic fields (Ryutova
and Scherrer, 1997). Here we extend our analysis and show that the
covariance of sum and difference of the reciprocal travel times is a
measure of large-scale, "climatological" heat flux, and covariance of
sum and difference of their departures from the mean, gives an estimate
for the magnetic energy flux. Using the reciprocal travel times measured
in North-South and West-East directions one can estimate the latitude
and longitude dependent energy fluxes. The possibility of the estimating
of the "eddy" fluxes, the heat and magnetic energy transport provided by
small scale motions, is outlined. We give the examples of the estimated
heat and magnetic energy flux using the data obtained from MDI-SOHO.
Title: Estimate of the Energy Flux from Time-Distance Analysis
Authors: Ryutova, M.
Bibcode: 1997ApJ...490L.111R
Altcode:
In this Letter we show that time-distance measurements in
helioseismology can be used to estimate the energy flux on the solar
surface. Nonreciprocity of travel time along the ray path and different
parity properties of sound speed, flow velocity, and magnetic field
allow one to obtain information on large-scale distribution of plasma
flows and magnetic fields. Here we extend our analysis and show that
the covariance of sum and difference of the reciprocal travel times is
a measure of large-scale, ``climatological'' heat flux and that the
covariance of sum and difference of their departures from the mean
gives an estimate for the magnetic energy flux. Using the reciprocal
travel times measured in north-south and west-east directions, one
can estimate the latitude- and longitude-dependent energy fluxes. The
possibility of estimating the ``eddy'' fluxes, the heat and magnetic
energy transport provided by small-scale motions, is outlined.
Title: On the Dynamics of Magnetic Flux Concentrations in Quiet
Photospheric Network.
Authors: Sakai, J. I.; Ryutova, M.; Schrijver, K.; Shine, R.; Tarbell,
T.; Berger, T.; Title, A.; Hagenaar, H.
Bibcode: 1997SPD....28.0260S
Altcode: 1997BAAS...29..904S
Magnetic flux concentrations in the quiet photospheric network show
a complex dynamics which includes merging of colliding fluxes, the
"total" or partial cancellation of neighboring fluxes, fragmentation
and others. We propose a mechanism to explain the observed phenomena
based on the idea that magnetic flux concentrations in the photospheric
network are essentially non-collinear. We show that non-collinearity
of colliding fluxes leads to the whole new class of effects which are
observed; for example, the apparent cancellation of opposite polarity
fluxes turns into the formation of horizontal magnetic fluxes (which
later may appear as a new weaker bipoles) and is accompanied by the
shock formation and mini-flares. In the case of shock formation
the reconnection area becomes a source of the acoustic emission;
mini-flares may be seen as bright points. The energetics of these
processes strongly depends on geometry of "collision" and physical
parameters of colliding fluxes. For example, if colliding fluxes have
comparable and "small" cross sections, the reconnection results in
complete reorganization of their magnetic fields; if merging fluxes
are large enough or considerably different, magnetic flux may be
only partially reconnected and partially survived. Reconnection of
non-collinear equal polarity fluxes leads to the "scattering" processes
which include the fragmentation into several smaller fluxes if initially
colliding concentrations carried different amount of magnetic flux. We
give the example of numerical simulation for the case of merging and
fragmentation process occurring during the collision of collinear
"strong" and "weak" magnetic flux concentrations. The calculation
results shown to be consistent with observational data from both
the SOHO/MDI instrument and the Swedish Vacuum Solar Telescope on
La Palma. This research is supported by NASA contract NAG5-3077 at
Stanford University and the MDI contract PR 9162 at Lockheed.
Title: Convective Flow Patterns in Time-Distance Measurements and
"Magnetic Corrections" in Vertically Stratified Atmosphere.
Authors: Ryutova, M.; Scherrer, P.
Bibcode: 1997SPD....28.0204R
Altcode: 1997BAAS...29..893R
Time-distance measurements for the reconstruction of subsurface flows
and horizontal magnetic fields proved to be very efficient. However,
if one can expect a reasonable accuracy of reconstructed maps for the
annuli of the radius small compared to the characteristic scale of
the convection, the situation changes when annular distances become
comparable with the scale of granular, mezogranular, or supergranular
convective motions: in each of these cases the uncertainty in the
measurements of travel time perturbations increases dramatically. We
present here a quantitative analysis of the problem for a particular
model of convective motions and compute the travel time perturbations as
a function of annular distances and the supergranule radius. It is shown
that at annular sizes close to the size of convective cell there occurs:
(1) the apparent reduction of the local velocity, and (2) appearance
of additional terms in the corrections to perturbation travel time
which cause a large error in reconstruction of the velocity field. We
discuss the importance of "directionally sensitive" measurements and
show that Fourier sin ntheta , cos ntheta transforms of travel times
measured as a function of direction, "kills" the largest source of
errors. We discuss the role of vertical motions. We also present the
expressions for the "magnetic corrections" in a vertically stratified
atmosphere. This research is supported by NASA contract NAG5-3077 at
Stanford University and the MDI contract PR 9162 at Lockheed.
Title: On the dynamics of magnetic flux concentrations in quiet
photospheric network.
Authors: Sakai, J. I.; Ryutova, M.; Schrijver, K.; Shine, R. A.;
Tarbell, T. D.; Berger, T. E.; Title, A. M.; Hagenaar, H. J.
Bibcode: 1997BAAS...29T.904S
Altcode:
No abstract at ADS
Title: On the Acoustic Emission in the Quiet Sun
Authors: Ryutova, M. P.; Tarbell, T. D.
Bibcode: 1997AAS...18912001R
Altcode: 1997BAAS...29..729R
The interaction of solar acoustic oscillations with magnetic regions on
the Sun strongly depends on the distribution of the random magnetic
fluxes in space and their physical parameters. The dynamics of
differently magnetized regions (sunspots, plages and quiet Sun), their
dispersion properties and their response to the propagation of acoustic
waves are completely different. For example, the enhanced absorption of
acoustic power by sunspot and plage regions is well established. Several
authors who have made similar measurements in quiet regions report that
the quiet Sun shows small but systematic acoustic emission. The effects,
enhanced absorption in active regions and "emission' of acoustic power
in quiet sun, are seen in the same range of wave numbers (0.2<=
k <= 0.6 Mm(-1) ). We report here that an excess of emission of
acoustic power in quiet regions is expected as a result of "inelastic"
scattering of acoustic waves by the random ensembles of widely spaced
magnetic flux tubes. The outcome of the effect strongly depends on the
magnetic filling factor of medium, phi (the total fraction of observed
area occupied by fluxes) and the parameters of acoustic wave. It is
most efficient in those regions of quiet Sun where k(2R^2<<) phi
, R being the characteristic radius of a magnetic flux tube. In this
case, resonant interaction is the most important of several physical
processes contribute to the energy exchange between the wave and
medium. Due to an effect similar to Landau damping, the energy of the
incident acoustic wave is accumulated in the system of magnetic flux
tubes and causes the acoustic wave (of frequency omega ) to damp at a
rate nu_L =~ phi omega . The energy remains for a long time in the form
of flux-tube oscillations. Then, in a time nu_ {rad}(-1) , the resonant
flux tubes radiate their energy as a secondary acoustic waves, where the
radiative damping rate (or the rate of the emission of secondary waves),
nu_ {rad} =~ omega k(2) R(2) . The power of emitted waves expressed
in terms of the parameters of the medium allows one to specify the
regions of an efficient energy input and corresponding range of wave
parameters. This research is supported by NASA contract NAG5-3077 at
Stanford University and NASA contract NAS8-39747 at Lockheed Martin.
Title: A Possible Mechanism for the Origin Emerging Flux in the
Sunspot Moat
Authors: Sakai, Jun-Ichi; Shine, R.; Title, A.; Ryutova, M.
Bibcode: 1996AAS...188.3502S
Altcode: 1996BAAS...28R.871S
Mass and energy flow near sunspots is associated with the emergence
of magnetic flux which then moves outward in the sunspot moat. We
present results of analytical and numerical studies of the interaction
of horizontal magnetic flux and plasma flows in 3D-geometry. We show
that nonlinear coupling of flux and plasma flows in the presence of
a gravitational field lead to nonlinear dissipative instabilities
which result in the formation of a solitary kink along the magnetic
flux. The stability of a kink and its further evolution depends on the
physical parameters of magnetic flux and surrounding medium. We discuss
two major cases, magnetic soliton- and shock-like propagation along
the magnetic flux, and specify the appropriate physical conditions for
their realization. For example, under conditions in a sunspot moat, when
the mass flow velocity exceeds about 0.5 v_A there occurs a magnetic
soliton-like kink, propagating with a velocity less than the external
mass flow velocity. The larger the radius of a flux tube, the larger the
``width'' of a soliton, and the lower the velocity of its propagation;
the width of a soliton corresponds to the separation of ``legs'' of a
kink which appear as magnetic field of the opposite polarities - the
nearest to sunspot has obviously the same polarity. When the external
mass flow velocity is less than about 0.5 v_A, a magnetic shock-like
perturbation can propagate with a velocity larger than the external
mass flow velocity. We apply these results to the observed properties
of emerging flux and find reasonable qualitative and quantitative
agreement. This research was supported by NASA contract NAG5-3077 at
Stanford University (M.R.) and NASA contract NAS8-39747 at
Title: A New Method for Diagnostics of Subsurface Magnetic Fields
and Flows from Time-Distance Analysis
Authors: Ryutova, M.
Bibcode: 1996AAS...188.7902R
Altcode: 1996BAAS...28..955R
We propose a new method of obtaining the information on plasma flows
and magnetic fileds below the visible surface using the time-distance
measurements. The recent advent of time-distance tomography (Duvall
et al. 1993) consisting in the discovery that allows to measure
directly the travel time between any point on the solar surface
and a surrounding annulus, opens the efficient ways to study the
structure and dynamics of the solar interior. We suggest to use sin
ntheta and cos ntheta convolutions of the propagation time tau_ θ
measured between any point inside the annulus with the prescribed
azimuthal angle theta : \bar {\tau}_c^{(n)} ;=;\frac{1}{2\pi}
\int\limits0^{2\pi} \tau(\theta)\cos n\theta d\theta \qquad
\bar {\tau}_s^{(n)} ;=;\frac{1}{2\pi} \int\limits0^{2\pi}
\tau(\theta)\sin n\theta d\theta Using the approximation of geometrical
acoustics and assuming that the magnetic effects are small, we find
that the first harmonics (n=1) contain an information predominantly
on the direction and absolute value of the horizontal flow velocity,
while the second harmonics (n=2) predominantly describes orientation
and absolute value of the horizontal magnetic field. The data obtained
for the different annuli give a topology and absolute values of the
mass flows and magnetic fields at the different depths. We discuss
the effects of discrete mesh on the accuracy in measurements of
propagation time. The advantage of the method consists in the fact
that we do not need any specific choice of the measurement mesh; the
method itself establishes a rule by which one can use any a priori
chosen mesh to find the distribution of horizontal magnetic fields
and flows. This research is supported by NASA contract NAG5-3077
at Stanford University. References Duvall, T..L.Jr., S.M.Jefferies,
J.W. Harvey and M.A.Pomerantz, 1993, Nature, 362, 430.
Title: The Evolution of Magnetic Structures Due to ``Magnetosonic
Streaming''
Authors: Ryutova, Margarita P.; Kaisig, M.; Tajima, T.
Bibcode: 1996ApJ...459..744R
Altcode:
The Faraday effect in gasdynamics called acoustic streaming and
its accompanying nonlinear phenomena have analogies in plasma
magnetohydrodynamics A natural place where these effects may occur
is the solar atmosphere with its strongly inhomogeneous magnetic
fields concentrated in random magnetic flux tubes. Unlike acoustic
streaming in the usual gasdynamics, nonlinear phenomena consisting in
the generation of plasma flows by an oscillating magnetic flux tube,
"magnetosonic streaming" (Ryutova 1986), is accompanied by a current
drive and results in a specific evolution of magnetic structures:
depending on the physical parameters of the medium a single magnetic
flux tube may be either split into thinner flux tubes or dissolved
diffusively into the ambient plasma. The effect of the "magnetosonic
streaming," on one hand, is an obvious candidate for the generation
of mass flows at magnetic flux tubes sites, and on the other hand, it
plays an essential role in the evolution of magnetic structures and
ultimately may determine their lifetime. The theory of magnetosonic
streaming is general and can be applied to other astrophysical objects
that maintain oscillatory motions and contain structured magnetic
fields or magnetic domains. We review analytical results and describe
the origin of the magnetosonic streaming in magnetic flux tubes due
to their interaction with acoustic waves. We study numerically the
regime of the "magnetosonic streaming" corresponding to splitting of
a magnetic flux tube. Our computer simulation supports and extends
the analytical result.
Title: The "Magnetosonic Streaming"
Authors: Ryutova, M.
Bibcode: 1996ApL&C..34...71R
Altcode:
No abstract at ADS
Title: The Effects on Mass Flows on the Dissipation of Alfven Waves
in the Upper Layers of the Solar Atmosphere
Authors: Ryutova, Margarita P.; Habbal, Shadia R.
Bibcode: 1995ApJ...451..381R
Altcode:
The influence of parallel plasma flows on the propagation of shear
Alfvén waves along magnetic structures is considered. It is shown that
even in a simple case of regular mass flows directed along the magnetic
field, their presence considerably modifies the dissipation of shear
Alfvén waves, affecting both the magnitude and the height of maximum
dissipation. The strongest effect occurs in the case of downflows when
the flow velocity at a certain height becomes equal to the Alfvén
velocity. Near that point, the wave comes to extinction and gives
off its energy completely. The axial extent of the absorption region
is evaluated. This effect can be directly associated with observed
high-velocity downflows in the transition region, and, in particular,
can serve as a qualitative explanation for the high variability of the
emission observed near 105 K. In the presence of upward
mass flows and moderate downflows, the dissipation of phase-mixed
Alfvén waves is accompanied by the radial redistribution of the
energy input across the magnetic structure, thus creating a mosaic
pattern in the emitting regions. The flow velocities are assumed to
be below the thresholds which correspond to the onset of hydrodynamic
and dissipative instabilities.
Title: Effects of highly intermittent magnetic fields and plasma
flows on solar wind dynamics
Authors: Ryutova, M.
Bibcode: 1995sowi.confR..27R
Altcode:
Filamentary magnetic fields and intermittent mass flows with highly
variant physical parameters as observed in coronal holes provide,
from a theoretical point of view, natural conditions for strongly
nonlinear dynamics. The presence of sheared mass flows along fine
scale magnetic structures results in strong nonlinear instability,
most important of which is the explosive instability. We specify
the physical conditions for several different manifestations of the
onset of explosive instability and its further evolution: (1) fully
developed explosive instability - explosive release of the energy; (2)
shock formation - stabilization of instability by small scale spatial
inhomogeneities leads to formation of subsequent shocks having a number
of peculiarities that is determined by the interplay of thermal and
viscous losses (for example, in predominance of thermal losses the
isothermal jump occurs); and (3) solitary waves - stabilization
of explosive instability by nonlinear dispersion effect leads to
formation of a 'gas' of solitons which are later either damped away
with characteristic time and energy input or evolve to solitons with
explosively growing amplitudes. Each scenario is completely determined
by the physical parameters of the medium, thus producing a quite
uneven distribution of energy in a coronal hole and, respectively,
an uneven outward propagation of the energy flux.
Title: Acoustic Waves in Random Ensembles of Magnetic Fluxes
Authors: Ryutova, M.
Bibcode: 1995ESASP.376b..83R
Altcode: 1995soho....2...83R; 1995help.confP..83R
To analyze the observational data and provide the appropriate diagnostic
procedure for photospheric manifestation of solar oscillations it is
necessary to take into account strong inhomogeneity of solar atmosphere
with respect to distribution of magnetic fields. The author studies the
collective phenomena in the propagation of acoustic waves and unsteady
wave-packets through quite regions, sunspots and plages including
time-dependent response of these regions to solar oscillations, the
energy transfer mechanisms, frequency shift effects and reradiation of
the acoustic waves in higher layers of the atmosphere. The author shows
that the dynamics of differently magnetized regions, their dispersion
properties, and their response to the propagation of acoustic waves
are completely different. The author describes the effects caused by
the specific distribution and randomness of magnetic flux tubes, which
can be observed and which can provide the tools for diagnostic goals.
Title: The Evolution of Magnetic Flux Tube Due to Magnetosonic
Streaming
Authors: Ryutova, M.; Kaisig, M.; Tajima, T.
Bibcode: 1994AAS...18512402R
Altcode: 1995BAAS...27..758R
No abstract at ADS
Title: Dynamics of Flux Tube Ensembles
Authors: Ryutova, Margarita
Bibcode: 1994ASPC...68..118R
Altcode: 1994sare.conf..118R
No abstract at ADS
Title: The Propagation of Sound Waves in a Randomly Magnetized
Medium. II. The Interaction of an Unsteady Wave Packet with an
Ensemble of Magnetic Flux Tubes
Authors: Ryutova, M. P.; Priest, E. R.
Bibcode: 1993ApJ...419..371R
Altcode:
The interaction of an unsteady wave packet of acoustic waves with plasma
containing ensembles of random magnetic flux tubes and the physical
mechanisms of energy transfer to the plasma are described. It is
shown that the propagation of an acoustic wave-packet in the randomly
magnetized solar atmosphere is accompanied by clear morphological
effects which include the spreading of the energy absorption region
over scales much larger than the size of the initial wave packet,
and which, in principle, can be observed. The regions of an efficient
energy input and their localization crucially depend on the distribution
of magnetic flux tubes in space and over their physical parameters
(including noncollinearity). The very existence of these effects is
determined by the fact that the solar atmosphere is randomly magnetized,
and magnetic flux tubes are essentially nonidentical. The results
may be useful for the diagnostics of the visible layers of the solar
atmosphere and magnetic helioseismology.
Title: A Possible Mechanism for Enhanced Absorption of p-Modes in
Sunspot and Plage Regions
Authors: Labonte, Barry J.; Ryutova, Margarita
Bibcode: 1993ApJ...419..388L
Altcode:
Magnetic regions on the Sun's surface are observed to absorb large
fractions of the p-mode (acoustic) wave power incident upon them. We
propose a mechanism to explain the absorption, based on the idea that
sunspots are assembled from many individual flux tubes with highly
variant physical conditions. Strong gradients in the (perturbed)
parameters of a wave propagating through such an inhomogeneous medium
result in enhanced absorption of the wave power. The gradients in the
wave parameters occur on the scale of the background flux tubes which
is smaller than the wavelength.
Title: The Propagation of Sound Waves in a Randomly Magnetized
Medium. I. General Considerations
Authors: Ryutova, M. P.; Priest, E. R.
Bibcode: 1993ApJ...419..349R
Altcode:
We study the time-dependent response of a randomly magnetized medium
(such as the solar atmosphere) to the propagation of acoustic waves,
including energy transfer to the medium due to different physical
processes. It is shown that the details of the interaction of a sound
wave with an ensemble of magnetic flux tubes, and, in particular,
the maximum energy input, crucially depends on the magnetic filling
factor of the medium as well as on the distribution of the random
tubes in space. The interaction of acoustic waves and unsteady wave
packets with an ensemble of magnetic flux tubes reveals some simple
and important features, which, in principle, are observable. A most
important role in these effects is played by resonant interaction both
absorption and scattering of the sound wave by flux tubes. We focus
on the case when the incident wavelength (λ) is much larger than the
separation (d) between tubes, which is in turn much larger than the
tube radii (R). In the case of resonant absorption (an effect
similar to Landau damping in the collisionless plasma) the energy of
the incident acoustic wave is accumulated in the system of magnetic
flux tubes and causes the acoustic wave (of frequency ω) to damp at
a rate νL ∼ (R2/d2)ω. The energy
remains for a long time in the form of flux-tube oscillations. Then,
in a time ν-1rad which is much longer than the
damping time of the sound wave, the resonant flux tubes radiate their
energy as secondary acoustic (or MHD) waves, where νrad
∼ ωk2R2. The incident acoustic wave can also
be resonantly scattered with the main contribution coming from the
kink mode; it leads to a linear frequency shift and to the appearance
of incoherent noise without a preliminary build up of wave energy in
flux-tube oscillations. When the distribution of flux-tube natural
frequencies is broader than νL the Landau-like resonant
absorption process is more important than resonant scattering, but when
the distribution is narrow the tubes are essentially identical and
resonant absorption is generally absent so that resonant scattering
dominates. A nonlinear analysis allows us to find the maximum energy
input and the frequency shift and their dependence on the parameters
of medium. Also, a detailed treatment is given of Landau-like damping
due to excitation of sausage modes.
Title: Nonlinear kink oscillations of a magnetic flux tube.
Authors: Ryutova, M.; Sakai, J. -I.
Bibcode: 1993JETPL..58..507R
Altcode: 1992JETPL..58..507R
The nonlinear equations which describe the long wavelength, weakly
dispersive, kink oscillations propagating along a magnetic flux tube
are derived. The character of nonlinearity appeared to be cubic,
with the coefficients which reflect the influence of a magnetic free
environment on the transverse oscillations of the flux tube.
Title: Enhanced absorption of p-modes in sunspot and plage regions.
Authors: Labonte, Barry J.; Ryutova, Margarita
Bibcode: 1993ppcn.conf..275L
Altcode:
Magnetic regions on the Sun's surface are observed to absorb large
fractions of the p-mode (acoustic) wave power incident upon them. The
authors propose a mechanism to explain the absorption, based on the
idea that sunspots are assembled from many individual flux tubes with
highly variant physical conditions. Strong gradients in the (perturbed)
parameters of a wave propagating through such an inhomogeneous medium
results in enhanced absorption of the wave power. The gradients in
the wave parameters occur on the scale of the background flux tubes
which is smaller than the wavelength.
Title: Unsteady Wave-Packet in the Random Ensemble of Magnetic Flux
Tubes: Acoustic Halos
Authors: Ryutova, M.; Priest, E.
Bibcode: 1993ASPC...46..554R
Altcode: 1993mvfs.conf..554R; 1993IAUCo.141..554R
No abstract at ADS
Title: Generation of Plasma Flows and Filamentation of Magnetic
Fields in Solar Atmosphere
Authors: Ryutova, M.
Bibcode: 1993ASPC...46..549R
Altcode: 1993IAUCo.141..549R; 1993mvfs.conf..549R
No abstract at ADS
Title: Propagation of Magnetoacoustic Waves in the Solar Atmosphere
with Random Inhomogeneities of Density and Magnetic Fields
Authors: Ryutova, M.; Kaisig, M.; Tajima, T.
Bibcode: 1991ApJ...380..268R
Altcode:
The dispersion properties and enhanced dissipation of hydromagnetic
waves in a random ensemble of closely packed flux tubes are
studied. The procedures which allow the averaged equations containing
the nonlinearity of the wave, dispersion properties of the system, and
dissipative effects to be obtained are presented. The obtained results
are addressed as applied to the solar atmosphere, with emphasis on
sunspot regions, plages, and other regions where random magnetic flux
bundles form a dense conglomerate. It is shown that in such regions the
enhanced dissipation of the wave energy takes place. The presence of
small-scale inhomogeneities is found to lead to the finite dispersion
of the wave, and in the case with weak but finite dispersion effects,
this gives rise to the cubic dependence on wavenumber of the frequency
shift of an acoustic wave. Different scenarios of the energy transfer of
primary magnetosonic waves to a certain region of the solar atmosphere
are considered.
Title: The Enhanced Dissipation of Sound Waves in Sunspot and
Plage Regions
Authors: Ryutova, M.; Kaisig, M.; Tajima, T.
Bibcode: 1991BAAS...23R1050R
Altcode:
No abstract at ADS
Title: Explosive Instability in Solar Coronal Loops
Authors: Ryutova, M.
Bibcode: 1991mcch.conf..159R
Altcode:
No abstract at ADS
Title: Absorption of Magnetoacoustic Waves in the Solar Atmosphere
with Random Inhomogeneities of Density and Magnetic Fields
Authors: Kaisig, M.; Tajima, T.; Ryutova, M.
Bibcode: 1991LNP...387..287K
Altcode: 1991fpsa.conf..287K
Effects of a collection of strong and random inhomogeneities of
the magnetic fields, plasma density, and temperature in the solar
atmosphere on the propagation of magnetoacoustic waves of arbitrary
amplitudes are numerically studied by using a one dimensional code
of ideal magnetohydrodynamics. It is shown that even in the presence
of strong, small scale background inhomogeneities long wavelength
perturbations ( R, where R is the scalelength of the inhomogeneities)
steepen and form shock waves. Furthermore, the presence of small
scale background fluctuations results in a much stronger dissipation
of long wavelength perturbations and a larger heating of the plasma
compared to the case of a homogneous medium. The limiting case of R
in which the wavelength of the perturbation is of the same order as
the length scale of the inhomogeneities (this case is beyond the realm
of the theoretical analysis of Ryutova et al. (1990)), dissipates its
energy even faster and in fact so fast that the waves do not steepen
into shocks. Compared to the case of long wavelength perturbations
the heating of the plasma is even larger. We discuss the relevance to
sunspots and magnetized regions of the solar atmosphere.
Title: Propagation of magnetoacoustic waves in the solar atmosphere
with random inhomogeneities of density and magnetic fields
Authors: Ryutova, M.; Kaisig, M.; Tajima, T.
Bibcode: 1990STIN...9110831R
Altcode:
Effects of strong and random inhomogeneities of the magnetic
fields, plasma density, and temperature in the solar atmosphere on
the properties of magnetoacoustic waves of arbitrary amplitudes are
studied. The procedure which allows one to obtain the averaged equation
containing the nonlinearity of a wave, dispersion properties of a
system, and dissipative effects is described. It is shown that depending
on the statistical properties of the medium, different scenarios of
wave propagation arise: in the predominance of dissipative effects the
primary wave is damped away in the linear stage and the efficiency of
heating due to inhomogeneities is much greater than that in homogeneous
medium. Depending on the interplay of nonlinear and dispersion effects,
the process of heating can be afforded through the formation of shocks
or through the storing of energy in a system of solitons which are
later damped away. Our computer simulation supports and extends the
above theoretical investigations. In particular the enhanced dissipation
of waves due to the strong and random inhomogeneities is observed and
this is more pronounced for shorter waves.
Title: Nonlinear magnetosonic waves in an inhomogeneous plasma.
Authors: Ryutova, M.; Kaisig, M.; Tajima, T.
Bibcode: 1990ESASP.311..339R
Altcode: 1990plas.work..339R
Effects of strong and random inhomogeneities of the magnetic fields,
plasma density, and temperature in the solar atmosphere on the
properties of magnetoacoustic waves of arbitrary amplitudes are
studied. Depending on the statistical properties of the medium,
different scenarios of wave propagation arise. In the predominance
of dissipative effects the primary wave is damped away in the linear
stage and the efficiency of heating due to inhomogeneities is much
greater than that in a homogeneous medium. The process of heating can
be afforded through the formation of shocks or through the storing
of energy in a system of solitons which are later dumped away. The
authors' computer simulations support and extend the above theoretical
investigations.
Title: Interaction of Acoustic Waves with Cluster of Solar Magnetic
Flux Tubes
Authors: Ryutova, M.; Kaisig, M.; Tajima, T.
Bibcode: 1990BAAS...22..854R
Altcode:
No abstract at ADS
Title: Waves and Oscillations in Magnetic Fluxtubes
Authors: Ryutova, M. P.
Bibcode: 1990IAUS..138..229R
Altcode:
No abstract at ADS
Title: Magnetic field generation by sound waves in the solar
atmosphere.
Authors: Ryutov, D. D.; Ryutova, M. P.
Bibcode: 1989JETP...69..965R
Altcode: 1989STIN...9019180R
The authors show that sound waves which are generated in the convective
zone of the Sun excite an electric current (and a magnetic field)
in the transition region from the chromosphere to the corona. The
excitation of the current is connected with the absorption of part
of the momentum of the waves by electrons as a result of the electron
thermal conductivity. When sound waves propagate in the direction of
decreasing density their leading front becomes steeper. This leads
to the formation of weak shock waves and-thanks to the fast energy
dissipation at the front-to a stronger magnetic field generation.
Title: MHD-waves and their nonlinear interaction in a plasma with
magnetic flux tubes.
Authors: Ryutova, M. P.
Bibcode: 1989plap.work...77R
Altcode:
A short survey of theoretical results related to the oscillations of
magnetic flux tubes with the main emphasis made on the discussion of
negative energy waves is presented. It is shown that the presence of
a shear flow along the magnetic field gives rise to a number of new
effects: the appearance of negative energy waves, reversal of the
sign of radiative damping, the development of explosive instability
at the nonlinear stage, etc. The results obtained are of interest in
connection with the problem of energy accumulation and its release in
the solar atmosphere.
Title: Negative-energy waves in a plasma with structured magnetic
fields
Authors: Ryutova, M. P.
Bibcode: 1988JETP...67.1594R
Altcode:
The properties of a plasma which contains structured magnetic fields
(magnetic tubes) are analyzed in the case with shear flows of matter
along the magnetic tubes. If the flows are sufficiently fast, they give
rise to several new effects: the appearance of negative-energy waves and
reversal of the sign of the radiative damping. In the nonlinear stage,
they drive an explosive instability. If the velocity exceeds an upper
threshold, they drive a gross (linear) hydrodynamic instability. The
corresponding processes are analyzed. Calculations of the growth rates
for dissipative instabilities associated with the excitation of sound
waves and anomalous absorption in a resonant layer are illustrated by
examples. Conditions for the occurrence of the explosive instability are
identified. The results derived here may be of interest in connection
with the problem of the buildup and release of energy in the solar
atmosphere and also for reaching an understanding of the dynamics
of various processes which occur in plasmas with structured magnetic
fields in space and in the laboratory.
Title: Generation of Plasma Flows by Oscillations of Magnetic
Flux Tubes
Authors: Ryutova, M. P.
Bibcode: 1986ESASP.251...71R
Altcode: 1986plas.work...71R
Nonlinear phenomena consisting in generation of plasma flows and
currents in structured magnetic fields are described. There are two
main effects leading to these phenomena. First, it takes place due
to the action of ponderomotive force on plasma, and second due to
the absorption of the momentum and angular momentum of oscillations
propagating along the magnetic flux tubes. If the absorption is provided
mostly with one of the plasma components, then besides the generation
of quite strong convective motions, it is accompanied by the excitation
of currents which can distort the initial magnetic fields and their
equilibrium conditions.
Title: The role of "magnetic threads" in the dynamics of the solar
chromosphere.
Authors: Ryutov, D. D.; Ryutova, M. P.
Bibcode: 1979IGAFS..48..118R
Altcode:
No abstract at ADS
Title: Sound oscillations in a plasma with "magnetic filaments"
Authors: Ryutov, D. A.; Ryutova, M. P.
Bibcode: 1976JETP...43..491R
Altcode:
No abstract at ADS