karlicky

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Author name code: karlicky
ADS astronomy entries on 2022-09-14
author:"Karlicky, Marian"

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Title: Filament Leg--Leg Reconnection as a Source of Prominent
Supra-Arcade Downflows
Authors: Dudik, Jaroslav; Aulanier, Guillaume; Kasparova, Jana;
Karlicky, Marian; Zemanova, Alena; Lorincik, Juraj; Druckmuller,
Miloslav
2022arXiv220900306D Altcode:
We report on interaction of the legs of the erupting filament
of 2012 August 31 and associated prominent supra-arcade downflows
(P-SADs) as observed by the Atmospheric Imaging Assembly onboard the
Solar Dynamics Observatory. We employ a number of image processing
techniques to enhance weak interacting features. As the filament erupts,
both legs stretch outwards. The positive-polarity leg also untwists
and splits into two parts. The first part runs into the conjugate
(negative-polarity) leg, tearing it apart. The second part then
converges into the remnant of the conjugate leg, after which both
weaken and finally disappear. All these episodes of interaction of
oppositely-oriented filament legs are followed by appearance of P-SADs,
seen in the on-disk projection to be shaped as loop-tops, along with
many weaker SADs. All SADs are preceded by hot supra-arcade downflowing
loops. This observed evolution is consistent with the three-dimensional
rr-rf (leg-leg) reconnection, where the erupting flux rope reconnects
with itself. In our observations, as well as in some models, the
reconnection in this geometry is found to be long-lasting. It plays
a substantial role in the evolution of the flux rope of the erupting
filament and leads to prominent supra-arcade downflows.

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Title: Zebra Stripes with High Gyro-Harmonic Numbers
Authors: Benáček, Jan; Karlický, Marian
2022SoPh..297..103B Altcode: 2022arXiv220810131B
Solar radio zebras are used in the determination of the plasma density
and magnetic field in solar flare plasmas. Analyzing observed zebra
stripes and assuming their generation by the double-plasma resonance
(DPR) instability, high values of the gyro-harmonic number are found. In
some cases they exceed one hundred, in disagreement with the DPR growth
rates computed up to now, which decrease with increasing gyro-harmonic
number. We address the question of how zebras with high values of the
gyro-harmonic numbers s are generated. For this purpose, we compute
the growth rates of the DPR instability in a very broad range of s ,
considering a loss-cone κ -distribution of superthermal electrons and
varying the loss-cone angle, electron energies, and background plasma
temperature. We have numerically calculated the dispersion relations
and the growth rates of the upper-hybrid waves and found that the
growth rates increase with increasing gyro-harmonic numbers if the
loss-cone angles are ∼80∘. The highest growth rates for
these loss-cone angles are obtained for velocity vκ=0.15 c
. The growth rates as a function of the gyro-harmonic number still show
well distinct peaks, which correspond to zebra-stripe frequencies. The
contrast between peak growth rates and surrounding growth rate levels
increases as the κ index increases and the background temperature
decreases. Zebras with high values of s can be generated in regions
where loss-cone distributions of superthermal electrons with large
loss-cone angles (∼80∘) are present. Furthermore, owing
to the high values of s , the magnetic field is relatively weak and
has a small spatial gradient in such regions.

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Title: Simulations of solar radio zebras
Authors: Karlický, M.
2022A&A...661A..56K Altcode:
Context. Solar radio zebras are used in diagnostics of solar flare
plasmas and it is of great importance to construct accurate models
to correctly characterize them. Aims: We simulated two zebras
to verify their double-plasma resonance (DPR) model. Methods:
In our zebra simulations, we used the DPR model in an expanding and
compressing part of the loop as well as with the wave propagating
along the loop. Results: Using the DPR model in such a loop, we
successfully simulated zebras from the 1 August 2010 and 21 June 2011
flares. We found that increasing the density or decreasing the magnetic
field in the part of the loop, where zebra-stripe sources are located,
the zebra stripes are shifted to higher frequencies and vice versa. In
the case of the 21 June 2011 flare, we confirm that small deviations
of zebra-stripe frequencies from their mean values can be explained by
waves propagating along the loop. We also confirm high values for the
gyro-harmonic number of zebra stripes. We explain an inconsistency in
the wave velocities derived from the plasma parameters and from the
frequency drift in combination with the density model of the solar
atmosphere. Finally, we discuss the high values of the gyro-harmonic
number found in the studied zebras.

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Title: Narrowband Spikes Observed During the 13 June 2012 Flare in
the 800 - 2000 MHz Range
Authors: Karlický, Marian; Rybák, Ján; Benáček, Jan; Kašparová,
Jana
2022SoPh..297...54K Altcode: 2022arXiv220409327K
Narrowband (∼5 MHz) and short-lived (∼0.01 s) spikes with three
different distributions in the 800 - 2000 MHz radio spectrum of the
13 June 2012 flare are detected and analyzed. We designate them as SB
(spikes distributed in a broad band or bands), SZ (spikes distributed
in zebra-like bands) and SBN (spikes distributed in broad and narrow
bands). On analyzing AIA/SDO images of the active region NOAA 11504,
a rough correspondence between groups of the spikes observed at 1000
MHz and peaks in the time profiles of AIA channels taken from the
flare subarea close to the leading sunspot is found. Among the types
of spikes the SZ type is the most interesting because it resembles
zebras. Therefore, using autocorrelation and crosscorrelation methods
we compare SZ and SBN spikes with the typical zebra observed in the
same frequency range. While the ratio of SZ band frequencies with their
frequency separation (220 MHz) is about 4, 5, and 6, in the zebra the
frequency stripe separation is about 24 MHz and the ratio is around
50. Moreover, the bandwidth of SZ bands, which consists of clouds of
narrowband spikes, is much broader than that of zebra stripes. This
comparison indicates that SZ spikes are generated in a different way
from the zebra, but in a similar way to SBN spikes. We successfully fit
the SZ band frequencies by the Bernstein modes. Based on this fitting
we interpret SZ and SBN spikes as those generated in the model of
Bernstein modes. Thus, the magnetic field and plasma density in the SZ
spike source are estimated to be about 79 G and 8.4 × 109
cm−3, respectively.

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Title: Dynamics and Characteristics of Waves in the Zebra Radio Source
Authors: Yasnov, L. V.; Karlický, M.
2022SoPh..297...35Y Altcode:
We analyzed the 17 August 1998 zebra event and showed that some
quasi-periodic oscillations modulate the zebra-stripe frequencies. We
determined the period of these oscillations as Pn=2.01 ±0.03
(in numbers of zebra stripes) and as Pf=11.8 ±0.17 MHz. In
the first part of the analyzed zebra, we found a stable density wave
that slowly propagated with the frequency drift less than 0.4 MHz
s−1. Then, a stationary density wave appeared followed
by a transformation of the waves to ones with longer periods. These
long-period waves were recorded before and after the time interval
when no zebra stripes were observed. We interpreted these density
waves as magnetosonic waves. We calculated their wavelength and
propagating velocity, considering two types of density models of the
solar atmosphere. We also estimated the characteristic density and
magnetic-field strength as N ≈9.2 ×108 cm−1
and B ≈0.73 G, respectively. We found similar velocities derived
from drifts of the density wave and velocities calculated from the
density and magnetic-field strength considering gyro-harmonic numbers
of zebra stripes.

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Title: Flare energy release and avalanche ionization of plasma by
runaway electrons in lower solar atmosphere
Authors: Tsap, Yuriy; Kopylova, Yulia; Karlický, Marian
2022OAst...30..216T Altcode:
The analysis of the electron acceleration by the quasi-stationary
sub-Dreiser electric fields in the lower solar atmosphere has been
done. It has been shown that the Dreiser electric field turned out
to be several orders of magnitude larger than coronal values due to
the inelastic collisions between electrons and hydrogen atoms. The
ionization of hydrogen atoms gives rise to the resulting secondary
electrons, which become runaway under the action of sub-Dreiser electric
fields. This causes an further avalanche-like ionization of the plasma
and leads to the acceleration of the large number of fast electrons
up to relativistic energies at small (≲ 100 km) distances.

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Title: KAPPA: A Package for the Synthesis of Optically Thin Spectra
for the Non-Maxwellian κ-distributions. II. Major Update to
Compatibility with CHIANTI Version 10
Authors: Dzifčáková, Elena; Dudík, Jaroslav; Zemanová, Alena;
Lörinčík, Juraj; Karlický, Marian
2021ApJS..257...62D Altcode:
KAPPA is a database and software for the calculation of the
optically thin spectra for the non-Maxwellian κ-distributions
that were recently diagnosed in the plasma of solar coronal loops,
flares, as well as in the transition region. KAPPA is based on the
widely used CHIANTI database and reproduces many of its capabilities
for κ-distributions. Here we perform a major update of the KAPPA
database, including a near-complete recalculation of the ionization,
recombination, excitation, and deexcitation rates for all ions in
the database, as well as an implementation of the two-ion model
for calculations of relative-level populations (and intensities) if
these are modified by ionization and recombination from or to excited
levels. As an example of KAPPA usage, we explore novel diagnostics of
κ, and show that O III lines near 500 and 700 Å provide a strong
sensitivity to κ, with some line intensity ratios changing by a
factor of up to 2-4 compared to Maxwellian. This is much larger than
previously employed diagnostics of κ.

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Title: Shock-wave Radio Probing of Solar Wind Sources in Coronal
Magnetic Fields
Authors: Koval, Artem; Karlický, Marian; Stanislavsky, Aleksander;
Wang, Bing; Bárta, Miroslav; Gorgutsa, Roman
2021ApJ...923..255K Altcode: 2021arXiv211015863K
The space weather effects in the near-Earth environment as well as
in atmospheres of other terrestrial planets arise by corpuscular
radiation from the Sun, known as the solar wind. The solar magnetic
fields govern the solar corona structure. Magnetic-field strength
values in the solar wind sources-key information for modeling and
forecasting the space weather climate-are derived from various solar
space- and ground-based observations, but so far not accounting for
specific types of radio bursts. These are "fractured" type II radio
bursts attributed to collisions of shock waves with coronal structures
emitting the solar wind. Here, we report on radio observations of two
"fractured" type II bursts to demonstrate a novel tool for probing of
magnetic-field variations in the solar wind sources. These results
have a direct impact on interpretations of this class of bursts and
contribute to the current studies of the solar wind emitters.

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Title: Narrowband Spikes Observed during the 2013 November 7 Flare
Authors: Karlický, Marian; Benáček, Jan; Rybák, Ján
2021ApJ...910..108K Altcode: 2021arXiv210401345K
Narrowband spikes have been observed in solar flares for several
decades. However, their exact origin is still discussed. To contribute
to understanding of these spikes, we analyze the narrowband spikes
observed in the 800-2000 MHz range during the impulsive phase of the
2013 November 7 flare. In the radio spectrum, the spikes started with
typical broadband clouds of spikes, and then their distribution in
frequencies changed into unique, very narrow bands having noninteger
frequency ratios. We successfully fitted frequencies of these narrow
spike bands by those, calculating dispersion branches and growth rates
of the Bernstein modes. For comparison, we also analyzed the model
where the narrow bands of spikes are generated at the upper-hybrid
frequencies. Using both models, we estimated the plasma density and
magnetic field in spike sources. Then, the models are discussed,
and arguments in favor of the model with the Bernstein modes are
presented. Analyzing frequency profiles of this spike event by the
Fourier method, we found the power-law spectra with the power-law
indices varying in the -0.8 to -2.75 interval. Because at some times
this power-law index was close to the Kolmogorov spectral index (-5/3),
we propose that the spikes are generated through the Bernstein modes
in turbulent plasma reconnection outflows or directly in the turbulent
magnetic reconnection of solar flares.

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Title: Spatial quasi-periodic variations of the plasma density and
magnetic field in zebra radio sources
Authors: Karlický, M.; Yasnov, L. V.
2021A&A...646A.179K Altcode:
Context. Radio bursts and their fine structures are an integral
part of solar flares. Fine structures in particular are used for
diagnostics of solar flare processes. The so-called zebras belong to
the most important of such fine structures. Aims: We analyze
seven zebra events in order to search for spatial variations in the
plasma density and magnetic field in zebra-stripe sources. 
Methods: We used an improved method for estimating the gyroharmonic
numbers of zebra-stripe frequencies. We compared observed zebra-stripe
frequencies with those calculated in the zebra model. The differences
in these frequencies vary and thus show spatial variations in the
plasma density and magnetic field. Results: In six out of
seven analyzed zebras, we found a rather high correlation coefficient
(about 0.7 and higher) between spatial variations in the density and
magnetic field and a strictly periodic function. These density and
magnetic field variations are explained by the torsional or sausage
magnetoacoustic waves in the loop in which zebra-stripe sources are
located. We present the wavelengths of these waves in dependence on
the zebra frequency and estimate their periods.

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Title: Flare Expansion to a Magnetic Rope Accompanied by Rare
Radio Bursts
Authors: Zemanová, Alena; Karlický, Marian; Kašparová, Jana;
Dudík, Jaroslav
2020ApJ...905..111Z Altcode: 2021arXiv210108633Z
We present multispectral analysis (radio, Hα, ultraviolet (UV)/extreme
ultraviolet (EUV), and hard X-ray) of a confined flare from 2015 March
12. This flare started within the active region NOAA 12 297 and then it
expanded into a large preexisting magnetic rope embedded with a cold
filament. The expansion started with several brightenings located
along the rope. This process was accompanied by a group of slowly
positively drifting bursts in the 0.8-2 GHz range. The frequency drift
of these bursts was 45-100 MHz s-1. One of the bursts had an
S-like form. During the brightening of the rope we observed a unique
bright EUV structure transverse to the rope axis. The structure was
observed in a broad range of temperatures and it moved along the rope
with the velocity of about 240 km s-1. When the structure
dissipated, we saw a plasma further following twisted threads in the
rope. The observed slowly positively drifting bursts were interpreted
considering particle beams and we show that one with the S-like
form could be explained by the beam propagating through the helical
structure of the magnetic rope. The bright structure transverse to
the rope axis was interpreted considering line-of-sight effects and
the dissipation-spreading process, which we found to be more likely.

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Title: The 2017 September 6 Flare: Radio Bursts and Pulsations in
the 22-5000 MHz Range and Associated Phenomena
Authors: Karlický, Marian; Rybák, Ján
2020ApJS..250...31K Altcode: 2020arXiv200905756K
For the 2017 September 6 flare (SOL2017-Sep-06T11:53) we present not
only unusual radio bursts but also their interesting time association
with the other flare phenomena observed in extreme ultraviolet (EUV),
white-light, X-ray, and γ-ray emissions. Using our new method based on
wavelets we found quasi-periodic pulsations (QPPs) in several locations
of the whole time-frequency domain of the analyzed radio spectrum
(11:55-12:07 UT and 22-5000 MHz). Among them the drifting QPPs are
new and the most interesting, especially a bidirectional QPP at the
time of the hard X-ray and γ-ray peaks and a sunquake start. In the
pre-impulsive phase we show an unusual drifting pulsation structure
(DPS) in association with the EUV brightenings caused by the interaction
of magnetic ropes. In the flare impulsive phase we found an exceptional
radio burst drifting from 5000 to 800 MHz. In connection with this
drifting burst, we show a U burst at about the onset time of an EUV
writhed structure and a drifting radio burst as a signature of a shock
wave at high frequencies (1050-1350 MHz). In the peak flare phase we
found an indication of an additional energy-release process located
at higher altitudes in the solar atmosphere. These phenomena are
interpreted considering a rising magnetic rope, magnetosonic waves,
and particle beams. Using a density model we estimated the density,
wave velocities, and source heights for the bidirectionally drifting
QPPs, the density for the pre-impulsive DPS and U burst, and the
density and magnetic field strength for the drifting radio burst.

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Title: Magnetic Field, Electron Density and Their Spatial Scales in
Zebra Pattern Radio Sources
Authors: Yasnov, L. V.; Karlický, M.
2020SoPh..295...96Y Altcode:
Zebra patterns (zebras) play an important role in the plasma diagnostics
during solar flares. Considering their double plasma resonance
(DPR) model, we present an improved method for the determination of
the gyro-harmonic numbers of the zebra stripes that are essential
in determining the electron density and magnetic field strength in
zebra sources. Furthermore, we present the magnetic field and density
spatial scales in zebra sources. Compared to the previous method,
we change the basic assumption of the method. Namely, the assumption
that the ratio R =Lbh/Lnh (Lbh and
Lnh are the magnetic field and density scales) is constant
in the whole zebra source is changed to its more generalized form,
where the ratio R is a linear function. Using this improved method,
first, we determine the gyro-harmonic numbers of several observed zebras
and variations of the spatial scales. Then, knowing the gyro-harmonic
numbers of zebra stripes, we compute the electron plasma density and
magnetic field strength in zebra sources. It is shown that in all
cases the gyro-harmonic numbers of zebra stripes are quite high (&gt;
≈50). This significantly reduces the magnetic field strength and thus
increases the plasma beta parameter in zebra sources. The change in
the ratio of the magnetic field and density scales along the axis of
the radiating tube for the studied zebras is within ± 5 percent. For
zebras at high frequencies, this ratio increases with the height,
and for zebras at lower frequencies it decreases. The ratio of the
magnetic field and density scales across the radiating tube is close
to 1 and varies in the range 0.87-1.20.

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Title: Estimating density and magnetic field turbulence in solar
flares using radio zebra observations
Authors: Karlický, M.; Yasnov, L.
2020A&A...638A..22K Altcode:
Context. In solar flares the presence of magnetohydrodynamic turbulence
is highly probable. However, information about this turbulence,
especially the magnetic field turbulence, is still very limited. Aims: In this paper we present a new method for estimating levels
of the density and magnetic field turbulence in time and space
during solar flares at positions of radio zebra sources. 
Methods: First, considering the double-plasma resonance model of
zebras, we describe a new method for determining the gyro-harmonic
numbers of zebra stripes based on the assumption that the ratio
R = Lb/Ln (Ln and Lb
are the density and magnetic field scales) is constant in the whole
zebra source. Results: Applying both the method proposed in
this work and one from a previous paper for comparison, in the 14
February 1999 zebra event we determined the gyro-harmonic numbers of
zebra stripes. Then, using the zebra-stripe frequencies with these
gyro-harmonic numbers, we estimated the density and magnetic field
in the zebra-stripe sources as n = (2.95-4.35) × 1010
cm-3 and B = 17.2-31.9 G, respectively. Subsequently,
assuming that the time variation of the zebra-stripe frequencies
is caused by the plasma turbulence, we determined the level of the
time varying density and magnetic field turbulence in zebra-stripe
sources as |Δn/n|t = 0.0112-0.0149 and |ΔB/B|t
= 0.0056-0.0074, respectively. The new method also shows deviations
in the observed zebra-stripe frequencies from those in the model. We
interpret these deviations as being caused by the spatially varying
turbulence among zebra-stripe sources; i.e., they depend on their
gyro-harmonic numbers. Comparing the observed and model zebra-stripe
frequencies at a given time, we estimated the level of this turbulence
in the density and magnetic field as |Δn/n|s = 0.0047
and |ΔB/B|s = 0.0024. We found that the turbulence levels
depending on time and space in the 14 February 1999 zebra event are
different. This indicates some anisotropy of the turbulence, probably
caused by the magnetic field structure in the zebra source.

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Title: Expansion of Hot Plasma with Kappa Distribution into Cold
Plasma
Authors: Benáček, Jan; Karlický, Marian
2020ApJ...896....9B Altcode: 2020arXiv200604479B
The X-ray emission of coronal flare sources can be explained by
considering the kappa electron distribution. Motivated by this fact,
we study the problem of how hot plasma with the kappa distribution of
electrons is confined in these sources. For comparison, we analyze
the same problem, but with the Maxwellian distribution. We use a
3D particle-in-cell code, which is large in one direction and thus
effectively only one-dimensional, but describe all electromagnetic
effects. In the case with the Maxwellian distribution, and in agreement
with the previous studies, we show a formation of the double layer
at the hot-cold transition region that suppresses the flux of hot
electrons from hot plasma into the cold one. In the case with the kappa
distribution, contrary to the Maxwellian case, we found that there
are several fronts with the double layers in the hot-cold transition
region. It is caused by a more extended tail in the kappa case than in
the Maxwellian one. The electrons from the extended tail freely escape
from the hot plasma into a cold one. They form a beam that generates
the return current and also Langmuir turbulence, where Langmuir waves
accumulated at some locations. At these locations, owing to the
ponderomotive force, Langmuir waves generate density depressions,
where the double layers with the thermal fronts that suppress the
hot electron flux, are formed. We also show how protons accelerate in
these processes. Finally, we compare the Kappa and Maxwellian cases
and discuss how these processes could be observed.

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Title: Transverse oscillations of a double-structured solar filament
Authors: Jelínek, P.; Karlický, M.; Smirnova, V. V.; Solov'ev, A. A.
2020A&A...637A..42J Altcode:
 Aims: We study the transverse oscillations of a double-structured
solar filament. Methods: We modelled the filament numerically
via a 2D magnetohydrodynamic (MHD) model, in which we solved a full set
of time-dependent MHD equations by means of the FLASH code, using the
adaptive mesh refinement method. We used the wavelet analysis method as
a diagnostic tool for analysing periods in simulated oscillations. Results: We present a model of a solar filament combined with
semi-empirical C7 model of the quiet solar atmosphere. This model is an
alternative model of a filament based on the magnetostatic solution of
MHD equations. We find that this double-structured filament oscillates
with two different eigen frequencies. The ratio is approximately 1.75
(∼7.4 min/∼4.2 min), which is characteristic for this type of
filament model. To show the details of these oscillations we present
a time evolution of the plasma density, temperature, plasma beta
parameter, and the ratio of gravity to magnetic pressure taken along
the vertical axis of the filament at x = 0. The periods found by
numerical simulations are then discussed in comparison with those
observed. The movie associated to Fig. 3 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936836/olm">https://www.aanda.org</A>

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Title: Drifting Pulsation Structure at the Very Beginning of the
2017 September 10 Limb Flare
Authors: Karlický, Marian; Chen, Bin; Gary, Dale E.; Kašparová,
Jana; Rybák, Jan
2020ApJ...889...72K Altcode: 2019arXiv191212518K
Drifting pulsation structures (DPSs) are important radio fine structures
usually observed at the beginning of eruptive solar flares. It has been
suggested that DPSs carry important information on the energy release
processes in solar flares. We study DPS observed in an X8.2-class flare
on 2017 September 10 in the context of spatial and spectral diagnostics
provided by microwave, EUV, and X-ray observations. We describe DPS
and its substructures that were observed for the first time. We use a
new wavelet technique to reveal characteristic periods in DPS and their
frequency bands. Comparing the periods of pulsations found in this DPS
with those in previous DPSs, we found new very short periods in the
0.09-0.15 s range. We present Expanded Owens Valley Solar Array images
and spectra of microwave sources observed during the DPS. This DPS at
its very beginning has pulsations in two frequency bands (1000-1300 MHz
and 1600-1800 MHz), which are interconnected by fast drifting bursts. We
show that these double-band pulsations started just at the moment when
the ejected filament splits apart in a tearing motion at the location
where a signature of the flare current sheet later appeared. Using the
standard flare model and previous observations of DPSs, we interpret
these double-band pulsations as a radio signature of superthermal
electrons trapped in the rising magnetic rope and flare arcade at the
moment when the flare magnetic reconnection starts. The results are
discussed in a scenario with the plasmoid in the rising magnetic rope.

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Title: Radio, EUV, and X-Ray Observations during a Filament Rise in
the 2011 June 7 Solar Flare
Authors: Karlický, Marian; Kašparová, Jana; Sych, Robert
2020ApJ...888...18K Altcode: 2020arXiv200400122K
The most energetic flares start with a filament rise followed by
magnetic reconnection below this filament. The start of the reconnection
corresponds to the beginning of the flare impulsive phase. In this
paper we study processes before this phase. During the filament rise
we recognize an unusual radio continuum with a starting boundary
drifting toward lower frequencies. The estimated velocity of the agent
generating this continuum boundary is about 400 km s-1,
similar to that of the rising filament. In association with this
filament rise, transient X-ray sources and extreme ultraviolet (EUV)
brightenings are found near the filament footpoint and outside the
locations where later two parallel flare ribbons appear. Moreover,
oscillations with a ∼30 s period are found simultaneously in radio,
EUV, and X-ray observations. Around the end of these oscillations the
flare impulsive phase starts as seen in observations of the drifting
pulsation structure and X-ray source located at the upper part of the
rising filament. We interpret the unusual radio continuum and transient
X-ray sources, which are located outside the two parallel flare ribbons,
as those generated during an interaction of the rising filament with
the above-lying magnetic loops. The EUV brightening at the filament
footpoint could be a signature of the magnetic reconnection inside the
magnetic rope carrying the filament. Possible scenarios of the ∼30
s period oscillations in radio, X-ray, and EUV are discussed.

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Title: Growth Rates of the Electrostatic Waves in Radio Zebra Models
Authors: Benáček, Jan; Karlický, Marian
2019ApJ...881...21B Altcode: 2019arXiv190412601B
Zebras were observed not only in the solar radio emission but also
in radio emissions of Jupiter and the Crab Nebula pulsar. In their
models, growth rates of the electrostatic waves play an important
role. Considering the plasma composed from the thermal background plasma
and hot and rare component with the Dory-Guest-Harris distribution, we
compute the growth rates γ and dispersion branches of the electrostatic
waves in the ω - k ⊥ domain. We show complexity of
the electrostatic wave branches in the upper-hybrid band. In order
to compare the results, which we obtained using the kinetic theory
and particle-in-cell (PIC) simulations, we define and compute the
integrated growth rate Γ, where the “characteristic width” of
dispersion branches was considered. We found a very good agreement
between the integrated growth rates and those from PIC simulations. For
maximal and minimal Γ we showed locations of dispersion branches in the
ω - k ⊥ domain. We found that Γ has a maximum when the
dispersion branches not only cross the region with high growth rates γ,
but when the dispersion branches in this region are sufficiently long
and wide. We also mentioned the effects of changes in the background
plasma and hot component temperatures.

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Title: Pulse-beam heating of deep atmospheric layers, their
oscillations and shocks modulating the flare reconnection
Authors: Jelínek, P.; Karlický, M.
2019A&A...625A...3J Altcode:
 Aims: We study the processes occurring after a sudden heating
of deep atmospheric layers at the flare arcade footpoints, which
is assumed to be caused by particle beams. Methods: For the
numerical simulations we adopt a 2D magnetohydrodynamic (MHD) model,
in which we solve a full set of the time-dependent MHD equations by
means of the FLASH code, using the adaptive mesh refinement (AMR)
method. Results: In the initial state we consider a model of
the solar atmosphere with densities according to the VAL-C model and
the magnetic field arcade having the X-point structure above, where the
magnetic reconnection is assumed. We found that the sudden pulse-beam
heating of deep atmospheric layers at the flare arcade footpoints
generates two magnetohydrodynamic shocks, one propagating upwards
and the second propagating downwards in the solar atmosphere. The
downward-moving shock is reflected at deep and dense atmospheric
layers and triggers oscillations of these layers. The period of these
oscillations in our case is about 174 s. These oscillations generate
the upward-moving magnetohydrodynamic waves that can influence the flare
magnetic reconnection in a quasi-periodic way. These processes require
a sudden heating in very localized regions in dense atmospheric layers;
therefore, they can be also associated with seismic waves.

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Title: Zebra-stripe sources in the double-plasma resonance model of
solar radio zebras
Authors: Karlický, M.; Yasnov, L.
2019A&A...624A.119K Altcode:
Context. Radio bursts with fine structures are used in diagnostics
of solar flare plasmas, of which zebra structures are the most
important. However, there is still a debate about their origin. 
Aims: The most probable model of zebras is that based on double-plasma
resonance (DPR) instability. The paper wants to contribute to
a verification of this model. Methods: We used analytical
methods. Results: We studied the DPR model in two scenarios:
a model with the zebra-stripe sources in a single loop and a model
with the zebra-stripe sources moving through a fan of magnetic field
lines. In the first case, we found several new relations among the
parameters of zebra stripes and their sources, which can be used to
analyze observed zebras and thus to verify if the zebra is generated
according to the DPR model. These relations were derived for the
zebra-stripe sources distributed along the loop and also for those
having some extent in the loop radius. In the scenario with the moving
zebra-stripe sources, we determined the parameters of the 14 December
2006 zebra and estimated a change of the ratio of magnetic field and
density scales causing the change of zebra-stripe frequencies. In this
case we found that this zebra can be also explained in the model with
the zebra-stripe sources in a single loop. Both the interpretations
are discussed.

---------------------------------------------------------
Title: Topological Structures of Velocity and Electric Field in the
Vicinity of a Cusp-type Magnetic Null Point
Authors: Nickeler, Dieter H.; Karlický, Marian; Kraus, Michaela
2019ApJ...873...41N Altcode: 2019arXiv190109913N
Topological characteristics reveal important physical properties of
plasma structures and astrophysical processes. Physical parameters and
constraints are linked with topological invariants, which are important
for describing magnetic reconnection scenarios. We analyze stationary
nonideal Ohm’s law concerning the Poincaré classes of all involved
physical fields in two dimensions by calculating the corresponding
topological invariants of their Jacobian (here: particularly the
eigenvalues) or Hessian matrices. The magnetic field is assumed to
have a cusp structure, and the stagnation point of the plasma flow
coincides with the cusp. We find that the stagnation point must be
hyperbolic. Furthermore, the functions describing both the resistivity
and the ohmic heating have a saddle-point structure, being displaced
with respect to the cusp point. These results imply that there is no
monotonous relation between current density and anomalous resistivity
in the case of a two-dimensional standard magnetic cusp.

---------------------------------------------------------
Title: Growth Rates of the Upper-Hybrid Waves for Power-Law and
Kappa Distributions with a Loss-Cone Anisotropy
Authors: Yasnov, L. V.; Benáček, J.; Karlický, M.
2019SoPh..294...29Y Altcode: 2019arXiv190405110Y
Fine structures of radio bursts play an important role in the
diagnostics of the solar flare plasma. Among them the zebras,
which are prevalently assumed to be generated by the double-plasma
resonance instability, belong to the most important ones. In this
paper we compute the growth rate of this instability for two types of
the electron distribution: a) for the power-law distribution and b)
for the kappa distribution, in both cases with the loss-cone type
anisotropy. We find that the growth rate of the upper-hybrid waves
for the power-law momentum distribution strongly depends on the
pitch-angle boundary. The maximum growth rate is found for the pitch
angle θc≈50∘. For small angles the growth
rate profile is very flat and for high pitch angles the wave absorption
occurs. Furthermore, analyzing the growth rate of the upper-hybrid
waves for the kappa momentum distribution we find that a decrease
of the characteristic momentum pκ shifts the maximum of
the growth rate to lower values of the ratio of the electron-plasma
and electron-cyclotron frequencies, and the frequency widths of
the growth rate peaks are very broad. But if we consider the kappa
distribution which is isotropic up to some large momentum pm
and anisotropic with loss-cone above this momentum then distinct
peaks of the growth rate appear and thus distinct zebra stripes can
be generated. It means that the restriction of small momenta for the
anisotropic part of distributions is of principal importance for the
zebra stripe generation. Finally, for the zebra stripes observed on
1 August 2010, the growth rates in dependence on the radio frequency
are computed. It is shown that in this case the growth rate peaks are
more distinct than in usually presented dependencies of growth rates
on the ratio of the plasma and cyclotron frequencies.

---------------------------------------------------------
Title: Pulse-beam heating of deep atmospheric layers triggering
their oscillations and upwards moving shocks that can modulate the
reconnection in solar flares
Authors: Jelínek, P.; Karlický, M.
2019arXiv190200292J Altcode:
We study processes occurring after a sudden heating of the chromosphere
at the flare arcade footpoints which is assumed to be caused by particle
beams. For the numerical simulations we adopt a 2-D magnetohydrodynamic
(MHD) model, in which we solve a full set of the time-dependent
MHD equations by means of the FLASH code, using the Adaptive Mesh
Refinement (AMR) method. In the initial state we consider a model
of the solar atmosphere with densities according to the VAL-C model
and the magnetic field arcade having the X-point structure above,
where the magnetic reconnection is assumed. We found that the sudden
pulse-beam heating of the chromosphere at the flare arcade footpoints
generates magnetohydrodynamic shocks, one propagating upwards and the
second one propagating downwards in the solar atmosphere. The downward
moving shock is reflected at deep and dense atmospheric layers and
triggers oscillations of these layers. These oscillations generate the
upwards moving magnetohydrodynamic waves that can influence the above
located magnetic reconnection in a quasi-periodic way. Because these
processes require a sudden heating in very localized regions in the
chromosphere therefore they can be also associated with seismic waves.

---------------------------------------------------------
Title: Determination of Plasma Parameters in Radio Sources of Solar
Zebra-patterns Based on Relations between the Zebra-stripe Frequencies
and Gyro-harmonic Numbers
Authors: Karlický, Marian; Yasnov, Leonid V.
2018ApJ...867...28K Altcode:
Solar radio zebras belong to the most important radio fine structures
used in diagnostics of solar flare plasmas. In the present paper,
assuming the double plasma-resonance model of zebras, we study
the relation between zebra-stripe frequencies and gyro-harmonic
numbers. We artificially generated two possible types of zebras:
the zebra with Sequence A and Sequence B, where an increase of the
zebra-stripe frequency corresponds to decrease or increase of the
gyro-harmonic number. Analyzing these ideal zebras, we found that the
frequency ratios of the neighboring zebra stripes increase in zebras
with Sequence A and decrease in zebras with Sequence B. This criterion
and corresponding diagrams were applied for nine observed zebras. All
these zebras were found to be with Sequence A. Then we checked and
confirmed these results by using the new numerical method, where the
gyro-harmonic numbers of the zebra stripes with the lowest frequency s
1 were also determined. We found that in all these zebras,
the spatial scale of the magnetic field in the zebra-stripe sources
was always shorter than that of the plasma density. Knowing the
gyro-harmonic numbers and corresponding zebra-stripe frequencies, we
determined the magnetic field and plasma density in zebra sources to
be 0.84-37.31 G and 0.026 × 1010-16.03 × 1010
cm-3, respectively. Finally, we found that with increasing
the gyro-harmonic number s 1, the ratio of perpendicular
and parallel scales of the magnetic field and plasma density in the
zebra-stripe sources also increases.

---------------------------------------------------------
Title: Fourier Power Spectra of Solar Noise Storms
Authors: Karlický, Marian; Rybák, Ján; Monstein, Christian
2018SoPh..293..143K Altcode:
We analyzed three noise storms recorded on 200 - 400 MHz Trieste
Callisto radio spectra on 2 July 2012, 8 July 2012, and 16 July 2012
by the Fourier method. We divided intervals of the noise storms into
five-minute intervals, and in these intervals we computed the mean
Fourier spectra as a function of the wave numbers in the frequency
and height-scale spaces. We found that these Fourier spectra, where
the spectrum from the quiet-activity interval was subtracted, are
power-law spectra. The mean power-law index of these spectra in the
range ln(kz)=[1.8 ,2.9 ] (where kz is the wave
number in the height-scale space) is −1.7 ±0.14 , −1.6 ±0.14 ,
and −1.5 ±0.12 for the 2 July 2012, the 8 July 2012, and the 16
July 2012 noise storms, respectively. It appears that as the number of
Type-I bursts in the studied interval increases, the power-law index
becomes closer to −5 /3 ; this is known as the Kolmogorov spectral
index. The power-law index of the noise storms is very similar to that
of the narrowband dm-spikes found in our previous studies. Furthermore,
we found a break in the power spectra at ln(kz)≈2.9 , and
the mean power-law index values above this break are −2.9 ±0.46 ,
−3.1 ±0.65 , and −3.4 ±0.98 , respectively.

---------------------------------------------------------
Title: Double plasma-resonance surfaces in flare loops and radio
zebra emission
Authors: Karlický, M.; Yasnov, L.
2018A&A...618A..60K Altcode:
 Aims: The zebra structures observed in radio waves during solar
flares are some of the most important structures used as diagnostics
of solar flare plasmas. We here not only analyze the so-called double
plasma-resonance (DPR) surfaces, but also estimate the effects of their
form on the size of the zebra sources and brightness temperature. 
Methods: To compute the DPR surfaces, we used numerical and analytical
methods. Results: We found that except for the case of a constant
magnetic field across the loop, the DPR surfaces deviate from the
constant plasma density surfaces. We found that the regime with a
finite height scale has three forms of resonance surfaces depending
on the magnetic field variation across the loop. This magnetic field
variation also determines if in the generated zebra structure, an
increase in gyro-harmonic number leads to an increase or decrease of
the zebra stripe frequency. In the case with an infinite height scale,
the resonance surfaces are parallel to the loop axis. Furthermore, we
found that for highly polarized zebra structures that are generated
at DPR surfaces close to the plasma frequency, the zebra emission
is limited to the narrow escaping cone and the emitting source
area increases with increasing viewing angle compared to the loop
axis. Moreover, with increasing deviation of the DPR surfaces from
those of constant density surfaces, the frequency bandwidth of the
DPR emission increases and can cause the zebra stripes to overlap,
which limits the zebra generation. For the zebra structures observed
on 14 February 1999, 6 June 2000, and 1 August 2010 and the observed
view perpendicular to the loop axis, we estimated that the brightness
temperature is 3.67 × 1014 K, 6.58 × 1013 K, and
7.35 × 1015 K, respectively. These brightness temperatures
are much lower than those derived for the view along the loop axis
(up to 1017 K), and thus are more realistic. The area of
the emitting source for coronal loops in the view perpendicular to
the loop axis can be larger by several orders of magnitude than that
in the view along the loop axis.

---------------------------------------------------------
Title: Effects of electron distribution anisotropy in spectroscopic
diagnostics of solar flares
Authors: Dzifčáková, E.; Karlický, M.
2018A&A...618A.176D Altcode:
 Aims: We analyzed effects of the bi-Maxwellian electron
distribution representing electron temperature anisotropy along
and across the magnetic field on the ionization and excitation
equilibrium with consequences on the temperature diagnostics of the
flare plasma. Methods: The bi-Maxwellian energy distributions
were calculated numerically. Synthetic X-ray line spectra of the
bi-Maxwellian distributions were calculated using non-Maxwellian
ionization, recombination, excitation and de-excitation rates. Results: We found that the anisotropic bi-Maxwellian velocity
distributions transform to the nonthermal energy distributions with
a high-energy tail. Their maximum is shifted to lower energies
and contains a higher number of the low-energy particles in
comparison with the Maxwellian one. Increasing the deviation of the
parameter p = T∥/T⊥ from 1, changes the
shape of bi-Maxwellian distributions and ionization equilibrium,
and relative line intensities also increase. The effects are more
significant for the bi-Maxwellian distribution with T∥
&gt; T⊥. Moreover, considering different acceleration
mechanisms and collisional isotropization it is possible that the
bi-Maxwellian distributions with high deviations from the Maxwellian
distribution are more probable for those with p &gt; 1 than for
those with p &lt; 1. Therefore, distributions with p &gt; 1 can be
much more easily diagnosed than those with p &lt; 1. Furthermore,
we compared the effects of the bi-Maxwellian distributions on the
ionization equilibrium and temperature diagnostics with those for the
κ-distributions obtained previously. We found that they are similar
and at the present state it is difficult to distinguish between the
bi-Maxwellian and κ-distributions from the line ratios.

---------------------------------------------------------
Title: Oscillations and Waves in Radio Source of Drifting Pulsation
Structures
Authors: Karlický, Marian; Rybák, Ján; Bárta, Miroslav
2018SoPh..293...62K Altcode: 2018arXiv180306148K
Drifting pulsation structures (DPSs) are considered to be radio
signatures of the plasmoids formed during magnetic reconnection
in the impulsive phase of solar flares. In the present paper
we analyze oscillations and waves in seven examples of drifting
pulsation structures, observed by the 800 - 2000 MHz Ondřejov
Radiospectrograph. For their analysis we use a new type of oscillation
maps, which give us much more information as regards processes
in DPSs than that in previous analyses. Based on these oscillation
maps, made from radio spectra by the wavelet technique, we recognized
quasi-periodic oscillations with periods ranging from about 1 to 108
s in all studied DPSs. This strongly supports the idea that DPSs are
generated during a fragmented magnetic reconnection. Phases of most
the oscillations in DPSs, especially for the period around 1 s, are
synchronized ("infinite" frequency drift) in the whole frequency range
of DPSs. For longer periods in some DPSs we found that the phases of the
oscillations drift with the frequency drift in the interval from −17
to +287 MHzs−1. We propose that these drifting phases can
be caused (a) by the fast or slow magnetosonic waves generated during
the magnetic reconnection and propagating through the plasmoid, (b) by
a quasi-periodic structure in the plasma inflowing to the reconnection
forming a plasmoid, and (c) by a quasi-periodically varying reconnection
rate in the X-point of the reconnection close to the plasmoid.

---------------------------------------------------------
Title: Double plasma resonance instability as a source of solar
zebra emission
Authors: Benáček, J.; Karlický, M.
2018A&A...611A..60B Altcode: 2017arXiv171104281B
Context. The double plasma resonance (DPR) instability plays a basic
role in the generation of solar radio zebras. In the plasma, consisting
of the loss-cone type distribution of hot electrons and much denser and
colder background plasma, this instability generates the upper-hybrid
waves, which are then transformed into the electromagnetic waves
and observed as radio zebras. Aims: In the present paper we
numerically study the double plasma resonance instability from the
point of view of the zebra interpretation. Methods: We use a
3-dimensional electromagnetic particle-in-cell (3D PIC) relativistic
model. We use this model in two versions: (a) a spatially extended
"multi-mode" model and (b) a spatially limited "specific-mode"
model. While the multi-mode model is used for detailed computations
and verifications of the results obtained by the "specific-mode"
model, the specific-mode model is used for computations in a broad
range of model parameters, which considerably save computational
time. For an analysis of the computational results, we developed
software tools in Python. Results: First using the multi-mode
model, we study details of the double plasma resonance instability. We
show how the distribution function of hot electrons changes during
this instability. Then we show that there is a very good agreement
between results obtained by the multi-mode and specific-mode models,
which is caused by a dominance of the wave with the maximal growth
rate. Therefore, for computations in a broad range of model parameters,
we use the specific-mode model. We compute the maximal growth rates
of the double plasma resonance instability with a dependence on the
ratio between the upper-hybrid ωUH and electron-cyclotron
ωce frequency. We vary temperatures of both the hot and
background plasma components and study their effects on the resulting
growth rates. The results are compared with the analytical ones. We
find a very good agreement between numerical and analytical growth
rates. We also compute saturation energies of the upper-hybrid waves
in a very broad range of parameters. We find that the saturation
energies of the upper-hybrid waves show maxima and minima at almost
the same values of ωUH/ωce as the growth
rates, but with a higher contrast between them than the growth
rate maxima and minima. The contrast between saturation energy
maxima and minima increases when the temperature of hot electrons
increases. Furthermore, we find that the saturation energy of the
upper-hybrid waves is proportional to the density of hot electrons. The
maximum saturated energy can be up to one percent of the kinetic energy
of hot electrons. Finally we find that the saturation energy maxima
in the interval of ωUH/ωce = 3-18 decrease
according to the exponential function. All these findings can be used
in the interpretation of solar radio zebras.

---------------------------------------------------------
Title: Solar Radio Burst Associated with the Falling Bright EUV Blob
Authors: Karlický, Marian; Zemanová, Alena; Dudík, Jaroslav;
Radziszewski, Krzysztof
2018ApJ...854L..29K Altcode: 2018arXiv180406206K
At the beginning of the 2015 November 4 flare, in the 1300-2000 MHz
frequency range, we observed a very rare slow positively drifting
burst. We searched for associated phenomena in simultaneous EUV
observations made by IRIS, SDO/AIA, and Hinode/XRT, as well as in H
α observations. We found that this radio burst was accompanied
with the bright blob, visible at transition region, coronal, and flare
temperatures, falling down to the chromosphere along the dark loop with
a velocity of about 280 km s-1. The dark loop was visible
in H α but disappeared afterward. Furthermore, we found
that the falling blob interacted with the chromosphere as expressed
by a sudden change of the H α spectra at the location
of this interaction. Considering different possibilities, we propose
that the observed slow positively drifting burst is generated by the
thermal conduction front formed in front of the falling hot EUV blob.

---------------------------------------------------------
Title: Very rare bursts observed in the 0.8-2.0 GHz solar radio
spectra
Authors: Jiřička, K.; Karlický, M.
2018CEAB...42....5J Altcode:
Besides typical and known radio bursts there are very rare bursts
that are not up to now commonly known and explained. In more than
twenty years of observations in the 0.8-2.0 GHz frequency range by the
Ondřejov radiospectrograph we found several such very rare bursts. In
this paper six examples of them are presented and described.

---------------------------------------------------------
Title: Brightness Temperature of Radio Zebras and Wave Energy
Densities in Their Sources
Authors: Yasnov, L. V.; Benáček, J.; Karlický, M.
2017SoPh..292..163Y Altcode: 2017arXiv170201278Y
We estimated the brightness temperature of radio zebras (zebra pattern -
ZP), considering that ZPs are generated in loops having an exponential
density profile in their cross section. We took into account that when
in a plasma there is a source emitting in all directions, then in the
escape process from the plasma the emission has a directional character
nearly perpendicular to the constant-density profile. Owing to the high
directivity of the plasma emission (for emission at frequencies close
to the plasma frequency), the region from which the emission escapes
can be very small. We estimated the brightness temperature of three
observed ZPs for two values of the density scale height (1 and 0.21
Mm) and two values of the loop width (1 and 2 arcsec). In all cases,
high brightness temperatures were obtained. For the higher value of
the density scale height, the brightness temperature was estimated to
be 1.1 ×1015 - 1.3 ×1017K, and for the lower
value, it was 4.7 ×1013 - 5.6 ×1015K. These
temperatures show that the observational probability of a burst with a
ZP, which is generated in the transition region with a steep gradient
of the plasma density, is significantly higher than for a burst
generated in a region with smoother changes of the plasma density. We
also computed the saturation energy density of the upper-hybrid waves
(according to the double plasma resonance model, they are generated in
the zebra source) using a 3D particle-in-cell model with a loss-cone
type of distribution of hot electrons. We found that this saturated
energy is proportional to the ratio of hot electron and background
plasma densities. Thus, comparing the growth rate and collisional
damping of the upper-hybrid waves, we estimated minimum densities of
hot electrons as well as the minimum value of the saturation energy
density of the upper-hybrid waves. Finally, we compared the computed
energy density of the upper-hybrid waves with the energy density of
the electromagnetic waves in the zebra source and thus estimated the
efficiency of the wave transformation.

---------------------------------------------------------
Title: Oscillations Excited by Plasmoids Formed During Magnetic
Reconnection in a Vertical Gravitationally Stratified Current Sheet
Authors: Jelínek, P.; Karlický, M.; Van Doorsselaere, T.; Bárta, M.
2017ApJ...847...98J Altcode: 2017arXiv170306674J
Using the FLASH code, which solves the full set of the 2D non-ideal
(resistive) time-dependent magnetohydrodynamic (MHD) equations,
we study processes during the magnetic reconnection in a vertical
gravitationally stratified current sheet. We show that during these
processes, which correspond to processes in solar flares, plasmoids are
formed due to the tearing mode instability of the current sheet. These
plasmoids move upward or downward along the vertical current sheet
and some of them merge into larger plasmoids. We study the density
and temperature structure of these plasmoids and their time evolution
in detail. We found that during the merging of two plasmoids, the
resulting larger plasmoid starts to oscillate with a period largely
determined by L/{c}{{A}}, where L is the size of the
plasmoid and c A is the Alfvén speed in the lateral parts
of the plasmoid. In our model, L/{c}{{A}} evaluates to ∼
25 {{s}}. Furthermore, the plasmoid moving downward merges with the
underlying flare arcade, which causes oscillations of the arcade. In
our model, the period of this arcade oscillation is ∼ 35 {{s}},
which also corresponds to L/{c}{{A}}, but here L means the
length of the loop and c A is the average Alfvén speed in
the loop. We also show that the merging process of the plasmoid with
the flare arcade is a complex process as presented by complex density
and temperature structures of the oscillating arcade. Moreover, all
these processes are associated with magnetoacoustic waves produced by
the motion and merging of plasmoids.

---------------------------------------------------------
Title: Hot-cold plasma transition region: collisionless case
Authors: Karlicky, Marian; Karlicky, Frantisek
2017arXiv170907622K Altcode:
We study processes at the transition region between hot (rare)
and cold (dense) plasma in the collisionless regime. We use a
3-dimensional electromagnetic particle-in-cell (3-D PIC) relativistic
code. Motivated by the transition region in the solar atmosphere the
temperature and density ratio of the plasmas is chosen as 100 and
0.01, respectively. For better understanding of studied processes
we make two types of computations: a) without any interactions among
plasma particles (free expansion) and b) with the full electromagnetic
interactions. In both the cases we found that the flux of cold plasma
electrons and protons from colder plasma to hotter one dominates
over the flux of hot plasma electrons and protons in the opposite
direction. Thus, the plasma in the hotter part of the system becomes
colder and denser during time evolution. In the case without any
interactions among particles the cold plasma electrons and protons
freely penetrate into the hot plasma. But, the cold plasma electrons
are faster than cold plasma protons and therefore they penetrate
deeper into the hotter part of the system than the protons. Thus,
the cooling of the electron and proton components of the plasma in the
hotter part of the system is different. On the other hand, in the case
with the electromagnetic interactions, owing to the plasma property,
which tries to keep the total electric current constant everywhere
(close to zero in our case), the cold plasma electrons penetrate into
the hotter part of the system together with the cold plasma protons. The
plasma waves generated at the transition region during these processes
reduce the number of electrons escaping from the hot plasma into the
colder one. Therefore these waves support a temperature jump between
hot and cold plasma.

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

---------------------------------------------------------
Title: Oscillations in the 45 - 5000 MHz Radio Spectrum of the 18
April 2014 Flare
Authors: Karlický, Marian; Rybák, Ján; Monstein, Christian
2017SoPh..292...94K Altcode: 2017arXiv170602836K
Using a new type of oscillation map, made from the radio spectra
by the wavelet technique, we study the 18 April 2014 M7.3 flare
(SOL2014-04-18T13:03:00L245C017). We find a quasi-periodic character
of this flare with periods in the range 65 - 115 seconds. At the
very beginning of this flare, in connection with the drifting
pulsation structure (plasmoid ejection), we find that the 65 - 115
s oscillation phase slowly drifts towards lower frequencies, which
indicates an upward propagating wave initiated at the start of the
magnetic reconnection. Many periods (1 - 200 seconds) are found in
the drifting pulsation structure, which documents multi-scale and
multi-periodic processes. On this drifting structure, fiber bursts
with a characteristic period of about one second are superimposed,
whose frequency drift is similar to that of the drifting 65 - 115 s
oscillation phase. We also checked periods found in this flare by the
EUV Imaging Spectrometer (EIS)/Hinode and Interface Region Imaging
Spectrograph (IRIS) observations. We recognize the type III bursts
(electron beams) as proposed, but their time coincidence with the
EIS and IRIS peaks is not very good. The reason probably is that the
radio spectrum is a whole-disk record consisting of all bursts from any
location, while the EIS and IRIS peaks are emitted only from locations
of slits in the EIS and IRIS observations.

---------------------------------------------------------
Title: Shock-reflected electrons and X-ray line spectra
Authors: Dzifčáková, E.; Vandas, M.; Karlický, M.
2017A&A...603A..17D Altcode: 2017arXiv170511007D
 Aims: The aim of this paper is to try to explain the physical
origin of the non-thermal electron distribution that is able to form
the enhanced intensities of satellite lines in the X-ray line spectra
observed during the impulsive phases of some solar flares. 
Methods: Synthetic X-ray line spectra of the distributions composed
of the distribution of shock reflected electrons and the background
Maxwellian distribution are calculated in the approximation of
non-Maxwellian ionization, recombination, excitation and de-excitation
rates. The distribution of shock reflected electrons is determined
analytically. Results: We found that the distribution of
electrons reflected at the nearly-perpendicular shock resembles,
at its high-energy part, the so called n-distribution. Therefore
it could be able to explain the enhanced intensities of Si xiid
satellite lines. However, in the region immediately in front of the
shock its effect is small because electrons in background Maxwellian
plasma are much more numerous there. Therefore, we propose a model in
which the shock reflected electrons propagate to regions with smaller
densities and different temperatures. Combining the distribution of
the shock-reflected electrons with the Maxwellian distribution having
different densities and temperatures we found that spectra with enhanced
intensities of the satellite lines are formed at low densities and
temperatures of the background plasma when the combined distribution
is very similar to the n-distribution also in its low-energy part. In
these cases, the distribution of the shock-reflected electrons controls
the intensity ratio of the allowed Si xiii and Si xiv lines to the Si
xiid satellite lines. The high electron densities of the background
plasma reduce the effect of shock-reflected electrons on the composed
electron distribution function, which leads to the Maxwellian spectra.

---------------------------------------------------------
Title: Chains of type-I radio bursts and drifting pulsation structures
Authors: Karlický, M.
2017A&A...602A.122K Altcode:
 Aims: Owing to similarities of chains of type-I radio bursts
and drifting pulsation structures the question arises as to whether
both these radio bursts are generated by similar processes. 
Methods: Characteristics and parameters of both these radio bursts
are compared. Results: We present examples of both types
of bursts and show their similarities and differences. Then, for
chains of type-I bursts, a similar model as for drifting pulsation
structures (DPSs) is proposed. We show that, similar to the DPS model,
the chains of type-I bursts can be generated by the fragmented magnetic
reconnection associated with plasmoid interactions. To support this new
model of chains of type-I bursts, we present an effect of merging two
plasmoids to form one larger plasmoid on the radio spectrum of DPS. This
process can also explain the `wavy' appearance of some chains of type-I
bursts. Further, we show that the chains of type-I bursts with the wavy
appearance can be used for estimation of the magnetic field strength
in their sources. We think that differences of chains of type-I bursts
and DPSs are mainly owing to different regimes of the magnetic field
reconnection. While in the case of chains of type-I bursts, the magnetic
reconnection and plasmoid interactions are in the quasi-separatrix
layer of the active region in more or less quasi-saturated regime, in
the case of DPSs, observed in the impulsive phase of eruptive flares,
the magnetic reconnection and plasmoid interactions are in the current
sheet formed under the flare magnetic rope, which moves upwards and
forces this magnetic reconnection.

---------------------------------------------------------
Title: Are chains of type I radio bursts generated by similar
processes as drifting pulsation structures observed during solar
flares?
Authors: Karlicky, Marian
2017arXiv170408532K Altcode:
We present examples of the both types of bursts and show their
similarities and differences. Then for chains of type I bursts a similar
model as for drifting pulsation structures (DPSs) is proposed. We
show that similarly as in the DPS, the chains of type I bursts can
be generated by the fragmented magnetic reconnection associated with
plasmoids interactions. To support this new model of chains of type I
bursts, we present an effect of merging of two plasmoids to one larger
plasmoid on the radio spectrum of DPS. This process can also explain the
"wavy" appearance of some chains of type I bursts. Then we show that
the chains of type I bursts with the "wavy" appearance can be used
for estimation of the magnetic field strength in their sources. We
think that differences of chains of type I bursts and DPSs are mainly
owing to different regimes of the magnetic field reconnection. While
in the case of chains of type I bursts the magnetic reconnection and
plasmoid interactions are in the quasi-separatrix layer of the active
region in more or less quasi-saturated regime, in the case of DPSs,
observed in the impulsive phase of eruptive flares, the magnetic
reconnection and plasmoids interactions are in the current sheet
formed under the flare magnetic rope, which moves upwards and forces
this magnetic reconnection.

---------------------------------------------------------
Title: Investigating the Origins of Two Extreme Solar Particle Events:
Proton Source Profile and Associated Electromagnetic Emissions
Authors: Kocharov, Leon; Pohjolainen, Silja; Mishev, Alexander; Reiner,
Mike J.; Lee, Jeongwoo; Laitinen, Timo; Didkovsky, Leonid V.; Pizzo,
Victor J.; Kim, Roksoon; Klassen, Andreas; Karlicky, Marian; Cho,
Kyung-Suk; Gary, Dale E.; Usoskin, Ilya; Valtonen, Eino; Vainio, Rami
2017ApJ...839...79K Altcode:
We analyze the high-energy particle emission from the Sun in two
extreme solar particle events in which protons are accelerated to
relativistic energies and can cause a significant signal even in the
ground-based particle detectors. Analysis of a relativistic proton event
is based on modeling of the particle transport and interaction, from a
near-Sun source through the solar wind and the Earth’s magnetosphere
and atmosphere to a detector on the ground. This allows us to deduce
the time profile of the proton source at the Sun and compare it with
observed electromagnetic emissions. The 1998 May 2 event is associated
with a flare and a coronal mass ejection (CME), which were well
observed by the Nançay Radioheliograph, thus the images of the radio
sources are available. For the 2003 November 2 event, the low corona
images of the CME liftoff obtained at the Mauna Loa Solar Observatory
are available. Those complementary data sets are analyzed jointly
with the broadband dynamic radio spectra, EUV images, and other data
available for both events. We find a common scenario for both eruptions,
including the flare’s dual impulsive phase, the CME-launch-associated
decimetric-continuum burst, and the late, low-frequency type III
radio bursts at the time of the relativistic proton injection into
the interplanetary medium. The analysis supports the idea that the
two considered events start with emission of relativistic protons
previously accelerated during the flare and CME launch, then trapped
in large-scale magnetic loops and later released by the expanding CME.

---------------------------------------------------------
Title: Electric Current Filamentation Induced by 3D Plasma Flows in
the Solar Corona
Authors: Nickeler, Dieter H.; Wiegelmann, Thomas; Karlický, Marian;
Kraus, Michaela
2017ApJ...837..104N Altcode: 2017arXiv170203986N
Many magnetic structures in the solar atmosphere evolve rather slowly,
so they can be assumed as (quasi-)static or (quasi-)stationary
and represented via magnetohydrostatic (MHS) or stationary
magnetohydrodynamic (MHD) equilibria, respectively. While exact 3D
solutions would be desired, they are extremely difficult to find in
stationary MHD. We construct solutions with magnetic and flow vector
fields that have three components depending on all three coordinates. We
show that the noncanonical transformation method produces quasi-3D
solutions of stationary MHD by mapping 2D or 2.5D MHS equilibria to
corresponding stationary MHD states, that is, states that display
the same field-line structure as the original MHS equilibria. These
stationary MHD states exist on magnetic flux surfaces of the original 2D
MHS states. Although the flux surfaces and therefore also the equilibria
have a 2D character, these stationary MHD states depend on all three
coordinates and display highly complex currents. The existence of
geometrically complex 3D currents within symmetric field-line structures
provides the basis for efficient dissipation of the magnetic energy
in the solar corona by ohmic heating. We also discuss the possibility
of maintaining an important subset of nonlinear MHS states, namely
force-free fields, by stationary flows. We find that force-free
fields with nonlinear flows only arise under severe restrictions of
the field-line geometry and of the magnetic flux density distribution.

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Title: Temperature dependent growth rates of the upper-hybrid waves
and solar radio zebra patterns
Authors: Benáček, J.; Karlický, M.; Yasnov, L. V.
2017A&A...598A.106B Altcode: 2017arXiv170106520B
Context. The zebra patterns observed in solar radio emission are very
important for flare plasma diagnostics. The most promising model
of these patterns is based on double plasma resonance instability,
which generates upper-hybrid waves, which can be then transformed
into the zebra emission. Aims: We aim to study in detail the
double plasma resonance instability of hot electrons, together with
a much denser thermal background plasma. In particular, we analyse
how the growth rate of the instability depends on the temperature of
both the hot plasma and background plasma components. Methods:
We numerically integrated the analysed model equations, using Python
and Wolfram Mathematica. Results: We found that the growth-rate
maxima of the upper-hybrid waves for non-zero temperatures of both
the hot and background plasma are shifted towards lower frequencies
comparing to the zero temperature case. This shift increases with an
increase of the harmonic number s of the electron cyclotron frequency
and temperatures of both hot and background plasma components. We
show how this shift changes values of the magnetic field strength
estimated from observed zebras. We confirmed that for a relatively
low hot electron temperature, the dependence of growth rate vs. both
the ratio of the electron plasma and electron cyclotron frequencies
expresse distinct peaks, and by increasing this temperature these peaks
become smoothed. We found that in some cases, the values of wave number
vector components for the upper-hybrid wave for the maximal growth
rate strongly deviate from their analytical estimations. We confirmed
the validity of the assumptions used when deriving model equations.

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Title: Oscillation Maps in the Broadband Radio Spectrum of the 1
August 2010 Event
Authors: Karlický, M.; Rybák, J.
2017SoPh..292....1K Altcode: 2016arXiv161102074K
We search for indications of waves in the 25 - 2000 MHz radio spectrum
of the 1 August 2010 event (SOL2010-08-01T08:57:00L075C013), where fast
propagating waves in the solar corona with periods of 181, 69, and 40
seconds were detected in UV observations. Using the wavelet technique,
we construct a new type of oscillation map for selected periods in the
whole domain of the radio spectrum. While an oscillation with a period
of 181 seconds was recognized in the whole 25 - 2000 MHz radio spectrum,
oscillations with periods of 69 and 40 seconds were only confirmed
in the 250 - 870 MHz frequency range. In the 800 - 2000 MHz range we
found periods of 50 and 80 seconds. Moreover, in the 250 - 870 MHz
frequency range, an oscillation with a period of about 420 seconds was
detected. We also made maps of phases of the 181-second oscillations in
order to analyze their frequency drift. At the beginning of the radio
event, the phase of the 181-second oscillation in the 2000 - 500 MHz
frequency range drifts toward lower frequencies. On the other hand,
we found that the phase is nearly synchronous at frequencies 25 - 500
MHz. While the phase drift at higher frequencies can be interpreted
as being caused by the UV wave, the synchronization of the phase
on lower frequencies is explained by the fast electron beams, whose
acceleration is modulated by the UV wave. Owing to this modulation,
the electron beams are accelerated with the period of the UV wave
(181 seconds). These beams propagate upward through the solar corona
and generate the 25 - 500 MHz radio emission with the 181-second
period. The 25 - 500 MHz radio emission, which corresponds to a large
interval of heights in the solar corona, is nearly synchronous because
of the high beam velocity (≈c /3 , where c is the light speed).

---------------------------------------------------------
Title: Origin of two extreme solar particle events
Authors: Mishev, A.; Kocharov, L.; Pohjolainen, S.; Reiner, M. J.;
Lee, J.; Laitinen, T.; Didkovsky, L. V.; Pizzo, V. J.; Kim, R.;
Klassen, A.; Karlicky, M.; Choj, K. S.; Kovaltsov, G. A.; Usoskin,
I. G.; Valtonen, E.; Vainio, R.
2017ICRC...35..146M Altcode: 2017PoS...301..146M
No abstract at ADS

---------------------------------------------------------
Title: Torsional oscillations and observed rotational period
variations in early-type stars
Authors: Krtička, J.; Mikulášek, Z.; Henry, G. W.; Kurfürst, P.;
Karlický, M.
2017MNRAS.464..933K Altcode: 2016arXiv160907914K
Some chemically peculiar stars in the upper main sequence show
rotational period variations of unknown origin. We propose that these
variations are a consequence of the propagation of internal waves in
magnetic rotating stars that lead to the torsional oscillations of the
star. We simulate the magnetohydrodynamic waves and calculate resonant
frequencies for two stars that show rotational variations: CU Vir and
HD 37776. We provide updated analyses of rotational period variations
in these stars and compare our results with numerical models. For CU
Vir, the length of the observed rotational period cycle, Π=67.6(5)
yr, can be well reproduced by the models, which predict a cycle length
of 51 yr. However, for HD 37776, the observed lower limit of the cycle
length, Π ≥ 100 yr, is significantly longer than the numerical models
predict. We conclude that torsional oscillations provide a reasonable
explanation at least for the observed period variations in CU Vir.

---------------------------------------------------------
Title: Differential rotation, flares and coronae in A to M stars
Authors: Balona, L. A.; Švanda, M.; Karlický, M.
2016MNRAS.463.1740B Altcode: 2016MNRAS.tmp.1226B
Kepler data are used to investigate flares in stars of all spectral
types. There is a strong tendency across all spectral types for
the most energetic flares to occur among the most rapidly rotating
stars. Differential rotation could conceivably play an important
role in enhancing flare energies. This idea was investigated,
but no correlation could be found between rotational shear and the
incidence of flares. Inspection of Kepler light curves shows that
rotational modulation is very common over the whole spectral type
range. Using the rotational light amplitude, the size distribution
of star-spots was investigated. Our analysis suggests that stars with
detectable flares have spots significantly larger than non-flare stars,
indicating that flare energies are correlated with the size of the
active region. Further evidence of the existence of spots on A stars
is shown by the correlation between the photometric period and the
projected rotational velocity. The existence of spots indicates the
presence of magnetic fields, but the fact that A stars lack coronae
implies that surface convection is a necessary condition for the
formation of the corona.

---------------------------------------------------------
Title: Flares on A-type Stars: Evidence for Heating of Solar Corona
by Nanoflares?
Authors: Švanda, Michal; Karlický, Marian
2016ApJ...831....9S Altcode: 2016arXiv160803494S
We analyzed the occurrence rates of flares on stars of spectral types
K, G, F, and A, observed by Kepler. We found that the histogram of
occurrence frequencies of stellar flares is systematically shifted
toward a high-energy tail for A-type stars compared to stars of cooler
spectral types. We extrapolated the fitted power laws toward flares
with smaller energies (nanoflares) and made estimates for total energy
flux to stellar atmospheres by flares. We found that, for A-type stars,
the total energy flux density was at least four-times smaller than for
G stars. We speculate that this deficit in energy supply may explain
the lack of hot coronae on A-type stars. Our results indicate the
importance of nanoflares for heating and formation of the solar corona.

---------------------------------------------------------
Title: Diagnosing the Source Region of a Solar Burst on 26 September
2011 by Using Microwave Type-III Pairs
Authors: Tan, B. L.; Karlický, M.; Mészárosová, H.; Kashapova,
L.; Huang, J.; Yan, Y.; Kontar, E. P.
2016SoPh..291.2407T Altcode: 2016SoPh..tmp..143T; 2016arXiv160605410T
We report a peculiar and interesting train of microwave Type-III pair
bursts in the impulsive rising phase of a solar flare on 26 September
2011. The observations include radio spectrometers at frequencies
of 0.80 - 2.00 GHz from the Ondřejov radiospectrograph in the
Czech Republic (ORSC), hard X-ray from the Ramaty High-Energy Solar
Spectroscopic Imager (RHESSI) and Gamma-Ray Burst Monitor onboard
the Fermi Space Telescope (Fermi/GRB), EUV images from the Sun
Watcher using APS detectors and image Processing instrument onboard
the Project for Onboard Autonomy 2 (SWAP/PROBA2), and magnetograms
from the Helioseismic and Magnetic Imager onboard the Solar Dynamic
Observatory (SDO/HMI). By using a recently developed method (Tan et al.,
Res. Astron. Astrophys.16, 82, 2016a), we diagnosed the plasma density,
temperature, plasma-β , magnetic field near the source region, the
energy of energetic electrons, and the distance between the acceleration
region and the emission start sites of Type-III bursts. From the
diagnostics, we find that i) The plasma density, temperature, magnetic
field, and the distance between the acceleration region and the emission
start sites have almost no obvious variations during the period of
Type-III pair trains, while the energy of electrons has an obvious
peak value that is consistent with the hard X-ray emission. ii) The
plasma-β is much higher than unity, showing a highly dynamic process
near the emission start site of Type-III bursts. iii) Although the
reversed-slope Type-III branches drift more slowly by one order of
magnitude than that of the normal Type-IIIs, the related descending
and ascending electrons still could have energy of the same order of
magnitude. These facts indicate that both the ascending and descending
electrons are possibly accelerated by a similar mechanism and in a
small source region. These diagnostics can help us to understand the
physics in the source region of solar bursts.

---------------------------------------------------------
Title: Shock-drift accelerated electrons and n-distribution
Authors: Vandas, Marek; Karlicky, Marian
2016usc..confE.124V Altcode:
Recently soft X-ray spectra observed during the impulsive phase of
several solar flares have been explained by the presence of the
n-distribution function of superthermal electrons. We examine if
electrons with such a distribution function can be produced in a
shock, e.g. in a flare termination shock. The distribution functions
of reflected electrons at quasi-perpendicular shocks are analytically
derived and compared with the n-distributions. We consider an influence
of the electrostatic cross-shock potential, shock curvature, and a
role of the upstream seed population on these distributions. We found
that a high-energy part of the distribution of electrons reflected
at a quasi-perpendicular shock could be very well fitted by the
n-distribution. It gives a chance to detect the flare termination shock.

---------------------------------------------------------
Title: Physical Conditions in the Source Region of a Zebra Structure
Authors: Yasnov, L. V.; Karlický, M.; Stupishin, A. G.
2016SoPh..291.2037Y Altcode: 2016SoPh..tmp..118Y
We analyze the physical conditions in the source region of a zebra
structure, observed with the Ondřejov radiospectrograph during the
1 August 2010 solar flare. To determine the gyro-frequency harmonic
numbers of the observed zebra lines, we compute the magnetic field
strength, the electron density, and their spatial scales in the source
region of the zebra structure. The region where the flare occurred is
analyzed using EUV (171 Å and 335 Å) observations. To determine the
conditions in the zebra source region, the magnetic field structure
is reconstructed using observed photospheric magnetic field data. By
computing the dependence of the magnetic field vs. height in this
reconstruction and by comparing the magnetic field strength derived
from the zebra structure, we determine the dependence of the electron
density vs. height in the zebra source-region. We identify the loops
where the zebra structure was generated at heights of about 2.5 -
3.3 Mm. Assuming the barometric law for the electron density, we
determine the temperature in the zebra source-region to be T ≈2.0
×104K. Comparing the obtained values of the temperature
and electron density in the zebra source-region with a model of the
solar atmosphere, we find that the zebra structure was generated in
the transition region, in agreement with our previous results.

---------------------------------------------------------
Title: Shock-drift accelerated electrons and n-distribution
Authors: Vandas, Marek; Karlicky, Marian
2016cosp...41E1982V Altcode:
Recently soft X-ray spectra observed during the impulsive phase of
several solar flares have been explained by the presence of the
n-distribution function of superthermal electrons. We examine if
electrons with such a distribution function can be produced in a
shock, e.g. in a flare termination shock. The distribution functions
of reflected electrons at quasi-perpendicular shocks are analytically
derived and compared with the n-distributions. We consider an influence
of the electrostatic cross-shock potential, shock curvature, and a
role of the upstream seed population on these distributions. We found
that a high-energy part of the distribution of electrons reflected
at a quasi-perpendicular shock could be very well fitted by the
n-distribution. It gives a chance to detect the flare termination shock.

---------------------------------------------------------
Title: Shock-drift accelerated electrons and n-distribution
Authors: Vandas, M.; Karlický, M.
2016A&A...591A.127V Altcode:
 Aims: By analyzing soft X-ray spectra observed during
the impulsive phase of several solar flares, the n-distribution
function of superthermal electrons has been detected. In the paper
we try to answer the question of whether electrons with this type of
distribution function can be produced in a shock, e.g. in a flare
termination shock. Methods: We use analytical and numerical
methods to compute distribution functions of electrons accelerated
by a shock. Results: We analytically derive the distribution
functions of reflected electrons at quasi-perpendicular shocks. We also
consider the influence of the electrostatic cross-shock potential,
shock curvature, and the role of the upstream seed population on
these distributions. The computed distributions are compared with the
n-distributions. We found that a high-energy part of the distribution
of electrons reflected at a quasi-perpendicular shock can be very
well fitted by the n-distribution in all the cases we studied. This
provides a chance to detect the flare termination shock.

---------------------------------------------------------
Title: Diagnosing physical conditions near the flare energy-release
sites from observations of solar microwave type III bursts
Authors: Tan, Bao-Lin; Karlický, Marian; Mészárosová, Hana;
Huang, Guang-Li
2016RAA....16...82T Altcode: 2016RAA....16e..13T; 2015arXiv151108863T
In the physics of solar flares, it is crucial to diagnose the physical
conditions near the flare energy-release sites. However, so far it is
unclear how to diagnose these physical conditions. A solar microwave
type III burst is believed to be a sensitive signature of primary energy
release and electron accelerations in solar flares. This work takes
into account the effect of the magnetic field on the plasma density and
develops a set of formulas which can be used to estimate the plasma
density, temperature, magnetic field near the magnetic reconnection
site and particle acceleration region, and the velocity and energy of
electron beams. We apply these formulas to three groups of microwave
type III pairs in an X-class flare, and obtained some reasonable and
interesting results. This method can be applied to other microwave
type III bursts to diagnose the physical conditions of source regions,
and provide some basic information to understand the intrinsic nature
and fundamental processes occurring near the flare energy-release sites.

---------------------------------------------------------
Title: Slipping Magnetic Reconnection, Chromospheric Evaporation,
Implosion, and Precursors in the 2014 September 10 X1.6-Class
Solar Flare
Authors: Dudík, Jaroslav; Polito, Vanessa; Janvier, Miho; Mulay,
Sargam M.; Karlický, Marian; Aulanier, Guillaume; Del Zanna, Giulio;
Dzifčáková, Elena; Mason, Helen E.; Schmieder, Brigitte
2016ApJ...823...41D Altcode: 2016arXiv160306092D
We investigate the occurrence of slipping magnetic reconnection,
chromospheric evaporation, and coronal loop dynamics in the 2014
September 10 X-class flare. Slipping reconnection is found to be present
throughout the flare from its early phase. Flare loops are seen to slip
in opposite directions toward both ends of the ribbons. Velocities
of 20-40 km s-1 are found within time windows where the
slipping is well resolved. The warm coronal loops exhibit expanding and
contracting motions that are interpreted as displacements due to the
growing flux rope that subsequently erupts. This flux rope existed and
erupted before the onset of apparent coronal implosion. This indicates
that the energy release proceeds by slipping reconnection and not via
coronal implosion. The slipping reconnection leads to changes in the
geometry of the observed structures at the Interface Region Imaging
Spectrograph slit position, from flare loop top to the footpoints in
the ribbons. This results in variations of the observed velocities of
chromospheric evaporation in the early flare phase. Finally, it is found
that the precursor signatures, including localized EUV brightenings as
well as nonthermal X-ray emission, are signatures of the flare itself,
progressing from the early phase toward the impulsive phase, with
the tether-cutting being provided by the slipping reconnection. The
dynamics of both the flare and outlying coronal loops is found to be
consistent with the predictions of the standard solar flare model in
three dimensions.

---------------------------------------------------------
Title: Quasi-periodic processes in the flare loop generated by sudden
temperature enhancements at loop footpoints
Authors: Karlický, M.; Jelínek, P.
2016A&A...590A...4K Altcode:
 Aims: During the impulsive flare phase, the plasma at the
flare loop footpoints is rapidly heated by particle beams. In the
present paper, we study processes that occur after this sudden heating
in a two-dimensional magnetic loop. Methods: We adopt a 2D
magnetohydrodynamic (MHD) model, in which we solve a full set of the
ideal time-dependent MHD equations by means of the FLASH code, using
the adaptive mesh refinement (AMR) method. Periods in the processes are
estimated by the wavelet analysis technique. Results: We consider
a model of the solar atmosphere with a symmetric magnetic loop. The
length of this loop in the corona is approximately 21.5 Mm. At both
loop footpoints, at the transition region, we initiate the Gaussian
temperature (pressure) perturbation with the maximum temperature 14,
7, or 3.5 times higher than the unperturbed temperature. In the corona,
the perturbations produce supersonic blast shocks with the Mach number
of about 1.1, but well below Alfvén velocities. We consider cases
with the same perturbations at both footpoints (symmetric case) and one
with different perturbations (asymmetric case). In the symmetric case,
the shocks move along both loop legs upwards to the top of the loop,
where they interact and form a transient compressed region. Then they
continue in their motion to the transition region at the opposite
side of the loop, where they are reflected upwards, and so on. At
the top of the loop, the shock appears periodically with the period
of about 170 s. In the loop legs during this period, a double peak of
the plasma parameters, which is connected with two arrivals of shocks,
is detected: firstly, when the shock moves up and then when the shock,
propagating from the opposite loop leg, moves down. Increasing the
distance of the detection point in the loop leg from the top of the
loop, the time interval between these shock arrivals increases. Thus,
at these detection points, the processes with shorter periods
can be detected. After ~500 s the process with the periodically
interacting shocks slowly changes to slow mode magnetosonic free
oscillation. Furthermore, we detected quasi-periodic processes, even in
the chromosphere under the location of the pressure perturbation. These
processes can be observed in intensities and Doppler shifts of optical
chromospheric lines. In the case with the asymmetric perturbations,
we found that the processes are even more complex.

---------------------------------------------------------
Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.

---------------------------------------------------------
Title: Magnetohydrodynamic Oscillations in the Solar Corona and
Earth's Magnetosphere: Towards Consolidated Understanding
Authors: Nakariakov, V. M.; Pilipenko, V.; Heilig, B.; Jelínek,
P.; Karlický, M.; Klimushkin, D. Y.; Kolotkov, D. Y.; Lee, D. -H.;
Nisticò, G.; Van Doorsselaere, T.; Verth, G.; Zimovets, I. V.
2016SSRv..200...75N Altcode: 2016SSRv..tmp....2N
Magnetohydrodynamic (MHD) oscillatory processes in different
plasma systems, such as the corona of the Sun and the Earth's
magnetosphere, show interesting similarities and differences, which
so far received little attention and remain under-exploited. The
successful commissioning within the past ten years of THEMIS, Hinode,
STEREO and SDO spacecraft, in combination with matured analysis of data
from earlier spacecraft (Wind, SOHO, ACE, Cluster, TRACE and RHESSI)
makes it very timely to survey the breadth of observations giving
evidence for MHD oscillatory processes in solar and space plasmas,
and state-of-the-art theoretical modelling. The paper reviews several
important topics, such as Alfvénic resonances and mode conversion;
MHD waveguides, such as the magnetotail, coronal loops, coronal
streamers; mechanisms for periodicities produced in energy releases
during substorms and solar flares, possibility of Alfvénic resonators
along open field lines; possible drivers of MHD waves; diagnostics of
plasmas with MHD waves; interaction of MHD waves with partly-ionised
boundaries (ionosphere and chromosphere). The review is mainly oriented
to specialists in magnetospheric physics and solar physics, but not
familiar with specifics of the adjacent research fields.

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

---------------------------------------------------------
Title: Microwave Type III Pair Bursts in Solar Flares
Authors: Tan, Baolin; Mészárosová, Hana; Karlický, Marian; Huang,
Guangli; Tan, Chengming
2016ApJ...819...42T Altcode: 2016arXiv160105312T
A solar microwave type III pair burst is composed of normal and
reverse-sloped (RS) burst branches with oppositely fast frequency
drifts. It is the most sensitive signature of the primary energy
release and electron accelerations in flares. This work reports
11 microwave type III pair events in 9 flares observed by radio
spectrometers in China and the Czech Republic at a frequency of
0.80-7.60 GHz during 1994-2014. These type III pairs occurred in
flare impulsive and postflare phases with separate frequencies in
the range of 1.08-3.42 GHz and a frequency gap of 10-1700 MHz. The
frequency drift increases with the separate frequency (fx),
the lifetime of each burst is anti-correlated to fx,
while the frequency gap is independent of fx. In most
events, the normal branches are drifting obviously faster than the RS
branches. The type III pairs occurring in flare impulsive phase have
lower separate frequencies, longer lifetimes, wider frequency gaps, and
slower frequency drifts than that occurring in postflare phase. Also,
the latter always has strong circular polarization. Further analysis
indicates that near the flare energy release sites the plasma density
is about {10}10{--}{10}11 cm-3 and
the temperature is higher than 107 K. These results provide
new constraints to the acceleration mechanism in solar flares.

---------------------------------------------------------
Title: Sources of Quasi-periodic Pulses in the Flare of 18 August 2012
Authors: Altyntsev, A.; Meshalkina, N.; Mészárosová, H.; Karlický,
M.; Palshin, V.; Lesovoi, S.
2016SoPh..291..445A Altcode: 2016SoPh..tmp...41A; 2016arXiv160102332A
We analyzed spatial and spectral characteristics of quasi-periodic
pulses (QPP) for the limb flare on 18 August 2012, using new data from
a complex of spectral and imaging instruments developed by the Siberian
Solar Radio Telescope team and the Wind/Konusγ -ray spectrometer. A
sequence of broadband pulses with periods of approximately ten seconds
were observed in X-rays at energies between 25 keV and 300 keV, and
in microwaves at frequencies from a few GHz up to 34 GHz during an
interval of one minute. The QPP X-ray source was located slightly above
the limb where the southern legs of large and small EUV loop systems
were close to each other. Before the QPPs occurred, the soft X-ray
emission and the Ramaty High Energy Solar Spectroscopic Imager signal
from the energy channels below 25 keV were gradually arising for several
minutes at the same location. It was found that each X-ray pulse showed
a soft-hard-soft behavior. The 17 and 34 GHz microwave sources were at
the footpoints of the small loop system, the source emitting in the 4.2
- 7.4 GHz band in the large system. The QPPs were probably generated
by modulated acceleration processes in the energy-release site. We
determined the plasma parameters in the radio sources by analyzing
the spectra. The microwave pulses might be explained by relatively
weak variations of the spectral hardness of the emitting electrons.

---------------------------------------------------------
Title: Flare evolution and polarization changes in fine structures
of solar radio emission in the 2013 April 11 event
Authors: Chernov, Gennady; Sych, Robert; Tan, Bao-Lin; Yan, Yi-Hua;
Tan, Cheng-Ming; Fu, Qi-Jun; Karlický, Marian; Fomichev, Valery
2016RAA....16...28C Altcode: 2016RAA....16b...8C; 2015arXiv150906487C
The measurement of positions and sizes of radio sources in observations
is important for understanding of the flare evolution. For the first
time, solar radio spectral fine structures in an M6.5 flare that
occurred on 2013 April 11 were observed simultaneously by several
radio instruments at four different observatories: Chinese Solar
Broadband Radio Spectrometer at Huairou (SBRS/Huairou), Ondřejov Radio
Spectrograph in the Czech Republic (ORSC/Ondřejov), Badary Broadband
Microwave Spectropolarimeter (BMS/Irkutsk), and spectrograph/IZMIRAN
(Moscow, Troitsk). The fine structures included microwave zebra patterns
(ZPs), fast pulsations and fiber bursts. They were observed during
the flare brightening located at the tops of a loop arcade as shown
in images taken by the extreme ultraviolet (EUV) telescope onboard
NASA's satellite Solar Dynamics Observatory (SDO). The flare occurred
at 06:58-07:26 UT in solar active region NOAA 11719 located close to
the solar disk center. ZPs appeared near high frequency boundaries of
the pulsations, and their spectra observed in Huairou and Ondřejov
agreed with each other in terms of details. At the beginning of the
flare's impulsive phase, a strong narrowband ZP burst occurred with a
moderate left-handed circular polarization. Then a series of pulsations
and ZPs were observed in almost unpolarized emission. After 07:00 UT
a ZP appeared with a moderate right-handed polarization. In the flare
decay phase (at about 07:25 UT), ZPs and fiber bursts become strongly
right-hand polarized. BMS/Irkutsk spectral observations indicated that
the background emission showed a left-handed circular polarization
(similar to SBRS/Huairou spectra around 3 GHz). However, the fine
structure appeared in the right-handed polarization. The dynamics of
the polarization was associated with the motion of the flare exciter,
which was observed in EUV images at 171 Å and 131 Å by the SDO
Atmospheric Imaging Assembly (AIA). Combining magnetograms observed
by the SDO Helioseismic and Magnetic Imager (HMI) with the homologous
assumption of EUV flare brightenings and ZP bursts, we deduced that the
observed ZPs correspond to the ordinary radio emission mode. However,
future analysis needs to verify the assumption that zebra radio sources
are really related to a closed magnetic loop, and are located at lower
heights in the solar atmosphere than the source of pulsations.

---------------------------------------------------------
Title: Comparison of 30 THz impulsive burst time development to
microwaves, Hα, EUV, and GOES soft X-rays
Authors: Miteva, R.; Kaufmann, P.; Cabezas, D. P.; Cassiano, M. M.;
Fernandes, L. O. T.; Freeland, S. L.; Karlický, M.; Kerdraon, A.;
Kudaka, A. S.; Luoni, M. L.; Marcon, R.; Raulin, J. -P.; Trottet,
G.; White, S. M.
2016A&A...586A..91M Altcode: 2015arXiv151201763M
The recent discovery of impulsive solar burst emission in the 30 THz
band is raising new interpretation challenges. One event associated with
a GOES M2 class flare has been observed simultaneously in microwaves,
Hα, EUV, and soft X-ray bands. Although these new observations confirm
some features found in the two prior known events, they exhibit time
profile structure discrepancies between 30 THz, microwaves, and hard
X-rays (as inferred from the Neupert effect). These results suggest a
more complex relationship between 30 THz emission and radiation produced
at other wavelength ranges. The multiple frequency emissions in the
impulsive phase are likely to be produced at a common flaring site lower
in the chromosphere. The 30 THz burst emission may be either part of a
nonthermal radiation mechanism or due to the rapid thermal response to
a beam of high-energy particles bombarding the dense solar atmosphere.

---------------------------------------------------------
Title: Frequency Oscillations of Drifting Pulsating Structures
Authors: Karlický, M.; Jiřička, K.; Bárta, M.
2016CEAB...40...93K Altcode:
Analyzing the solar radio spectra in the 0.8-4.5 GHz frequency range
observed at the Ondřejov Observatory during 2000-2015 we found 118
drifting pulsating structures (DPSs). Among them we found 8 DPSs with
distinct quasi-periodic oscillations in frequency. Periods of these
oscillations are in the range of 4-75 s. Based on the model of DPS and
numerical simulations we interpret these oscillations as a result of
merging of two plasmoids into one larger plasmoid that after merging
start to oscillate. The period of the plasmoid oscillation, P, can
be estimated as P ≈ L/v_A, where L is the characteristic size of
the plasmoid and v_A is the mean Alfvén speed in the plasmoid. This
enables us to roughly estimate the mean magnetic field strength in
the oscillating plasmoid (2.9-38.3 G).

---------------------------------------------------------
Title: Numerical RHD simulations of flaring chromosphere with Flarix
Authors: Heinzel, Petr; Kašparová, Jana; Varady, Michal; Karlický,
Marian; Moravec, Zdeněk
2016IAUS..320..233H Altcode: 2016arXiv160200016H
Flarix is a radiation-hydrodynamical (RHD) code for modeling of the
response of the chromosphere to a beam bombardment during solar
flares. It solves the set of hydrodynamic conservation equations
coupled with NLTE equations of radiative transfer. The simulations are
driven by high energy electron beams. We present results of the Flarix
simulations of a flaring loop relevant to the problem of continuum
radiation during flares. In particular we focus on properties of the
hydrogen Balmer continuum which was recently detected by IRIS.

---------------------------------------------------------
Title: SSALMON - The Solar Simulations for the Atacama Large
Millimeter Observatory Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson,
H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu,
B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.;
Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.;
Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier,
A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M.
2015AdSpR..56.2679W Altcode: 2015arXiv150205601W
The Solar Simulations for the Atacama Large Millimeter Observatory
Network (SSALMON) was initiated in 2014 in connection with two ALMA
development studies. The Atacama Large Millimeter/submillimeter Array
(ALMA) is a powerful new tool, which can also observe the Sun at
high spatial, temporal, and spectral resolution. The international
SSALMONetwork aims at co-ordinating the further development of solar
observing modes for ALMA and at promoting scientific opportunities
for solar physics with particular focus on numerical simulations,
which can provide important constraints for the observing modes and
can aid the interpretation of future observations. The radiation
detected by ALMA originates mostly in the solar chromosphere - a
complex and dynamic layer between the photosphere and corona, which
plays an important role in the transport of energy and matter and the
heating of the outer layers of the solar atmosphere. Potential targets
include active regions, prominences, quiet Sun regions, flares. Here,
we give a brief overview over the network and potential science cases
for future solar observations with ALMA.

---------------------------------------------------------
Title: Thermal Fronts in Solar Flares
Authors: Karlický, Marian
2015ApJ...814..153K Altcode:
We studied the formation of a thermal front during the expansion of hot
plasma into colder plasma. We used a three-dimensional electromagnetic
particle-in-cell model that includes inductive effects. In early phases,
in the area of the expanding hot plasma, we found several thermal
fronts, which are defined as a sudden decrease of the local electron
kinetic energy. The fronts formed a cascade. Thermal fronts with higher
temperature contrast were located near plasma density depressions,
generated during the hot plasma expansion. The formation of the main
thermal front was associated with the return-current process induced
by hot electron expansion and electrons backscattered at the front. A
part of the hot plasma was trapped by the thermal front while another
part, mainly with the most energetic electrons, escaped and generated
Langmuir and electromagnetic waves in front of the thermal front, as
shown by the dispersion diagrams. Considering all of these processes
and those described in the literature, we show that anomalous electric
resistivity is produced at the location of the thermal front. Thus,
the thermal front can contribute to energy dissipation in the
current-carrying loops of solar flares. We estimated the values of such
anomalous resistivity in the solar atmosphere together with collisional
resistivity and electric fields. We propose that the slowly drifting
reverse drift bursts, observed at the beginning of some solar flares,
could be signatures of the thermal front.

---------------------------------------------------------
Title: Electric Current Filamentation at a Non-potential Magnetic
Null-point Due to Pressure Perturbation
Authors: Jelínek, P.; Karlický, M.; Murawski, K.
2015ApJ...812..105J Altcode:
An increase of electric current densities due to filamentation is an
important process in any flare. We show that the pressure perturbation,
followed by an entropy wave, triggers such a filamentation in the
non-potential magnetic null-point. In the two-dimensional (2D),
non-potential magnetic null-point, we generate the entropy wave by a
negative or positive pressure pulse that is launched initially. Then,
we study its evolution under the influence of the gravity field. We
solve the full set of 2D time dependent, ideal magnetohydrodynamic
equations numerically, making use of the FLASH code. The negative
pulse leads to an entropy wave with a plasma density greater than
in the ambient atmosphere and thus this wave falls down in the
solar atmosphere, attracted by the gravity force. In the case of
the positive pressure pulse, the plasma becomes evacuated and the
entropy wave propagates upward. However, in both cases, owing to the
Rayleigh-Taylor instability, the electric current in a non-potential
magnetic null-point is rapidly filamented and at some locations the
electric current density is strongly enhanced in comparison to its
initial value. Using numerical simulations, we find that entropy waves
initiated either by positive or negative pulses result in an increase of
electric current densities close to the magnetic null-point and thus the
energy accumulated here can be released as nanoflares or even flares.

---------------------------------------------------------
Title: Determination of plasma parameters in solar zebra radio sources
Authors: Karlický, M.; Yasnov, L. V.
2015A&A...581A.115K Altcode:
 Aims: We present a new method for determining the magnetic field
strength and plasma density in the solar zebra radio sources. 
Methods: Using the double plasma resonance (DPR) model of the zebra
emission, we analytically derived the equations for computing the
gyroharmonic number s of selected zebra lines and then solved these
equations numerically. Results: The method was successfully
tested on artificially generated zebras and then applied to observed
ones. The magnetic field strength and plasma density in the radio
sources were determined. Simultaneously, we evaluated the parameter
Lnb = 2Lb/ (2Ln - Lb), where
Ln and Lb are the characteristic scale-heights
of the plasma density and magnetic field strength in the zebra source,
respectively. Computations show that the maximum frequency of the
low-polarized zebras is about 8 GHz, in very good agreement with
observations. For the high-polarized zebras, this limit is about
four times lower. Microwave zebras are preferentially generated
in the regions with steep gradients of the plasma density, such as
in the transition region. In models with smaller density gradients,
such as those with a barometric density profile, the microwave zebras
cannot be produced owing to the strong bremsstrahlung and cyclotron
absorptions. We also show that our DPR model is able to explain the
zebras with frequency-equidistant zebra lines.

---------------------------------------------------------
Title: Numerical simulations of flaring loops with Flarix
Authors: none Heinzel, Petr; Karlicky, Marian; Varady, Michal;
Kasparova, Jana; Moravec, Zdenek
2015IAUGA..2258466N Altcode:
Flarix is the radiation-hydrodynamical code for simulation of the
flare evolution. It solves the set of hydrodynamicval equations
coupled to NLTE equations of radiative transfer. The simulation is
driven by the accelerated electron beams. We present new results of
Flarix simulations for various types of flare loops, incorporating new
features like effects of the return current and particle re-acceleration
in the chromosphere.

---------------------------------------------------------
Title: On the Visibility of Prominence Fine Structures at Radio
Millimeter Wavelengths
Authors: Heinzel, P.; Berlicki, A.; Bárta, M.; Karlický, M.;
Rudawy, P.
2015SoPh..290.1981H Altcode: 2015SoPh..tmp...87H
Prominence temperatures have so far mainly been determined by analyzing
spectral line shapes, which is difficult when the spectral lines are
optically thick. The radio spectra in the millimeter range offer
a unique possibility to measure the kinetic temperature. However,
studies in the past used data with insufficient spatial resolution
to resolve the prominence fine structures. The aim of this article
is to predict the visibility of prominence fine structures in the
submillimeter/millimeter (SMM) domain, to estimate their brightness
temperatures at various wavelengths, and to demonstrate the feasibility
and usefulness of future high-resolution radio observations of
solar prominences with ALMA (Atacama Large Millimeter-submillimeter
Array). Our novel approach is the conversion of Hα coronagraphic images
into microwave spectral images. We show that the spatial variations
of the prominence brightness both in the Hα line and in the SMM
domain predominantly depend on the line-of-sight emission measure of
the cool plasma, which we derive from the integrated intensities of
the observed Hα line. This relation also offers a new possibility to
determine the SMM optical thickness from simultaneous Hα observations
with high resolution. We also describe how we determine the prominence
kinetic temperature from SMM spectral images. Finally, we apply the
ALMA image-processing software Common Astronomy Software Applications
(CASA) to our simulated images to assess what ALMA would detect at a
resolution level that is similar to the coronagraphic Hα images used
in this study. Our results can thus help in preparations of first
ALMA prominence observations in the frame of science and technical
verification tests.

---------------------------------------------------------
Title: Regions of Generation and Optical Thicknesses of dm-Zebra Lines
Authors: Yasnov, L. V.; Karlický, M.
2015SoPh..290.2001Y Altcode: 2015SoPh..tmp...88Y
Using a new model based on the double plasma resonance (DPR),
we show that the zebra structure seen in solar radio bursts is
generated in the transition region and at the tops of the magnetic
arcade. The magnetic field in zebra sources is probably weaker
than 150 gauss. According to this model, a generation of zebras in
stronger magnetic fields is improbable. The high-frequency boundary of
decimetric zebras depends on the background electron plasma density,
but not on the magnetic field strength in the generation regions. The
bremsstrahlung absorption in atmospheric layers above the DPR zebra
generation region and the cyclotron absorption in the DPR region and
in the gyroresonance layers at higher altitudes limit the spectrum
of zebras from both high-frequency and low-frequency sides. While
the bremsstrahlung reduces the emission from the high-frequency side,
the cyclotron absorption limits the low-frequency side. The observed
frequency range and the number of observed zebra lines are determined
not only by these absorptions, but also by appropriate distribution
functions of superthermal electrons and plasma conditions in this
region. Low-frequency (metric) zebra emissions can be generated at
high altitudes. Computations show that such emissions can escape from
the DPR generation region only at high gyro-harmonics (s &gt;10 )
and with many zebra lines.

---------------------------------------------------------
Title: Imaging and Spectroscopic Observations of a Transient Coronal
Loop: Evidence for the Non-Maxwellian K Distributions
Authors: Dudík, Jaroslav; Mackovjak, Šimon; Dzifčáková, Elena;
Del Zanna, Giulio; Williams, David R.; Karlický, Marian; Mason,
Helen E.; Lörinčík, Juraj; Kotrč, Pavel; Fárník, František;
Zemanová, Alena
2015ApJ...807..123D Altcode: 2015arXiv150504333D
We report on the Solar Dynamics Observatory/Atmospheric Imaging Assembly
(AIA) and Hinode/EUV Imaging Spectrograph (EIS) observations of a
transient coronal loop. The loop brightens up in the same location after
the disappearance of an arcade formed during a B8.9-class microflare
3 hr earlier. EIS captures this loop during its brightening phase,
as observed in most of the AIA filters. We use the AIA data to study
the evolution of the loop, as well as to perform the differential
emission measure (DEM) diagnostics as a function of κ. The Fe xi-Fe
xiii lines observed by EIS are used to perform the diagnostics of
electron density and subsequently the diagnostics of κ. Using ratios
involving the Fe xi 257.772 Å self-blend, we diagnose κ ≲ 2,
i.e., an extremely non-Maxwellian distribution. Using the predicted
Fe line intensities derived from the DEMs as a function of κ, we
show that, with decreasing κ, all combinations of ratios of line
intensities converge to the observed values, confirming the diagnosed
κ ≲ 2. These results represent the first positive diagnostics of
κ-distributions in the solar corona despite the limitations imposed
by calibration uncertainties.

---------------------------------------------------------
Title: The 2014 ALMA Long Baseline Campaign: An Overview
Authors: ALMA Partnership; Fomalont, E. B.; Vlahakis, C.; Corder,
S.; Remijan, A.; Barkats, D.; Lucas, R.; Hunter, T. R.; Brogan,
C. L.; Asaki, Y.; Matsushita, S.; Dent, W. R. F.; Hills, R. E.;
Phillips, N.; Richards, A. M. S.; Cox, P.; Amestica, R.; Broguiere,
D.; Cotton, W.; Hales, A. S.; Hiriart, R.; Hirota, A.; Hodge, J. A.;
Impellizzeri, C. M. V.; Kern, J.; Kneissl, R.; Liuzzo, E.; Marcelino,
N.; Marson, R.; Mignano, A.; Nakanishi, K.; Nikolic, B.; Perez,
J. E.; Pérez, L. M.; Toledo, I.; Aladro, R.; Butler, B.; Cortes,
J.; Cortes, P.; Dhawan, V.; Di Francesco, J.; Espada, D.; Galarza,
F.; Garcia-Appadoo, D.; Guzman-Ramirez, L.; Humphreys, E. M.; Jung,
T.; Kameno, S.; Laing, R. A.; Leon, S.; Mangum, J.; Marconi, G.;
Nagai, H.; Nyman, L. -A.; Radiszcz, M.; Rodón, J. A.; Sawada, T.;
Takahashi, S.; Tilanus, R. P. J.; van Kempen, T.; Vila Vilaro, B.;
Watson, L. C.; Wiklind, T.; Gueth, F.; Tatematsu, K.; Wootten, A.;
Castro-Carrizo, A.; Chapillon, E.; Dumas, G.; de Gregorio-Monsalvo, I.;
Francke, H.; Gallardo, J.; Garcia, J.; Gonzalez, S.; Hibbard, J. E.;
Hill, T.; Kaminski, T.; Karim, A.; Krips, M.; Kurono, Y.; Lopez, C.;
Martin, S.; Maud, L.; Morales, F.; Pietu, V.; Plarre, K.; Schieven,
G.; Testi, L.; Videla, L.; Villard, E.; Whyborn, N.; Zwaan, M. A.;
Alves, F.; Andreani, P.; Avison, A.; Barta, M.; Bedosti, F.; Bendo,
G. J.; Bertoldi, F.; Bethermin, M.; Biggs, A.; Boissier, J.; Brand,
J.; Burkutean, S.; Casasola, V.; Conway, J.; Cortese, L.; Dabrowski,
B.; Davis, T. A.; Diaz Trigo, M.; Fontani, F.; Franco-Hernandez, R.;
Fuller, G.; Galvan Madrid, R.; Giannetti, A.; Ginsburg, A.; Graves,
S. F.; Hatziminaoglou, E.; Hogerheijde, M.; Jachym, P.; Jimenez Serra,
I.; Karlicky, M.; Klaasen, P.; Kraus, M.; Kunneriath, D.; Lagos, C.;
Longmore, S.; Leurini, S.; Maercker, M.; Magnelli, B.; Marti Vidal,
I.; Massardi, M.; Maury, A.; Muehle, S.; Muller, S.; Muxlow, T.;
O'Gorman, E.; Paladino, R.; Petry, D.; Pineda, J. E.; Randall, S.;
Richer, J. S.; Rossetti, A.; Rushton, A.; Rygl, K.; Sanchez Monge,
A.; Schaaf, R.; Schilke, P.; Stanke, T.; Schmalzl, M.; Stoehr, F.;
Urban, S.; van Kampen, E.; Vlemmings, W.; Wang, K.; Wild, W.; Yang,
Y.; Iguchi, S.; Hasegawa, T.; Saito, M.; Inatani, J.; Mizuno, N.;
Asayama, S.; Kosugi, G.; Morita, K. -I.; Chiba, K.; Kawashima, S.;
Okumura, S. K.; Ohashi, N.; Ogasawara, R.; Sakamoto, S.; Noguchi, T.;
Huang, Y. -D.; Liu, S. -Y.; Kemper, F.; Koch, P. M.; Chen, M. -T.;
Chikada, Y.; Hiramatsu, M.; Iono, D.; Shimojo, M.; Komugi, S.; Kim,
J.; Lyo, A. -R.; Muller, E.; Herrera, C.; Miura, R. E.; Ueda, J.;
Chibueze, J.; Su, Y. -N.; Trejo-Cruz, A.; Wang, K. -S.; Kiuchi,
H.; Ukita, N.; Sugimoto, M.; Kawabe, R.; Hayashi, M.; Miyama, S.;
Ho, P. T. P.; Kaifu, N.; Ishiguro, M.; Beasley, A. J.; Bhatnagar,
S.; Braatz, J. A., III; Brisbin, D. G.; Brunetti, N.; Carilli, C.;
Crossley, J. H.; D'Addario, L.; Donovan Meyer, J. L.; Emerson, D. T.;
Evans, A. S.; Fisher, P.; Golap, K.; Griffith, D. M.; Hale, A. E.;
Halstead, D.; Hardy, E. J.; Hatz, M. C.; Holdaway, M.; Indebetouw, R.;
Jewell, P. R.; Kepley, A. A.; Kim, D. -C.; Lacy, M. D.; Leroy, A. K.;
Liszt, H. S.; Lonsdale, C. J.; Matthews, B.; McKinnon, M.; Mason,
B. S.; Moellenbrock, G.; Moullet, A.; Myers, S. T.; Ott, J.; Peck,
A. B.; Pisano, J.; Radford, S. J. E.; Randolph, W. T.; Rao Venkata,
U.; Rawlings, M. G.; Rosen, R.; Schnee, S. L.; Scott, K. S.; Sharp,
N. K.; Sheth, K.; Simon, R. S.; Tsutsumi, T.; Wood, S. J.
2015ApJ...808L...1A Altcode: 2015arXiv150404877P
A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA)
is to make accurate images with resolutions of tens of milliarcseconds,
which at submillimeter (submm) wavelengths requires baselines up to
∼15 km. To develop and test this capability, a Long Baseline Campaign
(LBC) was carried out from 2014 September to late November, culminating
in end-to-end observations, calibrations, and imaging of selected
Science Verification (SV) targets. This paper presents an overview
of the campaign and its main results, including an investigation of
the short-term coherence properties and systematic phase errors over
the long baselines at the ALMA site, a summary of the SV targets and
observations, and recommendations for science observing strategies at
long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz
are also compared to VLA 43 GHz results, demonstrating an agreement at
a level of a few percent. As a result of the extensive program of LBC
testing, the highly successful SV imaging at long baselines achieved
angular resolutions as fine as 19 mas at ∼350 GHz. Observing with
ALMA on baselines of up to 15 km is now possible, and opens up new
parameter space for submm astronomy. .

---------------------------------------------------------
Title: Sunspot waves and flare energy release
Authors: Sych, R.; Karlický, M.; Altyntsev, A.; Dudík, J.;
Kashapova, L.
2015A&A...577A..43S Altcode: 2014arXiv1409.2947S
Context. We study the possibility of flare process triggering by
waves propagating from the sunspot along a magnetic loop (channel)
to a nearby flare site. Aims: We present a relationship between
the dynamics of ~3-min slow magnetoacoustic waves in the sunspot and
flare emergence process. Waves propagating in the magnetic channel
whose one foot is anchored in the umbra represent the disturbing agent
responsible for triggering the flare energy release. Methods:
We applied time-distance plots and pixel wavelet filtration methods
to obtain spatio-temporal distribution of wave power variations in
radio and SDO/AIA data. To find the magnetic channel, we used potential
magnetic field extrapolation of SDO/HMI magnetograms. The propagation
velocity of wave fronts was measured from wave locations at specific
times. Results: In the correlation curves of the 17 GHz (NoRH)
radio emission, we found a monotonous energy amplification of the
3-min waves in the sunspot umbra before the 2012 June 7 flare. This
amplification was associated with an increase in the length of the
oscillatory wakes in coronal loops (SDO/AIA, 171 Å) prior to the flare
onset. A peculiarity of the flare is the constant level of the flare
emission in soft X-rays (RHESSI, 3-25 keV) for ~10 min after the short
impulsive phase, which indicates continuing energy release. Throughout
this time, we found transverse oscillations of the flare loop with a
30 s period in the radio-frequency range (NoRH, 17 GHz). This period
appears to be related to the 3-min waves from the sunspot. The magnetic
field extrapolation based on SDO/HMI magnetograms shows the existence
of the magnetic channel (waveguide) connecting the sunspot with the
energy release region. Conclusions: We analysed the sunspot
3-min wave dynamics and found a correlation between the oscillation
power amplification and flare triggering in the region connected to the
sunspot through the magnetic channel. We propose that this amplified
wave flux triggered the flare. The flare occurred because of this
amplified flux, however, and because a sufficient amount of free
magnetic energy was accumulated in close vicinity to the magnetic
channel prior to the flare. Furthermore, because of loop heating,
the wave velocity (sound velocity) increased with the penetration of
waves into the energy release site. The heating is shown to be able to
proceed after the flare main peak owing to a further energy pumping
in the form of waves from the sunspot and additional reconnection
episodes in the flare region.

---------------------------------------------------------
Title: Particle Acceleration in Plasmoid Ejections Derived from
Radio Drifting Pulsating Structures
Authors: Nishizuka, N.; Karlický, M.; Janvier, M.; Bárta, M.
2015ApJ...799..126N Altcode: 2014arXiv1412.7904N
We report observations of slowly drifting pulsating structures
(DPSs) in the 0.8-4.5 GHz frequency range of the RT4 and RT5 radio
spectrographs at Ondřejov Observatory, between 2002 and 2012. We
found 106 events of DPSs, which we classified into four cases:
(I) single events with a constant frequency drift (12 events), (II)
multiple events occurring in the same flare with constant frequency
drifts (11 events), (III) single or multiple events with increasing
or decreasing frequency drift rates (52 events), and (IV) complex
events containing multiple events occurring at the same time in a
different frequency range (31 events). Many DPSs are associated with
hard X-ray (HXR) bursts (15-25 keV) and soft X-ray (SXR) gradient
peaks, as they typically occurred at the beginning of HXR peaks. This
indicates that DPS events are related to the processes of fast energy
release and particle acceleration. Furthermore, interpreting DPSs
as signatures of plasmoids, we measured their ejection velocity,
their width, and their height from the DPS spectra, from which we
also estimated the reconnection rate and the plasma beta. In this
interpretation, constant frequency drift indicates a constant velocity
of a plasmoid, and an increasing/decreasing frequency drift indicates a
deceleration/acceleration of a plasmoid ejection. The reconnection rate
shows a good positive correlation with the plasmoid velocity. Finally
we confirmed that some DPS events show plasmoid counterparts in Solar
Dynamics Observatory/Atmospheric Imaging Assembly images.

---------------------------------------------------------
Title: Structured mass density slab as a waveguide of fast
magnetoacoustic waves
Authors: Jelínek, P.; Karlický, M.
2015CEAB...39...51J Altcode:
Coronal loops are waveguides for magnetohydrodynamic (MHD) waves. These
loops are expected to be structured. Therefore, in the present paper,
we numerically studied the propagation of the fast MHD waves in the
structured density slab (composed from a broad density slab with
one axisymmetric narrow sub-slab superposed), and analysed the wave
signals. Then, this structured slab was divided into its components,
i.e., to simple broad and narrow slabs and the same analysis was
made. We compared results of both these cases. For the calculations
we adopted a two-dimensional (2D) magnetohydrodynamic (MHD) model,
in which we solved a full set of ideal time-dependent MHD equations
using the FLASH code, applying the adaptive mesh refinement (AMR)
method. To initiate the fast sausage magnetoacoustic waves, we used
axisymmetric Gaussian velocity perturbation. Wave signals were detected
in different locations along the slab and as a diagnostic tool of these
waves, the wavelet analysis method has been used. We found that for
the structured density slab with sufficiently sharp boundaries, i.e.,
for good quality waveguides (without an energy leakage), the guided
waves in the structured slab behave similarly as in its separated
(simple slab) components.

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Title: High-frequency reverse drift bursts in 2012-2014 solar flares
Authors: Jiřička, K.; Karlický, M.
2015CEAB...39...59J Altcode:
During observations by the Ondřejov high-time resolution 0.8-2.0
GHz radio spectrograph in years 2012-2014, 33 high-frequency reverse
drift bursts with frequency drift less than 500 MHz s-1
were found. In 23 cases these bursts were observed before the GOES
flare maximum, while the remaining 10 after this GOES maximum. Using
the Aschwanden's density model of the solar atmosphere and assuming
the radio emission on the harmonic plasma frequency, the corresponding
velocities of the agents generating these bursts are less than 7000
km s-1. These velocities are too slow for electron beams,
therefore we propose that these bursts are generated by thermal
conduction fronts or by magnetohydrodynamic shocks.

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Title: Solar Radio Bursts with Spectral Fine Structures in Preflares
Authors: Zhang, Yin; Tan, Baolin; Karlický, Marian; Mészárosová,
Hana; Huang, Jing; Tan, Chengming; Simões, Paulo J. A.
2015ApJ...799...30Z Altcode: 2014arXiv1411.4766Z
Good observations of preflare activities are important for us to
understand the origin and triggering mechanism of solar flares, and
to predict the occurrence of solar flares. This work presents the
characteristics of microwave spectral fine structures as preflare
activities of four solar flares observed by the Ondřejov radio
spectrograph in the frequency range of 0.8-2.0 GHz. We found that
these microwave bursts which occurred 1-4 minutes before the onset of
flares have spectral fine structures with relatively weak intensities
and very short timescales. They include microwave quasi-periodic
pulsations with very short periods of 0.1-0.3 s and dot bursts with
millisecond timescales and narrow frequency bandwidths. Accompanying
these microwave bursts are filament motions, plasma ejection or loop
brightening in the EUV imaging observations, and non-thermal hard
X-ray emission enhancements observed by RHESSI. These facts may reveal
certain independent, non-thermal energy releasing processes and particle
acceleration before the onset of solar flares. They may help us to
understand the nature of solar flares and to predict their occurrence.

---------------------------------------------------------
Title: New Eyes Looking at Solar Activity: Challenges for Theory
and Simulations - Placing It into Context
Authors: Pohjolainen, S.; Karlický, M.; van Driel-Gesztelyi, L.;
Mandrini, C. H.
2015SoPh..290....1P Altcode: 2014SoPh..tmp..190P
Solar Cycle 24 has opened a new era in solar radio physics as we now
have instruments that can probe solar processes from submillimeter to
kilometer waves. New and upgraded instruments provide data that enable
studies of both energetic particles and thermal plasma, enhancing
our knowledge of solar eruptions and acceleration and propagation
of particles, through the solar chromosphere and corona and into
the interplanetary space. In this Topical Issue we highlight the new
observational capabilities and discuss the theoretical issues connected
to solar radio emission and interplanetary radio physics.

---------------------------------------------------------
Title: Fourier Analysis of Radio Bursts Observed with Very High
Time Resolution
Authors: DaÌ§browski, B. P.; Karlický, M.; Rudawy, P.
2015SoPh..290..169D Altcode:
Numerous solar radio bursts were observed in 2000 - 2001 using
the Toruń radio spectrograph with its unique time resolution of 80
microseconds. This high time resolution enables an in-depth analysis of
the time evolution of the power spectra and Fourier spectral indices of
selected short radio bursts. We analyze the power-spectrum parameters
and variability for two millisecond radio dm-spike events and one
drifting pulsation structure (DPS) event, for which the structures of
the recorded signals were analyzed with an effective time resolution
of 0.0008 s in five adjacent frequency bands of their radio spectra.

---------------------------------------------------------
Title: MHD flows at astropauses and in astrotails
Authors: Nickeler, D. H.; Wiegelmann, T.; Karlický, M.; Kraus, M.
2014ASTRP...1...51N Altcode: 2015arXiv150105122N
The geometrical shapes and the physical properties of stellar wind -
interstellar medium interaction regions form an important stage for
studying stellar winds and their embedded magnetic fields as well as
cosmic ray modulation. Our goal is to provide a proper representation
and classification of counter-flow configurations and counter-flow
interfaces in the frame of fluid theory. In addition we calculate flows
and large-scale electromagnetic fields based on which the large-scale
dynamics and its role as possible background for particle acceleration,
e.g., in the form of anomalous cosmic rays, can be studied. We find
that for the definition of the boundaries, which are determining the
astropause shape, the number and location of magnetic null points
and stagnation points is essential. Multiple separatrices can exist,
forming a highly complex environment for the interstellar and stellar
plasma. Furthermore, the formation of extended tail structures
occur naturally, and their stretched field and streamlines provide
surroundings and mechanisms for the acceleration of particles by
field-aligned electric fields.

---------------------------------------------------------
Title: Self-consistent stationary MHD shear flows in the solar
atmosphere as electric field generators
Authors: Nickeler, D. H.; Karlický, M.; Wiegelmann, T.; Kraus, M.
2014A&A...569A..44N Altcode: 2014arXiv1407.3227N
Context. Magnetic fields and flows in coronal structures, for
example, in gradual phases in flares, can be described by 2D and
3D magnetohydrostatic (MHS) and steady magnetohydrodynamic (MHD)
equilibria. Aims: Within a physically simplified, but exact
mathematical model, we study the electric currents and corresponding
electric fields generated by shear flows. Methods: Starting
from exact and analytically calculated magnetic potential fields,
we solved the nonlinear MHD equations self-consistently. By applying
a magnetic shear flow and assuming a nonideal MHD environment, we
calculated an electric field via Faraday's law. The formal solution
for the electromagnetic field allowed us to compute an expression
of an effective resistivity similar to the collisionless Speiser
resistivity. Results: We find that the electric field can be
highly spatially structured, or in other words, filamented. The electric
field component parallel to the magnetic field is the dominant component
and is high where the resistivity has a maximum. The electric field is a
potential field, therefore, the highest energy gain of the particles can
be directly derived from the corresponding voltage. In our example of a
coronal post-flare scenario we obtain electron energies of tens of keV,
which are on the same order of magnitude as found observationally. This
energy serves as a source for heating and acceleration of particles.

---------------------------------------------------------
Title: Quasi-Periodic Pulsations with Varying Period in
Multi-Wavelength Observations of an X-class Flare
Authors: Huang, Jing; Tan, Baolin; Zhang, Yin; Karlický, Marian;
Mészárosová, Hana
2014ApJ...791...44H Altcode:
This work presents an interesting phenomenon of the period variation
in quasi-periodic pulsations (QPPs) observed during the impulsive
phase of a coronal mass ejection-related X1.1 class flare on 2012
July 6. The period of QPPs was changed from 21 s at soft X-rays (SXR)
to 22-23 s at microwaves, to ~24 s at extreme ultraviolet emissions
(EUV), and to 27-32 s at metric-decimetric waves. The microwave,
EUV, and SXR QPPs, emitted from flare loops of different heights,
were oscillating in phase. Fast kink mode oscillations were proposed
to be the modulation mechanism, which may exist in a wide region in
the solar atmosphere from the chromosphere to the upper corona or
even to the interplanetary space. Changed parameters of flare loops
through the solar atmosphere could result in the varying period of
QPPs at different wavelengths. The first appearing microwave QPPs
and quasi-periodic metric-decimetric type III bursts were generated
by energetic electrons. This may imply that particle acceleration
or magnetic reconnection were located between these two non-thermal
emission sources. Thermal QPPs (in SXR and EUV emissions) occurred
later than the nonthermal ones, which would suggest a some time for
plasma heating or energy dissipation in flare loops during burst
processes. At the beginning of flare, a sudden collapse and expansion
of two separated flare loop structures occurred simultaneously with
the multi-wavelength QPPs. An implosion in the corona, including both
collapse and expansion of flare loops, could be a trigger of loop
oscillations in a very large region in the solar atmosphere.

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Title: A Very Small and Super Strong Zebra Pattern Burst at the
Beginning of a Solar Flare
Authors: Tan, Baolin; Tan, Chengming; Zhang, Yin; Huang, Jing;
Mészárosová, Hana; Karlický, Marian; Yan, Yihua
2014ApJ...790..151T Altcode: 2014arXiv1406.5209T
Microwave emission with spectral zebra pattern structures (ZPs)
is frequently observed in solar flares and the Crab pulsar. The
previous observations show that ZP is a structure only overlapped
on the underlying broadband continuum with slight increments and
decrements. This work reports an unusually strong ZP burst occurring
at the beginning of a solar flare observed simultaneously by two
radio telescopes located in China and the Czech Republic and by the
EUV telescope on board NASA's satellite Solar Dynamics Observatory
on 2013 April 11. It is a very short and super strong explosion whose
intensity exceeds several times that of the underlying flaring broadband
continuum emission, lasting for just 18 s. EUV images show that the
flare starts from several small flare bursting points (FBPs). There is
a sudden EUV flash with extra enhancement in one of these FBPs during
the ZP burst. Analysis indicates that the ZP burst accompanying an EUV
flash is an unusual explosion revealing a strong coherent process with
rapid particle acceleration, violent energy release, and fast plasma
heating simultaneously in a small region with a short duration just
at the beginning of the flare.

---------------------------------------------------------
Title: Solar flares: radio and X-ray signatures of magnetic
reconnection processes
Authors: Karlický, Marian
2014RAA....14..753K Altcode:
This review summarizes new trends in studies of magnetic reconnection in
solar flares. It is shown that plasmoids play a very important role in
this primary flare process. Using the results of magnetohydrodynamic and
particle-in-cell simulations, we describe how the plasmoids are formed,
how they move and interact, and how a flare current sheet is fragmented
into a cascade of plasmoids. Furthermore, it is shown that during the
interactions of these plasmoids electrons are not only very efficiently
accelerated and heated, but electromagnetic (radio) emission is also
produced. We also describe possible mechanisms for the triggering
of magnetic reconnection. The relevant X-ray and radio signatures
of these processes (such as radio drifting pulsation structures,
narrowband dm-spikes, and the loop-top and above-the-loop-top X-ray
sources) are then described. It is shown that plasmoids can also be
formed in kinked magnetic ropes. A mapping of X-points of the magnetic
reconnection on the chromosphere (as e.g. a splitting of flare ribbons)
is mentioned. Supporting EUV and white-light observations of plasmoids
are added. The significance of all these processes for the fast
magnetic reconnection and electron acceleration is outlined. Their
role in fusion experiments is briefly mentioned.

---------------------------------------------------------
Title: Magnetoacoustic Waves Propagating along a Dense Slab and
Harris Current Sheet and their Wavelet Spectra
Authors: Mészárosová, Hana; Karlický, Marian; Jelínek, Petr;
Rybák, Ján
2014ApJ...788...44M Altcode:
Currently, there is a common endeavor to detect magnetoacoustic
waves in solar flares. This paper contributes to this topic using an
approach of numerical simulations. We studied a spatial and temporal
evolution of impulsively generated fast and slow magnetoacoustic
waves propagating along the dense slab and Harris current sheet using
two-dimensional magnetohydrodynamic numerical models. Wave signals
computed in numerical models were used for computations of the temporal
and spatial wavelet spectra for their possible comparison with those
obtained from observations. It is shown that these wavelet spectra allow
us to estimate basic parameters of waveguides and perturbations. It was
found that the wavelet spectra of waves in the dense slab and current
sheet differ in additional wavelet components that appear in association
with the main tadpole structure. These additional components are new
details in the wavelet spectrum of the signal. While in the dense slab
this additional component is always delayed after the tadpole head, in
the current sheet this component always precedes the tadpole head. It
could help distinguish a type of the waveguide in observed data. We
present a technique based on wavelets that separates wave structures
according to their spatial scales. This technique shows not only
how to separate the magnetoacoustic waves and waveguide structure in
observed data, where the waveguide structure is not known, but also
how propagating magnetoacoustic waves would appear in observations
with limited spatial resolutions. The possibilities detecting these
waves in observed data are mentioned.

---------------------------------------------------------
Title: High-Resolution Time Profiles of Fiber Bursts at 1420 and
2695 MHz
Authors: Zlobec, P.; Karlický, M.
2014SoPh..289.1683Z Altcode:
To obtain constraints for models of fiber bursts, high-resolution time
(0.01 s) profiles of the fiber bursts recorded at 1420 and 2695 MHz by
the Trieste radiometers are studied in detail. The fiber bursts were
identified using Ondřejov radio spectra. During the years 2000 - 2005,
18 intervals with fiber bursts were selected; 26 groups were defined
and about 700 fibers were analyzed in detail. More than 300 pulsations,
present almost simultaneously with the fibers, were also selected and
studied in order to find similarities or differences between these
two types of fine structures. It was found that the polarization of
the associated continuum, both for fiber bursts and pulsations, is
practically the same. Evaluating the ratio between absorption over
emission of many single fibers we found that this parameter is very
different even for nearby bursts; however, we realized that this ratio
shows a tendency to decrease with time. Finally, the time profile of
one selected fiber burst was fitted using a recent model based on the
modulation of the broadband radio emission by fast magnetoacoustic
waves. The results are discussed.

---------------------------------------------------------
Title: Slipping Magnetic Reconnection during an X-class Solar Flare
Observed by SDO/AIA
Authors: Dudík, J.; Janvier, M.; Aulanier, G.; Del Zanna, G.;
Karlický, M.; Mason, H. E.; Schmieder, B.
2014ApJ...784..144D Altcode: 2014arXiv1401.7529D
We present SDO/AIA observations of an eruptive X-class flare of
2012 July 12, and compare its evolution with the predictions of a
three-dimensional (3D) numerical simulation. We focus on the dynamics of
flare loops that are seen to undergo slipping reconnection during the
flare. In the Atmospheric Imaging Assembly (AIA) 131 Å observations,
lower parts of 10 MK flare loops exhibit an apparent motion with
velocities of several tens of km s-1 along the developing
flare ribbons. In the early stages of the flare, flare ribbons consist
of compact, localized bright transition-region emission from the
footpoints of the flare loops. A differential emission measure analysis
shows that the flare loops have temperatures up to the formation of
Fe XXIV. A series of very long, S-shaped loops erupt, leading to a
coronal mass ejection observed by STEREO. The observed dynamics are
compared with the evolution of magnetic structures in the "standard
solar flare model in 3D." This model matches the observations well,
reproducing the apparently slipping flare loops, S-shaped erupting
loops, and the evolution of flare ribbons. All of these processes are
explained via 3D reconnection mechanisms resulting from the expansion
of a torus-unstable flux rope. The AIA observations and the numerical
model are complemented by radio observations showing a noise storm
in the metric range. Dm-drifting pulsation structures occurring
during the eruption indicate plasmoid ejection and enhancement of the
reconnection rate. The bursty nature of radio emission shows that the
slipping reconnection is still intermittent, although it is observed
to persist for more than an hour.

---------------------------------------------------------
Title: Modifications of thick-target model: re-acceleration of
electron beams by static and stochastic electric fields
Authors: Varady, M.; Karlický, M.; Moravec, Z.; Kašparová, J.
2014A&A...563A..51V Altcode: 2014arXiv1401.3329V
Context. The collisional thick-target model (CTTM) of the impulsive
phase of solar flares, together with the famous Carmichael, Sturrock,
Hirayama, and Kopp-Pneuman (CSHKP) model, presented for many years a
"standard" model, which straightforwardly explained many observational
aspects of flares. On the other hand, many critical issues appear when
the concept is scrutinised theoretically or with the new generation of
hard X-ray (HXR) observations. The famous "electron number problem"
or problems related to transport of enormous particle fluxes though
the corona represent only two of them. To resolve the discrepancies,
several modifications of the CTTM appeared. Aims: We study two
of them based on the global and local re-acceleration of non-thermal
electrons by static and stochastic electric fields during their
transport from the coronal acceleration site to the thick-target
region in the chromosphere. We concentrate on a comparison of the
non-thermal electron distribution functions, chromospheric energy
deposits, and HXR spectra obtained for both considered modifications
with the CTTM itself. Methods: The results were obtained using
a relativistic test-particle approach. We simulated the transport
of non-thermal electrons with a power-law spectrum including the
influence of scattering, energy losses, magnetic mirroring, and also
the effects of the electric fields corresponding to both modifications
of the CTTM. Results: We show that both modifications of the
CTTM change the outcome of the chromospheric bombardment in several
aspects. The modifications lead to an increase in chromospheric energy
deposit, change of its spatial distribution, and a substantial increase
in the corresponding HXR spectrum intensity. Conclusions: The
re-acceleration in both models reduces the demands on the efficiency
of the primary coronal accelerator, on the electron fluxes transported
from the corona downwards, and on the total number of accelerated
coronal electrons during flares.

---------------------------------------------------------
Title: Statistics and Classification of the Microwave Zebra Patterns
Associated with Solar Flares
Authors: Tan, Baolin; Tan, Chengming; Zhang, Yin; Mészárosová,
H.; Karlický, M.
2014ApJ...780..129T Altcode: 2013arXiv1311.5305T
The microwave zebra pattern (ZP) is the most interesting, intriguing,
and complex spectral structure frequently observed in solar flares. A
comprehensive statistical study will certainly help us to understand
the formation mechanism, which is not exactly clear now. This work
presents a comprehensive statistical analysis of a big sample with 202
ZP events collected from observations at the Chinese Solar Broadband
Radio Spectrometer at Huairou and the Ondŕejov Radiospectrograph
in the Czech Republic at frequencies of 1.00-7.60 GHz from 2000 to
2013. After investigating the parameter properties of ZPs, such as
the occurrence in flare phase, frequency range, polarization degree,
duration, etc., we find that the variation of zebra stripe frequency
separation with respect to frequency is the best indicator for a
physical classification of ZPs. Microwave ZPs can be classified into
three types: equidistant ZPs, variable-distant ZPs, and growing-distant
ZPs, possibly corresponding to mechanisms of the Bernstein wave
model, whistler wave model, and double plasma resonance model,
respectively. This statistical classification may help us to clarify
the controversies between the existing various theoretical models and
understand the physical processes in the source regions.

---------------------------------------------------------
Title: Frequency variations of solar radio zebras and their power-law
spectra
Authors: Karlický, M.
2014A&A...561A..34K Altcode:
Context. During solar flares several types of radio bursts are
observed. The fine striped structures of the type IV solar radio bursts
are called zebras. Analyzing them provides important information about
the plasma parameters of their radio sources. We present a new analysis
of zebras. Aims: Power spectra of the frequency variations
of zebras are computed to estimate the spectra of the plasma density
variations in radio zebra sources. Methods: Frequency variations
of zebra lines and the high-frequency boundary of the whole radio burst
were determined with and without the frequency fitting. The computed
time dependencies of these variations were analyzed with the Fourier
method. Results: First, we computed the variation spectrum of the
high-frequency boundary of the whole radio burst, which is composed of
several zebra patterns. This power spectrum has a power-law form with a
power-law index -1.65. Then, we selected three well-defined zebra-lines
in three different zebra patterns and computed the spectra of their
frequency variations. The power-law indices in these cases are found
to be in the interval between -1.61 and -1.75. Finally, assuming that
the zebra-line frequency is generated on the upper-hybrid frequency
and that the plasma frequency ωpe is much higher than
the electron-cyclotron frequency ωce, the Fourier power
spectra are interpreted to be those of the electron plasma density in
zebra radio sources.

---------------------------------------------------------
Title: Statistical Moments of Active-Region Images During Solar Flares
Authors: Šimberová, S.; Karlický, M.; Suk, T.
2014SoPh..289..193S Altcode:
We present new temporal-evolution diagnostics of solar flares. The
high-order statistical moments (skewness and kurtosis) of the Hα images
of active regions during solar flares were computed from their initial
phases up to their maxima. The same method was used for quiet active
regions for tests and comparison. We found that temporal profiles
of the Hα statistical moments during flares roughly correspond to
those observed in soft X-rays by the GOES satellite. Maxima of the
cross-correlation coefficients between the skewness and the GOES X-rays
were found to be 0.82 - 0.98, and the GOES X-rays are delayed 0 - 144
seconds against the skewness. We recognized that these moments are very
sensitive to pre-flare activities. Therefore we used them to determine
the flare starting-time and to study the pre-flare quasi-periodic
processes. We determined the periods of these pre-flare processes in
an interval of 20 - 400 seconds by using special convolution filters
and Fourier analysis. We propose to use this method to analyze active
regions during the very early phases of solar flares, and even in
real time.

---------------------------------------------------------
Title: Role of plasmoids in energy cascade in magnetic reconnection
in solar
Authors: Bárta, Miroslav; Büchner, Jörg; Karlicky, Marian;
Skala, Jan
2014cosp...40E.222B Altcode:
The key role of plasmoids for current sheet fragmentation and
filamentation in magnetic reconnection in high Lundquist-number systems
has been recently revealed. Their dynamics and mutual interaction
can provide efficient mechanism for energy cascade towards the
small scales where the fast kinetic reconnection process comes into
play. We will present results of our recent MHD and PIC simulations
in this direction. It will be shown that at medium and small scales
additional effect has to be taken into account: The mutual interaction
of plasmoids with reconnection flows. We shall also demonstrate that
formation and interaction of plasmoids is naturally involved in the
real solar flares. We will present an extension of the MHD simulations
providing simulated observations in optical, UV/EUV and radio domains
and their comparison with the data really observed during the solar
flares. The comparison clearly shows that the theory and modelling of
plasmoid-dominated regime of magnetic reconnection is applicable to
the physics of solar flares.

---------------------------------------------------------
Title: Report on the 2nd Solar ALMA Workshop
Authors: Dąbrowski, B.; Karlický, M.
2013Msngr.153...38D Altcode:
The Czech node is one of the ALMA European Regional Centres and is
the only one to support solar observations. The second workshop in the
series is briefly described: the main themes were the scope of solar
observation with ALMA, planning observations and the science that can
be achieved.

---------------------------------------------------------
Title: Flare line impact polarization. Na D2 589 nm line polarization
in the 2001 June 15 flare
Authors: Hénoux, J. C.; Karlický, M.
2013A&A...556A..95H Altcode:
Context. The impact polarization of optical chromospheric lines
in solar flares is still being debated. For this reason, additional
observations and improved flare atmosphere models are needed still. Aims: The polarization-free telescope THEMIS used in multiline 2
MulTiRaies (MTR) mode allows accurate simultaneous linear polarization
measurements in various spectral lines. Methods: In the 2001
June 15 flare, Hα, Hβ, and Mg D2 lines linear impact polarization
was reported as present in THEMIS 2 MTR observations. In this paper,
THEMIS data analysis was extended to the Na D2 line. Sets of I ± U
and I ± Q flare Stokes S 2D-spectra were corrected from dark-current,
spectral-line curvature and from transmission differences. Then, we
derived the linear polarization degree P and polarization orientation
angle α 2D-spectra. No change in relative positioning could be found
that would reduce the Stokes parameters U and Q values. No V and I
crosstalks could explain our results either. Results: The Na
D2 line is linearly polarized with a polarization degree exceeding 5%
at some locations. The polarization was found to be radial at outer
ribbons edges, and tangential at their inner edges. This orientation
change may be due to differences in electron distribution functions
on the opposite borders of flare chromospheric ribbons. Electron beams
propagating along magnetic field lines, together with return currents,
could explain both radial and tangential polarization. At the inner
ribbon edges, intensity profile-width enlargements and blueshifts
in polarization profiles are observed. This suggests chromospheric
evaporation. Appendix A is available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Fragmentation of electric currents in the solar corona by
plasma flows
Authors: Nickeler, D. H.; Karlický, M.; Wiegelmann, T.; Kraus, M.
2013A&A...556A..61N Altcode: 2013arXiv1306.5155N
 Aims: We consider a magnetic configuration consisting of an
arcade structure and a detached plasmoid, resulting from a magnetic
reconnection process, as is typically found in connection with solar
flares. We study spontaneous current fragmentation caused by shear and
vortex plasma flows. Methods: An exact analytical transformation
method was applied to calculate self-consistent solutions of the
nonlinear stationary magnetohydrodynamic equations. The assumption
of incompressible field-aligned flows implies that both the Alfvén
Mach number and the mass density are constant on field lines. We first
calculated nonlinear magnetohydrostatic equilibria with the help of
the Liouville method, emulating the scenario of a solar eruptive flare
configuration with plasmoids (magnetic ropes or current-carrying loops
in 3D) and flare arcade. Then a Mach number profile was constructed
that describes the upflow along the open magnetic field lines and
implements a vortex flow inside the plasmoid. This Mach number profile
was used to map the magnetohydrostatic equilibrium to the stationary
one. Results: We find that current fragmentation takes place
at different locations within our configuration. Steep gradients of
the Alfvén Mach number are required, implying the strong influence
of shear flows on current amplification and filamentation of the
magnetohydrostatic current sheets. Crescent- or ring-like structures
appear along the outer separatrix, butterfly structures between the
upper and lower plasmoids, and strong current peaks close the lower
boundary (photosphere). Furthermore, impressing an intrinsic small-scale
structure on the upper plasmoid results in strong fragmentation of the
plasmoid. Hence fragmentation of current sheets and plasmoids is an
inherent property of magnetohydrodynamic theory. Conclusions:
Transformations from magnetohydrostatic into magnetohydrodynamic
steady-states deliver fine-structures needed for plasma heating and
acceleration of particles and bulk plasma flows in dissipative events
that are typically connected to magnetic reconnection processes in
flares and coronal mass ejections.

---------------------------------------------------------
Title: Observational consequences of the local re-acceleration
thick-target model
Authors: Varady, M.; Moravec, Z.; Karlický, M.; Kašparová, J.
2013JPhCS.440a2013V Altcode:
In our contribution we compare the efficiency of the hard X-ray
production and the vertical sizes and positions of the hard X-ray
sources for the classical collisional thick-target model and for its
recently proposed modification, the local re-acceleration thick-target
model. The latter model has been proposed in order to ease some
of the severe theoretical problems of the collisional thick-target
model related to interpretation of the observational properties of the
foot-point HXR sources in solar flares. The results are obtained using
a relativistic test-particle approach for a fully ionised atmosphere
with a converging magnetic field and a single (compact) flare loop.

---------------------------------------------------------
Title: Modeling of Hα Eruptive Events Observed at the Solar Limb
Authors: Kotrč, P.; Bárta, M.; Schwartz, P.; Kupryakov, Y. A.;
Kashapova, L. K.; Karlický, M.
2013SoPh..284..447K Altcode: 2012SoPh..tmp..290K; 2012SoPh..tmp..269K
We present spectra and slit-jaw images of limb and on-disk eruptive
events observed with a high temporal resolution by the Ondřejov
Observatory optical spectrograph. Analysis of the time series of
full width at half-maximum (FWHM) in Hα, Hβ, and radio and soft
X-ray (SXR) fluxes indicates two phenomenologically distinct types
of observations which differ significantly in the timing of FWHM
and SXR/radio fluxes. We investigated one such unusual case of a
limb eruptive event in more detail. Synthesis of all observed data
supports the interpretation of the Hα broadening in the sense of
regular macroscopic plasma motions, contrary to the traditional
view (emission from warm dense plasma). The timing and observed
characteristics indicate that we may have actually observed the
initiation of a prominence eruption. We test this scenario via modeling
of the initial phase of the flux rope eruption in a magnetohydrodynamic
(MHD) simulation, calculating subsequently - under some simplifying
assumptions - the modeled Hα emission and spectrum. The modeled and
observed data correspond well. Nevertheless, the following question
arises: To what extent is the resulting emission sensitive to the
underlying model of plasma dynamics? To address this issue, we have
computed a grid of kinematic models with various arbitrary plasma
flow patterns and then calculated their resulting emission. Finally,
we suggest a diagnostics based on the model and demonstrate that it
can be used to estimate the Alfvén velocity and plasma beta in the
prominence, which are otherwise hard to obtain.

---------------------------------------------------------
Title: Fast Magnetoacoustic Waves in a Fan Structure Above a Coronal
Magnetic Null Point
Authors: Mészárosová, H.; Dudík, J.; Karlický, M.; Madsen,
F. R. H.; Sawant, H. S.
2013SoPh..283..473M Altcode: 2013arXiv1301.2485M
We analyze the 26 November 2005 solar radio event observed
interferometrically at frequencies of 244 and 611 MHz by the Giant
Metrewave Radio Telescope (GMRT) in Pune, India. These observations
are used to make interferometric maps of the event at both frequencies
with the time cadence of 1 s from 06:50 to 07:12 UT. These maps reveal
several radio sources. The light curves of these sources show that only
two sources at 244 MHz and 611 MHz are well correlated in time. The
EUV flare is more localized with flare loops located rather away from
the radio sources. Using SoHO/MDI observations and potential magnetic
field extrapolation we demonstrate that both the correlated sources
are located in the fan structure of magnetic field lines starting from
a coronal magnetic null point. Wavelet analysis of the light curves of
the radio sources detects tadpoles with periods in the range P=10 - 83
s. These wavelet tadpoles indicate the presence of fast magnetoacoustic
waves that propagate in the fan structure of the coronal magnetic null
point. We estimate the plasma parameters in the studied radio sources
and find them consistent with the presented scenario involving the
coronal magnetic null point.

---------------------------------------------------------
Title: Radio continua modulated by waves: Zebra patterns in solar
and pulsar radio spectra?
Authors: Karlický, M.
2013A&A...552A..90K Altcode:
 Aims: We aim to answer the question how waves with plasma density
variations affect the radio continua generated by the plasma emission
mechanism. Methods: We built a simple semi-empirical model of
the radio continuum modulation. Assuming that the waves with density
variations are in the source of this radio continuum, we modeled the
artificial radio spectrum, which we compared with observed spectra. Results: We show that the waves with density variations modulate the
radio continua generated by the plasma emission mechanism. Considering
a single slow magnetoacoustic wave, we model the radio spectra, which
resemble solar zebra patterns. We show that this modulation generates
zebra effects even when the radio continuum is composed of many spiky
bursts. Generalizing from one single wave to a wave turbulence we
find that the computed radio spectrum is similar to so-called lace
bursts. Finally, using the same procedure, but for fast magnetoacoustic
waves, we modeled the radio spectrum similar to that observed during
the interpulse phase of the radio emission of the Crab Nebula pulsar.

---------------------------------------------------------
Title: Dielectronic satellite lines and double layers in solar flares
Authors: Dzifčáková, E.; Karlický, M.; Dudík, J.
2013A&A...550A..60D Altcode:
Context. Particle acceleration during solar flares results
in departures of the distribution of particle energies from the
Maxwellian distribution. Apart from the high-energy tail, the bulk of
the distribution was recently also found to be significantly affected,
due, e.g., to the presence of double layers. Aims: We investigate
the influence of several proposed non-Maxwellian distribution functions
on the X-ray flare line spectra. The distribution functions considered
are sharply peaked and include the n-distribution, the moving Maxwellian
distribution, and the distribution formed in strong double layers in
the flaring plasma. Methods: Synthetic Si xiid-Si xiv spectra
involving allowed and dielectronic transitions at 5 - 6 Å are
calculated numerically. The parameters chosen for the calculations
correspond to the impulsive phase of solar flares, as inferred by
previous authors. Results: The Si xiid λ5.56/Si xiii λ5.68
and Si xiid λ5.82/Si xiii λ5.68 ratios depend on the relative number
of electrons at energies corresponding to the formation of the Si
xiid lines. Therefore, these ratios increase with the increasing
narrowness of the peak of the electron distribution function. The
highest ratios are achieved for the distribution formed in double
layers, while the moving Maxwellian distribution is less likely to
reproduce the observed enhancement of Si xiid intensities. However,
the ratio of the allowed Si xiv λ5.22/Si xiii λ5.68 transitions
depends on the ionization equilibrium. This ratio is very small for the
double-layer distribution. Combination of the double-layer distribution
with a Maxwellian distribution with the same mean energy significantly
enhances this ratio, while keeping the Si xiid intensities sufficiently
increased to explain the characteristics of the observed spectra. Conclusions: These results support the presence of double layers
in the plasma during impulsive phase of solar flares.

---------------------------------------------------------
Title: Radio fiber bursts and fast magnetoacoustic wave trains
Authors: Karlický, M.; Mészárosová, H.; Jelínek, P.
2013A&A...550A...1K Altcode: 2012arXiv1212.2421K
 Aims: We present a model for dm-fiber bursts that is based on
assuming fast sausage magnetoacoustic wave trains that propagate along
a dense vertical filament or current sheet. Methods: Eight groups
of dm-fiber bursts that were observed during solar flares were selected
and analyzed by the wavelet analysis method. To model these fiber
bursts we built a semi-empirical model. We also did magnetohydrodynamic
simulations of a propagation of the magnetoacoustic wave train in a
vertical and gravitationally stratified current sheet. Results:
In the wavelet spectra of the fiber bursts computed at different radio
frequencies we found the wavelet tadpoles, whose head maxima have the
same frequency drift as the drift of fiber bursts. It indicates that
the drift of these fiber bursts can be explained by the propagating
fast sausage magnetoacoustic wave train. Using new semi-empirical
and magnetohydrodynamic models with a simple radio emission model we
generated the artificial radio spectra of the fiber bursts, which are
similar to the observed ones.

---------------------------------------------------------
Title: Fragmented Reconnection and Narrowband Decimetric Spikes
Authors: Karlický, M.; Bárta, M.; Jiřička, K.
2013CEAB...37..521K Altcode:
Using numerical simulations, the fragmented reconnection process is
described. It is shown that during this reconnection process plasmoids
in a broad range of spatial scales are generated and form a cascade of
interacting plasmoids. These interactions then produce electromagnetic
waves. It is proposed that the observed narrowband dm-spikes are radio
signatures of these processes. Some properties of these cascades of
plasmoids are derived. Finally, it is discussed how these processes
can generate the above-the-loop-top hard X-ray sources as well as the
hard X-ray emission at footpoints of flare magnetic ropes.

---------------------------------------------------------
Title: Simulations of HXR Foot-point Source Sizes for Modified
Thick-target Models
Authors: Moravec, Z.; Varady, M.; Karlický, M.; Kašparová, J.
2013CEAB...37..535M Altcode:
We study vertical sizes of foot-point hard X-ray (HXR) sources using a
relativistic test particle approach in a flare loop with a converging
magnetic field. We compare results for the Collisional Thick Target
Model (CTTM) with recently proposed modifications of the CTTM comprising
a secondary acceleration of beam electrons. Our preliminary results
indicate that none of the proposed modifications of the CTTM can explain
the observed sizes of the HXR sources in a single loop flare scenario.

---------------------------------------------------------
Title: Observing the Sun with ALMA
Authors: Benz, A. O.; Brajsa, R.; Shimojo, M.; Karlicky, M.; Testi, L.
2012IAUSS...6E.205B Altcode:
The Atacama Large Millimeter Array (ALMA) is in the commissioning
phase for solar observations. A filter reduces the solar radiation
to a level suitable for solar observations. First observations
with one antenna have mapped the Sun by scanning. The results look
promising. The image of the quiet chromosphere shows large spatial
variations in emissivity. Interferometry is much more demanding and
not yet achieved. The current state and problems will be summarized. It
is clear that solar ALMA observations will take more developing time,
but will eventually be possible. The goal is subarcsecond resolution
of the quiet and active submillimeter continuum radiation originating
in the chromosphere and possibly in the flaring corona. A limiting
factor will be the temporal variability of the solar emission.

---------------------------------------------------------
Title: Magnetoacoustic waves in a vertical flare current-sheet in
a gravitationally stratified solar atmosphere
Authors: Jelínek, P.; Karlický, M.; Murawski, K.
2012A&A...546A..49J Altcode:
 Aims: We numerically studied evolution of impulsively
generated magnetoacoustic waves in the vertical flare current-sheet
that is embedded in the gravitationally stratified solar atmosphere
and compared it with its gravity-free counterpart. Methods:
We adopted a two-dimensional (2D) magnetohydrodynamic (MHD) model,
in which we solved a full set of ideal time-dependent MHD equations
by means of the FLASH code, using the adaptive mesh refinement (AMR)
method. To initiate the fast sausage magnetoacoustic waves, we used
axisymmetric Gaussian velocity perturbation. As a diagnostic tool of
these magnetoacoustic waves, we used the wavelet analysis method. 
Results: We present a model of magnetoacoustic wave propagation with
a gravity that is more realistic than that presented in previous
studies. We compare our results with those of a gravity-free
case. In equilibrium the current-sheet with gravity requires a
non-zero horizontal component of the magnetic field, contrary to
the gravity-free case. This causes differences in the parameters of
the wave signal that propagates along the current sheet. In addition
to these differences we find that wave signal variations and their
wavelet tadpoles are more complex in the case with gravity than in the
gravity-free case. Furthermore, for a shorter scale-height we found
a prolongation of the wavelet tadpoles. These differences result from
a variation of the dispersive properties and group velocities of the
propagating magnetoacoustic waves with height in the solar atmosphere
in the gravitational case. We show that these results can affect the
diagnostics of physical processes in solar flares.

---------------------------------------------------------
Title: Formation of Balmer Lines in Impulsively Heated Flare
Atmosphere by Neutral Beams
Authors: Varady, M.; Kašparová, J.; Moravec, Z.; Karlický, M.;
Heinzel, P.
2012ASPC..454..341V Altcode:
In the context of interpreting non-thermal hard X-ray emission and γ
lines emanating from the footpoints of flare loops, most contemporary
flare models assign a fundamental role during the flare energy release,
transport and deposition to the high energy non-thermal particle
beams. In this contribution we concentrate on modelling of the
spectroscopic properties of chromospheric flare emission in optical
hydrogen lines generated due to the bombardment of the chromosphere
and photosphere by neutral beams with power-law spectra. In order
to obtain an estimate of the neutral beam flare heating in the solar
atmosphere we produced a simple model describing the propagation and
thermalisation of neutral beams. We compare the neutral beam flare
heating with the flare heating produced by corresponding pure electron
and proton beams. Further we compare the contribution functions for
Hα line obtained for neutral and electron beam heating.

---------------------------------------------------------
Title: Electron acceleration during three-dimensional relaxation of
an electron beam-return current plasma system in a magnetic field
Authors: Karlický, M.; Kontar, E. P.
2012A&A...544A.148K Altcode: 2012arXiv1207.6248K
 Aims: We investigate the effects of acceleration during
non-linear electron-beam relaxation in magnetized plasma in the case of
electron transport in solar flares. Methods: The evolution of
electron distribution functions is computed using a three-dimensional
particle-in-cell electromagnetic code. Analytical estimations under
simplified assumptions are made to provide comparisons. Results:
We show that, during the non-linear evolution of the beam-plasma system,
the accelerated electron population appears. We found that, although
the electron beam loses its energy efficiently to the thermal plasma,
a noticeable part of the electron population is accelerated. For
model cases with initially monoenergetic beams in uniform plasma, we
found that the amount of energy in the accelerated electrons above the
injected beam-electron energy varies depending the plasma conditions and
could be around 10-30% of the initial beam energy. Conclusions:
This type of acceleration could be important for the interpretation
of non-thermal electron populations in solar flares. Its neglect could
lead to the over-estimation of accelerated electron numbers. The results
emphasize that collective plasma effects should not be treated simply
as an additional energy-loss mechanism, when hard X-ray emission in
solar flares is interpreted, notably in the case of RHESSI data.

---------------------------------------------------------
Title: Radio Diagnostics of Plasmoids in a Flare Current Sheet
Authors: Karlický, M.; Bárta, M.
2012ASPC..454..287K Altcode:
Examples of the drifting pulsating structures observed in solar
dm-radio spectra are presented. Their relationship to plasmoids in a
flare current sheet, and to their motions is explained. Then effects of
the plasmoids, especially those moving downwards and interacting with
an underlying flare-loop arcade, on a formation of flare ribbons are
shown. Finally, using a 2.5-D particle-in-cell modelling we present
the spectrum of the electromagnetic (radio) emission generated during
a coalescence of the plasmoids.

---------------------------------------------------------
Title: Processes of fragmentation cascade in large-scale magnetic
reconnection
Authors: Bárta, Miroslav; Büchner, Jörg; Karlicky, Marian
2012cosp...39..101B Altcode: 2012cosp.meet..101B
Magnetic field reconnection is now generally accepted as the key
mechanism for energy release in solar flares and other eruptive events
in astrophysical and space plasmas. However, direct application of
magnetic-reconnection theory to the physics of solar flares (and other
large-scale events) faces a crucial issue for a long time: All known
micro-physical processes leading to the change of magnetic field
topology (i.e. the reconnection) require very thin current sheets
(~1 m in the solar corona). On the other hand, the typical flare
current-layer width, estimated either from observations or from the
dimensional considerations, is about six orders of magnitude larger. It
is thus clear that some mechanisms of consecutive fragmentation of
the current density (and corresponding magnetic field) structure have
to play a role. In this contribution we aim at identifying all such
possible processes and studying some of them in more detail. In order
to cover a large range of scales we use high-resolution MHD simulations
combined with larger-scale kinetic (PIC) modelling. Our recent research
has shown that the cascade towards small scales is the result of mutual
positive feedback between the Lorentz-force driven instabilities
(such as tearing and the fragmenting coalescence), and their flow-
and pressure-field driven counterparts (typically Kelvin-Helmholtz
and ballooning instabilities).

---------------------------------------------------------
Title: Plasmoids in solar flares and their radio and X-ray diagnostics
Authors: Karlicky, Marian; Bárta, Miroslav
2012cosp...39..883K Altcode: 2012cosp.meet..883K
After introduction about a role of plasmoids in solar flare
reconnection, a concept of the successive merging of plasmoids and
fragmentation in the current sheet in the standard flare model is
presented. Using a 2.5-D electromagnetic particle-in-cell model these
processes are simulated. We recognized a formation of plasmoids and
their mutual interactions. During these interactions the electrons are
very effectively accelerated and heated. We recognized a fragmentation
in the current sheet formed between two merging plasmoids. We found
that this fragmentation is due to the tearing-mode instability
in this current sheet as well as by plasma flows and vortices. It
is shown that simultaneously the electromagnetic (radio) emission
is produced. Relevant X-ray, radio and H-alpha signatures of these
processes as e.g. the above-the-loop-top hard X-ray sources, merging of
X-ray source with the loop-top kernel, drifting pulsating structures,
narrowband dm-spikes, H-alpha ribbon motions are discussed.

---------------------------------------------------------
Title: Singularity spectra of decimetric solar bursts: The role of
higher spatial resolution observations
Authors: Rosa, Reinaldo; Karlicky, Marian; Sawant, Hanumant; Alves
Bolzan, Maur&ício José; Fernandes, Francisco
2012cosp...39.1624R Altcode: 2012cosp.meet.1624R
No abstract at ADS

---------------------------------------------------------
Title: The ALMA Regional Centre in the Czech Republic and the ALMA
Winter School in Prague
Authors: Dabrowski, B.; Karlický, M.
2012Msngr.148...47D Altcode:
The scope of the work of the Atacama Large Millimeter/submillimeter
Array (ALMA) Regional Centre in the Czech Republic is briefly outlined
and a short report is presented on the recent Winter School held
in Prague.

---------------------------------------------------------
Title: Fragmentation during merging of plasmoids in the magnetic
field reconnection
Authors: Karlický, M.; Bárta, M.; Nickeler, D.
2012A&A...541A..86K Altcode:
Context. Application of the magnetic-reconnection theory onto
large-scale events, such as solar flares, requires formation of very
thin (kinetic-scale) current sheets within the rather thick flare
current layer. Hence, some fragmentation/filamentation mechanisms
has to be in action. Aims: We aim at identifying fragmentation
mechanisms for magnetic field and current density structures. Namely,
we focus at detailed study of the processes during the merging
of plasmoids that had been formed in the current layer. 
Methods: A 2.5-D electromagnetic particle-in-cell model is used and
its results analysed. Results: It is shown that the merging
process of plasmoids is not a simple process as presented in some
previous studies. On the contrary, this process leads to a complex
fragmentation. We found two types of fragmentation processes: a)
fragmentation in the current sheet generated between the merging
plasmoids and b) fragmentation at the boundary of plasma outflow
from the reconnection between these plasmoids. While the first type of
fragmentation is generated by the tearing-mode (plasmoid) instability of
the secondary current sheet, the second one looks to be connected with
an increase of the plasma β parameter during these processes. Thus,
sheared high-β plasma flows produce this additional fragmentation. Conclusions: The fragmentation and energy transport from large
to small scales in a large-scale magnetic reconnection seem to be
the result of interplay and positive feedback between instabilities
driven by high gradients in both magnetic (intense current density)
and velocity (high vorticity) fields.

---------------------------------------------------------
Title: X-ray and EUV Filter Responses for Nonthermal κ-Distributions
Authors: Dzifčáková, E.; Dudík, J.; Karlický, M.
2012ASPC..456..135D Altcode:
We calculate the XRT and AIA filter responses to emission for
nonthermal electron kappa-distributions. The filter responses are in
general wider and shifted to higher temperatures. This can affect
temperature diagnostic during flares. We analyze the effect of
nonthermal kappa-distributions on the resulting forward models of AR
emission and show that their influence is small except for the extreme
nonthermal cases.

---------------------------------------------------------
Title: Influence of Static and Stochastic Electric Fields on Electron
Beams Bombarding the Chromosphere
Authors: Varady, M.; Karlický, M.; Moravec, Z.; Kašparová, J.
2012ASPC..456..203V Altcode:
Using a relativistic test-particle code we study and compare the
influence of static and stochastic electric fields on propagation
of electron beams along the magnetic fieldlines through the solar
atmosphere given by the VAL C model from the primary acceleration site
in the corona downwards to the chromosphere. The results are compared
with the most common, classical model of electron beam propagation,
scattering and thermalisation given by Emslie (1978). The effects
of the fields on the chromospheric heating and hard X-ray emission
are discussed.

---------------------------------------------------------
Title: The n-distribution of Electrons and Double Layers in the
Electron-beam-Return-current System of Solar Flares
Authors: Karlický, Marian
2012ApJ...750...49K Altcode:
We investigate processes in the electron-beam-return-current system
in the impulsive phase of solar flares to answer a question about the
formation of the n-electron distribution detected in this phase of solar
flares. An evolution of the electron-beam-return-current system with an
initial local density depression is studied using a three-dimensional
electromagnetic particle-in-cell model. In the system the strong double
layer is formed. Its electric field potential increases with the
electron beam flux. In this electric field potential, the electrons
of background plasma are strongly accelerated and propagate in the
return-current direction. The high-energy part of their distribution
at the high-potential side of the strong double layer resembles that
of the n-distribution. Thus, the detection of the n-distributions,
where a form of the high-energy part of the distribution is the most
important, can indicate the presence of strong double layers in solar
flares. The similarity between processes in solar flare loops and
those in the downward current region of the terrestrial aurora, where
the double layers were observed by FAST satellite, supports this idea.

---------------------------------------------------------
Title: The non-Maxwellian continuum in the X-ray, UV, and radio range
Authors: Dudík, J.; Kašparová, J.; Dzifčáková, E.; Karlický,
M.; Mackovjak, Š.
2012A&A...539A.107D Altcode:
 Aims: We investigate the X-ray, UV, and also the radio
continuum arising from plasmas with a non-Maxwellian distribution of
electron energies. The two investigated types of distributions are
the κ- and n-distributions. Methods: We derived analytical
expressions for the non-Maxwellian bremsstrahlung and free-bound
continuum spectra. The spectra were calculated using available
cross-sections. Then we compared the bremsstrahlung spectra arising from
the different bremsstrahlung cross-sections that are routinely used
in solar physics. Results: The behavior of the bremsstrahlung
spectra for the non-Maxwellian distributions is highly dependent
on the assumed type of the distribution. At flare temperatures and
hard X-ray energies, the bremsstrahlung is greatly increased for
κ-distributions and exhibits a strong high-energy tail. With decreasing
κ, the maximum of the bremsstrahlung spectrum decreases and moves
to higher wavelengths. In contrast, the maximum of the spectra for
n-distributions increases with increasing n, and the spectrum then
falls off very steeply with decreasing wavelength. In the millimeter
radio range, the non-Maxwellian bremsstrahlung spectra are almost
parallel to the thermal bremsstrahlung. Therefore, the non-Maxwellian
distributions cannot be detected by off-limb observations made by the
ALMA instrument. The free-bound continua are also highly dependent
on the assumed type of the distribution. For n-distributions, the
ionization edges disappear and a smooth continuum spectrum is formed
for n ≧ 5. Opposite behavior occurs for κ-distributions where
the ionization edges are in general significantly enhanced, with
details depending on κ and T through the ionization equilibrium. We
investigated how the non-Maxwellian κ-distributions can be
determined from the observations of the continuum and conclude that
one can sample the low-energy part of the distribution from the
continuum. Appendix A is available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: On the physical meaning of n-distributions in solar flares
Authors: Karlický, M.; Dzifčáková, E.; Dudík, J.
2012A&A...537A..36K Altcode:
 Aims: We investigate the physical meaning of the n-distributions
detected in solar flares. Methods: We consider a Maxwellian
velocity distribution with a velocity drift. This distribution is
analytically integrated to obtain the energy distribution, and its
stability is investigated numerically using a fully electromagnetic
particle-in-cell code. Results: It is shown that the
derived moving Maxwellian energy distribution is very similar to
the n-distribution, especially in their high-energy parts. Both
these distributions are mutually fitted and a relation between their
parameters found. Contrary to the n-distribution, the moving Maxwellian
distribution has a simple physical meaning, e.g., the electron component
of the return current in the beam-plasma system. However, for high drift
velocities of such a component, the moving Maxwellian distribution is
unstable. Therefore to keep the form of this distribution similar to
the n-distribution, some stabilization processes are necessary. If so,
then the high intensities of the Si xiid 5.56 Å and 5.82 Å satellite
lines and their evolution in solar flares can be explained by moving
Maxwellian distributions instead of the n-distributions. Thus, our
previous results connected with the n-distributions can be understood
in a new, physically profound way.

---------------------------------------------------------
Title: Magnetoacoustic waves in diagnostics of the flare current
sheets
Authors: Jelínek, P.; Karlický, M.
2012A&A...537A..46J Altcode:
 Aims: To obtain diagnostics tools for solar flare current sheets,
we numerically studied impulsively generated magnetoacoustic waves
in the Harris current sheet. Methods: We used two-dimensional
(2-D) magnetohydrodynamic (MHD) and wave dispersion models. Tests
of these models were performed for waves in the density slab, where
analytical solutions are known. In the MHD model, we solved the
full set of ideal MHD equations by means of the modified two-step
Lax-Wendroff algorithm. The initial perturbation was chosen to
generate preferentially the fast sausage magnetoacoustic waves. To
determine the dispersion characteristics of MHD waves in the Harris
current sheet, we numerically solved the equation of plasma motions
by means of the Runge-Kutta fourth order method together with the
bisection iteration one. To establish some diagnostics of these waves
and their corresponding flare current sheets, we used the wavelet
analysis method. Results: We find that the results of tests
of our 2-D MHD and wave dispersion models for the density slab are in
good agreement with analytical results. We analyze the magnetoacoustic
waves in the current sheet and compare them with those in the density
slab. In both cases, for similar geometrical and plasma parameters,
we find that wave trains were generated and propagated in a similar
way. Their signals registered at selected locations of the Harris
current sheet and density slab are also similar. Nevertheless, a
dependence of the period of the magnetoacoustic waves on the width of
the Harris current sheet differs from that for the density slab. The
form of the wave front inside the current sheet similarly differs
from that in the density slab. We find that the wavelet spectra of
the signals of incoming magnetoacoustic waves at selected locations
in the current sheet have the form of wavelet tadpoles. We distinguish
that the form of these wavelet tadpoles becomes longer and the heads of
the wavelet tadpoles are detected later in time as the distance of the
detection point from that of the initial wave perturbation increases. We
also find that the wavelet tadpole period depends on the plasma beta
parameter. The results are discussed from the point of view of their
use as diagnostics of the flare current sheets or flare loops.

---------------------------------------------------------
Title: Millisecond Radio Spikes in the Decimetric Band
Authors: Dąbrowski, B. P.; Rudawy, P.; Karlický, M.
2012esrs.book...71D Altcode:
We present the results of the analysis of thirteen events consisting
of dm-spikes observed in Toruń between 15 March 2000 and 30 October
2001. The events were obtained with a very high time resolution (80
microseconds) radio spectrograph in the 1352 - 1490 MHz range. These
data were complemented with observations from the radio spectrograph
at Ondřejov in the 0.8 - 2.0 GHz band. We evaluated the basic
characteristics of the individual spikes (duration, spectral width, and
frequency drifts), as well as their groups and chains, the location of
their emission sources, and the temporal correlations of the emissions
with various phases of the associated solar flares. We found that
the mean duration and spectral width of the radio spikes are equal
to 0.036 s and 9.96 MHz, respectively. Distributions of the duration
and spectral widths of the spikes have positive skewness for all
investigated events. Each spike shows positive or negative frequency
drift. The mean negative and positive drifts of the investigated spikes
are equal to -776 MHz s-1 and 1608 MHz s-1,
respectively. The emission sources of the dm-spikes are located mainly
at disk center. We have noticed two kinds of chains, with and without
frequency drifts. The mean durations of the chains vary between 0.067
s and 0.509 s, while their spectral widths vary between 7.2 MHz and
17.25 MHz. The mean duration of an individual spike observed in a
chain was equal to 0.03 s. While we found some agreement between
the global characteristics of the groups of spikes recorded with the
two instruments located in Toruń and Ondřejov, we did not find any
one-to-one relation between individual spikes.

---------------------------------------------------------
Title: Magnetoacoustic Wave Trains in the 11 July 2005 Radio Event
with Fiber Bursts
Authors: Mészárosová, H.; Karlický, M.; Rybák, J.
2012esrs.book...87M Altcode:
A dm-radio emission with fiber bursts observed on 11 July 2005 was
analyzed using wavelet filtration and spectral methods. In filtered
radio spectra we found structures with different characteristic
period P and frequency drift FD: i) fiber substructures (composed
of dot emissions) with P 1≈ 0.5 s, FD1=-
87 MHz s-1 on average, ii) fiber structures with
P 2≈1.9 s, and iii) drifting structures with P
3≈81.4 s, FD2=- 8.7, + 98.5, and - 21.8 MHz
s-1. In the wavelet spectra we recognized patterns having
the form of tadpoles. They were detected with the same characteristic
periods P as found for the filtered structures. The frequency
drift of the tadpole heads is found to be equal to the frequency
drift of some groups of fibers for the long-period wavelet tadpoles
(P 3) and to the frequency drift of individual fibers for
the short-period tadpoles (P 2). Considering these wavelet
tadpoles as signatures of propagating magnetoacoustic wave trains,
the results indicate the presence of several wave trains in the fibers'
source. While the long-period wave trains trigger or modulate a whole
group of fibers, the short-period ones look like being connected with
individual fiber bursts. This result supports the model of fibers based
on magnetoacoustic waves. Using a density model of the solar atmosphere
we derived the velocities of the magnetoacoustic waves, 107 and 562 km
s-1, and setting them equal to the Alfvén ones we estimated
the magnetic field in the source of fiber bursts as 10.7 and 47.8 G.

---------------------------------------------------------
Title: Magnetoacoustic Wave Trains in the 11 July 2005 Radio Event
with Fiber Bursts
Authors: Mészárosová, H.; Karlický, M.; Rybák, J.
2011SoPh..273..393M Altcode: 2011SoPh..tmp..128M; 2011SoPh..tmp..183M; 2011SoPh..tmp..252M
A dm-radio emission with fiber bursts observed on 11 July 2005 was
analyzed using wavelet filtration and spectral methods. In filtered
radio spectra we found structures with different characteristic
period P and frequency drift FD: i) fiber substructures (composed
of dot emissions) with P1≈ 0.5 s, FD1=−
87 MHz s−1 on average, ii) fiber structures
with P2≈1.9 s, and iii) drifting structures with
P3≈81.4 s, FD2=− 8.7, + 98.5, and − 21.8 MHz
s−1. In the wavelet spectra we recognized patterns having
the form of tadpoles. They were detected with the same characteristic
periods P as found for the filtered structures. The frequency
drift of the tadpole heads is found to be equal to the frequency
drift of some groups of fibers for the long-period wavelet tadpoles
(P3) and to the frequency drift of individual fibers for
the short-period tadpoles (P2). Considering these wavelet
tadpoles as signatures of propagating magnetoacoustic wave trains,
the results indicate the presence of several wave trains in the fibers'
source. While the long-period wave trains trigger or modulate a whole
group of fibers, the short-period ones look like being connected with
individual fiber bursts. This result supports the model of fibers
based on magnetoacoustic waves. Using a density model of the solar
atmosphere we derived the velocities of the magnetoacoustic waves,
107 and 562 km s−1, and setting them equal to the Alfvén
ones we estimated the magnetic field in the source of fiber bursts as
10.7 and 47.8 G.

---------------------------------------------------------
Title: Millisecond Radio Spikes in the Decimetric Band
Authors: DaÌ§browski, B. P.; Rudawy, P.; Karlický, M.
2011SoPh..273..377D Altcode: 2011SoPh..tmp..162D; 2011SoPh..tmp..231D; 2011SoPh..tmp...85D
We present the results of the analysis of thirteen events consisting
of dm-spikes observed in Toruń between 15 March 2000 and 30 October
2001. The events were obtained with a very high time resolution (80
microseconds) radio spectrograph in the 1352 - 1490 MHz range. These
data were complemented with observations from the radio spectrograph
at Ondřejov in the 0.8 - 2.0 GHz band. We evaluated the basic
characteristics of the individual spikes (duration, spectral width,
and frequency drifts), as well as their groups and chains, the
location of their emission sources, and the temporal correlations of
the emissions with various phases of the associated solar flares. We
found that the mean duration and spectral width of the radio spikes
are equal to 0.036 s and 9.96 MHz, respectively. Distributions of the
duration and spectral widths of the spikes have positive skewness for
all investigated events. Each spike shows positive or negative frequency
drift. The mean negative and positive drifts of the investigated spikes
are equal to −776 MHz s−1 and 1608 MHz s−1,
respectively. The emission sources of the dm-spikes are located mainly
at disk center. We have noticed two kinds of chains, with and without
frequency drifts. The mean durations of the chains vary between 0.067
s and 0.509 s, while their spectral widths vary between 7.2 MHz and
17.25 MHz. The mean duration of an individual spike observed in a
chain was equal to 0.03 s. While we found some agreement between
the global characteristics of the groups of spikes recorded with the
two instruments located in Toruń and Ondřejov, we did not find any
one-to-one relation between individual spikes.

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Title: Diagnostics of non-thermal distributions in solar flare
spectra observed by RESIK and RHESSI
Authors: Kulinová, A.; Kašparová, J.; Dzifčáková, E.; Sylwester,
J.; Sylwester, B.; Karlický, M.
2011A&A...533A..81K Altcode: 2011arXiv1109.1011K
Context. During solar flares an enormous amount of energy is released,
and the charged particles, like electrons, are accelerated. These
non-thermal electrons interact with the plasma in various parts
of solar flares, where the distribution function of electrons can
therefore be non-Maxwellian. Aims: We focus on the non-thermal
components of the electron distribution in the keV range and analyse
high-energy resolution X-ray spectra detected by RESIK and RHESSI for
three solar flares. Methods: In the 2-4 keV range we assume that
the electron distribution can be modelled by an n-distribution. Using
a method of line-intensity ratios, we analyse allowed and satellite
lines of Si observed by RESIK and estimate the parameters of this
n-distribution. At higher energies we explore RHESSI bremsstrahlung
spectra. Adopting a forward-fitting approach and thick-target
approximation, we determine the characteristics of injected electron
beams. Results: RHESSI non-thermal component associated with
the electron beam is correlated well with presence of the non-thermal
n-distribution obtained from the RESIK spectra. In addition, such an
n-distribution occurs during radio bursts observed in the 0.61-15.4
GHz range. Furthermore, we show that the n-distribution could also
explain RHESSI emission below ~5 keV. Therefore, two independent
diagnostics methods indicate the flare plasma being affected by
the electron beam can have a non-thermal component in the ~2-5 keV
range, which is described by the n-distribution well. Finally,
spectral line analysis reveals that the n-distribution does not
occupy the same location as the thermal component detected by RHESSI
at ~10 keV. Appendix A is available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>

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Title: Filament destabilization and CME release during a long
duration flare
Authors: Zuccarello, F.; Contarino, L.; Farnik, F.; Karlicky, M.;
Romano, P.; Ugarte-Urra, I.
2011A&A...533A.100Z Altcode:
Context. During complex and long duration solar flares, several filament
destabilizations or eruptions can occur that are often related to
coronal mass ejections (CMEs). Aims: We describe the study of
an X3.8 long duration event (LDE) that occurred in NOAA 10720 on 17
January 2005 and was characterized by three filament destabilizations
and two CMEs. Methods: Using multi-wavelength data provided
by both ground-based instruments and satellites, in addition to MDI
magnetograms, we investigated the morphological and magnetic evolution
of the active region before and during the LDE. Results: Our
analysis of Hα and 1600 Å images showed that initially a
two-ribbon structure developed in the central part of the active region,
where a filament was previously observed. At a later time, two bright
ribbons (in the most eastern side) and a strong brightness increase
(at the western outskirt of the active region) were simultaneously
observed. In a subsequent time interval, a new pair of ribbons was
observed in the western side of the active region. Moreover, a linear
force-free field extrapolation helped identify a null point in the
central part of the active region. Conclusions: The initial
filament destabilization that occurred in the central part of NOAA
10720 was probably due to magnetic flux emergence and photospheric
shearing motions, which caused a slow tether-cutting process beneath
the filament. The rearrangement of the magnetic field configuration,
occurring in the same area as the location of the null point, changed
the magnetic field connectivity in the active region, triggering two
filament eruptions in the eastern and western part of the active region
and two halo CMEs, in a kind of domino effect.

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Title: Spontaneous Current-layer Fragmentation and Cascading
Reconnection in Solar Flares. I. Model and Analysis
Authors: Bárta, Miroslav; Büchner, Jörg; Karlický, Marian;
Skála, Jan
2011ApJ...737...24B Altcode: 2010arXiv1011.4035B
Magnetic reconnection is commonly considered to be a mechanism of solar
(eruptive) flares. A deeper study of this scenario reveals, however,
a number of open issues. Among them is the fundamental question of how
the magnetic energy is transferred from large, accumulation scales to
plasma scales where its actual dissipation takes place. In order to
investigate this transfer over a broad range of scales, we address this
question by means of a high-resolution MHD simulation. The simulation
results indicate that the magnetic-energy transfer to small scales is
realized via a cascade of consecutively smaller and smaller flux ropes
(plasmoids), analogous to the vortex-tube cascade in (incompressible)
fluid dynamics. Both tearing and (driven) "fragmenting coalescence"
processes are equally important for the consecutive fragmentation
of the magnetic field (and associated current density) into smaller
elements. At the later stages, a dynamic balance between tearing and
coalescence processes reveals a steady (power-law) scaling typical
of cascading processes. It is shown that cascading reconnection
also addresses other open issues in solar-flare research, such as
the duality between the regular large-scale picture of (eruptive)
flares and the observed signatures of fragmented (chaotic) energy
release, as well as the huge number of accelerated particles. Indeed,
spontaneous current-layer fragmentation and the formation of multiple
channelized dissipative/acceleration regions embedded in the current
layer appear to be intrinsic to the cascading process. The multiple
small-scale current sheets may also facilitate the acceleration of a
large number of particles. The structure, distribution, and dynamics
of the embedded potential acceleration regions in a current layer
fragmented by cascading reconnection are studied and discussed.

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Title: Electron acceleration in a wavy shock front
Authors: Vandas, M.; Karlický, M.
2011A&A...531A..55V Altcode:
Context. It is known that electrons are accelerated at nearly
perpendicular shocks by the drift mechanism. And it is also known
that energy gain of electrons caused by this mechanism is not very
high. Therefore it was suggested in the past that the energy gain
might be increased if shocks had wavy fronts. For instance, there were
attempts to explain coronal type II burst and their fine structure by
electron acceleration in a wavy shock front. Aims: We studied
electron acceleration numerically at nearly perpendicular wavy shocks
for coronal conditions and compared it with analytical results on
electron acceleration at nearly perpendicular plane shocks. Methods: An analytical model of a wavy shock front was used
and trajectories of electrons in it and around it were calculated
numerically in a guiding centre approximation. Results: We found
that energy gains of electrons at a wavy shock front and a corresponding
smoothed-into-plane shock on the average were comparable. That is why
they do not depend significantly on the shock thickness, magnetic field
profile inside the shock, and shock wavy form. They do depend on the
angle between the smoothed shock front and ambient magnetic field. Conclusions: On average, a wavy shock front does not significantly
increase an acceleration efficiency. Energy gain remarkably exceeds an
average level for some combinations of initial parameters. Distribution
functions of accelerated electrons have a patchy structure, which
is prone to inducing plasma instabilities that will generate plasma
waves. This may have relevance to the problem of type II burst origin.

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Title: Is it possible to model observed active region coronal emission
simultaneously in EUV and X-ray filters?
Authors: Dudík, J.; Dzifčáková, E.; Karlický, M.; Kulinová, A.
2011A&A...531A.115D Altcode:
 Aims: We investigate the possibility of modeling the active
region coronal emission in the EUV and X-ray filters using one,
universal, steady heating function, tied to the properties of the
magnetic field. Methods: We employ a simple, static model to
compute the temperature and density distributions in the active region
corona. The model allows us to explore a wide range of parameters
of the heating function. The predicted EUV and X-ray emission in the
filters of EIT/SOHO and XRT/Hinode are calculated and compared with
observations. Using the combined improved filter-ratio (CIFR) method,
a temperature diagnostic is employed to compare the modeled temperature
structure of the active region with the temperature structure derived
from the observations. Results: The global properties of the
observations are most closely matched for heating functions scaling
as B_00.7-0.8/L_0^{0.5} that depend on the spatially
variable heating scale-length. The modeled X-ray emission originates
from locations where large heating scale-lengths are found. However,
the majority of the loops observed in the 171 and 195 filters can be
modeled only by loops with very short heating scale-lengths. These loops
are known to be thermally unstable. We are unable to find a model that
both matches the observations in all EUV and X-ray filters, and contains
only stable loops. As a result, although our model with a steady heating
function can explain some of the emission properties of the 171 and 195
loops, it cannot explain their observed lifetimes. Thus, the model does
not lead to a self-consistent solution. The performance of the CIFR
method is evaluated and we find that the diagnosed temperature can be
approximated with a geometric mean of the emission-measure weighted
and maximum temperature along the line of sight. Conclusions:
We conclude that if one universal heating function exists, it should
be at least partially time-dependent.

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Title: Fluctuation analysis of solar radio bursts associated with
geoeffective X-class flares
Authors: Veronese, T. B.; Rosa, R. R.; Bolzan, M. J. A.; Rocha
Fernandes, F. C.; Sawant, H. S.; Karlicky`, M.
2011JASTP..73.1311V Altcode:
High temporal resolution solar observations in the decimetric range (1-3
GHz) can provide additional information on solar active regions dynamics
and thus contribute to better understanding of solar geoeffective events
as flares and coronal mass ejections. The June 6, 2000 flares are a set
of remarkable geoeffective eruptive phenomena observed as solar radio
bursts (SRB) by means of the 3 GHz Ondrejov Observatory radiometer. We
have selected and analyzed, applying detrended fluctuation analysis
(DFA), three decimetric bursts associated to X1.1, X1.2 and X2.3
flare-classes, respectively. The association with geomagnetic activity
is also reported. DFA method is performed in the framework of a radio
burst automatic monitoring system. Our results may characterize the
SRB evolution, computing the DFA scaling exponent, scanning the SRB
time series by a short windowing before the extreme event. For the
first time, the importance of DFA in the context of SRB monitoring
analysis is presented.

---------------------------------------------------------
Title: Electron acceleration by a wavy shock front: details on
angular distribution
Authors: Vandas, Marek; Karlický, Marian
2011IAUS..274..201V Altcode:
We studied numerically electron acceleration by a perpendicular
wavy shock. Distribution function of accelerated electrons is
highly anisotropic, with many sharp peaks. The peaks are caused by
(usually single) reflections of electrons by the shock and subsequent
transmission.

---------------------------------------------------------
Title: ALMA and solar research
Authors: Karlický, Marian; Bárta, Miroslav
2011IAUS..274..284K Altcode:
The ALMA (Atacama Large Millimeter/sub-millimeter Array) is the large
interferometer that will consist up to 64 high-precision antennas
operating in the 31.3 - 950 GHz frequency range. In this range unique
observations in cosmology, cold universe, galaxies, stars and their
formations, and so on are expected. Among these objectives there is
a unique possibility to observe the Sun and to address outstanding
issues of solar physics. The ALMA is shortly described and then the
new ESO-ALMA European node (ARC) built at Ondřejov Observatory is
presented. The new ARC is the only one in Europe oriented to solar
physics. The requirements and limitations for ALMA solar observations,
as well as some examples of possible solar-oriented ALMA projects,
are mentioned.

---------------------------------------------------------
Title: Electromagnetic emission by subsequent processes L-&gt;L'+S
and L+L'-&gt;T
Authors: Karlický, Marian; Bárta, Miroslav
2011IAUS..274..252K Altcode:
Using a 2.5-D electromagnetic particle-in-cell (PIC) model, very
early stages of a generation of the electromagnetic emission produced
by a monochromatic Langmuir wave are studied. It is found that the
electromagnetic emission, which is dominant on the harmonic of the
plasma frequency, starts to be generated in a very small region of
k-vectors. Later on the k-vectors of this emission are scattered
around a `circle' (in our 2-D case), given by the relations for the
L+L'-&gt;T process. Analytical analysis of two subsequent processes
L-&gt;L'+S a L+L'-&gt;T confirms these results.

---------------------------------------------------------
Title: Separation of solar radio bursts in a complex spectrum
Authors: Mészárosová, Hana; Rybák, Ján; Karlický, Marian;
Jiřička, Karel
2011IAUS..274..150M Altcode:
Radio spectra, observed during solar flares, are usually very complex
(many bursts and fine structures). We have developed a new method to
separate them into individual bursts and analyze them separately. The
method is used in the analysis of the 0.8-2.0 GHz radio spectrum of the
April 11, 2001 event, which was rich in drifting pulsating structures
(DPSs). Using this method we showed that the complex radio spectrum
consists of at least four DPSs separated with respect to their different
frequency drifts (-115, -36, -23, and -11 MHz s-1). These
DPSs indicate a presence of at least four plasmoids expected to be
formed in a flaring current sheet. These plasmoids produce the radio
emission on close frequencies giving thus a mixture of superimposed
DPSs observed in the radio spectrum.

---------------------------------------------------------
Title: Successive Merging of Plasmoids and Fragmentation in a Flare
Current Sheet and Their X-Ray and Radio Signatures
Authors: Karlický, Marian; Bárta, Miroslav
2011ApJ...733..107K Altcode: 2011arXiv1101.4846K
Based on our recent MHD simulations, a conception of the successive
merging of plasmoids and fragmentation in the current sheet in the
standard flare model is presented. Then, using a 2.5-dimensional
electromagnetic particle-in-cell model with free boundary
conditions, these processes are modeled on the kinetic level
of plasma description. We recognize the plasmoids that mutually
interacted and finally merged into one large plasmoid. Between
interacting plasmoids, additional plasmoids and current sheets on
smaller spatial scales were formed, congruent with the fragmentation
found in MHD simulations. During interactions (merging-coalescences)
between the plasmoids, the electrons were very efficiently accelerated
and heated. We find that after a series of such merging processes, the
electrons in some regions reached the energies necessary for emission in
the hard X-ray range. Considering these energetic electrons and assuming
a plasma density of 109-1010 cm-3 and a
source volume equal to the 2007 December 31 flare, we compute the X-ray
spectra as produced by the bremsstrahlung emission process. Comparing
these spectra with observations, we think that these processes can
explain the observed above-the-loop-top hard X-ray sources. Furthermore,
we show that the process of fragmentation between two merging plasmoids
can generate narrow-band dm-spikes. Formulae for schematic fractal
reconnection structures are derived.

---------------------------------------------------------
Title: Quasi-periodic oscillations in solar X-ray sources
Authors: Mészárosová, Hana; Karlický, Marian; Fárník, František
2011IAUS..274..255M Altcode:
We have searched for quasi-periodic oscillations in the hard X-ray
emission of solar flares. We have selected 14 flare events which
were divided into two groups: a) the events with the X-ray sources
located at the flare loop footpoints and b) the events with the X-ray
source above the solar limb, i.e. with the loop-top X-ray source. We
found that while in the case with the footpoints X-ray sources the
quasi-periods of the recorded oscillations were in the interval 2-380 s,
in the events with loop-top sources only the quasi-periods longer than
50 s were recognized. These results are probably connected with the
MHD oscillation modes of the flaring loop. While the long periods,
which are dominant in loop-top sources, are produced by acoustic
oscillations along the whole long loop, in the layers close to the
loop footpoints also the MHD wave modes in shorter structures with
shorter periods are generated.

---------------------------------------------------------
Title: Magnetoacoustic waves in the narrowband dm-spikes sources
Authors: Karlický, M.; Jelínek, P.; Mészárosová, H.
2011A&A...529A..96K Altcode:
 Aims: A new type of analysis of the narrowband dm-spikes in
solar radio radiation is introduced to look for magnetoacoustic waves
in their sources. Methods: The Fourier and wavelet methods
were used. For the first time, the tadpole structures in the wavelet
spectra of this radio emission were searched for. Results:
Fifteen groups of the narrowband dm-spikes, observed during solar
flares, were selected and analyzed by the Fourier and wavelet analysis
methods. We found that the mean Fourier spectra of these spikes in
frequency space are the powerlaws with a power-law index in the range
-1.2 --1.8. Furthermore, their wavelet spectra based on time series
reveal tadpoles at some frequencies, which indicates the presence
of magnetoacoustic waves. These waves are interpreted as propagating
through a source of the narrowband dm-spikes. It is proposed that the
spikes are generated by driven coalescence and fragmentation processes
in turbulent reconnection outflow. This interpretation is supported
by a simultaneous observation of drifting pulsating structures (DPSs)
and spikes. Finally, modeling of the magnetoacoustic waves and tadpoles
in the Harris current sheet supports this interpretation.

---------------------------------------------------------
Title: The bound-bound and free-free radiative losses for the
nonthermal distributions in solar and stellar coronae
Authors: Dudík, J.; Dzifčáková, E.; Karlický, M.; Kulinová, A.
2011A&A...529A.103D Altcode:
Context. The radiative-loss function is an important ingredient
in the physics of the solar corona, transition region, and
flares. Aims: We investigate the radiative losses due to the
bound-bound transitions and bremsstrahlung for nonthermal κ- and
n-distributions. Methods: The bound-bound radiative losses are
computed by integrating synthetic spectra. An analytical expression is
derived for nonthermal bremsstrahlung. The bremsstrahlung is computed
numerically using accurate values of the free-free Gaunt factor. Results: We find that the changes in radiative-loss functions
due to nonthermal distributions are several times greater than the
errors due to the missing contribution of the free-bound continuum
or errors in atomic data. For κ-distributions, the radiative-loss
functions are in general weaker than for Maxwellian distribution,
with a few exceptions caused by the behavior of Fe. The peaks of the
radiative-loss functions are in general flatter. The situation is
opposite for n-distributions, for which the radiative-loss functions
have higher and narrower peaks. Local minima and maxima of the
radiative-loss functions may also be shifted. The contribution
from bremsstrahlung only changes by a few percent except in the
extreme nonthermal case of κ = 2. Stability analysis reveals that
the X-ray loops are stable against the radiatively-driven thermal
instability. The calculated radiative losses for nonthermal
distributions are available as two electronic tables at the CDS
via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/529/A103">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/529/A103</A>

---------------------------------------------------------
Title: Spontaneous Current-layer Fragmentation and Cascading
Reconnection in Solar Flares. II. Relation to Observations
Authors: Bárta, Miroslav; Büchner, Jörg; Karlický, Marian;
Kotrč, Pavel
2011ApJ...730...47B Altcode: 2010arXiv1011.6069B
In a paper by Bárta et al., the authors addressed by means of
high-resolution MHD simulations some open questions on the CSHKP
scenario of solar flares. In particular, they focused on the problem
of energy transfer from large to small scales in the decaying flare
current sheet (CS). Their calculations suggest that magnetic flux ropes
(plasmoids) are formed in a full range of scales by a cascade of tearing
and coalescence processes. Consequently, the initially thick current
layer becomes highly fragmented. Thus, the tearing and coalescence
cascade can cause an effective energy transfer across the scales. In
this paper, we investigate whether this mechanism actually applies in
solar flares. We extend the MHD simulation by deriving model-specific
features that can be searched for in observations. The results of
the underlying MHD model show that the plasmoid cascade creates a
specific hierarchical distribution of non-ideal/acceleration regions
embedded in the CS. We therefore focus on the features associated with
the fluxes of energetic particles, in particular on the structure
and dynamics of emission regions in flare ribbons. We assume that
the structure and dynamics of diffusion regions embedded in the CS
imprint themselves into the structure and dynamics of flare-ribbon
kernels by means of magnetic field mapping. Using the results of the
underlying MHD simulation, we derive the expected structure of ribbon
emission and extract selected statistical properties of the modeled
bright kernels. Comparing the predicted emission and its properties
with the observed ones, we obtain a good agreement between the two.

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Title: Radio Evidence of Break-out Reconnection?
Authors: Aurass, H.; Mann, G.; Zlobec, P.; Karlický, M.
2011ApJ...730...57A Altcode:
We reconsider the 2003 October 28 X17 flare/coronal mass ejection (CME),
studying the five minutes immediately before the impulsive flare phase
(not discussed in previous work). To this aim we examine complementary
dynamic radio spectrograms, single frequency polarimeter records, radio
images, space-based longitudinal field magnetograms, and ultraviolet
images. We find widely distributed faint and narrowband meter wave
radio sources located outside active regions but associated with
the boundaries of magnetic flux connectivity cells, inferred from the
potential extrapolation of the observed photospheric longitudinal field
as a model for coronal magnetic field structures. The meter wave radio
sources occur during the initial decimeter wave effects, which are well
known to be associated with filament destabilization in the flaring
active region (here NOAA 10486). Antiochos et al. predict in their
break-out model for CME initiation that "... huge phenomena ... may
be controlled by detailed plasma processes that occur in relatively
tiny regions." They suggest that the expected faint energy release
"... on long field lines far away from any neutral line ... may be
detectable in radio/microwave emission from nonthermal particles..." In
this paper, we describe meter wave sources whose properties correctly
coincide with the quoted predictions of the break-out reconnection
model of the CME initiation.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Radiative losses in solar and
stellar coronae (Dudik+, 2011)
Authors: Dudik, J.; Dzifcakova, E.; Karlicky, M.; Kulinova, A.
2011yCat..35290103D Altcode: 2011yCat..35299103D
The radiative losses due to bound-bound and free-free transitions
calculated for plasma with nonthermal {kappa}- and n-distributions of
electron energies are presented. The radiative losses are calculated
for the values of {kappa}=2, 3, 5, and 10 (rloss_k.dat) and n=1
(Maxwellian), 3, 5, and 11 (rloss_n.dat) as function of temperature (T)
or pseudo-temperature (tau) for the assumed value of electron density
ne=1016m-3. The ne*nH
factor is not included in the calculations. (2 data files).

---------------------------------------------------------
Title: Separation of drifting pulsating structures in a complex
radio spectrum of the 2001 April 11 event
Authors: Mészárosová, H.; Rybák, J.; Karlický, M.
2011A&A...525A..88M Altcode:
 Aims: We present new method of separating a complex radio
spectrum into single radio bursts. The method is used in the analysis
of the 0.8-2.0 GHz radio spectrum of the 2001 April 11 event, which
was rich in drifting pulsating structures. Methods: The method
is based on the wavelet analysis technique, which separates different
spatial-temporal components (radio bursts) that are difficult to
recognize in the original radio spectrum. Results: We show with
this method that the complex radio spectrum observed during the 2001
April 11 event consists of at least four drifting pulsating structures
(DPSs). These structures were separated with respect to their different
frequency drifts. The DPSs indicate at least four plasmoids that are
supposed to be formed in a flaring current sheet.

---------------------------------------------------------
Title: Solar Research with ALMA
Authors: Karlický, M.; Bárta, M.; DaÌ§browski, B. P.; Heinzel, P.
2011SoPh..268..165K Altcode: 2010SoPh..tmp..231K; 2010SoPh..tmp..207K
The Atacama Large Millimeter/sub-millimeter Array (ALMA) is a large
interferometer that will consist up to 64 high-precision antennas
operating in the 31.3 - 950 GHz frequency range. In this frequency
range, which is largely unexplored, unique observations with a broad
range of scientific objectives (cosmology, cold universe, galaxies,
stars and their formation, planets and so on) are expected. Among
these tasks there is a unique possibility to observe the Sun and to
address several outstanding issues of solar physics. First, the ALMA
is briefly described and then the new ESO-ALMA European node (ARC),
built at Ondřejov Observatory, is presented. In Europe, this ARC is
the only one oriented to solar physics. Consequently, the requirements
and limitations for ALMA solar observations, as well as some examples
of possible solar-oriented ALMA projects, are shown. A procedure of
the preparation and submission of proposals for ALMA observations
is mentioned.

---------------------------------------------------------
Title: Fine structures of radio bursts observed during the February
12, 2010 flare
Authors: Jiřička, K.; Karlický, M.
2011CEAB...35..215J Altcode:
Using the newly reconstructed Ondřejov radio spectrograph the radio
emission of the February 12, 2010 flare was studied in details. The
high-time resolution of the spectrograph (10 ms) reveals several
interesting fine structures in (a) type III burst, (b) reverse drift
burst and (c) drifting pulsating structures. Furthermore, an unique
type of short-lasting and narrowband spikes was recognized. These
fine structures give a more detailed information about superthermal
electrons producing these bursts and about the electron acceleration.

---------------------------------------------------------
Title: Kappa-distribúcie a ohrev koróny

---------------------------------------------------------
Title: Kappa-distribúcie
a ohrev koróny

---------------------------------------------------------
Title: Kappa-distributions and coronal heating.
Authors: Dudík, J.; Dzifčáková, E.; Kulinová, A.; Karlický, M.
2010nspm.conf..161D Altcode:
Particle energy kappa-distributions (distributions with non-thermal
tails) have been diagnosed in plasma of the transition region and
also in solar flares. Theoretical models suggest a link between
kappa-distributions and dynamic heating of the corona. Since
the presence of non-thermal distributions leads to changes in
intensities of emission lines, we have examined their effect on the
total radiation losses of the corona as well as responses of the EUV
and X-ray filters. Temperature responses of the filters are wider for
kappa-distributions than in the case of the Maxwell distribution, and
their respective maxima are shifted towards higher temperatures. On
the other hand, the total radiation losses of the corona are lower
compared to the Maxwell distribution except for the extreme non-thermal
case. This means that lower heating energy is needed to reach the
same corona temperature in case of kappa-distributions. In this work
we discuss the effect of element abundances and specific ions on the
total radiation losses of the corona.

---------------------------------------------------------
Title: Reconnection of a Kinking Flux Rope Triggering the Ejection
of a Microwave and Hard X-Ray Source II. Numerical Modeling
Authors: Kliem, B.; Linton, M. G.; Török, T.; Karlický, M.
2010SoPh..266...91K Altcode: 2010SoPh..tmp..149K; 2010arXiv1007.2147K
Numerical simulations of the helical (m=1) kink instability of an
arched, line-tied flux rope demonstrate that the helical deformation
enforces reconnection between the legs of the rope if modes with two
helical turns are dominant as a result of high initial twist in the
range Φ≳6π. Such a reconnection is complex, involving also the
ambient field. In addition to breaking up the original rope, it can
form a new, low-lying, less twisted flux rope. The new flux rope is
pushed downward by the reconnection outflow, which typically forces it
to break as well by reconnecting with the ambient field. The top part
of the original rope, largely rooted in the sources of the ambient
flux after the break-up, can fully erupt or be halted at low heights,
producing a "failed eruption." The helical current sheet associated with
the instability is squeezed between the approaching legs, temporarily
forming a double current sheet. The leg - leg reconnection proceeds
at a high rate, producing sufficiently strong electric fields that it
would be able to accelerate particles. It may also form plasmoids, or
plasmoid-like structures, which trap energetic particles and propagate
out of the reconnection region up to the top of the erupting flux rope
along the helical current sheet. The kinking of a highly twisted flux
rope involving leg - leg reconnection can explain key features of an
eruptive but partially occulted solar flare on 18 April 2001, which
ejected a relatively compact hard X-ray and microwave source and was
associated with a fast coronal mass ejection.

---------------------------------------------------------
Title: Reconnection of a Kinking Flux Rope Triggering the Ejection of
a Microwave and Hard X-ray Source I. Observations and Interpretation
Authors: Karlický, M.; Kliem, B.
2010SoPh..266...71K Altcode: 2010arXiv1007.2146K; 2010SoPh..tmp..139K
Imaging microwave observations of an eruptive, partially occulted solar
flare on 18 April 2001 suggest that the global structure of the event
can be described by the helical kink instability of a twisted magnetic
flux rope. This model is suggested by the inverse gamma shape of the
source exhibiting crossing legs of a rising flux loop and by evidence
that the legs interact at or near the crossing point. The interaction is
reflected by the location of peak brightness near the crossing point and
by the formation of superimposed compact nonthermal sources most likely
at or near the crossing point. These sources propagate upward along both
legs, merge into a single, bright source at the top of the structure,
and continue to rise at a velocity &gt;1000 km s−1. The
compact sources trap accelerated electrons which radiate in the radio
and hard X-ray ranges. This suggests that they are plasmoids, although
their internal structure is not revealed by the data. They exhibit
variations of the radio brightness temperature at a characteristic time
scale of ∼ 40 s, anti-correlated to their area, which also support
their interpretation as plasmoids. Their propagation path differs
from the standard scenario of plasmoid formation and propagation in
the flare current sheet, suggesting the helical current sheet formed
by the instability instead.

---------------------------------------------------------
Title: Modeling of Solar Flare Plasma and Its Radiation
Authors: Varady, Michal; Kasparova, Jana; Moravec, Zdeněk; Heinzel,
Petr; Karlicky, Marian
2010ITPS...38.2249V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Tearing, coalescence and fragmentation processes in solar
flare current sheet and drifting pulsating structures
Authors: Karlický, M.
2010AdSpR..46..377K Altcode:
The paper presents a summary of results from two different simulations
which study the tearing, coalescence and fragmentation of current
sheets, the associated production of energetic electrons and of plasma
waves from these electrons which could explain drifting pulsation
structures observed at radio wavelengths. Using a 2.5-D particle-in-cell
(PIC) model of the current sheet it is shown that due to the tearing
mode instability the current sheet tears into plasmoids and these
plasmoids later on coalesce into larger ones. During these processes
electrons are accelerated and they produce observable electromagnetic
waves. Furthermore, the 3-D PIC model with two current sheets extended
in the electric current direction shows their fast fragmentation
associated with the exponential dissipation of the free magnetic
field energy. An example of the drifting pulsating structure which is
considered to be a radio signature of the above mentioned processes
in solar flares is shown.

---------------------------------------------------------
Title: The X3.8 flare in NOAA 10720 : a new example of the domino
effect
Authors: Farnik, Frantisek; Contarino, L.; Romano, P.; Zuccarello,
F.; Karlicky, M.
2010shin.confE..16F Altcode:
We have studied an X3.8 flare occurred in NOAA 10720 on 17 January 2005
using chromospheric and photospheric images acquired at INAF - Catania
Astrophysical Observatory, TRACE images acquired at 1600 ?, full disk
MDI magnetograms, RHESSI hard X-ray data and Ondrejov radio data, in
order to investigate the morphological and magnetic evolution of the
active region before and during the flare. The analysis of H-alpha and
1600 ? images showed that initially a two-ribbon structure developed
in the central part of the active region, later two bright ribbons
(in the most eastern side) and a strong brightness increase (at the
western boundary of the active region) were observed contemporarily. In
the following time interval a new pair of ribbons was observed in
the central-western side of the region. The analysis of the magnetic
configuration and the location of a null point allowed us to single
out the sites where magnetic reconnection processes were most likely
to occur. Based on this result and on the analysis of H-alpha, TRACE,
RHESSI and Ondrejov data, we interpreted this behavior as due to an
initial filament eruption that occurred in the central part of NOAA
10720, where the null point was located, and later on, as in a domino
effect, other filament destabilization or eruption took place in the
eastern and western part of the active region.

---------------------------------------------------------
Title: Relation between the Spatial Distribution and Spectral Index
of Superthermal Electron Distribution in Solar cm-Radio Sources
Authors: Yasnov, L. V.; Karlický, M.
2010SoPh..264...93Y Altcode: 2010SoPh..tmp...90Y
A series of solar cm-radio bursts are analyzed by a new inverse method
estimating spatial changes of the superthermal electron distribution
in solar cm-radio burst sources. It is found that the measure of
the spatial change of superthermal electrons in the radio source
νn is always greater than that for the magnetic field
νB and it is linearly dependent on the spectral index of the
electrons δ as νn≈0.5δ. This relation is explained in
the simplified flare-loop model integrating the analytical solutions
of the Fokker - Planck equation. The mean value of νB
is found to be 0.36±0.04, which is very close to the value of
νB=0.38±0.02 derived from the dependence of the magnetic
field strength on the height in the active region measured by RATAN-600.

---------------------------------------------------------
Title: Radio spectra generated during coalescence processes of
plasmoids in a flare current sheet
Authors: Karlický, M.; Bárta, M.; Rybák, J.
2010A&A...514A..28K Altcode:
 Aims: Motivated by observations of the drifting pulsating
structures (DPSs) in solar radio spectra, we study the electromagnetic
(radio) emission generated during tearing and coalescence processes in a
flare current sheet. Methods: For numerical simulations, we used
a 2.5-D particle-in-cell electromagnetic relativistic code. Numerical
data were analyzed by the wavelet methods. Results: It is found
that the electromagnetic emission is generated during a coalescence of
plasmoids, and it has a quasi-periodic character. Detailed analysis
reveals that the electromagnetic emission is produced around the
interacting plasmoids just before their coalescence into a larger
one. The period in variations of electromagnetic emission corresponds
to that of magnetic field at the same region. Reflections of the
electromagnetic waves between interacting plasmoids are recognized. The
computed and observed periodicities are discussed. The similarity of
the DPSs with some radio bursts observed during star flares indicates
a broader applicability for this model.

---------------------------------------------------------
Title: Subsecond (0.1 s) Pulsations in the 11 April 2001 Radio Event
Authors: Karlický, M.; Zlobec, P.; Mészárosová, H.
2010SoPh..261..281K Altcode: 2010SoPh..tmp....9K
Radio pulsations observed during the 11 April 2001 event at six single
frequencies (237, 327, 408, 610, 1420, and 2695 MHz) by the Trieste
radio-polarimeter with a time resolution 10 ms are analyzed. A wavelet
analysis method as well as time delay and polarization measurements
are used. Both methods reveal pulsations with a period of about 0.1 s
at all observed frequencies. Furthermore, the 0.1 s pulsations drift
toward higher and lower frequencies, starting at about 1420 MHz. The
polarization of pulsations increases with frequency and time. The
remarkable fact that the detected 0.1 s period of pulsations does not
depend on frequency in a very broad frequency range is discussed in
terms of existing models of pulsations.

---------------------------------------------------------
Title: Nonlinear analysis of decimetric solar bursts
Authors: Rosa, Reinaldo R.; Bolzan, Mauricio J. A.; Fernandes,
Francisco C. R.; Sawant, H. S.; Karlický, Marian
2010IAUS..264..279R Altcode:
The solar radio emissions in the decimetric frequency range (above
1 GHz) are very rich in temporal and spectral fine structures due
to nonlinear processes occurring in the magnetic structures on
the corresponding active regions. In this paper we characterize the
singularity spectrum, f(α), for solar bursts observed at 1.6, 2.0 and
3 GHz. We interpret our findings as evidence of inhomogeneous plasma
turbulence driving the underlying plasma emission process and discuss
the nonlinear multifractal approach into the context of geoeffective
solar active regions.

---------------------------------------------------------
Title: Singularity Spectra and Generalized Extreme Value Distributions
of Decimetric Radio Bursts Associated with Flares
Authors: Rosa, Reinaldo; Veronese, Thalita; José Alves Bolzan,
Maurício; Fernandes, Francisco; Cecatto, José; Karlicky, Marian;
Sawant, Hanumant
2010cosp...38.2841R Altcode: 2010cosp.meet.2841R
The search for turbulent-like patterns and extreme dynamics from time
series of solar radio burts has recently advanced due to high-resolution
and high-sensitivity observations. Such so-lar radio emissions in the
decimetric frequency range (above 1 GHz) are very rich in temporal and
spectral fine structures due to nonlinear processes occurring in the
magnetic structures on the corresponding active regions. In this paper
we analize the decimetric fine structures of 8 X-Class Flares events
observed from Brazilian Solar Spectroscope (1-2.5 GHz) and On-drejov
radiospectrograph (3 GHz). The Singularity Spectra [1] and Generalized
Extreme Value (GEV) distribution [2] are obtained and we interpret our
findings as evidence of inhomogeneous lagrangian-like MHD turbulence
driving the underlying non-gaussian plasma emission process. Once
GEV statistical behavior was found for 75% of the events, the flare
ocurrence is discussed into the context of solar extreme events. [1]
Bolzan et al., Ann. Geophys., 27, 569-576, 2009. [2] S. Coles,
An Introduction to Statistical Modeling of Extreme Values, Springer
Series in Statistics, (2001) 228 pp., Springer-Verlag, Berlin, Germany.

---------------------------------------------------------
Title: Multi-scale MHD approach to the current sheet filamentation
in solar coronal reconnection
Authors: Bárta, M.; Büchner, J.; Karlický, M.
2010AdSpR..45...10B Altcode:
Magnetic field reconnection - considered now as a key process in the
commonly accepted standard scenario of solar flares - spans over many
mutually coupled scales from the global flare dimensions (≈10 Mm)
down to the scale, where non-ideal kinetic plasma effects takes place
(≈10 m). Direct numerical simulation covering all the scales
is, therefore, impossible. Nevertheless, the filamentary nature
of the current sheet fragmentation together with rescalability of
ideal-MHD equations - which governs the processes before reaching the
scales of non-ideal plasma response - allow to describe the large-
and intermediate-scale dynamics of reconnection flow with highly
reduced request for number of grid points. Since the smaller-scale
(and faster) dynamics sets-in only in regions of enhanced current
sheet filamentation, we focus just on these areas, which occupy only
a small fraction of the total volume. Generally, as the fragmentation
continues, it forms a cascade of filamentation until kinetic non-ideal
processes come to play. Information relevant for description of the
smaller-scale physics occupies only a small fraction of grid-cells
describing the large-scale dynamics. Thus, one can subsequently
zoom-in onto the regions of continuing current filamentation. The
current-sheet fragmentation cascade anticipated by Shibata and
Tanuma [Shibata, K., Tanuma, S. Plasmoid-induced-reconnection and
fractal reconnection. Earth, Planets, and Space 53, 473-482, 2001],
creates multiple dissipative regions in a single current sheet, which
can play a key role for DC-field particle acceleration in a flare
reconnection. The main goal of the paper is to numerically investigate
the relevance of cascading reconnection for solar flares. The numerical
algorithm implemented for that purpose and first results are presented
in this research note. Proposed algorithm - though motivated by the
self-similar nature of MHD equations - belongs in fact to the class
of block-structured Adaptive Mesh Refinement codes.

---------------------------------------------------------
Title: Spontaneous current sheet fragmentation and particle
acceleration in cascading magnetic reconnection in solar flares
Authors: Bárta, Miroslav; Büchner, Jörg; Karlicky, Marian
2010cosp...38.1955B Altcode: 2010cosp.meet.1955B
The question how is the magnetic energy -accumulated in solar eruptive
flares on relatively large scales (the thickness of the current layer
behind ejected CME is supposed to be approx. 1000 km) -transported
towards the dissipative scales (approx. 10 m in the solar corona)
re-mains as one of the main open issues in the solar flare theory. To
resolve this problem, Shibata and Tanuma (Earth, Planet Space 53, 2001)
have suggested a concept of cascading (or 'fractal') reconnection. We
studied this concept using numerical MHD simulations involving AMR
tech-nique in order to gain broader range of resolved scales. The
results of our simulations confirmed relevance of the mechanism of
tearing cascade suggested by Shibata and Tanuma. In addition to
that, we found further fragmentation of the current layer in the
perpendicular direction: secondary current sheets are formed between
interacting magnetic islands (plasmoids). These current layers are
possibly subjected to the same kind of processes (tearing cascade +
forced coalescence of tearing-formed plasmoids) as the original (global)
current layer formed as conse-quence of CME ejection. Thus, we suggest
to supplement the original cascading-reconnection scenario by the
possibility of spontaneous current sheet fragmentation in the second
dimen-sion. This finding is in agreement with general expectations of
spontaneous isotropisation of the turbulent cascade. Propagation of the
cascading process to he second dimension increases the efficiency of
the reconnection process and has also clear consequences for theory of
particle acceleration in the solar flares as such a fragmented current
sheet can host many non-ideal regions capable to accelerate particles.

---------------------------------------------------------
Title: An Estimation of Spatial Variations of Magnetic Field and
Superthermal Electron Distribution in cm-Radio Burst Sources
Authors: Yasnov, L. V.; Karlický, M.
2009SoPh..260..363Y Altcode:
The paper presents a new method of the estimation of spatial variations
of the magnetic field and superthermal electron distribution in solar
cm-radio burst sources. The method is based on minimization of the
difference between the theoretical and observed radio fluxes and on
the analysis of several burst spectra recorded in different moments of
time. Several solar cm-radio bursts are analyzed by this method. It is
found that the measure of the spatial variations of the superthermal
electron distribution in the radio source is always larger than that
for the magnetic field.

---------------------------------------------------------
Title: Electron beam - plasma system with the return current and
directivity of its X-ray emission
Authors: Karlický, M.; Kašparová, J.
2009A&A...506.1437K Altcode: 2009arXiv0909.0146K
Aims: An evolution of the electron distribution function in the
beam-plasma system with the return current is computed numerically for
different parameters. The X-ray bremsstrahlung corresponding to such an
electron distribution is calculated and the directivity of the X-ray
emission is studied. Methods: For computations of the electron
distribution functions we used a 3-D particle-in-cell electromagnetic
code. The directivity of the X-ray emission was calculated using
the angle-dependent electron-ion bremsstrahlung cross-section. Results: It was found that the resulting electron distribution
function depends on the magnetic field assumed along the electron
beam propagation direction. For small magnetic fields the electron
distribution function becomes broad in the direction perpendicular
to the beam propagation due to the Weibel instability and the return
current is formed by the electrons in a broad and shifted bulk of
the distribution. On the other hand, for stronger magnetic fields the
distribution is more extended in the beam-propagation direction and the
return current is formed by the electrons in the extended distribution
tail. In all cases, the anisotropy of the electron distribution
decreases rapidly due to fast collisionless processes. However, the
magnetic field reduces this anisotropy decrease. The X-ray directivity
shows the same trend and it is always closer to the isotropic case
than that in a simple beaming model.

---------------------------------------------------------
Title: EUV filter responses to plasma emission for the nonthermal
κ-distributions
Authors: Dudík, J.; Kulinová, A.; Dzifčáková, E.; Karlický, M.
2009A&A...505.1255D Altcode:
The responses to plasma emission of the TRACE EUV filters are
computed by integrating their spectral responses over the synthetic
spectra obtained from the CHIANTI database. The filter responses
to emission are functions of temperature, electron density, and the
assumed electron distribution function. It is shown here that, for the
nonthermal κ-distributions, the resulting responses to emission are
more broadly dependent on T, and their maxima are flatter than for the
Maxwellian electron distribution. The positions of the maxima can also
be shifted. Filter reponses to T are density-dependent as well. The
influence of the nonthermal κ-distributions on the diagnostics of T
from the observations in all three EUV filters is discussed.

---------------------------------------------------------
Title: Relationship between wave processes in sunspots and
quasi-periodic pulsations in active region flares
Authors: Sych, R.; Nakariakov, V. M.; Karlicky, M.; Anfinogentov, S.
2009A&A...505..791S Altcode: 2010arXiv1005.3594S
A phenomenological relationship between oscillations in a sunspot
and quasi-periodic pulsations (QPP) in flaring energy releases at an
active region (AR) above the sunspot is established. The analysis of
the microwave emission recorded by the Nobeyama Radioheliograph at 17
GHz shows a gradual increase in the power of the 3-min oscillation
train in the sunspot associated with AR 10756 before flares in this
AR. The flaring light curves are found to be bursty with a period of 3
min. Our analysis of the spatial distribution of the 3-min oscillation
power implies that the oscillations follow from sunspots along coronal
loops towards the flaring site. It is proposed that QPP in the flaring
energy releases can be triggered by 3-min slow magnetoacoustic waves
leaking from sunspots.

---------------------------------------------------------
Title: Stationary stagnation point flows in the vicinity of a 2D
magnetic null point: I. Systems with vanishing electric field and
an X-type magnetic null point
Authors: Nickeler, Dieter; Karlicky, Marian; Barta, Miroslav
2009arXiv0909.0836N Altcode:
The appearance of eruptive space plasma processes, e.g., in eruptive
flares as observed in the solar atmosphere, is usually assumed to be
caused by magnetic reconnection. The process of magnetic reconnection
is often connected with singular points of the magnetic field. We
therefore analyse the system of stationary resistive/non-ideal
magnetohydrodynamics (MHD) in the vicinity of singular points of flow
and field to determine the boundary between reconnection solutions
and non-reconnective solutions. We find conditions to enable the
plasma to cross the magnetic separatrices also inside the current
sheet, close to the current maximum. The results provide us with the
topological and geometrical skeleton of the resistive MHD fields. We
therefore have to perform a local analysis of almost all non-ideal MHD
solutions with a generalized non-idealness. We use Taylor expansions
of the magnetic field, the velocity field and all other physical
quantities, including the non-idealness, and with the method of a
comparison of the coefficients, the non-linear resistive MHD system
is solved analytically. It turns out that not every non-ideal flow is
a reconnective flow and that pure resistive/non-ideal MHD only allows
for reconnection-like solutions, even if the non-idealness is localized
to the region around the magnetic null point. It is necessary that the
flow close to the magnetic X-point is also of X-point type to guarantee
positive dissipation of energy and annihilation of magnetic flux. If
the non-idealness has only a one-dimensional, sheet-like structure,
only one separatrix line can be crossed by the plasma flow, similar
to reconnective annihilation solutions.

---------------------------------------------------------
Title: Successive Solar Flares and Coronal Mass Ejections on 2005
September 13 from NOAA AR 10808
Authors: Liu, Chang; Lee, Jeongwoo; Karlický, Marian; Prasad
Choudhary, Debi; Deng, Na; Wang, Haimin
2009ApJ...703..757L Altcode: 2009arXiv0908.0487L
We present a multiwavelength study of the 2005 September 13 eruption
from NOAA AR 10808 that produced total four flares and two fast
coronal mass ejections (CMEs) within ~1.5 hr. Our primary attention
is paid to the fact that these eruptions occurred in close succession
in time, and that all of them were located along an S-shaped magnetic
polarity inversion line (PIL) of the active region. In our analysis,
(1) the disturbance created by the first flare propagated southward
along the PIL to cause a major filament eruption that led to the
first CME and the associated second flare underneath. (2) The first
CME partially removed the overlying magnetic fields over the northern
δ spot to allow the third flare and the second CME. (3) The ribbon
separation during the fourth flare would indicate reclosing of the
overlying field lines opened by the second CME. It is thus concluded
that these series of flares and CMEs are interrelated to each other via
magnetic reconnections between the expanding magnetic structure and
the nearby magnetic fields. These results complement previous works
made on this event with the suggested causal relationship among the
successive eruptions.

---------------------------------------------------------
Title: “Drifting tadpoles” in wavelet spectra of decimetric radio
emission of fiber bursts
Authors: Mészárosová, H.; Karlický, M.; Rybák, J.; Jiřička, K.
2009A&A...502L..13M Altcode:
Aims: The solar decimetric radio emission of fiber bursts was
investigated searching for the “drifting tadpole” structures
proposed by theoretical studies. Methods: Characteristic periods
with the tadpole pattern were searched for in the radio flux time
series by wavelet analysis methods. Results: For the first time,
we have found drifting tadpoles in the wavelet spectra of the decimetric
radio emission associated with the fiber bursts observed in July 11,
2005. These tadpoles were detected at all radio frequencies in the
1602-1780 MHz frequency range. The characteristic period of the wavelet
tadpole patterns was found to be 81.4 s and the frequency drift of the
tadpole heads is -6.8 MHz s-1. These tadpoles are interpreted
as a signature of the magnetoacoustic wave train moving along a dense
flare waveguide and their frequency drift as a motion of the wave
train modulating the radio emission produced by the plasma emission
mechanism. Using the Aschwanden density model of the solar atmosphere,
only low values of the Alfvén speed and the magnetic field strength
in the loop guiding this wave train were derived which indicates a
neutral current sheet as the guiding structure. The present analysis
supports the model of fiber bursts based on whistler waves.

---------------------------------------------------------
Title: Analytical model of static coronal loops
Authors: Dudík, J.; Dzifčáková, E.; Karlický, M.; Kulinová, A.
2009A&A...502..957D Altcode:
By solving the energy-equilibrium equation in the stationary
case, we derive analytical formulae in the form of scaling laws
for non-uniformly heated and gravitationally stratified coronal
loops. The heating is assumed to be localized in the chromosphere
and to exponentially decrease with increasing distance along the loop
strand. This exponential behavior of the heating and pressure profiles
implies that we need to use the mean-value theorem, and in turn fit
the mean-value parameters of the scaling laws to the results of the
numerical simulations. The radiative-loss function is approximated by a
power-law function of the temperature, and its effect on the resulting
scaling laws for coronal loops is studied. We find that this effect
is more important than the effect of varying loop geometry. We also
find that the difference in lengths of the different loop strands in
a loop with expanding cross-section does not produce differences in
the EUV emission of these strands significant enough to explain the
observed narrowness of the coronal loops.

---------------------------------------------------------
Title: Highlights of the Brazilian Solar Spectroscope
Authors: Sawant, H. S.; Cecatto, J. R.; Mészárosová, H.; Faria,
C.; Fernandes, F. C. R.; Karlický, M.; de Andrade, M. C.
2009AdSpR..44...54S Altcode:
The digital, decimetric (950-2500 MHz) Brazilian Solar Spectroscope
(BSS, Sawant, H.S., Subramanian, K.R., Faria, C., et al. Brazilian
Solar Spectroscope (BSS). Solar Phys. 200, 167-176, 2001) with high
time (10-1000 ms) and frequency (1-10 MHz) resolution is in regular
operation since April, 1998, at the National Space Research Institute
(INPE) at São José dos Campos, Brazil. The BSS has now been upgraded
with a new digital data acquisition and data processing system. The new
version of the BSS has improved the observational possibilities with
the capability to record up to 200 frequency channels available in the
selectable frequency range 950-2500 MHz. The GPS receiver permits the
acquisition of data with time accuracy in the order of 0.1 ms. The
software system of the BSS is composed by two distinct modules:
the first, data acquisition system provides a flexible Graphical
User Interface (GUI) that allows one to choose the observational
parameters. The second module is the real time visualization system
that permits real time visualization of the observed dynamic spectrum
and additionally allows procedures for visualization and preliminary
analysis of the recorded solar spectra. Using the new visualization
system, we have realized two new types of dm-radio fine structures:
narrow band type III bursts with positive as well as negative group
frequency drift and dots emissions arranged in zebra-like and fiber-like
chains. Furthermore, we have found flare generated fast wave trains
according to their tadpole signature in wavelet power spectra for a
decimetric type IV radio event (June 6, 2000 flare).

---------------------------------------------------------
Title: Response of optical hydrogen lines to beam heating. I. Electron
beams
Authors: Kašparová, J.; Varady, M.; Heinzel, P.; Karlický, M.;
Moravec, Z.
2009A&A...499..923K Altcode: 2009arXiv0904.2084K
Context: Observations of hydrogen Balmer lines in solar flares remain an
important source of information on flare processes in the chromosphere
during the impulsive phase of flares. The intensity profiles of
optically thick hydrogen lines are determined by the temperature,
density, and ionisation structure of the flaring atmosphere, by the
plasma velocities and by the velocity distribution of particles in
the line formation regions. Aims: We investigate the role of
non-thermal electrons in the formation regions of Hα, Hβ, and Hγ
lines in order to unfold their influence on the formation of these
lines. We concentrate on pulse-beam heating varying on a subsecond
timescale. Furthermore, we theoretically explore possibility that a new
diagnostic tool exists indicating the presence of non-thermal electrons
in the flaring chromosphere based on observations of optical hydrogen
lines. Methods: To model the evolution of the flaring atmosphere
and the time-dependent hydrogen excitation and ionisation, we used a
1-D radiative hydrodynamic code combined with a test-particle code that
simulates the propagation, scattering, and thermalisation of a power-law
electron beam in order to obtain the flare heating and the non-thermal
collisional rates due to the interaction of the beam with the hydrogen
atoms. To not bias the results by other effects, we calculate only
short time evolutions of the flaring atmosphere and neglect the plasma
velocities in the radiative transfer. Results: All calculated
models have shown a time-correlated response of the modelled Balmer line
intensities on a subsecond timescale, with a subsecond timelag behind
the beam flux. Depending on the beam parameters, both line centres
and wings can show pronounced intensity variations. The non-thermal
collisional rates generally result in an increased emission from a
secondary region formed in the chromosphere. Conclusions: Despite
the clear influence of the non-thermal electron beams on the Balmer line
intensity profiles, we were not able on the basis of our simulations
to produce any unambiguous diagnostic of non-thermal electrons in the
line-emitting region, which would be based on comparison of individual
Balmer line intensity profiles. However, fast line intensity variations,
well-correlated with the beam flux variations, represent an indirect
indication of pulsating beams.

---------------------------------------------------------
Title: Tadpoles in Wavelet Spectra of a Solar Decimetric Radio Burst
Authors: Mészárosová, H.; Karlický, M.; Rybák, J.; Jiřička, K.
2009ApJ...697L.108M Altcode:
In the solar decimetric type IV radio event observed on 2001 June 13,
we have found wavelet tadpole patterns for the first time. They were
detected simultaneously at all radio frequencies in the 1.1-4.5 GHz
frequency range. The characteristic period of the wavelet tadpole
patterns was found to be 70.9 s. The parameters of the tadpoles on
different frequencies are very similar and the correlations between
individual radio fluxes are high. These tadpoles are interpreted as a
signature of the magnetoacoustic wave train moving along the flare loop
through the radio source and modulating its gyrosynchrotron emission.

---------------------------------------------------------
Title: Coronal fast wave trains of the decimetric type IV radio
event observed during the decay phase of the June 6, 2000 flare
Authors: Mészárosová, H.; Sawant, H. S.; Cecatto, J. R.; Rybák, J.;
Karlický, M.; Fernandes, F. C. R.; de Andrade, M. C.; Jiřička, K.
2009AdSpR..43.1479M Altcode:
The 22 min long decimetric type IV radio event observed during the
decay phase of the June 6, 2000 flare simultaneously by the Brazilian
Solar Spectroscope (BSS) and the Ondřejov radiospectrograph in
frequency range 1200-4500 MHz has been analyzed. We have found that
the characteristic periods of about 60 s belong to the long-period
spectral component of the fast wave trains with a tadpole pattern
in their wavelet power spectra. We have detected these trains in
the whole frequency range 1200-4500 MHz. The behavior of individual
wave trains at lower frequencies is different from that at higher
frequencies. These individual wave trains have some common as well as
different properties. In this paper, we focus on two examples of wave
trains in a loop segment and the main statistical parameters in their
wavelet power and global spectra are studied and discussed.

---------------------------------------------------------
Title: Kappa distribution and hard X-ray emission of solar flares
Authors: Kašparová, J.; Karlický, M.
2009A&A...497L..13K Altcode: 2009arXiv0902.3574K
Aims: We investigate whether the so-called kappa distribution, often
used to fit electron distributions detected in situ in the solar wind,
can describe electrons producing the hard X-ray emission in solar
flares. Methods: Using Ramaty High Energy Solar Spectroscopic
imager (RHESSI) flare data we fit spatially- and feature-integrated
spectra, assuming a kappa distribution for the mean electron flux
spectrum. Results: We show that a single kappa distribution
generally cannot describe spatially integrated X-ray emission
composed of both footpoint and coronal sources. In contrast, the kappa
distribution is consistent with mean electron spectra producing hard
X-ray emission in some coronal sources.

---------------------------------------------------------
Title: On spatial variations of magnetic field and superthermal
electron distribution in cm-radio burst source
Authors: Yasnov, Leonid V.; Karlický, Marian
2009IAUS..257..353Y Altcode:
The paper presents a new method of an estimation of spatial variations
of the magnetic field and superthermal electron distribution in solar
cm-radio burst sources. The method is based on the analysis of several
burst spectra recorded in the different moments of time and on the
minimization of the difference between the theoretical and observed
radio fluxes. It is found that the measure of the spatial variations
of superthermal electron distribution in the radio source is always
greater than that for the magnetic field. In most cases this measure
has a minimum at the impulsive phase of cm-radio bursts.

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Title: Cyclic Magnetic Field Reconnection
Authors: Karlický, Marian
2009ApJ...692L..72K Altcode:
Using a 2.5D electromagnetic particle-in-cell model, we study the
magnetic field reconnection around the rotating plasma embedded in
a magnetic field. Considering plasma rotation driven by an external
electric field, it was found that during one rotational cycle, first
the magnetic field energy increases and then decreases to its initial
value. The magnetic reconnection occurring during this cycle plays two
roles: first, it produces the closed magnetic islands and later on it
reopens them to the initial form of magnetic field lines. Thus, the
magnetic reconnection can be cyclically repeated in following plasma
rotations. Simultaneously, the kinetic particle energy in the system
increases due to dissipative processes in this externally driven
plasma system. We think that this cyclic reconnection can operate
around rapidly rotating stars and in the plasma vortices formed in
unstable plasma flows.

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Title: The X17.2 flare occurred in NOAA 10486: an example of filament
destabilization caused by a domino effect
Authors: Zuccarello, F.; Romano, P.; Farnik, F.; Karlicky, M.;
Contarino, L.; Battiato, V.; Guglielmino, S. L.; Comparato, M.;
Ugarte-Urra, I.
2009A&A...493..629Z Altcode:
Context: It is now possible to distinguish between two main models
describing the mechanisms responsible for eruptive flares : the standard
model, which assumes that most of the energy is released, by magnetic
reconnection, in the region hosting the core of a sheared magnetic
field, and the breakout model, which assumes reconnection occurs
at first in a magnetic arcade overlaying the eruptive features. Aims: We analyze the phenomena observed in NOAA 10486 before and
during an X17.2 flare that occurred on 2003 October 28, to study the
relationship between the pre-flare and flare phases and determine which
model is the most suitable for interpreting this event. Methods:
We performed an analysis of multiwavelength data set available for
the event using radio data (0.8-4.5 GHz), images in the visible range
(WL and Hα), EUV images (1600 and 195 Å), and X-ray data, as well
as MDI longitudinal magnetograms. We determined the temporal sequence
of events occurring before and during the X17.2 flare and the magnetic
field configuration in the linear force-free field approximation. Results: The active region was characterized by a multiple arcade
configuration and the X17.2 flare was preceded, by ~2 h, by the partial
eruption of one filament. This eruption caused reconnection at null
points located in the low atmosphere and a decrease in magnetic tension
in the coronal field lines overlaying other filaments present in the
active region. As a consequence, these filaments were destabilized and
the X17.2 flare occurred. Conclusions: The phenomena observed
in NOAA 10486 before and during the X17.2 flare cannot be explained
by a simple scenario such as the standard or breakout model, but
instead in terms of a so-called domino effect, involving a sequence
of destabilizing processes that triggered the flare.

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Title: Drifting Pulsating Structure in the Post-maximum Phase of
the May 13, 2005 Flare
Authors: Jiřička, K.; Karlický, M.
2009CEAB...33..217J Altcode:
A high-frequency drifting pulsating structure observed in the
post-maximum flare phase is analysed in detail. Using the Aschwanden
and Benz model (1997) of the solar atmosphere the altitude of the radio
source of this structure is estimated and compared with the loop height
derived from the distance of the Hα flare ribbons. It was found that
for the emission on the harmonic frequency the radio source is close to
the flare-loop top. It supports the idea that this drifting pulsating
structure is generated in the so-called termination shock.

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Title: Multi-scale MHD Modelling of the Current Sheet Fragmentation
in Turbulent Solar Flare Reconnection
Authors: Bárta, M.; Karlický, M.; Büchner, J.
2009CEAB...33..299B Altcode:
The concept of turbulent magnetic reconnection becomes now very
attractive in solar flare research as it can address many open
issues in that field. Nevertheless, it has not been explored yet
by numerical simulation since it requires a model which spans over a
broad scale-range of mutually coupled phenomena. Traditional simulation
approaches are not capable to cover a range of scales from the global
system dimensions down to the dissipation scale because of limited
number of grid points. A solution could be the development of an
appropriate recursive numerical algorithm which at different levels
of recursion solves the processes in current sheet fragmentation
on different spatial and temporal scales. For this sake we suggest a
numerical scheme, where the data representing the system under study are
stored in a dynamic hierarchically organized data structure (a tree)
which should reflect the self-similar properties of the anticipated
solution. To some extent such an algorithm can be considered as an
alternative approach to Adaptive Mesh Refinement (AMR) codes.

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Title: Electron Beam-Plasma Interaction and the Return-Current
Formation
Authors: Karlický, Marian
2009ApJ...690..189K Altcode:
Using a 3D electromagnetic particle-in-cell model, the plasma systems
with electron beams are studied. The model parameters are chosen
relevant to solar flares. To show the complexity of the problem
studied, in the first model, we present an evolution of two oppositely
propagating electron beams that escape from the localized acceleration
region. Then due to the limitations of this model, in other models
we consider a plasma system with one spatially homogeneous beam
and a neutralizing return current. The models without the initial
magnetic field revealed an importance of the Weibel instability
that very efficiently transferred the beam energy to the heating of
plasma electrons in the direction perpendicular to that of the beam
propagation. In this case, the return current evolved from the initially
shifted Maxwell distribution to the distribution with a broad flat
maximum. However, in the models with a sufficiently strong magnetic
field or those with shorter sizes of the numerical box (effectively
the 1D case), the Weibel instability was reduced, and the electron
distribution function mainly evolved in the beam-propagation direction
and the return current was given by a shift of some bulk electrons
and an extended tail.

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Title: Far-IR and Radio Thermal Continua in Solar Flares
Authors: Kašparová, J.; Heinzel, P.; Karlický, M.; Moravec, Z.;
Varady, M.
2009CEAB...33..309K Altcode: 2009arXiv0901.3465K
With the invention of new far-infrared (FIR) and radio mm and sub-mm
instruments (DESIR on SMESE satellite, ESO-ALMA), there is a growing
interest in observations and analysis of solar flares in this so far
unexplored wavelength region. Two principal radiation mechanisms play a
role: the synchrotron emission due to accelerated particle beams moving
in the magnetic field and the thermal emission due to the energy deposit
in the lower atmospheric layers. In this contribution we explore the
time-dependent effects of beams on thermal FIR and radio continua. We
show how and where these continua are formed in the presence of time
dependent beam heating and non-thermal excitation/ionisation of the
chromospheric hydrogen plasma.

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Title: Plasmoid Dynamics in Flare Reconnection and the Frequency
Drift of the Drifting Pulsating Structure
Authors: Bárta, M.; Karlický, M.; Žemlička, R.
2008SoPh..253..173B Altcode: 2008SoPh..tmp..131B
In the paper by Kliem, Karlický, and Benz (Astron. Astrophys.360, 715,
2000) it was suggested, that plasmoids formed during the bursty regime
of solar flare reconnection can be "visualised" in the radio spectra
as drifting pulsating structures via accelerated particles trapped
inside the plasmoid. In the present paper we investigate this idea in
detail. First, simple statistical analysis supporting this hypothesis
is presented. Then, by using the 2.5-D MHD (including gravity) model
solar flare reconnection in the inhomogeneous, stratified atmosphere is
simulated and the formation and subsequent ejection of the plasmoid is
demonstrated. The ejected plasmoid, which is considered to be a trap
for accelerated electrons, is traced and its plasma parameters are
computed. To estimate the associated plasma radio emission we need
to know locations of accelerated electrons and corresponding plasma
frequencies. General considerations predict that these electrons
should be distributed mainly along the magnetic separatrix surfaces
and this was confirmed by using a particle-in-cell simulation. Finally,
under some simplifying assumptions the model dynamic radio spectrum is
constructed. The relation between the global frequency drift and the
plasmoid motion in the inhomogeneous ambient atmosphere is studied. The
results are discussed with respect to the observed drifting pulsation
structures and their possible utilisation for flare magnetic field
diagnostics.

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Title: Narrowband Pulsating Decimeter Structure Observed by the New
Ondřejov Solar Radio Spectrograph
Authors: Jiřička, K.; Karlický, M.
2008SoPh..253...95J Altcode: 2008SoPh..tmp...18J
The new 0.8 - 2.0 GHz Ondřejov radio spectrograph with high time
resolution (10 ms) is presented. As an example of first observations
the 0.95 - 1.3 GHz narrowband pulsating structure with a characteristic
quasi-period of about 150 ms, observed during the impulsive phase of
the 9 June 2007 M1.0 flare, is shown. Some of the pulses show very fast
but measurable frequency drift of about −17 GHz s−1. The
model of this pulsating structure, based on the tearing and coalescence
processes in the current sheet, is briefly discussed.

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Title: Decimetric radio dot emissions
Authors: Mészárosová, H.; Karlický, M.; Sawant, H. S.; Fernandes,
F. C. R.; Cecatto, J. R.; de Andrade, M. C.
2008A&A...491..555M Altcode:
Context: We study a rare type of solar radio bursts called decimetric
dot emissions. Aims: In the period 1999-2001, 20 events of
decimetric dot emissions observed by the Brazilian Solar Spectroscope
(BSS) in the frequency range 950-2640 MHz are investigated statistically
and compared with radio fine structures of zebras and fibers. Methods: For the study of the spectral characteristics of the dot
emissions we use specially developed Interactive Data Language (IDL)
software called BSSView and basic statistical methods. Results: We
have found that the dm dot emissions, contrary to the fine structures of
the type IV bursts (i.e. zebras, fibers, lace bursts, spikes), are not
superimposed on any background burst emission. In the radio spectrum,
in most cases the dot emissions form chains that appear to be arranged
in zebra patterns or fibers. Because some zebras and fibers, especially
those observed with high time and high spectral resolutions, also show
emission dots (but superimposed on the background burst emission), we
compared the spectral parameters of the dot emissions with the dots
being the fine structure of zebras and fibers. For both these dots,
similar spectral characteristics were found. Some similarities of the
dot emissions can be found also with the lace bursts and spikes. For
some events the dot emissions show structural evolution from patterns
resembling fibers to patterns resembling zebras and vice versa,
or they evolve into fully chaotic patterns. Conclusions: For
the first time, we present decimetric dot emissions that appear to be
arranged in zebra patterns or fibers. We propose that these emissions
are generated by the plasma emission mechanism at the locations in
the solar atmosphere where the double resonance condition is fulfilled.

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Title: Multi-scale Numerical Approach to Solar Flare Magnetic
Reconnection
Authors: Bárta, M.; Karlický, M.; Nickeler, D.
2008ESPM...12.3.49B Altcode:
Magnetic reconnection - considered now commonly as the engine of
solar flares - spans over many mutually coupled scales from the
global flare dimensions (approximately 10 Mm) down to the scale,
where dissipation through kinetic effects take place (approximately 10
m). Direct numerical simulation covering all the scales is therefore
impossible for obvious reasons: full 3D numerical model would have
to involve 1018 grid points. Nevertheless, the filamentary nature of
the current sheet fragmentation give us the chance to describe the
process of reconnection with highly reduced request for number of grid
points. As the smaller-scale dynamics is interesting only in regions of
enhanced current sheet filamentation, we can focus just on these areas,
which occupy only a small fraction of the total volume. Generally,
as the fragmentation continues, it forms a cascade (finished by the
kinetic dissipation) where information relevant for description of
the smaller-scale level occupies only a small fraction of grid points
describing the higher level. Thus, one can subsequently zoom-in
onto the regions of continuing current filamentation. Anticipated
current-sheet-fragmentation cascade supposes multiple dissipative
regions formed in a single current sheet - this fact can play a key
role for direct particle acceleration in reconnection. The numerical
algorithm implementing this 'zooming' technique and the first results
will be presented.

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Title: Hydrogen Balmer Lines in the Solar Atmosphere Heated by
Electron Beams
Authors: Kasparova, J.; Varady, M.; Moravec, Z.; Heinzel, P.;
Karlicky, M.
2008ESPM...12.3.16K Altcode:
Accelerated particle beam are one of the mechanisms of the flare
energy transport from the corona to the transition region and the
chromosphere. Such beams heat ambient plasma and may affect atomic
population via collisions. Using 1D NLTE radiative hydrodynamics
we model influence of electron beams on hydrogen Balmer lines. In
the contribution we focus on the effect of so-called non-thermal
collisional rates on Halpha and Hbeta lines. Based on our results we
discuss diagnostic methods for determination of beam presence in the
formation regions of Halpha and Hbeta lines.

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Title: Gradient pattern analysis of short solar radio bursts
Authors: Rosa, R. R.; Karlický, M.; Veronese, T. B.; Vijaykumar,
N. L.; Sawant, H. S.; Borgazzi, A. I.; Dantas, M. S.; Barbosa,
E. B. M.; Sych, R. A.; Mendes, O.
2008AdSpR..42..844R Altcode:
We analyze the weak component of the localized temporal
pattern variability of 3 GHz solar burst observed by the Ondrejov
radiospectrograph. A complex, short and weak impulsive sample from the
time series was analyzed by applying a method based on the gradient
pattern analysis and discrete wavelet decomposition. By analyzing
canonical temporal variability patterns we show that the new method
can reliably characterize the phenomenological dynamical process of
short time series (N ⩽ 103 measurements) as the radio
burst addressed here. In the narrowest sense, by estimating the
mutual information distance in the gradient spectra, we show that the
fluctuation pattern of the short and weak 3 GHz impulsive solar burst,
with energetic amplitudes &lt;350 SFU, is closer to the intermittent
and strong MHD turbulent variability pattern.

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Title: Far-IR and Radio Continua in Solar Flares
Authors: Heinzel, P.; Kasparova, J.; Varady, M.; Karlicky, M.;
Moravec, Z.
2008ESPM...12.3.20H Altcode:
With the invention of new far-infrared (FIR) and radio mm and sub-mm
instruments (DESIR on SMESE satellite, ESO ALMA), there is a growing
interest in observations and analysis of solar flares in this so far
unexplored wavelength region. Two principal radition mechanisms play a
role: the synchrotron emission due to accelerated particle beams moving
in the magnetic field and the thermal emission due to energy deposit
in the lower atmospheric layers. The latter one was recently explored
for the case of semiempirical flare models, without considering the
temporal evolution. However, as the radiation-hydrodynamical simulations
do show, the lower atmosphere heated by beams exhibits fast temporal
changes which are typically reflected in variations of spectral-line
intensities. In this contribution we explore the time-dependent effects
of beams on FIR and radio continua. We show how and where these
continua are formed in the presence of time dependent beam heating
and non-thermal excitation/ionization of the chromospheric hydrogen
plasma. Our results should contribute to planning of new observations
in FIR and radio domain.

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Title: Flare Generated Coronal Fast Wave Trains of Decimetric Radio
Pulsations
Authors: Meszarosova, H.; Sawant, H. S.; Cecatto, J. R.; Rybak, J.;
Karlicky, M.; Fernandes, F. C. R.; Jiricka, K.; Andrade, M. C.
2008ESPM...122.105M Altcode:
The 22 minutes lasting interval of broadband dm-radio pulsations
observed simultaneously during a decay phase of the June 6, 2000 flare
by the Brazilian Solar Spectroscope (BSS) and Ondrejov radiospectrograph
in frequency range 1200-4500 MHz has been analyzed. We have realized
that dominant periods (32-64 s) belong to fast wave trains with a
tadpole pattern in their wavelet power spectra. The whole time interval
contains series of about 4 wave trains. These trains propagate in
whole frequency range 1200-4500 MHz. The propagation of individual
trains at lower levels of the solar atmosphere (higher frequencies) is
different from propagation of individual trains at higher ones (lower
frequencies). The wave trains at the same frequencies but in different
time subintervals have some common as well as different properties. The
main statistical parameters (periodical, quasi-periodical and decay
phase) of these wave trains in their wavelet power spectra have been
studied and the first results will be presented and discussed.

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Title: The Synthetic X-ray Flare Spectra for the Electron Beam and
the Return Current
Authors: Dzifcakova, E.; Karlicky, M.
2008ESPM...12.3.48D Altcode:
The electron beams accelerated during flare in low corona create return
currents of electrons in solar plasma. The accelerated electrons of the
electron beam and return current influence the electron distribution
function. The shape of the electron distribution which includes the
interaction of the electron beam with plasma and formation of the return
current has been modeled by PIC code. The synthetic X-ray spectra for
a such kind of the electron distributions have been computed by using
a modification of CHIANTI. The possibility to diagnose of the return
current from X-ray spectra is discussed.

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Title: 2D Stationary Reconnection Solutions in the Vicinity of a
Magnetic Null Point and a Stagnation Point
Authors: Nickeler, D.; Karlicky, M.
2008ESPM...12.3.43N Altcode:
The classical reconnection solutions propose an X-type inflow of
the plasma into the X-point structure of the magnetic field. We
analyse systematically the implications of the different magnetic
field structures of a field which depends linearly on the spatial
coordinates. The linear dependence is valid if the Jacobian matrix
of the magnetic field does not vanish at the null point. We solve
the complete set of the resistive MHD equations for the case that
the stagnation point has only a small offset to the magnetic null
point. We assume also that the Jacobian of the velocity field does not
vanish. This leads to the question which topological and geometrical
type of the flow corresponds to which type of magnetic field structure.

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Title: Hydrostatic Modelling of Active Region EUV and X-ray Emission
Authors: Dudik, J.; Dzifcakova, E.; Kulinova, A.; Karlicky, M.
2008ESPM...12.3.65D Altcode:
The hydrostatic modeling of active region NOAA 10963 coronal EUV and
X-ray emission is presented. The model considers three-dimensional
magnetic field structure obtained by the extraplation of
the longitudinal magnetogram in potential or linear force-free
approximation. We derived new scaling laws for loop apex temperature
and footpoint pressure as functions of loop length, volumetric
heating rate and heating scale height. These scaling laws assume a
power-law dependency of radiative loss function on the temperature,
a power-law dependency of the heating function on the loop length
and field strength at the loop base. The scaling laws are applied to
the results of the field extrapolations in AR NOAA 10963 in order to
calculate the temperature and density distributions in the active
region corona. The functions of filter response to emissivity has
been calculated by using the CHIANTI atomic database. Unlike previous
authors, we are able to get emitting loop structures in EUV. The results
show that the heating scale height plays important role in modeling
of the active region emission. The computed emission is compared with
observations and the implications on the heating function are discussed.

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Title: Return Current Formation in the Region of Escaping Electrons
from the Acceleration Space
Authors: Karlicky, M.
2008ESPM...12.3.47K Altcode:
In a 3-D electromagnetic particle-in-cell model the particle
distribution in the acceleration space with escaping accelerated
electrons is initiated. Then an evolution of the electron beam
penetrating into surrounding plasma and generating the return current
is studied. Besides the electrostatic effects at the beam front
and the beam-plasma instability a role of the Weibel instability is
recognized. Finally, the effects found are discussed in connections
to solar flares.

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Title: Numerical Modelling of Slow Standing Waves in a Solar
Coronal Loop
Authors: Jelinek, P.; Karlicky, M.
2008ESPM...12.3.59J Altcode:
In the paper we numerically investigate slow standing waves that
are impulsively generated in a solar coronal loop by the pressure
and density pulse. The solved problem is considered as one- and
two-dimensional and the results from both models are compared and
discussed. The corresponding computer models are described by the
ideal magnetohydrodynamic equations that are solved numerically on
uniformly structured mesh by means of the Lax-Wendroff and flux limiter
algorithms. The obtained numerical results show a time evolution
of the velocity, mass density, pressure or plasma energy density in
the model. Further results are the spatial profiles of velocity in
fundamental or first harmonic modes, depending on the position of
initial perturbations in the coronal loop, and for various positions
in the work area. Our presented work is aimed at the explanation of
coronal oscillations and its attenuation. These calculations are very
important for the explanation of the problem of coronal heating and
mechanisms of solar coronal oscillations. It is also important for an
interpretation of observations because the density perturbations can
produce corresponding perturbations in EUV or thermal X-ray emissions.

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Title: Influence of the Return Current on the EUV and X-Ray Flare
Line Emissions
Authors: Dzifčáková, Elena; Karlický, Marian
2008SoPh..250..329D Altcode: 2008SoPh..tmp..119D
Electron beams accelerated during solar flares carry electric currents
which should be neutralized by so-called return currents. Both the
electron beam and return current modify the electron distribution
function in the solar transition region and low corona. Thus, they
influence the intensities of the spectral lines formed in these
layers. Synthetic spectra for the solar flare atmosphere are computed
from model conditions and the possibilities of diagnostics of the
return current from the EUV and X-ray line spectra are discussed.

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Title: Particle-in-cell simulations of return current in solar flares
Authors: Karlický, M.; Nickeler, D. H.; Bárta, M.
2008A&A...486..325K Altcode:
Aims: We numerically study a formation of the return current generated
in solar flares. Methods: For simulations of the return current
in the beam-plasma system, a 3D particle-in-cell electromagnetic
code is used. Results: In conditions of solar flares with the
electron beam fluxes of EF = 9.1 × 109-4.55 ×
1010 erg s-1 cm-2, the beam-plasma
interaction with the return current is studied. We found that the
electron beam relaxes to the plateau distribution function as known
from electrostatic simulations. Simultaneously, due to electromagnetic
effects and the Buneman instability of the prescribed Maxwell-shifted
return current, the electron distribution function evolves to a
new stationary state with a new form of the return current. In this
final state the return current is formed not only by electrons in the
bulk of the electron distribution function, but also by electrons in
the extended tail. We use the results of simulations to estimate the
critical beam fluxes for the processes under study in the low corona,
the transition region and the upper chromosphere.

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Title: Solar Origin of the Radio Attributes of a Complex Type III
Burst Observed on 11 April 2001
Authors: Reiner, M. J.; Klein, K. -L.; Karlický, M.; Jiřička, K.;
Klassen, A.; Kaiser, M. L.; Bougeret, J. -L.
2008SoPh..249..337R Altcode: 2008SoPh..tmp...89R
We report here on the solar origin of distinctive radiation
characteristics observed for a decametric type III solar radio burst
that was associated with a major solar flare and CME on 11 April
2001. The associated decimeter (Ondřejov) and meter (Potsdam)
wavelength emissions, as well as the GOES soft X-ray lightcurve,
suggest that there were two successive events of energy release and
electron acceleration associated with this solar eruption. The Nançay
radioheliograph images and additional evidence of plasmoid propagation
suggest that the second event of electron acceleration resulted from
coronal reconfigurations, likely caused by the erupting CME. These
observational analyses provide new insights into the physical origin
of the distinguishing characteristics of complex type III-like radio
emissions that are typically observed at decameter wavelengths during
major solar eruptive events.

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Title: Solar decimetric type III bursts in semi-closed magnetic
field structures
Authors: Mészárosová, H.; Karlický, M.; Sawant, H. S.; Fernandes,
F. C. R.; Cecatto, J. R.; de Andrade, M. C.
2008A&A...484..529M Altcode:
Aims: We investigate statistically seventeen groups of solar type
III bursts, observed in the frequency range 950-2500 MHz using the
Brazilian Solar Spectroscope (BSS) during the period 1999-2002. Methods: Using specially-developed Interactive Data Language (IDL)
software called BSSView, the spectral characteristic properties of
the bursts were investigated. For illustration a semi-closed magnetic
field structure with trapped electron beams was modelled using the
particle-in-cell model. Results: Most of the type III bursts
studied in this paper have starting frequencies in the range 1100-1400
MHz and their average bandwidth, half-power duration, and interval
between adjacent bursts are 116 ± 59 MHz, 108 ± 41 ms, and 647 ±
643 ms, respectively. The number of bursts with negative frequency
drift, which is on average -914 ± 684 MHz s-1, is greater
than the number with positive frequency drift, which is on average
+807 ± 675 MHz s-1. The type III bursts have power-law
distribution function for their half-power duration H(f_start) = 4.79 ×
108~f_start-2.145± 0.015, bandwidth B_1(f_start)
= 1.95 × 10^7~f_start-1.697± 0.022 and B_2(f_start) = 7.07
× 10^5~f_start-1.154± 0.015, and frequency drift D(f_start)
= 0.43~f_start1.040± 0.031. Most of the groups of type III
bursts were also found to exhibit either positive or negative group
frequency drifts of on average +53 ± 38 MHz s-1 and -46 ±
42 MHz s-1, respectively. The detailed statistical analysis
suggests that in the frequency range studied there are two categories
of type III bursts, the average parameters of which we provide in
brackets for each type: a) numerous narrowband bursts (bandwidth
~100 MHz) with small frequency drift (~±500 MHz s-1) in
groups with visible group drift (~±50 MHz s-1) and b)
less numerous broader band bursts (bandwidth 171 MHz) with higher
frequency drift (~±1800 MHz s-1) in groups without group
drift. The statistics of the parameters of these drifting groups are
presented for the first time. The drifting groups of type III bursts
are interpreted as due to electron beams trapped in moving plasmoids,
which are semi-closed magnetic field structures.

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Title: On the validity of ideal MHD in the vicinity of stagnation
points in the heliosphere and other astrospheres
Authors: Nickeler, D. H.; Karlický, M.
2008ASTRA...4....7N Altcode:
The paradigm of ideal MHD is investigated in the vicinity of null points
of flows and magnetic fields. These null points determine the location
and geometrical shape of the heliopause (or other astropauses). We
investigate the question whether regular and stable solutions of the
ideal MHD equations in the vicinity of null points of flow and magnetic
field exist. This is done to test the validity of ideal MHD in the
vicinity of flow and magnetic field of the plasma boundaries of stellar
winds and their local interstellar medium. We calculate the general
solutions of ideal MHD in the vicinity of magnetic null points and use
the standard form of stagnation point flows to analyse all possible time
evolutions of these plasma environments. We show that the solution space
in 2-D consists almost exclusively of either exponentially (in time)
growing velocity or magnetic fields, or collapse solutions. Regular
solutions must be three-dimensional and seem to be unstable with
respect to small perturbations. This is an argument that reconnection
has to take place in such regions and that therefore nonideal terms
in Ohm's law are necessary, allowing for reconnection. We conclude
that the use of ideal MHD in the vicinity of singular points of flow
and magnetic field has to be analysed very carefully with respect to
simulation results as those simulations show numerical dissipation
(resistivity). These simulations can therefore produce unphysical
reconnection regimes. Thus one has to search for a realistic Ohm's law,
allowing for reconnection at the heliospheric boundaries.

---------------------------------------------------------
Title: Separation of Accelerated Electrons and Positrons in the
Relativistic Reconnection
Authors: Karlický, Marian
2008ApJ...674.1211K Altcode: 2007arXiv0709.0572K
We study the acceleration of electrons and positrons in a relativistic
magnetic field reconnection using a 2.5 dimensional particle-in-cell
electromagnetic relativistic code. We consider a model with two current
sheets and periodic boundary conditions. The electrons and positrons
are very effectively accelerated during the tearing and coalescence
processes of the reconnection. We found that near the X-points of the
reconnection the positions of electrons and positrons differ. This
separation process is in agreement with those studied in previous
papers analytically or by test particle simulations. We expect that
in dependence on the magnetic field connectivity this local separation
can lead to global spatial separation of the accelerated electrons and
positrons. A similar simulation in an electron-proton plasma with the
proton-electron mass ratio mi/me = 16 is made.

---------------------------------------------------------
Title: Fragmentation of the Current Sheet, Anomalous Resistivity,
and Acceleration of Particles
Authors: Karlický, M.; Bárta, M.
2008SoPh..247..335K Altcode: 2008SoPh..tmp...11K
The evolution of the current sheet in the electric current direction
(in the guiding magnetic field direction) is studied numerically in the
3-D particle-in-cell model with two current sheets and periodic boundary
conditions. In the regime with vD/v_{Te}≥ 1
(where vD and v_{Te} are the electric current
drift and electron thermal velocities, respectively) the current
sheets are unstable owing to the Buneman and kink instabilities and
become strongly fragmented. During their evolution, in addition
to an increase of the energy of the electric field component
in the guiding magnetic field direction, the energies of the
electric field components in the perpendicular direction are even
more enhanced. In the current sheet the anomalous resistivity
(ηanom/ηC∼7×105, where
ηC is the classical resistivity) is generated and thus
the magnetic field dissipates. Most of the dissipated magnetic energy
is transformed into the electron kinetic energy in the direction of
the electric current. The associated electric field accelerates the
electrons from the tail of the distribution function.

---------------------------------------------------------
Title: Resonant Transition Radiation and Solar Radio Bursts
Authors: Yasnov, L. V.; Karlický, M.; Modin, E. V.
2008SoPh..247..351Y Altcode: 2008SoPh..tmp....2Y
This paper presents general relations for the intensity of the resonant
transition radiation (RTR) and their detailed analysis. This analysis
shows that the spectrum amplitude of the x-mode at some frequencies
for high-energy electrons can grow with the magnetic field increase
in some interval from zero value; it can even dominate over that
for the o-mode. With further magnetic field increase, the intensity
of the RTR x-mode decreases in comparison with the intensity of
the o-mode and this decrease is higher for higher velocities of
energetic electrons. The polarization of the RTR depends on the
velocity of energetic electrons, too. For velocities lower than some
velocity limit v&lt;vi the RTR emission is unpolarized
in a broad interval of magnetic field intensities in the radio
source. For reasonable values of indices of the power-law distribution
functions of energetic electrons, the RTR is broadband in frequencies
(df/f≈0.2−0.4). Furthermore, we show various dependencies of
the RTR and its spectral characteristics. Assuming the same radio
flux of the transition radiation and the gyro-synchrotron one at
the Razin frequency, we estimate the limit magnetic field in the
radio source of the transition radiation. Then, we analyze possible
sources of small-scale inhomogeneities (thermal density fluctuations,
Langmuir and ion-sound waves), which are necessary for the transition
radiation. Although the small-scale inhomogeneities connected with
the Langmuir waves lead to the plasma radiation, which is essentially
stronger than RTR, the inhomogeneities of the ion-sound waves are
suitable for the RTR without any other radiation.

---------------------------------------------------------
Title: Modelling of Optical Emission in Solar Flares
Authors: Varady, M.; Kašparová, J.; Heinzel, P.; Karlický, M.;
Moravec, Z.
2008CEAB...32..101V Altcode:
We present recent progress achieved by our group in the field of flare
optical emission modelling. We concentrate on two problems. Firstly,
on the possibility of modelling of the time evolution of several Balmer
line profiles calculated for real electron fluxes obtained from the hard
X--ray observations of a particular flare with the prospect to compare
the theoretical results with the observed data for the corresponding
flare. Secondly, we discuss the influence of the non--thermal electrons
in the line emitting region on the formation and time evolution of
Balmer hydrogen line profiles.

---------------------------------------------------------
Title: Diagnostics of Magnetic Field in Solar Flare Reconnection Using
Authors: Bárta, M.; Karlický, M.
2008CEAB...32...51B Altcode:
Simultaneous Radio and SXR Observations Based on detailed analysis of
an earlier proposed relation between SXR plasmoid ejecta and Drifting
Pulsating Structures (DPS) in radio spectra we suggested the method
for the estimation of the magnetic field confining the plasmoid
ejected during the solar flare reconnection. After a brief summary of
the principles of the method, its applicability is demonstrated on the
case of a limb flare on October 5, 1992. Using the method, the strength
of the magnetic field confining the plasmoid/flux-rope was estimated
to be ≤ 5× 10^{-4} T for this event. General applicability of the
method is discussed at the end.

---------------------------------------------------------
Title: Dynamics of plasmoids formed by the current sheet tearing
Authors: Bárta, M.; Vršnak, B.; Karlický, M.
2008A&A...477..649B Altcode:
Context: Moving blob-like features observed in the soft X-ray and
EUV range above flare-loops are often interpreted as signatures of
plasmoids formed by the current sheet tearing in the flare-associated
reconnection process. Aims: We investigate the evolution of
the flare-associated current sheet numerically in order to analyse
the kinematics and dynamics of plasmoids. The goal is to explain the
broad diversity of kinematical properties of the plasmoid signatures
recorded by various observational techniques. Methods: We
performed a 2-dimensional resistive-MHD numerical simulation of
the reconnection starting from the Harris-type current sheet. After
identifying the plasmoids, we followed their motion to determine basic
kinematical parameters (velocity and acceleration), and we analysed
the associated magnetic field topology. Results: The simulation
reveals a broad variety of the kinematical/dynamical properties of
plasmoids - after formation, a plasmoid can move upward, downward, or
can even change its direction of propagation. The highest velocities,
in the range of the ambient Alfvén speed, are found in the case of
upward propagating plasmoids. The acceleration is determined by the
net magnetic field tension of the reconnected field lines. Downwardly
propagating plasmoids achieve only a fraction of the ambient Alfvén
speed. They strongly decelerate during the coalescence with low-lying
flare-loops, when distinct energy-release peaks occur and loop system
oscillations are excited. Conclusions: The presented results
explain, qualitatively and quantitatively, the broad spectrum of
kinematical properties of various observational features attributed
to the current-sheet plasmoids.

---------------------------------------------------------
Title: Period variations of radio pulsations observed during decay
phase of the June 06, 2000 flare
Authors: Sawant, Hanumant; Meszarosova, Hana; Cecatto, José;
Karlicky, Marian; Rybak, Jan; Fernandes, Francisco; Andrade, Maria;
Jiricka, Karel
2008cosp...37.2758S Altcode: 2008cosp.meet.2758S
The 22 minutes lasting interval of broadband dm-radio pulsations
observed during decay phase of the June 6, 2000 flare by Brazilian
Solar Spectroscope (BSS) and Ondrejov radiospectrograph in frequency
range 1200-4500 MHz have been analyzed for its complex temporal
variability. To understand the global relationship between radio
fluxes on lower and higher frequencies and to recognize different
emission mechanisms, we have made the cross-correlation of the radio
fluxes at different frequencies during time intervals under study. We
have realized that the dominant periods are not spread during whole
22 minutes time interval but their appearance is concentrated into 7
shorter time subintervals that we have then studied in detail. These
subintervals last 9-33 s, on average 21 s. The pulsations inside the
subintervals usually have higher intensity than the other ones and
characteristic dominant periods of these quasi-regular pulsations are
0.5-78.8 s. We were interested in possible differences among dominant
periods of individual time intervals as well as between the periods
at frequencies below and above 2000 MHz. Periods &gt; 60 s are rather
rare. The periods &lt; 40 s occur more frequently at frequencies below
2000 MHz than at frequencies above 2000 MHz. Occurrence of the periods
&gt; 40 s is similar at frequencies below and above 2000 MHz. Results
are compared with TRACE and EIT/SOHO images and discussed in framework
of multi-scaling flare loop interactions.

---------------------------------------------------------
Title: Return Current Simulations
Authors: Karlický, M.; Nickeler, D. H.
2008CEAB...32...39K Altcode:
The beam-plasma system is studied using a 3-D particle-in-cell
model. Because the electromagnetic effects are included a return current
is produced. The parameters are chosen to simulate a formation of the
return-current in conditions relevant to the transition region and
chromosphere during solar flares.

---------------------------------------------------------
Title: Separation of Accelerated Particles During Reconnection
Processes
Authors: Karlický, M.; Bárta, M.
2008CEAB...32...29K Altcode:
Using a 2.5 D relativistic electromagnetic particle-in-cell code the
acceleration of particles in the electron-positron and electron-"proton"
plasmas during the reconnection process is studied. It is found that
the electrons and positrons as well as electrons and protons appeared
during the tearing and coalescence processes in different locations. In
dependence on the local magnetic field connectivity it can lead to
spatial separation of the accelerated electrons and positrons or
electrons and protons.

---------------------------------------------------------
Title: The Interaction and Coalescence of a Loop-top Kernel with
a Plasmoid
Authors: Kołomański, S.; Karlický, M.
2008CEAB...32...93K Altcode:
We study the interaction and coalescence between a downward moving
plasmoid and a loop-top source recognized in the 30 Nov 2000
flare. Using observations from Yohkoh, GOES, SOHO and Ondřejov,
we performed a multi-wavelength analysis of this event. We found
that the interaction and coalescence of the two sources resulted
in reconnection of their magnetic fields, particle acceleration and
plasma heating. These observations are in agreement with predictions
of numerical modelling.

---------------------------------------------------------
Title: Multi-scale numerical modelling of the current sheet
fragmentation
Authors: Bárta, Miroslav; Karlicky, Marian; Büchner, Jörg
2008cosp...37..196B Altcode: 2008cosp.meet..196B
Magnetic reconnection - considered now commonly as the engine
of solar flares - spans over many mutually coupled scales from
the global flare dimensions (≈107 m) down to the scale, where
dissipation through kinetic effects take place (≈10 m). Direct
numerical simulation covering all the scales is therefore impossible
for obvious reasons: full 3D numerical model would have to involve
1018 grid points. Nevertheless, the filamentary nature of the current
sheet fragmentation give us the chance to describe the process of
reconnection with highly reduced request for number of grid points. As
the smaller-scale dynamics is interesting only in regions of enhanced
current sheet filamentation, we can focus just on these areas,
which occupy only a small fraction of the total volume. Generally,
as the fragmentation continues, it forms a cascade (finished by the
kinetic dissipation) where information relevant for description of
the smaller-scale level occupies only a small fraction of grid points
describing the higher level. Thus, one can subsequently zoom-in
onto the regions of continuing current filamentation. Anticipated
current-sheet-fragmentation cascade supposes multiple dissipative
regions formed in a single current sheet - this fact can play a key
role for direct particle acceleration in reconnection. The numerical
algorithm implementing this 'zooming' technique and the first results
will be presented.

---------------------------------------------------------
Title: Fragmentation of Current Sheet
Authors: Karlický, M.; Bárta, M.
2008CEAB...32...35K Altcode:
An evolution of the electric current in the current sheet along the
electric current direction (along the guiding magnetic field direction)
is studied numerically in the 3D PIC model of the current sheets. In
the regime of the Buneman and kink instabilities the current sheet
becomes strongly fragmented. Besides an increase of the energy of the
electric field component in the guiding magnetic field direction,
the energies of the electric field components in the perpendicular
direction are also enhanced. These processes are found to be connected
with the anomalous resistivity (η_{anom}/η_C = 10^5, where η_C
is the classical resistivity) in the current sheet and the magnetic
field dissipation.

---------------------------------------------------------
Title: Numerical simulations of solar flare processes
Authors: Karlicky, Marian
2008cosp...37.1448K Altcode: 2008cosp.meet.1448K
Using particle-in-cell models the processes of the current sheet
fragmentation, return current formation and electron beam interaction
with the current sheet are studied in details. Computations in the 3-D
model with two current sheets in the Buneman instability regime and
with the extended dimension in the electric current direction show that
the current sheets become very fragmented. The anomalous resistivity
is estimated. Furthermore, a formation of the return current due to
electromagnetic effects is presented. Finally, it is shown that the
electron beam can trigger the flare magnetic reconnection.

---------------------------------------------------------
Title: Interaction of non-thermal particles with solar chromosphere
and solar corona plasma
Authors: Radziszewski, Krzysztof; Rudawy, Pawel; Karlicky, Marian
2008cosp...37.2543R Altcode: 2008cosp.meet.2543R
In our paper we present the results of the simultaneous high temporal
resolution observations of the solar flares in the active region
NOAA 10786 observed on 12 and 13 July 2005. The visual data were
collected with the Multi-Channel Subtractive Double Pass (MSDP)
spectrograph and Solar Eclipse Coronal Imaging System (SECIS) in
Bialkow Observatory (University of Wroclaw, Poland) in H-alpha line
with high temporal resolution of 0.04-0.075 s. The radio observations
were collected in Ondrejov Observatory (Czech Republic) with 0.1 and
0.01 s cadence in 0.8- 2.0, 3.0 and 2.0-4.5 GHz bands using RT5, RT3
and RT4 radiotelescopes, respectively. The X-ray data were recorded
with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
satellite. We found high temporal correlation between the short
lived radio emissions of type III, hard X-ray flux variations and
short lasting variations of the brightness of the H- alpha flaring
kernels observed simultaneously in line center and both wings. High
cadence observations of solar flares has been used to investigate the
interaction of non-thermal particles with solar chromosphere and solar
corona plasma.

---------------------------------------------------------
Title: Highlights of the Brazilian Solar Spectroscope (bss)
Authors: Sawant, Hanumant; Cecatto, José; Meszarosova, Hana; Faria,
Claudio; Fernandes, Francisco; Karlicky, Marian; Andrade, Maria
2008cosp...37.2759S Altcode: 2008cosp.meet.2759S
The digital, decimetric (1000-2500 MHz) Brazilian Solar Spectroscope
(BSS) with high time (10- 1000 ms) and frequency (1-10 MHz) resolution
is in regular operation since April, 1998, at the National Space
Research Institute (INPE) at Sao Jose dos Campos, Brazil. The BSS
has now been upgraded with a new digital data acquisition and data
processing system. The new version of the BSS has a 14 bit A/D unit
which permits improved combination of the observational parameters
with a capability to record up to 200 frequency channels available
in a selectable frequency range of 1000-2500 MHz. It permits data
acquisition up to 5 ms time resolution with a limited number of
frequency channels. The software system of the BSS is composed by
two distinct modules: The first, data acquisition system provides a
flexible Graphical User Interface (GUI) that allows one to choose a
number of observational parameters. The second module is the real
time visualization system that permits real time visualization
of the observed dynamic spectrum and additionally has procedures
for visualization and preliminary analysis of the recorded solar
spectra. Using the new visualization system, we have realized two new
types of dm-radio fine structures: narrow band type III bursts with
positive/negative group frequency drift and dots-emissions arranged
in zebras and fibers.

---------------------------------------------------------
Title: Particle-in-cell simulations of shocks and band splitting of
type II solar radio bursts
Authors: Sakai, J. I.; Karlický, M.
2008A&A...478L..15S Altcode:
Aims:We investigate the emission process of electromagnetic waves
from proton beams reflected by the front of a fast magnetosonic
shock that propagates in a non-uniform density region, by changing
the propagation angle with respect to a uniform magnetic field from
90° to 45°. Methods: A two-dimensional, electromagnetic,
relativistic particle-in-cell (PIC) code is used. Results:
Near the shock front, some protons are reflected and accelerated. The
reflected protons can drag the background electrons to keep the charge
neutrality, resulting in electron acceleration. Due to the accelerated
electrons, the electrostatic waves (Z-modes in the oblique propagation)
can be excited where the reflected protons are generated. It is found
that for about 60° propagation, the extra-ordinary waves can be excited
from the shock front with a double oscillating structure. These waves
are excited both near the fundamental and second harmonic frequency
region of the local plasma frequency. The second harmonic waves have a
band splitting structure and the lower band is brighter than the upper
band part. For 45° propagation, the fundamental frequency region has
a band splitting structure.

---------------------------------------------------------
Title: Spike-like Bursts as Fine Structure of Zebras
Authors: Zlobec, P.; Karlický, M.
2007SoPh..246..419Z Altcode:
We studied the characteristics of the zebra-associated spike-like
bursts that were recorded with high time resolution at 1420 MHz in
four intervals (from 12:45 to 12:48 UT) during 5 August 2003. Our
detailed analysis is based on the selection of more than 500 such
spike-like bursts and it is, at least to our knowledge, the first
study devoted to such short-lived bursts. Their characteristics are
different from those pertinent to "normal" spike bursts, as presented
in the paper by Güdel and Benz (Astron. Astrophys.231, 202, 1990);
in particular, their duration (about 7.4 ms at half power) is shorter,
so they should be members of the SSS (super short structures) family
(Magdalenić et al., Astrophys. J.642, L77, 2006). The bursts were
generally strongly R-polarized; however, during the decaying part
of interval I a low R-polarized and L-polarized bursts were also
present. This change of polarization shows a trend that resembles
the peculiar form of the zebra lines in the spectral dominion ("V"
like). A global statistical analysis on the bursts observed in the
two polarimetric channels shows that the highest cross-correlation
coefficient (about 0.5) was pertinent to interval I. The zebras and the
bursts can be interpreted by the same double plasma resonance process
as proposed by Bárta and Karlický (Astron. Astrophys.379, 1045, 2001)
and Karlický et al. (Astron. Astrophys.375, 638, 2001); in particular,
the spikes are generated by the interruption of this process by assumed
turbulence (density or magnetic field variations). This process should
be present in the region close to the reconnection site (e.g., in the
plasma reconnection outflows) where the density and the magnetic field
vary strongly.

---------------------------------------------------------
Title: Shock drift electron acceleration and generation of waves
Authors: Karlický, M.; Vandas, M.
2007P&SS...55.2336K Altcode:
An analytically derived distribution function of reflected and
accelerated electrons at a nearly perpendicular shock is presented. Then
this distribution in a simplified form is introduced into a 1.5-D
relativistic electromagnetic particle-in-cell (PIC) model and a
generation of waves is studied. Numerical modeling shows not only a
generation of Langmuir and high-frequency electromagnetic waves as
expected, but also an efficient generation of whistler waves. Their
role in emission processes of type II solar radio bursts is discussed.

---------------------------------------------------------
Title: The Eruption from a Sigmoidal Solar Active Region on 2005
May 13
Authors: Liu, Chang; Lee, Jeongwoo; Yurchyshyn, Vasyl; Deng, Na; Cho,
Kyung-suk; Karlický, Marian; Wang, Haimin
2007ApJ...669.1372L Altcode: 2007arXiv0707.2240L
This paper presents a multiwavelength study of the M8.0 flare and
its associated fast halo CME that originated from a bipolar NOAA
AR 10759 on 2005 May 13. The source active region has a conspicuous
sigmoid structure at the TRACE 171 Å channel as well as in the SXI
soft X-ray images, and we mainly concern ourselves with the detailed
process of the sigmoid eruption, as evidenced by the multiwavelength
data ranging from Hα, WL, EUV/UV, radio, and hard X-rays (HXRs). The
most important finding is that the flare brightening starts in the
core of the active region earlier than that of the rising motion of
the flux rope. This timing clearly addresses one of the main issues in
the magnetic eruption onset of sigmoid, namely, whether the eruption
is initiated by an internal tether cutting to allow the flux rope
to rise upward, or a flux rope rises due to a loss of equilibrium to
later induce tether cutting below it. Our high time cadence SXI and Hα
data show that the first scenario is relevant to this eruption. As in
other major findings, we have the RHESSI HXR images showing a change
of the HXR source from a confined footpoint structure to an elongated
ribbon-like structure after the flare maximum, which we relate to the
sigmoid-to-arcade evolution. The radio dynamic spectrum shows a type II
precursor that occurred at the time of expansion of the sigmoid and a
drifting pulsating structure in the flare rising phase in HXRs. Finally,
type II and III bursts are seen at the time of maximum HXR emission,
simultaneous with the maximum reconnection rate derived from the flare
ribbon motion in UV. We interpret these various observed properties
with the runaway tether-cutting model proposed by Moore et al. in 2001.

---------------------------------------------------------
Title: The interaction of a plasmoid with a loop-top kernel
Authors: Kołomański, S.; Karlický, M.
2007A&A...475..685K Altcode:
Aims:We study the interaction between a downward moving plasmoid and
a loop-top kernel recognized in the 30 November 2000 flare. Such
an interaction is predicted by some numerical models of solar
flares. Methods: Using X-ray observations from Yohkoh and GOES,
EUV observations from SOHO, and radio observations from Ondřejov, we
perform multi-wavelength analysis of this interaction. Results:
The Yohkoh/SXT and SOHO/EIT images indicate that the growing flare loop
with the loop-top kernel and the above-lying plasmoid were formed as
a result of the interaction of two extended arcade-loops. While the
flare loop was growing upwards, the plasmoid moved downwards with the
velocity of about 16 km s-1 and interacted with the loop-top
kernel. Many details of this interaction are found, e.g., an increase
of the X-ray and decimetric radio fluxes and an increase of the plasma
temperature at the interaction site. Just after the coalescence of the
plasmoid with the loop-top kernel, the 1-2 GHz pulsating radio structure
and hard X-ray source above the coalescence site were observed. The
analyzed temperature maps indicate flows of heated plasma around
the plasmoid to the location of the X-ray and radio source. These
observations are in agreement with predictions from numerical modelling.

---------------------------------------------------------
Title: On Solar Intermediate Drift Radio Bursts at Decimeter and
Meter Wavelength
Authors: Rausche, G.; Aurass, H.; Mann, G.; Karlický, M.; Vocks, C.
2007SoPh..245..327R Altcode:
Fiber - or intermediate drift - bursts are a continuum fine structure
in some complex solar radio events. We present the analysis of such
bursts in the X17 flare on 28 Oct. 2003. Based on the whistler wave
model of fiber bursts we derive the 3D magnetic field structures that
carry the radio sources in different stages of the event and obtain
insight into the energy release evolution in the main flare phase,
the related paths of nonthermal particle propagation in the corona,
and the involved magnetic field structures. Additionally, we test the
whistler wave model of fiber bursts for the meter and the decimeter
wave range. Radio spectral data (Astrophysikalisches Institut Potsdam,
Astronomical Observatory Ondřejov) show a continuum with fibers for ≈
6 min during the main flare phase. Radio imaging data (Nançay Radio
Heliograph) yield source centroid positions of the fibers at three
frequencies in the spectrometer band. We compare the radio positions
with the potential coronal magnetic field extrapolated from SOHO/MDI
data. Given the detected source site configuration and evolution,
and the change of the fiber burst frequency range with time, we can
also extract those coronal flux tubes where the high-frequency fiber
bursts are situated even without decimeter imaging data. To this aim we
use a kinetic simulation of whistler wave growth in sample flux tubes
modeled by selected potential field lines and a barometric density
model. The whistler wave model of fiber bursts accurately explains
the observations on 28 Oct. 2003. A laterally extended system of low
coronal loops is found to guide the whistler waves. It connects several
neighboring active regions including the flaring AR 10486. For varying
source sites the fiber bursts are emitted at the fundamental mode of
the plasma frequency over the whole range (1200 - 300 MHz). The present
event can be understood without assuming two different generation
mechanisms for meter and decimeter wave fiber bursts. It gives new
insight into particle acceleration and propagation in the low flare
and post-CME corona.

---------------------------------------------------------
Title: Hydrogen Balmer line formation in solar flares affected by
return currents
Authors: Štepán, J. Å.; Kašparová, J.; Karlický, M.; Heinzel, P.
2007A&A...472L..55S Altcode: 2007arXiv0708.0265S
Aims:We investigate the effect of the electric return currents in
solar flares on the profiles of hydrogen Balmer lines. We consider the
monoenergetic approximation for the primary beam and runaway model of
the neutralizing return current. Methods: Propagation of the
10 keV electron beam from a coronal reconnection site is considered
for the semiempirical chromosphere model F1. We estimate the local
number density of return current using two approximations for beam
energy fluxes between 4 × 1011 and 1 × 1012
erg cm-2 s-1. Inelastic collisions of beam and
return-current electrons with hydrogen are included according to their
energy distributions, and the hydrogen Balmer line intensities are
computed using an NLTE radiative transfer approach. Results:
In comparison to traditional NLTE models of solar flares that neglect
the return-current effects, we found a significant increase emission
in the Balmer line cores due to nonthermal excitation by return
current. Contrary to the model without return current, the line
shapes are sensitive to a beam flux. It is the result of variation
in the return-current energy that is close to the hydrogen excitation
thresholds and the density of return-current electrons.

---------------------------------------------------------
Title: Joint Discussion 1 Particle acceleration from solar system
to AGN
Authors: Karlický, Marian; Brown, John C.
2007HiA....14...79K Altcode:
The scene is set for IAU JD01 on Cosmic Particle Acceleration: from
Solar System to AGNs

---------------------------------------------------------
Title: Radio and X-ray diagnostics of electrons accelerated in
solar flares
Authors: Bárta, Miroslav; Karlický, Marian
2007HiA....14...88B Altcode:
Starting from 2.5D MHD modelling of solar flares on a global scale we
calculate (using the PIC and test-particle simulations) the radio and
X-ray emissions generated in solar flare reconnection. Our results
the radio and X-ray spectra and brightness distributions, and their
dynamics are directly comparable with observations providing thus a
test of particle acceleration models as well as of the ‘standard’
global flare scenario.

---------------------------------------------------------
Title: Electron acceleration in a post-flare decimetric continuum
source
Authors: Subramanian, P.; White, S. M.; Karlický, M.; Sych, R.;
Sawant, H. S.; Ananthakrishnan, S.
2007A&A...468.1099S Altcode: 2007astro.ph..3612S
Aims:To calculate the power budget for electron acceleration and the
efficiency of the plasma emission mechanism in a post-flare decimetric
continuum source. Methods: We have imaged a high brightness
temperature (∼ 109 K) post-flare source at 1060 MHz with
the Giant Metrewave Radio Telescope (GMRT). We use information from
these images and the dynamic spectrum from the Hiraiso spectrograph
together with the theoretical method described in Subramanian &amp;
Becker (2006, Sol. Phys., 237, 185) to calculate the power input to the
electron acceleration process. The method assumes that the electrons
are accelerated via a second-order Fermi acceleration mechanism. Results: We find that the power input to the nonthermal electrons
is in the range 3× 1025-1026 erg/s. The
efficiency of the overall plasma emission process starting from electron
acceleration and culminating in the observed emission could range from
2.87× 10-9 to 2.38 × 10-8.

---------------------------------------------------------
Title: Hα with Heating by Particle Beams
Authors: Kašparová, J.; Varady, M.; Karlický, M.; Heinzel, P.;
Moravec, Z.
2007ASPC..368..441K Altcode: 2007astro.ph..3800K
Using 1D NLTE radiative hydrodynamics we model the influence of the
particle beams on the Hα line profile treating the beam propagation and
the atmosphere evolution self-consistently. We focus on the influence
of the non-thermal collisional rates and the return current. Based on
our results, we propose a diagnostic method for determination of the
particle beam presence in the formation regions of the Hα line.

---------------------------------------------------------
Title: Multiwavelength Study of the May 13, 2005 Flare Event
Authors: Rovira, M. G.; Šimberová, S.; Karlický, M.; Luoni,
M. L.; Fárnik
2007ASPC..368..461R Altcode:
A global view to the flare evolution via the image data of various parts
of electromagnetic spectra is introduced. Data from the ground-based
observations in Hα (HASTA, El Leoncito, Argentina) and radio spectra in
the 1-2-4.5 GHz range (Radiospectrographs, Ondřejov, Czech Republic)
have been analyzed. As to the space observations, there were involved
data of the event from SoHO (MDI, EIT, LASCO C2) and RHESSI (X-ray
sources). Some results of possible relations among various layers
of the Sun's atmosphere and following astrophysical interpretation
are presented.

---------------------------------------------------------
Title: Return Current and Energy Deposit in Flares
Authors: Varady, M.; Karlický, M.; Kašparová, J.
2007ASPC..368..473V Altcode:
The return current (RC) related effects represent in flares one
of the possible mechanisms of conversion of the kinetic energy of
electron beams into the thermal energy of flare plasma. Using a 1-D
current-in-cell model, details of formation and properties of the RC
driven by monoenergetic electron beams are calculated. Based on results
of the simulations, the influence of the RC on the energy deposit in
flares is discussed.

---------------------------------------------------------
Title: The Radio-Coronal Mass Ejection Event on 2001 April 15
Authors: Maia, Dalmiro Jorge Filipe; Gama, Ricardo; Mercier, Claude;
Pick, Monique; Kerdraon, Alain; Karlický, Marian
2007ApJ...660..874M Altcode:
On 2001 April 15, the Nançay radioheliograph observed fast-moving,
expanding loops in images taken in the wavelength range between 164
and 432 MHz. We were able to follow the progression of the radio loops,
starting from a few tenths to more than 1 Rsolar above the
solar limb, with a time cadence of order seconds. The loops seen in
radio agree very well with the features of the coronal mass ejection
(CME) seen later, more than 2.5 Rsolar above the limb,
in white-light images by the Large Angle Spectrometric Coronagraph
(LASCO) experiment on board the Solar and Heliospheric Observatory
(SOHO) spacecraft. The event is well associated with an energetic
electron event seen by the Electron, Proton, and Alpha Monitor
(EPAM) experiment on board the Advanced Composition Explorer (ACE)
spacecraft. A detailed transport model for the electrons shows that,
not only the inferred onset at the Sun, but also the duration of
the particle release, are similar for the radio loop and the in situ
electron event detected near the Earth.

---------------------------------------------------------
Title: Drifting pulsating structures generated during tearing and
coalescence processes in a flare current sheet
Authors: Karlický, M.; Bárta, M.
2007A&A...464..735K Altcode:
Aims:Based on particle-in-cell simulations, drifting pulsating
structures are interpreted as the radio emission generated during
tearing and coalescence processes in the current sheet of a flare. Methods: A 2.5D particle-in-cell electromagnetic relativistic code
was used considering two versions of the model: a) the model with
one current sheet with free boundary conditions and b) the model with
two current sheets and periodic boundary conditions. The dispersion
diagrams of electromagnetic waves we then constructed using the 2D
Fourier transform. Results: It is found that electrons are
accelerated most efficiently in the region near the x-point of the
magnetic field structure in the phase at the end of tearing process
and at the beginning of plasmoid coalescence. The most energetic
electrons are distributed mainly along the x-lines of the magnetic field
structure. During these processes, Langmuir waves are generated, along
with the electromagnetic (radio) ones. It looks as these electromagnetic
waves can be observed mainly on the second harmonics of the plasma
frequencies corresponding to the plasma densities in the external
parts of the plasmoids.

---------------------------------------------------------
Title: Collapsing magnetic trap as accelerator of electrons in
solar flares
Authors: Karlický, M.; Bárta, M.
2007AdSpR..39.1427K Altcode:
A collapsing trap in the cusp topology of solar flares is simulated
using a 2D MHD model. Then in this collapsing trap trajectories
of test electrons and their acceleration are studied in detail. In
the model we use the test particle technique with the guiding centre
approximation including also collisional losses and scattering of test
electrons. Computing the X-ray emission of the accelerated electrons
it is shown that the acceleration process in the collapsing trap easily
explains the formation of observed loop-top X-ray sources.

---------------------------------------------------------
Title: Magnetic reconnection in solar flares and corresponding
radio bursts
Authors: Karlický, M.; Bárta, M.
2007AdSpR..39.1415K Altcode:
The 2D MHD model of the flare magnetic reconnection shows that a
reconnection activity, changes of the magnetic field topology and
generation of waves are connected. It is found that after the phase of
a quasi-stationary reconnection in the extended current sheet above the
flare arcade the tearing mode instability produces the plasmoids which
then can interact and generate MHD waves. Results of particle-in-cell
simulations of the tearing processes, which accelerate electrons, are
mentioned. Then all these processes are discussed from the point of
view of possible radio emissions. While shocks can contribute to the
type II radio burst, the superthermal electrons trapped in plasmoids
can generate so called drifting pulsating structures. Furthermore,
regions with the MHD turbulence may manifest themselves as the lace
or dm-spike bursts.

---------------------------------------------------------
Title: High-Frequency Fiber Bursts Observed during The July 11,
2005 Flare
Authors: Karlický, M.; Jiřička, K.; Sawant, H. S.; Cecatto, J. R.;
Fernandes, F. C. F.; Andrade, M. C.
2007CEAB...31..181K Altcode:
A unique quasi-periodic activity of the 1-2 GHz fiber bursts observed
during the July 11, 2005, B4.0 flare is presented. Groups of fibers
and individual fibers occur with the period of about of 65 s and 1
s, respectively. The frequency drift of the fibers was found in the
interval -40 - -160 MHz s^{-1}. Unique cases of a sudden start and
sudden end of a group of fibers are shown. Considering the whistler or
Alfvén wave velocities for the interpretation of the frequency drift of
fibers and the Aschwanden's density model (2002) the magnetic field in
the fiber radio source was estimated as 8-9 G or 25-60 G, respectively.

---------------------------------------------------------
Title: Flare-Associated X-Ray Plasma Ejections and Radio Drifting
Structures
Authors: Kołomański, S.; Tomczak, M.; Ronowicz, P.; Karlický, M.;
Aurass, H.
2007CEAB...31..125K Altcode:
A suggestion that radio drifting structures (DSs) are emitted by
electrons trapped inside plasmoids that are seen as X-ray plasma
ejections (e.g. Khan et al., 2002) was illustrated for a small group of
events. We present preliminary results of a survey in which a list of
DSs observed in Ondřejov and Potsdam has been confronted with Yohkoh
Soft X-ray Telescope observations.

---------------------------------------------------------
Title: MHD Waves and Shocks Generated during Magnetic Field
Reconnection
Authors: Bárta, M.; Karlický, M.; Vršnak, B.; Goossens, M.
2007CEAB...31..165B Altcode:
We use a 2D MHD model of magnetic field reconnection to investigate
if and how bursts of reconnection activity, changes of the magnetic
field and shock wave generation are related. We found that major
bursts of power dissipated into Joule heat occur during topological
transitions of the magnetic field structure. These bursts are followed
by shocks and waves. Along the plasma outflow jet not only MHD waves,
but also ion-sound shocks are formed. After the phase of more or
less quiet reconnection (Petschek-type) the tearing mode produces
plasmoids. The interactions of these plasmoids are associated with
further bursts of the reconnection activity and a complex structure
of shock waves. Finally, all these processes are discussed as possible
sources of various radio bursts.

---------------------------------------------------------
Title: Spatial Structure and Spectra of X-Ray Sources During the
0.8 4.5 GHz Reverse Drift Bursts Observations
Authors: Fárník, F.; Karlický, M.
2007SoPh..240..121F Altcode:
In the years 2002 - 2005, 38 groups of the reverse drift bursts (RDBs)
were observed in the 0.8 - 4.5 GHz frequency range by the Ondřejov
radiospectrograph. In 21 cases, which were observed at the times
of the RHESSI observations, spatial structure, positional changes,
and spectra of X-ray sources during RDB observations are studied in
detail. First, based on the frequency drift and the spatial structure
of the associated X-ray source, the events are classified as: (a)
fast drifting RDBs with a compact X-ray source, (b) fast drifting RDBs
with a multiple X-ray source (FM), and slowly drifting RDBs. Then,
the spectra of X-ray sources at the times of RDBs are analyzed. It is
found that most fast drifting RDBs (16 of 17 cases) are associated with
the spectra having a distinct power-law (non-thermal) component. In
contrast, the X-ray spectra associated with the slowly drifting
RDBs are predominantly purely thermal (in three out of four cases;
in the 26 July 2004, case the X-ray spectrum is thermal and high
temperature, with non-thermal component). Two special cases of RDBs
observed during the 28 October 2003, and 23 July 2004, flares are
added for comparison. The most frequent events are those with fast
drifting RDBs, a compact short-lasting X-ray sources, and a power-law
X-ray spectrum. The individual reverse drift bursts (∼1 s duration)
do not show a clear temporal association with individual peaks of hard
X-ray bursts. During slowly drifting RDBs the shape of the associated
X-ray source changed or expanded. Among them the most interesting
one was observed in 26 July 2004, when the very slowly drifting RDBs
(+40 MHz s−1) were associated with an X-ray loop-like
source continuously elongating in the southwest direction. In the
most cases the model of RDBs with electron beams is compatible with
the observations, but in flares on 26 July 2004, and 28 October 2003,
the RDBs are probably generated by some other type of an agent; we
propose here a thermal conduction front.

---------------------------------------------------------
Title: Long period variations of dm-radio and X-ray fluxes in three
X-class flares
Authors: Mészárosová, H.; Karlický, M.; Rybák, J.; Fárník,
F.; Jiřička, K.
2006A&A...460..865M Altcode:
Aims.Long period (≥60 s) variations of the radio (0.8-4.5 GHz) and
X-ray fluxes observed during the July 14, 2000, April 12, 2001, and
April 15, 2001 flares by the Ondřejov radiospectrograph and Yohkoh
spacecraft are studied by statistical methods. Methods: .In
the flares under study, characteristic periods are searched for by the
Fourier and wavelet methods. To understand the origin of the 0.8-4.5 GHz
drifting burst with long period variations, observed at the beginning of
the April 15, 2001 flare, cross-correlations, time shifts, coherence,
and phase differences in its time series are computed. Results:
.The global statistical study of these flares revealed characteristic
periods in the interval of 60-513 s in the radio (0.8-4.5 GHz) and
60-330 s in the X-ray Yohkoh fluxes. Cross-correlations between the
radio fluxes at different frequencies helped us to determine the bursts
generated by plasma or gyro-synchrotron mechanisms. In the April 12,
2001 flare, soft X-ray fluxes of the sources located at the loop-top
and footpoints of a flare loop vary with the period of 60-320 s, and
they are highly correlated. But their relation to the radio (1.1 GHz -
plasma emission and 4.0 GHz - gyro-synchrotron emission) is complex. At
the beginning of the April 15, 2001 flare, in the 0.8-4.5 GHz range,
a broadband drifting radio burst with the time variation of 61-320 s
was observed at times of flare loop ejection. Its detailed statistical
analysis shows that this burst consists of two parts, and, that first
part is generated by the plasma emission mechanism and the second,
probably, by the gyro-synchrotron one. The characteristic period of
about 300 s found in three X-class flares in their dm-radio and X-ray
emissions is discussed.

---------------------------------------------------------
Title: Are heliospheric flows magnetic line- or flux-conserving?
Authors: Nickeler, D. H.; Karlický, M.
2006ASTRA...2...63N Altcode:
This article discusses and tests the validity of the frozen in magnetic
field paradigm (or 'ideal magnetohydrodynamics (MHD) constraint')
which is usually adopted by many authors dealing with heliospheric
physics. To show the problem of using ideal MHD in
such a counterflow configuration like the heliosphere, we first
recapitulate the basic concepts of freezing-in of magnetic fields,
respectively magnetic topology conservation and its violation (=
magnetic reconnection) in 3-D, already done by other authors with
different methods with respect to derivations and interpretations. Then
we analyse different heliospheric plasma environments. As a model of the
stagnation region/stagnation point in front of the heliospheric nose,
we present and discuss the general solution of the ideal MHD Ohm's law
in the vicinity of a 2-D stagnation point, which was found by us. We show that ideal MHD either leads necessarily to a diverging
magnetic field strength in the vicinity of such a stagnation point, or
to a vanishing mass density on the heliopause boundaries. In the case
that components of the electric field parallel to the magnetic field
do not exist due to the chosen form of the non-ideal Ohm's law, it is
always possible to formulate the transport equation of the magnetic
field as a modified ideal Ohm's law. We find that the
form of the Ohm's law which is often used in heliospheric physics (see
e.g. Baranov and Fahr, 2003), is not able to change magnetic topology
and thus cannot lead to magnetic reconnection, which necessarily has
to occur at the stagnation point. The diverging magnetic field, for
instance, implies the breakdown of the flux freezing paradigm for the
heliosphere. Its application, especially at the heliospheric nose,
is therefore rather doubtful. We conclude that it is necessary to
search for an Ohm's law which is able to violate magnetic topology
conservation.

---------------------------------------------------------
Title: Stationary Reconnection Of 2.5D Magnetic Fields And Localized
Non-Idealness In Incompressible MHD Flows
Authors: Nickeler, D. H.; Barta, M.; Karlicky, M.
2006IAUJD...3E..55N Altcode:
We construct 2D potential magnetic fields for modelling pre-flare
magnetic field structures. We ask the question how the application of
magnetic shear components, i.e. components of the magnetic field in the
invariant direction, could be a source of stationary reconnection. We
also ask how this is coupled to the localized non-idealness which
produces field aligned electric field components, indicating that
magnetic reconnection takes place.

---------------------------------------------------------
Title: Radio and X-ray Diagnostics of Electrons Accelerated in
Solar Flares
Authors: Bárta, M.; Karlický, M.
2006IAUJD...1E...7B Altcode:
It is well known fact that solar flares are efficient particle
accelerators - even several concurrent acceleration processes can
take place in a single flaring volume. Using hybrid and particle
simulations we study some of them, namely the direct acceleration
in the current sheet torn during the magnetic reconnection, the
acceleration in collapsing magnetic traps formed inside the cusp
structure, and pinch-effects in non-equilibrium plasmoids newly
created by the reconnection process. In order to relate our models
more directly to the real world we not only calculate the dynamics
of electron distribution functions but we extent our results to the
form comparable with observations. As accelerated particles in the
solar atmosphere manifest themselves most remarkably by the radio and
X-ray emissions the final outputs of our modelling are radio and X-ray
spectra and their dynamics as well as spatial structures of X-ray and
radio sources. The obtained results are, of course, sensitive to the
parameters of the used flare model. Conversely, fitting the observed and
the modelled data provides us with the diagnostic tool for investigation
of conditions under which the acceleration in the solar flares proceeds.

---------------------------------------------------------
Title: Electron Acceleration in a Wavy Shock Front
Authors: Vandas, M.; Karlicky, M.
2006IAUJD...1E..39V Altcode:
It is known that electrons are accelerated at nearly perpendicular
shocks by the drift mechanism. And it is also known that energy gain
of electrons caused by this mechanism is not very high. Therefore it
was suggested in the past that the energy gain might be increased if
shocks had wavy fronts. For instance, there were attempts to explain
coronal type II burst and their fine structure by electron acceleration
in a wavy shock front. We studied numerically electron acceleration at
nearly perpendicular shocks. We found that energy gains of electrons
at a wavy shock front and a corresponding smoothed plane shock were
comparable. That is why they do not depend significantly on the shock
thickness, magnetic field profile inside the shock, and shock wavy
form; they depend on the angle between the smoothed shock front and
ambient magnetic field.

---------------------------------------------------------
Title: Simulation of magnetic field dissipation in astrophysical jets
Authors: Topinka, M.; Topinka, M.; Karlický, M.
2006IAUJD...1E..43T Altcode:
We report first results of the numerical 3D MHD simulations of
magnetic field dissipation applied to magnetically driven astrophysical
jets. These simulations are considered to be a part of the gamma-ray
burst model based on Poynting flux dominated outflow.

---------------------------------------------------------
Title: Quasi-Static Sequences Of 2D Magnetic Potential Fields In
Barotropic Ideal MHD Flows
Authors: Nickeler, D. H.; Barta, M.; Karlicky, M.
2006IAUJD...3E..56N Altcode:
2D potential fields for modelling pre-flare magnetic field structures
have already often been used in the literature. The equation of motion
is often neglected as the plasma beta is assumed to be very small in
the regions above the photosphere. In contrast to that we analyse how
magnetic potential fields do evolve in the frame of barotropic ideal
MHD flows. Here neither the pressure gradient nor the equation of
motion can be neglected. We show special solutions by solving the set
of ideal MHD equations in the case of a quasi-static approach. This
implies that the non-linear term in the equation of motion is neglected.

---------------------------------------------------------
Title: X-Ray Loop-Top Source Generated by Processes in a Flare
Collapsing Trap
Authors: Karlický, M.; Bárta, M.
2006ApJ...647.1472K Altcode:
Using the two-dimensional MHD model of the magnetic reconnection,
the cusp structure with the collapsing trap is simulated. Scaling
these computational results into solar flare conditions, we study the
electron acceleration in the collapsing trap. We use the test-particle
technique with the guiding center approximation in which the collisional
losses and scattering of accelerated electrons are included. We found
that this “secondary” acceleration process essentially modifies the
distribution function of electrons preaccelerated in the reconnection
process. The collapsing trap consists of a structure with the return
current, which influences the spatial structure of the loop-top X-ray
source. The significance of the curvature drift of electrons in the
electric field direction for the electron acceleration is confirmed. The
acceleration is more efficient, and the X-ray loop-top source is more
intense, but spatially more prolonged than the X-ray source computed
in the model without this drift.

---------------------------------------------------------
Title: Collapsing magnetic trap as accelerator of electrons in
solar flares
Authors: Karlicky, M.; Barta, M.
2006IAUJD...1E..28K Altcode:
A collapsing trap in the cusp topology of solar flares is simulated
using a 2-D MHD model. Then in this collapsing trap trajectories
of test electrons and their acceleration are studied in detail. In
the model we use the test particle technique with the guiding centre
approximation including also collisional losses and scattering of test
electrons. Computing the X-ray emission of the accelerated electrons
it is shown that the acceleration process in the collapsing trap easily
explain a formation of observed loop-top X-ray sources.

---------------------------------------------------------
Title: Return Current And The Energy Deposit In Flares
Authors: Varady, M.; Karlicky, M.; Kasparova, J.
2006IAUJD...1E..51V Altcode:
The return current related effects in flares represent one of the
possible mechanisms of conversion of the kinetic energy of electron
beams into the thermal energy of flare plasma. Using a 1-D particle in
cell model details of formation and properties of the return current
driven by monoenergetic electron beams are calculated. Using the results
of the simulations the influence of the return current on the energy
deposit in flares are discussed.

---------------------------------------------------------
Title: Reverse Drift Bursts in the 0.8-4.5 GHz Band and their Relation
to X-rays
Authors: Fárnik, F.; Karlický, M.
2006ESASP.617E.127F Altcode: 2006soho...17E.127F
No abstract at ADS

---------------------------------------------------------
Title: Waves generated by reflected and accelerated electrons at a
nearly perpendicular shock
Authors: Karlický, M.; Vandas, M.
2006A&A...453.1089K Altcode:
Aims.We study a generation of waves by reflected and accelerated
electrons at a nearly perpendicular shock. Methods: .A shifted
loss-cone distribution of reflected and accelerated electrons at a
nearly perpendicular shock is derived analytically. Then in a simplified
form called here "cone" beam, this distribution is incorporated into
a 2D relativistic electromagnetic particle-in-cell model and the wave
generation is studied. Results: .Numerical modelling shows not
only a generation of Langmuir and high-frequency electromagnetic waves,
as expected, but also an efficient generation of whistler waves by the
normal Doppler resonance process. While the intensity of Langmuir waves
increases with the increase in the "cone" beam energy in a parallel
direction to the magnetic field, the whistlers are most effectively
generated for high values of the perpendicular beam energy. There are
indications that the whistlers participate in conversion processes
generating the high-frequency electromagnetic waves. Conclusions:
.Using a numerical model we found an efficient generation of Langmuir,
whistler, and electromagnetic waves by electrons reflected and
accelerated at a nearly perpendicular shock. Results are discussed in
connection with the herringbone structure of type II radio bursts. The
possible role of transmitted electrons is mentioned.

---------------------------------------------------------
Title: Simulation of Active Region Coronal Loops EUV Emission
Authors: Dudík, J.; Dzifčáková, E.; Karlický, M.; Wu, S. T.;
Wang, A. H.
2006ESASP.617E..57D Altcode: 2006soho...17E..71D
No abstract at ADS

---------------------------------------------------------
Title: Electron Acceleration and Transport During the November 5,
1998 Solar Flare At ∼13:34 UT
Authors: Trottet, G.; Correia, E.; Karlický, M.; Aulanier, G.; Yan,
Y.; Kaufmann, P.
2006SoPh..236...75T Altcode:
This paper deals with a detailed analysis of spectral and imaging
observations of the November 5, 1998 (Hα 1B, GOES M1.5) flare
obtained over a large spectral range, i.e., from hard X-rays to
radiometric wavelengths. These observations allowed us to probe electron
acceleration and transport over a large range of altitudes that is to
say within small-scale (a few 103 km) and large-scale (a few
105 km) magnetic structures. The observations combined with
potential and linear force-free magnetic field extrapolations allow
us to show that: (i) Flare energy release and electron acceleration
are basically driven by loop-loop interactions at two independent, low
lying, null points of the active region magnetic field; (ii) &lt;300 keV
hard X-ray-producing electrons are accelerated by a different process
(probably DC field acceleration) than relativistic electrons that
radiate the microwave emission; and (iii) although there is evidence
that hard X-ray and decimetric/metric radio-emitting electrons are
produced by the same accelerator, the present observations and analysis
did not allow us to find a clear and direct magnetic connection between
the hard X-ray emitting region and the radio-emitting sources in the
middle corona.

---------------------------------------------------------
Title: Evidence for Tether-Cutting Reconnection in a Quadrupole
Magnetic Configuration in the April 9, 2001, M7.9 Flare
Authors: Yurchyshyn, V.; Karlický, M.; Hu, Q.; Wang, H.
2006SoPh..235..147Y Altcode:
We studied the M7.9 flare on April 9, 2001 that occurred within a
δ-sunspot of active region NOAA 9415. We used a multi-wavelength
data set, which includes Yohkoh, TRACE, SOHO, and ACE spacecraft
observations, Potsdam and Ondřejov radio data and Big Bear Solar
Observatory (BBSO) images in order to study the large-scale structure
of this two-ribbon flare that was accompanied by a very fast coronal
mass ejection (CME). We analyzed light curves of the flare emission as
well as the structure of the radio emission and report the following:
the timing of the event, i.e., the fact that the initial brightenings,
associated with the core magnetic field, occurred earlier than the
remote brightening (RB), argue against the break-out model in the
early phase of this event. We thus conclude that the M7.9 flare and
the CME were triggered by a tether-cutting reconnection deep in the
core field connecting the δ-spot and this reconnection formed an
unstable flux rope. Further evolution of the erupted flux rope could
be described either by the "standard" flare model or a break-out
type of the reconnection. The complex structure of flare emission
in visible, X-ray, and radio spectral ranges point toward a scenario
which involves multiple reconnection processes between extended closed
magnetic structures.

---------------------------------------------------------
Title: Shrinking and Cooling of Flare Loops in a Two-Ribbon Flare
Authors: Vršnak, Bojan; Temmer, Manuela; Veronig, Astrid; Karlický,
Marian; Lin, Jun
2006SoPh..234..273V Altcode:
We analyze the evolution of the flare/postflare-loop system in the
two-ribbon flare of November 3, 2003, utilizing multi-wavelength
observations that cover the temperature range from several tens of
MK down to 104 K. A non-uniform growth of the loop system
enables us to identify analogous patterns in the height-time, h(t),
curves measured at different temperatures. The "knees," "plateaus,"
and "bends" in a higher-temperature curve appear after a certain time
delay at lower heights in a lower-temperature curve. We interpret such
a shifted replication as a track of a given set of loops (reconnected
field lines) while shrinking and cooling after being released from the
reconnection site. Measurements of the height/time shifts between h(t)
curves of different temperatures provide a simultaneous estimate of
the shrinkage speed and cooling rate in a given temperature domain,
for a period of almost ten hours after the flare impulsive phase. From
the analysis we find the following: (a) Loop shrinkage is faster at
higher temperatures - in the first hour of the loop-system growth,
the shrinkage velocity at 5 MK is 20 - 30 km s−1, whereas
at 1 MK it amounts to 5 km s−1; (b) Shrinking becomes
slower as the flare decays - ten hours after the impulsive phase,
the shrinkage velocity at 5 MK becomes 5 km s−1; (c) The
cooling rate decreases as the flare decays - in the 5 MK range it is
1 MK min−1 in the first hour of the loop-system growth,
whereas ten hours later it decreases to 0.2 MK min−1;
(d) During the initial phase of the loop-system growth, the cooling
rate is larger at higher temperatures, whereas in the late phases
the cooling rate apparently does not depend on the temperature; (e)
A more detailed analysis of shrinking/cooling around one hour after
the impulsive phase reveals a deceleration of the loop shrinkage,
amounting to ā ≈ 10 m s−2 in the T &lt; 5 MK range;
(f) In the same interval, conductive cooling dominates down to T ≈
3 MK, whereas radiation becomes dominant below T ≈ 2 MK; (g) A few
hours after the impulsive phase, radiation becomes dominant across the
whole T &lt; 5 MK range. These findings are compared with results of
previous studies and discussed in the framework of relevant models.

---------------------------------------------------------
Title: Interference patterns in solar radio spectra: high-resolution
structural analysis of the corona
Authors: Bárta, M.; Karlický, M.
2006A&A...450..359B Altcode:
Aims.We present a new method for high-resolution structural analysis
of the solar corona. Methods: .The relationship between the
spectral features of various types of solar radio bursts and the
physical properties of their sources have been extensively studied
by many authors. On the other hand, it is plausible to accept that
the spectral properties of the solar radio radiation received on the
Earth are - besides the physics of the radio source - influenced by an
inter-laying medium that radio waves propagate through. In particular,
the regular structures in the solar corona - such as coronal waves,
oscillations in shock fronts, the fine structures of coronal loops,
streamer current sheets, etc. - might efficiently filter transferred
radio radiation just as (broad-band) X-rays are filtered by a periodic
atomic structure of crystals; the difference is only in the spatial
scale. Using the wave optics methods, we investigate the prospective
influence of considered coronal structures on the propagating radio
waves originating in an external remote source. Results:
.Preliminary results have shown that the resulting modelled radio
emission may recall the spectra of observed zebra patterns for the
simple 1D density structure considered here and for a reasonable set of
parameters. Conversely, it is suggested that the spectra of the zebra
patterns might be used for an analysis of those coronal structures that
made these traces on the radiation by methods similar to those used
in crystallography. The possibility of the presence of such regular
small scale structures in the solar corona is demonstrated. For
completeness, a brief review of contemporary models of the zebra
patterns is provided.

---------------------------------------------------------
Title: Multi-wavelength study of coronal waves associated with the
CME-flare event of 3 November 2003
Authors: Vršnak, B.; Warmuth, A.; Temmer, M.; Veronig, A.;
Magdalenić, J.; Hillaris, A.; Karlický, M.
2006A&A...448..739V Altcode:
The large flare/CME event that occurred close to the west solar limb on
3 November 2003 launched a large-amplitude large-scale coronal wave that
was observed in Hα and Fe xii 195 Å spectral lines, as well as in the
soft X-ray and radio wavelength ranges. The wave also excited a complex
decimeter-to-hectometer type II radio burst, revealing the formation of
coronal shock(s). The back-extrapolation of the motion of coronal wave
signatures and the type II burst sources distinctly marks the impulsive
phase of the flare (the hard X-ray peak, drifting microwave burst,
and the highest type III burst activity), favoring a flare-ignited
wave scenario. On the other hand, comparison of the kinematics of
the CME expansion with the propagation of the optical wave signatures
and type II burst sources shows a severe discrepancy in the CME-driven
scenario. However, the CME is quite likely associated with the formation
of an upper-coronal shock revealed by the decameter-hectometer type II
burst. Finally, some six minutes after the launch of the first coronal
wave, another coronal disturbance was launched, exciting an independent
(weak) decimeter-meter range type II burst. The back-extrapolation
of this radio emission marks the revival of the hard X-ray burst,
and since there was no CME counterpart, it was clearly ignited by the
new energy release in the flare.

---------------------------------------------------------
Title: X-ray sources and magnetic reconnection in the X3.9 flare of
2003 November 3
Authors: Veronig, A. M.; Karlický, M.; Vršnak, B.; Temmer, M.;
Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W.
2006A&A...446..675V Altcode:
Context: .Recent RHESSI observations indicate an apparent altitude
decrease of flare X-ray loop-top (LT) sources before changing to the
commonly observed upward growth of the flare loop system. Aims:
.We performed a detailed study of the LT altitude decrease for one well
observed flare in order to find further hints on the physics of this
phenomenon and how it is related to the magnetic reconnection process in
solar flares. Methods: .RHESSI X-ray source motions in the 2003
November 3, X3.9 flare are studied together with complementary data
from SXI, EIT, and Kanzelhöhe Hα. We particularly concentrate on the
apparent altitude decrease of the RHESSI X-ray LT source early in the
flare and combine kinematical and X-ray spectral analysis. Furthermore,
we present simulations from a magnetic collapsing trap model embedded
in a standard 2-D magnetic reconnection model of solar flares. 
Results: .We find that at higher photon energies the LT source is
located at higher altitudes and shows higher downward velocities
than at lower energies. The mean downward velocities range from
14 km s-1 in the RHESSI 10-15 keV energy band to 45 km
s-1 in the 25-30 keV band. For this flare, the LT altitude
decrease was also observed by the SXI instrument with a mean speed of
12 km s-1. RHESSI spectra indicate that during the time
of LT altitude decrease the emission of the LT source is thermal
bremsstrahlung from a "superhot" plasma with temperatures increasing
from 35 MK to 45 MK and densities of the order of 1010
cm-3. The temperature does not significantly increase
after this early (pre-impulsive superhot LT) phase, whereas the
LT densities increase to a peak value of (3-4) × 1011
cm-3. Conclusions: .Modeling of a collapsing magnetic
trap embedded in a standard 2D magnetic reconnection model can reproduce
the key observational findings in case that the observed emission is
thermal bremsstrahlung from the hot LT plasma. This agrees with the
evaluated RHESSI spectra for this flare.

---------------------------------------------------------
Title: X-Ray Emission from Flare Collapsing Trap
Authors: Karlický, Marian
2006SSRv..122..161K Altcode:
An acceleration process in the collapsing magnetic trap, formed in the
flare with cusp magnetic field topology, is described. Computations
show that high-energy electrons are accumulated in the central part
of the collapsing magnetic trap due to an increase of their pitch
angles. The effect explains in a natural way the formation of X-ray
loop-top sources. Then, using the model with the collapsing trap and
considering only the adiabatic heating process, a possible explanation
for the motion of the X-ray loop-top source observed at the beginning
of some cusp-type flares is presented.

---------------------------------------------------------
Title: Investigations of spatially resolved 1.28 GHz radio activity
associated with solar X-Ray micro flares
Authors: Sawant, H. S.; Krucker, S.; Madsen, F. R. H.; Kane, S.;
Karlicky, M.; Ananthakrishnan, S.; Subramanian, P.
2006cosp...36.3365S Altcode: 2006cosp.meet.3365S
On 20 and 22 November 2005 Solar observations at 1280 MHz were carried
out from 04 00 to 11 30UT at the Giant Metrewave Radio Telescope --
GMRT - with time resolution of 512 ms and spatial resolution of sim
5 arc sec During GMRT observation time on both days micro flares have
been observed by RHESSI satellites in the range of 3 -- 10 keV Detailed
investigation of the X-ray emission shows the presence of both thermal
and non-thermal components Imaging analysis of one of the micro flares
in x ray shows the RHESSI data can produce image with resolution of 7
Here we report an investigation of simultaneous 1 28 GHz radio activity
and 3-10 keV X-ray observations of solar X-ray micro flares as observed
on 20 November during the interval 08 00-08 30 UT

---------------------------------------------------------
Title: Post-flare oscillation on November 17, 2001 flare at decimeter
wavelength
Authors: Sych, R.; Subramanian, P.; Karlicky, M.; Ananthakrishnan,
S.; Sawant, H.
2006cosp...36.1160S Altcode: 2006cosp.meet.1160S
On 17th November 2001 at GMRT observations were carried out at 1060
MHz with time resolution of 2 sec An M2 8 flare associated with active
region was observed from 04 45 UT to 06 11 UT In the main phase of the
flare the prominence eruption was observed at 17 GHz by the Nobeyama
Radioheliograph associated with ejection of halo CME Type III of radio
emission superimposed on drifting continuum was recorded by HIRAISO
dynamic spectrum in the frequency range of 25-1500 MHz from 05 00 UT
to 05 55 UT Post flare observations during the period 05 30-05 55 UT
of GMRT light curve indicates the long duration oscillation From GMRT
observation one can infer that these oscillations are originated in
a southern compact source In order to investigate time evolution of
GMRT radio sources we developed new method based on the continuous
wavelet transform which shows periodicities of the order of 100 sec
These results are discussed This research was supported by the grants
of RFFI 04-02-39003 05-07-90147

---------------------------------------------------------
Title: Model of Motion of the X-Ray Loop-Top Source at the Beginning
of Cusp-Type Flares
Authors: Karlický, M.; Veronig, A.; Vršnak, B.
2006CEAB...30...85K Altcode:
A model with a 1-D collapsing magnetic trap is proposed for
an explanation of the motion of the X-ray loop-top source at the
beginning of cusp-type flares. Considering plasma heating due to the
betatron mechanism an analytic formula for the temporal and spatial
evolution of heated plasma temperature in the trap is derived. Using
the formula and the relation for thermal bremsstrahlung flux, the
time evolution of the X-ray intensity profile in the trap is computed
numerically. The model explains not only the downward motion of the
X-ray loop-top source observed at the beginning of cusp-type flares,
but also the upward motion which follows.

---------------------------------------------------------
Title: Spectral and temporal properties of narrowband dm-spikes and
broadband pulses in the August 5, 2003 flare
Authors: Sych, R. A.; Sawant, H. S.; Karlický, M.; Mészárosová, H.
2006AdSpR..38..979S Altcode:
On August 5, 2003 the Ondřejov radiospectrograph and the Brazilian
Solar Spectrograph recorded simultaneously the narrowband dm-spikes
superimposed on broadband pulses in the frequency ranges of 0.8-4.5 and
1.75-2.25 GHz, respectively. Using a new method of wavelet filtering
broadband sub-second pulses with a frequency width of 0.48 GHz and
narrowband millisecond spikes with a frequency width 0.13 GHz were
recognized and analysed in detail. Filtered radio spectra showed that
the spikes were clustered in stripes at different frequencies. These
stripes drifted and their frequency ratios changed during short time
intervals. Periods of the narrowband spikes and their stripes were
∼0.4 s and 4, 8-10, and 16 s, respectively. The main period of
the broadband pulses was ∼4 s. Values of significant periods of the
narrowband spikes coincided with those of the broadband pulses. We found
significant peak-to-peak correlations with zero time lags among stripes
of the narrowband spikes on different frequencies. The characteristics
of the narrowband dm-spikes and broadband pulses indicate that mutually
linked emission processes generate both fine structures.

---------------------------------------------------------
Title: Collapsing magnetic trap as accelerator of electrons
Authors: Karlicky, M.; Barta, M.
2006cosp...36...20K Altcode: 2006cosp.meet...20K
A quasi-stationary collapsing trap is simulated using a 2-D MHD
model Then in this collapsing trap an acceleration of electrons
is studied in detail We used a test particle technique in which
collisional losses and pitch angle scattering of electrons in dense
plasma are included We found that this secondary acceleration process
efficiently accelerates electrons pre-accelerated in the reconnection
This acceleration process explains a formation of flare loop-top X-ray
sources in a very natural way

---------------------------------------------------------
Title: Harmonically related decimetric fine structures
Authors: Sawant, H. S.; Fernandes, F. C. R.; Karlický, M.;
Mészárosová, H.; Krishan, V.; Cecatto, J. R.; Madsen, F. R. H.;
Andrade, M. C.
2006AdSpR..38..406S Altcode:
We report rare events, above 1000 MHz, in which emission at the
fundamental and at second harmonic frequencies show nearly identical
fine structures. These high resolution observations are obtained from
the Brazilian Solar Radio Spectrograph operating in the frequency
range (2150 ± 100) MHz, and the Ondrejov observatory Solar Radio
Spectrograph operating in the frequency range of (800-2000) MHz. These
bursts have flux values of about 300 s.f.u. and total duration between
100 and 500 ms. The frequency and flux ratios of the harmonically
related narrow band bursts varied from 1.76 to 2.29 and 1.28 to 3.57,
respectively. The lower observed flux of the fundamental component in
comparison to the second harmonic could be due to its higher collisional
absorption assuming that the generation mechanism of these bursts is
due to the beam plasma interaction. The heights of the acceleration
regions estimated from the starting frequencies of the decimetric fine
structures are ⩽10 4 km.

---------------------------------------------------------
Title: Magnetic field reconnection initiating waves and shocks and
corresponding radio bursts
Authors: Karlicky, M.; Barta, M.
2006cosp...36...18K Altcode: 2006cosp.meet...18K
A 2D MHD model of the magnetic field reconnection shows that
reconnection activity changes of the magnetic field topology and
generation of waves and shocks are related For example it was found
that after the phase of quiet reconnection the tearing mode instability
produces plasmoids which then interact and generate MHD waves These
processes are analyzed from the point of view of a possible radio
emission While shocks can contribute to the type II radio burst the
superthermal electrons trapped in plasmoids can generate so called
drifting pulsating structures Furthermore possibly created turbulent
structure of density and magnetic field may manifest itself as a lace
or dm-spikes bursts

---------------------------------------------------------
Title: X-Ray Sources and Magnetic Reconnection in AN X-Class Flare
Authors: Veronig, A. M.; Vršnak, B.; Karlický, M.; Temmer, M.;
Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W.
2005ESASP.600E..32V Altcode: 2005ESPM...11...32V; 2005dysu.confE..32V
No abstract at ADS

---------------------------------------------------------
Title: Two Examples of the Flare in the Flare: X14.4 April 15,
2001 and X17.2 October 28, 2003 Flares
Authors: Karlický, M.; Fárník, F.; Mészárosová, H.; Jiřička, K.
2005ESASP.600E.125K Altcode: 2005ESPM...11..125K; 2005dysu.confE.125K
No abstract at ADS

---------------------------------------------------------
Title: Hard X-Ray Emission and its Relation to Reverse Drift Bursts
in the 0.8-4.5 GHZ Range
Authors: Fárník, F.; Karlický, M.
2005ESASP.600E.122F Altcode: 2005ESPM...11..122F; 2005dysu.confE.122F
No abstract at ADS

---------------------------------------------------------
Title: Problem of the Return Current in Energy Deposit in Flares
Authors: Varady, M.; Karlický, M.; Kašparová, J.
2005ESASP.600E.146V Altcode: 2005ESPM...11..146V; 2005dysu.confE.146V
No abstract at ADS

---------------------------------------------------------
Title: Current Sheet Dynamics at the Dissipation Scale
Authors: Bárta, M.; Karlický, M.
2005ESASP.600E.110B Altcode: 2005dysu.confE.110B; 2005ESPM...11..110B
No abstract at ADS

---------------------------------------------------------
Title: Hα Line in Solar Atmosphere Heated by Particle Beams
Authors: Kašparová, J.; Varady, M.; Karlický, M.; Moravec, Z.;
Heinzel, P.
2005ESASP.600E.127K Altcode: 2005dysu.confE.127K; 2005ESPM...11..127K
No abstract at ADS

---------------------------------------------------------
Title: Statistical Analysis of Pulsations and Pulsations with Fibers
in the Range 800-2000 MHZ
Authors: Mészárosová, H.; Rybák, J.; Zlobec, P.; Magdalenić,
J.; Karlický, M.; Jiřička, K.
2005ESASP.600E.133M Altcode: 2005dysu.confE.133M; 2005ESPM...11..133M
No abstract at ADS

---------------------------------------------------------
Title: Multi-Wavelength Analysis of High-Energy Electrons in Solar
Flares: A Case Study of the August 20, 2002 Flare
Authors: Kašparová, Jana; Karlický, Marian; Kontar, Eduard P.;
A. Schwartz, Richard; Dennis, Brian R.
2005SoPh..232...63K Altcode: 2005astro.ph..8636K
A multi-wavelength spatial and temporal analysis of solar high-energy
electrons is conducted using the August 20, 2002 flare of an unusually
flat (γ1 = 1.8) hard X-ray spectrum. The flare is studied
using RHESSI, Hα, radio, TRACE, and MDI observations with advanced
methods and techniques never previously applied in the solar flare
context. A new method to account for X-ray Compton backscattering in the
photosphere (photospheric albedo) has been used to deduce the primary
X-ray flare spectra. The mean electron flux distribution has been
analysed using both forward fitting and model-independent inversion
methods of spectral analysis. We show that the contribution of the
photospheric albedo to the photon spectrum modifies the calculated mean
electron flux distribution, mainly at energies below ∼100 keV. The
positions of the Hα emission and hard X-ray sources with respect to
the current-free extrapolation of the MDI photospheric magnetic field
and the characteristics of the radio emission provide evidence of the
closed geometry of the magnetic field structure and the flare process in
low altitude magnetic loops. In agreement with the predictions of some
solar flare models, the hard X-ray sources are located on the external
edges of the Hα emission and show chromospheric plasma heated by the
non-thermal electrons. The fast changes of Hα intensities are located
not only inside the hard X-ray sources, as expected if they are the
signatures of the chromospheric response to the electron bombardment,
but also away from them.

---------------------------------------------------------
Title: Radio Diagnostics of the Solar Flare Reconnection
Authors: Karlický, Marian; Bárta, Miroslav
2005SSRv..121..153K Altcode:
First, high-frequency (HF) slowly drifting pulsating structures
are interpreted as radio emissions of electron beams accelerated in
the magnetic reconnection volume and injected into magnetic islands
(plasmoids). Then, the time evolution of plasma parameters (density,
magnetic field, etc.) in a 2-D MHD model of solar flare reconnection
is computed numerically. Assuming plasma radio emission from locations
where the “double-resonance’’ instability generates upper-hybrid
(UH) waves due to unstable distribution function of suprathermal
electrons, the radio spectra and spatial source structures in the
reconnection region are modeled. By comparison of the modeled and
observed spectra a remarkable similarity has been found between the
computed narrow-band emission and the observed lace bursts. Finally,
a new diagnostics of the reconnection process is proposed.

---------------------------------------------------------
Title: Non-thermal processes associated with rising structures and
waves during a "halo" type CME
Authors: Lehtinen, N. J.; Pohjolainen, S.; Karlický, M.; Aurass,
H.; Otruba, W.
2005A&A...442.1049L Altcode:
We analyse structures and events connected with a flare-associated
"halo" type coronal mass ejection (CME) observed on December 18,
2000. A GOES C7.0 class X-ray flare started at 11:02 UT in NOAA Active
Region 9269, located at N14 E03. Yohkoh SXT observed slowly rising
soft X-ray loops already some 5 min before flare start. Hα images
show a two-ribbon flare, remote brightenings, and a partly disappearing
filament near the active region. A metric radio precursor was observed
to start at 11:06:30 UT, simultaneously with impulsive emission in hard
X-rays and microwaves. The frequency-drifting precursor envelope was
superposed with J- and reverse drift bursts. The radio bursts traced
large-scale soft X-ray loop structures about 160 000 km away from the
flare core, and hard X-ray emission was observed at the ends of some of
these loops. The precursor emission points to a rising structure where
electron acceleration takes place. Later on, a radio type II burst
(signature of a propagating shock, driven either by an ejecta or a
blast wave) and an EIT wave were observed. We conclude that possible
sources for the rising structure and accelerator of electron beams
are (1) large-scale loops that connect the flare core region and the
precursor site in the close vicinity of two separate rising filaments,
and (2) a growing shock that accelerates electrons along closed field
lines until the multipolar field is opened and the CME is lifted off. As
neither X-ray nor EUV ejecta could be observed whether in the direction
of the type II burst or near the radio precursor, we find some support
for the shock wave scenario.

---------------------------------------------------------
Title: Magnetic Field Dissipation in GRBs
Authors: Topinka, Martin; Spruit, Henk; Karlický, Marián
2005AIPC..801..141T Altcode:
We report on the first steps towards the three-dimensional simulation
of magnetic field dissipation in gamma-ray burst prompt emission. The
model is based on magnetically driven Poynting flux outflow.

---------------------------------------------------------
Title: Electron Acceleration by Coronal Shocks and Solar Type
II Bursts
Authors: Vandas, M.; Karlický, M.
2005ESASP.592..453V Altcode: 2005ESASP.592E..80V; 2005soho...16E..80V
No abstract at ADS

---------------------------------------------------------
Title: Characterization of solar multi-scaling magnetic loop
interactions
Authors: Rosa, Reinaldo R.; Karlický, Marian; Zanandrea, Ademilson;
Sych, Robert A.; Sawant, Hanumant S.; Krishan, Vinod
2005AIPC..784..567R Altcode:
Solar magnetic loop structures can exist in a broad range of
spatio-temporal scales and their mutual interactions are described
by nonlinear processes of magnetic reconnection triggered as a
secondary regime by a primary MHD instability. From the application
of wavelet analysis on decimetric time series as a counterpart of
spatio-temporal flare loop observations we derive, using Tajima's
model for quasi-periodic MHD coalescence, possible ranges of minimum
Sagdeev potential. From this parameter we obtain the Alfven period
of nonlinear oscillation for a typical mutual solar loop interaction
observed by SOHO and TRACE.

---------------------------------------------------------
Title: Radio Signatures of Solar Flare Reconnection
Authors: Bárta, M.; Karlický, M.
2005ApJ...631..612B Altcode:
The time evolution of plasma parameters (density, magnetic field,
etc.) in a two-dimensional MHD model of solar flare reconnection is
computed numerically. Then assuming plasma radio emission from locations
where the “double-resonance” instability generates upper hybrid
waves due to unstable distribution function of suprathermal electrons,
the radio spectra and spatial source structures in the reconnection
region are modeled. By comparison of the modeled and observed spectra,
a remarkable similarity has been found between the computed narrowband
emission and the observed lace bursts. Finally, a new radio diagnostic
of the reconnection process based on the model is proposed.

---------------------------------------------------------
Title: Multiwavelength Analysis of the Impact Polarization of 2001
June 15 Solar Flare
Authors: Xu, Z.; Hénoux, J. -C.; Chambe, G.; Karlický, M.; Fang, C.
2005ApJ...631..618X Altcode:
We report here on the temporal and spatial evolution of the
impact polarization of the Hα and Hβ lines during an M6.3 solar
flare observed on 2001 June 15 with the THEMIS telescope in the
multiwavelength spectropolarimetric mode. Typical spectral intensity
and polarization profiles are presented. Both lines are linearly
polarized. The Hαline degree of polarization exceeds 4% at line
center and in the near line wings. The Hβ line is also linearly
polarized, with a degree of polarization reaching 6%. The directions
of polarization are either parallel or perpendicular to the local
transverse magnetic field (i.e., either radial or tangential because the
transverse magnetic field is directed almost in the flare-to-disk center
direction). However, contrary to Hα, the Hβ polarization direction
is radial only. The Hα and Hβ polarization islands are located at the
edges of flare kernels. Only for radial polarization are these islands
cospatial. No Hβ polarization is found at the places where tangential
Hα polarization is present. The origin of the observed polarization is
discussed. Bombardment by low-energy protons or high-energy electrons
associated with return currents can explain the radial polarization
observed in the lowest flare kernel. The tangential Hα polarization
observed in the surge near the upper flare location is interpreted
as due to the electric current at the origin of the electromagnetic
force that lifts the surge.

---------------------------------------------------------
Title: Simulation of magnetic field dissipation in gamma-ray bursts
Authors: Topinka, M.; Karlický, M.; Hudec, R.
2005NCimC..28..455T Altcode:
We report on the first steps in 3D simulation of magnetic field
dissipation in gamma-ray burst (GRB) prompt emission. Our model is
based on magnetically driven Poynting flux outflow. We study the
evolution of multi-layered anti-parallel magnetic field in expanding
self-accelerated systems.

---------------------------------------------------------
Title: Time scales of the slowly drifting pulsating structure observed
during the April 12, 2001 flare
Authors: Karlický, M.; Bárta, M.; Mészárosová, H.; Zlobec, P.
2005A&A...432..705K Altcode:
First time scales of high-frequency (500-1500 MHz) slowly drifting
pulsating structures observed during the April 12, 2001 flare by the
Ondřejov (800-4500 MHz) and Potsdam (40-800 MHz) radiospectrographs
and by the 1420 and 610 MHz Trieste radiopolarimeters (with high time
resolution (1 ms)) are studied statistically. The Fourier method reveals
periods in the range of 0.9-7.5 s. For shorter periods the power spectra
show a power-law form, especially in the interval of about 0.06-0.2
s, where the power-law index is in the 1.3-1.6 range. The results
are interpreted using the flare model with plasmoid ejections. For
the first time, the multi-scale cascading reconnection process is
included in the interpretation. Corresponding time scales are estimated
analytically. Further, magnetic reconnection in the bursting regime is
simulated in a 2-D MHD model and variations of the dissipation power
and radio radiation measure are computed. Fourier spectra of these
numerical variations are determined and compared with those obtained
from observations.

---------------------------------------------------------
Title: Radio Diagnostics of Solar Flare Reconnection
Authors: Bárta, M.; Karlický, M.
2005HvaOB..29..205B Altcode:
A first attempt is made to describe theoretically a particular radio
emission from solar flare reconnection in full complexity and to use
obtained results for diagnostics of reconnection dynamics based on
radio observations. Firstly, the dynamics of flare reconnection
is studied numerically in the 2-D MHD model. Time evolution of plasma
parameters (density, magnetic field etc.) is found. Then, assuming
plasma radio emission from locations where the “double-resonance”
instability generates the upper-hybrid waves due to the unstable
distribution function of suprathermal electrons, the radio spectra are
modelled. Effects of the MHD turbulence in reconnection flows that
have major influence on the radio spectra dynamics are studied. The
resulting spectra are compared with those observed. It was found,
that the observed spectra of lace bursts are qualitatively well
reproduced. Finally, consequences of the model for plasma diagnostics
are discussed.

---------------------------------------------------------
Title: Analysis of Radio Emission Mechanisms Generating Preferentially
the Ordinary Mode of Electromagnetic Waves
Authors: Yasnov, M. N.; Karlický, M.
2005HvaOB..29..225Y Altcode:
Three radio emission mechanisms (radiation on the first and second
harmonic of the plasma frequency, and the resonant transition
radiation), which can preferentially generate electromagnetic waves
of the o-mode, are analysed. For the case of the transition radiation
various causes of density fluctuations (thermal, Langmuir and ion-sound
waves) are considered. It was found that the radiation on the frequency
of the upper-hybrid waves is always of the o-mode type. Radio emission
on the second harmonic of the upper-hybrid frequency can also be
polarized in the o-mode type, but this case is less probable than the
previous one. In the transition radiation the preference of the o-mode
type is also possible, but the small-scale turbulence in the radio
source is necessary. The most probable case is the resonant transition
radiation generated at density fluctuations produced by ion-sound waves.

---------------------------------------------------------
Title: Solar Narrowband Decimetric Spikes and Hard X-Rays
Authors: Jiřička, K.; Karlický, M.; Fárník, F.
2005HvaOB..29..149J Altcode:
Narrowband spikes observed by the Ondřejov radiospectrograph during
solar flares in the decimetric (1-2 GHz) range were analysed together
with the RHESSI observations. It was found that not the individual
dm-spikes, but the dm-spikes as a whole, are closely related with the
hard X-ray bursts (the correlation coefficient was 0.7-0.9) and their
time delays after X-rays were 2-14 s. The Fourier spectra of spikes
along the frequency were made and their spectral indices were found
to be in the -0.67 to -1.6 range. No correlation between power-law
spike and X-ray indices was found. The results were compared with those
obtained by Aschwanden and Güdel (1992) for spikes observed on lower
radio frequencies.

---------------------------------------------------------
Title: X-Ray and HαEmission of the 20 Aug 2002 Flare*
Authors: Kašparová, J.; Karlický, M.; Schwartz, R. A.; Dennis, B. R.
2005ASSL..320..187K Altcode: 2005smp..conf..187K
No abstract at ADS

---------------------------------------------------------
Title: Information on particle acceleration and transport derived
from solar flare spectropolarimetry
Authors: Xu, Z.; Hénoux, J. -C.; Chambe, G.; Karlický, M.; Fang, C.
2005AdSpR..35.1841X Altcode:
The hydrogen H α line has been found to be linearly polarized at
some locations and times during a June 15th 2001 flare observed with
THEMIS. This flare was accompanied by radio pulses and hard X-ray
emission. Linear polarization is below the noise level in the flare
kernels. However, it is present at the edges of these kernels, in
the line center and near wings where the polarization degree exceeds
4%. The directions of polarization are not random but close within
±15° to the tangential and radial directions. This polarization can
be due either to electron beams and their associated return currents
or to electron and proton beams.

---------------------------------------------------------
Title: Narrowband dm-spikes in the frequency range above 1 GHz and
hard X-ray emission
Authors: Fárník, F.; Karlický, M.
2005AdSpR..35.1799F Altcode:
Narrowband dm-spikes observed in nine intervals during five solar
flares in the 1-2 GHz range were analyzed together with the RHESSI and
HXRS observations. It was found that the over-frequency integrated
radio flux during the spike period is closely related with the hard
X-ray bursts (the correlation coefficient was 0.7-0.9) and their time
delays after X-rays were 2-14 s, with one exception (March 18, 2003)
where the time delay was opposite -15 s. Association of spikes with
X-ray spectral characteristics enabled us to divide the spikes into two
groups: (a) those observed before the soft X-ray flare maximum and,
(b) those observed after this maximum. While for the spikes observed
after the flare maximum no systematic spectral characteristics were
found, the spikes, observed before the flare maximum were at their
beginning associated with relatively hard X-ray spectra and their
hardness decreased with time. The RHESSI X-ray sources were compact,
only in the March 18, 2003 event an additional X-ray source appeared
just at the time of the dm-spikes observation. Fourier transformation
of the dynamic spectra of spikes was done to compare their dynamics
with the X-ray spectral indices. No correlation between power-law spike
and X-ray indices were found. It indicates that the MHD turbulence,
if it plays a role, does not represent a strong connection between
the spectral characteristics of the dm-spikes and associated X-ray
bursts. Furthermore, the results were compared with those obtained by
(Aschwanden, M.J., Güdel, M. The coevolution of decimetric millisecond
spikes and hard X-ray emission during solar flares. Astrophys. J. 401,
736-753, 1992) for spikes observed on lower radio frequencies. Contrary
to their results, no monotonic dependence between time delays and X-ray
intensities were found. Finally, the results were discussed using the
model of the narrowband dm-spikes and model of electron acceleration
in the collapsing magnetic trap.

---------------------------------------------------------
Title: Loop-Top Altitude Decrease in an X-Class Flare
Authors: Veronig, A.; Vršnak, B.; Karlický, M.; Temmer, M.;
Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W.
2005HvaOB..29..127V Altcode:
We study RHESSI X-ray source motions in the X3.9 flare of 2003 November
3. Particular attention is drawn to the apparent altitude decrease
of a distinct loop-top (LT) source at the early flare phase before
then changing to the commonly observed upward expansion of the flare
loop system. We obtain that the downward motion is more pronounced
at higher X-ray energies (peak values up to 50 km s^{-1}) consistent
with recent findings by Sui et al. (2004). RHESSI spectra indicate
that the emission process in the LT source is thermal bremsstrahlung
from a super hot plasma (∼40 MK) with high densities increasing from
∼10^{10} cm^{-3} early in the flare to several times 10^{11} cm^{-3}
at the end of RHESSI observations.

---------------------------------------------------------
Title: X-Ray Emission of the April 6, 2001 Flare Modelled by Processes
in a Collapsing Magnetic Trap
Authors: Karlický, M.
2005HvaOB..29..137K Altcode:
Using a test particle numerical model describing acceleration
processes in the collapsing magnetic trap the X-ray emission of
the April 6, 2001 flare was modelled. The Coulomb collisions and
scattering were included. The basic parameters of the collapsing trap
in the flare region was estimated from the potential magnetic field
extrapolation. Although all parameters used in the modelling cannot be
derived directly from observations a relatively good agreement between
the modelled and observed X-ray observations was found when a) the
collapse and trapping processes lasted 16 and 50 s, respectively, b)
the scattering of superthermal electrons was enhanced (5 times greater
than the Coulomb scattering), c) the injected electron distribution
function had the double power law form (energy power-law indices
γ_1^e = 8, γ_2^e = 1.3, the break energy E_{break}^e = 65 keV),
and d) the rate of injected electrons was 8.73×10^{34} s^{-1}.

---------------------------------------------------------
Title: Numerical Simulation of the Formation of the Return Current
Authors: Karlický, M.
2005HvaOB..29..215K Altcode:
First, a new 1D particle numerical code computing the formation of the
return-current is presented. Then the first results obtained by this
code are shown. Although the computations are made for very short time
intervals, they show details how the return current is formed. At the
beam head the electric field oscillating at the background plasma
frequency is generated. Their amplitude grows in time due to the
two-stream instability. It is found that at positions near the beam
injection the two-stream instability is forced by a continuation of
the injected beam, which gives higher values of the electric field
energy than in the normal saturation process due to the electron beam
trapping. During the beam propagation the background electrons are
accelerated in such a way that the electric current is neutralized. Most
of the beam electrons are decelerated, forming thus with the accelerated
background electrons a broad (in velocity space) distribution function.

---------------------------------------------------------
Title: Ten Types of Solar Radio Bursts and Fine Structures Observed
by the Ondřejov 0.8-2.0 GHz Radio-Spectrograph
Authors: Mészárosová, H.; Karlický, M.; Jiřička, K.
2005HvaOB..29..309M Altcode:
681 solar radio events observed by the Ondřejov 0.8--2.0 GHz
radio-spectrograph during 1992--2000 are analysed and corresponding
bursts and fine structures classified into ten different classes. A new
type of fine structure (laces) and a new sub-class of zebra patterns
were identified. Distribution of various types of fine structures in
dependence on the changes of solar activity during the cycles 22 and
23 and occurrences of studied types of burst in association with GOES
class flares are shown.

---------------------------------------------------------
Title: Influence of Electron Beam Pulses on Hα Line Formation
Authors: Varady, M.; Kašparova, J.; Karlický, M.; Heinzel, P.;
Moravec, Z.
2005HvaOB..29..167V Altcode:
In this contribution we present results of our simulations focused on
determination of spectroscopic signs of the presence of non--thermal
electrons in the formation region of Hα using three mutually
communicating codes. The originally autonomous and highly specialised
codes model three simultaneously acting processes in flares: the
precipitation and energy dissipation of the non-thermal power--law
electron beams in the solar atmosphere, the hydrodynamic response of
the atmosphere to the energy deposited by the beams, and the radiative
transfer in chromosphere and photosphere which determines the hydrogen
line profiles and their time evolution. The results show possible
existence of a new diagnostic method on presence of electron beams in
the formation region of the Hα line.

---------------------------------------------------------
Title: Loop-top gyro-synchrotron source in post-maximum phase of
the August 24, 2002 flare
Authors: Karlický, Marian
2004NewA....9..383K Altcode:
A region with a 17 GHz radio source with a decreased microwave spectral
index ( α∼-1.3) has been recognized at the top of the flare loop
in the post-maximum phase of the August 24, 2002 flare. The radio
emission from this region has been interpreted as optically thin
gyro-synchrotron emission. It looks that the region appeared at
the top of the flare loop as a consequence of the density decrease
which reduced the free-free emission component and thus revealed the
gyro-synchrotron one. The plasma parameters in the loop-top radio source
are estimated. Together with associated gyro-synchrotron sources at the
flare loop footpoints these phenomena indicate prolonged acceleration
processes in the post-maximum phase of this flare.

---------------------------------------------------------
Title: Acceleration and heating processes in a collapsing magnetic
trap
Authors: Karlický, M.; Kosugi, T.
2004A&A...419.1159K Altcode:
We study the acceleration processes in a collapsing magnetic trap
formed in the cusp structure of the flare model, using a test-particle
numerical method. Coulomb collisions and scattering are included. It
was found that if the trap collapse is sufficiently fast and the
energies of the injected electrons are sufficiently high, thus
overcoming the collisional losses, electrons can be accelerated in this
secondary acceleration process to very high energies depending on the
initial magnetic trap ratio R =Bmax/Binit. The
computations, made for R=10 and R=100 with isotropically injected 5-28.4
keV electrons and a background plasma density of about ne =
1010 cm-3, show that the high-energy electrons are
accumulated in the central part of the collapsing magnetic trap where
their velocities are nearly perpendicular to the magnetic field. This
effect gives us a new possibility to explain the formation of loop-top
sources observed in hard X-ray and radio emission. A further interesting
aspect is that these electrons later on escape from this collapsing
trap because its trap ratio decreases to R -&gt;1. The time evolution
of the energy of the trapped electrons and their energy flux at the
end points of the trap (footpoints) are computed for cases without
and with collisions. The effect of collisions on the energy spectrum
of the accelerated electrons is also shown. The X-ray spectra along
the collapsing trap are evaluated. Finally, we suggest a test of this
model considering radio waves in the decimetric frequency range.

---------------------------------------------------------
Title: Multi-Wavelength Analysis of the 29 September 2002 M2.6/2N
Flare
Authors: Kulinová, Alena; Dzifčáková, Elena; Bujňák, Rastislav;
Karlický, Marian
2004SoPh..221..101K Altcode:
Using TRACE EUV 171 Å line, Hα line, Zürich radio, RHESSI, and
HXRS observations the 29 September 2002 flare (M2.6), which occurred
in AR NOAA 0134, was analyzed. Flaring structures were compared with a
potential magnetic field model (field lines and quasi-separatrix layers)
made from SOHO/MDI full-disk magnetogram. Series of high-resolution
SOHO/MDI magnetograms and TRACE white-light images were used to
find changes in the active region at the photosphere during the
flare. The flare began with a rising of a small dark loop followed by
the flare brightening observed in 171 Å with TRACE and Hα lines. In
radio wavelengths, first type III bursts were observed 5 min prior
to the start of hard X-ray emission, indicating a pre-flare coronal
activity. The main hard X-ray emission peak (at 06:36 UT) was associated
with the second type III burst activity and several slowly negatively
drifting features, all starting from one point on the radio spectrum
(probably a shock propagating through structures with different plasma
parameters). After this time a huge loop formed and three minutes later
it became visible in absorption both in Hα and 171 Å EUV lines. The
phase of huge dark loop formation was characterized by long-lasting,
slowly negatively drifting pulsations and drifting continuum. Finally,
considering this huge loop as a surge an evolution of the event under
study is discussed.

---------------------------------------------------------
Title: High-frequency slowly drifting structures and X-ray sources
observed by RHESSI
Authors: Karlický, M.; Fárník, F.; Krucker, S.
2004A&A...419..365K Altcode:
Three solar flares (April 4, 2002, May 17, 2002, and August 30, 2002)
with the 0.4-2.0 GHz slowly drifting structures were selected and
analyzed together with RHESSI X-ray observations. Two events (April 4,
2002 and May 17, 2002) were observed above and one event (August 30,
2002) close to the solar limb. While in April 4, 2002 and August 30,
2002 the radio drifting structures with relatively high frequency
drifts (-32- -25 MHz s-1) were recorded at times of the
start of a motion of the X-ray flare source, in May 17, 2002 event
a splitting of the X-ray source into two sources was observed before
observation of the 0.8-1.8 GHz radio structure drifting with very slow
frequency drift (-0.4 MHz s-1). The X-ray source of the May
17, 2002 was much softer (&lt;40 keV) than those in April 4, 2002 and
August 30, 2002 (&gt;100 keV). Velocities of the X-ray sources in the
image plane were estimated as 12 km s-1 for April 4, 2002
and 10 km s-1 for August 30, 2002. Analyzing GOES data and
X-ray RHESSI spectra of the May 17, 2002 flare the plasma thermal and
non-thermal electron densities in the X-ray sources were determined. For
two cases (April 4, 2002 and May 17, 2002) it was found that the plasma
density in the coronal X-ray source is higher than maximum one derived
from the radio drifting structure. The cross-correlation of the radio
drifting structure and hard X-ray flux for the August 30, 2002 event
reveals that the hard X-ray emission is delayed 0.5-0.7 s after the
radio and it is partly correlated with an enhanced background of the
drifting structure. All these results are discussed and interpreted
considering the flare model with the plasmoid ejection.

---------------------------------------------------------
Title: Series of high-frequency slowly drifting structures mapping
the flare magnetic field reconnection
Authors: Karlický, M.
2004A&A...417..325K Altcode:
Rare series of the slowly drifting structures observed during two
solar flares (April 11, 2001 and March 18, 2003) in the 0.8-4.5 GHz
frequency range are studied. Their time-frequency evolution is compared
with topological and X-ray characteristics of the flares. Based on
recent modelling of the magnetic field reconnection in the bursting
and intermittent regime, it is proposed that these slowly drifting
structures map the flare magnetic field reconnection. In such a scenario
the drifting structures correspond to the radio emission from primary
and secondary plasmoids which are formed in the extended current sheet
due to tearing and coalescence processes and they move upwards in the
solar atmosphere. An increase and decrease of the frequency drifts
of the drifting structures in the initial and decaying flare phases
are interpreted as an increase and decrease of the reconnection rate,
respectively. On the other hand, individual bursts in the drifting
pulsating structures are considered to be radio manifestations of
separate electron beams accelerated during the secondary tearing
processes. The observed characteristic times are compared with those
theoretically predicted and the basic plasma parameters in the flare
process are estimated.

---------------------------------------------------------
Title: Collisional excitation and ionization of hydrogen by return
current in solar flares
Authors: Karlický, M.; Kašparová, J.; Heinzel, P.
2004A&A...416L..13K Altcode:
First a problem of the transport of electron beams with high energy
fluxes into the cold chromosphere during the flare is presented. Then
it is shown that the problem might be solved by the return current
formed by superthermal (runaway) electrons. In such a case the
return current electrons could influence hydrogen excitations and
ionizations. Therefore, we computed collisional rates of such a
return current and compared them with those of the thermal plasma
and of a monoenergetic (10 keV) electron beam with the energy flux
FE = 1012 erg cm-2 s-1
penetrating into the flare atmosphere described by the F1 model (Machado
et al. \cite{Machado1980}). We show that in this situation the return
current collisional rates can be dominant for some transitions.

---------------------------------------------------------
Title: The Growth rate of upper-hybrid waves and dynamics of microwave
zebra structures
Authors: Yasnov, Leonid V.; Karlický, Marian
2004SoPh..219..289Y Altcode:
The growth rate of the upper-hybrid waves with different velocities of
superthermal electrons is computed considering a finite temperature
of the background plasma and relativistic corrections. Based on
these computations two examples of high-frequency zebra structures
are interpreted. The sequence of the continuum, zebra structure,
and continuum observed in the 29 October 2000, event is explained as
an increase and following decrease of the velocity of superthermal
electrons in the range of v=0.1-0.3 c. On the other hand, the zebra
structure observed during the 18 March 2003 event represents an example
with fast electron acceleration.

---------------------------------------------------------
Title: Collisional Excitation and Ionization of Hydrogen by Return
Current in Solar Flares
Authors: Kašparová, J.; Heinzel, P.; Karlický, M.
2004IAUS..219..760K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Harmonically Related Decimetric Bursts
Authors: Sawant, H. S.; Fernandes, F. C. R.; Karlický, M.;
Meszarosova, H.; Krishan, V.; Cecatto, J. R.; Madsen, F. R. H.
2004cosp...35..528S Altcode: 2004cosp.meet..528S
High frequency observations with 3 MHz frequency and 20 ms time
resolutions were carried out in the frequency range of (2150 ± 100)
MHz from August 2001 for about two months by the Brazilian Solar
Spectroscope (BSS) totalling to of about 300 hours. About 30 groups
of solar bursts were recorded. Some of them were also recorded by the
Ondrejov Solar Spectroscopes. For the first time details of about
40 harmonically related decimetric narrowband type III bursts and
unclassified fine structures above 1000 MHz are reported. Flux values
are around 300 s.f.u. Total duration of all types of above bursts is
in between 100 -- 500 ms. Frequency ratio of the harmonically related
decimetric type III bursts including that of fine structures ranged
between 1.76 -- 2.29, where as ratios of the fluxes varied between 1.28
to 3.57, except one case where ratio is ∼ 0.98. The lower observed
flux of the fundamental component in comparison to the second harmonic
could be due to its stronger collisional absorption near source. We
have attempted to understand the formation of some of these structures
in terms of the four-wave scattering processes assuming whistlers to
be the low frequency waves.

---------------------------------------------------------
Title: What have we learned on non-thermal particle acceleration
and transport by optical spectropolarimetry
Authors: Hénoux, J. -C.; Karlicky, M.; Xu, Z.; Fang, C.
2004cosp...35..647H Altcode: 2004cosp.meet..647H
Most of the information on non-thermal particles is derived from
hard X-ray, gamma-ray or radio observations. Optical spectroscopic
polarimetry provides complementary information on the particle nature
and velocity distributions. Information is also provided on their
propagation conditions at chromospheric level. We will report here
on the information derived from measurements of the impact linear
polarization made in the Halpha and Hbeta lines with the French-Italian
solar telescope THEMIS.

---------------------------------------------------------
Title: Analysis of narrowband dm-spikes observed during the august
5,2003 flare.
Authors: Sawant, H.; Sych, R.; Karlicky, M.; Meszarosova, H.
2004cosp...35.1604S Altcode: 2004cosp.meet.1604S
Groups of narrowband dm-spikes superimposed on broadband pulsations,
observed in the 1-2 GHz frequency range, simultaneously by the
Brazilian Solar Spectroscope and Ondrejov radiospectrograph during
the August 5, 2003 flare are presented. Two methods of an analysis
of these spikes were used: a) The Fourier method searching frequency
structures in time integrated data, and b) detailed analysis of the
distribution of frequency and time structures using multiresolution
wavelet analysis. While the first approach is conceptually connected
with an expectation that the narrowband dm-spikes are generated in
the MHD plasma turbulence without any preferential spatial scales, the
wavelet analysis is searching for the preferential scales. Using the
Fourier method the power spectra with the power-law indices in the range
(-0.90 - -1.26) were found. On the other hand, the wavelet analysis
revealed three significant frequency sizes: 1) wideband pulses (about
0.5 GHz), 2) narrowband pulses (0.12 and 0.04 GHz) and 3) small scale
pulses (0.01 GHz). Moreover, the wavelet analysis shows a splitting
and drifting of specific harmonics, an increase of significant periods
of the narrowband pulses (e,g. from 3s to 7s, and from 9s to 19s),
and simultaneous decrease of significant periods of broadband pulses
(4.2s, 7.8s, 17.1s). But generally the significant periods of the
narrowband pulses coincide with those of the broadband pulses. The
results are interpreted within the model of spikes generated in a
non-stationary MHD plasma turbulence.

---------------------------------------------------------
Title: Decimetric fine structures and associated X-ray flares
Authors: Fernandes, F. C. R.; Kane, S. R.; Sych, R. A.; Andrade,
M. C.; Cecatto, J. R.; Sawant, H. S.; Karlický, M.; Meszarosova, H.
2004cosp...35.2984F Altcode: 2004cosp.meet.2984F
Brazilian Solar Spectroscope and Ondrejov radio spectrograph operate,
respectively, in the frequency range of 1250-1750 MHz and 800-2500
MHz. On 4 July 2003 the two instruments observed simultaneously radio
bursts associated with two solar flares, one at ∼ 1441 UT and the
other at ∼ 1637 UT. In both flares the radio bursts were found to
be rich in fine structures. The first flare was associated with a
C7.1 soft X-ray flare recorded by the GOES satellite from 1435 to
1520 UT with a peak at 1455 UT. An optical flare of importance 1F
occurred during 1435-1439 UT and was located at N05,E32 in the active
region 10400. During the period 1442-1508 UT the hard X-ray imaging
spectrometer on RHESSI recorded slowly decaying hard X-ray emission
in 10-20 keV range. X-ray emission at higher energies could not be
recorded due to the presence of terrestrial (magnetospheric) energetic
particles. 6-50 keV X-ray emission associated with the second flare
(1637 UT) was recorded by RHESSI during 1630-1650 UT. The emission
was characterized by several distinct maxima. Although no optical
flare has been reported at the time of this flare, hard X-ray images
obtained by RHESSI indicate that this flare occurred in the same active
region (10400) as the first flare. An analysis of the decimetric fine
structures has revealed positively drifting bursts in the frequency
range of 1380-2000 MHz with positive drift rates of 180-- 600 MHz/sec
at the beginning of the pulsating structures. Periodicity of pulsation
was found to be about 9 sec. Detailed radio and hard X-ray observations
of the two flares will be presented and the implications of these
observations with respect to the location of the electron acceleration
region in solar flares will be briefly discussed.

---------------------------------------------------------
Title: Narrowband dm-spikes and associated X-ray emission
Authors: Farnik, F.; Karlicky, M.
2004cosp...35.1166F Altcode: 2004cosp.meet.1166F
Narrowband dm-spikes observed in nine intervals during five solar flares
(20 May 2002, 18 March 2003, 10 June 2003, 22 June 2003 and 5 August
2003) were analyzed together with the RHESSI and HXRS observations. The
height scale spectra of the spikes were derived and their spectral
scale index was found to be between --0.67 and --1.6 . We divided the
studied events into two groups: a) the spikes observed before the soft
X-ray flare maximum and, b) the spikes observed after the maximum. While
the events with spikes after the flare maximum manifested no specific
characteristics, we found that during the events with spikes before the
flare (X-ray) maximum (10 June 2003 and 5 August 2003) the spikes were
associated with relatively hard X-ray spectra (spectral index gamma
was 3.0 and 3.7, respectively) and the spectral slope was increasing
afterwards (the X-ray spectrum was getting softer during the event
approaching the thermal equilibrium). All the observational results
are discussed in frame of our model of the narrowband dm-spikes.

---------------------------------------------------------
Title: High frequency decimetric pulsations and associated hard
X-ray emission in the 5 August 2003 (1249 UT) flare
Authors: Sawant, H. S.; Sych, R. A.; Kane, S. R.; Fernandes, F. C. R.;
Andrade, M. C.; Karlický, M.; Meszarosova, H.
2004cosp...35.2328S Altcode: 2004cosp.meet.2328S
The flare on 5 August 2003 (1243-1251 UT) was observed at a variety of
wavelengths. The H-alpha flare (importance SN) was located at S16, E33
in the active region NOAA 10424. The soft X-ray flare observed by GOES
has been classified as M1.7. The spatial and spectral characteristics
of the hard X-ray source were observed by the imaging spectrometer
on the RHESSI satellite. In addition, white light observations at
1600Å and EUV observations at 171Å (TRACE) and 195Å (EIT) are also
available. Ondrejov and BSS radio spectroscopes, operating in the
frequency ranges of 800-2000 MHz and 1750 - 2200 MHz respectively,
observed four groups of dm pulsations which covered the entire
frequency range and lasted for 30 to 50 sec. Wavelet and Fourier
analysis have shown that these groups of pulsations are composed of
broad band 0.5 GHz subsecond pulses and narrow band 0.12 MHz millisecond
spikes. Periodicity of these groups of pulsations is about 4 sec and
with 2 and 3 harmonics. The periodicity of the broad band component is
also same. Early in the flare RHESSI observed a double hard X-ray source
which later developed into a single source. The fluctuations in the hard
X-ray emission are similar to those at decimetric wavelengths. Big
and small loops are seen in TRACE data and their foot points are
nearly coincident with the appropriate polarity of magnetic field as
seen from MDI maps of the associated active region. An analysis of
these multi-wavelength observations of the 5 August 2003 flare will
be presented and their implications regarding the acceleration and
escape of energetic electrons will be briefly discussed.

---------------------------------------------------------
Title: Hard x-ray Pulsations in the Initial Phase of Flares
Authors: Fárník, F.; Karlický, M.; Švestka, Z.
2003SoPh..218..183F Altcode:
When analyzing light curves of hard X-ray bursts recorded by the Hard
X-Ray Spectrometer on board the MTI satellite, we have found three
events (all associated with major solar flares, two of them in the same
active region) which show pulsations in the very initial phase of the
burst. Periods of the pulsations range from 25 to 48 s. We compare them
with other observations of pulsations of radio waves and in X-rays
and conclude that pulsations of this kind have not been observed
before. We mention several possible causes and prefer interactions
between current-carrying loops as the most likely interpretation of
the observed variations.

---------------------------------------------------------
Title: The Unusual Hard X-ray Spectrum of the Flare of 20 August 2002
Authors: Schwartz, R. A.; Kasparova, J.; Dennis, B.; Karlicky, M.
2003AGUFMSH22A0171S Altcode:
An M3 Class flare was observed in x-rays with RHESSI and in H-alpha
with the Kanzelhohe Solar Observatory. The event was observed to
several hundreds of keV in X-rays and was marked by an unusually flat
spectrum observed from 20-70 keV. The measured power-law exponent
of this component was about 1.7, very close to the theoretical limit
for a thick-target injection of energetic electrons implying a near
cutoff below 80 keV. We will bound any systematic effects that may be
contributing to this result by analyzing the spectrum using multiple
techniques. We will also forward model the spatial/spectral x-ray
sources to further validate these observations.

---------------------------------------------------------
Title: Superluminal apparent velocities of relativistic electron
beams in the solar corona
Authors: Klassen, A.; Karlický, M.; Mann, G.
2003A&A...410..307K Altcode:
We present spectral and imaging observations of high frequency type
III bursts appearing in pairs: a primary fast drifting component and
a secondary “normal" drifting component. The primary bursts have
generally higher frequency drift and start at higher frequencies. They
show superluminal velocities up to 2.5 c (c, speed of light), while
the secondary component shows the usual &lt;0.5 c velocity expected for
type III burst exciters. These superluminal velocities are explained as
apparent velocities of relativistic electron beams propagating nearly
along the line of sight towards the observer with velocities close
to the speed of light. A model of type III burst pairs consisting of
subsequent fast drifting and “normal" drifting components is presented.

---------------------------------------------------------
Title: Radio manifestation of reconnection outflow jets
Authors: Bárta, Miroslav; Karlický, Marian
2003ESASP.535..471B Altcode: 2003iscs.symp..471B
As was already suggested in our previous models of the lace bursts
and the narrow-band dm-spikes both these spectral types are formed
in radio sources with MHD turbulence. Since such conditions are, as
commonly accepted, in the reconnection out-flow jets, it is reasonable
to locate radio sources of these bursts just there. The purpose of this
paper is to present global view on relevant plasma processes. Starting
from a 2-D MHD reconnection model the plasma density and magnetic field
are determined. Assuming a propagation of an unstable distribution
function outwards from the reconnection diffusion region along chosen
magnetic field lines, contributions to the radio flux due to the
double-resonance instability are computed. Integrating over an entire
source volume the artificial radio spectra are obtained. It is shown
that depending on MHD turbulence properties either the lace-burst or
the dm-spikes are observed.

---------------------------------------------------------
Title: On group velocity delays in microwave millisecond oscillating
events and radio spikes
Authors: Yasnov, L. V.; Karlický, M.
2003A&A...408..737Y Altcode:
Time delays between opposite polarizations, interpreted by a difference
between the ordinary and extraordinary modes, are studied. Two different
density and magnetic field models are used, and three emission
mechanisms generating radio waves in double upper-hybrid, plasma,
and gyro frequencies are considered. It is found that time delays and
their spectra can reach various values and forms depending on plasma
parameters in the radio wave emission and propagation. For the emission
in double upper-hybrid frequency the considerable decrease of the time
delay is due to an increase of the electron plasma density in the radio
wave generation. In a dense flare plasma the power index a of the time
delay spectrum is negative. On the other hand, in a diluted plasma
a becomes positive, but in this case it is much lower than observed
for dm-pulsations (a=3). Furthermore model values are compared with
the time delays presented by Fleishman et al. (\cite{Fleishman02}),
and it is shown that the best agreement is with the model assuming the
emission on double gyro-frequency. But, in this case the gyro-resonant
absorption limits the angle for escape of radio waves to Theta
&lt;3-10deg. Finally, an effect of the difference of the
group and light velocities on the frequency drift is analyzed. It is
shown that such an effect can be important for wave propagation along
magnetic field lines at frequencies close to the plasma frequency.

---------------------------------------------------------
Title: Regular variations of 3 GHz radio flux and current-loop
coalescence model of solar flares.
Authors: Karlický, M.; Jiřička, K.
2003ESASP.535..499K Altcode: 2003iscs.symp..499K
The 3 GHz radio flux records of two solar flares (April 7, 1997 and
March 29, 2001) with regular variations are presented. While the 3 GHz
flux record of the April 7, 1997 flare shows double-peaks periodicity,
the 3 GHz record of the March 29, 2001 flare reveals regular radio
flux steps at the ascending part of the radio burst. We interpret
the observed phenomena using the current loop coalescence model of
solar flares. In the case of the April 7, 1997 event we suggest that
the main period of the 3 GHz radio flux (about 100 s) corresponds to
the repetition of the current loop coalescence and the radio double
peaks are associated with the maxima of the electric field component
perpendicular to the interaction plane. In this case the plasma β
parameter in the current loop coalescence process is estimated to be
0.63. An increase of the β parameter during the flare is recognized. On
the other hand, the steps-like form of the 3 GHz flux record of the
March 29, 2001 event expresses an increasing amount of accelerated
electrons during periodic coalescence accelerations.

---------------------------------------------------------
Title: First detection of return currents in solar flares by
spectropolarimetry with THEMIS
Authors: Hénoux, J. -C.; Karlický, M.
2003A&A...407.1103H Altcode:
Using THEMIS French-Italien telescope with the MTR mode, the Hydrogen
Hα and Hβ lines have been observed to be linearly polarized up to a
few percent by impact during the impulsive phase of two solar flares
associated with high-frequency radio pulses. Two privileged directions
of linear polarization are present, respectively radial (in the disk
center to flare direction) and tangential (perpendicular to the radial
direction). This 90 degree change in the linear polarization direction
is interpreted as due to the chromospheric return current generated
by the penetration of a non-thermal electron beam into the chromosphere.

---------------------------------------------------------
Title: Analysis of solar narrow band dm-spikes observed at 1420
and 2695 MHz
Authors: Mészárosová, H.; Veronig, A.; Zlobec, P.; Karlický, M.
2003A&A...407.1115M Altcode:
Using both linear and nonlinear methods, narrow band dm-spikes recorded
at 1420 and 2695 MHz on June 6, 2000, July 8, 2000, July 12, 2000,
July 20, 2000, and March 28, 2001 were analyzed. In particular their
time profiles were studied statistically. The mean characteristic
times of the ascending and of the decaying parts of their profiles are
comparable, even if the dispersion of the values is very broad. For
selected spikes at 1420 MHz a more precise fitting technique using
exponential profiles was applied. While in the decaying part the
exponential trend can be generally found, in the ascending part the
exponential form can be confirmed only in few cases. The ascending
and decaying phase of spikes presumably correspond to the source
instability evolution and the plasma wave absorption. Furthermore,
durations and polarization values of both 1420 and 2695 MHz spikes
were determined and compared with the results in literature. All the
analyzed spike events were located near the solar disk center. The
polarization values and their trend in spike groups and the nearly
constant duration suggest that the polarization originates at the
source itself or near it. Selected time series of spikes were tested
with respect to low-dimensional determinism and nonlinearity. We
found that spikes recorded at fixed frequencies are not governed by a
linear stochastic process, as the underlying physical system contains
nonlinear signatures.

---------------------------------------------------------
Title: A Model of Zebra Emission in Solar Type IV Radio Bursts
Authors: LaBelle, J.; Treumann, R. A.; Yoon, P. H.; Karlicky, M.
2003ApJ...593.1195L Altcode:
Solar type IV radio bursts present a theoretical challenge because
they are composed of both continuum emission and fine structures. The
latter include “zebra bursts,” which appear as harmonically spaced
multiplets that shift in frequency with time. Similarities between
these features and terrestrial auroral emissions suggest a new model to
explain zebra-structured type IV emissions. In this model, the basic
generation mechanism is identical with that proposed by Winglee and
Dulk: mode conversion of Z-mode waves generated by the cyclotron maser
mechanism under the condition fuh=Nfce, with N an
integer; however, we propose a twist on this model whereby the “zebra
bursts” do not arise from multiple N-values. Rather, the presence of
localized density irregularities within the type IV source region leads
to trapping of the upper hybrid Z-mode waves in density enhancements,
which results in a discrete spectrum of upper hybrid modes with nearly
constant frequency spacing. The number m of quasi-harmonics is limited
by the trapping (quantization) conditions. The problem is described
by an equivalent Schrödinger equation for the trapped mode, which is
solved for an (idealized) cylindrical square density irregularity. In
this model, the eigenfrequency spacing matches the observed type
IV frequency spacings for less than 10% density enhancements with
individual scale sizes of 30-1000 thermal electron gyroradii,
corresponding to 1-100 m scales in coronal loops. To produce the
observed emitted power for a reasonable (&lt;1%) efficiency requires
a large number of such individual microscopic sources occurring over
a portion of a magnetic type IV loop at a restricted altitude within
which the magnetic field and density are approximately constant. The
loop plasma in the zebra emission source is thus highly turbulent in the
sense that it contains a large number of density fluctuations. In this
case transition radiation can effectively contribute to the radiation
background and may also provide the wave power required in the upper
hybrid range for generating zebra emissions.

---------------------------------------------------------
Title: Evolução temporal da explosão solar de 06 de junho de 2000
apresentando estruturas finas em rádio freqüências
Authors: Fernandes, F. C. R.; Sawant, H. S.; Cecatto, J. R.; Caracini,
A. G.; Vats, H. O.; Karlický, M.; Meszarosova, H.
2003BASBr..23..174F Altcode:
Em 06 de junho de 2000 (~15: 00-17: 00 UT), o Brazilian Solar
Spectroscope (BSS) registrou uma explosão solar intensa no intervalo
de freqüência de (1000-2000) MHz, com alta resolução temporal
(100 ms) e espectral (5 MHz). A atividade solar relacionada a esta
explosão associada à região ativa (AR) 9026 e classificada como
X2.3 foi grande. O Ondrejov Observatory registrou rádio emissões até
4,5 GHz. O satélite SOHO registrou uma série de erupções solares,
incluindo uma Ejeção de Massa Coronal (CME) tipo "full-halo" (~15:
54 UT). Explosões tipo II/IV também foram registradas. Na faixa
de ondas decimétricas, este evento apresentou dois picos distintos
(~15: 21 UT e ~16: 42 UT). O primeiro pico coincide com a explosão
registrada em raios-X moles (GOES) e em raios-X duros (Yohkoh). Os
espectros dinâmicos com alta resolução do BSS revelaram várias
estruturas finas, principalmente emissões tipo "zebra" e "fibra",
rádio pulsações, emissões tipo III e do único caso de emissões
"zebra" harmônicas observado na faixa decimétrica. Neste trabalho,
analisamos a evolução temporal e o comportamento global do evento
de 06 de junho de 2000, com ênfase na identificação e associação
da ocorrência de cada tipo de estrutura fina registrada em rádio
com cada etapa da explosão. Resultados preliminares mostraram que,
na fase pré-flare, as estruturas finas apresentaram taxa de deriva
negativa (~ 70-190 MHz/s). As emissões tipo "zebra" concentram-se na
fase de descida do primeiro pico impulsivo e na de subida do segundo
pico. Enquanto que as emissões tipo "fibra" ocorrem em ambas fases,
mas preferivelmente durante a fase de descida. Os resultados serão
apresentados e discutidos.

---------------------------------------------------------
Title: Investigation of april 4th, 2002 solar flare observed
simultaneously in X-rays and decimetric wavelengths
Authors: Fernandes, F. C. R.; Sawant, H. S.; Cecatto, J. R.; Andrade,
M. C.; Kane, S. R.; Karlický, M.; Meszarosova, H.
2003BASBr..23..173F Altcode:
The Brazilian Solar Spectroscope (BSS) is in operation at INPE, in
conjunction with a 9-m diameter antenna. BSS operates in the decimetric
frequency range (1000-2500 MHz) with high temporal (10-1000 ms) and
spectral (3 MHz) resolutions and the absolute timing accuracy of less
than 3 ms. Data can be digitized up to 100 frequency channels. From
March 2002, a couple of solar flares were simultaneous observed
in X-rays by the "Ramaty High Energy Solar Spectroscopic Imager"
(RHESSI) satellite and in radio frequencies by the BSS and by the
Ondrejov Solar Spectrographs (OSS). These flares have been selected for
multi-spectral investigations. The limb flare observed on April 4th,
2002, around 15: 28 UT was investigated. Hard X-ray and high frequency
decimetric narrow-band ( &lt; 200 MHz) type III-like radio bursts have
been observed in association with the impulsive phase of this flare. The
analysis of the RHESSI X-ray images indicates that the flare occurred
behind the south-east solar limb (~ 6o). The estimated occultation
height was ~4000 km. The X-ray spectrum (8-30 keV) was consistent with
a power-law slope with a negative exponent of ~6. These results are
presented and discussed. Moreover, we complement the analysis of the
flare of 4th April, 2002, by including studies of correlation between
radio structures and X-ray emission. A possible connection with the
plasmoid injection is also investigated, since the observation of
the limited frequency slowly drifting structures, as recorded by BSS
and OSS, is an evidence that the type III-like bursts were generated
inside the plasmoid.

---------------------------------------------------------
Title: High-Frequency Radio Signatures of Solar Eruptive Flares
Authors: Karlický, Marian
2003SSRv..107...81K Altcode:
Several examples of the radio emission of eruptive solar flares
with high-frequency slowly drifting structures and type II bursts
are presented. Relationships of these radio bursts with eruptive
phenomena such as soft X-ray plasmoid ejection and shock formation
are shown. Possible underlying physical processes are discussed in the
framework of the plasmoid ejection model of eruptive solar flares. On
the other hand, it is shown that these radio bursts can be considered
as radio signatures of eruptive solar flares and thus used for the
prediction of heliospheric effects.

---------------------------------------------------------
Title: X-ray and radio observations of the activation stages of an
X-class solar flare
Authors: Fárník, F.; Hudson, H. S.; Karlický, M.; Kosugi, T.
2003A&A...399.1159F Altcode:
We report interesting developments prior to the impulsive phase
of an X-class solar flare that occurred on September 24, 2001. Our
multiwavelength study makes use of X-ray data from the Yohkoh satellite,
the Ondřejov radio spectral observations in the decimetric band,
and the new Hard X-Ray Spectrometer instrument (HXRS) on board the MTI
satellite. The GOES time history of this event showed a “precursor”
phase starting as early as two hours prior to the impulsive phase,
and we have used various data sets to identify what parts of this
development could be associated with the flare itself. The most
interesting time interval was identified roughly one hour before
the main peak when an unusual drifting radio continuum was observed
together with two radio sources (at 327 and 164 MHz) in positions
corresponding to expanding loops seen in Yohkoh/SXT and SOHO/EIT images,
accompanied by a filament disappearence during the same period. Hard
X-ray observations revealed a soft spectrum that we interpret as
non-thermal, located within loop structures observed in soft X-rays
along the magnetic neutral line. The hard X-ray emission continued
for more than one hour, as observed in turn by the two spacecraft. In
the initial phase of the flare itself, the hard X-ray emission arose
in structures closely identifiable with the early soft X-ray loops,
which appeared to evolve smoothly into the post-flare loop system of
the flare maximum. The decimeter spectra showed loosely-correlated
spiky emission at frequencies consistent with the densities inferred
from soft X-rays, but with rapid drifts implying motions along field
lines. From all these data we infer that the initiation of the flare
involved non-thermal processes extending along the neutral line in
the photosphere, systematically including open magnetic field lines
as shown by the occurrence of interplanetary Type III bursts observed
by the WAVES spectrometer on board the WIND spacecraft.

---------------------------------------------------------
Title: Plasma Resonance Surfaces in the Magnetic Field Reconnection
and Radio Fine Structures
Authors: Karlický, Marian
2003SoPh..212..389K Altcode:
Using a 2-D MHD model, the magnetic field reconnection
in the current sheet and corresponding plasma
resonance lines (surfaces in 3-D), where the upper-hybrid
frequency equals one of harmonics of the electron gyrofrequency,
ωUH=(ωpe2+ωBe2)1/2=s
ωBe (ωUH, ωpe, and ωBe
are the upper hybrid, electron plasma, and cyclotron frequencies,
respectively, and s is the integer harmonic number) are computed. Then
at selected times and positions in the magnetic reconnection the
spatial and time spectra of upper hybrid frequencies along the
resonance lines are calculated. These spectra are discussed from
the point of view of radio fine structures as narrowband dm-spikes,
zebras, and lace bursts. It is shown that not only turbulent plasma
outflows, suggested in the paper by Bárta and Karlický (2001),
but also perturbed zones near the reconnection slow-mode shocks can
be locations of the narrowband dm-spikes (and/or continua). Sources
of the lace bursts (i.e. bursts with irregular lines) can be located
in the reconnection space, too. On the other hand, the zebras (bursts
with regular separations of zebra lines) need to be generated out of
strongly perturbed reconnection areas.

---------------------------------------------------------
Title: Transport of Energy from the Corona to the Chromosphere
During Flares
Authors: Heinzel, P.; Karlický, M.
2003LNP...612..161H Altcode: 2003ecpa.conf..161H
Hard X-ray (HXR) observations frequently exhibit fast temporal
variations during the impulsive phase of solar flares and this
is usually ascribed to the propagation of beams of accelerated
particles and to the dissipation of their energy in lower layers of
the solar atmosphere. As a result of fast heating and non-thermal
processes, several chromospheric lines show significant impulsive
brightenings. We first review observational attempts of detecting
such fast (sub-second) variations of the line intensities, namely
in the Halpha line, and discuss the problems associated with such
observations. Second, we describe new radiation-hydrodynamical (RHD)
simulations of the pulse-beam heating and show how they predict both
HXR and optical-line intensity variations on very short time scales. We
also discuss the effect of the return current on the energy deposit in
the atmosphere. Using new spatially-resolved HXR observations (RHESSI)
made simultaneously with a high-cadence detection of selected optical
lines, one should be able to diagnose the properties of particle beams,
provided that the response of the lower atmospheric layers to beam
pulses is strong enough.

---------------------------------------------------------
Title: Time profile, duration and polarization of high frequency
spikes
Authors: Zlobec, P.; Mészárosová, H.; Veronig, A.; Karlický, M.;
Magdaleníc, J.
2003HvaOB..27..115Z Altcode:
We analysed a large data set of spikes observed at frequencies 1420
and 2695 MHz recorded with high time resolution by the Trieste Solar
Radio System. Different types of analysis were performed in order to
determine duration, polarization and time profiles of single spikes.

---------------------------------------------------------
Title: High-frequency slowly drifting structures in the November 25,
2000 and April 15, 2001 solar flares
Authors: Karlický, M.; Fárník, F.
2003AdSpR..32.2539K Altcode:
Three slowly drifting structures observed during the November 25,
2000 and April 15, 2001 solar flares arepresented. Their relationship
to the hard X-ray emission is shown. While the April 15, 2001 X14.4
flare started with the high-frequency drifting structure associated
with a plasmoid ejection observed by TRACE in the 171 Å line, the
November 25, 2000 event commenced with two drifting structures in
two different frequency ranges; the high-frequency one consists of
fast positively drifting features with rapid frequency variations
of their high-frequency boundary. Due to fast drifting features the
slowly drifting structures are interpreted in the flare model with
a sequence of fast electron beams accelerated in the current sheet
below the ejected plasmoid. Drifting structures in the November 25,
2000 flare are explained by beams injected into the plasmoid and, at
the same time, by beams propagating downwards against the evaporation
or termination shocks.

---------------------------------------------------------
Title: High-Frequency Slowly Drifting Bursts and Plasmoid Ejections
Authors: Karlický, M.; Jiřička, K.
2003HvaOB..27..123K Altcode:
Two examples of radio emission of eruptive solar flares with
high-frequency slowly drifting structures are presented. The
relationship of these radio bursts with the soft X-ray plasmoid ejection
is shown. Possible underlying physical processes are discussed in the
framework of the model of eruptive solar flares. It is also shown that
these radio bursts can be considered as radio signatures of eruptive
solar flares and thus used for the prediction of heliospheric effects.

---------------------------------------------------------
Title: Hard X-ray and high-frequency decimetric radio observations
of the 4 April 2002 solar flare
Authors: Kane, S. R.; Sawant, H. S.; Cecatto, J. R.; Andrade, M. C.;
Fernandes, F. C. R.; Karlicky, M.; Meszarosova, H.
2003AdSpR..32.2503K Altcode:
Hard X-ray and high frequency decimetric type III radio bursts have been
observed in association with the soft X-raysolar flare (GOES class M
6.1) on 4 April 2002 (∼1532 UT). The flare apparently occurred ∼
6 degrees behind the east limb of the Sun in the active region NOAA
9898. Hard X-ray spectra and images were obtained by the X-ray imager
on RHESSI during the impulsive phase of the flare. The Brazilian Solar
Spectroscope and Ondrejov Radio Telescopes recorded type III bursts
in 800-1400 MHz range in association with the flare. The images of the
3-6, 6-12, 12-25, and 25-50 keV X-ray sources, obtained simultaneously
by RHESSI during the early impulsive phase of the flare, show that
all the four X-ray sources were essentially at the same location well
above the limb of the Sun. During the early impulsive phase, the X-ray
spectrum over 8-30 keV range was consistent with a power law with a
negative exponent of ∼ 6. The radio spectra show drifting radio
structures with emission in a relatively narrow (Δf ≤ 200 MHz)
frequency range indicating injection of energetic electrons into a
plasmoid which is slowly drifting upwards in the corona.

---------------------------------------------------------
Title: Time-dependent Flare Models with MALI
Authors: Kašparová, J.; Heinzel, P.; Varady, M.; Karlický, M.
2003ASPC..288..544K Altcode: 2003sam..conf..544K
Temporal variations of Hα line profile intensities related to electron
beams are presented. We show first results of time dependent simulations
of a chromospheric response to a 1 sec monoenergetic electron beam. 1-D
hydrodynamic code together with particle representation of the beam have
been used to calculate atmospheric evolution. Time dependent radiative
transfer problem has been solved for the resulting atmosphere in the
MALI approach, using the Crank-Nicholson implicit scheme. Non-thermal
collisional rates were included in linearised equations of statistical
equilibrium.

---------------------------------------------------------
Title: Southern hemisphere solar radio heliograph
Authors: Sawant, H. S.; Fernandes, F. C. R.; Neri, J. A. C. F.;
Cecatto, J. R.; Faria, C.; Stephany, S.; Rosa, R. R.; Andrade,
M. C.; Ludke, E.; Subramanian, K. R.; Ramesh, R.; Sundrarajan, M. S.;
Sankararaman, M. R.; Ananthakrishnan, S.; Swarup, G.; Boas, J. W. V.;
Botti, L. C. L.; Moron, C. E.; Saito, J. H.; Karlický, M.
2002ESASP.506..971S Altcode: 2002svco.conf..971S; 2002ESPM...10..971S
The Brazilian Decimetric Array (BDA) is being developed at National
Institute for Space Research (INPE) as an international collaborative
program. Initially, the BDA will operate in the tuneable frequency
range of 1.2-1.7 GHz. The initial planned baseline for BDA 'T' array
is 256×144 m and will be extended to 2.2×1.1 km. In this paper,
we present the results of developments concerning the prototype
of BDA (PBDA). The PBDA will initially operate in the frequency
range of 1.2-1.7 GHz, with a five-antenna array, using 4-meter
parabolic dishes with altitude and azimuth mountings and complete
tracking capability. The spatial resolution for solar images with
the PBDA will be about 3.5 arc-minutes leading to a sensitivity of
≍2×104 mJy/beam for an integration time of 1 sec. The
array will be installed at -22°41'19" latitude and 45°0'22" W
longitude and it is under operation between 9 and 21 UT for continuous
solar flux monitoring. Details of the PBDA system are presented.

---------------------------------------------------------
Title: Time dependent flare model with non-LTE radiative transfer
Authors: Varady, M.; Karlický, M.; Kašparová, J.; Heinzel, P.
2002ESASP.506..521V Altcode: 2002svco.conf..521V; 2002ESPM...10..521V
The first results of a time dependent simulation of chromospheric
response to a high energy electron beam are presented. The hybrid code,
i.e. a combination of a 1-D hydrodynamic code and a test particle code,
has been used to calculate the energy losses of a high energy electron
beam propagating through the solar atmosphere and the consequent
response of the ambient solar plasma to the energy deposition. The
resulting time evolution of the solar plasma temperature, density,
velocity and energy deposit on hydrogen has then been used as an input
for a time dependent radiative transfer code in the MALI approach
to determine the time variation of the Hα line profile. Non-thermal
collisional rates have been included in the linearised ESE.

---------------------------------------------------------
Title: Observation of harmonically related solar radio zebra patterns
in the 1-4 GHz frequency range
Authors: Sawant, H. S.; Karlický, M.; Fernandes, F. C. R.; Cecatto,
J. R.
2002A&A...396.1015S Altcode:
A unique case of two zebra patterns related harmonically with ratio
of ~ 1:2 was observed by distant radio telescopes at São José dos
Campos and Ondřejov Observatories. Accompanied zebras show that the
ratio of frequencies of the neighboring zebra lines is in the range
of 1.009-1.037. There is a tendency of a decrease of this ratio with
decreasing frequency within the specific zebra pattern. Both facts
speak in favour of plasma emission models for the zebra pattern fine
structure in radio burst continua.

---------------------------------------------------------
Title: Statistical analysis of high-frequency narrowband dm-spikes
Authors: Mészárosová, H.; Veronig, A.; Zlobec, P.; Karlický, M.
2002ESASP.506..347M Altcode: 2002ESPM...10..347M; 2002svco.conf..347M
Using linear and nonlienar methods narrowband dm-spikes recorded at
1420 and 2695 MHz were analyzed. In particular their time profiles were
studied statistically. For selected spikes at 1420 MHz a more precise
fitting technique using exponential profiles was applied. Generally,
while in the decaying part the exponential trend can be found, in
the ascending part the exponential form can be confirmed only in
few cases. Furthermore, durations of 1420 and 2695 MHz spikes were
determined and compared with the results in literature. Selected
time series of spikes were tested with respect to nonlinearity. We
found that spikes at fixed frequencies are not governed by a linear
stochastic process, as the underlying physical system contains nonlinear
signatures.

---------------------------------------------------------
Title: Prolonged millimeter-wave radio emission from a solar flare
near the limb
Authors: Pohjolainen, S.; Hildebrandt, J.; Karlický, M.; Magun, A.;
Chertok, I. M.
2002A&A...396..683P Altcode:
We present a multi-wavelength analysis of a gradual radio flare on
June 27, 1993 which showed emission at millimeter waves long after
the soft X-ray flux had peaked. The radio flare located at S12 E75
was associated with a GOES class M3.6 flare that lasted for more than
one hour and hard X-ray emission during the rising phase of the soft
X-ray/radio emission. The maximum radio flux density at 35 GHz was
60 sfu, but the calculated thermal bremsstrahlung flux from the GOES
soft X-rays was less than half of that. The possible explanations
for this prolonged millimeter wave emission could be accelerated
high-energy electrons gyrating along the field-lines (nonthermal
gyrosynchrotron emission) or thermal bremsstrahlung from evaporating
chromospheric warm and dense plasma (cool enough to go undetected by
GOES), or a mixture of these. Our model calculations show that even an
inhomogeneous source containing both kinds of particles would not be
able to produce such a spectral shape. A second source with extremely
high electron densities (&gt;1016 m-3), large
source dimensions (&gt;1015 m2), and very low
temperatures (&lt;106 K) must be assumed to explain the
observed radio spectra.

---------------------------------------------------------
Title: Interpretation of prolonged millimeter-wave emission from a
flare using model calculations
Authors: Hildebrandt, Joachim; Pohjolainen, Silja; Karlický, Marian
2002ESASP.506..299H Altcode: 2002svco.conf..299H; 2002ESPM...10..299H
The long-duration radio flare on June 27, 1993 was characterized
by strong emission at millimeter waves (up to 60 sfu at 35 GHz). It
was not possible to fit the spectrum by model calculations assuming
only one (even inhomogeneous and non-thermal) source because of the
increasing flux between 10 and 35 GHz. Either the low-frequency part
would be totally suppressed by the strong thermal bremsstrahlung
of cool (&lt;106K) plasma necessary for the high mm-flux
or the spectral slope would be always negative for ν &gt; 10 GHz if
gyrosynchrotron emission dominates. The only way to achieve a sufficient
fit was the assumption of two independent sources, one with energetic
electrons and enhanced plasma temperature (loop-like structure), the
other with rather high electron densities, large source dimensions,
and low temperatures (evaporated plasma), both located inside the
antenna beam of 2.4 arc min.

---------------------------------------------------------
Title: Radio signature of multi-scaling flare loop interactions
Authors: Rosa, Reinaldo R.; Ramos, Fernando M.; Sawant, Hanumant S.;
Fernandes, Francisco C. R.; Vijaykumar, Nandamudi L.; Zanandrea,
Ademilson; Karlický, Marian
2002ESASP.506..737R Altcode: 2002ESPM...10..737R; 2002svco.conf..737R
The solar radio emission at 3 GHz observed during the June 6, 2000
flare, at times when the EIT/SOHO and SXT/Yohkoh images indicate the
flare loop interactions, has been analyzed for its complex temporal
variability. Using the Fourier Power Spectrum (FPS) and the Global
Wavelet Spectrum (GWS) techniques the power spectra of the 3 GHz
signal, observed with time resolution of 0.6 s, have been determined:
a 1/f1.66±0.16 power law. The presence of a characteristic
power-law implies that the fluctuations are stochastically correlated
without a dominant characteristic spatio-temporal scale and contain
some self-similarity in time.

---------------------------------------------------------
Title: Sawtooth bursts: observations and model
Authors: Karlický, M.; Bárta, M.; Klassen, A.; Aurass, H.; Mann, G.
2002ESASP.506..303K Altcode: 2002ESPM...10..303K; 2002svco.conf..303K
An example of the sawtooth burst observed during the November 3, 1997
flare is shown. Basic parameters of the sawtooth bursts are summarized
and compared with those of fibers, fiber chains, zebras, EEL bursts
and lace bursts. The sawtooth bursts are found to be most similar to
the lace bursts, therefore the lace bursts model is proposed also for
them. Then using this model the dynamic spectrum with the sawtooth
burst is modelled. The model considers accelerated electrons with
an unstable distribution function on the double resonance frequency
and quasi-periodic variations of the electron plasma density and/or
magnetic field in the radio source.

---------------------------------------------------------
Title: The 1 October 2001 Eruptive Prominence: Observed and Modeled
Structures
Authors: Karlický, Marian; Kotrč, Pavel; Kupryakov, Yurij A.
2002SoPh..211..231K Altcode:
Using TRACE 171 Å image observations and Hα spectra and images
observed at the Ondřejov Observatory, the October 1, 2001, eruptive
prominence is studied. The evolution of this prominence is described and
velocities of specific parts of the prominence are determined. It was
found that, after the rising phase of the cold loop-like prominence,
its upper part expanded and below this expanding part, around one
of its legs a `ring' structure, visible in the TRACE images, was
formed. Then, at the same place, a tearing of the prominence leg was
recognized. Simultaneous spectral observations of this structure
reveal a very broad Hα line, which indicates strong turbulent
motion at these positions. These processes were accompanied by an
expanding Hα envelope. Due to the similarity of the observed `ring'
and tearing structures with those modeled by Lau and Finn (1996),
the prominence leg tearing is interpreted as a reconnection process
between two parallel magnetic ropes having parallel electric currents,
but anti-parallel axial magnetic fields.

---------------------------------------------------------
Title: Analysis of the expanding flare loops of C8.5/1F April 2,
2001 flare
Authors: Kulinová, A.; Dzifčáková, E.; Klačka, J.; Karlický, M.
2002ESASP.506..677K Altcode: 2002svco.conf..677K; 2002ESPM...10..677K
Evolution of the flare loops observed in TRACE 171 Å line, 1600
Å continuum and Hα line (Modra Observatory) during the C8.5/1F,
April 2, 2001 flare is analyzed (NOAA AR 9393). The expansion of the
flare loops at their tops is recognized nearly co-spatially at the
hot TRACE 171 Å as well as cold Hα line and 1600 Å continuum. Due
to the visibility of Hα structures in emission against the disc we
assume that this demands relatively high plasma electron densities
(~1012cm-3). Prior to the expansion of the loops
a high density plasma injection into them was observed. Detailed
analysis shows that plasma parameters are close to the ballooning
instability threshold, especially in regions close to the null point
of the extrapolated magnetic field.

---------------------------------------------------------
Title: Drifting decimetric pulsation structures in the initial phase
of solar flares
Authors: Karlický, M.; Kliem, B.; Mészárosová, H.; Jiřička, K.
2002ESASP.506..653K Altcode: 2002svco.conf..653K; 2002ESPM...10..653K
Two new cases of slowly negatively drifting pulsation structures in the
decimetric wavelength range are reported. It is shown that the August
18, 1998 flare started with a slowly drifting pulsation structure
associated with a plasmoid ejection observed by Yohkoh/SXT. This
drifting pulsation structure is an example of a narrow-band one,
which even shows intensity enhancements at its high- and low-frequency
edges. Using the cross-correlation method no significant relation
between the radio emission of this drifting structure and the hard
X-rays was found. On the other hand, the second drifting structure
observed during the hard X-ray decay phase of the March 24, 2000
flare shows a clear separation from the large-scale coronal shock
wave released by the flare (a partly simultaneous type II radio burst
occurred at much lower frequencies). The slowly drifting structures
are analyzed and possible underlying physical processes are discussed
assuming the plasmoid ejection model of eruptive solar flares.

---------------------------------------------------------
Title: Radio observations of the July 13, 2000 transequatorial
eruptive prominence
Authors: Karlický, M.; Shibasaki, K.
2002ESASP.506..657K Altcode: 2002ESPM...10..657K; 2002svco.conf..657K
Using the 17 and 34 GHz Nobeyama Radioheliograph observations the
July 13, 2000 transequatorial eruptive prominence was studied. It
was found that the eruption started near the bright equatorial
feature, which reappeared in the post-eruption phase. During 7
hours of observations of this feature periodic variations of its
brightness temperature were recognized, e.g. in the initial phase of
the prominence eruption their characteristic period was about of 12
minutes. Circular loops and helical structures of different scales,
indicating the presence of electric currents were observed during the
whole prominence eruption. The velocity of the upper boundary of the
prominence in the image plane, along the chosen line was estimated as
24 km s-1 in the first 15 minutes of the eruption and about
of 66 km s-1 in following times. Finally, the observations
are shortly discussed.

---------------------------------------------------------
Title: High-frequency slowly drifting structures in solar flares
Authors: Karlický, M.; Fárník, F.; Mészárosová, H.
2002A&A...395..677K Altcode:
Radio emission of four solar flares with high-frequency slowly drifting
structures is presented. Three sub-classes of these structures were
recognized. It is shown that the April 15, 2001 X14.4 flare started
with the slowly drifting structure associated with a plasmoid ejection
observed by TRACE in the 171 Å line. The August 18, 1998 event
presents an example of the drifting pulsation structure (DPS) which
is well limited in frequency extent at both sides. A further example
of the DPS, but followed by clouds of the narrowband dm-spikes, was
observed during the November 23, 2001 flare. Finally, in the case of
the April 12, 2001 flare, the drifting pulsation-continuum structure
was recorded at the same time as the metric type II radio burst,
i.e. in different frequency ranges. The slowly drifting structures
were analyzed and in two cases their relation to hard X-ray emission
was studied. Possible underlying physical processes are discussed
assuming the plasmoid ejection model of eruptive solar flares.

---------------------------------------------------------
Title: Magnetic fields, plasma densities, and plasma beta parameters
estimated from high-frequency zebra fine structures
Authors: Karlický, M.; Jiricka, K.
2002ESASP.505..437K Altcode: 2002solm.conf..437K; 2002IAUCo.188..437K
Using the recent model of the radio zebra fine structures
(Ledenev et al. 2001) the magnetic fields, plasma densities, and
plasma beta parameters are estimated from high-frequency zebra
fine structures. It was found that in the flare radio source of
high-frequency (1-2 GHz) zebras the densities and magnetic fields
vary in the intervals of (1-4)×1010 cm-3 and
40-230 G, respectively. Assuming then the flare temperature as about of
107K, the plasma beta parameters in the zebra radio sources
are in the 0.05-0.81 interval. Thus the plasma pressure effects in
such radio sources, especially in those with many zebra lines, are
not negligible.

---------------------------------------------------------
Title: Flare loops destabilization and expansion during the April 2,
2001 flare
Authors: Kulinová, A.; Dzifcáková, E.; Klacka, J.; Karlický, M.
2002ESASP.505..469K Altcode: 2002solm.conf..469K; 2002IAUCo.188..469K
An evolution of the flare loops observed in TRACE 171 Å line, 1600
Å continuum and Hα line (Modra Observatory) during the C8.5/1F,
April 2, 2001 flare is analyzed. The expansion of the flare loops
at their tops is recognized co-spatially at the hot (TRACE 171 Å,
0.9 MK) as well as cold (Hα and 1600 Å, 0.01 - 0.02 MK) lines. The
loop expansion started after an injection of the cold plasma into
the loops. At some parts of the expanding loops helical features were
found. At space of loop footpoints the umbrella handle shape features
can be seen. It was found that these structures are 3-dimensional ones,
i.e. not only layers in the chromosphere. Such an interpretation demands
relatively high plasma densities (~1012 cm-3)
in these structures due to their visibility in emission against the
disc in the Hα. Furthermore the linear bright structure, perpendicular
to the global magnetic field of the expanding loops, was observed. To
understand the whole process under the study, the observed structures
are compared with those extrapolated in the potential magnetic field
approximation. A possible role of the "ballooning" instability,
destabilizing the loops, is discussed.

---------------------------------------------------------
Title: X-ray and radio observations in the initial development of
an X-class solar flare
Authors: Fárnik, F.; Karlický, M.; Hudson, H.; Kosugi, T.
2002ESASP.508..441F Altcode: 2002soho...11..441F
The EIT/SOHO and SXT/YOHKOH plasma ejecta accompanied by an unusual
drifting radio continuum and early hard X-ray emission observed
prior to the impulsive phase of the September 24, 2001, X-class
flare are analyzed. The paper presents some of the first reported
observations from the new Hard X-ray Spectrometer instrument (HXRS),
as well as imaging data from YOHKOH plus radio spectral observations
in the decimetric band. The early hard X-ray observations revealed a
soft spectrum that we interpret as non-thermal, located within loop
structures observed in soft X-rays along the magnetic neutral line. The
hard X-ray emission continued for more than one hour. In the initial
phase of the flare, the hard X-ray emission arose in structures closely
identifiable with the early soft X-ray loops, which appeared to evolve
smoothly into the post-flare loop system of the flare maximum. At this
time the decimeter spectra showed loosely-correlated spiky emission at
frequencies consistent with the densities inferred from soft X-rays,
but with rapid drifts implying motions along magnetic field lines.

---------------------------------------------------------
Title: The EIT coil-like structure in the March 20, 2000 eruptive
prominence
Authors: Karlický, M.; Šimberová, S.
2002A&A...388.1016K Altcode:
The evolution of the March 20, 2000 prominence eruption observed in
the 195 Å(EIT/SOHO), Hα , (MDI/SOHO), 1-3 GHz radio and hard X-ray
(BATSE) was analyzed. A unique EIT coil-like structure with a hot core,
indicating an electric current, was observed at the beginning of the
prominence eruption. This structure with about 5 turns was associated
with the reverse drift radio bursts at 1.0-2.5 GHz and the 33-57 keV
hard X-ray emission. The hot core observation confirmed our recent
suggestion about heating inside the eruptive prominence. Comparing the
form of the EIT filament in the pre-eruption phase with the magnetic
field map the presence of the electric current was confirmed. It was
suggested that the relatively slow drifts of the reverse drift bursts
can be due to a beam propagating in a vertical coil-like (helical)
structure. Plasma processes and parameters in the eruptive prominence
were discussed.

---------------------------------------------------------
Title: Correlated Study of Decimetric Solar Radio Bursts and Solar
X-Ray Bursts Observed by RHESSI
Authors: Fernandes, F. C. R.; Cecatto, J. R.; Reinaldo, R. R.; Krishan,
V.; Sawant, H. S.; Karlicky, M.; Liricka, K.; Kane, S. R.
2002AAS...200.7609F Altcode: 2002BAAS...34..777F
High resolution sprectra and images of solar hard X-ray bursts in 3 keV
-- 15 MeV range obtained by the recently launched RHESSI spacecraft are
compared with decimetric solar radio bursts observed simultaneously
with high time and frequency resolution with the Brazilian Solar
Decimetric Telescope (1000 -- 2000 MHz) and Ondrejov Radio Telescope
(800 -- 4500 MHz). Preliminary results from a correlated study of
the type III bursts and other fine structures observed with the
ground-based radio instruments and the impulsive hard X-ray bursts
observed by RHESSI will be reported. These results are expected to
lead to a better understanding of the acceleration and propagation of
energetic electrons in the solar atmosphere.

---------------------------------------------------------
Title: A Mechanism for ZEBRA Burst Radio Emission in the Solar Corona
Authors: LaBelle, J.; Yoon, P. H.; Karlicky, M.; Treumann, R. A.
2002AGUSMSH21D..02L Altcode:
Solar ZEBRA radio bursts are one of the least understood solar radio
emissions. They occur irregularly during solar Type IV radio bursts
covering a relatively wide frequency range from 0.5-4 GHz. Their
instantaneous total bandwidth is narrow of the order of a fraction of
1 GHz. As the name suggests, they consist of a limited but sometimes
large number of emission lines which are about equally spaced in
frequency. The spacing is of the same order as the width of each
line emission. Their connection with type IV bursts suggests that
they occur in relatively strong magnetic field regions in the source
region of the type IV and are related to the generation of emission
by the trapped electron component in magnetic loop configurations. We
propose a mechanism which is based on trapping of the upper hybrid
mode in plasma density fluctuations in the loop plasma. Upper hybrid
waves are readily excited by the trapped electron populations in
the loop, whose distribution functions are characterized by loss
cones. Trapping causes a discrete spectrum of such modes and nearly
constant frequency spacing with the number of quasi-harmonics limited
by the trapping conditions. We derive an equivalent Schrödinger
equation for the trapped mode and solve it in cylindrical symmetry,
obtaining the eigenfrequencies. Trapping occurs for sufficiently large
density modulations. The expected frequency spacing is as narrow as
observed. The trapped upper hybrid modes may mode convert into radio
emission in order to radiate away; such mode conversion occurs in
several other space physics radio emissions, such as terrestrial
continuum radiation and auroral electron cyclotron harmonic waves
(“auroral roar”). This model of the ZEBRA emissions implies that
they can be used to remotely sense the fluctuating density structure
in the solar corona under type IV conditions.

---------------------------------------------------------
Title: Microwave Detection of Shock and Associated Electron Beam
Formation
Authors: Aurass, H.; Shibasaki, K.; Reiner, M.; Karlický, M.
2002ApJ...567..610A Altcode:
We use complementary European and Japanese solar radio ground-based
observations, together with Yohkoh soft X-ray and SOHO extreme-UV
images, to search for the signature of flare-related waves at different
heights above the Sun. The key data set for event selection is 40-800
MHz dynamic radio spectra from the Potsdam Astrophysical Institute,
whose radio spectral polarimeter is sensitive to the coronal shock
waves due to the associated type II radio bursts in the range between
0.2 and 1 Rsolar. Nobeyama Radio Heliograph images at 17
GHz show the chromosphere and the transition region to the corona with
unprecedented sensitivity and time resolution (1 s image cadence). Here
we focused on 17 GHz images in the time interval between flare onset
and the start of the metric type II burst. The decametric-hectometric
(Dm-Hm 1-14 MHz) radio experiment on board Wind completes the radio
spectral coverage. The spectra are used to check if the coronal shock
wave is also continuously visible in the range 3-8 Rsolar and
if the corona is open or closed for electron beams exciting hectometric
type III bursts. We selected two flare events that show metric type II
bursts, but with different associated 17 GHz features. For both events
we find flare disturbances in 17 GHz images that propagate earlier
than the type II bursts: a hot, dense blob (event 1; 1997 April 2)
or a cold, absorbing cloud (event 2; 1998 July 31). In event 1, the
hot and dense blob preceded the formation of a wave front segment that
appeared in SOHO/EIT images. In event 2, we observed the impact of
the 17 GHz absorbing cloud on a preexisting quiescent prominence far
out of the flaring active region after several minutes of propagation
without being disturbed. We demonstrate that the spectral pattern, as
well as the drift rate, of the given type II burst drastically changes
shortly before the cloud's impact. The Dm-Hm spectra in event 2 reveal
a typical shock-associated (SA) event in the outer corona during the
interaction between the absorbing cloud and the prominence. Finally,
we stress that there may be a common driver for the metric type II
bursts and simultaneous decimeter reverse-drift bursts between 1 and
2 GHz recorded on the radio spectrograph of Astronomical Observatory
Ondřejov.

---------------------------------------------------------
Title: Loop structures in the July 19, 1999 solar flare
Authors: Kulinová, A.; Karlický, M.
2002ESASP.477..143K Altcode: 2002scsw.conf..143K
Comparing the SOHO/EIT 195 Å and Hα images (Hvar and Modra
Observatories) with the magnetic field extrapolations of SOHO/MDI
magnetograms the loop structures of the July 19, 1999 flare were
analyzed. The presence of the current-carrying flux rope was identified
by its deviation from the current-free magnetic field extrapolation
and "umbrella hand" shape of the Hα ribbons. After the flare start
in the neighboring "cone" arcade this current-carrying flux rope
interacts (reconnects) with this arcade, forming thus flare loops
spanning over both these magnetic structures. During these processes
several cross-loop structures appeared. One of them indicates the
flare loop interaction. At this space the extended helical structure,
possibly a remnant of some current-carrying flux rope, was found. The
pitch angle of this helical thread θ = 61° was determined. Assuming
then the magnetic field as 10-4 - 10-3T, the
total electric current in the helical structure was estimated as J =
4.8×(109 - 1010)A.

---------------------------------------------------------
Title: Magnetic rope in the March 20, 2000 prominence eruption
Authors: Karlický, Marian; Simberová, Stanislava
2002ESASP.477..127K Altcode: 2002scsw.conf..127K
An evolution of the March 20, 2000 prominence eruption observed
in the Hα and 195 Å EIT was analyzed using the image processing
technique. The helical structure of the eruptive prominence (magnetic
rope) with a hot core was recognized and the electric current of
3.7×1010 Å inside this rope was estimated. The hot core
observation agrees with our recent spectroscopic observations. It
is interesting that the pre-eruptive filament was located above the
X-type photospheric magnetic field. During the eruption the magnetic
field changes around this X-type configuration have been found.

---------------------------------------------------------
Title: Occurrences of different types of 0.8-2.0 GHz solar radio
bursts and fine structures during the solar cycle
Authors: Jiřička, K.; Karlický, M.; Mészárosová, H.
2002ESASP.477..351J Altcode: 2002scsw.conf..351J
681 solar radio events observed by the Ondřejov 0.8-2.0 GHz
radiospectrograph during 1992-2000 are analyzed and corresponding
bursts and fine structures classified into ten different classes. For
all defined types of bursts and fine structures basic characteristics of
their parameters are presented. Distributions of various types of bursts
and fine structures in the years 1992-2000 in dependence on the changes
of solar activity during the cycles 22 and 23, occurrences of studied
types of bursts in association with GOES class flares as well as their
relationship to GOES flare maxima are shown. Finally, the association
of the analyzed bursts with the metric type III bursts is studied.

---------------------------------------------------------
Title: Impact Hα line polarization and return current
Authors: Karlický, M.; Hénoux, J. C.
2002A&A...383..713K Altcode:
Electron beams, bombarding the dense chromospheric layers during
solar flares, carry electric currents which need to be neutralized by
so-called return currents. Return currents are formed by background
plasma electrons having an anisotropic velocity distribution. Thus
they can generate impact Hα line polarization. First, a numerical
method of computation of the impact Hα line polarization for an
arbitrary electron distribution function is presented. Then the
polarization due to return current electrons associated with beam
electrons is computed. For low electron beam fluxes, the return
current is low and the polarization is only due to the electron beam,
i.e. it is perpendicular to the electron beam direction and it reaches
-8.0%. Increasing the return current and the beam flux leads to a
change of orientation of the polarization by 90deg and
the polarization degree can even reach a maximum of +22.4%. But this
change and the maximum of the polarization require very high electron
beam fluxes of 1.79 x 1012 and 4.8 x 1012
ergs cm-2 s-1, respectively. Therefore plasma
processes, which can reduce the high-energy flux requirement for the
polarization change observations, are briefly discussed.

---------------------------------------------------------
Title: 3 GHz Flux Variations of the April 7, 1997 Flare and
Current-Loop Coalescence Model
Authors: Fárník, F.; Karlický, M.
2002mwoc.conf..169F Altcode:
Very regular time variations of the 3 GHz radio flux observed during the
7 April 1997 flare are presented together with Yohkoh-SXT and SOHO-EIT
observations. On lower frequencies (40-800 MHz) the variations were
followed by several branches of type II radio burst. In the post-maximum
phase of this flare the Yohkoh images indicate I-type of the flare
loop interaction. The observations were analyzed and it was found that
the data can be described by the current-loop coalescence model: the
main period of the 3 GHz radio flux (about 100 s) corresponds to the
repetition of the current-loop coalescence, and the radio double-peaks
are associated with the maximum of the electric field component
perpendicular to the interaction plane. The plasma beta-parameter in
the current-loop coalescence process was estimated as 0.63. Indications
of the beta-parameter increase during the flare are found.

---------------------------------------------------------
Title: Flare Changes Associated with Peaks of Hard X-Ray Bursts
Authors: Farnik, F.; Svestka, Z.; Karlicky, M.
2002cosp...34E1403F Altcode: 2002cosp.meetE1403F
Using the high-resolution records made in four energy channels
by the Hard X-Ray Spectrometer (HXRS) on board the MTI spacecraft
(launched on 12 March 2000) we try to refine the study made by Dwivedi
et al. 18 years ago (Dwivedi, B.N., Hudson, H.S., Kane, S.R., and
Svestka, Z.: 1984, Solar Phys. 90, 331) who looked for changes in the
flare development associated with changes in the hard X-ray flux. In
addition to H-alpha and SOHO data we can, at least for some flares,
also use high-resolution TRACE images which make it possible to see
fine changes which could not be detected before. We try to find, in
particular, which parts of flares produce hard X ray peaks of various
hardness in the HXRS records and we also- compare them with peaks in
microwave records. Intense peaks often correspond to flaring structures
penetrating into strong magnetic fields (penumbrae and umbrae of
sunspots) which generally confirms Dwivedi et al.'s findings. However,
we can provide more details than they were able to obtain from their
data with worse space and time resolution.

---------------------------------------------------------
Title: High-Frequency Slowly Drifting Pulsation Structures in the
November 25, 2000 and April 15, 2001 Solar Flares.
Authors: Karlicky, M.; Farnik, F.
2002cosp...34E1404K Altcode: 2002cosp.meetE1404K
Radio and X ray emissions of the November 25, 2000 and April 15, 2001
solar- flares exhibiting the high-frequency slowly drifting pulsation
structures (DPS) are presented. The characteristic periods of the DPSs
are determined and their relationship to the hard X-ray emission is
analyzed. Possible physical processes are discussed under assumption
of the plasmoid ejection model of eruptive solar flares. It is shown
that the April 15, 2001 X14.4 flare started with the DPS which was
associated with a plasmoid ejection seen in the 171 A line (TRACE). The
November 25, 2000 event exhibits the DPS together with the bursts with
rapid frequency variations, indicating a different origin of the DPS.

---------------------------------------------------------
Title: Decimetric dot-like structures
Authors: Sawant, H. S.; Fernandes, F. C. R.; Cecatto, J. R.; Vats,
H. O.; Neri, J. A. C. F.; Portezani, V. A.; Martinon, A. R. F.;
Karlický, M.; Jiřička, K.; Mészárosová, H.
2002AdSpR..29..349S Altcode:
Various types of fine structures have been observed by the Brazilian
Solar Spectroscope (BSS) in the frequency range of (1000 - 2000) MHz,
since its regular operation from 1998. Here, we report for the first
time statistical analysis of the 165 isolated dot-like emissions and
their chains observed, from September 1999 to September 2000, in the
decimetric band. Dots are observed in groups spread over the frequency -
time plane. Rarely their chains are observed. Chains of dots cover the
frequency range of ∼ 150 MHz and hardly cover the entire frequency
range of observations. Isolated dot-like emission has been observed to
the limit of the BSS resolutions (3 MHz, 50 ms). In 50 % of the cases
the observed instantaneous bandwidth and flux values are 5 MHz and ∼
20 sfu, respectively. Also, in 90 % of the cases total duration is of
about 50 ms, equal to the limit of BSS time resolution. The groups of
the dots have been found to be associated with the rising part of the
impulsive flares and a radio-continuum. A model of dot-like emissions
based on the anisotropic beam instability is suggested.

---------------------------------------------------------
Title: Decimetric Reverse Drift and U-Type Bursts in the April 9,
2001 Flare
Authors: Cecatto, J. R.; Sawant, H. S.; Fernandes, F. C. R.; Krishan,
V.; Rosa, R. R.; Karlický, M.
2002mwoc.conf..313C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Electron acceleration, Decimetric Solar radio bursts and
Solar hard X-ray bursts observed by RHESSI
Authors: Kane, S.; Fernandes, F.; Cecatto, J.; Reinaldo, R.; Krishan,
V.; Sawant, H.; Karlicky, M.; Liricka, K.
2002cosp...34E.574K Altcode: 2002cosp.meetE.574K
Characteristics of the acceleration and propagation of electrons in the
solar corona during a solar flare are deduced from a correlated study
of decimetric radio bursts and impulsive hard X-ray bursts. Decimetric
type III bursts and other fine structures in the frequency range of
(1000-2000) MHz have been observed with the Brazilian Solar Decimetric
Spectroscope. Corresponding radio observations in the (800-4500) MHz
frequency range were made with the Ondrejov radio Telescopes. High
resolution sprectra and images of solar hard X-ray bursts in 3 keV
- 15 MeV range obtained by the recently launched RHESSI spacecraft
are compared with the radio observations to determine the temporal
relationship and its dependence on the characteristics of the radio
bursts and hard X ray bursts. Early results from this- correlated study
of ground-based radio observations and and spacecraft -observations
of solar X-ray flares will be reported.

---------------------------------------------------------
Title: Radio Shocks from Reconnection Outflow Jet? - New Observations
Authors: Aurass, H.; Karlicky, M.; Thompson, B. J.; Vršnak, B.
2002mwoc.conf..401A Altcode:
The common analysis of dynamic radio spectrograms with Yohkoh X-ray
images yields information about possible associations between
nonthermal electron acceleration and changes in hot and dense
plasma-magnetic field structures of the corona. Examples are correlated
X-ray-jet--electron beam injections (type III/U bursts), motions of
X-ray blobs and correlated shock-driven (type II) radio bursts, and
sigmoid evolution associated with characteristic type IV burst spectral
fine structures. Here, we demonstrate the first identification of the
radio signature of a reconnection outflow termination shock during a
dynamic flare. Reconnection of magnetic fields is one flare energy
release mechanism. During dynamic flares there is formed a system
of standing slow and - sometimes - also fast mode shock waves in the
space around the diffusion region. This standing fast mode shock is
revealed by a zero-drift type II burst between 300 and 400 MHz. It
exists more than 30 min starting 1 hour after the impulsive flare on
07 April 1997 in AR 8027. It shows herringbone fine structure and 10%
band splitted lanes. We argue for having detected fundamental mode
emission. No fundamental-harmonic pattern was observed. Simultaneous
imaging observations (Hα, Yohkoh SXT, SOHO EIT) show a postflare loop
arcade with a bright soft X-ray cusp. Preferable conditions for the
radio detection of the termination shock are a low plasma to magnetic
pressure ratio eta upstream of the slow shocks, a low diffusion region
rise velocity, and a low reconnection rate. The occurrence of the
termination shock is most probable in late stage of flares.

---------------------------------------------------------
Title: The 1.0-4.5 GHz Zebras in the June 6, 2000 Flare
Authors: Sawant, H. S.; Karlický, M.; Fernandes, F. C. R.; Cecatto,
J. R.
2002mwoc.conf..315S Altcode:
For the first time we are reporting harmonically related zebra
structures above 1000 MHz, having ratio of 1:2. Zebra structures show
up to 8 zebra lines. In individual zebra patterns the frequency ratio
of the neighbouring zebra lines are less than 1.03 and these ratios
decrease with the frequency decrease. The zebra patterns are analyzed
and interpreted assuming double plasma resonance instability as the
cause for their generation. The longitudinal upper hybrid waves are
excited at positions of cyclotron resonances and then transformed into
electromagnetic ones. Using this model the magnetic field strengths
in the flaring loops are estimated in the range of 110-230 G.

---------------------------------------------------------
Title: Drifting Pulsations, 3 GHz Oscillations and Loop Interactions
in the June 6, 2000 Flare
Authors: Karlický, M.; Sawant, H. S.; Fernandes, F. C. R.; Cecatto,
J. R.; Fárník, F.; Mészárosová, H.
2002mwoc.conf..173K Altcode:
During this long-lasting X2.3 flare (15:00-17:00 UT) two 3 GHz
maxima (impulsive phases) were recognized at 15:06:46-15:07:00 and
16:26:34-16:26:42 UT. Quasi-periodic oscillations with the periods of
160 s and 11 s, respectively, were found, during both these impulsive
phases. While in the first impulsive phase the 2.0-4.5 GHz broadband
pulsations superimposed on the continuum were recorded, during the
second one several quasi-periodic patches of narrowband spikes were
observed in the frequency range of 2.5-3.5 GHz. Moreover, at the onsets
of both impulsive phases the narrowband fast drift structures slowly
drifting towards lower frequencies and indicating the plasmoid ejection
were recorded. The SOHO and YOHKOH images of the flare show parallel
loops with brightenings among them. It shows that the flaring loops
interact. This view is supported by simultaneous observations of the
quasi-periodic oscillations at 3 GHz and the narrowband pulsations
in the second impulsive phase, which can be thus understood in the
framework of the current loop coalescence model.

---------------------------------------------------------
Title: Turbulent plasma model of the narrowband dm-spikes
Authors: Bárta, M.; Karlický, M.
2001A&A...379.1045B Altcode:
Starting from radio spectrum features of the narrowband dm-spikes,
it is suggested that they are generated at positions in the solar
flare atmosphere where the upper hybrid frequency is equal to the low
harmonics of the electron cyclotron frequency. It is assumed that a
radio source plasma is in a turbulent state. The upper hybrid waves
are generated by an anisotropic electron beam which propagates along
magnetic loop lines. Collisional damping and turbulent changes of
plasma parameters in the radio source cause strong intensity-frequency
variations of the upper hybrid waves. These waves are then transformed
into observed narrowband dm-spikes. Using this model, the artificial
radio spectra are computed. It is shown that a chain of narrowband
spikes is generated at a one cyclotron harmonic, in one turbulent
magnetic flux tube. On the other hand, a cloud of spikes (or their
harmonic clouds) results from a superposition of many chains of spikes
generated in many turbulent magnetic flux tubes (in several cyclotron
harmonics). Finally, further features of the narrowband dm-spikes are
discussed in the framework of the proposed model.

---------------------------------------------------------
Title: Bastille Day Event: A Radio Perspective
Authors: Reiner, M. J.; Kaiser, M. L.; Karlický, M.; Jiřička, K.;
Bougeret, J. -L.
2001SoPh..204..121R Altcode:
We describe the radio signatures that led up to and concluded the
solar eruptive event of 14 July 2000 (Bastille Day Event). These radio
signatures provide a means of remotely sensing the associated solar
activity and transient phenomena. For many days prior to the Bastille
Day Event kilometric Type III radio storm emissions were observed that
were presumably associated with the active region NOAA 9077. These storm
emissions continued until the X5.7 flare at ∼ 10 UT on 14 July 2000
that characterized the Bastille Day Event, then ceased abruptly. The
Bastille Day Event itself produced very intense, complex, long-duration
Type III-like radio emissions, which appear to have been associated
with electrons generated (accelerated) deep in the solar corona. The
coronal mass ejection (CME) associated with the Bastille Day Event
generated decametric to kilometric Type II radio emissions as the CME
propagated through the solar corona and interplanetary medium. The
frequency drift of these Type II radio emissions are related to the
dynamics of the propagating CME and indicate that the CME experienced
significant deceleration as it propagated from the high corona into
the interplanetary medium.

---------------------------------------------------------
Title: Radio bursts with rapid frequency variations - Lace bursts
Authors: Karlický, M.; Bárta, M.; Jiřička, K.; Mészárosová,
H.; Sawant, H. S.; Fernandes, F. C. R.; Cecatto, J. R.
2001A&A...375..638K Altcode:
The Ondřejov radiospectrograph operating in the 0.8-2.0 GHz frequency
range recorded in recent years (1998-2000), three (August 10, 1998;
August 17, 1999; June 27, 2000) unique bursts with rapid frequency
variations (lace bursts) lasting for several minutes. On August 17,
1999, the same burst was recorded simultaneously by the Brazilian
Solar Spectroscope in the 1.0-2.5 GHz frequency range. The frequency
variations of these bursts in four time intervals were analyzed by
the Fourier method and power-law spectra with power-law indices close
to -2 were found. The Fourier spectra show the presence of frequency
variations in the 0.01-3.0 Hz interval which indicate fast changes of
plasma parameters in the radio source. Due to the similarities in the
line features of these bursts with zebra pattern lines, a model similar
to that of the zebra pattern was suggested. The model radio spectra,
computed using this model with a turbulent state of the solar flare
atmosphere, are similar to those observed by the radiospectrographs.

---------------------------------------------------------
Title: Global statistics of 0.8-2.0 GHz radio bursts and
fine structures observed during 1992-2000 by the Ondřejov
radiospectrograph
Authors: Jiřička, K.; Karlický, M.; Mészárosová, H.; Snížek, V.
2001A&A...375..243J Altcode:
681 solar radio events observed by the Ondřejov 0.8-2.0 GHz
radiospectrograph during 1992-2000 are analyzed and corresponding bursts
and fine structures classified into ten different classes. A new rare
type of fine structure with rapid frequency variation we called lace
pattern was included. Drifting pulsation structures, observed usually
at the beginning of the impulsive flare phase, were recognized among
pulsations. Furthermore, a new sub-class of zebra patterns with many
zebra lines ( ~ 30) superimposed on fibers was identified. For all
defined types of burst and fine structures basic characteristics of
their parameters are presented. Distributions of various types of
burst and fine structures in the years 1992-2000 in dependence on the
changes of solar activity during the cycles 22 and 23, occurrences
of studied types of burst in association with GOES class flares as
well as their relationship to GOES flare maxima are shown. Finally,
the association of the analyzed bursts with the metric type III bursts
observed at Potsdam-Tremsdorf Observatory was studied.

---------------------------------------------------------
Title: An Estimation of the Coronal Magnetic Field Strength From
Spectrographic Observations in the Microwave Range
Authors: Ledenev, V. G.; Karlický, M.; Yan, Y.; Fu, Q.
2001SoPh..202...71L Altcode: 2001astro.ph..1360L
Solar radio emission observations in the microwave frequency range
show fine structures consisting of a number of almost parallel
narrow-frequency bands. We interpret these bands as plasma emission
at cyclotron harmonics. This emission is generated by the anisotropic
electron beam, which excites longitudinal waves at a normal Doppler
effect resonance. Subsequently, the longitudinal waves convert to radio
emission at the second harmonic of the longitudinal wave frequency,
and sometimes to the fundamental harmonic. The magnetic field strength
is estimated on the basis of such a model in the microwave burst sources
at ∼ 100-200 G. Estimates of the density variations are also made.

---------------------------------------------------------
Title: Locations of Footpoints of Transequatorial Interconnecting
Loops
Authors: Fárník, František; Karlický, Marian; Švestka, Zdeněk.
2001SoPh..202...81F Altcode:
We discuss footpoints of loops seen by Yohkoh in soft X-rays
that connect active regions across the equator (transequatorial
interconnecting loops - TILs). While most TILs are rooted in moderately
strong fields at peripheries of active regions, there are also cases
when these loops are anchored in very weak or very strong fields,
ranging from &lt; 30 G to several hundred gauss. Some have their
footpoints near sunspot penumbrae, creating `X-ray fountains' in a
combination with active region loops. But TILs are never rooted in
sunspots. The most likely explanation is that magnetic field lines
leave spots almost vertically so that TILs rooted in them extend high
into the corona and density in them is below the limit of visibility
in X-rays. The fact that in force-free modeling some TILs are rooted
in sunspots is most probably due to the difference between field-line
connections in `vacuum' and in the highly conductive plasma on the
Sun. Some TILs end before they reach active regions which sometimes
may indicate the real situation, but mostly this `gap' is probably due
to a temperature decrease near the loop footpoints which makes them
invisible in X-rays. In that case the fact that these cool lowest parts
of TILs are never found in TRACE or SOHO EIT images indicates that
plasma density in TILs must be very low. Still, the total absence of
any counterparts of X-ray TILs in TRACE and EIT images is puzzling and,
therefore, other possible interpretations of the `gap' origin are also
briefly mentioned.

---------------------------------------------------------
Title: New Solar Broad-Band Hard X-Ray Spectrometer: First Results
Authors: Fárník, František; Garcia, Howard; Karlický, Marian
2001SoPh..201..357F Altcode:
The scientific and operational aims of the Czech-made Hard X-Ray
Spectrometer (HXRS) launched onboard the U.S. Department of Energy
Multispectral Thermal Imager satellite (MTI), on 12 March 2000 are
discussed. The principal operating characteristics of the instrument
such as the temporal resolution, energy band selection, spectral
sensitivity, and the in-flight calibration procedure are described as
well as the technical details of the spectrometer including detectors,
shielding (against charged particles) and electronic design. The
MTI host satellite and its orbit are briefly described. Recent
observations by the 3 GHz Ondřejov radiometer are compared with
HXRS data to demonstrate one example of the HXRS data utilization:
the temporal relation between hard X-rays and radio emission. These
results show relatively long time delays (2-14 s) of the GHz broadband
radio pulses relative to the hard X-ray emission peaks. Access to the
HXRS data base via the Internet is provided.

---------------------------------------------------------
Title: Holes in the Hα Eruptive Prominence Structure
Authors: Šimberová, Stanislava; Karlický, Marian; Varady, Michal;
Rank, Gerhard
2001SoPh..201..119S Altcode:
The eruptive prominence observed on 27 May 1999 in Hα at Ondřejov
Observatory is analyzed using image-processing techniques. To understand
the physical processes behind the prominence eruption, heated structures
inside the cold Hα prominence material are sought. Two local minima of
intensity (holes), the first above and the second below the erupting Hα
prominence, have been found in the processed Hα images. A comparison
of Hα images with the SOHO/EIT and Yohkoh/SXT images showed: (a) the
cold Hα prominence is visible as a dark feature in the EIT images,
(b) the upper local minimum of intensity in the Hα image corresponds
to a hot structure seen in EIT, (c) the lower minimum corresponds
to a hot loop observed by SXT. The physical significance of the Hα
intensity minima and their relation to the hot structures observed by
EIT and SXT is discussed. The time sequence of observed processes is
in favor of the prominence eruption model with the destabilization of
the loop spanning the prominence. For comparison with other events the
velocities of selected parts of the eruptive prominence are determined.

---------------------------------------------------------
Title: Some aspects of radio and hard X-ray emissions of solar flares
Authors: Karlický, Marian
2001PBeiO..37...75K Altcode:
Two examples of the 1-2 GHz radio observations made by the Ondrejov
radiospectrograph are shown: a) The October 5, 1992 drifting pulsation
structure, and b) the November 9, 1998 high-frequency type II-like
burst. We propose a model in which the drifting pulsations are caused
by quasi-periodic particle accelerations in the magnetic reconnection
in space under the ejected plasmoid. Then a new model of the electron
component heating during the neutral beam bombardment of the dense
atmospheric layers is presented and its relevance to the hard X-ray
emission is discussed.

---------------------------------------------------------
Title: On an estimation of the coronal magnetic field strength from
spectrographic observations in the microwave range
Authors: Ledenev, V. G.; Karlický, M.; Yan, Yihua; Fu, Qijun
2001PBeiO..37...81L Altcode:
Observations of the solar radio emission in the microwave frequency
range show fine structures consisting of s number of the almost parallel
narrow frequency bands. We interpret these bands as the cyclotron
harmonics plasma emission. This emission is generated by the anisotropic
electron beam, which excites longitudinal waves on the normal Doppler
effect resonance. Then the longitudinal waves convert into the radio
emission on the second harmonic of the longitudinal waves frequency
and sometimes into the fundamental one. Estimations of the magnetic
field strength made on the basis of such a model give the values of
the magnetic field in the microwave burst sources as ~100-200 G.

---------------------------------------------------------
Title: Drifting radio bursts and fine structures in the 0.8-7.6
GHz frequency range observed in the NOAA 9077 AR (July 10-14, 2000)
solar flares
Authors: Karlický, M.; Yan, Y.; Fu, Q.; Wang, S.; Jiřička, K.;
Mészárosová, H.; Liu, Y.
2001A&A...369.1104K Altcode:
The 0.8-7.6 GHz global and detailed radio spectra of the four most
intense flares observed in the NOAA 9077 active region (July 10-14,
2000) are presented. The radio bursts of these flares and their
sequence reveal features indicative of topological similarities
among the flares under study. The drifting pulsation structures were
found to be the typical signatures of these flares. Furthermore,
many other fine structures such as narrowband drifting lines, drifting
harmonic structure with zebra patterns, drifting branches of narrowband
dm-spikes, and structures with fast positively and negatively drifting
bursts are shown in the context of the whole radio flares. Some of
them were observed for the first time. The relationships among them
and the resulting interpretations are summarized. The characteristic
periods of the drifting pulsation structures and the magnetic field
in the zebra radio source are determined.

---------------------------------------------------------
Title: The Magnetic Rope Structure and Associated Energetic Processes
in the 2000 July 14 Solar Flare
Authors: Yan, Yihua; Deng, Yuanyong; Karlický, Marian; Fu, Qijun;
Wang, Shujuan; Liu, Yuying
2001ApJ...551L.115Y Altcode:
In the reconstructed nonlinear force-free magnetic field of NOAA
Active Region 9077 before the X5.7/3B (10:24 UT) flare on 2000
July 14, we reveal for the first time the presence of a magnetic
rope from the extrapolation of the three-dimensional magnetic field
structure. This magnetic rope is located in a space above the magnetic
neutral lines of the filament. The calculated field lines of the rope
rotate around its axis for more than three turns. Overlying the rope
are multilayer magnetic arcades with different orientations. These
arcades are in agreement with the Transition Region and Coronal Explorer
observations. The estimated free magnetic energy in this rope system
is about 1.6×1032 ergs. Such magnetic field structure
provides a favorable model for the interpretation of the energetic
flare processes as revealed by Hα, EUV, and radio observations. In
particular, the intermittent cospatial brightening of the rope in
EUV 1600 Å image leading to the onset of the flare suggests that the
rope instability may have triggered the flare event, and the drifting
pulsation structure in the decimetric frequency range is considered
to manifest the initial phase of the coronal mass ejection.

---------------------------------------------------------
Title: Axially-symmetric Velocities in the 15 May 2000 Eruptive
Prominence
Authors: Karlický, Marian; Kotrč, Pavel; Kupryakov, Yurij A.
2001SoPh..199..145K Altcode:
Large Doppler velocities with unique, almost regular elliptical
features were observed in the Hα spectra of the May 15, 2000 eruptive
prominence. These features were interpreted in the frame of axially
symmetric models of the eruptive prominence. The rotational (7-60
km s−1), expansion (30-44 km s−1), axial
(3-19 km s−1), and global (66-160 km s−1)
prominence plasma velocities were derived. The plasma velocity
patterns were compared with the observed helical structures of the
Hα prominence. The velocities of selected Hα blobs in the image
plane were determined. The axially symmetric detwisting process of
the magnetic flux rope of the eruptive prominence was recognized.

---------------------------------------------------------
Title: Shock Drift Electron Acceleration in a Wavy Shock Front
Authors: Vandas, M.; Karlický, M.
2000SoPh..197...85V Altcode:
It is commonly believed that solar type II bursts are caused by
accelerated electrons at a shock front. Holman and Pesses (1983)
suggested that electrons creating type II bursts are accelerated by the
shock drift mechanism. Zlobec et al. (1993) dealt with a fine structure
of type II bursts (herringbones) and suggested a qualitative model
where electrons are accelerated by a nearly perpendicular wavy shock
front. Using this idea, we developed a model of electron acceleration
by such a wavy shock front. Electrons are accelerated by the drift
mechanism in the shock layer. Under simplifying assumptions it is
possible to obtain an analytical solution of electron motion in the
wavy shock front. The calculations show that electrons are rarely
reflected more than once at the wavy shock front and that their final
energy is mostly 1-3 times the initial one. Their acceleration does
not depend significantly on shock spatial parameters. In the present
model all electrons are eventually transmitted downstream where they
form two downstream beams. Resulting spectral and angular distributions
of accelerated electrons are presented and the relevance of the model
to the herringbone beams is discussed.

---------------------------------------------------------
Title: Hard X-Rays from Neutralized Ion Beams in Solar Flares
Authors: Brown, J. C.; Karlický, M.; Mandzhavidze, N.; Ramaty, R.
2000ApJ...541.1104B Altcode:
Under suitable conditions, hard X-rays (HXRs) may be emitted by a
neutralized proton beam due to the “heating” of the electrostatically
dragged electrons in collisions with a nearly neutral background
atmosphere. A simple estimate is made generalizing this HXR
emission mechanism to heavier ions dragging a neutralizing electron
current. Recent gamma-ray results on the energy content of flare ions
of &gt;=1 MeV nucleon-1 are used to estimate the total HXR
yield above 20 keV or so which would be expected from these processes,
and in 19 flares the results are compared with HXR data in the same
events. It is found that only in two flares are the neutral beam HXRs
clearly important and that in a few others they may be significant. In
most events, however, the neutral beam HXR contribution is small,
though the ion energy is comparable with that of electrons.

---------------------------------------------------------
Title: Linear and nonlinear statistical analysis of narrow-band
dm-spikes observed during the June 15, 1991 flare
Authors: Mészárosová, H.; Karlický, M.; Veronig, A.; Zlobec, P.;
Messerotti, M.
2000A&A...360.1126M Altcode:
Narrow-band dm-spikes observed during the June 15, 1991 flare
are statistically analysed. The character of their frequency
distributions at 237, 327, 408 and 610 MHz in both L- and R-handed
circular polarizations is studied. While for the complete time
intervals no simple distributions of spikes (either exponential or
power-law) are recognized, for shorter intervals both exponential
and power-law distributions are observed. No significant difference
is found in the distributions for L- and R-polarized data. Further
analysis reveals that spikes appearing in dense groups and with high
intensities preferentially have exponential distributions, while
the sparse spikes with lower intensities are rather characterized
by power-law distribution functions with high exponents. Groups of
independent spikes (cases with low rates and low intensities) have
power-law distributions trend in agreement with the coherent spike
mechanisms. Tests are provided regarding statistical analyses. The
nonlinear analysis reveals that the degree of complexity of the system
varies. It decreases when the attractor dimensions and the Lyapunov
exponents assume smaller values, which happens when very strong
spikes are present. The changing characteristics of the statistical
parameters are probably the result of a mutual interaction in the
source environment or a product of propagation conditions.

---------------------------------------------------------
Title: Solar flare radio pulsations as a signature of dynamic
magnetic reconnection
Authors: Kliem, B.; Karlický, M.; Benz, A. O.
2000A&A...360..715K Altcode: 2000astro.ph..6324K
Decimetric radio observations of the impulsive solar flare on October 5,
1992, 09:25 UT show a long series of quasi-periodic pulsations deeply
modulating a continuum in the 0.6-2 GHz range that is slowly drifting
toward lower frequencies. We propose a model in which the pulsations
of the radio flux are caused by quasi-periodic particle acceleration
episodes that result from a dynamic phase of magnetic reconnection in
a large-scale current sheet. The reconnection is dominated by repeated
formation and subsequent coalescence of magnetic islands (known as
"secondary tearing" or "impulsive bursty" regime of reconnection),
while a continuously growing plasmoid is fed by newly coalescing
islands. Such a model, involving a current sheet and a growing plasmoid,
is consistent with the Yohkoh observations of the same flare (Ohyama
&amp; Shibata ?). We present two-dimensional MHD simulations of dynamic
magnetic reconnection that support the model. Within the framework of
the proposed interpretation, the radio observations reveal details of
plasmoid formation in flares.

---------------------------------------------------------
Title: Power-law spectra of 1-2 GHz narrowband dm-spikes
Authors: Karlický, Marian; Jiřička, Karel; Sobotka, Michal
2000SoPh..195..165K Altcode:
Twelve examples of clouds of narrowband dm-spikes, observed by the
Ondřejov radiospectrograph in the 1-2 GHz frequency range, are
analyzed. After transforming of the frequency scales to heights in
the solar atmosphere, the indices of the power-law power spectra are
determined. The derived power-law indices are scattered in a broad
range of values (−0.80-−2.85). In some cases they considerably
deviate from the previously found value of −5/3. A change of the
power-law index above log k≈2.5 was also found in some cases. In the
two longest events the time evolution of their power spectra as well as
their indices were studied. While in most parts of the radio spectra
the spectral index remains constant, in one part its absolute value
increases with the spike intensity increase. Finally, the results,
especially the broad range of power-law indices, are briefly discussed.

---------------------------------------------------------
Title: Propagation of shock waves in the solar corona with 2-D
loop structures
Authors: Odstrčil, D.; Karlický, M.
2000A&A...359..766O Altcode:
Motivated by recent observations of type II radio bursts, we
study propagation of shock waves by the two-dimensional numerical
magnetohydrodynamic model. Explosion of a hot plasma is investigated
for various ratios of the mass density and magnetic field intensity in
a fan of coronal loops. Ducting of shock waves occurs along loop-like
structure and ducting of possible radio emission in under-dense coronal
loops is expected. This provides an alternative to classical explanation
that two distinctly separated type II radio bursts are caused by two
different shocks. The presented results support the idea that a single
solar flare energy release with a single shock can generate coronal
disturbances observed as two separate type II radio bursts.

---------------------------------------------------------
Title: Simultaneous SOHO and Ground-Based Observations of a Large
Eruptive Prominence and Coronal Mass Ejection
Authors: Plunkett, S. P.; Vourlidas, A.; Šimberová, S.; Karlický,
M.; Kotrč, P.; Heinzel, P.; Kupryakov, Yu. A.; Guo, W. P.; Wu, S. T.
2000SoPh..194..371P Altcode:
Coronal mass ejections (CMEs) are frequently associated with
erupting prominences near the solar surface. A spectacular eruption
of the southern polar crown prominence was observed on 2 June 1998,
accompanied by a CME that was well-observed by the LASCO coronagraphs
on SOHO. The prominence was observed in its quiescent state and was
followed throughout its eruption by the SOHO EIT and later by LASCO
as the bright, twisted core of the CME. Ground-based Hα observations
of the prominence were obtained at the Ondřejov Observatory in the
Czech Republic. A great deal of fine structure was observed within
the prominence as it erupted. The prominence motion was found to
rotate about its axis as it moved outward. The CME contained a helical
structure that is consistent with the ejection of a magnetic flux rope
from the Sun. Similar structures have been observed by LASCO in many
other CMEs. The relationship of the flux rope to other structures in
the CME is often not clear. In this event, the prominence clearly lies
near the trailing edge of the structure identified as a flux rope. This
structure can be observed from the onset of the CME in the low corona
all the way out to the edge of the LASCO field of view. The initiation
and evolution of the CME are modeled using a fully self-consistent,
3D axisymmetric, MHD code.

---------------------------------------------------------
Title: On the Solar Origin of Complex Type III-like Radio Bursts
Observed at and below 1 MHZ
Authors: Reiner, M. J.; Karlický, M.; Jiřička, K.; Aurass, H.;
Mann, G.; Kaiser, M. L.
2000ApJ...530.1049R Altcode:
By simultaneously analyzing decimetric, metric, and hectometric radio
observations, we provide evidence that a class of hectometric type
III-like radio events are associated with electrons accelerated during
the primary flare energy release process. We do this by demonstrating
that there is a good temporal correspondence between the hectometric
and decimetric radio emissions that are believed to involve the
acceleration of electrons in deep layers of the solar atmosphere
at heights estimated to be from 10,000 to 30,000 km (0.014 to 0.043
Rsolar). This class of hectometric type III-like events
may have simple or complex intensity-time profiles. When they have
complex profiles of long duration, the decimeter emissions also have
complex long-duration profiles. In this latter case they are also often
associated with metric type II radio bursts and coronal mass ejections
(CMEs). However, we argue on the basis of the observations that the
hectometric radio emissions are not necessarily associated with the
metric phenomena. Specifically, they are not likely generated by a
secondary acceleration process associated with the shock generating a
metric type II burst or with a shock driven ahead of the CME despite
the fact that the hectometric emission time profiles would (erroneously)
be morphologically classified as shock-accelerated (SA) events.

---------------------------------------------------------
Title: Collisional Heating of the Electron Component of Neutral Beams
Authors: Karlicky, M.
2000HvaOB..24...57K Altcode:
Using a 1-D test particle model with the collisional scattering the
numerical simulations of the collisional heating of the electron
component of neutral beams is studied. Namely, beam electrons lag
behind the protons, due to differential drag in collisions with the
background, but their longitudinal velocities are closely tied to
the beam protons by the electric field generated. However, collisions
with the background also scatter the beam electrons resulting in the
beam electron heating. The heating of these electrons up to 0.0125
of the initial proton energy was found. But, due to a decrease of
the energetic electron density to about of 0.11 of the initial one,
the real mean energy gain of these energetic electrons is 1/0.11 times
greater. Moreover, the electron distribution function deviates strongly
from the Maxwellian one.

---------------------------------------------------------
Title: Variations of 3 GHz Daily Radio Flux during the Years 1995-2000
Authors: Jiricka, K.; Karlicky, M.; Meszarosova, H.
2000ESASP.463..345J Altcode: 2000sctc.proc..345J
No abstract at ADS

---------------------------------------------------------
Title: Hard X-Rays from MeV Neutral Beams
Authors: Brown, J. C.; Karlicky, M.; Mandzhavidze, N.; Ramaty, R.
2000ASPC..206..210B Altcode: 2000hesp.conf..210B
No abstract at ADS

---------------------------------------------------------
Title: The 1-2 GHz Slowly Positively Drifting Bursts at the Beginning
of the May 2, 1998, September 23, 1998, and November 9, 1999 Solar
Flares
Authors: Kaltman, T.; Karlicky, M.; Jiricka, K.
2000HvaOB..24...35K Altcode:
At the beginning of three solar flares: May 2, 1998, September 23, 1998,
and November 9, 1999, slowly positively drifting bursts were observed
in the Ondrejov radiospectra frequency range 0.8-2.0 GHz. The frequency
drifts were estimated as 65-180 MHz s^-1, 20-40 MHz s^-1 and 40-125
MHz s^-1, respectively. Using the Aschwanden and Benz (1995) density
model for the low solar atmosphere, the corresponding velocities of
disturbances were determined as 650-1350 km s^-1, 120-340 km s^-1 and
300-850 km s^-1 respectively in the case of the fundamental radiation
and 1150-2440 km s^-1, 200-600 km s^-1 and 550-1550 km s^-1 in the
case of the harmonic radiation. These velocities are too low to be
associated with particle beams. Therefore, downwards propagating shock
waves, e.g. thermal conduction shock fronts, are suggested as possible
radio sources.

---------------------------------------------------------
Title: Energy mode distribution at the very beginning of parametric
instabilities of monochromatic Langmuir waves
Authors: Bárta, M.; Karlický, M.
2000A&A...353..757B Altcode:
Starting from a general form of the Zakharov equations the relations for
electric fields and wave energy distributions at the very beginning
of parametric instabilities are derived in dependence on initial
Langmuir wave parameters. The corresponding dispersion equations in
general and approximative forms are presented. These equations of
the order up to eleven, with a different level of physical effects
included (hydrodynamic-like, L_2 and L_3 distributions, non-linear
denominators, quasi-neutrality violation approximations) are solved
numerically. The growth rates, real frequencies and energy mode
distributions are obtained in five regimes of the modulational and
decay instabilities. A new description which is expressed by the
energy mode distribution clearly shows energies transferred into
up- and down-converted Langmuir and electromagnetic modes. Results
confirming those from previous studies as well as new and more general
ones are presented. Furthermore, it is found that in some commonly
used approximations of the dispersion equation, in the decay regime,
non-physically high real frequencies appear. It is shown that for more
general approximations this problem is effectually reduced. The role
of wave damping is considered, too. Finally, for a constant parent
Langmuir wave, it is found that the conversion efficiency into the
electromagnetic mode sharply increases with the temperature increase.

---------------------------------------------------------
Title: Radio Emission from Turbulent Flare Plasma
Authors: Barta, M.; Karlicky, M.
2000HvaOB..24...69B Altcode:
A model of radio emission from a localized turbulent flare plasma based
on the plasma emission mechanism is presented. This work is aimed
mainly to the transformation of wave modes, while incoming Langmuir
waves, generated by particle beams, are described phenomenologically by
various wave packets. The wave transformation is described by means
of the Zakharov equations, but, in contrast to previous studies,
where interacting wave modes filled the whole space, here only a
limited interaction area is supposed. Due to this approach the wave
energy movement effects are included. Our modelling starts with a
Langmuir wave packet moving toward the interaction region, where the
hydrodynamic turbulence, driven by outer (e.g. plasma outflows from the
magnetic field line reconnection site) rather than ponderomotive forces,
is supposed. The time evolution of the high-frequency electric field
is then governed by the first Zakharov equation. The electromagnetic
mode time dependence is calculated not only in the interaction region,
but also at some selected distant point, which represents the Earth
radiotelescope position. The aim of this modelling is the computation
of the model dynamic spectrum, which can be directly compared with
observed data, especially with the narrowband dm-spikes.

---------------------------------------------------------
Title: Global Coronal Waves: Implications for HESSI
Authors: Hudson, H. S.; Karlický, M.
2000ASPC..206..268H Altcode: 2000hesp.conf..268H
No abstract at ADS

---------------------------------------------------------
Title: Flare hard X-rays from neutral beams
Authors: Karlický, Marian; Brown, John C.; Conway, Andrew J.;
Penny, Gail
2000A&A...353..729K Altcode:
A new mechanism is presented for the production of bremsstrahlung
radiation from neutral beams (p+,e-) and its
possible relevance to flare heating and production of hard x-ray bursts
is discussed. Beam electrons lag behind the protons, due to differential
drag in collisions with the background, but their longitudinal
velocities are closely tied to the protons by the electric field
generated. However, collisions with the background also scatter the beam
electrons resulting in rms (quasi-thermal) transverse velocities well
in excess of the proton speed. We demonstrate the initial development
of this effect using an electrostatic particle simulation with scaled
collision rate and then study its full development using an approximate
analytic treatment. In particular, the heating of the beam electrons
under the bombardment effect of the background is limited by the warm
target effect but mean electron energies (`temperatures') of up to
E_e =~ 0.02Ep0 result during the propagation of a neutral
beam of initial proton energy Ep0. Thus, for example, HXR
bremsstrahlung in the range 20-200 keV can be generated by protons
in the range 1MeV-10MeV. The energy efficiency of the bremsstrahlung
production is also limited by the warm target effect but, depending on
the HXR spectrum, can exceed =~ 0.2 of the efficiency of the standard
thick target electron beam model. This suggests that the MeV neutral
beam model is, in terms of power requirements, unlikely to be the
source of `HXR-rich' flare bursts but that neutral beams able to
provide the impulsive flare heating will yield easily detectable HXR
burst signatures. Also, while the neutral beam model needs more power
( =~ 5x) than an electron beam to yield a given HXR burst flare, it
requires a much smaller beam number flux ( =~ 0.07 x). The issue of
the HXR spectral distribution expected from the neutral beam model is
also discussed.

---------------------------------------------------------
Title: Chromospheric Response to a Short-Duration Beam Heating:
Observing Programme and Numerical Simulations
Authors: Heinzel, P.; Karlický, M.; Kotrč, P.; Kupryakov, Yu. A.
2000ASPC..206..289H Altcode: 2000hesp.conf..289H
No abstract at ADS

---------------------------------------------------------
Title: The 1-4 GHz Zebras, Fibers, Reverse Drift Bursts and Slowly
Drifting Lanes Observed during the March 18, 1999 Flare
Authors: Zlobec, P.; Messerotti, M.; Karlický, M.; Mészárosová, H.
1999ESASP.448.1075Z Altcode: 1999ESPM....9.1075Z; 1999mfsp.conf.1075Z
No abstract at ADS

---------------------------------------------------------
Title: High-frequency Intermediate Drift Bursts and Zebra Patterns
Authors: Jiricka, K.; Karlický, M.; Mészárosová, H.
1999ESASP.448..829J Altcode: 1999ESPM....9..829J; 1999mfsp.conf..829J
No abstract at ADS

---------------------------------------------------------
Title: Radio Emission from Early Stages of Strong Langmuir Turbulence
Authors: Bárta, M.; Karlický, M.
1999ESASP.448..753B Altcode: 1999mfsp.conf..753B; 1999ESPM....9..753B
No abstract at ADS

---------------------------------------------------------
Title: Power-law and Exponential Distributions of Narrowband dm-Spikes
Observed During the June 15, 1991 Flare
Authors: Meszarosova, H.; Karlický, M.; Veronig, A.; Zlobec, P.;
Messerotti, M.
1999ESASP.448.1025M Altcode: 1999mfsp.conf.1025M; 1999ESPM....9.1025M
No abstract at ADS

---------------------------------------------------------
Title: Indications of Plasmoid Injection at the Beginning of an
Eruptive Flare
Authors: Fárnik, F.; Karlický, M.; Khan, J. I.
1999ESASP.448..791F Altcode: 1999ESPM....9..791F; 1999mfsp.conf..791F
No abstract at ADS

---------------------------------------------------------
Title: Physical Characteristics of the September 23, 1998 Solar Flare
Authors: Kotrc, P.; Karlický, M.; Kupryakov, Yu. A.; Kaltman, T. I.;
Kasparova, J.; Rompolt, B.
1999ESASP.448..841K Altcode: 1999ESPM....9..841K; 1999mfsp.conf..841K
No abstract at ADS

---------------------------------------------------------
Title: On a Herringbone Structure of Solar Type II Bursts
Authors: Vandas, M.; Karlický, M.
1999ESASP.448.1071V Altcode: 1999ESPM....9.1071V; 1999mfsp.conf.1071V
No abstract at ADS

---------------------------------------------------------
Title: Transequatorial Interconnecting Loops and Increase of Their
Length in the New Cycle
Authors: Fárnik, F.; Ŝvestka, Z.; Karlický, M.; Hudson, H. S.
1999ESASP.446..305F Altcode: 1999soho....8..305F
Using Yohkoh SXT data, we show that active regions of the new solar
cycle, appearing at high latitudes, can be connected across the
solar equator by loops as long as 60 heliographic degrees (730000
km). This length greatly exceeds the limit of 37 degrees found for
transequatorial interconnecting loops on Skylab and implies that the
Skylab limit was simply due to the low latitudes of active regions
during the period of Skylab observations. By modelling the loops in
force-free approximation using Kitt Peak magnetograms, we find strong
support for the interpretation that these long interconnecting loops
originate through reconnection of magnetic field lines which extend from
the two active regions towards and beyond the equator, and confirm the
earlier finding by Canfield, Pevtsov, and McClymont that a favourable
condition for the reconnection is the same chirality (i.e., same sign
of the force-free parameter alpha and same direction of current flow)
in the two active regions. As we were unable to find any longitudinal
(i.e., east-west) loops of a comparable length, we suggest that an
important component of the driving force for the reconnection of
transequatorial interconnecting loops may be the differential solar
rotation. It can help to drive the reconnection of loops extending in
the north- south direction, whereas it does not help in the case of
longitudinal loops. These conclusions are based on loop observations
in December 1997 and May 1998, when only short-lived transequatorial
loops connected the high-latitude active regions on the northern
and southern hemispheres. However, in February 1999 a rich system
of transequatorial loops as long as 550 000 km could be observed
during its whole transit across the visible solar disk. We are now
studying this system (not all supporting data have been available yet
when writing this Abstract), comparing it with a similar system of
much shorter transequatorial loops which crossed the solar disk in
March/April 1992 during the preceeding cycle. We again try to model
these long-lived loop systems in current-free approximation, using
both Kitt Peak and Big Bear magnetograms and, for the February 1999
transit, also the more frequent, high-resolution full-disk magnetic
maps from SOHO. This modelling verifies the location of the footpoints
of interconnecting loops in low magnetic fields at peripheries of the
interconnected active regions, indicates how some of the loops have
been formed, and provides information about some of the reasons which
lead to the shape and brightness variations in the loops system.

---------------------------------------------------------
Title: Acceleration Of Photoelectrons In A Return-Current Electric
Field And Ha Polarization
Authors: Karlický, Marian; Hénoux, Jean-Claude
1999ESASP.446..369K Altcode: 1999soho....8..369K
Chromospheric hydrogen Balmer Ha and Hb lines have been found to be
linearly polarized in the gradual phase of some solar flares. This
impact polarization is believed to be caused by low energy protons
(E&lt; 200 keV). However, we still must examine if low energy electrons
(E&lt; 200 eV) with an anisotropic velocity distribution function, if
presents, could also generate impact polarisation . In a recent paper
by H noux and Karlicky (1999), the evolution, in chromospheric layers,
of the ve-locity distribution function of high energy photoelectrons
produced by flare X-ray irradiation, was studied. A significant
anisotropy was found. However, due to the dominance of local electrons
in the line formation process, the resulting impact polarization
was one order of magnitude lower than ob-served. In this paper,
we look for the change of the photoelectrons anisotropy that could
result from the pre-sence of a return-current electric field. A 1-D
test particle code is used for computating both the re-turn-current
electric field generated by monoenergetic electron beams in flaring
chromospheric layers and the evolution of the photoelectron distribution
function. Using a 100 keV electron beam with a density of 2 and the MAVH
flare atmosphere, it is found that, at chromospheric level, low-energy
photoelectrons (E at 150 eV), produced by flare X-ray irradiation, can
be accelerated by the return-current electric field. This acceleration
is very sensi-tive to the exact density and temperature profile of the
solar atmosphere and the resulting effect as generation of impact Ha
polarization is discussed.

---------------------------------------------------------
Title: On two distinct shocks during the flare of 9 July 1996
Authors: Klassen, A.; Karlický, M.; Aurass, H.; Jiřička, K.
1999SoPh..188..141K Altcode:
Due to the emission of shock-accelerated electrons, broadband radio
observations display propagating super Alfvénic shock waves in the
low corona ('type II bursts'). We study the 9 July 1996 flare (AR
NOAA 7978) focusing on the aspect of shock generation. This event's
radio spectrogram shows two different type II bursts in sequence. Radio
imaging data (Paris, Meudon Observatory) reveal that both bursts appear
at different sites above the Hα flare. The driver of the first type II
burst seems to propagate with twice the speed of the second one. The
projected source site of the first type II burst (seen earlier and
at higher frequencies) is spatially situated further away from the
Hα flare site than the source of the second type II burst. We try to
understand this by comparing with Yohkoh soft X-ray images. The first
shock source occurs near the top of high soft X-ray loop structures. Its
driver can be a guided fast mode magnetic disturbance. The second type
II source appears in-between two high soft X-ray loop systems. This
might be a piston-driven disturbance powered by an evaporation front. We
get a consistent picture only by assuming a very inhomogeneous Alfvén
speed in the active region's atmosphere.

---------------------------------------------------------
Title: Fourier and wavelet analysis of type 42 SER and 41 F solar
radio bursts
Authors: Mészárosová, H.; JiřiČka, K.; Karlický, M.
1999A&A...348.1005M Altcode:
19 radio bursts (0.01 s time resolution) classified as 42 SER and 41
F types were selected from observations made by the Ondřejov 3 GHz
radiometer during 1990-1998. On the 2-4 GHz dynamic radio spectrum
in most cases these bursts were identified as decimetric DCIM and in
the metric range were accompanied by type III radio bursts indicating
the plasma emission origin of these bursts. This set of 3 GHz bursts
was analyzed by both the Fourier and the wavelet transform methods
searching for characteristic periodicities. Statistical parameters
of selected bursts were very similar and almost no difference between
42 SER and 41 F was found. The analysis of the 42 SER and 41 F radio
bursts on 3 GHz shows that the number of periods is increasing with
decreasing periods, forming a power-law distribution. The dominant
periods of the 3 GHz radiation are discussed in the framework of the
recent RLC-circuit model with current-carrying magnetic loops. On the
basis of this interpretation the electric current densities in the
magnetic loops were estimated in the 0.01-0.1 A m(-2) range.

---------------------------------------------------------
Title: The Radio-Silent Start of an Intense Solar Gamma-Ray Flare
Authors: Rieger, Erich; Treumann, Rudolf A.; Karlický, Marian
1999SoPh..187...59R Altcode:
Radio-silent γ-ray flares are solar flares that lack any significant
emission in the (non-thermal) radio wave band during their impulsive
hard X-ray and γ-ray emission phases. Flares with extremely suppressed
long-wavelength spectra have previously been reported by White et
al. (1992) and have been discussed in different context by Hudson
and Ryan (1995). A striking example of a radio-silent flare was
observed by SMM during the onset of the 6 March 1989 energetic γ-ray
flare. We argue that the absence of radio emission at wavelengths
longer than microwave wavelengths is an indication of the compactness
of the flare rather than that the flare did not exhibit non-thermal
properties. Probably the flare site was restricted to altitudes above
the photosphere in a newly emerging loop configuration lower than
the equivalent altitude corresponding to an emission frequency of 1.4
GHz. This implies the presence of a dense and highly magnetized closed
field configuration confining the electron component which causes the
impulsive γ-ray continuum. Reconnection in such a configuration did
not lead to open magnetic fields and streamer formation. Acceleration
of particles in the γ and hard X-ray bursts was restricted to closed
field lines. Thermal expansion of the loop system may subsequently
lead to the generation of radially propagating blast waves in the solar
corona which are accompanied by type II solar radio bursts and decimetre
emissions. The emission during the onset of the flare was dominated
by a continuum originating from electron bremsstrahlung at X-ray and
γ-ray energies with only little evidence for the presence of energetic
ions. It is, therefore, concluded that energetic electrons have been
primary and not secondary products of the particle acceleration process.

---------------------------------------------------------
Title: Solar type II bursts and shock drift electron acceleration
Authors: Vandas, M.; Karlický, M.
1999AIPC..471..657V Altcode: 1999sowi.conf..657V
It is generally believed that type II bursts are caused by electrons
accelerated at a shock front. Holman and Pesses (1) suggested that
type II bursts can be caused by electrons accelerated by the shock
drift mechanism. In order to explain a fine structure of type II
bursts (herringbones), Zlobec et al. (2) presented a qualitative model
where electrons are accelerated by a nearly perpendicular wavy shock
front. We discuss this possibility quantitatively, namely we present an
analytical solution of electron motion in a wavy shock front. Then we
perform a parametric study in order to determine which parameters of
the model are necessary for an appropriate electron energy gain. The
calculations show that electrons are rarely reflected more than once
at the wavy shock front and their final energy is mostly 1-3 times the
initial one. This is similar to the theoretical acceleration gain of
reflected electrons at the Earth's bow shock. In the present case all
electrons are eventually transmitted downstream where they form two
downstream beams.

---------------------------------------------------------
Title: Long transequatorial interconnecting loops of the new solar
cycle
Authors: Fárník, F.; Karlický, M.; Švestka, Z.
1999SoPh..187...33F Altcode:
We study two long transequatorial loops connecting high-latitude
regions of the new solar cycle. These loops (with lengths of 47 and
61 heliographic degrees) provide evidence that the upper length limit
of 37° found by Chase et al. (1976) from Skylab data was determined
simply by the typical distances between northern and southern active
regions during the period of Skylab observations. We find strong
support for the idea that these long interconnecting loops originate
through reconnection of field lines extending from the two active
regions towards and beyond the equator, and confirm the earlier
finding by Canfield, Pevtsov, and McClymont (1996) that only field
lines from active regions with the same chirality reconnect. As we
are not aware of any longitudinal (E-W) loops of comparable lengths,
we suggest that it is mainly the solar differential rotation which
drives the reconnection of latitudinal (N-S) field lines.

---------------------------------------------------------
Title: A spectropolarimetric estimate of energy deposition into the
chromosphere during solar flares
Authors: Kazantsev, S. A.; Karlicky, M.; Petrashen', A. G.; Hénoux,
J. -C.
1999ARep...43..340K Altcode:
The dependence of the degree of polarization of Hα and Hβ emission in
the solar chromosphere during solar flares on the energy of an incident
proton beam is calculated assuming that the origin of the observed
linear polarization is collisional. Estimates of the lower boundary
for the energy of the proton beam are obtained using a model for the
kinetics of the propagation of fast protons inside solar-flare magnetic
loops together with spectropolarimetric Hα and Hβ observations.

---------------------------------------------------------
Title: Velocity distribution function anisotropy of soft X-ray
generated photoelectrons and resulting Hα polarization in solar
flares
Authors: Hénoux, J. -C.; Karlický, M.
1999A&A...341..896H Altcode:
Soft X-rays irradiation of the solar atmosphere during solar
flares generates photoelectrons which have an anisotropic velocity
distribution. Using a 1-D test particle code, the anisotropy of the
photoelectrons velocity distribution is derived, and the maximum
degree of linear polarization in the hydrogen Hα and Hβ lines that
photoelectrons could generate by impact is estimated. Over a band
pass of 0.75 and 0.5 Angstroms, the net polarization degree expected
in both lines is predicted not to exceed 0.2%. Therefore, soft X-ray
irradiation cannot explain the one order of magnitude higher degree
of linear polarization observed in solar flares.

---------------------------------------------------------
Title: Intensity Distributions of Peak Fluxes of Radio Bursts at
Different Frequencies
Authors: Mészárosová, H.; Karlický, M.; Jiricka, K.
1999ASSL..239..243M Altcode: 1999msa..proc..243M
In this paper intensity distributions of peak fluxes of radio bursts
at frequencies of 3.0, 3.2, 5.2 and 8.4 GHz are studied. The exponents
of power-law distribution function are found in the range from -1.2
to -1.5. Comparisons of these results with results published for other
frequencies and with those predicted by avalanche models are made.

---------------------------------------------------------
Title: The NOAA AR 6718 magnetic field extrapolation with localized
current filaments.
Authors: Karlický, M.; Démoulin, P.; Aulanier, G.; van
Driel-Gesztelyi, L.; Hénoux, J. C.; Jirička, K.
1999joso.proc...97K Altcode:
The 3-D extrapolation of magnetic field lines of the July 11, 1991
Kitt Peak magnetogram shows a differential magnetic field shear in
the NOAA 6718 active region. A new combined extrapolation technique,
which includes localized current filaments is suggested and applied in
modelling of this shear. First, the potential field extrapolation is
made and then force-free current paths for several current filaments
in specific positions are computed. It is shown that with the electric
current increase the localized magnetic field shear is increasing. The
total electric current in 16 current filaments is considered up to
1.2×1012A.

---------------------------------------------------------
Title: Statistical analysis of 3 GHz solar radio bursts and estimation
of electric current densities in flare loops.
Authors: Mézsárosová, H.; Karlický, M.; Jiřička, K.
1999joso.proc..166M Altcode:
From observations made by the Ondřejov 3 GHz radiometer during
1990-1998, 15 radio bursts classified as 42 SER and 41 F types were
selected. (Most of these bursts were on the radio spectrum identified
with a group of high-frequency type III radio bursts). On the selected
bursts both the Fourier and the wavelet analyses were applied to
determine the periodicities. Then, using the RLC-circuit analog of
current-carrying magnetic loops the authors estimated electric current
densities in the acceleration space. As example they present results
for the radio burst of April 15, 1998.

---------------------------------------------------------
Title: Correction [to “A shock associated (SA) radio event and
related phenomena observed from the base of the solar corona to
1 AU”]
Authors: Bougeret, J. -L.; Zarka, P.; Caroubalos, C.; Karlický, M.;
Leblanc, Y.; Maroulis, D.; Hillaris, A.; Moussas, X.; Alissandrakis,
C. E.; Dumas, G.; Perche, C.
1998GeoRL..25.4103B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Evidence of Magnetic Field Reconnection in the Hα Eruptive
Prominence on 18 september 1995
Authors: Kotrč , P.; Karlický, M.; Šimberová, S.; Knížek, M.;
Varady, M.
1998SoPh..182..393K Altcode:
In this paper we present a detailed study of a violent evolution of the
18 September 1995 eruptive prominence observed by the Hα telescope
and the Multichannel Optical Flare Spectrograph in Ondřejov. The
fast changes of the prominence structure started immediately after
a weak radio burst at 3 GHz. This circumstance shows the presence of
non-thermal processes. In the later phase of the prominence evolution a
comparison of the Hα filtergrams with the Yohkoh Soft X-ray Telescope
pictures was made. For a search of fine structures in the Hα images,
an image processing technique was used. A detailed analysis of
observations indicates magnetic field line reconnection, mainly in
space below the rising Hα prominence. These reconnection processes
are manifested not only by structural changes of the Hα prominence and
X-ray loops but also by the character of Doppler velocities. Evidence of
splitting and rotation was found in the Hα spectrum formed close to the
reconnection space, and the typical velocities of such plasma movement
were evaluated. We estimated amplitudes of rotational velocities,
giving evidence about the rearrangement of helical structures during
the process of the eruptive prominence activation. In the conclusion
we discuss some implications of our results.

---------------------------------------------------------
Title: Narrowband dm-SPIKES Observed during the 15 June 1991 Flare
Authors: Zlobec, Paolo; Karlický, Marian
1998SoPh..182..477Z Altcode:
We performed a statistical analysis of the dm-spikes that were present
for an exceptionally long period (more than 10 min) during the 15 June
1991 flare. We realized that the polarization degree, the duration and
the mutual delay of the R- and L-components were nearly the same for
both CW and ACW cases. CW (ACW) means the clockwise (anti-clockwise)
sense of the loop in the R−L versus L+R plots, when the data of
a single spike are considered according to the time sequence. The
presence of such a loop is determined by the delay of the weaker
(stronger) polarimetric component in respect to the other one. The
increase of the polarization percentage started first at 610, then at
408 and afterwards at 327 MHz. It was found that the duration of spikes
was almost completely independent from the polarization degree. The mean
duration of spikes at different frequencies corresponds to that computed
using the formula of Güdel and Benz. Like the mean duration, also the
mean delay decreased with increasing frequency. The CW/ACW ratio varied
simultaneously for the frequencies we recorded during an interval of
about three minutes. Spikes were considered as the radio manifestation
of superthermal electrons accelerated in the MHD cascading waves. The
evolution of spikes and their parameters were qualitatively interpreted
within the flare reconnection model with turbulent plasma outflows.

---------------------------------------------------------
Title: Chromospheric evaporation shock and reduced optical thickness
drifting in the 1-4.5 GHz range
Authors: Karlicky, Marian
1998A&A...338.1084K Altcode:
Using a 1-D numerical hydrodynamic model, the evaporation shock
evolution is computed in the solar atmosphere having the density profile
derived from radioastronomical observations. Then the optical thickness
of the 1-4.5 GHz plasma emission on harmonic frequency is computed. It
is found that the optical thickness of the radio emission is reduced at
the evaporation shock. With a motion of this shock the optical thickness
reduction drifts towards lower frequencies with the frequency drift
which depends on the evaporation shock speed. The theoretical radio
spectrum caused by this optical thickness reduction is presented and
discussed in comparison with the July 9, 1996 radio spectrum.

---------------------------------------------------------
Title: Frequency gap between fast drift and type III associated
bursts.
Authors: Karlicky, M.; Zajtsev, V. V.
1998R&QE...41..639K Altcode:
The frequency gap between the high-frequency fast drift bursts
and metric type III associated bursts is interpreted using the
collisional absorption of the radio emission in dense layers of the
solar atmosphere. Studying the absorption of radio emission from the
narrow, cold and dense filament which is embedded in hotter plasma
and heated from the corona, it was found that the absorption causing
the frequency gap has a maximum at about 2 GHz, in agreement with
observations. Similar results were obtained also for the current
sheet structure.

---------------------------------------------------------
Title: The Solar Minimum Active Region 7978, Its X2.6/1B Flare, CME,
and Interplanetary Shock Propagation of 9 July 1996
Authors: Dryer, M.; Andrews, M. D.; Aurass, H.; DeForest, C.; Galvin,
A. B.; Garcia, H.; Ipavich, F. M.; Karlický, M.; Kiplinger, A.;
Klassen, A.; Meisner, R.; Paswaters, S. E.; Smith, Z.; Tappin,
S. J.; Thompson, B. J.; Watari, S. I.; Michels, D. J.; Brueckner,
G. E.; Howard, R. A.; Koomen, M. J.; Lamy, P.; Mann, G.; Arzner, K.;
Schwenn, R.
1998SoPh..181..159D Altcode:
The first X-class flare in four years occurred on 9 July 1996. This
X2.6/1B flare reached its maximum at 09:11 UT and was located in active
region 7978 (S10° W30°) which was an old-cycle sunspot polarity
group. We report the SOHO LASCO/EIT/MDI and SOONSPOT observations before
and after this event together with Yohkoh SXT images of the flare,
radio observations of the type II shock, and GOES disk-integrated soft
X-ray flux during an extended period that included energy build-up in
this active region.

---------------------------------------------------------
Title: A shock associated (SA) radio event and related phenomena
observed from the base of the solar corona to 1 AU
Authors: Bougeret, J. -L.; Zarka, P.; Caroubalos, C.; Karlický, M.;
Leblanc, Y.; Maroulis, D.; Hillaris, A.; Moussas, X.; Alissandrakis,
C. E.; Dumas, G.; Perche, C.
1998GeoRL..25.2513B Altcode:
We present for the first time an almost complete frequency coverage of a
Shock Associated (SA) radio event and related phenomena observed on May
6, 1996 at 9:27 UT. It is observed from the base of the solar corona
up to almost 1 Astronomical Unit (AU) from the Sun by the following
radio astronomical instruments: the Ondřejov spectrometer operating
between 4.5 GHz and 1 GHz (radiation produced near the chromosphere);
the Thermopyles Artemis-IV spectrograph operating between 600 MHz
and 110 MHz (distance range about 1.1-1.4 R⊙ from sun
center); the Nançay Decameter Array operating between 75 and 25 MHz
(distance range about 1.4-2 R⊙) and the RAD2 and RAD1
radio receivers on the WIND spacecraft covering the range from 14
MHz to about 20 kHz (distance range between 3 R⊙ and
about 1 AU). Observations at the Nançay Decameter Array clearly show
that the SA event starts from a coronal type II radio burst which
traces the progression of a shock wave through the corona above 1.8
R⊙-2 R⊙ from the sun center. This SA event
has no associated radio emission in the decimetric-metric range, thus
there is no evidence for electron injection in the low/middle corona.

---------------------------------------------------------
Title: Optical Thickness of the 2-4.5 GHz SOLAR PLASMA EMISSION
Authors: Karlický, Marian
1998SoPh..179..421K Altcode:
For radio emission at the frequency corresponding to the second
harmonic of the local plasma frequency, the optical thickness in the
solar atmosphere is calculated. Three types of models are assumed: the
model with radio emission from the narrow transition region, and models
with radio emission from a cool and dense plasma filament embedded in
hotter plasma at the transition region and in the corona. The optical
thickness is computed by integration of the collisional (free-free)
absorption along a radio-ray path radial in the solar atmosphere. In
all models considered the optical thickness can be sufficiently low
for appropriate parameters. For example, in the narrow (&lt;100 km)
transition region where the density scale height is much less than
that of the pressure one, the optical thickness can be lower than
1. Furthermore, the optical thickness can be decreased if the radio
emission is generated in the cool and dense plasma filament surrounded
by hotter and thinner plasma. But the models differ in density scale
heights and thus in distances between plasma emission levels. This
difference is essential for the interpretation of high-frequency type
III radio bursts.

---------------------------------------------------------
Title: Electrostatic effects during neutral beam propagation through
plasmas
Authors: Brown, John C.; Karlicky, Marian; Conway, Andrew J.;
Martland, Suzanne
1998A&A...331.1147B Altcode:
In this paper several aspects of the interaction of 1-D neutral beams
with plasmas are considered. In order to clearly understand the dual
roles of a background plasma in collisionally decelerating the beam
and its response to the consequently generated E-field, we examine two
cases: an artificial unresponsive background plasma, that corresponds
closely to the case of an unionized gas; and a realistic background
plasma, whose charges respond to the presence of any E-field. In the
former case, the electric field results solely in extremely small scale
oscillation of the beam electrons about the protons as both decelerate
collisionally and, although electron runaway is possible, the numbers
involved are found to be negligibly small. However, collisional
separation of the beam electrons and protons does occur in the case
of a realistic background plasma, since E easily drives a neutralizing
dense plasma electron current. Despite the charge separation, runaway
is found to be impossible in this case because of the masking effect
that the background plasma electrons have on the separated charges
unless the plasma is extremely tenuous compared to the beam, where the
plasma behaviour is close to that of a near-neutral gas. These effects
are shown by approximate analytic mean particle solutions and confirmed
by simulations from an electrostatic particle code, which can deal with
collective effects. Additional numerical simulations are also performed
to investigate the generation of Langmuir waves by a neutral beam. The
consequences of these results are discussed for flare neutral beams and
corresponding radiation signatures. As regards hard X-ray production
by runaways, although some very high energy electrons may result,
the number is far too small to be relevant to solar flare HXR burst
production. The beam and plasma oscillations may however be relevant
to radio bursts.

---------------------------------------------------------
Title: Interaction of Weak Shock Waves with Current Sheets in an
Active Region to Produce Nanoflares and Chains of Type I Radio Bursts
Authors: Odstrčil, Dušan; Karlický, Marian
1998SoPh..177..415O Altcode:
Interaction of weak shock waves with a current sheet is investigated by
a two-dimensional numerical magnetohydrodynamic model. In accordance
with solar coronal conditions, a ratio of thermal to magnetic
pressures of 0.1 and a shock Alfvén Mach number slightly above
1 are considered. It is found that even weak shock waves trigger
magnetic field reconnection in current sheets. Based on this result,
it is suggested that drifting chains of type I radio bursts are radio
manifestations of the interactions of weakly super-Alfvénic shock waves
with pre-existing current sheets distributed in an active region. This
model of type I noise storms is then discussed in connection with the
concept of nanoflares (localized reconnections) and the heating of
the solar corona.

---------------------------------------------------------
Title: On the source height of decimetre-wave burst emission
(abstract)
Authors: Krüger, A.; Kliem, B.; Hildebrandt, J.; Karlický, M.;
Zlobec, P.
1998PAICz..88...93K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Field Reconnection in the H-alpha Eruptive Prominence
on September 18, 1995
Authors: Karlicky, M.; Kotrc, P.; Simberova, S.; Knizek, M.; Varady, M.
1998ASPC..150..310K Altcode: 1998IAUCo.167..310K; 1998npsp.conf..310K
No abstract at ADS

---------------------------------------------------------
Title: Generation of Langmuir waves in neutral beam-plasma system
Authors: Karlický, M.; Messerotti, M.; Zlobec, P.
1998PAICz..88..133K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The narrowband dm-spikes observed during the 15 June 1991 flare
Authors: Zlobec, P.; Karlicky, M.
1998cee..workE..69Z Altcode:
We performed a statistical analysis of the dm-spikes that were present
for an exceptionally long period (more than 10 m) during the 15 June
1991 flare. We realized that the polarization degree, the duration
and the mutual delay of the R- and L-components were nearly the same
for both CW and ACW cases. CW (ACW) means clock-wise (anti-clock-wise)
sense of the loop in the R-L versus L+R plots when the data of a single
spike are considered according to the time sequence. The presence
of such a loop is determined by the delay of the weaker (stronger)
polarimetric component in respect to the other one. The increase
of the polarization percentage started first at 610, then at 408
and afterwards at 327 MHz. It was found that the duration of spikes
was almost completely independent from the polarization degree. The
mean duration of spikes at different frequencies corresponds to that
computed using the formula of Gudel and Benz. Like the mean duration,
also the mean delay was decreasing with increasing frequency. The
CW/ACW ratio varied simultaneously for the frequencies we recorded
during an interval of about three minutes. Spikes were considered as
the radio manifestation of superthermal electrons accelerated in the
MHD cascading waves. Evolution of spikes and their parameters were
qualitatively interpreted within the flare reconnection model with
the turbulent plasma outflows.

---------------------------------------------------------
Title: Force-free Electric Current Rope in the Solar Atmosphere
Authors: Karlický, M.
1998ESASP.417..301K Altcode: 1998cesh.conf..301K
No abstract at ADS

---------------------------------------------------------
Title: The narrowband dm--spikes observed during the September and
November 1997 solar flares
Authors: Karlicky, M.; Jivrivcka, K.; Aurass, H.; Klassen, A.; Mann, G.
1998cee..workE..44K Altcode:
During coordinated observations by radio spectrographs at AO Ondvrejov
(0.8 - 4.3 GHz) and AI Potsdam (40 - 800 MHz sweep and 693-740 MHz
high resolution multi-channel spectrometer) three flares were observed
with narrowband decimeter spikes clustered within a bandwidth of about
2 GHz. In all three cases the dm-spikes appear during the impulsive
flare phase above and near to the starting frequency range of meter
type III bursts. Date: || Associated Flare: || Narrowband Spikes:
September 12, 1997 || SF/--, N24W20, AR8084 || 0.6 -- 2.7 GHz; 16:05:35
-- 16:07 UT November 03, 1997 || 1B/M1.4, S20W15, AR 8100 || 0.4 --
2 GHz; 9:05:40 -- 9:09:30 UT November 03, 1997 || --/M4.2 || 0.25 --
1.2 GHz; 10:25:50 -- 10:27:40 UT The time coincidence found between
the narrowband dm-spikes and type III radio bursts show that dm-spikes
manifest the particle acceleration processes. Figure 1. The 03 November
1997, 10:25 UT event. 1 second with 0.01 s resolution; left-spectrum,
right--the time derivative of the spectrum.

---------------------------------------------------------
Title: Triggering of magnetic reconnection in the current sheet by
shock waves.
Authors: Odstrcil, D.; Karlicky, M.
1997A&A...326.1252O Altcode:
Interaction of a shock wave with a current sheet is investigated by
the two-dimensional numerical magnetohydrodynamic model. In accordance
with the solar coronal conditions, the ratio of the thermal to magnetic
pressures of 0.1 and the shock Alfven Mach number of about 1.25 are
used. It is found that the shock wave initiates magnetic reconnection
process in the current sheet. Further, it is found that the post-shock
situation rather than the shock compression is a cause of the magnetic
reconnection. Interaction of the shock with the current sheet results
in formation of two shocks that propagate away from the current sheet
on opposite sides followed by a rarefaction waves region. This dynamic
situation causes the current sheet to become gradually thinner and
the magnetic reconnection process is initiated probably due to the
tearing-mode instability. Presented results support the idea that the
solar flare can be triggered by the shock wave from a distant flare.

---------------------------------------------------------
Title: Optical and Radio Spectral Analysis of a Recurrent Surge
Authors: Kotrč, Pavel; Schmieder, Brigitte; Karlický, Marian;
Heinzel, Petr
1997SoPh..172..199K Altcode: 1997ESPM....8..199K
Coordinated observations obtained at Meudon (MSDP) and at Ondřejov
provide surge spectra in optical range (Hα, Hβ, Hγ, Hµ, Ca H and
K lines) and in radio range. The MSDP data allowed us to follow the
time evolution of the surge. The spectra of Balmer lines were used to
derive the electron density of the expelled cool material. The radio
bursts indicate that the acceleration of electrons took place in the
low and dense atmosphere, giving a good argument for a reconnection
near the transition region.

---------------------------------------------------------
Title: Ring Current Formed During the Bombardment of a Rotating Gas
Torus by Neutral Beams
Authors: Karlický, Marian
1997Ap&SS.257..249K Altcode:
A new mechanism for the generation of the electric ring current is
presented. During the radial bombardment of a rotating gas torus by a
neutral beam, electrons and protons are dragged by rotating gas. Due
to collisions electrons obtain the torus velocity faster than protons,
therefore in some layer there is a difference in electron and proton
beam toroidal velocities; the electric current is thus generated. This
current is discussed as the seed magnetic field in early stages of
evolving galaxies, which is then amplified by the dynamo process to
present values of the magnetic field.

---------------------------------------------------------
Title: Evolution of force-free electric currents in the solar
atmosphere.
Authors: Karlicky, M.
1997A&A...318..289K Altcode:
The new 3-D numerical model studying evolution of force-free electric
currents in the solar atmosphere is presented. The initial dipole
magnetic field is considered in a simplified active region. Starting
from a low electric current, which penetrates the photosphere, and
increasing the current intensity, the path of force-free electric
current and the corresponding magnetic field are computed. The virtual
mirror current representing the effect of the inertial photosphere is
considered. The single and the multiple current paths are compared. For
the single path case, it was found that an arch-shape electric current
is sheared with the increasing current intensity, then screwed into a
current loop with the helical structure and when the electric current
generates a magnetic field greater than the initial dipole magnetic
field the current path becomes unstable. During all this process the
current path moves upwards. Although the multiple current paths show
more complex internal structures of electric currents, the global
aspect of these processes remains the same. The relevance of this
modelling for processes in the solar atmosphere is discussed.

---------------------------------------------------------
Title: Effects of Particle Beams in the Solar Atmosphere
Authors: Karlicky, M.
1997HvaOB..21...43K Altcode:
This work addresses the observational and physical effects of
particle beams in the solar atmosphere. Mainly electron beams are
considered. Describing acceleration mechanisms of superthermal
particles, the main attention is devoted to effects influencing
the particle beam propagation. The collisional energy losses
and pitch angle scattering, the return current effects, and the
mirroring in the converging magnetic field in specific situations are
considered. Furthermore, the processes connected with the particle
beam bombardment of dense layers of the solar atmosphere are briefly
described. Finally, some open questions are summarized.

---------------------------------------------------------
Title: The Solar Minimum X2. 6/1B Flare and CME of 9 July 1996;
Part 2: Propagation
Authors: Dryer, M.; Andrews, M. D.; Aurass, H.; DeForest, C.; Karlicky,
M.; Kiplinger, A.; Klassen, A.; Meisner, R.; Ipavich, F. M.; Galvin,
A. B.; Paswaters, S. E.; Smith, Z.; Tappin, S. J.; Thompson, B. J.;
Watari, S. -I.; Michels, D. J.; Brueckner, G. E.; Howard, R. A.;
Koomen, M. J.; Lamy, P.; Mann, G.; Arzner, K.; Schwenn, R.
1997ESASP.404..331D Altcode: 1997cswn.conf..331D
No abstract at ADS

---------------------------------------------------------
Title: Shear Magnetic Field Reconnection near the 3-D Null Point
Authors: Karlicky, M.
1997HvaOB..21...91K Altcode:
Using a 3-D MHD numerical code the shear magnetic field reconnection
near the 3-D null point is studied. To demonstrate the topological
changes of magnetic field lines during the shear reconnection two cases:
(a) without and (b) with the anomalous resistivity are compared. For
simplicity a high beta plasma is assumed. It was found that during
this process magnetic field lines on one side of the "fan" structure
are reconnected with those on the opposite side of the fan. Thus,
the magnetic field lines reconnect places in a very broad range of
angles in the plane of the fan layer.

---------------------------------------------------------
Title: Triggering of Magnetic Reconnection in the Current Sheet by
Shock Waves - Nanoflares, and Chains of Type I Radio Bursts
Authors: Karlicky, M.; Odstrcil, D.
1997ESASP.404..451K Altcode: 1997cswn.conf..451K
No abstract at ADS

---------------------------------------------------------
Title: Effects of Particle Beams in the Solar Atmosphere
Authors: Karlicky, Marian
1997SSRv...81..143K Altcode:
This work addresses the observational and physical effects of particle
beams in the solar atmosphere. Mainly electron beams are considered, but
also some effects of proton and neutral beams are mentioned. Briefly
describing acceleration mechanisms of superthermal particles, the
main attention is devoted to effects influencing the particle beam
propagation. The collisional energy losses and pitch-angle scattering,
return current effects, mirroring in the converging magnetic field, and
the scattering in the Alfven and whistler wave turbulence in specific
situations are considered. The role of quasi-linear relaxation is
discussed. Examples of observations showing effects of particle beams
in the solar atmosphere are presented. Separate chapters are devoted
to processes connected with particle beam bombardment of dense layers
of the solar atmosphere: hard X-ray and gamma-ray flare emissions,
evaporation process, asymmetry of optical chromospheric lines,
and impact linear H-alpha line polarization. The beam induced energy
release processes are also included. The presented effects of particle
beams are summarized.

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Title: Interaction of shocks with a current sheet and reconnection
in the solar corona
Authors: Odstrcil, D.; Karlicky, M.
1997AdSpR..19.1895O Altcode:
Interaction of shocks with a current sheet is investigated within a 2D
MHD model based on an improved FCT numerical scheme. Basic parameters
of the problem are chosen to correspond to situations in the solar
corona with low plasma beta and moderate shock strength. Slow and fast
MHD shocks are introduced with shock normal parallel to magnetic field
lines. The interaction with the current sheet causes distortion of the
shock front and this distorts the magnetic field lines and generates
electric current. Large current densities are generated especially
when the fast MHD shock becomes the intermediate MHD shock at the
current sheet. Then peak values of the current density are about 3-4
times larger than the initial undisturbed values in the current sheet.

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Title: Narrowband dm-Spikes in the 2 GHz Frequency Range and MHD
Cascading Waves in Reconnection Outflows
Authors: Karlický, Marian; Sobotka, Michal; Jiřička, Karel
1996SoPh..168..375K Altcode:
Two examples of clouds of narrowband dm-spikes, observed by the
Ondřejov radiospectrograph in the 1-2 GHz frequency range, are
analyzed. After transformation of the frequency scales to distances in
the solar atmosphere, the power spectra analysis of size scales reveals
a spectral index of −5/3, resembling that of Kolmogorov spectra of
turbulent cascades. The narrowband dm-spikes are interpreted as radio
emission from electrons accelerated in MHD cascading waves, probably
generated in plasma outflows from magnetic field reconnection.

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Title: Transport of superthermal electrons in coronal loops and
U(N)-type solar radio bursts.
Authors: Karlicky, M.; Mann, G.; Aurass, H.
1996A&A...314..303K Altcode:
Electron beams travelling with about 1/3 of the velocity of light along
closed coronal loops can manifest themselves in decimeter and meter wave
solar type U or U(N) radio bursts. Using a 1-D test particle model,
we study trajectories of superthermal electrons in coronal loops with
the aim of understanding recently published detailed radio spectral and
imaging data about type U(N) bursts. The computations are carried out
in a static semi-circular loop of 1 solar radius length. For modeling
transport processes Coulomb collisions, mirroring of electrons in the
loop magnetic field, and scattering in zones of enhanced whistler wave
turbulence are taken into account. The formation of a finite zone of
enhanced whistler turbulence in the loop top is consistently explained
by the properties of loss-cone instability of a weak preexisting
energetic particle component. In a model run initially electrons
are injected upwards along the loop axis in one leg. Scanning the
trajectories of electrons through the loop and representing them
in space vs time and plasma frequency vs time plots, respectively,
we get synthetic radio source distributions and radio spectra. The
results can be analyzed in dependence on loop and particle parameters
including the strength of whistler turbulence. Thus, we are able to
model the essential aspects of observed U(N) bursts. We find that in
a zone of sufficiently strong whistler turbulence near the loop top
the initial electron beam is splitted up into two beams propagating
from the top back and forward into both loop legs. Thus two widely
separated radio sources brighten during the descending branch of U
burst spectra. Moreover, we find that U(N) type radio bursts can be
excited not only due to mirroring but also by scattering of electrons
in whistler turbulence near a leg of the loop. For demonstrating the
strength of the present model a simulation of an observed U(N) burst
(February 23, 1993) is given.

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Title: Proton transport in a magnetic loop and Hα impact line
linear polarization.
Authors: Karlicky, M.; Henoux, J. -C.; Smith, D.
1996A&A...310..629K Altcode:
Using a 1-D test particle model with 350000 numerical protons,
we study the evolution of the proton distribution function in a
magnetic loop. A continuous injection of low-energy 200-1500keV
protons with a distribution function proportional to a E^-3^
power-law is considered. The acceleration region is assumed to be
at the top of a flare loop where the protons are injected into a
cone of pitch angles centered along the loop axis. The computations
are made for a static loop of length 20880km with the parameters
in the chromosphere corresponding to the VAL-C model of the solar
atmosphere. Coulomb collisions, mirroring, and Alfven wave scattering
in an intermediate regime (W_a_^tot^=10^-1^erg/cm^3^) relative to
prior analyses corresponding to saturated scattering are taken into
consideration. The proton distribution function in the chromosphere
at the Hα formation layer is computed. The resulting anisotropy of
the proton distribution function in a quasi-stationary state of proton
bombardment is analyzed from the point of view of its expected effects
on the impact linear polarization of chromospheric lines.

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Title: Evidence for prolonged acceleration based on a detailed
analysis of the long-duration solar gamma-ray flare of June 15, 1991
Authors: Akimov, V. V.; Ambrož, P.; Belov, A. V.; Berlicki, A.;
Chertok, I. M.; Karlický, M.; Kurt, V. G.; Leikov, N. G.; Litvinenko,
Yu. E.; Magun, A.; Minko-Wasiluk, A.; Rompolt, B.; Somov, B. V.
1996SoPh..166..107A Altcode:
Gamma-ray emission extending to energies greater than 2 GeV and lasting
at least for two hours as well as 0.8-8.1 MeV nuclear line emission
lasting 40 min were observed with very sensitive telescopes aboard
the GAMMA and CGRO satellites for the well-developed post-flare loop
formation phase of the 3B/X12 flare on June 15, 1991. We undertook
an analysis of optical, radio, cosmic-ray, and other data in order to
identify the origin of the energetic particles producing these unusual
gamma-ray emissions. The analysis yields evidence that the gamma-rays
and other emissions, observed well after the impulsive phase of the
flare, appear to be initiated by prolonged nonstationary particle
acceleration directly during the late phase of the flare rather than by
a long-term trapping of energetic electrons and protons accelerated at
the onset of the flare. We argue that such an acceleration, including
the acceleration of protons up to GeV energies, can be caused by
a prolonged post-eruptive energy release following a coronal mass
ejection (CME), when the magnetic field above the active region,
strongly disturbed by the CME eruption, relaxes to its initial state
through magnetic reconnection in the coronal vertical current sheet.

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Title: Observations and Analysis of Surges in Chromosphere and
Lower Corona
Authors: Kotrc, P.; Schmieder, B.; Karlický, M.; Heinzel, P.
1996RoAJ....6...69K Altcode:
No abstract at ADS

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Title: H-alpha Eruptive Prominence and Evolution of Force-Free
Electric Currents in the Solar Atmosphere
Authors: Karlicky, M.
1996ASPC..111..365K Altcode: 1997ASPC..111..365K
Hα observations of the 18 Sep 1995 eruptive prominence indicating
magnetic field reconnection or electric current coalescence are
presented. To explain some aspects of these observations a 3-D numerical
model of the evolution of force-free electric currents in the solar
atmosphere was built.

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Title: Pinch Processes near the Transition Region and Electron
Bombardment of the Chromosphere in the Presence of Electric Current
Authors: Karlicky, M.
1996mpsa.conf..591K Altcode: 1996IAUCo.153..591K
No abstract at ADS

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Title: 1 4 GHz type II-like radio bursts and pinch processes near
the transition region
Authors: Karlický, Marian; Jiřička, Karel
1996SoPh..163..171K Altcode:
Analyzing 205 radio bursts observed by the Ondřejov radiospectrograph
in the 1-4 GHz frequency range during 1992 and 1993, we found 6 examples
of type II-like radio bursts coinciding with impulsive phases of
solar flares. These bursts were interpreted as radio manifestations
of MHD (shock) waves generated during impulsive phases of flares
in the vicinity of the transition region. Assuming a magnetic-field
perturbation origin of these waves, we studied pinch processes in the
current sheet near the transition region. In the 2-D MHD numerical model
of this current sheet we demonstrated that 2-D pinch processes induced
by radiative losses can trigger the impulsive phase of some flares
and so generate the observed high-frequency type II-like radio bursts.

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Title: Solar flares and related processes in active regions.
Authors: Karlický, M.
1996joso.proc..100K Altcode:
No abstract at ADS

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Title: Isolated narrowband dm-spikes in the 1 - 2 GHz frequency range.
Authors: Jiřička, K.; Mészárosová, H.; Karlický, M.
1996joso.proc..149J Altcode:
No abstract at ADS

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Title: Phenomena related to electron beams in solar flares
Authors: Karlický, Marian
1995CzJPh..45.1063K Altcode:
Starting from basic observational characteristics of solar flares
the flare physical processes are briefly described. The role of
electron beams in such a flare scenario is expressed. The observational
manifestations of electron beams as, e.g., type III and U radio bursts
are presented. Then results of numerical modelling of these processes
are shown. Besides the magnetic field-line reconnection process which is
considered to be a primary flare one, the main attention is devoted to
the evolution of electron beams in flare loops, to the interpretation
of U bursts, to the electron beam bombardment of deep and dense layers
of the solar atmosphere and to accompanied processes as the evaporation
process and the asymmetry of optical chromospheric lines.

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Title: Repeated activity of the 0.8 1.2 GHz radio source of March
20, 1993
Authors: Karlický, Marian; Jiřička, Karel
1995SoPh..160..121K Altcode:
During March 20, 1993, from 12:00 to 16:00 UT, repeated radio burst
activity was observed in the 0.8-1.2 GHz frequency range. `Periods'
in intervals 0.1-0.5, 0.7-1.0, 2.8-3.9, 75-170 s, and 15-25 min were
recognized. This long-lasting narrowband activity consisted mainly
of pulsations and continua. In some intervals it was accompanied
not only by spikes, broadband pulsations, and fibers in the 1-2
GHz frequency range, but also by type III and U burst activity at
lower frequencies as well as by hard X-ray bursts. From several radio
bursts, two characterized by different fine structures were selected
and compared. The observed differences are explained by different
distribution functions of superthermal electrons. The position of the
0.8-1.2 GHz radio source above the photosphere and the magnetic field
in the fiber burst source were estimated to be 66 000-75 000 km and
120-135 G, respectively.

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Title: Electron beam bombardment of the chromosphere in a flare loop
with electric currents.
Authors: Karlicky, M.
1995A&A...298..913K Altcode:
In a flare loop with electric current and corresponding Ohm electric
field the electron beam bombardment of chromospheric layers is
considered. It is assumed that the electric current, which is generated
during the slow evolution before a flare, flows along current filaments
in the flare loop and all current densities in these filaments are below
any thresholds of current instabilities. The convergence of magnetic
field below transition region and its influence on current densities
in current filaments are considered. The Ohm electric field in the
VAL-model chromosphere is determined and compared with the electric
field equivalent to collisional losses of the 30-100keV electrons
at these layers. It was found that for sufficiently high current
densities and electron energies the Ohm electric field can be greater
than that of collisional one, mainly at upper chromosphere. Using
a numerical model of electron beam bombardment in a flare loop, the
energy changes of initially 100keV electrons during their penetration
into the chromosphere in the case with and without the presence of
electric current are computed. The significance of these effects
and their influences on interpretations of hard X-ray emission and
evaporation process are discussed.

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Title: The generation of MHD shock wave during the impulsive phase
of the February 27, 1992 flare
Authors: Karlický, M.; Odstrcil, D.
1994ESASP.373..325K Altcode: 1994soho....3..325K
No abstract at ADS

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Title: Chromospheric and transition-region heating phenomena:
coordinated GBO and SOHO observations
Authors: Heinzel, P.; Kotrc, P.; Karlicky, M.; Nejezchleba, T.;
Knizek, M.
1994ESASP.373..369H Altcode: 1994soho....3..369H
No abstract at ADS

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Title: The Generation of Magnetohydrodynamic Shock Waves during the
Impulsive Phase of the 1992FEB27 Flare
Authors: Karlicky, Marian; Odstrcil, Dusan
1994SoPh..155..171K Altcode:
In this paper a unique 2.3-4.2 GHz radio spectrum of the flare impulsive
phase, showing fast positively drifting bursts superimposed on a slowly
negatively drifting burst, is presented. Analyzing this radio spectrum
it was found that the flare started somewhere near the transition
region, where upward propagating MHD waves were generated during the
whole impulsive phase. Moreover, it was found that behind a front of
these ascending MHD waves the downward propagating electron beams, which
bombarded dense layers of the solar atmosphere, were accelerated. It
seems that, simultaneously with the increase of beam bombardment
intensity, the intensity of MHD waves was increasing and thus the MHD
shock wave generation and the electron beam acceleration and bombardment
formed a self-consistently amplifying flare process. At higher coronal
heights this process was followed by a type II radio burst, i.e. by
the MHD flare shock. To verify this concept, the numerical modeling of
the shock-wave generation and propagation in space from a flare site
near the transition region up to 3 solar radii was made. Comparing the
thermal and magnetic field disturbances, it was found that those of
magnetic origin are more relevant in this case. Combining the results
of interpretation and numerical simulation, a model of the February 27,
1992 flare is suggested and new aspects of this model are discussed.

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Title: Magnetic field estimation in microwave radio sources
Authors: Ai-hua, Zhou; Karlický, M.
1994SoPh..153..441A Altcode:
Eliminating the termN L, useful formulae for the magnetic field
estimation in microwave radio sources are presented. Applications of
these formulae to observed solar microwave radio bursts are shown.

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Title: Magnetic field estimation in microwave radio sources
Authors: Zhou, Ai-Hua; Karlicky, M.
1994SoPh..153..441Z Altcode:
Eliminating the term N L, useful formulae for the magnetic field
estimation in microwave radio sources are presented. Applications of
these formulae to observed solar microwave radio bursts are shown.

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Title: On the Occurrence of Blue Asymmetry in Chromospheric Flare
Spectra
Authors: Heinzel, Petr; Karlicky, Marian; Kotrc, Pavel; Svestka, Zdenek
1994SoPh..152..393H Altcode:
We present observations of optical spectra of a flare in which blue line
asymmetry was seen for more than 4 min close to the flare onset. The
maximum blue asymmetry coincided with the maximum of a hard X-ray
and microwave burst. We discuss possible interpretations of the blue
asymmetry and conclude that the most plausible one is electron-beam
heating with return current. Although this process predicts downflows
in the lower transition region and upper chromosphere, its ultimate
effect on the line profiles can be blue asymmetry: the upper layers
moving away from us absorb the radiation of the red peak thus lowering
its intensity in comparison to the blue one.

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Title: Space and time distribution of hard X-ray emission in a loop
at the beginning of a flare
Authors: Karlicky, Marian; Henoux, Jean-Claude
1994A&A...283..202K Altcode:
Using a 1-D hybrid model of the electron bombardment in flare
loops, we study not only the evolution of densities, plasma
velocities and temperatures in the loop, but also the temporal and
spatial evolution of hard X-ray emission. In the present paper
a continuous bombardment by electrons isotropically accelerated
at the top of flare loop with a power-law injection distribution
function is considered. The computations included the effects of the
return-current that reduces signifcantly the depth of the chromospheric
layer which is evaporated. These computations were made to study
the contribution of various processes - chromospheric evaporation,
mirroring and high pitch angle of superthermal electrons - to the
hard X-ray emission at the top of a loop at the very beginning of
flares. Therefore the present modelling was made with superthermal
electron parameters coresponding to the classical resistivity regime
for an input energy flux of superthermal electrons of 109 erg
cm-2/sec. Chromospheric evaporation density waves generated
at both feet of the loop propagate up to the top, where they collide
and cause a temporary electron density enhancement. Electron mirroring
at magnetic mirrors increases the population of superthermal electrons
at the top loop. These two processes lead to hard X-ray emission at
the top of the loop and dominate over the effect of high pitch-angle
superthermal electrons.

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Title: Fast Drift Bursts; Spikes; and Continua Ohservations in the
100-4200 MHz Band
Authors: Jiricka, K.; Karlicky, M.; Kepka, O.; Tlamicha, A.
1994scs..conf..285J Altcode: 1994IAUCo.144..285J
New Ondřejov solar radio observational system consisting of a high-time
resolution 3000 MHz receiver and of a 100 - 4200 MHz radiospectrograph
is described and some results of observation of fast drift bursts,
spikes, and continua are presented.

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Title: Space and Time Distribution of Hard X-Ray Emission in a Loop
at the Beginning of a Flare
Authors: Karlicky, M.; Henoux, J. -C.
1994scs..conf..275K Altcode: 1994IAUCo.144..275K
Using a new 1D hybrid model of the electron bombardment in flare
loops, the authors study not only the evolution of densities, plasma
velocities and temperatures in the loop, but also the temporal and
spatial evolution of hard X-ray emission. In this paper a continuous
bombardment by electrons isotropically accelerated at the top of flare
loop with a power-law injection distribution function is considered.

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Title: The Superthermal Electrons in Flare Loops (Invited)
Authors: Karlicky, M.
1994scs..conf..235K Altcode: 1994IAUCo.144..235K
In this paper the collisional, return current, mirroring and
wave-particle interaction effects on the propagation of superthermal
electrons in flare loops are reviewed. Moreover, the electron
bombardment of dense layers of the solar atmosphere and corresponding
atmospheric response are presented. The accompanied X-ray, radio and
Hα emissions during the evaporation process are discussed.

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Title: Electron acceleration due to beam flux increase in a converging
magnetic field
Authors: Karlicky, M.; Henoux, J. -C.
1993A&A...278..627K Altcode:
The effects of the magnetic field mirroring and backscattering of beam
electrons in a time varying return-current electric field are studied
with a 1-D hybrid test particle model of the electron bombardment in
flare loops. These effects are analyzed for monoenergetic electron
beams with an energy flux increasing with time, for different widths
of their pitch-angle distribution. The consequence of a weak linear
increase of the magnetic field from the apex to the feet of the
loop is considered. The number and therefore the role of mirroring
electrons are increasing with the broadening of the pitch-angle
distribution. While in the case of bombardment by an unidirectional
beam only few particles are reflected by back-scattering in the dense
layers of the loop and then accelerated in the return-current electric
field, in the case of a broader pitch-angle distribution of beams
much more electrons are mirrored and accelerated. Part of them are
accelerated to energies higher than the initial ones. Consequently,
a collisionless return-current is formed, which decreases the beam
return-current losses. The possible role of these effects in the solar
flare scenario is shortly discussed.

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Title: Fast drift burst observations with the new Ondřejov
radiospectrograph
Authors: Jiricka, K.; Karlicky, M.; Kepka, O.; Tlamicha, A.
1993SoPh..147..203J Altcode:
The new 100-4200 MHz Ondřejov radiospectrograph and the high-time
resolution 3 GHz radiometer are described and the observations of fast
drift bursts during the increased solar activity of September 5-7,
1992 are presented and analyzed.

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Title: Return current losses in pulse beam heating of the solar
atmosphere
Authors: Karlický, Marian; Hénoux, Jean-Claude
1993AdSpR..13i.195K Altcode: 1993AdSpR..13..195K
The influence of return current losses on pulse beam heating of the
solar atmosphere is studied using a 1 D-hybrid code. While heating
of the coronal plasma by the penetrating electron beam is obtained,
as expected, strong return current losses of beam electrons at the
resistivity jump in the transition region are also found. The electron
beam energy is deposited at greater heights in the solar atmosphere
than in the case of pure collisional losses. At the starting time
of the flare, due to a strong return current heating, a very steep
transition region is formed where upwards and downwards plasma flows
are generated. However, this state has a transitory character. The
atmosphere is heated and a channel of hot, low resistivity plasma
is formed, by which the following electron beams can penetrate more
easily to deep chromospheric levels, where they are then thermalized.

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Title: An Analysis of SKYLAB X-Ray Pictures of a Giant Coronal Arch
Authors: Simberova, Stanislava; Karlicky, Marian; Svestka, Zdenek
1993SoPh..146..343S Altcode:
The limb event of 13/14 August, 1973, imaged by Skylab in soft X-rays,
proved to be a giant arch, quite similar to those observed in 1980-1986
on SMM. High spatial resolution (by a factor of 4-5 better than in SMM
data) made it possible to see the internal structure of the arch. Its
brightest part consisted of loops very similar to, but higher than,
post-flare loops, surrounded by a rich system of weak loop structures
extending up to altitudes of 260 000 km. While the main brightest
structure of the arch was newly formed, the weak very large loops had
existed above the active region before and were only enhanced during
the event.

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Title: New aspects of the April 27, 1981 flare
Authors: Karlicky, M.; Zhou, Ai-Hua
1993SoPh..146..199K Altcode:
Very interesting radio bursts, observed during the well-known solar
flare of April 27, 1981 are presented. While the sequence of reverse
drift bursts, U-bursts and radio flux depression on 9.375 GHz can
be explained within the beam bombardment and evaporation model, the
narrowband dm-spikes uniquely organized in "necklace" structures seem
to indicate the interaction of flare loops. Arguments in favour of
the plasma emission model of narrowband dm-spikes were found.

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Title: The acceleration of back-scattered beam electrons in a
return-current electric field
Authors: Karlicky, Marian
1993SoPh..145..137K Altcode:
Using a 1-D hybrid model of the electron beam bombardment in a flare
loop, it is demonstrated that beam electrons, back-scattered in dense
layers of the solar atmosphere, are accelerated in the return-current
electric field. This effect is shown in two regimes of the electron
beam bombardment: (a) with a monoenergetic quasi-steady beam, and (b)
with a sequence of 4 pulse beams. It is suggested that the mirroring of
electrons at loop magnetic mirrors can amplify this process. The role of
such acceleration for the formation of a collisionless return-current,
and thus for a decrease of return-current losses, is discussed.

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Title: Fine Structures in Time Profiles of Type-II Bursts at
Frequencies above 200-MHZ
Authors: Zlobec, P.; Messerotti, M.; Karlicky, M.; Urbarz, H.
1993SoPh..144..373Z Altcode:
We studied the properties of fine structures in 23 type II bursts
recorded at the Trieste Astronomical Observatory at frequencies above
200 MHz.

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Title: Pulse Beam Heating of the Solar Atmosphere (Abstract)
Authors: Karlicky, M.
1993HvaOB..17...33K Altcode:
No abstract at ADS

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Title: Mass motion of a heated plasma blob in a coronal loop.
Authors: Karlicky, M.; Simnett, George M.
1992ESASP.348..205K Altcode: 1992cscl.work..205K
A problem of the gravitational fall of dense plasma blob in the
semicircular coronal magnetic loop is studied using a 1-D hydrodynamic
code. Considering the thermal conduction and radiative losses are
fully compensated by an appropriate heating, it is shown that the
falling dense plasma blob compresses the underlying coronal plasma
and thus the blob is decelerated and reflected. This process together
with a decompression in the opposite side of coronal loop leads to
the oscillation movement of dense plasma blob and eventually to the
stop of this blob in some equilibrium position, in which the blob is
supported by the pressure of an underlying plasma. This process is very
sensitive to the deviation from full compensation of heating, radiative
and thermal conduction losses. Nevertheless, it seems that the pressure
with the appropriate heating can support the dense and cold plasma,
e.g. in solar prominences, where their magnetic field is stabilizing
the Rayleigh-Taylor instability of heavy gas above the lighter one.

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Title: Pulse-beam heating in flare loops.
Authors: Heinzel, Petr; Karlicky, M.
1992ESASP.348..237H Altcode: 1992cscl.work..237H
Using a 1D hydbrid code, the authors evaluate a response of the flare
loop atmosphere to a series of very short electron beam pulses with
subsecond duration. Loop dynamics and energy balance are treated by
solving the standard set of hydrodynamic equations, while the beam
deceleration in denser atmospheric layers is evaluated by using a
particle simulation technique. Ionization of hydrogen below T ≍
104K is obtained by solving simultaneously the time-dependent
non-LTE problem for a three-level hydrogen atom with continuum. The
resulting electron densities are then used to compute radiation losses
at each time step. The authors discuss the behaviour of time-dependent
heating, the ionization structure of the chromosphere, and the role of
relaxation processes. A series of short-duration electron beam pulses
represents schematically the non-stationary heating in the flare
loops. However, the time-dependent radiation-hydrodynamical approach
used in this paper can also be applied to study other processes taking
place in coronal loops.

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Title: Return current losses in pulse beam heating of the solar
atmosphere
Authors: Karlicky, M.; Henoux, J. -C.
1992A&A...264..679K Altcode:
A 1D-hybrid code is employed to examine the influence of return
current losses on pulse beam heating of the solar atmosphere. While
heating of the coronal plasma by the penetrating electron beam is
obtained as expected, strong return current losses of beam electrons
at the resistivity jump in the transition region are also found. The
electron beam energy is deposited at greater heights in the solar
atmosphere than in the case of pure collisional losses. At the
starting time of the flare, due to a strong return current heating,
a very steep transition region is formed where upward and downward
plasma flows are generated. The atmosphere is heated and a channel of
hot low-resistivity plasma is formed by which the following electron
beams can penetrate more easily to deep chromospheric levels where
they are then thermalized.

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Title: A simulation approach to neutral beam-plasma systems: analysis
of Langmuir waves generation
Authors: Messerotti, M.; Karlicky, M.
1992pdta.proc..115M Altcode:
Many authors suggested the acceleration of neutral beams in the primary
energy release site of solar flares (Simnett, 1986; Simnett and Heines,
1990; Martens and Young, 1990); such neutral beams would consist
of electrons and protons with the same drift velocity, so that the
protons carry the bulk of kinetic energy, and this would also overcome
most of the problems connected with the propagation of pure proton and
pure electron beams (Brown et Al., 1989). Numerical simulations in a
preliminary work (Karlicky, 1989) indicate that neutral beams can be
the result of current neutralization in accelerated proton beams or,
according to the model by Martens and Young (1990), their formation
can be due to the non-collisional, direct acceleration of protons and
electrons through the action of the electric field in the current sheet
formed at the top of a post-flare loop. Actually the real existence
of neutral beams in solar flares has to be proved yet and, among the
possible signatures, the emission of electromagnetic radiation was
considered in the literature. Proton beams were suggested by Benz and
Simnett (1986) as exciters of slowly-drifting solar radio bursts and
Smith and Benz (1989) proposed a model based on high-energy proton beams
to explain non-drifting radio emissions observed in the frequency band
1 - - 3 GHz with a lifetime ranging from 2 to 4 s, but many questions
concerning this point remain open (Messerotti, 1990). With regard to
that in the present work the generation of Langmuir waves in neutral
beam-plasma systems was studies using a 1-D electrostatic and a 1-D
electromagnetic particle code. For a weak and monoenergetic neutral
beam-plasma system a two-step saturation process of the electrostatic
beam instability was found to be operating, firstly driven by beam
electrons till their trapping and mixing in the phase space, when beam
protons undertake the role. The addition of a thermal spread in the
neutral beam resulted in the disappearance of the electron trapping
phase. The effect of an external magnetic field was also analyzed and
the simulations show that the saturation levels decrease according
to a square cosine law in the angle between the considered and the
beam propagation direction. Furthermore it was tried to estimate the
influence of electromagnetic waves on the generated Langmuir waves using
a 1-D electromagnetic relativistic code. Numerical results indicate
that such influence is negligible, as the level of em waves corresponds
roughly to the noise level of the background plasma. A comparison of
the parameters derived from the numerical experiments with those from
the theoretical estimations confirm the adequate accuracy of the above
results. In particular, the most relevant conclusion is that a real
neutral beam with monoenergetic protons can generate Langmuir waves
with a saturation level 150 times higher than that due to a pure
electron beam with the same density and velocity and this suggests
that observable radio emission could be produced.

---------------------------------------------------------
Title: Parametric model of interplanetary shock wave propagation
Authors: Voros, Z.; Karlicky, M.
1992sws..coll..675V Altcode:
The free parameters of the present simple model for the propagation of
a driven interplanetary shock wave are discussed, and the physically
meaningful range of 2D MHD numerical model input parameters is noted,
in view of experimentally obtained time intervals of soft, long-duration
X-radiation and type IVm radiation. It appears possible to improve
blast wave propagation forecasts by considering actual anisotropy
features of shock wave propagation.

---------------------------------------------------------
Title: Subsecond Variations of HXR and Hα Flare Emission
Authors: Heinzel, P.; Karlicky, M.
1992LNP...399..359H Altcode: 1992esf..coll..359H; 1992IAUCo.133..359H
For a series of electron beam pulses, we have computed the
time-dependent chromospheric heating and the corresponding hard X-ray
(HXR) flux. Moreover, by solving the time-dependent NLTE problem for
hydrogen, we theoretically predict the Ha-line intensity variations
on sub-second time scales. Both HXR-fluxes and Ha wing intensities
do exhibit a spiky behaviour, consistent with short pulse-beam
heating. However, the spikes in Ha are unexpectedly inverse, i.e. the
line intensity decreases during the beam heating. They correlate rather
well with HXR emission peaks computed for 24 keV channel. We compare our
theoretical results with recent observations of Kiplinger et al. (1991).

---------------------------------------------------------
Title: Radio Emission of Eruptive Flares
Authors: Karlicky, M.
1992LNP...399..171K Altcode: 1992esf..coll..171K; 1992IAUCo.133..171K
Radio spectra of some eruptive flares are described. Most of them do
not conform to the classical spectrum schema. Both the type I burst
chains associated with the filament activation phase of the May 16,
1981 flare, and the slow negative drift of the group of type III and
U bursts in the July 12, 1982 and June 15,1991 flares illustrate the
upwards expansion of complete magnetic structures. In some eruptive
flares, e.g. April 24, 1985, reverse drift bursts are observed prior to
the upwards expansion. In addition, narrowband dm-spikes and a variety
of positively drifting features are frequently observed. These are
believed to be radio signatures of localized reconnections and of
the spreading of flare dissipative processes. Results of numerical
simulations supporting these ideas are presented.

---------------------------------------------------------
Title: Radio Emission of the February 27, 1992 Flare
Authors: Karlicky, M.; Tlamicha, A.; Jiricka, K.; Aurass, H.;
Zlobec, P.
1992HvaOB..16...23K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Comparison of 2-Dimensional MHD and Semiempirical Models of
Interplanetary Shock Wave Propagation
Authors: Karlicky, M.; Smith, Z.; Dryer, M.
1991BAICz..42..320K Altcode:
A comparison was made between the 2D version of the 2 1/2-D MHD model
by Wu et al.(1983) and the semiempirical model of Voros and Karlicky
(1988). Although agreement in the exponential dependence (N is about
0.5) of shock wave velocities was found, the compared models differ in
the early stages of shock wave propagation and in the shock shapes. A
small E-W asymmetry of shock wave propagation was found in the MHD
simulations.

---------------------------------------------------------
Title: The Negative Frequency Drift of Microwave Bursts Due to
Collisional and Radiative Losses of Superthermal Electrons
Authors: Karlicky, M.
1991BAICz..42..260K Altcode:
An analytical estimate of negative frequency drift is compared to
observed values of microwave radio spectra with attention given to the
effects of microwave bursts. Observations of fast drift bursts (FDBs)
in the range 2-4.5 GHz are examined in terms of both radiative and
collisional losses, and the electron densities in the radio source are
reasonable and coincide with microwave bursts. Classical collisions
are sufficient to explain the negative frequency drift of FDBs, but
the frequency drift of the bursts from compact radio sources can be
used to estimate the plasma density in those sources.

---------------------------------------------------------
Title: Pulse Beam Heating of Solar Atmosphere
Authors: Karlicky, M.; Henoux, C.
1991BAICz..42...22K Altcode:
The response of the solar atmosphere to pulse beam heating was computed
using a one-dimensional hybrid code. Whereas the hydrodynamic part
of this program was used to compute the atmospheric response, the
pulse beam decelerated by electron-electron interactions in the dense
layers of the solar atmosphere is represented by particles. In this new
description of the electron beam, the finite transit time of electrons
accelerated in flare loops is taken into account and the hard X-ray
radiation has been computed directly.

---------------------------------------------------------
Title: The Role of the Magnetic Field in Intensity and Geometry in
the Type-Iii Burst Generation
Authors: Zlobec, P.; Ruždjak, V.; Vršnak, B.; Karlický, M.;
Messerotti, M.
1990SoPh..130...31Z Altcode:
We study the association of type III bursts related to Hα flares
in different magnetic environments in the period 1970-1981. Special
attention is paid to flares which partly cover a major spot umbra
(Z-flares). In particular we consider the location of the spots in the
active regions and the magnetic field intensities of spots covered by
a ribbon. The association rate with type III bursts decreases to 17%
when the flare is located inside the bipolar pattern of a large active
region, compared with an association rate of 54% when the flare is
situated outside it. The association rate increases with the magnetic
field intensity of the spot covered by Hα emission; this is most
clearly revealed for the flares occurring outside the bipolar pattern
of active regions. Ninety-three percent of the flare-associated type
III burst were accompanied by 10 cm radio bursts. For the most general
case in which a flare is developing anywhere in an active region,
the association with type III bursts generation increases with the
increasing magnetic field intensity of the main spot of the group.

---------------------------------------------------------
Title: Analysis of the Time Profile of Type-Iii Bursts at Meter
Wavelengths
Authors: Abrami, A.; Messerotti, M.; Zlobec, P.; Karlicky, M.
1990SoPh..130..131A Altcode:
The time profile of two sets of isolated type III bursts, observed in
the meter wavelength range at the Trieste Astronomical Observatory,
was analyzed using a Fourier transform technique in order to accurately
determine the decay constant of the exponential phase and to derive the
exciter time profile. The decay constant (τ) was found to be correlated
with the exciter duration (De), suggesting that the damping
of plasma waves is not of collisional origin and confirming results
obtained by previous authors at lower frequencies. In particular, two
distributions can be identified in the (τ − De) plane
and fitted by two nearly parallel lines, which could be the signature
of different decay processes. Moreover, the damping constant observed
at higher frequencies (327 and 408 MHz) has the same dependence on
exciter duration as that at the lower frequency (237 MHz), also in
disagreement with the collisional hypothesis.

---------------------------------------------------------
Title: Pulse Beam Heating of the Solar Atmosphere
Authors: Karlicky, Marian
1990SoPh..130..347K Altcode:
A response of the solar atmosphere to pulse beam heating is computed
using a 1-D hybrid code. While the hydrodynamic part of this program
is used to compute the atmospheric response, the pulse beam decelerated
by electron-electron and electron-neutral hydrogen interactions in the
dense layers of the solar atmosphere is represented by particles. In
this new description of an electron beam, the finite transit time of
accelerated electrons in the flare loops is taken into account and the
hard X-ray radiation is computed directly. Four different pulse beams
are considered and their effects are compared. Moreover, the return
current losses of the pulse beam are discussed.

---------------------------------------------------------
Title: Particle beams as a source of noise storm depression?
Authors: Aurass, H.; Boehme, A.; Karlicky, M.
1990SoPh..130...19A Altcode:
The February 5, 1986 flare-related radio continuum depression is
studied, compared with other noise storm depression events and discussed
in the framework of current type I storm models. The influence of flare
plasma flow or shocks and of superthermal electrons on noise storm
radiation is considered. The presence of fast drifting emission features
just before and during the decrease of the intensity, the association
between the depression onset and the microwave burst maximum, the
simultaneous appearance of the intensity minimum over a broad spectral
range as well as preflare evidence of an interconnection of the flare
site and the noise storm source are arguments for a preference of the
role of beams of superthermal electrons. We distinguish abrupt and slow
depressions (Figure 5). The abrupt depressions are in agreement with
Melrose's (1980) predictions. Slow depressions can only be understood by
invoking the diffusion of super-thermal electrons through the magnetic
field carrying the storm source.

---------------------------------------------------------
Title: Return Current and Collisional Effects in Nonthermal Electron
Beams with Pulsed Injection
Authors: Karlicky, M.; Alexander, D.; Brown, J. C.; MacKinnon, A. L.
1990SoPh..129..325K Altcode:
The evolution of a pulse of nonthermal electrons, with a truncated
power-law spectrum, injected into a uniformly dense coronal plasma,
is studied by the 1-D particle simulation of return current and direct
collisional effects. The beam pulse injection profile varies gradually
enough for total current neutrality, and a steady-state Ohm's law for
the return current, to apply at each point and time. Quasi-linear
relaxation of the beam is deliberately ignored in order to isolate
the modification of return current effects by pulsed injection.

---------------------------------------------------------
Title: Beam Heating in Solar Flares: Electrons or Protons?
Authors: Brown, J. C.; Karlicky, M.; MacKinnon, A. L.; van den Oord,
G. H. J.
1990ApJS...73..343B Altcode:
The current status of electron and proton beam models as candidates for
the impulsive phase heating of solar flares is discussed in relation to
observational constants and theoretical difficulties. It is concluded
that, while the electron beam model for flare heating still faces
theoretical and observational problems, the problems faced by low
and high energy proton beam models are no less serious, and there are
facets of proton models which have not yet been studied. At the present,
the electron beam model remains the most viable and best developed of
heating model candidates.

---------------------------------------------------------
Title: A survey of the peculiar radio emission of the solar
behind-limb event on 16th February 1984
Authors: Chertok, I. M.; Fomichev, V. V.; Gorgutsa, R. V.; Markeev,
A. K.; Podstrigach, T. S.; Aurass, H.; Hildebrandt, J.; Kliem, B.;
Krüger, A.; Kurths, J.; Karlický, M.; Tlamicha, A.; Urbarz, H. W.;
Zlobec, P.
1990AN....311...55C Altcode:
This paper presents radio emission measurements, taken from different
European stations, of the February 16th, 1984 solar behind-limb burst,
which started in the active region AR 4408 at a longitude of about 130
deg W. The event was related to a very strong relativistic particle
emission, the presence of cm-wave radiation from altitudes above
200,000 km above the photosphere, and an unusual U-shaped type II burst
pattern consisting of four simultaneous emission bands. The spectrum
in the cm-dm range exhibited different stages of evolution related
to the burst onset, the burst maximum, and the postburst increase. It
appears possible that, at dm-waves during the burst maximum, a partial
overlapping of plasma radiation with gyrosynchroton radiation governing
the cm-wave range took place.

---------------------------------------------------------
Title: Solar Flares and the Dynamics of Langmuir Waves in
Current-Carrying Plasmas
Authors: Karlicky, M.; Jungwirth, K.
1989SoPh..124..319K Altcode:
The dynamics of intense Langmuir waves in current-carrying plasmas is
studied both analytically and numerically. Starting with the widely
used Zakharov equations, adapted to these systems, specific features of
this problem are pointed out. Further, the role of resonant particles
is analyzed. By using 1-D macroparticle numerical code, nonlinear
regimes of the modified-decay and modulational instabilities are
then modelled. Efficient cooperation of essentially ponderomotive and
electron-ion drift effects its demonstrated.

---------------------------------------------------------
Title: Interpretation of a Special Fine Structure in Type-Iv Solar
Radio Bursts
Authors: Mann, G.; Baumgaertel, K.; Chernov, G. P.; Karlicky, M.
1989SoPh..120..383M Altcode:
A special fine structure (slowly drifting chains of narrowband fiber
bursts), firstly observed during the solar type-IV radio burst on
April 24, 1985, is interpreted as the radio signature of whistler waves
periodically excited by a switch-on/switch-off process of a loss-cone
instability in a localized wave packet of the fast magnetoacoustic mode.

---------------------------------------------------------
Title: The Route to Chaos during a Pulsation Event
Authors: Kurths, Juergen; Karlicky, Marian
1989SoPh..119..399K Altcode:
A time series analysis of a pulsation event in solar radio emission
provides an evolution from a regular doubly periodic phase to an
irregular behaviour. Applying some techniques developed in the theory
of nonlinear dynamic systems to this irregular stage suggests that
there exists a low-dimensional attractor. Estimates of the maximum
Lyapunov exponent give some evidence to deterministic chaos. The sudden
transition from a regular to a chaotic structure is identified as a
part of the Ruelle-Takens-Newhouse route to chaos which is typical
in nonlinear systems. It is checked whether this pulsation event may
be interpreted in terms of known pulsation models. Consequences for
models, which are suitable to describe such an evolution, are discussed.

---------------------------------------------------------
Title: Solar flares and dynamics of Langmuir waves in current-carrying
plasmas
Authors: Jungwirth, K.; Karlicky, M.
1989STIN...9021710J Altcode:
The dynamics of intense Langmuir waves in current-carrying plasmas is
studied both analytically and numerically. Starting with the widely
used Zakharov equations, adapted to these systems, specific features of
this problem are pointed out. Further, the role of resonant particles
is analyzed. By using 1-D macroparticle numerical code, nonlinear
regimes of the modified-decay and modulational instabilities are
then modelled. Efficient cooperation of essentially ponderomotive and
electron-ion drift effects is demonstrated. It appears that the heating
of a current-carrying plasma can be activated through releasing of the
inductively stored energy, due to the enhanced conversion of energy
associated with the electron drift motion. The underlying physics is
discussed and its relationship to the solar flare theory is suggested.

---------------------------------------------------------
Title: Effects of Shear Plasma Flow on Externally Induced Magnetic
Field Line Reconnection
Authors: Karlicky, M.
1989BAICz..40...23K Altcode:
A numerical study of the response of a current sheet to
resistivity enhancement in the presence of shear plasma flow is
presented. Simulations were conducted with two-dimensional model of
the current sheet and comparisons were made between cases with and
without the shear flow. The results show that the shear plasma flow in
the adjacent magnetic flux tubes forming the current sheet on their
tangential surface influences the resultant velocity field. Also, it
is found that the reconnection process in the vicinity of the X-point
becomes slower in the presence of shear flow.

---------------------------------------------------------
Title: The application of a 1-D electrostatic code for the analysis
of beam-plasma systems in the solar corona
Authors: Messerotti, M.; Zlobec, P.; Karlicky, M.
1989MmSAI..60..187M Altcode:
A one-dimensional electrostatic particle simulation code used for the
analysis of beam-plasma systems is investigated. The use of the code
in the preliminary study of an electrostatic streaming instability
(bump-on-tail type) in the nonlinear regime and the related choice of
system parameters is explained. The saturation of the instability
is analyzed for a proton as well as for an electron weak beam
having the same density and velocity in the cold approximation; the
corresponding energy levels are then compared to test the efficiency
of the process. The saturation level for protons was revealed to be
larger than that of electrons, thus suggesting possible radio emission
by protons.

---------------------------------------------------------
Title: Solar flares and dynamics of Langmuir waves in current-carrying
plasmas.
Authors: Karlický, M.; Jungwirth, K.
1989BAAS...21Q1027K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Chaotic Radiopulsations and Coronal Magnetic Field Estimates
Authors: Kurths, J.; Karlicky, M.
1989ESASP.285..175K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A simple model of propagation of driven interplanetary shock
waves and prediction of sudden commencements of geomagnetic storms.
Authors: Voros, Z.; Karlicky, M.
1988BAICz..39..250V Altcode:
On the basis of the results of magnetohydrodynamic models, observations
of type II radio burst and measurements of the interplanetary
plasma parameters of shock waves, a simple model relation has been
suggested for propagation of driven shock wave. The free parameters
in this relation, which has been constructed for a quick and simple
prediction of SSC, are determined and discussed with the aid of cases
of interplanetary shock waves already recorded.

---------------------------------------------------------
Title: Impulsive 6-cm Spikes and Langmuir Turbulence Caused by
Thick-target Electron Beams
Authors: Karlicky, M.
1988BAICz..39..146K Altcode:
The possibility that the 6-cm spikes observed during the May 16,
1981, solar flare are the microwave signature of Langmuir turbulence
generated by thick-target electron beams is discussed. The Langmuir
turbulence in the spike sources are estimated and compared with the
results of Emslie and Smith (1984). The short duration and small
extent of these 6-cm spikes are explained by the short lifetime of
the highly collimated thick-target electron beams in the small volumes
of the solar flare. It is suggested that the effects of gyroresonance
absorption must be taken into account with the increase of the magnetic
field in the spike sources.

---------------------------------------------------------
Title: Response of the Current Sheet to a Time-Limited Enhancement
of Electrical Resistivity
Authors: Karlicky, M.
1988BAICz..39...13K Altcode:
The initiation of a solar flare by an electron beam from a distant
previous flare via the mechanism proposed by Farnik et al. (1983) is
investigated by means of numerical simulations, extending the analysis
of Ugai (1980, 1982, and 1983) to focus on the evolution of the current
sheet after a rectangular pulse of increased electrical resistivity has
ended. The derivation of the governing equations is recalled, and the
simulation results are presented in extensive graphs. The reconnection
of magnetic-field lines after the pulse is found to be associated with
local field-line diffusion, an X-type field configuration, locally
enhanced Joule heating, and vortex formation near the X point (leading
to quasi-steady plasma flow). The current at the X point decreases
and changes sign during the period of vortex flow but then increases
rapidly when the vortex disappears.

---------------------------------------------------------
Title: On the Intermediate Drift Burst Model
Authors: Mann, G.; Karlicky, M.; Motschmann, U.
1987SoPh..110..381M Altcode:
A modification of the presently existing intermediate drift burst
model by Kuijpers (1975) and Bernold (1983) is suggested. It is shown
that whistler solitons cannot be responsible for intermediate drift
bursts. Here, they are interpreted as the radio signature of localized
formstable whistler wave packets propagating along the magnetic field
in a coronal loop. In the frame of this modified model, the magnetic
field strengths derived from fiber burst data agree with previous
estimates by Dulk and McLean (1978).

---------------------------------------------------------
Title: Hα diagnostics of (post)-flare loops based on narrow-band
filtergram observations
Authors: Heinzel, P.; Karlicky, M.
1987SoPh..110..343H Altcode:
Using narrow-band Hα filtergrams, we develop a quantitative
non-LTE approach to determine the physical conditions prevailing
at the tops of (post)-flare loops observed against the solar
disc. At temperatures 10000-15000 K, the tops of flare loops turn
to emission at Hα line center when the gas pressure Pg
reaches 1 dyn cm−2 and should be clearly visible for
Pg≳ 3 dyn cm−2, independently of the
loop diameter. This situation corresponds to the electron density
of the order 1012 cm−3. The contrast of
flare-loops (in projection on the disc) at Hα line center is mainly
the function of Pg, while in the line wings (Hα ± 1 Å)
the loop can be visible in absorption or emission only when rather
strong microturbulence is present or for unrealistically high gas
pressures. Finally, we briefly discuss our diagnostical results in
frame of the latest (post)-flare loop model.

---------------------------------------------------------
Title: On a sequence of remarkable fine structures in the type IV
burst of 24 April, 1985
Authors: Aurass, H.; Chernov, G. P.; Karlický, M.; Kurths, J.;
Mann, G.
1987SoPh..112..347A Altcode:
During the type IV burst on 24 April, 1985 we observed at 234 MHz
an untypical, strong, nearly six hours lasting continuum emission
incorporating several groups of broadband pulsations, zebra patterns,
fiber bursts, and a new fine structure phenomenon. The power spectra of
the groups of broadband pulsations reveal no simple structure. There
is only one common periodic component between 0.3 s and 0.4 s. Slowly
drifting chains of narrowband fiber bursts are described as a new fine
structure by spectrograms and simultaneously recorded single frequency
intensity profiles. A qualitative model of this new fine structure
is suggested.

---------------------------------------------------------
Title: Book Review: Radio continua during solar flares. / Reidel,
1986.
Authors: Karlicky, M.
1987SSRv...45..411K Altcode: 1987SSRv...45..411B
No abstract at ADS

---------------------------------------------------------
Title: Effects of Impulsively Heated Electrons in Solar Flares
Authors: Karlicky, M.
1987BAICz..38..201K Altcode:
Using a one-dimensional particle code, the evolution of impulsively
heated electrons in the flare loop is examined. The processes are
studied in two regimes: with and without the electric current. One run
was made for the system with the constant electric current, simulating
the large inductance of the current loop. It was shown that impulsive
electron heating leads to the formation of a double layer. Moreover,
this heating can trigger the ion-acoustic instability in the current
system of a flare loop. Both these effects increase the flare energy
release. The generated electrostatic high-frequency waves can be
observed as a radio burst.

---------------------------------------------------------
Title: Estimate of Plasma Parameters in a Coronal Loop by Means of
a Fiber Burst
Authors: Aurass, H.; Kurths, J.; Mann, G.; Chernov, G. P.; Karlicky, M.
1987SoPh..108..131A Altcode:
Analyzing a fiber burst occurring in the event on 19 August, 1981,
plasma parameters of the burst source volume are estimated by means
of Kuijpers' (1975) fiber burst model. The derived height dependence
of the density in a coronal loop agrees with an isothermal barometric
loop atmosphere.

---------------------------------------------------------
Title: Dm-Spikes and Their Relation to Other Flare Phenomena in the
October 14, 1983 Event
Authors: Karlický, M.; Messerotti, M.; Ruždjak, V.; Slottje, C.;
Tlamicha, A.; Urpo, S.; Zlobec, P.
1987BAICz..38...42K Altcode:
By using observations in H-alpha and radio frequencies between 169
MHz and 37 GHz, the October 14, 1983 two ribbon flare was analysed. A
coherent picture of the event is given using the standard topology
for two-ribbon flares and describing the dm-spikes as manifestations
of electron acceleration in a reconnection process (with stationary
shock wave). The drifting chains of these spikes are explained by
the movement of this "stationary" shock wave. It is shown that the
behaviour with time of the number density of the spikes is in agreement
with that of the 37 GHz flux and hence that the same population of
accelerated electrons that gave rise to the spikes, also produced the
37 GHz radiation.

---------------------------------------------------------
Title: Solar Radio Continua and the X-Ray Emission during Flares
Authors: Fárník, F.; Karlický, M.; Tlamicha, A.
1987BAICz..38...36F Altcode:
Radio continua measured by the Ondřejov solar radio spectrograph in
the frequency band of 100 - 1000 MHz are compared with the X-ray flux in
the 2 - 320 keV region, measured by the Czechoslovak photometer aboard
the Prognoz 8 satellite. The authors have chosen 20 flare-associated
events, recorded by both instruments from March to August 1981, and,
using the Solar Geophysical Data, they have determined source flares
and their optical characteristics.

---------------------------------------------------------
Title: Radio wave diagnostics of solar active regions. Part I -
mm-cm bands,part II - dm-m bands.
Authors: Karlicky, M.; Krueger, A.
1987PAICz..66..237K Altcode: 1987eram....1..237K
The results of different methods of observation of solar active regions
at mm and cm wavelengths when exploring the source structures and
parameters in the chromosphere and corona are reviewed. Calculations of
emission models which take into account bremsstrahlung and gyromagnetic
radiation are summarized. Diagnostic uses of different kinds of
microwave burst emission are briefly discussed. Decimetric and metric
radio spectral observations as diagnostic tools for the determination
of plasma parameters in the coronal areas of solar active regions
are also reviewed. Attention is given to the radio diagnostics of
solar flares. The most important types of dm and m radio bursts are
presented, and the most recent theoretical and observational results
are summarized.

---------------------------------------------------------
Title: Magnetic field line reconnection by localized enhancement of
resistivity and its interruption.
Authors: Karlicky, Marian
1987PAICz..66..253K Altcode: 1987eram....1..253K
The nonlinear development of magnetic reconnection in a current-sheet
system is studied numerically. The reconnection process, developing from
an initial localized enhancement of electrical resistivity, is at some
instants interrupted by a sharp decrease in electrical resistivity. The
development of this process is studied and the results discussed within
the scope of the solar flare theory.

---------------------------------------------------------
Title: Effects of Impulsively Heated Electrons in Solar Flares
Authors: Karlicky, M.
1987HvaOB..11..109K Altcode:
For the full text see Abstr. 44.073.004.

---------------------------------------------------------
Title: Electrical conductivity in the solar photosphere and
chromosphere
Authors: Kubat, J.; Karlicky, M.
1986BAICz..37..155K Altcode:
The method of computing of isotropic, Pedersen, Hall and Cowling
conductivities for the model of a quiet photosphere and chromosphere
(C-model of VAL) is developed. Numerical results and graphs are
calculated for magnetic fields of 10-2T and 10-4T
using new values of the proton-hydrogen scattering cross-section. In
addition, the graph of conductivities in the solenoid magnetic field
model is presented. A table of the Braginski coefficients calculated
from VAL is also presented.

---------------------------------------------------------
Title: Radio observations of the solar neutron flare of 3 June, 1982
Authors: Karlicky, M.; Aurass, H.; Mann, G.
1986SoPh..104..165K Altcode:
In this paper the solar neutron and white-light flare is studied
on the basis of radioastronomical observations. It is shown that
the 3 June, 1982 flare had an impulsive character. A strong shock
wave (MA ≥ 2.9) was observed unusually soon after the
impulsive phase of the flare. The radio spectrum of this event shows
that the primary acceleration process probably occurred in the region
with an electron density of ne = 4.4 × 1015
m−3. The pulsations of the type IV radio burst, observed
15 min after the mass ejection process, manifest the reconnection
process in the post-flare stage.

---------------------------------------------------------
Title: Plasma diagnosis by means of fiber bursts
Authors: Aurass, H.; Kurts, J.; Mann, G.; Chernov, G. P.; Karlický, M.
1986CoSka..15..327A Altcode:
During the type IV solar radio burst on August 19, 1981 a lot of fiber
bursts were observed. One of them is used for plasma diagnostic in the
source volume. The great frequency extension of the considered fiber
burst allows to estimate the height dependence of the plasma parameters.

---------------------------------------------------------
Title: Neutron increase at Lomnický štít, (June 3 1982) and
character of source flare
Authors: Křivský, L.; Karlický, M.; Kudela, K.
1986CoSka..15..161K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The role of narrowband dm-spikes in solar flares.
Authors: Karlicky, Marian
1986NASCP2449..155K Altcode: 1986rfsf.nasa..155K
The main observational characteristics of narrowband dm-spikes are
summarized. Since the spikes are observed in typical sequences of radio
bursts, a global model of these bursts is presented. The intensity of
the magnetic field in the spike source region, which is of principal
importance, is discussed.

---------------------------------------------------------
Title: White-light flare of 26 July 1981.
Authors: Gesztelyi, L.; Karlicky, M.; Farnik, F.; Gerlei, O.;
Valnicek, B.
1986lasf.conf..163G Altcode: 1986lasf.symp..163G
Making use of series of white light heliograms the authors studied
the development of a flare-active sunspot group in Hale region 17760,
where a white-light flare (WLF) was observed on 26 July 1981. The
WLF appeared in a disintegrating delta-configuration, where rapid
motion of newly emerged spots and of separating fragments of older
umbrae was shearing and distorting the magnetic field. On the basis
of optical, X-ray and radio observations the authors analysed the WLF
event. Some observational indications exist supporting the hypothesis
that the WLF knots are situated in the places of concentrated electric
current which electrically couples sub-photospheric, photospheric
and higher layers. Provided this is true the WL emission has been
interpreted as the response of deep layers of the solar atmosphere to
the dissipation-spreading process propagating along the electric current
system. Intensity of the WLF knots relatively to the photosphere has
been deduced and the power emitted between 545 and 555 nm estimated. The
total energy emitted by the WLF knots is roughly estimated.

---------------------------------------------------------
Title: Narrowband dm-Spikes, Intermediate Drift Bursts and Pulsations
in the Solar Flare of August 19, 1981
Authors: Karlicky, M.
1986BAICz..37....1K Altcode:
In the initial phase (12.51-12.53 UT) of the flare of August 19, 1981,
an interesting group of narrowband dm-spikes, intermediate drift bursts
and pulsations was observed. This paper tries to explain this group
of bursts by an uniform model. It is shown that all these bursts have
connections with acceleration and trapping of superthermal electrons
in the flare loop. The parameters of the flare loop and the electric
field in the acceleration process were estimated. The same 'period'
of intermediate drift bursts and pulsations has been explained. In the
following time, the flare loop under study explodes and a shock wave
(type II radio burst) is generated at the relatively high altitude
of about 100,000 km above the photosphere. This process was connected
with the radio flux decrease on 10 cm.

---------------------------------------------------------
Title: Analysis of the Flare of May 16th, 1981 with a Complex
Space-Time Structure Using Optical, X-Ray Data and Radio Observations
Authors: Ishkov, V. N.; Markeev, A. K.; Fomichev, V. V.; Chernov,
G. P.; Chertok, I. M.; Likin, O. B.; Pisarenko, N. F.; Karlický,
M.; Tlamicha, A.; Fárník, F.; Valniček, B.; Kalman, B.
1985BAICz..36...81I Altcode:
A comprehensive analysis of the flare event of May 16, 1981 was
carried out using burst records, heliograms, and dynamic spectra
of radio emission in the frequency band 1000-45 MHz. Observations
of X-ray emission obtained from the Prognoz-8 satellite were also
used in the analysis. Attention is given to the location and dynamic
characteristics of the H-alpha knots accompanied by a complicated
multicomponent time profile and a strongly varying spectrum of X-ray and
microwave bursts. A substantial change in the frequency spectrum of the
microwave emission was observed during the development of the flare,
with the maximum shifting towards the short-wave part of the cm band
when H-alpha emission approached the sunspots. In the pre-maximum phase
of the flare, sharp changes in the rate of increase of soft X-rays
were correlated with the brightening of existing and upsurging new
knots of H-alpha emission. The radio spectra for different frequency
bands are reproduced in photographic form.

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Title: Narrowband DM Spikes as Indication of Flare Mass Ejection
Authors: Karlicky, M.
1984SoPh...92..329K Altcode:
The paper presents the radio spectra of seven solar flares (May 16,
1981; August 19, 1981; January 31, 1982; February 1, 1982; June 3,
1982; June 7, 1982; and July 12, 1982), whose common feature is the
presence of narrowband dm-spikes. A close relationship was found among
dm-spikes, dm-pulsations and type II radio bursts. Moreover, all flares
under study showed indications of a mass ejection process. Based both
on these facts and on the theory of dm-spikes (Kuijpers et al., 1981),
our observations can be explained by runaway processes in several small
regions within the ejected and tearing magnetic structure of the flare.

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Title: On a model of relationship between type I and type III bursts
activity.
Authors: Karlicky, M.
1984ost1.conf..149K Altcode:
No abstract at ADS

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Title: Flare of March 28, 1980 and its Coronal Radio and Transient
Effects
Authors: Krivsky, L.; Karlicky, M.; Tlamicha, A.; Ruzdjak, V.;
Urbarez, H.
1984sii..conf..217K Altcode:
No abstract at ADS

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Title: X-ray, Hα, and radio observations of the two-ribbon flare
of 16 May, 1981
Authors: Fárník, F.; Kaastra, J.; Kálmán, B.; Karlický, M.;
Slottje, C.; Valniček, B.
1983SoPh...89..355F Altcode:
The paper is a contribution to the study of two-ribbon flares. A variety
of observational material, i.e. Hα pictures, radio spectrum in the
frequency band of 150-1000 MHz, radio map at 6 cm, fluxes at other
frequencies, magnetograms and X-ray flux in a broad energy interval,
enabled us to study the development of the 16 May, 1981 flare. The
onset of the flare could be described by the model of Van Tend and
Kuperus. A diminishing of the magnetic shear during the activation of
the filament was observed. From radio and X-ray data it was found that
pulsed acceleration took place in the region under the rising filament,
the electrons propagating in a limited region both upwards to greater
heights and downwards into the footpoints. Internal oscillations of
the filament were observed. A manifestation of the primary process of
interplanetary shock-wave generation was found. The 6 cm radio sources
could be localized in the footpoints of magnetic loops.

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Title: Book-Review - Solar Magnetohydrodynamics
Authors: Priest, E. R.; Karlicky, M.
1983BAICz..34..378P Altcode:
No abstract at ADS

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Title: Radio Spectrum and Model of White-Light Flare of July 4, 1974
Authors: Karlicky, M.
1983BAICz..34..355K Altcode:
The paper suggests a model of the white-light flare of July 4,
1974 which satisfies both the theoretical considerations and the
actual observations. The observed radio spectrum is interpreted as
an eruptive process that started at heights of more than 50000 km
above the photosphere and was activated by an electron beam. The
radio spectrum further shows that the activation is followed by a
dissipation-spreading process (Heyvaerts, 1981) propagating through
an electric current system towards the photosphere, to the place of
the emission in continuum. In conclusion the radio spectrum of the
white-light flare (1353 UT, July 4, 1974) is compared with the radio
spectrum of its "homologous" flare (0647 UT, July 4, 1974).

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Title: Magnetic Field Potential Approximation and Penumbral Fine
Structure before the White-Light Flare of July 4, 1974
Authors: Karlicky, M.; Suda, J.
1983BAICz..34..282K Altcode:
A comparison is made of the horizontal solar magnetic field component
distribution calculated at the photosphere, with the penumbral fine
structure of the large active group in the McMath active region 13
043 before the white-light flare of July 4, 1974. The magnetic field
is calculated as a potential approximation taking into account the
shape of individual spots in the group. Good agreement was found for
the peripheral portions of the flare activity regions, although strong
deviations were found in and near the location of white-light flare. The
discrepancies in the flare location support the conclusion that the
magnetic field structure in these regions before the white-light flare
have a non-potential component: that electric currents are present
even at the photospheric level. The disappearance of the discrepancies
implies that the direction of the penumbral fibrils after the flare
corresponds more to that of the potential magnetic field approximation.

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Title: Book-Review - Classics in Radio Astronomy
Authors: Sullivan, W. T., III; Karlicky, M.
1983BAICz..34..253S Altcode:
No abstract at ADS

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Title: Method of Estimating Langmuir's Turbulence in a Solar Flare
Authors: Karlicky, M.
1983BAICz..34..100K Altcode:
In principle, the theory of X hard and microwave solar bursts makes
it possible to determine the development of the 'mean' distribution
function of hot or superthermal electrons during the impulse phase
of a flare. On the basis of this development of the distribution
function of electrons, the method described in this paper can be used
to determine the parameters of Langmuir's turbulence, assumed to exist
in a solar flare.

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Title: Evolutionary Electron Beam and MHD Two Stream Instability in
Solar Radio Burst Models
Authors: Karlicky, M.; Krlin, L.
1983BAICz..34...18K Altcode:
This paper represents a contribution to the theory of type III and
IIIb solar radio bursts. It tries to clarify the role of the MHD two
stream instability in the case of the evolutionary electron beam. It
is shown that, in this case, the generation of the MHD two stream
instability depends on strong depression of quasilinear relaxation
(caused by a bump-on-tail instability). The results of this paper
are compared with the ideas used in Smith's and de la Noë's (1976)
model of type IIIb burst.

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Title: Drifting chains of type I radio bursts in the early stage of
the two-ribbon flare of May 16, 1981.
Authors: Karlický, M.; Jiřička, K.
1983ITABO..57...81K Altcode:
In the early stage of the two-ribbon flare of May 16, 1981, a close
relation between drifting chains of type I radio bursts and an
activated rising filament was found. The generation of a weak shock
wave is very probable in this phase of the flare, i.e. the model of
type I radio bursts by Spicer et al. (1981) is in good agreement with
the observations.

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Title: Peculiarities of the development of flare on May 16, 1981 as
observedin optical, X-rays and radio waves.
Authors: Ishkov, V. N.; Markeev, A. K.; Fomichev, V. V.; Chernov,
G. P.; Chertok, I. M.; Likin, O. B.; Pisarenko, N. F.; Valníček,
V.; Karlický, M.; Tlamicha, A.; Fárník, F.; Kálmán, B.
1983PDHO....5..193I Altcode: 1984PDHO....5..193I
On the basis of X-ray, visual and radio observations of the large
flare of 16 May 1981 the conclusion may be drawn that a large flare
is a long duration energy release process, and it can be interpreted
as a sum of smaller flares throughout the active region.

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Title: On the Relationship between the Chromospheric Flares and Type
I Noise Storm
Authors: Karlicky, M.; Kotrc, P.; Urbarz, H.
1982BAICz..33..331K Altcode:
No abstract at ADS

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Title: Radio Observation of Sudden Shock Wave Deceleration above
Solar Flare
Authors: Karlicky, M.; Jiricka, K.; Kepka, O.; Krivsky, L.; Tlamicha,
A.
1982BAICz..33...72K Altcode:
Sudden changes in frequency drift accompanied by broadening of the
frequency spectra and herringbone structure were observed in the initial
phase in three different cases of type II burst observations. The
phenomenon is interpreted as a sudden shock wave deceleration, which is
found to be the limiting factor for the existence of fast shock waves
under coronal conditions, and which may be connected with the second
phase of acceleration in the flare. Type II bursts with a frequency
ratio of about 1.5 and occasionally with a herringbone structure,
correspond to shock waves in turbulent states, while the laminar stage
corresponds to a narrow-band type II burst.

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Title: Drifting chains of Type I radio bursts in the early stage of
the Two Ribbon Flare of May 16, 1981
Authors: Karlicky, M.; JiřiČka, K.
1982nsco.work...81K Altcode:
No abstract at ADS

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Title: Five decades of radio astronomy.
Authors: Grygar, J.; Karlický, M.
1982Rise...63...45G Altcode:
No abstract at ADS

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Title: Type-Iii Bursts and Coronal Temperature
Authors: Karlicky, M.
1981SoPh...71..381K Altcode:
Numerical solution of the interaction of evolutionary electron
beam with coronal plasma shows that the velocity of packet of the
generated Langmuir's waves increases with the increase of coronal
temperature. This effect can be manifested by a dependence of the
drift of type III bursts on the coronal temperature.

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Title: Periodic Fluctuations in the Solar Millimeter Wave Burst
Associated with the Solar Flare on 1978SEP22
Authors: Urpo, S.; Tiuri, M.; Tlamicha, A.; Pracka, M.; Karlicky, M.
1981A&A....93..121U Altcode:
On September 22, 1978 the Sun was mapped at a wavelength of 8 mm
(37 GHz) at the Radio Research Station of the Helsinki University of
Technology in Finland. Enhanced radiation was found in the active region
McMath 15,551. This region was monitored and the time variation of the
radio flux was measured. During the observation a radio burst occurred
between 11 56 and 13 06 UT. It corresponded in time to a flare observed
in this region at N30 E49. The brightness temperature of the burst
was 7900±800 K. The spectrum analysis of the burst indicates that
there were pulsations with periodicities of 2.1 to 2.4s. Compatible
periodicities were also found from the sequence of type III radio
bursts which accompanied this flare. It is proposed that the observed
burst was caused by quasi-periodically accelerated electron beams.

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Title: Estimate of the Spectrum of Langmuir's Turbulence in a Solar
Flare from the X-emission Spectrum
Authors: Karlicky, M.; Farnik, F.
1980BAICz..31..111K Altcode:
With regard to estimating the spectrum and level of Langmuir's
turbulence in the region of a solar flare, the X-spectra of the
flare of October 12, 1977 is considered. Using Brown's (1971) model,
the distribution function of fast electrons has been determined
from three X-emission spectra derived at consecutive (10-second
interval) times. The monotonic increase of the distribution function of
electrons entering the X-emission area indicates that the electrons are
continuously accelerated in the region of the flare. The acceleration
is analyzed in the case where the effect of collision processes was
neglected, and for the case of a strong effect of the collision
processes. For the latter case, a model is outlined in which the
required distribution functions are accelerated by Langmuir's turbulence
in the acceleration region with a filamentary structure.

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Title: The Acceleration of the Electrons with Distribution Function
ƒ ~(v_{0)/v)^δ by Langmuir's Flare Turbulence
Authors: Karlicky, M.
1980BAICz..31..182K Altcode:
The process of acceleration of an evolutionary electron beam by
Langmuir's flare turbulence is studied in two ways. By means of the
diffusion equation in velocity space, Langmuir's turbulence (LT)
is described by the spectrum of a strong LT, and secondly, using
the Fokker-Planck equation, the LT is described by a soliton gas. In
addition, the time in which the original Maxwell distribution function
is accelerated to a distribution function is estimated with the aid
of a computed spectrum and of the soliton gas under the conditions of
the acceleration space. It is suggested that the acceleration space
has a filamentary structure, oriented in the direction of the magnetic
field and vertically.

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Title: Analysis and Interpretation of the Quasiperiodical Structure
of a Type IV Burst
Authors: Pracka, M.; Karlicky, M.
1979BAICz..30..257P Altcode:
This paper deals with the analysis of the type IV radio burst (with a
quasiperiodical structure), observed in the 270 to 470 MHz frequency
range with the radio spectrograph of the Ondrejov Observatory on July
3, 1974. The burst probably originated in the complicated magnetic
structure of active region McMath 13043 following a proton flare. The
method of spectral analysis and signal filtering was used to process the
event. The results were discussed from the point of view of statistical
likelihood. The observed periods of intensity modulation of the burst
are interpreted in the considered model as the periods of generation
and acceleration of electron beams in an X-type magnetic configuration,
as periods in electron beam injections into the coronal plasma taking
into account the finite velocities of propagation of electromagnetic
radiations.

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Title: On the Determination of the Solar Coronal Magnetic Field by
Using Type II Burst Observations and Theories
Authors: Karlicky, M.; Tlamicha, A.
1979BAICz..30..246K Altcode:
No abstract at ADS

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Title: Collision of Two Shock Waves as a Hypothetical Mechanism of
Producing Drifting Radio Bursts in the 400-500 MHz Range
Authors: Karlicky, M.
1978BAICz..29..313K Altcode:
After the proton flare of July 3, 1974 a hitherto unclassified
phenomenon with a diffusion 'banner' and with a considerably
decelerating drift within the type II and III burst drifts range was
observed in the radio dynamic spectrum between 410 and 470 MHz. The
hypothesis is presented that the phenomenon is due to the collision of
two shock waves, propagating against one another, during which the flux
of electromagnetic radiation is considerably enhanced relative to the
sum of the fluxes of the electromagnetic radiation of the individual
shock waves. The Newkirk 4-density model of the corona is used to
describe the phenomenon, the mechanism of plasmon-plasmon conversion in
electromagnetic radiation with a double plasma frequency is considered
and, according to the parameters derived from the dynamic spectrum,
the velocities, radii of curvature and direction of propagation of
the anticipated shock waves are analyzed in a simplified symmetric case.

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Title: Type III Radio Bursts in a Flaming Structure
Authors: Karlicky, M.; Tlamicha, A.
1977BAICz..28..117K Altcode:
This paper interprets the burst of July 3, 1974. The slowly drifting
fine structure in this type III burst is evidence of the existence
of very fast processes in large volumes of the corona. The concept
of a rapidly varying magnetohydrodynamically unstable 'blazing'
magnetic-field structure is developed. Based on this model, the
magnetic-field intensity at specific heights is computed for two times
separated by 1.4 sec.

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Title: Statistical Study of the Time Sequence of CA II Flocculae
and Series of Radio Fluxes During Solar Activity Cycle 20
Authors: Karlicky, M.
1977BAICz..28..200K Altcode:
Eleven one-year time series and an eleven-year time series of the Ca
II plage index and radio fluxes detected at frequencies of 600, 606,
1000, 2000, 2800, 3750, and 9400 MHz are analyzed statistically for the
interval from 1964 to 1974 (roughly the period of solar activity cycle
20). Power spectra, cross spectra, autocorrelation curves, and cross
correlations are computed for each one-year series, and 'mean' spectra
(integrated over 11 years) are obtained and compared with the spectra
for each individual year. Slowly varying components of the radio fluxes
are examined, and an attempt is made to relate the development of the
statistical characteristics of cycle 20 to large-scale manifestations
of their development, shifts in active-region longitudes, and maxima
as well as minima of solar activity. It is found that the closest
statistical relation exists between the Ca II and 1000-MHz series and
that solar cycle 20 can be divided into two phases with respect to the
cross correlations. The results also indicate that lower-frequency
radio sources tend to have longer lifetimes than higher-frequency
sources and that the average synodic rotation period of coronal layers
increases with height above the photosphere.

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Title: The Velocities of Type II Solar Radio Bursts
Authors: Tlamicha, A.; Karlicky, M.
1976BAICz..27....6T Altcode:
This paper is a summary of type II radio bursts identified at Ondrejov
between January 1973 and December 1974 in the frequency range of the
dynamic spectrum 70-810 MHz. The velocities of shock waves in the
individual cases of the type II bursts are given using the fourfold
Newkirk model. Some questions associated with type II radio bursts
and with the propagation of the shock wave into interplanetary space
and into the region of the earth are also discussed.

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Title: The Trajectories of U-type Solar Radio Bursts
Authors: Karlicky, M.; Tlamicha, A.
1976BAICz..27..223K Altcode:
This paper presents the computation of the trajectory of the U-type
solar radio burst observed on October 18, 1974. It also presents the
correction of this trajectory with respect to the finite velocity of
radio-wave propagation. An attempt is made at comparing the trajectory
arcs of the disturbance with the angular dimensions of a sunspot
group. In the special case where the sunspot group is located at the
solar limb, the comparison of the size of the corrected trajectory arcs
with the size of the sunspot group enables trajectories to be selected
by means of the elimination method, to determine the preference of
the trajectory for a certain direction and orientation relative to
the observer and, thus, to determine the possible actual trajectory.