arXiv subjects

Marian Karlicky

Publications and source records attributed to Marian Karlicky.

At least 19 recordsLinked to original sources

arXiv2026

Kinetic Processes to Radio Burst: First Observational-driven Study in Coronal Loops

Understanding the origin of coherent solar radio bursts requires linking macroscopic coronal structures with the kinetic processes responsible for wave generation. We investigate emissions from slowly positively drifting bursts (SPDBs), a specific type of solar radio emission. SPDBs provide observational constraints for modeling beam-plasma interactions in coronal loops, serving as a basis for a multiscale description. We employ a three--stage numerical framework that combines nonlinear force--free field (NLFFF) magnetic extrapolation, guiding--center simulations, and fully kinetic particle--in--cell (PIC) modeling. The background plasma density is described using a hydrostatic model consistent with active--region conditions, producing a plasma--frequency gradient comparable to that inferred from the observed SPDBs spectrum. Energetic electrons injected near the loop top evolve through magnetic mirroring, pitch--angle scattering, turbulence development, and partial precipitation. Evolved velocity distribution functions (EVDFs) are sampled after approximately one bounce period and used in PIC simulations to evaluate emission properties. The results show that the evolved beam distribution of energetic electrons predominantly excites beam--Langmuir waves and fundamental plasma emission along the loop, with the emission intensity gradually decreasing from the loop top toward the footpoint. The modest initial beam velocity of energetic electrons explains the inefficient generation of harmonic plasma emission. The temporal evolution of the modeled emission reproduces key SPDB characteristics, including the ~ 4s duration and frequency drift behavior. These results suggest plasma emission explains the mechanisms behind SPDB generation and demonstrate the feasibility of a unified model connecting coronal magnetic topology, particle transport, and radio emission.

astro-ph.SR↗

arXiv2022

Filament Leg--Leg Reconnection as a Source of Prominent Supra-Arcade Downflows

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.

astro-ph.SR↗

arXiv2020

Radio, EUV, and X-Ray Observations During a Filament Rise in the 2011 June 7 Solar Flare

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, similar to that of the rising filament. In association with this filament rise, transient X-ray sources and extreme ultaviolet (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.

astro-ph.SR↗

arXiv2019

Topological structures of velocity and electric field in the vicinity of a cusp-type magnetic null point

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 non-ideal Ohm's law concerning the Poincare classes of all involved physical fields in 2D 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 2D standard magnetic cusp.

physics.plasm-ph↗

arXiv2018

Solar radio burst associated with the falling bright EUV blob

At the beginning of the 4 November 2015 flare, in the 1300 -- 2000 MHz frequency range, we observed a very rare slowly positively drifting burst. We searched for associated phenomena in simultaneous EUV observations made by IRIS, SDO/AIA, Hinode/XRT and in H alpha 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 the velocity of about 280 km/s. The dark loop was visible in H alpha but disappeared afterwards. Furthermore, we found that the falling blob interacted with the chromosphere as expressed by a sudden change of the H alpha spectra at the location of this interaction. Considering different possibilities we propose that the observed slowly positively drifting burst is generated by the thermal conduction front formed in front of the falling hot EUV blob.

astro-ph.SR↗

arXiv2017

Hot-cold plasma transition region: collisionless case

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.

astro-ph.SR↗

arXiv2017

Shock-reflected electrons and X-ray line spectra

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. 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. 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.

astro-ph.SR↗

arXiv2017

Are chains of type I radio bursts generated by similar processes as drifting pulsation structures observed during solar flares?

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.

astro-ph.SR↗

arXiv2017

Electric current filamentation induced by 3D plasma flows in the solar corona

Many magnetic structures in the solar atmosphere evolve rather slowly so that they can be assumed as (quasi-)static or (quasi-)stationary and represented via magneto-hydrostatic (MHS) or stationary magneto-hydrodynamic (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 non-canonical transformation method produces quasi-3D solutions of stationary MHD by mapping 2D or 2.5D MHS equilibria to corresponding stationary MHD states, i.e., 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 provide the base 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 non-linear MHS states, namely force-free fields, by stationary flows. We find that force-free fields with non-linear flows only arise under severe restrictions of the field-line geometry and of the magnetic flux density distribution.

astro-ph.SR↗

arXiv2016

Diagnosing the Source Region of a Solar Burst on 26 September 2011 by Microwave Type III Pairs

This work reports a peculiar and interesting train of microwave type III pair bursts in the impulsive rising phase of a solar flare on 2011 September 26. The observations include radio spectrometers at frequency of 0.80 - 2.00 GHz, hard X-ray (RHESSI and FERMI), EUV images of SWAP/PROBA-2 and magnetogram of HMI/SDO. By using a recently developed method (Tan et al. 2016a), we diagnosed the plasma density, temperature, plasma beta, 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: (1) The plasma density, temperature, magnetic field, and the distance between the acceleration region and the emission start sites almost have no obvious variations during the period of type III pair trains, while the energy of electrons has an obvious peak value which is consistent to the hard X-ray emission. (2) The plasma beta is much higher than an unity showing a highly dynamic process near the emission start site of type III bursts. (3) Although the reversed-slope type III branches drift slower at one order of magnitude than that of the normal type III branches, the related downgoing and upgoing electrons still could have same order of magnitude of energy. These facts indicate that both of the upgoing and downgoing electrons are possibly accelerated by similar mechanism and in a small source region. This diagnostics can help us to understand the microphysics in the source region of solar bursts.

astro-ph.SR↗

arXiv2016

Slipping Magnetic Reconnection, Chromospheric Evaporation, Implosion, and Precursors in the 2014 September 10 X1.6-Class Solar Flare

We investigate the occurrence of slipping magnetic reconnection, chromospheric evaporation, and coronal loop dynamics in the 2014 September 10 X-class flare. The slipping reconnection is found to be present throughout the flare from its early phase. Flare loops are seen to slip in opposite directions towards 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 \textit{IRIS} 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 non-thermal X-ray emission are signatures of the flare itself, progressing from the early phase towards 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 3D.

astro-ph.SR↗

arXiv2016

Microwave Type III Pair Bursts in Solar Flares

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 reported 11 microwave type III pair events in 9 flares observed by radio spectrometers in China and the Czech Republic at frequency of 0.80 - 7.60 GHz during 1994 - 2014. These type III pairs occurred in flare impulsive and postflare phases with separate frequency in range of 1.08 - 3.42 GHz and frequency gap 10 - 1700 MHz. The frequency drift increases with the separate frequency (f_{x}), the lifetime of each burst is anti-correlated to f_{x}, while the frequency gap is independent to f_{x}. 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 frequency, longer lifetime, wider frequency gap, and slower frequency drift than that occurring in postflare phase. And 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 temperature higher than 10^{7} K . These results provide new constraints to the acceleration mechanism in solar flares.

astro-ph.SR↗

arXiv2015

Diagnose Physical Conditions Near the Flare Energy-release Sites from Observations of Solar Microwave Type III Bursts

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 do diagnose these physical conditions. Solar microwave type III burst is believed to be a sensitive signature of the primary energy release and electron accelerations in solar flares. This work takes into account the effect of magnetic field on the plasma density and developed s 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 applied these formulas to three groups of microwave type III pairs in a 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.

astro-ph.SR↗

arXiv2015

Quasi-periodic Fast-mode Magnetosonic Wave Trains Within Coronal Waveguides Associated with Flares and CMEs

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 within funnel-shaped waveguides in the wakes of coronal mass ejections (CMEs). QFPs can carry sufficient energy fluxes required for coronal heating during their occurrences. 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.

astro-ph.SR↗

arXiv2015

Flare processes evolution and polarization changes of fine structures of solar radio emission in the April 11, 2013 event

The measurement of positions and sizes of radio sources in the observations of solar radio spectral fine structures in an M6.5 flare on April 11, 2013 were observed simultaneously by several radio instruments at four different observatories: Chinese Solar Broadband Radio Spectrometers at Huairou (SBRS/Huairou), Ondrejov Radio spectrograph in the Czech Republic (ORSC/Ondrejov), Badary Broadband Microwave spectropolarimeter (BMS/Irkutsk), and spectrograph/IZMIRAN (Moscow, Troitsk). The fine structures include microwave zebra patterns (ZP), fast pulsations, and fibers. They were observed during the flare brightening located at the tops of a loop arcade. The dynamics of the polarization was associated with the motion of the flare exciter, which was observed in EUV images at 171A and 131A (SDO/AIA). Combining magnetograms observed by the SDO Helioseismic and Magnetic Imager (HMI) with the homologous assumption of EUV flare brightening 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.

astro-ph.SR↗

arXiv2015

Imaging and Spectroscopic Observations of a Transient Coronal Loop: Evidence for the Non-Maxwellian $κ$-Distributions

We report on the SDO/AIA and Hinode/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 three hours 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 DEM diagnostics as a function of $κ$. Fe XI--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 257.772Åselfblend, we diagnose $κ$ $\lesssim$ 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 $κ$ $\lesssim$ 2. These results represent the first positive diagnostics of $κ$-distributions in the solar corona despite the limitations imposed by calibration uncertainties.

astro-ph.SR↗

arXiv2015

MHD flows at astropauses and in astrotails

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.

astro-ph.SR↗

arXiv2014

A Very Small and Super Strong Zebra Pattern Burst at the Beginning of a Solar Flare

Microwave emission with spectral zebra pattern structures (ZPs) is observed frequently in solar flares and the Crab pulsar. The previous observations show that ZP is only a structure overlapped on the underlying broadband continuum with slight increments and decrements. This work reports an extremely unusual strong ZP burst occurring just at the beginning of a solar flare observed simultaneously by two radio telescopes located in China and Czech Republic and by the extreme ultraviolet (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 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 short duration just at the beginning of the flare.

astro-ph.SR↗