arXiv subjects

I. V. Zimovets

Publications and source records attributed to I. V. Zimovets.

At least 19 recordsLinked to original sources

arXiv2026

Electron Acceleration and Plasma Heating in an Impulsive Confined C-class Solar Flare

A detailed analysis of the impulsive C2.8 solar flare SOL2023-03-19T02:12 is presented, focusing on the microwave (MW) and X-ray domains. The flare was selected because of its impulsive nature, the relatively simple magnetic morphology of its parent active region (AR) NOAA 13256, its confined evolution, its moderate intensity, pronounced non-stationary temporal behaviour, and the availability of a unique multi-wavelength dataset. This dataset includes MW spectral observations in the frequency range 2.8-12 GHz obtained with the new Solar Radio Spectropolarimeter (SOLARSPEL), together with MW images from the Siberian Radioheliograph (SRH). The flare was also observed by two imaging X-ray telescopes, Solar Orbiter/STIX and ASO-S/HXI. Nonlinear force-free field extrapolations are used to reconstruct the three-dimensional magnetic configuration of the AR. We present evidence for a direct coupling between the thermal plasma and the non-thermal electron population in the frame of collisionless plasma during the initial flare stage. Some simple relationships about electron acceleration process are presented and discussed. Analysis of the extrapolated magnetic field indicates that the flare onset was associated with a system of low-lying sheared magnetic loops located along the polarity inversion line (PIL). Given the confined nature of the event and the reconstructed magnetic configuration, we infer that magnetic reconnection most likely occurred within current sheets possessing a substantial guide-field component. The observed non-stationary QPPs in the non-thermal emission, with periods decreasing from approximately 15 to 9 s, are interpreted as signatures of a sequence of magnetic reconnection episodes occurring in different magnetic structures and triggered quasi-periodically by a process that remains uncertain, but which may involve propagating slow magnetoacoustic waves.

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arXiv2025

On the possibility of using decayless kink oscillations of coronal loops to forecast powerful solar flares and coronal mass ejections

This work investigates the decayless kink oscillations of solar coronal loops and examines possible changes in their behaviour in active regions (ARs) before powerful solar flares (M- and X-class) and in the absence of powerful flares. To this end, we analysed 14 ARs with powerful flares and 14 ARs without powerful flares. For each event, images obtained in the 171 Åand 94 ÅAIA/SDO channels with 12-second cadence for 4 hours before the flare were retrieved and analysed. For ARs without powerful flares, arbitrary time intervals of similar duration were considered for comparison. Since the decayless oscillations have a very low amplitude (1-2 AIA/SDO pixels), we used the Motion Magnification technique to amplify the amplitude of these oscillations. Time-distance maps were constructed from the processed images in the 171 Åchannel, from which oscillatory patterns were extracted 'manually'. Wavelet analysis was performed to check for changes in the oscillation period. No systematic changes were found. No obvious differences in the behaviour of oscillations in ARs with and without powerful flares were detected either. Additional information was obtained on coronal mass ejections (CMEs) from ARs in the vicinity of the time intervals under consideration. Based on the results of the analysis of a small sample of events, we came to the preliminary conclusion that the registration and analysis of decayless kink oscillations of high (~ 100-600 Mm) coronal loops based on this methodology is not promising for predicting powerful flares and CMEs.

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arXiv2025

Investigation of possible precursors of solar flares in the active region 12230 On December 9, 2014

The question of the nature of precursors of solar flares, as well as their relationship with subsequent flares, still has no unambiguous answer. This is due, in particular, to the lack of systematic statistical work, the relative incompleteness (in isolation from the context of the development of the entire active region) of studies of individual events and the ambiguity of the term 'precursor' itself. In this paper, we consider the dynamics of the NOAA 12230 active region (AR), in which a series of homologous flares (C5-C9) occurred on December 9, 2014 within 12 hours, with an average frequency of about 2 hours. This AR was characterized by a rapid increase in flare activity followed by a rapid decay, which can be considered as a good example for studying potential precursors of flare series. We investigated the evolution of AR 12230 over a relatively long period (several days) and its transition from the 'no-flare' state to the flare-active regime. For this purpose, we study the magnetic field dynamics using SDO/HMI vector magnetograms, UV-EUV images based on SDO/AIA data, and X-ray observations from GOES/XRS and RHESSI data. We conclude that the significant increase in the chromospheric radiation variations against the background of a small flux of soft X-ray and UV emission from the corona observed on December 8, 2014, together with the magnetic flux emergence, can be considered as a precursor to a series of flares. The results show the importance and prospects of applying new methods of synoptic observations of the Sun in the context of collecting statistics ("history") of the AR energy release in different ranges of the electromagnetic spectrum.

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arXiv2025

Magnetic energies (and some other parameters) in solar active regions of different Hale and McIntosh classes: statistical analysis for 2010-2024

A statistical analysis of magnetic energies of the nonlinear force-free and potential fields, and their difference (a proxy for the free magnetic energy) in active regions (ARs) on the Sun of different Hale (Mount Wilson) and McIntosh classes for the period from May 1, 2010 to June 12, 2024 is presented. The magnetic fields in ARs are calculated using the GX Simulator based on the information about ARs contained in the daily Solar Region Summary (SRS) files provided by the NOAA SWPC and vector magnetograms by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Total unsigned and signed magnetic fluxes and vertical electric currents on the photosphere are also calculated. For the parameters considered, distributions have been determined in total for all ARs and separately for each Hale and McIntosh class. Minimum, maximum, mean values of the parameters and standard deviations were calculated for each class. The information about the parameters is presented in the form of graphs and tables. The magnetic energies, unsigned magnetic flux, unsigned vertical current, as well as the integral number of sunspots, number of ARs, and area of sunspots, integrated over ARs visible per day on the solar disk, exhibit similar approximately 11.6-year cyclicity. On average, magnetic energies of ARs increase with increasing Hale and McIntosh class, while the average fraction of the free magnetic energy in ARs of different classes differs weakly. We also found that the Poisson Flare Probabilities (PFPs) correlate with the parameters, and the Pearson correlation coefficient is up to 0.89. The results reveal relationships between various parameters of ARs and may be used in developing prediction of space weather effects.

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arXiv2021

Kink oscillations of coronal loops

Kink oscillations of coronal loops, i.e., standing kink waves, is one of the most studied dynamic phenomena in the solar corona. The oscillations are excited by impulsive energy releases, such as low coronal eruptions. Typical periods of the oscillations are from a few to several minutes, and are found to increase linearly with the increase in the major radius of the oscillating loops. It clearly demonstrates that kink oscillations are natural modes of the loops, and can be described as standing fast magnetoacoustic waves with the wavelength determined by the length of the loop. Kink oscillations are observed in two different regimes. In the rapidly decaying regime, the apparent displacement amplitude reaches several minor radii of the loop. The damping time which is about several oscillation periods decreases with the increase in the oscillation amplitude, suggesting a nonlinear nature of the damping. In the decayless regime, the amplitudes are smaller than a minor radius, and the driver is still debated. The review summarises major findings obtained during the last decade, and covers both observational and theoretical results. Observational results include creation and analysis of comprehensive catalogues of the oscillation events, and detection of kink oscillations with imaging and spectral instruments in the EUV and microwave bands. Theoretical results include various approaches to modelling in terms of the magnetohydrodynamic wave theory. Properties of kink oscillations are found to depend on parameters of the oscillating loop, such as the magnetic twist, stratification, steady flows, temperature variations and so on, which make kink oscillations a natural probe of these parameters by the method of magnetohydrodynamic seismology.

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arXiv2020

Flare Energy Release at the Magnetic Field Polarity Inversion Line During M1.2 Solar Flare of 2015 March 15. II. Investigation of Photospheric Electric Current and Magnetic Field Variations Using HMI 135-second Vector Magnetograms

This work is a continuation of Paper I [Sharykin et al., 2018] devoted to analysis of nonthermal electron dynamics and plasma heating in the confined M1.2 class solar flare SOL2015-03-15T22:43 revealing energy release in the highly sheared interacting magnetic loops in the low corona, above the polarity inversion line (PIL). The scope of the present work is to make the first extensive quantitative analysis of the photospheric magnetic field and photospheric vertical electric current (PVEC) dynamics in the confined flare region near the PIL using new vector magnetograms obtained with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) with high temporal resolution of 135 s. Data analysis revealed sharp changes of the magnetic structure and PVEC associated with the flare onset near the PIL. It was found that the strongest plasma heating and electron acceleration were associated with the largest increase of the magnetic reconnection rate, total PVEC and effective PVEC density in the flare ribbons. Observations and non-linear force-free field (NLFFF) extrapolations showed that the magnetic field structure around the PIL is consistent with the tether-cutting magnetic reconnection (TCMR) geometry. We gave qualitative interpretation of the observed dynamics of the flare ribbons, magnetic field and PVEC, and electron acceleration, within the TCMR scenario.

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arXiv2020

Relationships between Photospheric Vertical Electric Currents and Hard X-Ray Sources in Solar Flares: Statistical Study

There are still debates whether particle acceleration in solar flares may occur due to interruption of electric currents flowing along magnetic loops. To contribute to this problem, we performed the first statistical study of relationships between flare hard X-ray (HXR; $50-100$ keV) sources observed by the \textit{Ramaty High-Energy Solar Spectroscopic Imager} (RHESSI) and photospheric vertical electric currents (PVECs, $j_{r}$) calculated using vector magnetograms obtained with the Helioseismic and Magnetic Imager (HMI) on-board the \textit{Solar Dynamics Observatory} (SDO). A sample of 48 flares, from C3.0 to X3.1 class, observed in central part of the solar disk by both instruments in 2010--2015 was analyzed. We found that $\approx 70$\% of all HXR sources overlapped with islands or ribbons of enhanced ($\left| j_{r} \right| \gtrsim 10^{4}$ statampere~cm$^{-2}$) PVECs. However, less than $\approx 40$\% of the HXR sources overlapped with PVEC maxima, with an accuracy of $\pm 3^{\prime\prime}$. More than in half of the flares there were HXR sources outside regions of enhanced PVECs. We found no correlation between intensity of the HXR sources and PVEC density or total PVEC under them. No systematic dissipation of PVECs under the HXR sources was found during the flares. Collectively, the results do not support the current-interruption flare models. However, the results indicate the importance of the presence of longitudinal currents in flare regions. Understanding of their specific role in the processes of energy release, plasma heating, and acceleration of particles requires further investigation.

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arXiv2019

Density distribution of photospheric vertical electric currents in flare active regions of the Sun

Solar active regions contain electric currents. Information on the distribution of currents is important for understanding the processes of energy release on the surface of the Sun and in the overlying layers. The paper presents an analysis of the probability density function (PDF) of the absolute value of the photospheric vertical electric current density ($|j_z|$) in 48 active regions before and after flares in 2010--2017. Calculation of $|j_z|$ is performed by applying the differential form of Ampere's circuital law to photospheric vector magnetograms obtained from observations of the Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO). It has been established that for the studied active regions PDF($|j_z|$) is described by the Gauss function in the low-$|j_z|$ region ($|j_z| < 10110 \pm 1321$ statampere/cm$^2$) and the decaying power-law function in the region of higher $|j_z|$ values. Also, for some active regions PDF($|j_z|$) can be described by the special kappa-function. The distributions of the parameters of the approximating functions are obtained using the least squares method. The average absolute value of the power-law function index is $3.69 \pm 0.51$, and $3.99 \pm 0.51$ of the kappa-function. No systematic changes in parameters during the flares are detected. An explicit connection between the parameters and the flare X-ray class, as well as with the Hale magnetic class of the active regions, is not found. Arguments are presented in favor of the suggestion that the Gaussian distribution in the low-value region of PDF($|j_z|$) represents noise in the data, while the power-law "tail" reflects the nature of electric currents in the solar active regions.

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arXiv2018

Roles of photospheric motions and flux emergence in the major solar eruption on 2017 September 6

We study the magnetic field evolution in the active region (AR) 12673 that produced the largest solar flare in the past decade on 2017 September 6. Fast flux emergence is one of the most prominent features of this AR. We calculate the magnetic helicity from photospheric tangential flows that shear and braid field lines (shear-helicity), and from normal flows that advect twisted magnetic flux into the corona (emergence-helicity), respectively. Our results show that the emergence-helicity accumulated in the corona is $-1.6\times10^{43}~Mx^2$ before the major eruption, while the shear-helicity accumulated in the corona is $-6\times10^{43}~Mx^2$, which contributes about 79\% of the total helicity. The shear-helicity flux is dominant throughout the overall investigated emergence phase. Our results imply that the emerged fields initially contain relatively low helicity. Much more helicity is built up by shearing and converging flows acting on preexisted and emerging flux. Shearing motions are getting stronger with the flux emergence, and especially on both sides of the polarity inversion line of the core field region. The evolution of the vertical currents shows that most of the intense currents do not appear initially with the emergence of the flux, which implies that most of the emerging flux is probably not strongly current-carrying. The helical magnetic fields (flux rope) in the core field region are probably formed by long-term photospheric motions. The shearing and converging motions are continuously generated driven by the flux emergence. AR 12673 is a representative as photospheric motions contribute most of the nonpotentiality in the AR with vigorous flux emergence.

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arXiv2018

New estimation of non-thermal electron energetics in the giant solar flare on 28 October 2003 based on Mars Odyssey observations

A new estimation of the total number and energy of the non-thermal electrons produced in the giant ($>\text{X}17$) solar flare on 2003 October 28 is presented based on the analysis of the observations of the hard X-ray (HXR) emission by the High Energy Neutron Detector (HEND) onboard the Mars Odyssey spacecraft orbiting Mars. Previous estimations of the non-thermal electron energy based on the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) data were incomplete since RHESSI missed the peak of the flare impulsive phase. In contrast, HEND observed the whole flare. We used two models to estimate the energy of the non-thermal electrons: the cold thick target model and the warm thick target model. We found that, depending on the model used and the low-energy cutoff ($E_\mathrm{c}$) of the non-thermal electrons, the estimate of their total energy in the entire flare can vary from $2.3 \times 10^{32}$ to $6.2 \times 10^{33}$ ergs. The lowest estimate, $2.3 \times 10^{32}$ ergs, obtained within the cold thick target model and fixed $E_\mathrm{c}=43$ keV, is consistent with the previous estimate. In this case, non-thermal electrons accelerated in the peak of the flare impulsive phase missed by RHESSI contained approximately $40\%$ of the total energy of non-thermal electrons of the entire flare. The highest value, $6.2 \times 10^{33}$ ergs, obtained with the cold thick target model and fixed $E_\mathrm{c}=10$ keV, looks abnormally high, since it exceeds the total non-potential magnetic energy of the parent active region and the total bolometric energy radiated in the flare. Our estimates also show that the total number and energetics of the HXR-producing electrons in the flare region is a few orders of magnitude higher than of the population of energetic electrons injected into interplanetary space.

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arXiv2018

Radio, Hard X-Ray, and Gamma-Ray Emissions Associated with a Far-Side Solar Event

The SOL2014-09-01 far-side solar eruptive event produced hard electromagnetic and radio emissions observed with detectors at near-Earth vantage points. Especially challenging was a long-duration >100 MeV $γ$-ray burst probably produced by accelerated protons exceeding 300 MeV. This observation raised a question of how high-energy protons could reach the Earth-facing solar surface. Some preceding studies discussed a scenario in which protons accelerated by a CME-driven shock high in the corona return to the solar surface. We continue with the analysis of this challenging event, involving radio images from the Nançay Radioheliograph and hard X-ray data from the High Energy Neutron Detector (HEND) of the Gamma-Ray Spectrometer onboard the Mars Odyssey space observatory located near Mars. HEND recorded unocculted flare emission. The results indicate that the emissions observed from the Earth's direction were generated by flare-accelerated electrons and protons trapped in static long coronal loops. Their reacceleration is possible in these loops by a shock wave, which was excited by the eruption, being initially not CME-driven. The results highlight the ways to address remaining questions.

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arXiv2018

Flare Energy Release in the Magnetic Field Polarity Inversion Line During M1.2 Solar Flare of March 15, 2015. Paper I. Onset of Plasma Heating and Electrons Acceleration

We present the study of SOL2015-03-15 M1.2 flare, revealing acceleration of electrons and plasma heating in the sheared twisted magnetic structure in the polarity inversion line (PIL). The scope is to make the analysis of nonthermal electrons dynamics and plasma heating in the highly stressed magnetic loops interacting in the PIL by using X-ray, microwave, ultraviolet, and optical observations. It is found that the most probable scenario for the energy release in the PIL is the tether-cutting magnetic reconnection between the low-lying (3 Mm above the photosphere) magnetic loops within a twisted magnetic flux rope. Energetic electrons with the hardest spectrum were appeared at the onset of plasma heating up to the super-hot temperature of 40 MK. These electrons are localized in a thin magnetic channel with width of around 0.5 Mm with high average magnetic field of about 1200 G. The plasma beta in the super-hot region is less than 0.01. The estimated density of accelerated electrons is about 10^9 cm^-3 that is much less than the super-hot plasma density. The energy density flux of non-thermal electrons is estimated up to 3x10^12 ergs cm^-2s^-1 that is much higher than in the currently available radiative hydrodynamic models. These results revealed that one need to develop new self-consisting flare models reproducing 3D magnetic reconnection in the PIL with strong magnetic field, spatial filamentation of energy release, formation of high energy density populations of nonthermal electrons and appearance of the super-hot plasma.

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arXiv2018

Magnetic structure of solar flare regions producing hard X-ray pulsations

We present analysis of the magnetic field in seven solar flare regions accompanied by the pulsations of hard X-ray (HXR) emission. These flares were studied by Kuznetsov et al. (2016) (Paper~I), and chosen here because of the availability of the vector magnetograms for their parent active regions (ARs) obtained with the SDO/HMI data. In Paper~I, based on the observations only, it was suggested that a magnetic flux rope (MFR) might play an important role in the process of generation of the HXR pulsations. The goal of the present paper is to test this hypothesis by using the extrapolation of magnetic field with the non-linear force-free field (NLFFF) method. Having done this, we found that before each flare indeed there was an MFR elongated along and above a magnetic polarity inversion line (MPIL) on the photosphere. In two flare regions the sources of the HXR pulsations were located at the footpoints of different magnetic field lines wrapping around the central axis, and constituting an MFR by themselves. In five other flares the parent field lines of the HXR pulsations were not a part of an MFR, but surrounded it in the form of an arcade of magnetic loops. These results show that, at least in the analyzed cases, the "single flare loop" models do not satisfy the observations and magnetic field modeling, while are consistent with the concept that the HXR pulsations are a consequence of successive episodes of energy release and electron acceleration in different magnetic flux tubes (loops) of a complex AR. An MFR could generate HXR pulsations by triggering episodes of magnetic reconnection in different loops in the course of its non-uniform evolution along an MPIL. However, since three events studied here were confined flares, actual eruptions may not be required to trigger sequential particle acceleration episodes in the magnetic systems containing an MFR.

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arXiv2018

Flare Energy Release in the Lower Solar Atmosphere Near the Magnetic Field Polarity Inversion Line

We study flare processes in the solar atmosphere using observational data for a M1-class flare of June 12, 2014, obtained by New Solar Telescope (NST/BBSO) and Helioseismic Magnetic Imager (HMI/SDO). The main goal is to understand triggers and manifestations of the flare energy release in the photosphere and chromosphere using high-resolution optical observations and magnetic field measurements. We analyze optical images, HMI Dopplergrams and vector magnetograms, and use Non-Linear Force-Free Field (NLFFF) extrapolations for reconstruction of the magnetic topology and electric currents. The NLFFF modelling reveals interaction of two magnetic flux ropes with oppositely directed magnetic field in the PIL. These flux ropes are observed as a compact sheared arcade along the PIL in the high-resolution broad-band continuum images from NST. In the vicinity of PIL, the NST H alpha observations reveal formation of a thin three-ribbon structure corresponding to a small-scale photospheric magnetic arcade. The observational results evidence in favor of location of the primary energy release site in the chromospheric plasma with strong electric currents concentrated near the polarity inversion line. In this case, magnetic reconnection is triggered by the interacting magnetic flux ropes forming a current sheet elongated along the PIL.

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arXiv2017

Catalog of Hard X-ray Solar Flares Detected with Mars Odyssey/HEND from the Mars Orbit in 2001-2016

The study of nonstationary processes in the Sun is of great interest, and lately, multiwavelength observations and registration of magnetic fields are carried out by means of both ground-based telescopes and several specialized spacecraft (SC) on near-Earth orbits. However the acquisition of the new reliable information on their hard X-ray radiation remains demanded, in particular if the corresponding SC provide additional information, e.g. in regard to the flare observations from the directions other than the Sun-Earth direction. In this article we present a catalog of powerful solar flares registered by the High Energy Neutron Detector (HEND) device designed in the Space Research Institute (IKI) of Russian Academy of Sciences. HEND is mounted onboard the 2001 Mars Odyssey spacecraft. It worked successfully during the flight to Mars and currently operates in the near-Mars orbit. Besides neutrons, the HEND instrument is sensitive to the hard X-ray and gamma radiation. This radiation is registered by two scintillators: the outer one is sensitive to the photons above 40 keV and the inner one to the photons above 200 keV. The catalog was created with the new procedure of the data calibration. For most powerful 60 solar flares on the visible and on the far sides of the Sun (in respect to a terrestrial observer), we provide time profiles of flare radiation, summed over all the channels of X-ray and in some cases of gamma-ray bands as well as the spectra and characteristics of their power law approximation. We briefly discuss the results of the previous articles on the study of the Sun with HEND instrument and the potential of the further use of these data.

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arXiv2016

Spatio-temporal dynamics of sources of hard X-ray pulsations in solar flares

We present systematic analysis of spatio-temporal evolution of sources of hard X-ray (HXR) pulsations in solar flares. We concentrate on disk flares whose impulsive phase are accompanied by a series of more than three peaks (pulsations) of HXR emission detected in the RHESSI 50-100 keV channel with 4-second cadence. 29 such flares observed from February 2002 to June 2015 with time differences between successive peaks of 8-270 s are studied. The main observational result is that sources of HXR pulsations in all flares are not stationary, they demonstrate apparent displacements from pulsation to pulsation. The flares can be subdivided into two groups depending on character of dynamics of HXR sources. The group-1 consists of 16 flares (55%) with systematic dynamics of HXR sources from pulsation to pulsation with respect to a magnetic polarity inversion line (MPIL), which has simple extended trace on the photosphere. The group-2 consists of 13 flares (45%) with more chaotic displacements of HXR sources with respect to an MPIL having more complicated structure. Based on the observations we conclude that the mechanism of flare HXR pulsations is related to successive triggering of energy release in different magnetic loops. Group-1 flare regions consist of loops stacked into magnetic arcades extended along MPILs. Group-2 flare regions have more complicated magnetic structures and loops are arranged more chaotically. We also found that at least 14 (88%) group-1 flares and 11 (85%) group-2 flares are accompanied by coronal mass ejections, i.e. the majority of flares studied are eruptive events. This gives an indication that eruptive processes play important role in generation of HXR pulsations. We suggest that an erupting flux rope can act as a trigger of energy release. Its successive interaction with different loops can lead to apparent motion of HXR sources and to a series of HXR pulsations.

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arXiv2016

Observation of quasi-periodic solar radio bursts associated with propagating fast-mode waves

Radio emission observations from the Learmonth and Bruny Island radio spectrographs are analysed to determine the nature of a train of discrete, periodic radio \lq sparks\rq (finite-bandwidth, short-duration isolated radio features) which precede a type II burst. We analyse extreme ultraviolet (EUV) imaging from SDO/AIA at multiple wavelengths and identify a series of quasi-periodic rapidly-propagating enhancements, which we interpret as a fast wave train, and link these to the detected radio features. The speeds and positions of the periodic rapidly propagating fast waves and the coronal mass ejection (CME) were recorded using running-difference images and time-distance analysis. From the frequency of the radio sparks the local electron density at the emission location was estimated for each. Using an empirical model for the scaling of density in the corona, the calculated electron density was used to obtain the height above the surface at which the emission occurs, and the propagation velocity of the emission location. The period of the radio sparks, $δt_\mathrm{r}$=1.78$\pm$0.04 min, matches the period of the fast wave train observed at 171 $Å$, $δt_\mathrm{EUV}$=1.7 $\pm$ 0.2 min. The inferred speed of the emission location of the radio sparks, 630 km s$^{-1}$, is comparable to the measured speed of the CME leading edge, 500 km s$^{-1}$, and the speeds derived from the drifting of the type II lanes. The calculated height of the radio emission (obtained from the density) matches the observed location of the CME leading edge. From the above evidence we propose that the radio sparks are caused by the quasi-periodic fast waves, and the emission is generated as they catch up and interact with the leading edge of the CME.

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arXiv2016

Observational Investigation of Energy Release in the Lower Solar Atmosphere of a Solar Flare

We study flare processes in the lower solar atmosphere using observational data for a M1-class flare of June 12, 2014, obtained by New Solar Telescope (NST/BBSO) and Helioseismic Magnetic Imager (HMI/SDO). The main goal is to understand triggers and manifestations of the flare energy release in the lower layers of the solar atmosphere (the photosphere and chromosphere) using high-resolution optical observations and magnetic field measurements. We analyze optical images, HMI Dopplergrams and vector magnetograms, and use Non-Linear Force-Free Field (NLFFF) extrapolations for reconstruction of the magnetic topology. The NLFFF modelling reveals interaction of oppositely directed magnetic flux-tubes in the PIL. These two interacting magnetic flux tubes are observed as a compact sheared arcade along the PIL in the high-resolution broad-band continuum images from NST. In the vicinity of the PIL, the NST H alpha observations reveal formation of a thin three-ribbon structure corresponding to the small-scale photospheric magnetic arcade. Presented observational results evidence in favor of location of the primary energy release site in the dense chromosphere where plasma is partially ionized in the region of strong electric currents concentrated near the polarity inversion line. Magnetic reconnection may be triggered by two interacting magnetic flux tubes with forming current sheet elongated along the PIL.

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