Solar Flares Research Articles

The effect of data-driving and relaxation models on magnetic flux rope evolution and stability

Understanding the flux rope eruptivity and effects of data driving in modelling solar eruptions is crucial for correctly applying different models and interpreting their results. We aim to investigate these by analysing the fully data-driven modelled eruption of the active regions (ARs) 12473 and AR11176, as well as preforming relaxation runs for AR12473 (found to be eruptive) where the driving is switched off systematically at different time steps. We intend to analyse the behaviour and evolution of fundamental quantities that are essential for understanding the eruptivity of magnetic flux ropes (MFRs). The data-driven simulations were carried out with the time-dependent magnetofrictional model (TMFM) for AR12473 and AR11176. For the relaxation runs, we employed the magnetofrictional method (MFM) and a zero-beta magnetohydrodynamic (MHD) model to investigate how significant the differences between the two relaxation procedures are when started from the same initial conditions. In total, 22 simulations were studied. To determine the eruptivity of the MFRs, we calculated and analysed characteristic geometric properties such as the cross-section, MFR height, and physical stability parameters such as MFR twist and the decay index. Furthermore, for the eruptive cases, we investigated the effect of sustained driving beyond the point of eruptivity on the MFR properties and evolution. We find that the fully driven AR12473 MFR is eruptive, while the AR11176 MFR is not. For the relaxation runs, we find that the MFM MFRs are eruptive when the driving is stopped around the flare time or later, while the MHD MFRs show eruptive behaviour even if the driving is switched off one and a half days before the flare occurs. We also find that characteristic MFR properties can vary greatly even for the eruptive cases of different relaxation simulations. The results suggest that data driving can significantly influence the evolution of the eruption, with differences appearing even when the relaxation time is set to later stages of the simulation when the MFRs have already entered an eruptive phase. Moreover, the relaxation model affects the results significantly, as highlighted by the differences between the MFM and MHD MFRs, showing that eruptivity in MHD does not directly translate to eruptivity in the MFM, despite the same initial conditions. Finally, if the exact critical values of instability parameters are unknown, tracking the evolution of typical MFR properties can be a powerful tool for determining MFR eruptivity.

The Role of Magnetic Skeleton in Solar Flare Filaments Activity

We report an M9.3 flare and filaments activities from NOAA Active Region 11261 that are strongly modulated by the 3D magnetic skeleton. Magnetic field extrapolation from the vector magnetic field suggests complex magnetic connectivity and the existence of a high coronal null point southeast of the active region. A small filament over the inversed V-shaped polarity inversion line erupted and resulted in the M9.3 flare associated with a weak ejection in the EUV hot channel and the formation of a relatively large filament. Both the weak ejection and the eruption of the large filament were toward the southeast. Comparative analyses have disclosed the following new facts. First, the trajectory of looptop hard X-ray emission provides solid evidence that the magnetic reconnection site propagated up toward the coronal null point as the flare and filaments erupted. Second, the EVU observations show coronal mass ejection-like eruption features in the ejection region of the magnetic skeleton. Third, the closed fan confined the west end of the large filament and the corresponding flare ribbons. We demonstrate a spatiotemporal relationship between the magnetic skeleton and the flare filament activity. We conclude that the magnetic skeleton can modulate and determine almost all the characteristics of the studied activity in the corresponding scale.

Spatially resolved plasma composition evolution in a solar flare – The effect of reconnection outflow

Context. Solar flares exhibit complex variations in elemental abundances compared to photospheric values. These abundance variations, characterized by the first ionization potential (FIP) bias, remain challenging to interpret. Aims. We aim to (1) examine the spatial and temporal evolution of coronal abundances in the X8.2 flare on 2017 September 10, and (2) provide a new scenario to interpret the often observed high FIP bias loop top, and provide further insight into differences between spatially resolved and Sun-as-a-star flare composition measurements. Methods. We analyzed 12 Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) raster scans spanning 3.5 hours, employing both Ca XIV 193.87 Å/Ar XIV 194.40 Å and Fe XVI 262.98 Å/S XIII 256.69 Å composition diagnostics to derive FIP bias values. We used the Markov Chain Monte Carlo (MCMC) differential emission measure (DEM) method to obtain the distribution of plasma temperatures, which forms the basis for the FIP bias calculations. Results. Both the Ca/Ar and Fe/S composition diagnostics consistently show that flare loop tops maintain high FIP bias values of > 2–6, with peak phase values exceeding 4, over the extended duration, while footpoints exhibit photospheric FIP bias of ∼1. The consistency between these two diagnostics forms the basis for our interpretation of the abundance variations. Conclusions. We propose that this variation arises from a combination of two distinct processes: high FIP bias plasma downflows from the plasma sheet confined to loop tops, and chromospheric evaporation filling the loop footpoints with low FIP bias plasma. Mixing between these two sources produces the observed gradient. Our observations show that the localized high FIP bias signature at loop tops is likely diluted by the bright footpoint emission in spatially averaged measurements. The spatially resolved spectroscopic observations enabled by EIS prove critical for revealing this complex abundance variation in loops. Furthermore, our observations show clear evidence that the origin of hot flare plasma in flaring loops consists of a combination of both directly heated plasma in the corona and from ablated chromospheric material; and our results provide valuable insights into the formation and composition of loop top brightenings, also known as EUV knots, which are a common feature at the tops of flare loops.

Heliospheric Effect on Solar Activity Parameters during MaximumPhase of Solar Cycle 24 (2012-2015)

Abstract The time series of daily data of solar activity proxies, namely the sunspot number (SSN), sunspot area (SSA), solar radio flux (F10.7), modified coronal index (MCI), solar flare index (FI), and cosmic ray intensity (CRI), were analyzed to understand the solar activity modulations and short-term periodicities therein. Rieger-type, and other short-term periods, including the solar rotational period that covers the maximum activity phase period (maximum phase of solar cycle 24). The wavelet power spectra and Periodogram of SSN, SSA, F10.7, MCI, FI, and CRI exhibited a significant short-term period. The heliospheric effects exist for a particular period (~27 days) and it is related to the solar activity phenomena. The cross-correlation coefficients and time lags between the cosmic ray intensity and solar activity parameters were estimated to be 200, 46, 281, 39, and 47 days for SSN, SSA, F10.7, MCI, and FI respectively during the time series 2012-2015 (maximum phase of solar cycle 24).

Fast magnetohydrodynamic oscillations of a coronal loop embedded in a potential coronal arcade

Observations indicate variable widths exhibited by fan coronal loops and flare loops that tend to widen towards the apex. Short-period, quasi-periodic pulsations in solar flares are often interpreted in terms of the fast-sausage oscillations of flare loops and the collective vertical vibrations of arcade loops are attributed with the vertical kink mode. Both phenomena are used as a seismological tool to estimate the physical parameters in the corona. We performed an analytical study of fast sausage and kink oscillations in coronal loops, given the effects of loop curvature, expansion, and Alfv \'e n speed variation. We modelled a coronal loop as a dense expanding curved magnetic slab embedded within a potential coronal arcade, using a zero-beta plasma limit. We obtained the dispersion relation that governs fast waves in the model and studied it both numerically and analytically. The effects of loop expansion and variable Alfv \'e n speed reduce the cut-off frequency and increase the cut-off wavenumbers for fast sausage and kink waves. Moreover, the principal vertical kink mode has a cut-off and strongly attenuates in the leaky regime. The frequency increase is found to be minor for the global sausage mode both in the trapped and leaky regimes, with a frequency shift within a few percent. We found that in our model, where the Alfv \'e n speed increases from the footpoints to the loop top, the spatial profile of the longitudinal fundamental is broadened and the antinodes of the first overtone are shifted towards the footpoints. Using the classical expression for the cut-off wavenumber of the global sausage mode in a straight waveguide results in an underestimation of the density contrast constraint in flare loops. Instead, the suggested formula accounting for variations in loop widths provides more accurate results. The frequency of the global sausage mode can be correctly determined with the straight slab model.

Statistical study of the peak and fluence spectra of solar energetic particles observed over four solar cycles

Context. Solar energetic particles (SEPs) are an important space radiation source, especially for the space weather environment in the inner heliosphere. The energy spectrum of SEP events is crucial both for evaluating their radiation effects and for understanding their acceleration process at the source region, along with their propagation mechanism. Aims. In this work, we investigate the properties of the SEP peak flux spectra and the fluence spectra and their potential formation mechanisms using statistical methods. We aim to advance our understanding of SEP acceleration and propagation mechanisms. Methods. Employing a dataset from the European Space Agency’s Solar Energetic Particle Environment Modelling (SEPEM) program, we obtained and fit the peak-flux and fluence proton spectra of more than a hundred SEP events from 1974 to 2018. We analyzed the relationship among the solar activity, X-ray peak intensity of solar flares, and the SEP’s spectral parameters. Results. Based on the assumption that the initial spectrum of accelerated SEPs generally displays a power-law distribution and that the diffusion coefficient has a power-law dependence on the particle energy, we can assess both the source and propagation properties using the observed SEP event peak flux and fluence energy spectra. We confirm that the spectral properties of SEPs are influenced by the solar source and the interplanetary conditions, whereas their transportation process can be influenced by different phases of solar cycle. Conclusions. This study provides an observational perspective on the double power-law spectral characteristics of the SEP energy spectra, revealing their correlation with the adiabatic cooling and diffusion processes during the particle propagation from the Sun to the observer. This result contributes to forging a deeper understanding of the acceleration and propagation of SEP events, in particular, the possible origins of the double power law.

Revisiting the Superstorm on 6–7 April 2000 Caused by an Extraordinary Corotating Interaction Region (With an Embedded Coronal Jet?)

AbstractThe 6–7 April 2000 superstorm of SYM‐H intensity = −319 nT discussed in Meng et al. (2019; https://doi.org/10.1029/2018JA026425) was misidentified as being due to an interplanetary coronal mass ejection associated with a solar flare. The interplanetary cause was a highly unusual corotating interaction region (CIR) bounded by a strong fast forward shock (FS) with magnetosonic Mach number Mms = 4.6 and a fast reverse shock (RS) with Mms = 1.9. The exceptionally strong FS caused a ∼3‐factor interplanetary magnetic field (IMF) magnitude amplification in the leading half of the CIR with peak southward IMF Bz = −27 nT causing the superstorm. A plasma region between a tangential discontinuity and the stream interface had a scale size of ∼0.096 AU. We hypothesize that this is the first detection of a coronal jet at 1 AU. The jet/Gold magnetic tongue (1959; https://doi.org/10.1029/JZ064i011p01665) was embedded within the CIR, contained the southward Bz and caused the magnetic storm. We hypothesize that a shrinking coronal hole and magnetic reconnection caused the formation and release of the jet.

Ionospheric Absorption Variation Based on Ionosonde and Riometer Data and the NOAA D-RAP Model over Europe During Intense Solar Flares in September 2017

A novel method was developed based on the amplitude data of the EM waves measured by Digisondes to calculate and investigate the relative ionospheric absorption changes. The effect of 13 solar flares (>C8) that occurred from 4 to 10 September 2017 were studied at three European Digisonde stations (Juliusruh (54.63°N, 13.37°E), Průhonice (49.98°N, 14.55°E) and San Vito (40.6°N, 17.8°E)). The present study compares the results of the amplitude method with the absorption changes measured by the Finnish Riometer Network and determined by the NOAA D-RAP model during the same events. The X-class flares caused 1.5–2.5 dB of attenuation at 30–32.5 MHz based on the riometer data, while the absorption changes were between 10 and 15 dB in the 2.5–4.5 MHz frequency range according to the amplitude data. The impact caused by energetic particles after the solar flares are clearly seen in the riometer data, while among the Digisonde stations it can be observed only at Juliusruh in some certain cases. Comparing the results of the amplitude method with the D-RAP model it seems evident that the observed absorption values almost always exceed the values given by the model both at 2.5 MHz and at 4 MHz during the investigated period. According to the comparison between the riometer data with the D-RAP, generally, the model underestimates the absorption values obtained from the riometers during solar flares except at the highest latitude stations, while D-RAP overestimates the impact during the particle events.

Impacts of Data Preprocessing and Sampling Techniques on Solar Flare Prediction from Multivariate Time Series Data of Photospheric Magnetic Field Parameters

The accurate prediction of solar flares is crucial due to their risks to astronauts, space equipment, and satellite communication systems. Our research enhances solar flare prediction by employing sophisticated data preprocessing and sampling techniques for the Space Weather Analytics for Solar Flares (SWAN-SF) data set, a rich source of multivariate time series data of solar active regions. Our study adopts a multifaceted approach encompassing four key methodologies. Initially, we address over 10 million missing values in the SWAN-SF data set through our innovative imputation technique called fast Pearson correlation-based k-nearest neighbors imputation. Subsequently, we propose a precise normalization technique, called LSBZM normalization, tailored for time series data, merging various strategies (log, square root, Box–Cox, Z-score, and min–max) to uniformly scale the data set's 24 attributes (photospheric magnetic field parameters), addressing issues such as skewness. We also explore the “near decision boundary sample removal” technique to enhance the classification performance of the data set by effectively resolving the challenge of class overlap. Finally, a pivotal aspect of our research is a thorough evaluation of diverse oversampling and undersampling methods, including SMOTE, ADASYN, Gaussian noise injection, TimeGAN, Tomek links, and random undersampling, to counter the severe imbalance in the SWAN-SF data set, notably a 60:1 ratio of major (X and M) to minor (C, B, and FQ) flaring events in binary classification. To demonstrate the effectiveness of our methods, we use eight classification algorithms, including advanced deep-learning-based architectures. Our analysis shows significant true skill statistic scores, underscoring the importance of data preprocessing and sampling in time-series-based solar flare prediction.

Statistics of Solar White-light Flares. I. Optimization and Application of Identification Methods

White-light flares (WLFs) are energetic activity in the stellar atmosphere. However, observed solar WLFs are relatively rare compared to stellar WLFs or solar flares observed at other wavelengths, which limits our further understanding of solar/stellar WLFs through statistical studies. By analyzing flare observations from the Solar Dynamics Observatory, here we improve WLF identification methods to obtain more solar WLFs and their accurate light curves from two aspects: (1) imposing constraints defined by the typical temporal and spatial distribution characteristics of WLF-induced signals; and (2) setting the intrinsic threshold for each pixel in the flare ribbon region according to its inherent background fluctuation rather than a fixed threshold for the whole region. Applying the optimized method to 90 flares (30 C-class flares, 30 M-class flares, and 30 X-class flares) for a statistical study, we identified a total of nine C-class WLFs, 18 M-class WLFs, and 28 X-class WLFs. The WLF identification rate of C-class flares reported here reaches 30%, which is the highest to date to our best knowledge. It is also revealed that in each GOES energy level the proportion of WLFs is higher in confined flares than that in eruptive flares. Moreover, a power-law relation is found between the WLF energy (E) and duration (τ): τ ∝ E 0.22, similar to those of solar hard/soft X-ray flares and other stellar WLFs. These results indicate that we could recognize more solar WLFs through optimizing the identification method, which will lay a base for future statistical and comparison study of solar and stellar WLFs.

A type II radio burst associated with solar filament–filament interaction

Aims. Solar radio type II bursts are often associated with coronal shocks driven by solar eruptions. In this study, we report a type II burst associated with filament–filament interaction. Methods. Combining the high-quality multiwavelength observations from CHASE, SDO, STEREO, and CALLISTO, we conducted a detailed study of the type II burst associated with filament–filament interaction. Results. On 2023 September 11, an erupting filament (F1) likely disturbed a nearby long filament (F2), causing F2 to subsequently erupt. As a result of possible magnetic reconnection between ejective materials from the two filaments, loop-like structures formed perpendicular to them. Subsequently, the expansion of these loop-like structures triggered a strong coronal mass ejection (CME). Interestingly, a type II burst appeared on the solar spectrum around the time when the loop-like structures formed and the CME appeared above the occulting disk of STEREO/COR1. By converting the frequency of the type II burst to the coronal height using polarization brightness data recorded by the COR1 coronagraph and the spherically symmetric polynomial approximation technique, we determined the formation height of the type II burst to be around 1.45 R⊙, with a speed of approximately 440 km s−1. This is comparable to the observed height of the CME (∼1.43 R⊙), although slightly lower in speed (540 km s−1). Conclusions. All these results indicate that the type II burst was closely associated with filament–filament interactions and was possibly excited by the accompanying CME at the flank. We suggest that the filament–filament interactions played an important role in producing the type II burst by acting as a piston to trigger a strong CME.

Variations of flare energy release behaviour and magnetic loop characteristics versus absolute stellar parameters

ABSTRACT In this paper, we examine how stellar flare activity varies with evolution stage, rotation period, and spectral type. To do this, we examine the distributions of the flare equivalent duration on a logarithmic scale, which we consider as an indicator of the maximum energy level that a star can reach in white-light flares. We conduct these analyses using two distinct statistical models of data obtained from white-light flare patrols of 33 stars. These models are the one-phase exponential association (OPEA) and cumulative flare frequency models. The results show that the value of the OPEA model parameter Plateau has a linear relationship with the stellar B – V colour index and the rotation period. In addition, it is shown that flare time-scales, and therefore the maximum magnetic loop height that stars can have, vary according to the evolutionary stage of the star. Finally, it is concluded that the cumulative flare frequency parameters of the stars are not as effective as the OPEA parameters at exhibiting these variations.

A Rapid Sequence of Solar Energetic Particle Events Associated with a Series of Extreme-ultraviolet Jets: Solar Orbiter, STEREO-A, and Near-Earth Spacecraft Observations

A series of solar energetic electron (SEE) events was observed from 2022 November 9 to November 15 by Solar Orbiter, STEREO-A, and near-Earth spacecraft. At least 32 SEE intensity enhancements at energies >10 keV were clearly distinguishable in Solar Orbiter particle data, with 13 of them occurring on November 11. Several of these events were accompanied by ≲10 MeV proton and ≲2 MeV nucleon−1 heavy-ion intensity enhancements. By combining remote-sensing and in situ data from the three viewpoints (Solar Orbiter and STEREO-A were ∼20° and ∼15° east of Earth, respectively), we determine that the origin of this rapid succession of events was a series of brightenings and jetlike eruptions detected in extreme ultraviolet (EUV) observations from the vicinity of two active regions. We find a close association between these EUV phenomena, the occurrence of hard X-ray flares, type III radio bursts, and the release of SEEs. For the most intense events, usually associated with extended EUV jets, the distance between the site of these solar eruptions and the estimated magnetic connectivity regions of each spacecraft with the Sun did not prevent the arrival of electrons at the three locations. The capability of jets to drive coronal fronts does not necessarily imply the observation of an SEE event. Two peculiar SEE events on November 9 and 14, observed only at electron energies ≲50 keV but rich in ≲1 MeV nucleon−1 heavy ions, originated from slow-rising confined EUV emissions, for which the process resulting in energetic particle release to interplanetary space is unclear.

Stealth Non-standard-model Confined Flare Eruptions: Sudden Reconnection Events in Ostensibly Inert Magnetic Arches from Sunspots

We report seven examples of a long-ignored type of confined solar flare eruption that does not fit the standard model for confined flare eruptions. Because they are confined eruptions, do not fit the standard model, and unexpectedly erupt in ostensibly inert magnetic arches, we have named them stealth non-standard-model confined flare eruptions. Each of our flaring magnetic arches stems from a big sunspot. We tracked each eruption in full-cadence UV and EUV images from the Atmospheric Imaging Assembly of Solar Dynamics Observatory (SDO) in combination with magnetograms from SDO’s Helioseismic and Magnetic Imager. We present the onset and evolution of two eruptions in detail: one of six that each makes two side-by-side main flare loops, and one that makes two crossed main flare loops. For these two cases, we present cartoons of the proposed pre-eruption field configuration and how sudden reconnection makes the flare ribbons and flare loops. Each of the seven eruptions is consistent with being made by sudden reconnection at an interface between two internal field strands of the magnetic arch, where they cross at a small (10°–20°) angle. These stealth non-standard-model confined flare eruptions therefore plausibly support the idea of E. N. Parker for coronal heating in solar coronal magnetic loops by nanoflare bursts of reconnection at interfaces of internal field strands that cross at angles of 10°–20°.

Investigating the Behavior and Spatiotemporal Variations of Green-line Emission in the Solar Corona

Understanding coronal structure and dynamics can be facilitated by analyzing green-line emission, which enables the investigation of diverse coronal structures such as coronal loops, streamers, coronal holes, and various eruptions in the solar atmosphere. In this study, we investigated the spatiotemporal behaviors of green-line emissions in both low and high latitudes across nine solar cycles, ranging from Solar Cycle 17 to the current Solar Cycle 25, using the modified homogeneous data set. We employed methodologies such as cross correlation, power spectral density, and wavelet transform techniques for this analysis. We found distinct behaviors in green-line energy across various latitudinal distributions in the solar atmosphere. The trends observed at higher latitudes differ from those at lower latitudes. The emission behaviors show a close association with other solar phenomena like solar flares, sunspots, and coronal mass ejections throughout the solar cycles. The observed variations exhibit harmonic periods. The emission activity is significantly higher in the low latitudes, accounting for over 70% of the emissions, while the higher latitudes contribute less than 30%. The emissions exhibit asymmetric behavior between the northern and southern hemispheres, leading to a 44 yr cycle of solar hemispheric dominance shifts. Various factors, such as Alfvén waves, solar magnetic fields, sunspots, differential rotation, and reconnection events, influence the observed differences in behavior between lower and higher latitudes, suggesting the existence of potential underlying phenomena contributing to deviations in properties, intensity, temporal dynamics, and spatiotemporal lifetime.

Observation of super-Alfvénic slippage of reconnecting magnetic field lines on the Sun

AbstractSlipping motions of magnetic field lines are a distinct signature of three-dimensional magnetic reconnection, a fundamental process driving solar and stellar flares. While being a key prediction of numerical experiments, the rapid super-Alfvénic field line slippage driven by the ‘slip-running’ reconnection has remained elusive in previous observations. New frontiers into exploring transient flare phenomena were introduced by recently designed high cadence observing programs of the Interface Region Imaging Spectrograph (IRIS). By exploiting high temporal resolution imagery (~2 s) of IRIS, here we reveal slipping motions of flare kernels at speeds reaching thousands of kilometres per second. The fast kernel motions are direct evidence of slip-running reconnection in quasi-separatrix layers, regions where magnetic field strongly changes its connectivity. Our results provide observational proof of theoretical predictions unaddressed for nearly two decades and extend the range of magnetic field configurations where reconnection-related phenomena can occur.

Prompt Emission of Relativistic Protons up to GeV Energies from M6.4-Class Solar Flare on July 17, 2023

Prompt Emission of Relativistic Protons up to GeV Energies from M6.4-Class Solar Flare on July 17, 2023

Magnetic diffusion in solar atmosphere produces measurable electric fields

The efficient release of magnetic energy in astrophysical plasmas, such as during solar flares, can in principle be achieved through magnetic diffusion, at a rate determined by the associated electric field. However, attempts at measuring electric fields in the solar atmosphere are scarce, and none exist for sites where the magnetic energy is presumably released. Here, we present observations of an energetic event using the National Science Foundation’s Daniel K. Inouye Solar Telescope, where we detect the polarization signature of electric fields associated with magnetic diffusion. We measure the linear and circular polarization across the hydrogen Hε Balmer line at 397 nm at the site of a brightening event in the solar chromosphere. Our spectro-polarimetric modeling demonstrates that the observed polarization signals can only be explained by the presence of electric fields, providing conclusive evidence of magnetic diffusion, and opening a new window for the quantitative study of this mechanism in space plasmas.

Coronal and chromospheric activity of Teegarden's star

Teegarden's star is a late-type M-dwarf planet host, typically showing only rather low levels of activity. In this paper we present an extensive characterisation of this activity at photospheric, chromospheric, and coronal levels. We specifically investigated TESS observations of Teegarden's star, which showed two very large flares with an estimated flare fluence between 1029 and 1032\,erg comparable to the largest solar flares. We furthermore analysed nearly 300 CARMENES spectra and 11 ESPRESSO spectra covering all the usually used chromospheric lines in the optical from the Ca ii H K lines at 3930\ to the He i infrared triplet at 10830\ These lines show different behaviour: The He i infrared triplet is the only one absent in all spectra, some lines show up only during flares, and others are always present and highly variable. Specifically, the Halpha line is more or less filled in during quiescence; however, the higher Balmer lines are still observed in emission. Many chromospheric lines show a correlation with Halpha variability, which, in addition to stochastic behaviour, shows systematic behaviour on different timescales including the rotation period. Moreover, we found several flares and also report hints of an erupting prominence, which may have led to a coronal mass ejection. Finally, we present X-ray observations of Teegarden's star (i.e. a discovery pointing obtained with the Chandra observatory) and an extensive study with the XMM-Newton observatory, which observed two large flares. One of these showed clear signatures of the Neupert effect, suggesting the production of hard X-rays in the system.

Dynamic processes in current sheets and experimental laboratory astrophysics

The results of experimental research of the dynamics of current sheets, which are formed in laboratory experiments at the IOF RAS, are presented as a brief review. It is shown that the most significant features of phenomena like solar flares can be reproduced in laboratory conditions. These features include the relatively slow accumulation of the magnetic energy in the course of the current sheet formation, the rapid release of the energy during the disruption of the current sheet, acceleration of plasma flows, ultrafast plasma heating, and effective particle’s acceleration. A qualitative similarity has been established between the basic characteristics of current sheets in the tail region of the Earth’s magnetosphere and in laboratory conditions. A comparison of a number of fundamental dimensionless parameters indicates the possibility of quantitative laboratory modeling of processes occurring in the magnetosphere. It is concluded that experimental research of the dynamics of current sheets and magnetic reconnection processes represent one of the promising areas of the laboratory astrophysics.