We present analysis of magnetic field and vertical electric currents (VECs) in seven solar flare ... more We present analysis of magnetic field and vertical electric currents (VECs) in seven solar flare regions accompanied by pulsations of hard X-ray (HXR) emission. These flares were studied by Kuznetsov et al. (2016) and chosen here because of the availability of the vector magnetograms for their parent active regions (ARs) obtained with the SDO/HMI data. By extrapolation of magnetic field with the non-linear force-free field (NLFFF) method we found that before each flare there was a magnetic flux rope (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 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. Also, we found that in three out of seven events the s...
We study flare processes in the lower solar atmosphere using observational data for a M1-class fl... more 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...
We consider the relationship of electromagnetic radiation in the three most intense flares of sol... more We consider the relationship of electromagnetic radiation in the three most intense flares of solar cycle 23, more specifically, those of October 28, 2003, January 20, 2005, and September 7, 2005, to the acceleration and release of protons into interplanetary space. The impulsive phase of these flares lasted ∼ 20 min and consisted of at least three energy release episodes, which differed by their manifestation in the soft (1–8 �, GOES) and hard (>150 keV, INTEGRAL) X-ray ranges as well as at radio frequencies of 245 MHz and 8.8 GHz. The protons and electrons were accelerated in each episode, but with a different efficiency; the relativistic protons were accelerated only after 5–6min of impulsive-phase development after the onset of a coronal mass ejection. It is at this time that maximum hard X-ray fluxes were observed in the September 7, 2005 event, which exceeded severalfold those for the other two flares considered. We associate the record fluxes of protons with energies > 200MeV observed in the heliosphere in the September 7, 2005 event with the dynamics of the impulsive phase. The extreme intensities of the microwave emission in the October 28, 2003 and January 20, 2005 events were probably attributable to the high-energy electron trapping conditions and did not reflect the acceleration process.
Based on data obtained from numerical modeling of an active region (AR) of the Sun with the codes... more Based on data obtained from numerical modeling of an active region (AR) of the Sun with the codes of radiation magnetohydrodynamics (MURaM), the horizontal gradient of the vertical component of the magnetic field on three layers in the vicinity of the photosphere \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\nabla }_{h}}{{B}_{z}}$$\end{document} and the horizontal component of the electric current density \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{j}_{h}}$$\end{document} for the AR of the flare were calculated. It was found that ≈90% of the calculated pixels contain \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{j}_{h}}$$\end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\nabla }_{h}}{{B}_{z}}$$\end{document} of the same order, but these quantities are weakly correlated. The correlation coefficient is calculated for several groups of pixels that are distinguished by the magnitude of the horizontal current and the magnetic-field configuration. The correlation coefficients for these cases did not exceed 0.34 for the lower layer and 0.54 for the upper one. The contours of the strong \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{j}_{h}}$$\end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\nabla }_{h}}{{B}_{z}}$$\end{document} (in units of electric current density) are also weakly correlated. The result may indicate that caution must be taken when the horizontal-field gradient is used for approximation of the horizontal current in the photosphere (in particular, in the development of methods for the forecasting of flares). In additional, the probability-density functions \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$PDF({{\left| {{{j}_{h}}} \right|} \mathord{\left/ {\vphantom {{\left| {{{j}_{h}}} \right|} {\left| {{{j}_{z}}} \right|}}} \right. \kern-0em} {\left| {{{j}_{z}}} \right|}})$$\end{document} in AR photosphere are constructed. They show that the median value of the ratio of the horizontal current to the vertical current is 3.5. This is consistent with the few estimates of various components of currents in real solar ARs and indicates the importance of the further study of horizontal currents.
We present analysis of magnetic field and vertical electric currents (VECs) in seven solar flare ... more We present analysis of magnetic field and vertical electric currents (VECs) in seven solar flare regions accompanied by pulsations of hard X-ray (HXR) emission. These flares were studied by Kuznetsov et al. (2016) and chosen here because of the availability of the vector magnetograms for their parent active regions (ARs) obtained with the SDO/HMI data. By extrapolation of magnetic field with the non-linear force-free field (NLFFF) method we found that before each flare there was a magnetic flux rope (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 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. Also, we found that in three out of seven events the s...
We study flare processes in the lower solar atmosphere using observational data for a M1-class fl... more 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...
We consider the relationship of electromagnetic radiation in the three most intense flares of sol... more We consider the relationship of electromagnetic radiation in the three most intense flares of solar cycle 23, more specifically, those of October 28, 2003, January 20, 2005, and September 7, 2005, to the acceleration and release of protons into interplanetary space. The impulsive phase of these flares lasted ∼ 20 min and consisted of at least three energy release episodes, which differed by their manifestation in the soft (1–8 �, GOES) and hard (>150 keV, INTEGRAL) X-ray ranges as well as at radio frequencies of 245 MHz and 8.8 GHz. The protons and electrons were accelerated in each episode, but with a different efficiency; the relativistic protons were accelerated only after 5–6min of impulsive-phase development after the onset of a coronal mass ejection. It is at this time that maximum hard X-ray fluxes were observed in the September 7, 2005 event, which exceeded severalfold those for the other two flares considered. We associate the record fluxes of protons with energies > 200MeV observed in the heliosphere in the September 7, 2005 event with the dynamics of the impulsive phase. The extreme intensities of the microwave emission in the October 28, 2003 and January 20, 2005 events were probably attributable to the high-energy electron trapping conditions and did not reflect the acceleration process.
Based on data obtained from numerical modeling of an active region (AR) of the Sun with the codes... more Based on data obtained from numerical modeling of an active region (AR) of the Sun with the codes of radiation magnetohydrodynamics (MURaM), the horizontal gradient of the vertical component of the magnetic field on three layers in the vicinity of the photosphere \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\nabla }_{h}}{{B}_{z}}$$\end{document} and the horizontal component of the electric current density \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{j}_{h}}$$\end{document} for the AR of the flare were calculated. It was found that ≈90% of the calculated pixels contain \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{j}_{h}}$$\end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\nabla }_{h}}{{B}_{z}}$$\end{document} of the same order, but these quantities are weakly correlated. The correlation coefficient is calculated for several groups of pixels that are distinguished by the magnitude of the horizontal current and the magnetic-field configuration. The correlation coefficients for these cases did not exceed 0.34 for the lower layer and 0.54 for the upper one. The contours of the strong \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{j}_{h}}$$\end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\nabla }_{h}}{{B}_{z}}$$\end{document} (in units of electric current density) are also weakly correlated. The result may indicate that caution must be taken when the horizontal-field gradient is used for approximation of the horizontal current in the photosphere (in particular, in the development of methods for the forecasting of flares). In additional, the probability-density functions \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$PDF({{\left| {{{j}_{h}}} \right|} \mathord{\left/ {\vphantom {{\left| {{{j}_{h}}} \right|} {\left| {{{j}_{z}}} \right|}}} \right. \kern-0em} {\left| {{{j}_{z}}} \right|}})$$\end{document} in AR photosphere are constructed. They show that the median value of the ratio of the horizontal current to the vertical current is 3.5. This is consistent with the few estimates of various components of currents in real solar ARs and indicates the importance of the further study of horizontal currents.
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