Investigation of the mechanism of a solar flare by means of MHD simulations above the active region in real scale of time: The choice of parameters and the appearance of a flare situation

Abstract The observed primordial energy release of solar flare in the corona is explained by the mechanism of S. I. Syrovatskii, according to which the flare energy is accumulated in the current sheet. The flare release of the current sheet energy causes the observed manifestations of the flare, which are explained by the electrodynamical model of a solar flare proposed by I. M. Podgorny. According to this model, hard X-ray beam radiation on the solar surface is explained by the acceleration of electrons in field aligned currents caused by the Hall electric field in the current sheet. The study of the flare mechanism is impossible without performing magnetohydrodynamic (MHD) simulations above a real active region (AR), in which the calculation begins several days before the appearance of flares. When setting the problem, no assumptions were made about the flare mechanism. An absolutely implicit finite-difference scheme, conservative with respect to the magnetic flux, has been developed, which is implemented in the PERESVET code. MHD simulation in the real scale of time can only be carried out, thanks to parallel computations using compute unified device architecture (CUDA) technology. Methods have been developed that made it possible to stabilize the numerical instability arising near the boundary of the region. Calculation above AR 10365 for low viscosities ( Rm = 1 0 9 {\rm{Rm}}=1{0}^{9} , Re = 1 0 7 {\rm{Re}}=1{0}^{7} , ν Art Phoosphere = ν Magn Art Phoosphere = 1 0 − 4 {\nu }_{\text{Art Phoosphere}}={\nu }_{\text{Magn Art Phoosphere}}=1{0}^{-4} ) showed the appearance of a singular X-type line, in the vicinity of which a current sheet with accumulated magnetic energy for a flare can form. Also, by means of MHD simulation the appearance of singular lines above a real AR is shown, in which the magnetic field is a superposition of an X-type field and a diverging magnetic field. In such a superposition of configurations, even if the diverging field predominates, the formation of a current sheet is possible, which can explain the appearance of a flare of not very high power. The coincidence of the position of the source of the flare thermal X-ray radiation with the places of appearance of the current sheets confirms the mechanism of the solar flare, based on the accumulation of energy in the magnetic field of the current sheet.