A weak active region (NOAA 11158) appeared on the solar disk near the eastern limb. This region increased rapidly and, having reached the magnetic flux higher than 10²² Mx, produced an X-class flare. Only weak field variations at individual points were observed during the flare. An analysis of data with a resolution of 45 s did not indicate any characteristic features in the photospheric field dynamics during the flare. When the flux became higher than 3 × 10²² Mx, active region NOAA 10720 produced six X-class flares. The field remained quiet during these flares. An increase in the magnetic flux above ∼10²² Mx is a necessary, but not sufficient, condition for the appearance of powerful flares. Simple active regions do not produce flares. A flare originates only when the field distribution in an active region is complex and lines of polarity inversion have a complex shape. Singular lines of the magnetic field can exist only above such active regions. The current sheets, in the magnetic field of which the solar flare energy is accumulated, originate in the vicinity of these lines.

The use of parallel computations on Nvidia Tesla GPUs allows the magnetohydrodynamic (MHD) simulation of preflare situations in the solar corona above an active region in the real scale of time. The MHD simulation for AR 10 365 shows a significantly smaller number for the current density maxima, which mask real current sheets, i.e., the places of the primordial release of solar flare energy, as compared to previous MHD simulation on a reduced scale of time, where strong instabilities appeared near the photospheric boundary of the computational domain under the effect of an unnaturally rapid change in the photospheric magnetic field (the time scale was reduced by 10⁴ times). A more than 100× speedup of the numerical solution of a set of MHD equations is attained in comparison with successive calculations. The new results make it possible to determine a more precise magnetic configuration near current sheets, which can be used to improve the prediction of the appearance of charged particle fluxes accelerated to relativistic energies under the action of the Lorentz electromagnetic field, i.e., solar cosmic rays, which carry radiation dangerous for people and equipment in space and Earth’s polar latitudes.

Analysis of the solar cosmic ray measurements on the Geostationary Orbital Environmental Satellite (GOES) spacecraft indicated that the duration of solar flare relativistic proton large pulses is comparable with the solar wind propagation duration from the Sun to the Earth. The front of the proton flux from flares on the western solar disk approaches the Earth with a flight time along the Archimedean spiral magnetic field line of 15–20 min. The proton flux from eastern flares is registered in the Earth’s orbit 3–5 h after the flare onset. These particles apparently propagate across IMF owing to diffusion.

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 , Re = 1 0 7 , ν Art Phoosphere = ν 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.

The generation of solar cosmic rays occurs during explosive energy release in a solar flare, so in order to understand this phenomenon it is necessary to study both the mechanism of the solar flare and the process of particle acceleration by the generated electric field. During a solar flare in the solar corona above the active region (AR), the energy stored in the magnetic field of the current sheet is released. Using the results of numerical simulation and observations, I.M. Podgorny proposed an electrodynamic model of a solar flare, explaining its main observational manifestations, in particular, the appearance of X-ray emission on the surface of the Sun. The acceleration of protons occurs along a singular line of the magnetic field of the current sheet by the electric field E = -V×B/c. To obtain accurate results it is necessary to carry out MHD simulation in the real scale of time, which is only be done using parallel calculations. The parallelization of the program PERESVET carried out using graphics card (GPU), the calculations were accelerated by ~ 120 times. As a result of optimization of the approximation of the boundary conditions of free exit at the non-photospheric boundary, instability near the boundary was stabilized. The first results of MHD simulation in the real scale of time above the AR 10365 showed the appearance of a plasma flow near singular X-type lines, which have to cause to the formation of a current sheet.