Physics of auroral phenomena : proceedings of the 36th Annual seminar, Apatity, 26 February – 01 March, 2013 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2013. - 215 с. : ил., табл.

“Physics o f Auroral Phenomena", Proc. XXXVI Annual Seminar, Apatity, pp. 1 1 7 -1 2 0 , 2013 © Kola Science Centre, Russian Academy of Science, 2013 Polar Geophysical Institute POSITIONS OF X-RAY EMISSION SOURCES OF SOLAR FLARE OBTAINED BY MHD SIMULATION A.I. Podgom y1, I.M. Podgomy2 1Lebedev P hysical Institute RAS, Moscow, Russia, podgorny@ lebedev.ru, 2Institute f o r A stronom y RAS, Moscow, Russia, podgorny@ inasan.ru Abstract. Several mechanisms of solar flare production are considered by different authors. Usually the initial conditions are artificially set such a way that it is required for development of the proposed mechanism. The problem of used condition formation during evolution of a real active region is not considered in such approach. In our MHD simulation we does not use any hypotheses about the flare mechanism, but the flare mechanism is found from the numerical MHD simulations in which all the conditions are taken from observations. It is shown that flare energy accumulation occurs in the current sheet magnetic field created by disturbances focusing in the vicinity o f an X-type singular line. The electrodynamical model of the solar flare based on current sheet mechanism, which explains main flare manifestations, has been developed. Using this electrodynamical model the positions of sources of thermal X-ray radiation is found for the flare occurred May 27, 2003 at 02:53. To find positions of sources of soft X-ray radiation in the corona the graphical system is developed. The comparison with RHESSI X-ray observations is made. Introduction The primordial flare energy release takes place in the solar corona above an active region at the height 1 5 - 3 0 thousands kilometers. It is proved by flare X-rays observations on the solar limb [1,2]. MHD simulation with the real initial conditions on the photosphere [2, 3] show that flare energy accumulation can occur in the current sheet magnetic field created by disturbances focusing in the vicinity o f an X-type singular line. After the quasi-steady evolution the current sheet transfers into an unstable state [5]. As a result, explosive instability develops, which cause the flare energy release. A number o f papers consider several other mechanisms of solar flare: magnetic reconnection between the twisted magnetic flux tubes (helicity); compression of plasma by the self current (pinch- effect); different instabilities of current in plasma (see review [6, 7]). The most widely used mechanism is based on the assumption o f magnetic rope appearance [8]. If the rope current crosses the arch magnetic lines, then the 1/c jxB force accelerates plasma upward and stretches magnetic lines. As a result the current sheet appears under the rope. This sheet is analogous to one is created by disturbances focusing in the vicinity of X-type singular line. Occurrence of magnetic rope or other alternative mechanism requires appropriate conditions in the solar corona. It is difficult to explain how such conditions can appear due to slow evolution of magnetic field, which is observed on the solar surface. It is impossible to get instantly a powerful rope in the process of slow active region evolution before a flare. Slow grows o f the rope current in equilibrium state demands self-consistent grows of the arch magnetic field to conserve the stable equilibrium state, which really cannot be fulfilled. Usually simulations are performed in the assumption of existence some powerful equilibrium configuration with big amount of free energy, that suddenly becomes unstable. The possibility of creation such a system at slow evolution of an active region is not considered. Until now, nobody has been able to simulate the appearance o f magnetic rope for a real change of the magnetic field on the photosphere. Here another approach is proposed. Instead of hypothesizing, we find the flare mechanism directly from the numerical MHD simulations in which all the conditions are taken from observations. In such approach no assumption about the physical mechanism of investigated phenomenon is used. MHD simulation is carried out in the solar corona in the computational domain in the form of a parallelepiped, the lower boundary of which is located on the photosphere in the active region. The size of the computational domain is several times larger than the size of the active region of the Sun, so the photospheric boundary is located far from strong magnetic field sources and it produces no errors in the numerical simulation.. This small field adjacent to the active region can influence the field in the corona, as it is situated in a large area. The calculations are initiated several days before the flare, when strong disturbances in the corona are absent. Therefore, the potential magnetic field in the corona, calculated from the field distribution observed on the photosphere, is used for setting initial conditions. The magnetic field distributions measured on the photosphere are used for setting boundary conditions during period of simulated active region evolution. Others boundary conditions are approximated by free-exit conditions. The special numerical methods are developed to stabilize numerical instabilities. The methods are realized in the PERESVET code on the FORTRAN language. The absolutely implicit fmite-difference scheme with upwind approximation of transport terms is used. This scheme is also conservative relative to the magnetic flux. It is solved by the iteration method. 117