Physics of auroral phenomena : proceedings of the 38th annual seminar, Apatity, 2-6 march, 2015 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Издательство Кольского научного центра РАН, 2015. - 189 с. : ил., табл.

“P hysics o f Auroral P h e n o m e n a P ro c . XXXVIII A nnua l Sem inar, Apatity, pp. 79-82, 2 0 1 5 © Kola Science Centre, Russian Academy of Science, 2015 Polar Geophysical Institute MAGNETIC ENERGY ACUMULATION IN THE CORONAL CURRENT SHEET FOR A SOLAR FLARE I.M. Podgorny1, A.I. Podgomy 2 'institute fo r Astronomy RAS, Moscow, Russia 2Lebedev Physical Institute RAS, Moscow, Russia A b stract. The solar flare energy is accumulated above the active region (AR) in the solar corona in the magnetic field of a current sheet. For a current sheet creation the X-type magnetic field singular line should exist above AR with the magnetic flux (Ф > 10 22 M k c ) . The numerical magneto-hydrodynamic calculations performed by different authors and laboratory experiments showed that the current sheet creation and energy accumulation in its magnetic field are created due to the focusing of magnetic disturbances. The current sheet is only known object in the space, providing the slow accumulation of the huge amount of energy and its explosive release. Being high in the corona, the flare practically does not distort the magnetic field of AR. Introduction Solar flares - the explosive processes of energy release in the solar corona that occur on the background of stable work of the Sun fusion reactor and conservation of the solar constant. Unexpectedly, during a few minutes the energy 10 32 - 10 33 erg, which corresponds to the explosion of a million of hydrogen bombs, is released above AR. The existence of such gigantic explosions has remained long time outside the focus of attention of researchers because the power of Sun radiation (~10 33 erg/s) at the solar flare increases only by a fraction of the percent. The first information about the solar flare has been appeared in 1860 by Karington, who reported the sudden appearance two visible bright spots on the Sun, which is accompanied by a strong magnetic storm on the Earth after -18 hours. A similar phenomenon occurred repeatedly, and in 1941 it was named solar flare by H.W. Newton. In 1946 it was shown that instead of the Fraunhofer hydrogen line the bright hydrogen emission line Ha appears. There was impression that the energy release that causes the excitation of the hydrogen lines had been occurred by flare production on the Sun surface, and the term "chromospheric flare" was often used. Flares are observed on the solar disk in the AR. The AR is a place of concentration of dark spots (solar spots) with the temperature at 1000° - 2000° below the photosphere temperature. The transverse size of a large sunspot is about Ю 10 cm. The typical lifetime of a sunspot is about 10 days. The magnetic flux of northern or southern directions is concentrated in a sunspot. The magnetic field of a sunspot can reach several thousand gauss. The global solar magnetic field (~1 G) has dipole character. The direction of the dipole varies with a period o f 11 years. Observations of spots in the last 400 years have revealed the 11 year cycle of sunspot number change. At low solar activity usually about 10 spots is observed on the solar disk. In some rare cases, for example in the last activity minimum (2009 y), sunspots have been completely absent for a few weeks. During the big activity maximum the spot numbers exceed 150. Amplitude of the 11-year cycle undergoes strong modulation, and several authors drew attention to the existence of several long periods, which are superimposed on the clearly observed 11-year cycle. In periods of low activity, such as in the so-called Maunder minimum (1645 - 1715 years), 11 year maximums were virtually absent. During two cycles of activity in 1800 - 1820 years the number of spots does not exceed 50 (Dalton minimum). Unfortunately, reliable data on the number of sunspots became available only in the XX century. The last 70 years results of investigations of Royal Observatory of Belgium are shown in (Fig. 1). The attempts to establish empirical regularity modulation 1 1 -year cycle have not been a successful, and the forecast of the next cycle is not unique. The flare energy is released in the form of radiation in a wide frequency range, including thermal X ray with T ~ 10 keV, hard -100 keV beam X-rays, proton fluxes with relativistic energies and supersonic coronal mass ejections. The coronal mass ejection may exceed 10 15 g at the velocity of -10 8 cm/s, exceeding the solar wind velocity. A shock wave is formed at the front o f a supersonic coronal mass ejection. Coronal mass ejections perturb of the Earth magnetic field producing the magnetic storms and auroras. Long-term observations have shown that solar flares appearance on the solar disk in the AR. The impression that the flare occurs on the surface of the Sun entrenched the term "chromospheric flare". However, X-ray measurements on devices Yohkoh and RHESSI [1] revealed that the primary flare energy release occurs not on the surface o f the Sun, but in the corona above AR at the height order of 20 000 km. Opportunity for energy storage for a flare in the current sheet magnetic field in the solar corona was previously considered by S.I Syrovatskii and was confirmed in the numerical MHD calculations [2, 3]. The reviews [4, 5] describes three-dimensional MHD numerical experiments performed in 2 0 0 0 - 2013, in which it have been shown that the current sheet appears before the flare in the solar corona above AR, and the energy accumulated in the current sheet magnetic field is released during a flare. On the photospheric boundary the AR magnetic field distribution is set that measured in pre-flare state, and no assumptions 79