Physics of auroral phenomena : proceedings of the 35th Annual seminar, Apatity, 28 Februaru – 02 March, 2012 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2012. - 187 с. : ил., табл.

“Physics o f Auroral Phenomena", Proc. XXXV Annual Seminar, Apatity, pp. 9 -1 6 , 2012 © Koia Science Centre, Russian Academy of Science, 2012 Polar Geophysical Institute MAGNETOSPHERIC STORMS AND SUBSTORMS, NATURE AND TOPOLOGY OF HIGH LATITUDE CURRENT SYSTEMS E.E. Antonova1’2,1. P.Kirpichev2,1, V. V. Vovchenko2, M.O. Riazantseva1’2, M.S. Pulinets1, I.L. Ovchinnikov1, S.S. Znatkova1, M.V. Stepanova3 ‘Skobeltsyn Institute o f Nuclear Physics, Moscow State University, Moscow, 119991, Russia, antonova@orearm. msk. ru 2Space Research Institute (IKI) Russian Academy o f Science, Moscow, Russia 3Physics Department, Science Faculty, Universidad de Santiago de Chile, Chile Abstract. The nighttime region at geocentric distances ~7-10RE is ordinarily considered as the near tail region. However the results of observations including latest THEMIS mission clearly demonstrate the existence of surrounding the Earth plasma ring at these geocentric distances. The distribution of plasma pressure in the ring is near to azimuthally symmetric. Daytime compression of magnetic field lines and shift of minimal value of the magnetic field till high latitudes lead to splitting of daytime transverse currents in Z direction. As a result nighttime transverse currents in the surrounding the Earth plasma ring are concentrated near equator, daytime transverse currents are spread along compressed by solar wind field lines forming the cut ring current (CRC) which is the high latitude continuation of the ordinary ring current. CRC is supported by directed to the Earth plasma pressure gradients. The role of CRC in the development of magnetic storm and the creation of the Dst variation is analyzed. We stress that the development of partial ring current, which is one of the well-known features of magnetic storm, in the CRC region helps to eliminate paradox, appeared when it was suggested that tail current could have the considerable role in the Dst formation. The contribution CRC in the process of Dst formation during magnetic storms is evaluated for selected magnetic storms with known radial profile of plasma pressure. The magnetospheric substorm is one of the most extensively stydied magnetospheric phenomena for the most than 50 latest years. However the mechanism of observed energy explosion and localization of substorm onset continue to be widely discussed. We summarize the results of observations demonstrating the isolated substorm onset at geosentric distances smaller than 10RE. It is suggested that isolated substorm onset is localized in CRC. Introduction More than fifty years period of auroral researches reveal the main features of auroral dynamics (see Feldstein et al. [2010]). However, the main processes of auroral formation continue to be extensively debated. Later findings (see the review [Antonova et al., 2011]) show that even the wide-spread opinion about auroral oval mapping on the plasma sheet of the magnetosphere of the Earth requires more careful analysis. First results of particle observations in the magnetosphere of the Earth (see Vemov et al. [1969]) reviled the existence of the region from the geostationary orbit till ~10 RE named the region of quasitrapping. Trajectories of energetic particle in this region cross the magnetopause when the particle pitch angle is equal to 90° and the drift shell splitting effect is observed for particles with smaller pitch angles [Shabansky and Antonova, 1968]. Drift trajectories of such particles are closed inside the magnetosphere. Effect of drift echo is observed till -13 RE near midnight [Hori et al., 2003]. This means that the external boundary of the region of quasitrapping can be localized at such distances. Characteristics of plasma population in the region of quasitrapping are near to plasma sheet plasma (see discussion in Antonova [2007], Antonova et al. [2009a, 2011]). This statement is supported by results of low altitude and near equatorial observations. Newell and Meng [1992] using DMSP satellite data showed that plasma sheet-like particle precipitations near noon come from a region situated at the equator from the low latitude boundary layer. Created models of auroal particle precipitations (see [Vorobjev and Yagodkina, 2008; Newell et al., 2009] and ref. in these papers) demonstrate the existence of closed near noon ring of plasma sheet-like particle precipitations. Particle observations of THEMIS mission (see [Angelopoulos, 2008]) show the presence of plasma sheet-like plasma near noon at every crossing of the magnetopause to the equator from the low latitude boundary layer (LLBL). Analyzing statistical picture of Geotail observations obtained by Nagata et al. [2008] atXGSw<0 (where GSW is Geocentric Solar Wind coordinate system) it is also possible to select the ring-type distribution of plasma around the Earth. The existence of the surrounding the Earth plasma ring with quasitapped energetic particle population selects this ring as the magnetospheric domain, the study of which can be important for understanding of storm and substorm dynamics. In this paper, we shall try to analyze the distribution of plasma pressure in the ring and structure of transverse currents. We try to