ИСТИНА

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.