ИСТИНА

Region occupied by plasma sheet like plasma at geocentric distances from ~6 till ~ 12Re is ordinarily considered as the part of the plasma sheet. However its geometry is different from the plasma sheet proper where the field lines are greatly stretched in the antiearthward direction. Analyzed region has the ring-shaped form. Surface of minimal values of the magnetic field in this region is localized near the equatorial plane near midnight and shifted from the equatorial plane near noon. We obtained the averaged distributions of plasma pressure, of pressure anisotropy, and of magnetic field near the equatorial plane at geocentric distances >6Re using data of THEMIS mission. We calculate the values of plasma parameter beta (equal to the relation of the plasma pressure to the magnetic pressure) in the region of minimal values of the magnetic field using the Tsyganenko-2001 magnetic field model and demonstrate the existence of high-beta plasma ring surrounding the Earth. The obtained distribution of plasma pressure gradients is used for the evaluation of transverse currents in the ring. We calculate the transverse currents at the equatorial plane and at the surface of the minimal values of the magnetic field and show that the topology of current lines corresponds to the ring like current configuration compressed near noon. This finding supports the existence of the early suggested cut ring current (CRC) as the high latitude continuation of the ordinary ring current. The selection of plasma ring as a well defined structure in the high latitude magnetosphere requires the reanalysis of a number of positions in the physics of substorms and storm-substorm relationships. The isotropy of plasma pressure at large geocentric distances gives the possibility to use such value as a “natural tracer” of the magnetic field line as the pressure has the constant value along the field line in the condition of the magnetostatic equilibrium. Such feature provide the possibility to reanalyze the problem of the auroral oval mapping without using magnetic field models. Obtained distribution of plasma pressure over the equatorial plane is compared with the plasma pressure and the position of the electron precipitation boundaries at low altitudes. The pressure at low altitudes is obtained using data of the DMSP satellites. It is shown that most part of the auroral oval is mapped to the surrounding the Earth plasma ring. Such feature explains the well known ring like form of the auroral oval. Mapping of the most part of the auroral oval to the surrounding the Earth outer part of the ring current gives the possibility to clarify the substorm processes during magnetic storms when the auroral oval moves to low latitudes. We evaluated the contribution of the azimuthally symmetric part of the plasma ring to the Dst index for strong geomagnetic storms using the AMPTE/CCE radial profiles of plasma pressure published before, and showed that the contribution of the ring current including both RC and CRC is sufficient to obtain the observed Dst variation without the necessity to include the tail current system. We discuss the mechanisms of the formation of quite and active auroral arc during substorms and storms.