ИСТИНА

We analyze the properties of the surrounding the Earth plasma domain at geocentic distances till the magnetopause near noon and till geocentric distances till 10-12Re near midnigth. Plasma properties in this region are near to 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. We obtained the averaged distributions of plasma pressure, pressure anisotropy, and of magnetic field near the equatorial plane at geocentric distances >6Re using data of THEMIS mission. We calculate the transverse currents 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 which means that analyzed region is the high latitude continuation of the ordinary ring current. The observed isotropy of plasma pressure at large geocentric distances gives the possibility to use plasma pressure 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. We compare plasma pressure distribution at high and low altitudes and show that main part of discrete auroral oval can not be mapped to the plasma sheet. It is mapped to the surrounding the Earth plasma ring. We obtain the support of this statement analyzing the position of trapping boundary of energetic particles using data of METEOR satellites. The role of obtained findings in the solution of the problems of magnetospheric dynamics is discussed.