Radial penetration of a hot plasma associated with a large-scale electric field in the magnetosphere, and some related problems

Abstract

The inward penetration of a hot plasma as an energy accumulation process for magnetospheric substorms, and some related topics are discussed in the present paper. First, we consider the possibility that the large-scale electric field within the magnetosphere is induced as a result of the macroscopic interaction of the magnetic field disturbances in the solar wind with the magnetosphere. It is emphasized that the associated problem is essentially time dependent, and the change of the north-south component of the interplanetary magnetic field is interpreted as the incompressible Alfvén mode. Second, the problem of the inward penetration of the symmetric distributed energetic particles by the enhancement of the asymmetric electric field is quantitatively studied, using the drift kinetic approximation method. Taking account of the non-linear feedback effect of the asymmetric part of the particle distribution, we obtain the secular equation for the time development of the symmetric distribution function. Some numerical solutions of this equation are given as an application to the ring current proton penetration problem. For steady state penetration, the Earth's rotational motion and the tailward stretching of the field lines are important to the resonant protons with energy of 1–10 keV. Third, interrelation between the coherent adiabatic large-scale dynamical motion of the plasma as an energy accumulation process, and incoherent stochastic resonant wave-particle interactions, are discussed in relation to the energy accumulation and relaxation processes. The adiabatic drift instability condition, which would be satisfied in the front side of the penetrated proton ring current, is also considered. Finally, the possibility of runaway electrons in the topside ionosphere as a source of the magnetospheric electrons during the substorm is also considered, and the associated limiting flux intensity is estimated.