Wave-Particle Interactions Near the Geostationary Orbit

Abstract

It has become abundantly clear during the past decade of experimental observation of the near-Earth magnetosphere that many of the gross characteristics of its particle population and their temporal behavior can at least be qualitatively understood in terms of a large-scale convection of plasma from the geomagnetic tail towards the dayside, as originally postulated by Axford and Hines (1961) and Dungey (1961). Using the very simplest of models for the convective flow i.e., a uniform dawn-to-dusk electric field across the magnetosphere associated with the tail-to-dayside motion, plus a radial electric field associated with the rotation of the Earth, leads to a basic understanding of the populations of low energy (1 to 10⁴ eV) plasma within the magnetosphere, for the resulting flow pattern is divided into two parts. The flux tubes close to the Earth which corotate never become ‘open’ and are characterized by high densities of cold plasma from the ionosphere, while at larger distances flux tubes flow from the tail to the dayside carrying with them the hot plasma sheet particles which form the outer radiation zone and ring current. Thus the magnetosphere is divided into two regimes dominated by hot and cold plasma, respectively, and whose mutual boundary is the plasmapause (see, for example Russell and Thorne, 1970).