Polar Rain and the Question of Direct Particle Access.

摘要

Recent experimental findings on the weak, low-energy electron population found in the tail lobes and the low altitude polar regions to which they magnetically map are reviewed in light of two different polar rain models. In one model the field aligned solar wind electrons have direct entry to the magnetosphere in the distant tail where the field lines are assumed to be open. In the other, the polar rain is the potential-barrier-reflected electron component of the magnetosheath population that enters the magnetosphere at the cusp, and perhaps all along the magnetopause. The data do not fully support one model over the other, and it is possible that both entry mechanisms contribute depending on magnetopause position, on electron energy, and on the size and extent of boundary and barrier potentials. Keywords: Polar rain; Electron precipitation; Magnetotail; Polar caps; Reprints. (jhd)