Formation of plasmapause, or magnetospheric plasma knee, by the combined action of magnetospheric convection and plasma escape from the tail

TLDR

The revised Axford–Hines convective system incorporates recent geomagnetic data, showing that solar‑wind‑driven convection can penetrate the inner magnetosphere unless countered by Earth’s rotation, and that the magnetosphere’s tail is essentially open. The authors propose that the boundary between field‑line groups constitutes the plasmapause and aim to explain its observed characteristics. They argue that plasma on open field lines can escape into space during tail traversal, lowering density below equilibrium, while closed field lines prevent escape, maintaining diffusive equilibrium, creating a density discontinuity at the boundary. The analysis reveals a clear separation of magnetic lines into open and closed groups, a resulting plasma density discontinuity at their interface, and identifies this interface as the plasmapause, thereby accounting for its observed features.

Abstract

Magnetospheric convective system proposed by Axford and Hines is revised and made compatible with the view, based on the recently obtained geomagnetic data, that (1) the convective motion induced by the solar wind would penetrate to the innermost part of the magnetosphere, if it were not for the superposed effect of the earth's rotation, and the fact that (2) the earth's magnetosphere has an essentially open tail. Magnetic lines of force in the magnetosphere are then found separated into two groups: those that travel across the tail during the convective motion and those that are never transported to the tail. On field lines of the former group, the plasma density would be less than the value expected on the basis of the equilibrium theory, since the plasma along these field lines can escape to the outer space while the field line travels across the open magnetospheric tail and since the rate of plasma replenishment from lower levels is low. On field lines of the latter group, plasma escape is always prevented by closed field lines, so that the diffusive equilibrium would prevail. Hence at the boundary between these two groups of field lines, the plasma density is expected to show discontinuity. This boundary surface is suggested to be the plasmapause, and various observed features of the plasmapause are explained.