Axisymmetric Plasmasphere Resonances: Toroidal Mode

Authors:
Publisher website
Google Scholar
Abstract
The usual magnetohydromagnetic approach is used to investigate axisymmetric perturbations in a plasma permeated by a static dipole field. The model plasmasphere used has stationary, perfectly reflecting boundaries concentric with the dipole, and the plasma density is assumed to be spherically symmetric. The poloidal wave equation is reduced to a hierarchy of coupled differential equations in the radial variable. The toroidal wave equation is solved exactly using a density law which gives a good order of magnitude fit to recent whistler data. Because the extent of the plasma is finite, the eigenperiods are everywhere finite, including the poles. The stretched string model of vibrating lines of force is derived using the Wentzel-Kramers-Brillouin approximation, which fortuitously gives the exact periods for the density law utilized. Two unusual results are the prediction of shorter periods in the polar zones than at some high middle latitudes and discontinuous eigenperiods across the line of force which just grazes the outer plasma boundary. A general discussion of the results and the special significance of the toroidal and poloidal modes because of their symmetry is provided.

This publication has 20 references indexed in Scilit: