A revised (B, L) coordinate system to allow for distention of the magnetosphere by a symmetric ring current

Abstract

The McIlwain (B, L) coordinate system for describing physical points within the magnetosphere is modified to take account of magnetospheric distortions arising from symmetric ring currents, their associated induction fields, and a constant magnetopause boundary field on the day side of the earth. The goal in making such a modification is to develop a general procedure whereby stormtime magnetospheric distortions may be separated out of satellite particle data, making it possible to observe some of the more subtle aspects of particle behavior that otherwise may be hidden by larger effects. To demonstrate the usefulness of the modified (B, L) system, some new cases of Explorer 12 particle detector data are presented in which the particle configuration appears to be undergoing radial diffusion when plotted in the standard (B, L) system. However, when the counting rates are replotted in the modified system that accounts for ring currents, the diffusion is no longer evident. These cases are thus at least partially explained as being the effect of gross motion of the field lines themselves, rather than particle motion through the field lines.