Ion dynamics at the earthward termination of the magnetotail current sheet

Abstract

We investigate the dynamics of plasma sheet ions upon interaction with the magnetotail current sheet. During this interaction, ions can be subjected to prominent bunching in gyration phase because of enhanced tailward oriented centrifugal pull. We focus on the inner part of the plasma sheet and examine the consequences of this centrifugally driven phase bunching effect. In this region of space, as their Larmor radius is locally comparable to or smaller than the field variation length scale, ions experience nonadiabatic motion in a manner which differs from that in the distant tail where particles meander about the field minimum. Within the limits of the calculations which do not treat the particle dynamics in a self‐consistent manner, we show that phase bunching of plasma sheet ions leads to a distinctive current distribution in the near‐Earth tail, which is not found further out. In the equatorial vicinity, this distribution is characterized by a striated pattern of current both in the dawn‐dusk and in the Earth‐tail directions. The latter current leads to field line inclination in the dawn‐dusk direction at the earthward edge of the magnetotail current sheet, which may be viewed as characteristic of this region of space. We also show that in this region, off‐diagonal elements of the pressure tensor appear of importance to achieve stress balance.