Storm and substorm effects on magnetotail current sheet motion

Abstract

Passes through the mid‐region of the magnetotail by the Cluster spacecraft from 2001 to 2007 have been examined to study the dynamics of the cross‐tail current sheet. Cluster is ideally placed to study this region due to the orientation of the orbit in the magnetotail, such that the current sheet is sampled at distances downtail from about 8–19 RE. Multiple fluctuations of the X component of the magnetic field (BX) from positive to negative and vice versa, measured by Cluster as it crosses the nominal location of the current sheet, indicate that the current sheet is in motion. In this study we use the number of crossings of the current sheet by the Cluster 3 spacecraft as a measure of the dynamics of the magnetotail. The effects of substorm and magnetic storm activity on the dynamics during these orbits have been investigated using the AE and SYM‐H indices. Our results indicate that the current sheet is more often in motion during orbits when there is greater than average substorm activity and a quiet ring current. Results suggest that internal processes within the tail that initiate substorms may also initiate the flapping motion of the current sheet. In addition the more dipolar field that results from an enhanced ring current during magnetic storms may inhibit tail dynamics during substorm events.