Motion of the dipolarization front during a flow burst event observed by Cluster

TLDR

The flow burst coincided with a clear dipolarization front ahead of the Earthward‑directed high‑speed flow. The study investigates a flow burst event observed by Cluster on July 22, 2001 during enhanced geomagnetic activity in the postmidnight magnetotail. The authors analyze the event using Cluster four‑spacecraft observations collected during that period. The dipolarization front, about 2000 km thick, moves Earthward and dawnward at ~77 km/s, deflecting upstream plasma and aligning the high‑speed flow parallel to the front, indicating that the front’s evolution is directly coupled with the fast flow.

Abstract

In this paper we study a flow burst event which took place during enhanced geomagnetic activity on July 22, 2001, when Cluster was located in the postmidnight magnetotail. The flow burst was associated with a clear dipolarization ahead of the high‐speed part of the predominantly Earthward directed flow. Based on the analysis of the four spacecraft data, we found that a ∼2000 km thick dipolarization front moves Earthward and dawnward with a speed of ∼77 km/s. The plasma before this front is deflected, consistent with the plasma ahead of a localized plasma bubble centered at midnight side being pushed aside by the moving obstacle. The main body of the high‐speed flow is directed mainly parallel to the dipolarization front. These observations indicate that the evolution of the dipolarization front across the tail is directly coupled with the fast flow.