Mid-Tail Magnetic Reconnection Triggering Substorm: A Case Study

Abstract

Onset of a substorm is closely correlated with the current disruption in the near-Earth magnetotail, about 6 8 RE and magnetic reconnection in the middle magnetotail, around 20 30 RE. It is vital to understand the onset of a substorm by studying the time series among polar expansion of aurora, current disruption and magnetic reconnection. In this paper, with measurements from the Cluster spacecraft in the middle magnetotail, LANL-01 and LANL-97 at the synchronous orbit, POLAR in the near-earth magnetotail and IMAGE at polar region, a single substorm event is presented. The analysis indicates that magnetic reconnection is 3 minutes earlier than the current disruption in the near-earth magnetotail. Aurora brightening is observed by IMAGE 4 minutes after the current disruption. Simultaneously, the sharp increment of the AE index implies the substorm onset. The observational result is consistent with the Near Earth Neutral Line model (NENL).