The current sheet disruption model for substorm expansion phase onset: Background, arguments, and relationship to global substorm evolution

Abstract

The onset and evolution of substorms is viewed by many researchers to be a central question in magnetospheric physics. The most popular model for substorms is the Near-Earth Neutral Line model. This model asserts that the formation of a new, near-Earth reconnection region is the central feature of the onset of the expansion phase and that all other phenomena flow from this event. In recent years the Current Sheet Disruption model has been proposed as an alternative. This model asserts that the initiation of the substorm expansion phase is triggered by the disruption of the thin near-Earth current sheet that forms at and just beyond geosynchronous orbit in the late growth phase, and that the formation of a reconnection region proceeds from this event. In this paper we will review the history of and evidence for the Current Sheet Disruption model, especially with regard to recent evidence in favor of the NENL model. We will also review recent global MHD simulation results that provide an interesting perspective on the relationship between these two models.