Substorm dynamics in the magnetotail

Abstract

The large-scale dynamic evolution of the magnetotail in relation to substorms is most commonly understood and described in terms of magnetic reconnection, neutral line formation, and plasmoid ejection into the distant tail, as well as current disruption and diversion in the inner tail. Recent magnetohydrodynamic simulations have shown that the two aspects, which are often considered as alternative models, may well be part of one unstable process. We review the most recent update of this model. A new element, which has been strongly emphasized recently by observations as well as simulations, is the formation of a thin current sheet in the inner tail during the late substorm growth phase. This presumably eases the onset of instability, although the actual mechanism has not been clearly identified. The basic concept of a large-scale instability, involving the local breakdown of ideal MHD, has not changed significantly. However, recent MHD simulations as well as test particle investigations have put more emphasis on the role of the near tail region in providing current diversion ("disruption") and particle acceleration.