Recovery phase of magnetospheric substorms and its association with morning‐sector aurora

Abstract

In contrast to the extensively studied growth and expansion phases of magnetospheric substorms, the substorm recovery phase has not received much attention in the published literature. It has generally been considered as a period in which all disturbances caused by the previous two phases decay, the magnetosphere “recovers” to reach a quiet state again. Using mainly ground‐based data, we show that the “recovery phase” contains a number of features which are qualitatively different from the expansion phase, that is, not just a decay of previously excited forms of energy release. Typical recovery phase phenomena include intense electrojet activity in the morning sector, high‐energy particle precipitation, the development of large‐scale auroral vortex streets (so‐called Ω bands and associated magnetic Ps 6 pulsations), and very often new eastward expanding active auroral phenomena, not unlike evening‐sector expansion phase features but concentrated to the morning sector of the auroral oval. Such features must be associated with the substorm mechanism itself. We suggest that our observations during the substorm recovery phase are explained by the magnetospheric reorganization after the ejection of a plasmoid. We show that a more detailed investigation of the late substorm features can increase our understanding of the physical processes leading to the complete cycle of magnetospheric energy release.