Recurrent substorm activity during the passage of a corotating interaction region

Recent observations of magnetospheric dynamics driven by interaction with both high-speed solar wind streams (HSSs) and interplanetary coronal mass ejections (ICMEs) have shown periodic substonns to be common under strong driving, but with different periods of similar to 4 and 2-3 h, respectively. However, it is unclear what causes these substorms and what determines their periodicity. Observations during the passage of a corotating interaction region preceding a high-speed stream are presented here and the observed enhancements in the AE index are shown to be a quasi-periodic sequence of substorms. The occurrence times of these substorms and the variation of the AL index are shown to be consistent with a simple loading-unloading model without the need for external triggers. A possible explanation is given for the lengthening of the inter-substorm period during HSS relative to that of sawtooth events during ICMEs. (C) 2009 Elsevier Ltd. All rights reserved.

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