Repetitive substorms caused by Alfvénic waves of the interplanetary magnetic field during high-speed solar wind streams
Abstract
Substorms sometimes occur repetitively with a period of ∼1-4 hours. In this paper we examine repetitive substorms, identified using particle injections and positive H bays on the nightside, that we find to occur during corotating high-speed streams associated with coronal holes. The high-speed streams often last for several days and are accompanied by large amplitude Alfvén waves of the interplanetary magnetic field (IMF). We find that repetitive substorms occur every ∼1-4 hours, regardless of the solar cycle phase, whenever the Earth's magnetosphere is impinged by these high-speed streams. We further find that a significant number of these substorms are associated with repetitive northward turnings of the Alfvénic IMF, each northward turning preceded by weakly-to-moderately southward IMF, i.e., Bz ∼ -3.6 nT for ∼29 min on the average. We present eight example intervals where most of the repetitive substorms were associated with a northward turning. Statistically, for 63.5% of 312 substorms we are able to identify a reasonable association with a northward turning. While limitations of the Weimer-mapped IMF used here and the spatial structure of the Alfvénic IMF prevent us from estimating a precise figure for the percentage of IMF triggered substorms, our results indicate that many of the repetitive substorms are likely due to repetitive triggering by the Alfvénic IMF.
- Publication:
-
Journal of Geophysical Research (Space Physics)
- Pub Date:
- December 2006
- DOI:
- 10.1029/2006JA011685
- Bibcode:
- 2006JGRA..11112214L
- Keywords:
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- Magnetospheric Physics: Substorms;
- Magnetospheric Physics: Magnetic storms and substorms (7954);
- Interplanetary Physics: Corotating streams;
- Magnetospheric Physics: Plasma convection (2463);
- external triggering;
- high-speed solar wind;
- substorms