Repetitive substorms caused by Alfvenic waves of the interplanetary magnetic field during high-speed solar wind streams

Substorms sometimes occur repetitively with a period of similar to 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 Alfven waves of the interplanetary magnetic field ( IMF). We find that repetitive substorms occur every similar to 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 Alfvenic IMF, each northward turning preceded by weakly-to-moderately southward IMF, i.e., B-z similar to - 3.6 nT for similar to 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 Alfvenic 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 Alfvenic IMF.