The occurrence rate of magnetospheric‐substorm onsets: Random and periodic substorms

Particle-injection events are monitored on three geosynchronous satellites to determine the occurrences of magnetospheric substorms: for every consecutive pair of substorms found, the time interval [Delta]t between substorm onsets is determined. In this manner, 1001 values of [Delta]t are obtained. A statistical analysis of the [Delta]t values finds that the most-probable time between substorm onsets is [Delta]t [approx] 2.75 hours; this is interpreted to be the period between substorms when substorms occur cyclically. The statistical analysis of the [Delta]t values also finds a random probability for the occurrence of substorms with a mean time between random substorms of about 5 hours: it is speculated that this random occurrence may be caused by a property of the solar wind that varies randomly with an approximately 5-hour time scale. About 1500 substorms occur per year: about half are periodic and about half occur randomly. 59 refs., 5 figs.

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