Random and periodic substorms and their origins in the solar wind

R. D. Belian, J. Borovsky, R. J. Nemzek, and C. W. Smith

Proceedings of the Second International Conference on Substorms, pp. 463-465, 1994


Substorms occur (recur) in two fashions: periodically with time or randomly in time. A statistical analysis of the time intervals (Delta)t between subsequent substorm onsets clearly shows these two types of substorms. When substorms are recurring periodically, the period is 3.1 plus/minus 1.2 hours, and the distribution of periods is gaussian. When substorms are occurring randomly, the time intervals (Delta)t between successive substorm onsets are distributed according to the exponential distribution exp(-(Delta)t//5 hours), with a 5-hour mean interval between random onsets. With the use of the Los Alamos geosynchronous energetic-particle dam and the OMNI solar-wind data, it is shown that periodic substorms are associated with time intervals when the average value of the IMF is southward for extended periods of time and it is shown that randomly occurring substorms are statistically correlated with randomly occurring northward-to-southward reversals of the 1-hour-averaged values of the IMF B(sub z).

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