Abstract:

This paper has analyzed 2760 substorm events in the northern hemisphere by using IMAGE FUV observations in order to get the probability distribution of substorm wait time (time interval between substorm onsets). The effects of the satellite orbit have been taken in account. It is found: (1) the most probable substorm wait time is between 2 and 3 hours. The wait time is longer for substorms occurring at lower latitudes (near Earth) than those occurring at higher latitudes (far tail); (2) For substorms occurring in the near Earth region, the wait time satisfies Gauss distribution, while for those in the far tail, the wait time satisfy both Gauss and Poisson distribution. This may indicate that the near Earth substorm events are more periodic than far tail events; (3) the satellite orbit affects the wait time distribution mainly after 10 hours. And it causes one psudo-peak around 8 hours, which is more apparent in the lower latitude events than in the higher latitude.

Key words: substorm, wait time, IMAGE, satellite orbit