Seasonal-longitudinal variation of substorm occurrence frequency: Evidence for ionospheric control

Wang H., Luhr H.
Department of Atmospheric Oceanic and Space Science, University of Michigan, Ann Arbor, MI 48109, United States; College of Electronic Informatics, Wuhan University, Hubei, China; GeoForschungsZentrum Potsdam, Telegrafenberg D-14473 Potsdam, Germany

Abstract: Based on 2760 well-defined substorm onsets in the northern hemisphere and 1432 in the southern hemisphere observed by the FUV (Far Ultraviolet) Imager on board IMAGE (Imager for Magnetosphere-to-Aurora Global Exploration) spacecraft, a statistical study is performed for both hemispheres. The main emphasis is put on a possible dependence of the substorm occurrence frequency on season and longitude (S/L). It was found that around December solstice UT noon-time and around June solstice UT nighttimes are more favorable for substorms to occur. The occurrence frequency varies by a factor of 2. The sum of ionospheric Pedersen conductances of both hemispheres caused by solar illumination in the nightside auroral regions can account for the S/L dependence. Lower total conductivity seems to reduce the trigger level. We find that the IMF threshold for initiating a substorm is on average lower during favorable times, thus, substorms can occur more frequently. Copyright 2007 by the American Geophysical Union.

Year: 2007
Source title: Geophysical Research Letters
Volume: 34
Issue: 7
Art. No.: L07104
Cited by: 2
Link: Scorpus Link
Document Type: Article
Source: Scopus
Authors with affiliations:

1. Wang, H., Department of Atmospheric Oceanic and Space Science, University of Michigan, Ann Arbor, MI 48109, United States, College of Electronic Informatics, Wuhan University, Hubei, China
2. Lühr, H., GeoForschungsZentrum Potsdam, Telegrafenberg D-14473 Potsdam, Germany

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