Seasonal‐longitudinal variation of substorm occurrence frequency: Evidence for ionospheric control
Seasonal‐longitudinal variation of substorm occurrence frequency: Evidence for ionospheric control
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DOI：
10.1029/2007gl029423
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发表时间：
2007-04
影响因子：
5.2
通讯作者：
H. Wang;H. Lühr
中科院分区：
文献类型：
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作者：
H. Wang;H. Lühr
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.
