亚暴起始地磁指数判断的统计研究

Statistical Analysis of Substorm Onsets Determined by Geomagnetic Indices

利用2004年地磁西向电急流AL指数,亚暴电急流AE指数和场向电流AF指数来确定亚暴起始,并与2004.年亚暴极光起始进行对比.研究发现,如果以极光亚暴起始为时间零点,亚暴的西向电急流AL起始和电急流AE起始主要分布于-5～+6min的时间范围内,但在-9～+9min的时间范围内也有个别事例.场向电流AF起始分布较宽,可以分布于-8～+7min的时间范围内.平均西向电急流AL起始,电急流AE起始和场向电流AF起始分别为0.5,0.5,-0.1 min.通常西向电急流AL起始与极光起始同时的概率最高,而多数情况下电急流AE起始和场向电流AF起始提前极光起始1 min.这些地面磁场指数确定的亚暴起始分布,随着亚暴强度的增大(即最小AL指数减少,最大AE指数增大,最大AF指数增大)而向极光亚暴起始靠近.对于5个超级亚暴来说,其西向电急流AL起始和电急流AE起始都发生在极光起始之前.这些结果说明对于大亚暴,电急流的增加要早于极光爆发.

Using substorm AL index, substorm AE index and field-aligned current AF index in 2004, distribution of substorm AL, AE and AF onsets are studied with respect to substorm auroral onset. It is found that with auroral onsets being zero time, AL and AE onsets are mainly distributed between -5 and ＋6minute, with only few exceptions between -9 and ＋9minute. Field-aligned current AF onsets have a broader distribution from -8 to ＋7 minute. The average time differences of AL, AE, AF onsets are 0.5, 0.5, and -0.1 minute. The most probable AL onset is almost simultaneous with auroral onset, but the most probable onsets of AE and AF are about 1 min prior to auroral onsets. For those intense substorms, the onsets of AL, AE and AF approach to auroral onsets. For the five largest substorms, the onsets of AL and AE precede auroral onsets, suggesting during super substorms, substorm electric jet begin to increase before auroral breakup.