亚暴起始位置和膨胀相持续时间对行星际磁场Bz分量的响应

磁层亚暴是太阳风–磁层–电离层耦合过程中的重要爆发性事件，其特性受太阳风参数的影响很大。本文利用对IMAGE卫星在2000 － 2005年观测到的4193个亚暴起始事件，统计研究了在不同的行星际磁场（IMF）B_z 条件下亚暴起始位置和膨胀相持续时间。结果表明，南向IMF发生的亚暴比北向IMF下发生的亚暴要多。南向IMF条件下亚暴AE指数最大值的平均值基本上>600 nT，并有随南向IMF持续时间增大而增大的趋势。北向IMF条件下亚暴AE指数最大值的平均值基本上<500 nT，并有随北向IMF持续时间增大而减小的趋势。亚暴的起始磁纬度基本上位于65° － 70°之间。当南向IMF或北向IMF的持续时间增大，超过80 min时，北半球的亚暴起始磁纬度会降低。亚暴起始磁地方时大部分位于22:15 － 23:15 MLT之间。但整体分布比较分散，显示不出特别清晰的随IMF B_z持续时间变化的趋势。相比于南向的IMF，北向IMF期间发生亚暴的平均膨胀相持续时间增大了将近10 min，表明南向IMF期间，亚暴强度虽然较大，但其膨胀相持续时间较短，亚暴能量释放和耗散的速度更快。 

Response of Substorm Onset Location and Expansion Phase Duration to Interplanetary Magnetic Field Bz

A magnetospheric substorm is a significant process in solar wind-magnetosphere- ionosphere coupling. Substorm onset locations have a great dependence of solar wind parameters. Based on 4193 auroral breakup events identified by Frey et al. from about 5 years IMAGE FUV data, we statistically study the distribution of substorm onset locations and substorm expansion duration time under different Interplanetary Magnetic Field (IMF) conditions in southern and northern hemispheres. It is found that the occurrence rate of a substorm is relatively bigger under southward IMF than northward IMF. The maximum value of substorm AE index is above 600 nT under southward IMF, and increases with the evolution of southward IMF lasting time. While the maximum value of substorm AE index is beneath 500 nT under northward IMF, and decreases with the evolution of northward IMF lasting time. The substorm onset magnetic latitude is around 65°－70°. With the lasting time of northward/southward IMF exceeding 80 minutes, the substorm onset magnetic latitude in the northern hemisphere lower with the evolution of IMF lasting time. The substorm onset is around 22:15－23:15 MLT. It’s irregular under different IMF lasting time. The average expansion time of substorm is about 10 minutes larger under northward IMF than southward IMF. It indicates that the speed of substorm energy release and dissipation is faster under southward IMF with intense substorms.