亚暴起始位置和膨胀相持续时间对行星际磁场 B_z 分量的响应^*

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.