Cluster卫星观测的中高度极隙区中场向电流引起的磁场的扰动变化

CLUSTER OBSERVATIONS OF MAGNETIC FIELD DISTUR-BANCES CAUSED BY FACS IN THE MID-ALTITUDE CUSPS

本文分析了2002年9月10日Cluster四颗卫星穿越南极和北极极隙区期间的观测资料。这两次穿越是在弱而稳定的南向行星际磁场(IMF)条件下发生的。数据显示极隙区中的场向电流(FACs)引起了大的磁场扰动。本文采用了一种基于卫星多点测量来计算扰动界面方向和运动速度的方法。结果显示界面与磁力线大致平行,而它们的速度在卫星穿越南极极隙区时几乎朝向晨侧,在穿越北极极隙区时几乎朝向昏侧,并且其运动速度与相应卫星的速度相比其值很小。

Data from the four Cluster spacecraft during the mid-altitude cusp crossings on September 10 of 2002 are presented. The encounters occur under conditions of weak and steady southward Interplanetary Magnetic Field （IMF）. The data show that there are the field-aligned currents （FACs） in the cusp causing large magnetic field disturbances. The boundary structures of the cusps are characterized by the FACs interfaces. A method for calculating the velocities of the interface based on multi-point measurements of spacecraft are introduced. Results show that the interfaces are roughly parallel to magnetic field lines, and their velocities are almost dawnward for the southern crossing and almost duskward in the northern pass. The velocities have small values （0.36-0.80km/s） with respect to satellite＇ s velocity in the cusp crossings.