Transient Proccsses near the Dayside Magnetopause Associated with Solar Wind Changes

利用1992年10月17-18日和11月4日日侧磁层顶附近的Geotail观测资料，研究了磁层顶和磁层的振荡变化。研究结果总结如下：1。11月4日观测到的磁层顶交叉点与向北行星际磁场（IMF）有关，其特征是磁场中锯齿波形式的准周期脉冲和切向磁层顶的等离子体流分量。磁层顶电流层外的磁场方向为北向，并有反日倾斜，表明磁场在磁层顶上有包裹作用。波浪形磁层顶的边界法线在上游有系统地向太阳方向倾斜，而在下游有向反太阳方向倾斜的趋势，且存在较大偏差。2. 当观测到磁层顶交叉与向南的国际货币基金组织有关时，我们还观察到磁层顶方向明显的入/出依赖关系，这与磁层顶尾部移动的周期性凸起一致。然而，与IMF向北移动的情况相比，后向移动结构的重现不那么规律。此外，这也暗示了沿磁层顶的北（南）向流动发生在与磁层顶无关的向内（向外）磁场分量上。3. 10月17-18日在日侧磁层观测到Pc5和压缩Pc3脉动。Pc5的脉动特征符合以模态为基础的文件线驻振理论。观测到的Pc5脉动被认为是由磁层的突然压缩和膨胀引发的。另一方面，压缩Pc3脉动与向地球传播的快速磁声波一致。

Based on Geotail observations near the dayside magnetopause on October 17-18 and November 4,1992, we have studied oscillatory variations at the magnetopause and in the magnetosphere. The results are summarized as follows :1. Magnetopause crossings, associated with the northward interplanetary magnetic field (IMF) observed on November 4, were characterized by quasi-periodic pulses of a sawtooth wave form in the magnetic filed and the plasma flow components tangential to the magnetopause. The direction of magnetic field outside the magnetopause current layr was northward with antisunward tilt, indicating the draping of magnetic filed on the magnetopause. Boundary normals of wavy magnetopause systematically inclined sunward on the upstreamside, while they tend to incline antisunward with considerable deviation on the downstream side. 2. When the magnetopause crossings were observed in association with the southward IMF,we also observed a clear inbound/outbound dependence of the magnetopause orientation consistent with the tailward-moving recurrent bumps at the magnetopause. However, recurrence of tailward-moving structures is less regular than that for the case of northward IMF.In addition, there is an implication that the northward (southward) flow along the magnetopause occurred for the inward (outward) directed magnetic filed component nonnal to the magnetopause. 3. Pc5 and compressional Pc3 pulsations were observed in the dayside magnetosphere on October 17-18. The signature of the Pc5 pulsations agrees with the theory of file line standing oscillations with the mode being the fundamental. The observed Pc5 pulsations were regarded to be triggered by sudden compressions and expansions of the magnetosphere. On the other hand, compressional Pc3 pulsations are consistent with fast magnetosonic waves propagating earthward.