Computer Simulation of Earth's Magnetotail Dynamics

这是第一次。我们对磁尾的结构和动力学进行了全局性的MHD模拟，模拟结果与行星际磁场(IMF)在南北、东西向平面上的方向有关。结果表明，对于向南的IMF，磁中性线在等离子体片中形成，热等离子体向尾部喷射。当IMF存在较大的东西向分量时，约束热等离子体的磁力线形成螺旋形结构。当螺旋等离子体略向尾部移动时，它的两边逐渐卷曲，与地球的电离层同心。然后，在电离层和螺旋等离子体的边缘之间出现了一个类似磁通绳的结构，它限制了纵向磁场而不是等离子体。尾部重联在整个等离子体片区域进行，当所有场线断开时，热等离子体团以螺旋等离子体团的形式向尾部喷射。此外，为了研究边界层现象，我们在改进的跳蛙方法中引入了一个新的MHD程序，在两个时间网格点上进行了高分辨率的MHD模拟。磁层顶厚度向南偏薄，偏北偏厚。这是由于磁场沿磁层顶向北变化较小，而在日侧中性线上出现高压等离子体，使磁层顶变薄。随着时间的推移，边界层(或磁层顶)具有波浪型结构，以利于白天磁场合并的抖动。波状结构扩大了从磁鞘到磁层顶的动量传递。

For the first time. we carried out a global MHD simulation on the structure and dynamics of magnetotail depending on the orientation of the interplanetary magnetic field (IMF) in the plane of north-south, east-west. As a results, the magnetic neutral line forms in the plasma sheet for southward IMF and a hot plasma is ejected towards the tail. When there is a large east-west component of IMF during the southward interval of IMF, the magnetic field lines which confine hot plasma become a helical structure. Both edges of the helical plasmoid are gradually winded are concented to the earth's ionosphere as the helical plasmoid somewhat shifts towards the tail. Then a structure like magnetic flux rope, that confines a longitudinal magnetic field instead of plasma, appears between the ionosphere and the edges of the helical plasmoid. The tail reconnection proceeds in the whole plasma sheet region and the hot plasmoid is ejected tailward as a helical plasmoid when all the field lines are disconnected.Moreover we carried out a high resolution MHD simulation in two times grid points by introducing a newly developed MHD code in a modified leap-frog method in order to study a boundary layer phenomena. The thickness of magnetopause is thinner for southward IMF and it is thicker for northward IMF. Thiis is because the magnetic field varies mildly across the magnetopause for northward, on the other hand a high pressure plasma appears in the dayside neutral line to make thinner the magnetopause. When time elapses, the boundary layer (or magnetopause) has a wavy structure for the shake of dayside magnetic merging. The wavy structure enlarges the momentum transfer from magnetosheath to magnetopause.