Computer Simulation of Earth's Magnetotail Dynamics

第一次我们对磁尾的结构和动力学随行星际磁场（IMF）在南北、东西平面上的方向变化进行了全球MHD模拟。结果，磁场中性线形成的等离子体片向南IMF和热等离子体被喷向尾部。当在IMF向南的时间间隔内存在较大的东西分量时，束缚热等离子体的磁力线呈螺旋结构。螺旋等离子体团的两个边缘逐渐弯曲，并随着螺旋等离子体团向尾部的偏移而集中到地球电离层。然后，在电离层和螺旋等离子体团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。当所有场线断开时，尾重联在整个等离子体片区域内进行，热等离子体团以螺旋状向尾喷射.此外，为了研究边界层现象，我们采用改进的蛙跳方法，引入新开发的MHD程序，在两次网格点上进行了高分辨率的MHD模拟.磁层顶厚度在磁场向南方向较薄，磁场向北方向较厚。这是因为磁层顶的磁场向北变化不大，另一方面向阳面中性线处出现高压等离子体，使磁层顶变薄。随着时间的推移，边界层（或磁层顶）由于向阳面磁合并的震动而呈现波浪状结构。这种波状结构扩大了磁鞘向磁层顶的动量传递。

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.