磁层亚暴恢复期间等离子片边界层区的Kelvin—Helmholtz不稳定性

本文根据两个理想的磁流体力学模型研究了磁层亚暴恢复期间等离子体片边界层区的Kelvin-Helmholtz不稳定性。一个模型由三个均匀的等离子体区组成--北尾瓣、等离子体片和南尾瓣。在此模型里,不稳定模式在北(或南)尾瓣和等离子体片之间的边界面上激发。另一个模型由五个均匀的等离子体区组成--北尾瓣、等离子体片北边界层、等离子体片中间层、等离子体片南边界层和南尾瓣,在等离子体片边界层区存在着两种不稳定模式,一种在等离子体片的北(或南)边界层和中间层之间的边界表面上激发(模式Ⅰ);另一种在等离子体片北(或南)边界层和北(或南)尾瓣之间的边界面上激发(模式Ⅱ).模式Ⅰ多数时间是不稳定的。这些不稳定模式可能引起卫星观测到的等离子体边界层的一些特征。 

KELVIN-HELMHOLTZ INSTABILITY IN BOUNDARY LAYER REGIONS OF THE PLASMA SHEET DURING MAGNETOSPHERIC SUBSTORM RECOVERY

The Kelvin-Helmholtz instability in boundary layer regions of the plasma sheet during magnetospheric substorm recovery is studied based on two idealized MHDmodels.One model consists of three uniform plasma regions-the tail lobe,the plasma sheet,and the south tail lobe.In this model the unstable mode is excited at the boundary surface between the north (or south) tail lobe and the plasma sheet.The other model consists of five uniform plasma regions-the north tail lobe,the north boundary layer of the plasma sheet,the middle layer of the plasma sheet,the south boundary layer of the plasma sheet,and the sorth tail lobe.There are two unstable modes in boundary layer regions of the plasma sheet:one is excited at the boundary surface between the north (or south) boundary layer and the middle layer of the plasma sheet (Mode-I) and the other is excited at the boundary surface between the north (or south) boundary layer of the plasma sheet and the north (or south) tail lobe (Mode-II).Mode-Iis unstable most of the time.These unstable modes may cause some features of boundary layer regions of the plasma sheet observed oil satelittes.