地球磁层顶K-H不稳定性与撕裂模的耦合及涡旋撕裂模不稳定性

本文用二维MHD数值模拟研究了地球磁层顶同时存在速度剪切和磁场剪切时Kelvin-Helmholtz不稳定性（K-H）和撕裂模不稳定性（TM）的耦合过程。在雷诺数和磁雷诺数确定时,Alfvèn马赫数值（M_A）对耦合特性起决定性作用。在本文选取的参数条件下,若M_A<0.4,自发TM占主导地位;当0.4≤M_A<1.4时,TM受到K-H明显调制;如果M_A≥1.4,K-H引起的涡旋运动起控制作用,导致一种新的不稳定性产生。该不稳定性称作涡旋撕裂模不稳定性。其饱和后长时间渐近状态由一个大尺度的流体涡旋和同心磁岛组成。在地球磁层顶通量传输事件（FTEs）中它可能起着重要作用。

COUPLING OF KELVIN-HELMHOLTZ INSTABILITY AND TEARING MODE INSTABILITY AT EARTH'S MAGNETOPAUSE

A 2-D MHD simulation is performed to study the coupling of tearing mode instability （TM） with Kelvin-Helmholtz instability （K-H） when a B field shear exists at the magnetopause along with the velocity shear. It is found that the Alfvèn Mach number, MA plays an essential role in determining the properties of the coupled instability. In the case of B0 = 1.0, Rm-1 = 2.0 and R-1 = 0.1, if MA < 0.4, the spontaneous TM is dominated in the system. When 0.4 ≤ MA <1.4, TM is apparently modified by K-H. As MA ≥5 1.4,the coupled instability, called the vortex induced tearing mode instability （VITM）, appears to be intrinsically different from the conventional TM. The long time asymptotic quasi-static state for VITM is characterized by a large scale fluid vortex together with a co-centred magnetic island.