磁层顶电子剪切流K-H不稳定性

磁层顶是由经过舷激波的太阳风和地磁层相互作用而形成的边界层,其上有电流流动.本文将这种电流看成电子剪切流,来讨论夜侧磁层顶的电子剪切流所引起的Kelvin-Helmholtz(K-H)不稳定性问题.电子剪切流受到的洛仑兹力中包括了电场的作用,正是这种作用使得剪切不稳定性要复杂一些.本文对电子剪切流激发的K-H不稳定性进行了细致的分析,从而得知,电子流剪切引起的K-H不稳定性倾向于在磁层顶内侧激发,并且只有当剪切速率在上下两阈值之间时,才可能激发K-H不稳定性.本文对比了夜侧近地磁层顶和磁尾磁层顶,发现当磁层顶两侧电子数密度之比恒定时,高电子数密度的磁层顶侧易产生K-H不稳定性.而磁鞘侧电子数密度n2与磁层侧电子数密度n1之比n2/n1的改变对不稳定性的影响也很显著:较大的n2/n1产生的K-H波主要是在低速区域,其有效增长率较小.

The instability of water-mud interface in viscous two-layer flow with large viscosity contrast

The temporal instability of parallel viscous two-phase mixing layers is extended to current-fluid mud by considering a composite error function velocity profile. The influence of viscosity ratio, Reynolds number, and Froude number on the instability of the system are discussed and a new phenomenon never discussed is investigated based on our numerical results. It is shown that viscosity can enlarge the unstable wave number range, cause new instability modes, and certainly reduce the growth rate of Kelvin-Helmholtz （K-H） instability.