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Kelvin-Helmholtz vortices in the magneotail-flank

磁尾侧面的开尔文-亥姆霍兹涡流

基本信息

批准号：
15540426
负责人：
FUJIMOTO Masaki
金额：
$ 1.98万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

项目摘要

The Kelvin-Helmholtz (KH) vortices are a candidate agent for large-scale plasma transport across the magnetotail flank boundary. To understand the nature of MHD-scale KH vortices in non-llinear regimes, we have performed two-dimensional numerical simulations including finite electron inertia. Non-zero in-plan magnetic field is assumed to be present.When the stabilizing magnetic tension is weak, nicely rolled-up vortices are formed and field lines are so stretched to form an anti-parallel geometry within the vortices. Then reconnection is triggered. Such a process has been studied in resistive MHD approaches, however, this study is the first to prove the process from the cross-scale coupling point of view.On the other hand, when the tension is strong, the results are drastically dofferent depending on whether the sign of the magnetic field component changes across the shear layer or not.(1) When the magnetic component does not change sign across the shear layer, the effects of the instability is only to broaden the shear layer.(2) When the magnetic component changes sign across the shear layer, already in the early phase of the instability growth, a part of the current sheet is pinched by the flow and reconnection takes place. Then the flow produced by reconnection assists the vortex to grow and the size of the vortex obtained in this situation I smuch larger than the one without reconnection. What is more, the large vortex is filled with mixed plasma, that is, large scale plasma mixing across the boundary is attained in this situationWhat is even more interesting, we have found that the combination of strong magnetic tension and anti-parallel geometry is the best for creating large scale plasma mixing across the velocity shear layer.

开尔文-亥姆霍兹 (KH) 涡流是大规模等离子体传输穿过磁尾侧翼边界的候选媒介。为了了解非线性区域中 MHD 尺度 KH 涡旋的性质，我们进行了包括有限电子惯性在内的二维数值模拟。假设存在非零平面内磁场。当稳定磁张力较弱时，会形成良好卷起的涡旋，并且磁力线被拉伸以在涡旋内形成反平行几何形状。然后触发重连。这种过程已经在电阻MHD方法中进行了研究，然而，本研究首次从跨尺度耦合的角度证明了该过程。另一方面，当张力很强时，根据磁场分量的符号是否在剪切层上发生变化，结果会有很大不同。（1）当磁性分量在剪切层上没有改变符号时，不稳定性的影响只是扩大了剪切层的范围。 (2) 当磁性分量穿过剪切层改变符号时，已经处于不稳定性增长的早期阶段，电流片的一部分被流动挤压并发生重新连接。然后，重新连接产生的流动有助于涡流的增长，并且在这种情况下获得的涡流的尺寸比没有重新连接的涡流的尺寸大得多。更重要的是，大涡流中充满了混合等离子体，即在这种情况下实现了跨边界的大规模等离子体混合。更有趣的是，我们发现强磁张力和反平行几何结构的结合最适合在速度剪切层上产生大规模等离子体混合。