Single-spacecraft detection of rolled-up Kelvin-Helmholtz vortices at the flank magnetopause
Single-spacecraft detection of rolled-up Kelvin-Helmholtz vortices at the flank magnetopause
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DOI：
10.1029/2006ja011728
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发表时间：
2006-09-09
影响因子：
2.8
通讯作者：
Reme, H.
中科院分区：
文献类型：
--
作者：
Hasegawa, H.;Fujimoto, M.;Reme, H.
[ 1]最近的数值模拟表明，一旦开尔文-亥姆霍兹不稳定性（KHI）非线性增长形成高度卷起的涡流，涡流内就不可避免地实现了等离子体混合。因此，通过现场测量确定卷起的涡旋是一项重要任务，是确定太阳风等离子体进入磁层的机制和了解涡旋形成条件的一个步骤。在本研究中，我们表明，卷起的漩涡是可检测的，即使从单航天器的测量。KHI的数值模拟表明，在卷起的旋涡的一小部分低密度，磁层等离子体的尾部速度超过了磁鞘流。此特征仅在涡卷卷起后出现，因此可用作卷起的标记。在星团多航天器测量侧翼磁层顶卷起的涡旋时确实发现了这种特征。通过使用这个标记，我们已经搜索的事件一致的卷起从Geotail观测显示准周期等离子体和场波动的侧翼低纬度边界层（LLBL）下向北行星际磁场（IMF），推测与KH波。调查显示，这种卷起的事件确实发生在黎明和黄昏两侧，并不罕见的北IMF条件。此外，在所有卷起的情况下，磁鞘状离子检测到的磁层侧的边界。这些结果表明，KHI在北向IMF下侧翼LLBL的形成中起着不可忽视的作用。
[ 1] Recent numerical simulations suggest that as soon as the Kelvin-Helmholtz instability (KHI) has grown nonlinearly to form a highly rolled-up vortex, plasma mixing is inevitably achieved within the vortex. Identification of rolled-up vortices by in situ measurements is therefore an important task as a step to establish the mechanism by which solar wind plasmas enter the magnetosphere and to understand conditions under which the vortices form. In the present study we show that the rolled-up vortices are detectable even from single-spacecraft measurements. Numerical simulations of the KHI indicate that in the rolled-up vortex the tailward speed of a fraction of low-density, magnetospheric plasmas exceeds that of the magnetosheath flow. This feature appears only after a vortex is rolled up and thus can be used as a marker of roll-up. This signature was indeed found in the Cluster multispacecraft measurements of the rolled-up vortices at the flank magnetopause. By use of this marker, we have searched for events consistent with the roll-up from Geotail observations showing quasi-periodic plasma and field fluctuations in the flank low-latitude boundary layer (LLBL) under northward interplanetary magnetic field ( IMF), presumably associated with KH waves. The survey shows that such rolled-up events do occur on both dawn and dusk flanks and are not rare for northward IMF conditions. In addition, in all the rolled-up cases, magnetosheath-like ions are detected on the magnetospheric side of the boundary. These findings indicate that the KHI plays a nonnegligible role in the formation of the flank LLBL under northward IMF.