On the reformation at quasi- and exactly-perpendicular shocks: Full particle-in-cell simulations
On the reformation at quasi- and exactly-perpendicular shocks: Full particle-in-cell simulations
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关于准垂直和完全垂直冲击下的重组：完整的粒子内细胞模拟
DOI：
10.1029/2010ja015458
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
and R. Yamazaki
中科院分区：
文献类型：
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作者：
T. Umeda;Y. Kidani;M. Yamao;S. Matsukiyo;and R. Yamazaki
在较低的Alfven马赫数（MA= 5）下，对准垂直和完全垂直的无碰撞冲击下的重整进行了全粒子池（PIC）模拟研究。先前的自一致的一维（1 - D）混合和全PIC模拟表明，离子动力学对于垂直无碰撞冲击的非平稳性至关重要。这些结果表明，在离子回旋周期的时间尺度上，离子在激波锋面的反射导致了一个新的激波锋面的周期性坍缩和重建，这被称为激波改造。然而，最近的二维混合和全PIC模拟表明，在ma ~ 5的完全垂直冲击下，冲击重组不会发生。相比之下，另一个二维混合PIC模拟表明，在ma ~ 5的准垂直冲击下，激波重构仍然存在。虽然这两项工作似乎不一致，但由于数值模拟条件的几个差异，其原因并没有很好地理解。因此，本文给出了在几乎相同条件下准垂直和完全垂直冲击的全PIC模拟之间的直接比较。研究发现，冲击磁场在冲击切向上的平均时间发展表现出从重整阶段到非重整阶段的转变。另一方面，局部激波磁场表现出明显的激波锋的出现和消失，且周期在非重整阶段比重整阶段变长。
A full particle‐in‐cell (PIC) simulation study is carried out on the reformation at quasi‐ and exactly perpendicular collisionless shocks with a relatively low Alfven Mach number (MA= 5). Previous self‐consistent one‐dimensional (1‐D) hybrid and full PIC simulations have demonstrated that ion kinetics are essential for the nonstationarity of perpendicular collisionless shocks. These results showed that reflection of ions at the shock front is responsible for the periodic collapse and redevelopment of a new shock front on a timescale of the ion cyclotron period, which is called the shock reformation. Recent 2‐D hybrid and full PIC simulations, however, suggested that the shock reformation does not take place at exactly perpendicular shocks withMA∼ 5. By contrast, another 2‐D hybrid PIC simulation showed that the shock reformation persists at quasi‐perpendicular shocks withMA∼ 5. Although these two works seem to be inconsistent with each other, the reason is not well understood because of several differences in numerical simulation conditions. Thus this paper gives a direct comparison between full PIC simulations of quasi‐ and exactly perpendicular shocks with almost the same condition. It is found that the time development of the shock magnetic field averaged over the shock‐tangential direction shows the transition from the reformation to no‐reformation phase. On the other hand, local shock magnetic field shows the evident appearance and disappearance of the shock front, and the period becomes longer in the no‐reformation phase than in the reformation phase.