Transport Path of Cold‐Dense Plasmas in the Dusk Magnetotail Plasma Sheet: MMS Observations
Transport Path of Cold‐Dense Plasmas in the Dusk Magnetotail Plasma Sheet: MMS Observations
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黄昏磁尾等离子体片中冷密等离子体的传输路径：MMS 观测
DOI：
10.1029/2021ja029747
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Giles B. L.
中科院分区：
文献类型：
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作者：
Nishino M. N.;Hasegawa H.;Saito Y.;Kitamura N.;Miyashita Y.;Nagai T.;Yokota S.;Russell C. T.;Gershman D. J.;Giles B. L.
在行星际磁场（IMF）向北的条件下，近地等离子体片变得寒冷而致密，这表明太阳风等离子体有效地穿过磁层顶进入磁层，并可能是电离层氧离子外流的贡献。等离子体片的冷而密的特征在磁尾侧翼区域更为明显，磁尾侧翼区域是冷的太阳风等离子体和热的磁层等离子体的界面。已经提出了几种物理机制来解释太阳风等离子体穿过磁层顶的进入以及在尾翼区域形成冷密等离子体片（CDPS）。然而，磁尾内部冷密等离子体的传输路径还没有被理解。在这里，我们提出了一个案例研究的CDPS在黄昏磁尾的磁层多尺度（MMS）航天器在强向北IMF和高密度太阳风条件下。离子分布函数由高能和低能分量组成，低能分量间歇性地在与局部磁场平行和反平行的方向上显示能量分散。对能量分散的低能离子的飞行时间分析表明，这些离子起源于磁尾更远的区域，沿着磁场向电离层移动，然后通过镜面反射回到磁尾。俯仰角色散分析给出了关于能量分散离子的行进时间和路径长度的一致结果。在此基础上，讨论了低能离子在向北IMF过程中能量分散结构的可能产生机制。
The near‐Earth plasma sheet becomes cold and dense under northward interplanetary magnetic field (IMF) condition, which suggests efficient solar wind plasma entry into the magnetosphere across the magnetopause for northward IMF and a possible contribution of ionospheric oxygen ion outflow. The cold and dense characteristics of the plasma sheet are more evident in the magnetotail flank regions that are the interface between cold solar wind plasma and hot magnetospheric plasma. Several physical mechanisms have been proposed to explain the solar wind plasma entry across the magnetopause and resultant formation of the cold‐dense plasma sheet (CDPS) in the tail flank regions. However, the transport path of the cold‐dense plasma inside the magnetotail has not been understood yet. Here, we present a case study of the CDPS in the dusk magnetotail by magnetospheric multiscale (MMS) spacecraft under strongly northward IMF and high‐density solar wind conditions. The ion distribution function consists of high‐ and low‐energy components, and the low‐energy one intermittently shows energy dispersion in the directions parallel and antiparallel to the local magnetic field. The time‐of‐flight analysis of the energy‐dispersed low‐energy ions suggests that these ions originate in the region farther down the tail, move along the magnetic field toward the ionosphere and then come back to the magnetotail by the mirror reflection. The pitch‐angle dispersion analysis gives consistent results on the traveling time and path length of the energy‐dispersed ions. Based on these observations, we discuss possible generation mechanisms of the energy‐dispersed structure of the low‐energy ions during the northward IMF.