短磁结构中的离子尺度电流结构
Ion-scale current structures in Short Large-Amplitude Magnetic Structures
摘要：
我们研究了磁层多尺度任务观测到的地球离子前震区短大振幅磁结构（SLAMS）中的电流结构。具有强电流（|J| ~1 μA/m^2）的结构具有与局部离子惯性长度（di）相当的标度长度。一种电流结构类型是由于SLAMS的磁场旋转而产生的电流片，并且这些电流片的子集可以表现出包括电子流出射流和X线型磁拓扑的重联特征。SLAMS边缘附近的双尺度电流片的传播速度比整个SLAMS慢得多，这表明它可能是由压缩引起的。电流结构也以磁声哨声波的形式存在，其中fci < f < flh，fci和flh分别是离子回旋频率和低杂波频率。电流片和哨声波中的场旋转产生可比较的|J|和能量转换率。电子加热被清楚地观察到在一个哨声包嵌入在一个较大规模的电流片的SLAMS，其中的平行电场和曲率漂移相反的电场激发电子。研究结果揭示了激波过渡区薄电流结构的产生和能量转换过程。
英文摘要：
We investigate electric current structures in Short Large-Amplitude Magnetic Structures (SLAMS) in the terrestrial ion foreshock region observed by the Magnetospheric Multiscale mission. The structures with intense currents (|J|~1 μA/m^2) have scale lengths comparable to the local ion inertial length (di). One current structure type is a current sheet due to the magnetic field rotation of the SLAMS, and a subset of these current sheets can exhibit reconnection features including the electron outflow jet and X-line-type magnetic topology. The di-scale current sheet near the edge of a SLAMS propagates much more slowly than the overall SLAMS, suggesting that it may result from compression. The current structures also exist as magnetosonic whistler waves with fci < f < flh, where fci and flh are the ion cyclotron frequency and the lower-hybrid frequency, respectively. The field rotations in the current sheets and whistler waves generate comparable |J| and energy conversion rates. Electron heating is clearly observed in one whistler packet embedded in a larger-scale current sheet of the SLAMS, where the parallel electric field and the curvature drift opposite to the electric field energize electrons. The results give insight about the thin current structure generation and energy conversion at thin current structures in the shock transition region.
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