Evidence of an extended electron current sheet and its neighboring magnetic island during magnetotail reconnection
Evidence of an extended electron current sheet and its neighboring magnetic island during magnetotail reconnection
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DOI：
10.1029/2008ja013385
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发表时间：
2008-12
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通讯作者：
Li‐Jen Chen;N. Bessho;B. Lefebvre;H. Vaith;A. Fazakerley;A. Bhattacharjee;P. Puhl-Quinn;A. Runov;Y. Khotyaintsev;A. Vaivads;E. Georgescu;R. Torbert
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文献类型：
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作者：
Li‐Jen Chen;N. Bessho;B. Lefebvre;H. Vaith;A. Fazakerley;A. Bhattacharjee;P. Puhl-Quinn;A. Runov;Y. Khotyaintsev;A. Vaivads;E. Georgescu;R. Torbert
[1]在没有明显引导场的磁尾重联事件中，我们发现了空间扩展的电子电流片(ECS)及其邻近的磁岛。这一发现是基于来自四星团航天器的数据，并通过扩散区域内电子分布函数和直流电场的详细地图得以实现。这些地图是使用质量比mi/me=800的二维粒子单元模拟开发的。其中一艘航天器穿过重联零点的ECS，并与其他三艘航天器一起记录了以下特性：(1)ECS与一层垂直于ECS的双极电场并置，指向ECS，半宽小于8电子皮肤深度。(2)在流入区直至ECS和分离区，电子具有温度各向异性(Te∥/Te⊥&Gt；1)，并且向ECS方向的各向异性增加。(3)在ECS上下约1个离子皮肤深度(Di)范围内，电子密度向ECS方向减小3-4倍，在ECS边缘达到最小值，在ECS中心有一个局部明显的极大值。(4)双尺度磁岛连接到ECS，将其与另一重连接层隔开。我们的模拟表明，垂直于ECS的电场是由于电荷不平衡造成的，并且是ECS尺度的，离子对该电场的响应表现出电子尺度结构。
[1] We have identified a spatially extended electron current sheet (ECS) and its adjacent magnetic island during a magnetotail reconnection event with no appreciable guide field. This finding is based on data from the four Cluster spacecraft and is enabled by detailed maps of electron distribution functions and DC electric fields within the diffusion region. The maps are developed using two-dimensional particle-in-cell simulations with a mass ratio mi/me = 800. One spacecraft crossed the ECS earthward of the reconnection null and, together with the other three spacecraft, registered the following properties: (1) The ECS is colocated with a layer of bipolar electric fields normal to the ECS, pointing toward the ECS, and with a half width less than 8 electron skin depths. (2) In the inflow region up to the ECS and separatrices, electrons have a temperature anisotropy (Te∥/Te⊥ > 1), and the anisotropy increases toward the ECS. (3) Within about 1 ion skin depth (di) above and below the ECS, the electron density decreases toward the ECS by a factor of 3–4, reaching a minimum at edges of the ECS, and has a local distinct maximum at the ECS center. (4) A di-scale magnetic island is attached to the ECS, separating it from another reconnection layer. Our simulations established that the electric field normal to the ECS is due to charge imbalance and is of the ECS scale, and ions exhibit electron-scale structures in response to this electric field.