Construction of magnetic reconnection in the near-Earth magnetotail with Geotail
Construction of magnetic reconnection in the near-Earth magnetotail with Geotail
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DOI：
10.1029/2010ja016283
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发表时间：
2011-04-20
影响因子：
2.8
通讯作者：
Mukai, T.
中科院分区：
文献类型：
--
作者：
Nagai, T.;Shinohara, I.;Mukai, T.
2003年5月15日，当地面开始出现中度亚暴时，Geotail航天器在径向距离28 R-E的近地磁尾中对磁重联进行了现场观测。对于该事件，检测到与同时等离子体流和磁场反转相关的强烈交叉尾电子电流层，并获得了沿 GSM x 轴的尺度长度。这一观察使我们能够推断出近地磁尾磁重联基本结构的尺度。在电子流层的中心（一条可能的X线），携带交叉尾电流的黎明电子流的速度超过了电子流出速度的最大值（向地/向尾），并且是高度超阿尔芬尼的。该中心强交叉尾电子流层的整个范围在 x 方向上约为 1 lambda i（离子惯性长度），相当于磁尾中的 0.2 R-E。在距离X线小于1 lambda i处，电子流出速度达到最大值，也是超阿尔芬尼克，离中心越远，离子流出速度达到最大值。电子流出速度在下游区域减小，并且在距离为4 lambda i 时变得与离子速度相同。离子电子解耦区域在 x 方向上的完整范围为 8 lambda i，对应于磁尾中的 1.5 R-E，外部区域属于 MHD 区域。在离子-电子解耦区内，离子在流入过程中被加速至10 keV，并进一步向靠近中心的黄昏方向和沿稍微远离中心的x轴加速超过40 keV。这些对 X 线附近的离子和电子动力学的观察结果与此处和其他描述的二维细胞内粒子模拟的结果相当一致。目前的Geotail结果为近地磁尾磁重联结构提供了观测基础。
The Geotail spacecraft made in situ observations of magnetic reconnection on 15 May 2003 in the near-Earth magnetotail at a radial distance of 28 R-E when a moderate substorm started on the ground. For this event, the intense cross-tail electron current layer was detected in association with the simultaneous plasma flow and magnetic field reversals, and the scale length along the GSM x axis was obtained. This observation enables us to deduce scales for the basic structure of magnetic reconnection in the near-Earth magnetotail. In the center of the electron current layer (a possible X line), the speed of the dawnward electron flow carrying cross-tail current exceeds the maximum of the electron outflow speed (earthward/tailward), and it is highly super Alfvenic. The full extent of this central intense cross-tail electron current layer is approximately 1 lambda i (ion inertial length) in the x direction, which corresponds to 0.2 R-E in the magnetotail. Electron outflow speed reaches its maximum, which is also super Alfvenic, at distances of less than 1 lambda i from the X line, and ion outflow speed reaches its maximum farther away from the center. Electron outflow speed decreases in the downstream region, and it becomes the same as the ion speed at distances of 4 lambda i. The full extent of the ion-electron decoupling region is 8 lambda i in the x direction, which corresponds to 1.5 R-E in the magnetotail, and the outer region belongs to the MHD regime. Inside the ion-electron decoupling region, ions are accelerated up to 10 keV during inflow processes and further accelerated beyond 40 keV toward the duskward direction near the center and along the x axis slightly away from the center. These observations of the ion and electron dynamics in the close vicinity of the X line are fairly consistent with results from the two-dimensional particle-in-cell simulation described here and others. The present Geotail results provide the observational basis for the structure of magnetic reconnection in the near-Earth magnetotail.