Structure and dynamics of magnetic reconnection for substorm onsets with Geotail observations
Structure and dynamics of magnetic reconnection for substorm onsets with Geotail observations
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DOI：
10.1029/97ja02190
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发表时间：
1998-03-01
影响因子：
2.8
通讯作者：
Kokubun, S
中科院分区：
文献类型：
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作者：
Nagai, T;Fujimoto, M;Kokubun, S
在Geotail观测中，经常在磁尾午夜前20 - 30 R-E的中性片附近观测到具有强烈南向磁场的快速尾离子流，用于亚暴爆发。这些快速的尾流偶尔伴随着几个千电子伏的电子。利用这些事件，我们研究了磁场重联的结构和动力学。磁场重联点附近的等离子体片可以分为三个区域：中性片区域（靠近中性片，B-x的绝对值<5 nT）、边界区域（靠近等离子体片/尾瓣边界，B-x的绝对值接近或> 10 nT）和离赤道等离子体片（其余部分）。在中性片区域，等离子体以强对流方式传输，加速电子呈现出近似各向同性的分布。在离赤道等离子体片中，两种离子成分共存：离子在朝向中性片的对流过程中被加速和加热，离子几乎沿着磁场以高速流动。在这个区域，观察到高度加速的电子。虽然电子分布基本上是各向同性的，高能量（高于10千电子伏）的电子显示流远离重联网站沿着磁场线。在边界区域，离子也显示出两个组成部分：离子对流朝向中性片和场对准离子流出的重联区，虽然在对流过程中的加速和加热是弱的。在边界区域，高能（10 keV）电子流走，而中能（3 keV）电子流到重连部位。磁重联通常开始于磁尾午夜前的扇区，介于X-GSM =-20 R-E和X-GSM =-30 R-E之间，然后在地面上出现Pi 2脉动。磁重联进行的时间尺度为10分钟。磁重联结束后，相邻的等离子体被运送到postreconnection网站，等离子体可以成为固定的，即使在膨胀阶段。
Fast tailward ion flows with strongly southward magnetic fields are frequently observed near the neutral sheet in the premidnight sector of the magnetotail at 20-30 R-E for substorm onsets in Geotail observations. These fast tailward flows are occasionally accompanied by a few keV electrons. With these events, we study the structure and dynamics of magnetic reconnection. The plasma sheet near the magnetic reconnection site can be divided into three regions: the neutral sheet region (near the neutral sheet with the absolute magnitude of B-x of < 5 nT), the boundary region (near the plasma sheet/tail lobe boundary with the absolute magnitude of B-x is near or > 10 nT), and the off-equatorial plasma sheet (the rest). In the neutral sheet region, plasmas are transported with strong convection, and accelerated electrons show nearly isotropic distributions. In the off-equatorial plasma sheet, two ion components coexist: ions being accelerated and heated during convection toward the neutral sheet and ions flowing at a high speed almost along the magnetic field. In this region, highly accelerated electrons are observed. Although electron distributions are basically isotropic, high-energy (higher than 10 keV) electrons show streaming away from the reconnection site along the magnetic field line. In the boundary region, ions also show two components: ions with convection toward the neutral sheet and field-aligned ions flowing out of the reconnection region, although acceleration and heating during convection are weak. In the boundary region, high-energy (10 keV) electrons stream away, while medium-energy (3 keV) electrons stream into the reconnection site. Magnetic reconnection usually starts in the premidnight sector of the magnetotail between X-GSM = -20 R-E and X-GSM = -30 R-E prior to an onset signature identified with Pi 2 pulsation on the ground. Magnetic reconnection proceeds on a timescale of 10 min. After magnetic reconnection ends, adjacent plasmas are transported into the postreconnection site, and plasmas can become stationary even in the expansion phase.