Cluster observations of energetic electrons and electromagnetic fields within a reconnecting thin current sheet in the Earth's magnetotail
Cluster observations of energetic electrons and electromagnetic fields within a reconnecting thin current sheet in the Earth's magnetotail
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DOI：
10.1029/2008ja013511
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发表时间：
2008-12
影响因子：
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通讯作者：
A. Retinò;R. Nakamura;A. Vaivads;Y. Khotyaintsev;T. Hayakawa;Kentaro Tanaka;S. Kasahara;M. Fujimoto-M
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文献类型：
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作者：
A. Retinò;R. Nakamura;A. Vaivads;Y. Khotyaintsev;T. Hayakawa;Kentaro Tanaka;S. Kasahara;M. Fujimoto-M
[1]我们研究了加速的高能电子在磁尾重联通过使用集群同时测量三维电子分布函数，电场和磁场，和波在一个薄的电流片。我们提出了两个连续的电流片交叉点的观测，其中35-127千电子伏的电子通量的峰值在一个区间内的尾流。第一个交叉点显示了一个向尾部移动的磁通绳的特征。观测到的磁场和密度表明，磁通绳是非常动态的，与数值模拟的比较表明，交叉后合并的较小磁通绳。第二交叉发生在离子扩散区域内。电子的通量在通量绳内是最大的，其中它们主要垂直于磁场定向。在磁分界线处，磁通量较小，但能谱较硬，电子主要是场取向的。在扩散区观察到重联电场EY = 7 mV/m，而在磁绳中，EY要小得多。低混合频率附近的波与高能电子没有明显的相关性。我们解释的场对齐的电子在separatrices直接加速的重联电场在扩散区，而我们解释的垂直电子被困在磁通绳和加速电子感应加速器加速与非绝热俯仰角散射的组合。我们的观察表明，薄的电流片在动态重联过程中是重要的，在原位生产的高能电子和薄片内的电子和电磁场的同时测量是至关重要的，以了解加速机制。
[1] We study the acceleration of energetic electrons during magnetotail reconnection by using Cluster simultaneous measurements of three-dimensional electron distribution functions, electric and magnetic fields, and waves in a thin current sheet. We present observations of two consecutive current sheet crossings where the flux of electrons 35–127 keV peaks within an interval of tailward flows. The first crossing shows the signatures of a tailward moving flux rope. The observed magnetic field and density indicate that the flux rope was very dynamic, and a comparison with numerical simulation suggests a crossing right after coalescence of smaller flux ropes. The second crossing occurs within the ion diffusion region. The flux of electrons is largest within the flux rope where they are mainly directed perpendicular to the magnetic field. At the magnetic separatrices, the fluxes are smaller, but the energy spectra are harder and electrons are mainly field aligned. Reconnection electric fields EY ∼ 7 mV/m are observed within the diffusion region, whereas in the flux rope, EY are much smaller. Waves around lower hybrid frequency do not show a clear correlation with energetic electrons. We interpret the field-aligned electrons at the separatrices as directly accelerated by the reconnection electric field in the diffusion region, whereas we interpret the perpendicular electrons as trapped within the flux rope and accelerated by a combination of betatron acceleration with nonadiabatic pitch-angle scattering. Our observations indicate that thin current sheets during dynamic reconnection are important for in situ production of energetic electrons and that simultaneous measurements of electrons and electromagnetic fields within thin sheets are crucial to understand the acceleration mechanisms.