Turbulent magnetic field in the distant magnetotail: Bottom‐up process of plasmoid formation?
Turbulent magnetic field in the distant magnetotail: Bottom‐up process of plasmoid formation?
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DOI：
10.1029/94gl02094
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发表时间：
1994-12
影响因子：
5.2
通讯作者：
M. Hoshino;A. Nishida;T. Yamamoto;S. Kokubun
中科院分区：
文献类型：
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作者：
M. Hoshino;A. Nishida;T. Yamamoto;S. Kokubun
本文用湍流磁场重联过程研究了地球磁尾的GEOTAIL磁场观测。据发现，所观察到的湍流磁场的傅立叶功率谱密度可以近似的幂律谱，改变其斜率周围的翻转频率为0.04 Hz，尽管在遥远的磁尾等离子体片中观察到的各种各样的磁扰动之间的差异。湍流磁场数据分为两种情况（Nishida等人在本期）：一种是伴随着Bz磁场上的等离子体双极签名，另一种是没有双极签名。在Bz磁场分量中有和没有双极特征的情况下，翻转频率以上的较高频率区域总是显示出相似的谱斜率，尽管在较低频率区域中的谱特征在外观上表现出差异。当Bz磁场上没有双极信号时，低频范围几乎是一个平坦的频谱。另一方面，当观察到大尺度双极特征时，较低频率区域的斜率变得陡峭。观测结果表明：（1）在磁尾激发出等离子体片厚度尺度的小尺度撕裂模涡旋;（2）小尺度撕裂模涡旋合并形成大尺度等离子体团。
The GEOTAIL magnetic field observations in the earth's magnetotail are examined in terms of a turbulent magnetic reconnection process. It is found that the observed Fourier power spectral density of the turbulent magnetic fields can be approximated by a power-law spectrum which changes its slope around a turnover frequency with 0.04 Hz, in spite of the differences among a wide variety of magnetic perturbations observed in the distant magnetotail plasma sheet. The turbulent magnetic field data are classified into two cases (Nishida et al. in this issue): one is accompanied with a plasmoid bipolar signature on Bz magnetic field, and the other without the bipolar signature. The higher frequency regions above the turnover frequency always show similar spectral slope in the cases with and without a bipolar signature in Bz magnetic field component, although the spectral feature in the lower frequency regions exhibits differences in appearance. When there is no bipolar signature on Bz magnetic field, the lower frequency range is almost a flat spectrum. On the other hand, the slope of the lower frequency region becomes steep when a large scale bipolar signature is observed. The observations may indicate that 1) a small-scale tearing mode vortex with the scale of plasma sheet thickness is excited in the magnetotail, and 2) the large-scale plasmoid is coalescently formed from the small-scale tearing mode vortices.