Decrease in Bz prior to the dipolarization in the near‐Earth plasma sheet
Decrease in Bz prior to the dipolarization in the near‐Earth plasma sheet
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DOI：
10.1029/2005ja011144
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发表时间：
2005-09
影响因子：
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通讯作者：
K. Shiokawa;Y. Miyashita;I. Shinohara;A. Matsuoka
中科院分区：
文献类型：
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作者：
K. Shiokawa;Y. Miyashita;I. Shinohara;A. Matsuoka
[1]我们详细地研究了在(XGSM，YGSM)=(−8.3RE，−5.1RE)时，GeoTail卫星在近地等离子体片中观测到的偶极之前BZ的快速减小。观测使用了磁通门磁力仪(16赫兹样品)、搜索线圈磁力仪(128赫兹)和电场天线(赫兹)的高时间分辨率数据。在2分钟的短时间间隔内观察到两次偶极化。磁力BZ分量在偶极前突然减小2-4个S。在BZ突然下降时，在电场和磁场数据中观察到频率为5~20 Hz、振幅为1~3 mV m−1和5~15 nT S−1的特征波。我们讨论了偶极化前BZ突然减小的两个可能原因：(1)与亚暴电流楔形有关的场向线电流的通过；(2)由观测到的特征场振荡引起的爆炸性增长阶段和随后的尾流中断。
[1] We examine in detail the rapid decrease in Bz just before dipolarizations observed by the Geotail satellite in the near-Earth plasma sheet at (XGSM, YGSM) = (−8.3 RE, −5.1 RE). The observations were made using high-time-resolution data from a fluxgate magnetometer (16-Hz sample), a search-coil magnetometer (128 Hz), and an electric field antenna (64 Hz). Two dipolarizations were observed during a short time interval of 2 min. The magnetic Bz component suddenly decreased 2–4 s prior to the dipolarization. Characteristic waves with frequencies of 5–20 Hz and amplitudes of 1–3 mV m−1 and 5–15 nT s−1 were observed in the electric and magnetic field data at the time of the sudden decreases in Bz. We discuss two possible causes of the sudden decreases in Bz prior to the dipolarizations: (1) passage of a field-aligned line current associated with the substorm current wedge and (2) explosive growth phase and subsequent disruption of the tail current caused by the observed characteristic field oscillations.