Growth-Phase Thinning of the Near-Earth Current Sheet During the Cdaw-6 Substorm
Growth-Phase Thinning of the Near-Earth Current Sheet During the Cdaw-6 Substorm
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DOI：
10.1029/93ja03235
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发表时间：
1994-04
影响因子：
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通讯作者：
J. Sanny;R. McPherron;C. Russell;D. Baker;T. Pulkkinen;A. Nishida
中科院分区：
文献类型：
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作者：
J. Sanny;R. McPherron;C. Russell;D. Baker;T. Pulkkinen;A. Nishida
研究了CDAW 6磁层亚暴生长阶段近地电流片的变薄情况。亚暴的扩张开始于1979年3月22日1054 UT。在增长阶段，两个航天器，ISEE 1和ISEE 2，在电流片内约13 RE从地球，并获得同时在电流片的两个点的高分辨率磁数据。ISEE航天器还提供了等离子体数据，IMP 8提供了太阳风数据。为了便于分析，将GSM磁场数据转换为"中性片坐标系"，其中新的x轴平行于中性片上方和下方的平均磁场，新的y轴位于GSM赤道平面内。一个模型的基础上的假设，目前的表是一个时不变的结构无法预测中性片交叉时间。因此，哈里斯片模型，它允许一个删除的时间不变的限制，而不是使用。结果发现，在生长阶段，对应于电流片的厚度的模型参数呈指数下降，从约5RE到1RE，时间常数约为14分钟。此外，ISEE 1和ISEE 2中性片交叉后，膨胀发病表明，中性片向上移动在7公里/秒相对于航天器。由于两次穿越都发生在大约80秒内，因此目前的板块厚度估计约为500 km。这些结果表明，在亚暴生长阶段和扩张开始期间，近地电流片经历了戏剧性的变薄。
The thinning of the near-Earth current sheet during the growth phase of the CDAW 6 magnetospheric substorm is studied. The expansion onset of the substorm occurred at 1054 UT, March 22, 1979. During the growth phase, two spacecraft, ISEE 1 and ISEE 2, were within the current sheet approximately 13RE from the Earth and obtained simultaneous high-resolution magnetic data at two points in the current sheet. Plasma data were also provided by the ISEE spacecraft and solar wind data by IMP 8. To facilitate the analysis, the GSM magnetic field data are transformed to a “neutral sheet coordinate system” in which the new x axis is parallel to the average magnetic field above and below the neutral sheet and the new y axis lies in the GSM equatorial plane. A model based on the assumption that the current sheet is a time-invariant structure fails to predict neutral sheet crossing times. Consequently, the Harris sheet model, which allows one to remove the restriction of time invariancy, is used instead. It is found that during the growth phase, a model parameter corresponding to the thickness of the current sheet decreased exponentially from about 5RE to 1RE with a time constant of about 14 min. In addition, the ISEE 1 and ISEE 2 neutral sheet crossings after expansion onset indicate that the neutral sheet was moving upward at 7 km/s relative to the spacecraft. Since both crossings occurred in approximately 80 s, the current sheet thickness is estimated to be about 500 km. These results demonstrate that the near-Earth current sheet undergoes dramatic thinning during the substorm growth phase and expansion onset.