Earthward expansion of tail current disruption : Dual-satellite study
Earthward expansion of tail current disruption : Dual-satellite study
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尾流干扰向地球扩展：双卫星研究
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
S. Ohtani
中科院分区：
文献类型：
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作者：
S. Ohtani
本文件利用两颗相互靠近的卫星进行的磁场测量，讨论近地尾中尾电流中断的空间发展。本文由两部分组成：统计分析和对1986年8月30日发生的一次亚暴事件的个例分析。在第一部分中，对AMPTE/CCE（r < 8.8 RE）和GOES地球同步卫星的尾磁场重构（双极化）的起始时间进行了统计检查。结果表明，尾流扰动区在地球同步轨道外沿方位向扩展。另一个最出乎意料的发现是，尾电流干扰区域经常向地球扩展。1986年8月30日AMPTE/CCE和SCATHA卫星观测到的亚暴事件提供了一个很好的机会来研究尾流扰动区向地球的扩展。在这一事件中，AMPTE/CCE位于SCATHA的向地侧0.4 RE，并在SCATHA开始后15 s观察到磁波动的开始。向地球的膨胀速度估计为180 km/s，比快磁声波模式的传播速度慢得多，表明观测到的向地球的膨胀不是波传播的影响。AMPTE/CCE在这一事件中观察到的最初特征是南北磁分量的减少，伴随着高能离子通量的增强，这些离子的引导中心朝向尾部。这一结果表明，在尾电流中断的向地扩展区域的前部注入粒子增强了尾电流。这种增强的电流可以触发尾电流的局部中断，使得中断区域进一步向地扩展。
The present paper addresses the spatial development of tail current disruption in the near-Earth tail by making use of magnetic field measurements made by two satellites located close to each other. The paper consists of two parts: a statistical study and a case study of a substorm event that took place on August 30, 1986. In the first part the relative timing of the onsets of tail magnetic field reconfiguration (dipolarization) at the AMPTE/CCE (r < 8.8 RE) and GOES geosynchronous satellites is statistically examined. The result shows that the tail current disruption region expands azimuthally outside geosynchronous orbit. Another, and most unexpected, finding is that the tail current disruption region often expands earthward. The substorm event of August 30, 1986, observed by the AMPTE/CCE and SCATHA satellites provides a good opportunity to examine the earthward expansion of the tail current disruption region. In this event, AMPTE/CCE was located on the earthward side of SCATHA by 0.4 RE and observed the onset of magnetic fluctuations 15 s after the SCATHA onset. The earthward expansion velocity is estimated at 180 km/s, much slower than the propagation velocity of the fast magnetosonic mode, indicating that the observed earthward expansion is not an effect of the wave propagation. The very initial signature observed by AMPTE/CCE in this event is a decrease in the north-south magnetic component accompanied by the enhancement of the flux of energetic ions having their guiding centers tailward. This result suggests that the tail current is intensified by injected particles at the front of the earthward expanding region of the tail current disruption. This enhanced current may trigger the local disruption of the tail current, making the disruption region expand further earthward.