Preonset time sequence of auroral substorms: Coordinated observations by all‐sky imagers, satellites, and radars
Preonset time sequence of auroral substorms: Coordinated observations by all‐sky imagers, satellites, and radars
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DOI：
10.1029/2010ja015832
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发表时间：
2010-05
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通讯作者：
Y. Nishimura;L. Lyons;S. Zou;X. Xing;V. Angelopoulos;S. Mende;J. Bonnell;D. Larson;U. Auster;T. Hori;N. Nishitani;K. Hosokawa;G. Sofko;M. Nicolls;C. Heinselman
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作者：
Y. Nishimura;L. Lyons;S. Zou;X. Xing;V. Angelopoulos;S. Mende;J. Bonnell;D. Larson;U. Auster;T. Hori;N. Nishitani;K. Hosokawa;G. Sofko;M. Nicolls;C. Heinselman
[1] 使用事件时间历史和亚暴期间宏观相互作用（THEMIS）成像仪和航天器以及超级双极光雷达网络（SuperDARN）和扑克平地非相干散射雷达的两个合事件，我们表明，夜侧极冠中纵向狭窄的气流爆发可以先于极地边界增强（PBI），随后是赤道移动的南北（N-S）弧，包括那些导致近地等离子体层内亚暴爆发不稳定的因素。电离层流与 PBI 之间的关联表明，开放场线上的增强流可能有助于平行电势降增加、触发磁尾重新连接以及导致南北弧和亚暴爆发的向地流。我们还研究了导致和不导致亚暴扩展爆发的南北弧序列之间的差异。我们发现两种类型的N-S电弧具有相似的特征，这表明它们相应的等离子体片流特性也可能相似。然而，南北弧演化顺序之间存在一个差异。每个N-S弧都会导致生长期弧的小幅增强，并且当与爆发相关的N-S弧到达极光椭圆形的赤道部分时，先前存在的生长期弧比非爆发相关的N-S弧时明亮得多。假设生长相弧与等离子体片内边缘的压力梯度有关，这种差异表明等离子体片快速流动时的近地等离子体压力分布对于亚暴的触发至关重要。这些观察结果表明，只有当预先存在的内部等离子体层压力足够大时，亚暴爆发的不稳定才有可能发生。
[1] Using two conjunction events of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) imagers and spacecraft as well as the Super Dual Auroral Radar Network (SuperDARN) and Poker Flat Incoherent Scatter Radars, we show that longitudinally narrow flow bursts in the nightside polar cap can precede poleward boundary intensifications (PBIs) that are followed by equatorward moving north-south (N-S) arcs, including those leading to substorm onset instability within the near-Earth plasma sheet. The association between the ionospheric flows and PBIs indicates that enhanced flows on open field lines may contribute to parallel potential drop increase, triggering of magnetotail reconnection, and to the earthward flows leading to N-S arcs and to substorm onset. We also investigated differences between N-S arc sequences that do and do not lead to substorm expansion onset. We found that the two types of N-S arcs have similar characteristics, indicating that their corresponding plasma sheet flow properties could also be similar. There is, however, one difference between the sequences of N-S arc evolution. Each N-S arc leads to small intensification of the growth phase arc, and when the onset-related N-S arc reaches the equatorward portion of the auroral oval, the preexisting growth phase arc is much brighter than at the times of non-onset-related N-S arcs. Assuming that the growth phase arc is related to pressure gradients at the inner edge of the plasma sheet, this difference indicates that the near-Earth plasma pressure distribution at the time of plasma sheet fast flows is crucial in substorm triggering. These observations suggest that substorm onset instability is possible only when the preexisting inner plasma sheet pressure is sufficiently large.