Superposed epoch analysis of the ionospheric convection evolution during substorms:IMF BY dependence
Superposed epoch analysis of the ionospheric convection evolution during substorms:IMF BY dependence
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DOI：
10.1029/2010ja015728
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发表时间：
2010-05
影响因子：
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通讯作者：
A. Grocott;S. Milan;T. Yeoman;N. Sato;A. Yukimatu;J. Wild
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文献类型：
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作者：
A. Grocott;S. Milan;T. Yeoman;N. Sato;A. Yukimatu;J. Wild
我们提出了在不同的行星际磁场（IMF）方向下发生的磁层亚暴在北半球和南半球的平均电离层对流响应的叠加年代分析。电离层对流观测由超级双极光雷达网络（SuperDARN）提供，亚暴观测由磁层顶-极光全球探测（IMAGE）航天器上的远紫外（FUV）仪器确定。我们发现，在次暴生长阶段，在整个对流模式中观察到预期的与IMF BY相关的黎明-黄昏不对称性，但在膨胀阶段，这种不对称性仅在极帽和日侧极光区保留。在夜侧极光区，对流根据局部亚暴电动力学重新排序，任何剩余的黄昏-黎明不对称性与亚暴开始的磁局地时间更密切相关，其本身仅受IMF by的微弱支配。由于亚暴发生在磁极午夜之前的优势，亚暴的不对称性倾向于黄昏对流单元在午夜扇区的方位延伸，这是所谓的“哈朗不连续”的表现。这导致在亚暴期间北半球（南半球）的夜侧极光对流通常类似于负（正）IMF BY的预期模式。当北半球（南半球）先前存在的对流模式受到正（负）IMF by驱动时，夜侧极光对流在亚暴过程中发生显著变化，从而形成相同的“哈朗”构型。
We present superposed epoch analyses of the average ionospheric convection response in the northern and southern hemispheres to magnetospheric substorms occurring under different orientations of the interplanetary magnetic field (IMF). Observations of the ionospheric convection were provided by the Super Dual Auroral Radar Network (SuperDARN) and substorms were identified using the Far Ultraviolet (FUV) instrument on board the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) spacecraft. We find that during the substorm growth phase the expected IMF BY‐dependent dawn‐dusk asymmetry is observed over the entire convection pattern, but that during the expansion phase this asymmetry is retained only in the polar cap and dayside auroral zone. In the nightside auroral zone the convection is reordered according to the local substorm electrodynamics with any remaining dusk‐dawn asymmetry being more closely related to the magnetic local time of substorm onset, itself only weakly governed by IMF BY. Owing to the preponderance of substorms occurring just prior to magnetic midnight, the substorm‐asymmetry tends to be an azimuthal extension of the dusk convection cell across the midnight sector, a manifestation of the so‐called “Harang discontinuity.” This results in the northern (southern) hemisphere nightside auroral convection during substorms generally resembling the expected pattern for negative (positive) IMF BY. When the preexisting convection pattern in the northern (southern) hemisphere is driven by positive (negative) IMF BY, the nightside auroral convection changes markedly over the course of the substorm to establish this same “Harang” configuration.