Over‐Darkening of Pulsating Aurora
Over‐Darkening of Pulsating Aurora
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脉动极光过度变暗
DOI：
10.1029/2020ja028838
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Fujii R.
中科院分区：
文献类型：
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作者：
Hosokawa K.;Miyoshi Y.;Oyama S.‐I.;Ogawa Y.;Kurita S.;Kasahara Y.;Kasaba Y.;Yagitani S.;Matsuda S.;Ozaki M.;Tsuchiya F.;Kumamoto A.;Takashima T.;Shinohara I.;Fujii R.
最近对脉动极光（PsA）的高时间分辨率地面光学观测的分析报告说，PsA的亮度有时会在主脉动的ON阶段结束后立即下降到漫射背景水平以下。然而，迄今为止，这种“过暗化PsA”的产生机制仍然不清楚。在这项研究中，我们通过使用芬兰Sodankylä的电子倍增电荷耦合器件全天空相机和Arase卫星同时观测PsA来研究过暗PsA的特性。在2017年3月29日发生在斯堪的纳维亚半岛的一次会合事件中，几乎所有的PsA脉冲都表现出明显的过暗特征。通过分析过暗时的2D全天空图像，我们发现过暗区域出现在PsA斑块的后缘，并与向极传播的斑块一起移动。还发现，在位于PsA磁层对应物的Arase上的波浪仪器的合唱数据中没有看到类似的过度减少特征。这些结果表明，过暗化PsA不是由固定点处的合唱的时间变化引起的，而是由过暗化区域与PsA斑块的传播产生的。也就是说，过度暗化的PsA是PsA的空间结构和经常性传播的复合效应的结果。产生暗区的机制仍然是未知的，但过度暗化PsA的存在表明PsA的时间变化并不总是磁层中低波段合唱波调制的完美副本。
Recent analyses of high‐time resolution ground‐based optical observations of pulsating aurora (PsA) have reported that the brightness of PsA sometimes decreases below the diffuse background level immediately after the ON phase of the main pulsation finishes. To date, however, the generation mechanism of such an “over‐darkening PsA” is still unclarified. In this study, we investigated the characteristics of the over‐darkening PsA by using simultaneous observations of PsA with an electron multiplying charge coupled device all‐sky camera in Sodankylä, Finland and the Arase satellite. During one of the conjunction events in Scandinavia on March 29, 2017, almost all the PsA pulses showed clear over‐darkening characteristics. By analyzing the 2D all‐sky images at the times of over‐darkening we discovered that over‐darkening areas appeared in the trailing edge of PsA patches and moved in tandem with the poleward propagating patches. It was also found that similar over‐decreasing characteristics were not seen in the chorus data from the wave instruments onboard Arase located at the magnetospheric counterpart of PsA. These results indicate that the over‐darkening PsA is not caused by a temporal variation of chorus at a fixed point, but is produced by a propagation of over‐darkening area with PsA patches. That is, the over‐darkening PsA is a result of compounding effects of spatial structure and recurrent propagation of PsA. The mechanism creating the dark area is still unknown, but the existence of over‐darkening PsA suggests that the temporal variation of PsA is not always a perfect copy of the modulation of lower‐band chorus waves in the magnetosphere.