Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI
Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI
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在 Swarm 和 THEMIS ASI 交汇期间观察到的 Omega 带极向边界处的流切变
DOI：
10.1002/2017gl076485
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发表时间：
2018
影响因子：
5.2
通讯作者：
J. Weygand
中科院分区：
文献类型：
--
作者：
Jiang Liu;L. Lyons;W. E. Archer;B. Gallardo‐Lacourt;Y. Nishimura;Y. Zou;C. Gabrielse;J. Weygand
欧米伽带是弯曲的极光形式，从午夜沿着扩散极光带的极光边缘的安静弧线演化到晨边极光椭圆形。它们通常向东传播。由于欧米伽带是活跃磁尾的重要贡献者，了解它们的产生对于理解尾巴动力学很重要。以前的研究表明，极光流光--尾部快速流动的足迹--可以传播到欧米伽带。然而，这类事件是有限的，目前仍不清楚这些流动是否以及如何触发了波段。与欧米伽带有关的电离层流动可以提供有关欧米伽带驱动机制的有价值的信息。我们利用星群航天器和亚暴全天成像仪期间的事件和大尺度相互作用的时间历史之间的连接来检查这些流动，这使得我们能够第一次展示这些流动相对于omega带的明亮弧线的相对位置。我们发现，在欧米伽带明亮的弧线的两极附近，一直存在一个强烈的向东的电离层流动，导致在欧米伽带的极地边界附近有一个急剧的流动切变。这种电离层流动切变应对应于等离子体片内边缘附近的流动切变。这种等离子体片剪切可能会驱动开尔文-赫尔姆霍兹不稳定性，从而扭曲安静的弧线，形成欧米伽带。这似乎似乎是由与流光相关的快速流动或磁尾对流增强所驱动的强向东流动。
Omega bands are curved aurora forms that evolve from a quiet arc located along the poleward edge of a diffuse auroral band within the midnight to morningside auroral oval. They usually propagate eastward. Because omega bands are a significant contributor to an active magnetotail, knowledge about their generation is important for understanding tail dynamics. Previous studies have shown that auroral streamers, footprints of fast flows in the tail, can propagate into omega bands. Such events, however, are limited, and it is still unclear whether and how the flows trigger the bands. The ionospheric flows associated with omega bands may provide valuable information on the driving mechanisms of the bands. We examine these flows taking advantage of the conjunctions between the Swarm spacecraft and Time History of Events and Macroscale Interactions during Substorms all‐sky imagers, which allow us to demonstrate the relative location of the flows to the omega bands' bright arcs for the first time. We find that a strong eastward ionospheric flow is consistently present immediately poleward of the omega band's bright arc, resulting in a sharp flow shear near the poleward boundary of the band. This ionospheric flow shear should correspond to a flow shear near the inner edge of the plasma sheet. This plasma sheet shear may drive a Kelvin‐Helmholz instability which then distorts the quiet arc to form omega bands. It seems plausible that the strong eastward flows are driven by streamer‐related fast flows or enhanced convection in the magnetotail.