Radar Observations of Flows Leading to Substorm Onset Over Alaska
Radar Observations of Flows Leading to Substorm Onset Over Alaska
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DOI：
10.1029/2020ja028147
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发表时间：
2021-02
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影响因子：
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通讯作者：
L. Lyons;Jiang Liu;Y. Nishimura;A. Reimer;W. Bristow;D. Hampton;Xueling Shi;R. Varney;E. Donovan
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作者：
L. Lyons;Jiang Liu;Y. Nishimura;A. Reimer;W. Bristow;D. Hampton;Xueling Shi;R. Varney;E. Donovan
亚暴发现约40年后，利用极光观测提出亚暴的发生是由等离子体片流通道侵入低熵等离子体在等离子体片内部（极光椭圆的赤道部分）触发的。纵向定位使得这种流动通道很难用稀疏的航天器观测到，但它们可以通过地面雷达在电离层中更广泛的二维覆盖范围看到。我们分析了所有八次亚暴极光发生事件，在雷达运动中使用适当的极光和扑克平面雷达观测。这些和先前分析的五个事件一起提供了证据，表明侵入流通道在亚暴发生中起着重要作用。这种新等离子体的通量管积分熵必须低于周围等离子体的积分熵，这意味着等离子体片内熵分布的变化导致了亚暴开始时的不稳定性，这种不稳定性可以通过亚暴开始时不断增长的极光和电磁波看到。我们的分析还补充了先前的证据，即导致开始的流动通道从磁尾叶/极帽的开放极帽区域进入等离子体片/极光椭圆，这些流动通道沿着它们在极帽的白天边界附近的起源穿过极帽。与亚暴相关的地面地磁洼地并不是在亚暴开始时发生的而是在几分钟后与膨胀期流光相关联时发生的。
About 40 years after the discovery of the substorm, auroral observations were used to propose that substorm onset was triggered in the inner plasmas sheet (equatorward portion of the auroral oval) by an intrusion of the low entropy plasma by plasma sheet flow channels. Longitudinal localization makes such flow channels difficult to observe with sparse spacecraft, but they can be seen in the ionosphere via the broader, two‐dimensional coverage by ground‐based radars. We have analyzed all eight substorm auroral onset events with appropriate auroral and Poker Flat radar viewing during a radar campaign. These, together with five previously analyzed events provide evidence that intruding flow channels play an important role in substorm onsets. That the flux tube integrated entropy of this new plasma must be lower than that of the surrounding plasma implies that the change in the entropy distribution within the plasma sheet gives rises to the substorm onset instability that is seen via the growing auroral and electromagnetic waves seen with substorm auroral onset. Our analysis also adds to previous evidence that the flow channels leading to onset move into the plasma sheet/auroral oval from the open polar cap region of the magnetotail lobes/polar caps, that these flow channels move across the polar cap following their origin near the dayside boundary of the polar cap, and that substantial ground magnetic depressions associated with substorm do not occur with substorm onset but instead occur a few to several minutes later in association with expansion phase streamers.