Influence of Auroral Streamers on Rapid Evolution of Ionospheric SAPS Flows
Influence of Auroral Streamers on Rapid Evolution of Ionospheric SAPS Flows
复制标题
极光流对电离层 SAPS 流快速演化的影响
DOI：
10.1002/2017ja024198
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
N. Nishitani
中科院分区：
文献类型：
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作者：
B. Gallardo‐Lacourt;Y. Nishimura;L. Lyons;E. Mishin;J. Ruohoniemi;E. Donovan;V. Angelopoulos;N. Nishitani
亚极光极化流（SAPS）通常在其缓慢变化的成分之上显示出大幅、快速的增强。我们展示了来自地基全天空成像仪的同步观测以及来自超级双极光雷达网雷达的流数据，以研究极光现象与流增强之间的关系。我们首先识别出接近极光椭圆向赤道边界的极光射流，以检查亚极光流增加的频率。我们还从亚极光流增强开始进行反向查询，然后评估极光条件。在正向研究中，98%接近向赤道边界的射流都与SAPS流增强相关，其速度达到约700米/秒，通常比背景速度高出数百米/秒。反向研究表明，与射流相关的流增强（60%）以及增强的大尺度对流（37%）对SAPS流增强有贡献。极光射流与SAPS流的快速演变（约几分钟）的强相关性表明，瞬态快速向地球方向的等离子体片流常常会导致亚极光区域的向西SAPS流增强，而且由于在各种地磁条件下射流的发生更为频繁，这种增强远比仅在亚暴期间更为常见。我们还发现流持续时间与射流持续时间之间有很强的相关性，而SAPS流速与射流强度之间的相关性较弱。这一结果表明，等离子体片中的强烈流爆发（与强烈射流相关）可能通过在足够接近地球时增强环电流压力和局部压力梯度，从而与强烈的SAPS电离层流相关。
Subauroral polarization streams (SAPS) often show large, rapid enhancements above their slowly varying component. We present simultaneous observations from ground‐based all‐sky imagers and flows from the Super Dual Auroral Radar Network radars to investigate the relationship between auroral phenomena and flow enhancement. We first identified auroral streamers approaching the equatorward boundary of the auroral oval to examine how often the subauroral flow increased. We also performed the reverse query starting with subauroral flow enhancements and then evaluated the auroral conditions. In the forward study, 98% of the streamers approaching the equatorward boundary were associated with SAPS flow enhancements reaching ~700 m/s and typically hundreds of m/s above background speeds. The reverse study reveals that flow enhancements associated with streamers (60%) and enhanced larger‐scale convection (37%) contribute to SAPS flow enhancements. The strong correlation of auroral streamers with rapid evolution (approximately minutes) of SAPS flows suggests that transient fast earthward plasma sheet flows can often lead to westward SAPS flow enhancements in the subauroral region and that such enhancements are far more common than only during substorms because of the much more frequent occurrences of streamers under various geomagnetic conditions. We also found a strong correlation between flow duration and streamer duration and a weak correlation between SAPS flow velocity and streamer intensity. This result suggests that intense flow bursts in the plasma sheet (which correlate with intense streamers) are associated with intense SAPS ionospheric flows perhaps by enhancing the ring current pressure and localized pressure gradients when they are able to penetrate close enough to Earth.