Hemispheric asymmetry of the dayside aurora due to imbalanced solar insolation
Hemispheric asymmetry of the dayside aurora due to imbalanced solar insolation
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DOI：
10.1038/s41598-020-70018-w
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发表时间：
2020-08
影响因子：
4.6
通讯作者：
K. Liou;E. Mitchell
中科院分区：
文献类型：
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作者：
K. Liou;E. Mitchell
与主要受磁尾磁场重联控制的夜面极光不同，日面极光与日面磁层顶的磁场合并密切相关。大约二十年前，人们发现极光也受到太阳照射的控制。由于这一发现主要基于在北半球获得的数据，因此一个突出的问题是极光太阳辐射效应是否也存在于南半球。本研究通过研究两个半球的白天极光来解决这个问题。我们分析了 2002 年至 2007 年热层电离层中间层能量与动力学卫星上的全球紫外线成像仪获取的 6 年远紫外线波长的地球盘辐射。发现南半球也存在太阳日照效应。本质上，当极地半球阳光照射时，以电子沉淀形式沉积的能量通量较大，而当极地半球黑暗时，能量通量较小。由于极光主要是由电子沉淀产生的，而且电子是主要的电流载体，这种南北不对称性与之前的发现一致，即更大（更小）的场对准电流从阳光照射的（黑暗）半球流出。这种趋势与太阳风驱动无关，表明它是与太阳照射相关的效应。白天极光能量通量存在轻微的南北不对称性。我们讨论磁层电流和电压发生器的不对称性。
Unlike the nightside aurora, which is controlled mainly by magnetic field reconnection in the magnetotail, the dayside aurora is closely associated with magnetic field merging at the dayside magnetopause. About two decades ago, it was discovered that the aurora is also controlled by solar insolation. Because the finding was based on data acquired mainly in the Northern Hemisphere, an outstanding question is if the auroral solar insolation effect also exists in the Southern Hemisphere. The present study addresses this question by studying dayside auroras from both hemispheres. We analyze 6 years’ worth of Earth disk emissions at far ultraviolet wavelengths acquired by the Global UltraViolet Imager on-board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite from 2002 to 2007. It is found that the solar insolation effect also exists in the Southern Hemisphere. In essence, the energy flux deposited as electron precipitation, is larger when the polar hemisphere is sunlit and is smaller when the polar hemisphere is dark. Because auroras are produced mainly by electron precipitation and because electrons are the main current carrier, this north–south asymmetry is consistent with the previous finding that larger (smaller) field-aligned currents are flowing out of the sunlit (dark) hemisphere. This trend is independent of the solar wind driving, suggesting that it is an effect associated with solar insolation. A small north–south asymmetry in the dayside auroral energy flux was identified. We discuss the asymmetry in the context of magnetospheric current and voltage generators.