What Is Unusual About the Third Largest Geomagnetic Storm of Solar Cycle 24?
What Is Unusual About the Third Largest Geomagnetic Storm of Solar Cycle 24?
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DOI：
10.1029/2022ja030404
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发表时间：
2022-02
期刊：
影响因子：
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通讯作者：
N. Gopalswamy;S. Yashiro;S. Akiyama;H. Xie;P. Makela;M. Fok;C. Ferradas
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文献类型：
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作者：
N. Gopalswamy;S. Yashiro;S. Akiyama;H. Xie;P. Makela;M. Fok;C. Ferradas
我们报告了太阳周期24中第三大地磁风暴（2018年8月26日）的太阳和行星际（IP）原因。起源于静止暗条区的日冕物质抛射（CME）在0.5天后变为1 Au的440 km/s磁云（MC）。延长的CME加速（持续24小时）与喷发后拱廊强度和重新连接通量的时间曲线一致。Chen et al.（2019，https：//doi.org/10.3847/1538-4357/ab3f36）获得了较低的速度，因为他们假设CME在2012小时后不会加速。在暗条通道附近存在多个冕洞以及来自它们的高速风似乎具有在日冕和IP介质中产生复杂旋转的综合效应，从而导致高倾角MC。在主相的DST时间分布显着陡峭（风暴强度迅速增加）一致的密度增加（突出的材料）在MC的下半部分。使用综合内磁层-电离层模型进行的模拟表明，较高的环电流能量来自于MC中较大的动态压力（密度）。此外，Dst指数与包括密度的环电流注入的主相时间积分高度相关，与模拟一致。在IP磁场向南的时段内，如果下伏MC具有复杂的密度结构，则在风暴主相会产生复杂的时间结构。我们认为，强磁暴的形成是由于CME的长时间加速、CME磁绳的复杂旋转以及1-Au MC的高密度所致。
We report on the solar and interplanetary (IP) causes of the third largest geomagnetic storm (26 August 2018) in solar cycle 24. The underlying coronal mass ejection (CME) originating from a quiescent filament region becomes a 440 km/s magnetic cloud (MC) at 1 au after ∼5 days. The prolonged CME acceleration (for ∼24 hr) coincides with the time profiles of the post‐eruption arcade intensity and reconnected flux. Chen et al. (2019, https://doi.org/10.3847/1538-4357/ab3f36) obtain a lower speed since they assumed that the CME does not accelerate after ∼12 hr. The presence of multiple coronal holes near the filament channel and the high‐speed wind from them seem to have the combined effect of producing complex rotation in the corona and IP medium resulting in a high‐inclination MC. The Dst time profile in the main phase steepens significantly (rapid increase in storm intensity) coincident with the density increase (prominence material) in the second half of the MC. Simulations using the Comprehensive Inner Magnetosphere‐Ionosphere model show that a higher ring current energy results from larger dynamic pressure (density) in MCs. Furthermore, the Dst index is highly correlated with the main‐phase time integral of the ring current injection that includes density, consistent with the simulations. A complex temporal structure develops in the storm main phase if the underlying MC has a complex density structure during intervals of southward IP magnetic field. We conclude that the high intensity of the storm results from the prolonged CME acceleration, complex rotation of the CME flux rope, and the high density in the 1‐au MC.