Solar Irradiance Variability Due to Solar Flares Observed in Lyman-Alpha Emission
Solar Irradiance Variability Due to Solar Flares Observed in Lyman-Alpha Emission
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DOI：
10.1007/s11207-021-01796-3
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发表时间：
2021-02
期刊：
影响因子：
2.8
通讯作者：
R. Milligan
中科院分区：
文献类型：
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作者：
R. Milligan
由于中性氢的莱曼-α (Ly) 线是太阳光谱中最亮的发射线，因此由于背景非常高，检测该波长处的太阳耀斑导致的辐照度增加可能具有挑战性。先前针对最大耀斑的研究表明，即使是这些极端情况，Lyof 的增强效果也仅比背景高出几个百分点。在这项研究中，对约 8500 个大于 B1 级的耀斑进行了叠加历元分析，以确定它们对太阳 EUV 辐照度变化的贡献。以1 – 8 Å X射线发射峰值作为基准时间，对地球静止运行环境卫星15（GOES-15）上的EUV传感器在Lyemission中观测到的3123个B级和4972个C级耀斑的相应时间序列进行平均，以减少背景波动并改善耀斑信号。这些较弱事件的总和表明，它们平均使太阳辐射亮度增强了 0.1% - 0.3%。为了进行比较，相同的技术应用于 453 M 级和 31 X 级耀斑，导致 Lyemission 增加 1 – 4%。耀斑还根据其日照角度进行平均，以研究任何潜在的中心到肢体的变化。对于每个 GOES 类别，由于线的不透明度和/或足点的缩短，在靠近太阳边缘发生的耀斑中发现耀斑峰值的相对增强会减弱。研究中包括的一个温和事件，即 C6.6 耀斑，表现出 Lyof 7% 异常高的增长，这可能归因于灯丝喷发失败。迄今为止，这种幅度的增加仅与少数 X 级耀斑有关。
As the Lyman-alpha (Ly) line of neutral hydrogen is the brightest emission line in the solar spectrum, detecting increases in irradiance due to solar flares at this wavelength can be challenging due to the very high background. Previous studies that have focused on the largest flares have shown that even these extreme cases generate enhancements in Lyof only a few percent above the background. In this study, a superposed-epoch analysis was performed on ≈8500 flares greater than B1 class to determine the contribution that they make to changes in the solar EUV irradiance. Using the peak of the 1 – 8 Å X-ray emission as a fiducial time, the corresponding time series of 3123 B- and 4972 C-class flares observed in Lyemission by the EUV Sensor on the Geostationary Operational Environmental Satellite 15 (GOES-15) were averaged to reduce background fluctuations and improve the flare signal. The summation of these weaker events showed that they produced a 0.1 – 0.3% enhancement to the solar Lyirradiance on average. For comparison, the same technique was applied to 453 M- and 31 X-class flares, which resulted in a 1 – 4% increase in Lyemission. Flares were also averaged with respect to their heliographic angle to investigate any potential center-to-limb variation. For each GOES class, the relative enhancement in Lyat the flare peak was found to diminish for flares that occurred closer to the solar limb due to the opacity of the line and/or foreshortening of the footpoints. One modest event included in the study, a C6.6 flare, exhibited an unusually high increase in Lyof 7% that may have been attributed to a failed filament eruption. Increases of this magnitude have hitherto only been associated with a small number of X-class flares.