Elemental abundances in the solar corona are known to be different from those observed in the solar photosphere. The ratio of coronal to photospheric abundance shows a dependence on the first ionisation potential (FIP) of the element. We estimate FIP bias from direct measurements of elemental abundances from soft X-ray spectra using data from multiple space missions covering a range of solar activity levels. This comprehensive analysis shows clear evidence for a decrease in FIP bias around maximum intensity of the X-ray flare with coronal abundances briefly tending to photospheric values and a slow recovery as the flare decays. The departure from coronal abundances are larger for the low FIP elements Ca, Fe and Si than for S which have a mid FIP value. These changes in the degree of fractionation might provide inputs to model wave propagation through the chromosphere during flares.

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日冕元素丰度：来自太阳软 X 射线光谱的新结果

已知日冕中的元素丰度与在太阳光球中观察到的元素丰度不同。日冕丰度与光球丰度之比显示出对元素第一电离势 (FIP) 的依赖性。我们使用来自涵盖一系列太阳活动水平的多个太空任务的数据，通过从软 X 射线光谱中直接测量元素丰度来估计 FIP 偏差。这一综合分析显示了 FIP 偏差在 X 射线耀斑最大强度附近减少的明确证据，日冕丰度短暂趋于光球值，随着耀斑衰减缓慢恢复。与具有中等 FIP 值的 S 相比，低 FIP 元素 Ca、Fe 和 Si 与日冕丰度的偏离更大。