了解行星际日冕物质抛射中氦富集的整体方法：新的见解
A holistic approach to understand Helium enrichment in Interplanetary coronal mass ejections: New insights
摘要：
尽管氦的丰度（AHe = nH/nHe）在太阳光球/色球层高度约为8%，但在行星际日冕物质抛射（ICME）中，AHe可以在许多场合超过8%。虽然行星际激波、色球蒸发和“污泥去除”等因素在过去被分别用来解释ICME中AHe的增强，但这些过程都不能全面解释ICME中AHe的变化。通过对275个ICME事件的分析，我们发现ICME平均AHe值存在着太阳活动的变化。研究还表明，第一电离势效应以及日冕温度不是ICME中AHe增强的主要贡献因素。对63例太阳耀斑和ICME事件的研究表明，色球蒸发和重力沉降共同决定了ICME中AHe的增强和超过8%的变化。当色球蒸发将氦从色球层释放到日冕中时，重力沉降的氦在ICMEs期间被抛出。我们表明，来自CME爆发的同一活动区的先前耀斑的强度和时间是理解ICMEs中AHe增强的重要因素。
英文摘要：
Despite helium abundance (AHe = nH/nHe) is ~ 8 % at the solar photospheric/chromospheric heights, AHe can be found to exceed 8% in interplanetary coronal mass ejections (ICMEs) on many occasions. Although various factors like interplanetary shocks, chromospheric evaporation and "sludge removal" have been separately invoked in the past to address the AHe enhancements in ICMEs, none of these processes could explain the variability of AHe in ICMEs comprehensively. Based on extensive analysis of 275 ICME events, we show that there is a solar activity variation of ICME averaged AHe values. The investigation also reveals that the first ionization potential effect as well as coronal temperature are not the major contributing factors for AHe enhancements in ICMEs. Investigation on concurrent solar flares and ICME events for 63 cases reveals that chromospheric evaporation in tandem with gravitational settling determine the AHe enhancements and variabilities beyond 8% in ICMEs. While chromospheric evaporation releases the helium from chromosphere into the corona, the gravitationally settled helium is thrown out during the ICMEs.We show that the intensity and timing of the preceding flares from the same active region from where the CME erupts are important factors to understand the AHe enhancements in ICMEs.
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