{
  "id": "2111.10503",
  "version": "v1",
  "published": "2021-11-20T03:04:28.000Z",
  "updated": "2021-11-20T03:04:28.000Z",
  "title": "Comparison of Helium Abundance between ICMEs and Solar Wind near 1 AU",
  "authors": [
    "Hongqiang Song",
    "Xin Cheng",
    "Leping Li",
    "Jie Zhang",
    "Yao Chen"
  ],
  "comment": "9 pages, 3 figures, accepted for publication in ApJ",
  "categories": [
    "astro-ph.SR",
    "physics.space-ph"
  ],
  "abstract": "The Helium abundance, defined as $A_{He}=n_{He}/n_{H}\\times 100$, is $\\sim$8.5 in the photosphere and seldom exceeds 5 in fast solar wind. Previous statistics have demonstrated that $A_{He}$ in slow solar wind correlates tightly with sunspot number. However, less attention is paid to the solar cycle dependence of $A_{He}$ within interplanetary coronal mass ejections (ICMEs) and comparing the $A_{He}$ characteristics of ICMEs and solar wind. In this paper we conduct a statistical comparison of Helium abundance between ICMEs and solar wind near 1 AU with observations of \\textit{Advanced Composition Explorer} from 1998 to 2019, and find that the ICME $A_{He}$ also exhibits the obvious solar cycle dependence. Meanwhile, we find that the $A_{He}$ is obviously higher within ICMEs compared to solar wind, and the means within 37\\% and 12\\% of ICMEs exceed 5 and 8.5, respectively. It is interesting to answer where and how the high Helium abundance originates. Our statistics demonstrate that 21\\% (3\\%) of ICME (slow wind) $A_{He}$ data points exceed 8.5 around solar maximum, which decreases dramatically near minimum, while no such high $A_{He}$ values appear in the fast wind throughout the whole solar cycle. This indicates that the high $A_{He}$ (e.g., $>$8.5) emanates from active regions as more ICMEs and slow wind originates from active regions around maximum, and supports that both active regions and quiet-Sun regions are the sources of slow wind. We suggest that the high $A_{He}$ from active regions could be explained by means of the magnetic loop confinement model and/or photoionization effect.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-11-20T03:04:28.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "active regions",
      "solar cycle dependence",
      "slow wind",
      "comparison",
      "interplanetary coronal mass ejections"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}