{
  "id": "2006.09699",
  "version": "v1",
  "published": "2020-06-17T07:52:36.000Z",
  "updated": "2020-06-17T07:52:36.000Z",
  "title": "Characteristics and Importance of \"ICME-in-Sheath\" Phenomenon and Upper Limit for Geomagnetic Storm Activity",
  "authors": [
    "Ying D. Liu",
    "Chong Chen",
    "Xiaowei Zhao"
  ],
  "comment": "Accepted for publication in The Astrophysical Journal Letters",
  "categories": [
    "astro-ph.SR",
    "physics.space-ph"
  ],
  "abstract": "As an important source for large geomagnetic storms, an \"ICME-in-sheath\" is a completely shocked interplanetary coronal mass ejection (ICME) stuck in the sheath between a shock and host ejecta. Typical characteristics are identified from coordinated multi-sets of observations: (1) it is usually short in duration and lasts a few hours at 1 AU; (2) its solar wind parameters, in particular the magnetic field, seem to keep enhanced for a large range of distances; and (3) common ICME signatures are often lost. The host ejecta could be a single ICME or a complex ejecta, being fast enough to drive a shock. These results clarify previous misinterpretations of this phenomenon as a normal part of a sheath region. The \"ICME-in-sheath\" phenomenon, together with a preconditioning effect, produced an extreme set of the magnetic field, speed and density near 1 AU in the 2012 July 23 case, all around their upper limits at the same time. This is probably the most extreme solar wind driving at 1 AU and enables us to estimate the plausible upper limit for geomagnetic storm activity. With an appropriate modification in the southward field, we suggest that a geomagnetic storm with a minimum $D_{\\rm st}$ of about $-2000$ nT could occur in principle. The magnetopause would be compressed to about 3.3 Earth radii from the Earth's center, well inside the geosynchronous orbit.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-06-17T07:52:36.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "geomagnetic storm activity",
      "upper limit",
      "phenomenon",
      "icme-in-sheath",
      "characteristics"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}