{
  "id": "1712.05106",
  "version": "v1",
  "published": "2017-12-14T07:08:25.000Z",
  "updated": "2017-12-14T07:08:25.000Z",
  "title": "On the factors determining the eruptive character of solar flares",
  "authors": [
    "Christian Baumgartner",
    "Julia K. Thalmann",
    "Astrid M. Veronig"
  ],
  "comment": "17 pages, 7 figures, accepted for publication in ApJ",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We investigated how the magnetic field in solar active regions (ARs) controls flare activity, i.e., whether a confined or eruptive flare occurs. We analyzed 44 flares of GOES class M5.0 and larger that occurred during 2011--2015. We used 3D potential magnetic field models to study their location (using the flare distance from the flux-weighted AR center $d_{\\mathrm{FC}}$) and the strength of the magnetic field in the corona above (via decay index $n$ and flux ratio). We also present a first systematic study of the orientation of the coronal magnetic field, using the orientation $\\varphi$ of the flare-relevant polarity inversion line as a measure. We analyzed all quantities with respect to the size of the underlying dipole field, characterized by the distance between the opposite-polarity centers, $d_{\\mathrm{PC}}$. Flares originating from underneath the AR dipole $(d_{\\mathrm{FC}}/d_{\\mathrm{PC}}<0.5$) tend to be eruptive if launched from compact ARs ($d_{\\mathrm{PC}}\\leq60$ Mm) and confined if launched from extended ARs. Flares ejected from the periphery of ARs ($d_{\\mathrm{FC}}/d_{\\mathrm{PC}}>0.5$) are predominantly eruptive. In confined events the flare-relevant field adjusts its orientation quickly to that of the underlying dipole with height ($\\Delta\\varphi\\gtrsim40^\\circ$ until the apex of the dipole field), in contrast to eruptive events where it changes more slowly with height. The critical height for torus instability, $h_{\\mathrm{crit}}=h(n=1.5)$, discriminates best between confined ($h_{\\mathrm{crit}}\\gtrsim40$ Mm) and eruptive flares ($h_{\\mathrm{crit}}\\lesssim40$ Mm). It discriminates better than $\\Delta\\varphi$, implying that the decay of the confining field plays a stronger role than its orientation at different heights.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-12-14T07:08:25.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "solar flares",
      "eruptive character",
      "factors determining",
      "3d potential magnetic field models",
      "orientation"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 17,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}