Partially Open Fields and Solar Eruptions
Abstract
Partially Open Fields and Solar Eruptions*
Major solar eruptions such as X-class flares and coronal mass ejections (CMEs) are the progenitors of solar energetic particles and geomagnetic storms, and are thus key drivers of space weather at Earth. The solar magnetic field is the ultimate source of these massive events, the energy of which is believed to be stored as free magnetic energy (energy above the potential field state) prior to eruption. The amount of free magnetic energy available in a given region is therefore a crucial indicator of its propensity for eruption. However, solar active regions, from which the largest events originate, can store widely varying amounts of energy. Therefore, estimates of the free energy alone are likely to be insufficient for knowing when a region will erupt; we must also estimate the bounds on how much energy can be stored in a given region. The Aly-Sturrock theorem (Aly, ApJ 1991; Sturrock, ApJ 1991) shows that the energy of a fully force-free field cannot exceed the energy of the so-called open field. If the theorem holds, this places an upper limit on the amount of free energy that can be stored. In this paper, we describe how a closely related field, the partially open field (Wolfson & Low ApJ 1992; Hu, ApJ 2004; Aly & Amari, GAFD 2007), may place a much tighter bound on energy storage and yield insights as to when major eruptions from an active region are imminent (Amari et al., Nature, 2014). We demonstrate the idea for AR9077, the source of the July 14, 2000 "Bastille Day" flare/CME. *Research supported by NASA and AFOSR- Publication:
-
2018 Triennial Earth-Sun Summit (TESS)
- Pub Date:
- May 2018
- Bibcode:
- 2018tess.conf10905L