Coronal Mass Ejection Initiation: On the Nature of the Flux Cancellation Model
Abstract
We consider a three-dimensional bipolar force-free magnetic field with a nonzero magnetic helicity, occupying a half-space, and study the problem of its evolution driven by an imposed photospheric flux decrease. For this specific setting of the Flux Cancellation Model describing coronal mass ejections occurring in active regions, we address the issues of the physical meaning of flux decrease, of the influence on field evolution of the size of the domain over which this decrease is imposed, and of the existence of an energetic criterion characterizing the possible onset of disruption of the configuration. We show that (1) the imposed flux disappearance can be interpreted in terms of transport of positive and negative fluxes toward the inversion line, where they get annihilated. (2) For the particular case actually computed, in which the initial state is quite sheared, the formation of a twisted flux rope and the subsequent global disruption of the configuration are obtained when the flux has decreased by only a modest amount over a limited part of the whole active region. (3) The disruption is produced when the magnetic energy becomes of the order of the decreasing energy of a semi-open field, and then before reaching the energy of the associated fully open field. This suggests that the mechanism leading to the disruption is nonequilibrium as in the case where flux is imposed to decrease over the whole region.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2010
- DOI:
- 10.1088/2041-8205/717/1/L26
- arXiv:
- arXiv:1005.4669
- Bibcode:
- 2010ApJ...717L..26A
- Keywords:
-
- magnetohydrodynamics: MHD;
- stars: coronae;
- stars: flare;
- stars: magnetic field;
- Sun: coronal mass ejections: CMEs;
- Sun: flares;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- In press in ApJ Letters