The Association of Big Flares and Coronal Mass Ejections: What is the Role of Magnetic Helicity?
Abstract
In a recent study Andrews found that approximately 40% of M-class flares between 1996 and 1999, classified according to GOES X-ray flux, are not associated with Coronal Mass Ejections (CMEs). Using 133 events from his dataset for which suitable photospheric magnetograms and coronal images were available, we studied the pre-flare coronal helicity of the active regions that produced big flares. The coronal magnetic field of 78 active regions was modeled under the "constant α" linear force-free field assumption. We find that in a statistical sense the pre-flare value of α and coronal helicity of the active regions producing big flares that do not have associated CMEs is smaller than the coronal helicity of those producing CME-associated big flares. A further argument supporting this conclusion is that for the active regions whose coronal magnetic field deviates from the force-free model, the change of the coronal sign of α within an active region is twice more likely to occur when the active region is about to produce a confined flare than a CME-associated flare. Our study indicates that the amount of the stored pre-flare coronal helicity may determine whether a big flare will be eruptive or confined.
- Publication:
-
Coronal and Stellar Mass Ejections
- Pub Date:
- 2005
- DOI:
- 10.1017/S1743921305000475
- Bibcode:
- 2005IAUS..226..194N