The Association of Big Flares and Coronal Mass Ejections: What Is the Role of Magnetic Helicity?

Abstract

Recently, M. D. 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 data set for which suitable photospheric magnetograms and coronal images were available, we studied the preflare coronal helicity of the active regions that produced big flares. The coronal magnetic field of 78 active regions was modeled under the constant linear force-free field assumption. We find that in a statistical sense the preflare 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 as 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 preflare coronal helicity may determine whether a big flare will be eruptive or confined.