Sheared magnetic fields and eruptive phenomena: Prominences, flares, and coronal mass ejections

The underlying cause of all the giant manifestations of solar activity - CMEs, eruptive flares and filament ejections - is the disruption of a force balance between the upward pressure of the strongly sheared field of a filament channel and the downward tension of overlying field that is quasi-potential. A key point is that the upward pressure cannot increase rapidly, because the magnetic shear/twist is produced by the slow photospheric evolution (shear flows and/or flux emergence). Therefore, explosive events such as flares and CMEs must be due fundamentally to the catastrophic removal of the downward magnetic tension. Recent theory and simulation have focused on magnetic reconnection as the mechanism for the removal of the magnetic tension. This paper discusses critically the recent models for magnetic disruptions in the Sun's corona.