Magnetic 3-D Configurations of Energy Release in Solar Flares

Abstract

Basic concepts and principles usually used to interpret the solar flare phenomenon are summarized, and traditional classification schemes based on 2-D magnetic field representations are briefly reviewed. The extension to 3-D opens new aspects, some of which are sketched inthis paper: Inparticular two-loop interactions, two-ribbon flare geometry, and the plasmoid formationina current sheet are considered. It is shown that alternative onset processes exist beside the standard two-ribbon flare scenario in which the pre-flare arcade evolves slowly through a series of equilibrium states until the eruption. For example, the arcade can become unstable after an abrupt reformation of its core through a sequence of loop interactions. The restructuration results in animpulsive compact flare and the formationof anun stable ‘sigmoid’ whose eruption provides the two-ribbonphase aftermath. Possible modalities of mainphase are emphasized. Especially the secondary plasmoid formation is considered and its fate discussed stressing the 3-D aspect of the process and the effect of line-tying. Finally, complex events composed of several distinct, but causally related energy release processes are described.