Onset and Evolution of Solar Flares: Application of 2D and 3D Models of Magnetic Reconnection

Abstract

Contemporary multi-wavelength observations have revealed various important features during solar flares. On one hand, these observations support the two-dimensional (2D) “standard flare model,” while on other hand, they also call for exploration of three-dimensional (3D) magnetic field topologies involved in flares. Traditionally, the formation of parallel ribbons on both sides of the polarity inversion line (PIL) and associated overlying loop arcades have been recognized as the most prominent features of eruptive flares, forming the basis for the development of the standard model that provides a 2D description of flare-associated phenomena. However, the actual flare occurs within a more complicated 3D magnetic structure. Thus, despite its general applicability, the standard model has limited or no scope in explaining some features that exclusively require a 3D description. In this context, the observations of “circular ribbon flares” stand out, where one of the ribbons presents an almost fully closed quasi-circular or quasi-ellipsoidal shape, providing evidence of the involvement of a typical fan-spine magnetic configuration. In this article, we discuss observational features vis-à-vis theoretical understanding of solar flares in view of 2D and 3D models of magnetic reconnection. We highlight a few complex cases of circular ribbon flares exhibiting parallel ribbons, a coronal jet, and/or an erupting magnetic flux rope. Exploring various 3D topologies also enables us to probe similarities between the circumstances that govern the onset of jets, confined flares and CME-producing eruptive flares.