Onset and evolution of solar flares: Application of 2D and 3D models of magnetic reconnection

TL;DR

This paper reviews how 2D and 3D magnetic reconnection models explain the onset and evolution of solar flares, emphasizing complex features like circular ribbons and fan-spine configurations observed in multi-wavelength data.

Contribution

It compares observational features of solar flares with theoretical 2D and 3D models, highlighting the importance of 3D topologies in understanding complex flare phenomena.

Findings

3D magnetic topologies explain circular ribbon flares.

Complex flare features involve fan-spine magnetic configurations.

Onset mechanisms for jets, confined flares, and CMEs are linked to magnetic topology.

Abstract

The contemporary multi-wavelength observations have revealed various important features during solar flares which, on one hand, support the two-dimensional (2D) "standard flare model" while, on other hand, also urge for the exploration of three-dimensional (3D) magnetic field topologies involved in flares. Traditionally, the formation of parallel ribbons on both side of the polarity inversion line (PIL) and associated overlying loop arcades have been recognized as the most prominent features of eruptive flares which has formed the basis for the development of the standard model providing a 2D description of the flare-associated phenomena. The actual flare, however, occurs in a more complicated 3D magnetic structure. Thus, despite the general applicability, the standard model has limited or no scope in explaining some of the features which exclusively requires 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, evidencing the involvement of a typical fan-spine magnetic configuration. In this article, we discuss observational features vis \`a 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.