The unipolar solar flares as a manifestation of the 'topological' magnetic reconnection

TL;DR

This paper investigates unipolar solar flares, which occur in unexpected magnetic configurations, by analyzing observational data, proposing a topological magnetic reconnection model, and supporting it with theoretical and numerical simulations.

Contribution

It introduces a topological model of magnetic reconnection explaining unipolar flares, supported by observational evidence and numerical simulations.

Findings

Unipolar flares can occur due to topological magnetic reconnection.

Flares are not always directly linked to local magnetic sources.

The model explains flares with footpoints in same polarity regions.

Abstract

Solar flares - which are the most prominent manifestation of the solar activity - typically manifest themselves as a single or a set of luminous arcs (magnetic flux tubes) rooted in regions of opposite polarity in the photosphere. However, a careful analysis of the archival data by Hinode satellite sometimes reveals surprising cases of flaring arcs whose footpoints belong to regions of the same polarity or to areas without any appreciable magnetic field. Despite the counterintuitive nature of this phenomenon, it can be reasonably interpreted in the framework of the so-called 'topological model' of magnetic reconnection, where a magnetic null point is formed due to specific superposition of influences from remote sources rather than by local current systems. As a result, the energy release propagates along a separator of the flipping two-dome structure rather than along a fixed magnetic field line. Therefore, the luminous arc needs not to be associated anymore immediately with the magnetic sources. Here, we report both observational cases of the above-mentioned type as well as provide their theoretical model and numerical simulations.