Energy release in driven twisted coronal loops

Abstract

Magnetic reconnection in twisted magnetic flux tubes, representing coronal loops, is investigated. The main goal is to establish the influence of the field geometry and various thermodynamic effects on the stability of twisted flux tubes and on the size and distribution of heated regions. In particular, we aim to investigate to what extent the earlier idealised models, based on the initially cylindrically symmetric flux tubes, are different from more realistic models, including the large-scale curvature, atmospheric stratification, thermal conduction and other effects. In addition, we compare the roles of Ohmic heating and shock heating in energy conversion during magnetic reconnection in twisted loops. The models with straight flux tubes show similar distribution of heated plasma during the reconnection: it initially forms a helical shape, which subsequently becomes very fragmented. The heating in these models is rather uniformly distributed along flux tubes. At the same time, the hot plasma regions in curved loops are asymmetric, and concentrate close to the loop tops. Large-scale curvature has a destabilising in influence: lower twist is needed for instability. Footpoint convergence normally delays instability slightly, although, in some cases converging flux tubes can be less stable. Finally, introducing a stratified atmosphere gives rise to decaying wave propagation, which has destabilising effect.