Monday

We consider solar coronal heating in twisted magnetic flux ropes, which provide free magnetic energy which may be dissipated by magnetic reconnection (Klimchuk, 2015). An isolated individual flux rope may undergo reconnection and dissipate magnetic energy if it is unstable to the ideal kink instability, but heating could be much more efficient if energy could also be released from stable flux ropes. Previously, Tam et al (2015) and Hood et al (2015) undertook 3D MHD simulations demonstrating that a kink-unstable flux rope could trigger relaxation within nearby stable flux ropes. Furthermore, this could cause an avalanche effect.

The avalanche simulation simulated 23 flux ropes and is likely the extent of current computational capability whilst ensuring sufficient accuracy. Therefore, we developed a relaxation model (Hussain et al, 2017). The model used a Taylor relaxation model which determines the minimum energy state while conserving helicity. Our analysis shows good agreement between the analytical model and the simulation results.

The relaxation model is, however, blind to whether or not a relaxation event is physically likely to be initiated. Therefore, we have conducted MHD simulations of two flux ropes to determine a set of "rules" that could be applied to large scale avalanche relaxation models. Parameters that have been investigated include distance between a stable and unstable flux rope and the magnitude and direction of the twist. Furthermore, we have also investigated the reasons why a stable flux rope may undergo relaxation. Our investigations suggest that this might be due to triggering of a resistive instability by the expanding unstable flux rope coupled with a magnetic field perturbation that is a direct result of the unstable flux rope relaxing.