The Heating of the Solar Corona by Kink Instabilities

Abstract

The million-degree temperature of the solar corona might be due to the combined effectof barely distinguishable energy releases, called nanoflares, that occur throughoutthe solar atmosphere. Unfortunately, the high density of nanoflares, implied by thishypothesis, means that conclusive verification is beyond present observational capabilities.Nevertheless, it might be possible to investigate the plausibility of nanoflareheating by constructing a magnetohydrodynamic (MHD) model; one that can derivethe energy of nanoflares, based on the assumption that the ideal kink instability of atwisted coronal loop triggers a relaxation to a minimum energy state. The energy releasedepends on the current profile at the time when the ideal kink instability thresholdis crossed. Subsequent to instability onset, fast magnetic reconnection ensues in thenon-linear phase. As the flare erupts and declines, the field transitions to a lower energylevel, which can be modelled as a helicity-conserving relaxation to a linear force-freestate. The aim of this thesis is to determine the implications of such a scheme withrespect to coronal heating.Initially, the results of a linear stability analysis for loops that have net current arepresented. There exists substantial variation in the radial magnetic twist profiles for theloop states along the instability threshold. These results suggest that instability cannotbe predicted by any simple twist-derived property reaching a critical value. The modelis applied such that the loop undergoes repeated episodes of instability followed byenergy-releasing relaxation. Photospheric driving is simulated as an entirely randomprocess. Hence, an energy distribution of the nanoflares produced is collated. These resultsare discussed and unrealistic features of the model are highlighted. Subsequently,

Date of Award	31 Dec 2012
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Philippa Browning (Supervisor)