Development of Torus and Kink Instabilities in Eruptive Prominences

Abstract Several filament eruptions with pronounced writhing of the axis of the structure are analyzed. Initially, smooth arches of eruptive filaments are transformed into large-scale helical structures with at least one complete turn due to the development of kink instability. However, the initiation of the eruptions seems to be caused not by the kink instability but by catastrophic loss of equilibrium or torus instability. Calculations of the decay index of the coronal potential magnetic field indicate that the studied filaments began to rise rapidly at heights where the decay index was close to unity, the threshold for the catastrophic loss of equilibrium of straight flux ropes. Although it is often assumed that the kink instability precedes the subsequent torus instability leading to a full eruption, these examples testify to the possibility of the reverse order of the eruption development.