Magnetic reconnections as the underlying cause of spontaneous generation and annihilation of three-dimensional magnetic nulls

Abstract

Three-dimensional (3D) magnetic nulls are preferential sites for triggering solar coronal transients. Although these nulls are abundant in the solar atmosphere, their generation is yet to be thoroughly explored. This paper explores the mechanism of null generation as well as annihilation in detail by means of implicit large eddy simulations where magnetohydrodynamic equations are solved in the absence of an explicit magnetic diffusivity. The magnetofluid is idealized to be thermodynamically inactive, incompressible, and have perfect explicit electrical conductivity. The simulated dynamics is initiated by a prescribed flow in a magnetic configuration having an isolated current-free 3D null. The flow facilitates reconnections, which lead to the generation of primary null pairs in a way that preserves the topological degree. The formation process of these null pairs is novel and different from the standard pitchfork bifurcation. Contrarily, here we found creation of null pairs away from the central null, which we hypothesize is due to the interaction of the imposed flow and the reconnection outflow from the central current layer. Intriguingly, further evolution spontaneously generates new null pairs, which have a novelty by itself. As theorized, these spontaneously generated null pairs also preserve the net topological degree—adding credibility to the simulation. The simulation also shows null pair annihilation. Magnetic reconnections are identified to be responsible for the generation and annihilation of the nulls—opening up the possibility for the nulls to be self-organized structures. Furthermore, the reconnection being ubiquitous in the corona, it can explain the coronal abundance of magnetic nulls.