Generation and annihilation of three dimensional magnetic nulls in extrapolated solar coronal magnetic field: data-based Implicit Large Eddy simulation

Abstract

Three-dimensional (3D) magnetic nulls are the points where magnetic field vanishes and are preferential sites for magnetic reconnection: a fundamental process which converts magnetic energy into kinetic energy, heat, and energy of non-thermal particles along with a rearrangement of magnetic field lines. Reconnection is ubiquitous in nature and plays a major role in various magnetically confined laboratory and space/astrophysical plasmas. In the solar corona, the reconnection manifests as coronal transients including solar flares, coronal mass ejections and coronal jets—often associated with 3D nulls. The nulls are generally found to be collocated with complex active regions on the solar photosphere and merits further attention, particularly in terms of their generation. A recent idealized magnetohydrodynamics simulation initiated with an analytically constructed preexisting proper radial null has identified magnetic reconnection to be responsible for spontaneous generation of these 3D nulls. It is then imperative to further explore the plausibility of spontaneous generation of nulls in naturally occurring plasmas, identify the mechanism and verify the outcome vis-à-vis observations. An apt test bed for such an initiative is the solar atmosphere, as abundant space and ground-based observations are available. In the above backdrop, the paper attempts to investigate 3D null generation by carrying out a data-based simulation of a C6.6 class flare associated with the photospheric active region NOAA 11 977. The simulation confirms spontaneous pairwise generation of 3D nulls with magnetic reconnections as the underlying cause. Importantly, magnetic field lines associated with the spontaneously generated nulls are found to trace observed chromospheric bright points—highlighting their observational relevance. Overall, such spontaneous generation and annihilation of nulls through magnetic reconnections opens up a new avenue for solar coronal and chromospheric heating.