Field lines twisting in a noisy corona: implications for energy storage and release, and initiation of solar eruptions

TL;DR

This paper models how twisted magnetic field lines in the solar corona, influenced by photospheric motions, become unstable and develop turbulence, leading to energy storage and potential release in solar eruptions.

Contribution

It extends previous kink instability studies by including turbulent fluctuations, showing how energy accumulates and is released in a more realistic, turbulent coronal environment.

Findings

Kink instability occurs in laminar conditions but is suppressed in turbulent states.

Energy accumulates at large scales via inverse cascade in turbulent corona.

Twisted field lines can lead to micro-flares or larger eruptions upon interaction.

Abstract

We present simulations modeling closed regions of the solar corona threaded by a strong magnetic field where localized photospheric vortical motions twist the coronal field lines. The linear and nonlinear dynamics are investigated in the reduced magnetohydrodynamic regime in Cartesian geometry. Initially the magnetic field lines get twisted and the system becomes unstable to the internal kink mode, confirming and extending previous results. As typical in this kind of investigations, where initial conditions implement smooth fields and flux-tubes, we have neglected fluctuations and the fields are laminar until the instability sets in. But previous investigations indicate that fluctuations, excited by photospheric motions and coronal dynamics, are naturally present at all scales in the coronal fields. Thus, in order to understand the effect of a photospheric vortex on a more realistic corona, we continue the simulations after kink instability sets in, when turbulent fluctuations have already developed in the corona. In the nonlinear stage the system never returns to the simple initial state with ordered twisted field lines, and kink instability does not occur again. Nevertheless field lines get twisted, but in a disordered way, and energy accumulates at large scales through an inverse cascade. This energy can subsequently be released in micro-flares or larger flares, when interaction with neighboring structures occurs or via other mechanisms. The impact on coronal dynamics and CMEs initiation is discussed.