Flute and kink instabilities in a dynamically twisted flux tube with anisotropic plasma viscosity

TL;DR

This study investigates how dynamic boundary twisting and anisotropic plasma viscosity influence the development and interaction of flute and kink instabilities in solar coronal flux tubes through magnetohydrodynamic simulations.

Contribution

It demonstrates that boundary-driven twisting excites flute modes and that anisotropic viscosity enhances these instabilities, revealing their interplay with kink modes in a more realistic setting.

Findings

Flute instabilities are readily excited by boundary twisting.

Anisotropic viscosity significantly delays kink instability development.

Flute instability can coexist and compete with kink instability, especially under strong magnetic fields.

Abstract

Magnetic flux tubes such as those in the solar corona are subject to a number of instabilities. Important among them is the kink instability which plays a central part in the nanoflare theory of coronal heating, and for this reason in numerical simulations it is usually induced by tightly-controlled perturbations and studied in isolation. In contrast, we find that when disturbances are introduced in our magnetohydrodynamic flux tube simulations by dynamic twisting of the flow at the boundaries fluting modes of instability are readily excited. We also find that the flute instability, which has been theorised but rarely observed in the coronal context, is strongly enhanced when plasma viscosity is assumed anisotropic. We proceed to investigate the co-existence and competition between flute and kink instabilities for a range of values of the resistivity and of the parameters of the anisotropic and isotropic models of viscosity. We conclude that while the flute instability cannot prevent the kink from ultimately dominating, it can significantly delay its development especially at strong viscous anisotropy induced by intense magnetic fields.