Damping of nonlinear standing kink oscillations: a numerical study

TL;DR

This study uses high-resolution 3D MHD simulations to explore how nonlinear effects, especially Kelvin-Helmholtz instability, influence the damping of standing kink oscillations in coronal loops, revealing deviations from linear theory predictions.

Contribution

It demonstrates how nonlinear effects, particularly KHI, can accelerate damping beyond linear theory estimates, challenging current seismological methods.

Findings

KHI develops at higher amplitudes, accelerating damping.

Low amplitude oscillations match resonant absorption theory.

Nonlinear effects can significantly alter damping times.

Abstract

We aim to study the standing fundamental kink mode of coronal loops in the nonlinear regime, investigating the changes in energy evolution in the cross-section and oscillation amplitude of the loop which are related to nonlinear effects, in particular to the development of the Kelvin-Helmholtz instability (KHI). We run idea, high-resolution three-dimensional (3D) magnetohydrodynamics (MHD) simulations, studying the influence of the initial velocity amplitude and the inhomogeneous layer thickness. We model the coronal loop as a straight, homogeneous magnetic flux tube with an outer inhomogeneous layer, embedded in a straight, homogeneous magnetic field. We find that, for low amplitudes which do not allow for the KHI to develop during the simulated time, the damping time agrees with the theory of resonant absorption. However, for higher amplitudes, the presence of KHI around the oscillating loop can alter the loop's evolution, resulting in a significantly faster damping than predicted by the linear theory in some cases. This questions the accuracy of seismological methods applied to observed damping profiles, based on linear theory.