The dynamics and observability of circularly polarized kink waves

TL;DR

This study investigates circularly polarized kink waves in coronal loops, revealing that damping via resonant absorption is polarization-independent, but nonlinear effects and flow morphology differ between circular and linear polarizations, with implications for solar seismology.

Contribution

It is the first to compare properties of circularly polarized kink waves with linearly polarized ones in a 3D MHD framework, highlighting differences in flow morphology and nonlinear growth.

Findings

Resonant absorption damping is polarization-independent.

Flow morphology differs between circular and linear polarization.

Nonlinear growth rate depends on total energy, not perturbation amplitude.

Abstract

Context. Kink waves are routinely observed in coronal loops. Resonant absorption is a well-accepted mechanism that extracts energy from kink waves. Nonlinear kink waves are know to be affected by the Kelvin-Helmholtz instability. However, all previous numerical studies consider linearly polarized kink waves. Aims. We study the properties of circularly polarized kink waves on straight plasma cylinders, for both standing and propagating waves, and compare them to the properties of linearly polarized kink waves. Methods. We use the code MPI-AMRVAC to solve the full 3D Magnetohydrodynamic (MHD) equations for a straight magnetic cylinder, excited by both standing and propagating circularly polarized kink (m = 1) modes. Results. The damping due to resonant absorption is independent of the polarization state. The morphology or appearance of the induced resonant flow is different for the two polarizations, however, there are essentially no differences in the forward-modeled Doppler signals. For nonlinear oscillations, the growth rate of small scales is determined by the total energy of the oscillation rather than the perturbation amplitude. We discuss possible implications and seismological relevance.