Numerical Simulations of Torsional Alfv\'en Waves in Axisymmetric Solar Magnetic Flux Tubes

TL;DR

This paper numerically studies Alfvén wave propagation in an axisymmetric, non-isothermal solar flux tube, revealing how physical gradients influence wave behavior and reflection regions in the solar chromosphere.

Contribution

It presents a novel numerical analysis of Alfvén waves in a realistic solar flux tube with variable temperature and magnetic field divergence, highlighting differential wave variable behavior.

Findings

Velocity and magnetic perturbations behave differently due to physical gradients.

Wave reflection regions are identified in the solar chromosphere.

Cutoff periods for wave variables are calculated to explain wave reflection.

Abstract

We investigate numerically Alfv\'en waves propagating along an axisymmetric and non-isothermal solar flux tube embedded in the solar atmosphere. The tube magnetic field is current-free and diverges with height, and the waves are excited by a periodic driver along the tube magnetic field lines. The main results are that the two wave variables, the velocity and magnetic field perturbations in the azimuthal direction, behave differently as a result of gradients of physical parameters along the tube. To explain these differences in the wave behavior, the time evolution of the wave variables and the resulting cutoff period for each wave variable are calculated, and used to determine regions in the solar chromosphere where strong wave reflection may occur.