Torsional Alfven Waves in Solar Magnetic Flux Tubes of Axial Symmetry

TL;DR

This paper develops an analytical model and numerical simulations to study torsional Alfvén wave propagation in solar magnetic flux tubes, revealing complex magnetic and flow dynamics, energy transfer, and implications for solar atmospheric heating.

Contribution

It introduces a versatile analytical model for axisymmetric magnetic flux tubes and demonstrates nonlinear Alfvén wave propagation and energy transfer in the solar atmosphere.

Findings

Alfvén waves experience about 5% reflection at the transition region.

Magnetoacoustic waves carry 25% of Alfvén wave energy.

Localized mass transport and heating are possible due to wave interactions.

Abstract

Aims: Propagation and energy transfer of torsional Alfv\'en waves in solar magnetic flux tubes of axial symmetry is studied. Methods: An analytical model of a solar magnetic flux tube of axial symmetry is developed by specifying a magnetic flux and deriving general analytical formulae for the equilibrium mass density and a gas pressure. The main advantage of this model is that it can be easily adopted to any axisymmetric magnetic structure. The model is used to simulate numerically the propagation of nonlinear Alfv\'en waves in such 2D flux tubes of axial symmetry embedded in the solar atmosphere. The waves are excited by a localized pulse in the azimuthal component of velocity and launched at the top of the solar photosphere, and they propagate through the solar chromosphere, transition region, and into the solar corona. Results: The results of our numerical simulations reveal a complex scenario of twisted magnetic field lines and flows associated with torsional Alfv\'en waves as well as energy transfer to the magnetoacoustic waves that are triggered by the Alfv\'en waves and are akin to the vertical jet flows. Alfv\'en waves experience about 5 % amplitude reflection at the transition region. Magnetic (velocity) field perturbations experience attenuation (growth) with height is agreement with analytical findings. Kinetic energy of magnetoacoustic waves consists of 25 % of the total energy of Alfv\'en waves. The energy transfer may lead to localized mass transport in the form of vertical jets, as well as to localized heating as slow magnetoacoustic waves are prone to dissipation in the inner corona.