Alfv\'en waves in simulations of solar photospheric vortices

TL;DR

This study uses detailed magneto-hydrodynamic simulations to analyze plasma motions in solar photospheric vortices, revealing that observed vortex motions are wave-like Alfvén perturbations rather than tornado-like structures.

Contribution

It demonstrates that apparent vortex motions are actually torsional Alfvén waves propagating along magnetic field lines, challenging previous interpretations of vortex phenomena.

Findings

Vortex-like motions are wave-like Alfvén perturbations.

Test particles do not follow vortex-like structures.

Magnetic tension influences plasma motion significantly.

Abstract

Using advanced numerical magneto-hydrodynamic simulations of the magnetised solar photosphere, including non-grey radiative transport and a non-ideal equation of state, we analyse plasma motions in photospheric magnetic vortices. We demonstrate that apparent vortex-like motions in photospheric magnetic field concentrations do not exhibit "tornado"-like behaviour or a "bath-tub" effect. While at each time instance the velocity field lines in the upper layers of the solar photosphere show swirls, the test particles moving with the time-dependent velocity field do not demonstrate such structures. Instead, they move in a wave-like fashion with rapidly changing and oscillating velocity field, determined mainly by magnetic tension in the magnetised intergranular downflows. Using time-distance diagrams, we identify horizontal motions in the magnetic flux tubes as torsional Alfv\'en perturbations propagating along the nearly vertical magnetic field lines with local Alfv\'en speed.