Cut-off of transverse waves through the solar transition region

TL;DR

This study uses 3D MHD simulations to analyze how transverse kink waves propagate through the solar transition region, revealing a wave cut-off effect and identifying conditions under which waves can reach the corona and contribute to heating.

Contribution

The paper demonstrates the impact of the wave cut-off on kink wave propagation and compares analytical models with simulation results to predict wave behavior in the solar atmosphere.

Findings

Kink waves experience a cut-off in the transition region.

Waves with periods shorter than ~500 s can tunnel through the transition region.

Such waves can reach the corona and potentially heat it.

Abstract

Context. Transverse oscillations are ubiquitously observed in the solar corona, both in coronal loops and open magnetic flux tubes. Numerical simulations suggest that their dissipation could heat coronal loops, counterbalancing radiative losses. These models rely on a continuous driver at the footpoint of the loops. However, analytical works predict that transverse waves are subject to a cut-off in the transition region. It is thus unclear whether they can reach the corona, and indeed heat coronal loops. Aims. Our aims are to determine how the cut-off of kink waves affects their propagation into the corona, and to characterize the variation of the cut-off frequency with altitude. Methods. Using 3D magnetohydrodynamic simulations, we modelled the propagation of kink waves in a magnetic flux tube, embedded in a realistic atmosphere with thermal conduction, that starts in the chromosphere and extends into the corona. We drove kink waves at four different frequencies, and determined whether they experienced a cut-off. We then calculated the altitude at which the waves were cut-off, and compared it to the prediction of several analytical models. Results. We show that kink waves indeed experience a cut-off in the transition region, and we identified the analytical model that gives the best predictions. In addition, we show that waves with periods shorter than approximately 500 s can still reach the corona by tunnelling through the transition region, with little to no attenuation of their amplitude. This means that such waves can still propagate from the footpoints of loop, and result in heating in the corona.