Alfv\'en wave propagation, reflection and trapping in the solar wind

TL;DR

This study uses 1.5-D MHD simulations to investigate how Alfvén waves are reflected and trapped in the solar wind, revealing optimal conditions for wave trapping that could influence solar atmosphere energization.

Contribution

The paper introduces a semi-analytical model explaining wave interference effects and identifies specific density enhancement scales that maximize wave reflection and trapping.

Findings

Maximum wave reflection occurs when density enhancement width matches the Alfvén wavelength.

Extended density inhomogeneities enhance wave reflection and trapping.

Wave interference causes saturation of reflected energy in large inhomogeneous regions.

Abstract

Alfv\'en waves are known to be important carriers of magnetic energy that could play a role in coronal heating and/or solar wind acceleration. As these waves are efficient energy carriers, how they are dissipated still remains one of the key challenges. Using a series of 1.5-D magnetohydrodynamic (MHD) simulations, we explore wave energy trapping associated with field-aligned density enhancements. We examine the parameters which govern the wave reflection and trapping. The goal of our simulations is to find optimal conditions for wave trapping, which would ultimately promote the energisation of the solar atmosphere. In agreement with previous studies, we find that maximum wave reflections happen only for a narrow range of density enhancement widths, namely when it is comparable to the Alfv\'en wave wavelength. In our paper, we explain this scale-selectivity using a semi-analytical model that demonstrates the importance of wave interference effects. As expected, we find that spatially extended regions of density inhomogeneities favour enhanced wave reflection and trapping. However, wave interference causes saturation of the reflected energy for very extended regions of varying density.