MHD waves and instabilities in flowing solar structures in the framework of Hall magnetohydrodynamics

TL;DR

This paper studies how flows and Hall effects influence MHD surface waves and instabilities in solar plasma structures, revealing conditions for wave propagation limits and Kelvin-Helmholtz instability onset.

Contribution

It introduces a detailed analysis of surface wave propagation and instabilities in flowing solar plasma slabs within the Hall MHD framework, highlighting flow effects and instability criteria.

Findings

Flow alters wave phase velocities in plasma slabs.

Hall effect limits wave propagation range.

Kelvin-Helmholtz instability triggered at specific wave numbers.

Abstract

It is well established now that the solar atmosphere, from photosphere to the corona and the solar wind is a highly structured medium. Satellite observations have confirmed the presence of steady flows. Here, we investigate the parallel propagation of magnetohydrodynamic (MHD) surface waves travelling along an ideal incompressible flowing plasma slab surrounded by flowing plasma environment in the framework of the Hall magnetohydrodynamics. The propagation properties of the waves are studied in a reference frame moving with the mass flow outside the slab. In general, flows change the waves' phase velocities compared to their magnitudes in a static MHD plasma slab and the Hall effect limits the range of waves' propagation. On the other hand, when the relative Alfvenic Mach number is negative, the flow extends the waves propagation range beyond that limit (owing to the Hall effect) and can cause the triggering of the Kelvin--Helmholtz instability whose onset begins at specific critical wave numbers. It turns out that the interval of Alfvenic Mach numbers for which the surface modes are unstable critically depends on the ratio between mass densities outside and inside the flux tube.