Resonantly damped surface and body MHD waves in a solar coronal slab with oblique propagation

TL;DR

This paper investigates how oblique propagation enables surface and body MHD waves in solar coronal slabs, analyzing their properties, damping mechanisms, and excitation conditions through normal-mode and time-dependent analyses.

Contribution

It introduces the effects of oblique propagation on MHD wave modes in coronal slabs, revealing the existence of surface and body waves and their damping via resonant absorption.

Findings

Oblique propagation allows surface and body MHD waves in coronal slabs.

Resonant absorption damps surface and body modes.

Conditions for excitation of different wave modes are identified.

Abstract

The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a zero-$\beta$ configuration and for parallel propagation of waves does not allow the existence of surface waves. When oblique propagation of perturbations is considered both surface and body waves are able to propagate. When the perpendicular wave number is larger than a certain value, the body kink mode becomes a surface wave. In addition, a sausage surface mode is found below the internal cut-off frequency. When non-uniformity in the equilibrium is included, surface and body modes are damped due to resonant absorption. In this paper, first, a normal-mode analysis is performed and the period, the damping rate, and the spatial structure of eigenfunctions are obtained. Then, the time-dependent problem is solved, and the conditions under which one or the other type of mode is excited are investigated.