Magnetic Rayleigh-Taylor Instability at a Contact Discontinuity With Oblique Magnetic Field

TL;DR

This study analyzes the magnetic Rayleigh-Taylor instability at a density interface with an oblique magnetic field, deriving a dispersion relation and applying it to prominence structures to diagnose magnetic field inclinations.

Contribution

The paper derives a dispersion relation for the instability with an oblique magnetic field and demonstrates its application in diagnosing magnetic field angles in prominence threads.

Findings

Waves are unstable for all wavenumbers with inclined magnetic fields.

The critical wavenumber for instability disappears when the magnetic field is inclined.

Applied to prominence observations, the model estimates magnetic field inclinations from 0.5 to 30 degrees.

Abstract

Aims: In the present work we investigate the nature of the magnetic Rayleigh-Taylor instability at a density interface permeated by an oblique, homogeneous magnetic field in an incompressible limit. Methods: Using the system of linearised ideal incompressible magnetohydrodynamics (MHD) equations we derive the dispersion relation for perturbations of the contact discontinuity by imposing the necessary continuity conditions at the interface. The imaginary part of the frequency describes the growth rate of waves due to instability. The growth rate of waves is studied by solving numerically the dispersion relation. Results: The critical wavenumber at which waves become unstable, present for a parallel magnetic field, disappears, due to the inclination of the magnetic field and instead waves are shown to be unstable for all wavenumbers. Theoretical results are applied to diagnose the structure of the magnetic field in prominence threads. When applying our theoretical results to observed waves in prominence plumes, we obtain a wide range of field inclination angle; from 0.5 degrees up to 30 degrees. These results highlight the diagnostic possibility of our study.