Thermal and magnetically driven instabilities in a non-constantly stratified rapidly rotating fluid layer with azimuthal magnetic field

Abstract

Abstract The linear hydromagnetic stability problem for a horizontal non-constantly stratified fluid layer rapidly rotating about the z-axis and permeated by an azimuthal non-homogeneous magnetic field is investigated. A non-linear (parabolic) temperature profile Tequals;T(z) is used to simulate the lower part of the fluid core being unstably stratified and the upper part stably stratified. The problem is solved on the magnetic diffusion timescale and for q<1 (q is the ratio of the thermal and magnetic diffusivities). The model is investigated for various widths of the stably stratified part of the layer and for a wide range of values of the azimuthal magnetic field strength. Three kinds of instability have been found: thermally-driven propagating westward, magnetically-driven propagating westward and magnetically-driven propagating eastward. The most complicated case is with azimuthal wave number mequals;1 for which all three kinds of instabilities occur. For m≧2 only thermally-driven instabilities occur...