Hydromagnetic Surface Waves in a Conducting Liquid Surrounded by a Compressible Gas

Abstract

Those surface waves are studied that can propagate along a plane interface separating a conducting (incompressible) liquid from a nonconducting, compressible gas, when there is a static magnetic field parallel to the interface. For any given direction of propagation along the surface (except exactly perpendicular to the magnetic lines), and with the gas mass density small compared to that of the liquid, we find an approximate critical magnetic field strength above which the usual surface Alfvén waves cannot exist. Instead, at these strong magnetic fields, there are surface sound waves in the gas. The critical magnetic field at which the (actually smooth) transition from Alfvén-type to sound-type surface waves takes place is practically independent of the gas density, depending essentially only on its temperature.