Magneto-acoustic surface waves on current sheets

The theory of linear magneto-acoustic surface waves is investigated for current sheets across which the magnetic field has an arbitrary change of direction: in the first place discontinuously, and in the second place via a narrow transition region in which the magnetic field rotates with constant amplitude, so that the gas pressure remains constant. It is found that the effect of non-zero pressure is to eliminate the surface wave for certain angles of propagation and to allow the existence of an additional, slower, surface wave for other angles of propagation. The resonance damping of the surface waves when the current sheet is of small non-zero width is considered, and it is found that Alfven-resonance damping always occurs, as well as (for high β and certain angles of propagation) compressive- or cusp-resonance damping. (author)