ABSTRACT
This chapter discusses the propagation of MHD waves through a boundary between two uniform stationary plasmas. It deals with reflection and refraction of MHD waves incident on boundaries that are tangential discontinuities between two uniform MHD media at rest. Since the magnetic field, in either medium, is also parallel to the boundary, this means that, if a transverse Alfven wave is generated at a remote point, it can never reach the boundary. When the boundary is perturbed by a wave, it moves. It is necessary to take care over the choice of boundary conditions to be imposed on the perturbation fields. The wave in the second medium is an inhomogeneous wave, decaying evanescently with distance from the boundary but with phase advancing parallel to the boundary to match the phase advance of the incident wave. The appropriate boundary conditions at the discontinuity are that the total pressure and the displacement are continuous.
