Published online by Cambridge University Press: 28 March 2006
This paper investigates the perturbation modes of the steady parallel flow of a compressible fluid of finite constant viscosity and electrical conductivity in a uniform arbitrarily oriented magnetic field. In particular, in addition to the classical fast and slow sound and Alfvén modes, one obtains some waves whose amplitude is finite whenever the diffusive coefficients are finite and which resemble the diffusion of vorticity from stream surfaces in classical hydrodynamics. The paper also re-interprets upward-facing MHD waves and upstream wakes in a new way.