ABSTRACT
This chapter is concerned with Magnetohydrodynamic (MHD) waves. These waves are propagated in a variety of inhomogeneous MHD media. Frequently, the inhomegeneity has an effect on the nature of the wave, which is a first-order perturbation on the zero-order steady state. It is, therefore, necessary to understand the conditions that determine equilibrium states and steady-state flows. In a steady state, the plasma flows along streamlines that are everywhere tangential to the plasma velocity. The MHD equations allow the possibility of discontinuities in the various plasma parameters. These can be studied by applying equations describing the conservation of various quantities across a sharp boundary. A number of different types of discontinuity can occur in MHD flows. The boundary conditions of the previous section were derived for the general MHD equations and so discontinuities need not be stationary but may change shape as the plasma flows.
