ABSTRACT
The understanding of wave propagation in varying anisotropic media is complicated, even without the introduction of singular behaviour. This chapter discusses the propagation of fast and slow waves in anisotropic MHD situations where the transverse Alfven wave is decoupled from the other characteristic waves and can, therefore, be ignored. If one is seeking a solution describing only the propagated wave, then the evanescent wave may still lead to numerical swamping. In such cases, the numerical swamping may cause trouble and the equations must be manipulated analytically to remove the unwanted solution. Also the rays are all focused along the caustic and the approximations of geometrical optics diverge there—a full wave theory corrects for this. The general behaviour of the wave is similar to Airy function behaviour with modification to the phase and amplitude resulting from the deviations of the behaviour of G from linearity.
