Scattering of Alfven waves by random density fluctuations

The scattering of coherent Alfve'n waves by random density fluctuations is considered, using both the method of first-order smoothing and the first Born approximation. The method of first- order smoothing provides dispersion relations for the propagation of Alfven waves in an infinite medium in which the density is a spatially homogeneous random function. The Born approximation is used to solve the problem of the scattering of a coherent Alfven wave by a patch of density fluctuations and to calculate the mean square scattered dilatation (divergence of velocity) and vorticity and the ratio of average total energy scattered into magnetosonic modes to that scattered into Alfven modes. It is shown that in general a coherent Alfve'n wave undergoes damping while propagating through a medium which contains random density fluctuations, and several interesting properties of the mean scattered energy are discussed. Applications of the results to hydromagnetic wave propagation in the solar wind, scattering of Alfven waves by tangential discontinuities, and the problem of heating the solar wind are given. Subject headings: hydromagnetics - interplanetary medium