The effect of random Alfven waves on the propagation of hydromagnetic waves in a finite-beta plasma

Using first-order smoothing theory, Fourier analysis and perturbation methods, we obtain the evolution equation of the wave spectrum as well as the nonlinear forces generated by random Alfven waves in a finite-β plasma with phenomenological Landau-damping effects. The effect of microscale random Alfven waves on the propagation of large-scale hydromagnetic waves is also investigated by solving the mean-field equations. It is shown that parallel-propagating random Alfven waves are modulationally stable and that obliquely propagating Alfven waves can be modulationally unstable when the energy of random waves is converted to slow magnetic-acoustic waves that can be Landau-damped, providing a dissipation mechanism for the Alfven waves. (author)