Anisotropic MHD turbulence in the interstellar medium and solar wind

A theoretical model is given of anisotropic magnetohydrodynamic turbulence in the interstellar medium and the solar wind. The model is motivated by observations that show significant deviations from the Kolmogorov power-law. Dimensional and heuristic arguments are given and critically assessed. On the basis of the weak turbulence approximation in which three-wave interactions dominate, analytical and numerical results are obtained for the anisotropic energy spectrum produced by the random scattering of shear Alfven waves propagating parallel to a large-2 scale magnetic field. The energy spectrum is shown to be proportional to k(perpendicular to)(-2), qualitatively consistent with some observations and wave kinetic theory.