Anisotropy of small-scale inhomogeneities in the region of solar-wind acceleration

A model is proposed to explain observational data on the scattering of radi o signals, which indicate that small-scale plasma-density inhomogeneities i n the region of solar-wind acceleration are strongly elongated in the radia l direction, with the degree of elongation sharply decreasing at heliocentr ic distances of about six solar radii. The evolution of the energy spectra of the fluctuations of the magnetic field and plasma density is studied ass uming that the plasma-density fluctuations are generated locally by nonline ar interactions of high-frequency Alfven waves, and that the gradients of t he mean plasma parameters are smooth. The growth rates of the main nonlinea r processes are estimated. The strong elongation of the inhomogeneities fir st arises when the Alfven waves travel through the chromosphere-corona tran sition layer, then survives to considerable distances from the Sun because the associated nonlinear relaxation processes are fairly slow. Estimates of the degree of elongation of the inhomogeneities and the characteristic dis tance for chances in the angular wave spectra are in good agreement with ra dio propagation data. (C) 2001 MAIK "Nauka/Interperiodica".