Onset of anisotropy and Alfvén waves turbulence in the expanding solar wind

Solar Wind 8, AIP Conf. Proc. 382, p.306, 1996.

R. Grappin

Abstract

The expansion of the solar wind plasma modifies the linear and nonlinear evolution of the fluctuations advected by the solar wind. We use numerical simulations of MHD equations including expansion effects to study the formation of anisotropy in the wind and the interaction of Alfvén waves within a transverse magnetic structure. We find that (1) a large-scale isotropic Alfvénic eddy stretched by expansion naturally leads to streams mixed with smaller scale transverse Alfvén waves with a different anisotropy, (2) the expansion triggers the compressive decay of Alfvénicity in the vicinity of the current sheet but prevents the formation of a well-developed spectrum.