WAVES FROM THE SUN

Satellite observations of solar wind turbulence in the low frequency MHD domain show highly variable properties with respect to time and distance from the sun: one of the markers of this variability is the degree of “Alfvénicity,” which characterizes the relative level of quasi-incompressible waves propagating away from the sun. To answer the question of the origin and the evolution of this wave spectrum one must investigate the propagation of MHD fluctuations through the highly inhomogeneous and spherically expanding solar wind. Here we discuss some aspects both of the linear propagation before the critical point and of recent models for the evolution of the turbulence in the supersonic regions of the wind. © 1991, Taylor & Francis Group, LLC. All rights reserved.