Scaling, asymmetry and a Fokker–Planck model of the fast and slow solar wind as seen by WIND

Abstract

The solar wind plasma is a natural laboratory for studies of plasma turbulence. Long, evenly sampled satellite data sets are natural candidates for statistical studies and these are often performed in the context of magnetohydrodynamic (MHD) turbulence. In this paper, scaling properties of solar wind bulk plasma parameters are discussed. Low order probability density function (PDF) asymmetry analysis is applied to data that combines slow and fast solar wind. Results are compared to those obtained using a PDF rescaling technique. A break in scaling, identified by the rescaling method, is confirmed to occur at a temporal scale of ∼26 hours. Low asymmetry levels of the fluctuations PDF are identified for the quantities that also exhibit self-similar statistics. A generalized structure function analysis is then applied to the kinetic energy density obtained from slow and fast solar wind streams. The applicability of a Fokker–Planck model for slow and fast wind ρv2 fluctuations is investigated.