Intermittency, scaling and the Fokker-Planck approach to fluctuations of the solar wind bulk plasma parameters as seen by the WIND spacecraft

摘要

The solar wind provides a natural laboratory for observations of MHDturbulence over extended temporal scales. Here, we apply a model independentmethod of differencing and rescaling to identify self-similarity in theProbability Density Functions (PDF) of fluctuations in solar wind bulk plasmaparameters as seen by the WIND spacecraft. Whereas the fluctuations of speed vand IMF magnitude B are multi-fractal, we find that the fluctuations in the iondensity rho, energy densities B^2 and rho v^2 as well as MHD-approximatedPoynting flux vB^2 are mono-scaling on the timescales up to ~26 hours. Thesingle curve, which we find to describe the fluctuations PDF of all thesequantities up to this timescale, is non-Gaussian. We model this PDF with twoapproaches-- Fokker-Planck, for which we derive the transport coefficients andassociated Langevin equation, and the Castaing distribution that arises from amodel for the intermittent turbulent cascade.