Time-Dependent Perpendicular Transport in Goldreich-Sridhar MHD Turbulence

Abstract:

We derive analytically the time-dependent perpendicular diffusion coefficient of a charged particle in the anisotropic turbulence conjectured by Goldreich-Sridhar for time-scales smaller than the correlation time of the magnetic turbulence, as seen by the particle, where the quasi-linear theory is not valid. MHD fluctuations are assumed to be axi-symmetric. The perpendicular transport is assumed to be governed by the guiding-center motion. In a weak turbulence, we find that the separate contributions of the magnetic field line-random walk and the gradient/curvature drift away from the local field line become comparable at small spatial scales. The method applies to processes compatible with a significant departure of charged particles from field lines in the solar wind turbulence, such as longitudinal spread of SEP observed at 1 AU.