Superdiffusive Transport at Shocks in Space Plasmas

Abstract

Superdiffusion is characterized by a nonlinear growth of the mean square deviation with time. Superdiffusive transport can be interpreted in terms of a Lévy random walk, a stochastic process where a power-law distribution of free path lengths is allowed. Considering particles accelerated at interplanetary shocks, it is found that their intensity profile is a power-law in time in the case of superdiffusion, while it is an exponential decay for normal diffusion. Analysis of energetic particle fluxes from the Ulysses spacecraft at about 5 AU and from the Voyager 2 spacecraft at the solar wind termination shock shows that superdiffusive transport is found.