The Effect of Intermittent Turbulence on Cosmic-ray Transport

It has been suggested that intermittent regions of strong slab turbulence in the solar wind might be responsible for dropout events observed in solar energetic particle fluxes on small spatial scales. In this paper the large-scale transport of cosmic rays in three-dimensional magneto-hydrodynamic turbulence dominated by uniform two-dimensional turbulence, but including a minor intermittent slab turbulence component, is investigated theoretically. The main finding is that at late times both cosmic-ray transport parallel and perpendicular to the mean magnetic field are the net effect of an interplay between diffusive and nondiffusive (super or subdiffusive) transport effects as a consequence of this intermittency. In the case of subdiffusion diffusion dominates. When superdiffusion occurs, it dominates diffusive transport.