Anomalous and Gaussian transport regimes in anisotropic three-dimensional magnetic turbulence

The effects of the anisotropy of magnetic turbulence on the transport of ma gnetic field lines,are investigated numerically. The three-dimensional magn etic turbulence is represented by a Fourier expansion with a power law band spectrum, and anisotropy is introduced by considering different correlatio n lengths l(cx) and l(cy) in the plane perpendicular to the average magneti c field B-0=B0 (e) over cap(z), Transport in this plane is analyzed for dif ferent fluctuation levels delta B/B-0, and for various degrees of anisotrop y l(cx)/l(cy). The results of the simulation show that there are anomalous (subdiffusive and superdiffusive) transport regimes at low fluctuation leve ls, while Gaussian diffusive regimes are attained in the presence of high f luctuation levels, like in the isotropic case; as anisotropy is increased t he Gaussian regime is reached for higher fluctuation levels; for significan t degrees of anisotropy l(cx)/l(cy), a percolative regime is found at a low fluctuation level, with superdiffusion in the direction where the correlat ion length is shorter; conversely, in the diffusive regime transport is fas ter in the direction of the longer correlation length, and the obtained rat io of diffusion coefficients D-x/D-y is close to the ratio of anisotropy l( cx)/l(cy). The application of these results to energetic-particle propagati on in the solar wind is discussed. [S1063-651X(98)14511-7].