Small-scale Gradients and Large-scale Diffusion of Charged Particles in the Heliospheric Magnetic Field.

We have carried out numerical simulations of the propagation of energetic charged particles in a turbulent magnetic field similar to that observed in the solar wind. If the particles are released impulsively near the Sun, in a region small compared with the field coherence scale (a solar flare, for example), they exhibit characteristic fluctuations in intensity at 1 AU (dropouts) associated with very steep localized gradients. These numerical simulations are quantitatively very similar to recent observations by the Advanced Composition Explorer spacecraft and are the result of the convection of alternatively filled and empty flux tubes past the spacecraft. These fluctuations occur naturally as part of the particle transport in the same field, which results in large-scale cross field diffusion and which has previously been used to study the propagation of corotating interaction region-associated particles to high heliographic latitudes.