Solar energetic particles vs. global cosmic-ray diffusion

Abstract

We have addressed the problem of the discrepancy between observations of solar cosmic rays, often showing sharp-gradients, and observations of galactic and anomalous cosmic rays which are consistent with the diffusive-transport description. 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. The field coherence scale near the sun is the size of a supergranulation cell, and is about 0.01 AU at the orbit of Earth. These numerical simulations are quantitatively very similar to recent observations by the ACE spacecraft. These fluctuations occur naturally as part of the particle transport in the same field which results in large-scale cr...