Perpendicular Diffusion and Drift of Solar Energetic Particles in Heliospheric Magnetic Fields

Abstract

We present evidence for large perpendicular diffusive flows of solar energetic particles. Using anisotropy measurements of 40-90 MeV protons from the July 14th, 2000 event obtained by HET on Ulysses, we find periods of first order anisotropy directed at significant angles to the local magnetic field, which can only be satisfactorily explained by perpendicular diffusion. A large κ⊥ /κ|| of 0.25 is derived. We also find that the anisotropy is unaffected by the polarity of magnetic field. This puts an upper limit of κA /κ⊥ < 0.17 on the particle drift. The observation suggests that perpendicular diffusion is important to the transport of solar energetic particles in interplanetary magnetic fields.