The transport of energetic particles and cosmic rays in the heliosphere

We discuss recent observations of energetic particles and cosmic rays lending insight into how these particles are influenced by the interplanetary magnetic field and what can be learned about the field itself by using the energetic particles as probes. Two recent observations on which we focus attention are those by Ulysses at high heliographic latitudes and those by the Advanced Composition Explorer of impulsive solar flare events. The Ulysses observations of low-rigidity energetic particles at high latitudes associated with corotating interaction regions at lower latitudes are consistent with propagation in a stochastic field superimposed on a Parker spiral. These observations indicate that the particles undergo a significant cross-field diffusion. More-recent observation of energetic particles from impulsive solar flare events show structure on a fine scale which seems also to reflect the field-line meandering. Large small-scale gradients normal to the local magnetic field are shown to be completely consistent with significant cross-field diffusion on larger time scales. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.