Transport of charged particles in the heliosphere: Theory

Diffusion theory has proven enormously successful in explaining a wide range of cosmic ray phenomena, but a satisfactory explanation of how energetic charged particles are scattered in collisionless plasma (such as the solar wind) has remained elusive. This article summarizes recent advances in this field that have resulted from the use of more realistic models of magnetic turbulence in space. A special emphasis is placed on the strong influence turbulence geometry exerts on diffusion both parallel and perpendicular to the large-scale magnetic field. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.