ON THE CROSS-FIELD DIFFUSION OF GALACTIC COSMIC RAYS INTO AN ICME

We develop a numerical modelof the cross-fielddiffusion of galactic cosmicraysinto an interplanetary coronal mass ejection (ICME), on the assumption thatthe local part of the ICME is an expanding straight cylinder. It is found thatthe spatial distribution of cosmic ray density in the cylinder rapidly reachesa stationary state due to the balance between inward diffusion and adiabaticcooling in the expanding cylinder. By fitting the model to the Halloween ICMEevent observed with the network of muon detectors in October 2003, we evalu-ate the magnitude of the cross-field diffusion coefficient to be 1