Voyager Observations of Anomalous Cosmic Ray Gradients and the Role of Diffusion and Drifts in the Outer Heliosphere

Abstract

We find that the diffusion mean free path at 1.5 GV inferred from the gradient of anomalous cosmic rays (ACRs) observed by Voyager 1 and 2 (V1 and V2) has an approximately linear radial distance dependence at solar maximum. At solar minimum the mean free path is a factor of 10 or more larger than at solar maximum. We find that the expected dependence on current sheet tilt of the ACR O V1/V2 gradient has not become evident as of early 2003, likely because the tilt has yet to decrease below ˜40° . It appears that from mid-2000 up to day 104 of 2003 diffusion is the dominant particle transport mechanism in the far outer heliosphere at 1.5 GV.

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