Radial and Latitudinal Gradients of Anomalous Cosmic-Ray Oxygen and Helium from 1 to ~41 AU

Abstract

We have used data from the IMP 8, Voyager 1 (VI), Voyager 2 (V2), Pioneer 11 (Pll), and Pioneer 10 (PIO) spacecraft. to determine the radial and latitudinal gradients of anomalous cosmic ray oxygen in the energy range ~7 - 25 MeV/nuc and anomalous cosmic ray helium in the energy range ~20- 25 MeV/nuc for a time period near minimum solar modulation in 1987. We find that the radial gradients of both species are decreasing functions of radial distance, r, approximately r^(-1) for oxygen and r^(-0.7) for helium. The latitudinal gradient is large and negative, implying significant spherical asymmetry in the heliospheric distribution of these particles.

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