Radial and Latitudinal Gradients of Anomalous Cosmic Ray Oxygen Throughout the Heliosphere

Abstract

We have used data from the SAMPEX. Ulysses, Voyager 1 (Vl), Voyager 2 (V2), and Pioneer 10 (PIO) spacecraft to determine the radial and latitudinal gradients of anomalous cosmic ray oxygen at 10 MeV/nuc during 1994 days 209 - 313. These five spacecraft cover radial distances from 1 AU (SAMPEX) to 61 AU (PIO) and latitudes to 80° S (Ulysses) and 33° N (Vl). We find that the radial gradient is a decreasing function of radial distance, -r^(-n) , with n = 0.7 ± 0.7. The large-scale radial gradient between the inner and outer heliosphere is much smaller than it was during the last solar minimum period in ~1987. The latitudinal gradient is small and positive, 2.1 ± 0.6 %/deg, as opposed to the large and negative latitudinal gradients found during 1987, but similar to the small positive latitudinal gradient reported in a similar study for 1993 and also similar to that measured during 1976 for anomalous cosmic ray helium. These observations confirm that effects of curvature and gradient drift in the large scale magnetic field of the Sun are important for establishing the three-dimensional intensity distributions of these particles in the heliosphere during periods of solar minimum conditions.

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