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Published 1988 | Submitted
Book Section - Chapter Open

Composition, Gradients, and Temporal Variations of the Anomalous Cosmic-Ray Component


Recent measurements in the outer and inner heliosphere have provided new information on the composition, spatial distribution, and temporal variations of the anomalous component. Two additional elements, carbon and argon, are now found to be enhanced, and a method has been developed to derive the abundances of the neutral gas flowing into the heliosphere. In addition, latitudinal gradients recently observed in the outer heliosphere for both the anomalous and galactic cosmic-ray components are negative, opposite to the positive latitudinal gradients reported during the 1976 period when the solar magnetic field was reversed, as expected if the latitudinal gradients are due to effects of curvature and gradient drift in the solar magnetic field. Although the radial gradient remains positive in the outer solar system, there is evidence that the gradient decreases with distance from the Sun. Finally, current 26-day variations in the flux of anomalous cosmic-ray oxygen are large and regular in 1986-1987 at Voyager 1 at ~30° latitude but not at Voyager 2 near the ecliptic plane. We suggest that these variations may result from the combination of a latitudinal gradient with respect to magnetic latitude and the excursion of the spacecraft in latitude caused by a wavy current sheet.

Additional Information

We are grateful to R. E. Vogt for his contributions during his tenure as Principal Investigator for the Voyager CRS. We appreciate contributions from M. Allen who supplied some of the photoionization cross sections and to E. Christian who helped compile and analyze the cross section data. We acknowledge many helpful discussions with R. Mewaldt. We also appreciate the contributions of other Voyager CRS team members at Caltech, Goddard Space Flight Center, and the University of New Hampshire. This work was supported in part by NASA under contracts NAS 7-918 and NAG5-727, and grant NGR 05-002-160.

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August 19, 2023
January 13, 2024