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Published 1983 | Accepted Version
Book Section - Chapter Open

Temporal Variations of the Anomalous Oxygen Component


Data from the cosmic ray experiment on Voyagers 1 and 2 was used to examine anomalous oxygen in the time period from launch in 1977 to the end of 1981. Several time periods were found where large periodic (typically 26 day) temporal variations of the oxygen intensity between approximately 5 - 15 MeV/nuc are present. Variations in intensity by up to a factor of 10 are observed during these periods. Several characteristics of these variations indicate that they are not higher energy extensions of the low energy particle (approximately 1 MeV/nuc) increases found in many corotating interaction regions (CIR's). Many of these periodic temporal variations are correlated with similar, but much smaller, recurrent variations in the 75 MeV proton rate. Voyager 1 and Voyager 2 counting rates were compared to estimate the local radial gradient for both the protons and the oxygen. The proton gradients during periods of both maximum and minumum fluxes are consistent with the overall positive radial gradients reported by others from Pioneer and near-Earth observations, supporting the view that these variations are due to local modulation of a source outside the radial range of project measurements. In contrast, the oxygen gradients during periods of maximum proton flux differ in sign from those during minimum proton fluxes, suggesting that the origin of the oxygen variations is different from that of the protons.

Additional Information

We greatly appreciate the efforts of R. E. Vogt, both in his capacity as CRS Principal Investigator and as a colleague who has provided useful discussions. We care grateful to the Caltech and Goddard groups who have supported the CRS experiment. We thank E. C. Stone, R. A. Mewaldt, and S. P. Christon for many helpful discussions. We are grateful to Dr. Norm Ness and coworkers of the Goddard Space Flight Center Magnetometer Team and Dr. Herb Bridge and coworkers of the Massachusetts Institute of Technology Plasma Team for providing the Voyager magnetic field and solar wind data, respectively. This work was supported in part by NASA under contract NAS 7-918 and grants NAGW-200 and NGR 05-002-160.

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August 19, 2023
January 13, 2024