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Magnetic observations of the lunar cavity


  • D. S. Colburn,

  • J. D. Mihalov,

  • C. P. Sonett


Data from the Ames magnetometer experiment on the lunar orbiter Explorer 35 are examined for a period exceeding 4 months and covering more than 200 orbits. The main features of the diamagnetic cavity disclosed earlier are confirmed. The magnetic signature of the cavity is a variable phenomenon, sometimes vanishing entirely and on rare occasions displaying a decreased field in the interior in contrast to the more common increase. A positive correlation of cavity field increases with Kp and proton thermal speed is consistent with a model based on simple diamagnetism. Exterior small perturbations of the interplanetary field often occur outside the diamagnetic signature. Exterior peak occurrences do not correlate well with cavity signals or any obvious property of the interplanetary field, including magnitude, orientation, and noisiness; however, some control by orientation is not excluded. The peaks tend to occur at a lower proton thermal speed. The general lack of correlation and theoretical considerations indicate a solar-wind-limb interaction as the cause of the external peaks.