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Published October 1, 1971 | Published
Journal Article Open

The Electron Polar Cap and the Boundary of the Open Geomagnetic Field Lines


A total of 333 observations of the boundary of the polar access region for electrons (Ee > 530 kev) provides a comprehensive map of the electron polar cap. The boundary of the electron polar cap, which should occur at the latitude separating open and closed field lines, is consistent with previously reported closed field line limits determined from trapped-particle data. The boundary, which is sharply defined, seems to occur at one of three discrete latitudes. Although the electron flux is generally uniform across the polar cap, a limited region of reduced access is observed about 10% of the time.

Additional Information

Copyright © 1972 by the American Geophysical Union. (Received December 10, 1972; accepted June 28, 1972.) We gratefully acknowledge the collaboration and support of Drs. J. A. Simpson and C. Y. Fan during various stages of the joint University of Chicago and California Institute of Technology program. The instrument was constructed by the Laboratory for Astrophysics and Space Research of the University of Chicago. D. H. Fairfield and N. F. Ness kindly provided the interplanetary magnetic-field data. This work was performed under contract NAS 5-3095 and grant NGR 05-002-160. L. C. Evans received valuable support from the National Science Foundation and the State of California. The Editor thanks J. R. Burrows and A. Vampola for .their assistance in evaluating this report

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August 19, 2023
August 19, 2023