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Geomagnetic Cutoffs for Cosmic Ray Protons for Seven Energy Intervals Between 1.2 and 39 MeV

Fanselow, J. L. and Stone, E. C. (1972) Geomagnetic Cutoffs for Cosmic Ray Protons for Seven Energy Intervals Between 1.2 and 39 MeV. Journal of Geophysical Research A, 77 (22). pp. 3999-4009. ISSN 0148-0227. doi:10.1029/JA077i022p03999.

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The vertical geomagnetic cutoffs for cosmic-ray protons are presented for seven different energy intervals between 1.2 and 39 Mev. These data, representing approximately 160 passes through the cutoff, were taken during 1967 and 1968, between 408- and 912-km altitude, during times of K_p < 1^+. These passes provide nearly an order of magnitude more data during geomagnetically quiet times than have been previously reported at even one of these energies. In addition, the energy resolution of the instrument was significantly better than that of previous instruments. With these data, we find that the measured invariant latitudes for the cutoffs are 3° to 5° below previous calculations. We were unable to find any correlation of these observations with any physical phenomenon, including DST or the sun-earth-dipole angle. However, these data do indicate that even during ‘quiet’ times there are temporal changes in the geomagnetic field that cause the cutoff to fluctuate by 1° to 2°.

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Stone, E. C.0000-0002-2010-5462
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Additional Information:Copyright © 1972 by the American Geophysical Union. (Received February 16, 1972; accepted April 26, 1972.) We gratefully acknowledge the collaboration and support of Drs. J. A. Simpson and C. Y. Fan during various stages of this joint program of the University of Chicago and California Institute of Technology. The instrument was constructed by the Laboratory for Astrophysics and Space Research of the University of Chicago. We would also like to thank Dr. L. C. Evans and Mr. J. Brown for their helpful suggestions and for some of the subroutines used in the analysis. One of us (E.C.S.) was an Alfred P. Sloan research fellow during this work. Funding for the instrument and this analysis came from the National Aeronautics and Space Administration under contract NAS5-3095 and grants NGL 05-002-007 and NGR 05-002-160. The Editor wishes to thank H. Sauer and D. F. Smart for their assistance in evaluating this paper.
Group:Space Radiation Laboratory
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Alfred P. Sloan FoundationUNSPECIFIED
NASANGL 05-002-007
NASANGR 05-002-160
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Space Radiation Laboratory1972-02
Issue or Number:22
Record Number:CaltechAUTHORS:20140408-092506189
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ID Code:44736
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Deposited On:08 Apr 2014 21:37
Last Modified:10 Nov 2021 16:55

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