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Published 2001 | Published
Book Section - Chapter Open

A Direct Measurement of the Geomagnetic Cutoff for Cosmic Rays at Space Station Latitudes


We report new measurements of the vertical geomagnetic cutoff for cosmic rays with rigidities from ~500 to 1700 MV, made using data from the MAST instrument on SAMPEX. A total of ~10,000 nuclei were used to measure the latitude cutoff in nineteen separate rigidity intervals. These results show that cosmic rays and solar particles can penetrate several degrees lower in latitude than would be estimated from commonly used relations for the geomagnetic cutoff, which has implications for the radiation exposure expected on the Space Station. An excellent fit to our measured cutoffs is given by the relation Rc = 15.062cos4 (Λ) - 0.363 GV, where Rc is the geomagnetic cutoff in rigidity, and λ is the invariant latitude. We suggest that this relation is useful over invariant latitudes from Λ = 0° to 64°, corresponding to rigidity cutoffs from ~0.2 to 15 GV.

Additional Information

© Copernicus GmbH. This research was supported by NASA under grant NAS5-30704. During the summer of 1999, when most of this work was conducted, Ryan Ogliore was a student at Clarcmont-McKcnna College, working at Caltech as the recipient of a Caltech Summer Undergraduate Research Fellowship (SURF). We thank Georgia de Nolfo for helpful discussions and Jay Cummings for contributions to the data analysis routines.

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August 19, 2023
October 20, 2023