Geomagnetic Cutoff Variations During Solar Energetic Particle Events - Implications for the Space Station

Measurements of the time-variability of the location of the geomagnetic cutoff during the large solar energetic particle events of October and November 1992 using count rate data from the polar orbiting SAMPEX satellite are reviewed. Significant changes in the cutoff location of up to ~ 5° in less than one day are observed, even during periods with only moderate geomagnetic disturbances. We discuss the implications of such variations for the radiation hazard at the International Space Station, and we note that real-time monitoring of the cutoff location might be u~ed to provide a warning of the increased radiation levels, sometimes hours before the Space Station itself reaches high magnetic latitudes.