Proton Flux Anisotropy in Low Earth Orbit

Proton flux anisotropy as a function of altitude in the South Atlantic Anomaly (SAA) is investigated using data from the Compact Environment Sensor (CEASE) flown onboard the Tri-Service Experiment-5 (TSX-5) satellite from June 2000 to July 2006. In a 410 x 1710 km, 69 degree inclination orbit, TSX-5 spanned a broad range of the low Earth orbit regime. Using measurements of total dose, integral energy flux 40 MeV and the differential flux at 40 MeV sorted into 3 degree latitude x 3 degree longitude x 50 km altitude bins and averaged over the entire mission, the components arising from eastward and westward traveling protons have been determined in areas of the SAA where CEASE detection efficiency is not compromised. For the first time, ratios of these components have been compared to predictions of East-West effect models above 400 km. There is good agreement in general with the anisotropy becoming apparent at approximately 1200 km (moving down) and increasing rapidly starting at approximately 1000 km, the magnitude and rate depending on location within the anomaly. Measurement of the differential flux at 40MeV are compared to predictions of standard radiation belt models as a function of altitude and found to be substantially higher in magnitude than AP8, though a comprehensive survey has not yet been performed. Published in the Jnl. of IEEE Transactions on Nuclear Science v54 n6 p1975-1980 Dec 2007.