An Empirical Model of the South Atlantic Anomaly in Low Earth Orbit

The South Atlantic Anomaly is a region where the Earth's inner trapped radiation belt dips down. Low Earth orbit spacecraft experience hazardous levels of particle radiation in this region. Various models exist to describe the shape of this region (e.g., AP-8). Here we analyze data from 5 years of UV photometer data on a polar orbiting platform. While not a particle spectrometer, a UV photometer generates counts from particle hits, and thus can sense the intensity of the radiation flux. We present an empirical spherical harmonic based model that summarizes the in situ UV photometer data. Using the model, we derive the yearly intensity variation as well as the longer term solar cycle trend.