Shaun M Easley

Anisotropy in the South Atlantic Anomaly Shaun M Easley

Publisher Marketing: The South Atlantic Anomaly (SAA) is an area of increased radiation that poses a danger to satellites and manned spacecraft. From June 2000 through July 2006, the TSX-5 satellite measured proton fluxes in the SAA using its CEASE instrument. A review of the satellite data by scientists at AFRL/VSBX revealed an unanticipated, recurring bi-modal structure in histograms of the proton counts. This research identified the bi-modal behavior as anisotropic in nature, and the result of two separate processes. At low altitudes the anisotropy was well described by the classic "East-West Effect." Comparisons of the satellite data to simple analytical models are presented. At high altitudes, the anisotropy was the result of the detector measuring protons at different pitch angles when looking east vs. west. The sampled pitch angles were also found to be function of location, leading to a latitudinal variation to this anisotropy. Finally, we also examined a series of unusually high readings that affected some of the statistics in this study. These anomalous counts were found to have a possible solar cycle dependence leading to questions about the suitability of the current time-independent scheme used to sort the satellite's data set. Other possible explanations for the anomalous counts are also presented.