Seasonal variation and geomagnetic storm index effects on the proton flux response in the South Atlantic Anomaly by test particle simulations

In order to estimate the proton flux variations occurring in the South Atlantic Anomaly (SAA) caused by the geodipole tilting angle and the Dst index variations, we performed three dimensional relativistic test particle simulations to calculate the trajectories of high-energy protons (70–180 MeV), where the static background magnetic field was calculated by the Tsyganenko models T01/TS05 combined with IGRF-12. As various parameters characterize the SAA proton flux, the study considered the maximum proton flux and the area of the SAA. Among many different parameters that define the space weather conditions, we considered the geodipole tilting angle and the Dst index. The numerical results showed that (1) the proton flux intensity was increased in the SAA for small geodipole tilting angles, which was confirmed by observations, and that (2) the proton flux intensity was also increased for significantly low Dst index.