Simulations of Inner Proton Radiation Belt in the South Atlantic Anomaly during Geomagnetic Storms

Abstract:

The radiation environment of the Low-Earth Orbit (LEO) missions is greatly affected by the South Atlantic Anomaly (SAA), a permanent feature of the inner radiation belt due to geomagnetic field asymmetry. The geomagnetic storms affect greatly the inner magnetosphere configuration, which consequently influences the inner radiation belt activity, and thus the proton flux distribution inside the South Atlantic Anomaly. A three-dimensional relativistic test particle simulation code was developed to compute the trajectories of the protons with energy range 140-400 MeV by implementing Tao-Chan-Brizard guiding center model. The background time-varying magnetic field was provided by Tsyganenko model TS05, along with the inductive electric field calculated by Biot-Savart law. The selected geomagnetic storm event occurred on 15 May 2015. The main parameters of the SAA that we considered in this study are the maximum value of the proton flux and the area below a specific threshold.
It was found that the proton flux inside the SAA was intensified during the main phase of the storm and then totally decreased during the recovery phase. Numerical results were compared with observations made by NOAA 17 and ISS missions.