Mapping the South Atlantic Anomaly charged particle environment with the HEPD-01 detector on board the CSES-01 satellite

The South Atlantic Anomaly (SAA) is a region where the Earth’s magnetic field is lower by a factor of 2–3 with respect to the mean field value, resulting in a remarkably higher density of trapped charged particles. Updated surveys of this unique region are of capital importance to track the evolution of the geomagnetic field and improve models of the Earth’s ionosphere. The High-Energy Particle Detector (HEPD-01) on board the China Seismo-Electromagnetic Satellite (CSES-01), operational between the 24th and 25th Solar cycles, is one of the few instruments able to probe the radiation environment of the SAA at high energies. Sensitive to >1  MeV electrons and >10  MeV protons, HEPD-01 counters can reliably measure rates as large as several kHz/cm2, overcoming SAA saturation issues that often affect spaceborne detectors. By mapping the total particle flux observed within the SAA, we report here on the geographical shift of its center during the 2018–2022 period and deliver HEPD-01’s estimate of the associated integral particle flux, which validates NASA’s AP9-AE9 model. The present assessment of the SAA drift, besides featuring a notable accuracy, is unique in its time coverage, altitude, and energy range. In addition, our flux estimate covers the proton energy range above ∼200  MeV where the AP9 model relies on extrapolated data. The present results enrich the available observations of the radiation environment within the SAA, which are crucial for the investigation of the temporal evolution of the geomagnetic field, for models of geomagnetically trapped particles, and for the investigation of perturbations generated by space weather events. Knowledge of the SAA radiation environment is also relevant for spacecraft system design and to safeguard human crew health.