Spatial distribution characteristics of low-altitude medium-energy protons based on FY-3E satellite

This study utilizes data from the medium-energy proton detector (SME) aboard the Fengyun-3E(FY-3E) satellite (2022-2025), combined with the International Geomagnetic Reference Field (IGRF-13) and the AP8 radiation belt model, to systematically analyze the spatial distribution and periodic variation patterns of low-altitude medium-energy proton flux (0.1–5 MeV). The research focuses on the South Atlantic Anomaly (SAA), and by examining the latitudinal and longitudinal projection maps of medium-energy proton flux during different solar activity phases, it identifies a significant upward trend in proton flux over time, with the coverage gradually shifting westward each year. This is closely related to the decline in magnetic shielding ability caused by the decay of the geomagnetic dipole moment. Fourier series fitting reveals dominant periodicities of 364 days (annual cycle) and 91 days (seasonal cycle), confirming the coupling effect between solar activity and geomagnetic disturbances. A comparison of the AP8 model simulations with observed data demonstrates that models dynamically considering changes in the geomagnetic dipole moment (M value) show a significantly lower mean square error (MSE=0.161) compared to static models (MSE=0.328). Furthermore, these models more accurately reflect real data characteristics, as traditional models tend to underestimate near-Earth proton flux due to neglecting long-term geomagnetic variations. The study concludes that the decay of the magnetic field in the South Atlantic Anomaly is directly associated with the increase in proton flux, providing crucial reference and data support for radiation belt model optimization, spacecraft operational safety, and space weather forecasting, while also highlighting the far-reaching effects of magnetic field decay on the low Earth orbit particle environment.