In-depth analysis of selected major solar events with the HEPP-L particle detector onboard CSES-01 in low-Earth orbit

The characterization of the effects of solar disturbances on the Earth’s ionosphere is crucial for the monitoring and understanding of space weather. While satellites orbiting outside of the Van Allen belts allow for direct measurements of the ejected particles and of magnetic field perturbations, low Earth orbit spacecraft, such as the China Seismo-Electromagnetic Satellite (CSES-01), provide a direct assessment of the effect of these events on the Earth ionosphere. Here we present a detailed study of proton flux perturbations measured by the High-Energy Particle Package (HEPP-L) onboard CSES-01 during two major, prototypical solar events: the ground-level enhancement (GLE) of 2021-10-28, and an X3.3 flare occurred on 2024-02-09. The analysis of fluxes measured by HEPP-L, capable of detecting 2 MeV-20 MeV protons, relies on a robust statistical approach to model the expected background flux in ordinary conditions and identify anomalies attributable to space weather events. For the case studies outlined above, upon identification of anomalies, we assess the properties of the excess proton flux, including the temporal evolution of its spectral features. These results enrich the present knowledge of the effects of solar activity on the Earth’s ionosphere, demonstrating the crucial role that the CSES mission can play in space weather studies.