Characteristics of radiation belt energetic protons and the movement of their core location in response to geomagnetic disturbances.

This article focuses on the statistical analysis of the spatial and temporal distributions of energetic protons in the Earth's radiation belt, based on seven years (2012–2019) of observations from the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) onboard the Van Allen Probes. It finds that low-energy protons (55–148 keV) predominantly occupy higher L shells (L > 4) and exhibit significant fluctuations during geomagnetic storms, often penetrating to lower L shells, while higher-energy protons (221–489 keV) are mainly located at L < 4.5 and remain relatively stable. The study highlights the plasmapause location (Lpp) as a critical boundary influencing proton distributions: low-energy proton flux peaks (core locations, Lc) lie outside Lpp and shift rapidly during storms, high-energy proton cores lie inside Lpp and are less affected, and intermediate-energy proton cores fluctuate around Lpp, reflecting a balance between source and loss processes. Additionally, wave–particle interactions, particularly involving very-low frequency (VLF) waves, contribute to the gradual post-storm variations in proton fluxes.