Numerical simulation of chorus-driving acceleration of relativistic electrons at extremely low L-shell during geomagnetic storms* *Project supported by the National Natural Science Foundation of China (Grant Nos. 41904149 and 12173038), Stable-Support Scientific Project of ChinaResearch Institute of Radiowave Propagation (Grant No. A132001W07), and the National Institute of Natural Hazards, Ministry of Emergency Management of China (Grant No. 2021-JBKY-11).

Abstract

During 2018 major geomagnetic storm, relativistic electron enhancements in extremely low L-shell regions (reaching L∼3) have been reported based on observations of ZH-1 and Van Allen probes satellites, and the storm is highly likely to be accelerated by strong whistler-mode waves occurring near very low L-shell regions where the plasmapause was suppressed. It is very interesting to observe the intense chorus-accelerated electrons locating in such low L-shells and filling into the slot region. In this paper, we further perform numerical simulation by solving the two-dimensional Fokker–Planck equation based on the bounce-averaged diffusion rates. Numerical results demonstrate the evolution processes of the chorus-driven electron flux and confirm the flux enhancement in low pitch angle ranges (20°–50°) after the wave-particle interaction for tens of hours. The simulation result is consistent with the observation of potential butterfly pitch angle distributions of relativistic electrons from both ZH-1 and Van Allen probes.