Evolution of ion distribution functions in ionospheric plasmas perturbed by Alfvén waves

It is well known that electromagnetic (EM) processes can affect the trapped population of ionized particles in the Earth’s radiation belts and induce particle precipitations that can be measured by satellites. Moreover, in the last decades, several studies have suggested the concurrent occurrence of energetic particle flux variations (the so-called Particle Bursts, PBs) and ionospheric ELF-VLF electromagnetic activity in correspondence to (or even before) large earthquakes. However, to date, the underlying mechanisms connecting seismic-related electromagnetic processes to satellite-detected particle precipitation events remain elusive. In addition, a comprehensive model capable of explaining observed EM perturbations and PBs is still missing, especially during seismo-related phenomena. The lack of detailed investigation into these processes introduces uncertainties regarding the expected time delay between the two phenomena, which hinders the reproducibility and confirmation of reported findings across different studies, even when employing identical methodologies. Consequently, the temporal distribution of claimed seismo-related phenomena exhibits significant variability.

To address these challenges, we present novel numerical simulations investigating wave-particle interactions within a realistic topside ionospheric plasma environment. A hybrid code was successfully employed to simulate the topside ionosphere, incorporating realistic plasma parameters, including plasma beta and species composition. Simulation results demonstrate some modifications in the ion velocity distribution function, including the emergence of fast ion beams capable of inducing particle precipitation. These simulations provide, for the first time, an estimate of the time delay between the onset of EM waves and the resulting plasma modifications.