Collaborative Research: GEM--The Upper Limit of the Earth's Outer Radiation Belt Electron Fluxes

The Earth’s outer radiation belt electrons, also known as “killer electrons”, can pose a significant hazard to Earth-orbiting satellites and our unprecedented space-based connection-dependent society. The major acceleration mechanisms for these electrons include inward radial diffusion and local-wave particle interactions with whistler-mode chorus waves. Recent studies have demonstrated the approach of an upper limit of the fluxes of these electrons, which does not necessarily depend on the magnitude of the geomagnetic storm. However, the critical geomagnetic conditions and the underlying physical mechanisms that control this upper limit of the outer radiation belt electron fluxes still remain unknown. Assessing and forecasting the extreme case of these electron fluxes in the Earth’s outer radiation belt is important not only to the space science community but also to the space industry and economy. This proposal aims to unravel the driver and construct a prediction model for the upper limit of the Earth’s outer radiation belt electron fluxes during geomagnetically active times. The primary objective of this proposal is to investigate the upper limit of the Earth’s radiation belt electron fluxes. The science questions that will be answered include: (1) What are the critical geomagnetic conditions and the quantitative contributions of various geomagnetic indices to the observed flux upper limits in the Earth’s outer radiation belt using both statistical analysis and machine learning techniques? (2) What are the key input parameters in the quasi-linear diffusion simulation (e.g., wave parameters, total electron density, radial diffusion, background magnetic field) that produce higher flux upper limits driven by chorus waves? (3) What is the analytical estimate of the upper limits of fluxes that are due to local heating by whistler-mode chorus waves using quasi-linear theory and what are their correlations with the observed flux upper limits from satellite observations? To address these questions, the team will combine statistical satellite data analysis using measurements from NASA’s Van Allen Probes, numerical modeling, and an analytical approach using the quasi-linear regime and machine learning technique to identify the key factors that contribute to creating the upper limit of fluxes, and develop predictive models of the maximum outer belt electrons fluxes. The results of this project will provide insights regarding the cumulative impacts of storm and substorm activity on the radiation belt electron fluxes, the physical drivers of acceleration, and develop the necessary understanding to produce forecasting models of maximum electron fluxes in the outer radiation belt. Our proposal will have a secondary goal of exploring how we can learn to use machine learning models for scientific insight discovery. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.