Advances in plasma theory during the 1950s and 1960s led to the development of comprehensive models of Earth’s radiation belts capable of describing and forecasting many observational phenomena. These early models, developed with sparse and technically limited wave and particle measurements, were based on quasi-linear theory, treating particle transport as purely diffusive. However, recent high-fidelity spacecraft data (collected by Cluster, THEMIS, Van Allen Probes, Arase, MMS, SAMPEX, POES, GPS, CubeSat missions, and others) have repeatedly challenged this modelling approach, revealing discrepancies that highlight the need to incorporate non-diffusive irreversible processes that take place on small timescales. Addressing these gaps requires tackling fundamental questions on nonlinear particle acceleration, transport, and loss.
These advancements are critical not only for improving model accuracy but also for addressing societally important challenges, including forecasting radiation hazards in the near-Earth space environment and understanding the impact of energetic particle loss on the atmosphere. This project brings together a diverse team of leading international experts to: (i) unify current knowledge of relativistic particle dynamics in the radiation belts; (ii) investigate key processes beyond classical diffusion, such as radial advection and nonlinear wave-driven acceleration; and (iii) provide recommendations for future spacecraft missions to enable critical breakthroughs in radiation belt research.
Q1: What processes govern non-diffusive radial transport of energetic electrons in the outer radiation belt, and how can they be quantified?
Q2: How significant are nonlinear wave-particle resonances in local acceleration of electrons to relativistic (> 0.3 MeV) and ultrarelativistic (> 2 MeV) energies?
Q3: What are the required capabilities of new spacecraft instruments that would provide high-quality data for construction of nonlinear radiation belt models?