A Unified Understanding of the Earth's Radiation Environment

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Our society is increasingly reliant upon technological infrastructure that orbits in the harsh and highly dynamic radiation environment of near-Earth space. Low-cost access to space is driving a rapid increase in the number of satellites on orbit (e.g., Starlink, Oneweb), many of which use electronics that are untested during active solar conditions, such as the upcoming solar maximum in 2024-2025. This proposal will make a significant advance in the understanding of the radiation environment in which these satellites operate.Space was a £16.5 Bn UK industry in 2019/2020 and severe space weather was added to the National Risk Register in 2011, owned by the Met Office who provide space weather services to the satellite industry. However, current forecasting models, including the BAS Radiation Belt Model (BAS-RBM) that provides forecasts to the Met Office and European Space Agency, only forecast the highest energy electrons and the associated risk of damage from internal charging. The Met Office currently has no capability to forecast the lower energy electrons that can cause surface charging damage and be energised to become so-called 'killer' electrons.The radiation environment is highly dynamic and includes several different populations of electrons, identified by their energy ranges. The lowest energy electrons form the background plasma, medium energy electrons are found in the ring current, and the highest energy electrons form the radiation belts. These have historically been studied independently but the populations are interdependent, and recent research has highlighted that they need to be studied as a single system. For example, the highest energy killer electrons are produced when lower energy electrons are energised by electromagnetic waves. These waves are generated by the medium energy electrons and the acceleration is most effective in regions with a depleted background plasma. This proposal aims to establish how the populations and their interactions contribute to the variability of the radiation environment. We will determine which solar wind conditions produce the most effective wave-electron interactions, quantify the role of realistic magnetic fields on the loss and energisation of electrons, and determine how the interactions of the different populations affect the radiation environment in key types of space weather events. This will significantly increase our understanding of the conditions that lead to radiation environments that may damage satellites.These studies require a combination of data analysis and modelling. A few models can study multiple populations, but they all initially addressed a single population using an appropriate framework for that population. Extending to include another population meant incorporating an additional framework, introducing interpolation errors and inconsistencies. For example, although these models use realistic magnetic field models for part of the calculation, they assume a dipole magnetic field to model the wave-electron interactions. Building on our BAS-RBM experience, we will adopt a novel approach using a unifying framework for all three populations that can also include realistic magnetic and electric fields. To be consistent we will also develop the first comprehensive characterisations of wave-electron interactions in realistic magnetic fields. Using observations from spacecraft such as the Van Allen Probes, together with this new modelling framework, we will address the causes of variability in the radiation environment. The model created for these studies will also be able to provide improved predictions of the conditions leading to internal charging on satellites and a new ability to address surface charging.