A Unified Understanding of the Earth's Radiation Environment

我们的社会越来越依赖在恶劣和高度动态的近地空间辐射环境中运行的技术基础设施。进入太空的低成本正在推动轨道上卫星数量的迅速增加(例如，Starlink、OneWeb)，其中许多卫星使用的电子设备在活跃的太阳条件下未经测试，例如即将到来的2024-2025年太阳活动高峰。这项提议将在了解这些卫星运行时所处的辐射环境方面取得重大进展。2019/2020年，空间是英国16.5亿GB的产业，2011年，严重空间天气被列入英国气象局拥有的国家风险登记册，该办公室为卫星产业提供空间气象服务。然而，目前的预测模型，包括向英国气象局和欧洲航天局提供预测的BAS辐射带模型(BAS-RBM)，只预测最高能量的电子和相关的内部充电损害风险。英国气象局目前无法预测较低能量的电子，这些电子可能会导致表面电荷损伤，并被带电成为所谓的“杀手”电子。辐射环境是高度动态的，包括几种不同的电子，根据它们的能量范围进行识别。最低能电子形成背景等离子体，中能电子出现在环电流中，最高能电子形成辐射带。从历史上看，这些问题都是独立研究的，但这些群体是相互依存的，最近的研究强调，它们需要作为一个单一的系统来研究。例如，当较低能量的电子被电磁波激发时，就会产生最高能量的杀手电子。这些波是由中能电子产生的，在背景等离子体耗尽的地区加速最有效。这项建议旨在确定人口及其相互作用如何对辐射环境的可变性作出贡献。我们将确定哪些太阳风条件产生最有效的波-电子相互作用，量化现实磁场对电子损失和能量的作用，并确定在关键类型的空间天气事件中，不同群体的相互作用如何影响辐射环境。这将大大增加我们对导致可能损坏卫星的辐射环境的条件的了解。这些研究需要数据分析和建模相结合。一些模型可以研究多个种群，但它们最初都使用适合于该种群的框架来研究单个种群。扩大到包括另一个人口意味着纳入一个额外的框架，引入内插误差和不一致。例如，尽管这些模型在部分计算中使用了真实的磁场模型，但它们假定使用偶极磁场来模拟波-电子相互作用。在我们BAS-RBM经验的基础上，我们将采用一种新的方法，使用一个适用于所有三个群体的统一框架，该框架还可以包括真实的磁场和电场。为了保持一致，我们还将首先对现实磁场中的波-电子相互作用进行全面的描述。我们将利用范艾伦探测器等航天器的观测结果，再加上这一新的建模框架，解决辐射环境中可变性的原因。为这些研究创建的模型还将能够改进对导致卫星内部充电的条件的预测，并提供解决表面充电的新能力。

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.