The Importance of Nonlinear Physics in Radiation Belt Modelling

空间不是真空，而是弥漫着带电粒子。这种物质的第四种状态被称为等离子体，我们在地球上并不熟悉，因为它是在非常高的温度下产生的。最重要的等离子体来源是像太阳这样的恒星，等离子体既是燃料，也是由自我维持的热核聚变产生的。有一种无处不在的“太阳风”，它由等离子体组成，以每秒数百公里的速度从太阳四面八方流出，进入星际空间。虽然我们不像物质的前三种状态那样为我们所熟知和理解，但在宇宙的标准模型中，超过99%的物质是等离子体。固体、液体和气体的运动受常见的重力和压力所支配。相反，由于带电粒子的存在，等离子体动力学由电磁(电磁)力主导。地球的磁场类似于条形磁铁。这个磁场形成了一个保护边界，阻止了大多数原本危险的太阳风等离子体直接流向地球表面。除了作为保护屏障的主要功能外，地球磁场还通过许多复杂和动态的相互作用与充满等离子体的太阳风相互作用。这些不同的过程在几年到百万分之一秒的时间范围内运行。在全球范围内占主导地位的过程之一被称为“地下城循环”。通过地下城循环，起源于太阳风的等离子体可以通过进入地球黑夜而越过地球磁场最外层的保护屏障。然后，从这种机制和其他机制产生的等离子体从大气层的外围开始环绕地球，从白天到大约60,000公里，到晚上超过1,000,000公里。围绕地球的磁场和等离子体一起被称为磁层。如上所述，地球磁层是许多高能动力学的宿主，而这些动力学最终是由太阳风驱动的。通过地下城循环产生的等离子体本身可能是不稳定的，这些不稳定会产生电磁波(例如无线电波)，并在整个磁层中传播。这些无线电波可以继续与等离子体中的其他带电粒子相互作用，并改变它们的速度。这些粒子可以通过所谓的“共振相互作用”以接近光速的速度加速。地球磁层中含有这些高能粒子的区域被称为辐射带。卫星技术支撑着我们现代社会的大部分：导航、通信、防御和对地观测。数百颗运行中的卫星绕地球运行，必须穿越辐射带内的危险辐射环境。高能粒子给在轨航天器带来了许多操作和财务风险，包括完全损失。这些风险，以及其他相关的地面效应，导致空间天气被列入英国内阁办公室国家民用应急风险登记册。最近的卫星观测显示，电磁波的幅度可能比之前认为的要高得多(即携带更多能量)。这也意味着它们可以比之前想象的更快地将等离子体粒子激发到更高的能量。世界各地存在许多空间天气预报模型，但没有一个模型考虑到这些影响。英国南极调查局拥有一个世界领先的模型，它被授权给英国气象局。本研究会的最终目标是通过了解和包括高振幅波对粒子动力学的影响来提高这一业务模型的预测精度。随着社会变得越来越依赖卫星技术，这一点至关重要。

Space is not a vacuum, but is permeated with electrically charged particles. This fourth state of matter is called plasma, and is not familiar to us on Earth since it is created at very high temperatures. The most significant sources of plasma are stars such as our sun, with plasma both fuelling and being created by self-sustaining thermonuclear fusion. There is an ever-present 'solar wind' composed of plasma that flows out of the sun in all directions and into interstellar space at hundreds of kilometres per second. Whilst less well-known and understood to us than the first three states of matter, more than 99% of the material in the standard model of the universe is plasma. The motion of solids, liquids and gases is dominated by the familiar forces of gravity and pressure. In contrast, and due to the presence of charged particles, plasma dynamics are dominated by electric and magnetic (electromagnetic) forces. The Earth has a magnetic field similar to that of a bar magnet. This magnetic field forms a protective boundary that prevents the majority of the otherwise dangerous solar wind plasma from streaming directly towards the Earth's surface. In addition to its main function as a protective barrier, the Earth's magnetic field interacts with the plasma-filled solar wind via many complex and dynamic interactions. These different processes operate on a range of timescales from years to millionths of a second. One of the dominant global-scale processes is known as the 'Dungey Cycle'. Via the Dungey Cycle, plasma originating in the solar wind can be transported past the outermost protective barriers of the Earth's magnetic field by entering at the nightside of the Earth. Plasma originating from this, and other, mechanisms then proceeds to surround the Earth from altitudes ranging from the outer reaches of the atmosphere, up to around 60,000km on the dayside and beyond 1,000,000km on the nightside.The magnetic field and plasma surrounding the Earth are together known as a magnetosphere. As suggested above, the Earth's magnetosphere plays host to many highly energetic dynamics, and these dynamics are ultimately driven by the solar wind. Plasma sourced via the Dungey Cycle can itself be unstable, and these instabilities can generate electromagnetic waves (e.g. radio waves) that propagate throughout the magnetosphere. These radio waves can then go on to interact with other charged particles within the plasma and change their velocity. These particles can be accelerated close to the speed of light via so-called 'resonant interactions'. The regions of the Earth's magnetosphere containing these energetic particles are known as the radiation belts.Satellite technologies underpin much of our modern society: navigation, communication, defense and Earth observation. Hundreds of operational satellites orbit the Earth and must traverse the hazardous radiation environment in the radiation belts. Highly energetic particles pose many operational and financial risks to orbiting spacecraft, including total loss. These risks, and other associated ground-based effects, have led to the inclusion of Space Weather in the UK Cabinet Office National Risk Register of Civil Emergences.Recent satellite observations have revealed that electromagnetic waves can have significantly higher amplitudes (i.e. carry more energy) than previously thought. This also means that they can energise plasma particles to higer energies much more rapidly than previously thought. Numerous Space Weather forecasting models exist around the world, but none of them include these effects. The British Antarctic Survey hosts one world leading model, which is licenced to the UK Met Office. The ultimate objective of this Fellowship is to improve forecasting accuracy of this operational model by understanding and including the effects high amplitude waves have on particle dynamics. This is crucial as society becomes more and more dependent on satellite technologies.