Thermospheric Heating Modes and their Effects on Satellites

热层是我们在太空边缘(高度85到1000公里)的大气层的最上层。在这个区域内，围绕着价值数十亿英镑的数千颗卫星运行，这些卫星提供包括卫星导航、卫星通信和遥感在内的基本现代服务。还有数以千计的人造空间碎片在轨道上运行，由于碰撞的可能性，这些碎片对运行中的卫星构成重大风险。我们现在已经过了碰撞碎片增加超过损失的临界点，导致空间碎片数量净增长，从而导致碰撞风险不断增加。对卫星和碎片轨迹的短期和长期预测对于避免卫星在近地轨道上被摧毁至关重要。一个主要的限制因素是知道热层的密度，在极端情况下，热层的密度可以变化高达800%。这种变化是由于对太阳的扰动在近地空间产生的影响，统称为空间天气。在卫星最集中的极地地区，热层密度的最大不确定因素来自“焦耳”加热。这是由太空天气驱动的热层中带电粒子和中性粒子之间的碰撞造成的。至关重要的是，我们还没有正确地理解焦耳加热将在何时何地发生，以及它的可预测性如何。焦耳加热的准确模型和预测对于保护现代社会所依赖的空间资产至关重要。在这个项目中，我们将通过分析来自两个主要的国际极地仪器网络的十多年的数据来更好地理解焦耳加热。我们将使用气象学中发展起来的一种统计学方法，称为经验正交函数(EOF)分析，它能够揭示大型、噪声数据集中的潜在模式。通过这种方式，我们将以前所未有的细节解决焦耳加热问题，并将其分成不同的模式，这些模式或多或少取决于空间天气的太阳来源。由于这些源可以在它们在地球上造成空间天气之前被观测到，这将使我们能够量化焦耳加热的可预测限度。通过评估焦耳加热和卫星轨道之间的关系，这将使我们能够描述哪些轨道路径最容易受到空间天气的影响。

The thermosphere is the uppermost layer of our atmosphere at the edge of space (85 to 1000 km altitude). Within this region orbit thousands of satellites worth billions of pounds that provide essential modern services including satnav, satcomms, and remote sensing. There are also many thousands more orbiting pieces of man-made space debris which present a significant risk to operational satellites because of the chance of collision.We have now passed a tipping point where the increase in debris from collisions exceeds losses, leading to a net growth of the space debris population and thus ever-increasing risk of collisions.Short- and long-term predictions of satellite and debris trajectories are vital to avoid the destruction of satellites in low-Earth orbit. A major factor limiting factor is knowing the density of the thermosphere, which can vary by up to 800% during extreme times. The variability is due to effects in near-Earth space from disturbances on the Sun, collectively called space weather.In the polar regions, where there is the greatest concentration of satellites, the largest uncertainties in thermospheric density arise from "Joule" heating. This is caused by collisions between electrically-charged and neutral particles in the thermosphere, driven by space weather. Crucially, we have yet to properly understand when and where Joule heating will occur and how predictable it is. Accurate models and prediction of Joule heating are vital to safeguard the space assets on which modern society depends.In this project we will develop a better understanding of Joule heating by analysing more than a decade of data from two major international polar instrument networks. We will use a statistical method developed in meteorology called Empirical Orthogonal Function (EOF) analysis, which is capable of uncovering the underlying patterns in a large, noisy data set. In this way we will both resolve the Joule heating in unprecedented detail and separate it into patterns which depend to greater or lesser degrees on the solar sources of space weather. Since these sources can be observed before they cause space weather at Earth, this will allow us to quantify the limits of predictability of the Joule heating. By then assessing the relationship between the Joule heating and satellite trajectories, this will allow us to describe which orbital paths are most at risk from space weather.