Impacts of climate change in the troposphere, stratosphere and mesosphere on the thermosphere and ionosphere

越来越多的用于商业和科学目的的先进的基于卫星的技术在地球大气层的外层区域运作。为了保护这项技术，并确保我们能够安全有效地继续开发这一环境，对其未来状态，特别是其密度的可靠预测至关重要。为了做出可靠的预测，需要清楚地了解过去发生的长期(几十年到百年)变化的原因。地球上层大气(约90-500公里高度)既受到太阳上发生的过程(例如，将高能等离子体推向地球的日冕物质抛射)和下面大气中发生的过程(如雷暴)的影响。弄清这两类驱动因素的相对重要性是更好地了解高层大气的一个关键挑战。这一建议的重点是量化中低层(0-90公里高度)气候变化对高层大气状态长期变化的作用。中低层大气被认为主要通过向上传播大气波来影响高层大气。当大气波向上传播时，由于大气密度随高度呈指数下降，其幅度增加。因此，极大尺度的波动，如大气潮汐，构成了高层大气运动的重要组成部分。然而，海浪的幅度最终变得如此之大，以至于它们变得不稳定并破裂，类似于海滩上的海浪。当大气波破裂时，它们会将能量和动量转移到周围的大气中，从而驱动大规模的全球环流，并导致混合。波浪的特征和周围大气的状态决定了这些波能传播到多远(在高度和水平上)以及何时破裂。有证据表明，由于中低大气的人为气候变化，在过去的4-50年里，中低大气的造波过程和波的传播条件都发生了变化，预计未来还会有进一步的变化。这已经引起了低层大气大尺度环流模式的变化，并可能影响高层大气的气候。该项目将根据既定的排放情景，量化中低层大气人为气候变化对引起高层大气长期变化的重要性，包括过去(20世纪50年代至2000年代)和未来(20世纪50年代)。将使用最先进的全球三维气候模型进行计算机模拟，从地表延伸到大约500公里的高度，以实现这一点。这些模拟的结果将与观测到的高层大气的长期变化(例如，温度、密度)以及其他已知因素所做的贡献进行比较。其中包括高层大气中温室气体浓度的增加，这会产生降温效应，以及地球磁场的变化，这会导致更复杂的长期变化模式。还将研究由于气候变化而引起的地球磁场变化和大气潮汐变化之间的相互作用。这项研究将至少在最初阶段再次聚焦于1950年代至2020年代，但这一时间跨度可能会从850年扩大到现在。总而言之，该项目将确定中低层大气的气候变化在导致地球上层大气平均状态的长期变化中的重要性。这将提高我们对高层大气过去变化的理解，并使我们能够更好地预测未来。

An increasing amount of advanced, satellite-based technology, used for both commercial and scientific purposes, operates within the outer regions of the Earth's atmosphere. To safeguard this technology and ensure that we will be able to continue exploiting this environment safely and effectively, reliable predictions of its future state, especially its density, are essential. To make reliable predictions, a clear understanding of the causes of long-term (multi-decadal to centennial) changes that have taken place in the past is needed.The Earth's upper atmosphere (~90-500 km altitude) is influenced both by processes taking place on the Sun (e.g., so-called coronal mass ejections, which propel high-energy plasma towards the Earth) and by processes taking place in the atmosphere below (e.g., thunderstorms). Unravelling the relative importance of these two categories of drivers is a key challenge in achieving a better understanding of the upper atmosphere. This proposal focuses on quantifying the role of climatic changes in the lower and middle atmosphere (0-90 km altitude) in causing long-term changes in the state of the upper atmosphere.The lower and middle atmosphere are thought to affect the upper atmosphere mainly via upwardly propagating atmospheric waves. As atmospheric waves travel upwards, their amplitude increases due to the exponential decrease in atmospheric density with height. Very large-scale waves, such as atmospheric tides, therefore constitute an important part of the motion of the upper atmosphere. However, the amplitudes of the waves eventually become so large that they become unstable and break, similar to waves on a beach. When atmospheric waves break, they transfer energy and momentum to the surrounding atmosphere, which drives large-scale, global circulations and causes mixing. Both the characteristics of the waves, and the state of the surrounding atmosphere, determine how far these waves can propagate (in altitude as well as horizontally) and when they break.There is evidence that, as a result of man-made climate change in the lower and middle atmosphere, both wave generation processes and the wave propagation conditions in the lower and middle atmosphere have changed over the past 4-5 decades, with further changes expected in the future. This has already caused changes in large-scale circulation patterns in the lower atmosphere, and is likely to affect the climate of the upper atmosphere as well.This project will quantify the importance of man-made climate change in the lower and middle atmosphere in causing long-term changes in the upper atmosphere, both in the past (1950s-2000s) and projected into the future (2050s) according to established emission scenarios. Computer simulations with a state-of-the-art, global, 3-dimensional climate model, extending from the surface up to ~500 km altitude, will be used to do this. Results from these simulations will be compared to observed long-term changes in the upper atmosphere (e.g., in temperature, density) and to contributions made by other known factors. These include the increase in greenhouse gas concentration within the upper atmosphere itself, which has a cooling effect, and changes in the Earth's magnetic field, which cause more complicated patterns of long-term change. Interactions of changes in the Earth's magnetic field and changes in atmospheric tides due to climate change will also be investigated. This will focus at least initially again on the period of the 1950s to 2050s, but this may be broadened to a larger timespan from 850 to the present-day.In summary, this project will establish how important climate change in the lower and middle atmosphere is in causing long-term changes in the average state of the Earth's upper atmosphere. This will improve our understanding of past change in the upper atmosphere and enable better predictions for the future.