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

越来越多用于商业和科学目的的先进卫星技术是在地球大气层的外层区域运行的。为了保护这项技术，并确保我们能够继续安全有效地利用这一环境，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（几十年到几百年）变化的原因。地球的高层大气（~90-500公里高度）受到太阳上发生的过程（例如，所谓的日冕物质抛射，其将高能等离子体推向地球）和通过在下面的大气中发生的过程（例如，雷暴）。揭示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低层和中层大气（0-90公里高度）气候变化在造成高层大气状况长期变化方面的作用，据认为，低层和中层大气主要通过向上传播的大气波影响高层大气。当大气波向上传播时，由于大气密度随高度呈指数下降，它们的振幅增加。因此，大气潮汐等非常大规模的波构成了高层大气运动的重要组成部分。然而，波浪的振幅最终变得如此之大，以至于它们变得不稳定并破碎，类似于海滩上的波浪。当大气波破裂时，它们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。波的特性和周围大气的状态决定了这些波能传播多远有证据表明，由于低层和中层大气中人为的气候变化，在过去40 - 50年中，低层和中层大气中的波生成过程和波传播条件都发生了变化，预计未来会有进一步的变化。这已经引起了低层大气大规模环流模式的变化，并有可能影响高层大气的气候。本项目将量化低层和中层大气人为气候变化对高层大气长期变化的重要性，过去（1950 - 2000年代）和根据既定排放情景对未来（2050年代）的预测。为此，将使用最先进的全球三维气候模型进行计算机模拟，该模型从地表延伸到约500公里的高度。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）以及其他已知因素的贡献。这些因素包括具有冷却效应的高层大气中温室气体浓度的增加，以及地球磁场的变化，这会导致更复杂的长期变化模式。还将研究地球磁场变化与气候变化引起的大气潮汐变化之间的相互作用。这一项目将至少在最初阶段再次侧重于20世纪50年代至21世纪50年代的时期，但可能会扩大到从850年到现在的更大时间跨度。总之，这一项目将确定低层和中层大气的气候变化在导致地球高层大气平均状态长期变化方面的重要性。这将提高我们对高层大气过去变化的理解，并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.