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

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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.