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

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)...