The atmospheric circulation drives our weather and climate. But what makes the atmosphere circulate? In the lower atmosphere, it is the uneven distribution of the surface heating. Higher up, in the stratosphere and mesosphere at heights of 12-100km, atmospheric gravity waves (GWs) ascending from near the surface play a critical role in driving the global circulation.
You can sometimes see the effects of GWs when you look at the sky - their passage through clouds leaves visible ripples. The waves are created by winds blowing over mountains, instabilities in the jet streams and convection and weather systems. When they break, rather like ocean waves, they transfer momentum to the atmosphere. This drives the global circulation of the stratosphere and mesosphere important regions which exert a significant influence on surface weather and climate. They can also travel up hundreds of km to the electrically-charged ionosphere, where they cause travelling ionospheric disturbances (TIDs) which affect the propagation of radio waves used for communication and navigation systems. Understanding GWs is thus very important.
However, GWs are too small to simulate in climate models and notoriously difficult to observe with satellites. The contributions of different GW sources and the physics of how they interact with the atmosphere are thus poorly understood. There is a critical need for new techniques able to effectively measure these waves, allowing determination of their controlling physics and their effects on the atmosphere and ionosphere.
This project will meet this need by developing a new satellite method capable of measuring GWs in 3D. GWs are 3D phenomena, but conventional satellite measurements can only measure the GWs in 2D and so are seriously limited. I will combine data from different overlapping satellites to develop new 3D methods of measuring GWs. These data will let me determine fundamental GW properties not measured before at the global scale, such as their phase speed, frequency, and travel direction. I will use these data to answer three critical questions:
Q1: What is the nature of GWs in the global stratosphere and mesosphere, what are their sources and how do they vary?
Q2: How do these waves drive the global circulation of the atmosphere? Do a small number of very large GWs dominate the driving?
Q3: What is the connection between GWs and TIDs? What proportion of TID variability is caused by upward-propagating GWs? Answering the first two questions will advance model development, for both weather forecasting and predicting regional climate change. I will work to push such model developments forward to implementation with my network of modelling collaborators, including colleagues at Oxford University and the Met Office.
Answering the third question will have industrial impact, since GWs affect radio and GPS signals in the ionosphere; understanding this will help make GPS accurate enough for safety-critical applications like selfdriving cars. It will also enhance over-the-horizon radar, helping us track aircraft as they cross uninhabited regions. I will work with colleagues in Bath Engineering to push forward impact in this area.
Answering these questions is a fascinating blend of instrument science and geophysics. It not only capitalises on my unique skillset to produce science with clear real-world impact, but also provides the exciting opportunity to contribute to society in diverse ways, in both the short and long term.