A team from Bath's department of electronic and electrical engineering is testing the theory that, while the lower atmosphere is warming, the upper atmosphere, or mesosphere, is cooling by as much as 1C a year.
Very topical and important work.
The mesosphere, which is about 50 to 62 miles above the planet's surface, is notoriously difficult to investigate, but it is crucial in exploring climate change.
"The mesosphere has been called the miners' canary for climate change: it is very sensitive, and the changes there may be larger than in any other part of the atmosphere,' says Nick Mitchell, who leads the project at Bath.
"Evidence of such changes comes from sightings of unusual clouds in the polar mesosphere, which may mark the onset of long-term cooling of the upper atmosphere."
Those clouds also coincide with radar returns from many different types of ionospheric radars from HF to UHF. These polar mesospheric summer echoes (PMSE) seem to be related to both turbulence in the mesosphere and the formation of ice crystals. Experiments with the EISCAT facility in Norway have shed some light on their make-up with great sucess.
Similar looking radar returns also occur in the winter mesosphere, though in a different height regime. It is not clear what causes them since the winter mesopshere is much warmer than the summer and ice crystals should not form. Some interesting theories about turbulence and infrasound have been put forward but it is still all up in the air (excuse the pun).
I am fortunate enough to have run the first experiment using an ionospheric heater in conjunction with radar measurements at EISCAT on PMWE. This opened the door a little wider to the possibility of dust particles being the cause, but it is far from certain. If there are dust particles there where do they come from? It all still needs working out.
This is an area where ground-based instruments have proved vital in advancing our understanding. We have lost some of the infrastructure that would have been important for the UK to keep playing our role in these studies but thanks to the University of Bath and BAS, the UK will still have a role to play.