Prize for thesis in atmospheric physics

University of Oxford news release, 18 January 2005

A scientist who carried out his doctoral research in the Atmospheric, Oceanic and Planetary Physics group at the University of Oxford has been awarded the Royal Astronomical Society's Blackwell Prize for the best doctoral thesis in atmospheric physics in the UK.

Dr Paul Williams, who now holds a postdoctoral Research Fellowship in the Centre for Global Atmospheric Modelling at Reading University, won the award for his work studying the behaviour of waves in the Earth's atmosphere. As a Dphil student at Oxford he found that small-scale fluctuations, which are widespread in the atmosphere, may have a greater impact on weather systems than has previously been thought.

The fluctuations, known as inertia-gravity waves because they are sustained by a combination of inertial and gravitational forces, are prominent in the bottom 15 km of the atmosphere. They can often be seen from the surface of the Earth as 'stripy' features in clouds. Previously meteorologists assumed that inertia-gravity waves did not significantly interact with weather systems, such as warm and cold fronts, but this assumption had never been rigorously tested.

Motivated by the results of laboratory experiments, which seemed to challenge the meteorologists' assumption, Dr Williams and colleagues developed a computer model of a simple fluid system resembling the atmosphere. They represented the inertia-gravity waves as random noise in the model, since the fluctuations can be highly irregular, chaotic and transient. They found that the system could behave differently when the inertia-gravity wave representation was activated - in other words, the meteorologists' assumptions were not always justified.

In particular, the state of the fluid could undergo spontaneous transitions to quite different states, with a dramatic shift in the patterns of low and high pressure. Extrapolation of these results to the real atmosphere suggests that inertia-gravity waves could be a cause of significant errors in weather forecasts.

Dr Williams was presented with the Blackwell Prize and gave a short talk on his research at a ceremony at the Royal Astronomical Society HQ in London on Friday 14 January 2005.