I have sought to combine theoretical analysis and numerical computation in the study of fundamental aspects of atmospheric and oceanic fluid dynamics, in particular vortex dynamics. The atmosphere and oceans are hugely influenced by both the background planetary rotation as well as the density stratification. These effects, together with the shallow flow geometry (typical horizontal scales are 10 to 100 times larger than typical vertical scales), constrain the motion to be approximately layerwise two-dimensional. This means that vertical motion tends to be very weak compared to horizontal motion over much of the atmosphere and oceans, and stratification surfaces tend to be nearly flat. On these surfaces, a scalar quantity called the "potential vorticity" is often, to a good approximation, conserved following fluid "particles". That is, the potential vorticity (PV) is advected or transported by the nearly horizontal flow on these surfaces.

I have developed a series of lagrangian or partly-lagrangian numerical methods that allow one to accurately conserve potential vorticity, something which is not easy to do using commonly-used numerical methods. These methods have permitted a careful investigation of a range of fundamental processes, including vortex filamentation, stripping, merging, splitting, collapsing, etc, mainly in two-dimensional (height-independent) flows but recently also in three-dimensional flows . Further recent numerical developments have also permitted a careful assessment of the role of gravity waves in single-layer shallow-water flows and internal gravity waves in two- and three-dimensional Boussinesq (ocean-like) flows.

Current research is aimed at building more realistic atmospheric and oceanic models based in part on the numerical methods above, and in collaboration with the European Centre for Medium-range Weather Forecasting and the UK Meteorological Office.

For further information, see the Vortex Dynamics Research Group

Weather Forecasting