AN EXAMPLE OF CLIMATE-RELEVANT PROCESSES UNRESOLVED BY PRESENT-DAY GENERAL-CIRCULATION MODELS

A numerical study has been undertaken with a mesoscale atmospheric model to investigate whether dynamic and thermodynamic perturbations induced by the presence of an island in a Trade-wind flow can be sufficiently important to warrant some form of representation as a subgrid-scale phenomenon in a General Circulation Climate Model. The study has shown that the processes in the lee of the island - wake and vortices - have a definite influence on atmospheric processes downwind of the island compared with an unperturbed situation in which no island is present. A General Circulation Model would not 'see' a small island within its coarse grid, and as a result the island-induced perturbations would not be perceived by such a model. Attempts to quantify the transports of heat and moisture by the wake-and-vortex system indicate that they may be of climatic relevance if they act on sufficiently long time-scales.