Australian Southerly Busters. Part I. Analysis of a Numerically Simulated Case Study

Abstract

A diagnostic study Of the Australian southerly buster is performed using a numerical weather prediction model. It is demonstrated that the model, run at 50-km resolution, is capable of capturing the transition of a cold front into a southerly buster as it traverses the cut coast of the Australian continent. The main features of the modified front am identified through comparison of the simulation with an ?adiabatic simulation? from which precipitation and surface processes including orography have been removed. From this comparison, the southerly buster effect is defined in terms of the deformation of the front from its adiabatic ostentation and in terms of enhancement of temperature gradients and southerly winds along the coastal strip. Sensitivity experiments are then analyzed with a view to objectively determining the relative roles of mountains, precipitation, and land-sea contrasts of heating and friction in bringing about these perturbations. The major conclusions are that (i) the primary effect of northward movement of southerly winds along the Australian east coast is brought about by synoptic-scale frontal dynamics, and that (ii) the enhanced northward movement associated with the 5-shaped deformation of the frontal continuity is brought about solely by the interaction of the eastward-moving front with topography. The effects of surface heating and friction in modifying the front in the vicinity of the coast are also discussed.