Australian Southerly Busters. Part III: The Physical Mechanism and Synoptic Conditions Contributing to Development

Abstract

The physical mechanism responsible for the formation of the southerly busier is investigated using simulations from a version of the Australian Bureau of Meteorology's numerical weather prediction model. Froude number calculations are performed on a numerically simulated event to determine the blocking capacity of the mountains while the separate roles of the southern and eastern topography are explored through a series of idealized topography simulations. It is found that the topography along the southern coastline plays a crucial role in the formation of the southerly buster through blocking of the cold air and subsequent channeling around to the east coast where the southerly surge occurs. The interaction of four other summertime cold fronts with the southeastern Australian topography is studied. Only two of these events in reality produced southerly busters on the east coast. The model demonstrates ability to simulate the additional fronts accurately and hence distinguish between the southerly buster events and nonevents. The additional simulations are found to substantiate the results of the first part of the study in terms of demonstrating the importance of the orientation of the synoptic-scale front with respect to the southern coastline.