Numerical simulation of a cut-off low over southern Australia

Cut-off low pressure systems over southern Australia are synoptic scale low pressure systems which have a closed circulation at the surface and a deep trough at the 500 hPa level. They usually develop from a deep trough in th e westerlies, and often are companied by a Southern Ocean cold front. It is one of the most significant types of weather systems over southern Austral ia. Moderate or heavy rainfall is often associated with cut-off lows. Few s tudies so far have been conducted on them. In terms of prediction, the most interesting aspects are the position and intensity of the cut-off low pres sure systems, the rainfall amount and distribution and sharp winds, when th ey are present. In this paper, a numerical model developed at the University of New South W ales, HIRES (HIgh RESolution model), is employed to simulate the cut-off lo w of August 31 to September 2, 1997. The modeling results are encouraging, showing that HIRES can forecast very well the location and intensity of the cut-off low system and its associated precipitation. The impact of an impr oved, explicit physics scheme on the simulation is also examined. The expli cit scheme further improves the rainfall prediction.