Modeling Coastally Trapped Wind Surges over Southeastern Australia. Part II: Intensity and Depth

Abstract

A numerical weather prediction (NWP) model at the School of Mathematics, University of New South Wales, has been used to simulate the southerly buster, a southerly wind surge along the coast of New South Wales (NSW), which occurs during the spring and summer months. Three southerly buster events were simulated and comparison of the model results with observational data demonstrated that the NWP model was very good in simulating this type of event. These simulations were then used to consider the intensity, depth, and location of the southerly buster surges as they progressed northward. Both the strength and depth of the southerly buster surge decreased as it progressed farther north, particularly at the Hunter Valley. However, north of the Hunter Valley the intensity and depth increased again (in two of the three cases in this study) before dissipating completely. The location of the central part of the jet is adjacent to the Great Dividing Range, and the central jet splits at the northern side of the Hunter Valley to flow around either side of the mountains. The southerly flow into the Hunter Valley generally occurs before the continuation of the southerly buster up the coast. Sensitivity experiments, in which the topography at and north of the Hunter Valley was altered, were designed so that the southerly buster surge was able to develop naturally and then encounter different topographical features. These experiments indicate that the southerly buster is weaker and slower due to the natural break in the mountain barrier at the Hunter Valley and that the mountains to the north of the Hunter Valley act to delay the movement farther north with indications of reintensification in the region. It is concluded that the topography has a significant effect on the propagation of the southerly buster.