83rd Annual

Monday, 10 February 2003
Improved modeling of east Indian Ocean and Southern Ocean mid latitude cyclones
Bruce W. Buckley, Bureau of Meteorology, West Perth, WA, Australia; and L. M. Leslie
The low pressure systems that frequent the southern waters of the Indian Ocean between Ile de Kerguelen and the south of Western Australia are amongst the strongest depressions found outside tropical waters anywhere in the world. Near surface winds in excess of 25 m/s (50 knots) are common in these systems over large areas, posing a threat to shipping that ply these southern waters and occasionally producing bursts of severe weather over the populated south western corner of Australia. Little is known about the factors that contribute to the intensity of these storms. The results of a series of high resolution numerical simulations, using the HIRES model from the School of Meteorology at The University of Oklahoma, of a typical intense mid-winter southern ocean cyclone are presented. The sensitivity of the central pressure, maximum sustained wind speed, extent of storm force winds and structure of these storms to increased detail provided in the initial analysis provided by the ingestion of Quikscat scatterometer winds and of sea surface temperatures are presented. The combination of increased horizontal resolution and improved initial model states produced forecasts with far more accurate wind speeds than the coarser resolution operational global models. Finally, areas of future research are outlined, including coupling with ocean models to produce better simulations of the sea state, most notably the swell and wave heights.

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