12th Conference on Interactions of the Sea and Atmosphere


The effect of model initialised scatterometer data on the prediction of maritime cyclogenesis

Lance M. Leslie, University of Oklahoma, Norman, OK; and M. S. Speer and R. F. Abbey

The Tasman Sea is a large, historically data sparse area, of the Pacific Ocean between New Zealand and the east coast of Australia. It often is subject to synoptic and mesoscale weather systems that threaten life and property at sea or in coastal communities. These systems are highly diverse and include locally enhanced cold fronts such as the coastal southerly buster of southeastern Australia, low pressure troughs, small explosive low pressure systems near the Australian east coast and synoptic scale, maritime low pressure systems. They vary dynamically in intensity and structure across a spectrum that includes both weak or intense cold cored systems to warm cored systems such as tropical cyclones and the so-called "hybrid" systems.

In this study we concentrate on the prediction of the last class of system, that is, cyclones in open waters that threaten life and property as a result of the combined effects of wind, sea state and swell including both long fetch and storm surge. These systems at sea frequently are poorly forecast owing to the lack of data available for initializing the NWP models. In addition, the model predictions are often poorly verified, again owing to the lack of observational data. A ten year climatology of Tasman Sea cyclones from 1992 to 2001 has been developed and it reveals a rich array of the above-mentioned systems. There were 25 systems in total, including two explosive lows (or "bombs"), eleven lows that developed within easterly flow, seven lows that developed on frontal systems, four tropical cyclones and one hybrid low pressure system. Prior to the advent of routinely available scatterometer data (archived approximately since August 1999), verification of winds at sea close to the surface relied almost entirely on ships of opportunity. From the climatology we have generated we compared the wind predictions for several cases from a NWP model re-run with all available additional data, including scatterometer data. It was found that the predictions of near surface wind strength and central pressures of the systems were improved considerably. Future work will extend to predicting the sea state (wave height and swell) and storm surges for some of the climatological cases which were major forecast failures. This work involves the application of our coupled atmospheric-ocean models.

extended abstract  Extended Abstract (172K)

Poster Session 5, Microscale and Mesoscale Air-Sea Interaction
Tuesday, 11 February 2003, 9:45 AM-11:00 AM

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