AN OPERATIONAL SYSTEM FOR GENERATING CLOUD DRIFT WINDS IN THE AUSTRALIAN REGION AND THEIR IMPACT ON NUMERICAL WEATHER PREDICTION

The Australian Bureau of Meteorology has, since June 1992, produced cl oud drift wind data for operational use. These data are used in the an alysis cycle of the local operational numerical weather prediction sys tem. This paper describes the methodology used for automatically produ cing cloud drift winds and also for their application to numerical wea ther analysis and prediction. Local processing of Geostationary Meteor ological Satellite digital infrared data into cloud motion vectors has provided several advantages. It ensures timely availability of the da ta in the Australian National Meteorological Centre for the operationa l Regional Assimilation and Prediction (RASP) system. It allows qualit y control and, in particular, height assignment to be closely tied to the RASP system, which is consistent with the long-term requirement fo r the processing of these remotely sensed data to be done as part of t he assimilation system. Importantly, use of the data has resulted in c onsistent improvements both in forecasts from the RASP system over the Australian region in real-time trials over several months and in fore casts over the Southern Hemisphere in a two-month trial with the Burea u of Meteorology Research Centre Global Spectral Model.