THE GENERATION AND ASSIMILATION OF CLOUD-DRIFT WINDS IN NUMERICAL WEATHER PREDICTION

This paper describes the methods used to produce cloud-drift winds (CD Ws), concentrating, in particular, on their generation from sequential Geostationary Meteorological Satellite (GMS) imagery. It discusses th e estimation of these motion vectors from both infrared (IR) and visib le imagery at high spatial and temporal resolution and also records th eir accuracy and utility. The paper then discusses the assimilation of CDW data for numerical weather prediction (NWP). It does this by look ing at studies, both in the Australian Region and over a larger domain , showing the impact of CDWs on operational NWP using current conventi onal data assimilation techniques. Subsequent to this, the use of CDWs is examined in the context of tropical cyclone motion prediction, whe re intermittent assimilation, nudging and the use of a full variationa l technique are contrasted, using examples from the Tropical Cyclone M otion-90 (TCM-90) experiment in the tropical North-West Pacific and by examining the impact of hourly CDWs in the Australian region. It was found that the high spatial and temporal resolution winds clearly have the potential to improve the accuracy of NWP, however, full exploitat ion of their information content appears to require appropriate assimi lation techniques such as the variational method employed here.