The generation and assimilation of cloud-drift winds in numerical weather prediction

This paper describes the methods used to produce cloud-drift winds (CDWs), concentrating, in particular, on their generation from sequential Geostationary Meteorological Satellite (GMS) imagery. It discusses the estimation of these motion vectors from both infrared (IR) and visible imagery at high spatial and temporal resolution and also records their accuracy and utility. The paper then discusses the assimilation of CDW data for numerical weather prediction (NWP). It does this by looking at studies, both in the Australian Region and over a larger domain, showing the impact of CDWs on operational NWP using current conventional data assimilation techniques. Subsequent to this, the use of CDWs is examined in the context of tropical cyclone motion prediction, where intermittent assimilation, nudging and the use of a full variational technique are contrasted, using examples from the Tropical Cyclone Motion-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 exploitation of their information content appears to require appropriate assimilation techniques such as the variational method employed here.