THE NCEP GLOBAL ANALYSIS SYSTEM - RECENT IMPROVEMENTS AND FUTURE-PLANS

This paper describes significant changes to the U.S. National Centers for Environmental Prediction (NCEP, formerly NMC, the National Meteoro logical Center) global data assimilation system that were made operati onal in January, 1995. The emphasis is on changes to the 3D-variationa l analysis, which has been running operationally since June, 1991. The changes include additions of new data types, modifications to the bac kground error, and addition of a weak constraint on divergence tendenc y. A uniform improvement in fit of the 6 hour forecast guess to all ob servation types was observed in parallel tests over a period of 9 mont hs. Most of the improvement is believed to be due to the addition of t he divergence tendency constraint. The improved performance extends to medium range forecasts, as measured by anomaly correlation scores for geopotential height. Current research activities related to global an d regional data assimilation at NCEP are also briefly described.