Large-scale data assimilation systems: atmospheric applications to numerical weather prediction

Many developments have occurred in the large scale Numerical Weather Prediction (NWP) systems since the beginning of their operational use (end of the sixties). They have been pushed by scientific developments in data assimilation and modelling aspects as well as by the rapid progress in computer technology. After a quick description of the evolution of the operational data assimilation schemes since 1970, a review of the current state of the art in meteorological data assimilation is made. This review is limited to operational NWP performed for global modelling. Then the main algorithmic trends are outlined, and one tries to guess what operational data assimilation is likely to be in NWP centres in 2000 and beyond.