Overview of global data assimilation developments in numerical weather-prediction centres

Recent data assimilation developments which have taken place at numerical weather-prediction centres are briefly discussed, from the perspectives of both the importance of data and algorithmic developments. The increase in quality and quantity of satellite data is seen to play a major role in the improvement of forecast performance, particularly in the southern hemisphere. Further optimization of the use of observations is possible through the proper evaluation of data impact and the optimization of the amount of data to be assimilated. The generalized advent of four-dimensional variational assimilation is presented, and trends in the specification of error statistics are described. Finally, a more interactive forecasting system including an adaptive component is a new challenge to bring additional improvement to the forecasting of high-impact weather.