Research and Application News
20 years of 4D-Var: better forecasts through a better use of observations
20 November 2017
Twenty years ago ECMWF added an extra dimension – time – to the assimilation of observational data into weather models. This pioneering '4D-Var' technique has led to substantial improvements in the Centre's forecasts.
Developing a 4D variational data assimilation system was one of ECMWF's biggest-ever projects. It culminated in the operational implementation of 4D-Var on 25 November 1997, less than two years after the introduction of 3D-Var.
Image credit: ECMWF - Diagram illustrating the principle of 4D-Var.