A reformulation of the background error covariance in the RCMWF global data assimilation system
Une reformulation de la covariance des erreurs de départ dans le système d'assimilation des données global de RCMWF
Derber, J. ; Bouttier, F.
Année de publication
1999
The background error covariance plays an important role in modern data <br>assimilation and analysis systems by determining the distribution of the<br> information in the data in space and between variables. A new <br>formulation has been developed for use in the ECMWF system. The <br>non-separable structure functions depend on the horizontal and vertical <br>scales and a generalized linear balance operator to imply multivariate <br>structure functions. The balance operator is incorporated into the <br>definition of the analysis variables to ensure good preconditioning of <br>the problem. The formulation and structure of the background error <br>covariance are presented, and the implications for the analysis <br>increments are examined. This reformulation became the operational ECMWF<br> formulation in 3D-Var in May 1997 and in 4D-Var in November 1997</div>
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