A stategy for operational implementation of 4 D-VAR using an incremental approach
Une statégie pour l'implémentation opérationelle du modèle 4 D-VAR utilisant une approche incrémentale
Courtier, P. ; Thépaut, J.-N. ; Hollingsworth, A.
Année de publication
1994
An order of magnitude reduction in the cost of four-dimensional <br>variational assimilation (4D-Var) is required before operational <br>implementation is possible. Preconditioning is considered and, although <br>it offers a significant reduction in cost, it seems that it is unlikely <br>to provide a reduction as large as an order of magnitude. An <br>approximation to 4D-Var, namely the incremental approach, is then <br>considered and is shown to produce the same result at the end of the <br>assimilation window as an extended Kalman filter in which no <br>approximations are made in the assimilating model but in which instead a<br> simplified evolution of the forecast error is introduced. This approach<br> provides the flexibility for a costbenefit trade-off of 4D-Var to be <br>made.</div>
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