An overview of the variational assimilation in the ALADIN/FRANCE NWP system
Un aperçu de l'assimilation variationnelle dans le système de prévision numérique ALADIN/FRANCE
Fischer, C. ; Montmerle, T. ; Berre, L. ; Auger, L. ; Stefanescu, S.E.
We present an overview of the 3D-Var data assimilation in the framework of the ALADIN/France model.
The purpose of this system is to provide improved precipitation forecasts at mesoscale and in the short range,<br>up to 18 hours. The goal of the paper is threefold. Firstly, we present initial considerations for the design of<br>the 3D-Var system. Secondly, we discuss in more detail the specification of the background-error covariance<br>matrix, by comparing three different error simulation techniques, namely two variants of the NMC method and an<br>ensemble-based approach. The formal, diagnostic and impact studies have led to the selection of the ensemblebased<br>covariances for the ALADIN/France assimilation. Thirdly, scores of quantitative precipitation forecasts are<br>shown in order to illustrate the robustness and the preliminary meteorological performance of the ALADIN/France<br>assimilation suite. The results indicate that the tested configuration improves some aspects of the precipitation<br>forecast, while being neutral for others, when compared with the spin-up model.<br>We conclude the paper by providing a more explicit insight into the future evolution of limited-area<br>variational analysis towards convective-scale data assimilation.<br>
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