A parallel implementation of a 4DEnVar ensemble
Arbogast, Etienne ; Desroziers, Gérald ; Berre, Loïk
Année de publication
2017
<span style="color:#4b0082;"><font face="Garamond, serif"><font style="font-size: 12pt" size="3">Abstract</font></font></span></h2><p align="justify"><span style="color:#4b0082;"><font face="Garamond, serif"><font style="font-size: 12pt" size="3">The four-dimensional ensemble variational (4DEnVar) formulation has received a considerable attention during recent years, especially at Numerical Weather Prediction centres that are (or were) relying on a 3D/4D-Var formalism for their data assimilation systems. Since 4DEnVar background error covariances are by construction given by an ensemble of 4D non-linear trajectories, an important issue is the way to build this ensemble. The use of an ensemble of perturbed 4DEnVar to generate the ensemble is a natural approach but raises difficulties for the input and storage of 4D trajectories. A parallel implementation of such a 4DEnVar ensemble (En-4DEnVar) approach is proposed with distributed input and storage of ensemble perturbations. It takes benefit of an object oriented implementation of 4DEnVar, which has been recently developed at Météo-France. First results obtained with the French global model ARPEGE (Action de Recherche Petite Echelle Grande Echelle) show that such an approach is efficient and suggest that En-4DEnVar implementations are tractable.</font></font></span></p>
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