A posteriori validation applied to the 3D-Var ARPEGE and ALADIN data assimilations system
Une validation a-posteriori appliquée au système d'assimilation des données des modèles 3D-Var ARPEGE et ALADIN
Sadiki, W. ; Fischer, C.
Année de publication
2005
In this paper we present results from the application of a posteriori
diagnostics on existing data assimilation systems. The systems of
interest are the global data assimilation Arpège 3D-VAR of Météo-France,
and the limited-area 3D-VAR analysis of Aladin. First, we discuss how
the diagnostics can be ported from theory to practical applications,
using aggregates of analysis information over time. We then compare the
behaviour of the diagnostics in the two different data assimilation
systems, with a focus on the properties of the background and
observational error variances. Secondly, the a posteriori validation is
used for the off-line tuning of two scalar error parameters in the
Aladin 3D-VAR. The tuning provides error variances that better fit the
statistics of the innovation vector, without loss of quality in the
analyses. Finally, the link of this approach with ensemble-based
techniques is made. Especially, we propose to couple the a posteriori
diagnostics directly with the usual output of ensemble samples, which
could be done at no extra cost. If the results are then used to tune
error parameters, then an on-line adaptive assimilation system, based on
a posteriori considerations, is obtained.</div>
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