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| Titel |
A hybrid variational ensemble data assimilation for the HIgh Resolution Limited Area Model (HIRLAM) |
| VerfasserIn |
N. Gustafsson, J. Bojarova, O. Vignes |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 21, no. 1 ; Nr. 21, no. 1 (2014-02-26), S.303-323 |
| Datensatznummer |
250120893
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| Publikation (Nr.) |
 copernicus.org/npg-21-303-2014.pdf |
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| Zusammenfassung |
| A hybrid variational ensemble data assimilation has been developed on top of
the HIRLAM variational data assimilation. It provides the possibility of
applying a flow-dependent background error covariance model during the data
assimilation at the same time as full rank characteristics of the variational
data assimilation are preserved. The hybrid formulation is based on an
augmentation of the assimilation control variable with localised weights to
be assigned to a set of ensemble member perturbations (deviations from the
ensemble mean). The flow-dependency of the hybrid assimilation is
demonstrated in single simulated observation impact studies and the improved
performance of the hybrid assimilation in comparison with pure 3-dimensional
variational as well as pure ensemble assimilation is also proven in real
observation assimilation experiments. The performance of the hybrid
assimilation is comparable to the performance of the 4-dimensional
variational data assimilation. The sensitivity to various parameters of the
hybrid assimilation scheme and the sensitivity to the applied ensemble
generation techniques are also examined. In particular, the inclusion of
ensemble perturbations with a lagged validity time has been examined with
encouraging results. |
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