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| Titel |
An implementation of the Local Ensemble Kalman Filter in a quasi geostrophic model and comparison with 3D-Var |
| VerfasserIn |
M. Corazza, E. Kalnay, S. C. Yang |
| 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 ; 14, no. 1 ; Nr. 14, no. 1 (2007-02-22), S.89-101 |
| Datensatznummer |
250012130
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| Publikation (Nr.) |
 copernicus.org/npg-14-89-2007.pdf |
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| Zusammenfassung |
We perform data assimilation experiments with a widely used
quasi-geostrophic channel model and compare the Local Ensemble Kalman
Filter (LEKF) with a 3D-Var developed
for this model. The LEKF shows a large
improvement, especially in correcting the fast growing modes of the
analysis
errors, with a mean square error equal to
about half that of the
3D-Var. The improvement obtained in the analysis is maintained in
the forecasts, implying that the system is capable of correcting the
initial errors responsible for later
forecast error growth.
Different configurations of the LEKF are tested and compared. We
find that for this system, adding random perturbations after every
analysis step is more effective than the standard variance inflation
in order to avoid underestimating the background error covariance and
the consequent filter divergence.
Experiments indicate that optimal results are obtained with a
relatively small number
of vectors (~30) in the ensemble.
The LEKF is characterized by the "localization"
of the analysis process over local domains surrounding each gridpoint
of the model grid.
We find that, when using a fixed number of
ensemble vectors, there is an
optimal size of the local horizontal domain beyond which the results
do not change further. |
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