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| Titel |
A 20-year reanalysis experiment in the Baltic Sea using three-dimensional variational (3DVAR) method |
| VerfasserIn |
W. Fu, J. She, M. Dobrynin |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 8, no. 5 ; Nr. 8, no. 5 (2012-09-27), S.827-844 |
| Datensatznummer |
250005872
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| Publikation (Nr.) |
 copernicus.org/os-8-827-2012.pdf |
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| Zusammenfassung |
A 20-year retrospective reanalysis of the ocean state in the Baltic Sea is
constructed by assimilating available historical temperature and salinity
profiles into an operational numerical model with three-dimensional
variational (3DVAR) method. To determine the accuracy of the reanalysis, the
authors present a series of comparisons to independent observations on a
monthly mean basis.
In the reanalysis, temperature (T) and salinity (S) fit better with
independent measurements than the free run at different depths. Overall, the
mean biases of temperature and salinity for the 20 year period are reduced
by 0.32 °C and 0.34 psu, respectively. Similarly, the mean root mean
square error (RMSE) is decreased by 0.35 °C for temperature and 0.3 psu
for salinity compared to the free run. The modeled sea surface temperature,
which is mainly controlled by the weather forcing, shows the least
improvements due to sparse in situ observations. Deep layers, on the other
hand, witness significant and stable model error improvements. In
particular, the salinity related to saline water intrusions into the Baltic
Proper is largely improved in the reanalysis. The major inflow events such
as in 1993 and 2003 are captured more accurately as the model salinity in
the bottom layer is increased by 2–3 psu. Compared to independent sea level
at 14 tide gauge stations, the correlation between model and observation is
increased by 2%–5%, while the RMSE is generally reduced by 10 cm. It is
found that the reduction of RMSE comes mainly from the reduction of mean
bias. In addition, the changes in density induced by the assimilation of T/S
contribute little to the barotropic transport in the shallow Danish
Transition zone.
The mixed layer depth exhibits strong seasonal variations in the Baltic Sea.
The basin-averaged value is about 10 m in summer and 30 m in winter. By
comparison, the assimilation induces a change of 20 m to the mixed layer
depth in deep waters and wintertime, whereas small changes of about 2 m
occur in summer and shallow waters. It is related to the strong heating in
summer and the dominant role of the surface forcing in shallow water, which
largely offset the effect of the assimilation. |
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