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| Titel |
Assessment of the impact of HF radar current measurements on hydrodynamical model forecasts in the German Bight |
| VerfasserIn |
Johannes Schulz-Stellenfleth, Emil Stanev, Friedwart Ziemer, Klaus-Werner Gurgel |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042482
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| Zusammenfassung |
| The impact of high frequency (HF) radar measurements in the German Bight is investigated
using a statistical assessment approach as well as an assimilation method. Within the project
COSYNA (Coastal Observation SYstem for Northern and Arctic seas) three HF radar stations
located in Wangerooge, Büsum, and Sylt will provide continuous surface current
measurements. The presented study is about first steps towards the use of these data in an
assimilation system to improve forecasts with a three dimensional hydrodynamical
model.
To get a first idea about the impact of radar measurements, an optimal linear estimator is
used to re-construct the complete surface current field from HF radar observations taking
into account both the prior current distribution and radar measurement errors. The
prior current distribution is estimated using a three dimensional hydrodynamical
primitive equation model with 1 km resolution. The performance of the HF radar
observations is quantified in terms of the re-construction quality. Different combinations
of radar stations are investigated using synthetic observations. In particular the
impact of the additional two-dimensional information obtained with two stations
instead of one station is illustrated. The direct use of radial current components for
the re-construction is compared to the use of surface current vectors derived from
the combination of two or three radar stations. Apart from the capability of the
HF radar observations to provide estimates of the current field at the time of the
observations, the potential of the measurements to provide forecasts is investigated with the
linear re-construction approach as well. Furthermore the linear approach is used
to re-construct the surface elevation rate of change making use of the continuity
equation.
An assimilation method based on the ensemble Kalman filter is used for a first impact
assessment of HF radar measurements within a forecast system. Synthetic measurements with
different characteristics, e.g., different combinations of radar stations, different measurement
errors, are investigated. Twin runs are performed to compare forecasts with different
configurations of the assimilation system, e.g., different assimilation intervals or different
numbers of ensemble members.
First available measurements of the radial surface current component obtained by the
Wangerooge station are analyzed. Both the horizontal current field structure and the temporal
evolution of the current field are compared to the numerical model with a focus on the M2
tidal signal. The analysis will also provide a statistics on the frequency of missing values,
which is important for the assimilation of the data. |
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