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Ensemble-based assimilation of high-frequency radar surface currents in regional ocean models
Barth, Alexander; Alvera Azcarate, Aïda; Beckers, Jean-Marie et al.
20102010 The Meeting of the Americas
 

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Keywords :
data assimilation; ocean modelling; currents
Abstract :
[en] The results of coastal ocean models depend critically on the accuracy of boundary and initial conditions and atmospheric forcing. The precision of coastal ocean models is limited among others by uncertainty in those forcing fields. Since high-frequency (HF) radar installations provide measurements over a relatively large area, the assimilation of these data has a high potential to reduce the errors in ocean models and to provide a dynamically consistent estimation of the ocean circulation. The assimilation of HF radar data is not without its own challenges: the spatial variation of the surface currents uncertainty, the high temporal resolution of HF radar data, the simultaneous presence of a wide range of processes with distinct spatial and temporal scales (tides and other surface gravity waves, mesoscale and wind-driven circulation), and the generally strong sensitivity of regional models to errors in the boundary conditions and atmospheric forcings. These processess are important aspects to consider in the application of data assimilation methods to HF radar measurements. The results of two data assimilation experiments on the West Florida Shelf (WFS) and the German Bight are presented. HF radar currents are assimilated in a nested West Florida Shelf based on an ensemble of model realizations with different wind forcings. The model is sequentially updated and a filter is implemented to reduce spurious surface-gravity waves. Results of the WFS model assimilating surface currents show an improvement of the model currents not only at the surface but also at depth compared to independent ADCP observations. This West Florida Shelf assimilation experiment does not include tides. Tides are not generated within the domain, but are rather propagated inside the domain through the boundary conditions. The potential of using HF radar data to reduce errors in tidal boundary conditions is shown in a model setup of the German Bight. For improving the modeled tidal variability it is not sufficient to update the model state without updating the boundary conditions. An ensemble smoother to improve the tidal boundary values is presented and validated with independent HF radar measurements and tide-gage data. The ensemble-scheme is also applied to improve the wind forcing by assimilation of surface currents. The improvement of the analyzed wind forcing is assessed by using in-situ wind measurements.
Research center :
MARE - Centre Interfacultaire de Recherches en Océanologie - ULiège
GeoHydrodynamics and Environment Research
Disciplines :
Physical, chemical, mathematical & earth Sciences: Multidisciplinary, general & others
Earth sciences & physical geography
Author, co-author :
Barth, Alexander  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > GeoHydrodynamics and Environment Research (GHER)
Alvera Azcarate, Aïda  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > GeoHydrodynamics and Environment Research (GHER)
Beckers, Jean-Marie  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > GeoHydrodynamics and Environment Research (GHER)
Stanev, Emil V.;  GKSS - Germany
Weisberg, Robert H.;  University of South Florida - USA
Language :
English
Title :
Ensemble-based assimilation of high-frequency radar surface currents in regional ocean models
Publication date :
2010
Event name :
2010 The Meeting of the Americas
Event organizer :
American Geophysical Union
Event place :
Foz de Iguazu, Brazil
Event date :
8–12 August 2010
By request :
Yes
Audience :
International
Funders :
F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE]
Available on ORBi :
since 27 May 2011

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