Assimilation of sea level data over continental shelves: An ensemble method for the exploration of model errors due to uncertainties in bathymetry
Sea level model error statistics due to uncertainties in bathymetry in shallow seas are investigated through an original approach based on an ensemble method. The model is free-surface, barotropic and implemented over the entire European continental shelf. The main focus is the specific sea level re...
| Authors: | , , , |
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| Format: | article |
| Status: | Versión aceptada para publicación |
| Publication Date: | 2004 |
| Country: | España |
| Institution: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repository: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/414380 |
| Online Access: | http://hdl.handle.net/10261/414380 https://api.elsevier.com/content/abstract/scopus_id/23844506587 |
| Access Level: | Open access |
| Keyword: | Bathymetric errors Data assimilation Ensemble methods European shelf Meteorological forcing Model errors Shelf seas |
| Summary: | Sea level model error statistics due to uncertainties in bathymetry in shallow seas are investigated through an original approach based on an ensemble method. The model is free-surface, barotropic and implemented over the entire European continental shelf. The main focus is the specific sea level response of the ocean to meteorological forcing in the presence of bathymetric errors. The introduction of such errors is generally unavoidable considering our insufficient knowledge of bottom topography in most shallow regions of the world. These errors are likely to impact on ocean modeling. In particular, coastal gravity waves, which are responsible for an important part of sea level variability due to atmospheric forcing over shelves, are sensitive to bathymetric errors. An ensemble of perturbed bathymetric solutions is generated by first examining differences between selected existing bathymetric databases and then randomly combining perturbations generated from these differences. The objective is that the ensemble of simulations obtained by running the model over these bathymetries best represents the probability density of model states due to this particular source of errors. Interesting space-time characteristics of sea level error covariances in the perspective of sea-level data assimilation are pointed out. These statistics are shown to be neither homogeneous over shelves, nor Isotropic when approaching the coast. They are not even stationary, since they are very dependent on the meteorological regime. These features are of crucial importance since they impose heavy constraints on the choice of the scheme necessary to get dynamically consistent results from data assimilation over continental shelves. The question of the ability of this method to provide sensible bathymetry corrections is addressed in the last part of this paper. The correction is obtained by assimilating sea-level data generated by a simulated Wide Swath Ocean Altimeter system via a global inverse formulation using ensemble statistics. Twin experiments are carried out in that perspective. Results are encouraging, even if a significant part of bathymetric errors remains uncorrected after the analysis. © 2004 Elsevier B.V. All rights reserved. |
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