Study of the combined effects of data assimilation and grid nesting in ocean models – application to the Gulf of Lions

Vandenbulcke, Luc; Barth, Alexander; Rixen, M.; Alvera‐Azcárate, Aida; Bouallègue, Zied Ben; Beckers, Jean-Marie

doi:10.5194/os-2-213-2006

Cited by 16 publications

(11 citation statements)

References 27 publications

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“…SLA data are also assimilated by the coarse model providing boundary conditions to SCRM. For one-way nesting scheme as in our implementation, Vandenbulcke et al (2006) proved that the SLA signal coming from coarse model through the boundaries (assimilating SLA) is not sufficient to transfer the information throughout the whole nested high resolution domain, above all considering that SLA information concerns mesoscale features that can be resolved only by high resolution model. On the contrary, when the approach is a two-way nesting, the best results are reached assimilating data in the nested model only.…”

Section: Data and Analysismentioning

confidence: 95%

Impact of SLA assimilation in the Sicily Channel Regional Model: model skills and mesoscale features

et al. 2012

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Abstract. The impact of the assimilation of MyOcean sea level anomalies along-track data on the analyses of the Sicily Channel Regional Model was studied. The numerical model has a resolution of 1/32 • degrees and is capable to reproduce mesoscale and sub-mesoscale features. The impact of the SLA assimilation is studied by comparing a simulation (SIM, which does not assimilate data) with an analysis (AN) assimilating SLA along-track multi-mission data produced in the framework of MyOcean project. The quality of the analysis was evaluated by computing RMSE of the misfits between analysis background and observations (sea level) before assimilation. A qualitative evaluation of the ability of the analyses to reproduce mesoscale structures is accomplished by comparing model results with ocean colour and SST satellite data, able to detect such features on the ocean surface. CTD profiles allowed to evaluate the impact of the SLA assimilation along the water column. We found a significant improvement for AN solution in terms of SLA RMSE with respect to SIM (the averaged RMSE of AN SLA misfits over 2 years is about 0.5 cm smaller than SIM). Comparison with CTD data shows a questionable improvement produced by the assimilation process in terms of vertical features: AN is better in temperature while for salinity it gets worse than SIM at the surface. This suggests that a better a-priori description of the vertical error covariances would be desirable. The qualitative comparison of simulation and analyses with synoptic satellite independent data proves that SLA assimilation allows to correctly reproduce some dynamical features (above all the circulation in the Ionian portion of the domain) and mesoscale structures otherwise misplaced or neglected by SIM. Such mesoscale changes also infer that the eddy momentum fluxes (i.e. Reynolds stresses) show major changes in the Ionian area. Changes in Reynolds stresses reflect a different pumping of eastward momentum from the eddy to the mean flow, in turn influencing transports through the channel.

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Section: Data and Analysismentioning

confidence: 95%

Impact of SLA assimilation in the Sicily Channel Regional Model: model skills and mesoscale features

et al. 2012

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“…Considering that the model boundaries are provided by an assimilative model we think that for such a domain the information contained in the boundaries would propagate to the nested model without a substantial loss of information. On the contrary for larger off-line nested domains it was shown in literature (Vandenbulcke et al, 2006;Olita et al, 2012) that assimilation would be needed as information coming from boundaries quickly dissipates. Further, and maybe more important, in the present work we aim to observe changes generated by different parametrizations of surface physics: for this reason we should not hide this signal with any statistical correction.…”

Section: Methodsmentioning

confidence: 99%

Impact of currents on surface flux computations and their feedback on dynamics at regional scales

et al. 2015

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Abstract.A twin numerical experiment was conducted in the seas around the island of Sardinia (Western Mediterranean) to assess the impact, at regional and coastal scales, of the use of relative winds (i.e., taking into account ocean surface currents) in the computation of heat and momentum fluxes through standard (Fairall et al., 2003) bulk formulas. The Regional Ocean Modelling System (ROMS) was implemented at 3 km resolution in order to well resolve mesoscale processes, which are known to have a large influence in the dynamics of the area. Small changes (few percent points) in terms of spatially averaged fluxes correspond to quite large differences of such quantities (about 15 %) in spatial terms and in terms of kinetics (more than 20 %). As a consequence, wind power input P is also reduced by ∼ 14 % on average. Quantitative validation with satellite SST suggests that such a modification of the fluxes improves the model solution especially in the western side of the domain, where mesoscale activity (as suggested by eddy kinetic energy) is stronger. Surface currents change both in their stable and fluctuating part. In particular, the path and intensity of the Algerian Current and of the Western Sardinia Current (WSC) are impacted by the modification in fluxes. Both total and eddy kinetic energies of the surface current field are reduced in the experiment where fluxes took into account the surface currents. The main dynamical correction is observed in the SW area, where the different location and strength of the eddies influence the path and intensity of the WSC. Our results suggest that, even at local scales and in temperate regions, it would be preferable to take into account such a contribution in flux computations. The modification of the original code, substantially cost-less in terms of numerical computation, improves the model response in terms of surface fluxes (SST validated) and it also likely improves the dynamics as suggested by qualitative comparison with satellite data.

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“…The assimilation tool used for the experiments is the Ocean Assimilation Kit (OAK) [Vandenbulcke et al, 2006;Barth et al, 2007aBarth et al, , 2008Vandenbulcke et al, 2010]. The assimilation method provided in OAK is the square root analysis scheme of EnKF [Evensen, 2004].…”

Section: Assimilation Methodsmentioning

confidence: 99%

Ensemble assimilation of ARGO temperature profile, sea surface temperature, and altimetric satellite data into an eddy permitting primitive equation model of the North Atlantic Ocean

Yan

Barth

Beckers

et al. 2015

J. Geophys. Res. Oceans

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Sea surface height, sea surface temperature, and temperature profiles at depth collected between January and December 2005 are assimilated into a realistic eddy permitting primitive equation model of the North Atlantic Ocean using the Ensemble Kalman Filter. Sixty ensemble members are generated by adding realistic noise to the forcing parameters related to the temperature. The ensemble is diagnosed and validated by comparison between the ensemble spread and the model/observation difference, as well as by rank histogram before the assimilation experiments. An incremental analysis update scheme is applied in order to reduce spurious oscillations due to the model state correction. The results of the assimilation are assessed according to both deterministic and probabilistic metrics with independent/semiindependent observations. For deterministic validation, the ensemble means, together with the ensemble spreads are compared to the observations, in order to diagnose the ensemble distribution properties in a deterministic way. For probabilistic validation, the continuous ranked probability score (CRPS) is used to evaluate the ensemble forecast system according to reliability and resolution. The reliability is further decomposed into bias and dispersion by the reduced centered random variable (RCRV) score in order to investigate the reliability properties of the ensemble forecast system. The improvement of the assimilation is demonstrated using these validation metrics. Finally, the deterministic validation and the probabilistic validation are analyzed jointly. The consistency and complementarity between both validations are highlighted.

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Study of the combined effects of data assimilation and grid nesting in ocean models – application to the Gulf of Lions

Cited by 16 publications

References 27 publications

Impact of SLA assimilation in the Sicily Channel Regional Model: model skills and mesoscale features

Impact of SLA assimilation in the Sicily Channel Regional Model: model skills and mesoscale features

Impact of currents on surface flux computations and their feedback on dynamics at regional scales

Ensemble assimilation of ARGO temperature profile, sea surface temperature, and altimetric satellite data into an eddy permitting primitive equation model of the North Atlantic Ocean

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