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Scientific assessment of the IBI/NEMO configuration (MyOcean project)

Par ECOLA Dernière modification 09/10/2014 23:56

Scientific assessment of the quality of IBI simulations

C. Maraldi (post-doc), N. Ayoub, P. De Mey F. Lyard, in collaboration with MERCATOR-Océan and P. Marsaleix (Laboratoire d'Aérologie)

Contact: N. Ayoub, P. De Mey

In this work, the objective is to provide scientific consistency verification for the IBI (Irish Biscay Iberian) configuration of the NEMO model developed by MERCATOR-Ocean and Puertos del Estados (Spain) within the MyOcean project. This type of validation is often conducted upstream of the implementation of the system which will later be used for production and routinely validated; it is meant to guide model development in identifying gross deficiencies in the modelling of several key physical processes.

The figure (from Maraldi et al., 2013) shows the domain of study and the observations used for the comparisons. In this study, we analyse a one-year simulation (2008) of the IBI/NEMO model. In particular, a challenging issue is the consistency verification of high-frequency dynamics.

The representation of barotropic tides is first investigated with comparison to tide gauges and moorings on both elevations and depth averaged currents. In the Iroise Sea, we use HF radars surface velocity  to evaluate the model ability to represent the tidal currents' fine scales. The location and intensity of thermal fronts due to tides generated mixing on the European shelf and over the Armorican shelf break are examined in comparison to in situ temperature profiles and MODIS SST observations. The signature in sea surface elevation of M2 internal tides is analysed from altimetric along-track data and from simulated sea level. The agreement between the altimetric and model estimates is remarkable. They both suggest a stronger signature of mode 2 than mode 1.

We estimate volume, heat and freshwater transports across various sections to give broad lines of the model circulation and compare them to published values. A specific focus is made on the Mediterranean outflow, as the circulation in the Gibraltar Strait is strongly influenced by tides.

 A general assessment of the SST at diurnal to seasonal time scales and of the upper layers seasonal stratification is presented using satellite L3S SST products and in situ profiles over the whole area. A focus is then made on the southern Bay of Biscay with a more detailed investigation of the T/S profiles in the model and in the data from AZTI-Tecnalia moorings at Matxitxako and Donostia.

Simulated residual currents are compared to observations at the Puertos del Estado moorings along the northern Spanish coasts. The system ability to represent specific processes, such as the slope current in winter along the northern Spanish coasts, is also investigated. As very few data were available, this test is an illustration of the potential of the model as a complement to observations within an integrated approach.

Maraldi C., J. Chanut, B. Levier, N. Ayoub, P. De Mey, G. Reffray, F. Lyard, S. Cailleau, M. Drévillon, E. A. Fanjul, M. G. Sotillo, P. Marsaleix, and the Mercator Research and Development Team, 2013: ‘NEMO on the shelf: assessment of the Iberia–Biscay–Ireland configuration’, Ocean Sci., 9, 745-771, doi:10.5194/os-9-745-2013

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