Embedded Ocean Model Methods for Coastal Applications

Operational oceanography is presently a domain in great expansion. Accurate oceanic forecasts are becoming more necessary, whichever ocean scales are studied. An important difficulty in regional ocean modelling is the parametrization of the open sea boundary conditions. Various methods can be used, permitting inflows and outflows through theboundaries. In this study, we use a new and promising method, consisting in embedding a fine resolution model in a large scale coarser ocean model.Our region of interest is the Bay of Biscay. In order to simulate the circulationin this area, we use for the coarse model a 1/3 degree North Atlantic model, in which a 1/15 degree model of the Bay of Biscay and the Celtic shelf is embedded. Results from multi-year long simulations are analysed.For instance, with the fine grid, it becomes possible to see mesoscale structures such as SWODDIES (Slope Water Oceanic EDDIES) generated inside the Bay of Biscay, flowing along the slope current. We can also see events of intrusion of slope water onto theCeltic shelf. Given the difference in resolution between the coarse and the high resolution models, the cost of running the coarse model is low and this method appears to be routinely applicable.