Eric Grenier (CLS, France); Pierre-Yves Le Traon (Mercator Ocean, France)

We evaluate the impact of the future Surface Water and Ocean Topography mission (SWOT) on a high resolution ocean analysis and forecasting system. An Observing System Simulation Experiment (OSSE) is carried out with a high-resolution (1/12°) ocean analysis and forecasting system over the “Iberian-Biscay-Irish” (IBI) area, with tides included. The model is driven by high-frequency (3h) meteorological forcing data including atmospheric pressure. To simulate a “real” ocean and large swath observations like the SWOT data, we use a high resolution (1/36°) model run with different forcings and physics parametrization. The assimilation system is able to ingest 10 times more data than conventional altimeters. The results are better with large swath data, with a nadir altimeter, than with 3 conventional altimeters. The benefit is stronger in the Mediterranean Sea and in coastal areas. The system is able to sustain the right level of meso-scale activity in spite of the SWOT repetitivity. Large swath data, like the one that SWOT will provide, help the assimilation to create less artificial extrapolation than within the gaps of the conventional altimeters.