ALBERT

Description: The impact of forthcoming wide-swath altimetry missions on the ocean analysis and forecasting system was investigated by means of OSSEs (Observing System Simulation Experiments) performed with a regional data assimilation system, implemented in the Iberian-Biscay-Ireland (IBI) region, at 1/12° resolution using simulated observations derived from a fully eddy-resolving free simulations at 1/36° resolution over the same region. The objective was to asses the contribution of different satellite constellations to constrain the ocean analyses and forecasts, considering both along-track altimeters and future wide-swath missions, and as consequence the capability of the data assimilation techniques used in Mercator Ocean operational system to effectively combine the different kind of measurements. This was carried out as part of a European Space Agency (ESA) study on the potential role of wide-swath altimetry for the evolution of the European Union Copernicus programme. The impact of future wide-swath altimetry data is clearly evident investigating the reliability of sea-level in the OSSEs. The most significant results were obtained looking at the sensitivity of the system to wide-swath instrumental error: considering a constellation of three nadir and two accurate (small instrumental error) wide-swath altimeters, the error in the ocean analysis was reduced up to the 50%, with respect to conventional altimeters. Investigating the impact of the repetitivity of the future measurements, the results showed that two wide-swath missions had a major impact on the the sea-level forecasting increasing the accuracy over the entire time-window of the 5-day forecasts, with respect to a single wide-swath instrument. A spectral analysis underlined that the contributions of wide-swath altimetry data observed in the ocean analyses and forecasts statistics were mainly due to resolve more accurately (up to 〉25%), with respect to along-track data, the ocean variability at spatial scales smaller than 100km. Considering the ocean currents, the results confirmed that the information provided by wide-swath measurements at the surface is propagated also in the vertical and has a considerable impact (30%) on the ocean currents (up to 300 metres), with respect to the present constellation of altimeters. The ocean analysis and forecasting systems used here are currently adopted by Copernicus Marine Environment and Monitoring Service (CMEMS) to provide operational services and ocean re-analysis. The results obtained in the OSSEs considering along-track altimeters were consistent with those derived with real data (observing system experiments, OSEs). OSSEs also allow to evaluate the potential of new observing systems and in this study the results showed that future constellations of altimeters will have a major impact to constrain the CMEMS ocean analysis and forecasting systems and their applications.