Mediterranean Forecasting System: a new assimilation scheme for Sea Level Anomaly and its validation

The assimilation of satellite and in situ in the Mediterranean forecast system is based on an optimal interpolation scheme which uses EOFs to represent vertical modes of the background error correlation matrix. In this study we present a new methodology to estimate and the calculation of these multivariate EOFs. The EOFs are considered time and space varying (seasonal time scales and subregional). They consider the vertical error cross-variance between temperature, salinity, barotropic stream function and sea level anomaly. These EOFs are used to assimilate 5 years of along track sea level anomaly data. The validation of MFS analyses and forecasts using the assimilation system diagnostics and the comparison with independent observations show that, in relation to the old operational scheme, the use of the new background error correlation matrix significantly improves the accuracy of analyses and forecasts in the Mediterranean.