Mediterranean Surface Geostrophic Circulation from Satellite Gravity and Altimetry Observations

We present a data-based approach to study the mean and the climatology of the surface geostrophic currents (SGC) for the Mediterranean Sea, using satellite ocean surface altimetry observations for 22 years (1993-2014) in conjunction with the geoid solution derived from the space mission of GOCE (gravity field and steady-state ocean circulation explorer; Release 4). The resultant product is the Mediterranean SGC velocity field, that we denote by SGC and monthly time resolution. It exhibits smaller scales and lower dynamic intensities in comparison with open oceans, making the Mediterranean Sea a challenging test case for our satellite-based analysis. The mean SGC is largely consistent with previous findings but with additional circulation features in time and space. We also compare our results with the SGC output from the regional hydrodynamic model of Mercator that assimilates satellite altimetry, satellite sea surface temperature, and in situ observations. The prominent SGC features agree well not only on the large and subbasin scales but also in the widespread mesoscale dynamics. We find, however, comparatively lower intensities than the Mercator model in general, with differences that are on average around 7 cm/s, but might reach 13 cm/s in some coastal areas.