Circulation of the Surface Water in the Mediterranean Sea Inferred using Envisat ASAR
Reul, Nicolas¹; Chapron, bertrand¹; Collard, Fabrice²; Mouche, Alexis²; Poulain, Pierre-Marie³; Tournadre, jean¹; Menna, Milena^4
1IFREMER, FRANCE; ²cls, FRANCE; ³Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), ITALY; ⁴Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, ITALY

Significant advances have been made in the understanding of the thermohaline circulation and the forcings of the Mediterranean sea in recent years. However, there are still many issues to be addressed that should be seen as research priorities for the future. Can new measurements be made leading to an agreed description of the surface circulation in the Mediterranean, and particularly, in the eastern basin part is one of the remaining open questions. Sea surface range Doppler velocities from nearly 1500 Envisat Advanced Synthetic Aperture Radar (ASAR) acquisitions between 2007 and 2012, covering the Mediterranean Sea, and the Black Sea, have been examined to tentatively answer this question.
After systematic corrections and time-averaging, the inflow of Atlantic Water to the Mediterranean Sea and the further modified Atlantic water paths within the Western and Eastern basins, is investigated. Distinct expressions of the Alboran Gyres, Algerian current, Liguro-provencal and Northern currents as well as details about the circulation in the Ionian, Adriatic and levantine basins are revealed. The cyclonic Rim Current, surrounding the entire Black sea basin is also depicted. For the first time, mean seasonal variability of the surface circulation over the global basin can be estimated thanks to ASAR. At a spatial resolution of 10 km, the root mean square errors of these velocities are estimated to be less than 5 cm/s. The range Doppler velocity retrievals are assessed and compared to other direct and indirect estimates of the upper ocean current, including surface Lagrangian drifters, moored recording current meter measurements, and surface geostrophic current inverted from several mean dynamic topography fields. The results are promising and demonstrate that the synthetic aperture radar based range Doppler velocity retrieval method is applicable to monitoring the temporal and spatial variations of ocean surface circulation in the Mediterranean sea, provided the imaging geometry is favorable.