ALBERT

Description: Within the framework of the EGITTO/EGYPT program, the spatial structure and the temporal variability of the surface circulation in the eastern basin of the Mediterranean Sea was studied by means of satellite-tracked drifters. A total of 97 drifters drogued to 15-m nominal depth were released between September 2005 and March 2007, either regularly along ship-of-opportunity routes (Sicily Channel) or within specific structures during dedicated campaigns (Levantine sub-basin). After editing and low-pass filtering, the drifter trajectories were used to estimate pseudo-Eulerian statistics: mean current, variance ellipses, mean and eddy kinetic energies. A statistical analysis was also performed dividing the dataset in two extended seasons (winter and summer). This study completes previous ones in the Sicily Channel and in the Ionian. Several veins are evidenced, together with a seasonal variability inducing a reversal of the circulation in the southern part of the Ionian. However, in this latter area, data are too scarce and the dynamics too complex to achieve a circulation pattern yet. Eastward, the general circulation is described as a counterclockwise flow along the Libyo-Egyptian and Middle East slopes. Part of this flow is deflected toward the open sea by the anticyclones generated alongslope by the Libyo-Egyptian current (Libyan and Egyptian eddies), by the wind (Ierapetra) or by the topography (over the Eratosthenes Seamount and off Latakia). The entrainment of this flow around successive eddies (paddle-wheels effect) results in an open sea eastward transport of Atlantic water. When the Libyan eddies (anticyclonic) are close to the slope, the westward current is stronger than the mean eastward current and the circulation is temporally and locally reversed. The strong variability induced by the eddies and the meteorological conditions hinder evenly covering all the study area. Additional deployments are required to improve further our understanding of the circulation in this basin.

Description: Within the framework of the EGITTO/EGYPT programs, the spatial structure and the temporal variability of the surface circulation in the eastern basin of the Mediterranean Sea was studied with satellite-tracked drifters. A total of 97 drifters drogued to 15-m nominal depth were released between September 2005 and March 2007, regularly along ship-of-opportunity routes in the Sicily Channel and within specific structures during dedicated campaigns in the Levantine sub-basin. This study complements previous ones in the former and in the Ionian, but it is the first one in the latter. After editing and low-pass filtering, the drifter trajectories were used to estimate pseudo-Eulerian statistics: mean current, variance ellipses, mean and eddy kinetic energies. A statistical analysis was also performed dividing the dataset in two extended seasons (winter and summer). A branching behaviour of the surface water after passing through the Sicily Channel is evidenced, together with a seasonal variability inducing a reversal of the circulation in the southern part of the Ionian. In the Levantine, the surface circulation describes an eastward flow along the Libyan and Egyptian slopes (the Libyo-Egyptian Current: LEC) that continues in a cyclonic circuit along the Middle East and Turkish slopes. This general alongslope circuit can be perturbed locally and temporally by the numerous anticyclonic eddies that co-exist in the Levantine, mainly created by the instability of the LEC in the south (Libyo-Egyptian Eddies: LEEs), but also by the wind (Ierapetra and Pelops), and by the topography (over the Eratosthenes Seamount and off Latakia). The most frequent perturbation is the entrainment of part of the flow seaward: the LEEs close to the slope can interact with the LEC, which then spreads more or less around them, so that a series of contiguous LEEs (paddle-wheel effect) can possibly result in an eastward offshore transport (the so-called Mid Mediterranean Jet). Additionally, when LEEs are close enough to the slope, most of the surface flow is spread seaward. Along the slope the current is then induced by the LEEs southern side which results in a westward current. Locally and temporally the circulation along the slope can thus be reversed.