Circulation off Algeria inferred from the Médiprod-5 current meters

Eight moorings were deployed off Algeria (1–5°E) during the Médiprod-5 experiment (June 1986–March 1987). The 24 current meter time series recorded at nominal depths of 100, 300, 1000 and 2000 m are analysed together with hydrological data (May–June 1986) and satellite infrared images. As expected, the circulation features are markedly different inside and outside of a ∼ 50 km-wide coastal zone. At ∼ 25 km from the coast, five out of six moorings are well within the Algerian Current and the current profile is strongly sheared, with low correlations at depth. All water masses flow eastward along the Algerian slope, thus completing consitently our circulation diagrams. At ∼ 75 km, the currents are more correlated between 300 and 2000 m and more dependent on the occurrence of mesoscale (100–200 km) anticyclonic eddies called “open sea eddies”. nt was recorded, propagating eastward at ∼ 3 km/day across the mooring array. It is thought to consist of a meander (width 50–150 km) of the Algerian Current, extending to ∼ 100 km from the coast and associated with teo superimposed anticyclonic eddies. One eddy, enclosed within the meander, involved the surface layer and had the infra-red signature of what we previously called a “coastal eddy” (30–120 km apparent diameter). The other eddy seemingly involved the whole deep layer, rapidly became barotropic and large in diameter (up to ∼ 150 km) which made it coastal too. Sooner or later, both coastal eddies are expected to merge together. measurements have slightly modified our former hypotheses as, instead of assuming that “open sea eddies” are old stages of coastal surface eddies becoming larger and deeper, we now expect them to be old stages of the merged coastal eddies. This new understanding of such a coastal event is more similar to an open sea eddy and seems consistent with both theoretical models and laboratory experiments. Whatever this structure, recent data support our former hypotheses that mesoscale eddies generated by the Algerian Current can have a deep extent, propagate along the Algerian and then Sardinian slopes (where they entrap Levantine Intermediate Water) and strongly influence the circulation of all water masses.