CIRCULATION OFF ALGERIA INFERRED FROM THE MEDIPROD-5 CURRENT METERS

Eight moorings were deployed off Algeria (1-5 degrees E) during the Me diprod-5 experiment (June 1986-March 1987). The 24 current meter time series recorded at nominal depths of 100, 300, 1000 and 2000 m are ana lysed together with hydrological data (May-June 1986) and satellite in frared images. As expected, the circulation features are markedly diff erent inside and outside of a similar to 50 km-wide coastal zone. At s imilar to 25 km from the coast, five out of six moorings are well with in the Algerian Current and the current profile is strongly sheared, w ith low correlations at depth. All water masses flow eastward along th e Algerian slope, thus completing consistently our circulation diagram s. At similar to 75 km, the currents are more correlated between 300 a nd 2000m and more dependent on the occurrence of mesoscale (100-200 km ) anticyclonic eddies called ''open sea eddies''. An event was recorde d, propagating eastward at similar to 3 km/day across the mooring arra y. It is thought to consist of a meander (width 50-150 km) of the Alge rian Current, extending to similar to 100 km from the coast and associ ated with two superimposed anticyclonic eddies. One eddy, enclosed wit hin the meander, involved the surface layer and had the infra-red sign ature of what we previously called a ''coastal eddy'' (30-120 km appar ent diameter). The other eddy seemingly involved the whole deep layer, rapidly became barotropic and large in diameter (up to similar to 150 km) which made it coastal too. Sooner or later, both coastal eddies a re expected to merge together. These measurements have slightly modifi ed our former hypotheses as, instead of assuming that ''open sea eddie s'' are old stages of coastal surface eddies becoming larger and deepe r, we now expect them to be old stages of the merged coastal eddies. T his new understanding of such a coastal event is more similar to an op en sea eddy and seems consistent with both theoretical models and labo ratory experiments. Whatever this structure, recent data support our f ormer hypotheses that mesoscale eddies generated by the Algerian Curre nt can have a deep extent, propagate along the Algerian and then Sardi nian slopes (where they entrap Levantine Intermediate Water) and stron gly influence the circulation of all water masses. (C) 1997 Elsevier S cience Ltd.