CIRCULATION IN THE ALBORAN SEA AS DETERMINED BY QUASI-SYNOPTIC HYDROGRAPHIC OBSERVATIONS .1. 3-DIMENSIONAL STRUCTURE OF THE 2 ANTICYCLONIC GYRES

The circulation and dynamics of the Modified Atlantic Water have been studied using data from an intensive field experiment carried out betw een 22 September and 7 October 1992. Data included 134 CTD casts, ADCP , and satellite imagery. A well-defined wavelike front was observed wi th two significant anticyclonic gyres in the western and eastern Albor an Sea. Smaller-scale cyclonic eddies were also observed. The front se parates the more saline, older modified Atlantic water (S > 38) in the northern region from the fresher, more recent modified Atlantic water (S < 36.8) in the south. The associated baroclinic jet had a mean tra nsport of 1 Sv and maximum geostrophic velocities of 1.0 m s(-1). The three-dimensional structure and spatial scales of both gyres were simi lar, that is, 90 km long and 220 m deep. In the eastern Alboran, north east of Oran, the origin of the Algerian Current was also detected wit h an eastward transport of 1.8 Sv. The general picture can be presente d as a structure formed by a wavelike front coupled with two large ant icyclonic gyre-small cyclonic eddy systems. The relative importance of stratification, relative vorticity, and Froude number in the distribu tion of Ertel's potential vorticity has been examined, and potential v orticity conservation is used to infer vertical motion. The vertical v elocity forcing has been computed using the quasigeostrophic Q vector formulation of the omega equation. It is found that the differential v orticity advection due to mesoscale phenomena in the western Alboran p lays a main role in this forcing. The vertical velocities associated w ith these mesoscale structures reach maximum absolute values of 15 m d ay(-1).