MOMENTUM AND ENERGY-BALANCE OF THE MEDITERRANEAN OUTFLOW

Field data taken in the Gulf of Cadiz have been analyzed to describe s ome aspects of the momentum and energy balance of the Mediterranean ou tflow. A crucial component of the momentum balance is the total stress (entrainment stress and bottom drag), which has been estimated from a form of the Bernoulli function evaluated from density and current obs ervations. For the first 60 km west of the Camarinal Sill the outflow was confined within a narrow channel on the continental shelf. At abou t 70 km downstream the outflow crossed over the shelf-slope break and began to descend the continental slope. The buoyancy force increased s ubstantially, and the outflow underwent a geostrophic adjustment, albe it one heavily influenced by mixing and dissipation. The current direc tion turned 90 degrees to the right at a near-inertial rate. In this r egion, the estimated geostrophic velocity greatly underestimated the a ctual current, and the estimated curvature Rossby number was about 0.5 . Current speeds were in excess of 1 m s(-1) and the total stress was as large as 5 Pa. The entrainment stress, estimated independently from property fluxes, reached a maximum of about 1 Pa, or considerably sma ller than the inferred bottom stress. By about 130 km downstream, the current was aligned approximately along the local topography. The curr ent amplitude and the estimated stress were then much less, about 0.3 m s(-1) and 0.3 Pa. The entrainment stress was also very small in this region well downstream of the strait. This slightly damped geostrophi c flow continued on to Cape St. Vincent where the outflow began to sep arate from the bottom. Bottom stress thus appears to be a crucial elem ent in the dynamics of the Mediterranean outflow, allowing or causing the outflow to descend more than a kilometer into the North Atlantic. In the regions of strongest bottom stress the inferred drag coefficien t was about 2 - 12 (x 10(-3)) depending upon which outflow speed is us ed in the usual quadratic form. Entrainment stress was small by compar ison to the bottom stress, but the entrainment effect upon the density anomaly was crucial in eroding the density anomaly of the outflow. Th e observed entrainment rate appears to follow, roughly, a critical int ernal Froude number function.