Direct Observations of the Mean Circulation at 48°N in the Atlantic Ocean

Abstract

Eulerian velocity measurements carried out along 48°N in the Atlantic Ocean Provide averaged velocities with definite large-scale structure. This warrants an analysis of these mean velocity vectors within the framework of steady and large-scale dynamics: the dominant part played by the bottom forcing in the planetary vorticity balance is demonstrated. Combined use of vertical velocities derived from fills balance and the mean velocity spirals allows us to estimate advection in the heat equation and residual cros-isopycnal velocities. At the westernmost mooring site (35°W) heat losses to the atmosphere account for these residuals, while at the other sites (20°, 25° and 30°W) lateral heat fluxes induced by mesoscale eddues must be invoked. The hydrology of the region provides elements of comparison with the set of averaged velocities: qualitative through our knowledge of the motions of watermasses at this latitude, then more quantitative using geostrophic calculations. Beta-spiral inversions are carried out on climatological hydrographic data and the same dynamical analysis applied to the resulting velocity profiles. Some incompatibilities with the direct measurements are observed and possible masons for these differences discussed.