Barotropic and baroclinic tidal currents in the eastern basins of the North Atlantic

Abstract

Data from a large‐scale moored array in the Iberian and Canary basins are used to determine the energies of barotropic and baroclinic M 2 and S 2 tides. An analysis of time‐varying dynamical modes is performed. The results for barotropic modes confirm the global surface tide model results of Schwiderski (1980) for this region. The barotropic modes dominate in the deep basins, but increased baroclinic contributions are usually found over rough topography. At three locations near the continental slope in the southern Canary Basin the baroclinic modes dominate the barotropic mode. Results from an array of three moorings at the northern part of the Cape Verde Rise show an inverse behavior of barotropic and baroclinic energies, such that the baroclinic energy is steadily enhanced while the barotropic energy is reduced towards the continental margin. The increase in baroclinic energy is consistent with a generation of internal tides close to the shelf by surface tidal forcing over topography. Further evidence for this process is provided by the 2‐week periodicity of the first‐order baroclinic mode at the slope, corresponding to the spring‐neap cycle of the barotropic tide.