Mesoscale Eddies in the Tropical Atlantic Ocean

Habib Micaël Agnédjo Aguedjou1,2, Alexis Chaigneau2, Isabelle Dadou3, Yves Morel4, Gael Alory5 and Ezinvi Baloïtcha6, (1)CIPMA, UAC, Physical Oceanography, Cotonou, Benin, (2)LEGOS, Toulouse, France, (3)LEGOS, Toulouse Cedex 9, France, (4)Laboratoire d’Etudes Géophysiques et d’Océanographie Spatiale, LEGOS – UMR 5566 CNES-CNRS-IRD-UPS, Toulouse, France, (5)Observatory Midi-Pyrenees, Toulouse, France, (6)CIPMA, Cotonou, Benin
Abstract:
Abstract

Mesoscale eddy characteristics are studied in the Tropical Atlantic Ocean (30°N-30°S), using 23 years of daily altimetry sea level anomalies. From the analysis of more than 32000 coherent eddy trajectories, we found that these vortices are mainly generated both in the eastern part of the Atlantic ocean, especially in the Eastern Boundary Upwelling Systems (Canary and Benguela / Angola) and in the western part along the Brazil current region. Their westward propagating speed reaches 20 cm s-1 in equatorial areas and decreases with latitudes. They present typical amplitudes of 1-5 cm. The largest and most energetic eddies are observed in the equatorial region, in particular in the retroflection of the North Brazil Current (NBC). The seasonal cycle of the main eddy characteristics shows higher amplitudes along the NBC retroflection and the western part of the North Equatorial Countercurrent (NECC). We propose a criterion using altimetry only to analyze the mechanism responsible for eddy generation. In the NECC, we suggest that eddy generation is mainly due to barotropic instability of mean surface currents whereas other mechanisms must be invoked for the NBC. Moreover, eddy vertical characteristics are studied merging satellite altimetry and vertical temperature/salinity profiles from Argo floats. The temperature and salinity anomalies observed within the eddies reveals that they are surface-intensified in equatorial areas (20N-20S), whereas poleward of 20° they also present maximum subsurface anomalies down to 500-1000 m.

Keywords : Mesoscale eddies, Tropical Atlantic ocean, seasonal variability, eddy vertical structure

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