EDDIES IN THE NORTH BRAZIL CURRENT RETROFLECTION REGION OBSERVED BY GEOSAT ALTIMETRY

Mesoscale fluctuations in the western tropical Atlantic are analysed i n Geosat altimetry sea surface height (SSH) and geostrophic velocity a nomalies to investigate the role of eddies in the North Brazil Current (NBC) retroflection zone. The detachment of anticyclonic eddies from the NBC retroflection is observed during November through January, whe n the NBC retroflection into the North Equatorial Countercurrent (NECC ) weakens and finally breaks down. These eddies are traced over more t han 2 months between 50-degrees and 60-degrees-W on their way toward t he Caribbean, at average speeds of 15 cm s-1. In one case an apparent merger of two anticyclonic eddies occurs, one detached from the retrof lection zone and one detached from the NECC. Cyclonic eddies are also observed but are generally less persistent. Mesoscale SSH variance jus t west of the retroflection increases by a factor of 2 from early summ er to winter, mainly because of the anticyclonic eddies. Interhemisphe ric water mass transfer associated with the eddy flux out of the NBC r etroflection may amount to an average transport of 3 Sv.