A numerical study of the retroflection and rings of the North Brazil Current

. The North Brazil Current (NBC) is a western boundary current in the Tropical Atlantic, which plays a crucial role in the interhemispheric mass and heat exchange. Throughout the year, the CNB presents an intense seasonal variation. From March to June, most of the water transported by the CNB flows continuously along the western board, reaching the Caribean Sea. In the remaining of the year, however, the current separates abruptly from the coast, at approximately 6 - 7 N, in a pattern usually described as the NBC retroflection, feeding the North Equatorial Countercurrent (NECC). During the retroflecting phase, it is common to observe the formation of strong meandering, with the shedding of highly energetic anticyclonic rings. These rings move to the northwest, towards de Caribean.

As part of a Brazil-US bilateral project (Project RECONOB) the retroflection and eddy-shedding of the NBC is being investigated in a numerical framework. This include analyses of data generated by a high-resolution (1/12-degree) implementation of the Miami Isopycnic Coordinate Ocean Model (MICOM) to the Atlantic Ocean. Results from one of year data reproduce quite well the NBC annual cycle, with a very well defined retroflection in the period July-January. In the period annalyzed there was the formation and shedding of four rings, near 55W--7N. These rings, with diameter of approximately 270km, propagated northwestward with average speed of 26 cm/s, following trajectories very similar to those of observed rings. The continuation of this study will include the computation of volume and heat transported by the NBC rings, and the comparison of the numerical results with observed dat