Topic Area

Project Team Member

LCDR Marcus Simões Brazilian Navy

Major Findings

The North Brazilian Current (NBC) is a major western boundary current in the Tropical Atlantic. It plays two major roles. First closing the wind driven equatorial gyre and secondly providing conduit for cross equatorial transport of South Atlantic Surface Water(SASW) as part of the Meridional Overturning Cell (MOC). During July to February some retroflexions occur originating the North Brazil Current Rings/Eddies.

The ring moves northwestward toward the Caribbean roughly paralleling the South American coast line shedding as much as one-third of the net warm water transport across the equatorial tropical gyre boundary into the North Atlantic, in compensation for the southward export to North Atlantic Deep Water.

The ring generation is not well understood but some mechanism like retroflex paradox, local dynamics and remote propagating influences are being studied.

Having an average of more than 5 Rings per year with mean length scales of 100 km, some rings penetrated the thermocline to depths approaching 1000 m with mean translation velocities of 14km/day and speed of 8 to 12 cm/s.

Equatorial water mass volume trapped by rings in their core and transported into the subtropical North Atlantic has been estimated in 2.0 to 4.0 x 10 ¹³ m^3.

The annualized mass flux from all Rings/Eddies that are formed during a typical year is between 2.6 to 4.0 Sv, which carried amounts to roughly 20-30% of the total strength of the Atlantic MOC, indicating that these rings play an important role in the overturning cell and in the net meridional heat transport through the tropical Atlantic.

General and local circulation models have had varying levels of success in simulating NBC Rings. The new data set provided by the NBC experiment in the region and Remote Sensing tools will improve largely the next models generation.

Finally, the North Brazil current experiment and a set of multinational programs will create a new standard in the knowledge not only on NBC rings, NBC retroflexion and in the understanding of MOC but in a better understanding of the whole Atlantic dynamics,also.

References

• Goni, Gustavo J. ; Johns, William E. 2001, "A Census of North Brazil Current Rings Observed from TOPEX/POSEIDON Altimetry: 1992-1998
• Barnier, B., T. Reynaud, A. Beckmann, C. Böning,  J.-M. Molines, S. Barnard and Y. Jia, 1999: " On the seasonal variability and eddies in the North Brazil Current: Insights from model intercomparison experiments."
• D.M. Fratantoni and P.L. Richardson, W.E. Johns,S. Garzoli, W.D. Wilson, and G.J. Goni, "The North Brazil Current Rings Experiment, 2000"
• Johns, W.E., T.N. Lee, R. Beardsley, J. Candela and B. Castro, 1998: "Annual Cycle and Variability of the North Brazil Current", J.Phys.Oceano., 28(1), 103-128.
• http://www.aoml.noaa.gov/phod/nbc/proposal/node2 .html