On the dynamics of the Brazil Current site of origin

Soutelino, R.G. (1,2); Silveira, I.C.A. (1) and Gangopadhyay, A., (3)

1) IOUSP - University of São Paulo
2) IEAPM - Brazilian Navy
3) SMAST - University of Massachusetts at Dartmouth

The circulation of the Western Boundary Current (WBC) over the top 1200m is composed of two main jets: the Brazil Current (BC; upper) and the North Brazil Undercurrent (NBUC; lower). These two jets, one above the other, interact with the complex bathymetry creating intense mesoscale activity. We have reported this interaction in the literature recently. The circulation in the area is eddy-rich, and characterized by anticyclonic eddies, which are speculated to be stationary or recurrent. In this poster, we study possible formation mechanisms of these eddies.

Our hypothesis is that this mesoscale activity is due to the dynamical interaction of the mean currents with the local bathymetry. ROMS is used to investigate such interactions. The model is initialized using feature-modeled velocities with no atmospheric forcing and no remote forcing through the boundaries. The simulation results agree well with recent observations. An analysis of the results, in a quasi-geostrophic framework, is conducted to investigate the occurrence of baroclinic instability. The results indicate that there is a time lag between eddy formation at different depths. Baroclinic instability occurs first at intermediate levels and gradually moves upward in the water column, leading to the appearance of the mesoscale anticyclones at the surface. Hence, it is suspected that despite the complex topography, the BC-NBUC interaction is essential to explain the near-surface mesoscale activity.