A two-layer approximation to the Brazil Current–Intermediate Western Boundary Current System between 20°S and 28°S

Abstract

It has been shown that the vertical structure of the Brazil Current (BC)–Intermediate Western Boundary Current (IWBC) System is dominated by the first baroclinic mode at 22°S–23°S. In this work, we employed the Miami Isopycnic Coordinate Ocean Model to investigate whether the rich mesoscale activity of this current system, between 20°S and 28°S, is reproduced by a two-layer approximation of its vertical structure. The model results showed cyclonic and anticyclonic meanders propagating southwestward along the current axis, resembling the dynamical pattern of Rossby waves superposed on a mean flow. Analysis of the upper layer zonal velocity component, using a space-time diagram, revealed a dominant wavelength of about 450 km and phase velocity of about 0.20 ms −1 southwestward. The results also showed that the eddy-like structures slowly grew in amplitude as they moved downstream. Despite the simplified design of the numerical experiments conducted here, these results compared favorably with observations and seem to indicate that weakly unstable long baroclinic waves are responsible for most of the variability observed in the BC–IWBC system.