Near-surface circulation in the Tropical Atlantic Ocean

Abstract

A recent data set of surface drifter observations in the tropical Atlantic Ocean is analyzed with a methodology that groups the observations into bins and, within each bin, simultaneously decomposed them into a time-mean, annual and semiannual harmonics, and an eddy residual with non-zero integral time scale. Features of the time-mean circulation and its seasonal variations are resolved at unprecedented scales, for both total and Ekman-removed velocities. The drifter observations reveal the branches of the South Equatorial Current (SEC) which merge with the North Brazil Current (NBC), correlated annual fluctuations in the strengths of the NBC retroflection, western North Equatorial Countercurrent (NECC) and SEC, and flow along the Guyana Coast, and strong semiannual variations in the equatorial band of the central basin. Conduits are traced which link seasonal variations of the equatorial current system's strength with the northern and southern hemisphere subtropical gyres. These findings update key results of the two decade old SEQUAL/FOCAL programs, and allow generation of a new monthly climatology of near-surface currents in the tropical Atlantic Ocean.