Some aspects of the surface circulation south of 20°S revealed by First GARP Global Experiment Drifters

Abstract

Daily averaged positions from about 280 satellite‐tracked drifting buoys launched during the First GARP Global Experiment are used to estimate the sea surface current velocity field south of 20°S. The time‐averaged surface velocity field based on velocity averages over 4°×4° areas is used to construct the surface stream function. The gross features of the mean circulation are generally in agreement with other representations of the time‐averaged circulation although they do differ in details from the climatological relative surface dynamic topographies in the southern hemisphere subtropical gyres. Mean and eddy horizontal momentum fluxes based on a 2°×2° grid are estimated for the region south of 40°S. The zonally averaged momentum flux at the sea surface for the region of the Antarctic Circumpolar Current, from 40° to 60°S, leads to a momentum flux divergence of 60 cm2 s−2 indicating a meridional flux of eastward momentum away from the current axis. Given the relatively large errors associated with the zonally averaged momentum fluxes, the sign of the flux divergence remains uncertain.