Recent observations obtained in the South Atlantic suggest the existence of
a strong anticyclonic flow positioned over a major bottom topographic feat
ure known as the Zapiola Drift. Here a numerical simulation of the South At
lantic is described in which this anticyclone is reproduced, and the model
is used to diagnose the dynamics maintaining this flow. With a mean barotro
pic transport of 140 Sv and bottom velocities of 10 cm s(-1), the simulated
Zapiola Anticyclone compares well with in situ observations. Furthermore,
the model surface eddy kinetic energy shows a local minimum over the drift,
in agreement with observations from TOPEX/POSEIDON. Numerical experiments
show that the circulation feature is sensitive to the intensity of the eddy
field and to the particular value of the bottom friction. Both of these te
ndencies are in agreement with a theoretical explanation of the Zapiola Ant
icyclone that has recently appeared elsewhere. Thus we argue that the antic
yclone is maintained by eddy-driven potential vorticity fluxes accelerating
flow within topographically closed, ambient potential vorticity contours.
As far as we know, this is the first South Atlantic simulation to reproduce
the Zapiola Anticyclone in a realistic fashion. The quantitative success o
f this experiment is attributed to the use of a topography following (sigma
) coordinate in a spatially well resolved model.