Agulhas eddy fluxes in a 1/6° Atlantic model

A 1/6° resolution primitive equation model of the Atlantic circulation is analyzed in the Agulhas region. The model has a realistic level of eddy kinetic energy, and produces anticyclonic Agulhas rings as well as cyclonic structures. In the model as well as in the data, ring trajectories undergo a transition between a turbulent character in the Cape Basin and a steady propagation in the rest of the South Atlantic. The topography of the Walvis Ridge does not seem to play a part in generating this contrast in the model. The model shows that cyclones are primarily generated from the negative shear vorticity side of the Agulhas Current as it leaves the coast, and they are most of the time paired with anticyclones in dipolar or tripolar structures. Contribution of Agulhas rings to the transports has been estimated by two methods, either focussing on the amount of water trapped inside the eddies and carried with them, or as a perturbation to the time-mean flow. The second estimate always produces smaller mass fluxes than the first. Even so, the transient eddy flux (2 Sv of warm water over the Agulhas Ridge) is very large when compared to parameterizations of eddy fluxes used in low-resolution climate models.

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