| The early Sea Surface Height (SSH) decay of an Agulhas ring is studied using acircular symmetric, equivalent barotropic idealization of ring Astrid, which was measured duringthe first MARE-cruise. Observations indicate that the SSH of Agulhas rings most rapidly decays just after shedding.The goals of this study are 1) to investigate whether the observed initial SSH decay can be recovered by the model,2) to identify the processes responsible for the decay, and 3) to describe the mixing or stirring associated with the decay.It is found that the observed initial fast decay of ring Astrid can be recovered by a numerical model and thata mixed baroclinic/barotropic instability accounts for most of the observed decay of SSH.The simulation of ring Astrid shows that tracer loss from the core scales well with the decay of SSH. Tracer leakage manifestsitself through the formation of two filaments in the upper layers that reach down to the thermocline. In the deepest layers thereis no filamentation and tracer is mixed out of the ring due to Rossby wave radiation.The decay of tracer content in layers extending to the thermocline shows that up to 40% of ring water is lostdue to filamentation in the first 30 days. In deeper layers the decay of tracer content is even larger.We comment on the robustness of these results, the role of the baroclinic instability in the stirring of tracersand the role of buoyancy forcing in the mixing and stirring. |
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