Dynamics of Agulhas Retroflection and Ring Formation in a Numerical Model. Part I: The Vorticity Balance

Abstract

Abstract The Agulhas retroflection region of the wind-driven idealized South Atlantic–Indian Ocean model described by DeRuijter and Boudra is analyzed in detail. Here, in Part I, the physical mechanisms of the model retroflection are elucidated through illustration of Agulhas' vorticity balance among various experiments. In Part II, the ring formation process is described in terms of its vertical structure and the associated energy conversions. A one-layer model demonstration shows that both inertia and internal friction may account for a partial retroflection where a linear, weakly viscous system has none. In the nonlinear, weakly viscous one-layer model, the retroflection is accomplished through a free inertial boundary layer, as suggested originally by De Ruijter. When stratification is introduced and baroclinicity increased, using the Bleck and Boudra quasi-isopycnic coordinate model with 2 or 3 layers, the stretching term exerts an increasing influence. With 40-km resolution, terms included so that t...