Influence of the Cape Angle and Flow Speed on Eddy Formation and Detachment: Experimental Results and Comparison with North Brazil Current Eddies

Abstract

The quasi-periodic formation of eddies during retroflection of an initially steady surface current is addressed by experimental modeling and observations. The retroflection process was simulated for various conditions, corresponding to different combinations of a cape angle and surface current speed. The simulations were conducted on a stratified domain under rotation. Results indicate that eddy size and shape, and detaching frequency depend on cape angle, not on upstream speed. Eddies detach at a higher rate for 40$^\circ$ and 80$^\circ$ cape angles. Other configurations did not show either a regular eddy formation nor detaching. Eddy size was related to the internal Rossby radius of deformation ($R_{d}$) as predicted by theory. Current displacement toward the rotation axis in our experiments prior to eddy detachment was from 3.1 to 3.5$R_{d}$. Retroflection angle was proportional to detachment T for each cape angle: 6T for 80$^\circ$, and 3T for 40$^\circ$, where T is the rotation period of the turn table. We conclude that eddy detachment is a result of eddy angular momentum increase from the momentum flux of the steady current. Similarity was analyzed with retroflection present in the North Brazil Current. Eddy vorticity profile and dimensionless quantities related to moving speed and eddy size in the oceanic flow agree with our results.