Figure 1

Fig. 1. The nonlinear Ekman effect generates upwelling and downwelling in a Northern hemisphere anticyclonic eddy, as schematically depicted. The Ekman transport in the surface layer is at 90 degrees to the right of the wind and inversely proportional to the net rotation of the fluid. The rotation of the eddy is anticyclonic and opposite to Earth's rotation. It reduces the net spin, (f + )/2, felt by the fluid toward the inside of the eddy. At the periphery, the shear between the eddy and ambient fluid generates a spin in the fluid that is in the same sense as Earth's rotation, thus enhancing the net spin of the fluid. Hence, the Ekman transport is enhanced on the inside of the eddy and weakened toward the outside. The divergence/convergence of the Ekman transport drives up/down motion as shown. The vertical motion associated with an anticyclonic eddy is greater than that with a cyclonic eddy of similar strength because decreasing the magnitude of the net rotation solicits a greater response than increasing it by the same amount. [View Larger Version of this Image (192K JPEG file)]

 

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