Ekman Pumping & Suction: Examples

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We show examples of the flow patterns in cyclones and anticyclones created by the action of fans blowing air over the surface in the figures below. The rotation rate of the tank was 10rpm.

In Figs.1 and 2 we see a cyclonic circulation. The dye in Fig.1 is on the bottom and indicates deep flow converging inwards and upwards (see Fig.2) from the bottom. The paper dots on the surface, evident in the periphery of the tank, are driven outwards in the surface Ekman layer.

Fig.1 Evolution of bottom fluid dyed by potassium permanganate crystals at two successive times during the evolution of a cyclone driven by air flow from fans at the surface.

Fig.2 Side view showing fluid rising in the core of a cyclone from the bottom all the way up to the surface.

Figs.3 shows deep circulation in an anticyclone spiraling outwards in the bottom Ekman layer. The black paper dots on the surface are congregating in the center, indicative of convergent flow in the surface Ekman layer.

Fig.3 Bottom currents spiraling outward revealed by potassium permanganate streaks in an anticyclone. Note the paper dots gathered in the center consistent with convergence and Ekman pumping at the surface.

Real world example: The Great Pacific Garbage Patch