Ekman transport is the depth-integrated ageostrophic flow in a frictional rotating boundary layer. Beneath a surface stress ,with the stated orientation convention.
Spatial convergence or divergence of Ekman transport drives vertical motion at the base of the Ekman layer. With upward vertical coordinate,
In a thin Bottom Ekman layer, slowly evolving geostrophic flow drives upward Ekman pumping into a uniform-depth exterior layer. With , and , its balanced height satisfies . Small-scale Fourier modes decay on ; large-scale modes obey a diffusion equation with diffusivity . The balanced approximation requires .
Bottom Ekman pumping damps a horizontal quasi-geostrophic Fourier mode while its influence penetrates vertically only over . For a half-space with a vertically uniform initial mode, the boundary amplitude decays exponentially while the remote interior remains unchanged.
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Ekman transport is a concept in oceanography that refers to the net movement of water induced by wind stress over the surface of the ocean. When wind blows across the surface of the sea, it creates friction between the air and the water, causing the surface water to move in the direction of the wind. However, due to the Coriolis effect—resulting from the Earth's rotation—the surface water is deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.