Ekman Transport - Applications

Applications

• Ekman transport is a factor in coastal upwelling regimes which provide the nutrient supply for some of the largest fishing markets on the planet. Wind in these regimes blows parallel to the coast (such as along the coast of Peru, where the wind blows North). From Ekman transport, surface water has a net movement of 90 degrees to the left in such a location. Because the surface water flows away from the coast, the water must be replaced with water from below. It is important to remember that in shallow coastal waters, the Ekman spiral is normally not fully formed and the wind events that cause upwelling episodes are typically rather short. This leads to many variations in the extent of upwelling, but the ideas are still generally applicable.
• Ekman transport is similarly at work in equatorial upwelling, where, in both hemispheres, a trade wind component towards the west causes a net transport of water towards the pole, and a trade wind component towards the east causes a net transport of water away from the pole.
• On smaller scales, cyclonic winds induce Ekman transport which causes net divergence and upwelling, or Ekman pumping, while anti-cyclonic winds cause net convergence and downwelling, or Ekman suction
• Ekman transport is also a factor in the circulation of the ocean gyres. Ekman transport causes water to flow toward the center of the gyre in all locations, creating a sloped sea-surface, and initiating geostrophic flow (Colling p 65). Harald Sverdrup applied Ekman transport while including pressure gradient forces to develop a theory for this (see Sverdrup balance).