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What is Ekman transport ?

by Olga K and helmut s.

In order to understand the term Ekman transport it is necessary to have a clear understanding of the concept known as Ekman spiral. The Ekman spiral is a theoretical model of the effect on water of wind blowing over the ocean. Because of the Coriolis effect the surface layer is expected to drift at a right angle in the Northern Hemisphere and to the left in the Southern Hemisphere. Water in the lower layers drifts as well however not as fast as the surface water.

"The Ekman spiral is one of the oldest results in dynamical oceanography. It was first proposed (conceptually) by the great Norwegian explorer Fridtjof Nansen. As part of a polar expedition in the late 1890s, Nansen froze his ship Fram into the ice north of Spitzbergen Island and allowed it to drift for more than two years. During the expedition he noticed that the drift of the boat was generally to the right of the wind. Nansen proposed that this motion was the result of the Coriolis force, which causes objects to veer to the right in the northern hemisphere and to the left in the southern hemisphere. He supposed further that as the ice pushed on the water immediately below it, that water would move still further to the right of the wind, though a little more slowly. Extended down through the water column, the result would be a spiral structure. The mathematics behind this spiral were formalized by V. Walfrid Ekman in 1905, the spiral itself was not seen in the open ocean until 1986, by Jim Price, Robert Weller, and Becky Schudlich of the Woods Hole Oceanographic Institution ." (above article was published by http://www.gfdl.gov/~a1g/Ekman_spiral.html   )

Have a look at an interesting model of the Ekman spiral.

Now about Ekman transport, the text book says  "net water transport, the sum of layer movement due to the Ekman spiral. Theoretical Ekman transport is 90 degree to the right of the wind direction in the Northern Hemisphere."

Let's look at a number of questions and a diagram found on the web.

More about upwelling from the fisheries websites.

In the Ekman layer caused by winds blowing across the sea's surface, if the viscosity coefficient is not dependent on depth, the current on the sea's surface will point 45 degrees to the right of the wind's direction (in the Northern hemisphere).

Now after you have studied this information take a quick look at http://micmac.gso.uri.edu/gfd_exp/exp_e/glossary/images/et.gif

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04/02/13