What is ekman transport

Figure 9. Sailors of ships noticed that icebergs move in a different direction than the wind. Walfrid Ekman , a Swedish physicist resolved the problem of why wind currents and water currents were not the same. The problem is that this straight line does not look straight when referenced to a spinning Earth. There are many on-line resources for the Coriolis effect, so I won't try to duplicate visualizations here, but there are a few things to get straight before looking at a few of them.

For a three-dimensional body, this angle is a solid angle, and we can use the formulas developed from plate tectonics and spherical trigonometry to determine the solid angle. But fortunately, we don't need to use these, because the rotation axis corresponds to Earth's north pole, thus, we can just use the latitude.

If you want more background and examples, I can recommend the Wikipedia page which is very well done. I can also recommend: Coriolis explained. The left panel of the figure below is is an excellent summary of how the Coriolis effect red arrows combines with pressure driven wind blue arrows to produce the anticlockwise rotation black arrows around a low pressure system in the Northern Hemisphere What is the wind pattern, and sense of rotation, around a low pressure system in the Southern Hemisphere?

The right panel is a wonderful image of the wind pattern around a Low Pressure system over Iceland. Wind-driven Currents and Ekman Transport The wind blows across the ocean and moves its waters as a result of its frictional drag on the surface. Ripples or waves cause the surface roughness necessary for the wind to couple with surface waters.

A wind blowing steadily over deep water for 12 hrs at an average speed of about cm per sec 2. If Earth did not rotate, frictional coupling between moving air and the ocean surface would push a thin layer of water in the same direction as the wind. This surface layer in turn would drag the layer beneath it, putting it into motion.

This interaction would propagate downward through successive ocean layers, like cards in a deck, each moving forward at a slower speed than the layer above.

However, because Earth rotates, the shallow layer of surface water set in motion by the wind is deflected to the right of the wind direction in the Northern Hemisphere and to the left of the wind direction in the Southern Hemisphere. This deflection is known as the Coriolis effect.

Except at the equator, where the Coriolis effect is zero, each layer of water put into motion by the layer above shifts direction because of Earth's rotation.

The Ekman spiral describes how the horizontal wind sets surface waters in motion. As represented by horizontal vectors, the speed and direction of water motion change with increasing depth.

He thought that trapped in sea ice, which moves with ocean currents, he would get to the North Pole eventually. For three years, Nansen and his ship drifted through the Arctic. But he did have lots of time to make observations of the environment. One of his observations was that the ice was not moving in the same direction as the wind.

It was moving consistently to the right of the wind direction. This phenomenon would later become known as Ekman transport.