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Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water.
A Wind generated current is a flow in a body of water that is generated by wind friction on its surface. Wind can generate surface currents on water bodies of any size. The depth and strength of the current depend on the wind strength and duration, and on friction and viscosity losses, [1] but are limited to about 400 m depth by the mechanism, and to lesser depths where the water is shallower. [2]
Wind-driven upwelling brings nutrients from deep waters to the surface which leads to biological productivity. Therefore, wind stress impacts biological activity around the globe. Two important forms of wind-driven upwelling are coastal upwelling and equatorial upwelling.
Thus, some water is rising, in what is known as upwelling. Its speeds are very slow even compared to the movement of the bottom water masses. It is therefore difficult to measure where upwelling occurs using current speeds, given all the other wind-driven processes going on in the surface ocean.
Another important factor to take into account, especially when considering ocean-wind interaction, is the role played by eddy-induced Ekman pumping. [7] Some other limitations of the explanation above are due to the idealised, quasi circular linear dynamical response to perturbations that neglects the vertical displacement that a particle can ...
The driving forces of the Ekman transport is wind-stress or "τ" (wind stress on the seasurface). The driving winds are divided in multiple areas; East of 68°W has relative stable wind speeds (>6 m s − 1 {\displaystyle s^{-}1} ), and slightly lower during August–November (4 – 6 m s − 1 {\displaystyle s^{-}1} ).
Were the earth climate symmetric about the equator, cross-equatorial wind would vanish, and the cold tongue would be much weaker and have a very different zonal structure than is observed today. [8] The Walker cell is indirectly related to upwelling off the coasts of Peru and Ecuador.
Additionally, extensive upwelling of colder sub-surface waters occurs, caused by the prevailing northwesterly winds acting through the Ekman Effect. The winds drive surface water to the right of the wind flow, that is offshore, which draws water up from below to replace it. The upwelling further cools the already cool California Current.