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Coastal upwelling is the best known type of upwelling, and the most closely related to human activities as it supports some of the most productive fisheries in the world. Coastal upwelling will occur if the wind direction is parallel to the coastline and generates wind-driven currents.
Coastal upwelling is the main factor contributing to the high biological productivity of the Humboldt current. [1] Upwelling within the current is not uniform across the entire system. Three notable upwelling subsystems are produced by this current:
Ekman transport is the net motion of fluid as the result of a balance between Coriolis and turbulent drag forces. In the picture above, the wind blowing North in the northern hemisphere creates a surface stress and a resulting Ekman spiral is found below it in the water column.
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. This is the mechanism that produces California's characteristic coastal fog and cool ocean waters. As a result, ocean surf temperatures are much colder in ...
In addition to coastal upwelling, strong upwelling also occurs along the equator. In this case, the Coriolis force is small near the equator as it changes sign between the hemispheres. The westward trade winds then lead to an Ekman transport that moves the surface waters away from the equator in both hemispheres.
Coastal upwelling occurs when the wind stress is directed with the coast on its left (right) in the Northern (Southern) Hemisphere. If so, Ekman transport is directed away from the coast forcing waters from below to move upward. Well known coastal upwelling areas are the Canary Current, the Benguela Current, the California Current, the Humboldt ...
Schematic of coastal downwelling in the Northern Hemisphere. Downwelling is the downward movement of a fluid parcel and its properties (e.g., salinity, temperature, pH) within a larger fluid. It is closely related to upwelling , the upward movement of fluid.
Two figures showing the surface Ekman spiral. The figure on the left is the 3D Ekman spiral, the figure on the right 2D. The solution for the flow forming the bottom Ekman spiral was a result of the shear stress exerted on the flow by the bottom.