- Boundary current
Boundary currents are
ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents.
Eastern boundary currents
Eastern boundary currents are relatively shallow and slow-flowing. They are found on the eastern side of
oceanic basins (adjacent to the western coasts of continents). Subtropical eastern boundary currents flow equatorward, transporting cold water from higher latitudes to lower latitudes; examples include the Benguela Current, the Canary Current, the Peru Current, and the California Current. Coastal upwelling often brings nutrient-rich water into eastern boundary current regions, making them productive areas of the ocean.
Western boundary currents
Western boundary currents are warm, deep, narrow, and fast flowing currents that form on the west side of ocean basins due to "western intensification". They carry warm water from the tropics poleward. Examples include the
Gulf Stream, the Agulhas current, and the Kuroshio.
Western intensification is the intensification of the western arm of an
oceanic current, particularly a large gyre in an ocean basin. The trade windsblow westward in the tropics, and the westerliesblow eastward at mid-latitudes. This wind pattern applies a stress to the subtropical ocean surface with negative curl in the northern hemisphere and a positive curl in the southern hemisphere. The resulting Sverdrup transportis equatorward in both cases. That transport is balanced by a narrow, intense poleward current, which flows along the western boundary of the ocean basin, allowing the vorticityintroduced by coastal friction to balance the vorticity input of the wind. Western intensification also occurs in the polar gyres, where the sign of the wind stress curl and the direction of the resulting currents are reversed. It is because of western intensification that the currents on the western boundary of a basin (such as the Gulf Stream, a current on the western side of the Atlantic Ocean) are stronger than those on the eastern boundary (such as the California Current, on the eastern side of the Pacific Ocean). Western intensification was first explained by the American oceanographer Henry Stommel.
Notes, links and references
*Thurman, Harold V., Trujillo, Alan P. Introductory Oceanography Tenth Edition. ISBN 0-13-143888-3
*AMS glossary: amsglossary.allenpres.com
*Professor Raphael Kudela, UCSC, lectures OCEA1 Fall 2007
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