Western intensification

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Western intensification is the intensification of the western arm of an oceanic current, particularly a large gyre in an ocean basin, due to the Coriolis effect, and the variation of Coriolis force with latitude (the beta effect). It is for this reason 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). First explained by the American oceanographer Henry Stommel.

The cause is at least partially, if not mostly the difference in the Coriolis effect at different latitudes. Coriolis effect is stronger nearer the poles, so as the North Atlantic Current is driven east by the Westerly Winds, it wants to curve to the right, or South toward the center of the North Atlantic Gyre becoming the broad Canary Current. The Canary Current also wants to curve to the right toward the center of the gyre broadening the current even further. The North Equatorial Current heading west has the least influence from Coriolis effect and the water literally piles up along the western side of the basin (which can be seen by looking at a sea surface elevation satellite data picture). The Gulf Stream flows north out of this pile of water in a narrow intense current.