Equatorial undercurrent

From Glossary of Meteorology

Equatorial Undercurrent

(Abbreviated EUC.) A subsurface current flowing eastward along the equator.

A narrow, swift-flowing ribbon with a thickness of 200 m and a width of at most 400 km, it displays the largest current speeds of the equatorial current system. In the Pacific, where it is also known as the Cromwell Current, it flows with a speed of 1.5 m s-1 at a depth of 200 m in the west, rising to a depth of 40 m in the east. In the Atlantic its core is at a depth of 100 m and its speed exceeds 1.2 m s-1. In the Indian Ocean it exists as a flow ribbon centered on a depth of 200 m during the northeast monsoon season (December–April); during the remainder of the year this flow gets incorporated into the eastward flowing southwest monsoon current. In all oceans the EUC swings back and forth between two extreme positions 90–150 km either side of the equator with a two- to three-week period.