The Equatorial Undercurrent in the Light of the Vorticity Equation

The Equatorial Undercurrent, recently observed in the central Pacific Ocean by Cromwell, Montgomery, and Stroup, is a narrow eastward current occupying the lower part of the surface layer at the equator. In the present study the Undercurrent, treated as a permanent feature of the oceanic circulation, is found to be consistent with the conservation of absolute cyclonic vorticity in the equatorward flow comprising one segment of the meridional circulation. The continental barriers permit the formation of the longitudinal pressure-gradient component essential for the existence of the Undercurrent.