The link between western boundary currents and equatorial undercurrents

Abstract

A constant potential vorticity model is used to investigate the relation between the properties of an equatorward-directed western boundary current and the formation of the Equatorial Undercurrent (EUC) in the western equatorial oceans. It is shown that the value of the Bernoulli function at the equator, undetermined in earlier purely inertial EUC models, is fixed by the bifurcation latitude of the western boundary current that feeds the EUC. This is an additional example of the nonlocal forcing of the EUC by the subtropical gyre. The constant potential vorticity model yields reasonable values for the initial EUC core velocities for a bifurcation latitude on the order of 6 degrees from the equator. (A)