Wind Forcing and the Zonal Structure of the Equatorial Undercurrent

Abstract

A recently developed nonlinear inviscid model of the equatorial undercurrent is coupled to a wind-driven surface layer. Wind stress drives a poleward Ekman flow, causing equatorial divergence of surface layer transport. This divergence is balanced by upwelling of fluid. In this manner, the imposed wind stress controls the zonal structure of the undercurrent transport. The meridional structure of the undercurrent is determined from the undercurrent transport, the thermocline structure outside the undercurrent, and conservation of potential vorticity and Bernoulli function by the inviscid undercurrent. Westward wind stress increasing linearly westward, eastward transport increases nearly linearly westward. For westward wind stress with a midbasin maximum, eastward transport has a maximum just west of the basin middle, and there is recirculation along t...