THE INFLUENCE OF LAYER OUTCROPPING ON THE SEPARATION OF BOUNDARY CURRENTS .1. THE WIND-DRIVEN EXPERIMENTS

The influence of outcropping isopycnal layers on the separation of wes tern boundary currents is investigated in a series of wind-driven eddy -resolving multilayer primitive equation numerical experiments. The ou tcropping mechanism of Parsons allows the midlatitude jet to separate south of the zero wind-stress curl line (ZWCL), an important property when one considers that most realistic numerical experiments to date e xhibit an over-shooting subtropical western boundary current. If the i nertial terms are removed from the momentum equations, the Sverdrup re lation for the interior flow emerges as the dominant constraint on the placement of the upper-layer jet separation latitude. As long as the upper/lower layer ratio is small enough, a good agreement is obtained with the analytical theory, namely a separation south of the ZWCL. If the ratio is large, the resulting flow pattern changes drastically by favoring a configuration that satisfies the Sverdrup relation and main tains a jet separation at the ZWCL. As soon as the inertial terms are included, the Sverdrup constraint becomes less dominant, allowing the upper-layer midlatitude jet separation latitude to shift southward whe never the upper layer is chosen sufficiently shallow to cause large-sc ale outcropping. The degree to which this southward shift depends on t he amount of mass in the top layer and on the parameterization of the wind-induced stress profile in the water column is explored in detail.