Open Collections

Abstract

The circulation and cross-shelf exchanges in a coastal ocean are studied using a primitive equation, non-linear, two-layer model with irregular bathymetry. Tracer advection is evaluated with the Tremback-Bott transport scheme and a post-treatment of the transport fluxes to achieve monotonicity. During upwelling events, alongshore variability of the topography, which here is mostly confined over the shelf-edge, is shown to have a first order effect on the circulation. The topography generates a countercurrent force on the deep flow. This effect is not reproduced by two-dimensional models. Enhanced cross-shelf mixing of passive scalar is also found at the shelf-edge. Rough shelf-breaks can be expected to generate more cross-shelf exchange of passive properties than smooth topographies during upwelling events. A stochastic wind stress forcing is applied to a barotropic version of the model in order to study the statistical equilibrium of the coastal ocean. The fundamental distinction between potential vorticity and passive scalar behavior in a vigorous eddy field is demonstrated. The cross-shelf gradient of eddy kinetic energy generates a strong upgradient pumping of potential vorticity over the shelf. Two mean alongshore jets are then observed. A poleward jet-arises at the shelf-break as predicted by the maximum entropy theory while an equatorward jet balances the momentum budget over the shelf. The passive scalar eddy-diffusivity exhibits large spatial variability. It is found to be qualitatively related to the eddy kinetic energy and the cross-shelf gradient of potential vorticity. It is shown that scalar concentration fronts naturally tend to form at the shelfedge. Small scale topography also locally enhances the cross-shelf passive scalar exchange by introducing some additional eddy kinetic energy into the velocity field.