The effects of the alongshore wind stress on the top-to-bottom front along the Southern Brazilian coast: a two-dimensional modelling approach

In this study a two-dimensional version of the Princeton Ocean Model is used to investigate the effects of both idealised upwelling and downwelling favourable winds on a top-to-bottom front along the Southern Brazilian coast. The thermohaline field implemented in the model is reconstructed from temperature and salinity data collected in the region in mid-May 1978. Both the salinity and density fields show a continuous stratification from the coast while there is a well-defined thermal front separating colder shelf waters from the warmer waters offshore. Upwelling favourable winds tend to deform the frontal structure horizontally along the boundary layers. The continuous density stratification inhibits large deformation in the bulk of the front as the vertical stratification increases on the bottom of the surface mixed layer and on top of the bottom boundary layer. Opposite winds tend to destroy completely the original S-shape. In this case, the convective mixing is significant and a vertical isopycnal field develops if the forcing is applied for a sufficiently long time. The cross-shore circulation, and hence the cross-frontal exchange of properties, is controlled by the generation of the boundary layers and its dependency on the vertical stratification and the characteristics of the bottom topography.