Stationary Shock Fronts in a Continuously Stratified Thermocline Model

Abstract

Fronts are ubiquitous in the ocean. Recent work by Dewar has considered the formation of oceanic fronts in a simple layered model. In this contribution, the position and structure of similar fronts within a coupled mixed layer-thermocline model are studied. A subtropical gyre is considered. The mixed layer is chosen to be warm and light along the southern boundary of this gyre but cooler and denser to the east and north. This contrast in mixed layer properties drives the formation of a front within the southern flank of the subtropical gyre. For the model dynamics require the mixed layer to be deeper where it is dense and shallower where it is less dense. The more rapid northward Ekman drift due to the concentration of the Ekman transport within the thinner mixed layer to the south tries to override the weaker drift associated with the thicker mixed layer to the north. There are sharp jumps in mixed layer thickness and isopycnal depths over this front. It also carries substantial transports. This front is of particular interest because it is a site of anomalously strong subduction driven by the buoyancy yielded up by the northward Ekman drift as it moves across the front into cooler, denser waters.