The Circulation Dynamics and Thermodynamics of Upper Ocean Density Fronts

Abstract

This paper extends a previous hydrodynamic circulation model of established,persistent upper ocean density fronts by including a thermodynamicor buoyancy equation in the intergral treatment. An analysis is alsoconducted of the variables related to the kinetic and potential energybudgets in the frontal zone. A comparison of the new results withprevious ones shows satisfactory agreement. The new model is usedto explore three frontal types of widely different scale or rotationeffect, a river plume front, a Sargasso Sea front and the Gulf Streamfront. As the scale increases, the influence of rotation increasesand the effect of interfacial turbulent transport diminishes. Also,with increasing scale the strength of the down-stream (alongfront)flow increases while the cross-stream flow diminishes, but alwaysshows a two-sided convergence near the surface front. The kineticenergy dissipation decreases rapidly with dissipation times of residentkinetic energy increasing from ten minutes for the river plume frontto a week for the Gulf Stream front. The model results indicate thatthe direction of turbulent mass entrainment is always downward, thatfronts always spread, even if slowly, relative to the ambient fluid,and that the cross-stream flow near the surface front always showsa tow-sided convergence