Numerical simulations of the baroclinic dynamics of density‐driven coupled fronts and eddies on a sloping bottom

Abstract

Numerical simulations of the baroclinic dynamics of density‐driven coupled fronts and eddies are described. The simulations are based on a two‐layer intermediate length scale model which filters out barotropic instability and focuses on the subinertial baroclinic evolution of density‐driven flows within the context of allowing finite‐amplitude height variations in the lower layer. The baroclinic destabilization of a bottom‐trapped coupled front on a sloping bottom is described. In the overlying fluid the instability takes the form of amplifying topographic Rossby waves. In the coupled front the perturbations to the downslope incropping are preferentially amplified compared to those on the upslope incropping. The perturbations to the downslope incropping develop into downslope propagating plumes which eventually evolve into relatively coherent along‐slope propagating domes. We discuss the propagation characteristics of these domes. We also simulate the evolution of density‐driven eddies or domes. The first eddy simulation we describe is for an initial eddy configuration which satisfies a zero topographic Rossby wave condition in the upper layer. We show that these traveling solutions remain remarkably coherent over a period of about 40 eddy circulation times or about 250 days for typical continental slope values. For a sufficiently large initial eddy height, upper layer fluid parcels can be transported in the along‐slope direction by the baroclinic eddy. We also simulate the evolution of an initial eddy configuration which does not satisfy a zero topographic Rossby wave condition in the upper layer. A relatively intense cyclonic circulation develops in the overlying fluid over the traveling dome as does a topographic Rossby wave tail. However, even these solutions remain surprisingly coherent over many eddy circulation times.