The Role of a Finite Density Jump at the Bottom of the Quasi-Continuous Ventilated Thermocline

Abstract

The ocean thermocline is resolved in a very large number of layers by means of a recursive relation that extends the LPS model of the ventilated flow from a small to an arbitrary number of layers. In order to have simplified dynamics, the basin is semi-infinite in the zonal direction, the thermocline is fully ventilated, and its thickness vanishes at the northern boundary. In this model, the potential vorticity of each layer is shown to be inversely proportional to the Bernoulli function. The high vertical resolution adopted for the thermocline allows the study of the dependence of its motion on the ratio between the density contrast at the sea surface and the density step separating the thermocline bottom from the underlying quiescent abyss. This ratio controls both the nonlinearity and the baroclinicity of the solution. The behavior of the solution as this ratio varies from zero (linear and barotropic case) to infinity (?fully nonlinear? and baroclinic case) is described. The singularity that is found in the fully nonlinear case is discussed.