The role of a finite density jump at the bottom of the quasi-continuous ventilated thermocline

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 thermoclin e is fully ventilated, and its thickness vanishes at the northern boundary. In this model, the potential vorticity of each layer is shown to be invers ely proportional to the Bernoulli function. The hi,oh vertical resolution a dopted 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 densi ty step separating the thermocline bottom from the underlying quiescent aby ss. This ratio controls both the nonlinearity and the baroclinicity of the solution. The behavior of the solution as this ratio varies from zero (line ar and barotropic case) to infinity ("fully nonlinear" and baroclinic case) is described. The singularity that is found in the fully nonlinear case is discussed.