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

P.Lionello, Univ. of Padua, Dep. of Physics
and J.Pedlosky, WoodsHole Oceanographic Institution

The ocean thermocline is resolved in a very large number of layers by means of  a recursive relation which extends the LPS model of the ventilated flow from 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, denoted as a in the paper, 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.

Schematic of the layer model: meridional section of the gyre

Meridional of the stratification in the ventilatted thermocline. The lowermost dashed line is the bottom of the thermocline. The thick line shows the top of the deepest moving layer.  Top-left: linear case, a=0. Top-right: a=10. Bottom-left: a=1000. Bottom-right a=100000. (The parameter a is inversely proportional to the density step at the bottom of the thermocline)