Equilibration and lateral spreading of a strip-shaped convective region

The authors investigate the spreading stage of the deep ocean convection fo r a strip-shaped convective region to study the law of spreading and sensit ivity of the eddy exchange efficiency parameter to the shape of the region and the background stratification. To simulate this convection process a tw o-layer quasigeostrophic model is used and the input of buoyancy due to sur face cooling is parameterized through creation of pairs of baroclinic point vortices with opposite signs of potential vorticity (hetons) at a constant rate. It is shown that the eddy exchange efficiency parameter for lateral fluxes of potential density out of the convective region is not universal b ut essentially depends on the shape of the region and the relative layer th icknesses. The horizontal spreading of the potential density anomaly shows a faster than diffusive, quasi-linear dependence on time at moderate values of the surface buoyancy flux. This behavior is due to the specific dynamic s of hetons and heton clusters.