In recent years many LES studies have been performed to investigate the entrainment process in Stratocumulus (Sc) clouds (e.g. Lock and MacVean, Lewellen and Lewellen, vanZanten et al, all in press). Despite this effort a unified entrainment parametrization applicable to both clear and cloudy boundary layers is still not available. The main difficulty is the complex interaction of different processes in these clouds; i.e. the simultanous occurence of radiative and surface-based forcing, condensation and evaporation. To tackle the effect of radiation a so-called smoke boundary layer has been studied extensively; this cloud is radiatively active but doesn't have any phase changing effects.
As a next step we are currently studying entrainment in a layer in which the Sc cloud extends down to the surface. We call this a Stratocumulus-fog layer: Scf. The advantage of such a cloud is that evaporational and condensational effects are taken into account but that the complexity of the two layer structure of Sc clouds (i.e. cloud and subcloud layer) is eliminated. Preliminary results show that Scf cloud show similar behaviour as the smoke boundary layer in that the entrainment flux tends to be a certain fraction of the forcing. The forcing being either at the bottom (surface fluxes) or at the top (radiative cooling) of the boundary layer