A NUMERICAL-MODEL OF THE CLOUD-TOPPED PLANETARY BOUNDARY-LAYER - RADIATION, TURBULENCE AND SPECTRAL MICROPHYSICS IN MARINE STRATUS

A numerical model of the cloud-topped planetary boundary-layer is pres ented. The model is one-dimensional with special emphasis on a detaile d description of cloud microphysical processes. Aerosols and cloud dro plets are treated in a two-dimensional particle-distribution whereby t he activation of aerosols is calculated explicitly by solving the drop let-growth equation at all relative humidities. Atmospheric radiation is determined with a S-two-stream radiation scheme. Turbulent fluxes a re parametrized as a function of the turbulent kinetic energy. Numeric al results are presented which are obtained by utilizing measurements made over the North Sea. The interaction between radiation, turbulence and cloud processes for maintaining the quasi-steady state of stratif orm cloud fields is emphasized.