A numerical model of the cloud‐topped planetary boundary‐layer: Radiation, turbulence and spectral microphysics in marine stratus

Abstract

Abstract A numerical model of the cloud‐topped planetary boundary‐layer is presented. The model is one‐dimensional with special emphasis on a detailed description of cloud microphysical processes. Aerosols and cloud droplets are treated in a two‐dimensional particle‐distribution whereby the activation of aerosols is calculated explicitly by solving the droplet‐growth equation at all relative humidities. Atmospheric radiation is determined with a δ‐two‐stream radiation scheme. Turbulent fluxes are parametrized as a function of the turbulent kinetic energy. Numerical 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 stratiform cloud fields is emphasized.