Turbulent Structure of a Shear-Driven Stratus-Topped Atmospheric Boundary Layer: A Comparison of Model Results with Observations

Abstract

An observational study of the cloud-topped atmospheric boundary layer (ABL) during a strong gale reveals that the turbulent boundary layer was dominated by shear instead of convection. A one-dimensional ensemble-averaged model is used to study this type of cloud-topped ABL. Turbulence closure is formulated by using an equation for both the turbulent kinetic energy and the viscous dissipation. The radiation model consists of an emissivity model for the longwave radiation and a two-stream model for the shortwave radiation. Both model results and observations indicate that the longwave radiative cooling at cloud top is mainly balanced by entrainment of warm air from above the inversion. A parameterization for the rainfall is included and the effect of this on the liquid water content is studied.