An observational study of stratocumulus entrainment and thermodynamics

Abstract

The rate of entrainment of air from the free troposphere into the cloud-topped planetary boundary layer is estimated using a technique based on measurement of ozone flux and mean distribution. The average measured value of entrainment velocity is 3.0 mm s-1 with a range of 1.0 to 5.0 mm s-1 for cloudy cases. Variation in the rate between cases is not well correlated with variations in buoyancy or moisture fluxes in the boundary layer. Thermodynamic budgets are constructed for eight cases. Divergence of the solar radiative flux is an important component of the boundary-layer energetics during midday. The net longwave (terrestrial) radiative flux profiles consistently show good agreement with theoretical models, but an unambiguous partitioning of the flux divergence between inversion and mixed layers could not be established. Examples of stratocumulus breakup and reformation are also examined. -from Authors