Entrainment and the fine structure of the stratocumulus cloud top

This work is to obtain a better understanding of cloud-top entrainment through an in-depth analysis of entrainment-zone structure. Using in situ aircraft measurements from Atlantic Stratocumulus Transition Experiment (ASTEX), the presence of an interfacial layer in-between the top of the cloud mixed-layer and the base of the free atmosphere is identified and consequently defined as the entrainment zone. The depth of the entrainment zone is on the order of tens of meters, where turbulence and sometimes cloud droplets are detectable. Inhomogeneous mixing was found to occur within the entrainment zone. Parcels of inversion-layer air and boundary-layer air are identified within the entrainment zone. Analyses suggest that turbulence intensity and cloud amount in the entrainment zone vary depending on the distribution of entrainment mixing fraction. Furthermore, continuous mixing in the entrainment zone appears to dissipate the upper-cloud layer. Implication of the findings in this study on the cloud evolution will be discussed.