A Model for Entrainment into a Cloud-Topped Marine Boundary Layer. Pad II: Discussion of Model Behavior and Comparison with Other Models

Abstract

The model for the cloud-topped marine boundary layer presented by Stage and Businger (1981) is discussed and compared with previous models. Our model gives a considerably different interpretation of the energetics of the layer and indicates that a much higher fraction (20%) of the layer turbulence kinetic energy production is available to drive entrainment than previously supposed. In a test case, the Lilly (1968) minimum entrainment model gives entrainment rates similar to ours; however, this model is based on physically unrealistic assumptions about layer energetics. It is noted that two soundings from the International Field Year for the Great Lakes (IFYGL) exhibit behavior not allowed by Deardorff?s (1976) model. In these cases our model gives a good fit to the data and Deardorff?s model predicted a boundary layer much deeper than observed. The depth of the layer of radiative cooling at cloud top is shown to be important only if it is a significant fraction of the mixed-layer depth zB. Layer energetics are shown to prevent the cloud-top entrainment instability condition from causing much difference in theentrainment rate