A multiple mixed layer model of the cloud-topped boundary layer is developed to investigate the diurnal variation of stratocumulus. A simple representation of the microphysical properties of the cloud layer is included which enables high resolution, interactive radiation calculations to be made. A constraint on the buoyancy flux profile is introduced which permits the previously well-mixed layer to separate into two independently driven layers, thereby avoiding many of the unrealistic aspects of single-layer models and enabling the model to reproduce features seen in observational studies. the diagnosis of this decoupling, which generally occurs during the morning, is discussed and is shown to have a seasonal and latitudinal sensitivity due to its dependence on cloud layer short-wave absorption. Comparisons of results with those obtained when separation is not permitted show significant differences. In particular, the cloud layer displays a much enhanced diurnal variation in thickness when separation is allowed, with the minimum occurring in the afternoon. These results are shown to produce much better agreement with observations. the likely consequences of separation for boundary layer evolution are discussed. the surface energy balance can be quite strongly affected, suggesting that it is important to resolve this diurnal variation, especially in areas where stratocumulus is a dominant climatological feature. The sensitivity of the results to model assumptions are investigated and the limitations of the model are also assessed.
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TURTON et al. (1987) studied this question.