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Validation of a mixed‐layer closure. II: Observational tests
Author(s) -
Lilly Douglas K.
Publication year - 2008
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.183
Subject(s) - entrainment (biomusicology) , environmental science , drizzle , atmospheric sciences , parametrization (atmospheric modeling) , cloud base , meteorology , cloud top , mixed layer , climatology , radiative transfer , precipitation , cloud computing , geology , physics , computer science , quantum mechanics , rhythm , acoustics , operating system
Data from the DYCOMS2 observational campaign are used to test a mixed‐layer entrainment model presented previously by the author. The model is extended to include the effects of drizzle precipitation and radiative warming from the surface. The most consistent results are obtained under the assumption that the mixed‐layer top is unsaturated, that is, the cloud top is below the top of the turbulent flow. With this assumption, the predicted entrainment rates lie near those obtained by Faloona et al. , and are well correlated with them, but are sensitive to the evaluation of temperature and moisture jumps and other parameters. The predicted entrainment rates are substantially smaller than those observed by Gerber et al. , and are not correlated with them. Drizzle precipitation, as evaluated by VanZanten et al. , reduces entrainment rates due to evaporative cooling below cloud base. This effect appears to improve the comparisons with observations. Tests of the robustness of the model calculations show mostly encouraging results. The effect of surface radiation into cloud base is found to be almost negligible. A new criterion for cloud‐top entrainment instability, based on the entrainment closure, indicates stability for most observed conditions. The homogeneity of the DYCOMS2 data is beneficial for obtaining reliable measures of entrainment, but limits the ability to test closure predictions over a wide range of conditions. Use of this model for parametrization of marine stratiform cloud layers in large‐scale or climate prediction models is considered plausible with limitations. Copyright © 2008 Royal Meteorological Society