Simple, large-eddy, buoyancy flux model for cloudy boundary layers

In cloudy boundary layers the circulation structure, buoyancy flux profile, and cloud-top entrainment rate are strongly interdependent. This complicates attempts at formulating simple unified 1D models that will be valid for quite different layer dynamics (e.g., stratocumulus versus shallow cumulus). In this work we address these issues, summarizing results from a recent paper to appear in JAS (available on our website, http://eiger.mae.wvu.edu/cloud.html), and more recent extensions to that work. An approximate expression for the buoyancy flux is formulated solely in terms of the liquid potential temperature and total water profiles and their respective flux profiles. The predictions compare favorably with the results of an extensive set of large eddy simulations, including simulations of stratocumulus, shallow cumulus, and transitional behavior in between. This formulation is combined with previous results on the relation between cloud-top entrainment rate and circulation structure to predict the behavior of quasi-steady cumulus-coupled boundary layers as a function of a basic set of physical input parameters. These predictions also compare favorably with LES results. Efforts aimed at extending these results to a fully-coupled, unsteady 1D model are underway, and their current status will be discussed.