Testing alternative formulations of the double-Gaussian PDF closure in CLUBB
Authors
Heng Xiao — Pacific Northwest National Laboratory
Mikhail Ovchinnikov — Pacific Northwest National Laboratory
Category
Warm low clouds, including aerosol interactions
Description
In the Cloud Layers Unified By Binormals (CLUBB) parameterization, in addition to the assumption of a double-Gaussian joint probability density function (PDF) for subgrid-scale variability, several other assumptions are made about the PDF shape for simplification and for better constraints on the parameterized higher moments. In this study, we develop and test alternative formulations of these additional assumptions. Our goal is (1) to remove the unrealistic assumptions of equal in-plume vertical velocity variances and of zero in-plume vertical fluxes of temperature and moisture and (2) to better constraint several higher-order terms, e.g., the third moment of vertical velocity and the “flux of flux” terms. The impact of these alternative formulations is tested first by feeding “perfect” statistical moments calculated from large¬-eddy simulations into the PDF closure scheme and then in a single-column model for DYCOMS, BOMEX and LBA cases.
