Evaluating the CLUBB PDF closure for shallow convection

Abstract:

Assumed-probability density function (PDF) higher-order turbulence closures (APHOCs) like the Cloud Layers Unified By Bi-normals (CLUBB) have been implemented in global atmospheric models as the parameterization for boundary layer turbulence and shallow convection. In this study, we evaluate in detail the performance of the PDF closure used in CLUBB for both quasi-steady marine shallow convection (BOMEX) and shallow convection periods of continental diurnal convection cases over Southern Great Plains in the U.S. (ARM97) and over Amazon (LBA). The evaluation looks at the behavior of the PDF closure in an offline mode with input supplied by statistics from large-eddy simulations (LESs) as well as in a single-column model (SCM) to quantify the deficiencies related to the PDF closure with and without interactions with other parameterized processes of CLUBB. We mainly focus on the biases of parameterized moisture and temperature skewnesses and related cloud property biases near shallow cloud base and top and their manifestation in different shallow convection regimes.