Climate Simulations Using the Community Atmosphere Model Coupled with a Multi-Variate PDF-Based Cloud Scheme

Abstract:

Supported by funding through a Climate Process Team (CPT), we have implemented a multi-variate probability density function (PDF) cloud and turbulence scheme into NCAR’s Community Atmosphere Model (CAM). The parameterization is known as Cloud Layers Unified by Bi-normals (CLUBB) and is an incomplete third-order turbulence closure centered around a double-Gaussian assumed PDF. CLUBB replaces the existing planetary boundary layer, shallow convection, and cloud macrophysics schemes in CAM with a unified parameterization that drives one double moment microphysics scheme.

This presentation documents the performance of CAM-CLUBB for both prescribed sea surface temeprature (SST) and coupled simulations. We will discuss the improved mean state climate, such as improved stratocumulus to cumulus transitions, that can result when compared to CAM5. In addition, CAM-CLUBB is able to improve many long-standing issues that many general circulation models (GCMs) struggle to realistically simulate; such as the Madden-Julian Oscillation (MJO), diurnal cycle of precipitation, and the frequency and intensity of precipitation. We will also discuss preliminary work being done to use CLUBB as a deep convection scheme in CAM.