Improved Climate Simulation by Using a Double‐Plume Convection Scheme in a Global Model

Abstract

AbstractConvective parameterization can drastically regulate the mean climate and tropical transient activity of a General circulation model (GCM). In this study, the physics suite of the NCAR Community Atmosphere Model, version 5 (CAM5) was first ported to the Global‐to‐Regional Integrated Forecast System model. Then, the original convective parameterization of CAM5—with a separate representation of deep convection Zhang–Mcfarlane (ZM) and shallow convection University of Washington (UW)—was replaced by a double‐plume (DP) scheme. This DP scheme adopts a quasi‐unified representation of shallow and deep convection within a single framework. Results demonstrate that the new scheme brings about several improvements in the modeled climate. The differences in the trigger and closure assumptions, lateral mixing rate, and cloud model for the deep convection result in systematic regional differences in the simulated precipitation pattern, cloud vertical structure, and the associated radiative forcing. Compared with ZM‐UW, DP reduces the biases in precipitation over the Indian Ocean, ameliorates the “high‐frequency and low‐intensity” problem of tropical precipitation, and leads to an improved representation of tropical variability, including the Madden–Julian Oscillation. Double‐plume reduces low clouds and increases high clouds in the tropics, due to its internal parallel‐split convective processes and smaller cumulus cloud fraction. Discussions related to parametric tuning of convective parameterization are also presented.