Convection Parameterization and Climate Simulation in the National Center for Atmospheric Research (NCAR) Community Climate System Model

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

Two deficiencies in the NCAR Community Climate System Model (CCSM) are believed to be related to the parameterization of convection in the model. The model is thus biased toward weak intraseasonal variability in the tropical atmosphere and excessive precipitation in the Arabian Peninsula, compared to observations. Because of the wide use of the CCSM, it is important to conduct research to address them. The goal of this research project is to address these issues by focusing on convective parameterization in the model. Specifically, the investigation aims to achieve the following fundamental scientific objectives: (i) Understand how convection interacts with the large-scale processes in different climate regimes; (ii) Incorporate observational data to improve convective parameterization in CCSM; (iii) Improve the simulated temporal variability of convection and the atmospheric state in CCSM; (iv) Determine the cause of the erroneous precipitation simulation over the Arabian Peninsula in CCSM and eliminate it. The basic research tools used in this work are the NCAR CCM3, which is the atmospheric component of CCSM, and the Zhang-McFarlane convection scheme, together with field observational data from different convection regimes in the tropics and midlatitudes. Simulations with improved convective parameterization will be analyzed using statistical and composite techniques to examine the improvement in the tropical intraseasonal variability. Systematic initial tendency error analysis will be applied to simulations from a series of carefully designed numerical experiments to understand the causes of large summer precipitation bias in the Arabian Peninsula in CCM3. The research should result in an improved convective parameterization, a better understanding of the role of convection and a better simulation in tropical climate and its variability in the NCAR CCM3. This research is important because it has potential to improve climate predictions and projections, which are of great value to world societies.