The Sensitivity of Surface Energy Balance to Convective Parameterization in a General Circulation Model

Abstract

This study investigates the interaction between convection and the surface energy fluxes, and its sensitivity to convective parameterization schemes using a general circulation model. Two simulations of the global circulation averaged annually from 1 June 1985 to 31 May 1986 are performed, with particular emphasis on the tropical Pacific. In the control simulation, a convective scheme that parameterizes convection based on low-level moisture convergence is used. A second experiment employs a parameterization scheme that uses the time rate of change of convective available potential energy (CAPE) to determine convection. When the low-level moisture convergence is used as the closure for convective parameterization, convection and low-level convergence occur near the landmass of Southeast Asia. The large-scale circulation is such that a fairly strong surface wind that provides moisture to fuel convection is located in the western tropical Pacific warm pool regions, giving rise to relatively high latent heat flux there. When the time rate of change of CAPE is used to close convective parameterization, convection and its associated low-level large-scale convergence and weak surface, wind speed occur in the warm pool region, resulting in low latent heat flux there. Response of surface solar radiative flux to convection is found to be the largest in the surface energy budget. Convection affects surface radiation through the generation of clouds. In the experiment, more clouds are produced over the tropical oceans, leading to less solar radiation received on the surface. More clouds in the experiment also load to less net emission of longwave radiation from the ocean surface due to the cloud green-house effect albeit the magnitude is much smaller than that for solar radiation. The large changes in surface latent heat and solar radiative fluxes from the control run to the experiment suggest that the surface energy balance in the atmospheric general circulation model is highly sensitive to convective parameterization.