A51D-0084
Development of a unified turbulence scheme with a statistical cloud fraction scheme in Community Atmosphere Model
Friday, 18 December 2015
Poster Hall (Moscone South)
Yi Qin, Center for Earth System Science, Tsinghua University, Beijing, China, Yanluan Lin, Tsinghua Univ, Beijing, China and Bin Wang, IAP Insititute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Abstract:
Most GCMs have difficulty in the simulation of marine stratocumulus. Simulated stratocumulus coverage in Community Atmosphere Model version 5 (CAM5) is too small with an abrupt transition to shallow cumulus in the subtropical eastern ocean. To improve the simulation of the smooth transition between stratocumulus and shallow cumulus and reduce the inherent model bias, a unified boundary layer scheme, merging the moist turbulence scheme and shallow cumulus scheme of University of Washington, is proposed. The unified scheme separates the turbulent mass flux into a local transport part by the turbulent process and a nonlocal transport part by the shallow convection in the convective boundary layers. Specific criterion is used to achieve a smooth transition between stratocumulus and shallow cumulus. The new unified scheme with a statistical cloud fraction scheme is able to improve the marine stratocumulus cloud simulation in CAM5. The sub-grid variabilities caused by the convective and turbulent processes are considered in the cloud fraction scheme to improve the coupling process between cloud formation and convective and boundary layer mixing processes.
