Further Improvement to the Convection Scheme in CCSMFurther Improvement to the Convection Scheme in CCSM

Xiaoliang Song, Liping Deng, Sunwook Park and Ray Arritt Xiaoliang Song, Liping Deng, Sunwook Park and Ray Arritt (ISU) (ISU) Guang Jun ZhangGuang Jun Zhang ( (Scripps Institution of Oceanography)Scripps Institution of Oceanography)Guido Vettoretti and Richard Peltier (University of Toronto)Guido Vettoretti and Richard Peltier (University of Toronto)

Xiaoqing WuXiaoqing Wu

Department of Geological and Atmospheric SciencesDepartment of Geological and Atmospheric SciencesIowa State UniversityIowa State University

Partly by DOE CCPP and ARM

1. The tropical biases

2. Improvement to convection and cloud schemes

3. Effects on global climate simulations

Convection

Radiation

Clouds

1. The tropical biases

Seasonal variation of precipitation

Madden-Julian Oscillation (MJO)

Double ITCZ problem in Coupled Models

2. Improvement to convection and cloud schemes

Revised ZM Closure assumption Quasi-equilibrium between convection and large-scale forcing

Zhang (2002, 2003 JGR)

Conv

LSb CAPE

CAPEm

ECAP CAPELS

Conv

LS: Large-scale advection and radiative heating/cooling

Conv: Convective processes

Non-squall cluster Squall cluster Scattered convection

Wu and Moncrieff (1996)

Cloud-Resolving Model (CRM) simulations

Activation of deep convection

In-cloud water concentration derived from the CRM simulation (solid) compares with that used by the standard CCM3 (dashed). Circles are normalized CRM cloud (liquid and ice) water paths.

Wu and Liang (2005, GRL)

Convective Momentum Transport (CMT)

Zhang and Cho (1991, JAS)Wu and Yanai (1994, JAS)Wu, Zhang and Liang (2003, GRL)

xp

zuMuuF c

ccx

)(

yp

zvMvvF c

ccy

)(

Cloud-scale pressure

Cloud mass fluxDetrainment of mass

In-cloud momentum

Convective momentum tendency:, yx FF:, cc vu

::cM

:cp

Fractional area of clouds:c

3. Effects on global climate simulations

Coupled GCM simulations

SummarSummaryy

• Statistical analysis of CRM simulations together with Statistical analysis of CRM simulations together with the theoretical consideration of subgrid-scale the theoretical consideration of subgrid-scale processes offer a unique opportunity to reduce the processes offer a unique opportunity to reduce the uncertainties, especially tropical biases, in the climate uncertainties, especially tropical biases, in the climate simulations.simulations.

• The seasonal variation and global distribution of The seasonal variation and global distribution of precipitation and the MJO simulation are improved precipitation and the MJO simulation are improved and closer to observations. and closer to observations.

• Preliminary coupled simulations show strong effects Preliminary coupled simulations show strong effects of the modified convection and cloud schemes on the of the modified convection and cloud schemes on the double ITCZ problem. double ITCZ problem.