Improved Climate Simulations with Modified Convection Scheme: What’s Next?

Xiaoqing Wu (ISU) and Guang Jun Zhang (SIO)

Supported by DOE CCPP, ARM and NSF

Xiaoliang Song and Liping Deng (ISU)Xiaoliang Song and Liping Deng (ISU)

Guido Vettoretti and W.R. Peltier (UT)Guido Vettoretti and W.R. Peltier (UT)

Modified Zhang-McFarlane (ZM) Convection Scheme

• Revised convection closure assumption

Convection is tied to the destabilization of the tropospheric layer above PBL by the large-scale processes

• Trigger condition of deep convection

Convection is activated when the relative humidity is larger than certain threshold, or the increase of CAPE due to the large-scale processes exceeds certain threshold

• Convective momentum transport

Convection redistributes the horizontal momentum through the compensating subsidence, detrainment and perturbation pressure gradient

Detrainment of excess momentum from clouds

Subsidence of environmental air that compensates the cloud mass flux

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

x

p

z

uMuuF c

ccx

)(

y

p

z

vMvvF c

ccy

)(

Convective Momentum Transport (CMT)

Cloud-scale pressure

Cloud mass flux

Detrainment of mass

In-cloud momentum

Convective momentum tendency:, yx FF

:, cc vu::cM:cp

Fractional area of clouds:c

Convection-induced pressure gradient force

CAM3 Spectral CCSM3 (T31)

CCM3 Spectral CSM1.4 (T31)

CAM3.3 FV CCSM3.1

Atmospheric Models Fully Coupled Models

Double ITCZ problem

CSM1.4 with modified ZM

CCSM3 with modified ZM

Seasonal variation

CSM1.4 with modified ZM CCSM3 with modified ZM

Variability Diagnostics for 6-Hourly Data

CAM3.3 FV

Standard CAM3 CAM3 with revised closure and rh=0

CAM3 with revised closure and rh=0.8 CAM3 with modified ZM

Variability Diagnostics for 6-Hourly Data

CAM3.3 FV

isufvcam6

cam_fvz Histograms of daily precipitation rate

Standard CAM3 CAM3 with revised closure and rh=0

CAM3 with revised closure and rh=0.8 CAM3 with modified ZM

Histograms of daily precipitation rate

MJO

cam3_3_fv_1.9x2.5

isufvcam6

cam_fvz

NCEP

MJO

CCSM3 with modified ZM

Standard CCSM3

CCSM3.1 with modified ZM

b31.007 (years 79-98)

ENSO

b31.001 b31.006 b31.007

Standard CSM1.4 CSM1.4 with modified ZM

ENSO

Standard CCSM3 CCSM3 with modified ZM

ENSO