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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
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
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