Further Improvement to the Convection Scheme in CCSM

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Further Improvement to the Convection Scheme in
CCSM
Xiaoqing Wu
Department of Geological and Atmospheric Sciences
Iowa State University

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

Partly by DOE CCPP and ARM
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• The tropical biases
• Improvement to convection and cloud schemes
• 3. Effects on global climate simulations

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1. The tropical biases
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Seasonal variation of precipitation
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Madden-Julian Oscillation (MJO)
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Double ITCZ problem in Coupled Models
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2. Improvement to convection and cloud schemes
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Revised ZM Closure assumption Quasi-equilibrium
between convection and large-scale forcing
LS Large-scale advection and radiative
heating/cooling
Conv Convective processes
Zhang (2002, 2003 JGR)
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Cloud-Resolving Model (CRM) simulations
Non-squall cluster
Squall cluster
Scattered convection
Wu and Moncrieff (1996)
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Activation of deep convection
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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)
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Convective Momentum Transport (CMT)
Convective momentum tendency
In-cloud momentum
Detrainment of mass
Cloud mass flux
Cloud-scale pressure
Fractional area of clouds
Zhang and Cho (1991, JAS) Wu and Yanai (1994,
JAS) Wu, Zhang and Liang (2003, GRL)
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3. Effects on global climate simulations
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Coupled GCM simulations
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Summary

• Statistical analysis of CRM simulations together
  with the theoretical consideration of
  subgrid-scale processes offer a unique
  opportunity to reduce the uncertainties,
  especially tropical biases, in the climate
  simulations.
• The seasonal variation and global distribution of
  precipitation and the MJO simulation are improved
  and closer to observations.
• Preliminary coupled simulations show strong
  effects of the modified convection and cloud
  schemes on the double ITCZ problem.