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© Crown copyright Met Office Cloudier Evaluating a new GCM prognostic cloud scheme using CRM data Cyril Morcrette, Reading University, 19 February 2008
© Crown copyright Met Office The need for a cloud scheme Clouds exists well before grid-box reaches 100% relative humidity. But clouds exists on scales much smaller than GCM grid boxes. Cant represent them explicitly. Need to parameterize them.
© Crown copyright Met Office Summary of moisture variables in our Cloud Scheme VariableCurrent schemePC2 q cl (Liquid Water Content) DiagnosticPrognostic q cf (Ice Water Content) Prognostic q t (Total water content) Prognosticq t =q cl +q cf C l (Liquid cloud fraction) DiagnosticPrognostic C f (Ice cloud fraction) DiagnosticPrognostic
© Crown copyright Met Office Fields from LEM simulation of TOGA-COARE (Tropical convection) Mean qcl in envMean qcf in env Liquid cloud fraction Ice cloud fraction Height (km) Time (hours) Height (km) 20 144 0.1 g/kg
© Crown copyright Met Office Tendencies from the LEM fields d (qcl) / dt d (qcf) / dt d (Cl) / dt d (Cf) / dt 0.36 / hr 0.036 g/kg/hr
© Crown copyright Met Office Increments from Convection Detrainment dx/dt=D(x plume -x env ) Detrainment Also consider: vertical transport by compensating subsidence evaporation following warming due to compensating subsidence. (These are small effects)
© Crown copyright Met Office Increments from Convection d (qcl) / dt d (Cl) / dt d (qcf) / dt d (Cf) / dt
© Crown copyright Met Office Microphysical effects on d(qcf)/dt Deposition Sublimation Autoconversion of ice crystals to snow Fall of ice 0.036 g/kg/hr
© Crown copyright Met Office Effects on d(qcf)/dt All microphysics Advection by compensating subsidence
© Crown copyright Met Office Effects on d(Cf)/dt Fall of ice Sublimation Advection by compensating subsidence
© Crown copyright Met Office Effects on d(qcl)/dt Adiabatic warming by compensating subsidence Advection by compensating subsidence Large-scale forcing Boundary-layer processes
© Crown copyright Met Office Effects on d(Cl)/dt Adiabatic warming by compensating subsidence Boundary-layer processes Large-scale forcing Advection by compensating subsidence
© Crown copyright Met Office Parameterized tendencies d (qcl) / dt d (qcf) / dt d (Cl) / dt d (Cf) / dt
© Crown copyright Met Office Comparing Tendencies d (qcl) / dt d (qcf) / dt d (Cl) / dt d (Cf) / dt Truth from LEM Parametrization
© Crown copyright Met Office Conclusions (work in progress) General methodology seems promising. Source from convective detrainment appears to be too high. (This may be due to way detrainment is calculated from LEM data) Future work Consider using a diagnostic cloud fraction for shallow convection which doesnt have large anvils.
© Crown copyright Met Office Questions and answers
© Crown copyright Met Office Extra figures Massflux
© Crown copyright 2006Page 1 CFMIP II sensitivity experiments Mark Webb (Met Office Hadley Centre) Johannes Quaas (MPI) Tomoo Ogura (NIES) With thanks.
Page 1© Crown copyright 2007 Initial tendencies of cloud regimes in the Met Office Unified Model Keith Williams and Malcolm Brooks Met Office, Hadley Centre.
© Crown copyright Met Office Towards understanding the mechanisms responsible for different cloud-climate responses in GCMs. Mark Webb, Adrian Lock (Met.
Page 1© Crown copyright 2007 Constraining the range of climate sensitivity through the diagnosis of cloud regimes Keith Williams 1 and George Tselioudis.
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GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey AM2 cloud sensitivity to details of convection and cloud.
Chapter 24 Water in the Atmosphere $200 $400 $600 $800 $1000 $200 $400 $600 $800 $1000 $200 $400 $600 $800 $1000 $200 $400 $600 $800 $1000 Category 1Category.
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