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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.

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Presentation on theme: "© Crown copyright Met Office Cloudier Evaluating a new GCM prognostic cloud scheme using CRM data Cyril Morcrette, Reading University, 19 February 2008."— Presentation transcript:

1 © Crown copyright Met Office Cloudier Evaluating a new GCM prognostic cloud scheme using CRM data Cyril Morcrette, Reading University, 19 February 2008

2 © 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.

3 © 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

4 © 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) g/kg

5 © Crown copyright Met Office Tendencies from the LEM fields d (qcl) / dt d (qcf) / dt d (Cl) / dt d (Cf) / dt 0.36 / hr g/kg/hr

6 © 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)

7 © Crown copyright Met Office Increments from Convection d (qcl) / dt d (Cl) / dt d (qcf) / dt d (Cf) / dt

8 © Crown copyright Met Office Microphysical effects on d(qcf)/dt Deposition Sublimation Autoconversion of ice crystals to snow Fall of ice g/kg/hr

9 © Crown copyright Met Office Effects on d(qcf)/dt All microphysics Advection by compensating subsidence

10 © Crown copyright Met Office Effects on d(Cf)/dt Fall of ice Sublimation Advection by compensating subsidence

11 © Crown copyright Met Office Effects on d(qcl)/dt Adiabatic warming by compensating subsidence Advection by compensating subsidence Large-scale forcing Boundary-layer processes

12 © Crown copyright Met Office Effects on d(Cl)/dt Adiabatic warming by compensating subsidence Boundary-layer processes Large-scale forcing Advection by compensating subsidence

13 © Crown copyright Met Office Parameterized tendencies d (qcl) / dt d (qcf) / dt d (Cl) / dt d (Cf) / dt

14 © Crown copyright Met Office Comparing Tendencies d (qcl) / dt d (qcf) / dt d (Cl) / dt d (Cf) / dt Truth from LEM Parametrization

15 © 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.

16 © Crown copyright Met Office Questions and answers

17 © Crown copyright Met Office Extra figures Massflux


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