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RICO single column model simulations

Benjamin Devenish

Met Office, UK

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Outline of talk

Summary of model

Sensitivity to vertical resolution

Sensitivity to cloud microphysics parameterisations

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Summary of model

Met Office GCM: Unified Model (UM)Turbulence mixing scheme

First-order closure Non-local/explicit entrainment (Lock 2001)

Cumulus parameterisation Based on Gregory and Rowntree (1990) mass flux

scheme and Grant and Brown (1999) Cloud fraction

Based on Smith (1990)Cloud microphysics

Autoconversion based on Tripoli and Cotton (1980) Assumed droplet number concentration

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RICO simulations

Mass fluxDetrainment begins at approximately 2000m

L38

Forced shallow convectionNo clear inversionAir parcel virtual potential temperature (dashed) vs ambient potential temperature (solid) adiabatic ascent

No mid-level convection

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Large-scale cloud fraction

L38 L80

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Convective cloud fraction

L38 L80

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Mass flux

L38 L80

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Surface fluxes

Sensible heat flux

Latent heat flux

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Total surface precipitation

Average precipitation L38: 1.34 mm/day L80: 1.17 mm/day

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Precipitation (ctd)

Large-scale precipitation

Convective precipitation

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Potential temperature

L38 L80

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Relative humidity

L38 L80

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Zonal wind

L38 L80

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Sensitivity to cloud microphysics

PC2 cloud scheme (UKMO)Prognostic cloud and prognostic condensate (PC2)Prognostic equations for vapour, liquid and ice

contents and liquid, ice and total cloud fractionsAssess impact of each physical and dynamical

process on clouds and condensate e.g. convection

KK autoconversion schemeBased on Khairoutdinov and Kogan (2000) Bulk microphysics parameterisationKessler-type parameterisation (liquid water

partitioned into cloud water and drizzle)

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Total surface precipitation: PC2 + KK

PC2 KK

PC2 + KKAll simulations L38

Average precipitation PC2: 1.68 mm/day

Average precipitation KK: 1.35 mm/day

Average precipitation PC2+KK: 1.47 mm/day

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Convective and large-scale precipitation

KK PC2 PC2 + KK

Conv.

LS

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Cloud cover

PC2

PC2 + KK

KK large-scale

KK convective

Large-scalecloud only

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Conclusions

Difficulty in diagnosing shallow convection

Fairly insensitive to model resolution

Sensitivity to cloud microphysicsPC2 scheme rains too much