Met Office GPCI simulationsAdrian Lock

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UK Met Office simulations in GPCI

HadGAM1 climate – for IPCC AR4 38 levels (~300m at 1km), N96 (~150km)

HadGAM1a climate – development version for AR5

Operational forecast ~ HadGAM1a but different! 38 levels, N216 (~70km) 5 day forecasts from ECMWF analyses (2003)

Dynamics and Physics ~same in both: Grid-point model: semi-implicit semi-lagrangian scheme PBL: K-profile+explicit entrainment; Ri scheme for SBL Massflux: Gregory-Rowntree + aspects of Grant & Brown for shallow Cloud: diagnostic RH scheme, Smith Radiation: Edwards-Slingo

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Recent Model ChangesForecast upgrade 15th March 2006

•In both forecast and HadGAM1a but NOT HadGAM1:•Convection

•Adaptive detrainment (A. Maidens, S. Derbyshire)

•Boundary Layer•Revised marine scalar surface exchange (J. Edwards)•Non-gradient stress (A. Brown)•Sharp tailed stability functions over Sea (R. Beare)

•Additional changes in HadGAM1a•Major overhaul of aerosols

•Differences between forecast and HadGAM1•cumulus cloud cover parametrization (esp. significant for shallow)•Interactive aerosols

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GPCI cross-section: problem

Problem with SSTs in the forecast model: Unable to use ECMWF SSTs Can’t use climate SSTs because those are for a 360 day calendar

Both these should become possible soon - rerun Can’t easily include Met Office operational SSTs My GPCI forecasts used a multi-year climatology

[I discovered afterwards!]

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GPCI cross-section: JJA cloud cover

Colder SSTs in forecast model imply reduced surface fluxes compared to the climate simulations

Spin-up in surface fluxes during forecast (as atmosphere cools down to new SST?)

Sen

sib

le h

eat

flux

(W/m

2)

Late

nt h

eat

flux

(W/m

2)

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GPCI cross-section: JJA cloud cover

Deep cumulus cloud-top falls during forecast, to ~ climate model level“Anvil” cloud cover increases during forecast to ~ HG1a amount < HG1 = Ad Detr

Mean field

Differences

0 100

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GPCI cross-section: JJA cloud cover

Stratocu cloud-top rises during forecast to reach ~ level in climate modelCloud cover increasesCloud cover excessive in 5 day forecast “transition region” – lack of GB CF

Cu

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GPCI cross-section: JJA cloud cover

Higher stratocu top associated with deepening BL during the forecastBL also becomes more well mixed:

•reduced near-surface RH•recall increase in surface fluxes

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Omega

Rise in cloud top not due to reduced subsidenceAscent in ITCZ increases during forecast > climate

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GPCI cross-section: JJA cloud amounts

•Reduced stratocumulus in HadGAM1a – reduced aerosol concentrations?•Cu cloud in forecast “transition region” gives large LWP by day 5

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Climate model TCA

Cross-section representivity? Some quantitative difference

between 5 and 1 year JJA HadGAM1a still loses some Sc Correctly reduced marine

aerosol gives excessive precipitation at low LWP

Precip needs retuning?

JJA 2003 JJA 5 years

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Zonal winds

Forecast spins up easterlies in tropics HadGAM1a has weaker easterlies than HadGAM1

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Summary

Deep convection doesn’t penetrate high enough (as high as ECMWF analysis)

Stratocumulus thickens up and rises from EC analysisAerosol change between climate model versions

highlights importance of drizzlePersistent problems with Met Office models in Sc-Cu

transition regions GB shallow cu cloud fraction parametrization helps Still tends to be too cloudy Further work on interaction between cumulus and inversion

Thanks!Questions?

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Tropical Temperature Errors vs SondesSummer 2005

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Tropical R. Humidity Errors vs SondesSummer 2005

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Tropical Wind Errors vs SondesSummer 2005