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Adrian Lock. Met Office GPCI simulations. 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)
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Adrian Lock Met Office GPCI simulations
UK Met Office simulations in GPCI • HadGAM1 climate – forIPCCAR4 • 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
Recent Model Changes Forecast 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
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!]
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?) Sensible heat flux (W/m2) Latent heat flux (W/m2)
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 0 100 Differences
GPCI cross-section: JJA cloud cover Stratocu cloud-top rises during forecast to reach ~ level in climate model Cloud cover increases Cloud cover excessive in 5 day forecast “transition region” – lack of GB CFCu
GPCI cross-section: JJA cloud cover • Higher stratocu top associated with deepening BL during the forecast • BL also becomes more well mixed: • reduced near-surface RH • recall increase in surface fluxes
Omega • Rise in cloud top not due to reduced subsidence • Ascent in ITCZ increases during forecast > climate
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
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
Zonal winds • Forecast spins up easterlies in tropics • HadGAM1a has weaker easterlies than HadGAM1
Summary • Deep convection doesn’t penetrate high enough (as high as ECMWF analysis) • Stratocumulus thickens up and rises from EC analysis • Aerosol change between climate model versions highlights importance of drizzle • Persistent 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
Questions? Thanks!