1. Met Office GPCI simulations Adrian Lock

2. © Crown copyright 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

3. © Crown copyright Recent Model Changes Forecast upgrade 15 th 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

4. © Crown copyright 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!]

5. © Crown copyright 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/m 2 ) Latent heat flux (W/m 2 )

6. © Crown copyright 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 0100

7. © Crown copyright 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 C F Cu

8. © Crown copyright 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

9. © Crown copyright Omega  Rise in cloud top not due to reduced subsidence  Ascent in ITCZ increases during forecast > climate

10. © Crown copyright 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

11. © Crown copyright 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

12. © Crown copyright Zonal winds  Forecast spins up easterlies in tropics  HadGAM1a has weaker easterlies than HadGAM1

13. © Crown copyright 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

14. Thanks! Questions?

15. © Crown copyright Tropical Temperature Errors vs Sondes Summer 2005

16. © Crown copyright Tropical R. Humidity Errors vs Sondes Summer 2005

17. © Crown copyright Tropical Wind Errors vs Sondes Summer 2005