Presentation on theme: "1 Evaluating climate model using observations of tropical radiation and water budgets Richard P. Allan, Mark A. Ringer Met Office, Hadley Centre for Climate."— Presentation transcript:
1 Evaluating climate model using observations of tropical radiation and water budgets Richard P. Allan, Mark A. Ringer Met Office, Hadley Centre for Climate Prediction and Research, U.K. Tony Slingo (ESSC, Reading University) 1) Are the unexpected observed changes in the tropical radiation budget real? 2) Using cloud forcing ratio to infer cloud properties 3) Radiance simulations within the climate model
2 Are the large observed decadal changes in the tropical radiation budget artefacts of the instrumentation? [ Wielicki et al. (2002) Science, 295, 841-844]
3 Total Channel Offset ERBS orbit drift Offset increase expected. 1993 Jump in offset due to power-off - also expected. Deep-space checks in calibration over 15 years suggest uncertainty < 0.5 Wm -2 Are the changes in semi-annual SW flux cycle artefacts of orbit? Yes. Combination of 36-day precession cycle AND drift in ERBS orbit:
4 Decadal variability still appears robust and significantly larger than climate models predict Updated seasonal flux changes Updated interannual time-series
5 Multi-spectral evaluation of simulated cloud properties (!) Ratio of cloud albedo effect to cloud greenhouse effect. Removes to first order dependence on cloud fraction Improves interpretation of cloud properties from radiation budget Sub-sample dynamic regime
6 Analysing cloud radiative effect in tropical convective regime (a) ERBS radiation + ERA40 vertical velocity + ISCCP cloud (f) New dynamics model (atmos) (h) New dynamics, coupled Not enough cloud cover, too bright?
8 Conclusions Unexpected changes in semi-annual cycle of top of atmosphere albedo is an artefact: combination of, –Drift in orbit of ERBS satellite –Mismatch between 72 day precession cycle and monthly means Still believe decadal variation in tropical radiation budget which climate models cannot reproduce Cloud forcing ratio and dynamic regime analysis - techniques to evaluate the climate model 20-year radiance simulations completed - how reliable is the Bates et al. HIRS data?