Evaluation of the Surface Radiation Budget in HadGEM1

1. Evaluation of the Surface Radiation Budget in HadGEM1 A. Bodas-Salcedo, M. A. Ringer, A. Jones Hadley Centre, Met Office, UK RADAGAST meeting. Reading, ESSC, 19-20 July 2007

2. Contents • Introduction • Motivation • Model and data • Climatology • Seasonal cycles: global and hemipheric • Energy distribution and cloud effects • Regional means • Comparison against ground measurements • Tropical interannual variability • Land-surface albedo • Global dimming • Conclusions

3. Impact on atmosphere and ocean • The vertical distribution and overlap of cloud layers determine the magnitude and vertical profile of radiative heating => influence in the large-scale circulation. • By modulating the distribution of heating between the atmosphere and the surface, clouds influence the circulation of the oceans. (Gleckler, GRL, 2005)

4. Model and observations • MODEL • HadGAM1 (Atmosphere-only) • 1.875o lon x 1.25o lat • 38 atmospheric levels • 20 years: 1981 - 2000 • Monthly means • 5-member ensemble • ISCCP-FD • Satellite-derived SRB • 2.5ox2.5o approximately equal-area grid • 20 years: 1984 - 2003 • Monthly means • BSRN • Downwelling fluxes from 28 ground stations • ~1800 monthly means • MODIS • Land-surface white-sky albedo • 16-day 0.05 degree albedo product (MOD43C1) • MODIS spatially complete albedo • 2-yr 16-day averages

5. Seasonal cycle (60oS – 60oN) 201.9 210.2 361.1 355.7 9.2 11.2 413.6 418.6

6. Seasonal cycle (Hemispheric)

7. Net fluxes and CRF SW Solid lines: ISCCP-FD LW NET NET SW LW SW NET SW NET LW LW SW LW NET NET SW LW

8. SW fluxes

9. LW downward flux

10. BSRN stations Climate classification based on Trewartha and Horn (1980)

11. HadGAM1 vs BSRN – Scatter plots LW SW

12. HadGAM1 vs BSRN

13. BSRN HadGAM1 ISCCP HadGAM1 vs BSRN – Seasonal cycles SW LW

14. Interannual variability ISCCP SWdn ISCCP LWdn HadGAM1 SWdn HadGAM1 LWdn

15. Surface albedo HadGAM1 MOD43C1 HadGAM1 Minus MODIS January July

16. Surface albedo – Europe (January) HadGAM1 Snow amount HadGAM1 HadGAM1 minus MOD43C1 MOD43C1 HadGAM1 minus MODIS-SC MODIS-SC

17. Surface albedo – Seasonal cycle

18. Global dimming

19. Conclusions • HadGAM1 simulates reasonably well present day SRB (and the distribution of energy at TOA, ATM and SFC), although notable differences appear at regional level. • The biggest differences are found in the Northern Hemisphere. • The simulation of LWdn is closer to observations than that of SWdn. • SWdn: • Overestimation over land masses (ISCCP and BSRN). Bias (StDv): 17.2 (28.6) W m-2. • Very good agreement over polar regions. • LWdn: • HadGAM1 tends to underestimate LWDN. Bias (StDv): -6.0 (19.6) W m-2. • Underestimation less consistent than overestimation in SWdn. • No significant dependence with latitude, which seemed to be common in previous models. • Good representation of the response to El Niño events. • Land-surface albedo vs MODIS: • +ve bias in January over NH landmasses when compared with. • +ve bias over deserts in South Africa, Australia and South America. • Lack of structure over the Sahara and Arabian Peninsula. • Concerns on the amplitude and phase of the seasonal cycle. • Need for comprehensive intercomparison of datasets. • Model in line with studies that suggest that ‘global dimming’ is far from being a uniform phenomenon across the globe.

20. Thanks!

21. BSRN stations