1. THOR Annual Meeting - Bergen 9-11 November 2011 1/25 On the impact of initial conditions relative to external forcing on the skill of decadal predictions: preliminary results with the ECMWF coupled system Susanna Corti European Centre for Medium-Range Weather Forecasts With contributions from Magdalena Balmaseda, Per Kållberg, Linus Magnusson and Tim Palmer

2. THOR Annual Meeting - Bergen 9-11 November 2011 2/25

3. THOR Annual Meeting - Bergen 9-11 November 2011 3/25 (EXP1) Surface Temperature Anomaly Correlation Coefficients YR 2-5 12-month average

4. THOR Annual Meeting - Bergen 9-11 November 2011 4/25 (EXP1) Near Surface Temperature Anomaly Correlation Coefficients YR 2-5 12-month average- Linear Climate trend out

5. THOR Annual Meeting - Bergen 9-11 November 2011 5/25 (EXP1) Near Surface Temperature Anomaly Correlation Coefficients YR 2-5 12-month average Climate trend in Climate trend out Anom. Init. Flux Cor. Full Init. Flux Cor. Volc. in Full Init. Volc. in Full Init. Anom. Init. Flux Cor. Full Init. Volc. in Flux Cor. Volc. in

6. THOR Annual Meeting - Bergen 9-11 November 2011 6/25 (EXP1) Near Surface Temperature Anomaly Correlation Coefficients YR 6-9 12-month average Climate trend in Climate trend out Anom. Init. Flux Cor. Full Init. Flux Cor. Volc. in Full Init. Volc. in Full Init. Anom. Init. Flux Cor. Full Init. Volc. in Flux Cor. Volc. in

7. THOR Annual Meeting - Bergen 9-11 November 2011 7/25 (EXP2) Near Surface Temperature Anomaly Correlation Coefficient [Climate trend out] YR 2-5 12-month averageYR 6-9 12-month average Grand Ensemble of all (EXP1) experiments - 27 Ensemble members Near Surface Temperature Anomaly Correlation Coefficients [Climate trend out] YR 2-5 12-month averageYR 6-9 12-month average

8. THOR Annual Meeting - Bergen 9-11 November 2011 8/25 Grand Ensemble of all (EXP1) experiments - 27 Ensemble members YR 2-5 12-month average Cor=0.95, SPREAD/RMSE=0.63 YR 2-5 12-month average Cor=-0.01, Climate forcing out AMO index YR 2-5 12-month average Cor=0.78, SPREAD/RMSE=0.82 YR 2-5 12-month average Cor=0.9, Climate forcing out T2m

9. THOR Annual Meeting - Bergen 9-11 November 2011 9/25 10-year integrations with 5-member ensembles from: A 1965 initial conditions, observed forcing (GHG & aerosols) from 1965 (control1) B 1995 initial conditions, observed forcing (GHG & aerosols) from 1995 (control2) C 1965 initial conditions, observed forcing from 1995 D 1995 initial conditions, observed forcing from 1965 By comparing A with D, and B with C, we have two estimates of decadal predictability (arising from having different initial conditions and the same GHG forcing). By comparing A with C, and B with D, we have two estimates of the impact of GHG forcings (since initial conditions are the same). 1965-1995 Experiment

10. THOR Annual Meeting - Bergen 9-11 November 2011 10/25 1yr Running mean - Global SSTs FOR INI 1965-1975 1995-2005

11. THOR Annual Meeting - Bergen 9-11 November 2011 11/25 1yr Running mean - Indian Ocean SSTs INI FOR 1965-19751995-2005

12. THOR Annual Meeting - Bergen 9-11 November 2011 12/25 1yr Running mean - North Atlantic SSTs INI FOR 1965-1975 1995-2005

13. THOR Annual Meeting - Bergen 9-11 November 2011 13/25 ReanalysisControl SSTs: [1995-2005] - [1965-1975] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

14. THOR Annual Meeting - Bergen 9-11 November 2011 14/25 ReanalysisControl SSTs: [1995-1996] - [1965-1966] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

15. THOR Annual Meeting - Bergen 9-11 November 2011 15/25 ReanalysisControl SSTs: [1995-1997] - [1965-1967] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

16. THOR Annual Meeting - Bergen 9-11 November 2011 16/25 ReanalysisControl SSTs: [1995-1998] - [1965-1968] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

17. THOR Annual Meeting - Bergen 9-11 November 2011 17/25 ReanalysisControl SSTs: [1995-1999] - [1965-1969] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

18. THOR Annual Meeting - Bergen 9-11 November 2011 18/25 RianalysisControl SSTs: [1995-2000] - [1965-1970] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

19. THOR Annual Meeting - Bergen 9-11 November 2011 19/25 ReanalysisControl SSTs: [1995-2005] - [1965-1975] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

20. THOR Annual Meeting - Bergen 9-11 November 2011 20/25 ReanalysisControl SSTs: [1995-1996] - [1965-1966] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

21. THOR Annual Meeting - Bergen 9-11 November 2011 21/25 ReanalysisControl SSTs: [1995-1997] - [1965-1967] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

22. THOR Annual Meeting - Bergen 9-11 November 2011 22/25 ReanalysisControl SSTs: [1995-1998] - [1965-1968] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

23. THOR Annual Meeting - Bergen 9-11 November 2011 23/25 ReanalysisControl SSTs: [1995-1999] - [1965-1969] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

24. THOR Annual Meeting - Bergen 9-11 November 2011 24/25 ReanalysisControl SSTs: [1995-2000] - [1965-1970] Ctl95-FOR65 FOR95-Ctl65 Ctl95-INI65 INI95-Ctl65

25. THOR Annual Meeting - Bergen 9-11 November 2011 25/25 Summary The decadal prediction experiments show a positive forecast quality that can be statistically significant over several areas. When the linear climate trend is subtracted some regions (common to all the experiments carried out) of more pronounced predictability have been identified. Preliminary results of the 1965-1995 experiment indicate that over time scales longer than 5 years predictability arises mainly from the forcing. The correct initialisation has a strong impact up to about 1 year on a global domain, but it seems to affect the predictability over the North Atlantic up to 5 years.

26. THOR Annual Meeting - Bergen 9-11 November 2011 26/25 Reliability diagram Poor resolution Good resolution Reliability score (the smaller, the better) Resolution score (the bigger, the better) c c Size of red bullets represents number of forecasts in probability category (sharpness)

27. THOR Annual Meeting - Bergen 9-11 November 2011 27/25 Brier Skill Score & Reliability Diagram How to construct the area of positive skill? perfect reliability Observed Frequency Forecast Probability line of no skill area of skill (RES > REL) climatological frequency (line of no resolution)

28. THOR Annual Meeting - Bergen 9-11 November 2011 28/25 Grand Ensemble of all (EXP1) experiments - 27 Ensemble members Reliability diagrams - T2m - 2-5 yr T2m anomaly below the lower tercile - Global T2m anomaly above the upper tercile - Global

29. THOR Annual Meeting - Bergen 9-11 November 2011 29/25 Grand Ensemble of all (EXP1) experiments - 27 Ensemble members Reliability diagrams - T2m - 2-5 yr T2m anomaly below the lower tercile - Global T2m anomaly above the upper tercile - Global

30. THOR Annual Meeting - Bergen 9-11 November 2011 30/25 T2m anomaly below the lower tercile - Global Linear Climate trend out T2m anomaly above the upper tercile - Global Linear Climate trend out Grand Ensemble of all (EXP1) experiments - 27 Ensemble members Reliability diagrams - T2m - 2-5 yr

31. THOR Annual Meeting - Bergen 9-11 November 2011 31/25

32. THOR Annual Meeting - Bergen 9-11 November 2011 32/25

33. THOR Annual Meeting - Bergen 9-11 November 2011 33/25