1. © Crown copyright Met Office Improving seasonal forecasting: role of teleconnections Madrid. Febrero 2009. Alberto Arribas

2. © Crown copyright Met Office The new Met Office Seasonal Forecasting System: GloSea4 Huge team effort! Expected to become operational in April 2009 Main drivers: Adaptation to climate change: Seasonal-to-Decadal system Bridge NWP-CR: Facilitate model development …. And improved seasonal forecasts!

3. © Crown copyright Met Office The new Met Office Seasonal Forecasting System: GloSea4 GloSea4 is not a model GloSea4 is an ensemble prediction system (build around our latest model: HadGEM3) Initialization (+ uncertainties) Model Model uncertainties Post-processing (eg. Calibration) Probabilistic Forecast

4. © Crown copyright Met Office Outline … or, why are we changing? GloSea4: the new Ensemble Prediction System HadGEM3: the new model (improving teleconnections)

5. © Crown copyright Met Office Skill of seasonal forecasts

6. © Crown copyright Met Office Scope for improvement Perfect model skill – ECMWF model Potential skill – Atlantic SST, climate Change, El Nino and volcanoes Greenhouse gases are missing (Doblas et al. 2006) Atlantic SST response is weak (Rodwell et al. 2004) El Nino teleconnection is missing (Toniazzo and Scaife 2006) Volcanic influence is weak (Stenchikov et al. 2006)

7. © Crown copyright Met Office Why do we need to change the system to improve the model?

8. © Crown copyright Met Office What are we changing? GloSea3GloSea4 Model HadCM3 (N48L19 – 1/3L40) HadGEM3 (N96L38-ORCA1L42) Initialization Atmos/soil: reconf. of ECMWF 4D-Var Ocean: UM-ocean 3D-OI Atmos/soil/sea-ice: reconf. of Met Office 4D-Var Ocean: NEMO 3D-OI IC uncertainties Wind stress and SST perturbations added to a central analysis Weekly lagged approach Model uncertainties NoneRP + SKEB2 Forecast ensemble 41-members (monthly bursts from 1 st ) ~ 30 members (weekly bursts) Hindcast ensemble Run a priori off-line 15-members / 15-years (1987-2001) ERA-40 Run on real-time with forecast ~10-members / ~15-years (1993-2007) ERA-interim

9. © Crown copyright Met Office Why are we changing the ensemble? Current system (GloSea3). Forecast: 1 st Jan 2009 1 st Feb 2009 Once a month Perturbations to initial conditions added to a central analysis No model uncertainties 40 ensemble members 6-month forecasts

10. © Crown copyright Met Office Forecast biases How to separate the signal from the bias? Obs. clim. fcst Temperature probability

11. © Crown copyright Met Office Dealing with model biases:

12. © Crown copyright Met Office Why are we changing the hindcast? Current system (GloSea3). Hindcast: 1 st Jan 1987, 1988, 1989 … 2001 1 st Feb 1987, 1988, 1989 … 2001 Run apriori 15 years; 15 members 6-month forecasts Estimate mean errors to calibrate forecast

13. © Crown copyright Met Office How to remove model biases How to separate the signal from the bias? Obs. clim. fcst Temperature probability fcst clim (estimated from hindcast!)

14. © Crown copyright Met Office Why are we changing the ensemble? New system (GloSea4). Forecast: Once a week No perturbations to ICs. Lagged approach Includes model uncertainties 29 th Jan 2009 15 th Jan 2009 22 th Jan 2009 8 th Jan 2009 1 st Jan 2009 40 ensemble members 6-month forecasts 10 ensemble members 6-month forecasts

15. © Crown copyright Met Office Why are we changing the hindcast? New hindcast (GloSea4). Fcst & Hcst: Run on real-time 15 years; 10 members 15 th Jan 2009 22 th Jan 2009 8 th Jan 2009 1 st Jan 2009 15 th Jan 22 th Jan 8 th Jan 1 st Jan 1991-2005 Calibration on the fly!! Forecast Hindcast

16. © Crown copyright Met Office The new system gives us: Flexibility to introduce model changes Stand-alone hindcast suite for model improvement

17. © Crown copyright Met Office The new model: HadGEM3 Improved physics, dynamics. Increased resolution Further development until end 2010 linked to: Improvement of skill for seasonal-to-decadal Improvement of skill for regional prediction

18. © Crown copyright Met Office Improved teleconnections: ENSO-Europe and the role of the stratosphere (Adam Scaife, Sarah Ineson, Jeff Knight, Andrew Marshall)

19. © Crown copyright Met Office ObservationsL38 Model Observations show low pressure Not well captured by model Response to El Nino Observations Ineson and Scaife, Nature Geoscience, (2009)

20. © Crown copyright Met Office Weak El Nino Strong El Nino Response to El Nino Observations Toniazzo and Scaife, GRL, (2006)

21. © Crown copyright Met Office Hypothesis: Models capture ENSO-Europe trop. teleconnection but fail to reproduce strat. teleconnection

22. © Crown copyright Met Office Arctic polar vortex:  Most intense during winter; steepest temperature gradient; sudden stratospheric warmings  Planetary (Rossby) waves typically propagate upward and equatorward, contributing to vortex breakdown European response to El Niño in late winter and connection to Sudden Stratospheric Warmings Winter 05/06 (08/09 similar) Baldwin and Dunkerton 2001; Kodera et al 1990, Boville 1984

23. © Crown copyright Met Office Standard and Extended model Standard (L38)Extended (L60) 39.3km 84.1km Stratosphere (midlatitude mean profile)

24. © Crown copyright Met Office Role of stratosphere Zonal WindTemperature Role of stratosphere Ineson and Scaife, Nature Geoscience, (2009)

25. © Crown copyright Met Office Response to El Nino Observations L60 Model Response to El Nino Ineson and Scaife, Nature Geoscience, (2009)

26. © Crown copyright Met Office No active Active stratosphere Response to El Nino Ineson and Scaife, Nature Geoscience, (2009)

27. © Crown copyright Met Office Active strat. No active Strong Nino Trop. only

28. © Crown copyright Met Office Winter 2005/6 Adam Scaife No Strat. Stratosphere Observed Scaife and Knight, QJRMS, 2008

29. © Crown copyright Met Office Concluding … New Seasonal Forecasting System: – Improved initialization, representation of uncertainties and calibration – Flexible and focused on improving latest model: e.g. ENSO-Europe teleconnection only properly represented when stratosphere is included

30. © Crown copyright Met Office Perdon por el ingles, Muchas gracias … Alguna pregunta?