The ECMWF Monthly and Seasonal Forecast Systems

1. The ECMWF Monthly and Seasonal Forecast Systems D. Anderson, M. Balmaseda, L. Ferranti, F. Molteni, T. Stockdale, F. Vitart ECMWF, Reading, UK

2. Main topics • Monthly forecast system: • merging with VAREPS • new atmospheric model cycle : improved simulation of tropical intra-seasonal variability • some recent results from the operational version • Seasonal forecast system: from System 2 to System 3 • improved ocean data assimilation • better predictions of tropical SST • reduced systematic errors in atmospheric fields

3. Monthly Forecasting System • Real-time forecast: • Coupled ocean-atmosphere integrations: a 51-member ensemble is integrated for 32 days every Thursday. • Atmospheric component: IFS with the latest operational cycle and with a TL159L62 resolution • Oceanic component: HOPE (from Max-Planck Institute) with a zonal resolution of 1.4 degrees and 29 vertical levels • Coupling: OASIS (CERFACS). Coupling every ocean time step (1 hour) • Background statistics: • 5-member ensemble integrated at the same day and same month as the real-time time forecast over the past 12 years

4. Model changes during the past year • New versions of IFS : • Cycle 29R2 in June 2005 + new sea ice treatment* • Cycle 30R1 in Feb 2006 + change of vertical resolution (62 vertical levels) • The sea-ice cover is persisted from the atmospheric initial conditions till day 10, then relaxed towards climatology. After day 30, the sea-ice cover is the climatologocal sea-ice cover (from ERA40). • Other changes: • Archiving of probabilities • Verification web site • New products (Madden Julian Oscillation, products for the Southern Hemisphere)

5. Future developments: Merging the monthly forecasting system with VAREPS Present situation: 2 separate systems EPS: TL399L62 twice a day uncoupled Day 10 Day 0 TL159L62 once a week MOFC: Day 0 Day 32 Ocean model

6. Future developments: Merging the monthly forecasting system with VAREPS Q1 2007: single system VAREPS: Once a week TL399L62 TL255L62 Day 32 Day 0 Day 10 MOFC: Day 10 Day 0 Day 32 Ocean model

7. 48 5-ensemble member cases, CY30R1 Prob. 2m temp. in upper tercile. NH. Day 12-18 VAREPS Op. TL159 32/16 92% significance ROC Area: 0.640.61 Tl159 VAREPS

8. Madden Julian Oscillation experiments: 15/12/92 - 31/01/93 ERA40 Analysis: Velocity Pot. 200 hPa OLR U 850 hPa

9. MJO simulation: Spectra of tropical velocity potential (in seasonal exper.) ERA-40 Cy 30R2 Cy 23R4

10. Madden-Julian oscillation Forecast starting on 31 December 1992 CY29R1 Analysis CY30R2

11. MJO EOF analysis The combined EOFs (vel. pot. 200-hPa, U 850 hPa, OLR) have been computed on ERA40 daily data from 2002 to 2004.

12. MJO EOF analysis PC1 PC2 29R1 30R2

13. Precipitation over India 08/05-15/05 15/05-22/05 22/05-29/05 29/05-05/06 ANA Day 5-11 Day 12-18

14. Precipitation over India 08/05-15/05 15/05-22/05 22/05-29/05 29/05-05/06 ANA Day 19-25 Day 26-32

15. ECMWF seasonal forecast System-2 • COUPLED MODEL • Atmospheric model cycle 23R4 • Atmospheric resolution TL95 and 40 levels • Hope ocean model (1x1) • Oasis coupler • INITIALIZATION • ERA-15 data to initialize ocean and atmosphere • Assimilation of subsurface temperature only • “Multivariate” corrections to the salinity and velocity fields • Ensemble of 5 ocean analyses back to 1987. • ENSEMBLE GENERATION • Real time FC: 40 ensemble members (SST and wind perturbations) • Back integrations: • 5 members, 1987-2001 for calibration. • 40 members (Nov and May starts) for skill assessment.

16. System-3(expected late 2006) • COUPLED MODEL • New cycle of atmospheric model (Cy31R1) • Higher atmospheric resolution TL159 and 62 levels • Green house gasses and new aerosols. • New sea-ice specification algorithm • Include ocean currents in wave model • INITIALIZATION • ERA-40 data to initialize ocean and atmosphere • Include bias correction in ocean assimilation. • Include assimilation of salinity and altimeter data. • Ocean reanalysis back to 1959, using ENACT/ENSEMBLES ocean data • ENSEMBLE GENERATION • Extended range of back integrations: 11 members, 1981-2005. • Revised wind and SST perturbations. • Use EPS Singular Vector perturbations in atmospheric initial conditions. • Forecasts out to 12 months (4x per year)

17. EUROSIP: EUROpean multi-modelSeasonal-to-Interannual Prediction system • Currently composed of ECMWF (System 2), Meteo-France (Arpege/ORCA) and UK MetOffice (GloSea) coupled systems • Ensemble integrations performed at ECMWF • Multi-model products to be computed and made available to member states • Graphical products available on the ECMWF web site • Data access/distribution policy to be agreed

18. System-3 New ECMWF operational ocean (re)analysis • Basic (existing) Setup: • Ocean model: HOPE (~1x1 going to 1x.3 at the equator) • Assimilation Method OI • Assimilation of T + Balanced relationships (T-S, ρ-U) • 10 days assimilation windows, increment spread in time • Ensemble of 5 ocean analyses to represent uncertainty • +New Features • ERA-40 fluxes to initialize ocean • Retrospective Ocean Reanalysis back to 1959. • Multivariate on-line Bias Correction . • Assimilation of salinity data. • Assimilation of altimeter-derived sea level anomalies. • 3D OI

19. North Atlantic: T300 anomaly North Atlantic: S300 anomaly Reanalysis time series : trends and variability (with uncertainty from 5 ocean analysis) Climate signals….

20. Values from Bryden et al 2005 THC: Atlantic Meridional Transport(30N)

21. Tropical Pacific SST indices: bias ---- System 2 ---- System 3 (exp.)

22. Tropical Pacific SST indices: skill scores ---- System 2 ---- System 3 (exp.)

23. Tropical Pacific SST indices: error time series ---- System 2 ---- System 3 (exp.)

24. JFM rainfall standard deviation and regression against the Nino3.4 index: GPCP

25. JFM rainfall standard deviation and regression against the Nino3.4 index: System 2

26. JFM rainfall standard deviation and regression against the Nino3.4 index: System 3

27. Systematic errors in atmospheric fields:500-hPa geopotential height in JFM (m.4-6) System 3 System 2

28. Systematic errors in atmospheric fields:sea level pressure in JAS (m.4-6) System 3 System 2

29. Systematic errors in atmospheric fields:2-m. temperature in JAS (m.4-6) System 3 System 2

30. Latest Niño 3.4 Forecast EuroSIP ECMWF

31. ECMWF: Prob. 2m temp. > upper tercile

32. EUROSIP: Prob. 2m temp. > upper tercile

33. Seasonal forecasting of tropical storms ECMWF Forecasts starting on 1st June 2005: JASON OBS: JASON 2005 EuroSIP WNP ENP Atl

34. Tropical storm seasonal forecast for JASON 2006 ECMWF forecast issued in May

35. Tropical storm seasonal forecast for JASON 2006 ECMWF forecast issued in June

36. Summary • Integration of VarEPS and monthly forecast: a step towards a “seamless prediction” system. • Improvements in physical parametrizations (to be included in cy 31R1) reduce systematic errors and improve tropical intra-seasonal variability in monthly and seasonal forecasts. • New ocean (re-)analysis beneficial to both seasonal forecasting and climate research • Multi-model predictions moving from experimental (DEMETER, ENSEMBLES) to operational phase (EUROSIP).