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

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

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 Yes/no, error bars, probabilities? Users should be told about past records of forecast quality

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)

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

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

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: 0.64 0.61 Tl159 VAREPS

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

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

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

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.

MJO EOF analysis PC1 PC2 30R2 29R1

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

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

Indian monsoon Probability of precipitation in the upper tercile 27 real-time cases covering the period May-June-July-August 2002, 2003, 2004 , 2005 Monthly Forecast Persistence of the probabilities of the previous week DAY 19-25 DAY 26-32 DAY 12-18 ROC score: 0.58 0.49 ROC score: 0.46 0.48 ROC score: 0.64 0.49

System-2 ECMWF seasonal forecast 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.

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)

EUROSIP: EUROpean multi-model Seasonal-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

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 System-3 +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 ECMWF has a new operational ocean (re)analysis to initialize seasonal and monthly forecasts To the basic setup (existing SYSTEM 2), we have added new features. The new system assimilates salinity and altimeter.

Reanalysis time series : trends and variability (with uncertainty from 5 ocean analysis) North Atlantic: T300 anomaly Climate signals…. North Atlantic: S300 anomaly The shading in the figures is a representation of the uncertainty in our analysis. It comes from the ensemble of 5 analysis in which the wind stress has been perturbed.

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

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

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

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

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

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

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

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

Systematic errors in atmospheric fields: sea level pressure in JAS (m

Systematic errors in atmospheric fields: 2-m. temperature in JAS (m

Latest Niño 3.4 Forecast EuroSIP ECMWF The EUROSIP NINO plumes for the forecast started in March06 indicate a fast return to near-normal conditions by May and the tendency of warm after that. Here is the latest collection of forecasts of 20 ENSO models. Time Series of predicted sea surface temperature anomalies (SSTA) for the Niño 3.4 index (°C) from various dynamical and statistical models for nine overlapping 3-month periods. Figure provided by the Forecasting and Prediction Research Group of the IRI. Plume of 20 ENSO forecast models from March 2006. There is quite a range of forecasts from later northern spring onward. Some clustering of model forecasts is apparent. Four models (NCEP/CFS, ECHAM/MOM, CPC Markov and Zhang intermediate coupled model) see the mild cold even continuing into and beyond the middle of 2006, while the others generally call for a return to neutral by around June, with a few warming to weak El Nino anomaly levels by July or August. IRI defines La Nina as SSTs in the Nino3.4 region being more than the following anomaly amounts, varying as a function of the season: DJF -0.65 AMJ -0.45 ASO -0.55 JFM -0.55 MJJ -0.50 SON -0.75 FMA -0.45 JJA -0.50 OND -0.75 MAM -0.40 JAS -0.50 NDJ -0.70 The above anomaly thresholds approximately mark the 25%iles for the 1950-2000 distributions of the respective seasons.

ECMWF: Prob. 2m temp. > upper tercile

EUROSIP: Prob. 2m temp. > upper tercile

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

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

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

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).