1. Page 1© Crown copyright 2004 Seasonal forecasting activities at the Met Office Long-range Forecasting Group, Hadley Centre Presenter: Richard Graham ECMWF Forecast Products Users Meeting, 15-17th June 2005

2. Page 2© Crown copyright 2004 Outline Brief summary 2004/5 Recent Met Office (GloSea) seasonal forecasts New website products Multi-model forecast combination/calibration

3. Page 3© Crown copyright 2004 Overview, 2004/5 Met Office GloSea model (version of HadCM3) main tool for seasonal prediction – used in conjunction with statistical methods now runs in parallel configuration with system2 in ECMWF Op. suite (multi-model) 15-member hindcasts 1987-present have been completed (12 starts/year) Met Office seasonal forecast website update - planned for July multi-model products (temperature and precipitation) probability for outer-quintile categories extensive upgrade of verification/validation information (research on multi-model combination/calibration) Use of ECMWF monthly system Met Office post-processed products supplied to various end users Talks: Bernd Becker and Stefan Meulemans - later today EU ENACT project completed 43-year global ocean re-analyses, different models and ODA methods analysis quality assessed through seasonal forecast impacts

4. Page 4© Crown copyright 2004 Recent forecasts: Nino3.4 SST anomaly, Dec04 – May05 Dec04Jan05 Feb05 Mar05Apr05 May05

5. Page 5© Crown copyright 2004 Recent forecasts: Outer-quintile temperature forecasts and verif DJF04/05 P(outer quintile) >40% IRI verification

6. Page 6© Crown copyright 2004 Skill assessment for outer quintiles – new website products

7. Page 7© Crown copyright 2004 Hindcast datasets used BACKRUNS (operational set) period: 1987-present (16 yrs, 1987-2002, used here) 15-member ensemble allows skill assessment for higher order (than tercile) categories DEMETER (research set) period: 1959-2001 (43 yrs) 9-member ensemble

8. Page 8© Crown copyright 2004 BACKRUNS verification: temperature, ROC: selectable by region/initial date/lead time: tercilesouter-quintiles Example for Central America, JJA, 1-month lead (1987-2002)

9. Page 9© Crown copyright 2004 BACKRUNS verification: precipitation, ROC: selectable by region/initial date/lead time: tercilesouter-quintiles Example for Central America, JJA, 1-month lead (1987-2002)

10. Page 10© Crown copyright 2004 BACKRUNS: ROC skill maps Example for 2m temperature, JJA, 1m lead from GloSea hindcasts 1987-2002 (16 yrs) local gridpoint ROC scores (area under the curve) Skill for outer-quintile extremes similar to that for outer terciles NB. But sample of events is smaller Event = temperature in upper tercile Event = temperature in upper quintile

11. Page 11© Crown copyright 2004 DEMETER: ROC skill maps Example for 2m temperature, JJA, 1m lead from GloSea DEMETER hindcasts 1959-2001 (43 yrs) local gridpoint ROC scores (area under the curve) Event = temperature in upper tercileEvent = temperature in upper quintile

12. Page 12© Crown copyright 2004 BACKRUNS verification: precipitation, reliability: selectable by region/initial date/lead time: tercilesouter-quintiles Example for Central America, JJA, 1-month lead (1987-2002)

13. Page 13© Crown copyright 2004 European multi-model GloSea GloSea+ECMWF multi-model probability of well-above/below temperatures, Jun-Jul-Aug well above well below

14. Page 14© Crown copyright 2004 multi-model combination, calibration prediction of decile extremes

15. Page 15© Crown copyright 2004 Discriminant Analysis for multi-model combining/calibration Generalised squared distance; where, tcategory of interest (eg. upper quintile) x vector of predictor variables (elements = eg. t2m from different models) m t corresponding vector of mean predicted values (from hindcasts) when category t was observed (cross validated) S covariance matrix for different predictors (models) Predicted probability of category t given by… Take average of p t (x) over all ensemble members

16. Page 16© Crown copyright 2004 Area with BS > 95% significant for 2m temp outer quintiles DEMETER (1959-1999) Black: Raw Ensemble GloSea. Red: Raw Ensemble Multi-model Blue: Discriminant GloSea. Green: Discriminant Multi-model. All seasons 0,1,2,3 months lead

17. Page 17© Crown copyright 2004 Area with ROC skill > 95% significant 2m temp DEMETER (1959-1999) Black: Raw Ensemble GloSea. Red: Raw Ensemble Multi-model Blue: Discriminant GloSea. Green: Discriminant Multi-model. All seasons 0,1,2,3 months lead

18. Page 18© Crown copyright 2004 European multi-model GloSeaGloSea calibrated probability of well-above/below temperatures, Jun-Jul-Aug well above well below

19. Page 19© Crown copyright 2004 ROC significance for calibrated forecasts of outer deciles: temperature, Europe, JAS (1959-1999) >95% significance GloSea GloSea+ system2+ Meteo- France Multi-model

20. Page 20© Crown copyright 2004 ROC significance for calibrated forecasts of outer deciles: temperature, Europe, AMJ (1959-1999) >95% significance GloSea GloSea+ system2+ Meteo- France Multi-model

21. Page 21© Crown copyright 2004 Summary + key plans New website products – July 05 Multi-model Outer-quintiles probabilities Expanded verification information Next year Calibrated products Higher order extremes (deciles) Need to resolve trade off between reliability and resolution EU ENSEMBLES project Investigate multi-annual/decadal skill Compare ensemble initialisation strategies Next generation GloSea Investigate/prepare new Hadley Centre climate model (HadGEM1) for use in seasonal prediction

22. Page 22© Crown copyright 2004 ENSEMBLES project: Met Office seasonal/multi-annual/decadal runs Model DePreSys (HadCM3) Current oper. range decadal assimilation method GloSea (HadCM3) Seasonal (6months) Conventional (OI type) calibrated anomalies 9-ensemble experiments 1991-2001 pert. ODA pert. phys. lagged avge pert. phys. lagged avge Hindcasts period: 1991 - 2001 GloSea: ->7m:1 st /15 th May/Nov 1 st June/Dec ->14m:1 st May/June/Nov/Dec -> 10y:1 st May 1964, 1994 DePreSys: -> 10y:1 st May/Nov (all years)

23. Page 23© Crown copyright 2004 Questions & Answers

24. Page 24© Crown copyright 2004 Seasonal forecasting activities at the Met Office Long-range Forecasting Group, Hadley Centre Presenter: Richard Graham ECMWF Forecast Products Users Meeting, 15-17th June 2005

25. Page 25© Crown copyright 2004 Outer quintile temperature forecasts and verif FMA 05 P(outer quintile) >40% IRI verification

26. Page 26© Crown copyright 2004 Seasonal forecasting system : GloSea Enhanced version of the Hadley Centre Climate model HadCM3 Six month real-time 41 member ocean atmosphere global forecast ensemble 5 ocean analyses from perturbed wind stresses Ocean analyses further perturbed with instantaneous SST perturbations hindcast (BACKRUN) period, 1987-present (1987-2002 used here) Ocean Analysis - 5 member ensemble Real - Time Forecast 41 member ensemble Retrospective Forecasts - 15 member ensemble 198720041988 Atmosphere NWP/re- analyses 15 member

27. Page 27© Crown copyright 2004 BACKRUNS verification: temperature, reliability: selectable by region/initial date/lead time: tercilesouter-quintiles Example for Central America, JJA, 1-month lead (1987-2002)

28. Page 28© Crown copyright 2004 Discriminant Analysis -used to calibrate dynamical forecasts and combine ensembles from multi-model -Multi-variate: different predictors (models) considered together, relative skill taken into account Pdfs for above, middle and below terciles, given value of a predictor (illustration) Calculated using historical data and hindcasts