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Seasonal forecasting activities at the Met Office Long-range Forecasting Group, Hadley Centre

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. Outline. Brief summary 2004/5 Recent Met Office (GloSea) seasonal forecasts New website products

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Seasonal forecasting activities at the Met Office Long-range Forecasting Group, Hadley Centre

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  1. 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. Outline • Brief summary 2004/5 • Recent Met Office (GloSea) seasonal forecasts • New website products • Multi-model forecast combination/calibration

  3. 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. Recent forecasts: Nino3.4 SST anomaly, Dec04 – May05 Dec04 Jan05 Feb05 May05 Mar05 Apr05

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

  6. Skill assessment for outer quintiles – new website products

  7. 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. BACKRUNS verification: temperature, ROC: selectable by region/initial date/lead time: Example for Central America, JJA, 1-month lead (1987-2002) terciles outer-quintiles

  9. BACKRUNS verification: precipitation, ROC: selectable by region/initial date/lead time: Example for Central America, JJA, 1-month lead (1987-2002) terciles outer-quintiles

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

  11. DEMETER: ROC skill mapsExample 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 tercile Event = temperature in upper quintile

  12. BACKRUNS verification: precipitation, reliability: selectable by region/initial date/lead time: Example for Central America, JJA, 1-month lead (1987-2002) terciles outer-quintiles

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

  14. multi-model combination, calibration prediction of decile ‘extremes’

  15. Discriminant Analysis for multi-model combining/calibration Generalised squared distance; where, t category of interest (eg. upper quintile) x vector of predictor variables (elements = eg. t2m from different models) mtcorresponding 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 pt(x) over all ensemble members

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

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

  18. European multi-model probability of well-above/below temperatures, Jun-Jul-Aug GloSea GloSea calibrated well above well below

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

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

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

  23. Questions & Answers

  24. 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. Outer quintile temperature forecasts and verif FMA 05 P(outer quintile) >40% IRI verification

  26. 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) Retrospective Forecasts - 15 member ensemble Atmosphere NWP/re- analyses Real - Time Forecast 41 member ensemble 15 member Ocean Analysis - 5 member ensemble 1987 1988 2004

  27. BACKRUNS verification: temperature, reliability: selectable by region/initial date/lead time: Example for Central America, JJA, 1-month lead (1987-2002) terciles outer-quintiles

  28. 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

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