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Met Office seasonal predictions and applications Richard Graham

Met Office seasonal predictions and applications Richard Graham Chris Gordon, Matt Huddleston, Mike Davey, Alberto Arribas, Bernd Becker, Anca Brookshaw, Andrew Colman, Stephen Cusack, Margaret Gordon, Bruce Ingleby, Peter McLean (Adam Scaife, Malcolm Macvean)

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Met Office seasonal predictions and applications Richard Graham

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  1. Met Office seasonal predictions and applications Richard Graham Chris Gordon, Matt Huddleston, Mike Davey, Alberto Arribas, Bernd Becker, Anca Brookshaw, Andrew Colman, Stephen Cusack, Margaret Gordon, Bruce Ingleby, Peter McLean (Adam Scaife, Malcolm Macvean) ECWMF Forecast Users Meeting, 16 June 2006

  2. Outline • Met Office systems & basic products • Europe/UK winter 2005/06 (first major operational UK seasonal forecast statement) • Accounting for climate trends in forecasts and their communication • If time: forecasts for Regional Climate Outlook Forums (RCOFs)

  3. Global prediction: Dynamical Seasonal forecasting system : GloSea • Enhanced version of the Hadley Centre Climate model HadCM3 • AGCM: 2.5° x 3.75° x 19L • OGCM: (1.25° to 0.3°) x 1.25° x 40L • 41-member ocean-atmosphere global forecast ensemble • run to 6 months ahead from initial conditions on 1st of each month • 5 ocean analyses from perturbed wind stresses • Ocean analyses further perturbed with instantaneous SST perturbations • hindcast (‘BACKRUN’) period, 1987-present (1987-2001 calibration) • run at ECMWF as part of developing European multi-model – EURO-SIP Real - Time Forecast 41 member ensemble Atmosphere NWP/re- analyses 15 member Ocean Analysis - 5 member ensemble 1987 1988 2005

  4. Global JJA temperature probability (tercile categories) JJA temperature probability – ‘extremes’ (outer-quintile categories) GloSea EURO-SIP P(above) P(well-above) P(avge) P(well-below) P(below) Example website products for GloSea & EURO-SIP Latest (May) GloSea ensemble forecast for tropical Pacific (Niño3.4) Sea Surface Temperature (SST) Products available at: www.metoffice.gov.uk/research/seasonal

  5. Statistical forecasts for specific regions – based on historical SST anomaly relationships winter NAO Used in objective and subjective combination with GloSea model output

  6. winter 2005/6 forecast 2005/6

  7. Met Office winter forecast 2005/6 A two in three chance of a colder-than-average winter for much of Europe. If this holds true, parts of the UK – especially southern regions – are expected to have temperatures below normal There is also an indication for a drier-than-average winter over much of the UK. • Customers: • public • government (Cabinet office) • planners in utilities, transport, finance & insurance, defence, aviation, local authorities • biggest ‘story’ ever run by Met Office press office • 71% of public aware, 14% took action Observed temperature anomalies DJF 2005/6

  8. NAO statistical/empirical forecast, winter 2005/06 N. Atlantic May SST anomaly associated with +ve NAO NAO index: difference between normalised pressure anomaly Azores - Iceland Predicts correct sign in 2 out of 3 winters N. Atlantic May SST anomaly 2005

  9. Met Office decadal prediction system (DePreSys)DJF forecast from June 2005

  10. Model skill/’response’ ‘average’ DJF hindcast skill 1987-2002 (ROC) HadAM3 response to idealised (‘May05-like’) forcing courtesy W. Norton GloSea & HadAM3 skill and ‘response’

  11. From September FromOctober From November OSTIA anomaly 1985-2001 climatology GloSea predictions: Temperature forecast for DJF. Ensemble mean relative to 1987-2001 climatology

  12. GloSea: 500 hPa forecast for DJF – Ensemble mean From September From October M M From November Model ~ 40% observed NCEP Analysis M DAM

  13. ‘average’ DJF hindcast skill 1987-2002 (ROC) Most-likely precipitation category, DJF05/06 Observed precip anomalies DJF05/06 (IRI) Precipitation winter 05/06: ‘…some indication of drier-than-average’ GloSea prediction from Sep05

  14. Met Office (GloSea) ECMWF EURO-SIP multi-model Meteo-France EURO-SIP: probability of lower temperature tercile category: NDJ 2005 (from September) Forecast is made available on the 15th of each month.

  15. May 2005 October 2005 Below the surface 60-90m October 2005 August 2005 Monitoring the forecast – ocean temperatures

  16. Monitoring the forecast 0m Gulf Stream region January 1996 50m 100m 150m May Dec January 2006 South of Newfoundland region Sub-tropical region Note impact of ARGO array

  17. Statistical forecasting model Analysis of climate trends Research studies (e.g. PREDICATE, COAPEC) Dynamical forecasting models Analysis of current ocean observations Skill assessed by past performance of the forecast methods The forecast process ‘This forecast is produced using a combination of statistical models and complex climate models with interpretation by operational forecasters.’ (Met Office,EURO-SIP) Monthly conference of experts (forecasting, research & comms staff) What other forecasts are saying

  18. Summary • The statistical forecast suggested colder than average winter (it was supported by the experimental decadal forecast system). • GloSea September and October forecasts suggested cold conditions over Europe. • GloSea forecast the SST tripole and geopotential height patterns consistent with a negative NAO situation – but the signal is weak ~ 40% of observed amplitude (as expected). • Real time analysis of sub-surface ocean temperatures supported the re-emergence of tripole SST anomalies in winter. This was closely (weekly) monitored to see if the forecast was ‘on track’. • Expert interpretation (by research and forecast staff) was used to draw all this together into the headline forecast and to subsequently decide if the forecast should be revised.

  19. Accounting for climate trends & Communication issues

  20. Some press (over)reactionThe ‘how cold is cold?’ issue 31st October 2005 27th October 2005

  21. Choice of climatology determines the forecast message!Statistical forecast for summer 2006 relative to 3 climatologies Relative to 1987-2001 (CGCM hindcast period) ‘Most likely cold’ Relative to 1971-2000 ‘Most likely average’ Relative to 1961-1990 ‘Most likely average’

  22. 2003/04 2004/05 2005/06 1989/90 1984/85 1962/63 Winter (DJF) 2005/6 forecast ‘re-stated’:forecast probabilities for Southern England, from Sept Skill-calibrated combination of predicted NAO index and GloSea 2m temperature 2002/03 1995/96 (4.72 ºC) +0.015ºC/year 1975 on, +0.0075ºC/year before 1975 Climate 1915 to 2005

  23. Concluding remarks • Advice was favourably received by UK government – raised profile of SF • Met Office now contracted for routine ‘operational’ seasonal forecast briefings to Cabinet Office • …and to Environment Agency re drought in SE UK. • transfer of ‘operational’ tasks from Research to Operations Centre • Need ‘pull-through’ of existing understanding to improve CGCMs • new post focused on improving European skill, also NERC knowledge transfer post • ENSEMBLES project comparison of decadal and seasonal models • Improve communication being developed for next winter • ‘how cold is cold?’ • based on feedback (in part from April RMS meeting) • issue more detailed probability information • avoid confusion caused by displaying component forecasts on the website (NAO and GloSea output) • ‘consolidated’ forecast maps (combining forecasts) • Hindcasts do not give full skill picture – need to know how the models perform under different modes of forcing • this impacts on model calibration/combining strategies • Need ways of accounting for climate trend in the preparation and communication of the forecast

  24. Forecasts for Africa Regional Climate Outlook Forums

  25. CGCM ‘large-scale’ quality sufficient for downscaling? ability of downscaling to improve regional skill? benefits of dynamical Vs statistical methods? GloSea probabilities RCOF forecast Verification Observed (IRI) West Africa Regional Climate Outlook Forum for precipitation JAS 2005 GloSea skill 2m lead wet avge dry

  26. June issue forecasts of Jul-Oct inflow Corr=0.69 Real-time forecasts forecast Regression:GloSea+statistical+catchment observations verification Low inflow forecasts viewed with caution Operational forecasts for 2005 Applications: water volume inflow, lake Volta:learning to use in decision making Limit of catchment Lake Volta Akosombodam: 1000MWatt Hydro-plant

  27. Observed OND precipitation anomalies GPC forecasts for OND available for GHACOF16, the published consensus, the verification IRI GloSea ECMWF Euro-SIP Published Consensus (SOND)

  28. Additional slides

  29. Accounting for climate trends in seasonal forecasts:Japan December 2005 • Figure from Koichi Kurihara, JMA

  30. Calibrated using hindcast performance Use of hindcasts: calibration can dilute CGCM ‘signal’ relevant to the current forecast situation ‘Raw’ GloSea ensemble Reliability for outer-quintile temperature categories, northern exttratropics Resolution ‘ability to detect outer-quintile temperature events’

  31. Skill at 1 month lead: ROC scores based on hindcasts 1987-2002 Upper tercile category Upper quintile category Temp: MAM Precip: JJA

  32. User requirement for regional detail:Example: observed regional impact of negative NAO Average number of days with mean temperature < 0°C When –ve NAO is observed 10 winters with –ve NAO, 1970/1 – 2000/1 9 winters since 1995/96 • more ‘cold’ days in all districts (factor 3 to 8) • increase largest in south and west Based on station observations

  33. User requirement for regional detail Average number of days with mean temperature < 0°C When –ve NAO is forecast 10 winters with –ve NAO, 1970/1 – 2000/1 9 winters since 1995/96 • more ‘cold’ days in all districts (factor 2 to 5) • increase largest in south and west

  34. Inputs: Underpinning scientific understanding From Warwick Norton (Reading Uni): HadAM3 forcing experiments Solid contours are significant at 95% • Rossby wave train over Atlantic, ridge over northern Europe gives cold temps.

  35. Previous Dec-Jan with strong Atlantic dipole SST pattern (9 years) Solid contours are significant at 95%

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