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Page 1© Crown copyright 2005 Met Office seasonal predictions and applications Richard Graham Chris Gordon, Matt Huddleston, Mike Davey, Alberto Arribas,

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Presentation on theme: "Page 1© Crown copyright 2005 Met Office seasonal predictions and applications Richard Graham Chris Gordon, Matt Huddleston, Mike Davey, Alberto Arribas,"— Presentation transcript:

1 Page 1© Crown copyright 2005 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 Page 2© Crown copyright 2005 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 Page 3© Crown copyright 2005 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 1 st of each month 5 ocean analyses from perturbed wind stresses Ocean analyses further perturbed with instantaneous SST perturbations hindcast (BACKRUN) period, 1987-present ( calibration) run at ECMWF as part of developing European multi-model – EURO-SIP Ocean Analysis - 5 member ensemble Real - Time Forecast 41 member ensemble Atmosphere NWP/re- analyses 15 member

4 Page 4© Crown copyright 2005 Example website products for GloSea & EURO-SIP Latest (May) GloSea ensemble forecast for tropical Pacific (Niño3.4) Sea Surface Temperature (SST) Products available at: P(above) P(avge) P(below) Global JJA temperature probability (tercile categories) JJA temperature probability – extremes (outer-quintile categories) GloSea EURO-SIP P(well-below) P(well-above)

5 Page 5© Crown copyright 2005 Statistical forecasts for specific regions – based on historical SST anomaly relationships winter NAO Used in objective and subjective combination with GloSea model output

6 Page 6© Crown copyright 2005 winter 2005/6 forecast 2005/6

7 Page 7© Crown copyright 2005 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. Observed temperature anomalies DJF 2005/6 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

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

9 Page 9© Crown copyright 2005 Met Office decadal prediction system (DePreSys) DJF forecast from June 2005

10 Page 10© Crown copyright 2005 GloSea & HadAM3 skill and response average DJF hindcast skill (ROC) courtesy W. Norton Model skill/response HadAM3 response to idealised (May05-like) forcing

11 Page 11© Crown copyright 2005 GloSea predictions: Temperature forecast for DJF. Ensemble mean relative to climatology OSTIA anomaly climatology From September From November From October

12 Page 12© Crown copyright 2005 GloSea: 500 hPa forecast for DJF – Ensemble mean NCEP Analysis From SeptemberFrom October From November M DAMM M Model ~ 40% observed

13 Page 13© Crown copyright 2005 Precipitation winter 05/06: …some indication of drier- than-average average DJF hindcast skill (ROC) GloSea prediction from Sep05 Most-likely precipitation category, DJF05/06 Observed precip anomalies DJF05/06 (IRI)

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

15 Page 15© Crown copyright 2005 Monitoring the forecast – ocean temperatures May 2005October 2005 August 2005 Below the surface 60-90m October 2005

16 Page 16© Crown copyright 2005 Monitoring the forecast January 1996 January 2006 Gulf Stream region Sub-tropical region Note impact of ARGO array South of Newfoundland region 0m 100m 50m May Dec 150m

17 Page 17© Crown copyright 2005 The forecast process This forecast is produced using a combination of statistical models and complex climate models with interpretation by operational forecasters. Dynamical forecasting models Analysis of current ocean observations Statistical forecasting model Analysis of climate trends Skill assessed by past performance of the forecast methods Monthly conference of experts (forecasting, research & comms staff) (Met Office,EURO-SIP) Research studies (e.g. PREDICATE, COAPEC) What other forecasts are saying

18 Page 18© Crown copyright 2005 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 Page 19© Crown copyright 2005 Accounting for climate trends & Communication issues

20 Page 20© Crown copyright 2005 Some press (over)reaction The how cold is cold? issue 27 th October st October 2005

21 Page 21© Crown copyright 2005 Choice of climatology determines the forecast message! Statistical forecast for summer 2006 relative to 3 climatologies Relative to (CGCM hindcast period) Most likely cold Relative to Most likely average Relative to Most likely average

22 Page 22© Crown copyright 2005 Winter (DJF) 2005/6 forecast re-stated: forecast probabilities for Southern England, from Sept 1962/ / / / / /851989/90 (4.72 ºC) ºC/year 1975 on, ºC/year before 1975 Climate 1915 to /06 Skill-calibrated combination of predicted NAO index and GloSea 2m temperature

23 Page 23© Crown copyright 2005 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 Page 24© Crown copyright 2005 Forecasts for Africa Regional Climate Outlook Forums

25 Page 25© Crown copyright 2005 West Africa Regional Climate Outlook Forum for precipitation JAS 2005 CGCM large-scale quality sufficient for downscaling? ability of downscaling to improve regional skill? benefits of dynamical Vs statistical methods? GloSea skill 2m leadGloSea probabilitiesRCOF forecast wet dry avge Observed (IRI) Verification

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

27 Page 27© Crown copyright 2005 GPC forecasts for OND available for GHACOF16, the published consensus, the verification Observed OND precipitation anomalies GloSea Euro-SIP ECMWF IRI Published Consensus (SOND)

28 Page 28© Crown copyright 2005 Additional slides

29 Page 29© Crown copyright 2005 Accounting for climate trends in seasonal forecasts: Japan December 2005 Figure from Koichi Kurihara, JMA

30 Page 30© Crown copyright 2005 Use of hindcasts: calibration can dilute CGCM signal relevant to the current forecast situation Reliability for outer-quintile temperature categories, northern exttratropics Resolution ability to detect outer- quintile temperature events Raw GloSea ensemble Calibrated using hindcast performance

31 Page 31© Crown copyright 2005 Precip: JJA Skill at 1 month lead: ROC scores based on hindcasts Upper tercile categoryUpper quintile category Temp: MAM

32 Page 32© Crown copyright 2005 User requirement for regional detail: Example: observed regional impact of negative NAO Average number of days with mean temperature < 0°C 10 winters with –ve NAO, 1970/1 – 2000/1 9 winters since 1995/96 Based on station observations more cold days in all districts (factor 3 to 8) increase largest in south and west When –ve NAO is observed

33 Page 33© Crown copyright 2005 User requirement for regional detail Average number of days with mean temperature < 0°C 10 winters with –ve NAO, 1970/1 – 2000/1 9 winters since 1995/96 When –ve NAO is forecast more cold days in all districts (factor 2 to 5) increase largest in south and west

34 Page 34© Crown copyright 2005 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 Page 35© Crown copyright 2005 Previous Dec-Jan with strong Atlantic dipole SST pattern (9 years) Solid contours are significant at 95%


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