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© Crown copyright 2005 Page 1
Met Office seasonal predictions and applicationsRichard 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
© Crown copyright 2005 Page 2
Outline
Met Office systems & basic productsEurope/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)
© Crown copyright 2005 Page 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
Ocean Analysis - 5 member ensemble
Real - TimeForecast
41 memberensemble
1987 20051988
Atmosphere NWP/re- analyses
15 member
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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
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)
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Statistical forecasts for specific regions – based on historical SST anomaly relationships
winter NAO
Used in objective and subjective combination with GloSea model output
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winter 2005/6 forecast 2005/6
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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
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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
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Met Office decadal prediction system (DePreSys)DJF forecast from June 2005
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GloSea & HadAM3 skill and ‘response’
‘average’ DJF hindcast skill1987-2002 (ROC)
courtesy W. Norton
Model skill/’response’
HadAM3 response to idealised (‘May05-like’) forcing
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GloSea predictions: Temperature forecast for DJF. Ensemble mean relative to 1987-2001 climatology
OSTIA anomaly 1985-2001 climatology
From September
From November
From October
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GloSea: 500 hPa forecast for DJF – Ensemble mean
NCEP Analysis
From September From October
From November
M
DAMM
M
Model ~ 40% observed
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Precipitation winter 05/06: ‘…some indication of drier-than-average’
‘average’ DJF hindcast skill1987-2002 (ROC)
GloSea prediction from Sep05
Most-likely precipitation category, DJF05/06
Observed precip anomalies DJF05/06 (IRI)
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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
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Monitoring the forecast – ocean temperatures
May 2005 October 2005
August 2005Below the surface 60-90m
October 2005
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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
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The forecast process
‘This forecast is produced using a combination of statistical models and complex climate models with interpretation by operational forecasters.’
Dynamicalforecasting models
Analysis ofcurrent oceanobservations
Statisticalforecasting model
Analysis ofclimate 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
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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.
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Accounting for climate trends
&
Communication issues
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Some press (over)reactionThe ‘how cold is cold?’ issue
27th October 2005 31st October 2005
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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’
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Winter (DJF) 2005/6 forecast ‘re-stated’:forecast probabilities for Southern England, from Sept
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
-6 -5 -4 -3 -2 -1 0 1 2 3
Temperature anomaly degC
Pro
ba
bili
ty
trend adjusted climatology forecast
1962/63
2002/03
1995/96
2003/042004/05
1984/85
1989/90
(4.72 ºC)
+0.015ºC/year 1975 on,
+0.0075ºC/year before 1975
Climate 1915 to 2005
2005/06
Skill-calibrated combination of predicted NAO index and GloSea 2m temperature
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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
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Forecasts for Africa Regional Climate Outlook Forums
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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 lead GloSea probabilities RCOF forecast
wet
dry
avgeObserved (IRI)
Verification
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Predicted, observed 2005 and LTA inflow
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
June - Nov July - Nov Aug - Nov Sept - Nov Oct - Nov
Mill
ion
Ac
re F
ee
t (M
AF
)
2005 UK-Met Inflow (MAF)
2005 Actual Inflow (MAF)
LTA
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
0
10
20
30
40
50
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
perc
ent o
f ann
ual t
otal
rainfall
inflow
Low inflow forecasts viewed with caution
0
50
100
150
200
250
300
1965 1970 1975 1980 1985 1990 1995 2000 2005
year
infl
ow
an
om
aly
(%
of
no
rmal)
Real-time forecasts
Corr=0.69
June issue forecasts of Jul-Oct inflow
forecast
verificationRegression:GloSea+statistical+catchment observations
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GPC forecasts for OND available for GHACOF16, the published consensus, the verification
Observed OND precipitation anomalies
GloSea Euro-SIP ECMWFIRI
Published Consensus (SOND)
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Additional slides
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Accounting for climate trends in seasonal forecasts:Japan December 2005
•Figure from Koichi Kurihara, JMA
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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
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Precip: JJA
Skill at 1 month lead: ROC scores based on hindcasts 1987-2002
Upper tercile category Upper quintile category
Temp: MAM
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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
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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
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Inputs: Underpinning scientific understandingFrom 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.
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Previous Dec-Jan with strong Atlantic dipole SST pattern (9 years)
Solid contours are significant at 95%