page 1© crown copyright 2004 seasonal forecasting activities at the met office long-range...
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© Crown copyright 2004 Page 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
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Outline
Brief summary 2004/5
Recent Met Office (GloSea) seasonal forecasts
New website products
Multi-model forecast combination/calibration
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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
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Recent forecasts: Nino3.4 SST anomaly, Dec04 – May05
Dec04 Jan05 Feb05
Mar05 Apr05 May05
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Recent forecasts:Outer-quintile temperature forecasts and verif DJF04/05
P(outer quintile)
>40%
IRI verification
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Skill assessment for outer quintiles – new website
products
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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
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BACKRUNS verification: temperature, ROC: selectable by region/initial date/lead time:
terciles outer-quintiles
Example for Central America, JJA, 1-month lead (1987-2002)
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BACKRUNS verification: precipitation, ROC: selectable by region/initial date/lead time:
terciles outer-quintiles
Example for Central America, JJA, 1-month lead (1987-2002)
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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)
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
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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
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BACKRUNS verification: precipitation, reliability: selectable by region/initial date/lead time:
terciles outer-quintiles
Example for Central America, JJA, 1-month lead (1987-2002)
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European multi-model
GloSea GloSea+ECMWF multi-modelprobability of well-above/below temperatures, Jun-Jul-Aug
well above
well below
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multi-model combination, calibration
prediction of decile ‘extremes’
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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) mt 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 pt(x) over all ensemble members
)()()(2 t1
t mxSmxx tD
))(5.0exp()( 2 xx tt Dp
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Area with BS > 95% significant for 2m tempouter 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
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Area with ROC skill > 95% significant 2m tempDEMETER (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
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European multi-model
GloSea GloSea calibrated
probability of well-above/below temperatures, Jun-Jul-Aug
well above
well below
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ROC significance for calibrated forecasts of outer deciles: temperature, Europe, JAS (1959-1999)
>95% significance
GloSea
GloSea+ system2+ Meteo-France
Multi-model
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ROC significance for calibrated forecasts of outer deciles: temperature, Europe, AMJ (1959-1999)
>95% significance
GloSea
GloSea+ system2+ Meteo-France
Multi-model
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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
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ENSEMBLES project: Met Office seasonal/multi-annual/decadal runs
ModelDePreSys(HadCM3)
Currentoper. range
decadal
assimilationmethod
GloSea(HadCM3)
Seasonal(6months)
Conventional (OI type)
calibrated anomalies
9-ensembleexperiments1991-2001
pert. ODA
pert. phys.
lagged avge
pert. phys.
lagged avge
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)
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Questions & Answers
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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
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Outer quintile temperature forecasts and verif FMA 05
P(outer quintile)
>40%
IRI verification
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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 - TimeForecast
41 memberensemble
Retrospective Forecasts - 15 member ensemble
1987 20041988
Atmosphere NWP/re- analyses
15 member
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BACKRUNS verification: temperature, reliability: selectable by region/initial date/lead time:
terciles outer-quintiles
Example for Central America, JJA, 1-month lead (1987-2002)
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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