caio a. s. coelho centro de previsão de tempo e estudos climáticos (cptec) instituto nacional de...
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Caio A. S. CoelhoCentro de Previsão de Tempo e Estudos Climáticos (CPTEC)
Instituto Nacional de Pesquisas Espaciais (INPE)[email protected]
1st EUROBRISA workshop, Paraty, 17-19 March 2008
Deriving South America seasonal rainfall from upper level circulation predictions
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Conceptual framework
)y(p
)x(p)x|y(p)y|x(p
i
iiiii
Data Assimilation “Forecast Assimilation”
)x(p
)y(p)y|x(p)x|y(p
f
fffff
Stephenson et al. (2005)
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Calibration and combination experiment
Common hindcast period: 1987-2005 (19 years)
y: observed rainfall (GPCP, Adler et al. 2003)x: predicted upper level (200 hPa) circulation
Use two EUROSIP model predictions: • ECMWF System 3• UK Met Office
Target season: DJFStart date: November (i.e. 1-month lead predictions for DJF)
NCEP/NCAR Reanalysis (Kalnay et al. 1996) is used to verify predicted upper level circulation
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dy
du
dx
dv
Upper level circulation
u: zonal windv: meridional wind: stream function
': zonal mean of
: perturbed (eddy) stream function
'
uv
)v,u(V
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Observed perturbed stream function
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ECMWF perturbed stream function
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UKMO perturbed stream function
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Perturbed stream function verification
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El Niño
Observed perturbed stream function anomaly
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La Niña
Observed perturbed stream function anomaly
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La Niña
El Niño
Observed perturbed stream function anomaly
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El Niño
ECMWF perturbed stream function anomaly
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La Niña
ECMWF perturbed stream function anomaly
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El Niño
La Niña
ECMWF perturbed stream function anomaly
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El Niño
UKMO perturbed stream function anomaly
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La Niña
UKMO perturbed stream function anomaly
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El Niño
La Niña
UKMO perturbed stream function anomaly
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Perturbed stream function anomaly verification
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)C,Y(N~Y b
)S),YY(G(N~Y|X o
Prior:
Likelihood:
Posterior:
),(~| DYNXY a
Calibration and combination procedure: Forecast Assimilation
qq:D
qn:Y
pn:X
qq:C q1:Yb
pp:S qn:Ya
Matrices
Stephenson et al. (2005)
Forecast assimilation uses first three leading MCA modes of the matrix YT X.
X: circulation predictions (ECMWF + UKMO)Y: DJF rainfall
)(
)()|()|(
Xp
YpYXpXYp
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Forecast Assimilation: First MCA mode
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Forecast Assimilation: Second MCA mode
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Forecast Assimilation: Third MCA mode
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Correlation between predicted and observed anomalies
Forecast AssimilationECMWF UKMO
Issued: November, Valid for DJF, Hindcast period: 1987-2005
Upper level circulation derived predictions obtained with forecast assimilation have comparable level of skill to indiv. model predictions
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ECMWF UKMO Forecast Assimilation
Ranked Probability Skill Score (tercile categories)
Issued: November, Valid for DJF, Hindcast period: 1987-2005
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Gerrity Score (tercile categories)
ECMWF UKMO Forecast Assimilation
Issued: November, Valid for DJF, Hindcast period: 1987-2005
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Issued: November, Valid for DJF, Hindcast period: 1987-2005
ROC Skill Score (positive or negative anomaly)
ECMWF UKMO Forecast Assimilation
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Issued: November, Valid for DJF, Hindcast period: 1987-2005
Reliability diagram (positive or negative anomaly)
ECMWF UKMO Forecast Assimilation
Forecast assimilation improves prediction reliability
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ROC plot (positive or negative anomaly)
Issued: November, Valid for DJF, Hindcast period: 1987-2005
ECMWF UKMO Forecast Assimilation
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Summary
• Forecast assimilation is a useful framework for exploring atmospheric teleconnections in seasonal forecasts
• ENSO atmospheric teleconnections is the main source of skill for South America rainfall predictions
• Combined and calibrated circulation derived predictions obtained with forecast assimilation have comparable level of skill to single model rainfall prediction
• Additional skill improvements can be investigated by including humidity predictions in the forecast assimilation procedure