The Impacts of the Indian Ocean warming trend on African Climate.
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The Impacts of the Indian Ocean warming trend on
African Climate.
Dan Hodson and Rowan Sutton
NCAS Centre for Global Atmospheric ModellingDepartment of Meteorology
University of Reading
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OutlineObservations.Experiments I
– Atmosphere model forced with:• Historical Observed Sea Surface Temperatures.• 1°C Anomaly in the Indian Ocean
Indian Ocean Temperature TrendExperiments II
– Atmosphere model force with Observed Indian Ocean warming Trend
ResultsConclusions and Caveats
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Observations
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Hoerling et al. J. Climate 2006
1950-1999 Trend in Rainfall
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Experiments I
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AGCM forced with Observed SSTs
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AGCM Forced with Obs SSTs 1950-1999
Hoerling et al. J. Climate 2006
FMA
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AGCM Forced with Obs SSTs 1950-1999
Hoerling et al. J. Climate 2006
JAS
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AGCM forced with 1°C Indian Ocean
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+1°C
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AGCM Forced with 1C Indian Ocean Anomaly
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AGCM Forced with 1C Indian Ocean Anomaly
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Indian Ocean Temperature Trend
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Indian Ocean SST Trend
C
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Indian Ocean SST trend
Annual mean SST trend 1951-1990 C/year
0.02
-0.02
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Atmosphere model force with Observed Indian Ocean
warming Trend
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Jan
May
Sept
SST Anomalies
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Indian Ocean SST Trend
CIOP
ION
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Experiment
Five AGCMs– Arpege – CAM3– Echam5– GAM (IAP)– HadAM3
Indian Ocean Positive (IOP) Indian Ocean Negative (ION)
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Results
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FMAVertical velocity Rainfall Surface Temperature
ARP
CAM
ECH
GAM
HAD
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JASVertical velocity Rainfall Surface Temperature
ARP
CAM
ECH
GAM
HAD
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Caveats?
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Observed MSLP trends
Copsey et al GRL 2006
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MSLP Trends
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Conclusions
AGCMs forced with warm Indian Ocean capture some of the trends in African rainfall (both FMA and JAS).
Trends associated with changes in subsidence/ changes in Walker Circulation.
Can we use AGCMs to model past changes in this way?
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Vertical Structure JAS
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Vertical Structure FMA
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Station rainfall trends 1950-1999
(JAS/FMA)