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

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

Observations

Hoerling et al. J. Climate 2006

1950-1999 Trend in Rainfall

Experiments I

AGCM forced with Observed SSTs

AGCM Forced with Obs SSTs 1950-1999

Hoerling et al. J. Climate 2006

FMA

AGCM Forced with Obs SSTs 1950-1999

Hoerling et al. J. Climate 2006

JAS

AGCM forced with 1°C Indian Ocean

+1°C

AGCM Forced with 1C Indian Ocean Anomaly

AGCM Forced with 1C Indian Ocean Anomaly

Indian Ocean Temperature Trend

Indian Ocean SST Trend

C

Indian Ocean SST trend

Annual mean SST trend 1951-1990 C/year

0.02

-0.02

Atmosphere model force with Observed Indian Ocean

warming Trend

Jan

May

Sept

SST Anomalies

Indian Ocean SST Trend

CIOP

ION

Experiment

Five AGCMs– Arpege – CAM3– Echam5– GAM (IAP)– HadAM3

Indian Ocean Positive (IOP) Indian Ocean Negative (ION)

Results

FMAVertical velocity Rainfall Surface Temperature

ARP

CAM

ECH

GAM

HAD

JASVertical velocity Rainfall Surface Temperature

ARP

CAM

ECH

GAM

HAD

Caveats?

Observed MSLP trends

Copsey et al GRL 2006

MSLP Trends

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?

Vertical Structure JAS

Vertical Structure FMA

Station rainfall trends 1950-1999

(JAS/FMA)