1. The Impacts of the Indian Ocean warming trend on African Climate. Dan Hodson and Rowan Sutton NCAS Centre for Global Atmospheric Modelling Department of Meteorology University of Reading

2. Outline Observations. Experiments I –Atmosphere model forced with: Historical Observed Sea Surface Temperatures. 1°C Anomaly in the Indian Ocean Indian Ocean Temperature Trend Experiments II –Atmosphere model force with Observed Indian Ocean warming Trend Results Conclusions and Caveats

3. Observations

4. Hoerling et al. J. Climate 2006 1950-1999 Trend in Rainfall

5. Experiments I

6. AGCM forced with Observed SSTs

7. AGCM Forced with Obs SSTs 1950-1999 Hoerling et al. J. Climate 2006 FMA

8. AGCM Forced with Obs SSTs 1950-1999 Hoerling et al. J. Climate 2006 JAS

9. AGCM forced with 1°C Indian Ocean

10. +1°C

11. AGCM Forced with 1C Indian Ocean Anomaly

13. Indian Ocean Temperature Trend

14. Indian Ocean SST Trend C

15. Indian Ocean SST trend Annual mean SST trend 1951-1990 C/year 0.02 -0.02

16. Atmosphere model force with Observed Indian Ocean warming Trend

17. Jan May Sept SST Anomalies

18. Indian Ocean SST Trend C IOP ION

19. Experiment Five AGCMs –Arpege –CAM3 –Echam5 –GAM (IAP) –HadAM3 Indian Ocean Positive (IOP) Indian Ocean Negative (ION)

20. Results

21. FMA Vertical velocityRainfallSurface Temperature ARP CAM ECH GAM HAD

22. JAS Vertical velocityRainfallSurface Temperature ARP CAM ECH GAM HAD

23. Caveats?

24. Observed MSLP trends Copsey et al GRL 2006

25. MSLP Trends

26. 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?

28. Vertical Structure JAS

29. Vertical Structure FMA

30. Station rainfall trends 1950-1999 (JAS/FMA)