1. Respective forcing of the Indian Ocean And Western Pacific warming on the Northern hemisphere atmospheric circulation Bologna, Feb. 2008Cassou, Sanchez, Hodson, Keenlyside, Okumura, Zhou, Sutton

2. SST [1950-1975] – SST[1960-1990] SST [1976-2001] – SST[1960-1990] 1. Quick summary of the experimental design SST [1976-2001] – SST[1960-1990] SST averaged over the entire basin Goal: quantify the influence of the INDO-PAC warming on the Northern hemisphere circulation 1.ARPEGE4.4 2.HADAM 3.ECHAM5 4.IAP 5.CAM3 40-year WIP 40-year CIP CIP WIP NCEP Z500 JJA [1976-2001] – [1950-1975] NCEP Z500 DJF [1976-2001] – [1950-1975] BL NAO+

3. 2. Models responses for DJF Precip ARPEGE HADAM ECHAMIAP [40-yr WIP]-[40-yr CIP] CAM Multi 2 groups of models: ARP / HAD / ECH : Increased precip Along a Madagascar/Sumatra line IAP / CAM : Weak local response

4. 3. Models responses for DJF Z500 ARPEGE HADAM ECHAM IAP CAM Multi [40-yr WIP]-[40-yr CIP]

5. 4. Models responses for DJF Z500 ARPEGE HADAM ECHAMIAP CAM Multi NCEP Z500 DJF [1976-2001] – [1950-1975] [40-yr WIP]-[40-yr CIP]

6. 5. Models responses for JJA Precip ARPEGE HADAM ECHAMIAP Northward shift of the ITCZ In all the models [40-yr WIP]-[40-yr CIP] CAM Multi Regional discrepancies are associated with different mean states

7. 6. Relationship between response and climatology ARPEGEHADAM ECHAMIAP CAM Multi Impossible to have a clear/deterministic response over monsoon regions [40-yr WIP]-[40-yr CIP]

8. ARPEGE HADAM ECHAM IAP CAM Multi 7. Models responses for JJA Precip over Africa [40-yr WIP]-[40-yr CIP] Similar conclusions to e.g. Giannini et al (2003) Large decrease of rainfall Over Africa

9. ARPEGEHADAM ECHAM IAP CAM Multi 8. Models responses for JJA VP200 [40-yr WIP]-[40-yr CIP] Large change in Walker cells

10. 10. Models responses for JJA Z500 ARPEGE HADAM ECHAMIAP CAM Multi [40-yr WIP]-[40-yr CIP]

11. 9. Models responses for JJA Z500 ARPEGE HADAM ECHAMIAP CAM Multi NCEP Z500 JJA [1976-2001] – [1950-1975] [40-yr WIP]-[40-yr CIP]

12. 1. West Pac : OUT WIP-CIP WIO-CIO Western Pacific removed and set to [1961-1990] Indian SSTs are strictly identical

13. 2. Model response for JJA precip ARPEGE HADAM ECHAMIAP CAMMulti INDO-PACINDO-ONLY Northward shift of the ITCZ In all the models Southward shift of the ITCZ In all the models

14. 3. Model response for JJA Precip ARPEGEHADAM ECHAMIAP CAMMulti INDO-PACINDO-ONLY NO SIGNIFICANT CHANGES

15. 4. Model response for JJA VP200 ARPEGEHADAM ECHAM IAP CAMMulti INDO-PAC INDO-ONLY LOCAL CHANGES

16. 5. JJA Z500 ARPEGEHADAM ECHAM Multi IAP CAM INDO-PAC INDO-ONLY WEAK AND NO CONSISTENT CHANGES

17. 6. DJF Z500 ARPEGEHADAM ECHAM Multi IAP CAM INDO-PAC INDO-ONLY VERY STRONG AND UNREALISTIC CHANGES

18. 7. DJF U200(clim)+V200 ARPEGEHADAM ECHAMIAP CAM INDO-PAC Zonally chains of anomalies associated with Disturbances in the vicinity of the mean jets (particulartly the jet that stretches across South Asia Branstator (2002) The Pacific Route along the wave guide

19. 8. DJF U200(clim)+V200 ARPEGEHADAM ECHAMIAP CAM INDO-PAC INDO-ONLY The Pacific Route Along the wave guide

20. 9. Conclusions 1. We need to be very careful in what we call “indian ocean” 2. Differences in responses to Indian ocean warming in literature are due to model climatologies and also to the selected forcing domain 3. Indian-West-Pacific warming leads to changes in the North Atlantic that projects Onto the positive phase of the NAO. 4. True NAO in two models (HAD/ARP) and two wavy patterns (CAM/ECHAM)… two mechanisms (direct route via the Pacific –jet wave guide) and indirect via the walker Cell (still under investigation) 5. Removing the west Pacific warming leads to unrealistic results (very strong in winter, Very weak in summer)… The WP warming tends to counteract the direct Indian warming… Separating the two of them might be not physical.