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Respective forcing of the Indian Ocean And Western Pacific warming on the

Respective forcing of the Indian Ocean And Western Pacific warming on the Northern hemisphere atmospheric circulation. Cassou, Sanchez, Hodson, Keenlyside, Okumura, Zhou, Sutton. Bologna, Feb. 2008. SST [1976-2001] – SST[1960-1990]. ARPEGE4.4 HADAM ECHAM5 IAP CAM3. WIP. 40-year WIP

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Respective forcing of the Indian Ocean And Western Pacific warming on the

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

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

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

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

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

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

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

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

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

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

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

  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 HADAM ARPEGE ECHAM IAP Southward shift of the ITCZ In all the models CAM Multi Northward shift of the ITCZ In all the models INDO-PAC INDO-ONLY

  14. 3. Model response for JJA Precip ARPEGE HADAM ECHAM IAP NO SIGNIFICANT CHANGES CAM Multi INDO-PAC INDO-ONLY

  15. 4. Model response for JJA VP200 ARPEGE HADAM ECHAM IAP INDO-PAC CAM Multi LOCAL CHANGES INDO-ONLY

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

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

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

  19. 8. DJF U200(clim)+V200 ARPEGE HADAM ECHAM IAP The Pacific Route Along the wave guide CAM INDO-ONLY INDO-PAC

  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.

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