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Bruce T. Anderson, Boston University ( brucea@bu )

Wherefore El Niño : The impact of extra-tropical atmospheric circulations upon the tropical Pacific. Bruce T. Anderson, Boston University ( brucea@bu.edu ). Introduction.

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Bruce T. Anderson, Boston University ( brucea@bu )

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  1. Wherefore El Niño:The impact of extra-tropical atmospheric circulations upon the tropical Pacific Bruce T. Anderson, Boston University (brucea@bu.edu)

  2. Introduction • Previous research has shown that the northern hemisphere wintertime climate is strongly forced by large-scale boundary conditions associated with the concurrent El Niño/Southern Oscillation (ENSO) • Impacts local, regional and global atmospheric dynamics • Influences various climatological fields such as temperature, precipitation, and “storminess” • As such, researchers have spent considerable time investigating forcing mechanisms for the ENSO as well as the evolution of the atmospheric and oceanic components of the ENSO system

  3. Introduction con’t. • One intriguing set of results involves fields in the extra-tropics that may be related to the initiation of ENSO events • In this talk, we will summarize results from the last few years that tell a compelling story of how the extra-tropics can influence the tropical Pacific : • Influence of upper-tropospheric circulations upon the global and regional Hadley cell • Signature of these changes in the surface pressure and wind patterns • Impact upon surface and subsurface temperature fields • Subsequent influence upon the upper-tropospheric circulations (?)

  4. Non-ENSO ENSO Global-Scale Hadley Cell Circulation Caballero, 2007 (GRL)

  5. Overturning Circulation Stationary Wave Stress Role of Stationary Wave Activity Caballero, 2007 (GRL)

  6. High Overturning Role of Stationary Wave Activity Weak Overturning Caballero and Anderson, 2009 (GRL)

  7. Upper-air Stationary Waves Anderson, 2004 (J.Clim)

  8. Upper-tropospheric Circulations Anderson, 2004 (J.Clim)

  9. Surface Signature Anderson, 2004 (J.Clim)

  10. Intraseasonal Variability and Seasonal Mean Anderson, 2007 (J.Clim)

  11. Intraseasonal Variability Anderson, 2007 (J.Clim)

  12. Intraseasonal Variability and SLP Anderson, 2007 (J.Clim)

  13. Intraseasonal Variability and Winds Anderson, 2007 (J.Clim)

  14. Surface and Subsurface Temperatures Anderson, 2004 (J.Clim)

  15. Recharge/Discharge Paradigm for ENSO (Meinen and McPhaden, 2000)

  16. Surface and Subsurface Temperatures Anderson, 2004 (J.Clim)

  17. Evolution of Thermocline Depth and SSTs Model (Anderson and Maloney, 2006) Obs. 1993-99 (Meinen and McPhaden, 2001)

  18. Evolution of ENSO System Anderson, 2004 (J.Clim)

  19. Midlatitude forcing and Rossby Wave Breaking (Woollings et al, 2008) (Croci-Maspoli et al., 2007) (Anderson, 2004)

  20. Conclusions • Equatorial Pacific SST anomalies appear to be partly related to changes in large-scale, extra-tropical atmospheric circulations 12-15 months prior to boreal winter ENSO events • Related to changes in hemispheric-scale upper-air circulations • Associated with anomalous equatorward propagation of stationary wave activity over the North Pacific • Generates vertical circulation patterns over the sub-tropical and extratropical Pacific, which are co-located with variations in surface pressure and wind stress fields over the central sub-tropical and tropical North Pacific • Surface circulations can initiate the recharge/discharge mechanism that serves as the onset (or “trigger”) for ENSO events • Role of tropical, sub-tropical, and/or extratropical processes in forcing/maintaining large-scale mode of variability • Central Pacific SST anomalies • Internal atmospheric variability associated with Rossby wave breaking

  21. El Nino/Southern Oscillation

  22. El Nino/Southern Oscillation Impacts

  23. El Nino/Southern Oscillation Impacts

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