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Volcanic source of decadal predictability in the North Atlantic

Volcanic source of decadal predictability in the North Atlantic. Didier Swingedouw, Juliette Mignot, Sonia Labetoulle , Eric Guilyardi, Gurvan Madec. DJF SST in GIN Seas ( HadISST ). A 20-yr cycle in the North Atlantic?. Swingedouw et al., in rev .

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Volcanic source of decadal predictability in the North Atlantic

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  1. Volcanicsourceofdecadalpredictabilityin the NorthAtlantic Didier Swingedouw, Juliette Mignot, Sonia Labetoulle, Eric Guilyardi, Gurvan Madec

  2. DJF SST in GIN Seas (HadISST) A 20-yr cycle in the North Atlantic? Swingedouw et al., in rev.

  3. A 20-yr cycle in the North Atlantic? Chylek et al. 2011

  4. A 20-yr cycle in the North Atlantic? April seaiceedge in the NordicSeas Divine et al. 2006 Sicre et al. 2008

  5. 20-yr cycle in IPSLCM5 10 yrs Seaicecover -, SLP- negativedelayedfeeedback EGC + 5yrs 3yrs convection + T,’ S’ + 2yrs 9yrs AMOC + Escudier et al., in rev.

  6. Advection as in Great Salinity Anomalies

  7. How canweintializethis 20-yr cycle in the model?

  8. Experimentaldesign • 5-member historical ensemble withnatural and antrhopogenicradiatiuve forcing • 5-member initialised ensemble nudgedwith SST anomalies (Reynolds et al. 2007) superimposed on eachhistorical simulation over the period 1949-2005: • 3-member hindcast ensemble every 5 years (with white noise on SST) and forecast or projection ensemble • 3-member ensemble withonlynatural and anthropogenic forcing Agung Pinatubo El Chichon

  9. AMOC Initialisation Reconstruction Obs. (Huck et Nudged • Reconstructions of the AMOC using NODC hydrographic data (Huck et al. 2008) and Latif et al. (2003) • Agreement betweennudged and reconstructions • Synchronisation also in the historical simulations Historical Control

  10. CV sites response • Convection sites explain AMOC variations

  11. Mechanisms • Agung eruption 1963-1966 • GIN SST and sea-icecover • Wind stress & EGC • SSS Labrador Sea • CV sites • AMOC • Phasing of the second maximum GSA GSA GSA • Labrador Sea SSS = 7-10 yearspredictor of the AMOC • EGC = more than 10 yearspredictor

  12. Initialisation du cycle à 20 ans 10 yrs Seaicecover -, SLP- negativedelayedfeeedback EGC + 5yrs 3yrs convection + T,’ S’ + 2yrs Agung eruption 9yrs AMOC + Escudier et al. In rev.

  13. Attribution simulations • Agung eruption in 1963 resets the 20-yr cycle in natural simulations as in historicalones, not the case in anthropogenicones

  14. Impact of volcanic forcing Climatic index Agung Model free 15 yrs Model free Time 1963 1982 1991 2006

  15. Impact of volcanic forcing Climatic index Agung El Chichon Model free 15 yrs Time 1963 1982 1991 2006

  16. Impact of volcanic forcing Climatic index Kanzow et al. 2010 Agung El Chichon Pinatubo Model free 15 yrs Destructive interference Time 1963 1982 1991 2006

  17. Impact of volcanic forcing Model free Need of simulations withoutPinatubo to confirmthisidea

  18. A simple physical model The purplecurveis a simple model of the 20-yr response to the 3 major volcanoes plus a weakening due to anthropogenic forcing:

  19. Conclusions • A 20-yr favoredfrequency in the North Atlantic in IPSL-CM5: agreement with a few data • Simple initialisation technique succeeds in synchronizing the AMOC • Due to volcanictriggering of the 20-yr cycle • And the effect of the NAO in the 1980s and 1990s • Effect of Pinatubo: destructive interference?

  20. Thankyou Didier.Swingedouw@lsce.ipsl.fr Photo by Bruno Ferron, OVIDE 2010

  21. Hindcasts AMOC 48°N • Only one member of the nudged ensemble (planned to apply to each) • 3-member ensemble of free run • Good predictiveskill for the AMOC in perfect model analysis (Persechino et al., sub.) • 90’s max. missed

  22. Hindcasts AMOC 48°N • Only one member of the nudged ensemble (planned to apply to each) • 3-member ensemble of free run • Good predictiveskill for the AMOC in perfect model analysis (Persechino et al., sub.) • 90’s max. missed

  23. Hindcasts Hind.

  24. Another ensemble

  25. CV sites response in projections

  26. Escudier et al. mechanism in projections

  27. Discussion Iwi et al.

  28. Discussion Iwi et al.

  29. Propagation of SST anomalies Box 1 • Wefollow the mininimum of SST along the gyre • 7yearsbetween Labrador and GIN • True in the model (known) • And in the SST Reynolds data! Box 2 Box 3 GSA GSA GSA Box 4

  30. Air-seaice interactions NCEP & HadISST • Anomalouswind stress in the NCEP and HadISST seaice, similar to whatisobtained in the simulations. • An indication of the existence of the air-sea-seaice interaction fromour 20-yr cycle. Nudged ensemble Historical ensemble % seaicecover

  31. Hindcasts

  32. What do weexpectfrom initialisation? Climatic index Observations Model free Model initialised Time • Assumptions: • Climatic oscillations correctlyrepresented in model (frequency, amplitude)? • There existsways to phase the twosignalsusingcoupledmodels?

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