1. Volcanic source of decadal predictability in the North Atlantic Didier Swingedouw, Juliette Mignot, Sonia Labetoulle, Eric Guilyardi, Gurvan Madec

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

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

4. Sicre et al. 2008 Divine et al. 2006 April sea ice edge in the Nordic Seas

5. T,’ S’ + EGC + 5yrs 3yrs negative delayed feeedback AMOC + 9yrs 10 yrs 20-yr cycle in IPSLCM5 2yrs convection + Sea ice cover -, SLP- Escudier et al., in rev.

6. Advection as in Great Salinity Anomalies

7. How can we intialize this 20-yr cycle in the model?

8. Experimental design 5-member historical ensemble with natural and antrhopogenic radiatiuve forcing 5-member initialised ensemble nudged with SST anomalies (Reynolds et al. 2007) superimposed on each historical 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 with only natural and anthropogenic forcing Agung El Chichon Pinatubo

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

10. CV sites response Convection sites explain AMOC variations

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

12. T,’ S’ + EGC + 5yrs 3yrs negative delayed feeedback AMOC + 9yrs 10 yrs Initialisation du cycle à 20 ans 2yrs convection + Sea ice cover -, SLP- Escudier et al. In rev. Agung eruption

13. Attribution simulations  Agung eruption in 1963 resets the 20-yr cycle in natural simulations as in historical ones, not the case in anthropogenic ones

14. Impact of volcanic forcing Climatic index Time Model free Agung 15 yrs 196319821991 2006

15. Impact of volcanic forcing Climatic index Time Model free Agung 15 yrs El Chichon 196319821991 2006

16. Impact of volcanic forcing Time Model free Agung 15 yrs El Chichon Pinatubo 196319821991 2006 Destructive interference Kanzow et al. 2010 Climatic index

17. Impact of volcanic forcing Model free Need of simulations without Pinatubo to confirm this idea

18. A simple physical model The purple curve is 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 favored frequency in the North Atlantic in IPSL- CM5: agreement with a few data Simple initialisation technique succeeds in synchronizing the AMOC Due to volcanic triggering of the 20-yr cycle And the effect of the NAO in the 1980s and 1990s Effect of Pinatubo: destructive interference?

20. Thank you 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 predictive skill 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 predictive skill 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.

29. Propagation of SST anomalies  We follow the mininimum of SST along the gyre  7 years between Labrador and GIN  True in the model (known)  And in the SST Reynolds data! Box 1 Box 2 Box 3 Box 4 GSA

30. Air-sea ice interactions  Anomalous wind stress in the NCEP and HadISST sea ice, similar to what is obtained in the simulations.  An indication of the existence of the air-sea- sea ice interaction from our 20-yr cycle. NCEP & HadISST Nudged ensemble Historical ensemble % sea ice cover

31. Hindcasts

32. What do we expect from initialisation? Climatic index Time Observations Model free Model initialised Assumptions: 1.Climatic oscillations correctly represented in model (frequency, amplitude)? 2.There exists ways to phase the two signals using coupled models?