1. NACLIM CT1-3 meeting, at MPI, 19-20/03/2014 On the predictability of the winter North Atlantic Oscillation: lagged influence of autumn Arctic sea-ice and Eurasian snow J. García-Serrano, C. Frankignoul LOCEAN-IPSL, Paris, France with contributions from: G. Gastineau (LOCEAN-IPSL) and A. de la Cámara (LMD-IPSL)

2. further explore the covariability by means of describing the spatial patterns and the associated dynamics; two key elements for assessing model reproducibility and performing sensitivity experiments NACLIM CT1-3 meeting, at MPI, 19-20/03/2014 On the predictability of the winter North Atlantic Oscillation: lagged influence of autumn Arctic sea-ice and Eurasian snow

3. NACLIM CT1-3 meeting, at MPI, 19-20/03/2014

5. extended-MCA (EMCA) weekly snow cover extent in October (40th-44th) (Cohen and Jones 2011)

6. correlation skill for cross-validated hindcasts 1979/80–2012/13 NACLIM CT1-3 meeting, at MPI, 19-20/03/2014

7. correlation skill for cross-validated hindcasts 1979/80–2012/13 NACLIM CT1-3 meeting, at MPI, 19-20/03/2014

9. upward-propagating wave activity (stratospheric mechanism) NACLIM CT1-3 meeting, at MPI, 19-20/03/2014

10. upward-propagating wave activity (stratospheric mechanism) NACLIM CT1-3 meeting, at MPI, 19-20/03/2014

11. transient-eddy feedback (tropospheric mechanism) NACLIM CT1-3 meeting, at MPI, 19-20/03/2014

12. Summary: September Arctic sea-ice variability (MCA-SIC), in particular over the Barents-Kara Seas, is associated with a wave-like anomaly crossing Eurasia in November that (i) impacts vertical wave activity over both the North Pacific and northern European sectors, thus modulating the stratospheric vortex strength; and (ii) induces a positive transient- eddy feedback over the eastern North Atlantic helping to maintain the tropospheric anomaly. Negative SIC anomalies (i.e. sea-ice reduction) over the Barents-Kara Seas are followed by a negative NAO phase in winter. Time-evolving October Eurasian snow variability (EMCA-SCE) shows a south-westward progression from eastern to central Siberia, with larger SCE anomalies preceding a negative NAO phase in winter. This time-evolving SCE pattern leads to changes in the Siberian High, which further lead to enhanced/reduced vertical wave activity over eastern Eurasia affecting the stratospheric polar vortex over the North Pacific sector. These observational, surface-boundary forcings (Arctic SIC; Eurasian SCE) can be used to formulate empirical predictions of the winter NAO index (>50%) and European surface climate, as benchmark for dynamical predictions. NACLIM CT1-3 meeting, at MPI, 19-20/03/2014

13. J. García-Serrano and C. Frankignoul (2014) - Nature Geoscience, 7, 10.1038/NGEO2118 J. García-Serrano, C. Frankignoul, G. Gastineau, A. de la Cámara (2014) - J. Climate (almost-submitted) The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 (NACLIM – www.naclim.eu) NACLIM CT1-3 meeting, at MPI, 19-20/03/2014

14. EXTRA SLIDES

15. wave-like anomaly preceding the establishment of the winter NAO vortex split preceding the establishment of the winter NAO

16. vortex splits are followed by negative NAO-like at surface (Mitchell et al. 2013, JCLIM) wave-like anomaly precedes NAO-like (Kuroda & Kodera 1999, GRL) leading to enhanced vertical propagation of wave actvity (Garfinkel et al. 2010, CDYN)

17. upward-propagating wave activity (stratospheric pathway)

18. transient-eddy feedback (tropospheric mechanism) LEFE workshop, at LOCEAN, 05/12/2013

20. Honda et al. (2009, GRL)

21. SIC (oct)SIC (nov)

22. The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 NACLIM www.naclim.euwww.naclim.eu