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

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. 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 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

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

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

5. NACLIM CT1-3 meeting, at MPI, 19-20/03/2014 extended-MCA (EMCA) weekly snow cover extent in October (40th-44th) (Cohen and Jones 2011)

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

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

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

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

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

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

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

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

14. EXTRA SLIDES

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

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

17. upward-propagating wave activity (stratospheric pathway)

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

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.eu