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)

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

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

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

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)

correlation skill for cross-validated hindcasts 1979/80–2012/13

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

correlation skill for cross-validated hindcasts 1979/80–2012/13

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

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

upward-propagating wave activity

(stratospheric mechanism)

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

upward-propagating wave activity

(stratospheric mechanism)

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

transient-eddy feedback

(tropospheric mechanism)

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.

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)

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

EXTRA SLIDES

wave-like anomaly preceding the

establishment of the winter NAO

vortex split preceding the

establishment of the winter NAO

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)

upward-propagating wave activity (stratospheric pathway)

transient-eddy feedback

(tropospheric mechanism)

LEFE workshop, at LOCEAN, 05/12/2013

Honda et al. (2009, GRL)

SIC (oct) SIC (nov)

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