NACLIM Annual Meeting, 14-15/10/2014

J. García-Serrano, C. Frankignoul

LOCEAN-IPSL, Paris, France

On the feedback of the winter NAO-driven sea ice anomalies

NACLIM Annual Meeting, 14-15/10/2014

[Strong et al. 2009, JCLIM]

[Strong et al. 2009, JCLIM]

There is a negative feedback of the NAO-driven sea-ice anomalies to the atmosphere (in winter);

which is due to its long damping time-scale

NACLIM Annual Meeting, 14-15/10/2014

[Strong et al. 2009, JCLIM]

[Strong et al. 2009, JCLIM]

[e.g. Magnusdottir et al. 2004, JCLIM; Deser et al. 2004, JCLIM]

Z500 (DJFM)

NACLIM Annual Meeting, 14-15/10/2014

[Strong et al. 2009, JCLIM]

(detrended) SIC anomalies in the Atlantic basin persist for more than 2-3 months

NACLIM Annual Meeting, 14-15/10/2014

feedback with December-SIC is dominated by anomalies east of Greenland, especially

over the Greenland Sea

feedback with January-SIC is dominated by anomalies west of Greenland

NACLIM Annual Meeting, 14-15/10/2014

NACLIM Annual Meeting, 14-15/10/2014

NACLIM Annual Meeting, 14-15/10/2014

NACLIM Annual Meeting, 14-15/10/2014

- January: westward tilt with height over Europe, suggestive of Rossby wave; at 200hPa wave-like anomaly

- February: hemispheric scale; projecting on the NAO + annular structure at 50hPa

- negative feedback!

NACLIM Annual Meeting, 14-15/10/2014

- February: regional scale; showing a dipole-like anomaly at 200hPa + wave-1 signature at 50hPa

- negative feedback!

NACLIM Annual Meeting, 14-15/10/2014

Summary:

• The negative feedback of the winter NAO-driven SIC anomalies to the atmosphere can be observed with monthly data, which is consistent with its long decaying time-scale (longer than 2-3 months). The feedback is statistically significant on the atmosphere of February, thereby January is a transition month.

• There appears to be an intra-seasonal behaviour in this feedback (atmospheric response): with SIC-forcing in December dominated by anomalies east of Greenland (i.e. the Greenland Sea), and SIC-forcing in January dominated by anomalies west of Greenland (i.e. Davis Strait/Labrador Sea).

• If there is a persistent NAO in December, SIC anomalies are followed, in February, by a NAO-like pattern in the troposphere and an annular structure in the stratosphere.

• If there is a persistent NAO in January, SIC anomalies are followed by a regional atmospheric anomaly over the North Atlantic, and a wave-1 structure in the stratosphere.

• The existence of the winter NAO-driven SIC dipolar anomaly might represent an additional source of uncertainty in the atmospheric response (AGCM) to current sea-ice trends and projected changes.

NACLIM Annual Meeting, 14-15/10/2014

• The existence of the winter NAO-driven SIC dipolar anomaly might represent an additional source of uncertainty in the atmospheric response (AGCM) to current sea-ice trends and projected changes.

Nov-Dec Jan-Feb

[Deser et al. 2010, JCLIM]

[Screen et al. 2013, JCLIM]

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