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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
- 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]