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

Satellite-derived sea-ice concentration (SIC) and re-analysed atmospheric data are used to analyse the potential feedback of the North Atlantic Oscillation (NAO)-driven sea-ice anomalies in winter onto the atmosphere during 1979–2013. A maximum covariance analysis shows that this feedback can be detected with monthly data. When SIC leads, the covariability between Atlantic SIC and the Euro-Atlantic atmospheric circulation in February is statistically significant, but shows intra-seasonal differences: the December SIC influence is dominated by anomalies east of Greenland, with maximum amplitude in the Greenland Sea (GS); while the January SIC influence is dominated by anomalies west of Greenland, in the Davis Strait-Labrador Sea (DL) region. The lagged atmospheric anomalies are likewise different. A reduction of SIC over GS in December is followed in February by a negative NAO-like pattern near the surface and a hemispheric signature in the upper-troposphere, thus acting as a negative feedback. On the other hand, a reduction of SIC over DL in January is followed by an atmospheric anomaly over the North Atlantic that projects on the positive phase of the East Atlantic pattern. The dynamics associated with these atmospheric anomalies is described, indicating that transient-eddy activity is likely at work in settling the large-scale patterns. The role of concomitant North Atlantic sea surface temperature anomalies is discussed.