Comparison of NAO-related changes in the North Atlantic sea ice and associated surface quantities on different time scales

The sea ice variation in the high latitude northern oceans is connected to the Arctic warming. The North Atlantic Oscillation (NAO) is a climate mode in the North Atlantic Ocean.The NAO and the northern Atlantic sea ice variations are connected with each other.Both the Arctic sea ice and NAO displays variations on various time scales, including long-term trends and interdecadal changes. In the present study, Wu and Wang (2020) distinguished variations on different time scales and revealed important differences in the NAO-related sea ice concentration (SIC), surface air temperature (SAT) and sea surface temperature (SST) patterns for trend, interdecadal and interannual variations.

The SIC has a prominent decreasing trend in the Greenland Sea and the Barents Sea (Fig. 1a), collocating with an increasing SAT trend and a weak increasing SST trend in the high-latitude North Atlantic (Fig. 1b). The wind trends display a weak NAO signal (Fig. 1a). Corresponding to the positive interdecadal NAO phase, the SIC shows a decreasing trend in the Greenland and Barents Seas (Fig. 1c). The SAT change features a west negative-east positive pattern along with positive anomalies extending to the Greenland Sea (Fig. 1d). The SST change is very weak in the Greenland Sea. Corresponding to the positive interannual NAO phase, the SIC change is opposite between the Greenland/Barents Seas and the Labrador Sea (Fig. 1e). The SAT change is characterized by a broad west-east pattern over the mid-high latitudes (Fig. 1f). The SST change features an east-west dipole pattern in the mid-latitude North Atlantic Ocean (Fig. 1f). In both interdecadal and interannual variations, NAO-related meridional wind anomalies induce anomalous advection that contributes to the SAT change together with upward longwave radiation. The SIC and SAT changes are coupled closely through surface heat fluxes in all the three time scales.

Most of previous studies did not separate variations on different time scales when analyzing the NAO-Arctic sea ice relationship. The present results suggest that it is necessary to distinguish time scales in studying the relationship among SIC, SAT and SST variations.

Wu, R.*, and Y.-Q. Wang, 2020: Comparison of North Atlantic Oscillation-related changes in the North Atlantic sea ice and associated surface quantities on different time scales. International Journal of Climatology, 40(5), 2686-2701, doi:10.1002/joc.6360.

Figure 1 Linear trend of 9-year running mean (a) SIC (%/decade, shading) and 10-m wind (m/s/decade, vector, scale at top), (b) SAT (10ºC/decade, shading) and SST (ºC/decade, red contour) in March for the period 1957-2014. The thick contours denote that the linear trend is significant at the 95% confidence level. Anomalies of detrended 9-year running mean (a) SIC (0.1%, shading) and 10-m wind (m/s, vector, scale at top), (b) SAT (ºC, shading) and SST (0.2ºC, red contour) in March obtained by regression with detrended 9-year running mean January-March NAO index for the period 1957-2014. The thick contours denote that the anomalies are significant at the 95% confidence level. Anomalies of 9-year running mean removed (a) SIC (0.1%, shading) and 10-m wind (m/s, vector, scale at top), (b) SAT (ºC, shading) and SST (0.2ºC, red contour) in March obtained by regression with 9-year running mean removed January-March NAO index for the period 1957-2014. The thick blue contours denote 50% climatological mean SIC.