Relationships between Arctic sea-ice concentration, temperature, and specific humidity in the lower troposphere during 1980–2021

Abstract. Understanding of the local effects of sea-ice concentration (SIC) variations on the Arctic atmosphere is a prerequisite for assessing the role of Arctic sea-ice decline in the climate system, including its influence on mid-latitudes. In this study, we analysed the relationships between SIC and both temperature and specific humidity at the surface and 2 m level, as well as at 950, 850, 750, and 600 hPa across the circumpolar Arctic. The role of wind speed and direction in the relationships between SIC and both temperature and specific humidity is discussed. We applied linear ordinary-least-square-regression analysis to detrended anomalies of monthly means of data from the NCEP/CFSR atmospheric reanalysis for 1980–2021. The results show the strongest correlations between SIC and temperature, as well as between SIC and specific humidity, in the marginal ice zone during the cold seasons (November–April) with the coefficient of determination (R2) around 0.6 at the surface and near-surface levels and around 0.3 at 950 and 850 hPa. We interpret the statistical results for these cold seasons so that SIC affects air temperature and specific humidity, while the effects of air temperature variations are limited. SIC correlates somewhat better with specific humidity than with temperature, which can be attributed to the exponential dependence of saturation specific humidity on temperature. In the Central Arctic, physical conditions are favourable for high R2 values, but low variability in SIC reduces the correlations. In contrast, in regions such as the northern Barents Sea, increased November–April SIC variability from 1980–2000 to 2001–2021 strengthens the correlations, even though previous studies showed that surface heat and moisture fluxes become less sensitive to SIC in a warming climate. This finding suggests that statistical effects can outweigh the physical sensitivity in shaping observed relationships. During the warm seasons (May–October), high enough air temperatures reduce SIC via melting, while the effect of SIC on air temperature and specific humidity cannot be large, as the surface temperature of the sea ice is very close to that of the open ocean. The relationships between SIC and both temperature and specific humidity are generally weaker during these warm seasons with R2 at the surface and near-surface levels around 0.4 over the marginal ice zone during May–July and across the entire sea-ice zone during August–October.