Factors contributing to rapid decline of Arctic sea ice in autumn

Autumn Arctic sea ice has been declining since the beginning of the era of satellite sea ice observations.In this study,we examined the factors contributing to the decline of autumn sea ice concentration.From the Beaufort Sea to the Barents Sea,autumn sea ice concentration has decreased considerably between 1982 and 2020,and the rates of decline were the highest around the Beaufort Sea.We calculated the correlation coefficients between sea ice extent(SIE)anomalies and anomalies of sea surface temperature(SST),surface air temperature(SAT)and specific humidity(SH).Among these coefficients,the largest absolute value was found in the coefficient between SIE and SAT anomalies for August to October,which has a value of−0.9446.The second largest absolute value was found in the coefficient between SIE and SH anomalies for September to November,which has a value of−0.9436.Among the correlation coefficients between SIE and SST anomalies,the largest absolute value was found in the coefficient for August to October,which has a value of−0.9410.We conducted empirical orthogonal function(EOF)analyses of sea ice,SST,SAT,SH,sea level pressure(SLP)and the wind field for the months where the absolute values of the correlation coefficient were the largest.The first EOFs of SST,SAT and SH account for 39.07%,63.54%and 47.60%of the total variances,respectively,and are mainly concentrated in the area between the Beaufort Sea and the East Siberian Sea.The corresponding principal component time series also indicate positive trends.The first EOF of SLP explains 41.57%of the total variance.It is mostly negative in the central Arctic.Over the Beaufort,Chukchi and East Siberian seas,the zonal wind weakened while the meridional wind strengthened.Results from the correlation and EOF analyses further verified the effects of the ice-temperature,ice-SH and ice-SLP feedback mechanisms in the Arctic.These mechanisms accelerate melting and decrease the rate of formation of sea ice.In addition,stronger meridional winds favor the flow of warm air from lower latitudes towards the polar region,further promoting Arctic sea ice decline.

Recent Rapid Decline of the Arctic Winter Sea Ice in the Barents–Kara Seas Owing to Combined Effects of the Ural Blocking and SST

This study investigates why the Arctic winter sea ice loss over the Barents–Kara Seas（BKS） is accelerated in the recent decade. We first divide 1979–2013 into two time periods： 1979–2000（P1） and 2001–13（P2）, with a focus on P2 and the difference between P1 and P2. The results show that during P2, the rapid decline of the sea ice over the BKS is related not only to the high sea surface temperature（SST） over the BKS, but also to the increased frequency,duration, and quasi-stationarity of the Ural blocking（UB） events. Observational analysis reveals that during P2, the UB tends to become quasi stationary and its frequency tends to increase due to the weakening（strengthening） of zonal winds over the Eurasia（North Atlantic） when the surface air temperature（SAT） anomaly over the BKS is positive probably because of the high SST. Strong downward infrared（IR） radiation is seen to occur together with the quasi-stationary and persistent UB because of the accumulation of more water vapor over the BKS. Such downward IR favors the sea ice decline over the BKS, although the high SST over the BKS plays a major role. But for P1, the UB becomes westward traveling due to the opposite distribution of zonal winds relative to P2, resulting in weak downward IR over the BKS. This may lead to a weak decline of the sea ice over the BKS. Thus, it is likely that the rapid decline of the sea ice over the BKS during P2 is attributed to the joint effects of the high SST over the BKS and the quasi-stationary and long-lived UB events.