Spatiotemporal variation and freeze-thaw asymmetry of Arctic sea ice in multiple dimensions during 1979 to 2020

Arctic sea ice is broadly regarded as an indicator and amplifier of global climate change.The rapid changes in Arctic sea ice have been widely concerned.However,the spatiotemporal changes in the horizontal and vertical dimensions of Arctic sea ice and its asymmetry during the melt and freeze seasons are rarely quantified simultaneously based on multiple sources of the same long time series.In this study,the spatiotemporal variation and freeze-thaw asymmetry of Arctic sea ice were investigated from both the horizontal and vertical dimensions during 1979–2020 based on remote sensing and assimilation data.The results indicated that Arctic sea ice was declining at a remarkably high rate of–5.4×10^(4) km^(2)/a in sea ice area(SIA)and–2.2 cm/a in sea ice thickness(SIT)during 1979 to 2020,and the reduction of SIA and SIT was the largest in summer and the smallest in winter.Spatially,compared with other sub-regions,SIA showed a sharper declining trend in the Barents Sea,Kara Sea,and East Siberian Sea,while SIT presented a larger downward trend in the northern Canadian Archipelago,northern Greenland,and the East Siberian Sea.Regarding to the seasonal trend of sea ice on sub-region scale,the reduction rate of SIA exhibited an apparent spatial heterogeneity among seasons,especially in summer and winter,i.e.,the sub-regions linked to the open ocean exhibited a higher decline rate in winter;however,the other sub-regions blocked by the coastlines presented a greater decline rate in summer.For SIT,the sub-regions such as the Beaufort Sea,East Siberian Sea,Chukchi Sea,Central Arctic,and Canadian Archipelago always showed a higher downward rate in all seasons.Furthermore,a striking freeze-thaw asymmetry of Arctic sea ice was also detected.Comparing sea ice changes in different dimensions,sea ice over most regions in the Arctic showed an early retreat and rapid advance in the horizontal dimension but late melting and gradual freezing in the vertical dimension.The amount of sea ice melting and freezing was disequilibrium in the Arctic during the considered period,and the rate of sea ice melting was 0.3×10^(4) km^(2)/a and 0.01 cm/a higher than that of freezing in the horizontal and vertical dimensions,respectively.Moreover,there were notable shifts in the melting and freezing of Arctic sea ice in 1997/2003 and 2000/2004,respectively,in the horizontal/vertical dimension.

Characteristics of change in the Antarctic sea ice area and its relation to SST in the tropical Pacific

In this paper, the characteristics of change in the Antarctic sea ice area are analysed by using the observed data from 1973 1986. The analysed results show that the monthly and annual change of the Antarctic sea ice area is obvious, the biggest change value is in 160°E 120°W and 60°W 100°E, the smallest value is in 110°E 160°E and 120°W 60°W. The relation between the Antarctic sea ice area and the Sea Surface Temperature(SST) in tropical Pacific is close, and the relation between the Antarctic sea ice area in each longitude belt and SST in tropical Pacific shows a clear difference. It is obvious that the Antarctic sea ice areas in 0° 90°E and 100°E 110°W have a different feedbacking relation with SST in the tropical Pacific. The notable relationship occurs in the 3 4 and 41 45 months, that quite tallies with the occurrence of El Nino.

Seasonal and inter-annual variations of Arctic cyclones and their linkage with Arctic sea ice and atmospheric teleconnections

The seasonal and inter-annual variations of Arctic cyclone are investigated. An automatic cyclone tracking algorithm developed by University of Reading was applied on the basis of European Center for Medium-range Weather Forecasts（ECMWF） ERA-interim mean sea level pressure field with 6 h interval for 34 a period. The maximum number of the Arctic cyclones is counted in winter, and the minimum is in spring not in summer.About 50% of Arctic cyclones in summer generated from south of 70°N, moving into the Arctic. The number of Arctic cyclones has large inter-annual and seasonal variabilities, but no significant linear trend is detected for the period 1979–2012. The spatial distribution and linear trends of the Arctic cyclones track density show that the cyclone activity extent is the widest in summer with significant increasing trend in CRU（central Russia）subregion, and the largest track density is in winter with decreasing trend in the same subregion. The linear regressions between the cyclone track density and large-scale indices for the same period and pre-period sea ice area indices show that Arctic cyclone activities are closely linked to large-scale atmospheric circulations, such as Arctic Oscillation（AO）, North Atlantic Oscillation（NAO） and Pacific-North American Pattern（PNA）. Moreover,the pre-period sea ice area is significantly associated with the cyclone activities in some regions.

Spatiotemporal characteristics of sea ice transport in the Baffin Bay and its association with atmospheric variability

Sea ice export through the Baffin Bay plays a vital role in modulating the sea ice cover variability in the Labrador Sea.In this study,satellite-derived sea ice products are used to obtain the sea ice area flux(SIAF)through the three passages in the Baffin Bay(referred to as A,B,and C for the north,middle,and south passages,respectively).The spatial variability of the monthly sea ice drift in the Baffin Bay is presented.The interannual variability and trends in SIAF via the three passages are outlined.The connection to several large-scale atmospheric circulation modes is assessed.Over the period of 1988-2015,the average annual(October to the following September)SIAF amounts to 555×10^(3) km^(2),642×10^(3) km^(2),and 551×10^(3) km^(2) through Passages A,B,and C,respectively.These quantities are less than that observed through the Fram Strait(FS,707×10^(3) km^(2))of the corresponding period.The positive trends in annual SIAF,on the order of 53.1×10^(3) km^(2)/(10 a)and 43.2×10^(3) km^(2)/(10 a)(significant at the 95%confidence level),are identified at Passages A and B,respectively.The trend of the south passage(C),however,is slightly negative(-13.3×10^(3) km^(2)/(10 a),not statistically significant).The positive trends in annual SIAF through the Passages A and B are primarily attributable to the significant increases after 2000.The connection between the Baffin Bay sea ice export and the North Atlantic Oscillation is not significant over the studied period.By contrast,the association with the cross-gate sea level pressure difference is robust in the Baffin Bay(R equals 0.69 to 0.71,depending on the passages considered),but relatively weaker than that over FS(R=0.74).

EFFECTS OF VARIATION OF WINTER SEA-ICE AREA IN KARA AND BARENTS SEAS ON EAST ASIA WINTER MONSOON

By analyzing the observation data and performing the numerical simulation tests,it is shown that the Kara and the Barents Sea area is a key region to influence climate variation over the Northern Hemisphere.The variation of winter sea-ice area in the key region is closely associated with that of the EU teleconnection pattern at 500 hPa and East Asia winter monsoon(EAWM) intensity.When a heavy sea-ice prevails in the key region,the EU teleconnection pattern at 500 hPa is excited easily(there are positive 500 hPa height anomalies over around Japan and West Europe),and winter Siberia high is weakened,meanwhile,sea level pressure(SLP)has positive anomalies over the Northern Pacific.Therefore,EAWM will be weakened,winter temperature over East Asia is above normal and the frequency of cold-air activity in February in China will be decreased.When the light sea-ice occurs in the key region,the results will be opposite.

加拿大北极地区航运对气候变暖的影响

This paper presents a detailed account of the effect of shipping activity on the increasing trends of air temperatures in the Canadian Arctic region for the period of 1980–2018.Increasing trend of temperature has gained significant attention with respect to shipping activities and sea ice area in the Canadian Arctic.Temperature,sea ice area and shipping traffic datasets were investigated,and simple linear regression analyses were conducted to predict the rate of change(per decade)of the average temperature,considering winter(January)and summer(July)seasons.The results indicate that temperature generally increased over the studied region.Significant warming trend was observed during July,with an increase of up to 1℃,for the Canadian Arctic region.Such increasing trend of temperature was observed during July from the lower to higher latitudes.The increase in temperature during July is speculated to increase the melting of ice.Results also show a decline in sea ice area has a significant positive effect on the shipping traffic,and the numbers of marine vessel continue to increase in the region.The increase in temperature causes the breaking of sea ice due to shipping activities over northern Arctic Canada.