Multi-time-scale Variability And Attribution Of Arctic Sea Ice Over The Past 41 Years

Based on the daily observations of sea ice data,timing of Arctic sea ice melt onset and freeze up data,as well as the daily atmospheric and oceanic data from 1979 to 2019,the characteristics of freezing and thawing process of Arctic sea ice are firstly analyzed in this study.And then,the characteristics of intraseasonal oscillation(ISO)in sea ice concentration(SIC)and sea ice thickness(SIT)are analyzed respectively.Further,the variation of ISO characteristics of SIC and SIT in the context of rapid Arctic sea ice melting was studied.In addition,the effects of high latitude atmosphere and ocean ISO on sea ice in the northern hemisphere are also discussed.Finally,the simulation effect of 20 Earth system models in CMIP6 on ISO of sea ice is evaluated.The main conclusions are as follows:1.In the past 41 years,sea ice in the Arctic margin has melted earlier and frozen later,and even more so in the Atlantic sector.The interannual increase of the total energy absorbed by the sea ice surface in the Arctic marginal during the melting period leads to the earlier melting and later freezing of the sea ice there.Moreover,the increase of the melting pool since 2002 has led to a jump in the amount of energy absorbed during the melting period and the amount of sea ice melting.As a result,the Arctic has more seasonal ice and thin ice to produce.The seasonal melting and freezing of sea ice are closely related to the seasonal variation of radiation flux,while the intraseasonal variation of sea ice has a good inverse correlation with the intraseasonal variation of sensible heat flux and net long wave radiation.In addition,wind also plays an important role in the changes of sea ice.Taking the 2007 melt season as an example,the large-scale circulation field and the wind field affect the movement of sea ice and the polarity transport of heat.Wind speed and arctic cyclones,on the other hand,have significant effects on sea ice on intraseasonal time scale.Wind speed varies inversely with the area and thickness of sea ice.Strong winds associated with Arctic cyclones can make sea ice move quickly and break up,bring water vapor and warm air,and promote sea ice melting by affecting the vertical mixing of regional oceans.With the decline of sea ice in recent decades,sea ice has become more sensitive to atmospheric dynamic and thermal forcing and is more prone to change on an intraseasonal time scale.2.The ISO signal of SIC first moved north and then south from April to March of the next year.The ISO intensity of SIC and SIT were stronger in the winter half year of the Arctic(Octover-March).The strong ISO of SIC occurred in the SIC range of0.15-0.8,and the strong ISO of SIT occurred in the SIT range of 1-1.7m.The ISO period of SIC and SIT shows spatial inhomogeneity: for SIC,the period of Region 1(20°E-90°W,55°N-90°N)is 50-60 days,and that of Region 2(90°W-0°,55°N-80°N)is 60-70 days.For SIT,the periods of Region 3(100°E-90°W,70°N-80°N)and Region 4(60°W-100°E,75°N-85°N)are both 50-60 days,but Region 3 is closer to 60 days and Region 4 is closer to 50 days.Within an ISO period of SIC and SIT,both the ISO signals of SIC and SIT moved eastward.Under the background of rapid reduction of sea ice,the region where the strong ISO of SIC occurs shifts northward,and the ISO period of SIC in Region1 decreased from 60 days to approximately 50 days;The intensity of SIT ISO in Arctic marginal is weakened,the ISO of SIT in central sea ice area becomes stronger;Moreover,the ISO signal of SIT in Region 3 moves slowly,the SIT ISO signal east of 160°E becomes stronger,and the eastward shift of the SIT ISO signal in Region 4 disappears.The ISO of the sea level pressure(SLP)in the northern hemisphere winter half year is similar to the AO mode,with a period of 50-60 days.When AO-(+),positive(negative)surface air temperature(SAT)and sea surface temperature(SST)anomalies are more likely to occur in the Arctic marginal sea area.The positive(negative)SAT anomalies are caused by southerly(north)wind.SST anomalies are caused by wind-driven ocean currents and heat transfer between sea and air.During the weakening of AO-(+),the negative(positive)abnormal strengthening and moving of SLP in the Barents and Kara Sea(B-K Sea)resulted in the strengthening and moving of cyclonic(anticyclonic)wind field in the region,and then,the occurrence of positive(negative)air temperature and SST anomalies and the eastward movement along the marginal sea,leading to the intra-seasonal melting and freezing of sea ice in the marginal sea region.3.The ability of the Earth System Model to simulate ISO of sea ice directly determines its overall ability to simulate sea ice.Compared with the 20 models,the model with CICE as the sea ice component is a better model to simulate the ISO spatial state of SIT.EC-EARTH3,EC-EARTH3-VEG(sea ice component is NEMO-LIM)and three MPI models(sea ice component is unnamed)can better simulate ISO spatial distribution of SIC.In addition,the models which sea ice component is NEMO-LIM,the MPI models and the MRI-ESM2.0 model performed better in simulating the ISO period of SIC and SIT.Moreover,most of the 20 models failed to simulate the movement characteristics of SIT ISO,but 11 models simulated the eastward shift of SIC ISO signal,including 4 models with CICE sea ice component and 4 with NEMO-LIM sea ice component.