The Impact Of Arctic Oscillation And Cloud Attributes In Spring And Summer On September Sea Ice Retreat In The Arctic

Satellite observations show that Arctic sea ice keeps shrinking beyond the expectation of natural variability,especially in September,the end of the melting period.The results of a large number of diagnostic analysis and numerical models show that the retreat of Arctic sea ice is not only a sensitive indicator of Arctic amplification and the Arctic energy balance,but also an important factor in the extreme weather in middle and low latitudes and the global atmospheric circulation.Therefore,a detailed understanding of the Arctic sea ice change is important to understand and predict the global climate change in the future.Arctic clouds have raised widely concern since the radiation feedback effects between the Arctic cloud and solar radiation have been discovered.Previous studies have found that as the most direct cloud property that affect the Arctic surface radiation balance,cloud radiation forcing(CRF)is closely related to Arctic sea ice.In addition,as the leading mode of Northern Hemisphere atmospheric circulation,the Arctic Oscillation(AO)also has an important impact on the variation of Arctic sea ice.However,current researches mainly focus on the dynamic processes of the impact of the AO on Arctic sea ice variation.Research about the thermodynamic mechanism in the processes of the AO influences Arctic sea ice variation is in short.Whether the AO can regulate Arctic sea ice variability by affecting Arctic CRF remains unknown.In addition,thanks to the global warming and rapid climate change,the interactions between AO and Arctic sea ice remain a complex problem.Therefore,based on the cloud attributes and temperature data from ERA5 reanalysis datasets,sea ice concentration(SIC)data from NSIDC,Arctic Oscillation Index(AOI)data from Climate Prediction Center(CPC)from 1979-2020,the paper analyzes the climate characteristics of the Arctic cloud properties in spring and summer.Then the paper discusses the mechanism of the impact of the AO on CRF.Finally,the paper focuses on the spatial and temporal characteristics of September sea ice change as well as the responses of the sea ice variability over the ROI(Region of Interest)to springtime and summertime cloud properties and AO.Main conclusions are drawn as follows:1.In spring,in terms of the average spatial distribution,the maximum of the LW CRF(Long Wave Cloud Radiative Forcing)and TWC(Total Cloud Water Content)appears in the Pacific sector of the Arctic Ocean,which may be closely related to the severe condition of sea ice retreat in this region.The low CF(Cloud Fraction)in the solid ice area is less than that in the open water.The high CF in the solid ice area is more than that in the solid ice area,which may be related to the higher temperature and stronger convection of the open water in spring.In terms of the relationship between CRF and CF as well as TWC,the CF and LW CRF have positive and negative correlations in different regions.As the height increases,the positive correlation strengthens,and the region expands to the open water of the Pacific Ocean.Meanwhile,the negative correlation decreases,and the region tends to narrow.The TWC is positively correlated with LW CRF,which is stronger and more extensive than the positive correlation between CF and LW CRF.That may be related to the direct radiation effects of the water vapor.2.In summer,in terms of the average spatial distribution,the minimum of the SW CRF(Short Wave Cloud Radiative Forcing)appears in the Pacific sector of the Arctic Ocean.That may be related to the enhanced cloud albedo effects,which is the result of the sea ice retreat.The distribution patterns of CF and TWC are similar.Generally,the value of CF and TWC are larger in summer than in spring.That is tightly connected with the seasonal sea ice retreat.In addition,the minimum value of low-level CF(TWC)and maximum value of middle and high-level CF(TWC)are observed over Eastern Siberian Sea and Laptev Sea which might be caused by the divergence of low-level water vapor and the convergence of middle and high-level water vapor over the region.In terms of the relationship between CRF and CF as well as TWC in summer,significantly positive and negative correlation between CRF and CF(TWC)are both observed.The correlation between CRF and CF(TWC)tends to decrease with altitude.The correlation between CRF and TWC is weaker than the correlation between CRF and CF in terms of both strength and significance.Summertime cloud is of vital importance in regulating the variability of SW CRF.3.The springtime AOI and the LW CRF anomaly are generally positive,and the summertime AOI and the SW CRF anomaly are generally negative.This correlations in spring and summer are particularly significant over ROI.But under the control of the Northern Hemisphere atmospheric circulation,the responses of springtime LW CRF and summertime SW CRF to atmospheric conditions are different.During the positive AOI,the instability of the springtime low-level atmosphere and the growth of the springtime CF as well as the low-level TWC tend to promote the growth of LW CRF.However,during the positive AOI,he instability of the summertime low-level atmosphere and the growth of the summertime CF as well as the low-level TWC can’t explain the growth of SW CRF.The growth of SW CRF over ROI related to positive AOI may be caused by other dynamics and/or thermodynamic processes.4.In the past 42 years,the September sea ice in the Arctic Ocean has experienced several sea ice minimum events,and sea ice extent(SIE)has decreased at an average rate of 4.4 10 6)8)/.Since 2006,the decline rate has slowed down.From the perspective of spatial variation,the decrease trend of sea ice concentration(SIC)over ROI is very significant,and the average decline rate of SIC is more than 0.3%/.However,sea ice density has increased,rather than decreased,in solid ice areas near the Canadian islands and northern Greenland in the Arctic Ocean.The average Arctic SIC of42 years increases with the increase of latitude,and the overall distribution of the western hemisphere is larger than that of the eastern hemisphere.5.Over the ROI,the positive anomaly of springtime LW CRF and the positive AOI both have significant effects to promote September sea ice decline.The springtime LW CRF makes up about 32.5% of the SIE variability The springtime AOI makes up about11.70% of the SIE variation.The impact of LW CRF and AO on sea ice is not independent.In fact,the positive(negative)AOI can accelerate(decelerate)the loss of sea ice by promoting the increase(decrease)of the LW CRF.Similarly,the strong(weak)springtime LW CRF can also increase(reduce)AOI to speed up the decline of sea ice.However,springtime CF and TWC can’t pre-regulate September sea ice change,due probably to the indirect radiative effects of CF and TWC on the Arctic sea ice.6.Over the ROI,the increased(decreased)summertime SW CRF and increased(decreased)AOI promote the growth of September sea ice.The SW CRF makes up about39.7% of the SIE variability,which is even more important than the spring LW CRF.The summertime AOI makes up about 8.6% of the SIE variability,which is more important than the spring AOI.The impact of SW CRF and AOI on sea ice in summer are not independent.Positive(negative)AOI can increase(decrease)the SW CRF in promoting the growth(retreat)of September sea ice.Similarly,the increased(decreased)summertime SW CRF can also increase(decrease)AOI to accelerate(decelerate)the growth of sea ice.In addition,the increased TWC can also reduce the sea ice over ROI.TWC makes up about 10.8% of the SIE variability.However,the influence of summertime TWC on September sea ice is through direct or indirect effects by other thermal and/or dynamic processes,rather than the short-wave cloud radiative effects.