Study On The Variation Of Summer Arctic Sea Ice Region Albedo And Its Relationship With Climate Factors

Albedo represents the ability of the earth to reflect the short-wave radiation from the sun and plays an important role in the energy distribution between the atmosphere and the surface.Arctic sea ice has changed significantly in recent decades,mainly in the decrease of sea ice area and sea ice thickness,and the increase of open water region in the Arctic.Because sea ice albedo is much larger than that of sea water,the ocean absorbs more solar energy,and some of which is used to melt the sea ice,so the sea ice is further reduced.The change of sea ice and albedo will have an important impact on the global climate.Therefore,it is of great significance to analyze the temporal and spatial variation of Arctic albedo with the remote sensing observation data of long time series.The spatiotemporal variations in the sea ice region albedo over the entire Arctic region and its eight sea areas?the Central Arctic Ocean?CAO?,the Beaufort and Chukchi Seas?BC?,the East Siberian and Laptev Seas?ESL?,the Baffin Bay and Labrador Sea?BL?,the Canadian Archipelago?CA?,the Greenland Sea?GS?,the Hudson Bay?HB?and the Kara and Barents Seas?KB??in the summer of 1982-2015are analyzed with CLARA-A2-SAL data.The variation trends of sea ice parameters such as the sea ice concentration?SIC?,the sea ice extent?SIE?and the sea ice melt onset and the relationship with albedo are also analyzed.Furthermore,the spatial and temporal response of summer albedo to near-surface air temperature,long-wave and short-wave radiation fluxes and sea level pressure in winter,spring and summer are further analyzed,and the following conclusions are drawn:?1?The average albedo over the Arctic sea ice region from 1982 to 2015 was46%,showing a significant downward trend of-1.6%/decade,and the downward trend in August was-2.1%/decade,which was greater than that in June and July.The BC had the largest decline in the albedo with the trend of-2.2%/decade,while the albedo in the GS region showed an insignificant growth trend.After 2005,the Arctic Sea ice region albedo began to decline obviously.In summer,the SIC also showed a downward trend and the downward speed was-2.5%/decade,showing a significant positive correlation with albedo with a correlation coefficient of 0.79,and the spatial change trend of which was also consistent with albedo.The SIE representing the coverage of sea ice also showed a significant downward trend and had a correlation coefficient of 0.72 with the albedo.This indicatesd that the average albedo in the range decreased as the sea ice coverage decreased.The Arctic melt onset showed a significant advance trend of-4.5 days/decade and a significant positive correlation with the summer albedo with a coefficient of 0.45,indicating that the earlier melting would reduce the albedo in the summer sea ice area.?2?Two kinds of near-surface air temperature data from ERA-Interim and NCEP/NCAR are used to compare and analyze the spatial distribution,vatiation trend and spatial-temporal response to summer albedo.The two kinds of temperature showed significant trends of increase in summer,spring and winter,and significant negative correlations with the albedo.The regression analysis results of near-surface air temperature and albedo showed that the regression equation coefficients of ERA-Interim data in summer,spring and winter were-6.39,-0.43 and-0.62,respectively,and those of NCEP/NCAR data were-4.63,-0.26 and-0.67,respectively,indicating that the response relationship between summer near-surface air temperature and albedo was good.The CA,BL and HB had the largest regression equations determination coefficients,indicating that the albedo was closely related to the temperature,while the GS had the smallest determination coefficient.The results of the sliding multiple regression analysis with a sliding window of 19 years showed that the determination coefficients in the BL,KB,BC and ESL showed a minimum value in the sliding center year of 1996 and then gradually increased,indicating that the relationship between temperature and albedo in these regions had been gradually strengthened since 2005.?3?Based on the analysis of ERA-Interim data,it was found that the downward long-wave radiation showed significant growth trends in summer,spring and winter,with the growth rates of 2.3,4.1 and 4.7 Wm^-2/decade respectively,showing significant negative correlations with the summer albedo,and the correlation coefficients were-0.90,-0.68 and-0.65 respectively.The long-wave net radiation increased significantly only in summer with a growth rate of 1.9 Wm^-2/decade,and showed a significant negative correlation with the albedo with a coefficient of-0.77.The trend values of the long-wave cloud radiation force in summer,spring and winter were 0.3,0.9 and 1.6 Wm^-2/decade,respectively,only that in the spring and winter were significant,showing significant negative correlations with the summer albedo,and the correlation coefficients are were-0.36,-0.44 and-0.54,respectively.As the sea ice melts,the SIC and albedo decrease,and the absorption of solar short-wave radiation increases,as a result,the cloud or atmospheric temperature increases,the downward longwave radiation increases,and the upward longwave radiation is also enhanced at the same time.In summer,due to more heat absorbed by sea ice melting,sea surface temperature and near-surface air temperature increase less,so the increasing trend of upward long-wave radiation is small,therefore,the long-wave net radition in summer increased significantly.The influence of cloud on downward long-wave radiation and long-wave net radiation was greater in winter and spring than that in summer,so it can be inferred that the increase of downward long-wave radiation in summer was mainly affected by atmospheric temperature and humidity.In summer and spring,the downward short-wave radiation showed significant downward trends and positive correlations with albedo,with correlation coefficients of 0.82 and0.36,respectively.The short-wave net radiation in summer and spring showed significant upward trends,and wre negatively correlated with summer albedo,with correlation coefficients of-0.66 and-0.74,respectively.However,the short-wave cloud radiation force in summer and spring showed strengthed trends,with the trend values of-3.7 and-0.4 Wm^-2/decade,respectively,showing significant positive correlations with summer albedo,with the correlation coefficients of 0.89 and 0.43,respectively.This may be due to the intensified melting of sea ice in summer,and the early melting in spring,which made the evaporation on the ocean surface intensified,and the rising of water vapor made the cloud block the downward short-wave radiation.?4?There was no significant correlation between the winter AO index and the Arctic summer albedo from 1982 to 2015,but there wre significant positive correlatios in the BL,HB and GS regions,and negative correlations in BC and ESL regions,indicating that the positive phase of winter AO is conducive to the import of Arctic sea ice into the North Atlantic,but the relationship between the winter AO and the Arctic summer albedo is uncertain in general.The summer AO index showed a downward trend with the increasing of negative phase years and a significant positive correlation with the Arctic summer albedo,the correlation coefficient was 0.47,which also showed significant positive correlations with albedo in the BC,CAO ESL,KB and BL regions,but inapparent negative correlation in the GS region,showing a"seesaw"structure.The results of sliding correlation analysis showed that there were significant positive correlations between summer AO and albedo in the Arctic and BC region,which indicated that AO was one of the most important factors that dominated the change of albedo in the Arctic and the dominating factor in the BC region.The summer AD index showed an upward trend with the increasing of positive phase years,and showed a significant negative correlation with summer albedo,the correlation coefficient was-0.44,which also showed significant negative correlations in the BC,ESL,CA and KB.The results of the sliding correlation analysis with a sliding window of 19 years showed that the negative correlation between summer AD and Arctic albedo had been gradually strengthened since the sliding center year of1996,and the negative correlations between summer AD and Arctic albedo were significant in the central year from 2002 to 2006.This indicated that the influence of summer AD on albedo had experienced a process from weak to strong and gradually became one of the most important air circulation factors as summer AO.The winter AD index showed a downward trend with the increasing of negative phase,and showed a significant positive correlation with summer albedo,with a correlation coefficient of 0.37.It can be seen from the sliding correlation analysis that the correlation between winter AD index and albedo weakened gradually and became insignificant,but the winter AD was positively correlated with albedo in most time periods.