Arctic Sea Ice Variability And Its Response To Spring Downwelling Longwave And Shortwave Radiation

Arctic sea ice is an important part of the global climate system.Its change has great influence on the hydrological system,the thermal cycle,the ocean current and the ecosystem in the high latitudes.In the context of global warming,the influence of the Arctic amplification effect on the Arctic sea ice is increasing.Nearly forty years of microwave radiometer satellite observations show that the coverage of Arctic sea ice is shrinking,especially in 2007 and 2012.The thickness of sea ice in the Arctic is thinning,the melting period of sea ice is prolonged in summer,and the seasonal sea ice coverage ratio continues to increase,and the interannual change of sea ice intensifies.It has become the consensus of polar scientific circles that Arctic sea ice is decreasing at an alarming rate.The research on Arctic sea ice has become the key to study global climate change.First of all,we use daily sea ice concentration data from National Snow and Ice Data Center?NSIDC,1979-2016?,the altimeter satellite observations for years of 2003-2008 and years of 2011-2016 sea ice thickness data,two meter air temperature reanalysis data provided by National Centers for Environmental Prediction?NCEP?and the European Centre for Medium-Range Weather Forecasts?ECMWF?,analysis variation characteristics of sea ice concentration,area,thickness and early melt onset day.The results showed that there was no significant change in the ice concentration of the Arctic Ocean in the winter of 38 years,and a continuous downward trend in summer.The Arctic sea ice coverage and area overall showed a decreasing trend.The decrease trend of SIE and SIA in 2013-2016 years is the most significant,which is 11.6%and7.4%less than that in the first stage.The SIE and SIA of each area declined,and the anomaly of SIE and SIA was negative after 2005.The sea ice thickness in the ICESat phase?2003-2008?showed a downward trend,the thick ice?>3.0m?has reduced ice?<1.5m?was increased,decreased significantly in autumn than winter.The Cryosat-2phase?2012-2014?has recovered,and then tends to be stable.Arctic sea ice early melt onset day began to ahead of time,the maximum value appeared in Kara sea and Laptev Sea,about 20 days in advance,followed by Barents Sea,Beaufort Sea,Chukotka sea,and East Siberian sea,ahead of time about 8¹2 days.Secondly,based on longwave and shortwave radiation flux data from NCEP and ECMWF,the characteristics of the change of the downward longwave and shortwave radiation flux in the Arctic spring for 1979-2016 are analyzed.The flux trend of longwave radiation from NCEP and ECMWF is very consistent in spring.Except for the Bering Sea,the trend of longwave radiation flux in the Arctic and all sea areas is characterized by positive anomalies.The downward longwave radiation flux has a three-peak structure.The maximum value appears in mid-April and is about twice as high as the first peak?mid-March?and the third peak?at the end of May?,about 1.0W·m^-2·decade^-1.Compared with the trend of the downward longwave radiation flux,the shortwave radiation is quite different.However,it is also characterized by negative anomalies in the Arctic Ocean.The trend of the downward shortwave radiation flux is a bimodal structure with the maximum occurring at the end of May.The main manifestations are significant negative in the Chukchi Sea,East Siberian Sea and Baffin Bay.The trend of longwave radiation flux in each sea area is the same,with positive anomalies in the central Arctic,the Greenland Sea,and the glacier sea,averaging about5 W·m^-2·decade^-1.Finally,the effects of longwave and shortwave radiation flux anomalies to sea ice early melt onset day in the Arctic were discussed.The results showed that the early melt onset day of sea ice was negatively correlated with the longwave radiation flux in the spring and positively correlated with the shortwave radiation flux.The earlier the sea ice begins to melt,the larger the downward longwave radiation flux and the less the shortwave radiation flux.The unusual downward longwave radiation flux in the spring is the key thermodynamic process that determines the sea ice early melt onset day.