| Microwave remote sensing has become one of the indispensable means in polar sea ice observation,mainly due to its capability of all time and all-weather coverage at large scales,the penetration of clouds,and the high sensitivity to the dielectric properties of ice and water.Polar sea ice change is an indicator of cryosphere and polar environmental change,and plays an important role in regional and global climate change research.Sea ice concentration(SIC)and sea ice thickness(SIT)are two sea ice parameters that describe the variation characteristics of sea ice in "horizontal direction" and "vertical direction" respectively.However,due to the lack of reliable and long-term SIT data,previous studies have mostly only focused on the analysis of SIC.Based on the long-term SIC retrieved by microwave radiometers and the SIT retrieved by radar altimeters,the European Space Agency(ESA)has obtained a long time series and high-precision SIC and SIT data sets(namely the ESA CCI data)by using the fusion algorithms.These data sets provide a reliable remote sensing data source for quantitative study of the temporal and spatial variation characteristics of Arctic sea ice.By using the ESA CCI data,this dissertation studies the spatio-temporal variation of sea ice in the Arctic from 2002 to 2017,and analyzes the response relationship between SIC,SIT and several environmental parameters(i.e.,2 meter temperature,sea level pressure,and 10 meter wind speed,etc.).The main results and conclusions are as follows:(1)Based on the ship-based observation data and airborne IceBridge observation data,the performance of ESA CCI SIC and SIT were comprehensively analyzed and evaluated respectively.The results show that the error of ESA CCI SIC and SIT data is small,and the RMSE is 8.82%and 0.48 m respectively,which demonstrates the good accuracy and reliability of the ESA CCI sea ice data.(2)The interannual and seasonal variation,and the spatial distribution of Arctic SIC,sea ice extent(SIE),sea ice area(SIA)and SIT were studied by means of regression analysis and catastrophe test.The results show that the interannual variations of SIC,SIE,SIA and SIT all exhibit a decrease trend,and the decreasing rate of multi-year ice extent(area)is about twice as fast as that of one-year ice extent(area).Spatially,the SIC of the Kara Sea and the Barents Sea decreases the most significantly,reaching-1.11%ˇyear-1.The Arctic SIC,SIE and SIA reach the maximum in winter and the minimum in summer.The Arctic SIT shows a decrease trend in the study period,especially in Hudson Bay,reaching-0.051mˇyear-1.The average annual SIT abruptly occurred in 2007,from a slight rise in 2003-2017 to a significant downward trend from 2007-2017.(3)Combined with a variety of environmental parameters,the causes of sea ice changes were analyzed,with emphasis on the response of atmospheric circulation anomalies to sea ice in 2007,2012 and 2016.It is found that the increasing trend of 2 meter temperature is 0.057?,which is an important driving factor for the decrease of Arctic sea ice.The Arctic dipole anomaly appears in 2007,and the SIT decreases on a large scale,which accelerates the reduction of sea ice.In the winter of 2012,unusual positive temperature and pressure anomalies appear in the eastern Arctic Ocean,resulting in a significant reduction of sea ice in the Barents Sea and the Kara Sea.In 2016,the positive anomalies of temperature and wind speed occupy an obvious dominant position,which cause the divergence effect of sea ice and reduce the multi-year ice and SIT in the Arctic Ocean.These results preliminarily reveal the meteorological causes of the change of Arctic sea ice.This study preliminarily reveals the temporal and spatial evolution law of Arctic sea ice change in the past 15 years and its possible causes,and further provides reference for the future polar regional and global regional climate change research. |
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