Arctic Sea Ice Thickness Change Inversion Using 2015 ~2018 Cryosat-2 Altimetry Data

Affected by the feedback effect of sea ice albedo,Arctic sea ice is most sensitive to climate change.The decrease of sea ice reduces the amount of heat that sea ice reflects into space,and raises the temperature of sea water,which leads to the rise of Arctic temperature and hence global average temperature.The Arctic region is at an accelerated rate which is of twice about the global average since 1979.Meanwhile,sea ice has decreased by about 30-50%.As one of the important parameters,sea ice thickness affects the heat exchange between the Arctic Ocean and the atmosphere,the deformation and the circulation of sea ice.Furthermore,it affects the thermodynamics and dynamics of sea ice.Therefore,it is particularly important to accurately measure the thickness and its distribution.Due to the special geographical location and climate conditions in the Arctic region,mooring sonar,submarine sonar,airborne electromagnetic induction,airborne laser altimetry can hardly monitor long-term sea ice in the Arctic region on a large scale,which result in not enough to fully understand the feature and trends of the arctic sea ice thickness.The development of satellite altimetry makes it possible to continuously observe arctic sea ice in space and time.As one of satellite altimetries,ESA's Cryosat-2 satellite carries a synthetic aperture Interferometric Radar System(SIRAL)that covers almost the entire Arctic Ocean(88°N).In this paper,the altimetry data of Cryosat-2 satellite baseline C from January2015 to December 2018 are used to extract and calculate the residual elevation from Cryosat-2 data in the Arctic area(50-88°N).Threshold and standard deviation are used to eliminate gross errors.The sea level along the orbit is determined,and the sea ice freeboard is obtained.Finally,the sea ice thickness is obtained by buoyancy law and necessary parameters.Using the Beaufort Gyre Exploration Project's up-Looking-sonar sea ice draft and the sea ice thickness product of the NASA OIB in the United States,the accuracy of the results was evaluated.On this basis,the spatial distribution and seasonal variation of sea ice thickness in the Arctic and its surrounding waters were evaluated.Combined with meteorological elements(atmospheric temperature and ocean surface wind speed),the causes of changes in Arctic sea ice thickness were discussed.In this paper,the reference of thin ice and thick ice is 2m,thick ice is more than 2m,and thin ice is below 2m.The main results and conclusions are as follows:(1)The Barents Sea,Kara Sea,Lapjev Sea,Labrador Sea,Hudson Bay,Baffin Bay,Davis Strait,Okhotsk Sea and other sea areas in the study area are ice-free in summer.After the freezing of sea ice in autumn and winter,the sea ice thickness increases by no more than 2 m.The sea ice in northern Greenland and Northern Canada is thicker,there are more than 3 m of sea ice in winter and summer.In addition,the sea ice is thicker in the Beaufort Sea close to the Canadian Arctic Islands and the Arctic Pole.There is a mixed ice type in winter at the Fram Strait,and the sea ice is thicker in the north or near it in summer.(2)In spring,the proportion of sea ice whose thickness is more than 2m is more than 60%.In summer,the proportion of sea ice less than 2m in thickness is more than 50%,more than 80% in 2015,less than 10% in 3m and about 1% in2015.The proportion of sea ice above and below 2m in autumn and winter is approximately the same,about 50%.The difference is that compared with the previous autumn and the following winter,the proportion of sea ice above 4m in winter is larger,except that the difference between autumn 2016 and winter 2017 is not big or slightly small.(3)From the summer of 2015 to 2018,the proportion of sea ice above 2m is in the order of 2017,2016,2018 and 2015.The proportion of sea ice in different years in lower temperature areas is in the order of 2015,2017,2016 and 2018.The sea wind from Eastern Greenland in 2015 is larger and the sea wind in the Fram Strait is smaller.The wind direction is from high latitude to low latitude.In 2018,the wind in the Fram Strait is similar to that in 2015.In the summer of 2016 and2017,the wind speed from the eastern part of Greenland is still higher,but the wind direction from the lower latitude to the higher latitude in the Strait of Fram strait.The difference is that the wind speed in the Fram Strait is relatively high.The summer wind in 2015 and 2018 promotes the circulation of sea ice from the Fram Strait,and hinders the circulation of sea ice in 2016 and 2017.This indicates that the sea surface wind has a great influence on the distribution of sea ice thickness in the summer of 2015-2018.