Observation And Simulation Research On Growth And Decay Processes Of Ice Cover On Lake Wuliangsuhai

The seasonal lake ice is an important part of the cryosphere of the pan-third polar regions that located in the middle latitude,and its change is an important indicator of the regional climate.Compared with the lakes of high latitude,the lake ice in this region has the characteristics of strong solar radiation,less precipitation,thin ice thickness and surface with high sediment concentration in winter.The study of lake ice in this area has great significance on the climate changes of the pan-third polar regions and the construction of "Belt and Road Initiatives".In this paper,Wuliangsuhai,a typical representative of shallow lake in arid and semi-arid regions,is selected to carry out on-site observation of lake ice generation and dissipation in winters during 2015-2018.Make deep analysis of the optical properties and thermodynamic process of its lake ice in different stages,and at the same time,make use of the observation and analysis results to optimize some related ice lake models and validate the computing results.First,the air temperature ranged from-29.7? to 16.3?,the maximum ice thickness ranged from 39 cm to 57 cm,the maximum snow thickness ranged from 5.2 cm to 13.0 cm.The lake ice albedo was affected by the snow,sediment and melt water on the ice surface.The average albedo and transmittance of lake ice at different stages were 0.54 and 0.08(bare ice),0.74 and 0.04(snow),0.30 and 0.12(melting),respectively.Affected by the sediment covering the surface,the surface albedo of lake ice decreases with the increasing sediment concentration.Based on the lake ice thickness,surface sediment content and the number of days after snowfall,the researcher established the parameterized albedo formula of Wuliangsuhai lake ice during bare ice,snow-covering and melting stage.Second,the surface heat flux of lake ice on Wuliangsuhai is mainly determined by the solar radiation and long-wave radiation.During the freezing period,the surface heat flux loss of lake ice was about 20?40 W/m2.The solar radiation absorbed by the lake ice was mainly affected by the thickness of ice and snow,and it was about 9?22 W/m2.Under the combined action of solar radiation,air temperature and water temperature,the ice temperature on Lake Wuliangsuhai has obvious diurnal variation characteristics.Use actually-measured data to modify the interior optical parameters of lake ice in the Delta-Eddington model.The results showed that the absorption of radiation by lake ice decreases with the depth.The calculated results of which were used to fit the relation expression of lake ice equivalent extinction coefficient varying with the depth.Third,adding the item of solar radiation absorbed by lake ice in Stefan formula improves the calculation accuracy of the ice thickness.The HIGHTSI model was optimized by using the Wuliangsuhai lake ice's parameterized albedo formula and the relation expression of equivalent extinction coefficient varying with the depth,and the calculated results of which are agreed with the actually-measured ice thickness and temperature.Use analytic model,numerical model and MERRA-2 reanalysis data to calculate the thickness changes of Wuliangsuhai lake ice in the winters of 2015-2018.It was found that the analytical model can be used to calculate the ice thickness changes and the maximum ice thickness during the freezing period,and the numerical model can be used to calculate the ice thickness and temperature during the whole ice growth and decay processes.In this paper,based on field observation and numerical simulation,the growth and decay processes of lake ice on Lake Wuliangsuhai is studied.The results show the influence of strong solar radiation and high ice sediment content on the optical properties and thermodynamics of lake ice in arid and semi-arid regions of middle and low latitudes.The lake ice albedo parameterization and equivalent extinction coefficient with ice thickness in different stages are established.The analytical model and numerical model are developed for the arid and semiarid regions of middle and low latitudes.These results are of great significance for the analysis of lake ice changes in the pan third polar regions under the background of global warming.