The in situ observation of modelled sea ice drift characteristics in the Bohai Sea

Sea ice drift is mainly controlled by ocean currents, local wind, and internal ice stress. Information on sea ice motion, especially in situ synchronous observation of an ice velocity, a current velocity, and a wind speed, is of great significance to identify ice drift characteristics. A sea ice substitute, the so-called "modelled ice", which is made by polypropylene material with a density similar to Bohai Sea ice, is used to complete a free drift experiment in the open sea. The trajectories of isolated modelled ice, currents and wind in the Bohai Sea during non-frozen and frozen periods are obtained. The results show that the currents play a major role while the wind plays a minor role in the free drift of isolated modelled ice when the wind is mild in the Bohai Sea. The modelled ice drift is significantly affected by the ocean current and wind based on the ice–current–wind relationship established by a multiple linear regression. The modelled ice velocity calculated by the multiple linear regression is close to that of the in situ observation, the magnitude of the error between the calculated and observed ice velocities is less than12.05%, and the velocity direction error is less than 6.21°. Thus, the ice velocity can be estimated based on the observed current velocity and wind speed when the in situ observed ice velocity is missing. And the modelled ice of same thickness with a smaller density is more sensitive to the current velocity and the wind speed changes. In addition, the modelled ice drift characteristics are shown to be close to those of the real sea ice, which indicates that the modelled ice can be used as a good substitute of real ice for in situ observation of the free ice drift in the open sea, which helps solve time availability, safety and logistics problems related to in situ observation on real ice.

Comparisons of passive microwave remote sensing sea ice concentrations with ship-based visual observations during the CHINARE Arctic summer cruises of 2010–2018

In order to apply satellite data to guiding navigation in the Arctic more effectively,the sea ice concentrations(SIC)derived from passive microwave(PM)products were compared with ship-based visual observations(OBS)collected during the Chinese National Arctic Research Expeditions(CHINARE).A total of 3667 observations were collected in the Arctic summers of 2010,2012,2014,2016,and 2018.PM SIC were derived from the NASA-Team(NT),Bootstrap(BT)and Climate Data Record(CDR)algorithms based on the SSMIS sensor,as well as the BT,enhanced NASA-Team(NT2)and ARTIST Sea Ice(ASI)algorithms based on AMSR-E/AMSR-2 sensors.The daily arithmetic average of PM SIC values and the daily weighted average of OBS SIC values were used for the comparisons.The correlation coefficients(CC),biases and root mean square deviations(RMSD)between PM SIC and OBS SIC were compared in terms of the overall trend,and under mild/normal/severe ice conditions.Using the OBS data,the influences of floe size and ice thickness on the SIC retrieval of different PM products were evaluated by calculating the daily weighted average of floe size code and ice thickness.Our results show that CC values range from 0.89(AMSR-E/AMSR-2 NT2)to 0.95(SSMIS NT),biases range from−3.96%(SSMIS NT)to 12.05%(AMSR-E/AMSR-2 NT2),and RMSD values range from 10.81%(SSMIS NT)to 20.15%(AMSR-E/AMSR-2 NT2).Floe size has a significant influence on the SIC retrievals of the PM products,and most of the PM products tend to underestimate SIC under smaller floe size conditions and overestimate SIC under larger floe size conditions.Ice thickness thicker than 30 cm does not have a significant influence on the SIC retrieval of PM products.Overall,the best(worst)agreement occurs between OBS SIC and SSMIS NT(AMSR-E/AMSR-2 NT2)SIC in the Arctic summer.

Albedo of Coastal Landfast Sea Ice in Prydz Bay,Antarctica:Observations and Parameterization

The snow/sea-ice albedo was measured over coastal landfast sea ice in Prydz Bay, East Antarctica（off Zhongshan Station）during the austral spring and summer of 2010 and 2011. The variation of the observed albedo was a combination of a gradual seasonal transition from spring to summer and abrupt changes resulting from synoptic events, including snowfall, blowing snow, and overcast skies. The measured albedo ranged from 0.94 over thick fresh snow to 0.36 over melting sea ice. It was found that snow thickness was the most important factor influencing the albedo variation, while synoptic events and overcast skies could increase the albedo by about 0.18 and 0.06, respectively. The in-situ measured albedo and related physical parameters（e.g., snow thickness, ice thickness, surface temperature, and air temperature） were then used to evaluate four different snow/ice albedo parameterizations used in a variety of climate models. The parameterized albedos showed substantial discrepancies compared to the observed albedo, particularly during the summer melt period, even though more complex parameterizations yielded more realistic variations than simple ones. A modified parameterization was developed,which further considered synoptic events, cloud cover, and the local landfast sea-ice surface characteristics. The resulting parameterized albedo showed very good agreement with the observed albedo.

Aerial observations of sea ice and melt ponds near the North Pole during CHINARE2010

An aerial photography has been used to provide validation data on sea ice near the North Pole where most polar orbiting satellites cannot cover. This kind of data can also be used as a supplement for missing data and for reducing the uncertainty of data interpolation. The aerial photos are analyzed near the North Pole collected during the Chinese national arctic research expedition in the summer of 2010（CHINARE2010）. The result shows that the average fraction of open water increases from the ice camp at approximately 87°N to the North Pole, resulting in the decrease in the sea ice. The average sea ice concentration is only 62.0% for the two flights（16 and 19 August 2010）. The average albedo（0.42） estimated from the area ratios among snow-covered ice,melt pond and water is slightly lower than the 0.49 of HOTRAX 2005. The data on 19 August 2010 shows that the albedo decreases from the ice camp at approximately 87°N to the North Pole, primarily due to the decrease in the fraction of snow-covered ice and the increase in fractions of melt-pond and open-water. The ice concentration from the aerial photos and AMSR-E（The Advanced Microwave Scanning Radiometer-Earth Observing System） images at 87.0°–87.5°N exhibits similar spatial patterns, although the AMSR-E concentration is approximately 18.0%（on average） higher than aerial photos. This can be attributed to the 6.25 km resolution of AMSR-E, which cannot separate melt ponds/submerged ice from ice and cannot detect the small leads between floes. Thus, the aerial photos would play an important role in providing high-resolution independent estimates of the ice concentration and the fraction of melt pond cover to validate and/or supplement space-borne remote sensing products near the North Pole.

The signature analysis of summer Antarctic sea-ice distribution by ship-based sea-ice observation

Based on the Chinese 19th National Antarctic Research Expedition,we carried out ship-based Antarctic sea-ice observa-tion on icebreaker Xue Long using Antarctic sea-ice process and climate (ASPeCt) criteria during austral summer.Sea-ice distribution data were obtained along nearly 6,500 km of the ship’s track.The measurement parameters included sea-ice thickness,sea-ice concentration,snow thickness,and floe size.Analysis showed the presence of the large spatial varia-tions of the observed sea-ice characteristics.Sea-ice concentration varied between 0 and 80 percent and reached its peak value in Weddell Sea because of the specific dynamical process affecting in summer sea-ice melting.There are large areas of open water along the study section.Sea ice and the upper snow thickness of the section varied between 10 cm and 210 cm and 2 cm and 80 cm,respectively,and each reaches its peak values near Amery ice shelf.The floe size varied from less than 10 cm and the maximum of more than 2,000 km along the section.

Arctic multiyear sea ice variability observed from satellites:a review

In comparison with seasonal sea ice(first-year ice,FY ice),multiyear(MY)sea ice is thicker and has more opportunity to survive through the summer melting seasons.Therefore,the variability of wintertime MY ice plays a vital role in modulating the variations in the Arctic sea ice minimum extent during the following summer.As a response,the ice-ocean-atmosphere interactions may be significantly affected by the variations in the MY ice cover.Satellite observations are characterized by their capability to capture the spatiotemporal changes of Arctic sea ice.During the recent decades,many active and passive sensors onboard a variety of satellites(QuikSCAT,ASCAT,SSMIS,ICESat,CryoSat-2,etc.)have been used to monitor the dramatic loss of Arctic MY ice.The main objective of this study is to outline the advances and remaining challenges in monitoring the MY ice changes through the utilization of multiple satellite observations.We summarize the primary satellite data sources that are used to identify MY ice.The methodology to classify MY ice and derive MY ice concentration is reviewed.The interannual variability and trends in the MY ice time series in terms of coverage,thickness,volume,and age composition are evaluated.The potential causes associated with the observed Arctic MY ice loss are outlined,which are primarily related to the export and melting mechanisms.In addition,the causes to the MY ice depletion from the perspective of the oceanic water inflow from Pacific and Atlantic Oceans and the water vapor intrusion,as well as the roles of synoptic weather,are analyzed.The remaining challenges and possible upcoming research subjects in detecting the rapidly changing Arctic MY ice using the combined application of multisource remote sensing techniques are discussed.Moreover,some suggestions for the future application of satellite observations on the investigations of MY ice cover changes are proposed.

Characteristics of sea ice kinematics from the marginal ice zone to the packed ice zone observed by buoys deployed during the 9th Chinese Arctic Expedition

Sea ice growth and consolidation play a significant role in heat and momentum exchange between the atmosphere and the ocean.However,few in situ observations of sea ice kinematics have been reported owing to difficulties of deployment of buoys in the marginal ice zone(MIZ).To investigate the characteristics of sea ice kinematics from MIZ to packed ice zone(PIZ),eight drifting buoys designed by Taiyuan University of Technology were deployed in the open water at the ice edge of the Canadian Basin.Sea ice near the buoy constantly increased as the buoy drifted,and the kinematics of the buoy changed as the buoy was frozen into the ice.This process can be determined using sea ice concentration,sea skin temperature,and drift speed of buoy together.Sea ice concentration data showed that buoys entered the PIZ in mid-October as the ice grew and consolidated around the buoys,with high amplitude,high frequency buoy motions almost ceasing.Our results confirmed that good correlation coefficient in monthly scale between buoy drift and the wind only happened in the ice zone.The correlation coefficient between buoys and wind was below 0.3 while the buoys were in open water.As buoys entered the ice zone,the buoy speed was normally distributed at wind speeds above 6 m/s.The buoy drifted mainly to the right of the wind within 45°at wind speeds above 8 m/s.During further consolidation of the ice in MIZ,the direct forcing on the ice through winds will be lessened.The correlation coefficient value increased to 0.9 in November,and gradually decreased to 0.7 in April.

Sustainable observations of landfast sea ice in the cryosphere:a case study at the Liaodong Bay,Bohai Sea,North China

Sustainable monitoring of sea ice is crucial for better understanding air-ice-ocean interactions and identifying new processes.However,it is an expensive process particularly for the polar cryosphere environment.The seasonal ice-covered sea area can be used as a test bed for cryosphere-related process studies due to convenient access and conduction of field work,and the seasonal regime variation of the Arctic sea ice resulting from climate changes.In this paper,a small landfast sea ice monitoring program has been carried out for four consecutive seasons at Jiangjunshi Port,the Bohai Sea,North China,analyzing the temperature and salinity of air,ice and ocean and discussing the influence on mechanical properties.The effect of air temperature on sea ice temperature is focused.During low-temperature periods,the maximum correlation coefficient between air temperature and ice temperature,along with temperature fluctuation within ice,decreases as ice depth increases.Ice salinity was measured using ice core sampling and ice crumb sampling,with ice crumb salinity twice larger compared to ice core sampling when the ice temperature is−3℃.Ice salinity variations with ice temperature and the salinity profiles were fitted.Analysis of the profiles of under-ice seawater salinity reveals the presence of a high-salinity layer near the bottom of sea ice during the initial stage of sea ice growth.Based on the dynamic changes in sea ice temperature and sea ice salinity,this study evaluates the mechanical properties of sea ice,with the fitting determination coefficients of the obtained parameterized formulas significantly better than those reported in current research.

Application of the HY-1 satellite to sea ice monitoring and forecasting

The HY-1A satellite is the first oceanic satellite of China. During the winter of 2002-2003, the data of the HY-1A were applied to the sea ice monitoring and forecasting for the Bohai Sea of China for the first time. The sea ice retrieval system of the HY-1 A has been constructed. It receives 1B data from the satellite, outputs sea ice images and provides digital products of ice concentration, ice thickness and ice edge, which can be used as important information for sea ice monitoring and the initial fields of the numeric sea ice forecast and as one of the reference data for the sea ice forecasting verification. The sea ice retrieval system of the satellite is described, including its processes, methods and parameters. The retrieving results and their application to the sea ice monitoring and forecasting for the Bohai Sea are also discussed.

Review of research on Arctic sea ice physics based on the Chinese National Arctic Research Expedition

China launched its Arctic research program and organized the first Chinese National Arctic Research Expedition （CHINARE-Arctic） in 1999. By 2016, six further expeditions had been conducted using the R/V Xuelong. The main region of the expeditions has focused on the Pacific sector of the Arctic Ocean for sea ice observations. The expeditions have used icebreaker, helicopter, boat, floe, and buoy platforms to perform these observations. Some new technologies have been developed, in particular, the underway auto-observing system for sea ice thickness using an electromagnetic instrument. The long-term measurement systems, e.g., the sea ice mass balance buoy, allow observations to extend from summer to winter. Some international cooperation projects have been involved in CHINARE-Arctic, especially the ＂Developing Arctic Modeling and Observing Capabilities for Long-Term Environmental Studies＂ project funded by the European Union during the International Polar Year. Arctic sea ice observations have been used to verify remote sensing products, identify changes in Arctic sea ice, optimize the parameterizations of sea ice physical processes, and assess the accessibility of ice-covered waters, especially around the Northeast Passage. Recommendations are provided as guidance to future CHINARE-Arctic projects. For example, a standardized operation system of sea ice observations should be contracted, and the observations of sea ice dynamics should be enhanced. The upcoming launch of a new Chinese icebreaker will allow increased ship time in support of future CHINARE Arctic oceanographic investigations.

利用CCD成像技术进行渤海海冰观测探讨

利用CCD成像技术进行走航海冰观测是国际南极科学委员会海冰过程与气候项目制定的南极海冰观测方法的一部分。本文介绍了利用CCD成像技术进行海冰观测及其图像信息提取的基本原理,分析了该项技术在南北极海冰走航观测应用实践中的成功经验及问题所在,讨论了南北极与渤海冰情和调查作业环境的差异,探讨了利用CCD成像技术进行渤海海冰观测的应用前景。

On the turbulent heat fluxes:A comparison among satellite-based estimates,atmospheric reanalyses,and in-situ observations during the winter climate over Arctic sea ice

The surface energy budget is crucial for Arctic sea ice mass balance calculation and climate systems,among which turbulent heat fluxes significantly affect the airesea exchanges of heat and moisture in the atmospheric boundary layer.Satellite observations(e.g.CERES and APPX)and atmospheric reanalyses(e.g.,ERA5)are often used to represent components of the energy budget at regional and pan-Arctic scales.However,the uncertainties of the satellite-based turbulent heat fluxes are largely unknown,and cross-comparisons with reanalysis data and insitu observations are limited.In this study,satellite-based turbulent heat fluxes were assessed against in-situ observations from the N-ICE2015 drifting ice station(north of Svalbard,JanuaryeJune 2015)and ERA5 reanalysis.The turbulent heat fluxes were calculated by two approaches using the satellite-based ice surface temperature and radiative fluxes,surface atmospheric parameters from ERA5,and snow/sea ice thickness from the pan-Arctic Ice Ocean Modeling and Assimilation System(PIOMAS).We found that the bulk-aerodynamic formula based results could better capture the variations of turbulent heat fluxes,while the maximum entropy production based estimates are comparable with ERA5 in terms of root-mean-square error(RMSE).CERES-based estimates outperform the APP-X-based ones but ERA5 performs the best in all seasons(RMSE of 18 and 7 W m^(-2)for sensible and latent heat flux,respectively).The aireice temperature/humidity differences and the surface radiation budget were found the primary driving factors in the bulk-formula method and maximum entropy production(MEP)method,respectively.Furthermore,errors in the surface and near-surface temperature and humidity explain almost 50%of the uncertainties in the estimates based on the bulk-formula,whereas errors in the net radiative fluxes explain more than 50%of the uncertainties in the MEP-based results.

Evaluation of the relationships and uncertainties of airborne and ground-based sea ice surface temperature measurements against remotely sensed temperature records

Sea ice surface temperature(IST)is an important indicator of environmental changes in the Arctic Ocean.In this study,the relative performance of four mainstream IST records,i.e.airborne IST,infrared radiometer measured IST(IR IST),longwave radiation derived IST(LWR IST),and snow and ice mass balance array buoy derived IST(Buoy IST),were evaluated against the MODIS IST product.Bias,standard deviation(STD),and root mean square error(RMSE)were used to evaluate the data quality.Results revealed that airborne IST had the best accuracy,which was 0.21 K colder than MODIS IST,with STD of 1.46 K and RMSE of 1.47 K.Ground-based ISTs were biased with each other but all warmer than the MODIS IST.The IR IST had the best overall accuracy(bias=0.55 K;STD=1.52 K;RMSE=1.61 K),while the LWR IST was the noisiest measurement with the largest outlier data percent.Besides,co-located IR and LWR ISTs were more consistent than any type of evaluated IST against MODIS IST(correlation coefficient=0.99).Airborne and IR ISTs are thus the premier choice for monitoring the rapidly changing Arctic sea ice,together with satellite observations.