On Thermodynamic Growth And Decay Processes Of Ice Cover: Field Measurements And Determination Of Crucial Parameters

Global warming and its resulting events, special for sea level rising, would make some directly or indirectly impacts on costal and offshore engineers in China. Reasonable forecast of climatic change is crucial to put forward corresponding policy. Sea ice and fresh ice in polar or sub-polar regions are primary factors in global climate system; also serve as proxy climate records as their sensitivity to climatic change. The optimization of parameterization and the arithmetic are more important than the model strategy to develop the ice thermodynamic model. Based on the data derived from the field campaigns of landfast sea-ice thermodynamic observation off Zhongshan Station in Prydz Bay, East Antarctica from November 2005 to December 2006, and lake-ice optical observation in seven lakes located in the drainage basin of Baltic Sea (with 5 lakes in Finland and 2 lakes in Estonia) from February to April, 2009, the growth and decay processes of ice cover have been studied. Some key thermodynamic parameters have been quantified and analyzed. The author took all field works involved in this study.In the first chapter, global warming and its possible impacts on coastal and offshore engineers in China were evaluated. Significance of study on landfast sea ice and lake ice has been explored. Studies on the growth and decay processes of sea ice and fresh ice, field work of landfast sea-ice thermodynamic observation in Antarctica, and lake-ice optical properties have been reviewed.In the second chapter, the field campaigns and the involved monitoring techniques of landfast sea-ice thermodynamic observation off Zhongshan Station and lake-ice optical observation in the drainage basin of Baltic Sea have been presented. The former field campaign is characterized as the most comprehensive one for landfast sea-ice thermodynamic study in Prydz Bay to date. A new apparatus for monitoring sea-ice and snow thickness has been developed based on the magnetostrictive-delay-line principle. The apparatus has a precision of±2 mm, which is higher than that of the previous techniques for monitoring ice thickness.In third chapter, the growth and decay processes of landfast ice off Zhongshan Station have been studied. The thermal conductivity of snow cover has been quantified based on the air-snow-ice temperature profile. The recoiling of fast-ice marginal line toward the shore promoted the decay of landfast sea ice during summer, and vice versa. Ice-growth season lasted from February to November in 2006. The first step to study intraday variation in ice-growth rate for Antarctic landfast ice has been launched based on the field data of ice thickness with high resulotion. The results show that there was no obvious intraday variation in ice-growth rate during polar night, while an obvious minimal ice-growth rate can be detected at postmeridiem (12:00～15:00) during the two months preceding or after the polar night. The ice salinity profile was a "C-shape" profile, and then turned into a "?-shape" profile after brine drainage due to warm air and ice temperatures around March, this profile was kept to November, when melt-onset turned it into a "I-shape" profile. Strong winds and the consequent blowing snow played a pivotal role for snow redistribution at the experimental site, which resulted in a relatively thin snow cover on the ice. The thermal conductivity of the snow did not exhibit any seasonal dependence.In the fourth chapter, based on the so-called residual method, ice temperature profiles, combined with measurements of ice bottom ablation or accretion were used to estimate oceanic heat flux under landfast ice off Zhongshan Station, which is the first time to using this method to estimate oceanic heat flux under landfast ice in Prydz Bay completely based on the field data. The oceanic heat flux decreased from initial values of 11.8(±3.5)W/m~2 in April to an annual minimum in September with a value of 1.9(±2.4)W/m~2. It remained low through to late November, in mid December it increased sharply. The seasonal evolvement of the oceanic heat flux was similar with that of sea-ice concentration in Prydz Bay. Taking into account the oceanic heat, the calculated ice growth based on the Stefan's Law improved except at times when the oceanic heat or the ice-growth rate approaching to zero.In the fifth chapter, the relationship between snow/ice optical properties related to the spectral region of photosynthetically active radiation (PAR) and their stratigraphical structure has been discussed based on lake-ice observation in the drainage basin of Baltic Sea, The optical properties of snow, granular ice and columnar ice have been compared quantitatively. The growth and decay processes of lake ice in the drainage basin of Baltic Sea have been compared in brief with those of landfast ice off Zhongshan Station. The PAR flux through ice cover was controlled by snow principally. When snow was removed or melted as the spring coming, the PAR flux would increase distinctly. The decline of snow albedo was more notable than that of snow extinction coefficient as spring coming. The snow albedo in spring was one fourth that in winter. Extinction coefficient of ice was about one tenth to on third that of snow, which was determined by the thickness ratio of granular ice basically as extinction coefficient of granular ice was twice to trebly that of columnar ice. The snow cover and the formation of snow ice complexed the ice growth and decay for the lake ice in the drainage basin of Baltic Sea, while as the snow was thin and no snow ice occurred over the landfast ice off Zhongshan Station, snow cover cannot make a significant impact on the ice growth and decay. The season vatiations in the heat from water under the lake ice in the drainage basin of Baltic Sea was stable and no short-term change can be detected. While, both the season vatiations and short-term changes in the oceanic heat under landfast ice off Zhongshan Station were vary distinct.The results derived from this study can provide background data and validation data for numerical simulation on the growth and decay processes of ice, support the optimization of the parameterization for ice thermodynamic modelling, and support the development of ice thermodynamic model coupled in the synoptic and climatic model.