【Title】【Author】Snowpack is a combination of several snow layers. Accordingly, snowpack natural metamorphism is composed of several stages. The aim of this study is to investigate the natural snow metamorphism at t...【Title】【Author】Snowpack is a combination of several snow layers. Accordingly, snowpack natural metamorphism is composed of several stages. The aim of this study is to investigate the natural snow metamorphism at the snow layer unit. The field investigation was conducted at the Tianshan Station for Snow Cover and Avalanche Research, Chinese Academy of Sciences （43°16＇ N, 84°24＇ E, and 1,776 m a.s.l.）, during the winter of 2010-2011. A complete metamorphic procedure and the corresponding microstructure of a target snow layer were tracked. The results indicate that： the ideal and complete metamorphic process and the corresponding predominant snow grain shape have 5 stages： 1） unstable kinetic metamorphism near the surface; 2） unstable kinetic metamorphism under pressure; 3） stable kinetic metamorphism; 4） equilibrium metamorphism; 5） wet snow metamorphism. Snow grain size sharply decreased in the surface stage, and then changed to continuously increase. Rapid increase of grain size occurred in the stable kinetic metamorphism and wet snow metamorphism stage. The characteristic length was introduced to represent the real sizes of depth hoar crystals. The snow grain circularity ratio had a variation of “rapid increase – slow decrease – slow increase”, and the snow aggregations continuously increased with time. Snow density grew stepwise and remained steady from the stable kinetic to the equilibrium metamorphism stage. The differences in metamorphism extent and stages among snow layers, led to the characteristic layered structure of snowpack.展开更多
Reliablemicrostructuremeasurement of snow is a requirement for microwave radiative transfer model validation.Snow specific surface area(SSA)can be measured using stereological methods,in which snow samples are cast in...Reliablemicrostructuremeasurement of snow is a requirement for microwave radiative transfer model validation.Snow specific surface area(SSA)can be measured using stereological methods,in which snow samples are cast in the field and photographed in the laboratory.Processing stereology photographs manually by counting intersections of test cycloids with air-ice boundaries reduces the problems in binary segmentation.This paper is a case study to evaluate the repeatability of the manually stereology interpretation by two independent research groups.We further assessed how uncertainty in snow SSA influences simulated brightness temperature(TB)driven by the Microwave Emission Model of Layered Snowpacks(MEMLS),and how stereology compares to Near Infrared(NIR)camera and hand lens.Data was obtained from two alpine snow profiles from Steamboat Springs,Colorado.Results showed that stereological SSA values measured by two groups are highly consistent,and the ground radiometer measured T_(B)at 19 and 37 GHz was successfully predicted(RMSE<3.8 K);simulations using NIR SSA and hand-lens geometric grain size(Dg)measurements have larger errors.This conclusion was not sensitive to uncertainty in the free parameters of TB modeling.展开更多
基金supported by National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant No.2012BAC23B01)National Natural Science Foundation of China (Grant No.41171066)the R&D Special Fund for Public Welfare Industry of China(Grant No.GYHY201206026)
文摘【Title】【Author】Snowpack is a combination of several snow layers. Accordingly, snowpack natural metamorphism is composed of several stages. The aim of this study is to investigate the natural snow metamorphism at the snow layer unit. The field investigation was conducted at the Tianshan Station for Snow Cover and Avalanche Research, Chinese Academy of Sciences （43°16＇ N, 84°24＇ E, and 1,776 m a.s.l.）, during the winter of 2010-2011. A complete metamorphic procedure and the corresponding microstructure of a target snow layer were tracked. The results indicate that： the ideal and complete metamorphic process and the corresponding predominant snow grain shape have 5 stages： 1） unstable kinetic metamorphism near the surface; 2） unstable kinetic metamorphism under pressure; 3） stable kinetic metamorphism; 4） equilibrium metamorphism; 5） wet snow metamorphism. Snow grain size sharply decreased in the surface stage, and then changed to continuously increase. Rapid increase of grain size occurred in the stable kinetic metamorphism and wet snow metamorphism stage. The characteristic length was introduced to represent the real sizes of depth hoar crystals. The snow grain circularity ratio had a variation of “rapid increase – slow decrease – slow increase”, and the snow aggregations continuously increased with time. Snow density grew stepwise and remained steady from the stable kinetic to the equilibrium metamorphism stage. The differences in metamorphism extent and stages among snow layers, led to the characteristic layered structure of snowpack.
基金supported by NASA Terrestrial Hydrology Program[grant number NNX09AM10G]Strategic Priority Research Program of Chinese Academy of Sciences[grant number XDA20100300].
文摘Reliablemicrostructuremeasurement of snow is a requirement for microwave radiative transfer model validation.Snow specific surface area(SSA)can be measured using stereological methods,in which snow samples are cast in the field and photographed in the laboratory.Processing stereology photographs manually by counting intersections of test cycloids with air-ice boundaries reduces the problems in binary segmentation.This paper is a case study to evaluate the repeatability of the manually stereology interpretation by two independent research groups.We further assessed how uncertainty in snow SSA influences simulated brightness temperature(TB)driven by the Microwave Emission Model of Layered Snowpacks(MEMLS),and how stereology compares to Near Infrared(NIR)camera and hand lens.Data was obtained from two alpine snow profiles from Steamboat Springs,Colorado.Results showed that stereological SSA values measured by two groups are highly consistent,and the ground radiometer measured T_(B)at 19 and 37 GHz was successfully predicted(RMSE<3.8 K);simulations using NIR SSA and hand-lens geometric grain size(Dg)measurements have larger errors.This conclusion was not sensitive to uncertainty in the free parameters of TB modeling.
