Due to the existence of thermal offsets,global solar irradiances measured by pyranometers are smaller than actual values,and errors are larger in the daytime.Until now,there is no universally-recognized correction met...Due to the existence of thermal offsets,global solar irradiances measured by pyranometers are smaller than actual values,and errors are larger in the daytime.Until now,there is no universally-recognized correction method for thermal offset errors.Therefore,it is imperative to identify a convenient and effective correction method.Five correction methods were evaluated based on the data measured from a field experiment from 23 January to 15 November,2011.Results have shown:1) Temporal variation characteristics of thermal offsets in the four tested pyranometers are consistent.2) Among the five methods,non-dimensional quantity method is suggested for use to correct thermal offsets,because it is convenient and no modification of instruments is required.If collocated net longwave radiation and wind speed data are available and their uncertainties are small,the historical solar radiation datasets can also be corrected.And correction effects by the method are better.展开更多
Recently, the degradation of permafrost and marsh environments in the Da and Xiao Hinggan Mountains has become a great concern as more human activities and pronounced climate warming were observed during the past 30 y...Recently, the degradation of permafrost and marsh environments in the Da and Xiao Hinggan Mountains has become a great concern as more human activities and pronounced climate warming were observed during the past 30 years and projected for the near future. The distr/bution patterns and development mechanisms of the permafrost and marshes have been examined both in theories and in field observations, in order to better understand the symbiosis of permafrost and marshes. The permafrost and marshes in the Da and Xiao Hinggan Mountains display discernible zonations in latitude and elevation. The marsh vegetation canopy, litter and peat soil have good thermal insulation properties for the underlying permafrost, resulting in a thermal offset of 3 ℃ to 4℃ and subsequently suppressing soil temperature. In addition, the much higher thermal conductivity of frozen and ice-rich peat in the active layer is conducive to the development or in favor of the protection of permafrost due to the semi-conductor properties of the soils overlying the permafrost. On the other hand, because permafrost is almost impervious, the osmosis of water in marsh soils can be effectively reduced, timely providing water supplies for helophytes growth or germination in spring. In the Da and Xiao Hinggan Mountains, the permafrost degradation has been accelerating due to the marked climate warming, ever increasing human activities, and the resultant eco-environmental changes. Since the permafrost and marsh environments are symbiotic and interdependent, they need to be managed or protected in a well-coordinated and integrated way.展开更多
基金National Science Foundation of China for Young Scholars(40905071)National Natural Science Foundation of China for General Program(41275114)
文摘Due to the existence of thermal offsets,global solar irradiances measured by pyranometers are smaller than actual values,and errors are larger in the daytime.Until now,there is no universally-recognized correction method for thermal offset errors.Therefore,it is imperative to identify a convenient and effective correction method.Five correction methods were evaluated based on the data measured from a field experiment from 23 January to 15 November,2011.Results have shown:1) Temporal variation characteristics of thermal offsets in the four tested pyranometers are consistent.2) Among the five methods,non-dimensional quantity method is suggested for use to correct thermal offsets,because it is convenient and no modification of instruments is required.If collocated net longwave radiation and wind speed data are available and their uncertainties are small,the historical solar radiation datasets can also be corrected.And correction effects by the method are better.
基金Under the auspices of National Natural Science Foundation of China (No. 40701031,40225001,J0630966)3rd-term Knowledge Innovation Program of Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences (No. O650445)
文摘Recently, the degradation of permafrost and marsh environments in the Da and Xiao Hinggan Mountains has become a great concern as more human activities and pronounced climate warming were observed during the past 30 years and projected for the near future. The distr/bution patterns and development mechanisms of the permafrost and marshes have been examined both in theories and in field observations, in order to better understand the symbiosis of permafrost and marshes. The permafrost and marshes in the Da and Xiao Hinggan Mountains display discernible zonations in latitude and elevation. The marsh vegetation canopy, litter and peat soil have good thermal insulation properties for the underlying permafrost, resulting in a thermal offset of 3 ℃ to 4℃ and subsequently suppressing soil temperature. In addition, the much higher thermal conductivity of frozen and ice-rich peat in the active layer is conducive to the development or in favor of the protection of permafrost due to the semi-conductor properties of the soils overlying the permafrost. On the other hand, because permafrost is almost impervious, the osmosis of water in marsh soils can be effectively reduced, timely providing water supplies for helophytes growth or germination in spring. In the Da and Xiao Hinggan Mountains, the permafrost degradation has been accelerating due to the marked climate warming, ever increasing human activities, and the resultant eco-environmental changes. Since the permafrost and marsh environments are symbiotic and interdependent, they need to be managed or protected in a well-coordinated and integrated way.
