Zhang Q.,Institute of Arid Meteorology of CMA |
Zhang Q.,Key Laboratory of Arid Climatic Change and Disaster Reduction of Gansu Province |
Zhang Q.,Key Open Laboratory of Arid Climatic Change and Disaster Reduction of CMA |
Yao T.,Institute of Arid Meteorology of CMA |
And 6 more authors.
Science China Earth Sciences | Year: 2015
Aerodynamic roughness length is an important physical parameter in atmospheric numerical models and micrometeorological calculations, the accuracy of which can affect numerical model performance and the level of micrometeorological computations. Many factors influence the aerodynamic roughness length, but formulas for its parameterization often only consider the action of a single factor. This limits their adaptive capacity and often introduces considerable errors in the estimation of land surface momentum flux (friction velocity). In this study, based on research into the parameterization relations between aerodynamic roughness length and influencing factors such as windflow conditions, thermodynamic characteristics of the surface layer, natural rhythm of vegetation growth, ecological effects of interannual fluctuations of precipitation, and vegetation type, an aerodynamic roughness length parameterization scheme was established. This considers almost all the factors that affect aerodynamic roughness length on flat land surfaces with short vegetation. Furthermore, using many years’ data recorded at the Semi-Arid Climate and Environment Observatory of Lanzhou University, a comparative analysis of the application of the proposed parameterization scheme and other experimental schemes was performed. It was found that the error in the friction velocity estimated by the proposed parameterization scheme was considerably less than that estimated using a constant aerodynamic roughness length and by the other parameterization schemes. Compared with the friction velocity estimated using a constant aerodynamic roughness length, the correlation coefficient with the observed friction velocity increased from 0.752 to 0.937, and the standard deviation and deviation decreased by about 20% and 80%, respectively. Its mean value differed from the observed value by only 0.004 m s−1 and the relative error was only about 1.6%, which indicates a significant decrease in the estimation error of surface-layer momentum flux. The test results show that the multifactorial universal parameterization scheme of aerodynamic roughness length for flat land surfaces with short vegetation can offer a more scientific parameterization scheme for numerical atmospheric models. © 2015 Science China Press and Springer-Verlag Berlin Heidelberg
Yue P.,Institute of Arid Meteorology |
Yue P.,Key Laboratory of Arid Climatic Change and Reducing Disaster of Gansu Province |
Yue P.,Key Open Laboratory of Arid Climatic Change and Disaster Reduction of CMA |
Yue P.,Lanzhou University |
And 19 more authors.
Science China Earth Sciences | Year: 2015
On the basis of information from the project “Land-surface Processes and their Experimental Study on the Chinese Loess Plateau”, we analyzed differences in land-surface water and heat processes during the main dry and wet periods of the semiarid grassland growing season in Yuzhong County, as well as the influences of these environmental factors. Studies have shown that there are significant differences in changes of land-surface temperature and humidity during dry and wet periods. Daily average normalized temperature has an overall vertical distribution of “forward tilting” and “backward tilting” during dry and wet periods, respectively. During the dry period, shallow soil above 20-cm depth is the active temperature layer. The heat transfer rate in soil is obviously different during dry and wet periods. During the dry period, the ratio of sensible heat flux to net radiation (H/Rn) and the value of latent heat flux to net radiation (LE/Rn) have a linear relationship with 5-cm soil temperature; during the wet period, these have a nonlinear relationship with 5-cm soil temperature, and soil temperature of 16°C is the critical temperature for changes in the land-surface water and heat exchange trend on a daily scale. During the dry period, H/Rn and LE/Rn have a linear relationship with soil water content. During the wet period, these have a nonlinear relationship with 5-cm soil water content, and 0.21 m3 m−3 is the critical point for changes in the land-surface water and heat exchange trend at daily scale. During the dry period, for vapor pressure deficit less than 0.7 kPa, H/Rn rises with increased vapor pressure deficit, whereas LE/Rn decreases with that increase. When that deficit is greater than 0.7 kPa, both H/Rn and LE/Rn tend to be constant. During the wet period, H/Rn increases with the vapor pressure deficit, whereas LE/Rn decreases. The above characteristics directly reflect the effect of differences in land-surface environmental factors during land-surface water and heat exchange processes, and indirectly reflect the influences of cloud precipitation processes on those processes. © 2015, Science China Press and Springer-Verlag Berlin Heidelberg.
Yu L.,Northwest University for Nationalities |
Yu L.,Institute of Arid Meteorology |
Longqing L.,University of Sichuan |
Qiang Z.,Institute of Arid Meteorology |
And 6 more authors.
Chemistry and Ecology | Year: 2013
The aim of the present study was to investigate the possible effects of temperature on cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn) accumulation in five vegetable species collected at different sites (Shuichuan, Beiwan, Dongwan and Wufe) in northwest China. The meteorological data of air and soil temperatures were recorded daily during the period from sowing to harvest for the five vegetables. The air and soil temperatures affected the capacity of pumpkin, cabbage, brassica napus and Chinese cabbage to accumulate Zn, Cd, Cu and Pb. Principal component analysis showed that temperature, photosynthetic and physiological factors all contributed to the soil-plant transfer properties of DTPA-extractable heavy metals. Temperature played a more important role in Cd, Pb, Cu and Zn accumulation in four vegetables in this semiarid area. However, the enormous surface area of spinach was likely to elevate heavy metal loads owing to atmospheric deposits. For most vegetables studied, there was a striking dissimilarity in the uptake and translocation ability of Cd, Zn and Cu in soil, but similar accumulation to translocation for Pb in soil. © 2013 Copyright Taylor and Francis Group, LLC.