植被总初级生产力(Gross primary productivity,GPP)是陆地生态系统碳循环的关键环节,对维持全球碳平衡至关重要。基于Google Earth Engine平台,利用NASA LP DAAC发布的MOD17A2H产品,研究分析了塔里木河生态输水期间陆地生态系统生长季...植被总初级生产力(Gross primary productivity,GPP)是陆地生态系统碳循环的关键环节,对维持全球碳平衡至关重要。基于Google Earth Engine平台,利用NASA LP DAAC发布的MOD17A2H产品,研究分析了塔里木河生态输水期间陆地生态系统生长季的GPP变化。结果表明:(1)生态输水后,塔里木河生态环境整体得到改善。输水前期,塔里木河生长季GPP平均为3675.51 g C·m^(-2)·季^(-1),输水中期,生长季GPP增加到4024.09 g C·m^(-2)·季^(-1),输水后期,该值跃升为4896.61 g C·m^(-2)·季^(-1)。2000—2020年塔里木河生长季GPP表现出明显的增加趋势,增长幅度约为每个生长季增加90.25 g C·m^(-2)。2010年后,上、中、下游日GPP增加幅度亦更明显,分别为每10 a增加2.54 g C·m^(-2)、2.17 g C·m^(-2)和1.74 g C·m^(-2)。(2)塔里木河陆地生态系统生长季(5—10月)的日GPP变化在不同区域存在明显差异。上游区日GPP变化总体上表现出先增加后减小的单峰趋势,下游区则以双峰变化趋势为主。(3)塔里木河生态输水工程有益于生长季GPP的变化,其中对6、8月的GPP变化影响更显著。展开更多
Intense human activities in arid areas have great impacts on groundwater hydrochemical cycling by causing groundwater salinization.The spatiotemporal distributions of groundwater hydrochemistry are crucial for studyin...Intense human activities in arid areas have great impacts on groundwater hydrochemical cycling by causing groundwater salinization.The spatiotemporal distributions of groundwater hydrochemistry are crucial for studying groundwater salt migration,and also vital to understand hydrological and hydrogeochemical processes of groundwater in arid inland oasis areas.However,due to constraints posed by the paucity of observation data and intense human activities,these processes are not well known in the dried-up river oases of arid areas.Here,we examined spatiotemporal variations and evolution of groundwater hydrochemistry using data from 199 water samples collected in the Wei-Ku Oasis,a typical arid inland oasis in Tarim Basin of Central Asia.As findings,groundwater hydrochemistry showed a spatiotemporal dynamic,while its spatial distribution was complex.TDS and δ18O of river water in the upstream increased from west to east,whereas ion concentrations of shallow groundwater increased from northwest to southeast.Higher TDS was detected in spring for shallow groundwater and in summer for middle groundwater.Pronounced spatiotemporal heterogeneity demonstrated the impacts of geogenic,climatic,and anthropogenic conditions.For that,hydrochemical evolution of phreatic groundwater was primarily controlled by rock dominance and evaporation-crystallization process.Agricultural irrigation and drainage,land cover change,and groundwater extraction reshaped the spatiotemporal patterns of groundwater hydrochemistry.Groundwater overexploitation altered the leaking direction between the aquifers,causing the interaction between saltwater and freshwater and the deterioration of groundwater environment.These findings could provide an insight into groundwater salt migration under human activities,and hence be significant in groundwater quality management in arid inland oasis areas.展开更多
With the development of computational power and numerical algorithms,computational fluid dynamics(CFD) has become an important strategy for the design of aircraft,which significantly reduces the reliance on wind-tunne...With the development of computational power and numerical algorithms,computational fluid dynamics(CFD) has become an important strategy for the design of aircraft,which significantly reduces the reliance on wind-tunnel and flight tests.In this paper,we conducted a numerical investigation on the flow past a full commercial aircraft at Mach number 0.2 and 14 degrees angle of attack by means of Reynolds-averaged Navier-Stokes(RANS),detached-eddy simulation(DES) and our newly developed constrained large-eddy simulation(CLES).The objective of this paper is to study the capability of these models in simulating turbulent flows.To our knowledge,this is the first large-eddy simulation method for full commercial aircraft simulation.The results show that the CLES can predict the mean statistical quantities well,qualitatively consistent with traditional methods,and can capture more small-scale structures near the surface of the aircraft with massive separations.Our study demonstrates that CLES is a promising alternative for simulating real engineering turbulent flows.展开更多
文摘植被总初级生产力(Gross primary productivity,GPP)是陆地生态系统碳循环的关键环节,对维持全球碳平衡至关重要。基于Google Earth Engine平台,利用NASA LP DAAC发布的MOD17A2H产品,研究分析了塔里木河生态输水期间陆地生态系统生长季的GPP变化。结果表明:(1)生态输水后,塔里木河生态环境整体得到改善。输水前期,塔里木河生长季GPP平均为3675.51 g C·m^(-2)·季^(-1),输水中期,生长季GPP增加到4024.09 g C·m^(-2)·季^(-1),输水后期,该值跃升为4896.61 g C·m^(-2)·季^(-1)。2000—2020年塔里木河生长季GPP表现出明显的增加趋势,增长幅度约为每个生长季增加90.25 g C·m^(-2)。2010年后,上、中、下游日GPP增加幅度亦更明显,分别为每10 a增加2.54 g C·m^(-2)、2.17 g C·m^(-2)和1.74 g C·m^(-2)。(2)塔里木河陆地生态系统生长季(5—10月)的日GPP变化在不同区域存在明显差异。上游区日GPP变化总体上表现出先增加后减小的单峰趋势,下游区则以双峰变化趋势为主。(3)塔里木河生态输水工程有益于生长季GPP的变化,其中对6、8月的GPP变化影响更显著。
基金This research was funded by the Natural Science Foundation of Xinjiang Uygur Autonomous Region,China(2021D01D01).
文摘Intense human activities in arid areas have great impacts on groundwater hydrochemical cycling by causing groundwater salinization.The spatiotemporal distributions of groundwater hydrochemistry are crucial for studying groundwater salt migration,and also vital to understand hydrological and hydrogeochemical processes of groundwater in arid inland oasis areas.However,due to constraints posed by the paucity of observation data and intense human activities,these processes are not well known in the dried-up river oases of arid areas.Here,we examined spatiotemporal variations and evolution of groundwater hydrochemistry using data from 199 water samples collected in the Wei-Ku Oasis,a typical arid inland oasis in Tarim Basin of Central Asia.As findings,groundwater hydrochemistry showed a spatiotemporal dynamic,while its spatial distribution was complex.TDS and δ18O of river water in the upstream increased from west to east,whereas ion concentrations of shallow groundwater increased from northwest to southeast.Higher TDS was detected in spring for shallow groundwater and in summer for middle groundwater.Pronounced spatiotemporal heterogeneity demonstrated the impacts of geogenic,climatic,and anthropogenic conditions.For that,hydrochemical evolution of phreatic groundwater was primarily controlled by rock dominance and evaporation-crystallization process.Agricultural irrigation and drainage,land cover change,and groundwater extraction reshaped the spatiotemporal patterns of groundwater hydrochemistry.Groundwater overexploitation altered the leaking direction between the aquifers,causing the interaction between saltwater and freshwater and the deterioration of groundwater environment.These findings could provide an insight into groundwater salt migration under human activities,and hence be significant in groundwater quality management in arid inland oasis areas.
基金supported by the National Natural Science Foundation of China(Grant Nos.10921202 and 91130001)the National Basic Research Program of China(Grant No. 2009CB724101)
文摘With the development of computational power and numerical algorithms,computational fluid dynamics(CFD) has become an important strategy for the design of aircraft,which significantly reduces the reliance on wind-tunnel and flight tests.In this paper,we conducted a numerical investigation on the flow past a full commercial aircraft at Mach number 0.2 and 14 degrees angle of attack by means of Reynolds-averaged Navier-Stokes(RANS),detached-eddy simulation(DES) and our newly developed constrained large-eddy simulation(CLES).The objective of this paper is to study the capability of these models in simulating turbulent flows.To our knowledge,this is the first large-eddy simulation method for full commercial aircraft simulation.The results show that the CLES can predict the mean statistical quantities well,qualitatively consistent with traditional methods,and can capture more small-scale structures near the surface of the aircraft with massive separations.Our study demonstrates that CLES is a promising alternative for simulating real engineering turbulent flows.
