Previous studies have demonstrated that offline land surface models(LSMs)and global hydrological models(GHMs)can reasonably reproduce streamflow in large river basins.Global reanalyses supply fine spatiotemporal runof...Previous studies have demonstrated that offline land surface models(LSMs)and global hydrological models(GHMs)can reasonably reproduce streamflow in large river basins.Global reanalyses supply fine spatiotemporal runoff estimates,but they are not fully intercompared and evaluated in China.This study assesses the routed-runoff from five offline LSM/GHM runs(VIC-CN05.1,CLM-CFSR,CLM-ERAI,CLM-MERRA,and CLM-NCEP)and three reanalysis datasets(ERAI/Land,JRA55,and MERRA-2)against the gauged streamflow(26 stations)in major Chinese river basins during 1980–2008.The Catchment-based Macro-scale Floodplain model(CaMa-Flood)is employed to route those runoff datasets to the hydrological stations.Four statistical quantities,including the correlation coefficient(R),standard deviation(STD),Nash–Sutcliffe efficiency coefficient(NSE),and relative error(RE),along with a ranking method,are used to quantify the quality of those products.The results show that the spatial patterns of both modeled and observed streamflow in summer are similar,but their magnitudes are different.Except for MERRA-2,the other products can reproduce well the interannual variability of streamflow in both the Yangtze and Yellow River basins.All products generally underestimate the magnitude and variance of monthly streamflow,while VIC-CN05.1 and JRA55 are closer to observations compared to other products.The correlation coefficients for all products are overall larger than 0.61,with the highest value(0.85)from VIC-CN05.1.In addition to CLM-MERRA,MERRA-2,and CLM-NCEP with relatively small precipitation,other products can simulate peak flow well with positive NSEs up to 0.41(ERAI/Land).Considerable uncertainties exist among the eight products at the Yellow River outlet,which might be because the LSMs ignore frequent human activities.Based on the above statistics,performances of the eight runoff products are ranked in descending order as follows:VIC-CN05.1,ERAI/Land,JRA55,CLM-CFSR,CLM-ERAI,MERRA-2,CLM-MERRA,and CLM-NCEP,which provides a reference for flood/hydro展开更多
Seismic wave propagation in fluid-solid coupled media is currently a popular topic. However, traditional wave equation-based simulation methods have to consider complex boundary conditions at the fluid-solid interface...Seismic wave propagation in fluid-solid coupled media is currently a popular topic. However, traditional wave equation-based simulation methods have to consider complex boundary conditions at the fluid-solid interface. To address this challenge, we propose a novel numerical scheme that integrates the lattice Boltzmann method(LBM) and lattice spring model(LSM). In this scheme, LBM simulates viscoacoustic wave propagation in the fluid area and LSM simulates elastic wave propagation in the solid area. We also introduce three different LBM-LSM coupling strategies, a standard bounce back scheme, a specular reflection scheme, and a hybrid scheme, to describe wave propagation across fluid-solid boundaries. To demonstrate the accuracy of these LBM-LSM coupling schemes, we simulate wave propagation in a two-layer model containing a fluid-solid interface. We place excitation sources in the fluid layer and the solid layer respectively, to observe the wave phenomena when seismic waves propagate to interface from different sides. The simulated results by LBM-LSM are compared with the reference wavefields obtained by the finite difference method(FDM) and the analytical solution(ANA).Our LBM-LSM coupling scheme was verified effective, as the relative errors between the LBM-LSM solutions and reference solutions were within an acceptable range, sometimes around 1.00%. The coupled LBM-LSM scheme is further used to model seismic wavefields across a more realistic rugged seabed,which reveals the potential applications of the coupled LBM-LSM scheme in marine seismic imaging techniques, such as reverse-time migration and full-waveform inversion. The method also has potential applications in simulating wave propagation in complex two-and multi-phase media.展开更多
Effective medium methods for the attribution of micro-structures to macro elastic properties of shales are important for the prediction of sweet spots in the shale-gas production.With X-ray micro-computed tomography(X...Effective medium methods for the attribution of micro-structures to macro elastic properties of shales are important for the prediction of sweet spots in the shale-gas production.With X-ray micro-computed tomography(XMCT),the micro-structures of shale core samples from Longmaxi Formation are visualized and characterized by 3D digital images.As an efficient alternative to conventional effective medium methods for estimating elastic properties,we propose a consistent workflow of lattice spring modeling(LSM)to emulate the digital cores using three types of lattices.Particular attention is paid to investigate the effective Young’s moduli,Poisson’s ratios,and preferred orientations,by uniaxial compression tests along two directions.Within elastic deformation,the impact of lattice arrangements on the anisotropy is even more than those of stress disturbances and micro-structural features.Compared with analytical approximations and theoretical predictions,the LSM numerical scheme shows general applicability for heterogeneous porous rocks.展开更多
Land data assimilation(DA)is an effective method to provide high-quality spatially and temporally continuous soil moisture datasets that are crucial in weather,climate,hydrological,and agricultural research.However,mo...Land data assimilation(DA)is an effective method to provide high-quality spatially and temporally continuous soil moisture datasets that are crucial in weather,climate,hydrological,and agricultural research.However,most existing land DA applications have used remote sensing observations,and are based on one-dimensional(1 D)analysis,which cannot be directly employed to reasonably assimilate the recently expanded in-situ soil moisture observations in China.In this paper,a two-dimensional(2 D)localized ensemble-based optimum interpolation(En OI)scheme for assimilating in-situ soil moisture observations from over 2200 stations into land surface models(LSMs)is introduced.This scheme uses historical LSM simulations as ensemble samples to provide soil moisture background error covariance,allowing the in-situ observation information to be propagated to surrounding pixels.It is also computationally efficient because no additional ensemble simulations are needed.A set of ensemble sampling and localization length scale sensitivity experiments are performed.The En OI performs best for in-situ soil moisture fusion over China with an ensemble sampling of hourly soil moisture from the previous 7 days and a localization length scale of 100 km.Following the evaluation,simulations for in-situ soil moisture fusion are also performed from May 2016 to September 2016.The En OI analysis is notably better than that without in-situ observation fusion,as the wet bias of 0.02 m3 m-3 is removed,the root-mean-square error(RMSE)is reduced by about 37%,and the correlation coefficient is increased by about 25%.Independent evaluation shows that the En OI analysis performs considerably better than that without fusion in terms of bias,and marginally better in terms of RMSE and correlation.展开更多
Since the North American and Global Land Data Assimilation Systems(NLDAS and GLDAS) were established in2004, significant progress has been made in development of regional and global LDASs. National, regional, projectb...Since the North American and Global Land Data Assimilation Systems(NLDAS and GLDAS) were established in2004, significant progress has been made in development of regional and global LDASs. National, regional, projectbased, and global LDASs are widely developed across the world. This paper summarizes and overviews the development, current status, applications, challenges, and future prospects of these LDASs. We first introduce various regional and global LDASs including their development history and innovations, and then discuss the evaluation, validation, and applications(from numerical model prediction to water resources management) of these LDASs. More importantly, we document in detail some specific challenges that the LDASs are facing: quality of the in-situ observations, satellite retrievals, reanalysis data, surface meteorological forcing data, and soil and vegetation databases; land surface model physical process treatment and parameter calibration; land data assimilation difficulties; and spatial scale incompatibility problems. Finally, some prospects such as the use of land information system software, the unified global LDAS system with nesting concept and hyper-resolution, and uncertainty estimates for model structure,parameters, and forcing are discussed.展开更多
Recently, a four-dimensional lattice spring model(4D-LSM) was developed to overcome the Poisson’s ratio limitation of the classical LSM by introducing the fourth-dimensional spatial interaction. In this work, some as...Recently, a four-dimensional lattice spring model(4D-LSM) was developed to overcome the Poisson’s ratio limitation of the classical LSM by introducing the fourth-dimensional spatial interaction. In this work, some aspects of the 4D-LSM on solving problems in geomechanics are investigated, such as the ability to reproduce elastic properties of geomaterials, the capability of solving heterogeneous problems,the accuracy on modelling stress wave propagation, the ability to solve dynamic fracturing and the parallel computational efficiency. Our results indicate that the 4D-LSM is promising to deal with problems in geomechanics.展开更多
基金Supported by the National Key Research and Development Program of China(2016YFA0602401)National Natural Science Foundation of China(41875106).
文摘Previous studies have demonstrated that offline land surface models(LSMs)and global hydrological models(GHMs)can reasonably reproduce streamflow in large river basins.Global reanalyses supply fine spatiotemporal runoff estimates,but they are not fully intercompared and evaluated in China.This study assesses the routed-runoff from five offline LSM/GHM runs(VIC-CN05.1,CLM-CFSR,CLM-ERAI,CLM-MERRA,and CLM-NCEP)and three reanalysis datasets(ERAI/Land,JRA55,and MERRA-2)against the gauged streamflow(26 stations)in major Chinese river basins during 1980–2008.The Catchment-based Macro-scale Floodplain model(CaMa-Flood)is employed to route those runoff datasets to the hydrological stations.Four statistical quantities,including the correlation coefficient(R),standard deviation(STD),Nash–Sutcliffe efficiency coefficient(NSE),and relative error(RE),along with a ranking method,are used to quantify the quality of those products.The results show that the spatial patterns of both modeled and observed streamflow in summer are similar,but their magnitudes are different.Except for MERRA-2,the other products can reproduce well the interannual variability of streamflow in both the Yangtze and Yellow River basins.All products generally underestimate the magnitude and variance of monthly streamflow,while VIC-CN05.1 and JRA55 are closer to observations compared to other products.The correlation coefficients for all products are overall larger than 0.61,with the highest value(0.85)from VIC-CN05.1.In addition to CLM-MERRA,MERRA-2,and CLM-NCEP with relatively small precipitation,other products can simulate peak flow well with positive NSEs up to 0.41(ERAI/Land).Considerable uncertainties exist among the eight products at the Yellow River outlet,which might be because the LSMs ignore frequent human activities.Based on the above statistics,performances of the eight runoff products are ranked in descending order as follows:VIC-CN05.1,ERAI/Land,JRA55,CLM-CFSR,CLM-ERAI,MERRA-2,CLM-MERRA,and CLM-NCEP,which provides a reference for flood/hydro
基金supported in part by R & D Department of China National Petroleum Corporation (2022DQ0604-01)National Natural Science Foundation of China (42204132)+3 种基金the China Postdoctoral Science Foundations (2020M680667, 2021T140661)Harvard-CUP Joint Laboratory on Petroleum Science“111” project (B13010)the financial support from the CAS Special Research Assistant Project。
文摘Seismic wave propagation in fluid-solid coupled media is currently a popular topic. However, traditional wave equation-based simulation methods have to consider complex boundary conditions at the fluid-solid interface. To address this challenge, we propose a novel numerical scheme that integrates the lattice Boltzmann method(LBM) and lattice spring model(LSM). In this scheme, LBM simulates viscoacoustic wave propagation in the fluid area and LSM simulates elastic wave propagation in the solid area. We also introduce three different LBM-LSM coupling strategies, a standard bounce back scheme, a specular reflection scheme, and a hybrid scheme, to describe wave propagation across fluid-solid boundaries. To demonstrate the accuracy of these LBM-LSM coupling schemes, we simulate wave propagation in a two-layer model containing a fluid-solid interface. We place excitation sources in the fluid layer and the solid layer respectively, to observe the wave phenomena when seismic waves propagate to interface from different sides. The simulated results by LBM-LSM are compared with the reference wavefields obtained by the finite difference method(FDM) and the analytical solution(ANA).Our LBM-LSM coupling scheme was verified effective, as the relative errors between the LBM-LSM solutions and reference solutions were within an acceptable range, sometimes around 1.00%. The coupled LBM-LSM scheme is further used to model seismic wavefields across a more realistic rugged seabed,which reveals the potential applications of the coupled LBM-LSM scheme in marine seismic imaging techniques, such as reverse-time migration and full-waveform inversion. The method also has potential applications in simulating wave propagation in complex two-and multi-phase media.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences,the National Natural Sciences Foundation and China Postdoctoral Science Foundation(Grant Nos.XDA14010303,XDB10010400,41804134,2018M640176).
文摘Effective medium methods for the attribution of micro-structures to macro elastic properties of shales are important for the prediction of sweet spots in the shale-gas production.With X-ray micro-computed tomography(XMCT),the micro-structures of shale core samples from Longmaxi Formation are visualized and characterized by 3D digital images.As an efficient alternative to conventional effective medium methods for estimating elastic properties,we propose a consistent workflow of lattice spring modeling(LSM)to emulate the digital cores using three types of lattices.Particular attention is paid to investigate the effective Young’s moduli,Poisson’s ratios,and preferred orientations,by uniaxial compression tests along two directions.Within elastic deformation,the impact of lattice arrangements on the anisotropy is even more than those of stress disturbances and micro-structural features.Compared with analytical approximations and theoretical predictions,the LSM numerical scheme shows general applicability for heterogeneous porous rocks.
基金Supported by the China Meteorological Administration Special Public Welfare Research Fund(GYHY201506002)National Key Research and Development Program of China(2018YFC1506601)+1 种基金National Natural Science Foundation of China(91437220)National Innovation Project for Meteorological Science and Technology(CMAGGTD003-5)。
文摘Land data assimilation(DA)is an effective method to provide high-quality spatially and temporally continuous soil moisture datasets that are crucial in weather,climate,hydrological,and agricultural research.However,most existing land DA applications have used remote sensing observations,and are based on one-dimensional(1 D)analysis,which cannot be directly employed to reasonably assimilate the recently expanded in-situ soil moisture observations in China.In this paper,a two-dimensional(2 D)localized ensemble-based optimum interpolation(En OI)scheme for assimilating in-situ soil moisture observations from over 2200 stations into land surface models(LSMs)is introduced.This scheme uses historical LSM simulations as ensemble samples to provide soil moisture background error covariance,allowing the in-situ observation information to be propagated to surrounding pixels.It is also computationally efficient because no additional ensemble simulations are needed.A set of ensemble sampling and localization length scale sensitivity experiments are performed.The En OI performs best for in-situ soil moisture fusion over China with an ensemble sampling of hourly soil moisture from the previous 7 days and a localization length scale of 100 km.Following the evaluation,simulations for in-situ soil moisture fusion are also performed from May 2016 to September 2016.The En OI analysis is notably better than that without in-situ observation fusion,as the wet bias of 0.02 m3 m-3 is removed,the root-mean-square error(RMSE)is reduced by about 37%,and the correlation coefficient is increased by about 25%.Independent evaluation shows that the En OI analysis performs considerably better than that without fusion in terms of bias,and marginally better in terms of RMSE and correlation.
基金Supported by the US Environmental Modeling Center(EMC)Land Surface Modeling Project(granted to Youlong Xia)National Natural Science Foundation of China(51609111,granted to Baoqing Zhang)
文摘Since the North American and Global Land Data Assimilation Systems(NLDAS and GLDAS) were established in2004, significant progress has been made in development of regional and global LDASs. National, regional, projectbased, and global LDASs are widely developed across the world. This paper summarizes and overviews the development, current status, applications, challenges, and future prospects of these LDASs. We first introduce various regional and global LDASs including their development history and innovations, and then discuss the evaluation, validation, and applications(from numerical model prediction to water resources management) of these LDASs. More importantly, we document in detail some specific challenges that the LDASs are facing: quality of the in-situ observations, satellite retrievals, reanalysis data, surface meteorological forcing data, and soil and vegetation databases; land surface model physical process treatment and parameter calibration; land data assimilation difficulties; and spatial scale incompatibility problems. Finally, some prospects such as the use of land information system software, the unified global LDAS system with nesting concept and hyper-resolution, and uncertainty estimates for model structure,parameters, and forcing are discussed.
基金financially supported by the National Natural Science Foundation of China (Grant No. 1177020290)
文摘Recently, a four-dimensional lattice spring model(4D-LSM) was developed to overcome the Poisson’s ratio limitation of the classical LSM by introducing the fourth-dimensional spatial interaction. In this work, some aspects of the 4D-LSM on solving problems in geomechanics are investigated, such as the ability to reproduce elastic properties of geomaterials, the capability of solving heterogeneous problems,the accuracy on modelling stress wave propagation, the ability to solve dynamic fracturing and the parallel computational efficiency. Our results indicate that the 4D-LSM is promising to deal with problems in geomechanics.
