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Effects of sample density on the assimilation performance of an explicit four-dimensional variational data assimilation method

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Science China Earth Sciences 2009年第11期52卷 1849-1856页

作者： TIAN XiangJun xie zhenghui ICCES/LASE Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China

The concepts of sample sphere radius and sample density are proposed in this paper to help illustrate that different vector transformations result in diverse sample density with the same sample ensemble, which finally affects their assimilation performance. Several numerical experiments using a onedimensional (1-D) soil water equation and synthetic observations are conducted to evaluate this new theory in land data assimilation.

关键词： POD/SVD-E4DVAR data assimilation sample density

A land surface soil moisture data assimilation framework in consideration of the model subgrid-scale heterogeneity and soil water thawing and freezing

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Science China Earth Sciences 2008年第7期51卷 992-1000页

作者： TIAN XiangJun xie zhenghui Institute of Atmospheric Physics Chinese Academy of SciencesBeijing 100029China

The Ensemble Kalman Filter (EnKF) is well known and widely used in land data assimilation for its high precision and simple operation. The land surface models used as the forecast operator in a land data assimilation system are usually designed to consider the model subgrid-heterogeneity and soil water thawing and freezing. To neglect their effects could lead to some errors in soil moisture assimilation. The dual EnKF method is employed in soil moisture data assimilation to build a soil moisture data as- similation framework based on the NCAR Community Land Model version 2.0 (CLM 2.0) in considera- tion of the effects of the model subgrid-heterogeneity and soil water thawing and freezing: Liquid volumetric soil moisture content in a given fraction is assimilated through the state filter process, while solid volumetric soil moisture content in the same fraction and solid/liquid volumetric soil moisture in the other fractions are optimized by the parameter filter. Preliminary experiments show that this dual EnKF-based assimilation framework can assimilate soil moisture more effectively and precisely than the usual EnKF-based assimilation framework without considering the model subgrid-scale heteroge- neity and soil water thawing and freezing. With the improvement of soil moisture simulation, the soil temperature-simulated precision can be also improved to some extent.

关键词： dual EnKF NCAR/CLM soil moisture assimilation framework subgrid-heterogeneity soil water thawing and freezing

An explicit four-dimensional variational data assimilation method based on the proper orthogonal decomposition: Theoretics and evaluation

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Science China Earth Sciences 2009年第2期52卷 279-286页

作者： TIAN XiangJun xie zhenghui Institute of Atmospheric Physics Chinese Academy of SciencesBeijing 100029China

The proper orthogonal decomposition (POD) method is used to construct a set of basis functions for spanning the ensemble of data in a certain least squares optimal sense. Compared with the singular value decomposition (SVD), the POD basis functions can capture more energy in the forecast ensemble space and can represent its spatial structure and temporal evolution more effectively. After the analysis variables are expressed by a truncated expansion of the POD basis vectors in the ensemble space, the control variables appear explicitly in the cost function, so that the adjoint model, which is used to de-rive the gradient of the cost function with respect to the control variables, is no longer needed. The application of this new technique significantly simplifies the data assimilation process. Several as-similation experiments show that this POD-based explicit four-dimensional variational data assimila-tion method performs much better than the usual ensemble Kalman filter method on both enhancing the assimilation precision and reducing the computation cost. It is also better than the SVD-based ex-plicit four-dimensional assimilation method, especially when the forecast model is not perfect and the forecast error comes from both the noise of the initial filed and the uncertainty of the forecast model.

关键词： POD data assimilation 4DVAR explicit method

Impacts of hydraulic redistribution on eco-hydrological cycles： A case study over the Amazon basin

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Science China Earth Sciences 2018年第9期61卷 1330-1340页

作者： Yuanyuan WANG Binghao JIA zhenghui xie Beijing Meteorological Observatory Beijing 100089 China State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China

Hydraulic redistribution(HR)refers to the process of soil water transport through the low-resistance pathway provided by plant *** has been observed in field studies and proposed to be one of the processes that enable plants to resist water ***,most land-surface models(LSMs)currently do not include this underground root *** this study,a HR scheme was incorporated into the Community Land Model version 4.5(CLM4.5)to investigate the effect of HR on the eco-hydrological *** paired numerical simulations(with and without the new HR scheme)were conducted for the Tapajos National Forest km83(BRSa3)site and the *** for the BRSa3 site in the Amazon showed that HR during the wet season was small,<0.1 mm day^(–1),transferring water from shallow wet layers to deep dry layers at night;however,HR in the dry season was more obvious,up to 0.3 mm day^(–1),transferring water from deep wet layers to shallow dry layers at *** incorporating HR into CLM4.5,the new model increased gross primary production(GPP)and evapotranspiration(ET)by 10%and 15%,respectively,at the BRSa3 site,partly overcoming the *** the Amazon,regional analysis also revealed that vegetation responses(including GPP and ET)to seasonal drought and the severe drought of 2005 were better captured with the HR scheme incorporated.

关键词： Land-surface model CLM4.5 Hydraulic redistribution Gross primary production Evapotranspiration

Numerical simulation based on two-directional freeze and thaw algorithm for thermal diffusion model

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Applied Mathematics and Mechanics(English Edition) 2016年第11期37卷 1467-1478页

作者： Junqiang GAO zhenghui xie Aiwen WANG Zhendong LUO State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of Sciences School of Mathematics and Physics North China Electric Power University School of Applied Science Beijing Information and Science Technology University

Freeze-thaw processes significantly modulate hydraulic and thermal char- acteristics of soil. The changes in the frost and thaw fronts （FTFs） affect the water and energy cycles between the land surface and the atmosphere. Thus, the frozen soil com- prising permafrost and seasonally frozen soil has important effects on the land surface hydrology in cold regions. In this study, a two-directional freeze and thaw algorithm is incorporated into a thermal diffusion equation for simulating FTFs. A local adaptive variable-grid method is used to discretize the model. Sensitivity tests demonstrate that the method is stable and FTFs can be tracked continuously. The FTFs and soil tempera- ture at the Qinghai-Tibet Plateau D66 site are simulated hourly from September 1, 1997 to September 22, 1998. The results show that the incorporated model performs much better in the soil temperature simulation than the original thermal diffusion equation, showing potential applications of the method in land-surface process modeling.

关键词： freeze and thaw algorithm frost and thaw front (FTF) sensitivity test,thermal diffusion equation

Evaluation and Projection of Population Exposure to Temperature Extremes over the Beijing−Tianjin−Hebei Region Using a High-Resolution Regional Climate Model RegCM4 Ensemble

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Advances in Atmospheric Sciences 2024年第6期41卷 1132-1146页

作者： Peihua QIN zhenghui xie Rui HAN Buchun LIU State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG) Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China Institute of Environment and Sustainable Development in Agriculture Chinese Academy of Agricultural Sciences(CAAS)Beijing 100081China

Temperature extremes over rapidly urbanizing regions with high population densities have been scrutinized due to their severe impacts on human safety and *** of all,the performance of the regional climate model RegCM4 with a hydrostatic or non-hydrostatic dynamic core in simulating seasonal temperature and temperature extremes was evaluated over the historical period of 1991–99 at a 12-km spatial resolution over China and a 3-km resolution over the Beijing−Tianjin−Hebei(JJJ)region,a typical urban agglomeration of *** of spatial distributions of temperature extremes over the JJJ region using RegCM4 with hydrostatic and non-hydrostatic cores showed high spatial correlations of more than 0.8 with the *** a warming climate,temperature extremes of annual maximum daily temperature(TXx)and summer days(SU)in China and the JJJ region showed obvious increases by the end of the 21st century while there was a general reduction in frost days(FD).The ensemble of RegCM4 with different land surface components was used to examine population exposure to temperature extremes over the JJJ *** exposure to temperature extremes was found to decrease in 2091−99 relative to 1991−99 over the majority of the JJJ region due to the joint impacts of increases in temperature extremes over the JJJ and population decreases over the JJJ region,except for downtown ***,changes in population exposure to temperature extremes were mainly dominated by future population ***,we quantified changes in exposure to temperature extremes with temperature increase over the JJJ *** study helps to provide relevant policies to respond future climate risks over the JJJ region.

关键词： CMIP6 convection-permitting population exposure RegCM4 temperature extremes

Incorporation of a Dynamic Root Distribution into CLM4.5： Evaluation of Carbon and Water Fluxes over the Amazon

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Advances in Atmospheric Sciences 2016年第9期33卷 1047-1060页

作者： Yuanyuan WANG zhenghui xie B inghao JIA State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029 University of Chinese Academy of Sciences Beijing 100049

Roots are responsible for the uptake of water and nutrients by plants and have the plasticity to dynamically respond to different environmental conditions. However, most land surface models currently prescribe rooting profiles as a function only of vegetation type, with no consideration of the surroundings. In this study, a dynamic rooting scheme, which describes root growth as a compromise between water and nitrogen availability, was incorporated into CLM4.5 with carbon-nitrogen （CN） interactions （CLM4.5-CN） to investigate the effects of a dynamic root distribution on eco-hydrological modeling. Two paired numerical simulations were conducted for the Tapajos National Forest km83 （BRSa3） site and the Amazon, one using CLM4.5-CN without the dynamic rooting scheme and the other including the proposed scheme. Simulations for the BRSa3 site showed that inclusion of the dynamic rooting scheme increased the amplitudes and peak values of diurnal gross primary production （GPP） and latent heat flux （LE） for the dry season, and improved the carbon （C） and water cycle modeling by reducing the RMSE of GPP by 0.4 g C m^-2 d^-1, net ecosystem exchange by 1.96 g C m^-2 d^-1, LE by 5.0 W m^-2, and soil moisture by 0.03 m^3 m^-3, at the seasonal scale, compared with eddy flux measurements, while having little impact during the wet season. For the Amazon, regional analysis also revealed that vegetation responses （including GPP and LE） to seasonal drought and the severe drought of 2005 were better captured with the dynamic rooting scheme incorporated.

关键词： CLM4.5 dynamic root distribution carbon cycle water cycle Amazon

A soil moisture assimilation scheme based on the ensemble Kalman filter using microwave brightness temperature

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Science China Earth Sciences 2009年第11期52卷 1835-1848页

作者： BingHao Jia zhenghui xie XiangJun Tian ChunXiang Shi ICCES/LASG Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China Graduate University of Chinese Academy of Sciences Beijing 100049 China National Satellite Meteorological Center China Meteorological Administration Beijing 100081 China

This study presents a soil moisture assimilation scheme, which could assimilate microwave brightness temperature directly, based on the ensemble Kalman filter and the shuffled complex evolution method (SCE-UA). It uses the soil water model of the land surface model CLM3.0 as the forecast operator, and a radiative transfer model (RTM) as the observation operator in the assimilation system. The assimilation scheme is implemented in two phases: the parameter calibration phase and the pure soil moisture assimilation phase. The vegetation optical thickness and surface roughness parameters in the RTM are calibrated by SCE-UA method and the optimal parameters are used as the final model parameters of the observation operator in the assimilation phase. The ideal experiments with synthetic data indicate that this scheme could significantly improve the simulation of soil moisture at the surface layer. Further- more, the estimation of soil moisture in the deeper layers could also be improved to a certain extent. The real assimilation experiments with AMSR-E brightness temperature at 10.65 GHz (vertical polariza- tion) show that the root mean square error (RMSE) of soil moisture in the top layer (0―10 cm) by as- similation is 0.03355 m3·m-3, which is reduced by 33.6% compared with that by simulation (0.05052 m3·m-3). The mean RMSE by assimilation for the deeper layers (10―50 cm) is also reduced by 20.9%. All these experiments demonstrate the reasonability of the assimilation scheme developed in this study.

关键词： land data assimilation soil moisture ensemble Kalman filter SCE-UA method radiative transfer model AMSR-E

A moving boundary problem derived from heat and water transfer processes in frozen and thawed soils and its numerical simulation

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Science China Mathematics 2008年第8期51卷 1510-1521页

作者： xie zhenghui SONG LiYe FENG XiaoBing Institute of Atmospheric Physics Chinese Academy of SciencesBeijing 100029China Graduate School of the Chinese Academy of Sciences Beijing 100049China Department of Mathematics the University of TennesseeKnoxvilleTN 37996USA

The seasonal change in depths of the frozen and thawed soils within their active layer is reduced to a moving boundary problem, which describes the dynamics of the total ice content using an independent mass balance equation and treats the soil frost/thaw depths as moving (sharp) interfaces governed by some Stefan-type moving boundary conditions, and hence simultaneously describes the liquid water and solid ice states as well as the positions of the frost/thaw depths in soil. An adaptive mesh method for the moving boundary problem is adopted to solve the relevant equations and to determine frost/thaw depths, water content and temperature distribution. A series of sensitivity experiments by the numerical model under the periodic sinusoidal upper boundary condition for temperature are conducted to validate the model, and to investigate the effects of the model soil thickness, ground surface temperature, annual amplitude of ground surface temperature and thermal conductivity on frost/thaw depths and soil temperature. The simulated frost/thaw depths by the model with a periodical change of the upper boundary condition have the same period as that of the upper boundary condition, which shows that it can simulate the frost/thaw depths reasonably for a periodical forcing.

关键词： frost and thaw depth moving boundary Stefan problem heat and water transfer numerical solution 80A22