Application of Nonlinear Balance Scheme in Three-Dimensional Variational Data Assimilation

The dynamical constrains in three-dimensional variational data assimilation are discussed when consid- ering the impact of stream divergence and convergence on the pressure and wind fields.For the analysis of severe tropical cyclone,frontal structures,and other rapidly changing structures,the geostrophic balance and linear balance cannot properly represent the relationship between wind and pressure fields.However,the nonlinear balance incremental equation takes into account the information of flow-dependent background, and makes response to the flow-dependent background covariance in the 3D-Var system.Results indicate that the application of the nonlinear balance equation to 3D-Var system improves the quality of severe trop- ical cyclone assimilation system,which has some positive effects on intensity prediction of tropical cyclones.     

SURFACE IMBALANCE ENERGY CALCULATED AND ANALYZED WITH THE DATA OF EBEX-2000*

Mainly.three methods have been developed to calculate turbulence heat flux.They are eddy covariance method,Bowen ratio/energy balance method and aerodynamic method.In this paper, all the three methods have been used to calculate sensible heat flux,latent heat flux and imbalance energy near the surface with the experiment data of EBEX-2000.Then comparisons of the three methods and some possible explanations of the surface imbalance energy are given.     

Automatic Modeling of (Cross) Covariance Tables Using Fast Fourier Transform

Covariance models provide the basic measure of spatial continuity in geostatistics. Traditionally, a closed-form analytical model is fitted to allow for interpolation of sample Covariance values while ensuring the positive definiteness condition. For cokriging, the modeling task is made even more difficult because of the restriction imposed by the linear coregionalization model. Bochner's theorem maps the positive definite constraints into much simpler constraints on the Fourier transform of the covariance, that is the density spectrum. Accordingly, we propose to transform the experimental (cross) covariance tables into quasidensity spectrum tables using Fast Fourier Transform (FFT). These quasidensity spectrum tables are then smoothed under constraints of positivity and unit sum. A backtransform (FFT) yields permissible (jointly) positive definite (cross) covariance tables. At no point is any analytical modeling called for and the algorithm is not restricted by the linear coregionalization model. A case study shows the proposed covariance modeling to be easier and much faster than the traditional analytical covariance modeling, yet yields comparable kriging or simulation results.     

最小二乘配置方法确定局部大地水准面的研究

从最小二乘配置方法的原理出发 ,描述了最小二乘配置法中经验协方差函数的确定方法。在此基础上 ,以我国西部高山地区为例 ,利用实测点重力数据、30″× 30″数值地面模型和EGM96地球重力场模型 ,确定了该地区 2 .5′× 2 .5′大地水准面     

CO2湍流通量误差的修正和不确定性研究进展

目前国内外对能量和CO₂涡动相关通量的测量误差的谱修正缺乏一致性，导致各测量站之间的资料对比难以进行，给全球尺度资料的合成造成很大困难。因此在强调长期CO₂通量测量精度的同时，还应该注重确定对测量误差修正的首选方法和研究重点。该文主要介绍了两种用于修正测量仪器误差的谱方法；二维和三维的气流运动对通量误差的影响；资料处理中的误差；夜间CO₂通量的测量问题。     

Flux Corrections Revisited

In a horizontally homogeneous atmosphere, the calculation of thevertical fluxes of mass, momentum, and heat from point measurementsare to lowest order calculated as the standard eddy covariance.Additional terms primarily related to the mean vertical velocity areadded to improve the accuracy of the calculation. A review ofprevious work is undertaken. The fluxes are reformulated beginningwith the equations of conservation of mass, momentum, and energy. Aformula for the mean vertical velocity is found that is accurate tothe ideal gas approximation. Relations are developed between fluxesat different heights. In addition to the relations for fluxes ofmass, sensible heat, and latent heat, the fluxes of momentum andturbulent kinetic energy are also considered.     

Coregionalization by Linear Combination of Nonorthogonal Components

This paper applies the relationship between the matrix multivariate covariance and the covariance of a linear combination of a single attribute to analyze modeling with nested structures. This analysis for modeling of covariances is introduced to the multivariate case for nonorthogonal vector spatial components. Results validate the classic linear model of coregionalization for a more general case of nonorthogonality, that produces additional terms including cross-covariance in the nested structures. Linear combinations of nested structures have been applied in the frequency domain to a more general case where the coefficients are nonconstant but valid transfer functions. This allows for a tool for the production of cross-covariance and covariance models that are convolutions of valid models. An example for modeling of the hole effect is illustrated.     

拟合推估两步极小解法

在回顾了最小二乘拟合推估的“综合极小”解法（正常拟合推估）后，分析了正常拟合推估存在的问题。考虑到随机场信号不一定完全表现为随机性，其中可能含有趋势性，顾而提出了拟合推估的“两步极小”解法，即将随机场分成趋势性部分和随机性部分，对趋势性部分采用函数拟合，对随机性部分采用协方差函数拟合。给出了“分两步极小”拟合推估的2种解法。计算表明，两步极小解法能部分地改善拟合推估的精度。     

用最小二乘配置获得地形变应变场动态图像的几个问题研究

针对应用于地壳形变应变推估拟合的最小二乘配置实现过程中的几个关键问题,利用模拟等距测边网及大面积水准监测网实测资料,获得了基本上符合高斯型函数特征的位移协方差图形,并给出了确定高斯型函数中参数的方法。在此基础上,将空间域的最小二乘配置内插推广应用于时间域来产生连续变化的动态图像。最小二乘配置具有可以评定精度的优点,已测点分布越密,精度越高。