全球变化与中国东北样带(NECT)

全球变化陆地样带是从机理上理解陆地生态系统对全球变化的响应 ,预测全球变化对陆地生态系统的可能影响 ,实现预警、调节和减小全球变化不良影响 ,科学地规划和管理陆地生态系统的有效研究平台。在介绍国际全球变化陆地样带提出的背景与选定标准、中国东北样带的位置与特征的基础上 ,较系统地总结了近年来中国东北样带的研究进展 :建立了用于模型发展和比较的不同时间和空间尺度的中国东北样带数据集 ,从机理上初步探讨了全球变化对于森林、草甸草原和典型草原的可能影响 ,发展了用于古植被气候重建的植物种与表土花粉类型的定量关系模型、多尺度耦合的羊草草原生态系统动态模型和基于林窗原理的森林生态系统动态模型 ,并对全球变化对中国东北样带的影响进行了初步评估 ,进而针对我国作为发展中国家 ,财力有限的特点 ,提出未来中国东北样带研究拟充分利用我国特殊的生态环境与区域特色 ,围绕“生态过程与生态安全及其对全球变化的响应与反馈”这一关键科学问题 ,做出一些在国际上既有显示度 ,又服务于我国社会经济可持续发展的研究成果。     

Evaluating Models Of The Neutral, Barotropic Planetary Boundary Layer Using Integral Measures: Part Ii. Modelling Observed Conditions

The steady-state, horizontally homogeneous, neutral, barotropiccase forms the foundation of our theoretical understanding of the planetary boundary layer (PBL).While simple analytical models and first-order closure models simulate atmospheric observationsof this case well, more sophisticated models, in general, do not. In this paperwe examine how well three higher-order closure models, E - - l, E - l, and LRR - l,which have been especially modified for PBL applications, perform in predicting the behaviour of thecross-isobaric angle ₀, the geostrophic drag coefficient C_g, and the integral of the dissipationrate over the boundary layer, as a function of the surface Rossby number Ro. For comparison we alsoexamine the performance of three first-order closure mixing-length models, two proposed byA. K. Blackadar and one by H. H. Lettau, and the performance of the standard model forsecond-order closure and a modification of it designed to reduce the overprediction of turbulence inthe upper part of the boundary layer.     

我国地球空间数据框架的设计思想与技术路线

根据当前我国基础地理信息系统的发展态势,较为详尽地讨论了１∶１万至１∶５万基础地理信息系统的设计思路,提出了地球空间数据框架（ＤＧＤＦ）的概念,即基于数字正射影像和ＤＥＭ及与若干层矢量框架数据（如大地控制、交通图、水系、境界、行政边界、注记等）的整体集成的栅格－矢量一体化空间数据库,目的在于尽快建立起有活力的和可更新的国家和省级基础地理信息系统。还详尽讨论了建立基础地理信息系统的主要技术路线和数据采集与数据处理的工艺流程。     

Estimation of dynamic ocean topography in the Gulf Stream area using the Hotine formula and altimetry data

Two modifications of the Hotine formula using the truncation theory and marine gravity disturbances with altimetry data are developed and used to compute a marine gravimetric geoid in the Gulf Stream area. The purpose of the geoid computation from marine gravity information is to derive the absolute dynamic ocean topography based on the best estimate of the mean surface height from recent altimetry missions such as Geosat, ERS-1, and Topex. This paper also tries to overcome difficulties of using Fast Fourier Transformation (FFT) techniques to the geoid computation when the Hotine kernel is modified according to the truncation theory. The derived absolute dynamic ocean topography is compared with that from global circulation models such as POCM4B and POP96. The RMS difference between altimetry-derived and global circulation model dynamic ocean topography is at the level of 25cm. The corresponding mean difference for POCM4B and POP96 is only a few centimeters. This study also shows that the POP96 model is in slightly better agreement with the results derived from the Hotine formula and altimetry data than POCM4B in the Gulf Stream area. In addition, Hotine formula with modification (II) gives the better agreement with the results from the two global circulation models than the other techniques discussed in this paper. Received: 10 October 1996 / Accepted: 16 January 1998     

A comparison of drainage networks derived from digital elevation models at two scales

Automated generation of drainage networks has become increasingly popular with powerful analytical functions in geographic information systems (GIS) and with the increased availability of digital elevation models (DEMs). This paper compares drainage networks derived from DEMs at two scales, 1:250 000 (250K) and 1:24 000 (24K), using various drainage parameters common in hydrology and geomorphology. The comparison of parameters derived from the 250K DEMs with those from the 24K DEMs in 20 basins ranging from 150 to 1000 km² in West Virginia shows that the goodness-of-fit between parameter estimates based on the DEMs varies. Results clearly show that superior estimations are produced from the 24K DEMs. Better estimates can be obtained from the 250K DEMs for stream length and frequency parameters than for gradient parameters. However, the estimation of the mean gradient parameters based on the 250K DEMs seems to improve with increasing terrain complexity. Finally, basin size does not strongly affect the accuracy of parameter estimates based on the 250K DEMs.     

Statistical estimation of corner frequency and its application to seismic event-identification

A statistical method is proposed for estimation of the corner frequency. It is based on inference for a stochastic model whose short-term behavior resembles the established source time functions. Properties of the estimates are investigated and some numerical examples are presented. A discussion concerning earthquake–explosion discrimination and the way corner frequency can be related to the rate of zero-crossings is also included. The paper is concluded with some numerical examples.     

Computer-simulation models of scoria cone degradation

Long-term erosional modifications of the relatively simple morphology of scoria (‘cinder') cones are ideally suited for study by field and computer-simulation methods. A series of temporally-distinct cones in the San Francisco and Springerville volcanic fields of Arizona provides the foundation for documenting the degradational evolution of scoria cones in a semi-arid climate. Progressive changes due to erosion are illustrated by the systematic decrease with increasing age of various morphometric parameters, including scoria cone height, cone height/width ratio (H_co/W_co), crater depth/width ratio, and slope angle. For example, Holocene–latest Pleistocene cones in the San Francisco field have a mean H_co/W_co value of 0.178±0.041, a mean maximum slope angle of 29.7±4.2°, and a mean average slope angle of 26.4±7.3°, whereas the group of Pliocene cones have values of 0.077±0.024, 20.5±5.8°, and 8.7±2.7°, respectively. Comparative morphology of scoria cones is a potentially useful dating tool for mapping volcanic fields.In order to better understand the degradational modifications of these volcanic landforms, we have developed a numerical approach to simulate the surficial processes responsible for the erosion of a typical scoria cone. The simulation algorithm can apply either a linear diffusion-equation model or a model with a nonlinear transport law. Using a finite-difference formulation, the simulation operates upon a three-dimensional scoria cone input as a matrix of elevation values. Utilizing both field and model results, the correlation between changing H_co/W_co value, cone age, and computer time step was expressed graphically to derive comprehensive values of the transport or diffusion coefficient (D_f) for both volcanic fields. For the San Francisco volcanic field, D_f had a calculated value of 21.4 m²/kyr for the linear model and 5.3 m/kyr for the nonlinear model, while for the Springerville volcanic field D_f had a calculated value of 24.4 m²/kyr for the linear model and 6.3 m/kyr for the nonlinear model.     

Formulation of discontinuous deformation analysis (DDA) — an implicit discrete element model for block systems

Continuum-based numerical methods have played a leading role in the numerical solution of problems in rock mechanics and engineering geology. However, for fractured rocks, a continuum assumption often leads to difficult parameters to define and over-simplified geometry to be realistic. In such case, discrete representations of fractures and individual blocks must be adopted. In this paper, a newly emerged member in the family of discrete element methods (DEM), the discontinuous deformation analysis (DDA), is presented, including its variational principle, governing equations, solution techniques and contact representation and detection algorithms. Its relative advantages and shortcomings are compared with the explicit distinct element method and the finite element method. An example of the analysis of tunnel stability is provided to demonstrate the capability of this new method.     

应用CARMA模型评价矿井疏水对泉流量的影响

受控自回归滑动平均模型是用来描述随机现象中输入与输出关系的一类线性动态模型。本文以大柳塔井田双沟泉域为例,应用该模型分别对双沟泉域在天然条件和矿井疏水条件下的泉流量进行预测,并据此评价矿井疏水对泉流量的影响。     

川东地区天然气勘探开发的三种模式

本文根据川东地区天然气勘探开发历史,系统归纳和总结了成组气田整体勘探开发、多高点滚动勘探开发和多产层立体勘探开发三种模式的勘探程序、勘探部署以及开发特点和原则。以供后续天然气勘探开发决策时参考。