电离层预报模型研究

当利用无线电电磁波进行远程通信、卫星导航时,传递信号要受到电离层的影响,因此,对电离层中电子含量的研究显得特别重要.虽然国际上有几种电离层的电子含量预报模型,但其预报只能精确到电子含量的50%～60%.本文提出了一种新的电离层电子含量预报方法:即用球谐函数对IGS(国际GPS服务)所给出的离地面450 km高的球面上的每一网点的电离层电子含量进行拟合,对不同的时间所得到的拟合系数所形成的时间序列用时间序列分析理论中的ARMA(p,q)模型进行预报,从而实现全球的电离层电子含量预报.利用本方法对2004年和2005年IGS所给电离层电子含量资料在地理框架中做了分析预报,5天内电子含量预报相对精度在90%左右.     

NUMERICAL STUDY ON THE MIXING OF UNSORTED SEDIMENT PARTICLES DISCHARGED INTO A CROSS-FLOW BY MULTIPHASE PARTICLE-IN-CELL （MP-PIC） METHOD

The mixing characteristics of dredged sediments of variable size discharged into cross-flow are studied by an Eulerian-Lagrangian method. A three-dimensional (3D) numerical model has been developed by using the modified k-ε parameterization for the turbulence in fluid phase/water and a Lagrangian method for the solid phase/sediments. In the model the wake turbulence induced by sediments has been included as additional source and sink terms in the k-ε model; and the trajectories of the sediments are tracked by the Lagrangian method in which the sediment drift velocities in cross-flow are computed by a multiphase particle-in-cell (MP-PIC) method and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumped sediment cloud is governed by the total buoyancy on the cloud, the drag force on each particle and velocity of cross-flow. The cross-flow destroys more or less the double vortices occurred in stagnant ambience and dominates the longitudinal movement of sediment cloud. The computed results suggest satisfactory agreement by comparison with the experimental results of laboratory.     

Adjustments in river channel geometry associated with hydraulic discontinuities across the fluvial–tidal transition of a regulated river

Major hydraulic discontinuities along lowland rivers may be caused by water impoundment behind weirs, by tributary floods, and by tides. An analysis of the geometry of 122 surveyed channel cross-sections located on an 18 km reach of the lower River Dee identifies up to three levels in the bank profile representing minima in the width:mean depth ratio, and distinct changes in the geometric properties of the channel to these three levels in a downstrem direction and within four stretches influenced to varying degrees by hydraulic discontinuities created by a weir and by tidal overtopping of the weir. Simple modelling combined with field observations suggest possible processes that may control the observed changes in channel morphology. © 1997 John Wiley & Sons, Ltd.     

应力减小引起的岩石破坏与地震

最近完成的岩石力学三轴实验表明,岩石的破坏既能由最大主应力的增加引起,又能由中等主应力的变化(增加或减小)或最小主应力的减小引起,因此联系到地震的发生也是如此。地震前必须有一个应力和能量的增加过程,但地震不一定发生在应力和能量的增加过程中,地震也可以发生在应力和能量的减小过程中。文章还讨论了能够引起地壳中应力减小的作用,並从地震活动性方面探索应力减小引起地震的可能性。     

Characterisation of Tensile Damage in Rock Samples Induced by Different Stress Paths

Cracks, induced by different stress states, are studied systematically on thin slices of crinoidal limestone samples. Samples damaged by tension are compared to samples in which first damage is induced by compressive stresses, followed by tensile stresses. To quantify the effect of the compressive stresses, samples only damaged by compression are also studied. The tensile stresses cause the occurrence of an intergranular crack. When the sample is first damaged by compressive stresses, former induced damage influences the growth of this crack. It results in an intergranular crack with a zigzag profile. The average orientation of the intergranular crack is, however, the same as in the samples damaged by tension only.     

A new method of migration imaging for MT data

Introduction The migrationof electromagnetic field is like that of elastic wave in seismic prospecting, butthere are some differences between them (Lee et al, 1989). The elastic wave field satisfies thegeneral wave equation, while the electromagnetic field in our study satisfies the diffusion equation.Both the electromagnetic field and the elastic wave field have a similar mechanism. The imagingfunction named map can characterize the interface of different mediums (MA, 1989), that is …     

Debris from the basal ice of the Agassiz ice cap,Ellesmere Island,arctic Canada

This article describes the characteristics of debris obtained from the basal ice in a borehole in the Agassiz ice cap, Ellesmere Island, Northwest Territories by the Canadian Polar Continental Shelf Project in 1979. The debris appears to have been incorporated by basal freezing at a time when the base of the glacier upstream was near the pressure melting point and some 19°C warmer than at the present site. Such an occurrence may be explained by a different flow regime, by a thicker ice sheet, by the influence of irregular bedrock topography on basal ice conditions at some stage in the past, or by a combination of these factors.     

大地电磁资料偏移成像

在研究Zhdanov的二维电磁场偏移成像的基础上, 针对它在某些方面的不足, 研究并提出了改进算法. 首先, 用一维反演结果确定初始背景电阻率, 然后在延拓计算过程中, 利用迭代算法进行逐层修正、 延拓计算, 从而获得较准确的电阻率; 第二, 研究了有限差分方程的改进算法, 根据大地电磁场变化的特点, 设计了纵向以等比级数变网格的迭代算法. 通过以上两方面技术的改进, 经理论模型和实际资料试算验证, 取得了较好的结果.      

渗透率场敏感系数的数值计算

由渗流微分方程定解问题，利用格林互易定理从理论上导出了渗透率场敏感系数 的计算公式，并借助于数值积分和差分方法给出了渗透率场敏感系数的离散形式. 由Peacem an方程建立了井压渗透率场敏感系数与网格压力渗透率场敏感系数的关系. 对理论模型利用 三维不均匀非稳定渗流场的压强数值解计算了井压对渗透率场的敏感系数，并用敏感系数的 直接计算方法进行了验证，结果表明本文的计算方法与直接计算方法相吻合.     

The Use of Invertebrates in Ground Water Monitoring: A Rising Research Field

The use of invertebrates as biomonitors of ground water quality is a relatively new approach that has come of age with the development of ground water ecology. The benefits of such an approach are illustrated by four examples of field biomonitoring from several sites in various hydrogeological settings. Contamination of the interstitial zone by heavy metals in some sectors of the Rhóne River (France) was shown by the scarcity of insect species; sewage pollution in the saturated zone of a karstic aquifer was indicated by the low relative abundances of stygobites as compared with those of stygophiles and stygoxenes; and enrichment with organic matter of an underflow was clearly demonstrated by the extremely high density of ground water invertebrates such as oligochaetes, ostracods, and isopods. Examination of the spatial changes in the composition and abundance of invertebrate assemblages was also useful in determining the direction and intensity of water fluxes between a river and its underflow, as well as in delineating the reduced or oxidized zones in a manganese-polluted aquifer. Finally, the selected case studies emphasized the variety of methodological approaches that could be developed in ground water contamination biomonitoring, as well as the complementary and sometimes new information provided by this innovative method in comparison with that obtained by conventional pollution monitoring techniques.     

Evaluation of the ventilated chamber for measuring evaporation from a forest

Evaporation from a regenerating forest was determined concurrently by atmospheric measurements of the Bowen ratio, soil water depletion, and by weighing lysimeter. The methods agreed closely over 18 days in spring and 11 days in summer. Accordingly, the Bowen ratio technique was then used as the control against which any effect on evaporation by enclosure of the lysimeter with a chamber of varied ventilation rate could be quantified hourly and daily. Accuracy of gas analysis was checked against lysimeter values. Daily evaporation by the lysimeter was generally unaffected by enclosure—on a few afternoons there was a statistically significant enhancement of hourly values by the chamber. This was accounted for by difference in turbulence between chamber and forest. The general agreement in daytime hourly values is attributed to the frequent occurrence of equilibrium evaporation (rate at which evaporation is independent of ventilation). At night, evaporation was higher during enclosure. Comparisons were not possible with rain or dew. Determination of evaporation by gas analysis agreed within about 5 per cent of lysimeter values during a dry period. We conclude that the ventilated chamber as used provides realistic estimates of evaporation by forests. We show how periods of bias can be anticipated and corrected by theory.     

Study of the Difference between Seismogenic Deformation and Deformation by Permanent Tectonic Movement

Ground deformation may be caused by crustal movement and non-crustal movement.The non-crustal movements include those caused by temperature,rainfall,ground water,etc.Deformation caused by crustal movement includes seismogenic deformation(that appearing in the process of earthquake preparation and that directly caused by the earthquake)and general tectonic activities.The key point in the study of the relationship between ground deformation and earthquakes is how to eliminate information of deformation caused by non-crustal movement and permanent(or slow)tectonic deformation in observed data.In this paper an analysis is made on the short leveling data recorded at Dahuichang Deformation-Observing Station,Beijing,for 22 years(1970-1991)by using the LMS algorithm method after lateral adaptive filtering of the modern digital signal processing technique.Eliminating the approximate annual variation in deformation caused by non-crustal movement such as temperature,rainfall,ground water,etc.,a unified standard is     

上海地震台阵与台网的定位及视慢度研究

阐述了台阵的地震定位原理和视慢度在台阵与台网定位中的一些重要特性，并比较了相同位置上的上海地震台阵与台网对同一地震的定位结果。最后，对上海台队与台网导致定位误差的横向速度变化的位置和范围给出了矢量校正的结果并进行了初步讨论。     

Numerical study of seasonal circulation and variability over the inner shelf of the northern South China Sea

This study examines seasonal circulation, hydrography, and associated spatial variability over the inner shelf of the northern South China Sea (NSCS) using a nested-grid coastal ocean circulation model. The model external forcing consists of tides, atmospheric forcing, and open boundary conditions based on the global ocean circulation and hydrography reanalysis produced by the Hybrid Coordinate Ocean model. Five numerical experiments are conducted with different combinations of external forcing functions to examine main physical processes affecting the seasonal circulation in the study region. Model results demonstrate that the monthly mean circulation in the study region features the Guangdong Coastal Current (GCC) over coastal waters and the South China Sea Warm Current (SCSWC) in the offshore deep waters. The GCC produced by the model flows nearly southwestward in winter months and northwestward in summer months, which agrees with previous studies. The SCSWC flows roughly northeastward and is well defined in summer months. In winter months, by comparison, the SCSWC is superseded by the southwestward strong wind-driven currents. Analysis of model results in five different experiments demonstrates that the monthly mean circulation over coastal and inner shelf waters of the NSCS can be approximated by barotropic currents forced by the southwestward monsoon winds in winter months. In summer months, by comparison, the monthly mean circulation in the study region is affected significantly by baroclinic dynamics associated with freshwater runoff from the Pearl River and advection of warm and saline waters carried by the SCSWC over the NSCS.     

昆仑山口西8．1级地震前兆异常时空特征初探

通过对青藏高原北部地区前兆观测手段共88个台点的资料系统分析、整理、汇总,认为在昆仑山口西8．1级地震中短期内前兆异常具有明显的特征,并认为8．1级地震的发生不仅仅是大构造断裂带活动的产物,更是在某种特殊的力源作用下,大区域构造应力发生显变化,并在几条边界构造大断裂的相互作用下发生的1次强震活动。     

Synthesized Poisson and renewal model and its application in seismic hazard analysis

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裂缝诱导双相HTI介质地震波场错格伪谱法模拟与波场特征分析

裂缝诱导的双相具有水平对称轴的横向各向同性(HTI)介质模型是由一组平行排列的垂直裂缝嵌入到统计各向同性的流体饱和多孔隙岩石中而组成的,它综合考虑了裂缝型储层岩石的各向异性和孔隙性.高精度的地震波场数值模拟技术是研究该介质中地震波传播规律的主要方法.本文结合错格伪谱法和时间分裂法,求解描述该介质中地震波传播的一阶速度-应力方程.模拟了单层和双层模型中的地震波场,并对其进行了特征分析.研究结果表明:错格伪谱法能有效消除标准网格伪谱法波场模拟结果中出现的数值伪影现象,与时间分裂法结合能够获得稳定的、高精度的模拟结果;裂缝诱导双相HTI介质中的地震波场兼具裂缝各向异性介质和双相介质中传播的地震波的波场特征.     

应力减小引起地震

最近完成的岩石力学实验表明,在三轴应力状态下最大主应力的增加、中等主应力的变化(增加或减小)和最小主应力的减小都能导致岩石的破坏。由此启示,地震的发生既可能由地壳中的最大主应力的增加引起,又可能由中等主应力或最小主应力的减小引起。讨论了地壳中可能引起应力减小的作用,并从地震活动的规律性探讨了应力减小引起地震的可能性。指出在地震研究的各个领域中,不仅应考虑应力增加和能量积累过程中发生的地震,还应考虑在应力减小和能量减小过程中引起的地震。      

Reduced heat transfer in saltwater by a magnetic field: do oceans have a “geomagnetic brake”?

Seawater is the major heat transporter in our global environment, covering more than two-thirds of the surface of the earth. With an average salinity of ～3.5%, it is a moderate electric conductor, which is permanently in motion by thermal and hydrodynamic forces. A magnetic field exerts a Lorentz force on seawater that principally influences both the dissipation of turbulence and the flow properties by magnetic friction. Here we show by experiments on laboratory scale that convection in seawater is slowed down by an external static magnetic field and leads to a reduced heat flux resulting in an increased or decreased heat content in the volume in response to influx or drain of heat, respectively. Experimentally, the application of a vertical magnetic field of 60 mT reduces the convective heat transport on the liquid-air surface within in 5 min by about 8% perpendicular to the field and up to 14% parallel to it. The effect is strongly correlated with the magnetic interaction parameter of the system, which relates the magnetic to the viscous volume force. In the natural environment, the geomagnetic field is omnipresent. It is weaker by about three orders of magnitude compared with the magnetic field applied in the experiments. It has, however, an undisturbed and long-lasting impact on the convection, at low Reynolds numbers, in the large body of water in the deeper ocean below the mixed layer. There are no investigations regarding a possible contribution of this effect to natural saltwater flows, neither by proxy experiments nor by model calculations. The data presented raise the possibility that convective heat transport in the sea could be always slowed down by the geomagnetic field to a certain extent, besides it could be modulated by the geomagnetic secular variation on relatively short timescales like decades.     

Internal elemental cycles affecting the long-term alkalinity status of lakes: implications for lake restoration

Although the major processes affecting the acid-base balance of a lake are directly linked to reactions involving nitrogen and sulphur they are also influenced by the carbon cycle which is regulated by the supply of phosphorus. Changes in the long-term alkalinity of a lake are brought about by redox reactions in solution and through interactions with the atmosphere and sediments. Adding organic material or nutrients may help to restore acidified lakes, by generating base and by the increased carbon turnover creating a self-regulating ecosystem which is resistant to change.