共查询到20条相似文献，搜索用时 171 毫秒
1.
在岩石物理实验的基础上，综合运用水岩相互作用、表面物理、电化学等方面的理论，研究水型及矿化度变化对阿尔奇模型中的m、n值以及Waxman-Smits模型中B参数的影响及作用机理.结果表明，水型及矿化度的变化不仅对m、n、B值产生影响，由于在不同的浓度范围内，地层水矿化度对岩石颗粒表面偶电层厚度及平衡离子活动性的影响不同，还导致Archie公式中的m、n值以及Waxman-Smits模型中的B参数在不同矿化度范围内表现出不同的特征：低矿化度情况下，m、n、B值随着矿化度的降低而迅速减小；而当矿化度升高到一定程度以后，m、n、B值趋于稳定，此时的岩电参数是偶电层中扩散层消失后岩石电学特征的反映. 相似文献
2.
3.
针对长江中下游中尺度地形特点以及暴雨过程发生发展期间风垂直切变的主要观测特征,设计了一系列中尺度地形的三维理想数值试验,分析了干大气地形流和重力波特征,探讨了条件不稳定湿大气地形对流降水的模态分布,在此基础上研究了圆形、直线风垂直切变和切变厚度对中尺度地形对流降水强度和模态分布的影响.结果发现:在 Fr≈1的干大气条件下,气流遇到地形后分支、绕流和爬升现象同时存在,地形激发的重力波在水平和垂直方向上传播,其在迎风坡、背风坡、地形上游和下游的振幅不同,并组织出不同强度的垂直上升运动.在Fr > 1的条件不稳定湿大气下,地形对流降水主要存在三种模态,即迎风坡和背风坡准静止对流降水以及地形下游移动性对流降水,地形对流降水的形成与重力波在低层组织的上升运动密切相关.风垂直切变对地形对流降水的强度和模态分布有重要作用,其中圆形风垂直切变(风随高度旋转)不仅影响地形下游对流降水系统的移动方向,而且影响迎风坡和背风坡山脚处对流降水中心的分布和强度;直线风垂直切变(风随高度无旋转)主要影响地形对流降水的移动速度和强度.风随高度自下而上顺(逆)时针旋转,地形对流系统向下游传播时向右(左)偏移.风垂直切变主要通过影响地形重力波的结构和传播以及对流系统的形成、移动方向和速度,来影响地形对流降水的模态分布,其中对流层中低层的风垂直切变对地形对流降水强度和模态分布有重要影响. 相似文献
4.
利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟实验室研发的全球海洋－大气－陆面过程气候系统耦合模式（IAP/LASG GOALS 40）,对比分析了考虑和不考虑气候的外强迫因子（太阳活动、温室气体及硫酸盐气溶胶）变化对2003年夏季中国区域的短期气候预测的影响.结果发现,由于外强迫因子变化的影响,模式模拟的中国区域2003年夏季降水距平的分布比不考虑这种变化时更接近实况,它有效地改善了无外强迫变化时模式模拟预测的中国区域降水不真实偏大的缺点,使一些地区的模拟降水量值减小,范围扩大,位置北抬.更重要的是,由于考虑了外强迫的变化,GOALS耦合模式很好地模拟出了2003年夏季淮河流域较大的降水正距平区,同时相应的500 hPa环流场的模拟也有较大的改进. 相似文献
5.
青藏高原为亚洲季风区的典型代表区域,研究其水汽进入平流层的过程和机理对认识全球气候和大气环境变化具有一定的现实意义. 本文基于中尺度气象模式(WRF)的模拟输出结果(2006年8月20日至8月26)驱动拉格朗日大气输送模式FLEXPART,通过追踪并解析气块的三维轨迹以及温度、湿度等相关物理量的相关变化特征,初步分析了夏季青藏高原地区近地层-对流层-平流层的水汽输送特征. 研究结果表明,源于高原地区近地层的水汽在进入平流层的过程中受南亚高压影响下的大尺度环流和中小尺度对流的共同影响.首先,在对流抬升作用下,气块在短时间内(24 h)可抬升到9~12 km的高度,然后在南亚高压闭合环流影响下,相当部分气块在反气旋的东南侧穿越对流层顶进入平流层中,并继续向低纬热带平流层输送,进而参与全球对流层-平流层的水汽循环过程. 在对流抬升高度上气块位置位于高原的西北侧,然而气块拉格朗日温度最小值主要分布于高原南侧,两个位置上气块的平均位温差值可达15~35 K,这种显著的温度差异将导致气块进入平流层时"脱水". 比较而言,夏季青藏高原地区近地层水汽进入平流层的多寡主要和大尺度汽流的垂直输送有关,而深对流的作用相对较弱. 相似文献
6.
位涡因在绝热无摩擦大气中具有守恒性而被当作一个较好的示踪物广泛的应用．然而位涡本身,对于大尺度“慢流形”更为有效．因此,需要寻找另外的守恒的不变量来描述速度和气压场等快速变化的强天气过程,比如增长期和成熟的热带气旋．本文将湿大气中的焓和熵引入绝对运动方程来消除气压梯度项,并利用Weber变换和Ertel形式的连续方程,推导了湿大气中的斜压Ertel—Rossby不变量,并证明了其守恒性．推得的湿斜压Ertel-Rossby不变量的表达式除了包含传统的位涡项,它还包括气压梯度、位能和动能梯度项等能反映“快流形”特征的因子,以及干Ertel—Rossby不变量所没有的湿度因子,因此能更完善地描述湿过程中强天气现象快速变化的动力学特征．通过个例分析,与湿位涡和干大气中的Ertel-Rossby不变量相比,这个守恒的不变量对于台风这类真实湿大气中快速变化的强天气过程是一个较好的诊断分析工具,能表征几个共存台风组成的多台风系统的移动和强度变化．湿Ertel-Rossby不变量在真实湿大气中有较为广泛的应用前景． 相似文献
7.
过去50年中国西部气候和径流变化的区域差异 总被引：12，自引：0，他引：12
通过对过去50年中国西部降水和主要河流径流变化的对比分析, 研究降水和径流的区域变化差异, 结果表明, 黄河上游径流和降水与新疆北部和青藏高原南部雅鲁藏布江流域径流、降水呈显著的反相关关系. 中国西部降水变化大体上以青藏高原唐古拉山和天山为界, 表现出南北一致, 中部(西部的喀喇昆仑山除外)相反, 即从南到北呈现出干-湿-干或湿-干-湿的区域变化差异; 在河流径流上表现为北部伊犁河流域和南部雅鲁藏布江流域径流变化的一致性, 而与黄河上游径流变化呈反位相变化; 同时, 新疆和黄河径流的反位相变化表现在年代际上, 而黄河和雅鲁藏布江径流变化表现在年际变化上. 黄河上游径流的变化与西北太平洋季风指数的变化比较一致, 这表明黄河上游径流变化受到较强的东亚季风的影响; 新疆总径流分别与西北太平洋季风指数和西风指数存在显著的正负相关关系, 寻找不同地区径流变化异同对于认识和预测径流未来变化具有重要的指导意义. 相似文献
8.
9.
10.
2001年8月19日2011～2030UT，AE指数相对较小(40～130 nT)，Cluster 卫星穿越磁尾电流片.利用Cluster 观测资料分析，发现宁静期间有双峰电流片存在，这期间没有明显的高速流，没有明显的电流片振荡. 同时，进一步分析双峰电流片中的离子特性发现:质子数密度Np在中性线（<Bx> = 0）附近相对较大，呈非对称性分布；质子温度分布比较均匀；在中性线两侧，质子y方向上的流速Vy方向相反. 最后讨论LHDI（低混杂漂移不稳定性）的非线性演化可能是形成宁静期间双峰电流片的主要机制. 这些对进一步完善电流片形成机制可能有很重要的意义. 相似文献
11.
Masoud Rostami 《地球物理与天体物理流体动力学》2017,111(1):1-31
Analysis of the influence of condensation and related latent heat release upon developing barotropic and baroclinic instabilities of large-scale low Rossby-number shielded vortices on the f-plane is performed within the moist-convective rotating shallow water model, in its barotropic (one-layer) and baroclinic (two-layer) versions. Numerical simulations with a high-resolution well-balanced finite-volume code, using a relaxation parameterisation for condensation, are made. Evolution of the instability in four different environments, with humidity (i) behaving as passive scalar, (ii) subject to condensation beyond a saturation threshold, (iii) subject to condensation and evaporation, with three different parameterisations of the latter, are inter-compared. The simulations are initialised with unstable modes determined from the detailed linear stability analysis in the “dry” version of the model. In a configuration corresponding to low-level mid-latitude atmospheric vortices, it is shown that the known scenario of evolution of barotropically unstable vortices, consisting in formation of a pair of dipoles (dipolar breakdown) is substantially modified by condensation and related moist convection, especially in the presence of surface evaporation. No enhancement of the instability due to precipitation was detected in this case. Cyclone-anticyclone asymmetry with respect to sensitivity to the moist effects is evidenced. It is shown that inertia-gravity wave emission during the vortex evolution is enhanced by the moist effects. In the baroclinic configuration corresponding to idealised cut-off lows in the atmosphere, it is shown that the azimuthal structure of the leading unstable mode is sensitive to the details of stratification. Scenarios of evolution are completely different for different azimuthal structures, one leading to dipolar breaking, and another to tripole formation. The effects of moisture considerably enhance the perturbations in the lower layer, especially in the tripole formation scenario. 相似文献
12.
An efficient methodology for estimating irrigation return flow coefficients of irrigated crops at watershed and seasonal scale 总被引：1，自引：0，他引：1
Irrigation return flow coefficients, i.e. the ratio between the quantity of water returned from the cultivated area to the groundwater system and the amount of abstraction, vary by more than 50% for rice cultivation using standing water irrigation to 0% in the case of drip irrigation technique. This component of the groundwater budget plays an important role, particularly in intensively irrigated areas. Thus, to avoid any inaccurate aquifer budgeting, modelling and consequently any erroneous watershed management, this component needs to be accurately assessed for a particular time‐step (e.g. weekly, seasonally) onto the studied area. The present paper proposes a cost‐effective and useful methodology for assessing irrigation return flow coefficients (Cf = irrigation return flow/pumping flow) based on (i) basic crops field survey and meteorological data and (ii) the use of a simple hydraulic model that combines both water balance technique and unsaturated/saturated flow theory. An attempt to estimate the uncertainty of irrigation return flow coefficient estimates based on the uncertainty introduced by the pumping and the natural spatial variability of the soil characteristics is also proposed. Results have been compared to real field conditions and allow us to (i) estimate the uncertainty and (ii) validate and demonstrate the robustness of the applied methodology. The proposed methodology allows relatively good estimates of the irrigation return flow coefficients at watershed and seasonal scale. The irrigation return flow coefficients are calculated as: 51 ± 8% in rainy season (Kharif) and 48 ± 4% in summer (Rabi) for rice; 26 ± 11% in rainy season and 24 ± 4% in summer for vegetables; 13 ± 8% in rainy season and 11 ± 3% in summer for flowers. These results were found to be consistent with the existing literature. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
13.
The validity of a previously proposed but untested modification to equations for flow to a horizontal well is assessed using a specially developed finite-difference model. This modification extends confined flow equations to allow the head in the well and the saturated depth at the well to be estimated in unconfined conditions. The study is limited to the case of two-dimensional flow with no flow in the direction parallel to the line of the well. The results show that the modified equations for both a finite unconfined aquifer and, by inference, an infinite unconfined aquifer are adequately accurate for practical application. 相似文献
14.
Esteban G. Jobbágy Santiago Lorenzo Nicolás Buono Ricardo Páez Yésica Diaz Victoria Marchesini Marcelo D. Nosetto 《水文研究》2021,35(5):e14188
Our understanding of how groundwater mediates evapotranspiration/streamflow partitioning is still fragmented and catchment studies under changing vegetation conditions can provide a useful frame for integration. We explored this partition in a flat sedimentary dry catchment in central Argentina in which the replacement of native vegetation with rainfed crops was accompanied by the abrupt formation of groundwater-fed streams by subsurface erosion (i.e., sapping) episodes. Historical records indicated widespread water table rises (~0.3 m y−1 on average). Groundwater level and stream baseflow fluctuated seasonally with minima in the warm rainy season, indicating that evaporative discharge rather than rainfall shapes saturated flows. Diurnal groundwater level fluctuations showed that plant uptake was widespread where water tables are shallow (<3 m) but restricted to deep-rooted Prosopis forests where they are deep (7–10 m). MODIS and LANDSAT NDVI revealed a long-term greening for native vegetation, new wetlands included, but not for croplands, suggesting more limited evapotranspiration-groundwater level regulation under agriculture. Close to the deepest (20 m) and most active incisions, groundwater level and greenness declined and stream baseflow showed no seasonal fluctuations, hinting decoupling from evapotranspiration. Intense ecological and geomorphological transformations in this catchment exposed the interplay of five mechanisms governing evapotranspiration/streamflow partition including (a) unsaturated uptake and both (b) riparian and (c) distributed uptake from the saturated zone by plants, as well as (d) deepening incisions and (e) sediment deposits over riparian zones by streams. Acknowledging the complex interplay of these mechanisms with groundwater is crucial to predict and manage future hydrological changes in the dry plains of South America. 相似文献
15.
In a compound meandering channel, patterns of flow structures and bed variations change with increasing water depth owing to complex momentum exchange between high-velocity flow in a main channel and low-velocity flows in flood plains. We have developed a new quasi-three-dimensional model without the shallow water assumption, i.e., hydrostatic pressure distribution; our method is known as the general bottom velocity computation (BVC) method. In this method, a set of depth-integrated equations, including depth-integrated momentum and vorticity equations, are prepared for evaluating bottom velocity and vertical velocity distributions. The objective of this study is to develop a bed variation calculation method for both single and compound meandering channels by using the BVC method coupled with a sediment transport model. This paper shows that the BVC method can reproduce the pattern change of bed variation in a compound meandering channel flow with increasing relative depth. The variation in sediment transport rate due to overbank flow is explained by experimental and computational results. 相似文献
16.
Marius Todsen 《Journal of Hydrology》1973,20(4):311-326
The partial differential equation which governs the seepage of water in unsaturated and saturated porous media is solved numerically by a generalized Newton iteration technique for two models, one ditch drainage model and one earth dam model. For each model, which is two-dimensional, a few hypothetical soils with different moisture retention curves are considered. In both models only drainage from an initially saturated soil occurs; thus, the problem of hysteresis is avoided. The results of the computations are compared with those of corresponding saturated (pure groundwater) models; solutions obtained earlier by this author and others.
Computational instability phenomena appear when the slope of the retention curves is made steep, i.e., for poorly-graded soils. 相似文献
17.
层状饱水软土地基三维非轴对称动力响应分析方法 总被引：1，自引：0，他引：1
将饱水软土地基视为两相介质、考虑水的渗流和土骨架9变形的耦合作用，用Fourier展开和Hankel积分变换分析三维非称对称饱和弹性土层波动方程，用刚度矩阵方法，建立了层状饱和软土地基三维非轴对称动力响应的解析分析方法。以数值算例对比分析了单相土介质与两相饱和土介质三维非轴对称稳态动力响应，结果表明：在饱水软土地基动力响应分析中应该考虑土体中孔隙流体的影响。 相似文献
18.
Combination of CFCs and stable isotopes to characterize the mechanism of groundwater–surface water interactions in a headwater basin of the North China Plain 
下载免费PDF全文
下载免费PDF全文 Shiqin Wang Ruiqiang Yuan Changyuan Tang Xianfang Song Matthew Currell Zhenglun Yang Zhuping Sheng 《水文研究》2018,32(11):1571-1587
Mountainous areas are characterized by steep slopes and rocky landforms, with hydrological conditions varying rapidly from upstream to downstream, creating variable interactions between groundwater and surface water. In this study, mechanisms of groundwater–surface water interactions within a headwater catchment of the North China Plain were assessed along the stream length and during different seasons, using hydrochemical and stable isotope data, and groundwater residence times estimated using chlorofluorocarbons. These tracers indicate that the river is gaining, due to groundwater discharge in the headwater catchment both in the dry and rainy seasons. Residence time estimation of groundwater using chlorofluorocarbons data reveals that groundwater flow in the shallow sedimentary aquifer is dominated by the binary mixing of water approximating a piston flow model along 2 flow paths: old water, carried by a regional flow system along the direction of river flow, along with young water, which enters the river through local flow systems from hilly areas adjacent to the river valley (particularly during the rainy season). The larger mixing ratio of young water from lateral groundwater recharge and return flow of irrigation during the rainy season result in higher ion concentrations in groundwater than in the dry season. The binary mixing model showed that the ratio of young water versus total groundwater ranged from 0.88 to 0.22 and 1.0 to 0.74 in the upper and lower reaches, respectively. In the middle reach, meandering stream morphology allows some loss of river water back into the aquifer, leading to increasing estimates of the ratio of young water (from 0.22 to 1). This is also explained by declining groundwater levels near the river, due to groundwater extraction for agricultural irrigation. The switch from a greater predominance of regional flow in the dry season, to more localized groundwater flow paths in the wet season is an important groundwater–surface water interactions mechanism, with important catchment management implications. 相似文献
19.
定量解析污染源对水质影响的贡献是水环境精细化管理的重要基础。目前多通过水质和土地利用类型的关系以解析水体污染源的研究,忽略了空间尺度的差异性,引发景观配置不合理的后果。为此,本研究依据考虑空间尺度效应的污染源解析方法,基于异龙湖流域3条主要入湖河流的入湖口监测断面对雨季和旱季的水质数据进行研究。同时利用绝对主成分—多元线性回归模型(APCS-MLR)和bioenv分析揭示河道不同尺度缓冲区的土地利用变化对水质的影响并解析河流主要污染源。研究结果表明:(1)异龙湖主要入湖河流水质表现出季节性差异,旱季期间3条主要入湖河流的浊度、化学需氧量(CODCr)、氨氮(NH3-N)、总磷(TP)和总氮(TN)浓度平均值相比于雨季减幅分别为39.53%、39.93%、94.48%、38.29%和1.72%。其中,入湖河流水体中的TN在旱季和雨季的超标率分别为58%和74%,成为首要污染物;(2)在旱季,20 m缓冲区尺度内河流水质受耕地和裸地占比影响较大,随着空间尺度的扩大,至50～300 m缓冲区尺度时建设用地、林地及水体占比对水质的影响增加;在雨季,C... 相似文献
20.
The derivation of moist baroclinic Ertel-Rossby invariant in fast manifold and its application to typhoons 总被引：1，自引：0，他引：1
Potential vorticity(PV)has been widely applied as a tracer because of its property of conservation in frictionless,dry adiabatic flow.However,PV itself is more effective in describing the slow-manifold flow at large scale.Therefore,we wish to find a materially conserved invariant other than PV to diagnose severe weather such as growing and mature tropical cyclones,whose velocity and dynamic pressure vary rapidly and locally.Starting from the absolute motion equation after elimination of the pressure gradient term by introducing moist entropy and moist enthalpy,the baroclinic Ertel-Rossby invariant(ERI)in moist flow is derived by the Weber transformation.Furthermore,the material conservation property of moist ERI is proven.Besides the traditional moist potential vorticity(MPV)term,the invariant includes the moisture factor that is excluded in dry ERI and the term related to gradients of pressure,kinetic energy and potential energy that reflects the"fast-manifold"property.Therefore,it is more complete to describe the fast motions off the slow manifold for severe weather than is the MPV term.The moist ERI is then applied to diagnose a triple-typhoon system,and is compared with MPV and dry ERI.Contrastive analysis shows that moist ERI is a better tool to diagnose the movements and intensity variations of several coexisting typhoons.The moist ERI can signify the movement and development of a multi-typhoon system.It has wide application prospects for a real moist atmosphere. 相似文献