Stochastic modelling of groundwater flow and solute transport in aquifers     

T.-C. Jim Yeh 《水文研究》1992,6(4):369-395

This paper presents an introductory overview of recently developed stochastic theories for tackling spatial variability problems in predicting groundwater flow and solute transport. Advantages and limitations of the theories are discussed. Lastly, strategies based on the stochastic approaches to predict solute transport in aquifers are recommended.  相似文献   

Axial convergence in a well-mixed estuary     

R.A. Nunes  J.H. Simpson 《Estuarine, Coastal and Shelf Science》1985,20(5):637-649

Transverse secondary circulations involving surface convergence, observed in a well-mixed estuary in North Wales, are made visible by the collection of surface material along an axial line which extends continuously for many kilometres through the estuary. The circulation and axial convergence, however, are seen only during the flood phase of the tide and no similar behaviour has been observed during the ebb phase.Convergent circulations in the estuary are associated with small but steady transverse density gradients in the cross-section, produced by non-uniform advection of the longitudinal gradient through the channel. A diagnostic model, using measured mean distributions of cross-sectional density, indicates surface transverse velocities (～0.1 ms^?1) similar to those observed in the estuary. The model further predicts appreciable transverse divergent currents at a fractional depth of 0.75: a prediction which has been tested in the estuary using a vertical array of accurately resolving current direction indicators.  相似文献   

Investigating the mechanisms leading to the deglaciation of past continental northern hemisphere ice sheets with the CLIMBER–GREMLINS coupled model     

Sylvie Charbit  Masa Kageyama  Didier Roche  Catherine Ritz  Gilles Ramstein 《Global and Planetary Change》2005,48(4):1887

A coupling procedure between a climate model of intermediate complexity (CLIMBER-2.3) and a 3-dimensional thermo-mechanical ice-sheet model (GREMLINS) has been elaborated. The resulting coupled model describes the evolution of atmosphere, ocean, biosphere, cryosphere and their mutual interactions. It is used to perform several simulations of the Last Deglaciation period to identify the physical mechanisms at the origin of the deglaciation process. Our baseline experiment, forced by insolation and atmospheric CO₂, produces almost complete deglaciation of past northern hemisphere continental ice sheets, although ice remains over the Cordilleran region at the end of the simulation and also in Alaska and Eastern Siberia. Results clearly demonstrate that, in this study, the melting of the North American ice sheet is critically dependent on the deglaciation of Fennoscandia through processes involving switches of the thermohaline circulation from a glacial mode to a modern one and associated warming of the northern hemisphere. A set of sensitivity experiments has been carried out to test the relative importance of both forcing factors and internal processes in the deglaciation mechanism. It appears that the deglaciation is primarily driven by insolation. However, the atmospheric CO₂ modulates the timing of the melting of the Fennoscandian ice sheet, and results relative to Laurentide illustrate the existence of threshold CO₂ values, that can be translated in terms of critical temperature, below which the deglaciation is impeded. Finally, we show that the beginning of the deglaciation process of the Laurentide ice sheet may be influenced by the time at which the shift of the thermohaline circulation from one mode to the other occurs.  相似文献   

On salinity regimes and the vertical structure of residual flows in narrow tidal estuaries     

D. Prandle 《Estuarine, Coastal and Shelf Science》1985,20(5):615-635

An examination is made of the circulation in narrow estuaries subject to a predominant tidal forcing. Velocity structures are derived separately for residual flow components associated with (a) river flow, (b) wind stress, (c) a well-mixed longitudinal density gradient and (d) a fully stratified saline wedge. Dimensionless parameters are introduced to indicate the magnitude of each component and these parameters are evaluated for 9 major estuaries, thereby revealing their sensitivity to each component.For a channel of constant breadth and depth, formulae are deduced for the length of saline intrusion, L. Comparisons with observed data show that such formulae may be used with confidence to predict changes in L arising from variations in river flow, tidal range or channel depths.The level of stratification is shown to be related to a product of two parameters, one associated with velocity structure and a second involving the square of the ‘flow ratio’ $\text{u}\text{u}\text{?}$ (i.e. residual velocity/amplitude of the tidal velocity). This relationship provides a simple classification system for estuarine stratification which can be used to indicate the sensitivity of any particular estuary to changing conditions.  相似文献   

Southern Meridional Atmospheric Circulation Associated with IOD     

LIU Na CHEN Hongxia 《中国海洋大学学报(英文版)》2006,5(2):99-105

Using the monthly wind and sea surface temperature （SST） data, southern meridional atmospheric circulation cells associated with the Indian Ocean Dipole Mode （IOD） events in the Indian Ocean are for the first time described and examineS. The divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells. During the four different phases of the positive IOD events, the anomalous meridional Hadley circulation over the western Indian Ocean shows that the air rises in the tropics, flows poleward in the upper troposphere, sinks in the subtropics, and returns back to the tropics in the lower troposphere. The anomalous Hadley circulation over the eastern Indian Ocean is opposite to that over the western Indian Ocean. During positive IOD events, the meridional Hadley circulation over the eastern Indian Ocean is weakened while it is strengthened over the western Indian Ocean. Correlation analysis between the IOD index and the indices of the Hadley cells also proves that, the atmospheric circulation patterns are evident in every IOD event over the period of record.  相似文献   

The Upper Pleistocene to Holocene sediments on the Mediterranean island of Lampedusa (Italy)     

C. Giraudi 《第四纪科学杂志》2004,19(6):537-545

The island of Lampedusa lies on the northern edge of the African continental shelf, but during some Quaternary marine lowstands it was joined to the African continent. The study and dating of the aeolian, alluvial, detrital sediments, calcareous crusts and speleothems have established that the climatic–environmental variations recorded on the island can be related chronologically to those known for northern Libya, Tunisia and the Italian peninsula. During the Last Glacial Maximum, phases of Saharan dust accumulation on Lampedusa occurred, and were coeval with dust accumulation in crater lakes and on high mountains in central‐southern Italy, and with phases of glacial advance in the Apennines and in the Alps. During the late Holocene, accumulation of Saharan dust on Lampedusa occurred but there was little accumulation of dust on the northern side of the Mediterranean Sea. With the new data from Lampedusa, it is possible to envisage two different scenarios of atmospheric circulation relating to the Last Glacial Maximum and to the late Holocene. During the Last Glacial Maximum, southerly atmospheric circulation brought rainfall to the southern slopes of the Alps and to the Apennines. During the late Holocene, a prevalent westerly atmospheric circulation became established in the northern Mediterranean. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

WEKU – a GIS-Supported stochastic model of groundwater residence times in upper aquifers for the supraregional groundwater management     

R. Kunkel  F. Wendland 《Environmental Geology》1997,30(1-2):1-9

 The supraregional GIS-supported stochastical model, WEKU, for the determination of groundwater residence times in the upper aquifers of large groundwater provinces is presented. Using a two-dimensional analytical model of groundwater flow, groundwater residence times are determined within two extreme cases. In the first case, maximal groundwater residence times are calculated, representing the part of groundwater, that is drained by the main surface water of a groundwater catchment area. In the second case, minimal groundwater residence times for drainage into the nearest surface water are determined. Using explicit distribution functions of the input parameters, mean values as well as potential ranges of variations of the groundwater residence times are derived. The WEKU model has been used for the determination of groundwater residence times throughout Germany. The model results – mean values and deviations of the groundwater velocity and the maximal and minimal groundwater residence times in the upper aquifers – are presented by general maps and discussed in detail. It is shown that the groundwater residence times in the upper aquifer vary regionally, differentiated between less than 1 year and more than 2000 years. Using this information, the time scales can be specified, until measures to remediate polluted groundwater resources may lead to a substantial groundwater quality improvement in the different groundwater provinces of Germany. With respect to its supraregional scale of application, the WEKU model may serve as a useful tool for the supraregional groundwater management on a state, federal or international level. Received: 15 August 1995 · Accepted: 15 October 1995  相似文献   

用层次分析法决策地下水库回灌方案的排序问题     

李云峰  王文科  李志刚  王希宁 《地球科学与环境学报》1992,(2)

本文引用了一种新的系统分析方法(层次分析法)对地下水库人工回灌的复杂系统进行了择优排序研究,取得了满意的结果。实践证明,层次分析法对于地下水库人工回灌方案的择优是一种简捷实用的决策方法。  相似文献   

Subtidal sea level and current variations in the northern reach of San Francisco Bay     

Roy A. Walters  Jeffrey W. Gartner 《Estuarine, Coastal and Shelf Science》1985,21(1):17-32

Analyses of sea level and current-meter data using digital filters and a variety of statistical methods show a variety of phenomena related to non-local coastal forcing and local tidal forcing in the northern reach of San Francisco Bay, a partially mixed estuary. Low-frequency variations in sea level are dominated by non-local variations in coastal sea level and also show a smaller influence from tidally induced fortnightly sea level variations. Low-frequency currents demonstrate a gravitational circulation which is modified by changes in tidal-current speed over the spring-neap tidal cycle. Transients in gravitational circulation induce internal oscillations with periods of two to four days.  相似文献   

Distinct climate change synchronous with Heinrich event one, recorded by stable oxygen and carbon isotopic compositions in stalagmites from China   总被引：2，自引：0，他引：2  

Houyun Zhou  Jianxin Zhao  Michael K. Gagan  Jun Yan 《Quaternary Research》2008,69(2):306-315

Uranium-series dating of oxygen and carbon isotope records for stalagmite SJ3 collected in Songjia Cave, central China, shows significant variation in past climate and environment during the period 20-10 ka. Stalagmite SJ3 is located more than 1000 km inland of the coastal Hulu Cave in East China and more than 700 km north of the Dongge Cave in Southwest China and, despite minor differences, displays a clear first-order similarity with the Hulu and Dongge records. The coldest climatic phase since the Last Glacial Maximum, which is associated with the Heinrich Event 1 in the North Atlantic region, was clearly recorded in SJ3 between 17.6 and 14.5 ka, in good agreement in timing, duration and extent with the records from Hulu and Dongge caves and the Greenland ice core. The results indicate that there have been synchronous and significant climatic changes across monsoonal China and strong teleconnections between the North Atlantic and East Asia regions during the period 20-10 ka. This is much different from the Holocene Optimum which shows a time shift of more than several thousands years from southeast coastal to inland China. It is likely that temperature change at northern high latitudes during glacial periods exerts stronger influence on the Asian summer monsoon relative to insolation and appears to be capable of perturbing large-scale atmospheric/oceanic circulation patterns in the Northern Hemisphere and thus monsoonal rainfall and paleovegetation in East Asia. Climatic signals in the North Atlantic region propagate rapidly to East Asia during glacial periods by influencing the winter land-sea temperature contrast in the East Asian monsoon region.  相似文献