bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon isotopic disequilibrium in polar planktonic foraminifera and its impact on modern and Last Glacial Maximum reconstructions
Authors: Kohfeld K. E. , Anderson R. F. , Lynch‐Stieglitz J.
Published: September 2002

Calibration studies of Neogloboquadrina pachyderma (sinistral coiling, hereinafter referred to as N. pachyderma (s.)) in the South Atlantic raise questions about the interpretation of this species' carbon isotope composition as a paleoceanographic tracer of Southern Ocean surface nutrient contents. Carbon isotope disequilibrium between δ13C of total CO2 (TCO2) of seawater and δ13C of N. pachyderma (s.) increases systematically between 70° and 40°S. Several effects could cause the observed carbon isotope disequilibrium, including a combination of foraminiferal diet, calcification temperature, and carbonate ion chemistry. Combining these corrections to the δ13C of N. pachyderma (s.) improves the reconstruction of the δ13C of seawater TCO2 between 0 and 200 m in the modern South Atlantic. With these corrections applied, the δ13C for equilibrium calcite reconstructed from N. pachyderma (s.) at the Last Glacial Maximum is very similar to preindustrial values, suggesting that one cannot rule out the possibility that surface nutrient concentrations in the South Atlantic Ocean were comparable to today. However, the magnitude of the uncertainties associated with these corrections make it difficult to assess absolute paleonutrient concentrations with much confidence.
Abundances and charge states of particles in the solar wind
Authors: Bochsler Peter
Published: September 2002

The Sun is the only star from which matter can be collected in order to investigate its elemental and isotopic composition. Solar elemental abundances provide the most important benchmark for the chemical evolution of the galaxy. They can be derived from photospheric observations, from in situ investigations of the solar wind, and from solar energetic particles. Solar isotopic abundances provide an important reference for the galactic evolution and if available with sufficient precision, also for the chemical and physical evolution of the solar system. The abundances of isotopes in the solar atmosphere can only be inferred from in situ observations of solar particles. This review makes an attempt to summarize current knowledge about the composition of the solar wind and shows how the elemental, isotopic, and charge state composition of solar wind particles is shaped as the solar corona expands throughout the heliosphere.
The lunar atmosphere: History, status, current problems, and context
Authors: Stern S. Alan
Published: September 2002

After decades of speculation and fruitless searches by observers, the lunar atmosphere was first observed by Apollo surface and orbital instruments beginning in 1971. With the end of Apollo missions in 1972 and the termination of funding for Apollo lunar ground station observations in 1977 the field withered for many years, but it has recently enjoyed a renaissance. This renewal was initiated by the discovery of lunar atmospheric sodium and potassium by ground‐based observers and was furthered by the in situ detection of metal ions derived from the Moon in interplanetary space, the possible discoveries of H2O ice at the poles of the Moon and Mercury, and the detection of tenuous atmospheres around other remote sites in the solar system, including Mercury and several Galilean satellites. In this review I attempt to summarize the present state of knowledge about the lunar atmosphere, describe the important physical processes taking place within it, and compare the lunar atmosphere with other tenuous atmospheres in the solar system.
Using wire grid structures in the combination of uniform geometric theory of diffraction and method of moments for near‐field analysis
Authors: Harms Harm‐Friedrich
Published: September 2002

The combination of the uniform geometric theory of diffraction and the method of moments is a useful tool for analyzing electromagnetic fields. Many problems in analysis cannot be examined either by the uniform geometric theory of diffraction or by the method of moments. In combining both it is possible to solve a lot of these problems. In this paper, special attention is given to the use of this combination for near‐field analysis.
Equivalent boundary conditions for a perfectly conducting periodic surface with a cover layer
Authors: Holloway Christopher L. , Kuester Edward F.
Published: September 2002

Using the method of homogenization, effective electromagnetic properties for a two‐dimensional, perfectly conducting, periodic rough surface with a thin periodic cover layer are derived. This allows for the development of an equivalent boundary condition for the “effective” fields at such a surface. It is shown that the coefficients in this equivalent boundary condition can be interpreted as electric and magnetic polarizability densities. We apply this boundary condition to calculate the reflection coefficient of H‐ and E ‐polarized plane waves incident at a rough, perfectly conducting surface. The reflection coefficients derived here are compared with previous results from the literature for surfaces with no cover layer, demonstrating the accuracy of the new equivalent boundary condition. We also obtain previously known equivalent boundary conditions for a flat perfectly conducting plane with a thin cover layer as a special case of our result. This work is a first step in the derivation of generalized impedance‐type boundary conditions for conducting rough interfaces (to be published separately).
Matched filtering for the measurement of conjugately ducted VLF transmissions
Authors: Starks M. J. , Lee M. C.
Published: September 2002

The application of matched filtering to the problem of very low frequency (VLF) radio signals ducted between magnetically conjugate points on the Earth by ionospheric plasma structures has been examined theoretically and implemented in recent field experiments. With accurate knowledge of the source VLF transmission the subionospheric component of the received waveform can be effectively removed, and the characteristics of the remaining ducted signal can be accurately estimated. Although the technique has been shown not to produce strictly consistent estimates of the subionospheric and ducted signal amplitudes, it is able to efficiently recover the transit delays and amplitudes of ducted man‐made whistler mode emissions for reasonable values of the relevant signal‐to‐noise ratios. This is substantiated by the use of matched filtering to analyze data collected by radio receivers placed at the conjugate ends of a magnetic field line, thereby recovering the amplitudes and transit delays of ducted signals with time resolution as small as 30 s. An arbitrary degree of accuracy can be obtained in these measurements through the use of bit stream extraction and comparison. Further correlation analysis can be performed to extract Doppler shifts due to drifting ducts, and the small time resolution makes possible studies of ducting under rapidly changing conditions.
Dense media radiative transfer theory based on quasicrystalline approximation with applications to passive microwave remote sensing of snow
Authors: Tsang Leung , Chen Chi‐Te , Chang Alfred T. C. , Guo Jianjun , Ding Kung‐Hau
Published: September 2002

Dense media radiative transfer (DMRT) equations based on quasicrystalline approximation (QCA) for densely distributed moderate size particles are developed. We first compute the effective propagation constant and coherent transmission into a dense medium on the basis of the generalized Lorentz‐Lorenz law and the generalized Ewald‐Oseen extinction theorem. The absorption coefficient of the dense media is then calculated. The distorted Born approximation is next applied to a thin layer to determine the bistatic scattering coefficients and the scattering coefficient. The phase matrix in DMRT is then obtained as bistatic scattering coefficient per unit volume. The model is applied to multiple sizes and for sticky particles. Numerical results are illustrated for extinction and brightness temperatures in passive remote sensing using typical parameters in snow terrain. The QCA‐based DMRT is also used to compare with satellite Special Sensor Microwave Imager (SSM/I) brightness temperatures for four channels at 19 and 37 GHz with vertical and horizontal polarizations and for two snow seasons. It shows reasonable agreement to snow depth of 1 m.
An optimization approach to two‐dimensional time domain electromagnetic inverse problems
Authors: Gustafsson Mats , He Sailing
Published: September 2002

An optimization approach to a two‐dimensional electromagnetic inverse problem in the time domain is considered. Wave‐splitting is integrated in the optimization algorithm. The permittivity, permeability, and conductivity are reconstructed by minimizing an objective functional. To speed up the computation time, an explicit expression for the gradient of the objective functional is derived by introducing dual functions and using the Gauss surface divergence theorem. The parameters are then reconstructed by an iterative conjugate gradient algorithm. Numerical results for a simultaneous reconstruction of the permittivity, permeability, and conductivity are presented.
Calibration of zenith hydrostatic delay model for local GPS applications
Authors: Liu Y. , Iz H. Baki , Chen Y.
Published: September 2002

Determination of dry zenith delay, DZD, is important for separating wet zenith delay with high accuracy from Global Positioning System (GPS) measurements. The existing models are usually for the calculation of the zenith hydrostatic delay, ZHD. Because the zenith hydrostatic delay includes the contribution of water vapor and is also not accurate enough, the DZD, approximately replaced by ZHD, will induce ∼2 cm error into local GPS applications. In this study we calibrate a popular ZHD model, namely, the Saastamoinen model for local GPS meteorology, using radiosonde data. We test the calibrated model by comparing the predicted delays from the calibrated model against the observed delays from radiosonde data that are not included in the calibration solution. The calibrated model shows 20 mm improvement over the uncalibrated model predictions over the same period. A comparison of the DZDs calculated from GPS measurements over a month period with calibrated and uncalibrated ZHD model predictions shows 15 mm average improvement.
Asymptotic high‐frequency Green's function for a planar phased sectoral array of dipoles
Authors: Capolino F. , Maci S. , Felsen L. B.
Published: September 2002

This paper deals with the derivation and physical interpretation of a uniform high‐frequency Green's function for a planar right‐angle sectoral phased array of dipoles. This high‐frequency Green's function represents the basic constituent for the full‐wave description of electromagnetic radiation from rectangular periodic arrays and scattering from rectangular periodic structures. The field obtained by direct summation over the contributions from the individual radiators is restructured into a double spectral integral whose high‐frequency asymptotic reduction yields a series of propagating and evanescent Floquet waves (FWs) together with corresponding FW‐modulated diffracted fields, which arise from FW scattering at the array edges and vertex. Emphasis is given to the analysis and physical interpretation of the vertex diffracted rays. The locally uniform asymptotics governing this phenomenology is physically appealing, numerically accurate, and efficient, owing to the rapid convergence of both the FW series and the series of corresponding FW‐modulated diffracted fields away from the array plane. A sample calculation is included to demonstrate the accuracy of the asymptotic algorithm.
Partition between collision and subduction accretionary prisms along an inherited transcurrent fault zone: New insights on the Taiwan fold and thrust belt
Authors: Brusset Stéphane , Souquet Pierre , Déramond Joachim , Sibuet Jean‐Claude , Hsu Shu‐Kun , Deffontaines Benoît , Chu Hao‐Tsu
Published: September 2002

A new geotectonic framework of the Taiwan orogen is presented in accordance with the hypothesis of an oblique arc‐arc collision. The colliding Luzon arc is physically connected to the eastern Coastal Range in which a subduction complex remnant is preserved and backthrust with intra‐arc sediments in a small retroforeland basin. A southern and extinct extension of the Ryukyu arc is characterized in western Taiwan. It displays a duplex structure (Tananao and Backbone horses and Lishan triangle zone) between a buried floor thrust located in the arc crust and a roof thrust developed in the arc cover (Hsüehshan Range and South Backbone Range). Westward the basal thrust climbs in the sedimentary series of the western proforeland (Foothills and Hengchun Peninsula) and dies out hi a buried tip line. The northern part of the orogen, including all the Tananao arc core, is shown as an intra‐oceanic‐continental arc‐arc collision belt characterized by an unroofed duplex culmination above a leading floor thrust and both proforeland and retroforeland basins. The southern part, which displays a roof thrust sequence above a buried duplex, is shown as an accretionary prism built in a transition zone between continent and oceanic subduction (transition from the Asian continental crust, including the former Ryukyu arc, to the oceanic Old Philippine Sea crust). The partition is believed to be induced by a deep intracontinental transcurrent fault zone able to influence the difference in shortening, duplex pattern, and leading thrust depth. The evolution was controlled by the Ryukyu subduction (backarc extension, arc magmatism extinction, and cooling and intra‐arc collapse) until the early middle Miocene (around 15 Ma) and then it was controlled by the Luzon arc progression (continental subduction, collision, indentation, and hinterland uplift and frontal thrust propagation).
Evolution of the Kap Cannon Thrust Zone (north Greenland)
Authors: von Gosen W. , Piepjohn K.
Published: September 2002

In North Greenland, early Paleozoic metamorphic successions of the north Greenland fold belt are carried along the Kap Cannon Thrust Zone northward over the Late Cretaceous Kap Washington Group and Permo‐Carboniferous strata. Ellesmerian deformations and metamorphism occurred prior to ductile deformation in the Kap Cannon mylonites, which developed from shear zones in the hanging wall metamorphics. Heterogeneous shearing affects the Ellesmerian structures, with shear sense indicators suggesting top‐to‐north displacements in the mylonites. Late Cretaceous mafic dikes and sills record intense ductile deformation in the mylonites and incipient shearing within distinct zones of the hanging wall metamorphics. In the footwall of the mylonite zone, approximately NW directed thrusting with the formation of imbricates in Permo‐Carboniferous strata on Lockwood Ø is related to an oblique ramping beneath and in front of the Kap Cannon Thrust Zone. Since the Kap Washington volcanics are mostly affected by brittle deformation, the onset of thrusting occurred in a deeper crustal level. Condensed ductile deformation within the mylonites, shear zones, and an additional oblique to lateral ramp suggest that shear/strain heating contributed to a local rise in temperature. Continuing displacement led to uplift of the thrust zone bounded block of metamorphic rocks with a final emplacement over the northern volcanics under brittle conditions. According to the age of the magmatic rocks in the footwall, the evolution of the Kap Cannon Thrust Zone probably took place during early Tertiary (Eurekan) times. The regional implications are briefly discussed.
Green and Ampt infiltration into soils of variable pore size with depth
Authors: Selker John S. , Duan Jinfan , Parlange Jean‐Yves
Published: September 2002

Most expressions for infiltration rely upon the assumption of vertical uniformity in soil texture and hydraulic properties. We present an extension of the results of Beven [1982, 1984] for infiltration and lateral flow in soils with decreasing permeability with depth. Unlike Beven, we base the derivations upon joint changes in soil properties based on an overall change in characteristic pore size via Miller scaling. A set of very simple expressions for the time rate of infiltration are obtained using a Green and Ampt approach for soils with permeability that decreases with depth following linear, power law, and exponential relationships.
Derived functions of time domain reflectometry for soil moisture measurement
Authors: Yu C. , Warrick A. W. , Conklin M. H.
Published: September 2002

This paper gives a systematic framework for evaluating the time domain reflectometry (TDR) response of soil. TDR measures the soil composite dielectric constant (Ka); thus any factor that has an influence on Ka measurement can affect soil moisture determination. On the basis of known dielectric constants of air, soil, water, and ice, as well as the volumetric fraction of each phase in a bulk soil, functional relationships between volumetric water content (θυ, cm3/cm−3) and Ka are derived in the form of θv=aKa0.5+b. In general, the TDR functions derived from this study are in good agreement with the “universal equation” developed through experiments by Topp et al. [1980] and other available TDR calibration data. This paper demonstrates that (1) soil solid and porosity have little effect on dielectric constant measurement; (2) temperature has a minor influence except for very wet soils; and (3) surface area is an important factor affecting the water content measurement.
A Procedure for classifying textural facies in gravel‐bed rivers
Authors: Buffington John M. , Montgomery David R.
Published: September 2002

Textural patches (i.e., grain‐size facies) are commonly observed in gravel‐bed channels and are of significance for both physical and biological processes at subreach scales. We present a general framework for classifying textural patches that allows modification for particular study goals, while maintaining a basic degree of standardization. Textures are classified using a two‐tier system of ternary diagrams that identifies the relative abundance of major size classes and subcategories of the dominant size. An iterative procedure of visual identification and quantitative grain‐size measurement is used. A field test of our classification indicates that it affords reasonable statistical discrimination of median grain size and variance of bed‐surface textures. We also explore the compromise between classification simplicity and accuracy. We find that statistically meaningful textural discrimination requires use of both tiers of our classification. Furthermore, we find that simplified variants of the two‐tier scheme are less accurate but may be more practical for field studies which do not require a high level of textural discrimination or detailed description of grain‐size distributions. Facies maps provide a natural template for stratifying other physical and biological measurements and produce a retrievable and versatile database that can be used as a component of channel monitoring efforts.
Water distribution network optimization using a modified genetic algorithm
Authors: Montesinos Pilar , Garcia‐Guzman Adela , Ayuso Jose Luis
Published: September 2002

A modified genetic algorithm (GA) is proposed for water distribution network optimization. Several changes are introduced in the selection and mutation processes of a simple GA. In each generation a constant number of solutions is eliminated, the selected ones are ranked for crossover, and the new solutions are allowed to undergo at most one mutation. All these modifications greatly increase the algorithm convergence. The modified GA is tested on the New York City water supply expansion problem. It obtains the lowest‐cost feasible solution reported in the literature in far fewer generations than any previous GA.
Analysis of flood damages from the 1993 and 1995 Meuse Floods
Authors: Wind H. G. , Nierop T. M. , de Blois C. J. , de Kok J. L.
Published: September 2002

This paper addresses uncertainties pertaining to damage assessments made for the floodings of the Meuse River in 1993 and 1995. The analysis is based on flood damage data that were collected by damage experts and consist of large sample sizes within each municipality. The most interesting aspect of these two floods is that although the volume of flooding and the inundated area were comparable in order of magnitude, the flood damage estimates in 1995 were 35% lower than in 1993. We conclude that part of the reduction in flood damage during the 1995 flood was due to a reduction in the damage to household goods. This may be explained by a marginal increase in flood warning time and experiences gained from the flood of 1993. As flood damage assessments are the cornerstone in the evaluation of flood damage mitigation schemes, empirical data of previous floods should be used to improve the foundations of the methods to assess flood damages.
Reactive solute transport in flow between a recharging and a pumping well in a heterogeneous aquifer
Authors: Dagan Gedeon , Indelman Peter
Published: September 2002

Steady flow between a fully penetrating recharging and pumping well (doublet) takes place in a heterogeneous aquifer. The spatially variable hydraulic conductivity is modeled as a lognormal stationary random function, of anisotropic two‐point covariance. The latter is characterized by the horizontal and vertical integral scales I and Iυ respectively. A tracer, or a reactive solute obeying first‐order kinetics, is injected as a pulse or continuously in the recharging well. Our aim is to determine the flux‐averaged concentration (the breakthrough curve) in the pumping well as a function of time and of the various parameters of the problem, i.e., σY2 (the logconductivity variance), l′ = l/I (l is the distance between wells), and e = Iυ/I (the anisotropy ratio). A simple solution of this difficult problem is achieved by adopting a few simplifying assumptions: (1) the wells are fully penetrating, of length much larger than Iυ and of radius rw much smaller than I, (2) a first‐order solution in σY2 of the flow and transport equations is sought, (3) the anisotropy ratio is small, say e < 0.2, and (4) neglect of the effect of pore‐scale dispersion. After determining the travel time τ mean and variance, the mean flux‐averaged concentration is found by assuming that τ is lognormal. In a homogeneous medium there is a large spreading of the solute signal in the pumping well owing to the variation of the travel time among the streamlines connecting the two wells. The effect of heterogeneity is similar to that of pore‐scale dispersion; that is, it leads to enhanced spreading and in particular to an early breakthrough. The solution has potential applications to aquifer tests and to evaluation of efficiency of remediation schemes and may serve as a benchmark for numerical models.
Combining binary decision tree and geostatistical methods to estimate snow distribution in a mountain watershed
Authors: Balk Benjamin , Elder Kelly
Published: September 2002

We model the spatial distribution of snow across a mountain basin using an approach that combines binary decision tree and geostatistical techniques. In April 1997 and 1998, intensive snow surveys were conducted in the 6.9‐km2 Loch Vale watershed (LVWS), Rocky Mountain National Park, Colorado. Binary decision trees were used to model the large‐scale variations in snow depth, while the small‐scale variations were modeled through kriging interpolation methods. Binary decision trees related depth to the physically based independent variables of net solar radiation, elevation, slope, and vegetation cover type. These decision tree models explained 54–65% of the observed variance in the depth measurements. The tree‐based modeled depths were then subtracted from the measured depths, and the resulting residuals were spatially distributed across LVWS through kriging techniques. The kriged estimates of the residuals were added to the tree‐based modeled depths to produce a combined depth model. The combined depth estimates explained 60–85% of the variance in the measured depths. Snow densities were mapped across LVWS using regression analysis. Snow‐covered area was determined from high‐resolution aerial photographs. Combining the modeled depths and densities with a snow cover map produced estimates of the spatial distribution of snow water equivalence (SWE). This modeling approach offers improvement over previous methods of estimating SWE distribution in mountain basins.
Prediction of watershed runoff using Bayesian concepts and modular neural networks
Authors: Zhang Bin , Govindaraju Rao S.
Published: September 2002

Artificial neural networks have been widely used as models for a variety of nonlinear hydrologic processes including that of predicting runoff over a watershed. In this paper such networks were organized in a modular architecture to handle complex sets of rainfall‐runoff data. Such data often contain examples corresponding to different rules that may be associated with high, low, and medium streamflows. Different modules within the network were trained to learn subsets of the input space in an expert fashion. A gating network was used to mediate the response of all the experts. The problem was posed as one of Bayesian statistics combined with maximum likelihood estimation of network parameters. The training of the gating network was equivalent to the classification problem (i.e., identification of the expert), while the experts trained to minimize the absolute difference between predicted and target monthly discharges. The performance of modular networks in predicting runoff over three medium‐sized watersheds was examined. Average monthly rainfall of current and previous months and average monthly temperatures were treated as network inputs, and monthly runoff was treated as output. Three different modular network architectures were examined in this paper: two based on hard classification and one based on soft classification. In addition, a fully connected feed forward network was utilized for comparison purposes. On the basis of the results, modular networks appear to be good alternatives for predicting runoff. The role of these networks on issues regarding probabilistic interpretability and classification are discussed.
Five centuries of interannual sediment yield and rainfall‐induced erosion in the Canadian High Arctic recorded in lacustrine varves
Authors: Lamoureux Scott
Published: September 2002

A 487‐year sediment yield record based on the varves from Nicolay Lake, Nunavut, Canada, is used to investigate long‐term yield variability. A general extreme value model, estimated with probability‐weighted moments, was used to identify the magnitude and timing of the low‐probability events. Exceptional sediment yields in 1951 and 1962 coincided with the two largest rainfalls on record. Smaller multiday rainfalls were also recorded in the varves as subannual rhythmites, although rhythmites were not generated by rainfall events that occurred during the nival flood or after prolonged warm weather. By accounting for probable soil moisture conditions and the timing of nival floods compared to major rainfall, rhythmites in all but 3 years of the sediment record can be explained by storms exceeding ∼13 mm total. Generally, more frequent extremes and increased variance in yield occurred during the 17th and 19th centuries, likely due to increased occurrences of cool, wet synoptic types during the coldest periods of the Little Ice Age.
Sediment deposition and transport patterns following a reservoir sediment release
Authors: Wohl Ellen E. , Cenderelli Daniel A.
Published: September 2002

A reservoir sediment release on the North Fork Poudre River supplied ∼7000 m3 of silt‐ to pebble‐sized sediment to an originally boulder bed channel. Deposition along the 12 km of channel downstream from the reservoir occurred primarily in pools. During the subsequent snowmelt hydrograph, sediment was progressively scoured from the upstream and then the downstream pools. Initial sediment reworking in the pools created a deep, narrow thalweg scoured to the original pool bed, with additional sediment deposition in lateral eddies. Continued reworking reduced but did not completely remove these eddy deposits. The channel became supply‐limited with respect to finer grain‐sized fractions (clay to medium sand) first at upstream and then at downstream sites and eventually became supply‐limited with respect to coarser grain‐sized fractions (coarse sand to pebbles). Bedload transport rates at a site were strongly linked to the depletion of sediment stored in upstream pools. Magnitude, duration, and sequence of flows were all important controls on bedload transport and return of the channel to its prerelease state.
Characteristic rate scale and timescale of supply‐limited transpiration under a Richards‐Cowan Framework
Authors: Levine John B. , Salvucci Guido D.
Published: September 2002

A combined Richards‐Cowan model of transpiration and soil moisture flux is used to analyze the relationship between stage‐one (atmosphere limited) and stage‐two (stressed) transpiration during a series of simulated dry downs. The duration of stage‐one transpiration is found to be controlled by the storage capacity of the root zone, the potential transpiration rate, and the soil desorptivity and drainage properties, which in turn influence the net of upward and downward moisture fluxes through the bottom of the root zone. During stage‐two transpiration the root zone lower boundary behaves like a dry surface, and the transpiration rate is supply‐limited by the upward flux to this boundary. These findings are combined with a similarity solution for the upward flux rate (including the influence of gravity) in order to derive an analytic approximation for the time to onset of stage‐two transpiration. This estimated time to stressts, along with a rate scale defined by the time average flux in the root zone prior to stress, can be used to nondimensionalize the relation between stage‐two transpiration and time in similar fashion to the bare soil evaporation analysis ofSalvucci[1997]. The resulting expressions allow prediction, under simplified event‐based initial and boundary conditions, of the second stage of transpiration from soil desorptivity and drainage properties.
Comparison of models for transient storage of solutes in small streams
Authors: Wörman Anders
Published: September 2002

Biogeochemical mechanisms in rivers and streams give rise to a transient storage of solute substances in hyporheic zones and hence retard the solute transport. Analytical solutions to the temporal moments of the residence times are used as the basis to compare three different transient storage models with respect to deviation in higher‐order moments, model bias, and relationships between the parameters of the different models. The transient storage was formulated using either first‐order mass transfer equations or a one‐dimensional diffusion process in which the storage capacity of the storage zone is limited by an impermeable surface or groundwater seepage into the stream. In all three cases the mean residence time due to a solute pulse (Dirac type) at the upstream boundary increases linearly with the size ratio of the storage zone and the stream. The three models provide an identical representation up to the first three temporal moments, which implies that at least four moments must be taken into account to distinguish between the physical biases of the models and to estimate the deviation in model characteristics. By evaluating the results from three tracer experiments, limits of acceptable model bias could be estimated. Evaluation of the tracer experiments also indicated that the temporal moments can function as indicators of underlying physics. Groundwater infiltration may significantly decrease the skewness of the residence times.
Predicting stream transient storage zone characteristics from tracer data
Authors: Manson J. Russell
Published: September 2002

A method for predicting solute transport in streams with transient storage is presented. The method uses the principle of superposition to generate general solutions for an arbitrary inflow boundary condition based on a fundamental solution for a constant finite duration loading. The principle of superposition is shown to give excellent results for the cases studied here. The method can be used to compute stream and transient storage characteristics from measured concentration versus time data from stream tracer studies.
Optimal fund assignment and allocation models for pipe repair maintenance in leaky water distribution networks
Authors: Bach Nguyen Luong , Fujiwara Okitsugu , Luong Huynh Trung
Published: September 2002

In pipe repair maintenance operations for leaky water distribution networks in cities, it is usually the practice that whenever pipe leaks are detected, repair actions are undertaken until the funds assigned are exhausted. The allocation of limited repair funds to different pipe sections is normally done without careful quantitative analysis but according to an intuitive rule, whereby the section of the larger leak volume receives the larger share of funds. This paper proposes a new modeling approach to determine optimal repair fund allocation to different sections of a city. A basic periodic‐review stochastic demand inventory model is first applied to ascertain the optimal funds to be assigned to a city under an assumption of no fund limitation. The model is then extended to determine the optimal allocation of the limited funds to different sections of a city. The models minimize the expected total system cost composed of repair cost, storage cost (of spare parts and materials), and penalty cost for water loss due to lack of funds. Numerical experiments are then conducted to illustrate the applicability of the proposed models, and the characteristics of the optimal solutions with regard to parameter variations are investigated. Data used in the numerical example are taken from actual data of the secondary network of Ho Chi Minh City in Vietnam.
Transport of a two‐member decay chain in a single fracture: Simplified analytical solution for two radionuclides with the same transport properties
Authors: Cormenzana J.
Published: September 2002

The analytical solution presented by Sudicky and Frind [1984] for the problem of transport of a two‐member decay chain through a single fracture in a porous rock matrix for the general case was correct. However, when this analytical solution was applied to several examples, a mistake was made in its evaluation, and all the results are incorrect. In particular, the surprising effect identified [Sudicky and Frind, 1984, p. 1028] “the second member of the decay chain can penetrate further along the fracture than the first, even though the diffusion coefficients and the retardation factors are the same for both species” is an artifact. In this paper the errors of Sudicky and Frind are identified, and a simple analytical solution is derived for the particular case in which both members of the chain have the same retardation and diffusion properties. This simple analytical solution has been applied to their examples, and results show that for a decay chain of two radionuclides with the same retardation and sorption properties, if a pulse of the parent radionuclide is injected into a single fracture, the ratio of concentrations of the two members of the chain at any point along the fracture or into the matrix is equal to the ratio of total masses of both radionuclides in the system.
Stochastic determination of well capture zones conditioned on regular grids of transmissivity measurements
Authors: van Leeuwen Matthijs , Butler Adrian P. , te Stroet Chris B. M. , Tompkins Jacob A.
Published: September 2002

A stochastic approach is adopted for characterizing the uncertainty in time‐related well capture zones in heterogeneous formations. Transmissivity is modeled as a random space function, conditioned on regular grids of evenly distributed transmissivity measurements. Monte Carlo analysis is used to infer the probability distribution of the resulting stochastic capture zones. Three measures of conditioning performance are defined and evaluated for several combinations of conditioning density, transmissivity variance, and transmissivity integral scale. Furthermore, a connection is made with previous work on transport theory. Simulation results show that conditioning performance increases with an increasing conditioning density, an increasing transmissivity integral scale, and a decreasing transmissivity variance. However, there is a threshold combination of conditioning density and integral scale beyond which conditioning performance stagnates. The practical implications of the results in general and the threshold in particular are discussed.
Analytical determination of power‐law index for the Chapman et al. sandpile (FSOC) analog for magnetospheric activity — A renormalization‐group analysis
Authors: Tam Sunny W. Y. , Chang Tom , Chapman S. C. , Watkins N. W.
Published: September 2002

Recent suggestion and experimental indications that the magnetotail dynamics exhibit self‐organized critical behavior have re‐motivated interest in sandpile (avalanche) models. Some examples of specific interest for geomagnetic activity have the property that internal avalanches exhibit inverse power law statistics whereas systemwide avalanches have a well‐defined mean. Here, we apply the concept of renormalization group to such a model. We demonstrate that invariant analysis based on the renormalization‐group theory can explain the power law distribution of energy release by internal avalanches in the large‐scale regime of these systems.
Bottom water throughflows at the Rio de Janeiro and Rio Grande Fracture Zones
Authors: Mercier Herlé , Weatherly Georges L. , Arhan Michel
Published: September 2002

Bottom water throughflows at the Rio de Janeiro Fracture Zone (22°S) and Rio Grande Fracture Zone (26°S) of the Mid‐Atlantic Ridge are identified from hydrographic anomalies observed along 9°W in the Angola Basin. The throughflow water is supplied by a meridional band of cold and fresh water lying against the western flank of the Ridge.
The simulation of the coronal mass ejection‐shock system in the inner corona
Authors: Zhang Bei‐Chen , Wang Jing‐Fang
Published: September 2002

In the concept that coronal mass ejections (CME) are usually originated in large closed magnetic field regions which are found in the coronal streamer belt near the solar surface, we have used a thermal driving force so strong that portions of the closed magnetic fields were carried away by the strong disturbance. A CME‐shock system is obtained in the inner corona. The “legs” of loop‐like CMEs are again obtained at the interface between the coronal open and closed magnetic fields. However, there is no counterpart in outer space. The shock is a combined one with an intermediate shock near the equator at its early stage. Ultimately, it becomes a pure fast shock. A plasmoid with higher density and bubble‐like magnetic fields is formed behind the MHD shock wave. It propagates at high speed. The results show that the high‐speed plasmoid does not propel the MHD shock in front of it; rather, the plasmoid forms behind the MHD shock.
Magnetic field depressions in the solar wind
Authors: Fränz M. , Burgess D. , Horbury T. S.
Published: September 2002

Depressions in the interplanetary magnetic field strength occur on a wide range of temporal scales, starting with magnetic holes with a duration of several seconds and extending to larger‐scale structures of more than 30 min duration. Using the magnetic field measurements of the Ulysses spacecraft, we quantify the statistical significance of the occurrence rate of depressions in the magnetic field compared to a lognormal distribution. On this basis we introduce measures for the length and depth of magnetic depressions. There is a weak indication for a change in the character of the length distribution at 20–40 s in the high‐speed solar wind. An analysis of 115 depressions with a length > 2 min showed that (1) they are bounded by tangential discontinuities in 78% of all cases, (2) normals to the structure boundaries have no strong orientation with respect to background field or global geometry, and (3) an increased proton temperature anisotropy is the only bulk ion parameter correlating with the depressions.
Underdamped responses of a well to nearby swarm earthquakes off the coast of Ito City, central Japan, 1995
Authors: Kunugi Takashi , Fukao Yoshio , Ohno Masao
Published: September 2002

We observed coseismic and noncoseismic water level changes of an underdamped well‐aquifer system at epicentral distances of ∼5 km during the 1995 earthquake swarm activity off the coast of Ito City, Shizuoka Prefecture, central Japan. Each water level change consists of a static offset with a linear trend component followed by a damped harmonic oscillation. The characteristic frequency and decay parameter of these oscillations are 18.3 s and 0.024 s−1, respectively. We detected 14 such events within 8 days during the activity. The offset values are mostly 2 mm or less, but there were two exceptionally large offsets of 4 and 6 mm. The observed waveforms are consistent with an analytical expression for the theoretical well level response to step‐like pressure head change in an underdamped well‐aquifer system. This consistency allowed us to estimate the parameters of the well‐aquifer system and the offset component of pressure head changes from the observed hydrographs. The seismic records at the nearest station indicate that among the 14 events only seven, including the two exceptionally large events, were apparently synchronous with swarm earthquakes. Among these seven events the largest two are quantitatively explained as the consequence of the coseismic volumetric strain changes. The other five are interpreted as either the effect of coseismic strain change near a node of the volumetric strain field or some other coseismic effects. The seven well events not synchronous with earthquakes indicate the occurrence of abrupt local pressure disturbances in the aquifer within a distance of a few tens of meters from the well.
Evidence for a recently abandoned shear margin adjacent to ice stream B2, Antarctica, from ice‐penetrating radar measurements
Authors: Clarke Ted S. , Liu Chen , Lord Neal E. , Bentley Charles R.
Published: September 2002

Satellite imagery of the area between ice streams B1 and B2, Antarctica, shows a lineation on the surface of the ice sheet of uncertain origin. Ice motion in the area (2 m yr−1) is 2 orders of magnitude slower than that of the surrounding streams and shows no significant variation that could explain the feature. A low‐power, high‐resolution radar system was used to image the upper 80 m of the ice sheet between the two ice streams; the survey shows that the lineation is associated with what is likely an abandoned shear margin. The radar data show that a set of chaotic diffractors lies buried beneath two thirds of the area, while the remaining one third is undisturbed to 80 m depth. The chaotic ice ends abruptly along a boundary that is parallel to, but offset 2.5 km from, the surface lineation. Also, isolated linear diffractors are commonly observed in the otherwise undisturbed ice immediately adjacent to the boundary. The depth, location, orientation, and curved form of the diffractors strongly suggest they are the tops of crevasses that were active at the time the chaotic ice was being strained and that they were formed by left‐lateral shear. This is the same sense of shear that is presently active in the B2 margin, 6 km away. The depth to the chaotic diffractors suggests that the shear margin abandoned its prior position ∼190 years B.P.; the burial depth decreases toward the B2 margin and suggests a migration rate of ∼100 m yr−1. In addition, a separate high‐power radar system was used to image the entire thickness of the ice sheet (∼1 km) in the same area. These data show numerous linear diffractors near the base of the ice sheet. It is very likely that at least some of these diffractors are entrained morainal debris. Others may be bottom crevasses or zones of wet, reflective ice that developed in the high‐strain environment of the now‐abandoned shear margin.
Static stress transfer and earthquake triggering: No lower threshold in sight?
Authors: Ziv Alon , Rubin Allan M.
Published: September 2002

The main objective of this study is to see if a lower threshold for earthquake triggering exists. Resolving this issue is important for the understanding of earthquake mechanics and for the purpose of hazard analysis. We compute the cumulative static stress changes imposed on 63 M ≥ 4.5 earthquakes in central California between 1969 and 1998, by adding the stress changes imposed by all previous M ≥ 4.5 earthquakes as a function of time prior to the events. We find that 85% of the cumulative stress changes at the time of rupture are positive for stress change magnitudes of >10 kPa (>0.1 bar), and 70% are positive for stress changes of <10 kPa (< 0.1 bar) as well as <1 kPa (<0.01 bar). A comparison between these results and those obtained for synthetic catalogs, in which the timing or focal mechanisms of the earthquakes were randomized, shows that this degree of triggering is very unlikely to be found in a random catalog. Thus we conclude that no lower threshold for earthquake triggering in central California has been found. We show that the temporal distribution of stress changes that discourage failure is consistent with the theoretical prediction that the time delay increases with the magnitude of the stress change.
Characteristics of three‐dimensional quasi‐geostrophic transient eddy propagation in the vicinity of a simulated Gulf Stream
Authors: Nakamura Mototaka , Chao Yi
Published: September 2002

Output of an eddy‐resolving model of the North Atlantic is diagnosed in the vicinity of the Gulf Stream (GS), using the three‐dimensional quasi‐geostrophic transient wave activity flux diagnostic developed by Plumb [1986]. The model North Atlantic shows large transient wave activity along the model GS and along the edge of the Mediterranean Outflow. The fluxes show advection of wave activity by the GS from the separation point and radiation of wave activity from the GS in the top 1000 m. The wave radiation from the model GS is particularly clear to its south and points southwestward in general. The fluxes in and around the Mediterranean Outflow appear to be generated and dissipated locally. The vertical component of the transient wave activity flux is downward on average at all depths, suggesting conversion of baroclinic energy supplied near the surface into kinetic energy distributed throughout the depth. Eddy fields show that transient eddies tend to reinforce quasi‐stationary meanders in the GS just downstream of the separation point. We also find evidence for eddy forcing of the northern recirculation generated in the model, in agreement with the available observations.