bluuebunny/crossref_metadata_2025 huggingface dataset:
El Niño‐Southern Oscillation sea surface temperature and wind anomalies, 1946–1993
Authors: Harrison D. E. , Larkin Narasimhan K.
Published: February 2004

El Niño‐Southern Oscillation (ENSO) periods, which occur irregularly every few years, are a major perturbation of the Earth's climate system that involves large‐scale changes in winds, rainfall, sea surface temperature (SST), and surface pressure. In some areas of the world there are disastrous droughts, and in others there is serious flooding. North American weather patterns are also affected. It is important to develop skillful forecasts for ENSO periods. Our goal here is to provide an overview of the global ocean and atmosphere surface changes that typically occur during ENSO periods. Knowledge of these anomaly patterns is needed in order to improve our understanding and forecasts of ENSO. With a global surface data set we describe the statistically significant patterns of SST, surface wind, and surface pressure changes that on average are associated with the 10 post‐World War II ENSO periods. We present these average anomaly results as an “ENSO composite.” It is useful to identify phases of the typical ENSO and examine the statistically significant elements phase by phase. An ENSO by ENSO period search indicates that about two thirds of these elements occur in 90% or more of the ENSO periods: we define a “Robust ENSO Composite” from these frequently occurring elements and find it to be an Indo‐Pacific phenomenon. Limitations in the surface data set make it possible that this study has not identified all the important aspects of ENSO periods; data are very sparse in both space and time over much of the tropics and the southern hemisphere. However, we suggest that any theory or model of ENSO should at least exhibit the features of this robust composite, and is unlikely to able to represent adequately the large‐scale environmental impacts of ENSO unless it does so.
Postglacial variations in the level of the sea: Implications for climate dynamics and solid‐Earth geophysics
Authors: Peltier W. R.
Published: February 2004

Throughout the latter half of the Pleistocene epoch of Earth history, beginning ∼900 kyr ago, the climate system has been dominated by an intense oscillation between full glacial and interglacial conditions. During each glacial stage, global sea level fell by ∼120 m on average, as extensive ice sheets formed and thickened on the surfaces of the continents at high northern (primarily) and southern latitudes. Within each cycle this glaciation phase lasted ∼90 kyr and was followed by a much more rapid deglaciation event which terminated after ∼10 kyr and which returned the system to the interglacial state. The period of the canonical glacial cycle has remained very close to 100 kyr since its inception in mid‐Pleistocene time. Because of the magnitude of the mass that was redistributed over the surface of the Earth during each such glacial cycle and because of the viscoelastic nature of the rheology of the planetary mantle, these shifts in surface mass load induced variations in the shape of the planet that have been indelibly transcribed into the geological record of sea level variability. Indeed, the geological, geophysical, and even astronomical signatures of this process, which is continuing today, are now being measured with unprecedented precision using the methods of space geodesy and have thereby begun to provide important new scientific insight and understanding, both of the interior of the solid Earth and of the climate system variability with which the ice ages themselves are associated. In this article my purpose is to bring together, in a single review, an assessment of where we currently stand scientifically with regard to understanding both of these aspects of the ice ages. Although the discussion will not address in any detail the fascinating issue of ice age climate, since this topic is sufficiently complex of itself to require a detailed review of its own, I will nevertheless attempt to briefly summarize the current state of understanding of the physical processes that are responsible for the occurrence of the ice age cycle, by way of providing a more complete context in which to appreciate the main lines of argument that will be developed.
An improved method of synthesizing ground backscatter ionograms for spherical ionospheres
Authors: Ong C. Y. , Bennett J. A. , Dyson P. L.
Published: February 2004

Synthesis of ground backscatter ionograms is a useful technique for studying the structure of the ionosphere. By synthesizing backscatter ionograms from a known ionosphere, knowledge can be obtained on how variations in the ionosphere affect the shape of a backscatter ionogram. A method allowing the rapid synthesis of ground backscatter ionograms is presented. The vertical ionospheric profile is represented by a series of smoothly joined quasi‐parabolic segments which can accurately reproduce both measured and model profiles. The ionosphere is, however, restricted to being spherically symmetric. The synthesis includes corrections for geometrical and time delay focusing. The speed of the technique is valuable when ionospheric state is to be determined by seeking a match between measured and synthesized backscatter ionograms. The restriction of the synthesis to spherically symmetric ionospheres means that the best choice can only be made from this class. Residual differences can be a useful indication of the significance of departures from spherical symmetry. The calculations involved in the synthesis are closely related to those necessary to establish coordinate registration in the location of targets for over‐the‐horizon radar.
Ground‐based microwave radiometry and long‐term observations of atmospheric water vapor
Authors: Elgered Gunnar , Jarlemark Per O. J.
Published: February 2004

Microwave radiometer data and radiosonde data from the time period 1981–1995 have been used to study long‐term trends in the integrated precipitable water vapor (IPWV). The two instruments have operated 37 km apart on the Swedish west coast. Model parameters are estimated for the entire data sets as well as for subsets of the data. The IPWV model parameters are a mean value, a linear drift with time, and the amplitude and phase of an annual component. The radiosonde data, which are uniformly sampled in time, show an increase in the IPWV of 0.03 mm/yr with a statistical standard deviation of 0.01 mm. The microwave radiometer data, which are not at all uniformly sampled in time, show −0.02±0.01 mm/yr. We show that the disagreement is caused by the different sampling of the data for the two instruments. When the two data sets are reduced to include only data that are sampled simultaneously, we find an agreement between all estimated model parameters, given their statistical uncertainties. This suggests that if the microwave radiometer had also been operating continuously over the 15‐year period, its data would have implied a linear trend similar to the result obtained from the radiosonde data. The general quality of the data, in terms of the short time scatter, has been improved over the time period. The root mean square (RMS) difference between the IPWV measured by the radiometer and by the radiosondes was 2.1 mm during the first 5 years and was reduced to 1.6 mm during the last 4 years. These values include the real difference in the IPWV between the two sites. The bias, radiometer‐radiosonde, was 0.1 mm for the whole data set and varied between −0.2 and 0.9 mm for smaller data sets of a few years.
Water vapor microwave continuum absorption: A comparison of measurements and models
Authors: Rosenkranz Philip W.
Published: February 2004

Measurements, made in different laboratories, of absorption by water vapor in microwave windows are compared with models for the water vapor continuum. A reanalysis of some of these measurements leads to the conclusion that the laboratory data are best represented by a combination of Liebe's [1987] millimeter‐wave propagation model (MPM) for the foreign‐broadened component of the water continuum and the 1993 version of MPM for the self‐broadened component. This combined model is validated by comparison with measurements of atmospheric microwave emission.
Characteristics of plasma structuring in the cusp/cleft region at Svalbard
Authors: Basu S. , Weber E. J. , Bullett T. W. , Keskinen M. J. , MacKenzie E. , Doherty P. , Sheehan R. , Kuenzler H. , Ning P. , Bongiolatti J.
Published: February 2004

Satellite scintillation, all‐sky optical imager, and digisonde observations were coordinated during a cusp campaign conducted at Ny Alesund, Svalbard (78.9°N, 11.8°E 75.7°N corrected geomagnetic latitude, over the period January 4–15, 1997. This paper is focused on a study of the distribution and dynamics of mesoscale (tens of kilometers to tens of meters) electron density irregularities in the dayside auroral region. This study has been performed at Ny Alesund, Svalbard, by measuring the effects of these irregularities on the amplitude scintillation of 250‐MHz transmissions from a quasi‐stationary polar satellite as well as the amplitude and phase scintillation of 1.6‐GHz signals from Global Positioning System (GPS) satellites. These GPS scintillation measurements were augmented by the use of dual‐frequency (1.2 and 1.6 GHz) GPS phase data acquired at the same station by the Jet Propulsion Laboratory for the International GPS Geodynamic Service (IGS). The continuous 250‐MHz scintillation observations explored the daytime auroral ionosphere 2° poleward of Ny Alesund and showed that the scintillation spectra are often broad, as may be expected for irregularities in a turbulent flow region. Such irregularity dynamics were detected poleward of the nominal cusp region over the interval of 0600–1500 magnetic local time. The period of observations included the magnetic storm of January 10–11, 1997, when GPS observations of the IGS detected polar cap patches with total electron contents of 3×1016 m−2 and large‐scale (tens of kilometers) phase variations at the GPS frequency of 1.6 GHz that corresponded to temporal gradients of 2×1016 m−2 min−1. However, amplitude scintillations at the GPS frequency of 1.6 GHz could not be detected in association with these large‐scale phase variations, indicating that the irregularities with wavelengths less than the Fresnel dimension of 400 m were below the detectable limit. This is shown to be consistent in the context of enhanced ionospheric convection determined by digisonde and scintillation spectra.
Strip, slot, air, inverted patch (SSAIP): A cavity‐backed alternative to broadband communication antennas
Authors: Melcón A. Alvarez , Mosig Juan R.
Published: February 2004

In this paper, a new cavity‐backed antenna configuration, called strip, slot, air, inverted patch (SSAIP) is proposed. The SSAIP is the cavity‐backed version of the standard strip, slot, foam, inverted patch (SSFIP) antenna concept, and this paper compares the electrical performances of both types of antennas. Results reveal that similar to their SSFIP counterparts, SSAIP antennas also exhibit large frequency bandwidth but now combined with clean and versatile radiation patterns and can thus be used in broadband communication applications. The analysis of these antennas is carried out with a specific integral equation formulation, described in the paper. To facilitate the physical understanding of the new structure, an equivalent filter model of the real SSAIP antenna is also derived. This equivalent model allows standard filter design techniques to be used for an easy electrical design of the antenna. In addition to theoretical results, experimental results are also presented showing good agreement between numerical predictions and measurements.
Measurements of transionospheric radio propagation parameters using the FORTE satellite
Authors: Massey Robert S. , Knox Stephen O. , Franz Robert C. , Holden Daniel N. , Rhodes Charley T.
Published: February 2004

We report initial measurements of ionospheric propagation parameters, particularly the total electron content (TEC), using the recently launched FORTE satellite. FORTE, which orbits the Earth at an altitude of 800 km and an inclination of 70°, contains a set of wideband radio receivers whose output is digitally recorded. A specialized triggering circuit identifies transient, broadband radio events, which include radiation from lightning, transionospheric pulse pairs, and man‐made sources. Event data are transmitted to the ground station for analysis. In this paper we examine signals transmitted from an electromagnetic pulse generator operated at Los Alamos. The transmitter produces nearly impulsive signals in the VHF range. The received signal is dispersed by the ionosphere, and the received signal can be analyzed to deduce the total electron content along the path. By comparing the slant TEC thus measured with results from a ray‐tracing code, we can deduce the vertical TEC to 800 km. Data from eight passes are presented. These types of data (in larger quantities) are of interest to operators of radar altimeters, who need data to corroborate their corrections for the ionospheric TEC. The combination of FORTE TEC data to 800 km and TEC measurements to 20,000 km (the Global Positioning System orbital altitude) can provide useful information for assessing the validity of models of plasmaspheric electron density. Initial estimates of the plasmaspheric density, on two daytime passes, are about 6 TECU. The signal received by FORTE, which is linearly polarized at the transmitter, is split into two magnetoionic modes by the ionosphere. The receiving antenna is also linearly polarized and therefore receives both modes. By measuring the beat frequency between the two modes, we can deduce the product of the geomagnetic field and the cosine of the angle between the field and the propagation vector. The possibility of using the measured slant TEC and the beat frequency to geolocate impulsive signals is discussed.
Model of red sprites due to intracloud fractal lightning discharges
Authors: Valdivia J. A. , Milikh G. M. , Papadopoulos K.
Published: February 2004

A new and improved model of red sprites is presented. Emphasis is placed on accounting for the puzzling observation of the spatial structure in the emissions. The model relies on the electromagnetic pulse (EMP) fields created by a horizontal lightning discharge and includes the observed fractal structure of such discharges in the computation of the EMP power density. It is shown that the model can account for the observed spatial structure of the red sprites while reducing the typical charge required to approximately 100 C.
Gradient drift instability growth rates from global‐scale modeling of the polar ionosphere
Authors: Sojka J. J. , Subramanium M. V. , Zhu L. , Schunk R. W.
Published: February 2004

The winter polar ionosphere, under southward interplanetary magnetic field (IMF) conditions, experiences irregularity development leading to consequences such as scintillation on transionospheric communication links. These irregularities are associated with antisunward convecting polar ionospheric patches. The gradient drift instability (GDI) has been considered a primary candidate for the generation of these irregularities, or at least the long‐wavelength energy source of the irregularity‐wave cascade process. The Utah State University time‐dependent ionospheric model (TDIM) enables the polar cap ionosphere and its patches to be modeled on a large scale in a time‐evolving manner. Hence, at each point in space and time, the TDIM has adequate information to compute the growth rate of the gradient drift instability. The spatial gradients are based on a 92×92 km TDIM grid resolution, while the time resolution can be as short as 30 s. In this study, we present results of the GDI linear growth rate calculations for the F region. For a first time, snapshots of the instantaneous GDI linear growth rates over the polar ionosphere are shown. These show, in part, the correlation of the GDI with polar cap patches. Then we present the time evolution of the linear growth rate as plasma flux tubes convect. It is shown that a flux tube of plasma can, in fact, change between being unstable and stable to the GDI as the plasma convection pattern switches in response to changing IMF conditions. These convective results are essential information if an assessment of whether or not a plasma flux tube is stable to the gradient drift mechanism is to be made.
Crustal shortening and vertical strain partitioning in the Middle Atlas Mountains of Morocco
Authors: Gomez Francisco , Allmendinger Richard , Barazangi Muawia , Er‐Raji Ahmed , Dahmani Mohammed
Published: February 2004

The NE‐SW trending Middle Atlas Mountains of Morocco are obliquely oriented within the late Cenozoic regional stress field, resulting in deformation that is partitioned into strike‐slip faulting and thrust‐related folding. In the central Middle Atlas, thrusting is confined to a 20 km wide fold belt between two relatively rigid crustal blocks that are obliquely converging. We suggest that in addition to strain partitioning observed in plan view, a partitioning of deformation between the upper and lower crust may be necessary to reconcile estimated crustal thickening and horizontal shortening within the fold belt. Cross‐section balancing based on field observations demonstrates a relatively modest amount of Cenozoic horizontal shortening (∼ 4.7 km) normal to the fold belt producing 800 m of structural relief. Yet, geophysical data suggest this contraction has not produced a significant crustal root beneath the fold belt; that is, the belt does not appear to be isostatically compensated. Assuming all horizontal shortening was accommodated by crustal thickening beneath the fold belt implies much greater thickening than is suggested by constraints on the preshortened crustal thickness. It thus appears that thickening does not accommodate all of the contraction. We suggest one possible solution: The upper crust shortens by thickening (faulting and folding), whereas the lower crust deforms laterally.
Eocene‐early Miocene foreland basin development and the history of Himalayan thrusting, western and central Nepal
Authors: DeCelles Peter G. , Gehrels George E. , Quade Jay , Ojha T. P.
Published: February 2004

Sedimentologic, petrographic, and U‐Pb detrital zircon ages from middle Eocene through early Miocene sedimentary rocks in the Lesser Himalayan zone of western and central Nepal indicate that a peripheral foreland basin system had developed in the eastern Himalayan collision zone by middle Eocene time. The shallow‐marine, Eocene Bhainskati Formation accumulated in a back‐bulge depozone between a southward migrating forebulge and the Indian craton. Migration of the forebulge through this region during Eocene‐Oligocene time produced a regional unconformity that spans ∼15–20 Myr. By early Miocene time, the forebulge unconformity was onlapped by the distal fringes of the southward migrating foredeep depozone, represented by fluvial deposits of the Dumri Formation. Continued southward migration of the foredeep during the Neogene accommodated the fluvial Siwalik Group. Light mineral provenance data and U‐Pb detrital zircon ages suggest that the Bhainskati was derived partly from Tethyan sedimentary rocks of the Tibetan Himalayan zone during initial growth of the Himalayan fold‐thrust belt. The Dumri was derived from metasedimentary and crystalline rocks of the Greater Himalayan zone during emplacement of the Main Central thrust and contemporaneous tectonic unroofing by normal faulting along the South Tibetan detachment system. The Lesser Himalayan crystalline thrust sheets were emplaced soon after deposition of the Dumri Formation, ∼15–10 Ma. Paleocurrent and lithofacies data from the Dumri Formation indicate deposition by west‐southwestward flowing rivers that drained into the Indus portion of the Himalayan foreland basin system during the early Miocene. Thick channel sandstones in the lower Dumri may represent the early Miocene counterpart of the modern Ganges River. Eastward diversion of the Ganges drainage system to near its present location had occurred by ∼15 Ma, as the high‐standing Aravalli Range on the northern Indian shield approached the front of the fold‐thrust belt. Assuming reasonable values for the flexural rigidity of Indian lithosphere, the time span of the forebulge unconformity yields a velocity of ∼14–33 mm/yr for the southward migration of the fold‐thrust belt relative to India. This range of values is consistent with Neogene and present‐day estimates and suggests that only one third to one half of India‐Eurasia convergence has been accommodated by shortening in the Himalayan fold‐thrust belt since the onset of collision.
Collision and extrusion at the Kuril‐Japan arc junction
Authors: Kusunoki Kaori , Kimura Gaku
Published: February 2004

Hokkaido (Japan) is a region where collision tectonics is ongoing at an arc‐arc junction and where lower crust is presently exposed as a result of the collision of the forearc sliver of the Kuril Arc with the Northeast Japan Arc. Deep‐seated ductile deformation in metamorphic rocks has already been described, but more shallow deformation is not sufficiently well observed to clarify a total history of the collision. We focus on the shallow deformation in the Cape Erimo area in central Hokkaido and discuss in detail the process of collision at this arc‐arc junction. Four phases of deformation are discriminated in the study area as follows: (1) ENE‐WSW extension immediately after sediment deposition, (2) NW trending dextral strike slip, (3) NE‐SW compression in association with the formation of conjugate sets of strike‐slip faults, and (4) E‐W compression represented by the formation of low‐angle reverse faults. The first and the second phases of faulting may be a manifestation of the Oligo‐Miocene dextral transform plate boundary between the Eurasia and Okhotsk Plates. A conjugate system of strike‐slip faults formed in the third phase, newly clarified in this study, by NE trending horizontal compression nearly normal to the NW trending dextral strike‐slip fault zone of the previous phase. Development of the strike‐slip faults, especially the predominance of sinistral strike‐slip faults in the southern half of the arc‐arc junction, must be explained by extrusion in association with collision of the forearc sliver of the Kuril Arc. Such extrusion may be a common tectonic feature even in the case of a small‐scale collision at an arc‐arc junction.
Northeastward growth of the Tibet plateau deduced from balanced reconstruction of two depositional areas: The Qaidam and Hexi Corridor basins, China
Authors: Métivier François , Gaudemer Yves , Tapponnier Paul , Meyer Bertrand
Published: February 2004

We address the problem of late Cenozoic uplift, erosion, and growth of northeastern Tibet by reconstructing, from isopach maps and drill holes, the volumes and masses of sediments deposited in the Qaidam and Hexi Corridor basins since ∼35 Myr ago. The mass budget is based on simple geometrical assumptions such as regional similarity of the thickness ratios between strata of different ages. In the Qaidam, where our record extends back to the Oligocene, the budget shows a huge rise of the accumulation rates after the beginning of the Pliocene (5.3 Ma). The early Pliocene seems to be the period of maximum deposition with accumulation rates in excess of 1 mm yr−1 (∼ 2.7 kg m−2 yr−1) of compacted rocks throughout the basin. There also seems to be a southeastward shift of the largest depocenters between the upper Pliocene (3.4–1.6 Ma) and the Quaternary. In the Hexi Corridor, sedimentation is confined to small foreland flexural depressions associated with the frontal thrusts of the Qilian Shan and occurs at an average rate one order of magnitude smaller than in the Qaidam basin. The accumulation rate is maximum in the Quaternary. The sedimentation history appears to support a plateau‐building mechanism resulting from the combination of two geologicallly common processes: crustal‐scale thrusting and sedimentary basin infilling. The time needed to completely fill the Qaidam basin and make its catchment a plateau closely resembling that of the highest part of Tibet (Qangtang) is of the order of 9 Myr. The mechanism now at work north of the Kunlun, which involves rapid infilling of broad, flat areas separated by relatively narrow mountain ranges, has thus probably been important in producing the high, smooth topography that characterizes much of central Tibet.
A Monte Carlo assessment of Eulerian flow and transport perturbation models
Authors: Hassan Ahmed E. , Cushman John H. , Delleur Jacques W.
Published: February 2004

Monte Carlo studies of flow and transport in two‐dimensional synthetic conductivity fields are employed to evaluate first‐order flow and Eulerian transport theories. Hydraulic conductivity is assumed to obey fractional Brownian motion (fBm) statistics with infinite integral scale or to have an exponential covariance structure with finite integral scale. The flow problem is solved via a block‐centered finite difference scheme, and a random walk approach is employed to solve the transport equation for a conservative tracer. The model is tested for mass conservation and convergence of computed statistics and found to yield accurate results. It is then used to address several issues in the context of flow and transport. The validity of the first‐order relation between the fluctuating velocity covariance and the fluctuating log conductivity is examined. The simulations show that for exponential covariance, this approximation is justified in the mean flow direction for log conductivity variance, σf2, of the order of unity. However, as σf2 increases, the relation for the transverse velocity component deviates from the fully nonlinear Monte Carlo results. Eulerian transport models neglect triplet correlation functions that appear in the nonlocal macroscopic flux. The relative importance of the triplet correlation term for conservative chemicals is examined. This term appears to be small relative to the convolution flux term in mildly heterogeneous media. As σf2 increases or the integral scale grows, the triplet correlation becomes significant. In purely convective transport the triplet correlation term is significant if the heterogeneity is evolving. The exact nonlocal macroscale flux for the purely convective case significantly differs from that of the convective‐dispersive transport. This is in agreement with recent theoretical analysis and numerical studies, and it suggests that neglecting local‐scale dispersion may lead to large errors. Localization errors in the flux term are evaluated using Monte Carlo simulations. The nonlocal in time model significantly differs from the fully nonlocal model. For small variance and integral scale there is a slight difference between the fully localized flux and the fully nonlocal convolution flux. This is also in agreement with recent theories that suggest that moments through the second for the two models are nearly identical for conservative tracers. The fully localized model does not perform well in the purely convective cases.
Production of CO2 in the capillary fringe of a deep phreatic aquifer
Authors: Affek Hagit P. , Ronen Daniel , Yakir Dan
Published: February 2004

CO2 profiles obtained along a 30‐m‐thick unsaturated zone under land irrigated with sewage effluents show two production regions: a seasonal one in the root zone and another, at steady state, near the water table (29 m). On an annual basis the CO2 flux from the deep source toward the atmosphere (6.3 g C m−2 yr−1) is balanced by a similar influx of soluble organic carbon (SOC) from sewage effluents. The δ13C values of soil CO2 indicate that CO2 is produced from plant material in the root zone and from biodegradation of total sedimentary organic carbon in the capillary fringe. High CO2 concentration in the capillary fringe (up to 2%) is likely to reflect a decrease in diffusivity relative to the unsaturated zone due to increase in both water content and tortuosity induced by the capillary fringe structure. The long residence time of SOC and CO2 in the unsaturated zone (29 years at the study site) suggests that the unsaturated zone of deep aquifers may have a significant storage capacity for carbon and may act as a temporary carbon sink.
Anisotropic scaling in braided rivers: An integrated theoretical framework and results from application to an experimental river
Authors: Foufoula‐Georgiou Efi , Sapozhnikov Victor B.
Published: February 2004

Dynamic scaling in braided rivers is reexamined under an extended theoretical framework, developed herein, which explicitly incorporates the self‐affinity (scaling anisotropy) in the spatial structure of braided rivers. It is shown that in structures exhibiting anisotropic spatial scaling, dynamic scaling (if present) is necessarily anisotropic. Through analysis of the behavior of an experimental braided river, the presence of anisotropic dynamic scaling in braided rivers was revealed. This implies that there exists a pair of dynamic exponents Zx and Zy enabling one to rescale space (differently in the direction X of the slope and in the perpendicular direction Y) and time, such that the evolution of a smaller part of a braided river looks statistically identical to that of a larger one. The presence of such a space‐time scale invariance provides an integrated framework for describing simultaneously the spatial and temporal structure of braided rivers and may be explored toward statistical prediction of large and rare changes from the statistics of smaller and frequent ones.
The dependence of the electrical conductivity measured by time domain reflectometry on the water content of a sand
Authors: Ferré P. A. , Redman J. D. , Rudolph D. L. , Kachanoski R. G.
Published: February 2004

We present paired measurements of the water content and electrical conductivity collected in a laboratory column packed with a homogeneous, clean sand over a wide range of water content and pore water electrical conductivity (EC) conditions. The EC was determined using the method of Nadler et al. [1991] from waveforms collected with two‐rod time domain reflectometry (TDR) probes with and without baluns and with three‐rod probes without baluns. Following Heimovaara et al. [1995], we calibrated the probes in saline solutions to account for the series resistance of the cable and connectors. The calibrated EC shows a nonlinear dependence on the water content that is well described by a simple power relationship [Archie, 1942]. Recognizing that calibration in saline solutions is impractical for some TDR probes, we demonstrate that the EC response can be calibrated directly using the results of drainage events, incorporating only a separate calibration of the cable resistance. None of the probe designs shows any clear advantage for EC measurement.
Chemistry of unsaturated zone gases sampled in open boreholes at the crest of Yucca Mountain, Nevada: Data and basic concepts of chemical and physical processes in the mountain
Authors: Thorstenson Donald C. , Weeks Edwin P. , Haas Herbert , Busenberg Eurybiades , Plummer Niel , Peters Charles A.
Published: February 2004

Boreholes open to the unsaturated zone at the crest of Yucca Mountain, Nevada, were variously sampled for CO2 (including 13C and 14C), CH4, N2, O2, Ar, CFC‐11, CFC‐12, and CFC‐113 from 1986 to 1993. Air enters the mountain in outcrops, principally on the eastern slope, is enriched in CO2 by mixing with soil gas, and is advected to the mountain crest, where it returns to the atmosphere. The CFC data indicate that travel times of the advecting gas in the shallow Tiva Canyon hydrogeologic unit are ≤5 years. The 14C activities are postbomb to depths of 100 m, indicating little retardation of 14CO2 in the shallow flow systems. The 14C activities from 168 to 404 m in the Topopah Spring hydrogeologic unit are 85–90 pMC at borehole USW‐UZ6. The CFC data show that the drilling of USW‐UZ6 in 1984 has altered the natural system by providing a conduit through the Paintbrush Nonwelded unit, allowing flow from Topopah Spring outcrops in Solitario Canyon on the west to USW‐UZ6, upward in the borehole through the Paintbrush, to the shallow Tiva Canyon flow systems, and out of the mountain.
In situ estimation of soil hydraulic functions using a multistep soil‐water extraction technique
Authors: Inoue M. , Šimunek J. , Hopmans J. W. , Clausnitzer V.
Published: February 2004

Estimation of the retention and unsaturated hydraulic conductivity functions is essential to effectively provide input for water flow and transport simulation and prediction. A parameter optimization procedure is shown as a promising tool to estimate inversely these hydraulic function parameters from transient soil matric potential and cumulative soil solution extraction measurements. Sensitivity analyses from synthetic data generated from forward numerical model simulations showed that optimum tensiometer locations will depend on soil type. Experiments were carried out in both a laboratory column (Columbia sandy loam) and in the field (Yolo silt loam). In both cases a series of vacuum extraction pressures was applied to a ceramic soil solution sampler, and cumulative soil solution extraction volume and matric potentials at various positions near the extraction device were monitored as the soil solution was extracted. In the laboratory a zero‐flux boundary condition was maintained at the bottom of the column, whereas matric potential measurements were used in the field to define the lower boundary. In both the field and laboratory experiments, flow at the upper boundary was zero. Cumulative extraction volume and matric potential data were included in the objective function to be minimized to estimate the hydraulic function parameters. We determined that the optimized solution was sensitive to the contact between the ceramic ring and the surrounding soil. By also optimizing the hydraulic resistance of the ceramic ring of the extraction device, optimization improved the fit between measured and optimized flow variables. Comparison of the optimized with the independently measured hydraulic functions indicated that the in situ estimation using a multistep extraction procedure can provide accurate soil hydraulic data.
Public perceptions regarding water quality and attitudes toward water conservation in the lower Fraser Basin
Authors: McDaniels Timothy L. , Axelrod Lawrence J. , Cavanagh Nigel
Published: February 2004

This paper concerns public judgments regarding water quality, public attitudes about water conservation, and related issues in the Lower Fraser Basin of southwest British Columbia, Canada. A written survey was administered to 183 lay subjects in four communities within the Lower Fraser Basin. The results show that subjects generally perceive water quality in specific water bodies as worse than indicated in technical studies of those water bodies. Respondents also indicated a high willingness to engage in water conservation activities. Discussion and conclusions complete the paper.
Taieri river data to test channel network and river basin heterogeneity concepts
Authors: Ibbitt R. P. , McKerchar A. I. , Duncan M. J.
Published: February 2004

The paper describes data collected in a 158‐km2 basin for testing hypotheses underpinning the optimal channel network concept. Over a 4‐day period, discharge, channel cross sections, and longitudinal slope were measured at 300 sites. Measured channel widths range from 0.050 to 16.60 m, mean depths range from 0.010 to 0.546 m, and mean water velocities range from 0.004 to 0.575 m/s. Bias in the site selection was checked by comparing measurements made at predefined distances upstream or downstream of the measurement section. Slope measurements were based on channel reach lengths typically of the order of 0.5 km. Since the data may be of use to other researchers, we have archived them on the World Wide Web (site http://www.cri.nz/hydrology/taieripage.htm) along with a 1:50,000 scale map and the associated time series of streamflow at the basin outlet during the measurement interval.
A mathematical formulation for reactive transport that eliminates mineral concentrations
Authors: Saaltink Maarten W. , Ayora Carlos , Carrera Jesús
Published: February 2004

We present a concise and general mathematical formulation for reactive transport in groundwater for general applications. By means of linear algebraic manipulations of the stoichiometric coefficients of the chemical reactions we are able to reduce the number of unknowns of the equations to be solved to the number of degrees of freedom according to thermodynamic rules. We present six formulations that differ from each other by number and type of unknowns and discuss their advantages and disadvantages with respect to the two most important numerical solution methods, the Sequential Iteration Approach (SIA) and the Direct Substitution Approach (DSA). Our conclusion is that the proposed reduction of the number of variables is of special interest for the DSA. We have applied one of these formulations to an example of the flushing of saline water by fresh water.
Effect of removal of Juniperus ashei on evapotranspiration and runoff in the Seco Creek Watershed
Authors: Dugas W. A. , Hicks R. A. , Wright P.
Published: February 2004

The water balance of a watershed may be affected by replacing deep‐rooted woody species with shallow‐rooted herbaceous vegetation. The objective of this study was to measure the effect of removing an individual species of tree, Juniperus ashei (Bucch.), on the runoff (RO) and evapotranspiration (ET) from two adjacent, unreplicated 15‐ha areas (termed untreated and treated) in northeast Uvalde County, Texas, U.S.A. Daily ET from the two areas, measured from 1991 through 1995 using the Bowen ratio–energy balance method, varied from near 0 to 6 mm/d. All J. ashei taller than 0.5 m were cut with a chain saw in the treated area in September 1992. During both the pretreatment period (prior to September 1992) and the posttreatment period, the slope of treated ET as a function of untreated ET was ∼1, suggesting that for the entire period of measurements, brush removal had no significant effect on ET. Average daily ET from the area to be treated was 0.05 mm/d lower than that from the untreated area during the 2‐year pretreatment period, while it was 0.12 mm/d lower during the 3‐year posttreatment period. The ET difference (untreated minus treated) was 0.3 mm/d in the first 2 years following removal of J. ashei and decreased thereafter. Removal of J. ashei had no consistent effect on RO. Vegetation management increased the potential for greater water yields in the short term from these rangelands by decreasing ET for the first 2 years after imposition of treatment.
Evaluation of hydrodynamic scaling in porous media using finger dimensions
Authors: Selker John S. , Schroth Martin H.
Published: February 2004

The use of dimensionless scaling is ubiquitous to hydrodynamic analysis, providing a powerful method of extending limited experimetnal results and generalizing theories. Miller and Miller [1956] contributed a scaling framework for immiscible fluid flow through porous media that relied on consistency of the contact angle between systems to be compared. It is common to assume that the effective contact angle will be zero in clean sand material where water is the wetting liquid. The well‐documented unstable wetting process of fingered flow is used here as a diagnostic tool for the scaling relationships for infiltration into sandy media. Through comparison of finger cross sections produced using three liquids as well as various concentrations of anionic surfactant, it is shown that the zero contact angle assumption is very poor even for laboratory cleaned silica sand: Experimental results demonstrate effective contact angles approaching 60°. Scaling was effective for a given liquid between sands of differing particle size. These results suggest that caution should be exercised when applying scaling theory to initial wetting of porous media by liquids of differing gas‐liquid interfacial tensions.
Enhanced lower bounds for the global optimization of water distribution networks
Authors: Sherali Hanif D. , Totlani Rajiv , Loganathan G. V.
Published: February 2004

In this paper we address a global optimization approach to the problem of designing a water distribution network that satisfies specified flow demands at stated pressure head requirements. The nonlinear, nonconvex network problem is transformed into the space of certain design variables. By relaxing the nonlinear constraints in the transformed space via suitable polyhedral outer approximations, we derive a linear lower bounding problem. This problem provides an enhancement of Eiger et al.'s [1994] lower bounding scheme and takes advantage of the monotone concave‐convex nature of the nonlinear constraints. Upper bounds are computed by solving a projected linear program that uses the flow conserving solution generated by the lower bounding problem. These bounding strategies are embedded within a branch‐and‐bound algorithm. The partitioning scheme employed reduces the gap from optimality, inducing a convergent process to a feasible solution that lies within any prescribed accuracy tolerance of global optimality. The approach is illustrated using two standard test problems from the literature. For the larger (Hanoi network) problem a better incumbent than previously reported in the literature is obtained and is proven to be within 0.486% of optimality over the specified feasible domain used for this problem.
Reliability analysis of water distribution networks in consideration of equity, redistribution, and pressure‐dependent demand
Authors: Fujiwara Okitsugu , Li Jun
Published: February 2004

A goal programming model has been developed to analyze the system behavior for the water distribution networks under contingency situations due to failures of pipes and pumps, taking into account three aspects: (1) equity, or sharing inconvenience equally among consumers; (2) redistribution of the network flows to reduce the negative consequences of a failure of one portion on other portions of the network; and (3) consideration of pressure‐dependent demand delivery due to insufficient head, namely, if a nodal head falls below a desired level, the flow delivered to that node is reduced. The first priority of the goal program is to maximize the lowest nodal demand supply ratio (or the ratio of actually delivered demand to the required demand at a node). The second priority is to maximize the system demand supply ratio (or the ratio of actually delivered water to the required total system demand). Link flow directions in the model are not fixed but are determined by a set of criteria. The system behaviors with respect to the three aspects of reliability factors are examined through extensive numerical experiments. The impact of equity requirements on redistribution of network flows, link flow directions, nodal demand supply ratio, and system demand supply ratio when failure events become serious is examined in particular detail. It is found that equity requirements can satisfactorily bring about fair sharing of inconvenience among consumers. The model proposed also suggests that network operations should reverse some link flow directions in order to meet equity requirements under severe contingencies.
An analysis of energy expenditure in Goodwin Creek
Authors: Molnár Peter , Ramírez Jorge A.
Published: February 2004

The local optimality hypothesis that natural river systems adjust their average channel properties toward an optimal state in which the rate of energy dissipation per unit channel area, Pa, is constant throughout the river network is explored on an analysis of Goodwin Creek, Mississippi. River network parameters describing the variation of channel forming and maintaining discharge, channel downstream hydraulic geometry, bed slope, and sediment concentration as a function of cumulative drainage area are estimated from Goodwin Creek data. Optimal channel characteristics that produce constant Pa are determined and superposed onto the digital elevation model‐;extracted river network with reach averaged bed slopes, and the spatial distribution of the energy dissipation rate Pa throughout the network is analyzed. Channel reaches with average energy dissipation rates different from the constant value of the optimal network are identified. We argue that these reaches are potentially unstable relative to the remainder of the network, and that their average channel properties will adjust in the direction of constant Pa. Qualitative statements are made about the direction of this adjustment through differences between the observed and optimal channel widths, and comparisons are made with recent observations of channel change in Goodwin Creek. This energy expenditure analysis suggests that the hypothesis of local optimality can be a useful tool for studying the relative stability and potential channel adjustment of river networks.
Energy dissipation theories and optimal channel characteristics of river networks
Authors: Molnár Peter , Ramírez Jorge A.
Published: February 2004

The effects of energy dissipation on channel properties of a river network are explored. On the basis of a local and global hypothesis of optimality in energy expenditure, we investigate the relationships between channel hydraulic geometry, flow velocity, channel bed slope, and streamflow conditions in optimal river networks. Expressions for the rate of energy dissipation per unit channel area Pa are derived as functions of cumulative drainage area and river network parameters. Optimal channel characteristics are developed that satisfy the hypothesis of local optimality, and provide constant Pa throughout the river network. We show that these optimal channel characteristics are remarkably similar to those of many natural river systems in their downstream hydraulic geometry exponents, channel bed slope scaling, spatial distribution of average flow velocity, boundary shear, resistance to flow, etc. Optimal combinations of channel downstream hydraulic geometry and basin topography were analyzed on data from Goodwin Creek. We found ranges of optimality for the combination of the downstream hydraulic geometry exponent for width of Leopold and Maddock [1953] (0.32 < b < 0.74), and the channel bed slope scaling exponent (−0.65 < z < −0.29), and argue that river networks develop average channel properties within these ranges in order to attain constant Pa throughout the network. We propose that the hypothesis of local optimality is a central principle that explains the average behavior and adjustment of channel characteristics in natural river systems.