bluuebunny/crossref_metadata_2025 huggingface dataset:
Ground‐based radiometric measurements of atmospheric brightness temperature and water contents in Italy
Authors: Barbaliscia F. , Fionda E. , Masullo P. G.
Published: February 2004

This paper presents the results of the analysis carried out of ground‐based zenith measurements of atmospheric brightness temperature acquired by a dual‐channel radiometer at 23.8 and 31.4 GHz at Rome, Italy, uninterruptedly during 4 years, from 1992 to 1996. The cumulative distributions of the atmospheric brightness temperature, as well as of the total water vapor and liquid water contents retrieved via the inversion of radiometric measurements, are presented and discussed. The analysis is performed for various time bases: years, months, and hours of the day, allowing indications of both design parameters and meteorological aspects. Comparison is made of the radiometric data with those calculated on the basis of long‐term radiosonde profiles by means of current literature models. Model‐oriented analysis is also attempted concerning the separate contributions of the two individual water phases and the possibility of deriving the status of the sky from the measured brightness temperature.
Radiometric and structural measurements of snow samples
Authors: Wiesmann Andreas , Mätzler Christian , Weise Thomas
Published: February 2004

The interaction of microwaves with the natural snow cover strongly depends on the complex structure of the snowpack. In order to quantify this dependency, dedicated experiments were performed with homogeneous slabs of dry, natural snow samples measured over a frequency range from 11 to 94 GHz. A new method introduced by Mätzler and Wegmüller [1995] and Weise [1996a] for determining the scattering and absorption behavior of test samples was applied and further developed by application of a multiple scattering model. Homogeneous samples of dry snow were (1) investigated using a set of portable, linearly polarized Dicke radiometers at frequencies of 11, 21, 35, 48 and 94 GHz, (2) characterized by temperature, grain size and shape, density and permittivity, and (3) structurally analyzed by digitized snow sections in order to obtain statistical information of the snow structure i.e. the autocorrelation function. During the winters 1994/1995 and 1995/1996 additional measurements of snow samples were made to extend the variability of the investigated snow types. Up to now, 20 samples, representing alpine snow in winter (that is, without melt metamorphism) have been collected during three winter campaigns. Here, we present the method and the radiative transfer model and show how it can be inverted to obtain scattering and absorption coefficients. A first assessment of the snow sample data is also presented. The results show good agreement between the measured and the theoretical absorption coefficient. The scattering coefficient turns out to be a strong function of frequency and correlation length as expected from Rayleigh scattering. However, distinct differences can be noted.
On the reality of upper mesospheric/lower thermospheric turbulent “eddies”
Authors: Roper R. G.
Published: February 2004

The structure of atmospheric turbulence and its relationship to the refractive index discontinuities responsible for the scattering of radio waves are discussed. Emphasis is placed more on the nature of the intermittent scatterers observed at upper mesospheric/lower thermospheric altitudes than on volume scattering. The preferred model is of transient patches composed of vortex strings. An overview of the methods used to estimate the rate of dissipation of turbulent energy using MF radar data which emphasizes the advantages of imaging Doppler interferometry is presented, together with a review of pertinent laboratory investigations of coherent structures. An attempt is made to remove the contamination by gravity waves from imaging Doppler interferometry fluctuating velocity data. Emphasis is given to the fact that all radar measurements of turbulent intensity to date are upper estimates, not only because of the presence of gravity wave fluctuations contaminating the data, but also because the turbulence itself is not stationary and homogeneous but intermittent in both space and time. The intermittent nature of the turbulence, in which the refractive index discontinuities responsible for the radar backscatter are associated with decaying, homogeneous turbulent coherent structures, is in contrast to the theory of volume scattering, which assumes the radar pulse volume to be partially filled with stationary, homogeneous turbulence.
Modulation instability at the upper hybrid layer in high‐power radio wave ionospheric heating
Authors: Keskinen M. J. , Rodriguez P.
Published: February 2004

A model of the evolution of finite amplitude upper hybrid waves generated at the upper hybrid resonance height during high‐power radio wave ionospheric heating is presented. We show that the threshold for modulation instability can be exceeded for upper hybrid wave amplitudes of the order of a few tens of millivolts per meter and will be excited for scale sizes, perpendicular to the geomagnetic field, of the order of a few tens of electron gyroradii.
Physical modeling of passive polarimetric microwave observations of the atmosphere with respect to the third Stokes parameter
Authors: Kutuza B. G. , Zagorin G. K. , Hornbostel A. , Schroth A.
Published: February 2004

Measurements of upwelling and downwelling rain brightness temperatures show significant differences between horizontal and vertical polarization, which depend on wavelength and rain rate. These measurements are related to the first and second Stokes parameter. Also, the third Stokes parameter of atmospheric microwave emission will have measurable values under certain conditions. A polarimetric model for the description of the microwave emission and scattering by hydrometeors, including all four Stokes parameters, is presented. This model is applied to the scenario of plane layers of ice crystals and rain above a rough surface. The magnitudes of the third Stokes parameter for microwave emission from oriented nonspherical rain drops and for scattering by ice crystals are estimated. It is shown that the third Stokes parameter for rain is dominated by the first azimuthal harmonic of the emission vector. Finally, an algorithm for the computation of polarized brightness temperatures emanating from cylindrical rain cells above a surface is developed.
A multiple phase screen technique for electromagnetic wave propagation through random ionospheric irregularities
Authors: Grimault Christophe
Published: February 2004

In some cases, natural or man made, the ionospheric electron density is highly disturbed and becomes a random medium. Satellite signals propagating through such a medium suffer rapid phase and amplitude variations called scintillations. The coherence time and bandwidth of the channel are therefore reduced, and the fading can reach Rayleigh type in the most severe cases. The design of communication systems able to operate in such conditions requires a precise knowledge of these parameters. The aim of this paper is to present a new numerical technique, based on the multiple phase screens (MPS) approach, which allows the evaluation of the channel characteristics. The method, called MPC, avoids the plane wave hypothesis and is especially designed for upward links, where the electromagnetic wave source may be close to the turbulent medium and the receiver is far away (geostationary satellite case). The source antenna gain pattern is included in the modeling, along with the medium drift speed, which can vary with height. Interesting results show that the scintillation index and scattering loss at the receiver are closely related to the transmitter antenna directivity and tracking precision.
Episodic development of a convergent margin inferred from structures and processes along the southern Chile margin
Authors: Bangs Nathan L. , Cande Steve C.
Published: February 2004

Seismic reflection data acquired in the vicinity of Isla Mocha across the southern coast of Chile image structures formed along the continental margin and reveal an episodic history of accretion, nonaccretion, and possibly erosion. Structures formed at the toe of the continental slope suggest frontal accretion of ¾ to 1 ¾ km of trench fill. Seismic images also reveal that a small accretionary wedge, 20–30 km wide, abuts the truncated continental metamorphic basement that extends seaward from beneath the shelf. The small size of the accretionary wedge on three profiles examined here is not consistent with a long history of accretion with the current deformational style, as current rates of frontal accretion could have accumulated all of the existing accretionary wedge in less than 1–2 m.y. This is a small fraction of convergence history along this margin, and the current accretionary mode has not been consistently maintained in the past. The Isla Mocha region is located between the temperate climate of central Chile and the glacial climate of southern Chile, and climatic conditions in this region have likely fluctuated sufficiently to cause significant variation in trench sediment supply. Accretionary and nonaccretionary or erosional episodes are probably linked to temporal variations in trench sediment thickness, as suggested by observations along the Chile margin. Currently, thick trench sediment correlates with accretion along the southern Chile margin, and thin trench sediment correlates with nonaccretion/tectonic erosion as near the Chile Ridge and from the Juan Fernandez Ridge to northern Chile. The Isla Mocha region also lies 900 – 1000 km north of the Chile triple junction, and the Chile Ridge lies approximately 2000 km to the west and has not yet collided and affected the margin near Isla Mocha. This part of the precollision zone provides an excellent reference to examine the effects of Chile Ridge collision in the development of the Chile margin. The most apparent effect of subduction of the buoyant, young crust of the Chile Ridge is a shallow trench that is nearly devoid of sediment. Consequently, the triple junction is undergoing nonaccretion or erosion, and the accretionary complex near the triple junction remains smaller than to the north or south because the current phase of rapid accretion elsewhere in the trench has bypassed the triple junction region. The interplay of subduction zone processes, such as trench sedimentation and ridge collision, has resulted in an episodic development of the margin and produced a discontinuous record of convergence history within the accretionary wedge.
Estimation of intraplate strain accumulation in the New Madrid seismic zone from repeat GPS surveys
Authors: Weber John , Stein Seth , Engeln Joseph
Published: February 2004

The New Madrid seismic zone (NMSZ), a region within the eastern portion of the North American plate where great earthquakes occurred in 1811–1812, provides a type example of large earthquakes within a relatively stable continental interior. Assessing the scale and causes of deformation in such regions, as well estimation of the recurrence interval for the large earthquakes within them, has long been recognized as an important but challenging issue, for which the advent of space‐based geodesy provides an important new tool. Here we report initial results from two Global Positioning System (GPS) surveys of a geodetic network spanning the New Madrid seismic zone. Because the expected strain signal is small, the data were analyzed in three different ways. First, site velocities were estimated and analyzed for spatial gradients parallel and perpendicular to the trend of the major strike‐slip faults inferred from seismicity. This analysis suggests, but does not require, a few millimeters per year of right‐lateral shear across the southern portion of the seismic zone, consistent with the earthquake focal mechanisms. Second, we divided the network into near‐field subnetworks and found possibly significant shear associated with approximately E‐W shortening within the southern NMSZ and possible N‐S shortening across the left step connecting the presumed strike‐slip faults. Third, we compared the strain observed along individual baselines to that predicted from the results of earlier near‐field surveys which combined GPS and triangulation data. In the southern part of the seismic zone, we found general agreement with the earlier study, although our data suggest lower strain rates. Hence after only 2 years of measurements, the GPS data suggest but do not yet require detectable strain accumulation. However, given that great earthquakes occur in the area and that our results are reasonably consistent with the results of other geodetic studies using different data and with earthquake mechanisms, it seems likely that we are seeing strain accumulation in the southern NMSZ. A simple interpretation of the data as showing about 3 to 5 mm yr−1of right‐lateral fault‐parallel motion implies a 1000 to 3300‐year recurrence for great earthquakes with 5 to 10‐m slip, assuming all the accumulating strain is released seismically. This recurrence interval may be an underestimate, if the observed strains are largely postseismic effects of the 1811–1812 earthquakes, a possibility suggested by the observation that plate‐wide data show less motion across the NMSZ. Future surveys should resolve this issue as the longer measurement spans yield more precise velocity estimates.
Steady infiltration flows with sloping boundaries
Authors: Philip J. R. , Knight J. H.
Published: February 2004

General theorems are established that enable immediate solution of the quasilinear steady infiltration equation for any distribution of line and point sources at or beneath a sloping upper soil surface, or on or above a sloping impermeable base. The required solutions are readily deduced from the known simple solutions for buried line and point sources. Corollary to the theorems, similar relations hold for downslope and cross‐slope flux density components. Illustrative solutions are presented for line and point sources in the various configurations. Distributions of both potential and stream function are mapped for line sources and also for point sources at or beneath a horizontal surface. For other point sources, potential is mapped in the normal plane through the source. For sources beneath a surface, distortion due to the surface is relatively small, even for dimensionless normal source depth as small as 1. On the other hand, for sources above a sloping base, the base strongly skews the distributions of both potential and streamlines. Far downslope the flow is purely (line sources) or primarily (point sources) parallel to the base. Upper bounds exist on total source strength, beyond which a saturated region emerges, perched on a horizontal base. Consistent with earlier results and theorems, physically acceptable steady flows do not exist above the base.
Stochastic analysis of three‐phase flow in heterogeneous porous media: 2. Numerical simulations
Authors: Abdin Alaa E. , Kaluarachchi Jagath J.
Published: February 2004

The first paper of this two‐part series [Abdin and Kaluarachchi, this issue] developed a spectral/perturbation analysis to predict the variability of individual and capillary pressures of three‐phase (water, oil, and air) flow in heterogeneous porous media. The work in this manuscript is an extension of that work to validate the applicability of the perturbation analysis and to study the stochastic behavior of three‐phase flow. The input stochastic variables were soil grain size distribution index, α, and log k where k is the permeability. In this work a one‐dimensional numerical solution was developed to solve the three coupled nonlinear flow equations. The results using three different combinations of input stochastic variables showed good agreement between perturbation and numerical analyses over a wide range of flow conditions. In addition, the results showed a large influence of subsurface heterogeneity on the predicted capillary pressure variability. In general, this variability was highest with the uncorrelated α and log k case followed by deterministic α (stochastic log k) and correlated cases. The results suggest that subsurface heterogeneity is important in predicting three‐phase flow in heterogeneous porous media. Finally, the results of this work can be used as a preliminary step for stochastic analysis of three‐fluid phase flow.
Modeling the spatial variability of subsurface runoff using a topographic index
Authors: Woods Ross A. , Sivapalan Murugesu , Robinson Justin S.
Published: February 2004

We propose a new topographic index for use in regions with rapid subsurface runoff which is spatially variable. By considering field measurements we suggest that the pattern of recharge to the saturated zone is controlled by both the prestorm catchment‐average wetness and the pattern of saturated zone thickness. The major distinguishing assumptions of this index are that (1) the soil lies above an impermeable layer; (2) saturated hydraulic conductivity does not vary with depth; (3) the pattern of recharge can be estimated using a simple nonlinear function of both local and catchment‐average saturated zone thickness. The index predicts patterns of both subsurface runoff and saturated zone thickness: spatial patterns change as catchment wetness varies. Subsurface runoff is predicted to be most uniform when the catchment is wettest, and as the catchment dries out, runoff decreases most quickly at the driest locations in the catchment. This index is able to reproduce significant features of observed spatial patterns of subsurface stormflow for a variety of prestorm conditions and can also be used as the basis for a rainfall‐runoff model.
Simulation of radar reflectivity fields: Algorithm formulation and evaluation
Authors: Anagnostou Emmanouil N. , Krajewski Witold F.
Published: February 2004

A hybrid stochastic physics‐based and polarization‐diverse radar reflectivity simulation procedure for rainfall studies is described. The procedure begins with the generation of two‐dimensional rainfall intensity fields from a space‐time stochastic model with a statistical parametrization of drop‐size distribution. The two‐dimensional fields are complemented with a vertical structure of hydrometeors by choosing a precipitation cloud type model, which results in size, shape, and phase (mixed or single) distribution at discrete elevations. Given these three‐dimensional fields, the sampling volume integration process involved in radar measurements is simulated to give the radar‐observed parameters. Effects such as antenna beam pattern, horizontal and vertical gradients, atmospheric gases, and rain attenuation are represented. The radar observables are corrupted with a random measurement error to represent the radar hardware system noise and other sources of uncertainty. The simulated radar reflectivities are qualitatively evaluated using actual radar data. The simulator is a useful tool for engineers and hydrometeorologists in the study of radar‐rainfall measurement and estimation errors and their effects.
Is dominant use management compatible with basin‐wide economic efficiency?
Authors: Ward Frank A. , Lynch Thomas P.
Published: February 2004

Managing reservoir systems for economic efficiency requires maximizing total economic benefits over all water uses, time periods, and locations. This paper presents results derived from a basin optimization model that solves both multiple use and dominant use management objective functions. Application of the model to New Mexico's Rio Chama basin for the uses of river recreation, lake recreation, and hydropower indicates a negligible difference in system benefits between managing for multiple use and for a dominant use. However, there is a substantial difference in the distribution of water across reservoirs and economic benefits across uses. Results suggest that in basins where nonconsumptive uses are dominant, managers may have more latitude than previously believed in managing for dominant uses while still meeting a larger economic efficiency objective.
A tensiometer for measuring hydraulic potentials on surfaces of porous rock
Authors: Tokunaga Tetsu K.
Published: February 2004

A laboratory method for obtaining tensiometer measurements on surfaces of porous rock and soil is presented. The construction and performance of two versions of the “surface tensiometer,” developed for determining near‐zero values of matric potential on rock surfaces, are described. Laboratory surface tensiometer measurements were made on a natural fracture surface of a Bishop Tuff block equilibrated with a water table boundary set at elevations ranging from −51 to +25 mm relative to the tensiometers. All equilibrium readings were within 10 Pa of ideal values, and most were within 5 Pa. Response times associated with this instrument‐rock system were in qualitative agreement with the matric potential–dependent hydraulic properties of the rock block.
How regional are the regional fluxes obtained from lower atmospheric boundary layer data?
Authors: Sugita Michiaki , Hiyama Tetsuya , Kayane Isamu
Published: February 2004

The contribution of the upwind source area to the surface fluxes determined from lower boundary layer profiles was studied. Use was made of the boundary layer data obtained from a 213‐m meteorological tower and from a tethered sonde, and of surface fluxes from five stations deployed during the 3‐week Tsukuba 92 intensive field experiment whose 16 by 16 km experimental area can be characterized by its generally flat topography and by its complex surface land usages. The profile‐derived regional sensible heat fluxes were compared with the area‐averaged fluxes from the flux data of the surface stations, evaluated for the upwind areas of different sizes from approximately 3 × 10−3 km2 to 70 km2. The best agreement was found for the comparison with the results for the upwind area of around 17 km2. This roughly corresponds to the height to fetch ratio of 200 when one considers the mean surface layer height of 40 m.
Flow to a well of finite diameter in a homogeneous, anisotropic water table aquifer
Authors: Moench Allen F.
Published: February 2004

A Laplace transform solution is presented for the problem of flow to a partially penetrating well of finite diameter in a slightly compressible water table aquifer. The solution, which allows for evaluation of both pumped well and observation piezometer data, accounts for effects of well bore storage and skin and allows for the noninstantaneous release of water from the unsaturated zone. For instantaneous release of water from the unsaturated zone the solution approaches the line source solution derived by Neuman as the diameter of the pumped well approaches zero. Delayed piezometer response, which is significant during times of rapidly changing hydraulic head, is included in the theoretical treatment and shown to be an important factor in accurate evaluation of specific storage. By means of a hypothetical field example it is demonstrated that evaluations of specific storage (Ss) using classical line source solutions may yield values of Ss that are overestimated by a factor of 100 or more, depending upon the location of the observation piezometers and whether effects of delayed piezometer response are included in the analysis. Theoretical responses obtained with the proposed model are used to suggest methods for evaluating specific storage.
Design for an inexpensive continuous digital output water level recorder
Authors: Reedyk S. , Cooke S. , Burchett G. , Prepas E. E.
Published: February 2004

This note introduces a design for a low‐cost continuous digital output water level recorder. The Stowaway™ volt data logger from Onset Computer Corporation is modified to incorporate a steady voltage input. A simple float‐pulley system can be constructed, or the logger can be attached to existing analog recorders. Laboratory and field accuracy tests indicate that the recorder is capable of producing reliable estimates of stage. In‐field accuracy is a function of the float‐pulley system and the choice of accuracy in the electronic components employed in the modification of the data logger.
Global distributions of glacier properties: A stochastic scaling paradigm
Authors: Bahr David B.
Published: February 2004

Many problems in global climate and Earth systems science require knowledge of regional‐ or global‐scale distributions of glacier properties, which includes mass balance, ice velocity, flux, thickness, volume, and surface area, among others. With roughly 160,000 glaciers worldwide, obtaining information on the global probability distributions of most ice properties is expensive and often infeasible. Only surface area distributions are relatively easy to measure, either by direct observation or remote sensing. While other properties are difficult to observe, this work shows that scaling relationships from the continuum dynamics of ice can link the distribution of surface areas to the global and regional distributions of any other continuum property. Some data inventories already exist for constructing reasonable distributions of glacier sizes, and this analysis presents theoretical arguments based on glacier network topologies (similar in concept to river networks) to suggest a power law times an exponential distribution of surface areas (in agreement with the data). Therefore, by using existing data or the theoretical distributions of surface areas, specific distributions for other glacier properties in any region of the world can be constructed. As an example, predictions (up to a scaling constant) are made for the distribution of glacier volumes, characteristic thicknesses, characteristic velocities, and characteristic response times in the Alps.
Radially convergent flow in heterogeneous porous media
Authors: Sánchez‐Vila Xavier
Published: February 2004

We present an analytical solution for apparent effective transmissivity under radially convergent steady state flow conditions, produced by constant pumping from a single well of finite radius, rw. Apparent effective transmissivity, Te, is defined as the value that relates the expected values of flow and head gradient at a certain location. The domain is two‐dimensional, of annular shape, and the size of the pumping well is explicitly taken into account. The solution for the steady state heads is obtained by solving the perturbed flow equation and substituting it into Darcy's law to obtain a consistent second‐ order expansion for Te. We show that apparent effective transmissivity is a scalar for any choice of isotropic covariance model, with an expression given in integral form. Our main result is that Te in a heterogeneous, statistically isotropic random field, under radial steady state flow conditions, is a monotonie increasing function of r (distance from the well) that rises from the harmonic mean of the point transmissivity values (close to the well) and tends asymptotically towards the geometric mean (far from the well). The asymptotic value is reached at a distance of a few integral scales (1.5–2 for the Gaussian model and 3–5 for the exponential one). The apparent effective transmissivity versus normalized r curves are in excellent agreement with previously published numerical work carried out using Monte Carlo method.
Potential theory for dual‐depth subsurface drainage of ponded land
Authors: Kirkham Don , van der Ploeg R. R. , Horton Robert
Published: February 2004

Dual‐depth subsurface drainage is considered to be more effective in removing excess water from soil than single‐depth drainage, but this problem has not been analyzed in detail. Therefore, assuming that uniform, water‐saturated soil covered by ponded water and overlying an impervious barrier is drained by equally spaced, alternating deep circular drain tubes, existing potential flow theory for a single‐depth drainage system was extended. Sample calculations with the newly derived equations show that a dual‐depth subsurface drainage system can be highly effective to remove excess water from soil. For example, a relative drain discharge of 160% is calculated when new drain tubes, added at the 0.60 m depth, are placed midway between the original drain tubes, which are 25 m apart and at the 1.20 m depth. In this calculation we have assumed that the impervious layer is at the 3.0 m depth, the radius of the tubes is 0.05 m, the soil hydraulic conductivity is 1 m/d, and the thickness of the ponded water is 0.0 m. For the same conditions, but with the additional tubes at the 1.20 m depth (same depth as original tubes), the relative drain discharge becomes nearly 200%, and with the additional tubes at the 2.40 depth (1.20 m below original tubes) it is more than 250%. When the impervious layer is at a greater depth and when the original drain spacing is more than 25.0 m, the relative drain discharge becomes even larger. The effectiveness of the dual‐depth tube system becomes particularly large, if the second tube system is placed below the level of the first one.
Determining permeability of tight rock samples using inverse modeling
Authors: Finsterle Stefan , Persoff Peter
Published: February 2004

Data from gas‐pressure‐pulse‐decay experiments have been analyzed by means of numerical simulation in combination with automatic model calibration techniques to determine hydrologie properties of low‐permeability, low‐porosity rock samples. Porosity, permeability, and Klinkenberg slip factor have been estimated for a core plug from The Geysers geothermal field, California. The experiments were conducted using a specially designed permeameter with small gas reservoirs. Pressure changes were measured as gas flowed from the pressurized upstream reservoir through the sample to the downstream reservoir. A simultaneous inversion of data from three experiments performed on different pressure levels allows for independent estimation of absolute permeability and gas permeability which is pressure‐dependent due to enhanced slip flow. With this measurement and analysis technique we can determine matrix properties with permeabilities as low as 10−21 m2. In this paper we discuss the procedure of parameter estimation by inverse modeling. We will focus on the error analysis, which reveals estimation uncertainty and parameter correlations. This information can also be used to evaluate and optimize the design of an experiment. The impact of systematic errors due to potential leakage and uncertainty in the initial conditions will also be addressed. The case studies clearly illustrate the need for a thorough error analysis of inverse modeling results.
Solute channeling in unsaturated heterogeneous porous media
Authors: Birkholzer Jens , Tsang Chin‐Fu
Published: February 2004

Numerical simulations have been performed to study flow and solute transport phenomena in strongly heterogeneous, variably saturated porous media. Different saturation scenarios were applied varying from fully saturated to highly unsaturated conditions, corresponding to different infiltration rates into the soil. It was found that the solute travels along preferred flow paths, which may be called channels. The degree of channeling, the location of channels, and the hydraulic properties along channels are a function of the mean saturation in the flow domain. Strong channeling effects were obtained in both fully saturated and in low‐saturation cases. At intermediate saturation values, channeling effects are less significant, and the system exhibits a more homogeneous flow pattern. The dispersion of solutes as shown in the calculated tracer breakthrough curves essentially reflects the degree of channeling and thus is saturation dependent; in cases when flow channeling is less evident we observe much smaller dispersion than in cases with strong channeling. The hydraulic properties of the channels appeared to be an invariant of the actual location and geometry, indicating that they may be an intrinsic characteristic of the soil heterogeneity and the water saturation.
Biogeochemistry of a cirque‐lake landscape: An interdisciplinary study in a catchment of the northern Black Forest, Germany
Authors: Sommer Michael , Thies Hansjörg , Kolb Eckart , Bächle Herbert , Stahr Karl
Published: February 2004

The pedological analysis of the soil continuum in a catchment can yield substantial insight in flow paths, transport processes, and possible linkages between terrestrial and aquatic ecosystems. In an interdisciplinary study we investigated precipitation, lake tributaries, and soils of three sandstone‐dominated subcatchments of a dystrophic cirque lake during 1989 and 1990. The chemistry of tributary 1 is characterized by relatively higher pH values, positive alkalinity at base flow, higher concentrations of Ca, Mg, and K, and lower dissolved organic carbon (DOC). It does not fit to the chemistry of the very acid, leached, podzolized soils in its subcatchment (weak linkage). The dominance of base flow and lower intra‐annual variations in discharge and temperature further confirm the conclusion of a dominating vertical flow path of soil water into the regolith and bedrock zone with substantial buffering in that zone (groundwater flow). Tributary 2 shows the lowest pH values and the highest concentrations of DOC, Fe, Al, and P, which fits very well the chemistry of the very acid, leached, permanently wet soils of its catchment (strong linkage). The dominance of storm flow water with high intra‐annual variations in discharge corresponds with the high soil moisture and prevalent lateral flow path of water in the soil cover (lateral subsurface flow). Tributary “mix” behaves intermediate between tributaries 1 and 2 but is more similar to that of tributary 1. This is due to the dominance of podzolized over reductomorphic soils in the subcatchment. Lateral transport of matter can be inferred from the soil pattern in all catchments, but its relevance for lake inlet chemistry depends on the existence of downslope immobilization zones.
On the Brutsaert temperature roughness length model for sensible heat flux estimation
Authors: Cahill Anthony T. , Parlange Marc B. , Albertson John D.
Published: February 2004

The scalar roughness length for temperature, z0h, is necessary to estimate the sensible flux from atmospheric surface layer similarity theory in conjunction with skin temperature measurements. A theoretical relationship for z0h as a function of the roughness Reynolds number z0+ which was developed by Brutsaert [1975] for rough‐bluff surfaces is often used to link infrared skin temperature measurements to atmospheric temperature measurements. Measurements of sensible heat flux and temperature at two semiarid sites are used to evaluate and test the temperature roughness length model coefficients. Consideration of the measurement error is important to derive an accurate set of coefficients. These new field‐based coefficients correct for some of the underprediction of sensible heat flux at high flux rates that occurred with past formulations.
Design of a Piezometer Network for estimation of the sample variogram of the hydraulic gradient: The role of the instrument
Authors: Conwell P. M. , Silliman S. E. , Zheng L.
Published: February 2004

The process of designing a piezometer network for estimating the sample variogram of the hydraulic gradient is used to illustrate one strategy for designing a sampling network which is both appropriate for the estimation of spatial statistics and efficient in terms of the measurement instrument. Constraints which impacted this design can be broken into three categories: (1) constraints discussed by previous authors and related to increasing confidence in the estimate of the sample variogram, (2) new constraints related to the spatial distribution of sample location for the purpose of estimating the sample variogram, and (3) constraints related to the measurement instrument. After assessing a number of sampling strategies, including uniform grids, randomized grids, various geometric patterns, and scaled sampling patterns, an acceptable design for the present application was developed from a scaled sampling pattern which was modified to utilize the instrument more efficiently. In this situation the final design could not have been established except through consideration of both the statistics to be derived from the sampling effort and the instrument used to obtain the measurements.
Two‐phase flow infiltration equations accounting for air entrapment effects
Authors: Wang Zhi , Feyen Jan , Nielsen Donald R. , van Genuchten Martinus T.
Published: February 2004

Water infiltration into the unsaturated zone is potentially affected by air compression ahead of the wetting front. Analytical infiltration equations accounting for air compression, air counterflow, and flow hysteresis in a porous medium were derived on the basis of the Green and Ampt [1911] assumptions. Air compression ahead of the wetting front was predicted using the perfect gas law. The capillary pressure at the wetting front was found to vary between the dynamic water‐bubbling value and the dynamic air‐bubbling value of the material. These equations, accounting also for the effects of macropores near the soil surface, turned out to be simpler than the traditional Kostiakov [1932] and the Philip [1957a, b, c, d] equations. The equation parameters are physically meaningful and can be readily obtained from field measurements of the natural saturated hydraulic conductivity and soil water retention or pressure infiltrometer data. Experimental testing showed that the equations are reasonably accurate.
Control models for hydroelectric energy optimization
Authors: Georgakakos Aris P. , Yao Huaming , Yu Yongqing
Published: February 2004

The optimization of hydroelectric energy is addressed via a new multilevel control model, which is used to derive estimates of system firm energy with or without dependable capacity commitments. The model is able to optimize individual turbine operation as well as overall system operation on an hourly and daily basis. The mechanism by which the various models are linked and exchange information ensures full compatibility among the control levels and guarantees operational consistency across all timescales. The model is applied to the Lanier‐Allatoona‐Carters system, located in the southeastern United States, and is suitable for planning as well as operational applications.
Temporal scales and hydrological regimes: Implications for flood frequency scaling
Authors: Robinson Justin S. , Sivapalan Murugesu
Published: February 2004

This paper investigates the interactions among storm, within‐storm, between‐storm, and seasonal variabilities of rainfall and catchment response time and how these interactions can help identify different hydrological regimes. Using the theoretical framework provided by a simple linear rainfall‐runoff model and intuitive reasoning, five hydrological regimes, ranging from very fast to very slow, are identified on the basis of two dimensionless ratios of the constituent timescales. For each regime, the paper addresses the question of how the interactions between the timescales in rainfall and in the runoff response manifest in the flood peak response and in the shape of the flood frequency curve, and the resulting implications for the scaling of the flood frequency curve between catchments. It is found that, for example, in fast regimes, within‐storm patterns are the important determinant of flood peaks, while in slow regimes multiple storms and seasonality are critical. The latter result is verified by means of simulations with a derived flood frequency model for an actual catchment, Salmon Creek, in Western Australia. Slow regimes are characterized by low values of the coefficient of variation, CV[Qp], of the flood peaks, while fast regimes are characterized by higher values of CV[Qp]. Analysis of the simulation results on the Salmon catchment, which belongs to the slow regime and exhibits a nonlinear rainfall‐runoff response, also shows that nonlinearity in catchment response substantially increases CV[Qp] and may even dominate the scaling of CV[Qp] with catchment size. The scaling exponent in the relationship between mean annual flood and catchment size, for a linear runoff response, is higher for slow catchments and lower for fast catchments, and in both cases it remains constant with catchment area. A major conclusion of the paper is that the combined effects of within‐storm patterns, multiple storms, and seasonality have an important control on the observed scaling behavior in empirical flood frequency curves, each being dominant over a different range of catchment sizes.
Adjusting benefits transfer values for inflation
Authors: Eiswerth Mark E. , Shaw W. Douglass
Published: February 2004

This paper analyzes assumptions that are implicitly made in updating estimates of nominal values for environmental goods produced by previous valuation studies, especially adjustments made through use of the consumer price index (CPI). The paper illustrates that the underlying form of preferences for the selected values from a past study may have a significant influence on the updated environmental values. We show why care is necessary in updating past welfare or value estimates in the face of changes in the demand and supply for environmental amenities when using the CPI.
Interpretation of two‐region model parameters
Authors: Griffioen J. W. , Barry D. A. , Parlange J.‐Y.
Published: February 2004

Apart from advection and diffusion/dispersion, other physical and chemical processes can affect the movement of solute through a porous medium. The classical advection‐dispersion equation does not usually model adequately the breakthrough curves resulting from such effects. The two‐region model (TRM) is an attempt to model succinctly and easily the effects of physical and/or chemical nonequilibrium. Physical nonequilibrium is the focus of this paper. The additional parameters appearing in the TRM are the ratio of mobile to total pore fluid, β, and the apparent transfer rate of the solute between the mobile and the immobile regions, α. Meaning is ascribed to these parameters by identifying the various ways in which physical nonequilibrium can arise. An examination of published data shows that the dominant trend is a linear variation of the transfer rate α with mobile fluid velocity Vm. In order to develop an approach incorporating all porous media types, timescales of solute transport are identified and compared to the mass transfer timescale (1/α). It was found that the local advection timescale best characterizes the mass transfer timescale. Two trends were observed for the mobile water fraction β. For aggregated/saturated porous media, β was found to be constant or decreased with increasing pore water velocity, while for partially saturated soils, β was constant or increased with increasing moisture content.
Multifractal analyses of hydraulic conductivity distributions
Authors: Liu H. H. , Molz F. J.
Published: February 2004

The concept of a universal multifractal, a generalization of a monofractal, is a recently developed scaling model for natural phenomena characterized by irregularity. Presented herein is an effort to use universal multifractal concepts to deal with spatial variations of hydraulic conductivity K, which have a significant effect on contaminant transport in the subsurface. Structure function analyses of four K data sets show that some vertical variations of K display multifractal structures, while others are consistent with monofractal behavior. In order to make multifractal concepts more useful, multifractal noise is introduced and defined as the increments of a multifractal. It is concluded that the multifractal formalism of Schertzer and Lovejoy [1987] has provided a rather general approach for modeling In K variations in the vertical. With the exception of horizontal variations of the Borden data, all results fell within the domain of universal multifractal behavior, which includes the monofractal case. Parameters were well‐defined in an empirical sense and easy to calculate, indicating a robust formalism. Results were consistent with the recent finding of Liu and Molz [1997, also Non‐Gaussian and scale‐variant behavior in hydraulic conductivity distributions, submitted to Water Resources Research, 1997, hereinafter referred to as submitted paper] that K variations display increasing heterogeneity at decreasing scales.
Effect of colloids on volatile contaminant transport and air‐water partitioning in unsaturated porous media
Authors: Choi Heecheul , Corapcioglu M. Yavuz
Published: February 2004

The presence of mobile colloids in subsurface environments can enhance subsurface contaminant migration by reducing retardation effects. We developed a mathematical model based on mass balance equations to describe the transport and fate of colloidal particles and a volatile contaminant in an unsaturated porous medium. When colloids are present in an unsaturated medium, the system representation include four phases: an aqueous phase, a carrier phase, a stationary solid matrix phase, and the air phase. Colloidal mass transfer between the aqueous and solid matrix phases and between the aqueous phase and the air‐water interface, and the contaminant mass transfer between aqueous and colloidal phases and between the aqueous phase and the air‐water interface are represented by kinetic expressions. Nondimensionalized governing equations are solved to analyze colloid and contaminant transport in an unsaturated column. A sensitivity analysis of the transport model was utilized to assess the effects of several parameters on model behavior. Results show that the effect of colloids on a volatile contaminant transport is highly dependent on the properties of the contaminant and the colloidal surfaces. The presence of an air‐water interface retards the volatile contaminant migration because of mass transfer rate across the air‐water interface, offsetting the facilitating effect of colloids. We tested the effects of varying Henry's constant and the contaminant mass transfer across the air‐water interface. The equilibrium assumption for the contaminant mass transfer across the air‐water interface may be valid for volatile contaminants with dimensionless Henry's constants less than one. As Henry's constant increases, the contaminant mass transferred across the air‐water interface is approximately 20% larger at 46% air saturation than at 15% air saturation because of a larger volume of air. At 15% air saturation, air phase contaminant reaches the equilibrium concentration at about 18 pore volumes with a large dimensionless Henry's constant (H+=). However, at 46% air saturation, it takes over 20 pore volumes to reach the equilibrium concentration, even with a smaller Henry's constant (H+quals;1).
Controls of strength and rate of downstream fining above a river base level
Authors: Hoey Trevor B. , Ferguson Robert I.
Published: February 2004

We report sensitivity tests on a numerical model of the development of downstream fining by size‐selective transport and deposition above a base level in a gravelbed river with no lateral inputs of water or sediment. Strong fining requires deposition mainly to the surface; otherwise, its amount and streamwise distribution are not highly sensitive to any single factor but vary somewhat with hiding factor, excess shear stress, and bed sorting. Low initial concavity inhibits fining, but different higher concavities generate fairly similar fining profiles. Lower sediment supply leads to a coarser bed with less fining, but there is no simple relationship between fining and aggradation rate. The rate of development of fining is sensitive to all these factors but is always rapid initially, followed by a far slower approach towards final equilibrium. Surface grain size adjustment is potentially an important degree of freedom in river response to any environmental change or human impact which causes overloading.