bluuebunny/crossref_metadata_2025 huggingface dataset:
Testing Part‐Whole Valuation Effects in Contingent Valuation of Instream Flow Protection
Authors: Brown Thomas C. , Duffield John W.
Published: February 2004

A review of studies of part‐whole valuation effects in contingent valuation highlights the difficulty of distinguishing part‐whole bias from the effect of substitution among goods. A contingent valuation of instream flow preservation indicates that respondents with more information about substitutes were more sensitive in their valuations to the number of rivers protected than were respondents with less information. These results, in combination with those of other studies of part‐whole valuation effects, suggest that contingent valuation researchers must design guidelines for deciding what information about substitutes should be presented to respondents and how that information should be presented.
On the relative roles of hillslope processes, channel routing, and network geomorphology in the hydrologic response of natural catchments
Authors: Robinson Justin S. , Sivapalan Murugesu , Snell John D.
Published: February 2004

We consider catchment hydrologic response as if determined from the two independent processes of hillslope and channel network transport, operating across all the hillslopes and stream channels forming a catchment. This raises a number of interesting questions. Which process response characterizes a catchment's response? What governs the importance of one process over another? Is catchment response linear and time invariant, despite inherent nonlinearity in the runoff transport processes? Such questions, fundamental to an understanding of the nature of catchment response, are examined in this paper. We use a theoretical framework provided by geomorphology‐based models of runoff routing to examine the hydrologic response over a range of catchment sizes. We demonstrate the effects of catchment size upon the relative roles of hillslope processes, channel routing, and network geomorphology in the hydrologic response of natural catchments. Motivated by the concept of geomorphological dispersion, we parameterize these processes in terms of catchment wave celerity and a catchment dispersion coefficient. We show that these catchment parameters vary with catchment size and provide insights into the nonlinearity of catchment response and the relative roles of the constituent processes.
Processes Controlling the Chemistry of Two Snowmelt‐Dominated Streams in the Rocky Mountains
Authors: Campbell Donald H. , Clow David W. , Ingersoll George P. , Mast M. Alisa , Spahr Norman E. , Turk John T.
Published: February 2004

Time‐intensive discharge and chemical data for two alpine streams in the Loch Vale watershed, Colorado, were used to identify sources of runoff, flow paths, and important biogeochemical processes during the 1992 snowmelt runoff season. In spite of the paucity of soil cover the chemical composition of the streams is regulated much as in typical forested watersheds. Soils and other shallow groundwater matrices such as boulder fields appear to be more important in controlling surface‐water chemistry than their abundance would indicate. The chemical composition of the major source waters (usually thought of as end‐members whose chemical composition is relatively constant over time) changes at the same time that their mixing ratio in streams changes, confounding use of end‐member mixing models to describe stream‐water chemistry. Changes in the chemical composition of these source waters are caused by the ionic pulse of solutes from the snowpack and the small size of the shallow groundwater reservoir compared to the volume of snowmelt passing through it. The brief hydrologic residence time in the shallow groundwater indicates that concentrations of most dissolved constituents of stream water were controlled by fast geochemical processes that occurred on timescales of hours to days, rather than slower processes such as weathering of primary minerals. Differences in the timing of snowmelt‐related processes between different areas of the watershed also affect the stream‐water chemical composition. Cirque lakes affect discharge and chemical composition of one of the streams; seasonal control on stream‐water NO3 and SiO2 concentrations by diatom uptake in the lakes was inferred. Elution of acidic waters from the snowpack, along with dilution of base cations originating in shallow groundwater, caused episodes of decreased acid‐neutralizing capacity in the streams, but the streams did not become acidic.
Use of a Reactive Gas Transport Model to Determine Rates of Hydrocarbon Biodegradation in Unsaturated Porous Media
Authors: Baehr Arthur L. , Baker Ronald J.
Published: February 2004

A mathematical model is presented that simulates the transport and reaction of any number of gaseous phase constituents (e.g. CO2, O2, N2, and hydrocarbons) in unsaturated porous media. The model was developed as part of a method to determine rates of hydrocarbon biodegradation associated with natural cleansing at petroleum product spill sites. The one‐dimensional model can be applied to analyze data from column experiments or from field sites where gas transport in the unsaturated zone is approximately vertical. A coupled, non‐Fickian constitutive relation between fluxes and concentration gradients, together with the capability of incorporating heterogeneity with respect to model parameters, results in model applicability over a wide range of experimental and field conditions. When applied in a calibration mode, the model allows for the determination of constituent production/consumption rates as a function of the spatial coordinate. Alternatively, the model can be applied in a predictive mode to obtain the distribution of constituent concentrations and fluxes on the basis of assumed values of model parameters and a biodegradation hypothesis. Data requirements for the model are illustrated by analyzing data from a column experiment designed to determine the aerobic degradation rate of toluene in sediments collected from a gasoline spill site in Galloway Township, New Jersey.
Field‐based determination of air diffusivity using soil air and atmospheric pressure time series
Authors: Rojstaczer Stuart , Tunks John P.
Published: February 2004

Air diffusivity in two zones over a 4.6‐m interval of the unsaturated zone was determined through analysis of atmospheric pressure and soil air pressure time series. Regression analysis was used to calculate the ratio of amplitudes (admittance) and phase lag between these series at diurnal and semidiurnal frequencies. The admittance for each of the monitoring zones was close to unity for both frequencies. Phase lags between the two time series were statistically equivalent to zero at the diurnal frequency but were as large as 20° ± 7° at the semidiurnal frequency. The phase lag at diurnal and semidiurnal frequencies for each zone was compared to a diffusional model of soil air pressure response to atmospheric loading. From this comparison a composite air diffusivity was determined for each zone. The absence of large variability in air diffusivity and the trends in phase shift with depth suggest that macropores or fractures propagate through a clay layer at a depth of 0.5–1.2 m. The length of the time series (110 days) allowed for the examination of the magnitude of temporal changes in phase shift and air diffusivity. Temporal and spatial trends in phase lag are smaller than the error bounds in the phase estimates. Air diffusivity determined from the entire time record deviated only slightly from the average diffusivity determined from the analysis of a sequence of partial records.
Colloid‐facilitated contaminant transport in discretely fractured porous media: 2. Fracture network examples
Authors: Ibaraki M. , Sudicky E. A.
Published: February 2004

Numerical simulations of colloid‐facilitated contaminant transport in fractured porous media were performed to examine the influence of mobile colloids on contaminant migration through a network of fractures. Simulations involving transport through fracture networks in a clay and a sandstone rock indicate that colloid‐facilitated contaminant transport can be an important factor leading to the rapid exceedance of water quality standards at large distances from the contaminant source. If the colloids are highly mobile in open fractures and there is a strong affinity for a reactive contaminant to remain adsorbed onto them, then low but environmentally significant contaminant concentration levels can quickly propagate through an interconnected network of fractures. The total concentration plumes that are produced are highly irregular in regions in advance of the zone of bulk aqueous phase contaminant transport. Because of this feature, colloid‐enhanced solute transport is likely to increase prediction uncertainty compared to the case when colloids are absent because field data on fracture network interconnectivity, aperture values, and values of parameters such as colloid filtration coefficients in the fractures are typically lacking.
A Geostatistical Approach to the Conditional Estimation of Spatially Distributed Solute Concentration and Notes on the Use of Tracer Data in the Inverse Problem
Authors: Ezzedine Souheil , Rubin Yoram
Published: February 2004

This paper presents a theoretical framework for deriving the moments of the concentration, based on the Lagrangian approach and using a stochastic framework, conditional to measurements of conductivity and hydraulic head. The method consists of deriving the spatial correlations between concentration and travel time and hydrologic variables such as the conductivity and the hydraulic head. These correlations allow the conditioning of the moments of the concentration on measurements. By conditioning the concentration the uncertainty associated with its estimation can be reduced substantially. Consequently, difficulties associated with estimation of the extent of contamination can be alleviated. The theoretical framework and derivations may also be used to condition the moments of the conductivity on tracer data such as concentrations, travel times, and displacements. An application of such an approach would require a configuration of sources and samplers. We show that measured concentration is inferior to travel time and displacements in terms of efficient conditioning.
Steady State Groundwater Flow Simulation With Imprecise Parameters
Authors: Dou Chunhua , Woldt Wayne , Bogardi Istvan , Dahab Mohamed
Published: February 2004

A methodology based on fuzzy set theory is developed to incorporate imprecise parameters into steady state groundwater flow models. In this case, fuzzy numbers are used to represent parameter imprecision. As such, they are also used as a measure for the uncertainty associated with the hydraulic heads due to the imprecision in the input parameters. The imprecise input parameters may come from indirect measurements, subjective interpretation, and expert judgment of available information. In the methodology, a finite difference method is combined with level set operations to formulate the fuzzy groundwater flow model. This fuzzy modeling technique can handle imprecise parameters in a direct way without generating a large number of realizations. Two numerical solution methods are used to solve the fuzzy groundwater flow model: the groundwater model operator method proposed in this methodology and the iterative algorithm based on conventional interval arithmetics. The iterative method is simple but may overestimate the uncertainty of hydraulic heads. The groundwater model operator method not only provides the hull of the solution set for the hydraulic heads but also considers the dependence of hydraulic head coefficients which are functions of imprecise parameters. Sensitivity analysis shows that the dependence of hydraulic head coefficients has a critical impact on the model results, and neglecting this dependence may result in significant overestimation of the uncertainty of hydraulic heads. A numerical model based on the methodology is tested by comparing it with the analytical solution for a homogeneous radial flow problem. It is also applied to a simplified two‐dimensional heterogeneous flow case to demonstrate the methodology.
New manuscript guidelines for the reporting of stable hydrogen, carbon, and oxygen isotope ratio data
Authors: Hornberger George M.
Published: February 2004

In accordance with recommendations by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry [IUPAC, 1994; Coplen, 1994], Water Resources Research requests that authors (in all cases where feasible) (1) discontinue reporting isotopic abundances relative to SMOW (standard mean ocean water) and PDB (Peedee belemnite), (2) express hydrogen isotopic ratios of all substances relative to VSMOW (Vienna standard mean ocean water) on a normalized scale such that the δ2H of SLAP (standard light antarctic precipitation) relative to VSMOW is −428‰, (3) express carbon isotopic ratios of all substances relative to VPDB (Vienna Peedee belemnite) on a scale defined by adopting a δ13C value of +l.95‰ for NBS 19 carbonate relative to VPDB, (4) express oxygen isotopic ratios relative to either VSMOW or VPDB on a normalized scale such that the δ18O of SLAP is −55‰ relative to VSMOW, and (5) indicate values of isotopic fractionation factors if isotopic abundances of a mineral or compound depend upon such a factor.
Introduction to special section: Dreiss Memorial Special Section
Authors: Hornberger George M. , Anderson Mary P.
Published: February 2004

On December 14, 1993, Shirley Dreiss died in a car crash while driving to the San Francisco airport. In the ensuing weeks the news spread through the hydrological community accompanied by profound shock and sadness. We all lost a colleague, and many of us also lost a friend. At the time of her death, Shirley was a professor of hydrogeology and chair of the Department of Earth Sciences at the University of California at Santa Cruz. She was only 44 years old and in the prime of her career.
Flux and Resident Injection in Gaseous Advection Experiments
Authors: Gimmi T. , Flühler H.
Published: February 2004

The occurrence of gaseous pollutants in soils has stimulated many experimental activities, including forced ventilation in the field as well as laboratory transport experiments with gases. The dispersion coefficient in advective‐dispersive gas phase transport is often dominated by molecular diffusion, which leads to a large overall dispersivity γ. Under such conditions it is important to distinguish between flux and resident modes of solute injection and detection. The influence of the inlet type on the macroscopic injection mode was tested in two series of column experiments with gases at different mean flow velocities υ. First we compared infinite resident and flux injections, and second, semi‐infinite resident and flux injections. It is shown that the macroscopically apparent injection condition depends on the geometry of the inlet section. A reduction of the cross‐sectional area of the inlet relative to that of the column is very effective in excluding the diffusive solute input, thus allowing us to use the solutions for a flux injection also at rather low mean flow velocities υ. If the whole cross section of a column is exposed to a large reservoir like that of ambient air, a semi‐infinite resident injection is established, which can be distinguished from a flux injection even at relatively high velocities υ, depending on the mechanical dispersivity of the porous medium.
Application of Fractal Techniques to the Comparative Evaluation of Two Methods of Extracting Channel Networks from Digital Elevation Models
Authors: Ichoku Charles , Karnieli Arnon , Verchovsky Irina
Published: February 2004

The extraction of channel networks from digital elevation models was carried out using two different techniques: the “flow accumulation method” (which is based on the now almost traditional steepest descent flow routing) and the “multilevel skeletonization method“ (which is based on curvatures in contours). Series of networks representing the same drainage basin were extracted with each of the methods using different extraction thresholds. Various stream ratios and fractal dimensions were determined from these networks based on three different hierarchical models. The study shows that for each extraction method, all ratios irrespective of hierarchical model exhibit similar variation with respect to extraction threshold. On the other hand, for the flow accumulation method of extraction, the different types of fractal dimensions vary in different ways with extraction threshold while in the case of the multilevel skeletonization method all the fractal dimensions decrease as extraction threshold increases. We attribute this difference in the behavior of fractal dimensions to the difference in approach between the two methods of extraction. Apparently the multilevel skeletonization method employs a more natural scheme.
Fuzzy Learning Decomposition for the Scheduling of Hydroelectric Power Systems
Authors: Saad M. , Bigras P. , Turgeon A. , Duquette R.
Published: February 2004

This paper presents a nonlinear multivariable fitting model to decompose the optimal policies obtained by dynamic programming of a unique aggregated reservoir. The nonlinear functions are generated using radial basis functions (RBF) neural networks. In this method the potential energy of all the reservoirs in the hydropower system is added to form one equivalent reservoir. The operating policy of the equivalent reservoir is determined by stochastic dynamic programming, and finally the operating rules of each reservoir are determined using RBF neural networks. To improve the multivariable representation of the data, a series of piecewise RBF neural networks is determined using clustering analysis. A fuzzy clustering approach is used to determine the RBF's parameters. This approach has the advantages of being fast and simple to implement with well‐established convergence properties. It also has a good representation of the covariance matrix, since all the data belong to all the classes at the same time with different membership grades. A comparison with the back propagation learning and principal components techniques is also reported for Québec's La Grande River installations. As a result, the proposed approach gives satisfactory operating rules compared with principal component analysis, and the CPU time is reduced by a factor of 15 to 20 compared with the back propagation technique.
Distribution and Variability of 7Be in Soils Under Different Surface Cover Conditions and its Potential for Describing Soil Redistribution Processes
Authors: Wallbrink P. J. , Murray A. S.
Published: February 2004

Measurements of 7Be in soils can be used to indicate movement of topsoil, and this study aims to contribute to this technique by examining 7Be in soils under a range of conditions. The penetration and areal concentration of 7Be have been measured in bare soil, grassland, and eucalypt forest and compared with total measured fallout. Inventories in the bare soil decreased progressively from 64 to 46% of total fallout over the sampling period, probably owing to a decrease in infiltration capacity. This may have an effect on the interpretation of 137Cs inventories under similar conditions. For grassed soil, average inventories were 96–142% of total fallout; for eucalypt litter plus soil, inventories were 73–95%. Natural variability of areal concentration of the nuclide was calculated to be about 20% (relative standard deviation), irrespective of soil type and/or surface cover. However, soil disturbance following logging operations increased variability to about 50%, even after more than 7 half‐lives of 7Be had elapsed. Penetration could be approximated by an exponential in bare soil and in eucalypt forest soil without litter, and average penetration half depths (Ph) in these soils were calculated to be 0.7 and 3.4 mm, respectively. Beryllium 7 concentration was found to increase as particle size decreased. The nuclide was not found below 20 mm depth in any soil or surface cover condition, thus confirming its utility in qualitative models that infer erosion processes by its use as a tracer of surface soil.
Stochastic Interpolation of Aquifer Properties Using Fractional Lévy Motion
Authors: Painter Scott
Published: February 2004

This paper describes a new technique for conditional simulation of aquifer properties in unobserved regions. The technique utilizes a recently introduced model for heterogeneity based on the Lévy‐stable family of probability distributions to achieve a higher degree of realism than is possible with Gaussian‐based techniques. Specifically, permeability and porosity variations are modeled using fractional Lévy motion. A new algorithm for producing fractional Lévy motion conditioned to match known data is introduced. Two‐dimensional simulations using actual permeability measurements as input demonstrate that this algorithm produces random fields with the specified properties. Simulations using a subset of a detailed permeability map of an outcrop as input illustrate how the new method can be used to estimate important flow and transport properties and to quantify uncertainties in these estimates.
Stream and Pseudopotential Functions in Visualizing Groundwater Flow and Transport Processes
Authors: Matanga George B.
Published: February 2004

Scientific visualization is increasingly being applied in many large‐scale groundwater modeling efforts as an effective means of presentation and interpretation of model results. An interpolation or statistical approach is applied to develop three‐dimensional spatial distributions of geologic, hydraulic, and chemical data from a model or field measurements. The distributions become the basis for evaluating spatial variation of data. The evaluation is accomplished by displaying data in the form of isosurfaces of values of data Or as contours of data on a surface or plane. This approach of analyzing data is known as data visualization. In addition to data visualization, some of the problems encountered in groundwater hydrology require visualization of groundwater flow and transport processes. Display of hydraulic and chemical data for analysis of groundwater flow and transport processes is herein referred to as process visualization. In both data and process visualization, hydraulic and chemical data are displayed as color contours or isolines on surfaces. However, in data visualization the surface on which data are displayed may be oriented in any direction, whereas in process visualization the surfaces need to be tangential or orthogonal to the direction of groundwater flow. In three‐dimensional groundwater flow, stream surfaces and pseudopotential surfaces are tangential and orthogonal, respectively, to the direction of groundwater flow. Therefore stream and pseudopotential surfaces provide natural platforms on which to visualize groundwater flow and transport processes. To demonstrate application of stream and pseudopotential surfaces in process visualization, the three‐dimensional groundwater flow beneath the Borden Landfill is considered.
Scale Dependence of Soil Permeability to Air: Measurement Method and Field Investigation
Authors: Garbesi Karina , Sextro Richard G. , Robinson Allen L. , Wooley John D. , Owens Jonathan A. , Nazaroff William W.
Published: February 2004

This work investigates the dependence of soil permeability to air on sampling scale in near‐surface unsaturated soils. A new dual‐probe dynamic pressure technique was developed to measure permeability in situ over different length scales and different spatial orientations in the soil. Soils at three sites were studied using the new technique. Each soil was found to have higher horizontal than vertical permeability. Significant scale dependence of permeability was also observed at each site. Permeability increased by a factor of 20 as sampling scale increased from 0.1 to 2 m in a sand soil vegetated with dry grass, and by a factor of 15 as sampling scale increased from 0.1 to 3.5 m in a sandy loam with mature Coast Live Oak trees (Quercus agrifolia). The results indicate that standard methods of permeability assessment can grossly underestimate advective transport of gas phase contaminants through soils.
Adapted Fick's Law Applied to Soil Respiration
Authors: Freijer J. I. , Leffelaar P. A.
Published: February 2004

In soil respiration studies the diffusive gas fluxes are often calculated using Fick's law. However, results obtained with Fick's law deviate from those obtained with the theoretically sound Stefan‐Maxwell equations. In the present study a numerical model based on an adapted form of Fick's law is applied to soil respiration. A pressure adjustment flux to maintain isobaric equilibrium in the system is employed to correct errors related to the usage of Fick's law. The results of the above‐mentioned model are compared with those of analytical solutions of Fick's law and the Stefan‐Maxwell equations to check the model's accuracy. The analytical solutions are derived for steady state transport at constant respiration rates in a hypothetical ternary system with N2, O2, and CO2. Calculations are performed at various constant rates of CO2 production and O2 consumption throughout the soil. Differences between the mole fraction gradients calculated with Fick's law and the Stefan‐Maxwell equations are substantial. If Fick's law is combined with the isobaric equilibrium correction procedure, the similarity with the Stefan‐Maxwell equations is much better. The numerical model employing the adapted Fick's law is subsequently tested against field measurements. Field measurements were carried out in large outdoor lysimeters filled with oil‐contaminated soil containing nonvolatile hydrocarbons. Nonsteady gas transport due to dynamic soil respiration during biodegradation of the hydrocarbons in the lysimeters is modeled at known boundary conditions. The result of the model agree with measurements of CO2 fluxes and O2 and CO2 concentration profiles in the lysimeters.
Contaminant Transport at a Waste Residue Deposit: 1. Inverse Flow and Nonreactive Transport Modeling
Authors: Sonnenborg Torben O. , Engesgaard Peter , Rosbjerg Dan
Published: February 2004

An application of an inverse flow and transport model to a contaminated aquifer is presented. The objective of the study is to identify physical and nonreactive flow and transport parameters through an optimization approach. The approach can be classified as a statistical procedure, where a flow and transport simulation model is combined with nonlinear least squares multiple regression. The U.S. Geological Survey method of characteristics model is used to simulate flow and transport, and the optimization part is solved using a Levenberg‐Marquardt algorithm. The sensitivity of the optimization approach to steady state versus transient flow conditions and to the amount of hydraulic and solute data used is investigated. The flow parameters, transmissivity and leakage factor, are estimated simultaneously with the transport parameters: source strength, porosity, and longitudinal dispersivity. This paper is the first in a two‐paper series describing contaminant transport at a waste residue site. In the second paper, reactive transport at the site is investigated.
Closed‐Form Solutions for Steady State Density‐Dependent Flow and Transport in a Vertical Soil Column
Authors: Park Namsik
Published: February 2004

Closed‐form solutions are derived for steady state density‐dependent fluid flow and solute transport problems in a one‐dimensional vertical soil column. Transport mechanisms considered are advection, molecular diffusion, and velocity‐dependent dispersion. Solutions can be obtained for a wide variety of cases. Characteristics of density‐dependent solutions, including effects of variations in density and the thickness of transition zones, are investigated for a simple case. Unique features not found in density‐independent solutions are observed. Nonuniform concentration profiles with vanishing density effects are also identified.
Winter methane dynamics in a temperate peatland
Authors: Melloh Rae A. , Crill Patrick M.
Published: February 2004

Methane (CH4) dynamics in pore water, snow pore air, and surface emissions were investigated in a temperate poor fen in New Hampshire over several winters. Total snowfall and average air temperatures during winter months (defined as December, January, and February) were climatologic indicators of significant flux rates from this midlatitude poor fen. Average winter emissions, for the five winters ending in 1994–1995, were 20, 39, 53, 56, and 26 mg m−2 d−1, amounting to 2.0, 5.2, 6.6, 9.2, and 2.0% of the total annual fluxes, respectively. Totaling emissions over 5 years that represent low to average snowfall, winter accounted for 4.3% of emissions to the atmosphere. Winter flux rates were near 55 mg m−2 d−1 for years with average snowfall, and 25 mg m−2 d−1 for years with low snowfall. Concentrations of CH4 sampled in pore water immediately beneath the ice were highly variable (0 to 1.1 mM). The concentration magnitude and standard deviation increased toward the fen center and correlated with spatial variation in hydrology, peat texture, and peat depth. CH4 stores increased in the near‐surface pore water as the ice cover formed. Seasonal CH4 buildup in deeper peat began near the end of the growing season, probably due to changing transport mechanisms and temperature effects on solubility. Stored CH4 in the 25‐ to 75‐cm peat layer decreased by 2.7 g m−2 between January and June 1995.
A 1° × 1° distribution of carbon dioxide emissions from fossil fuel consumption and cement manufacture, 1950–1990
Authors: Andres Robert J. , Marland Gregg , Fung Inez , Matthews Elaine
Published: February 2004

One degree latitude by one degree longitude (1° × 1°) data sets of carbon dioxide emissions from fossil fuel consumption and cement manufacture were produced for 1950, 1960, 1970, 1980, and 1990. National estimates of carbon emissions were combined with 1° × 1° data sets of political units and human population density to create the new 1° × 1° carbon emissions data sets. The human population density data set has an effective resolution of the country/state level. This resolution translates to the 1° × 1° carbon emissions data set. Latitudinal distribution of emissions have also been calculated. The data show continual growth with time over most of the world, with increased growth rates in major urban areas. A slow southerly shift in the bulk of the emissions is apparent as Asian countries increase their energy consumption to support their growing economies and populations. The digital data sets are available by anonymous ftp.
Estimation of methane emission from rice paddies in Mainland China
Authors: Yao Heng , Zhuang Ya‐hui , Chen Zong Liang
Published: February 2004

Methane emission from rice paddies in mainland China is estimated by the method of regional classification. Rice paddies in mainland China were classified into five major ecoclimatic regions and seven subregions according to regional ecological and agricultural parameters. The direct statistical agricultural data based on the 2484 county level records and climatic parameters of 160 meteorological stations in 1991 were employed for the classification and estimation. Methane emission rates obtained from six experimental sites representing 10 eco‐agricultural conditions were taken into consideration for the estimation. Using this method, the total methane emission from mainland China turned out to be 15.3 Tg/yr. Seasonally, methane was found to be emitted mainly (up to 95%) between April and October with an emission peak in June. Geographically, methane emission was intensively (up to 80%) concentrated in the central part of China and in the middle and lower reaches of the Yangtze River. The three counties with highest methane emission are all located in Sichuan province, they are Daxian (0.105 Tg/yr, 107°24′E, 31°12′N), Yuechi (0.091 Tg/yr, 106°24′E, 30°30′N), and Guangan (0.089 Tg/yr, 106°36′E, 30°24′N), altogether accounting for 2% of the total methane emission from rice paddies of the country. Single‐season rice (midrice in this paper) which was found mainly distributed in the southwest and southeast parts of the country plays the most important role in rice paddy methane compared with other rice methane sources. For comparison, several other known estimation methods employed by other authors were also used to make a comparison with the method of our data source. The estimated emissions from these studies are in the range of 7.7–24.6 Tg/yr. Trend analysis showed that methane emission in rice paddies from mainland China would remain at the present level in the near future.
Historical variations in terrestrial biospheric carbon storage
Authors: Post Wilfred M. , King Anthony W. , Wullschleger Stan D.
Published: February 2004

Changes in carbon storage in terrestrial ecosystems are a consequence of shifts in the balance between net primary production (NPP) and heterotrophic respiration (RH). Historical climatic variations which favored NPP over RHmay have led to increased ecosystem carbon storage and might account for at least part of the “missing” sink required to balance the current century's global carbon budget. To test this hypothesis, we employed a georeferenced global terrestrial biosphere model of 0.5° spatial resolution. The model was driven from an assumed equilibrium in 1900 using gridded historical time series of monthly temperature and precipitation and the historical record of changes in atmospheric CO2concentration. Interannual variability in climate induced interannual changes in terrestrial biospheric carbon storage and net carbon exchange with the atmosphere of the order of 1–2 Gt C yr−1. With climate change alone, global biospheric carbon storage declined by 1% (23 Gt C) over the period 1900–1988. With the addition of a moderate CO2fertilization response, biospheric carbon storage increased by 3% (57 Gt C), primarily as a consequence of changes in NPP and litter inputs to the soil system. With CO2fertilization, the model's cumulative carbon sink for the period 1900–1988 accounts for about 69% of the missing sink derived by deconvolution. For the period 1950–1988, the modeled sink is about 56% of the missing sink. Our results suggest that the temporal evolution of the missing sink over the period 1900–1988 could be a response of the terrestrial biosphere to changes in climate and atmospheric CO2or perhaps climate change alone. The discrepancy in the magnitudes of the modeled and deconvolved sinks may be due to limitations of the biospheric model or to overestimates of the land‐use source flux.
Crustal deformation around the Gulf of California
Authors: Dunn P. J. , Robbins J. W. , Bosworth J. M. , Kolenkiewicz R.
Published: February 2004

A number of Satellite Laser Ranging (SLR) sites in the southwest United States and Mexico, in operation for over ten years, have been supporting the global laser network measuring tectonic plate motion and providing information for studies of regional crustal deformation. Observations of the Laser Geodetic Satellite (LAGEOS) collected in 1994 by the transportable satellite laser ranging system, TLRS‐4, at two sites on the Baja peninsula now provide the means to extend the network of fixed stations at Monument Peak and Otay Mountain in southern California and Mazatlan on mainland Mexico. After the third SLR occupation of Ensenada, it's estimated site motion exhibits nearly the full plate rate predicted by the NNR‐NUVEL1A model for a location on the Pacific plate. At the southern tip of the Baja, the motion of Cabo San Lucas has an azimuth that is more westerly than that expected from Pacific modeled motion. This discrepancy in azimuth, in conjunction with the slower SLR recovered velocity for Mazatlan, results in an apparent 6 mm/yr faster spreading rate across the mouth of the Gulf of California than that predicted by the NUVEL‐1A model. The velocities of the Monument Peak and Otay Mountain sites show the expected long‐term difference from Pacific plate motion, due to their proximity to the San Andreas Fault system.
Decadal oscillations driven by the annual cycle in a zonally‐averaged coupled ocean‐ice model
Authors: Yang Jiayan , Huang Rui Xin
Published: February 2004

The role of the annual cycle in driving long‐term variations in high‐latitude oceans is studied in a zonally‐averaged ocean model coupled with a thermodynamic sea‐ice model. When the model is forced by surface fluxes whose seasonalities are idealized sinusoidally, subharmonic oscillations on interdecadal time scales arise due to a delicate interplay between surface heat and freshwater fluxes, sea‐ice extent, oceanic heat transport, and convective overturning. It is shown that the seemingly zero‐net‐gain annual cycle of winter freezing and summer melting may actually drain salts from the surface layer to the deeper ocean, leading to freshening of the upper ocean. This mechanism, when coupled with sea‐ice feedback, produces a self‐sustaining inter‐decadal oscillation. Parallel numerical experiments that use steady surface forcings do not generate such oscillations. This study highlights an important aspect of the annual cycle in forcing inter annual to decadal time scale climate variations.
A two‐stream, four‐sector, recurrence pattern: Implications from WIND for the 22‐year geomagnetic activity cycle
Authors: Crooker N. U. , Lazarus A. J. , Lepping R. P. , Ogilvie K. W. , Steinberg J. T. , Szabo A. , Onsager T. G.
Published: February 2004

Continuous solar wind data from WIND reveals a new recurrence pattern which implies that speed variations contribute to the 22‐year cycle of geomagnetic activity. Near December 1994 solstice, in keeping with expectation, a four‐sector interplanetary magnetic field pattern was accompanied by four streams. As the season advanced toward March equinox, however, the streams in the two sectors with away polarity diminished, leaving a strikingly unusual two‐stream, four‐sector pattern until late April. Since the magnetic field pointed toward the sun in both streams, the polarity effect of Russell and McPherron [1973] combined with the high‐speed flow resulted in a recurrent pattern of sustained geomagnetic activity during these sector passages. The solar wind pattern is consistent with Earth's excursion to southern heliographic latitudes at March equinox enabling WIND to sample high‐speed flow from only the southern coronal hole. The WIND data imply that the 22‐year variation in geomagnetic activity results not only from longer immersion in toward sectors in March and away sectors in September during even solar cycles, as proposed by Russell and McPherron [1973], but also from higher flow speeds in those sectors.
Comparison of NOAA‐11 SBUV/2 ozone vertical profiles with correlative measurements
Authors: Planet W. G. , Miller A. J. , DeLuisi J. J. , Hofmann D. J. , Oltmans S. J. , Wild J. D. , McDermid I. S. , McPeters R. D. , Connor B. J.
Published: February 2004

Vertical profiles of ozone have been determined from observations with the Solar Backscatter Ultraviolet (SBUV/2) instrument on the NOAA‐11 operational satellite. These observations began in January 1989 and continue to early 1995. Comparisons have been made with selected sets of ozone vertical profiles derived from an ensemble of satellite and land‐based measurements. These include; 1) lidar and microwave measurements performed at Table Mountain, CA. 2) Umkehr observations with a mid‐northern latitude set of Dobson spectrophotometers. 3) balloon ozonesondes launched from Boulder, CO. 4) measurements with the NASA SBUV on Nimbus‐7. Overall, the SBUV/2 profiles within the altitude range of 1–20mb agree with the other measurements to about ±5% with a −3 to −5% bias, the SBUV/2 values being lower. This level of agreement is consistent with the expected performance of the SBUV/2 instrument based on an extensive characterization of the instrument both in pre‐launch calibration and in‐orbit performance and also with current understanding of the test optical components used in pre‐flight calibration.
Investigation of the inner‐outer core boundary structure from the seismograms of a deep earthquake recorded by a regional seismic array
Authors: Huang Bor‐Shouh
Published: February 2004

PKP(Cdiff), the PKP diffraction waves after PKP‐C cut‐off, was identified in the PKIKP (or PKP(DF)) wave coda of teleseismic seismograms from a deep earthquake in western Brazil. An array stacking technique was applied to the short‐period waveforms from a regional seismic network in Taiwan to retrieve the weak PKP(Cdiff) waves between 159° and 162°. The differential travel times and slowness of PKP(Cdiff) and PKP(DF) were used to constrain the P‐velocity structure near the inner‐outer core boundary (ICB). The results of this study demonstrate that in some cases the ICB structure can be constrained by data from a single event using presently available short‐period regional seismic data and applying suitable array techniques. With a correction for axi‐symmetric anisotropy applied to the inner core, the results of this study agree with the PKP properties of model VMOI, a regional ICB model revised from PREM covering the ICB sampled area of this study, and model AK135, a new proposed earth model. The C‐cusp position was reported at 151.4° from this event. Theoretical predictions for another new proposed earth model SP6 is in significant disagreement with the observed differential travel times between PKP(Cdiff) and PKP(DF). At a distance of 159°, the residuals (observation‐prediction) included the observation errors (±0.2 sec) are approximately +0.17 sec, −0.31 sec and +0.69 sec for VMOI, AK135 and SP6, respectively. Neither model predicts a significant differential slowness residual. This misfit along this path may be the result of the lateral heterogeneity of the sampled region near the ICB relative to both spherically symmetric models or the complications imposed by the non‐axi‐symmetric anisotropy of the inner core.
Record low ozone at Mauna Loa Observatory during winter 1994–1995: A consequence of chemical and dynamical synergism?
Authors: Hofmann D. J. , Oltmans S. J. , Koenig G. L. , Bodhaine B. A. , Harris J. M. , Lathrop J. A. , Schnell R. C. , Barnes J. , Chin J. , Kuniyuki D. , Ryan S. , Uchida R. , Yoshinaga A. , Neale P. J. , Hayes D. R. , Goodrich V. R. , Komhyr W. D. , Evans R. D. , Johnson B. J. , Quincy D. M. , Clark M.
Published: February 2004

During two days in late December 1994, total ozone measured at the Mauna Loa Observatory on the island of Hawaii, dropped below 200 Dobson Units (DU) for the first time since ozone measurements began at this site over 30 years ago. Total ozone values this low have not previously occurred over populated areas except on rare occasions when the edges of the springtime Antarctic ozone hole temporarily pass over the southern tip of Argentina. The monthly total ozone average for January 1995 was 216 DU, about 14% below the 1964–1981 baseline value. Ultraviolet radiation measured at Mauna Loa on clear days during this period increased inversely with ozone as expected, more than tripling in relative intensity at 295 nm. The normal annual minimum in total ozone occurs in winter at Mauna Loa; however, some winters experience considerably lower values than others. This was the case during the winter of 1994–1995. Although the general decline in global ozone, which began about 1980 and also appears in the Mauna Loa record, may be related to chemical ozone depletion, the unusually low values during some winters at Mauna Loa appear to be related to ozone transport from the tropics, and the timing of phase transitions of the QBO. This analysis provides an accurate method of forecasting low‐ozone, high‐UV winters in Hawaii.
UARS measurements of CIO and NO2 at 40 and 46 km and implications for the model “ozone deficit”
Authors: Dessler A. E. , Kawa S. R. , Considine D. B. , Waters J. W. , Froidevaux L. , Kumer J. B.
Published: February 2004

We present the first diurnally‐resolved measurements of ClO and NO2 at 3.1 and 1.4 hPa, approximately 40 and 46 km. Comparisons between the measurements of ClO and a zero‐dimensional box model utilizing standard photochemistry and constrained by Upper Atmosphere Research Satellite (UARS) tracer measurements show that photochemical models overpredict ClO by a factor of two or more at 3.1 hPa and by a factor of 1.5–2.0 at 1.4 hPa. NO2 is well simulated by the model at 3.1 hPa, but systematically overestimated at 1.4 hPa. The model overestimate of ClO results in an overestimate of ozone loss in the upper stratosphere of 10–40%.
Distortion of the heliospheric plasma sheet by interplanetary shocks
Authors: Odstrčil D. , Smith Z. , Dryer M.
Published: February 2004

A 2½D MHD model is used to investigate mutual interactions between interplanetary shocks with the interplanetary magnetic field (IMF), An ambient solar wind is considered with a flat equatorial heliospheric current sheet (HCS) that is embedded within a finite thickness heliospheric plasma sheet (HPS). Two different velocity pulses are introduced with four different latitudinal positions at 0.1 AU. We found that large values of the meridional IMF originate when the shock interacts with the HPS. This is caused by field‐line draping around the highly distorted shock driver and by deflection of the HCS in asymmetric situations.
Solar ultraviolet irradiance at Tierra Del Fuego: Comparison of measurements and calculations over a full annual cycle
Authors: Diaz Susana B. , Frederick John E. , Lucas Timothy , Booth C. Rocky , Smolskaia Irina
Published: February 2004

A spectroradiometer located at Ushuaia, Tierra del Fuego, Argentina obtained a high quality data set on the solar ultraviolet (UV) spectral irradiance for a full annual cycle during 1992. The unique aspect of the ground‐based irradiances is their ability to characterize the effects of cloudiness. Measured irradiances at 340 nm can be used to characterize the attenuation provided by cloudy skies. When irradiances at shorter wavelengths, 302.5–320.0 nm, are adjusted for this attenuation, they show good agreement with radiative transfer calculations which assume clear skies and utilize data from the Total Ozone Mapping Spectrometer (TOMS) as inputs. The differences which exist are qualitatively consistent with the neglect of spherical geometry in the calculated irradiances.
Crustal shear‐wave splitting from local earthquakes in the Hengill Triple Junction, southwest Iceland
Authors: Evans John R , Foulger G. R. , Julian Bruce R. , Miller Angus D.
Published: February 2004

The Hengill region in SW Iceland is an unstable ridge‐ridge‐transform triple junction between an active and a waning segment of the mid‐Atlantic spreading center and a transform that is transgressing southward. The triple junction contains active and extinct spreading segments and a widespread geothermal area. We evaluated shear‐wave birefringence for locally recorded upper‐crustal earthquakes using an array of 30 three‐component digital seismographs. Fast‐polarization directions, ϕ, are mostly NE to NNE, subparallel to the spreading axis and probably caused by fissures and microcracks related to spreading. However, there is significant variability in ϕ throughout the array. The lag from fast to slow S is not proportional to earthquake depth (ray length), being scattered at all depths. The average wave‐speed difference between qS1 and qS2 in the upper 2–5 km of the crust is 2–5%. Our results suggest considerable heterogeneity or strong S scattering.