bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting Two‐ and Three‐Fluid Capillary Pressure‐Saturation Relationships of Porous Media With Fractional Wettability
Authors: Bradford Scott A. , Leij Feike J.
Published: February 2004

Knowledge of the capillary pressure‐saturation (Pc−S) relations of porous media is essential for the research and management of multiphase flow and transport. Indirect methods have often been used to predict Pc−S curves, since the actual measurement of all Pc−S curves may be cumbersome. Existing methods to predict the Pc−S relations for porous media with fractional wettability, however, are generally inadequate. This paper reports on methods to quantify Pc−S curves of such media that contain two or three fluids (air, oil, and water). The prediction of oil‐water Pc−S relations from air‐oil or air‐water Pc−S data through mere scaling is not possible since the oil‐water capillary pressure may be positive or negative in fractional wettability media. We successfully predicted the oil‐water Pc−S curve using a linear transformation of air‐oil Pc−S data. In three‐fluid media with fractional wettability the prediction of three‐fluid from two‐fluid Pc−S relations using only Leverett's assumption is unreliable, since both water and oil act as intermediate fluid. We predicted the three‐fluid oil‐water Pc from two‐fluid oil‐water or linearly transformed air‐oil Pc−S data. The three‐fluid air‐oil Pc could be readily predicted from the two‐fluid air‐oil Pc−S relation for a variable oil saturation and a constant water saturation. In contrast, when the water saturation was varied, at a constant oil saturation, the air‐oil Pc could only be predicted using an empirical correction for the two‐fluid air‐oilPc−S data. The three‐fluid air‐water Pc is obtained as the sum of the oil‐water Pc and the air‐oil Pc (both water and oil pressures are measured with respect to atmospheric pressure).
Macrotransport of a Biologically Reacting Solute Through Porous Media
Authors: Dykaar Bruce B. , Kitanidis Peter K.
Published: February 2004

A physically based model is developed to study the transport of a solute utilized by microorganisms forming a biofilm coating on soil grains in a porous medium. A wavy‐walled channel is used as a geometrical model of a porous medium and a biofilm is attached to the channel wall. Within the biofilm the solute is consumed according to a first‐order volumetric rate. A numerical study is performed to obtain the dependence of the macrotransport coefficients on the Peclet number and Damkohler number. It is found that in some cases of practical importance the pore fluid is not well mixed, and mass transport limitations can control macroreaction rates. For diffusion‐limited cases (large Damkohler numbers) increased solvent velocity can enhance the macroreaction rate by a factor of almost 3. Mean solute and mean solvent velocities are, in general, not equal, and mean solute velocities can exceed mean solvent velocities by 60% at high Damkohler numbers. These results agree qualitatively with those of a previous numerical study by Edwards et al. [1993]. The results also suggest that due to the spatially variable pore geometry, the biomass nearest the pore throat is more effective at consuming the solute than biomass in the pore chamber. A comparison is made between mass transfer correlations and the results determined for the macroreaction rate coefficient. We find that over a limited range of Peclet numbers a macroscale Sherwood number follows the Pe⅓ behavior determined from experimental mass transfer correlations and predicted by boundary layer theory.
Measuring the Economic Benefits of Removing Dams and Restoring the Elwha River: Results of a Contingent Valuation Survey
Authors: Loomis John B.
Published: February 2004

The contingent valuation method was used to obtain estimates of willingness to pay for removing the two dams on the Elwha River on the Olympic Peninsula in Washington State and restoring the ecosystem and the anadromous fishery. Using the dichotomous choice voter referendum format, the mean annual value per household is $59 in Clallam County, $73 for the rest of Washington, and $68 for households in the rest of the United States. The aggregate benefits to residents of the State of Washington is $138 million annually for 10 years and between $3 and $6 billion to all U.S. households. These estimates suggest that the general public would be willing to pay to remove old dams that block salmon migration.
On the Incorporation of Drains into Three‐Dimensional Variably Saturated Groundwater Flow Models
Authors: MacQuarrie K. T. B. , Sudicky E. A.
Published: February 2004

Subsurface drains are important features in many problems involving shallow groundwater flow and have generally been represented in two‐dimensional numerical models by specifying hydraulic head or fluid flux at one or more nodes in the computational grid. Here we describe a new approach for representing drains in three‐dimensional variably saturated flow models. The method is based on a one‐dimensional flow equation for the drain which is analogous to a one‐dimensional open‐channel flow equation; the numerical contributions to the system of global equations from the one‐dimensional discretized equation are added to the three‐dimensional, porous medium contributions. The inclusion of drain flow by this technique is readily adaptable to any three‐dimensional numerical simulator. The accuracy of the method is demonstrated by comparing results obtained with the new method to steady state and transient results presented by Fipps et al. [1986]. The numerical formulation naturally accommodates flow in heterogeneous media and demonstrates excellent mass balance. Illustrative examples are presented which highlight the usefulness of the algorithm for studying the influence of drains in problems involving subsurface effluent disposal in heterogeneous aquifers and agricultural land drainage. The method will have application to many studies involving water and contaminant movement in drained soils.
Are Water Table Variations in a Shallow Forest Soil Consistent with the TOPMODEL Concept?
Authors: Moore R. D. , Thompson J. C.
Published: February 2004

The TOPMODEL concept provides a simple method for parameterizing the effect of topography on the distribution of subsurface moisture and runoff production, and has been incorporated into models of catchment hydrology and forest ecology. Most evaluations of the TOPMODEL concept have been based on comparisons of stream flow hydrographs and do not necessarily provide a test of the predictions of subsurface flow and saturated source area dynamics. The objective of this study was to evaluate whether water table predictions based on the TOPMODEL concept agree with observed water table depths for a shallow forest soil in a small subcatchment drained by an ephemeral stream. Observed water table depths were fitted well by a linear statistical model that is mathematically consistent with the TOPMODEL assumptions and that specifies time and location effects independently. That is, the water table does not change shape but shifts uniformly up or down in response to changes in saturated zone storage. Residuals from the fitted model were generally less than 10 cm in absolute value, compared to observed ranges of water table depths up to 100 cm. The TOPMODEL concept predicts that the relation between the estimated location effects for the wells and the values of In (a/tan β) should be linear, where a is the drainage area per unit contour length, and tan β is the surface slope. Regression analysis revealed that the fitted linear relation was statistically significant (P=0.001), but weak (R2= 0.26). This weak fit could be caused by (1) significant spatial variability in soil transmissivity (assumed negligible in many applications of TOPMODEL) and/or (2) errors in specifying In (a/tan β) from a digital elevation model of the surface topography. Considering the increasingly common application of the TOPMODEL concept in hydrologic and ecological models, further research should be carried out to specify more clearly the bounds of applicability of its underlying assumptions and to identify workable extensions and modifications to the concept, where necessary.
Groundwater Inflow Measurements in Wetland Systems
Authors: Hunt Randy J. , Krabbenhoft David P. , Anderson Mary P.
Published: February 2004

Our current understanding of wetlands is insufficient to assess the effects of past and future wetland loss. While knowledge of wetland hydrology is crucial, groundwater flows are often neglected or uncertain. In this paper, groundwater inflows were estimated in wetlands in southwestern Wisconsin using traditional Darcy's law calculations and three independent methods that included (1) stable isotope mass balances, (2) temperature profile modeling, and (3) numerical water balance modeling techniques. Inflows calculated using Darcy's law were lower than inflows estimated using the other approaches and ranged from 0.02 to 0.3 cm/d. Estimates obtained using the other methods generally were higher (0.1 to 1.1 cm/d) and showed similar spatial trends. An areal map of groundwater flux generated by the water balance model demonstrated that areas of both recharge and discharge exist in what is considered a regional discharge area. While each method has strengths and weaknesses, the use of more than one method can reduce uncertainty in the estimates.
The Solution of Groundwater Quality Management Problems with a Nonconvex Feasible Region Using a Cutting Plane Optimization Technique
Authors: Karatzas George P. , Finder George F.
Published: February 2004

In groundwater quality management problems the concentration constraints have a nonlinear behavior which may be described either as a convex or a nonconvex function. Therefore the feasible region, which is defined as the intersection of all of these constraints, can be either a convex or a nonconvex set. A review of existing optimization algorithms for the solution of the groundwater quality management problem indicates that the majority of them have an inability to determine a global optimum when nonconvexity occurs. In an earlier paper that appeared in this journal [Karatzas and Finder, 1993], the outer approximation method, a global optimization technique, was presented for the solution of groundwater management problems with convex constraints. The problem was formulated to minimize a concave objective function over a compact convex set of constraints. In the present study the same concept is applied to problems with nonconvex constraints. While the main concept of the current approach remains the same as that in our earlier study, there is a significant difference in the determination of the cutting hyperplane. The nonconvexity of the domain requires a special approach to insure that the introduction of the cutting hyperplane does not eliminate any part of the nonconvex feasible region. In this work the theory of the developed algorithm is presented and subsequently applied to two groundwater quality problems. In the first example a hypothetical aquifer is considered to illustrate the performance of the methodology. In the second example a groundwater quality management problem in Woburn, Massachusetts, is solved. Results obtained are compared with those generated by MINOS 5.1.
A new tracer experiment to estimate the methane emissions from a dairy cow shed using sulfur hexafluoride (SF6)
Authors: Marik Thomas , Levin Ingeborg
Published: February 2004

Methane emission from livestock and agricultural wastes contribute globally more than 30% to the anthropogenic atmospheric methane source. Estimates of this number have been derived from respiration chamber experiments. We determined methane emission rates from a tracer experiment in a modern cow shed hosting 43 dairy cows in their accustomed environment. During a 24‐hour period the concentrations of CH4, CO2, and SF6, a trace gas which has been released at a constant rate into the stable air, have been measured. The ratio between SF6 release rate and measured SF6 concentration was then used to estimate the ventilation rate of the stable air during the course of the experiment. The respective ratio between CH4 or CO2 and SF6 concentration together with the known SF6 release rate allows us to calculate the CH4 (and CO2) emissions in the stable. From our experiment we derive a total daily mean CH4 emission of 441 LSTP per cow (9 cows nonlactating), which is about 15% higher than previous estimates for German cows with comparable milk production obtained during respiration chamber experiments. The higher emission in our stable experiment is attributed to the contribution of CH4 release from about 50 m3 of liquid manure present in the cow shed in underground channels. Also, considering measurements we made directly on a liquid manure tank, we obtained an estimate of the total CH4 production from manure: The normalized contribution of methane from manure amounts to 12–30% of the direct methane release of a dairy cow during rumination. The total CH4 release per dairy cow, including manure, is 521–530 LSTP CH4 per day.
Diffusional flux of CO2 through snow: Spatial and temporal variability among alpine‐subalpine sites
Authors: Sommerfeld Richard A. , Massman William J. , Musselman Robert C. , Mosier Arvin R.
Published: February 2004

Three alpine and three subalpine sites were monitored for up to 4 years to acquire data on the temporal and spatial variability of CO2 flux through snowpacks. We conclude that the snow formed a passive cap which controlled the concentration of CO2 at the snow‐soil interface, while the flux of CO2 into the atmosphere was controlled by CO2 production in the soil. Seasonal variability in the flux at all sites was characterized by early winter minima followed by a rise in flux that averaged 70% above the minima over about a 1‐month period. The seasonal variability was not related to soil temperatures which remained relatively constant. Interannual variability was small, and spatial variability was smaller than previously reported. Spatial variability on a scale of 1 to 10 m was less than 30% of the average fluxes and not significantly greater than estimated error in most cases. Spatial variability on a scale of 10‐ to 100‐m was about a factor of 2 and on a scale of 100 to 1000 m was about a factor of 4. The 100‐ to 1000‐m variability was complicated by the fact that the sites were in different ecosystems, alpine and subalpine, and at different elevations. We attribute the small variability at the 1‐ to 10‐m scale to the deep snow cover, from 1.4 to 5 m. We hypothesize that horizontal diffusion under the snow cover reduced small‐scale horizontal gradients, while the insulating effect of the deep snow cover kept the soil temperature and moisture relatively constant. Equivalent annual wintertime flux averaged about 95 g C m−2 yr−1 in the alpine and about 232 g C m−2 yr−1 in the subalpine sites. Measurements of CO2 concentrations at 0.2 and 0.5 m in the soil of one of the subalpine sites indicated that production early in the snow season occurred at or below 0.5 m while production between 0.5 m, and the surface became important after the start of the melt season.
Variations in modeled atmospheric transport of carbon dioxide and the consequences for CO2 inversions
Authors: Law R. M. , Rayner P. J. , Denning A. S. , Erickson D. , Fung I. Y. , Heimann M. , Piper S. C. , Ramonet M. , Taguchi S. , Taylor J. A. , Trudinger C. M. , Watterson I. G.
Published: February 2004

Carbon dioxide concentrations due to fossil fuel burning and CO2 exchange with the terrestrial biosphere have been modeled with 12 different three‐dimensional atmospheric transport models. The models include both on‐line and off‐line types and use a variety of advection algorithms and subgrid scale parameterizations. A range of model resolutions is also represented. The modeled distributions show a large range of responses. For the experiment using the fossil fuel source, the annual mean meridional gradient at the surface varies by a factor of 2. This suggests a factor of 2 variation in the efficiency of surface interhemispheric exchange as much due to differences in model vertical transport as to horizontal differences. In the upper troposphere, zonal mean gradients within the northern hemisphere vary in sign. In the terrestrial biotic source experiment, the spatial distribution of the amplitude and the phase of the seasonal cycle of surface CO2 concentration vary little between models. However, the magnitude of the amplitudes varies similarly to the fossil case. Differences between modeled and observed seasonal cycles in the northern extratropics suggest that the terrestrial biotic source is overestimated in late spring and underestimated in winter. The annual mean response to the seasonal source also shows large differences in magnitude. The uncertainty in hemispheric carbon budgets implied by the differences in interhemispheric exchange times is comparable to those quoted by the Intergovernmental Panel on Climate Change for fossil fuel and ocean uptake and smaller than those for terrestrial fluxes. We outline approaches which may reduce this component in CO2 budget uncertainties.
An integrated biosphere model of land surface processes, terrestrial carbon balance, and vegetation dynamics
Authors: Foley Jonathan A. , Prentice I. Colin , Ramankutty Navin , Levis Samuel , Pollard David , Sitch Steven , Haxeltine Alex
Published: February 2004

Here we present a new terrestrial biosphere model (the Integrated Biosphere Simulator ‐ IBIS) which demonstrates how land surface biophysics, terrestrial carbon fluxes, and global vegetation dynamics can be represented in a single, physically consistent modeling framework. In order to integrate a wide range of biophysical, physiological, and ecological processes, the model is designed around a hierarchical, modular structure and uses a common state description throughout. First, a coupled simulation of the surface water, energy, and carbon fluxes is performed on hourly timesteps and is integrated over the year to estimate the annual water and carbon balance. Next, the annual carbon balance is used to predict changes in the leaf area index and biomass for each of nine plant functional types, which compete for light and water using different ecological strategies. The resulting patterns of annual evapotranspiration, runoff, and net primary productivity are in good agreement with observations. In addition, the model simulates patterns of vegetation dynamics that qualitatively agree with features of the natural process of secondary succession. Comparison of the model's inferred near‐equilibrium vegetation categories with a potential natural vegetation map shows a fair degree of agreement. This integrated modeling framework provides a means of simulating both rapid biophysical processes and long‐term ecosystem dynamics that can be directly incorporated within atmospheric models.
Comparison of soil acetate concentrations and methane producton, transport, and emission in two rice cultivars
Authors: Sigren L. K. , Byrd G. T. , Fisher F. M. , Sass R. L.
Published: February 2004

The amount of methane emitted from irrigated rice paddies is dependent on the variety of rice grown. In this study we examined two varieties of rice with differing methane emission rates to determine if the primary mechanism for these differences was related to transport processes or the rate of methane production. The cultivars used were Mars and Lemont, with 1994 seasonal emissions of 34 and 18 g m−2, respectively. Seasonal methane emission and soil acetate concentration data were measured weekly over two seasons in both varieties. In addition, gas transport through the two rice varieties was investigated in both field and laboratory experiments in 1995. We found no significant differences in gas transport between the two varieties. However, significant differences between the two varieties were detected in the soil acetate concentrations during the vegetative growth stage. Mars exhibited higher seasonal methane emissions and higher soil acetate concentrations than Lemont. This suggests that the intervarietal differences in methane emissions are the result of different soil substrate levels and hence different rates of methane production. The turnover time of soil acetate was found to be small, about 1 hour in the last half of the season. Calculations of methane oxidation, using two methods, support previous findings that the fraction of methane oxidized in the soil prior to emission increases from 10 to 30% before heading to 30–70% after heading.
An inverse modeling approach to investigate the global atmospheric methane cycle
Authors: Hein Ralf , Crutzen Paul J. , Heimann Martin
Published: February 2004

Estimates of the global magnitude of atmospheric methane sources are currently mainly based on direct flux measurements in source regions. Their extrapolation to the entire globe often involves large uncertainties. In this paper, we present an inverse modeling approach which can be used to deduce information on methane sources and sinks from the temporal and spatial variations of atmospheric methane mixing ratios. Our approach is based on a three‐dimensional atmospheric transport model which, combined with a tropospheric background chemistry module, is also employed to calculate the global distribution of OH radicals which provide the main sink for atmospheric methane. The global mean concentration of OH radicals is validated with methyl chloroform (CH3CCl3) observations. The inverse modeling method optimizes the agreement between model‐calculated and observed methane mixing ratios by adjusting the magnitudes of the various methane sources and sinks. The adjustment is constrained by specified a priori estimates and uncertainties of the source and sink magnitudes. We also include data on the 13C/12C isotope ratio of atmospheric methane and its sources in the model. Focusing on the 1980s, two scenarios of global methane sources are constructed which reproduce the main features seen in the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL) methane observations. Differences between these two scenarios may probably be attributed to underestimated a priori uncertainties of wetland emissions. Applying the inverse model, the average uncertainty of methane source magnitudes could be reduced by at least one third. We also examined the decrease in the atmospheric methane growth rate during the early 1990s but could not uniquely associate it with changes in particular sources.
Sources of spatial variation in methane emission from mires in northern Sweden: A mechanistic approach in statistical modeling
Authors: Granberg Gunnar , Mikkelä Catharina , Sundh Ingvar , Svensson Bo H. , Nilsson Mats
Published: February 2004

Methane emissions from six mires in northern Sweden were measured using a closed chamber technique during the frost free season in 1992. The average methane flux over the measurement period, calculated either for each mire or for different plant communities within one mire, ranged from 9 to 83 mg CH4 m−2 d−1. The emission rate on each occasion was related to physical and chemical environmental variables, both in a general data set for all mires (n = 836) and in subdata sets for individual mires, using multiple linear regression. The variables with significant contributions to the models were water table, standing water above the vegetation surface, peat temperatures, and principal components of the near infrared reflectance spectra of peat samples reflecting variations in organic chemical composition. To account for the actual contribution of methane production and methane oxidation, variables describing the active parts of the vertically distributed potentials of methane production or oxidation were constructed. The interaction terms between these variables, respectively, describing the active proportion of methanogens and methanotrophs, and the temperature values representing the anoxic and oxic parts of the profile were significantly correlated to the methane emission rate; positively for the production zone and negatively for the consumption zone. By using this mechanistic approach, a significant temperature effect in both the methane production and consumption zone was detected. These constructed temperature variables explain 21% of the variance in the logarithmically transformed methane fluxes using the entire data set (n = 836) but only 5% of the variance using peat temperatures from fixed depths. Adding variables describing the organic chemical composition of the peat to the models improved the predictability in 10 of the 11 model sets tested, decreasing the unexplained variance by maximally 50% for a poor fen community model and increasing R2 from 0.40 to 0.68. In the general model, R2 increased from 0.42 to 0.49 with the inclusion of organic chemical composition. The explained variance in the final models, including the substrate variables, ranged from R2 = 0.49 to R2 = 0.75, with one exception, Torsmyran (R2 = 0.36) which is a mire that most closely relates to an eccentric ombrotrophic bog among the mires studied.
Terrestrial carbon storage during the past 200 years: A Monte Carlo Analysis of CO2 data from ice core and atmospheric measurements
Authors: Bruno Michele , Joos Fortunat
Published: February 2004

We have updated earlier deconvolution analyses using most recent high‐precision ice core data for the last millennium [Etheridge et al., 1996] and direct atmospheric CO2 observations starting in 1958 [Keeling and Whorf, 1994]. We interpreted nonfossil emissions, that is, the difference between the increase in observed atmospheric plus modeled oceanic carbon inventory and fossil emissions, as biospheric carbon storage (release). We have assessed uncertainties in the CO2 ice core data using a Monte Carlo approach and found a 2‐σ uncertainty for the nonfossil emissions (20‐year averages) of 0.2–0.4 GtC yr−1. Overall uncertainties of the nonfossil emissions were estimated to be 0.5 GtC yr−1 before 1950 and ˜1 GtC yr−1 during the last decade. We found a large and rapid change of −0.8 GtC yr−1 in the nonfossil emissions (approximate net air‐biota flux) between 1933 and 1943. Before 1933, the land biota acted as carbon source of order 0.5 GtC yr−1 in agreement with independent estimates of carbon emissions by land use changes [Houghton, 1993a]. After 1943, the land biota was a net sink of about 0.3 GtC yr−1. This implies an average biospheric sink of 1.5 GtC yr−1 during the last 5 decades to compensate estimated carbon emissions by land use changes. We could not attribute this sink to a single mechanism. We found that the temporal evolution of the required biota sink is not compatible with conventional modeling of CO2 fertilization. We estimated potential terrestrial carbon storage due to nitrogen fertilization to be 1 GtC yr−1 for 1960, that is, smaller than the required sink, and 1.5–3 GtC yr−1 for 1990. To assess the potential impact of climate variations, we deconvolved the preindustrial CO2 concentrations which fluctuated around 280 ppm. We found a maximum nonfossil sink of 30 GtC within 50 years. Thus it seems not likely that the cumulative sink of 76 GtC which is required to balance land use emissions during 1935 to 1990 can be explained by climate variations only.
Methane emission from rice: Stable isotopes, diurnal variations, and CO2exchange
Authors: Chanton J. P. , Whiting G. J. , Blair N. E. , Lindau C. W. , Bollich P. K.
Published: February 2004

The importance of vegetation in supporting methane production and emission within flooded rice fields was demonstrated. Methane emission from Lousiana, United States, rice fields was correlated to the quantity of live aboveground biomass and the rate of CO2exchange. The quantity of belowground methane was greater in vegetated plots relative to plots maintained free of vegetation. The diurnal maximum in the rate of methane emission was coincident with the release of the most13C‐enriched methane and a maximum in transpiration rate rather than stomatal conductance, suggesting that diurnal variations in methane emission rate are linked with transpiration, in addition to temperature. Results of isotopic measurements of belowground, lacunal, and emitted methane indicate that methane is transported from rice predominantly via molecular diffusion with a small component due to transpiration‐induced bulk flow. Samples of methane collected from air‐filled internal spaces within the rice culm were13C‐enriched (−53.1 ± 0.3‰) relative to emitted (−64.5 ± 1.0‰) and belowground methane (−59 ± 1.0‰) . Reproduction of these observed13C values with a numerical model required isotopic fractionation effects associated with transport of methane into and from rice plants. The model could not conclusively confirm rhizospheric methane oxidation. However,13C‐enriched methane was observed in the floodwater overlying the flooded soil (−44.4 ± 2.2‰), consistent with the oxidation of substantial quantities of methane as it diffused across the soil‐water interface.
Discrimination against C18O16O during photosynthesis and the oxygen isotope ratio of respired CO2 in boreal forest ecosystems
Authors: Flanagan Lawrence B. , Brooks J. Renee , Varney Gregory T. , Ehleringer James R.
Published: February 2004

Our objective was to analyze factors that influence changes in the oxygen isotope ratio (δ18O) of atmospheric CO2 within boreal forest ecosystems. We made measurements in the three major forest types (black spruce, jack pine, and aspen) at the southern and northern ends of the boreal forest in central Canada. This research was part of a larger study, the Boreal Ecosystem‐Atmosphere Study (BOREAS). In terrestrial ecosystems the δ18O value of atmospheric CO2 is strongly influenced by isotope effects that occur during photosynthesis and respiration. Of primary importance is an equilibrium isotope effect that occurs between oxygen in CO2 and oxygen in soil water and plant chloroplast water. During the equilibrium reaction the oxygen isotope ratio of CO2 becomes enriched in 18O relative to that of water. We measured seasonal changes in the oxygen isotope ratio of (1) water input to the ecosystems (precipitation), (2) water taken up by the major plant species from the soil (plant stem water), and (3) water in plant leaves. We used this information in calculations of isotope discrimination during photosynthesis and soil respiration. Discrimination against C18O16O during photosynthetic gas exchange (ΔA) (influenced by equilibration with chloroplast water) averaged approximately 21‰ at midday and was similar for all forest types. In contrast, CO2 released during plant and soil respiration had an average δ18O value of −14.4‰ but was less depleted in 18O than would be expected for respired CO2 in isotopic equilibrium with soil water. This effect was most pronounced in black spruce sites because of the extensive coverage of moss on the ground surface and the observation that water in the upper moss layers can have an oxygen isotope ratio substantially different from water in deeper soil layers.
An unusual pattern of recurring seismic quiescence at Kalapana, Hawaii
Authors: Dieterich James H. , Okubo Paul G.
Published: February 2004

An unusual pattern of recurring seismic quiescence is observed in the Kalapana, Hawaii region of Kilauea Volcano. Statistically significant intervals of quiescence preceded the Kalapana earthquakes of 1975 (M7.2) and 1989 (M6.1) and a third quiescence is presently underway. The sensitivity of the volcano flank to continuing magmatic activity in the nearby east rift zone complicates interpretation of these observations. The current quiescence episode may be caused by magmatic processes in the east rift zone or by changes within the flank of Kilauea. The latter possibility, if correct, may represent a precursor to another earthquake.
Remotely triggered microearthquakes at the Geysers Geothermal Field, California
Authors: Stark Mitchel A. , Davis Scott D.
Published: February 2004

Microearthquake (MEQ) activity recorded on a local network at The Geysers geothermal field has been observed to increase dramatically within seconds to minutes after the arrival of surface waves from large regional earthquakes. This behavior was observed not only following the 1992 Landers earthquake, for which remotely triggered seismicity (at The Geysers and elsewhere) has been documented, but also for the following events: Gulf of Alaska (Ms 7.6, March 6, 1988); Loma Prieta (Ms 7.1, October 17, 1989); two events within the Gorda Plate (Ms 6.9 on July 13, 1991 and Ms 7.1 on August 17, 1991); Petrolia ( Ms 7.0, April 25, 1992); and Northridge (M s 6.6, January 17, 1994). The exact onset times of most swarms are difficult to pinpoint, but all start within minutes of the passage of seismic waves and in at least one case (Gulf of Alaska) the onset appears to coincide with the expected arrival of the surface waves. These swarms generally last for a few hours at most, and decay with time in a manner similar to aftershock sequences. We propose that the dynamic stresses associated with seismic waves emanating from these earthquakes may trigger the onset of these swarms. The Landers event may have been particularly efficient at generating remotely triggered swarms throughout the western U.S. because of its size and shallow focal depth, which would promote large surface waves. Our data demonstrate, however, that the phenomenon is not unique to the Landers event.
Forcing and biological impact of onset of the 1992 El Niño in central California
Authors: Chavez Francisco P.
Published: February 2004

The physical, chemical and biological effects related to onset of the 1992 El Niño in central California are described. Oceanic Kelvin waves link atmospheric events in the western equatorial Pacific and onset of temperature and primary productivity anomalies. The perturbations observed off California, with a deeper thermocline and nutricline reducing the supply of nutrients and regulating productivity, are similar to those observed along the coast of Peru during El Niño.
A reexamination of the role of solar heating in the O2 atmospheric and infrared atmospheric bands
Authors: Mlynczak Martin G. , Marshall Benjamin T.
Published: February 2004

The role of heating due to absorption of solar radiation by molecular oxygen (O2) in the A, B, and γ atmospheric bands and in the infrared atmospheric band is reviewed. Prior studies have demonstrated the importance of heating by these O2 bands in the vicinity of the tropopause. In the middle mesosphere, the heating associated with O2 atmospheric bands is shown to rival that of the numerous individual solar and chemical heat sources. We show that heating in the O2 atmospheric bands increases the total diabatic (i.e., solar plus exothermic chemical reaction) heating by 5 to 15 percent between 60 and 80 km.
Global, collisional model of high‐energy photoelectrons
Authors: Khazanov G. V. , Moore T. E. , Liemohn M. W. , Jordanova V. K. , Fok M. ‐C.
Published: February 2004

A previously‐developed colissional, interhemispheric flux tube model for photoelectrons (PE) [Khazanov et al., 1994] has been extended to three dimensions by including transport due to and magnetic gradient‐curvature drifts. Using this model, initial calculations of the high‐energy (≥50 eV) PE distribution as a function of time, energy, pitch angle, and spatial location in the equatorial plane, are reported for conditions of low geomagnetic activity. To explore both the dynamic and steady behaviors of the model, the simulation starts with the abrupt onset of photoelectron excitation, and is followed to steady state conditions. The results illustrate several features of the interaction of photoelectrons with typical magnetospheric plasmas and fields, including collisional diffusion of photoelectons in pitch angle with flux tube filling, diurnal intensity and pitch angle asymmetries introduced by directional sunlight, and energization of the photoelectron distribution in the evening sector. Cross‐field drift is shown to have a long time scale, taking 12 to 24 hours to reach a steady state distribution. Future applications of the model are briefly outlined.
Blue jets produced by quasi‐electrostatic pre‐discharge thundercloud fields
Authors: Pasko V. P. , Inan U. S. , Bell T. F.
Published: February 2004

Pre‐discharge quasi‐electrostatic (QE) fields immediately above the thundercloud lead to the formation and upward propagation of streamer type ionization channels with features in good agreement with recent video observations of Blue Jets.
Ponderomotive acceleration of ions by circularly polarized electromagnetic waves
Authors: Lee Nam C. , Parks George K.
Published: February 2004

The ponderomotive acceleration of multi‐species ions due to circularly polarized electromagnetic waves propagating parallel to the magnetic field is calculated. When applied to a low frequency left‐hand circularly polarized wave, the results show differential accelerations among the different ion species. We demonstrate that differential acceleration of ion species by the ponderomotive force can occur even in the absence of a parallel electric field component. Our work extends the results previously obtained by Li and Temerin (1993) who considered the ponderomotive acceleration due to obliquely propagating Alfvén waves.
Comparison of proxy records of climate change and solar forcing
Authors: Crowley Thomas J. , Kim Kwang‐Yul
Published: February 2004

The role of solar variability as a cause of decadal‐centennial scale climate change continues to be a topic of debate. Herein we compare two estimates of solar variability since 1600 with two estimates of northern hemispheric temperature change. Sun‐climate correlations vary between 0.57–0.74 and are significant at the 95% level. However, the small number of oscillations in the time series suggests to us that longer records are needed for a more convincing demonstration of a significant sun‐climate linkage. Forcing of an energy balance model with the solar time series indicates that modest amounts of solar variability and climate sensitivity yield temperature variations that represent a significant fraction of the inferred changes during the Little Ice Age. This latter result further supports the hypothesis that solar variability may be significantly contributing to climate change on decadal‐centennial time scales.
Moon‐solar wind interactions: First results from the WIND/3DP Experiment
Authors: Bosqued J. M. , Lormant N. , Rème H. , d'Uston C. , Lin R. P. , Anderson K. A. , Carlson C. W. , Ergun R. E. , Larson D. , McFadden J. , McCarthy M. P. , Parks G. K. , Sanderson T. R. , Wenzel K.‐P.
Published: February 2004

Launched on November 1, 1994, the WIND spacecraft passed behind the moon on December 27, 1994 and remained in its optical shadow for ∼41 minutes. At the time the moon was immersed in the interplanetary medium and a large amount of new data has been collected by the WIND/3DP experiment. The nature of the flow near the moon is described by presenting detailed electron and ion plasma parameters in various regions; a structured lunar plasma umbra is clearly observed downstream of the moon at XSSE ∼ −6 RM, characterized by a gradual decrease of electron and ion densities to values of <0.5 cm−3 near the center of the optical umbra. The plasma umbra is surrounded by a penumbra region in which plasma densities and magnetic field magnitude decrease and plasma flow undergoes small but noticeable variations. Analysis of magnetic shielding effects show that medium energy electrons follow the interplanetary magnetic field lines and are partially occulted by the moon. These first WIND results on the detailed properties of the downstream flow and the cavity extent are compared with fluid descriptions of the global moon‐solar wind interaction.
Interstitial water chemistry of sediments of the Costa Rica Accretionary Complex off the Nicoya Peninsula
Authors: Zuleger E. , Gieskes J. M. , You C.‐F.
Published: February 2004

Interstitial water analyses from numerous piston, gravity, and Alvin push cores show that fluid flow at the Costa Rica Accretionary Prism is spatially limited and can only be detected by visually directed cores in zones of biogenic activity. Most of the sites cored show evidence for normal diagenetic processes in rapidly deposited, organic carbon‐rich sediments, with little evidence for fluid advection. However, in visually directed Alvin push cores, obtained from black sulfidic sediments characterized by the presence of Calyptogena clams or tubeworms, evidence for fluids advected upward from greater depth horizons is shown. These zones are associated with a large mudvolcano on the prism and with the zoes of Out Of Sequence Thrusts. As changes from sea water concentrations are still relatively small, substantial mixing with sea water must have occurred during this upward fluid movement.
Kilometric irregularities in the E and F regions of the daytime equatorial ionosphere observed by a high resolution HF radar
Authors: Blanc Elisabeth , Mercandalli Brigitte , Houngninou Etienne
Published: February 2004

During the International Equatorial Electrojet Year, high resolution vertical HF coherent radar experiments were performed in the Ivory Coast (9°24′62″N, 5°37′38″W) at frequencies in the range 1–8 MHz. Kilometric scale irregularities were observed in the E and F regions of the daytime equatorial ionosphere. These irregularities constitute a large sporadic E layer within the altitude range 100 to 150 km, larger than the width of the equatorial electrojet. The higher part of this irregular region is detached in the morning and evening forming an intermediate region at 150–160 km. These 150 km echoes overtakes the E region electrojet echoes at 100–120 km at noon. The echolocation shows that the reflections arise from the vertical direction up to 150 km with a significant contribution of reflections from East West directions above 110 km. The F1 region irregularities are characterized by time and height scales significantly larger than the E region irregularities scales. As in the E region, the F1 region reflections arise from the vertical and from East West directions when the reflection distance increases. The variations of the Doppler frequency versus the observation distance at several sounding frequencies are well explained by a horizontal motion of the irregular plasma flow both in the E and F regions with velocities of 100 m/s and 130 m/s respectively.
Initial results from the ICEMELT Experiment: Body‐wave delay times and shear‐wave splitting across Iceland
Authors: Bjarnason Ingi Th. , Wolfe Cecily J. , Solomon Sean C. , Gudmundson Gunnar
Published: February 2004

We present results from the first stage of the ICEMELT broadband seismometer experiment designed to determine upper mantle structure beneath Iceland, a hotspot located on the Mid‐Atlantic Ridge. Relative delays of teleseismic body waves across Iceland are in excess of l s for P waves and as large as 3 s for S waves. The patterns of P and S wave delays suggest a low‐velocity anomaly in the upper few hundred kilometers beneath central Iceland, consistent with the signature of mantle upwelling beneath a hotspot. Shear‐wave splitting measurements of the fast polarization direction ϕ and the delay time δt between the fast and slow shear waves have been obtained at several network stations. Splitting times range from 0.7 to 1.7 s, and fast directions are generally between N20°W and N45°W. While splitting times of this magnitude must be primarily signatures of the anisotropy of the Icelandic upper mantle, the directions of fast polarization are inconsistent with simple models of horizontally diverging flow either in the plate spreading direction or radially from the center of the hotspot. A hypothesis consistent with splitting data obtained to date is that the dominant contribution to upper mantle anisotropy is from the large‐scale mantle flow field of the North Atlantic.
Low stable isotope ratios of tropical cyclone rains
Authors: Lawrence Robert James , Gedzelman David Stanley
Published: February 2004

Tropical cyclone rains have distinctly lower stable isotope ratios than rains in other tropical and summer precipitation systems, with a mean value slightly above that of water vapor near the sea surface. The isotope ratios also decrease radially inward to the eye wall, but appear to be anomalously low even near the periphery of the rain shield. These findings indicate that tropical cyclones are highly efficient precipitation systems and suggest the use of stable isotope ratios as dynamic tracers of a tropical cyclone's water and energy budgets.
Self‐diffusion of water in a natural hypersaline solution (Dead Sea brine)
Authors: Yechieli Yoseph , Ronen Daniel
Published: February 2004

The self‐diffusion of H218O has been studied empirically in Dead Sea brine (TDS ≈ 340 g/l), a natural, very saline solution composed of mainly Mg and Na chlorides. Experiments were conducted in dialysis cells with 18O‐depleted water at an ambient temperature of 22±1°C. The self‐diffusion coefficient in DS water is 1.8 × 10−5 cm²/sec, about 25% lower than the known self‐diffusion coefficient in distilled water. Knowledge of the self‐diffusion coefficient in hypersaline solutions is of importance for the determination of mass transfer in brines, at sediment‐water interfaces in lakes and in interstitial solutions of saturated and unsaturated porous media in aquifers.
Are low‐latitude Pi2 pulsations cavity/waveguide modes?
Authors: Allan W. , Menk F. W. , Fraser B. J. , Li Y. , White S. P.
Published: February 2004

The plasmasphere seems the most likely magnetospheric region in which compressional hydromagnetic waves may be trapped to form cavity modes. It has been suggested that substorm‐associated Pi2 magnetic pulsations have a cavity mode character at low latitudes. Recent detailed observations of night‐side Pi2 events at low latitudes have also suggested a cavity or waveguide character. We apply a well‐tried numerical hydromagnetic wave coupling model at low latitudes, and compare the model output with these observations. We find that the qualitative amplitude and phase characteristics of the model magnetic fields in latitude and longitude fit well with the observations, provided the ionospheric boundary condition at low latitudes gives negligible rotation of magnetic field components between ionosphere and ground. The comparison supports the idea that low‐latitude Pi2 pulsations are cavity/waveguide modes. It also suggests that the magnetic H component observed at the ground near the equator may be a combination of the radial and compressional components above the ionosphere.
Grain boundary melt films in an experimentally deformed olivine‐orthopyroxene rock: Implications for melt distribution in upper mantle rocks
Authors: Drury Martyn R. , Fitz Gerald John D.
Published: February 2004

An unexpected microstructure, with important implications for melt distribution in the upper mantle, has been found in a 70% olivine +30% orthopyroxene rock experimentally deformed at 1500K, 300 MPa, where incipient partial melting occurred. As found in previous studies of comparable systems, most melt in the olivine‐orthopyroxene sample resided in a network of grain‐edge tubes and occasional thick (50–500 nm) layers. We infer, using electron microscopy at its highest resolution, that melt also existed in another form as glass films 1.0–1.5 nm thick, along all grain boundaries, with total film fraction (F) of 0.0002. All of these melts are unusually SiO2‐rich. Further work is needed to confirm that the thin films are not transient, although their coexistence with smoothly curved solid‐melt interfaces and flat crystal faces suggests they are stable. If thin high‐silica melt films are stable they might influence physical properties and melt extraction processes in regions of incipient melting and metasomatism in the upper mantle.