bluuebunny/crossref_metadata_2025 huggingface dataset:
Solute dilution at the Borden and Cape Cod groundwater tracer tests
Authors: Thierrin Joseph , Kitanidis Peter K.
Published: February 2004

This study presents an analysis of the rate of dilution of a conservative nonreactive tracer in two well‐known field experiments: The Borden (Ontario, Canada) experiment and the Cape Cod (Massachusetts) experiment. In evaluating the dilution of injected sodium bromide, in addition to computing the second spatial moments, we have used the dilution index and the reactor ratio. The dilution index is a measure of the formation volume occupied by the solute plume, and the reactor ratio is a shape factor, which measures how stretched and deformed the plume is. Unlike the second moments, which may go up or down during an experiment, the dilution index should increase monotonically. The results for both plumes were quite similar. After an initial period the dilution index increased linearly with time, which is macroscopically equivalent to transport in two‐dimensional uniform flow. The reactor ratio was relatively constant during the period of the experiments. Their values, about 0.72 for the Borden test and 0.63 for the Cape Cod test, indicate that the Cape Cod plume was more stretched and deformed than the Borden plume. The maximum concentration, which is an alternative to the dilution index for quantifying dilution, was found to be more erratic and more susceptible to sampling error.
Long‐Term Hydrologic and Biogeoehemieal Responses of a Soft Water Seepage Lake in North Central Wisconsin
Authors: Wentz Dennis A. , Rose William J. , Webster Katherine E.
Published: February 2004

Hydrologic and chemical budgets were determined for the period October 1980 through September 1988 for Vandercook Lake, a 43‐ha soft water seepage lake located in predominantly sandy outwash in northern Wisconsin. The 1951–1980 mean annual precipitation for the lake, based on nearby National Weather Service (NWS) stations, was 825 mm; volume‐weighted pH of bulk atmospheric deposition during the 8‐year study averaged 4.7. From October 1980 through September 1983, annual precipitation was 108% of the 30‐year NWS average, annual recharge was 144% of the 8‐year study period average, and annual groundwater inflow to the lake ranged from 5 to 9% of the total inflow. From October 1986 through September 1988, annual precipitation was 90% of the NWS average, annual recharge was 30% of the study period average, and the lake received no groundwater inflow. During the study, the lake changed from a system whose buffering mechanism was significantly influenced by mineral weathering in inflowing groundwater to one dominated by in‐lake sulfate reduction. The functional differences exhibited by this lake during the 8 years of study demonstrate the tenuousness with which conclusions based on shorter‐term studies of similar systems must be considered.
Flooding Hydrology and Mixture Dynamics of Lake Water Derived from Multiple Sources in an Amazon Floodplain Lake
Authors: Lesack Lance F. W. , Melack John M.
Published: February 2004

The temporal dynamics in the lake water mixture derived from river flooding, local rainfall and runoff, exchange with an adjacent lake, groundwater exchange, and evaporation was computed from detailed measurements over an annual cycle for a permanent lake on the central Amazon floodplain. River water invaded the lake at the start of rising water, but by mid‐rising water, lake water steadily flowed out from the lake and into the river, while river levels continued to rise. Despite a relatively low ratio of catchment area to water surface area, the lake exported to the river three times the amount of water originally received from the river. The lake water mixture was dominated by river water early during the water year, increasing to 70% of the mixture. When lake water began flowing out from the lake, the river water fraction was steadily diluted as runoff became dominant. By the end of the water year, runoff contributed 57% of the total water input, river inflow 21%, rainfall 11%, inflow from an adjacent lake 6%, and seepage inflow 4%. However, local runoff, river inflow, and lake water carried over between water years have the potential for considerable interannual variation. The finding that runoff from relatively small local catchments can be sufficiently large to prevent flood waters from entering the lakes during periods of rising water may critically limit our ability to characterize the long‐term frequency and duration of flooding in lakes on the floodplains of large rivers in the wet tropics.
A Three‐Dimensional Miscible Transport Model For Seawater Intrusion in China
Authors: Xue Yuqun , Xie Chunhong , Wu Jichun , Liu Peimin , Wang Jianji , Jiang Qingbo
Published: February 2004

A three‐dimensional miscible transport model for seawater intrusion in a phreatic aquifer with a transition zone is presented. This model considers many important factors, such as the effect of variable density on fluid flow, the effect of precipitation infiltration and phreatic surface fluctuation on the process of seawater intrusion, the existence of great discharge pumping wells, etc. The difficulty in solving this problem can be tackled by the presented numerical method and iteration technique. This model is used to describe seawater intrusion in Huangheying, Longkou, People's Republic of China. The simulated values agree very well with the field data (e.g., the total mean values of the absolute error of Cl− concentration are 46.13 mg/L and 55.67 mg/L, respectively, and those of the water head are 0.24 m and 0.08 m, respectively).
Unsaturated Hydraulic Conductivity Measured by Time Domain Reflectometry Under a Rainfall Simulator
Authors: Parkin Gary W. , Kachanoski R. Gary , Elrick David E. , Gibson Richard G.
Published: February 2004

We used time domain reflectometry (TDR) probes installed vertically at the soil surface beneath a constant‐rate rainfall simulator to measure cumulative water storage and the soil's unsaturated hydraulic conductivity. The slope from linear regression of water storage on time before any applied water infiltrates to the bottom of the TDR probe gives an estimate of the local infiltration rate. Local infiltration rates measured by TDR in the field were plotted against the corresponding local steady state water contents to give an estimate of the soil's unsaturated hydraulic conductivity over a range in water content of 20% using only two applied rainfall rates. The spatial variability in local infiltration rates may be the result of infrequent high‐intensity pulses of rainfall leading to temporary ponding and redistribution of water at the soil surface. Nonlinear optimization was used to estimate the saturated hydraulic conductivity and inverse capillary length scale from TDR data.
Water Recharge and Solute Transport Through the Vadose Zone of Fractured Chalk Under Desert Conditions
Authors: Nativ Ronit , Adar Eilon , Dahan Ofer , Geyh Mebus
Published: February 2004

This study focuses on water flow and solute migration through unsaturated fractured chalk in an arid area. The chalk underlies a major industrial complex in the northern Negev desert, where groundwater contamination has been observed. Four dry‐drilling holes were bored through the vadose zone. Core and auger samples, collected at 30‐ to 50‐cm intervals, were used for chemical and isotopic analyses, enabling the construction of the following profiles: (1) a tritium profile, to estimate the rate of water flow through the unsaturated zone; (2) oxygen 18 and deuterium profiles, to assess the evaporation of water at land surface before percolation, and in the upper part of the vadose zone after infiltration; and (3) chloride and bromide profiles, as tracers for inert solutes and pollutants. The tritium and bromide profiles showed the rate of infiltration through the unsaturated matrix to be very slow (1.6–11 cm/yr). The chemical and isotopic data from the core holes suggested that the pore water changes characteristics with depth. Close to land surface, the pore water is strongly evaporated (δ18O = +5.94‰) and highly concentrated (∼29 meq Cl/100 g rock), but changes gradually with depth to amore dilute concentration (∼4 meq Cl/100 g rock) and isotopically depleted composition (δ18O = −4.4‰), closer to the isotopic composition of precipitation and groundwater. Nearby monitoring wells have shown anthropogenic contribution of heavy metals, organic compounds, and tritium (Nativ and Nissim, 1992). A conceptual model is proposed in which a small portion of the rainwater percolates downward through the matrix, while a larger percentage of the percolating water moves through preferential pathways in fractures. The water flowing through the fractures penetrates the matrix across the fracture walls, where it increases the tritium concentrations, depletes the stable isotopic composition, and dilutes the salt concentrations. The observed rapid downward migration of tritium and heavy metals through the profuse fractures makes the chalk inefficient as a hydrologic barrier.
Parameter Estimation and Stochastic Interpretation of the Transient Storage Model For Solute Transport in Streams
Authors: Hart Deborah R.
Published: February 2004

A stochastic model for solute transport in streams with transient storage zones is presented. This model has an analytic solution in terms of a rapidly converging infinite series. Besides being computationally efficient, this solution is of interest because the terms of the series can be interpreted physically. Simple methods for roughly estimating storage zone parameters directly from tracer injection data are introduced. These methods give quick estimates of these parameters without requiring solutions to the model equations.
Three‐Dimensional Analytical Models of Contaminant Transport From Nonaqueous Phase Liquid Pool Dissolution in Saturated Subsurface Formations
Authors: Chrysikopoulos Constantinos V.
Published: February 2004

Closed form analytical solutions are derived for three‐dimensional transient contaminant transport resulting from dissolution of single‐component nonaqueous phase liquid pools in saturated porous media. The solutions are suitable for homogeneous porous media with unidirectional interstitial velocity. The dissolved solute may undergo first‐order decay or may sorb under local equilibrium conditions. The solutions are obtained for rectangular and elliptic as well as circular source geometries, assuming that the dissolution process is mass transfer limited, by applying Laplace and Fourier transforms. Although the solutions contain integral expressions, these integrals are easily evaluated numerically. These solutions are useful for verifying the accuracy of numerical solutions to more comprehensive models and for design and interpretation of experiments in laboratory‐packed beds and possibly some field studies. The results of several simulations indicate that for short downstream distances, predictions of contaminant concentrations are sensitive to the source structure and orientation with respect to the direction of interstitial flow.
Approximate Mixed‐Integer Nonlinear Programming Methods for Optimal Aquifer Remediation Design
Authors: McKinney Daene C. , Lin Min‐Der
Published: February 2004

An optimal aquifer remediation design model employing a nonlinear programming algorithm was developed to find the minimum cost design of a pump‐and‐treat aquifer remediation system. The mixed‐integer nonlinear programming model includes the discontinuous fixed costs of system construction and installation as well as operation and maintenance. The fixed cost terms in the objective function have been approximated by continuous functions of the decision variables using a polynomial penalty coefficient method resulting in a nonlinear programming formulation of an otherwise mixed‐integer nonlinear programming model. Results of applying the new polynomial penalty coefficient method to an example design problem show that a combined well field and treatment process model hat includes fixed costs has a significant impact on the design and cost of aquifer remediation systems, reducing system costs by using fewer, larger flow rate wells. Previous pump‐and‐treat design formulations have resulted in systems with numerous, low flow rate wells due to the use of simplified cost functions that do not exhibit economies of scale or fixed costs. The polynomial penalty coefficient method results were compared to two alternative approximate mixed‐integer nonlinear programming methods for solving optimal quifer remediation design problems, the pseudo‐integer method and the exponential penalty coefficient method. The polynomial penalty coefficient method obtains the same solutions and performs as well as or better than the exponential penalty coefficient method. The polynomial penalty coefficient method almost always results in better, less expensive designs and requires significantly less computer time than the pseudo‐integer method.
The Effect of Constant Anisotropy on Capillary Barrier Performance
Authors: Stormont J. C.
Published: February 2004

Ross' solution for the divergence capacity of a capillary barrier is modified to incorporate constant hydraulic conductivity anisotropy of the fine layer. The analysis assumes steady infiltration and that the principal directions of the hydraulic conductivity tensor are parallel and normal to the fine‐coarse contact. The solutions for divergence capacity and length have two terms. The first term, similar to the solution of Ross, represents the diversion due to the presence of the capillary barrier and is proportional to the hydraulic conductivity parallel to the contact. The second term, which arises from infiltration into an anisotropic medium independent of the capillary barrier, is a function of the fine layer thickness and will be small for engineered barriers. Thus an anisotropic fine layer with a greater hydraulic conductivity in the direction parallel to the fine‐coarse contact will extend the performance of a capillary barrier as measured by its divergence capacity and length.
Pool Spacing in Forest Channels
Authors: Montgomery David R. , Buffington John M. , Smith Richard D. , Schmidt Kevin M. , Pess George
Published: February 2004

Field surveys of stream channels in forested mountain drainage basins in southeast Alaska and Washington reveal that pool spacing depends on large woody debris (LWD) loading and channel type, slope, and width. Mean pool spacing in pool‐riffle, plane‐bed, and forced pool‐riffle channels systematically decreases from greater than 13 channel widths per pool to less than 1 channel width with increasing LWD loading, whereas pool spacing in generally steeper, step‐pool channels is independent of LWD loading. Although plane‐bed and pool‐riffle channels occur at similar low LWD loading, they exhibit typical pool spacings of greater than 9 and 2–4 channel widths, respectively. Forced pool‐riffle channels have high LWD loading, typical pool spacing of <2 channel widths, and slopes that overlap the ranges of free‐formed pool‐riffle and plane‐bed channel types. While a forced pool‐riffle morphology may mask either of these low‐LWD‐loading morphologies, channel slope provides an indicator of probable morphologic response to wood loss in forced pool‐riffle reaches. At all study sites, less than 40% of the LWD pieces force the formation of a pool. We also find that channel width strongly influences pool spacing in forest streams with similar debris loading and that reaches flowing through previously clear‐cut forests have lower LWD loading and hence fewer pools than reaches in pristine forests.
A Two‐Component Mixing Model for Predicting Regional Episodic Acidification of Surface Waters During Spring Snowmelt Periods
Authors: Eshleman Keith N. , Davies Trevor D. , Tranter Martyn , Wigington Parker J.
Published: February 2004

A two‐component mixing model of acid neutralizing capacity (ANC) is proposed for explaining two observed features related to the episodic acidification of surface waters during snowmelt periods: (1) maximum episodic declines in ANC are largest in high ANC systems and increase linearly with antecedent ANC and (2) relative depressions in ANC attributable to increases in nitric acid concentrations are larger in low ANC systems, while relative depressions in ANC attributable to dilution of base cations are larger in high ANC systems. Conceptually, the model represents the physical mixing of two hydrochemical end‐members within a surface water environment, although the physical sources of water in the model are undefined. The model is shown to explain 55–72% of the total variation of these characteristics among various surface water systems within the Catskill and Adirondack mountain regions of New York. In addition, the model also explains 11–47% of the relative depression in ANC attributable to natural organic acidity in surface waters in these regions. The model is subsequently linked to an empirical equilibrium acidification model for predicting the long‐term episodic acidification response of Adirondack lakes during snowmelt periods. Model predictions suggest that percentage decreases in sulfuric acid concentrations of the magnitude mandated by the 1990 Clean Air Act Amendments (40%) will not restore to positive values the ANC of all Adirondack lakes which are currently acidic (ANC < 0) during spring snowmelt periods. Long‐term increases in nitric acid concentrations may counterbalance the expected increases in ANC attributable to reductions in sulfur deposition.
Evaluation of the ERS 1/Synthetic Aperture Radar Capacity to Estimate Surface Soil Moisture: Two‐Year Results Over the Naizin Watershed
Authors: Cognard Anne‐Laure , Loumagne Cécile , Normand Michel , Olivier Philippe , Ottlé Catherine , Vidal‐Madjar Daniel , Louahala Sami , Vidal Alain
Published: February 2004

One of the possible applications of satellite radar remote sensing is to estimate surface soil moisture. To evaluate the capacity of ERS 1/synthetic aperture radar (SAR), a European Space Agency (ESA) pilot project has been set up. The test site is a small agricultural watershed situated in the central part of French Brittany. During 1992 and 1993, almost all possible SAR images were acquired together with two types of ground truths: intensive ground measurements during 14 field campaigns and point automatic measurements over the entire period. From the comparison of those ground truth data with the ERS 1 images, the following results are obtained. On a field scale the relation between the radar signal and the surface soil moisture depends strongly on the type of culture: Correlation is poor for the different cultures except for wheat. On a basin scale, it is shown that during the period of low vegetation density, there is a linear correlation between the mean radar data and the point automatic measurements. This last result is very encouraging and could open the way to hydrological applications.
Tree ring width and density evidence of climatic and potential forest change in Alaska
Authors: Jacoby Gordon C. , D'Arrigo Rosanne D.
Published: February 2004

Ring width and density measurements from the same trees can produce distinctly different climatic information. Ring width variations and recorded data in central and northern Alaska indicate annual temperatures increased over the past century, peaked in the 1940s, and are still near the highest level for the past 3 centuries. Density variations indicate summer temperatures are now warm but not above some previous levels occurring prior to this century. The early cooler period, corresponding to the Little Ice Age, was interrupted by brief warm intervals. The recent increase in temperatures combined with drier years may be changing the tree response to climate and raising the potential for some forest changes in Alaskan and other boreal forests.
Assimilation of surface data in a one‐dimensional physical‐biogeochemical model of the surface ocean: 1. Method and preliminary results
Authors: Prunet Pascal , Minster Jean‐François , Ruiz‐Pino Diana , Dadou I.
Published: February 2004

A new method to transform satellite ocean color data into estimates of primary production and carbon fluxes is presented. A one‐dimensional coupled physical‐bio‐geochemical model of the surface ocean is constrained to reproduce the seasonal evolution of surface chlorophyll concentration by adjusting the parameters of the 10‐compartment trophic system using a variational technique. The method is applied to in situ surface chlorophyll data from station Papa, but averaged over the characteristic depth of ocean color measurements, and affected by errors compatible with those of satellite values. Using 35 measurements for the year 1976, it is found that five linear combinations of the trophic parameters can be adjusted. This adjustment is also valid for 1975 chlorophyll data. In general, the adjusted values of the trophic parameters are sensitive to their a priori values, but consistent results are found for the grazing rate (0.35 to 0.6 d−1), the phytoplankton mortality rate (very small), and the minimum concentration of zooplankton in winter (less than 0.16 mmolC m−3). Some carbon fluxes, namely photosynthetic carbon production in the euphotic layer (95 to 110 gC m−2 yr−1), its regeneration by grazing (60 % of the latter), and the recycling efficiency of nitrogen (60%) seem to be robustly constrained, though primary production is apparently underestimated compared to the most recent ones. The export flux amounts to 35 to 40% of primary production, but its value depends on the particle sinking rate, which is not adjustable from chlorophyll data. This study suggests that simplified biological models, compared to the model used here, would be sufficient to achieve this task.
Magnetic hysteresis in young mid‐ocean ridge basalts: Dominant cubic anisotropy?
Authors: Gee Jeff , Kent Dennis V.
Published: February 2004

Magnetic hysteresis data from young mid‐ocean ridge basalts include samples with saturation remanence to saturation magnetization (Mrs/Ms) ratios greater than 0.5, the theoretical limit for an assemblage of single domain grains with uniaxial anisotropy. Under the usual assumption of dominant uniaxial anisotropy, the narrow single domain grain size distribution implied by these high Mrs/Ms values is difficult to reconcile with petrographic and remanence data that suggest the presence of larger multidomain grains. Dominant cubic anisotropy provides a plausible explanation for the high Mrs/Ms ratios, and if generally valid, requires reinterpretation of granulometric and domain state inferences made from hysteresis data.
Fault zone strength and failure criteria
Authors: Marone Chris
Published: February 2004

This paper discusses Coulomb failure criteria for brittle deformation of intact rock and fault gouge. Data are presented from laboratory experiments designed to identify the critical gouge layer thickness required to effect a transition from the standard Coulomb criterion to a modified failure law (referred to as Coulomb plasticity) appropriate for simple shear of a gouge layer. Experiments were carried out using tension fractures and quartz powder to simulate granular fault gouge. Fractures sheared without gouge obey the standard Coulomb law. A 0.6mm‐thick gouge layer was required to effect the transition to Coulomb plasticity. I test and reject the hypothesis that fault zone strength and apparent coefficient of internal friction can be predicted from fracture of intact rock simply by accounting for differences in the failure laws and without considering variations in the Coulomb parameters. The data presented indicate that the stress state required for Coulomb plasticity is not developed within very thin gouge layers. This work implies that brittle fault zones have lower friction than predictions based on the strength of intact rock. However, the magnitude of this weakening effect is small (for example, a coefficient of sliding friction of 0.75 would be reduced to 0.6) and thus it is not an independent explanation of the apparent weakness of mature faults.
Three‐dimensional magnetic reconnection and the magnetic topology of coronal mass ejection events
Authors: Gosling J. T. , Birn J. , Hesse M.
Published: February 2004

Measurements of suprathermal electron fluxes in the solar wind indicate that field lines within coronal mass ejections, CMEs, near and beyond 1 AU are normally connected to the Sun at both ends. However, on occasion some field lines embedded deep within CMEs appear to be connected to the Sun at only one end. Here we propose an explanation for how such field lines arise in terms of 3‐dimensional reconnection close to the Sun. Such reconnection also provides a natural explanation for the flux rope topology characteristic of many CMEs as well as the coronal loops formed during long‐duration, solar soft X‐ray events. Our consideration of the field topologies resulting from 3‐dimensional reconnection indicates that field lines within and near CMEs may on occasion be connected to the outer heliosphere at both ends.
Isentropic mixing in the Arctic stratosphere during the 1992–1993 and 1993–1994 winters
Authors: Dahlberg Steven P. , Bowman Kenneth P.
Published: February 2004

Dynamic isolation of the winter Arctic circumpolar vortex during 1992–1993 and 1993–1994 (the second and third northern hemisphere winters of the UARS mission) is studied using quasi‐horizontal isentropic trajectories. Ejection of vortex air and entrainment of mid‐latitude air into the vortex are quantified and compared with climatological values obtained from the analysis of 16 Arctic winters. A number of unusual features of both winters are discussed. The most notable features are the anomalous isolation experienced by the vortex during December 1992 and the unusual degree of isolation and persistence of the vortex during February and March of both years. The 1992–1993 winter season is the most consistently isolated vortex on record. Only during January 1993, when entrainment is large, is this pattern of extreme isolation broken.
Greenland Ice Sheet over the next 5000 years
Authors: Loutre Marie‐France
Published: February 2004

The two‐dimensional climate model developed by Gallée et al. [1991, 1992] in Louvain‐la‐Neuve (2‐D‐LLN climate model) has been used to test the long‐term response of the climate system to carbon dioxide (CO2) concentration changes induced by fossil fuel energy consumption. Three scenarios of future atmospheric CO2 concentration have been designed : in the first two, the concentration is kept constant over the next 5000 years (5 ka), first to the pre‐industrial value (280 parts per million volume, 280 ppmv) and second, to the double of the present‐day value (710 ppmv). In a third scenario, it has been assumed that the pre‐industrial CO2 concentration will rise from 280 to 710 ppmv within the next 500 years and then decrease progressively to reach 450 ppmv and 350 ppmv, respectively 1000 years and 1500 years from now. In such a scenario, the mean annual and hemispheric temperature is shown to increase by about 3°C due to the increase in the atmospheric CO2 concentration from 280 ppmv to 710 ppmv. High latitudes are more sensitive than low latitudes, this being related to important albedo changes over these regions. While the Greenland ice sheet does not change significantly if the pre‐industrial CO2 concentration is assumed to remain constant, it rapidly collapses with a CO2 concentration of 710 ppmv kept constant over the next 5 ka. Even in the third scenario where the CO2 concentration progressively returns to the present‐day value at the end of the simulation (5 ka after present (5 ka AP)), the Greenland ice sheet disappears also.
Relativistic electron precipitation enhancements near the outer edge of the radiation belt
Authors: Nakamura R. , Baker D. N. , Blake J. B. , Kanekal S. , Klecker B. , Hovestadt D.
Published: February 2004

We examined characteristics of relativistic electron precipitation bursts observed by the Heavy Ion Large Telescope (HILT) experiment onboard the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite. We report on relatively narrow, persistent, latitudinal bands of precipitation with time scales of 10∼30 sec near the outer edge of the radiation belt: these develop and decay with a time scale of a few hours. Acceleration processes more effective than the usual radial diffusion process or scattering process would be needed to explain this strong precipitation band phenomenon. Another prominent signature is microbursts with a time scale down to a few hundred milliseconds. It is suggest that these microbursts are due to wave‐particle interaction involving a relaxation‐oscillator type of mechanism.
Satellite observations of transionospheric pulse pairs
Authors: Holden D. N. , Munson C. P. , Devenport J. C.
Published: February 2004

The BLACKBEARD payload aboard the ALEXIS satellite has been making broadband observations in the VHF band of the radio spectrum. Since November of 1993 several hundred unusual signals have been recorded. The peculiar nature of these bursts of radio noise is that they have a duration of approximately 10 µsec, are typically 20 to 40 dB brighter than the average background, and occur in pairs separated by approximately 50 µsec. We have dubbed these emissions TransIonospheric Pulse Pairs, or TIPP events. We do not know what the source of these emissions is, but the dispersion of these signals is consistent with an origin at or near the earth's surface. The satellite field of view and time of day when TIPP events are generally detected are consistent with regions of thunderstorm activity such as south‐central Africa or Indonesia.
Discrimination of geophysical phenomena in satellite radar interferograms
Authors: Massonnet Didier , Feigl Kurt L.
Published: February 2004

Various geophysical phenomena are recorded in the interference patterns formed by differencing two synthetic aperture radar (SAR) images. The fringes generated by the topographic relief can be removed using a digital elevation model (DEM). The remaining fringes map the change in satellite‐to‐ground range which occurred between the acquisition times of the two images. By comparing different pairs of images spanning different intervals of time, it is possible to discriminate between geophysical signal and interferometric artifact. Here we apply this pair‐wise logic to the area around the 1992 Landers, California earthquake using SAR images acquired by the ERS‐1 satellite. The range varies with time as a constant, step, impulsive, or sloping function. Examples of each type include a DEM error, an aftershock, two atmospheric perturbations, and postseismic afterslip, respectively. Their signatures are identified and separated using the pair‐wise logic.
Overlapping fault planes of the 1971 San Fernando and 1994 Northridge, California earthquakes
Authors: Mori Jim , Wald David J. , Wesson Robert L.
Published: February 2004

Aftershocks of the 1971 San Fernando and 1994 Northridge earthquakes were relocated using a three‐dimensional velocity model that was derived from inverting P‐wave travel time data. The hypocenters show clear orientations of the dipping fault planes. The San Fernando aftershocks form a plane extending from a depth of 15 km to the surface, dipping toward the northeast at about 40°. The Northridge aftershocks delineate a fault extending from a depth of 18 km up to about 5 km, dipping toward the southwest at about 40°. In the region the aftershocks overlap in map view, the San Fernando plane cuts off the Northridge plane at a depth of 5 to 8 km, preventing it from reaching the surface. The similar but oppositely dipping fault planes suggest a pair of conjugate planes reflecting a horizontal northeast‐southwest compression.
Comparison of longterm greenhouse projections with the geologic record
Authors: Crowley Thomas J. , Kim Kwang‐Yul
Published: February 2004

Previous climate modeling studies suggest that temperature increases beyond 2100 AD due to greenhouse gas changes could be comparable to the Cretaceous. However, these projections have not been tested against a range of emission scenarios, nor have estimates of past temperature change been well restrained quantitatively. Herein we use a 1D energy balance model (EBM) with an upwelling‐diffusion ocean model to explore the temperature response to extreme cases of unrestricted and severely restricted greenhouse gas increases. Results are compared against revised estimates of global temperature change over the last 100 million years. For four of the six scenarios, global temperature projections by the years 2400–2700 equal or exceed levels of the Eocene or Cretaceous warm periods. The two exceptions involve scenarios with relatively low climate sensitivity and stringent conservation measures, but even in these projections temperatures are as warm as any time in the last 30 million years. These calculations suggest that regardless of emission scenario or system sensitivity, future greenhouse warming will be large even on a geological scale.
Moment tensor estimation using regional seismograms from a Tibetan Plateau portable network deployment
Authors: Randall George E. , Ammon Charles J. , Owens Thomas J.
Published: February 2004

We present the results of moment tensor inversions using regional seismograms recorded during the 1991–1992 PASSCAL passive seismic experiment on the Tibetan Plateau. Using data recorded over a one‐year period, we estimate the source mechanisms for 38 earthquakes within and near the Tibetan Plateau with moment‐magnitudes (Mw) ranging from 3.8 to 5.0. With only one exception, all the events within the Plateau, but away from the Plateau boundary, indicate either strike‐slip or extensional faulting, a result consistent with previous studies. Three‐fourths of all the events occurred at depths less than 10 km, and all but two depths less than 15 km. Several events, located near the southeastern section of the Plateau, exhibit an unusual mb‐Mw difference of approximately one magnitude unit.
Seasonality of precipitation along a meridian in the western United States
Authors: Rajagopalan Balaji , Lall Upmanu
Published: February 2004

We investigate seasonality of daily precipitation along a meridian in the Western U.S. using a nonparametric technique. The occurrence of daily precipitation is treated as a nonhomogeneous Poisson process and the time varying intensity function is estimated for every calendar day using a kernel estimator. The technique is fully data adaptive. We apply this technique to selected long record stations along a meridional transect spanning from Tucson, AZ to Priest River ID. Differences in the seasonality of precipitation occurrence and magnitude are revealed as a function of latitude and topographic factors. A monotonic trend in the seasonality of precipitation over the length of record is also observed.
Discharge rate of SO2 from Unzen Volcano, Kyushu, Japan
Authors: Hirabayashi Jun‐ichi , Ohba Takeshi , Nogami Kenji , Yoshida Minoru
Published: February 2004

The discharge rate of SO2 from Unzen volcano, which started erupting in November 1990, has been measured with a correlation spectrometer (COSPEC) at a fixed ground‐based station about 2.3 km SSW from the summit lava dome. The discharge rate of SO2 increased greatly after the explosive eruptions on June 8th and 11th, 1991. High discharge rates of SO2 (an average of 180 ton/day) were observed from July 1991 to January 1992, followed by a general decrease to an average of 110 ton/day during March 1992 and May 1994. The discharge rate of SO2 correlates with the extrusion rate of magma. Judging from the sulfur inventory, i.e., 130–450 g of discharged SO2 per ton of erupted magma, and the sulfur content of the extruded lava, the proportion of sulfur degassed from the magma is estimated to be ca. 80%, suggesting an efficient volatile degassing. The discharge rate of the total volatiles is calculated to be 7,700 ton/day by combining the SO2 discharge rate with the chemical composition of volcanic gases.
Magnetic stratigraphy of Chinese Loess as a record of natural fires
Authors: Kletetschka Günther , Banerjee Subir K.
Published: February 2004

Magnetic susceptibility records of paleosols and loess show high correlation with oxygen‐isotope stratigraphy of ocean sediments [Kukla, 1987], providing a global paleoclimatic record. Different models have been put forth to explain the nature and cause of susceptibility variations, but consensus has not yet been achieved. Our low‐temperature studies reveal a secondary magnetite component in paleosols that is characterized by a higher Verwey transition (115K) than that for the magnetite (100 K) in unaltered loess. The same shift in the Verwey transition can be achieved by heating and cooling loess samples. This is consistent with a new hypothesis that the magnetic signal from paleosols may be produced by natural fires in the past. Natural fire intensity is sensitive to the amount of annual precipitation, so that increased fire‐induced susceptibilities should reflect an increase in the humidity of regional climate.
Pore‐scale heterogeneity, energy dissipation and the transport properties of rocks
Authors: Bernabé Yves , Revil André
Published: February 2004

The pore structure of rocks is highly complex, with wide variations in pore size and shape. In this work, pore‐scale heterogeneity was simulated by distributing spheres, tubes and cracks with variable dimensions on a square lattice. The transport properties of 100 such network realizations, covering 11 orders of magnitude in permeability, were calculated. Seeking the appropriate averaging procedure to calculate the permeability and electrical conductivity from the local pore parameters, we computed the energy locally dissipated in each bond during fluid or electric flow and the energy globally dissipated in the whole network. By equating the latter to the sum of the former, we obtained averaging expressions exactly predicting the transport properties of the network realizations. Since these relations hold on a wide variety of heterogeneous networks covering a broad range of permeabilities and electrical conductivities, we propose that they should also be valid on rocks. We can thus gain insights into how pore‐scale heterogeneity affects the transport properties of rocks.
10 micron mapping of Jupiter on the CFHT after the impacts of comet P/Shoemaker‐Levy 9
Authors: Billebaud F. , Drossart P. , Vauglin I. , Merlin P. , Sibille F. , Lognonné P. , Lellouch E. , Mosser B.
Published: February 2004

We have observed Jupiter on July 24, 25, 26 and 27, 1994, in thermal infrared, using the French National 10 micron array camera “C10µ”, mounted on the Canada‐France‐Hawaii 3.6 meter telescope. The observations were made using both broad‐band and narrowband filters, as well as a Circular Variable Filter (CVF). Two observing programs were scheduled, one concerning atmospheric observations and the other one focusing on seismological observations (Lognonné et al., 1994). We present here preliminary results concerning the atmospheric program. The main result is that persistent brightness temperature enhancements still exist several days after the impacts at several wavelengths, corresponding to a long term perturbation associated to the impact sites.
Radionuclide migration experiments under laboratory conditions
Authors: Vandergraaf T. T.
Published: February 2004

Arguments are given in favour of performing non‐conservative radionuclide migration experiments in natural and artificial fractures under laboratory conditions. Results are presented from a series of migration experiments performed in a natural fracture in a quarried block of granite with overall dimensions of 81 × 90 × 75 cm. These experiments were conducted in a dedicated experimental facility and were designed to complement field migration experiments, to develop and test methodologies and to evaluate transport models. The flow path in the fracture was selected from the hydraulic characterization of the fracture using borehole to borehole pumping tests. Following migration experiments with stable, conservative tracers Br− and uranine, migration experiments were performed with a number of radionuclides at a flow rate of 3 mL/h. At the completion of the migration experiments, the fracture surfaces were scanned using a Ge(Li) gamma detector and an alpha probe to determine the sorbed radioisotope distributions on the fracture surfaces. The results from these experiments show that the behaviour of radioisotopes is usually more complex than can be represented by a simple, reversible sorption coefficient (Ka). However, the transport models that use this simple Ka tend to give conservative estimates of contaminant transport in environmental and safety assessment calculations.
Observations of Jupiter's synchrotron radiation at 18 cm during the comet Shoemaker‐Levy/9 impacts
Authors: Bolton S. J. , Foster R. S. , Waltman W. B.
Published: February 2004

The results of observations of Jupiter's synchrotron radiation during the period surrounding the impacts of comet Shoemaker‐Levy/9 are reported. The observations were made at the Naval Research Laboratory's Maryland Point Observatory 85 foot radio antenna operating at 1665 MHz (18 cm). The data indicate that an increase in the intensity of the synchrotron emission of 23% took place over the full duration of the impact period. The increase was accompanied by two characteristic changes in the beaming curve: a flattening and the creation of brightness temperature variations on hourly timescales. We interpret the latter as longitudinal variations in the beaming curve which suggests a localized mechanism resulting in a redistribution of the radiating electrons in the Jovian radiation belts.
Long‐term observations of keV ion and electron variability in the outer radiation belt from CRRES
Authors: Friedel R. H. W. , Korth A.
Published: February 2004

The distribution of energetic electrons and ions with L‐value (L≤8) as measured by the Electron‐Proton Angle Spectrometer onboard CRRES over the whole mission lifetime (July 1990 to October 1991) is presented. The outer radiation belt is shown to be highly dynamic, both in position and in strength. Substantial enhancements of electron and ion flux on short timescales are seen throughout most of the magnetosphere sampled by CRRES, and are strongly related to the Kp index and the ring current as measured by DST. These enhancements decay over less than 30 days. There is evidence of a magnetospheric electron and ion acceleration mechanism of considerable strength and efficiency. Very intense periods of activity (such as the March, 1991 storm) can lead to the creation of an additional, high‐energy belt in the slot region, which persists over a period of many months.
Radon emissions from mud volcanoes in northern Italy: Possible connection with local seismicity
Authors: Martinelli G. , Albarello D. , Mucciarelli M.
Published: February 2004

Data concerning Radon emission in waters filling mud volcanoes of Northern Apennines (Northern Italy) sampled from 1986 until 1989 have been analyzed. Possible connections between shallow environmental conditions and Rn emission from mud volcanoes have been explored. A linear relationship between air temperature and Rn count rates has been determined. After the removal of temperature related Rn variations, a significant correlation has been pointed out between anomalous spike‐like Rn emissions at one of the station considered and the occurrence of low magnitude (M<4.5) local earthquakes.
Is the slip rate variation on the Great Sumatran Fault accommodated by fore‐arc stretching?
Authors: Bellier O. , Sébrier M.
Published: February 2004

In oblique convergent subduction areas, an obliquity increase should produce a slip rate increase on trench parallel strike‐slip faults and thus the fore‐arc platelet should be stretched. Along the Great Sumatran Fault (GSF), that is associated with the oblique convergent Sunda Arc, a northward increase of the GSF slip rate occurs parallel with the convergence obliquity. Transpressional back‐arc deformation accommodates part of the GSF slip rate variation while no significant fore‐arc stretching is observed. The Sumatran case shows that oblique convergence may be accommodated by deformation of a 500‐km‐wide zone, from the fore‐arc to the back‐arc domains.
Simultaneous optical and HF radar observations of the ionospheric cusp
Authors: Rodger A. S. , Mende S. B. , Rosenberg T. J. , Baker K. B.
Published: February 2004

Simultaneous optical all‐sky imager and photometer data from South Pole station and the PACE HF radar at Halley, Antarctica from two case studies are used to show that their respective ionospheric signatures of the magnetospheric cusp are collocated to better than about 1° latitude. The plasma convection reversal as identified in the PACE data is usually observed within the region showing cusp precipitation, as expected from contemporary models of this region of geospace.
A plate cooling model relating rates of plate motion to the age of the lithosphere at trenches
Authors: Carlson R. L.
Published: February 2004

Previous studies have shown that the observed correlation between the age of the lithosphere and rate of ‘absolute’ motion of subducting oceanic plates at trenches can be explained by a net slab‐pull force derived from a halfspace cooling model for the thermal lithosphere. Rates of motion are proportional to the square root of age. However, depth / age trends suggest that the ‘plate’ thermal structure applies to much of the seafloor; rate and age data for trenches where the oldest seafloor is subducted in the western Pacific should reflect the ‘plate’ structure. Fitting rate and age data from 16 trenches to net slab‐pull models based on both halfspace and plate cooling models shows that rates of plate motion at the five western Pacific trenches where the lithosphere entering the trench is oldest are systematically lower than the rates predicted by the best fitting halfspace model. In contrast, these data do fit a slab‐pull model based on plate cooling with R²=0.97, and an RMS error of 4.7 mm/a. Thus the plate model represents a statistically significant improvement over the halfspace model, and the plate‐like ‘flattening’ of depth/age trends is reflected in the relationship between the rate of subduction and the age of the seafloor at Pacific trenches.
The 40Ar/36Ar ratio of the undepleted mantle; A reevaluation
Authors: Matsuda Jun‐ichi , Marty Bernard
Published: February 2004

The 40Ar/36Ar ratio of the mantle bears important information about the extent of early degassing of the earth. Many researchers have agreed that 40Ar/36Ar ratio in the depleted mantle as sampled by Mid‐Ocean Ridge Basalts (MORB) is as high as 28000. However, the 40Ar/36Ar ratio in the undepleted mantle has been strongly debated. We have reexamined the noble gas data of He and Ar in MORB and hot spot volcanics using 4He/40Ar vs. 36Ar/40Ar and 4He/40Ar vs. ³He/40Ar diagrams. In these diagrams, mixing lines between two components result in straight lines, which enable us to interpret data more easily than using diagrams with different denominators like a 40Ar/36Ar vs. ³He/4He plot where all mixing lines appear as curves. We conclude that the 40Ar/36Ar ratio in the undepleted mantle is much higher than the atmospheric value and should be higher than the observed highest values in the hot spot volcanics. We also suggest that high 4He/40Ar ratios observed in MORB result from kinetic disequilibrium during partial melting.