bluuebunny/crossref_metadata_2025 huggingface dataset:
A combined algorithm for automated drainage network extraction
Authors: Chorowicz Jean , Ichoku Charles , Riazanoff Serge , Kim Youn‐Jong , Cervelle Bernard
Published: February 2004

Based on existing principles of automated drainage network extraction we have developed two methodological algorithms, the “profile scan” and “hydrological flow modeling,” and used them to extract networks from digital elevation models (DEMs). The “hydrological flow modeling” algorithm specializes in the extraction of well‐connected hierarchically arranged skeletal channel networks. On the other hand, the channels extracted by the “profile scan” algorithm lack adequate connectivity, but this algorithm is suitable for the extraction of wide valley bottoms and other flat areas. A combination of the two algorithms gives a more versatile algorithm capable of yielding networks which are not only well connected but also portray the surface character of the drainage network thus generated. The good functioning of our algorithm is not inhibited by the presence of pits in the DEM. There is therefore no preprocessing of the DEM prior to drainage extraction. Rather, at the end of extraction, isolated spots are eliminated since these are the ones most probably representing artifacts.
Dissolved organic carbon fractions in soil and stream water during variable hydrological conditions at Birkenes, southern Norway
Authors: Easthouse Kent B. , Mulder Jan , Christophersen Nils , Seip Hans M.
Published: February 2004

Spatial and temporal variations in the composition of dissolved organic carbon (DOC) in stream and soil water of the acidified Birkenes catchment were studied during summer and autumn 1990. Hydrophobic and hydrophilic acids were the dominant fractions in the soils (dominated by podzols and peats) and brook, accounting for ∼90% of total DOC. The podzol displayed a vertical gradation of DOC fractions, with hydrophobic acids dominating in the O horizon (∼65%) and hydrophilic acids dominating in the E and B horizons (∼60%). In the bogs, hydrophilic acids were the dominant fraction at all depths. Temporal variations in the relative contributions of the various DOC fractions were most pronounced in the podzol O horizon and the brook during successive autumn rainstorms, and small in the mineral soils and bogs. In the brook, DOC increases at peak discharge were dominated by hydrophilic acids. If stream water was assumed to be a conservative mixture of water from the podzol O and B horizons and from the deeper layers in the bog surrounding the stream, 92% of the variability in the concentration of hydrophobic and hydrophilic acids in the stream could be explained. This mixing analysis suggested that base flow largely originated in the deeper layers of the bogs, while peak flow was primarily made up of B horizon (∼50–65%) and O horizon (∼35–50%) water.
A note on head and velocity covariances in three‐dimensional flow through heterogeneous anisotropic porous media
Authors: Rubin Yoram , Dagan Gedeon
Published: February 2004

A procedure for the characterization of the head and velocity fields for saturated flow in heterogeneous, statistically anisotropic formations is developed. The fields are characterized through a series of spatial covariances as well as the velocity‐head, velocity‐log conductivity and head‐log conductivity cross covariances. All these functions are given in terms of the parameters which characterize the input log conductivity field and the average head garadient. A general procedure is outlined, followed by explicit derivation of head and velocity covariances for heterogeneous, statistically anisotropic formations. Closed form analytic results are obtained for the statistically isotropic formations, while the results for the anisotropic ones required taking quadrature over analytic expressions. The results may be used for transport predictions and for conditioning on measurements, and may be particularly useful for testing of numerical codes.
Models for disc infiltrometers
Authors: Warrick A. W.
Published: February 2004

Disc infiltrometers are popular devices for determining in situ hydraulic properties of unsaturated soils. This paper compares alternative solutions of Richards' equation for both steady state and time‐dependent cases. The steady state solutions were in general agreement using alternative hydraulic conductivity functions of the same capillary length scale. Small‐time solutions for the nonlinear cases were consistent with linear diffusion from a disc source using an average diffusivity value which is simply related to the capillary length. This offers a refinement over the one‐dimensional solution for short times in that the geometric effect of the circular source is included. Simulations for two examples indicate that the approach to the steady state solution may take considerably longer than what is commonly reported in the literature for field applications.
Econometric estimation of groundwater pumping costs: A simultaneous equations approach
Authors: Kanazawa Mark T.
Published: February 2004

Recent studies have attempted econometric estimation of the effect of changing groundwater costs on various dimensions of agricultural behavior. These studies assume parametric cost values, ignoring the possibility that marginal pumping costs may be endogenous to the extent of pumping activity. Under the alternative assumption of increasing marginal pumping costs, existing estimates of various elasticities may be suspect due to specification bias. This paper investigates this possibility, modeling a pumping technology based on hydrologic principles which incorporates constant pumping costs as a limiting case. The model also allows for common pool externalities when agents pump groundwater from the same aquifer. The results of the econometric analysis strongly suggest the presence of increasing marginal pumping costs for farmers in our data sample.
Energy budget evaporation from Williams Lake: A closed lake in north central Minnesota
Authors: Sturrock A. M. , Winter T. C. , Rosenberry D. O.
Published: February 2004

Evaporation from Williams Lake, computed by the energy budget method for the five open‐water seasons of 1982–1986, varied from a maximum seasonal rate of 0.282 cm/d in 1983 to a minimum seasonal rate of 0.219 cm/d in 1982. The pattern of monthly values of evaporation is not consistent from year to year. The normally expected pattern of low evaporation values in May, followed by increasing values in June to maximum values in July is true for only 3 of the 5 years. Comparison of annual evaporation calculated by the energy budget and mass transfer methods indicates that energy budget values varied from 13% greater to 11% less than mass transfer values. Furthermore, there is no seasonal bias in the pattern. Large differences exist in the magnitude of energy fluxes to and from Williams Lake. By far the greatest energy fluxes, having magnitudes of hundreds of watts per square meter, are incoming solar radiation, incoming atmospheric radiation, and outgoing long‐wave radiation emitted by the lake water. The least energy fluxes are related to advection, which generally have magnitudes less than 5 W m−2.
An evaluation of boundary conditions for one‐dimensional solute transport: 2. Column experiments
Authors: Novakowski Kent S.
Published: February 2004

As the result of a theoretical comparison of analytical models for one‐dimensional solute transport (Novakowski, this issue), it has been found that to reconcile the substantial differences observed between the models under conditions of large dispersion, a physical modeling study of the processes of solute transport in the vicinity of boundaries must be undertaken. The physical modeling is conducted using columns ranging in diameter from 76 to 352 mm and length from 300 to 400 mm. Geological materials of either large or small coefficient of dispersion are employed as packing for the columns. Reservoirs of finite volume are located at the inlet and outlet boundaries of each column. Using a conservative fluorescent tracer, experiments are conducted to investigate the use of macroscopic continuity in concentration at the boundaries, and the use of the flux‐averaged transformation for this boundary value problem. Concentration of the tracer was determined noninvasively from both the inlet and outlet reservoirs and, for some experiments, resident concentration was determined from within the interior of the column by excavation. Results of the experiments conducted using different volumes of the outlet reservoir show that the analytical model for flux concentration accounting for macroscopic continuity in concentration at the boundaries only poorly simulates the physical mixing process in the outlet reservoir. In addition, the results of the experiments conducted in which resident concentrations were determined from the interior of the column show that the concept of macroscopic continuity is not supported by physical evidence at either the inlet or outlet boundary. Thus, the analytical model in which concentration at the boundaries is macroscopically discontinuous best simulates the solute transport processes for this boundary value problem. Unfortunately, the solutions for resident and flux concentration with these boundary conditions are identical and further distinction between these models cannot be undertaken. Analytical inversion of the Laplace domain solution is also presented.
The form of the dispersion equation under recharge and variable velocity, and its analytical solution
Authors: Serrano Sergio E.
Published: February 2004

In this article an attempt is made to describe field scale solute transport parameters in terms of regional hydrologic and aquifer hydraulic properties, such as recharge rate, transmissivity, hydraulic gradient, aquifer thickness and soil porosity. Aquifers subject to natural recharge from rainfall exhibit groundwater velocities which vary with distance and with the recharge intensity. This in turn generates an evolving transport dispersion coefficient which increases with distance even in a homogeneous aquifer with constant dispersivity. The dispersion equation in an aquifer subject to recharge and variable groundwater velocity is one with coefficients given as variable functions of distance. A new stable analytical solution of this equation is presented along with numerical comparisons with the classical convection dispersion equation and sensitivity tests on the effect of hydrologic‐hydraulic variables on the contaminant evolution. It was found that the recharge rate substantially affects the contaminant distribution and may partially explain the scale dependence of dispersion parameters. Transmissivity and hydraulic gradient values also determine the velocity distribution and therefore the rate of migration. It would appear that constant, laboratory scale, dispersivities may be sufficient for the modeling of field scale concentrations if an equation which accounts for the effects of hydrologie and hydraulic variables is used.
Measurements in a Braided River chute and lobe: 2. Sorting of bed load during entrainment, transport, and deposition
Authors: Ashworth P. J. , Ferguson R. I. , Ashmore P. E. , Paola C. , Powell D. M. , Prestegaards K. L.
Published: February 2004

Grain size distributions of bed material, bed load, and bar head deposition were sampled during the evolution of a chute and lobe in the braided gravel bed Sunwapta River, Alberta. Although bed shear stress and total bed load transport rate varied substantially within the reach and from day to day (Ferguson et al., this issue), the median diameter D50 of bed load was remarkably constant. The bed initially fined from chute to bar head but became more uniform. Sediment deposited on the bar head also had a near constant D50, similar to that of the bed load truncated at the same lower size limit. Both load and deposition were finer on average than the bed, suggesting overall selective transport despite little sign of local sorting. In contrast to median diameters, maximum sizes (Dmax) of sediment in motion and deposited on the bar head varied substantially and showed a weak but significant dependence on shear stress. Inferring selective entrainment from this evidence alone would be dubious because Dmax was also found to increase systematically with the mass of sediment sampled. However, two different methods of analysis of fractional transport rates throughout the size range also showed size‐selective entrainment and transport. In the marginal transport conditions of this study, size sorting appears to occur but only weakly and mainly in the coarser fractions.
Oscillation phenomena in gravity‐driven drainage in coarse porous media
Authors: Pražák J. , Šír M. , Kubík F. , Tywoniak J. , Zarcone C.
Published: February 2004

Correlations between rainfall amount and water content in coarse soils were studied. Situations were registered in which the intensity of the gravity‐driven flow in the soil exhibited irregular oscillations which could not be explained within the scope of the standard Richards' theory. The problem was analyzed by means of a set of laboratory experiments. It seems that the observed global (macroscopic) oscillations can be qualitatively explained as a result of correlated behavior of the local (microscopic) flows. The search for a satisfactory quantitative description of those effects promises to be a field of useful and interesting research activities.
The influence of airflow on the vertical infiltration of water into soil
Authors: Weir Graham J. , Kissling Warwick M.
Published: February 2004

The vertical flow of air and water into a Gardner soil is investigated numerically and analytically. Instantaneously applying a constant head of water to the soil surface initially produces a rapid diffusive change in air pressure in the soil, and a slower diffusive change in water content. Fluid flow comprises a region of descending water at air entry conditions, below which is a transitional layer of both airflow and water flow, which connects to a region with essentially the initial value of capillary pressure. Four flow regimes are identified. The initial compressive and resistive regimes are associated with air compressibility and viscosity. The well‐known sorptive and gravity regimes are established later. During the resistive regime, the main effect of air viscosity arises from airflows in the lower region which cause the water content profile to lag behind the corresponding profiles predicted without effects of air viscosity. A Green and Ampt infiltration law may accurately describe the infiltration process, provided the suction head suggested by Bouwer is selected. Approximate agreement is obtained between the theoretical predictions, and the corresponding accurate numerical results.
Regional geohydrologic‐geomorphic relationships for the estimation of low‐flow statistics
Authors: Vogel Richard M. , Kroll Charles N.
Published: February 2004

Many investigators have sought to develop regional multivariate regression models which relate low‐flow statistics to watershed characteristics. Normally, a multiplicative model structure is imposed and multivariate statistical procedures are employed to select suitable watershed characteristics and to estimate model parameters. Since such procedures have met with only limited success, we take a different approach. A simple conceptual stream‐aquifer model is extended to a watershed scale and evaluated for its ability to approximate the low‐flow behavior of 23 unregulated catchments in Massachusetts. The conceptual watershed model is then adapted to estimate low‐flow statistics using multivariate regional regression procedures. Our results indicate that in central western Massachusetts, low‐flow statistics are highly correlated with the product of watershed area, average basin slope and base flow recession constant, with the base flow recession constant acting as a surrogate for both basin hydraulic conductivity and drainable soil porosity.
Modeling biotic uptake by periphyton and transient hyporrheic storage of nitrate in a natural stream
Authors: Kim Brian K. A. , Jackman Alan P. , Triska Frank J.
Published: February 2004

To a convection‐dispersion hydrologic transport model we coupled a transient storage submodel (Bencala, 1984) and a biotic uptake submodel based on Michaelis‐Menten kinetics (Kim et al., 1990). Our purpose was threefold: (1) to simulate nitrate retention in response to change in load in a third‐order stream, (2) to differentiate biotic versus hydrologie factors in nitrate retention, and (3) to produce a research tool whose properties are consistent with laboratory and field observations. Hydrodynamic parameters were fitted from chloride concentration during a 20‐day chloride‐nitrate coinjection (Bencala, 1984), and biotic uptake kinetics were based on flume studies by Kim et al. (1990) and Triska et al. (1983). Nitrate concentration from the 20‐day coinjection experiment served as a base for model validation. The complete transport retention model reasonably predicted the observed nitrate concentration. However, simulations which lacked either the transient storage submodel or the biotic uptake submodel poorly predicted the observed nitrate concentration. Model simulations indicated that transient storage in channel and hyporrheic interstices dominated nitrate retention within the first 24 hours, whereas biotic uptake dominated thereafter. A sawtooth function for Vmax ranging from 0.10 to 0.17 μg NO3‐N s−1 gAFDM−1 (grams ash free dry mass) slightly underpredicted nitrate retention in simulations of 2–7 days. This result was reasonable since uptake by other nitrate‐demanding processes were not included. The model demonstrated how ecosystem retention is an interaction between physical and biotic processes and supports the validity of coupling separate hydrodynamic and reactive submodels to established solute transport models in biological studies of fluvial ecosystems.
Evolution of coarse gravel bed forms: Field measurements at flood stage
Authors: Dinehart Randy L.
Published: February 2004

Field measurements to investigate the origin and growth of mesoscale gravel bed forms in deep flows were made in the North Fork Toutle River, Washington. Sonar observations of the gravel streambed at a stationary point were recorded during two storm flows in December 1989 and January 1990 with concurrent bed load sampling and continuous velocity measurements. Mean diameter of bed load was about 3 cm, flow depths were 1.4–2.4 m, and bed shear stresses were 2–5 times the critical stress of mean bed load diameter, as computed from the depth‐slope product. These records document the hydrodynamic conditions under which dunelike coarse gravel bed forms were observed. Coarse gravel dunes (height, 20 cm; length, 6–15 m) evolved more than 24 hours after peak stage, primarily by accretion, as inferred from bed form changes revealed in dual sonar records. Dune heights increased to 40 cm as mean trough elevation rose about 50 cm over several hours. Smaller dunes (wavelength, 1–3 m), transitional from bed load sheets, migrated on the backs of the large dunes. The superposed dunes finally became indistinguishable from the large dunes, which diminished in height by increasing the mean level of troughs. Gravel deposition occurred at the observation point in conjunction with migration of gravel dunes. The direct comparison of known bed form regimes and gravel bar facies provides alternative interpretations of gravelly deposits.
Modeling long‐term solute transport in drained unsaturated zones
Authors: Kandil Hesham , Miller Cass T. , Skaggs R. Wayne
Published: February 2004

Long‐term assessment of solute transport in the unsaturated zone is an important consideration for irrigation management, pesticide management, and subsurface contaminant restoration analysis and design. Mathematical models are often used to perform such analyses. Modeling fluid flow and solute transport in the unsaturated zone typically requires solution of the nonlinear Richards equation and an advective‐dispersive equation for contaminant transport as a function of time. Such solutions are possible but computationally expensive. A simplified water balance approach to solve fluid flow in shallow, drained unsaturated zones has been developed and refined over the last 15 years. The objectives of this study were to use results from a water balance model to obtain solutions for solute transport in drained, shallow water table soils, and to compare the results with solutions based upon Richards' equation. Transient soil water flux rates computed with a water balance model were used as input to a Petrov‐Galerkin advective‐dispersive transport model to simulate solute transport in unsaturated soils. The transport model was checked for consistency by comparison with an analytical solution. Sample simulations showed good agreement between a Richards' equation‐based transport model and a water balance‐based transport model. Simulations were performed to show predicted trends in water quality over 1‐year periods.
A mass conservative numerical solution for two‐phase flow in porous media with application to unsaturated flow
Authors: Celia Michael A. , Binning Philip
Published: February 2004

A numerical algorithm for simulation of two‐phase flow in porous media is presented. The algorithm is based on a modified Picard linearization of the governing equations of flow, coupled with a lumped finite element approximation in space and dynamic time step control. Numerical results indicate that the algorithm produces solutions that are essentially mass conservative and oscillation free, even in the presence of steep infiltrating fronts. When the algorithm is applied to the case of air and water flow in unsaturated soils, numerical results confirm the conditions under which Richards's equation is valid. Numerical results also demonstrate the potential importance of air phase advection when considering contaminant transport in unsaturated soils. Comparison to several other numerical algorithms shows that the modified Picard approach offers robust, mass conservative solutions to the general equations that describe two‐phase flow in porous media.
Recreation value of water to wetlands in the San Joaquin Valley: Linked multinomial logit and count data trip frequency models
Authors: Creel Michael , Loomis John
Published: February 2004

The recreational benefits from providing increased quantities of water to wildlife and fisheries habitats is estimated using linked multinomial logit site selection models and count data trip frequency models. The study encompasses waterfowl hunting, fishing and wildlife viewing at 14 recreational resources in the San Joaquin Valley, including the National Wildlife Refuges, the State Wildlife Management Areas, and six river destinations. The economic benefits of increasing water supplies to wildlife refuges were also examined by using the estimated models to predict changing patterns of site selection and overall participation due to increases in water allocations. Estimates of the dollar value per acre foot of water are calculated for increases in water to refuges. The resulting model is a flexible and useful tool for estimating the economic benefits of alternative water allocation policies for wildlife habitat and rivers.
Iowa climate reconstructed from tree rings, 1640–1982
Authors: Cleaveland M. K. , Duvick D. N.
Published: February 2004

Tree ring indices from an expanded network of 17 white oak (Quercus alba} sites in eastern and central Iowa were used to reconstruct state average July Palmer hydrological drought index (PHDI), annual precipitation (previous August to current July), and other climate variables for 1640–1982. We removed nonclimatic variance trends caused by changing sample size and senescent growth. July PHDI correlated better with tree growth than annual precipitation. Occurrence of prolonged droughts throughout the reconstruction suggests that decades like the 1930s occur about twice per century in Iowa. Iowa climate is correlated with the Southern Oscillation Index (SOI) from June in the year of El Niño onset (Yr0) through the next February (Yr+1), with negative SOI (El Niño) associated with wetter conditions. When the June (Yr0) to February (Yr+1) average SOI reaches extremes ≥ + 1.0 or ≤−1.0, it correlates significantly with observed and reconstructed July PHDI (r = −0.37 and −0.56, respectively). Climate during solar cycles centered on sunspot minima alternates between wet and dry regimes that differ by an average of 1.21 units of observed July PHDI and 46.7 mm of annual precipitation for 1877–1982. The solar relationship has been stable since 1640. Combining solar and SOI influences in forecasts may improve prediction of Iowa climate.
Moving finite element model for one‐dimensional infiltration in unsaturated soil
Authors: Gottardi G. , Venutelli M.
Published: February 2004

The numerical integration of Richards' equation for infiltration into homogeneous unsaturated soil is carried out by a moving finite element (MFE) method. Accurate solution of this one‐dimensional nonlinear partial differential equation by standard finite difference (FD) or finite element (FE) methods can be obtained by using a fine discretization on space and time. This can lead to large computer times. With the MFE method, grid points are moved during computation along the wetting front, so that accuracy can be maintained by using a small number of nodes for simulating cases several meters in depth. For these cases the MFE method is faster than FD and FE methods. The numerical MFE model is verified through comparison with the quasi‐analytical solution by Philip (1957). Moreover, we compare, for some other test problems, the computational efficiency of this method with that of two efficient pressure head‐based FD and FE fixed grid formulations.
Continuous groundwater velocity fields and path lines in linear, bilinear, and trilinear finite elements
Authors: Cordes Christian , Kinzelbach Wolfgang
Published: February 2004

Darcy velocity fields obtained from finite element solutions of heads in groundwater flow exhibit discontinuities at element boundaries, thus giving rise to inaccuracies in path line construction. Several methods have been developed to resolve those inaccuracies including global postprocessing of velocity fields, mixed hybrid finite element formulations, and stream function formulations. All of these techniques either lead to a considerable increase in the computational effort or are not general enough for all purposes. The point of view taken here is that standard finite element flow models yield exact water balances, which in the usual approach to path line computation are not fully used. By starting out from patches with flux‐conserving boundaries, a new postprocessing procedure is derived that allows construction of a continuous flux distribution over the whole model domain. In this procedure only the head gradients of adjacent elements are used, thus avoiding the solution of another global system of equations. Furthermore, application of a stream function interpolation inside each patch allows the fast computation of path lines without any time stepping. The path lines computed with the proposed procedure are compared to path lines computed by usual particle tracking and examples are presented showing that the new method is vastly superior to traditional particle tracking.
Representation of basin scale in flood peak distributions
Authors: Smith James A.
Published: February 2004

A lognormal cascade model is developed for representing basin scale in flood peak distributions. The model is developed from the multiplicative cascade modeling framework developed by Gupta and Waymire (1990) for spatial hydrologic processes. The lognormal cascade model has a simple parameterization of basin scale that can represent either simple scaling or multiscaling processes. Likelihood‐based statistical inference procedures are developed for parameter estimation and hypothesis testing for the lognormal cascade model. The lognormal cascade model is used to examine scale properties of annual flood peaks from 104 stations in the central Appalachian region of Maryland and Virginia. Drainage area for the basins ranges from 0.3 square miles (0.78 km2) to nearly 10,000 square miles (26,100 km2). The empirical results suggest two hypotheses concerning scaling properties of central Appalachian flood peaks: (1) the multiscaling hypothesis holds over the entire range of scales (for this hypothesis, some anomalous properties of flood peaks in small basins must be dealt with), and (2) scaling properties of rainfall and the channel/floodplain system impose a peak in variability of flood magnitudes for basins with drainage area between 10 and 100 square miles (between 26 and 260 km2).
Groundwater lens dynamics of Atoll Islands
Authors: Underwood Mark R. , Peterson Frank L. , Voss Clifford I.
Published: February 2004

A variable‐density groundwater model is used to analyze the effects of various controls on the size of the freshwater lens, the structure of the transition zone, and the propagation of tidal fluctuations in a two‐layer atoll island groundwater system. Modeling results indicate that mixing of fresh water and saltwater occurs primarily as a result of oscillating vertical flow due to tidal fluctuations and depends to a lesser extent on transverse dispersion along the dominantly horizontal recharge‐discharge path of flow. The controls on the amount of mixing are: (1) the accumulated vertical distance, which increases with tidal range and is restricted by vertical permeabilities, and (2) vertical longitudinal dispersion. Comparison of cross‐sectional simulations of atoll islands using nontidal and tidal models shows that the nontidal model must use artificially high values of transverse dispersivity to compensate for the lack of tidally driven, vertical mixing processes. Although the tidal model has high computational requirements, it can be used to calibrate vertical permeabilities and is best suited for problems dealing with groundwater resource evaluations, hydrologic events, and hydrologic processes. The limitations of the nontidal model are that it cannot be used for calibration of vertical permeabilities and will not realistically simulate those cases in which transition zones are thick or recharge low.
Photosynthetic climate in selected regions during the northern hemisphere growing season
Authors: Pinker R. T. , Laszlo I. , Miskolczi F.
Published: February 2004

The feasibility of deriving photosynthetically active radiation (PAR) from satellite observations on global scale was previously demonstrated (Pinker and Laszlo, 1992). The methodology used was evaluated against available ground truth (Pinker et al., 1993). The objective of this study was to provide, for a first time, consistent information on the temporal and spatial variability in PAR on a continental scale during a growing season; such information can be used to develop new parameterizations of net primary productivity and evapotranspiration, that till now were not possible.
N2O as an indicator of Arctic vortex dynamics: Correlations with O3 over Thule, Greenland in February and March, 1992
Authors: Emmons L. K. , Reeves J. M. , Shindell D. T. , de Zafra R. L.
Published: February 2004

We have recovered vertical profiles of stratospheric N2O from spectra observed using a ground‐based mm‐wave spectrometer during the Arctic spring. The measurements were made from Thule, Greenland (76.3°N, 68.4°W) on nine occasions from late February to late March, 1992 as part of the Upper Atmosphere Research Satellite (UARS) Correlative Measurements Program and the European Arctic Stratospheric Ozone Experiment (EASOE). During late February Thule was under the inside edge of the Arctic vortex and mixing ratio profiles measured in that period are substantially reduced from typical high‐latitude summer values. By late March the polar vortex had moved well away from Thule and N2O mixing ratios were greatly increased, coinciding with a basic change in circulation that brought in air from the Aleutian high. The motion of the vortex is also illustrated in the change in potential vorticity above Thule. A correlation with ozone balloonsonde data from Thule is made and compared to similar analyses of the Airborne Arctic Stratospheric Expedition (AASE) measurements. Within the sensitivity of our analysis, the correlation of N2O and O3 shows no evidence of ozone depletion within the vortex during this period; however, there is a distinct difference in the correlation inside and outside the vortex.
First results of ground‐based FTIR measurements of atmospheric trace gases in north Sweden and Greenland during EASOE
Authors: Adrian G. P. , Baumann M. , Blumenstock T. , Fischer H. , Friedle A. , Gerhardt L. , Maucher G. , Oelhaf H. , Scheuerpflug W. , Thomas P. , Trieschmann O. , Wegner A.
Published: February 2004

Zenith column amounts of N2O, CH4, CFC‐12, O3, HNO3, ClONO2, HCl, and HF were measured by ground‐based FTIR spectrometers at Kiruna in November 1991 and from January to March 1992, and in January and March 1992 in Sondre Stromfjord, Greenland. They were correlated to the dynamical situation of the stratosphere and interpreted in terms of chemical processes, with respect to the position of the vortex, the stratospheric temperatures, and the trajectories of the air masses for the last ten days. One of the most remarkable results is the increasing ClONO2 burden from the end of January to mid‐March, reaching the extremely high value of 7.2 × 1015 molec./cm².
Reaction of ClO with NO3: OClO formation and night‐time O3 loss
Authors: Toumi R.
Published: February 2004

The atmospheric importance of the reaction of ClO with NO3 has been tested in a one‐dimensional photochemical model. This reaction has two product channels which are of atmospheric importance. The channel which forms Cl and NO2 can destroy ozone in a catalytic cycle. This cycle constitutes the main ozone loss mechanism during the night near 40 km. The other channel forms OClO and is a significant source of OClO in the upper stratosphere during the night. In the polar lower stratosphere this reaction does not significantly enhance OClO.
Total nitrogen dioxide at the Arctic Polar Circle since 1990
Authors: Goutail Florence , Pommereau Jean Pierre , Sarkissian Alain , Kyro Esko , Dorokhov Valery
Published: February 2004

Daily ground‐based NO2 column measurements have been conducted with UV‐visible SAOZ diode‐array spectrometers at Sodankyla in northern Finland since January 1990 and at 3 additional stations during EASOE. Inspection of the data indicates: a total NO2 reduction by 30% by the Pinatubo aerosol in spring and summer 1992 compared to the previous years; a poor correlation in winter with potential vorticity indicative of motion of the vortex and of advection of air from mid‐latitude, frequent during EASOE; an absence of significant global denitrification by sedimentation of nitric acid on PSC particles inside the vortex; and a high correlation between total NO2 and 30–50 hPa temperature. The latter is unexpected in winter 1991–92, since most of NOx (NO + NO2 + ClONO2 + 2N2O5) at the altitude of the aerosol layer should have been converted into liquid nitric acid. This is expected to revert only slowly to NOx at high latitude in winter. The correlation suggests a temperature dependent saturation of the aerosol water / sulfuric acid droplets and / or a temperature dependent mechanism of restitution of NOx to the gas phase.
Airborne measurements during the European Arctic Stratospheric Ozone Experiment: Observation of OClO
Authors: Brandtjen Ronald , Klüpfel T. , Perner D. , Knudsen B. M.
Published: February 2004

Within the European Arctic Stratospheric Ozone Experiment (EASOE) 1991/92, airborne UV‐VIS spectral measurements of stratospheric OClO, NO2, and O3 were made by DOAS (Differential Optical Absorption Spectroscopy). The TRANSALL C160 was operated for the observation of the polar stratosphere from Kiruna (67°N), Sweden, during four campaigns from December 1991 to March 1992. Inside the vortex, the highest vertical column densities of OClO, up to 12 * 1012 molec cm−2 at a solar zenith angle of 90°, were observed during January and February 1992. The last OClO was detected on March 11 (4 * 1012 molec cm−2). Cross sections of the vortex showed the largest amounts of OClO within the core and lesser amounts in the vortex boundary. OClO was not detected outside the vortex within the detection limit which was 5*1012 molec cm−2 in December 1991 and about 2.5*1012 molec cm−2 in spring 1992.
Solar ultraviolet radiation and total ozone, as derived from satellite and ground‐based instrumentation
Authors: Varotsos C.
Published: February 2004

Daily broad‐band measurements of solar ultraviolet radiation reaching the ground at Athens, Greece (38°N, 24°E) during 1989–1991 in conjunction with daily total ozone measurements deduced from satellite and ground‐based instrumentation were used to investigate their association. Furthermore, employing a parametric model, the spectral and broad‐band solar ultraviolet radiation for the period 1979–1991 were calculated considering the total ozone values, derived from the satellite Nimbus‐7.

Total ozone reductions of 2.5% during summertime and 7% during wintertime per decade, cause an increase in erythemally active UV‐B irradiance of 5% and 14% respectively.
Geotail observation of cold ion streams in the medium distance magnetotail lobe in the course of a substorm
Authors: Mukai T. , Hirahara M. , Machida S. , Saito Y. , Terasawa T. , Nishida A.
Published: February 2004

We observed cold ion beams in the magneto‐tail lobe at XGSM ∼ −42 Re in the initial operations of the Low Energy Particle (LEP) experiment onboard the GEOTAIL satellite on August 22, 1992, when multiple onsets of substorms took place. These ion beams generally consisted of protons and singly‐charged oxygen ions (O+), flowing tailward with nearly the same velocities ∼ 100–200 km/s. The H+ number density was generally of order 10−2 cm−3, while the O+ density was of order 10−3 cm−3 but at times increased sporadically by an order of magnitude. These ions presumably would be transported along magnetic field lines through the polar mantle from the dayside polar ionosphere and convected to the mid‐magnetotail where the observation was made. That different ion species had equal velocities is consistent with the velocity filter effect due to E × B convection. Three‐dimensional determinations of their velocity distributions have revealed off‐ecliptic angles of the flow directions as large as several tens of degrees. We discuss this feature in terms of the enhanced convection velocity that is associated with the plasma‐sheet thinning confined to a limited region in the Y direction. Characteristic changes in the flow velocity are also found in association with a substorm plasmoid passage.
Some observations of gravity‐wave‐induced structure in ozone and water vapour during EASOE
Authors: Teitelbaum H. , Ovarlez J. , Kelder H. , Lott F.
Published: February 2004

During the EASOE campaign, measurements were made of temperature and different minor constituents, with the help of instrumented balloons. The vertical profiles nearly always show small scale structures. Here we show that on two different days a large part of these small scale structure can be explained by the transport induced by waves. The rôle of waves is supported by a good correlation found between the small scale structure of the minor constituents profiles and the temperature profile. Furthermore on 11 December 1991 lidar measurements show the trace of a wave on a polar stratospheric cloud (Godin et al. 1993).Comparison of some of its characteristics with what was found in water vapour and ozone measurement profiles carried out the same day, confirm the rôle of the wave in the minor constituent fluctuations.
Vertical ocean loading amplitudes from VLBI measurements
Authors: Sovers O. J.
Published: February 2004

Vertical ocean loading amplitudes are determined by analysis of IRIS geodetic VLBI data. The 4 nearly diurnal (K1, P1, O1, Q1) and 4 nearly semidiurnal (K2, S2, M2, and N2) component amplitudes can be inferred from the data with accuracies of 1–2 mm. Uncertainties of total displacements can approach 1 cm. Empirically determined total displacements are considerably larger than the values calculated from two geophysical models. The Scherneck model is found to give a better representation of VLBI delay data than the model of Pagiatakis by about 3 mm in residuals at 6 sites. Empirical estimation of the ocean loading amplitudes reduces χ2 by 3067 for the 96 additional degrees of freedom in a fit to 273,000 IRIS VLBI observations, and reduces the RMS residuals by 3 mm relative to a fit using the fixed Scherneck model. Vertical ocean loading amplitudes can thus be inferred from VLBI data at a level which improves the overall model, but detailed assessment of individual tidal components is presently obscured by incomplete modeling at the tidal frequencies.
The eddy radiation field of the Gulf Stream as measured by ocean acoustic tomography
Authors: Chester David , Malanotte‐Rizzoli Paola , Lynch James , Wunsch Carl
Published: February 2004

The Gulf Stream System is one of the most important components of the North Atlantic Circulation. Reciprocal acoustic transmissions have been analyzed to determine the structure and variability of temperature, current velocity, and relative vorticity in a region just south of the Gulf Stream. Observational evidence is presented that the Gulf Stream is the source of the energetic eddy variability found in the Atlantic interior. Through highly nonlinear processes, eddy activity (energy) radiates away from the Stream southward via Rossby wave packets.
Equatorial electromagnetic emission with discrete spectra near harmonics of oxygen gyrofrequency during magnetic storm
Authors: Liu H. , Kokubun S. , Hayashi K.
Published: February 2004

Equatorial electromagnetic ELF emissions at a frequency range around the oxygen ion gyrofrequency were observed in the low altitude plasmasphere (L = 1.5∼2.5) during magnetic storms with high activity of the ring current by triaxial search coil and single component electric field instruments on board the Akebono satellite. We find that a particular type of the ELF emissions occur with a multi‐band spectral structure around the local gyrofrequency (Fo+) of the oxygen ion (O+) during the main phase of magnetic storm. Our finding includes the following; The multi‐band emissions are localized in the morning sector and often consist of several spaced frequency bands closely related the local gyro‐harmonics of oxygen ion (O+) with a fundamental frequency of Fo+ or 2Fo+. The frequency of each band is dependent on the local magnetic field variation along the satellite orbit and the spacing between the bands is almost equal to Fo+ or 2Fo+. It is suggested that emissions are generated by terrestrial oxygen ion composing the ring current area during the main phase of magnetic storm.
Lidar measurements of Mt. Pinatubo aerosols at Aberystwyth from August 1991 through March 1992
Authors: Vaughan G. , Wareing D. P. , Jones S. B. , Thomas L. , Larsen N.
Published: February 2004

Measurements of stratospheric aerosols were conducted at Aberystwyth (52.4°N, 4.0°W) from 14 August 1991 to 30 March 1992, using a dual‐polarisation lidar at 532 nm. The backscatter ratios show that volcanic aerosols, present below 22 km in August, built up steadily during the autumn and extended to higher altitudes. During 7–9 December a large increase in aerosol amounts was observed, with maximum backscatter ratios of 17 and aerosols reaching 34 km. Thereafter, peak backscatter ratios remained around 8, with aerosols extending up to 28 km. Optical depths increased tenfold during the period of measurements, from .02 in August to about 0.2 in March. A notable feature of the aerosol cloud was a layer of depolarising particles, first seen near 19 km on October 1st, which gradually subsided during the course of the autumn and winter.
Airborne lidar observation of mountain‐wave‐induced polar stratospheric clouds during EASOE
Authors: Godin S. , Mégie G. , David C. , Haner D. , Flesia C. , Emery Y.
Published: February 2004

The airborne backscatter lidar Leandre was flown during the EASOE campaign on board the French ARAT‐Fokker 27, to provide mesoscale observations of scattering layers in the stratosphere. The use of cross‐polarization channels at the 532 nm laser emitted wavelength, allowed discrimination between the quasi‐spherical particles of the Pinatubo aerosol and the non‐spherical frozen particles of polar stratospheric clouds. Measurements taken on December 11th 1991 revealed mountain‐wave‐induced polar stratospheric clouds at 21 km altitude, extending over 300 km west and 300 km east from Kiruna. The wavelength and amplitude of the perturbation imply local cooling ranging from 3°K to 10°K in the stratosphere, taking the temperature below the threshold of formation of polar stratospheric clouds.
Effects of stratospheric aerosols from the Mt. Pinatubo eruption on ozone measurements at Sodankylä, Finland in 1991/92
Authors: Dahlback A. , Rairoux P. , Stein B. , Del Guasta M. , Kyrö E. , Stefanutti L. , Larsen N. , Braathen G.
Published: February 2004

Total ozone amount is measured at Sodankylä, Finland using a Brewer spectrophotometer and a SAOZ instrument. The effect on these measurements of the stratospheric aerosols from the Pinatubo eruption is estimated, using a radiative transfer model. The aerosols is modelled as spherical particles of 75% sulphuric acid, with a size distribution inferred from lidar measurements. With the Brewer instrument looking directly at the sun or moon, measurements of ozone amount are not significantly affected by aerosols; the effect of aerosols on measurements looking at the zenith sky depends on the height of the aerosol layer and on the solar zenith angle. Ozone measurements from SAOZ observations of zenith skylight at sunrise and sunset are very sensitive to aerosol effects. Total ozone may be underestimated by up to 30% if airmass factors calculated for a clear sky are used. The SAOZ measurements can be brought into better agreement with the Brewer direct sun and moon measurements when airmass factors calculated taking account of aerosol scattering are used. A sensitivity test indicate that TOMS measurements are also affected by Pinatubo aerosols. For moderate and small solar zenith angles TOMS tends to overestimate the total ozone. For large solar zenith angle TOMS underestimates the total ozone significantly.
Microseismicity of back‐arc rifting in the Middle Okinawa Trough
Authors: Sato Toshinori , Koresawa Sadayuki , Shiozu Yasumasa , Kusano Fujio , Uechi Seiichi , Nagaoka Osamu , Kasahara Junzo
Published: February 2004

A one month microearthquake survey was conducted at Iheya Knolls in the middle Okinawa Trough in 1992 to reveal microearthquake characteristics of back‐arc rifting. We deployed five ocean bottom seismometers and observed over 1700 events during 30 days. Hypocenters were determined for 48 earthquakes with good resolution. From this survey, we conclude that the survey area with 100km × 100km has high seismicity, many earthquakes occur in the western part of Iheya Knolls, and few occur in the central part. The earthquakes are distributed in an en echelon shape and throughout the entire depth of the crust. There is no evidence for the existence of transform faults, suggesting that the middle Okinawa Trough is in a stage of back‐arc rifting.
Ultraviolet actinic flux in the stratosphere: An overview of balloon‐borne measurements during EASOE, 1991/92
Authors: Schiller C. , Hofzumahaus A. , Müller M. , Klein E. , Röth E.‐P. , Schmidt U.
Published: February 2004

Filter radiometers sensitive in the spectral intervals 290–310 nm and at 280–400 nm were used to measure the actinic flux in the stratosphere. Data were obtained from seven balloon flights during the European Arctic Stratospheric Ozone Experiment (EASOE). Measurements were made at solar zenith angles between 95° and 68° and at altitudes from 0 up to 33 km. The observations are compared to values calculated by a radiation flux model.