bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrology and alkalinity regulation of soft Florida waters: An integrated assessment
Authors: Stauffer Robert E. , Canfield Daniel E.
Published: February 2004

Natural waters in ridge provinces of Florida and southeast Georgia were classified geographically, by degrees of cultural disturbance, and according to the dominant hydrologic and biogeochemical processes controlling chemistry. The ionic composition of lakes, upland streams, and surficial aquifer (water table) springs in relatively undeveloped catchments reflects the geographic variations in bulk deposition corrected for evapotranspiration (Na, Cl), plus a slight gain (net watershed mobilization) of Mg, and partial to nearly complete losses (net retention) of nitrate, sulfate, Ca, and K. Recharge to the Floridan aquifer in infertile, forested, sandy ridge provinces of northern Florida contains 360–580 μmol CO2. On the basis of indirect geochemical evidence, sulfate retention appears less important in lake sediments than in the region's highly weathered, ferruginous, kaolinitic, sand soils. Silica concentrations in upland streams and water table springs closely reflect the predicted equilibrium between kaolinite and gibbsite. Along with other evidence, the Si concentrations in ridge lakes indicate that seepage inflow is much more important than assumed in Baker et al.'s (1988) regional model. Lakes and streams are acidified either by humic acids or nonmarine sulfate but rarely by both, as reflected by the significant inverse correlation between these two components. Contrary to previous reports, there is no significant difference in alkalinity for culturally undisturbed lakes in the northern Trail versus southern Highlands Ridge areas.
Migration of radionuclides from a granite repository
Authors: Krishnamoorthy T. M. , Nair R. N. , Sarma T. P.
Published: February 2004

Migration of radionuclides in the fracture of a host rock matrix surrounding a high‐level waste repository is discussed in terms of two coupled one‐dimensional equations, one for the fracture and the other for the porous rock matrix. The processes considered are advection, dispersion, radioactive decay and adsorption on the surface of the fracture, and diffusion, radioactive decay and adsorption in the microfissures of the host rock. The temporal and spatial distribution of concentration and flux at the outlet of the fracture for some typical radionuclides encountered in high‐level radioactive waste has been computed using two‐component leaching from the waste matrix and budgeting the total inventory. It is observed that the concentration of 90Sr and 239Pu markedly decreases with distance along the fracture due to sorption and decay. However, either travel time or sorption do not present enough delay for significant decay of 129I in fracture water. While the peak flux of 129I shows insignificant variation at different fracture lengths for varied fracture apertures, that of 239Pu has functional dependence on both parameters.
Predicting episodic stream acidification in the southeastern United States: Combining a long‐term acidification model and the end‐member mixing concept
Authors: Hooper Richard P. , Christophersen Nils
Published: February 2004

The model of acidification of groundwater in catchments (MAGIC) was applied to data from the Panola Mountain Research Watershed located near Atlanta, Georgia, in the southern Piedmont physiographic province of the United States. In contrast to past applications, MAGIC was calibrated directly to two soil environments using information gained from an independent mixing model rather than to the stream water. A third soil environment, the deeper soil horizons which provide base flow, was identified from the mixing model, but its chemistry was assumed to be invariant during the forecast period, and hence it was not included in MAGIC. This mixing model identified soil environments that appear to be important in determining present stream water chemistry, determined the hydrologic routing parameters necessary for the model, and permitted predictions of stream water chemistry during future storm events. Annual average stream water acid neutralizing capacity (ANC) was predicted to decrease during the next 50 years in a manner largely consistent with a regional analysis of the nearby southern Blue Ridge province performed by the U.S. Environmental Protection Agency. The two upper soil layers, however, were predicted to acidify substantially within the next 20 years so that the stream water may become unsuitable for sensitive aquatic biota for much of the year, despite a positive annual average ANC. This approach, which combines a predictive model and a mixing model, provides testable hypotheses because actual soil environments are modeled; field experiments to test the processes contained in the model are suggested.
Input of fecal coliform bacteria to an upland stream channel in the Yorkshire Dales
Authors: Hunter Colin , McDonald Adrian , Beven Keith
Published: February 2004

The input of fecal coliform bacteria to the River Skell stream from a small, approximately 0.5 ha, instrumented research site on Pateley Moor in the Yorkshire Dales was investigated. Bacterial concentrations were determined for a total of 433 water samples collected between October and December 1984 from 31 stream bank sites representing three types of near‐surface water flow: matrix through flow, nonmatrix through flow, and overland flow. Bacterial concentrations in matrix through flow were found to be very low, but much higher input rates were found in both nonmatrix through flow and overland flow. Overland flow sites were the most important group for the input of bacteria to the channel, both between and during storm events. The rate of fecal coliform input was found to increase during storm events, and there was a strong, positive correlation between bacterial input rate and stream stage height.
A mathematical model for the one‐dimensional transport and fate of oxygen and substrate in a water‐saturated sorbing homogeneous porous medium
Authors: Lindstrom F. Tom
Published: February 2004

Dissolved oxygen and substrates are transported and processed abiotically and biotically in aquifers. A mathematical model for the one‐dimensional simultaneous transport and fate of dissolved oxygen and substrate in an aerobic water‐saturated linear equilibrium sorption homogeneous porous medium is presented. Transport is by coupled one‐dimensional advection‐dispersion equations. Modified Monod kinetics are used to define the substrate and oxygen utilization rates. The dynamically aerobic microbe population is simultaneously modeled. The resulting coupled system of nonlinear oxygen‐substrate‐microbe population equations is solved via an Eulerian‐Lagrangian method. This is based upon splitting the time operator and using Lagrange cubic splines across the entire domain to solve the advective portion first. The diffusive portion is then solved. An explicit time integration algorithm is sketched. Two numerical validation scenarios are discussed. Three realistic field scenarios are presented based upon published literature kinetic parameters.
Transport of rate‐limited sorbing solutes in heterogeneous porous media: Application of a one‐dimensional multifactor nonideality model to field data
Authors: Brusseau Mark L.
Published: February 2004

The results of several experiments reported in the literature indicate that the assumptions of porous media homogeneity and instantaneous sorption are generally invalid for transport of sorbing solute at the field scale. In addition, it is probable that the “nonideal” transport observed is caused by more than one factor. The purpose of this work was to evaluate the ability of a one‐dimensional, multifactor nonideality model to represent the nonideal transport of sorbing solutes at the field scale. For this model the two‐domain approach is used to represent heterogeneity, and sorption is represented as being essentially instantaneous for a portion of the sorbent and rate limited for the remainder. Data (breakthrough curves) obtained from four field experiments reported in the literature were used to test the performance of the model. With one exception, data from laboratory or field experiments were used to identify values for input parameters; the exception concerned an assumption of a uniform distribution of sorbent between the advective and nonadvective pore water domains. Specification of input parameters independent of the data being simulated allowed the model to be used in a predictive mode. On the basis of the good match between predictions produced with the model and the data, it appears that the model provides a valid representation of sorption dynamics and solute transport for field‐scale systems influenced by heterogeneity and rate‐limited sorption. The model should be useful in situations where the extensive input data required for more complex models (e.g., stochastic) are not available.
An analytical solution for one‐dimensional transport in porous media with an exponential dispersion function
Authors: Yates S. R.
Published: February 2004

An analytical solution describing the transport of dissolved substances in heterogeneous porous media with an asymptotic distance‐dependent dispersion relationship has been developed. The solution has a dispersion function which is linear near the origin (i.e., for short travel distances) and approaches an asymptotic value as the travel distance becomes infinite. This solution can be used to characterize differences in the transport process relative to both the classical convection‐dispersion equation which assumes that the hydrodynamic dispersion in the porous medium remains constant and a dispersion solution which has a strictly linear dispersion function. The form of the hydrodynamic dispersion function used in the analytical solution is
, where α(x) = a L[1 − e−bx/L] and
is the average pore water velocity. The proposed model may provide an alternate means for obtaining a description of the transport of solutes in heterogeneous porous media, when the scale dependence of the dispersion relationship follows the behavior given by α(x). The overall behavior of the model is illustrated by several examples for constant concentration and flux boundary conditions.
Diffusive matrix fracture coupling including the effects of flow channeling
Authors: Dykhuizen R. C.
Published: February 2004

It is important to predict the transport of solute in fractured systems. In these systems the majority of solute advection occurs within the fractures. However, the diffusive coupling with the large storage contained within the rock matrix often significantly slows down the effective solute velocity below that of the physical fluid velocity within the fractures. The coupling between these two porosity systems is further complicated by the fact that the fluid within the fractures flows in distinct channels which occupy a small percent of the fracture plane. This paper extends the work of Rasmuson and Neretnieks (1986) and Johns and Roberts (1991) in analyzing the consequences of the channeling on the solute coupling between these two porosity systems. It has been found by Rasmuson and Neretnieks that the amount of coupling can be significantly reduced due to the fracture channeling if the time scales of interest are short when compared to diffusive time scales in the rock matrix system. This study shows that for longer time scales this reduction in the coupling is greatly reduced. Experimental measurements are still required to enable verification of the assumptions made in this and other analytical studies of fracture matrix coupling.
The use of macroscopic percolation theory to construct large‐scale capillary pressure curves
Authors: Kueper Bernard H. , McWhorter David B.
Published: February 2004

This paper introduces a macroscopic invasion percolation process suitable for simulating the displacement of one immiscible fluid by another through porous media under conditions of capillary‐dominated flow. The theory is similar to classical percolation theory in that the structure of a real porous medium is represented as an ordered lattice, but differs in that each point of the lattice is assigned a local‐scale porosity, permeability, and capillary pressure‐saturation relationship, rather than microscale pore and pore throat dimensions. Unlike pore‐scale percolation theory, each node of the lattice may be occupied by either one or two phases, thereby allowing bicontinua of fluids in two dimensions. To illustrate an application of the theory, both wetting and non wetting fluids are percolated through a heterogeneous porous medium while accounting for fluid trapping such that a hysteretic, large‐scale capillary pressure‐saturation curve is constructed. The simulations are carried out in spatially correlated, random permeability fields assuming that the local‐scale capillary pressure‐saturation relationships are perfectly correlated with permeability. The resulting large‐scale capillary pressure curves are found to be influenced by the mean and variance of the assigned lognormal distribution of permeabilities. Very little sensitivity to the ratio of correlation lengths was observed. It is found that the threshold saturation giving rise to an initial percolating cluster of nonwetting fluid across the lattice corresponds to between 18.8% and 29.5% nonwetting saturation, depending on the statistics of the permeability field. Comparison of the percolation‐derived capillary pressure curves to those based on a direct arithmetic average demonstrates that an arithmetic average is only valid through the range of fluid saturations where no trapping occurs.
Physically based hydrologic modeling: 1. A terrain‐based model for investigative purposes
Authors: Grayson Rodger B. , Moore Ian D. , McMahon Thomas A.
Published: February 2004

THALES, a simple distributed parameter hydrologic model is presented and applied to two catchments in Australia and the United States, each with different dominant hydrologic responses. The model simulates Hortonian overland flow and runoff from saturated source areas and is used to identify some of the barriers to modeling the hydrology of small catchments. At Wagga Wagga in New South Wales, Australia, runoff is produced from saturated source areas, whereas on the Lucky Hills catchments at Walnut Gulch in Arizona, Hortonian overland flow processes dominate. Simulations at Wagga Wagga are based on published parameters and field data measured as part of an intensive field program and result in a relatively poor fit of the outflow hydrographs for a series of storms. The simulated position and growth of saturated areas coincides with the limited available information, indicating that at least the gross effects of subsurface water movement are being represented. For the Lucky Hills catchments, the hydrographs at the catchment outlet and points within the catchment are simulated for a storm series. The results are highly dependent on the parameter values, which are poorly defined, highlighting the lack of measured field data and lack of methodology for the collection of data at a scale appropriate for such models. The model structure is also shown to have a major influence on the output. The influence of simulating surface flow as sheet flow or rill flow or through a series of ephemeral gullies, as well as the choice of the surface roughness parameter and antecedent soil water conditions, is shown to have a profound effect on the distributed flow depth and velocity predictions. By fitting model parameters, a simulation assuming Hortonian overland flow produced similar results at the catchment outlet to those based on partial area runoff. These results are of concern since it is common to calibrate and verify hydrologic models based on the accuracy with which the catchment outflow is predicted. The internal estimates of flow characteristics following such a calibration often provide the input to sediment and nutrient transport models. Models such as THALES produce an enormous amount of information and have the theoretical potential to provide a “universal” tool for the representation of hydrologic response. However, problems of verification and validation of such models are acute. These problems relate to the difficulty in measuring/deriving parameters a priori, measurement of the catchment response in sufficient detail for testing, and the validity of the fundamental assumptions and algorithms used in model development.
Parameter estimation of hydraulic properties from one‐step outflow data
Authors: Toorman A. F. , Wierenga P. J. , Hills R. G.
Published: February 2004

The one‐step outflow method was presented by Kool et al. (1985a, b) as a fast procedure to estimate unsaturated soil hydraulic properties. Many investigators, however, encountered difficulties obtaining a unique solution to the problem. The purpose of this paper is to evaluate some of the problems related to this method by looking at response surfaces and to make recommendations for improvements in the methodology. The one‐step outflow procedure was investigated using synthetic data sets generated for 7.6‐cm‐diameter by 7.6‐cm‐high soil cores. A finite difference solution of Richards' equation was used to generate the synthetic data sets. Response surfaces were calculated for the van Genuchten parameters α, n, and Ks for various combinations of matric potential, water content, and outflow data from initially saturated soil cores subjected to a step change in pressure at one of its boundaries. The results clearly show that with outflow data alone, the parameter estimation procedure will have difficulty converging. However, if matric potential data are available for a point in the core at some distance from the outflow boundary, parameter estimation sensitivity is greatly improved. The procedure used was found to be most helpful for determining which auxiliary variables should be measured for parameter estimation from outflow experiments.
Effects of uncertainties on the limits of on‐farm improvement in irrigation rehabilitation
Authors: Sritharan Subramania Iyer , Clyma Wayne
Published: February 2004

Procedures for analyzing the effects of uncertainties on the on‐farm time of application and applied depth of irrigation have been presented using two parameter‐gamma densities for the different variables. The critical coefficient of variation (CV) in delivered farm flow rate beyond which variations in targeted depths cause more deviations in time of application is found to be 0.25. For a typical set of values for on‐farm variables, reducing the CV of farm flow below 0.12 does not improve the variance in applied depth for the case of fixed CV values of 0.10 for farm area and time of application. A distribution function for time of application has been derived which will enable the computation of reliable levels of application time. Solving the yield problems considering the application system hydraulics in a deterministic mode does not lead to large errors when the variances in the on‐farm variables do not exceed 0.20. Generally, for shorter basins which are common in many countries, higher efficiencies can be achieved. Efficiencies less than 85% begin to occur when the length of the basin exceeds 275 ft (84 m) for typical values of field parameters in soils belonging to the Soil Conservation Service infiltration family of 3.0.
Extension of the Heaslet‐Alksne Technique to arbitrary soil water diffusivities
Authors: Parlance M. B. , Prasad S. N. , Parlange J.‐Y. , Römkens M. J. M.
Published: February 2004

The Heaslet‐Alksne technique solved the nonlinear diffusion equation by expansion around the wetting front for power law diffusivities. Essentially the same technique has been applied when a well‐defined wetting front exists at a finite distance. In this paper, the method is extended for an arbitrary diffusivity and to the case when there is no well‐defined wetting front at a finite distance. Two illustrations for exponential and power law diffusivities show the excellent accuracy of the method.
Field study of dispersion in a heterogeneous aquifer: 4. Investigation of adsorption and sampling bias
Authors: Boggs J. Mark , Adams E. Eric
Published: February 2004

The declining mass balance trend observed for bromide and three fluorobenzoate tracers during a natural gradient experiment at a site near Columbus, Mississippi, prompted investigations related to the reactivity of the tracers and the representativeness of the tracer samples obtained from multilevel samplers. A laboratory soil column study indicated that adsorption of bromide during the field experiment was of the order of 20% and that up to 10% of the three fluorobenzoates was adsorbed. The presence of iron oxides and kaolinite in the alluvial aquifer combined with the low ground water pH of 4.8 produced geochemical conditions conducive to adsorption of the anionic tracers. Multilevel samplers (MLS) used in the field experiment were evaluated by comparing bromide concentrations from the MLS with water samples extracted from adjacent soil cores. Vertically averaged bromide concentrations for the MLS were 21% lower than those for the cores. A matrix diffusion process in conjunction with a natural tendency for preferential sampling from permeable regions in the heterogeneous alluvial sediments is proposed as an explanation for the apparent bias in the MLS sample concentrations. This process is shown to be qualitatively consistent with the tracer mass balance observed during the natural gradient experiment.
Carbon isotope fractionation by marine phytoplankton in culture: The effects of CO2 concentration, pH, temperature, and species
Authors: Hinga Kenneth R. , Arthur Michael A. , Pilson Michael E. Q. , Whitaker Dania
Published: February 2004

Closed cultures of marine phytoplankton were established under variable conditions of CO2 concentration, temperature, growth rate (by light limitation), and pH (but with nearly identical [CO2aq]) in order to assess the relative influence of these variables on the extent of carbon isotope fractionation relative to dissolved inorganic carbon sources. Culture biomass was not allowed to increase beyond levels that would significantly affect the dissolved carbon system in the closed cultures. In experiments with Skeletonema costatum and Emiliania huxleyi, increasing CO2 concentrations led to increased carbon isotope discrimination (resulting in organic matter progressively depleted in δ13C, i.e., a greater, more negative ϵp). ϵp values for E. huxleyi were 8–10‰ less than for S. costatum under identical conditions. For the S. costatum cultures, there was nearly a 20 ‰ range in [CO2aq]‐dependent ϵp. The effect was nonlinear with a leveling off at high [CO2aq]. Over a pH range of 7.5–8.3 but at a constant [CO2aq] there was a variation in carbon isotope fractionation by S. costatum of about 9 ‰ with a minimum at pH 7.8–7.9. There was a temperature effect of ∼8‰ on fractionation even after equilibrium temperature dependency of δ13C of CO2aq was taken into account. No growth rate effect was found for S. costatum over a modest range of growth rates. Culture experiments used to determine the carbon isotope fractionation by phytoplankton species must be conducted under well‐defined conditions of temperature, pH, and CO2 concentrations. Hindcasts of ancient atmospheric pCO2 from measurements of δ13C of organic carbon in marine sediments will require careful calibration because of the variety of possible factors that influence δ13Corg.
Sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization
Authors: Altabet Mark A. , Francois Roger
Published: February 2004

In two contrasting regions of the ocean, the equatorial Pacific and the southern ocean, the δ15N of core top sediments were strongly related to [NO3−] in surface waters. With distance from the equator in the equatorial Pacific, δ15N increased from 7‰ to 16‰ as [NO3−] decreased from 8μM to < 0.1 μM. Going from 60° to 30° S in the SE Indian Ocean, core top δ15N increased from 5‰ to 11‰ as surface [NO3−] decreased from 25μM to < 0.1 μM. These results are strong evidence that sedimentary δ15N in these regions is recording the increasing isotopic enrichment of near‐surface NO3− with its depletion by phytoplankton. In the case of the equatorial Pacific, δ15N values for sinking particles collected at 150 m matched well the core top sediment values, demonstrating little diagenetic alteration of the near‐surface generated isotopic signal. These equatorial Pacific data sets have variations with near‐surface [NO3−] consistent with Rayleigh fractionation kinetics for a fractionation factor (ϵu) of 2.5‰. This value is substantially lower than previously found for temperate or polar regions, perhaps as a result of differences in phytoplankton species assemblage or growth condition. In the southern ocean south of the polar front, comparison of δ15N values for opal‐rich sediments south and sinking particles indicates an apparent +5‰ diagenetic enrichment relative to the surface‐generated signal that requires further investigation. This exception aside, our observations show that the surface‐water relationship of increasing δ15N with increasing NO3− depletion is generally transmitted to and preserved in the sediments, an important requirement for further development and application of this important paleoceanographic tool.
Monitoring the vertical structure of the Arctic Polar Vortex over northern Scandinavia during EASOE: Regular N2O profile observations
Authors: Bauer Reimar , Engel Andreas , Franken Herbert , Klein Erich , Kulessa Gerhard , Schiller Cornelius , Schmidt Ulrich , Borchers Reinhard , Lee Julia
Published: February 2004

Different whole air samplers were flown on large balloons launched from Kiruna (67.9°N; 21.1°E) in the period from 30 November 1991 until 20 March 1992. Thirteen vertical profiles of the N2O mixing ratio were obtained from the analyses of the stratospheric air samples collected at altitudes between about 10 km and 31 km. The series of profile observations illustrates the temporal variation of the vertical structure of the Arctic polar vortex over Northern Scandinavia during EASOE. Already by mid December the N2O mixing ratios observed at the 600 K isentropic level (about 24–25 km) were as low as 20 ppbv, due to the effect of diabatic subsidence. In December subsidence rates of about 100–180 m/day were observed. Dynamic wave activity at the edge of the vortex led to significant sideways erosion at lower altitudes. However, inside the vortex, at altitudes above 600 K, N2O mixing ratios of less than 10 ppbv were observed until the end of March.
Stratospheric ClONO2 and HNO3 profiles inside the Arctic vortex from MIPAS‐B limb emission spectra obtained during EASOE
Authors: Oelhaf H. , Clarmann T.V. , Fischer H. , Friedl‐Vallon F. , Fritzsche Ch. , Linden A. , Piesch Ch. , Seefeldner M. , Völker W.
Published: February 2004

Vertical profiles of ClONO2 and HNO3 inside the Arctic vortex have been retrieved from infrared limb emission spectra recorded during balloon flights on January 13 and in the night of March 14/15, 1992 from Esrange, Sweden (68°N) as part of the European Arctic Stratospheric Ozone Experiment (EASOE). The instrumentation used was the cryogenic Michelson Interferometer for Passive Atmospheric Sounding, Balloon‐borne version (MIPAS‐B). Low ClONO2 abundances in mid‐January indicate that a significant portion of ClONO2 had already been converted at that time. An unexpectedly high ClONO2 amount (1.8 to 3.1 ppbv between 16.1 and 21.5 km altitude) has been inferred from the March flight data. This implies that obviously most of the total available chlorine (ClOy) in the lower stratosphere was then in this reservoir molecule. The measured HNO3 profiles give no hint of any significant layered removal of gaseous HNO3 by condensation on particles or/and sedimentation.
Evidence for an upper mantle low velocity zone beneath the southern Basin and Range‐Colorado Plateau transition zone
Authors: Benz H. M. , McCarthy J.
Published: February 2004

A 370‐km‐long seismic refraction/wide‐angle reflection profile recorded during the Pacific to Arizona Crustal Experiment (PACE) detected an upper mantle P‐wave low‐velocity zone (LVZ) in the depth range 40 to 55 km beneath the Basin and Range in southern Arizona. Interpretation of seismic data places constraints on the sub‐crustal lithosphere of the southern Basin and Range Province, which is important in light of the active tectonics of the region and the unknown role of the sub‐crustal lithosphere in the development of the western United States. Forward travel time and synthetic seismogram techniques are used to model this shallow upper mantle LVZ. Modeling results show that the LVZ is defined by a 5% velocity decrease relative to a Pn velocity of 7.95 km s−1, suggesting either a ∼3–5% mafic partial melt or high‐temperature, sub‐solidus peridotite.
Distribution of ozone laminae during EASOE and the possible influence of inertia‐gravity waves
Authors: Reid S. J. , Vaughan G. , Mitchell N. J. , Prichard I. T. , Smit H. J. , Jorgensen T. S. , Varotsos C. , de Backer H.
Published: February 2004

The distribution of laminae in ozone has been determined from the EASOE ozonesonde archive as a function of potential temperature and potential vorticity. Results confirm previous studies that laminae are absent above ∼450K within the vortex, and are most abundant near its edge. Observations of inertia‐gravity waves in the lower stratosphere appear to suggest that such waves are not of sufficiently large amplitude to cause the kinds of laminae that are observed.
Depletions in winter total ozone values over southern England
Authors: Hughes P. A. , Lapworth A. , Smout R. E.
Published: February 2004

The time series of total ozone measured over Southern England showed anomalously low monthly mean values in the winter of 1992/93. It is shown that the causes for these low values are unlikely to be of meteorological origin, but are possibly related to the volcanic eruption of Pinatubo in 1992.
Removal of meteorological synoptic‐scale disturbances from TOMS total ozone fields
Authors: Price J. D. , Howells A. , Vaughan G.
Published: February 2004

It is expected from theoretical considerations that synoptic‐scale variations in total ozone should be correlated with the absolute vorticity field near the tropopause. A similar correlation is expected with potential vorticity on larger scales and comparisons between these two correlations can provide an insight into stratospheric dynamics. This paper uses TOMS total ozone fields and vorticity derived from ECMWF analyses for 1987, to reveal the evolution of the lower stratospheric stability structure, and the presence of the polar vortex. The possibility of using total ozone data to study the chemical evolution of the northern polar vortex is also discussed.
Total ozone measured during EASOE by a UV‐visible spectrometer which observes stars
Authors: Fish D. J. , Jones R. L. , Freshwater R. A. , Roscoe H. K. , Oldham D. J. , Harries J. E.
Published: February 2004

Total ozone was measured from Abisko, Sweden (68.4°N, 18.8°E) from January to early March 1992, by a new instrument which uses stars and the Moon as sources of UV‐visible light for absorption spectroscopy. In addition, some zenith‐sky observations were made. Ozone measurements obtained using both techniques are presented and compared with those from other instruments. Good agreement with simultaneous ozonesonde measurements is observed, but the stellar measurements appear systematically higher than total ozone measured by both SAOZ and TOMS.
Restoring post‐impact deformation at Sudbury: A circular argument
Authors: Roest Walter R. , Pilkington Mark
Published: February 2004

Recent seismic reflection observations have shown a considerable shortening of the Sudbury Structure in a direction roughly perpendicular to its long axis. Using a kinematic reconstruction technique for gridded geophysical data, which takes into account non‐uniformly distributed strain, we reconstruct the pre‐deformation shape of the Sudbury Structure and show that it could have been circular at the time of its formation (∼1.85 Ga). This supports an impact origin.
Three component vertical seismic profiling (VSP) experiment in the Sudbury Basin
Authors: Miao X. , Moon W. M. , Milkereit B. , Mwenifumbo C. J.
Published: February 2004

A three component VSP experiment was carried out in the metasedimentary Whitewater group of the Sudbury Structure. Processing of the VSP data focused on velocity analysis, wavefield separation, shear‐wave analysis, waveform modelling, hodogram analysis, and integration of surface‐seismic and borehole geophysical data. Wavefield separation processing and synthetic VSP modelling resulted in a realistic velocity model and the corridor‐stacked compressional section correlates well with the surface seismic reflection data. The shear wave section provides an additional constraint on the subsurface structure. Besides establishing a direct link between borehole lithologies and surface seismic images, the VSP data, using three component particle motion velocity hodograms, provide an independent estimate of true reflector dip in the subsurface of the Sudbury Structure.
Velocity and reflection structure of the Sudbury Structure from laboratory measurements
Authors: Salisbury M. H. , Iuliucci R. , Long C.
Published: February 2004

Compressional wave velocities and densities have been measured to hydrostatic confining pressures of 600 MPa for 120 drill core samples representing all major lithologies exposed in the Sudbury Structure (SS) in order to constrain petrologic interpretations of seismic reflection, refraction and logging data obtained along the Sudbury Lithoprobe Transect. A composite acoustic impedance section, constructed for the centre of the structure by stacking the drilled sections on the basis of petrology, shows that the Chelmsford greywacke/Onwatin shale and shale/Onaping tuff contacts near the top of the section should be strong reflectors, the Granophyre/Norite contact should be a moderate reflector and the tuff/Granophyre contact will not reflect seismic energy at all. The Norite/Levack gneiss contact at the base of the section will be a strong reflector locally. These results are in excellent agreement with Lithoprobe seismic reflection results and provide a means for interpreting the reflection data in terms of petrology across most of the structure. Since both of the major types of ore bodies found in the SS are coincident with reflective contacts, seismic reflection profiling should be a valuable tool for base metal exploration in the region.
Laboratory simulation of polar stratospheric clouds
Authors: Callaghan R. , Lim I. J. , Murdock D. E. , Sloan J. J. , Donaldson D. J.
Published: February 2004

A flow cell built to simulate heterogeneous reactions in the stratosphere is described. Small particles (∼1 μm diameter) have been made from nitric acid solutions and distilled water. These have many of the important physical properties of types I and II polar stratospheric clouds (PSCs), respectively. The FTIR spectra of the ice particles are compared with calculated extinction (scattering plus absorption) spectra to obtain an estimate of their size distributions. The average particle size can be controlled by varying the flow conditions. The nitric acid particles have not been as well characterized, because the required optical constants are not yet available. Their spectra, however, have the characteristics expected for type I PSCs, and resemble those previously reported for thin‐film nitric acid trihydrate.
Correlated observations of the boundary between polar cap and nightside auroral zone by HF radars and the DMSP satellite
Authors: Senior C. , Delcourt D. , Cerisier J.‐C. , Hanuise C. , Villain J.‐P. , Greenwald R. G. , Newell P. T. , Rich F. J.
Published: February 2004

Simultaneous observations from HF radars and the DMSP satellite have been used to relate the ionospheric convection pattern and the nightside precipitation at the polar cap‐auroral zone boundary. The convection is eastward in the poleward part of the radars field of view and predominantly westward at lower latitudes. The DMSP‐F9 particle spectrograms exhibit energetic precipitating protons at the poleward edge of an “inverted V”. The downward H+ flow displays spatial filtering effects with a clear energy‐latitude dispersion. Single‐particle trajectory simulations in appropriate field models demonstrate that these ions were ejected from the neutral sheet near 120 RE geocentric distance. Most notably, the simulations reveal significant azimuthal dispersion during transport, and the source region in the magnetotail is found to extend over several Earth radii in the dawn‐dusk direction, less energetic particles originating duskward of the high‐energy ones. The longitudinal spread of the tail source suggests particle precipitation in the ionosphere over at least one hour magnetic local time. Also, as the downflowing protons travel near the lobeward edge of the plasma sheet, the observations suggest that the convection reversal lies inside the boundary layer plasma sheet (PSBL).
Ground‐based stratospheric NO2 monitoring at Keflavik (Iceland) during EASOE
Authors: Van Roozendael Michel , Fayt Caroline , Bolsée David , Simon Paul C. , Gil Manuel , Yela Margarita , Cacho Javier
Published: February 2004

Measurements of nitrogen dioxide total amounts have been performed by ground‐based visible spectrometry at Keflavik, Iceland (64.0°N, 22.6°W) during EASOE. NO2 column amounts below 1×1015 molec/cm² are measured between December 1991 and mid‐February 1992, the lowest values being reached inside the polar vortex during the coldest period of the campaign. The usual correlation between sunset NO2 total columns and 20 hPa temperatures was not observed during the warming of the stratosphere in February. This indicates low N2O5 amounts outside the vortex, possibly related to heterogeneous reactions on Pinatubo aerosol particles. However the low NO2 contents observed could be attributed partly to the advection of air masses from the polar night region.
Towards an improved seismic imaging technique for crustal structures: The Lithoprobe Sudbury experiment
Authors: Milkereit B. , White D. J. , Green A. G.
Published: February 2004

Under the Canadian Lithoprobe program, conventional low‐ (10–55 Hz) and high‐frequency (30–140 Hz) vibroseis reflection surveys were conducted across the Sudbury Structure. The main objective of the study was to evaluate the performance of seismic exploration techniques in a complex, mainly crystalline geological setting. The Sudbury experiment demonstrated that high input frequencies can be preserved through appropriate acquisition and processing procedures. Consequently, the high‐frequency seismic data proved capable of imaging complex shallow crustal structures not ‘seen’ by the conventional low‐frequency seismic survey. In crystalline environments, improved high‐frequency seismic exploration technology will provide a better link between seismic images and surface geology.
periodic bursts of electrostatic electron cyclotron harmonic (ESCH) waves in the boundary plasmasheet region of the magnetosphere tail
Authors: Oya Hiroshi , Iizima Masahide , Morioka Akira
Published: February 2004

Periodic bursts of very intense electrostatic electron cyclotron harmonic waves have been discovered by the PWP (Plasma Wave Spectra Probe) onboard the Sakigake spacecraft while the spacecraft was crossing the plasma sheet boundary layer within the distance range from 40 to 50 earth radii. The observed pulsive bursts of the plasma waves show very intense nature which is characterized by BEN (broadband electrostatic noise) with the maximum intensity of about 200mV/m and the bursts axe enhanced periodically with the period around 1.5 minutes suggesting large volume (within the inferred size from 100km to about 1000 km) of plasma cloud periodically flowing toward tail region. There were also periodic variation of ESCH wave spectra suggesting the velocity space modulation in the plasma flow with period of ranging from 300 to 400sec; the magnetic field intensity shows the periodic variation with the same characteristic periods from 300 to 400sec.
SAFIR operation and evaluation of it's performance
Authors: Kawasaki Z.‐I. , Yamamoto K. , Matsuura K. , Richard P. , Matsui Toshiaki , Sonoi Yasuo , Shimokura Naoyoshi
Published: February 2004

SAFIR (Surveillance et d'Alerte Foudre par Interferometrie Radioelectrique) has been equipped and operated in Japan since June 12th, 1991 as a cooperative project among Osaka University, Kansai Electric Power Co. INC.(KEPCO), and the French manufacturer DIMENSIONS. The operational coverage covers Northern Kinki District, Wakasa District, and Hokuriku District. Hokuriku District is well known for its winter thunderstorm activity. The method for the evaluation was to take the cross‐correlation between the meteorological radar echo pattern and the distribution pattern of lightning discharges detected by SAFIR. We obtained high cross‐correlation coefficients and concluded that the SAFIR locations were shown to have statistically high accuracy. We also show the case study of the occurrence of the lightning strike, which is recorded by KEPCO, to evaluate the usefulness of the warning by SAFIR.
Low energy particle signature of substorm dipolarization
Authors: Liu Chao , Perez J. D. , Moore T. E. , Chappell C. R.
Published: February 2004

The low energy particle signature of substorm dipolarization is exhibited through a case study of RIMS data on DE‐1 at ∼2100 MLT, ILAT = 59°∼65°, L = 3.8∼5.4 RE, and geocentric distances 2.6∼2.9 RE. A strong cross‐field‐line, poleward outflow that lasts for a few minutes with a velocity that reaches at least 50 km/s is correlated with substorm activity evidenced in the AE index and the MAG‐1 data. All the major species (H+, He+, O+) are observed to have the same bulk velocity. The parallel velocities are strongly correlated with the perpendicular velocities. The parallel acceleration is shown to result from the centrifugal force of the E×B drift induced by the dipolarizing perturbation of the magnetic field‥
Multiwavelength lidar measurements of stratospheric aerosols above Spitsbergen during winter 1992/93
Authors: Beyerle Georg , Neuber Roland , Schrems Otto , Wittrock Folkard , Knudsen Bjørn
Published: February 2004

Within the period of December 1992 to March 1993 lidar investigations of stratospheric aerosols were performed at Ny‐Ålesund, Spitsbergen (79°N, 12°E). Backscatter signals at wavelengths of 353, 532 and 1064 nm and depolarization signals at 532 nm in altitudes ranging from the tropopause up to 30 km were analyzed. Throughout the whole measurement period we observed an aerosol layer of volcanic origin in the lower stratosphere. Depolarization profiles suggest that the volcanic aerosol layer consisted mainly of liquid droplets. Comparison with model calculations indicate median particle radii between 0.1 and 0.2 µm. Surface densities exceeded approximately 40 µm²/cm³ in the lower part of the layer around 12 km. In January 1993 polar stratospheric clouds (PSCs) were frequently observed at altitudes up to 22 km. We analyzed the backscatter and depolarization data with respect to the temperature history of backward trajectories reaching Ny‐Ålesund. Signatures for micron sized crystalline PSC particles appear for cooling rates of −1 to −3 K day−1. Larger cooling rates of −4 to −10 K day −1 produced submicron sized aerosols, presumably supercooled droplets, characterized by enhanced backscatter ratios and reduced depolarization.
Ozone profiles at McMurdo Station, Antarctica during the austral spring of 1992
Authors: Johnson Bryan J. , Deshler Terry , Rozier William R.
Published: February 2004

Thirty‐seven vertical profiles of ozone and temperature were measured at McMurdo Station, Antarctica (78°S) from 23 August to 31 October 1992. Total column ozone dropped from an initial 223 Dobson Units (DU) on 24 August to 158 DU on 27 September. The 12–20 km column reached a record low of 17 DU on 9 October, an 84% loss compared to the initial value of 106 DU. The most severely depleted layer was between 12 and 16 km which coincided with the volcanic aerosol layer (11–16 km) observed by aerosol counter flights and the Italian Lidar at McMurdo. By the end of September the polar vortex elongated and shifted away from McMurdo. Subsequent profiles, above 20 km altitude, were typically 15–20°C warmer and ozone concentrations were 50–100% higher for the remainder of the measurement period. The 12–16 km layer, however, remained 80 to 97% depleted compared to the initial profile.
Latitudinal distribution of stratospheric aerosols during the EASOE winter 1991/92
Authors: Neuber R. , Beyerle G. , Fiocco G. , di Sarra A. , Fricke K. H. , David Ch. , Godin S. , Knudsen B. M. , Stefanutti L. , Vaughan G. , Wolf J.‐P.
Published: February 2004

Lidar measurements of stratospheric aerosols were made at several Arctic and mid‐latitude stations as part of the European Arctic Stratospheric Ozone Experiment (EASOE) in 1991/92. Volcanic aerosols were observed throughout the winter at all stations. High latitude stations observed an aerosol‐free stratosphere during most of the winter at altitudes above 450 K potential temperature (above 16 km). An even latitudinal distribution of volcanic aerosols was observed below this level. This is interpreted as indicative of latitudinal transport into the polar region throughout the winter.
Lidar observations of the Pinatubo aerosol layer at Thule, Greenland
Authors: Di Girolamo Paolo , Cacciani Marco , di Sarra Alcide , Fiocco Giorgio , Fuà Daniele
Published: February 2004

Lidar measurements of the stratospheric aerosol content have been carried out in Thule (Greenland), in connection with the European Arctic Stratospheric Ozone Experiment (EASOE). Aerosols attributable to the Pinatubo eruption were detected in the stratosphere late in September; during autumn and early winter the stratospheric aerosol load slowly increased. In the region above approximately 18 km the aerosol load depended on the location of the station relative to the polar vortex. A temporary increase of the aerosol concentration was detected up to about 26 km at the beginning of February, when Thule was located for a few days outside the vortex. A final increase of the aerosol load was related with the final breakup of the vortex. The aerosol integrated backscatter values ranged between 0.001 and 0.005 sr−1 during most of the winter, and increased up to 0.007 sr−1 in early spring; in this period the aerosol columnar mass was estimated to be as high as 0.1 g m−2.
Stochastic analysis of mantle convection experiments using two‐point correlation functions
Authors: Puster Peter , Jordan Thomas H.
Published: February 2004

This paper discusses the stochastic analysis of spatially complex, time‐dependent flows in spherical and cylindrical geometries where the reference states, internal heating rates, and boundary conditions are temporally invariant and rotationally symmetric. Snapshots of the aspherical temperature anomalies δT (r,Ω,t) from a single convection run are taken to be samples of a stationary, rotationally invariant random field, and the spatial two‐point correlation function CTT(r,r′,Δ) is constructed by averaging over rotational transformations of this ensemble. Three subfunctions are extracted: the rms variation,
the radial correlation function, RT(r,r′) = CTT(r,r′,0)/ σT(r)σT(r′), and the angular correlation function
All three are useful in assessing the structural differences among mantle convection simulations, but the diagnostic properties of RT and its robustness with respect to low‐pass filtering recommend it as a tool for testing stratification hypotheses against whole‐mantle tomographic models.
Box model studies of ClOx deactivation and ozone loss during the 1991/92 northern hemisphere winter
Authors: Lutman E. R. , Toumi R. , Jones R. L. , Lary D. J. , Pyle J. A.
Published: February 2004

Calculations using a photochemical box model from mid‐January to early March 1992 show the return from perturbed levels of ClOx to near background levels, and the associated rise of ClONO2. The calculated values of ClONO2 in an in‐vortex, background aerosol scenario are in good agreement with those observed by the balloon borne MIPAS‐B limb sounder. Implications for ozone loss are discussed.