bluuebunny/crossref_metadata_2025 huggingface dataset:
A simple analytical model of aerosol properties with account for hygroscopic growth: 1. Equilibrium size spectra and cloud condensation nuclei activity spectra
Authors: Khvorostyanov Vitaly I. , Curry Judith A.
Published: September 2002

A microphysical model of aerosol size spectra that includes hygroscopic growth is presented. In the presence of atmospheric humidity, an aerosol size spectrum of the Junge [1952] type transforms into a superposition of two equilibrium power law spectra with indices determined by the original Junge index and the fraction of soluble material contained in the aerosol. The aerosol size distributions are presented as explicit functions of relative humidity H for three different humidity regimes: (1) moderate humidity, (2) high humidity but subsaturation, and (3) interstitial cloud aerosol. On the basis of this model of aerosol hygroscopic growth, the Twomey [1959] cloud condensation nuclei (CCN) power law is then derived so that its coefficients are related to the aerosol microstructure and humidity dependence under subsaturation. This simple aerosol model can be used in cloud and climate models that do not treat explicitly CCN activation and for evaluation of aerosol optical properties. An application for aerosol optical properties is considered by Khvorostyanov and Curry [this issue].
Gravity wave characteristics in the lower atmosphere at south pole
Authors: Pfenninger Matt , Liu Alan Z. , Papen George C. , Gardner Chester S.
Published: September 2002

A 4‐year (1993–1996) temperature and wind data set obtained from over 2000 high‐resolution balloon soundings at South Pole is used to study gravity wave characteristics in the troposphere and lower stratosphere. Extensive analyses of energy density, spectra, and static stability are performed to present a comprehensive view of the gravity wave characteristics in the lower atmosphere at South Pole. Our results show that the gravity waves are ubiquitous and often fairly strong at South Pole, even though the generation mechanisms are not clear. Gravity wave characteristics are, in general, similar to those obtained at other high‐latitude southern hemisphere stations. Potential energies vary between about 0.5 J/kg and 5 J/kg with season and altitude. Variations in kinetic energies are not well correlated with potential energy variations and range from 1 J/kg to 11 J/kg. We observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations, especially in the stratosphere. In general, the gravity waves in the stratosphere are stronger (weaker) in austral spring (fall). Wave activity in the troposphere has little seasonal dependence. Stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere. The probability of wave instability is 13.7% in the troposphere and 5.4% in the stratosphere. This is due to the less stable stratification in the troposphere, where the buoyancy period averages 8.3 min compared to 4.9 min in the stratosphere. Dynamic (shear) instability is more likely to occur than convective instability (11% versus 2.6% in the troposphere and 4.7% versus 0.7% in the stratosphere), due to the prevailing strong wind shear. The instability probabilities vary seasonally with the austral winter exhibiting the highest probability of instabilities (dynamic and convective instabilities combined) in both the troposphere and stratosphere.
Measurements of atmospheric layers from the NASA DC‐8 and P‐3B aircraft during PEM‐Tropics A
Authors: Stoller P. , Cho J. Y. N. , Newell R. E. , Thouret V. , Zhu Y. , Carroll M. A. , Albercook G. M. , Anderson B. E. , Barrick J. D. W. , Browell E. V. , Gregory G. L. , Sachse G. W. , Vay S. , Bradshaw J. D. , Sandholm S.
Published: September 2002

Tropospheric vertical structure was analyzed using in situ measurements of O3, CO, CH4, and H2O taken on board the NASA DC‐8 aircraft during three Pacific Exploratory Missions (PEMs): PEM‐West A, September‐October 1991 in the western Pacific; PEM‐West B, February‐March 1994 in the western Pacific; and PEM‐Tropics A, September‐October 1996 in the central and eastern Pacific. PEM‐Tropics A added measurements from the NASA P3‐B aircraft. We used a new mode‐based method to define a background against which to find layers. Using only O3 and H2O, we found 472 layers in PEM‐Tropics A (0.72 layers per vertical kilometer profiled), 237 layers in PEM‐West A (0.54 layers/km), and 158 layers in PEM‐West B (0.41 layers/km). Using all constituents, we found 187 layers in PEM‐Tropics A (0.43 layers/km), 128 layers in PEM‐West A (0.29 layers/km), and 80 layers in PEM‐West B (0.21 layers/km). Stratospheric air, sometimes mixed with trapped pollution, was the dominant layer source in all three missions. The larger number of layers per kilometer in PEM‐Tropics A was probably due to repeated profiling of several “superlayers” visible in many of the mission lidar and potential voracity profiles. The thickness of the superlayers was of order 1 km, and the horizontal extent was of order 1000 km. We found that layers have an important effect on the thermal structure. An example based on ozonesonde data from Tahiti is shown, where a dry, subsiding layer was stabilized by much greater radiative cooling at the base than at the top. The stabilized layer can trap pollution and force vertical plumes to spread into horizontal layers.
Observed and model‐simulated diurnal cycles of precipitation over the contiguous United States
Authors: Dai Aiguo , Giorgi Filippo , Trenberth Kevin E.
Published: September 2002

We analyzed diurnal variations in precipitation, surface pressure, and atmospheric static energy over the United States from observations and NCAR regional climate model (RegCM) simulations. Consistent with previous studies, the mean (1963–1993) pattern of the diurnal cycle of summer U.S. precipitation is characterized by late afternoon maxima over the Southeast and the Rocky Mountains and midnight maxima over the region east of the Rockies and the adjacent plains. Diurnal variations of precipitation is weaker in other seasons, with early to late morning maxima over most of the United States in winter. The diurnal cycle in precipitation frequency accounts for most of the diurnal variations, while the diurnal variations in precipitation intensity are small. The broad pattern of the diurnal cycle of summer precipitation is fairly stable, but the interannual variability in the diurnal cycle of winter precipitation is large. The diurnal cycle of July connective available potential energy (CAPE) is dominated by a solar driven march of a high‐CAPE (2–4 kJ kg−1 ) tongue moving from the Southeast into the Northwest, with maximum values in the late afternoon to early evening over most of the United States. The solar driven diurnal and semidiurnal cycles of surface pressure result in significant large‐scale convergence over most of the western United States during the day and over the region east of the Rockies at night. The diurnal cycle of low‐level large‐scale convergence suppresses daytime convection and favors nighttime moist convection over the region east of the Rockies and the adjacent plains. The nocturnal maximum in the region east of the Rockies is also enhanced by the eastward propagation of late afternoon thunderstorms generated over the Rockies. Over the Southeast and the Rockies, both the static instability and the surface convergence favor afternoon moist convection in summer, resulting in very strong late afternoon maxima of precipitation over these regions. RegCM simulations of 1993 summer precipitation with three different cumulus convection schemes (Grell, Kuo, CCM3) all had deficiencies in capturing the broad pattern of the diurnal cycle of precipitation over the United States. The model also overestimated precipitation frequency and underestimated precipitation intensity. The simulated diurnal cycles of surface pressure and CAPE were weak compared to observations. All the schemes produced too much cloudiness over the Southeast for July 1993 which reduced surface solar radiation and thus daytime peak warming at the surface. The model's criteria for onset of moist convection appear to be too weak, so moist convection in the model starts too early and occurs too often with all the three schemes.
Velocity shear impoundment of the Io plasma torus
Authors: Pontius Duane H. , Wolf R. A. , Hill T. W. , Spiro R. W. , Yang Y. S. , Smyth W. H.
Published: September 2002

The Io plasma torus apparently has a much longer lifetime than anticipated on the basis of simple theoretical stability analyses. This quandary is particularly evident at the outer edge of the torus, the plasma ramp, where the steep radial gradient in plasma content indicates the presence of some confining influence. Previous attempts to explain this feature have focused on the possibility that high‐energy particles could impound the colder, Iogenic plasma, but these studies have proved inconclusive. We consider an alternative mechanism whereby the development of an unstable perturbation is interrupted by the observed shear in the rotational velocity. An example in simplified geometry demonstrates how the relative azimuthal displacement of radially adjacent perturbations might eliminate their coherency and impose a finite saturation amplitude. Fully nonlinear numerical simulations using the Rice convection model at Jupiter produce analogous results, suggesting that perturbations are suppressed where the shear is strong. The crucial parameter is the ratio of the classic, linear growth rate to a rate that characterizes the velocity shear. The electric fields produced by unstable perturbations farther out are effectively shielded from the shear region. We suggest that this effect helps impound the plasma torus and is at least partly responsible for producing the ramp.
Jupiter's exogenic dust ring
Authors: Colwell Joshua E. , Horányi Mihály , Grün Eberhard
Published: September 2002

Interplanetary and interstellar dust particles stream through the Jovian magnetosphere where their orbits are perturbed by the Lorentz force. Energy and angular momentum exchange with the magnetosphere can lead to capture of some submicron dust particles into dynamically stable orbits around Jupiter. The captured grains can be on prograde or retrograde orbits, and their final orbits are usually in the semimajor axis range of 2 to 20 Jupiter radii, with eccentricities ∼0.1–0.8 and inclinations ≲20°. Captured grains have radii between about 0.5 and 1.5 μm. These captured dust particles form a diffuse band of material around Jupiter, outside the main Jovian ring, with a peak normal optical depth of τ≲10−9 While this is too low for optical detection, the Galileo dust detector has detected particles on prograde and retrograde orbits around Jupiter whose sizes, orbital properties, and number density are consistent with captured interplanetary and interstellar dust.
An intercomparison of three‐dimensional reconstruction techniques using data and models of Jupiter's synchrotron radiation
Authors: de Pater Imke , Sault R. J.
Published: September 2002

We present and compare results from two different tomographic reconstruction techniques: a backprojection technique [from de Pater et al., 1997b] and a three‐dimensional (3‐D) Fourier technique [from Sault et al., 1997]. We applied both techniques to very large array (VLA) data of Jupiter's synchrotron radiation and to models which simulate 2‐D images of Jupiter's radio emission [from de Pater et al., 1997a]. The 3‐D images thus constructed represent the apparent radio emissivity. Results from the two techniques are quite compatible. A comparison between the tomographic reconstructions of the data and model yields information on models of the electron flux,j(L, αe, E), and the magnetic field configuration. At first glance, results from the data and model agree quite well. Longitudinal differences between the data and model suggest the need for modifications to the magnetic field model, while differences in the radial profile are caused by imperfections in the radial profile of the electron flux. We suggest that the magnetic equatorial surface should be less warped than in the O6 model. We further find that the change in the modeled pitch angle distribution at Amalthea's orbit [from de Pater et al., 1997a] should be modified by, for example, the inclusion of diffusion both in pitch angle and L, while there also appear to be more emitters at high latitudes outside of Amalthea's orbit than assumed in the model.
OH in Saturn's magnetosphere: Observations and implications
Authors: Richardson J. D. , Eviatar A. , McGrath M. A. , Vasyliũnas V. M.
Published: September 2002

The discovery of OH in Saturn's inner magnetosphere changed our view of this region from one where plasma dominated the physics to one where neutrals are dominant. We revisit Hubble Space Telescope observations of OH and derive revised OH brightnesses for observations in 1992, 1994, and 1995. These OH observations as well as Voyager observations are used as constraints on a model of neutral and plasma interactions. We find that the neutral source required to produce the observed OH brightnesses is 1.4×1027H2O s−1, with a sharp peak in the neutral source rate near 4.5 RS. A good fit to the data requires OH densities of over 700 cm−3 at 4.5 RS. Rapid diffusion times, about 5 days at 6 RS, are required to match the observed ion densities. We find that the plasma and neutral composition vary with distance from Saturn, and make predictions for the ion and neutral densities as a function of radius.
Energetic ion populations and periodicities near Jupiter
Authors: Anagnostopoulos G. C. , Marhavilas P. K. , Sarris E. T. , Karanikola I. , Balogh A.
Published: September 2002

The HISCALE experiment, during Ulysses' approach to Jupiter, observed a ∼10 hour periodic softening in ion spectrum outside the plasma sheet that (1) is not related to the approach of the plasma sheet, (2) is in phase with the «clock» relativistic electron modulation, and (3) is related to flux increase at low energies (≤200 keV) and flux decrease at high energies (≥200 keV); the observations suggest the existence of an ion population with energy spectrum that is in general softer than the spectrum of the plasma sheet population. Detailed examination of the data shows that series of short duration (from a few up to some tens of minutes) energetic ion (∼0.06 to ∼3.00 MeV) bursts is a global phenomenon of the dayside Jovian magnetosphere and its environment. The bursts are often periodic at ∼40 min, although a second harmonic at ∼20 min is also evident in some cases. The energetic (≥∼60 keV) ion observations suggest that the plasma sheet was the main source of the upstream events inbound. The upstream observations (intensity‐time profiles, energy spectra, velocity dispersion, angular distributions and composition) made by Ulysses (and earlier observations by Voyager missions, i.e. inverse velocity dispersion) are well explained in terms of magnetospheric periodicities (10/5 hours and 40/20 min) and a leakage model for magnetospheric ions. During the outbound trajectory, Ulysses detected a low energy (≤∼200 keV) ion population, that is discussed in terms of shock drift acceleration.
Bulk flows of hot plasma in the Jovian magnetosphere: A model of anisotropic fluxes of energetic ions
Authors: Hawkins S. Edward , Cheng Andrew F. , Lanzerotti Louis J.
Published: September 2002

Since the Ulysses flyby of Jupiter in February 1992, a consistent picture of the bulk flows of hot plasma has yet to be formed. The present study reports a comprehensive analysis of energetic particle anisotropies from the Ulysses mission. We present an empirical model which separates flow from gradient anisotropies. The model employs a multidimensional minimization routine to fit simultaneously 13 free parameters using 98 measurements. The large number of independent measurements is possible because the Ulysses Heliosphere Instrument for Spectra, Composition, and Anisotropy at Low Energy (HI‐SCALE) has nearly full angular coverage at high time resolution and moderately high angular resolution. The model uses the full energy range (∼50–3000 keV) of the low‐energy magnetic spectrometers and also the pure proton channels of the composition aperture on the instrument. We present flow results during the inbound pass of Ulysses in which the radial velocity component shows a persistent radial outflow. The azimuthal component is in the sense of planetary rotation but generally below rigid corotation, and the azimuthal velocity is greater near the plasma current sheet than at higher magnetic latitudes. Outbound, the flows in the high‐latitude duskside magnetosphere inferred from the particle anisotropies indicate, surprisingly, sunward flows opposite to planetary rotation. We find evidence of gradient anisotropies especially near the magnetospheric current sheet on the dayside. We present a picture of the global magnetic field configuration and flows of hot plasma, consistent with our model results, dominated by subcorotation at low latitudes but by sunward flow at high latitudes.
Saturn's hydrogen aurora: Wide field and planetary camera 2 imaging from the Hubble Space Telescope
Authors: Trauger John T. , Clarke John T. , Ballester Gilda E. , Evans Robin W. , Burrows Christopher J. , Crisp David , Gallagher John S. , Griffiths Richard E. , Hester J. Jeff , Hoessel John G. , Holtzman Jon A. , Krist John E. , Mould Jeremy R. , Sahai Raghvendra , Scowen Paul A. , Stapelfeldt Karl R. , Watson Alan M.
Published: September 2002

Wide field and planetary camera 2/Hubble Space Telescope (WFPC2/HST) images of Saturn's far ultraviolet aurora reveal emissions confined to a narrow band of latitudes near Saturn's north and south poles. The aurorae are most prominent in the morning sector with patterns that appear fixed in local time. The geographic distribution and vertical extent of the auroral emissions seen in these images provide the first new observational insights into the physical mechanisms that power Saturn's aurora since the Voyager encounters 17 years ago.
Ventifacts at the Pathfinder landing site
Authors: Bridges N. T. , Greeley R. , Haldemann A. F. C. , Herkenhoff K. E. , Kraft M. , Parker T. J. , Ward A. W.
Published: September 2002

About half of the rocks at the Mars Pathfinder Ares Vallis landing site appear to be ventifacts, rocks abraded by windborne particles. Comparable resolution images taken by the Imager for Mars Pathfinder (IMP) camera and the Viking landers show that ventifacts are more abundant at the Pathfinder site. The ventifacts occur in several forms, including rocks with faceted edges, finger‐like projections, elongated pits, flutes, grooves, and possible rills. The trends of elongated pits, flutes, grooves, and rills cluster at ∼280–330° clockwise from north and generally dip 10–30° away from their trend direction. These orientations are indicative of southeast to northwest winds and differ from the trend of wind tails at the landing site, the direction of local wind streaks, and predictions of the Global Circulation Model, all of which indicate northeast to southwest winds. The disparity between these data sets strongly suggests that local circulation patterns have changed since the abrasion of the ventifacted rocks. The greater number of ventifacts at the Pathfinder site compared to either of the Viking sites is most easily explained as being due to a larger supply of abrading particles, composed of either sand‐sized grains or indurated dust aggregates, and higher surface roughness, which should increase the momentum of saltating grains. The Pathfinder ventifacts may have formed shortly after the deposition of outflow channel sediments nearly 2 Gry ago, when a large local supply of abrading particles should have been abundant and atmospheric conditions may have been more conducive to rock abrasion from saltating grains. Based on how ventifacts form on Earth, the several ventifact forms seen at the Pathfinder site and their presence on some rocks but not on others are probably due to local airflow conditions, original rock shape, exposure duration, rock movement, and to a lesser extent, rock lithology. The abundance of ventifacts at the Pathfinder site, together with other evidence of weathering, indicates that unaltered rock surfaces are rare on Mars.
Debris‐flow origin for the Simud/Tiu deposit on Mars
Authors: Tanaka Kenneth L.
Published: September 2002

A late Hesperian smooth plains deposit on Mars interpreted as a debris flow extends more than 2000 km from Hydraotes Chaos, through Simud and Tiu Valles, and into Chryse Planitia. The Simud/Tiu deposit widens out to >1000 km and embays streamlined landforms and knobs made up of sedimentary and perhaps volcanic deposits that were carved by earlier channeling activity. Morphologic features of the Simud/Tiu deposit observed in Viking and Pathfinder images are generally consistent with a debris‐flow origin, but some of the deposit's salient features are not readily explained by catastrophic flooding or ice flow. Internal depressions appear to be bounded by linear scarps along flow margins where differential shearing may have occurred and in areas where flow spreading may have produced zones of extensional breakup and thinning within the flow. Possible flow lobes within the deposit may have formed by successive flow surges within the flow unit. The Pathfinder landing site is on the Simud/Tiu deposit, and the observations there are consistent with debris flow. The low, longitudinal ridges at the site may have formed by clast interactions as the flow ground to a halt. Imbricated, planar rocks on the ridges, such as in the Rock Garden, also may have been emplaced by debris or ice flow. However, stream energy calculations at Ares Vallis and channel geology indicate that flooding probably was incapable of emplacing the meter‐size boulders observed at the Pathfinder site. Dewatering of pressurized zones in the debris flow or underlying material may be responsible for mud eruptions that formed a couple of patches of low pancakelike shields up to 5 km in diameter and for probable water flows that formed two small rille channels a few kilometers long. Local irregular grooves may be cracks that resulted from later desiccation and contraction of the flow material. The debris‐flow unit apparently coalesced from outflows of water‐fluidized debris originating from beneath chaotic and hummocky terrains within and along the margins of Simud and Tiu Valles. The deposit is onlapped from the north by another flow deposit originating from Acidalia Planitia. If the Simud/Tiu debris flow had entered a standing body of water, a turbidity current may have arisen from the debris flow and then backflowed over the debris flow to account for the Acidalia deposit.
A novel acceleration algorithm for the computation of scattering from rough surfaces with the forward‐backward method
Authors: Chou Hsi‐Tseng , Johnson Joel T.
Published: September 2002

The forward‐backward method has been shown to be an effective iterative technique for the computation of scattering from one‐dimensional rough surfaces, often converging rapidly even for very large surface heights. However, previous studies with this method have computed interactions between widely separated points on the surface exactly, resulting in anO(N2) computational algorithm that becomes intractable for large rough surface sizes, as are required when low grazing incidence angles are approached. An acceleration algorithm for more rapidly computing interactions between widely separated points in the forward‐backward method is proposed in this paper and results in an O(N) algorithm with increasing surface size. The approach is based on a spectral domain representation of source currents and the Green's function and is developed for both perfectly conducting and impedance boundary surfaces. The method is applied in a Monte Carlo study of low grazing incidence backscattering from very rough (up to 10 m/s wind speed) ocean‐like surfaces at 14 GHz and is found to require only a small fraction of the CPU time required by other competing methods; such as the banded matrix iterative approach/canonical grid and fast multipole methods.
Partial area coverage distribution for flood frequency analysis in arid regions
Authors: Marco Juan B. , Valdés Juan B.
Published: September 2002

Convective rainfalls of high intensity are largely responsible for most large floods occurring in arid regions. Convective storms are limited in size and rarely cover an entire basin. Therefore flood frequency is affected by the distribution of storm coverage c, which is the fraction of basin area upon which rainfall occurs. Analytical probability density function (pdf) estimates of partial storm coverage are presented as a function of basin area sc and the probability distribution function for storm radius rs Conditional pdfs for the covered area fraction c, given the storm radius f(c/rs), are obtained as a compound distribution with finite probability for maximum coverage and continuous density for smaller values. The conditionality assumption is removed by assuming an exponential storm radius marginal distribution to obtain the catchment coverage pdf. This pdf is compound, with discrete probability for complete catchment coverage P(c=1) and a continuous function for partial overlap. The continuous function combines a Weibull pdf and linear functions of c. Both P(c=1) and f(c)) depend on χ, the average catchment‐to‐storm radius ratio. The distribution explains the partial coverage data for the Walnut Gulch basin in Arizona. Departures were observed, however, for slightly less than complete coverage, namely, for 0.9 < c < 1. A conceptual event classification and a method were designed to include partial coverage effects on flood frequency distribution.
Significance of porosity variability to transport in heterogeneous porous media
Authors: Hassan Ahmed E. , Cushman John H. , Delleur Jacques W.
Published: September 2002

We use Monte Carlo simulations of flow and transport in two‐dimensional random conductivity, porosity, and geochemistry fields to explore the influence of their spatial variability on flow and transport processes for both conservative and reactive chemicals. For conservative transport, results show that when the porosity is correlated to the hydraulic conductivity (which may be expected in geologic formations); the dispersion process is significantly affected. Positive cross correlation between the porosity and the conductivity decreases dispersion, while a negative correlation tends to increase dispersion in the longitudinal direction. For reactive transport in physically and chemically heterogeneous media, the geochemical variability alone yields results that are significantly different than when both geochemistry and porosity are random space variables correlated to the conductivity field. These results suggest that it is necessary to examine the role porosity variability and its correlation to the conductivity play in transport theories. The stochastic perturbation transport theory, previously developed by our group for conservative chemicals, is modified to account for the porosity variability and its correlation with the hydraulic conductivity. The results of the modified theory support the Monte Carlo simulations and indicate that porosity variability significantly affects the second longitudinal moment. The implication of the study for field problems depends on the existence of cross correlation between porosity and conductivity.
Identification of large‐scale hydraulic conductivity trends and the influence of trends on contaminant transport
Authors: Eggleston Jack , Rojstaczer Stuart
Published: September 2002

We examine the identification of large‐scale spatial trends in hydraulic conductivity and the influence of these trends on contaminant transport. Using three different trend identification methods, polynomial regression and Kaiman filtering, which fit smooth functions, and hydrofacies delineation, which constructs a geologic model, we try to identify the hydraulic conductivity patterns controlling solute transport in a heavily sampled heterogeneous aquifer on Columbus Air Force Base, Mississippi. Even with >2400 hydraulic conductivity measurements, unambiguous determination of large‐scale trends is not possible. None of the estimated hydraulic conductivity trends gives transport simulations that reproduce the observed non‐Gaussian transport behavior. Hydrofacies delineation and Kalman filtering give the best results. While the influence of the identified large‐scale trends on advective transpo) hydraulic conductivity structures.
Data from selected U.S. Geological Survey National Stream Water Quality Monitoring Networks
Authors: Alexander Richard B. , Slack James R. , Ludtke Amy S. , Fitzgerald Kathleen K. , Schertz Terry L.
Published: September 2002

A nationally consistent and well‐documented collection of water quality and quantity data compiled during the past 30 years for streams and rivers in the United States is now available on CD‐ROM and accessible over the World Wide Web. The data include measurements from two U.S. Geological Survey (USGS) national networks for 122 physical, chemical, and biological properties of water collected at 680 monitoring stations from 1962 to 1995, quality assurance information that describes the sample collection agencies, laboratories, analytical methods, and estimates of laboratory measurement error (bias and variance), and information on selected cultural and natural characteristics of the station watersheds. The data are easily accessed via user‐supplied software including Web browser, spreadsheet, and word processor, or may be queried and printed according to user‐specified criteria using the supplied retrieval software on CD‐ROM. The water quality data serve a variety of scientific uses including research and educational applications related to trend detection, flux estimation, investigations of the effects of the natural environment and cultural sources on water quality, and the development of statistical methods for designing efficient monitoring networks and interpreting water resources data.
Scales of fluctuation and the propagation of uncertainty in random porous media
Authors: Ghanem Roger
Published: September 2002

The mechanics of transport and flow in a random porous medium are addressed in this paper. The hydraulic properties of the porous medium are modeled as spatial random processes. The heterogeneity of the medium is modeled as a superposition of scales of heterogeneity that are statistically uncorrelated. The stochastic process making up a hydraulic property is thus represented as a linear combination of normalized deterministic shapes multiplied by a set of uncorrelated random variables. The Karhunen‐Loeve expansion is used to formalize this representation. The uncertainty contained in each of these scales is then propagated through the system using the governing differential equation as a constraint. The solution process will thus consist of the original scales used to represent the porous medium as well as various interaction between these scales. The objective of this paper is to develop a procedure for quantifying the uncertainty in the field variables using the scales of fluctuation of the porous medium as the measuring stick.
Estimation of soil moisture and groundwater recharge using the TOPOG_IRM Model
Authors: Zhang L. , Dawes W. R. , Hatton T. J. , Reece P. H. , Beale G. T. H. , Packer I.
Published: September 2002

A distributed parameter ecohydrological model (TOPOG_IRM) was applied to a 1.6 km2 pastoral catchment in southeast Australia for estimating soil moisture and groundwater recharge, for a period of 1992–1994. The main objective of TOPOG_IRM is to provide a realistic description of the key processes which control the soil moisture dynamics, evapotranspiration, and to investigate hydrological and ecological responses at a catchment scale. The model was not fitted but parameterised with field data and literature values. The soil moisture content at various depths was well simulated for six sites in the catchment representing different soil types and landscape positions. The spatial patterns of the soil moisture content appear to be controlled mainly by the soil types, and the results indicated that there is little lateral movement of water in the catchment. Average groundwater recharge was found to be 5% of the annual rainfall, and its spatial patterns were dominated by the soil types. The study has demonstrated potential application of TOPOG_IRM in simulating catchment scale responses under different land management options in the context of salinity control.
Seasonal and spatial variations in infiltration rates in badland surfaces under Mediterranean climatic conditions
Authors: Cerdà A.
Published: September 2002

This paper investigates the spatial and temporal variations of infiltration rates on badland landscapes under Mediterranean climatic conditions of the eastern Iberian Peninsula. Soil infiltration was measured under simulated rainfall and by cylinder infiltrometer for typical winter, spring, summer, and autumn conditions. The spatial variability of infiltration within the badland landscapes is determined by the two main geomorphological units: slopes and pediments. Slopes show greater steady state infiltration rates than pediments (averaging 6.6 and 11.9 mm h−1, respectively), but they generate faster runoff and the runoff curves are steeper than on the slopes. For short thunderstorms, pediments generate more runoff because soils on the slopes have a wider and deeper crack network, which favors higher infiltration rates at the beginning of the rainfall. However, for simulated storms of 40 min duration, the runoff rate on the slopes (74.3%) is slightly greater than on the pediments (72.5%) due to their lower steady state infiltration rate. For both slopes and pediments, greater steady state infiltration rates were measured under simulated rainfall (fc) for summer (18.9 and 11.6 mm h−1) than for winter (11.8 and 6.8 mm h−1), spring (3.8 and 8.7 mm h−1), and autumn (4.1 and 8.3 mm h−1) for slope and pediment positions, respectively. Measurements by means of cylinder infiltrometer (ifc) confirm these seasonal trends. On the pediment plots, ifc varies from 43 mm −1 in winter to 26 mm h−1 in spring, rises to 62 mm h−1 in summer, and finally drops to 26 mm h−1 in autumn. For the slope positions, ifc has a similar seasonal trend: 18 mm h−1 in winter, 9 mm h−1 in spring, 52 mm h−1 in summer, and 10 mm h−1 in autumn. Measurements by means of cylinder infiltrometer results in 3 times greater steady state infiltration rates due to the effect of water depth pressure and crust development under simulated rainfall. In summer the development of wide and deep cracks results in macropore flow, and these are important factors in pipe initiation.
open‐channel flow through simulated vegetation: Suspended sediment transport modeling
Authors: López Fabián , García Marcelo
Published: September 2002

A two‐equation turbulence model, based on the k‐ϵ closure scheme, was used to determine the mean flow and turbulence structure of open channels through simulated vegetation, thus providing the necessary information to estimate suspended sediment transport processes. Dimensional analysis allowed identification of the dimensionless parameters that govern suspended sediment transport in the presence of vegetation and thus helped in the design of numerical experiments to investigate the role of different flow properties, sediment characteristics, and vegetation parameters upon the transport capacity. A reduction of the averaged streamwise momentum transfer toward the bed (i.e., shear stress) induced by the vegetation was identified as the main reason for lower suspended sediment transport capacities in vegetated waterways compared to those observed in nonvegetated channels under similar flow conditions. Computed values of kinematic eddy viscosity were used to solve the sediment diffusion equation, yielding distributions of relative sediment concentration slightly in excess of the ones predicted by the Rousean formula. A power law was found to provide a very good collapse of all the numerically generated data for suspended sediment transport rates in vegetated channels.
Laboratory investigations of effective flow behavior in unsaturated heterogeneous sands
Authors: Wildenschild D. , Jensen K. H.
Published: September 2002

Two‐dimensional unsaturated flow and transport through heterogeneous sand was investigated under controlled laboratory conditions. The unsaturated hydraulic conductivity of five homogeneous sands and three heterogeneous systems composed of these five sands was measured using a steady state flux controlled method. The heterogeneous sand systems were established in a laboratory tank for three realizations of random distributions of the homogeneous sands comprising a system of 207 grid cells. The water flux was controlled at the upper boundary, while a suction was applied at the lower boundary such that on the average a uniform pressure profile was established and gravity flow applied. Solute breakthrough curves measured at discrete points in the tank using time domain reflectometry, as well as dye tracer paths, showed that flow and transport took place in a very tortuous pattern where several grid cells were completely bypassed. The degree of tortuosity appeared to be dependent on the degree of saturation, as the tortuosity increased with decreasing saturation. Despite the tortuous flow patterns, we found that the effective unsaturated hydraulic conductivity as well as the retention curves for the three realizations of the heterogeneous sand were quite similar, thus suggesting that this type of heterogeneous flow system can be treated as an equivalent homogeneous medium characterized by effective parameters.
Soil structure development and preferential solute flow
Authors: Vervoort R. W. , Radcliffe D. E. , West L. T.
Published: September 2002

Soil structure and preferential flow are thought to be highly related, but quantification of this relationship has remained problematic. A combination of experiments on two soils at local and field scale was used to study the relationships between the degree of structural development, saturated conductivities Ks, moisture release, breakthrough parameters, and observations of preferential flow at the field scale. The convection dispersion equation and mobile‐immobile model were fitted to breakthrough curves, and flow channels were stained with dye. Well‐developed structure was associated with high dispersivities, a high coefficient of variation of Ks, and low mobile water contents, low exchange coefficients, and a low dyed area. Field‐scale observations matched the differences in structure and preferential flow parameters observed at the local scales. Local‐scale preferential flow appeared to highly influence field‐scale solute transport, indicating that this is an important local‐scale process which is not dampened at the field scale. A conceptual model of subsoil structural development was expanded with physical parameters matching the structural development stage to predict the likelihood of preferential flow on the basis of the saturation regime of the horizon or pedon.
Low‐frequency oscillations in precipitation, temperature, and runoff on a west facing mountain front: A hydrogeologic interpretation
Authors: Shun Tongying , Duffy Christopher J.
Published: September 2002

This paper examines the space‐time patterns of annual, interannual, and decadal components of precipitation, temperature, and runoff (P‐T‐R) using long‐record time series across the steep topographic gradient of the Wasatch Front in northern Utah. This region forms the major drainage area to the Great Salt Lake. The approach is to use multichannel singular spectrum analysis as a means of detecting dominant oscillations and spatial patterns in the data and to discuss the relation to the unique mountain and basin hydrologic setting. Results of the analysis show that high‐elevation runoff is dominated by the annual and seasonal harmonics, while low‐elevation runoff exhibits strong interannual and decadal oscillations. For precipitation and temperature, only the annual/seasonal spectral peaks were found to be significantly different from the underlying noise floor, and these components increase with altitude similar to the mean orographic pattern. Spectral peaks in runoff show a more complex pattern with altitude, with increasing low‐frequency components at intermediate and lower elevation. This pattern is then discussed in terms of basin storage effects and groundwater‐stream interaction. A conceptual hydrogeologic model for the mountain and basin system proposes how losing streams and deep upwelling groundwater in the alluvial aquifer could explain the strong low‐frequency component in streams entering the Great Salt Lake. The phase‐plane trajectories of the dominant components for P‐T‐R are reconstructed as a function of altitude showing the relation of hydrogeologic conditions to the strongest oscillations in mountain runoff and discharge to the Great Salt Lake. The paper shows that weak interannual and decadal oscillations in the climate signal are strengthened where groundwater discharge dominates streamflow.
Daily streamflow conditions map now online
Authors: Lins Harry F.
Published: September 2002

A new daily streamflow conditions map for the United States is now available online from the U.S. Geological Survey (USGS). The map depicts streamflow as a percentile of its longterm value for each day Located at http://water.usgs.gov/public/dwc/national_map.html, it is updated every 3 hours.

The flows are grouped into seven color‐coded percentile categories. More than 2000 realtime stations from the USGS stream gaging network, each having at least 30 years of continuous records, are represented. Changes in daily streamflow over the past several weeks can be viewed in an animated sequence.
Rhodococcus equi infection in transplant recipients: a case of mistaken identity and review of the literature
Authors: Perez M.G.V. , Vassilev T. , Kemmerly S.A.
Published: September 2002

Abstract The incidence of Rhodococcus equi infection in solid‐organ transplant recipients continues to rise throughout the world. Unfortunately, this opportunistic pathogen is still underestimated and potentially disregarded by physicians and microbiology laboratories due to its morphology on Gram staining. Pulmonary involvement is the most common finding in the immunocompromised host. We report a case of a 63‐year‐old heart‐transplant recipient who presented with increasing fatigue and nonproductive cough for 3 weeks. After full evaluation, a lung abscess was demonstrated by thoracic computerized tomography (CT). Blood and sputum cultures were remarkable for heavy “diphtheroids.” Although the Gram‐stain result was initially interpreted as a contaminant, a clinical suspicion for Rhodococcus assisted in further investigation. Broncheoalveolar lavage and CT‐guided biopsy of the lung abscess revealed heavy growth of diphtheroids. However, further evaluation by a reference laboratory demonstrated mycolic acid staining consistent with R. equi. Surgical drainage and prolonged antibiotic therapy resulted in complete remission of the pneumonia and abscess. This represents the fourth reported case of R. equi infection in a heart transplant recipient. It is imperative that all physicians and laboratory staff consider R. equi when an immunocompromised patient has any type of pneumonia, especially with abscess formation.
Safety and tolerability of caspofungin acetate in the treatment of fungal infections
Authors: Sable C.A. , Nguyen B‐Y T. , Chodakewitz J.A. , DiNubile M.J.
Published: September 2002

Abstract Caspofungin acetate is the first member of the novel echinocandin class of antifungal drugs to be marketed in the United States. It has recently been approved for use in patients with invasive aspergillosis who are refractory to or intolerant of conventional therapy. Accordingly, its safety profile is particularly important to review. The safety and tolerability of caspofungin have been examined in 623 persons, including 295 patients who received ≥ 50 mg/day for at least one week in clinical studies. In the 263 patients, given caspofungin in randomized double‐blind active‐control trials to date, there have been no serious clinical or laboratory drug‐related adverse events; caspofungin was discontinued in only 2% of these patients because of drug‐related adverse experiences. Caspofungin may have potentially important drug interactions with cyclosporine and tacrolimus.
Legionellosis in a lung transplant recipient obscured by cytomegalovirus infection and Clostridium difficile colitis
Authors: Nichols L , Strollo D.C. , Kusne S.
Published: September 2002

Abstract: A 52‐year‐old‐white male underwent double lung transplantation for severe emphysema due to alpha‐1‐antitrypsin deficiency and heavy tobacco use. Following a postoperative course complicated by renal insufficiency, pulmonary emboli, and Clostridium difficile colitis, he was discharged in stable condition. Two months later, he was admitted to a local hospital with a fever, abdominal pain, diarrhea, nausea, and dyspnea. Computerized tomography (CT) of the chest revealed bilateral pleural effusions. Sigmoidoscopy was grossly normal but biopsy demonstrated cytomegalovirus (CMV) colitis, and the patient was placed on intravenous ganciclovir. Over the next week, he became progressively hypoxemic and was transferred to the University of Pittsburgh Medical Center (post‐transplant day 81) for further evaluation. His medications on transfer included: ganciclovir, prednisone, tacrolimus, dapsone, fluconazole, ondansetron, lansoprazole, digoxin, and coumadin.
Ca2+entry blocking and contractility promoting actions of norbormide in single rat caudal artery myocytes
Authors: Fusi Fabio , Saponara Simona , Sgaragli Giampietro , Cargnelli Gabriella , Bova Sergio
Published: September 2002

Aim of the present study was to investigate the effects of norbormide, a selective vasoconstrictor agent of the rat peripheral vessels, on the whole‐cell voltage‐dependent L‐type Ca2+current (ICa(L)) of freshly isolated smooth muscle cells from the rat caudal artery, using either the conventional or the amphotericin B‐perforated whole‐cell patch‐clamp method.

Norbormide decreased L‐type Ca2+current in a concentration‐ and voltage‐dependent manner, without modifying the threshold and the maximum of the current‐voltage relationship. Norbormide‐induced ICa(L)inhibition was reversible upon wash‐out.

Norbormide both shifted the voltage dependence of the steady‐state inactivation curve to more negative potentials by about 16 mV, without affecting the activation curve, and decreased the slope of inactivation. Norbormide, however, did not modify both the activation and the inactivation kinetics of the ICa(L).

Norbormide decreased ICa(L)progressively during repetitive step depolarizations, with inhibition depending on the stimulation frequency (use‐dependent block) as well as on the holding potential.

Addition of 50 μMnorbormide caused the contraction of all freshly isolated cells and also of those impaled with the perforated method, but not of those impaled with the conventional method (i.e. dialysed).

In conclusion, these results prove norbormide to be a vascular L‐type Ca2+channel inhibitor, which preferentially acts on the inactivated and/or open state of the channel. In rat caudal artery smooth muscle, however, this mechanism does not result in a vasodilating effect since it is overwhelmed by the mechanism underlying norbormide‐induced vasoconstriction.

British Journal of Pharmacology(2002)137, 323–328. doi:10.1038/sj.bjp.0704877