bluuebunny/crossref_metadata_2025 huggingface dataset:
Radon 222 Emanometry: A relevant methodology for water well siting in hard rock aquifers
Authors: Lachassagne Patrick , Pinault Jean‐Louis , Laporte Pierre
Published: February 2004

To improve the understanding of soil gas emanations with the aim of groundwater prospecting in fractured substrates, radon anomalies were mapped in a tropical region (French Guyana) where the structural features of a potential gas source are masked owing to the thick regolith cover. Two anomalies were located. Two probes were then installed, one (Bl) on the border of the north anomaly and the second (B2) at the center of the south anomaly, as well as a meteorological station, and monitoring was carried out for 6 months extending from the dry to the rainy season. Signal processing of radon signal–atmospheric pressure time series allowed us to determine the physical processes causing migration of the gases in the soil and the subsoil. The radon anomalies are very probably associated with the presence, in the hard rock substratum, of a permeable structure that permits the transit of “deep” origin gas to the surface. This transport by advection disturbs the radon diffusion profile from the first meters of soil into the atmosphere. The radon thus behaves as a marker of deeper gases percolating through the regolith cover. Indeed, in such a context with low‐permeability weathered formations, because of its short half‐life (3.8 days) the radon measured in the first decimeters of the soil displays an exclusively superficial origin. Hence the measurement of the radon content in soil, at an identical depth from one sampling site to another, helps locate the zones affected by advective gas transfers which explains why the radon anomalies in soil gases, identified at the scale of a hydrogeological prospecting site located in a hard rock context, usually coincide vertically in hydraulically active fracture zones. This fully justifies the use of this method to site water wells, provided some precautions are observed, particularly pertaining to the spatial and temporal variability of the signal associated with different types of soils and changes in the meteorological parameters and soil moisture contents. The methodology is simple since only robust equipment is required. The estimation of gas transport parameters also helped identify the extent of advection areas. During the dry season they are characterized by low gas velocity. These zones shrink with the early rains, and the advection area is confined vertically up the fault where a channeling effect occurs: Soil gas preferably follows the less constricted pores, and the increased pressure gradient offsets the decrease in permeability.
Effect of initial step height on headcut development in upland concentrated flows
Authors: Bennett Sean J. , Casalí Javier
Published: February 2004

Experiments were conducted to examine the effect of initial step height on growth, development, and upstream migration of headcuts in concentrated flows typical of rills, crop furrows, and ephemeral gullies. In a laboratory channel, packed soil beds were constructed with preformed headcuts ranging in height from 5 to 50 mm. Each bed was subjected to the same simulated rain, which produced a protective surface seal, followed by an overland flow, which caused soil erosion exclusively at the headcut. After a brief period of bed adjustment, migration rate, scour hole geometry, and sediment yield reached asymptotic values, but the time and length required to reach these asymptotes decreased as the initial step height increased. Steady state headcut dimensions, sediment yield, and the slope of the sediment deposit increased as initial step height increased, but sediment sorting patterns downstream of the migrating headcut remained unchanged.
Partitioning tracer transport in a hydrogeochemically heterogeneous aquifer
Authors: Zhang Yan , Graham Wendy D.
Published: February 2004

In this paper a stochastic model is developed to predict the behavior of partitioning tracers in a three‐dimensional aquifer subject to spatial heterogeneities of nonaqueous phase liquid (NAPL) and Darcy flux. Stochastic Eulerian perturbation methods are applied to derive a system of six coupled partial‐differential first‐order moment equations from the traditional advection‐dispersion‐retardation equation. These equations describe the transient behavior of the concentration moments that explicitly accounts for the effects of the considered heterogeneities on prediction uncertainty and spatiotemporal correlation between tracer concentration, Darcy flux, and NAPL distribution. A finite difference technique is used to solve these equations numerically. Three different cases are presented to evaluate the impact of various statistical relationships between the random fields of natural log conductivity and natural log volumetric NAPL content. It is found that strong negative correlation between NAPL content and hydraulic conductivity leads to increased prediction uncertainty, whereas strong positive correlation between NAPL content and hydraulic conductivity leads to decreased prediction uncertainty over the uncorrelated case. For all cases, cross correlations between tracer concentration and Darcy flux or NAPL saturation are more extensive in the direction of mean flow than transverse to the mean flow. Furthermore, the magnitude of these correlations is approximately constant over the duration of the tracer experiment, implying that all concentration measurements taken at a particular location contain approximately equal information about Darcy flux or NAPL distribution within the experimental domain. The cross correlation between tracer concentration and Darcy flux is relatively insensitive to the degree of the conductivity‐NAPL correlation. However, the correlation between tracer concentration and NAPL concentration is much larger for strongly (positively or negatively) correlated hydraulic conductivity and NAPL distributions. In a comparison paper [Zhang and Graham, this issue] these correlations, together with tracer measurements, are incorporated into a parameter estimation algorithm to produce site‐specific conditional estimates of NAPL and Darcy flux distribution.
Estimation of turbulent kinetic energy dissipation
Authors: Chen Huey‐Long , Hondzo Miki , Rao A. Ramachandra
Published: February 2004

The kinetic energy dissipation rate is one of the key intrinsic fluid flow parameters in environmental fluid dynamics. In an indirect method the kinetic energy dissipation rate is estimated from the Batchelor spectrum. Because the Batchelor spectrum has a significant difference between the highest and lowest spectral values, the spectral bias in the periodogram causes the lower spectral values at higher frequencies to increase. Consequently, the accuracy in fitting the Batchelor spectrum is affected. In this study, the multitaper spectral estimation method is compared to conventional methods in estimating the synthetic temperature gradient spectra. It is shown in the results that the multitaper spectra have less bias than the Hamming window smoothed spectra and the periodogram in estimating the synthetic temperature gradient spectra. The results of fitting the Batchelor spectrum based on four error functions are compared. When the theoretical noise spectrum is available and delineated at the intersection of the estimated spectrum, the fitting results of the kinetic energy dissipation rate corresponding to the four error functions do not have significant differences. However, when the noise spectrum is unknown and part of the Batchelor spectrum overlaps the region where the noise spectrum dominates, the weighted chi‐square distributed error function has the best fitting results.
Variability of Gardner's α for coarse‐textured sediments
Authors: Khaleel Raziuddin , Relyea John F.
Published: February 2004

Vadose zone soils in arid regions often contain a high gravel fraction (>2 mm size). This paper examines, for coarse‐textured soils, variability of the slope α of Gardner's [1958] unsaturated hydraulic conductivity K versus matric potential ψ relation, K = Kseαψ. The steady state head control method was used to obtain unsaturated K for tensions as high as 386 cm. A total of 79 samples were analyzed in the laboratory; the gravel fraction for the 41 gravelly samples ranged from 20 to 71% (by weight); the remaining 38 samples were sandy with no gravel fraction. The measured K values for the gravelly samples fall within a narrow range and are well within the range of measured K values for the sandy samples. The bulk of both gravelly and sandy samples can be described using a single‐slope exponential model; Gardner's α and the intercept K0 are based on a least squares fit to the late time measurements at lower ψ. The mean and variance of α for the gravelly samples are lower compared with the sandy type. The α values for the gravelly soils follow a normal distribution, whereas the K0 estimates and the laboratory‐measured Ks follow lognormal distributions. For the sandy type, α, K0, and Ks follow lognormal distributions. The α values appear to be related to the median particle diameter d50 and the slope of the particle size distribution. A clear reduction in variability of α is apparent with an increase in d50, suggesting that the unsaturated K and α variability for the gravelly soils can be estimated within narrow ranges. The flow‐weighted characteristic pore size λm is clearly dependent on the soil type; λm values for the gravelly soils are characterized by a smaller mean and variance than for the sandy type. This helps explain the finding that the range in unsaturated K for the gravelly soils is less than for the sandy type. At higher tensions the mean and variance of α and lnK0 as well as the cross correlation between α and lnK0 are important inputs to stochastic models of unsaturated flow. The implications of their variability on flow in heterogeneous media are discussed.
Tidal fluctuations in a leaky confined aquifer: Dynamic effects of an overlying phreatic aquifer
Authors: Li L. , Barry D. A. , Jeng D.‐S.
Published: February 2004

Tidal fluctuations in a leaky confined coastal aquifer are damped significantly due to leakage into an overlying phreatic aquifer. Jiao and Tang [1999] presented an analytical solution to a simple model describing this phenomenon. Their solution assumes that the tidal fluctuations in the overlying phreatic aquifer are negligible (i.e., a static phreatic aquifer). Here we examine dynamic effects of the overlying aquifer based on a new approximate analytical solution. The numerical results indicate that the dynamic effects can be significant for a relatively large leakage and a high transmissivity of the phreatic aquifer.
An integrated crustal velocity field for the central Andes
Authors: Kendrick Eric , Bevis Michael , Smalley Robert , Brooks Benjamin
Published: February 2004

We present an integrated velocity field for the central Andes, derived from GPS observations collected between January 1993 and March 2001 that eliminates the velocity bias between the South America‐Nazca Plate Project (SNAPP) and central Andes GPS Project (CAP) velocity fields published by Norabuena et al. [1998] and Bevis et al. [1999]. The reference frame is realized by minimizing the motion of eight continuous GPS stations and one rover GPS station located in the stable core of the South American plate. The RMS horizontal motion of these stations is just 1.1 mm/yr. The amplitude of these residual motions is roughly compatible with expected levels of measurement error. In our new solution, five of the six SNAPP stations located just outside the orogenic belt are effectively stationary, and the velocities for adjacent CAP and SNAPP stations now agree at a level consistent with their formal uncertainties.
Impact of 837 GPS/MET bending angle profiles on assimilation and forecasts for the period June 20–30, 1995
Authors: Liu Hui , Zou X. , Shao H. , Anthes R. A. , Chang J. C. , Tseng J.‐H. , Wang B.
Published: February 2004

With a ray‐tracing procedure and variational data assimilation techniques, it is now possible to make direct use of radio occultation bending angles, rather than their derived temperature and moisture retrievals, in atmospheric data analysis and assimilation. This paper describes results obtained from including more than 800 GPS/MET bending angle profiles, available over an 11‐day period, 20–30 June 1995, into the National Centers for Environmental Prediction spectral statistical interpolation analyses. The methodology for assimilating the bending angles (including an impact parameter offset correction) is briefly summarized. Verified with 56 collocated radiosonde profiles, the assimilation of only GPS/MET bending angles improves the temperature and specific humidity analysis above 850 mbar. Even though the number of GPS/MET soundings is still far less than conventional data and operational satellite soundings, our results from two continuous 11‐day data assimilation cycles demonstrate a closer fit of both GPS/MET and conventional observations to the analyses between 850 and 200 hPa when the bending angles are incorporated. Including the bending angles also results in a small but consistent improvement in the short‐range (6 hours) and medium‐range (1–5 days) forecast skills, especially in the Southern Hemisphere.
Comparing independent estimates of carbon dioxide exchange over 5 years at a deciduous forest in the southeastern United States
Authors: Wilson Kell B. , Baldocchi Dennis D.
Published: February 2004

At a deciduous forest in the southeast United States (Walker Branch Watershed, Oak Ridge, Tennessee), as at other sites with tall vegetation and/or complex terrain, it is difficult to temporally integrate eddy covariance data to obtain long‐term estimates of net ecosystem exchange of carbon dioxide (NEE), primarily because of suspected systematic nocturnal errors. Therefore, although eddy covariance data can be invaluable, additional tools such as empirical gap‐filling methods, independent measurements of CO2 flux using chambers, and simulations using canopy process models are often necessary to obtain reliable annual carbon uptake estimates. Two independent approaches for estimating annual NEE using these tools at the Walker Branch site are discussed. One approach is to cumulatively sum the full set of eddy covariance measurements over time. The second approach is to sum the output of NEE from a biophysical canopy exchange model (CANOAK). CANOAK incorporates independent chamber measurements on leaves, soil, and stems and is driven using the observed canopy architecture, meteorology, soil water content, and soil temperatures to predict NEE. Both methods estimate similar trends and magnitudes of daytime (daylight hours) soil respiration and NEE over 5 years. Both methods also suggest similar differences among years (interannual variability). These two estimates of NEE are used to address possible measurement bias errors at this site and to provide plausible estimates of annual NEE. The estimated mean annual NEE at this site is −574 g C m−2 yr−1 between 1995 and 1999, ranging from −470 g C m−2 y−1 (1995) to −629 g C m−2 yr−1 (1999) (negative NEE indicates uptake by forest).
Mechanisms in the development of anomalous sea ice extent in the western Arctic: A case study
Authors: Lynch Amanda H. , Maslanik James A. , Wu Wanli
Published: February 2004

Interannual cycles and trends in Arctic ice cover are dominated by strong regional variability. Arctic sea ice extent exhibited a record minimum within the Arctic Basin during September 1990, dominated by a rapid retreat in the Chukchi, East Siberian, and Laptev Seas. Simulations using a coupled regional model reproduced the enhanced cyclonic activity and enhanced ice melt which led to this large retreat in sea ice cover. Sensitivity experiments showed that accurate initial ice conditions are crucial for a realistic simulation of the ice anomaly, pointing to the need for adequate spin‐up in coupled model experiments. It was also found that thermodynamic melt can account for the bulk of the total loss in ice mass over the summer season in 1990, but without dynamics, the spatial patterns characteristic of the ice reductions are not reproduced well. Also, transport of ice was crucial to initiate the formation of the anomaly, even if the formation was delayed until later in the season. The ice‐albedo feedback is important in allowing the continued formation of the ice anomaly throughout the summer. Interannual variations in atmospheric circulation that yield regional differences in ice thickness provide a preconditioning that significantly affected development of the ice anomaly. This suggests that circulation modes play an important role in determining ice severity along the Siberian coast.
Chemical transport across the ITCZ in the central Pacific during an El Niño‐Southern Oscillation cold phase event in March‐April 1999
Authors: Avery Melody A. , Westberg David J. , Fuelberg Henry E. , Newell Reginald E. , Anderson Bruce E. , Vay Stephanie A. , Sachse Glen W. , Blake Donald R.
Published: February 2004

We examine interhemispheric transport processes that occurred over the central Pacific during the PEM‐Tropics B mission (PTB) in March‐April 1999 by correlating the observed distribution of chemical tracers with the prevailing and anomalous windfields. The Intertropical Convergence Zone (ITCZ) had a double structure during PTB, and interhemispheric mixing occurred in the equatorial region between ITCZ branches. The anomalously strong tropical easterly surface wind had a large northerly component across the equator in the central Pacific, causing transport of aged, polluted air into the Southern Hemisphere (SH) at altitudes below 4 km. Elevated concentrations of chemical tracers from the Northern Hemisphere (NH) measured south of the equator in the central Pacific during PTB may represent an upper limit because the coincidence of seasonal and cold phase ENSO conditions are optimum for this transport. Stronger and more consistent surface convergence between the northeasterly and southeasterly trade winds in the Southern Hemisphere (SH) resulted in more total convective activity in the SH branch of the ITCZ, at about 6°S. The middle troposphere between 4–7 km was a complex shear zone between prevailing northeasterly winds at low altitudes and southwesterly winds at higher altitudes. Persistent anomalous streamline patterns and the chemical tracer distribution show that during PTB most transport in the central Pacific was from SH to NH across the equator in the upper troposphere. Seasonal differences in source strength caused larger interhemispheric gradients of chemical tracers during PTB than during the complementary PEM‐Tropics A mission in September‐October 1996.
Radiative properties of aerosols in Saharan dust outbreaks using ground‐based and satellite data: Applications to radiative forcing
Authors: Díaz Juan P. , Expósito Francisco J. , Torres Carlos J. , Herrera Félix , Prospero Joseph M. , Romero María C.
Published: February 2004

We report on measurements of atmospheric transmission (ATT) and aerosol optical depth (AODT) made at three wavelengths (368, 500, and 778 nm) with a spectroradiometer placed on Tenerife (28.5°N, 16.3°W), Canary Islands. Using the National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) channel 1, we also measured the aerosol optical depth (AODS) and albedo over a region of the North Atlantic Ocean extending from 15°–35°N to 12°–25°W. We observe large changes in ATT and AODT when dust outbreaks pass over this region. Using all these data, we derive the asymmetry factor (g), the single‐scattering albedo (ω), and the local mean AODT and we compute the direct radiative forcing ΔF attributable to mineral dust. The local radiative forcing obtained is over the ocean ΔF = −9.7 W/m2 and for the land ΔF = −4.5 W/m2 with an error of ±25%. Extending these results to global‐scale averages, we obtain values of ΔF of −1.22 W/m2 over the ocean and −0.57 W/m2 over land. The forcings attributable to dust are comparable in magnitude to those reported in the literature for anthropogenic sulphate and for biomass burning aerosols.
Characteristics of the spatial distribution and yearly variation of aerosol optical depth over China in last 30 years
Authors: Yunfeng Luo , Daren Lu , Xiuji Zhou , Weiliang Li , Qing He
Published: February 2004

The yearly and monthly mean aerosol optical depth (AOD) at 0.75 μm were retrieved using a new method improved from Qiu's algorithm from the data of daily direct solar radiation, sunshine duration, surface pressure, and vapor pressure at 46 A class solar radiation stations over China from 1961 to 1990, as well as the Total Ozone Mapping Spectrometer (TOMS) derived ozone data from 1979 to 1990. Then the analysis on the distribution of yearly mean AOD and its variation over China in the last 30 years were made from the derived AOD data. It was found that the yearly mean AOD has pattern related to the geographical features with the maximums over basins. One of the maximum centers at Sichuan Basin, southwest of China, and the other is in the south Xinjiang Basin, northwest of China. In most areas of China the maximum of AOD occurs in spring, but the season of reaching the minimum varies with regions. The monthly mean AOD distributions are similar to the annual mean pattern, having strong ”basin“ effect, but the month‐to‐month differences are still obvious. In addition, AOD increased dramatically over China mainland from 1961 to 1990, particularly in the middle and lower reaches area of the Yangzi River and the east part of southwest China. In north China, Shandong peninsula, the east part of Qinghai Province, and coastal areas of Guangdong Province, a significant increasing trend of AOD is shown, while in most parts of northwest China and northeast China, the increase trend is less significant. However, in the western part of Xinjiang autonomous region and part of Yunnan Province, only a decreasing tendency is shown. Of the total 46 stations, the yearly averaged AOD variation curve can be briefly divided into two periods. One period is from 1961 to 1975, when AOD is smaller than the 30 year mean value; the other period is from 1976 to 1990, when AOD is higher than the mean value. Except for the peak in 1982 and 1983, which may be attributed to the eruptions of El Chichon, the curve shows a significant increasing trend from 1961 to 1990. The monthly averaged AODs of the total 46 stations also obviously increased.
Double ITCZs
Authors: Zhang Chidong
Published: February 2004

This study examines where and when double InterTropical Convergence Zones (ITCZs) exist and whether double ITCZs, defined in terms of monthly precipitation distributions, are significant climatological features in the tropics. The most identifiable double ITCZ is found over the eastern Pacific during boreal spring, mainly in March and April. Weak signals of a double ITCZ exist over the Indian Ocean during November, but only infrequently. Over the western and central Pacific, signatures of a double ITCZ can often be found, but mostly during June through September. No double ITCZ is found over the Atlantic Ocean. The boreal‐spring double ITCZ over the eastern Pacific fails to exist only during El Niño‐Southern Oscillation warm phases, when it is replaced by a single ITCZ at the equator as the cold tongue disappears and the maximum sea surface temperature emerges at the equator. It is therefore concluded that double ITCZs are significant features of the tropical climate even though they undergo spatial and temporal variations. Simple composites of double ITCZs and associated surface conditions indicate that double ITCZs, at least over the Pacific Ocean, exist when there are local minima in surface humidity and temperature along the equator. On the basis of the limited observations, it is proposed that double ITCZs in the Pacific are more causally related to surface thermal conditions than atmospheric internal dynamics alone. During boreal spring a special distribution in sea surface temperature with its local minimum at the equator (i.e., the cold tongue) and two maxima at each side is necessary for the double ITCZ over the eastern Pacific. The westward advection of cold and dry surface air by the easterlies from the cold‐tongue region is instrumental in the double ITCZ over the central and western Pacific.
Seasonal variation of water vapor in the lower stratosphere observed in Halogen Occultation Experiment data
Authors: Randel William J. , Wu Fei , Gettelman Andrew , Russell J. M. , Zawodny Joseph M. , Oltmans Samuel J.
Published: February 2004

The seasonal cycle of water vapor in the lower stratosphere is studied based on Halogen Occultation Experiment (HALOE) satellite observations spanning 1991–2000. The seasonal cycle highlights fast, quasi‐horizontal transport between tropics and midlatitudes in the lowermost stratosphere (near isentropic levels ∼380–420 K), in addition to vertical propagation above the equator (the tropical “tape recorder”). The rapid isentropic transport out of the tropics produces a layer of relatively dry air over most of the globe throughout the year, and the seasonal cycle in midlatitudes of both hemispheres (and over the Arctic pole) follows that in the tropics. Additionally, the Northern Hemisphere summer monsoon has a dominant influence on hemispheric‐scale constituent transport. Longitudinal structures in tropical water vapor and ozone identify regions of strong coupling to the troposphere; an intriguing result is that the solstice minima in water vapor and ozone are spatial separated from maximum convection and coldest tropical temperatures. Detailed comparisons with tropical aircraft measurements and the long record of balloon data from Boulder, Colorado, demonstrate the overall high quality of HALOE water vapor data.
Theory of charge and mass transfer in ice‐ice collisions
Authors: Dash J. G. , Mason B. L. , Wettlaufer J. S.
Published: February 2004

A new model describes charge and mass transfer in ice‐ice collisions in terms of fundamental molecular physics. Drawing on clues from results of recent and earlier experiments, the theory treats the collisions as interlinked events acting in three stages: before collision, during contact, and withdrawal. The theory provides quantitative descriptions of charge and mass transfer and their dependence on growth rate, temperature, and impact energy. Application of the theory to experimental simulations of thunderstorm charging explains general trends in terms of basic microscopic processes.
Accumulation over the Greenland ice sheet from historical and recent records
Authors: Bales Roger C. , McConnell Joseph R. , Mosley‐Thompson Ellen , Csatho Beata
Published: February 2004

Water accumulation, defined as precipitation minus evaporation, was estimated over all of Greenland as part of a program to understand changes in ice sheet mass and elevation. Over 360 historical and recent point accumulation estimates on the Greenland ice sheet were evaluated, and 276 estimates that were judged to be high quality were used to develop the accumulation map. The data set includes 99 points developed as part of four investigations of the past 5–15 years; these are judged to have the greatest accuracy. Using kriging, the average accumulation over Greenland is estimated to be ∼30 g cm−2 yr−1. For the interior part of the ice sheet above 1800 m elevation, where most of the data were acquired, the average accumulation is also estimated to be ∼30 g cm−2 yr−1. There are still many areas on the ice sheet, including northwest, southeast, and southern Greenland, where accumulation is highly uncertain, exceeding the mean ice sheet uncertainty at a point of ∼20–25%. In these regions, further sampling will be required to reduce uncertainty in both regional and ice‐sheet‐wide accumulation.
Modeling modern methane emissions from natural wetlands: 2. Interannual variations 1982–1993
Authors: Walter Bernadette P. , Heimann Martin , Matthews Elaine
Published: February 2004

A global run of a process‐based methane model [Walter et al., this issue] is performed using high‐frequency atmospheric forcing fields from the European Centre for Medium‐Range Weather Forecasts (ECMWF) reanalyses of the period from 1982 to 1993. Modeled methane emissions show high regional, seasonal, and interannual variability. Seasonal cycles of methane emissions are dominated by temperature in high‐latitude wetlands, and by changes in the water table in tropical wetlands. Sensitivity tests show that globally, ±1°C changes in temperature lead to ±20% changes in methane emissions from wetlands. Uniform changes of ±20% in precipitation alter methane emissions by about ±8%. Limitations in the model are analyzed and the effects of sub‐grid‐scale variations in model parameters and errors in the input data are examined. Simulated interannual variations in methane emissions from wetlands are compared to observed atmospheric growth rate anomalies. Our model simulation results suggest that contributions from sources other than wetlands and/or the sinks are more important in the tropics than north of 30°N. In high northern latitudes it seems that a large part of the observed interannual variations can be explained by variations in wetland emissions. Our results also suggest that reduced wetland emissions played an important role in the observed negative methane growth rate anomaly in 1992.
A sensitivity study of the discrete Kalman filter (DKF) to initial condition discrepancies
Authors: Gilliland Alice , Abbitt Pamela J.
Published: February 2004

In several previous studies the discrete Kalman filter (DKF) has been used in an adaptive‐iterative mode to deduce time‐varying air quality emissions. While it is not expressly stated in previous literature on this method, the DKF assumes that the initial modeled and observed concentrations are equal. Careful consideration of this assumption is critical for urban or regional scale air quality models because agreement of initial concentrations with observations is not always a requirement or priority when using these models. The purpose of this paper is to clarify the initial condition assumption in the DKF and to investigate potential implications when the assumption is violated. We focus on the adaptive‐iterative implementation of the DKF since we are specifically interested in deducing time‐varying air quality emissions. A complete description of the adaptive‐iterative DKF as implemented by other authors is provided. A case study in the form of a pseudodata test or identical twin experiment is presented to show that if the initial condition assumption is violated, the adaptive‐iterative DKF can produce biased emissions to compensate for the initial modeled and observed concentration differences. The magnitude and longevity of the resulting compensating error depends on the influence of the initial concentrations, as the error is removed more quickly for highly reactive species than for less reactive species (e.g., isoprene versus CO).
Coherent radar ice thickness measurements over the Greenland ice sheet
Authors: Gogineni S. , Tammana D. , Braaten D. , Leuschen C. , Akins T. , Legarsky J. , Kanagaratnam P. , Stiles J. , Allen C. , Jezek K.
Published: February 2004

We developed two 150‐MHz coherent radar depth sounders for ice thickness measurements over the Greenland ice sheet. We developed one of these using connectorized components and the other using radio frequency integrated circuits (RFICs). Both systems are designed to use pulse compression techniques and coherent integration to obtain the high sensitivity required to measure the thickness of more than 4 km of cold ice. We used these systems to collect radar data over the interior and margins of the ice sheet and several outlet glaciers. We operated both radar systems on the NASA P‐3B aircraft equipped with GPS receivers. Radar data are tagged with GPS‐derived location information and are collected in conjunction with laser altimeter measurements. We have reduced all data collected since 1993 and derived ice thickness along all flight lines flown in support of Program for Regional Climate Assessment (PARCA) investigations and the North Greenland Ice Core Project. Radar echograms and derived ice thickness data are placed on a server at the University of Kansas (http://tornado.rsl.ukans.edu/Greenlanddata.htm) for easy access by the scientific community. We obtained good ice thickness information with an accuracy of ±10 m over 90% of the flight lines flown as a part of the PARCA initiative. In this paper we provide a brief description of the system along with samples of data over the interior, along the 2000‐m contour line in the south and from a few selected outlet glaciers.
Application of an optimal estimation inverse method to GPS/MET bending angle observations
Authors: Palmer Paul I. , Barnett John J.
Published: February 2004

Palmer et al. [2000] describes an optimal estimation inverse method for radio occultation (RO) bending angle measurements to retrieve simultaneously temperature, humidity, and surface pressure; outlines quality control procedures for retrieved profiles; and investigates the results from numerical simulations. Here we present retrievals that use bending angle observations from the Global Positioning System Meteorology (GPS/MET) satellite instrument and a priori information from the European Centre for Medium‐Range Weather Forecasts analyses. Retrieved profiles are compared with correlative radiosondes, United Kingdom Meterological Office (UKMO) model analyses, and retrievals from the conventional inverse method. Retrieved temperature profiles are generally colder than analyses but agree with the conventional inverse method to within 1 K. Water vapor retrievals are generally drier than the UKMO analyses and wetter than the radiosonde profiles. Quality of retrieved surface pressure values are related to the extent to which RO observations reach into the troposphere. Low‐latitude retrievals make large adjustments to surface pressure and tropospheric temperatures, which are directly linked to the lack of water vapor above 300 hPa in the inverse model, consistent with previous studies. A study of individual occultations at low and high latitude shows that the optimal retrievals are able to resolve small‐scale atmospheric structure exhibited by the conventional inverse method and collocated radiosondes, not shown by analyses.
Observations and trends of clouds based on GOES sounder data
Authors: Schreiner Anthony J. , Schmit Timothy J. , Menzel W. Paul
Published: February 2004

A 26 month (November 1997 through December 1999) data set of Geostationary Operational Environmental Satellite (GOES) sounder‐derived cloud parameters has been analyzed to discern annual and monthly trends. An important outcome of this study is the identification of diurnal trends made possible by the geostationary satellite frequent observations over specific locations. The area of coverage is 20°N to 50°N and 60°W to 160°W, which corresponds to the continental United States and the surrounding waters. The satellite cloud observations were compared to manually observed Pilot Reports (PIREPs) and were found to be, on average, 35 hPa lower. Comparing the frequency of GOES sounder observations of high cloudiness with observations from the National Oceanic and Atmospheric Administration (NOAA) series of polar orbiting weather satellites reveals a correlation coefficient of 0.79 and a bias of 3.4% for the frequency of occurrence (GOES with a mean higher height). The frequency of occurrence and distribution of clouds, cloud top pressure (CTOP), and effective cloud amount are based on a spatial resolution of ∼40 km (3×3 field of view box) and are shown for eight regions. High clouds (CTOP ≤300 hPa) are found to be more prevalent during the Northern Hemisphere summer than winter for all regions. High clouds for 1998 comprise 8.5% of all observations. Also, in 1998 clear conditions are observed ∼34% of the time. Focusing on the strength of the hourly GOES sounder data, it is found that thin high clouds are most prevalent during the summer and fall seasons, occurring most frequently in the late morning and early afternoon.
Seasonal variations of PAN, PPN, and O3 at the upper Midwest PROPHET site
Authors: Pippin Margaret , Bertman Steve , Thornberry Troy , Town Michael , Carroll Mary Anne , Sillman Sanford
Published: February 2004

Continuous measurements of peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), and ozone (O3) were made from June 1997 through August 1999 at a ground site in the upper Midwest as part of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET). Relatively clean air originating in Canada is transported to the site from the northwest, while more polluted air originating in the metropolitan regions of the Midwest is transported mainly from the southwest and the southeast. Monthly averages of PAN are a minimum in summer /early winter (July‐January) with mixing ratios ranging from 125 to 259 parts per trillion by volume (pptv), while maximum monthly average PAN levels are observed in February through June with mixing ratios of 325–390 pptv. Monthly average ozone mixing ratios ranged from 42 to 46 ppbv in the spring/summer months and 23–32 ppbv in the autumn/early winter months. Correlation among species were examined on a monthly basis. There is a dramatic variation in the PPN/PAN slope from summer to winter with the general trend a maximum slope in the winter ranging from 0.20 to 0.23 and a minimum slope during the summer months ranging from 0.09 to 0.13. The degree of association, r2, is strong in all months, ranging from 0.76 to 0.96. A photochemical box model was used to determine if the seasonal variation could be attributed solely to the summertime production of PAN from isoprene. Box model results indicate that the seasonal variation in the PPN/PAN slope when produced from anthropogenic precursors can be explained by seasonal changes in temperature and photolysis rates, and the production of PAN from isoprene in the summer only serves to increase the seasonal difference in slope.
Neogene to Quaternary sedimentary basins in the south Adriatic (Central Mediterranean): Foredeeps and lithospheric buckling
Authors: Bertotti Giovanni , Picotti Vincenzo , Chilovi Cristina , Fantoni Roberto , Merlini Saverio , Mosconi Alessandro
Published: February 2004

Up to several kilometers deep sedimentary basins of Neogene to Quaternary age are found in the south Adriatic between the Apennines and the Dinarides/Albanides. They are the Apennines foredeep, the Central Adriatic Basin, and the South Adriatic Basin. Two regional seismic lines, 260 and 170 km long, across the entire system provide hitherto unavailable constraints on the kinematics and dynamics of basin development. The Apennine foredeep imaged along the lines, formed in middle to late Pliocene times through a rapid westward tilting of the basin floor. A paleobathymetry of few kilometers was created in which allochthonous bodies were emplaced and sediments deposited unaffected by deformation and farther rotations. The Central and South Adriatic Basins formed in Neogene to Quaternary times and are both characterized by strong subsidence in their central parts, gradually diminishing toward the edges in the SW and NE. Depocenters did not shift laterally through time. Subsidence rates increase through time, and subsidence continued also following the end of main shortening episodes in the Dinarides/Albanides. The Central and South Adriatic Basins form two crustal‐scale synclines with subsidence concentrated in their central parts. Basins' geometries and subsidence patterns indicate that the Adriatic crust has undergone (episodes of) buckling since Miocene times. Wavelengths and amplitudes of such folds change along strike corresponding to mechanical changes of the folded medium.
On the relative role of hydrodynamic dispersion for river water quality
Authors: Gandolfi C. , Facchi A. , Whelan M. J.
Published: February 2004

Neglecting hydrodynamic dispersion in models of river water quality has important implications in terms of simplifying the equations which describe the system and for model calibration. In this paper we analyze the behavior of a river system subjected to a time‐variable point source input of a degradable solute using frequency response techniques applied to one‐dimensional solute transport models, considering the combined effect of amplitude attenuation and phase shift due to hydrodynamic dispersion. We derive exact and simplified expressions that can be used for establishing whether dispersion is negligible at a desired level of accuracy. Finally, we present an application of the analysis to the river Lambro in northern Italy which receives diurnally varying solute loads from an undersized sewage treatment plant. The results obtained show the following: (1) In the case of a time‐constant solute input, exact analytical expressions of the error incurred by neglecting dispersion can be derived which show that dispersive transport is negligible in most quasi steady state cases. (2) When solute input varies sinusoidally with time, the error due to neglecting dispersion is strongly dependent on the input frequency and may be significant if the input frequency is high. The error is practically independent of the decay rate coefficient, k, except when k is significantly greater than the input frequency. (3) Ignoring solute transport upstream from the outfall, due to dispersion, in the solution to the advection dispersion equation (ADE) can result in significant errors if the input frequency is sufficiently high. In some cases the choice of the ADE solution employed may have a larger impact than neglecting dispersion altogether.
Hydrogeological characterization of the south oyster bacterial transport site using geophysical data
Authors: Hubbard Susan S. , Chen Jinsong , Peterson John , Majer Ernest L. , Williams Kenneth H. , Swift Donald J. , Mailloux Brian , Rubin Yoram
Published: February 2004

A multidisciplinary research team has conducted a field‐scale bacterial transport study within an uncontaminated sandy Pleistocene aquifer near Oyster, Virginia. The overall goal of the project was to evaluate the importance of heterogeneities in controlling the field‐scale transport of bacteria that are injected into the ground for remediation purposes. Geochemical, hydrological, geological, and geophysical data were collected to characterize the site prior to conducting chemical and bacterial injection experiments. In this paper we focus on results of a hydrogeological characterization effort using geophysical data collected across a range of spatial scales. The geophysical data employed include surface ground‐penetrating radar, radar cross‐hole tomography, seismic cross‐hole tomography, cone penetrometer, and borehole electromagnetic flowmeter. These data were used to interpret the subregional and local stratigraphy, to provide high‐resolution hydraulic conductivity estimates, and to provide information about the log conductivity spatial correlation function. The information from geophysical data was used to guide and assist the field operations and to constrain the numerical bacterial transport model. Although more field work of this nature is necessary to validate the usefulness and cost‐effectiveness of including geophysical data in the characterization effort, qualitative and quantitative comparisons between tomographically obtained flow and transport parameter estimates with hydraulic well bore and bromide breakthrough measurements suggest that geophysical data can provide valuable, high‐resolution information. This information, traditionally only partially obtainable by performing extensive and intrusive well bore sampling, may help to reduce the ambiguity associated with hydrogeological heterogeneity that is often encountered when interpreting field‐scale bacterial transport data.
Dual‐mode modeling of competitive and concentration‐dependent sorption and desorption kinetics of polycyclic aromatic hydrocarbons in soils
Authors: Zhao Dongye , Pignatello Joseph J. , White Jason C. , Braida Washington , Ferrandino Francis
Published: February 2004

A radial dual‐mode diffusion model is proposed for mass transfer of hydrophobic compounds in soil organic matter (SOM) that is able to predict competitive and concentration effects on sorption and desorption rates. On the basis of dual‐mode sorption theory for glassy polymers the model assumes a population of specific adsorption sites (“holes”) interspersed uniformly in the dissolution (partition) domain of SOM. It further assumes Fickian diffusion in the dissolution domain and immobilization in the holes, with microscopic local equilibrium between the two domains. The model is solved numerically (Crank‐Nicolson implicit method). Using parameters from single‐solute equilibrium and kinetic experiments, the model adequately predicts batch transient sorption and desorption of phenanthrene (primary solute) as a function of pyrene (cosolute) concentration, and batch transient sorption of phenanthrene as a function of its own concentration, in two soils. The model shows that phenanthrene sorption approaches equilibrium faster with increasing cosolute or self‐concentration owing to the concentration dependence of the apparent diffusivity, as predicted by a simple hole‐plugging mechanism (i.e., fewer and fewer holes are available). Simulations show the effect to be greatest under infinite bath uptake conditions. Under finite bath conditions this positive effect on rate may be opposed by a batch process temporal bias present when the water:soil ratio is kept constant in a series of experiments. The bias is due to gradient driving force effects that slow the rate as a result of the decrease in percent of solute finally taken up by the solid as cosolute or concentration increases.
Evaporation From rain‐wetted forest in relation to canopy wetness, canopy cover, and net radiation
Authors: Klaassen Wim
Published: February 2004

Evaporation from wet canopies is commonly calculated using EPM, the Penman‐Monteith equation with zero surface resistance. However, several observations show a lower evaporation from rain‐wetted forest. Possible causes for the difference between EPM and experiments are evaluated to provide rules for the simulation of rainfall interception by forest canopies. The evaluation is executed using a micrometeorological model with a detailed representation of the forest canopy. Simulated results are compared with experimental results. In spite of theoretical reservations the evaporation of completely wet forest appears to agree with EPM. Evaporation from wet forest appears mainly dependent on net radiation. Rainfall interception is related to evaporation from the canopy. Evaporation from the canopy appears proportional with the square root of canopy cover and sensitive to canopy wetness. An accurate estimate of canopy wetness is needed to use EPM for the calculation of evaporation from rain‐wetted forest.
The Nerrigundah Data Set: Soil moisture patterns, soil characteristics, and hydrological flux measurements
Authors: Walker Jeffrey P. , Willgoose Garry R. , Kalma Jetse D.
Published: February 2004

This paper presents a data set that describes the spatial and temporal variability of soil moisture within the 6 ha Nerrigundah catchment, located in a temperate region of eastern Australia. The data set includes high‐resolution elevation data; high‐ resolution (20 m) near‐surface soil moisture maps; soil moisture profile measurements at 13 locations, with one being applicable for one‐dimensional modeling; soil moisture measurements from four different measurement devices at a single location; soil temperature profile measurements; soil heat flux and supporting meteorological measurements, including data obtained with two pluviometers and four collecting rain gauges; surface roughness measurements; soil information for 19 locations, including field measurements of saturated hydraulic conductivity; and catchment runoff measurements. These data are available on the World Wide Web at http://www.civag.unimelb.edu.au/∼jwalker/data/nerrigundah.