bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors affecting the measurement of mercury emissions from soils with flux chambers
Authors: Wallschläger Dirk , Turner Ralph R. , London Jacqueline , Ebinghaus Ralf , Kock Hans H. , Sommar Jonas , Xiao Zifan
Published: December 2003

Air‐surface exchange of mercury (Hg) above an arid geothermal area was measured with three parallel flux chamber experiments. The different experimental designs were intercompared with each other, with regard to the magnitude of the measured Hg fluxes and their response to environmental changes. Qualitatively, the measured Hg fluxes agreed well throughout the diurnal cycle, and in their response to environmental events and experimental manipulations, but quantitatively, there were significant discrepancies between the individual flux results. On average, the three designs yielded Hg fluxes agreeing within a factor of 2, but even more pronounced differences were observed during midday high emission periods and during apparent nighttime deposition events. The chamber flushing rate appears to have a very significant impact on the measured fluxes and on the response behavior to environmental change. This study demonstrates that both experimental differences and small‐scale regional variability introduce large uncertainty in the estimation of natural Hg air‐surface exchange by different flux chamber techniques. Also, the impact of environmental parameters on Hg air‐surface exchange was studied. Rain events led to a strong increase in the Hg emissions, even when the covered soil remained dry, suggesting that the apparent chamber footprint is larger than the actually covered area. Exclusion of sunlight led to decreases in Hg emissions. Statistical analysis revealed the strongest correlations between the measured Hg fluxes and radiation and wind speed. Weaker correlations were observed with air and soil temperature and wind direction (probably due to local Hg sources). Fluxes were also inversely correlated with relative humidity.
Biases of the observed atmospheric water budgets over the central United States
Authors: Yarosh Evgeney S. , Ropelewski Chester F. , Berbery Ernesto H.
Published: December 2003

Analysis of the mean annual cycle of the observed water budget based on radiosonde data for the 20 year period 1973–1992 reveals a negative bias in the atmospheric estimate of mean moisture flux convergence over the central United States when compared to mean river discharge for the same period. Several possible sources of this bias are examined through the analysis of radiosonde, wind profiler, and river discharge data as well as water budget estimates from NCEP's mesoscale Eta Model. The analysis suggests that 20 years of radiosonde observations are sufficient to get stable mean water vapor flux convergence estimates. The analysis also shows that the bias between averaged vapor flux convergence and river discharge likely does not depend on changes in the locations of upper‐air observations or on changes in the radiosondes observational technique. Components of the atmospheric water budget diurnal cycle are estimated from hourly wind profiler data and from 3‐hourly Eta Model output. The analyses show that monthly mean atmospheric water budget quantities calculated from twice a day sampling, on average, significantly underestimate magnitudes of these quantities compared to estimates based on hourly or 3‐hourly analyses. The magnitude of the underestimation is more than 60% of the difference between mean observed terrestrial and atmospheric components of the hydrological cycle over the central United States, in agreement with earlier studies suggesting that temporal sampling may account for part of this bias. The effect of spatial sampling was evaluated using differences between atmospheric water budget terms from the Eta Model at its full 48 km resolution compared to Eta Model water budget estimates sampled at the radiosonde spatial resolution. These analyses show that the magnitude of the effect of spatial resolution is about 40% of the magnitude of the mean bias between the average moisture flux convergence and river discharge. The combined effect of temporal and spatial undersampling by radiosondes over the central United States is estimated to be 0.44 mm d−1. This value is within 8% of the estimated mean difference between river discharge and moisture flux convergence for the central United States.
A space‐time downscaling model for rainfall
Authors: Venugopal V. , Foufoula‐Georgiou Efi , Sapozhnikov Victor
Published: December 2003

Interpretation of the impact of climate change or climate variability on water resources management requires information at scales much smaller than the current resolution of regional climate models. Subgrid‐scale variability of precipitation is typically resolved by running nested or variable resolution models or by statistical downscaling, the latter being especially attractive in ensemble predictions due to its computational efficiency. Most existing precipitation downscaling schemes are based on spatial disaggregation of rainfall patterns, independently at different times, and do not properly account for the temporal persistence of rainfall at the subgrid spatial scales. Such a temporal persistence in rainfall directly relates to the spatial variability of accumulated local soil moisture and might be important if the downscaled values were to be used in a coupled atmospheric‐hydrologic model. In this paper we propose a rainfall downscaling model which utilizes the presence of dynamic scaling in rainfall [Venugopal et al., 1999] and which in conjunction with a spatial disaggregation scheme preserves both the temporal and spatial correlation structure of rainfall at the subgrid scales.
River basin hydrology in a global off‐line land‐surface model
Authors: Bosilovich Michael G. , Yang Runhua , Houser Paul R.
Published: December 2003

Land‐surface hydrology has been examined for the Off‐line Land‐surface GEOS Assimilation (OLGA) system and Goddard Earth Observing System (GEOS‐1) data assimilation system using a river routing model. The GEOS‐1 land‐surface parameterization is very simple, using an energy balance prediction of surface temperature and prescribed soil water. OLGA uses atmospheric data from GEOS‐1 to drive a more comprehensive parameterization of the land‐surface processes. Using a global river routing model, OLGA's hydrology is evaluated against GEOS‐1 (which serves as a control case) and observations. The river routing model moves monthly mean climatologic source runoff through river networks to simulate the river discharge from many river basins around the world, which can be compared to observed climatologic river discharge. Because of the soil hydrology, the OLGA system shows a general improvement in the simulation of river discharge, compared to the GEOS‐1, by slowing the discharge of water. Snowmelt processes included in OLGA also have a positive effect on the annual cycle of river discharge and source runoff. The timing of the snowmelt in river discharge, however, still needs improvement in the annual cycle. Preliminary tests of a coupled land‐atmosphere model indicate improvements to the hydrologic cycle compared to the uncoupled system. The river routing model has provided a useful tool in the evaluation of the GCM hydrologic cycle and has helped quantify the influence of the more advanced land‐surface model.
Spectral parameters for the ν6 region of HCOOH and its measurement in the infrared tropospheric spectrum
Authors: Perrin A. , Rinsland C. P. , Goldman A.
Published: December 2003

New spectral parameters (line positions and intensities) have been generated for the ν6 band of HCOOH, which agree well with 0.002 cm−1 resolution infrared laboratory spectra. The line positions were derived from previously published spectroscopic constants [Bumgarner et al., 1988]. New relative intensities were derived from the analysis of A type and B type transitions. The new line parameters allow improved quantitative analysis of atmospheric spectra from the 1105 cm−1 Q branch, provided that the previously neglected HDO strong tropospheric absorption in this region is taken into account.
Future atmospheric methane concentrations in the context of the stabilization of greenhouse gas concentrations
Authors: Kheshgi Haroon S. , Jain Atul K. , Kotamarthi V. R. , Wuebbles Donald J.
Published: December 2003

Tropospheric CH4 concentration depends, according to modeled tropospheric processes, on many factors, including emissions of CH4 as well as NOx and CO. Illustrative analyses of the relation between emissions and CH4 concentration give some guidance on the role of CH4 in the stabilization of greenhouse gas concentrations. The contribution of CH4 to radiative forcing at the time of stabilization is expected to be modest, provided CH4 and CO emissions do not go far beyond current rates. However, in cases leading to stabilization the potential mitigation of increases in radiative forcing by methane control could be comparable to that of CO2 control over the next century. Whether or not this potential is realized will depend partially on the cost of deep reductions of CH4, NOx, CO, or CO2 emissions over the next century, which is not known.
A climate database for Mars
Authors: Lewis Stephen R. , Collins Matthew , Read Peter L. , Forget François , Hourdin Frédéric , Fournier Richard , Hourdin Christophe , Talagrand Olivier , Huot Jean‐Paul
Published: December 2003

A database of statistics which describe the climate and surface environment of Mars has been constructed directly on the basis of output from multiannual integrations of two general circulation models developed jointly at Laboratoire de Météorologie Dynamique du Centre National de la Recherche Scientifique, France, and the University of Oxford, United Kingdom, with support from the European Space Agency. The models have been developed and validated to reproduce the main features of the meteorology of Mars, as observed by past spacecraft missions. As well as the more standard statistical measures for mission design studies, the Mars Climate Database includes a novel representation of large‐scale variability, using empirical eigenfunctions derived from an analysis of the full simulations, and small‐scale variability using parameterizations of processes such as gravity wave propagation. The database may be used as a tool for mission planning and also provides a valuable resource for scientific studies of the Martian atmosphere. The database is described and critically compared with a representative range of currently available observations.
Topography, roughness, layering, and slope properties of the Medusae Fossae Formation from Mars Orbiter Laser Altimeter (MOLA) and Mars Orbiter Camera (MOC) data
Authors: Sakimoto Susan E. H. , Frey Herbert V. , Garvin James B. , Roark James H.
Published: December 2003

The enigmatic Medusae Fossae Formation (MFF) is one of the youngest surficial deposits on Mars. Previously proposed modes of origin include pyroclastic volcanism, eolian mantling, polar sedimentation, carbonate platform, and paleoshorelines. In order to assess mapped member boundaries and constrain likely origin processes we analyze five topographic transects from the Mars Orbiter Laser Altimeter (MOLA) collected during the aerobraking hiatus orbit period of the Mars Global Surveyor (MGS) mission together with several simultaneously acquired Mars Orbiter Camera (MOC) images to examine the regional and local variations in the relief, slopes, vertical roughness, and relative elevations of mapped MFF members. We find that the members are not particularly flat or level but have average thicknesses of many hundreds of meters and substantially more internal relief than previously thought. Locally, the MFF members are sometimes distinguishable by slope, elevation, and surface roughness characteristics, but no unique formation‐wide characteristics are apparent in this analysis of the limited initial data. The relative elevations of the mapped members are not consistent with undeformed planar horizontal layers but may be consistent with layers draped over preexisting topography with subsequent partial removal. Analysis of the initial coincident MOC and MOLA hiatus data suggests the possible presence of local layers, as well as the mislocation of at least a few MFF member and formation boundaries. We conclude that carbonate and shoreline deposit origins are not as well supported in the initial MGS data as they were in the Viking data and that the MFF formation and member boundaries should be reexamined in conjunction with the incoming new MGS data.
Actinic fluxes in Titan's atmosphere, from one to three dimensions: Application to high‐latitude composition
Authors: Lebonnois Sébastien , Toublanc Dominique
Published: December 2003

We present a study on diurnally and annually averaged values of the actinic fluxes used in one‐dimensional (1‐D) photochemical models, as well as a 3‐D radiative transfer model, based on Monte Carlo calculations with application to the atmosphere of Titan. This study shows that the commonly used value <θ> = 30° for the mean incident angle at the equator in photochemical models of Titan is not the best choice, though changing the value has no dramatic effects on photochemistry. The results of the 3‐D code give direct access to the photolysis rates at any point in the atmosphere. The necessity of 3‐D values in a deep atmosphere such as Titan's is demonstrated particularly for high‐latitude winter conditions. These 3‐D photolysis rates are used to model the latitudinal variations of the chemical composition of Titan's atmosphere in a 1‐D photochemical model adapted to different latitudes. This study shows that these kinds of simple photochemical models cannot reproduce the observed latitudinal behavior and that we need to develop real 2‐D photochemical models of Titan's atmosphere.
The high‐resolution gravity anomaly of the lunar topography
Authors: Arkani‐Hamed Jafar
Published: December 2003

By lowering the altitude of Lunar Prospector to about 10–20 km the spacecraft will provide measures of the Moon's gravity field at very high resolution, enabling us to derive a spherical harmonic representation that includes harmonics of degree 360 and demanding precise calculation of the gravity field of the topography at such low altitudes. We present a method to determine the gravity field of the topography at low altitudes, which is very efficient even for higher degree harmonics and is also applicable for topography with laterally and radially varying density. The method is applied to three simple models; namely, an unfilled basin, a basin with mare filling, and a topography specified by a tesseral harmonic of degree 60 and order 30, before applying it to the actual topography of the Moon. It is shown that the gravity of the topography calculated by the surface‐mass density approximation (a conventional method) is sufficient for harmonics of degree up to about 100 but becomes increasingly inadequate as the degree of the harmonics increases. The method is also applied to internal density interfaces, such as a possible Moho undulation, and it is concluded that the surface‐mass density approximation becomes less appropriate once the degree of the harmonics exceeds about 20. We also calculate the free air gravity anomaly of the lunar topography at 10 km altitude using this method and the available 90 degree spherical harmonic model of the topography. Although the surface topography of Venus has been expanded in terms of the spherical harmonics of degree up to 360 [Rappaport and Plaut, 1994], its gravity field is measured at altitudes greater than 150 km [Sjogren et al., 1997], which is much larger than the surface topography or possible undulation of the crust‐mantle boundary. The results of our method and the conventional method may not differ significantly for Venus.
Circular‐polarization radar properties of high‐altitude ice: Western Kunlun Shan and central Andes
Authors: Haldemann Albert F. C. , Muhleman Duane O.
Published: December 2003

Full polarization synthetic aperture radar images of high‐altitude glaciers and ice fields in the Western Kunlun Shan of Tibet and the central Andes near Santiago, Chile, made with the shuttle imaging radar, display regions with circular‐polarization ratios, μc, in excess of unity. The mountainous topography at both locales allows reconstruction of the angular scattering behavior. The behavior is very similar to that displayed by Greenland's percolation zone. Glaciologic evidence from the Tibetan site confirms ice pipes and lenses embedded in the firn, which have been identified as the scatterers producing μc>1 in Greenland. This demonstrates that the cold snow percolation facies radar signature exists outside of Greenland. The Greenland radar behavior had been suggested as an analogue for that of the icy Galilean satellites. We, like previous workers, find that the near‐nadir backscatter is too specular to be considered analogous to that of the Jovian moons. We also present a crevasse region in Tibet that exhibits μc>1 and a possible detection of the ice substrate of a rock‐covered glacier in the Andes.
Combined coccolith, foraminiferal, and biomarker reconstruction of paleoceanographic conditions over the past 120 kyr in the northern North Atlantic (59°N, 23°W)
Authors: Weaver P. P. E. , Chapman M. R. , Eglinton G. , Zhao M. , Rutledge D. , Read G.
Published: December 2003

We present data for North Atlantic core Biogeochemical Ocean Flux Study (BOFS) 16K (59°N, 23°W, water depth 2370 m) including coccolith flora, ∂18O, planktonic foraminiferal sea surface temperatures (SSTs) by FA20 and SIMMAX methods, and alkenone‐based U37K and U37K′ SSTs. A good correlation exists between the abundances of cold water coccolith species and foraminifera, and a broad correlation exists between coccolith and alkenone abundances except in the Holocene. Reworked Cretaceous coccoliths at the Last Glacial Maximum are coincident with warm deviations of the U37K′ signal. Assessment of various calibrations of U37K and U37K′ with paleotemperature shows the inappropriateness of a global correlation. We have produced a North Atlantic U37K′ calibration on the basis of North Atlantic data alone (U37K′=0.026T+0.186), which produces SST data for summer season at 0 m water depth, comparable to the warm season foraminiferal SSTs, except during the intervals 26–36, 58–65, and 100–120 ka when the alkenones indicate somewhat cooler surface waters.
Response of the tropical Atlantic thermocline to Late Quaternary Trade Wind changes
Authors: Wolff Tobias , Mulitza Stefan , Rühlemann Carsten , Wefer Gerold
Published: December 2003

We applied the modern analog technique to foraminiferal counts from three equatorial Atlantic gravity cores to estimate paleothermocline depths in the eastern and western tropical Atlantic during the past 250 kyr. The eastern equatorial core GeoB 1105‐4 is characterized by variations in the 23‐kyr cycle, whereas the western sediment cores show a dominant periodicity at the 41‐kyr band. The phase relationships with respect to insolation and ice volume suggest that thermocline fluctuations in the east are primarily driven by the intensity of the monsoon due to variations in low‐latitude insolation. In contrast, changes of the thermocline depth in the western tropical Atlantic, which lead global ice volume at the 41‐kyr band by 3‐4 kyr, seem to depend on the strength of the SE trade winds in response to the meridional temperature gradients in the South Atlantic.
Oceanic primary productivity and dissolved oxygen levels at the Cretaceous/Tertiary Boundary: Their decrease, subsequent warming, and recovery
Authors: Kaiho Kunio , Kajiwara Yoshimichi , Tazaki Kazue , Ueshima Masato , Takeda Nobuyori , Kawahata Hodaka , Arinobu Tetsuya , Ishiwatari Ryoshi , Hirai Akio , Lamolda Marcos A.
Published: December 2003

Thirty‐six different geochemical and foraminiferal analyses were conducted on samples collected at closely spaced intervals across the Cretaceous/Tertiary (K/T) boundary exposed at Caravaca, Spain. A rapid reduction in the gradient between δ13C values in fine fraction carbonate and benthic foraminiferal calcite and a decrease in the abundance of phosphorus (a proxy for organic carbon) and calcium were recorded in sediments 0–0.5 cm above the K/T boundary. These trends imply that an abrupt mass mortality occurred among pelagic organisms, leading to a significant reduction in the flux of organic carbon to the seafloor. In addition, variations in sulfur isotope ratios, the hydrocarbon‐generating potential of kerogen (measured as the hydrogen index), and foraminiferal indices of dissolved oxygen level all imply that a rapid decrease in dissolved oxygen was coincident with the δ13C event. Evidence of the low oxygen event has also been recognized in Japan and New Zealand, suggesting that intermediate water oxygen minima were widely developed during earliest Danian time. A threefold increase in the kaolinite/illite ratio and a 1.2‰ decrease in δ18O (carbonate fine fraction) were recorded in the basal 0.1–2 cm of Danian age sediments. These trends suggest that atmospheric warming and an increase in surface water temperature occurred 0–3 kyr after the δ13C event. Recovery in the difference between δ13C values in the carbonate fine fraction and in benthic foraminiferal calcite as well as increases in phosphorus and calcium contents occur at the base of planktonic foraminiferal Zone Pla, implying that an increase in primary productivity commenced some 13 kyr after the K/T boundary.

Tables A1‐A3 are available on diskette or via Anonymous FTP from kosmos.agu.org directory APENO (Username = anonymous, Password = guest). Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009 or by phone at 800‐966‐2481; $15.00. Payment must accompany order.
The surface‐bounded atmospheres of Mercury and the Moon
Authors: Killen Rosemary M. , Ip Wing‐H.
Published: December 2003

Surface‐bounded exospheres have been detected at the Moon, Mercury, and Europa and almost certainly exist about other objects. Historically, the first of these systems to be observed was the lunar exosphere, where He and Ar were detected by the Apollo spacecraft. The Hermean exosphere is archetypical of these systems in that it is part of a coupled system including the surface and magnetosphere interacting dynamically with the solar wind and fields. Studies of the Hermean exosphere heretofore have neglected or only superficially considered these interactions. We will review the current state of knowledge of the exospheres of Mercury and the Moon and discuss areas in which our knowledge is most incomplete. We will focus on the exosphere as part of a coupled system including the surface at its base and the particle, field, and interplanetary environment as both a source and sink for neutrals. Apollo era instruments made unambiguous detections of 36Ar, 40Ar, and He and placed stringent upper limits on other species [Hodges, 1975; Hodges and Hoffman, 1973]. Post‐Apollo work began with the discovery of Na and K using ground‐based techniques [Potter and Morgan, 1988]. There have also been attempts to use the International Ultraviolet Explorer and the Hubble Space Telescope to detect additional species. The Mariner 10 mission included two encounters with Mercury and one distant flyby in 1974–1975: (1) March 29, 1974 (nightside pass with closest approach at 723‐km altitude), (2) September 21, 1974 (distant dayside pass), and (3) March 16, 1975 (nightside pass with closest approach at 327‐km altitude). Since then there has been no other spacecraft mission to Mercury. In the 2 decades since the Mariner 10 mission, slow but steady progress has been made in understanding the Hermean system, but our knowledge of this innermost terrestrial planet is extremely limited. It is clear that many theories about the origin and evolution of Mercury that were proposed before Mariner 10 are inconsistent with what we now know about the system. Substantial progress will be made only by returning to the planet. This review aims to present a tool for mission planning as well as an introduction and overview of the exosphere.
Stratospheric ozone depletion: A review of concepts and history
Authors: Solomon Susan
Published: December 2003

Stratospheric ozone depletion through catalytic chemistry involving man‐made chlorofluorocarbons is an area of focus in the study of geophysics and one of the global environmental issues of the twentieth century. This review presents a brief history of the science of ozone depletion and describes a conceptual framework to explain the key processes involved, with a focus on chemistry. Observations that may be considered as evidence (fingerprints) of ozone depletion due to chlorofluorocarbons are explored, and the related gas phase and surface chemistry is described. Observations of ozone and of chlorine‐related trace gases near 40 km provide evidence that gas phase chemistry has indeed currently depleted about 10% of the stratospheric ozone there as predicted, and the vertical and horizontal structures of this depletion are fingerprints for that process. More striking changes are observed each austral spring in Antarctica, where about half of the total ozone column is depleted each September, forming the Antarctic ozone hole. Measurements of large amounts of ClO, a key ozone destruction catalyst, are among the fingerprints showing that human releases of chlorofluorocarbons are the primary cause of this change. Enhanced ozone depletion in the Antarctic and Arctic regions is linked to heterogeneous chlorine chemistry that occurs on the surfaces of polar stratospheric clouds at cold temperatures. Observations also show that some of the same heterogeneous chemistry occurs on the surfaces of particles present at midlatitudes as well, and the abundances of these particles are enhanced following explosive volcanic eruptions. The partitioning of chlorine between active forms that destroy ozone and inert reservoirs that sequester it is a central part of the framework for our understanding of the 40‐km ozone decline, the Antarctic ozone hole, the recent Arctic ozone losses in particularly cold years, and the observation of record midlatitude ozone depletion after the major eruption of Mount Pinatubo in the early 1990s. As human use of chlorofluorocarbons continues to decrease, these changes throughout the ozone layer are expected to gradually reverse during the twenty‐first century.
The feasibility of studying the solar wind magnetosphere interaction by active electromagnetic sounding from outside the magnetosphere
Authors: Doudkin F. L. , Gough M. P.
Published: December 2003

A space experiment is proposed to make continuous remote electromagnetic soundings of the solar wind bow shock interaction with the magnetosphere of the Earth. We discuss the feasibility of construction of a system that will allow us to carry out the bow shock sounding and study solar wind local obstacles tens of minutes before their interaction with the bow shock. The sounding system, placed at a distance about 26 RE from the bow shock, with average transmitter active power of 20 W at a maximum antenna length of 3 km and antenna weight of about 100 kg, would provide bow shock‐solar wind monitoring with spatial resolution of 0.25–1 RE in the frequency range 9–225 kHz and a 10% electron density resolution. Such a system, located at the Lagrange point L1, could provide continuous monitoring of the solar wind interaction with the Earth's magnetosphere.
Equatorial ionospheric electron density below the F2 peak
Authors: Radicella S. M. , Adeniyi J. O.
Published: December 2003

True height profile analysis below the F2 peak was employed in this study. Diurnal, seasonal, and solar cycle variations in electron density were examined from 100 km up the F2 peak. Some results obtained for the equatorial region in the Indian and American sectors were confirmed in this study. The departure of the daytime electron density from that of a simple Chapman variation begins from an altitude of about 190 km at low solar activity and from 210 km at high solar activity. The midday minimum is observable from about 100 km below the F2 peak at low solar activity. It is noticeable from about 40 to 90 km below the F2 peak at high solar activity, except in April, when a postnoon peak is not developed. Most of the features observed find their explanation in the vertical E × B plasma drift variation.
Geometry of thin‐skinned tectonic systems in relation to detachment layer thickness in sedimentary basins
Authors: Stewart S. A.
Published: December 2003

Characterizing features of both extensional and compressional thin‐skinned systems may be controlled by the thickness of the underlying mobile material. Within extensional fault arrays, detachment layer thickness, in conjunction with detachment dip, controls variations in fault spacing and polarity because rigid fault blocks are only free to rotate as long as there is enough underlying mobile material to redistribute between the fault block keels. Different styles of extensional fault array range from single polarity arrays with closely spaced faults (thin detachment) to arrays where the fault blocks rotate until the fault blocks separate from one another (thick detachment). Departure from this relationship depends on the amount of internal deformation that can be sustained by the domino fault blocks. Within contractional zones, detachment folds occur where the amount of mobile material can fill the evolving fold core via redistribution; thrusts occur where there is insufficient mobile material to sustain detachment fold growth. The variations in extensional and contractional style that are described here in relation to mobile layer thickness can be combined to give an idealized model of regional variation in structural style in relation to regional variation in stratigraphy. Applying this model to a salt basin, an allochthon in the area of thickest salt may be characterized by updip raft tectonics and downdip detachment fold belts; this style would be laterally transitional toward areas of thinner or lower net salt to updip domino fault arrays and downdip thrust systems.
Extensional deformation across an active margin, relations with subsidence, uplift, and rotations: The Hikurangi subduction, New Zealand
Authors: Chanier Frank , Ferrière Jacky , Angelier Jacques
Published: December 2003

On the basis of field studies in the forearc domain of the Hikurangi subduction margin, in the eastern North Island of New Zealand, we analyze the evolution of the subduction since its onset 25 Myr ago. Analyses of brittle deformation within this forearc domain have revealed evidence of extensional deformation, contemporaneous with the subduction of the Pacific plate beneath the North Island. The type and origin of extensional deformation during the development of the active margin are discussed. The problem is crucial because this forearc domain was previously considered as having undergone almost continuous compression during the late Cenozoic. Two distinct events of late Cenozoic extensional deformation are identified. The youngest one is Quaternary in age; it affects limited areas where important uplift prevails. The orientation of extensional paleostress axes is perpendicular to that of uplift axes, hence consistent with the classical hypothesis of gravitational collapse affecting the upper part of the margin. Of particular interest is the older extensional event, middle‐late Miocene in age. It affected most of the forearc domain during a long time span that was also characterized by widespread margin subsidence. Some structures attributed to this event are syndepositional, including rollover structures, and there are mainly high‐angle normal faults that affect not only the Miocene sediments but also the pre‐Miocene basement. The orientations of paleostress axes obtained by inversion of fault data sets are multiple; after corrections taking into account the rotational history of the margin during the late Cenozoic, they are found to be generally consistent with two major trends. Because these extensional structures developed throughout a long period of the margin subsidence, it is proposed that they reflect the process of tectonic erosion that affected the Hikurangi active margin during the middle and late Miocene, between about 15 and 5 Myr ago.
Transport of nitrogen and phosphorus from rhode river watersheds during storm events
Authors: Correll David L. , Jordan Thomas E. , Weller Donald E.
Published: December 2003

We studied storm discharges of nitrate and dissolved and particulate forms of ammonium, organic N, phosphate, and organic P from four adjacent small watersheds of differing land use on the Atlantic Coastal Plain in Maryland. We used V‐notch weirs and automated storm samplers to measure discharges and collect samples at flow intervals during 76 storms. The watershed aquifers are perched on an impervious clay layer slightly above sea level, so that combined groundwater and surface water discharges were measured at the weirs. The concentrations of particulate forms of organic N (PON), organic P (POP), and inorganic P (PPi) increased up to 3 orders of magnitude during storm events and usually peaked prior to the peak water discharge, while concentrations of dissolved forms of organic N (DON), organic P (DOP), inorganic P (DPi), and nitrate did not change very much. Dissolved and particulate ammonium (DNH4 and PNH4, respectively) concentrations increased up to fivefold in storm events but remained low compared to other N forms. The watershed with the most cropland discharged the highest concentrations of total N, PON, DNH4, nitrate, POP, and PPi. A forested watershed discharged the highest concentrations of DON, PNH4, and DOP. The watershed with the most grazed land discharged the highest concentration of DPi. PON and POP were the dominant forms of N and P in storm discharges from all watersheds. Concentrations of nitrogen were higher in spring and summer storms than in winter storms, but phosphorus concentrations were much higher in the summer storms than in spring or winter. The concentrations of PPi, POP, PON, DNH4, and PNH4 increased significantly with peak water discharge among storms, while concentrations of DPi, DOP, DON, and nitrate were not correlated with peak discharge. The ratios of TN/TP and TIN/TIP declined significantly with peak water discharge among storms.
Sediment transport along lower Fraser River: 1. Measurements and hydraulic computations
Authors: McLean David G. , Church Michael , Tassone Bruno
Published: December 2003

A comprehensive program of sediment transport measurements was conducted along lower Fraser River, British Columbia, between 1966 and 1986. The data yield a detailed sediment budget. Annual total suspended loads at three stations are virtually identical, averaging 17 × 106 tonnes/year (t yr−1). The suspended sand load is about 5.5 × 106 t yr−1, about one third of the total. In the gravel bed reach of the river the sand behaves as wash load. Significant transport of gravel begins at Agassiz at a discharge of about 5000 m3 s−1. The annual gravel transport was estimated to be about 0.23 × 106 t yr−1, only 1% of the total load. All of this material is deposited in the reach upstream of Mission. At Mission, sands finer than 0.177 mm make up more than 50% of the suspended sand load but are virtually absent from the sand bed. Therefore a portion of the sand load at Mission is wash load. The total bed material load here was estimated to be 3.0 × 106 t yr−1, about 18% of the total sediment load. Virtually all of the bed material load was transported in intermittent suspension near the bed, less than 5% occurring as bed load. In the long term the suspended sand load upstream is approximately equal to the total sand load at Mission. However, within individual years some of the sand is stored within the reach temporarily and then reentrained later.
Conditioning a multiple‐patch SVAT Model using uncertain time‐space estimates of latent heat fluxes as inferred from remotely sensed data
Authors: Franks Stewart W. , Beven Keith J.
Published: December 2003

It has been shown that the calibration of soil vegetation‐atmosphere transfer (SVAT) models is inherently uncertain, even when data are available over a relatively limited homogeneous area. The representation of subgrid‐scale variability of fluxes is not easily achieved because of the lack of information available about appropriate parameter distributions and their covariance. However, remote sensing of thermal surface responses offers the possibility of obtaining distributed estimates of surface fluxes. In this paper, multiple Landsat‐Thematic Mapper (TM) images of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) site are used to derive uncertain estimates of the land surface–atmosphere sensible and latent fluxes over a period of time. Employing a framework based on fuzzy set theory, the parameter space representing all feasible parameterizations of a SVAT model are examined with respect to these image estimates. Areal weightings for a number of functional types of flux behavior are then derived through which the temporal evolution of surface fluxes can be estimated.
Theoretical model of a multisection time domain reflectometry measurement system
Authors: Feng W. , Lin C. P. , Deschamps R. J. , Drnevich V. P.
Published: December 2003

A multisection model is presented to simulate electromagnetic wave propagation in an unmatched time domain reflectometry (TDR) probe and layered soil system. The model uses a linear‐time‐invariant feedback system to model each section and links each section in a bottom‐up fashion. Multiple sections can be incorporated in this model by a simple extension of a single‐section system. An unmatched TDR probe system is modeled by dividing it into equivalent sections and matching the simulated waveform with the actual waveform. The excellent match between the simulated and the recorded waveforms verifies the model. This model eliminates the requirement of a matched 50‐Ω probe handler in probe design for dielectric measurement. It can also be used to assist probe design and TDR data interpretation. The reflected waveforms in layered soil specimens are modeled, and the simulated waveforms are compared to those obtained from experiments. The method of using apparent dielectric constant to obtain average volumetric water content is examined for the layered soil system. The results show that apparent dielectric constant is applicable for the measurement of average volumetric water content for a layered soil, but caution has to be used when interpreting the waveforms.
An analytical probabilistic approach to sizing flood control detention facilities
Authors: Guo Yiping , Adams Barry J.
Published: December 2003

Flood control detention facilities have been traditionally designed using the design storm approach. Because of the deficiencies associated with the design storm approach, continuous simulation using long‐term historical rainfall data has been recommended for the planning and design of these facilities in order to examine the performance of the system under a wide range of meteorological and hydrological conditions. An analytical probabilistic approach is presented as a computationally efficient alternative to continuous simulation. In this approach the probability distribution of the peak outflow rate from a detention facility servicing an urban catchment is derived from the probability distribution of the rainfall event characteristics that generate the runoff received by the detention facility. These derived mathematical expressions are used to determine analytically the storage‐discharge relationship required for a detention facility to achieve the desired level of flood control. Comparison with long‐term continuous simulation modeling demonstrates that the closed‐form mathematical expressions of the analytical probabilistic approach provide reasonable approximation of the continuous simulation results. The analytical probabilistic approach overcomes some of the conceptual problems of the design storm approach and is therefore proposed for the planning and design of flood control detention facilities.
Analyzing the potential for water quality externalities as the result of market water transfers
Authors: Connor Jeffery D. , Perry Gregory M.
Published: December 2003

This article presents a comparative static framework for predicting the water quality outcomes of water trade. The focus is on a comprehensive treatment of water quality processes. Previous work has assumed that reductions in agriculturally induced water quality externalities are an increasing function of irrigation application rates. The comparative static framework used here allows for the possibility that water transfer can result in both positive and negative water quality externalities as the result of dilution, even when the rate of loading decreases. We apply our model to the Owyhee aquifer of eastern Oregon, an area where nitrate concentrations exceeded the EPA standard of 10 ppm in over 30% of area test wells in 1991. In conclusion, we describe conditions when water trade is most likely to generate positive versus negative water quality externalities. We also draw policy conclusions about the kinds of institutional rules best suited to balance trade‐offs between gains to trade, water quality externalities, and transactions costs.
Sediment production from forest roads in western Oregon
Authors: Luce Charles H. , Black Thomas A.
Published: December 2003

Prevention and estimation of soil erosion from forest roads requires an understanding of how road design and maintenance affect sediment production. Seventy‐four plots were installed on forest roads in the Oregon Coast Range to examine the relationship between sediment production and road attributes such as distance between culverts, road slope, soil texture, and cutslope height. An additional comparison was made between road segments with cutslopes and ditches freshly cleared of vegetation and segments with established vegetation on cutslopes and in ditches. All road segments were 5 m wide and insloped with aggregate surfacing, light traffic, and no overhanging forest cover. Sediment production was correlated to the product of segment length times road slope squared. Sediment production from aggregate covered roads on a silty clay loam was about 9 times greater than that from roads constructed on a gravelly loam. Sediment production was not correlated to the cutslope height. Road segments where vegetation was cleared from the cutslope and ditch produced about 7 times as much sediment as road segments where vegetation was retained, showing the potential reduction in erosion by revegetation following construction and the potential impact of ditch cleaning during maintenance. Relationships and estimates from this study provide a basis for improved erosion estimates by commonly used empirical procedures.
Bivariate extreme value distributions: an application of the Gibbs Sampler to the analysis of floods
Authors: Adamson P. T. , Metcalfe A. V. , Parmentier B.
Published: December 2003

The quantitative definition of the magnitude of a flood episode exclusively in terms of its peak rate of discharge is often insufficient. In common with most episodic hydrological phenomena, floods are intrinsically multivariate random events, characterized not only by their peak flow, but also by their volume and the duration of discharge above critical thresholds. A complete definition in terms of these three component random variables has not found its way into standard analytical practice. This may be partly because the theory of multivariate extremes is not straightforward, and partly because no intuitively attractive way of presenting the component variables in a probabilistic framework has been put forward. We propose that the Gibbs sampler, a member of the new generation of computer intensive methods in computational statistics, bypasses the theoretical difficulties. We demonstrate the Gibbs sampler, and provide graphical presentations of the results, for the annual flood hydrograph on the Mekong River at Vientiane, Laos. We extend the results to evaluate the potential distribution of flood damage to the city.
Screening model for the contamination of a well in a uniform flow field
Authors: Kennedy Christopher , Lennox William C.
Published: December 2003

Explicit solutions are developed for the steady state concentration of a contaminant at a water supply well, because of a continuous source within the capture zone. The solutions are based on the streamline equation for a well in a uniform flow field [Todd, 1959] and account for the dilution of contaminated waters at the well where streamlines are converging. Integration along a streamline also yields expressions for the travel time and distance to the well, which may be used to calculate the concentration of an exponentially decaying contaminant. In a sensitivity analysis with fixed source location, travel times decrease with higher values of hydraulic conductivity down to a minimum value. This minimum is given by a hydraulic conductivity just under the limiting value that places the source on the capture zone boundary.
Runoff from a cornfield as affected by tillage and corn canopy: A large‐scale simulated‐rainfall hydrologic data set for model testing
Authors: Wauchope R. D. , Sumner H. R. , Truman C. C. , Johnson A. W. , Dowler C. C. , Hook J. E. , Gascho G. J. , Davis J. G. , Chandler L. D.
Published: December 2003

A rainfall simulator was used to apply 5 cm of rainfall in 2 hours to two replicate 624 m2plots at six times during each of the growing seasons of 1992 and 1993. Because the simulator generated reproducible and time‐invariant rainfall intensities, the resulting 24 hydrographs reproducibly reveal the effects of tractor wheel compaction, tillage, soil reconsolidation, surface sealing, and corn canopy development. A time series data set including weather, crop development, soils properties, evapotranspiration, and antecedent soil water is available. These data should provide hydrologie modelers, particularly those interested in modeling runoff with time resolutions of <1 day, with a useful validation data set.
Underthrusting at the Hjort Trench, Australian‐Pacific plate boundary: Incipient subduction?
Authors: Meckel T. A. , Coffin M. F. , Mosher S. , Symonds P. , Bernardel G. , Mann P.
Published: December 2003

The southernmost portion of the Macquarie Ridge Complex (MRC) comprises the Hjort Ridge, Trench, and Plateau, the topographic expression of the Australian‐Pacific plate boundary south of New Zealand. On the basis of marine geophysical (swath bathymetry/reflectivity, seismic reflection, gravity, magnetic) data, teleseismic data, and gravity modeling, we argue that the Australian plate is actively underthrusting the Pacific plate along the Hjort Trench, but self‐sustaining subduction does not yet appear to have commenced. We interpret a crustal discontinuity in the Trench as a shallowly dipping thrust splay off a sub‐vertical transform fault in the crest of the Hjort Ridge (Hjort Fault). The Hjort Fault separates oceanic crust generated at the Southeast Indian Ridge (SEIR crust), located to the south, from oceanic crust generated at the extinct Australian‐Pacific spreading center located to the north (MRC crust). Oblique convergence on the transform has initiated a significant plate boundary decollement in the Trench, but our estimate of ∼50 km of underthrusting does not support the existence of an eastwardly dipping Australian slab below ∼20 km depth. For the length of the Hjort Ridge and Trench system, oblique convergence is partitioned between the decollement in the Trench and the Hjort Fault. South of 57.5°S, the trench decollement accommodates thrusting. North of 57.5°S, the boundary‐parallel component of convergence becomes dominant, the Trench gradually shallows, and the trench decollement evolves into a low‐angle, oblique‐slip fault. The trench decollement and strike‐slip system in the Hjort Ridge are structural boundaries that contain tectonic slivers of inferred SEIR crust of the western flank of the Hjort Ridge that currently belong to neither the Australian nor the Pacific plates.