bluuebunny/crossref_metadata_2025 huggingface dataset:
El Niño Southern Oscillation (ENSO) and decadal‐scale climate variability at 10°N in the eastern Pacific from 1893 to 1994: A coral‐based reconstruction from Clipperton Atoll
Authors: Linsley Braddock K. , Ren Lei , Dunbar Robert B. , Howe Stephen S.
Published: September 2002

We have developed a 101 year (1893–1994) subseasonal oxygen (δ18O) and carbon (δ13C) isotopic time series from Clipperton Atoll in the eastern Pacific using the coral Porites lobata. In agreement with Linsley et al. [1999] we find that seasonal and interannual coral δ18O variability at Clipperton results from variability in both water temperature and salinity. Three new coral time series demonstrate the reproducibility of a secular coral δ18O trend of −0.35‰ since 1910 but show varying δ13C trends. Strong decadal‐scale variability in the δ18O record appears related to the Pacific Decadal Oscillation (PDO) through postulated changes in the strengths of the Equatorial Counter Current and North Equatorial Current. Interannual variability in this coral δ18O record is directly related to the El Niño Southern Oscillation (ENSO) and isolation of this frequency band indicates reduced ENSO variability in the eastern equatorial Pacific in the period 1925 to ∼1940, in agreement with instrumental and other Pacific coral records.
Glacial deep water geometry: South Atlantic benthic foraminiferal Cd/Ca and δ13C evidence
Authors: Oppo Delia W. , Horowitz Michael
Published: September 2002

A depth transect of cores from 1268 to 3909 m water depth in the western South Atlantic are ideally situated to monitor the interocean exchange of deep water and variations in the relative strength of northern and southern sources of deep water production. Benthic foraminiferal Cd/Ca and δ13C data suggest that Glacial North Atlantic Intermediate Water (GNAIW) extended at least as far south as 28°S in the western South Atlantic. The core of nutrient‐depleted water was situated at ∼1500 m, above and below water masses with higher nutrient concentrations. When examined in conjunction with published paired Cd/Ca and δ13C from intermediate depth cores from other basins, it appears that the extent of GNAIW influence on the intermediate waters of the world's oceans was less than suggested previously. Differentiating among possible pathways for the glacial deep ocean (>3 km) requires a better understanding of the controls on Cd/Ca and δ13C values of benthic foraminifera.
Late glacial diatom accumulation at 9°S in the Indian Ocean
Authors: Broecker Wallace S. , Clark Elizabeth , Lynch‐Stieglitz Jean , Beck Warren , Stott Lowell D. , Hajdas Irena , Bonani Georges
Published: September 2002

A continuous 10‐m‐long section consisting of roughly two thirds Ethmodiscus rex (a diatom) and one third mixed planktonic foraminifera was identified in a core from 3800 m depth at 9°S on the Indian Ocean's 90°E Ridge. Radiocarbon dates place the onset of deposition of this layer at >30,000 years B.P. and its termination at close to 11,000 years B.P. However, precise dating of the foraminifera from the Ethmodiscus layer itself proved to be impossible owing to the presence of secondary calcite presumably precipitated from the pore waters. During the Holocene, high calcium carbonate content ooze free of diatoms was deposited at this locale. As the site currently lies beneath the pathway taken by upper ocean waters entering the Indian Ocean from the Pacific (via the Indonesian Straits), it appears that during glacial time, thermocline waters moving along this same path provided the silica and other nutrients required by these diatoms.
Millennial reoccurrence of century‐scale abrupt events of East Asian Monsoon: A possible heat conveyor for the global deglaciation
Authors: Wang Luejiang , Sarnthein Michael , Grootes Pieter M. , Erlenkeuser Helmut
Published: September 2002

High‐resolution sediment records from the South China Sea reveal a winter monsoon dominated glacial regime and a summer monsoon dominated Holocene regime during the last glacial cycle. A fundamental change between regimes occurred during deglaciation through a series of millennial reoccurrences of century‐scale changes in the East Asian monsoon (EAM) climate. These abrupt events centered at 17.0, 15.9, 15.5, 14.7, 13.5, 13.9, 13.3, 12.1, 11.5, and 10.7 14C ka correlate well with the millennial‐scale events in the Santa Barbara Basin and the Arabian Sea, i.e. a relationship between EAM and El Niño/Southern Oscillation systems. The abrupt increases in summer monsoon imply enhanced heat transport from low‐latitude sea area to the midlatitude/high‐latitude land area. The phase relationship between events of EAM and ice sheet may reflect a faster EAM response and a slower ice sheet response to the insolation change. A far‐reaching conclusion is that the EAM might have triggered the Northern Hemisphere deglaciation.
Onset of the Mid‐Cretaceous greenhouse in the Barremian‐Aptian: Igneous events and the biological, sedimentary, and geochemical responses
Authors: Larson Roger L. , Erba Elisabetta
Published: September 2002

Basalts and biostratigraphy dated at 125–120 Ma from the Ontong Java and Manihiki Plateaus in the western Pacific evidence the largest volcanic event in Earth history in at least the past 160 m.y. The intervening Nova‐Canton Trough rifted at about 121–118 Ma, and a number of guyots and seamounts formed concurrently or slightly later. Geological events that probably were responses to these volcanic/tectonic events occurred in the following chronostratigraphic order. Biotic fluctuations began at about 122.5 Ma. At about 122.0 Ma, 87Sr/86Sr began to decline slowly. Metal concentrations of Co, Mn, Pb, Yb, and Cu in sediments peaked at about 121.5–121.2 Ma. Changes in planktonic communities and sedimentation culminated in a nannoconid “crisis” just prior to 120.5 Ma and in the Selli black shale (OAE la) at about 120.5–119.5 Ma. A sharp drop in δ13C occurred at the beginning of the Selli event and rebounded into a longer positive excursion that reached a peak after the Selli event at about 119.5–118.5 Ma. At 120.5 Ma, 87Sr/86Sr declined rapidly and reached a minimum at about 116–113 Ma. We speculate that the intensity of these latter responses suggests a corresponding peak in volcanic/tectonic activity at about 121–119 Ma.
Sea‐surface temperatures of the southwest Pacific Ocean during the Last Glacial Maximum
Authors: Barrows T. T. , Juggins S. , De Deckker P. , Thiede J. , Martinez J. I.
Published: September 2002

The southwest Pacific Ocean covers a broad range of surface‐water conditions ranging from warm, salty water in the subtropical East Australian Current to fresher, cold water in the Circumpolar Current. Using a new database of planktonic foraminifera assemblages (AUSMAT‐F2), we demonstrate that the modern analog technique can be used to accurately reconstruct the magnitude of sea‐surfacetemperature (SST) in this region. We apply this technique to data from 29 deep‐sea cores along a meridional transect of the southwest Pacific Ocean to estimate the magnitude of SST cooling during the Last Glacial Maximum. We find minimal cooling in the tropics (0°–2°C), moderate cooling in the subtropical midlatitudes (2°–6°C), and maximum cooling to the southeast of New Zealand (6°–10°C). The magnitude of cooling at the sea surface from the tropics to the temperate latitudes is found to generally be less than cooling at the surface of adjacent land masses.
Topography of the transition zone seismic discontinuities
Authors: Helffrich George
Published: September 2002

Phase transformations in mantle mineralogies probably cause the transition zone seismic discontinuities, nominally at 410, 520, and 660 km depth. Thermodynamic principles govern phase transformations, making them sensitive to changes in the mantle's ambient conditions through the thermodynamic response: Changes in temperature or composition shift the transformation to a different pressure, creating topography on a level discontinuity. With this use as an exploratory tool for the mantle in mind, we review the basic seismological and phase equilibrium concepts underlying the detection and interpretation of the seismic wave arrivals associated with the transition zone discontinuities. Reviewing the evidence for and against the phase transition model, we conclude that it is viable and describe how discontinuities have been and can be used to probe the physical and chemical state of the transition zone.
What caused the glacial/interglacial atmospheric pCO2 cycles?
Authors: Archer David , Winguth Arne , Lea David , Mahowald Natalie
Published: September 2002

Fifteen years after the discovery of major glacial/interglacial cycles in the CO2 concentration of the atmosphere, it seems that all of the simple mechanisms for lowering pCO2 have been eliminated. We use a model of ocean and sediment geochemistry, which includes new developments of iron limitation of biological production at the sea surface and anoxic diagenesis and its effect on CaCO3 preservation in the sediments, to evaluate the current proposals for explaining the glacial/interglacial pCO2 cycles within the context of the ocean carbon cycle. After equilibration with CaCO3 the model is unable to generate glacial pCO2 by increasing ocean NO3− but predicts that a doubling of ocean H4SiO4 might suffice. However, the model is unable to generate a doubling of ocean H4SiO4 by any reasonable changes in SiO2 weathering or production. Our conclusions force us to challenge one or more of the assumptions at the foundations of chemical oceanography. We can abandon the stability of the “Redfield ratio” of nitrogen to phosphorus in living marine phytoplankton and the ultimate limitation of marine photosynthesis by phosphorus. We can challenge the idea that the pH of the deep ocean is held relatively invariant by equilibrium with CaCO3. A third possibility, which challenges physical oceanographers, is that diapycnal mixing in ocean circulation models exceeds the rate of mixing in the real ocean, diminishing the model pCO2 sensitivity to biological carbon uptake.
Surface air temperature and its changes over the past 150 years
Authors: Jones P. D. , New M. , Parker D. E. , Martin S. , Rigor I. G.
Published: September 2002

We review the surface air temperature record of the past 150 years, considering the homogeneity of the basic data and the standard errors of estimation of the average hemispheric and global estimates. We present global fields of surface temperature change over the two 20‐year periods of greatest warming this century, 1925–1944 and 1978–1997. Over these periods, global temperatures rose by 0.37° and 0.32°C, respectively. The twentieth‐century warming has been accompanied by a decrease in those areas of the world affected by exceptionally cool temperatures and to a lesser extent by increases in areas affected by exceptionally warm temperatures. In recent decades there have been much greater increases in night minimum temperatures than in day maximum temperatures, so that over 1950–1993 the diurnal temperature range has decreased by 0.08°C per decade. We discuss the recent divergence of surface and satellite temperature measurements of the lower troposphere and consider the last 150 years in the context of the last millennium. We then provide a globally complete absolute surface air temperature climatology on a 1° × 1° grid. This is primarily based on data for 1961–1990. Extensive interpolation had to be undertaken over both polar regions and in a few other regions where basic data are scarce, but we believe the climatology is the most consistent and reliable of absolute surface air temperature conditions over the world. The climatology indicates that the annual average surface temperature of the world is 14.0°C (14.6°C in the Northern Hemisphere (NH) and 13.4°C for the Southern Hemisphere). The annual cycle of global mean temperatures follows that of the land‐dominated NH, with a maximum in July of 15.9°C and a minimum in January of 12.2°C.
A hybrid uniform geometrical theory of diffraction–moment method for efficient analysis of electromagnetic radiation/scattering from large finite planar arrays
Authors: Çivi Ö. Aydin , Pathak Prabhakar H. , Chou Hsi‐Tseng , Nepa Paolo
Published: September 2002

A hybrid uniform geometrical theory of diffraction (UTD)‐moment method (MOM) approach is introduced to provide an efficient analysis of the electromagnetic radiation/scattering from electrically large, finite, planar periodic arrays. This study is motivated by the fact that conventional numerical methods become rapidly inefficient and even intractable for the analysis of electrically large arrays containing many antenna or frequency‐selective surface (FSS) elements. In the present hybrid UTD‐MOM approach, the number of unknowns to be solved is drastically reduced as compared to that which is required in the conventional MOM approach. This substantial reduction in the MOM unknowns is essentially made possible by introducing relatively few, special ray‐type (or UTD) basis functions to efficiently describe the unknown array currents. The utility of the present hybrid approach is demonstrated here for the simple case of a large rectangular phased array of short and thin metallic dipoles in air, which are excited with a uniform amplitude and linear phase distribution. Some numerical results are presented to illustrate the efficiency and accuracy of this hybrid method.
The application of GPS observations to equatorial aeronomy
Authors: Mendillo Michael , Lin Bosheng , Aarons Jules
Published: September 2002

Routine observations of the ionospherically imposed propagation effects upon GPS satellite signals are available online from the International GPS Service for Geodynamics. With over 200 ground‐based stations now reporting data, ionospheric studies ranging from the analysis of single‐site observations to the full global network have demonstrated the geophysical science yield possible from this remarkable resource. In this paper we expand on the use of GPS data for comprehensive “regional studies” at low latitudes. Using the GPS observing sites in South America, we show how routine observations are processed to form reliable total electron content (TEC) values capable of describing the latitudinal, longitudinal, local time, and storm time behavior over the full span of the continent. To study the dominant F region structure at low latitudes, the Appleton anomaly, two indices are developed to assess its strength (Is) and asymmetry (Ia). TEC data at 30 s intervals are used to form phase fluctuation indices that capture plasma irregularity patterns at 15‐min (fp) and hourly (Fp) time resolution. Tests of Fp at Atlantic and Pacific sector locations show them to reproduce accurately all known occurrence patterns for equatorial spread F (ESF). The use of the three indices (Is,Ia, and Fp) to formulate predictive capabilities for ESF on the basis of the enhancement or suppression of growth rate indicators was not particularly successful.
Applying Padé via Lanczos to the finite element method for electromagnetic radiation problems
Authors: Slone Rodney Daryl , Lee Robert
Published: September 2002

Recently there has been a great deal of interest in using the Padé via Lanczos (PVL) technique to analyze the transfer functions and impulse responses of large‐scale linear circuits. In this paper, matrix‐Padé via Lanczos (MPVL), which can be used on multiple‐input multiple‐output systems, is applied to solve models resulting from applying the finite element method (FEM) to electromagnetic wave propagation problems in the frequency domain. The resulting solution procedure of using MPVL to solve FEM equations allows for wideband frequency simulations with a reduction in total computation time. Several issues arise during this application, and each is addressed in detail. Numerical simulations using this method are shown along with traditional methods using an LU decomposition at each frequency point of interest. Comparisons in accuracy as well as computation time are also given.
Low‐latitude field‐aligned irregularities observed in the E region with the Piura VHF radar: First results
Authors: Woodman Ronald F. , Chau Jorge L. , Aquino Fredy , Rodriguez Rodolfo R. , Flores Luis A.
Published: September 2002

We have used the Piura VHF radar (5°12'S, 80°38'W, ∼7.5°N geomagnetic latitude, just outside the magnetic equator) in northern Peru to gather echoes from 3‐m E region field‐aligned irregularities. We present statistical results of these echoes: percentage of occurrence and histograms of radial velocities and spectral widths, obtained with a 15‐day data set gathered in 1996. These E region echoes are confined to 95‐ to 120‐km altitude and present spectral characteristics similar to equatorial electrojet (EEJ) echoes generated by a gradient drift instability, i.e., type 2. However, they appear mainly at nighttime and early morning (1800–0800 LT) and therefore do not present a temporal similarity to EEJ echoes. Moreover, we observe the existence of two well‐defined types of echoes: (1) lower E region echoes (95–105 km) and upper E region echoes (105–120 km). Both regions show different spectral and temporal characteristics. It is difficult to determine at this point the physical mechanisms responsible for the formation of the irregularities without measurements of E fields and density gradients, which we plan to do in a future experiment.
Simulation of radiometric and attenuation measurements along Earth‐satellite links in the 10‐ to 50‐GHz band through horizontally finite convective rain cells
Authors: Marzano Frank S. , Fionda Ermanno , Ciotti Piero
Published: September 2002

An iterative solution is illustrated of the three‐dimensional radiative transfer equation for a horizontally finite and vertically inhomogeneous precipitating cloud. The method is applied to modeling a convective rain cell of cylindrical shape, characterized by spherical raindrops having a negative‐exponential drop size distribution. The realistic model also takes into account the presence of a cloud and an ice layer above the rain cell itself. The simulated brightness temperature, the mean radiative temperature, and the path attenuation are evaluated in a three‐dimensional geometry from a surface observation point in order to simulate a ground‐based station with a beacon receiver and a multichannel radiometer. Numerical results are shown to illustrate the potential of the proposed model for different sets of frequency channels, observation geometries, cloud sizes and types, and precipitation intensities. After generating a large data set by varying the relevant rain cell parameters, regression analysis is applied to derive a statistical estimation of the total path attenuation from surface rain rate and ground‐based radiometric measurements together with the frequency scaling factors for cumuliform clouds in the 10‐ to 50‐GHz band.
Analysis and validation of GPS/MET radio occultation data in the ionosphere
Authors: Schreiner William S. , Sokolovskiy Sergey V. , Rocken Christian , Hunt Douglas C.
Published: September 2002

Global Positioning System (GPS) radio occultation signals received by a low Earth orbit (LEO) satellite provide information about the global distribution of electron density in the ionosphere. We examine two radio occultation inversion algorithms. The first algorithm utilizes the Abel integral transform, which assumes spherical symmetry of the electron density field. We test this algorithm with two approaches: through the computation of bending angles and through the computation of total electron content (TEC) assuming straight line propagation. We demonstrate that for GPS frequencies and for observations in LEO, the assumption of straight‐line propagation (neglecting bending) introduces small errors when monitoring the F2 layer. The second algorithm, which also assumes straight‐line propagation, is a three‐dimensional (3‐D) inversion constrained with the horizontal structure of a priori electron density fields. As a priori fields we use tomographic solutions and the parameterized real‐time ionospheric specification model (PRISM) when adjusted with ionosonde data or ground‐based GPS vertical TEC maps. For both algorithms we calibrate the occultation data by utilizing observations from the part of the LEO that is closer to the GPS satellite. For inversions we use dual‐frequency observational data (the difference of Ll and L2 phase observables) which cancel orbit errors (without applying precise orbit determination) and clock errors (without requiring synchronous ground data) and thus may allow inversions to be computed close to real time in the future. The Abel and 3‐D constrained algorithms are validated by statistically comparing 4 days of inversions with critical frequency (ƒ0F2) data from a network of 45 ionosonde stations and with vertical TEC data from the global network of GPS ground receivers. Globally, the Abel inversion approach agrees with the ƒ0F2 correlative data at the 13% rms level, with a negligible mean difference. All tested 3‐D constrained inversion approaches possess a statistically significant mean difference when compared with the ionosonde data. The vertical TEC correlative comparisons for both the Abel and 3‐D constrained inversions are significantly biased (∼30%) by the electrons above the 735‐km LEO altitude.
VLF scattering from red sprites: Vertical columns of ionization in the Earth‐ionosphere waveguide
Authors: Rodger Craig J. , Thomson Neil R. , Wait James R.
Published: September 2002

Red sprites were discovered by chance in 1989 when a low‐light TV system was pointed above an active thunderstorm. Optically, they are observed as clusters of short‐lived (∼50 ms) pinkish‐red luminous events, sometimes stretching from ∼40 to ∼85 km altitude. Red sprites are associated with ionization in the Earth‐ionosphere waveguide, which can persist for up to ∼100 s at higher altitudes. The structured ionization associated with red sprites has been observed through “VLF sprites,” perturbations of the phase and/or amplitude of subionospheric VLF transmissions, which can be used to study the electrical properties of the red sprite plasma. Previous theoretical studies have simplified the problem by assuming the red sprite associated ionizations were columns of infinite length, or inside a “flat‐Earth” waveguide. In this paper we present an approach for examining the scattering of VLF transmissions by a finite‐length column of ionization inside the Earth‐ionosphere waveguide, including the effect of realistic curvature of the waveguide. These expressions are applied to the detection and study of red sprites by assuming that the associated ionization can be treated as a (cluster of) truncated columns in the Earthionosphere waveguide. An example calculation is presented, examining the farthest distance from the red sprite from which it might be detected as a VLF sprite.
Coupling of electromagnetic energy to a scatterer inside a cavity: A combined statistical and integral representation approach
Authors: Lefèbvre J. , Hagen J. V. , Lecointe D. , Tabbara W.
Published: September 2002

We consider an electromagnetic compatibility problem, where an electromagnetic plane wave, incident on an aperture in the wall of a cavity, is coupled to a set of enclosed metallic plates and a monopole is connected to the base of the cavity and loaded with an impedance. For an aperture of moderate dimensions, one can define an equivalent problem where the incident wave is the one radiated by electric and magnetic dipoles placed inside the cavity with the aperture short‐circuited. To predict the voltage induced on the load, an integral representation of the electric field combined with the Green's function of the cavity is used to model the electric field. This reduces the set of unknowns to the values of the currents on the monopole and on the plates. A method of moments is then used to solve the related integral equation. The analysis of the variations of the average and maximum values of the voltage over a given frequency band, as a function of the parameters of the structure, is conducted in an unusual manner. We use statistical tools such as experiment design, regression, and kriging to determine the prevailing parameters and their degree of correlation and to provide a fast prediction of the average and maximum values of the voltage.
Radio wave active Doppler imaging of space plasma structures: Arrival angle, wave polarization, and Faraday rotation measurements with the radio plasma imager
Authors: Reinisch Bodo W. , Sales Gary S. , Haines D. Mark , Fung Shing F. , Taylor William W. L.
Published: September 2002

Radio sounding in the magnetosphere by the radio plasma imager on the IMAGE spacecraft will determine the dimensions and shape of the cavity between the magnetopause and the plasmapause. Omnidirectional transmission of pulsed radio signals results in echoes arriving from many directions. Quadrature sampling and Doppler analysis of the signals received on three orthogonal antennas will make it possible to determine the angles of arrival of the echoes, their polarization ellipses, and the Faraday rotation. Decomposition of the echo signals into the two characteristic waves is used to identify the O‐ and X‐wave components.
Electromagnetic scattering by a triaxial homogeneous penetrable ellipsoid: Low‐frequency derivation and testing of the localized nonlinear approximation
Authors: Perrusson G. , Lambert M. , Lesselier D. , Charalambopoulos A. , Dassios G.
Published: September 2002

The field resulting from the illumination by a localized time‐harmonic low‐frequency source (typically a magnetic dipole) of a voluminous lossy dielectric body placed in a lossy dielectric embedding is determined within the framework of the localized nonlinear approximation by means of a low‐frequency Rayleigh analysis. It is sketched (1) how one derives a low‐frequency series expansion in positive integral powers of (jk), where k is the embedding complex wavenumber, of the depolarization dyad that relates the background electric field to the total electric field inside the body; (2) how this expansion is used to determine the magnetic field resulting outside the body and how the corresponding series expansion of this field, up to the power 5 in (jk), follows once the series expansion of the incident electric field in the body volume is known up to the same power; and (3) how the needed nonzero coefficients of the depolarization dyad (up to the power 3 in (jk)) are obtained, for a general triaxial ellipsoid and after careful reduction for the geometrically degenerate geometries, with the help of the elliptical harmonic theory. Numerical results obtained by this hybrid low‐frequency approach illustrate its capability to provide accurate magnetic fields at low computational cost, in particular, in comparison with a general purpose method‐of‐moments code.
Mechanisms for accommodation of Miocene extension: Low‐angle normal faulting, magmatism, and secondary breakaway faulting in the southern Sacramento Mountains, southeastern California
Authors: Campbell‐Stone Erin , John Barbara E. , Foster David A. , Geissman John W. , Livaccari Richard F.
Published: September 2002

The Colorado River extensional corridor (CREC) accommodated up to 100% crustal extension between ∼23 and 12 Ma. The southernmost Sacramento Mountains core complex lies within this region of extreme extension and exposes a footwall of Proterozoic, Mesozoic, and Miocene crystalline rocks as well as Miocene volcanic and sedimentary rocks in the hanging wall to the regionally developed Chemehuevi‐Sacramento detachment fault (CSDF) system. New structural, U‐Pb‐zircon, Ar‐Ar, and fission track geochronologic and paleomagnetic studies detail the episodic character of both magmatic and tectonic extension in this region. Extension in this part of the CREC was initiated with tectonic slip along a detachment fault system at a depth between 10 and 15 km. Magmatic extension at these crustal levels began at ∼20–19 Ma and directly account for 5–18 km of extension (10–20% of total extension) in the southern Sacramento Mountains. Three discrete magmatic episodes record rotation of the least principal stress direction, in the horizontal plane, from 55° to 15° over the following ∼3 Myr. The three intrusions bear brittle and semibrittle fabrics and show no crystal‐plastic fabric development. The final 3–4 Myr of stretching were dominated by amagmatic or tectonic extension along a detachment fault system, with extension directions rotating back toward 75°. The data are consistent with extremely rapid cooling and uplift of Miocene footwall rocks; the ∼19 Ma Sacram suite was emplaced at a mean pressure of ∼3.0 kbars and uplifted rapidly to a level in the crust where brittle deformation was manifested by movement on the detachment fault at ∼16 Ma. By ∼14 Ma the footwall was exposed at the surface, with detritus shed off and deposited in adjacent hanging wall basins.
Field examples of strike‐slip fault terminations in Mongolia and their tectonic significance
Authors: Bayasgalan Amgalan , Jackson James , Ritz Jean‐François , Carretier Sebastien
Published: September 2002

Deformation at the ends of large intracontinental strike‐slip faults that do not simply link other major structures often involves rotations about a vertical axis. We use earthquake slip vectors, surface rupture in earthquakes, and geomorphology to examine the ends of three major strike‐slip faults in Mongolia. In these places a simple pattern is seen, consisting of a thrust fault on one side, with a displacement that decreases away from the strike‐slip fault, consistent with local rotational deformation. Strike‐slip faults that terminate in this way allow the style of faulting to change spatially within a deforming area, for example, from dominantly strike‐slip to dominantly dip‐slip, while still accommodating the overall deformation required by larger‐scale regional motions. Such a change in fault style should also be accompanied by a change in the rotation rate about a vertical axis, which may be detected paleomagnetically. The kind of strike‐slip fault termination described here may have consequences for how large strike‐slip fxaults evolve and grow and for the variation in displacement along their length.
Lithosphere folding: Primary response to compression? (from central Asia to Paris basin)
Authors: Cloetingh S. , Burov E. , Poliakov A.
Published: September 2002

We examine the role of lithosphere folding in the large‐scale evolution of the continental lithosphere. Analysis of the record of recent vertical motions and the geometry of basin deflection for a number of sites in Europe and worldwide suggests that lithospheric folding is a primary response of the lithosphere to recently induced compressional stress fields. Despite the widespread opinion, folding can persist during long periods of time independently of the presence of many inhomogeneities such as crustal faults and inherited weakness zones. The characteristic wavelengths of folding are determined by the presence of young lithosphere in large parts of Europe and central Asia and by the geometries of the sediment bodies acting as a load on the lithosphere in basins. The proximity of these sites to the areas of active tectonic compression suggests that the technically induced horizontal stresses are responsible for the large‐scale warping of the lithosphere. Wavelengths and persistence of folding are controlled by many factors such as rheology, faulting, time after the end of the major tectonic compression, nonlinear effects, and initial geometry of the folded area. In particular, the persistence of periodical undulations in central Australia (700 Myr since onset of folding) or in the Paris basin (60 Myr) long after the end of the initial intensive tectonic compression requires a very strong rheology compatible with the effective elastic thickness values of about 100 km in the first case and 50–60 km in the second case.
Arc‐continent collision in Papua Guinea: Constraints from fission track thermochronology
Authors: Hill Kevin C. , Raza Asaf
Published: September 2002

The Papua New Guinea (PNG) Mobile Belt adjacent to the Finisterre Arc was formerly the leading NE corner of the Australian plate that converged obliquely with the Pacific plate. Forty new apatite and zircon fission track analyses of Mobile Belt rocks previously dated by K‐Ar and Rb‐Sr analyses constrain Neogene time‐temperature paths and tectonic models. The Paleogene arc along the southern margin of the Caroline plate was juxtaposed against PNG in the early Miocene, coeval with locking up of the west dipping Solomon subduction zone by the Ontong Java Plateau. These events initiated wrenching along the northern PNG margin and increased westward subduction of the Solomon Sea plate beneath the eastern margin. The Mobile Belt underwent extension above the downgoing slab with rapid cooling of metamorphic rocks at ∼17 Ma, immediately prior to emplacement of the Maramuni Arc from 17 to 12 Ma. A change in plate motion at ∼12–10 Ma terminated the arc and caused PNG‐Caroline plate convergence, creating the orogenic belt in New Guinea from 12 to 4 Ma. This resulted in ∼4.5 km of uplift and ∼3 km of denudation and cooling of the entire Mobile Belt in the late Miocene, propagating westward along the Mobile Belt at 8–5 Ma and southward into the Fold Belt at 5–4 Ma. The compression caused thrusting of Miocene strata within the Mesozoic type section. A further change in plate motion at 4–3 Ma returned the margin to transpression with local compression along strike‐slip faults and ongoing collision of the Finisterre Arc terrane.
Morphometry of late Pleistocene‐Holocene faulting and volcanotectonic relationship in the southern Andes of Colombia
Authors: Tibaldi Alessandro , Leon Jaime Romero
Published: September 2002

Diffuse seismicity and the active Galeras Volcano characterize the southern Andes of Colombia, whose inhabitants are prone to a high natural risk. We used field geological, structural, and quantitative morphological data to define the geometry and kinematics of late Quaternary faults and the volcanotectonic relationships in this area. The main NE‐SW Buesaco Fault has a late Pleistocene‐Holocene 29‐km rupture length. Offset of dated landforms yields 188 ± 13 m of horizontal, right‐lateral, long‐term cumulative component of slip, the vertical component of uplift of the NW block being 67 ± 12 m. The long‐term net slip rate is 1.48 ± 0.12 mm/yr. The other main structure, here named Aranda Fault, also strikes NE‐SW and is 13 km long. Offset of landforms yields 160 ± 10 m of horizontal, right‐lateral, long‐term component of slip and 3.9 ± 1.9 m of vertical component of uplift of the NW block. The long‐term net slip rate is 1.19 ± 0.08 mm/yr. On the Galeras edifice E‐W to NW‐SE faults have normal motions and slip rates from 0.02 to 0.23 mm/yr. Both the Galeras and a late Pleistocene pyroclastic cone lie along the ideal extension of the Buesaco Fault. Magma uprising in the crust can occur along the NE striking fractures when magma pressure (σmp) is greater than the normal‐to‐fault component of tectonic σ1. Magma uprising in the uppermost crust (i.e., in the cone) can occur by rock cracking along E‐W planes with σmp > σ3 up to NW‐SE planes with σmp greater than shear stress component of the horizontal greatest principal stress (σHmax).
Plant canopy interception of rainfall and its significance in a banded landscape, arid western New South Wales, Australia
Authors: Dunkerley D. L. , Booth T. L.
Published: September 2002

The canopy interception storage capacity of three plants in an arid, banded (runoff‐runon) landscape was determined in the field from weight gain under artificial rain. The plants, two shrubs and a grass, were the bladder saltbush Atriplex vesicaria (Heward ex Benth.), the pearl bluebush Maireana sedifolia (F. Muell.) P. G. Wilson, and perennial Mitchell grass Astrebla lappacea (Lindl.) Domin. For saltbush and Mitchell grass, canopy water storage capacity (1.3 mm) correlated strongly with projected canopy area, while for the dense canopy of the bluebush (2.0 mm capacity), plant weight was a better predictor. In view of canopy cover amounts in each plant community, and the mean rain day rainfall of 5.7 mm, estimated annual water losses amount to 32% for Mitchell grass communities, 5% for saltbush communities, and <1% for bluebush communities. Canopy interception loss is shown to be a significant influence on the water redistribution that supports banded landscapes in the arid Broken Hill area.
Modeling the effects of systematic variation in ionic strength on the attachment kinetics of Pseudomonas fluorescens UPER‐1 in saturated sand columns
Authors: Deshpande P. A. , Shonnard D. R.
Published: September 2002

We report the effects of salt type and concentration on the change in attachment kinetics when bacteria are pumped through a column of water‐saturated clean sand over relatively long periods of time (up to 35 pore volumes). The species Pseudomonas fluorescens UPER‐1 was found to exhibit three different kinds of attachment kinetics: first order, second order, and an intermediate order. The attachment kinetics of bacteria was modeled by using the advection‐dispersion equation coupled with a set of equations for each kind of attachment kinetics while using colloid filtration theory to predict collector efficiencies. At low or zero salt concentrations (≤10−4 M) a second‐order kinetics model (“blocking”), a “first‐order” kinetics model, and an intermediate‐order kinetics model (“ripening”), were all found to fit the data equally well. At intermediate and high salt concentrations (≥10−3 M) the ripening model was found to fit the data best. We report values for collision efficiencies of bacteria in the range 0.01–0.2, depending upon the salt type and concentration. This study points out the importance of long‐term experiments to study the effect of ionic strength on bacteria attachment kinetics in saturated porous media and the phenomenon of cell‐to‐cell attachment at high ionic strength. This study further points out the range of kinetics to expect when bacteria attach to natural porous media and suggests a modeling framework.
Dam nation: A geographic census of American dams and their large‐scale hydrologic impacts
Authors: Graf William L.
Published: September 2002

Newly available data indicate that dams fragment the fluvial system of the continental United States and that their impact on river discharge is several times greater than impacts deemed likely as a result of global climate change. The 75,000 dams in the continental United States are capable of storing a volume of water almost equaling one year's mean runoff, but there is considerable geographic variation in potential surface water impacts. In some western mountain and plains regions, dams can store more than 3 year's runoff, while in the Northeast and Northwest, storage is as little as 25% of the annual runoff. Dams partition watersheds; the drainage area per dam varies from 44 km2 (17 miles2) per dam in New England to 811 km2 (313 miles2) per dam in the Lower Colorado basin. Storage volumes, indicators of general hydrologic effects of dams, range from 26,200 m3 km−2 (55 acre‐feet mile−2) in the Great Basin to 345,000 m3 km−2 (725 acre‐feet mile−2) in the South Atlantic region. The greatest river flow impacts occur in the Great Plains, Rocky Mountains, and the arid Southwest, where storage is up to 3.8 times the mean annual runoff. The nation's dams store 5000 m3 (4 acre‐feet) of water per person. Water resource regions have experienced individualized histories of cumulative increases in reservoir storage (and thus of downstream hydrologic and ecologic impacts), but the most rapid increases in storage occurred between the late 1950s and the late 1970s. Since 1980, increases in storage have been relatively minor.
Estimation of physical variables from multichannel remotely sensed imagery using a neural network: Application to rainfall estimation
Authors: Hsu Kuo‐lin , Gupta Hoshin V. , Gao Xiaogang , Sorooshian Soroosh
Published: September 2002

Satellite‐based remotely sensed data have the potential to provide hydrologically relevant information about spatially and temporally varying physical variables. A methodology for estimating such variables from multichannel remotely sensed data is presented; the approach is based on a modified counterpropagation neural network (MCPN) and is both effective and efficient at building complex nonlinear input‐output function mappings from large amounts of data. An application to high‐resolution estimation of the spatial and temporal variation of surface rainfall using geostationary satellite infrared and visible imagery is presented. Test results also indicate that spatially and temporally sparse ground‐based observations can be assimilated via an adaptive implementation of the MCPN method, thereby allowing on‐line improvement of the estimates.
Modeling the effect of wetlands, flooding, and irrigation on river flow: Application to the Aral Sea
Authors: Ferrari Michael R. , Miller James R. , Russell Gary L.
Published: September 2002

As the world's population continues to increase, additional stress is placed on water resources. This stress, coupled with future uncertainties regarding climate change, makes arid and semiarid regions particularly vulnerable. One example is the Aral Sea where the freshwater inflow, which is dominated by snowmelt runoff, has decreased significantly since the expansion of intensive irrigation in the 1960s. The purpose of this paper is to use a river routing scheme from a global climate model to examine the flow of the Amu Dar'ya River into the Aral Sea. The river routing scheme is modified to include groundwater flow, flooding, and evaporative losses in the river's wetlands and floodplain and anthropogenic withdrawals for irrigation. A set of scenarios is designed to test the sensitivity of river flow to the inclusion of these modifications into the river routing scheme. When riverine wetlands and floodplains are present, the river flow is reduced significantly and is similar to the observed flow. In addition, the model results show that it is essential to incorporate human diversions to represent accurately the inflow to the Aral Sea, and they also indicate potential management strategies that might be appropriate to maintain a balance between inflow to the sea and upstream diversions for irrigation.
Three‐dimensional hydrofacies modeling based on soil surveys and transition probability geostatistics
Authors: Weissmann Gary S. , Carle Steven F. , Fogg Graham E.
Published: September 2002

Typical hydrogeologic data sets consisting of information from boreholes provide excellent information on vertical variability of sedimentary deposits but very limited information on lateral distribution and variability. In cases where surface geomorphic features reflect processes similar to those responsible for past deposition, the soil survey offers a resource for assessing the lateral sediment variability. Facies mean length and transition probability measurements of C horizon textures from the soil maps on the Kings River alluvial fan, California, provide a basis for Markov chain models of spatial variability in the principal lateral directions and facies orientation information for the horizontal plane. Incorporation with a Markov chain model of vertical‐direction transitions based on well data yields a three‐dimensional Markov chain model of sediment variability which includes cross correlation between sediment types and representation of asymmetry (e.g., fining upward tendencies). Use of the model in geostatistical conditional simulation and simulated annealing produces a detailed, geologically plausible image of the subsurface hydrofacies distribution.
Distributed modeling of storm flow generation in an Amazonian rain forest catchment: Effects of model parameterization
Authors: Vertessy Robert A. , Elsenbeer Helmut
Published: September 2002

We describe a process‐based storm flow generation model, Topog_SBM consisting of a simple bucket model for soil water accounting, a one‐dimensional kinematic wave overland flow scheme, and a contour‐based element network for routing surface and subsurface flows. Aside from topographic data and rainfall the model has only six input parameters: soil depth (z), saturated hydraulic conductivity at the soil surface (K0), the rate of decay in K0 with depth (m), the Manning surface roughness parameter (n), the maximum (saturated) soil water content (θs), and the minimum (residual) soil water content (θr). However, the model is fully distributed, so these values can vary in magnitude across space. The model was applied to La Cuenca, a very small rainforest catchment in western Amazonia that has been well characterized in several hydrometric and hydrochemical investigations. Total runoff, peak runoff, time of rise, and lag time were predicted for 34 events of varying magnitudes and antecedent moisture conditions. We compared results for eight different model parameterizations or “sets”; four of these were freely calibrated to yield the best possible model fit to runoff data, whereas the other four were constrained (in various ways) by the use of actual K0 data gathered for the catchment. The eight sets were calibrated on either one of three events or on the three events jointly to illustrate the importance of calibration event selection on model performance. Model performance was evaluated by comparing observed and predicted (1) storm flow hydrograph attributes and (2) spatiotemporal patterns of overland flow occurrence across the catchment. The model generally predicted the right amount of runoff but usually underpredicted the peak runoff rate and overpredicted the time of rise. The “best” parameterization could credibly predict hydrographs for only about half of the events. Significant, and sometimes gross, errors were encountered for about one fourth of the events modeled, raising concerns in our minds about the a priori simulation of events that diverge too far from the conditions that the model was calibrated for. For the best parameterization we were able to predict an overland flow frequency distribution that accorded with field observations, though the model almost always overpredicted the spatial extent of overland flow. We concluded that model performance for the La Cuenca conditions could be enhanced by adding a “fast” subsurface flow pathway and/or by modifying the K0 versus depth decay function.
Solute transport with residence‐time‐dependent sink/source reaction coefficients
Authors: Flury Markus , Jury William A.
Published: September 2002

Solutes and colloids moving through porous media often undergo kinetic reactions, such as sorption or degradation. The kinetic reactions are mathematically described by rate laws and their associated rate coefficients. Rate coefficients are often considered to be time invariant, but there is experimental evidence that the coefficients may depend on the travel or residence time of the dissolved or suspended substance. In this paper we present a theoretical approach to describe transport with residence‐time‐dependent sink/source reaction coefficients. The solution to the transport problem with an arbitrary functional form for the reaction term is expressed in terms of the solution to the nonreactive transport problem. The solution is therefore independent of the nature of the transport process and independent of any specific representation of the reaction coefficients. Applications to a convective‐dispersive transport regime are given, and differences between time‐dependent and residence‐time‐dependent reaction coefficients are illustrated with solute breakthrough curves. Depending on the boundary conditions of a specific problem, time‐dependent and residence‐time‐dependent reaction coefficients can lead to very different transport behavior.