bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects on stratospheric ozone from high‐speed civil transport: Sensitivity to stratospheric aerosol loading
Authors: Weisenstein Debra K. , Ko Malcolm K. W. , Rodriguez Jose M. , Sze Nien‐Dak
Published: February 2008

The potential impact of high‐speed civil transport (HSCT) aircraft emissions on stratospheric ozone and the sensitivity of these results to changes in aerosol loading are examined with a two‐dimensional model. With aerosols fixed at background levels, calculated ozone changes due to HSCT aircraft emissions range from negligible up to 4–6% depletions in column ozone at northern high latitudes. The magnitude of the ozone change depends mainly on the NOx increase due to aircraft emissions, which depends on fleet size, cruise altitude, and engine design. The partitioning of the odd nitrogen species in the lower stratosphere among NO, NO2, N2O5, and HNO3 is strongly dependent on the concentration of sulfuric acid aerosol particles, and thus the sensitivity of O3 to NOx emissions changes when the stratospheric aerosol loading changes. Aerosol concentrations 4 times greater than background levels have not been unusual in the last 2 decades. Our model results show that a factor of 4 increase in aerosol loading would significantly reduce the calculated ozone depletion due to HSCT emissions. Because of the natural variability of stratospheric aerosols, the possible impact of HSCT emissions on ozone must be viewed as a range of possible results.
Thermally distinct ejecta blankets from Martian craters
Authors: Betts Bruce H. , Murray Bruce C.
Published: February 2008

Utilizing the Termoskan data set of the Phobos '88 mission we have recognized a new feature on Mars: ejecta blanket distinct in the thermal infrared (EDITH). Virtually all of the more than 100 features discovered in the Termoskan data are located on the plains near Valles Marineris. EDITHs have a startlingly clear dependence upon terrains of Hesperian age, implying a spatial or temporal dependence on Hesperian terrains. Almost no thermally distinct ejecta blankets are associated with any of the thousands of craters within the data set that occur on the older Noachian units. EDITHs also do not appear on the portions of the younger Tharsis Amazonian units seen in the data. The Hesperian terrain dependence cannot be explained by either atmospheric or impactor variations; Noachian and Hesperian terrains must have experienced identical atmospheric and impactor conditions during Hesperian times. Thermally distinct ejecta blankets therefore reflect target material differences and/or secondary modification processes. Not all lobate ejecta blankets are thermally distinct, but all EDITHs correlated with visibly discernible ejecta blankets are associated with lobate ejecta blankets. The boundaries of the thermally distinct areas usually follow closely the termini of the fluidized lobate ejecta blankets, even when the ejecta blankets show a high degree of sinuosity. Thus, the thermally distinct nature of EDITHs must be due to the primary ejecta formation process. The coupling of these thermal anomalies to morphology is unlike most sharp Martian inertia variations which are decoupled from observed surface morphology. Some thermally distinct ejecta blankets occur near otherwise similar craters that do not have thermally distinct ejecta blankets. Thus, wind patterns or locally available aeolian material cannot provide a single overall explanation for the observed variations. We compiled a data base of 110 EDITH and non‐EDITH craters ranging in diameter from 4.2 km to 90.6 km. There are almost no correlations within the data base other than occurrence on Hesperian terrains. We postulate that most of the observed EDITHs are due to excavation of thermally distinctive Noachian age material from beneath a relatively thin layer of younger, more consolidated Hesperian volcanic material. The plausibility of this theory is supported by much geological evidence for relatively thin near‐surface Hesperian deposits overlying massive Noachian megabreccias on the EDITH‐rich plains units. We suggest that absence of thermally distinct ejecta blankets on Noachian and Amazonian terrains is due to absences of distinctive near‐surface layering. Thermally distinct ejecta blankets are excellent locations for future landers and remote sensing because of relatively dust free surface exposures of material excavated from depth.
Photometric and spectroscopic observations of 5145 pholus
Authors: Hoffmann Martin , Fink Uwe , Grundy William M. , Hicks Michael
Published: February 2008

Light curve observations carried out in January and February 1992 are presented. We find an amplitude of 0.2 magnitude and a period of 0.4157 day. Fine structures of the light curve and their variability with time are discussed in terms of the changing phase angle and deviations of the object's shape from a regular ellipsoid. The present orbital and physical properties alone for 5145 Pholus do not provide a clue for either a cometary or an asteroidal origin. It seems to have properties in common with both and thus could form a bridge between these two groups.
Adsorption of HOx on aerosol surfaces: Implications for the atmosphere of Mars
Authors: Anbar A. D. , Leu M‐T. , Nair H. A. , Yung Y. L.
Published: February 2008

The potential impact of heterogeneous chemistry on the abundance and distribution of HOx in the atmosphere of Mars has been assessed by combining observational data of dust and ice aerosol distributions with an updated photochemical model. Critical parameters include the altitude distributions of aerosols, and the surface loss coefficients (γ) of HO2 on dust and ice in the lower atmosphere, and H on ice above 40 km. We find that adsorption of HO2 on dust (γHO2 ≥ 0.01), or ice near 30 km (γHO2 ≥ 0.1), can deplete OH abundances in the lower atmosphere by 10% or more. Such depletions approach those obtained by lowering the water vapor abundance by an order of magnitude below the global average observed by Viking (≈ 25%). Since the oxidation of CO is catalyzed by HOx in the lower atmosphere via the reaction CO + OH → CO2 + H, loss of OH due to adsorption of HO2 on dust or ice at low altitudes could have a significant effect on the ratio CO : CO2. The adsorption of H on ice at 50 km (γH ≥ 0.01) can result in even larger OH depletions. However, this effect is localized to altitudes > 40 km, where CO oxidation is relatively unimportant. Laboratory data suggest that γHO2 ≈ 0.01 is a reasonable estimate for adsorption on dust. Larger values are plausible, but are not stongly supported by experimental evidence. The reactivity of HO2 on ice is unknown, while γH on ice appears to be < 0.001. There is a need for measurements of HOx adsorption on surfaces representative of Martian aerosols at temperatures < 220 K.
Ice in the northern lowlands and southern highlands of Mars and its enrichment beneath the Elysium lavas
Authors: Cave Julie A.
Published: February 2008

A comprehensive study of the Elysium region has revealed evidence of widespread ground‐ice, whose concentration and depth has varied considerably. Ejecta mobility and crater morphology analyses of a database of 7289 craters (which range in diameter from 1.875 to over 160 km) have been used to investigate the distribution of ice between longitudes 245°–155° and latitudes 20°S–45° N, an area incorporating all of the Elysium Quadrangle and large portions of Amenthes, Amazonis, Mare Tyrrhenum, Aeolis, Memnonia, Cebrenia and Diacria Quadrangles. Assuming that the observed variations in the crater characteristics are the result of the incorporation of varying concentrations of subsurface volatiles, the ice distribution is shown to be strongly dependent upon latitude, though its concentration varies with depth and is strongly influenced by geological setting. Important differences have been detected in the distribution of southern and northern lowland ground‐ice. While there is substantial evidence of near‐surface ice in the northern lowlands, where near‐surface limits are strongly influenced by latitude, the greatest concentrations of subsurface ice occur at much greater depths in the southern highlands. In addition, the ice appears to be enriched at depth in the Elysium Lavas, and nearer to the surface in deposits located to the northwest of Elysium Mons and in the Vastitas Borealis Formation. This distribution suggests that several ice‐emplacement mechanisms have operated on Mars, including the enrichment of the deeper ice by juvenile water from beneath the Elysium volcanic province, and the redistribution to the lowlands of a highly concentrated ice reservoir from a great depth within the highlands.
Lunar ferroan anorthosites: Mineralogy, compositional variations, and petrogenesis
Authors: McGee J. J.
Published: February 2008

Detailed petrologic study of a suite of lunar ferroan anorthosites indicates that their mineral compositional variations are generally consistent with derivation of these anorthosites from a common parent magma. There are continuous compositional variations in major elements and smooth trends in minor elements (Mg, Fe in plagioclase; Al, Ti, Cr in pyroxene). Relict textures, zoning, and possible primary trends of mineral compositional variations are preserved in many of the anorthosites. The presence of heterogeneous, bimodal, and/or trimodal pyroxene compositions suggests that some of the anorthosites are polymict rocks; however, they are composed entirely of ferroan‐anorthosite‐suite lithologies. Some aspects of the mineral composition data suggest that complex processes operated during formation of the ferroan anorthosites. The lack of a well‐defined, positive or negative trend of pyroxene Mg/(Mg + Fe) versus plagioclase anorthite content, the homogenization of mineral compositions in some anorthosites, and the varied and apparently enriched Mn contents of pyroxenes in some anorthosites suggest that original igneous compositional characteristics have been altered during and/or after crystallization. Processes operative during anorthosite formation may have included some mixing of different melts, trapping of variable amounts of intercumulus liquid, postcrystallization redistribution of elements, or perturbations both during adcumulus growth and subsequent to crystallization by impact events. FeO and MgO contents of the highly calcic plagioclase typical of these anorthosites suggest that the plagioclase‐melt distribution coefficients for these elements need to be reassessed.
Isotopic fractionation of hydrogen in planetary exospheres due to ionosphere‐exosphere coupling: Implications for Venus
Authors: Hodges R. Richard
Published: February 2008

Planetary D/H fractionation factors for ionosphere‐exosphere coupling through D‐H+, H‐D+, and H‐H+ interactions have been computed for a variety of ion and neutral temperatures. These results strongly support differential escape of H relative to D, in stark contrast to the almost indiscriminate nature of collisional ejection by hot O atoms. The competitive effects of these processes is most important on Venus, where differential escape has created a hundredfold enhancement of the D to H ratio. It is argued that, since exospheric equilibrium concentrates neutral hydrogen in the night hemisphere where ion temperatures are maximum, the creation of fast hydrogen by charge exchange flourishes. On the other hand, hot O is produced by dissociative recombination of O2+ on the day side of the planet, in a region where hydrogen is depleted and thermospheric O is the primary collision partner. Oxygen exosphere models show that O‐O collisions suppress the high energy component of the hot O distribution by more than a factor of 10. More important, the ballistic trajectories of fast O atoms that reach the nighttime reservoir of exospheric hydrogen favor downward scatter of D and H rather than their escape. Owing to the severe limits placed on the effectiveness of collisional ejection, it is concluded that the differential escape of D and H from Venus is determined by charge exchange interactions.
New dust opacity mapping from Viking infrared thermal mapper data
Authors: Martin Terry Z. , Richardson Mark I.
Published: February 2008

Global dust opacity mapping for Mars has been carried forward using the approach described by Martin (1986) for Viking IR Thermal Mapper data. New maps are presented for the period from the beginning of Viking observations, until Ls 210° in 1979 (1.36 Mars years). This range includes the second and more extensive planet‐encircling dust storm observed by Viking, known as storm 1977b. Improvements in approach result in greater time resolution and smaller noise than the earlier work. A strong local storm event filled the Hellas basin at Ls 170°, prior to the 1977a storm. Dust is retained in equatorial regions following the 1977b storm far longer than in mid‐latitudes. Minor dust events appear to raise the opacity in northern high latitudes during northern spring. Additional mapping with high time resolution has been done for the periods of time near the major storm origins in order to search for clues to the mechanism of storm initiation. The first evidence of the start of the 1977b storm is pushed back to Ls 274.2°, preceding signs of the storm in images by about 15 hours.
Recent multispectral observations of Jupiter from 0.6 to 2.4 μm
Authors: Moreno F. , Molina A. , Ortiz J. L.
Published: February 2008

Recent results obtained from observations of the Jovian atmosphere during the 1992 apparition are shown and discussed in a preliminary fashion. The observational data were acquired from two observing campaigns during very good seeing conditions. Charge‐coupled device images were obtained on February 1992 at the Cassegrain focus of the 1.52‐m telescope at Calar Alto Observatory, Spain. These images were taken using narrow‐band interference filters in the 0.62‐ to 0.95‐μm region. Also, we present images of Jupiter in the region 1.5–2.4 μm that were acquired on May 1992 using an InSb 58 × 62 array at the Cassegrain focus of the 4.2‐m William Herschel telescope at La Palma, Spain. This work is intended to be a continuation of an extended program on ground‐based observations of the Jovian planet atmospheres.
On the haze model for Triton
Authors: Krasnopolsky Vladimir A.
Published: February 2008

Some improvements are introduced into the haze model by Krasnopolsky et al. (1992), which describes growth and precipitation of particles formed by methane photolysis. These improvements take into account a possible termination of the Voyager Ultraviolet Spectrometer (UVS) occultation observations by clouds and a more accurate presentation of the surface reflection by a modified Hapke function. All changes are within the uncertainties of the previous model, though not negligible. The particle mean radius and number density for global mean conditions vary from 0.1±0.01 μm and 2.4 cm−3 at 30 km to 0.135±0.015 pm and 10.4 cm−3 near the surface. The scale height of the volume extinction coefficient in the visible varies from 7 km at h=25 km to 15 km at h=5 km. The vertical optical thickness of haze is equal to (5±1) × 10−3 at 0.47 μm.
Erosion of ejecta at Meteor Crater, Arizona
Authors: Grant John A. , Schultz Peter H.
Published: February 2008

New methods for estimating erosion at Meteor Crater, Arizona, indicate that continuous ejecta deposits beyond 1/4–1/2 crater radii from the rim (0.25R‐0.5R) have been lowered less than 1 m on the average. This conclusion is based on the results of two approaches: coarsening of unweathered ejecta into surface lag deposits and calculation of the sediment budget within a drainage basin on the ejecta. Preserved ejecta morphologies beneath thin alluvium revealed by ground‐penetrating radar provide qualitative support for the derived estimates. Although slightly greater erosion (2–3 m) of less resistant ejecta locally has occurred, such deposits were limited in extent, particularly beyond 0.25R‐0.5R from the present rim. Subtle but preserved primary ejecta features (e.g., distal ejecta lobes and blocks) further support our estimate of minimal erosion of ejecta since the crater formed ∼50,000 years ago. Unconsolidated deposits formed during other sudden extreme events (e.g., landslides) exhibit similarly low erosion over the same time frame; the common factor is the presence of large fragments or large fragments in a matrix of finer debris. At Meteor Crater, fluvial and eolian processes remove surrounding fines leaving behind a surface lag of coarse‐grained ejecta fragments that armor surfaces and slow vertical lowering.
The effect of surface roughness on lunar thermal emission spectra
Authors: Johnson Paul E. , Vogler Karl J. , Gardner Jeffrey P.
Published: February 2008

Although attempts have been made to interpret mid‐infrared spectra of the Moon and other atmosphereless bodies in terms of surface composition, we show that surface roughness plays an equally important role when interpreting low to moderate resolution mid‐infrared spectra of the Moon. In order to understand this influence, we model surface roughness as a distribution of paraboloidal craters parameterized by fractional coverage and depth‐to‐diameter ratio. This model explains, to first order, the differences in spectral radiance seen in ratios of one lunar spectrum to another which have been attributed to differences in composition by some authors. We have also developed a technique by which surface roughness can be measured with infrared colors, in such a way that the result is insensitive to compositional effects.
Paleotemperatures versus sea level: Oxygen isotope signal from fish bone phosphate of the Miocene Calvert Cliffs, Maryland
Authors: Barrick Reese E. , Fischer Alfred G. , Bohaska David J.
Published: February 2008

The use of skeletal oxygen isotopic records for use in paleotemperature reconstruction has been hampered by the lack of independent evidence for ocean water oxygen isotopic composition. The δ18O record from homeothermic cetaceans has provided an independent estimate of ocean δ18O values represented by the Calvert and Choptank formations of Maryland. Fish teeth and bones (especially shark and ray teeth) were also collected from these sediments and provide the basis for paleotemperature estimates for represented time slices of the middle Miocene. Trends in δ18O values of the fish phosphate throughout the Calvert Formation are of opposite polarity to the trends from the cetacean bone phosphate. Paleotemperatures calculated using the cetacean proxies for ocean δ18O values sharpen the already present trend, indicating that ocean temperatures increased during episodes of greater glaciation and decreased during periods of lesser or no glaciation. When using modern average ocean values of 0‰ SMOW in the paleotemperature calculation, however, corrected paleotemperatures for the Choptank Formation do not alter the existing pattern of temperatures.
Past climate and the role of ocean heat transport: Model simulations for the Cretaceous
Authors: Barron Eric J. , Peterson William H. , Pollard David , Thompson Starley
Published: February 2008

A series of general circulation model experiments using Global Environmental and Ecological Simulation of Interactive Systems (GENESIS) were executed to evaluate the sensitivity of simulated mid‐Cretaceous climate to small perturbations in ocean heat transport. Three experiments were performed: (1) mixed layer ocean with no ocean heat transport, ZEROQ, (2) ocean heat transport specified as required for GENESIS to best match modern observations, ONEQ, and (3) doubled ocean heat transport, TWOQ. The ONEQ experiment represents an ocean heat transport which is actually about 15% of the values given by Carissimo et al. (1985) from modern observations. As a sensitivity experiment these model simulations represent a doubling of the role of the ocean. However, relative to the observations, they represent small perturbations to the total poleward heat transport in the model. With the exception of the tropics, no major changes in the structure of the general circulation of the atmosphere resulted from the modification of the ocean heat transport. However, relatively small increases in ocean heat transport resulted in a number of significant differences between simulations, including tropical cooling, polar warming, weakened equator‐to‐pole surface temperature gradients, weakened midlatitude jets, decreased land‐sea pressure contrast, and decreased midlatitude storminess. The experiments indicate that changes in ocean heat transport which are well within the realm of possibility for Earth history can have significant climatic impact. Although ocean heat transport may be a significant factor in explaining Cretaceous polar warmth, the changes specified in these experiments alone are not sufficient to explain the polar warmth of the Cretaceous.
Simplified ionospheric regional model for telecommunication applications
Authors: Zolesi Bruno , Cander Ljiljana R. , De Franceschi Giorgiana
Published: February 2008

A simplified model of the key ionospheric characteristics of vertical incidence such as fo F2 M(3000)F2, h′F, foF1, and f0E that are used for prediction of operational parameters of HF telecommunication systems in a restricted area has been developed. The simplified ionospheric regional model (SIRM), is based upon the Fourier analysis of the monthly median values of these characteristics from seven ionospheric stations in Europe. It is shown that only 12 dominant Fourier coefficients, expressed as a function of local time (LT), solar activity and geographic latitude are sufficient to reproduce the main features of the diurnal, seasonal, and solar cycle behavior of the mid‐latitude ionosphere under median conditions. The model is in a very suitable form for digital computer calculation of the characteristics for a given position, instant of time, and solar activity.
A computer simulation of the production of an artificially ionized layer using the Arecibo facility
Authors: Milikh G. M. , Hinds J. M. , Duncan L. M.
Published: February 2008

A computer model simulating the formation of an artificially ionized layer in the atmosphere by a series of microwave pulses was developed and is presented. A modified version of the kinetic theory of the breakdown of air by a powerful microwave emission was incorporated into a model of electromagnetic propagation through the atmosphere by a converging ionizing microwave pulse. This model takes into consideration radio wave self‐action as well as absorption and produces profiles of electron concentration formed in the atmosphere by both an isolated pulse and a series of pulses. Effects of varying the shape of the ionizing pulse are considered as well as the influence of the ambient electron concentration. Also, the dependence of the electron concentration on the energy and duration of the pulse is investigated. The possible increase in the rate of electron production is considered when using an intense pulse to initiate the breakdown followed by a series of pulses of lesser energy. The influence of the refraction of the microwave beam is estimated. The computer model presented shows that an artificial ionized layer of electrons reaching concentrations of the order of 108 cm−3 could be formed over a height range of 40–70 km, if the Arecibo antenna and radio facility were reconfigured so that it would be able to generate microwaves with f = 2.38 GHz and a power of approximately 1–4 MW. In addition, a pulse compressor would be used to form pulses with durations of approximately 0.1–0.15 μs with a repetition frequency of 103 Hz.
A 50‐MHz radio Doppler experiment for midlatitude E region coherent backscatter studies: System description and first results
Authors: Haldoupis C. , Schlegel K.
Published: February 2008

Contrary to equatorial and auroral electrojet plasmas, studies on scattering of VHF waves from midlatitude E region field‐aligned irregularities are limited, and the physics of the phenomena is not well understood. In this paper we provide first an update of the subject and then present a new experiment, denoted as Sporadic E Scatter Experiment (SESCAT), designed for high‐time resolution coherent backscatter measurements of 3‐m E region irregularities from a middle latitude location. The technique, which is used successfully in auroral latitudes for years, is capable of measuring the Doppler spectrum of the echoing signal at a fixed range with great accuracy. The experiment is a state of the art bistatic CW Doppler radar operating at 50.52 MHz with the transmitting and receiving arrays beaming northward to a region perpendicular to the Earth's magnetic field at the E region peak. The viewing area, determined by the narrow beam intersecting patterns and the field‐aligned character of the irregularities, is fixed at about 15×40 km2 and located over the southern Aegean at 30.8° invariant magnetic latitude (L = 1.35). First results show that 50‐MHz backscatter events, with snrs as large as 25 dB and lifetimes of several minutes to more than an hour, do exist at midlatitudes in accordance with previous experiments which related these echoes to sporadic E layers. The observed events, except for an early afternoon case, occurred during dark hours in the period between a few hours before and after local midnight. The backscatter can be continuous but in some events a quasi‐periodic behavior was found with periods between 2 and 10 min. Associated to the backscatter are symmetric narrow Doppler spectra with mean velocities in the ±80 m s−1 range and mean widths about 30 to 60 m sminus;1. In terms of spectrum width, the midlatitude E region echoes do not compare to the low‐velocity type 2 echoes observed in the equatorial and auroral electrojets. Finally, very strong meteor‐induced backscatter with abrupt onsets and short lifetimes up to 3 min were also detected. These echoes have relatively large velocities at onset and in one case an ion acoustic velocity component was seen briefly at 320 m s−1, suggesting that the Farley‐Buneman instability may also be functioning at times in the midlatitude E region.
Attenuation and countermeasures in millimeter‐wave point‐to‐multipoint networks
Authors: Jones S. M. R. , Watson P. A.
Published: February 2008

Whilst most propagation studies for line‐of‐sight links in the millimeter‐wave range have in the past concentrated on point‐to‐point performance prediction, this study is specifically directed to point‐to‐multipoint aspects, with a special interest in the possibility of using intelligent resource sharing techniques at the central node. Dual‐polarization radar data, covering a 2‐year period, are used to make predictions of attenuation and interference in the 20 to 50 GHz range for 1 to 20‐km radius networks employing either adaptive gain, adaptive time division multiple access, or both techniques combined.
Rigorous full‐wave analysis of electric and dielectric waveguides embedded in a multilayered bianisotropic medium
Authors: Olyslager F. , De Zutter D.
Published: February 2008

In this contribution we determine the eigenmodes propagated along structures consisting of a waveguide embedded in a general multilayered bianisotropic medium. This includes for example microstrips or strip dielectric waveguides on bianisotropic substrates. The analysis presented here is a generalization to bianisotropic layered media of the boundary integral equation technique described in previous publications for isotropic layered media. The set of integral equations is solved by a spectral domain technique. In this spectral technique the layered medium is taken into account by determining the scattering of plane waves in the layered medium. Hence the major part of this publication deals with the scattering of plane waves in a multilayered bianisotropic medium. The described analysis is illustrated with the dispersion curves for thick microstrip lines on various bianisotropic substrates.
Generation of ELF and VLF waves by a thermal instability excited in the HF heater‐modulated polar electrojet
Authors: Kuo S. P.
Published: February 2008

A thermal instability responding to the modulation of polar electrojet by HF heater as a potential efficient mechanism for the generation of ELF and VLF waves has been investigated. It is shown that a positive feedback through the electron‐neutral collisional heating process can cause the transient response of the plasma to the modulated HF heater to grow exponentially. Considering a sinusoidally modulated HF heater wave having its field amplitude proportional to | cosω1t/2 |, the threshold fields of the thermal instability under normal electrojet conditions are found to be about 1.6 V m−1 and 0.8 V m−1 for the o mode and x mode operation respectively. For a heater wave field of 2 V m−1, the instability can be excited by the x mode heater within a few milliseconds and also by the o mode heater but taking about 9 times as long.
Episodic reactivation of a Late Precambrian mylonite zone on the Gondwanan Margin of the Appalachians, southern Newfoundland
Authors: O'Brien B. H. , O'Brien S. J. , Dunning G. R. , Tucker R. D.
Published: February 2008

The Grand Bruit Fault Zone of southern Newfoundland is a fundamental structure within Late Precambrian basement on the Gondwanan margin of the Appalachian orogen. Within the fault zone, a sequence of structures documents changes in the sense of ductile displacement from (1) reverse dip slip, to (2) dextral strike slip, to (3) sinistral oblique slip, and, finally, to (4) dextral lateral offsets. Fault movements along this structure were punctuated by emplacement of a variety of plutons and minor intrusions which, when precisely dated, allow these movements to be bracketed at between 571 Ma and 564 Ma, 497 Ma and 427 Ma, 424 Ma and 420 Ma, and 421 Ma and 387 Ma, respectively. The tectonic evolution of the Gondwanan inlier of southern Newfoundland is mirrored, in large part, by the record of mylonite development within the Grand Bruit Fault Zone. These tectonic events are attributable to well‐constrained, regional orogenic events of both the Pan‐African and Appalachian cycles. Newly formed shear zones in the fault zone reactivate parts of much older faults of similar regional orientation and are, in some cases, kinematically indistinguishable from the ancestral structures. Integration of precise geochronological data with the sequence of overprinted fault structures demonstrates that, although the role of progressive deformation in shear zone development was important, the observed disposition of structures and rock units is primarily a function of polyorogenic accretion. As a multiple‐reactivated structural lineament in a Gondwanan basement inlier, the fault zone exerted fundamental control over the tectonic development of the leading edge of the convergent southeast margin of the orogen.
Eocene‐Oligocene tectonics and kinematics of the Rhine‐Saone Continental Transform Zone (eastern France)
Authors: Lacombe O. , Angelier J. , Byrne D. , Dupin J. M.
Published: February 2008

A tectonic analysis of brittle deformation was performed in the Rhine‐Saône transform in order to decipher and understand the deformation processes in a typical continental transfer zone. Cenozoic major and minor fault patterns are described, and brittle structures are interpreted in terms of paleostress orientations. The Eocene N‐S compression related to Africa‐Eurasia convergence is marked mainly by strike‐slip faults. It was followed by a major phase of crustal extension, mainly Oligocene in age, related to the west European rifting. This extensional phase is expressed by normal faults, tension gashes, and extensional strike‐slip faults which are especially abundant in the transform zone. These two events are found to be quite different in terms of distribution of horizontal stress trajectories. The trend of σ1 axes is very homogeneous for the N‐S compression, whereas σ3 orientations associated with the major extension vary from E‐W in most of the Rift system to NW‐SE within the transform zone. Finally, the Mio‐Pliocene tectonic emplacement of the Jura fold‐and‐thrust belt is marked in the field by strike‐slip faults associated with a well‐defined trend of σ1 oriented W‐NW‐E‐SE to NW‐SE. The preexisting basement fracture pattern between the grabens was also considered in order to estimate which faults were likely to have been reactivated during the Oligocene transform kinematics, and the theoretical shear motion on these inherited fault surfaces, when submitted to E‐W extension, was calculated. Left‐lateral/extensional reactivation of a preexisting 60°N trending fault system in the brittle upper crust is likely to have accommodated the shear strain arising between the rift segments in response to crustal stretching. Two independent numerical modelings, based on distinct element and finite element analyses, respectively, enabled us to verify and to refine the hypothesis of transform kinematics related to E‐W extension and inducing regional perturbations of extensional stress trajectories. The overall mechanism and the transtensional kinematics of the Rhine‐Saône transform zone are thus tightly constrained. The inherited crustal anisotropy, the large‐scale perturbations of extensional stress trajectories, and the development of distributed brittle deformation within the sedimentary cover are found to play a major role in the tectonic evolution of continental rift‐transform systems.
Crustal structure and reflectivity of the Swiss Alps from three‐dimensional seismic modeling: 2. Penninic Nappes
Authors: Litak R. K. , Marchant R. H. , Pfiffner O. A. , Brown L. D. , Sellami S. , Levato L. , Wagner J.‐J. , Olivier R.
Published: February 2008

Surface geological mapping, laboratory measurements of rock properties, and seismic reflection data are integrated through three‐dimensional seismic modeling to determine the likely cause of upper crustal reflections and to elucidate the deep structure of the Penninic Alps in eastern Switzerland. Results indicate that the principal upper crustal reflections recorded on the south end of Swiss seismic line NFP20‐EAST can be explained by the subsurface geometry of stacked basement nappes. In addition, modeling results provide improvements to structural maps based solely on surface trends and suggest the presence of previously unrecognized rock units in the subsurface. Construction of the initial model is based upon extrapolation of plunging surface structures; velocities and densities are established by laboratory measurements of corresponding rock units. Iterative modification produces a best fit model that refines the definition of the subsurface geometry of major structures. We conclude that most reflections from the upper 20 km can be ascribed to the presence of sedimentary cover rocks (especially carbonates) and ophiolites juxtaposed against crystalline basement nappes. Thus, in this area, reflections appear to be principally due to first‐order lithologic contrasts. This study also demonstrates not only the importance of three‐dimensional effects (sideswipe) in interpreting seismic data, but also that these effects can be considered quantitatively through three‐dimensional modeling.
Shallow magnetic inclinations in the Cretaceous Valle Group, Baja California: remagnetization, compaction, or terrane translation?
Authors: Smith Douglas P. , Busby Cathy J.
Published: February 2008

Paleomagnetic data from Albian to Turonian sedimentary rocks on Cedros Island, Mexico (28.2° N, 115.2° W) support the interpretation that Cretaceous rocks of western Baja California have moved farther northward than the 3° of latitude assignable to Neogene oblique rifting in the Gulf of California. Averaged Cretaceous paleomagnetic results from Cedros Island support 20 ± 10° of northward displacement and 14 ± 7° of clockwise rotation with respect to cratonic North America. Positive field stability tests from the Vizcaino terrane substantiate a mid‐Cretaceous age for the high‐temperature characteristic remanent magnetization in mid‐Cretaceous strata. Therefore coincidence of characteristic magnetization directions and the expected Quaternary axial dipole direction is not due to post mid‐Cretaceous remagnetization. A slump test performed on internally coherent, intrabasinal slump blocks within a paleontologically dated olistostrome demonstrates a mid‐Cretaceous age of magnetization in the Valle Group. The in situ high‐temperature natural remanent magnetization directions markedly diverge from the expected Quaternary axial dipole, indicating that the characteristic, high‐temperature magnetization was acquired prior to intrabasinal slumping. Early acquisition of the characteristic magnetization is also supported by a regional attitude test involving three localities in coherent mid‐Cretaceous Valle Group strata. Paleomagnetic inclinations in mudstone are not different from those in sandstone, indicating that burial compaction did not bias the results toward shallow inclinations in the Vizcaino terrane.
Stratigraphic interpretation of the Ordovician of the Appalachian Basin and implications for Taconian flexural modeling
Authors: Diecchio Richard J.
Published: February 2008

Models that reconcile the thicknesses of various Appalachian stratigraphic sequences in terms of subsidence associated with thrust loading are based on various assumptions about regional stratigraphy. Different assumptions, based on a different interpretation of Middle and Upper Ordovician stratigraphy, suggest that the geometry of lithospheric flexure due to Taconian thrust loading may have been different than predicted by existing models. Taconian flysch facies restricted to the eastern margin of the outcrop belt is the basis for identifying a thrust load‐induced foredeep. Coeval shallow marine facies were probably beyond the limit of thrust load influence. Stratigraphic thinning near the transition between the flysch and shallow marine facies is interpreted as a peripheral bulge and is located within the Valley and Ridge. Comparison is made with the Timor area north of Australia. Thrust load‐induced foredeeps and peripheral bulges predicted by this model are much narrower than predicted by previous models.
Experimental and Numerical Investigation of Soil Vapor Extraction
Authors: Fischer Ulrich , Schulin Rainer , Keller Martin
Published: February 2008

In recent years soil vapor extraction (SVE) has been used extensively to remove volatile organic compounds (VOCs) from the vadose zone. In order to investigate processes limiting the removal of VOCs during the later stages of SVE operations, multicomponent soil‐venting experiments were performed at different water contents in a sand tank (80 × 66 × 5 cm) in the absence of a liquid organic phase. Four chlorinated VOCs were used as the model compounds. A homogeneous packing of quartz sand was used as the model soil. Gas phase concentrations were measured at several locations with different water saturations during each experiment. The compounds did not adsorb onto the sand. Volatilization was the key process for VOC removal. Gas concentrations decreased more slowly at locations with high water saturation and for compounds having a small Henry's law constant. Gas concentrations observed for experiments conducted at low water content were found to be a function of dimensionless time. Tailing in gas concentration distributions at large dimensionless times was attributed solely to diffusion in interparticle water and suggested that local nonequilibrium conditions prevailed. This hypothesis was supported by numerical simulations based on the local equilibrium assumption (LEA) and a first‐order kinetics approach. For the experiments conducted at low water saturations the LEA was valid only for small dimensionless times. Tailing in the gas concentration distributions could then be described quite well by means of a first‐order kinetic approach using calibrated mass transfer coefficients.
Bayesian Estimation of Uncertainty in Runoff Prediction and the Value of Data: An Application of the GLUE Approach
Authors: Freer Jim , Beven Keith , Ambroise Bruno
Published: February 2008

This paper addresses the problem of evaluating the predictive uncertainty of TOPMODEL using the Bayesian Generalised Likelihood Uncertainty Estimation (GLUE) methodology in an application to the small Ringelbach research catchment in the Vosges, France. The wide range of parameter sets giving acceptable simulations is demonstrated, and uncertainty bands are presented based on different likelihood measures. It is shown how the distributions of predicted discharges are non‐Gaussian and vary in shape through time and with discharge. Updating of the likelihood weights using Bayes equation is demonstrated after each year of record and it is shown how the additional data can be evaluated in terms of the way they constrain the uncertainty bands.
Stochastic analysis of three‐phase flow in heterogeneous porous media: 1. Spectral/perturbation approach
Authors: Abdin Alaa E. , Kaluarachchi Jagath J.
Published: February 2008

Stochastic analysis of steady state three‐phase (water, oil, and air) flow in heterogeneous porous media was performed using the perturbation theory and spectral representation technique. The governing equations describing flow of water, oil, and air are coupled and nonlinear. The key stochastic input variables are intrinsic permeability, k, and the soil grain size distribution index, α. Three different stochastic combinations of these two input parameters were considered in the analysis. The spectral/perturbation approach was used to develop closed‐form expressions to describe stochastic variability of key output processes, such as capillary and individual phase pressures. The second paper of this two‐part series [Abdin and Kaluarachchi, this issue] will discuss the applicability and the validity of the spectral/perturbation technique to study the stochastic behavior of three‐phase flow using numerical simulations.
Analysis of temporal variations of the polarization of Venus observed by Pioneer Venus Orbiter
Authors: Knibbe Willem Jan J. , de Haan Johan F. , Hovenier Joop W. , Travis Larry D.
Published: February 2008

Time variations of the disk‐averaged polarization of Venus at wavelengths of 270, 365, 550, and 935 nm have been analyzed in terms of average haze optical thickness, cloud‐top pressure, and cloud absorption optical thickness at 270 nm (presumably due to gaseous SO2 absorption). The polarization data were deduced from observations made by the Pioneer Venus Orbiter between 1978 and 1990. Newton‐Raphson iteration was used to derive the atmospheric parameter values from these observations. The required multiple scattering calculations were performed using the adding/doubling method. The atmospheric model consists of a cloud layer and a haze layer. The cloud and haze particles are composed of a concentrated sulfuric acid solution and have an effective radius of 1.05 μm and 0.25 μm, respectively. It was found that the disk‐averaged haze optical thickness, cloud‐top pressure, and cloud absorption optical thickness at 270 nm varied irregularly between 1978 and 1990. No trends were identified for the cloud‐top pressure and cloud absorption optical thickness at 270 nm, but we did deduce a decrease in haze optical thickness during this 12 year period. Specific numbers are: (1) a haze optical thickness at 365 nm of about 0.25 in 1978 and less than 0.1 in 1990, (2) a cloud‐top pressure that varies between 5 and 20 mbar, and (3) a cloud absorption optical thickness that varies between 0.0 and 4.0. Finally, our analysis revealed that the disk‐averaged cloud‐top pressure and haze optical thickness behaved anomalously in 1983.
Salt marsh hydrology: Implications for biogeochemical fluxes to the atmosphere and estuaries
Authors: Nuttle William K. , Hemand Harold F.
Published: February 2008

Rates of gas emissions and solute fluxes from salt marsh sediments are influenced by sediment hydrology. A comprehensive water balance study in a New England salt marsh reveals that evapotranspiration and infiltration during tidal inundation and precipitation are the dominant hydrological processes in the sediment on a marsh‐wide scale. Water loss by drainage through the sediment into tidal creeks is effectively limited to within 10 m to 15 m of the creek bank; however, drainage is responsible for 40% of the water loss within 10 m of the creek during nonflooding, neap tide periods. The rate and extent of advective transport by pore water drainage is controlled by the topography of the marsh surface. Tidal fluctuations in creek level drive larger, oscillating water fluxes across the creek bank, which results in a dispersive transport of the solutes in the sediment, but these fluxes are attenuated in the first meter. Convexities in the marsh surface, for example, the crests of the creek banks, are the location of maximum water loss by drainage and probably the highest degree of desaturation and aeration, which can, in turn, increase gas emissions locally. The spring‐neap tide cycle modulates wetting and drying of the sediment and, by inference, gas emissions in the interior of the marsh. The limited extent of solute transport by drainage implies that an as yet undescribed mechanism is responsible for controlling the concentration of conservative solutes in salt marshes.
Cycling of dissolved rare earth elements in Chesapeake Bay
Authors: Sholkovitz E. R. , Elderfield H.
Published: February 2008

The measurement of dissolved rare earth elements (REE) in the surface waters, water column of anoxic basins, and pore waters in Chesapeake Bay has provided new insights to the biogeochemistry and estuarine chemistry of REE. All dissolved REE from the riverine source show large‐scale removal in the lower salinity zone (0‐10‰). The shale‐normalized pattern of dissolved Susquehanna River water is opposite in form to that of surface sediments in the Bay. The former is enriched in heavy REE (HREE) while the latter are enriched in light REE (LREE). Neither component has a flat pattern normally assumed for river‐ transported REE to the ocean. The dissolved LREE (i.e., La, Ce, Nd, Sm, and Eu) are enriched 3 to 9 times) in the oxygen‐depleted deep waters over their concentrations in the oxic surface waters. In contrast, HREE (Er, Yb, and Lu) are slightly depleted. All REE concentrations in the two surface (0‐2 cm) pore waters are greatly enriched (8‐17 times; 43 times for Ce) relative to oxygen‐depleted bottom waters and have relative abundances opposite to those of their sediments. While Ce has a positive anomaly in the pore waters, negative anomalies exist in the oxygen‐depleted bottom waters. The REE are participating in a set of complex biogeochemical cycles within the water column and surface sediments. Fractionation of REE during these cycles leads to the preferential enrichment of LREE in the seasonally oxygen‐depleted bottom waters. It is proposed that this fractionation is coupled to redox cycles of Mn and Fe and the interaction of dissolved REE with suspended particles and surficial sediments.
Measurements and interpretation of δ13C of methane from termites, rice paddies, and wetlands in Kenya
Authors: Tyler Stanley C. , Zimmerman Patrick R. , Cumberbatch Colin , Greenberg James P. , Westberg Curtis , Darlington Johanna P. E. C.
Published: February 2008

Ratios of 13C/12C have been measured in methane from a variety of sources in tropical Kenya. Ranges of δ13C in CH4 for termites (most values range from −56 to −64‰, one is at −44‰ one is at ∼−73‰), rice paddies (range −57 to −63‰), and wetlands (range −45 to − 50‰ for Lake Baringo, ∼−55‰ in the Moloi River, ∼−62‰ and ∼−31‰ in two swamp areas) are presented. The data are interpreted with the help of additional measurements of δ13C of CO2 gas, and organic carbon in plant material, termite bodies, and termite fungus combs. The implications of these findings are related to the problem of studying the atmospheric methane budget.