bluuebunny/crossref_metadata_2025 huggingface dataset:
Crustal shortening and Eocene extension in the southeastern Canadian Cordillera: Some thermal and rheological considerations
Authors: Liu Mian , Furlong Kevin P.
Published: February 2008

Metamorphic core complexes in the southeastern Canadian Cordillera were formed during Eocene crustal extension, shortly (within a few millions of years) after Late Jurassic‐Paleocene crustal shortening. Thermal‐rheological modeling, constrained by geological and geochronological studies of the Valhalla core complex and other core complexes in this region, is used to investigate two major problems concerning the formation of these core complexes: (1) the dynamic links between crustal shortening and extension and (2) the cooling history and unroofing rates during extension. Thermal‐rheological effects associated with crustal shortening are integrated through the history of crustal compression, since crustal shortening in this region was a long and slow process and cannot be treated as an instantaneous event. Our results suggest that crustal shortening may have played an important role in Eocene extension in the southeastern Canadian Cordillera by (1) producing a thickened and therefore unstable crust and (2) thermally weakening the lithosphere. However, heat generated by crustal shortening is not enough to account for the thermal state of the Valhalla complex, and additional heat sources at depth may be necessary. We then investigate thermal evolution during extension in both a simple shear model and a progressive pure stretching model. We show that the geotherm in an extensional region is time‐and space‐dependent and is affected by many variables including the preextensional thermal history and the mode of extension. Thus caution needs to be exercised when inferring unroofing rates from thermochronologic data. The cooling history of the Valhalla core complex may be explained by unroofing at rates of 1–2 mm/yr.
Evolution of a conjugate passive margin pair in Mesozoic southern Turkey
Authors: Dilek Yildririm , Rowland Joel C.
Published: February 2008

In the western Tauride belt of southern Turkey, a north pointing cusp (Isparta Angle) occurs along the Mesozoic carbonate axis and encompasses passive continental margin sequences, rift assemblages, mantle peridotites, an ophiolite complex, and platform fragments. The contacts between these tectonostratigraphic units are commonly tectonic with the carbonate platforms forming the autochthonous basement to the west and east directed thrust sheets both in the west and the east. Rift assemblages consist of chert, pelagic limestone, mudstone, sandstone, and alkaline lavas ranging in age from Upper Triassic to Upper Cretaceous and locally include serpentinite lenses. Mantle peridotites are commonly harzburgitic, cut by numerous doleritic dikes, and underlain by a syntectonic mélange. The ophiolite complex occurs in the south, adjacent to and overlying the western platform (Bey Daglari), and consits mainly of peridotites and cumulate gabbros with a poorly developed dike complex and rare extrusive rocks. Platform fragments are represented by north‐south trending slivers of limestones that have affinity with the western platform. They are technically overlain by the rift assemblages and/or mantle rocks within the Isparta Angle. Rock types and associated structures within the Isparta Angle indicate a progressive evolution from continental rifting and passive margin development to ocean basin formation in the Tauride belt of the Neotethyan realm during Triassic to Late Cretaceous time. The pronounced asymmetry in the crustal architecture of the conjugate margins suggests that initial stages of rifting and subsequent extension were probably facilitated by crustal failure along an east dipping (in present coordinates) low‐angle fault. Continued rifting and associated crustal thinning resulted in upwelling and emplacement of the mantle beneath the lower plate and in partial melting of this elevated mantle generating alkaline lavas. Further extension in the south established a spreading system along which Cretaceous oceanic crust, now represented by the Tekirova ophiolite, was created. Contractional deformation in Late Cretaceous to Late Tertiary time caused telescoping of rock units within the Isparta Angle and emplacement of thrust sheets onto the platform carbonates both in the east and the west. The opening and closure stages of the ocean basin within the Isparta Angle were diachronous while the bounding carbonate platforms were probably revolved around a pivoting pole located at or near the apex of this sharp bend in the Tauride belt.
Evidence and mechanisms for forearc extension at the accretionary Costa Rica Convergent Margin
Authors: McIntosh Kirk , Silver Eli , Shipley Thomas
Published: February 2008

Seismic reflection data across the upper trench slope off the Nicoya Peninsula, Costa Rica, reveal a wide zone of nearly trench‐parallel normal faults. Although work in the last decade has shown that normal faults are present at many convergent margins, most examples (e.g., Japan, Peru‐Chile, and Guatemala) have been associated with margins experiencing subduction erosion or non‐accretion. In contrast, extension in the Costa Rica study area apparently is coeval with frontal accretion and underplating. The normal faults across the Costa Rica forearc are striking in seismic section due to the well‐layered, 2‐km‐thick upper slope apron. Fault plane reflections and reflector terminations show that the faults extend through the sedimentary apron and apparently into the underlying accretionary prism, indicating a deep‐seated deformation process. The zone of extension is from the midslope area to within 10 km of the shelf edge, a minimum width of about 20 km; the estimated extension across the zone is at least 1.5 to 3 km. Within the apron section, spacing between the faults is generally 200–500 m, and nominal fault dip is 20°–40° and predominantly landward. Activity on the normal faults appears to have occurred over a significant period of time based on increased displacement with depth and on fault‐controlled sedimentary thickening. At least some of the faults may be presently active; shallow reflectors and possibly the seafloor are displaced by faulting. Contemporary sediment accretion is documented by the same seismic reflection profiles showing offscraping and underplating near the toe of the wedge and out‐of‐sequence thrusting primarily below the midslope area. The consistent landward normal fault dip may be influenced by structural anisotropy in the prism and possible extensional reactivation of earlier thrust faults associated with accretion processes. With the available data it is not possible to conclusively determine the cause of the stress field leading to the upper prism and apron extension. However, the three most likely causes are underplating, changes in basal shear stress, or a brief episode of subduction erosion.
A model for water transport and ice lensing in freezing soils
Authors: Konrad J.‐M. , Duquennoi C.
Published: February 2008

A one‐dimensional model for water transport and ice lensing in incompressible saturated and solute‐free soil specimens is proposed for the simulation of small‐scale frost heave tests in the laboratory. The model considers (1) open‐system freezing in which the variables T and Pw are independent, (2) an ice lens that continues to grow as long as enough energy is available in the frozen fringe to produce the work required for mass transfer to the ice lens, and (3) a new ice lens that forms when the vertical strain in the frozen soil reaches the instantaneous tensile failure strain. The proposed frost heave model is amenable to computer simulation procedures which provide predictions of rate of frost heave and rate of pore freezing front penetration as functions of applied load, thermal and water flow regimes, and soil properties. Position, time of initiation, and ultimate thickness of individual ice lenses emerge also as a part of the solution. A quantitative comparison of observed and simulated responses for various boundary conditions is shown for a reference soil known as Devon silt. The model was found to exhibit many of the characteristics observed in frost heave tests on Devon silt and predicted the effects of overburden pressure on frost heave rate.
Mean flow and turbulence fields over two‐dimensional bed forms
Authors: Nelson Jonathan M. , McLean Stephen R. , Wolfe Stephen R.
Published: February 2008

Detailed laser‐Doppler velocity and Reynolds stress measurements over fixed two‐dimensional bed forms are used to investigate the coupling between the mean flow and turbulence and to examine effects that play a role in producing the bed form instability and finite amplitude stability. The coupling between the mean flow and the turbulence is explored in both a spatially averaged sense, by determining the structure of spatially averaged velocity and Reynolds stress profiles, and a local sense, through computation of eddy viscosities and length scales. The measurements show that there is significant interaction between the internal boundary layer and the overlying wake turbulence produced by separation at the bed form crest. The interaction produces relatively low correlation coefficients in the internal boundary layer, which suggests that using local bottom stress to predict bed load flux may not only be erroneous, it may also disregard the essence of the bed form instability mechanism. The measurements also indicate that topographically induced acceleration over the bed form stoss slope has a more significant effect in damping the turbulence over bed forms than was previously supposed, which is hypothesized to play a role in the stabilization of fully developed bed forms.
Stochastic Analysis of Transport and Decay of a Solute in Heterogeneous Aquifers
Authors: Miralles‐Wilhelm F. , Gelhar L. W.
Published: February 2008

A stochastic analysis of transport and first‐order decay for a solute plume in a three‐dimensionally heterogenous aquifer shows that a spatially variable decay rate produces effects both in the transient and steady state characteristics of the effective decay rate, effective solute velocity, and longitudinal macrodispersivity. The effective decay rate is found to be less than the mean, which implies that decay predictions that employ spatial averages of observations will tend to overestimate the rates of mass transformation due to decay. The effective solute velocity is found to be the only field scale coefficient dependent on the correlation between decay and log hydraulic conductivity. The longitudinal macrodispersivity is found to be reduced relative to that of a conservative/nondecaying solute. The characteristic timescale of the transient development of all field‐scale coefficients is reduced by the presence of a heterogeneous decay rate. All of these trends are accentuated with increasing decay rate variability. Increased peak concentrations, earlier arrival times, and decreased plume spreading are practical consequences of the derived results. The stochastic analysis presented here provides a vehicle to link laboratory‐scale measurements with these field‐scale predictions.
Connectivity of random fault networks following a power law fault length distribution
Authors: Bour Olivier , Davy Philippe
Published: February 2008

We present a theoretical and numerical study of the connectivity of fault networks following power law fault length distributions, n(l) ∼ αl−a, as expected for natural fault networks. Different regimes of connectivity are identified depending on a. For a > 3, faults smaller than the system size rule the network connectivity and classical laws of percolation theory apply. On the opposite, for a < 1, the connectivity is ruled by the largest fault in the system. For 1 < a < 3, both small and large faults control the connectivity in a ratio which depends on a. The geometrical properties of the fault network and of its connected parts (density, scaling properties) are established at the percolation threshold. Finally, implications are discussed in the case of fault networks with constant density. In particular, we predict the existence of a critical scale at which fault networks are always connected, whatever a smaller than 3, and whatever their fault density.
A systematic analysis of eight decades of incipient motion studies, with special reference to gravel‐bedded rivers
Authors: Buffington John M. , Montgomery David R.
Published: February 2008

Data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size,
. Calculated
. values were stratified by initial motion definition, median grain size type (surface, subsurface, or laboratory mixture), relative roughness, and flow regime. A traditional Shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition;
. values determined from reference bed load transport rates and from visual observation of grain motion define subparallel Shields curves, with the latter generally underlying the former; values derived from competence functions define a separate but poorly developed field, while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous, rather than time‐averaged, critical shear stresses. The available data indicate that for high critical boundary Reynolds numbers and low relative roughnesses typical of gravel‐bedded rivers, reference‐based and visually based studies have
ranges of 0.052–0.086 and 0.030–0.073, respectively. The apparent lack of a universal
for gravel‐bedded rivers warrants great care in choosing défendable
values for particular applications.
The shallow oxygen maximum in the tropical Atlantic Ocean (Guinea Dome Area): Physical or biological origin?
Authors: Oudot Claude
Published: February 2008

The Guinea Dome area (12°N, 22°W) is characterized by a summertime O2 maximum which lies at the top of the thermocline. The vertical distributions of molecular nitrogen and argon are used to discuss the physical and biological contributions to oxygen supersaturation in that region. Whereas this subsurface O2 maximum is as sharp as those encountered elsewhere in the ocean, it is not at a high supersaturation level (maximum 4.4% on average). Thus the O2 maximum does not seem to be mainly due to photosynthesis and hence Reid's [1962] physical hypothesis appears to be like the major explanation.
Sources and routing of the Amazon River Flood Wave
Authors: Richey Jeffrey E. , Mertes Leal A. K. , Dunne Thomas , Victoria Reynaldo L. , Forsberg Bruce R. , Tancredi Antônio C. N. S. , Oliveira Eurides
Published: February 2008

We describe the sources and routing of the Amazon River flood wave through a 2000‐km reach of the main channel, between São Paulo de Olivença and Obidos, Brazil. The damped hydrograph of the main stem reflects the large drainage basin area, the 3‐month phase lag in peak flows between the north and south draining tributaries due to seasonal differences in precipitation, and the large volume of water stored on the floodplain. We examined several aspects of the valley floor hydrology that are important for biogeochemistry. These include volumes of water storage in the channel and the floodplain and the rates of transfer between these two storage elements at various seasons and in each segment of the valley. We estimate that up to 30% of the water in the main stem is derived from water that has passed through the floodplain. To predict the discharge at any cross section within the study reach, we used the Muskingum formula to predict the hydrograph at downriver cross sections from a known hydrograph at upstream cross‐sections and inputs and outputs along each reach. The model was calibrated using three years of data and was successfully tested against an additional six years of data. With this model it is possible to interpolate discharges for unsampled times and sites.
Pattern of particulate nitrogen transport in world rivers
Authors: Ittekkot Venugopalan , Zhang Shuo
Published: February 2008

Samples from several major world rivers were analyzed for their particulate nitrogen (PN) contents, C/N ratios, and total particulate amino acid (TPAA) contents. The results show a global PN transport of 33 × 1012 g N yr−1, more than 80% of which occurs in rivers carrying high suspended matter concentrations such as the Ganges, Brahmaputra, Mekong, and Huanghe. Quantitatively, nitrogen transported in the particulate fraction exceeds that reported for dissolved inorganic nitrogen. The bulk of the PN transport is associated with material having relatively low C/N ratios and low TPAA contents. TPAA accounted for about 20% of the total PN transport. Although natural processes leading to high rates of erosion in Asian rivers might have partly contributed to the observed PN transport pattern, our results suggest that human activities such as deforestation and increased use of nitrogen fertilizer in their drainage basins are also an important factor. The biogeochemical nature of the remaining 80% is only poorly known, but should be of relevance in studying the response of estuaries and coastal seas to human activities in the terrestrial environment.
Consumption of atmospheric methane in soils of central Panama: Effects of agricultural development
Authors: Keller Michael , Mitre Martin E. , Stallard Robert F.
Published: February 2008

Laboratory and in situ measurements of soil methane consumption in a moist forest area of central Panama indicate that the conversion of forests to agricultural lands diminishes the soil sink for atmospheric methane. Rates of microbial methane consumption in agricultural soils were one fourth those of undisturbed forest soils. This reduction in soil methane consumption may partially account for past and future increases in atmospheric methane concentrations.
Helicopter launching of surface and sea‐bed drifters
Authors: Paskausky D. F. , Nalwalk A. J. , Murphy D. L. , Kollmeyer R. C.
Published: February 2008

The semi‐enclosed nature of Long Island Sound makes it ideal for surface and sea‐bed drifter studies. A U.S. Coast Guard H‐3 helicopter provided a “synoptic” launch within a half tidal cycle. Drifter releases were conducted on 18 June 1973 at a total of 50 stations in Long Island and Block Island Sounds. Drops were made at various altitudes and speeds in order to determine optimum release conditions.
Post‐shock spikes: A new feature of proton and alpha enhancements associated with an interplanetary shock wave
Authors: Gloeckler G. , Ipavich F. M. , Fan C. Y. , Hovestadt D.
Published: February 2008

Abrupt and prolonged enhancements in the intensities of 100 to ∼2000 keV/nucleon protons and alpha particles observed in interplanetary space are interpreted as particle populations confined between an interplanetary shock front and a magnetic field discontinuity. Prominent intensity “spikes” observed only below ∼400 keV per charge for both protons and alpha particles several hours behind the shock front suggest that some fraction of the confined particles is accelerated by an energy per charge dependent process.
Deep lunar interior inferred from recent seismic data
Authors: Nakamura Yosio , Latham Gary , Lammlein David , Ewing Maurice , Duennebier Frederick , Dorman James
Published: February 2008

Analysis of recent lunar seismic data from distant meteoroid impacts, high‐frequency teleseismic events and deep moonquakes shows several significant deviations of P‐ and S‐wave travel times from those expected if the lunar interior were homogeneous below the crust. These data are interpreted resulting in a lunar model consisting of at least four and possibly five distinguishable zones: (I) the 50 to 60 km thick crust characterized by seismic velocities appropriate for plagioclase‐rich materials, (II) the 250 km thick upper mantle characterized by seismic velocities consistent with an olivine‐pyroxene composition, (III) the 500 km thick middle mantle characterized by a high (0.33 ‐ 0.36) Poisson's ratio, (IV) the lower mantle characterized by high shear‐wave attenuation and possibly (V) a core of radius between 170 and 360 km characterized by a greatly reduced compressional wave velocity.
Plasma wave turbulence at distant crossings of the plasma sheet boundaries and the neutral sheet
Authors: Scarf F. L. , Frank L. A. , Ackerson K. L. , Lepping R. P.
Published: February 2008

The orbit of IMP 7 frequently takes the spacecraft across the neutral sheet in the geomagnetic tail at a downstream distance of about 35 Re. In this preliminary report we discuss the detection of strong low frequency electromagnetic signals and moderate electrostatic noise enhancements near local midnight. We use data from a substorm period on October 28, 1972 when there were multiple crossings of the neutral sheet and the boundary of the plasma sheet.
Shear wave birefringence in dilating granite
Authors: Bonner B. P.
Published: February 2008

Laboratory observations of ultrasonic shear waves indicate splitting along the direction of minimum principal stress of ∼11% for confined (20 MPa) and ∼16% for unconfined specimens of Westerly granite loaded in uniaxial stress. Dilatant strains increase birefringence except at > 80‐90% of the ultimate strength, when processes related to shear failure apparently become important. If seismic birefringence observed in the field can be related to anisotropic dilatant strains, these laboratory measurements of precursory velocity changes should prove useful in predicting earthquakes.
Ice particulates in the mesosphere
Authors: Chesworth E. T. , Hale L. C.
Published: February 2008

The observations of noctilucent clouds, the measurements of hydrated and of large immobile ions, and the light‐scattering layer detected by the OGO‐6 satellite suggest the presence of particulates, probably ice, in the mesosphere. The correlation between temperature and positive ion conductivity where the vapor pressure over ice becomes greater than atmospheric pressure in the stratopause region indicates the presence of ice crystals throughout the mesosphere over a wide range of latitudes during all seasons. Between 109 and 1010 ice crystals per m³ of order 10 nanometers in diameter can dominate ionization loss processes in the mesosphere, and can explain a variety of experimental observations, including observed solar angle dependence and seasonal variability of electron density.
Rapidly accumulating manganese deposit from the Median Valley of the Mid‐Atlantic Ridge
Authors: Scott Martha R. , Scott Robert B. , Rona Peter A. , Butler Louis W. , Nalwalk Andrew J.
Published: February 2008

A manganese oxide crust from an extensive deposit in the median valley of the Mid‐Atlantic Ridge was found to be unusually high in manganese (up to 39.4% Mn), low in Fe (as low as .01% Fe), low in trace metals and deficient in Th230 and Pa231 with respect to the parent uranium isotopes in the sample. The accumulation rate is 100 to 200 mm/106 y, or 2 orders of magnitude faster than the typical rate for deep‐sea ferromanganese deposits. The rapid growth rate and unusual chemistry are consistent with a hydrothermal origin or with a diagenetic origin by manganese remobilized from reduced sediments. Because of the association with an active ridge, geophysical evidence indicative of hydrothermal activity, and a scarcity of sediment in the sampling area, we suggest that a submarine hot spring has created the deposit.
Lunar evolution: The first 600 million years
Authors: Husain Liaquat , Schaeffer O. A.
Published: February 2008

From a stepwise‐heating experiment to neutron‐irradiated samples of whole rock and a plagioclase separate, we have determined an 40Ar ‐ 39Ar age of 4.26 ± 0.02 G.y. for the Apollo 17 troctolite 76535. This rock is believed to have formed as a result of very slow cooling at a depth of 10 ‐ 40 km, and hence furnishes direct evidence that the moon was chemically zoned before 4.26 G.y. The age of the rock is associated with the Serenitatis Basin forming event. The age of formation of the Serenitatis Basin is then deduced at 4.26 ± 0.02 G.y. ago, about 300 million years before the Imbrium event. It appears that the major basin forming era on the near side of the moon lasted longer than 300 million years. The grouping of many lunar rock ages at 3.9 ‐ 4.0 G.y. is most likely due to the fact that the Imbrium ejecta predominates all highland landing sites.
H2SO4‐HNO3‐H2O ternary aerosol formation mechanism in the stratosphere
Authors: Kiang C. S. , Cadle R. D. , Yue Glenn K.
Published: February 2008

An order‐of‐magnitude calculation of the characteristic time required for the homogeneous heteromolecular nucleation of new stratospheric particles involving the H2SO4‐HNO3‐H2O ternary system is presented. This characteristic time is compared with the characteristic time required for the homogeneous heteromolecular nucleation of sulfuric acid particles involving the H2SO4‐H2O binary system and with the characteristic time for the sulfuric acid vapor condensing on the preexisting particles. From the comparison of these characteristic times, we show that this formation of new particles involving H2SO4 ‐HNO3‐H2O may be the most favorable mechanism for the formation of “sulfuric acid particles” in the stratosphere.
A model of the Venus ionosphere
Authors: Nagy A. F. , Liu S. C. , Donahue T. M. , Atreya S. K. , Banks P. M.
Published: February 2008

Results of model calculations of the Venus ionosphere covering the altitude range from 120 km to 300 km are presented. The chemical scheme and the reaction rates adopted for the model are the same as given in a recent paper by Kumar and Hunten [1974], except that the electron temperature dependence of the dissociative recombination rates is taken into account. The calculations were carried out for ‘low’ and ‘high’ atomic oxygen models, corresponding to an [O]/[CO2] ratio of 0.4 percent and 4 percent respectively at 140 km. The results of the calculations agree well in both shape and magnitude with the Mariner 5 and 10 occultation results in the chemically controlled region; at the higher altitudes reasonable agreement with the observation is obtained if diffusive equilibrium and high vertical flow velocities (10 km/sec) are assumed as upper boundaries for the Mariner 5 and 10 conditions, respectively, although solar wind‐ionosphere interactions are the likely controlling mechanism for the Mariner 10 case.
Statistical evidence of tropospheric mid‐latitude tropical interactions
Authors: Miller A. J. , Gruber A.
Published: February 2008

Utilizing the daily analyzed zonal and meridional wind components at 200 mb for the year 1970 (available from the tropical analysis program of the National Meteorological Center) daily estimates of the meridional eddy momentum transfer have been computed at 33, 29, 24, 20, 15, 10, 5 and 0°N. The momentum transfers were then subjected to conventional spectrum analysis and the results indicate a coherent relationship from 33N into the subtropics at 14–16 and 4.35 days. This suggests a form of mid‐latitude tropical interaction that should be considered in investigation of tropical variations at these periods.
Lidar observations of a stratospheric dust cloud layer in the tropics
Authors: Fegley Ronald W. , Ellis Howard T.
Published: February 2008

A transparent whitish cloud veil was observed over Hawaii from early October throughout January 2, 1975, the date of submission of this paper. Lidar measurements made from the Mauna Loa Observatory during this period established the height of the layer at about 19.5 km MSL with a typical thickness at half maximum of 800 meters. The nearest Rawinsonde data clearly indicated this height to be above the tropopause. During the month of November, a stratospheric layer was observed by several other workers in the United States which has been attributed to the eruption of Fuego volcano in Guatemala during the month of October. However, the backscatter coefficient observed in the layer over Hawaii was occasionally 20 times greater than that observed at other locations. Although our data support the volcanic hypothesis, there are still some unanswered questions. For example, we observed the layer prior to the major eruption period and the time of appearance of the layer over other observatories in the United States. Furthermore, high altitude aircraft were operating in the stratosphere over Hawaii during the first two weeks of October which may have influenced the cloud formation.
Westward ionospheric currents over the dip equator during geomagnetic disturbances
Authors: Rastogi R. G.
Published: February 2008

During geomagnetic disturbed periods, the q type of sporadic E layer near the dip equator is shown to disappear with maximum error of five minutes during the period when the difference of the geomagnetic H field between the equatorial and non‐equatorial station decreases below the night level. These periods are identified with the reversal to westward direction of the electrojet currents at the base of the E region around 100 km level irrespective of the changes in the Sq current system which might be produced by the disturbance.
The chemistry of atmospheric bromine
Authors: Wofsy Steven C. , McElroy Michael B. , Yung Yuk Ling
Published: February 2008

Bromine may act as a catalyst for recombination of ozone and could be more efficient than either nitric oxide or chlorine. The lower atmosphere contains small concentrations of gaseous bromine produced in part by marine activity, in part by volatilization of particulate material released during the combustion of leaded gasoline, with an additional contribution due to the use of methyl bromide as an agricultural fumigant. Observations by Lazrus et. al. (1975) indicate small concentrations of bromine, ∼ 10−11 (v/v) in the contemporary stratosphere and appear to imply a reduction of approximately 0.3% in the global budget of O3. Estimates are given for future reductions in O3 which might occur if the use of CH3Br as an agricultural fumigant were to continue to grow at present rates.
Twilight transition spectra of atmospheric O2 Ir emissions
Authors: Baker Doran , Steed Allan , Huppi Ronald , Baker Kay
Published: February 2008

Resolved spectra have been obtained from the ground of the O2(a¹Δg) emissions from the upper atmosphere utilizing a wide‐field interferometer with a cryogenically cooled germanium detector. The rotational structure of both the (0, 0) band at 1.27 µm and the (0, 1) band at 1.58 µm are clearly separable from the hydroxyl airglow. The decay rate of the O2(a¹Δg) during the twilight transition has been observed.
Atomic nitrogen measurements in the upper atmosphere
Authors: Mauersberger K. , Engebretson M. J. , Potter W. E. , Kayser D. C. , Nier A. O.
Published: February 2008

The open source neutral mass spectrometer (OSS) on the Atmosphere Explorer‐C satellite (AE‐C) measures the neutral constituents of the upper atmosphere. It has been found that atomic nitrogen densities can be determined at altitudes above 380 km. Most of the nitrogen atoms combine with oxygen adsorbed on the walls of the ion source to form NO. The measured net peaks at 14 amu and 30 amu show the scale height expected for atomic nitrogen; both peaks have a pronounced diurnal variation. We computed absolute number densities at 400 km for a time period between February and April 1974 when measurements were taken in the northern hemisphere. Minimum and maximum densities of atomic nitrogen occur between 4 and 6 hr LST in the morning and around 16 hr LST in the afternoon, respectively. At 400 km the minimum particle density is 1.0 × 105 cm−3 and the maximum density 1.5 × 106 cm−3. In contrast to the response of N2 to geomagnetic activity, atomic N shows no appreciable effect.
Mathematical representation of the auroral oval
Authors: Holzworth R. H. , Meng C.‐I.
Published: February 2008

A curve fitting procedure for mathematically representing the auroral oval is described. It is shown that the Feldstein ovals and quiet auroral ovals of the night side in DMSP photographs can be approximated by an offset circle, plus a small (≲ 1° magnitude) Fourier component in corrected geomagnetic coordinates. Parameters are introduced, Θ and (θo, ϕo), that indicate the dynamic motion of the auroral oval size and center location, respectively. Using the parameter Θ, an analysis of several DMSP photographs shows a strong correlation between the southward interplanetary magnetic field (−Bz) and the size of the auroral oval.
On the stability of open hydraulic fractures in the Earth's crust
Authors: Secor Donald T. , Pollard David D.
Published: February 2008

It has been suggested that a substantial amount of heat energy could be extracted from dry hot rocks near the earth's surface by circulating a fluid through large hydraulic fractures. However a theoretical analysis of propagation and closure of hydraulic fractures subject to realistic stress gradients indicates an upper limit for the size of a stable fracture. For example, if the vertical gradient of the least principal stress exceeds the unit weight of the fluid by ∼100 dynes/cm³ a stable vertical fracture in granite held open by fluid pressure may not be more than ∼2 × 104 cm high. This limit should be taken into account in the design of dry hot rock heat recovery systems.
New cross sections for the absorption of near ultraviolet radiation by nitrous oxide (N2O)
Authors: Johnston H. S. , Selwyn G. S.
Published: February 2008

A re‐investigation of the ultraviolet absorption spectrum of nitrous oxide (N2O) agrees with previous results in the range 210 to 235 nm, but contrary to previous results it indicates a vanishingly small cross section above 260 nm. The absence of the relatively long wave length absorption implies a negligible rate of photolysis of nitrous oxide in the troposphere. These results plus the previously estimated atmospheric mean residence times of N2O indicate that there is a large, unknown tropospheric sink for nitrous oxide.
Demonstration of 26 Mg excess in Allende and evidence for 26 Al
Authors: Lee Typhoon , Papanastassiou D. A. , Wasserburg G. J.
Published: February 2008

We report the discovery of a large anomaly in the isotopic composition of Mg in a Ca‐Al rich chondrule from the Allende meteorite. This anomaly is manifest independently of instrumental fractionation and is due to an enrichment of about 1.3 percent in 26Mg while the abundances of 25Mg and 24Mg are terrestrial in value. There is a strong correlation in this chondrule between the 26Mg excess and the Al/Mg ratio so that the most plausible cause of the anomaly is the in situ decay of now extinct 26Al (τ½ = 0.72 × 106 yr). Mineral phases extracted from a Ca‐Al‐rich aggregate have distinct Al/Mg but show identical, small Mg anomalies which are apparent after correction for fractionation (δ26Mg = 0.3%). These data indicate that this aggregate was isotopically homogenized in a high Al/Mg environment after the decay of 26Al had occurred or that some of the Mg anomalies are due to effects other than in situ decay of 26Al.
Observations of interaction regions and corotating shocks between one and five AU: Pioneers 10 and 11
Authors: Smith Edward J. , Wolfe John H.
Published: February 2008

Interaction regions between adjacent solar wind streams have been identified between 1 and 5 AU using Pioneer 10 and 11 magnetic field and plasma measurements. Beyond 1 AU, a relatively large fraction of the interaction regions have been found to be accompanied by either forward shocks, reverse shocks, or shock pairs. The observations are consistent with previous theoretical proposals that the interaction between adjacent streams leads to the development of corotating interplanetary shocks.
Recombination of NO+ in the ionosphere
Authors: Torr D. G. , Torr M. R. , Walker J. C. G. , Brace L. H. , Brinton H. C. , Hanson W. B. , Hoffman J. H. , Nier A. O. , Oppenheimer M.
Published: February 2008

The rate coefficient for dissociative recombination of NO+ with electrons is determined as a function of electron temperature using a large sample (∼3000) of simultaneous measurements of ion and neutral concentrations and temperatures made by the Atmosphere Explorer‐C satellite at night. The derived recombination coefficient can be represented by the expressions

urn:x-wiley:00948276:media:grl316:grl316-math-0001
for 1000 < Te < 2500°K and

urn:x-wiley:00948276:media:grl316:grl316-math-0002
for 700 ≤ Te ≤ 1000°K where the uncertainty values apply to the temperature dependence of α. The uncertainty value in the coefficient should be used with the uncertainty value with the same sign in the exponent in going from the lower to the higher temperature regime. The uncertainty in the absolute value of α is about ±30%, i.e., the α vs. Te curve may be shifted by ±30%.
A direct measurement of the winter helium bulge
Authors: Mauersberger K. , Potter W. E. , Kayser D. C.
Published: February 2008

In late December 1975, the orbital configuration of the Atmosphere Explorer‐D satellite made possible the measurement of the winter helium bulge within a single perigee pass. Shortly after the winter solstice, the perigee of the polar orbiting AE‐D satellite crossed the equator, at which time descending and ascending portions of the orbit stretched symmetrically over the southern and northern hemispheres. The open source neutral mass spectrometer (OSS) on board AE‐D measured helium densities between the perigee (about 150 km) and altitudes of 650 km. During the time the perigee was at the equator, altitudes above approximately 550 km were located north and south at latitudes greater than 50°, Helium showed, in the winter hemisphere, a factor of 20 higher densities than at corresponding altitudes and latitudes in the southern, summer hemisphere. Absolute densities of helium agree well with previous measurements.
Determination of maximum earthquake magnitude
Authors: Smith Stewart W.
Published: February 2008

A method is proposed to utilize the geologic record of fault displacement along with fault length to estimate the maximum magnitude earthquake that can be expected on an active fault. The method uses seismic moment as the link between geologic data and earthquake statistics. Several examples illustrate that faults of comparable length but different total slip in Holocene time have significantly different earthquake potentials.
Nonlinear equatorial spread F
Authors: Scannapieco Anthony J. , Ossakow Sidney L.
Published: February 2008

A numerical simulation of the non‐linear evolution of the collisional Rayleigh‐Taylor instability using a set of equations appropriate for the equatorial F region ionosphere has been performed. Our results show that the irregularities produced by the instability grow on the bottomside of the F region peak, as predicted by linear theory, and then the irregularities nonlinearly bubble through to the topside, where linear theory predicts no irregularities. Fourier analysis of the irregularities show one dimensional power law power spectrum for both the vertical and horizontal directions.
Atmospheric nitrogen fixation by lightning
Authors: Noxon J. F.
Published: February 2008

Nitrogen fixation in the atmosphere has been observed during a lightning storm by means of absorption spectra associated with NO2. A rough estimate of the efficiency of fixation yields the value of 1026 NO2 molecules per lightning stroke.
High resolution infrared absorptivities for gaseous chlorine nitrate
Authors: Graham R. A. , Tuazon E. C. , Winer A. M. , Pitts J. N. , Molina L. T. , Beaman L. , Molina M. J.
Published: February 2008

High resolution infrared absorptivities of chlorine nitrate (ClONO2) are required in order to quantitatively evaluate, by examination of infrared spectra obtained recently from balloon‐borne spectrometers, the possible occurrence of this compound in the stratosphere. In the present study, infrared absorptivities for four absorption bands of gaseous ClONO2 have been measured at 0.0625 cm−1 spectral resolution with a Fourier transform infrared (FT‐IR) system. Spectra were obtained at two pressures (0.05 and 1.05 torr) of pure ClONO2 and with 125 torr of N2 added to a 0.50 torr sample. Absorptivities for a range of spectral resolutions (0.0625, 0.125, 0.25 and 0.50 cm−1) have been calculated from the data.
Analyzing worldwide total ozone for trends
Authors: Hill William J. , Sheldon Paul N. , Tiede James J.
Published: February 2008

Total ozone data are statistically analyzed to estimate the trend detection capability which would provide early warning of ozone depletion. Based on a worldwide sample of nine stations, an abnormal global ozone change of 0.26% per year persisting over 6 years would be judged statistically significant, if it were to occur and could not be explained by historical patterns. A resulting 1.56% early warning can limit maximum reversible depletion to 2.3%, if the cause were due to chlorofluoromethanes FC‐11 and FC‐12. The analysis shows no evidence of an abnormal global trend persisting in the 1970's. The potential exists for detecting even smaller changes by using data from all the current land‐based stations and satellites.
The lower‐hybrid‐drift instability as a source of anomalous resistivity for magnetic field line reconnection
Authors: Huba J. D. , Gladd N. T. , Papadopoulos K.
Published: February 2008

It is shown that the lower‐hybrid‐drift instability can be unstable over a large region of the magnetotail where collisionless reconnection is expected to occur. For typical quiescent tail parameters the instability threshold is much lower than the ion acoustic instability. Preliminary considerations indicate that it can produce anomalous resistivity substantially larger than classical, reconnection rates of the order 10−1 VA, electromagnetic noise is the frequency range ωLH < ω ≪ Ωe and field aligned relativistic electron fluxes.
A new source of lunar electromagnetic induction: Forcing by the diamagnetic cavity
Authors: Sonett C. P. , Wiskerchen M. J.
Published: February 2008

A new source of electromagnetic excitation of the Moon is identified. It is distinct from the known spherical transverse electric (TE) mode forced by time variations of the interplanetary magnetic field. This new source is a consequence of the extension of the diamagnetic cavity field into the lunar interior and is detected on the sunlit lunar surface as a strong induction signal, directed preferentially east and west, and superimposed upon the global TE mode. The induction signal is hypothesized to be the time‐dependent part of the diamagnetic cavity fringing field within the Moon. The signal results from overall expansion and contraction of the lunar cavity measured here in the frequency range of 10−5 ≤ f ≤ 10−4 Hz. This "breathing" mode of the Moon‐cavity system is in turn based upon large scale hydromagnetic pressure variations of the solar wind. Confinement of the cavity fringing field to the lunar interior results in the lines of force being folded over just above the lunar surface and swept downstream above a region of reduced field intensity in the cavity walls. This is consistent with earlier observation. The associated current layer extends upstream over the face of the Moon. The diamagnetic contribution to induction seen on the sunlit lunar surface also suggests a resolution of the long‐standing difference between the excess induction noted experimentally on the darkside of the Moon (Kuckes, 1974) and that computed from TE mode theory.
Possible effects on fropospheric O 3 and OH due to No emissions
Authors: Liu Shaw Chen
Published: February 2008

The effects of NO emissions on non‐urban tropospheric ozone and OH concentrations are investigated. It is shown that ozone is not likely to increase with the increase in the injection of NO alone into an otherwise clean ambient atmosphere. Ambient OH concentrations would be increased by NO emissions through the NO + HO 2 reaction.
The spatio‐temporal variation of seismicity before the 1971 San Fernando Earthquake, California
Authors: Ishida Mizuho , Kanamori Hiroo
Published: February 2008

The spatio‐temporal variation of seismicity prior to the 1971 San Fernando, California, earthquake is studied for the area within 35 km of the epicenter. During the period from 1932 to 1961, the seismicity in this area was relatively low and random. A remarkable NE‐SW trending alignment of activity occurred during the period from 1961 to 1964, the period corresponding to the inferred onset of the Palmdale uplift. During the period from 1965 to 1968, the seismicity around the epicentral area became extremely low; no event was located within 13 km from the epicenter. During the period from 1969 to the occurrence of the San Fernando earthquake, activity around the epicentral area increased. This activity may be considered to be foreshock activity in a broad sense.
Organic carbon in marine atmospheric particulate matter: Concentration and particle size distribution
Authors: Hoffman Eva J. , Duce Robert A.
Published: February 2008

Organic carbon (OC) was determined in atmospheric particulate matter collected at several remote marine locations in the northern and southern hemispheres (Bermuda, Hawaii, Samoa). The OC concentrations were rather similar at all three locations, generally ranging from 0.2 to 0.4 µg/m³ STP. The major mass of the OC at all three locations was found on the smallest particles (radii less than 0.5 µm). However, the major mass of OC on laboratory generated atmospheric sea salt particles was found on particles with radii from 1‐3 µm, the same size as the major mass of the sea salt in both the laboratory experiments and in ambient marine air. This suggests that most of the organic material in marine atmospheric particulate matter is not associated with sea salt. Gas‐particle interactions involving organic compounds could explain the observed size distribution of the OC‐containing particles and the rather constant concentrations of organic carbon found in marine atmospheric particulate matter at the locations studied.
Seismicity in the vicinity of the Farallon Escarpment
Authors: Uhrhammer Robert
Published: February 2008

On April 30, 1977, at 1903 UTC an earthquake (ML = 2.6) occurred in the vicinity of the Farallon Escarpment (37.7°N ‐ 123.3°W), approximately 25 km west of the Farallon Islands. This well located earthquake is of particular interest in that it establishes earthquake activity along the California continental margin as far as 65 km west of the San Andreas fault. The significance is that the active seismic zone west of the San Andreas fault extends up to the edge of the continental margin but not past it into the oceanic crust. The occurrence rate is very low with an inter‐occurrence time for earthquakes with ML ≥ 1.9, in a 3000 square kilometer area in the vicinity of the escarpment, of about two years. The first motions recorded at local seismographic stations are consistent with a right‐lateral strike‐slip mechanism orientated parallel to the strike of the San Andreas fault.
Gabbros from Mare Crisium: An analysis of the Luna 24 soil
Authors: Bence A. E. , Grove T. L. , Scambos T.
Published: February 2008

Monomineralic and lithic fragments from the Luna 24 drill core are samples of a mare ferrogabbro and a rarer gabbro of possible highlands origin. Mineral phase chemistries of the mare ferrogabbro suggest the crystallization near the lunar surface of an evolved Fe‐rich (Fe/Fe+Mg = 0.68 to 0.70) multiply saturated liquid. This low‐Ti liquid, also represented in the core by basalt and brown glass fragments, crystallized at the Mare Crisium site as a lava flow or intrusive and underwent little differentiation at the cooling site.
Stratospheric sulfate at high altitudes
Authors: Lazrus A. L. , Gandrud B. W.
Published: February 2008

Sulfate ion was measured on air filtration samples obtained between 14 and 37 km at 33°N. One concentration profile was determined each season in 1976. An average maximum mixing ratio of 1.4 ppbm was observed at 19 km. Sulfate was also observed on the filters exposed at the higher altitudes. The values at 24 km and above were quite variable, with an average value of 0.6 ppbm.