bluuebunny/crossref_metadata_2025 huggingface dataset:
A determination of the infrared optical depth of the El Chichon volcanic cloud
Authors: Pollack James B. , Witteborn Fred C. , O'Brien Kevin , Flynn Brian
Published: February 2008

Infrared transmission spectra of the atmosphere above 11‐km altitude were obtained in December 1982 and April/May 1983 from a NASA Convair 990 aircraft. The observations on the first flight series encompassed low and middle latitudes in the northern hemisphere, while the observations on the second series covered a wide range of latitudes in both hemisphere. We have analyzed these data to derive the optical depth of the El Chichon volcanic cloud at a wavelength of 8.4 μm. Comparison of these values with concurrent measurements by Dutton and DeLuisi of the cloud's optical depth at 0.5 μm leads to the ratio of the cloud's infrared to visible optical depth, R. We analyzed the observed spectra by ratioing pairs of spectra taken at similar latitudes, but different air masses and comparing these ratio spectra with synthetic ones. The synthetic spectra allow for absorption by gases (O3, H2O, CO2, CH4, and N2O) as well as extinction by the cloud particles. Extinction by the cloud particles is particularly important in the 8‐ to 9‐μm region. We obtain an average value for R of 0.25±0.05. Our data imply that concentrated sulfuric acid was the dominant source of aerosol extinction in the 8‐to 12‐μm window region of the Earth's atmosphere and that the volume modal particle radius equalled 0.6±0.1 μ at the time of our observations. At these times, the volcanic particles produced a significant warming of the lower stratosphere and had a nontrivial impact on the radiation budget of the troposphere and ground in the northern hemisphere.
Reactions of OH with α‐pinene and β‐pinene in air: Estimate of global CO production from the atmospheric oxidation of terpenes
Authors: Hatakeyama Shiro , Izumi Katsuyuki , Fukuyama Tsutomu , Akimoto Hajime , Washida Nobuaki
Published: February 2008

Reactions of OH with α‐pinene and β‐pinene were studied for the purpose of obtaining the basic data to estimate the emission rate of CO from the photooxidation of terpenes in the atmosphere. In the presence of NO the main product was pinonaldehyde and 6,6‐dimethyl‐bicyclo[3.1.1]heptan‐2‐one from α‐ and β‐pinene, respectively, and the yield was 56±4 and 79±8%, respectively. In the absence of NO the yield was remarkably lower, and the yield of organic aerosols was enhanced. For α‐pinene 56±3% was obtained as a yield of aerosols on the carbon number basis. Gross annual emission of CO from the reactions of OH with terpenes was estimated to be 22 Tg C yr−1 (50 Tg CO yr−1) by regarding α‐pinene as the representative of terpenes, on the basis of the annual emission rate of terpenes, estimated lifetime of pinenes in the atmosphere, the apparent rate constant for the intermediate to form CO, and the estimated yield of CO from the secondary oxidation of pinonaldehyde. The ultimate yield of CO from the tropospheric oxidation of terpenes (including both ozone and OH reactions) was estimated to be 20% on the carbon number basis, and the total annual emission of CO was evaluated to be 96 Tg C yr−1 (222 Tg CO yr−1).
Fluid flow near the surface of Earth's outer core
Authors: Bloxham Jeremy , Jackson Andrew
Published: February 2008

Maps of the fluid flow at the core surface are important for a number of reasons: foremost they may provide some insight into the workings of the geodynamo and may place useful constraints on geodynamo models; from the flow, the force balance at the top of the core can, at least in part, be deduced; the flow can provide short‐term predictions of the secular variation; the flow is important in understanding changes in the length of day; and constraints on lateral temperature variations and topography at the core‐mantle boundary may be derived. Unlike the case of mantle convection, only very small lateral variations in core density are required to drive the flow; these density variations are too small (by several orders of magnitude) to be imaged seismically, so instead we use the geomagnetic secular variation to infer the flow. Despite considerable recent progress in mapping the core flow, substantial differences exist between maps produced by different researchers. Here we examine the possible underlying reasons for these differences, paying particular attention to the inherent problems of nonuniqueness. We focus on the aspects of the flow which do seem to be well determined and discuss their geophysical implications.
Seismicity of the Sunda Strait: Evidence for crustal extension and volcanological implications
Authors: Harjono Hery , Diament Michel , Dubois Jacques , Larue Michel , Zen Mudaham Taufick
Published: February 2008

The Sunda Strait is located in the transitional zone between two different modes of subduction: the Java frontal subduction and the Sumatra oblique subduction. This setting implies that the Sunda Strait region is a key to the understanding of the geodynamic processes involved. In order to study the shallow seismicity, a microearthquake survey was carried out in that region. Twelve stations, accurately located by the aim of satellite positionning, recorded about 300 local events in the summer 1984. From this set, 174 shallow earthquakes have been precisely located. The results of this study reveal that the crustal earthquakes in the Sunda Strait area occurs in three main areas: (1) beneath the Krakatau complex, where earthquakes are generated by double‐couples and are of tectonic origin; (2) inside a graben in the western part of the strait; and (3) in a more diffused zone to the south of Sumatra. The individual and composite focal mechanisms from the events inside the strait show an extensional regime. A stress tensor, which have been deduced from the individual focal mechanisms of earthquakes of the Krakatau group shows that the tensional axis is oriented N130°E. This study confirms that the Sunda Strait is in an extensional tectonic regime as a result of the northwestward movement of the Sumatra sliver plate along the Semangko fault zone.
A northwest trending, Jurassic Fold Nappe, northernmost Zacatecas, Mexico
Authors: Anderson Thomas H. , McKee James W. , Jones Norris W.
Published: February 2008

The Caopas, Rodeo, and Nazas formations exposed in the San Julián uplift of northern Zacatecas are distinguished principally on the basis of style and intensity of deformation; they are parts of the same early Mesozoic(?) volcanogenic suite. This suite was the source for overlying volcaniclastic conglomerate and sandstone (La Joya Formation) that appears transitional into succeeding Late Jurassic (Oxfordian?) Zuloaga Limestone. Deformation that was contemporaneous with the deposition of the lower part of the Zuloaga produced an asymmetrical northwest trending fold nappe that was driven southwestward. The massive quartz‐porphyry core of the structure (Caopas Formation) moved somewhat independently of the encasing, more ductile rocks (Rodeo and Nazas formations). Phyllonite developed in the nose of the nappe; the upright limb was attenuated and ruptured. In zones where deformation due to the nappe‐forming process was weaker, a gently dipping foliation, possibly related to an older episode of recumbent folding, is preserved. Orientation, age, and location of the nappe suggest that it is a manifestation of transpressional stress developed along the Mojave‐Sonora megashear as left‐lateral movement carried the Jurassic arc toward the southeast.
Amount and style of Late Cenozoic Deformation in the Liupan Shan Area, Ningxia Autonomous Region, China
Authors: Zhang Peizhen , Burchfiel B. C. , Molnar Peter , Zhang Weiqi , Jiao Dechen , Deng Qidong , Wang Yipeng , Royden Leigh , Song Fangmin
Published: February 2008

The structures of the Liupan Shan area are characterized by numerous active thrust and strike‐slip faults that suggest thin‐skinned deformation. The structural history of this area can be divided into three phases that probably overlap one another in time and are parts of a single protracted deformation. The oldest Cenozoic deformational phase occurred probably between late Pliocene and early Quaternary time and produced some of the folds and thrust faults in the Liupan Shan and Yueliang Shan. During this phase, deformation was the result of approximately N50°E shortening, and the amount of shortening seems to have been about 1–2 km. The second phase of deformation was dominated by left‐lateral strike‐slip faulting (left slip) on the N60°W striking Haiyuan fault zone and shortening on north‐south trending structures; shortening was associated with a transfer of the left‐slip displacement on the Haiyuan fault zone to shortening in areas farther east. Shortening occurred by thrust faulting in the Liupan Shan and Xiaoquan Shan and by folding in the Madong Shan. During this phase the orientation of shortening changed to N60°W. The average amount of shortening on the north‐south trending folds in the Madong Shan is about 6.3–7.8 km. Most of the shortening on the Liupan Shan and Xiaoguan Shan thrust faults also occurred during this phase and amounted to a minimum of 4.8–6.3 km and 6.6–7.6 km, respectively, also with an orientation of N60°W. During the third phase of deformation, about 1–1.5 km of late Pleistocene to Recent left slip occurred on the Xiaokou fault, which was transferred into oblique left‐slip thrusting in the Liupan Shan. At this time, deformation in the Madong Shan and Xiaoguan Shan ceased or was reduced to a very slow rate. The present, active left‐slip on the Haiyuan fault zone is accommodated by shortening in the Liupan Shan area. The total displacement along the Haiyuan fault is essentially the same as the total amount of shortening in the Liupan Shan area. The sequence and interaction of strike‐slip and thrust faults in the Liupan Shan area seem to apply to the folds and thrust faults farther north in the southern Ningxia region. Thus the northeastern margin of the Tibetan Plateau appears to grow by shortening oriented northeast and by left slip faulting that transfers material from farther to the west. The total left‐slip in the entire southern Ningxia region probably is less than 20–25 km and may be absorbed by shortening within this region. Thus the eastward translation of crustal fragments in the northern part of the Tibetan Plateau may not extend east of southern Ningxia, and if large‐scale eastward displacement has occurred, it must lie farther south.
The role of deformation in the formation of metamorphic gradients: Ridge subduction beneath the Oman Ophiolite
Authors: Hacker Bradley R.
Published: February 2008

Two tectonic scenarios have been proposed for genesis and emplacement of the Oman ophiolite. One suggests that the ophiolite was generated at a spreading center, the other suggests generation within an intraoceanic arc. An integrated thermal and kinematic model of the temperature, stress, rock type, and displacement fields during early stages of the emplacement of the Oman ophiolite was developed to test these two possibilities. The thermal evolution was calculated by a finite difference algorithm for heat conduction, considering heats of metamorphic reactions, deformational heating, heat advection by flowing rock, mantle heat flow, and radioactive heating. The stress and displacement fields were calculated by an analytical model using a velocity boundary condition, power law constitutive relations, and a brittle frictional sliding relationship. Field observations in Oman can be satisfied with the spreading center model but not with the arc model. Moreover, simulations indicate that the ophiolite was probably <2 m.y. old at the time of intraoceanic thrusting and that shear stresses of ∼100 MPa were attained during thrusting. In addition to satisfying currently available field constraints, these simulations also indicate specific further work that will help resolve the controversy over thevolution of this unique orogen. Future work should be directed toward (1) using thermobarometry and thermochronology to constrain the spatial variation in PTt paths of the metamorphic sole; (2) dating the igneous genesis of the ophiolite; and (3) using quartzite and dunite recrystallized grain size paleopiezometers to infer stresses during thrusting. These simulations point out the important effect synmetamorphic deformation can have on the formation of metamorphic field gradients. In contractional fault zones, metamorphic field gradients may be normal or inverted and contracted or extended relative to the initial thermobarometric gradient, and adjacent fault zone rocks may display crossing PT paths. Unusually contracted or extended metamorphic field gradients may also develop in the footwalls of normal fault zones where portions of the heating hangingwall accrete to the uplifting, cooling footwall.
Downward transport and fate of organic matter in the ocean: Simulations with a general circulation model
Authors: Najjar Raymond G. , Sarmiento Jorge L. , Toggweiler J. R.
Published: February 2008

A phosphorus‐based model of nutrient cycling has been developed and used in conjunction with a general circulation model to evaluate the roles of the dissolved and sinking particulate phases in the downward transport of organic matter in the ocean. If sinking particles dominate the downward transport and remineralize in accord with observations made primarily with sediment traps, we find in equatorial upwelling regions that particle fluxes and thermocline nutrient concentrations are higher than observed. These enhanced fluxes and concentrations are a result of what we term “nutrient trapping,” a positive feedback whereby high upwelling produces high new production that results in remineralization and enhanced nutrient concentrations in the upwelling water, which further increases new production. Nutrient trapping in shallow upwelling zones can be eliminated by increasing the particle flux length scale, which suggests that if sinking particles dominate the downward transport of organic matter then the flux length scale is longer than observed. Even with a longer particle flux length scale, we find that nutrients are trapped in some deep convective regions of the southern ocean, where new production is predicted to be much higher than the observed primary production. In simulations where the downward transport of organic matter takes place primarily in a dissolved phase, nutrient trapping is completely eliminated, in both upwelling and convective regions. The models with dissolved organic matter also agree fairly well with nutrient transports in the north Atlantic Ocean calculated from observed nutrient and hydrographic data (Rintoul and Wunsch, 1991). Our results therefore support the dissolved organic nitrogen and carbon measurements made with the high‐temperature combustion technique of Suzuki et al. (1985) and Sugimura and Suzuki (1988) and suggest that there exists an as‐yet undiscovered pool of dissolved organic phosphorus in the ocean. We also use the various models to make an estimate of global new production of 2.9 to 3.6 mol C/m2/yr (12 to 15 Gt C/yr).
High‐lattitude convection patterns for various large‐scale field‐aligned current configurations
Authors: Blomberg L. G. , Marklund G. T.
Published: February 2008

The large‐scale field‐aligned current system for persistent northward interplanetary magnetic field (IMF) is typically different from that for persistent southward IMF. One characteristic difference is that for northward IMF there is often a large‐scale field‐aligned current system poleward of the main auroral oval. This current system (the NBZ current) typically occupies a large fraction of the region poleward of the region 1 and 2 currents. The present paper models the high‐latitude convection as a function of the large‐scale field‐aligned currents. In particular, a possible evolution of the convection pattern as the current system changes from a typical configuration for southward IMF to a configuration representing northward IMF (or vice versa) is presented. Depending on additional assumptions, for example about the y‐component of the IMF, the convection pattern could either turn directly from a two‐cell type to a four‐cell type, or a three‐cell type pattern could show up as an intermediate state. An interesting although rather surprising result of this study is that different ways of balancing the NBZ currents has a minor influence on the large‐scale convection pattern.
Diurnal variations on a plasmaspheric flux tube: Light ion flows and F region temperature enhancements
Authors: Guiter S. M. , Gombosi T. I. , Rasmussen C. E.
Published: February 2008

Diurnal variations on a plasmaspheric flux tube were modelled using a time‐dependent, multi‐species, one‐stream, interhemispheric model for plasmaspheric flows. In the model the coupled time‐dependent hydrodynamic equations (continuity, momentum, and energy) of a two ion (H+ and O+) quasineutral, currentless plasma are solved for a closed geomagnetic field line; no diffusive equilibrium assumptions are made. For this work an L=2 field line with conjugate points displaced in latitude and longitude was used in order to model the tilt of the geomagnetic field. The simulation was done for June solstice conditions during solar minimum. In general the results reproduce those found by Richards and Torr [1986]. However, a striking new result is the presence of large downward H+ velocities (∼2.2 km/s) at about 320 km altitude in the winter (southern) hemisphere, in early morning when the summer hemisphere is already sunlit but the winter hemisphere is still in darkness. These are accompanied by large H+ temperature enhancements, reaching 5600 K, at about 280 km altitude. The large velocities are a resilt of an increase in the H+ pressure gradient coupled with a decrease in the friction encountered by the H+ ions. These flows are stopped at lower altitudes where the neutral densities are higher; the bulk kinetic energy is converted to thermal energy, resulting in the temperature enhancements.
Dynamic tensile‐failure‐induced velocity deficits in rock
Authors: Rubin Allan M. , Ahrens Thomas J.
Published: February 2008

Planar impact experiments were employed to induce dynamic tensile failure in Bedford limestone. Rock discs were impacted with aluminum and polymethyl methacralate (PMMA) flyer plates at velocities of 10 to 25 m/s. Tensile stress magnitudes and duration were chosen so as to induce a range of microcrack growth insufficient to cause complete spalling of the samples. Ultrasonic P‐ and S‐wave velocities of recovered targets were compared to the velocities prior to impact. Velocity reduction, and by inference microcrack production, occurred in samples subjected to stresses above 35 MPa in the 1.3 μs PMMA experiments and 60 MPa in the 0.5 μs aluminum experiments. Using a simple model for the time‐dependent stress‐intensity factor at the tips of existing flaws, apparent fracture toughnesses of 2.4 and 2.5 MPa m½ are computed for the 1.3 and 0.5 μs experiments. These are a factor of ∼ 2 to 3 greater than quasi‐static values. The greater dynamic fracture toughness observed may result from microcrack interaction during tensile failure. Data for water‐saturated and dry targets are indistinguishable.
Late Jurassic to Eocene geochemical evolution of volcanic rocks in Puerto Rico
Authors: Schellekens Johannes H.
Published: February 2008

The Late Jurassic to Eocene deformed volcanic, volcaniclastic and sedimentary rocks of Puerto Rico are divided into three igneous provinces, the southwestern, central, and northeastern igneous province. Based on the stratigraphic position approximate ages could be assigned to the flow rocks in these provinces. Ba/Nb and La/Sm diagrams are presented to illustrate the origin and evolution of the flow rocks. The oldest rock in the southwestern province may include MORB. Early Cretaceous volcanic rocks in the central and northeastern province have low Ba/Nb and La/Sm, that are interpreted as an early island arc stage, with none or only minor contribution of slab‐derived material. The Late Cretaceous to Eocene volcanic rocks have a wide range of values for the Ba/Nb and La/Sm that are interpreted as the result of admixture of a variable amount of slab‐derived material. The Maricao Basalt (Maastrichtian to Eocene) in the southeastern igneous province has the geochemical signature of magmas formed in an extensional setting.
Paleomagnetic evidence for Late Miocene counterclockwise rotation of North Coast carbonate Sequence, Puerto Rico
Authors: Reid Jane A. , Plumley Peter W. , Schellekens J. H.
Published: February 2008

A paleomagnetic study of the essentially undeformed middle Tertiary carbonate sequence along the north coast of Puerto Rico reveals statistically significant pre‐Pliocene discordance of characteristic component directions against those expected from cratonic North America for much of the section. Despite generally weak to moderately weak magnetic intensities, confirmation of the magnetization as primary in origin comes from the presence of two distinct components of magnetization, intrasite bipolarity, and/or the reproducibility of measurements.
Clay mineral and zeolite diagenesis in the Toa Baja Well, Puerto Rico
Authors: Tribble Jane S.
Published: February 2008

Several diagenetic reactions typical of volcaniclastic sediments have been identified in the Toa Baja well. The zeolites heulandite and (less commonly) analcite, present in the upper half of the drilled section, give way to laumontite at depth. A decrease with depth in the expandability of mixed layer chlorite/smectite was observed. Corrensite was detected over the depth range 1676–2286 m. Temperatures implied by the depth ranges of diagenetic and indicator minerals are consistent with a paleothermal gradient of about 30–50°C/km, assuming little or no erosion of section.
The Toa Baja Drilling PRoject and current studies in Puerto Rican geology: Introduction and summary
Authors: Larue D. K.
Published: February 2008

This volume concerns information learned by drilling the Toa Baja well on the north coast of Puerto Rico, and current studies of Puerto Rican geology and tectonics.

The Toa Baja Drillsite is located in the North Coast basin of Puerto Rico about 10 km west of San Juan. The hole was spudded on August 23, 1989, and plugged and abandoned on November 7,1989 at a total depth of 2704m. Two lithologies were encountered during drilling: an upper series consisting of Oligocene‐Miocene shallow‐water limestone and sandstone facies, and a lower series consisting of Eocene deep‐water volcaniclastic strata, including some lava flows or shallow intrusions, pelagic marls, and altered igneous rocks or coarsegrained sandstones. Principal findings made during drilling include: 1) the important unconformity separating the upper and lower series at about 579 m; 2) 8 faults defined clearly by dipmeter log; 3) changes in rock type probably associated with reflection events in seismic reflection profiles crossing the drillsite; 4) confirmation of overall low geothennal gradients and heat flow, but presence of a thermal anomaly near 2683 m; 5) documentation of high paleogeothermal gradients using petrographic, isotopic, X‐Ray diffraction and electron microprobe studies; 6) presence of fractures indicating a current extensional tectonic setting.

Current studies in the Puerto Rico region include: 1) paleomagnetic evidence for Late Miocene counterclockwise rotation; 2) geochemical evolution of Cretaceous and Eocene igneous rocks; 3) evidence of transtension in the northeast Caribbean plate boundary zone; 4) results of studies of ancient fault zones on Puerto Rico; and 5) stratigraphic studies of the Tertiary of Puerto Rico.
Structural analysis of cores and cuttings from the Toa Baja (Puerto Rico) Borehole
Authors: Lallemant Hans G. Avé
Published: February 2008

Deformation structures in core samples and well cuttings from the Toa Baja borehole in Puerto Rico, obtained from depths of 580 to 2700 meters, can be divided into two major categories: (1) structures resulting from compression and shear and (2) structures formed by extension. Generally, the first ones are older and they are somewhat more abundant at horizons where fault zones occur as deduced from dipmeter readings and televiewer log. These structures may have formed during an Eocene thrusting event, recognized regionally in Puerto Rico. The extensional structures which almost always crosscut the compressional ones are filled with zeolite, calcite, prehnite, or quartz. There is poor correspondence between the abundance of these fractures and the position of the major fault zones. The largest abundance of veins occurs between 1700 and 2100 meters depth. They may be related to a phase of regional extension during the Late Paleogene.
Ground deformation associated with volcanic tremor at Izu‐Oshima Volcano
Authors: Oikawa Jun , Ida Yoshiaki , Yamaoka Koshun , Watanabe Hidefumi , Fukuyama Eiichi , Sato Kaoru
Published: February 2008

Izu‐Oshima volcano had summit and fissure eruptions in November, 1986 after 12 years of dormancy, and three small eruptions followed these events within one year. Episodic and continuous volcanic tremors were observed for the period containing these eruptions. It is a remarkable discovery that the episodic volcanic tremor was accompanied by a small but sharp ground deformation, the polarity of which was variable. The distribution of tilt vectors reveals that the source of ground deformation was always located beneath the northwestern flank of the volcano, where a magma reservoir was predicted by other studies. On the other hand, the seismologically detected tremor source was determined to be at a shallow depth below the central pit crater, a few kilometers away from the predicted magma reservoir. It is thus inferred that the tremor source near the crater generated pressure increases or decreases that were simultaneously transmitted through the vent to the magma reservoir and lead to its expansion or contraction.
Comparison of semikinetic and generalized transport models of the polar wind
Authors: Demars H. G. , Schunk R. W.
Published: February 2008

A comparison has been made, in as consistent a manner as possible, of a transport (bi‐Maxwellian based 16‐moment equations) and a semikinetic description of the terrestrial polar wind. The comparison shows a remarkably close agreement in the corresponding predictions for the altitude variation of the density, drift velocity, parallel and perpendicular (to B) temperatures, and the flow of parallel and perpendicular thermal energies. This close agreement provides further evidence that the bi‐Maxwellian based transport equations are a powerful tool for studying thermal space plasmas that develop non‐Maxwellian features.
Comment on “Atmospheric contamination: A possible source for heavy noble gases in basalts from Loihi Seamount, Hawaii” by D. B. Patterson, M. Honda, and I. McDougall
Authors: Staudacher Thomas , Sarda Philippe , Allègre Claude J.
Published: February 2008

Allègre et al. (1983), Staudacher et al. (1986) and Sarda et al. (1988) reported noble gas concentrations and isotopic ratios of basalt glasses from Loihi seamount and Hualalai, Hawaii. The 4He/3He and 40Ar/36Ar ratios of ∼25,000 and 390 ± 50 respectively are different than the air ratio and typical ratios found in MORB glasses. The Ne, Kr and Xe isotopic ratios are the same as those found in air or deep seawater. Based on the different isotopic ratios and the different noble gas concentration patterns of Ne, Ar, Kr and Xe compared to air, deep seawater and MORB, these authors concluded that the noble gases enclosed in vesicles from Loihi and Hualalai basalts are not significantly contaminated by atmospheric noble gases, and that the Loihi and Hualalai basalts came from a separate source, namely the lower mantle, with a distinct noble gas signature. In contrast to the upper mantle, which is highly depleted in noble gases, this lower mantle should be not or only slightly outgassed (Allègre et al., 1986).

In a recent publication, Patterson et al. (1990), based on our noble gas data (Staudacher et al., 1986; Sarda et al., 1988), propose that Ne, Ar, Kr and Xe noble gas concentrations in basalt glasses could be plausibly explained by a) contamination of the Loihi plume magma prior to eruption with atmospheric noble gases disolved in deep seawater (which they model by elemental noble gas fractionation of a tholeiitic melt that was equilibrated with seawater derived noble gases), and b) elemental fractionation of noble gases during vesicle formation and vesicle loss. We completely disagree with such an interpretation and show here that their argumentation is inconsistent and incorrect.
NO2 overnight decay and layer height at Halley Bay, Antarctica
Authors: Keys J. G. , Gardiner B. G.
Published: February 2008

Ground‐based measurements of stratospheric slant column NO2 amounts made at Halley Bay, Antarctica in 1987 are compared with ozone and temperature profiles from balloon‐borne sondes. Sunrise‐to‐sunset (am/pm) ratios of NO2 have been calculated in autumn and spring by using the sonde data in conjunction with a simple photochemical model for the conversion of NO2 to N2O5. These calculations can be reconciled with the spectrometric measurements of column NO2, provided that the bulk of the NO2 layer is assumed to lie at a height of about 25km. The small amounts of NO2 that are present in the stratospheric column during the first 6 weeks of spring are therefore confined to altitudes above the ozone depletion region. Slow recovery of the NO2 column in spring compared with the rate of its decline in autumn indicates slow photolysis of depleted levels of N2O5 inside the polar vortex.
Effect of varying fluid composition on mass and energy transport in the Earth's crust
Authors: Bodnar R. J. , Costain J. K.
Published: February 2008

The ability of fluids flowing through a given volume of crustal rock to affect mass and energy transfer is controlled by the physical and chemical nature of the fluid. Most numerical simulations of fluid‐flow and fluid‐rock interaction approximate the mass and energy transfer characteristics of crustal fluids using the physical, thermodynamic and transport properties of H2O. Results of fluid inclusion studies indicate that H2O is, in fact, the dominant component of fluids from most shallow to intermediate depth crustal environments, with other components usually present in varying amounts. In many crustal environments, properties of the fluids are adequately represented by those of the system H2O‐CO2‐NaCl.

In the pure H2O system, mass and energy transport properties reach extrema and become very sensitive to small variations in temperature or pressure in a restricted region of P‐T space near the critical point. This “critical region” migrates to higher and lower temperatures as NaCl or CO2, respectively, are added to water, and mass and energy transport properties become less sensitive to temperature or pressure variations when either NaCl or CO2 are added to water.

The effect of fluid composition on mass transfer is illustrated by the system SiO2‐H2O‐NaCl. The SiO2‐H2O sub‐system is characterized by a solubility maximum, or region of retrograde solubility, at temperatures and pressures slightly above the critical point of water. Addition of NaCl increases the solubility of silica and shifts the quartz solubility maximum to higher temperatures and pressures relative to pure H2O.
SEM/STEM observations of magnetite in carbonates of eastern North America: Evidence for chemical remagnettzation during the Alleghenian Orogeny
Authors: Suk Dongwoo , Van der Voo Rob , Peacor Donald R.
Published: February 2008

Early to middle Paleozoic carbonates of eastern North America have been pervasively remagnetized. In order to determine the process of remagnetization, scanning and scanning transmission electron microscopy have been used to characterize magnetite in thin sections and in concentrated separates. Samples included Ordovician Knox carbonates from east Tennessee, Ordovician Trenton limestone and Devonian Onondaga and Helderberg limestones from New York, and Ordovician Trenton carbonates from Michigan. Inclusions of authigenic minerals within magnetite grains, lack of cations other than iron, and a variety of textural relations all imply that the magnetite is authigenic. These data are consistent with estimates that paleotemperatures never exceeded values that would reset magnetic directions. The remagnetization is thus a chemical remanent magnetization (CRM) rather than viscous remanent magnetization (VRM). As the timing of remagnetization corresponds to the Alleghenian orogeny, the observed relations imply stress‐induced crystallization of magnetite that was mediated by fluids, consistent with but not requiring fluid flow on a regional basis.
Effect of fluid viscosity and saturation on the ultrasonic velocities in a Fontainebleau sandstone
Authors: Khalatbari Azar , Vo‐Thanh Dung , Poirier Jean‐Paul
Published: February 2008

Simultaneous measurements of the P‐ and S‐wave velocities at 1MHz frequency as a function of temperature from −80°C to 80°C have been made in a Fontainebleau sandstone saturated with glycerol. We investigated 8 saturation degrees, from fully saturated to almost dry state. Generally, the velocity decreases with increasing temperature; it is large between ≈ −40°C and ≈ 40°C. The velocity dispersion is attributed to viscous shear relaxation. The model of O'Connell and Budiansky modified by introducing the saturation parameter and a Gaussian distribution of crack aspect ratios is used to interpret the data. A trial and error method is used to estimate the model parameters. The model satisfactorily accounts for the data at high saturation.
Seismic pulses suggesting an implosive source at the 1989 Ito‐Oki Submarine Eruption, central Japan
Authors: Ukawa Motoo , Obara Kazushige , Fukuyama Eiichi
Published: February 2008

Four unusual seismic pulses of magnitude about 2 were observed at the 1989 Ito‐oki submarine eruption on July 13, 1989. Their seismograms show two distinct characteristics; ineffective shear wave excitation and downward motions of P onsets for all azimuths. Source mechanisms are studied by using data obtained on the local seismic network. Hypocenters were estimated to be in a very shallow part of the upper crust beneath a new crater found after the eruption. The downward first motion and ineffective shear wave excitation are difficult to explain simultaneously by a double couple type source mechanism, suggesting an implosive type source.
Kozeny‐Carman relation for a medium with tapered cracks
Authors: Dvorkin Jack , Gvirtzman Haim , Nur Amos
Published: February 2008

We examine the permeability of a medium with thin tapered cracks to a single‐phase fluid flow in the presence of immobile matter which is accumulated in the tips of cracks. The original Kozeny‐Carman relation shows an increase in permeability of such a material relative to the case when tips are free of accumulated matter. To resolve this paradox we introduce a corrected version of the Kozeny‐Carman relation for the case when the shape of a crack cross‐section can be described by a power law. This class of crack shapes includes the important cases of triangular cracks and space between two contacting circular grains. The revised relation includes the original porosity Φ and specific surface area S of the material without accumulated matter as well as the degree of filling a crack space by accumulated matter Z. The permeability is proportional to Φ3 and S−2, and decreases with increasing Z.
A simple explanation for the depth distribution of deep earthquakes
Authors: Willemann Raymond J.
Published: February 2008

In a model for the depth distribution of deep earthquakes, I assume that deep earthquakes occur only above a critical deviatoric stress and that where the stress is achieved the seismicity rate is proportional to the strain rate. The model seismicity rate increases sharply before terminating, in agreement with the observed depth distribution. Since the assumptions are valid for most plausible seismic processes, no large stresses or unusual earthquake mechanisms near the termination of seismicity are required.
Major and trace element mass flux in fumarolic deposits, Valley of Ten Thousand Smokes, Alaska: Rhyolite‐rich protolith
Authors: Papike J. J. , Keith T. E. C. , Spilde M. N. , Shearer C. K. , Galbreath K. C. , Laul J. C.
Published: February 2008

Three fossil fumaroles in rhyolite‐rich ash‐flow tuff from the lower Valley of Ten Thousand Smokes (VTTS) have been studied to ascertain chemical losses and gains and mineralogical evolution during fumarolic alteration and subsequent cooling and weathering processes. Major oxide and trace element data were interpreted using the isocon method of Grant (1986).
Horizontal and vertical structure of the major sporadic sodium layer events observed during ALOHA‐90
Authors: Kane Timothy J. , Hostetler Chris A. , Gardner Chester S.
Published: February 2008

Sporadic Na (Nas) layers have been observed frequently at low‐ and high‐altitude sites primarily in the Northern Hemisphere. Nas layers are very dense and very thin (∼1 km FWHM) and can form over periods ranging from a few minutes to several hours. Radar and lidar observations by our group at Arecibo have shown conclusively that Nas layers are linked to the formation of sporadic E (Es) layers. Large Nas events were observed on several flights during ALOHA‐90 to extend over horizontal distances of approximately 1800 km. Atmospheric tides and gravity waves were observed to have an effect on the vertical motion of these layers. We describe the 22 March event which was observed from Maui (21°N) to near the equator (5°N) and the 27 March event which was observed from Maui (156°W) to almost the International Date Line (∼172°W).
Gravity wave modulation of gradient drift instabilities in mid‐latitude sporadic E irregularities
Authors: Woodman R. F. , Yamamoto M. , Fukao S.
Published: February 2008

Recent E region VHF backscatter echoes observed by the MU radar at mid‐latitudes show quasi‐periodic striations with a fairly constant range vs. time tilt in a RTI display. These features are explained in terms of gravity waves with frequencies close to the Brunt‐Väisälä frequency which modulate the shape of sporadic E layers. The conditions of instability, when the magnetic field has a significant dip angle, is revised. Differing from previous work, we argue that conditions of local gradient drift instability are not sufficient and one has to consider the integrated properties of each magnetic filed tube. Stratified sporadic E layers are stable using this new criteria, unless they are distorted to produce unstable integrated gradients. Gravity waves with phase fronts parallel to the magnetic dip angle are capable of producing such distortion, imposing its own temporal and spatial periodicity on the echoes.
Multifractal structure of speed fluctuations in recurrent streams at 1 AU and near 6 AU
Authors: Burlaga L. F.
Published: February 2008

This paper demonstrates the existence of multifractal structure in the velocity fluctuations associated with recurrent streams at 1 AU and near 6 AU. There is a significant evolution of the multifractal spectrum from 1 AU to 6 AU. At 1 AU the fluctuations on all scales in the indicated range are related to the local speed gradients associated with the stream structure. Near 6 AU the multifractal structure of the speed fluctuations approaches the universal form for intermittent turbulence for moments q>5, and it has approximately the value expected for a set of discontinuities for q=2.
Mean winds and waves in the troposphere during ALOHA‐90
Authors: Avery S. K. , Palo S. E.
Published: February 2008

Measurements of the tropospheric horizontal wind field at Christmas Island during the ALOHA‐90 campaign are presented in this paper. A diurnal cycle is observed on several days but is not consistent from day‐to‐day. Significant variance associated with the high frequency wave motions occurred between March 22 and 26, 1990. This large wave activity in the troposphere is consistent with mesospheric wave activity during the same time interval.
Simultaneous balloonborne measurements of stratospheric water vapor and ozone in the polar regions
Authors: Hofmann D. J. , Oltmans S. J. , Deshler T.
Published: February 2008

Vertical profiles of stratospheric water vapor and ozone were measured together at McMurdo and South Pole Stations in Antarctica, and at Kiruna, Sweden, on several occasions during the austral spring of 1990 and the boreal winter of 1991. The Antarctic data indicated that major dehydration had occurred on a continental scale over the winter stratospheric cloud formation period leaving only 2 to 3ppmv water vapor between 11 and 19km. Measurements before and after movement of the boundary of the polar vortex across McMurdo detected increases in both water vapor and ozone in the 17 to 20km region. This injected layer was still observed at South Pole Station a month later suggesting continental proportions. In early November, with the vortex still intact, South Pole measurements indicated a substantial degree of inhomogeneity in both water vapor and ozone in the lower stratosphere. In comparison, stratospheric water vapor measurements in the Arctic gave values of 4 to 5 ppmv indicating the absence of the gross stratospheric dehydration effects obvious in the Antarctic, and they did not reveal significant structure except on one occasion with very cold temperatures (−90°C) at 25km and nacreous cloud displays.
Mapping the crust in southeastern Germany using Rayleigh waves in the period range 6–16 S
Authors: Hadiouche Ouiza , Kruger Frank , Kind Rainer
Published: February 2008

Rayleigh waves generated from seismic events in southern Germany and recorded at the broad‐band GRF array, have been analysed. The group velocities have been determined from 6 to 16 s along more than 100 carefully selected seismic paths. A regionalization method, based on the classical approach for surface wave propagation, has been applied to this data set. The lateral heterogeneities, inferred from the lateral variations of the group velocities after the 2‐D inversion, present an excellent correlation with the known geological features. The effects on group velocities involved by these lateral heterogeneities may exceed ±10%. Azimuthal anisotropy might exist beneath the region in agreement with earlier results inferred from Pn‐wave travel times.
Compositional control of anisotropy of remanent and induced magnetization in synthetic samples
Authors: Johns Mary , Jackson Mike
Published: February 2008

Anisotropy of remanent and induced magnetization was found to be compositionally controlled in synthetic samples of varying proportions of chlorite (a platy paramagnet), manganese oxide (an isotropic paramagnet), and magnetite (an anisotropic ferrimagnet). Grains were magnetically aligned in a 100 mT field, then uniaxially compressed at 27.6 MPa to produce an L‐S fabric. Anisotropy of anhysteretic susceptibility (AAS) and anisotropy of magnetic low‐field susceptibility (AMS) are coaxial, and anhysteretic susceptibility is consistently more anisotropic than low‐field susceptibility. AMS increases with the addition of oblate magnetite, but decreases with addition of isotropic Mn2O3 to chlorite. These experiments demonstrate that magnetic anisotropy depends on the shape, relative magnetic intensity, and proportion of the magnetic minerals.
Potential effects of ongoing postglacial adjustment on very long baseline interferometry measurements
Authors: Tushingham A. Mark
Published: February 2008

Very long baseline interferometry (VLBI) has the potential to estimate the rates of postglacial adjustment across northern North America. By employing glacial isostatic adjustment theory, the radial rates of uplift or subsidence were computed at five VLBI sites. The expected rates of baseline extension or reduction between these sites and seven static sites (with respect to postglacial adjustment) were estimated. These first‐order estimates may act as a guide in organizing a VLBI network to measure ongoing postglacial adjustment and help determine how many years would be required to observe the deglaciation signal. Ideally, using a network which includes sites in the region of maximum postglacial uplift and sites in the southern United States, this signal should be observed in ∼10 years of annual measurements.
Similitude modeling of internal gravity wave spectra
Authors: Dewan Edmond M.
Published: February 2008

Internal gravity waves are present in both the ocean and atmosphere. The oceanic gravity wave power spectra have been modeled semi‐empirically by Garrett and Munk (1972, 1975) and shown to have “universal” properties. Their model seems to be useful also for atmospheric waves. Recently a similitude type of “saturation” model for vertical wave number horizontal velocity fluctuation spectra has met with empirical support in the atmosphere. The present paper employs a further similitude argument related to “cascade” properties which would apply to the frequency and horizontal wave number spectra. Testable consequences are exhibited. If validated the model would provide useful insight into the physics of these waves.
On the embedding‐dimension analysis of AE and AL time series
Authors: Shan Lin‐Hua , Goertz Christoph K. , Smith Robert A.
Published: February 2008

Several authors have employed the embedding‐dimension method to analyze time series of geomagnetic indices, with differing results for the value of the correlation dimension ν. It is argued that these differences may arise from corresponding differences in the length and construction of the various data sets used. Practical application of the method to sets of discretized data requires use of a delay time scale set by the autocorrelation time of the data set. It is found that a particular data set containing 35 days of AE exhibits an autocorrelation time τc longer by an order of magnitude than that of a short‐duration (<5 days) set, raising the possibility that extant analyses of long‐duration sets may have employed delay times shorter than τc. In addition, the power spectrum of AE reveals modulation at a period of 24 hr. A numerical experiment on the logistic map shows that such modulation introduces an extra degree of freedom in the data, resulting in an augmented correlation dimension.
Airglow rotational temperature measurements during the ALOHA Campaign
Authors: Niciejewski R. J. , Yee J. H.
Published: February 2008

Two instruments sensitive to nocturnal airglow emissions were flown aboard the NCAR Electra aircraft during the 1990 ALOHA campaign—a Fourier transform spectrometer and a 1/4 meter grating spectrometer. The two instruments were chosen to provide complementary data in the near infrared spectral region, the former between 6000 and 10000 cm−1, and the latter between ∼11300 and ∼11600 cm−1. Coordinated measurements were acquired by both instruments of several ro‐vibrational transitions within the ground state of the Meinel band of hydroxyl and one electronic transition of the O2 At system. Rotational temperatures were deduced from both species, including several transitions within the Meinel system. It is usually assumed that the mean height of the O2 At layer is several kilometers above the mean height of the OH layer, implying a means of determining a neutral temperature height profile, albeit coarsely. Data from two flights show an interesting behavior: temperatures inferred from OH and O2 At emissions from the March 31, 1990, mission are equal, T(OH) ∼ T(O2), within error bars during the start of the west‐to‐east flight while T(OH) > T(O2) during the latter part of the flight. For the March 22, 1990, mission, the dependences are reversed with T(OH) > T(O2) during the first part of the south‐to‐north flight, and temperatures similar at the end. A comparison with a standard temperature profile model for April at various latitudes indicates that the best fit is for an altitudinal temperature profile for 30 N latitude. A lower T(O2) indicates a high mesopause existed during the ALOHA experiment.