bluuebunny/crossref_metadata_2025 huggingface dataset:
Genereration of magnetospheric radiation by decay of Bernstein waves
Authors: Rönnmark Kjell
Published: February 2008

Recent observations show that extremely narrow emission lines are present in the spectrum of the terrestrial myriametric radiation, which on the basis of earlier observations has been characterized as nonthermal continuum radiation. The occurance of these monochromatic emissions is not predicted by previously published theories for the radiation. A linear instability, exciting low frequency electrostatic turbulence, is required by theories invoking a nonlinear coalescence to produce the radiation, but there are no conclusive observations associating low frequency electrostatic waves with the sources of myriametric radiation. In this study, the possibility that the radiation is produced by a nonlinear decay of electrostatic Bernstein waves with frequency near the upper hybrid frequency is considered. This mechanism can explain the narrow spectral lines, and does not require a linear instability at low frequencies.
The Jakobshanvs effect
Authors: Hughes T.
Published: February 2008

The Jakobshavns Effect may have been a significant factor in hastening the collapse of palaeo ice sheets with the advent of climatic warming after 18,000 years ago and may precipitate partial collapse of the present‐day Greenland and Antarctic Ice Sheets following CO2‐induced climatic warming in the decades ahead. The Jakobshavns Effect is observed today on Jakobshavns Glacier, which is located at 69°10′N on the west coast of Greenland. The Jakobshavns Effect is a group of positive feedback mechanisms which allow Jakobshavns Glacier to literally pull ice out of the Greenland Ice Sheet at a rate exceeding 7 km/a across a floating terminus 800 m thick and 6 km wide. The pulling power results from an imbalance of horizontal hydrostatic forces in ice and water columns at the grounding line of the floating terminus. Positive feedback mechanisms that sustain the rapid ice discharge rate are ubiquitous surface crevassing, high summer rates of surface melting, extending creep flow, progressive basal uncoupling, progressive lateral uncoupling, and rapid iceberg calving.
MHD turbulence in the solar wind‐comet interaction region
Authors: Sagdeev R. Z. , Shapiro V. D. , Shevchenko V. I. , Szego K.
Published: February 2008

One of the most striking features discovered during the encounter of space probe ICE and comet Giacobini‐Zinner was the presence of intensive MHD turbulence even at large distances from the comet. In this paper it is shown that the mass loading of the solar wind with cometary ions can cause such a phenomenon.
Formation of the volcanic front in subduction zones
Authors: Tatsumi Yoshiyuki
Published: February 2008

A model is proposed to understand the magma genesis beneath the volcanic front which overlies the dipping seismic zone with a constant depth of about 110 km in most subduction zones. It is suggested that the constant depth of 110 km is governed by the decomposition of amphibole in the mantle wedge. Hydrous phases in the subducted slab decompose at levels shallower than 100 km, that is, beneath the fore‐arc region. The slab‐derived H2O, enriched in incompatible elements with larger ionic radii, reacts with the overlying mantle wedge materials to form polluted amphibole peridotite. The polluted peridotite is transported downward on the slab by the induced convection in the mantle wedge. Amphibole in the dragged peridotite decomposes at a depth of about 110 km, just beneath the volcanic front. H2O released migrates upward to reform amphibole peridotite in the higher‐temperature and lower‐pressure region. When the front of amphibolization reaches a level at which the solidus temperature of amphibole peridotite is distributed, initial magmas are produced and rise as a form of mantle diapir. The mantle diapir stops rising to segregate a primary magma for lavas on the volcanic front.
A new mechanism for stable viscous remanent magnetization and overprinting during long magnetic polarity intervals
Authors: Moon Tom , Merrill Ronald T.
Published: February 2008

A new mechanism by which viscous remanent magnetization, VRM, can be acquired is proposed. This VRM probably is the major cause of overprinting during long magnetic polarity intervals.
Solar wind carbon, nitrogen and oxygen abundances measured in the Earth's magnetosheath with AMPTE/CCE
Authors: Gloeckler G. , Ipavich F. M. , Hamilton D. C. , Wilken B. , Stüdemann W. , Kremser G. , Hovestadt D.
Published: February 2008

The solar wind number density ratios of C6+ + C5+ and N7+ + N6+ + N5+ relative to O8+ + O7+ + O6+ have been measured for the first time using data from the Charge‐Energy‐Mass (CHEM) Spectrometer on the AMPTE/CCE spacecraft during four solar active periods from Sept. 19 to Nov. 1, 1984 when CCE traversed the subsolar magnetosheath of the compressed magnetosphere. We find the average values of the density ratios of C/O and N/O to be 0.43±0.03 and 0.15±0.06, respectively. These ratios, as well as our average He2+/O ratio of 43±5 for these same time periods, are in excellent agreement with Solar Energetic Particles (SEP) abundance ratios as well as SEP‐derived coronal abundances of these elements. Our solar wind C/O ratio is substantially below the generally accepted photospheric value of 0.60.
Ice plasma wave measurements in the ion pick‐up region of comet Halley
Authors: Scarf F. L. , Coroniti F. V. , Kennel C. F. , Sanderson T. R. , Wenzel K‐P , Hynds R. J. , Smith E. J. , Bame S. J. , Zwickl R. D.
Published: February 2008

In late March 1986 the plasma wave instrument on the International Cometary Explorer (ICE) detected sporadic bursts of strong plasma turbulence with average wave characteristics very similar to those detected six months earlier, during the ICE traversal of the Comet Giacobini‐Zinner (G‐Z) heavy ion pick‐up region. In both cases the observations of enhanced wave levels were generally correlated with simultaneous detection of energetic ions. We interpret the 1986 activity in terms of plasma instabilities associated with solar wind pick‐up of ions produced by heavy neutrals from Comet Halley. On March 25, when the distance between Comet Halley and ICE was 28.1 million kilometers, the ICE‐to‐comet range was about six times greater than the distance that marked the measured outer boundary of the turbulent heavy ion pick‐up region for G‐Z. Based on comparison with G‐Z data and with earlier Halley observations, plausible arguments suggest that in late March, Halley should have produced detectable levels of energetic ions and associated plasma turbulence in a region with a spatial extent of 30‐40 million kilometers.
the two‐faced mica
Authors: York Derek , Martinez Margarita Lopez
Published: February 2008

We explain two common 40Ar/39Ar age spectra shapes in biotite. One features a dip in ages at mid‐temperature regions of the spectrum. The other has exactly the opposite characteristic, i.e. a bump upwards in age at the same position. The explanation assumes that the vast majority of biotites consist of two almost completely independent K‐Ar phases. During laboratory step‐heating of irradiated biotite, the argon from these two phases is separated via release over two different temperature ranges. Biotite is therefore a clock with two faces.
On crustal seismicity of the Amazonian foothill of the central Peruvian Andes
Authors: Dorbath C. , Dorbath L. , Cisternas A. , Deverchere J. , Diament M. , Ocola L. , Morales M.
Published: February 2008

A microearthquake survey of crustal seismicity conducted in 1985 on the Eastern Cordillera and the Amazonian foothills in Central Peru gives a description of the present tectonic activity related to the uplift of the Andes. Hypocenters on the Huaytapallana fault are shallower than 10 km, and their focal mechanism is in agreement with the fault trace corresponding to the earthquakes of 1969 and suggests a reverse strike slip movement on a plane striking N130°. An active tectonic zone is evidenced along a NW‐SE direction passing through the Amauta Subandean region. The vertical distribution of hypocenters and the comparison of shallow and deep focal mechanisms suggest a reverse fault dipping to the west. Depths vary between 0 and 20 km. and never exceed 32 km. The Huaytapallana Cordillera is uplifted by thrust faults on both sides.
Palaeoclimatic and sedimentary history from magnetic susceptibility of loess in China
Authors: Heller Friedrich , Tung‐sheng Liu
Published: February 2008

The magnetostratigraphic age of the oldest loess sediments in the central Chinese loess plateau investigated so far has recently been placed at ca. 2.4 million years B.P. Thus, glaciations in Central Asia, which are believed to provide the detritus for the formation of Chinese loess, commenced at the same time as the first ice‐rafted debris sank into the ocean basins of the northern hemisphere [Shackleton et al., 1984], Lithologic, palaeontologic, geochemical and especially rock‐magnetic variations throughout the loess column are indicative of palaeoclimatic fluctuations during loess deposition. The variations of magnetic low field susceptibility in loess closely resemble those of the marine oxygen‐isotope record [Shackleton and Opdyke, 1976] and establish for the first time a continuous record of the Pleistocene glacial and interglacial stages in a continental section. Spectral analysis of the rock‐magnetic time series indicates slow apparent sedimentation during interglacial periods which are characterized mainly by calcium dissolution and related compaction of the soils. Variable aeolic sediment influx as well as erosion and/or polygenetic soil formation may also strongly influence the sedimentary history.
Conjugacy of proton and electron auroras observed near L=6.1
Authors: Sato N. , Fujii R. , Ono T. , Fukunishi H. , Hirasawa T. , Araki T. , Kokubun S. , Makita K. , Saemundsson Th.
Published: February 2008

Simultaneous observations using two‐channel meridian scanning photometers were carried out at geomagnetically conjugate‐pair stations, Syowa Station in Antarctica and Husafell in Iceland (L=6.1), during August‐September 1984. The photometers were equipped with interference filters for OI 5577A and Hß 4861A emissions. During the conjugate campaign, the data obtained on September 26, 1984 was of the highest quality with a clear sky and no moon. The initial results on the conjugacy of Hß proton auroras and their relations to 5577A electron auroras are as follows; i) During the pre‐breakup phase the Hß auroras observed at Syowa were mostly located at a lower latitude than the simultaneous conjugate auroras observed at Husafell. Such Hß auroras showed high intensities at Syowa relatively to those at Husafell, ii) During the auroral breakup phase, enhancement of Hß emissions occurred almost simultaneously in the both hemispheres. However, the intensities of Hß auroras were higher at Husafell than at Syowa, iii) During the pre‐breakup phase, Hß auroras observed continuously in the equator boundary were associated with weak diffuse 5577A auroras in the conjugate regions, (iv) In the regions and time intervals where 5577A auroras showed poor conjugacy, the Hß auroras also showed poor conjugacy.
Correlation between the surfaces of natural rock joints
Authors: Brown Stephen R. , Kranz Robert L. , Bonner Brian P.
Published: February 2008

Cores from two natural joints were studied to estimate the degree of correlation between the surfaces and the distribution of apertures. Matched pairs of profiles were taken from both surfaces of each joint. These profiles were then placed together to produce a linear trace of the apertures. Power spectra of the individual surfaces were compared to that of the apertures. Correlation between the surfaces is evidenced by the lack of long wavelength power in the aperture traces relative to the individual surfaces. The correlation lengths for the two joints studied are between 0.5‐5 mm. It is clear that the correlation between the surfaces must be considered, when studying the mechanical and transport properties of rock joints.
Small comets: Implications for interplanetary Lyman α
Authors: Donahue T. M.
Published: February 2008

If small comets are as numerous in the inner solar system as Frank et al. [1986a] have recently proposed, large and easily detectable amounts of hydrogen would be generated in interplanetary space. Inhibition of water vapor production by a factor of 3 × 10−9 by very thick dust mantles would be necessary to prevent excitation of a detectable interplanetary Lyman α glow. Other optical problems associated with the cometesimals are also discussed.
Analysis of the microseismicity induced by a fluid injection in a granitic rock mass
Authors: Talebi Shahriar , Cornet François‐Henri
Published: February 2008

The microseismicity induced by a fluid injection at a depth of 443 m in a granitic rock mass has been monitored with a 16 station network. The location of the five events observed on the near totality of the network suggests that flow away from the well occurred along a preexisting fracture nearly parallel to the maximum horizontal principal stress direction and not along the fractures observed at the wellbore. Focal mechanisms of these events are coherent with shear motions along fissures which intersect the main flow path. A difficulty has been encountered in the determination of source parameters from spectral analysis of signals because of attenuation effects. Indeed, for uncorrected spectra the corner frequency was found to decrease as the source to station distance increased. This demonstrates the effect of attenuation on the signals and therefore the necessity of correcting spectra for attenuation effects before estimating source parameters.
Heat flow ‐ heat production relationships in the UK and the vertical distribution of heat production in granite batholiths
Authors: Webb P. C. , Lee M. K. , Brown G. C.
Published: February 2008

Recently the UK heat flow ‐ heat production data‐base has been expanded. The linear correlation formerly recognised for southern Britain is now in doubt and there seems no justification for recognising heat flow provinces with characteristic q* and D in the UK. Interpretation of heat flow ‐ heat production data from two voluminous granite batholiths is consistent with geochemical evidence that depth distributions of heat production differ according to magma type.
Late Archaean/Early Proterozoic CO2streaming through the lower crust and geochemical segregation
Authors: Newton R. C.
Published: February 2008

Considerable evidence exists for large‐scale migration of CO2‐rich fluids through the lower continental crust in the Late Archaean and Early Proterozoic, with transfer of heat producing elements and H2O to higher levels. The evidence manifest in the large charnockitic terrains of this age includes deformation‐related charnockitic alteration of gneisses, nearly ubiquitous CO2‐rich fluid inclusions in minerals, depletion of large‐ion‐lithophile elements (LILE), particularly Rb, relative to typical upper crustal rocks, similar depletion of18O in paragneisses and petrographic and geochemical evidence of open‐system replacement of amphibole gneiss by charnockite. A conveyor‐belt upper mantle source appears to have been necessary for prolonged CO2supply in high‐grade crustal metamorphism, most plausibly by deep subduction of marine carbonate under continental interiors. This plate tectonic mode seems consonant with crustal thickening and orogenic patterns inferred for most charnockitic terrains and with CO2transport mechanisms constrained by experimental petrology.
The depth dependence of heat production in the continental lithosphere, derived from seismic velocities
Authors: Rybach Ladislaus , Cermák Vladimír
Published: February 2008

An experimentally established relationship enables the conversion of compressional seismic velocity to heat production (A). The conversion, performed for 47 characteristic seismic sections from various tectonic units in Central and Eastern Europe, yields a general decrease of A with depth (z). The pattern of decrease depends on geological age: young tectonic units with high heat flow exhibit a more rapid decrease. The depth dependence of A does not follow the simple exponential law A(z) = A(O)exp(−z/D). The logarithmic decrement D has the dimension length; in general, D decreases with depth, from 20‐30 km at 10 km depth to less than 10 km at the Moho. In the uppermost 10 km of the crust a certain redistribution of the heat producing radioelements U and Th can occur by deep groundwater migration through microcrack networks. Below the Moho, heat production attains values which represent only insignificant contributions to heat flow through or to temperature field changes in the lithosphere.
Is the mantle geotherm subadiabatic?
Authors: Jeanloz Raymond , Morris S.
Published: February 2008

Internal heating and secular cooling are expected to decrease the geothermal gradient away from an adiabat. A scaling analysis that is quantified on the basis of published numerical models indicates that the interior geotherm should be nearly isothermal through the lower mantle if all heating is from within. For the more realistic condition that the mantle is partly heated from within and partly from below, we still expect the average thermal gradient to be significantly subadiabatic through much of the interior of the mantle. Values of the seismologically observable inhomogeneity parameter η ∼ 1.04 to 1.07 should characterize the subadiabatic regions of the lower mantle.
Interplanetary magnetic field enhancements: Further evidence for an association with Asteroid 2201 Oljato
Authors: Russell C. T.
Published: February 2008

In 1980 and 1983 the asteroid 2201 Oljato passed inside the orbit of Venus, respectively 65 and 21 days prior to the passage of Venus, apparently causing disturbances in the interplanetary magnetic field, possibly through the interaction of its debris trail with the solar wind. In July 1986 the asteroid passed through the inner solar system 25 days after Venus and we expected to find similar disturbances if the debris trail extended in front of the asteroid. The expected disturbances were observed. All data from the longitude range of the disturbances have been examined for all Venus years as well as from a control period over the same solar longitudes but at different ecliptic longitudes. No enhancements in the rate of occurrence of events were seen in the control periods during 1980, 1983 and 1986, and the rate was uniformly low at all other times. The new data reaffirm the association of solar wind disturbances with the asteroidal passage and imply a debris trail that extends perhaps 1 AU both in front of and behind the asteroid.
Waveform effects of a high‐velocity, subducted slab
Authors: Vidale John E.
Published: February 2008

Creager and Jordan [1986] propose that penetration of subducting slabs under the Kurile Islands and other subduction zones to depths of at least 1000 km is necessary to explain travel time anomalies of deep earthquakes. Such penetration would also be expected to affect the amplitudes and waveforms of the body waves from earthquakes. Synthetic seismograms appropriate for a record section in a plane perpendicular to the strike of the slab are presented using a coupled finite‐difference and Kirchhoff method. Our shear‐wave version of the compressional‐wave velocity structure of Creager and Jordan [1986] produces an amplitude decrease up to a factor of four and waveform broadening up to 20 seconds for SH arrivals with a take‐off angle pointing straight down the slab. Slabs that extend only 300 km below the earthquake but are half as thick and twice as anomalously fast as Creager and Jordan's [1986] velocity model will roughly preserve the travel time variation pattern, and show less waveform broadening, but produce first arrivals that are emergent. Slabs that become thicker with depth show less waveform broadening. Reconciliation of the amplitude, waveform distortion, and timing of body waves from deep events is necessary to understand the geometry of slabs in the upper mantle and near and below the 650 km discontinuity.
Growth of contact area between rough surfaces under normal stress
Authors: Stesky R. M. , Hannan S. S.
Published: February 2008

The contact area between deforming rough surfaces in marble, alabaster, and quartz was measured from thin sections of surfaces bonded under load with low viscosity resin epoxy. The marble and alabaster samples had contact areas that increased with stress at an accelerating rate. This result suggests that the strength of the asperity contacts decreased progressively during the deformation, following some form of strain weakening relationship. This conclusion is supported by petrographic observation of the thin sections that indicate that much of the deformation was cataclastic, with minor twinning of calcite and kinking of gypsum. In the case of the quartz, the observed contact area was small and increased approximately linearly with normal stress. Only the irreversible cataclastic deformation was observed; however strain‐induced birefringence and cracking of the epoxy, not observed with the other rocks, suggests that significant elastic deformation occurred, but recovered during unloading.
Frictional behavior of granite at low and high sliding velocities
Authors: Blanpied M. L. , Tullis T. E. , Weeks J. D.
Published: February 2008

To study how the velocity dependence of steady state friction of granite varies as a function of sliding rate, we slid initially bare surfaces of Westerly granite at rates of from 0.001 µm/s (32 mm/yr) to over 3 mm/s, accumulating 376 mm of total displacement; the normal stress was 50 MPa. We find that the velocity dependence, measured by a‐b, changes from negative (velocity weakening) at <10 µm/s to positive (velocity strengthening) at >32 µm/s. Modeling of experimental data using a simple constitutive law shows that the magnitude of a, the direct dependence of friction on velocity, remains nearly constant at all rates up to at least 100 µm/s. The increase in a‐b with velocity is due to a reduction in the magnitude of b. Our results are consistent with the view that a measures the deformation rate sensitivity of the fault zone material and that b measures the amount of change of some fault zone property.
Statistical tests for closure of plate motion circuits
Authors: Gordon Richard G. , Stein Seth , DeMets Charles , Argus Donald F.
Published: February 2008

The standard method of testing whether data describing the relative motion of three plates meeting at a triple junction are consistent with rigid plate tectonics uses the condition of plate circuit closure: the Euler vectors or angular velocities describing the relative motion of each plate pair must sum to zero. Deviations from closure suggest that the data are systematically in error, or that the plate boundaries have been identified incorrectly, or that the plates are non‐rigid. We examine two methods, one based on a chi‐square test and the other based on an F‐ratio test, of testing whether plate motion circuits close. We find the latter test is useful, but the former is of limited value because of the common practice of systematically overestimating errors in plate motion data. We apply the F‐ratio test to Minster and Jordan's data for the boundaries dividing the Pacific, Cocos, and Nazca plates, which prove consistent with plate circuit closure. Application of the test to their data for the boundaries dividing the Australian, Antarctic, and African plates shows nonclosure even after deletion of data from the Carlsberg Ridge, which recently has been suggested to divide the African plate from an Indo‐Arabian plate. This nonclosure suggests systematic errors in the data or internal deformation of one or more of the plates meeting at the Indian Ocean Triple Junction.
Plasma Transport Near the Magnetic Cavity Surrounding Comet Halley
Authors: Haerendel Gerhard
Published: February 2008

The dominant forces resisting the transport of magnetic field into the inner coma of a comet are ion mass loading from and friction with the expanding neutral atmosphere. A magnetic cavity is thereby created. Close to it the frictional force is most important. Careful interpretation of the magnetic field profile measured during the Giotto flyby of comet P/Halley reveals the existence of an inward directed component of plasma flow of a few km/s, which drops to zero at the boundary of the cavity. The energy transferred from the neutral gas to the plasma by friction and mass loading is responsible for the strongly elevated ion temperatures outside the magnetic cavity. Fitting of the observed magnetic profile and ion temperature distribution yields quantitative determinations of some crucial parameters of the coma.
The absence of region 1/Region 2 field‐aligned currents during prolonged quiet times
Authors: Rich Frederick J. , Gussenhoven M. S.
Published: February 2008

Using magnetic field and precipitating particle data from the DMSP/F7 satellite, we have found that, during extended periods of geomagnetic quiet, the large‐scale field‐aligned current (FAC) system known as Region 1/Region 2 either does not exist or is too small to be observable. A clear dayside cleft FAC system is observed on the preferred side of local noon for the indicated by the IMF By component and the cleft electron precipitation extends far into the region normally considered to be the polar cap. These quiet periods represent times when energy input from the solar wind is low; the IMF is maintained at near zero or slightly northward levels and the solar wind speed is low. For such times, the Kp index is ≤ 1 for several consecutive 3 hour periods. In these cases, the auroral zone is marked by diffuse electron precipitation, and only small‐scale or fine‐scale FAC's. In the polar cap, electron precipitation is characterized by polar rain and there are no FAC systems (including the NBZ system). Some previous reports imply that one should always find this large‐scale Region 1/Region 2 system during quiet times. We suggest that the Region 1/Region 2 system vanishes 10's of mins to hrs after the IMF has turned northward.
Comparisons of measured sulfate production due to ozone oxidation in clouds with a kinetic rate equation
Authors: Hegg Dean A. , Hobbs Peter V.
Published: February 2008

A comparison is made between sulfate production rates predicted by the kinetic rate expression of Hoffman [1986] and measurements of O3‐induced sulfate production in real and simulated clouds. Reasonable agreement is found and the Hoffman rate expression is recommended for interim use in numerical models to predict sulfate production due to O3 oxidation in clouds.
No short reversals of Brunhes Age recorded in the Toba Tuffs, north Sumatra, Indonesia
Authors: Diehl J. F. , Onstott T. C. , Chesner C. A. , Knight M. D.
Published: February 2008

Paleomagnetic and 40Ar/39Ar data indicate that two tuffs are present at Siguragura, North Sumatra, Indonesia: a reversely magnetized tuff (the earliest eruptive unit of the Toba caldera) of Matuyama age (0.84 Ma) and a normally magnetized tuff (the last eruptive unit of the Toba caldera) of late Brunhes age. No reversely magnetized tuffs of late Brunhes age are present at this location as suggested by previous investigators.
The derivation of 40Ar/39Ar age spectra of single grains of hornblende and biotite by laser step‐heating
Authors: Layer Paul W. , Hall Chris M. , York Derek
Published: February 2008

We present the first examples of 40Ar/39Ar age spectra for hornblende and biotite derived by the laser step‐heating of individual grains. It is straightforward to use a continuous laser to produce detailed (>20 steps), reproducible and precise age spectra in this way. An infra‐red microscope is used to monitor the sample temperature changes so that a judicious heating schedule can be chosen. Such a system can be readily automated. The biotite spectra shown exhibit large age differences (∼60 m.y.) between co‐existing flakes differing in mass by a factor of ∼70.
Comment on the letter “On the influx of small comets into the Earth's atmosphere II: Interpretation”
Authors: Wasson John T. , Kyte Frank T.
Published: February 2008

Frank et al. (1986a) inferred a terrestrial mass influx of 108 g icy comets of ∼1015g a−1. About 20‐40% of the mass of known comets is comprised of chondritic rocky matter, thus the associated influx of chondritic matter is inferred to be at least 2 · 1014 g a−1. Iridium‐accumulation evidence indicates a total influx of chondritic extraterrestrial matter having masses in the range 10−14 to 1017 g of 7.8 · 1010 g a−1, 2500 times smaller; >99% of this infalling matter is in masses <10−2 g or >1011 g. For bodies in the 107‐109 g range the inferred flux is 108 g a−1, a factor of 2 · 106 lower than that inferred for the Frank et al. comets. Because there must be devolatilized objects in the same population, the actual discrepancy is larger, probably ∼3 · 109.
Locating microearthquakes induced by hydraulic fracturing in crystalline rock
Authors: House Leigh
Published: February 2008

Microearthquakes induced by hydraulic fracturing in crystalline rock at a depth of 3.5 km were located with a precision of better than 30 m to obtain information about the geometry and dimensions of the fracture system produced. The induced microseismicity was monitored by a network of five borehole seismic stations; a total of about 800 induced events were reliably located from arrival times. Event locations show a tabular distribution that strikes 350° and dips 65° east, subparallel to the injection well. The injection was intended to produce a fracture system that would hydraulically connect two subparallel wells. A lack of fluid communication between them is consistent with a lack of induced microearthquakes near the target wellbore. The 150 m thickness of the zone of seismicity far exceeds the relative locational uncertainties. The injected fluid appears to have stimulated a zone of rock, rather than simply a single fracture. The distribution of microseismic events presumably envelops the zone of fluid paths created by the fracture experiment.
Mesospheric temperature inversion and gravity wave breaking
Authors: Hauchecorne A. , Chanin M. L. , Wilson R.
Published: February 2008

More than 500 nightly mean temperature profiles have been obtained since 1981 by two Rayleigh lidars located in south of France 550 km apart. In the mesosphere a temperature inversion, a feature persisting for several days, is frequently observed simultaneously at both sites. From a statistical study of the inversion characteristics, it is shown that its altitude ranges from 55‐72 km in winter to 70‐83 km in summer, while its probability of occurrence presents a semi‐annual variation with a maximum higher in winter than in summer and a minimum lower in May than in September. The seasonal variation of the temperature inversion is shown to be very similar to that of the MST radar echoes in the mesosphere associated to turbulent layers generated by the breaking of gravity waves. A crude estimate of the amplitude growth with height of a gravity wave in the presence of an inversion layer indicates that the wave will break preferably inside and above this layer. The persistence of a temperature inversion during several days, with amplitude as large as 40 K, is tentatively explained by the heating of the turbulent layers generated by the continuous breaking of gravity waves above the secondary minimum of temperature.
Temperatures and shear stresses in the upper part of a subduction zone
Authors: van den Beukel Jilles , Wortel Rinus
Published: February 2008

The temperature structure of the upper part of a subduction zone, i.e. the region between the trench and the volcanic line, has been investigated by means of numerical modelling. Published heat flow measurements are used to constrain the thermal structure of this region and the shear stresses at the plate contact. A pressure and temperature dependent rheology is used to model shear stresses. It is shown that temperatures at the plate contact and within the upper plate are primarily determined by frictional heating. Except for the subduction of very young oceanic lithosphere (less than 30 Myr old), these temperatures, as well as shear stresses, are essentially independent of the age of the subducting oceanic lithosphere and the convergence velocity between the two plates. Pressure‐temperature conditions at the upper surface of the slab for the proposed thermal model are in good agreement with conditions inferred from high‐pressure metamorphic material of regional extent in the Franciscan Complex of California.
Decay of the El Chichon perturbation to the stratospheric aerosol layer: Multispectral ground‐based radiometric observations
Authors: Pearson E. W. , LeBaron B. A. , Michalsky J. J.
Published: February 2008

A 9‐year time series of multispectral radiometric observations taken at Rattlesnake Mountain Observatory (46.4 N, 119.6 W) is analyzed to determine the long‐term behavior of the El Chichon‐induced perturbation to the stratospheric aerosol layer. A technique for determining the volcanic enhancement is described. Time series data for the volcanic enhancement in stratospheric optical depth at wavelengths of 1010, 785, 535, 486, and 428 nm are presented. The main features of the results, slight wavelength dependence and a seasonal oscillation superimposed on the expected exponential decay at all wavelengths, are discussed.
Resonance scattering by sodium in mercury's atmosphere I. The effect of phase and atmospheric smearing
Authors: Killen R. M.
Published: February 2008

We present the dependence of the intensity in the sodium D1 and D2 lines on the planetary phase and position on the disk. Theoretical intensities are convolved with an atmospheric point spread function with FWHM of 0″.5 and 2″.0 for planetary phases 60° and 90°. We show that although the absolute intensities are extremely dependent on seeing, the I(D2)/I(D1) ratio remains a reliable indicator of column abundance regardless of the seeing function. For a uniform distribution of sodium, limb brightening will be apparent for a seeing disk with FWHM of 0″.5 but will not be apparent for a FWHM of 2″.0.
On the utilization of ionosonde data to analyze the latitudinal penetration of ionospheric storm effects
Authors: Forbes Jeffrey M. , Codrescu Mihail , Hall Timothy J.
Published: February 2008

Upper atmosphere science is placing increased emphasis on global coupling between the magnetosphere, ionosphere, and thermosphere systems, particularly with regard to the penetration of dynamic, chemical, and electrodynamic effects from high to low latitudes during magnetically disturbed periods. An emerging potential exists for latitudinal and longitudinal chains of ionosondes to contribute uniquely to this thrust in ways complementary to the capabilities and shortcomings of other ground‐based sensors and satellites. Here we illustrate a methodology whereby the fullest potential of such ionosonde data can be realized. Data from a chain of stations close to the −165° magnetic meridian and separated by about 5° in magnetic latitude are used to study the relationships between magnetic activity, hmF2, foF2, and inferred meridional winds during 17‐28 April, 1979. Hourly values are fit in latitude using Legendre polynomials, and variations from quiet‐time values are displayed in latitude ‐ U.T. coordinates using a color graphics method which provides an illuminating illustration of the penetration of ionospheric disturbances in latitude and their dependence on Kp, storm time, and local time. Observed effects are interpreted in terms of plausible electric field, neutral wind, and neutral composition changes during the storm period. For instance, net depletions in foF2 occur over the entire disturbed interval down to about 25°‐30° latitude, apparently due to such increased N2 densities that the resulting enhanced plasma loss rates overcompensate any “positive” storm effects whereby southward winds elevate the F‐layer peak to altitudes of reduced chemical loss. Positive storm effects are, however, observed at lower latitudes, and may also reflect the influence of electric fields as well as winds. Interestingly, besides reflecting the anticipated southward flows and equatorward extensions in conjunction with magnetically disturbed conditions, the 24‐hour average meridional winds exhibit a northward return flow after the magnetic disturbance has relaxed; this is a new feature of thermosphere dynamics which should be further investigated using general circulation models and other means of inferring the wind field.
Implications of large flow velocity signatures in nearly isotropic ion distributions
Authors: Williams D. J. , Mitchell D. G. , Christon S. P.
Published: February 2008

We have compared ISEE‐1 energetic (≥24 keV) ion distributions with previously published, lower‐energy (≤17 keV/e) ISEE‐1 H+ and He++ distributions [Peterson et al., 1981] in the quiet‐time plasma sheet at ∼15 RE radial distance, ∼0430 local time, and within ∼1 RE of the expected neutral sheet position. Moment calculations carried out over the nearly isotropic H+ and He++ plasma distributions yield low (≲14 km/sec) bulk velocities. However, the spectral shapes of these same distributions are indicative of high flow speeds (∼500–700 km/sec). We argue that these seemingly contradictory results within a given measurement of the plasma distribution are consistent and can be explained by the evolution of plasma distributions flowing along a geomagnetic field line. Isotropization of the (observed) distributions while preserving their spectral signatures can result from the effects of single‐particle motion and pitch angle diffusion. Whether the dual properties of isotropy and high‐velocity spectra are observed depends on the position of the observation point along the field line and on the ambient plasma number density, bulk velocity, and temperature. For the case presented we conclude that H+ and He++ ions of solar wind origin were accelerated through an electrostatic potential of ∼2.4 kV prior to their observation by ISEE‐1 in the plasma sheet on a closed magnetospheric field line. From energetic ion observations we infer that a second, independent plasma sheet population existed at this ISEE‐1 position in the geomagnetic field.
A few parts in 108geodetic baseline repeatability in the Gulf of California using the Global Positioning System
Authors: Tralli David M. , Dixon Timothy H.
Published: February 2008

Global Positioning System (GPS) geodetic measurements of 350–650 km baselines across the Pacific‐North America plate boundary in the Gulf of California are presented. The analysis employs a four‐station U.S. fiducial network and combined carrier phase and pseudorange data. Water vapor radiometer (WVR) data at the Gulf sites are used to calibrate the GPS signal for wet tropospheric path delays. Residual tropospheric delays are modeled as first‐order exponentially correlated stochastic processes. The measurement precision for horizontal components is a few parts in 108or better. Comparison of the Gulf data with other geodetic techniques is not yet possible, however the system accuracy appears to be about 1 part in 107based on simultaneous GPS solutions of a baseline in California collocated with VLBI. The results are encouraging because a high level of precision with GPS is demonstrated even with stations located outside a fiducial network and when wet tropospheric path delays are significant, typically exceeding 20 cm at zenith.
Nd isotopic variations in Precambrian banded iron formations
Authors: Jacobsen Stein B. , Pimentel‐Klose Mario R.
Published: February 2008

The isotopic composition of Nd is reported for 8 banded iron formations (BIFs) ranging in age from 0.65 to 3.4 Ga. The data suggest a trend of increasingly positive ϵNd values with age and is interpreted to reflect isotopic variations in Precambrian seawater. The Urucum (0.65 Ga) and the Gunflint (1.9 Ga) BIFs yield negative ϵNd values between −6 and 0. The remaining BIFs, with ages of 1.84 to 3.4 Ga, have predominantly positive values between −1 and +4. The Nd isotopic signature of BIFs changes from a principally continental source to a dominantly depleted mantle source from the present into the Archean. The positive, mantle‐like values of Archean BIFs contrast strongly with the negative, continental‐like values of Phanerozoic seawater. Therefore, the REE budget of the oceans during most of the Archean was probably dominated by hydrothermal circulation of seawater through mid‐ocean ridge basalts and not by river waters, as today.
“Space weather forecast”: Prediction of relativistic electron intensity at synchronous orbit
Authors: Nagai Tsugunobu
Published: February 2008

Long‐term variations in high‐energy (greater than 2 MeV) electron flux at synchronous orbit are examined to reveal their close relationship to geomagnetic activity. The electron flux diminishes rapidly in association with an enhancement of geomagnetic activity (storm) and then increases. The flux becomes higher than the pre‐storm level and its peak occurs approximately 4–5 days after the enhancement of geomagnetic activity. A linear prediction filter is designed for daily sums of Kp as input data and corresponding daily averages of the electron flux (Log value) as output data. The data are those taken in 1984–1985. This filter can successfully reproduce the electron flux behavior observed not only in 1984–1985 but also in 1978–1981.
Hot oxygen atoms in the upper atmospheres of Venus and Mars
Authors: Nagy Andrew F. , Cravens Thomas E.
Published: February 2008

The altitude distribution of the hot oxygen density was calculated for the upper atmospheres of Venus and Mars for solar cycle maximum and minimum conditions, respectively. The calculated values for Venus are in good agreement with the observed values and are about a factor of twenty larger than the calculated values for Mars at the exobase.
Observations of ion cyclotron harmonic structure in type 1 to 4 VHF auroral echoes
Authors: Prikryl P. , André D. , Sofko G. J. , Koehler J. A. , McKibben M. J.
Published: February 2008

The understanding of E region plasma instabilities is crucial for the interpretation of the enormous stream of data from large ongoing projects like STARE and SABRE in Europe, and BARS in Canada, in which measurements of radar scatter from E region plasma waves are used to infer the electric fields, hydromagnetic waves, and field‐aligned currents in the E region. Auroral echoes measured by 50 MHz CW Doppler radars strongly indicate that the electrostatic ion cyclotron (EIC) mechanism may be more important in auroral irregularity formation than was previously suspected. Doppler spectra taken over 64 ms intervals are highly structured, showing as many as seven or eight discrete frequency components whose frequency separation is often approximately the cyclotron frequency of one of the principal ions in the E region. In this note, we show that when examples of each of the four standard spectral types (1 to 4), whose classification is based upon time‐averaging over several seconds, are examined with the finer time resolution of 64 ms (i.e. a resolution of the same order as the lifetime of the individual plasma irregularities), all four types appear to be composites of many harmonically structured bursts as described above. Since the spectral components in individual bursts may occur at frequencies that are not exact multiples of the ion gyrofrequency, time averaging over many bursts usually smears out the harmonic content, resulting in broader spectral peaks. The resulting smoothed spectra then appear to be caused by instabilities other than the EIC instability.
Magnetotelluric observations along the lithoprobe southeastern Canadian Cordilleran Transect
Authors: Jones Alan G. , Kurtz Ron D. , Oldenburg Doug W. , Boerner David E. , Ellis Rob
Published: February 2008

As part of the LITHOPROBE Southern Cordilleran Transect investigations, twenty‐seven wideband magnetotelluric (MT) responses were obtained along 150 km of the reflection seismic lines. The MT profile begins to the east on the Rocky Mountain Trench above autochthonous North American basement, traverses across the Purcell anticlinorium, the Kootenay Arc, the Nelson batholith, and ends on the east side of the Valhalla gneiss complex.

Sites near Kootenay Lake respond to a major near‐surface conductivity anomaly that is probably due to either graphitic schists or to an extension of the silver‐bearing mineralization found further north. The short period (<1 s) data from above the Nelson batholith indicate its thickness extent, whereas the long period (>1 s) data are highly complex and exhibit 3D regional features. Inversions of the data from the two sites on the Valhalla complex yield 1D models with interfaces in electrical conductivity at depths that agree with an increase in the number of reflectors at ≈9 km, “the base of layered reflections” at ≈22 km, and the Mono at ≈35 km.

Of major significance to our understanding of the current composition and state of the lower continental crust is that although for the Valhalla complex there are few reflections below ≈22 km the MT responses indicate that the zone is conducting. This is the only location known to the authors where the lower crust is seismically transparent but electrically conductive.
lightning‐related fields in the ionosphere
Authors: Baginski M. E. , Hale L. C. , Olivero J. J.
Published: February 2008

Lightning‐related transient electric fields and conduction current densities due to the redistribution of charge by the return stroke, but not directly associated with the high‐intensity current channel, are investigated via a simulation of Maxwell's equations. The investigation presents evidence to suggest that the lightning‐related charge redistribution and subsequent relaxation, rather than the high intensity current, is the source of the major component of the transient field and energy coupled to the ionosphere. A time domain finite element analysis is employed in the simulation, using a conductivity profile obtained simultaneously with electric field measurements which agree, in general terms, with the simulations. It is concluded that prior depictions of these phenomena underestimate the fraction of the total energy that couples to and dissipates within the ionosphere and magnosphere.
Kinetics and product studies of the BrO + ClO Reaction: Implications for Antarctic chemistry
Authors: Sander Stanley P. , Friedl Randall R.
Published: February 2008

The reaction of ClO with BrO has been investigated by two independent techniques, discharge flow‐mass spectrometry and flash photolysis‐UV spectrometry, over the temperature range 220‐400 K and the pressure range 1‐760 torr. Rate constants have been determined for three product channels; a) Br + ClOO, b) Br + OClO, and c) BrCl + O2. The rate constants for the overall reaction and each reaction branch were found to be inversely dependent on temperature and independent of pressure. The results for the temperature dependence of the overall rate constant from the discharge flow and flash photolysis studies are in excellent agreement, and collectively disagree substantially with the only previous temperature dependence study. Also, in contrast to previous studies, the channel forming BrCl is found to be significant (≃ 8%). These kinetic measurements have an important impact on the modeling of Antarctic chemistry; for temperatures found in the Antarctic stratosphere the rate coefficients for the channels yielding ClOO and OClO are a factor of 2‐3 larger than previously estimated. In addition, the BrCl channel, which has an impact on the nighttime partitioning of BrOX and the diurnal variability of OClO, has been omitted from previous atmospheric models.