bluuebunny/crossref_metadata_2025 huggingface dataset:
Methane flux fromPeltandra virginica:stable isotope tracing and chamber effects
Authors: Chanton Jeffrey P. , Whiting Gary J. , Showers William J. , Crill Patrick M.
Published: February 2008

Methane flux from plots ofPeltandra virginicain a bottomland hardwood swamp in southeast Virginia varied from 270 to 670 mg CH4m−2d−1from May to August and was 6 times greater than the flux from unvegetated adjacent open waters. Variations in chamber temperature, light, and CO2levels failed to produce systematic changes in CH4flux rate or its isotopic composition from vegetated plots, suggesting that CH4flux fromPeltandrais independent of stomatal aperture or hourly variations in photosynthetic rate. Comparisons of different chamber techniques for the collection of CH4for isotopic analysis and for flux measurements fromPeltandrasuggest that the effect of using simple uncontrolled chambers is small relative to temporal and spatial variations in methane emission and its isotopic composition. These results may be extended to other aquatic macrophytes which also transport gas primarily by molecular diffusion such asOryza, Carex, Pontederia, Sagittaria, and Cladium.The δ13C of CH4released fromPeltandravaried between −61 and −71 °/oo. Isotopic variations in CH4associated withPeltandraappeared to be controlled by transport effects. Methane withdrawn fromPeltandrastems was considerably13C enriched relative to sedimentary CH4and was not an indicator of the isotopic composition of CH4emitted by these plants. Hence emergent aquatic macrophytes rooted in organic‐rich sediments do not appear to be a source of13C enriched methane to the atmosphere. Emitted CH4was13C depleted relative both to the CH4within stems (−49 to −55 °/oo) and within sediments (‐56 to ‐58 °/oo), suggesting isotopic fractionation associated with the release of CH4by the plants. The preferential release of12CH4by the plants is partly compensated for by the enrichment of13C in CH4contained within the plant stem. Although the presence of methanotrophic bacteria within the rhizosphere ofPeltandrawas demonstrated, the stable isotopic composition of methane emitted from these plants or collected from sedimentary bubbles and plant stems presents no evidence for extensive oxidation of methane withinPeltandraor its rhizosphere. Either stable isotopes are not a good indicator of rhizopheric methane oxidation or the microbes' in situ respiration is limited by competition for oxygen with the demands of root respiration, oxidation of complex organic matter, ferrous iron oxidation, and nitrification.
Indications of low dimensionality in magnetospheric dynamics
Authors: Roberts D. A. , Baker D. N. , Klimas A. J. , Bargatze L. F.
Published: February 2008

Using three separate but related approaches, we examine the question of whether the dynamic response of the magnetosphere to the solar wind input may be described by a low‐order system of equations. First, we determine that the dimension of the subset (the “attractor”) in the high‐dimensional magnetospheric phase space associated with the westward auroral electrojet (AL) index for some of the data sets compiled by Bargatze et al. [1985] is 4.0 ±0.2, seemingly independent of activity level. Second, direct modeling of the magnetosphere considering the bulk properties of the tail plasma leads to a system of equations that is similar to those previously reported as a dripping faucet model; here we focus specifically on the prediction of a natural frequency in this model. Finally, we identify a peak with the predicted frequency in power spectra of AL computed for intervals with both low and high activity. Peaks at other frequencies also appear in the spectra, and such resonances would be expected for a chaotic non‐linear oscillator. Combining these approaches we conclude that at least some aspects of magnetospheric dynamics may be meaningfully modeled by low‐dimensional sets of equations.
Oxygen isotope fractionation in stratospheric CO2
Authors: Thiemens M. H. , Jackson T. , Mauersberger K. , Schueler B. , Morton J.
Published: February 2008

A new cryogenic collection system has been flown on board a balloon gondola to obtain separate samples of ozone and carbon dioxide without entrapping major atmospheric gases. Precision laboratory isotopic analysis of CO2 samples collected between 26 and 35.5km show a mass‐independent enrichment in both 17O and 18O of about 11 per mil (‰) above tropospheric values. Ozone enrichment in its heavy isotopes was 9 to 16% in 50O3 and 8 to 11% in 49O3, respectively [Schueler et al., 1990]. A mechanism to explain the isotope enrichment in CO2 has been recently proposed by Yung et al. [1991]. Their model is based on the isotope exchange between CO2 and O3 via O(1D), resulting in a transfer of the ozone isotope enrichment to carbon dioxide. Predicted enrichments and measured values agree well.
Nitrogen airglow sources: Comparison of Triton, Titan, and Earth
Authors: Strobel Darrell F. , Meier R. R. , Summers Michael E. , Strickland Douglas J.
Published: February 2008

Detailed calculations of the emission rates of nitrogen airglow in the upper atmospheres of Triton and Titan by direct solar excitation, photoelectrons, and magnetospheric electrons are compared with the Voyager Ultraviolet Spectrometer (UVS) observations. The principal spectral features of Triton's airglow are shown to be consistent with precipitation of magnetospheric electrons with power dissipation − 5 × 108 W. Solar excitation rates of the dominant N2 and N+ emission features are factors of 2–7 weaker than magnetospheric electron excitation. On Titan the calculated disk center and bright limb N+(1085 Å) intensities by solar excitation agree with observed values, whereas if the 970Å feature is mostly N2 c4 band emission, the calculated photoelectron excitation intensity is only 40% of the observed value. The difference could be due to magnetospheric electron precipitation. But the calculated LBH intensity by photoelectrons is in agreement with observations and suggests that magnetospheric electrons play a minor role in Titan's UV airglow. On the Earth solar/photoelectron excitation explains the observed N+(1085 Å) and LBH intensities, accounts for only 40% of the N+(916 Å) intensity, and overpredicts substantially the N2 c4 (0–0) band intensity.
Sheared field tearing mode instability and creation of flux ropes in the Earth magnetotail
Authors: Büchner J. , Kuznetsova M. , Zelenyi L. M.
Published: February 2008

Spontaneous disruptions of magnetotail energy are supposed to be caused by a tearing mode instability. We show how the tail current sheet becomes unstable in the presence of a sufficiently large magnetic shear. The instability occurs because the magnetic shear removes the stabilizing influence of the gyroscopic electrons. Ion Landau damping determines the growth rate of the instability. A violation of the magnetic line conservation in a narrow region due to finite electron inertia would allow three—dimensional reconnection and flux rope formation. The resulting flux topes are smaller in size and cause, therefore, weaker and more localized perturbations of the magnetosphere.
Isotopic fractionation of dissolved ammonium at the oxygen‐hydrogen sulfide interface in anoxic waters
Authors: Velinsky David J. , Fogel Marilyn L. , Todd James F. , Tebo Bradley M.
Published: February 2008

The δ15N of dissolved ammonium was determined in three anoxic marine basins: Black Sea, Saanich Inlet, B.C., Canada, and Framvaren Fjord, Norway. In each basin, the δ15N‐NH4+ was greatest near the 02/H2S interface, with δ15N as high as +21‰. The depth distributions of NH4+ and δ15N‐NH4+ for Black Sea and Framvaren Fjord were examined with a one‐dimensional, steady‐state, vertical advection‐diffusion model to calculate the isotope fractionation during the consumption of NH4+ by bacteria. Isotope enrichments, ϵ, for Black Sea were between 5 and 15 ‰, whereas in Framvaren Fjord ϵ ranged from 20 to 30 ‰. These differences are related mainly to the ambient concentration of NH4+. Biosynthetic uptake of NH4+ rather than nitrification was responsible for the fractionation. The δ15N‐NH4+ in Saanich Inlet appears related to in‐situ regeneration of NH4+ with little isotopic fractionation between dissolved and particulate nitrogen (PN).
Observations of wellbore failure in the Toa Baja Well—Implications for the state of stress in the North Coast Tertiary Basin, Puerto Rico
Authors: Moos Daniel , Morin Roger H.
Published: February 2008

Borehole televiewer (BHTV) and 4‐arm caliper (dipmeter) logs were obtained in the Toa Baja well (drilled to a depth of 2704 m into sediments of the North Coast Tertiary Basin, Puerto Rico) from 704 to 2676 m depth. The only observations suggesting that stress‐induced wellbore failure (breakouts) had occurred were small intermittent features at a depth of approximately 2600 m with azimuths of 70° and 250° and the fact that, during drilling, wellbore stability became a problem near total depth. An increase in mud weight to 10 Lb/gal required to stabilize the deteriorating wellbore was accompanied by loss of drilling fluid into the formation, suggesting that hydraulic fracturing or the reopening of pre‐existing near vertical fractures had occurred. A series of vertical fractures at a variety of azimuths (averaging N3l°W) was detected by the BHTV. The loss of circulation due to an increase in mud weight, combined with the absence of well‐developed breakouts, enables us to estimate stress magnitudes near the well for reasonable values of rock strength: S1=Sv; S3=Shmin≈ 0.5v; SHmax≈ (0.55–0.63)Sv, and an associated incipient normal faulting stress regime. This stress regime is consistent with focal mechanisms determined for earthquakes with epicenters near the drillsite.
Real time monitoring of vertical ground deformations during eruptions at Piton de la Fournaise
Authors: Toutain Jean‐Paul , Bachelery Patrick , Blum Pierre‐Antoine , Cheminee Jean‐Louis , Delorme Hugues , Fontaine Laurent , Kowalski Philippe , Taochy Philippe
Published: February 2008

Tilt changes related to a summit dike emplacement at Piton de la Fournaise volcano have been recorded by a 4 continuously recording electronic tiltmeters network during the April 18, 1990 eruption. The real‐time processing of these data at the Observatory allows to calculate during the emplacement the relative position of the inflation center from the tilt vectors supplied by the nearby stations. Two main steps have been identified: an initial subvertical intrusion step, followed by a lateral dike migration from the summit cone. This monitoring allows to calculate a high average intrusion velocity of about 0.2 m.sec−1 which can related to the highly fracturated pattern of the summit area.
Recent warming in eastern Canada inferred from geothermal measurements
Authors: Beltrami Hugo , Mareschal Jean‐Claude
Published: February 2008

Borehole temperature measurements from several sites in eastern Canada were analyzed to determine recent step changes in ground surface temperature. Inversion of the data suggests a warming by 1 to 2°C in the last 100 years for most of the sites analyzed.
The origin of the tsunami excited by the 1989 Loma Prieta Earthquake —Faulting or slumping?
Authors: Ma Kuo‐Fong , Satake Kenji , Kanamori Hiroo
Published: February 2008

We investigated the tsunami recorded at Monterey, California, during the 1989 Loma Prieta earthquake (MW=6.9). The first arrival of the tsunami was about 10 min after the origin time of the earthquake. Using an elastic half space, we computed vertical ground displacements for many different fault models for the Loma Prieta earthquake, and used them as the initial condition for computation of tsunamis in Monterey Bay. The synthetic tsunami computed for the uniform dislocation model determined from seismic data can explain the arrival time, polarity, and amplitude of the beginning of the tsunami. However, the period of the synthetic tsunami is too long compared with the observed. We tested other fault models with more localized slip distribution. None of the models could explain the observed period. The residual waveform, the observed minus the synthetic waveform, begins as a downward motion at about 18 min after the origin time of the earthquake, and could be interpreted as due to a secondary source near Moss Landing. If the large scale slumping near Moss Landing suggested by an eyewitness observation occurred about 9 min after the origin time of the earthquake, it could explain the residual waveform. To account for the amplitude of the observed tsunami, the volume of sediments involved in the slumping is approximately 0.013km3· Thus the most likely cause of the tsunami observed at Monterey is the combination of the vertical uplift of the sea floor due to the main faulting and a large scale slumping near Moss Landing.
The degassing flux from the solid earth: Release by fracturing
Authors: Torgersen Thomas , O'Donnell James
Published: February 2008

A simple 1‐D model is developed for the release of He (and Ar) from a solid lithology to the intervening porefluid as a result of fracturing. The results indicate that fracturing can release the solid phase accumulated He on a geologically short time‐scale (<1500yrs) for large crustal sections and can lead to the (observed) decoupling of He and Ar degassing fluxes from a homogeneous crust. Measurement of regional variations in the crustal degassing fluxes may therefore provide a useful constraint on time‐dependent hydraulic control of large‐scale fluid transport in the Earth's crust.
Fluid flow connections to basement rocks below sedimentary basins: Evidence from the base metal deposits in Ireland
Authors: Dixon Paul R. , Rye Danny M. , Janecky D. R.
Published: February 2008

Lead isotope systematics in Irish base metal deposits and basement rocks indicate that lead and other metals were derived from local basement rocks with little or no addition from basinal sediments hosting the deposits. Thus, a fluid circulation model involving simple basin brine expulsion and an impermeable boundary at the basin‐basement interface cannot be invoked to explain the origin of the mineralization. Production of ore deposits as a result of transport out of the basement would involve a relatively trivial integrated heat addition as compared to the total heat transported within the basin on the time scale of deposit formation.
ULF magnetic signatures at the Earth surface due to ground water flow: A possible precursor to earthquakes
Authors: Draganov A. B. , Inan U. S. , Taranenko Yu. N.
Published: February 2008

Magnetic field fluctuations at the earth's surface of
at <1 Hz are shown to result from motion with a peak velocity of ∼4 cm/s of ground water (∼4 S/m) at ∼5 km depth. Surface field changes can occur due to either divergence free fluid motion with transverse spatial wavelengths of a few tens of km, and/or homogeneous flow which displaces local inhomogeneities in the earth magnetic field.
Examination of time‐variable input effects in a nonlinear analogue magnetosphere model
Authors: Baker D. N. , Klimas A. J. , Roberts D. A.
Published: February 2008

Our previously developed nonlinear dynamical models of the magnetosphere exhibit deterministic chaotic behavior as the solar wind input which drives the systems increases from low to high levels. In this paper we employ the plasma physical analogue model (an extention of the damped, harmonic‐oscillator dripping faucet model) to consider explicitly the effect of time‐varying the inputs. This work is equivalent to considering the effects of northward and southward turnings of the interplanetary magnetic field for various periods of time. We find that relatively extended episodes (≥2 hours) of turned on input with shorter (∼1 hour) periods of turned off input lead to model behavior much like the continuously driven case. However, going to short input intervals with longer periods of zero input leads to highly irregular and dramatically fluctuating episodes of magnetotail unloading. These results give us insight into the diversity of apparent magnetospheric responses during relatively isolated substorm conditions. This work shows the absolutely critical interdependence (in a nonlinear dynamical system) of input phasing and internal magnetospheric response cycles.
Tests of random density models of terrestrial planets
Authors: Kaula William M. , Asimow Paul D.
Published: February 2008

Random density models are analyzed to determine the low degree harmonics of the gravity field of a planet, and therefrom two properties: an axiality Pl, the percent of the degree variance in the zonal term referred to an axis through the maximum for degree l; and an angularity Eln, the angle between the maxima for two degrees l, n. The random density distributions give solutions reasonably consistent with the axialities and angularities for the low degrees, l < 5, of Earth, Venus, and Moon, but not for Mars, which has improbably large axialities and small angularities. Hence the random density model is an unreliable predictor for the non‐hydrostatic second‐degree gravity of Mars, and thus for the moment‐of‐inertia, which is more plausibly close to 0.365MR2.
Improving ocean tide predictions by using additional semidiurnal constituents from spline interpolation in the frequency domain
Authors: Le Provost Christian , Lyard Florent , Molines Jean‐Marc
Published: February 2008

The improvement in accuracy that can be obtained by increasing the number of constituents in the model at present used for tidal height corrections in the GDRs of satellite altimetric measurements is analysed by referring to the performance of the Harmonic Method in predicting tides at a selected number of locations in the world where observations of sea level variations are available. Given the interest in such improvements, a way of extending the existing data set is proposed, without the need to run a new model of the world's oceans: the method relies on the concept of admittance. World's oceans maps are derived for five additional constituents, and the differences in predicted heights resulting from these improvements are evaluated.
Electromagnetic emissions during rock blasting
Authors: O'Keefe S. G. , Thiel D. V.
Published: February 2008

Radio emissions during quarry blasting have been recorded in the audio frequency band. Three distinct mechanisms are suggested to explain the observed results; rock fracture at the time of the explosion, charged rocks discharging on impact with the pit floor and micro‐fracture of the remaining rock wall due to pressure adjustment of the bench behind the blast. The last mechanism was evident by a train of discrete impulses recorded for up to one minute after the blast. It is assumed that during this time the rock behind the blast was subjected to a significant change in pressure. This may be related to ELF observations during earthquakes.
Reactions on sulphuric acid aerosol and on polar stratospheric clouds in the Antarctic stratosphere
Authors: Wolff E. W. , Mulvaney R.
Published: February 2008

Heterogeneous chemistry producing active chlorine has been identified as crucial to Antarctic ozone depletion. Most attention has focussed on reactions on solid polar stratospheric cloud (PSC) particles, although there is still no satisfactory understanding of the microchemical incorporation of HCl in PSCs. The alternative mechanism involving sulphuric acid aerosol as the reaction surface has been considered at lower latitudes, but its role in the special conditions of the polar stratosphere has been largely ignored. Recent data from the Antarctic stratosphere have suggested that HCl is present in sulphuric acid aerosol that remains liquid even at the lowest stratospheric temperatures. The available laboratory data show that cold, relatively dilute, sulphuric acid is particularly able to take up HCl that is available for reaction provided the aerosol remains liquid. Fast heterogeneous reaction rates compared to those at mid‐latitudes will produce active chlorine rapidly. Since the aerosol is present with significant surface area throughout the lower stratosphere, it should be very effective for heterogeneous reaction once temperatures drop. These surfaces, rather than PSCs, could host the initial conversion of Cl to its active form over the Antarctic.
Enigma of earthquakes at ridge‐transform‐fault plate boundaries distribution of non‐double couple parameter of Harvard CMT Solutions
Authors: Kawakatsu Hitoshi
Published: February 2008

The distribution of the non‐double couple parameter of shallow earthquakes reported in the Harvard CMT catalogue shows systematic characteristics depending on the epicentral locations and types of fault mechanisms. We suggest that they can be explained by the presence of subevents with different double couple mechanisms in a single rupture sequence. The earthquakes at the ridge‐transform‐fault plate boundaries show a particularly interesting pattern. It is suggested that two types of faulting expected in the area (i.e., normal faults at ridges and strike slip faults at transform‐faults) tend to occur almost simultaneously, although this hypothesis needs to be delineated by careful analyses using bodywave waveforms.
Near infrared imaging of hydroxyl wave structure over an ocean site at low latitudes
Authors: Taylor M. J. , Hill M. J.
Published: February 2008

Coordinated observations of wave structure in the near infrared hydroxyl (OH) nightglow emission have been made from Maui, Hawaii using a suite of narrow angle and all‐sky TV cameras. Two sets of data were obtained, the first in conjunction with the ALOHA‐90 campaign and the second during the subsequent new moon period. Well formed, short period (<20 min) wave patterns of comparable morphology, dynamics and abundance to those regularly imaged from mid‐latitude mountain sites were detected on several occasions. Although the Hawaiian islands comprise several high volcanic peaks, the patterns were not consistent with gravity waves generated by the interaction of strong winds with the local island topography. This suggests that other mid‐latitude wave patterns may also not be of mountain origin. The wave patterns imaged during ALOHA‐90 were of significantly lower contrast than those detected later. This effect may be related to changes in the characteristics of the middle atmosphere that occur shortly after the spring equinox.
Triton's atmosphere: A source of N and H for Neptune's magnetosphere
Authors: Summers Michael E. , Strobel Darrell F.
Published: February 2008

Mass loading of the Neptunian magnetosphere occurs primarily by thermal escape of H, H2, and N from Triton's upper atmosphere. The global escape rate of hydrogen is ∼ 7 × 1025s−1, determined by the global average methane photolysis rate, whereas the escape rate of nitrogen for our preferred model is ∼ 3.4 × 1025s−1, and is controlled by the global and orbital average energy deposition rate due to precipitating magnetospheric electrons. The escape rate of H+ and N+ is <4% of the neutral escape rate and implies that mass loading of the Neptunian magnetosphere is not localized to Triton's corona. The ratio of hydrogen to nitrogen escape rates for our preferred model is ∼2:1, comparable to the [H+]/[N+] abundance ratio inferred for Neptune's magnetosphere.
Na temperature lidar measurements of gravity wave perturbations of wind, density and temperature in the mesopause region
Authors: She C. Y. , Yu J. R. , Huang J. W. , Nagasawa C. , Gardner C. S.
Published: February 2008

High resolution temperature profiles of the mesopause region above Fort Collins, CO (40.6°N,105°W) were measured with a Na lidar on the nights of March 2–3 and April 15–16, 1990, during the ALOHA‐90 campaign. This paper reports the initial scientific analysis of these data which were used to compute (1) the altitude profiles of relative atmospheric temperature perturbations, (2) the mean Brunt‐Vaisala frequency in the mesopause region, and (3) the vertical shear variance of horizontal winds. On March 2–3 and April 15–16, the rms temperature perturbations were 5.7% and 7.1%, the average Brunt‐Vaisala periods were 4.9 min and 4.6 min, and the wind shear variances were 878 (ms−1/km)² and 967 (ms−1/km)², respectively.
Neutral line chaos and phase space structure
Authors: Burkhart Grant R. , Martin Richard F. , Dusenbery Paul B. , Speiser Theodore W.
Published: February 2008

Numerical surface of section techniques and analytic methods are used to study phase space structure and chaos near a neutral line. We find that, for −(2h)1/2 ≤ Py ≤ (2h)1/2, the ratio of fields, bn, rather than κ, is the appropriate chaos parameter, where Py and h are the normalized canonical momentum and energy. We find that the action integral adiabatic constant is approximately conserved and can be used to describe particle motion as long as bn ≪ 1 or bn ≫ 1.
Quantitative comparison of bathymetric survey systems
Authors: Goff John A. , Kleinrock Martin C.
Published: February 2008

Spatially coincident Deep‐Tow, Sea Beam, and SeaMARC II bathymetric data are statistically analyzed to determine the scales at which each system is reliable for mapping seafloor features. The methods we employ, including ruler measures of contours and profiles, and the covariance function and power spectrum of profiles, allow us to investigate the size of features measured as a function of scale.
An equatorial temperature and wind anomaly (ETWA)
Authors: Raghavarao R. , Wharton L. E. , Spencer N. W. , Mayr H. G. , Brace L. H.
Published: February 2008

Data obtained from the WATS (Wind and Temperature Spectrometer) and LP (Langmuir Probe) experiments on board DE‐2 (Dynamic Explorer) during high solar activity show evidence of anomalous latitudinal variations in the zonal winds and temperature at low latitudes. The zonal winds exhibit a broad maximum centered around the dip equator, flanked by minima on either side around 25 degrees; while the temperature exhibits a pronounced bowl‐shaped minimum at the dip equator which is flanked by maxima. The two minima in the zonal winds and the corresponding maxima in the temperature are nearly collocated with the crests of the well known Equatorial Ionization Anomaly (EIA). The maximum in the zonal winds and the minimum in the gas temperature are collocated with the trough of the EIA. The differences between the maxima and minima in temperature and zonal winds, on many occasions, are observed to exceed 100 K and 100 m/s, respectively. The characteristics of this new phenomenon have eluded present day empirical models of thermospheric temperature and winds. The connection among these variables can be understood from the ion‐neutral drag effect on the motions of the neutrals that in turn affect their energy balance.
Evidence of a transverse Langmuir modulational instability in a space plasma
Authors: Ergun R. E. , Carlson C. W. , McFadden J. P. , Clemmons J. H. , Boehm M. H.
Published: February 2008

Electric field amplitude modulations of Langmuir waves were observed in the auroral ionosphere. The data are consistent with a transverse modulational instability resonant with lower hybrid or ion Bernstein waves. The envelopes appear to have been nearly saturated.
Point defects in (Mg,Fe)SiO3 perovskite
Authors: Hirsch L. M. , Shankland T. J.
Published: February 2008

Equilibrium concentrations of point defects in Fe‐bearing MgSiO3 perovskite are calculated using a quantitative defect chemistry approach. Dependences of defect concentrations on temperature, oxygen activity, and pressure are illustrated. These calculations demonstrate how differences in the control of experimental conditions can lead to significant differences in point defect‐controlled properties.
The dependence of seafloor roughness on spreading rate
Authors: Hayes Dennis E. , Kane Kimberlee A.
Published: February 2008

Bathymetric profiles taken parallel to flowlines across the mid‐ocean ridges of the South Atlantic and South Pacific strongly suggest an approximate linear relationship (slope 30–50 m cm−1 yr) between the RMS amplitude roughness of small scale features and spreading rate. This relationship is best demonstrated for spreading half rates <35 mm/yr. The RMS roughness‐spreading rate dependence is most clearly defined for that component of the ridge flank relief with spatial wavelengths of less than about 25 km. The RMS roughnesses calculated for constant spreading rate intervals of ∼10 my across a single flowline profile from the South Atlantic show that significant and consistent opposite flank roughness differences are typically associated with asymmetric spreading. This important observation has profound implications regarding the nature of the faulting and volcanic processes acting near the ridge axis to form the small scale asymmetric roughness.
Initial measurements of CO2 concentrations (1530 to 1940 AD) in air occluded in the GISP 2 Ice Core from central Greenland
Authors: Wahlen M. , Allen D. , Deck B. , Herchenroder A.
Published: February 2008

Initial measurements of CO2 in the air of bubbles in the GISP 2 (Greenland Ice Sheet Project 2) ice core were performed using a dry extraction technique and tunable diode laser absorption spectroscopy. The record spans the years 1530 to 1940, and includes part of the little ice age. Absolute dating of the air was obtained from the location of the 14CO2 bomb peak in the bubble air, relative dating from the seasonal variations of H218O and electro‐conductivity. The results for preindustrial times indicate constant atmospheric CO2 levels of 280±5 ppmv between 1530 and 1810 AD. Thereafter the concentrations rise rather abruptly. The record smoothly connects to the direct atmospheric observations from Mauna Loa.
Geodynamic parameters derived from 7 years of laser data on Lageos
Authors: Gegout Pascal , Cazenave Anny
Published: February 2008

Seven years (1984 through 1990) of Laser data on Lageos have been.analysed to recover absolute stations velocities and j2. Relative motions between stations located in stable tectonic regions agree well with the NUVEL‐1 model predictions within 5 mm/yr rms. Relative motion across the San Andreas Fault is found to be − 33.±1. mm/yr. Solution for the secular variation of J2 is (−2.8±0.04) × 10−11/yr.
Paleomagnetism of three upper Jurassic ash‐flow sheets in southeastern Arizona: Implications for regional deformation
Authors: Hagstrum Jonathan T. , Lipman Peter W.
Published: February 2008

A sequence of three petrologically distinct Upper Jurassic ash‐flow tuffs has been sampled for paleomagnetic analysis in the Huachuca Mountains, Canelo Hills, and Mustang Mountains of southeastern Arizona. Site‐mean paleomagnetic directions for these units indicate significant vertical‐axis rotations between sampling localities (≃15°–40°), and a comparison of these and previously published data with reference directions from the Colorado Plateau implies that the Jurassic rocks in southeastern Arizona have been rotated in a clockwise sense with respect to stable North America. These new data are consistent with paleomagnetic results showing clockwise rotation of Upper Cretaceous rocks in south central Arizona, and further indicate that studies of North American apparent polar wander based on rocks from southern Arizona could be subject to error. The clockwise rotations in southern Arizona are likely related to Late Cretaceous and early Tertiary strike‐slip movement on northwest‐trending high‐angle faults in the region, and this movement may be linked to an increase in oblique Farallon‐North American plate convergence at that time.
A medium term precursor to the Loma Prieta Earthquake?
Authors: Gladwin M. T. , Gwyther R. L. , Higbie J. W. , Hart R. G.
Published: February 2008

The Loma Prieta earthquake (Ms=7.1, 17 October 1989) provided unique near field borehole tensor strain observations. The medium term data at the San Juan Bautista site showed a clear anomalous change in the fault parallel shear strain rate beginning about a year before the event. The anomaly ultimately reached 30% of the coseismic offset. The signal shows similarities with changes in strain rates reported from the geodetic record, suggesting a broad regional anomaly. The limited spacial sampling available prevents determination of a causal link useful for prediction between these data and the earthquake.
homogeneous freezing nucleation of stratospheric solution droplets
Authors: Jensen Eric J. , Toon Owen B. , Hamill Patrick
Published: February 2008

We have used the classical theory of homogeneous nucleation to calculate the freezing rate of sulfuric acid solution aerosols under stratospheric conditions. The freezing of stratospheric aerosols would be important for the nucleation of nitric acid trihydrate particles in the Arctic and Antarctic stratospheres. In addition, the rate of heterogeneous chemical reactions on stratospheric aerosols may be very sensitive to their state. Our calculations indicate that homogeneous freezing nucleation of pure water ice in the stratospheric solution droplets would occur at temperatures below about 192 K. However, the physical properties of H2SO4 solution at such low temperatures are not well known, and it is possible that sulfuric acid aerosols will freeze out at temperatures ranging from about 180–195 K. We also show that the temperature at which the aerosols freeze is nearly independent of their size.
Large and small scale structures in the plasma sheet: A signature of chaotic motion and resonance effects
Authors: Ashour‐Abdalla Maha , Berchem Jean , Büchner Jörg , Zelenyi Lev M.
Published: February 2008

Solar wind ion trajectories were computed using the Tsyganenko magnetic field model and assuming the presence of a uniform dawn‐dusk electric field. As a result of the energization and scattering produced by stochastic processes near the tail midplane, two distinct regions are formed, the plasma sheet boundary layer (PSBL) and the addition to these large scale structures the existence of new small scale structures, called beamlets, in the PSBL are predicted. Beamlets correspond to a structuring of the plasma distributions both in configuration and in velocity space. Beamlets consist of particles which experienced relatively small scattering when interacting with the tail neutral sheet and have Speiser or open trajectories at the point of observation.
The effects of site response on source parameters deduced for the 1980 Long Valley, California earthquake sequence
Authors: Peppin William A.
Published: February 2008

Data taken from the University of Nevada (UNR) array of surface‐located wideband, digital, displacement seismographs placed over the 1980 Long Valley earthquake sequence show very strong site effects, which control spectral parameters and hence inferred source parameters, up to ML 5.0. Observations from 4,000 seismograms show that differences in site effects can lead to inferred seismic moments at least a factor of two lower than previously reported. Observed S‐wave spectral corner frequencies show upper‐bound cutoffs which are widely disparate at different sites (e.g., 15 Hz at MG1 and 6 Hz at WT1), thus fmax is quite variable by site. This high‐ frequency cutoff, clearly a site effect at WT1, could be misinterpreted as an apparent departure from source similarity for seismic moments below 1021 dyn‐cm. Estimates of seismic moment and source duration from the UNR ‘rock’ sites may be more accurate than those previously published, both because the UNR instrumentation has greater resolution at longer periods (0.1 to 1.0 Hz) and because of less near‐site signal distortion at high frequencies.
The velocity profile at the base of the liquid core from PKP(BC+Cdiff) data: An argument in favour of radial inhomogeneity
Authors: Souriau Annie , Poupinet Georges
Published: February 2008

The velocity profile at the base of the core is derived from the mean travel time of the PKP(BC+Cdiff) data collected by the International Seismological Centre. PKP(BC) corresponds to rays having their turning points in the lower third of the liquid core, which give at great distance a branch Cdiff diffracted along the inner core boundary. Travel time residuals are computed with respect to the Earth model PREM (Dziewonski and Anderson, 1981), whose liquid core nearly follows the Adams‐Williamson equation at any depth, implying a neutral density stratification. Positive values of PKP(BC+Cdiff) residuals are obtained for epicentral distances greater that 151°. They are well explained by a liquid core model in which the velocity is constant in the lowermost 150 km. This strong decrease of the velocity gradient is in favour of a stable stratification at the base of the liquid core. It cannot be explained by thermal effects only but may correspond to a departure from homogeneity, probably in relation to the crystallization of the inner core.
Partitioning behavior of NI, CO, MO, and W between basaltic liquid and Ni‐rich metal: Implications for the origin of the moon and lunar core formation
Authors: Hillgren Valerie J.
Published: February 2008

A recent model of the origin of the Moon in a giant impact put forth by O'Neill [1991a and b] states that the bulk abundances of siderophile elements in the Moon would be provided by the impactor plus a late reduced veneer. A small Ni‐rich core would then separate setting the siderophile element abundance pattern in the lunar mantle. I test this hypothesis using simple mass balance and the results of an experimental study that I have conducted on the partitioning of moderately siderophile elements between basalt and Ni‐rich metal. I find this hypothesis to be viable under a limited set of conditions.
An unusual change in the Jovian Lyman‐alpha bulge
Authors: McGrath M. A.
Published: February 2008

A very unusual change is reported in the morphology of the Jovian Ly‐α bulge, a region of enhanced Ly‐α emission near the Jovian spin equator at a fixed system III magnetic longitude (λIII) that has persisted since its discovery in the late 1970s. Observations from 1979‐March 1989 consistently showed Ly‐α emission that peaked near λIII∼100° then dropped and remained constant in the nonbulge region from λIII∼200‐360°. During this time the bulge had a full width half maximum (FWHM) of ∼100‐130°. In September 1989 and March and May 1991 this nominal morphology was substantially different: the Ly‐α brightness showed a much broader peak (FWHM ∼200°) centered near 40° meaning that the bulge encompassed nearly the entire equatorial region of the planet and the previously flat nonbulge region was virtually nonexistent. These observations show a fundamental change in the morphology of the Ly‐α bulge which was not observed in the previous 11 years. Present theories for the bulge invoke asymmetric processes or densities in the Jovian ionosphere. The change in bulge morphology may imply a significant change in the pattern of large‐scale magnetospheric convection, in turn implying a possible change in longitudinal density structure of the Io plasma torus between March and Sept 1989. The possibility that the observed change in bulge morphology is related to long‐term solar activity also cannot be ruled out.
Waveform effects of a metastable olivine tongue in subducting slabs
Authors: Vidale John E. , Williams Quentin , Houston Heidi
Published: February 2008

We constructed velocity models of subducting slabs with a kinetically‐depressed olivine → β‐ and γ‐spinel transition, and examined the effect that such structures would have on teleseismic P waveforms using a full‐wave finite‐difference method. These two‐dimensional calculations yielded waveforms at a range of distances in the downdip direction. The slab models included a wedge‐shaped, low‐velocity metastable olivine tongue (MOTO) to a depth of 670 km, as well as a plausible thermal anomaly; one model further included a 10‐km‐thick fast layer on the surface of the slab. The principal effect of MOTO is to produce grazing reflections at wide angles off the phase boundary, generating a secondary arrival 0 to 4 seconds after the initial arrival depending on the take‐off angle. The amplitude and timing of this feature vary with the lateral location of the seismic source within the slab cross‐section. Careful analysis of waveforms from earthquakes with depths near 400 km, simple sources, and adequate station coverage in appropriate geometries will be required to resolve whether MOTO is present.
Measurements of ClO and O3 from 21°N to 61°N in the lower stratosphere during February 1988: Implications for heterogeneous chemistry
Authors: King J. C. , Brune W. H. , Toohey D. W. , Rodriguez J. M. , Starr W. L. , Vedder J. F.
Published: February 2008

The decline in stratospheric ozone at northern midlatitudes in wintertime may be caused by chlorine photochemistry that has been enhanced by heterogeneous reactions. We examine the possibility that the heterogeneous reaction of N2O5 on sulfate aerosols is the cause of this decadal ozone decline by comparing ClO and O3 measurements made in the lower stratosphere during February, 1988, with results from a two‐dimensional model. At midlatitudes, the abundances, latitudinal, and seasonal gradients of the observed ClO are similar to the results of a model with heterogeneous chemistry, but are in strong disagreement with the results from the model with only gas‐phase chemistry. At low latitudes, agreement is best with the results of the model with only gas‐phase chemistry. These limited observations indicate that the amount of reactive chlorine is being enhanced, and that heterogeneous chemistry is a likely cause, but the details of the heterogeneous chemistry and the possibility of other mechanisms still need to be considered.
Direct conversion of ordinary mode into upper hybrid wave by density irregularities in the ionosphere
Authors: Antani S. N. , Rao N. N. , Kaup D. J.
Published: February 2008

We investigate direct conversion of ordinary mode into upper hybrid (UH) waves by pre‐existing electron density irregularities during ionospheric heating. The electric field amplitude and the average power absorbed by the excited UH waves are calculated when the irregularity distribution is (i) coherent, and (ii) incoherent with a broad band power spectrum modelled by a drift wave type scaling. For the typical parameters of the experiments, we find that the direct conversion process can be quite efficient.
Paleomagnetism of mesozoic red chert from Cedros Island and the San Benito Islands, Baja California, Mexico revisited
Authors: Hagstrum Jonathan T. , Sedlock Richard L.
Published: February 2008

Previous paleomagnetic study of Mesozoic subduction‐complex rocks on Cedros Island and the San Benito Islands, Mexico, shows that these rocks have been remagnetized; a single‐polarity magnetization was found in chert sections and underlying pillow basalt deposited during a mixed‐polarity interval of the geomagnetic field. Reanalysis of the Cedros and San Benito chert samples (101 total) shows that 13 samples also retain a high blocking‐temperature component of magnetization (600° to 680°C) indicating a polarity stratigraphy and deposition of the bedded chert near 2° ± 3° paleolatitude. These data are similar to those for red chert in California and Japan implying that many of the Mesozoic ophiolitic chert sequences now exposed around the Pacific rim were initially deposited within the equatorial zone of high biologic productivity. These new data also support accretion of the Cedros and San Benito chert to the American margin at tropical paleolatitudes requiring significant northward translation (and clockwise rotation) to bring them to their present position with respect to the continental interior.
Electromagnetic ELF radiation from earthquake regions as observed by low‐altitude satellites
Authors: Serebryakova O. N. , Bilichenko S. V. , Chmyrev V. M. , Parrot M. , Rauch J. L. , Lefeuvre F. , Pokhotelov O. A.
Published: February 2008

Seismo‐Electromagnetic (SEM) waves observed by low‐altitude satellites passing over seismic regions were studied. The data of the COSMOS‐1809 satellite were analysed over the earthquake region in Armenia during the period from January 20 to February 17, 1989. Intense EM radiation at frequencies below 450 Hz was observed at the L‐shells of the earthquake, during 12 orbits out of the 13 that passed within 6° in longitude from the epicenter, and during 1 out of 6 in the range of 6°–8° longitude away from this region. The other orbits, which passed 10°–12° from the epicentre, showed no effect. To complete this study, we used the emissions observed by another low‐altitude satellite (AUREOL‐3).It is shown that during the event the seismic region is permanently radiating; the intensity and the envelope shape of the wave depend on its time relatively to the time of the earthquake. Their frequency spectra are compared to the average spectrum recorded in the same geomagnetic regions. Similar wave intensities and spectral distributions were observed on the two satellites during the seismic periods.
In situ stratospheric measurements of CH4, 13CH4, N2O, and OC18O using the Bliss tunable diode laser spectrometer
Authors: Webster Christopher R. , May Randy D.
Published: February 2008

Simultaneous in situ measurements of stratospheric CH4, 13CH4, N2O, OC18O, pressure, and temperature have been made from Palestine, Texas (32°N) in September 1988 with the JPL Balloon‐borne Laser In Situ Sensor (BLISS). Measurements of CH4 and N2O in the altitude range 30–35 km agree well with other measurements, except for an anomalously high value for the N2O at 31 km. Measurements of CH4 support earlier observations of a fold in the vertical profile. A ratio for stratospheric 13CH4/CH4 of 0.0105 ± 0.0010 implies an enrichment of δ13C = −45 ± 92 parts per thousand over the PDB value, in agreement with previous measurements in the troposphere. A large mixing ratio of 1.9 ± 0.2 ppmv for OC18O is measured, corresponding to an enrichment of δ18O = 280 ± 50 parts per thousand for the 18O isotopic species over the SMOW value.
Global warming: Evidence for asymmetric diurnal temperature change
Authors: Karl Thomas R. , Kukla George , Razuvayev Vyacheslav N. , Changery Michael J. , Quayle Robert G. , Heim Richard R. , Easterling David R. , Fu Cong Bin
Published: February 2008

Analyses of the year‐month mean maximum and minimum surface thermometric record have now been updated and expanded to cover three large countries in the Northern Hemisphere (the contiguous United States, the Soviet Union, and the People's Republic of China). They indicate that most of the warming which has occurred in these regions over the past four decades can be attributed to an increase of mean minimum (mostly nighttime) temperatures. Mean maximum (mostly daytime) temperatures display little or no warming. In the USA and the USSR (no access to data in China) similar characteristics are also reflected in the changes of extreme seasonal temperatures, e.g., increase of extreme minimum temperatures and little or no change in extreme maximum temperatures. The continuation of increasing minimum temperatures and little overall change of the maximum leads to a decrease of the mean (and extreme) temperature range, an important measure of climate variability.

The cause(s) of the asymmetric diurnal changes are uncertain, but there is some evidence to suggest that changes in cloud cover plays a direct role (where increases in cloudiness result in reduced maximum and higher minimum temperatures). Regardless of the exact cause(s), these results imply that either: (1) climate model projections considering the expected change in the diurnal temperature range with increased levels of the greenhouse gases are underestimating (overestimating) the rise of the daily minimum (maximum) relative to the maximum (minimum), or (2) the observed warming in a considerable portion of the Northern Hemisphere landmass is significantly affected by factors unrelated to an enhanced anthropogenically‐induced greenhouse effect.