bluuebunny/crossref_metadata_2025 huggingface dataset:
Moment tensor inversions and dipping slabs
Authors: Langston Charles A. , Arnold Walter A.
Published: February 2008

Moment tensor inversions were performed on synthetic teleseismic P and SH body wave data for two plausible orientations of intermediate depth earthquakes located in a slab. A ray method was used to generate the synthetic P and SH data for dipping slab models. Plane layered Green's functions were assumed in the inversions even though the synthetic data contained the effect of slab dip. This was done to simulate the typical situation where horizontal plane layers are assumed in mechanism studies. The inversion of data from an oblique‐slip source, for dipping slabs up to 45°, gave the assumed double couple source. When the initial mechanism was a near vertical dip‐slip type, results from the inversion showed significant departures from the assumed mechanism. A surprising result was that even though the presence of a dipping slab can occasionally distort the radiation pattern enough to yield fictitious source orientations, amplitudes and polarities were satisfactorily explained within typical variations seen in real data. Thus, the non‐double couple terms in the moment tensor can compensate for the perturbing effects of slab dip.
The effect of fluid flow on the magnetic field in low porosity crystalline rock
Authors: Martin R. J. , Haupt R. W. , Greenfield R. J.
Published: February 2008

Changes in the local geomagnetic field have been observed and documented in several seismically active areas prior to, during, and following earthquakes. Mizutani and Ishido (1975) proposed that groundwater may diffuse through a hypocentral region and that the fluid flow can produce an electric potential by means of electrokinetic phenomena. The resulting current flow, in turn, will generate a magnetic field.

Fluid flow tests conducted on samples of Westerly granite demonstrated that the diffusion of an electrolytic fluid causes a measurable magnetic field change. At high fluid flow rates, a magnetic field change was observed that was in agreement with theoretically predicted and numerically calculated values. In addition, the sign of the magnetic field changes as the fluid flow direction through the sample was reversed. Moreover, the tests showed that the magnitude of the magnetic field change is dependent upon (1) the porosity of the rock; (2) the pore wall surface area; (3) the permeability of the rock; and (4) zeta potential of the fluid‐pore wall system.
The sensitivity of upper ocean structure to time varying wind direction
Authors: Dickey T. D. , Simpson J. J.
Published: February 2008

Observations and models show that sudden changes in the magnitude of the wind stress which occur within a time interval of one‐half inertial period are most effective in increasing surface current speeds and mixing the upper layers of the ocean. The purpose of the present study is to quantify the effects of concurrent time dependent wind direction. The Mellor‐Yamada level 2 1/2 turbulence closure model is used. A series of model runs was executed in order to determine the relative sensitivity of mixed layer depth and sea surface temperature to wind speed as compared with the rate of change of wind direction. The results indicate that the accuracy and time resolution of wind direction should be given special consideration in the design and interpretation of field experiments which will be used for testing prognostic mixed layer models.
Altitudinal and temporal variation of hydrocarbons and other gaseous tracers of Arctic haze
Authors: Rasmussen R. A. , Khalil M. A. K. , Fox R. J.
Published: February 2008

Springtime concentrations of hydrocarbons and chlorocarbons in the arctic atmosphere (70°N, Barrow) are reported. Concentrations of the following gases were determined: acetylene (C2H2), ethene (C2H4), ethane (C2H6), propane (C3H8), benzene (C6H6), toluene (C7H8), perchloroethylene (C2Cl4), and trichloroethylene (C2HCl3). Vertical distributions of these gases were also determined on flights during May 1982. The results show that C2Cl4, C2H2, and C2H6 may be gaseous tracers of arctic haze. Their vertical profiles suggest that polluted air may be transported to the arctic 1‐2 km above ground, and perhaps also in layers higher than this level.
Can ‘pure‐path’ models explain free oscillation data?
Authors: Kawakatsu Hitoshi
Published: February 2008

Several recently published regionalized models of the earth’s lateral heterogeneity obtained by ‘pure‐path’ analysis are compared to free oscillation data of Masters et al [1982]. Among these models, Okal’s [1977] model shows a strongly dominant pattern of angular order l = 2 heterogeneity that is strikingly similar to Masters et al’s data. This suggests that Okal’s model may explain the free oscillation data as well as the "transition‐zone" model of Masters et al. and that shallow lateral heterogeneity may be responsible for the simple pattern of Masters et al. The apparent success of Okal’s model suggests the importance of lateral heterogeneity within oceanic regions. The instability of ‘pure‐path’ analysis is also demonstrated by spectral analysis of the lateral heterogeneities of different ‘pure‐path’ models.
Mesospheric ozone depletion during the Solar Proton Event of July 13, 1982 Part II. Comparison between theory and measurements
Authors: Solomon S. , Reid G. C. , Rusch D. W. , Thomas R. J.
Published: February 2008

The solar proton event of July 13, 1982 was the largest to date in the current solar cycle. Proton fluxes observed by the NOAA‐6 satellite have been used to calculate ionization rates during the event, which have been found to be almost as large as those of the August, 1972 event near 70 km, but much smaller at lower altitudes. This ionization leads to the production of odd hydrogen radicals (H+OH+HO2) which catalytically destroy odd oxygen in the mesosphere and stratosphere. A one‐dimensional time‐dependent model has been used to calculate the percentage change in ozone resulting from this event. The calculated ozone depletion is compared to that observed by the Solar Mesosphere Explorer (SME) satellite.
Stratospheric ozone observations simultaneous with NO2 at 45°S
Authors: McKenzie R. L. , Johnston P. V.
Published: February 2008

A least squares data reduction technique for extracting stratospheric ozone abundances concurrently with NO2 abundances is described. The observational technique used is ground based long path absorption spectroscopy in the wavelength range 435‐450nm. Sources of error are discussed and the overall accuracy of ozone retrievals is quantified in terms of the maximum residual errors accepted. Results obtained from our clean air site at Lauder New Zealand (−45°S, 170°E) are presented for the period December 1980 to April 1982, and compared with Dobson total ozone values. Although less accurate (∼±20%) than the Dobson values, the technique may find use because both NO2 and O3 amounts are obtained simultaneously from the same sampled volume. Thus there is the potential for providing observational evidence for modelled coupling between these two species.
Upper mantle oxidation state: Evidence from olivine‐orthopyroxene‐ilmenite assemblages
Authors: Eggler David H.
Published: February 2008

Oxygen fugacities of olivine‐orthopyroxene‐ilmenite‐bearing, high‐pressure megacrysts, mineral intergrowths, and peridotites from kimberlites and from a minette have been calculated from the equilibrium 2Fe2O3 + 4FeSiO3 = 8FeSi0.5O2 + O2. Resultant fO2's, which are interpreted to reflect the subcontinental source regions of alkalic magmas, are clustered between the quartz‐fayalite‐magnetite and magnetite‐wustite buffers. These relatively oxidized conditions are compatible with at least some estimates of fO2 of typical basalts. They are also compatible with existence of carbonate minerals and diamond or graphite and, if fluids are present, with water‐rich H2O‐CO2 fluids rather than CH4‐H2O fluids.
Equatorial disturbance dynamo electric fields
Authors: Fejer B. G. , Larsen M. F. , Farley D. T.
Published: February 2008

F‐region vertical drift data from Jicamarca, Peru show that equatorial east‐west electric fields are sometimes perturbed 16‐24 hours after the onset of geomagnetic storms. These disturbance dynamo electric fields, which must be caused primarily by the action of neutral winds at low and middle latitudes, decrease and sometimes even reverse the quiet time electric field pattern during both daytime and nighttime. The long delay excludes the possibility that gravity waves are responsible and suggests that the thermospheric circulation is disturbed. The data also show that after some storms there are no such delayed disturbances, a fact which may be due to the longitudinal structure of the disturbances at high latitudes and/or that only very strong storms can produce major thermospheric perturbations that extend to middle and low latitudes.
On the Injection Boundary Model and dispersing ion signatures at near‐geosynchronous altitudes
Authors: Strangeway R. J. , Johnson R. G.
Published: February 2008

A simple particle drift model is used to investigate the applicability of the injection boundary concept to the ion dispersion event observed on March 22 (day 81), 1979. The model consists of a dipole magnetic field with a uniform cross‐tail electric field plus a corotation field. A full spectrum of particles from 100 eV to 32 keV is injected at the Kp = 6 ‐ Mauk and McIlwain injection boundary at the time of substorm onset on this day (1100 UT). A new approach is presented for displaying the model‐produced ion drift trajectories to make the large scale spatial characteristics of the evolving energy distributions easier to envision and to facilitate the comparison of the model results with experimental observations. The resultant prediction for the dispersion signature is compared with Scatha mass spectrometer measurements, and a 2.0 kV/Re cross‐tail convection electric field is found to give a good fit to the observed dispersion signature. It is determined that for this particular event, injection only at that portion of the injection boundary close to 1800 local time is required to produce the dispersion curve.
The rate of occurrence of dayside Pc 3,4 pulsations: The L‐value dependence of the IMF cone angle effect
Authors: Russell C. T. , Luhmann J. G. , Odera T. J. , Stuart W. F.
Published: February 2008

The normalized rate of occurrence of dayside Pc 3,4 pulsations from L=2.4 to 4.3 has a strong enhancement for low cone angles of the interplanetary magnetic field. When the angle of the IMF to the earth sun line, θBX, is 15° or less the occurrence rate is 7‐8 times the average rate at L=2.4 to 2.8 and 2.2 to 3.5 times the average rate at L=4 to 4.3. These waves disappear when the IMF is nearly at right angles to the sun‐earth‐line. This absence of pulsations occurs over the widest range of angles at lowest L‐values. These observations are consistent with a source originating in the waves upstream of the subsolar bow shock which are transported by convection to the magnetopause where they couple to oscillations of magnetospheric field lines. Since the index of refraction of the magnetospheric plasma decreases with decreasing radial distance, except at the plasmapause, inward propagating waves should be refracted away from the radial direction. Thus, to reach low L‐values the waves should couple near the stagnation point and propagate nearly radially inwards. Upstream waves should be convected to the stagnation point for only a limited range of θBX. However, to reach higher L‐values the coupling may be at later local times where cross streamline propagation can bring waves from a larger range of θBX. The streamline geometry and its connection to the foreshock region is illustrated for a variety of IMF orientations using a simple approximation to the magnetosheath flow field.
The mean life of continents: Estimates of continent recycling rates from Nd and Hf isotopic data and implications for mantle structure
Authors: DePaolo Donald J.
Published: February 2008

An analysis of the initial neodymium and hafnium isotopic compositions of modern and ancient mantle‐derived rocks shows that the divergence of the mantle 143Nd/144Nd and 176Hf/177Hf ratios from the chondritic ratios over the past 2 billion years has been much less than would be expected based on the Sm/Nd and Lu/Hf ratios of the mantle source of mid‐ocean ridge basalt. The most likely explanation is that rock material from the continents has been recycled semi‐continuously back into the mantle over this time period. The required rate of return of continents to the mantle, calculated from a simple transport model, is about 0.35±0.15 of the continental mass per billion years (∼2.5 km³/year). This result is consistent with the hypothesis that the mass of the continents has been approximately constant since the late Archean, and implies that recycled continental material must be an important component of the upper mantle.
Multi‐beam Doppler sonar observation of tidal flow turbulence
Authors: Lhermitte Roger , Poor Henry
Published: February 2008

Preliminary results on tidal flow turbulence acquired from multi‐beam Doppler sonar observations are presented. The Doppler sonar is a high resolution system capable of observing the spectrum of radial velocities in the scattering volume with a precision greatly exceeding the Doppler spectrum bandwidth. Such capability provides access to small scale water turbulence observations if foreign contributions to velocity variance are removed. This preliminary analysis of the data is primarily concerned with vertical and horizontal velocity turbulence as related to longitudinal mean flow velocity.
Daytime variation of atmospheric NO2 from ground based infrared measurements
Authors: Flaud J.‐M. , Camy‐Peyret C. , Cariolle D. , Laurent J. , Stokes G. M.
Published: February 2008

During the day of September 20, 1982 16 high resolution atmospheric spectra were recorded at regularly spaced time intervals from sunrise to sunset using the Fourier transform spectrometer of the McMath solar telescope of Kitt Peak National Observatory. Using well isolated NO2 absorption peaks appearing in the 2850‐2950 cm−1 region, it has been possible to measure precisely the daytime variation of the NO2 vertical column density. A rapid increase from sunrise to noon is observed followed by a slower increase in the afternoon. A comparison with the predictions of a photochemical model is given.
A numerical model of centrifugal wind in a rapidly rotating magnetosphere
Authors: Sato T. , Murakami M.
Published: February 2008

A numerical model of studying the plasma flow dynamics in a rapidly rotating, axisymmetric magnetosphere has been developed. Starting from a corotating dipole magnetosphere where the plasma density radially decreases as r−3 but the pressure is uniform, we have studied the evolution of the outward plasma flow (centrifugal wind) and the associated conformation of the magnetosphere for two cases; (1) a high pressure case where the corotation speed is smaller than the magnetosonic speed and (2) a low pressure case where the corotation speed exceeds the magnetosonic speed beyond a certain distance. It is found that whether or not the magnetosphere can form a disklike structure depends largely on the pressure distribution in the magnetosphere. It is also confirmed that a super magnetosonic centrifugal wind is generated beyond the critical point where the rotational energy equals the sum of the magnetic and thermal energies. Furthermore, in the case where the disklike structure is formed, a sharp increase in the plasma density appears in the disklike region. Comparisons with the observed Jovian magnetosphere are made.
The October 1980 earthquake sequence near the New Hebrides
Authors: Vidale John , Kanamori Hiroo
Published: February 2008

Four large earthquakes occurred in 1980 in a seismic gap near the Loyalty Islands in the New Hebrides. At 3:25 UT on October 24 an event with Ms = 6.7 initiated the sequence. Three events, Ms = 6.7, 7.2, and 6.5, followed on the next day. We investigated this sequence by using the seismicity, first‐motion, and waveform data and long‐period surface waves. The first‐motion data constrain one of each pair of nodal planes. With this constraint, inversion of Rayleigh‐ and Love‐wave spectra at 256 seconds determines the other nodal plane. The mechanisms of all four events are almost pure thrust on a plane dipping about 20 degrees east and striking parallel to the local strike of the New Hebrides trench. The first‐day aftershocks indicate an initial rupture zone of about 2,000 km², which is consistent with the estimated seismic moment of 3 × 1027 dyne‐cm. During the next two days, the aftershock activity expanded to an area of 10,000 to 20,000 km² in the directions both along and perpendicular to the trench. Within 5 hours after the third and largest event, the initial rupture zone had become mostly quiescent. Modeling of waveforms suggests a body‐wave moment of between 0.5 and 1.0 × 1027 dyne‐cm and a source process time of 11 seconds. This pattern suggests that the initial rupture zone represents a zone of increased strength (i.e. an asperity), and the stress change due to failure of this asperity subsequently migrated outward. During the two‐year period before the main event, seismicity in the initial rupture zone was very low except near the point where the first mainshock initiated. A very tight clustering of activity occurred there. This pattern indicates gradual stress concentration near the asperity which finally failed during the mainshock sequence.
A rapidly travelling planetary‐scale instability in the atmosphere
Authors: Lynch Peter
Published: February 2008

The hydrodynamic instability of the zonally averaged circulation of the atmosphere is investigated using a primitive equation model on a global domain. The classical baroclinically unstable modes are examined and a new mode of instability is found. This mode has phase‐speed greater than the maximum zonal flow velocity (such a solution is impossible within the framework of quasi‐geostrophic theory). It draws energy from the mean flow in the troposphere through baroclinic conversion and it penetrates deeply into the middle atmosphere, its growth there being supported by convergence of vertical wave energy flux. With zonal wavenumber one it has a period of two days and an e‐folding time of six days. Such instabilities may play an important role in the dynamics of the middle atmosphere.
Field‐aligned ion beams upstream of the Earth's bow shock: Evidence for a magnetosheath source
Authors: Thomsen M. F. , Gosling J. T. , Bame S. J. , Feldman W. C. , Paschmann G. , Sckopke N.
Published: February 2008

High time resolution ISEE‐1 and ‐2 observations of upstream field‐aligned ion beams at several crossings of the Earth’s bow shock indicate that some beams are due to high‐energy magnetosheath particles leaking through the shock into the upstream region. The distribution immediately downstream of these oblique (θBn ∼ 50°) shocks consists of a ‘core’ of directly transmitted, slightly heated ions plus a crescent‐shaped, high‐velocity distribution, centered roughly on the magnetic field in the direction toward the upstream region, with a fairly well‐defined low velocity cut‐off.
Observations of interplanetary energetic ion enhancements near magnetic sector boundaries
Authors: Briggs Patrick R. , Armstrong Thomas P.
Published: February 2008

We have examined all energetic medium nuclei (carbon, nitrogen, and oxygen) flux increases observed by the satellites IMP 7 and IMP 8 at 1 AU during Bartels rotations 1906‐1974. After removing flare‐related increases, the remaining 145 "events" were compared to interplanetary magnetic field and solar wind parameters. We have discovered a class of flux enhancements in which the ion increases occur close to the onset of magnetic sector boundary crossings. We interpret this observation as a facilitated access to 1 AU of energetic ions from the corona or chromosphere via the magnetic sector structure. It appears that this access is more significant for medium than for lighter nuclei, suggesting a possible charge‐ or rigidity‐dependent transport mechanism.
Mid‐latitude stratospheric aerosol layer enhancement by El Chichon: The first year
Authors: Michalsky J. J. , Herman B. M. , Larson N. R.
Published: February 2008

Measurements are reported in this paper which indicate the nature of the enhancement of the stratospheric aerosol layer by month for the first full year following the Spring 1982 eruptions of El Chichon. The aerosol optical depths as a function of wavelength are obtained by differencing mean monthly values obtained before and after the eruptions. The first enhancement above background was detected in September 1982. The inverted size distributions indicate a steady increase to larger mean size particles each month with a radius near 0.6 micrometers during the last reported month of March 1983. This size is considerably larger than that which is generally assumed for the sulfuric acid aerosols which form following an eruption.
A volcanomagnetic observation on Mount St. Helens, Washington
Authors: Davis P. M. , Pierce D. R. , McPherron R. L. , Dzurisin D. , Murray Thomas , Johnston Malcolm J. S. , Mueller Robert
Published: February 2008

Total magnetic fields were recorded at five sites on Mt. St. Helens between 23 October and 11 November 1981, an interval which included an extrusive dome‐building eruption of the volcano. Two of the magnetometers located in the volcano's crater measured reversible magnetic changes, which correspond to fluctuations in tilt measured nearby. However, the relationship is highly nonlinear. Electric fields were measured on the east flank of the volcano near its summit to search for electrokinetic effects. They show no correlation with the magnetic changes and, in the long term, are uncorrelated with eruptive activity. Our favored interpretation of the magnetic changes is that they result from stress‐induced changes in the magnetization of the volcano. Magnetic field values returned to pre‐anomaly values. This reversibility rules out pressure‐induced magnetization as the dominant mechanism and places an upper limit of σ ∼300 bars on the stress changes. The limited spatial extent of the magnetic anomaly field places the source of stress at shallow depth beneath the crater floor consistent with models based on strain data.
Composition of the upper mantle: Geophysical tests of two petrological models
Authors: Bass Jay D. , Anderson Don L.
Published: February 2008

The elastic properties of candidate mantle phases are used to test the viability of olivine‐rich (pyrolitic) and CaO + Al2O3‐rich (eclogitic) assemblages for the mantle. High temperature adiabats for each phase of interest are constructed and compared to mantle seismic properties. Both pyrolitic and eclogitic assemblages satisfy the seismic properties between ∼ 200 and 400 km. Between 400 and 670 km depth an eclogitic assemblage yields a superior match to velocities and velocity gradients. The 400 km seismic discontinuity may represent a chemical boundary between pyrolite and picritic eclogite (“piclogite”) or phase transformations in the olivine + orthopyroxene components of a piclogitic assemblage containing about 16% olivine. High velocity gradients in the transition zone may be explained by the transformation of Ca‐rich cpx to majorite garnet. Seismic properties at the top of the lower mantle are consistent with pyrolite, piclogite or perovskite, implying that the 670 km discontinuity may be a chemical boundary.
A simple model of the 1982‐83 Californian "El Nino"
Authors: Simpson James J.
Published: February 2008

Steric height, steric height anomaly, sea level and sea level anomaly show that the 1940‐41 and the 1982‐83 Californian "El Niño" events were resonant responses of the California Current to the expansion and intensification of the Aleutian low and decrease in strength of the North Pacific high. In both cases, the subsurface anomalies were dynamically produced by onshore transport of Subarctic water and a downward tilt of the inshore thermocline. Sea surface temperature anomalies, however, resulted from thermodynamic as well as dynamic processes. Most previous Californian "El Niño" or "anti‐El Niño" events probably were resonant or anti‐resonant responses of the seasonal cycle of the California Current to anomalous large‐scale atmospheric forcing.
Atomic oxygen concentrations in the auroral ionosphere
Authors: McDade I. C. , Llewellyn E. J.
Published: February 2008

The most recent laboratory rate coefficients for the reactions of N2(A³∑u+) with O(³P) and O2 are used to determine atomic oxygen concentrations in the lower ionosphere from previously published measurements of the quenching of auroral N2(A³∑u+). It is shown that the derived atomic oxygen concentrations are in good agreement with those of the CIRA 72 model atmosphere in the 100‐160 km altitude range, and not significantly smaller as has been previously suggested.
Interaction between VLF waves and the turbulent ionosphere
Authors: Titova E. E. , Di V. I. , Yurov V. E. , Raspopov O. M. , Trakhtengertz V. Yu , Jiricek F. , Triska P.
Published: February 2008

The effects of broadening of frequency spectra of quasi‐monochromatic very low frequency (VLF) signals were observed in the polar ionosphere when VLF transmitter signals were registered on the satellite "Intercosmos‐19". Broadening of the spectrum was mainly registered on the electric antenna to the extent of Δf ≤ ± 1 kHz. Broadening of the VLF signal and intensive extra low frequency (ELF) noise with f < 1 kHz were observed simultaneously. Such effects can be explained by a transformation of the initial whistler‐wave, into whistler‐mode waves with wave‐normals very near the resonant cone, by small‐scale ionospheric irregularities. These irregularities can be caused by ion‐acoustic or ion‐cyclotron waves. The effect of the broadening of the VLF signal spectrum can be used as a diagnostic of ionospheric turbulence and field‐aligned electric currents in the upper ionosphere.
A wave model for the aurora
Authors: Bingham R. , Bryant D. A. , Hall D. S.
Published: February 2008

A wave‐particle interaction model is proposed for the electron acceleration that leads to discrete aurora. Measurements of accelerated electrons are used to deduce the wave spectrum and the nature of the waves responsible for acceleration. The waves are identified as lower‐hybrid waves. Generation of the waves by various free energy sources is considered and the wave energy required to account for the aurora is calculated and compared with observations.
Lightning activity and severe storm structure
Authors: Taylor W. L. , Brandes E. A. , Rust W. D. , MacGorman D. R.
Published: February 2008

Space‐time mapping of VHF sources from four severe storms on 19 June 1980 reveals that lightning processes for cloud‐to‐ground (CG) and large intracloud (IC) flashes are confined to an altitude below about 10 km and closely associated with the central regions of high reflectivity. Another class of IC flashes produces a splattering of sources within the storms' main electrically active volumes and also within the large divergent wind canopy aloft. There is no apparent temporal association between the small high altitude IC flashes that occur almost continuously and the large IC and CG flashes that occur sporadically in the lower portions of storms.
The OI 989‐Å tropical nightglow
Authors: Abreu V. J. , Dalgarno A. , Yee J. H. , Chakrabarti S. , Solomon S. C.
Published: February 2008

We present the first observations of the OI 989Å (2p4 ³P ‐ 3s′ ³D°) emission in the tropical nightglow. The morphology and origin of the emission are discussed. Dielectronic recombination of O+ is suggested as the mechanism responsible for populating the 3s′ ³D° state.
Interannual variability versus seasonal variability in the Tropical Atlantic
Authors: Picaut Joël , Servain Jacques , Busalacchi Antonio J. , Seva Marc
Published: February 2008

Monthly fields of sea surface temperature and wind stress for the tropical Atlantic are constructed for January 1964 to December 1979. Inside the Gulf of Guinea the amplitude of the seasonal variability of SST ranges between 2.5 and 4 times greater than the interannual variability. In the remainder of the equatorial Atlantic this measure is less than 2. Standard deviations of wind stress anomalies indicate that, except near the Intertropical Convergence Zone, the magnitude of interannual fluctuations are greater than seasonal ones. The joint analyses of these SST and wind stress fields indicate the largest positive SST anomaly in the Gulf of Guinea (July, 1968) was immediately preceded by the only reversal of the trade winds west along the equator.
Formation of CS2 and OCS from decomposition of metal sulfides
Authors: Stedman Donald H. , Creech Michael Z. , Cloke Paul L. , Kesler Stephen E. , Gardner Michael
Published: February 2008

The unexpected observation that the common mineral iron sulfide FeS2 produces CS2 and OCS when incubated with water has been further investigated by testing either untreated pyrite or pyrite cleaned with acid and an organic solvent. OCS and CS2 were produced in all experiments except those excluding oxygen or those thoroughly cleaned with acetonitrile. These results indicate that both oxygenated water and organic matter are needed to produce OCS and CS2. Oxygenated groundwater with dissolved organic matter is widespread in most geologic environments, as are metal sulfides, suggesting that oxidative decomposition of pyrite should be investigated as a source of OCS and CS2 to the atmosphere.
Observation of interplanetary magnetic field and of ionospheric plasma convection in the vicinity of the dayside polar cleft
Authors: Clauer C. R. , Banks P. M. , Smith A. Q. , Jorgensen T. S. , Friis‐Christensen E. , Vennerstrom S. , Wickwar V. B. , Kelly J. D. , Doupnik J.
Published: February 2008

Dayside ionospheric convection at high latitudes has been examined during a series of experiments using the Sondrestrom radar together with ancillary observations of the interplanetary magnetic field (IMF) by the IMP‐8 spacecraft. The radar experiments obtained a latitude coverage of 67.6° Λ to 81.30° Λ and a temporal resolution of between 14 to 25 minutes. A total of 17 rotations through the dayside cleft region during April, June and July, 1983 have been examined. The observations show two convection cells with sunward flow at lower latitudes and antisunward flow at higher latitudes. The flow commonly rotates through a 180° angle resulting in the predominant appearance of east‐west flows. Rapid temporal variations in the convection velocities are frequently observed. Many of the high latitude variations in convection velocity appear to be directly related to variations in the IMF By component, with eastward (westward) velocity associated with negative (positive) By. This is strong evidence for a direct electrical coupling between the solar wind and dayside high latitude ionosphere.
Radar and satellite measurements of an F‐region ionization enhancement in the post‐noon sector
Authors: Robinson R. M. , Evans D. S. , Potemra T. A. , Kelly J. D.
Published: February 2008

A post‐noon enhancement in F‐region ionization has been studied using data from the Sondrestrom radar and the NOAA‐7 and Triad satellites. This enhancement is seen quite often in Sondrestrom radar data. It is extended in the east‐west direction and is the site of elevated electron temperatures. Data from the Triad satellite indicate that the enhancement observed on 9 September 1983 was collocated with intense upward field‐aligned currents. The NOAA‐7 satellite measured an electron spectrum in association with the event that was peaked at about 1 keV. The appearance of the spectrum suggests that the electrons were accelerated through a potential drop of 1.3 kV. The temperature and density of the source electrons was estimated to be 350 eV and 3.5 cm−3, respectively. The spatial relationship between the currents, electric field and electron precipitation is similar to that observed in evening sector auroral arcs. We argue that the F‐region arc on the dayside is produced by the same process as the more intense evening sector arcs except that the accelerating potential above the arc is lower. This difference in accelerating potential is a result of the higher source densities in the magnetosphere to which field lines from the dayside arc connect.
Millstone Hill incoherent scatter observations of exospheric temperature over 25 to 60 degrees north latitude
Authors: Oliver W. L.
Published: February 2008

Elevation scan observations made by the Millstone Hill incoherent scatter radar are analyzed to produce local‐time/latitude maps of exospheric temperature. By lowering the antenna elevation to 4 degrees, observations in the thermosphere are possible over the latitude range 25 to 60 degrees north. These radar maps of exospheric temperature provide a new capability for the simultaneous monitoring of the detailed temporal and spatial morphology of the thermosphere. The combination of such maps from different radars promises to provide a powerful new tool for global thermospheric studies. The results for two multi‐day experimental periods in March and November 1982 are presented and described. During magnetically quiet periods the latitudinal variation of exospheric temperature is observed to be small in comparison with the diurnal variation. During disturbed periods large ion frictional heating events are observed at high latitudes and may extend even to mid latitudes during the more energetic events. These frictional heating effects upon the ions severely contaminate and exaggerate the deduced neutral temperatures. The second of the two November days showed substantially higher temperatures than the first even at mid and low latitudes. It is suggested that the high level of magnetic activity commencing on the prior evening and persisting for more than 24 hours served to generate an aurorally driven circulation cell that deposited auroral energy throughout the radar field of view.
Thermospheric neutral wind at −39° azimuth during the daytime sector at Sondrestrom
Authors: Wickwar Vincent B.
Published: February 2008

Measurements with the Sondrestrom radar have been used to examine the daytime thermospheric neutral wind and to relate that wind to other geophysical parameters. Ion drag is found to be particularly important for determining the wind pattern. However, evidence is presented that the wind pattern is significantly influenced by soft particle precipitation and, possibly, by Joule heating.
Age of oceanic plates at subduction and volatile recycling
Authors: Abbott Dallas , Lyle Mitchell
Published: February 2008

The age of the subducting plate as it enters the trench controls the maximum depth of volatile transport by the downgoing plate. As the slab descends and heats up, decarbonation and dehydration reactions cause alteration minerals and sediments to release volatiles. Our calculations show that subducting oceanic plates <11 m.y. old in oceanic arcs and <34 m.y. old in continental arcs heat up so rapidly that no H2O or CO2 can return to the asthenosphere. Instead, these volatiles rise into the over‐riding lithospheric plate. CO2 and H2O are released differently during subduction. A thickly‐sedimented plate subducting beneath an oceanic arc will return H2O to the asthenosphere only if the subducting plate is older than 11 m.y. and CO2 only if it is older than 25 m.y. If Archaean oceanic lithosphere had a maximum age of 30‐50 m.y. and an average age of 10‐18 m.y., then the amount of volatile recycling to the asthenosphere could have been much lower than at present, despite a greater total consumption rate.
The eclogite to garnetite transition — Experimental and thermodynamic constraints
Authors: Bina Craig R. , Wood Bernard J.
Published: February 2008

We have found that the forms of the experimentally determined phase diagrams for pyroxene‐garnet transformations require the volume changes for these reactions to be much smaller at 130 kbar (400 km) than at 1 atm. Using these volume data we calculated the width of the eclogite‐garnetite transition in natural quartz tholeiite and alkali olivine basalt compositions taking account of mixing in multicomponent pyroxene and garnet phases. We find that the eclogite‐garnetite transition does not exhibit any discontinuity in bulk sound velocity in the pressure range 110 to 230 kbar. In addition, this velocity, when plotted as a function of pressure, possesses a curvature which is in the opposite sense to that given by the Preliminary Reference Earth Model (PREM). This phase transition, therefore, does not appear to be a satisfactory model for the 400 km seismic discontinuity.
Seismotectonics of the Guinean Earthquake of December 22, 1983
Authors: Dorbath C. , Dorbath L. , Gaulon R. , George T. , Mourgue P. , Ramdani M. , Robineau B. , Tadili B.
Published: February 2008

Field geological and seismological investigations conducted after the Guinean earthquake on December 22, 1983 show a shallow dextral strike‐slip fault with a large normal component. The NW‐SE horizontal compressive stress deduced from this event is consistent with measurements made at other places in this region. Old fissures, some of them reactivated during this earthquake, show that this intraplate area constitutes a localized weakness zone in the crust.
Permeability changes during time‐dependent deformation of silicate rock
Authors: Kranz Robert L. , Blacic James D.
Published: February 2008

Permeability was measured during creep deformation of a tight sandstone and a granite at upper crustal conditions. With water at 100°C as the pore fluid, permeability first decreased then increased during loading to peak stress. Thereafter, permeability decreased as much as 50% over time, even though sample volumetric strain indicated continuous dilatant creep. A silica‐rich precipitate was found at the ends of the specimens and etch pits found on quartz grain surfaces. From these observations, we infer that permeability changes during creep are a result of the competing processes of dissolution, precipitation and dilatant microcracking. Depending upon deformation rates, this could have ramifications which are beneficial for waste isolation, but deleterious for geothermal energy extraction schemes.
Optical Doppler imaging of the Aurora Borealis
Authors: Shepherd G. G. , Gault W. A. , Koehler R. A. , McConnell J. C. , Paulson K. V. , Llewellyn E. J. , Anger C. D. , Cogger L. L. , Haslett J. W. , Moorcroft D. R. , Gattinger R. L.
Published: February 2008

The Fabry‐Perot spectrometer method of measuring upper atmospheric winds and temperatures has now been firmly established. The Michelson interferometer offers an alternative approach that has so far received little attention. A brief description is given of a stable achromatic field‐widened Michelson interferometer, that uses a CCD detector. Four phase‐stepped images are reduced to images of phase (leading to velocity), of fringe visibility (leading to temperature), and intensity. Preliminary results on the 557.7 nm emission in aurora, made during field trials in February, 1984 are presented. During an auroral brightening three scale sizes of event were observed in the velocity images: a "pulsation" filling the whole field of view and having a period of 200 s, a linear structure with an apparent wavelength of about 50 km, and a linear wavelike structure with an apparent wavelength of 10 km.
Bursts of electron waves modulated by oblique ion waves
Authors: Boswell R. W.
Published: February 2008

Experimental evidence is presented which shows small packets of electron plasma waves modulated by large amplitude obliquely propagating non‐linear ion plasma waves. Very often, but not always, the whole system is modulated by an oscillation near the ion gyro frequency or its harmonics. The ion waves seem to be similar to those measured in the current carrying auroral plasma. These results suggest that the generation of ion and electron waves in the auroral plasma may be correlated.
Energetic ion observations of a large scale vortex in the distant geotail
Authors: Sanderson T. R. , Daly P. W. , Wenzel K.‐P. , Hones E. W. , Bame S. J.
Published: February 2008

We present first observations in the deep tail of the magnetosphere of a vortex structure in both energetic ions (E > 35 keV) and plasma. We observe a vortex, with period about 15 minutes, at X = −217 Re within the energetic ion boundary layer which marks the boundary between the plasma sheet and the southern lobe. The vortex, which was coplanar with the boundary layer, was observed between a region of tailward flow of energetic ions (i.e. the plasma sheet) and a region with no tailward flow (i.e. the southern lobe).
A causal relationship between lightning and explosive spread F
Authors: Woodman Ronald F. , Kudeki Erhan
Published: February 2008

Experimental evidence for a causal relationship between lightning and explosive equatorial spread F is presented. It is proposed that explosive spread F is produced by rapidly growing plasma instabilities, which are triggered by sudden increases of the F region ambient electric fields due to the penetration of lightning fields into regions of weak or marginal instability.
A model for equatorial explosive spread F
Authors: Kelley M. C. , Farley D. T. , Kudeki E. , Siefring C. L.
Published: February 2008

Explosive spread F was first described by Woodman and LaHoz [1976]. In such events the 50 MHz radar signal rises at Jicamarca to 10‐20 db above the noise level within a few milliseconds but then disappears within 100 ms or less. Woodman has suggested that electric fields from thunderstorms might drive a plasma instability which could cause these echoes, and recent observations [Woodman and Kudeki, 1984] provide convincing evidence for this triggering. Here we discuss the instability mechanism and show that transient thunderstorm electric fields comparable to those recently observed by rockets in the midlatitude ionosphere could excite a rapidly growing two‐stream plasma instability that is driven by the E×B drift of the F region electrons in the short period (less than the ion gyroperiod) before the ions reach the same velocity.
Low latitude Pc3 pulsations and associated ionospheric oscillations measured by a digital chirp ionosonde
Authors: Sutcliffe P. R. , Poole A. W. V.
Published: February 2008

It is shown that oscillations of ionospheric Doppler velocity are associated with Pc3 geomagnetic pulsations recorded at ground level. Two mechanisms are proposed to account for this association, namely, variations in the refractive index of the ionosphere due to the oscillating
and vertical
drift of the ionosphere as a whole. The latter is used to determine the east‐west component of pulsation electric field in the ionosphere.
Electrostatic hiss and the beam driven electron acoustic instability in the dayside polar cusp
Authors: Tokar Robert L. , Gary S. Peter
Published: February 2008

In this study it is shown that the upward moving electron beams observed by DE‐1 in the dayside polar cusp at 2 to 5 RE drive an electrostatic electron acoustic mode, rather than the whistler mode near resonance, as previously concluded. The characteristics of this instability are compared with the properties of hiss in the polar cusp observed by DE‐1. The hiss frequencies and funnel shaped frequency‐time spectra are consistent with the electron acoustic mode. However, because the hiss often has a fluctuating magnetic field component near the axis of the funnel shape, the hiss is probably composed of both electron acoustic and whistler mode waves.
Seismic to ultrasonic velocity drift: Intrinsic absorption and dispersion in crystalline rock
Authors: Murphy William F.
Published: February 2008

An intrinsic velocity dispersion of 5% has been measured from 2 to 7 kHz in a water saturated crystalline rock. The porosity of the granite is 0.008 and consists of microcracks. Specific attenuation was observed to be weakly dependent on frequency over the same band. We also measured longitudinal and shear specific attenuation as a continuous function of water saturation at 1‐2 kHz. The constant‐Q model inadequately describes the dispersion. The dispersion mechanism is hydrodynamic relaxation of the microcracks. An effective pressure of 10 MPa reduces the dispersion to less than 1% per decade, or 4% from 1 Hz to 1 MHz. The intrinsic dispersion is insufficient to account for the discrepancies between seismic, sonic, and ultrasonic velocities which are observed in the field. The in‐situ velocity drift is a factor of four greater than the maximum intrinsic dispersion. We conclude that such a velocity drift in crystalline rocks is caused by sampling resolution of macroscopic fractures.
The vertical distribution of CHClF2 (CFC‐22) in the stratosphere
Authors: Fabian P. , Borchers R. , Krüger B. C. , Lal S. , Penkett S. A.
Published: February 2008

This paper presents the first measurements of the vertical distribution of CFC‐22 in the stratosphere resulting from gas chromatography‐mass spectrometry (GC‐MS) of air samples collected cryogenically between 10 and 33 km altitude, at 44°N. Results from 2 balloon flights carried out on September 20, 1982, and on September 10, 1983, are shown and compared with a theoretical profile computed by means of a 1‐D model. Our results demonstrate that CFC‐22 mixing ratios decrease more slowly with height than many other halocarbons indicating that this hydrohalocarbon may become an important source of ClOx radicals in the upper stratosphere.
Is hydrogen cyanide (HCN) a progenitor of acetonitrile (CH3CN) in the atmosphere?
Authors: Brasseur G. , Zellner R. , De Rudder A. , Arijs E.
Published: February 2008

The possibility of a link between HCN and CH3CN in the atmosphere has been suggested recently. A new chemical analysis of this problem as well as model calculations indicate that, most probably, these gases are produced at the Earth's surface and destroyed by oxidation in the middle atmosphere. The strength of the photodestruction of these 2 molecules seems to be weak. It is unlikely that HCN is an atmospheric source of CH3CN.
Variable field‐to‐normal angles in the shock foreshock boundary observed by ISEE 1 and 2
Authors: Greenstadt E. W. , Mellott M. M.
Published: February 2008

Saturated ULF waves in the foreshock, with amplitudes comparable to the magnitude of the average field, are convected by the solar wind to the quasi‐parallel shock where the average field‐normal angle is less than, or about, 45°. Several examples from ISEE 1 and 2 magnetometer data show waves that defined local, instantaneous field‐normal angles very different periodically from the average. Local geometric conditions at the nominally quasi‐parallel shock varied from nearly parallel to nearly perpendicular, at the periods of typical upstream waves. Clear magnetic shock transitions occurred under temporarily quasi‐perpendicular geometry.
Preliminary results from vertical seismic profiling of Oroville microearthquake S‐waves
Authors: Malin P. E. , Waller J. A.
Published: February 2008

Seismograms recorded along a 0.5 km‐deep borehole in Oroville, CA., show that ground‐level s‐wave velocity spectra at this location are a product of site effects. In the 6.25 to 50 hz range studied, both the Cleveland Hill fault, through which the borehole was drilled, and the rock above it contribute to a substantial loss of s‐wave energy. In first‐order approximation, the average apparent s‐wave quality factor, Qsa, along the well is 9. Across the fault zone the Qsa drops to a low of 3. Downhole, the seismograms can readily be separated into longitudinal and transverse components. Particle motion diagrams show that the s‐arrival is made up of two differently polarized waves. This splitting is possibly an effect of wave propagation in the highly cracked and probably anisotropic rock of the region.