bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferroelectricity in natural samples of chalcocite, Cu2S
Authors: Bieniulis Mark Z. , Corry Charles E. , Hoskins Earl R.
Published: February 2008

A structural phase transition, conductivity and dielectric permittivity anomalies, together with a polarization hysteresis loop which collapses above the Curie temperature (∼ 105°C) provide converging lines of evidence for ferroelectricity in the single and polycrystalline natural samples of chalcocite, Cu2S, investigated. Chalcocite is an important ore of copper, and its electrical properties are a factor both in exploration for the mineral and processing the ore.
Corotating convection revisited
Authors: Hill T. W. , Liu W. W.
Published: February 2008

The corotating convection model invokes a systematic large‐scale pattern of plasma motion through the Jovian magnetosphere, a pattern fixed in corotating (System III) coordinates and established by an observed longitudinal asymmetry of the S+ ion distribution in the inner Io torus. In its various versions published to date, the corotating convection model would preserve this longitudinal asymmetry throughout the magnetospheric convection system; the model is thus in conflict with the high degree of longitudinal symmetry that is observed to exist in the hot outer Io torus and presumed to exist also in the magnetosphere outside the torus. We propose to solve this difficulty by superimposing on the corotating convection system a strong retrograde flow confined to the torus region, representing the corotation lag associated with ion production and charge exchange in the Io torus. The addition of this azimuthal flow in the torus region renders the plasma density distribution almost symmetric with respect to longitude in the outer torus and beyond (as required by direct observation), while retaining a corotating convection pattern outside the torus (whose existence is supported indirectly by a number of observations). Serendipitously, the condition of approximate azimuthal symmetry of the plasma density distribution permits an analytic solution of the otherwise intractable equations governing the corotating convection pattern.
The influence of lower stratospheric forcing on the October Antarctic ozone decrease
Authors: Nagatani Ronald M. , Miller Alvin J.
Published: February 2008

The vertical component of the Eliassen‐Palm (E‐P) fluxes for the seven Septembers of 1979 to 1985 are shown to have a pattern correlation to 30 mb mean latitudinal ozone and temperature at 70°S for October, suggesting a dynamical influence on the long term trend of ozone and temperature values in the Southern Hemisphere for the period. For the August E‐P fluxes and September parameters the relationship still appears to hold for temperature, but the ozone relationship is much weaker.
Shear‐wave velocity and Poisson's ratio structure of the upper lithosphere in southwest Germany
Authors: Holbrook W. Steven , Gajewski Dirk , Prodehl Claus
Published: February 2008

Knowledge of shear‐wave velocity structure, when used with compressional‐wave velocity, can help constrain interpretations of composition from seismic refraction results. We present shear‐velocity (vs) models from high‐quality S‐wave data from Southwest Germany, which combine with existing P‐wave velocity (vp) models to give Poisson's ratio in the crust and uppermost mantle. In general, Poisson's ratio is 0.25 in the uppermost crust, 0.22‐0.23 in the mid‐crust, and varies laterally from 0.24‐0.30 in the lower crust; the average Poisson’s ratio for the whole crust is everywhere about 0.25. The laminated signature of the lower crust prominent on reflection and P‐wave refraction data is absent on the S‐wave refraction data, suggesting strong vertical variations of Poisson's ratio within the lower crust. No shear‐wave refractions from the upper mantle are present, even where strong P‐wave refractions are observed, possibly indicating an increase of Poisson's ratio with depth in the upper mantle. We interpret these results to indicate a high quartz content or fluid phases at low pore pressure in the mid‐crust, a high feldspar content in the lower crust, and an increase in depletion of basaltic components with depth in the upper mantle.
Origin of magnetization in the Phosphoria Formation at Sheep Mountain, Wyoming: A possible relationship with hydrocarbons
Authors: Benthien R. H. , Elmore R. D.
Published: February 2008

Hydrocarbon impregnated fenestral dolomites of the Phosphoria Formation were sampled on both flanks of Sheep Mountain Anticline, Wyoming. Demagnetization results indicate one dominant component that is either synfolding (Laramide in age) or predates folding (Cretaceous in age). Thermal demagnetization yields stable decay to temperatures between 500°C and 550°C and rock magnetic experiments suggest that the magnetization is dominated by a low coercivity component. Magnetic extracts contain spheres (<15 µ diameter) as well as other authigenic forms. Energy dispersive analysis demonstrates that Fe is the only detectable element present in the spheres and X‐ray diffraction analysis indicates that magnetite is present in the extracts; the spheres are interpreted to be authigenic magnetite. The magnetization is interpreted as a chemical remanent magnetization (CRM) residing in this authigenic magnetite. Chemical conditions created by the hydrocarbons may have caused precipitation of the authigenic magnetite and acquisition of the associated CRM.
Phase velocity distribution in the Indian Ocean and Indonesian region inferred from GEOSCOPE records
Authors: Roult G. , Rouland D. , Montagner J. P.
Published: February 2008

To improve the lateral resolution of 3 dimensional models of seismic wave velocities in the Indian Ocean and surrounding regions we analyzed direct earthquake to station Rayleigh waves observed on the vertical long‐period components of four GEOSCOPE stations [TAM (Algeria), PCR (La Réunion), PAF (Kerguelen) and AGR (Djibouti)].

The phase velocities along 51 well‐distributed paths are obtained in the period range 40‐350 s after corrections for the phase pattern at the source and for the instrumental response. A tomographic method is then applied (Montagner, 1986a) to compute the geographical distribution of phase velocities, without any a priori regionalization.

The location of velocity anomalies is quite stable and well resolved. The phase velocity distributions are compared with global results from Nakanishi and Anderson (1984b), Woodhouse and Dziewonski (1984), Tanimoto (1985), Nataf et al. (1986) and with regional studies using group velocities for the same region (Montagner, 1986a,b,c).
A search for fast planetary‐scale instabilities in the equatorial stratosphere
Authors: Lait Leslie R. , Stanford John L.
Published: February 2008

A method proposed by Salby for computing space‐time Fourier transforms of asynoptic satellite data has been applied to stratospheric brightness temperature measurements from January and February 1979 in a search for two fast‐moving low‐wavenumber instabilities predicted in a numerical study by Lynch. The method is capable of producing spectra down to periods of approximately one day with no distortion due to the asynopticity of the data. No spectral peaks corresponding to the predicted modes were found; taking the noise level as the upper limit for their amplitudes at the altitudes observed, an upper limit of approximately 0.6 to 1.2 degrees Kelvin may be set for their peak amplitudes near the mesopause.
North‐south structures in the midnight sector auroras as viewed by the Viking imager
Authors: Rostoker Gordon , Lui A. T. Y. , Anger C. D. , Murphree J. S.
Published: February 2008

During auroral substorms, active auroras involving field‐aligned electric fields appear at the poleward border of the auroral oval. Equatorward of these active discrete auroras, a diffuse region of luminosity develops which often features imbedded localized structures which can have distinctively north‐south orientations. In this paper we study the behaviour of such longitudinally confined northsouth oriented auroral arc structures which may turn on and off sporadically during the substorm lifetime. In particular, we show observations which suggest that these structures may be the projection on the ionosphere of the drift paths of energetic electrons as they drift from the magnetotail into the more dipolar inner magnetosphere. Our results suggest that injection of auroral particles into the central plasma sheet occurs in quite localized regions over lengthy periods of time. The injected particles drift earthward in the central plasma sheet where those electrons with pitch angles close to the loss cone are sporadically caused to precipitate into the ionosphere causing the fingers of luminosity. North‐south aligned structures near the equatorward edge of the oval are believed to represent precipitation of a spatially localized population of energetic electrons for which the westward convective drift velocity in the evening sector nearly balances the eastward gradient and curvature drift velocity thus leading to purely earthward convective drift of the energetic electrons.
Polar cap arcs observed by the Viking satellite
Authors: Eliasson L. , Lundin R. , Murphree J. S.
Published: February 2008

The Viking orbit has been well suited for studies of polar cap phenomena in the altitude range 5000 to 13500 km. A variety of particle features have been observed. Signatures of acceleration below the spacecraft altitude by field‐aligned potentials such as narrow beams of upflowing ions and an increased electron loss cone angle are typically observed. Polar arc events are caused by accelerated particle distributions in regions with characteristics similar to those in the plasma sheet boundary layer. The shape of the electron angular distributions indicates that the arcs occur on closed magnetic field lines. Many "polar cap" arcs are better described as the poleward edge of an expanded oval during magnetic quiet conditions.
Stratospheric distribution of HCN from far infrared observations
Authors: Abbas M. M. , Guo J. , Carli B. , Mencaraglia F. , Carlotti M. , Nolt I. G.
Published: February 2008

Far infrared limb thermal emission measurements of the earth's stratosphere were made with a high resolution spectrometer on a balloon payload launched from Palestine, Texas, on October 5, 1982. Several limb sequences of a portion of the observed spectra have been analyzed for retrieval of the stratospheric HCN profile from a number of spectral lines in the 32 to 56 cm−1 region. The mixing ratio profile in the 20 to 37 km altitude range has been retrieved with 2σ uncertainties of ∼ 15 to 20% and with an altitude resolution of ∼ 4‐5 km. The HCN volume mixing ratio is found to be ∼ 139 pptv at 20 km, 127 pptv at 25 km, and increasing to 172 pptv at 37 km. The results are compared with measurements by other groups and with photochemical model calculations reported in the literature.
Regional linear cross‐strike discontinuities in western Aphrodite Terra, Venus
Authors: Crumpler L. S. , Head James W. , Harmon John K.
Published: February 2008

Western Aphrodite Terra, Venus, is characterized by a series of parallel linear structural discontinuities 2000‐4000 km in length and 100‐200 km wide, which strike at high angles to the general topographic trend of the highlands. The detailed characteristics of these features are similar to terrestrial oceanic fracture zones and strike‐slip fault zones. Either interpretation implies the presence of large‐scale horizontal tectonic movement on Venus.
Magnetic field draping in the comet Halley coma: Comparison of Vega observations with computer simulations
Authors: Schwingenschuh K. , Riedler W. , Yeroshenko Ye. , Phillips J. L. , Russell C. T. , Luhmann J. G. , Fedder J. A.
Published: February 2008

During the VEGA‐1 encounter with comet Halley, the magnetometer observed draping and compression of the interplanetary magnetic field (IMF). These are reproduced well by a 3‐D MHD simulation of the cometary interaction. Rotations in the magnetic field similar to those at closest approach are also observed 2.75 hours earlier. We suggest that both rotations correpond to the same IMF interval and that the spacecraft had overtaken the plasma and encountered "older" magnetic field as it penetrated the coma. Analysis of the MHD model indicates that it should take ∼ 3 to 5 hours for a solar wind parcel to pass from the unperturbed solar wind to VEGA‐1 at closest approach. A simulated magnetic field profile composed of nested sections for different IMF orientations closely resembles the observations. This result supports the hypothesis of layered magnetic orientations in the coma.
Mirror instability in the magnetosphere of comet Halley
Authors: Russell C. T. , Riedler W. , Schwingenschuh K. , Yeroshenko Ye.
Published: February 2008

High resolution VEGA 1 and 2 magnetic measurements in the cometary magnetosphere and magnetosheath of Halley reveal the presence of fluctuations with the signature expected for the mirror instability. This instability is a mechanism by which homogeneously produced cometary ions with a large perpendicular temperature anisotropy can be concentrated into discrete linear features. Thus, the mirror instability may provide a new mechanism for the generation of cometary rays. To our knowledge the presence of this instability in the cometary plasma was not predicted.
Fingerprint structure PC 1 geomagnetic pulsations
Authors: Sato Natsuo , Hirasawa Takeo , Shirokura Yoshihiko
Published: February 2008

A new type of Pc 1 pulsation is found. The emission is called "fingerprint" structure Pc 1 from the shape of the frequency ‐time (f‐t) spectra. The characteristics of the emissions obtained at geomagnetically conjugate statieons (Syowa Station in Antarctica and Husafell in Iceland) are as follows: The fine structure of the emission consists of many horizontal lines on f‐t spectra, up to 25 different lines. The frequency separation of adjacent lines remains constant and the frequency differences are 15‐25 mHz, mostly around 16‐20 mHz. The enhanced bands of each harmonic structure change their frequencies simultaneously. The fine structures of the emissions show good geomagnetic conjugacy when the emissions are observed with enough intensity at both stations.
The effect of counter electrojet on the plasma distribution of the topside ionosphere
Authors: Alex S. , Roy M. , Rastogi R. G.
Published: February 2008

Evidence of strong correlation between the counter electrojet and the behaviour of the topside ionosphere is presented here. The reality of the counter electrojet is established by the magnetic field variations of the H‐component and the bottom side ionograms at Huancayo. For the same event, the latitudinal plasma distributions of the topside ionosphere are studied. It is shown that the E‐region electric field associated with the counter electrojet pushed the plasma downwards even on the topside as high as 600 km. The well known crest‐trough formation is also shown to be absent on the counter electrojet day.
Methylamines in the marine atmosphere
Authors: Van Neste Antoinette , Duce Robert A. , Lee Cindy
Published: February 2008

There is growing recognition of the possible importance of organic nitrogen compounds in the global atmospheric nitrogen cycle. Concentrations of gaseous methylamines (MAs) have been measured for the first time in the atmosphere of two non urban regions‐coastal Hawaii and Rhode Island. In Hawaii gaseous MA concentrations were as follows: monomethylamine (MMA), 11±5 pmol/m³ dimethylamine (DMA), 93±51 pmol/m³ and trimethylamine (TMA), 30±19 pmol/m³. Concentrations of these compounds were also measured in coastal seawater in Hawaii and Massachusetts and in rainwater from Rhode Island. Calculations of the fluxes of MAs across the air‐sea interface indicate that the oceans are a source for MMA and TMA but may be a sink for dimethylamine (DMA). The concentrations of MAs observed in rain can largely be explained by scavenging of gaseous MAs. Another important removal process for atmospheric MAs appears to be oxidation by OH radicals. Wet and dry removal combined with OH oxidation appear to balance oceanic production of MMA and TMA in the Hawaii region. Significant uncertainties remain about the cycling of DMA.
Air‐ and oxygen‐broadening coefficients for the O2 rotational line at 60.46 cm−1
Authors: Jennings D. A. , Evenson K. M. , Vanek M. D. , Nolt I. G. , Radostitz J. V. , Chance K. V.
Published: February 2008

Using an NBS laser‐based tunable far infrared spectrometer, we have measured the air‐ and oxygen‐broadening coefficients for the J = 10←10, N = 11←9 O2 rotational transition at 60.46 cm−1 (1.812 THz). The air‐broadening coefficient is 5.04 ± 0.38 × 10−7 cm−1Pa−1 (0.0511±0.0039 cm−1atm−1) (HWHM) at 245±6 K; the oxygen‐broadening coefficient is 4.92±0.47 × 10−7 cm−1Pa−1 (0.0499±0.0048 cm−1 atm−1) (HWHM) at 259±2 K. These direct experimental measurements of the air‐broadening coefficient should improve the accuracy of retrieval calculations for far infrared stratospheric balloon experiments which use O2 rotational lines to calibrate the viewing geometry.
Effect of variable bathymetry on the amplitude of teleseismic tsunamis: A ray‐tracing experiment
Authors: Woods Mark T. , Okal Emile A.
Published: February 2008

We apply surface wave ray‐tracing techniques to tsunami propagation in an ocean of variable depth. Because tsunami velocities are proportional to the square root of the depth of the water column, the juxtaposition of oceanic plateaux and basins generates strong lateral velocity gradients, and bathymetric features can act as lenses focusing or defocusing the tsunami waves. We present a reconstruction of the tsunami wave field from the great Chilean earthquake of 1960: an order‐of‐magnitude computation based on the concept of ray‐density provides qualitative agreement with observations at several sites in the Pacific Ocean. We also demonstrate the possibility of using “reciprocal” maps to identify tsunamigenic zones that present particular danger for a given receiving shore.
Comment on “A statistical study of the central plasma sheet: Implications for substorm models”
Authors: Cattell C. A. , Elphic R. C.
Published: February 2008

We show that the conclusions of the above paper are seriously compromised by flaws in the methodology of the statistical study. In addition, the authors' definition of a physically significant flow is not consistent with the physics of the magnetotail.
Model geoid anomalies due to subduction of inextensible lithosphere
Authors: Willemann Raymond J. , Anderson Charles A.
Published: February 2008

We compute geoid slopes from models of subduction in which the subducted lithosphere is much stronger than the surrounding mantle. Geoid slope contributions from both the lithospheric slab and mantle boundary deformations are computed from finite element analysis of mantle flow. The finite element model includes a slab of finite length and a depth dependent Newtonian rheology for the surrounding mantle. We find that observed geoid anomalies at subduction zones, which are positive, cannot be matched by models with uniform mantle viscosity. However, even with a strong subducted lithosphere, the ratio of driving load to boundary deformation is significantly increased by a ten‐fold increase of viscosity with depth, resulting in a geoid high. We find that the sign of the geoid slopes within 3000 km of the trench are independent of maximum depth of the slab for maximum depths from 700 km to 2800 km.
A technique to obtain a Q(f) model from microearthquake swarms
Authors: Carpenter P. J. , Sanford A. R. , Ake J. P.
Published: February 2008

The frequency dependence of the seismic quality factor, Q, is important in interpreting seismic wave spectra for nuclear test discrimination, earthquake damage studies, and in exploration. In this study, P and S wave spectra from 18 events recorded during three 1977 microearthquake swarms are used to compute Q(f) (frequency range = 3‐40 Hz) for a seismically active geothermal region of disturbed upper crust in the central Rio Grande rift near Socorro, New Mexico. Numerically differentiated spectra are fit with a model of the form Q(f) = Qofη and standard linear regression techniques used to compute Qo and η, along with their uncertainties. Only two out of 18 events in these swarms exhibit significant Qp or Qs frequency dependence at the 95% confidence level. This is primarily due to large uncertainties in η generated by upper‐crustal reverberations. Averaging Qp and Qs over events in each swarm shows that for two swarms, a significant frequency dependent Qp exists with η ranging from 0.29 to 0.67 and Qop ranging from 5 to 17 (95% confidence intervals). A strong decrease in Qp or Qs with frequency (η < −0.2) appears to be ruled out. Likewise, the frequency dependence of Qp and Qs does not appear to change with event distance over the range 15.4‐16.9 km. Smoothed spectra produce less frequency dependence and higher Qo values than unsmoothed spectra (the only significant Q(f) is Qos = 123 and η = 0.33 for one swarm). This suggests that much of the apparent frequency dependence may be due to ripple in the spectra (caused by scattered phases in the time window, or the process of windowing itself) and that this technique should only be used with "smooth" spectra.
Mm: Use of a variable‐period mantle magnitude for the rapid one‐station estimation of teleseismic moments
Authors: Talandier Jacques , Reymond Dominique , Okal Emile A.
Published: February 2008

Broadband records of the first passage of Rayleigh waves at Papeete, Tahiti from large circum‐Pacific earthquakes are used to recover in real time their seismic moments. The magnitude concept is used at periods varying from 50 to 300 s. Adequate corrections are made for distance and period. Typical standard deviations are 0.2 orders of magnitude on Mo. This mantle scale Mm can be extended continuously with no additional corrections over 4 orders of magnitude. It can be measured in the frequency‐ or time‐domains, and we describe briefly the automation of the method, with obvious applications in tsunami warning.
Numerical simulation of the generation of turbulence from cometary ion pick‐up
Authors: Goldstein M. L. , Roberts D. A. , Matthaeus W. H.
Published: February 2008

Observations of magnetic field fluctuations near comet Halley have revealed a rapid development of a Kolmogoroff‐like turbulence spectrum extending from below 10−2 Hz to above 0.1 Hz. Spectra obtained far from the comet have a strong peak in power near the Doppler‐shifted ion‐cyclotron frequency of singly ionized water. Closer to the comet, the spectrum at higher frequencies is enhanced in power level over the background solar wind spectrum by approximately an order of magnitude. We solved the equations of incompressible MHD using a two‐dimensional 256×256 mode spectral method code to simulate this spectral evolution as an inertial range turbulent cascade. The initial conditions contained a constant magnetic field and a single coherent wave mode at a low wave number. The solar wind turbulence was modelled by a background noise spectrum having a Kolmogoroff spectral index. The coherent mode decayed into an inertial range spectrum with Kolmogoroff slope within a few eddy‐turnover times. Both the time scale and the increase in power level of the turbulence seen in the simulation are in accord with the Giotto observations.
Magnetic helicity of the IMF and the solar modulation of cosmic rays
Authors: Bieber John W. , Evenson Paul , Matthaeus William H.
Published: February 2008

Using interplanetary magnetic field data acquired at 1 AU, we show that the distribution of magnetic helicity in the heliosphere is asymmetric about the current sheet, in accord with recent theoretical predictions. Such an asymmetric distribution of helicity can in principle explain the sensitivity of the solar modulation of cosmic rays to the sun's magnetic polarity, as observed in charge sign dependent modulation, Jovian electrons, and anomalous 4He.
Paleomagnetic evidence for rotation in opposite senses of adjacent blocks in northeastern Aegea and Western Anatolia
Authors: Kissel C. , Laj C. , Şengör A. M. C. , Poisson A.
Published: February 2008

Paleomagnetic data from western Anatolia and from the island of Lesbos demonstrate significant counterclockwise, clockwise or null rotations of coherent blocks which occurred during the neotectonic period. These results suggest that the brittle carapace of the lithosphere may not everywhere follow the motion of the ductile lower part but that its movement arises from adjustment to the extensional tectonic regime.
The magmatic Rayleigh number and time dependent convection in cooling lava lakes
Authors: Carrigan Charles R.
Published: February 2008

Estimates of the Rayleigh number are necessary for determining the thermal and dynamic states of convecting magma. Calculation of a temperature based Rayleigh number, RaT, is complicated by the thermal coupling that exists between an intrusion and its host. However, the typically greater thermal resistance of the host regime compared to that of convecting magma can allow the host to control heat flux from a magma chamber in a manner somewhat independent of the state of convection in the chamber. In a system where heat flux is controlled rather than temperature, a heat flux based Rayleigh number, RaF, is a more natural parameter to employ, although it has not been used in most magmatic convection models. While the insulating properties of the host regime tend to reduce the value of the thermal Rayleigh number, whether temperature or flux based, this value can be very large compared to any critical value of the Rayleigh number that might exist. The quantity RaF is used to obtain useful relationships for estimating the thermal and kinematic regime in magma. Conservative models of a cooling lava lake, which include temperature dependent viscosity, show that convection will be vigorous enough to circulate phenocrysts. However, the time dependent nature of magmatic convection and the tendency of whole body convection to vanish before crystallization is complete severely complicate any attempt to infer convective amplitudes from the observed distribution of crystals “frozen” into the interior of the body.
A new interpretation of plasma‐line overshoot phenomena
Authors: Kuo S. P. , Lee M. C. , Djuth F. T.
Published: February 2008

The temporal evolution of Langmuir waves excited by high‐power, high‐frequency (HF) radio waves in the ionosphere is studied theoretically. This study is motivated by past observations made with the 450 MHz radar at Arecibo Observatory in Puerto Rico. Two kinds of nonlinear damping to the parametric decay instability are considered in the derivation of the rate equation for the spectral intensity of enhanced Langmuir waves. They are Langmuir wave cascading caused by nonlinear Landau damping and cross‐field electron diffusion. The first damping process leads to the saturation of individual unstable Langmuir wave. The second process, which results from the incoherent scattering of electron orbits by the total excited Langmuir waves, yields anomalous damping that applies to each Langmuir wave. Consequently, Langmuir waves with smaller growth rates will be suppressed by those with larger growth rates. Such a mode competition process may cause the overshoot of the HF‐enhanced plasma line observed with the Arecibo 430 MHz radar. Favorable agreement is obtained between theory and the Arecibo observations.
Are fast atmospheric pulsations optical signatures of lightning‐induced electron precipitation?
Authors: LaBelle J.
Published: February 2008

Fast Atmospheric Light Pulsations (FAP's) consist of millisecond time‐scale bursts of light which have been observed at L = 1.5–2.2 during searches for atmospheric light emissions associated with supernovae. Their statistics of occurrence resemble those of Lightning‐induced Electron Precipitation (Trimpi events) observed at somewhat higher L‐shells. Here we propose that FAP's are in fact optical signatures of LEP events associated with the ≥ 2 MeV electrons of the inner radiation belt (L ≈ 1.4). These electrons would precipitate at low altitudes and could be modulated with time scales the order of 1 ms. The total loss rate of electrons from the inner belt resulting from these events would be comparable to, but somewhat smaller than, the loss rate due to Coulomb scattering.
New silicate perovskites
Authors: Liu Lin‐gun
Published: February 2008

The previously reported non‐quenchable phases of the compositions of diopside and omphacite, or the diopside‐II phase, have been observed to crystallize in the cubic perovskite structure at pressures greater than ∼230 kbar and at ∼1000°C by in situ experiments using a gasketed diamond‐anvil cell coupled with laser heating. The lattice parameter for the perovskite phase of (Ca0.5Mg0.5)SiO3 is a = 3.437 ± 0.004Å and that of ½ (0.75CaMgSi2O6·0.25NaAlSi2O6) a = 3.492 ± 0.004Å at pressure range 230‐245 kbar and room temperature. Diopside‐II is the most likely host of both Ca and Na, and probably the second most abundant mineral phase, in the lower mantle.
Magnetization gaps associated with tearing in the Central America Subduction Zone
Authors: Counil Jean‐Louis , Achache José
Published: February 2008

Vector magnetic anomaly maps derived at sea‐level from Magsat data show a large positive anomaly above the Middle America Trench Relative highs and lows correlate with variations in the seismicity of the subducted Cocos plate. These anomalies can only be modelled assuming complete demagnetization of the slab near seismic discontinuities. We propose that demagnetization is necessarily associated with tearing of the plate. Magnetic anomalies indicate tearing of the Cocos plate beneath Mexico and near Panama but further east than previously proposed on the basis of seismic data. Although the demagnetization process is likely to be related to the temperature increase, it is shown that thermal diffusion is not sufficient to produce the observed anomaly and that the slab must be heavily fractured in the vicinity of teared zones.
Mass transfer from smooth alabaster surfaces in turbulent flows
Authors: Opdyke Bradley N. , Gust Giselher , Ledwell James R.
Published: February 2008

The mass transfer velocity for alabaster plates in smooth‐wall turbulent flow is found to vary with the friction velocity according to an analytic solution of the advective diffusion equation. Deployment of alabaster plates on the sea floor can perhaps be used to estimate the viscous stress, and transfer velocities for other species.
The effect of model structure on projections of greenhouse‐gas‐induced climatic change
Authors: Wigley T. M. L.
Published: February 2008

The transient response of global‐mean temperature to greenhouse‐gas forcing between 1765 and 2030 is studied using two types of ocean model, a pure diffusion model and an upwelling‐diffusion model. The results are almost the same for both types of model. If the greenhouse‐gas contribution to global warming over the period 1880‐1985 is Δ, then the contribution to future warming over the period 1985‐2030 is shown to be approximately 1.6 Δ independent of model type and model parameters (viz. climate sensitivity and ocean mixing rate).
A nonlinear model of wave‐particle interactions in the trapped radiation belts: Auroral pulsation solutions
Authors: Davidson G. T. , Chiu Y. T.
Published: February 2008

The interactions of waves and trapped electrons are described by a closed system of three nonlinear coupled equations. The model has applications to many aspects of wave‐particle interactions in the magnetosphere. Nonlinear numerical solutions pertinent to auroral pulsations have been computed for realistic ranges of physical parameters. The results confirm that precipitation pulsations can be initiated by either an injection of energetic trapped particles or an increase in the plasma ionization density. Relaxation of the system results in cyclic phase trajectories about a (quasi equilibrium) point that is not located at the initial equilibrium point. That observation may explain the tendency of auroral pulsations to appear superimposed upon an increase in the general rate of electron precipitation. The results also imply that precipitation pulsations are most readily initiated by an encounter of drifting energetic electrons with a region of enhanced cold plasma density.
Mesospheric measurements using the EISCAT VHF system : First results and their interpretation
Authors: Hall C. , Hoppe U.‐P. , Williams P. J. S. , Jones G. O. L.
Published: February 2008

The first attempts to use the EISCAT VHF radar to make incoherent scatter measurements of the mesosphere took place in February 1987 and some of the results are presented. Measurements of the electron concentration were made together with tentative calculations of the ratio of negative ions to free electrons. The vertical motion of the neutral atmosphere was also deduced and both chaotic and well‐defined wave structures were observed. One particularly well‐defined wave is examined and possible mechanisms are discussed, including generation by the solar terminator.
Improved sea level monitors for measuring vertical crustal deformation in the Shumagin Seismic Gap, Alaska
Authors: Hurst Ken , Beavan John
Published: February 2008

We have improved the relative vertical deformation detection capability of a network of sea level gauges in the Shumagin seismic gap, Alaska. An examination of the present noise levels suggests that the network is now capable of providing relative vertical deformation data that is quieter than data from leveling, the Global Positioning System, Very Long Baseline Interferometry, or Satellite Laser Ranging.
Non methane hydrocarbons chemistry in the atmosphere of an equatorial forest: A case of indirect photochemical production of OH radicals
Authors: Bonsang B. , Kanakidou M. , Lambert G.
Published: February 2008

An experiment was conducted in the Guyana forest in March 1985, during which C2 ‐ C6 non methane hydrocarbons (NMHC) were measured in the air, together with CO2 and its associated 13C isotopic composition. Owing to the very high atmospheric stability, strong vertical concentration gradients were observed close to the soil surface. Simple assumptions allow showing that NMHC are mainly destroyed by OH radicals whose concentration seems to be surprisingly high, around 1×107 radicals cm−3. An indirect photochemical production of these radicals is proposed.

On the other hand, the fluxes of the different NMHC emitted from the litter were found to be small, in the range of 10−7 to 10−6 g of carbon per hour and per m².
Upper limit on the rate constant for isotope exchange between molecular oxygen and ozone at 298K
Authors: Anderson S. M. , Morton J. , Mauersberger K.
Published: February 2008

The gas phase bimolecular isotope exchange reaction between molecular oxygen and ozone has been investigated directly for the first time. Its rate coefficient is found to be less than 2 × 10−25 cm³‐sec−1 at 298 K, over six orders of magnitude below recent estimates. Much faster exchange was observed over condensed ozone at 77K, suggesting isotopic scrambling is catalyzed under these conditions. The low rate coefficient implies that homogeneous exchange between ground state oxygen and ozone molecules cannot play a significant role in heavy ozone chemistry.
Paleomagnetic results from the Shasta Bally Plutonic Belt in the Klamath Mountains Province, northern California
Authors: Mankinen Edward A. , Irwin William P. , Grommé C. Sherman
Published: February 2008

Available paleomagnetic data show approximately 100° of clockwise rotation for Permian and Triassic strata of the Eastern Klamath terrane. Jurassic strata of this terrane are rotated approximately 60° clockwise, which is comparable to rotations reported for Jurassic plutons that occur elsewhere in the Klamath Mountains province. Paleomagnetic data obtained during the present study from the Shasta Bally belt of Cretaceous plutons indicate 25.7° ± 13.6° of clockwise rotation for the province since Early Cretaceous time (≃ 136 Ma). The waning stages of rotation at the time of emplacement of the Shasta Bally belt plutons, which was closely followed by deposition of basal strata (Lower Cretaceous) of the Great Valley sequence, probably represents completion of accretion of the province to cratonic North America.
Gas phase collisional excitation of infrared emissions in the vicinity of the space shuttle
Authors: Torr Marsha R. , Torr Douglas G.
Published: February 2008

Recent models of the gas concentrations around orbiting vehicles have predicted concentration enhancements of up to 50 times ambient near ram surfaces for the shuttle at altitudes of 200 km. For some models, the mean free path decreases by a factor of ∼100 below that of the undisturbed ambient gas. The predicted scale length for the induced enhancement is relatively large, 5 m, which results in large column concentrations. In this paper we explore the possible implications of such a gas buildup in terms of induced photon emissions. When a large variety of interactions involving the enhanced local shuttle atmosphere are considered, it is predicted that significant effects arise from gas phase collisions between the relatively energetic ambient atoms and molecules and the atoms and molecules in the shuttle environment, particularly in front of ram surfaces. It is shown that such collisions have the potential to transfer considerable energy to the gases in the shuttle environment. Using reasonable estimates for cross sections we find that the most likely emission outcome will be vibrational and rotational radiation losses in the infrared due to direct collisional excitation. Estimates are made of the anticipated intensities of this radiation as a function of vehicle altitude or neutral atmosphere concentration.
Growing ion holes as the cause of auroral double layers
Authors: Tetreault David J.
Published: February 2008

The nonlinear ion‐hole instability is proposed as the cause of intermittent double layers observed in the auroral particle acceleration region. A novel feature of the instability is its occurance in plasma that is stable to linear ion acoustic waves. A growing ion‐hole has a double layer potential structure. We demonstrate here that nonlinear hole instability is consistent with S3‐3 and Viking satellite data. Instability thresholds, as well as characteristic double layer amplitudes, potential drops, speeds, and scale sizes are calculated. The inadequacy of conventional linear instability models in explaining the data is discussed.
An investigation of small‐offset fracture zone geoid waveforms
Authors: Shaw Peter R.
Published: February 2008

Approximately 1,500 geoid cross sections across 15 small‐offset South Atlantic fracture zones (FZ's) are compiled from Seasat altimeter data and organized according to crustal age; these profiles provide a basis for the comparison of the different FZ's, and the evolution of each over geological time. I use an empirical orthogonal function decompostion to investigate the dependence of profile shape and amplitude upon crustal age. The geoid cross sections are found to be coherent in form down the length of each FZ, and possess amplitudes that are inversely related to the relative spreading rate at the time of formation. This observation is consistent with a simple model in which the active portion of a fracture zone (the transform fault) remains a fixed spatial length, yielding a variable age offset across the FZ.
Correction to “Are fast atmospheric pulsations optical signatures of lightning‐induced electron precipitation?”
Authors: LaBelle J.
Published: February 2008

Owing to a production error, a significant portion of the text of “Are Fast Atmospheric Pulsations Optical Signatures of Lightning‐Induced Electron Precipitation?” by J. LaBelle (Geophys. Res. Lett., 14, 1023, 1987) was printed out of sequence. GRL regrets the error and is printing the paper again, with the correct order of the text restored.

Fast Atmospheric Light Pulsations (FAP's) consist of millisecond time‐scale bursts of light which have been observed at L=1.5‐2.2 during searches for atmospheric light emissions associated with supernovae. Their statistics of occurrence resemble those of Lightning‐induced Electron Precipitation (Trimpi events) observed at somewhat higher L‐shells. Here we propose that FAP's are in fact optical signatures of LEP events associated with the ≥ 2 MeV electrons of the inner radiation belt (L ≈ 1.4). These electrons would precipitate at low altitudes and could be modulated with time scales the order of 1 ms. The total loss rate of electrons from the inner belt resulting from these events would be comparable to, but somewhat smaller than, the loss rate due to Coulomb scattering.
Similarity of anomalous sea level pressure fields during the July 1986 and September 1987 southern California Quakes—Accidental or Indicative?
Authors: Namias Jerome
Published: February 2008

Moderate size earthquakes in Southern California in July 1986 and October 1987 were associated with similar antecedent monthly mean anomaly patterns of sea level pressure over the far western contiguous United States and eastern North Pacific. This apparent relationship and a long time series of such patterns in past Julys and Octobers suggest that further research of this nature might be of value in earthquake prediction.
A comparison of surface friction velocities estimated by dissipation and iterative bulk aerodynamic methods during gale
Authors: Akkarappuram Anto F. , Raman Sethu
Published: February 2008

Energy dissipation method and an Iterative Bulk Aerodynamic Method (IBAM) are used to estimate friction velocity (u*) for a wide wind speed range (5.66 to 21.6 ms−1) with convective atmospheric conditions over the ocean during the Genesis of Atlantic Lows Experiment (GALE). Values of u* obtained by the IBAM are in reasonably good agreement with those from the dissipation method. The iterative bulk method appears to do well for wind speeds up to about 21 ms−1.
Gulf Stream remote forcing of shelfbreak currents in the Mid‐Atlantic Bight
Authors: Bane John M. , Brown Otis B. , Evans Robert H. , Hamilton Peter
Published: February 2008

The “Slope Sea” is a narrow band of ocean that lies between the Gulf Stream and the continental shelf edge in the Mid‐Atlantic Bight. It is composed primarily of slopewater, and a closed cyclonic gyre circulates within the upper few hundred meters of its western end. A two‐year time series of current measurements in this region has shown that the southwestward flowing shelfbreak currents along the shoreward flank of the gyre are directly related to the position of the Gulf Stream, which is typically some 150 to 300 km seaward of the shelfbreak. The mean monthly shelfbreak currents are strongest, towards the southwest at about 30–40 cm s−1, when the Stream is within 150 km of the shelf edge, whereas those currents are close to zero when the Stream is about 300 km away.
The solar cycle and the QBO influences on the latitude of storm tracks in the North Atlantic
Authors: Tinsley Brian A.
Published: February 2008

It is shown that if data on the latitude variation of winter storm tracks in the North Atlantic are sorted according to the phase of the quasi‐biennial oscillation (QBO) of stratospheric winds in the tropics, then a clear solar cycle variation emerges without any need to smooth the data. For the west phase of the QBO the peak to peak amplitude of the solar cycle variation is about 6° of latitude, with storm tracks occurring equatorward at solar maximum and poleward at solar minimum. This is consistent with the recent work of Labitzke and van Loon, and extends to dynamical effects at the surface the pattern of atmospheric responses that they found. Problems with the acceptance of the concept of solar variability effects on weather are discussed. To relate the solar variable energy inputs to the weather effects which are energetically several orders of magnitude larger, scenarios for a class of mechanisms with two or three stages of amplification are outlined, involving middle atmospheric energy inputs, in contrast to the tropospheric inputs of solar luminosity changes.
Partial anhysteretic remanence and its anisotropy: Applications and grainsize‐dependence
Authors: Jackson Mike , Gruber William , Marvin Jim , Banerjee Subir K.
Published: February 2008

The distribution of remanence coercivities in a rock sample can be obtained by differentiating alternating field (AF) demagnetization curves of anhysteretic remanent magnetization (ARM); however, significant errors can be introduced by grain interactions and by the noise inherent in differentiation. We have found that 1) this error can be significantly reduced by measuring partial ARM's (pARM's) and 2) pARM patterns show a strong empirical correlation with grain‐size. pARM's are imparted by exposing a sample to a small direct magnetic field in the presence of a large, decreasing AF; the direct field is switched on over a specified range of AF's, thus magnetizing a fraction of the magnetite grains in the corresponding coercivity range. We have further found in both synthetic and natural sediments that measurement of the anisotropy of pARM enables us to detect the preferred orientations of distinct subpopulations of magnetite particles, related to the size and shape of the grains.
Effects of compressibility on the temperature jump at the interface of layered, spherical‐shell convection
Authors: Yuen David A. , Zhang Shuxia , Langenberger Sherri E.
Published: February 2008

Large temperature jumps at the interface of layered convection are important to the argument used against the likelihood of separate circulations in the upper and lower mantles. We study this problem within the framework of a compressible, constant viscosity spherical‐shell model. Both mechanical and thermal coupling configurations are considered. Although the temperature jumps are reduced by compressibility, their magnitudes remain quite large, 0(10³°C), in the case of mechanical coupling. For thermal coupling the temperature jumps become smaller but still are substantial, between 500 to 1000 °C. In layered spherical‐shell convection, flows in the lower mantle are several times greater than the surface velocities.
Comment on “MHD Wave breaking in the outer plasmasphere”
Authors: Lanzerotti L. J. , Uberoi C.
Published: February 2008

We point out that the physical implications of the plasma and magnetic field gradients in the Earth's magnetosphere include both resonance absorption of energy and nonlinear effects such as wave steepening and breaking. We conclude, by consideration of the relative timescales for the two processes, that hydromagnetic resonance absorption effects are more important in the Earth's magnetospheric plasma environment.
Magnetization of a dolomite bed in the Monterey Formation: Implications for diagenesis
Authors: Hart Melissa , Fuller M.
Published: February 2008

The effect of diagenesis upon natural remanent magnetization (NRM) has been studied at two sites within a single bed of dolomite from the Monterey Formation in Santa Barbara County, California. Paleomagnetic direction demonstrates that the NRM is primary at one site and remagnetized at the other site. Magnetic separates from samples carrying a primary NRM yielded detrital magnetite. Separates from samples carrying secondary NRM yielded an unusual form of authigenic magnetite. Evidence suggests that the formation of the authigenic magnetite accompanied late stage dolomite diagenesis. Correlating the remagnetization direction to the paleomagnetic history of the region gives a probable age of 0.72–2.47 m.y.b.p. for both of these diagenetic events.