bluuebunny/crossref_metadata_2025 huggingface dataset:
The auroral kilometric radiation: DE 1 direction finding studies
Authors: Mellott M. M. , Huff R. L. , Gurnett D. A.
Published: February 2008

We have determined the directions of arrival of auroral kilometric radiation during three separate intervals using data from the DE 1 plasma wave instrument. In the case of the dominant extraordinary mode component, these directions were consistent with generation at the local electron cyclotron frequency on nightside auroral field lines. The ordinary mode component appeared to have a similar source in one case, but in other cases came from different directions. These other cases were consistent with reflection at the plasmapause and the wall of the auroral plasma cavity.
Effect of H2O on phase transformations of mantle silicates at high pressures and temperatures
Authors: Liu Lin‐gun
Published: February 2008

The effect of H2O on the high‐pressure phase transformations in a 1∶1 mixture of forsterite and enstatite has been investigated on the basis of experimental data available in the MgO‐SiO2‐H2O system at pressures up to 280 kbar. It has been found that the modified spinel phase of Mg2SiO4 does not occur at high pressure in this system, where more than about 4 wt % H2O is present. In addition, the spinel phase of Mg2SiO4 does not appear at its equilibrium transition boundary (modified spinel ↔ spinel) if more than about 3 wt % H2O is present in the system. Thus, if more than about 4 wt % H2O is present in the chemical composition of downgoing slabs, the so‐called 400 km seismic discontinuity in the normal mantle may not occur in the subduction zone at all.
Observations of shear‐coupled P waves
Authors: Zandt George , Randall George E.
Published: February 2008

Teleseismic SV waves couple to P waves in the lithosphere in several ways. P waves converted from discontinuities in the lithosphere precede the main SV arrival as small amplitude Sp precursors. Large amplitude P waves follow the main SV arrival after conversion by reflection at the free surface, and post‐critical reflection from a discontinuity in the lithosphere. SPdiff denotes a converted P wave diffracted along the underside of the crust when a teleseismic SV wave strikes it from below near the critical angle of incidence.

We observed several of these shear‐coupled P waves on seismograms of deep earthquakes recorded at broadband seismic stations (RSTN) in North America. For these paths, large amplitudes relative to SV characterize the lithospheric multiple near 50°, with amplitudes decreasing rapidly beyond 60°. Calculation of synthetic seismograms indicate that a post‐critical reflection from a discontinuity at 70‐80 km depth where compressional velocity increases abruptly to about 8.5 km/s produce the largest amplitude P arrival. The observations of these shear‐coupled P waves presents a previously untapped source of information about the fine structure of the upper mantle.
Photolysis rates based on Schumann‐Runge band approximations and irradiance measurements
Authors: Herman J. R. , Mentall J. E.
Published: February 2008

The photolysis rate (J3) for CF2Cℓ2, (F‐12) in the stratosphere has been computed for three altitudes using measured solar fluxes from a balloon borne spectrometer. The rate is compared with that obtained by computing the attenuated flux using effective cross sections appropriate for the Schumann‐Runge bands (J1) [Allen and Frederick, 1982]. The result shows that the error in the F‐12 photolysis rate caused by using the Allen and Frederick approximation is about 10% (J1 < J3) for altitudes between 32 and 38 km with solar zenith angles less than about 62 degrees. For species other than O2, this implies that the discrepancy in photolysis rates associated with the Schumann‐Runge band approximations are not likely to be important. Within the Schumann‐Runge band region the computed errors for F‐12 photolysis are about 10.5% at 38.13 km and increase with decreasing altitude. If this error applies to O2 photolysis, there may be the possibility of an incorrect calculation of net odd oxygen production in photochemical models.
Atmospheric carbontetrafluoride (CF4): Sources and trends
Authors: Khalil M. A. K. , Rasmussen R. A.
Published: February 2008

Concentrations of carbontetrafluoride (CF4) observed at the south pole suggest that this inert trace gas is accumulating in the earth's atmosphere at about 1.3 (0.8‐2) pptv/yr. This amounts to an average increase of about 1.8 (1‐3) × 1010 gms/yr and can be explained by the estimated emissions of CF4 from aluminum manufacturing. Although it is still not possible to determine how much, if any, of the present atmospheric content of CF4 is from natural sources, it appears that these sources are small (≦109 gm/yr) and therefore will be extremely difficult to identify and evaluate.
Excess carbon‐14 abundances in uranium ores: Possible evidence for emission from uranium‐series isotopes
Authors: Barker D. , Jull A. J. T. , Donahue D. J.
Published: February 2008

Significant levels of 14C have been detected in uranium‐bearing minerals using the tandem accelerator mass spectrometer at the University of Arizona. The amount of 14C detected in a given mineral is proportional to the concentration of uranium in that mineral. The average value of 14C atoms/uranium atom is (2.2±0.5)×10−15 (2σ). These data are consistent with the assumption of direct 14C emission from one or more nuclei in the 238U decay chain with a branching ratio of 1.0 to 2.0×10−9, relative to alpha decay. The uncertainty results from the possible production of 14C from 11B(α,p)14C.
High pore pressure generation in sediments in front of the Barbados Ridge Complex
Authors: Shi Yaolin , Wang Chi‐Yuen
Published: February 2008

DSDP data for the Barbados Ridge complex show the existence of high pore pressures in sediments both oceanward and arcward of oceanic trenches. We model the evolution of pore pressure by using a finite element procedure. Three consecutive stages are recognized: (1) In the oceanic basin, sedimentation rate is low; there is little excess pore pressure. (2) Approaching the trench but before being incorporated into the accretionary prism, sediments are subjected to increasing tectonic compression as well as greater sediment overburden. Thus, high pore pressure can be created. An important result is that the lowest effective stress occurs within the sedimentary layer instead of at its base and a decollement may develop along this weakened zone. (3) Arcward of the trench, sediments above the decollement are offscraped while those beneath it are subducted. Fast sedimentation combined with tectonic compression can create pore pressures so high as to cause porosity to increase with depth. This facilitates the formation of mud volcanoes, even oceanward of the deformation front.
The implication for the presence of a magnetosphere on Uranus in the relationship of EUV and radio emission
Authors: Shemansky D. E. , Smith G. R.
Published: February 2008

Two apparent contradictory sets of facts exist concerning the presence of a magnetosphere at Uranus. The Voyager planetary radio astronomy experiment has not detected a Uranus signal at a range <0.7 AU, whereas IUE satellite observations show relatively strong emission indicating the presence of substantial particle excitation of the atmosphere. The character of the EUV emission implies the presence of an ionosphere, and mass‐loading of the extended system comparable to that of Saturn. If the ingredient for production of an active magnetosphere is present, the non detection of radio emission then suggests that Uranus has a very weak or non existent magnetosphere. The apparent paradox of an excited atmosphere in the absence of an active magnetosphere may possibly be explained in terms of the peculiar characteristics of the excited sunlit equatorial exospheres of Jupiter and Saturn. We suggest that 1) the observed Uranus EUV emission may be a similar phenomenon to those observed in the sub‐solar equatorial regions of Jupiter and Saturn, which appear to be disconnected from auroral or magnetospheric activity, and 2) the Uranus intrinsic magnetic field is probably weak or nonexistent because of the availability of substantial mass for producing an active magnetosphere as derived from the nature of the EUV emission. We predict a substantial escape rate of atomic hydrogen (∼2 × 1028 S−1).
The generation of broadband electrostatic noise by an ion beam in the magnetotail
Authors: Akimoto Kazuhiro , Omidi Nojan
Published: February 2008

The results of a theoretical investigation of the generation of broadband electrostatic noise (BEN) by an ion beam in the Earth's magnetotail are presented. It is shown that at low beam temperatures an ion beam can generate BEN at wave normal angles (θ) between zero and 80°, with the maximum growth occurring at θ = 0° when the beam velocity is small and at large θ (∼ 70°) for higher beam velocities. It is also shown that two types of instability are responsible for the wave amplification. One is the ion acoustic instability associated with the electron‐ion beam relative drift, and the other is the ion‐ion instability. The broad frequency and angular spectra of BEN can be explained by the presence of the two instabilities. These instabilities are shown to be insensitive to the presence of a background magnetic field.
Estimate of carbonyl sulfide (OCS) volcanic source strength deduced from OCS/CO2 ratios in volcanic gases
Authors: Belviso Sauveur , Nguyen Ba Cuong , Allard Patrick
Published: February 2008

Measurements of the concentration ratio of OCS and CO2 were made in fumaroles of several volcanoes in Italy and Nicaragua. The values obtained, together with previous published data, demonstrate that the OCS/CO2 ratio is positively correlated with the emission temperature of the gases. It ranges from 10−7.1 to 10−2.7 at the Vulcano (90°C) and Erta'Ale (1130°C) volcanoes, respectively. The global OCS volcanic source strength, deduced from SO2 emission rates, CO2/SO2 and OCS/CO2 ratios in volcanic gases, is estimated to be in the range 6‐90 ×109 gOCS per year.
Single station CMT; Application to the Michoacan, Mexico, Earthquake of September 19, 1985
Authors: Ekström Göran , Dziewonski Adam M. , Steim Joseph M.
Published: February 2008

Observations of three‐dimensional ground motion at a single point on the surface of the Earth following an earthquake can be sufficient to determine the zeroth order moment tensor of the event. We adapt the centroid‐moment tensor (CMT) method [Dziewonski et al., 1981] of analysis to single station data and apply it to the September 19, 1985 Michoacan earthquake. The obtained mechanism indicates faulting on a shallow plane, consistent with the ongoing subduction of the Cocos plate. The scalar moment is 1.3 × 1028 dyne‐cm. A direct deconvolution of the observed P‐wave train indicates that the moment release occurred in two subevents, each of 20 seconds duration with a peak‐to‐peak separation in time of 25 seconds.
The comet/solar wind transition region at Giacobini‐Zinner
Authors: Thomsen M. F. , Bame S. J. , Feldman W. C. , Gosling J. T. , McComas D. J. , Young D. T.
Published: February 2008

Between about 7 and 12 × 104 km from the nucleus of Comet Giacobini‐Zinner, the International Cometary Explorer (ICE) found a region in which the solar wind flow speed decreased and the electron density and temperature increased by factors of ∼2. This transition region was characterized by large fluctuations in the plasma parameters and by highly variable electron velocity distributions. Electron temperature and density variations through the transition region reveal that ICE never crossed a short‐scalelength bow shock during the encounter, although the scalelength for the gross transition in plasma properties is not incompatible with a shock dominated by the length scales of cometary ions. However, many of the electron distributions in the transition region and sheath are similar to those seen behind weak collisionless shocks elsewhere in the heliosphere. A model of the comet/solar wind interaction is suggested in which a standing shock exists sunward of the ICE trajectory, but, due to large variations in the upstream conditions, it is highly variable and perhaps only intermittent along the flanks.
Immobility of reduced carbon along grain boundaries in dunite
Authors: Watson E. Bruce
Published: February 2008

Carbon‐14 radiotracer experiments at 10 kbar (1 GPa) and 1000°‐1200°C reveal that, due to low diffusivity or low solubility (or both), carbon is immobile in the grain boundary regions of natural dunite. Within the resolution of the beta‐track mapping technique, grain boundary diffusion of carbon from a pure graphite source is not detectable in experiments of up to 10 days duration at 1200°C, even though measurable volume diffusion profiles are generated at these conditions (D ∼ 3‐4 × 10−10 cm²/s, in agreement with previous estimates). The documented immobility of carbon in dunite grain boundaries precludes development of a continuous carbon film by diffusion from an initially localized source. If such a film is the cause of the mantle high‐conductivity layer, it probably originated by a process involving fluid (CO/CO2) infiltration and subsequent reduction.
Measurement of frequency dependent Lg attenuation in the Great Basin
Authors: Chávez David E. , Priestley Keith F.
Published: February 2008

Measurement of the spatial decay of spectral amplitudes of the higher‐mode seismic surface wave train Lg indicates that in the Great Basin the apparent seismic quality factor, Q, is a function of frequency. Observations along a 300 km profile recording of a nuclear explosion yield the function Q(ƒ)=206ƒ0.68 over the band 0.3 ⩽ ƒ ⩽ 10.0 Hz. Similar analysis using numerous recordings of earthquakes along paths which provide a good average sampling of the Great Basin crust gives Q(ƒ) = 214(± 15)ƒ0.54(±0.09), for 0.3 ⩽ ƒ ⩽ 5.0 Hz. If the crustal sampling by Lg energy from nuclear explosions (surface sources) is primarily in the shallow crust, as has been suggested, then these results indicate a greater frequency dependence of apparent Q there than at depth.
A statistical study of the central plasma sheet: Implications for substorm models
Authors: Huang C. Y. , Frank L. A.
Published: February 2008

The University of Iowa Lepedea on board ISEE 1 is used to investigate the characteristics of the central plasma sheet under all levels of geomagnetic activity. Positive ion responses from 1 eV to 45 keV are used in this study. All the periods during 1978 when the central plasma sheet is encountered are included. Our study excludes all boundary layer samples. The results of this study show that the central plasma sheet consists of plasma with high thermal energy (several keV) but low bulk speeds. This remains true even during high geomagnetic activity. The main effect of increasing activity is heating of the plasma sheet, preferentially at the high‐latitude boundaries.
Estimation of the probability of earthquake occurrence on the basis of logistic models: High probability of an earthquake of M≥6.5 near the Arc Junction off northeast Japan
Authors: Kuge Keiko , Honkura Yoshimori
Published: February 2008

The probability of the occurrence of an earthquake of M≥6.5 is estimated by applying logistic models to seismicity in the Hokkaido‐Tohoku region, northeast Japan. It is found that the probability of an earthquake occurrence near the arc junction off northeast Japan is high when a specific seismicity pattern appears; that is, seismic activity increases 7∼10 years or decreases 3∼6 years before an event of M≥6.5. Because seismic activity is currently extremely low near the arc junction, it is possible that an earthquake of M≥6.5 may occur there within a few years. Specifically, the probability estimated on the basis of logistic models is higher than 0.9 for the year of 1988.
Cretaceous paleomagnetism of the Methow‐Pasayten Belt, Washington
Authors: Granirer Julian L. , Burmester Russell F. , Beck Myrl E.
Published: February 2008

Detailed demagnetization experiments isolated a characteristic remanent magnetization in ten stable sites from the upper Cretaceous Winthrop and Midnight Peak Formations in the Methow‐Pasayten belt of north‐central Washington. This remanence agrees best between opposite limbs of a fold (the Goat Peak syncline) when corrected for 46% of tilt. This is consistent with magnetization acquired during deformation. Synfolding magnetization may have been facilitated by a thermo‐chemical event associated with synkinematic intrusions along the axis of folding. The mean direction (D=12.0°, I=61.1°, Alpha‐95=4.8°) is highly discordant with respect to the expected direction for north‐central Washington. This discordance points to about 1,400 km of poleward transport and 48° of clockwise rotation between 93 and 45‐48 Ma.
The Sakigake and Suisei encounters with comet Halley
Authors: Itoh T. , Hirao K.
Published: February 2008

Included in this issue are several papers that discuss results obtained from the two Japanese spacecraft missions to comet Halley. This introductory article summarizes the highlights of the research.
A disturbance of the ion tail of comet Halley and the heliospheric structure as observed by Sakigake
Authors: Saito Takao , Yumoto Kiyohumi , Hirao Kunio , Saito Keiji , Nakagawa Tomoko , Smith Edward J.
Published: February 2008

In order to study the interaction between the solar wind measured by Sakigake and ion tail disturbances of comet Halley, more than 500 photographs of the comet taken on the ground during this apparition are surveyed. The focus of the present study is the December 31, 1985, event, when various types of disturbances occurred, including an outstanding disconnection event (DE)‐ like knot. Analysis of the Sakigake/IMF data reveals that comet Halley did not encounter the heliospheric neutral sheet on that day, demanding a new explanation for the DE‐like event, different from the Niedner‐Brandt model. During this event the comet encountered a high‐speed solar wind stream from a coronal hole tongue of the sun. The event can be explained by a dynamic pressure model, according to which the DE‐like plasmoid was caused by a sudden increase in the dynamic pressure of the solar wind. A result of the simulation work by Ogino is found to support this interpretation.
Comet Giacobini‐Zinner: Comparison of a post‐encounter image with in‐situ and groundbased observations
Authors: Mendillo Michael , Baumgardner Jeffrey
Published: February 2008

An unfiltered image of Comet Giacobini‐Zinner was obtained 16 hours after the ICE encounter. While it is not possible to separate the dust, gas and plasma components of the "white light" image, comparisons of the visible structures with ICE in‐situ plasma and field observations, groundbased optical data, and computer simulation results suggest that the image shows emission from plasma structures along the equivalent ICE trajectory.
Acoustic noise measurements on Axial Seamount, Juan De Fuca Ridge
Authors: Bibee L. D. , Jacobson R. S.
Published: February 2008

Anomalously high ambient acoustic noise was observed within the caldera of Axial Seamount, located on the Juan de Fuca Ridge at 46°N. Noise spectra from 2 to 30 Hz were calculated from hydrophone signals from four separate seismic recording systems. Noise levels varied up to 25 dB over 6 km. This observation suggests the noise source is at or near the sea floor. By assuming spherical spreading, we estimate the source of the noise to be within 400 m of one of the instruments. A low temperature hydrothermal vent field, located within 600 m of this instrument, has been previously mapped with submersibles and is likely the source of the anomalous noise. A high temperature, black smoker, vent field, also located within the caldera, shows no evidence of anomalous acoustic noise.
Radar interferometer estimate of zonal drift variability during spread F
Authors: Kudeki Erhan , Franke Steven J.
Published: February 2008

Zonal drift velocity variations with 30% amplitudes and several minute time scales are observed in Jicamarca radar interferometer data collected from bottomside F region altitudes during two different periods with 70‐90 m/s and 100‐155 m/s mean zonal drifts. These fluctuations are indicative of intermediate scale vertical structuring of F region plasma to be expected in periods of Rayleigh‐Taylor bubble formation, and may contribute significantly to the decorrelation of forward scattered satellite signals detected for scintillation spaced receiver analysis.
Antarctic ozone change correlated to the stratospheric temperature field
Authors: Sekiguchi Yoshiro
Published: February 2008

Total ozone and ozonesonde data obtained at the Japanese Antarctic Station, Syowa, are analyzed together with radiosonde data in the lower stratosphere at the same station. Very high correlation coefficients between monthly mean values of ozone and stratospheric temperature suggest a clear relation between stratospheric circulation and ozone amount. The rapid decrease of the Antarctic ozone in recent years might be caused by the extraordinary change in the circulation, because there is also a rapid decrease of the temperature in the lower stratosphere above the Syowa station in spring months of recent years. This conclusion is endorsed by analysis of ozonesonde observations in 1982. The year‐to‐year change of both total ozone and stratospheric temperature suggests the influence of changes in solar activity.
The close relation between Antarctic total‐ozone depletion and cooling of the Antarctic low stratosphere
Authors: Angell J. K.
Published: February 2008

Nearly 5500 mean‐monthly low‐stratospheric temperatures at 100, 50 and 30 mb at 16 Antarctic stations have been extracted from "Monthly Climatic Data for the World" for the interval 1958‐1985. About 450 mean‐monthly total‐ozone values at 4 Antarctic stations have been extracted from "Ozone Data for the World" for the same interval. There has been an impressive in‐phase relation between seasonal variations in low‐stratospheric temperature and total ozone in Antarctica. This relation extends not only to the large total‐ozone and low‐stratospheric temperature decreases since 1978 in the Southern Hemisphere spring (approximately 30% and 6‐8°C, respectively, based on smoothed data), but also to relatively minor fluctuations in this and other seasons. The springtime stratospheric temperature decreases since 1978 are indicated to have been greatest along the Antarctic coast between about 30°W and 60°E, including the stations of Halley Bay and Syowa; there has been practically no low‐stratospheric temperature decrease at stations 10 degrees of latitude further north on the Antarctic Peninsula. The springtime temperature decrease has been pretty much confined to the Antarctic stratosphere, or to levels above about 300 mb.
Total ozone decrease at South Pole, Antarctica, 1964‐1985
Authors: Komhyr W. D. , Grass R. D. , Leonard R. K.
Published: February 2008

Mean monthly total ozone data obtained at South Pole, Antarctica, during 1964‐1985 are presented. Preliminary analysis of the data suggests that total ozone has decreased at South Pole by roughly 20% since the mid‐1960's. Largest decreases have occurred during October and November months, but autumn and winter months also exhibit a decrease. During February months, ozone has increased slightly. Superimposed on the long‐term downward ozone trend are episodic decreases in ozone dating back to 1965 that have occurred at intervals of 4‐6 years. These decreases are shown to be related to delays in stratospheric warmings in Antarctica and the transport of ozone into Antarctica each spring.
Atmospheric trace gas trends at Palmer Station, Antarctica: 1982‐1985
Authors: Cronn D. R. , Bamesberger W. L. , Menzia F. A. , Waylett S. F. , Waylett A. S. , Ferrara T. W. , Howard H. M. , Robinson E.
Published: February 2008

Measurements of CFCl3, CF2Cl2, CH3CCl3 CCl4 and N2O at Palmer Station, Antarctica (64°46′S, 64°04′W) from February 4, 1982 to November 30, 1985 are reported. For the week beginning January 1, 1984, the averages of the hourly measurements were 199.6 ppt for CFCl3, 329.0 ppt for CF2Cl2, 124.2 ppt for CH3CCl3, 150.2 ppt for CCl4, and 301.3 ppb for N2O. The mixing ratios increased at an annual rate of 5.87% y−1 for CFCl3, 5.45% y−1 for CF2Cl2, 5.31% y−1 for CH3CCl3, 1.29% y−1 for CCl4, and 0.24% y−1 for N2O.
Characteristics of polar stratospheric clouds during the formation of the Antarctic ozone hole
Authors: Hamill Patrick , Toon O. B. , Turco R. P.
Published: February 2008

We describe measured properties of Antarctic polar stratospheric clouds and consider the possible relationship between the clouds and the formation of the ozone hole. We show that the ozone hole develops and the clouds dissipate in the same place and at the same time. There may be a causal relationship between cloud particle evaporation and ozone depletion. A heterogeneous mechanism involving chemical reactions in the cloud droplets is suggested.
The onset of time‐dependent convection in spherical shells as a clue to chaotic convection in the Earth's mantle
Authors: Machetel Philippe , Yuen David A.
Published: February 2008

This work presents a detailed numerical study of the dynamical behavior of convection in a spherical shell, as applied to mantle convection. From both 2‐dimensional (120 radial and 360 tangential points) and 3‐dimensional (60 radial levels and spherical harmonics up to order and degree l=33, m=33), we show that for a spherical shell (with inner to outer radii ratio η=.62) convection becomes time‐dependent, with l=2 dominating, at a Rayleigh number of about 31 times supercritical for a constant viscosity, base‐heated configuration. This secondary instability is characterized by oscillatory time‐dependence, with higher frequencies involved, at slightly higher Rayleigh numbers. In the process of illustrating the onset of time‐dependence, we extend our analysis to show that the onset of weak turbulence in spherical‐shell convection takes place at about 60 times the critical Rayleigh number via a quasi‐periodic mode.
Adcumulus growth of the inner core
Authors: Morse S. A.
Published: February 2008

The earth's core is contained in an oxide bottle, the mantle. With regard to any dissolved oxygen, therefore, the outer core (OC) is in a reactive relationship to its container. The mantle contains only trivial amounts of sulfur compared to its solubility in the liquid OC, so the bottle is effectively inert to sulfur. This difference affects whether the diluent convects freely away from the freezing inner core (sulfur) or moves under constraint of saturation at the interface with the container (oxygen). The motion of oxygen is limited by diffusion; it requires double freezing and hence release of latent heat at both top and bottom of the OC, or else (if the top of the OC is a heat sink) no escape of heat to the mantle. The motion of sulfur allows rapid transport of latent heat away from the inner core boundary by compositional convection and implies major heat loss from the core. The velocity of compositional convection (due to sulfur) may be as much as 104 times that of diffusion of oxygen, so sulfur in the outer core should be far more important in driving the dynamo than oxygen.
Acceleration of energetic ions by a nearly perpendicular interplanetary shock
Authors: Ohsawa Yukiharu
Published: February 2008

The theory of resonant ion acceleration which has been recently developed is compared quantitatively with the acceleration of energetic ions by a quasiperpendicular shock observed by Voyager 2 at a distance of ∼ 1.9 AU from the Sun. The theory explains many important features of the experimental results.
Ion distributions in a two‐dimensional reconnection field geometry
Authors: Curran D. B. , Goertz C. K. , Whelan T. A.
Published: February 2008

ISEE observations have shown trapped ion distributions in the magnetosphere along with streaming ion distributions in the magnetosheath. The more energetic ion beams are found to exist further away from the magnetopause than lower‐energy ion beams. In order to understand these properties of the data, we have taken a simple two‐dimensional reconnection model which contains a neutral line and an azimuthal electric field and compared its predictions with the experimental data of September 8, 1978. Our model explains trapped particles in the magnetosphere due to non‐adiabatic mirroring in the magnetosheath and streaming ions in the magnetosheath due to energization at the magnetopause. The model also shows the higher‐energy ions extending further into the magnetosheath, away from the magnetopause than the lower‐energy ions. This suggests the ion data of September 8, 1978 are consistent with a reconnection geometry.
Transition from double to single Wadati‐Benioff seismic zone in the Shumagin Islands, Alaska
Authors: Hudnut K. W. , Taber J. J.
Published: February 2008

A discontinuity exists in the moderate‐depth seismicity located by the Shumagin seismic network in the eastern Aleutian subduction zone. The boundary is nearly perpendicular to the arc and has a double planed Wadati‐Benioff zone to the west and a single planed zone to the east. The transition does not appear to be an artifact of mislocations, as shown by three‐dimensional ray trace modeling and examination of phases of representative earthquakes. Current theory on the presence or absence of double seismic zones suggests a change in stress across the boundary. If so, the east and west regions may either have different aseismic to seismic slip ratios, or be in different stages of the earthquake cycle.
Investigations and interpretations of the vertical distribution of U, TH, and K: South Africa and Canada
Authors: Schneider R. V. , Roy R. F. , Smith A. R.
Published: February 2008

Investigations of the distribution of U, Th, and K in deep profiles exposed by Precambrian doming have been presented for Vredefort, South Africa and have recently been completed for a similar structure near Sudbury, Ontario, Canada. An evaluation of the Vredefort data shows evidence of a major crustal repetition of the vertical radioelement distribution with depth. A simple explanation is that the South African basement is geochemically layered, with repetition occurring from layer to layer. This implies a sawtooth, or “serrated” distribution with depth.

Preliminary results from the Sudbury investigation show a rise in heat production with distance from the Sudbury Structure, corresponding to decreasing depth in the basement rocks. The repetition of the radioelement distribution observed at Vredefort does not appear in the Sudbury data. Although Th and K make a jump at nearly the same depth, the U data show no corresponding increase. U loss is suspected in the project area, affecting the overall distribution of heat production in the Sudbury basement. Given its complex history and geographic location, the material in the sample area may not be representative of the Superior Province.
Steady state heat flow in a random medium and the linear heat flow‐heat production relationship
Authors: Nielsen Søren B.
Published: February 2008

The heat transfer in the earth's crust is described by three‐dimensional steady state heat conduction in a heterogeneous medium with randomly varying thermal conductivity and heat production. The heat flow‐heat production relationship generally emerges as the regression of the surface heat flow on surface heat production. The case of normally distributed thermal conductivity and heat production in an upper heterogeneous slab yields a linear relation, the slope and intercept of which depend on the horizontal and vertical correlation scales of heterogeneity, the correlation between thermal conductivity and heat production, and the ratio of heat produced within the zone of heterogeneity to heat from deeper origin. The model is a stochastic extension of the traditional homogeneous slab model, and the intercept of the linear relationship predicts the true average heat flow at a depth equal to the slope, when this depth is smaller than the true slab thickness.
The Antarctic ozone depletion caused by heterogeneous photolysis of halogenated hydrocarbons
Authors: Krüger Bernd C. , Wang GuiQin , Fabian Peter
Published: February 2008

Corresponding to measurements made in the Arctic, assumptions have been made on the atmospheric concentrations of reactive halogenated hydrocarbons in Antarctica. These concentrations have been used in a one‐dimensional photochemical model calculation carried out for Antarctic conditions. When the photolysis rates of these compounds are increased, which is likely to be expected due to an acceleration by heterogeneous photolysis, total ozone columns are calculated well in agreement with the recently observed low Antarctic ozone values.
Toms observations of total ozone in the 1986 Antarctic spring
Authors: Krueger A. J. , Schoeberl M. R. , Stolarski R. S.
Published: February 2008

Total ozone measurements by the Total Ozone Mapping Spectrometer (TOMS) aboard the Nimbus 7 satellite show the reappearance in 1986 of the extreme springtime Antarctic ozone minimum during September and October. The minimum total ozone amounts descended to 156 Dobson Units; the minimum October average of 185 DU was 27 DU higher than the corresponding average in 1985 and 5 DU less than the 1984 average. This behavior indicates a pause in the downward trend of recent years.
Mantle devolatilization and convection: Implications for the thermal history of the Earth
Authors: Jackson Michael J. , Pollack Henry N.
Published: February 2008

The depletion of volatiles from the earth's mantle over its history may have had significant effects on thermal convection, due to the effects of volatiles on silicate rheology. Experimental data suggest that the activation energy for solid‐state creep in a volatile‐free environment is as much as 25% greater than in a volatile‐rich environment, and thus devolatilization can lead to a substantial increase in viscosity. In a devolatilizing system, gradually increasing temperatures (relative to those in a system with volatile‐independent rheology) may be required to maintain moderate viscosities and convection. We investigate this postulated effect by incorporating a time‐dependent increase in activation temperature, simulating progressive mantle devolatilization, in a parameterized convection model. Volatiles significantly affect the earth's thermal evolution when the dependence of mantle rheology upon volatile content is sufficiently strong, the total volatile loss is sufficiently large, and devolatilization is relatively slow and continuous. For models with an increase of 20% in activation energy over earth history, the present‐day ratio of heat production to heat loss (Urey ratio) approaches or exceeds 1.0 when volatile loss is relatively continuous. With rapid early volatile loss, the upper bound on the present‐day Urey ratio is about 0.8 to 0.9, comparable to the limit with volatile‐independent rheology. Present uncertainties in these factors permit an earth that may be close to a steady thermal state or perhaps even warming up.
Shallow seismic reflection profile of the Meers Fault, Comanche County, Oklahoma
Authors: Myers Paul B. , Miller Richard D. , Steeples Don W.
Published: February 2008

A high‐resolution seismic‐reflection survey was conducted across the Meers fault in Comanche County, Oklahoma, in an attempt to determine the shallow structure associated with the fault zone. A downhole .50‐caliber rifle was used as the seismic‐energy source. Two 100‐Hz geophones were connected in series at each receiver station. A 1.22‐m station spacing was used for both source and receiver. Field recording parameters were set to optimize seismic reflections in the 40–150 millisecond range. A pre‐analog‐to‐digital low‐cut filter (24 dB/octave rolloff with −3 dB point of 220 Hz) resulted in dominant frequencies in excess of 150 Hz. Several interpretable reflection events between 40 and 120 msec on the processed seismic section provide a clear picture of the shallow structure. Reverse faulting is evident not only at the scarp itself but also on both the upthrown (north) and downthrown (south) portions of the line. This suggests the fault zone extends at least 180 m in both directions (north and south) from the scarp itself. Recent movement appears only to have occurred along the major fault associated with the scarp. The northern portion of the seismic line is characterized by gentle folding, which is not present on the southern portion.
A comparison of two sets of synthetic reflection seismograms for a complex two‐dimensional model of the oceanic crust‐mantle transition
Authors: Brocher Thomas M. , Frazer L. Neil
Published: February 2008

The algorithm chosen for the calculation of synthetic seismograms often represents a compromise between the realistic representation of complex geology and economy. Comparison of synthetic seismic reflection sections calculated using a relatively inexpensive ray theory and a relatively expensive generalized reflectivity algorithm for a complex, laterally inhomogeneous model of the oceanic Moho demonstrates that ray theory provides a close approximation to the full‐wave theory. The chief difference between the two synthetic sections is the more accurate variation in amplitude with horizontal range predicted by the reflectivity synthetics, due to its inclusion of the horizontal smoothing of the reflected amplitudes over the width of the First Fresnel Zone. While this Fresnel zone smoothing will become increasingly important with increasing reflector depth, the results shown here suggest that inexpensive ray theory synthetics may have sufficient accuracy in many similar applications.
Magnetic field and remanent magnetization effects of basin‐forming impacts on the Moon
Authors: Hood L. L.
Published: February 2008

Maps of the distribution of lunar surface magnetic fields produced by the electron reflection method have shown that the largest observed concentrations of lunar crustal magnetization occur antipodal (diametrically opposite) to 4 relatively young large impact basins: Imbrium, Orientale, Serenitatis, and Crisium. A model is proposed here for the formation of these magnetization concentrations (or ‘magcons’) in which the partially ionized vapor cloud produced in a hypervelocity (> 10 km s−1) basin‐forming impact expands around the moon forcing a pre‐existing ambient magnetic field to be concentrated for a brief (< 1 day) time period in the antipodal zone. Acquisition of magnetic remanence during the period of compressed field amplification may occur by one of several mechanisms including shock remanence by impact of solid secondaries ejected from the basin‐forming event. The model implies that basin‐forming impacts have played a major role in determining the large‐scale distribution of crustal magnetization detectable from lunar orbit.
Penetration of magnetospheric convective electric field to the equatorial ionosphere during the substorm of March 22, 1979
Authors: Somayajulu V. V. , Reddy C. A. , Viswanathan K. S.
Published: February 2008

The possible penetration of magnetospheric convective electric field to low latitudes is investigated with the help of VHF radar measurements of equatorial electrojet electric fields during the 1054 UT substorm of March 22, 1979. The observed time relationship of these electric fields with the southward component of the interplanetary magnetic field and the polar‐auroral magnetic activity suggests that the magnetospheric convective electric fields may penetrate to low latitudes, at least on certain occasions during the growth phase of a substorm before screening by ring current becomes effective.
Deformation of the core‐mantle boundary induced by spherical‐shell, compressible convection
Authors: Zhang Shuxia , Yuen David A.
Published: February 2008

We derive the single‐mode, mean‐field equations for spherical‐shell convection with variable viscosity and compressibility included. Core‐mantle boundary (CMB) topography produced by whole mantle convection is computed for various rheologies and different thermal boundary conditions at CMB. Results for long‐wavelength undulations show the extreme sensitivity of these signatures to rheological and equation of state parameters. In order to obtain excess ellipticity of about 1 km, the activation energy and volume in the lower mantle should be low and the temperatures at CMB around 4,500 K, in accord with recent experimental findings.
Minor source of ozone in the lower thermosphere
Authors: Bates David R.
Published: February 2008

The binary collision ozone source
is considered. It cannot remove the apparent deficiency in model ozone above 95 km.
Elasticity and equation of state of MgSiO3 perovskite
Authors: Cohen Ronald E.
Published: February 2008

The elastic constants and equation of state of MgSiO3 perovskite and MgO are calculated as functions of pressure and temperature using the potential induced breathing (PIB) model, which is an ab initio model in the sense that no experimental data are used. Excellent agreement with experiment is found for the equation of state of perovskite. The calculated thermal expansivity is lower than determined experimentally. PIB provides pressure derivatives of elastic constants that are probably more accurate than experimental results, so that PIB pressure derivatives may be used with experimental elastic moduli when these become available for MgSiO3 perovskite. A fourth‐order finite strain equation is required to fit the elastic moduli, since the shear modulus has only a small pressure dependence at high pressures. The calculated elastic properties are used to discuss the composition of the lower mantle. The results are consistent with a lower mantle composition enriched in Fe.
Alteration of the coercivity spectrum and paleointensity determination
Authors: Dunlop David J. , Reid Brian , Hyodo Hironobu
Published: February 2008

A restudy of 13 bricks from a 19th‐century kiln, using the Shaw AF‐demagnetization method of paleointensity determination, revealed alteration of the magnetite carrying natural remanent magnetization (NRM) during heating to the Curie point. Anhysteretic remanences before heating (ARM1) and after heating (ARM2) had similar intensities, but the ARM2 coercivity spectrum was softer than the ARM1 spectrum. The coercivity spectrum of thermoremanence (TRM) softened in a similar way after heating. We therefore calculated a "corrected TRM", TRMc = (ARM1/ARM2)TRM at each AF demagnetization step. The NRM vs. TRMc plot was in most cases more nearly linear than the original NRM vs. TRM plot. However, the paleointensities determined using uncorrected total NRM/TRM ratios (57 µT) and using our TRMc values (55.5 µT) agreed equally well with a recent Thellier‐method determination of 56 µT by Aitken and others. Grain‐size alteration of the magnetites has changed their fundamental TRM/ARM ratios as well as their coercivities, making our correction procedure untrustworthy. Lack of significant changes in TRM or ARM coercivity spectra after heating is evidence of minimal grain‐size alteration, and remains the best criterion for reliable Shaw‐method paleointensities.
Comment on “Fingerprint structure PC 1 geomagnetic pulsations”
Authors: Fraser‐Smith A. C.
Published: February 2008

Sato et al. [1987] recently drew attention to a new form of Pc 1 pulsations, which they refer to as ‘fingerprint structure’ Pc 1 pulsations because of their distinctive appearance in frequency‐time (f‐t) spectrograms. The new pulsations were observed on moderately high latitude geomagnetic field lines (L≈6) and the authors suggested that the considerable number of spectral lines and their constant frequency separation might provide evidence for non‐linear effects in the Pc 1 pulsation generation region. It is suggested here, on the contrary, that the fine frequency structure is not a non‐linear effect but is simply a manifestation of field line resonances of the kind suggested by Fraser‐Smith [1967].
On the nature of pressure‐induced coordination changes in silicate melts and glasses
Authors: Stolper Edward M. , Ahrens Thomas J.
Published: February 2008

Progressive decreases in the Si‐O‐Si angles between corner‐shared silicate tetrahedra in glasses and melts with increasing pressure can lead to arrangements of oxygen atoms that can be described in terms of edge‐ or face‐shared octahedra. This mechanism of compression can account for the gradual, continuous increases in melt and glass densities from values at low pressure that indicate dominantly tetrahedral coordination of Si to values at several tens of GPa that suggest higher coordination. It also can explain the unquenchable nature of octahedrally coordinated Si in glasses, the absence of spectroscopically detectable octahedrally coordinated Si in glasses until they are highly compressed, the gradual and reversible transformation from tetrahedral to octahedral coordination in glasses once the transformation is detectable spectroscopically, and the fact that this transformation takes place in glass at room temperature. It may also have relevance to pressure‐induced transformations from crystalline to glassy phases, the difficulty in retrieving some metastable high pressure crystalline phases at low pressure, and the observed differences between the pressures required for phase transformations in shock wave experiments on glasses and crystals.
Nitrous oxide in the tropical middle atmosphere, observed by ground‐based MM‐wave spectrometry
Authors: Connor Brian J. , de Zafra R. L. , Solomon P. M. , Parrish A. , Barrett J. W. , Jaramillo M.
Published: February 2008

Measurements of stratospheric N2O were made from Mauna Kea in Hawaii in June, 1983 and in May and June, 1986, by observing thermal emission of the molecule in a rotational transition at ∼ 1 mm wavelength. Analyses of the data yield altitude profiles in the middle and upper stratosphere. Useful measurements of N2O may be made in one to two hours. The N2O profiles agree reasonably well with model predictions and with published satellite data, though we report significantly more N2O near the stratopause than shown by the satellite measurement, and significantly more N2O in the middle stratosphere than in one of the models. The discrepancy between our data and the satellite measurement may be due in part to variations induced by the solar cycle.
Prediction of radio frequency power generation of Neptune's magnetosphere from generalized radiometric Bode's law
Authors: Million M. A. , Goertz C. K.
Published: February 2008

Magnetospheric radio frequency emission power has been shown to vary as a function of both solar wind and planetary values such as magnetic field by Kaiser and Desch. Planetary magnetic fields have been shown to scale with planetary variables such as density and angular momentum by numerous researchers. This paper combines two magnetic scaling laws (Busse's and Curtis Ness') with the radiometric law to yield ‘Bode's’‐type laws governing planetary radio emissions. Further analysis allows the reduction of variables to planetary mass and orbital distance. These generalized laws are then used to predict the power output of Neptune to be about 1.6 × 107W; with the intensity peaking at about 3MHz.
High pressure shear moduli—A many body model for oxides
Authors: Agnon Amotz , Bukowinski M. S. T.
Published: February 2008

We have constructed a parametric many‐body potential that gives accurate predictions of high pressure properties of alkali‐earth oxides. The model incorporates ionic deformational energy and a repulsive potential that are sensitive to the crystal environment. This feature is accomplished by an explicit dependence of the size of oxygen on the crystal potential. The parameters of the model are constrained by equation of state and zero pressure elastic constants of the B1 (NaCl) phases. The model predicts accurate B1‐B2 transition pressures and densities of the B2 (CsCl) phases. Elastic moduli are reproduced exactly, and accurate pressure derivatives are predicted.