bluuebunny/crossref_metadata_2025 huggingface dataset:
A nonlinear least‐squares inverse analysis of strike‐slip faulting with application to the San Andreas Fault
Authors: Williams Charles A. , Richardson Randall M.
Published: February 2008

A nonlinear weighted least‐squares inverse analysis was performed for a synthetic elastic layer over viscoelastic half‐space model of strike‐slip faulting, and an inversion of strain rate data was attempted for the locked portions of the San Andreas fault in California. The model parameters were: elastic layer thickness (H); fault locking depth (D); earthquake recurrence time (T); average shear modulus of the elastic layer and viscoelastic half‐space (μ); half‐space viscosity (η); and coseismic offset (DU). Only the ratio of viscosity to shear modulus can be resolved, and thus shear modulus was held constant. Based on an eigenvector analysis of synthetic data, it is not possible to resolve all of the five remaining parameters with the current observations, which are very close to the fault and vary only with time since the last earthquake. A suite of inversions was therefore performed for the San Andreas, holding recurrence time and locking depth fixed at particular values for each inversion. These inversions resulted in nearly the same data misfit. Thus, a range of estimated values, rather than a particular set of values, was found for the remaining three parameters. Inversions on data from the northern San Andreas resulted in predicted parameter ranges similar to those produced by inversions on data from the whole fault. The addition of observations which vary with distance from the fault should help to constrain these ranges, and perhaps allow resolution of recurrence time and locking depth.
Rupture extent of the 1978 Miyagi‐Oki, Japan, earthquake and seismic coupling in the northern Honshu Subduction Zone
Authors: Tichelaar Bart W. , Ruff Larry J.
Published: February 2008

Underthrusting at subduction zones can cause large earthquakes at shallow depths, but is always accommodated by aseismic creep below a certain depth. This transition depth is referred to as the depth of seismic coupling and can be directly observed in a subduction zone as the lower depth extent of significant moment release of the deepest large underthrusting earthquakes. In 1978, a large (Ms=7.5) earthquake occurred off the coast of Miyagi Prefecture in northern Honshu. Its focal mechanism represents underthrusting of the Pacific plate beneath Honshu. Since the hypocenter is located 150 km landward from the trench and there are no other large interplate earthquakes further landward from the trench axis, this event defines the maximum depth of the coupled zone.

The lower limit of significant moment release of the Miyagi‐Oki earthquake is obtained by analysis of the long‐period P waves. The deconvolved source time function consists of a dominant single pulse with peak moment release at 12 s and a total duration of 18 s. The rupture extent of this dominant pulse does not extend deeper than 40 km, thus the transition from coupled to uncoupled in northern Honshu occurs at or above 40 km depth.
Lattice‐gas automata for modeling acoustic wave propagation in inhomogeneous media
Authors: Huang Jau‐Inn , Chu Yu‐Hua , Yin Chuan‐Sheng
Published: February 2008

We report recent developments in using lattice‐gas automata to simulate acoustic wave propagation in inhomogeneous media, and give experimental results that include transmitted and reflected waves. Two sets of rules are adopted to govern the evolution of particles in the lattice; one applicable to lattice sites on the interface, the other to interior sites. Both sets of rules are simple and deterministic, thereby preserving the computational advantages of lattice‐gas automata. Further investigation bears long‐term promise of yielding a novel and efficient forward modeling tool for geologically realistic models.
A new model for substorm onsets: The pre‐breakup and triggering regimes
Authors: Rothwell P. L. , Block L. P. , Silevitch M. B. , Fälthammar C. ‐G.
Published: February 2008

This model explains why breakup has been observed as low as L = 5‐6 and predicts that a higher concentration of O+ in the plasma sheet will permit breakup at such low L values. The establishment of a coupled current structure within a single arc leads to a quasi‐stable system i.e. the pre‐breakup regime. Perturbation of the pre‐breakup structure leads to an instability criterion. Certain quiescent configurations are inherently unstable. Transitions from a stable to an unstable situation can trigger a rapid poleward expansion of the quiescent arc or substorm breakup. The kinetic energy of injected plasma from the magnetotail supplies the energy for breakup.
Charge states of substorm particle injections
Authors: Sibeck D. G. , Ross K. S. , McEntire R. W.
Published: February 2008

The drift velocities of ions injected during substorms depend upon their energy and charge state. We use Medium Energy Particle Analyzer (MEPA) observations to time the arrival of peak proton, helium, and oxygen fluxes at the Charge Composition Explorer (CCE) satellite and determine the dominant ion charge states of these species in the energy range 72‐1000 KeV. The results indicate that freshly‐injected helium (72‐240 KeV) and oxygen (137‐365 KeV) are singly‐ionized, but that more energetic oxygen (>365 KeV) is multiply‐charged. This suggests either a dominant ionospheric source at the lower energies and a solar wind source at the higher energies or an energization of the pre‐existing ring current population.
Counter‐streaming electrons at the geomagnetic equator near 9 RE
Authors: Klumpar D. M. , Quinn J. M. , Shelley E. G.
Published: February 2008

Observations from the AMPTE/CCE satellite are used to study short‐lived, highly anisotropic electron distributions in the relatively unexplored region of the equatorial magnetosphere between 6.6 RE and the CCE apogee at 8.8 RE. Remarkably intense (∼1×109/cm²‐sec‐sr‐keV) bursts of highly collimated (within 5° of B) counterstreaming electrons have been observed at keV energies with durations of a few tens of seconds to a few minutes near the geomagnetic equator on L‐shells that intersect the high latitude ionosphere in the region normally associated with the auroral zone. Simultaneous deep depressions of the locally mirroring fluxes accompany the counterstreaming electrons at energies below the peak energy. The field‐aligned electrons have mirror points deep in both the northern and southern hemispheres. We suggest these equatorial electrons may result from the release of auroral electrons trapped beneath the auroral accelerating potentials at lower altitudes along the same magnetic flux tubes.
AMPTE/CCE observations of shell‐like He2+ and O6+ distributions in the magnetosheath
Authors: Fuselier S. A. , Shelley E. G. , Klumpar D. M.
Published: February 2008

We present the first simultaneous observations of solar wind He2+ and O6+ shell‐like distributions in the magnetosheath. The He2+ and O6+ distributions are centered on the downstream H+ bulk velocity and have radii proportional to mass/charge. These observations are consistent with the electrostatic cross‐shock potential model discussed in the text.
Wave propagation in a fluid‐filled fracture — An experimental study
Authors: Tang X. M. , Cheng C. H.
Published: February 2008

A laboratory experimental study has been carried out to investigate the mode trapping characteristics of a fluid‐filled fracture between two elastic solids. Using a small circular cylindrical receiver of 2.7 mm diameter, we were able to measure the wave motion directly inside a 2.8 mm thick fracture and to obtain array data for the propagating waves. The data was processed using Prony's method to give velocity of the wave modes as a function of frequency. The experimental results agree with the theoretical predictions quite well. Specifically, in a “hard” (aluminum) fracture where the shear velocity of the solid is greater than the fluid velocity, four normal modes were detected in the frequency range up to 2.4 MHz. Whereas in a “soft” (lucite) fracture where the shear velocity is smaller than the fluid velocity, four leaky‐P modes were detected in the same frequency range. In both cases, a fundamental mode analogous to Stoneley waves in a borehole was detected. In particular, the velocity of this mode approaches zero in the low frequency limit, as indicated by the theory and confirmed by the experiment in a low frequency range down to 25 kHz.
Solubility and equilibrium vapor pressures of HCl dissolved in polar stratospheric cloud materials: Ice and the trihydrate of nitric acid
Authors: Hanson David , Mauersberger Konrad
Published: February 2008

Measurements of the pressure‐solubility behaviour of HCl in water ice and in the nitric acid trihydrate (NAT) crystal at 200 K are reported. It was found that HCl is about 20 times more soluble in NAT than in ice for stratospheric conditions. A relation between HCl pressure and substrate composition based on the Gibbs‐Duhem equation is developed. This relation, along with other thermodynamic data, can be used to obtain the HCl pressure‐solubility behaviour at different temperatures. Implications of these results for the south polar ozone hole are discussed.
Possible explanations of north‐south plasma flow in the outer heliosphere and meridional transport of magnetic flux
Authors: McNutt R. L.
Published: February 2008

Observed meridional plasma flow and its connection with other plasma parameters in the outer heliosphere are discussed. The dynamics of the flow are examined locally and compared with observed plasma parameters and a global flow model which predicts such flows in a steady solar wind. The observational evidence supports stream dynamics and associated pressure gradients as responsible for driving the flow. Such a meridional flow may result in a net transport of magnetic flux from regions near the heliographic equator. The amplitude of the observed meridional component of solar wind flow is consistent with observed magnetic flux deficits in the outer heliosphere. The limited coverage of heliographic latitude by Voyager 2 precludes a direct measurement of the full flow pattern; however, the magnitude of reported magnetic flux deficits and the unambiguous, regular variations in the meridional flow suggest that the stream interactions do produce a net movement of magnetic flux away from the heliographic equator.
First VHF radar measurements of mesopause summer echoes at mid‐latitudes
Authors: Reid Iain M. , Czechowsky Peter , Rüster Rüdiger , Schmidt Gerhard
Published: February 2008

Observations of the summer mesosphere using the stationary SOUSY VHF (53.5 MHz) radar located in the Harz mountains of Germany (52°N, 10°E) indicate the presence of very strong radar returns from heights near 85–86 km on some occasions. These echoes occur in the form of a layer with a full‐power half‐width of less than about 1 km, and exhibit an aspect sensitivity of about 1 dB deg−1. These features are very similar to those of the so‐called Polar Mesopause Summer Echo (PMSE) known to occur at high latitudes and suggest a common production mechanism.
Crustal diffusion of gases out of Mercury and the Moon
Authors: Killen R. M.
Published: February 2008

I have calculated an upper limit to the rate of diffusion of sodium and potassium out of Mercury and the Moon and have compared the resulting flux to that required to maintain the known exospheres. I find that diffusion rates are inadequate by 12 orders of magnitude on the Moon and 9 orders of magnitude on Mercury for diffusion out of orthoclase minerals. Diffusion will be more rapid out of pure glass by 5 to 6 orders of magnitude and out of shocked basalt by an amount depending on the microstructure of the mineral. The observed abundance and distribution of volatiles in small glass spherules on the Moon indicates that diffusion is very inefficient after solidification and cooling. At Mercury, the limitation on sodium flux to the atmosphere is shown to be the rate at which new regolith is created. The discrepancy between the observed column abundnace of sodium in the Mercurean atmosphere and the known sources may indicate that either Mercury's crust has a larger volatile content than the Moon or that a recycling mechanism exists in the Mercurean atmosphere which is not present for the Moon.
Pioneer and Voyager observations of the solar wind at large heliocentric distances and latitudes
Authors: Gazis P. R. , Mihalov J. D. , Barnes A. , Lazarus A. J. , Smith E. J.
Published: February 2008

The Pioneer 10, 11 and Voyager 2 spacecraft are well suited for exploring spatial gradients in the distant solar wind. Between 1984 and 1986 Pioneer 11 and Voyager 2 were located at nearly the same heliocentric distance (≃20 AU) and longitude but were widely separated in latitude; Pioneer 11 was at a heliographic latitude of ≥15° while Voyager 2 was near the solar equator. Pioneer 10 was located near the solar equator but at a considerably greater heliocentric distance (≃40 AU). IMP observations at 1 AU provide an inner heliosphere baseline.

Prior to mid‐1985, Pioneer 11 and Voyager 2 observed nearly identical solar wind structures. The characteristics and arrival times of these structures were similar at both spacecraft.

After day 150 of 1985 this situation changed dramatically. The velocity structure at Voyager 2 became flatter. The velocities seen at Voyager 2 also fell with respect to Pioneer 11; the difference in velocities observed by the two spacecraft grew to 200 km s−1 by late 1986. In late 1985 Pioneer 10 observed a change in the solar wind similar to that observed at Voyager 2. These changes in the solar wind at low latitudes may be related to a change which occurred in the coronal hole structure in early 1985.
Modeling of Atmosphere Explorer‐D Return Flux Experiment
Authors: Gordon T. D. , Seebaugh W. R.
Published: February 2008

Codes for the prediction of spacecraft environments are currently in widespread use; however, few if any comparisons of code results with experimental measurements have been performed. In this paper we report the results of calculations performed for the Atmosphere Explorer‐D satellite at an altitude of approximately 250 km. Measurements of the atmospheric composition at the ram surface of the spacecraft were obtained by a closed source mass spectrometer before and during the operation of a return flux experiment in which a neon plume was directed into the spacecraft velocity vector. Calculations using the Integrated Spacecraft Environment Model (ISEM) reproduced the measured fluxes of the ambient species immediately before and during the venting operation. The presence of the neon plume reduced the flux of ambient species reaching the detector. The model reproduced these trends and gave a range of calculated neon return flux with a mean approximately equal to the value derived from the measurements. The model predicted a surface density of ambient species approximately 33 times the ambient level with and without the plume and nonnegligible scattering of neon into the wake of the spacecraft during plume operation.
Trapped‐particle evacuation: Source of magnetotail bursts and tailward flows?
Authors: Lyons L. R. , Schulz M. , Fennell J. F.
Published: February 2008

Theoretical considerations and observational evidence suggest that the polar cap (which marks the boundary between closed and open field lines) can expand rapidly enough during the growth phase of a substorm to release geomagnetically trapped particles from previously closed drift shells and thus enable them to escape into the tail. This scenario requires induced electric fields sufficient to yield E · J < 0 along the nightside x‐line, whereas standard reconnection theory would hold that E · J > 0 there at all times. In support of our concept we cite observations which suggest that the moving separatrix can overtake convecting nightside plasma during intervals of polar‐cap expansion, and we illustrate the occurrence of this phenomenon with a simple model which suggests that closed nightside field lines containing trapped particles can become open and thus be evacuated of their particle populations. Such evacuation seems to account for the occurrence of energetic‐particle bursts in the tail (for which impulsive energization is therefore unnecessary) and for some of the plasma flows that occur in the region adjacent to the plasma‐sheet boundary layer. Expansion of the dayside portion of the polar cap should contribute to the transition of particles from closed to open field lines there and thus should increase the fluxes of magnetospheric ions in the magnetosheath.
Effects of the drag force on the rise height of particles in the gas‐thrust region of volcanic eruption columns
Authors: Bursik Marcus
Published: February 2008

In a two‐phase jet, the rise height of particles is strongly dependent on initial particle concentration and particle size because the magnitude of the drag force varies with these two factors. Large particles (those with terminal fall velocities comparable to initial jet velocity) and small particles (terminal fall velocities much less than jet velocity) react to the drag force in different ways. As their concentration is varied, small particles reach a minimum in rise height when their initial particle‐field density equals the fluid density. The rise height of large particles varies little with concentration. The results may be applicable to explosive volcanic eruptions because the lower part of an eruption column is jetlike rather than plumelike. One implication is that eruption column collapse and pyroclastic flow formation, caused by gradual changes in initial particle concentration or gas content, may be modified by drag effects, perhaps accounting for column height fluctuations during collapse and some of the bedding characteristics of coignimbrite lag breccias.
Core‐mantle boundary topography and whole‐mantle convection
Authors: Forte Alessandro M. , Peltier W. Richard
Published: February 2008

The seismically observed topography on the core‐mantle boundary (CMB) and the velocities of the surface tectonic plates together constitute important observational constraints on viscous flow models of the Earth's mantle. We show here that the CMB deflections inferred by Morelli and Dziewonski (1987) may be explained in terms of a simple model of whole‐mantle convection and in the process we provide a new method for inferring the penetration depths of subducted slabs.
A comparison of magnetite particles produced anaerobically by magnetotactic and dissimilatory iron‐reducing bacteria
Authors: Moskowitz Bruce M. , Frankel Richard B. , Bazylinski Dennis A. , Jannasch Holger W. , Lovley Derek R.
Published: February 2008

We compare the magnetic properties of fine‐grained magnetite produced by two newly isolated anaerobic bacteria, a magnetotactic bacterium (MV‐1) and a dissimilatory iron‐reducing bacterium (GS‐15). Although room‐temperature magnetic properties are generally different between the two microorganisms, MV‐1 and GS‐15 magnetites can be most easily distinguished by the temperature variation of saturation remanence obtained at liquid helium temperatures. Magnetite produced by MV‐1 displays a sharp discontinuity in intensity at 100 K related to the Verwey transition. Magnetite produced by GS‐15 displays a gradual decrease in intensity with temperature due to the progressive unblocking of magnetization. The differing behavior is due exclusively to different grain size distributions produced by these microorganisms. MV‐1 produces magnetite with a narrow grain size distribution that is within the stable single domain size range at room temperature and below. GS‐15 produces magnetite with a wide grain size distribution extending into the superparamagnetic (SPM) size range. Our results show that a substantial fraction of particles produced by GS‐15 are SPM at room temperature.
Fortuna Tessera, Venus: Evidence of horizontal convergence and crustal thickening
Authors: Bruegge R. W. Vorder , Head J. W.
Published: February 2008

Structural and tectonic patterns mapped in Fortuna Tessera are interpreted to reflect a change in the style and intensity of deformation from east to west, beginning with simple tessera terrain at relatively low topographic elevations in the east and progressing through increasingly complex deformation patterns and higher topography to Maxwell Montes in the west. These morphologic and topographic patterns are consistent with east‐to‐west convergence and compression and the increasing elevations are interpreted to be due to crustal thickening processes associated with the convergent deformational environment. Using an Airy isostatic model, crustal thicknesses of approximately 35 km for the initial tessera terrain, and crustal thicknesses of over 100 km for the Maxwell Montes region are predicted. Detailed mapping with Magellan data will permit the deconvolution of individual components and structures in this terrain.
Mid‐latitude lidar observations of large sporadic sodium layers
Authors: Senft Daniel C. , Collins Richard L. , Gardner Chester S.
Published: February 2008

During the early morning of October 31, 1988 two large sporadic Na (Nas) layers were observed near the mesopause above Urbana, IL (40°N, 88°W) with a Na lidar system. The layers began forming near 102 km at 0026 LST and 0110 LST and moved downward with vertical velocities as high as 4 ms−1 before dissipating between 94 and 96 km. The duration of each layer was approximately 80 min. The layers were narrow (∼ 1 km FWHM) and dense with maximum densities approaching 7800 cm−3. The characteristics of these two Nas layers are very similar to those of similar phenomena observed recently at Andoya, Norway [von Zahn et al., 1987] and Mauna Kea, Hawaii [Kwon et al., 1988]. Lidar observations of the mesospheric Na layer have been conducted routinely by several groups at mid‐latitudes for almost 20 years. Although large Nas layers now appear to be relatively common at low‐ and high‐latitudes, to our knowledge the two layers described in this letter are only the second observation of this puzzling phenomenon at mid‐latitudes.
Aurora on Triton?
Authors: Hill T. W. , Dessler A. J.
Published: February 2008

If the planetary magnetic field of Neptune lies within the range of values that have been predicted for it (or even if the field is considerably smaller), Voyager 2 will find Triton immersed within the plasmasphere of a rotationally dominated magnetosphere. We expect the ionosphere of Triton to be highly conducting, which, coupled with Triton's 40 km/sec velocity relative to the magnetospheric plasma, leads to a limiting current that produces an induced magnetosphere, as occurs with solar‐wind flow past Venus or Mars. The induced magnetosphere, analogous to that observed near Saturn's satellite Titan, serves to deviate the flowing plasma and reduce the potential across Triton. The limiting current in this case can probably be carried by the local plasma with drift speeds below the thermal speed. For these conditions, we do not expect current‐driven instabilities to occur, and any auroral emissions would probably not be detectable against the background airglow of Triton's atmosphere. However, if Triton were to have a weak intrinsic magnetic field (for example, application of Blackett's law to Triton indicates a surface field of 400 nT, although a 20–80 nT surface field on Triton would suffice), the current would be funneled into an auroral zone. This would produce a concentration of current that may trigger specific auroral acceleration processes, such as double‐layer formation, and produce auroral optical and radio emissions detectable by Voyager instruments. Thus the presence of an aurora, particularly one that is localized, will argue for the presence of an intrinsic field on Triton.
Amazon Capims (floating grassmats): A source of 13C enriched methane to the troposphere
Authors: Chanton Jeffrey , Crill Patrick , Bartlett Karen , Martens Christopher
Published: February 2008

The 13C isotopic composition of methane emitted to the troposphere from Amazon capims (floating grassmats) ranged from −36.9 to −48.0‰, averaging −44.4 ± 4.2‰. All pools of methane associated with the grassmats were 13C enriched; methane withdrawn from plant stems ranged from −39 to −49‰ while bubbles stirred from the root mat averaged −41.4‰. As the CH4 flux from these habitats makes up some 40% of the total flux from the Amazon floodplain, CH4 emissions from the region as a whole must be enriched in the heavy carbon isotope. Methane withdrawn from the stems of five genera of rooted macrophytes ranging in latitude from the Florida Everglades to the Alaskan Arctic exhibited 13C enrichment relative to the sedimentary methane bubble reservoir. Several hypotheses based upon isotopic fractionation by methane transport, oxidation and production processes are proposed to explain this phenomenon.
Seasat‐derived gravity constraints on stress and deformation in the northeastern Indian Ocean
Authors: Stein Carol A. , Cloetingh Sierd , Wortel Rinus
Published: February 2008

We use SEASAT‐derived gravity data to investigate crustal deformation in the NE Indian Ocean. Gravity highs reflecting crustal undulations vary in orientation from E‐W in the Central Indian Basin to NE‐SW in the Wharton Basin. The undulations vary in trend similarly to the variation of the maximum compression directions predicted by a plate driving force model [Cloetingh and Wortel, 1985], and are essentially restricted to the area of predicted compression for both principal horizontal stresses. This agreement implies that the stress model describes the basic features of the deformation observed in the gravity as well as the seismicity. The gravity data also provide insight into two enigmatic tectonic features. The transition in the morphology of the 90°E Ridge at 10°S from a continuous high to a complex blocky structure appears related to the deformation, since undulations in the Central Indian Basin can be projected eastward to blocks on the Ridge. The morphology, formerly interpreted as a fossil feature, may reflect the recent deformation. The discrepancy between the trends of the southernmost 85°E Ridge and the 90°E Ridge, previously thought to exclude similar hot spot track origins, appears to result from treating a crustal undulation as part of the 85°E Ridge. Earthquakes do not appear to be preferentially located with respect to the peaks and troughs of the undulations.
Persistence of the ring current, 1958–1984
Authors: Wrenn Gordon L.
Published: February 2008

Statistical evidence for a solar cycle modulation in storm‐time ring current particle lifetimes is presented. Linear regression of Dst with respect to ap(τ), and an optimisation of τ to maximise correlation, gives characteristic persistence times for each year through 2.5 solar cycles. These average persistences vary between less than 10 h at solar minimum (1962, 1975) to greater than 16 h at solar maximum (1970, 1981). The analysis is biassed toward the later stages of recovery when the rate of decay has reduced, but the result is not a function of mean current strength or frequency of large storms. Increased abundance of O+ is postulated as the most probable explanation of longer particle lifetimes at solar maximum, this strongly supports the proposition that a large fraction of the ring current is of ionospheric origin, and underlines the importance of dynamic coupling between the ionosphere and magnetosphere during disturbed periods.
Broadband electrostatic noise due to field‐aligned currents
Authors: Schriver David , Ashour‐Abdalla Maha
Published: February 2008

There are observations of broadband electrostatic noise in the plasma sheet boundary layer that are associated with field‐aligned currents (electron beams), which often have an upper cutoff frequency above the electron plasma frequency. In this paper, using linear theory and numerical simulations we present results from a study of instabilities caused by an electron beam in a thermally mixed plasma. It is shown that two instabilities, the electron acoustic and electronion instabilities can combine to form a broadbanded wave spectrum that rapidly destroys the electron beam.
Predictions of lightning activity at Neptune
Authors: Borucki W. J.
Published: February 2008

Spacecraft observations of the seven innermost planets suggest that lightning is present on all planets with dense atmospheres. Thus lightning may be expected to occur on Neptune as well. Based on the level of lightning activity observed on Jupiter and on the assumption that the lightning energy dissipation rate is a constant fraction of the dissipation rate of the convective energy, the lightning rate on Neptune is estimated to be 1/19 that observed on Jupiter. It is predicted that approximately 60 events should be recorded by the Voyager imager during its search of the nightside of Neptune.
Magnetosphere of Neptune: auroral zone field‐aligned potential drops?
Authors: Cheng Andrew F.
Published: February 2008

This paper explores some possibilities for plasma populations, field‐aligned currents, and field‐aligned potentials in the magnetosphere of Neptune. Observed plasma populations at Saturn and Uranus may provide reasonable upper and low limits, respectively, to those at Neptune. Field‐aligned current densities comparable to those at Earth may be observed by the Voyager magnetometer above Neptune's auroral zone. Inverted‐V events reaching energies of several tens of keV may also be observed by the Voyager Low Energy Charged Particle experiment.
European tidal gravity: An improved agreement between observations and models
Authors: Baker T. F. , Edge R. J. , Jeffries G.
Published: February 2008

Tidal gravity observations were made at 5 sites in Europe using improved LaCoste and Romberg ET gravimeters. Special attention was paid to improving the accuracy of determining both the amplitude and phase in tidal gravity measurements. The measuring screws of the gravimeters were calibrated on the well established short range vertical gravity calibration lines at Hannover, FRG. For M2 and O1, it is shown that there is a very significant improvement in the agreement between observations and models compared to previous European tidal gravity measurements. For O1, the ocean tide loading and attraction is very small in Europe and our observations verify that the Dehant‐Wahr anelastic body tide gravimetric factor is accurate to within 0.2%. There is no dependence upon lateral changes of Earth structure, at least within the accuracy of our measurements.
Spectral analysis of high resolution temperature profiles in the stratosphere
Authors: Cot Charles , Barat Jean
Published: February 2008

We present in this paper one of the first high resolution analysis of temperature profiles measured in the lower stratosphere. The temperature fluctuations level is shown to depend only on the static stability. Moreover, in the 12 ‐ 1,500 m vertical wavelength range, the temperature spectrum has a mean slope around ‐ 2.3, a value significantly above the ‐ 3 saturated model value.
Dielectric stratigraphy of ice: A new technique for determining total ionic concentrations in polar ice cores
Authors: Moore J. C. , Mulvaney R. , Paren J. G.
Published: February 2008

A 133 m deep Antarctic ice core from Dolleman Island, Antarctic Peninsula, has been profiled by dielectric measurements in the AF‐LF (20 Hz ‐ 100 kHz) frequency range. This has revealed large variations in dielectric relaxation and conductivity down the core. A comparison with the chemical stratigraphy along 45 m of the core demonstrates for the first time the decisive role played by acids and salts in determining the electrical behaviour of natural ice. The total ionic concentration along the ice core can be deduced from the dielectric response. This technique may be applied rapidly in the field and, as it requires no contact between ice core and electrodes, the core is maintained in pristine condition for later chemical analysis.
1960 Chile: New estimate of polar motion excitation
Authors: Slade M. A. , Yoder C. F.
Published: February 2008

A recent reanalysis of the ILS polar motion data has been processed using Kalman filtering techniques to generate the polar motion excitation function over the time‐span from 1960 to 1965. The resulting excitation function has been examined for the effects of 1960 Chile in an attempt to determine experimentally how large earthquakes affect polar motion. The examination was deliberately not placed in the context of any theory of seismic or postseismic excitation. The resulting upper bound of ∼75. × 1022 N‐m. for a 10° dip (∼36. × 1022 N‐m for 20° dip) is consistent with results obtained from previous seismic studies, including a recent normal mode excitation result. Following future great earthquakes, monitoring of polar motion by space‐based techniques such as VLBI should continue at high temporal resolution for several weeks in order to directly measure the rheological parameters of the upper mantle.
Models of Pluto‧s upper atmosphere
Authors: McNutt Ralph L.
Published: February 2008

Best guesses as to the thermal structure and composition of Pluto‧s atmosphere have led to speculations of substantial loss rates (∼1028 s−1) of methane from the planet over cosmogonic time scales. Results from recent stellar occultation measurements, and using a Parker‐type hydrodynamic calculation, show that the loss rates may actually be lower by as much as a factor ∼5, depending upon the efficiency of heating of the atmosphere via the absorption of solar EUV and upon the true atmospheric composition, if the thermal structure of the upper atmosphere is properly taken into account. The loss rate may even be less (by another factor ∼10) if there is minimal heating of the upper atmosphere.
Pluto‧s interaction with the solar wind
Authors: Bagenal Fran , McNutt Ralph L.
Published: February 2008

If Pluto‧s atmospheric escape rate is significantly greater than 1.5 × 1027 molecules s−1 then the interaction with the tenuous solar wind at 30 A. U. will be like that of a comet: there will be extensive ion pick‐up upstream and the size of the interaction region will vary directly with variations in the solar wind flux. If the escape flux is much less, then one expects that the solar wind will be deflected around Pluto‧s ionosphere in a Venus‐like interaction. In either case, the weak interplanetary magnetic field at 30 A. U. results in very large gyroradii for the picked up ions and a thick bow shock, necessitating a kinetic treatment of the interaction. Strong variations in the size of the interaction region are expected on time scales of days due to changes in the solar wind.
Effect of irradiation on the surface of Pluto
Authors: Johnson R. E.
Published: February 2008

The surface of Pluto is exposed to cosmic ray particles which slowly alter the reflectance of the condensed methane and the UV absorbed in the atmosphere may produce precipitates. Depending on the rates of the competing regolith processes and the rate of replenishment of the methane the surface can appear bright, ‘red‧, or ‘dark‧. Here the relevant laboratory data show that, in the absence of any local particle precipitation, the amount of darkening occurring in one orbit is small.
Infrared radiative transfer calculations for volcanic ash clouds
Authors: Prata A. J.
Published: February 2008

Radiative transfer calculations are performed for volcanic ash clouds assumed to consist of mixtures of ash particles, ice spheres, water droplets and ash particles coated with sulphuric acid. The results show that for nascent volcanic eruption clouds a reverse absorption effect is noticeable in the infrared window between 10µm and 13µm, for which absorption of infrared radiation increases with increasing wavelength. This effect may be of use in detecting hazardous volcanic clouds from space.
Mean residence time of the shelf water in the East China and the Yellow Seas determined by 228Ra/226Ra measurements
Authors: Nozaki Yoshiyuki , Kasemsupaya Vimonrut , Tsubota Hiroyuki
Published: February 2008

Increasing attention of oceanographers has recently been paied on East Asian marginal seas regarding their role on the global environment, yet geochemical investigations have been few to date. We here report new data on the distribution of 228Ra and 226Ra in the surface water of the East China and the Yellow seas in an effort to constrain the time necessary for the coastal and shelf waters to exchange with offshore waters. Such information is needed in evaluating the exchange of heat and water across the air‐sea interface that affects the local climate and the fate of pollutants, nutrients and weathering products supplied from the continent. Based on the Ra isotope signals, we have estimated that the shelf water component contributes ∼ 20 % of the Tsushima Current water passing through the Tsushima Strait and the mean residence time for the shelf water to mix with the Kuroshio surface water is ∼ 2.3 years. As many of materials derived from the continent such as heavy metals and the nutrients have their mean residence times less than a few months in the nearshore and shelf waters, they must largely deposit on the shelf sediments prior to the transport from the shelf to the open sea by mixing.
Effects of near source seafloor topography on long‐period teleseismic P waveforms
Authors: Okamoto Taro , Miyatake Takashi
Published: February 2008

In the study of the shallow earthquakes in the subduction zones, reverberations inside the water layer near the source are known to affect very significantly the far field body waveforms. The usual correction is to take a horizontally layered model as the near source structure, but it is not realistic for the trench geometry. Therefore finite‐difference simulation combined with far‐field ray‐theory is employed in order to examine the effects of the realistic non‐flat seafloor topography.

As a realistic trench model the Japan trench is selected. The response of the structure near the source is calculated by two‐dimensional finite‐difference simulation. Then teleseismic P waveforms are calculated by using reciprocal theorem. Our results suggest that (1) around the trench bottom, effects of non‐planar structure are remarkable and the realistic seafloor cannot be approximated by any model of planar structure, however, (2) effects of the continental slope are well approximated by a model of planar dipping seafloor of appropriate dip. Therefore, the near source structure must include the realistic seafloor topography, or the waveform analyses may lead to spurious subevents in a later stage of rupture process and mislocation of events. Our results also show that present knowledge about the seafloor topography is enough to incorporate the complicated geometry.
Fault‐zone attenuation of high‐frequency seismic waves
Authors: Blakeslee Sam , Malin Peter , Alvarez Marcos
Published: February 2008

We have developed a technique to measure seismic attenuation within an active fault‐zone at seismogenic depths. Utilizing a pair of stations and pairs of earthquakes, spectral ratios are performed to isolate attenuation produced by wave‐propagation within the fault‐zone. This empirical approach eliminates common source, propagation, instrument and near‐surface site effects. The technique was applied to a cluster of 19 earthquakes recorded by a pair of downhole instruments located within the San Andreas fault‐zone, at Parkfield California. Over the 1‐40 Hz bandwidth used in this analysis, amplitudes are found to decrease exponentially with frequency. Furthermore, the fault‐zone propagation distance correlates with the severity of attenuation. Assuming a constant Q attenuation operator, the S‐wave quality factor within the fault‐zone at a depth of 5‐6 kilometers is 31 (+7,−5).

If fault‐zones are low‐Q environments, then near‐source attenuation of high‐frequency seismic waves may help to explain phenomenon such as fmax. Fault‐zone Q may prove to be a valuable indicator of the mechanical behavior and rheology of fault‐zones. Specific asperities can be monitored for precursory changes associated with the evolving stress‐field within the fault‐zone. The spatial and temporal resolution of the technique is fundamentally limited by the uncertainty in earthquake location and the interval time between earthquakes.
Seismic tomography of Jasper Seamount
Authors: Hildebrand J. A. , Dorman L. M. , Hammer P. T. C. , Schreiner A. E. , Cornuelle B. D.
Published: February 2008

A vertical section of the interior structure of Jasper Seamount was modeled using a spectral tomographic inversion of P wave travel times. An array of ocean bottom seismographs (OBSs) deployed over the seamount detected the arrivals from a series of ocean bottom shots. A reference velocity model reveals that average compressional velocities within the seamount are similar to those found within Kilauea and are consistently slower than velocities at equivalent depths in typical oceanic crust. This suggests Jasper Seamount has a high average porosity. Perturbations from the reference model were imaged by tomographic inversion. A high velocity zone within the northwest flank of the seamount may result from dikes associated with a radial rift or from a shallow solidified magma reservoir. A low velocity summit may result from shallow, explosive eruptions. The tomographic model is consistent with the results of gravity, magnetic and dredging analyses.
Balloon borne in‐situ detection of OH in the stratosphere from 37 to 23 km
Authors: Stimpfle R. M. , Lapson L. B. , Wennberg P. O. , Anderson J. G.
Published: February 2008

The OH number density in the stratosphere has been measured over the altitude interval of 37 to 23 km at midday via a balloon‐borne gondola launched from Palestine, Texas on July 6, 1988. OH radicals are detected with a laser induced fluorescence instrument employing a 17 kHz repetition rate copper vapor laser pumped dye laser optically coupled to an enclosed flow, in‐situ sampling chamber. OH abundances ranged from 88±31 pptv (1.1 ± 0.4 × 107 molec cm−3) in the 36 to 35 km interval to 0.9 ± 0.8 pptv (8.7 ± 7.7 × 105 molec cm−3) in the 24 to 23 km interval. The stated uncertainty (±1σ) includes that from both measurement precision and accuracy. Simultaneous detection of ozone and water vapor densities was carried out with separate on‐board instruments.
Bookshelf faulting and horizontal block rotations between overlapping rifts in southern Afar
Authors: Tapponnier Paul , Armijo Rolando , Manighetti Isabelle , Courtillot Vincent
Published: February 2008

Lateral slip on initially rift‐parallel normal faults may be a particularly efficient mechanism to accomodate strain between overlapping oceanic rifts. It occurs in southern Afar, where clockwise block rotations result from distributed dextral shear between the overlapping Ghoubbet Asal‐Manda Inakir and Manda Hararo‐Abhe Bad rifts. Faulting observed during the 1969, Serdo earthquakes and on SPOT images is consistent with the shear being taken up by left‐lateral slip on steep NW‐SE striking faults, which formed as normal faults before extensional strain became localized in the two rifts. This bookshelf faulting accounts quantitatively for the 14.5°± 7.5° rotation documented by paleomagnetism in the 1.8 ± 0.4 Ma old Afar stratoid basalts, given the 17.5 ± 5 mm/yr rate of separation between Arabia and Somalia.
Rheology of olivine and the strength of the lithosphere
Authors: Mackwell S. J. , Bai Q. , Kohlstedt D. L.
Published: February 2008

In order to throw some light on the rheological behavior of the upper mantle of the Earth, a detailed series of high‐temperature deformation experiments has been performed on olivine single crystals at 1 atm pressure under highly controlled thermodynamic conditions. The effects of stress, temperature, oxygen fugacity and orthopyroxene activity on the deformation rate of olivine have been carefully measured for the major high‐temperature slip systems. These experimental results have been extrapolated to the pressures and strain rates of the upper mantle to provide new insight into the mechanical behavior of the mantle and a better constrained approach to extrapolation of laboratory deformation data to the conditions present in the upper mantle. We suggest that extrapolations in stress provide the most reliable means for extending laboratory creep data to upper mantle strain rates. We also predict that, in the dislocation creep field, the bulk of the strain in olivine in the upper mantle is accommodated by the (010)[100] slip system. In addition, true mantle strengths are probably most accurately modelled using the experimental data for samples oriented favoring the (010)[001] slip system. However, the reliable prediction of mantle strengths requires highly accurate temperature versus depth relationships and good indications of the local oxygen fugacity in the mantle.
Pressure balance between lobe and plasma sheet
Authors: Baumjohann Wolfgang , Paschmann Götz , Lühr Hermann
Published: February 2008

Using eight months of AMPTE/IRM plasma and magnetic field data, we have done a statistical survey on the balance of total (thermal and magnetic) pressure in the Earth's plasma sheet and tail lobe. About 300,000 measurements obtained in the plasma sheet and the lobe were compared for different levels of magnetic activity as well as different distances from the Earth. Our data show that lobe and plasma sheet pressure balance very well. Even in the worst case they do not deviate by more than half of the variance in the data itself. Approximately constant total pressure was also seen during a quiet time pass when IRM traversed nearly the whole magnetotail in the vertical direction, from the southern hemisphere lobe through the neutral sheet and into the northern plasma sheet boundary layer.
Release Of liquid water from the space shuttle
Authors: Pike C. P. , Knecht D. J. , Viereck R. A. , Murad E. , Kofsky I. L. , Maris M. A. , Tran N. H. , Ashley G. , Twist L. , Gersh M. E. , Elgin J. B. , Berk A. , Stair A. T. , Bagian J. P. , Buchli J. F.
Published: February 2008

Groundbased and onboard video images of a sunlit Shuttle Orbiter water dump are interpreted as showing that the continuous ∼1 mm diameter liquid stream quickly breaks up in near‐vacuum to form ice/snow particles of two characteristic sizes. Discrete large droplets (shown from laboratory measurements, to have diameters comparable with that of the initial coherent quasicylinder) are most evident in the close‐in photographs, and unresolved submicron “fog” from recondensation of overexpanded evaporated water appears to dominate the ground‐telescope photographs of the ∼2½ km long optically detectable trail. We estimated the mean diameter of the smaller particles from the spatial distribution of visible radiance using a model of their energy balance, (small) surface roughening as they sublime, and Mie scattering of pre‐dawn sunlight. The results are consistent with those from recent space‐tank simulations.
Lidar observations of mesospheric Fe and sporadic Fe layers at Urbana, Illinois
Authors: Bills Richard E. , Gardner Chester S.
Published: February 2008

Lidar measurements of mesospheric Fe were conducted at Urbana, IL (40°N, 88°W) during 4 nights in late October 1989. The average Fe abundances, layer centroid heights and rms widths varied between 1.0 – 2.0×1010 cm−2, 89.0 – 90.5 km and 3.2 – 4.1 km, respectively. The peak densities of the layer near 90 km varied between 15 – 25×103 cm−3. Considerable gravity wave and tidal activity was observed in the Fe profiles. On 3 nights the formation and dissipation of 3 large sporadic Fe (Fes) layers was observed. These are the first observations of this phenomenon. The 2 largest Fes layers formed at 102.4 km and 91.4 km over a period of about 20 min and their widths were approximately 2.3 km FWHM. The peak densities of the Fes layers were as high as 31×103 cm−3 and the abundances were as high as 5.8×109 cm−2. The observations are compared with previous measurements of mesospheric Fe and with recent observations of sporadic Na (Nas) layers.