bluuebunny/crossref_metadata_2025 huggingface dataset:
The gravitational field of Phobos
Authors: Chao B. Fong , Rubincam David Parry
Published: February 2008

The external gravitational field produced by a rigid body of uniform density but irregular shape is formulated in terms of spherical harmonics. The formalism is applied to the Martian satellite Phobos. Based on a 3‐dimensional shape model of Phobos by Duxbury, the gravitational coefficients up to degree and order 4 for a homogeneous Phobos are computed. In particular, we find J2 = 0.105. The in‐plane libration amplitude of a homogeneous Phobos is predicted to be 0.97°, within the rather large uncertainty of the observed value of 0.78 ± 0.4°.
Observations and statistical simulations of a proposed solar cycle/qbo/weather relationship
Authors: Baldwin Mark P. , Dunkerton Timothy J.
Published: February 2008

The 10.7 cm solar flux is observed to be highly correlated with north pole stratospheric temperatures when partitioned according to the phase of the equatorial stratospheric winds (the quasi‐biennial oscillation, or QBO) (Labitzke and van Loon, 1988a). We supplement their observations with calculations showing that temperatures over most of the northern hemisphere are highly correlated or anticorrelated with north pole temperatures. The observed spatial pattern of solar cycle correlations at high latitudes is shown to be not unique to the solar cycle. We present results similar to the observed solar cycle correlations, with simulated harmonics of various periods replacing the solar cycle. These calculations demonstrate that correlations at least as high as those for the solar cycle results may be obtained using simulated harmonics.
Current dynamo effect of 3‐D time‐dependent reconnection in the dayside magnetopause
Authors: Song Yan , Lysak Robert L.
Published: February 2008

The increase of twist helicity by the curl of the Lorentz force in 3‐D time‐dependent reconnection implies a current dynamo effect, which transfers electromagnetic energy into the magnetosphere. Therefore magnetic reconnection is not only a dissipation process (J·E >0) but also a dynamo process (J·E <0), which corresponds to the generation of the field‐aligned current. The dynamo effect is effective if the level of the fluctuations, irregularities and non‐linearity of the plasma in the reconnection region is high. In this case the turbulent plasma with a finite diffusivity can be reorganized to a near force‐ and torque‐free state in the multiple reconnection sites. The current dynamo effect during reconnection gives an explanation for the diversion and disruption of the magnetopause current and the formation of large and small twisted magnetic flux tubes (so called FTEs, mini‐FTEs or impulsive penetration) at the magnetopause. An “overlap‐reconnect‐twist” dynamo process is suggested. The theory of the conversion and approximate conservation of the magnetic helicity during reconnection is used to estimate the average dynamo effect. During magnetic reconnection, the induced electric field consists of the convection electric field (Ec) and the time‐dependent electric field (Ei(X, t)), which correspond to the diffusion (J·Ec > 0) and dynamo processes (<∫J·EidV> <0)respectively.
Effects of interplanetary shocks on kilometric type III radio bursts
Authors: MacDowall R. J.
Published: February 2008

Interplanetary (IP) type III bursts that undergo sudden intensity changes when their electron beams traverse the vicinity of an IP shock are examined. Three types of intensity changes are discussed: cutoffs in which the type III intensity is abruptly reduced and remains at the reduced level for all lower frequencies, narrow‐band intensifications that frequently occur on the high‐frequency edge of a cutoff, and narrow‐band intensity reductions. Pitch angle scattering of the beam electrons in the enhanced magnetic turbulence downstream of shocks is proposed as a principal cause of the intensity cutoffs and, possibly, the intensifications. These observations suggest that one type III emission mode (fP or 2fP) is frequently at least 10 times more intense than the other mode.
Moist convection on Neptune
Authors: Stoker Carol R. , Toon Owen B.
Published: February 2008

We present a study of methane moist convection on Neptune. We examine the stability conditions to initiate moist convection of methane clouds. Temperature lapse rates that are unstable to moist convection are subadiabatic by a factor of two or more while adiabatic and superadiabatic lapse rates are stable. In the observed Neptune temperature structure, vertical velocities ≥ 40 m s−1 are required to lift moist air above the stable region and initiate moist convection. Alternatively, moist convection could be initiated by air that is slightly drier than its surroundings. Moist convective clouds achieve altitudes up to 100 mb, thereby exceeding the temperature minimum and depositing methane in the Neptune stratosphere. We predict that at least 2000 such clouds penetrate the Neptune stratosphere per hour.
Spontaneous small‐scale melt segregation in partial melts undergoing deformation
Authors: Stevenson David J.
Published: February 2008

A partial melt undergoing large scale deformation is shown to be unstable with respect to small scale redistribution of melt, provided the shear viscosity of the matrix depends on melt fraction. In the physically realistic case where melt “softens” the matrix, melt migrates along the direction parallel to the axis of minimum compressive stress and accumulates in “veins” (melt‐rich lenses). The maximum growth rate of the instability is of order —⋵od ln η/df (⋵o ≡ largest component of the principal strain tensor, η = shear viscosity, f = melt fraction), and plausibly fast enough to invalidate the conventional applications of Darcy's law (e.g., mid‐ocean ridges, subduction zones) since melt migrates into veins in preference to being pervasively flushed vertically. The preferred lengthscale of the instability is poorly determined but probably ∼ meters. Veins may eventually form an interconnected drainage network, allowing rapid vertical flushing of melt.
Location performance of a sparse regional network
Authors: Ballard Sanford , Walck Marianne C. , Chael Eric P.
Published: February 2008

A key element in successful seismic verification of a nuclear test ban treaty is the capability of a sparse network of seismic stations to accurately locate regional events. We have investigated the regional location accuracy of the Regional Seismic Test Network (RSTN), a five‐element, three‐component network in eastern North America, using 62 events varying in size from magnitude 3.0 to 5.1. Applying an algorithm which allows inclusion of back‐azimuth estimates as well as travel times, we determined a median location error of 23 km for the data set relative to the PDE locations. Considering the large station spacing (1500 km) and few data used in the locations (2 to 4 stations), the RSTN location accuracy is remarkably good; the results imply that a widely spaced network of single, three‐component stations could reliably locate regional seismic events.
Nonlinear interaction of energetic ring current protons with magnetospheric hydromagnetic waves
Authors: Chan Anthony A. , Chen Liu , White Roscoe B.
Published: February 2008

In order to study nonlinear wave‐particle interactions in the Earth‧s magnetosphere we have derived Hamiltonian equations for the gyrophase‐averaged nonrelativistic motion of charged particles in a perturbed dipole magnetic field. We assume low frequency (less than the proton gyrofrequency) fully electromagnetic perturbations, and we retain finite Larmor radius effects. Analytic and numerical results for the stochastic threshold of energetic protons (≳ 100 keV) in compressional geomagnetic pulsations in the Pc 5 range of frequencies (150‐600 seconds) are presented. These protons undergo a drift‐bounce resonance with the Pc 5 waves which breaks the second (longitudinal) and third (flux) adiabatic invariants, while the first invariant (the magnetic moment) and the proton energy are approximately conserved. The proton motion in the observed spectrum of waves is found to be strongly diffusive, due to the overlap of neighboring primary resonances.
Constraints on impact rates in the Pluto‐Charon system and the population of the Kuiper Comet Belt
Authors: Weissman Paul R. , Dobrovolskis Anthony R. , Stern S. Alan
Published: February 2008

Impact rates in the Pluto‐Charon system are dominated by comets from the proposed Kuiper Belt, 30 to 50 AU from the Sun. Such collisions excite the eccentricity of Charon‧s orbit, which then decays due to tidal dissipation. Charon‧s eccentricity approaches a quasi‐steady state, which can be used to constrain the total number and mass of comets in the Kuiper Belt. Unfortunately, the current upper limit on Charon‧s orbital eccentricity must be reduced by more than a factor of ten before useful constraints can be set.
The deep planetary magnetotail revisited
Authors: Macek Wieslaw M.
Published: February 2008

We extend a previously presented magnetotail model [Grzedzielski and Macek, 1988] to great distances in the antisolar direction. For typical solar wind parameters at ∼ 1 AU and the most probable set of parameters of the model as determined for the ISEE 3 region of ∼ 200 Earth radii (RE), the open geotail extends to at least (3 − 4) × 10³ RE downstream from Earth where it forms a cavity filled with a dense (∼ 1 cm−3), hot ( ≲ 106K) plasma and low magnetic field strengths (1.2 − 0.4 nT). The cross section of this cavity in the plane perpendicular to the Earth‐Sun line has dimensions of 300 − 400 RE parallel to the ecliptic plane, but only ∼ 5 RE in the direction normal to the ecliptic. It seems likely that the magnetotail would become filamentary at such distances. Our results indicate that the Phobos spacecraft could have observed tail associated phenomena at distances of ∼ 3900 RE downstream from Earth during a September 1988 transit. We compare model predictions for the characteristics of planetary magnetotails (including Neptune) in our solar system.
Regional stress field in the Lesser Antilles between Guadeloupe and Barbuda Islands
Authors: Julien Philippe , Bonneton Jean‐Roger
Published: February 2008

Microtectonic and extensometric measurements on the island of Basse‐Terre in Guadeloupe are coherent with a homogeneous stress system (Julien and Bonneton, 1984).

In order to compare the stress field obtained from the deep seismicity and the stress directions deduced from superficial observations, a method for determining the aspect ratio and the principal directions of the regional stress field from a set of focal mechanisms has been used (Julien and Cornet, 1987).

When applied to a group of large earthquakes, this method provides means for computing the stress field in a lithospheric block. The inversion of the focal mechanisms located in the eastern part of the crust in the Caribbean plate between the Guadeloupe and the Barbuda islands shows a maximum principal stress oriented nearly horizontally in the direction N 120°E. These results are in full agreement with microtectonic measurements and observed deformations. This direction corresponds to the convergence direction of the western Atlantic plate towards the Caribbean plate.
More about the moment of inertia of Mars
Authors: Kaula William M. , Sleep Norman H. , Phillips Roger J.
Published: February 2008

The maximum allowable mean moment‐of‐inertia I of Mars is 0.3650 · MR² because the rate‐of‐adjustment of the rotation axis is much faster than the rate‐of‐generation of density heterogeneities, as with any planet. But Mars differs from the other terrestrial planets in that its gravity field is rougher, in the sense of stress‐difference implication, and its global tectonics is dominated by one feature, centered on the Tharsis Plateau. Plausible tectonic models of Mars require generation and support that are almost axially symmetric about Tharsis. Hence, unlike other terrestrial planets, Mars likely has two non‐hydrostatic components of moments‐of‐inertia that are nearly equal, and the most probable value of I/MR² is slightly less than 0.3650.
A comparison of the spatio‐temporal distribution of moment release for the 1986 Andreanof Islands Earthquake with relocated seismicity
Authors: Houston Heidi , Engdahl E. R.
Published: February 2008

We compare relocated, teleseismically recorded seismicity before and after the May 7, 1986, Andreanof Islands earthquake (Mw= 8) to the spatial and temporal distribution of seismic moment release during the mainshock. Relocated seismicity from 1964 through April 1987 clusters strongly along the main thrust zone, in similar locations for the pre‐ and post‐mainshock periods.

We performed simultaneous iterative inversions of broadband teleseismic GDSN and NARS P‐waveforms using the method of Kikuchi and Fukao [1987]. Fault plane parameters (e.g., strike, dip, depth, and extent of fault plane) consistent with regional tectonics and aftershock locations were specified. The results of the inversions are spatial and temporal maps of moment release on the fault plane. Most of the moment found by the inversion is localized in several regions of the fault plane. Resolution of the location and timing of the major subevents is good. The rupture was bilateral, with a highly variable rupture velocity. A shallow, updip region of the fault plane ruptured toward the end of the mainshock process.

The mainshock moment release tended to occur in regions of the fault plane in which no or few aftershocks or preshocks are located. This tendency suggests that regions of high moment release in the 1986 Andreanof Islands earthquake resulted from rupture of mechanically strong regions (i.e., asperities) on the fault plane, which exhibited little seismicity before or after the mainshock that ruptured them. We infer that the asperity regions were locked and quiescent before the mainshock, while surrounding seismically active areas did not store as much strain and slipped mostly aseismically.
The OI844.6 nm emission in evening twilight
Authors: Bahsoun‐Hamade F. , Wiens R. H. , Shepherd G. G.
Published: February 2008

Ground‐based measurements of the atomic oxygen multiplet emission at 844.6nm were made during evening twilight through the fall and winter of 1988/89, from Toronto using a low‐resolution Fabry‐Perot interferometer. Observations were made in the azimuth of the sun at 20° above the horizon, over a local solar zenith angle range from 94° to 99°. The radiance variation as a function of SZA is presented, with correction for atmospheric extinction. These are the first ground based measurements of the 844.6 nm emission ever reported for early twilight. The measurements are an important first step in obtaining the atomic oxygen density as well as the ratio of the integrated photoelectron flux to the solar EUV flux. The results are compared with previous measurements by others.
Phlogopite and K‐amphibole in the upper mantle: Implication for magma genesis in subduction zones
Authors: Sudo Akira , Tatsumi Yoshiyuki
Published: February 2008

High‐pressure phase relations have been examined for phlogopite + diopside with and without enstatite under vapor absent conditions in the pressure range of 5 to 13 GPa and in the temperature range of 1000 to 1300°C. Phlogopite in these systems can be stable up to 6–7 GPa and decomposes through pressure‐dependent reactions to crystallize phases including potassic amphibole. The experimental results suggest that phlogopite, which is one of main hydrous phases in the downdragged hydrated peridotite at the base of mantle wedge, plays an important role in the formation of magmas at the backarc side of a volcanic arc. The existence of potassic amphibole at higher pressure regions may imply the involvement of subduction component in magma generation in the region far away from the trench axis.
The evolution from weak to strong geomagnetic activity: An interpretation in terms of deterministic chaos
Authors: Baker D. N. , Klimas A. J. , McPherron R. L. , Büchner J.
Published: February 2008

Linear prediction filtering techniques have shown that the magnetospheric response to energy transfer from the solar wind contains both driven and unloading components. Filter elements ordered with respect to geomagnetic activity have shown a peak at 20 minutes due to the driven component and a second peak at 1 hour which has been interpreted in terms of the magnetotail unloading component. The peak at 1 hour was found to increase in strength with increasing activity up to a critical activity level beyond which the peak vanished. We study these features of geomagnetic activity in terms of a nonlinear dynamical model of the magnetospheric system. We base our model on the leaky faucet analogy of plasmoid formation (Hones, 1979) and the dripping faucet experiment and model of Shaw (1984). We have constructed a mechanical analogue to the magnetosphere which models both the driven and the loading‐unloading energy release mechanisms. This model is elementary, but is dynamically complete in that it is able to represent the entire cycle of substorm growth, expansion, and recovery. The model is able to explain many of the features of the linear filter results. In particular, the model suggests that the disappearance of the 1 hour peak is due to a chaotic transition beyond which the loading‐unloading mechanism continues, but aperiodically. This work suggests that, using the tools of chaos theory, we may gain considerable insight into the stormtime behavior of the magnetosphere.
Wave‐induced burst precipitation events detected with a digital ionosonde
Authors: Jarvis M. J. , Smith A. J. , Berkey F. T. , Carpenter D. L.
Published: February 2008

Initial results are presented from two methods whereby burst precipitation events in the lower ionosphere, almost certainly induced by VLF wave‐particle interactions in the magnetosphere, have been detected using a ground‐based digital ionosonde. In the first method, HF echoes are received above the critical frequency of the surrounding plasma; particle energies and the location and extent of the plasma enhancement may be deduced. In the second method, a rapid decrease in the phase of ionospheric echoes is observed due to refractive index changes along the echo path; particle energies, the duration of the precipitation event and the precipitation energy flux can be estimated.
The prediction of the magnitude of sunspot maxima for Cycle 22 using abnormal quiet days in Sq(H)
Authors: Butcher E. C.
Published: February 2008

Analysis of abnormal quiet days (or AQDs) in Sq(H) near years of sunspot minimum have successfully been used to predict the maximum annual mean sunspot number Ra‐max at the following sunspot maximum. In this paper, the method is used for cycle 22 and predicts a value of Ra‐max of 187 ± 36 and a value of the maximum monthly value of R of 254 ± 49.
ROLE OF ANISOTROPIC AND/OR LAYERED PERMEABELITY IN HYDROTHERMAL CONVECTION
Authors: Rosenberg N. D. , Spera F. J.
Published: February 2008

The spatial variation and degree of anisotropy of the permeability field (k) is an important parameter affecting the dynamics of convective fluid flow in saturated geologic media. We report results from time‐dependent, two‐dimensional numerical simulations, with constant fluid properties, for k fields that are anisotropic, layered or both. Streamlines and isotherms are given for domains with permeable and impermeable tops for Ra (100–300), kz/kx (0.33–40) and for a system with two isotropic layers of equal height, kt/kb (0.1–10). The kinetic energy (KE) and Nusselt number (Nu) monotonically decrease as kz/kx increases at constant Rayleigh number, defined with respect to kz. In two‐layer systems, KE increases linearly and Nu increases asymptotically as kt/kb increases at constant Rayleigh number, defined with respect to kb. For otherwise identical cases, KE and Nu are greater for permeable top than impermeable top boundary conditions. Time to steady‐state is inversely proportional to KE1/2. Results are also presented for k Fields that are both anisotropic and layered as an analog to oceanic crust permeability.
Thermal Isotasy in the South Atlantic: A New Approach
Authors: Gibert Dominique , Courtillot Vincent
Published: February 2008

We present a new way to estimate the thermal diffusivity and the thickness of the oceanic lithosphere based on admittances computed from geoid and bathymetry profiles which roughly parallel the ridge. This method appears to operate in die medium wave band (500 ‐ 1500 km), and may be of help in remote oceanic areas where only poor bathymetry is available. We apply the method to 32 profiles on each flank of the South Atlantic spreading ridge between the equator and 35°S, and obtain the solution domain for both the plate thickness and the thermal diffusivity Anomalously high admittance values obtained for the west flank (at wavelengths around 700 km) may be due to deeper asthenospheric density heterogeneities.
Simultaneous Disturbance of Conjugate Ionospheric Regions in Association With Individual Lightning Flashes
Authors: Burgess W. C. , Inan U. S.
Published: February 2008

Characteristic whistler‐associated amplitude perturbations of subionospheric VLF or LF signals (“Trimpi events”) observed within one second of each other at Palmer Station, Antarctica and at Arecibo, Puerto Rico suggest that ionospheric regions in both northern and southern hemispheres are disturbed together in association with individual lightning flashes. During a one hour period on March 21, 1989, the onsets of 44 out of 47 perturbations measured on a 21.4 kHz signal from Maryland to Arecibo occurred within l s of perturbation onsets measured on a 23.4 kHz signal from Hawaii to Palmer Station. Similar activity occurred before and after this period, and on the preceding and following days. The observations are consistent with the disturbance of geomagnetically conjugate ionospheric regions by multiple bounces between hemispheres of bursts of radiation belt electrons, scattered in pitch angle by whistlers in the magnetosphere. Analysis of patterns of perturbations with corresponding whistler and lightning information from this period suggests that there were at least two distinct ionospheric disturbances in each hemisphere.
Isotropized Magnetic‐Moment Equation of State for the Central Plasma Sheet
Authors: Kan J. R. , Baumjohann W.
Published: February 2008

The AMPTE/IRM plasma and magnetic field data show that the compression in the central plasma sheet (< 20 RE radial distance) near the equatorial plane is governed by the isotropized magnetic‐moment equation of state, P/(NBZ) = constant, derived from the invariance of the magnetic moment under the assumption of isotropic ion pressure P where N is the number density and Bz is the normal field component in the plasma sheet. The adiabatic equation of state, P/N5/3 = constant, can be expected to govern the compression in the distant plasma sheet (> 20 RE) or the plasma sheet boundary layer where fewer particles are likely to escape from a flux tube through the loss cone to meet the particle conservation requirement of the adiabatic condition.
Observation of auroral secondary electrons in the Jovian magnetosphere
Authors: McNutt Ralph L. , Bagenal Fran , Thome Richard M.
Published: February 2008

Localized enhancements in the flux of suprathermal electrons were observed by the Voyager 1 Plasma Science instrument near the outer boundary of the Io plasma torus between L ∼7.5 and L ∼10. This localization, which occurs within the general region of hot electrons noted by Sittler and Strobel (1987), and the spectral characteristics of the observed electrons are consistent with secondary (backscattered) electron production by intense Jovian auroral energetic particle precipitation and support the hypothesis that such electrons may contribute to the processes that heat the plasma in this region of the magnetosphere.
Variations of mesospheric equatorial ozone as observed by the Solar Maximum Mission
Authors: Aikin Arthur C. , Henze William , Kendig David J. , Nakatsuka Roy , Smith Henry J. P.
Published: February 2008

Tropical lower mesospheric ozone concentrations determined from ultraviolet sunset occultations demonstrate latitude dependent variations from 1985 through 1988. Although there is no detectable secular change at the equator, at 20°N there is an increase of 1.4% per year, while at 20°S there is a decrease of 0.6% per year. At all observed latitudes, annual and semiannual oscillations are evident, but the amplitude of the oscillations is a factor of four smaller at 20°S than at 20°N. The annual and semiannual ozone behavior is caused primarily by equatorial temperature waves. Secular changes are the result of variations in mesospheric temperature, solar flux, and trace constituents which are involved in the ozone chemistry. The variation with latitude of the observed ozone trends between 1985 and 1989 is different from predictions of some models which simulate stratospheric and lower mesospheric ozone behavior over a sunspot cycle. This is the result of differences between the actual temperature structure of the atmosphere and that adopted in the models, rather than an error in the underlying photochemistry.
SAM II aerosol measurements during the 1989 AASE
Authors: Osborn M. T. , Pitts M. C. , Powell K. A. , McCormick M. P.
Published: February 2008

The Stratospheric Aerosol Measurement II (SAM II) satellite experiment measures 14 daily L.O‐μm aerosol extinction profiles in the high northern latitudes. These SAM II data were used to spot the locations of polar stratospheric clouds (PSCs) and provide an overview of the vertical structure of the upper tropospheric and stratospheric aerosols during the 1989 Airborne Arctic Stratospheric Expedition (AASE). Contour plots of aerosol extinction vs. longitude and altitude are shown for 24 days during AASE which summarize these measurements. PSC sightings occurred during the first week of January and from January 18 through February 2, 1989. Although SAM II measured a higher than average number of PSCs in January 1989 as compared to the previous 10 years, The number of PSCs sighted during the entire 1989 winter season is only slightly above average. Also discussed is the vertical gradient in aerosol extinction which occurs as the SAM II measurement locations cross the polar vortex.
A survey of particle measurements in the Arctic from the Forward Scattering Spectrometer Probe MODEL 300
Authors: Dye J. E. , Gandrud B. W. , Baumgardner D. , Sanford L. , Ferry G. V.
Published: February 2008

A new instrument, the Forward Scattering Spectrometer Probe (FSSP) 300, was used on the NASA ER‐2 during the Airborne Arctic Stratospheric Expedition (AASE) to count and size particles in the size range of approximately 0.4 to 24 μm diameter. A brief description of the instrument is presented and observations for each ER‐2 flight are summarized. Measurements were made in both type I and type II polar stratospheric clouds as well as in the background sulfuric acid particles. Total particle concentrations up to 16 cm−3 with total particle volumes up to 10 μm3 cm−3 were observed in some of the polar stratospheric cloud events.
Airborne measurements of stratospheric constituents over the Arctic in the winter of 1989
Authors: Mankin William G. , Coffey M. T. , Goldman Aaron , Schoeberl Mark R. , Lait Leslie R. , Newman Paul A.
Published: February 2008

We have used a Fourier transform spectrometer aboard the NASA DC‐8 aircraft during the Airborne Arctic Stratospheric Expedition (AASE) to record infrared absorption spectra of the polar stratosphere. From these high resolution spectra we have derived vertical column amounts above flight altitude of O3, CH4, N2O, H2O, HCl, HF, NO, NO2, ClONO2, and HNO3 for eleven flights poleward of 60°N. We report here measurements on the flight of 26 January 1989 when the flight path during the observations crossed from outside the polar vortex to inside. This allowed a clear comparison of the conditions of the air within the vortex with that outside. Observations of passive tracers such as CH4 and HF indicate that air of a certain composition within the polar vortex occurs at lower altitude than air outside. Within the vortex, we observed markedly reduced columns of HCl and NO2. The ratio of HCl to HF column dropped from its typical nidlatitude value of 4.5 to as low as 1.7 within the vortex, implying that the HCl had been chemically or physically removed from the air in the vortex. NO2 values within the vortex were near 3.0×1014 molecules‐cm−2, about a factor of two less than columns outside. In contrast to the Antarctic observations, HNO3 values were elevated within the vortex. HNO3 columns inside the vortex reached values of 30×1015 molecules‐cm−2. The ClONO2 column was largest within the vortex, peaking at 4×l015 molecules‐cm−2 near the boundary of the vortex, and decreasing farther into the vortex.
Rotational instabilities of the Earth induced by mantle density anomalies
Authors: Ricard Yanick , Sabadini Roberto
Published: February 2008

From the seismic tomographic models, we estimate the offset between the geographic pole and the main inertial axis. This offset, which is large for a static Earth, is drastically reduced when the dynamical behaviour of the mantle is taken into account. For a mantle stratification with a viscosity increase by a factor of about 50, this offset is comparable to what can be estimated on the basis of remanent post‐glacial depression. We also discuss the rate of polar drift induced by both internal mass heterogeneities and Pleistocenic deglaciation. Contributions from internal sources and ice‐sheets disintegration are consistent with the observed secular trend. For high viscosity contrasts, our results are quite insensitive to the phase transition or chemical nature of the upper‐lower mantle interface. This study shows that there is no contradiction between the tomographic models of the Earth and their implications for the rotational stability of our planet; our findings also agree with recent analyses of paleomagnetic data.
The relationship between QE−1 and dispersion in extensional modulus, E
Authors: Lienert Barry R. , Manghnani Murli H.
Published: February 2008

We have measured the extensional modulus (ratio of stress to strain, E) and the fractional energy loss per radian (QE‐1) as functions of frequency in cylindrical samples of two solids: a room‐dry sandstone (Berea) and an acrylic plastic (Lucite). In the seismic frequency range (0.1–100 Hz), QE‐1
for the sandstone is constant, while the sandstone modulus follows a power law of frequency,

 

allowing QE‐1 to be independently estimated from the slope of log E versus log f. In the same frequency range, QE‐1 for the acrylic plastic is not constant but exhibits a slight relaxation peak centered about 2 Hz. In this case
QE‐1 can be estimated from the derivative, d log E/d log f, i.e., the above power law appears to hold independently at each point in the frequency domain even when QE‐1 is varying.
Thermal expansivity versus pressure at constant temperature: A re‐examination
Authors: Anderson O. L. , Chopelas A. , Boehler R.
Published: February 2008

Results from recent high pressure experiments have shown δT in the relationship

 

to be constant over significant compressions, one of the original assumptions required to make this relationship valid. We have re‐examined the original derivation of this equation and present a simpler derivation eliminating the previous assumptions. Furthermore, high pressure experiments find (∂lnα/∂lnρ)T is equal in value to l/αKT(∂KT/∂T)P derived from experiments at ambient pressures. From values of −δT = l/αKT(∂KT/∂T)P at high temperatures, it is asserted that −(∂lnα/∂lnρ)T must lie between 4 and 6 in the lower mantle, a value significantly higher than previously assumed in earth models.
Nonadiabatic ion diamagnetic drift instability in the neutral sheet
Authors: Mu Jian‐lin , Pu Zu‐yin , Fang Zheng‐zhi
Published: February 2008

There are two kinds of drift motion associated with AC ions in the neutral sheet: orbital drift and diamagnetic drift. Both of the motions can reach the order of the thermal velocity. An electrostatic instability can thus be driven by the AC ion diamagnetic drift velocity and enhanced by the orbital drift resonance with the wave. The associated anomalous resistivity reaches the order of 104 mΩ.
Titanomagnetite granulometry and rockmagnetism of some Plio‐Pleistocene volcanic rocks
Authors: Robertson D. J.
Published: February 2008

Particle size distribution and composition of iron‐titanium oxides have been measured in four samples of volcanic rock from the Lesser Antilles. Magnetic hysteresis properties are predicted for these samples on the basis of available data for synthetic analogues, and the predictions are compared with laboratory measurements of the same parameters.
The occurrence and transport of radon in the natural environment
Authors: Reimer G. M.
Published: February 2008

Radon—a colorless, odorless, tasteless, radioactive gas known to accumulate in homes.

Within the last two years, those words have appeared in probably every newspaper in the country, informing the public that they may have an increased risk of lung cancer due to exposure to radon. Although the actual health risks of the slightly elevated concentrations found in the vast majority of homes is a matter of current scientific study, there are clearly some areas of the country where indoor levels and individual exposures can approach those found in underground mines. In these cases, the risks are not in doubt, but questions concerning the occurrence and transport of radon abound.
Radium regionalization in California
Authors: Wollenberg H. A. , Revzan K. L.
Published: February 2008

The amount of 222Rn that enters a house depends to a large extent on the concentration of radon's parent, 226Ra in the soil. With the assumption that radium is in radioactive equilibrium with its ultimate parent, 238U, we used the National Aerial Radiometric Reconnaisance (NARR) data and a database covering the concentration and distribution of uranium in California rocks to estimate the regional distribution of radium. A north‐to‐south increase in radium occurs between 42° and 36°N, then radium decreases southward. This pattern is explained by the distribution of rock types. The overall mean radium concentrations estimated from the aeroradiometric and lithologic data are similar, but there is a significant discrepancy between aeroradiometric and lithologic‐estimated radium in central California. Ground measurements suggest that the radium values from aeroradiometric measurements there are erroneously high, pointing out the necessity of verifying aeroradio‐metrically‐determined data before they are used to help predict radon production.
Pedologic and climatic controls on RN‐222 concentrations in soil gas, Denver, Colorado
Authors: Asher‐Bolinder Sigrid , Owen Douglass E. , Schumann R. Randall
Published: February 2008

Soil‐gas radon concentrations are controlled seasonally by factors of climate and pedology. In a swelling soil of the semiarid Western United States, soil‐gas radon concentrations at 100 cm depth increase in winter and spring due to increased emanation with higher soil moisture and the capping effect of surface water or ice. Increased soil moisture results from a combination of higher winter and spring precipitation and decreased insolation in fall and winter, lowering soil temperatures so that water infiltrates deeper and evaporates more slowly. Radon concentrations in soil drop markedly through the summer and fall. The increased insolation of spring and summer warms and dries the soil, limiting the amount of water that reaches 100 cm. As the soil dries, radon emanation decreases, and deep soil cracks develop. These cracks aid convective transport of soil gas, increase radon's flux into the atmosphere, and lower its concentration in soil gas. Probable controls on the distribution of uranium within the soil column include its downward leaching, its precipitation or adsorption onto B‐horizon clays, concretions, or cement, and the uranium content and mineralogy of the soil's granitic and gneissic precursors.
The magnetic properties of the Soviet spacecraft “Phobos‐2”
Authors: Auster H.‐U. , Fornacon K.‐H. , Rustenbach J. , Roatsch Th. , Schroedter R. , Schwingenschuh K. , Auster V.
Published: February 2008

An analysis of the magnetic properties of “Phobos‐2,” a new type of Soviet spacecraft, is presented. It has been based on measurements carried out on the ready‐for‐launch spacecraft, and on zero level interpretations of the two magnetometers on board during 255 days of flight. In this context, a method is described for identifying and estimating magnetic disturbance sources under unfavorable conditions. The magnetic moment of the spacecraft and of a spring which is responsible for moving the boom have been determined. An influence of different orientation modes on the zero levels is shown at both magnetometers. The total influence of all sources of disturbances amounts to 2–4 nT per component.
An experiment in the use of trained neural networks for regional seismic event classification
Authors: Pulli Jay J. , Dysart Paul S.
Published: February 2008

A neural network employing the back propagation learning paradigm has been developed as an experiment in the automatic classification of small regional earthquakes and quarry explosions. The network has been used in the analysis of 66 events recorded by the NORESS array in southern Norway. The input vector consists of three broadband discriminants including the spectral ratios of Sn/Pn and Lg/Pn waves, and the mean cepstral variance of Pn, Sn, and Lg. Two hidden layers are used, consisting of 8 and 2 units. The output vector consists of two units which correspond to the classification of explosion or earthquake.

The network was first trained using input vectors from the entire dataset. The network was able to perfectly model the training set with no classification errors. For comparison, an optimum linear classifier used with the same dataset resulted in 5 errors and 19 uncertain classifications. Next, the network was trained with half of the events and tested with the remaining half. This resulted in 5 errors and 2 uncertain classifications. This compares with 5 errors and 18 uncertain events for the optimum linear classifier. The apparent advantage of the neural network over the optimum linear classifier is the network's ability to model complex decision regions and in the reduction of the number of uncertain events.
Regional transport of the urban workweek: Methylchloroform cycles in the Nevada‐Arizona Desert
Authors: White Warren H. , Macias Edward S. , Miller David F. , Schorran David E. , Hoffer Thomas E. , Rogers David P.
Published: February 2008

The halocarbons CFCl3, CH3CCl3, CCl4, and C2Cl4 have been monitored at four locations in southern California, southern Nevada, and northwestern Arizona. Summertime concentrations of CH3CCl3 and C2Cl4 at the Nevada and Arizona sites exhibit strong weekly cycles that lag similar cycles observed in the Los Angeles Basin by 1–2 days. The observed patterns imply a nearly complete weekend shutdown of emissions, and remarkably consistent long‐range (300–400 km) transport through complex terrain. The average amplitude of the summertime CH3CCl3 cycle is about 1200 ppt in air leaving the Los Angeles Basin, 80 ppt at the mountain‐top Nevada observatory, and 40 ppt at the level‐terrain Arizona observatory.
Current plate velocities relative to the hotspots incorporating the NUVEL‐1 global plate motion model
Authors: Gripp Alice E. , Gordon Richard G.
Published: February 2008

NUVEL‐1 is a new global model of current relative plate velocities [DeMets et al., 1990], which differ significantly from those of prior models. Here we incorporate NUVEL‐1 into HS2‐NUVEL1, a new global model of plate velocities relative to the hotspots. HS2‐NUVEL1 was determined from the hotspot data and errors used by Minster and Jordan [1978] to determine AM1‐2, which is their model of plate velocities relative to the hotspots. AM1‐2 is consistent with Minster and Jordan's relative plate velocity model RM2. Here we compare HS2‐NUVEL1 with AM1‐2 and examine how their differences relate to differences between NUVEL‐1 and RM2. HS2‐NUVEL1 plate velocities relative to the hotspots are mainly similar to those of AM1‐2. Minor differences between the two models include the following: (1) in HS2‐NUVEL1 the speed of the partly continental, apparently non‐subducting Indian plate is greater than that of the purely oceanic, subducting Nazca plate; (2) in places the direction of motion of the African, Antarctic, Arabian, Australian, Caribbean, Cocos, Eurasian, North American, and South American plates differs between models by more than 10°; (3) in places the speed of the Australian, Caribbean, Cocos, Indian, and Nazca plates differs between models by more than 8 mm/yr. Although 27 of the 30 RM2 Euler vectors differ with 95% confidence from those of NUVEL‐1, only the AM1‐2 Arabia‐hotspot and India‐hotspot Euler vectors differ with 95% confidence from those of HS2‐NUVEL1. Thus, substituting NUVEL‐1 for RM2 in the inversion for plate velocities relative to the hotspots changes few Euler vectors significantly, presumably because the uncertainty in the velocity of a plate relative to the hotspots is much greater than the uncertainty in its velocity relative to other plates.
Triggered slip on the Calaveras Fault during the magnitude 7.1 Loma Prieta, California, Earthquake
Authors: McClellan P. H. , Hay E. A.
Published: February 2008

After the magnitude (M) 7.1 Loma Prieta earthquake on the San Andreas fault we inspected selected sites along the Calaveras fault for evidence of recent surface displacement. In two areas along the Calaveras fault we documented recent right‐lateral offsets of cultural features by at least 5 mm within zones of recognized historical creep. The areas are in the city of Hollister and at Highway 152 near San Felipe Lake, located approximately 25 km southeast and 18 km northeast, respectively, of the nearest part of the San Andreas rupture zone. On the basis of geologic evidence the times of the displacement events are constrained to within days or hours of the Loma Prieta mainshock. We conclude that this earthquake on the San Andreas fault triggered surface rupture along at least a 17‐km‐long segment of the Calaveras fault. These geologic observations extend evidence of triggered slip from instrument stations within this zone of Calaveras fault rupture.
On determining ice accumulation rates in the past 40,000 years using in situ cosmogenic 14C
Authors: Lal D. , Jull A. J. T.
Published: February 2008

Radiocarbon is produced in situ in ice by nuclear spallations of oxygen by cosmic ray neutrons. As the firn accumulates, it acquires a predictable concentration of in situ14C, inversely proportional to the rate of accumulation. Most of this production occurs when the amount of overlying ice is less than (2–3) Λ, where Λ is the absorption mean free path for cosmic radiation in ice, about 150 g · cm−2, i.e. within the top 10 m. In most accumulation areas, this is firn. In situ produced 14C is added to the firn as it accumulates, and is not expected to be lost by diffusion. During the firnice transition, atmospheric CO2 is trapped, adding 14CO2 to the ice. The signature of in situ14C is however not obliterated since ∼ 60% of in situ14C is instantly oxidized to 14CO in the ice. We discuss the results available to date and propose that this in situ14CO can be used to determine ice accumulation rates back to 40,000 yrs in the past.
azimuthal variation of Coda Q in northern Taiwan
Authors: Wang Jeen‐Hwa , Liu Kun‐Sung
Published: February 2008

Seismograms of local earthquakes recorded on the short‐period sensor of the TATO station (one of the SRO stations) near Taipei, northern Taiwan are used to determine values of coda Q (Qc). Results show the azimuthal dependence of the values of Qc. A correlation between the values of Qc and the tectonics of the region is determined.The value of Qc is small in the oceanic lithosphere, intermediate in the plate boundaries and large in the continental lithosphere.
Role of the Eastern California Shear Zone in accommodating Pacific‐North American Plate motion
Authors: Dokka Roy K. , Travis Christopher J.
Published: February 2008

The newly recognized Eastern California shear zone (ECSZ) of the Mojave Desert‐Death Valley region has played a major, but previously underappreciated role in accommodating the dextral shear between the Pacific and North American plates in late Cenozoic time. Comparison of integrated net slip along the shear zone with motion values across the entire transform boundary indicates that between 9% and 23% of the total relative plate motion has occurred along the ECSZ since its probable inception ∼10–6 Ma. Long‐term integrated shear along the ECSZ (6–12 mm yr−1) is similar to historic measurements (6.7±1.3 mm yr−1). Time‐space patterns of faulting suggest that shear was concentrated in the eastern part of the Mojave Desert block and Death Valley during late Miocene and early Pleistocene time, but that the locus of faulting in the south‐central Mojave jumped westward between 1.5 and 0.7 Ma.
Upper‐mantle velocity structure of the Great Basin
Authors: Dueker Ken , Humphreys Eugene
Published: February 2008

Teleseismic P‐wave travel‐times measured in the eastern Great Basin show ∼1 sec variations in travel‐time residuals. Inversion of these data images an alternating sequence of high‐ and low‐velocity upper‐mantle bodies trending NE across the eastern margin of the Great Basin. Low‐velocity mantle lies beneath the volcanic trends of the eastern Snake River Plain and the St. George volcanic field. These two low‐velocity trends are separated by high‐velocity mantle extending from northern Utah to SW Wyoming. Combining these results with seismic data from the western Great Basin reveals a continuation of these upper‐mantle trends across the Great Basin.
Aseismic slip on the San Andreas Fault south of Loma Prieta
Authors: Behr J. , Bilham R. , Bodin P. , Burfoid R. O. , Bürgmann R.
Published: February 2008

Two digital creepmeters installed within the San Andreas fault zone after the 18 Oct 1989 Loma Prieta main shock show less than 1 cm of post seismic right‐lateral slip in the four months following the earthquake. At Mt. Madonna road a 23 mm coseismic fracture slipped a further 3 mm after heavy rain, and at Nyland Ranch near San Juan Bautista the fault slipped approximately 9 mm starting 42 days after the main shock. If the current trend at Nyland Ranch persists, more than 2 cm of post seismic slip will develop by 1991. At both sites minor left‐lateral displacements occurred which are attributed to near‐surface soil effects. The abutments of the railroad bridge across the Pajaro River at Chittenden, which were extended by the 1906 earthquake, were not extended during the Loma Prieta event although they have evidently moved apart by more than 7 cm since bridge reconstruction in 1940. This corresponds to 10 cm of right‐lateral slip which could be related to M>5 events in mid‐century or could be due to aseismic slip at a mean rate of 2.1 mm/a. The absence of significant surface slip within the fault zone in the decades before and the months following the Loma Prieta event suggests either that near‐surface deformation is distributed over a wide zone or that a slip deficit remains. Several authors have proposed this region as a future location for M≈5 events.
Seismic anisotrdpy in granuulte facies rocks of the Arunta Block, central Australia
Authors: Greenhalgh S. A. , Wright Cedric , Goleby Bruce , Soleman Sugiharto
Published: February 2008

Using travel times from explosive sources recorded at distances less than 36 km, evidence for P‐wave anisotropy was obtained in an area of central Australia where granulite facies rocks from the lower crust are exposed at the surface; these rocks form the hanging wall of one of the most prominent ancient thrust structures seen anywhere in a continental interior. The azimuthal variation in seismic velocity for rocks at depths less than about 1 km is about 5%, and is comparable in magnitude to values reported for both continental and oceanic upper mantle. The maximum velocity (east‐west) is parallel to the predominant strike direction of gneissic foliation observed in outcrop in the survey region, which was produced during granulite facies metamorphism at about 1,800 Ma.