bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical wind shears, turbulence and non‐turbulence in the troposphere and stratosphere
Authors: Weinstock Jerome
Published: February 2008

A theoretical calculation is made of σ(h), the standard deviation of vertical wind shears, in terms of the turbulence energy dissipation rate ε and Brunt‐Väisälä frequency ωB. This calculation provides a theoretical basis for the empirical power law relation σ(h) = A hm obtained by rocket and balloon wind soundings; it also provides a scaling of σ(h) with atmospheric conditions. The intervals h ranging from about 50m to 1000m are determined by buoyancy subrange turbulence, and smaller shear intervals are determined by inertial subrange turbulence. The theoretical σ(h) allows ε to be predicted from vertical wind soundings in the troposphere and stratosphere. The predicted value of ε in the troposphere agrees with the value obtained by Kung. However, the predicted stratospheric value of ε is larger than obtained by Lilly et al. from HICAT flights. This discrepancy in stratospheric ε is attributed to non‐turbulent, low frequency, short scale, quasi‐horizontal motions of the stratosphere; motions that contribute to vertical wind soundings but not to gust measurements by horizontal HICAT flights.
Kelvin‐Helmholtz instability and the variation of geomagnetic pulsation activity
Authors: Lee L. C. , Olson J. V.
Published: February 2008

It is shown that the observed local time variation of dayside geomagnetic micropulsations is consistent with the Kelvin‐Helmholtz generation mechanism operating at the magnetopause. The variation of the angle between the interplanetary magnetic field and the magnetopause around the magnetosphere causes variations in the magnetosheath magnetic field, which in turn lead to local time variations in micropulsation amplitudes. Morning sector pulsations are expected to be larger than afternoon sector pulsations. Furthermore, large‐amplitude pulsations are expected to be more frequently observed when the angle between the interplanetary magnetic field and the solar wind velocity in front of the bow shock is small.
Chemical composition of Mount St. Helens volcanic ash
Authors: Taylor H. E. , Lichte F. E.
Published: February 2008

Volcanic ash samples from the May 18, 1980, Mount St. Helens eruption were analyzed for major, minor, and trace composition by a variety of analytical techniques. Results indicate that the basic composition of the ash consists of approximately 65% SiO2, 18% Al2O3, 5% FetO3, 2% MgO, 4% CaO, 4% Na2O, and 0.1% S. Thirty seven trace metals are reported including Ba, Cu, Mn, Sr, V, Zn, and Zr. A change in the chemical composition of the ash as a function of distance from the volcano is related to a similar change in physical characteristics of the ash. Water soluble components were also determined after column leaching experiments were performed. Concentration levels of soluble salts were found to be moderately high (1500‐2000 µg/g) with molar ratios suggesting the presence of NaCl, KCl, CaSO4, and MgSO4. Heavy metals such as Cu, Co, Mn, and Zn were found at appreciable concentrations (10‐1000 µg/g). Unexpectedly high concentration levels of ammonium (45 µg/g) and nitrate (100 µg/g) ions as well as dissolved organic carbon (130 µg/g) were observed in several ash leachates. Results for fluoride and boron show low average levels of ∼5 and ∼ 0.5µg/g, respectively.
Paleomagnetism of the Leucite Hills volcanic field, southwestern Wyoming
Authors: Sheriff Steven D. , Shive Peter N.
Published: February 2008

Paleomagnetic results have been determined for 41 sites, in lava flows and plug domes, in the 300 km² Leucite Hills volcanic field (1.1 ± .4 mybp), southwest Wyoming. Rock magnetic and petrographic studies show that magnetite is the important remanence carrier. Primary spinel and rhombohedral phases are both present. Analysis of VGP positions from 35 of these sites yields a paleomagnetic pole at 113.3°E, 87.4°N (α95 = 7.2°, δ = 23.0°) which, as expected, is coincident with the present day rotation axis. Generally, the ultrapotassic rocks of the Leucite Hills are magnetically stable; both polarities are recorded in the field along with a few directions which may be transitional. About 90% of the sites are reversely magnetized. Due to a lack in precision of the age determination for the Leucite Hills, the normal flows cannot be constrained to the Brunhes epoch or either the Cobb Mountain or Jaramillo events.
Tunable diode laser measurement of nitrous oxide in air
Authors: Connell Peter S. , Perry Robert A. , Howard Carleton J.
Published: February 2008

Infrared derivative spectroscopy using a tunable diode laser coupled to a multipass absorption cell has been used to measure the nitrous oxide mole fraction in tropospheric air samples. The individual measurement precision was 1.5% (1σ). No temporal variation outside the statistical error limits was observed in 26 measurements over a two month period. Absolute values were obtained by comparison to manometrically calibrated standards prepared by static dilutions of N2O in air to ambient levels. The mean mole fraction of N2O in dry air was determined to be 298±5 ppb where the error includes an estimate of possible systematic errors in standard preparation.
Dynamic and static moduli
Authors: Cheng C. H. , Johnston David H.
Published: February 2008

Static and dynamic bulk moduli (Ks and Kd) are measured as continuous functions of pressure from zero to 2‐3 kilobars for two sandstones, a tuff, limestone, granite, and oil shale. Results for the sandstones and granite are in good agreement with previously reported data with Ks/Kd varying from about 0.5 at atmospheric pressure to close to unity at pressures 2 kilobars and above. For rocks behaving elastically under static loading, the Ks/Kd ratio is inversely related to the microcrack density. For the limestone, time dependent deformation associated with pore collapse results in Ks/Kd ratios approaching 0.1 at high pressure. Upon unloading, while initially high ( ∼ 1.0) at high pressures, Ks/Kd becomes lower than values obtained during loading at low pressures ( < 1 kilobar) due to opening of microcracks generated during pore collapse. For the oil shale, in which few microcracks exist, Ks/Kd remains relatively constant with pressure at a value of about 0.7.
High‐frequency Pn,Sn velocities: Some comparisons for the western, central, and South Pacific
Authors: Walker Daniel A.
Published: February 2008

High‐frequency Pn,Sn velocities for earthquakes originating in the subduction zones of the Western Pacific suggest that the travel paths of these phases, recorded in the range of 12° to 30°, may be significantly different from those of Pn,Sn phases recorded at distances less than 12° or greater than 30°. This suggestion is supported by high‐frequency Pn,Sn velocities for intra‐plate earthquakes in the Central and South Pacific.
Thermal property measurements in a fresh pumice flow at Mt. St. Helens
Authors: Hardee H. C.
Published: February 2008

A thermal penetrator that was air dropped into a freshly emplaced pumice flow at Mt. St. Helens yielded information on the in‐situ thermal properties of the pumice. The in‐situ conductivity‐density‐specific heat product at a depth of 60 cm was found to be 7.24 × 10−5cal²/cm4s−°C² at an average pumice temperature of 200°C. Using this data, values for the average in‐situ thermal conductivity (2.9 × 10−4cal/cm−s−°C) and thermal diffusivity (1.2 × 10−3cm²/s) were estimated. These thermal properties are of use in studies of pumice cooling and in the interpretation of infrared remote sensing data.
Possible tilt phenomena observed as water level anomalies along the Los Angeles aqueduct
Authors: Leary Peter C. , Malin Peter E. , Strelitz Richard A. , Henyey Thomas L.
Published: February 2008

Water levels in the Los Angeles Aqueduct in southern California fluctuate in a manner that are not easily attributable to normal aqueduct operations. Simple hydraulics suggests that large scale earth tilt can register as water level anomalies with a sensitivity of about .01 ft/microradian. Two aqueduct anomalies which coincide spatially and temporally with independently observed deformational phenomena are used to explore this suggestion.
Anti‐solar acceleration of ionospheric plasma across the Venus terminator
Authors: Knudsen William C. , Spenner Karl , Miller Kent L.
Published: February 2008

We demonstrate that the horizontal ionospheric particle pressure gradient across the Venus terminator is the principal body force accelerating the plasm to the observed anti‐solar velocity. The large scale horizontal
electromagnetic body force is typically an order of magnitude smaller than the particle pressure gradient. The viscous body forces above 300 km—drag or acceleration—are also an order of magnitude smaller than the pressure gradient body force. In the immediate vicinity of the ionopause where the ionospheric plasma density decreases below 10³ ions/cm³ and the magnetic field strength increases, the electromagnetic body force may become significant. The electromagnetic body force may also be significant in the nightside ionosphere. The bulk of the ionospheric flow momentum is not derived from the ionosheath momentum.
Voyager measurement of the rotation period of Saturn's magnetic field
Authors: Desch M. D. , Kaiser M. L.
Published: February 2008

We determine Saturn's radio rotation period using measurements made by the Planetary Radio Astronomy experiment onboard the Voyager spacecraft. The sidereal period deduced is 10 hr 39 min 24 sec ±7 sec. The radio rotation period is presumably that of the planet's magnetic field. We propose a provisional Saturn longitude convention, and we provide equations to compute a longitude ephemeris and to transform between the proposed system and the (10 hr 14 min) system used for the Pioneer 11/Saturn encounter. In addition, we evaluate the degree of longitude smearing which could result over the long term from the merging of data sets organized in this system. Finally, no evidence of control of the radio emission by any of Saturn's satellites is found.
A rapid method for magnetic granulometry with applications to environmental studies
Authors: Banerjee Subir K. , King John , Marvin James
Published: February 2008

We have developed a rapid method of characterizing the fine‐scale variation (sub‐micron to hundreds of microns, µm) in the grain size of magnetite in long sediment cores. This method is a new rock magnetic tool and can be readily applied to the following disciplines: (1) environmental studies; (2) hydrology; (3) petrology; and (4) geomagnetism.

The method consists of a comparative plot of the depth variation of two magnetic parameters. The first parameter, low field (less than 0.1 millitesla, mT, or 1 Oe) susceptibility in a steady field is plotted on the abscissa. The second parameter, anhysteretic remanent magnetization (ARM) imparted by a smoothly decreasing AF of peak value 100 mT (1,000 Oe) in the presence of a weak steady field (0.01‐0.1 mT, or 0.1‐1 Oe) is plotted on the ordinate. For a sediment column in which the magnetic mineral is magnetite, a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points (χ, ARM).
Earthward transport of energetic protons in the Earth's plasma sheet
Authors: Lui A. T. Y. , Krimigis S. M.
Published: February 2008

The transport of magnetospheric energetic protons (Ep ∼ 0.29‐0.50 MeV) in the earth’s plasma sheet at downstream distances of ∼ 30‐45 Re is studied on a statistical basis with 5.5 min average data from the APL/JHU Charged Particle Measurement Experiment on the IMP 7 and IMP 8 spacecraft. The analysis shows that there is a net earthward transport of these particles, although tailward streaming is observed as frequently as earthward streaming. The net transport is earthward for all Kp conditions and for low as well as high flux thresholds. The averaged net particle flux is ∼ 2 × 10²cm−2sec−1, which translates into averaged particle and energy fluxes over the plasma sheet region of ∼ 4 × 1022sec−1 and ∼ 2 × 1016ergs sec−1, respectively. It is suggested that this particle influx could be a possible source of protons for the earth’s outer radiation belt.
Potential for geophysical experiments in large scale tests
Authors: Dieterich James H.
Published: February 2008

Potential research applications for large‐specimen geophysical experiments include measurements of scale dependence of physical parameters and examination of interactions with heterogeneities, especially flaws such as cracks. In addition, increased specimen size provides opportunities for improved recording resolution and greater control of experimental variables. Large‐scale experiments using a special purpose low stress (<40 MPa) biaxial apparatus demonstrate that a minimum fault length is required to generate confined shear instabilities along pre‐existing faults. Experimental analysis of source interactions for simulated earthquakes consisting of confined shear instabilities on a fault with gouge appears to require large specimens (˜1m) and high confining pressures (> 100 MPa).
Large scale laboratory testing of hydraulic fracturing
Authors: Haimson Bezalel C.
Published: February 2008

A large scale laboratory testing facility for hydraulic fracturing studies is strongly recommended. The theory behind the fracturing mechanism is well developed, the field utilization of the method is multifaceted and rapidly growing; yet laboratory verification of many of the assumptions and theoretical results is lacking. The main reason for the scarcity of experimental work is that until now only small size specimens (linear dimensions approx. 10 cm) could be tested in existing facilities, a size not suitable for studying fracture extension and control. Large scale testing of 1 m³ rock samples should provide the experimental backing that is missing in our interpretation of fracturing events.
Positive cloud‐to‐ground lightning flashes in severe storms
Authors: Rust W. David , MacGorman Donald R. , Arnold Roy T.
Published: February 2008

The occurrence of cloud‐to‐ground flashes that effectively lower positive charge to earth (+CG flash) over flat terrain has been documented in the mature stage of severe thunderstorms. Of the 31 documented +CG flashes, most had only one return stroke. Zero‐to‐peak rise times for the strokes averaged 7 µs. The +CG flashes averaged 520 ms in duration, with 25 percent lasting more than 800 ms. Many of these had field changes suggestive of continuing current. Positive flashes have been observed to emanate from several regions of severe storms: high on the back of the main storm tower, through the wall cloud, and from the downshear anvil. Visually most of these positive flashes have emanated from high in the storm, and acoustic mapping of two shows thunder sources to a height of about 15 km.
Seismic anisotropy observed in upper oceanic crust
Authors: Stephen R. A.
Published: February 2008

Seismic anisotropy in the upper 1500m. of oceanic basement has been observed by polarization analysis of three‐component borehole seismometer records. The most convincing evidence for the anisotropy is shear wave splitting for explosive sources at four azimuths. Compressional wave particle motion deviations suggestive of anisotropy are also observed but they may be caused by lateral inhomogeneities. The anisotropy was not resolved by travel‐time analysis. The observed velocities and particle motions in the horizontal plane can be modelled to within a standard deviation by assuming a perfectly elastic, homogeneous, anisotropic layer 2 with hexagonal symmetry and a horizontal symmetry axis. The most probable cause of the anisotropy is preferred crack orientation.
Two‐layer mantle convection and the depletion of radioactive elements in the lower mantle
Authors: Schubert G. , Spohn T.
Published: February 2008

Only a small percentage of the mantle’s total content of radioactive elements can be in the lower mantle if this region convects steadily and separately from the upper mantle. Recent geochemical models of a depleted upper mantle and an undepleted lower mantle are thus inconsistent with a steady thermal model involving distinct upper and lower mantle convection cells. Steady two‐layer mantle convection requires a depleted lower mantle and an undepleted upper mantle to match the observations of surface heat flow and mantle viscosity. The constraint on the abundance of radioactive elements in the lower mantle depends on the existence of at least one thermal boundary layer at the upper mantle‐lower mantle interface with thickness comparable to that of the surface thermal boundary layer. Since the temperature drop across an interface boundary layer is limited by the relatively small difference between the solidus temperature and the upper mantle temperature, the amount of heat which can be transferred across this layer is small compared with the surface heat flow. The upper limit on the concentration of radioactive elements in the lower mantle can be relaxed only if both the lower boundary layer of the upper mantle cell and the upper boundary layer of the lower mantle cell are extremely thin or absent altogether, which we consider, however, highly unlikely.
Size distribution of 210Pb aerosols over oceans
Authors: Sanak J. , Gaudry A. , Lambert G.
Published: February 2008

We have studied the size distribution of 210Pb aerosols collected by a cascade impactor during a cruise from Marseille (France) to Amsterdam Island (South Indian Ocean). It was shown that 70 to 90% of the activity is measured in particles with a diameter smaller than 1.2 µm either in a continental atmosphere or in open ocean. This result confirms that 210Pb is a good tracer for aerosols produced by gas‐to‐particle conversion.
A scattering model to explain seismic Q observations in the lithosphere between 1 and 30 Hz
Authors: Dainty A. M.
Published: February 2008

Observations of lithospheric Q for shear waves in the range 1‐30 Hz reported in the literature are examined using a scattering model consisting of randomly distributed spheres. For the single scattering approximation I have assumed 1/Q = 1/Qi + gv/ω, where Qi is the intrinsic Q due to anelasticity, v is the velocity of shear waves, ω is angular frequency and g is the turbidity. g is taken as a constant in this paper; since g = ∫ n(a)σda, where n(a)da is the number of scattering spheres of radius a/unit volume and σ is the scattering cross‐section for a sphere, this suggests that geometrical scattering dominates. This will be true for ka > 1, where k is wavenumber. Based on this criterion and the observation that Q is large (i.e. g small) at a frequency of 0.05 Hz, a is of the order of magnitude 1‐10 km. Fits of observations of shear wave Q from Japan and Central Asia indicate that Qi = 2000 ± 500 for the lithosphere of both regions; g = 0.01 km−1 for the Japan observations and g = 0.005 km−1 for Central Asia.
Evidence for a short tropospheric residence time for carbon disulfide
Authors: Bandy Alan R. , Maroulis Peter J. , Shalaby Lamaat , Wilner Lane A.
Published: February 2008

Our recent measurements of the concentrations of CS2 in the background troposphere suggest that the atmospheric residence time of this substance is short, probably on the order of ten days. This conclusion is based on the very low CS2 concentrations found in the free troposphere (<3 pptv) and the relatively large concentrations (30 pptv) found in the boundary layer. Such a rapid decrease in concentration with altitude can be explained in a straightforward way only if the residence time of CS2 is less than the characteristic vertical mixing time of the troposphere, which is of the order of ten days.
Magnetic anomaly maps from 40°N to 83°N derived from MAGSAT satellite data
Authors: Coles R. L. , Haines G. V. , van Beek G. Jansen , Nandi A. , Walker J. K.
Published: February 2008

Stringent selection criteria using Kp indices, local magnetic activity estimates, and visual intercomparisons, followed by a statistical screening procedure have enabled the production of preliminary scalar and vector component magnetic anomaly maps derived from Magsat data at northern high latitudes, in spite of frequent external field disturbances. Comparisons between the maps and with other magnetic maps and geological information confirm their general validity.
The spectrum of atmospheric velocity fluctuations at 8 km and 86 km
Authors: Balsley B. B. , Carter D. A.
Published: February 2008

Power spectra of wind variability (power spectral density vs. period) between roughly 3m and 8d are presented for the high‐latitude summer troposphere (8 km) and mesosphere (86 km). These results were obtained from an essentially continuous record of wind measurements using the Poker Flat MST radar in Alaska.
Upper stratospheric photolysis of NaOH
Authors: Rowland F. Sherwood , Makide Yoshihiro
Published: February 2008

The ultraviolet absorption cross sections for NaOH have been calculated from the flame absorption spectroscopic data of Daidoji, and used for estimates of solar ultraviolet photodissociation rates in the stratosphere. One cross section maximum of 1.8 × 10−17 cm² occurs at 234 nm, and another of 1.0 × 10−17 cm² is found at 320 nm. Absorption in the 200‐265 nm band corresponds to a photodissociation coefficient for NaOH of 2 × 10−3 sec−1 at 50 km decreasing to 10−4 sec−1 at 35 km, both for overhead sun. If absorption in the 285‐350 nm band leads to molecular decomposition, the photodissociation coefficient is approximately 6 × 10−2 sec−1 at all altitudes in both the stratosphere and troposphere. The major photodissociation pathway leads to Na(²S) plus OH, and has a wavelength threshold of 346±12 nm.
Observations of large electric fields near the plasmasheet boundary by ISEE‐1
Authors: Cattell C. A. , Kim M. , Lin R. P. , Mozer F. S.
Published: February 2008

We report the first observations of large electric field spikes (up to ∼ 80 mV/m) at distances of 7 ‐ 23 RE. Almost all of these spikes are detected within one minute of encountering the high latitude plasmasheet boundary, as identified by energetic particle detectors. These strong electric fields occur in regions of enhanced low frequency turbulence and in regions of field‐aligned current flow. Individual electric field spikes are well‐correlated with small‐scale gradients in particle fluxes and small‐scale currents. If these high altitude events are mappings of the low altitude electrostatic shocks, these data provide evidence that poleward auroral field lines map to the boundary of the plasmasheet.
Determination of acoustic velocities in xenon and methane hydrates by Brillouin Spectroscopy
Authors: Whiffen B. L. , Kiefte H. , Clouter M. J.
Published: February 2008

The technique of Brillouin spectroscopy has, for the first time, been used to determine the longitudinal sound velocities in pure methane hydrate and xenon hydrate. The samples were artificially grown and polycrystalline. The velocity in methane hydrate, which on theoretical grounds is relatively independent of the degree of cage occupancy, was determined experimentally to be approximately 0.88 that of ice.
Plasma behavior during energetic electron streaming events: Further evidence for substorm‐associated magnetic reconnection
Authors: Bieber J. W. , Stone E. C. , Hones E. W. , Baker D. N. , Bame S. J.
Published: February 2008

A recent study showed that streaming energetic (〉200 keV) electrons in Earth's magnetotail are statistically associated with southward magnetic fields and with enhancements of the AE index. It is shown here that the streaming electrons characteristically are preceded by a ∼15 minute period of tailward plasma flow and followed by a dropout of the plasma sheet, thus demonstrating a clear statistical association between substorms and the classical signatures of magnetic reconnection and plasmoid formation. Additionally, a brief upward surge of mean electron energy preceded plasma dropout in several of the events studied, providing direct evidence of localized, reconnection‐associated heating processes.
Voyager ultraviolet stellar occultation measurements of the composition and thermal profiles of the Saturnian upper atmosphere
Authors: Festou M. C. , Atreya S. K.
Published: February 2008

Occultation of the star δ‐Scorpii by Saturn as recorded by the Voyager Ultraviolet Spectrometer yields the value of the exospheric temperature in the equatorial region to be 800 (+150, −120) K at an altitude of 1540 km above the 1‐bar atmospheric pressure level; the H2‐density at 1540 km is determined to be 5 (+3.6, −1.8) × 109 cm−3. Temperature gradient in the thermosphere is found to be 1.25 (+0.05, −0.07) K km−1. Methane volume mixing ratio at 965 km above the 1‐bar pressure level is determined to be 1.5 × 10−4.
Seasonal variations in stratospheric NO2at 45°S
Authors: McKenzie R. L. , Johnston P. V.
Published: February 2008

We present daily twilight measurements of stratospheric NO2at latitude 45°S for the period from December 1980 to May 1982. The technique used is ground based long path absorption spectroscopy. The deduced column abundances are in general agreement with comparable measurements in the Northern Hemisphere, with evening abundances exhibiting a seasonal variation from 3.2 × 1015mol.cm−2to 6.4 × 1015mol.cm−2in phase with the cycle of annual variation in length of day. The corresponding range in morning abundances is from 2 × 1015mol.cm−2to 4.5 × 1015mol.cm−2. The lower morning values are generally consistent with an overnight decay of NO2with a time constant of about a day.
Mechanism of the olivine to spinel phase transformation in Ni2SiO4
Authors: Boland J. N. , Liebermann Robert C.
Published: February 2008

An electron microscope study of the olivine to spinel transformation in Ni2SiO4 has revealed the nature of the defect structures in the transforming olivine immediately ahead of the migrating olivine‐spinel interphase boundary. The residual olivine has a high density of [100] and [001] Burger's‐vector dislocations (1 to 5 × 109 cm−2). No stacking faults or dissociated dislocations are observed in the residual olivine, although a significant number (∼108 cm−2) of [010] dislocations are activated by the extreme synthesis conditions (52 kbar, 1100° C). This result may have important applications in the study of paleo‐deformation of olivine. The mechanism of the transformation in the fine‐ground sample appears to be a nucleation and growth process with no evidence to support a martensitic mechanism.
Identifying the coordination of silicon by magic‐angle‐spinning NMR: Thickness of the Venus lithosphere estimated from topography and gravity” by A. Cazenave and K. Dominh
Authors: Thomas John M. , Gonzalez‐Calbert Jose M. , Fyfe Colin A. , Gobbi Gian C. , Nicol Malcolm
Published: February 2008

Six‐coordinated Si in stishovite yields a sharp 29Si MASNMR signal at −191.3 ±0.2 ppm from TMS, well‐removed from the characteristic signal associated with tetrahedral coordination in quartz, cristobalite, and other, less crystalline siliceous solids.
Heat flux induced by gravity waves
Authors: Weinstock J.
Published: February 2008

A derivation is given of the heat flux induced by large amplitude gravity waves; the case where nonlinear or turbulent damping exceeds molecular damping. This case is typical of the middle atmosphere. The derivation is based on a simple algorithm for converting the linear dispersion relation for gravity waves into a nonlinear one, and generalizes a recent derivation by Walterscheid. The derived heat deposition flux is shown to cause local cooling where the waves are close to saturation, but could cause heating where the waves are far from saturation. It is then proven that the heat flux is related to the diffusivity and to the wave momentum deposition flux by simple expressions. Hence, knowledge of one transport coefficient is practically equivalent to knowledge of the other two. The derivation is limited to waves that have some randomicity.
Seismic activity related to the March‐April, 1982 eruptions of El Chichon Volcano, Chiapas, Mexico
Authors: Havskov J. , De la Cruz‐Reyna S. , Singh S. K. , Medina F. , Gutiérrez C.
Published: February 2008

Interesting seismic activity occurred before, during, and following the recent eruptions of El Chichon Volcano in southeastern Mexico. Several eruptions took place in late March and early April 1982, ejecting large amounts of andesitic ash and pumice. The first eruption was preceded by one month of intense shallow seismicity (h∼5km). Two days before the first eruption of March 29, the seismicity changed character and was most likely shallow (h∼2km). This shallow seismicity continued until the last and probably largest eruption on April 4, after which only deep seismicity was observed (h∼15km). The different nature of shallow events and deep events suggest that the former are directly related with the magma movements and ground water interactions while the latter are probably controlled by regional tectonic stresses, acting on the weakened region left by the eruption at those depths.
Collisionless dissipation processes in quasi‐parallel shocks
Authors: Quest K. B. , Forslund D. W. , Brackbill J. U. , Lee K.
Published: February 2008

The evolution of collisionless, quasi‐parallel shocks (θBn < 45°, where θBn is the angle between the shock normal and the upstream magnetic field) is examined using two dimensional particle simulations. Reflected ions upstream from the shock are observed with average guiding center velocity and gyrational energy which agree well with the prediction of simple specular reflection. Strong ion heating through the shock ramp is apparently caused by large amplitude whistler turbulence. A flux of suprathermal electrons is also observed upstream with increased flux oblique to the magnetic field direction. Much stronger ion heating occurs in the shock than electron heating. The relevance of this work to the earth's bow shock is discussed.
Paleomagnetic evaluation of the Orocline Hypothesis in the central and southern Appalachians
Authors: Schwartz Susan Y. , Van der Voo Rob
Published: February 2008

The axial traces of the major Appalachian folds change azimuthal direction from a NE‐SW orientation to a N‐S orientation in the area of the Pennsylvania Salient and swing back to a NE‐SW orientation in the vicinity of the Virginia Reentrant. All available paleomagnetic data from the folded Appalachians have been examined to test the Appalachian orocline hypothesis. Pre‐deformational site‐mean directions from suitable studies were rotated by the amount required to bring the strike of the sampled beds into coincidence with an average trend of the Central and Southern Appalachians (N35E). A comparison of clustering of site‐means before and after this correction, reveals that in all cases unbending of the arc causes site‐mean directions to disperse. This dispersal demonstrates that the curvature of the Appalachian orogen is to a very large degree a primary feature rather than a feature which resulted from the bending of initially straight fold axes.
Origin of lunar meteorite ALHA 81005: Clues from the presence of Terrae clasts and a very low‐titanium mare basalt clast
Authors: Treiman Allan H. , Drake Michael J.
Published: February 2008

Petrographic data and pyroxene compositions indicate that meteorite ALHA 81005 is a breccia from the terrae of the Earth's Moon. Thin section ALHA 81005,9 includes ferroan anorthositic clasts, a lone clast of Mg‐suite plutonic composition, fragments which are intermediate in composition between ferroan anorthosite and Mg‐suite plutonics, and a clast of very low‐titanium mare basalt. Fragments of norite and harzburgite have mineral compositions like ferroan anorthosite, and a clast of ferroan anorthosite has pyroxenes with lower molar Mg/(Mg+Fe) than in known pristine rocks. The Mg‐suite protoliths for the clasts of intermediate composition are inferred to be magnesian troctolites, spinel troctolites and feldspathic lherzolites. Although clasts of these lithologies are not present in ALHA 81005,9, mineral fragments from them are present. A single basaltic clast is of mare origin, based on the molar Mg/(Mg+Fe) ratio and Cr content of its pyroxenes. The composition of its plagioclase and the molar Ti/(Ti+Cr) ratios of its pyroxenes indicate that the clast is a fragment of very low‐titanium (VLT) mare basalt. If this basalt is significantly younger than the last basin‐forming impact event (≃ 3.9 × 109 years ago), its presence probably constrains the source crater for ALHA 81005 to be within a hundred kilometers of a VLT mare basalt flow.
Trapped noble gases indicate lunar origin for Antarctic Meteorite
Authors: Bogard D. D. , Johnson P.
Published: February 2008

The isotopic abundances of the noble gases (He, Ne, Ar, Kr, Xe) are reported for Antarctic meteorite ALHA81005. It contains solar wind‐implanted gases whose absolute and relative concentrations are quite similar to lunar regolith samples but not to other meteorites. ALHA81005 also contains a large excess 40Ar component which is identical to the component in lunar fines implanted from the lunar atmosphere. Large concentrations of cosmogenic 21Ne, 82Kr and 126Xe in ALHA81005 indicate a total cosmic ray exposure age of ≥ 2×108 years. The noble gas data alone are strong evidence for a lunar origin of this meteorite.
Large‐scale thermal anomalies in the California Current during the 1982‐1983 El Niño
Authors: Simpson James J.
Published: February 2008

The large‐scale thermal structure of the California Current during 1982‐83 shows several anomalous conditions: warm sea surface temperature anomalies (∼1‐2°C), depression of the thermocline by 50 m or more, and pronounced subsurface warming (∼3‐4°C) relative to the 30‐year mean. The subsurface anomaly is much greater than the surface anomaly. These persistent (>6 months) structures, coupled with unusually high sea levels along the North American coast, show that a major Californian "El Niño" occurred during 1982‐83. The data support the conclusion that the expansion and intensification of the Aleutian low and the decrease in strength of the Pacific high produced an anomalous basin‐wide atmospheric circulation which coupled directly to the large‐scale oceanic wind‐driven circulation to produce the Californian "El Niño." The enhanced transport from the west (offshore California) and south (Baja California), which such a circulation would produce, is consistent with the observed water properties. The equatorial 1982‐83 El Niño is probably related to the Californian "El Niño" through an atmospheric teleconnection between equatorial sea surface temperature and the atmospheric Hadley circulations.
The El Chichon volcanic cloud: An introduction
Authors: Pollack James B. , Toon Owen B. , Danielsen Edwin F. , Hofmann David J. , Rosen James M.
Published: February 2008

Background information is provided on the nature and importance of the El Chichon volcanic cloud and an introduction is given to the papers of this special issue.
Contact stiffness in granular porous materials: Comparison between theory and experiment
Authors: Winkler Kenneth W.
Published: February 2008

Propagation of acoustic waves in earth materials is controlled to a large extent by the properties of the solid frame of the material. In sedimentary materials, interactions at the grain contacts provide a key to understanding the frame properties. In this note, a recent theoretical model by Digby (1981) for acoustic velocities in dry, disordered sphere packs is discussed and applied to experimental data. Central to the model are the normal and tangential stiffnesses at the contacts between grains. We have inverted Digby’s results to give equations for the contact stiffnesses in terms of the measured velocities. These equations have been applied to experimental data from the literature for both unconsolidated glass beads and Berea sandstone at various confining pressures. Taken literally, these results indicate that interactions at real grain contacts are not well described by conventional Hertz‐Mindlin contacts or by modified Digby contacts. Alternatively, the results indicate that the theory requires modifications such as additional contact interactions or distributions of grain sizes, coordination numbers, or contact stiffnesses.
Wave structure in the Venus ionosphere downstream of the terminator
Authors: Brace L. H. , Elphic R. C. , Curtis S. A. , Russell C. T.
Published: February 2008

In the lower ionosphere of Venus, just nightward of the terminator, instruments on the Pioneer Venus Orbiter have revealed nearly coherent wave trains in the electron density, Ne, temperature, Te, and in the east‐west component of the magnetic field, BE. These waves exist primarily below 200 km. They have north‐south wavelengths of the order of 150 km and amplitudes in Ne and Te of about a factor of 2 or 3. BE has an amplitude of about 30 nT but no net value averaged over the waves. A unique phase relationship exists between these three parameters. Ne and Te vary approximately inversely, suggesting that the waves represent vertical plasma motions. Ne maxima and minima tend to occur at zero crossings of BE; i.e., within regions of vertical current. The plasma pressure is roughly constant within the wave and is several times larger than the magnetic pressure. The wave energy is believed to be derived from the steep plasma pressure gradient at the terminator which accelerates ionospheric plasma nightward. The generation process is unknown, but it may involve gradient driven interchange instabilities, or shear instabilities produced by ion‐neutral drag at lower altitudes. Whatever their origin, the waves are important because they represent an energy sink for the transterminator flow that is largely responsible for the maintenance of the nightside ionosphere.
Investigation of a lower mantle shear wave triplication using a broadband array
Authors: Zhang Jiajun , Lay Thorne
Published: February 2008

SH signals recorded by an array of four broadband (Benioff 1‐90) instruments, run by Caltech, are inspected for evidence of a lower mantle shear wave velocity discontinuity previously detected using WWSSN data. Deep focus earthquakes beneath Argentina span the distance range 78° to 82° from the array, where the triplication in the travel time curve produced by the discontinuity is expected to result in an arrival between the direct shear wave, S, and the reflection off of the core‐mantle boundary, ScS. The SH data for these events do show evidence of the arrival; however, the broadband signals also show significant receiver structure complexity. Empirical receiver functions are determined for each station by stacking observations for events in South America closer than 75° from the array. Incorporating these receiver functions into the synthetic modeling demonstrates that lower mantle shear velocity models with a discontinuity fit the observations better than models without one.
Basin wide thermocline displacements along the equator of the Atlantic in 1983
Authors: Katz Eli Joel
Published: February 2008

Observations from five inverted echo sounders deployed between 10°W and 38°30′W along the equator during the spring and summer of 1983 are presented. The annual development of the eastward acting zonal pressure gradient is described and related to the observed zonal wind stress. The minimum and maximum basin wide gradients are observed in mid‐April and in the latter part of July, respectively. The upwelling season in the Gulf of Guinea is identified at the easternmost sounder during May, June, and July. Pulses in thermocline displacement (first deepening, then shallowing) propagate eastward across the basin at speeds of 2.8 and 2.1 m s−1. They arrive at 10°W at the onset and just after the cessation of the seasonal upwelling at that location. Their initialization is related to relaxation periods in the zonal wind. For four of the last five years, the time of the pulse preceding the upwelling is tentatively identified.
A relationship between the height of the tropical tropopause and the global angular momentum of the atmosphere
Authors: Reid George C. , Gage Kenneth S.
Published: February 2008

The angular momentum budget of the atmosphere requires that there be an upward transport of angular momentum in the tropics and a downward transport at midlatitudes. The vertical transport in the tropics is thought to take place in the cores of deep convective clouds, and the same convective activity is thought to play a dominant role in determining the height of the tropopause in the tropics. Accordingly, the average height of the tropical tropopause ought to be positively correlated with the angular momentum of the atmosphere relative to the earth’s surface. The existence of such a correlation on both annual and interannual time scales is shown.
Plasma wave spectra near slow mode shocks in the distant magnetotail
Authors: Scarf F. L. , Coroniti F. V. , Kennel C. F. , Smith E. J. , Slavin J. A. , Tsurutani B. T. , Bame S. J. , Feldman W. C.
Published: February 2008

Recently Feldman et al. (1984), used ISEE‐3 data to analyze variations in charged particle and magnetic field characteristics near plasma sheet boundaries in the distant magnetotail and they demonstrated that several of the crossings had the properties of slow mode shocks. Here we discuss ISEE‐3 plasma wave measurements at two of these crossings, and show that all conventional characteristics of fast collisionless shock spectra are present. Upstream (lobe side) electron plasma oscillations are detected in association with electron heat flux enhancements, and pronounced spectral peaks at lower frequencies are found within the shock layer.
Drift mirror Mode waves in the distant (X ≃ 200 Re) magnetosheath
Authors: Tsurutani B. T. , Richardson I. G. , Lepping R. P. , Zwickl R. D. , Jones D. E. , Smith E. J. , Bame S. J.
Published: February 2008

Drift mirror waves have been detected 207 Re downstream in the distant magnetosheath by instrumentation onboard ISEE‐3. The MHD structures have estimated scale sizes of 4.6 × 104 to 2.3 × 105 km or 130 to 700 proton gyroradii, assuming 1 keV protons. Simultaneous measurements on IMP‐8 indicate that at the time of the events, the earth's magnetosphere was enveloped by a solar flare‐associated interplanetary shock and driver gas. The (shocked) driver gas was characterized by an unusually low plasma density with a β (plasma pressure/magnetic pressure) of ∼ 0.2. From the instability criterion, β ⊥/β11>1+1/β⊥, the magnetosheath plasma should not go mirror‐mode unstable unless the anisotropy, β⊥ / β11 is large, >6. These unusual conditions are met by the demonstrated presence of highly anisotropic, energetic 35‐384 keV ions with P⊥ /P11 ≃ 30. It is calculated that most of the plasma energy density can be due to >1 keV ions. The source of the ions is not well understood, but an appealing possibility is magnetic annihilation of the northward magnetosheath fields with southern hemisphere polar cusp magnetic fields.
Gravity anomalies and the structure of western Tibet and the Southern Tarim Basin
Authors: Lyon‐Caen Hélène , Molnar Peter
Published: February 2008

Gravity anomalies across the western part of the Tarim Basin and the Kunlun mountain belt show that this area is not in local isostatic equilibrium. These data can be explained if a strong plate underlying the Tarim Basin extends southwestward beneath the belt at least 80 km and supports part of the topography of northwest Tibet. This corroborates Norin's inference that late Tertiary crustal shortening has occurred in this area by southward underthrusting of the Tarim Basin beneath the Kunlun. This study places a lower bound on the amount of underthrusting.
Source pulse enhancement by deconvolution of an empirical Green's function
Authors: Mueller Charles S.
Published: February 2008

Observations of the earthquake source‐time function are enhanced if path, recording‐site, and instrument complexities can be removed from seismograms. Assuming that a small earthquake has a simple source, its seismogram can be treated as an empirical Green's function and deconvolved from the seismogram of a larger and/or more complex earthquake by spectral division. When the deconvolution is well posed, the quotient spectrum represents the apparent source‐time function of the larger event. This study shows that with high‐quality locally recorded earthquake data it is feasible to Fourier transform the quotient and obtain a useful result in the time domain. In practice, the deconvolution can be stabilized by one of several simple techniques.

In this paper, the method is implemented and tested on high‐quality digital recordings of aftershocks of the Jan. 9, 1982 Miramichi (New Brunswick) earthquake. In particular, seismograms from a Jan. 17 aftershock (017 13:33 GMT, local mag.=3.5) exhibit path or site effects which complicate the determination of source parameters. After deconvolution, the apparent far‐field source of this event is a simple pulse in displacement with duration ≈ 0.07 second for both P and S.
In‐situ sampling of clouds with a droplet to aerosol converter
Authors: Ogren John A. , Heintzenberg Jost , Charlson Robert J.
Published: February 2008

Cloud droplets are separated from atmospheric trace gases, rain drops and submicrometer aerosol particles on the basis of their aerodynamic properties and evaporated by dry air. The evolved trace gases and residual particles can be analyzed by in‐situ methods and collected for subsequent chemical analysis.
Solar cycle dependence of the location of the Venus bow shock
Authors: Alexander C. J. , Russell C. T.
Published: February 2008

Initial measurements of the Venus bow shock obtained by Pioneer Venus in 1979 near solar maximum indicated that the bow shock was on average 2.44 RV from the center of the planet in the terminator plane. This is 0.35 RV further from Venus than observed by Venera 9/10 in 1976. In the past this discrepancy has been attributed to some effect of the solar cycle. Recent measurements by Pioneer Venus support this interpretation. In 1980 the distance to the bow shock reached a maximum of 2.45 RV and since then has been almost steadily declining toward the distance measured by Venera near solar minimum. The variation in bow shock position is well correlated with the sunspot number and the F 10.7 cm flux over this period. We attribute this behavior to the variation in the neutral atmosphere of Venus with the solar cycle and its subsequent effect on the mass‐loading of the solar wind.
A diffuse plate boundary model for Indian Ocean tectonics
Authors: Wiens Douglas A. , DeMets Charles , Gordon Richard G. , Stein Seth , Argus Don , Engeln Joseph F. , Lundgren Paul , Quible Dan , Stein Carol , Weinstein Stuart , Woods Dale F.
Published: February 2008

Australia and India are conventionally thought to be contained in a single plate divided from an Arabian plate by the Owen Fracture Zone. We propose instead that motion along the nearly aseismic Owen Fracture Zone is negligible and that Arabia and India are contained within a single Indo‐Arabian plate, divided from the Australian plate by a diffuse boundary. This boundary, which trends E‐W from the Central Indian Ridge near Chagos Bank to the Ninetyeast Ridge, and north along the Ninetyeast Ridge to the Sumatra Trench, is a zone of concentrated seismicity and deformation heretofore characterized as “intraplate”. Plate motion inversions and an F‐ratio test show that relative motion data along the Carlsberg Ridge are fit significantly better by the new model. The misclosure of the Indian Ocean triple junction is reduced by 40%. The rotation vector of Australia relative to Indo‐Arabia is consistent with the seismologically observed ∼2 cm/yr of left‐lateral strike‐slip along the Ninetyeast Ridge, N‐S compression in the Central Indian Ocean, and the N‐S extension near Chagos. This boundary, possibly initiated in late Miocene time, may be related to the opening of the Gulf of Aden and the uplift of the Himalayas. The convergent segment of this boundary may represent an early stage of convergence preceding the initiation of subduction.