bluuebunny/crossref_metadata_2025_split huggingface dataset:
A tomographic image of mantle structure beneath Southern California
Authors: Humphreys Eugene , Clayton Robert W. , Hager Bradford H. 
Published: February 2008

We determined the variations in seismic structure beneath southern California by using a tomographic method of inversion on teleseismic P delays recorded with the Southern California Array. The algorithm employed was a modified form of an Algebraic Reconstruction Technique (ART) used in medical X‐ray imaging. Deconvolution with an empirically estimated point spread function was also used to help in focusing the image.The inversion reveals two prominent features beneath the region. The first is a thin, vertical wedge directly beneath the Transverse Ranges that is 2‐3% faster than the surrounding region. This feature deepens to the east, attaining a maximum depth of about 250 km beneath the San Bernardino Mountains. The second feature is a major zone of low velocity material that is 2‐4% slow under the Salton Trough rift valley, extending to a depth of about 125 km. Two possible explanations for the spatial association of the Transverse Ranges with the velocity anomaly below are lithospheric subduction or small‐scale sublithospheric convection in the region of the Big Bend of the San Andreas Fault. The low velocity anomaly beneath the Salton Trough is consistent with convective upwelling there.
methane concentrations and source strengths in urban locations
Authors: Blake Donald R. , Woo Van H. , Tyler Stanley C. , Rowland F. Sherwood 
Published: February 2008

Higher atmospheric concentrations of methane are found in air samples from urban locations than in contemporary samples at the same latitude in remote locations. Higher concentrations of several trace chlorocarbon gases are also found in the same urban samples than in the corresponding remote samples. The “urban excess”, i.e. urban concentration minus remote concentration, is generally 1000 to 2000 times larger on a molar basis for CH4 than for CCl3F. Because almost all CCl3F is emitted in urban environments, the urban release of CH4 is estimated from the observed molar ratios to be 30 to 60 megatons per year world‐wide.The fraction of world‐wide methane release occurring in the urban environment can be estimated from the concentration ratios, urban to remote, for CH4 vs. CCl3F. About 8% to 15% of the atmospheric methane release is observed to occur in urban locations.
Strong hydromagnetic turbulence associated with comet Giacobini‐Zinner
Authors: Tsurutani Bruce T. , Smith Edward J. 
Published: February 2008

The turbulence surrounding comet Giacobini‐Zinner reached intensities three orders of magnitudes above that of “intermediate” solar wind conditions, was characterized by Δ B/Bo almost equal to one, and extended to cometocentric distances beyond 106 km. The strong spectral peak at f ∼ 10−2 Hz and the general intensity profile of the turbulence (a lack of emissions close to the nucleus [< 2.5 × 104 km], peak intensities near the bow wave, and a spatial extend > 106 km) are in excellent agreement with generation by plasma instabilities associated with the pickup of H2O+ group ions.The total energy of the magnetic turbulence near f ∼ 10−2 Hz is estimated to be ∼ 5 × 1015 joules and that of ion energization due to solar wind pickup ∼6 × 1013 watts. It thus takes a minimum of ∼ 100 s to build up the magnetic turbulence. This scale is approximately the linear growth rate of the ion pickup instability, giving a consistent picture of the energy source of the turbulence.
A comparison of broadband source spectra, seismic energies, and stress drops of the 1989 Loma Prieta and 1988 Armenian earthquakes
Authors: Houston Heidi 
Published: February 2008

Broadband source spectra of the 1989 Loma Prieta (MW = 6.9) and 1988 Armenian (MW = 6.7) earthquakes are computed at periods from 1 to 50 sec using digitally‐recorded teleseismic P body waves. The effects of attenuation, geometrical spreading, and radiation pattern are removed from the spectra of individual stations, which are then averaged. The source spectra of the Loma Prieta and Armenian earthquakes are higher for their seismic moments than the spectra of 11 intraplate earthquakes studied by Zhuo and Kanamori [1987], which in turn are 2 to 4 times larger than average spectra of interplate subduction zone earthquakes.The seismically radiated energy can be computed from the source spectrum using Haskell's [1964] formulation assuming a point source with no directivity. An Orowan stress drop can be obtained from the seismic energy and moment. The Orowan stress drops for the Loma Prieta and Armenian earthquakes are both about 20 bars, significantly higher than Orowan stress drops of recent large interplate earthquakes. There is a positive correlation between the Orowan stress drops and the estimated repeat times, consistent with the notion that mechanical fault strength increases with increasing interseismic period.
Field‐aligned electric field accompanied by drift Alfvén waves in an inhomogeneous plasma
Authors: Hasegawa Akira , Maclennan Carol G. 
Published: February 2008

A field‐aligned electric field, δE‖↑ which is accompanied by drift Alfvén wave perturbations in an inhomogeneous plasma, can be expressed in simple terms as where ψ and δψ are the magnetic flux function and its perturbation, Te is the electron temperature, n(ψ) is the plasma density, k⟂ is the perpendicular wave number, li is the ion Larmor radius and l is the coordinate along a magnetic line of force.
The pressure dependence of the reaction between ClO and OClO at 226K
Authors: Parr A. D. , Wayne R. P. , Hayman G. D. , Jenkin M. E. , Cox R. A. 
Published: February 2008

The reaction between ClO and OClO (1), has been studied using the molecular modulation technique at 226K over the pressure range 4.8 – 29.0 torr. The reaction has a strong pressure dependence and the termolecular rate constant obtained at this temperature is The importance of the reaction is discussed in the context of the large ozone depletions observed in the Antarctic springtime. An explanation for the unexpected behaviour observed in earlier studies of the OClO/N02 system is also given.
On the solar source of transient cosmic ray intensity variations
Authors: Duggal S. P. , Pomerantz M. A. 
Published: February 2008

Studies of the mechanisms that produce transient cosmic ray intensity variations have been in progress for many years. It has long been recognized that classical nonrecurrent Forbush decreases (FD's), characterized by an abrupt reduction in the flux (typically over several hours) followed by a slow recovery (often lasting several weeks), are generally the result of processes initiated by solar flares. Thus, for example, it has been demonstrated that anisotropic cosmic ray flow patterns during FD's reflect the configuration of the flare‐associated interplanetary shocks that produce them [Duggal and Pomerantz, 1976].Much confusion has resulted from the logically incorrect premise that every transient intensity modulation (TIM) is a Forbush decrease. Thus analyses based upon the subjective assignment of a large number of TIM's to their presumed initiating flares have yielded disparate conclusions [Iucci et al, 1977; Krivsky et al, 1977].
Tidal perturbations on the satellite 1967–92A
Authors: Felsentreger T. L. , Marsh J. G. , Williamson R. G. 
Published: February 2008

The orbit of the 1967‐92A satellite has been studied to ascertain the extent to which tidal forces contribute to orbital perturbations. This study has permitted an estimation of the magnitudes of ocean tide effects on the satellite's inclination, in particular for the M2 and S2 constituents. The ocean tide estimates are based upon the use of a value of 0.3 for the solid earth tide Love number k2 and a lag angle of 0° in the orbit determination procedure. The amplitudes and phases of these tidal effects are in good agreement with those calculated from numerical models of the M2 and S2 tides derived from surface data. The results are as follows:
Supplement table is available with entire article on microfiche. Order from American Geophysical Union, 1909 K Street, N. W., Washington, D. C. 20006. Document J78‐002; $1.00. Payment must accompany order.
Distribution of Reverberant Subbottom Layers in the Southwest Pacific Basin
Authors: Houtz Robert E. , Ludwig William J. 
Published: February 2008

Vertical reflection profiles made with a large volume (7628 cm3) sound source and airgun‐sonobuoy reflection and refraction profiles in the southwest Pacific Ocean basin reveal significant accumulations of acoustically reverberant material that is difficult to penetrate with small (328–656 cm3) airguns.An isopach map of the reverberant layers, called ‘smooth acoustic basement’ or the ‘opaque layer’ in earlier studies, is presented along with an isopach map of the overlying weakly stratified (and low velocity) sediment. The map shows that misidentification of the reverberant material as igneous basement would result in average basement depth about 500 m too shallow, and in three separate areas, 1500 to 2000 m too shallow. The new data generally agree with depth versus age curves of basement in the oldest Pacific crust as determined by DSDP boreholes.DSDP cores from the reverberant layer in the central part of the study area show that it is volcanogenic in some places and calcareous in others. These drill sites are in areas where the reverberant layer is relatively thin, so that thick accumulations to the south have not been sampled. The calcareous nature of these thick beds is implied by the lack of consistently nearby seamount clusters, which could provide volcanogenic materials. If the thick reverberant layers are calcareous, that is, deposited at or near the equator, the net northward drift during the past 130 m.y. (or more) has been only 7–8° of latitude.
Seismicity and fault plane solutions of intermediate depth earthquakes in the Pamir‐Hindu Kush Region
Authors: Roecker S. W. , Soboleva O. V. , Nersesov I. L. , Lukk A. A. , Hatzfeld D. , Chatelain J. L. , Molnar P. 
Published: February 2008

Relocations of earthquakes, recorded by a local network of stations in Afghanistan and Tadjikistan in 1966 and 1967, indicate a narrow seismic zone (width ≲30 km) dipping steeply into the mantle to a depth of 300 km beneath the Pamir and Hindu Kush ranges. Very low seismicity was observed at depths less than about 70 km, the approximate depth of the Moho. Clear gaps in activity exist also within the zone of intermediate depth seismicity. One gap, about 50 km wide near 37°N and at depths greater than 100 km, separates a steeply northward dipping zone to the southwest from a steeply southeastward dipping zone to the northeast. This gap probably marks either a tear in the downgoing slab or a gap between two oppositely dipping slabs. Fault plane solutions, determined by Soboleva for events between 1960 and 1967, generally show steeply plunging T axes approximately within the planar seismic zone. They therefore are grossly similar to those at island arcs where no deep earthquakes occur and presumably result from gravitational body forces acting on a relatively dense slab of lithosphere. At the same time there is a very large variation in the fault plane solutions, much larger than is common at island arcs.Appendix is available with entire article on microfiche. Order from the American Geophysical Union, 2000 Florida Ave., N.W., Washington, DC 20009. Document J80‐003; $1.00. Payment must accompany order.
K‐Ar dating, geological and paleomagnetic study of a 5‐km lava succession in northern Iceland
Authors: Saemundsson Kristjan , Kristjansson Leo , McDougall Ian , Watkins N. D. 
Published: February 2008

A 5‐km section of basalt lavas exposed at Tröllaskagi on the western flank of the Eyjafjördur structural dome in northern Iceland has been subjected to K‐Ar age and paleomagnetic analysis from which detailed results are tabulated (34 dated lavas, 455 paleomagnetic directions). The upper 4 km of the sequence was erupted between about 11 and 9 m.y. ago. The rate of growth of the lava pile changed about 9.5 m.y. ago. Growth rates in the lower part were of the order of 1 km/m.y., whereas growth rates in the upper part may have been as high as 4 km/m.y. A 1.8 km‐thick normal polarity interval in the middle part of the section is correlated with marine magnetic anomaly 5. A good match is observed between the polarity sequence of the Trðllaskagi section and the marine magnetic polarity pattern above and below anomaly 5. Regression analysis of the K‐Ar data gives an age of 10.5 m.y. for the older boundary of anomaly 5 but a questionable 9.3‐m.y. age for its younger limit. Structural characteristics of the lava pile indicate that eruption of the sequence was associated with a now extinct rift axis in the western part of northern Iceland. A mean paleomagnetic field direction from 292 lavas is slightly far sided and right handed. Low‐latitude virtual poles are more prevalent in this survey than in two comparable recent surveys on younger Icelandic lavas and much more common than may be expected from a Fisherian distribution. There is no evidence to confirm that such transitional poles are predominantly due to nondipole fields. No significant difference was found in overall strength or stability between normal and reverse geomagnetic fields, as recorded in over 1000 lava flows in Iceland.Table is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Ave., N.W.,Washington, D.C. 20009. Document J80‐004; $1.00. Payment must accompany order.
Orbital forcing, climatic interactions, and glaciation cycles
Authors: Le Treut Hervé , Ghil Michael 
Published: February 2008

We consider forced oscillations of a nonlinear climatic oscillator. The oscillator includes radiation balance, oceanic thermal inertia, a highly simplified hydrological cycle, the mass balance and plastic flow of ice sheets, the elasticity of the earth's crust, and the viscosity of its upper mantle, as well as their various interactions. This system exhibits self‐sustained periodic oscillations with amplitude of a few degrees Celsius in the absence of any periodic forcing. The oscillator's free period, depending on model parameters, lies roughly between 5000 yr and 15000 yr (5–15 ka). The model is subjected to forcing at the astronomical periodicities of precession, 19 and 23 ka, obliquity, 41 ka, and eccentricity, 100 ka and 400 ka. The forcing is assumed to act on the climatic system by variations in mean annual insolation, in the case of eccentricity, as well as by its effect on the ice‐mass balance through the nonlinear precipitation‐temperature feedback.The effects investigated only cause small changes in ice mass V and global temperature T when self‐sustained oscillations are absent. In their presence, nonlinearly resonant response to the forcings leads to large changes in T and V; this response obtains at the frequency of the forcing, due to the mechanism of entrainment. The nonlinear character of the response also leads to combination tones. These are linear combinations of the forcing frequencies with integer coefficients, among which the largest occur near 100 and 10 ka. Sharp peaks in spectral density at the forcing frequencies and at their combination tones are superimposed on a continuous background. The spectral power in the background decreases with increasing frequency, like random red noise. This deterministic aperiodic behavior limits the predictability of glaciation cycles.
Polar auroras, polar substorms, and their relationships with the dynamics of the magnetosphere
Authors: Feldstein Y. I. 
Published: February 2008

Comparison is made between the position of the auroral oval during both night and day and that of the boundaries of trapped radiation according to observations from the satellite Alouette 2. We show that visual auroras are located on the poleward side of the boundary of smoothly closed field lines. From the data on auroral dynamics, information is obtained on some parameters of the geomagnetic field, i.e., field intensity in the magnetospheric tail, cross‐sectional dimensions of the tail at various geocentric distances, and the length of the tail. The density of low‐energy plasma at geocentric distances of 5 to 9 RE is estimated for various periods of the solar activity cycle. The influence of the magnetospheric ring current on the position of the auroral oval is considered. On the basis of polar auroral observations, estimates are made of variations in ring current parameters at times of ring current enhancement. DP and DPC magnetic field variations at high latitudes, linked with the structure of the geomagnetic field in the magnetosphere, are also discussed.DPvariations are characterized by current electrojets, a western one within the auroral oval and an eastern one in the evening hours at Φ ∼ 65°, where Φ is the invariant latitude. The DPC variations of greatest intensity are noted on the daytime side of the earth. The field variations are due to a counterclockwise current. We show that the current system of Chapman's SD variations is a superposition of two different types of variations, DP and DPC.
Crustal resistivity anomalies from geomagnetic deep‐sounding studies
Authors: Porath H. , Dziewonski A. 
Published: February 2008

A number of magnetic variation anomalies observed in geomagnetic deep‐sounding studies can be attributed to inhomogeneities of electrical resistivity in the upper crust. The electromagnetic induction in isolated conductors is usually too small to explain anomalies associated with crustal inhomogeneities, and anomalous variation fields mainly arise from concentration and channeling of currents induced elsewhere. These systems of currents are induced over a large region of the earth and have dimensions comparable to those of the source field. Most of the crustal anomalies are associated with deep conducting sedimentary basins or with regions of rapid change of sedimentary conductivity.Examples of anomalies of this origin are the North German basin, the Anadarko basin in Oklahoma and a region in north‐central Texas where more resistive paleozoic sediments are adjacent to conductive sediments in the Gulf coast plains. Other anomalies are related to currents concentrated in channels of conducting sea water located between two resistive continental blocks. Anomalous fields arising in this way have been observed on both sides of the Bonifacio Straits between Corsica and Sardinia. It is also thought that the Alert anomaly in the Canadian Arctic is closely related to the channeling of current through the Robeson Channel. An additional inland anomaly seems to be due to leakage of currents induced in the oceans into conductive structures in the upper crust. A magnetic variation anomaly with an amplitude larger than any other reported in the literature has been found in the northern Great Plains province of the United States. It extends along the eastern edge of the Black Hills north to the Williston basin. Higher conductivities than those characteristic of sediments are needed to explain this anomaly, which has been tentatively attributed to a zone of conducting graphite schists in the basement. Examples of magnetotelluric observations near current concentrations compared with two‐dimensional model calculations show that plane‐layered solutions are rarely adequate as representations of magnetotelluric resistivity curves in the vicinity of these features. In spite of these difficulties, the geomagnetic deep‐sounding technique can yield information about the lateral variations of resistivities of the upper mantle, providing that the conductivities at the surface are not too high or are relatively uniform, or both.
Selenodesy
Authors: Kaula William M. 
Published: February 2008

In the last 4 years, knowledge of the gravitational field and shape of the moon greatly improved through the Apollo 15–17 subsatellites, metric photography, and altimeter systems and the continued programs of laser ranging and radio interferometry from the earth. This summary is divided into three sections: gravity, rotational dynamics, and geometry. For a more detailed review, see Kaula [1975].Of the global gravity field, only the second‐ and third‐degree harmonics are known reliably. The best determination was by Sjogren [1971], who used tracking of Lunar Orbiter 4, the 2700‐ to 6100‐km altitude of which effectively filtered out higher harmonics. Other solutions for higher‐degree harmonics [Liu and Laing, 1971; Michael and Blackshear, 1972] give severely distorted representations of the far side gravity field. Ferrari [1975a, b] and Ananda [1975] have recently obtained a more plausible result, using improved statistical techniques on Apollo 15 and 16 subsatellites plus Lunar Orbiter 5 data.
Structure of the Earth's core
Authors: Engdahl E. R. , Dziewonski A. M. , Flinn Edward A. 
Published: February 2008

Recent advances in the identification of normal mode data [Dziewonski and Gilbert, 1972, 1973a, b; Gilbert and Dziewonski, 1975; Mendiguren, 1972, 1973] have allowed new constraints to be imposed on the distribution of elastic parameters within the earth's interior. In particular, the new overtone modes identified have an effective control over possible models of the structure of the inner and the outer core. Aniong recent studies using these new data, those of Gilbert et al. [1973], Jordan and Anderson [1974], and Gilbert and Dziewonski [1975] are the most relevant, since these workers made an attempt to invert simultaneously the entire available seismic data set to model the deep structure of the earth's interior.Body wave studies have concentrated on the fine structure and the anelasticity of the core. Differential travel times (the difference between the arrival times of two body phases) have been used in inversion studies and in making independent estimates of the radii of the outer and the inner core. Differential travel times have the advantage of being independent of the base line bias always present in absolute travel times and of virtually eliminating the effects both of inhomogeneities in the upper mantle and of uncertainties due to source mislocation [Jordan, frequency waves near 1 Hz, Q ≥ 5000, P7KP being consistently higher in frequency than P4KP. This latter effect is likely to be caused by a PmKP tunneling phenomenon, discussed by Richards [1973], which predicts a frequency dependent transmission coefficient through the core that selectively removes low frequencies. Because of tunneling, the estimates of Q in the outer core from PmKP waves may be somewhat too high.
The Global Atmospheric Research Program
Authors: Perry John S. 
Published: February 2008

While this report was in preparation an international force of about 40 ships, 13 aircraft, and 4000 scientists and technicians was engaged in measuring the atmosphere and ocean of the tropical Atlantic in unprecedented detail. This followed by a few months the efforts of a smaller armada in the China Sea which studied energy exchanges between the warm Kuroshio current and cold Asian air masses. These large field programs, Garp Atlantic Tropical Experiment (Gate) and Air Mass Transformation Experiment (Amtex), respectively, were visible manifestations of the Global Atmospheric Research Program (Garp), an international undertaking which has formed the unifying focus for a large fraction of the world's meteorological research during the past decade and a half.The primary objective of this report is to highlight the activities and accomplishments of Garp—and among these, primarily the United States' contributions—during the last 4 years. These and their supporting rationale are familiar to most meteorologists. For the broader audience of this report, however, it is appropriate to begin by outlining the genesis and conceptual framework of Garp.