bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropy and shear‐velocity heterogeneities in the upper mantle
Authors: Nataf H.‐C. , Nakanishi I. , Anderson Don L.
Published: February 2008

Long‐period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle. The dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure. The data are corrected for the effect of surface layers and both Love and Rayleigh waves are used. Shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km. The shear wave velocity distribution to 200 km depth correlates with surface tectonics, except in a few anomalous regions. Below that depth the correlation vanishes. Cold subducted material shows up weakly at 350 km as fast S‐wave anomalies. In the transition region a large scale pattern appears with fast mantle in the South‐Atlantic. S‐anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones. The Pacific shows a NW‐SE fabric.
Venus dayside ionospheric conditions: Effects of ionospheric magnetic field and solar EUV flux
Authors: Elphic R. C. , Brace L. H. , Theis R. F. , Russell C. T.
Published: February 2008

The Venus ionosphere is influenced by both solar EUV and solar wind conditions. Using in situ measurements of solar EUV flux, we investigate the extent of the EUV‐contributed modulation of dayside conditions as measured by the Pioneer Venus orbiter Langmuir probe experiment. We use data from the low altitude dayside ionosphere (150‐200 km altitude, 0600‐1800 local solar time), normalized by a new empirical model of the ionosphere. We also introduce a new method for measuring the EUV flux at Venus that relies on the photoelectron emission from the Langmuir probe sensor in regions far above the ionosphere. Using these data we find that the EUV flux strongly affects ionospheric electron number density, Ne, but influences electron temperature, Te, very little. After removing this EUV dependence from the data, we examine the role of ionospheric magnetic fields in modulating dayside conditions, and we find that the presence or absence of large scale horizontal fields has no significant affect on Ne and Te at these altitudes. This is because the ions are collision dominated at these altitudes, and vertical diffusive transport is unimpeded by magnetic fields of the observed magnitudes.
Relativistic dispersion and the generation of auroral kilometric radiation
Authors: Pritchett P. L.
Published: February 2008

Auroral kilometric radiation (AKR) is known to be produced in a region in which the plasma sheet electrons have speeds v²/c² > ωp²/Ωe² « 1. Under such conditions, relativistic effects on the dispersion of extraordinary‐mode waves near the electron cyclotron frequency are found to be very significant. Linear theory and computer simulation applied to a model distribution indicate that a k ∥ = 0 extraordinary mode with Re ω ≲ Ωe dominates the radiation emission resulting from the cyclotron maser instability. These results suggest that the hot electrons determine the propagation characteristics of AKR and that larger growth rates are possible for direct amplification of extraordinary waves in the auroral region than predicted by calculations using cold‐plasma dispersion.
Domain wall nucleation as a controlling factor in the behaviour of fine magnetic particles in rocks
Authors: Boyd J. R. , Fuller M. , Halgedahl S.
Published: February 2008

Difficulties in domain wall nucleation have been shown to affect the domain state of the fine magnetic particles in rocks. Particles, large enough to contain a domain wall, remain saturated in remanence and only nucleate a wall when a backfield is applied. In this paper, nucleation is described during hysteresis, stress cycles and cycles through the low temperature anisotropy transition in magnetite. It is suggested that much of the grain size dependence of magnetic behaviour in the pseudosingle domain grain size range can be attributed to the increasing difficulty with which walls are nucleated, as particle size decreases.
A kinky heliospheric current sheet: Cause of CDAW‐6 substorms
Authors: Tsurutani Bruce T. , Russell Christopher T. , King Joseph H. , Zwickl Ronald D. , Lin Robert P.
Published: February 2008

Two magnetospheric substorms and the intensification of the second are caused by interplanetary magnetic field and ram pressure changes associated with a kinky heliospheric current sheet (KHCS). The responsible interplanetary features occur in a highly compressed region between a solar flare‐associated shock wave and the cold driver gas. The possbility that the interplanetary structure is a “magnetic cloud” is ruled out.
Vertical and horizontal characteristics of Arctic haze during AGASP: Alaskan Arctic
Authors: Schnell R. C. , Raatz W. E.
Published: February 2008

Vertical and horizontal distributions of ozone, extinction due to aerosol light scattering, condensation nucleus concentrations, aerosol spectra, and meteorological parameters were measured with a NOAA WP‐3D research aircraft over the Alaskan Arctic in March 1983. Multiple layers of haze, varying in thickness from a few 10's to 100's of meters, were observed throughout the troposphere. A maximum concentration of aerosols was located between 600 and 800 mb. Distribution of the haze layers was associated with distinct meteorological boundaries. The characteristics of the haze changed in response to stages in the progression of a major Arctic haze episode. On March 17, 1983, the Arctic anticyclone was penetrated and its meteorological and aerosol properties determined.
Surface aerosol measurements at Barrow during AGASP
Authors: Bodhaine B. A. , Dutton E. G. , DeLuisi J. J.
Published: February 2008

Surface aerosol measurements were made at the Barrow GMCC Observatory during the AGASP flight series in March 1983. The condensation nucleus, scattering extinction coefficient, size distribution, and total aerosol optical depth measurements all clearly show conditions of background Arctic haze for March 9‐11, a series of haze episodes during March 12‐16, and a return to background haze for March 17‐18. Angstrom exponents calculated from scattering coefficient data were low during March 9‐11, relatively higher during March 12‐14, and highest during March 15‐18. Surface aerosol data and aerosol optical depth data are in good qualitative agreement for the 10‐day period studied. Background haze was present when trajectories circled the Arctic basin, and haze episodes occurred when trajectories originated in western Asia and Europe.
Airborne observations of Arctic aerosols. I: Characteristics of Arctic haze
Authors: Radke Lawrence F. , Lyons Jamie H. , Hegg Dean A. , Hobbs Peter V. , Bailey Ian H.
Published: February 2008

In airborne measurements in the vicinity of Barrow, Alaska and over the Beaufort and Chukchi Seas visible hazes were found in layers typically hundreds of meters thick and extending 20‐200 km horizontally. Volume distributions of the particles in the hazes had distinct peaks in the accumulation and coarse particle modes at 0.25, 0.6 and 4 µm diameter. The principal aerosol component of the hazes was sulfate and this was associated with the accumulation mode.
Statistical analysis of trace gases in Arctic haze
Authors: Khalil M. A. K. , Rasmussen R. A.
Published: February 2008

A large number of anthropogenic trace gases arising from combustion processes such as in power plants and automobiles are found to be more abundant in regions of arctic haze when compared to their concentrations in cleaner background air. The excess of concentrations of a trace gas observed in the haze is greatest for short‐lived gases and least for the longer‐lived species. Included among these gases are CO2, CO, C2‐C6 hydrocarbons, and N2O. High concentrations of anthropogenic chlorofluorocarbons and chlorocarbons are also found in arctic haze, including F‐11, F‐12, CCl4, CH3CCl3, perchloroethylene, trichloroethylene, dichloromethane, and chloroform. The lack of excess CH3Cl in the haze suggests that low temperature combustion such as burning of wood does not contribute to arctic haze. The Soviet Union and Europe, because they are industrialized and have large populations at higher latitudes (>50°N), are potential source regions for both these groups of anthropogenic trace gases.
The absorption of solar radiation by the Arctic atmosphere during the haze season and its effects on the radiation balance
Authors: Valero Francisco P. J. , Ackerman Thomas P. , Gore Warren J. Y.
Published: February 2008

In this letter we report measurements of broadband spectral absorption of solar radiation by the Arctic atmosphere during haze events. A preliminary analysis of our data indicates that large changes occur in the radiative transfer processes in the Arctic during haze events. For example, the planetary albedo is estimated to increase by 2.5% over the ocean and to decrease by 9% over the ice cap. Changes of such magnitude in the radiative parameters have the potential for significant climatic effects. The need for further experimental and modeling efforts is emphasized.
Observation of double‐layer‐like structures at rocket altitudes
Authors: Kellogg P. J. , Monson S. J. , Whalen B. A.
Published: February 2008

We have observed 230 large amplitude electric field pulses in a rocket flight to an apogee of 585 km over an aurora. While the limitations of the instrumentation only allow limits to be set on the characteristics of these pulses, the limits are nevertheless significant. A typical lower limit on the potential jump of the pulses (see Figure 3) is about .4 volts. Many of the pulses show structure at a frequency very close (<2%) to the proton‐cyclotron frequency.
EUV (800‐1400 Å) observations of the tropical airglow
Authors: Chakrabarti Supriya
Published: February 2008

We have obtained the first spectrum of the tropical airglow in the 800‐1400 Å range. The data were obtained at 8 Å resolution by the EUV spectrometer on board the STP78‐1 satellite. The time‐averaged downlooking spectrum within the arc shows strong OI features at 1304 and 1356 Å. We have detected the oxygen recombination continuum at 911 Å, which provides the first conclusive evidence that radiative recombination is the primary excitation mechanism for the tropical ultraviolet emissions. We have also discovered a weak OI 989 Å emission from the tropical arc region, which is not expected in ordinary radiative recombination spectrum. Such observation indicates that other processes, such as dielectronic recombination or mutual neutralization, might be present in these regions.
Tomographic imaging of the earthquake rupture process
Authors: Ruff Larry J.
Published: February 2008

To advance our understanding of the earthquake rupture process, we must develop methods that will map observations into the space‐time variation of seismic moment release on the fault plane. While the temporal history of overall moment release is relatively easy to obtain from P‐waves, there has been no objective quantitative method available to directly determine the spatial variation in moment release. The theoretical connection between spatially varying moment release and the resultant seismogram is a linear integral relationship (specifically, a Radon transform). This paper outlines a linear inverse method that provides a high‐resolution tomographic image of the space‐time varying moment density function. Application of the method to P‐waves from the large 1976 Mindanao earthquake demonstrates the ability of this method to reliably extract coherent pulses of moment release in space and time.
Density‐versus‐depth models from multimode surface waves
Authors: Cara M. , Lévèque J. J. , Maupin V.
Published: February 2008

Multimode Love and Rayleigh wave data related to the Pacific Ocean and to North America are inverted using two sets of parameters: 1) the isotropic P and S velocities plus the density and 2), five elastic parameters describing a transversely isotropic medium, plus the density. It is found that the assumption of isotropy leads to very unrealistic upper‐mantle models while much more realistic models are obtained under the assumption of transverse isotropy. The lateral variations in density between the Pacific Ocean and North America are then less than 1.5% and, in both regions, a large density gradient is well resolved at a depth near 360 km.
Continuum radiation and electron plasma oscillations in the distant geomagnetic tail
Authors: Coroniti F. V. , Scarf F. L. , Kennel C. F. , Gurnett D. A.
Published: February 2008

ISEE‐3 electric field measurements are used to examine the properties of electromagnetic continuum radiation in the distant geomagnetic tail. Continuum is observed in all the tail's plasma regions and in the magnetosheath. The power spectrum at 210 RE is nearly identical to that at 40 RE, indicating that the tail cavity forms a reasonably loss‐free waveguide. The angular distribution exhibits both anisotropy, which is similar to that observed nearer the earth, and isotropy for high frequencies (f > 31.6 kHz) in the magnetosheath and for low frequencies (f ≤ 17.8 kHz) in the tail lobes and boundary layer. Isotropic radiation suggests that, in addition to the near earth source, continuum is also generated over a large spatial region in the tail. Electrostatic electron plasma oscillations are also detected in the in the distant tail, and these could represent the local source of the continuum.
Effect of parallel refraction on magnetospheric upper hybrid waves
Authors: Engel John , Kennel Charles F.
Published: February 2008

Large amplitude (⩾10 mV/m) electrostatic plasma waves near the upper hybrid (UH) frequency have been observed from 0° to 50° magnetic latitude (MLAT) during satellite plasma‐pause crossings. A three‐dimensional numerical ray tracing calculation, based on an electron distribution measured during a GEOS 1 dayside intense upper hybrid wave event, suggests how UH waves might achieve such large amplitudes away from the geomagnetic equator. Refractive effects largely control the wave amplification and, in particular, the unavoidable refraction due to parallel geomagnetic field gradients restricts growth to levels below those observed. However, a cold electron density gradient parallel to the field can lead to upper hybrid wave growth that can account for the observed emission levels.
Plasma characteristics of polar cap F‐layer arcs
Authors: Carlson H. C. , Wickwar V. B. , Weber E. J. , Buchau J. , Moore J. G. , Whiting W.
Published: February 2008

First results are reported of a comprehensive campaign to measure ionospheric structure and dynamics of nighttime polar cap F‐layer or F‐region arcs. Airborne optical and digital ionosonde data were collected simultaneously with ground based incoherent scatter radar data, continuously over many hours in time and 500 to 1000 km in space. Polar cap F‐region sub‐visual auroral arcs, which are commonly observed during quiet magnetic conditions, are found to represent boundaries (or shears) in the polar cap plasma circulation pattern. F‐region electron concentration enhancements are found in these features and can be of significance to polar thermospheric circulation, composition, and thermal structure. The quiet polar ionosphere is so structured that high time resolution intensified optical images of thermospheric emmissions can make a major contribution to interpretation of incoherent scatter radar data.
Thermospheric gravity waves near the source: Comparison of variations in neutral temperature and vertical velocity at Sonore Stromfjord
Authors: Herrero Federico A. , Mayr Hans G. , Harris Isadore , Varosi Frank , Meriwether John W.
Published: February 2008

A computation of the atmospheric response to heat sources in the thermosphere has shown that the local perturbations produced by impulsive sources depend critically on the parameter being observed (e.g., temperature), on the distance from the source, and on the source shape and time variation. A simulation has been done with a source at an altitude of 130 km, and it has been compared with nighttime observations of the neutral temperature and vertical wind velocity variations occurring between 250 and 300 km above Sondre Stromfjord. The data show two heating events, the first occurring away from the zenith and the second in the zenith, thus yielding observations away from and directly above the heated region. The computations reproduced all of the features observed but underestimated the vertical velocity amplitudes and the rapidity of the temperature decay. The observations also support the theoretical finding that the vertical velocity near the source shows maxima (minima) simultaneous with temperature increases (decreases), roughly resembling the time derivative of the source.
Characteristics of suprathermal H+ and He++ in plasmoids in the distant magnetotail
Authors: Gloeckler G. , Ipavich F. M. , Hovestadt D. , Scholer M. , Galvin A. B. , Klecker B.
Published: February 2008

We have obtained rest frame distribution functions of suprathermal (∼6 to ∼150 keV/amu) H+ and He++ ions during 20 particle intensity increases observed in the distant magnetotail (≳80 RE) using data from the University of Maryland/Max‐Planck Institut ULECA sensor on ISEE‐3. All twenty increases were characterized by isotropic ∼100 keV electrons preceded by beaming electrons and velocity‐dispersed proton distributions, signatures typically associated with plasmoids. In each of these 20 plasmoids we find both H+ and He++ to be convected tailward with speeds ranging from 200 to 1000 km/s. The distribution functions of H+ and He++ in each event are well represented by an exponential dependence on particle speed. The sample averages of the proton number density, n, energy density, u, and effective temperature, kTeff = (2/3)(u/n), are respectively 0.018 cm−3, 160 eV/cm³ and 6.1 keV, while the He++ to H+ number density and effective temperature sample average ratios are 0.03 and 3.25 respectively. We conclude that the acceleration mechanism is fairly efficient, depends on the particle velocity, and that the solar wind is a dominant plasma source. Furthermore, our observations indicate that the plasmoids are expanding at speeds of ∼100 km/s during their tailward propagation.
Direct observations of passages of the distant neutral line (80‐140 RE) following substorm pnsets: ISEE‐3
Authors: Baker D. N. , Bame S. J. , Birn J. , Feldman W. C. , Gosling J. T. , Hones E. W. , Zwickl R. D. , Slavin J. A. , Smith E. J. , Tsurutani B. T. , Sibeck D. G.
Published: February 2008

Detailed plasma and field data are examined for a period of time when ISEE‐3 is in the range −140 ≲ XGSM ≲ −80 RE. Several clear examples, at a frequency of ∼ once per day, of strong southward magnetic field followed by strong northward field occur when ISEE‐3 is in the plasma sheet. During the southward field intervals, the bulk plasma flow is strongly tailward while during the northward field episodes the plasma flow is generally very weak. In all instances of this kind, the signatures at ISEE‐3 follow (by 5‐10 minutes) the initial impulsive injection of energetic ions at geostationary orbit. It is suggested that the south‐to‐north field transitions and plasma flow patterns are produced by the passage over ISEE‐3 of the distant neutral line immediately following near‐earth substorm onset.
Sounding of the plasma sheet in the deep geomagnetic tail using energetic particles
Authors: Daly P. W. , Wenzel K.‐P. , Sanderson T. R.
Published: February 2008

Energetic ions (E > 35 keV) at 90° to the magnetic field line are measured on ISEE‐3 in the distant geomagnetic tail and are used as tracers of the particle density during two encounters with the plasma sheet at 210 and 128 earth radii from the earth. Because of the finite gyroradius (2400 km) of these (assumed) protons, different orientations about the magnetic field measure the intensity at different locations, allowing a separation of spatial from temporal variations. Density contour maps of the plasma sheet are constructed, demonstrating the wavy nature of this regime, as well as the existence of density layers within it.
The relationship between the IMF By and the distant tail (150‐238 Re) lobe and plasmasheet By fields
Authors: Tsurutani B. T. , Jones D. E. , Lepping R. P. , Smith E. J. , Sibeck D. G.
Published: February 2008

The relationships between the Solar Magnetospheric (SM) y‐ component of the interplanetary magnetic field (IMF) and the lobe and plasmasheet magnetic fields have been studied for the two ISEE‐3 deep tail passes. It is found that for positive sector IMFs, 13% of the interplanetary magnetic field penetrates into the aberrated north‐dawn and south‐dusk lobe quadrants, and about the same amount in the north‐dusk and south‐dawn lobe quadrants for negative sector IMFs. For the above cases, field penetration is significantly less for opposite polarity IMFs. The former results are generally consistent with open magnetospheric models, but the latter (the lack of response in certain quadrants) are unexplained by theory at this time. If the magnitude of the plasmasheet By fields are related to plasma pressure anisotropies, very small anisotropies of P⊥/P∥ ≃ 1.01 are expected.
Magnetotail flux ropes
Authors: Sibeck D. G. , Siscoe G. L. , Slavin J. A. , Smith E. J. , Bame S. J. , Scarf F. L.
Published: February 2008

ISEE‐3 magnetometer observations are presented that are consistant with flux ropes within the magnetotail. Three instances have been found. The flux ropes are identified by a strong magnetic field in their core, a bipolar magnetic field signature, and a double peaked field signature indicative of an off‐center crossing. The axes of the flux ropes lie nearly parallel to the magnetotail axis. Inside the flux ropes, a hot plasma streams tailward and there is an increase in the flux of energetic protons and the intensity of plasma waves. When the flux ropes were observed, ground magnetograms near local midnight were highly disturbed.
Features of ion trajectories in the polar magnetosphere
Authors: Horwitz J. L.
Published: February 2008

The trajectories of mainly low‐energy ionospheric ions injected near the polar cusp into the polar magnetosphere are presented for a model polar magnetosphere including the effects of convection electric fields and gravitation. The trajectories display the ion mass and energy differentiation which has been seen in recent satellite observations of low‐energy ionospheric ions injected into the polar magnetosphere, and indicate that for reasonable ranges of injection energy, pitch angle and convection electric field: 1. Transport of low‐energy ‘polar cusp’ O+ to the ∼1 Re altitude nightside auroral acceleration region is feasible; and 2. Preferential trapping of energetic O+ relative to H+ and He+ energetic ions occurs in the closed field line region of the magnetotail plasma sheet. Two interesting classes of polar region very low‐energy heavy ion trajectories are noted: 1. ‘Parabolic’ trajectories, in which heavy ions injected at the polar cusp at small pitch angles rise then fall into the polar cap atmosphere, and 2. ‘Hopping’ trajectories, in which heavy ions injected at large pitch angles at the polar cusp mirror between the gravitational stopping location and magnetic mirror point as they convect at low to intermediate altitudes across the polar cap. It is also illustrated how during conditions of sunward convection in the central polar cap, a pronounced ‘spray’ of ions injected on the nightside may occur, in which such ions may appear in the nightside or dayside magnetosphere depending upon injection characteristics and dusk‐to‐dawn convection electric field magnitude; such ion dynamics may be of interest in connection with theta auroras.
Polarization of spacecraft generated plasma clouds
Authors: Katz I. , Parks D. E. , Cooke D. L. , Lilley J. R.
Published: February 2008

Observations made on the space shuttle during the STS‐3 flight indicate that generation of dense plasma from sources aboard the orbiter was accompanied by substantial reduction of electric potential measured by probes fixed on the orbiter. In a separate experiment increased plasma densities were observed to follow the release of neutral gas. In this letter, it is argued that both observations are consistent with the shielding of the electric field,
, associated with the motion of the orbiter across the earth's field from the interior of the spacecraft generated plasma. As a consequence the downstream drift of the part of the plasma cloud near the vehicle may be much less than the drift speed
experienced by a single charged particle released from rest in the vehicle's frame. Since the ion thermal velocities with which plasma expands along field lines are typically much less than
, this consequence can have a substantial impact on the determination of spacecraft generated plasma densities near the orbiter.
Aircraft latitude survey measurements of the El Chichon eruption cloud
Authors: Shah G. M. , Evans W. F. J.
Published: February 2008

Aerosol optical thicknesses were derived from solar spectral extinction measurements. These were made with a sunphotometer on board the NASA Convair 990 aircraft during May, July and December 1982 over a range of latitudes covered by the flight mission. Large increases in the optical thicknesses over the background levels for the stratosphere were found at all latitudes where observations were made; these are attributed to the El Chichon eruption cloud. The latitudinal variation of the optical thickness in May and July shows a maximum in the vicinity of the eruption, a minimum near 30°N and no appreciable change further north of the minimum. This is indicative of a thick portion of the cloud being confined between 0° and 30°N latitude. In December, the maximum was found near 8°N, the minimum near 25°N and an increase north of the minimum. The spectral dependence of the aerosol optical thickness which is different on one side of the 30°N latitude from the other suggests that the two portions of the cloud have different size distributions of aerosols.
Observations of atmospheric ozone: 38° to 76° north latitude at altitudes from 8 km to the surface
Authors: Gregory Gerald L. , Beck Sherwin M. , Hudgins Charles H.
Published: February 2008

Ozone data were obtained from 8 km to the surface and at latitudes from 38° to 76° N during January and February 1983. Flight lines covered northeastern U.S., Canada, and Greenland. The results of the latitudinal survey at 5‐ to 8‐km altitude showed O3 mixing ratios to be ≃ 40 ppbv with little variation in latitude. One region of elevated O3 was observed and extended from 54° N to 57° N latitude. Ozone reached 150 ppbv at 6.4‐km altitude. This sampling was stratospheric air as the tropopause height was 5.6‐km altitude. Profiles at 76°, 67°, and 53° N showed O3 to be well mixed from about 5 km to the surface. In some cases, profiles identified a layer of 1 km to 100 m vertical dimension at the surface, in which O3 destruction had occurred.
Mapping alluvial fans in Death Valley, California, using multichannel thermal infrared images
Authors: Gillespie Alan R. , Kahle Anne B. , Palluconi Frank D.
Published: February 2008

We have mapped alluvial fans in Death Valley, California using NASA's 8‐12 µm six‐channel airborne Thermal Infrared Multispectral Scanner (TIMS). We are able to recognize both composition and relative age differences. Age unit boundaries are generally consistent with those obtained by conventional mapping. Composition was verified by field investigation and comparison with existing geologic maps. Bedrock and its young derived fan gravels have similar emissivities. The original composition of the fans is modified by differential erosion and weathering, permitting relative age mapping with TIMS.
Characteristics of the spacecraft optical glow
Authors: Yee Jeng‐Hwa , Abreu V. J. , Dalgarno A.
Published: February 2008

The optical glow induced by spacecraft‐environment interaction under daytime conditions is analyzed using photometric data obtained by the Visible Airglow Experiment on board the Atmosphere Explorer Satellite. Because of the increased ambient oxygen density, the glow is more intense in the daytime. The daytime production efficiency, measured in Rayleighs per oxygen atom, is similar to the nighttime value. No dependence of the glow intensity on the ambient plasma density was found. The production efficiency increased with time throughout the duration of the spacecraft in orbit.
Free tropospheric measurements of CS2over a 45°N to 45°S latitude range
Authors: Tucker Brian J. , Maroulis Peter J. , Bandy Alan R.
Published: February 2008

Free tropospheric measurements of CS2were made over a latitude range 45°N to 45°S. The mean of 52 measurements was 5.7 pptv. The standard deviation and standard error of the mean were 1.9 and 0.3 pptv respectively. The amounts of CS2in the northern and southern hemispheres were statistically the same.
Stress in a stratified crust overlying a buried screw dislocation
Authors: Leary Peter C.
Published: February 2008

A Haskell matrix solution to the equation of stress equilibrium is used to describe the crustal response to a screw dislocation source lying beneath a uniform elastic crust capped by a region of layered rigidity. The solution is used to illustrate the effect a stratified crustal rigidity has on the near surface in situ stress field. Without accounting for this effect, it is possible to overestimate the deep tectonic stress levels inferred from in situ vertical gradients measured in the uppermost crust.
Paleomagnetism of Late Paleozoic igneous rocks from southern Portugal
Authors: Perroud H. , Bonhommet N. , Ribeiro A.
Published: February 2008

The Upper Devonian Beja Gabbro yields a stable characteristic magnetization with dual polarities. Inclinations are moderate to steep, while declination vary systematically along the arcuate trend of the Massif, suggesting pretectonic magnetization and oroclinal bending. The inclination differs from those of other Devonian results from Europe suggesting a separation between Southern and Northern Iberia. Lower Carboniferous volcanics from the "Pyrite Belt" were remagnetized in Middle Carboniferous, but a few sites were found with a high temperature component which might represent the primary magnetization. The paleolatitudinal movement computed from these magnetizations is in excellent agreement with that of Africa from Late Devonian to Middle Carboniferous. We suggest therefore that southermost parts of Spain and Portugal were part of Africa until the final collision events of the Hercynian orogeny.
The neutral wind “flywheel” as a source of quiet‐time, polar‐cap currents
Authors: Lyons L. R. , Killeen T. L. , Walterscheid R. L.
Published: February 2008

The neutral wind pattern over the summer polar cap can be driven by plasma convection to resemble the convection pattern. For a north‐south component of the interplanetary magnetic field Bz directed southward, the wind speeds in the conducting E‐region can become ∼ 25% of the electric field drift speeds. If convection ceases, this neutral wind distribution can drive a significant polar cap current system for ∼ 6 hours. The currents are reversed from those driven by the electric fields for southward Bz, and the Hall and field‐aligned components of the current system resemble those observed during periods of northward Bz. The current magnitudes are similar to those observed during periods of small, northward Bz; however observations indicate that electric fields often contribute to the currents as much as, or more than, the neutral winds.
Latitude variation of recurrent Mev‐energy proton flux enhancements in the heliocentric radial range 11 to 20 AU and possible correlation with solar coronal hole dynamics
Authors: Christon S. P. , Stone E. C.
Published: February 2008

Recurrent low energy ( ≳0.5 MeV) proton flux enhancements, reliable indicators of corotating plasma interaction regions in interplanetary space, have been observed on the Voyager 1 and 2 and Pioneer 11 spacecraft in the heliographic latitude range 2°S to 23°N and the heliocentric radial range 11 to 20 AU. After a period of rather high correlation between fluxes at different latitudes in early 1983, distinct differences develop. The evolution of the fluxes appears to be related to the temporal and latitudinal dynamics of solar coronal holes, suggesting that information about the latitudinal structure of solar wind stream sources propagates to these distances.
New results on the Pioneer Venus Orbiter February 10‐11, 1982 events: A solar wind disturbance not a comet
Authors: Intriligator D. S.
Published: February 2008

We study the characteristics of a series of disturbances observed on February 10‐11, 1982 by the plasma analyzer and the magnetometer on the Pioneer Venus Orbiter (PVO) obtained in the solar wind upstream of Venus. We conclude that the events were associated with the propagation of a solar wind disturbance of coronal origin and not with an encounter with a comet or other local outgassing object (Russell et al., 1983). The plasma analyzer spectra clearly show the presence of increases in He++ and they argue strongly against Russell et al.'s interpretation. The peak in magnetic field magnitude on February 11 is identified as the magnetic signature of a thin, trailing "filament" at the end of a series of solar initiated events. Corresponding increases in He++ and magnetic field fluctuations were observed near earth by ISEE‐3 about a day later, and this strongly supports the concept of a solar origin.
Auroral kilometric radiation triggered by type II solar radio bursts
Authors: Calvert W.
Published: February 2008

The previously‐reported triggering of auroral kilometric radiation (AKR) during type III solar radio bursts was attributed to the incoming radio waves rather than other aspects of the burst's causative solar flare. This conclusion has now been confirmed by ISEE‐1 and ISEE‐3 observations showing AKR which seems to have been triggered also by a subsequent type II solar radio burst, up to eleven hours after the flare.
Stacking investigations of higher‐order mantle Rayleigh waves
Authors: Okal Emile A. , Jo Bong‐Gon
Published: February 2008

We present the initial results of an ongoing study of higher‐order mantle overtones of Rayleigh waves. The main problem is to separate overtone branches (3R,4R,5R), traveling with identical group velocities at similar frequencies. Global stacking is used, both for traveling waves and normal modes, with dispersion results in generally excellent agreement with both theoretical models and values published for a well‐separated part of the 3R branch.
Shear‐wave splitting and anisotropy in the Charlevoix Seismic Zone, Quebec
Authors: Buchbinder Goetz G. R.
Published: February 2008

During the month of August 1984 an experiment was undertaken in the Charlevoix Seismic Zone to test the hypothesis that shear‐wave splitting could be observed in a seismically active region. Seismograms, recorded by digital 3‐component seismographs, located very close to the epicentres of three earthquakes, showed shear‐wave splitting. The amount of splitting was estimated to be 1.6% to 2% of the shear wave velocity from particle motion diagrams. The average azimuth of the direction of polarization was 30°. These observations can be explained by the presence of vertical cracks striking 30° east of north, with a minimum crack density of ε = 0.03.
Wave signature in stratospheric aerosols
Authors: Ackerman Marcel , Lippens Carlos , De Muer Dirk
Published: February 2008

Regularly spaced vertical structures have been observed in stratospheric aerosols revealed by the observation of scattered sunlight. The simultaneous observations of this phenomenon and of regularly spaced vertical fluctuations of temperature is presented. The aerosol structure is interpreted in terms of particle size as a function of temperature on the basis of the limited theoretical studies available about the effects of temperature and humidity on the growth and optical properties of sulfuric acid‐water dropplets in the stratosphere.
Effect of the interplanetary magnetic field Y component on the high‐latitude nightside convection
Authors: de la Beaujardière O. , Wickwar V. B. , Kelly J. D. , King J. H.
Published: February 2008

Sondrestrom radar observations reveal that the dawn‐dusk (By) component of the interplanetary magnetic field (IMF) strongly influences the nightside polar convection. This effect is quite complex. The convection for one orientation of By is not the mirror image of the other orientation. A positive By (i.e., pointing toward dusk) seems to organize the velocities such that, at all local times, they are predominantly westward within the radar field‐of‐view (≃68°‐to‐82° invariant latitude). Between dusk and midnight, on one such occasion, sunward flow is observed within the polar cap. In the midnight and dawn sectors, when By is negative, the plasma velocities often appear random. For large negative By, the afternoon cell appears shifted toward early hours such that large southward velocities are observed about 3 hours before midnight. These are the only times when the predominant velocity component is southward.
Three spacecraft measurements of an unusual disturbance in the solar wind: Further evidence for a cometary encounter
Authors: Russell C. T. , Schwingenschuh K. , Phillips J. L. , Arghavani M. R.
Published: February 2008

On February 11, 1982 the Pioneer Venus orbiter detected an unusual disturbance of the interplanetary magnetic field and solar wind plasma. While this disturbance was being detected at Venus, Venera 13 and 14 were making measurements of the interplanetary magnetic field about 6 million km away. These spacecraft observed at most a very weak disturbance several hours after the peak of the event at Pioneer Venus. Had the event been a solar initiated disturbance it should have been seen almost unaltered by the Venera spacecraft. Thus the Venera 13 and 14 data provide further evidence for the cometary nature of this event.
Vertical distortion in Long Valley, California, associated with the January 1983 earthquake swarm
Authors: Whitcomb James H. , Rundle John B.
Published: February 2008

Beginning in the summer of 1982, a series of repeated, high‐precision, gravity measurements have been undertaken in Long Valley, California. Benchmarks have been established from south of Crowley Lake outside the caldera, to Mono Craters in the north. Stations are reobserved at frequent intervals with three Model G, LaCoste‐Romberg gravity meters. We observed significant changes in surface gravity associated with the January 1983 earthquake swarm in the south moat of Long Valley caldera. These changes indicate that the ground around the Casa Diablo hot springs area was uplifted at the time of the swarm. The uplift pattern agrees with that predicted by the model of Rundle and Whitcomb, that is, injection of magma into two chambers at 5 to 8 km depth beneath Long Valley Caldera.
Affirmation of triggered Jovian radio emissions and their attribution to corotating radio lasers
Authors: Calvert W.
Published: February 2008

The diverse criticisms of jovian radio triggering, by Desch and Kaiser, are considered invalid primarily because they stemmed from ignoring the original event criteria. Moreover, attributing the observed triggerings to accidental encounters with a constant rotating beam is unjustified, as should have been obvious from the original analysis, since they occurred at the wrong jovian phases. On the other hand, there is nothing wrong with a rotating source also being triggerable, and it is proposed that the triggered emissions originate from just such sources.
Observations of double arch formation in the Bering Strait
Authors: Torgerson Lenora J. , Stringer William J.
Published: February 2008

During the time that ice is present in the Bering Strait, it is constantly moving, both northward and southward, subject to wind and current stresses. There were, however, several times in the last decade when the ice was prevented from travelling through the Strait. The blockage of ice was due to the formation of fairly stable double arches that extended across the Strait.

Six episodes of double arch formation, resulting in ice blockage in the Bering Strait, were recorded on NOAA satellite imagery spanning the last eleven years; one additional episode was seen on Landsat imagery. All of the incidences of double arching occurred between February and May. In the most extreme case the arches prevented the southward flow of ice through the Strait for at least 27 days during April and May 1980.
Heat flow and lithospheric thinning in the Ligurian Basin (N. W. Mediterranean)
Authors: Jemsek J. , Von Herzen R. , Rehault J.‐P. , Williams D. L. , Sclater J.
Published: February 2008

We present preliminary results of 78 new heat flow measurements collected on a transect across the central Ligurian Basin (South France to Corsica margins). The basin‐wide flux has an average of 79 ± 21 mWm−2 with significant local and regional variability. Correction for the deposition of up to 5 km of post‐rift sediment gives a mean value of 102 mWm−2 which is similar to values for normal oceanic crust of the same age (21 Ma). The total tectonic subsidence (TTS) calculated for the region with probable oceanic crustal structure is comparable to or somewhat greater than 21 Ma crust of the major ocean basins. The heat flow data overall are compatible with the observed TTS in showing substantial lithospheric thinning, but do not tightly constrain thermal models of continental extension and rifting.
Surface deformation and geoid anomalies over single and double‐layered convective systems
Authors: Koch Manfred , Yuen D. A.
Published: February 2008

Using a primitive variable formulation of the finite‐element method, we have compared the differences in the surface observables, such as topography and geoid, produced by single‐ and double‐layered thermal convection. Both constant and depth‐dependent viscosities have been considered. For the same Rayleigh number larger surface perturbations are produced by single‐cell convection. For the same Nusselt number the magnitudes of the surface observables are greater for double‐layered convection. For the same surface heat‐flux, surface topographies have similar magnitudes, but the relative amplitudes of geoid anomalies depend greatly on the style of viscosity stratification. This difference in the geoid between the two systems increases with greater surface heat‐flow, regardless of viscosity structure.
Identification of aftershocks of deep earthquakes by a new ratios method
Authors: Frohlich Cliff , Davis Scott
Published: February 2008

We describe a new statistical method for identifying pairs or groups of related events in sequences which resemble, but are not identical to, a Poisson process. For a particular earthquake, we form the ratior(Nb,Na)of the relative origin times of theNath subsequent event and theNbth previous event. We then find the probability that such a ratio could occur if the sequence were a Poisson process. Presumably, sequences where the ratio is too small to be probable contain related events, and the subsequent events are aftershocks. Since the method requires knowledge of the origin times of only a few preceding and subsequent events, it is more powerful than methods which require knowledge of the mean activity rate of the Poisson process. Using this ratios method, we searched the ISC catalog for aftershocks of earthquakes with focal depths exceeding 70 km. From the world as a whole, events with at least one aftershock can be found in all depth ranges, including 250 km to 450 km. However, the incidence of aftershocks is significantly lower for events between 100 and 450 km than for shallower or deeper events.
Calculation of charge‐state ratios for satellite Tori
Authors: Summers Danny , Siscoe George L.
Published: February 2008

We model the diffusion of ions in a satellite plasma torus by means of a symmetric one dimensional random walk in which the particle source is at O, the particle sink is at N (an integer ⩾ 2), and the scale size of the diffusion cell is unity. We obtain the probability distribution function of the number of steps to exit for an ion or, equivalently, the probability distribution of ion residence times. This distribution is used in a model incorporating ionization by electron impact to derive steady state expressions for the ratio of the numbers of doubly to singly ionized ions, and the total number of ions in the torus. These expressions involve the diffusion time scale τs, the ionization time scale τi, and N. We compare the result for the charge‐state ratio with its corresponding value based on the assumption that all ions reside in the torus for the mean residence time, the latter being the standard assumption. Typically, we find that for given values of τs, τi and N our result is twice that obtained with the standard assumption. We apply the results to the torus of the Jovian satellite Io to predict mean residence times for sulphur and oxygen ions. A factor of two reduction in the time required to produce the observed charge state partitioning gives residence time estimates closer to those found by considering power requirements.
Modelling polarity transitions with radial dipole sources: Geomagnetic field behavior at northern mid‐latitudes
Authors: Kaiser Alen D. , Verosub Kenneth L.
Published: February 2008

The behavior of the geomagnetic field during polarity transitions has been studied by modelling Parker‐Levy cyclonic convection cells with radial dipole sources located at the core/mantle boundary. The polarity transitions are generated by inverting the dipoles in an ever‐increasing spherical cap. Initial results for observation sites at northern mid‐latitudes demonstrate the dependence of the observed behavior of the geomagnetic field on the location of the center of the spherical cap. Although the modelling reproduces certain features of earlier models, it also accounts for observed phenomena not predicted by the other models. By initiating the reversal at 70°S, 30°W, we obtain a good fit to the available data for the Brunhes‐Matuyama transition as observed at northern‐latitude sites.
The ice flow velocity profile for Dye‐3, Greenland
Authors: Shoji Hitoshi , Langway Chester C.
Published: February 2008

Uniaxial compression tests were made on 72 deep ice core specimens taken from 14 depth intervals between 247 m and 2021 m on the Dye‐3 Greenland ice core. Test results give stress exponent values ranging from 2.7 to 3.2, which are in close agreement to the 3.0 measured on laboratory‐manufactured polycrystalline ice specimens. These test results are compared with similar measurements made in a field laboratory immediately after the ice core was recovered. The data sets showed no significant differences over the four‐year time span. The horizontal velocity profile is calculated for Dye‐3 using a strain‐rate enhancement factor relationship and using stress exponent and activation energy values measured for artificial laboratory ice. The calculated profile is in good agreement with the results from direct borehole tilting measurements. This is the first time such a close correlation has been affected between laboratory‐generated experimental data and field measurements in the analysis of a horizontal velocity profile for a large ice sheet.
The Pioneer Venus Orbiter event of February 11, 1982: Of cometary or solar origin?
Authors: Russell C. T. , Luhmann J. G. , Elphic R. C. , Barnes A. , Mihalov J. D.
Published: February 2008

On February 11, 1982, an unusual cusp‐shaped temporal variation in the interplanetary magnetic field was detected by the Pioneer Venus orbiter. While variations of the Helium content of the solar wind were detected on the preceding day, these changes had no obvious relationship to the occurrence of the cusp‐shaped temporal variation in the IMF on February 11. In fact the solar wind He content was quite nominal on February 11. The magnetic variations were also quite unlike those previously reported to be magnetic clouds. Moreover, the scale size of the disturbance had to be smaller than 4×106 km and thus of cometary dimensions rather than of dimensions usually found in solar initiated events. Thus, we see no need to alter our original interpretation that the observations of Pioneer Venus on February 11, 1982 were consistent with the passage of a comet close to Venus.