bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic profiling of suspended sediments in the marine bottom boundary layer
Authors: Young Robert A. , Merrill John T. , Clarke Thomas L. , Proni John R.
Published: February 2008

An acoustic (3 MHz) backscattering profilometer has been developed for study of sediment transport in the bottom boundary layer. Laboratory experiments indicate reasonable correlations between backscattering intensity and mass concentrations for well‐sorted fine to coarse quartz sands typical of those found in marine sediments. Departure of the calibration curves from their expected values is thought to be due to the non‐spherical shape of the quartz grains. Field experiments on the inner shelf using the profilometer combined with velocity profiles show individual profiles (taken at 1 Hz) during erosion events are characterized by highly variable concentrations. Surface wave groups rather than individual waves appear to be correlated with groups of profiles with high concentrations extending 25‐100 cm above bottom. Averaging produces smooth profiles which fit well log‐normal distributions predicted by steady flow suspended load theories.
The MAGSAT mission
Authors: Langel Robert , Ousley Gilbert , Berbert John , Murphy James , Settle Mark
Published: February 2008

The MAGSAT spacecraft was launched on October 30, 1979, into a twilight, sun‐synchronous, orbit with inclination 96.76°, perigee 352 km and apogee 561 km. The Cesium vapor scalar and fluxgate vector magnetometers together measured the field magnitude to better than 2 nanotesla (nT) and each component to better than 6nT. Two star cameras, a high‐accuracy sun sensor and a pitch axis gyro provided the 10‐20 arc‐second attitude measurements necessary to achieve this accuracy. The magnetometers were located at the end of a boom to eliminate the effect of spacecraft fields. An optical system measured the attitude of the vector magnetometer and sun sensor (at the end of the boom) relative to the star cameras (on the main spacecraft). The data are available in several formats from the National Space Science Data Center and are undergoing analysis by a team of investigators.
Sensitivity of selected geomagnetic properties to truncation level of spherical harmonic expansions
Authors: Benton Edward R. , Estes Ronald H. , Langel Robert A. , Muth Lorant A.
Published: February 2008

A two day selection of MAGSAT data is fit by spherical harmonic series truncated at increasing levels NF in the range 2<NF<14 to determine the extent to which the geomagnetic Gauss coefficients depend upon truncation level of the fit. The dependence is found to be concentrated in the range n<NF≲n+4 decreasing rapidly in magnitude to a few nanotesla as n increases to about 6.

Several geomagnetic properties are then examined by evaluating them at various truncation levels N with NF fixed and N<NF. The spectrum of magnetic energy (outside the core and outside the earth) as determined by the NF=23 MAGSAT model MGST 1/81 is evaluated. It suggests that the crustal anomaly contribution to magnetic energy outside the core will not exceed 0.1%, when the expansion is truncated at N=8. The positions of certain contours of the geomagnetic elements on the core‐mantle boundary and their intersections needed for magnetic determination of the core motions, are examined and found to be relatively stable when N changes from 7 to 8, but to exhibit greater sensitivity for both larger and smaller values of N.

This article contains supplementary material.
Pole‐strength of the Earth from MAGSAT and magnetic determination of the core radius
Authors: Voorhies Coerte V. , Benton Edward R.
Published: February 2008

The unsigned magnetic flux linking earth's surface is evaluated numerically from a model of two days of MAGSAT data and found to be 16.054 GWb. Comparison with values calculated from earlier geomagnetic field models dating back to 1930 reveals a smooth, monotonic and recently accelerating decrease in earth's pole‐strenth at a fifty year average rate of 8.3 MWb/year or 0.052% per year.

Hide's magnetic technique for finding the radius of earth's electrically conducting core is tested in two ways. Main field models for 1960 and 1965 are first extrapolated downward through the nearly insulating mantle and then separately compared to equivalent extrapolated models of MAGSAT data. For each of these two earlier epochs, the unsigned flux is found to equal the MAGSAT value at a unique radius which is within 2% of the seismic core radius.

Main field models at the earlier epochs 1950, 1940, and 1930 are then derived from the 1960 main field, secular variation and secular acceleration coefficients of the GSFC 12/66 model. Truncation at degree N=8 and comparison with an equivalent MAGSAT model again yields magnetic values of the core radius within 2% of the seismic value. These results support the customary geophysical approximations that the mantle is nearly a perfect insulator and the core a perfect conductor on the decade time scale.
A preliminary comparison of the MAGSAT data and aeromagnetic data in the continental U.S.
Authors: Won I. J. , Son K. H.
Published: February 2008

A preliminary regional scale magnetic anomaly map derived from the MAGSAT data over the continental U.S. shows reasonably good correlations when compared with the corresponding aeromagnetic map. This conclusion is based upon the analysis of the fine attitude scalar MAGSAT data of about a two‐month duration starting November 2, 1979 and the analysis of the Project MAGNET U.S. aeromagnetic data in the same region.
Preliminary interpretation of magnetic anomalies over Japan and its surrounding area
Authors: Yanagisawa Masahisa , Kono Masaru , Yukutake Takesi , Fukushima Naoshi
Published: February 2008

The anomalies of geomagnetic total force over Japan and its surrounding area (20°‐50°N and 120°‐160°E) were interpreted by a magnetization of the earth's surface layer in a direction parallel to the main magnetic field. A negative magnetization anomaly in the Japan Sea may be attributable to the thinness of the magnetized part of the crust in comparison with the Japan Island. This is in accordance with the underground high temperature gradient suggested from the observed high heat flow values in the Japan Sea area.
New evidence of a meridional current system in the equatorial ionosphere
Authors: Maeda H. , Iyemori T. , Araki T. , Kamei T.
Published: February 2008

An interesting variation in the geomagnetic D‐component has been found by analysis of the Magsat data. Characteristics of this variation are: that it appears everyday on the low‐latitude duskside and is antisymmetric about the dip equator (negative in the northern hemisphere); that the magnitude (from 5 to 25 nT) depends upon the geographic longitude and altitude; and that no corresponding change can be seen on the ground magnetic data. The change suggests a meridional current system in the equatorial ionosphere, produced in association with the electrojet current along the dip equator. This effect should be taken into account in the study of geomagnetic anomaly of internal origin with the Magsat data.
Model predictions of magnetic perturbations observed by MAGSAT in dawn‐dusk orbit
Authors: Hughes Terence J. , Wallis D. D. , Burrows J. R. , Wilson Margaret D.
Published: February 2008

One use to which Magsat data can be put is to test the various models of auroral current flow which have been generated in the past. To do this, predictions of the perturbation magnetic field can be calculated from a current model, and these can be critically examined in light of the Magsat data. In this progress report, current models derived from the electric field models of Heppner (1977) and the conductivity models of Wallis and Budzinski (1981) are used to predict the field at Magsat orbit. Some features of the predictions are compared with Magsat data.
A technique for modeling the magnetic perturbations produced by field‐aligned current systems
Authors: Klumpar D. M. , Greer D. M.
Published: February 2008

A computational procedure is introduced for calculating the magnetic fields produced by virtually any distributed system of electrical currents. This procedure is being applied to the modeling of magnetic fields produced near the earth and on its surface by horizontal currents flowing in the ionosphere and by the so‐called Birkeland currents flowing along the geomagnetic field at high magnetic latitudes. This report describes briefly the principles that underlie the technique and illustrates the results obtained when the model is applied to the interpretation of perturbation fields being measured by the polar‐orbiting magnetic fields satellite (MAGSAT). Even for a very simple assumed current distribution we calculate magnetic field residuals whose large‐scale features are similar to those deduced from MAGSAT measurements. A predominately sunward magnetic perturbation is obtained over the region poleward of the Region 1 current system as a natural consequence of balanced Region 1 and Region 2 currents. The model predicts the existence of low‐latitude magnetic effects of auroral currents that represent potential sources of error for spherical harmonic representations of the geomagnetic field.
The 1981 microearthquake swarm near Moodus, Connecticut
Authors: Ebel John E. , Vudler Vladimir , Celata Michael
Published: February 2008

From August through October, 1981 an intense microearthquake swarm of over 500 events was detected near Moodus, Connecticut, the site of persistent small earthquake activity throughout the historical record. The swarm consisted of 39 foreshocks which preceeded the magnitude 2.1 mainshock, a normal pattern of aftershocks which immediately followed the main shock, and later smaller bursts of microearthquakes associated with migrations of the event epicenters. The shocks were all within 1 km of the earth's surface and located along a 5 km long segment of the Salmon River. Earthquakes of magnitude less than 1 were felt and events as small as magnitude 0 were heard by people living near the epicenters.
A multi‐frequency radiometric measurement of soil moisture content over bare and vegetated fields
Authors: Wang J. R. , Schmugge T. J. , Gould W. I. , Glazar W. S. , Fuchs J. E. , McMurtrey J. E.
Published: February 2008

An experiment on soil moisture remote sensing over bare, grass and alfalfa fields was conducted during July ‐ September 1981 with 0.6 GHz, 1.4 GHz, 5.0 GHz, and 10.6 GHz microwave radiometers mounted on mobile towers. Ground truth acquisition of soil moisture content, ambient air and soil temperatures was made concurrently with the radiometric measurements. Biomass of the vegetation cover was sampled about once a week. Soil density for each of the three fields was measured several times during the course of the experiment. The results of the radiometric measurements confirm the frequency dependence of moisture sensing sensitivity reduction reported earlier by Kirdiashev et al. (1979). The present work extends the frequency range of earlier measurements down to 0.6 GHz. Observations over the bare, wet field show that the measured brightness temperature is lowest at 5.0 GHz and highest at 0.6 GHz frequency, a result contrary to the expectation based on the estimated dielectric permittivity of soil‐water mixtures and current radiative transfer model in that frequency range.
Induction in a transatlantic cable at periods between 20 minutes and one day
Authors: Lanzerotti L. J. , Meloni A. , Medford L. V. , Gregori G. P.
Published: February 2008

Power spectral anaylses are presented of the voltage fluctuations in a transatlantic cable on two days of moderate geomagnetic activity and four days of magnetic quiet. The voltage fluctuations with periods from about twenty minutes to a day are predominantly of geomagnetically‐induced origin, with similar peaks often found in the geomagnetic and voltage spectra. The voltage spectral power Sv at a given frequency f can be expressed in terms of the horizontal field spectral power SH as βSHfγ.
Single vortex current system in the polar region generated by an interplanetary shock wave
Authors: Iyemori Toshihiko , Araki Tohru
Published: February 2008

The equivalent current of an SC main impulse in the polar region is found to be a single vortex current system which encircles the cusp region when the interplanetary magnetic field is continuously northward in the vicinity of an interplanetary shock wave. The twin vortex current pattern hitherto believed as the current system of the main impulse tends to appear when the IMF is southward. We present evidence suggesting that this IMF dependence of the current pattern comes from the superposition of the twin vortex structure of the DP2 current or the substorm current system on the single vortex system of the main impulse.
Gravity‐wave generation by thunderstorms observed with a vertically‐pointing 430 MHz radar
Authors: Larsen M. F. , Swartz W. E. , Woodman R. F.
Published: February 2008

During September of 1979, the Arecibo Observatory 430 MHz Doppler radar was used to study the upper troposphere and lower stratosphere during thunderstorm activity in the afternoon hours. It was found that when the clouds developed sufficiently in the vertical direction to reach the height of the tropopause, gravity‐wave oscillations in the vertical velocity above the tropopause would develop. The amplitude was 2 m/s, and the period was close to 6 min.
Formation of sulfur dioxide and methanesulfonic acid in the photooxidation of dimethyl sulfide in the air
Authors: Hatakeyama Shiro , Okuda Michio , Akimoto Hajime
Published: February 2008

Photooxidation of dimethyl sulfide (DMS) in air in the presence of NO was studied. Sulfur dioxide (SO2) and methanesulfonic acid (CH3SO3H) are major sulfur‐containing products. In the reaction systems of DMS‐NO‐air with low initial NO concentration and DMS‐CH3ONO‐air, in which OH radical‐initiated photooxidation prevails, the yield of SO2 was determined to be 20.7 ± 1.2 %. The yield of methanesulfonic acid is more than 50 % of the consumed DMS. Sulfuric acid was also detected as a minor product with a yield of less than 2 %. The implications of these results on the atmospheric sulfur cycle are discussed.
Venus nightside ionosphere: A model with KeV electron impact ionization
Authors: Kumar Shailendra
Published: February 2008

A model of the ‘full up’ nightside ionosphere of Venus is presented for the equatorial midnight region. We propose keV electron impact as the strongest source of ionization leading to peak ion density of ≃105 cm−3 which was observed by the PV‐OIMS experiment on several occasions. The observed altitude profiles of CO2+, O+, O2+, H+ and H2+ (or D+) can be reproduced with this model if available keV electron flux is approximated by øe(E) ∼ 100 E e −E/1000 in 0.3 ‐ 3.0 keV range. This is a reasonable extrapolation of fluxes observed at lower energies.
Venus: Comparison of gravity and topography in the vicinity of Beta Regio
Authors: Reasenberg R. D. , Goldberg Z. M. , Shapiro I. I.
Published: February 2008

The Doppler tracking data obtained from the Pioneer Venus Orbiter when it passed near Beta Regio yielded a peak vertical anomaly of 150 mGal when analyzed by our two stage procedure. A comparison of maps of the gravity and topography at comparable resolution shows a striking correlation. A scatter plot shows that the observed gravity anomaly is approximately 0.4 of that expected from uncompensated topography of half the mean density of Venus. However, the spectral admittance shows that the gravity anomalies can not be explained either by Airy compensation at fixed depth or by a model comprising an elastic plate atop an inviscid fluid. The gravity and topography variations may signify deep compensation or dynamic support for Beta Regio and more shallow compensation for other features.
Vertical column abundance of atmospheric OH at solar maximum from Fritz Peak, Colorado
Authors: Burnett Clyde R. , Burnett Elizabeth B.
Published: February 2008

New measurements of the vertical column abundance of atmospheric hydroxyl have been taken at Fritz Peak Observatory, Colorado, through the period of maximum solar activity of Solar Cycle 21. The OH abundance increase of about 12%/year observed since 1976 ended with the peak solar activity in 1980. The overhead‐sun column abundance increased from 5.4 × 1013/cm² in 1977 to 9.5 × 1013/cm² in 1980. The 1981 observations show a subsequent average decrease of about 3%. The seasonal average abundances for the entire 1976–1981 period show a good linear correlation with the corresponding sunspot number averages. A high‐sun enhancement of about 2 × 1013/cm² occurred during the 1979–1980 period; the resulting steep sec χ‐distribution has persisted into 1981.
Unreliable paleomagnetic results from the Wilkins Peak Member of the Eocene Green River Formation, Wyoming
Authors: Sheriff Steven D. , Shive Peter N.
Published: February 2008

A paleomagnetic investigation of in‐situ and exploration drill core samples of the Wilkins Peak Member of the Eocene Green River Formation in the Green River Basin of Wyoming yielded poor and unreliable paleomagnetic results. X‐ray and thermomagnetic analysis of samples from the study shows that pyrrhotite is the dominant magnetic mineral in the samples; pyrrhotite is known to be a common authigenic phase in Green River Basin sediments. Two earlier studies of the Green River Formation suggest unexpected behavior of the Eocene magnetic field; magnetite was identified in one sample of the former study. Similar lithologies have been sampled by all three studies. Because magnetic mineralogy may vary from authigenic to primary within one rock type, it is important for future paleomagnetic studies of the Green River Formation to carefully investigate the mineralogy and timing of remanence acquisition.
On the emission of carbon, nitrogen and sulfur in the atmosphere during bushfires in intertropical savannah zones
Authors: Delmas Robert
Published: February 2008

The fluxes of carbon, nitrogen and sulfur emitted to the atmosphere during bushfires in intertropical savannah zones are evaluated by measuring these three elements in various samples of plants and ashes collected before and after the fires in a savannah of Ivory Coast. We show that almost all the carbon and nitrogen, and over half the sulfur contained in the vegetation are released into the atmosphere during bushfires. Owing to the great extent of the areas burnt annually, this phenomenon constitutes an important spurge of C, N and S for the atmosphere : 1‐3.1×109 ton carbon, 5‐15×106 ton nitrogen and 0.4‐1.2×106 ton sulfur.
Two‐component proton spectra in the inner Saturnian magnetosphere
Authors: Krimigis S. M. , Armstrong T. P.
Published: February 2008

The Low Energy Charged Particle (LECP) experiment onboard the Voyager‐2 spacecraft performed extensive measurements of energetic (∼28 keV ≲ Ep ≲ 150 MeV; ∼ 22 keV ≲ Ee ≲ 20 MeV) protons and electrons during spacecraft passage through the inner magnetosphere of Saturn in August 1981. Analysis of the measurements inside the orbits of Enceladus and Mimas reveals the presence of a two‐component proton spectrum consisting of a low‐energy population at ≲ 500 keV identified for the first time and described by dj/dE = KE−2.5, and a high‐energy part at E ≳ 16 MeV whose spectral form is similar to that expected from cosmic ray neutron albedo decay (CRAND), as previously inferred by the Pioneer‐11 investigators from integral measurements. In addition, there exist large fluxes of high (≳ 1.5 MeV) and low (22 to 35 keV) energy electrons (∼3.7 × 105 and ∼1.1 × 105 cm−2sec−1sr−1, respectively) throughout this region. The pitch angle distribution of low energy protons changes from a simple sin2/3 α dependence to one where intensities near 90° become depleted as the spacecraft approached the planet’s ring plane at ∼ 2.88 RS. It is likely that the pitch angle depletion is due to proton interactions with the tenuous G‐ring. These observations also resolve a number of uncertainties regarding the presence of energetic protons and electrons inside the orbits of Enceladus and Mimas, arising from the analysis of Pioneer‐11 measurements.
Ion two‐stream and modified two‐stream instabilities in the magnetic neutral sheet
Authors: Lee L. C.
Published: February 2008

We study the stability of a magnetic neutral sheet that separates two regions of magnetized plasma. The particle species in the neutral sheet consists of: (a) trapped ions and electrons, which are confined within the current sheet, and (b) background ions and electrons, which partially penetrate into the current sheet. The diamagnetic currents of trapped particles and of background particles are in opposite directions, which produces an ion two‐stream distribution in the neutral sheet. It is found that, in addition to the lower hybrid drift instability, the ion two‐stream and modified two‐stream instabilities may occur in the neutral sheet with a thickness on the order of or smaller than the ion inertial length. These instabilities are also expected to occur in the dynamic diffusion region of magnetic reconnection.
ISEE‐1 and ‐2 observations of laminar bow shocks: Velocity and thickness
Authors: Russell C. T. , Hoppe M. M. , Livesey W. A. , Gosling J. T. , Bame S. J.
Published: February 2008

Thirteen bow shock crossings observed by ISEE‐1 and ‐2 have been used to determine the thickness and velocity of the quasi‐perpendicular laminar bow shock, i.e., those for which the Mach number and beta are low and the magnetic field is at large angles to the shock normal. The shock velocity ranges from a few kilometers per second to over 100 km/sec for these events. The shock thickness is found to be close to an ion inertial length, about 100 km for the conditions studied herein. In contrast to supercritical shocks, there is approximate equipartition of thermal energy between ions and electrons behind these shocks. Finally, there is a weak correlation between shock thickness and the angle between the interplanetary magnetic field and the shock normal, with more perpendicular shocks being thinner.
Atmospheric sodium chemistry I. The altitude region 70‐100 km
Authors: Sze N. D. , Ko M. K. W , Swider W. , Murad Edmond
Published: February 2008

Recent measurements indicate that the rate coefficient for
is three orders of magnitude faster than previously reported. Use of this new rate coefficient in current models will lead to Na concentrations in the upper mesosphere significantly lower than the observations. We propose that the restoration of the proper Na concentrations necessitates the reduction of NaO2 by O, particularly at night when photolysis of NaOH or NaO2 become ineffective Na sources.
Atmospheric photooxidation of methyl sulfide
Authors: Grosjean Daniel , Lewis Roger
Published: February 2008

Major gas phase products of the photooxidation of methyl sulfide (CH3SCH3) under atmospheric conditions are sulfur dioxide, formaldehyde, ozone and nitric acid, along with smaller amounts of methyl nitrate. Substantial formation of light‐scattering aerosols was observed, with inorganic sulfate and methane sulfonic acid as major components of the aerosol. Experimental results are discussed in terms of reaction pathways initiated by reaction of methyl sulfide with the hydroxyl radical.
Spectra of nuclear explosions, earthquakes, and noise from Wake Island bottom hydrophones
Authors: McCreery Charles S. , Walker Daniel A. , Sutton George H.
Published: February 2008

Spectral characteristics of P phases from 4 shallow focus earthquakes and 8 underground explosions, and of 52 samples of ocean bottom background noise, are examined by using tape recordings of ocean bottom hydrophones near Wake Island from July 1979 through March 1981. Significant differences are found between spectra of large shallow focus earthquakes and explosions (5.7 ≤ mb ≤ 6.3) observed at 61° to 77° epicentral distance. For similar magnitudes, explosions were found to have less energy at frequencies below 1.5 Hz and more energy at frequencies above 2.0 Hz. Earthquakes were found to have a spectral slope of −28 dB/octave (relative to pressure) over the band 1 to 6 Hz. Explosions were found to have the same spectral slope over the band 2.2 to 6 Hz, but a different slope of −12 dB/octave over the band 1.1 to 2.2 Hz. High frequencies (> 6 Hz) observed in the teleseismic P phases indicate high Q values for the deep mantle. Ambient noise levels on the ocean bottom near Wake are comparable to levels at the quietest continental sites for frequencies between 3 and 15 Hz. Also high levels of coherence (at least as high as 0.85) have been observed for P phases recorded on sensors with 40‐km separation.
A shear velocity discontinuity in the lower mantle
Authors: Lay Thorne , Helmberger Donald V.
Published: February 2008

A lower mantle S‐wave triplication is detected using short‐ and long‐period SH seismograms in the distance range 70° to 95°. Modeling of the observations with synthetic seismograms indicates that the triplication is produced by a 2.75 ± 0.25% shear velocity increase about 280 km above the core‐mantle boundary. The SH data from intermediate and deep focus events for three distinct source region‐receiver array combinations show generally consistent travel time and relative amplitude behavior of the triplication. There are small, systematic travel time shifts between the source regions which suggest regional variations in the depth of the discontinuity of up to 40 km.
Prediction of Fe2+ ‐ Mg2+ site occupancies in pigeonite
Authors: Castagna John P.
Published: February 2008

In the simple system CaSiO3‐FeSiO3‐MgSiO3, pyroxene M1 and M2 sites can be treated as distinct but interpenetrating solutions. In order to study the thermodynamics of the cation exchange between these sites, the simple mixture model is used as a first approximation of their nonideality. The intracrystalline cation distribution of iron and magnesium in synthetic pigeonite predicted in this way agrees well with experimental data.
Velocity and attenuation in sandstone at elevated temperatures and pressures
Authors: Jones Terry , Nur Amos
Published: February 2008

New measurements of seismic velocity and attenuation have been made in the kiloHertz frequency range to temperatures of 120°C, confining and pore pressure to 200 bars in Berea sandstone. With increasing temperature, shear velocity and attenuation decrease at all pressures in a fully saturated rock. The data suggest that thermal relaxation is not a significant loss mechanism under these conditions. We propose that dissipation is controlled by a viscous fluid flow mechanism, in which a sharp frequency peak in attenuation is shifted from 2kHz at room temperature to 8 kHz at 120°C as the pore fluid viscosity is decreased with increasing temperature. However, the velocity decrease is too great to be accounted for by a change of relaxation times. A non‐dispersive temperature softening in shear may control the velocities.
Nighttime VHF and GHz scintillations in the East‐Asian sector of the equatorial anomaly
Authors: Wernik A. W. , Franke S. , Liu C. H. , Fang D. J.
Published: February 2008

Measurements made during solar maximum years in the East Asian sector of the equatorial anomaly show different seasonal patterns of night‐time scintillation occurrence at 137 MHz at Lunping and 4 GHz at Hong Kong. These seasonal variations are very similar to that observed at the equatorial station in Guam, indicating strong coupling between equatorial and anomaly irregularities. Model computations indicate that the GHz scintillation observed at Hong Kong is much stronger than one would expect based on VHF scintillation measured at Lunping. It is suggested that this might be an indication of strong latitudinal dependence of scintillation in the anomaly region. We also discuss the possible difference in local ionospheric conditions that were responsible for generating GHz scintillation causing irregularities in the anomaly region and at the equator.
On the equatorial transport of Saturn's ionosphere as driven by a dust‐ring current system
Authors: Ip W.‐H. , Mendis D. A.
Published: February 2008

The diurnal modulation of the dust ring current of Saturn's D‐ring causes field‐aligned Birkeland currents to flow near the dawn and dusk terminators and close across the mid‐latitude ionosphere. One consequence of this current system is the establishment of a global convection pattern in the equatorial outer ionosphere. Outward motion of the dayside ionospheric plasma as well as the corresponding absorption effect of the inner ring system might be one physical cause of the depletion of the ionospheric content of Saturn.
The driving mechanism of plate tectonics: Relation to age of the lithosphere at trenches
Authors: Carlson R. L. , Hilde T. W. C. , Uyeda S.
Published: February 2008

Sea‐floor age‐depth and age‐trench‐depth relations suggest that the oceanic lithosphere continues to thicken and subside with age beyond 80 Ma. If so, slab‐pull (FS) and ridge‐push (FR) forces can be calculated from the age of the sea floor at trenches (t), and if the shear stress acting on the base of the plate increases with absolute velocity (νa), the approximate force balance equation is

math image
where D, S and R are constants related to drag, slab pull and ridge push, respectively. The relation between velocity and age is

urn:x-wiley:00948276:media:grl2256:grl2256-math-0002
We have tested this model by linear regression using rate and age data for 15 trenches:

urn:x-wiley:00948276:media:grl2256:grl2256-math-0003
The strength of this correlation (r² = 0.98) is strong evidence in favor of the validity of this simple model. These results suggest that ridge push is just sufficient to overcome drag at the base of the plate, and does not contribute significantly to the motions of oceanic plates, though the value of R′ is consistent with the motions of plates not attached to subducted slabs.
Sulfuric acid vapour derivations from negative ion composition data between 25 and 34 km
Authors: Arijs E. , Nevejans D. , Ingels J. , Frederick P.
Published: February 2008

Negative ion composition measurements obtained during a valve controlled balloon flight were used to derive (H2SO4 + HSOy) number densities between 25 and 34 km altitude. The data are compared to similar results obtained for other stratospheric temperatures. The implications of the results on our present ideas about aerosol formation are briefly discussed.
Dielectric currents in the low‐latitude boundary layer and geomagnetic tail
Authors: Cole K. D.
Published: February 2008

We consider a collisionless plasma with E (the electric field) parallel to the y‐axis of a cartesian frame of reference and B (the magnetic induction) parallel to the z‐axis. When there is a gradient, orthogonal to B, of the quantity ϵE², where ϵ = 1 + 4πρm c²/B², where ρm is the plasma mass density and c the speed of light, there is driven a (dielectric) current (j) given in the following two cases, by

urn:x-wiley:00948276:media:grl2299:grl2299-math-0001
(i) When ▽(ϵE²) is parallel to E, j is in the direction of E × B, and (ii) when ▽(ϵE²) is in the direction E × B, j is in the direction of E. In the former case it follows that, in a steady state,

urn:x-wiley:00948276:media:grl2299:grl2299-math-0002
along a line in the y‐direction, and in the latter case

urn:x-wiley:00948276:media:grl2299:grl2299-math-0003
on a line in the x‐direction where p⊥ is the pressure perpendicular to B. The currents related to ϵE² are geophysically significant in the region of interaction of the solar wind and geomagnetic field in the low latitude boundary layer and geomagnetic tail. The last written equation enables a realistic estimate of the cross‐tail electric field to be made.
Upstream electron oscillations and ion overshoot at an interplanetary shock wave
Authors: Potter Douglas W. , Parks G. K.
Published: February 2008

During the passage of a large interplanetary shock on 13 October 1981, the ISEE‐1 and ‐2 spacecraft were in the solar wind outside of the upstream region of the bow shock. The high time resolution data of the University of California particle instruments enable us to pinpoint the expected electron spike as occurring just before the magnetic ramp. In addition, two features that occur at this shock have not been observed before: 1) electron oscillations associated with low frequency waves upstream of the shock and 2) sharp ‘overshoot’ (∼1 sec) in the ion fluxes that occur right after the magnetic ramp. This interplanetary shock exhibits many of the same characteristics that are observed at the Earth’s bow shock.
Solar wind disturbances in the outer heliosphere, caused by six successive solar flares from the same active region
Authors: Akasofu S.‐I. , Hakamada K.
Published: February 2008

Solar wind disturbances caused by six hypothetical flares from the same active region are traced out to about 15 au, using a simple, empirical modeling method developed by Hakamada and Akasofu [1982]. Our method provides a first order construction, temporal and spatial, of flare‐induced shocks and their multiple interactions with each other, as well as with the corotating interaction regions. The results are discussed in connection with recent cosmic ray observations by space probes.
Remote determination of the outer radial limit of stormtime Pc5 wave occurrence using geosynchronous satellites
Authors: Barfield J. N. , Lin C. S.
Published: February 2008

Magnetic field data from the geostationary satellites GOES 2 and GOES 3 have shown the characteristics of stormtime Pc5 waves to vary dramatically with local magnetic field inclination angle. To investigate this effect, we scanned data from GOES 2 and GOES 3 for the twelve‐month period March 1979‐February 1980. During this time GOES 2 was at 104±4° west geographic longitude (9.6±0.4° north magnetic latitude), and GOES 3 was at 135° west geographic longitude (4.7° north magnetic latitude). 105 Pc5 events were observed at GOES 3, and 28 events at GOES 2. During the period of study, only one event was observed at GOES 2 when no waves were observed at GOES 3. Using the GOES 3 Pc5 events as a control set, we investigated the dependence of GOES 2 Pc5 occurrence on the local magnetic field inclination angle. Further, using a simple partial ring current model to produce field distortion at GOES 2, we determined the equivalent L value of GOES 2 for each 10‐minute interval during which Pc5 waves were observed at both satellites. During 93% of the Pc5 wave intervals, the local magnetic field inclination angle was less than 40°, corresponding to an outer limit of L=7.4.
Reflection of MHD‐waves in the Pc4‐5 period range at ionospheres with non‐uniform conductivity distributions
Authors: Glaßmeier Karl‐Heinz
Published: February 2008

A theoretical model is proposed which describes the influence of non‐uniform ionospheric conductivity distributions on ULF‐pulsations. The assumption is made that the field‐aligned currents carried by the wave‐field are closed by polarisation currents in the magnetosphere and by the irrotational part of the ionospheric currents. Current continuity at the magnetosphere‐ionosphere boundary provides for a differential equation for the reflected electric field for arbitrary non‐uniform conductivity distributions. A solution of the equation for two simple but realistic conductivity and electric field distributions shows that anomalies in the reflected electric field can occur which are confined to the conductivity gradient region. Under certain conditions also double peak electric field disturbances have been obtained.
Geometry of magma bodies beneath Long Valley, California determined from anomalous earthquake signals
Authors: Sanders Chris O. , Ryall Flori
Published: February 2008

One hundred and ninety‐two small earthquakes which occurred recently near the southern edge of Long Valley caldera at depths from 1 to 13 km are used to map the subsurface geometry of magma bodies in the caldera. Seismograms of these events recorded northwest, north, northeast, and east of Long Valley with ray paths through the caldera are often anomalous in that S‐wave arrivals are absent and high frequency P‐wave energy is missing. These anomalous ray paths intersect in an area of the south‐central caldera which we interpret to be a region of molten or partially molten rock. This magma body lies between about 4 1/2 and at least 13 km depth and is 10 km long by 5 km wide beneath 7 km. The magma appears to be relatively contiguous below 7 km and more dispersed above. Another magma body may be present in the northwest caldera coincident with an interpreted 7‐8 km deep reflection from the top of a magma chamber.
Local earthquakes on three‐component seismographs: Heterogeneity in the aftershock zone of El Asnam, Algeria (10.10.1980, M = 7.3)
Authors: Nercessian A. , Sapin M. , Hirn A. , Wittlinger G. , Djeddi M.
Published: February 2008

Seismograms of aftershocks of the El Asnam earthquake recorded by three‐component stations of a local array provide direct evidence of structural heterogeneity in the aftershock zone. Inversion of arrival times for three dimensional velocity structure is thus needed for the relocation of hypocenters. These fall within a reduced depth interval from 6 to 12 km in the underthrust block.
Simulation of auroral current sheet equilibria and associated V‐shaped potential structures
Authors: Singh N. , Thiemann H. , Schunk R. W.
Published: February 2008

Results from numerical simulations of auroral current sheet equilibria and associated V‐shaped potential structures are presented. It is shown that with allowance for both hot magnetospheric ion and cold ionospheric ion populations, the perpendicular potential drop, Φm, associated with a non‐neutral auroral current sheet is critically controlled by the temperature of the ‘heated’ ionospheric ions. The heating is caused by the wave turbulence excited by the auroral current sheet. In the presence of heated ionospheric ions, a relatively large variation in the temperature of the hot magnetospheric ion population causes a very small variation in the potential drop Φm. The perpendicular potential drop acts to produce a V‐shaped double layer with multiple potential steps parallel to the magnetic field when a zero potential boundary condition is imposed at the ionospheric boundary. Outside the V‐shaped potential structure, ionospheric return currents develop self‐consistently.
Siderophile, lithophile and mobile trace elements in the Lunar Meteorite Allan Hills 81005
Authors: Verkouteren R. Michael , Dennison Jane E. , Lipschutz Michael E.
Published: February 2008

Contents of siderophilic As, Au, Co, Ga and Sb, volatile/mobile Ag, Bi, Cd, In, Se, Te, Tl and Zn and lithophilic Cs, Rb and U determined by radiochemical neutron activation analysis in ALH A81005 are similar to those of lunar highlands samples returned by Apollo missions, indicating this meteorite's lunar origin. Five elements (Co, Ga and lithophiles) reflect lunar crustal processes while the remaining 11 siderophile and mobile elements (including the most mobile ones) indicate 1.4 ± 0.5% micrometeorite (Cl equivalent) admixture or enrichment by thermal redistribution on the moon. Thus, in contrast to L chondrites where severe shock caused trace element loss, impact‐launching of ALH A81005 to Earth was free of substantial (≤20 GPa) shock loading. In this light, a Martian origin for severely shocked SNC meteorites is plausible.
Composition of bulk samples and a possible pristine clast from Allan Hills A81005
Authors: Boynton William V. , Hill Dolores H.
Published: February 2008

Abundances of thirty‐five elements were determined in two bulk samples and a white clast in the Allan Hills A81005 meteorite. High siderophile element content indicates that the sample is a regolith breccia. An Fe/Mn ratio of 77 in this meteorite eliminates parent bodies of known differentiated meteorites as the source of ALHA 81005. The incompatible elements are very similar to those found in most lunar highlands rocks, and provide very strong evidence that the sample is lunar in origin. The clast sample has the trace element pattern of a lunar anorthosite and is very low in KREEP and siderophile elements. It may be a fragment of a pristine lunar rock.
Some dynamical properties of vortex streets in Saturn's atmosphere from analyses of Voyager images
Authors: Godfrey David , Hunt Garry E. , Suomi Verner E.
Published: February 2008

We present the first observations of a vortex street in an atmosphere other than that of the Earth made from a sequence of images of Saturn taken by Voyager 2 in August 1981. The analysis of these images shows that the feature sits at the maximum of the westward jet and suggests that it may be produced by material rising up from below the level of the visible clouds.
Ray trace model of the Santa Barbara, California, Land‐Sea Seismic Refraction Experiment
Authors: Keller B. , Prothero W. A. , Trehu A. M. , Stierman D. J.
Published: February 2008

A seismic refraction profile utilizing shots at sea and receivers on land and on the ocean bottom lies on a north‐south line from the southernmost Coast Ranges, across the western Transverse Ranges, to the northern Borderland at the longitude of Santa Barbara. Computer ray tracing to model the data from this profile shows significant lateral P velocity variations extending to at least 15 km depth. Although fault dips cannot be resolved by these data, most major faults mapped on the surface have a signature in the deeper crustal structures. A deep low velocity trough underlies the Montalvo trend in the Santa Barbara Channel. A narrow high velocity ridge is associated with basement rocks south of the Santa Cruz Island fault. These lateral velocity variations suggest that earthquake hypocenters and fault plane solutions calculated assuming a laterally homogenous crust‐model may be significantly in error.
One‐year Lidar observations of the stratospheric aerosol at Frascati, March 1982 ‐ March 1983
Authors: Adriani A. , Congeduti F. , Fiocco G. , Gobbi G. P.
Published: February 2008

Lidar measurements of the stratospheric aerosol burden over Frascati (42°N ‐ 13°E) in the period March '82 ‐ March '83 are reported. The arrival of the dust cloud generated by the El Chichon eruption was detected on late April 1982. Scattering ratios up to 10 were observed. The integrated backscatter between 12 and 28 km shows a fairly regular increasing trend over the whole period. The aerosol appeared at first stratified in thin layers; later, the entire region became fairly homogeneously filled.
Further paleomagnetic results from the Jurassic Topley Intrusives in the Stikinia Subterrane of British Columbia
Authors: Symons David T. A.
Published: February 2008

The 142 Ma old Jurassic Topley Intrusions are exposed in the middle of the Intermontane Belt or Stikinia subterrane of composite Terrane I of the Canadian Cordillera in central British Columbia. Thermal demagnetization at 560°C leads to the isolation of a single stable magnetic component directed at 324.2°, 54.1°, α95 = 8.6° in 17 of the 22 sites. The pole position of 238,2°W, 58.4°N, δp = 8.3°, δm = 11.8° for the component is discordant relative to the North American craton. This position supports previous work in suggesting that Stikinia has been translated northward by 14 ± 2° or about 1400 km between mid‐Cretaceous and pre‐Miocene time. It also suggests that the central portion of Stikinia has not been rotated about a vertical axis by a statistically significant amount whereas minor marginal blocks of the subterrane have been subjected to large and variable amounts of both clockwise and counterclockwise rotation.
Multiple ion streams in the near vicinity of the space shuttle
Authors: Stone N. H. , Samir U. , Wright K. H. , Reasoner D. L. , Shawhan S. D.
Published: February 2008

Differential measurements of ion flow direction and energy during the third Space Shuttle mission (STS‐3) have revealed the existence of ion streams in the near vicinity of the Orbiter at angles of attack as great as 50° with respect to the ram direction and typically with 10% of the ram current intensity. Neither the source nor the mechanism by which these secondary ion streams were created are known at present; however, it is reasonably certain that they are not of geophysical origin, but result from the interaction of the Orbiter with its environmental ionospheric plasma. The energy of the secondary streams was observed to be very close to the ion ram energy and they were, therefore, not detected by a standard planar Retarding Potential Analyzer (RPA) instrument. This leaves open the question as to their existence in the vicinity of orbiting spacecraft in general. Possible connections between secondary ion streams and phenomena previously observed in the vicinity of ionospheric spacecraft are mentioned.
Interferometric phase velocity measurements
Authors: Kintner P. M. , LaBelle J. , Kelley M. C. , Cahill L. J. , Moore T. , Arnoldy R.
Published: February 2008

Phase velocities of plasma waves near the lower hybrid frequency were measured with an interferometer composed of two spatially separated electron density probes. The plasma waves were produced in the F‐region ionosphere by an argon ion beam. By calculating the normalized cross spectrum of the plasma waves a coherency of .98 was estimated along with a maximum phase difference of π/3 radians between the two probes. This implies that the wavelength was 6 meters compared to an O+ gyroradius of 3.8 meters and that the phase velocity was 45 km/sec compared to an ion beam velocity of 12.4 km/sec. These numbers compare favorably with recent predictions of a nonresonant mode produced by a dense ion beam.
Polar cap vertical currents associated with northward interplanetary magnetic field
Authors: Araki Tohru , Kamei Toyohisa , Iyemori Toshihiko
Published: February 2008

Magnetic field data observed by MAGSAT at altitude between 250‐550 km clearly showed that a pair of vertical currents appears in the dayside polar cap when the interplanetary magnetic field (IMF) has a strong northward component. The currents were approximately symmetric with respect to the noon meridian, and flowed into the ionosphere on the duskside and away from it on the dawnside. These currents were very clearly seen on May 10, 1980, when the IMF was kept strongly northward all day long. The horizontal magnetic field along 10 successive orbits on the day indicated the signature. The distribution of the vertical magnetic field observed along the same orbits was reasonably explained in terms of the ionospheric Hall currrent which was produced when the vertical current flowed into or away from the ionosphere. The existence of such vertical currents was also confirmed by the statistical analysis over the whole MAGSAT data period.
Lithospheric stress near a ridge‐transform intersection
Authors: Morgan Jason Phipps , Parmentier E. M.
Published: February 2008

Oceanic lithosphere at a ridge‐transform intersection has distinct structural characteristics. The spreading axis and normal fault scarps, which parallel the ridge axis away from the intersection, locally curve towards the transform fault. This implies that the least compressive stress direction becomes oblique to the spreading direction near a ridge‐transform intersection. This stress field may be the result of a tensile ridge axis stress resisting plate separation and a transform shear stress resisting relative plate motion. A plane stress plate model with prescribed plate boundary stresses is formulated to explore this hypothesis. The orientation of the least compressive horizontal stress near an intersection depends strongly on the ratio of the applied boundary stresses. Thus ridge axis curvature may place an important constraint on plate boundary forces.