bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultimate strength of solids and formation of planetary cores
Authors: Davies Geoffrey F.
Published: February 2008

Some previous experiments and theory have suggested that the ultimate strengths of silicates are 1 ‐ 2 GPa (10 ‐ 20 kbar), that the ultimate strength of ice is about 0.1 GPa (1 kbar), and that the confining pressures of planetary interiors (∼100 GPa) would not increase these strengths by more than a factor of two. Deviatoric stresses of these magnitudes are easily generated in planetary interiors by density heterogeneities of tens of kilometers radius. This implies that once such heterogeneities had formed, core segregation would not be further inhibited by the strength of a cold protoplanetary interior. It is further suggested that core segregation may be initiated by heterogeneous impact heating well before extensive near surface melting occurs, and that in the most favorable circumstance segregation could begin in a 700 km‐radius protoplanet or a 500 km‐radius icy satellite. These considerations increase the likelihood that core segregation in larger planets and satellites was essentially contemporaneous with accretion.
A model for crystal development in dry snow
Authors: Adams E. E. , Brown R. L.
Published: February 2008

Calculations are made to determine the approximate excess pore vapor density in snow due to a temperature gradient and pore geometry. The approximate excess vapor density is found to be in part produced by the presence of a temperature gradient. This in turn effects the type of crystal which develops in the snowpack in the presence of a temperature gradient. Comparison with experimental evidence shows excellent agreement. Results presented here indicate that the prediction of crystal habit as determined by temperature and temperature gradient may be possible if the pore geometry can be adequately described.
Arid soils as a source of atmospheric carbon monoxide
Authors: Conrad Ralf , Seiler Wolfgang
Published: February 2008

CO fluxes between soil and atmosphere were measured by field studies under arid conditions in Germany as well as in a semidesert (Karoo) and a desert (Namib) in South and Southwest Africa. Arid soils usually acted as a net source of atmospheric CO. The CO emission rates were dependent on soil temperature and soil organic carbon content. CO emission turned into CO deposition, when the soils were irrigated. CO deposition was due to microbial CO consumption, whereas CO emission was due to chemical processes.
A Pioneer‐Voyager study of the solar wind interaction with Saturn
Authors: Slavin J. A. , Smith E. J. , Gazis P. R. , Mihalov J. D.
Published: February 2008

Voyager 1/2 observations are used to confirm and quantify the unusual bluntness of the dayside Saturn magnetopause suggested by the earlier Pioneer 11 measurements. Once corrected for variations in solar wind pressure, the Saturn observations are found to indicate a magnetospheric radius in the terminator plane equal to 1.8 times the nose distance. This ratio is 30% greater than the terrestrial value and is corroborated by the very blunt shape of the Saturn bow shock and large width of the forward magnetosheath. Possible causes and ramifications of these results for the solar wind interaction with Saturn are discussed.
Implication for stratospheric composition of a reduced absorption cross section in the Herzberg continuum of molecular oxygen
Authors: Brasseur G. , De Rudder A. , Simon P. C.
Published: February 2008

Recent determinations of O2 absorption cross sections in the Herzberg continuum, obtained from in situ solar irradiance measurements, have shown that the corresponding laboratory values might be overestimated by 30 to 50 percent. The change in the stratospheric composition due to such a reduction in these cross sections has been calculated by means of a steady state one dimensional chemical model. An accurate determination of the O2 absorption spectrum in the 200‐220 nm range is required since the distribution of several trace species is very sensitive to the atmospheric transmissivity in this wavelength region.
Current plate motions based on Doppler satellite observations
Authors: Anderle R. J. , Malyevac C. A.
Published: February 2008

About 50% of the Doppler observations made on a Navy Navigation Satellite over a 9 year period were analyzed to determine the motion of 8 sites on the North American plate and 12 sites on 7 other plates. The computed plate motions were not statistically significant compared with the standard errors of measurement of 1 to 5 cm/yr except for the Australian plate, European plate and Pacific plate. The measured motions of these plates are about twice those inferred from geologic records, but are in the proper direction.

Processing of the balance of the data on one satellite over the 9 year time interval would improve the accuracy of the determination by about 60%, improving the possibility of detecting additional statistically significant motions.

Unreasonable altitude changes at most sites are probably due to neglected higher order ionospheric refraction effects on the observations.
Reply to M. Berberian's Comment on the Paper, A. Mohajer‐Ashjai and A. A. Nowroozi “The Tabas Earthquakes of September 16, 1978 in east central Iran,” G.R.L. No. 9L0391
Authors: Mohajer‐Ashjai A. , Nowroozi A. A.
Published: February 2008

The Tabas earthquake of September 16, 1978, M=7.7, has been associated with extensive thrust faulting; there has been some confusion about the fault‐length associated with this earthquake. At least 70 km of fresh surface faulting is associated with this earthquake together with several branches of secondary faulting.

We thank Mr. Berberian for his interest in our paper, however, his aberrant comments have provided this opportunity for us to clarify several points. See Berberian (1982).
Exit of boundary layer plasma from the distant magnetotail
Authors: Heikkila Walter J.
Published: February 2008

It is pointed out that the boundary layer plasma must somehow leave the magnetospheric system. We propose that the boundary layers on the dawn and dusk flanks are continued into the far magnetotail, becoming joined together far downstream, still on closed magnetic field lines. Within the combined layer there would be a dusk to dawn electric field for antisunward convection (as is the case for the boundary layers on the dawn and dusk flanks nearer to the earth). It is suggested that the boundary layer flow is so massive that the flow itself can generate the right electric field for continued flow. Most of the plasma in the mantle over the polar caps would also be convected out in a similar manner, rather feeding the plasma sheet. There would be a stagnation point inside the magnetotail, with any boundary or mantle plasma diffusing earthward of this point becoming the plasma sheet. It is deduced that no steady state solution is possible.
Atmospheric turbidity over Africa ‐ Disturbed by the El Chichon Eruption?
Authors: Jaenicke R. , d'Almeida G. A.
Published: February 2008

In a network, the atmospheric turbidity over Africa is observed for two years. The most recent data from a central Sahara station show increased values but horizontal visibility remained unchanged. This large turbidity seems to be produced not only regionally, rather the temporal development points toward the eruption of El Chichon in Mexico.
Analysis of coregistered Landsat, Seasat and SIR‐A images of varied terrain types
Authors: Rebillard Philippe , Evans Diane
Published: February 2008

Multisensor image data (SIR‐A, Seasat SAR and Landsat MSS) over areas in northern Algeria and eastern Utah have been coregistered in order to assess the complementary effects of the orbital sensors for geologic mapping in two very different terrains. This first attempt at registering such a data set shows that the radar backscatter information provided by the SIR‐A image increases the classification accuracy of several geologic units over the Landsat image alone, and over combined Landsat and Seasat images.
Precise measurement of seismic traveltimes ‐ Investigation of variation from tidal stress in shallow crust
Authors: Liu Hsi‐Ping , Westerlund Robert E. , Fletcher Jon B.
Published: February 2008

We have conducted 8 precise seismic surveys near Hollister, CA, over a period of 1 y in an attempt to detect the traveltime variation caused by the solid‐earth tidal stress. The surveys were conducted along a 600 m baseline located in quartz monzonite hills 2 km west of the San Andreas fault. A 656 cm³ air gun fired in a mud‐filled pit 2 m deep provided a repeatable seismic source. The signals from two 2.3 Hz vertical‐component geophones 600 m apart were digitized at a nominal rate of 600 samples/s by two cassette recorders modified for precise synchronization of data sampling against a master clock. Each survey consists of ∼ 100 traveltime measurements over the 12 h period between 6 p.m. and 6 a.m. local time; the time frame of each experiment was limited by daytime cultural noises. Analysis of traveltime variation is done either by timing of amplitude extrema or by cross‐correlation of a waveform constructed from the digital data by a cubic‐spline interpolation. Fractional error of the repeatability of traveltime measurement is typically ±3.3 × 10−4 for the first high‐frequency, large amplitude arrival following the direct body waves. The first survey, conducted at a spring tide in August, 1981, showed a variation of Δt/t ∼ 2 × 10−3 and correlated in time with the extensional tidal strain component along the baseline direction. The next two surveys, conducted at two neap tides, showed variation of Δt/t ∼ 6 × 10−4 and also correlated with the same tidal strain component. However, the other 5 surveys conducted after the onset of 1981 rainy season and into the 1982 dry season, 4 at spring tides and 1 between a spring and a neap tide, showed traveltime constant to within 1 standard deviation. These results corroborate only partially the previously reported tidal stress variation of traveltimes in the shallow crust.
The Indian ocean gravity low: Evidence for an isostatically uncompensated depression in the upper mantle
Authors: Ihnen S. M. , Whitcomb J. H.
Published: February 2008

The broad gravity low in the equatorial Indian Ocean south of Sri Lanka is the largest and most striking feature in the gravitational field of the earth. The most negative long‐wavelength free‐air gravity anomalies are found there and the sea surface (geoid) lies more than 100 meters below the best fitting ellipsoid. We propose a model of the lithosphere and upper mantle which accurately predicts the observed free‐air gravity and geoid elevation. This model is consistent with bathymetry and sediment thickness data and suggests that the crust south of India currently floats as much as 600 meters lower than would be expected if the region were isostatically compensated. This residual depression of the crust is apparently confirmed by observations of ocean depth. An uncompensated depression is consistent with the downgoing arm of a convection cell, and also with the presence of a mechanical wake left in the upper mantle behind India as it traveled toward Asia.
An analysis of periodicities in the 1470 to 1974 Beijing precipitation record
Authors: Hameed S. , Yeh W. M. , Li M. T. , Cess R. D. , Wang W. C.
Published: February 2008

An analysis of a time series consisting of an annual index of dryness/wetness for the years 1470 to 1974 in Beijing, China is presented. Its power spectrum shows that dominant cycles occur with long periods of the order of 80 years. Cycles with periods of 11 and 22 years are weak or non‐existent, but a significant signal at 18.7 years (which is also the period of a component of the lunar tide generating force) is detected. The long term variations in Beijing precipitation appear to lag long term (Gleissberg) variations in solar activity by nearly 75 years. A pattern which spans nearly 150 years in the Beijing record is found to be repeated with notable similarity.
Dynamic compression of diopside and salite to 200 GPa
Authors: Svendsen Bob , Ahrens Thomas J.
Published: February 2008

New Hugoniot data on single crystal diopside, CaMgSi2O6 (Di), suggest that transformation to a high‐pressure thermomechanical state begins at ∼50 GPa and is complete above 100 GPa, in agreement with other pyroxenes and silicates of geophysical interest. Comparison of the new high pressure phase (HPP) data for Di and salite, CaMg0.82Fe0.18Si2O6 (Sa) with appropriate mixed oxide and perovskite models implies compatibility between either model and the data. Conversely, least‐squares fits to the HPP Di data favor lower (3.6 ‐ 3.9 Mg/m³) values of zero‐pressure, room‐temperature density than the models (4.0 ‐ 4.1 Mg/m³). Similar comments apply to porosity‐corrected HPP hedenbergite (Hd) data. The HPP Di, Sa, and Hd data also imply much larger density differences between these compositions in the HPP regime (e.g., ≈0.8 Mg/m³ between Di and Hd) than at STP (0.38 Mg/m³). This may represent the influence of multiple transition processes (e.g., polymorphism and Fe2+ high‐low spin) as a function of Fe content across the Di‐Hd series. The new HPP Sa data closely parallel (≈0.1 Mg/m³ less dense) the lower mantle density profile from ∼90 GPa to 136 GPa. Our results are consistent with the speculations of Jeanloz and Ahrens on the possibility of significant Ca in the lower mantle.
tropospheric oxalate
Authors: Norton R. B. , Roberts J. M. , Huebert B. J.
Published: February 2008

The existence of oxalate (COO)2= in tropospheric aerosols and in precipitation has been demonstrated using ion chromatography. Mixing ratios have been observed up to 50 pptv in air samples and 0.3 ppm in precipitation. Correlation of airborne oxalate with airborne nitrate suggests a pollution source.
Ion cyclotron waves in the io plasma torus: Polarization reversal of whistler mode noise
Authors: Gurnett D. A. , Goertz C. K.
Published: February 2008

Because of the presence of multiple ion species in the Io plasma torus whistler mode noise can be converted to ion cyclotron waves via a polarization reversal process at the local crossover frequency. Using whistler mode intensity measurements in the Jovian magnetosphere from Voyager 1 we estimate the pitch‐angle diffusion rates that would occur if the noise is converted to ion cyclotron waves. Typical pitch‐angle diffusion coefficients range from Dαα ≃ 10−6 sec−1 for protons resonating near the equator to Dαα ≃ 10−4 sec−1 for 10 keV O+ ions resonating at high latitudes. Although complete bounce averaged diffusion coefficients have not yet been computed, preliminary estimates indicate that the energetic ion precipitation caused by these waves may be able to account for the EUV auroral emissions at the foot of the torus field lines.
Transfer of pulsation‐related wave activity across the magnetopause: Observations of corresponding spectra by ISEE‐1 and ISEE‐2
Authors: Greenstadt E. W. , Mellott M. M. , McPherron R. L. , Russell C. T. , Singer H. J. , Knecht D. J.
Published: February 2008

Comparison of power spectra of magnetic field data from ISEE‐1 and ‐2 recorded simultaneously on both sides of the magnetopause showed that power level inside the magnetosphere varied with power level outside in the magnetosheath and suggested that the same frequencies were enhanced on the two sides of the boundary. Power levels were two to three orders of magnitude lower inside than outside the magnetosphere, indicating that wave energy was transmitted inside from the sheath, through a locally stable magnetopause.
Matching long term periodicities of geomagnetic reversals and galactic motions of the solar system
Authors: Negi J. G. , Tiwari R. K.
Published: February 2008

To understand the phenomenon of frequent reversals of axial geocentric dipole fields it is essential to understand the spectral structure of geomagnetic reversal series and search for possible exogenetic (cosmic) factors associated with its dynamic behaviour. A scheme of Walsh spectrum analysis (which is more efficient and appropriate for binary processes as compared to Fourier Spectrum Analysis and Maximum Entropy Method), has been applied, for the first time, to the available world‐wide paleomagnetic measurements during phanerozoic (last 570 million years). The results postulate long‐term cyclicity in magnetic stratigraphy with reversal periods of 285, 114, 64, 47 and 34 million years with distinct resolution. The similar analysis was further repeated by dividing the total record in two sub‐series. These results indicate mean periods of 71, 47 and 32‐ m.y. These peaks are statistically significant at 90% confidence level. These results, thus, question the widely accepted theory of randomness of geomagnetic reversal for long‐period sequence. Surprisingly, the maximum spectral power is found for the Cosmic year (285 m.y.) Term (period of complete revolution of solar system around the Milky way galactic centre). The other reversal periods correspond nicely with the solar system's periods of galactocentric radial motion, interaction of spiral density wave with galactic orbit and solar oscillation in and outside of orbital plane. Such a remarkable correlation and harmony between observed gravitational phenomena and terrestrial records of electromagnetic processes on the cosmic scale appear to be of fundamental importance in macroscopic physics.
Upward electron beams measured by DE‐1: A primary source of dayside region‐1 birkeland currents
Authors: Burch J. L. , Reiff P. H. , Sugiura M.
Published: February 2008

Measurements made by the High Altitude Plasma Instrument on DE‐1 have shown that intense upward electron beams with energies from ≈20 eV to ≈200 eV are a common feature of the region just equatorward of the morning‐side polar cusp. Computations of the currents carried by these beams and by the precipitating cusp electrons show excellent agreement with the simultaneous DE‐1 magnetometer measurements for both upward and downward Birkeland currents. The data indicate that cold ionospheric electrons, which carry the downward region‐1 Birkeland currents on the morning side, are accelerated upward by potential drops of a few tens of eV at altitudes of several thousand kilometers. This acceleration process allows spacecraft above those altitudes to measure routinely the charge carriers of both downward and upward current systems.
The role of compressive forces in intracratonic basin formation and mid‐plate orogenies
Authors: Lambeck Kurt
Published: February 2008

Lithospheric buckling due to compressive forces requires excessively large stresses. With some modifications of the elastic plate buckling problem, significant deformation can occur at compressive stresses of a few kbars, an order of magnitude less than required to induce elastic buckling. Three modifications are proposed. (i) The plate is considered as an effective viscoelastic layer subjected to an initial perturbation. (ii) When a compressive force is applied these perturbations are magnified and then grow with time. (iii) Uplifted areas are eroded and sediments are deposited in the downwarped areas. This mechanism appears to be relevant to the formation of some intracratonic basins such as those in central Australia. The mechanism can lead to significant orogenies away from plate boundaries such as the Petermann Ranges Orogeny and the Alice Springs Orogeny of central Australia.
Plasma regimes in the deep geomagnetic tail: ISEE 3
Authors: Bame S. J. , Anderson R. C. , Asbridge J. R. , Baker D. N. , Feldman W. C. , Gosling J. T. , Hones E. W. , McComas D. J. , Zwickl R. D.
Published: February 2008

Using a lunar gravitation‐assisted orbit, the ISEE‐3 spacecraft remained close to and within a previously unexplored part of the distant (60‐220 RE) geomagnetic tail nearly continuously from 1 January to 30 March 1983. An initial analysis of data obtained with the Los Alamos plasma electron analyzer onboard ISEE‐3 reveals that all of the plasma regimes identified previously with near‐earth measurements (i.e., plasma sheet, low‐latitude boundary layer, plasma mantle, lobe, and magnetosheath) remain recognizable entities in the distant tail as well. However, these regimes appear to be intermingled in a more chaotic fashion than near the earth. Typical flow velocities within the plasma sheet at ∼200 RE in this preliminary analysis are ∼500 km s−1 tailward, considerably higher than is characteristic of the near‐earth plasma sheet. Earthward flow within the plasma sheet has been observed occasionally, suggesting the temporary presence of a neutral line beyond 220 RE. Strong bi‐directional electron anisotropies are found throughout much of the distant plasma sheet, boundary layer, and magnetosheath.
The reaction of gas phase N2O5 with water vapor
Authors: Tuazon Ernesto C. , Atkinson Roger , Plum Christopher N. , Winer Arthur M. , Pitts James N.
Published: February 2008

The reaction of N2O5 with water vapor, a potentially important nighttime loss reaction for NOx and formation pathway for nitric acid, has been investigated at 298 ± 1 K in two environmental chambers of 3800 and 5800 L volume. From the N2O5 decay rates as a function of water vapor concentration, an upper limit to the N2O5 + H2O rate constant of less than 2.4 × 10−21 cm³ molecule−1 s−1 is derived. However, while gas phase nitric acid was observed to be a major product, its yield, especially at low water vapor concentrations, was significantly lower than the value of 2 expected, indicating that the overall reaction in these chambers involved both homogeneous and heterogeneous components. After allowing for the contribution of the heterogeneous reaction, an estimate of the gas phase homogeneous rate constant for N2O5 + H2O of 1.3 × 10−21 cm³ molecule−1 s−1 was obtained. While this value must still be regarded as an upper limit to the homogeneous rate constant, it is a factor of 10 lower than the only directly measured upper limit reported previously.
Identification of deuterium ions in the ionosphere of Venus
Authors: Hartle R. E. , Taylor H. A.
Published: February 2008

The dominant mass 2 ion in the ionosphere of Venus is identified as D+ through analysis of the height variation of [mass 2 ion]/[H+] measured in the chemical equilibrium region by the ion mass spectrometer on the Pioneer Venus Orbiter. This result leads to [D]/[H] = (2.2 ± 0.6) × 10−2 at the turbopause, which agrees with the ratio measured in the lower atmosphere by the large probe mass spectrometer. The 100‐fold deuterium enrichment supports previous suggestions that Venus has lost at least 0.3 percent of a terrestrial ocean.
Average configuration of the distant (<220 Re) magnetotail: Initial ISEE‐3 magnetic field results
Authors: Slavin J. A. , Tsurutani B. T. , Smith E. J. , Jones D. E. , Sibeck D. G.
Published: February 2008

Magnetic field measurements from the first two passes of the ISEE‐3 GEOTAIL Mission have been used to study the structure of the trans‐lunar tail. Good agreement was found between the ISEE‐3 magnetopause crossings and the Explorer 33,35 model of Howe and Binsack. Neutral sheet location was well ordered by the hinged current sheet models based upon near earth measurements. Between X=−20 Re and −120 Re the radius of the tail increases by about 30% while the lobe field strength decreases by approximately 60%. Beyond X=−100 to −120 Re the tail diameter and lobe field magnitude become nearly constant at terminal values of approximately 60 Re and 9 nT, respectively. These results are consistent with pressure balance across the distant magnetopause equating lobe field pressure, B²L/8π, and external solar wind thermal and magnetic pressure, nk(Te+Ti) + B²/8π. The distance at which the tail was observed to cease flaring, 100‐120 Re, is in close agreement with the predictions of the analytic tail model of Coroniti and Kennel. Overall, the findings of this study suggest that the magnetotail retains much of its near earth structure out to X=−220 Re.
Effect of the eruption of El Chichon on stratospheric aerosol size and composition
Authors: Oberbeck V. R. , Danielsen E. F. , Snetsinger K. G. , Ferry G. V. , Fong W. , Hayes D. M.
Published: February 2008

Dominant effects of the El Chichon eruption on stratospheric aerosols at 19.8 to 20.7 km are: (1) vapor depositional growth of the small‐aerosol (background) mode; (2) development of a large‐particle mode by sedimentation from the highest altitudes in the cloud; (3) a change in the large‐particle mode from sulfate‐coated silicates to sulfate aerosols, some with silicate cores; (4) a 100‐fold increase in sulfate mass in the large particle mode. Terminal velocities of large silicate particles, maximum r = 2.3 µm, sampled 1 month after eruption, and calibrated with the aid of lidar data, indicate initial injection to 26 to 27 km. Smaller velocities of sulfate aerosols, median r = 0.5 µm, are compatible with major growth in 2 to 3 months at 27 to 28 km. Aerosol settling accounts for the descent of the main lidar return to 26.5 km in August and to 20 to 21 km in December. Additional growth by condensation and/or coalescence during descent is required to explain the largest aerosols, r = 0.5 to 0.9 µm. Although sedimentation is the dominant cause of bimodality, mixing of air from low and high latitudes can produce bimodal or trimodal distributions.
Measurements of the aerosol size distributions in the El Chichon cloud
Authors: Knollenberg Robert G. , Huffman Dale
Published: February 2008

Three particle size spectrometers were flown aboard the NASA‐U2 on numerous flights before and after the eruption of El Chichon to determine the effects of the eruption. Measurements of aerosol particles between 20° ‐ 50° north latitude over the North American continent show strong orders of magnitude enhancements in number and mass. Our analyses and supporting measurements by others, indicate that the aerosol between 0.1 ‐ 2.0 µm is largely H2SO4 while the aerosol larger than 2 µm is likely ash. Comparisons of measurements using a spectrometer with an aerodynamically sensitive (particle size sorting) inlet with a second one that operated “in situ”, and a third one that operated isokinetically, indicate that the larger ash particles are of low bulk density. Observations of particles as large as 30 µm four months after the eruption are only compatible with very low bulk densities. The H2SO4 droplet populations show decreasing number density with altitude but increasing mass. The distribution is largely bimodal with 0.4 and 1.2 µm modes typically observed. The mass is dominated by the 1.2 µm mode.
Changes in the sub‐2.5 micron diameter aerosol observed at 20 km altitude after the eruption of El Chichon
Authors: Wilson J. C. , Blackshear E. D. , Hyun J. H.
Published: February 2008

Measurements of sub‐2.5 µm aerosol concentration were made from a NASA U‐2 aircraft by several experimenters before and after the eruptions of El Chichon in March and April of 1982. Concentrations of sub‐2.5 µm diameter particles encountered between 19.6 and 21.6 km altitude were nearly uniform over large distances in regions thought to be unaffected by El Chichon. Comparisons of measurements made with three instruments suggest that particles smaller than .1 µm in diameter contributed significantly to the number distribution of these non‐El Chichon aerosols. Measurements of large concentrations of sub 0.1 µm particles in April and May 1982 imply that new particle formation occured following the eruption. Measurements made in November and December of 1982 showed decreased numbers of sub‐0.1 µm particles compared to the non‐El Chichon measurements. Simultaneous measurements of SO2 and aerosol volume concentrations made on the lower edge of the volcanic cloud two weeks after the eruption permitted a range of SO2 conversion rates to be estimated.
El Chichon volcanic ash in the stratosphere: Particle abundances and size distributions after the 1982 eruption
Authors: Gooding James L. , Clanton Uel S. , Gabel Elizabeth M. , Warren Jack L.
Published: February 2008

Volcanic ash particles collected from the stratosphere after the March/April, 1982 explosive eruption of El Chichòn volcano, Mexico, were mostly 2‐40‐µm vesicular shards of silicic volcanic glass that varied in abundance, at 16.8‐19.2 km altitude, from 200 m−3 (30‐49°N lat.) in May to 1.3 m−3 (45‐75°N) in October. At the minimum, the ash cloud covered latitudes 10‐60°N in July and 10°S‐75°N in October. In May and July, ash particles were mostly free, individual shards (and clusters of shards) but, by October, were intimately associated with liquid droplets (presumably, sulfuric acid). In May 1982, the total stratospheric burden of ash was at least 240 tons (2.2 × 108 g) although the total ash injected into the stratosphere by the eruption was probably 480‐8400 tons.
A two‐dimensional model simulation of the El Chichon volcanic eruption cloud
Authors: Capone Louis A. , Toon Owen B. , Whitten Robert C. , Turco Richard P. , Riegel Christopher A. , Santhanam Krishnamurthy
Published: February 2008

Using a two‐dimensional model of sulfate photochemistry, transport, and aerosol microphysics, we have simulated a 2‐year period following the eruptions of El Chichon. Our calculations suggest that the residence time of the cloud in the stratosphere exceeds 2 years. The model reproduces the observed optical depth, lidar backscatter, and infrared extinction coefficients if about 10 megatonnes of SO2 are injected. The major deficiency of the model is a somewhat too rapid transport.
Sondrestrom radar—Initial results
Authors: Kelly John D.
Published: February 2008

Operation of an incoherent‐scatter radar at Sondre Stromfjord, Greenland, began in early February 1983, marking the beginning of a new effort in ground‐based ionospheric research in the vicinity of the polar cusp and polar cap. The Sondrestrom Radar is located north of the arctic circle on the west coast of Greenland near the Sondrestrom Air Base at an invariant latitude of 75°. The effects of the polar cusp may frequently be observed at local noon: the radar‐measured signature in the F region is an increase of more than a factor of two in electron density. Additionally, the daytime variations in the F1‐region electron density are dramatic. In contrast to auroral zone measurements, enhanced electron density at 150‐km altitude has been observed, and a marked absence of detectable E‐region ionization at night has also been noticed.
Electron Beam Injection Experiments: Replication of flight observations in a laboratory beam plasma discharge
Authors: Bernstein W. , McGarity J. O. , Konradi A.
Published: February 2008

Recent electron beam injection experiments in the lower ionosphere have produced two perplexing results:

1. At altitudes from 140 km to 220 km, the beam associated 391.4 nm intensity is relatively independent of altitude despite the decreasing N2 abundance.

2. The radial extent (⊥B) of the perturbed region populated by beam associated energetic electrons significantly exceeds the nominal gyrodiameter for 90° injection.

A series of laboratory measurements is described in which both of these flight results appear to have been closely reproduced. The laboratory results are reasonably consistent with the transition from a collision dominated to collisionless beam‐plasma discharge configuration.
An application of ray theory to the propagation of waves along a laterally heterogeneous spherical surface
Authors: Jobert N. , Jobert G.
Published: February 2008

A simple transformation, for a point on the surface of a spherical model and for the corresponding local velocity, has been used to study the propagation of a disturbance along the surface. Using a Gaussian beam computation scheme, rays are traced and seismograms obtained for a few spherical models with lateral heterogeneities. In the results, deviations from the first order perturbation theory for normal modes are displayed.
Anomalous neon‐helium ratios in the Arctic Ocean
Authors: Top Zafer , Clarke W. B. , Moore R. M.
Published: February 2008

Measurements of dissolved helium and neon were made on seawater samples collected at the Lomonosov Ridge Experiment site (LOREX, 1979) and at the FRAM III drifting ice station (1981) in the Arctic Ocean. The most striking feature of the results is the high values of Ne/He in the shallow depths compared to previous results in other oceans. Ice formation and refreezing of meltwater appear to be the mechanisms which could explain the observed Ne/He anomaly.
Synthetic aperture radar observation of ocean roughness from rolls in an unstable marine boundary layer
Authors: Thompson T. W. , Liu W. T. , Weissman D. E.
Published: February 2008

Simultaneous synthetic aperture radar (SAR) and cloud photographic observations of the Atlantic Ocean off the coast of Florida were made from a high‐altitude aircraft when there was an unstable marine boundary layer. The synthetic aperture radar images show unusual kilometer‐sized features on the ocean surface which are related to clouds. The ocean near shore was cloud‐free and had no radar features, while from 30 to 330 km offshore there were clouds and prominent kilometer‐sized features in the SAR image. These radar features are most prominent when the radar was looking upwind, are less prominent when the radar was looking downwind, and disappear entirely when the radar was looking crosswind. Since ocean radar echo strengths are believed to be controlled primarily by ocean waves satisfying the Bragg relation, these radar features most likely resulted from local enhancements of short gravity waves with 17‐ to 34‐cm wavelengths, which in turn are surface expressions of roll convections in a kilometer‐thick unstable marine boundary layer.
Magnetic structure of the distant geotail from −60 to −220 Re: ISEE‐3
Authors: Tsurutani B. T. , Slavin J. A. , Smith E. J. , Okida R. , Jones D. E.
Published: February 2008

Magnetic field observations during the first ISEE‐3 pass into a previously unexplored region of the geotail (−80 to −220 Re) are discussed. The tail structures customarily detected closer to Earth are also identifiable in the distant tail field data: two lobes separated by a plasma sheet and embedded neutral sheet. A plasma sheet boundary layer, characterized by small diamagnetic field decreases and the presence of large amplitude (5 nT p‐p) electromagnetic waves, is often, but not always present. It is found that the tail maintains a well‐ordered magnetic field structure out to −220 Re. Near‐earth (−40 to −80 Re), the magnetic field in the plasma sheet is directed southward only 5% of the time, but this percentage gradually increases with distance until it is southward 50% the time at X = −220 Re. The implications of the above observations for reconnection models are discussed. Significant By fields are detected within the neutral sheet and the field rotation often takes place primarily in the X‐Y plane. These transverse fields may be associated with tailward moving plasmoids or with a shearing of the lobes.
Evidence for an Early Archean Geomagnetic Field: A paleomagnetic study of the Komati Formation, Barberton Greenstone Belt, South Africa
Authors: Hale C. J. , Dunlop D. J.
Published: February 2008

3.5 Ga old peridotitic komatiites of the Komati formation, Barberton greenstone belt, South Africa have a characteristic NRM (natural remanent magnetization) that is stable during alternating field and thermal demagnetization. The thermal nature of this remanence is demonstrated by successful Thellier‐type paleo‐intensity determinations on some samples in the temperature range 350 to 575°C. The characteristic NRM is an almost total thermal overprint acquired during unroofing and cooling following pervasive greenschist metamorphism at 3470±20 Ma. The mean direction of magnetization after cleaning is D=326° I=81° (k=60, α95=8°, N= 7 sites), with a paleopole at 11°S, 21°E (δp=δm=15°). The paleopole falls in southern Africa; ancestral southern Africa was therefore in polar latitudes around 3.5 Ga, the same position it occupied in the late Archean and early Proterozoic. Paleofield intensities are about one‐half present‐day intensities for polar latitudes. A vigorous earth's magnetic field was already in existence in the early Archean, implying that the core had a suitable size, composition and convective flow to support dynamo action.
Limitation of electrostatic charging of dust particles in a plasma
Authors: Goertz C. K. , Ip W.‐H.
Published: February 2008

We show that in a dusty plasma consisting of a plasma (density n and temperature T) and dust grains (density N and radius a) the charge on a grain is not given by its free‐space value Qo = Va, where V is its surface potential. Instead the charge is reduced by a factor 1 + x, with x = 4πNaλD², where λD is the plasma Debye length. Except in the optically thin E and G rings this factor is large. Usually electromagnetic forces on dust particles in Saturn's ring system are too small to produce observable effects. The current carried by dust particles moving relative to the plasma with a speed w is to a good approximation given by j = NQw. Thus magnetic perturbations by the F ring should be much smaller than previously estimated.
Theory of chorus‐related electrostatic bursts
Authors: Bujarbarua S. , Sarma S. N. , Nambu M. , Fujiyama H.
Published: February 2008

We present here a theory of the emission of electrostatic bursts along with the whistler waves observed recently in the Earth's outer magnetosphere. We show that these electrostatic bursts are due to a high frequency plasma instability which occurs because of a new mode coupling effect in plasma turbulence (plasma maser). The theory agrees with the observations in the space.
Dynamics of lava flow: Thickness growth characteristics of steady two‐dimensional flow
Authors: Park Seung , Iversen James D.
Published: February 2008

The thickness growth characteristics of flowing lava are investigated using a heat balance model and a two‐dimensional model for flow of a Bingham plastic fluid down an inclined plane. It is found that yield strength plays a crucial role in the thickening of a lava flow of given flow rate. To illustrate this point, downstream thickness profiles and yield strength distributions were calculated for flows with mass flow rates of 104 and 105 kg/m‐sec. Higher flow rates led to slow cooling rates which resulted in slow rate of increase of yield strength and thus greater flow lengths.
Late acquisition of “primary” remanence in some fresh basalts: A cause of spurious paleomagnetic results
Authors: Hoffman Kenneth A.
Published: February 2008

Although rarely reported, the principal magnetic carrier associated with rocks of basaltic composition can be titanomagnetite (Fe3−xTixO4) very rich in titanium (x>.75). If not oxidized during cooling, such a pristine magnetic carrier will possess a Curie temperature too low to insure the acquisition of a stable thermoremanent magnetization (TRM). A stable chemical remanent magnetization (CRM) ultimately may be acquired through room temperature oxidation of the titanomagnetite to titanomaghemite; however, such a process can occur during a time interval far removed from that of initial cooling. A case study is presented which dramatically illustrates the spurious nature of paleomagnetic results associated with such an occurrence.
Zonal pressure gradient, velocity and transport in the Atlantic Equatorial Undercurrent from focal cruises (July 1982‐February 1984)
Authors: Hisard Philippe , Hénin Christian
Published: February 2008

The zonal pressure gradient (ZPG) along the Atlantic equator and the Equatorial Undercurrent (EUC) transport are discussed for four cruises representative of each season. A very clear sea surface slope reversal occurred in the eastern area during autumn as far west as 14°W. An early onset of the equatorial thermocline rising was evident during spring 1983. An eastward equatorial surface jet clearly distinct from the EUC was observed at 35°W and 29°W. The greatest ZPG but the lowest EUC transport were observed during summer 1983. A nearly total absence of the ZPG and a large surfacing of the EUC as far as 10°W characterized the 1984 winter.
The precise computation of geoid undulation differences with comparison to results obtained from the Global Positioning System
Authors: Engelis Theo , Rapp Richard H. , Tscherning C. C.
Published: February 2008

Ellipsoidal height differences have been determined for 13 station pairs in the central Ohio region using measurements made with the Global Positioning System. This information was used to compute geoid undulation differences based on known orthometric heights. These differences were compared to gravimetrically computed undulations (using a Stokes integration procedure and least squares collocation having an internal r.m.s. agreement of ±1 cm in undulation differences). The two sets of undulation differences have an r.m.s. discrepancy of ±5 cm while the average station separation is of the order of 14 km. This good agreement suggests that gravimetric data can be used to compute accurate geoid undulation differences that can be used to convert ellipsoidal height differences obtained from GPS to orthometric height differences.
Very high electron temperatures in the daytime F region at Sondrestrom
Authors: Kofman Wlodek , Wickwar Vincent B.
Published: February 2008

Sondrestrom observations show that a characteristic F‐region signature of the interaction between the magnetosphere and ionosphere is a narrow band of elevated electron temperatures. Its location is associated with the ion convection reversal in the morning and evening convection cells. Typically, near 500 km altitude, the temperature is 3500 to 4000 K. However, on 24 April 1983, a geomagnetically very active day with Kp values of 6‐ during the period of interest, the electron temperature reached 6000 K in the afternoon convection reversal. The ion velocities were between 1 and 2 km/s on both sides of the reversal. There was considerable soft particle precipitation and a large downward heat flux of 0.3 erg/cm²‐s at 450 km. These high temperature electrons then transferred 0.5 erg/cm²‐s to ions and neutrals between 175 and 550 km, which represents a very sizeable perturbation to the thermosphere.
Net mass transport by internal waves near the Strait of Gibraltar
Authors: Kinder Thomas H.
Published: February 2008

Current measurements revealed that nonlinear internal waves, generated within the Strait of Gibraltar, propagated eastward about 50 km into the western Mediterranean Sea and appeared as energetic packets of 30 minute period waves. The waves had a net eastward transport in the upper layer such that during a ten day period the waves carried one‐third of the climatic transport. This partitioning of transport, normally carried by a narrow current, may have altered the strengths of the Atlantic inflow current and the anticyclonic Alboran Sea gyre.
Acceleration of electrons in strong beam‐plasma interactions
Authors: Wilhelm Klaus , Bernstein William , Kellogg Paul J. , Whalen Brian A.
Published: February 2008

The sounding rocket payload SCEX (Several Compatible Experiments to utilize an electron accelerator; NASA flight 27.045) launched on January 27, 1982 from the Churchill Research Range provided an opportunity to observe the effects of strong beam‐plasma interactions on the electron population in a region of space remote from the main payload carrying the accelerator. We present observations demonstrating that electron energies of up to four times the injection energy occurred during accelerator operations in high‐current mode. Detailed instrumental performance characteristics in flight and in the laboratory will be discussed. The acceleration events occurred at reception pitch angles between 54° and 126°. Long confinement times seem to be a necessary condition for generating the energetic electrons. It is proposed that they result from the length of the interaction region.
Satellite observation of SO2 from El Chichon: Identification and measurement
Authors: McPeters R. D. , Heath D. F. , Schlesinger B. M.
Published: February 2008

Absorption bands between 300 nm and 315 nm were observed in spectral scans of the atmospheric albedo made by the solar backscattered ultraviolet instrument (SBUV) on Nimbus 7 following the eruption of El Chichon. We show that these bands coincide with peaks in the absorption coefficient spectrum of SO2 and use the magnitude of the absorption to estimate the column content of SO2 present. A maximum concentration of 15 matm‐cm of SO2 was observed west of Hawaii on April 15; the minimum detectable amount of SO2 in a single scan is about 1 matm‐cm. The disappearance of the band structure at wavelengths below 300 nm indicates that the SO2 was between 20 km and 30 km altitude. We also observe excess albedo near 300 nm which we attribute to increased scattering from volcanic aerosols; the wavelength of the scattering feature indicates that the aerosols also were near 25 km altitude.
Shear wave velocity and attenuation in ocean bottom sediments from acoustic log waveforms
Authors: Toksöz M. Nafi , Wilkens R. H. , Cheng C. H.
Published: February 2008

In boreholes where formation shear wave velocity is lower than borehole fluid velocity neither refracted shear waves nor pseudo‐Rayleigh waves can propagate. When frequency response of the sonde does not extend to low frequencies (e.g. 2 kHz) Stoneley waves are not excited. In such cases refracted P and leaking PL modes become dominant phases on a full waveform acoustic log. The P wave velocity can be determined from the first arrivals. Then, using synthetic seismograms and a waveform matching technique, formation shear wave velocity and attenuation can be estimated. This method is demonstrated using data from DSDP Site 612 in the Baltimore Canyon Trough area of the Atlantic margin.
Magnetic polarity stratigraphy and stratigraphic completeness
Authors: May Steven R. , Butler Robert F. , Roth Frances A.
Published: February 2008

A fundamental limiting factor in the precision of magnetostratigraphic correlation is stratigraphic completeness. Sadler [1981] has suggested a method by which the expected completeness of any given stratigraphic section can be calculated given the thickness, duration, and depositional environment. The technique is probabilistic and requires the investigator to specify a meaningful short‐term time scale at which completeness is to be estimated. For magnetostratigraphy, the short‐term time scale is defined by the duration of the polarity chron or other polarity feature of interest. Sadler's method allows the probability of observing such features to be quantified. It is a useful tool for evaluating the reliability of magnetostratigraphic correlations and for judging between alternative correlations.
Sawtooth segmentation and deformation processes on the southern San Andreas Fault, California
Authors: Bilham Roger , Williams Patrick
Published: February 2008

Five contiguous 12‐13 km fault segments form a sawtooth geometry on the southernmost San Andreas fault. The kinematic and morphologic properties of each segment depend on fault strike, despite differences of strike between segments of as little as 3 degrees. Oblique slip (transpression) of fault segments within the Indio Hills, Mecca Hills and Durmid Hill results from an inferred 8:1 ratio of dextral slip to convergence across the fault zone. Triggered slip and creep are confined almost entirely to transpressive segments of the fault. Durmid Hill has been formed in the last 28 ± 6 ka by uplift at an average rate of 3 ± 1 mm/a.
Observation and interpretation of the seafloor vertical electric field in the eastern North Pacific
Authors: Chave Alan D. , Filloux Jean H.
Published: February 2008

A 37 day long recording of the seafloor vertical electric field collected on the East Pacific Rise and south of the mouth of the Gulf of California is examined. The principal barotropic ocean tides are detected by regression analysis and display electric field values that yield typical open ocean water velocities of 1 cm/s or less. Spectral analysis and modeling indicate that internal wave‐induced electric fields consistent with the Garrett‐Munk kinematic description explain the data between the local inertial frequency of 0.033 cph and about 1 cph. At lower frequencies, a variance enhancement near 90 h period of unknown origin is also present. Low but significant coherence of the VEF with land magnetic observatory data is also demonstrated; this is probably due to motion of the electric field instrument in ambient water currents.