bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alfvénic noise and transient reconfiguration in a simulated current sheet
Authors: Rogers Catherine H. , Christiansen Peter J. 
Published: February 2008

A magnetotail‐like structure is modelled using a 2‐dimensional, single‐ion species, electromagnetic, Darwin (no displacement current), particle‐in‐cell (PIC) code, which is a modified version of that described by Hamilton and Eastwood [1982]. The modifications include new boundary conditions for the magnetic fields which allow a non‐symmetrical topology to be modelled.The work presented here is aimed at the construction and testing of a self‐consistent ‘steady‐state’ model. It is found that the model supports significant magnetic perturbations, arising as a consequence of cyclotron resonance interactions with ion beam‐like features. When subjected to transient changes in the convection electric field, the model also exhibits field reconfiguration and particle responses reminiscent of near‐Earth substorm behaviour.
A model for the computation of thermal expansivity at high compression and high temperatures: MGO as an example
Authors: Anderson Orson L. , Oda Hitoshi , Isaak Donald 
Published: February 2008

We compute the value of the thermal expansivity α over a wide range of compression (η ≡ V/V0, 0.6 ≤ η ≤ 1.0) and temperature (300 K ≤ T ≤ 2500 K). Three methods are combined to find α. We utilize: 1) the high P,T data base from the PIB ab initio model for MgO, which specifies the Helmholtz energy and the volume and temperature derivatives; 2) the measured thermal expansivity and its various pressure and temperature derivatives; and 3) several thermodynamic identities relating T and V dependence of various physical properties.We present a simple equation relating α to η along isochores and suggest values of α. for MgO over V, P, T conditions, including those of the earth's lower mantle. The parameters in the equation are evaluated by using the ab initio data base. We find that α varies from about 1.40αa to 0.40αa along a geotherm through the upper and lower mantle, where αa is α at ambient conditions.
Pressure gradient structures in the tail neutral sheet as “roots of the arcs” with some effects of stochasticity
Authors: Galperin Yu. I. , Volosevich A. V. , Zelenyi L. M. 
Published: February 2008

Westward cross‐tail current at the earthward edge of the plasma sheet is enhanced due to strongly stochastic (rLi ∼ Rc) ion motions. A narrow elongated magnetic field depression arises which leads to further stochastication of the ions convecting through it, and to a local increase of magnetostatic plasma pressure, enhanced lateral transport and removal of higher energy ions. This plasma structure can be stationary in the magnetospheric frame.It is the “root” of sheet‐like auroral currents of stable auroral homogeneous arcs/bands (inverted‐V's) located at the equatorial edge of the steady premidnight auroral oval. The magnetic field minimum can be the location of a sub‐storm onset when it deepens below the stability threshold for reconnection/tearing.
Southwest Pacific temperatures: Diurnal and seasonal trends
Authors: Salinger M. James , Hay John , McGann Ron , Fitzharris Blair 
Published: February 2008

Temperature trends are presented for a large part of the southwest Pacific. The trends differ from those documented for Northern Hemisphere land areas, where warming has occurred mainly through increases in minimum temperature. The New Zealand patterns are derived from recently completed analyses of monthly and annual mean maximum and minimum surface temperature records for a newly homogenised historical climate data series for New Zealand and outlying islands. They indicate that the warming in the New Zealand region over the past five decades can be attributed to increases in both mean maximum (mostly daytime) and mean minimum (mostly night time) temperature. All seasons show a temperature increase, with the largest occurring in summer (DJF).Northern Hemisphere evidence suggests that changes in cloud cover and the presence of sulfate aerosols plays a direct role. The present results imply that, while the observed warming in a large portion of the Northern Hemisphere landmass may be significantly affected by both these factors, sulfate aerosol effects may be less important in the Southern Hemisphere.
Background levels of formate and other ions in ice cores from inland Greenland
Authors: Osada Kazuo , Langway Chester C. 
Published: February 2008

Concentration levels of the organic acids HCOO− and CH3SO3−, inorganic acids NO3− and excess SO42− and ammonium were measured in pre‐1900 AD ice layers from seven geographically dispersed inland sites in Greenland. Average multiple‐year background concentration levels are calculated for each ion at each site from laboratory measurements of continuous core samples representing from 4 to 10 years of snow accumulation (32 to 80 individual measurements) from various time intervals.The HCOO− concentration level increases from 6 ng/g in the most northern colder site to 36 ng/g in the most southern warmer site; CH3SO3− increases from 0.9 ng/g to 2.8 ng/g; NO3− decreases from 83 ng/g to 37 ng/g; excess SO42− decreases from 43 ng/g to 19 ng/g, all with variability. The distribution of the NH4+ ion shows a nearly constant level at about 6 ng/g for all sites except Dye‐2 where it reaches 10 ng/g. The deposition patterns for HCOO− and NH4+ on the ice sheet suggest major contributions arrive from sources originating from the southwest of Greenland.
The configuration of Asia prior to the collision of India: Cretaceous paleomagnetic constraints
Authors: Chen Yan , Courtillot Vincent , Cogné Jean‐Pascal , Besse Jean , Yang Zhenyu , Enkin Randy 
Published: February 2008

Paleomagnetic data from Central Asia show that 1700±610 km of shortening of southern Asia since Cretaceous time have been absorbed by distributed deformation between southern Tibet and the Siberia craton. This result is based on a compilation of Cretaceous poles from the Junggar, Tarim, Tibet, Indochina, South China, North China, and Mongolia blocks, complementing the recent compilation of Enkin et al. (1992a). We propose a paleogeographic reconstruction of Asia in the Cretaceous, in which the position of Siberia is derived from the synthetic apparent polar wander path of Besse and Courtillot (1991). The resulting map, which likely represents Asia as it remained throughout the Cretaceous until the collision with India began, features an “unbent” Tibet, with an east‐west trending Andean margin at tropical latitudes and a rather continuous belt of continental red bed basins extending from Sichuan to Tarim through Tibet. The map allows one to estimate continental shortening and rotations between the blocks, which are attributed to the collision. Despite large uncertainties, these have amounts and senses which are in all cases compatible with some recent kinematic models such as that of Avouac (1991).Appendix is available with entire paper on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W.,Washington, DC 20009. Document B93‐007; $2.50. Payment must accompany order.
Physical properties of the aerosol at the South Pole
Authors: Hogan Austin W. , Barnard Stephen , Bortiniak J. 
Published: February 2008

The size distribution of aerosol arriving at the South Pole was measured several times during four days of relatively homogeneous meteorological transport conditions. This aerosol had a maximum number concentration in the 10−6cm < r < 8×10−6cm radius rangeand a maximum volume concentration in the 2×10−5 − 2×10−4cm radius rangea total number concentration of 106/cm³ and a total volume concentration of 10−6cm³/m³which would correspond to a mean mass concentration of about 1‐2 µgm/m³. Almost all particles of r ⪖ 1.5×10−5cm were hygroscopicwith refractive index near 1.54. No particles of r ≥ 6×10−4cm were found in 75m³ of airand an average of 44/cm³ carried charges.This aerosol represents the background aerosol which occurs at the end point of a long series of meteorological precipitation processes; aerosols suffering a similar chain of processes while being transported vertically in the troposphere may also approach the same end point.
Incoherent scatter observations of mesospheric dynamics at Arecibo
Authors: Ganguly Suman 
Published: February 2008

Incoherent scatter spectral observations at Arecibo have been extended down to 59 km. For the first time vertical velocities in the mesosphere have been observed using this technique. The velocities unambiguously reveal a wavelike structure growing with height and varying in time. Above around 75 km, the vertical wavelength is around 16 km and the time period about 4 hours ± 20 minutes. Vertical velocities near 90 km were as large as 1 ms−1 and the apparent vertical energy flux was reasonably constant above 75 km. Below 75 km the energy flux was substantially lower, suggesting a mechanism where the gravity waves acquire significant energy from the diurnal tidal component trapped below the mesopause.The estimated adiabatic density and temperature changes near 90 km, estimated using simple idealized theories, were around 11%. The observed changes in spectral width were also found to be in harmony with estimated density and temperature changes to within 25%.
Four similar earthquakes in central California
Authors: Geller Robert J. , Mueller Charles S. 
Published: February 2008

We study four ML ‐ 2.7 earthquakes on the San Andreas Fault in Central California. The first two events occurred within five minutes of each other in November 1978; the two events in January 1979 occurred within a nine hour period. The CALNET (USGS local array) seismograms of these four events display only some general similarity. However, when low ‐ pass filtered below 5 Hz, the four events have nearly identical seismograms. The similarity is even more striking in the pass‐band below 2 Hz. This suggests that all four events are within a radius of no more than a quarter wavelength, or about 200 ‐ 400 m.Although no definitive conclusion can be reached from a study of only four earthquakes, our results strongly suggest that the following hypothesis should be further tested: Small to moderate earthquakes may commonly be much more tightly clustered in both hypocentral location and depth than is suggested by routine locations from local arrays. The physical basis of this clustering is that the earthquakes represent repeated stress release at the same asperity, or stress concentration, along the fault surface. Identification of such asperities might be useful in understanding the sequence of events leading to the initiation of a larger earthquake.
The arrival of the Mount St. Helens eruption cloud over Europe
Authors: Meixner F. X. , Georgii H.‐W. , Ockelmann G. , Jäger H. , Reiter R. 
Published: February 2008

The stratospheric aerosol layer between 15 and 25 km altitude is an important factor in the balance of the global radiation budget. The eruption of the Mount St. Helens in Washington, USA, on 18 May 1980 violated the quasi stationary situation in the stratosphere which was established after the decay of the post‐Fuego aerosol during the years 1974 to 1976. At tropopause level the cloud was observed over the east coast of the US and Canada on 21 May 1980. The further transport over the Atlantic was estimated by first guess trajectory constructions. The arrival of the eruption cloud over Europe was observed by the authors employing in‐situ techniques and remote sensing. The in‐situ measurements of atmospheric SO2 were performed during an aircraft ascent up to 13.7 km on 26 May 1980 over southern Scandinavia. In contrast to an aircraft ascent over southern Germany on 24 May 1980 a tenfold increase in SO2 mixing ratio at tropopause level was observed.Remote sensing by ground based ruby lidar at Garmisch‐Partenkirchen (47.5°N, 11°E) from 25 May to 29 May 80 indicates an aerosol peak at a height of 11 to 12 km, which was initially coupled to the tropopause, but later clearly separated from that level.
Rock properties for which large scale tests may be necessary
Authors: Hustrulid William 
Published: February 2008

The potential application of large scale geomechanical testing results to the following five mining/civil engineering problem areas; roof spans, design of rock support‐reinforcement systems, design of rock compression members, development/optimization of fragmentation systems, and design of slopes is discussed. It is concluded that such testing does have an application but to be meaningful it must be accompanied by significant field observation measurement programs.The type of testing facility required is not universal but depends upon the problem to be examined.
Sunlight absorption by aerosols in Jupiter's upper atmosphere
Authors: West Robert A. 
Published: February 2008

The amount of sunlight deposited in the Jovian upper atmosphere is estimated from reflectivity measurements at 2400 Å by the Voyager 2 Photopolarimeter experiment and at visible and near‐IR wavelengths observed by Pioneer 10 and ground‐based instruments.Zero to about one percent of the incident energy is absorbed at altitudes above the 100 mbar level in models with mean values for haze optical depth and single scattering albedo. Several percent of the incident energy could be absorbed, if limiting values are used, and if an additional absorbing layer is incorporated below the high altitude haze in Pioneer models. Maximum absorption occurs at the edge of the polar regions near ±65° latitude. Most of the absorbed energy is derived from visible and near‐IR radiation rather than UV radiation.
The effect of fluid flow on the magnetic field in low porosity crystalline rock
Authors: Martin R. J. , Haupt R. W. , Greenfield R. J. 
Published: February 2008

Changes in the local geomagnetic field have been observed and documented in several seismically active areas prior to, during, and following earthquakes. Mizutani and Ishido (1975) proposed that groundwater may diffuse through a hypocentral region and that the fluid flow can produce an electric potential by means of electrokinetic phenomena. The resulting current flow, in turn, will generate a magnetic field.Fluid flow tests conducted on samples of Westerly granite demonstrated that the diffusion of an electrolytic fluid causes a measurable magnetic field change. At high fluid flow rates, a magnetic field change was observed that was in agreement with theoretically predicted and numerically calculated values. In addition, the sign of the magnetic field changes as the fluid flow direction through the sample was reversed. Moreover, the tests showed that the magnitude of the magnetic field change is dependent upon (1) the porosity of the rock; (2) the pore wall surface area; (3) the permeability of the rock; and (4) zeta potential of the fluid‐pore wall system.
Phase velocity distribution in the Indian Ocean and Indonesian region inferred from GEOSCOPE records
Authors: Roult G. , Rouland D. , Montagner J. P. 
Published: February 2008

To improve the lateral resolution of 3 dimensional models of seismic wave velocities in the Indian Ocean and surrounding regions we analyzed direct earthquake to station Rayleigh waves observed on the vertical long‐period components of four GEOSCOPE stations [TAM (Algeria), PCR (La Réunion), PAF (Kerguelen) and AGR (Djibouti)].The phase velocities along 51 well‐distributed paths are obtained in the period range 40‐350 s after corrections for the phase pattern at the source and for the instrumental response. A tomographic method is then applied (Montagner, 1986a) to compute the geographical distribution of phase velocities, without any a priori regionalization.The location of velocity anomalies is quite stable and well resolved. The phase velocity distributions are compared with global results from Nakanishi and Anderson (1984b), Woodhouse and Dziewonski (1984), Tanimoto (1985), Nataf et al. (1986) and with regional studies using group velocities for the same region (Montagner, 1986a,b,c).
Non methane hydrocarbons chemistry in the atmosphere of an equatorial forest: A case of indirect photochemical production of OH radicals
Authors: Bonsang B. , Kanakidou M. , Lambert G. 
Published: February 2008

An experiment was conducted in the Guyana forest in March 1985, during which C2 ‐ C6 non methane hydrocarbons (NMHC) were measured in the air, together with CO2 and its associated 13C isotopic composition. Owing to the very high atmospheric stability, strong vertical concentration gradients were observed close to the soil surface. Simple assumptions allow showing that NMHC are mainly destroyed by OH radicals whose concentration seems to be surprisingly high, around 1×107 radicals cm−3. An indirect photochemical production of these radicals is proposed.On the other hand, the fluxes of the different NMHC emitted from the litter were found to be small, in the range of 10−7 to 10−6 g of carbon per hour and per m².
Correction to “Are fast atmospheric pulsations optical signatures of lightning‐induced electron precipitation?”
Authors: LaBelle J. 
Published: February 2008

Owing to a production error, a significant portion of the text of “Are Fast Atmospheric Pulsations Optical Signatures of Lightning‐Induced Electron Precipitation?” by J. LaBelle (Geophys. Res. Lett., 14, 1023, 1987) was printed out of sequence. GRL regrets the error and is printing the paper again, with the correct order of the text restored.Fast Atmospheric Light Pulsations (FAP's) consist of millisecond time‐scale bursts of light which have been observed at L=1.5‐2.2 during searches for atmospheric light emissions associated with supernovae. Their statistics of occurrence resemble those of Lightning‐induced Electron Precipitation (Trimpi events) observed at somewhat higher L‐shells. Here we propose that FAP's are in fact optical signatures of LEP events associated with the ≥ 2 MeV electrons of the inner radiation belt (L ≈ 1.4). These electrons would precipitate at low altitudes and could be modulated with time scales the order of 1 ms. The total loss rate of electrons from the inner belt resulting from these events would be comparable to, but somewhat smaller than, the loss rate due to Coulomb scattering.
Regional stress field in the Lesser Antilles between Guadeloupe and Barbuda Islands
Authors: Julien Philippe , Bonneton Jean‐Roger 
Published: February 2008

Microtectonic and extensometric measurements on the island of Basse‐Terre in Guadeloupe are coherent with a homogeneous stress system (Julien and Bonneton, 1984).In order to compare the stress field obtained from the deep seismicity and the stress directions deduced from superficial observations, a method for determining the aspect ratio and the principal directions of the regional stress field from a set of focal mechanisms has been used (Julien and Cornet, 1987).When applied to a group of large earthquakes, this method provides means for computing the stress field in a lithospheric block. The inversion of the focal mechanisms located in the eastern part of the crust in the Caribbean plate between the Guadeloupe and the Barbuda islands shows a maximum principal stress oriented nearly horizontally in the direction N 120°E. These results are in full agreement with microtectonic measurements and observed deformations. This direction corresponds to the convergence direction of the western Atlantic plate towards the Caribbean plate.
A comparison of the spatio‐temporal distribution of moment release for the 1986 Andreanof Islands Earthquake with relocated seismicity
Authors: Houston Heidi , Engdahl E. R. 
Published: February 2008

We compare relocated, teleseismically recorded seismicity before and after the May 7, 1986, Andreanof Islands earthquake (Mw= 8) to the spatial and temporal distribution of seismic moment release during the mainshock. Relocated seismicity from 1964 through April 1987 clusters strongly along the main thrust zone, in similar locations for the pre‐ and post‐mainshock periods.We performed simultaneous iterative inversions of broadband teleseismic GDSN and NARS P‐waveforms using the method of Kikuchi and Fukao [1987]. Fault plane parameters (e.g., strike, dip, depth, and extent of fault plane) consistent with regional tectonics and aftershock locations were specified. The results of the inversions are spatial and temporal maps of moment release on the fault plane. Most of the moment found by the inversion is localized in several regions of the fault plane. Resolution of the location and timing of the major subevents is good. The rupture was bilateral, with a highly variable rupture velocity. A shallow, updip region of the fault plane ruptured toward the end of the mainshock process.The mainshock moment release tended to occur in regions of the fault plane in which no or few aftershocks or preshocks are located. This tendency suggests that regions of high moment release in the 1986 Andreanof Islands earthquake resulted from rupture of mechanically strong regions (i.e., asperities) on the fault plane, which exhibited little seismicity before or after the mainshock that ruptured them. We infer that the asperity regions were locked and quiescent before the mainshock, while surrounding seismically active areas did not store as much strain and slipped mostly aseismically.
The relationship between QE−1 and dispersion in extensional modulus, E
Authors: Lienert Barry R. , Manghnani Murli H. 
Published: February 2008

We have measured the extensional modulus (ratio of stress to strain, E) and the fractional energy loss per radian (QE‐1) as functions of frequency in cylindrical samples of two solids: a room‐dry sandstone (Berea) and an acrylic plastic (Lucite). In the seismic frequency range (0.1–100 Hz), QE‐1
for the sandstone is constant, while the sandstone modulus follows a power law of frequency, allowing QE‐1 to be independently estimated from the slope of log E versus log f. In the same frequency range, QE‐1 for the acrylic plastic is not constant but exhibits a slight relaxation peak centered about 2 Hz. In this case
QE‐1 can be estimated from the derivative, d log E/d log f, i.e., the above power law appears to hold independently at each point in the frequency domain even when QE‐1 is varying.
Thermal expansivity versus pressure at constant temperature: A re‐examination
Authors: Anderson O. L. , Chopelas A. , Boehler R. 
Published: February 2008

Results from recent high pressure experiments have shown δT in the relationship to be constant over significant compressions, one of the original assumptions required to make this relationship valid. We have re‐examined the original derivation of this equation and present a simpler derivation eliminating the previous assumptions. Furthermore, high pressure experiments find (∂lnα/∂lnρ)T is equal in value to l/αKT(∂KT/∂T)P derived from experiments at ambient pressures. From values of −δT = l/αKT(∂KT/∂T)P at high temperatures, it is asserted that −(∂lnα/∂lnρ)T must lie between 4 and 6 in the lower mantle, a value significantly higher than previously assumed in earth models.
The occurrence and transport of radon in the natural environment
Authors: Reimer G. M. 
Published: February 2008

Radon—a colorless, odorless, tasteless, radioactive gas known to accumulate in homes.Within the last two years, those words have appeared in probably every newspaper in the country, informing the public that they may have an increased risk of lung cancer due to exposure to radon. Although the actual health risks of the slightly elevated concentrations found in the vast majority of homes is a matter of current scientific study, there are clearly some areas of the country where indoor levels and individual exposures can approach those found in underground mines. In these cases, the risks are not in doubt, but questions concerning the occurrence and transport of radon abound.