bluuebunny/crossref_metadata_2025 huggingface dataset:
Isoprene and its oxidation products, methyl vinyl ketone and methacrolein, in the rural troposphere
Authors: Montzka S. A. , Trainer M. , Goldan P. D. , Kuster W. C. , Fehsenfeld F. C.
Published: February 2008

The mixing ratios of methyl vinyl ketone (CH2=CHCOCH3) and methacrolein (CH2=C(CH3)COH) were measured at a site located in the Kinterbish Wildlife Management Area in western Alabama. The measurements were made between June 15 and July 20, 1990. Considering all the data over the whole measurement period, the concentrations of these two carbonyls were approximately equal at this isolated rural site. The average mixing ratios for methyl vinyl ketone and methacrolein were 0.98 parts per billion by volume (ppbv) and 0.66 ppbv, respectively, while the medians were 0.87 ppbv and 0.57 ppbv. The methyl vinyl ketone mixing ratio varied from 3.4 ppbv to the detection limit of the instrument, ≈0.01 ppbv, while the methacrolein mixing ratio varied from 2.6 ppbv to 0.027 ppbv. These carbonyls constituted a significant fraction of the volatile organic compounds observed at the site: their mixing ratios, measured 2 m above the top of the forest canopy, were less than that of the dominant compound isoprene but were considerably greater than the mixing ratios of anthropogenic compounds (e.g., benzene). The mixing ratios of methyl vinyl ketone and methacrolein were found to be highly correlated and exhibited a systematic variation with respect to each other. On average, during the day, methyl vinyl ketone was larger than methacrolein, while methacrolein tended to be slightly larger during the night. The systematic behavior of these compounds with respect to each other and other compounds measured at the site were simulated using a one‐dimensional photochemical model. These observations were consistent with the production and loss of isoprene, methyl vinyl ketone, and methacrolein by photochemical oxidation reactions.
On the accuracy of the Eddington approximation for radiative transfer in the microwave frequencies
Authors: Kummerow Christian
Published: February 2008

Radiative transfer calculations in the presence of clouds and precipitation simplify as the wavelengths of the radiation approach the Rayleigh scattering regime. In particular, the transfer of microwave radiation is often simpler than the equivalent calculations at shorter wavelengths because the order of quadrature and moments of the phase function needed for the treatment of scattering decrease as the wavelength increases. The purpose of this paper is to examine how well an Eddington approximation can reproduce brightness temperatures obtained from a more complete, N‐stream discrete ordinate solution in the microwave regime. Radiation propagating through a plane parallel medium will be considered in this discussion. Although model discrepancies are complicated functions of the cloud constituents, the differences between an eight‐stream discrete ordinate solution and an analytical Eddington solution were generally small, ranging from 0 to 6°K when only one uniform layer of hydrometeors was considered. When realistic, multilayered cloud hydrometeor profiles were used, the differences between these two models never exceeded 3°K over the entire range of microwave frequencies considered (6.6–183 GHz). The models agreed to within 0.2°K in the absence of scattering constituents.
Inferring middle atmospheric ozone height profiles from ground‐based measurements of molecular oxygen emission rates: 3. Can twilight measurements of the atmospheric band be used to retrieve an ozone density profile?
Authors: Sica R. J.
Published: February 2008

Measurements of emissions from atoms and molecules during twilight have been used to infer height profiles of various species in the atmosphere. The visible and near‐infrared emissions from molecular oxygen can be used to retrieve a density height profile of ozone in the middle atmosphere. A time‐dependent, four‐species model of the volume emission rate of O2(1Δg) and O2(1Σg) and the density profile of O(1D) and O3 is used to determine the suitability of the O2(1Σg) emission to infer the O3 density. Previous studies in this series have shown the sensitivities of the model to input parameters other than ozone (part 1) and the usefulness of the O2(1Δg) emission rate to infer the shape of the O3 density profile from 50‐ to 110‐km (part 2). The O2(1Δg) emission rate is favorable for this retrieval in part due to its long radiative lifetime (about 65 min). However, the O2(1Σg) emission has a short radiative lifetime (12 s) and the emission rate changes rapidly during twilight. This paper details the difficulties in using the O2(1Σg) emission to retrieve O3 profiles in the middle atmosphere. Whereas in principle the O2(1Σg) emission can be used to retrieve O3 density profiles, in practice the temporal resolution required for the measurements may be beyond that of current airglow instrumentation.
Heterogeneous nighttime production and deposition of particle nitrate at a rural site in North America during summer 1988
Authors: Li Shao‐Meng , Anlauf K. G. , Wiebe H. A.
Published: February 2008

Measurements at a rural site in central Ontario, Canada, in August 1988 showed gradual increases in particle nitrate (pNO3−) concentration from 1800 hours to midnight and a decrease thereafterward toward the early morning. A time‐dependent Lagrangian box model, which included homogeneous and heterogeneous chemical reactions of nitrogen species, dry deposition of O3, NO2, HNO3 and pNO3−, and sources of NOx, was used to simulate the observed nighttime increase of pNO3− for four nights in August. The model results indicate that the nighttime pNO3− was mainly formed by reactions of the nitrate radical (NO3) and N2O5 with particles, with these species contributing on average more than 80% and about 10% of the total nightly pNO3− formation, respectively. Conversion of HNO3 to pNO3− was found to be negligible compared to these two processes, contributing less than 5%. By assuming steady‐state concentrations, a simplified approach to fit nighttime pNO3− concentrations using only NOx and O3 observations gave results similar to the box model. As expected, the pseudo‐first‐order rate constants for the formation of pNO3− on particles from NO3 and N2O5 were found to be linear functions of the particle mass. When assuming an extended Junge distribution for the particles, the rate constants indicated a near unity sticking coefficient (α1) for NO3 but a substantially smaller sticking coefficient (α2) of about 0.02 for N2O5, consistent with results from laboratory studies. Sensitivity tests showed that the ranges of 0.8–1.0 for α1 and 0.01–0.04 for α2 gave reasonable model fits for pNO3− and HNO3. The box model showed that the heterogeneous reactions were the major sinks for NO3 and N2O5. The dry deposition velocities for O3, NO2, pNO3−, and HNO3 derived from the model simulations were similar to observed values over similar vegetation. The dry deposition rate constant of pNO3− appeared to be a function of the near‐surface wind speed, although the dry deposition velocity of pNO3− was quite variable. The box model predicted similar amounts of dry deposition for HNO3 and pNO3− during each of the four nights.
Observations of the atmospheric sulfur cycle on SAGA 3
Authors: Huebert B. J. , Howell S. , Laj P. , Johnson J. E. , Bates T. S. , Quinn P. K. , Yegorov Vladimir , Clarke A. D. , Porter J. N.
Published: February 2008

During the Soviet/American Gases and Aerosols (SAGA) 3 program in February and March 1991 we measured a wide variety of sulfur compounds simultaneously in the equatorial Pacific marine boundary layer. We made measurements of atmospheric dimethyl sulfide (DMS), sulfur dioxide (SO2), and size‐resolved aerosol non‐sea‐salt sulfate (NSS), and methane sulfonate (MSA). Some of our observed ratios contradict commonly held views of the marine sulfur cycle: the large DMS/NSS ratio implies that NSS may not be the primary product of DMS oxidation under some conditions. We also found much more DMS than SO2, which may suggest that SO2 is not always an intermediate in DMS oxidation. The small SO2/NSS ratio also supports the idea that most NSS was not formed from SO2. Although our measured ratios of MSA/NSS were similar to previous observations in this region, much of the MSA was contained on supermicron particles, in contrast to both the NSS and the earlier MSA observations at higher latitudes. This implies that MSA/NSS ratios in ice cores may not accurately reflect the MSA/NSS ratios in their source areas.
Reaction of N2O5 on tropospheric aerosols: Impact on the global distributions of NOx, O3, and OH
Authors: Dentener Frank J. , Crutzen Paul J.
Published: February 2008

Using a three‐dimensional global model of the troposphere, we show that the heterogeneous reactions of NO3 and N2O5 on aerosol particles have a substantial influence on the concentrations of NOx, O3, and OH. Due to these reactions, the modeled yearly average global NOx burden decreases by 50% (80% in winter and 20% in summer). The heterogeneous removal of NOx in the northern hemisphere (NH) is dominated by reactions on aerosols; in the tropics and southern hemisphere (SH), with substantial smaller aerosol concentrations, liquid water clouds can provide an additional sink for N2O5 and NO3. During spring in the NH subtropics and at mid‐latitudes, O3‐concentrations are lowered by 25%. In winter and spring in the subtropics of the NH calculated OH concentrations decreased by up to 30%. Global tropospheric average O3 and OH burden (the latter weighted with the amount of methane reacting with OH) can drop by about 9% each. By including reactions on aerosols, we are better able to simulate observed nitrate wet deposition patterns in North America and Europe. O3 concentrations in springtime smog situations are shown to be affected by heterogeneous reactions, indicating the great importance of chemical interactions resulting from NOx and SO2 emissions. However, a preliminary analysis shows that under present conditions a change in aerosol concentrations due to limited SO2 emission control strategies (e.g., reductions by a factor of 2 in industrial areas) will have only a relatively minor influence on O3 concentrations. Much larger reductions in SO2 emissions may cause larger increases in surface O3 concentrations, up to a maximum of 15%, if they are not accompanied by a reduction in NOx or hydrocarbon emission.
Identification and yield of carbonic acid and formaldehyde in irradiated ices
Authors: DelloRusso Neil , Khanna R. K. , Moore M. H.
Published: February 2008

Carbonic acid ((OH)2CO) was tentatively identified in the infrared spectrum of a proton irradiated CO2 + H2O ice mixture [Moore and Khanna, 1991]. In this report we present additional evidence for a more definitive identification of (OH)2CO with (1) the infrared spectrum of a residue obtained by proton irradiation of CO2 + D2O ice mixture, and (2) the infrared spectra of solid phases of formaldehyde (H2CO), acetone [(CH3)2CO], and dimethyl carbonate [(OCH3)2CO], which are structurally similar to (OH)2CO. Infrared characteristics (peak frequencies and complex refractive indices of the compounds in point 2) are also reported. In particular, the integrated absorption coefficients for the C=O band for the compounds in point 2 do not vary by more than 20%. Based on these values, we estimate the yields of H2CO and (OH)2CO by proton irradiation of ice mixtures. Both H2CO and (OH)2CO are possible irradiation products of cometary and planetary ices.
A coupled subsurface‐boundary layer model of water on Mars
Authors: Zent Aaron P. , Haberle Robert M. , Houben Howard C. , Jakosky Bruce M.
Published: February 2008

We have written a one‐dimensional numerical model of the exchange of H2O between the atmosphere and subsurface of Mars through the planetary boundary layer (PBL). Our goal is to explore the mechanisms of H2O exchange and to elucidate the role played by the regolith in the local H2O budget. The atmospheric model includes effects of Coriolis, pressure gradient, and frictional forces for momentum: radiation, sensible heat flux, and advection for heat. The model differs from Flasar and Goody by use of appropriate Viking‐based physical constants and inclusion of the radiative effects of atmospheric dust. The pressure gradient force is specified or computed from a simple slope model. The subsurface model accounts for conduction of heat and diffusion of H2O through a porous adsorbing medium in response to diurnal forcing. The model is initialized with depth‐independent H2O concentrations (2 kg m−3) in the regolith and a dry atmosphere. The model terminates when the atmospheric H2O column abundance stabilizes to 0.1% per sol. Results suggest that in most cases, the flux through the Martian surface reverses twice in the course of each sol. In the midmorning, the regolith begins to release H2O to the atmosphere and continues to do so until midafternoon, when it once more becomes a sink. It remains an H2O sink throughout the Martian night. In the early morning and late afternoon, while the atmosphere is convective, the atmosphere supplies H2O to the ground at a rapid rate, occasionally resulting in strong pulses of H2O into the ground. The model also predicts that for typical conditions, perhaps 15–20 sols are required for the regolith to supply an initially dry atmosphere with its equilibrium load. The effects of surface albedo, thermal inertia, solar declination, atmospheric optical depth, and regolith pore structure are explored. Increased albedo cools the regolith, so less H2O appears in the atmospheric column above a bright surface. The friction velocity is higher above a dark surface, so there is more diurnal H2O exchange; relative humidities are much higher above a bright surface. Thermal inertia I affects the propagation of energy through a periodically heated homogeneous surface. Our results suggest that higher thermal inertia forces more H2O into the atmosphere because the regolith is warmer at depth. Surface stresses are higher above a low I surface, but there is less diurnal exchange because the atmosphere is dry. The latitude experiment predicts that the total diurnal insolation is more important to the adsorptively controlled H2O column abundance than the peak daytime surface temperature. Fogs and high relative humidity will be far more prevalent in the winter hemisphere. The dust opacity of the atmosphere plays a very significant role; the PBL height, column abundances, relative humidity, and surface stresses all increase very strongly as the optical depth approaches zero. The dust opacity of the atmosphere must be considered in subsequent PBL models.
Radio observations of the planets: The importance of laboratory measurements
Authors: De Pater Imke , Mitchell David L.
Published: February 2008

In this paper we summarize the needs of planetary radio astronomers regarding future laboratory measurements. We present a short review of our present knowledge regarding planetary atmospheres and surfaces, and show our progression in data analysis over time when more and better laboratory data became available. To further constrain elemental abundances and understand the dynamics and cloud physics in the giant planet's atmospheres, we need laboratory data on the line broadening parameters of H2S gas under Uranian/Neptunian conditions, on the far wings of the H2S and NH3 line profiles, and on the dielectric properties of CH4−, NH3−, H2S−, and NH4SH‐ice. To obtain a better understanding of Venus' atmosphere, we need measurements of the absorption coefficient of gaseous H2SO4 at millimeter wavelengths. Accurate measurements of the center frequencies of the CO lines are necessary to determine wind velocity fields in Venus' and Mars' atmospheres. The modeling of radiative transfer through particulate material is the most difficult aspect of the analysis of microwave observations of planetary surfaces. Laboratory experiments that separately measure the absorption and scattering properties of lunar soils and/or terrestrial rock powders at frequencies from ∼1 to 200 GHz would provide a valuable addition to existing data at 450 MHz, 35 GHz, and far infrared frequencies. These data would be applied to the analysis of microwave spectra of planetary surfaces to help separate the effects of radiative transfer from those of nonlinear heat conduction and internal heat sources.
Xenological constraints on the impact erosion of the early Martian atmosphere
Authors: Zahnle Kevin J.
Published: February 2008

The roughly uniform hundredfold depletion of observable Martian atmophiles (nonradiogenic noble gases and reconstituted nitrogen) with respect to Earth implies that Mars lost its atmosphere by a relatively efficient, nonfractionating process. Impact erosion (expulsion of atmosphere by impacts) is an appealing candidate. Noble gases can be used to test this hypothesis. Xenon in particular can be used to impose three constraints on how Mars lost its atmosphere: its very low abundance compared to Earth, Venus, and likely meteoritic sources; its distinctive isotopic composition compared to likely meteoritic sources; and the relatively high absolute abundance of radiogenic 129Xe, daughter of the extinct radionuclide 129I (half‐life 17 m.y.). A fourth useful constraint is imposed by radiogenic 40Ar. If produced by impact erosion, the first two constraints become constraints on the composition, mass distribution, and orbital elements of the impactors. The third and fourth constraints imply that Mars lost its nonradiogenic noble gases early, perhaps before it was 100 Myr old. Impact erosion can be invoked to explain Mars by any of three stories: (1) Mars is unlikely. In a sort of planetary brinkmanship, impact erosion almost removed the entire atmosphere but was arrested just in time. (2) Martian noble gases are cometary and cometary Xe is as isotopically mass fractionated as Martian and terrestrial Xe. This is most easily accomplished if a relatively thick geochemically controlled CO2 atmosphere protected trace atmophiles against escape. It is not known if comets actually have the desired composition. (3) Mars was indeed stripped of its early atmosphere but a small remnant was safely stored in the regolith, later released as a by‐product of water mobilization.
Glacial carbonate dissolution cycles and atmospheric pCO2: A view from the ocean bottom
Authors: Emerson Steven , Archer David
Published: February 2008

We present a calculation of the global calcium carbonate dissolution response to glacial/interglacial changes in seawater carbonate chemistry inferred from Cd/Ca and carbon isotope ratios in benthic foraminifera. Our model is based on the relationship between the carbonate dissolution flux and the degree of calcite saturation in the three main ocean basins. The rate of carbonate dissolution is derived using mechanisms inferred from studies of surface sediment pore water geochemistry. The model predicts a change in the relative importance of CaCO3 burial among the Atlantic, Indian, and Pacific oceans between glacial and interglacial times. Chemical rearrangement of deep waters appears to be a viable mechanism for driving interocean differences in carbonate accumulation, and observed CaCO3 burial trends constrain alkalinity changes that accompanied deepwater nutrient redistribution. Our model predicts atmospheric pCO2 lowering during glacial times caused by the carbonate dissolution response to be less than 10 ppm suggesting that this mechanism is not a viable candidate for explaining a large fraction of the observed 80 ppm decrease observed in ice cores.
Carbon isotopic variations on glacial‐to‐interglacial time scales in the ocean: Modeling and implications
Authors: Ku Teh‐Lung , Luo Shangde
Published: February 2008

Downcore variations in the deep‐sea δ13C signal as recorded in benthic foraminifera are a function of past changes in global organic carbon inventory and ocean circulation. Thus the carbon isotopic composition of fossil benthic foraminifera constitutes a valuable geochemical proxy for reconstructing paleooceanographic conditions. This study examines the mean ocean 13C/12C variations due to the climatically induced changes in the size of the two organic carbon pools: terrestrial biomass (forest‐soil) and continental shelf sediment. Through modeling the paired foraminiferal δ13C‐δ18O data in the literature, it is estimated that during the past several hundred thousand years in late Quaternary, transfer of organic carbon between these two pools and the ocean in response to glacial‐interglacial climate and sea level changes has resulted in global oceanic δ13C fluctuations with a mean amplitude of about 0.32‰. The transfer has accounted for about two thirds of the observed carbon isotopic shift in the deep eastern Pacific (ocean circulation accounting for the remaining one‐third of δ13C amplitude variations). In the deep North Atlantic Ocean, it has accounted for about one‐third of the shift. Of the two organic carbon reservoirs, forest‐soil is roughly 2.5 times more responsible than shelf sediment in altering the mean carbon isotopic composition of the Quaternary oceans. Destruction of organic matter from the shelf sediment reservoir is responsible for raising the oceanic nutrient inventory during glacial times by about 4% relative to the present (interglacial) level, a level which is difficult to be assessed by the cadmium proxy. Marine deposition of organic carbon in glacial oceans increased by 3–10%, in spite of a reduction in terrestrial biomass during ice ages. Isolating out the global climatic signals in δ13C records shows that since about 300 kyr ago, there has been a trend of increasing organic carbon accumulation toward the present, at least in the equatorial E. Pacific. It also shows that the contrast between the δ13C values (hence nutrient content) of deep water in the Atlantic and Pacific observed in today's ocean was smaller during glacial periods. In the northwestern Indian Ocean, the global climate‐corrected δ13C results reveal interglacial intensification of the monsoon‐driven upwelling and productivity, back to at least oxygen isotopic stage 11 circa 400 kyr B.P.
Ab initio methods in mineral surface reactions
Authors: Lasaga Antonio C.
Published: February 2008

The methodology of nonempirical ab initio quantum mechanical calculations is reviewed as applied to the field of mineral surface chemistry and water‐rock geochemical kinetics. The ab initio treatment of adsorption deals with the covalent forces between surface atoms and molecules either in solution or in the gas phase. This new information on the bonding of surface atoms can now extend the classical theory of adsorption. Furthermore, reactions on mineral surfaces can also be understood with the aid of ab initio results. The theory can predict reaction potential surfaces as a function of the position of various surface species. In turn, such entities as the activated complex of transition state theory and the reaction coordinate can now be described in a nonempirical way for geochemical reactions, such as the dissolution of quartz or feldspar. Other important reaction variables such as the kinetic isotope effects, the catalytic effect of pH, the catalytic or inhibitory role of dissolved ions and of organic molecules, and the effect of impurities and coordination number of the surface atoms on the water‐rock kinetics can be uniquely studied with ab initio techniques. The initial success of the ab initio approach opens up a new and powerful method of investigating surface reactions.
Application of stochastic inverse theory to ionospheric tomography
Authors: Fremouw E. J. , Secan James A. , Howe Bruce M.
Published: February 2008

Tomographic processing of path integral electron density records is emerging as a viable tool for ionospheric research. Tomographic processors fall into at least two major classes: those applying the Radon transform and those employing linear algebraic matrix inversion. In this paper we apply one of the latter, the “weighted, damped, least squares” technique of stochastic inversion, to two simulated but realistic data sets. This method, which repeatedly has been applied successfully to ocean acoustic tomography, is particularly suited to solving inverse problems in geophysics because it provides an orderly mechanism for judicious use of a priori or external information to complement sparse or nonuniform path integral data. The limited range of angles through which the ionosphere may be viewed on satellite‐to‐ground paths represents such a nonuniformity in ionospheric tomography. The method also provides means for estimating uncertainty in the image field, uncertainty which itself is nonuniform.
Comparison between particle simulation and full‐wave analysis for wave propagation in a nonuniform plasma
Authors: Yagitani S. , Nagano I. , Omura Y. , Matsumoto H.
Published: February 2008

Full‐wave analysis has been applied to the study of wave propagation in a nonuniform plasma, especially where WKB approximation becomes invalid. Because of several approximations assumed, however, it cannot be applied to problems involving particle kinetic effects or nonlinear processes. To evaluate such complicated effects on wave propagation in a nonuniform plasma, we have performed particle simulations with a one‐dimensional nonuniform electron plasma, in which a wave propagates parallel to the static magnetic field. Good agreement is found between the wave fields in the particle simulations and the full‐wave solutions under the same plasma conditions. We also found that two interesting phenomena occur in the particle simulations with plasma conditions different from those allowed in full‐wave analysis. One is a particle kinetic effect, which is due to a large thermal velocity of the plasma. A whistler mode wave is spatially attenuated in a nonuniform plasma through cyclotron damping. The other is a nonlinear effect arising when the incident wave has a large amplitude. Several electromagnetic modes propagating in a nonuniform plasma interact nonlinearly with one another to excite electrostatic oscillations at the local plasma frequencies and at twice the wave frequency. Particle simulation and full‐wave analysis can be used together to characterize wave propagation under a fuller range of plasma conditions and to clarify the limitation of each.
Symmetry properties in polarimetric remote sensing
Authors: Nghiem S. V. , Yueh S. H. , Kwok R. , Li F. K.
Published: February 2008

This paper presents the relations among polarimetric backscattering coefficients from the viewpoint of symmetry groups. Symmetry of geophysical media encountered in remote sensing due to reflection, rotation, azimuthal, and centrical symmetry groups is considered for both reciprocal and nonreciprocal cases. On the basis of the invariance under symmetry transformations in the linear polarization basis, the scattering coefficients are related by a set of equations which restrict the number of independent parameters in the polarimetric covariance matrix. The properties derived under these transformations are general and apply to all scattering mechanisms in a given symmetrical configuration. The scattering coefficients calculated from theoretical models for layer random media and rough surfaces are shown to obey the derived symmetry relations. Use of symmetry properties in remote sensing of structural and environmental responses of scattering media is discussed. As a practical application, the results from this paper provide new methods for the external calibration of polarimetric radars without the deployment of man‐made calibration targets.
Glacier study using wavenumber domain synthetic aperture radar
Authors: Hamran Svein‐Erik , Aarholt Eldar
Published: February 2008

New developments of frequency synthesizers and digital phase detectors make it possible to produce digital radars with high dynamic range that operate in the frequency domain. These radars are especially well suited for ground‐penetrating use. This contribution presents the theoretical basis for frequency domain radars and develops a wavenumber domain‐based synthetic aperture radar algorithm for inverting the data. The effect of the propagation medium is taken into account, and experimental results from a subpolar glacier are given.
Deep earthquakes beneath central Taiwan: Mantle shearing in an arc‐continent collision
Authors: Lin C. H. , Roecker S. W.
Published: February 2008

The island of Taiwan owes its existence to the collision of an island arc on the Philippine Sea Plate with the Eurasian continental shelf. Most of the earthquakes in the mantle beneath Taiwan clearly are related to one of these plates subducting beneath the other, but beneath the central part of the island there is a zone of subcrustal seismicity that is not obviously related to any subduction zone. We investigated the uncertainties in the locations of these anomalous earthquakes by rereading P and S wave arrival times and computing information density functions for several of these events. The seismic zone itself is then defined through a joint probability function incorporating the entire data set. Individual information density functions show that several events are likely to be located at depths exceeding 60 km, with two events exceeding 80 km depth. The joint probability function shows a narrow zone of seismicity, about 20 km wide along strike, plunging to the east. Combining these results with evidence from surface geology, focal mechanisms and subsurface tomography, we suggest that these events are caused by an eastward displacement of the Eurasian mantle north of 24°N which juxtaposes it against colder subducted crust to the south. Moreover, the heat produced by this type of shearing in the mantle must be insignificant for brittle failure to exist at these depths.
Production and accumulation of calcium carbonate in the ocean: Budget of a nonsteady state
Authors: Milliman John D.
Published: February 2008

Present‐day production of CaCO3 in tne world ocean is calculated to be about 5 billion tons (bt) per year, of which about 3 bt accumulate in sediments; the other 40% is dissolved. Nearly half of the carbonate sediment accumulates on reefs, banks, and tropical shelves, and consists largely of metastable aragonite and magnesian calcite. Deep‐sea carbonates, predominantly calcitic coccoliths and planktonic foraminifera, have orders of magnitude lower productivity and accumulation rates than shallow‐water carbonates, but they cover orders of magnitude larger basin area. Twice as much calcium is removed from the oceans by present‐day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity (1.6 bt), suggesting that outputs have been overestimated or inputs underestimated, that one or more other inputs have not been identified, and/or that the oceans are not presently in steady state. One “missing” calcium source might be groundwater, although its present‐day input is probably much smaller than that of rivers. If, as seems likely, CaCO3 accumulation presently exceeds terrestial and hydrothermal input, this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level: shallow‐water accumulation decreases by an order of magnitude with a 100 m drop in sea level, while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow‐water carbonates.
Atmospheric carbonyl sulfide exchange in bog microcosms
Authors: Fried Alan , Klinger Lee F. , Erickson David J.
Published: February 2008

Measurements of Carbonyl sulfide (OCS) fluxes were carried out on bog microcosms using chamber sampling and tunable diode laser analysis. Intact bog microcosms (vascular plants, mosses, and peat) removed ambient levels of OCS in the light and dark with rates from −2.4 to −8.1 ng S min−1 m−2. Peat and peat plus mosses emitted OCS in the light with rates of 17.4 and 10.9 ng S min−1 m−2, respectively. In the dark, the mosses apparently removed OCS at a rate equivalent to the peat emissions. A 3‐D numerical tracer model using this data indicated that boreal bog ecosystems remove at most 1% of ambient OCS, not sufficient to account for an observed OCS depletion in boreal air masses.
Accurate locations of nuclear explosions in Balapan, Kazakhstan, 1987 to 1989
Authors: Thurber C. H. , Quin H. R. , Richards P. G.
Published: February 2008

Locations of 20 nuclear explosions from 1987 to 1989 at the Balapan test site, Kazakhstan, are derived with a precision of about 100 m from time‐sequence SPOT satellite images combined with teleseismic epicenter estimates. For most events, there is little or no ambiguity in the association between seismic events and image features. The locations determined by JED are associated with formal error estimates (95% confidence ellipses) that are significantly too small. In 16 out of 19 cases, the events are found from satellite imagery to lie outside these ellipses. Possible causes are nonuniform observation, poor azimuthal coverage, and source region heterogeneity. Our results should prove valuable for studies of seismic waveforms, arrival time and amplitude tomography, event location, tectonic release, and seismic coupling at Balapan, and demonstrate the utility of combined seismic and satellite image analyses for seismic verification studies.
Source characteristics and locations of hectometric radio emissions from the northern Jovian hemisphere
Authors: Reiner M. J. , Fainberg J. , Stone R. G.
Published: February 2008

Northern Jovian hectometric (HOM) radio emissions, detected from high Jovian latitudes by the Unified Radio and Plasma Wave (URAP) experiment on the Ulysses spacecraft, were observed at all Jovian longitudes. This emission was observed to be predominantly right‐hand circularly polarized, but some left‐hand circular polarization was observed implying the presence of O mode emissions from the northern Jovian hemisphere. Intense HOM emissions, with well‐defined directions and polarizations, were often confined to similar longitudinal regions where intense HOM emissions were previously observed at low latitudes. The present analysis confirms that these northern HOM sources lie in the Jovian polar regions on magnetic field lines that pass through the Io plasma torus. The observations may be consistent with emission from either a filled cone beam or a longitudinal distribution of thin hollow cones.
Temperature dependent UV absorption spectra of carbonyl chloro‐fluoride
Authors: Nölle Andreas , Heydtmann Horst , Meller Richard , Moortgat Geert K.
Published: February 2008

The absorption cross‐sections of COClF have been measured in the wavelength range 200–260 nm at temperatures ranging from 298 to 223 K with a spectral resolution of 0.05 nm using diode array spectroscopy. The absorption cross‐sections were used to calculate photodissociation rate constants at different solar zenith angles as a function of altitude. Temperature effects of the photodissociation rate constants are discussed.
An earthquake model with magnitude‐sensitive dynamics
Authors: McCloskey John , Bean C. J. , O'Reilly B.
Published: February 2008

Considerations of the dimensionality of earthquake generating mechanisms, as assessed by prediction‐regression analysis, show that complete earthquake populations are best described by complex, high‐dimensional dynamics. Cellular automata which allow individual degrees of freedom to many small areal increments of a fault face reproduce realistic event sequences which follow the Gutenberg‐Richter relation.

Simple, spring‐block models with as few as two blocks have been shown, however, to neatly explain the coupling between adjacent segments of transform faults which has been observed in the stratigraphic record.

Here we propose a hierarchical earthquake model in which there is an explicit change in the generating dynamics with magnitude and which may be appropriate for seismicity on a section of a transform fault which includes more than one active segment. In the model a high‐dimensional cellular automaton is responsible for the production of low‐energy events and a low‐dimensional double‐block model represents the dynamics of events in which an entire fault face slips. Frequency magnitude distributions of the model seismicity show a change in b‐value with magnitude which is the result of the change in universality class of the underlying dynamics. Similar changes in b‐value (related to the finite width of the seismogenic layer) have been reported in the literature.
Regional moment:magnitude relations for earthquakes and explosions
Authors: Patton Howard J. , Walter William R.
Published: February 2008

We present Mo:mb relations using mb(Pn) and mb(Lg) for earthquakes and explosions occurring in tectonic and stable areas. The observations for mb(Pn) range from about 3 to 6 and show excellent separation between earthquakes and explosions on Mo:mb plots, independent of the magnitude. The scatter in Mo:mbobservations for NTS explosions is small compared to the earthquake data. The Mo:mb(Lg) data for Soviet explosions overlay the observations for U. S. explosions. These results, and the small scatter for NTS explosions, suggest weak dependence of Mo:mb relations on emplacement media. A simple theoretical model is developed which matches all these observations. The model uses scaling similarity and conservation of energy to provide a physical link between seismic moment and a broadband seismic magnitude. Three factors, radiation pattern, material property, and apparent stress, contribute to the separation between earthquakes and explosions. This theoretical separation is independent of broadband magnitude. For U.S. explosions in different media, the material property and apparent stress contributions are shown to compensate for one another, supporting the observations that Mo:mb is nearly independent of source geology.
Constraints on interseismic deformation at Japan Trench from VLBI data
Authors: Argus Donald F. , Lyzenga Gregory A.
Published: February 2008

We use space geodetic data from very long baseline interferometry to estimate the velocity relative to the plates of two sites near Tokyo. We use these results and elastic models of interseismic deformation to put constraints on the slip rate along the main thrust at the Japan subduction zone. The sites at Kashima and Tsukuba lie 150 and 200 km, respectively, west of the axis of the Japan trench, where the Pacific plate subducts at ∼97 mm/yr. The two sites also lie 160 km from the Sagami trough, where the Philippine plate subducts obliquely at ∼32 mm/yr. Relative to the North American plate Kashima moves at 13±2 mm/yr toward N46±4°W and Tsukuba moves at 9±3 mm/yr toward N42±19°W. These observed velocities are intermediate between the velocities of the Pacific and Eurasian plates, consistent with the overriding plate being the Eurasian plate. In this case the observed velocities reflect the sum of (a) permanent west‐northwest shortening in northern Honshu and (b) elastic deformation due to locking the main thrust fault at Japan trench. But the observed velocities are also part way between the velocities of the Philippine and North American plates, and they may result from Philippine‐North American deformation. Nevertheless, the observed velocities limit the locked segment of the main thrust at Japan trench to no more than 27 km vertically or 100 km along dip. Thus, the main Pacific plate thrust fault is not strongly coupled, part of it must creep, and it probably does not generate great earthquakes.
Artificial auroras in the upper atmosphere 1. Electron beam injections
Authors: Burch J. L. , Mende S. B. , Kawashima N. , Roberts W. T. , Taylor W. W. L. , Neubert T. , Gibson W. C. , Marshall J. A. , Swenson G. R.
Published: February 2008

Artificial electron beams from the Space Experiments with Particle Accelerators (SEPAC) on the ATLAS 1 Spacelab payload were used to stimulate auroral emissions at southern auroral latitudes. The emitted electron beams were monoenergetic at 6.25 keV and were fired in one‐second pulses every fifteen seconds with currents of 1.21 A. Optical measurements of the beam were made in the vicinity of the Shuttle Orbiter by its on‐board television camera and in the upper atmosphere by the Atmospheric Emissions Photometric Imager (AEPI). AEPI imaged auroral emissions in both white light and at the 427.8 nm N2+ emission line. Energy deposition calculations and the results of previous sounding‐rocket experiments had suggested that emissions with scale sizes of about 130 meters would result from the artificial electron beams with the visible emissions extending from about 110 to 130 km altitudes. In the ATLAS 1 experiments the auroral imaging was performed from the Shuttle, providing a new perspective on the artificial auroras and allowing the emissions to be traced from altitudes near the 295 km Shuttle altitude down to the 110 km level along the curved magnetic field lines.
A model for Gouge Deformation: Implications for remanent magnetization
Authors: Roux Stéphane , Hansen Alex , Herrmann Hans J. , Vilotte Jean‐Pierre
Published: February 2008

Using a two‐dimensional construction for space‐filling bearings (SFB) recently proposed by Herrmann et al.[1990], as an idealized description of the texture of gouge‐like material, we study the effect of grain rotations in a shear band. The SFB model is by construction self‐similar and the disk‐size distribution follows a power‐law in good agreement with the observed particle‐size distribution of natural gouges. The kinematics of the model is described by a single degree of freedom, i.e.. each disk can only rotate, with no slip at the contact points. We investigate the isothermal remanent magnetization (IRM) reduction during such a cataclastic shearing. The problem can be solved analytically for this model. The magnetization loss, due to a disorientation of the grains can be shown to be a power‐law as a function of the shear. The exponent of the power law is simply related to the fractal dimension of the particle‐size distribution in the gouge. This result may stimulate experimental investigations using IRM to gain new insight into the gouge texture and kinematics.
New data from Hadar (Ethiopia) support orbitally tuned time scale to 3.3 MA
Authors: Renne Paul , Walter Robert , Verosub Kenneth , Sweitzer Monica , Aronson James
Published: February 2008

Support for the astronomically calibrated geomagnetic polarity time scale is provided by new 40Ar/39Ar dating and magnetostratigraphic data from the Hadar Formation, Ethiopia. Three tuffs and a basalt flow at Hadar span the Mammoth subchron of the Gauss chron, and range in age from 3.18±0.01 to 3.40 ±0.03 Ma. Interpolation of sediment accumulation rates in two magnetostratigraphic sections yields an estimated age range of 3.30±0.02 to 3.21±0.01 Ma for the Mammoth subchron, closely coinciding with orbitally based predictions of 3.33 to 3.22 Ma rather than with previous estimates of 3.15 to 3.05 Ma.
CS2 absorption cross‐section measurements from 187 nm to 230 nm
Authors: Xu Huan , Joens Jeffrey A.
Published: February 2008

Absorption cross‐sections are reported for CS2 for wavelengths between 187 nm and 230 nm at a temperature of 300K and a spectral bandwidth of 0.20 nm. The results are compared to previous cross‐section determinations for CS2, and to the absorption spectrum of SO2, which exhibits a strongly structured absorption band in the same region of the spectrum. The effect of spectral bandwidth and temperature on the absorption cross‐sections is also discussed.
Automotive tire wear as a source for atmospheric OCS and CS2
Authors: Pos W. H. , Berresheim H.
Published: February 2008

The emission of CS2, OCS and traces of SO2 from mixtures of fifteen different ground tire treads has been detected in laboratory experiments using gas chromatography/flame photometric detection (GC/FPD) and gas chromatography/mass spectrometry (GC/MS). Samples of ground tire particles (60–100 mesh) were flushed at different temperatures using either clean nitrogen gas or a mixture of 100 ppb O3 in N2. CS2 was the dominant sulfur gas detected in all of the experiments. OCS and CS2 emissions increased strongly with temperature and were independent of the presence of O3. In contrast, SO2 was observed only at high ozone levels. It is roughly estimated that tire wear may produce as much as 0.04 ± 0.004 Tg S (OCS) yr−1 or about 6.7% of the total OCS flux into the atmosphere. Therefore, this as yet undescribed automotive source may make a small but significant contribution to the atmospheric OCS budget.
Magnetic fabric determined from Arm and IRM anisotropies in Paleozoic carbonates, Southern Appalachian Basin
Authors: Lu Gang , McCabe Chad
Published: February 2008

We have undertaken a comparative study of ARM and IRM anisotropies in Paleozoic carbonate rocks from the Nashville and Jessamine Domes in the Southern Appalachian Basin. The ARMA ellipsoids differ markedly from the IRMA ellipsoids. ARMA appears to reflect a pre‐deformation magnetic fabric due to deposition and/or compaction with minimum axes near vertical and a weak lineation. Conversely, IRMA has minimum axes near horizontal and oriented NE‐SW, which is compatible with a tectonic fabric due to Alleghanian deformation. Percent ARMA is consistently greater than IRMA. ARM was imparted at low alternating fields (30 mT), and thus ARMA may reflect the fabric residing in low and intermediate coercivity (coarse grained) magnetite. However, the IRM was imparted in saturating fields (300 mT) and appears to be dominated by the single domain fraction, which is believed to carry the observed Kiaman Superchron remagnetization.
Generalized Omori law for aftershocks and foreshocks from a simple dynamics
Authors: Shaw Bruce E.
Published: February 2008

A theory of the time dependence of earthquake foreshocks and aftershocks is presented. The theory involves the response to sudden forcing of a dynamics of self‐driven acceleration to failure. The empirically observed Omori law, which says that the rate of aftershocks as a function of time falls as a power law in time, is derived theoretically. The exponent of the falloff in time is shown to generically give a value close to one, for rapidly accelerating dynamics. To see if the theory is consistent with other features of real data, foreshocks and aftershocks of small magnitude mainshocks are analyzed in a catalogue of real earthquakes. Results show that the spatial and temporal distribution of aftershocks is separable into a dependence on space and a dependence on time, that the spatial distribution of aftershocks is consistent with the hypothesis that stress changes from the mainshock cause aftershocks, and that the number of foreshocks approaches the number of aftershocks as the magnitude of the mainshock becomes smaller.
Comparison of HRDI wind measurements with radar and rocket observations
Authors: Burrage M. D. , Skinner W. R. , Marshall A. R. , Hays P. B. , Lieberman R. S. , Franke S. J. , Gell D. A. , Ortland D. A. , Morton Y. T. , Schmidlin F. J. , Vincent R. A. , Wu D. L.
Published: February 2008

Wind fields in the mesosphere and lower thermosphere are obtained with the High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) by observing the Doppler shifts of emission lines in the O2 Atmospheric band. The validity of the measured winds depends on an accurate knowledge of the positions on the detector of the observed lines in the absence of a wind induced Doppler shift. These positions have been determined to an accuracy of approximately 5 ms−1 from the comparison of winds measured by HRDI with those obtained by MF radars. Excellent agreement is found between HRDI measured winds and winds observed with radars and rockets. In addition, the sensitivity of HRDI to migrating tides and other large scale waves is demonstrated.