bluuebunny/crossref_metadata_2025 huggingface dataset:
The microstructural response of quartz and feldspar under shock loading at variable temperatures
Authors: Huffman Alan R. , Brown J. Michael , Carter Neville L. , Reimold W. Uwe
Published: February 2008

Shock recovery experiments were carried out on Westerly granite and Hospital Hill quartzite targets in the peak pressure range 8 to 25 GPa, preshock temperatures of 25°, 450°, and 750°C and pulse durations of 2 to 7 μs using internally heated momentum traps and explosive plane wave generators. Optical and transmission electron microscopy analyses of quartz and feldspar shocked at 25°C revealed the previously documented progression, with increasing pressure: (1) fracturing; (2) planar fractures and shock mosaicism; (3) shock mosaicism and planar deformation features (PDFs); and (4) isotropization. This same sequence is observed for experiments at elevated preshock temperature but with specific microstructures occurring at lower pressures than those in previous experiments at room temperature. At 750°C, strong shock mosaicism, partially thermally recovered, is characteristic of feldspar shocked to 8 GPa, whereas 15 GPa is required for its development in quartz and for the generation of PDFs in both minerals. The results suggest that threshold pressures for formation of the various microstructures and phases are expected to vary systematically as a function of the preshock temperature of the target material. We suggest that PDFs are generated in the shock transition by progressive, heterogeneous, phase transformation of the crystal structure to form dense glass or high pressure polymorphs. The onset pressures for PDFs in specific crystallographic orientations is not influenced strongly by temperature, but the character of the PDFs does change as preshock temperature is increased at the same peak shock stress. The change from multiple sets of thin PDFs at low temperature to thicker single sets of PDFs at moderate temperature, and finally to complete isotropization at high temperatures, reflects a change in the phase transformation mechanism as a function of temperature. In contrast, development of shock mosaicism in quartz and feldspar occurs throughout the duration of shock loading and is better developed at elevated temperatures where the kinetics are enhanced by the additional thermal energy in the target.
Magma ascent rates from amphibole breakdown: An experimental study applied to the 1980–1986 Mount St. Helens eruptions
Authors: Rutherford Malcolm J. , Hill Peter M.
Published: February 2008

Recent 1980–1986 Mount St. Helens dacites contain the phenocryst assemblage, plagioclase, amphibole, low‐Ca pyroxene, magnetite, ilmenite, and rare high‐Ca pyroxene, which indicates that they all originated from an 8 km deep reservoir at 900°±20°C with XH2O= 0.67 in fluid according to experimental data. Iron‐titanium oxide phenocryst compositions indicate that all post May 18 dacitic magmas erupted at 900°±20°C except for the final lava extrusion in October 1986; the magma reservoir may have cooled to 866°C by October 1986. Amphiboles in the post May 18, 1980, magma contain one or more amphibole populations characterized by reaction rims of different thicknesses. The development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir. Constant P and T and isothermal decompression experiments show that during a 900°C constant rate decompression from 8 km to the surface, no reaction rim develops on amphibole in 4 days, a 10‐μm rim develops in 10 days, and a 35‐μm rim develops in 20 days. These experimental data and histograms of rim widths in 1980–1986 Mount St. Helens dacites show that post May 18 eruptions are composed in large part of magma represented by a population of thin‐rimmed amphiboles, magma which ascended from the deep (8 km) reservoir in 6 to 10 days. The remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 μm, magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly (millimeter scale) into the erupting magma. The mixing in a viscous, slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population. The experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post May 18 dacites of about 15–30 m/h for magma represented by the thick‐rimmed amphiboles and from 35 to 50 m/hr for magma represented by the thin‐rimmed crystals. An ascent rate of >66 m/h is indicated for the May 18, 1980, eruption, which contains amphiboles with no reaction rims. The volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath Mount St. Helens in 1981–1982 was equivalent to a cylinder 8 km long and 8–9 m in radius.
Three‐dimensional spherical models of layered and whole mantle convection
Authors: Glatzmaier Gary A. , Schubert Gerald
Published: February 2008

We present numerical calculations of three‐dimensional spherical shell thermal convection for constant viscosity and stratified viscosity models of whole‐layer and two‐layer mantle convection. These four examples are intended to provide theoretical guidance for determining the style of convection that is occurring in Earth's mantle. An impermeable interface between the upper and lower converting shells in the two‐layer solutions is placed at a depth of 670 km to coincide with the mantle seismic discontinuity that divides the upper and lower mantle. The interface results in an internal thermal boundary layer that raises the mean temperature in the lower shell by about 1400 K compared to the whole‐layer solutions. The patterns of convection in the upper part of the whole‐layer solutions are dominated by narrow arcuate sheetlike downflows in a background of weak upflow. In contrast, the upper shells of the two‐layer solutions have complicated networks of convective rolls with the upflows and downflows having very similar structure. The structure of convection in the lower shells is similar to that in the lower part of the whole‐layer solutions. An increase (decrease) in the viscosity in the lower (upper) shell decreases (increases) the convective velocity in the lower (upper) shell and increases (decreases) the horizontal scale in the lower (upper) shell. The upper and lower shells are viscously coupled at the 670‐km interface when viscosity is the same in the two shells. However, when viscosity in the lower shell is 30 times greater than that in the upper shell, the coupling is partially viscous and partially thermal. Based on the horizontal structure of subduction zones on Earth's surface and on tomographic images of temperature variations in Earth's mantle, we conclude that the style of convection in Earth's mantle is more like that of the whole‐mantle models.
An intermediate one‐dimensional thermodynamic sea ice model for investigating ice‐atmosphere interactions
Authors: Ebert Elizabeth E. , Curry Judith A.
Published: February 2008

A one‐dimensional thermodynamic model of sea ice is presented that focuses on those features that are most relevant to interactions with the atmosphere, namely the surface albedo and leads. It includes a surface albedo parameterization that interacts strongly with the state of the surface, and explicitly includes meltwater ponds. The lead parameterization contains a minimum lead fraction, absorption of solar radiation in and below the leads, lateral accretion and ablation of the sea ice, and a prescribed sea ice divergence rate. The model performed well in predicting the current climatic sea ice conditions in the central Arctic when compared with observations and other theoretical calculations. Results of parameter sensitivity tests produced large equilibrium ice thicknesses for small values of ice divergence or large values of minimum lead fraction as a result of positive feedback mechanisms involving cooling of water in the leads. The ice thickness was also quite sensitive to the meltwater runoff fraction and moderately sensitive to the other parameters in the melt pond parameterization, a result of the strong dependence of the surface albedo, and hence the net flux, on the surface conditions. To further investigate the physical interactions and internal feedback processes governing the sea ice‐lead system, sensitivity tests were also performed for each of the external forcing variables. The model's equilibrium sea ice thickness was extremely sensitive to changes in the downward longwave and shortwave fluxes and atmospheric temperature and humidity, moderately sensitive to the value of the ocean heat flux, and insensitive to values of wind speed, snowfall, and rainfall in the immediate vicinity of the baseline forcing, although significant changes in thickness occurred for larger variations in wind speed and snowfall. Four important positive feedback loops were identified and described: (1) the surface albedo feedback, (2) the conduction feedback, (3) the lead solar flux feedback, and (4) the lead fraction feedback. The destabilizing effects of these positive feedbacks were mitigated by two strong negative feedbacks: (1) the outgoing longwave flux feedback, and (2) the turbulent flux feedback. Considering the strong influence which sea ice has on global atmospheric and oceanic circulation patterns, it is essential that climate models be able to treat these feedback processes appropriately.
Spatial and temporal scales in altimetric variability in the Brazil‐Malvinas current confluence region: Dominance of the semiannual period and large spatial scales
Authors: Provost Christine , Le Traon Pierre‐Yves
Published: February 2008

Two years of Geosat data are used to investigate the space and time scales of the mesoscale variability in the Brazil‐Malvinas Current confluence region. The mesoscale activity is highly inhomogeneous and anisotropic. The inhomogeneity is characterized by low values of sea level variability in the Malvinas Current (less than 8 cm, i.e., eddy kinetic energy less than 150 cm2 s−2), intermediate values in the Brazil Current (typically 16 cm/800 cm2 s−2) and high values in the Brazil‐Malvinas frontal region (30 cm/1700 cm2 s−2). The anisotropy is marked with meridional variances of velocity that are typically three times larger than zonal ones in the region of maximum variability. Mesoscale variations are dominated by relatively large spatial scales and low‐frequency fluctuations. Contrary to similar spectra derived from Geosat data over the North Atlantic (Le Traon, 1991; Le Traon et al., 1990) or over the whole southern ocean (Chelton et al., 1990) there is very little energy at the annual period. In the mean spectrum, the energy is at least 3 times smaller at the annual period than at the semiannual period or at shorter periods. The semiannual signal, with length scales of about 400–500 km, has a clear northward propagation and is maximum in the frontal region. It is probably associated with the semiannual wave that dominates the atmospheric circulation in the southern hemisphere. However, the mechanism responsible for this semiannual signal in the frontal region remains unclear. Beyond this dominant semiannual frequency, the altimetry‐derived mesoscale fluctuations exhibit other energetic signals, especially signals at periods between 75 and 150 days and spatial scales of 500–600 km with a westward propagation which have characteristics consistent with the dynamics of barotropic Rossby waves.
Movement of the surface front induced by Kuroshio frontal eddy
Authors: Toda Takashi
Published: February 2008

Analysis of successive satellite thermal images in Tosa Bay, Japan, along the Kuroshio, showed that a cyclonic frontal eddy is formed due to the topographic effect of Cape Ashizuri when the Kuroshio axis moves offshore. Unlike those found in the South Atlantic Bight (SAB) along the Gulf Stream, the frontal shape induced by the eddy is asymmetric. Comparison with the previous description on the eddy in the SAB shows a possibility that cold, nutrient‐rich deep water is not easily pumped up by the upwelling induced by the eddy in Tosa Bay and the surface temperature distribution is not affected much. Time series of water temperatures recorded on a ferryboat show that this phenomenon occurs about three times in a month but is not periodic.
Comparison of dynamic height variations in the tropical Atlantic during 1987–1989 as viewed in sections Hydrography and Geosat altimetry
Authors: Carton James A. , Chepurin Gennady A. , Korotaev Gennady K. , Zhu Tong
Published: February 2008

During the 1980s the Soviet Union conducted a series of 25 hydrographic cruises in the tropical Atlantic under the Sections (acronym for Energetically Active Zones of the Ocean and Climate Variability) program. As one of its objectives, Sections has produced the most extensive hydrographic data set ever collected in the tropical Atlantic. Here we examine dynamic topography from seven cruises during the years 1987 through 1989 and compare them to corresponding maps of sea level from the Geosat satellite mission. The two independent estimates of sea level variation are well correlated, with the sea level fields explaining approximately half of the variance of dynamic height fields. There is a seasonal variation to the agreement, so that the correlation increases somewhat in summer and fall, as the variability of the height field increases. Wavenumber spectra of both dynamic height and sea level are quite red for wavelengths greater than 400–600 km. Smaller wavelengths cannot be resolved by the hydrographic sampling program. A comparison of the dynamic height and sea level spectra indicates that sea level has somewhat less variability than dynamic height at all wavenumbers.
Some statistical and dynamical properties of turbulence in the oceanic pycnocline
Authors: Wijesekera Hemantha W. , Dillon Thomas M. , Padman Laurie
Published: February 2008

Statistics of turbulence length scales in individual mixing patches are used to describe the nature of mixing in the oceanic pycnocline near steep bottom topography. The majority of the observed mixing events can be explained with the conventional ideas of shear‐driven turbulence. The statistics of some large patches, however, deviate substantially from expected values, suggesting that there is at least one other significant source of turbulent kinetic energy besides small‐scale shear production. On the basis of inertial subrange energy arguments, it is proposed that the overturning seen in these events is a release of potential energy to kinetic energy which is consistent with advective instability in a finite‐amplitude internal wave field. We find that within large turbulent patches the turbulent kinetic energy dissipation rate εr averaged over a region of height r has a lognormal distribution consistent with Kolmogorov's third hypothesis, σ2ln(εr) = A + μ, ln (LP/r), where σ2ln(εr) is the variance of ln (εr); r satisfies LP ≫ r ≫ η; LP is the size of the mixing patch; η is the Kolmogorov scale; A depends on the large‐scale flow field; and μ is the intermittency coefficient, which is found to be approximately 0.4 in large patches. The variance of ln (εr) also depends on the Reynolds number and the characteristic length scales of the mixing patches.
Behavior of precipitating water drops under the influence of electrical and aerodynamical forces
Authors: Coquillat Sylvain , Chauzy Serge
Published: February 2008

The present work performs a realistic modeling of precipitating charged water drops under the influence of electrical and dynamical forces in the vertical and downward electric field of a thundercloud. The following factors which control the shape of an individual raindrop are taken into account: surface tension, internal hydrostatic pressure, aerodynamic pressure, and electrostatic pressure. Unlike a recent and notable work by Chuang and Beard (1990) in which this problem is approached by adjusting an empirical pressure distribution for the distortion, our model considers simple local pressure balance to determine the drop shape. This computation aims at characterizing drop distortion, falling speed modification, and disruption. The overall present results are similar to those of Chuang and Beard's more sophisticated model, and the predicted critical fields are even closer to wind tunnel measurements by Richards and Dawson (1971). The disruption of positively charged drops requires lower ambient fields than that of the negatively charged drops, and for highly charged and large drops they are of the order of those commonly measured within thunderclouds. At last, the terminal velocity is highly affected by net charge and ambient field. These processes are probably important in lightning initiation during drop disruption.
The high‐resolution doppler imager on the Upper Atmosphere Research Satellite
Authors: Hays Paul B. , Abreu Vincent J. , Dobbs Michael E. , Gell David A. , Grassl Heinz J. , Skinner Wilbert R.
Published: February 2008

The high‐resolution Doppler imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) is a triple‐etalon Fabry‐Perot interferometer designed to measure winds in the stratosphere, mesosphere, and lower thermosphere. Winds are determined by measuring the Doppler shifts of rotational lines of the O2 atmospheric band, which are observed in emission in the mesosphere and lower thermosphere and in absorption in the stratosphere. The interferometer has high resolution (0.05 cm−1), good offband rejection and excellent stability. This paper provides details of the design and capabilities of the HRDI instrument.
Solar‐Stellar Irradiance Comparison Experiment 1: 2. Instrument calibrations
Authors: Woods Thomas N. , Rottman Gary J. , Ucker Gregory J.
Published: February 2008

The science objective for the Solar‐Stellar Irradiance Comparison Experiment (SOLSTICE) is to accurately measure the full disk solar spectral irradiance in the ultraviolet (UV) spectral region over a long time period. The SOLSTICE design was driven by the requirement for long‐term, precise solar photometry conducted from space. The SOLSTICE 1 is on the Upper Atmosphere Research Satellite (UARS), launched in September 1991 with the possibility for a 10‐year operational mission. The in‐flight calibration for SOLSTICE to meet its primary objective is the routine measurements of the UV radiation from a set of early‐type stars, using the identical optical elements employed for the solar observations. The extensive preflight calibrations of the instrument have yielded a precise characterization of the three SOLSTICE channels. Details of the preflight and in‐flight SOLSTICE calibrations are discussed in this paper.
Preface [to special section on 'The Tropical Experiment of the Stratosphere‐Troposphere Exchange Project (STEP Tropical)]
Authors: Pfister Leonhard , Russell Philip B.
Published: February 2008

The Tropical Experiment of the Stratosphere‐Troposphere Exchange Project (STEP) was an international effort to answer two major questions: (1) How is air moved from the tropical troposphere to the overlying stratosphere and (2) Why is the stratosphere so dry? These issues are in fact coupled, since, excepting the lower middle stratosphere during Antarctic winter, only the tropical tropopause is cold enough to dehydrate air (by freezing and subsequent precipitation) to the zonally averaged mixing ratios of 2.5–3 parts per million by volume (ppmv) observed in the tropical lower stratosphere. Indeed, the dryness of the global stratosphere has historically been the key piece of evidence indicating that the tropics are the region of upward mass transfer.
Land surface temperatures derived from the advanced very high resolution radiometer and the along‐track scanning radiometer: 1. Theory
Authors: Prata A. J.
Published: February 2008

The problem of deriving accurate land surface temperatures (LSTs) using infrared satellite measurements is considered. The radiative transfer equation over the land is solved by linearization of the Planck function in temperature and wavenumber in the same manner as is done for obtaining the so‐called split‐window algorithm for sea surface temperature estimation. The effects of the atmosphere and of surface emissivity are both considered in the derivation. By making further assumptions, an approximate split‐window algorithm which shows explicitly how atmospheric absorption by water vapor and surface emissivity both affect the accuracy of LSTs is derived. A new algorithm has been formulated for use with National Oceanic and Atmospheric Administration advanced very high resolution radiometer data and is compared with previously published algorithms. It has a global form with coefficients that depend upon local conditions. Dual angle algorithms are also derived. These may be used to estimate LST using data from the along‐track scanning radiometer on board the first European remote‐sensing satellite.
Circulation anomaly mechanisms in the tropical Atlantic sector during the northeast Brazil rainy season: Results from the GISS general circulation model
Authors: Hastenrath Stefan , Druyan Leonard
Published: February 2008

The role of the sea surface temperature (SST) pattern in the tropical Atlantic on the overlying atmosphere is studied from a 7‐year run of the general circulation model (GCM) of the Goddard Institute for Space Studies (GISS) (period 1980–1986) and in comparison to upper air analyses of the European Centre for Medium‐Range Weather Forecasts (ECMWF), surface ship observations of the SST and wind fields (COADS), and rainfall measurements in Northeast Brazil (Nordeste). Observations for March to April show that reduced northward SST decrease in the tropical Atlantic is accompanied by reduced northward decrease of lower‐tropospheric thickness, which accounts for an inverse change in the meridional pressure gradient and reduced northerly wind component; this in turn entails a northward displaced Intertropical Convergence Zone and drought in the Nordeste. The GCM simulation reproduces the thermal and hydrostatic forcing of SST on the meridional gradients of lower‐tropospheric thickness and pressure in the proper sense, albeit more weakly than observed. The modeled meridional wind component follows the meridional pressure gradient in the proper sense, but mean and range are smaller than observed, and the modeled interannual variability is not altogether consistent with observational evidence. The modeled March to April precipitation in the Nordeste shows little relation to the observed rainfall, although it is weakly related with the observed interhemispheric SST contrast and with the modeled near‐surface meridional wind component. Both modeled and observed March to April Nordeste rainfall are negatively related with SST anomalies in the equatorial Pacific in March to April as well as in the immediately preceding January. Both in January and in March to April the modeled soil moisture exhibits a strong dependence on the modeled precipitation, but neither resembles in interannual variability nor in absolute amounts of the observed rainfall. Overall the GISS GCM seems to reproduce reasonably well the response of lower‐tropospheric thickness and near‐surface pressure to SST, while the simulation of wind and rainfall is somewhat deficient.
Factors influencing dry season ozone distributions over the tropical South Atlantic
Authors: Anderson B. E. , Gregory G. L. , Barrick J. D. W. , Collins J. E. , Sachse G. W. , Hudgins C. H. , Bradshaw J. D. , Sandholm S. T.
Published: February 2008

Airborne measurements of trace gas and aerosol species were obtained in the lower troposphere (<5km) over the western Atlantic Ocean between 13°S and 40°N during the August/September 1990 NASA Chemical Instrument Test and Evaluation (CITE 3) experiment. The largest background O3 mixing ratios, averaging 35 and 70 ppbv within the mixed layer (ML) and free troposphere (FT; altitudes >2.4 km), respectively, were found over the tropical South Atlantic. Several competing processes were observed to regulate O3 budgets in this region. Within the ML, rapid photochemical destruction produced a diurnal O3 variation of 8 ppbv and an O3/altitude gradient between the surface and 5 km of almost 10 ppbv(O3) km−1. ML O3 concentrations were replenished by atmospheric downwelling which occurred at rates of up to and exceeding 1 cm s−1. Ozone values within the subsiding FT air were enriched both by long‐range transport of O3 produced photochemically within biomass combustion plumes and the downward propagation of dry, upper tropospheric air masses. Overall, the tropospheric O3 column below 3.3 km averaged 13.5 Dobson units (DU) over the South Atlantic region, which is 8–9 DU higher than observed during CITE 3 ferry flights over the northern tropical Atlantic Ocean or measured by ozonesondes over coastal Brazil during the wet season. An examination of simultaneous dew point and combustion tracer (e.g., CO) measurements suggests that the dry subsiding layers and biomass burning layers make approximately equal contributions to the observed O3 enhancement.
An updated model for O2(a1Δg) concentrations in the mesosphere and lower thermosphere and implications for remote sensing of ozone at 1.27 μm
Authors: Mlynczak Martin G. , Solomon Susan , Zaras Daphne S.
Published: February 2008

An updated kinetic model for the calculation of daytime steady state O2(a1Δg) concentrations in the mesosphere and lower thermosphere is presented. In addition to the usual source from ozone photolysis in the Hartley band, energy transfer from O(1D) produced by photolysis of molecular oxygen in the Lyman alpha and Schumann‐Runge continuum spectral intervals is shown be a significant source of O2(a1Δg) as well. Numerous changes and additions to the basic O2(a1Δg) kinetic model have been included. These new sources and kinetic parameters imply that lower mesospheric ozone concentrations as inferred by near‐infrared emission techniques are to be decreased by as much as 10% while lower thermospheric ozone concentrations are to be increased by as much as 20%.
Redox chemistry of iron in fog and stratus clouds
Authors: Erel Yigal , Pehkonen Simo O. , Hoffmann Michael R.
Published: February 2008

The redox chemistry of Fe in fog and cloudwater has been investigated at coastal and inland locations in the Los Angeles basin, in Bakersfield California, and in Delaware Bay. Samples were collected and analyzed for Fe (Fe(II)), Fe(III), total(Fe), sulfur (S(IV), S(VI)), organic ligands (formate, acetate, oxalate), total organic carbon (TOC), pH, major cations (sodium, calcium, magnesium, potassium, ammonium), chloride, sulfate, nitrate, peroxides, and aldehydes (HCHO); the amount of sunlight was also measured. The ratio Fe(II)/Fe(total) varied between 0.02 and 0.55. The concentration of Fe(II) varied between 0.1 and 5 micromole, and the concentration of total Fe varied between 2 and 27 micromole. The atmospheric redox cycle of Fe involves both dissolved and aerosol surface species and appears to be related to the presence of organic compounds which act as electron donors for the reduction of Fe(III). Fe(III) reduction is enhanced by light but significant Fe(II) levels were observed in the dark. We suggest that reduction of Fe(III) species by organic electron donors may be an important pathway that affects the speciation of Fe in both urban and rural atmospheres. It is possible that reactions involving Fe and organic compounds might be an important source of carboxylic acids in the troposphere.
Detection of water vapor in the stratosphere over very high clouds in the tropics
Authors: Fritz Sigmund , Laszlo Istvan
Published: February 2008

Satellite observations, above very high clouds in the tropics, are analyzed. These observations reveal the influence of warm water vapor in the stratosphere; above those clouds, the radiance (equivalent temperature) in the water vapor channel (6.7 μm) is warmer than the equivalent temperature in the window channel (11.1 μm). When the clouds are well below the tropopause, the temperature in the water vapor channel is colder than the window channel temperature. Theoretical radiative calculations support the interpretation of the satellite observations.
Measurements of dimethyl sulfide and SO2 during GTE/CITE 3
Authors: Ferek Ronald J. , Hegg Dean A.
Published: February 2008

As part of NASA's Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation (GTE/CITE 3) Sulfur Gas Intercomparison, we conducted measurements of dimethyl sulfide (DMS) and SO2 using two techniques well suited for sampling from an aircraft due to their simplicity of design. DMS was collected by preconcentration on gold wire preceded by a KOH‐impregnated filter oxidant scrubber, and analyzed by gas chromatography with flame photometric detection. SO2 was collected on K2CO3/glycerol‐impregnated filters and analyzed by ion chromatography. In blind tests, both techniques produced excellent agreement with National Institutes of Standards and Technology (NIST) standards. For field measurements, the DMS technique produced excellent correlation with the mean of the six different techniques intercompared. For SO2, the five techniques intercompared were rather poorly correlated, but correlations between the three techniques which passed NIST standards tests were somewhat better. Our SO2 filter measurements exhibited rather large uncertainties due to higher than normal variability of the filter blanks, which we believe was caused by extended storage in the field. In measurements conducted off the coast of Natal, Brazil, a diurnal afternoon minimum in DMS concentrations accompanied by a corresponding maximum in SO2 concentrations was observed. However, due to rather large uncertainties in the SO2 measurements, any conclusions about the SO2 trend must be considered tentative.
Atmospheric depositional fluxes of 7Be and 210Pb at Galveston and College Station, Texas
Authors: Baskaran M. , Coleman Charles H. , Santschi Peter H.
Published: February 2008

The bulk depositional fluxes of 210Pb and 7Be were measured at a coastal (Galveston) and an inland (College Station) station for about 3 years, between 1989 and 1991. The annual depositional fluxes of 7Be and 210Pb at Galveston during this period varied by a factor of about 2.5, between 8.9 and 23.2 disintegrations per minute (dpm) cm−2 yr−1, with a mean of 14.7 dpm cm−2 yr−1 for 7Be, and 0.67 and 1.71 dpm cm−2 yr−1, with a mean of 1.03 dpm cm−2 yr−1 for 210Pb, respectively. The precipitation‐normalized 7Be flux increases with increasing amount of precipitation. There is no systematic and consistent seasonal trend in the depositional fluxes for 7Be or for 210Pb. The volume‐weighted 210Pb concentrations, when normalized to the amount of precipitation, seem to be constant over the time period of this study. Four to six heavy rain events (> 5 cm) in a single day account for 20–30% of the annual deposition of 7Be and 210Pb. Such events account, however, for only about 4–6% of the total number of rainy days in a year. The dry depositional fluxes of these nuclides appear to be a significant fraction of the bulk depositional flux only during the months when there is very little rain. The fraction of dry to total depositional flux of 210Pb appears to be higher than that of 7Be. The strong positive correlation between 7Be and 210Pb depositional fluxes indicates that the flux of both nuclides is controlled by scavenging processes by local precipitation. This correlation also indicates that a major portion of the air masses that brings precipitation to Galveston and College Station is of continental origin. Our data therefore suggest that 7Be and 210Pb cannot be used as independent atmospheric tracers in our coastal station. This observation is consistent with those observed at many other continental and coastal stations.
Origins of the rings of Uranus and Neptune: 2. Initial conditions and ring moon populations
Authors: Colwell Joshua E. , Esposito Larry W.
Published: February 2008

The smallest moons of the Jovian planets are unlikely to survive intact the flux of cometary impactors in the outer solar system for billions of years. In paper 1 (Colwell and Esposito, 1992) we showed that the small moons of Uranus and Neptune are fragments or rubble pile agglomerations left over from some older, larger population of satellites. Catastrophic fragmentation occurs in ∼ 108 years for these ring moons. The fate of the debris following a fragmenting impact is central to understanding the evolution of these satellites and the hypothesized origin of rings from their debris. In this extension of our earlier work we examine the possible effects of the velocity distribution of fragments following a catastrophic fragmentation on satellite diminution via a collisional cascade. We compare our results with those presented in paper 1. Fragment velocities are critical in the evolution of the collisional cascade because of the possibility of reaccretion following disruption. Using our simulations of the collisional cascade including the effects of the fragment velocity distribution we estimate an unseen population of moons in the 1 to 10 km size range of ∼ 1000 at Uranus and at Neptune. Using our model fragment velocity distribution we calculate the initial phase space distribution of the new ring particles. This provides a physically realistic initial condition for simulations of the collisional evolution of planetary rings. We find that a narrow ring with a characteristic width of ∼ 50 km is a natural outcome of the catastrophic disruption of satellites.
Estimating modal abundances from the spectra of natural and laboratory pyroxene mixtures using the modified Gaussian model
Authors: Sunshine Jessica M. , Pieters Carlé M.
Published: February 2008

Spectra of samples containing multiple pyroxene components are explored as a function of modal abundance using the modified Gaussian model (MGM). The MGM, unlike other approaches, allows spectra to be analyzed directly, without the use of actual or assumed end‐member spectra and therefore holds great potential for remote applications. Quantitative understanding of the spectral characteristics of lithologies which include mixtures of two or more pyroxenes is fundamental to analyzing remotely acquired spectra of terrestrial and extra‐terrestrial targets. A series of mass fraction mixtures created from several different particle size fractions were analyzed with the MGM to quantify the properties of pyroxene mixtures as a function of both modal abundance and grain size. Results of this MGM analysis indicate that band centers, band widths, and relative band strengths of absorptions from individual pyroxenes in mixture spectra are largely independent of particle size. In addition, systematic changes in relative band strength as a function of modal abundance are observed, which yield particle size independent relationships that can be used to estimate modal abundances from the spectra of unknown samples. Spectra of natural samples exhibiting both zoned and exsolved pyroxenes are evaluated as examples of spectra likely to be measured from actual lithologies. Spectral properties of both pyroxene components are resolved in exsolved samples using the MGM, and modal abundances are accurately estimated to within 5–10% without predetermined knowledge of the end‐member spectra. In contrast, the spectra of samples exhibiting zoned compositions are consistent with one dominant pyroxene component. This single pyroxene component has anomalously wide absorption bands and appears to represent an average composition.
Temporal behavior of cloud morphologies and motions in Saturn's atmosphere
Authors: Sanchez‐Lavega A. , Lecacheux J. , Colas F. , Laques P.
Published: February 2008

Saturn's atmosphere displays a variety of temporal changes in its cloud morphology at synoptic and planetary scales. Hemispheric long‐term albedo variations, which are more pronounced at ultraviolet and blue wavelengths, have been well established and are apparently linked to the seasonal insolation cycle. Short‐term changes, of the order of months, have been observed in the spectral reflectivity of the belt/zone pattern mainly at mid‐latitudes. Some appear to be related to discrete spot activity, but for the majority of the changes, no such signs of spot activity were detected up to a resolution ∼2000 km. In particular, the “ribbon” structure at 45°N could have been affected by this activity and probably is a transient phenomenon. The polar belts at ∼65° north and south and those at 75° north (hexagon) and south show a long‐term stability in their location, perhaps for more than a century. The most prominent belts located in the Equator and the Equatorial Zone are persistent features of Saturn's globe; their main changes took place during the development of a rare, planetary‐scale disturbance known as Great White Spots. Only five such events have been observed at repetitive regular intervals of about one Saturn year since the first report in 1876, and at different latitudes from the equator to 60°N. They are probably convective in origin, with the seasonal heating of the upper atmosphere acting as a trigger mechanism. During its life cycle of 2–3 years, the disturbance shows turbulent planetary‐scale patterns of clouds that might be related to a wave dynamical phenomenon. Other distinct nonaxisymmetric cloud systems at synoptic scale are very scarce in Saturn's atmosphere. We observed new isolated features at several latitudes during 1990 and 1991. These spots, together with those available from historical records, are used as tracers for determining the latitude dependence and time variability of Saturn's zonal winds. The winds tend to exhibit a long‐term stability in their latitudinal positions and average wind speed, although some significant departures from the zonal mean Voyager profile have been detected during the development of the equatorial disturbance in 1990 and 1991.
Correlated variations of UV and radio emissions during an outstanding Jovian auroral event
Authors: Prangé R. , Zarka P. , Ballester G. E. , Livengood T. A. , Denis L. , Carr T. , Reyes F. , Bame S. J. , Moos H. W.
Published: February 2008

An exceptional Jovian aurora was detected in the FUV on December 21, 1990, by means of Vilspa and Goddard Space Flight Center (GFSC) International Ultraviolet Explorer (IUE) observations. This event included intensification by a factor of three between December 20 and 21, leading to the brightest aurora identified in the IUE data analyzed, and, in the north, to a shift of the emission peak towards larger longitudes (these variations are even more dramatic once the actual source brightness distribution is retrieved from the raw data). The Jovian radio emission simultaneously recorded at decameter wavelengths in Nançay also exhibits significant changes, from a weak and short‐duration emission on December 20 to a very intense one, lasting several hours, on December 21. Confirmation of this intense radio event is also found in the observations at the University of Florida on December 21. The emissions are identified as right‐handed Io‐independent “A” (or “non Io‐A”) components from the northern hemisphere. The radio source region deduced from the Nançay observations lies, for both days, close to the UV peak emission, exhibiting in particular a similar shift of the source region toward larger longitudes from one day to the next. A significant broadening of the radio source was also observed and it is shown that on both days, the extent of the radio source closely followed the longitude range for which the UV brightness exceeds a given threshold (∼3 kW m−1). The correlated variations, both in intensity and longitude, strongly suggest that a common cause triggered the variation of the UV and radio emissions during this exceptional event. On one hand, the variation of the UV aurora could possibly be interpreted according to the Prangé and Elkhamsi (1991) model of diffuse multicomponent auroral precipitation (electron and ion): it would arise from an increase in the precipitation rate of ions together with an inward shift of their precipitation locus from L ≈ 10 to L ≈ 6. On the other hand, the analysis of Ulysses observations in the upstream solar wind suggests that a significant disturbance in the solar wind, involving the generation of an interplanetary shock and the presence of a CME have interacted with the Jovian magnetosphere at about the time of the auroral event. Both arguments suggest that we may have observed for the first time a magnetic storm‐type interaction in an outer planet magnetosphere, affecting simultaneously several auroral processes. Conversely, the observed relationship between the level of UV auroral activity and the detection of decameter emission (DAM), if it were a typical feature, might argue in favour of a more direct and permanent association between the auroral processes leading to UV and radio aurorae, possibly related to “discrete‐arc”‐like activity and electron precipitation.
Thermodynamic influences on the marine carbon isotope record
Authors: Charles Christopher D. , Wright James D. , Fairbanks Richard G.
Published: February 2008

Air‐sea exchange represents an important controlling factor for the distribution of carbon isotopes in the modern ocean, even below the surface mixed layer. Here we show that this thermodynamic influence varies between water masses with a magnitude which is large relative to the amplitude of typical deep sea sediment δ13C records. Thus, changes in air‐sea exchange processes must be regarded as a significant source of variability for any marine δ13C signal.
Tomographic reconstruction of ionospheric electron density with European incoherent scatter radar verification
Authors: Raymund T. D. , Pryse S. E. , Kersley L. , Heaton J. A. T.
Published: February 2008

A campaign was conducted in late September 1991 to obtain experimental measurements for use in ionospheric tomography. Four stations receiving signals from the Navy Navigation Satellite System satellites were set up in a meridional chain in Scandinavia covering some 10° of latitude. Measurements of total electron content were made for six satellite passes over a 2‐day period coinciding with an extended run of the CP3f latitudinal scan common program of the European incoherent scatter radar. A new reconstruction technique involving the use of two‐dimensional basis vectors has been used to convert the total electron content measurements to images of electron density in a height versus latitude plane. Comparisons of the tomographic images and the independent measurements of electron density from the radar show good general agreement. Broadly similar troughs and enhancements are observed by the two techniques, and a latitudinal gradient in the height of the peak density is reproduced in both data sets.
Near‐field patterns of circular aperture antennas
Authors: Hansen R. C. , Libelo Louis F.
Published: February 2008

An accurate representation of circular aperture near fields, including those in the projected aperture region, is obtained through a modification of the geometrical theory of diffraction launching coefficient.
The psychology of drinking water quality: An exploratory study
Authors: Syme Geoffrey J. , Williams Katrina D.
Published: February 2008

Perceptions of drinking water quality were measured for residents at four locations in Western Australia. The total dissolved solid levels for the locations varied. Four scales of drinking water satisfaction were measured: acceptability of water quality; water quality risk judgment; perception of neighborhood water quality; and attitudes toward fluoride as an additive. Responses to each of these scales did not appear to be highly related to total dissolved solids. The relationship between attitudes toward water quality and a variety of psychological, attitudinal, experiential, and demographic variables was investigated. It was found that responses to the acceptability of water quality and water quality risk judgment scales related to perceived credibility of societal institutions and feelings of control over water quality and environmental problems. For the remaining two scales few significant correlations were found. The results support those who advocate localized information and involvement campaigns on drinking water quality issues.
Modeling Colloid Transport in Unsaturated Porous Media and Validation with Laboratory Column Data
Authors: Corapcioglu M. Yavuz , Choi Heecheul
Published: February 2008

Colloidal particles can act as carriers to enhance the transport of contaminants in porous media by reducing retardation effects. When colloids are present, especially in the vadose zone, the system can be treated as consisting of four phases: an aqueous phase, the stationary soild matrix phase, a carrier (colloidal particles) phase, and a stagnant air phase. In the work reported a mathematical model based on mass balance equations was developed to describe the transport and fate of colloids in an unsaturated porous medium. Colloidal particles can sorb onto the air‐water interface as well as to the solid matrix surfaces. Colloid/matrix mass transfer rate is represented by first‐order kinetics, while the colloid/air‐water interface mass transfer mechanism is formulated by second‐order kinetics. The model was applied to simulate the migration of colloids through an unsaturated finite column. Numerical solutions were obtained to provide estimates of colloidal concentrations. A sensitivity analysis of the transport model was utilized to assess the effect of several parameters on model behavior. The aqueous phase colloid concentration is quite sensitive to changes in the rate coefficient of colloidal deposition on the solid matrix. However, the colloidal capture on the air‐water interface is affected by the fraction of air‐water interface available for particle deposition as well as by the rate coefficient of colloidal capture on the air‐water interface, k3. As k3 increases, the available sorption site reduces quickly. Furthermore, increasing colloidal sorption capacity significantly retards the colloidal migration. The model results match successfully with experimental data of Wan and Wilson [1994a] and Wan et al. [1994]. A comparison between the breakthrough curves of hydrophobic and hydrophilic colloids suggests that the hydrophobic colloids have less affinity for both solid matrix and the air‐water interface. Experimental data and model results show that the presence of the air‐water interface retards the colloid transport very significantly. Finally, the proposed model is extended to simulate the colloid transport under transient water flow conditions. Simulations show that aqueous phase colloid concentration varies along the column following a trend similar to the saturation profile for both hydrophobic and hydrophilic colloids. However, the migration profile of hydrophilic colloid suspension is faster than the hydrophobic one.