bluuebunny/crossref_metadata_2025 huggingface dataset:
Tracer filamentation generated by small‐scale Rossby wave breaking in the lower stratosphere
Authors: Bradshaw N. G. , Vaughan G. , Busen R. , Garcelon S. , Jones R. , Gardiner T. , Hacker J.
Published: December 2002

An airborne monitoring system has been used to observe fine‐scale filamentation in the ozone field between 370 and 390 K isentropic levels. The Australian long‐range, high‐altitude research aircraft, the Egrett, was used to record multiple atmospheric properties with a high spatial resolution. Toward the end of 5 June 2000, an intrusion of low‐ozone air was recorded over Aberystwyth, between 360 and 390 K. On the same day, a Rossby wave was observed to be breaking over western Europe with both poleward and equatorward components. We suggest that the low ozone at ∼380 K was caused by the poleward component of the breaking Rossby wave, stretching from southwestern Ireland to Iceland. On the eastern flank of the subtropical intrusion the in situ ozone measurements observed by the Egrett showed distinctive step and trough structures that were not expected from conventional model analyses. Using Reverse Domain‐Filled (RDF) trajectory analyses to produce a fine‐scale view of potential vorticity, we show how breaking of small‐scale Rossby waves along the flank of the main wave over the northeastern United States, followed by a strong zonal compression, produced fine‐scale filaments responsible for the structures observed in the Egrett ozone measurements.
Polar vortex concentricity as a controlling factor in Arctic denitrification
Authors: Mann G. W. , Davies S. , Carslaw K. S. , Chipperfield M. P. , Kettleborough J.
Published: December 2002

Recent in situ observations in the Arctic stratosphere have detected nitric acid–containing particles with sizes up to 10‐μm radius and number concentrations between 10−5 and 10−3 cm−3. Here we quantify the effect of these particles on Arctic denitrification by using a new three‐dimensional (3‐D) model which can couple particle growth and sedimentation with the full dynamics of the Arctic polar vortex. We show that the very long growth times of large nitric acid trihydrate (NAT) particles lead to a highly nonlinear dependence of Arctic denitrification on the growth and evaporation cycles of individual particles, thus making denitrification dependent on the precise meteorological conditions in a given winter. Using 3‐D wind and temperature fields from December 1999, we identify a period that was optimum for denitrification, in which the cold pool and vortex were nearly concentric and in which a large proportion of the particles were able to sediment over about 8 days through the full depth of the cold pool without evaporating. We then show that small departures from concentric conditions can lead to substantial reductions in denitrification. A case is presented in which denitrification was completely shut off even with over half of the cold pool area remaining within the vortex. Under the same conditions, a model in which the particles were assumed to be in continuous equilibrium with the gas phase caused extensive denitrification. Our results show that low Arctic vortex temperatures in themselves are unlikely to be a reliable indicator of potential denitrification if large NAT particles are involved.
Primary sulfate aerosol and associated emissions from Masaya Volcano, Nicaragua
Authors: Allen A. G. , Oppenheimer C. , Ferm M. , Baxter P. J. , Horrocks L. A. , Galle B. , McGonigle A. J. S. , Duffell H. J.
Published: December 2002

Existing studies of the composition of volcanic plumes generally interpret the presence of sulfate aerosol as the result of comparatively slow oxidation of gaseous SO2. We report here new observations from Masaya Volcano, Nicaragua, which demonstrate that sulfate aerosol may also be emitted directly from volcanic vents. Simultaneous aerosol and gaseous S, Cl, and F compounds were collected at the rim of the passively degassing crater in May 2001. Mean concentrations of SO42−, Cl−, and F− within the plume were 83, 1.2, and 0.37 μg m−3, respectively (fine aerosol fraction <2.5 μm) and 16, 2.5, and 0.56 μg m−3, respectively (coarse aerosol fraction >2.5 μm). The aerosols were highly acidic, with estimated pH of <1.0 in the fine aerosols. Sulfate was present mainly in smaller particles, with the fine fraction accounting for ≈80% of the mass. The bulk of the sulfate was emitted directly from the magmatic vent. Acidity in the aerosols derived from the presence of sulfuric acid and, to a lesser extent, hydrofluoric acid, with [H+]/[SO42−] equivalent values of 0.5–0.8 and 0.3–3 for fine and coarse aerosols, respectively. Gas phase/aerosol phase mass ratios were, on average, 458 (S), 330 (F), and 186 (Cl), with ranges of 95–1178, 37–659, and 43–259, respectively. These observations of highly acidic aerosol emitted directly from crater vents have implications for plume chemistry and environmental and health impacts of volcanic degassing.
In situ measurements of carbon dioxide, 0.37–4.0 μm particles, and water vapor in the stratospheric plumes of small rockets
Authors: Gates Amelia M. , Avallone Linnea M. , Toohey Darin W. , Rutter Andrew P. , Whitefield Philip D. , Hagen Donald E. , Hopkins A. Raymond , Ross Martin N. , Zittel Paul F. , Thompson Thomas L. , Herman Robert L. , Friedl Randall R.
Published: December 2002

Carbon dioxide (CO2) and large particles (0.37–4.0 μm) were measured in the stratospheric plume wakes of three rockets, an Atlas IIAS, a Delta II, and an Athena II. The correlations between CO2 mass and particle number densities in each plume are consistent with the unique combination of solid and liquid engine emissions of each rocket. Measured size distributions indicate a 1.1 μm mode with density of 2 g cm−3, consistent with spherical alumina particles emitted by solid rocket motors. Disagreement between the measured size distributions and the mean sizes inferred from the known alumina and CO2 emission indices and an observed increase in the particle number emission index with altitude are evidence for large particle oversampling effects and the presence of condensed volatile compounds within the particle population. Direct evidence for the latter is a persistent ∼0.5–1 part per million (ppm) shortfall of water vapor relative to CO2 measured in the plume of the Athena II rocket based on the expected H2O/CO2 emission ratio. Although pure ice particles would not persist at the conditions of the measurements, a more stable coating of HNO3 (as either nitric acid trihydrate or as a liquid layer) could have reduced the sublimation rate of the underlying ice, thereby increasing the lifetimes of volatile particles within the plume. If confirmed, such a process would have important implications for the radiative and chemical properties of rocket plumes, including global ozone depletion associated with rocket launch activities.
Global budget of atmospheric carbonyl sulfide: Temporal and spatial variations of the dominant sources and sinks
Authors: Kettle A. J. , Kuhn U. , von Hobe M. , Kesselmeier J. , Andreae M. O.
Published: December 2002

The spatial and temporal variability of the global fluxes of carbonyl sulfide (COS) is discussed together with possible implications for total column atmospheric COS loading. The input of COS into the atmosphere is calculated as the sum of all known direct sources of COS plus the conversion of carbon disulfide (CS2) and dimethyl sulfide (DMS) to COS by atmospheric oxidation processes. Recent models are used to predict COS, CS2, and DMS release from the oceans and COS uptake by soils, plants, and oceans. This forward approach to constructing global integrated COS fluxes has a large associated range of uncertainty. The best guess global annual‐integrated COS net flux estimate does not differ from zero within the range of estimated uncertainty, consistent with the observed absence of long‐term trends in atmospheric COS loading. Interestingly, the hemispheric time‐dependent monthly fluxes are very close in phase for the Northern and Southern Hemispheres. The monthly variation of the Northern Hemisphere flux seems to be driven primarily by high COS vegetation uptake in summer, while the monthly variation of the Southern Hemisphere flux appears to be driven mostly by high oceanic fluxes of COS, CS2, and DMS in summer.
Airborne observations of dry particle absorption and scattering properties over the northern Indian Ocean
Authors: de Reus Marian , Formenti Paola , Ström Johan , Krejci Radovan , Müller Detlef , Andreae Meinrat O. , Lelieveld Jos
Published: December 2002

Airborne measurements of the absorption and scattering coefficients of dry aerosols, at 525 and 545 nm, respectively, were performed over the northern Indian Ocean during the Indian Ocean Experiment (INDOEX). In the marine boundary layer the dry absorption coefficient decreased from about 25 Mm−1 close the Indian subcontinent to 2 Mm−1 close to the Intertropical Convergence Zone (ITCZ), which reflects the removal and dilution of anthropogenically produced aerosols during their transport over the Indian Ocean. The dry scattering coefficient initially decreased with distance from the Indian subcontinent, from 70 Mm−1 at 8°N to 10 Mm−1 at 2°N, resulting in a dry single scattering albedo between 0.6 and 0.8 (0.7–0.9 at ambient relative humidity). At further distance from the Indian subcontinent the scattering coefficient and single scattering albedo increased, indicating the increasing importance of aerosols of natural origin. Using Mie theory, the refractive index of the anthropogenically produced aerosols has been estimated to be 1.50–0.06i.
Evidence of the Pinatubo volcanic eruption on the distribution of ozone over the tropical Indian region
Authors: Beig G. , Saraf N. , Peshin S. K.
Published: December 2002

Three independent sets of experimental data for ozone obtained by balloon‐borne ozonesondes and Dobson spectrophotometer during the period 1979–1998 are analyzed over the tropical Indian region covering two stations, Delhi (28°N, 77°E) and Pune (18°N, 73.5°E), in search of volcanic signals after the Mount Pinatubo eruption of 1991. These data sets are analyzed using a regression model, based on multiple function regression theory, which takes into account several natural and anthropogenic signals in order to detect a relatively smaller magnitude, sporadic effect. To study the volcanic effects on the vertical structure of ozone, data sets are independently analyzed for four different predefined Umkehr layers from 15 to 33 km. The total ozone amounts obtained by Dobson spectrophotometer over these two stations are revisited and analyzed using the above regression model. A maximum decrease of the order of 4–7 Dobson units (DU) in the altitude range 15–24 km following 3–4 months of eruption and a maximum increase of the order of 2–3 DU for the altitude range 24–33 km immediately after the eruption have been observed in ozone amounts over these two tropical stations. The total ozone amount measurement indicates a decrease of about 5–6% during the period effected by the Pinatubo eruption. The decreasing trend in ozone content is found to exist up to a maximum of 1.5 years from the time of eruption. The similarity of the results obtained from the three sets of data analyzed affirms the effect of volcanic eruption over the tropical Indian region.
Aerosol elemental concentrations in the tropopause region from intercontinental flights with the Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container (CARIBIC) platform
Authors: Papaspiropoulos Giorgos , Martinsson Bengt G. , Zahn Andreas , Brenninkmeijer Carl A. M. , Hermann Markus , Heintzenberg Jost , Fischer Herbert , van Velthoven Peter F. J.
Published: December 2002

This study with the Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container (CARIBIC) platform investigates the aerosol elemental concentrations at 9–11 km altitude in the northern hemisphere. Measurements from 31 intercontinental flights over a 2‐year period between Germany and Sri Lanka/Maldives in the Indian Ocean are presented. Aerosol samples were collected with an impaction technique and were analyzed for the concentration of 18 elements using particle‐induced X‐ray emission (PIXE). Additional measurements of particle number concentrations, ozone and carbon monoxide concentrations, and meteorological modeling were included in the interpretation of the aerosol elemental concentrations. Particulate sulphur was found to be by far the most abundant element. Its upper tropospheric concentration increased, on average, by a factor of 2 from the tropics to midlatitudes, with another factor 2 higher concentrations in the lowermost stratosphere over midlatitudes. Correlation patterns and source profiles suggest contributions from crustal sources and biomass burning, but not from meteor ablation. Coinciding latitudinal gradients in particulate sulphur concentrations and emissions suggest that fossil fuel combustion is an important source of the aerosol in the upper troposphere and lowermost stratosphere. The measurements indicate aerosol transport along isentropic surfaces across the tropopause into the lowermost stratosphere. As a result of the prolonged residence time, ageing via oxidation of sulphur dioxide in the lowermost stratosphere was found to be a likely high‐altitude, strong source that, along with downward transport of stratospheric air, could explain the vertical gradient of particulate sulphur mass concentration around the extratropical tropopause.
Underestimation of solar global and diffuse radiation measured at Earth's surface
Authors: Philipona Rolf
Published: December 2002

Climate change perspectives intensified investigations of the radiative balance of the Earth‐atmosphere system. At the top of the atmosphere, solar irradiance is known with absolute uncertainty of 0.3% and theoretical models agree with albedo measurements, but solar shortwave radiation observations at Earth's surface are less than those calculated by radiative‐transfer models. This model observation discrepancy (10–25 Wm−2) led to a decade‐long controversy on unexplained enhanced absorption of shortwave radiation in clear sky atmospheres as well as in clouds. Here we show evidence for underestimation of surface shortwave irradiance by traditional “unconditioned” global and diffuse pyranometer measurements. Reinvestigations of pyranometer calibration in conjunction with thermal offsets and pyranometer thermal control demonstrate an underestimation of clear sky solar global, as well as diffuse irradiance by 8–20 Wm−2, caused by pyranometer differential cooling. Field measurements with “conditioned” and “unconditioned” pyranometers demonstrate that the so‐called night offset is present and considerably larger during daytime measurements, and this not only for diffuse but also for global pyranometer measurements. Long‐term comparisons between traditional unconditioned and well‐conditioned pyranometer measurements at Davos (midlatitude, 1580 m a.s.l.) show differences of several percent on the annual mean of global irradiance. Even though we are aware that measurements at higher altitudes are subject to larger thermal offsets and not representative for the global average, the results of our experiment lead us to believe that surface solar irradiance, measured in the past throughout the globe by traditional unconditioned pyranometers, is underestimated.
Year‐round records of bulk and size‐segregated aerosol composition and HCl and HNO3 levels in the Dumont d'Urville (coastal Antarctica) atmosphere: Implications for sea‐salt aerosol fractionation in the winter and summer
Authors: Jourdain Bruno , Legrand Michel
Published: December 2002

Year‐round composition of bulk and size‐segregated aerosol was examined at a coastal Antarctic site (Dumont d'Urville). Sea‐salt particles display a summer depletion of chloride relative to sodium, which reaches ∼10%. The mass chloride loss is maximum on 1‐ to 3‐μm‐diameter particles, nitrate being often the anion causing the chloride loss. The summer SO42−/Na+ ratio exceeds the seawater value on submicron particles due to biogenic sulfate and on coarse particles due to ornithogenic (guano‐enriched soils) sulfate and to heterogeneous uptake of SO2 (or H2SO4). HCl levels range from 47 ± 28 ng m−3 in the winter to 130 ± 110 ng m−3 in the summer, being close to the mass chloride loss of sea‐salt aerosols. In the winter, sea‐salt particles exhibit Cl−/Na+ and SO42−/Na+ mass ratios of 1.9 ± 0.1 and 0.13 ± 0.04, respectively. Resulting from precipitation of mirabilite during freezing of seawater, this sulfate‐depletion‐relative sodium takes place from May to October. From March to April, warmer temperatures and/or smaller sea ice extent offshore the site limit the phenomenon. A range of 14–50 ng m−3 of submicron sulfate is found, confirming the existence of nssSO42− in the winter at a coastal Antarctic site, highest values being found in the winters of 1992–1994 due to the Pinatubo volcanic input. Apart from these three winters, nssSO42− levels range between 15 and 30 ng m−3, but its origin is still unclear (quasi‐continuous SO2 emissions from the Mount Erebus volcano or local wintertime dimethyl sulfide [DMS] oxidation, in addition to long‐range transported by‐product of DMS oxidation).
Frost flowers: Implications for tropospheric chemistry and ice core interpretation
Authors: Rankin Andrew M. , Wolff Eric W. , Martin Seelye
Published: December 2002

This paper discusses the chemical composition of frost flowers and their accompanying slush layers and the evidence for their role as a salt source in processes important to atmospheric chemistry and ice core interpretation. Analysis of Antarctic frost flowers shows that they are highly saline and fractionated in sea‐salt ions, with sulfate being depleted strongly relative to sodium. Because frost flowers give a bright return on satellite scatterometer images, the times and places of their formation can be identified. When winds blow towards an aerosol sampling station from areas identified by the scatterometer as covered with flowers, the collected aerosol is also depleted in sulfate. Because the flowers have a large salinity, bromide concentrations are elevated in frost flowers relative to seawater. With their high surface area, it is possible that bromine is released to the atmosphere from frost flowers, with consequent implications for tropospheric ozone depletion. The finding that quantities of fractionated sea salt are available at the sea–ice interface in the winter months and may be transported inland as aerosol also has implications for the interpretation of ice core records. Analysis of one near‐coastal core shows that the majority of the sodium comes from a fractionated source rather than from open water. Hitherto, strong sea‐salt signals in ice cores have been attributed to increased open water and more efficient transport inland, perhaps due to stormier weather. At least in coastal regions, however, these signals may be related instead to the increased formation of sea ice and frost flowers.
Low‐pressure dependency of the isotopic enrichment in ozone: Stratospheric implications
Authors: Bhattacharya S. K. , Chakraborty Subrata , Savarino Joel , Thiemens Mark H.
Published: December 2002

Stratospheric ozone is enriched in the heavy isotopes (17O and 18O) relative to the ambient oxygen from which it is formed. This enrichment varies with altitude, attaining very high values between 30 and 40 km. A recent theory of Y. Q. Gao and R. A. Marcus explores the reasons for isotopic enrichment in the process of ozone formation and is particularly useful to understand the laboratory results. The stratospheric variations are sought to be explained in terms of temperature dependence of isotopic enrichment, but the magnitude of variation does not match with predictions accurately. We demonstrate here that isotopic enrichment in ozone generated by oxygen photolysis depends on the pressure of the oxygen reservoir and can have very high values (at about 15 torr), comparable to the highest observed stratospheric values. Analysis of the data shows that secondary enrichment through ozone dissociation can add to the primary enrichment associated with ozone formation. The effect of dissociation is found to be more pronounced in the pressure range of 15 to 50 torr, resulting in high enrichment. It is shown that the relative kinetics, pressure and temperature conditions of ozone formation and dissociation play an important role in determining the ultimate value of the enrichment. The results are particularly useful to understand the stratospheric data and resolve the observed discrepancy.
Ground‐based infrared spectroscopic measurements of carbonyl sulfide: Free tropospheric trends from a 24‐year time series of solar absorption measurements
Authors: Rinsland C. P. , Goldman A. , Mahieu E. , Zander R. , Notholt J. , Jones N. B. , Griffith D. W. T. , Stephen T. M. , Chiou L. S.
Published: December 2002

Solar absorption spectra recorded over a 24‐year time span have been analyzed to retrieve average free tropospheric mixing ratios of carbonyl sulfide (OCS). The measurements were recorded with the Fourier transform spectrometer located in the U.S. National Solar Observatory McMath solar telescope facility on Kitt Peak (altitude 2.09 km, lat. 31.9°N, long. 111.6°W), southwest of Tucson, Arizona, and were obtained on 167 days between May 1978 and February 2002, typically at 0.01‐cm−1 spectral resolution. A best fit to the time series shows an average mixing ratio of 566 pptv (1 pptv = 10−12 per unit volume) between 2.09 and 10 km, a small but statistically significant long‐term decrease equal to (−0.25 ± 0.04)% yr−1, 1 sigma, and a seasonal variation with a summer maximum, a winter minimum, and a peak amplitude of (1.3 ± 0.4)%, 1 sigma, relative to the mean. Although a statistically significant decline and seasonal variation have been detected, both are exceedingly small. The present results confirm and extend earlier studies showing that the OCS free tropospheric abundance at northern midlatitudes has remained nearly constant over the last decades.
Stress differences in the Martian lithosphere: Constraints on the thermal state of Mars
Authors: Arkani‐Hamed Jafar , Riendler Lucas
Published: December 2002

Depth‐dependent density perturbations are determined inside the elastic part of the Martian lithosphere (assumed to be 300 km thick) using a thick elastic shell model, such that the deformed model under the loads of surface topography and the density perturbations gives rise to the observed topography and gravity anomalies of Mars specifies by spherical harmonics of degree 3–50. Large positive density perturbations, as high as ∼150 kg/m3, exist in the crust that are associated with Hellas, Isidis, Argyre, and Utopia basins, reflecting the mantle uplift in response to the impact excavation. Also, large positive density perturbations exist in the crust beneath Olympus (∼350 kg/m3) and Tharsis monts (∼200 kg/m3), indicating that these shield volcanoes are not isostatically compensated. On the other hand, negative density perturbations are associated with Alba Patera, Elysium rise, and the highland surrounding Hellas basin. The density perturbations gradually diminish with depth, becoming less than 20 kg/m3 by 250–300 km depth. The resulting stress differences within the crust and upper mantle are dominated by Olympus (up to 100 MPa), whereas other shield volcanoes create lesser stress differences. We estimate the brittle‐ductile transition temperature in the lithosphere, adopting the creep law of dry olivine for the rheology of the Martian lithosphere. The brittle‐ductile transition temperature beneath Olympus is ∼800C throughout the lithosphere, indicating that the upper parts of Mars must have been cold to support this volcano for 1–2 Gyr.
Numerical modeling for target water depth estimation of marine‐target impact craters
Authors: Ormö Jens , Shuvalov Valery V. , Lindström Maurits
Published: December 2002

Marine impacts can develop a crater in the seafloor if the target water depth is shallow in relation to the size of the impactor. The geology of this marine‐target crater is influenced by the layer of water in the upper part of the target. The influence increases with increased water depth. The target water depth is essential when calculating the magnitude of the impact event as the seafloor crater merely expresses some of the expended energy. The target water depth for a marine‐target crater is often estimated by facies analysis of sediments related to the impact crater, unfortunately often with ambiguous results. We propose to combine the conventional methods with numerical modeling of the target water depth based on the special target‐water‐related features of the crater. We used geological data from the Lockne crater as constraints in a simulation with the SOVA hydrocode. The simulations were done for three different target water depths (200 m, 500 m, and 1000 m) within the likely depth range for the Middle Ordovician sea, in which the impact occurred. In order to obtain the minimum estimated size of the Lockne crater by an asteroid impact at 20 km/s, the water depth must have been slightly less than 1 km, and the impactor radius must have been about 400 m. It was not possible to generate a crater with the geological features of Lockne for target water depths of less than about 500 m. However, the ratio may be further constrained by factors such as impactor density, impact angle, and impact velocity.
Late Cenozoic tectonic development of the intramontane Alai Valley, (Pamir‐Tien Shan region, central Asia): An example of intracontinental deformation due to the Indo‐Eurasia collision
Authors: Coutand I. , Strecker M. R. , Arrowsmith J. R. , Hilley G. , Thiede R. C. , Korjenkov A. , Omuraliev M.
Published: December 2002

The Pamir indentor of the northwestern Himalayan syntaxis is a first‐order feature demonstrating partly the northward extent of deformation due to the Cenozoic Indo‐Eurasia collision. The Alai Valley of Kyrgyzstan at the northern end of the indentor is a strategically positioned, E‐W trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone. To quantify the convergence accommodated across the Alai Valley during the Late Cenozoic, we collected structural and stratigraphic field data, reviewed existing Soviet literature, and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin. Our study suggests that the development, progressive closure, and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events: (1) Distributed north‐south contraction took place during the late Oligocene–early Miocene, accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface; and (2) N‐S shortening resumed in the mid‐Miocene and continues today. During this second episode the thrust front migrated southward, localized along the Trans Alai ranges, and failed to reactivate earlier Neogene structures. Horizontal shortening of about 35% across the Alai Valley implies relatively low strain rates and displacement rates of about 4.18–4.69 × 10−16 s−1 and 0.66–0.78 mm yr−1, respectively, for the last 25 Myr. Our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the Asian continent as early as the late Oligocene.
Boron isotope signatures in the coastal groundwaters of French Guiana
Authors: Negrel Philippe , Petelet‐Giraud Emmanuelle , Kloppmann Wolfram , Casanova Joël
Published: December 2002

Drinking water used by the population of French Guiana comes mostly from rivers and can induce major health impacts. Consequently, groundwaters are being studied in terms of an alternative drinking water supply. In this context, boron isotopes were applied to the coastal aquifers to better constrain the water‐rock interactions. We found that the δ11B signatures vary between −2.98 and 49.35‰ in the groundwaters and between 36.35 and 42.41‰ in the river waters and that the local seawater gave a value of 40.76‰. We also noted an inverse correlation between groundwater pH and δ11B: this relationship, previously demonstrated experimentally, is particularly well defined in the French Guiana coastal aquifer because of the wide pH range (4.18 to 7.64) naturally present in the groundwaters. It would appear that the variations in δ11B values are linked to water‐rock interaction processes (e.g., dissolution/precipitation of silicates).
Oxygen 18 fractionation during snowmelt: Implications for spring flood hydrograph separation
Authors: Laudon Hjalmar , Hemond Harry F. , Krouse Roy , Bishop Kevin H.
Published: December 2002

Isotopic hydrograph separation (IHS) to define sources of event and preevent water during hydrological episodes has greatly improved the understanding of water, solute, and contaminant transport to streams during recent decades. However, the large variation in snowmelt isotopic composition, caused by fractionation during melting, has impeded an accurate separation of streamflow during spring flood episodes. Here we present a method that greatly improves the separation of event and preevent water during snowmelt by accounting for both the temporal change in the snowmelt isotopic signal and the temporary storage of meltwater in the catchment. Comparison of results of this technique with previous results, using isotopic data from the 1997 spring flood on a small catchment in northern Sweden, suggests that earlier techniques significantly underestimate the preevent contribution. This paper also explores the importance of lateral mixing across the catchment of temporally varying event inputs for the IHS results.
Cross correlations among estimators of shape
Authors: Martins Eduardo S. , Stedinger Jery R.
Published: December 2002

The regional variability of shape parameters (such as κ for the GEV distribution) may be described by generalized least squares (GLS) regression models that allow shape parameters to be estimated from basin characteristics recognizing the sampling uncertainty in available shape estimators. Implementation of such GLS models requires estimates of the cross‐site correlation of the shape parameter estimators for every pair of sites. Monte Carlo experiments provided the information needed to identify simple power approximations of the relationships between the cross correlation of estimators of skewness γ from [log] Pearson type 3 (P3) data and of the shape parameter κ of both generalized Pareto (GP) and generalized extreme value (GEV) distributions, as functions of the intersite correlation of concurrent flows.
IUPAC-NIST Solubility Data Series. 78. Acetonitrile Binary Systems
Authors:   Volume Editors, Sazonov Valerii P. , Shaw David G. ,   With the assistance of Evaluators:, Sazonov Valerii P. , Sazonov Nikolai V. , Skrzecz Adam ,   Compilers, Sazonov Valerii P. , Sazonov Nikolai V. , Lisov Nikolai I.
Published: December 2002

The mutual solubilities and liquid–liquid equilibria of acetonitrile binary systems with different compounds exhaustively and critically are reviewed. The compounds include water, inorganic compounds, and a variety of organic compounds (hydrocarbons, halogenated hydrocarbons, alcohols, carboxylic acids and esters, nitrogen, and sulfur compounds). A total of 353 systems reported in the primary literature through 2000 are compiled. For 25 systems sufficient data are available to allow critical evaluation. All data are expressed as mass and mole fractions as well as the originally reported units. Similar reviews of gas, liquid, and solid solubilities for other systems are published in the of Solubility Data Series. This is the 78th volume of this series.
Electron Interactions With BCl3
Authors: Christophorou L. G. , Olthoff J. K.
Published: December 2002

In this paper we review and assess the cross sections for collisions of low-energy electrons with boron trichloride (BCl3). The only available experimental cross section data are for partial and total ionization and electron attachment, and the electron attachment cross sections are uncertain. Calculated values are available for the total elastic, differential elastic, and momentum transfer cross sections, and derived cross sections have been published for vibrational excitation and dissociation. Other than some rather uncertain data on electron attachment rate constants and some measurements of electron drift velocities in BCl3/Ar and BCl3/He mixtures, there are no measurements of the electron attachment, ionization, or transport coefficients for this gas. Analysis of the experimental data on the electron affinity, electron attachment, and electron scattering, enabled identification of negative ion states of BCl3 at about −0.3, 1.0, 2.8, 5.2, 7.6, and 9.0 eV. Because the existing electron collision data are few and uncertain, relevant data are provided for photon impact on BCl3..
Correlated line broadening in multidimensional vibrational spectroscopy
Authors: Venkatramani Ravindra , Mukamel Shaul
Published: December 2002

The third-order optical response of two coupled anharmonic vibrations interacting with a Brownian oscillator bath that induces energy level fluctuations with arbitrary time scales and degree of correlation is calculated. Two-dimensional correlation plots show distinct signatures of these fluctuations in the various possible three pulse, infrared, femtosecond techniques.
Temperature dependent partition functions and equilibrium constant for HCN and HNC
Authors: Barber R. J. , Harris Gregory J. , Tennyson Jonathan
Published: December 2002

Ab initio vibration-rotation energy levels are summed to estimate a partition function for the total HCN system. By assigning individual levels to HCN and HNC, separate partition functions are obtained for the isomers. These are used to give a temperature dependent equilibrium constant which suggests that at temperatures typical of cool carbon stars, about 20% of the HCN system is actually HNC. Errors in the partition functions and equilibrium constant are estimated.
Single-molecule spectroscopy: The road ahead
Authors: Orrit Michel
Published: December 2002

The spectroscopy of single molecules in frozen matrices at liquid helium temperatures reveals very narrow lines, often with lifetime-limited widths. The sensitivity of such sharp lines provides a wealth of information about the molecules, their environment, and their interaction with electromagnetic fields. As compared to more conventional bulk investigations, single molecules reveal the full extent of inhomogeneity at small scales, in the static or structural sense as well as in the time-resolved or dynamical sense. A few examples from the recent literature, on single molecules as sources of single photons, as probes for molecular or electronic motion, or as beacons in structural studies of biological molecules, illustrate these general features of the technique. The author’s best hopes for advances in the field include bridging between room and liquid helium temperatures, investigating structural problems on frozen biomolecules, using a single molecule as a tip for near-field optics, or as an input or output gate for quantum cryptography and quantum computing, and probing and exploiting the multiple possible interactions between single molecules.
Single-molecule chemistry
Authors: Ho W.
Published: December 2002

The ability to probe individual atoms and molecules have made it possible to reveal properties which otherwise would be hidden in the study of an ensemble of atoms and molecules. The scanning tunneling microscope (STM) with its unmatched spatial resolution and versatility literally allows us to touch atoms and molecules one at a time and to carry out experiments which previously were only imagined. One of the great attributes of the STM is that it provides a real space view of the individual molecules and the atomic landscape of their environment, thus removing many of the uncertainties surrounding the nature of the system under study. Combining its imaging, manipulation, spectroscopic characterization, and chemical modification capabilities, the STM has enabled direct visualization of chemistry by revealing the fundamental properties of atoms and molecules and their interactions with each other and the environment. While femtosecond lasers have made it possible to study chemistry at the temporal limit, the STM provides an understanding of chemistry at the spatial limit.
Probing single-molecule dynamics photon by photon
Authors: Yang Haw , Xie X. Sunney
Published: December 2002

We present the theoretical rationales for data analysis protocols that afford an efficient extraction of conformational dynamics on a broad range of time scales from single-molecule fluorescence lifetime trajectories. Based on correlation analyses, a photon-by-photon approach on one hand provides the highest time resolution, whereas a minimal-binning method on the other hand is most suitable for experiments experiencing external fluorescence intensity variations. Applications of the two methods are illustrated via computer simulations. In cases where fluorescence quenching is either due to Förster fluorescence resonance energy transfer or due to the excited-state electron transfer, the fluorescence lifetime is dependent on donor-acceptor distance, thereby providing a window through which conformational dynamics are revealed. To assist in interpreting experimental data derived from the new protocols, analytical expressions relating fluorescence lifetime fluctuation correlations to a Brownian diffusion model and to an anomalous diffusion model are discussed.
Direct measurements of memory effects in single-molecule kinetics
Authors: Yang Shilong , Cao Jianshu
Published: December 2002

Statistics and correlations of single-molecule sequences of modulated reactions are explicitly evaluated in the stochastic rate representation. The memory function, introduced through the Gaussian approximation of the stochastic rate expression, characterizes the correlation in single-molecule rate processes in a formalism similar to the stochastic line shape theory. Within this formalism, the on-time correlation is shown to approximate the memory function of the fluctuating rate at discretized effective time separations. A new measurement, the two-event number density, is proposed as a means to map out the memory function over the complete time range. Confirmed by numerical calculations, these relations quantify dynamic disorder caused by conformational fluctuations and hence are useful for analyzing single-molecule kinetics.
Single-molecule approach to dispersed kinetics and dynamic disorder: Probing conformational fluctuation and enzymatic dynamics
Authors: Sunney Xie X.
Published: December 2002

This article reviews our efforts in understanding dynamical fluctuations of both conformation and enzymatic reactivity in single biomolecules. The single-molecule approach is shown to be particularly powerful for studies of dispersed kinetics and dynamic disorder. New single-molecule observations have revealed conformational transitions occurring on a broad range of timescales, 100 μs–10 s, offering new clues for understanding energy landscape of proteins, as well as the structural and chemical dynamics therein.
Granular flow down a rough inclined plane: Transition between thin and thick piles
Authors: Silbert Leonardo E. , Landry James W. , Grest Gary S.
Published: December 2002

The rheology of granular particles in an inclined plane geometry is studied using three dimensional molecular dynamics simulations. The flow–no-flow boundary is determined for piles of varying heights over a range of inclination angles θ. Three angles determine the phase diagram: θr, the angle of repose, is the angle at which a flowing system comes to rest; θm, the maximum angle of stability, is the inclination required to induce flow in a static system; and θmax is the maximum angle for which stable, steady state flow is observed. In the stable flow region θr<θ<θmax, three flow regimes can be distinguished that depend on how close θ is to θr: (i) θ≫θr: Bagnold rheology, characterized by a mean particle velocity vx in the direction of flow that scales as vx∝h3/2, for a pile of height h, (ii) θ≳θr: The slow flow regime, characterized by a linear velocity profile with depth, and (iii) θ≈θr: Avalanche flow characterized by a slow underlying creep motion combined with occasional free surface events and large energy fluctuations. We also probe the physics of the initiation and cessation of flow. The results are compared to several recent experimental studies on chute flows and suggest that differences between measured velocity profiles in these experiments may simply be a consequence of how far the system is from jamming.
The 248 nm photolysis of NO2/N2O4: Time-resolved Fourier transform infrared emission from NO and NO2, and quenching of NO (v=5–8)
Authors: Morrell Claire , Breheny Ciara , Haverd Vanessa , Cawley Aimee , Hancock Gus
Published: December 2002

The photolysis of NO2 and N2O4 has been studied at 248 nm by observations of time-resolved Fourier transform infrared emission from the photofragments. The photolysis of NO2 produces emission in the Δv=−1 and −2 fundamental and overtone bands of NO(X 2Π), and spectral analysis yields a broad Gaussian-type distribution in the vibrational levels v=2–8, in good agreement with one of two previously reported initial nascent quantum state distributions. Quenching of the higher levels (v=5–8) of NO in collisions with NO2 produces rate constants which increase with increasing v with values between 0.91 and 3.5×10−11 cm3 molecule−1 s−1. The process is shown to have a larger component of resonance energy transfer from NO(v) to NO2(0,0,1) than previously reported values for the rate constants at lower v which are further from resonance. A fast component of IR emission from the nascent excited states of NO2 is observed, together with slower decaying emissions near 1450 and 2750 cm−1, assigned as Δν3=−1 and Δν1=Δν3=−1 transitions from high vibrational levels of the ground state formed by quenching of electronically excited NO2 produced from the photolysis of N2O4. A comparison is made of these IR bands with similar features seen in the IR emission from NO2 following electronic excitation in the visible region below its dissociation limit. Further emission near 1880 cm−1 accompanies the photolysis of N2O4, and is tentatively assigned to the direct formation of NO as a photolysis product, with a non-negligible quantum yield in low vibrational levels.
Elastic and rotationally inelastic differential cross sections for He+H2O collisions
Authors: Brudermann Jesko , Steinbach Christof , Buck Udo , Patkowski Konrad , Moszynski Robert
Published: December 2002

Elastic and rotationally inelastic cross sections have been measured for He+H2O scattering at two collision energies, 66.3 and 99.0 meV, using the crossed molecular beam technique. The inelastic events are detected by time-of-flight analysis of the scattered He atoms. The data are converted to elastic differential cross sections and inelastic angular-dependent energy loss spectra in the center-of-mass system. They are compared with averaged, full close-coupling calculations of state-to-state cross sections for rotational excitation based on a newly calculated ab initio potential using symmetry-adapted perturbation theory. The agreement with the elastic differential cross sections is excellent. The energy loss spectra are reproduced satisfactorily and among the largest differential cross sections that contributed to the measurements are excitations around all three possible axes for ΔJ=1 but a preference of the excitation around the in-plane C axis for ΔJ=2 transitions.
Analysis of the small-scale structure of turbulence on smooth and rough walls
Authors: Poggi D. , Porporato A. , Ridolfi L.
Published: December 2002

Energy spectra and structure functions of the streamwise and wall-normal turbulent velocity components in an open channel flow are experimentally investigated as a function of the distance from the wall. Both smooth- and rough-wall conditions are considered, with special attention to the zone close to the wall. In the core region, the small-scale turbulent flow field is always characterized by a high level of isotropy, while a strong anisotropy is found at small scales in the near-wall region. In the smooth-wall case, the extent of the scaling range increases as the wall is approached, but with exponents which are different from the classical ones. In the rough-wall case, the roughness strongly interacts with turbulence, destroying the scaling regions at small scales through the imposition of its characteristic scales. A lower level of intermittency and anisotropy is also observed at the small scales for rough-wall conditions. Energy spectra and structure functions suggest a connection of these behaviors with the turbulent energy directly injected into the flow by the roughness elements. The integral structure functions show that roughness effects exceed the sole modification of local shear and reveal the direct impact of wakes and vortices generated by the roughness in the near-wall region.
Heats of formation of phosphorus compounds determined by current methods of computational quantum chemistry
Authors: Haworth Naomi L. , Bacskay George B.
Published: December 2002

The heats of formation of a range of phosphorus containing molecules (P2, P4, PH, PH2, PH3, P2H2, P2H4, PO, PO2, PO3, P2O, P2O2, HPO, HPOH, H2POH, H3PO, HOPO, and HOPO2) have been determined by high level quantum chemical calculations. The equilibrium geometries and vibrational frequencies were computed via density functional theory, utilizing the B3LYP/6-31G(2df,p) functional and basis set. Atomization energies were obtained by the application of ab initio coupled cluster theory with single and double excitations from (spin)-restricted Hartree–Fock reference states with perturbative correction for triples [CCSD(T)], in conjunction with cc-pVnZ basis sets (n=T, Q, 5) which include an extra d function on the phosphorus atoms and diffuse functions on the oxygens, as recommended by Bauschlicher [J. Phys. Chem. A 103, 11126 (1999)]. The valence correlated atomization energies were extrapolated to the complete basis limit and corrected for core–valence (CV) correlation and scalar relativistic effects, as well as for basis set superposition errors (BSSE) in the CV terms. This methodology is effectively the same as the one adopted by Bauschlicher in his study of PO, PO2, PO3, HPO, HOPO, and HOPO2. Consequently, for these molecules the results of this work closely match Bauschlicher’s computed values. The theoretical heats of formation, whose accuracy is estimated as ranging from ±1.0 to ±2.5 kcal mol−1, are consistent with the available experimental data. The current set of theoretical data represent a convenient benchmark, against which the results of other computational procedures, such as G3, G3X, and G3X2, can be compared. Despite the fact that G3X2 [which is an approximation to the quadratic CI procedure QCISD(T,Full)/G3Xlarge] is a formally higher level theory than G3X, the heats of formation obtained by these two methods are found to be of comparable accuracy. Both reproduce the benchmark heats of formation on the average to within ±2 kcal mol−1 and, for these molecules at least, they are superior to the basic G3 method. The performance of G3X2 is further improved, however, by the incorporation of BSSE corrections in the CV component of the energies. All the G3n methods have difficulties, however, with molecules which have multiple or highly strained P–P bonds, such as P2 and P4.