Role Of Water Vapor Research Articles

Organization of Tropical Convection in Low Vertical Wind Shears: The Role of Water Vapor

A modeling study is conducted to gain insight into the factors that control the intensity and organization of tropical convection, and in particular to examine if organization occurs in the absence of factors such as vertical wind shear or underlying sea surface temperature (SST) gradient. The control experiment integrates a cloud-resolving model for 15 days using a 3D domain exceeding 1000 km in length, with no imposed winds, and horizontally uniform SST and forcing for convection. After 2 days of random activity, the convection organizes into clusters with dimensions of approximately 200 km. Convective systems propagate through the clusters at speeds of 2–3 m s−1, while the clusters themselves propagate at minimal speeds of around 0.5 m s−1. Examining the thermodynamic structure of the model domain, it is found that the convective free bands separating the clusters are very dry throughout the troposphere, and due to virtual temperature effects, are correspondingly warmer in the lower troposphere and boundary layer. This suggests a positive feedback between convection and water vapor, where convective moistening of the local atmosphere renders it more favorable to future convection. The existence of this feedback is demonstrated by experiments in which the free-tropospheric water vapor is perturbed in convective regions, and it is found that the lower-atmospheric water vapor is most critical in controlling convection, most likely through the role of downdrafts. Examination of the boundary layer in the control experiment also indicated that convectively generated cold pools also play a key role in the organization of convection, possibly by their influence on the boundary layer water vapor field. In order to see how the water vapor feedback modifies established convective organization, a further experiment was conducted with an SST gradient imposed, which established a mock Walker cell type circulation, with ascending motion over the warmest SSTs. After 5 days, the SST gradient is reversed to see how the convection would establish itself over the new SST maximum. This highly idealized experiment therefore represents a surrogate for the atmospheric response to SST “hotspots,” that observations have shown to form under the descending branch of large-scale tropical circulations such as the Madden–Jullian oscillation, due to increased incident solar radiation and decreased latent heat fluxes at the surface. It is found that the convection does not spontaneously initiate over the new SST maximum, but instead must propagate toward it. After a further 5 days, much longer than the boundary layer adjustment timescale, the warmest SSTs are still completely free from convection. This is directly due to the dryness of the atmosphere caused by the initial period of subsidence. A further set of experiments examines the robustness of the feedback in cases of imposed vertical wind shear. It is found that strong wind shears prevent the feedback by effectively mixing water vapor. However, the feedback is still very important in cases of weak wind shears.

The role of water vapour in the oxidation of glass in the YSiAlON system

Abstract The effect of water vapour on the oxidation of an oxynitride glass in the system YSiAlON has been studied in the temperature range 1050–1200°C. Three categories of oxidising atmospheres were used; dry oxygen/nitrogen, nitrogen plus water vapour and oxygen plus water vapour. The water vapour pressure was varied within the range 360–2690 Pa. The oxidation kinetics, derived from thermogravimetric data, and the reaction products, examined by XRD and SEM, were analysed in order to understand the reaction mechanisms. The reaction kinetics and product morphology indicate that the rate of oxidation is controlled by the chemical reaction at the internal interface (oxide scale/substrate). The oxidation of the glass is found to be much faster in an atmosphere of nitrogen plus water vapour than in pure oxygen, showing that water vapour is an effective independent oxidant. The oxidation rate for oxygen plus water vapour is greater than the sum of the individual oxidation rates, indicating a synergy. The relationships between the reaction rate and the water vapour pressure and oxidation temperature are determined.

The role of water vapour in the atmosphere. A short overview from a climate modeller's point of view

Water vapour plays a dominant role in the radiative balance and the hydrological cycle. It is a principal element in the thermodynamics of the atmosphere, it transports latent heat, it contributes to absorption and emission in a n umber of bands and it condenses into clouds that reflect and adsorb solar radiation, thus directly affecting the energy balance. In the lower atmosphere, the water vapour concentrations can vary by orders of magnitude from place to place. This variability creates a fundamental problem in climate modelling due to the very high temporal and spatial resolution needed to resolve all processes creating the sharp gradients which are related to the variability. The contribution of water vapour to atmospheric phenomena on different time and space scales for today's and future climates are discussed as well as the importance of water vapour monitoring. The latter is a prerequisite for model validation and an important contribution to the understanding of the behaviour of the atmosphere. It is shown that only the validation of more than one component of the hydrological cycle leads to a better understanding and an improvement of the simulations.

Climatic impact of future supersonic aircraft: role of water vapour and ozone feedback on circulation

Assessment studies of future supersonic aircraft impact on the chemical composition of the atmosphere have generally been made using two- or three-dimensional chemical transport models (CTM). Typical products of these calculation are ozone profile and column changes produced by NOx, H2O and particle emissions from supersonic aircraft (HSCT). These have to be interpreted as pure chemical perturbations, being the atmospheric circulation kept fixed in the models. On the other hand, steady state accumulation of H2O from HSCT can produce significant anomalies in the lower stratospheric water vapour mixing ratio (about 10% at Northern mid-latitudes). Stratospheric H2O and O3 absorb long-wave planetary radiation, so that HSCT driven changes may upset the residual circulation and produce a radiative forcing at the tropopause. A climate-chemistry model is used here to study this effect, using an iterative procedure for the chemistry and radiation modules that are not simultaneously interactive. The major findings are the following: (a) lower stratospheric vertical fluxes of H2O and other atmospheric tracers are significantly affected by water vapour and ozone radiative feedback on the stratospheric circulation. (b) H2O accumulation patterns change significantly in the tropical lower stratosphere, with respect to the case with no radiative feedback on circulation of HSCT additional H2O and perturbed O3 (baseline case). (c) The tropopause radiative forcing of this additional water vapour is greatly reduced with respect to the baseline case.

Water vapor's role in climate revisited at follow‐up Chapman Conference

Water vapor is the most significant atmospheric trace constituent vis‐a‐vis climate, atmospheric chemistry, and hydrology. Without water vapor, the most important atmospheric greenhouse gas, the planet's surface temperature would be well below freezing.Water vapor is the prime source of atmospheric hydroxyl radical (OH), which, as an oxidizing agent for many air pollutants, serves as the atmosphere's detergent. The large latent energy associated with water's phase changes significantly affects the vertical stability of the atmosphere, the structure and evolution of storm systems, and the energy balance of the atmosphere.Yet, despite recent advances, some essential aspects of the distribution and variability of atmospheric water vapor are poorly documented, and key areas of uncertainty in our understanding of the climate system and its potential changes hinge on a more complete understanding of the behavior of water vapor.

Uncertainties linked to water vapor's role in climate change

ADVERTISEMENT RETURN TO ISSUEPREVNewsNEXTUncertainties linked to water vapor's role in climate changeCatherine M. CooneyCite this: Environ. Sci. Technol. 1999, 33, 23, 489APublication Date (Web):June 9, 2011Publication History Published online9 June 2011Published inissue 1 December 1999https://doi.org/10.1021/es993120jRIGHTS & PERMISSIONSArticle Views75Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-AlertsSUBJECTS:Climate change,Water vapor Get e-Alerts

Role of water vapour in the interaction of SnO 2 gas sensors with CO and CH 4

New aspects of the influence of water vapour in the interaction of SnO 2 gas sensors with different reducing gases are evidenced by an original experimental method. This consists in measuring the conductance transients during and after rapid transitions from dry into humid air containing identical concentrations of methane and CO, respectively. The results indicate that while methane and water compete in reacting with one type of oxygen ions on the surface, CO reacts mainly with another type of surface oxygen, almost insensitive to water.

Scanning force microscope observations of particle detachment from substrates: The role of water vapor in tribological debonding

The tip of a scanning force microscope was used to detach nanometer-scale, single crystal NaCl particles from a glass substrate under controlled atmospheres of known humidity. After characterizing a particle at low contact force, a single line scan at high contact force was used to apply stresses to the attached particle. The lateral force during the line scan showed a sharp discontinuity associated with detachment of the particle from the substrate. The peak lateral force during this procedure is a strong function of particle contact area and humidity. As the relative humidity is raised from low values, the strength of the particle-substrate bond decreases dramatically. We interpret these results in terms of detachment by chemically assisted crack growth along the NaCl-glass interface.

Injection-seeded optical parametric oscillator for airborne water vapour DIAL

Any detailed understanding of the role of water vapour in the global climate system requires precise measurements in the atmosphere with high temporal and spatial resolution. A technique that is appropriate to deliver these data is airborne differential absorption lidar (DIAL) applied in the near-infrared spectral range. In order to accurately determine atmospheric water vapour concentrations by means of the DIAL technique tunability and spectral properties of the lidar transmitter are very important. It is demonstrated that the spectral and energy requirements are achieved using optical parametric oscillators (OPOs) that are line-narrowed by the technique of injection seeding with radiation from dye lasers or from laser diodes. When the OPO is unseeded its spectral width is broad enough to suffer only negligible absorption from the absorption lines. Therefore, the unseeded OPO radiation can be used for off-line measurement, which simplifies the DIAL set-up significantly. In addition, the laser diodes were employed to measure line parameters of a selected absorption line in the near-IR. Their precise determination is important in order to make accurate DIAL measurements.

Conjugated polymer surfaces and interfaces

The doping of a conjugated polymer, polyacetylene, to a state of high electrical conductivity in 1977 marked a distinct step in interest in the electronic and transport properties of electrically conducting organic materials. Since 1990, however, undoped semiconducting conjugated polymers have emerged as potentially useful electronic materials in a variety of electronic and optoelectronic applications. In the context of polymer–based electronic device applications, it is of critical importance to understand the nature of the electronic structure of the polymer surface and the polymer–metal interface. It has been shown that, especially for conjugated polymers, photoelectron spectroscopy provides a maximum amount of both chemical and electronic structural information within a single measurement technique. This contribution contains an overview of some details of the early stages of interface formation with metals on the surfaces of conjugated polymers and model molecular solids, as studied using photoelectron spectroscopy. The materials chosen are especially of interest in connection with polymer-based light emitting devices, or LEDs. Specifically, the materials involved include poly( p –phenylenevinylene), or PPV, and a series of substituted PPVs, as well as a diphenylpolyene molecule for PPV, namely, α,ω–diphenyltetradecaheptaene. Some general trends in the behaviour of light–metal atoms on the clean surfaces of conjugated polymers are pointed out. Some consequences, based upon the information obtained in the studies reviewed, are highlighted. Finally, two recent issues, which are studied by the methods used for the metal–on–polymer interfaces studies, are covered: the role of water vapour on the electronic structure of PPV; and the use of phase–separated polymer blends to increase the quantum efficiency of blue light emitting diodes.

Role of water vapor on the wear of MnZn ferrite heads sliding against magnetic tapes

Friction and wear behavior of metallic (mu-metal) and ceramic (MnZn ferrite) head materials sliding against CrO 2 magnetic tape was investigated. Accelerated tape drive tests were conducted in air at various relative humidity levels. Knoop indentation and nano-scratch techniques were used to measure wear. Friction force was measured simultaneously using a strain gage load beam. To investigate static fatigue induced fracture at high humidities, static tests were conducted on MnZn ferrite in an environment chamber. The head specimens were observed optically and with a scanning electron microscope (SEM). The results showed a strong influence of humidity on the tribological behavior of the materials tested. Wear mechanisms of metal and ceramic head materials were found to be different. In the case of mu-metal heads, water was believed to act as a lubricant in the mid-RH (relative humidity) range and to mitigate friction and wear. At high humidities, friction and wear increased dramatically and patches of debris were observed at the head gap. This increase is attributed to formation of menisci bridges at asperity contacts resulting in high adhesive friction and increased abrasive wear due to agglomeration of debris. In the case of MnZn ferrite, friction and wear increased steadily up to 65% RH and then increased catastrophically. The fracture stress of ceramics is known to reduce at high humidities (moisture-assisted fracture or static fatigue). This phenomenon is thought to initiate brittle fracture at the location of surface defects resulting in increased wear. The static tests with MnZn ferrite at high humidity resulted in formation of loose debris, which confirms the static fatigue theory.

Role of Water Vapor in the Partial Oxidation of Propene

The role of water vapor was explored for the partial oxidation of propene over antimony–tin–vanadium oxide (SB/Sn/V oxide) catalyst at 1 atm pressure and 340°C using a microcatalytic packed bed reactor. Steady-state, transient kinetics, TPD, and isotopic transient experiments were performed. Water suppresses the formation of CO2by blocking the most active sites which are responsible for CO2formation but water also enhances the rate of the catalytic oxidation by keeping the catalyst surface at a high oxidation state and preventing the formation of strongly bonded oxygenates. Isotopic transient experiments with labeled O2in the presence of water indicate a strong interaction between water and the catalyst surface. Water exchanges oxygen slowly with the surface of the catalyst.

The role of water vapor and convection during the Central Equatorial Pacific Experiment from observations and model simulations

Field measurements from the Central Equatorial Pacific Experiment (CEPEX) conducted from March 7 to April 5, 1993, are used to study the link between water vapor, convection, and sea surface temperature (SST) in a region of particular importance to global climate. The data are compared with results from a general circulation model (GCM). Three high‐resolution simulations were carried out with slightly different initial conditions using European Centre for Medium Range Weather Forecasts (ECMWF) analyses from March 1, 1993, and forced with the observed SST as lower boundary condition. Radiosondes released between the equator and 5°S show a dry region east of the dateline collocated with a clear sky region observed from the Japanese Geostationary Meteorological Satellite (GMS) in the first 2 weeks of CEPEX, which both vanish in the second 2 weeks. The model is able to reproduce this change in convective activity. Moreover, a comparison of the anomalies of the relative humidity profiles grouped according to SST and infrared brightness temperature (IRBT) indicates that the GCM correctly simulates the observed behavior. The atmosphere is relatively moist when the SST is warm and low IRBTs occur at the same time, that is, when convection takes place, and dryer than on average for the opposite case. In general, however, the model is too dry in the midtroposphere and too wet in the upper troposphere. Very good agreement is found between the simulated and observed ice water content, in particular with respect to its increase with in cloud temperature.

Time-Resolved Studies of the Effects of Water Vapor in Glow Discharge Mass Spectrometry

The role of water vapor as an impurity in glow discharge mass spectrometry is examined by means of pulsed injection of water into an argon discharge. The effect of water vapor on both analyte and intrinsic gas species is determined. Water dissociates in the discharge to produce reactants that can influence analytical results. The extent of this effect is dependent on the reactivity of the cathode sample with water and its dissociation products. Metal oxides are observed during and shortly after the pulsed water injection. Three different cathode materials (titanium, iron, and copper) are studied, with a range of metal oxide bond strengths. Titanium, which has strong gettering action in the glow discharge plasma, exhibits the shortest perturbation time after addition of water vapor. The experiments show the need to remove trace water from glow discharges for best analytical results.

Multielement analysis of geological and related non-conducting materials using spark ablation and a sequential spectrometer

Spark ablation (SA) coupled to a sequential inductively coupled plasma atomic emission spectrometer (ICP-AES) is evaluated for multielement analysis of geological and related non-conducting materials. Long-term stability conditions were established which allowed the determination of major, minor, and trace elements (Si, Ca, Ti, Al, Mg, Fe, Mn, Sr, Ba, Zr, Cr, V and Zn). The influence of the observation height was determined and the role of water vapor in the plasma evaluated. In the latter case the presence of water vapor resulted in a reduction of intensity and magnification of interference effects. The intensity and RSDs increased and improved, respectively, with decreasing particle size from about 3% to 1%. In the case of fine grained sediments, intensities for the involatile elements were relatively higher, possibly due to more efficient atomization and ablation rates. Scanning electron micrographs indicate that while melting still played a role in the ablation process, materials were also removed by mechanical ablation. The accuracy was determined using a wide range of geological standard reference materials. The use of Si I 251.611 nm as the internal standard resulted in a significant improvement in accuracy and compensation of particle size effects. Without Si as the internal standard the mean correlation coefficient was 0.62 ± 0.37; with Si the mean coefficient was 0.97 ± 0.36.

Effect of Oxidizing and Reducing Gas Atmospheres on the Iron-Catalyzed Formation of Filamentous Carbon from Methanol

Iron-catalyzed formation of filamentous carbon from methanol was studied at 500--600 C by exposing iron wire to methanol partial pressures of 1.33--300 kPa in the presence of added partial pressures of water vapor, carbon dioxide, and hydrogen. Filamentous carbon formed from feedstreams containing only methanol, and this process was accompanied by metal dusting corrosion. Addition of a sufficient water vapor partial pressure prevented both carbon deposition and corrosion. The role of water vapor is viewed as being to maintain the iron surface in an oxide state, which is inactive for the catalytic formation of filamentous carbon. Carbon dioxide was found to be a much less effective oxidant than water vapor, while hydrogen did not prevent filamentous carbon formation. Carbon deposition from methanol occurs under conditions where it would not be expected from the equilibrium products of its gas-phase decomposition (CO, CO[sub 2], H[sub 2]O, H[sub 2], and CH[sub 4]).

Selectivity Mechanisms in Low Pressure Selective Epitaxial Silicon Growth

Selective silicon processing at 775 and 850°C using an based chemistry was studied. The selectivity of each experimental condition was quantified by measuring the silicon nuclei density/cm2 on large blanket areas of . The morphology of the selective silicon films was examined for texture and hillocks. The roles of water vapor and atomic hydrogen on the microchemistry of an surface was investigated. Thermodynamic modeling of the effect of different atmospheric leak rates on the water vapor and atomic hydrogen concentrations was carried out with the aid of the SOLGAS program. A new understanding of selectivity is proposed. An surface is an interruption of the bulk continuous random network structure and, as such, has a characteristic density of defect sites. The degree of selectivity observed is determined by the type of species which terminate these defect sites, i.e., by the number of defect sites which are not chemically passivated against the adsorption of silicon species. A universal selective silicon processing regime is predicted and good agreement with a wide range of published selective silicon processes is shown.

Time-dependence of the conductance of SnO 2: Pt: Sb in atmospheres containing oxygen, carbon monoxide and water vapour I. Non-oscillatory behaviour

The time-dependence of the conductance G( t) of SnO 2: Pt: Sb gas sensors after introducing CO in atmospheres containing oxygen and water vapour was investigated. Depending on experimental conditions, different G( t) behaviours were observed over different temperature ranges: either monotonic increases towards steady-state values, or self-sustained oscillations. Part I describes and analyzes the non-oscillatory behaviour, Part II the oscillatory behaviour. A unitary model is proposed, which offers a qualitative explanation for both, by taking into account an assembly of interdependent surface phenomena, including adsorption, desorption, spill-over and chemical reactions of oxygen, carbon monoxide and water. The role of water vapour is emphasized. Though speculative, the model is consistent with a broad range of experimental results and it also allows for some general considerations about utilizing the SnO 2: Pt: Sb material as CO sensor and as oxidation catalyst.

The global energy budget and satellite observations

During the last 30 years, space observations have provided new information about (a) the energy from our Sun, (b) the radiative exchange between our earth-atmosphere system and space, (c) required poleward energy transports by our atmosphere and oceans, (d) seasonal and interannual variations of (b) and (c), (e) the role of clouds in the global energy budget, and (f) preliminary information about the role of water vapor in the global energy budget. After a review of what we now know about these topics, the paper concludes with a discussion of major unknowns including the vertical variation of cloud forcing, the “CO 2 fingerprint,” the “missing petawatt” of energy transport, and the role of non-cloud aerosols and surface features in the global budget.

T. C. Chamberlin and H2O climate feedbacks: A voice from the past

The interaction of positive and negative climate feedbacks has become a central issue for the global change science community. With many expecting surface air temperatures to rise several degrees due to increases in anthropogenic greenhouse gases, the response of H2O (water vapor, liquid, solid) is critical. Will higher temperatures and increased evaporation lead to an enhanced greenhouse effect, especially over the tropical oceans, or will increased cloudiness effectively cap the increase in temperatures? [see Ramanathan and Collins, 1991, 1992; Stephens and Slingo, 1992].“Greenhouse Warming and Cloud Thermostats” is the name of a talk to be given by V. Ramanathan during the Atmospheric Sciences Section luncheon at the AGU 1992 Fall Meeting on December 8. This topic invites comparison between the current H2O feedback hypotheses and work begun almost a century ago by the celebrated geologist Thomas Chrowder Chamberlin (1843–1928) at the University of Chicago [Gillispie, 1970–1980; Schultz, 1976]. Briefly, here are some of Chamberlin's ideas on the roles of water vapor and clouds.