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Air Mass (air + mass)
Selected AbstractsEncapsulating Eu3+ complex doped layers to improve Si-based solar cell efficiencyPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 8 2009Alessia Le Donne Abstract This paper reports the electrical characterization of commercially available crystalline silicon solar cells encapsulated with poly-vinylacetate doped with different Eu3+ organic complexes. The inclusion of these complexes in the encapsulating matrix allows down-shifting of the solar spectrum components below 420,nm toward the maximum quantum efficiency of the solar cells. This effect has been proven under Air Mass 1·5 conditions (simulating terrestrial applications) where an increase of the total power delivered by the encapsulated cells has been observed. Moreover, this enhancement has been obtained using very low percentage by weight of organolanthanide dopants, allowing a reduction in the Watt peak price. At higher concentrations a strong quenching of the energy transfer from the organic antenna to the lanthanide ion has been observed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Aerosol growth and activation in polluted air masses over a tropical metropolis in the Indian sub-continentATMOSPHERIC SCIENCE LETTERS, Issue 2 2009S. Varun Raj Abstract Air pollution can affect cloud formation in more than one way. When the pollutant gases are condensable (e.g. oxides of sulphur), then the process of aerosol activation is eased to a certain extent aiding cloud formation. However, polluted days are often characterised by low updraught speeds which inhibit aerosol growth. In this study, we have critically examined the aerosol activation process in a polluted coastal environment where both effects are present. We have concentrated on the Chennai region (one of the largest cities in the world) of the Indian sub-continent because its pace of industrialisation is increasing rapidly, adding to increasing SO2 pollution over the years. Air masses over Chennai contain a mixture of aerosol particles including NaCl, because of its proximity to the Bay of Bengal, along with ammonium sulphate. We have used observational data along with a detailed microphysical chemical parcel model to study cloud activation effects. We find that over Chennai, often the presence of the condensable pollutant vapour (SO2) more than compensates for the low updraught speeds by lowering the level of maximum super saturation significantly. This latter effect favours the activation of ammonium sulphate as well as NaCl aerosol particles. We have undertaken a systematic analysis to quantify the relative strengths of these two competing effects and find that even with low updraught speeds, oxides of sulphur can perturb the activation domain comprising a mixture of aerosol particles to such an extent that aerosol particles in polluted environments often grow efficiently. This effect is non-intuitive in the sense that one associates smaller cloud droplet sizes with polluted air masses. This is the first microphysical modelling study for the Indian sub-continent where National Environmental Engineering Research Institute (NEERI) observations have been applied to cloud microphysical processes. Copyright © 2009 Royal Meteorological Society [source] Dye-Sensitized Solar Cells Based on a Novel Fluorescent Dye with a Pyridine Ring and a Pyridinium Dye with the Pyridinium Ring Forming Strong Interactions with Nanocrystalline TiO2 FilmsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2010Yousuke Ooyama Abstract As new-type donor,acceptor ,-conjugated dyes capable of forming a strong interaction between the electron-acceptor moiety of the sensitizers and a TiO2 surface, fluorescent dye OH11 and pyridinum dye OH12 with a pyridine and pyridinium ring as the electron-accepting group, respectively, have been designed and synthesized as photosensitizers for use in dye-sensitized solar cells (DSSCs). The fluorescent dye OH11 exhibits an absorption band at around 410 nm and a fluorescence band at around 530 nm. On the other hand, the pyridinum dye OH12 shows an absorption maximum at around 560 nm, assigned to a strong intramolecular charge-transfer excitation from the dibutylamino group to the pyridinium ring. The short-circuit photocurrent densities of the DSSCs prepared by using OH11 and OH12 are 4.33 and 1.74mA cm,2, and the solar energy-to-electricity conversion yields are 1.33 and 0.51,%, respectively, under simulated solar light [AM (air mass) 1.5, 100 mW,cm,2]. The open-circuit photovoltage for OH11 (525 mV) is higher than that of OH12 (444 mV). The effects of the configuration of the dyes on the TiO2 surface and of their chemical structures on the photovoltaic performances are discussed on the basis of semi-empirical molecular orbital calculations (AM1 and INDO/S), spectral analyses and cyclic voltammetry. [source] Charge Generation and Photovoltaic Operation of Solid-State Dye-Sensitized Solar Cells Incorporating a High Extinction Coefficient Indolene-Based SensitizerADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Henry J. Snaith Abstract An investigation of the function of an indolene-based organic dye, termed D149, incorporated in to solid-state dye-sensitized solar cells using 2,2,,7,7,-tetrakis(N,N -di- p -methoxypheny-amine)-9,9,-spirobifluorene (spiro-OMeTAD) as the hole transport material is reported. Solar cell performance characteristics are unprecedented under low light levels, with the solar cells delivering up to 70% incident photon-to-current efficiency (IPCE) and over 6% power conversion efficiency, as measured under simulated air mass (AM) 1.5 sun light at 1 and 10,mW cm,2. However, a considerable nonlinearity in the photocurrent as intensities approach "full sun" conditions is observed and the devices deliver up to 4.2% power conversion efficiency under simulated sun light of 100,mW cm,2. The influence of dye-loading upon solar cell operation is investigated and the thin films are probed via photoinduced absorption (PIA) spectroscopy, time-correlated single-photon counting (TCSPC), and photoluminescence quantum efficiency (PLQE) measurements in order to deduce the cause for the non ideal solar cell performance. The data suggest that electron transfer from the photoexcited sensitizer into the TiO2 is only between 10 to 50% efficient and that ionization of the photo excited dye via hole transfer directly to spiro-OMeTAD dominates the charge generation process. A persistent dye bleaching signal is also observed, and assigned to a remarkably high density of electrons "trapped" within the dye phase, equivalent to 1.8,×,1017,cm,3 under full sun illumination. it is believed that this localized space charge build-up upon the sensitizer is responsible for the non-linearity of photocurrent with intensity and nonoptimum solar cell performance under full sun conditions. [source] Compact Inverse-Opal Electrode Using Non-Aggregated TiO2 Nanoparticles for Dye-Sensitized Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Eun Sik Kwak Abstract Compact inverse-opal structures are constructed using non-aggregated TiO2 nanoparticles in a three-dimensional colloidal array template as the photoelectrode of a dye-sensitized solar cell. Organic-layer-coated titania nanoparticles show an enhanced infiltration and a compact packing within the 3D array. Subsequent thermal decomposition to remove the organic template followed by impregnation with N-719 dye results in excellent inverse-opal photoelectrodes with a photo-conversion efficiency as high as 3.47% under air mass 1.5 illumination. This colloidal-template approach using non-aggregated nanoparticles provides a simple and versatile way to produce efficient inverse-opal structures with the ability to control parameters such as cavity diameter and film thickness. [source] Polymer Solar Cells Based on a Low-Bandgap Fluorene Copolymer and a Fullerene Derivative with Photocurrent Extended to 850,nm,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2005F. Zhang Abstract Polymer solar cells have been fabricated from a recently synthesized low band-gap alternating polyfluorene copolymer, APFO-Green2, combined with [6,6]-phenyl-C61 -butyric acid methyl ester (PCBM) from organic solutions. External quantum efficiencies (EQEs) of the solar cells show an onset at 850,nm and a peak of >,10,% located at 650,nm, which corresponds to the extended absorption spectrum of the polymer. Photocurrent of 3.0,mA,cm,2, photovoltage of 0.78,V, and power conversion efficiency of 0.9,% have been achieved in solar cells based on this new low-bandgap polymer under the illumination of air mass,1.5 (AM,1.5) (1000,W,m,2) from a solar simulator. [source] ,Distribution of oxygen-18 and deuterium in river waters across the United StatesHYDROLOGICAL PROCESSES, Issue 7 2001Carol Kendall Abstract Reconstruction of continental palaeoclimate and palaeohydrology is currently hampered by limited information about isotopic patterns in the modern hydrologic cycle. To remedy this situation and to provide baseline data for other isotope hydrology studies, more than 4800, depth- and width-integrated, stream samples from 391 selected sites within the USGS National Stream Quality Accounting Network (NASQAN) and Hydrologic Benchmark Network (HBN) were analysed for ,18O and ,2H (http://water.usgs.gov/pubs/ofr/ofr00-160/pdf/ofr00-160.pdf). Each site was sampled bimonthly or quarterly for 2·5 to 3 years between 1984 and 1987. The ability of this dataset to serve as a proxy for the isotopic composition of modern precipitation in the USA is supported by the excellent agreement between the river dataset and the isotopic compositions of adjacent precipitation monitoring sites, the strong spatial coherence of the distributions of ,18O and ,2H, the good correlations of the isotopic compositions with climatic parameters, and the good agreement between the ,national' meteoric water line (MWL) generated from unweighted analyses of samples from the 48 contiguous states of ,2H=8·11,18O+8·99 (r2=0·98) and the unweighted global MWL of sites from the Global Network for Isotopes in Precipitation (GNIP) of the International Atomic Energy Agency and the World Meteorological Organization (WMO) of ,2H=8·17,18O+10·35. The national MWL is composed of water samples that arise in diverse local conditions where the local meteoric water lines (LMWLs) usually have much lower slopes. Adjacent sites often have similar LMWLs, allowing the datasets to be combined into regional MWLs. The slopes of regional MWLs probably reflect the humidity of the local air mass, which imparts a distinctive evaporative isotopic signature to rainfall and hence to stream samples. Deuterium excess values range from 6 to 15, in the eastern half of the USA, along the northwest coast and on the Colorado Plateau. In the rest of the USA, these values range from ,2 to 6,, with strong spatial correlations with regional aridity. The river samples have successfully integrated the spatial variability in the meteorological cycle and provide the best available dataset on the spatial distributions of ,18O and ,2H values of meteoric waters in the USA. Published in 2001 by John Wiley & Sons, Ltd. [source] Empirical models of UV total radiation and cloud effect studyINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2010David Mateos Villán Abstract Several empirical models of hourly ultraviolet total radiation (UVT) have been proposed in this study. Measurements of UVT radiation, 290,385 nm, have been recorded at ground level from February 2001 to June 2008 in Valladolid, Spain (latitude 41°40,N, longitude 4°50,W and 840 m a.s.l.). The empirical models have emerged due to the lack of some radiometric variables in measuring stations. Hence, good forecasts of them can be obtained from usual measures in these stations. Therefore, some advantages of the empirical models are that they allow the estimation of past missing data in the database and the forecast of future ultraviolet solar availability. In this study, reported models in the bibliography have been assessed and recalibrated. New expressions have been proposed that allow obtaining hourly values of ultraviolet radiation from global radiation measures and parameters as clearness index and relative optical air mass. The accuracy of these models has been assessed through the following statistical indices: mean bias, mean-absolute bias and root-mean-square errors whose values are close to zero, below 7% and below 10%, respectively. Two new clear sky models have been used to evaluate two new parameters: ultraviolet and global cloud modification factors, which can help to understand the role of the clouds on solar radiation. The ultraviolet cloud modification factor depends on cloudiness in such a way that its value under overcast skies is half of the cloudless skies one. Exponential and potential fits are the best relationships between both cloud factors. Finally, these parameters have been used to build new UV empirical models which show low values of the statistical indices mentioned above. Copyright © 2009 Royal Meteorological Society [source] Reconstruction of winter climate variations during the 19th century in JapanINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2008Junpei Hirano Abstract An attempt was made to reconstruct winter climate conditions in Japan for the period 1810/1811 to 1858/1859 on the basis of daily weather records documented in old diaries. Daily weather maps for each winter were drawn using 19th century weather records collected by our research group. Maps were divided into five types by classifying daily snowfall and rainfall distributions and the occurrence frequencies of each weather pattern for the period 1810/1811 to 1858/1859 were analysed. It was found that the occurrence frequencies of winter monsoon weather patterns were high from the late 1820s to the early 1840s. This period almost coincided with a summer cold period in the 19th century. The result implies that strengthening of a cold air mass around Japan occurred in the late 1820s, not only in summer but also in winter. The frequencies of the typical winter monsoon patterns correspond with the freezing dates of Lake Suwa, which have been used as an indicator of winter coldness in previous studies. On the basis of the frequencies of the winter monsoon weather patterns, mean January temperatures for western Japan were estimated. In the time series of estimated temperatures, a cooling period from the late 1820s to the early 1830s was revealed. Copyright © 2007 Royal Meteorological Society [source] A synoptic-scale climate analysis of anomalous snow water equivalent over the Northern Great Plains of the USAINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2003Andrew Grundstein Abstract The Northern Great Plains is a region where variations in seasonal snow accumulation can have a dramatic affect on regional hydrology. In the past, one of the problems in studying snow hydrology has been obtaining information of sufficiently high temporal and spatial resolution on the water content of the snowpack. This project used a hybrid climatology of snow water equivalent (SWE) that incorporated both model and observed data. This climatology has a long time series (49 years) and a high spatial resolution (1° × 1°) sufficient for use in a climatic analysis. The long and complete time series of SWE generated in this project allowed for a comprehensive analysis of the meteorological and climate forcing mechanisms that influence the amount of SWE. The five largest (high SWE) and five smallest SWE (low SWE) accumulations on 1 March were examined. High SWE years received greater snowfall and fewer accumulated melting degree days throughout the season. Large SWE accumulations at the end of the season, however, were not always associated with deep snowpacks early in the season. Also, all five high SWE years had above normal snowfall in February. Years with small or no SWE had below-average snowfall but greater than average accumulated melting degree days. A synoptic analysis examined both atmospheric circulation and air mass frequencies to assess impacts on ablation and snowfall. A distinct difference in the frequency of different air mass during high SWE versus low SWE years was evident. High SWE years were characterized by substantially greater intrusions of the coldest and driest air mass type (dry polar). Low SWE years, in contrast, had a greater frequency of more moderate air masses (dry moderate and moist moderate). In years with above average SWE, negative departures in November,December,January,February composite 700 hPa field were evident across the continental USA and indicate a greater frequency of troughing across the study area. Low SWE years were characterized by a ridging pattern that reduced the likelihood of precipitation and may have aided in the intrusion of more moderate air masses. Copyright © 2003 Royal Meteorological Society [source] A 4,% Efficient Dye-Sensitized Solar Cell Fabricated from Cathodically Electrosynthesized Composite Titania Films,ADVANCED MATERIALS, Issue 21 2003J. Yamamoto Cathodically electrosynthesized TiO2 films (see Figure) containing occluded Degussa P-25 titania particles can yield short-circuit current densities as high as 10.5 mA,cm,2, an open-circuit photovoltage of 690 mV, a fill factor of 57.3,%, and a photovoltaic efficiency of 4.13,% under simulated air mass 1.5 (100 mW,cm,2) sunlight in a dye-sensitized solar cell device. [source] Synthesis and characterization of cyclopentadithiophene-based low bandgap copolymers containing electron-deficient benzoselenadiazole derivatives for photovoltaic devicesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2010In Hwan Jung Abstract We have synthesized two cyclopentadithiophene (CDT)-based low bandgap copolymers, poly[(4,4-bis(2-ethyl-hexyl)-4H -cyclopenta[2,1- b:3,4- b,]dithiophene-2,6-diyl)- alt -(benzo[c][1,2,5]selenadiazole-4,7-diyl)] (PCBSe) and poly[(4,4-bis(2-ethyl-hexyl)-4H -cyclopenta[2,1- b:3,4- b,]dithiophene-2,6-diyl)- alt -(4,7-dithiophen-2-yl-benzo[c][1,2,5]selenadiazole-5,5,-diyl)] (PCT2BSe), for use in photovoltaic applications. Through the internal charge transfer interaction between the electron-donating CDT unit and the electron-accepting benzoselenadiazole, we realized exceedingly low bandgap polymers with bandgaps of 1.37,1.46 eV. The UV,vis absorption maxima of PCT2BSe were subjected to larger hypsochromic shifts than those of PCBSe, because of the distorted electron donor,acceptor (D,A) structures of the PCT2BSe backbone. These results were supported by the calculations of the D,A complex using the ab initio Hartree-Fock method with a split-valence 6-31G* basis set. However, PCT2BSe exhibited a better molar absorption coefficient in the visible region, which can lead to more efficient absorption of sunlight. As a result, PCT2BSe blended with [6,6]-phenyl-C61 -butyric acid methyl ester (PC61BM) exhibited a better photovoltaic performance than PCBSe because of the larger spectral overlap integral with respect to the solar spectrum. Furthermore, when the polymers were blended with PC71BM, PCT2BSe showed the best performance, with an open circuit voltage of 0.55 V, a short-circuit current of 6.63 mA/cm2, and a power conversion efficiency of 1.34% under air mass 1.5 global illumination conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1423,1432, 2010 [source] Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2010Hatim O. Sharif Sharif, Hatim O., Almoutaz A. Hassan, Sazzad Bin-Shafique, Hongjie Xie, and Jon Zeitler, 2010. Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas. Journal of the American Water Resources Association (JAWRA) 1-11. DOI: 10.1111/j.1752-1688.2010.00459.x Abstract:, Many of the storms creating the greatest rainfall depths in Texas, measured over durations ranging from one minute to 48 hours, have occurred in the Texas Hill Country area. The upstream portion of the Guadalupe River Basin, located in the Texas Hill Country, is susceptible to flooding and rapid runoff due to thin soils, exposed bedrock, and sparse vegetation, in addition to the Balcones Escarpment uplift contributing to precipitation enhancement. In November 2004, a moist air mass from the Gulf of Mexico combined with moist air from the Pacific Ocean resulted in the wettest November in Texas since 1895. Although the peak discharges were not the highest on record, the U.S. Geological Survey (USGS) stream gauge on the Guadalupe River at Gonzales, Texas reported a daily mean discharge of 2,304 m3/s on November 23, 2004 (average discharge is 53 m3/s). In this paper, we examine the meteorological conditions that led to this event and apply a two-dimensional, physically based, distributed-parameter hydrologic model to simulate the response of a portion of the basin during this event. The study results clearly demonstrate the ability of physically based, distributed-parameter simulations, driven by operational radar rainfall products, to adequately model the cumulative effect of two rainfall events and route inflows from three upstream watersheds without the need for significant calibration. [source] Spectral response and energy output of concentrator multijunction solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2009Geoffrey S. Kinsey Abstract The spectral response of concentrator multijunction solar cells has been measured over a temperature range of 25,75°C. These data are combined with reference spectra representing the AM1·5 standard as well as annual spectral irradiance at representative geographical locations. The results suggest that higher performance in the field may be obtained if multijunction cells are designed for an effective air mass higher than AM1·5. Copyright © 2008 John Wiley & Sons, Ltd. [source] Eulerian backtracking of atmospheric tracers.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 615 2006I: Adjoint derivation, parametrization of subgrid-scale transport Abstract The problem of identification of sources of atmospheric tracers is most classically addressed through either Lagrangian backtracking or adjoint integration. On the basis of physical considerations, the retro-transport equation, which is at the basis of Lagrangian backtracking, can be derived in a Eulerian framework as well. Because of a fundamental time symmetry of fluid transport, Lagrangian or Eulerian backtracking can be used for inverting measurements of the concentration of an atmospheric tracer. The retro-transport equation turns out to be the adjoint of the direct transport equation, with respect to the scalar product defined by integration with respect to air mass. In the present paper, the exact equivalence between the physically-derived retro-transport and adjoint equations is proved. The transformation from the direct to the retro-transport equation requires only simple transformations. The sign of terms describing explicit advection is changed. Terms describing linear sources or sinks of tracers are kept unchanged. Terms representing diffusion by unresolved time-symmetric motions of the transporting air are also unchanged. This is rigorously shown for turbulent eddy-diffusion or mixing length theory. The case of subgrid-scale vertical transport by non-time-symmetric motions of air is studied using the example of the Tiedtke mass-flux scheme for cumulus convection. The retro-transport equation is then obtained by simply inverting the roles of updraughts and downdraughts, as well as of entrainment and detrainment. Conservation of mass of the transporting air is critical for all those properties to hold. Copyright © 2006 Royal Meteorological Society [source] Turbulent length-scales in the marine atmospheric mixed layerTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 566 2000P. Durand Abstract The spectra of turbulence signals can be characterized by several independent scales. To provide a parametrization of these spectra requires knowledge of the relationships between these scales. This paper focuses on three independent scales: the integral scale (which is influenced by the low-frequency behaviour of the spectra); the wavelength of the spectrum peak (which characterizes the energy-containing domain); and the dissipation scale (which is relevant for the inertial subrange). First, we present definitions of these various scales, and the possible relationships between them. The profiles of the scales were computed from airborne measurements made in the atmospheric mixed layer over the open ocean, in a region where horizontal homogeneity can be assumed, at least for several tens of km. Furthermore, the diurnal cycle being very weak in this oceanic area, and aircraft moving at high speed through the air mass, stationarity is well verified on the runs, and Taylor's hypothesis may be used. The meteorological conditions correspond to a slightly unstable mixed layer, with weak to moderate winds. In a first part, we analyse the integral scales of various parameters on a 180-km run and demonstrate that these parameters cannot be computed with any soundness from horizontal-wind, temperature and moisture signals, because of the continuous increase in the spectral energy when moving towards lower frequencies. For the same reasons, the spectrum peak and the corresponding wavelength cannot be determined for these parameters. The computation of the integral and energy-containing scale is therefore restricted to the vertical velocity, and to the various covariances. The turbulence field is characterized by a stretching of the eddies along the mean wind direction which results in greater integral and energy-containing scales (but not in greater dissipation scales) when computed for along-wind runs than for the cross-wind runs. The profiles of the various scales increase with altitude and are well defined in the lower half of the mixed layer, but are much more scattered in the upper half. This behaviour is related to the source of turbulence, which lies in the surface buoyancy flux in the lower half of the mixed layer, and comes from higher altitude sources in the upper half. The integral scales have values comparable with those found in previous work, except for parameters related to temperature fluctuations, which have lower values. The ratio of the energy-containing scale to the integral scale, which determines the sharpness of the ,spectral knee', varies considerably from one parameter to another, and sometimes with altitude. This demonstrates that a single unique parametrization cannot be defined for turbulence spectra. As a consequence, the eddy-exchange coefficients, which depend on a characteristic length-scale, should vary from one parameter to another. This would then have to be taken into account in model parametrization based on mixing length-scales. [source] Field optimization and CCD data simulation for the antarctic International Concordia Explorer Telescope (ICE-T)ASTRONOMISCHE NACHRICHTEN, Issue 4 2009D. Fügner Abstract We performed extensive data simulations for the planned ultra-wide-field, high-precision photometric telescope ICE-T (International Concordia Explorer Telescope). ICE-T consists of two 60 cm-aperture Schmidt telescopes with a joint field of view simultaneously in two photometric bandpasses. Two CCD cameras, each with a single 10.3k × 10.3k thinned back-illuminated device, would image a sky field of 65 square degrees. Given a location of the telescope at Dome C on the East Antarctic Plateau, we searched for the star fields that best exploit the technical capabilities of the instrument and the site. We considered the effects of diurnal air mass and refraction variations, solar and lunar interference, interstellar absorption, overexposing of bright stars and ghosts, crowding by background stars, and the ratio of dwarf to giant stars in the field. Using NOMAD, SSA, Tycho-2 and 2MASS-based stellar positions and BVIJH magnitudes for these fields, we simulated the effects of the telescope's point-spread-function, the integration, and the co-addition times. Simulations of transit light curves are presented for the selected star fields and convolved with the expected instrumental characteristics. For the brightest stars, we showed that ICE-T should be capable of detecting a 2 REarth Super Earth around a G2 solar-type star, as well as an Earth around an M0-star , if these targets were as abundant as hot Jupiters. Simultaneously, the telescope would monitor the host star's surface activity in an astrophysically interpretable manner (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Layer-by-Layer Deposition of Rhenium-Containing Hyperbranched Polymers and Fabrication of Photovoltaic CellsCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2007Chui Wan Tse Abstract Multilayer thin films were prepared by the layer-by-layer (LBL) deposition method using a rhenium-containing hyperbranched polymer and poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (PTEBS). The radii of gyration of the hyperbranched polymer in solutions with different salt concentrations were measured by laser light scattering. A significant decrease in molecular size was observed when sodium trifluoromethanesulfonate was used as the electrolyte. The conditions of preparing the multilayer thin films by LBL deposition were studied. The growth of the multilayer films was monitored by absorption spectroscopy and spectroscopic ellipsometry, and the surface morphologies of the resulting films were studied by atomic force microscopy. When the pH of a PTEBS solution was kept at 6 and in the presence of salt, polymer films with maximum thickness were obtained. The multilayer films were also fabricated into photovoltaic cells and their photocurrent responses were measured upon irradiation with simulated air mass (AM) 1.5 solar light. The open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of the devices were 1.2 V, 27.1 ,,A,cm,2, 0.19, and 6.1×10,3,%, respectively. The high open-circuit voltage was attributed to the difference in the HOMO level of the PTEBS donor and the LUMO level of the hyperbranched polymer acceptor. A plot of incident photon-to-electron conversion efficiency versus wavelength also suggests that the PTEBS/hyperbranched polymer junction is involved in the photosensitization process, in which a maximum was observed at approximately 420 nm. The relatively high capacitance, determined from the measured photocurrent rise and decay profiles, can be attributed to the presence of large counter anions in the polymer film. [source] Hydrologic response of the Greenland ice sheet: the role of oceanographic warmingHYDROLOGICAL PROCESSES, Issue 1 2009E. Hanna Abstract The response of the Greenland ice sheet to ongoing climate change remains an area of great uncertainty, with most previous studies having concentrated on the contribution of the atmosphere to the ice mass-balance signature. Here we systematically assess for the first time the influence of oceanographic changes on the ice sheet. The first part of this assessment involves a statistical analysis and interpretation of the relative changes and variations in sea-surface temperatures (SSTs) and air temperatures around Greenland for the period 1870,2007. This analysis is based on HadISST1 and Reynolds OI.v2 SST analyses, in situ SST and deeper ocean temperature series, surface-air-temperature records for key points located around the Greenland coast, and examination of atmospheric pressure and geopotential height from NCEP/NCAR reanalysis. Second, we carried out a novel sensitivity experiment in which SSTs were perturbed as input to a regional climate model, and document the resulting effects on simulated Greenland climate and surface mass balance. We conclude that sea-surface/ocean temperature forcing is not sufficient to strongly influence precipitation/snow accumulation and melt/runoff of the ice sheet. Additional evidence from meteorological reanalysis suggests that high Greenland melt anomalies of summer 2007 are likely to have been primarily forced by anomalous advection of warm air masses over the ice sheet and to have therefore had a more remote atmospheric origin. However, there is a striking correspondence between ocean warming and dramatic accelerations and retreats of key Greenland outlet glaciers in both southeast and southwest Greenland during the late 1990s and early 2000s. Copyright © 2008 John Wiley & Sons, Ltd. [source] Development of a spatial synoptic classification scheme for western EuropeINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2007Donna Bower Abstract This paper presents a new spatial air-mass climatology for western Europe (WE) based upon the analysis of daily data for 48 climate stations for the period 1974,2000. Referred to as the spatial synoptic classification for western Europe (SSCWE), the new air-mass climatology not only facilitates the examination of both spatial and temporal climate variations but also provides, for the first time, a physically based synoptic classification for a wide variety of applications at the western European scale. The SSCWE is based on the philosophy of the spatial synoptic classification (SSC), which was first introduced to the synoptic climatological community in the mid-1990s and later refined as the SSC2 for application across North America. As for the SSC2, establishing the physical characteristics for six generic air masses is the basis of the SSCWE. In this paper, the procedures for identifying air-mass characteristics are described and an analysis of the spatial and temporal variation of the six generic air-mass types across western Europe is presented. Copyright © 2007 Royal Meteorological Society [source] Pressure gradient force, atmospheric circulation and climate in western Europe (1899,2002)INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2007Pierre P. Kastendeuch Abstract One mission of synoptic climatology is to quantify the link between atmospheric circulation and surface environment. The pressure gradient force (PGF) is used as a multiple index to summarize the monthly atmospheric circulation for a site in western Europe (5°E and 50°N). The study of the temporal evolution of the PGF components (direction, magnitude, X and Y components) was carried out for the period 1899,2002. The results reflect the variability in atmospheric circulation and reveal some trends. The magnitude of the PGF is particularly affected by several successive periods where the strength of the atmospheric flow was lower (negative trend) or higher (positive trend) than normal. During the last decades of the twentieth century the atmospheric flow appears stronger than before (positive trend), except in summer. As the direction of the PGF can be related to the trajectory of the flow via the Buys,Ballot law, its anomalies are directly related to anomalies in the advection of air masses. No definite trend can be detected for this variable. However, it seems that the northerly flow becomes rare in winter. The relevance of the PGF is also examined with regard to the evolution of monthly temperatures and precipitations via some series of multiple regressions. The best results are obtained for the precipitations, with an explained variance lying between 47 and 73% (respectively in May and February). For temperatures, the explained variance oscillates between 34 and 73% (in September and January). The fact that the meridional and zonal components of the PGF, and the absolute pressure at the site are explicitly taken into account, ensures a good quantification of the atmospheric circulation ,anomalies', that are largely responsible for the annual, seasonal or monthly singularities of temperature and precipitation over western Europe. Copyright © 2007 Royal Meteorological Society [source] Measurement of climate complexity using sample entropyINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2006Li Shuangcheng Abstract A climate system is a complex nonlinear system. Estimation of the complexity is of great interest in climatic forecast and prediction. In this paper, we propose the use of sample entropy (SampEn), an entropy-based algorithm, to measure the complexity of daily temperature series. Estimations of SampEn were calculated for 50 meteorological stations in the mountains of Southwest China, particularly in Yunnan Province. On the basis of these data, stations were grouped in climatically homogenous regions (climate provinces), and the spatial pattern of SampEn for each climate province was investigated. The SampEn value of spatial distribution of climate provinces reflects the varying degree of influence of the monsoonal air masses. High SampEn values occur in interactive regions of different air masses, owing to large regional differences in weather processes, while the southwest region is under the influence of the Southwest Monsoon leading to a homogenous climatic environment, low SampEn values and small spatial variations of SampEn. The results suggest that SampEn is an alternative nonlinear approach for analyzing and predicting complexity of climatic time series. Copyright © 2006 Royal Meteorological Society [source] A synoptic-scale climate analysis of anomalous snow water equivalent over the Northern Great Plains of the USAINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2003Andrew Grundstein Abstract The Northern Great Plains is a region where variations in seasonal snow accumulation can have a dramatic affect on regional hydrology. In the past, one of the problems in studying snow hydrology has been obtaining information of sufficiently high temporal and spatial resolution on the water content of the snowpack. This project used a hybrid climatology of snow water equivalent (SWE) that incorporated both model and observed data. This climatology has a long time series (49 years) and a high spatial resolution (1° × 1°) sufficient for use in a climatic analysis. The long and complete time series of SWE generated in this project allowed for a comprehensive analysis of the meteorological and climate forcing mechanisms that influence the amount of SWE. The five largest (high SWE) and five smallest SWE (low SWE) accumulations on 1 March were examined. High SWE years received greater snowfall and fewer accumulated melting degree days throughout the season. Large SWE accumulations at the end of the season, however, were not always associated with deep snowpacks early in the season. Also, all five high SWE years had above normal snowfall in February. Years with small or no SWE had below-average snowfall but greater than average accumulated melting degree days. A synoptic analysis examined both atmospheric circulation and air mass frequencies to assess impacts on ablation and snowfall. A distinct difference in the frequency of different air mass during high SWE versus low SWE years was evident. High SWE years were characterized by substantially greater intrusions of the coldest and driest air mass type (dry polar). Low SWE years, in contrast, had a greater frequency of more moderate air masses (dry moderate and moist moderate). In years with above average SWE, negative departures in November,December,January,February composite 700 hPa field were evident across the continental USA and indicate a greater frequency of troughing across the study area. Low SWE years were characterized by a ridging pattern that reduced the likelihood of precipitation and may have aided in the intrusion of more moderate air masses. Copyright © 2003 Royal Meteorological Society [source] Snow cover in western Poland and macro-scale circulation conditionsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2002Ewa Bednorz Abstract The aim of the study was to find out the connection between the nature of winters in the western part of Poland (excluding the Sudety mountains) and the fluctuation in the atmospheric circulation in the North Atlantic region determined by the North Atlantic Oscillation (NAO) index. An attempt was made to establish the correlation between the NAO index and specific meteorological parameters in Pozna,. The strongest positive correlation was obtained for the mean winter temperature (December,March) and strong negative correlation was found for the number of days with snow cover. Winter precipitation in Pozna, was least associated with the NAO. The correlation coefficient was small and not significant. In the next stage of the study, the area of western Poland was examined; however, only one parameter, i.e. the number of days with snow cover, was taken into consideration. At each of 29 stations distributed in the study area the number of days with snow cover was proved to be strongly negatively correlated with the NAO index. Finally, the frequency of air flow directions was taken into consideration and their association with the NAO was examined. A strong negative correlation was obtained for the frequency of northeasterly and easterly air flow directions and a strong positive correlation was calculated for the frequency of westerly and northwesterly airflow directions. Such findings are consistent with the westerly flow of air masses during the positive phase and with the northerly and easterly flows during the negative phase. The results lead to the conclusion that the positive phase of the NAO causes mild and less snowy winters, whereas the negative phase increases the probability of severe and snowy winters in western Poland. Copyright © 2002 Royal Meteorological Society. [source] The influence of large-scale atmospheric circulation on the surface energy balance of the King George Island ice capINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2001Matthias Braun Abstract During the austral summer 1997,1998 three automatic weather stations were operated at different altitudes on the sub-Antarctic ice cap of King George Island (South Shetland Islands). Snowmelt was derived from energy balance computations. Turbulent heat fluxes were calculated from meteorological measurements using the bulk aerodynamic approach, with net radiation being measured directly. Modelled ablation rates were compared with readings at ablation stakes and continuously measured snow height at a reference site. Snow depletion and daily snowmelt cycles could be well reproduced by the model. Generally, radiation balance provided the major energy input for snowmelt at all altitudes, whereas sensible heat flux was a second heat source only in lower elevations. The average latent heat flux was negligible over the entire measuring period. A strong altitudinal gradient of available energy for snowmelt was observed. Sensible heat flux as well as latent heat flux decreased with altitude. The measurements showed a strong dependence of surface energy fluxes and ablation rates on large-scale atmospheric conditions. Synoptic weather situations were analysed based on AVH RR infrared quicklook composite images and surface pressure charts. Maximum melt rates of up to 20 mm per day were recorded during a northwesterly advection event with meridional air mass transport. During this northwesterly advection, the contribution of turbulent heat fluxes to the energy available for snowmelt exceeded that of the radiation balance. For easterly and southerly flows, continentally toned, cold dry air masses dominated surface energy balance terms and did not significantly contribute to ablation. The link between synoptic situations and ablation is especially valuable, as observed climatic changes along the Antarctic Peninsula are attributed to changes in the atmospheric circulation. Therefore, the combination of energy balance calculations and the analysis of synoptic-scale weather patterns could improve the prediction of ablation rates for climate change scenarios. Copyright © 2001 Royal Meteorological Society [source] Use of METEOSAT water-vapour images for the diagnosis of a vigorous stratospheric intrusion over the central MediterraneanMETEOROLOGICAL APPLICATIONS, Issue 3 2000K Lagouvardos The diagnosis of a vigorous dry intrusion over the central Mediterranean is performed using water-vapour images from METEOSAT. This dry intrusion was located on the rear side of a cold front (propagating from Italy to Greece) and played an important role in the onset of thunderstorms over the western Greek coasts. A combination of satellite imagery and potential vorticity analyses showed that the dry air originated in the lower-stratospheric and higher-tropospheric layers. The interaction of the dry air with the moist air masses within the warm conveyor belt ahead of the cold front (overrun of warm air by low equivalent potential temperature air) produced a potentially unstable region over the area of reported thunderstorms. Copyright © 2000 Royal Meteorological Society [source] Föhn as a response to changing upstream and downstream air massesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 635 2008Georg J. Mayr Abstract Observations of föhn from the field phase of the Mesoscale Alpine Programme (MAP) are used to study how differences between the air masses upstream and downstream of the central Alpine crest determine whether the flow can descend to the lee as either shallow föhn, when it passes through passes in the mountains, or deep föhn, when it overflows the Alpine crest. First, the föhn case of 30 October 1999 is examined using ECMWF analyses and radiosonde data at various upstream and downstream locations. Additional measurements from aircraft, dropsondes, an instrumented car and automatic weather stations are then used for a detailed study of the föhn flow across the Brenner Pass. Advection of cold air around the eastern edges of the Alps and warm air around the western edge of the Alps ahead of a synoptic ridge set up a reservoir of colder air on the south side of the Alps and a reservoir of warmer air to the north. The depth to where the air was colder on the southern side was sufficient for a shallow föhn to flow through the pass. After the passage of the ridge axis, synoptic cold air advection provided another source of colder air, this time from the southwest, growing deeper with time and having a synoptically imposed cross-barrier flow component. The maximum depth to where the air upstream was colder than downstream extended just above the peaks of the highest mountains. An analysis of the detailed measurements across the Brenner Pass showed that this depth was also the top of the layer that descended and accelerated down the lee slopes of the Wipp Valley. Upstream, air above the föhn layer had an even stronger cross-barrier component yet did not descend because it did not have lower potential temperatures than the downstream side at that level. Deep föhn never developed. An examination of other well-documented MAP föhn cases confirmed the conclusion from the 30 October event that shallow and deep föhns , at least for the central Alps , are mostly a response to differences in air masses between the upstream and downstream side. A cross-barrier component of the flow was only a modification but in itself not sufficient to cause the flow to both descend and accelerate down the lee slope, unless potential temperatures on the upstream side were lower in this layer than on the downstream side. Copyright © 2008 Royal Meteorological Society [source] Aerosol growth and activation in polluted air masses over a tropical metropolis in the Indian sub-continentATMOSPHERIC SCIENCE LETTERS, Issue 2 2009S. Varun Raj Abstract Air pollution can affect cloud formation in more than one way. When the pollutant gases are condensable (e.g. oxides of sulphur), then the process of aerosol activation is eased to a certain extent aiding cloud formation. However, polluted days are often characterised by low updraught speeds which inhibit aerosol growth. In this study, we have critically examined the aerosol activation process in a polluted coastal environment where both effects are present. We have concentrated on the Chennai region (one of the largest cities in the world) of the Indian sub-continent because its pace of industrialisation is increasing rapidly, adding to increasing SO2 pollution over the years. Air masses over Chennai contain a mixture of aerosol particles including NaCl, because of its proximity to the Bay of Bengal, along with ammonium sulphate. We have used observational data along with a detailed microphysical chemical parcel model to study cloud activation effects. We find that over Chennai, often the presence of the condensable pollutant vapour (SO2) more than compensates for the low updraught speeds by lowering the level of maximum super saturation significantly. This latter effect favours the activation of ammonium sulphate as well as NaCl aerosol particles. We have undertaken a systematic analysis to quantify the relative strengths of these two competing effects and find that even with low updraught speeds, oxides of sulphur can perturb the activation domain comprising a mixture of aerosol particles to such an extent that aerosol particles in polluted environments often grow efficiently. This effect is non-intuitive in the sense that one associates smaller cloud droplet sizes with polluted air masses. This is the first microphysical modelling study for the Indian sub-continent where National Environmental Engineering Research Institute (NEERI) observations have been applied to cloud microphysical processes. 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