ALBERT

Description: [1]  Different solutions have been proposed to solve the ‘faint young Sun problem’, defined by the fact that the Earth was not fully frozen during the Archean despite the fainter Sun. Most previous studies were performed with simple 1D radiative convective models and did not account well for the clouds and ice-albedo feedback or the atmospheric and oceanic transport of energy. We apply a Global Climate Model (GCM) to test the different solutions to the faint young Sun problem. We explore the effect of greenhouse gases (CO 2 and CH 4 ), atmospheric pressure, cloud droplet size, land distribution and Earth's rotation rate. We show that, neglecting organic haze, 100 mbars of CO 2 with 2 mbars of CH 4 at 3.8 Ga and 10 mbars of CO 2 with 2 mbars of CH 4 at 2.5 Ga allow a temperate climate (mean surface temperature between 10 °C and 20 °C). Such amounts of greenhouse gases remain consistent with the geological data. Removing continents produces a warming lower than +4 °C. The effect of rotation rate is even more limited. Larger droplets (radii of 17  µm versus 12  µm ) and a doubling of the atmospheric pressure produce a similar warming of around +7 °C. In our model, ice-free waterbelts can be maintained up to 25° N/S with less than 1 mbar of CO 2 and no methane. An interesting cloud feedback appears above cold oceans, stopping the glaciation. Such a resistance against full glaciation tends to strongly mitigate the faint young Sun problem.

Description: [1]  The Cross-track Infrared Sounder (CrIS) is the high spectral resolution spectroradiometer on the Suomi National Polar-Orbiting Partnership (NPP) satellite, providing operational observations of top-of-atmosphere thermal infrared radiance spectra for weather and climate applications. This paper describes the CrIS radiometric calibration uncertainty based on pre-launch and on-orbit efforts to estimate calibration parameter uncertainties, and provides example results of recent post-launch validation efforts to assess the predicted uncertainty. Pre-launch Radiometric Uncertainty (RU) estimates computed for the laboratory test environment are less than ~0.2 K 3-sigma for blackbody scene temperatures above 250 K, with primary uncertainty contributions from the calibration blackbody temperature, calibration blackbody reflected radiance terms and detector nonlinearity. Variability of the pre-launch RU among the longwave band detectors and midwave band detectors is due to different levels of detector nonlinearity. A methodology for on-orbit adjustment of nonlinearity correction parameters to reduce the overall contribution to RU and to reduce FOV-to-FOV variability is described. The resulting on-orbit RU estimates for Earth view spectra are less than 0.2 K 3-sigma in the midwave and shortwave bands, and less than 0.3 K 3-sigma in the longwave band. Post-launch validation efforts to assess the radiometric calibration of CrIS are underway; validation results to date indicate that the on-orbit RU estimates are representative. CrIS radiance products are expected to reach “Validated” status in early 2014.

Description: [1]  An extended Tracking Radar Echo by Correlation (TREC) technique, called T-TREC technique, has been developed recently to retrieve horizontal circulations within tropical cyclones (TCs) from single Doppler radar reflectivity ( Z ) and radial velocity ( V r , when available) data. This study explores, for the first time, the assimilation of T-TREC-retrieved winds for a landfalling typhoon, Meranti (2010), into a convection-resolving model, the WRF (Weather Research and Forecasting). The T-TREC winds or the original V r data from a single coastal Doppler radar are assimilated at the single time using the WRF 3DVAR, at 8, 6, 4 and 2 hours before the landfall of typhoon Meranti. In general, assimilating T-TREC winds results in better structure and intensity analysis of Meranti than directly assimilating V r data. The subsequent forecasts for the track, intensity, structure and precipitation are also better, although the differences becomes smaller as the V r data coverage improves when the typhoon gets closer to the radar. The ability of the T-TREC retrieval in capturing more accurate and complete vortex circulations in the inner-core region of TC is believed to be the primary reason for its superior performance over direct assimilation of V r data; for the latter, the data coverage is much smaller when the TC is far away and the cross-beam wind component is difficult to analyze accurately with 3DVAR method.

Description: [1]  Given its large population, vigorous and water-intensive agricultural industry, and important ecological resources, the western United States presents a valuable case study for examining potential near-term changes in regional hydroclimate. Using a high-resolution, hierarchical, five-member ensemble modeling experiment that includes a global climate model (CCSM), a regional climate model (RegCM), and a hydrological model (VIC), we find that increases in greenhouse forcing over the next three decades result in an acceleration of decreases in spring snowpack and a transition to a substantially more liquid-dominated water resources regime. These hydroclimatic changes are associated with increases in cold-season days above freezing and decreases in the cold-season snow-to-precipitation ratio. The changes in the temperature and precipitation regime in turn result in shifts toward earlier snowmelt, baseflow, and runoff dates throughout the region, as well as reduced annual and warm-season snowmelt and runoff. The simulated hydrologic response is dominated by changes in temperature, with the ensemble members exhibiting varying trends in cold-season precipitation over the next three decades, but consistent negative trends in cold-season freeze days, cold-season snow-to-precipitation ratio, and April 1 st snow water equivalent. Given the observed impacts of recent trends in snowpack and snowmelt runoff, the projected acceleration of hydroclimatic change in the western U.S. has important implications for the availability of water for agriculture, hydropower and human consumption, as well as for the risk of wildfire, forest die-off, and loss of riparian habitat.

Description: [1]  The consequences of different Quasi-Biennial Oscillation (QBO) nudging widths on stratospheric dynamics and chemistry are analyzed by comparing two model simulations with NCAR's WACCM model where the width of the QBO is varied between 22° and 8.5°N and S. The sensitivity to the nudging width is strongest in Northern Hemisphere (NH) winter where the Holton-Tan effect in the polar stratosphere, i.e., stronger zonal mean winds during QBO west phases, is enhanced for the wider compared to the narrower nudging case. The differences between QBO west and east conditions for the two model experiments can be explained with differences in wave propagation, wave-mean flow interaction and the residual circulation. In the wider nudging case a divergence anomaly in the mid-latitude upper stratosphere/lower mesosphere occurs together with an equatorward anomaly of the residual circulation. This seems to result in a strengthening of the meridional temperature gradient and hence a significant strengthening of the polar night jet (PNJ). In the narrower nudging case these circulation changes are weaker and not statistically significant, consistent with a weaker and less significant impact on the PNJ. Chemical tracers like ozone, water vapour and methane react accordingly. From a comparison of westerly minus easterly phase composite differences in the model to reanalysis and satellite data we conclude that the standard WACCM configuration (QBO22) generates more realistic QBO effects in stratospheric dynamics and chemistry during NH winter. Our study also confirms the importance of the secondary mean meridional circulation associated with the QBO for the Holton-Tan effect.

Description: [1]  The microphysical properties of ice fog were measured at two sites during a small IOP in January and February of 2012 in the Interior Alaska. The NCAR Video Ice Particle Sampler (VIPS) probe and formvar (polyvinyl formal) coated microscope slides were used to sample airborne ice particles at two polluted sites in the Fairbanks region. Both sites were significantly influenced by anthropogenic emission and additional water vapor from nearby open water power plant cooling ponds. Measurements show that ice fog particles were generally droxtal-shaped (faceted, quasi-spherical) for sub-10 µm particles, while plate shaped crystals were the most frequently observed particles between 10 and 50 µm. A visibility cutoff of 3 kilometers was used to separate ice fog events from other observations which were significantly influenced by larger (50–150 µm) diamond dust particles. [2]  The purpose of this study is to more realistically characterize ice fog microphysical properties in order to facilitate better model predictions of the onset of ice fog in polluted environments. Parameterizations for mass and projected area are developed and used to estimate particle terminal velocity. Dimensional characteristics are based on particle geometry and indicated that ice fog particles have significantly lower density values than water droplets as well as reduced cross-sectional areas, the net result being that terminal velocities are estimated to be less than half the value of those calculated for water droplets. Particle size distributions are characterized using gamma functions and have a shape factor (μ) of between −0.5 and −1.0 for polluted ice fog conditions.

Description: [1]  In our recent paper [6], the sensitivity of infrasound to the upper atmosphere is investigated using impulsive signals from the Tungurahua volcano in Ecuador. We reported on the coherent variability of thermospheric travel times, with periods equal to those of the tidal harmonics. Moreover, it was shown that the error in predicted thermospheric travel time is in accord with typical uncertainties in the upper atmospheric wind speed models. Given the observed response of the infrasound celerities to upper atmospheric tidal variability, it was suggested that infrasound observations may be used to reduce uncertainty in the knowledge of the atmospheric specifications in the upper atmosphere. In this paper, we discuss the estimation of upper atmospheric wind model updates from the infrasound data described in the aforementioned paper. The parameterization of the model space by empirical orthogonal functions is described; it is found that the wind model in the upper mesosphere and lower thermosphere can be described by a four-parameter model. Due to the small dimensionality of the model space, a grid search method can be used to solve the inverse problem. A Bayesian method is used to assess the uncertainty in the inverse solution given the a priori uncertainty in the data and model spaces and the non-linearity of the inverse problem at hand. We believe that this is the first study in which such methods are applied to real infrasound data, allowing for a rigorous analysis of this inverse problem. It is found that the complexity of the a posteriori model distribution increases for a larger dimensional model space and larger uncertainties in the data. A case study is presented in which the non-linear propagation from source to receiver is simulated using an updated wind model and non-linear ray theory. As non-linear propagation effects further constrain the propagation path, this is a way to check the physical self-consistency of the travel time inversion approach. We obtain excellent agreement between the simulated and observed waveforms.

Description: [1]  Thirty years of balloon-borne measurements over Boulder (40 ∘ N, 105 ∘ W) are used to investigate the water vapor trend in the tropopause region. This analysis extends previously published trends, usually focusing on altitudes greater than 16km, to lower altitudes. Two new concepts are applied: 1) Trends are presented in a thermal tropopause (TP) relative coordinate system from − 2km below to 10km above the TP. 2) Sonde profiles are selected according to TP height. Tropical (TP z  〉 14km), extratropical (TP z  〈 12km), and transitional air mass types (12km 〈 TP z  〈 14km), reveal three different water vapor reservoirs. The analysis based on these concepts reduces the dynamically–induced water vapor variability at the TP and principally favors refined water vapor trend studies in the upper troposphere and lower stratosphere. Nonetheless, this study showshow uncertain trends are at altitudes −2 to + 4km around the TP. This uncertainty in turn has an influence on the uncertainty and interpretation of water vapor radiative effects at the TP, which are locally estimated for the 30 year period to be of uncertain sign. The much discussed decrease in water vapor at the beginning of 2001 is not detectable between −2 to 2km around the TP. On lower stratospheric isentropes, the water vapor change at the beginning of 2001 is more intense for extratropical than for tropical air mass types. This suggests a possible link with changing dynamics above the jet stream such as changes in the shallow branch of the Brewer–Dobson circulation.

Description: [1]  Retrievals of sulfur dioxide (SO 2 ) from space-based spectrometers are in a relatively early stage of development. Factors such as interference between ozone and SO 2 in the retrieval algorithms often lead to errors in the retrieved values. Measurements from the Ozone Monitoring Instrument (OMI), SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY), and Global Ozone Monitoring Experiment −2 (GOME-2) satellite sensors, averaged over a period of several years, were used to identify locations with elevated SO 2 values and estimate their emission levels. About 30 such locations, detectable by all three sensors and linked to volcanic and anthropogenic sources, were found, after applying low- and high- spatial frequency filtration designed to reduce noise and bias and to enhance weak signals to SO 2 data from each instrument. Quantitatively, the mean amount of SO 2 in the vicinity of the sources, estimated from the three instruments is in general agreement. However, it's better spatial resolution makes it possible for OMI to detect smaller sources and with additional more detail as compared to the other two instruments. Over some regions of China, SCIAMACHY and GOME-2 data show mean SO 2 values that are almost 1.5 times higher than those from OMI but the suggested spatial filtration technique largely reconciles these differences.

Description: [1]  Dust is an important indicator of climate change. In paleo-climate research, sediments bearing signals of dust deposition offer a rich archive for climate-change history. However, the dust-climate link is very complex due to the various direct and indirect feedbacks in the Earth system. In this study, we examine two issues: (1) given the recent global warming, what are the dust variations, both globally and in key dust regions? and, (2) what are the climate drivers behind the variations? Using synoptic data for the period 1974-2012, we analyzed the global trend of dust frequency and visibility-derived dust concentrations and their characteristics in key dust regions, including North Africa, the Middle East, Southwest Asia, Northeast Asia, South America and Australia. We also examined the likely climate drivers for dust variations in the different regions by computing the correlations between the time series of dust and of major climate indices – the MEI (Multivariate El Niño/Southern Oscillation Index), NAO (North Atlantic Oscillation) and AMO (Atlantic Multi-decadal Oscillation). It was found that over the period 1984–2012, the global-mean (excluding North America and Europe) near-surface dust concentration decreased at 1.2% yr -1 . This decrease is mainly due to reduced dust activities in North Africa, accompanied by reduced activities in Northeast Asia, South America, and South Africa. A significant negative correlation between Saharan dust and AMO was detected and it seems reasonable to suggest that under present climate, the global dust trend is determined by the climate systems governing the Atlantic and North African regimes.

Description: [1]  We show measurements of middle atmospheric water vapor as measured by two ground-based Water Vapor Millimeter-wave Spectrometer (WVMS) instruments, and three satellite-based instruments: the Aura Microwave Limb Sounder (MLS), the Atmospheric Chemistry Experiment (ACE), and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). We also show CH 4 measurements from the MIPAS and ACE instruments and use these to help interpret the H 2 O variations. We find that interannual changes in stratospheric H 2 O of ~0.5 ppmv, observed from Table Mountain, California at 26 km and 40 km from 2010–2012, are caused primarily by dynamically driven changes in CH 4 during this period. The interannual variations in H 2 O observed over Mauna Loa, Hawaii, are shown to be quite similar to the average variations observed over 50 o S-50 o N in the lower mesosphere, thus we conclude that a single ground-based microwave instrument can provide a useful estimate of interannual globally averaged lower mesospheric H 2 O variations, even when such changes are as small as ~0.2-0.3 ppmv. We find that the increase of ~0.2-0.3 ppmv in H 2 O in the lower mesosphere since 2006 is qualitatively consistent with an increase in tropical tropopause temperature since ~2001.

Description: [1]  An adjoint version of the HARC neighborhood air quality model with 200 m horizontal resolution, coupled offline to the QUIC-URB fast response urban wind model, was used to perform 4D variational (4Dvar) inverse modeling of an industrial release of formaldehyde (HCHO) and sulfur dioxide (SO 2 ) in Texas City, Texas during the 2009 Study of Houston Atmospheric Radical Precursors (SHARP). The source attribution was based on real-time observations by the Aerodyne mobile laboratory and a high resolution 3D digital model of the emitting petrochemical complex and surrounding urban canopy. The inverse model estimate of total primary HCHO emitted during the incident agrees very closely with independent remote sensing estimates based on both Imaging and Multi-Axis Differential Optical Absorption Spectroscopy (DOAS). Whereas a previous analysis of Imaging DOAS data attributed the HCHO release to a Fluidized Catalytic Cracking Unit (FCCU), the HARC model attributed most of the HCHO and SO 2 release to a neighboring hydrotreater unit that desulfurizes the feed to the FCCU. Other facilities implicated by the source attribution were ultraformer and distillate desulfurization units and two flares. The inferred HCHO-to-SO 2 molar emission ratio was similar to that computed directly from ambient air measurements during the release. The model-estimated HCHO-to-CO molar emission ratio for combustion units with significant inferred emissions ranged from 2% to somewhat less than 7%, consistent with other observationally-based estimates obtained during SHARP. A model sensitivity study demonstrated that the inclusion of urban morphology has a significant, but not critical, impact on the source attribution.

Description: [1]  Carbonaceous aerosols have the potential to impact climate directly through absorption of incoming solar radiation and indirectly by affecting cloud and precipitation. To quantify this impact, recent modeling studies have made great efforts to simulate both the spatial and temporal distribution of carbonaceous aerosol's optical properties and associated radiative forcing. This study makes the first observationally constrained assessment of the direct radiative forcing of carbonaceous aerosols over California. By exploiting multiple observations (including ground sites and satellites), we constructed the distribution of aerosol optical depths and aerosol absorption optical depths (AAOD) over California for a ten-year period (2000–2010). We partitioned the total solar absorption into individual contributions from elemental carbon (EC), organic carbon (OC), and dust aerosols, using a newly developed scheme. Our results show that AAOD due to carbonaceous aerosols (EC and OC) at 440 nm was 50%–200% larger than natural dust, with EC contributing the bulk (70%–90%). Observationally constrained EC absorption agrees reasonably well with estimates from global and regional chemical transport models, but the models underestimate the OC AAOD by at least 50%. We estimated that the top of the atmosphere (TOA) forcing from carbonaceous aerosols was 0.7 W/m 2 and the TOA forcing due to OC was close to zero. The atmospheric heating of carbonaceous aerosol was 2.2–2.9 W/m 2 , of which EC contributed about 80–90%. We estimated the atmospheric heating of OC at 0.1–0.4 W/m 2 , larger than model simulations. EC reduction over the last two decades may have caused a surface brightening of 1.5–3.5 W/m 2 .

Description: [1]  The tropospheric seasonal cycles of N 2 O, CFC-11 (CCl 3 F), and CFC-12 (CCl 2 F 2 ) are influenced by atmospheric dynamics. The interannually varying summertime minima in mole fractions of these trace gases have been attributed to interannual variations in mixing of stratospheric air (depleted in CFCs and N 2 O) with tropospheric air with a few months lag. The amount of wave activity that drives the stratospheric circulation and influences the winter stratospheric jet and subsequent mass transport across the tropopause appears to be the primary cause of this interannual variability. We relate the observed seasonal minima of species at three Northern Hemisphere sites (Mace Head, Ireland; Trinidad Head, USA and Barrow, Alaska) with the behavior of the winter stratospheric jet. As a result, a good correlation is obtained between zonal winds in winter at 10 hPa, 58 o N-68 o N and the de-trended seasonal minima in the stratosphere-influenced tracers. For these three tracers, individual Pearson correlation coefficients (r) between 0.51 and 0.71 were found, with overall correlations of between 0.67 and 0.77 when ‘composite species’ were considered. Finally we note that the long-term observations of CFCs and N 2 O in the troposphere provide an independent monitoring method complementary to satellite data. Furthermore they could provide a useful observational measure of the strength of stratosphere-troposphere exchange and thus, could be used to monitor any long-term trend in the Brewer-Dobson Circulation which is predicted by climate models to increase over the coming decades.

Description: Homogenous liquid precursor for ZrC – SiC was prepared by blending of Zr ( OC 4 H 9 ) 4 and Poly[(methylsilylene)acetylene]. This precursor could be cured at 250°C and converted into binary ZrC – SiC composite ceramics upon heat treatment at 1700°C. The pyrolysis mechanism and optimal molar ratio of the precursor were investigated by XRD. The morphology and elements analyses were conducted by SEM and corresponding energy-dispersive spectrometer. The evolution of carbon during ceramization was studied by Raman spectroscopy. The results showed that the precursor samples heat treated at 900°C consisted of t- ZrO 2 (main phase) and m- ZrO 2 (minor phase). The higher temperature induced phase transformation and t- ZrO 2 converted into m- ZrO 2 . Further heating led to the formation of ZrC and SiC due to the carbothermal reduction, and the ceramic sample changed from compact to porous due to the generation of carbon oxides. With the increasing molar ratios of C / Zr , the residual oxides in 1700°C ceramic samples converted into ZrC and almost pure ZrC – SiC composite ceramics could be obtained in ZS-3 sample. The Zr , Si , and C elements were well distributed in the obtained ceramics powders and particles with a distribution of 100 ~ 300 nm consisted of well-crystallized ZrC and SiC phases.

Description: [1]  Monthly temperature and precipitation data from 41 global climate models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5) were compared to observations for the 20 th century, with a focus on the United States Pacific Northwest (PNW) and surrounding region. A suite of statistics, or metrics, was calculated, that included correlation and variance of mean seasonal spatial patterns, amplitude of seasonal cycle, diurnal temperature range, annual- to decadal- scale variance, long-term persistence, and regional teleconnections to ENSO. Performance, or credibility, was assessed based on the GCMs’ abilities to reproduce the observed metrics. GCMs were ranked in their credibility using two methods. The first simply treated all metrics equally. The second method considered two properties of the metrics: 1) redundancy of information (dependence) among metrics, and 2) confidence in the reliability of an individual metric for accurately ranking models. Confidence was related to how robust the estimate of the metric was to ensemble size, given that for most of the models only a small number of ensemble members (i.e. realizations of the 20 th century) were available. A cursory comparison with 24 CMIP3 models revealed few differences between the two generations of models with respect to the statistics analyzed.

Description: [1]  In this paper, the effects of temperature, pressure, winds, moisture and molecular content on the propagation of blast waves at high altitudes are investigated. These cause refractions and attenuations which modify the recorded ground overpressures from the ideal predictions. By coupling these effects together, the non-ideal corrections to the overpressures are estimated by applying approximations which are dependent on the angle of propagation of the blast wave.

Description: [1]  The most severe thunderstorms, producing extreme precipitation, occur over subtropical and midlatitude regions. Atmospheric conditions conducive to organized, intense thunderstorms commonly involve the coupling of a low-level jet (LLJ) with a synoptic short wave. The midlatitude synoptic activity is frequently modulated by the circumglobal teleconnection (CGT) – in which meridional gradients of the jet stream act as a guide for short Rossby waves. Previous research has linked extreme precipitation events with either the CGT or the LLJ, but has not linked the two circulation features together. In this study, a circulation-based index was developed by combining (a) the degree of the CGT and LLJ coupling, (b) the extent to which this CGT-LLJ coupling connects to regional precipitation, and (c) the spatial correspondence with the CGT (short-wave) trending pattern over the most recent 32 years (1979-2010). Four modern-era global reanalyses, in conjunction with four gridded precipitation datasets, were utilized to minimize spurious trends. The results are suggestive of a link between several recent extreme precipitation events and the CGT/LLJ trends, including those leading to the 2008 Midwest flood in U.S., the 2011 tornado outbreaks in southeastern U.S., the 2010 Queensland flood in northeastern Australia and the 2010 Pakistan flood. Moreover, an analysis of three CMIP5 models from the historical experiments points to the role of greenhouse gases in forming the CGT trends during the warm season.

Description: [1]  Mineral aerosols are produced during the erosion of soils by wind and are a common component of the total atmospheric particle load (dust) in arid and semi-arid regions. The size of these particles can vary widely from clay particles less than 2 µm to larger silt and sand-sized particles that can exceed 50 µm in diameter. In this study, we present two continuous records of total suspended particle (TSP) concentrations at sites in Mesa Verde and Canyonlands National Parks in Colorado and Utah, USA, respectively, and compare those values to measurements of fine and coarse particle concentrations made from nearby IMPROVE-network samplers. Average annual concentrations of TSP at Mesa Verde were 90 µg m -3 in 2011 and at Canyonlands were 171 µg m -3 in 2009, 113 µg m -3 in 2010, and 134 µg m -3 in 2011. In comparison, annual concentrations of fine (diameter of 2.5 µm and below) and coarse (2.5-10 µm diameter) particles at these sites were well below 10 µg m -3 in all years. The high concentrations of TSP appear to be the result of regional dust storms that result in elevated concentrations of very coarse particles greater than 10 µm in diameter. These conditions regularly occur from early spring until early fall with two-week mean TSP periodically in excess of 200 µg m -3 at Canyonlands. Measurement of particle sizes embedded on filters indicates that the median particle size of all particles varies between approximately 10 µm in winter and 40 µm during the spring dust-storm season. These persistently elevated concentrations of large particles indicate that regional dust emission as dust storms and events are important determinants of air quality in this region.

Description: [1]  Nitrogen oxide radicals (NO x ) produced by lightning are natural precursors for the production of the dominant tropospheric oxidants, OH and ozone. Observations of the interannual variability (IAV) of tropical ozone and of global mean OH (from the methylchloroform proxy) offer a window for understanding the sensitivity of ozone and OH to environmental factors. We present the results of simulations for 1998-2006 using the GEOS-Chem chemical transport model with IAV in tropical lightning constrained by satellite observations from the Lightning Imaging Sensor (LIS). We find that this imposed IAV in lightning NO x improves the ability of the model to reproduce observed IAV in tropical ozone and OH. Lightning is far more important than biomass burning in driving the IAV of tropical ozone, even though the IAV of NO x emissions from fires is greater than that from lightning. Our results indicate that the IAV in tropospheric OH is highly sensitive to lightning relative to other emissions, and suggest that lightning contributes an important fraction of the observed IAV in OH inferred from the methylchloroform proxy. Lightning affects OH through the HO 2 +NO reaction, an effect compounded by positive feedback from the resulting increase in ozone production and in CO loss. We can account in the model for the observed increase in OH in 1998-2004 and for its IAV, but the model fails to explain the OH decrease in 2004-2006. We find that stratospheric ozone plays little role in driving IAV in OH during 1998-2006, in contrast to previous studies that examined earlier periods.

Description: [1]  The gravity wave field in the lower stratosphere (between 15 km and 22 km altitude) above Mount Pleasant Airport (51°49’S, 58°26’W), on the Falkland Islands is studied using over 2100 high-resolution radiosonde soundings from 2002-2010. The seasonal variation in vertical direction of propagation shows a small decrease in numbers of upward propagating waves that is related to critical level filtering, however there is a very large increase in numbers of downward propagating waves between July and September; this is attributed to the proximity of the edge of the polar vortex. There is a seasonal variation in gravity wave energy density, with a large peak during the austral autumn equinox; this is markedly different to results in the literature both from Rothera, on the Antarctic Peninsula, and stations on the main Antarctic continent. This seasonal pattern has been shown to be linked to variations in the sources of upward propagating gravity waves. The seasonal variation in gravity wave characteristics above Mount Pleasant Airport seen in our results suggest that the gravity wave field in this region is determined by a combination of different gravity wave sources located above and below the lower stratosphere.

Description: [1]  Observed evaporative demand has decreased worldwide during the past several decades. This trend is also noted on the Tibetan Plateau, a region that is particularly sensitive to climate change. However, patterns and trends of evapotranspiration and their relationship to drought stress on the Tibetan Plateau are complex and poorly understood. Here, we analyze spatiotemporal changes in evapotranspiration and effective moisture (defined as the ratio of actual evapotranspiration ( ET a ) to reference crop evapotranspiration ( ET o )) based on the modified Lund–Potsdam–Jena Dynamic Global Vegetation Model (LPJ). Climate data from 80 meteorological stations on the Tibetan Plateau were compiled for the period 1981–2010 and future climate projections were generated by a regional climate model through the 21 st century. The results show regional trends towards decreasing ET o and statistically significant increases in ET a ( p  〈 0.05) and effective moisture during the period 1981–2010 ( p  〈 0.001). A transition from significant negative to positive ET o occurred in 1997. Additionally, a pronounced increase in effective moisture occurred during the period 1981–1997 because of significant decreased ET o before 1997. In the future, regional ET o and ET a are projected to increase, thus reducing drought stress, because of generally increased effective moisture. Future regional differences are most pronounced in terms of effective moisture, which shows notable increases in the northwestern plateau and decreases in the southeastern plateau. Moreover, the reduced magnitude of effective moisture is likely to intensify in the long term, due mainly to increased evaporative demand.

Description: [1]  Changes in the hydrological cycle being caused by human-induced global warming are triggering variations in observed spatiotemporal distributions of precipitation and temperature extremes, and hence in droughts and floods across China. Evaluation of future climate extremes based on General Circulation Models (GCMs) outputs will be of great importance in scientific management of water resources and agricultural activities. In this study, 5 precipitation extreme and 5 temperature extreme indices are defined. This study analyzes daily precipitation and temperature data for 1960-2005 from 529 stations in China and outputs of GCMs from the Coupled Model Intercomparison Project Phase 3 (CMIP3) and Phase 5 (CMIP5). Downscaling methods, based on QQ-plot and transfer functions, are used to downscale GCMs outputs to the site scale. Performances of GCMs in simulating climate extremes were evaluated using the Taylor diagram. Results showed that: (1) the multimodel CMIP5 ensemble performs the best in simulating observed extreme conditions; (2) precipitation processes are intensifying with increased frequency and intensity across entire China. The southwest China, however, is dominated by lengthening maximum consecutive dry days and also more heavy precipitation extremes; (3) warming processes continue with increasing warm nights, decreasing frost days and lengthening heat waves during the 21 st century; (4) changes in precipitation and temperature extremes exhibit larger changing magnitudes under RCP85 scenario; (5) for the evolution of changes in extremes, in most cases, the spatial pattern keeps the same, even though changing rates vary. In some cases, area with specific changing properties extends or shrinks gradually. The directions of trends may alter during the evolution; and (5) changes under RCP85 become more and more pronounced as time elapses. Under the peak-and-decline RCP26, changes in some cases don't decrease correspondingly during 2070-2099 even though the radiative forcing during 2070-2099 is less than during 2040-2069. The increase of radiative forcing triggers considerable regional variations in consecutive dry days, but causes only slight changes in the areal average in China. The results of this study imply higher flood risk across entire China but intensifying droughts in south China in the 21 st century, and also more heat-related losses in east coasts of China.

Description: [1]  Marine cloud brightening through sea spray injection has been proposed as a method of temporarily alleviating some of the impacts of anthropogenic climate change, as part of a set of technologies called geoengineering. We outline here a proposal for three coordinated climate modeling experiments to test aspects of sea spray geoengineering, to be conducted under the auspices of the Geoengineering Model Intercomparison Project (GeoMIP). The first, highly idealized, experiment ( G1ocean-albedo ) involves a uniform increase in ocean albedo to offset an instantaneous quadrupling of CO 2 concentrations from preindustrial levels. Results from a single climate model show an increased land-sea temperature contrast, Arctic warming, and large shifts in annual mean precipitation patterns. The second experiment ( G4cdnc ) involves increasing cloud droplet number concentration in all low-level marine clouds to offset some of the radiative forcing of an RCP4.5 scenario. This experiment will test the robustness of models in simulating geographically heterogeneous radiative flux changes and their effects on climate. The third experiment ( G4sea-salt ) involves injection of sea spray aerosols into the marine boundary layer between 30°S and 30°N to offset 2 W m -2 of the effective radiative forcing of an RCP4.5 scenario. A single model study shows that the induced effective radiative forcing is largely confined to the latitudes in which injection occurs. In this single model simulation, the forcing due to aerosol–radiation interactions is stronger than the forcing due to aerosol–cloud interactions.

Description: Ce -doped BaTiO 3 -based ceramics were prepared and studied to satisfy ultra-broad temperature stability (from −55°C to 300°C, capacitance variation rate based on C 20°C is within ±15%). The sample with 0.6 mol% CeO 2 succeeds to achieve this performance with a remarkably high ceiling temperature of 300°C. Meanwhile, the sample has good dielectric and electrical properties at room temperature (ε r  = 1667, tanδ = 1.478%, ρ V  = 5.9 × 10 12  Ω·cm). Ce ion can substitute for Ti ion as Ce 4+ or Ba ion as Ce 3+ . The substitution decreases the spontaneous polarization of BaTiO 3 , and then weakens the ferroelectricity of BaTiO 3 . As a result, the temperature stability of samples is improved obviously. Besides, CeO 2 addition promotes the formation of exaggerated grains, which are consisting of Ba 6 Ti 17 O 40 .

Description: This study aims to optimize quantitative X-ray diffraction (XRD) mineralogical analysis of the minority phases in clinker. The proposed method consists of applying Rietveld quantitative refinement to the XRD patterns for both clinker and the insoluble residue remaining after it is attacked with methanol and salicylic acid (Takashima method). The method was tested with industrial clinker and the same material after modifying its mineralogy by refiring at 1500°C followed by slow cooling. The findings showed that the C 4 AF / C 3 A ratios for quickly and gradually cooled clinker were much higher when the clinker diffractograms were refined with the Rietveld procedure than when the proposed method was used. The proportion of C 3 A found with the proposed method was ≈2.8-fold higher than when Rietveld only was applied to the diffractograms for clinkers. Taken together, the refinement data for the two materials (clinker and Takashima residua) revealed that Rietveld quantitative XRD applied to clinker underestimates the low C 3 A content. These findings are supported by postsulfate attack durability studies conducted on cements prepared with the two clinkers.

Description: The effect of increasing poling fields on the properties of (1− x )BZT– x BCT compositions across the morphotropic phase boundary (MPB) is studied using large signal polarization and strain, small signal permittivity and piezoelectric coefficient, and XRD measurements. Successive poling causes charge carrier migration inducing an internal bias field, which becomes large with respect to the coercive field resulting in biased ferroelectric and ferroelastic switching. Improvements in piezoelectric coefficient of 9% are significantly smaller in the tetragonal 60BCT composition compared with the improvement of approximately 50% in the rhombohedral 40BCT and MPB 50BCT compositions. While the properties continue to change with increased poling fields, the remnant ferroelastic domain texture parallel to the field direction, as observed from XRD, stays approximately constant. The improvement in overall domain alignment leading to largely enhanced intrinsic piezoelectricity originates from the alignment of 180° domains and possibly non-180° domains in grains with orientations inclined to the electric field. As a result, poling is most effective in BZT–BCT materials that have low coercive fields, show low distortions and possess more polarization orientations, such as compositions in the rhombohedral phase field or near the MPB.

Description: The defect chemistry-modulated dielectric properties of dense yttria-doped zirconia ceramics prepared by conventional sintering (at 1350°C–1500°C) and electric field-assisted flash sintering (55 V/cm at 900°C) were studied by impedance spectroscopy. While the bulk dielectric properties from both sets of samples showed only small and insignificant changes in conductivity and permittivity, respectively, a huge increase of these properties was measured for the grain boundaries in the flash sintered specimens. A close analysis of these results suggests that flash sintering reduced grain-boundary thickness (by about 30%), while increasing the concentration of oxygen vacancies near these interfaces (by about 49%). The underlying mechanism proposed is electric field-assisted generation and accommodation of defects in the space-charge layers adjacent to the grain surface. The changes in measured permittivity are attributed to the boundary thickness effect on capacitance, while conductivity involved variations in its defect density-dependent intrinsic value, accounting for changes also observed in grain-boundary relaxation frequencies. Therefore, in terms of modifications to the specific dielectric properties of these materials, the overall consequence of flash sintering was to considerably lower the semi-blocking character of the grain boundaries.

Description: This article presents a detailed study on the nanoscaled interface between microelongated gold particles (GP) and biphase leucite/feldspar glass-ceramic matrix. The glass-ceramic composite with a nonuniform GP distribution was processed through hot-pressing under vacuum using a commercial dental ceramic furnace for glass-ceramic dental crown manufacturing. Heat treatments at 900°C, 1100°C, and 1300°C were conducted, and microstructural features along the interface were used to verify the chemical reactions between GP and glass-ceramic matrix. It was observed that the amorphous glass-ceramic matrix had nanoscaled biphase structures, and the distributed nanoscaled amorphous leucite phase was attracted to GP during hot-pressing, and was more reactive with GP than the feldspar phase. The thickness of the interfacial phase formed through chemical reactions between GP and glass-ceramic matrix is around 30 nm. The chemically bonded interface has contributed significantly toward the substantial improvements in both strength and toughness of the GP-reinforced glass-ceramic matrix composite. Characterization techniques, including X-ray diffraction and field-emission scanning electron Microscopy, incorporating X-ray microanalysis using energy dispersive spectrometry, have been employed in this study.

Description: [1]  The problem of diurnal variation in surface emissivity over the Sahara Desert during non-raining days is studied and assessed with observations from the Infrared Atmospheric Sounding Interferometer (IASI). The analysis has been performed over a Sahara Desert dune target area during July 2010. Spinning Enhanced Visible and Infrared Imager observations from the European geostationary platform Meteosat-9 (Meteorological Satellite 9) have been also used to characterize the target area. Although the amplitude of this daily cycle has been shown to be very small, we argue that suitable nighttime meteorological conditions and the strong contrast of the reststrahlen absorption bands of quartz (8–14 μ m) can amplify its effect over the surface spectral emissivity. The retrieval of atmospheric parameters show that at nighttime an atmospheric temperature inversion occurs close to the surface yielding a thin boundary layer which acts like a lid, keeping normal convective overturning of the atmosphere from penetrating through the inversion. This mechanism traps water vapour close to the land and drives the direct adsorption of water vapour at the surface during the night. The diurnal variation in emissivity at 8.7 μ m has been found to be as large as 0.03 with high values at night and low values during the day. At 10.8 μ m and 12 μ m the variation has the same sign as that at 8.7 μ m, but with a smaller amplitude, 0.019 and 0.014, respectively. The impact of these diurnal variations on the retrieval of surface temperature and atmospheric parameters has been analyzed.

Description: [1]  Retrieval of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) using the Collection 5 (C005) algorithm provides large-scale (10x10 km) estimates that can be used to predict surface layer concentrations of particulate matter with aerodynamic diameter smaller than 2.5 microns (PM 2.5 ). However, these large-scale estimates are not suitable for identifying intra-urban variability of surface PM 2.5 concentrations during wildfire events when individual plumes impact populated areas. We demonstrate a method for providing high-resolution (2.5 km) kernel-smoothed estimates of AOD over California during the 2008 northern California fires. The method uses high-resolution surface reflectance ratios of the 0.66 µm and 2.12 µm channels, a locally derived aerosol optical model characteristic of fresh wildfire plumes, and a relaxed cloud filter. Results show that the AOD derived for the 2008 northern California fires outperformed the standard product in matching observed aerosol optical thickness (AOT) at three coastal AERONET sites and routinely explained more than 50% of the variance in hourly surface PM 2.5 concentrations observed during the wildfires.

Description: Recent investigations have revealed the great potential of Raman spectroscopy for the characterization of clinker minerals and commercial Portland cements. The usefulness of this technique for the identification of anhydrous, hydrated, and carbonated phases in cement-based materials has been demonstrated. In the present work, the application of micro-Raman spectroscopy for the characterization of the main clinker phases of calcium aluminate cements and calcium sulfoaluminate cement is explored. The main stable hydrated phases as well as several important carbonated phases are investigated. Raman measurements on the following phases are reported: (i) pure, unhydrated phases: CA, C 12 A 7 , CA 2 , C 2 AS, cubic- C 3 A , C 4 AF, and C 4 A 3 ; (ii) hydrated phases: ettringite, monosulfoaluminate, and hydrogarnet ( C 3 AH 6 ); (iii) carboaluminate phases: hemicarboaluminate and monocarboaluminate. The present results, which are discussed in terms of the internal vibrational modes of the aluminate, carbonate, and sulfate molecular groups as well as stretching O–H vibrations, show the ability of Raman spectroscopy to identify the main hydrated and unhydrated phases in the aluminate and sulfoaluminate cements. The Raman spectra obtained in this work provide an extended database to the existing data published in the literature.

Description: Acmite ( NaFeSi 2 O 6 ) films were formed on steel coupons via solvothermal reaction of silica, sodium hydroxide, and 1, 4-butanediol in an autoclave under autogenous pressure. Systematic variation in processing variables led to homogenous coatings comprised of pinacoidal acmite grains with an average grain size of ~33 μm. The coatings were produced on the steel coupons from reactant conditions of 0.635 m SiO 2 , 2.546 m NaOH , and 3.087 m 1,4-butanediol for 72 h at 240°C.

Description: [1]  An observational study of nonlinear interaction between the quasi two-day wave (QTDW) and the diurnal and semidiurnal tides from meteor radar measurements at Maui is reported. The diurnal and semidiurnal tides show a short-term variation with the QTDW activity. The variation of amplitude of the semidiurnal tide is opposite to that of the QTDW. The minimum amplitudes of the diurnal tide appear several days later than the maximum amplitudes of the QTDW, and the diurnal tide obviously strengthens when the QTDW drops to small amplitudes. The bispectrum analysis shows significant nonlinear interactions among the QDTW and the tidal components. The two quasi 16-h modes with periods of 16.2 h and 15.8 h generated in the interactions of the QTDW with the diurnal and semidiurnal tides can clearly be distinguished because of the slight deviation of the QTDW period from 48 h. The bicoherence spectrum demonstrates that the QTDW and the semidiurnal tide have quite strong levels of coherence, indicating that the nonlinear interaction is a mechanism responsible for the variability of the semidiurnal tide. Although there is also some interaction between the QTDW and the diurnal tide, their coherence level is low. When the QTDW drops to very weak amplitudes, the background wind decreases and reverses. During this time, the diurnal tide holds large amplitudes. These results support the notion that the variability of the diurnal tide is mainly attributable to the strong QTDW-induced changes in the background atmosphere, which was shown in the modeling study by Chang et al . [2011]. Hence, both the nonlinear interaction and the background flow changes are responsible for the observed variation of the diurnal tide.

Description: [1]  We conducted three-member ensemble simulations using a global atmospheric model with a high-horizontal resolution of a 60-km grid size for the period 1872-2099 (228 years). Between 1872 and 2005, the model was forced with observed historical sea surface temperatures (SST), while between 2006 and 2099 the boundary SST data were estimated using the multi-model ensemble (MME) of the Coupled Model Intercomparison Project phase 3 (CMIP3) models and assuming A1B emission scenario. Annual mean precipitation (PAVE), the Simple Daily Precipitation Intensity Index (SDII), and the maximum 5-day precipitation total (R5d) averaged over East Asia increase almost monotonically through the 21st century. The statistically significant area of precipitation intensity increase is larger for 2080-2099 than for 2046-2065. In particular, intense rainfall will increase over northern and southern China during 2080-2099. The conversion rate from water vapor to precipitation per 1 °C rise in surface air temperature for SDII and R5D is much larger than that for PAVE during the 21st century. This suggests that extreme rainfall events will occur more frequently than moderate rainfall events even if the amount of temperature rise is same. Future changes in the horizontal transport of water vapor also leads to more intense precipitation over East Asia. In particular, the increase in clockwise water vapor transport due to intensification of the subtropical high contributes to increased intense precipitation over southern China.

Description: [1]  An aircraft field study [POST; Physics Of Stratocumulus Top] was conducted off the central California Coast in July and August of 2008 to deal with the known difficulty of measuring entrainment rates in the radiatively important stratocumulus [Sc] prevalent in that area. The CIRPAS Twin Otter research aircraft flew 15 quasi-Lagrangian flights in unbroken Sc and carried a full complement of probes including three high data-rate probes UFT-M [Ultra-Fast Temperature probe], PVM [Particulate Volume Monitor] probe, and gust probe. The probes’ co-location near the nose of the Twin Otter permitted estimation of entrainment fluxes and rates with an incloud resolution of 1 m. [2]  Results include the following: Application of the conditional-sampling variation of classical mixed layer theory for calculating the entrainment rate into cloud top for POST flights is shown to be inadequate for most of the Sc. Estimated rates resemble previous results after theory is modified to take into account both entrainment and evaporation at cloud top given the strong wind shear and mixing at cloud top. Entrainment rates show a tendency to decrease for large shear values, and the largest rates are for the smallest temperature jumps across the inversion. Measurements indirectly suggest that entrained parcels are primarily cooled by infrared flux divergence rather than cooling from droplet evaporation, while detrainment at cloud top causes droplet evaporation and cooling in the EIL [Entrainment Interface Layer] above cloud top.

Description: A 50:50 vol% MgO – Y 2 O 3 nanocomposite with ~150 nm grain size was prepared in an attempt to make 3–5 μm infrared-transmitting windows with increased durability and thermal shock resistance. Flexure strength of the composite at 21°C is 679 MPa for 0.88 cm 2 under load. Hardness is consistent with that of the constituents with similar grain size. For 3-mm-thick material at 4.85 μm, the total scatter loss is 1.5%, forward scatter is 0.2%, and absorptance is 1.8%. Optical scatter below 2 μm is 100%. Variable intensity OH absorption (~6% absorptance) is observed near 3 μm. The refractive index is ~0.4% below the volume-fraction-weighted average of those of the constituents. Thermal expansion is equal to the volume-fraction-weighted average of expansion of the constituents. Specific heat capacity is equal to the mass-fraction-weighted average of heat capacities of the constituents. Thermal conductivity lies between those of the constituents up to 1200 K. Elastic constants lie between those of the constituents. The Hasselman mild thermal shock resistance parameter for the composite is twice as great as that of common 3–5 μm window materials, but half as great as that of c -plane sapphire.

Description: [1]  We present new measurements of the time-dependence of the ice nucleating ability of a wide range of materials including the minerals montmorillonite and kaolinite, the biological proxy ice nuclei Icemax, and flame soot generated from the incomplete combustion of ethylene gas. We also present time-dependence for ambient ice nuclei collected from rain water samples. Our data show that the time-dependence for all materials studied here is weak, suggesting that the modified singular approximation is valid over the range of times and temperatures encountered for mixed-phase clouds.

Description: [1]  Attributing changes in extreme daily precipitation to global warming is difficult, even when based on global climate model simulations or statistical trend analyses. The question about trends in extreme precipitation and their causes has been elusive because of climate models’ limited precision and the fact that extremes are both rare and occur at irregular intervals. Here a newly discovered empirical relationship between the wet-day mean and percentiles in 24-hr precipitation amounts was used to show that trends in the wet-day 95th percentiles world-wide have been influenced by the global mean temperature, consistent with an accelerated hydrological cycle caused by a global warming. A multiple regression analysis was used as a basis for an attribution analysis by matching temporal variability in precipitation statistics with the global mean temperature.

Description: [1]  We implement a new isoprene oxidation mechanism in a global 3-D chemical transport model (GEOS-Chem). Model results are evaluated with observations for ozone, isoprene oxidation products, and related species from the ICARTT aircraft campaign over the eastern United States in summer 2004. The model achieves an unbiased simulation of ozone in the boundary layer and the free troposphere, reflecting canceling effects from recent model updates for isoprene chemistry, bromine chemistry, and HO 2 loss to aerosols. Simulation of the ozone-CO correlation is improved relative to previous versions of the model and this is attributed to a lower and reversible yield of isoprene nitrates, increasing the ozone production efficiency (OPE) per unit of nitrogen oxides (NO x  ≡ NO + NO 2 ). The model successfully reproduces the observed concentrations of organic nitrates (∑ANs) and their correlations with HCHO and ozone. ∑ANs in the model is principally composed of secondary isoprene nitrates, including a major contribution from nighttime isoprene oxidation. The correlations of ∑ANs with HCHO and ozone then provide sensitive tests of isoprene chemistry and argue in particular against a fast isomerization channel for isoprene peroxy radicals. ∑ANs can provide an important reservoir for exporting NO x from the US boundary layer. We find that the dependence of surface ozone on isoprene emission is positive throughout the US, even if NO x emissions are reduced by a factor of 4. Previous models showed negative dependences that we attribute to erroneous titration of OH by isoprene.

Description: [1]  The extent to which the rain rate from shallow, liquid-phase clouds is microphysically influenced by aerosol, and therefore drop concentration N d perturbations, is addressed through analysis of the precipitation susceptibility, S o . Previously published work, based on both models and observations, disagrees on the qualitative behavior of S o with respect to variables such as liquid water path L or the ratio between accretion and autoconversion rates. Two primary responses have emerged: (i) S o decreases monotonically with increasing L and (ii) S o increases with L , reaches a maximum, and decreases thereafter. Here we use a variety of modeling frameworks ranging from box models of (size-resolved) collision-coalescence, to trajectory ensembles based on large eddy simulation to explore the role of time available for collision-coalescence t c in determining the S o response. The analysis shows that an increase in t c shifts the balance of rain production from autoconversion (a N d -dependent process) to accretion (roughly independent of N d ), all else (e.g., L ) equal. Thus with increasing cloud contact time warm rain production becomes progressively less sensitive to aerosol, all else equal. When the time available for collision-coalescence is a limiting factor, S o increases with increasing L whereas when there is ample time available, S o decreases with increasing L . The analysis therefore explains the differences between extant studies in terms of an important precipitation-controlling parameter, namely the integrated liquid water history over the course of an air parcel's contact with a cloud.

Description: [1]  In previous studies, the Yonsei University (YSU) planetary boundary layer (PBL) scheme implemented in the Weather Research and Forecasting (WRF) model was reported to perform less well at night, while performing better during the day. Compared to observations, predicted nocturnal low-level jets (LLJs) were typically weaker and higher. Also, the WRF model with Chemistry (WRF/Chem) with the YSU scheme was reported to sometimes overestimate near-surface ozone (O 3 ) concentration during the nighttime. The updates incorporated in WRF version 3.4.1, include modifications of the nighttime velocity scale used in the YSU boundary-layer scheme. The impacts of this update on the prediction of nighttime boundary layers and related implications for wind resource assessment and air quality simulations are examined in this study. The WRF/Chem model with the updated YSU scheme predicts smaller eddy diffusivities in the nighttime boundary layer, and consequently lower and stronger LLJs over a domain focusing on the southern Great Plains area, showing a better agreement with the observations. As a result, related overestimation problems for near-surface temperature and wind speeds appear to be resolved, and the nighttime minimum near-surface O 3 concentrations are better captured. Simulated vertical distributions of meteorological and chemical variables for weak wind regimes (e.g., in the absence of LLJ) are less impacted by the YSU updates.

Description: [1]  We introduce novel methodology to examine the ability of six regional climate models (RCMs) in the North American Regional Climate Change Assessment Program (NARCCAP) ensemble to simulate past extreme precipitation events seen in the observational record over two different regions and seasons. [2]  Our primary objective is to examine the strength of daily correspondence of extreme precipitation events between observations and the output of both the RCMs and the driving reanalysis product. To explore this correspondence, we employ methods from multivariate extreme value theory. These methods require that we account for marginal behavior, and we first model and compare climatological quantities which describe tail behavior of daily precipitation for both the observations and model output before turning attention to quantifying the correspondence of the extreme events. Daily precipitation in a west coast region of North America is analyzed in two seasons, and it is found that the simulated extreme events from the reanalysis-driven NARCCAP models exhibit strong daily correspondence to extreme events in the observational record. Precipitation over a central region of the United States is examined, and we find some daily correspondence between winter extremes simulated by reanalysis-driven NARCCAP models and those seen in observations, but no such correspondence is found forsummer extremes. Furthermore, we find greater discrepancies among the NARCCAP models in the tail characteristics of the distribution of daily summer precipitation over this region than seen in precipitation over the west coast region. We find that the models which employ spectral nudging exhibit stronger tail dependence to observations in the central region.

Description: [1]  Atmospheric organic aerosol concentrations depend in part on the gas-particle partitioning of primary organic aerosol (POA) emissions. Consequently, heating and dilution were used to investigate the volatility of biomass burning smoke particles from combustion of common North American trees/shrubs/grasses during the third Fire Lab at Missoula Experiment (FLAME-III). Fifty to eighty percent of the mass of biomass burning POA evaporated when isothermally diluted from plume (~1000 µg m -3 ) to ambient-like concentrations (~10 µg m -3 ), while roughly eighty percent of the POA evaporated upon heating to 100 °C in a thermodenuder with a residence time of ~14 seconds. Therefore, the majority of the POA emissions were semi-volatile. Thermodenuder measurements performed at three different residence times indicated that there were not substantial mass transfer limitations to evaporation (i.e., the mass accommodation coefficient appears to be between 0.1 and 1). An evaporation kinetics model was used to derive volatility distributions and enthalpies of vaporization from the thermodenuder data. A single volatility distribution can be used to represent the measured gas-particle partitioning from the entire set of experiments, including different fuels, organic aerosol concentrations, and thermodenuder residence times. This distribution, derived from the thermodenuder measurements, also predicts the dilution-driven changes in gas-particle partitioning. This volatility distribution and associated emission factors for each fuel studied can be used to update emission inventories and to simulate the gas-particle partitioning of biomass burning POA emissions in chemical transport models.

Description: [1]  We investigate the variations in tropospheric circulation over Asia associated with the stratospheric quasi-biennial oscillation (QBO) during Northern Hemisphere (NH) autumn (September-November) using the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis and NCEP-Department of Energy (DOE) Reanalysis II data sets for a 25-year period (1980-2004). The anomaly fields in this study are expressed as the easterly years minus the westerly years of the QBO. The zonal wind distribution at 200 hPa indicates easterly anomalies at low latitudes from India through Taiwan, statistically significant westerly anomalies at mid-latitudes including the Tibetan Plateau to northern China, and significant easterly anomalies in the high-latitude Eurasia north of 50°N. A momentum balance analysis indicates that these anomalies over Asia are attributable to atmospheric waves and residual mean meridional flow. Significant northward and descending anomalies are observed in the lower stratosphere over Asia, with detectable signals in the troposphere around Tibet. The adiabatic heating due to descending motions in the region centering on India and Bangladesh is consistent with the distribution of rainfall anomalies. The formation of zonal wind anomalies over South Asia seems to be associated with not only wave activities but also adiabatic heating and thermal advection. We suggest that the QBO may be linked to tropospheric circulation over Asia through wave activities and convective activities in autumn, and the wave activities in the low latitudes associated with the QBO seem to be connected with the rainfall distribution over the Asian monsoon region.

Description: [1]  Subtropical cyclogenesis and tropical transitions (TT) over the South Atlantic Ocean only received attention after the first documented Hurricane Catarina occurred close to the Southern Brazilian coast in March 2004. However, due to the lack of studies in this part of Atlantic Ocean, it is still unclear what the main environmental conditions and dynamical processes associated with TT or even subtropical cyclogenesis are over the region. This study presents a synoptic and dynamical analysis of the Subtropical Cyclone Anita which occurred in March 2010 near Brazilian coast. This system started as a pure subtropical cyclone, evolved to a condition favorable to TT, later developed a cold-cored structure and decayed as an extratropical cyclone. During the period favorable for TT, the turbulent heat fluxes (latent plus sensible) from the ocean decreased and Anita started interacting with another extratropical disturbance preventing the TT to happen. This interaction, in turn, increased the vertical wind shear, let the extratropical transition to occur and promoted the westward displacement of Anita to colder waters thus decreasing the turbulent heat fluxes. The results suggest that the combination of a dipole blocking pattern aloft, with contribution from barotropic energy conversions, and strong turbulent fluxes are important ingredients for tropical storms development. Hybrid storms in such environmental conditions can be one form of precursors of hurricanes over the South Atlantic.

Description: In this work, novel Y 2 Si 2 O 7 / ZrO 2 composites were developed for structural and coating applications by taking advantage of their unique properties, such as good damage tolerance, tunable mechanical properties, and superior wear resistance. The γ- Y 2 Si 2 O 7 / ZrO 2 composites showed improved mechanical properties compared to the γ- Y 2 Si 2 O 7 matrix material, that is, the Young's modulus was enhanced from 155 to 188 GPa (121%) and the flexural strength from 135 to 254 MPa (181%); when the amount of ZrO 2 was increased from 0 to 50 vol%, the γ- Y 2 Si 2 O 7 / ZrO 2 composites also presented relatively high facture toughness (〉1.7 MPa·m 1/2 ), but this exhibited an inverse relationship with the ZrO 2 content. The composition–mechanical property–tribology relationships of the Y 2 Si 2 O 7 / ZrO 2 composites were elucidated. The wear resistance of the composites is not only influenced by the applied load, hardness, strength, toughness, and rigidity but also effectively depends on micromechanical stability properties of the microstructures. The easy growth of subcritical microcracks in Y 2 Si 2 O 7 grains and at grain boundaries significantly contributes to the macroscopic fracture toughness, but promotes the pull-out of individual grains, thus resulting in a lack of correlation between the wear rate and the macroscopic fracture toughness of the composites.

Description: [1]  The Suomi National Polar-orbiting Partnership (NPP) satellite was launched on October 28, 2011 and carries the Advanced Technology Microwave Sounder (ATMS) on board. ATMS is a cross-track scanning instrument observing in 22 channels at frequencies ranging from 23 to 183 GHz, permitting the measurements of the atmospheric temperature and moisture under most weather conditions. In this study, the ATMS radiometric calibration algorithm used in the operational system is first evaluated through independent analyses of prelaunch thermal vacuum data. It is found that the ATMS peak nonlinearity for all the channels are less than 0.5 K, which is well within the specification. For the characterization of the ATMS instrument sensitivity or noise equivalent differential temperatures (NEDT), both standard deviation and Allan variance of warm counts are computed and compared. It is shown that NEDT derived from the standard deviation is about three to five times larger than that from the Allan variance. It is shown that this difference results from a non-stationary component in the standard deviation of warm counts. The Allan variance is better suited than the standard deviation for describing NEDT. In the ATMS sensor brightness temperature data record (SDR) processing algorithm, the antenna gain efficiencies of main beam, cross-polarization beam and side lobes must be derived accurately from the antenna gain distribution function. However, uncertainties remain in computing the efficiencies at ATMS high frequencies. Thus, ATMS antenna brightness temperature data records (TDR) at channels 1 to 15 are converted to SDR with the actual beam efficiencies whereas those for channels 16 to 22 are only corrected for the near-field side-lobe contributions. The biases of ATMS SDR measurements to the simulations are consistent between GPS RO and NWP data and are generally less than 0.5 K for those temperature sounding channels where both the forward model and input atmospheric profiles are reliable.

Description: [1]  The operational ALADIN-France 3D-Var system is based on static background error covariances calculated off-line during a few-week past period. In this study, the impact of an on-line updated specification of background error covariances is evaluated in the ALADIN-France system. This evaluation is done by comparing three experiments, respectively based on (i) covariances calculated from a monthly average over a past period, (ii) covariances calculated from a monthly average over the period of study, and (iii) covariances calculated from a sliding daily average over the period of study. Firstly, it is shown through a comparison between experiments (i) and (ii) that updating the monthly average of error covariances has a positive impact on the short-range forecast quality. This is related to the specification of covariances which are more representative of average weather regimes at play during the period of study. Secondly, a comparison between experiments (ii) and (iii) indicates that additional positive impacts of a daily update of error covariances are also visible, although they tend to be somewhat localized and modest during this period. These impacts are illustrated by case studies for humidity during an anticyclonic situation, and for wind during a cyclonic event. These results support the idea to consider an on-line updated specification of background error covariances.

Description: [1]  On 5 August 2008, a localized heavy rainfall event caused a rapid increase in drainpipe discharge, which killed five people working in a drainpipe near Zoshigaya, Tokyo. This study compared the effects of artificial land cover and anthropogenic heat on this localized heavy rainfall event based on three ensemble experiments using a cloud-resolving model that includes realistic urban features. The first experiment (CTRL) considered realistic land cover and urban features, including artificial land cover, anthropogenic heat, and urban geometry. In the second experiment (NOAH), anthropogenic heat was ignored. In the third experiment (NOLC), urban heating from artificial land cover was reduced by keeping the urban geometry but with roofs, walls, and roads of artificial land cover replaced by shallow water. The results indicated that both anthropogenic heat and artificial land cover increased the amount of precipitation and that the effect of artificial land cover was larger than that of anthropogenic heat. However, in the middle stage of the precipitation event, the difference between the two effects became small. Weak surface heating in NOAH and NOLC reduced the near-surface air temperature and weakened the convergence of horizontal wind and updraft over the urban areas, resulting in a reduced rainfall amount compared with that in CTRL.

Description: The as-prepared BiFeO 3 ceramic shows a piezoelectric d 33 coefficient of −14 pC/N, that is, an obvious ferroelectric self-poling phenomenon. The temperature gradient between the two surfaces of BiFeO 3 ceramic was intentionally enlarged when BiFeO 3 was prepared with a rapid liquid sintering method. This temperature gradient and the corresponding thermal strain can introduce defect dipoles through separating bismuth vacancies from oxygen vacancies. A mass of these dipoles introduce a macroscopic internal electric field ( E in ) which downward poles BiFeO 3 ceramic during its cooling down process. As expected, an E in of 〉10 kV/cm is confirmed by the asymmetrical polarization/strain versus electric field curves.

Description: The effect of Ba content on the stress sensitivity of the antiferroelectric to ferroelectric phase transition in ( Pb 0.94− x La 0.04 Ba x )[( Zr 0.60 Sn 0.40 ) 0.84 Ti 0.16 ] O 3 ceramics is investigated through monitoring electric field-induced polarization and longitudinal strain under compressive prestresses. It is found that incorporation of Ba significantly suppresses the stress sensitivity of the phase transition, as manifested by slight decreases under prestresses up to 100 MPa in the maximum polarization ( P m ) and longitudinal strain ( x m ). The energy storage density is even increased under the mechanical confinement in compositions x  = 0.02 and 0.04. X-ray diffraction, transmission electron microscopy, and dielectric measurements indicate that the suppressed stress sensitivity is associated with the disruption of micrometersized antiferroelectric domains into nanodomains and the transition from antiferroelectric to relaxor behavior.

Description: Powders and nanoceramics composed of composites of CoFe 2 O 4 , CoFe 2 , and a small amount of FeO were prepared by heating CoFe 2 O 4 powder in reducing atmosphere and by sintering the product of reducing reaction at 350°C via spark plasma sintering technology. In the powders, increase in the molar ratios of CoFe 2 : CoFe 2 O 4 and a great change in magnetic parameters were observed with the change in heating temperature from 300°C to 400°C, and the dominance of dipole interaction over exchange coupling in the interparticle interactions was confirmed by the steps in magnetic hysteresis loops and the negative Henkel plots. However, in the nanoceramics, significant enhancement in exchange coupling was found when the sintering temperature was raised to 500°C and 650°C, which was confirmed by both the positivity of Henkel plot and the single-phase style of the magnetic hysteresis loop.

Description: [1]  Extratropical cyclones and their associated frontal systems are well known to be related to heavy precipitation events. Here an objective method is used to directly link extreme precipitation events with atmospheric fronts, identified using ECMWF Interim Reanalysis data, to quantify the importance of fronts for precipitation extremes globally. In some parts of the major midlatitude storm track regions, over 90% of precipitation extremes are associated with fronts, with slightly more events associated with warm fronts than cold fronts. On average 51% of global precipitation extremes are associated with fronts, with 75% in the midlatitudes and 31% in the tropics. A large proportion of extreme precipitation events occur in the presence of both a cyclone and a front, but remote fronts are responsible for many of the “front-only” events. The fronts producing extreme precipitation events are found to have up to 35% stronger frontal gradients than other fronts, potentially providing some improved forecasting capabilities for extreme precipitation events.

Description: Gas adsorption porosity measurement of geopolymers (GPs) is required for quantitative understanding of such mesoporous structures, but the complex nature of the GP system makes analysis difficult. Previous results in the literature are often ambiguous or contradictory. A systematic investigation of metakaolin GP gas adsorption results was conducted to optimize the use of this measurement technique and verify that results match known theory about GP structure. It was found that GP undergoes structural change upon degassing at 100°C or higher. If and only if this change is prevented by degassing at a lower temperature could it be shown that specific surface area and total gas adsorption increases with both increasing curing temperature and decreased Si : Al ratio. This observation is consistent with previous suggestions of increased zeolitic character under these conditions, where previous gas adsorption investigations had not observed this expected relationship. Hydrogen physisorption is proposed as a substitute technique for micropore isotherms in GPs due to the difficulty of removing trace gasses from GPs and the measurement effect of such gasses at high vacuum. A hydrogen physisorption isotherm qualitatively resembled an equivalent nitrogen micropore isotherm.

Description: In this work, the role of europium doping of glasses formulated in the ternary system ZnO – CdO – TeO 2 is described. The Eu -doped oxide glasses were prepared by the conventional melt-quenching method and by using three different compositions. Structural studies reveal that there exists a good affinity between Cd and some rare earth (RE) ions to form the crystalline phase. The X-ray diffraction (XRD) diagrams display that the structure of these glasses is amorphous and with the increase in CdO content and the compatibility of Eu 3+ , there is a tendency to form nanocrystals of CdTe 2 O 5 . The scanning electron microscopic (SEM) observation of their microstructure confirms the presence of phase separation. Differential thermal analysis (DTA) of these glasses showed small exothermic peaks noted around 450°C for the V2 glass and 480°C for V1 and V3 glasses, which could be attributed to the formation of these crystals. The infrared spectra showed a main absorption band around 800–600 cm −1 corresponding to the Te – O stretching mode in TeO 4 and TeO 3 groups. By optical absorption (OA), the band gap ( E g ) for each glass was determined; these values were 3.27, 3.14, and 3.3 eV for the V1–V3 glasses, respectively. Furthermore, the presence of Eu 3+ was detected in the 370–470 nm short-range wavelengths. The photoluminescence (PL) experiments of the glasses showed light emission due to the following transitions: 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4.

Description: The conductivity of nominal CaWO 4 , CaW 0.99 Ta 0.01 O 4–δ , 0.7( CaWO 4 )–0.3( La 0.99 Ca 0.01 NbO 4–δ ), and Ca 0.9 La 0.1 WO 4+δ has been studied by means of a.c. impedance measurements. Proton conductivity was observed for CaW 0.99 Ta 0.01 O 4–δ , which displayed exothermic hydration with enthalpy and entropy of –82 kJ/mol and –120 J/molK, respectively. The proton mobility in CaW 0.99 Ta 0.01 O 4–δ was low, with enthalpy and preexponential factor of mobility of 82 kJ/mol and 0.7 cm 2 K/Vs. The high enthalpy of mobility is interpreted to reflect association between the acceptor dopant and protonic defects, whereas the low preexponential factor of mobility may reflect a lower proton concentration than assumed. Rietveld refinement indicated low solubilities of La on Ca -site and Ta on W-site. Proton conductivity was also observed in undoped CaWO 4 , however, not in Ca 0.9 La 0.1 WO 4+δ . The conductivity of 0.7( CaWO 4 )–0.3( La 0.99 Ca 0.01 NbO 4–δ ) behaved much like that of undoped LaNbO 4 , likely due to a very low acceptor dopant concentration.

Description: A new lead-free BNT-based piezoelectric ceramics of (1 −  x ) Bi 0.5 Na 0.5 TiO 3 – x Bi ( Al 0.5 Ga 0.5 ) O 3 ( x  = 0, 0.02, 0.03, 0.04, and 0.05) were synthesized using a conventional ceramic fabrication method. Their structures and electrical properties were investigated. All the samples show a typical ferroelectric P ( E ) loops and S ( E ) curves at room temperature. The optimal properties are obtained at the composition of the x  = 0.03. The substitution of Bi ( Al 0.5 Ga 0.5 ) O 3 enhances piezoelectric constant and increases Curie temperature from 58 pC/N and 310°C of pure BNT to 93 pC/N and 325°C of the x  = 0.03. The temperature-dependent P ( E ) loops and S ( E ) curves of 0.97BNT–0.03BAG indicate that phase transition from ferroelectric to antiferroelectric takes place over a very wide temperature region from 80°C to 180°C. The results show that the introduction of BAG improves the electrical properties of BNT.

Description: [1]  The initial breakdown stage of 10 intracloud lightning flashes that may have produced terrestrial gamma-ray flashes (TGFs) are studied with wideband E-change, multi-band B-change, and VHF lightning mapping data; these flashes fit published criteria known to be associated with TGFs. The (x, y, z, t) locations of fast initial breakdown pulses (IBPs) were determined with E-change data using a time-of-arrival (TOA) technique. Each IBP includes one or more fast-rising sub-pulses. Previous research has shown that a typical intracloud flash initiates just above the main negative cloud charge (MNCC), then an initial negative leader propagates upward in 1 – 20 ms to the bottom of the upper positive cloud charge (UPCC), thereby establishing a conducting path between the MNCC and UPCC. TOA locations indicate that IBPs are directly related to the initial negative leader. The IBPs primarily occur in short (〈 750 µs) bursts of 2 – 5 pulses, and each burst produces a slow, monotonic E-change. Typically 1 – 3 IBP bursts are needed to span the vertical gap from the MNCC to the UPCC, with successive bursts separated by 1 – 5 ms. In the B-change data each IBP burst has an associated ULF pulse and several LF pulses, and these are caused by the same physical events that produce the slow, monotonic E-change and fast-rising IBP sub-pulses, respectively. Based on similarities with known TGF-associated signals, we speculate that a relativistic electron avalanche causes each LF pulse/IBP sub-pulse pair; thus each pair has the potential to cause a TGF.

Description: [1]  Stratospheric Sudden Warming (SSW) events are typically, but not always, accompanied by negative Northern Annular Mode anomalies in the troposphere. However, large uncertainties remain as to which dynamical processes are responsible for those anomalies.In order to highlight sources of variability in stratosphere-troposphere coupling amongst SSW events, we present a case study of three selected events and show detailed Transformed Eulerian Mean diagnostics for momentum changes in the stratosphere and troposphere in the course of those events. Our results suggest that planetary-scale waves, especially the zonal wavenumber two component, may not only play an important role for the onset of tropospheric anomalies in response to SSW events, but also for introducing variability in the vertical coupling, i.e., whether the tropospheric circulation anomalies lag, lead or occur simultaneous to the weakening of the vortex. Particularly, the meridional propagation of those waves in the upper troposphere could be an important factor that determines whether SSW events lag or lead tropospheric anomalies.

Description: [1]  Three years of gravity wave observations from the HIRDLS instrument on NASA's Aura satellite are examined. We produce estimates of the global distribution of gravity wave momentum flux as a function of individual observed wave packets. The observed distribution at the 25 km altitude level is dominated by the small proportion of wave packets with momentum fluxes greater than ~0.5 mPa. Depending on latitude and season, these wave packets only comprise ~7–25% of observations, but are shown to be almost entirely responsible for the morphology of the observed global momentum flux distribution. Large-amplitude wave packets are found to be more important over orographic regions than over flat ocean regions, and to be especially high in regions poleward of 40S during austral winter. The momentum flux carried by the largest packets relative to the distribution mean is observed to decrease with height over orographic wave generation regions, but to increase with height at tropical latitudes; the mesospheric intermittency resulting is broadly equivalent in both cases. Consistent with previous studies, waves in the top 10% of the extratropical distribution are observed to carry momentum fluxes more than twice the mean and waves in the top 1% more than 10× the mean, and the Gini coefficient is found to characterise the observed distributions well. These results have significant implications for gravity wave modelling.

Description: [1]  Aerosol optical properties simulated by the global 3-D tropospheric chemistry and transport model GEOS-Chem (GC) from 2008 to 2010 over the contiguous United States were evaluated with ground observations from Aerosol Robotic Network (AERONET) sites and aerosol products reported by the Multi-angle Imaging SpectroRadiometer (MISR). Overall, the correlation coefficient (r) and regression slope between AERONET and GC 2° x 2.5° (2 ° latitude x 2.5 ° longitude) daily total column aerosol optical depth (AOD) was 0.6 and 0.51, respectively. After using the nested GC 0.5° x 0.667° model to control for spatial variability, removing several outliers, and averaging over a monthly timescale, the agreement was significantly improved to an r of 0.84 and a slope of 0.75. Seasonal, hourly, and geographical statistics for GC 0.5° x 0.667° and AERONET AODs show a similar data range and variation, with higher mean values in the summer, the evening, and in the eastern U.S. Smaller correlation coefficients are seen in the summer and winter, in the evening, and in the western U.S. To investigate the optical properties of major GC tracers, MISR Level 2 aerosol products were used to calculate inorganic aerosol, dust, and absorbing non-dust AOD. Both GC and MISR suggest that, on average, inorganic aerosol has the highest AOD (GC: 0.071, MISR: 0.089) nationally, followed by absorbing non-dust species (GC: 0.025, MISR: 0.041), and dust (GC: 0.013, MISR: 0.014). The large discrepancies in our inter-comparison are due to GC underestimation of inorganic aerosol levels during all four seasons in the western U.S., and dust during summer in the eastern U.S., along with overestimation of summertime absorbing non-dust species over the northwestern U.S. These uncertainties are attributed to underestimation of inorganic aerosol emissions in more polluted western regions, the transport of Sahara dust in the summer, misuse of the fire files, and MISR retrieval uncertainties in the surface and choice of aerosol models.

Description: [1]  The eruption of the Icelandic volcano Eyjafjallajökull in the spring of 2010 lasted for 39 days with an explosive phase (14–18 April), an effusive phase (18 April–4 May) and a phase with renewed explosive activity (5–17 May). Images every 5 seconds from a camera mounted 34 km from the volcano are available for most of the eruption. Applying the maximum cross-correlation method (MCC) on these images, the velocity structure of the eruption cloud has been mapped in detail for four time intervals covering the three phases of the eruption. The results show that on average there are updrafts in one part of the cloud, and lateral motion or downdrafts in another. Even within the updraft part, there are alternating motions of strong updrafts, weak updrafts and downward motion. These results show a highly variable plume driven by intermittent explosions. The results are discussed in the context of integral plume models, and in terms of elementary parcel theory.

Description: [1]  The Madden–Julian oscillation (MJO) is the dominant mode of intraseasonal variability in tropical rainfall on the large scale, but its signal is often obscured in individual station data, where effects are most directly felt at the local level. The Fly River system, Papua New Guinea, is one of the wettest regions on Earth and is at the heart of the MJO envelope. 16-year time series of daily precipitation at 15 stations along the river system exhibit strong MJO modulation in rainfall. At each station, the difference in rainfall rate between active and suppressed MJO conditions is typically 40% of the station mean. The spread of rainfall between individual MJO events was small enough such that the rainfall distributions between wet and dry phases of the MJO were clearly separated, at the catchment level. This implies that successful prediction of the large-scale MJO envelope will have a practical use for forecasting local rainfall. In the steep topography of the New Guinea Highlands, the mean and MJO signal in station precipitation is twice that in the satellite TRMM 3B42HQ product, emphasising the need for ground truthing satellite-based precipitation measurements. A clear MJO signal is also present in the river level, which peaks simultaneously with MJO precipitation input in its upper reaches, but lags the precipitation by approximately 18 days on the flood plains.

Description: [1]  Many challenges remain for estimating the Antarctic ice sheet surface mass balance (SMB), which represents a major uncertainty in predictions of future sea-level rise. Validating continental scale studies is hampered by the sparse distribution of in-situ data. Here we present a 26-year mean SMB of the Fimbul ice shelf in East Antarctica between 1983–2009, and recent interannual variability since 2010. We compare these data to results of large-scale SMB studies for similar time periods, obtained from regional atmospheric modeling and remote sensing. Our in-situ data include ground penetrating radar, firn cores and mass balance stakes, and provide information on both temporal and spatial scales. The 26-year mean SMB on the Fimbul ice shelf varies between 170 and 620 kg m -2 a -1 giving a regional average value of 310 ±70 kg m -2 a -1 . Our measurements indicate higher long-term accumulation over large parts of the ice shelf compared to the large-scale studies. We also show that the variability of the mean annual SMB, which can be up to 90 %, can be a dominant factor in short-term estimates. The results emphasize the importance of using a combination of ground based validation data, regional climate models and remote sensing over a relevant time period in order to achieve a reliable SMB for Antarctica.

Description: [1]  A global model of sodium in the mesosphere and lower thermosphere has been developed within the framework of the National Center for Atmospheric Research's Whole Atmosphere Community Climate Model (WACCM). The standard fully-interactive WACCM chemistry module has been augmented with a chemistry scheme that includes 9 neutral and ionized sodium species. Meteoric ablation provides the source of sodium in the model and is represented as a combination of a meteoroid input function (MIF) and a parameterized ablation model. The MIF provides the seasonally and latitudinally varying meteoric flux which is modeled taking into consideration the astronomical origins of sporadic meteors and considers variations in particle entry angle, velocity,mass and the differential ablation of the chemical constituents. WACCM simulations show large variations in the sodium constituents over timescales from days to months. Seasonality of sodium constituents is strongly affected by variations in the MIF and transport via the mean meridional wind. In particular, the summer to winter hemisphere flow leads to the highest sodium species concentrations and loss rates occurring over the winter pole. In the Northern Hemisphere, this winter maximumcan be dramatically affected by stratospheric sudden warmings. Simulations of the January 2009 major warming event show that it caused a short term decrease in the sodium column over the polar cap that was followed by a factor of three increase in the following weeks. Overall, the modeled distribution of atomic sodium in WACCM agrees well with both ground-based and satellite observations. Given the strong sensitivity of the sodium layer to dynamical motions, reproducing its variability providesa stringent test of global models, and should help to constrain key atmospheric variables in this poorly sampled region of the atmosphere.

Description: [1]  The hydrological impact of enhancing Earth's albedo by solar radiation management is investigated using simulations from 12 Earth System models contributing to the Geoengineering Model Intercomparison Project (GeoMIP). We contrast an idealized experiment,G1, where the global mean radiative forcing is kept at pre-industrial conditions by reducing insolation while the CO 2 concentration is quadrupled, to a 4xCO 2 experiment. The reduction of evapotranspiration over land with instantaneously increasing CO 2 concentrations in both experiments largely contributes to an initial reduction in evaporation. A warming surface associated with the transient adjustment in 4xCO 2 generates an increase of global precipitation by around 6.9% with large zonal and regional changes in both directions, including a precipitation increase of 10% over Asia and a reduction of 7% for the North American summer monsoon. Reduced global evaporation persists in G1 with temperatures close to pre-industrial conditions. Global precipitation is reduced by around 4.5% and significant reductions occur over monsoonal land regions: East Asia (6%), South Africa (5%), North America (7%) and South America (6%). The general precipitation performance in models is discussed in comparison to observations. In contrast to the 4xCO 2 experiment, where the frequency of months with heavy precipitation intensity is increased by over 50% in comparison to the control, a reduction of up to 20% is simulated in G1. These changes in precipitation in both total amount and frequency of extremes, point to a considerable weakening of the hydrological cycle in a geoengineered world.

Description: [1]  Atmospheric circulation in a Snowball Earth is critical for determining cloud behavior, heat export from the tropics, regions of bare ice, and sea glacier flow. These processes strongly affect Snowball Earth deglaciation and the ability of oases to support photosynthetic marine life throughout a Snowball Earth. Here we establish robust aspects of the Snowball Earth atmospheric circulation by running six general circulation models with consistent Snowball Earth boundary conditions. The models produce qualitatively similar patterns of atmospheric circulation and precipitation minus evaporation. The strength of the Snowball Hadley circulation is roughly double modern at low CO 2 and greatly increases as CO 2 is increased. We force a 1D axisymmetric sea glacier model with GCM output and show that, neglecting zonal asymmetry, sea glaciers would limit ice thickness variations to O (10%). Global mean ice thickness in the 1D sea glacier model is well-approximated by a 0D ice thickness model with global mean surface temperature as the upper boundary condition. We then show that a thin-ice Snowball solution is possible in the axysymmetric sea glacier model when forced by output from all the GCMs if we use ice optical properties that favor the thin-ice solution. Finally, we examine Snowball oases for life using analytical models forced by the GCM output and find that conditions become more favorable for oases as the Snowball warms, so that the most critical time for the survival of life would be near the beginning of a Snowball Earth episode.

Description: [1]  Extensive measurements of aerosol number size distributions (in the size range 10 to 875 nm) carried out over the oceanic regions of Bay of Bengal and Arabian Sea during two large cruise experiments (one during pre-monsoon and the other during winter) are used to investigate the spatial distribution of aerosol size distributions in general, and that of fine particles in particular, within the marine atmospheric boundary layer. The size distributions, over northwestern Bay of Bengal, lying downwind of the continental outflow from Indo-Gangetic Plain, and over the Eastern Bay of Bengal, under the influence of East Asian outflow, showed a bimodal structure with prominent mode (100–125 nm) in the accumulation regime and weak mode (30–40 nm) in the Aitken regime during both pre-monsoon and winter seasons. While the Aitken mode was found to be relatively quite weak in the Indo Gangetic Plain outflow during both the seasons, it was prominent in the East Asian outflow regions, especially during the winter season. The distributions over the northern Arabian Sea, a region quite prone to advection of dust during pre-monsoon and summer season, showed a prominent Aitken mode (~45 nm) followed by a weaker accumulation mode during pre-monsoon season. Analysis of SeaWiFS data revealed a systematic collocation of Aitken mode aerosols and the high chlorophyll concentration in the northern Arabian Sea implying the role of ocean biogeochemistry in influencing the aerosol size distributions. Such a feature implying biogeochemical influence was not seen over eastern and northern Bay of Bengal during pre-monsoon and winter season.

Description: [1]  Understanding future changes in the frequency, intensity and duration of extreme events in response to increased greenhouse gas forcing is important for formulating adaptation and mitigation strategies that minimize damages to natural and human systems. We quantify transient changes in daily-scale seasonal extreme precipitation events over the U.S. using a 5-member ensemble of nested, high-resolution climate model simulations covering the 21 st century in the IPCC SRES A1B scenario. We find a strong drying trend in annual and seasonal precipitation over the Southwest in autumn, winter and spring, and over the central U.S. in summer. These changes are accompanied by statistically significant increases in dry day frequency and dry spell lengths. Our results also show substantial increases in the frequency of extreme wet events over the northwestern U.S. in autumn, winter and spring, and the eastern U.S. in spring and summer. In addition, the average precipitation intensity increases relative to the extreme precipitation intensity in all seasons and most regions, with the exception of the Southeast. Therefore, most regions receive a greater fraction of total seasonal precipitation from extreme events. These results imply fewer but heavier precipitation events in the future, leading to more frequent wet and dry extremes in most regions of the U.S. Our simulations suggest that many of these changes are likely to become statistically significant by the mid-21 st century. Given current vulnerabilities, such changes in extreme precipitation could be expected to increase stress on water resources in many areas of the U.S., including during the near-term decades.

Description: [1]  Two data assimilation (DA) methods, a simple rule-based direct insertion (DI) approach and an one-dimensional ensemble Kalman filter (EnKF) method, are evaluated by assimilating snow cover fraction observations into the Community Land surface Model (CLM). The ensemble perturbation needed for the EnKF resulted in negative snowpack biases. Therefore, a correction is made to the ensemble bias using an approach that constrains the ensemble forecasts with a single unperturbed deterministic LSM run. This is shown to improve the final snow state analyses. The EnKF method produces slightly better results in higher elevation locations, whereas results indicate that the DI method has a performance advantage in lower elevation regions. In addition, the two DA methods are evaluated in terms of their overall impacts on the other land surface state variables (e.g., soil moisture) and fluxes (e.g., latent heat flux). The EnKF method is shown to have less impact overall than the DI method, and causes less distortion of the hydrological budget. However, the land surface model adjusts more slowly to the smaller EnKF increments, which leads to smaller but slightly more persistent moisture budget errors than found with the DI updates. The DI method can remove almost instantly much of the modeled snowpack, but this also allows the model system to quickly revert to hydrological balance for non-snowpack conditions.

Description: We studied ancient enamels on gilded copper from a collection of archeological horse harness pendants of the Museo Instituto Valencia de Don Juan (Madrid, Spain) to test the benefits of a new, nondestructive analytical methodology based on chemometric analysis (i.e., Principal Component Analysis, PCA) on micro-ATR-FTIR spectral data and chemical quantification using SEM-EDS. The novelty of this approach was threefold: (i) PCA allowed the discrimination of the different harness pendants of known origin and attributed to the 14th and 15th centuries according to the chemical complex composition, nanostructure, glass weathering, and/or coloring mechanisms of each colored enamel, separately (i.e., red, purple, blue, and white), (ii) it is a cheap, easily available and nondestructive methodology that enables us to (iii) draw archeological conclusions about the quality of the manufacturing process, reassess the chronology of these objects and attempt to attribute them to different workshops according to the different traditional recipes identified. In particular, the enamels were made of alkali and/or alkaline earth lead-glass with a wide range of chemical compounds in the form of pigments or opacifiers. Two types of coloring mechanisms were identified, colloidal particles such as copper-ruby for red enamels, and ionic mechanisms such as Fe (II) and Co (II) to achieve a blue pigments; Mn (III) in the purple pigment; and two kind of white enamels were identified, i.e., tin oxide as an opacifier and uranium oxide. In addition, we established the reason for the poor state of conservation of some of the enamels by means of the identification of depolymerization and ion exchanges, well-known harmful effects of glass weathering, and finally a chronology was assigned for some of these pieces according to the enamel composition.

Description: Novel glass-ceramics with embedded thermoelectric Bi 2 Se 3 crystals were prepared from glass matrices in the Ge 20 Se 100− x Bi x ( x  = 5, 10, 12 mol%) system. Based on DSC results performed at different heating rates, characteristic activation energies ( E c ) and Avrami exponents ( n ) were obtained and analyzed by using Kissinger's relation, Ozawa's method, Augis–Bennett approximation and Matusita–Sakka theory. XRD results showed that pure Bi 2 Se 3 crystalline phase precipitated upon annealing at different temperatures for various time. The crystal size and crystalline fraction in the samples could be tuned by controlling the annealing time.

Description: In the present investigations nano size high alumina cements (HAC) were prepared by very effective co-melt precursor sintering technique from their metal nitrate precursors. The prime cementing phases observed were CA, CA 2 , and C 12 A 7 . The addition of nano structured cements in refractory castables has improved the thermo-chemical-mechanical properties to a significant extent. Each batch of low cement castables (LCC) was prepared from calcined Chinese bauxite, HAC, and superfine additives. The effect of HAC in bauxite castable with the additives similar to Silicon Carbide, reactive alumina, and micro-fine silica on the sinterability and properties of these castables was investigated. Physical properties such as apparent porosity and bulk density, mechanical properties such as hot modulus of rupture (HMOR), cold and hot modulus of rupture (CMOR), and cold crushing strength (CCS) of hydrated and sintered castables were studied. The sintered castables were also characterized for their solid phase compositions and microstructure using X-ray diffraction (XRD) and FE-SEM, respectively. In the castables new phases such as mullite, α-alumina were formed at the expense of bauxite and silica. Solid solution of mullite formed at high temperature acts as a bonding phase and is accounted for high HMOR, CMOR, and CCS values. These excellent properties of such castables may enable their uses in various applications such as refractory lining for fabrication of steel, aluminium, copper, glass, cement, chemicals, and ceramics.

Description: [1]  Airborne Multi-AXis Differential Optical Absorption Spectroscopy (AMAX-DOAS) measurements of NO 2 tropospheric vertical columns were performed over California for two months in summer 2010. The observations are compared to the NASA Ozone Monitoring Instrument (OMI) tropospheric vertical columns (data product v2.1) in two ways: (1) Median data was compared for the whole time period for selected boxes and the agreement was found to be fair (R = 0.97, slope = 1.4 ± 0.1, N = 10). (2) A comparison was performed on the mean of coincident AMAX-DOAS measurements within the area of the corresponding OMI pixels with the tropospheric NASA OMI NO 2 assigned to that pixel. The effects of different data filters were assessed. Excellent agreement and a strong correlation (R = 0.85, slope = 1.05 ± 0.09, N = 56) was found for (2) when the data was filtered to eliminate large pixels near the edge of the OMI orbit, the cloud radiance fraction was 〈 50 %, the OMI overpass occurred within 2 hr of the AMAX-DOAS measurements, the flight altitude was 〉 2 km, and a representative sample of the footprint was taken by the AMAX-DOAS instrument. The AMAX-DOAS and OMI data sets both show a reduction of NO 2 tropospheric columns on weekends by 38 ± 24 % and 33 ± 11 %, respectively. The assumptions in the tropospheric satellite air mass factor simulations were tested using independent measurements of surface albedo, aerosol extinction and NO 2 profiles for Los Angeles for July 2010 indicating an uncertainty of 12 %.

Description: Zn 2 GeO 4 ceramic materials were synthesized by the solid-state method. Zn 2 GeO 4 powders were investigated with X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Oxygen defects in the Zn 2 GeO 4 ceramics were investigated by photoluminescence, Raman, and EDS spectra. Conductivity of Zn 2 GeO 4 was 0.18 S/cm at low temperature of 773 K, and its activation energy was 0.49 eV. The results showed that Zn 2 GeO 4 was a promising low-temperature electrolyte with high conductivity.

Description: [1]  This study presents a nonlinear spatio-temporal analysis of 1167 station temperature records from the United States Historical Climatology Network covering the period from 1898 through 2008. We use the Empirical Mode Decomposition (EMD) method to extract the generally nonlinear trends of each station. The statistical significance of each trend is assessed against three null models of the background climate variability, represented by stochastic processes of increasing temporal correlation length. We find strong evidence that more than 50 percent of all stations experienced a significant trend over the last century with respect to all three null models. A spatio-temporal analysis reveals a significant cooling trend in the South-East and significant warming trends in the rest of the contiguous US. It also shows that the warming trend appears to have migrated equatorward. This shows the complex spatio-temporal evolution of climate change at local scales.

Description: [1]  Despite growing interest in the visible light absorbing organic component of atmospheric aerosols, referred to as “brown” carbon, our knowledge of its chemical composition remains limited. It is well accepted that biomass burning is one important source of “brown” carbon in the atmosphere. In this study, cloud water samples heavily affected by biomass burning were collected at Mount Tai (1534 m, ASL), located in Shandong province in the North China Plain in summer 2008. The samples were analyzed with high performance liquid chromatography equipped with a UV/Vis absorbance detector immediately followed by electrospray ionization and analysis using a time-of-flight (ToF) mass spectrometer. The high mass resolution and accuracy provided by the ToF mass spectrometer allows determination of the elemental composition of detected ions. Using this approach the elemental compositions of 16 major light absorbing compounds, which together accounted for approximately half of measured sample absorption between 300 and 400 nm, were determined. The most important classes of light absorbing compounds were found to be nitrophenols and aromatic carbonyls. Light absorption over this wavelength range by reduced nitrogen compounds was insignificant in these samples.

Description: [1]  Remote sensing techniques offer the unique possibility to continuously and automatically monitor the atmospheric state from ground and space. Ground based microwave radiometers (MWRs), for example, are frequently used for temperature and humidity profiling of the lower troposphere. In order to improve the profiles in the middle and upper troposphere, further information is needed. In this respect, satellite measurements are expected to be very useful. In this study, the synergy benefit in temperature and humidity clear-sky profiling using different combinations of state-of-the-art microwave and infrared ground and satellite based instruments is assessed. The synergy benefit is regarded as the information gain in light of ground based MWR observations together with some climatological a priori knowledge. The maximum information content for this kind of synergy is estimated by assuming optimum conditions, e.g., no forward model uncertainties and a horizontal homogeneous atmosphere. For a mid-latitude site, the ground based MWR gives about 4.4 and 2.4 independent pieces of information on the temperature and humidity profile, respectively. For the temperature profile, the combination with IASI and AMSU-A/MHS increases the information by a factor of about 1.8 and 1.5, respectively, with highest benefit in warm and/or humid conditions. The vertical information on humidity is significantly improved by highly spectrally resolved IR observations from ground or space, when the atmosphere is cold and dry; the vertical information is more than tripled. If measurements from AMSU-A/MHS, IASI or SEVIRI are included, retrieval uncertainties in the middle and upper troposphere are significantly reduced by up to 68%.

Description: [1]  Detailed tracing of an exhaust plume from a rocket's initial trajectory is a scientifically and diagnostically useful technique. It can provide detailed information on the atmosphere's mean winds, wind shears, turbulent regime and physical state over a wide altitude range from 50 to 200 km. We analyze Soyuz rocket exhaust plumes from Plesetsk on 21 May 2009 and 27 June 2011, which uncovered significantly different atmospheric states and underlying dynamics. The first case showed highly dynamical conditions in the mesosphere, characterized by vortex structures, wind shears and small-scale turbulent eddies. The estimated turbulent energy dissipation rates ranged 330-460 mW kg −1 . A characteristic balloon-shaped trail was observed at altitudes between 105 and 160 km, having rapid expansion rates of 500-800 m s −1 over the time period of 2 min which can be explained by complex gas dynamic processes in the rocket wake involving the collision of shock waves. In the second case, we show evidence that the rocket exhaust trail persisted without any changes during its motion from Plesetsk via Denmark to the UK for 9 hours, indicating extremely stable atmospheric conditions. This case introduces a new state of the summer mesosphere – remarkably quiet conditions, probably never observed before. The rocket plumes studied, related to the initial rocket trajectory, are essentially twilight phenomena as seen from the ground using wideband spectrum cameras, that is the Sun should be below the horizon by 6°. For the first time, we analyze the dynamics of rocket exhaust products at the initial trajectory in the mesosphere and lower thermosphere using detailed photographic imaging taken from the ground.

Description: [1]  Rust and bunt spores that act as ice nuclei could change the formation characteristics and properties of ice-containing clouds. In addition, ice nucleation on rust and bunt spores, followed by precipitation, may be an important removal mechanism of these spores from the atmosphere. Using an optical microscope, we studied the ice nucleation properties of spores from four rust species ( Puccinia graminis , Puccinia triticina , Puccinia allii , Endocronartium harknesssii ) and two bunt species ( Tilletia laevis , Tilletia tritici ) immersed in water droplets. We show that the cumulative number of ice nuclei per spore is 5 × 10 -3 , 0.01 and 0.10 at temperatures of roughly -24 °C, -25 °C and -28 °C, respectively. Using a particle dispersion model, we also investigated if these rust and bunt spores will reach high altitudes in the atmosphere where they can cause heterogeneous freezing. Simulations suggest that after 3 days and during periods of high spore production, between 6-9 % of 15  μ m particles released over agricultural regions in Kansas (U.S.), North Dakota (U.S.), Saskatchewan (Canada) and Manitoba (Canada) can reach at least 6 km in altitude. An altitude of 6 km corresponds to a temperature of roughly -25 °C for the sites chosen. The combined results suggest that (a) ice nucleation by these fungal spores could play a role in the removal of these particles from the atmosphere and (b) ice nucleation by these rust and bunt spores are unlikely to compete with mineral dust on a global and annual scale at an altitude of approximately 6 km.

Description: This article details the influence of zirconium doping on the piezoelectric properties and relaxor characteristics of 94( Bi 1/2 Na 1/2 ) TiO 3 –6 Ba ( Zr x Ti 1− x ) O 3 (BNT–6BZT) bulk ceramics. Neutron diffraction measurements of BNT–6BZT doped with 0%–15% Zr revealed an electric-field-induced transition of the average crystal structure from pseudo-cubic to rhombohedral/tetragonal symmetries across the entire compositional range. The addition of Zr up to 10% stabilizes this transition, resulting in saturated polarization hysteresis loops with a maximum polarization of 40 μC/cm 2 at 5.5 kV/mm, while corresponding strain hysteresis measurements yield a maximum strain of 0.3%. With further Zr addition, the ferroelectric order is progressively destabilized and typical relaxor characteristics such as double peaks in the current density loops are observed. In the strain hysteresis, this destabilization leads to an increase of the maximum strain by 0.05%. These changes to the physical behavior caused by Zr addition are consistent with a reduction of the transition temperature T F-R , above which the field-induced transformation from the relaxor to ferroelectric state becomes reversible.

Description: Precursor glasses for the ferroelectric barium bismuth titanate ( BaBi 4 Ti 4 O 15 ) (BBiT) have been prepared by the melt-quench technique in the SiO 2 – K 2 O – BaO – Bi 2 O 3 – TiO 2 (SKBBT) glass system with and without Eu 2 O 3 doping. BBiT glass–ceramic (GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X-ray diffraction (XRD), electron microscopy (FE-SEM, TEM), and FT-IR reflectance spectroscopy. FE-SEM images show the formation of randomly oriented hexagonal rod-shaped crystals of 200–400 nm and TEM images show 10–20 nm crystallites. FT-IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680 cm −1 . The activation energy of crystallization ( E c ) varies from 295 to 307 kJ/mol. The dielectric constants (ε r ) of glass and GC nanocomposites increase with an increase in frequency up to 3.0 MHz and then decrease up to 5.0 MHz. Heat-treated GCs show higher ε r values, in the range 25–55, compared to the precursor glasses (20–37). Dielectric losses (tan δ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100 Hz to 5.0 MHz. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5 D 0 → 7 F 2 transition. An intense 466 nm excitation band corresponding to the 7 F 0 → 5 D 2 transition was observed. Emission spectra were then recorded by exciting the glass samples at 466 nm. Longer heat-treatment times led to a 15-fold increase in the intensity of the red emission at 612 nm, attributed to the segregation of Eu 3+ ions into the low phonon energy BBiT crystallites. The hardness (3.8–5.1 GPa) and fracture toughness (1.8–3.5 MPam 0.5 ) values obtained in the GCs are high and suitable for structural applications.

Description: Carbon doping is known to be very effective for enhancing the high-field properties of magnesium diboride, MgB 2 , but not for the low-field properties. Here, we report that both the high- and the low-field properties can be improved simultaneously without doping by increasing the initial magnesium partial pressure, by simply reducing the size of the magnesium particles. It is shown that in situ processed bulk MgB 2 sintered with fine magnesium powders has superior superconducting properties compared with a bulk sample fabricated using coarse magnesium lumps. The change in the lattice parameters was almost negligible; however, a clear increase in lattice strain can be observed for the sample sintered with fine magnesium powders. The increase in the lattice strain results in an enhancement of the high-field properties. Furthermore, it has also been found that the low-field critical current density is not reduced, but rather slightly increased for the fine magnesium powder sample. This is due to a closer linkage among the grains that drastically improves grain connectivity. These findings demonstrate that the initial growth mechanism of MgB 2 is very crucial for its superior superconducting properties, and it especially indicates the importance of magnesium vapor pressure.

Description: Revisiting classic phase diagrams and chemical phase relations in the solid state of a very well-studied oxide system, such as the lithium aluminosilicate (LAS) system, can open a new window for the design of new advanced materials with improved properties. Crystal chemistry and phase equilibria are used to demonstrate the ability to design materials with particular desired properties in the alumina-rich corner of the LAS phase diagram. The experimental results demonstrate the alumina and β-eucryptite solid-state compatibility.

Description: This work reports the crystallization, microstructure, and surface composition of Cu In 0.7 Ga 0.3 Se 2 (CIGS) thin films grown by femtosecond pulsed laser deposition at different annealing temperatures. The structural and optical properties of the CIGS films were characterized by X-ray diffraction, Raman scattering, UV-visible spectroscopy, and Hall effect measurement. The results indicate that binary crystals of CuS e initially formed on the as-deposited film, but then completely turned into a quaternary chalcopyrite structure after annealing at 400°C. Phase transformation significantly affects the surface morphology, Hall properties, and band gap. Transmission electron microscopy further revealed that an interface between the Mo substrate and CIGS crystallites contains an amorphous layer even at the high temperature of 500°C. For the application of photovoltaic devices, we also report on the photoresponse of both as-deposited and annealed films as demonstrated by preliminary tests.

Description: Reactive sintering of 3 Ti : Sn :2 C and 3Ti:Sn:2C:0.6Fe powder mixtures is studied in the temperature range 510°C–1200°C under argon. It is demonstrated that the recently discovered Ti 3 SnC 2 phase is formed, provided that Fe is added to a 3 Ti : Sn :2 C reactant mixture within the synthesis conditions used. Using dilatometric and X-Ray diffraction analyses, the formation mechanism of Ti 3 SnC 2 is discussed. Results show that at low temperature (about 510°C), tin is consumed to form Fe x Sn y intermetallics. At high temperature (about 1060°C), tin is newly available to form Ti 3 SnC 2 due to the melting of Fe x Sn y . Then, the intermediate phases, TiC and Ti 2 SnC , and/or Ti 5 Sn 3 , TiC , C , and Ti are dissolved in the ( Fe  +  Sn ) liquid phase and Ti 3 SnC 2 very likely precipitate from the melt. The second part of the study deals with the optimization of the Fe content in the initial 3Ti:Sn:2C reactant powder mixture to synthesize samples with larger Ti 3 SnC 2 content by hot isostatic pressing.

Description: The effects of non-stoichiometry on the microstructure, oxygen vacancies, and piezoelectric properties of ( Na 0.5 K 0.5 ) x NbO 3 (NK x N, where x  =   0.98, 1.00, 1.01, and 1.02) ceramics doped with sintering aid CuTa 2 O 6 (CT) doping were investigated. X-ray diffraction (XRD) patterns indicated that a secondary phase formed in CT-doped NK x N (NK x NCT) ceramics with x  〈   1.00 and that a pure phase was obtained with x  ≥   1.00. The grain size of NK x NCT ceramics increased with increasing x value due to the formation of a liquid phase. The internal bias field, activation energy, and Raman analysis for NK x NCT ceramics showed that the number of induced oxygen vacancies increased with decreasing x value. The high mechanical quality factor ( Q m ) value obtained for NK x NCT ceramics did not correspond to a higher concentration of oxygen vacancies, illustrating that the suitable compensation (excess Na and K ) is more important than the concentration of oxygen vacancies to obtain the ceramics with high Q m values. The NK x NCT ceramics with x  =   1.01 exhibited excellent piezoelectric properties, with k p and Q m values of 39.9% and 2,070, respectively.

Description: Low-temperature sintering of β-spodumene ceramics with low coefficient of thermal expansion (CTE) was attained using Li 2 O – GeO 2 sintering additive. Single-phase β-spodumene ceramics could be synthesized by heat treatment at 1000°C using highly pure and fine amorphous silica, α-alumina, and lithium carbonate powders mixture via the solid-state reaction route. The mixture was calcined at 950°C, finely pulverized, compacted, and finally sintered with or without the sintering additive at 800°C–1400°C for 2 h. The relative density reached 98% for the sample sintered with 3 mass% Li 2 O – GeO 2 additive at 1000°C. Its Young's modulus was 167 GPa and flexural strength was 115 MPa. Its CTE (from R.T. to 800°C) was 0.7 × 10 −6  K −1 and dielectric constant was 6.8 with loss tangent of 0.9% at 5 MHz. These properties were excellent or comparative compared with those previously reported for the samples sintered at around 1300°C–1400°C via melt-quenching routes. As a result, β-spodumene ceramics with single phase and sufficient properties were obtained at about 300°C lower sintering temperature by adding Li 2 O – GeO 2 sintering additive via the conventional solid-state reaction route. These results suggest that β-spodumene ceramics sintered with Li 2 O – GeO 2 sintering additive has a potential use as LTCC for multichip modules.

Description: Pyrochlore-structured lanthanide stannate ceramic ( Ln 2 Sn 2 O 7 ) has been synthesized via a new complex precipitation method. A suite of characterization techniques, including FTIR, Raman, X-ray, and electron diffraction as well as nitrogen sorption were employed to investigate the structural evolution of the synthesized and calcined powder. Raman, XRD, and selected area electron diffraction results confirm the presence of the pyrochlore structure after calcination of the powder above 1200°C. TEM imaging shows fine crystallites gradually increased in size from approximately 100 nm to about 500 nm with higher calcination temperatures. Grain growth and powder densification upon increasing the calcination temperature was confirmed by nitrogen sorption results. This aqueous synthetic method provides a simple pathway for the preparation of homogeneous lanthanide stannate ceramics.

Description: [1]  In this paper we outline a new objective dust source detection method for the central and western Sahara (CWS), based on the automated tracking of individual dust plumes in data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI), available every 15 minutes at ~0.03 o spatial resolution. The method is used to map the origin of summertime dust storms in the CWS for June to August 2004 – 2010. It reveals the sources of these events in unprecedented detail, allowing for the identification of specific, highly active source areas. The study of collocated surface features reveals that many of the dominant sources are likely associated with palaeo-lakes and outwash plains, many in close proximity to the Saharan mountains. Extensive non-source areas are associated with low albedo and elevated terrain, pointing to the mountainous regions of the Sahara. Additionally, sand seas are not identified as important source areas, but their margins sometimes are. The automated tracking method also facilitates analysis of the transport direction of dust plumes from key source regions, and the inference of emission mechanisms. It is found that there are two broad domains within the CWS: one in southwest Algeria and northwest Mali, characterised primarily by transport towards the southwest and very likely dominated by low-level jets embedded in the northeasterly Harmattan winds; and a second in southern Algeria, northwest Niger and northeast Mali where there is no preferred transport direction and a strong potential association between dust events and deep convection, pointing towards cold pool outflows as the likely deflation mechanism.

Description: [1]  The Role of aerosols effect on two tropical cyclones over Bay of Bengal are investigated using a convection permitting model with two-moment mixed-phase bulk cloud microphysics scheme. The simulation results show the role of aerosol on the microphysical and dynamical properties of the cloud and bring out the change in efficiency of the clouds in producing precipitation. The tracks of the TCs are hardly affected by the changing aerosol concentrations, but the intensity exhibits significant sensitivity due to the change in aerosol concentration. It is also clearly seen from the analyses that higher heating in the middle troposphere within the cyclone center is in [2]  response to latent heat release as a consequence of greater graupel formation. Greater heating in the middle level is particularly noticeable for the clean aerosol regime which causes enhanced divergence in the upper level which, in turn, forces the lower level convergence. As a result, the cleaner aerosol perturbation is more unstable within the cyclone core and produces a more intense cyclone as compared to the other two aerosol perturbations. This study along with previous simulations show the robustness of the concept of TC weakening by storm ingestion of high concentrations of CCN. The consistency of these model results gives us confidence in stating there is a high probability that ingestion of high CCN concentrations in a TC will lead to weakening of the storm but has little impact on storm direction . Moreover, as pollution is increasing over the Indian sub-continent, this study suggests pollution may be weakening TCs over the Bay of Bengal.

Description: [1]  Land surface hydrological modeling is sensitive to near-surface air temperature, which is especially true for the cryosphere. The lapse rate of near-surface air temperature is a critical parameter when interpolating air temperature from station data to gridded cells. To obtain spatially distributed, fine-resolution near-surface (2 m) air temperature in the mainland China, monthly air temperature from 553 Chinese national meteorological stations (with continuous data from 1962 to 2011) are divided into 24 regional groups to analyze spatio-temporal variations of lapse rate in relation to surface air temperature and relative humidity. The results are as follows: (1) Evaluation of estimated lapse rate shows that the estimates are reasonable and useful for temperature-related analyses and modeling studies. (2) Lapse rates generally have a banded spatial distribution from southeast to northwest, with relatively large values on the Tibetan Plateau and in northeast China. The greatest spatial variability is in winter with a range of 0.3–0.9 °C·100 m -1 , accompanied by an inversion phenomenon in the northern Xinjiang Province. In addition, the lapse rates show a clear seasonal cycle. (3) The lapse rates maintain a consistently positive correlation with temperature in all seasons, and these correlations are more prevalent in the north and east. The lapse rates exhibit a negative relationship with relative humidity in all seasons, especially in the east. (4) Substantial regional differences in temporal lapse rate trends over the study period are identified. Increasing lapse rates are more pronounced in northern China, and decreasing trends are found in southwest China, which are more notable in winter. An overall increase of air temperature and regional variation of relative humidity together influenced the change of lapse rate.

Description: [1]  A laboratory investigation of the electric charge separated in collisions between vapor grown ice crystals and a target growing by riming is presented in this work, with the goal of studying the performance of the non–inductive mechanism under microphysical conditions similar to some of those which occur in the stratiform regions of the Mesoscale Convective Systems. A series of experiments was conducted by using a target 2 mm in diameter, for ambient temperatures between −7 °C and −13 °C, effective liquid water content between 0.05 and 0.5 g m -3 and air speeds between 1 and 3 m s -1 . Charge diagrams of the sign of the electric charge transfer on the rimer as a function of the ambient temperature and the effective liquid water content for each velocity are presented. The results show that the riming target charges positive for temperatures above −10 °C. For temperatures below −10 °C the charging is positive for high liquid water content, and negative for low liquid water content. The magnitude of the charge transfer per collision under the studied conditions ranges from 0.01 to 0.2 fC. The implications of these results to the electrification processes are discussed.

Description: [1]  We describe a method to evaluate cloud microphysics simulated with a global cloud resolving model against CloudSat and CALIPSO satellite data. Output from the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) is run through a satellite-sensor simulator (Joint Simulator for satellite sensors), then directly compared to the radar and lidar signals from CloudSat and CALIPSO. The forward approach allows for consistency in cloud microphysical assumption involved in the evaluation. To investigate the dependence of the signals on the temperature, we use temperature extensively as the vertical coordinate. The global statistical analysis of the radar reflectivity shows that the simulation overestimates all the percentiles above –50 °C, and that snow category contributes significantly to low reflectivity values between –80 and –40 °C. The simulated lidar signals have two modes associated with cloud ice and snow categories, though the observations have only one mode. The synergetic use of radar reflectivity and lidar backscatter enables us to determine the relative magnitudes of ice/liquid water contents and effective radii without use of retrievals. The radar-and-lidar diagnosis for cloud tops shows that, due to snow category, NICAM overestimates the mass-equivalent effective radius and underestimates ice water content. Also, the diagnosis was shown to be useful to investigate sensitivities of the parameters of bulk microphysical schemes on the water contents and sizes. The non-spherical scattering of ice particles was shown to affect the above radar-and-lidar diagnosis for large reflectivity ranges, but not to alter most of the other diagnoses for this simulation.

Description: Ceramics have played a crucial role in the development of fission based nuclear power, in glass & glass composite high level wasteforms, in composite cements to encapsulate intermediate level wastes (ILW) and also for oxide nuclear fuels based on UO 2 and PuO 2 /UO 2 mixed oxides. They are also used as porous filters with the ability to absorb radionuclides (RN) from air and liquids and are playing a key role in the cleanup at Fukushima. Non-oxides also find current fission applications including in graphite moderators and B 4 C control rods. Ceramics will continue to be significant in the near-term expansion of nuclear power via next-step developments of fuels with inert matrices or based on thoria and in wasteforms using alternative composite cements or single or multiphase ceramics that can host Pu & other difficult RN. Longer term advances for Generation IV reactors, which will operate at higher temperatures & with higher fuel burn-up require innovative fuel developments potentially via carbides & nitrides or composite fuel systems. Novel non-thermal (cement-like) and thermal techniques are currently being developed to treat some of the difficult legacy wastes. Non-thermally derived wasteforms developed from geopolymers, composite cements, hydroceramics, and phosphate-bonded ceramics and thermally derived wasteforms made by Hot Isostatic Pressing and fluidized bed steam reforming (FBSR) as well as vitrification techniques based on cold crucible melting (CCM), Joule-heater in-container melting and plasma melting (PM) are described. Future developments in waste treatment will be based on separation technologies for partitioning individual RN along with design & construction of RN-containing ceramic targets for inducing transmutation reactions. Near demonstration actinide-hosting ceramic wasteforms including multiphase Synroc systems are described. Opportunities also exist for ceramics in structural applications in Generation IV reactors such as composite SiC / SiC and C / C for fuel cladding and control rods and MAX phases and ultrahigh-temperature ceramics (UHTCs) may find near core fuel coating and cladding applications. Uses of ceramics in fusion reactor systems will be both functional (ceramic superconductors in magnet systems for plasma control and in Li silicate breeder blankets in tokamaks) and structural including as sapphire diagnostic windows, graphite diverters, and plasma facing C and UHTCs. In all these cases, performance is limited by poorly understood radiation damage and interface controlled processes, which demands a combined modeling/experimental approach.

Description: [1]  Tonle Sap Lake is the largest freshwater lake in Southeast Asia. During the post-monsoon season, a small linear cloud system has been observed over this lake in early morning, while the sky above the surrounding land is clear. Although this cloud system is apparently generated by land breezes, previous studies on land–lake (sea) circulation have suggested that environmental factors at low latitudes inhibit development of nocturnal land breezes. In this study, we investigate the mechanism of these early-morning clouds through numerical simulation. The simulations show a linear updraft system over the lake, forming along the southwest lakeshore around 22:00 and moving northeast to the middle of the lake. The heavier air mass from the land meets the extraordinarily warm and humid air mass over the lake, triggering updrafts under the conditionally convective instability. The characteristic high surface water temperature was favorable for generation of the land breeze and updraft systems. That high surface water temperature of the lake is produced by the tropical climate along with efficient energy absorption, because of shallowness of the water body. This unique feature can generate a clear nocturnal land breeze circulation accompanying a migrating updraft system over the lake, despite its low latitude.

Description: [1]  This paper explores the use of a parametric geostatistical model for combining rainfall characteristics derived from raingauge data with the same characteristics derived from remote-sensed data-sets. Hypotheses can then be tested about which predictors significantly increase precision of an estimated characteristic. Although applicable wherever ground-level data and remote-sensed data are to be combined, the statistical procedure set out in the paper is developed for two examples of rainfall characteristics: (i) G , the mean annual rainfall at an ungauged site, conditional on knowledge of two predictor variables T (the mean annual rainfall calculated from the TRMM 3B42 data-set for 1998–2009 ), and C (mean annual rainfall derived from the CMORPH data-set for 2003–2009 ); (ii) the mean annual maximum one-day rainfall H , interpolated using the same modelling procedure with predictor variables T and C derived from annual maximum one-day rainfalls in the same remote-sensed data-sets. Prediction errors showed no bias, skewness of distribution, or spatial heterogeneity. The model's generality means that it could be used with any predictors other than T and C , possibly derived from other satellite data-sets or radar. Provided that predictor variables are correlated with the variable to be predicted, it is not necessary for the model relating them to be fitted using data from identical periods, nor for the grid spacing of T and C to be identical. Model performance was evaluated by using a “leave-one-site-out” procedure, which showed that the RMSE of model predictions at omitted sites was smaller than RMSEs obtained from five other well-known spatial predictors.