41 research outputs found
The efficacy of aerosolâcloud radiative perturbations from near-surface emissions in deep open-cell stratocumuli
Aerosolâcloud radiative effects are determined and quantified in simulations
of deep open-cell stratocumuli observed during the VAMOS Ocean-Cloud-Atmosphere-Land
Study Regional Experiment (VOCALS-REx) campaign off
the west coast of Chile. The cloud deck forms in a boundary
layer 1.5 km deep, with cell sizes reaching 50 km in diameter. Global databases of ship
tracks suggest that these linear structures are seldom found in boundary
layers this deep. Here, we quantify the changes in cloud radiative properties
to a continuous aerosol point source moving along a fixed emission line
releasing 1017 particles per second. We show that a spatially coherent
cloud perturbation is not evident along the emission line. Yet our model
simulates an increase in domain-mean all-sky albedo of 0.05, corresponding to
a diurnally averaged cloud radiative effect of 20 Wâmâ2, given the
annual mean solar insolation at the VOCALS-REx site. Therefore, marked
changes in cloud radiative properties in precipitating deep open cells may be
driven by anthropogenic near-surface aerosol perturbations, such as those
generated by ships.
Furthermore, we demonstrate that these changes in cloud radiative properties
are masked by the naturally occurring variability within the organised cloud
field. A clear detection and attribution of cloud radiative effects to a
perturbation in aerosol concentrations becomes possible when sub-filtering of
the cloud field is applied, using the spatio-temporal distribution of the
aerosol perturbation. Therefore, this work has implications for the detection
and attribution of effective cloud radiative forcing in marine stratocumuli,
which constitutes one of the major physical uncertainties within the climate
system. Our results suggest that ships may sometimes have a substantial
radiative effect on marine clouds and albedo, even when ship tracks are not
readily visible.</p
Bounding global aerosol radiative forcing of climate change
Aerosols interact with radiation and clouds. Substantial progress made over the past 40 years in observing, understanding, and modeling these processes helped quantify the imbalance in the Earth's radiation budget caused by anthropogenic aerosols, called aerosol radiative forcing, but uncertainties remain large. This review provides a new range of aerosol radiative forcing over the industrial era based on multiple, traceable, and arguable lines of evidence, including modeling approaches, theoretical considerations, and observations. Improved understanding of aerosol absorption and the causes of trends in surface radiative fluxes constrain the forcing from aerosol-radiation interactions. A robust theoretical foundation and convincing evidence constrain the forcing caused by aerosol-driven increases in liquid cloud droplet number concentration. However, the influence of anthropogenic aerosols on cloud liquid water content and cloud fraction is less clear, and the influence on mixed-phase and ice clouds remains poorly constrained. Observed changes in surface temperature and radiative fluxes provide additional constraints. These multiple lines of evidence lead to a 68% confidence interval for the total aerosol effective radiative forcing of -1.6 to -0.6 W mâ2, or -2.0 to -0.4 W mâ2 with a 90% likelihood. Those intervals are of similar width to the last Intergovernmental Panel on Climate Change assessment but shifted toward more negative values. The uncertainty will narrow in the future by continuing to critically combine multiple lines of evidence, especially those addressing industrial-era changes in aerosol sources and aerosol effects on liquid cloud amount and on ice clouds
A model intercomparison of CCN-limited tenuous clouds in the high Arctic
We perform a model intercomparison of summertime high Arctic (â>â80°N) clouds observed during the 2008 Arctic Summer Cloud Ocean Study (ASCOS) campaign, when observed cloud condensation nuclei (CCN) concentrations fell below 1cmâŸÂł. Previous analyses have suggested that at these low CCN concentrations the liquid water content (LWC) and radiative properties of the clouds are determined primarily by the CCN concentrations, conditions that have previously been referred to as the tenuous cloud regime. The intercomparison includes results from three large eddy simulation models (UCLALES-SALSA, COSMO-LES, and MIMICA) and three numerical weather prediction models (COSMO-NWP, WRF, and UM-CASIM). We test the sensitivities of the model results to different treatments of cloud droplet activation, including prescribed cloud droplet number concentrations (CDNCs) and diagnostic CCN activation based on either fixed aerosol concentrations or prognostic aerosol with in-cloud processing.
There remains considerable diversity even in experiments with prescribed CDNCs and prescribed ice crystal number concentrations (ICNC). The sensitivity of mixed-phase Arctic cloud properties to changes in CDNC depends on the representation of the cloud droplet size distribution within each model, which impacts autoconversion rates. Our results therefore suggest that properly estimating aerosolâcloud interactions requires an appropriate treatment of the cloud droplet size distribution within models, as well as in situ observations of hydrometeor size distributions to constrain them.
The results strongly support the hypothesis that the liquid water content of these clouds is CCN limited. For the observed meteorological conditions, the cloud generally did not collapse when the CCN concentration was held constant at the relatively high CCN concentrations measured during the cloudy period, but the cloud thins or collapses as the CCN concentration is reduced. The CCN concentration at which collapse occurs varies substantially between models. Only one model predicts complete dissipation of the cloud due to glaciation, and this occurs only for the largest prescribed ICNC tested in this study. Global and regional models with either prescribed CDNCs or prescribed aerosol concentrations would not reproduce these dissipation events. Additionally, future increases in Arctic aerosol concentrations would be expected to decrease the frequency of occurrence of such cloud dissipation events, with implications for the radiative balance at the surface. Our results also show that cooling of the sea-ice surface following cloud dissipation increases atmospheric stability near the surface, further suppressing cloud formation. Therefore, this suggests that linkages between aerosol and clouds, as well as linkages between clouds, surface temperatures, and atmospheric stability need to be considered for weather and climate predictions in this region
Opportunistic experiments to constrain aerosol effective radiative forcing
Aerosolâcloud interactions (ACIs) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The nonlinearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can be challenging when meteorological variability also drives both aerosol and cloud changes independently. Natural and anthropogenic aerosol perturbations from well-defined sources provide âopportunistic experimentsâ (also known as natural experiments) to investigate ACI in cases where causality may be more confidently inferred. These perturbations cover a wide range of locations and spatiotemporal scales, including point sources such as volcanic eruptions or industrial sources, plumes from biomass burning or forest fires, and tracks from individual ships or shipping corridors. We review the different experimental conditions and conduct a synthesis of the available satellite datasets and field campaigns to place these opportunistic experiments on a common footing, facilitating new insights and a clearer understanding of key uncertainties in aerosol radiative forcing. Cloud albedo perturbations are strongly sensitive to background meteorological conditions. Strong liquid water path increases due to aerosol perturbations are largely ruled out by averaging across experiments. Opportunistic experiments have significantly improved process-level understanding of ACI, but it remains unclear how reliably the relationships found can be scaled to the global level, thus demonstrating a need for deeper investigation in order to improve assessments of aerosol radiative forcing and climate change
Berry Flesh and Skin Ripening Features in Vitis vinifera as Assessed by Transcriptional Profiling
Background
Ripening of fleshy fruit is a complex developmental process involving the differentiation of tissues with separate functions. During grapevine berry ripening important processes contributing to table and wine grape quality take place, some of them flesh- or skin-specific. In this study, transcriptional profiles throughout flesh and skin ripening were followed during two different seasons in a table grape cultivar âMuscat Hamburgâ to determine tissue-specific as well as common developmental programs.
Methodology/Principal Findings
Using an updated GrapeGen Affymetrix GeneChipÂź annotation based on grapevine 12Ăv1 gene predictions, 2188 differentially accumulated transcripts between flesh and skin and 2839 transcripts differentially accumulated throughout ripening in the same manner in both tissues were identified. Transcriptional profiles were dominated by changes at the beginning of veraison which affect both pericarp tissues, although frequently delayed or with lower intensity in the skin than in the flesh. Functional enrichment analysis identified the decay on biosynthetic processes, photosynthesis and transport as a major part of the program delayed in the skin. In addition, a higher number of functional categories, including several related to macromolecule transport and phenylpropanoid and lipid biosynthesis, were over-represented in transcripts accumulated to higher levels in the skin. Functional enrichment also indicated auxin, gibberellins and bHLH transcription factors to take part in the regulation of pre-veraison processes in the pericarp, whereas WRKY and C2H2 family transcription factors seems to more specifically participate in the regulation of skin and flesh ripening, respectively.
Conclusions/Significance
A transcriptomic analysis indicates that a large part of the ripening program is shared by both pericarp tissues despite some components are delayed in the skin. In addition, important tissue differences are present from early stages prior to the ripening onset including tissue-specific regulators. Altogether, these findings provide key elements to understand berry ripening and its differential regulation in flesh and skin.This study was financially supported by GrapeGen Project funded by Genoma España within a collaborative agreement with Genome Canada. The authors also thank The Ministerio de Ciencia e Innovacion for project BIO2008-03892 and a bilateral collaborative grant with Argentina (AR2009-0021). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewe
Opportunistic experiments to constrain aerosol effective radiative forcing
Aerosolâcloud interactions (ACIs) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The nonlinearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can be challenging when meteorological variability also drives both aerosol and cloud changes independently. Natural and anthropogenic aerosol perturbations from well-defined sources provide âopportunistic experimentsâ (also known as natural experiments) to investigate ACI in cases where causality may be more confidently inferred. These perturbations cover a wide range of locations and spatiotemporal scales, including point sources such as volcanic eruptions or industrial sources, plumes from biomass burning or forest fires, and tracks from individual ships or shipping corridors. We review the different experimental conditions and conduct a synthesis of the available satellite datasets and field campaigns to place these opportunistic experiments on a common footing, facilitating new insights and a clearer understanding of key uncertainties in aerosol radiative forcing. Cloud albedo perturbations are strongly sensitive to background meteorological conditions. Strong liquid water path increases due to aerosol perturbations are largely ruled out by averaging across experiments. Opportunistic experiments have significantly improved process-level understanding of ACI, but it remains unclear how reliably the relationships found can be scaled to the global level, thus demonstrating a need for deeper investigation in order to improve assessments of aerosol radiative forcing and climate change
Diffraction-limited gradient-index (GRIN) microlenses with high numerical apertures produced by silver ion exchange in glass: Diffusion modeling and process optimization
Cylindrical and rod gradient-index lenses with numerical apertures of 0.5 are produced by silver ion exchange in a sodium-aluminosilicate glass. Choosing the appropriate glass composition enables the generation of refractive index changes of 0.145 in the glass without coloration in the visible range. Diffraction-limited optical performance of lenses of up to 1.3 mm in thickness or diameter is achieved by ion exchange modeling which comprises the following steps: (1) The concentration-dependent diffusion coefficient of the glass is experimentally determined by the Boltzmann-Matano method, (2) Process control is provided by the measured dopant concentration/refractive index relation and the glass/salt equilibrium dependence, (3) The ion exchange process is optimized by solving the non-linear diffusion equation for two steps under different boundary conditions, (4) Diffraction-limited lenses up to numerical apertures of 0.5 are generated by applying the optimized process parameters to the ion exchange
Diffraction-limited gradient-index lenses with high numerical aperture for applications in laser beam-shaping and medicine
Diffraction-limited focusing lenses with a numerical aperture of 0.52 and diverging lenses with a numerical aperture of 0.62 were fabricated by silver-sodium ion exchange in cylindrical and rod geometry. The silver ion exchange in a sodium-aluminosilicate glass was optimized by the simulation of the diffusion equation for concentration-dependent diffusion coefficients and by direct measurement of the index profile by the refracted -near-field-method. The performance of the lenses was proved by interferometrical measurements of wavefront aberrations. Applications of gradient-index lenses to the fast-axis-collimation (FAC) of high-power lasef diodes and in endoscopic systems are discussed
Microoptical modulators and switches for multimode fiber applications
External modulators and switches for multimode fiber transmission systems are required for a plenty of applications in optical metrology and communication systems. We show that a confocal arrangement of microlens arrays with certain filter elements in the common focal plane of the arrays, which are moved with the help of piezoelectrical actuators, is a very simple and flexible concept to met the needs of a number of very different applications. The focal length, lens pitch and width of the arrays have to be chosen properly. We discuss which optical elements (collimation optics, microlens array, focussing optics) are required for certain applications. We present experiments for an intensity modulator