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  • 1
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    Sensitivity of a continental nighttime stratocumulus-topped boundary layer to varying environmental conditions (2016)
    Wiley
    Details
    Publication Date: 2016-07-21
    Description: Large-eddy simulation of a nocturnal stratocumulus-topped boundary layer in a continental mid-latitude environment has been performed to examine the sensitivity of the cloud to a number of different environmental parameters. The simulations showed that the stratocumulus cloud was strongly affected by the presence of an overlying free tropospheric cirrus cloud (FTC), in agreement with previous studies of marine nighttime stratocumulus. When introducing an FTC with an optical thickness of 2, stratocumulus liquid water path decreased by 30%. Enhancing the optical thickness of the FTC to 8 further decreased the liquid water path by almost 10%. The presence of an FTC decreased the cloud-top radiative cooling which decreased the turbulent mixing in the boundary layer so that the liquid water content and cloud depth were reduced. The sensitivity of the stratocumulus cloud to an overlying FTC was found to be affected by the moisture content in the free troposphere. When a clear positive or negative moisture gradient above the inversion was imposed, and an overlying FTC with an optical thickness of 8 was introduced, the stratocumulus cloud LWP decreased by more than 40%. Furthermore, the effect of changes in free tropospheric moisture content and an overlying FTC on the stratocumulus cloud properties was found to be non-linear, the combined response was in general weaker than the two responses added together. The modeled response to changes in cloud condensation nuclei (CCN) concentrations was found to be non-significant, unless the CCN concentrations were so low that drizzle was induced (r 50 cm −3 ).
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 2
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    A safe operating space for humanity (2009)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2009-09-26
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Rockstrom, Johan -- Steffen, Will -- Noone, Kevin -- Persson, Asa -- Chapin, F Stuart 3rd -- Lambin, Eric F -- Lenton, Timothy M -- Scheffer, Marten -- Folke, Carl -- Schellnhuber, Hans Joachim -- Nykvist, Bjorn -- de Wit, Cynthia A -- Hughes, Terry -- van der Leeuw, Sander -- Rodhe, Henning -- Sorlin, Sverker -- Snyder, Peter K -- Costanza, Robert -- Svedin, Uno -- Falkenmark, Malin -- Karlberg, Louise -- Corell, Robert W -- Fabry, Victoria J -- Hansen, James -- Walker, Brian -- Liverman, Diana -- Richardson, Katherine -- Crutzen, Paul -- Foley, Jonathan A -- England -- Nature. 2009 Sep 24;461(7263):472-5. doi: 10.1038/461472a.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Stockholm Resilience Centre, Stockholm University, Kraftriket 2B, 10691 Stockholm, Sweden.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19779433" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biodiversity ; Civilization ; Conservation of Natural Resources/*methods/trends ; *Earth (Planet) ; Ecology/*methods/*trends ; *Ecosystem ; Extinction, Biological ; Fossils ; Green Chemistry Technology/*methods/trends ; Greenhouse Effect ; History, 20th Century ; History, 21st Century ; History, Ancient ; *Human Activities/history ; Humans ; Nitrogen/metabolism ; Phosphorus/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Climate-induced changes in sea salt aerosol number emissions: 1870 to 2100 (2013)
    Wiley
    Details
    Publication Date: 2013-01-04
    Description: [1]  Global climate model output is combined with an emission parameterization to estimate the change in the global and regional sea salt aerosol number emission from 1870 to 2100. Global average results suggest a general increase in sea salt aerosol number emission due to increasing surface wind speed. However, the emission changes are not uniform over the aerosol size spectrum due to an increase in sea surface temperature. From 1870 to 2100 the emission of coarse mode particles (dry diameter D p  〉 655 nm) increase by approximately 10 % (global average), whereas no significant change in the emission of ultrafine mode aerosols (dry diameter D p  〈 76 nm) was found over the same period. Significant regional differences in the number emission trends were also found. Based on CAM-Oslo global climate model output, no straight-forward relationship was found between the change in the number emissions and changes in the sea salt aerosol burden or optical thickness. This is attributed to a change in the simulated residence time of the sea salt aerosol. For the 21st century, a decrease in the residence time leads to a weaker sea salt aerosol-climate feedback that what would be inferred based on changes in number emissions alone. Finally, quantifying any potential impact on marine stratocumulus cloud microphysical and radiative properties due to changes in sea salt aerosol number emissions is likely to be complicated by commensurate changes in anthropogenic aerosol emissions and changes in meteorology.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    In Situ Observations of Cirrus Cloud Microphysical Properties Using the Counterflow Virtual Impactor (1993)
    American Meteorological Society
    Details
    Publication Date: 1993-06-01
    Print ISSN: 0739-0572
    Electronic ISSN: 1520-0426
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 5
    Electronic Resource
    Electronic Resource
    Single Particle Analysis of Aerosols, Observed in the Marine Boundary Layer during the Monterey Area Ship Tracks Experiment (MAST), with Respect to Cloud Droplet Formation (2000)
    Springer
    Journal of atmospheric chemistry 37 (2000), S. 299-329 
    Details
    ISSN: 1573-0662
    Keywords: aerosols ; cloud formation ; microanalysis ; ship tracks ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The chemical composition of individual particles 〉0.2 μm sampled duringthe MAST-experiment wereanalysed by SEM-EDX, in combination with multivariatetechniques. The objective of this experiment was toidentify the mechanisms responsible for themodification of marine stratocumulus clouds byemissions from ships and in a wider sense to provideinformation on the global processes involved inatmospheric modification of cloud albedo. Aerosolswere examined under different MBL pollution levels(clean, intermediately polluted and moderatelypolluted) in five different reservoirs: backgroundbelow-cloud and above-cloud aerosol; background clouddroplet residual particles; below-cloud ship plumeaerosol and ship track cloud droplet residualparticles.In this study a relation was provided between theaerosol emitted from the ship's stack to an effect incloud. Additionally, a large fraction of the ambientaerosol was found to be composed of organic materialor other compounds, consisting of low Z-elements,associated with chlorine. Their number fraction waslargest in clean marine boundary layers, and decreasedwith increasing pollution levels. The fraction of`transformed sea salt' (Na, Cl, S), on the other hand,increased with the pollution level in the MBL. Only20% of the particles fell within the detectable rangeof the analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006416600722
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  • 6
    Electronic Resource
    Electronic Resource
    Computer modelling of clouds at Kleiner Feldberg (1994)
    Springer
    Journal of atmospheric chemistry 19 (1994), S. 189-229 
    Details
    ISSN: 1573-0662
    Keywords: Cloud model ; airflow model ; cloud chemistry ; cloud microphysics ; aerosols ; Henry's Law ; nitric acid ; cloud-water acidity ; turbulence ; mixing ; scavenging ; Kleiner Feldberg ; GCE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The airflow, cloud microphysics and gas- and aqueous-phase chemistry on Kleiner Feldberg have been modelled for the case study of the evening of 1 November 1990, in order to calculate parameters that are not easily measured in the cloud and thus to aid the interpretation of the GCE experimental data-set. An airflow model has been used to produce the updraught over complex terrain for the cloud model, with some care required to ensure realistic modelling of the strong stable stratification of the atmosphere. An extensive set of measurements has been made self-consistent and used to calculate gas and aerosol input parameters for the model. A typical run of the cloud model has calculated a peak supersaturation of 0.55% which occurs about 20 s after entering cloud where the updraught is 0.6 m s−1. This figure has been used to calculate the efficiency with which aerosol particles were scavenged; it is higher than that calculated by other methods, and produces a cloud with slightly too many droplets. A broad cloud droplet size spectrum has been produced by varying the model inputs to simulate turbulent mixing and fluctuations in cloud parameters in space and time, and the ability of mixing processes near cloud-base to produce a lower peak supersaturation is discussed. The scavenging of soluble gases by cloud droplets has been observed and departures from Henry's Law in bulk cloud-water samples seen to be caused by variation of pH across the droplet spectrum and the inability of diffusion to adjust initial distributions of highly soluble substances across the spectrum in the time available. Aqueous-phase chemistry has been found to play a minor role in the cloud as modelled, but circumstances in which these processes would be more important are identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696589
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  • 7
    Electronic Resource
    Electronic Resource
    The Kleiner Feldberg Cloud Experiment 1990. An overview (1994)
    Springer
    Journal of atmospheric chemistry 19 (1994), S. 3-35 
    Details
    ISSN: 1573-0662
    Keywords: orographic clouds ; cloud chemistry and microphysics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract An overview is given of the Kleiner Feldberg cloud experiment performed from 27 October until 13 November 1990. The experiment was carried out by numerous European research groups as a joint effort within the EUROTRAC-GCE project in order to study the interaction of cloud droplets with atmospheric trace constituents. After a description of the observational site and the measurements which were performed, the general cloud formation mechanisms encountered during the experiment are discussed. Special attention is given here to the process of moist adiabatic lifting. Furthermore, an overview is given regarding the pollutant levels in the gas phase, the particulate and the liquid phase, and some major findings are presented with respect to the experimental objectives. Finally, a first comparison attempts to put the results obtained during this campaign into perspective with the previous GCE field campaign in the Po Valley.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696581
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  • 8
    Electronic Resource
    Electronic Resource
    Microphysics of clouds at Kleiner Feldberg (1994)
    Springer
    Journal of atmospheric chemistry 19 (1994), S. 59-85 
    Details
    ISSN: 1573-0662
    Keywords: cloud ; droplet size distribution ; microphysics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract During a field measuring campaign at Kleiner Feldberg (Taunus) in 1990, microphysical characteristics of clouds have been measured by Forward Scattering Spectrometer Probes (FSSP). The aim was to study the influence of aerosol and meteorological factors on droplet size and number. The results are: More mass in the accumulation size range of the aerosol leads to more droplets in stratocumulus clouds and to higher soluble masses in droplets of stratus clouds. However, the aerosol distribution was coarser in the stratus clouds compared to the stratocumulus clouds. Within the first 200 m from cloud base, the droplets grow while their number decreases. The growth results in a stable size of about 14 µm diameter over a large distance from cloud base in many stratocumulus clouds. Two types of mixing processes were observed: processes with reductions in the number of droplets (inhomogeneous mixing) and with reductions in the size of the droplets (homogeneous mixing).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696583
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  • 9
    Electronic Resource
    Electronic Resource
    Phase partitioning of aerosol particles in clouds at Kleiner Feldberg (1994)
    Springer
    Journal of atmospheric chemistry 19 (1994), S. 107-127 
    Details
    ISSN: 1573-0662
    Keywords: Partitioning ; aerosol particles ; cloud ; scavenging ; CVI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The partitioning of aerosol particles between cloud droplets and interstitial air by number and volume was determined both in terms of an integral value and as a function of size for clouds on Mt. Kleiner Feldberg (825 m asl), in the Taunus Mountains north-west of Frankfurt am Main, Germany. Differences in the integral values and the size dependent partitioning between two periods during the campaign were observed. Higher number and volume concentrations of aerosol particles in the accumulation mode were observed during Period II compared to Period I. In Period I on average 87±11% (±one standard deviation) and 73±7% of the accumulation mode volume and number were incorporated into cloud droplets. For Period II the corresponding fractions were 42±6% and 12±2% in one cloud event and 64±4% and 18±2% in another cloud event. The size dependent partitioning as a function of time was studied in Period II and found to have little variation. The major processes influencing the partitioning were found to be nucleation scavenging and entrainment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696585
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  • 10
    Electronic Resource
    Electronic Resource
    The influence of aerosol particle composition on cloud droplet formation (1994)
    Springer
    Journal of atmospheric chemistry 19 (1994), S. 153-171 
    Details
    ISSN: 1573-0662
    Keywords: Partitioning ; sulphur ; elemental carbon ; nucleation scavenging ; single particle analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A difference in partitioning between cloud droplets and interstitial air for two chemical species (elemental carbon and sulphur) with different expected behaviour in nucleation scavenging was observed in clouds at Mt. Kleiner Feldberg (825 m asl), near Frankfurt, Germany. The fraction of sulphur incorporated in cloud droplets was always higher than the fraction of elemental carbon. This difference in partitioning has also been observed in fog but under different pollution conditions in the Po Valley, Italy. Both these studies were based on bulk samples. In the present study at Kleiner Feldberg, impactor samples of the particles in the interstitial air and the cloud droplet residuals were taken and a single particle analysis was done on the samples. It was found that, for a given particle size, the majority of particles forming cloud droplets were soluble and that insoluble particles preferentially remained in the interstitial air.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696587
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