• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 394
  • 94
  • 79
  • 76
  • 73
  • 33
  • 27
  • 15
  • 9
  • 6
  • 3
  • 3
  • 2
  • 2
  • 2
  • Tagged with
  • 960
  • 151
  • 142
  • 95
  • 93
  • 92
  • 92
  • 90
  • 89
  • 85
  • 78
  • 76
  • 74
  • 73
  • 73
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
311

Different approaches for constraining global climate models of the anthropogenic indirect aerosol effect: Different approaches for constraining global climate models of theanthropogenic indirect aerosol effect

Lohmann, Ulrike, Quaas, Johannes, Kinne, Stefan, Feichter, Johann January 2007 (has links)
Strategies to detect and attribute aerosol global impacts on clouds and climate from synergetic approaches involving modeling and observational evidence at different spatial and temporal scales.
312

Evaluating parameterisations of subgrid-scale variability

Quaas, Johannes, Grützun, Verena, Schemann, Vera, Weber, Torsten 26 November 2015 (has links)
Parameterisations of fractional cloudiness in large-scale atmospheric models rely on information about the subgrid-scale variablity of the total water specific humidity, qt , provided in form of a probability density function (PDF). In this contribution, four different approaches to evaluate such total-water PDFs are discussed: (i) Satellite spectroradiometers with high spatial resolution allow to construct at the scale of model grid boxes a histogram, and subsequently to derive the moments of the PDF, of the vertical integral of qt . This can be compared to the same quantity diagnosed from the model parameterisation. Although the vertical integral mostly focuses on the boundary layer, and involves issues in grid-boxes with orographic variability, it allowed nevertheless in the example presented to pinpoint deficiencies of a model parameterisation. (ii) Assuming a simple PDF shape and saturation within clouds, the simple “critical relative humidity” metric can be derived from infrared sounders and/or cloud lidar in combination with reanalysis data with a vertical resolution. It allows to evaluate the underlying PDF of any cloud scheme, but is sensitive to the assumptions. (iii) Supersites with a combination of ground-based lidar, radar and microwave data provide high-resolution high-quality reference data. In a “virtual reality” framework, we showed, however, that it is difficult to evaluate higher moments of a spatial PDF with this temporally-varying data. (iv) From a hierarchy of models from general circulation models to direct numerical simulations, we find that the variance of the qt follows a power-law scaling with an exponent of about -2. This information is very useful to improve the parameterisations.
313

The aerosol indirect effect: parameterization in large-scale models and evaluation with satellite data

Quaas, Johannes 17 November 2003 (has links)
Global climate change is considered to be one of the most serious concerns of humankind (United Nations, 1992; United Nations, 2002). Anthropogenic greenhouse gases and aerosols impact considerably the energy balance of the Earth system, possibly provoking adverse effects on social, ecological, and economical equilibria. This is one of the main reasons why the understanding of the Earth’s climate system is of major importance. If better predictions of the response of the climate system to anthropogenic perturbations were available, political decisions against negative impacts could be taken, and social adaptations to changed climate conditions would be possible.
314

Mobiler Aerosolstandard - Entwicklung eines mobilen Aerosolstandards

Birmili, Wolfram, Tuch, Thomas, Wiedensohler, Alfred, Sonntag, André 16 February 2010 (has links)
Ein mobiler Aerosolstandard für ultrafeine Partikel wurde als neue Möglichkeit zur Qualitätskontrolle für innovative Umweltmessungen in Luftgütemessnetzen entwickelt. Die Bestimmung der Anzahl ultrafeiner Partikel in Ergänzung zur Überwachung von Feinstaub PM10 oder PM2.5 eröffnet neue Möglichkeiten, die Luftqualität zukünftig besser beurteilen zu können. Ultrafeine Partikel sind ein zweckmäßiger Indikator, um z. B. die positive Wirkung einer Umweltzone in Luftreinhalteplänen nachzuweisen.
315

Lagrangeovský disperzní model / Lagrangian dispersion model

Lejdar, Lukáš January 2015 (has links)
In a field of environmental protection there is a very important question about the options to determine impact of different pollution sources on air quality in areas more or less distant from those sources. For those predictions we can use physical or computer modelling. In this paper a computer model (Lagrangian Dispersion Model, or LDM) of air pollution propagation is developed and described. The LDM was created in order to work within the CLMM - Charles University Large-Eddy Microscale Model. In this paper we discuss theory of those models as well as technical solutions used to develop the LDM. The model is validated and subsequently applied on several cases with different degree of geometry complexity. Powered by TCPDF (www.tcpdf.org)
316

DAG- OCH GRÅVATTEN TILLSPOLNING AV TOALETTER- risker och energibesparingar / URBAN RUNOFF AND GREY WATER FOR FLUSHING OF TOILETS- risks and energy savings

Johansson, August, Karlsson, Pontus January 2020 (has links)
Då klimatförändringarna runt om i världen accelererar med torka så behöver man under regnperioder ta tillvara på dag- och gråvatten istället för att släppa ut det i dagvattensystemet. I Örebro, Sverige, finns en byggnad vid namn Citypassagen, som använder sig av ett system som spolar toaletter med uppsamlat regnvatten. Att spara dagvatten och använda som spolvatten är en smart lösning på vattenbrist, det kan dock föra in risker in i byggnaden som skulle kunna smitta människor som befinner sig vid och använder toaletterna. Detta tillsammans med riskerna vid gråvattenanvändning undersöks närmare i den här rapporten, samt att det undersöks om implementering av ett sådant system som använder dag- och gråvattnet för toalettspolning kan vara energieffektivt.Rapporten kommer fram till att det främst är bakterier och patogener som skulle kunna orsaka smitta hos människor vid användning av dessa dag- och gråvattenspolande toaletter, då de kan förekomma som aerosoler medan de andra undersökta områdena inte kan förekomma som aerosoler. Det fastställs även att energibesparing kan göras med ett spolvattensystem som använder sig av regnvatten då reningen inte kommer att bli lika omfattande som vid ett traditionellt reningsverk. Slutsatsen är att risker som legionella pneumophila kan smitta som aerosoler. Andra smittorisker är E-coli, Cryptosporidium och Giardia, patogener som kan återfinnas i gråvatten. Energibesparingar kan främst göras vid reningsprocessen, då samma rigorösa reningsprocess som återfinns i reningsverk inte krävs. / With accelerating climate change bringing droughts around the world, the necessity to use urban runoff and grey water as a resource grows. In Örebro, Sweden, there is a building called Citypassagen, which uses a system of collected rainwater for flushing of toilets. To use urban runoff for toilet flushing is a smart solution to shortage of water availability, though it can also mean the exposure of health risks to people who use the toilets. These risks, accompanied by the risks of grey water usage, are examined in this report, and also if the implementation of a system that uses urban runoff and grey water for toilet flushing can be viewed as a means to energy savings.This report finds that bacteria and pathogens are the primary source of potential infection when using urban runoff or grey water flushing toilets, because of their ability to occur as aerosols, unlike the other examined risks. It is also established that energy savings can be made with a flushing system that uses rainwater, because the purification process is not as extensive compared to the process used in a traditional treatment plant. The conclusion is that risks such as legionella pneumophila can infect as an aerosol. Other risks of infection are E-coli, Cryptosporidium and Giardia, pathogens that can be traced in grey water. Energy savings can primarily be achieved in the purification process, because the same rigorous process used in traditional treatment plants is not necessary.
317

Studium velikostně rozlišeného atmosférického aerosolu pomocí kaskádních impaktorů / Study of size-resolved atmospheric aerosol using cascade impactors

Kozáková, Jana January 2018 (has links)
This dissertation includes two main research projects: 1) the investigation of the intermodal fraction and 2) the influence of regional air pollution transport on Ostrava. Introduction and aim of the first project. Fine and coarse particulate matter (PM) of atmospheric aerosol are considered as separate pollutants and overlap in the particle size range of about 1 - 2.5 μm (aerodynamic diameter dae; PM1-2.5) which represents the intermodal fraction. Sources of both fine and coarse fractions contribute to PM1-2.5 to different extents due to changing meteorological and spatial conditions. Therefore, there is an ongoing discussion as to whether PM1 should be included for monitoring as an additional fine particulate pollutant by the ambient air quality standard. The intrusion of the one fraction to the other one can lead to some inaccuracies in the source apportionment, epidemiological and exposure studies. The aim of the first project was to examine the associations between PM1-2.5 and the coarse (PM2.5-10 or PM>2.5)/fine (PM1) fraction under different meteorological conditions at various sites in the Czech Republic during winter and summer seasons. Introduction and aim of the second project. The EU air quality standards have been frequently exceeded in one of the European air pollution hot spots:...
318

Optische Eigenschaften von Wüstenaerosol

Wenzel, Karin, Schienbein, Sigurd, Posse, Peter, Hoyningen-Huene, Wolfgang von 01 November 2016 (has links)
Durch Messungen von spektraler optischer Dicke, Sonnenaureole und Himmelshelligkeit in Kombination mit den Programmen CIRATRA und BILANZ werden die optischen Eigenschaften von Sahara-Wüstenaerosol und dessen klimatische Wirkung unter Berücksichtigung der Nichtsphärizität der Aerosolpartikel untersucht. / By combining measurements of spectral optical thickness, solar aureole and sky brightness with the programs CIRATRA and BILANZ the optical porperties of Saharan desert aerosol and its climatic effects are investigated, including a consideration of the Nonsphericity of the aerosol particles.
319

Spektraler Extinktionsgang und Größenverteilung des Pinatubo-Aerosols

Hoyningen-Huene, Wolfgang von, Posse, Peter 08 November 2016 (has links)
Spektralradiometermessungen (spektrale optische Dicke und Himmelshelligkeitsfunktion) unter Hochgebirgsbedingungen (Zugspitze, 2965 m) wurden zur Bestimmung der klirnarelevanten Aerosolparameter des stratosphärischen Vulkanaerosols (speziell des Pinatubo) verwendet. Die erhaltenen klirnarelevanten Aerosolparameter aus den Meßkampagnen werden mit Angaben der Aerosolklimatologien verglichen und zur Abschätzung des kurzwelligen Strahlungsforcings durch das Pinatubo-Aerosol verwendet. / Spectral radiometer measurements (spectral optical thickness and sky brightness function) under high mountain conditions (Zugspitze, 2965 m) have been used for the determination of climate-relevant aerosol parameters of the stratospheric volcanic aerosol (columnar size distribution, refractive index, phase function and asymmetry parameter - especially of the aerosol of the Pinatubo volcano eruption in 1991). The climate-relevant aerosol parameters of the measurement campaigns and their temporal change have been compared with data of the aerosol climatologies and have been used for the estimation of the short wave radiative forcing of the Pinatubo event.
320

Lässt sich die Aerosolbelastung von Stadtgebieten aus Satellitenbildern ableiten?

Schmidt, Christian, Ziemann, Astrid, Schlink, Uwe 26 September 2017 (has links)
The use of contrast reducing Mie scattering for the derivation of aerosol optical thickness (AOT) of the atmosphere is described in this article. With the aid of Differential Texture Analysis (DTA) the contrast between two visual satellite images will be determined and the AOT will be deduced. An assessment of the DTA algorithm with Landsat 5 TM satellite images for the Munich area is presented here. Problems like false AOT values caused by surface albedo changes and uncertainties in pollution loading are discussed, and proposed solutions will also be presented. Two methods for solving these difficulties, the histogram method and the regression method, will be displayed. / Zur Ableitung der Aerosol optischen Dicke (AOT) der Atmosphäre erweist sich die kontrastreduzierende Wirkung der Mie-Streuung an Aerosolpartikeln als nützlich. Zwischen zwei unterschiedlich belasteten visuellen Satellitenbildern wird mit Hilfe der Differentiellen Texturanalyse (DTA) der Kontrastunterschied beider berechnet und daraus die AOT abgeleitet. In dieser Arbeit geht es um die Bewertung des DTA-Algorithmus' anhand von Landsat 5 TM Satellitenbildern vom Großraum München. Im Folgenden werden auch Probleme des DTA-Codes, wie z.B. falsch detektierte AOT auf Grund von Änderungen der Bodenalbedo und zu niedrig ermittelte AOT-Werte bedingt durch Ungereimtheiten der Belastungssituationen der Satellitenbilder, diskutiert und Lösungsvorschläge, u.a. die Histogramm- und Regressionsmethode, präsentiert.

Page generated in 0.0328 seconds