The thin border between cloud and aerosol: sensitivity of several ground 1 based observation techniques

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Mostra el registre parcial de l'element Calbó Angrill, Josep Long, Charles N. González Gutiérrez, Josep Abel Augustine, John McComiskey, Allison 2017-11-01
dc.identifier.issn 0169-8095
dc.description.abstract Cloud and aerosol are two manifestations of what it is essentially the same physical phenomenon: a suspension of particles in the air. The differences between the two come from the different composition (e.g., much higher amount of condensed water in particles constituting a cloud) and/or particle size, and also from the different number of such particles (10–10,000 particles per cubic centimeter depending on conditions). However, there exist situations in which the distinction is far from obvious, and even when broken or scattered clouds are present in the sky, the borders between cloud/not cloud are not always well defined, a transition area that has been coined as the “twilight zone”. The current paper presents a discussion on the definition of cloud and aerosol, the need for distinguishing or for considering the continuum between the two, and suggests a quantification of the importance and frequency of such ambiguous situations, founded on several ground-based observing techniques. Specifically, sensitivity analyses are applied on sky camera images and broadband and spectral radiometric measurements taken at Girona (Spain) and Boulder (Co, USA). Results indicate that, at these sites, in more than 5% of the daytime hours the sky may be considered cloudless (but containing aerosols) or cloudy (with some kind of optically thin clouds) depending on the observing system and the thresholds applied. Similarly, at least 10% of the time the extension of scattered or broken clouds into clear areas is problematic to establish, and depends on where the limit is put between cloud and aerosol. These findings are relevant to both technical approaches for cloud screening and sky cover categorization algorithms and radiative transfer studies, given the different effect of clouds and aerosols (and the different treatment in models) on the Earth's radiation balance
dc.description.sponsorship This research is developed within the framework of the project NUBESOL (CGL2014-55976-R) which is funded by the Spanish Ministry of Economy and Competitiveness. The work was mostly carried out while the first author was enjoying a research stay at NOAA-ESRL-GMD, which was partly funded by the Spanish Ministry of Education, Culture and Sports, through grant PRX16/00161. Many people from the Global Radiation Group at NOAA-ESRL GMD assisted in this research by providing data, software, and in particular, expertise and educated insight
dc.format.mimetype application/pdf
dc.language.iso eng
dc.publisher Elsevier
dc.relation MINECO/PE 2015-2017/CGL2014-55976-R
dc.relation.isformatof Reproducció digital del document publicat a:
dc.relation.ispartof © Atmospheric Research, 2017, vol. 196, p. 248-260
dc.relation.ispartofseries Articles publicats (D-F)
dc.rights Tots els drets reservats
dc.subject Núvols
dc.subject Clouds
dc.subject Radiació terrestre
dc.subject Terrestrial radiation
dc.subject Aerosols atmosfèrics
dc.subject Atmospheric aerosols
dc.title The thin border between cloud and aerosol: sensitivity of several ground 1 based observation techniques
dc.type info:eu-repo/semantics/article
dc.rights.accessRights info:eu-repo/semantics/embargoedAccess
dc.embargo.lift 2019-07-28T07:20:44Z
dc.embargo.terms 24 mesos info:eu-repo/date/embargoEnd/2019-11-01
dc.type.version info:eu-repo/semantics/acceptedVersion
dc.contributor.funder Ministerio de Economía y Competitividad (Espanya)

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