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dc.contributor.authorAnsmann, A.
dc.contributor.authorTesche, Matthias
dc.contributor.authorSeifert, P.
dc.contributor.authorAlthausen, D.
dc.contributor.authorEngelmann, R.
dc.contributor.authorFruntke, J.
dc.contributor.authorWandinger, U.
dc.contributor.authorMattis, I.
dc.contributor.authorMueller, D.
dc.date.accessioned2013-08-01T09:33:11Z
dc.date.available2013-08-01T09:33:11Z
dc.date.issued2009-09-16
dc.identifier.citationAnsmann , A , Tesche , M , Seifert , P , Althausen , D , Engelmann , R , Fruntke , J , Wandinger , U , Mattis , I & Mueller , D 2009 , ' Evolution of the ice phase in tropical altocumulus : SAMUM lidar observations over Cape Verde ' Journal of Geophysical Research: Atmospheres , vol 114 , D17208 . DOI: 10.1029/2008JD011659
dc.identifier.issn2169-897X
dc.identifier.otherPURE: 1980441
dc.identifier.otherPURE UUID: 7c3968f3-edb3-45bf-8074-696417d38d0b
dc.identifier.otherWOS: 000269756900005
dc.identifier.otherScopus: 72049085025
dc.identifier.urihttp://hdl.handle.net/2299/11261
dc.description.abstractThe formation of the ice phase in tropical altocumulus has been studied with multiwavelength aerosol-cloud Raman lidar, wind Doppler lidar, and radiosonde, providing information on geometrical and optical properties, cloud phase, cloud top temperature, updraft and downdraft velocity, and fall speed of ice crystals. The observations were conducted at Praia (15 degrees N, 23.5 degrees W), Cape Verde, in the tropical North Atlantic in the framework of the Saharan Mineral Dust Experiment (SAMUM) project in January and February 2008. More than 200 different altocumulus layers were analyzed. The coldest liquid cloud had a temperature of -36 degrees C and appeared at a height of 9800 m. Tropical altocumulus is found to be geometrically (262 +/- 137 m) and optically thin (0.69 +/- 0.61), mostly short-lived, and horizontally small with extents of less than 50 km in 80% of the cases. A clear relationship between the occurrence of the ice phase in altocumulus and cloud top temperature is observed, even more clear after the removal of effects of cloud seeding, which is found to be an important process of ice production in lower layers of multilayer altocumulus systems. Because almost all altocumulus layers (99%) showed a liquid cloud top (region in which ice nucleation begins), we conclude that deposition and condensation ice nucleation are unimportant processes during the initial phase of altocumulus glaciation. A pronounced impact of aerosols such as mineral particles known to be favorable ice nuclei is not found in this region with strong dust-smoke outbreaks from Africa. The different phases of an almost complete life cycle of an altocumulus were monitored over 5 hours. The observed processes of droplet and ice formation are discussed based on height-resolved depolarization-ratio (cloud phase) and vertical-velocity time series.en
dc.format.extent20
dc.language.isoeng
dc.relation.ispartofJournal of Geophysical Research: Atmospheres
dc.subjectMULTIPLE-SCATTERING
dc.subjectAIRCRAFT OBSERVATIONS
dc.subjectBACKSCATTER
dc.subjectRAMAN LIDAR
dc.subjectDESERT DUST
dc.subjectEXTINCTION
dc.subjectSAHARAN DUST
dc.subjectTERMINAL VELOCITIES
dc.subjectOROGRAPHIC WAVE CLOUDS
dc.subjectFORMING NUCLEI
dc.titleEvolution of the ice phase in tropical altocumulus : SAMUM lidar observations over Cape Verdeen
dc.contributor.institutionSchool of Physics, Astronomy and Mathematics
dc.contributor.institutionScience & Technology Research Institute
dc.contributor.institutionCentre for Atmospheric and Climate Physics Research
dc.description.statusPeer reviewed
dc.relation.schoolSchool of Physics, Astronomy and Mathematics
rioxxterms.versionofrecordhttps://doi.org/10.1029/2008JD011659
rioxxterms.typeJournal Article/Review
herts.preservation.rarelyaccessedtrue
herts.rights.accesstyperestrictedAccess


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