Discrimination of water, ice and aerosols by light polarisation in the CLOUD experiment

  • Cloud microphysical processes involving the ice phase in tropospheric clouds are among the major uncertainties in cloud formation, weather and General Circulation Models (GCMs). The simultaneous detection of aerosol particles, liquid droplets, and ice crystals, especially in the small cloud-particle size range below 50 µm, remains challenging in mixed phase, often unstable ice-water phase environments. The Cloud Aerosol Spectrometer with Polarisation (CASPOL) is an airborne instrument that has the ability to detect such small cloud particles and measure their effects on the backscatter polarisation state. Here we operate the versatile Cosmics-Leaving- OUtdoor-Droplets (CLOUD) chamber facility at the European Organisation for Nuclear Research (CERN) to produce controlled mixed phase and other clouds by adiabatic expansions in an ultraclean environment, and use the CASPOL to discriminate between different aerosols, water and ice particles. In this paper, optical property measurements of mixed phase clouds and viscous Secondary Organic Aerosol (SOA) are presented. We report observations of significant liquid – viscous SOA particle polarisation transitions under dry conditions using CASPOL. Cluster analysis techniques were subsequently used to classify different types of particles according to their polarisation ratios during phase transition. A classification map is presented for water droplets, organic aerosol (e.g., SOA and oxalic acid), crystalline substances such as ammonium sulphate, and volcanic ash. Finally, we discuss the benefits and limitations of this classi- fication approach for atmospherically relevant concentration and mixtures with respect to the CLOUD 8–9 campaigns and its potential contribution to Tropical Troposphere Layer (TTL) analysis.

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Author:Leonid Nichman, Claudia Fuchs, Emma Järvinen, Karoliina Ignatius, Niko Florian Höppel, Antonio Dias, Martin HeinritziORCiDGND, Mario SimonORCiD, Jasmin Tröstl, Andrea Christine WagnerGND, Robert WagnerORCiDGND, Christina Williamson, Chao Yan, Federico Bianch, Paul J. Connolly, James Robert Dorsey, Jonathan DuplissyORCiD, Sebastian Ehrhart, Carla Frege, Hamish Gordon, Christopher Robert Hoyle, Thomas Bjerring Kristensen, Gerhard Steiner, Neil McPherson DonahueORCiDGND, Richard C. FlaganORCiD, Martin William Gallagher, Jasper KirkbyORCiD, Ottmar MöhlerORCiDGND, Harald Saathoff, Martin Schnaiter, Frank StratmannORCiDGND, Antonio Tomé
Parent Title (English):Atmospheric chemistry and physics. Discussions
Publisher:European Geosciences Union
Place of publication:Katlenburg-Lindau
Document Type:Article
Date of Publication (online):2016/11/17
Date of first Publication:2015/11/10
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2016/11/17
Page Number:37
First Page:31433
Last Page:31469
© Author(s) 2015. CC Attribution 3.0 License.
Institutes:Geowissenschaften / Geographie / Geowissenschaften
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften
Licence (German):License LogoCreative Commons - Namensnennung 3.0