Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

Show full item record



Nichman , L , Järvinen , E , Dorsey , J , Connolly , P , Duplissy , J , Fuchs , C , Ignatius , K , Sengupta , K , Stratmann , F , Möhler , O , Schnaiter , M & Gallagher , M 2017 , ' Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment ' , Atmospheric Measurement Techniques , vol. 10 , no. 9 , pp. 3231-3248 .

Title: Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment
Author: Nichman, Leonid; Järvinen, Emma; Dorsey, James; Connolly, Paul; Duplissy, Jonathan; Fuchs, Claudia; Ignatius, Karoliina; Sengupta, Kamalika; Stratmann, Frank; Möhler, Ottmar; Schnaiter, Martin; Gallagher, Martin
Contributor: University of Helsinki, Department of Physics
Date: 2017-09-04
Language: eng
Number of pages: 18
Belongs to series: Atmospheric Measurement Techniques
ISSN: 1867-1381
Abstract: Optical probes are frequently used for the detection of microphysical cloud particle properties such as liquid and ice phase, size and morphology. These properties can eventually influence the angular light scattering properties of cirrus clouds as well as the growth and accretion mechanisms of single cloud particles. In this study we compare four commonly used optical probes to examine their response to small cloud particles of different phase and as-phericity. Cloud simulation experiments were conducted at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at European Organisation for Nuclear Research (CERN). The chamber was operated in a series of multi-step adiabatic expansions to produce growth and sublimation of ice particles at super-and subsaturated ice conditions and for initial temperatures of -30, -40 and -50 degrees C. The experiments were performed for ice cloud formation via homogeneous ice nucleation. We report the optical observations of small ice particles in deep convection and in situ cirrus simulations. Ice crystal asphericity deduced from measurements of spatially resolved single particle light scattering patterns by the Particle Phase Discriminator mark 2 (PPD-2K, Karlsruhe edition) were compared with Cloud and Aerosol Spectrometer with Polarisation (CASPOL) measurements and image roundness captured by the 3View Cloud Particle Imager (3V-CPI). Averaged path light scattering properties of the simulated ice clouds were measured using the Scattering Intensity Measurements for the Optical detectioN of icE (SIMONE) and single particle scattering properties were measured by the CASPOL. We show the ambiguity of several optical measurements in ice fraction determination of homogeneously frozen ice in the case where sublimating quasi-spherical ice particles are present. Moreover, most of the instruments have difficulties of producing reliable ice fraction if small aspherical ice particles are present, and all of the instruments cannot separate perfectly spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R-2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds.
114 Physical sciences

Files in this item

Total number of downloads: Loading...

Files Size Format View
amt_10_3231_2017.pdf 2.931Mb PDF View/Open

This item appears in the following Collection(s)

Show full item record