Articles | Volume 17, issue 19
Atmos. Chem. Phys., 17, 12219–12238, 2017

Special issue: The ACRIDICON-CHUVA campaign to study deep convective clouds...

Special issue: VERDI – Vertical ​Distribution of Ice ​in Arctic Clouds...

Atmos. Chem. Phys., 17, 12219–12238, 2017

Research article 13 Oct 2017

Research article | 13 Oct 2017

Classification of Arctic, midlatitude and tropical clouds in the mixed-phase temperature regime

Anja Costa1, Jessica Meyer1,a, Armin Afchine1, Anna Luebke1,b, Gebhard Günther1, James R. Dorsey2, Martin W. Gallagher2, Andre Ehrlich3, Manfred Wendisch3, Darrel Baumgardner4, Heike Wex5, and Martina Krämer1 Anja Costa et al.
  • 1Forschungszentrum Jülich GmbH, Jülich, Germany
  • 2Centre for Atmospheric Science, University of Manchester, Manchester, UK
  • 3Leipziger Institut für Meteorologie, Universität Leipzig, Germany
  • 4Droplet Measurement Technologies, Longmont, CO 80503, USA
  • 5Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • anow at: Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, Dortmund, Germany
  • bnow at: Atmosphere in the Earth System Department, Max Planck Institute for Meteorology, Hamburg, Germany

Abstract. The degree of glaciation of mixed-phase clouds constitutes one of the largest uncertainties in climate prediction. In order to better understand cloud glaciation, cloud spectrometer observations are presented in this paper, which were made in the mixed-phase temperature regime between 0 and −38 °C (273 to 235 K), where cloud particles can either be frozen or liquid. The extensive data set covers four airborne field campaigns providing a total of 139 000 1 Hz data points (38.6 h within clouds) over Arctic, midlatitude and tropical regions. We develop algorithms, combining the information on number concentration, size and asphericity of the observed cloud particles to classify four cloud types: liquid clouds, clouds in which liquid droplets and ice crystals coexist, fully glaciated clouds after the Wegener–Bergeron–Findeisen process and clouds where secondary ice formation occurred. We quantify the occurrence of these cloud groups depending on the geographical region and temperature and find that liquid clouds dominate our measurements during the Arctic spring, while clouds dominated by the Wegener–Bergeron–Findeisen process are most common in midlatitude spring. The coexistence of liquid water and ice crystals is found over the whole mixed-phase temperature range in tropical convective towers in the dry season. Secondary ice is found at midlatitudes at −5 to −10 °C (268 to 263 K) and at higher altitudes, i.e. lower temperatures in the tropics. The distribution of the cloud types with decreasing temperature is shown to be consistent with the theory of evolution of mixed-phase clouds. With this study, we aim to contribute to a large statistical database on cloud types in the mixed-phase temperature regime.

Short summary
The paper presents 38 h of in situ cloud spectrometer observations of microphysical cloud properties in the Arctic, midlatitudes and tropics. The clouds are classified via particle concentrations, size distributions, and – as a novelty – small particle aspherical fractions. Cloud-type profiles are given for different temperatures and locations. The results confine regions where different cloud transformation processes occurred and emphasise the importance of small particle shape detection.
Final-revised paper