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Volume 16, issue 9 | Copyright

Special issue: ML-CIRRUS – the airborne experiment on natural cirrus...

Atmos. Chem. Phys., 16, 5793-5809, 2016
https://doi.org/10.5194/acp-16-5793-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 May 2016

Research article | 12 May 2016

The origin of midlatitude ice clouds and the resulting influence on their microphysical properties

Anna E. Luebke1, Armin Afchine1, Anja Costa1, Jens-Uwe Grooß1, Jessica Meyer1,a, Christian Rolf1, Nicole Spelten1, Linnea M. Avallone2,b, Darrel Baumgardner3, and Martina Krämer1 Anna E. Luebke et al.
  • 1Forschungszentrum Jülich, Institut für Energie und Klimaforschung (IEK-7), Jülich, Germany
  • 2National Science Foundation, Arlington, Virginia, USA
  • 3Droplet Measurement Technologies, Boulder, Colorado, USA
  • anow at: Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, Unit “Exposure Scenarios”, Dortmund, Germany
  • bformerly at: University of Colorado, Boulder, Colorado, USA

Abstract. The radiative role of ice clouds in the atmosphere is known to be important, but uncertainties remain concerning the magnitude and net effects. However, through measurements of the microphysical properties of cirrus clouds, we can better characterize them, which can ultimately allow for their radiative properties to be more accurately ascertained. Recently, two types of cirrus clouds differing by formation mechanism and microphysical properties have been classified – in situ and liquid origin cirrus. In this study, we present observational evidence to show that two distinct types of cirrus do exist. Airborne, in situ measurements of cloud ice water content (IWC), ice crystal concentration (Nice), and ice crystal size from the 2014 ML-CIRRUS campaign provide cloud samples that have been divided according to their origin type. The key features that set liquid origin cirrus apart from the in situ origin cirrus are higher frequencies of high IWC ( > 100ppmv), higher Nice values, and larger ice crystals. A vertical distribution of Nice shows that the in situ origin cirrus clouds exhibit a median value of around 0.1cm−3, while the liquid origin concentrations are slightly, but notably higher. The median sizes of the crystals contributing the most mass are less than 200µm for in situ origin cirrus, with some of the largest crystals reaching 550µm in size. The liquid origin cirrus, on the other hand, were observed to have median diameters greater than 200µm, and crystals that were up to 750µm. An examination of these characteristics in relation to each other and their relationship to temperature provides strong evidence that these differences arise from the dynamics and conditions in which the ice crystals formed. Additionally, the existence of these two groups in cirrus cloud populations may explain why a bimodal distribution in the IWC-temperature relationship has been observed. We hypothesize that the low IWC mode is the result of in situ origin cirrus and the high IWC mode is the result of liquid origin cirrus.

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Short summary
In this study, we present observational evidence to show that two distinct types of cirrus clouds exist – in situ origin and liquid origin cirrus. These two types differ by their formation mechanism and other properties. Airborne, in-cloud measurements of cloud ice water content (IWC), ice crystal concentration (Nice), and ice crystal size from the 2014 ML-CIRRUS campaign provide cloud samples that have been divided and analyzed according to their origin type.
In this study, we present observational evidence to show that two distinct types of cirrus...
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