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Discussion papers
https://doi.org/10.5194/acp-2019-447
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-447
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 16 May 2019

Submitted as: research article | 16 May 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Ice-nucleating particle versus ice crystal number concentration in altocumulus and cirrus embedded in Saharan dust: A closure study

Albert Ansmann1, Rodanthi-Elisavet Mamouri2, Johannes Bühl1, Patric Seifert1, Ronny Engelmann1, Julian Hofer1, Argyro Nisantzi2, James D. Atkinson3,a, Zamin A. Kanji3, Berko Sierau3,b, Mihalis Vrekoussis4,5,6, and Jean Sciare4 Albert Ansmann et al.
  • 1Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 2Cyprus University of Technology, Dep. of Civil Engineering and Geomatics, Limassol, Cyprus
  • 3Institute for Atmospheric and Climate Science, ETH Zürich, Zurich, Switzerland
  • 4Energy, Environment and Water Research Center, The Cyprus Institute, Nicosia, Cyprus
  • 5Institute of Environmental Physics and Remote Sensing, University of Bremen, Bremen, Germany
  • 6Center of Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany
  • anow at: Ethical Power, Exeter, UK
  • bnow at: Notime, Zurich, Switzerland

Abstract. For the first time, a closure study of the relationship between ice-nucleating particle concentration (INPC) and ice crystal number concentration (ICNC) in altocumulus and cirrus layers, solely based on ground-based active remote sensing, is presented. Such aerosol-cloud closure experiments are required (a) to better understand aerosol-cloud interaction in the case of mixed-phase clouds, (b) to explore to what extend heterogeneous ice nucleation can contribute to cirrus formation which is usually controlled by homogeneous freezing, and (c) to check the usefulness of available INPC parameterization schemes, applied to lidar profiles of aerosol optical and microphysical properties up to tropopause level. The INPC-vs-ICNC closure studies were conducted in Cyprus (Limassol and Nicosia) during a six-week field campaign in March–April 2015 and during the 17-month CyCARE (Cyprus Clouds Aerosol and Rain Experiment) campaign. Focus is on altocumulus and cirrus layers which developed in pronounced Saharan dust layers at heights from 5–11 km. Cloud top temperatures ranged from −20 °C to −57 °C. INPC was estimated from polarization/Raman lidar observations in combination with published INPC parameterization schemes for immersion and deposition nucleation. ICNC was estimated from combined Doppler lidar, aerosol lidar, and cloud radar observations of the terminal velocity of falling ice crystals, radar reflectivity and lidar backscatter in combination with modeling of backscattering at 532 nm and 8.5 mm wavelength. Good to acceptable agreement between INPC (observed before and after the occurrence of the cloud layer under investigation) and ICNC values was found in three proof-of-concept closure experiments. In these case studies, INPC and ICNC values matched within an order of magnitude (i.e., within the uncertainty ranges of the INPC and ICNC estimates), and ranged from 0.1–10 per liter in the altocumulus layers and 1–50 per liter in the cirrus layers observed between 8–11 km height.

Albert Ansmann et al.
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Short summary
For the first time, a closure study of the relationship between ice-nucleating particle concentration (INPC) and ice crystal number concentration (ICNC) in altocumulus and cirrus layers, solely based on ground-based active remote sensing, is presented. The closure studies were conducted in Cyprus. Focus was on altocumulus and cirrus layers which developed in pronounced Saharan dust layers. The closure studies show that heterogeneous ice nucleation can play a dominant role in ice formation.
For the first time, a closure study of the relationship between ice-nucleating particle...
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