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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Aug 2018

Research article | 02 Aug 2018

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This discussion paper is a preprint. A revision of the manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP).

The impact of mineral dust on cloud formation during the Saharan dust event in April 2014 over Europe

Michael Weger1, Bernd Heinold1, Ina Tegen1, Christa Engler2,a, Patric Seifert1, Holger Baars1, Fabian Senf1, Corinna Hoose3, Romy Ullrich3, Axel Seifert4, Ulrich Blahak4, Martina Krämer5, Ulrich Schumann6, Christiane Voigt6,7, and Stephan Borrmann7,8 Michael Weger et al.
  • 1Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 2Leipzig Institute for Meteorology, University of Leipzig, Leipzig, Germany
  • 3Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 4Deutscher Wetterdienst, Offenbach, Germany
  • 5Forschungszentrum Jülich, Jülich, Germany
  • 6Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 7Johannes Gutenberg-Universität, Mainz, Germany
  • 8Max-Planck-Institut für Chemie, Mainz, Germany
  • aformerly at: Leibniz Institute for Tropospheric Research, Leipzig, Germany

Abstract. A regional modeling study on the impact of desert dust on cloud formation is presented for a major Saharan dust outbreak over Europe from 2 April to 5 April 2014. The dust event coincided with an extensive and dense cirrus cloud layer, suggesting an influence of dust on atmospheric ice nucleation. Using interactive simulation with the regional dust model COSMO-MUSCAT, we investigate cloud and precipitation representation in the model and test the sensitivity of cloud parameters to dust-cloud and dust-radiation interactions of the simulated dust plume. We evaluate model results with ground-based and space-borne remote sensings of aerosol and cloud properties, as well as the in situ measurements obtained during the ML-CIRRUS aircraft campaign. A run of the model with single-moment bulk microphysics without online dust feedback considerably underestimated cirrus cloud cover over Germany in the comparison with infrared satellite imagery. This was also reflected in simulated upper-tropospheric ice water content (IWC), which accounted only for 20% of the observed values. The interactive dust simulation with COSMO-MUSCAT, including a two-moment bulk microphysics scheme and dust-cloud as well as dust-radiation feedback, in contrast, led to significant improvements. The modeled cirrus cloud cover and IWC were by at least a factor of two higher in the relevant altitudes compared to the non-interactive model run. We attributed these improvements mainly to enhanced deposition freezing in response to the high mineral dust concentrations. This was corroborated further in a significant decrease in ice particle radii towards more realistic values, as compared to in situ measurements from the ML-CIRRUS aircraft campaign. By testing different empirical ice nucleation parameterizations, we further demonstrate that remaining uncertainties in the ice nucleating properties of mineral dust affect the model performance at least as significantly as to whether including the online representation of the mineral distribution. Dust-radiation interactions played a secondary role for cirrus cloud formation, but contributed to a more realistic representation of precipitation by suppressing moist convection in southern Germany. In addition, a too low specific humidity in the 7 to 10km altitude range in the boundary conditions was identified as a main reason of misrepresentation of cirrus clouds in this model study.

Michael Weger et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Michael Weger et al.
Michael Weger et al.
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Short summary
The impact of desert dust on cloud formation is investigated for a major Saharan dust event over Europe by interactive regional dust modeling. Dust particles are very efficient ice nucelating particles promoting the formation of ice crystals in clouds. The simulations show, that the observed extensive cirrus development was likely related to the above-averge dust load. The interactive dust-cloud feedback in the model significantly improves the agreement with aircraft and satellite observations.
The impact of desert dust on cloud formation is investigated for a major Saharan dust event over...