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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 21 | Copyright
Atmos. Chem. Phys., 18, 15767-15781, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Nov 2018

Research article | 02 Nov 2018

Additional global climate cooling by clouds due to ice crystal complexity

Emma Järvinen1,a, Olivier Jourdan2, David Neubauer3, Bin Yao4, Chao Liu4, Meinrat O. Andreae5,6, Ulrike Lohmann3, Manfred Wendisch7, Greg M. McFarquhar8,9, Thomas Leisner1, and Martin Schnaiter1 Emma Järvinen et al.
  • 1Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Karlsruhe, Germany
  • 2Laboratoire de Météorologie Physique, Université Clermont Auvergne, OPGC, UMR/CNRS 6016, Clermont-Ferrand, France
  • 3Institute of Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland
  • 4Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing 210044, China
  • 5Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
  • 6Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
  • 7Leipzig Institute for Meteorology, University of Leipzig, Leipzig, Germany
  • 8Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, Norman, OK, USA
  • 9School of Meteorology, University of Oklahoma, Norman, OK, USA
  • anow at: National Center for Atmospheric Research (NCAR), Boulder, CO, USA

Abstract. Ice crystal submicron structures have a large impact on the optical properties of cirrus clouds and consequently on their radiative effect. Although there is growing evidence that atmospheric ice crystals are rarely pristine, direct in situ observations of the degree of ice crystal complexity are largely missing. Here we show a comprehensive in situ data set of ice crystal complexity coupled with measurements of the cloud angular scattering functions collected during a number of observational airborne campaigns at diverse geographical locations. Our results demonstrate that an overwhelming fraction (between 61% and 81%) of atmospheric ice crystals sampled in the different regions contain mesoscopic deformations and, as a consequence, a similar flat and featureless angular scattering function is observed. A comparison between the measurements and a database of optical particle properties showed that severely roughened hexagonal aggregates optimally represent the measurements in the observed angular range. Based on this optical model, a new parameterization of the cloud bulk asymmetry factor was introduced and its effects were tested in a global climate model. The modelling results suggest that, due to ice crystal complexity, ice-containing clouds can induce an additional short-wave cooling effect of −1.12Wm2 on the top-of-the-atmosphere radiative budget that has not yet been considered.

Publications Copernicus
Short summary
Using light diffraction it is possible to detect microscopic features within ice particles that have not yet been fully characterized. Here, this technique was applied in airborne measurements, where it was found that majority of atmospheric ice particles have features that significantly change the way ice particles interact with solar light. The microscopic features make ice-containing clouds more reflective than previously thought, which could have consequences for predicting our climate.
Using light diffraction it is possible to detect microscopic features within ice particles that...