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Additional Global Climate Cooling by Clouds due to Ice Crystal Complexity

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Järvinen Emma, Jourdan Olivier, Neubauer David, Yao Bin, Liu Chao, Andreae Meinrat O., Lohmann Ulrike, Wendisch Manfred, McFarquhar Greg M., Leisner Thomas, Schnaiter Martin,
Project A new parameterization scheme for ice and snow in climate models
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Original article (peer-reviewed)

Journal Atmospheric Chemistry and Physics Discussions
Page(s) 1 - 24
Title of proceedings Atmospheric Chemistry and Physics Discussions
DOI 10.5194/acp-18-15767-2018

Open Access

URL http://doi.org/10.5194/acp-18-15767-2018
Type of Open Access Publisher (Gold Open Access)

Abstract

Ice crystal submicron structures have a large impact on the optical properties of cirrus clouds and conse- quently 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 mea- surements 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 −1.12 W m2 on the top-of-the-atmosphere radiative budget that has not yet been considered.
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