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https://doi.org/10.5194/acp-2020-365
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-365
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  27 Apr 2020

27 Apr 2020

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This preprint is currently under review for the journal ACP.

Cold cloud microphysical process rates in a global chemistry-climate model

Sara Bacer1,a, Sylvia C. Sullivan2, Holger Tost3, Jos Lelieveld1,4, and Andrea Pozzer1,5 Sara Bacer et al.
  • 1Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
  • 2Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 3Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany
  • 4Energy, Environment and Water Research Center, The Cyprus Institute, Nicosia, Cyprus
  • 5International Centre for Theoretical Physics, Trieste, Italy
  • anow at: LEGI, Université Grenoble Alpes, CNRS, Grenoble INP, Grenoble, France

Abstract. Microphysical processes in cold clouds which act as sources or sinks of hydrometeors below 0 °C control the ice crystal number concentrations (ICNCs) and in turn the cloud radiative effects. Estimating the relative importance of the cold cloud microphysical process rates is of fundamental importance to underpin the development of cloud parameterizations for weather, atmospheric chemistry and climate models and compare the output with observations at different temporal resolutions. This study quantifies and investigates the cold cloud microphysical process rates by means of the chemistry-climate model EMAC and defines the hierarchy of sources and sinks of ice crystals. The analysis is carried out both at global and at regional scales. We found that globally the freezing of cloud droplets, along with convective detrainment over tropical land masses, are the dominant sources of ice crystals, while aggregation and accretion act as the largest sinks. In general, all processes are characterised by highly skewed distribution. Moreover, the influence of (a) different ice nucleation parameterizations and (b) a future global warming scenario on the rates has been analysed in two sensitivity studies. In the first, we found that the application of different parameterizations for ice nucleation changed only slightly the hierarchy of ice crystal sources. In the second, all microphysical processes followed an upward shift (in altitude) and an increase by up to 10 % in the upper troposphere towards the end of the 21st century. This increase could have important feedbacks, such as leading to enhanced longwave warming of the uppermost atmosphere.

Sara Bacer et al.

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Latest update: 27 Sep 2020
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Short summary
We investigate the relative importance of the rates of cold cloud microphysical processes which act as sources or sinks of ice crystals (ICs) and control IC number concentration. By means of numerical simulations performed with a global chemistry-climate model, we assess the relevance of these processes at global and regional scales. This estimation is of fundamental importance to assign priority to the development of microphysics parameterizations and compare model output with observations.
We investigate the relative importance of the rates of cold cloud microphysical processes which...
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