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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 17 Sep 2019

Submitted as: research article | 17 Sep 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).

The impact of Secondary Ice Production on Arctic Stratocumulus

Georgia Sotiropoulou1, Sylvia Sullivan2, Julien Savre3, Gary Lloyd4, Thomas Lachlan-Cope5, Annica M. L. Ekman6, and Athanasios Nenes1,7 Georgia Sotiropoulou et al.
  • 1Laboratory of Atmospheric Processes and Their Impacts, School of Architecture, Civil & Environmental Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerland
  • 2Department of Earth and Environmental Engineering, Columbia University, New York, 10027, USA
  • 3Meteorological Institute, Faculty of Physics, Ludwig-Maximilians-University, Munich, Germany
  • 4Centre for Atmospheric Science, University of Manchester, Manchester, M139P, UK
  • 5British Antarctic Survey, Cambridge, CB3 0ET, UK
  • 6Department of Meteorology & Bolin Center for Climate Research, Stockholm University, Stockholm, 11419, Sweden
  • 7Institute of Chemical Engineering Sciences, Foundation for Research and Technology-Hellas, Patras 26504, Greece

Abstract. In-situ measurements of Arctic clouds frequently show that ice crystal number concentrations (ICNCs) are much higher than the available ice-nucleating particles (INPs), suggesting that Secondary Ice Production (SIP) may be active. Here we use a Lagrangian Parcel Model and a Large Eddy Simulation to investigate the impact of three SIP mechanisms (rime-splintering, break-up from ice-ice collisions and droplet-shattering) on a summer Arctic stratocumulus case observed during the Cloud Coupling And Climate Interactions in the Arctic (ACCACIA) campaign. Primary ice alone cannot explain the observed ICNCs, and droplet-shattering is an ineffective SIP mechanism for the conditions considered. Rime-splintering, a mechanism that usually dominates within the studied temperature range, is also weak owing to the lack of large droplets to initiate this process. In contrast, break-up enhances ICNCs by 1–1.5 orders of magnitude, bringing simulations in good agreement with observations. Combining both processes can further explain some of the largest ICNCs observed. The main conclusions of this study show low sensitivity to the assumed INP and Cloud Condensation Nuclei (CCN) conditions. Our results indicate that collisional break-up may be an important ice-multiplication mechanism that is currently not represented in large-scale models. Finally, we also show that a simplified treatment of SIP, using a LPM constrained by a LES and/or observations, provides a realistic yet computationally efficient description of SIP effects that can eventually serve as an efficient way to parameterize this process in large-scale models.

Georgia Sotiropoulou et al.
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Georgia Sotiropoulou et al.
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Publications Copernicus
Short summary
Arctic clouds consist a large source of uncertainty in predictions of the future climate. Observations indicate that the number concentration of cloud ice crystals exceeds the concentration of aerosols that can act as ice nucleating particles (INP). We show that ice multiplication due to mechanical break-up upon collisions between the few primary ice crystals (formed from INP) can explain this discrepancy. Including a description of this process in climate models can improve cloud representation.
Arctic clouds consist a large source of uncertainty in predictions of the future climate....