Mixed-phase clouds are a large source of uncertainty in projections of the Arctic climate. This is partly due to the poor representation of the cloud-ice formation processes. Implementing a parameterization for ice multiplication due to mechanical break-up upon collision of two ice particles in a high resolution model improves cloud-ice phase representation. However, the results are sensitive to poorly constrained microphysical parameters (e.g. ice habit, rimed fraction, autoconversion rate).
Mixed-phase clouds are a large source of uncertainty in projections of the Arctic climate. This...
Review status: this preprint is currently under review for the journal ACP.
Ice multiplication from ice-ice collisions in the high Arctic: sensitivity to ice habit, rimed fraction and the spectral representation of the colliding particles
Georgia Sotiropoulou1,2,Luisa Ickes3,Athanasios Nenes2,4,and Annica M. L. Ekman1Georgia Sotiropoulou et al.Georgia Sotiropoulou1,2,Luisa Ickes3,Athanasios Nenes2,4,and Annica M. L. Ekman1
1Department of Meteorology, Stockholm University & Bolin Center for Climate Research, Stockholm, Sweden
2Laboratory of Atmospheric Processes and their Impacts, School of Architecture, Civil & Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
3Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden
4Institue for Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, Greece
1Department of Meteorology, Stockholm University & Bolin Center for Climate Research, Stockholm, Sweden
2Laboratory of Atmospheric Processes and their Impacts, School of Architecture, Civil & Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
3Department of Space, Earth and Environment, Chalmers University of Technology, Gothenburg, Sweden
4Institue for Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, Greece
Received: 28 Jul 2020 – Accepted for review: 29 Sep 2020 – Discussion started: 02 Oct 2020
Abstract. Atmospheric models often fail to correctly reproduce the microphysical structure of Arctic mixed-phase clouds and underpredict ice water content, even when simulations are constrained by the observed levels of ice nucleating particles. In this study we investigate whether ice multiplication from ice-ice collisions, a process missing in most models, can account for the observed cloud ice in a stratocumulus cloud observed during the Arctic Summer Cloud Study campaign. Our results indicate that including ice-ice collisions can improve the modeled cloud water properties, but the degree of influence depends on other poorly constrained microphysical aspects that include ice habit, rimed fraction and cloud ice-to-snow autoconversion rate. Simulations with dendrites are less sensitive to variations in the assumed rimed fraction of the particle that undergoes break-up, compared to those with planar ice. Activating cloud ice-to-snow autoconversion decreases the sensitivity of the break-up process to both the assumed ice habit and rimed fraction. Finally, adapting a relatively small value for the threshold diameter at which cloud ice is converted to snow enhances break-up efficiency and improves the macrophysical representation of the cloud.
Mixed-phase clouds are a large source of uncertainty in projections of the Arctic climate. This is partly due to the poor representation of the cloud-ice formation processes. Implementing a parameterization for ice multiplication due to mechanical break-up upon collision of two ice particles in a high resolution model improves cloud-ice phase representation. However, the results are sensitive to poorly constrained microphysical parameters (e.g. ice habit, rimed fraction, autoconversion rate).
Mixed-phase clouds are a large source of uncertainty in projections of the Arctic climate. This...