Articles | Volume 19, issue 20
https://doi.org/10.5194/gmd-19-10185-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Special issue:
https://doi.org/10.5194/gmd-19-10185-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Model description paper
| 
27 Oct 2026
Model description paper |
| 27 Oct 2026
| 27 Oct 2026
Stochastic homogeneous freezing of supercooled droplets in mixed-phase clouds in particle-based idealised microphysics framework (exemplified with PySDM v3.0)
Tim Lüttmer
CORRESPONDING AUTHOR
Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany
Sylwester Arabas
Faculty of Physics and Applied Computer Science, AGH University of Krakow, Kraków, Poland
Peter Spichtinger
Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany
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An important mechanism for the appearance of ice particles in the upper troposphere at low temperatures is homogeneous nucleation. This process is commonly described by the
Koop line, predicting the humidity at freezing. However, laboratory measurements suggest that the freezing humidities are above the Koop line, motivating the present study to investigate the influence of different physical parameterizations on the homogeneous freezing with the help of a detailed numerical model.
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Short summary
Homogeneous freezing describes the spontaneous freezing of supercooled droplets, with the probability depending on temperature, droplet size, and elapsed time. Droplets freeze across a range of temperatures rather than all at once, and faster updrafts and larger droplets lead to freezing at warmer temperatures. Once some droplets freeze, the growing ice crystals deplete the surrounding vapour, causing the remaining droplets to evaporate. This affects the number of ice crystals in the cloud.
Homogeneous freezing describes the spontaneous freezing of supercooled droplets, with the...
