Preprints
https://doi.org/10.5194/acp-2021-728
https://doi.org/10.5194/acp-2021-728

  14 Oct 2021

14 Oct 2021

Review status: this preprint is currently under review for the journal ACP.

Formation of ice particles through nucleation in the mesosphere

Kyoko K. Tanaka1, Ingrid Mann2, and Yuki Kimura3 Kyoko K. Tanaka et al.
  • 1Astronomical Institute, Tohoku University, 6-3, Aza Aoba, Aramaki, Aoba-ku, Sendai, 985-8578, Japan
  • 2Institute of Physics and Techonlogy, Department of Physics and Technology, University of Tromsø
  • 3Institute of Low Temperature Sciences, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo, 060-0819, Japan

Abstract. Observations of polar mesospheric clouds have revealed the presence of solid ice particles in the upper mesosphere at high latitudes; however, their formation mechanism remains uncertain. In this study, we investigated the formation process of ice particles through nucleation from small amounts of water vapor at low temperatures. Previous studies that used classical nucleation theory have shown that amorphous solid water particles can nucleate homogeneously at conditions that are present in the mesosphere. However, the rate predictions for water in classical nucleation theory disagree with experimental measurements by several orders of magnitude. We adopted a semi-phenomenological model for the nucleation process, which corrects the evaluation of the molecular cluster formation energy using the second virial coefficient, which agrees with both experiments and molecular dynamics simulations. To calculate the nucleation process, we applied atmospheric conditions for the temperature, pressure, numerical density of dust grains, and cooling rate. The results indicate that homogeneous water nucleation is extremely unlikely to occur in the mesosphere, while heterogeneous nucleation occurs effectively. Dust grains generated by meteor ablation can serve as nuclei for heterogeneous nucleation. We also showed that the ice can form directly in a crystalline state, rather than an amorphous state.

Kyoko K. Tanaka et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Kyoko K. Tanaka et al.

Kyoko K. Tanaka et al.

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Short summary
We investigated ice particle nucleation with classical nucleation and semi-phenomenological models, in relation to the origin of noctilucent clouds observed in the mesosphere. In previous studies, homogeneous nucleation was suggested to occur. However, we found that homogeneous nucleation is very unlikely to occur in the mesosphere, while heterogeneous nucleation occurs effectively.
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