What Is Triggering Ice in Mixed‐Phase Clouds: A Process Analysis With ECHAM6.1‐HAM2.3 Using the Factorial Method.
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| Title: | What Is Triggering Ice in Mixed‐Phase Clouds: A Process Analysis With ECHAM6.1‐HAM2.3 Using the Factorial Method. |
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| Authors: | Ickes, L.1,2 (AUTHOR) luisa.ickes@chalmers.se, Neubauer, D.2,3 (AUTHOR), Proske, U.2,4 (AUTHOR), Villanueva, D.2 (AUTHOR), Lohmann, U.2 (AUTHOR) |
| Source: | Journal of Geophysical Research. Atmospheres. 6/16/2026, Vol. 131 Issue 11, p1-19. 19p. |
| Subject Terms: | *Vertical mixing (Earth sciences), *Meteorological precipitation, Ice formation & growth, Atmospheric models, Cloud physics, Ice nuclei, Stratus clouds |
| Abstract: | Mixed‐phase clouds can be found at temperatures between 0 and −38° ${}^{\circ}$C and consist of supercooled cloud droplets and ice crystals. The phase of mixed‐phase clouds is crucial for the radiation budget, which determines the atmosphere's energy balance. The transition of a supercooled cloud to a mixed‐phase or ice cloud is triggered by different processes that form or introduce ice crystals into a supercooled cloud. Once ice crystals are present, they grow at the expense of the cloud droplets due to the Wegener‐Bergeron‐Findeisen process. This causes a partial or complete glaciation of the mixed‐phase cloud. In the global climate model ECHAM6.1‐HAM2.3, three trigger processes introduce initial ice crystals into a supercooled stratiform cloud: heterogeneous freezing, sedimentation of ice crystals from upper cloud layers (in‐cloud seeding or seeder‐feeder process), and vertical transport (vertical diffusion and vertical advection) of ice crystals. The role of these three ice‐triggering processes was investigated by conducting a set of simulations and analyzing them using a statistical framework (factorial method). For that framework, the supercooled liquid fraction of a mixed‐phase cloud was used as an indicator of the microphysical structure and phase of the cloud. It was found that the sedimentation of the ice crystals is crucial for triggering the ice in mixed‐phase stratiform clouds in ECHAM6.1‐HAM2.3. Our results affect the model's sensitivity to freezing parameterizations and variations in aerosol‐cloud interactions. Plain Language Summary: Clouds are made of tiny water droplets or ice crystals, and some clouds—called mixed‐phase clouds—have both. Clouds are important because they affect Earth's climate by influencing how much sunlight is reflected or trapped. But scientists still struggle to understand which mechanisms in these clouds turn water into ice under different meteorological and dynamical conditions. This study used a climate model to test three ways ice might form in this model and the importance of each process: (a) Freezing aided by particles, (b) Falling ice crystals from higher clouds or higher cloud layers (called sedimentation), and (c) Air movements that carry ice crystals up and down (vertical transport). It was shown that sedimentation and vertical transport are important to distribute ice crystals throughout clouds, especially in warmer parts of the mixed‐phase range (above −25° ${}^{\circ}$C). Freezing only becomes important at colder temperatures (below −30° ${}^{\circ}$C). In thicker clouds, ice moves around more, making sedimentation and vertical transport even more important. It is suggested to investigate the matter with other models and complement with observations to derive more conclusions for further model development. Key Points: Sedimentation of ice crystals triggers most of the water‐to‐ice phase transition in warm mixed‐phase clouds (>−25° ${}^{\circ}$C)Freezing is the least important ice‐triggering process in warm mixed‐phase clouds (>−25° ${}^{\circ}$C) with increasing importance for colder cloudsThe factorial analysis is a suitable framework to analyze the effect of ice‐triggering processes and facilitates model intercomparison [ABSTRACT FROM AUTHOR] |
| Copyright of Journal of Geophysical Research. Atmospheres is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
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| Items | – Name: Title Label: Title Group: Ti Data: What Is Triggering Ice in Mixed‐Phase Clouds: A Process Analysis With ECHAM6.1‐HAM2.3 Using the Factorial Method. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Ickes%2C+L%2E%22">Ickes, L.</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<i> luisa.ickes@chalmers.se</i><br /><searchLink fieldCode="AR" term="%22Neubauer%2C+D%2E%22">Neubauer, D.</searchLink><relatesTo>2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Proske%2C+U%2E%22">Proske, U.</searchLink><relatesTo>2,4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Villanueva%2C+D%2E%22">Villanueva, D.</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Lohmann%2C+U%2E%22">Lohmann, U.</searchLink><relatesTo>2</relatesTo> (AUTHOR) – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Atmospheres%22">Journal of Geophysical Research. Atmospheres</searchLink>. 6/16/2026, Vol. 131 Issue 11, p1-19. 19p. – Name: Subject Label: Subject Terms Group: Su Data: *<searchLink fieldCode="DE" term="%22Vertical+mixing+%28Earth+sciences%29%22">Vertical mixing (Earth sciences)</searchLink><br />*<searchLink fieldCode="DE" term="%22Meteorological+precipitation%22">Meteorological precipitation</searchLink><br /><searchLink fieldCode="DE" term="%22Ice+formation+%26+growth%22">Ice formation & growth</searchLink><br /><searchLink fieldCode="DE" term="%22Atmospheric+models%22">Atmospheric models</searchLink><br /><searchLink fieldCode="DE" term="%22Cloud+physics%22">Cloud physics</searchLink><br /><searchLink fieldCode="DE" term="%22Ice+nuclei%22">Ice nuclei</searchLink><br /><searchLink fieldCode="DE" term="%22Stratus+clouds%22">Stratus clouds</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: Mixed‐phase clouds can be found at temperatures between 0 and −38° ${}^{\circ}$C and consist of supercooled cloud droplets and ice crystals. The phase of mixed‐phase clouds is crucial for the radiation budget, which determines the atmosphere's energy balance. The transition of a supercooled cloud to a mixed‐phase or ice cloud is triggered by different processes that form or introduce ice crystals into a supercooled cloud. Once ice crystals are present, they grow at the expense of the cloud droplets due to the Wegener‐Bergeron‐Findeisen process. This causes a partial or complete glaciation of the mixed‐phase cloud. In the global climate model ECHAM6.1‐HAM2.3, three trigger processes introduce initial ice crystals into a supercooled stratiform cloud: heterogeneous freezing, sedimentation of ice crystals from upper cloud layers (in‐cloud seeding or seeder‐feeder process), and vertical transport (vertical diffusion and vertical advection) of ice crystals. The role of these three ice‐triggering processes was investigated by conducting a set of simulations and analyzing them using a statistical framework (factorial method). For that framework, the supercooled liquid fraction of a mixed‐phase cloud was used as an indicator of the microphysical structure and phase of the cloud. It was found that the sedimentation of the ice crystals is crucial for triggering the ice in mixed‐phase stratiform clouds in ECHAM6.1‐HAM2.3. Our results affect the model's sensitivity to freezing parameterizations and variations in aerosol‐cloud interactions. Plain Language Summary: Clouds are made of tiny water droplets or ice crystals, and some clouds—called mixed‐phase clouds—have both. Clouds are important because they affect Earth's climate by influencing how much sunlight is reflected or trapped. But scientists still struggle to understand which mechanisms in these clouds turn water into ice under different meteorological and dynamical conditions. This study used a climate model to test three ways ice might form in this model and the importance of each process: (a) Freezing aided by particles, (b) Falling ice crystals from higher clouds or higher cloud layers (called sedimentation), and (c) Air movements that carry ice crystals up and down (vertical transport). It was shown that sedimentation and vertical transport are important to distribute ice crystals throughout clouds, especially in warmer parts of the mixed‐phase range (above −25° ${}^{\circ}$C). Freezing only becomes important at colder temperatures (below −30° ${}^{\circ}$C). In thicker clouds, ice moves around more, making sedimentation and vertical transport even more important. It is suggested to investigate the matter with other models and complement with observations to derive more conclusions for further model development. Key Points: Sedimentation of ice crystals triggers most of the water‐to‐ice phase transition in warm mixed‐phase clouds (>−25° ${}^{\circ}$C)Freezing is the least important ice‐triggering process in warm mixed‐phase clouds (>−25° ${}^{\circ}$C) with increasing importance for colder cloudsThe factorial analysis is a suitable framework to analyze the effect of ice‐triggering processes and facilitates model intercomparison [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Journal of Geophysical Research. Atmospheres is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1029/2025JD045160 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 19 StartPage: 1 Subjects: – SubjectFull: Vertical mixing (Earth sciences) Type: general – SubjectFull: Meteorological precipitation Type: general – SubjectFull: Ice formation & growth Type: general – SubjectFull: Atmospheric models Type: general – SubjectFull: Cloud physics Type: general – SubjectFull: Ice nuclei Type: general – SubjectFull: Stratus clouds Type: general Titles: – TitleFull: What Is Triggering Ice in Mixed‐Phase Clouds: A Process Analysis With ECHAM6.1‐HAM2.3 Using the Factorial Method. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Ickes, L. – PersonEntity: Name: NameFull: Neubauer, D. – PersonEntity: Name: NameFull: Proske, U. – PersonEntity: Name: NameFull: Villanueva, D. – PersonEntity: Name: NameFull: Lohmann, U. IsPartOfRelationships: – BibEntity: Dates: – D: 16 M: 06 Text: 6/16/2026 Type: published Y: 2026 Identifiers: – Type: issn-print Value: 2169897X Numbering: – Type: volume Value: 131 – Type: issue Value: 11 Titles: – TitleFull: Journal of Geophysical Research. Atmospheres Type: main |
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