Repurposing weather modification for cloud research showcased by ice crystal growth
Open accessAbstract
The representation of cloud processes in models is one of the largest sources of uncertainty in weather forecast and climate projections. While laboratory settings offer controlled conditions for studying cloud processes, they cannot reproduce the full range of conditions and interactions present in natural cloud systems. To bridge this gap, here we leverage weather modification, specifically glaciogenic cloud seeding, to investigate ice growth rates within natural clouds. Seeding experiments were conducted in supercooled stratus clouds (at −8 to −5∘C) using an uncrewed aerial vehicle, and the created ice crystals were measured 4–10 min downwind by in situ and ground-based remote sensing instrumentation. We observed substantial variability in ice crystal growth rates within natural clouds, attributed to variations in ice crystal number concentrations and in the supersaturation, which is difficult to reproduce in the laboratory and which implies faster precipitation initiation than previously thought. We found that for the experiments conducted at −5.2∘C, the ice crystal populations grew nearly linearly during the time interval from 6 to 10 min. Our results demonstrate that the targeted use of weather modification techniques can be employed for fundamental cloud research (e.g. ice growth processes, aerosol–cloud interactions), helping to advance cloud microphysics parameterizations and to improve weather forecasts and climate projections.
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Although CLOUDLAB's primary goal was not related to the MCT technique, its results are highly relevant for this SRM method.
“Although CLOUDLAB's primary goal was not related to the MCT technique, its results are highly relevant for this SRM method (CORDIS, 2021; Ramelli et al., 2024)”
From Past Field Experiments of Solar Radiation Modification: A Review of the Scientific and Technical Aspects for Governance (2026) · cites this paper as Ramelli et al., 2024
The Materials and methods section says CLOUDLAB used seeding to understand ice formation and growth, rather than to pursue a climate-intervention goal. The Results report seeding-induced depletion of cloud droplets, and the Conclusion mentions climate intervention as another use of weather modification. The paper does not identify MCT or assess how relevant its results are to that specific SRM method. (LLM, conf=0.82)
Experimental — accuracy not yet measuredCLOUDLAB examined the role of the WBF process in modulating cloud glaciation, precipitation formation, and mixed-phase cloud lifetimes.
“Additionally, CLOUDLAB examined the role of the WBF process in modulating cloud glaciation, precipitation formation, and mixed-phase cloud lifetimes (Henneberger et al., 2023; Ramelli et al., 2024)”
From Past Field Experiments of Solar Radiation Modification: A Review of the Scientific and Technical Aspects for Governance (2026) · cites this paper as Ramelli et al., 2024
The Results and Conclusion report that CLOUDLAB observed WBF-related droplet depletion, local glaciation, and growth of precipitation-sized ice particles. The Introduction notes that ice crystals influence cloud lifetime, but this paper does not report an examination of how WBF modulates mixed-phase cloud lifetimes. (LLM, conf=0.86)
Experimental — accuracy not yet measuredThe HOLIMO imager on the TBS resolved ice crystal habits (pristine vs. rimed) and quantified concentrations up to 2,000 L^-1.
“The HOLIMO imager on the TBS resolved ice crystal habits (pristine vs. rimed) and quantified concentrations up to 2,000 L -1 (Fuchs et al., 2025; Henneberger et al., 2023; Ramelli et al., 2024)”
From Past Field Experiments of Solar Radiation Modification: A Review of the Scientific and Technical Aspects for Governance (2026) · cites this paper as Ramelli et al., 2024
The Instrumentation section describes HOLIMO on the tethered HoloBalloon and says its ice-crystal images were classified as pristine or aggregated, not pristine or rimed. The Results section reports HOLIMO-measured ice-crystal concentrations up to 2,000 L−1 during passage of the seeding plume. (LLM, conf=0.91)
Experimental — accuracy not yet measuredCLOUDLAB primarily targeted MCT processes such as ice nucleation dynamics and glaciation in low-altitude supercooled stratus clouds.
“CCT/MCT research remains the least explored, exemplified by the CLOUDLAB project (2022-ongoing), which primarily targeted MCT processes (CORDIS, 2021; Ramelli et al., 2024) such as ice nucleation dynamics and glaciation in low-altitude supercooled stratus clouds (Fuchs et al., 2025; Henneberger et al., 2023).”
From Past Field Experiments of Solar Radiation Modification: A Review of the Scientific and Technical Aspects for Governance (2026) · cites this paper as Ramelli et al., 2024
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Cites
Miller, A. J., Ramelli, F., Fuchs, C., Omanovic, N., Spirig, R., Zhang, H., Lohmann, U., Kanji, Z. A., & Henneberger, J. (2024) · Atmospheric Measurement Techniques · doi:10.5194/amt-17-601-2024 · Cited by 26 · see citing works
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Research works printed but not linked: 13
- [7]Morrison H, et al. 2020. Confronting the challenge of modeling cloud and precipitation microphysics. J Adv Modeling Earth Syst. 12: e2019MS001689. PMC7507216 32999700
- [11]Sazaki G, Zepeda S, Nakatsubo S, Yokomine M, Furukawa Y. 2012. Quasi-liquid layers on ice crystal surfaces are made up of two different phases. Proc Natl Acad Sci U S A. 109: 1052– 1055. 22232653 PMC3268306
- [23]Korolev A, Milbrandt J. 2022. How are mixed-phase clouds mixed? Geophys Res Lett 49: e2022GL099578. PMC9540255 36246738
- [24]Korolev A, Leisner T. 2020. Review of experimental studies of secondary ice production. Atmos Chem Phys. 20: 11767– 11797.
- [25]Hofer S, et al. 2023. Realistic representation of mixed-phase clouds increases future climate warming. PREPRINT (Version 1) available at Research Square.
- [38]French JR, et al. 2018. Precipitation formation from orographic cloud seeding. Proc Natl Acad Sci U S A. 115: 1168– 1173. 29358387 PMC5819430
- [39]Castellano NE, Ávila EE, Bürgesser RE, Saunders CP. 2014. The growth of ice particles in a mixed phase environment based on laboratory observations. Atmos Res. 150: 12– 20.
- [48]Pruppacher HR, Klett JD, Wang PK. 1998. Microphysics of clouds and precipitation. Taylor & Francis.
- [52]Bruintjes RT. 1999. A review of cloud seeding experiments to enhance precipitation and some new prospects. Bull Am Meteorol Soc. 80: 805– 820.
- [53]Flossmann AI, et al. 2019. Review of advances in precipitation enhancement research. Bull Am Meteorol Soc. 100: 1465– 1480.
- [62]Beck A. 2017. Observing the microstructure of orographic clouds with HoloGondel [PhD thesis]. ETH Zurich.
- [65]Ramelli F, et al 2024. Data for the publication “Repurposing weather modification for cloud research showcased by ice crystal growth”. 10.5281/zenodo.13712737. PMC11423147 39323981 · DOI
- [66]Ramelli F, et al. 2024. Software for the publication “Repurposing weather modification for cloud research showcased by ice crystal growth”. 10.5281/zenodo.13715279. PMC11423147 39323981 · DOI
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Quantifying ice crystal growth rates in natural clouds from glaciogenic cloud seeding experiments
Fuchs, C., Ramelli, F., Miller, A. J., Omanovic, N., Spirig, R., Zhang, H., Seifert, P., Ohneiser, K., Lohmann, U., & Henneberger, J. (2025) · Atmospheric Chemistry and Physics · doi:10.5194/acp-25-12177-2025 · Cited by 4 · see citing works
Self-citationHernandez‐Galindo, I., Määttänen, A., Redmond Roche, B. H., Boucher, O., Irvine, P. J., & Moore, J. C. (2026) · Earth's Future · doi:10.1029/2025ef007254 · Cited by 2 · see citing works
“Although CLOUDLAB's primary goal was not related to the MCT technique, its results are highly relevant for this SRM method (CORDIS, 2021; Ramelli et al., 2024).”
Influential
- Authors
- Ramelli, F., Henneberger, J., Fuchs, C., Miller, A. J., Omanovic, N., Spirig, R., Zhang, H., David, R. O., Ohneiser, K., Seifert, P., & Lohmann, U.
- Affiliations
- ETH Zurich (CH)
- University of Oslo (NO)
- Leibniz Institute for Tropospheric Research (DE)
- Corresponding author
- Ramelli, Fabiola
- ORCID
- Venue
- PNAS Nexus
- Publisher
- Oxford University Press (OUP)
- Published
- 2024-09
- Volume
- 3
- Issue
- 9
- Pages
- pgae402-pgae402
- ISSN
- 2752-6542 (ISSN-L)
- PMC
- PMC11423147
- OpenAlex
- W4402595900
- Cited by
- 12
- References
- 1
- Citations by year
- 2026: 6 · 2025: 4 · 2024: 2
- FWCI
- 2.12
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- PNAS Nexus (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- Repository for Publications and Research Data (ETH Zurich) (submittedVersion, cc-by)
- ETH Zürich Research Collection
- Funders
- European Research Council (101021272)
- Horizon 2020 (654109)
- German Research Foundation (408027490)
- Horizon Europe (101079385)
- Topics
- Physical Sciences › Environmental Science › Global and Planetary Change › Atmospheric aerosols and clouds
- Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Meteorological Phenomena and Simulations
- Physical Sciences › Environmental Science › Global and Planetary Change › Climate Change and Geoengineering
- Keywords
- weather modification, ice crystal growth, ice crystal number concentration, supersaturation, precipitation initiation, cloud microphysics parameterization, aerosol-cloud interactions
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