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A Turbulence‐Informed Parameterization of Phase Partitioning in Stratiform Mixed‐Phase Clouds for the LMDZ Model.

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Title: A Turbulence‐Informed Parameterization of Phase Partitioning in Stratiform Mixed‐Phase Clouds for the LMDZ Model.
Authors: Raillard, Lea1 (AUTHOR) lea.raillard@lmd.ipsl.fr, Vignon, Étienne1 (AUTHOR), Rivière, Gwendal1 (AUTHOR), Madeleine, Jean‐Baptiste1 (AUTHOR)
Source: Journal of Advances in Modeling Earth Systems. Jun2026, Vol. 18 Issue 6, p1-23. 23p.
Subject Terms: Phase partition, Atmospheric models, Stratus clouds, Supercooled liquids, Ice crystals, Turbulence, Arctic climate
Geographic Terms: Arctic regions
Abstract: High‐latitude clouds, present over the Arctic Ocean, the Southern Ocean and the Antarctic continent, are very often mixed‐phase clouds (MPCs), that is, composed of both supercooled liquid droplets and ice crystals. Despite being essential for the climate of the poles, they remain a major modeling challenge for climate models. In this study, we present a new cloud phase partitioning parameterization developed for the LMDZ atmospheric model. This parameterization is based on the theory of the evolution of supersaturation in a turbulent environment and is inspired by previous theoretical and modeling works. This scheme completely abandons the standard temperature dependent phase partitioning used in the model to predict the amount of supercooled liquid water in clouds as a function of turbulent kinetic energy, resolved vertical velocity and pre‐existing ice crystal properties. This new scheme is evaluated over the Southern Ocean with observation from the MARCUS campaign and results show an improvement in the simulation of the cloud phase spatial variability. The sensitivity to the crystal number concentration, determined by a prescribed concentration of ice nucleating particles, is also assessed. A second evaluation is performed in the Arctic region with observations collected in mid‐level frontal clouds during the RALI‐Thinice campaign and a perturbed parameter ensemble experiment is conducted to assess the parametric sensitivity. The new scheme suppresses the systematic overestimation of liquid far from cloud top and shows the ability to simulate patches and thin layers of supercooled liquid water as commonly observed in polar frontal clouds. Plain Language Summary: Mixed‐phase clouds—containing both ice crystals and supercooled liquid droplets—are widespread in the polar regions and play a major role in the high‐latitude climate. At subzero temperature the coexistence of solid and liquid water depends on a delicate balance between the characteristics of ice crystals (number, shape...) and vertical motions in the atmosphere. This complexity is challenging for climate models which still have difficulty in representing these clouds and especially the correct ratio between water phases, namely supercooled liquid droplets and ice crystals. This study proposes to revise the parameterization of the phase partitioning in the LMDZ atmospheric model, by making the amount of liquid in the clouds dependent on the ice properties and vertical motions. The performance of this new scheme is then assessed by comparing simulations over the Arctic regions with measurements from the RALI‐THINICE airborne campaign on the one hand, and simulations over the Southern Ocean to ship‐based observations from the MARCUS campaign on the other. These simulations show an improvement in the vertical structure of liquid quantity, with a high spatial variability of the liquid patches in the clouds, both vertically and horizontally. Key Points: A cloud phase partitioning parameterization based on supersaturation evolution in a turbulent environment is implemented in the ICOLMDZ GCMThe evaluation, in the Svalbard region and Southern Ocean, shows improvements in content and spatial variability of supercooled liquid waterGeneralized parametric sensitivity is explored and quantified through the realisation of perturbed parameters ensembles [ABSTRACT FROM AUTHOR]
Copyright of Journal of Advances in Modeling Earth Systems 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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  Label: Title
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  Data: A Turbulence‐Informed Parameterization of Phase Partitioning in Stratiform Mixed‐Phase Clouds for the LMDZ Model.
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Advances+in+Modeling+Earth+Systems%22">Journal of Advances in Modeling Earth Systems</searchLink>. Jun2026, Vol. 18 Issue 6, p1-23. 23p.
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  Data: <searchLink fieldCode="DE" term="%22Arctic+regions%22">Arctic regions</searchLink>
– Name: Abstract
  Label: Abstract
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  Data: High‐latitude clouds, present over the Arctic Ocean, the Southern Ocean and the Antarctic continent, are very often mixed‐phase clouds (MPCs), that is, composed of both supercooled liquid droplets and ice crystals. Despite being essential for the climate of the poles, they remain a major modeling challenge for climate models. In this study, we present a new cloud phase partitioning parameterization developed for the LMDZ atmospheric model. This parameterization is based on the theory of the evolution of supersaturation in a turbulent environment and is inspired by previous theoretical and modeling works. This scheme completely abandons the standard temperature dependent phase partitioning used in the model to predict the amount of supercooled liquid water in clouds as a function of turbulent kinetic energy, resolved vertical velocity and pre‐existing ice crystal properties. This new scheme is evaluated over the Southern Ocean with observation from the MARCUS campaign and results show an improvement in the simulation of the cloud phase spatial variability. The sensitivity to the crystal number concentration, determined by a prescribed concentration of ice nucleating particles, is also assessed. A second evaluation is performed in the Arctic region with observations collected in mid‐level frontal clouds during the RALI‐Thinice campaign and a perturbed parameter ensemble experiment is conducted to assess the parametric sensitivity. The new scheme suppresses the systematic overestimation of liquid far from cloud top and shows the ability to simulate patches and thin layers of supercooled liquid water as commonly observed in polar frontal clouds. Plain Language Summary: Mixed‐phase clouds—containing both ice crystals and supercooled liquid droplets—are widespread in the polar regions and play a major role in the high‐latitude climate. At subzero temperature the coexistence of solid and liquid water depends on a delicate balance between the characteristics of ice crystals (number, shape...) and vertical motions in the atmosphere. This complexity is challenging for climate models which still have difficulty in representing these clouds and especially the correct ratio between water phases, namely supercooled liquid droplets and ice crystals. This study proposes to revise the parameterization of the phase partitioning in the LMDZ atmospheric model, by making the amount of liquid in the clouds dependent on the ice properties and vertical motions. The performance of this new scheme is then assessed by comparing simulations over the Arctic regions with measurements from the RALI‐THINICE airborne campaign on the one hand, and simulations over the Southern Ocean to ship‐based observations from the MARCUS campaign on the other. These simulations show an improvement in the vertical structure of liquid quantity, with a high spatial variability of the liquid patches in the clouds, both vertically and horizontally. Key Points: A cloud phase partitioning parameterization based on supersaturation evolution in a turbulent environment is implemented in the ICOLMDZ GCMThe evaluation, in the Svalbard region and Southern Ocean, shows improvements in content and spatial variability of supercooled liquid waterGeneralized parametric sensitivity is explored and quantified through the realisation of perturbed parameters ensembles [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Journal of Advances in Modeling Earth Systems 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:
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    Identifiers:
      – Type: doi
        Value: 10.1029/2025MS005100
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 23
        StartPage: 1
    Subjects:
      – SubjectFull: Phase partition
        Type: general
      – SubjectFull: Atmospheric models
        Type: general
      – SubjectFull: Stratus clouds
        Type: general
      – SubjectFull: Supercooled liquids
        Type: general
      – SubjectFull: Ice crystals
        Type: general
      – SubjectFull: Turbulence
        Type: general
      – SubjectFull: Arctic climate
        Type: general
      – SubjectFull: Arctic regions
        Type: general
    Titles:
      – TitleFull: A Turbulence‐Informed Parameterization of Phase Partitioning in Stratiform Mixed‐Phase Clouds for the LMDZ Model.
        Type: main
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          Name:
            NameFull: Raillard, Lea
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            NameFull: Vignon, Étienne
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            NameFull: Rivière, Gwendal
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            NameFull: Madeleine, Jean‐Baptiste
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          Dates:
            – D: 01
              M: 06
              Text: Jun2026
              Type: published
              Y: 2026
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            – TitleFull: Journal of Advances in Modeling Earth Systems
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