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https://doi.org/10.5194/egusphere-2025-3876
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-3876
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
19 Aug 2025
| 19 Aug 2025
The Arctic Low-Level Mixed-Phase Haze Regime and its Microphysical Differences to Mixed-Phase Clouds
Abstract. A comprehensive in-situ dataset of low-level Arctic clouds was collected in the Fram Strait during the HALO-(AC)3 campaign in spring 2022 using the research aircraft Polar 6. The clouds observed at altitudes below 1000 m were frequently in a mixed-phase state. We demonstrate that despite comparable optical properties, classic mixed-phase clouds (MPC) and mixed-phase haze (MPH) can be distinguished on the basis of their microphysical properties. While the thermodynamic phases of the particles within the MPH are similar to those in the MPC, the supercooled droplets observed in MPC are replaced by large (> 3 µm) wet aerosol particles in MPH. Furthermore, the particle number concentration measured in MPH is reduced by approximately 3 orders of magnitude compared to MPC. MPH is observed in subsaturated air with respect to water, suggesting that the small liquid particles are haze droplets and are in equilibrium below the activation threshold to form cloud droplets. Chemical analysis suggested that the haze particles contained significant amounts of sea salt. Additional in-situ measurements with an optical particle counter indicated that their number concentration was two times larger over the sea ice compared to the open ocean. Furthermore, measurements of the vertical distribution of the thermodynamic phases in low-level Arctic clouds revealed a characteristic structure, with a liquid regime frequently occurring at the top of the atmospheric boundary layer, followed by MPCs, and an MPH layer below.
The findings from this study enhance our understanding of the microphysical composition of clouds in mixed-phase conditions.
How to cite. Moser, M., Voigt, C., Eppers, O., Lucke, J., De La Torre Castro, E., Mayer, J., Dupuy, R., Mioche, G., Jourdan, O., Clemen, H.-C., Schneider, J., Joppe, P., Mertes, S., Wetzel, B., Borrmann, S., Klingebiel, M., Mech, M., Lüpkes, C., Crewell, S., Ehrlich, A., Herber, A., and Wendisch, M.: The Arctic Low-Level Mixed-Phase Haze Regime and its Microphysical Differences to Mixed-Phase Clouds, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-3876, 2025.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
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CC1: 'Community Comment on egusphere-2025-3876', Martina Krämer, 25 Aug 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3876/egusphere-2025-3876-CC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2025-3876-CC1 -
RC1: 'Comment on egusphere-2025-3876', Anonymous Referee #1, 16 Sep 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3876/egusphere-2025-3876-RC1-supplement.pdf
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RC2: 'Comment on egusphere-2025-3876', Anonymous Referee #2, 30 Sep 2025
Review of “The Arctic Low-Level Mixed-Phase Haze Regime and Its Microphysical Differences to Mixed-Phase Clouds”
This manuscript presents an observational study of Arctic low-level mixed-phase haze (MPH), distinguishing it from Arctic mixed-phase clouds (MPC). Overall, the manuscript is well-structured, with thorough scientific analysis and clear visualizations through figures and charts. I recommend publication after the authors address the following comments.
Major Comments
- Clustering and Physical Interpretation
The authors employ clustering and statistical analysis to interpret the underlying mechanisms of the observed phenomena. However, observational data alone do not directly confirm physical processes (e.g., during HALO-(AC)³, the synoptic situation primarily controls the ABL top temperature, while surface-driven processes determine its vertical extent). The logical connections could be strengthened by incorporating back-trajectory analyses—especially in Section 2.3, and at Lines 183 and 207 in Section 3.1.1. - Clustering Justification and Consistency
In Table 1, MPH is divided into sub-clusters 2a and 2b, which are later recombined for microphysical comparisons with MPC. The rationale for creating sub-clusters (e.g., 2a vs. 2b, or 1a vs. 1c) is unclear. Line 136 mentions that Table 1 lists the thresholds defining each regime, but the basis for these choices isn't fully explained. Additionally, there's no figure provided to support Lines 288–289. It appears that in many sections, sub-clusters are merged (e.g., 2a+2b → 2), raising the question of whether the initial subdivision is necessary. While Lines 200–221 are logically structured, please clarify the importance of including these sub-clusters in the context of the central narrative. Why are these regime details crucial for the main scientific conclusions? - Suggestions for Figure 2
Figure 2 shows large variability, and the gray lines do not provide as much value as intended. I suggest replotting the three profile types in separate panels with a shared axis range, using the color scheme from Figure 3. Each panel can include all dropsondes of that type along with an averaged profile. This restructuring would facilitate cross-comparison with Figure 3, support the discussion on “exceptions and normals” (p. 8), and better illustrate inversion frequency. - Further Analysis of Figure 4 by Environment Type
Figure 4 is already informative, but the analysis could be enhanced by breaking it down by environment—such as marginal ice zone (MIZ), open ocean, and sea ice. Including additional subplots by surface type would provide valuable insights for readers and future studies. - Clarity in Figure 5
Figure 5 is the most difficult to interpret due to the complexity of the color-coded “step” histograms. Would it be possible to separate Ice and MPH into an additional column or panel to reduce visual clutter? - Clarify Novelty and Contribution in Introduction
Please clearly state the novelty of this study in the Introduction, ideally around Line 50. For example: "In this study, we conduct a detailed investigation of a previously unclassified cloud regime, which we refer to as the mixed-phase haze (MPH)." Is this the first study to define MPH as a unique regime? Does the novelty stem from high-resolution in-situ observations? How does this work advance beyond previous research? These elements are hinted at throughout the Introduction, but an explicit statement would help readers better understand the contribution. - Line 340–341: Secondary Ice Production?
The statement that NINP is lower than the haze droplet number (Line 340) might also suggest the influence of secondary ice production. If so, the "Therefore" at Line 341 feels misleading. Please clarify the logical flow here.
Minor Comments
- Line 6: "The particle number concentration" — specify what kind of particles (e.g., hydrometeors?).
- Line 17–24: Consider shortening this part of the Introduction. The discussion begins focusing on clouds at Line 25, so the earlier text may be unnecessarily long.
- Line 49: Add citation for the Wegener–Bergeron–Findeisen (WBF) process.
- Line 63: "Three research aircrafts" → should be "three research aircraft".
- Abstract: Consider combining the two paragraphs into one for better flow.
- Lines 90–100: The description of instruments could benefit from a summary chart. This could include size ranges, acronyms, uncertainties, transmission efficiency, and lower/upper limits.
- Indentation inconsistencies: e.g., Lines 280–281. Please ensure consistent formatting throughout the manuscript.
Summary:
This is a scientifically rich and well-organized study. The observational analysis is impressive, and the topic—especially the distinction of the MPH regime—is of great interest. Addressing the issues above, particularly those related to clustering logic, figure clarity, and novelty statement, will significantly improve the manuscript and make it more accessible to a broader scientific audience.Citation: https://doi.org/10.5194/egusphere-2025-3876-RC2 - Clustering and Physical Interpretation
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Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt, Weßling, Germany
Christiane Voigt
Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt, Weßling, Germany
Institut für Physik der Atmosphäre, Johannes Gutenberg-Universität, Mainz, Germany
Oliver Eppers
Max Planck Institute for Chemistry, Mainz, Germany
Johannes Lucke
Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt, Weßling, Germany
Faculty of Aerospace Engineering, Delft University of Technology, Delft, Netherlands
Rail Tec Arsenal, Vienna 1210, Austria
Elena De La Torre Castro
Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt, Weßling, Germany
Johanna Mayer
Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt, Weßling, Germany
Regis Dupuy
Laboratoire de Météorologie Physique, Université Clermont Auvergne, Clermont-Ferrand, France
Guillaume Mioche
Laboratoire de Météorologie Physique, Université Clermont Auvergne, Clermont-Ferrand, France
Olivier Jourdan
Laboratoire de Météorologie Physique, Université Clermont Auvergne, Clermont-Ferrand, France
Hans-Christian Clemen
Max Planck Institute for Chemistry, Mainz, Germany
Johannes Schneider
Max Planck Institute for Chemistry, Mainz, Germany
Philipp Joppe
Institut für Physik der Atmosphäre, Johannes Gutenberg-Universität, Mainz, Germany
Max Planck Institute for Chemistry, Mainz, Germany
Stephan Mertes
Leibniz–Institut für Troposphärenforschung, Leipzig, Germany
Bruno Wetzel
Leibniz–Institut für Troposphärenforschung, Leipzig, Germany
Stephan Borrmann
Institut für Physik der Atmosphäre, Johannes Gutenberg-Universität, Mainz, Germany
Max Planck Institute for Chemistry, Mainz, Germany
Marcus Klingebiel
Leipziger Institut für Meteorologie, Universität Leipzig, Leipzig, Germany
Mario Mech
Institut für Geophysik und Meteorologie, Universität zu Köln, Cologne, Germany
Christof Lüpkes
Alfred–Wegener–Institut, Helmholtz–Zentrum für Polar– und Meeresforschung, Bremerhaven, Germany
Susanne Crewell
Institut für Geophysik und Meteorologie, Universität zu Köln, Cologne, Germany
André Ehrlich
Leipziger Institut für Meteorologie, Universität Leipzig, Leipzig, Germany
Andreas Herber
Alfred–Wegener–Institut, Helmholtz–Zentrum für Polar– und Meeresforschung, Bremerhaven, Germany
Manfred Wendisch
Leipziger Institut für Meteorologie, Universität Leipzig, Leipzig, Germany
Short summary
In this study we analyzed Arctic mixed-phase clouds using airborne in-situ measurements in spring 2022. Based on microphysical properties, we show that within these clouds a distinction must be made between classic mixed-phase clouds and a mixed-phase haze regime. Instead of supercooled droplets, the haze regime contains large wet sea salt aerosols. These findings improve our understanding of Arctic low-level cloud processes.
In this study we analyzed Arctic mixed-phase clouds using airborne in-situ measurements in...