Distinct Microphysical Characteristics of Ice Particles in Convective versus Stratiform Regions of Stratocumulus Clouds: A Case Study

Shen, Zhuoxuan; Liu, Xiaoli; Li, Yan; Xiong, Jingyuan; Min, Kerui; Cai, Hengjia; Wang, Nan

doi:https://doi.org/10.5194/egusphere-2025-3034

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https://doi.org/10.5194/egusphere-2025-3034

Preprints

14 Jul 2025

| 14 Jul 2025

Distinct Microphysical Characteristics of Ice Particles in Convective versus Stratiform Regions of Stratocumulus Clouds: A Case Study

Zhuoxuan Shen, Xiaoli Liu, Yan Li, Jingyuan Xiong, Kerui Min, Hengjia Cai, and Nan Wang

Abstract. In stratocumulus cloud systems, where convective areas are embedded within extensive stratiform regions, significant differences exist in microphysical properties and ice particle growth processes across these zones. This heterogeneity creates gaps in understanding precipitation mechanisms and cloud microphysics parameterization. To explore the distinct microphysical characteristics of ice particles in convective regions (CR) and stratiform regions (SR) of stratocumulus clouds, this study analyzes a stratocumulus rainfall event over northern China on 22 May 2017, using airborne data, mesoscale numerical simulations (WRF model), and Lagrangian particle-based simulations (McSnow model). The results show that in CR, stronger updrafts and higher liquid water content promote riming and aggregation, resulting in larger, denser ice particles (maximum rime density reaches 0.5 to 0.55 g cm^-3) and a deeper melting layer (ML). In SR, the riming process is weaker, leading to a thinner ML (400 to 500 m thinner). When ice-phase particles enter the supercooled water region, riming starts with medium-to-large ice particles, followed by smaller ones. The wider rimed particle spectra lead to a broader range of melted liquid drops, thus intensify precipitation. By fitting the gamma distribution to the ice-phase particle spectra, it is found that the spectral parameter N₀(shape parameter μ and slope parameter λ) in CR above 5000 m is generally larger (smaller) than in SR. The quantitative relationships among the spectral parameters were also fitted through regression analysis: lg(N₀) = -5.48 λ - 3.1, lg(N₀) = -0.46 μ - 3.25, λ = 0.06 μ + 0.06. These correlations show minimal variation between temperatures above and below 0 °C.

Received: 26 Jun 2025 – Discussion started: 14 Jul 2025

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Zhuoxuan Shen, Xiaoli Liu, Yan Li, Jingyuan Xiong, Kerui Min, Hengjia Cai, and Nan Wang

Status: final response (author comments only)

RC1:
'Comment on egusphere-2025-3034', Anonymous Referee #1, 04 Aug 2025
Review of “Distinct Microphysical Characteristics of Ice Particles in Convective versus Stratiform Regions of Stratocumulus Clouds: A Case Study” by Shen et al.
This is a comprehensive study that combines aircraft in-situ observations and modeling tools to investigate the distinct microphysical characteristics of ice particles in CR vs. SR portions of stratocumulus clouds. The reviewer truly enjoyed reading this manuscript. However, a rejection is recommended because of the following reasons.
All the major findings presented in this study have been documented elsewhere as cited by the authors. Then what is the point of innovation brought by this follow-up study?

For microphysics studies, WRF simulations is commonly used to compensate for the limited spatiotemporal coverage of aircraft observations and validate the newly discovered hypothesis. However, the modeling results do not provide additional insights or novel understanding, as the simulation results largely reiterate the findings of in-situ observations, e.g., CR having stronger updrafts and more riming. The manuscript's core arguments and conclusions would remain entirely unaffected if the WRF component were removed, suggesting these simulations contribute little substantive value to the study.

While the paper provides a detailed microphysical analysis of ice particles in stratocumulus clouds, its fundamental limitation lies in being a single case study (22 May 2017 over northern China). This narrow scope significantly restricts the broader applicability and scientific impact of the findings.

Specific comments
Line 40. Should be “Research has”.
“McFarquhar” is incorrect cited as “Mcfarquhar”.
Citation: https://doi.org/10.5194/egusphere-2025-3034-RC1
- AC1: 'Reply on RC1', Zhuoxuan Shen, 24 Aug 2025
  
  Dear Reviewer,
  We thank you for your thoughtful review and helpful suggestions.
  We appreciate the recognition of our work. However, we still need to provide some responses and clarifications regarding the paper.
  Both observations and WRF simulations have revealed that the convective regions exhibit higher supercooled water content and broader ice particle spectra, yet there remains a lack of quantitative understanding of the riming characteristics and microphysical properties of ice particles in different cloud regions.
  Therefore, based on observations and WRF, McSnow model is introduced in Sec4.2. It is found that the aggregation process strengthens, forming denser aggregates (especially riming crystals) at about 500 m above the 0 ℃ isotherm. The most heavily rimed particles fall within the 1000 μm to nearly 0.02 cm range, with the highest density of rimed particles primarily in the 1000 μm to about 5000 μm range. Additionally, the maximum rime density can reach 0.5 to 0.55 g cm⁻³ (0.1 to 0.15 g cm⁻³ higher than in stratiform regions), resulting in a thicker melting layer and more active ice particle growth in the upper melting layer (ML). Overall, the riming and melting layers in convective regions are 400 to 500 m thicker than those in stratiform regions. Therefore, the WRF simulation is intended mainly to provide the initial fields for integrating the McSnow model, primarily including vertical profiles of pressure, water vapor, and temperature.
  In our study, it was found that both the supercooled water content and supercooled layer thickness in the convective regions are significantly greater than those in the stratiform regions, potentially resulting in markedly different riming characteristics of ice particles compared to the stratiform regions. To better understand and explore the impact of supercooled water content and layer thickness on the riming growth of ice particles, we have also added a sensitivity experiment. The results show that when both parameters increase, the spectrum of rimed snow shifts toward larger diameters, whereas decreases in either parameter lead to the opposite trend. Regarding supercooled water content and supercooled layer thickness, stratiform regions and convective regions are more sensitive to increases in the former than in the latter, but more sensitive to decreases in the latter than in the former. In addition, convective regions are generally more sensitive to such variations than stratiform regions, and rimed snow is more sensitive than rimed crystals. This section was not included in the original manuscript due to space constraints. The results of the sensitivity experiments are provided in the supplement (SensitivityExperiment.pdf). If there is an opportunity to further revise the paper, we will include these results in the manuscript as well.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3034-AC1
- AC3: 'Reply on RC1', Zhuoxuan Shen, 10 Sep 2025
  
  Thank you once again for your valuable suggestions. After carefully considering and integrating the comments from both reviewers, we have prepared a more comprehensive and detailed revision. Please find the updated response in the attached file “Revision.pdf”.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3034-AC3
RC2:
'Comment on egusphere-2025-3034', Anonymous Referee #2, 27 Aug 2025
Review of Distinct Microphysical Characteristics of Ice Particles in Convective vs Stratiform Regions of Stratocumulus Clouds: A Case Study
Zhuoxuan Shen, Xiaoli Liu, Yan Li, Jingyuan Xiong, Kerui Min, Hengjia Cai, and Nan Wang
Summary: This paper presents a study of a rain event consisting of stratus clouds and convective clouds over northern China. The analysis consists of three components, the first an analysis of five spiral descents of a research aircraft, the second a modeling study using the WRF model, and the third an analysis from a 1-D Lagrangian model called McSnow. The goal of the study is to investigate the difference in microphysical processes occurring in the stratiform vs convective clouds. The convection is relatively weak (vertical velocities of +/- 3 m/s at best from Fig. 4c). In the first component, the authors fit gamma distributions to the observed particle size distributions at points all along the spiral descent, and then examine the relation of the gamma fit parameters to temperature and to each other. In the second component, they examine the microphysical evolution of ice and liquid water content from the WRF simulations in convective areas at approximate geographic locations where the planes flew the spirals. In the third component, then examined 1-D particle evolution with cloud depth using the McSnow model. Their conclusions about microphysical processes in the convective vs stratiform regions largely agree with findings from past studies, specifically that convective regions have more supercooled water, more riming, more efficient aggregation near the melting layer, and secondary ice production in the Mossop-Hallett temperature range, while stratiform areas have the opposite, less to no riming, and no secondary ice production.
Major comments
The novelty of the study is never stated, but to me is the geographic region of the study-few studies have been published, at least in English, of stratiform vs convective clouds in the northern China region. That said, the microphysical evolution described in the paper conforms to studies in similar cloud systems in other regions of the world, some of which the authors refer to in their intro.

The authors fail to relate their findings to past studies. There is no discussion section after the analyses are presented. What is unique about this study that makes it a novel contribution to the literature? How do the findings relate to past work regarding microphysical evolution in stratiform vs convective regions? This is what is missing in this paper, and should be developed if the editor decides to return the paper for major revisions.

The figures need a lot of work to make them easier to understand. Specifically:

Figure 2: An inset of where this is in China would be helpful. International readers would have no idea where this is within the country.

The flight track is hard to see in Fig. 3, and the reflectivity scale numbers are microscopic. You only need one scale and you can make it large with readable text. A white instead of black background wound enhance the figure.

Figure 4 needs a temperature scale. Without it, it is hard to make any sense of the other data. I can’t make any sense of which dots are which on the first panel, and the data on vertical wind are all a jumble on the last panel. Why not show each spiral separately. Make a 4 by 5 panel figure. The vertical motions look pretty much the same in all spirals (+3 to -3 m/s). How do you know there was convection? I would think the vertical motions would be very different in the stratiform vs convective regions. Maybe if they were plotted separately, they might differentiate better? The table does show some differentiation, but the convection is pretty weak for a mid-May storm.

Figure 5: Radius, not Radium. Because the diagrams are small and cover 2.5 orders of magnitude on the x axis, the first four look pretty much the same to me at altitude above 2C. There is more differentiation at altitudes below 2C.

6: The many lines on each panel criss-cross so many times that I had a hard time making sense out of any of it

7 shows the gamma distribution fit parameters for different points on the spiral descents for three temperature ranges. For most of the panels, the data are scattered quite a bit. Linear fit equations are given as a function of temperature in each panel for the three temperature ranges, but to me, the data are anything but linear. How good are these fits? What is the point of the fit equations if the data are not a linear function of temperature to begin with? How are these fit equations supposed to be used? There is no discussion of the application of all these fit equations. What is the point of the fits?

15: There are so many particle size distributions on the tiny figures, that it is difficult to make sense out of them.

Overall, the figures are too small and crammed with too much information. The text on many figures is small and hard to read.
I had a hard time associating the three components of the study into a common theme. The relationship between the data and the modeling studies was not clear. It seemed like the three components were somewhat independent. The conclusions, for example, don’t really tie the components of the study together at all.

Other comments
Table 1: change the dash is the temperatures from -16.3-10.3 to -16.3 to +10.3 on all lines.
206: What do you mean by “microphysical dynamics”

The evolution of the parameters in Fig. 6 seems more complicated than the explanations given. I had a hard time sorting out what the figures showed, and I’m not sure I understand it. Having all 5 spirals on top of one another and lines going back and forth with spirals crossing one another made the figure different to sort out, at least for me.
Please check the following sentences for grammar or missing space or other characters:
47, Sentence beginning L. 60, L. 82, L121,

64: I think you have it backwards – Heymsfield found that at low RH, Ice particles survived to warmer temperatures. This was also found in MCSs (see papers by Grim et al. and Stechman et al.).

128: There is no coefficient “a” in the equation above

Summary: This paper needs a lot of work to be publishable in ACP.
Citation: https://doi.org/10.5194/egusphere-2025-3034-RC2
- AC2: 'Reply on RC2', Zhuoxuan Shen, 08 Sep 2025
  
  We would like to express our sincere gratitude for your recognition of our work and for the valuable comments and suggestions you provided. Based on your feedback, we have carefully re-examined the manuscript and made substantial revisions to improve its overall quality and clarity. In the revised manuscript, we have strengthened the analysis of the MCSNOW model results regarding the evolution of ice particles. Sensitivity experiments are addede to better understand the effects of supercooled water content and supercooled layer thickness on the ice particle size distribution and related spectral parameters. In addition, we have strengthened the comparison with previous studies, provided a clearer explanation of the novelty of our work, and refined several figures and textual details according to your suggestions. A detailed summary of the revisions and responses to each comment can be found in "Revision.pdf" inside the submitted ZIP file.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3034-AC2

Zhuoxuan Shen, Xiaoli Liu, Yan Li, Jingyuan Xiong, Kerui Min, Hengjia Cai, and Nan Wang

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Short summary

This research combines aircraft observations and numerical simulations, particularly using the McSnow model, to track ice particle growth and evolution in stratocumulus clouds. Our findings show that the maximum rime density in convective regions reaches 0.5 to 0.55 g cm^-3, leading to a thicker melting layer (400 to 500 m thicker than in stratiform regions). The study also identifies key relationships between spectral parameters, offering insights into cloud microphysical parameterization.


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