Examination of varying mixed-phase stratocumulus clouds in terms of their properties, ice processes and aerosol-cloud interactions between polar and midlatitude cases: An attempt to propose a microphysical factor to explain the variation

Lee, Seoung Soo; Jung, Chang-Hoon; Yoon, Young Jun; Um, Junshik; Zheng, Youtong; Guo, Jianping; Manoj, Manguttathil G.; Song, Sang-Keun

doi:https://doi.org/10.5194/egusphere-2023-862

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https://doi.org/10.5194/egusphere-2023-862

Preprints

22 May 2023

| 22 May 2023

Examination of varying mixed-phase stratocumulus clouds in terms of their properties, ice processes and aerosol-cloud interactions between polar and midlatitude cases: An attempt to propose a microphysical factor to explain the variation

Seoung Soo Lee, Chang-Hoon Jung, Young Jun Yoon, Junshik Um, Youtong Zheng, Jianping Guo, Manguttathil G. Manoj, and Sang-Keun Song

Abstract. This study examines the ratio of ice crystal number concentration (ICNC) to cloud droplet number concentration (CDNC), which is ICNC/CDNC, as a microphysical factor that induces differences in cloud development, its interactions with aerosols and impacts of ice processes on them among cases of mixed-phase clouds. This examination is performed using a large-eddy simulation (LES) framework and one of efforts toward a more general understanding of mechanisms controlling those development and impacts in mixed-phase clouds. For the examination, this study compares a case of polar mixed-phase clouds to that of midlatitude mixed-phase clouds with weak precipitation. It is found that ICNC/CDNC plays a critical role in making differences in cloud development with respect to the relative proportion of liquid and ice mass between the cases by affecting in-cloud latent-heat processes. Note that this proportion has an important implication for cloud radiative properties and thus climate. It is also found that ICNC/CDNC plays a critical role in making differences in clouds and their interactions with aerosols and impacts of ice processes on them between the cases by affecting in-cloud latent-heat processes. Findings of this study suggest that ICNC/CDNC can be a simplified general factor that contributes to a more general understanding of mixed-phase clouds and roles of ice processes and aerosols in them and thus, to the development of more general parameterizations of those clouds and roles.

Received: 29 Apr 2023 – Discussion started: 22 May 2023

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Journal article(s) based on this preprint

20 Jan 2025

Role of a key microphysical factor in mixed-phase stratocumulus clouds and their interactions with aerosols

Seoung Soo Lee, Chang Hoon Jung, Jinho Choi, Young Jun Yoon, Junshik Um, Youtong Zheng, Jianping Guo, Manguttathil G. Manoj, and Sang-Keun Song

Atmos. Chem. Phys., 25, 705–726, https://doi.org/10.5194/acp-25-705-2025,https://doi.org/10.5194/acp-25-705-2025, 2025

Short summary

Seoung Soo Lee, Chang-Hoon Jung, Young Jun Yoon, Junshik Um, Youtong Zheng, Jianping Guo, Manguttathil G. Manoj, and Sang-Keun Song

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-862', Anonymous Referee #1, 10 Jul 2023

This study examines the impact of ICNC and CDNC on the properties of mixed-phase clouds using large-eddy simulations. However, I do not see new and exciting findings in this study, and some results are not convincing. Therefore, I recommend rejecting this paper in the current format.
Major comments:
1. The authors seem to be not familiar with the literature in the field. The impact of ICNC and CDNC on the properties of mixed-phase clouds, which arises from the efficiency of INP and CCN, has been explored extensively in the past. Key conclusions of this study are very similar to some previous studies, e.g, by Solomon et al. 2018 (doi: 10.5194/acp-18-17047-2018). I do not see any new or exciting results out of this study.
2. The authors stated “ICNC/CDNC can be a simplified general factor that contributes to a more general understanding of mixed-phase clouds”. If the authors can establish "a general principle" for the mixed-phase cloud, I think it would be very useful and this study would be worth for a publication. However, this argument is not convincing for the following reasons:
2.1. The author conducted nine idealized simulations of the mixed-phase clouds. It is not convincing to me how results from nine idealized simulations can be helpful to establish a general principle or a general parameterization for the mixed-phase cloud.
2.2. Observations are missing to justify the model setup and evaluate simulation results. For example, it said that “a system of mixed-phase stratocumulus clouds was observed to exist over a period between 02:00 local solar time (LST) and 20:00 LST on March 29th, 2017. On average, the bottom and top of these clouds are at ~400 m and ~3 km in altitude, respectively.” Is there any ground-based observations to support this statement? See Fig. 1 in Solomon’s paper as a good example.
2.3. Model setup for the initial CCN and INP measurements is also not convincing. One weird result is the extremely high IWC for the control run. As far as I know, IWC in the mixed-phase stratocumulus cloud is usually much smaller than LWC. However, in the control run, IWC/LWC is 26.28, which is extremely high. Do you have any observations to support this result? Can you find any literature to support such high ratio exist in the mixed-phase cloud? If you cannot find observations to support such high IWC/LWC value, it means that the control run might not be setup correctly, and the goal to establish “a general principle” from those simulation results is not convincing.
Here is one suggestion to improve the paper quality: whenever you refer to the observation (cloud, CCN, INP, LWP, IWP...), you should either cite a reference if the results are published or add it in the paper to support your statement. If you don't have those observations, you should provide reasonable assumptions. If results are quite different from previous studies (e.g., extremely high IWC/LWC), you should provide strong justifications.

Citation: https://doi.org/10.5194/egusphere-2023-862-RC1
- AC1: 'Reply on RC1', Seoung Soo Lee, 08 Oct 2023
  
  The authors appreciate the valuable comments and suggestions of the reviewer. The authors' responses are in the supplemental pdf file.
  
  Citation: https://doi.org/10.5194/egusphere-2023-862-AC1
RC2:
'Comment on egusphere-2023-862', Anonymous Referee #2, 06 Sep 2023
Review of the manuscript “EGUsphere-2023-862” entitled “Examination of varying mixed-phase stratocumulus clouds in terms of their properties, ice processes and aerosol-cloud interactions between polar and midlatitude cases: An attempt to propose a microphysical factor to explain the variation” written by Lee, Jung, Yoon, Um, Zheng, Guo, Manoj, and Song.
This study shows simulation results of idealized clouds that can occur in a polar region using the Weather Research and Forecasting model with a bin cloud microphysics scheme at a spatially fine resolution. The authors endeavor to examine how variations in cloud development are influenced by changes in cloud condensation nuclei (CCN) and ice-nucleating particle (INP) concentrations.
The authors propose that the ratio between the concentrations of ice crystals and cloud droplets may constitute a pivotal factor influencing cloud development. However, substantiating such a claim is challenging due to the scarcity of supporting evidence, and numerical experiments do not appear to be appropriately designed to substantiate this assertion. Furthermore, despite simulations of stratocumuli in a polar region are conducted, there is a notable absence of evidence regarding the adequacy of the model's cloud representation. Additionally, the experimental design lacks sufficient information for simulating stratocumuli adequately. The authors also introduce logical leaps in their arguments at several junctures. Consequently, for these reasons, the reviewer recommends against the publication of this paper. Detailed discussions on specific issues are provided below.

Major:
To convincingly demonstrate that the ratio between ICNC and CDNC (ICNC/CDNC) is indeed a critical factor in cloud development, as emphasized by the authors, it is imperative to systematically vary this ratio and conduct numerical experiments. This research, however, has scarcely undertaken such an approach. The ratios presented in Table 1 vary across all experiments, rendering it challenging to discern whether the differences revealed in each experiment stem simply from disparities in CCN and INP or from the ICNC/CDNC. To substantiate the authors' claims, it is essential that similar outcomes emerge in experiments with matched ICNC/CDNC but differing CCN and INP concentrations, thereby providing evidence for the significance of this ratio. Furthermore, as depicted in Figure 7, all four experiments—200_2, 2000_20, 200_20, and 2000_2—exhibit similar profiles for IWC and LWC. However, the ICNC/CDNC ratios vary significantly among these experiments, ranging from 0.108 to 0.512. Therefore, based on these findings, it is challenging to assert that ICNC/CDNC is a critical factor.

The authors present cloud development based solely on profiles of horizontally (and temporally) averaged IWC and LWC. However, it should be noted that cloud development is influenced by a multitude of physical quantities beyond these metrics. Offering results exclusively in the form of averaged IWC and LWC profiles is not considered appropriate.

The authors numerically simulate clouds in a polar region using the UM data as initial conditions. However, the adequacy of the model's cloud representation cannot be assessed as there is no comparison between the simulated clouds and those that can form under the actual conditions. For instance, in the control run, the averaged total water path of the simulated clouds is approximately 33 g m^–2. Without a comparison to the total water path of clouds formed under the corresponding conditions in the corresponding region, it is impossible to gauge the fidelity of the model's cloud simulation.

According to Figure 2, the potential temperature in the near-surface atmosphere is approximately 257 K, which, assuming a pressure of 1000 hPa, corresponds to an extremely low temperature of approximately –16°C. However, the way SST (and/or surface heat fluxes) is prescribed under these atmospheric conditions remains undisclosed. For example, if the SST is assumed to be near 0°C, this would anticipate significant sensible heat flux. In this situation, it becomes vital to provide details on many cloud-related quantities and synoptic conditions, such as SST evolution, surface heat fluxes, large-scale subsidence, and cloud top height development.

In some points of the paper, the authors present arguments with substantial logical leaps. For instance, at L351, the authors assert that drop sedimentation “increases” total cloud mass. However, this assertion is neither logical nor supported by simulation results. The experimental findings merely demonstrate that in the comparison between the 200_2 run and the 200_2_noice run, the former exhibits greater total cloud mass and greater drop sedimentation. This can be attributed to the inherent fact that denser clouds yield more precipitation. In addition, at L403, the authors describe that a higher IWC/LWC ratio in the 200_2 run than in the 200_2_noice run results in more water content (WC), but no logical rationale for this claim is provided, and it is evident only that the inclusion of INP leads to an increase in total water mass.

Minor:
I strongly recommend refine the writing. The authors excessively use sentences beginning with "There" and passive voice constructions.

Although the authors have discussed the strong correlation between IWC and IWP in the early sections of the paper (e.g., Table 2), they consistently describe them as "IWC (IWP)" throughout the manuscript, which diminishes the readability of the paper. If the correlation is indeed evident, it is advisable to mention either IWC or IWP alone for clarity.
Citation: https://doi.org/10.5194/egusphere-2023-862-RC2
- AC2: 'Reply on RC2', Seoung Soo Lee, 08 Oct 2023
  
  The authors' appreciate the comments and suggestions of the reviewer. The authors' responses are in the supplementary file.
  
  Citation: https://doi.org/10.5194/egusphere-2023-862-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-862', Anonymous Referee #1, 10 Jul 2023

This study examines the impact of ICNC and CDNC on the properties of mixed-phase clouds using large-eddy simulations. However, I do not see new and exciting findings in this study, and some results are not convincing. Therefore, I recommend rejecting this paper in the current format.
Major comments:
1. The authors seem to be not familiar with the literature in the field. The impact of ICNC and CDNC on the properties of mixed-phase clouds, which arises from the efficiency of INP and CCN, has been explored extensively in the past. Key conclusions of this study are very similar to some previous studies, e.g, by Solomon et al. 2018 (doi: 10.5194/acp-18-17047-2018). I do not see any new or exciting results out of this study.
2. The authors stated “ICNC/CDNC can be a simplified general factor that contributes to a more general understanding of mixed-phase clouds”. If the authors can establish "a general principle" for the mixed-phase cloud, I think it would be very useful and this study would be worth for a publication. However, this argument is not convincing for the following reasons:
2.1. The author conducted nine idealized simulations of the mixed-phase clouds. It is not convincing to me how results from nine idealized simulations can be helpful to establish a general principle or a general parameterization for the mixed-phase cloud.
2.2. Observations are missing to justify the model setup and evaluate simulation results. For example, it said that “a system of mixed-phase stratocumulus clouds was observed to exist over a period between 02:00 local solar time (LST) and 20:00 LST on March 29th, 2017. On average, the bottom and top of these clouds are at ~400 m and ~3 km in altitude, respectively.” Is there any ground-based observations to support this statement? See Fig. 1 in Solomon’s paper as a good example.
2.3. Model setup for the initial CCN and INP measurements is also not convincing. One weird result is the extremely high IWC for the control run. As far as I know, IWC in the mixed-phase stratocumulus cloud is usually much smaller than LWC. However, in the control run, IWC/LWC is 26.28, which is extremely high. Do you have any observations to support this result? Can you find any literature to support such high ratio exist in the mixed-phase cloud? If you cannot find observations to support such high IWC/LWC value, it means that the control run might not be setup correctly, and the goal to establish “a general principle” from those simulation results is not convincing.
Here is one suggestion to improve the paper quality: whenever you refer to the observation (cloud, CCN, INP, LWP, IWP...), you should either cite a reference if the results are published or add it in the paper to support your statement. If you don't have those observations, you should provide reasonable assumptions. If results are quite different from previous studies (e.g., extremely high IWC/LWC), you should provide strong justifications.

Citation: https://doi.org/10.5194/egusphere-2023-862-RC1
- AC1: 'Reply on RC1', Seoung Soo Lee, 08 Oct 2023
  
  The authors appreciate the valuable comments and suggestions of the reviewer. The authors' responses are in the supplemental pdf file.
  
  Citation: https://doi.org/10.5194/egusphere-2023-862-AC1
RC2:
'Comment on egusphere-2023-862', Anonymous Referee #2, 06 Sep 2023
Review of the manuscript “EGUsphere-2023-862” entitled “Examination of varying mixed-phase stratocumulus clouds in terms of their properties, ice processes and aerosol-cloud interactions between polar and midlatitude cases: An attempt to propose a microphysical factor to explain the variation” written by Lee, Jung, Yoon, Um, Zheng, Guo, Manoj, and Song.
This study shows simulation results of idealized clouds that can occur in a polar region using the Weather Research and Forecasting model with a bin cloud microphysics scheme at a spatially fine resolution. The authors endeavor to examine how variations in cloud development are influenced by changes in cloud condensation nuclei (CCN) and ice-nucleating particle (INP) concentrations.
The authors propose that the ratio between the concentrations of ice crystals and cloud droplets may constitute a pivotal factor influencing cloud development. However, substantiating such a claim is challenging due to the scarcity of supporting evidence, and numerical experiments do not appear to be appropriately designed to substantiate this assertion. Furthermore, despite simulations of stratocumuli in a polar region are conducted, there is a notable absence of evidence regarding the adequacy of the model's cloud representation. Additionally, the experimental design lacks sufficient information for simulating stratocumuli adequately. The authors also introduce logical leaps in their arguments at several junctures. Consequently, for these reasons, the reviewer recommends against the publication of this paper. Detailed discussions on specific issues are provided below.

Major:
To convincingly demonstrate that the ratio between ICNC and CDNC (ICNC/CDNC) is indeed a critical factor in cloud development, as emphasized by the authors, it is imperative to systematically vary this ratio and conduct numerical experiments. This research, however, has scarcely undertaken such an approach. The ratios presented in Table 1 vary across all experiments, rendering it challenging to discern whether the differences revealed in each experiment stem simply from disparities in CCN and INP or from the ICNC/CDNC. To substantiate the authors' claims, it is essential that similar outcomes emerge in experiments with matched ICNC/CDNC but differing CCN and INP concentrations, thereby providing evidence for the significance of this ratio. Furthermore, as depicted in Figure 7, all four experiments—200_2, 2000_20, 200_20, and 2000_2—exhibit similar profiles for IWC and LWC. However, the ICNC/CDNC ratios vary significantly among these experiments, ranging from 0.108 to 0.512. Therefore, based on these findings, it is challenging to assert that ICNC/CDNC is a critical factor.

The authors present cloud development based solely on profiles of horizontally (and temporally) averaged IWC and LWC. However, it should be noted that cloud development is influenced by a multitude of physical quantities beyond these metrics. Offering results exclusively in the form of averaged IWC and LWC profiles is not considered appropriate.

The authors numerically simulate clouds in a polar region using the UM data as initial conditions. However, the adequacy of the model's cloud representation cannot be assessed as there is no comparison between the simulated clouds and those that can form under the actual conditions. For instance, in the control run, the averaged total water path of the simulated clouds is approximately 33 g m^–2. Without a comparison to the total water path of clouds formed under the corresponding conditions in the corresponding region, it is impossible to gauge the fidelity of the model's cloud simulation.

According to Figure 2, the potential temperature in the near-surface atmosphere is approximately 257 K, which, assuming a pressure of 1000 hPa, corresponds to an extremely low temperature of approximately –16°C. However, the way SST (and/or surface heat fluxes) is prescribed under these atmospheric conditions remains undisclosed. For example, if the SST is assumed to be near 0°C, this would anticipate significant sensible heat flux. In this situation, it becomes vital to provide details on many cloud-related quantities and synoptic conditions, such as SST evolution, surface heat fluxes, large-scale subsidence, and cloud top height development.

In some points of the paper, the authors present arguments with substantial logical leaps. For instance, at L351, the authors assert that drop sedimentation “increases” total cloud mass. However, this assertion is neither logical nor supported by simulation results. The experimental findings merely demonstrate that in the comparison between the 200_2 run and the 200_2_noice run, the former exhibits greater total cloud mass and greater drop sedimentation. This can be attributed to the inherent fact that denser clouds yield more precipitation. In addition, at L403, the authors describe that a higher IWC/LWC ratio in the 200_2 run than in the 200_2_noice run results in more water content (WC), but no logical rationale for this claim is provided, and it is evident only that the inclusion of INP leads to an increase in total water mass.

Minor:
I strongly recommend refine the writing. The authors excessively use sentences beginning with "There" and passive voice constructions.

Although the authors have discussed the strong correlation between IWC and IWP in the early sections of the paper (e.g., Table 2), they consistently describe them as "IWC (IWP)" throughout the manuscript, which diminishes the readability of the paper. If the correlation is indeed evident, it is advisable to mention either IWC or IWP alone for clarity.
Citation: https://doi.org/10.5194/egusphere-2023-862-RC2
- AC2: 'Reply on RC2', Seoung Soo Lee, 08 Oct 2023
  
  The authors' appreciate the comments and suggestions of the reviewer. The authors' responses are in the supplementary file.
  
  Citation: https://doi.org/10.5194/egusphere-2023-862-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Seoung Soo Lee on behalf of the Authors (08 Oct 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (27 Oct 2023) by Odran Sourdeval

RR by Anonymous Referee #3 (21 Dec 2023)

Suggestions for revision or reasons for rejection

I have carefully read the paper “Examination of varying. Iced-phase stratocumulus clouds in terms of their properties, ice processes and aerosol-cloud interactions between polar and midlatitude cases: An attempt to propose a microphysical factor to explain the variation”. The paper proposes a series of simulations to compare the mid-latitude and polar cases of mixed-phase clouds. The motivations of the paper are indeed important, most of the studies are focused on warm clouds and not on mixed-phase clouds, as mentioned by the authors, even if there are more and more studies about them currently. The analysis is based on LES simulations to better understand the aerosol-cloud interactions. Interesting results have been derived from the study, for example ice processes increase the total cloud mass for the polar case compared to the polar warm cloud counterpart when ICNC/CDNC and IWC/LWC are high (and the opposite for mid-latitude clouds). The study is very comprehensive and the authors have done a lot of different simulations to explain their analysis, but I have concerns about the methods and the conclusions seem to be rushed or more clarification is needed. Also, I think clarifications are needed to better understand the paper as it is currently difficult to follow with the names of the simulations which are not clear to understand and remember what is associated with what. The current version needs to be rewritten to make it clearer. I do not have a strong expertise in models so I focused my review on the other parts. My concerns are detailed below.

General Comments
- Mixed phase clouds are different in the Arctic and mid-latitudes: In the Arctic, the liquid layer is usually on top of the ice layer, whereas in mid-latitudes mixed-phase clouds consist of pockets of liquid and ice within the clouds. These differences are not mentioned in the paper and have implications for ice processes, especially Wegener Bergeron process. How are mixed-phase clouds represented in the model? Can the authors comment on the possible biases arising from this?
- It is usually difficult to disentangle the dynamical, microphysical changes and natural variability in model simulations, as both are bound in the parameterisation. I wonder if we can disentangle the effect of cloud evolution on ACI just by looking at different simulations, can the authors comment on that?
- The study is difficult to read with all the different names of simulations that are not explicit about what they correspond to, and considering the number of simulation, it became difficult to figure out the corresponding simulation. I suggest that the names are renamed to better understand.
- There are many sentences with the use of brackets to express two ideas in the same sentence, making it difficult to read. For example in lines 621, 632, 635,... I recommend simplifying those.
- I did not find many details about the measurements (CCN measurements, Cloudnet...). Can the authors add information on where the data come from? How it is retrieved? Also, I would have liked the authors to show some plots comparing the model output with the observations when it is possible.
- On line 721, the authors say that ICNC/CDNC increases with IWC/LWC and base their analysis on this. But this is not true for the 200_2 simulations, as the authors state. So I do not understand why they infer results and generalize it when one of the situations does not work. Can the authors comment on that?
- The authors infer different glaciation processes from the change in ICNC/CDNC, but I am not convinced that this is not directly related to the temperature difference between the Arctic and mid-latitudes. Can the authors make the argument explicit to rule out the temperature dependence?
- The nucleation mode between the Arctic and the mid-latitudes is very different due to the moisture regime. The Arctic region is less prone to immersion freezing and condensation freezing compared to the mid-latitudes because of the expected supersaturation of water vapour with respect to liquid. Is this related to the authors' conclusion? If so, would the information on relative humidity be helpful?
- I think the authors' conclusion is too general (e.g., when the authors refer to polar regions, it actually corresponds to a region around Svalbard, which is a region of the Arctic). The conclusion should not be so promising because it could mislead readers.

Specific comments
-Line 94: Mixed-phase clouds can also be found in convective clouds in the tropics.
- Line 105: "The radiative properties of liquid particles are substantially different from those of ice particles", I slightly disagree with this sentence. It is true that the radiative properties are not exactly the same, but the main difference is that ice crystals are larger and less numerous than cloud droplets (due to lower concentration of INP compare to CCN), so ice clouds tend to be less reflective than liquid clouds, and ice crystals precipitate, potentially altering the cloud lifetime.
- Lines 134-136: "Many factors, such as environmental conditions..." The spatial distribution of the liquid and ice phases is also important as mentioned in the general comments.
- Line 165: "Get us the fully established principle": What would be needed to get the fully established principle?
- Lines 197 to 203: I do not understand the logic, the authors refer to hydrometeors, then to aerosols, then back to aerosols. Can the authors rephrase the sentence?
- Line 205: So aerosols do not sediment, is this true? Can the authors confirm that this hypothesis is close to reality?
- Line 247: Since the altitude bins are not linear, would it be possible to have them in the supporting information? Otherwise it would be difficult to replicate the study.
- Line 266 and line 281: Aerosol concentration is assumed to be constant with time and altitude in the PBL, can the authors confirm that this is an appropriate hypothesis?
- Line 291: The dust concentration is higher than the observed INP concentration, as is the INP concentration from the presentation. Can the authors state whether the INP concentration from the study is of the same order of magnitude as the dust events?
- Line 385, is the temperature range from Choi et al. (2014) at the top of the cloud? Also, is the temperature range the same as the temperature range from the present study?
- Line 462: The authors refer to the Lee et al. (2022) study for the mid-latitude case. Are the model and method similar and is CTH similar? I think the authors should describe this paper and the method used a bit more.
- Line 478-482. The much higher IWC than LWC in the polar case compared to midlatitude. The polar case is also associated with lower temperature, so I am not sure what more information can be derived from this.
- Line 495: The authors present new simulations here, which is confusing, why did they not present them in section 2.2.2?
- The process associated with cloud formation and evolution does indeed depend on geographical regions. The Arctic is known to be prone to radiative cooling, whereas the mid-latitudes are prone to convective processes, so it is difficult to compare the two regions. Can the authors comment on this?
- Line 597: 200_2_fac10, 100_2_fac10_CCN10, 200_2_fac10_INP10 represent mid-latitude cases. I thought the mid-latitude cases were from Lee et al. (2022) (line 159). Can the authors explicit that?
- Line 786: Should IFN be INP?

Hide

RR by Anonymous Referee #2 (14 Feb 2024)

Suggestions for revision or reasons for rejection

The second review of the manuscript “EGUsphere-2023-862” entitled “Examination of varying mixed-phase stratocumulus clouds in terms of their properties, ice processes and aerosol-cloud interactions between polar and midlatitude cases: An attempt to propose a microphysical factor to explain the variation” written by Lee, Jung, Yoon, Um, Zheng, Guo, Manoj, and Song.

The authors have tried to make answers to my questions in the previous review. While some of them are adequately answered, others are not yet. Moreover, I would like to add some minor comments.

Major
1. The question in the previous review that points out the causality between the sedimentation and the total cloud mass is not properly answered. As sedimentation obviously acts as a sink term of cloud mass, the sentence “the droplet sedimentation tends to increase the total cloud mass in the 200_2 run” should be revised. In other words, to state the drop sedimentation as a cause of the increase in the total cloud mass, neither just mentioning some previous studies nor simply saying “it is not important” is not sufficient. The sentence should be revised like as: “Of the two runs, the drop sedimentation is greater in the case with the greater total cloud mass”. I can find similar expressions at many points throughout the manuscript.
Related with this, I do not understand the phrase “changing sedimentation” in L527. Does changing mean increasing or decreasing? Also, I do not think that neither increasing nor decreasing of total cloud mass cannot be yielded by “changing sedimentation”.

2. By conducting additional experiments, the question that points out the importance of ICNC/CDNC is answered to some extent. However, it is still questionable whether ICNC/CDNC is indeed the critical factor. The experiments in the manuscript do not show any “intermediate” IWC/LWC values, saying 2–20 although ICNC/CDNC increases relatively gradually (Table 4). This means that the IWC/LWC shows an abrupt change, like a regime shift. I strongly recommend that the authors should clarify this in a relevant point of the manuscript.

3. I strongly suggest the authors to show more diverse types of analysis in the manuscript (not as supplementary). For example, the authors should add time-height plots of IWC or time series of IWP. For L585, the authors can add drop (ice) size distributions as the authors utilized a spectral bin microphysics model. For the description in the Section 3.1.1, the authors should add vertical profiles, time series, or time-height plots of RH with respect to liquid and ice.

Minor
1. In the manuscript, the authors should specify the model integration time and the period where the average is calculated. Note that the first a few hours of simulation are generally excluded from calculating average as they are regarded as spin-up in a typical idealized cloud simulation.

2. The authors should describe about the model in more detail. For example, does the model include the source of aerosol concentration other than turbulent mixing and advection, such as regeneration by drop evaporation or surface emission? Otherwise, how can the aerosol concentration be maintained throughout the model integration? In addition, whether the model consider freezing of activated drops should be described, considering the experimental condition. Moreover, the way large-scale subsidence (L254) is considered in the model should also be described.

3. L424 and others: How is the entrainment rate defined? Why does it have a unit of cm s–1? The entrainment rate has the unit of s–1 in general.

4. L621: All of the studies mentioned consider drop autoconversion, not ice autoconversion. Therefore, it is not proper to presume that ice autoconversion is roughly proportional to ice concentration based on these studies.

5. Is stating INP meaningful in “noice” experiments? I suggest that the authors replace “200_2_noice” with ”200_0” and “2000_2_noice” with “2000_0”. In the same way, I suggest to replace “200_2_fac10” with “200_0.07” (also the others including “_fac10”) as the names are neither intuitive nor consistent with others.

6. As the descriptions about the “norad” experiments are very simple, I suggest not to include them in Table 1 for simplicity.

7. The authors stated that the reanalysis has a temporal resolution of 6 hours (L248). However, in another line, they stated that Figure 2c shows the time series of surface temperature in the reanalysis (L257), which varies with a temporal resolution of 1 hour.

8. I strongly suggest the authors to split the L343–391 and to make them as another subsection, named “model validation”. Related with this, if there is no other problem, I suggest the authors to include Fig. S1 in the manuscript.

9. L214: the most widely used -> a

10. L303: IFN -> INP

11. L398, 400: The order of IWC and LWC should be reversed

12. L405: this -> that, L406: this -> the

Hide

ED: Reconsider after major revisions (15 Feb 2024) by Odran Sourdeval

AR by Seoung Soo Lee on behalf of the Authors (23 May 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (05 Jun 2024) by Odran Sourdeval

RR by Anonymous Referee #3 (24 Jun 2024)

Suggestions for revision or reasons for rejection

I thank the authors for the changes they made to the manuscript, which improved the article, especially in the presentation of the results. As mentioned in my previous review, I think the paper is suitable for publication in ACP. However, I have minor comments that I would like the authors to address before the article is published.

I am still concerned about the representation of the mixed phase in the model compared to the observation. I do not understand what the authors mean by ice and liquid pockets in the sentence: “pockets of ice particles and those of liquid particles are mixed together”. What is the size of the pockets considered? Usually, in models, ice and liquid hydrometeors are homogeneously mixed in mixed phase clouds. My problem is that this is not what observations show, as in Coopman and Tan (2023), Tan and Storelvmo (2016), Korolev and Milbrandt (2022), D'Alessandro et al. (2021), D'Alessandro et al. (2023), Schima et al. (2022). The different representation of homogeneously mixed hydrometeors or the presence of pockets has an impact on the microphysical processes (e.g., WBF…). Therefore, it should be highlighted in the article that the representation of mixed-phase clouds considered in the model of the study has hypotheses that do not agree with observations (the study that the authors refer to Lee et al. (2021) is also from models).

Coopman, Q., & Tan, I. (2023). Characterization of the Spatial Distribution of the Thermodynamic Phase Within Mixed‐Phase Clouds Using Satellite Observations. Geophysical Research Letters, 50(24), e2023GL104977.
Korolev, A., & Milbrandt, J. (2022). How are mixed‐phase clouds mixed?. Geophysical Research Letters, 49(18), e2022GL099578.
D'Alessandro, J. J., McFarquhar, G. M., Wu, W., Stith, J. L., Jensen, J. B., & Rauber, R. M. (2021). Characterizing the occurrence and spatial heterogeneity of liquid, ice, and mixed phase low‐level clouds over the Southern Ocean using in situ observations acquired during SOCRATES. Journal of Geophysical Research: Atmospheres, 126(11), e2020JD034482.
D’Alessandro, J. J., & McFarquhar, G. M. (2023). Impacts of drop clustering and entrainment‐mixing on mixed phase shallow cloud properties over the Southern Ocean: Results from SOCRATES. Journal of Geophysical Research: Atmospheres, 128(15), e2023JD038622.
Schima, J., McFarquhar, G., Romatschke, U., Vivekanandan, J., D’Alessandro, J., Haggerty, J., ... & Schnaiter, M. (2022). Characterization of Southern Ocean boundary layer clouds using airborne radar, lidar, and in situ cloud data: Results from SOCRATES. Journal of Geophysical Research: Atmospheres, 127(21), e2022JD037277.
Tan, I., & Storelvmo, T. (2016). Sensitivity study on the influence of cloud microphysical parameters on mixed-phase cloud thermodynamic phase partitioning in CAM5. Journal of the Atmospheric Sciences, 73(2), 709-728.

Regarding my first specific comment, I suggest that the difference between stratiform and convective clouds be clarified and changed: “When mixed-phase stratiform clouds are associated with convective clouds, they can form even in the tropical region.” to “When mixed-phase clouds are associated with convective clouds, they can form even in the tropical region.”

I thank the authors for their efforts to remove the brackets, as mentioned in my previous review, but they should be careful that the sentences remain coherent. For example, the three repetitions of "respectively" in lines 122, 123, 124 make reading too difficult.

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RR by Anonymous Referee #2 (05 Aug 2024)

Suggestions for revision or reasons for rejection

The second review for the manuscript EGUsphere-2023-862 entitled “Examination of varying mixed-phase stratocumulus clouds in terms of their properties, ice processes and aerosol-cloud interactions between polar and midlatitude cases: An attempt to propose a microphysical factor to explain the variation” written by Lee et al..

The authors have adequately improved the manuscript. I suggest a few minor modifications before publishing.

1. Title: almost all contents of this manuscript are focused on the “polar case”, instead of “the midlatitude case”, with which was dealt by a previous study of the authors. I suggest the phrase “between polar and midlatitude cases” in the title simply to “a polar cloud case”.

2. I think that the most important result of this manuscript is the strong relationship between IWC/LWC and ICNC/CDNC, which is shown as a list of numbers in Tables 2, 3 and 5. I strongly suggest adding a figure that shows the relationship (e.g., ICNC/CDNC for x axis and IWC/LWC for y axis).

3. L497: We cannot know whether pockets of ice particles and those of liquid particles are “mixed together” or “separated in a specific layer” from Figure 4, which just shows the horizontally averaged vertical mass contents profile of ice particles and liquid particles.

4. L500–507: “higher”, “more”, “higher”, “more”, “higher”, and “more” than what?

5. L507: I expect not only high ICNC/CDNC but also greater capacitance of ice particles than that of liquid drops can impact the more active growth of ice particles by vapor deposition.

6. Some paragraphs are too long and contain too many ideas so I suggest splitting them into two or more: for example, L479 and L533.

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ED: Reconsider after major revisions (21 Aug 2024) by Odran Sourdeval

Dear authors,

Thank you for revising your manuscript according to the referee's comments and for thoroughly responding to their various concerns. I recognize that this required significant effort on your part, and I am pleased to note that the manuscript is now much improved. Adding and discussing observations in comparison to your modeling results was particularly important.

Both referees have provided additional comments based on your responses, and I would ask you to review these and further revise your manuscript accordingly. In particular, I would like to emphasize two specific points from these comments:

- Representation of the mixed phase in the model compared to the observation: Your assumptions do not seem to align with current literature based on observations. This should, at a minimum, be acknowledged and discussed in the manuscript.

- Relationship between IWC/LWC and ICNC/CDNC: This is a significant highlight of your paper, yet it is not clearly represented in any figures. As suggested by the referee, a visual representation of the relationship (e.g., one ratio as a function of the other) could be very useful.

Additionally, I would like to provide a few more comments:

- The title of the manuscript is becoming too long and should be made more concise for better impact and readability. Please refer to our Guidelines for Authors (https://www.atmospheric-chemistry-and-physics.net/policies/guidelines_for_authors.html). Similarly, your conclusion has also increased in length, and I suggest adapting it to provide a more concise summary for the readers. Again, please refer to the guidelines. This could for instance be achieved by moving some content to your "discussion" section, which is comparatively shorter than the conclusion.

- The "data availability" section should include a statement about where the data you used can be accessed (https://www.atmospheric-chemistry-and-physics.net/policies/data_policy.html). You mention that the data processed on your private computer system is private, but you have also utilized publicly available data. An access statement for this original data should be provided, particularly for CloudNet, and perhaps for the reanalysis and CCN data (if it is not based on publicly available data, please state so in that section).

- As mentioned earlier, comparisons to observations are a crucial aspect of your work. However, I still find that insufficient details are provided regarding these observations. For example, how many CloudNet stations are available in your simulated region, and where are they located (this could be useful to include in Fig 1)? What is the spatial resolution of the retrievals? Are they continuously available accross your simulation or are there discontinuities? For Fig. 5 and related discussions, have you compared domain-averaged model outputs with the observations from the one or few station(s), or have you co-located the simulations with the observations? Additionally, have CloudNet data been used / evaluated before for mixed-phase clouds, and do they provide simultaneous ice and liquid cloud properties in a single vertical pixel or only one at a time? All these aspects should be further described and discussed to enhance the relevance of the model-observation comparisons.

Overall, both referees have suggested that minor revisions are needed. Considering that I am also providing my own list of comments in addition, I will request reconsideration of the manuscript after (moderate) major revisions. Please note that these revisions are primarily aimed at further clarifying your manuscript.

Kind regards,
Odran Sourdeval

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AR by Seoung Soo Lee on behalf of the Authors (20 Sep 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (11 Oct 2024) by Odran Sourdeval

AR by Seoung Soo Lee on behalf of the Authors (27 Oct 2024) Manuscript

Journal article(s) based on this preprint

20 Jan 2025

Role of a key microphysical factor in mixed-phase stratocumulus clouds and their interactions with aerosols

Seoung Soo Lee, Chang Hoon Jung, Jinho Choi, Young Jun Yoon, Junshik Um, Youtong Zheng, Jianping Guo, Manguttathil G. Manoj, and Sang-Keun Song

Atmos. Chem. Phys., 25, 705–726, https://doi.org/10.5194/acp-25-705-2025,https://doi.org/10.5194/acp-25-705-2025, 2025

Short summary

Seoung Soo Lee, Chang-Hoon Jung, Young Jun Yoon, Junshik Um, Youtong Zheng, Jianping Guo, Manguttathil G. Manoj, and Sang-Keun Song

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Sep 2023	33	11	4	48
Oct 2023	34	12	5	51
Nov 2023	9	1	3	13
Dec 2023	14	9	5	28
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Apr 2024	22	1	2	25
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Jun 2024	35	7	4	46
Jul 2024	10	1	6	17
Aug 2024	18	2	4	24
Sep 2024	11	4	5	20
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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Short summary

This study is motivated by the fact that there are no general factors that represent the overall properties of mixed-phase clouds. The absence of these factors contributes to the high uncertainty in the prediction of climate change. Hence, this study finds a general factor that explains differences in the properties of different mixed-phase clouds, using a modeling tool. This factor is useful to develop a general way of using climate models to better predict climate change.


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