Distinctive aerosol-cloud-precipitation interactions in marine boundary layer clouds from the ACE-ENA and SOCRATES aircraft field campaigns

Zheng, Xiaojian; Dong, Xiquan; Xi, Baike; Logan, Timothy; Wang, Yuan

doi:https://doi.org/10.5194/egusphere-2023-2608

Preprints

https://doi.org/10.5194/egusphere-2023-2608

Preprints

14 Nov 2023

| 14 Nov 2023

Distinctive aerosol-cloud-precipitation interactions in marine boundary layer clouds from the ACE-ENA and SOCRATES aircraft field campaigns

Xiaojian Zheng, Xiquan Dong, Baike Xi, Timothy Logan, and Yuan Wang

Abstract. The aerosol-cloud-precipitating interaction within the cloud-topped Marine Boundary Layer (MBL), are being examined using aircraft in-situ measurements from Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) and Southern Ocean Clouds Radiation Aerosol Transport Experimental Study (SOCRATES) field campaigns. SOCRATES clouds have a larger number of smaller cloud droplets compared to ACE-ENA summertime and wintertime clouds. The ACE-ENA clouds, especially in wintertime, exhibit pronounced drizzle formation and growth, attributed to the strong in-cloud turbulence that enhances the collision-coalescence process. Furthermore, the Aerosol-Cloud Interaction (ACI) indices from the two aircraft field campaigns suggest distinct sensitivities. The aerosols during ACE-ENA winter are more likely to be activated into cloud droplets due to more larger aerosols and strong vertical turbulence. The enriched aerosol loading during SOCRATES generally leads to smaller cloud droplets competing for available water vapor and exhibiting a stronger ACI. The ACI calculated near the cloud base was noticeably larger than the layer-mean and near-cloud-top, owing to the closer connection between the cloud layer and sub-cloud aerosols. Notably, the sensitivities of cloud base precipitating rates to cloud-droplet number concentrations are more pronounced during the ACE-ENA than during the SOCRATES campaigns. The in-cloud drizzle evolutions significantly alter sub-cloud cloud condensation nuclei (CCN) budgets through the coalescence-scavenging effect, and in turn, impact the ACI assessments. The results of this study can enhance the understanding and aid in future model simulation and assessment of the aerosol-cloud interaction.

Received: 04 Nov 2023 – Discussion started: 14 Nov 2023

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Journal article(s) based on this preprint

18 Sep 2024

Distinctive aerosol–cloud–precipitation interactions in marine boundary layer clouds from the ACE-ENA and SOCRATES aircraft field campaigns

Xiaojian Zheng, Xiquan Dong, Baike Xi, Timothy Logan, and Yuan Wang

Atmos. Chem. Phys., 24, 10323–10347, https://doi.org/10.5194/acp-24-10323-2024,https://doi.org/10.5194/acp-24-10323-2024, 2024

Short summary

Xiaojian Zheng, Xiquan Dong, Baike Xi, Timothy Logan, and Yuan Wang

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-2608', Anonymous Referee #1, 11 Dec 2023
Comment on EGU-2023-2608 titled “Distinctive aerosol-cloud-precipitation interactions in marine boundary layer clouds from the ACE-ENA and SOCRATES aircraft field campaigns”
GENERAL COMMENTS:
This study uses aircraft in-situ measurements from the ACE-ENA and SOCRATES field campaigns to illustrate vertical profiles of cloud microphysical and precipitation properties and their relationships with above- and below-cloud aerosols. The paper is well-written with appropriate references. There is tremendous detail in Section 2 (uncertainties in airborne observations, formulae used to calculate cloud properties, thresholds used to define in-cloud and above/below-cloud regions) to ensure the results can be reproduced. The discussion of the results is well structured, and the text is backed up with appropriate figures. The study draws proper conclusions and provides appropriate evidence. This is a comprehensive study that deals with numerous elements of aerosol-cloud-precipitation interactions – a single paper is used to show findings that could have spread across multiple studies if the individual elements were investigated further.
While the work is comprehensive, the novelty of this study comes from the fact that these in-situ observations come from regions that have not been sampled extensively by aircraft or the data examined in detail. Additionally, very distinct regions with unique cloud and aerosol characteristics are compared. In isolation, many findings might not strictly be new as they corroborate results from many previous studies that have used aircraft observations. Nevertheless, this study is an important addition to the literature because of the wide range of topics discussed and the fact that the authors contrast cloud and aerosol properties from multiple field campaigns from two different locations. The effort put into this work is commendable and the paper would be a valuable addition to the journal and the literature. Given the number of topics discussed and potential for deeper dives into each topic, I can see multiple studies coming out of further investigation into the results presented here.
I have some considerations for the authors before the study is published:
The introduction felt a bit too broad and generic - the authors could better motivate and highlight the unique aspect of this work by guiding the reader through the distinct nature of these regions, by contrasting the existing knowledge of cloud properties from these regions - somewhat done for SOCRATES but not for ACE-ENA, highlighting the ‘climatic significance’ of clouds observed in these two regions – this was only done for MBL clouds in general, and the need for in situ observations from these locations.

Is there a reason behind comparing these two specific field campaigns? Are we comparing apples to apples? - describing the cloud regime, type, or morphology in these regions could help interpret the differences in the results presented in later sections.
2. The authors could better and use terminology to refer to cloud processes discussed throughout the text. Terms like “collision-coalescence”, “in-cloud coalescence”, “coalescence-scavenging” are used (often interchangeably it seems) - they can be merged or defined using more commonly used terminology.
Line 57: the authors could separate what they term the ‘coalescence-scavenging effect’ into two parts. While the drizzle drops are within the cloud layer, the process described in Line 58 can be described as the ‘collision-coalescence’ process. Once the drizzle drops are below cloud base, the process described in Line 59 can be described as the ‘precipitation scavenging’ process. Using such terminology would prevent confusion caused by using the same term for two separate processes that occur in-cloud and out-of-cloud, respectively. Please ensure consistency in using the terms as the paper currently uses “collision-coalescence process” in some spots and different terms at other spots while describing a similar process.
SPECIFIC COMMENTS:
ABSTRACT:
Line 15: Could you provide quantitative estimates with the number and size used to state “larger number” and “smaller cloud droplets”?
SECTION 1:
Line 34: The authors mention ‘cloud-top longwave radiative cooling’ here which is very important and should be mentioned but it is not discussed later. In contrast, there is an excellent discussion of cloud top entrainment mixing and droplet evaporation near cloud top later, but it is not introduced here. The authors could better motivate their results by introducing cloud processes in Section 1 if they are discussed later.
Line 42: This statement is only true under conditions of comparable cloud water content. Please update accordingly and provide appropriate references.
Line 44: Instead of listing references at the end of the sentence, a reader would benefit much more if references for specific elements followed the corresponding text. For example, “…investigated by different observational platforms, such as aircraft (Diamond et al., 2018; Painemal et al., 2020), model simulations (Hill et al. 2009)…”.
Please directly state some of the “different maritime regions”. Something like “….over different maritime regions like the southeast Pacific (Painemal and Zuidema, 2011), northeast Pacific (Braun et al., 2018), southeast Atlantic (Diamond et al., 2018), and eastern North Atlantic (Zheng et al., 2022a).”
Line 53: More recent studies of precipitation susceptibility (e.g., Gupta et al., 2022; Jung et al., 2016; Terai et al., 2012) have been built upon the studies cited here. To my knowledge, Feingold and Seibert (2009) introduced the term precipitation susceptibility and the study should be cited here. I see the authors briefly compared their results with some of these previous studies (good to see) - but the studies should be cited in the introductory text. Also suggest discussing the different issues with estimating/interpreting S_o based on results from previous studies.
Line 75: Please also provide the months for the ACE-ENA IOPs along with the years.
Line 80: Please provide the duration for the SOCRATES austral summer IOP.
SECTION 2:
I want to commend the authors for the discussion in this section. However, the section does lack some context about the cloud sampling locations. A map of the sampling locations/flights tracks or a list of the range of latitude-longitude coordinates where clouds were sampled during the IOPs would be very useful.
Line 106: I believe by “resolutions” you actually mean - “the size bins of the probe were 1 to 3 um wide”?
Line 111: Can you provide a reference for the phase classification product? If not, a short description of the methodology for it would be useful.
Line 128: Can cite Hansen and Travis, 1974 where the term “effective radius” and the associated formula were introduced.
Line 160: Do your results depend on the selection of the value of 200 m to determine the distance for above-cloud aerosols that are important for the analysis? Gupta et al. (2021) conducted a sensitivity test to determine if their analysis of cloud microphysical properties was affected by this number for distance from above-cloud aerosols. A comment on the sensitivity of the results on this value would be useful.
SECTION 3:
Line 192: These aerosol concentrations for SOCRATES seem high for the Southern Ocean, which was typically viewed to be a pristine environment. The authors refer to previous studies from SOCRATES to explain the aerosol size distribution or composition, do these studies have similar aerosol concentrations?
Line 213: Do you mean that the ‘sub-cloud Nacc values’ are more than double the ‘above-cloud Nacc values’? Suggest rewording this sentence.
Line 268: “These results have further improved the understanding of the aerosol first indirect effect”. This statement is a bit overreaching. There are many studies that have shown similar results. I suggest rewording to “These results are consistent with the understanding of the aerosol first indirect effect”
Line 271: It is interesting that the average Nc for ACE-ENA winter is greater than both the sub-cloud Nacc and Nccn. Do you have any comments on why this is the case? Has this been observed elsewhere? Are the values of Nc influenced by above-cloud aerosols or sub-cloud Na?
Line 310: This is an excellent discussion of entrainment mixing and its competing influence on droplet size/liquid water content and likely highlights two different modes of cloud top mixing – homogeneous and inhomogeneous mixing that depend on the entrainment rate (Lehmann et al., 2009; Lu et al., 2011) – do the authors have any comments based on their calculated entrainment rates? The authors could cite examples of previous studies that show similar vertical profiles of cloud properties where the effects of entrainment mixing on cloud microphysical properties were evident.
Line 370: The skewness of a distribution can actually be calculated as a statistical parameter rather than having a visual comparison. I leave it to the authors to decide if they would like to add this parameter to the study.
SECTION 4:
Line 434: This statement would be more accurate if the Liquid Water Path (LWP; vertical integral of the LWC) values were compared across campaigns rather than the mean LWC. Suggest adding LWP values or rewording the sentence.
Line 468: Do you want to mention some of these aircraft campaigns - VOCALS, ORACLES, ACTIVATE, etc.?
Line 475: These are some very interesting results. While the ACI_r,CT values are close to what one might expect (droplets are too large near cloud top for above-cloud aerosols to exert a significant influence on r near cloud top), it is interesting to note the ACI_{N, CT} values reported here. Do the authors have any explanation or hypotheses for what causes these values to not be closer to 0 like ACI_{r, CT}?
Line 480: I think the authors should also mention cloud top entrainment mixing over here.
Line 484: As mentioned earlier, would be good to also cite Feingold and Seibert, 2009 when defining S_o, which to my knowledge was the first study to define the term.
Line 491: The authors should provide the correlation coefficient values for the S_o calculations and contrast these with previous studies. At least two recent studies did this – Jung et al. 2016 and Gupta et al. 2022.
Line 501: “…due to decreasing 𝑆𝑜 within the thicker cloud (Terai et al., 2012)”. This is oversimplifying the problem. The value of S_o depends not only on cloud thickness but also on the calculation methodology as shown by Terai et al, the cloud type – cumulus versus stratocumulus (Sorooshian et al., 2009; Jung et al., 2016) and the above- and below-cloud aerosol concentration (Duong et al., 2011; Jung et al., 2016; Gupta et al., 2022). Having more information on cloud type/morphology in the introduction would give context to these S_o values and other results in the study.
Line 531: What are the units of the CCN loss rate? Here, the values are reported with units of “cm^-3” which does not include a unit of time, this is likely an error?
SECTION 5:
Line 568: The differences can also be attributed to the different size distributions which are then due to the sources discussed in the following sentences. That would then nicely lead to the discussion of aerosol modes toward the end of the paragraph.
Line 569: I don’t think using the words ‘pristine natural environment’ is appropriate when the previous sentence claimed the aerosol concentrations are highest for SOCRATES.
Line 580: Can you also list the percentage increase in r from cloud base to top since these campaigns had different cloud thickness values?
Lines 255 and 576: How does in-cloud coalescence cause an increase in the size of sub-cloud aerosols? In-cloud coalescence would increase the size of a cloud drop as it accumulates water by colliding and coalescing with other droplets. Once this drop evaporates in the sub-cloud to expose the residual aerosol, the aerosol/CCN core size should be the same unless the CCN is modified during droplet growth. Is this related to the condensation of sulfuric gas onto aerosol cores as described in Line 245? If so, is there a way to verify this based on these observations? If not, this should be stated as a hypothesis rather than a conclusion?
Lines 591-597: I don’t fully understand or agree with the conclusion drawn here. The studies that the authors cited here/earlier (among many others) have calculated f_ad using in-situ aircraft data from other locations and shown that assuming f_ad = 0.8 could lead to errors in satellite estimates of droplet concentration. While the calculation of f_ad and stating the regional values is important, these f_ad values do not “shed light on the further understanding of the satellite retrievals, particularly the satellite-based aerosol-cloud interaction assessment”. The authors can state the f_ad values and perhaps add a comment on the need to use these values when calculating droplet concentration for these regions using satellite retrievals, but I suggest removing lines 594-597.
Line 614: I don’t understand what is meant by “the aircraft assessment provides more connected circumstances between the aerosols and cloud layer.”
TECHNICAL CORRECTIONS/CLARIFICATIONS:
Line 12: Could use the term “aerosol-cloud-precipitation” given the terminology in the title? Also, change to “interactions” given the verb “are” in the next sentence?
Line 94: “aerosol, cloud, and drizzle”?
Line 105: “onboard the aircraft”?
Line 110: “large, ice particles”? Large ice particles would be a lot larger than 200 um.
Line 286: “To ensure the representativeness of the vertical profiles”?
Line 443: The sentence should probably end with “during the winter”.
Line 582: Do you mean “The mean cloud-top entrainment rates (𝑤𝑒 ) are a function of cloud top virtual potential temperature and vertical velocity and their values are….”
Figure 1: Please mention which statistical metrics are provided in the legends. Suggest adding that to the figure caption.
Figure 2: The caption lists the incorrect size range for the inner plots. Should be “Aitken mode size distribution (𝐷𝑝 = 0.01 to 0.06 µm)”
REFERENCES:
Feingold, G. and Siebert, H.: Cloud – Aerosol Interactions from the Micro to the Cloud Scale, from the Strungmann Forum Report, Clouds in the Perturbed Climate System: Their Relationship to Energy Balance, Atmospheric Dynamics, and Precipitation, 2, edited by: Heintzenberg, J. and Charlson, R. J., MIT Press, ISBN 978-0-262-01287-4, 2009.
Gupta, S., McFarquhar, G. M., O’Brien, J. R., Delene, D. J., Poellot, M. R., Dobracki, A., Podolske, J. R., Redemann, J., LeBlanc, S. E., Segal-Rozenhaimer, M., and Pistone, K.: Impact of the variability in vertical separation between biomass burning aerosols and marine stratocumulus on cloud microphysical properties over the Southeast Atlantic, Atmos. Chem. Phys., 21, 4615– 4635, https://doi.org/10.5194/acp-21-4615-2021, 2021.
Gupta, S., McFarquhar, G. M., O'Brien, J. R., Poellot, M. R., Delene, D. J., Miller, R. M., and Small Griswold, J. D.: Factors affecting precipitation formation and precipitation susceptibility of marine stratocumulus with variable above- and below-cloud aerosol concentrations over the Southeast Atlantic, Atmos. Chem. Phys., 22, 2769–2793, https://doi.org/10.5194/acp-22-2769-2022, 2022.
Hansen, J. and Travis, L. D.: Light scattering in planetary atmospheres, Space Sci. Rev., 16, 527–610, 1974.
Lehmann, K., Siebert, H., and Shaw, R. A.: Homogeneous and inhomogeneous mixing in cumulus clouds: dependence on local turbulence structure, J. Atmos. Sci., 66, 3641–3659, https://doi.org/10.1175/2009JAS3012.1, 2009.
Lu, C., Liu, Y., and Niu, S.: Examination of turbulent entrainment-mixing mechanisms using a combined approach, J. Geophys. Res., 116, D20207, https://doi.org/10.1029/2011JD015944, 2011
Citation: https://doi.org/10.5194/egusphere-2023-2608-RC1
- AC1: 'Reply on RC1', Xiaojian Zheng, 15 Apr 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2608/egusphere-2023-2608-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2023-2608-AC1
RC2:
'Comment on egusphere-2023-2608', Anonymous Referee #2, 09 Jan 2024

See attached.

Citation: https://doi.org/10.5194/egusphere-2023-2608-RC2
- AC2: 'Reply on RC2', Xiaojian Zheng, 15 Apr 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2608/egusphere-2023-2608-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2023-2608-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-2608', Anonymous Referee #1, 11 Dec 2023
Comment on EGU-2023-2608 titled “Distinctive aerosol-cloud-precipitation interactions in marine boundary layer clouds from the ACE-ENA and SOCRATES aircraft field campaigns”
GENERAL COMMENTS:
This study uses aircraft in-situ measurements from the ACE-ENA and SOCRATES field campaigns to illustrate vertical profiles of cloud microphysical and precipitation properties and their relationships with above- and below-cloud aerosols. The paper is well-written with appropriate references. There is tremendous detail in Section 2 (uncertainties in airborne observations, formulae used to calculate cloud properties, thresholds used to define in-cloud and above/below-cloud regions) to ensure the results can be reproduced. The discussion of the results is well structured, and the text is backed up with appropriate figures. The study draws proper conclusions and provides appropriate evidence. This is a comprehensive study that deals with numerous elements of aerosol-cloud-precipitation interactions – a single paper is used to show findings that could have spread across multiple studies if the individual elements were investigated further.
While the work is comprehensive, the novelty of this study comes from the fact that these in-situ observations come from regions that have not been sampled extensively by aircraft or the data examined in detail. Additionally, very distinct regions with unique cloud and aerosol characteristics are compared. In isolation, many findings might not strictly be new as they corroborate results from many previous studies that have used aircraft observations. Nevertheless, this study is an important addition to the literature because of the wide range of topics discussed and the fact that the authors contrast cloud and aerosol properties from multiple field campaigns from two different locations. The effort put into this work is commendable and the paper would be a valuable addition to the journal and the literature. Given the number of topics discussed and potential for deeper dives into each topic, I can see multiple studies coming out of further investigation into the results presented here.
I have some considerations for the authors before the study is published:
The introduction felt a bit too broad and generic - the authors could better motivate and highlight the unique aspect of this work by guiding the reader through the distinct nature of these regions, by contrasting the existing knowledge of cloud properties from these regions - somewhat done for SOCRATES but not for ACE-ENA, highlighting the ‘climatic significance’ of clouds observed in these two regions – this was only done for MBL clouds in general, and the need for in situ observations from these locations.

Is there a reason behind comparing these two specific field campaigns? Are we comparing apples to apples? - describing the cloud regime, type, or morphology in these regions could help interpret the differences in the results presented in later sections.
2. The authors could better and use terminology to refer to cloud processes discussed throughout the text. Terms like “collision-coalescence”, “in-cloud coalescence”, “coalescence-scavenging” are used (often interchangeably it seems) - they can be merged or defined using more commonly used terminology.
Line 57: the authors could separate what they term the ‘coalescence-scavenging effect’ into two parts. While the drizzle drops are within the cloud layer, the process described in Line 58 can be described as the ‘collision-coalescence’ process. Once the drizzle drops are below cloud base, the process described in Line 59 can be described as the ‘precipitation scavenging’ process. Using such terminology would prevent confusion caused by using the same term for two separate processes that occur in-cloud and out-of-cloud, respectively. Please ensure consistency in using the terms as the paper currently uses “collision-coalescence process” in some spots and different terms at other spots while describing a similar process.
SPECIFIC COMMENTS:
ABSTRACT:
Line 15: Could you provide quantitative estimates with the number and size used to state “larger number” and “smaller cloud droplets”?
SECTION 1:
Line 34: The authors mention ‘cloud-top longwave radiative cooling’ here which is very important and should be mentioned but it is not discussed later. In contrast, there is an excellent discussion of cloud top entrainment mixing and droplet evaporation near cloud top later, but it is not introduced here. The authors could better motivate their results by introducing cloud processes in Section 1 if they are discussed later.
Line 42: This statement is only true under conditions of comparable cloud water content. Please update accordingly and provide appropriate references.
Line 44: Instead of listing references at the end of the sentence, a reader would benefit much more if references for specific elements followed the corresponding text. For example, “…investigated by different observational platforms, such as aircraft (Diamond et al., 2018; Painemal et al., 2020), model simulations (Hill et al. 2009)…”.
Please directly state some of the “different maritime regions”. Something like “….over different maritime regions like the southeast Pacific (Painemal and Zuidema, 2011), northeast Pacific (Braun et al., 2018), southeast Atlantic (Diamond et al., 2018), and eastern North Atlantic (Zheng et al., 2022a).”
Line 53: More recent studies of precipitation susceptibility (e.g., Gupta et al., 2022; Jung et al., 2016; Terai et al., 2012) have been built upon the studies cited here. To my knowledge, Feingold and Seibert (2009) introduced the term precipitation susceptibility and the study should be cited here. I see the authors briefly compared their results with some of these previous studies (good to see) - but the studies should be cited in the introductory text. Also suggest discussing the different issues with estimating/interpreting S_o based on results from previous studies.
Line 75: Please also provide the months for the ACE-ENA IOPs along with the years.
Line 80: Please provide the duration for the SOCRATES austral summer IOP.
SECTION 2:
I want to commend the authors for the discussion in this section. However, the section does lack some context about the cloud sampling locations. A map of the sampling locations/flights tracks or a list of the range of latitude-longitude coordinates where clouds were sampled during the IOPs would be very useful.
Line 106: I believe by “resolutions” you actually mean - “the size bins of the probe were 1 to 3 um wide”?
Line 111: Can you provide a reference for the phase classification product? If not, a short description of the methodology for it would be useful.
Line 128: Can cite Hansen and Travis, 1974 where the term “effective radius” and the associated formula were introduced.
Line 160: Do your results depend on the selection of the value of 200 m to determine the distance for above-cloud aerosols that are important for the analysis? Gupta et al. (2021) conducted a sensitivity test to determine if their analysis of cloud microphysical properties was affected by this number for distance from above-cloud aerosols. A comment on the sensitivity of the results on this value would be useful.
SECTION 3:
Line 192: These aerosol concentrations for SOCRATES seem high for the Southern Ocean, which was typically viewed to be a pristine environment. The authors refer to previous studies from SOCRATES to explain the aerosol size distribution or composition, do these studies have similar aerosol concentrations?
Line 213: Do you mean that the ‘sub-cloud Nacc values’ are more than double the ‘above-cloud Nacc values’? Suggest rewording this sentence.
Line 268: “These results have further improved the understanding of the aerosol first indirect effect”. This statement is a bit overreaching. There are many studies that have shown similar results. I suggest rewording to “These results are consistent with the understanding of the aerosol first indirect effect”
Line 271: It is interesting that the average Nc for ACE-ENA winter is greater than both the sub-cloud Nacc and Nccn. Do you have any comments on why this is the case? Has this been observed elsewhere? Are the values of Nc influenced by above-cloud aerosols or sub-cloud Na?
Line 310: This is an excellent discussion of entrainment mixing and its competing influence on droplet size/liquid water content and likely highlights two different modes of cloud top mixing – homogeneous and inhomogeneous mixing that depend on the entrainment rate (Lehmann et al., 2009; Lu et al., 2011) – do the authors have any comments based on their calculated entrainment rates? The authors could cite examples of previous studies that show similar vertical profiles of cloud properties where the effects of entrainment mixing on cloud microphysical properties were evident.
Line 370: The skewness of a distribution can actually be calculated as a statistical parameter rather than having a visual comparison. I leave it to the authors to decide if they would like to add this parameter to the study.
SECTION 4:
Line 434: This statement would be more accurate if the Liquid Water Path (LWP; vertical integral of the LWC) values were compared across campaigns rather than the mean LWC. Suggest adding LWP values or rewording the sentence.
Line 468: Do you want to mention some of these aircraft campaigns - VOCALS, ORACLES, ACTIVATE, etc.?
Line 475: These are some very interesting results. While the ACI_r,CT values are close to what one might expect (droplets are too large near cloud top for above-cloud aerosols to exert a significant influence on r near cloud top), it is interesting to note the ACI_{N, CT} values reported here. Do the authors have any explanation or hypotheses for what causes these values to not be closer to 0 like ACI_{r, CT}?
Line 480: I think the authors should also mention cloud top entrainment mixing over here.
Line 484: As mentioned earlier, would be good to also cite Feingold and Seibert, 2009 when defining S_o, which to my knowledge was the first study to define the term.
Line 491: The authors should provide the correlation coefficient values for the S_o calculations and contrast these with previous studies. At least two recent studies did this – Jung et al. 2016 and Gupta et al. 2022.
Line 501: “…due to decreasing 𝑆𝑜 within the thicker cloud (Terai et al., 2012)”. This is oversimplifying the problem. The value of S_o depends not only on cloud thickness but also on the calculation methodology as shown by Terai et al, the cloud type – cumulus versus stratocumulus (Sorooshian et al., 2009; Jung et al., 2016) and the above- and below-cloud aerosol concentration (Duong et al., 2011; Jung et al., 2016; Gupta et al., 2022). Having more information on cloud type/morphology in the introduction would give context to these S_o values and other results in the study.
Line 531: What are the units of the CCN loss rate? Here, the values are reported with units of “cm^-3” which does not include a unit of time, this is likely an error?
SECTION 5:
Line 568: The differences can also be attributed to the different size distributions which are then due to the sources discussed in the following sentences. That would then nicely lead to the discussion of aerosol modes toward the end of the paragraph.
Line 569: I don’t think using the words ‘pristine natural environment’ is appropriate when the previous sentence claimed the aerosol concentrations are highest for SOCRATES.
Line 580: Can you also list the percentage increase in r from cloud base to top since these campaigns had different cloud thickness values?
Lines 255 and 576: How does in-cloud coalescence cause an increase in the size of sub-cloud aerosols? In-cloud coalescence would increase the size of a cloud drop as it accumulates water by colliding and coalescing with other droplets. Once this drop evaporates in the sub-cloud to expose the residual aerosol, the aerosol/CCN core size should be the same unless the CCN is modified during droplet growth. Is this related to the condensation of sulfuric gas onto aerosol cores as described in Line 245? If so, is there a way to verify this based on these observations? If not, this should be stated as a hypothesis rather than a conclusion?
Lines 591-597: I don’t fully understand or agree with the conclusion drawn here. The studies that the authors cited here/earlier (among many others) have calculated f_ad using in-situ aircraft data from other locations and shown that assuming f_ad = 0.8 could lead to errors in satellite estimates of droplet concentration. While the calculation of f_ad and stating the regional values is important, these f_ad values do not “shed light on the further understanding of the satellite retrievals, particularly the satellite-based aerosol-cloud interaction assessment”. The authors can state the f_ad values and perhaps add a comment on the need to use these values when calculating droplet concentration for these regions using satellite retrievals, but I suggest removing lines 594-597.
Line 614: I don’t understand what is meant by “the aircraft assessment provides more connected circumstances between the aerosols and cloud layer.”
TECHNICAL CORRECTIONS/CLARIFICATIONS:
Line 12: Could use the term “aerosol-cloud-precipitation” given the terminology in the title? Also, change to “interactions” given the verb “are” in the next sentence?
Line 94: “aerosol, cloud, and drizzle”?
Line 105: “onboard the aircraft”?
Line 110: “large, ice particles”? Large ice particles would be a lot larger than 200 um.
Line 286: “To ensure the representativeness of the vertical profiles”?
Line 443: The sentence should probably end with “during the winter”.
Line 582: Do you mean “The mean cloud-top entrainment rates (𝑤𝑒 ) are a function of cloud top virtual potential temperature and vertical velocity and their values are….”
Figure 1: Please mention which statistical metrics are provided in the legends. Suggest adding that to the figure caption.
Figure 2: The caption lists the incorrect size range for the inner plots. Should be “Aitken mode size distribution (𝐷𝑝 = 0.01 to 0.06 µm)”
REFERENCES:
Feingold, G. and Siebert, H.: Cloud – Aerosol Interactions from the Micro to the Cloud Scale, from the Strungmann Forum Report, Clouds in the Perturbed Climate System: Their Relationship to Energy Balance, Atmospheric Dynamics, and Precipitation, 2, edited by: Heintzenberg, J. and Charlson, R. J., MIT Press, ISBN 978-0-262-01287-4, 2009.
Gupta, S., McFarquhar, G. M., O’Brien, J. R., Delene, D. J., Poellot, M. R., Dobracki, A., Podolske, J. R., Redemann, J., LeBlanc, S. E., Segal-Rozenhaimer, M., and Pistone, K.: Impact of the variability in vertical separation between biomass burning aerosols and marine stratocumulus on cloud microphysical properties over the Southeast Atlantic, Atmos. Chem. Phys., 21, 4615– 4635, https://doi.org/10.5194/acp-21-4615-2021, 2021.
Gupta, S., McFarquhar, G. M., O'Brien, J. R., Poellot, M. R., Delene, D. J., Miller, R. M., and Small Griswold, J. D.: Factors affecting precipitation formation and precipitation susceptibility of marine stratocumulus with variable above- and below-cloud aerosol concentrations over the Southeast Atlantic, Atmos. Chem. Phys., 22, 2769–2793, https://doi.org/10.5194/acp-22-2769-2022, 2022.
Hansen, J. and Travis, L. D.: Light scattering in planetary atmospheres, Space Sci. Rev., 16, 527–610, 1974.
Lehmann, K., Siebert, H., and Shaw, R. A.: Homogeneous and inhomogeneous mixing in cumulus clouds: dependence on local turbulence structure, J. Atmos. Sci., 66, 3641–3659, https://doi.org/10.1175/2009JAS3012.1, 2009.
Lu, C., Liu, Y., and Niu, S.: Examination of turbulent entrainment-mixing mechanisms using a combined approach, J. Geophys. Res., 116, D20207, https://doi.org/10.1029/2011JD015944, 2011
Citation: https://doi.org/10.5194/egusphere-2023-2608-RC1
- AC1: 'Reply on RC1', Xiaojian Zheng, 15 Apr 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2608/egusphere-2023-2608-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2023-2608-AC1
RC2:
'Comment on egusphere-2023-2608', Anonymous Referee #2, 09 Jan 2024

See attached.

Citation: https://doi.org/10.5194/egusphere-2023-2608-RC2
- AC2: 'Reply on RC2', Xiaojian Zheng, 15 Apr 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2608/egusphere-2023-2608-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2023-2608-AC2

Peer review completion

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

AR by Xiaojian Zheng on behalf of the Authors (16 Apr 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (25 Apr 2024) by Tak Yamaguchi

RR by Anonymous Referee #1 (07 May 2024)

RR by Anonymous Referee #2 (14 May 2024)

ED: Publish subject to minor revisions (review by editor) (15 May 2024) by Tak Yamaguchi

AR by Xiaojian Zheng on behalf of the Authors (11 Jun 2024) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (13 Jul 2024) by Tak Yamaguchi

After reading the revised manuscript, I found several unclear sentences, English mistakes, typos, and errors such as cross-referencing. Below is the list of my suggestions and questions. I don't think I found all mistakes and typos. Please do very careful reading and perform corrections and adjustments. Also, I found in some places the explanation of the physical processes mostly come from the existing studies and these explanations are not investigated by your analysis so there is no guarantee that these physical explanations hold for these IOPs. You seem to be making "sound reasonable" arguments without showing evidence. For these parts, please clearly make a separation from what your analysis shows to what other studies show and clearly state the arguments with other studies are reasonable/seems applicable but not necessarily true. I also suggest to use ACE-ENA Sum and ACE-ENA Win in the text.

L13: are being examined => are examined
L16: larger number => larger number concentration
L17: cloud droplets => cloud droplet effective radius
L19: drizzle formation and growth due to => drizzle formation via droplet growth through
L23: sufficient water => sufficient water vapor (or moisture)
L24: You have not defined the aerosol-limited regime, yet. Maybe "ACE-ENA winter is in the aerosol-limited regime such that aerosols are more likely activated..." (L22-L24)
L26: water-vapor-limit regime => water-vapor-limited regime
L27: Please use more appropriate verb in stead of "pronounced" or describe how pronounced.
L51: "more and smaller cloud droplets not only extend cloud longevity and spatial coverage" I don't think this always holds. Please clarify it.
L57: "Aerosols have been found to suppress the precipitation frequency and strength by constantly buffering cloud droplet number concentrations via activation, hence increasing cloud precipitation susceptibility" doesn't make sense. Buffering implies that multiple process work together to reduce the response to an aerosol perturbation but aerosol should increase cloud droplet number after it is activated. Also, how does this increase cloud precipitation susceptibility? Please clarify in plain language.
L67: cloud top => cloud-top
L80: CCN budgets also via => CCN budget via
L88: for such studies => for studying ACPIs / for studies of ACPIs
L94: were => was
L95: Remove "(ACE-ENA Sum)" and "(ACE-ENA Win)" since these are not used in other part of the text. Or use these names in stead of, e.g., ACE-ENA winter, ACE-ENA summer, winter ACE-ENA, and summer ACE-ENA in the text. The latter may be better so that you list like "SOCRATES, ACE-ENA Sum, and ACE-ENA Win" in stead of "SOCRATES, ACE-ENA winter and summer."
L115: as well as => and
L117: aerosol, clouds and precipitation => aerosol, clouds, and precipitation
L134: numerous => many
L136: colder nature => colder weather/climate/atmospheric condition? near-freezing condition?
L137: "compositely speaking" sounds odd to me. "our composite analysis of ... shows that" is better
L139: The region of selected... => Because/Since the region of selected...
L162: ...(Glienke and Mei, 2000). While... => ...(Glienke and Mei, 2000), while... Or remove "while" and start with "SOCRATES..." "the" in front of "SOCRATES" is unnecessary here. This should be generally applicable throughout the text.
L166: will be => are
L207: along with => , and
L208: cloud base heights (zt), cloud top heights (zb) and => cloud-base heights (zb), cloud-top heights (zt), and
L213: g/kg => g kg^-1 (superscript)
L224: g/kg => g kg^-1
L235: which counts => which count
L243: ACE-ENA is => ACE-ENA are
L262: "separated profiles" Please make it clear.
L265: decreasing profile => decreasing aerosol profile
L266: during summertime, will induce => during summertime, induce
L266: What is the typical distance between the bottom of the elevated aerosol layer and the cloud top for both ACE-ENA and SOCRATES? Why is 200 m chosen in stead of 100 m which is used by the referenced study? Some clarification is necessary here.
L268: SOCRATES will significantly => SOCRATES significantly
L268: aerosol budget, they would need => aerosol budget, and (or which?) they need
L310: Figure 1a reveals => Figures 1a and 1d reveal
L313: 1a&b => 1a and 1b
L314: 1b&c => 1b and 1c
L320: during SOCRATES => for SOCRATES
L321: 1e&f => 1e and 1f
L322: Section 3.1 => Section ? The paragraph is in Section 3.1.
L343: entrained down => entrained
L369: Bulk cloud microphysical properties distribution => Distribution of bulk cloud microphysical properties
L372: "The results in Figure 1 have demonstrated that aerosol/CCN sources and concentrations, especially from the sub-cloud regime, play an important role in cloud droplet formation and evolution." I don't see any discussion regarding this point in Section 3.1. Are you mentioning about L318-L320? If you are mentioning the sentences following this sentence, then adjust the sentence appropriately.
L387: "Note that the NCCN0.35% and NC values are lower than NC values during the ACE-ENA winter IOP, which is also confirmed in previous studies" I don't get this. Which NCCN and NC are you comparing with NC of ACE-ENA winter?
L406: "due to cloud-top entrainment" requires an immediate explanation. I think some text re-organization may be necessary to combine the sentences in the next paragraph. Or maybe just removing "due to cloud-top entrainment" from the sentence just work nicely, i.e., use the current paragraph to describe the general shape of the profile and use the next paragraph to give physical insights/interpretations.
L429: Define DSD here.
L435: "In addition, the cloud adiabaticity is defined as ..." is not connected well to the previous sentence. Please elaborate it.
L450: cloud top => cloud-top
L455: "generally weaker cloud-top inversions" In L461, the temperature jumps are listed, which should be listed here for clarity. Or move "Within the above-cloud inversion layer, the temperature (water vapor mixing ratio) differences ΔT (Δq) are 1.76 K (-1.75 g kg-1), 1.54 K (-1.66 g kg-1) and 1.48 K (-1.09 g kg-1) for SOCRATES, ACE-ENA summer and winter, respectively." right after the sentence.
L455: "stronger near-cloud top turbulence" In Fig. 5, TKE near the cloud top for ACE-ENA Win is strongest. So add a cross-reference of (Figure 5).
L457: cloud top => cloud-top
L460: How about influence on the water vapor jump? ACE-ENA Win is lowest and SOCRATES is strongest so entrained air could be dryer? It is better to use virtual potential temperature.
L462: Remove "Therefore".
L465: exhibited => exhibit
L490: droplet size distributions (DSD) => DSDs. DSD should be defined at L429.
L515: Move "For the four cloud portions from cloud base to cloud top, the skewness of summertime (wintertime) cloud DSDs are 0.627 (0.271), 0.358 (0.175), 0.098 (-0.063), and -0.362 (-0.554), respectively." to L508 before "Notably, the cloud DSDs..." and adjust both sentences.
L520: Make new paragraph starting with "Note that in the upper region..." and adjust the sentence.
L541: m/s => m s^-1
L546: 5c & d => 5c and 5d
L554: might be slightly => is
L578: are elongated => would become longer (a time scale does not have width)
L578: growth can be => growth could be
L581: which disturb => which would disturb
L583: "As a result, the ACE-ENA..." The discussion above the sentence is all hypothesis/speculations based on past studies and there is no guarantee that these occur in ACE-ENA. Please correct it.
L630: higher => higher than ACE-ENA
L632: "relatively less Nccn,0.35% condition for SOCRATES" In Fig. 1f, Nccn,0.35% is largest for SOCRATES. Please clarify this.
L636: According to Fig.1 "under the relatively more CCN condition" is not true for ACE-ENA compared with SOCRATES. Please clarify this.
L640: add appropriate references for VOCALS, CSET, ORACLES, ACTIVATE
L645: Move "The AI indices from three IOPs are ..." between "...the cloud base)." and "Note that the availability..." in L607 or move it to a better place before discussing these indices
L648: Include Fig. S5 into Fig. 6. Also state that the LWC near cloud top for the three IOPs are not comparable each other.
L682: near the cloud base => near the cloud base in ACE-ENA winter
L682: "the ACE-ENA winter featured enhanced collision-coalescence and drizzle-recirculating processes" has not been shown by data analysis. Or are you mentioning L617-L621? But it still lacks drizzle-recirculating process. Please clarify it.
L684: "the higher ambient aerosol and CCN concentrations ... may induce effective aerosol buffering effects" is unclear. Are you saying that aerosol of SOCRATES is mainly composed of fine Aitken mode aerosol (I think you mentioned somewhere in the text), which results in smaller cloud droplets, thus collision-coalescence is not effective, which means that the warm-rain processes are suppressed? Please explain clearly.
L695: Do you really think the difference of R^2 between 0.165 and 0.295 for SOCRATES is significant and think SOCRATES are more related to Nc? These numbers as well as correlation coefficients for S0 (L672) are generally small and I am not sure if these are statistically meaningful. How reliable are these values with uncertainty of observed data?
L754: Sentences below this line are unclear and need elaboration. "Hence ..." This is unclear and need better explanation. "the time needed, ..." is also unclear to me. What budget are you talking about? The sub-cloud CCN budget? "restore the sub-cloud CCN to the budget" sounds strange since these units are different.
L756: Thus, => This
L775: "Physical processing like in-cloud Brownian capture can reduce Aitken mode aerosols, while the chemical processes transform Aitken mode aerosols to larger sizes, moving them toward the accumulation mode. In addition, the in-cloud coalescence processes shift sub-cloud aerosol residuals to larger sizes, as multiple aerosols combine into a single aerosol core inside the cloud droplet during collision-coalescence" These are not shown from your analysis. These from the existing studies are used so that "the observed increase in the tail-end of the aerosol distribution for all IOPs" is somehow explained. So, these statements are speculation or can be hypothesis for future research. Please distinguish the existing studies from your findings.
L794: "which substantially enhances the collision-coalescence and the drizzle re-circulating processes" is not demonstrated by your analysis and this is another speculation.
L802: cloud base => cloud-base
L807: "a result of turbulence-driven in-cloud droplet interactions, especially under low NC condition" is not shown by your analysis and this is a speculation/hypothesis.
L809: "The relationships established in this study indicate that ACE-ENA clouds, are largely determined by Hc, while SOCRATES clouds are more influenced by the Nc." This needs to be corrected because of small R2.
L810: "The combination of a deeper cloud layer and relatively lower ambient aerosol concentration, eventually leading to stronger drizzle production and
evolution during ACE-ENA, especially during the winter season, results in more robust precipitation susceptibility" Even this is a sort of speculation. This has not been demonstrated by your analysis. A sound reasonable explanation doesn't mean that that is true or happening without evidence.

Fig. 1: "ACE-ENA summer, winter and SOCRATES" => "ACE-ENA Sum, ACE-ENA Win, and SOCRATES"; "pink, purple and green" => "pink, purple, and green"
Fig. 2: "Accumulation mode, Aitken mode and Coarse mode" => "Accumulation mode, Aitken mode, and Coarse mode"; "ACE-ENA summer, winter and SOCRATES" => "ACE-ENA Sum, ACE-ENA Win, and SOCRATES"; "pink, purple and green" => "pink, purple, and green"
Fig. 3: "ACE-ENA summer, winter and SOCRATES" => "ACE-ENA Sum, ACE-ENA Win, and SOCRATES"; "pink, purple and green" => "pink, purple, and green"
Fig. 4: "ACE-ENA summer, winter and SOCRATES" => "ACE-ENA Sum, ACE-ENA Win, and SOCRATES"; "pink, purple and green" => "pink, purple, and green"
Fig. 5: "u'2 (c) and v'2" => "u'2 (c), and v'2": "ACE-ENA summer, winter and SOCRATES" => "ACE-ENA Sum, ACE-ENA Win, and SOCRATES"; "pink, purple and green" => "pink, purple, and green"
Fig. 6: Add label (a) and (b). Include Fig. S5 here; "ACE-ENA summer, winter and SOCRATES" => "ACE-ENA Sum, ACE-ENA Win, and SOCRATES"; "pink, purple and green" => "pink, purple, and green"
Fig. 7: "ACE-ENA summer, winter and SOCRATES" => "ACE-ENA Sum, ACE-ENA Win, and SOCRATES"; "pink, purple and green" => "pink, purple, and green"

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AR by Xiaojian Zheng on behalf of the Authors (06 Aug 2024) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (07 Aug 2024) by Tak Yamaguchi

AR by Xiaojian Zheng on behalf of the Authors (13 Aug 2024) Author's response Manuscript

Journal article(s) based on this preprint

18 Sep 2024

Distinctive aerosol–cloud–precipitation interactions in marine boundary layer clouds from the ACE-ENA and SOCRATES aircraft field campaigns

Xiaojian Zheng, Xiquan Dong, Baike Xi, Timothy Logan, and Yuan Wang

Atmos. Chem. Phys., 24, 10323–10347, https://doi.org/10.5194/acp-24-10323-2024,https://doi.org/10.5194/acp-24-10323-2024, 2024

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Xiaojian Zheng, Xiquan Dong, Baike Xi, Timothy Logan, and Yuan Wang

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Xiaojian Zheng, Xiquan Dong, Baike Xi, Timothy Logan, and Yuan Wang

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The marine boundary layer aerosol-cloud interactions (ACI) are examined using in-situ measurements from two aircraft campaigns over the eastern North Atlantic (ACE-ENA) and Southern Ocean (SOCRATES). The SOCRATES clouds have more and smaller cloud droplets. The ACE-ENA clouds exhibit pronounced drizzle formation and growth. Results found distinctive aerosol-cloud interactions for two campaigns. The drizzle processes significantly alter sub-cloud aerosol budgets, and impact the ACI assessments.

Distinctive aerosol-cloud-precipitation interactions in marine boundary layer clouds from the ACE-ENA and SOCRATES aircraft field campaigns

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