Review of Measurement Report: A survey of meteorological and cloud properties during ACTIVATE’s postfrontal flights and their suitability for Lagrangian studies by Tornow et al.

This measurement report is about marine cold-air outbreak flights during the ACTIVATE campaign. The authors report on the synoptic and meteorological conditions during flights,  cloud properties, and choose specific flights of interest for Lagrangian modelling studies.

Overall, I think that this is a nice measurement report that is certainly helpful for anyone interested in choosing specific cases for a modelling study. My main concern is that that the selected cases all appear rather similar. Below I made some comments that the authors should consider before publication.

General Comments

1. My largest concern is that it appears that all the ‘selected’ flights are fairly similar in terms of their characteristics, yet some potentially interesting cases such as 29 Jan 2021 and 28 Feb 2020 are not selected. Given that some of the selected cases have already been studied in published work, I think the report could benefit from some additional discussion about what makes each selected case unique and what would be interesting to study about them. At the moment it seems that no matter which of the selected cases is chosen one would get similar results while other cases with more different characteristics are left out. For instance, what would be the difference between choosing the 1 Mar 2020 and the 13 Mar 2022 flights, they seem very similar. Intentionally or not the authors might be steering the research to specific types of cases that then might end up being overrepresented in the literature, while other relevant cases are not studied.
2. Although the authors mention that users can adjust the criteria, I think some justification or more description of how the authors arrived at the selected thresholds for the parameters in Table 1 is needed. Also were any other criteria considered by the authors that might be relevant, but were not included (such as surface fluxes)?
3. 72-74: In the context of this report, it is important to mention what these studies have already done. At a later point it should also be mentioned which cases have been studied in which of these publications. Possibly add an indication in Figure 4?

Specific Comments

1. 1, 29: The statements make it sound like marine cold-air outbreaks are purely a cloud phenomenon. Please consider revising: e.g., ‘often appearing as part of […]’
2. 43-45: I am confused by this sentence since it seems to suggest that inhibition of vertical transport leads to the development of convection.
3. 58: Are there any references or links for CAESAR already?
4. 59: These field campaigns could be mentioned by name.
5. 70: Is that the maximum or average MCAO index > 0 K for these 71 flights.
6. Section 2.1: I am quite confused with some things here since notation does not appear to be consistent. Potential temperature is mentioned but derivatives are written as dT . Meridional wind speed changes are expressed as dv/dt which I interpret as the temporal change of the full wind (so it is neither the change in the meridional direction nor the change of the meridional wind). Please edit these things for clarity.
7. 102: ‘connect […] as lines’ might be better.
8. 131: How accurate is it to assume that all clouds are within the BL? How frequent was contamination by higher clouds and what impact did it have?
9. 162-165: It would be good to add to Table 1 which of the qualities mentioned here each criteria in the table corresponds to.
10. 182: Mention that you mean the identified front at the bottom of the image. 
11. 229: ‘All flights have at least three scores’ sounds confusing. Please consider revising wording: ‘fulfil at least three scores’. 
12. 277-278: Both of those flights were not selected. Why if they cover most criteria and the cloud transition. I think a 10 K threshold for the MCAO index is quite high. Was the value for these two cases close to 0 K?
13. Fig. 4: NA and TRUE have the same symbol. Further, it is quite hard to figure out the correct line for each case. Possibly, ticks on the left and a line connecting the cloud distributions to the score sheet could be added? The caption should also mention what the shaded areas in the score sheet mean. 
14. For future submissions the authors should include all figures in the main text near where they are mentioned as instructed in the ACP submission guidelines. 

Typographical:

1. 73: Try to be consistent with MCAO vs CAO.
2. 228: Fig. 4
3. 312: ‘favorable to certain’
4. Fig. 4 caption: ‘gray areas'

Review for Measurement Report: A survey of meteoroloigcal and cloud properties during ACTIVATE’s postfrontal flights and their suitability for Lagrangian case studies by Tornow et al.

This report discusses the importance of representing marine cold-air outbreaks (MCAOs) in weather and climate models and how recent field campaigns can help improve that. It provides a summary of the undertaken flights and how they could be used for future modelling studies.

In general, I enjoyed reading the manuscript as it provides a solid overview of the flights and the functional instruments during the single flights. I do have some comments that should be addressed before publication.

Major comments

1. I believe the discussion of suitable cases for Lagrangian studies should be revisited and articulated more clearly. Currently, this is to some degree confusing as it is difficult to follow the single dates. I would introduce a numbering from 1 to XX flights and reference these numbers as looking for the single dates mentioned in the text and compare it to the figures is quite cumbersome. An idea would also be to cluster the flights by the chosen criteria instead of having a chronological order.
2. As discussed in Sect. 3.4, the selected case studies show some quite large variations with respect to cloud droplets, cloud heights, and cloud top temperature. This variety should be discussed more especially in the context of constraining weather and climate models.

Minor comments

1. Line 9/10: “were better aligned with the MBL flow” – I do not understand what you mean by MBL flow
2. Line 18: there must be more reference to the cloud-climate feedback than only McCoy et al, 2023
3. Line 35: “MBL downwind” – downwind from what?
4. Line 40: I disagree with the “thereby” here coming from the previous sentence. I would turn the sentence around.
5. Line 51: “shaping prevalent aerosol with fetch” – what does this mean?
6. Line 50 – 61: I think it could be beneficial to have an overview figure with all campaigns marked and highlighting the measurement area of ACTIVATE
7. Line 88 – 90: can you split up this long sentence in two?
8. Line 105: “at time steps around the time of interest” – be more specific
9. Line 114: “which we assume is representative of MBL” – add references or more justification why this is applicable
10. Line 133: “load” – please change the verb
11. Line 145: use CCN as abbreviation as you have already introduced it
12. Line 166-168: I think the criteria in Table 1 need to be more clearly introduced, as I was surprised and confused by this paragraph, and did not think it was helpful. A proper discussion of Table 1 would be good.
13. Line 176-180: switch around the two criteria to be consistent with the explanation in Section 2.1 and give a paragraph title, e.g., “1. Hewson (1998): searching for spatial … “
14. Line 188 – 193: split up this single sentence
15. Line 204: orange should be grey?
16. Line 209: “and MCAO indices” – you already said that in the beginning of the sentence
17. Line 210: give some more background information to the turbulent surface fluxes
18. Line 212: As far as I can see, the data population is very sparse for the appended figures – can you add the number of data points going into your box whiskers, and discuss that as well? For case late 2020, early 2021 it looks like only 3 or 4 flights are selected, which are not enough to have box whiskers for that.
19. Line 219: what do you mean by process signatures?
20. Line 222: remove that sentence “Additionally, we indicate whether flights capture”
21. Line 226: While I do understand that some work is still in progress, here a bit more explanation is required how this is done for new particle formation
22. Line 234: “not shown” is not a good practice anymore remove and add to appendix
23. Line 265: I believe Figure A1 was never referenced, please double-check
24. Line 268-269: I do not understand this part with where the aircraft was located downwind and farther downwind.
25. Line 307: I expect there to be also other references for the CCN dilution in the MBL – please add.

Technical comments

1. Line 19: “contributes” to contribute
2. Line 65: wrong citation style (\citet{} vs \citep{})  this also goes for other instances: line 69, 105, 157
3. Line 73/161: stay consistent with MCAOs and not CAOs
4. Line 110: degree sign needs to go after the numerical value
5. Line 127: space between < and 6.0
6. Line 228: I believe the wrong figure is referenced here.
7. Line 240: space between number and unit (%)
8. Line 312: remove space between 9 and 5
9. Figure 1: please check that all colors are also explained in the figure caption, e.g., the yellow line? Dashed and solid lines? Green lines?
10. Figure 2: why did you choose vertical velocities at 700 hPa? Please discuss
11. Table 1: check that there is spacing between numerical values and units
12. Figure 3: MCAO index subplot could benefit from a dashed black line at 0 (as in w_{700 hPa}) for readability; the box whiskers should be in the same order as the labels, ideally actually blue, grey and then orange.
13. Figure 4: As said above, I believe a proper numbering of the flights would be useful, instead of the single dates. Please also explain the orange and blue shading in the score sheet. It is very hard to distinguish TRUE and NA – can you adapt that, such that maybe NA is represented by a cross or triangle? I would also color the selected flights labels and not only the score sheet. I would also sort the flight chronologically from top to down. There is a missing space in the figure caption in “gray areas”. The numbers in the legend are not needed.
14. Figure 5: similar comments as for figure 4.
15. Figure A1: not referenced?
16. Figure A2: can you choose colors for cloud formation and breakup that are consistent with Figure 4? Also red and green is not color vision deficiency friendly. Please avoid that combination for line plots.
17. Figure A3: as mentioned above, I would like to have the number of data points going into the box whiskers. Especially the late 2020, early 2021 case seems like very few flights which do not warrant a box plot – please discuss that. Further, when data is missing such as for late 2020, early 2021 a connecting line should be not plotted. Please adjust that.
18. Figure A4: have a caption that fully explains the figure.