Review Reports

Round 1

Reviewer 1 Report

Review report of

Validation of a contrail life cycle model in central Europe

By Rosenow et al.

Summary of paper:

Global civil aviation affects the Earth’s radiation balance through a combination of CO2 emissions and non-CO2 effects including the formation of contrail and contrail-cirrus. The studies on contrails become very important and urgent for potential mitigation scenarios. This paper presents a new method to model the contrail life cycle in central Europe by combining a nice and comprehensive review of the current state of algorithms describing the contrail formation and evolution. Compared with former models, they include ambient turbulence and humidity in the atmospheric conditions in the new model. Based on individual flights, the authors calculated the contrail life cycle with either measured or modeled input variables and validated the results with the ground-based camera observations, reaching an overall good agreement.

 

The research topic of contrail life cycle modeling is very interesting and important and certainly relevant to the readers of Sustainability. The authors have a unique dataset with multiple models and instruments at their disposal that are certainly valuable for the corresponding research. I applaud their efforts. The manuscript is well written and organized, except for a missing subsection (4.1). Hence in a sense, this is an uncompleted manuscript.  Nevertheless, there are several points should be clarified before publication.

 

1.       Line 16, from the context, should it be 90% accuracy? The same expressions are found elsewhere. Please double check.

2.       Line 18, contrail = condensation trail, the abbreviation and the full name are both used in the manuscript. It’s better to use “contrail” with a short description of condensation trail.

3.       Line 72, “between 7 and 30 min”, any reference for this? Why is the age chosen?

4.       Lines 90-92, please rephrase the sentence.

5.       Line 114, what do the authors mean by using “worse”?

6.       Line 117, the wind -> wind.

7.       Lines 124-127, very confusing, please rephrase the sentence.

8.       Line 175, during the radiosonde probing, the balloon may be drifted to a faraway place by wind. Any short description of the balloon trajectory will help for the accuracy.

9.       Line 210, live -> life.

10.   Line 223, what is the symbol “vmathrmTAS”? Typo?

11.   Figure 2, what can we learn from Figure 2? Why do the profiles are so different (up to 2 magnitudes)? Is it meaningful to have this figure?

12.   Figure2, 6 p.pm. -> 6 p.m.

13.   Line 244, the right parentheses are missing for the saturation vapor pressures “e*”.

14.   Lines 270-271, the turbulence intensity in the atmosphere is denoted by the turbulent energy dissipation rate epsilon.

15.   Lines 273-274, any reference for the lognormal distribution of epsilon?

16.   Line 274, what does this mean? Why is there a linear correlation between epsilon and vertical velocity? Any reference supports this?

17.   Lines 276-277, confusing

18.   Line 309, For 0.02535 -> For 0.0235; Please check again.

19.   Line 366, what is the definition for \sigma_i(t)?

20.   Line 425, ice water content and the abbreviation IWC are both used in the manuscript. Why don’t the authors just use “IWC” for the sake of simplicity.

21.   Line 426, “According to Stokes”, do the authors mean Stokes equation or any reference?

22.   Line 435, Does the sedimentation speed increase or decrease under the influence of the wind drift? Please make the expression more unambiguous.

23.    Lines 441-442, “Note that …”, the sentence is mentioned above and should be removed.

24.   Line 453, the subsection 4.1 is empty.

25.   Line 467, see Table 1 for what? I just realized that there are two Table 1. Please make corrections.

26.   Line 472, epsilon = 0.057 m^2s^-3? The intensity of turbulence is way too strong to be real. Please carefully check the number. See, for example, Schumann et al. 1995.

27.   Figure 10, I recommend the authors to indicate the different panels with letters (like a-h) for make the description earlier. The same for Figure 11.

28.   Line 483, please carefully check the value of the energy dissipate rate.

29.   Figure 11 (caption), please check the value of epsilon.

30.   Line 497, please rephrase the sentence.

31.   Line 517, observes -> observed.

32.   Lines 517-518, met -> reached. Should it be 90% accuracy?

33.   Line 523, from the results, it should be downward vertical wind.

34.   Lines 524-525, this is not well understood. Please rephrase the sentence.

35.   Line 527, contrails -> contrail.

36.   Lines 531-532, “From this follows for”???

 

 

 

 

Author Response

Dear Reviewer 1,

thank you for your valuable hints. 

Please find attached our response to all of your comments.

 

Best wishes

Judith Rosenow

Reviewer 2 Report

I recommend processing the following comments:

-       -  You state that you have achieved the observed lifetime with an accuracy of 10 % on average slightly underestimating the lifetime, have you compared this value with other studies?

-       -  Add a discussion section to discuss results and findings with other studies on the topic.

-       -  The conclusion missing the future direction.

-      -  Most literature reviews are out of date.

-        - English check should be required.

it is necessary to go through the contribution and pay attention to small grammatical mistakes and typographical mistakes which can reduce the quality of the article

Author Response

Dear Reviewer 2,

thank you for your kind review and the good ideas to improve the manuscript. As you find in the attached response, we considered all comments. Specifically, we asked a native speaker for checking the English grammar and spelling.

With kind regards,

Judith Rosenow

Author Response File: Author Response.docx

Reviewer 3 Report

 

Review of "Validation of a Contrail Life Cycle Model in Central Europe" by Rosenow

 

 

This manuscript provides a detailed description of a plume model coupled to a contrail initiation model from data. If looks at a small number of samples from one location. Also does a nice job of looking into key uncertainties. The paper could use some corrections as noted in my detailed comments below but is likely publishable with minor revisions. The results should probably be phrased a bit differently, since the range of contrail cases sampled is pretty narrow (lifetimes are all 5-10 min).

 

My main general comment is that it would be useful to do a more statistical treatment of the criteria to see if the model predicts contrails when there are none. The authors have only shown that in clear skies when a contrail forms it can be modeled, and this is a particular lifetime. Would it predict a lot of contrails when there were none if you ran it for many cases (e.g. a whole month). This is obviously perhaps something for future work, but it could be mentioned/noted in the conclusions (see detailed comments below.

 

Specific Comments:

 

Page 1, L16: What does accuracy mean? Even here might have to define it.

 

Page 1, L25: You should probably cite the more recent Lee et al 2021 aviation assessment paper.

 

Lee, D. S., D. W. Fahey, A. Skowron, M. R. Allen, U. Burkhardt, Q. Chen, S. J. Doherty, et al. 2021. “The Contribution of Global Aviation to Anthropogenic Climate Forcing for 2000 to 2018.” Atmospheric Environment 244 (January): 117834. https://doi.org/10.1016/j.atmosenv.2020.117834.

 

Page 1, L36: Global contrail estimates are typically built from individual contrails that have different lifetimes and time of day. Some of these contrails do have a cooling effect.

 

Page 2, L47: I’m not sure it’s ‘most’ (most are probably using detailed plume models), but you should provide references for some studies here.

 

Page 2, L49: They are partially abstracted in global models, but there are some global trajectory based models that have individual contrails. (E.g. Schumann, COCIP noted below).

 

Page 2, L80: suggest volatile —> highly variable (volatile has a specific chemical meaning)

 

Page 2, L82: note that global models do NOT have typical lifetimes, but they can track the entire evolution. Also they can track aviation induced cloudiness which is no longer linear in shape.

 

Page 3, Figure 1: Please make the numbers follow the numbers in the text. The figure could be improved to focus on the steps: identification, data into contrail initialization steps then contrail lifecycle. There are connections on figure 1 that don’t seem to make sense. Are you using radiosondes separately or through the GFS analysis? You don’t really input time into the GFS, etc.

 

Page 3, L114: maybe delete ‘worse’ here.

 

Page 3, L114: nature —> natural

 

Page 4, L158: It’s not ‘many’ aircraft, it’s only a few aircraft. The data is not that available (but enough, I guess you can remove the question mark).

 

Page 4, L174: Also note the IAGOS program which does have quality controlled humidity sensors on a small number of aircraft.

 

Page 5, L193: push —> assimilate

 

Page 5, L195: might just state every 6 hours (the ‘cycles’ correspond to UTC time).

 

Page 5, L211: what do you do about temporal mismatches if the radiosonde profile is every 12 hours? Why do you need the GFS at all if you are using radiosonde data?

 

Page 5, L218: what are they dependent on? I think only on an efficiency factor right? Please clarify.

 

Page 6, L237: is all this really necessary? You know the aircraft type, location, temperature and humidity, and that it is at cruise altitude. Isn’t that sufficient to decide whether a persistent contrail will form or not?

 

Page 7, L261: Please clarify ‘In the last hours to days’ does not make sense. Do you mean ‘On the timescale of hours to days’?

 

Page 7, L274: is upper tropospheric grid scale vertical velocity from the GFS realistic for defining turbulence?

 

Page 8, L280: when is the dissipation regime again? After 100s?

 

Page 8, L295: Is v_TAS the true air speed (relative to the air)?

 

Page 11, L360: Variance of what? What are the physical units here?

 

Page 12, L369: Given the scale of the GFS, doesn’t that introduce a large uncertainty?

 

Page 15, L473: can you mark the location of the radiosonde station on Figure 8 please.

 

Page 16, L481: so this contrail disappeared because of being ‘lofted’ into a sub-saturated region?

 

Page 17, L508: So your method is biased towards observations of 5-10 minute contrails.

 

It would be interesting to do a more statistical sampling of all aircraft in sight of the cameras to see if the contrail ID model has false positives and false negatives and what that looks like (obviously if you cannot observe them due to cloud cover that would be useful to know too).

 

Even if there were clouds, it would be interesting to see if the model has a wider diversity of lifetime, or is biased towards 5-10 min lifetimes….

 

Page 18, L523: upward or downward wind? Or both?

 

Page 18, L531: Maybe comment on this: does it work in your 13 examples? It would also be useful to run more cases (even if a contrail was not observed but when the model predicted one) and see if it holds over a wide range of lifetimes. At least add some caveats here. 

There are some minor edits needed (I have suggested a few other words). The language usage is okay. I recognize English is a challenging written language for non native speakers. 

Author Response

Dear Reviewer 3, thank you for your valuable hints and comments. Please find attached a response to all of your hints and concerns.

Author Response File: Author Response.docx

Reviewer 4 Report

The paper deals with a method to validate the Contrail Life Cycle model considering data from ADS-B, camera observation and weather data The article is of interest to Sustainability readers and it is within the scope of the journal. I have just a couple of comments.

The introduction should better introduce the problem of the contrail for the environment so that the reader can better understand the importance of the method, which is, however, really well described in the following chapter. In addition, the authors may explain why the Contrail Life Cycle assessment is important in solving the environmental problem of contrails. Also in the introduction they should spend a few words on the ADS-B data and explain the advantage to use this data acquisition system.

Finally, in the conclusions, the authors should explain why the method is useful to reduce the negative impact of the contrail on the weather.

 Minor comments.

The authors define the acronym ADS-B at line 92, but they cite it in the abstract (line 12) and in the introduction (line 42). I think that they should define the acronym the first time that they cite it.

 Line 158: There is a typing mistake: there is a question mark not appropriate

Author Response

Dear Reviewer 4,

thank you very much for your kind and helpful comments. Please find attached a response to all of your concerns.

With kind regards

Judith Rosenow

Author Response File: Author Response.docx