This paper uses radiosonde observations and flight Automatic Dependent Surveillance-Broadcast (ADS-B) telemetry to estimate the potential contrail occurrence by altitude and seasonality. The paper is very well written, the methodology is appropriate, and the results are reasonable. It is relevant to the scope of Atmospheric Chemistry and Physics, and I recommend it for publication with minor revisions.

Major Comments

1. [Sections 4.1 and 4.4] Are these results (i.e., ISSR properties, potential contrail formation, and their respective seasonal variabilities) consistent with existing publications that used radiosonde measurements and in-situ water-vapour measurements from aircraft^1–3? It would be great if the authors can compare and quantify the differences in their results relative to existing studies and include a short discussion on the potential reasons causing these discrepancies.
2. [Section 4.6] The authors estimate the change in the non-persistent and persistent contrail formation from different fuel types. However, as pointed out, these fuels have differences in the water vapour emissions index and nvPM number emissions index, both of which are expected to change the various contrail properties such as the lifetime and radiative forcing^4–6. While I understand that the changes in contrail properties are beyond the scope of this study, it would still be appropriate to add a short discussion on the potential changes in contrail properties due to the use of different fuel types.
3. [Section 4.7] The results in this section were very well described. However, the authors can improve it further by highlighting the potential factors that contribute to the seasonal difference in flight altitude changes in minimising persistent contrail formation. For example, it would be great if these results can be related to the seasonal cycle of the thermal tropopause height, as illustrated in Figure 5.

Minor Comments

4. [Line 43] It would be great to add a short sentence describing the second-order effects of contrails in affecting the natural cirrus properties^7,8.
5. [Line 53] The terms “terrestrial RF” and “solar RF” that were used in this paper are not commonly used in the literature. The authors can consider renaming them to “shortwave (SW)” and “longwave (LW)” RF here and in other parts of the paper to conform to the terminology that is used in the literature.
6. [Line 272] There is a typo where “R1-NOC” should be “R1-NPC”.
7. [Lines 430 - 432] This statement conflicts with Figure 5c. The stratosphere is generally dry and identified where the background H2O is below 10 ppm. Ice supersaturation in the stratosphere is a rare event and Figure 5c shows that persistent contrails generally form below the troposphere.
8. [Lines 477 – 485] It would be a great for the authors to highlight that the contrail climate forcing from NPC are generally negligible, and that PC’s are the significant contributor to contrail climate forcing.

REFERENCES

1. Petzold A., Neis P., Rütimann M., Rohs S., Berkes F., G. J. Smit H., Krämer M., Spelten N., Spichtinger P., Nédélec P., Wahner A. Ice-supersaturated air masses in the northern mid-latitudes from regular in situ observations by passenger aircraft: Vertical distribution, seasonality and tropospheric fingerprint. Atmos Chem Phys. 2020;20(13):8157-8179. doi:10.5194/ACP-20-8157-2020
2. Agarwal A., Meijer VR., Eastham SD., Speth RL., Barrett SRH. Reanalysis-driven simulations may overestimate persistent contrail formation by 100-250%. Environ Res Lett. 2022;17(1):1-14. doi:10.1088/1748-9326/AC38D9
3. Rädel G., Shine KP. Evaluation of the use of radiosonde humidity data to predict the occurrence of persistent contrails. Q J R Meteorol Soc. 2007;133(627):1413-1423. doi:10.1002/QJ.128
4. Voigt C., Kleine J., Sauer D., Moore RH., Bräuer T., Le Clercq P., Kaufmann S., Scheibe M., Jurkat-Witschas T., Aigner M., Bauder U., Boose Y., Borrmann S., Crosbie E., Diskin GS., DiGangi J., Hahn V., Heckl C., Huber F., et al. Cleaner burning aviation fuels can reduce contrail cloudiness. Commun Earth Environ 2021 21. 2021;2(1):1-10. doi:10.1038/s43247-021-00174-y
5. Kärcher B. Formation and radiative forcing of contrail cirrus. Nat Commun. 2018;9(1):1824. doi:10.1038/s41467-018-04068-0
6. Teoh R., Schumann U., Gryspeerdt E., Shapiro M., Molloy J., Koudis G., Voigt C., Stettler M. Aviation Contrail Climate Effects in the North Atlantic from 2016-2021. AtmosChemPhysDiscuss. 2022. doi:https://doi.org/10.5194/acp-2022-169
7. Ponater M., Bickel M., Bock L., Burkhardt U. Towards Determining the Contrail Cirrus Efficacy. Aerospace. 2021;8(2):42. doi:10.3390/AEROSPACE8020042
8. Burkhardt U., Kärcher B. Global radiative forcing from contrail cirrus. Nat Clim Chang. 2011;1(1):54-58. doi:10.1038/nclimate1068

This study investigates the presence of conditions favorable to the occurrence of persistent and non-persistent contrails. Radiosonde ascents in the vicinity of Paris, which are combined with flight altitudes of aircraft in this area, serve as the basis for this investigation. In this way, for example, a common probability can be estimated that an aircraft flies through an area that fulfills the conditions for the formation of condensation trails. 

This is a conscientiously conducted study with interesting results that fit very well into the scope of ACP. I recommend publication with minor revisions.

Comments

• Is there a reason that for the calculations of the saturation water vapor pressure over liquid water the equation after Sonntag (1994) is used? Wouldn't it be more consistent to use the Murphy and Koop (2005) method  also for e_sat_liq (as it is already done fore_sat_ice)?
• In order to help readers better understand the results, a rough quantitative estimate of the possible disadvantages of higher / lower altitudes would be helpful.
• The illustrations are very clear and meaningful. Nevertheless, an indication of the percentiles for the tropopause (Fig. 5) and jet stream height (Fig. 6) would be desirable in order to gain an impression of their variability. 
• P11L258: „Profiles for which the temperature inversion was weak and the TT altitude was not clearly identifiable are removed from the analysis.“ What exactly do you mean with „weak“? How do you define this „weakness“?
• P14L332: "The smallest distances are identified in March and November with the jet stream at the same altitude as for R2.“ For me it seems that the distance in April is smaller than the distance in March. Typo?
• P12 L278 "similarly to R2-PC conditions“ - you mean R1-NPC? Typo?
• P14L331: "Similarly Fig 6b…"  you mean Fig 6c?

Misc.

•  P12 L273.  R1-NOC should be R1-NPC
• Sometimes R2 is used, other times R2-PC (same for R1 and R1-NPC). Please use consistent labeling in the text and graphics.