I have read your manuscript with great interest. While reading it I found a few things that I would like to give you feedback on.

First of all, I was wondering why no one from the ACE-FTS team is a co-author on such a study? Have you offered them the co-authorship? If not, a good point of contact for ACE-FTS is Kaley Walker from the University of Toronto (kaley.walker@utoronto.ca).

A major point that does not become clear from your study is if you are assessing the accuracy of the ACE-FTS isotope measurements or the accuracy airborne in-situ instruments? What actually is the intention of the study should be more clearly pointed out. Regarding the accuracy or quality of the ACE-FTS delta D measurements there are already several studies documenting this (although these are rather satellite-satellite comparison) and should be considered in your study. See my specific comments below.

Another study that may be of interest to you is the study by Thurnherr et al. (2024) where TROPOMI delta D was compared with airborne in situ observations.

Specific comments:

P1, L17: There is a more recent paper giving an overview on polar stratospheric clouds by Tritscher et al. (2021). I would thus suggest to additionally cite this paper.

P2, L23: There is another review paper by Yoshimura (2015). Although the focus of this review is somewhat different it may be worth citing or at least it will provide you with some other useful additional  references.

P2, L55: Add “e.g.” before Eichinger since there are many more isotope enabled models and studies that would be worth to be cited here as e.g.  deVries et al. (2022) for the COSMO-iso model, Eckstein et al. (2018) for the ICON-ART-iso model and Risi et al. (2021) for the LMDZ-iso model.

P3, L61: More recent papers on isotope measurements from Odin/SMR are the studies by Lossow et al. (2011) and Wang et al. (2018). Thus, I would suggest to add these here.

P3, L70: There are more recent intercomparison studies by Högberg et al. (2019) and Lossow et al (2020) that should also be cited here.

P19, L355: As already mentioned above, how do your results fit/compare to previous comparison studies?

P20, L379: I would suggest to add here additionally some newer references.

Technical corrections:

P3, L60: ODIN -> Odin

P3, L66: space between reference and “observes” missing.

P3, L70: ODIN -> Odin

P6, L142: of appears twice, thus one is obsolete.

P7, L163: space between “clouds” and the reference of Boone missing.

P22, L462ff: Use regular font for the reference by Hagemann et al.

P24, L524ff: Same here for the Randel et al. reference.

References:

de Vries, A. J., Aemisegger, F., Pfahl, S., and Wernli, H.: Stable water isotope signals in tropical ice clouds in the West African monsoon simulated with a regional convection-permitting model, Atmos. Chem. Phys., 22, 8863–8895, https://doi.org/10.5194/acp-22-8863-2022, 2022.

Eckstein, J., Ruhnke, R., Pfahl, S., Christner, E., Diekmann, C., Dyroff, C., Reinert, D., Rieger, D., Schneider, M., Schröter, J., Zahn, A., and Braesicke, P.: From climatological to small-scale applications: simulating water isotopologues with ICON-ART-Iso (version 2.3), Geoscie. Model Dev., 11, 5113–5133, https://doi.org/10.5194/gmd-11-5113-2018, 2018.

Högberg, C., Lossow, S., Khosrawi, F., Bauer, R., Walker, K. A., Eriksson, P., Murtagh, D. P., Stiller, G. P., Steinwagner, J., and Zhang, Q.: The SPARC water vapour assessment II: profile-to-profile and climatological comparisons of stratospheric delta D(H₂O) observations from satellite Atmos. Chem. Phys., 19, 2497–2526, https://doi.org/10.5194/acp-19-2497-2019, 2019.

Lossow, S., Steinwagner, J., Urban, J., Dupuy, E., Boone, C. D., Kellmann, S., Linden, A., Kiefer, M., Grabowski, U., Glatthor, N., Höpfner, M., Röckmann, T., Murtagh, D. P., Walker, K. A., Bernath, P. F., von Clarmann, T., and Stiller, G. P.: Comparison of HDO measurements from Envisat/MIPAS with observations by Odin/SMR and SCISAT/ACE-FTS, Atmos. Meas. Tech., 4, 1855–1874, https://doi.org/10.5194/amt-4-1855-2011, 2011.

Lossow, S., Högberg, C., Khosrawi, F., Stiller, G. P., Bauer, R., Walker, K. A., Kellmann, S., Linden, A., Kiefer, M., Glatthor, N., von Clarmann, T., Murtagh, D. P., Steinwagner, J., Röckmann, T., and Eichinger, R.: A reassessment of the discrepancies in the annual variation of δD-H₂O in the tropical lower stratosphere between the MIPAS and ACE-FTS satellite data sets, Atmos. Meas. Tech,, 13, 287–308, https://doi.org/10.5194/amt-13-287-2020, 2020.

Risi, C., et al. (2012), Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopic observations: 2. Using isotopic diagnostics to understand the mid and upper tropospheric moist bias in the tropics and subtropics, J. Geophys. Res., 117, D05304, doi:10.1029/2011JD016623

Thurnherr, I., Sodemann, H., Trent, T., Werner, M., and  Bösch, H. (2024). Evaluating TROPOM Delta D column retrievals with in situ airborne field campaign measurements using expanded collocation criterion, Earth and Space Science, 11,  e2023EA003400, https://doi.org/10.1029/2023EA003400

Tritscher, I., Pitts, M. C., Poole, L. R., Alexander, S. P., Cairo, F., Chipperfield, M. P., et al. (2021). Polar stratospheric clouds: Satellite observations, processes, and role in ozone depletion. Review of Geophysics, , 59, e2020RG000702. https://doi.org/10.1029/2020RG000702.

Wang, T., Zhang, Q., Lossow, S., Chafik, L., Risi, C., Murtagh, D., & Hannachi, A. (2018). Stable Water Isotopologues in the Stratosphere Retrieved from Odin/SMR Measurements. Remote Sensing, 10(2), 166. https://doi.org/10.3390/rs10020166.

Yoshimura, K., Stable Water Isotopes in Climatology, Meteorology, and Hydrology: A Review, Journal of the Meteorological Society of Japan, 2015, Volume 93, Issue 5, Pages 513 533, https://doi.org/10.2151/jmsj.2015-03.