the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Apr 2025
A systematic comparison of ACE-FTS δD retrievals with airborne in situ sampling
Abstract. The isotopic composition of water vapor in the upper troposphere and lower stratosphere (UTLS) can be used to understand and constrain the budget and pathways of water transport into that region of the atmosphere. Measurements of the water isotopic composition help further understanding of the region's chemistry, radiative budget, and the sublimation and growth of polar stratospheric clouds and high-altitude cirrus, both of which are also important to stratospheric chemistry and Earth's radiation budget. Here we present the first intercomparison of water isotopic composition δD using in situ measurements from the ChiWIS, Harvard ICOS, and Hoxotope instruments and satellite retrievals from ACE-FTS. The in situ data comes from the AVE-WIIF, TC4, CR-AVE, StratoClim, and ACCLIP field campaigns, and satellite retrievals of isotopic composition are derived from the ACE-FTS v5.2 data set. We find that in all campaign intervals, the satellite retrievals above about 14 km altitude are depleted by up to 150 ‰ with respect to in situ measurements. We also use in situ measurements from the ChiWIS instrument, which has flown in both the Asian Summer Monsoon (AM) and the North American Monsoon (NAM), to confirm the isotopic enhancement in δD observed in satellite retrievals above the NAM.
Competing interests: One of the co-authors is a member of the AMT editorial board.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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CC1: 'Comment on egusphere-2025-1190', Farahnaz Khosrawi, 23 Apr 2025
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CC2: 'Reply on CC1', Benjamin Clouser, 15 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1190/egusphere-2025-1190-CC2-supplement.pdf
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CC2: 'Reply on CC1', Benjamin Clouser, 15 May 2025
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RC1: 'Comment on egusphere-2025-1190', Chris Boone, 01 May 2025
My review is provided in the attached pdf file.
- AC2: 'Reply on RC1', Benjamin Clouser, 06 Sep 2025
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RC2: 'Comment on egusphere-2025-1190', Anonymous Referee #2, 09 Jun 2025
The paper illustrates a series of relevant results, tackling the problem of comparing heterogeneous in situ measurements of D/H with ACE-FTS satellite data products. This itself is a complicated problem, and the paper serves as an effort to cross-validate several datasets, illustrating consistencies and potential issues.
I only have a few, mostly minor comments that the authors should address, and which are reported here below:
1) In the introduction, the authors should also consider adding results from nadir hyperspectral sensors such as IASI, which allow for HDO and D/H vertical profile retrieval on a global scale. Specifically the following works:
https://acp.copernicus.org/articles/9/9433/2009/
https://essd.copernicus.org/articles/14/709/2022/
https://www.sciencedirect.com/science/article/pii/S0022407316301248?via%3Dihub
provide a good overview of results whoch would be beneficial to this introductory discussion.
2) Line 156: to be more precise, and to distinguish ACE-FTS from instruments like MIPAS, "limb-sounding" should be replaced by "solar occultation"
3) Figure 4: It would be useful to report the variability of ACE-FTS profiles averaged here with errorbars.4) Lines 270 - 272: this is one of the core points of the paper. I wonder if the authors checked the possibility that temperature dependency of line strengths in different spectral regions cause this. This would clearly be another factor beside the already noted difference in sampling techniques between ACE-FTS and in situ techniques.
5) Lines 309 - 311: to better discuss this, the manuscript should report the exact space and time box considered for ACE-FTS, and eventually include comparison with a restricted dataset of ACE-FTS profiles.
6) Sometimes UT/LS is used, some other times UTLS. Please make the notation uniform across the paper.
Citation: https://doi.org/10.5194/egusphere-2025-1190-RC2 - AC1: 'Reply on RC2', Benjamin Clouser, 06 Sep 2025
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- 1
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.