The article presents a temporal series of the isotopic composition of water vapor during the austral summer 2023/2024 at Dome C, East Antarctica. The data have been obtained using two different laser spectrometers: a Picarro Cavity Ring-Down Spectrometer (CRDS) and an AP2E Optical-Feedback Cavity Enhanced Absorption Spectrometer (OF-CEAS). According to Lauwers et al. (2024), the low-humidity OF-CEAS analyzer, which was supposedly deployed in the field for this paper, should perform better than the CRDS at low humidity, but in this study it seems to give worse results.

A comparison between the measured and the LMDZ6-iso simulated isotopic composition of water vapor has also been carried out in this paper. The modeled and measured data show a good agreement for humidity and also show an overall agreement for d¹⁸O, dD and, to a certain extent, for deuterium excess, but LMDZ6-iso, while capturing the general variability, fails to obtain the correct isotopic values as well as the magnitude of the observed diurnal cycles.

Line 15 the measurement period is more than 3 months rather than 2.5 months

Line 46-47 change “such as encountered on the East Antarctic Plateau, is a technical challenge since most laser spectrometers are designed for measuring accurately within a range of humidities between 5,000 and 30,000 ppmv” with “such as those encountered on the East Antarctic Plateau, presents a technical challenge, as most laser spectrometers are designed for measuring accurately within a range of humidities between 5,000 and 30,000 ppmv”

Line 57-58 how is the commercially available Picarro laser spectrometer adapted for low humidity measurements?

Line 63 same as line 15

Line 91-91 I think it would be better to specify the Picarro model (L2130-i? L2140-i?) instead of the identifier of your instrument. The same for the AP2E instrument: is it a ProCeas?

Line 139 change “closest” with “close”

Line 140 Is it possible for the deuterium excess to be +90‰ (based on a d¹⁸O=-80‰ and a dD=-550‰)?

Line 160-161 Although you give an explanation in line 180-183, I am still wondering why you used two laboratory standards mostly outside the range of the measured water vapor isotopic values. Couldn’t you use, for example, the VSAEL standard with the FP5 standard?

Line 201-202 “i” is not subscript

Line 273 What model is the Picarro HIDS2319?

Line 284-285 change “Below 500 ppmv, both 𝛿¹⁸O and 𝛿D show a divergence with decreasing humidity levels, in the opposite direction as for both Picarro analysers” with “Below 500 ppmv, both 𝛿¹⁸O and 𝛿D diverge as humidity levels decrease, but in the opposite direction observed in both Picarro analysers”

Figure 4 d¹⁸Ohumcorr-d¹⁸Ohumcorr [‰] and dDhumcorr-dDhumcorr [‰] for the y axis is not very clear

Line 374-375 and 381-382 what does it mean that “both analysers capture the linearity between the true 𝛿¹⁸O value of the two laboratory standards”? A line passing through two point is always a linear equation

Figure 7 I can’t find “AP2E, raw” in panel a), which should be a blue dashed line; is it present in the graph? Was air temperature not available in the first and the last period of measurements? Where does the temperature come from? Is it AWS temperature or modeled temperature? You should specific it in the main text and in the figure caption

Line 455-456 there is a divergence between the two instruments between mid-February and mid-March. I know it’s due to the very low humidity which makes it hard for the laser spectrometers to correctly measure the isotopic composition, but how do you explain the different behavior of the Picarro and the AP2E laser spectrometers and which one is more reliable? I think this is an important point if you wish to measure the isotopic composition of water vapor in other seasons

Line 483 change “to correctly capture” with “in correctly capturing”

Line 485-486 change “Because of the large correction linked to the humidity-dependence on the 𝛿¹⁸O signal, even the 𝛿¹⁸O could be challenged” with “Due to the significant correction associated with the humidity dependence of the 𝛿¹⁸O signal, even the 𝛿¹⁸O measurement could be questioned”

Line 486-487 why you stopped the comparison at mid-February when you have data up to mid-March 2024? Is it because of the unreliability of the isotope data due to the very low humidity? I think it should be explained in the text

Line 490 change “show” with “shows”

Line 491 change “including for the amplitude of the observed diurnal cycle” with “including in terms of the amplitude of the observed diurnal cycle”

Line 495-496 change “the modelled 𝛿¹⁸O shows an overall positive bias during the period December to mid-February compared to the observations” with “the modelled 𝛿¹⁸O shows an overall positive bias during the entire period compared to the observations”

Line 538 change “during the summertime” with “during summertime”

Line 547-549 The higher deuterium excess in the measurements with respect to LMDZ6-iso could also be explained by sublimation

Line 556-557 change “might not be well representing the in-situ conditions” with “they may not accurately represent the in-situ conditions”

Line 570-571 change “Combining the observations of the water vapour isotopic composition” with “Combining observations of water vapour isotopic composition”

Lauwers, T., Fourré, E., Jossoud, O., Romanini, D., Prié, F., Nitti, G., Casado, M., Jaulin, K., Miltner, M., Farradèche, M., Masson-Delmotte, V., and Landais, A.: OF-CEAS laser spectroscopy to measure water isotopes in dry environments: example of application in Antarctica, https://doi.org/10.5194/egusphere-2024-2149, 15 August 2024.