The authors compare ice clouds properties measured using the airborne WALES lidar system during the HALO (AC)3 campaign in the Arctic in undisturbed arctic conditions (AC) and in prevailing warm air intrusion conditions (WAI). They focus on comparisons of water vapor mixing ratios profiles and inferred relative humidity over ice (RH_i) in the ice clouds, near the ice clouds and further in the cloud-free atmosphere. The retrieved RH_i values are organized in 3 ranges named low HET, high HET, and HOM defined according to possible nucleation processes. They find differences between AC and WAI clouds, in terms of top and base altitude. Cloud optical depth is larger in WAI clouds as well as RH_I. Large super saturation is seen at cloud base for WAI clouds but not AC clouds, while both AC and WAI clouds exhibit large super saturation at cloud top.

This study shows unprecedented measurement in cirrus clouds in the Arctic with comparisons of cirrus clouds properties in AC and WAI conditions possibly suggesting different formation processes. This manuscript is fully relevant for publication in ACP. However, I recommend that the authors address the following questions before publication.

General comments

1. Given that the paper is about differences between undisturbed arctic conditions (AC) and prevailing warm air intrusion conditions (WAI), I was expecting more details about flights grouping. “We studied the synoptic situation for each flight”, as written in Sect. 2.3.1, should be developed. What are the criteria for the classification? Please explain the information provided in Fig. 2.
2. In Table 3, what does “± value” mean? Is “value” a standard deviation or other?
3. Figure 3 is a very good illustration of the cloud masking. I note that this illustration is for flight RF17, which is in the AC category according to Fig. 2. I see cloud tops up to 9.5 km, which seems in contradiction with the fact that AC clouds have top height = 6376 ± 1195 m in Table 3. Please clarify. Which part of the flight do we see in Fig. 3 in terms of latitude and longitude ranges?
4. Regarding Table 3 and related text, it would be informative to show ECMWF temperature vs. altitude in AC and WAI conditions (perhaps add a figure?). I suggest comparing temperatures at base and top heights.
5. Nucleation process:
   • Unlike in Dekoutsidis et al. (2023), which present a similar analysis but by comparing in situ and liquid origin cirrus clouds at mid-latitude, cloud temperature is not required to be smaller than 235 K (according for instance to Table 2 and as seen in Fig. 4), and it seems that the statistics provided in Table 4 and the discussions are by considering all temperatures. The wording “HOM regime” is misleading because it seems to actually mean “RHi > 147 %”, and the line for HOM threshold extending up to 265 K in Fig. 5 is confusing. Please clarify.
   • In Figure 5 and related text, as well as in Sects. 4 and 5, the interpretation in terms of “HOM regime” is complicated by the fact that temperatures might be larger than 235 K. It is likely that T < 235 K near cloud top, but it is no sure near cloud base. Additional information related to temperature seems necessary.
   • Can the authors clarify the statement in lines 397-398?
6. Sections 4 and 5 could be shortened, I felt that there were repetitions.

Other comments

1. Line 11: backscatter coefficient: at which wavelength? 532 nm?
2. Line 159: please define the backscatter ratio
3. Line 163: PLDR > 20 % => could mixed-phase clouds be included at the warmest temperatures?
4. Lines 220-222: can you include a reference for this study? And/or for HAMP?
5. Lines 232, line 263, and caption of Fig. 5: should Sect. 2.3.4 be 2.3.5?
6. Lines 264: should Sect. 2.3.3 be 2.3.4?
7. Lines 371-375: is there evidence that high latitude cirrus clouds in De La Torre Castro et al. (2023) are WAI? Note that in this study, T is smaller than 235 K.
8. Line 375: do you confirm that the “Rolf et al. (2022)” reference is a short abstract?

Technical comments

1. Fig.1: typo: collumn => column
2. Fig. 5: top left panel: we cannot see the value for high HET (orange) in the 20-30 % range. Move the caption?
3. Lines 359-360: the sentence ends with “,0.23%”. Can you rephrase?
4. Kärcher, B.: Supersaturation, dehydration, and denitrification in Arctic cirrus, Atmos. Chem. Phys., 2005 => the reference is incomplete