Measurements of Ice Crystal Fluxes from the Surface at a Mountain Top Site
, Michael Flynn 1 and Martin Gallagher 1Round 1
Reviewer 1 Report
The paper reports on ice crystal fluxes measured by eddy covariance method at a high altitude mountain site. Operating this type of method at such a site is ambitious. Still, the authors have managed to obtain useful results that advance our understanding of ice crystal flux from frozen surfaces. The observations are scientifically sound and are analysed in a meaningful way. Generally, the paper is well written. Once a few minor issues have been addressed, it will make an excellent contribution to the journal.
Minor issues
Concerning the location of the surface source of small ice crystals observed at Jungfraujoch: how far is 'far upwind' (line 27)? Can you be more specific? Perhaps combine windspeed with what is known about growth rates of ice crystals to arrive at a semi-quantitative estimate (cf. Fukuta & Takahashi, 1999; https://doi.org/10.1175/1520-0469(1999)056<1963:TGOAIC>2.0.CO;2 )
Another study reporting high ice crystal number concentrations at a mountain top (Sonnblick, Austria) is Beck et al. (2018; https://doi.org/10.5194/acp-18-8909-2018). Their insights are based on an approach different from that used in the present study and should be considered in the introduction or in the discussion section.
I would appreciate to see at the end of the paper a few lines regarding possible implications of the observed fluxes of ice particles. Are the positive fluxes reported in Table 2 in an order of magnitude that is relevant for seeding from below supercooled clouds skimming mountain ridges or tops? And, could this make a difference to the precipitation downwind the seeding ridge?
Figure 1 - Perhaps add a scalebar?
Line 67: Replace 'fully' with 'full'
Line 89: Replace 'Demott' with 'DeMott'
Line 133: I would suggest to replace 'evaluated' with 'applied'
Line 135: Does 'homogenous' imply 'flat'?
Line 173: I am not sure whether 'non-vertical' is correct or whether it should be 'non-horizontal'
Table 2: For clarity, I would suggest to add a '+' to upper positive flux range values (e.g. first line: -67 - +23), as is promised in the legend of the Table. The same applies to the y-axis legend of Figure 4d.
Line 211: What 'Ice number concentrations...' (high or low or else)?
Line 215: 'Outlying' of the population of trustworthy measurements? If not, replace 'outlying' with 'extreme' (same applies to the legend of Figure 3).
Figure 3: Increase the line thickness of the whiskers to make then distinguishable from vertical grid lines.
Line 247: 'In contrast' or 'Constrastingly', not 'In contradiction'
Line 248: Perhaps rephrase the sentence in this way: 'The same was observed for particles smaller 50 um.'
The sentence starting in line 252 ('A similar relationship ...') needs rephrasing to be understandable.
Line 255: The maximum flux value is 10 to the 5, not 10 to the -5.
Lines 262-263: Complete sentence by adding 'observation': 'Almost no observation of fluxes from the south exist...'
Line 303: Should be '...the riming effect that has not been ruled out...'
Line 318: In 'gm-3' the '-3' should be superscript.
Line 340: 'thy' should be 'they'
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments on “Measurements of ice crystal fluxes from the surface at a mountain top site”
This study presents observations of clouds at the Jungfraujoch station. Ice particle number concentration fluxes are calculated based on the eddy covariance method. Results suggest that the origin of anomalously high cloud ice crystal concentration is due to a strong surface source generated by the interaction of turbulent deposition of supercooled droplets to fragile ice-covered snow surfaces. In general, the manuscript is easy to read and follow. However, not all methods and results are adequately described. My comments are listed below and they should be addressed properly before it it is suitable for the scope and quality of the Atmosphere journal.
Major comments:
1. Please justify why ignoring the terminal velocity of particles when calculating ice crystal fluxes.
2. In the abstract, it said that “a detailed analysis of the cloud ice crystal sizes and habits with respect to with respect to wind speed and growth regimes confirms…” However, habits and growth regimes are poorly discussed in the manuscript.
3. In the abstract “the most likely explanation is due to a strong surface source generated by the interaction of turbulent deposition of supercooled droplets to fragile ice-covered snow surfaces.”, as well as in the summary, Line 334: “We, therefore conclude that frost crystals growing on the snow surface are the likely source of the ice crystals following Lloyd et al.” I am not convinced by this conclusion after reading the manuscript. Rejecting one hypothesis (e.g., blowing snow mechanism) is not enough to confirm other hypotheses (e.g., frost crystals growing on the snow surface). More discussions are needed in section 3 to explain the potential mechanism, especially what observational evidence supports this mechanism (not just rejecting other mechanisms).
Other comments:
1. Line 33: “Lloyd et al., 2015” be consistent with the citation format throughout the manuscript.
2. Line 38-39: “In other cases, it was not…” Please add references.
3. Line 43-46: “Although the EC method is …” Please add references.
4. Line 52: “highlighting” -> “highlight”
5. Figure 1 caption: “withing” -> “with”
6. Line 60: “and aerosol composition” -> “such as aerosol composition”?
7. Line 69: Add a period after “a hose”.
8. Figure 2: what is the meaning of those black lines and the black circle in the figure?
9. Figure 2 caption: Can the author provide the GPS of the research station?
10. Table 1: “Size range (um)” is not suitable for Metek.
11. Line 113: “water vapour freezes and produces part of the crystal-clusters”. “Water vapour freezes” is not a correct physical statement. Do you want to say “depositional growth of ice crystal”?
12. Line 114: “the sublimation of snow does not lead to a mass loss but to a formation of sublimation crystals.” This sentence is confusing. What is the difference between “sublimation snow” and “sublimation crystals”?
13. Line 128: “the vertical exchange” of what?
14. Line 130: “15.5 um” radius or diameter?
15. Line 130: “…of fog, and aerosol particles”. Need to rephrase.
16. Line 136: “exchange” of what?
17. Line 152: “the remaining term…” What is the remaining term of equation 4?
18. Line 189: “An ogive test, as already described, established a suitable average time of typically 8 minutes for flux calculations.” I would recommend the author show the plots of the ogive test.
19. Figure 4: (c) and (d) are upward fluxes? (e) and (f) are downward fluxes?
20. Line 255: “10-5”->”105”
21. Figures 7 and 8 are not discussed in the manuscript.
22. Line 340: “thy” -> “they”
23. Line 342: “In cloud” -> “In-cloud”
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors have addressed my comments properly. I think it is suitable for publication.
