the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Jan 2025
Using Formvar to Capture Ice Crystals and Retrieve Roughness Parameters
Abstract. Ice crystal roughness is a poorly observed and understood parameter, yet it significantly influences crystal’s scattering properties and consequently impacts radiative transfer in the atmosphere, contributing to uncertainties in weather and climate forecasting. In this study, we introduce a novel approach to obtain high-resolution roughness measurements, building on the traditional formvar method for capturing ice crystals. Ice crystals were grown in the Manchester Ice Cloud Chamber, collected, and subsequently imaged using various techniques, including a scanning optical profilometer, which enabled the identification of roughness features as small as 0.8 µm. This approach provides critical insights into roughness characteristics that are significant for improving radiative transfer models and forecasts.
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RC1: 'Comment on amt-2024-200', Anonymous Referee #1, 03 Feb 2025
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Review of ‘Using Formvar to Capture Ice Crystals and Retrieve Roughness Parameters’
from Celebi et al. (2025)
Celebi et al. present a proof-of-concept for using the formvar replica technique to preserve the shape of ice crystals to analyze the surface roughness offline, e.g. using an optical profilometer. SEM imaging was also done. The comparison of roughness parameter derived from salt crystals and their replica showed agreement despite of the skewness. By testing the technique with real ice crystals generated in the Manchester ice cloud chamber (MICC), it turned out that the mean roughness increased by increasing crystal length and levels off at around 50 µm, which can be considered as a reasonable result. However, I don’t fully understand what the aim of this study is. Is it planned as an add-on measurement technique for MICC to determine surface roughness of ice crystals which were formed in the chamber? How many ice crystals have to be analyzed to gain a representative statistic of the crystals and their roughness in the chamber? Is it possible to achieve this with the here presented method? Or what is the objective? I think it has to be shown that this method is robust to study a large number of ice crystals. I guess this is needed for any application. In principle, I see the potential of the here presented method as proof-of-concept. However, as there are some shortcomings using the actual formvar method and the fact that the objective is not defined, the value of the study needs to be presented more clearly. After overcoming these problems, which are probably largely due to the formulation and description of the study, the manuscript can be published in AMT, as the formvar replica technique has potential and fits within the scope of the journal.
Specific comments:
Abstract: It would strengthen the paper if the abstract stated that this was a proof-of-concept study. In addition, giving information of the comparison between salt and salt replica as a test would eventually increase confidence in this method.
Introduction: The introduction is well written and gives a good overview about the necessity to study ice crystal surface roughness and the state-of-the-art of surface roughness determination with formvar. However, a short paragraph of the state-of-the-art of surface roughness using other methods is missing. I am sure there are more methods and publications on that topic, but the study of Magee et al. (2014) [1] applying ESEM, Ulanowski et al. (2014)[2] Voigtländer et al. (2018)[3] and Järvinen et al. (2018)[4] using SID-3 instrument could be mentioned.
Methodology part & Figure 1: The methodology part is very detailed. There are some repetitions. In my opinion Figure 1 is not important. I suggest to shorten the section and leave Fig. 1 out.
P9 l208-210: The authors gave the information that many features in the formvar are not a result of accreted ice crystals but artefacts from the formvar process. Do the artefacts affect the determination of surface roughness of ice crystals? Can always be distinguished between artefact and ice crystal? Do the artefacts influence the counting statistics of ice crystals when the fall on a spot with an artifact? Can the process been improved in order to reduce or avoid these artefacts?
P9 l210-215: I do not understand why it solves the problem that ice crystals do not sink when using a thicker formvar layer.
Fig. 5: What relevance do those ice crystals have that not fully sink into the formvar? Could it be that a certain type of ice crystals always not sink into formvar and would be missing in the analyzes leading to basis of this method?
P12 Fig.5: Please add a scale bar.
P13 l283-286: I agree, but it would be good to have more information of the formation and history of the ice crystals which were examined (later it is discussed, but I missed the information already at this point in the text). Maybe the roughness is different due to different environmental conditions the ice crystals experienced [3, 4] before settled on the formvar. Further, the number of investigated ice crystals is not very high (caption of Fig. 9 ‘n=7 for each size bin’). It seems that this offline method -using formvar for ice crystal surface roughness detection- is very complex and time-consuming. How will it be possible to analyse a larger sample size? What are the advantages of this introduced method compared to online measurements of single airborne ice crystals such as e.g. SID-3?
P14 l316-317: ‘However, if appropriate mitigation methods are implemented, the occurrence of these artefacts can be greatly reduced, resulting in the most accurate possible roughness measurements.’ For such a statement a comprehensive analysis of already published methods is needed, which should be given in the introduction, see comment introduction of this review. And maybe it should be reformulated to ‘one of the most accurate…’. I would expect SEM to have a higher spatial resolution.
Technical corrections:
P2 l49: Insert a blank between ‘(1951)used’.
P5 l115: Insert a half blank ‘0.6wt%’.
References: The AMT citation style has to be used.
[1] N. B. Magee, A. Miller, M. Amaral, and A. Cumiskey, "Mesoscopic surface roughness of ice crystals pervasive across a wide range of ice crystal conditions," Atmos. Chem. Phys., 2014, doi: 10.5194/acp-14-12357-2014.
[2] Z. Ulanowski, P. H. Kaye, E. Hirst, R. S. Greenaway, R. J. Cotton, E. Hesse, and C. T. Collier, "Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements," Atmos. Chem. Phys., 2014, doi: 10.5194/acp-14-1649-2014.
[3] J. Voigtländer, C. Chou, H. Bieligk, T. Clauss, S. Hartmann, P. Herenz, D. Niedermeier, G. Ritter, F. Stratmann, and Z. Ulanowski, "Surface roughness during depositional growth and sublimation of ice crystals," Atmospheric Chemistry and Physics, 2018, doi: doi:10.5194/acp-18-13687-2018.
[4] E. Järvinen, H. Wernli, and M. Schnaiter, "Investigations of Mesoscopic Complexity of Small Ice Crystals in Midlatitude Cirrus," Geophysical Research Letters, 2018, doi: https://doi.org/10.1029/2018GL079079.
Citation: https://doi.org/10.5194/amt-2024-200-RC1
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