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the Creative Commons Attribution 4.0 License.
| 09 Jan 2025
Improved Formulation of Fragmentation of Snow during Collision with Graupel/Hail based on Observations at Jungfraujoch: Cold Non-Dendritic Regime of Temperature
Abstract. Much of the initiation of ice particles in deep precipitating clouds has been attributed to Secondary Ice Production (SIP). Fragmentation during collisions among particles of ice precipitation is one of the known SIP processes. Some recent studies have used our theoretical formulation of this SIP process in the cloud microphysics scheme of numerical atmospheric models published in 2017. However, there has been a lack of observational data for better understanding of the SIP process. The focus of the present study is on fragmentation of naturally falling snowflakes during their collisions with graupel/hail particles, based on observations conducted at Jungfraujoch, a mountain pass in the Alps and located about 3.6 km above Mean Sea Level. The cloud-top was at about −25° to −32 °C. The study used a portable chamber specially designed to observe the fragmentation of snow particles outdoors. Fixed ice spheres in the chamber were used to mimic graupel or hail. Based on the observational study, we optimised the theoretical formulation for prediction of the number of fragments arising from collisions between snow and graupel/hail. The observations reveal an average number of fragments per collision of about 5. The study improved the prediction of SIP by this type of fragmentation compared to our original theoretical formulation, for snow consisting of mostly aggregates of crystals from the ‘non-dendritic habit regime’ of temperatures colder than −17 °C.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2024-3800', Anonymous Referee #1, 04 Feb 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3800/egusphere-2024-3800-RC1-supplement.pdf
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RC2: 'Comment on egusphere-2024-3800', Anonymous Referee #2, 07 Feb 2025
Review for “Improved Formulation of Fragmentation of Snow during Collision with Graupel/Hail based on Observations at Jungfraujoch: Cold NonDendritic Regime of Temperature” by Paul et al.
General comment:
This paper investigates the fragmentation of naturally falling “non-dendritic” ice particles at the Jungfraujoch station using the portable instrument developed in Gautam et al. (2022, 2024). The results of the experiments are fitted to the Phillips et al. (2017) formulation and some numerical tests are performed. The overall concept of the study is interesting, especially as only a limited number of studies have explored this SIP mechanism. Examining the fragmentation of naturally falling ice particles is particularly relevant, as it enables the observation of numerous collisions without the need for artificially generated ice particles.
However, I have significant concerns about the major limitations of the experiments, which are not addressed in the paper. A key issue is the use of a GoPro camera, which is not a research instrument and is therefore not designed for measuring ice particles (It is primarily used for filming sports). Consequently, a substantial proportion of fragments is likely undetected, yet this limitation is not discussed in the study. Additionally, the properties of the ice particles such as fall speed, mass, rime fraction, and collision kinetic energy (CKE) are subject to large uncertainties due to the methodology employed. Important elements regarding the numerical modelling setup are not provided. The presentation of the figures could be improved to enhance clarity and readability.
Overall, while the study’s concept and topic are relevant, the paper exhibits several methodological weaknesses that undermine its rigour. Without substantial improvements, I cannot recommend publication in ACP. If the authors thoroughly address these issues, the study could become suitable for publication. I therefore recommend a major revision.
Major comments:
The resolution of the GoPro must be explicitly stated in the paper. Is it the same as reported in Gautam et al. (2024) (150 µm)?
The detection limit is given as 300 µm (line 238). However, if the resolution is 150 µm, this corresponds to only two pixels, which is insufficient for reliable detection. In situ aircraft probes typically require at least three pixels to identify hydrometeors, suggesting that the detection limit should be no less than 450 µm.
Strong evidence indicates that SIP generates fragments smaller than 300 or 450 µm. Numerical simulations by Lawson et al. (2015) and Huang et al. (2021), where SIP was turned off, revealed a lack of ice crystals around 100 µm compared to in situ aircraft observations. This suggests that small fragments are likely missed during your experiment. This limitation should be clearly addressed in the abstract, results, and conclusions.
Previous studies demonstrate the challenge of detecting small ice particles produced by SIP. Lauber et al. (2018) and Keinert et al. (2020) used a 20 000 fps camera with around 1 µm pixel resolution. Even with such advanced imaging, Kleinheins et al. (2021) found that during some pressure release event likely producing secondary ice splinters, fragments were not detected. The recent experiment of Seidel et al. (2024) employed a sophisticated ice counter for the Hallet–Mossop process, using the impaction of splinters on a supercooled sucrose solution. Grzegorczyk et al. (2023) employed both holography (10 µm resolution) and microscopy (3 µm resolution) to study ice fragmentation. Compared to these approaches, the current setup (only 120 fps and 150 µm resolution) is limited, and improvements should be considered. I strongly recommend improving this aspect for any future observations.
The inability to capture small ice particles produced by fragmentation in your experiments is an important limitation. Grzegorczyk et al. (2023) demonstrated that fragmentation generates fragments smaller than 300/450 µm, reinforcing the need for discussion on this limitation.
The use of a single camera is insufficient, as out-of-focus ice crystals may be missed. Grzegorczyk et al. (2023) showed that a high-speed camera detected only ~10 ice crystals, whereas microscope and holography measurements captured significantly more (~100) in the same experiment. This again suggests that the current study likely underestimates the number of detected fragments.
Given these limitations and the evidence of the presence of smaller ice fragments, the paper should explicitly state the number of fragments is a ‘minimum number of ice fragments’ larger than the threshold size in the abstract, results, and conclusions. Caution is needed when interpreting the findings, and I strongly recommend adding a discussion section addressing these limits based on the relevant references mentioned previously.
The original formulation of Phillips et al. (2017) suggests that the mass of fragments of 0.001 times that of the parent particle (except for hail). Based on the findings of this study, did you modify the mass of the fragment? If so, does it modify the particle size distribution of ice crystals obtain with the AC model?
Line 51-73: There are repetitions; I suggest reorganising this paragraph. Additionally, more studies that have implemented the Phillips et al. (2017) parameterisation and demonstrated improved ice crystal number concentration compared to observations should be cited (e.g. Huang et al., 2022; Karalis et al., 2022; Han et al., 2024; Grzegorczyk et al., 2025).
Line 60-61: Mention the Grzegorczyk et al. (2023) study, which observed a large number of fragments during graupel-snow collisions.
Line 97: Was the camera able to capture all ice spheres where ice breakup occurred? Given that the distance between spheres was 2 cm, was any rebound of snowflakes between the spheres observed when they were around 1 cm in diameter? What was the reason for using a 2 cm ice sphere as a proxy for graupel/hail instead of a smaller target size?
Line 110: It is written that the cloud top was between -25 and -32 °C while the ground was at -5°C and RH=27%. Regarding the distance between the cloud base and dry conditions at the ground, I think that sublimation might affect the shape of the particle and therefore the fragility of the ice particles.
Line 114: On what observations is this statement based?
Figure 2: The ice crystal images are of poor quality, please provide better quality images and, if possible, include video of breakup events or at least some images.
Line 160: The mass of the particles is estimated based on the integrated mass, which is used to derive the m-D relationship. How were these ice particles observed? Was a GoPro camera used? More details are needed. Given the significant variability in ice particle properties, the uncertainty in mass as well as parameters in Table 1 should be assessed.
Line 166-167: Was the size and number of fragments inspected manually for 100 collisions? Please provide more details about the method and some images.
Section 2.6: The simulation performed to obtain the rime fraction was initially design for California which is a completely different from the situation at Jungfraujoch in Switzerland, why using it? Please clarify that, give more details about the simulation setup, results and how the mean rime fraction was calculated.
The number of asperities which is a key parameter relies on the rime fraction while this parameter is only estimated from numerical simulation. This is very dependent on the ability of the microphysics scheme to reproduce the real cloud situation. The uncertainty about rime fraction and its importance must be more discussed.
Griggs et al. (1986) show that riming tends to inhibit fragmentation while it is the opposite in Phillips et al. (2017) formulation, did you have some information about that from the apparent shape of the particle observed during your experiments?
Line 227-228: Larger ice particles may fall faster, have higher mass and CKE, and contain more asperities that could break. How do you explain, then, that larger ice particles produce fewer fragments? One possible reason is that higher CKE may generate fragments that are too small to be detected.
Line 229: Change "number" to "minimum number is about 5."
Figure 3: The figure appears to be average, while line 222 indicates that approximately 100 collisions were observed. Could you show all the raw measurements?
Line 237-238: This cannot be stated, see my previous comments.
Figure 4: Why are there so few data points? A line density plot or a bar plot with a smaller bin width might improve clarity. Additionally, the unit on the y axis is missing.
Line 250-251: How was the 13% fall speed error calculated? 120 fps resolution suggests it may be higher.
Line 252: Gautam et al. (2024) report a 30% CKE error, while this study reports 46%. How was this estimated?
Figure 5: Why so few measurement points? Improve this figure by showing raw measurements of N vs. CKE. Also, why do some collisions have identical CKE values, given the variability in fall speed and particle mass?
Line 265: You cannot state that the rime fraction is estimated from the “snow sampled” if it is derived from simulations.
Line 283: Was the rime fraction constant in the simulation? Please provide relevant results to clarify this.
Line 296-297: Better in prediction compared to what? Compared to the measurements used initially for the fit?
Section 6: What type of simulation is conducted using the AC model? What is the cloud numerical setup employed? Please provide further details.
Line 346: It is unfortunate that the effect of rime fraction on the number of fragments cannot be studied based on your measurements. There are some instruments like the MASC probe that could provide information about the rime fraction of ice particles.
Line 371-373: Please exercise caution when referring to the detection of fragments and revise this sentence accordingly.
Figure 6, 7 and 8: Could you clarify how these plots are obtained from the simulations?
Conclusion: Update this section based on the previous comments.
Minor comments:
- Only a few studies about fragmentation in ice-ice collision have been made, please cite all of them (add Griggs et al., 1986, Takahashi et al., 1994, Grzegorczyk et al., 2023) in the introduction.
- The quality of all figures needs to be improved (increase the dpi please).
- Line 69-71: Cite references that support that.
- Line 74: Mention that Takahashi et al. (1995) experiment is also used by Phillips et al. (2017) formulation.
- Line 180-183: Please precise which parameter needs the rime fraction.
- Figure 3: The legend in the upper right corner is empty. The resolution of the figure might be improved.
- Suggestion: plotting x and y axes on a log scale instead of using Log N for clarity.
References:
Gautam, M.: Fragmentation in graupel snow collisions, Master of Science dissertation, Dept of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden, 2022.
Gautam, M., D. Waman, S. Patade, A. Deshmukh, V. T. J. Phillips, M. Jackowicz-Korczynski, P. Smith, and A. Bansemer: Fragmentation in graupel-snow collisions: new formulation from field observations. J. Atmos. Sci., in press, 2024.
Phillips, V. T., Yano, J.-I., and Khain, A.: Ice multiplication by breakup in ice–ice collisions. Part I: Theoretical formulation, J. Atmos. Sci., 74, 1705–1719, 2017a.
Lawson, R.P., Woods, S., Morrison, H., 2015. The microphysics of ice and precipitation development in tropical cumulus clouds. J. Atmos. Sci. 72, 2429–2445. https://doi.org/10.1175/jas-d-14-0274.1.
Huang, Y., Wu, W., McFarquhar, G.M., Wang, X., Morrison, H., Ryzhkov, A., Hu, Y., Wolde, M., Nguyen, C., Schwarzenboeck, A., Milbrandt, J., Korolev, A.V., Heckman, I., 2021. Microphysical processes producing high ice water contents (hiwcs) in tropical convective clouds during the haic-hiwc field campaign: evaluation of simulations using bulk microphysical schemes. Atmos. Chem. Phys. 21, 6919–6944. https://doi.org/10.5194/acp-21-6919-2021.
Lauber, A. Kiselev, T. Pander, P. Handmann, and T. Leisner, "Secondary Ice Formation during Freezing of Levitated Droplet," Journal of the Atmospheric Sciences, vol. 75, no. 8, pp. 2815-2826, Aug 2018, doi: 10.1175/jas-d-18-0052.1.
Keinert, D. Spannagel, T. Leisner, and A. Kiselev, "Secondary Ice Production upon Freezing of Freely Falling Drizzle Droplets," Journal of the Atmospheric Sciences, vol. 77, no. 8, pp. 2959-2967, 2020, doi: 10.1175/jas-d-20-0081.1.
Kleinheins, A. Kiselev, A. Keinert, M. Kind, and T. Leisner, "Thermal Imaging of Freezing Drizzle Droplets: Pressure Release Events as a Source of Secondary Ice Particles," (in English), Journal of the Atmospheric Sciences, vol. 78, no. 5, pp. 1703-1713, 01 May. 2021 2021, doi: https://doi.org/10.1175/JAS-D-20-0323.1.
S. Seidel, A. A. Kiselev, A. Keinert, F. Stratmann, T. Leisner, and S. Hartmann, "Secondary ice production – no evidence of efficient rime-splintering mechanism," Atmos. Chem. Phys., vol. 24, no. 9, pp. 5247-5263, 2024, doi: 10.5194/acp-24-5247-2024.
Grzegorczyk, P., Yadav, S., Zanger, F., Theis, A., Mitra, S. K., Borrmann, S., and Szakall, M.: Fragmentation of ice particles: laboratory experiments on graupel–graupel and graupel–snowflake collisions, Atmospheric Chemistry and Physics, 23, 13 505–13 521, https://doi.org/10.5194/acp-23-13505-2023, 2023.
Huang, Y., Wu, W., McFarquhar, G.M., Xue, M., Morrison, H., Milbrandt, J., Korolev, A. V., Hu, Y., Qu, Z., Wolde, M., Nguyen, C., Schwarzenboeck, A., Heckman, I., 2022. Microphysical processes producing high ice water contents (hiwcs) in tropical convective clouds during the haic-hiwc field campaign: dominant role of secondary ice production. Atmos. Chem. Phys. 22, 2365–2384. https://acp.copernicus.org/art icles/22/2365/2022/. https://doi.org/10.5194/acp-22-2365-2022.
Karalis, M., Sotiropoulou, G., Abel, S.J., Bossioli, E., Georgakaki, P., Methymaki, G., Nenes, A., Tombrou, M., 2022. Effects of secondary ice processes on a stratocumulus to cumulus transition during a cold-air outbreak. Atmos. Res. 277, 106302. https://doi.org/10.1016/j.atmosres.2022.106302.
Han, C., Hoose, C., Dürlich, V., 2024. Secondary ice production in simulated deep convective clouds: a sensitivity study. J. Atmos. Sci. 81, 903–921. https://doi.org/10.1175/jas-d-23-0156.1.
Grzegorczyk, P.,Wobrock,W., Canzi, A., Niquet, L., Tridon, F., and Planche, C.: Investigating secondary ice production in a deep convective cloud with a 3D bin microphysics model: Part I - Sensitivity study of microphysical processes representations, Atmospheric Research, 313, 107 774, https://doi.org/10.1016/j.atmosres.2024.107774, 2025.
Griggs, D. J. and Choularton, T. W.: A laboratory study of secondary ice particle production by the fragmentation of rime and vapour-grown ice crystals, Q. J. Roy. Meteor. Soc., 112, 149–163, https://doi.org/10.1002/qj.49711247109, 1986.
Takahashi, T., Nagao, Y., and Kushiyama, Y.: Possible High Ice Particle Production during Graupel–Graupel Collisions, J. Atmos. Sci., 52, 4523–4527, https://doi.org/10.1175/1520-0469(1995)052<4523:phippd>2.0.co;2, 1995.
Citation: https://doi.org/10.5194/egusphere-2024-3800-RC2
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