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| 20 Nov 2024
Measurement Report: Influence of particle density on secondary ice production by graupel and ice pellet collisions
Abstract. We present a laboratory study dedicated to fragmentation due to graupel-graupel and ice pellet-ice pellet collisions and their role in augmenting ice particle concentration in clouds. For this, graupels of different sizes and densities were created utilizing dry growth condition in a cold chamber at -7 °C and -15 °C using a setup that simulates the natural rotation and tumbling motion of freely falling graupels. Ice pellets were generated by freezing water in 3D-printed spherical molds. We conducted collision experiments inside the cold chamber utilizing a fall tube that ensures central and repeatable collision of ice particles at different collision kinetic energies. The number of fragments generated in the collisions were analyzed following a theoretical framework as a function of the collision kinetic energy. Our results revealed a strong dependency of the fragment number on the density of the colliding ice particles, which can be attributed to the particles’ structure. The number of fragments varies between 1 and 20 and, thus, comparable or larger than those resulted in drop freezing experiments. The size of the fragments was in the sub-mm range for graupels, and up to 3 mm for ice pellets. Another set of experiments, focusing on multiple collision of graupel revealed that the number of fragments generated becomes zero when the particle suffers more than three collisions in a row.
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RC1: 'Comment on egusphere-2024-3222', Anonymous Referee #1, 22 Dec 2024
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Review for: Measurement Report: Influence of particle density on secondary ice production by graupel and ice pellet collisions
General comments:
In their experimental study Yadav et al. quantify the number of fragments generated upon collisions between ice pellet and graupel particles and their dependency on particle density. This study extends the work of Grzegorczyk et al. (2023), enhancing our understanding of the collisional break-up mechanism—a critical process in mixed-phase cloud microphysics that is increasingly supported by observational and modeling evidence. Current parameterizations of this process rely on limited and outdated laboratory data, underscoring the importance of this study in providing updated experimental insights to improve its representation in cloud models. Prior to publication, the following major comments should be addressed, followed by minor suggestions and editorial remarks:Specific comments:
• In the Experimental section, the authors should discuss the extent to which the ice particles used in the study reflect natural atmospheric conditions. For example: Under what synoptic conditions and cloud configurations would graupel and ice pellets of the sizes used (2.45 mm for graupel; 5 mm and 7 mm for ice pellets) form? Is the liquid water content (LWC) used in the experiments realistic for these scenarios? Additionally, the prevailing supersaturation with respect to ice is not mentioned, yet this parameter is important for ensuring a more accurate implementation of the results in cloud models.• The study contains several limitations that should be discussed more thoroughly in the results and conclusions sections:
- First, the experiments focus solely on central collisions, unlike Grzegorczyk et al. (2023), which also examined edge collisions. The potential impact of this choice on the number of fragments generated (e.g., whether head-on collisions are expected to produce more fragments than oblique ones), should be addressed.
- Second, the authors acknowledge that the collisional kinetic energies (CKEs) used in their experiments represent the upper range of natural CKE values (Lines 124-129), which could influence the applicability of the results to natural conditions.
- Finally, the detection limit for identifying small fragments (20 μm; Lines 137-140) imposes a constraint, particularly on the observed size of fragments in graupel collisions mentioned in Lines 159-160.
These limitations should be explicitly acknowledged and discussed in both the results and conclusions sections to provide a balanced interpretation of your findings.• The statements made in Lines 192-194 and 216-217 are rather bold and should be tempered by a discussion of the experimental limitations. Specifically, the limited number of experiments conducted, the use of artificial graupel and ice pellets, which may not fully represent natural particles, and the need to examine a broader range of ice particle sizes to cover the phase space relevant for numerical cloud models. Recent work by Gautam et al. (2024) used field observations to constrain the empirical parameters in the theoretical framework developed by Phillips et al. (2017). Comparing the experimental results in this study against these new findings would strengthen the discussion and enhance the robustness of the conclusions.
• Both the abstract and conclusion sections should better articulate the motivation (the importance of ice multiplication and the understudied contribution of ice pellets within this context), as well as the broader implications of your study.
Minor comments:
• Line 11 and Line 226: Consider replacing “suffers” with “undergoes” or “experiences” to improve phrasing.
• Line 15: Maybe use “formed” instead of “generated” here, to avoid repetition.
• Lines 17-19: Specify the expected temperature range within the mixed-phase regime where SIP is anticipated to address discrepancies between ice crystal number and ice nucleating particle concentrations.
• Line 20: Here we could acknowledge not only the lack of systematic laboratory studies but also the challenges in identifying SIP in field observations and accurately representing these small-scale cloud processes in model grid cells across different horizontal resolutions (through empirical parameterizations).
• Line 22: Note that both droplet diameters <13 µm and >24 µm should coexist in Hallett and Mossop (1974).
• Line 52: Are you referring to a specific publication here about the importance of SIP in thunderstorm clouds?
• Line 55: Please clarify “underestimated” environment. Did you mean “undersaturated”?
• Lines 55-59: Please include references to support this part of the introduction. Are you referring to observational studies (e.g., Korolev et al., 2022; Lachapelle et al., 2024; Lachapelle and Thériault, 2022) or laboratory-based research?
• Line 62: Could you clarify what you mean by “fragmentation outcome” here? The number and/or size distribution of the particles produced?
• Line 70: Maybe “lower” instead of “less”
• Line 72: Please define what GEORG stands for here.
• Figure 1 caption: Please provide additional details for the ice pellet shown in panel c, including its density and the temperature at which it was formed, to align with the information given for graupel particles in panels a and b.
• Table 1: For GG collisions (Experiments 9-11), please confirm whether the density of 0.46 g/cm³ for graupel particles is accurate. It does not appear in Figure 4, Table 3, or the main text. Could this be a typo?
• Table 3: Please confirm whether results for a density of 0.21 g/cm³ from Grzegorczyk et al. (2023) are also included in Figure 3.
• Figure 4: Consider adding legends to enhance readability. Additionally, include the temperature at which the experiments were conducted alongside the density information. This will help readers more easily identify the points referenced, such as those mentioned in Lines 207-208.
• Line 112: Line 112: Have you specified these predefined conditions used for generating graupel particles somewhere in the text?
• Line 252: “possess”
• Line 256: Maybe you could reiterate the Hallett-Mossop temperature range here to avoid potential confusion with the wider -20°C < T < -5°C range mentioned earlier.References
- Gautam, M., Waman, D., Patade, S., Deshmukh, A., Phillips, V., Jackowicz-Korczynski, M., Paul, F. P., Smith, P., and Bansemer, A.: Fragmentation in Collisions of Snow with Graupel/Hail: New Formulation from Field Observations, J Atmos Sci, 81, 2149–2164, https://doi.org/10.1175/JAS-D-23-0122.1, 2024.
- Grzegorczyk, P., Yadav, S., Zanger, F., Theis, A., Mitra, S. K., Borrmann, S., and Szakáll, M.: Fragmentation of ice particles : laboratory experiments on graupel-graupel and graupel-snowflake collisions, Atmospheric Chemistry and Physics Discussion, https://doi.org/10.5194/egusphere-2023-1074, 2023.
- Hallett, J. and Mossop, S. C.: Production of secondary ice particles during the riming process, Nature, 249, 26–28, https://doi.org/10.1038/249026a0, 1974.
- Korolev, A., Demott, P. J., Heckman, I., Wolde, M., Williams, E., Smalley, D. J., and Donovan, M. F.: Observation of secondary ice production in clouds at low temperatures, Atmos Chem Phys, 22, 13103–13113, https://doi.org/10.5194/acp-22-13103-2022, 2022.
- Lachapelle, M. and Thériault, J. M.: Characteristics of Precipitation Particles and Microphysical Processes during the 11-12 January 2020 Ice Pellet Storm in the Montréal Area, Québec, Canada, Mon Weather Rev, 150, 1043–1059, https://doi.org/10.1175/MWR-D-21-0185.1, 2022.
- Lachapelle, M., Thompson, H. D., Leroux, N. R., and Thériault, J. M.: Measuring Ice Pellets and Refrozen Wet Snow Using a Laser-Optical Disdrometer, J Appl Meteorol Climatol, 63, 65–84, https://doi.org/10.1175/JAMC-D-22-0202.1, 2024.
- Phillips, V. T. J., Yano, J. I., and Khain, A.: Ice multiplication by breakup in ice-ice collisions. Part I: Theoretical formulation, J Atmos Sci, 74, 1705–1719, https://doi.org/10.1175/JAS-D-16-0224.1, 2017.Citation: https://doi.org/10.5194/egusphere-2024-3222-RC1
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Experimental data for "Measurement Report: Influence of particle density on secondary ice production by graupel and ice pellet collisions" S. Yadav et al. https://doi.org/10.5281/zenodo.14140846
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