the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Mar 2025
Influence of Secondary Ice Production on cloud and rain properties: Analysis of the HYMEX IOP7a Heavy Precipitation Event
Abstract. A significant part of precipitation originates from ice crystals while the representation of the cloud mixed phase by atmospheric models remains a challenging task. One of the well-known problem is the discrepancy between the concentration of ice nucleating particles (INPs) and the ice crystal number concentration. This study explores the effect of secondary ice production (SIP) on the properties of the intense precipitation event IOP7a observed during the HYMEX campaign. The effect of SIP on cloud and rain properties is assessed by turning on or off SIP mechanisms in the 3D bin microphysics scheme DESCAM. Our results indicate that including SIP gives better agreement with in situ aircraft observations in terms of ice crystal number concentration and supercooled drop number fraction. During the mature cloud stage, and for temperatures warmer than -30 °C, 59 % of ice crystals are produced by fragmentation due to ice-ice collisions, 38 % by Hallet-Mossop process, 2 % by fragmentation of freezing drops and only 1 % by heterogeneous ice nucleation. Furthermore, ours results shows that the production of small ice crystals by SIP induces a redistribution of the condensed water mass toward particles smaller than 3 mm rather than larger ones. As ice crystals melt, this effect is also visible in the precipitating liquid phase. The shift toward smaller particles results in a reduced precipitation flux of both ice crystals and drops. Consequently, SIP induces a decrease of the accumulated precipitation at the surface by 8 % and reduces heavy rainfall exceeding 40 mm by 20 %.
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RC1: 'Comment on egusphere-2025-819', Anonymous Referee #1, 19 Apr 2025
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Review of the manuscript titled Influence of Secondary Ice Production on cloud and rain properties: Analysis of the HYMEX IOP7a Heavy Precipitation Event
The authors of this manuscript examined the impact of SIP processes, including Hallett-Mossop, drop shattering during freezing and ice-ice collision breakup, in a real case model simulation with a 3D bin microphysics scheme (DESCAM). It is found that including SIP, the model produced slightly higher TWC, and higher ice number concentration for T>-20°C. Adding SIP improvement of the agreement between simulation results and the observations for ice number concentration, TWC, drop number fraction (> 300 microns) as well as size distributions for both ice and liquid at the altitudes where SIP is active (5-6 km). The contributions of each SIP process, based on the current parameterizations, at different altitudes were quantified. Simulated precipitation amounts from both SIP and noSIP runs are generally lower than the observations. The SIP run produced lower precipitation amount, more smaller drops and less larger drops compared to noSIP run. Adding SIP in the simulation will also modify the mass distribution of hydrometeors with more mass for the smaller particle/drop sizes.
The manuscript is well written. The experiment and the results are well presented. The scope of the study aligns well with the focus of the journal. I therefore recommend the publication of this manuscript after addressing the following comments.
General:
Fig 2a: what’s the range of the invalid range of radar signal just above and below the aircraft. I didn’t see any data being masked out in the near-aircraft region.
L139: please also add descriptions of the temperature range and dependency for H-M process.
L176-177: How was the averaging of the model results performed? Only for in-cloud region or the entire zone highlighted in Fig. 1b? Or is there any selection of the areas close to the aircraft track?
Fig. 3: should the shade area of noSIP simulation be added as well?
L200: however, there are values at ~7.5 and 9 km though. One is closer to noSIP, another one much higher than both simulations.
196-198: good point.
Fig. 4: the aircraft observed different altitudes/regions. Some flight legs were continuously in-cloud, and some others sampled updraft like towers especially at higher altitudes. These clouds might be quite different in terms of microphysical properties. Using a single average model profile for the comparison with the aircraft data might miss a lot of detailed information. In the comparison here, I would suggest exploring to have more categorized comparisons depending on different altitudes & cloud types (continued, updrafts, etc.) which might help to better understand the differences between simulations and observations.
L205-206: Need more justifications here. How about the number of drops with sizes between 100 and 300 microns?
L277-278: as mentioned previously, another factor of changed connectiveness for deep convective cases should be discussed as well.
L293-294: For the selection of the model grid, in addition to the similar altitude within ±150m, are the distance to these two stations considered?
L391-393: Good to have this statement as the SIP parameterizations are largely uncertain, even for the Hallett-Mossop process!!
Other comments:
L1: “cloud mixed phase” à mixed-phase cloud.
L4, L6, L39: please add explanation of the acronyms: IOP7a, HYMEX, DESCAM.
L59: “the HYMEX-IOP7a heavy precipitation event” à the HYMEX-IOP7a is a heavy precipitation event
L69: The HYMEX program (HYdrological Cycle in the Mediterranean EXperiment), HYMEX was already explained previously.
L84: the ARAMIS not explained.
Fig 1: I believe adding some satellite images might help to understand the weather condition for this case study.
L150: “The simulations are performed on Sept. 26, 2012” à “The simulations are performed for Sept. 26, 2012”? I guess this is the date of the flight, not the date when the simulation was run.
L161: “Fig. 1b” à “Fig. 2b”?
L264: “at the south of the two domain” à “at the south of the two stations”?
Citation: https://doi.org/10.5194/egusphere-2025-819-RC1
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