Continuous secondary ice production initiated by updrafts through the melting layer in mountainous regions

Abstract. An accurate prediction of the ice crystal number concentration in clouds is important to determine the radiation budget, the lifetime, and the precipitation formation of clouds. Secondary ice production is thought to be responsible for the observed discrepancies between the ice crystal number concentration and the ice nucleating particle concentration in clouds. The Hallett-Mossop process is active between −3 °C and −8 °C and has been implemented into several models while all other secondary ice processes are poorly constrained and lack a well-founded quantification. During two hours of measurements taken on a mountain slope just above the melting layer at temperatures warmer than −3 °C, a continuously high concentration of small plates identified as secondary ice was observed. The presence of drizzle drops suggests droplet fragmentation upon freezing as the responsible secondary ice mechanism. The constant supply of drizzle drops can be explained by a recirculation theory, suggesting that melted snowflakes, which sedimented through the melting layer, were reintroduced into the cloud as drizzle drops by orographically forced updrafts. Here we introduce a parametrization of droplet fragmentation at high temperatures when primary ice nucleation is basically absent and the first ice is initiated by collision of drizzle drops with aged ice crystals sedimenting from higher altitudes. Based on previous measurements, we estimate that a droplet of 200 µm in diameter produces 18 secondary ice crystals when it fragments upon freezing. The application of the parametrization to our measurements shows high uncertainties, but the estimated number of splinters produced per fragmenting droplet (18–43) lies within the range of uncertainty if we assume that all droplets larger than 40 µm fragment when they freeze.

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Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-3855-2021 ◽

2021 ◽

Vol 21 (5) ◽

pp. 3855-3870

Author(s):

Annika Lauber ◽

Jan Henneberger ◽

Claudia Mignani ◽

Fabiola Ramelli ◽

Julie T. Pasquier ◽

...

Keyword(s):

Number Concentration ◽

Ice Crystals ◽

Radiation Budget ◽

Ice Crystal ◽

High Concentration ◽

Melting Layer ◽

Mountainous Regions ◽

Order Of Magnitude ◽

Ice Production ◽

Droplet Fragmentation

Abstract. An accurate prediction of the ice crystal number concentration in clouds is important to determine the radiation budget, the lifetime, and the precipitation formation of clouds. Secondary-ice production is thought to be responsible for the observed discrepancies between the ice crystal number concentration and the ice-nucleating particle concentration in clouds. The Hallett–Mossop process is active between −3 and −8 ∘C and has been implemented into several models, while all other secondary-ice processes are poorly constrained and lack a well-founded quantification. During 2 h of measurements taken on a mountain slope just above the melting layer at temperatures warmer than −3 ∘C, a continuously high concentration of small plates identified as secondary ice was observed. The presence of drizzle drops suggests droplet fragmentation upon freezing as the responsible secondary-ice mechanism. The constant supply of drizzle drops can be explained by a recirculation theory, suggesting that melted snowflakes, which sedimented through the melting layer, were reintroduced into the cloud as drizzle drops by orographically forced updrafts. Here we introduce a parametrization of droplet fragmentation at slightly sub-zero temperatures, where primary-ice nucleation is basically absent, and the first ice is initiated by the collision of drizzle drops with aged ice crystals sedimenting from higher altitudes. Based on previous measurements, we estimate that a droplet of 200 µm in diameter produces 18 secondary-ice crystals when it fragments upon freezing. The application of the parametrization to our measurements suggests that the actual number of splinters produced by a fragmenting droplet may be up to an order of magnitude higher.

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Model emulation to understand the joint effects of ice-nucleating particles and secondary ice production on deep convective anvil cirrus

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-17315-2021 ◽

2021 ◽

Vol 21 (23) ◽

pp. 17315-17343

Author(s):

Rachel E. Hawker ◽

Annette K. Miltenberger ◽

Jill S. Johnson ◽

Jonathan M. Wilkinson ◽

Adrian A. Hill ◽

...

Keyword(s):

Temperature Dependence ◽

Production Efficiency ◽

Crystal Size ◽

Particle Production ◽

Number Concentration ◽

Mixed Phase ◽

Ice Crystals ◽

Ice Crystal ◽

Ice Crystal Size ◽

Ice Production

Abstract. Ice crystal formation in the mixed-phase region of deep convective clouds can affect the properties of climatically important convectively generated anvil clouds. Small ice crystals in the mixed-phase cloud region can be formed by heterogeneous ice nucleation by ice-nucleating particles (INPs) and secondary ice production (SIP) by, for example, the Hallett–Mossop process. We quantify the effects of INP number concentration, the temperature dependence of the INP number concentration at mixed-phase temperatures, and the Hallett–Mossop splinter production efficiency on the anvil of an idealised deep convective cloud using a Latin hypercube sampling method, which allows optimal coverage of a multidimensional parameter space, and statistical emulation, which allows us to identify interdependencies between the three uncertain inputs. Our results show that anvil ice crystal number concentration (ICNC) is determined predominately by INP number concentration, with the temperature dependence of ice-nucleating aerosol activity having a secondary role. Conversely, anvil ice crystal size is determined predominately by the temperature dependence of ice-nucleating aerosol activity, with INP number concentration having a secondary role. This is because in our simulations ICNC is predominately controlled by the number concentration of cloud droplets reaching the homogeneous freezing level which is in turn determined by INP number concentrations at low temperatures. Ice crystal size, however, is more strongly affected by the amount of liquid available for riming and the time available for deposition growth which is determined by INP number concentrations at higher temperatures. This work indicates that the amount of ice particle production by the Hallett–Mossop process is determined jointly by the prescribed Hallett–Mossop splinter production efficiency and the temperature dependence of ice-nucleating aerosol activity. In particular, our sampling of the joint parameter space shows that high rates of SIP do not occur unless the INP parameterisation slope (the temperature dependence of the number concentration of particles which nucleate ice) is shallow, regardless of the prescribed Hallett–Mossop splinter production efficiency. A shallow INP parameterisation slope and consequently high ice particle production by the Hallett–Mossop process in our simulations leads to a sharp transition to a cloud with extensive glaciation at warm temperatures, higher cloud updraughts, enhanced vertical mass flux, and condensate divergence at the outflow level, all of which leads to a larger convectively generated anvil comprised of larger ice crystals. This work highlights the importance of quantifying the full spectrum of INP number concentrations across all mixed-phase altitudes and the ways in which INP and SIP interact to control anvil properties.

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Characterization of Arctic mixed-phase cloud properties at small scale and coupling with satellite remote sensing

10.5194/acp-2017-93 ◽

2017 ◽

Cited By ~ 3

Author(s):

Guillaume Mioche ◽

Olivier Jourdan ◽

Julien Delanoë ◽

Christophe Gourbeyre ◽

Guy Febvre ◽

...

Keyword(s):

Remote Sensing ◽

Crystal Size ◽

Mixed Phase ◽

Ice Crystals ◽

Small Scale ◽

Vertical Profiles ◽

Liquid Droplets ◽

Ice Crystal ◽

High Concentration ◽

Ice Crystal Size

Abstract. This study aims to characterize the microphysical and optical properties of ice crystals and supercooled liquid droplets within low-level Arctic mixed-phase clouds (MPC). We compiled and analyzed cloud in situ measurements from 4 airborne campaigns (18 flights, 71 vertical profiles in MPC) over the Greenland Sea and the Svalbard region. Cloud phase discrimination and representative vertical profiles of number, size, mass and shapes of ice crystals and liquid droplets are assessed. The results show that the liquid phase dominates the upper part of the MPC with high concentration of small droplets (120 cm−3, 15&tinsp;μm), and averaged LWC around 0.2 g m−3. The ice phase is found everywhere within the MPC layers, but dominates the properties in the lower part of the cloud and below where ice crystals precipitate down to the surface. The analysis of the ice crystal morphology highlights that irregulars and rimed are the main particle habit followed by stellars and plates. We hypothesize that riming and condensational growth processes (including the Wegener-Bergeron-Findeisein mechanism) are the main growth mechanisms involved in MPC. The differences observed in the vertical profiles of MPC properties from one campaign to another highlight that large values of LWC and high concentration of smaller droplets are possibly linked to polluted situations which lead to very low values of ice crystal size and IWC. On the contrary, clean situations with low temperatures exhibit larger values of ice crystal size and IWC. Several parameterizations relevant for remote sensing or modeling are also determined, such as IWC (and LWC) – extinction relationship, ice and liquid integrated water paths, ice concentration and liquid water fraction according to temperature. Finally, 4 flights collocated with active remote sensing observations from CALIPSO and CloudSat satellites are specifically analyzed to evaluate the cloud detection and cloud thermodynamical phase DARDAR retrievals. This comparison is valuable to assess the sub-pixel variability of the satellite measurements as well as their shortcomings/performance near the ground.

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Development and characterization of an ice-selecting pumped counterflow virtual impactor (IS-PCVI) to study ice crystal residuals

Atmospheric Measurement Techniques ◽

10.5194/amt-9-3817-2016 ◽

2016 ◽

Vol 9 (8) ◽

pp. 3817-3836 ◽

Cited By ~ 5

Author(s):

Naruki Hiranuma ◽

Ottmar Möhler ◽

Gourihar Kulkarni ◽

Martin Schnaiter ◽

Steffen Vogt ◽

...

Keyword(s):

Transmission Efficiency ◽

Number Concentration ◽

Ice Crystals ◽

Ice Crystal ◽

Cloud Droplets ◽

Virtual Impactor ◽

Wide Range ◽

Aerosol Cloud Interactions ◽

Cloud Activation ◽

Dynamics Simulations

Abstract. Separation of particles that play a role in cloud activation and ice nucleation from interstitial aerosols has become necessary to further understand aerosol-cloud interactions. The pumped counterflow virtual impactor (PCVI), which uses a vacuum pump to accelerate the particles and increase their momentum, provides an accessible option for dynamic and inertial separation of cloud elements. However, the use of a traditional PCVI to extract large cloud hydrometeors is difficult mainly due to its small cut-size diameters (< 5 µm). Here, for the first time we describe a development of an ice-selecting PCVI (IS-PCVI) to separate ice in controlled mixed-phase cloud system based on the particle inertia with the cut-off diameter ≥  10 µm. We also present its laboratory application demonstrating the use of the impactor under a wide range of temperature and humidity conditions. The computational fluid dynamics simulations were initially carried out to guide the design of the IS-PCVI. After fabrication, a series of validation laboratory experiments were performed coupled with the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) expansion cloud simulation chamber. In the AIDA chamber, test aerosol particles were exposed to the ice supersaturation conditions (i.e., RHice > 100 %), where a mixture of droplets and ice crystals was formed during the expansion experiment. In parallel, the flow conditions of the IS-PCVI were actively controlled, such that it separated ice crystals from a mixture of ice crystals and cloud droplets, which were of diameter ≥  10 µm. These large ice crystals were passed through the heated evaporation section to remove the water content. Afterwards, the residuals were characterized with a suite of online and offline instruments downstream of the IS-PCVI. These results were used to assess the optimized operating parameters of the device in terms of (1) the critical cut-size diameter, (2) the transmission efficiency and (3) the counterflow-to-input flow ratio. Particle losses were characterized by comparing the residual number concentration to the rejected interstitial particle number concentration. Overall results suggest that the IS-PCVI enables inertial separation of particles with a volume-equivalent particle size in the range of ~ 10–30 µm in diameter with small inadvertent intrusion (~ 5 %) of unwanted particles.

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Impacts of Secondary Ice Production on Arctic Mixed-Phase Clouds based on ARM Observations and CESM2

10.5194/acp-2020-1276 ◽

2020 ◽

Author(s):

Xi Zhao ◽

Xiaohong Liu ◽

Vaughan T. J. Phillips ◽

Sachin Patade

Keyword(s):

Global Climate Model ◽

Single Layer ◽

Ice Nucleation ◽

Number Concentration ◽

Mixed Phase ◽

Department Of Energy ◽

Cloud Base ◽

Ice Crystal ◽

Ice Production ◽

Mixed Phase Clouds

Abstract. For decades, measured ice crystal number concentrations have been found to be orders of magnitude higher than measured ice nucleating particles in moderately cold clouds. This observed discrepancy reveals the existence of secondary ice production (SIP) in addition to the primary ice nucleation. However, the importance of SIP relative to primary ice nucleation remains highly unclear. Furthermore, most weather and climate models do not represent well the SIP processes, leading to large biases in simulated cloud properties. This study demonstrates a first attempt to represent different SIP mechanisms (frozen raindrop shattering, ice-ice collisional break-up, and rime splintering) in a global climate model (GCM). The model is run in the single column mode to facilitate comparisons with the Department of Energy (DOE)'s Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment (M-PACE) observations. We show the SIP importance in the four types of clouds during M-PACE (i.e., multilayer, and single-layer stratus, transition, and front clouds), with the maximum enhancement in ice crystal number concentration by up to 4 orders of magnitude in the moderately-cold clouds. We reveal that SIP is the dominant source of ice crystals near the cloud base for the long-lived Arctic single-layer mixed-phase clouds. The model with SIP improves the occurrence and phase partitioning of the mixed-phase clouds, reverses the vertical distribution pattern of ice number concentration, and provides a better agreement with observations. The findings of this study highlight the importance of considering the SIP in GCMs.

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Development and characterization of an ice-selecting pumped counterflow virtual impactor (IS-PCVI) to study ice crystal residuals

10.5194/amt-2016-102 ◽

2016 ◽

Author(s):

Naruki Hiranuma ◽

Ottmar Möhler ◽

Gourihar Kulkarni ◽

Martin Schnaiter ◽

Steffen Vogt ◽

...

Keyword(s):

Transmission Efficiency ◽

Number Concentration ◽

Ice Crystals ◽

Ice Crystal ◽

Cloud Droplets ◽

Large Size ◽

Virtual Impactor ◽

Wide Range ◽

Aerosol Cloud Interactions ◽

Cloud Activation

Abstract. Separation of particles that play a role in cloud activation and ice nucleation from interstitial aerosols has become necessary to further understand aerosol-cloud interactions. The pumped counterflow virtual impactor (PCVI), which uses a vacuum pump to accelerate the particles and increase their momentum, provides an accessible option for dynamic and inertial separation of cloud elements. However, the use of a traditional PCVI to extract large size cloud hydrometeors is difficult mainly due to its small cut-size diameters (< 5 µm). Here, for the first time we describe a development of an ice-selecting PCVI (IS-PCVI) to separate ice in the controlled mixed-phase cloud system based on the particle inertia with the cut-off diameter > 10 µm. We also present its laboratory application demonstrating the use of the impactor under a wide range of temperature and humidity conditions. The computational fluid dynamics (CFD) simulations were initially carried out to guide the design of the IS-PCVI. After fabrication, a series of validation laboratory experiments were performed coupled with the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) expansion cloud simulation chamber. In the AIDA chamber, test aerosol particles were exposed to the ice supersaturation conditions (i.e., RHice > 100 %), where a mixture of droplets and ice crystals was formed during the expansion experiment. In parallel, the flow conditions of the IS-PCVI were actively controlled, such that it separated ice crystals from a mixture of ice crystals and cloud droplets, which were of size ≥ 10 µm. These large ice crystals were passed through the heated evaporation section to remove the water content. Afterwards, the residuals were characterized with a suite of online and offline instruments downstream of the IS-PCVI. These results were used to assess the optimized operating parameters of the device in terms of (1) the critical cut-size diameter, (2) the transmission efficiency and (3) the counterflow-to-input flow ratio. Particle losses were characterized by comparing the residual number concentration to the rejected interstitial particle number concentration. Overall results suggest that the IS-PCVI enables inertial separation of particles with a volume-equivalent particle size in the range of ~ 10–30 µm in diameter with small inadvertent intrusion (~ 5 %) of unwanted particles.

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Cold cloud microphysical process rates in a global chemistry–climate model

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-1485-2021 ◽

2021 ◽

Vol 21 (3) ◽

pp. 1485-1505

Author(s):

Sara Bacer ◽

Sylvia C. Sullivan ◽

Odran Sourdeval ◽

Holger Tost ◽

Jos Lelieveld ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Climate Models ◽

Climate Model ◽

Ice Nucleation ◽

Ice Crystals ◽

Ice Crystal ◽

Microphysical Process ◽

Future Global Warming ◽

Microphysical Processes ◽

Ice Production

Abstract. Microphysical processes in cold clouds which act as sources or sinks of hydrometeors below 0 ∘C control the ice crystal number concentrations (ICNCs) and in turn the cloud radiative effects. Estimating the relative importance of the cold cloud microphysical process rates is of fundamental importance to underpin the development of cloud parameterizations for weather, atmospheric chemistry, and climate models and to compare the output with observations at different temporal resolutions. This study quantifies and investigates the ICNC rates of cold cloud microphysical processes by means of the chemistry–climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) and defines the hierarchy of sources and sinks of ice crystals. Both microphysical process rates, such as ice nucleation, aggregation, and secondary ice production, and unphysical correction terms are presented. Model ICNCs are also compared against a satellite climatology. We found that model ICNCs are in overall agreement with satellite observations in terms of spatial distribution, although the values are overestimated, especially around high mountains. The analysis of ice crystal rates is carried out both at global and at regional scales. We found that globally the freezing of cloud droplets and convective detrainment over tropical land masses are the dominant sources of ice crystals, while aggregation and accretion act as the largest sinks. In general, all processes are characterized by highly skewed distributions. Moreover, the influence of (a) different ice nucleation parameterizations and (b) a future global warming scenario on the rates has been analysed in two sensitivity studies. In the first, we found that the application of different parameterizations for ice nucleation changes the hierarchy of ice crystal sources only slightly. In the second, all microphysical processes follow an upward shift in altitude and an increase by up to 10 % in the upper troposphere towards the end of the 21st century.

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Two-year statistics of columnar-ice production in stratiform clouds over Hyytiälä, Finland: environmental conditions and the relevance to secondary ice production

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-14671-2021 ◽

2021 ◽

Vol 21 (19) ◽

pp. 14671-14686

Author(s):

Haoran Li ◽

Ottmar Möhler ◽

Tuukka Petäjä ◽

Dmitri Moisseev

Keyword(s):

Single Layer ◽

Number Concentration ◽

Ice Crystals ◽

Liquid Water Path ◽

Ice Particles ◽

Stratiform Clouds ◽

Shallow Clouds ◽

Linear Depolarization Ratio ◽

Generation Mechanisms ◽

Ice Production

Abstract. Formation of ice particles in clouds at temperatures of −10 ∘C or warmer was documented by using ground-based radar observations. At these temperatures, the number concentration of ice-nucleating particles (INPs) is not only expected to be small, but this number is also highly uncertain. In addition, there are a number of studies reporting that the observed number concentration of ice particles exceeds expected INP concentrations, indicating that other ice generation mechanisms, such as secondary ice production (SIP), may play an important role in such clouds. To identify formation of ice crystals and report conditions in which they are generated, W-band cloud radar Doppler spectra observations collected at the Hyytiälä station for more than 2 years were used. Given that at these temperatures ice crystals grow mainly as columns, which have distinct linear depolarization ratio (LDR) values, the spectral LDR was utilized to identify newly formed ice particles. It is found that in 5 %–13 % of clouds, where cloud top temperatures are −12 ∘C or warmer, production of columnar ice is detected. For colder clouds, this percentage can be as high as 33 %; 40 %–50 % of columnar-ice-producing events last less than 1 h, while 5 %–15 % can persist for more than 6 h. By comparing clouds where columnar crystals are produced and to the ones where these crystals are absent, the columnar-ice-producing clouds tend to have larger values of liquid water path and precipitation intensity. The columnar-ice-producing clouds were subdivided into three categories, using the temperature difference, ΔT, between the altitudes where columns are first detected and cloud top. The cases where ΔT is less than 2 K are typically single-layer shallow clouds where needles are produced at the cloud top. In multilayered clouds where 2 K < ΔT, columns are produced in a layer that is seeded by ice particles falling from above. This classification allows us to study potential impacts of various SIP mechanisms, such as the Hallet–Mossop process or freezing breakup, on columnar-ice production. To answer the question whether the observed ice particles are generated by SIP in the observed single-layer shallow clouds, ice particle number concentrations were retrieved and compared to several INP parameterizations. It was found that the ice number concentrations tend to be 1–3 orders of magnitude higher than the expected INP concentrations.

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A new look at the environmental conditions favorable to secondary ice production

10.5194/acp-2019-611 ◽

2019 ◽

Cited By ~ 2

Author(s):

Alexei Korolev ◽

Ivan Heckman ◽

Mengistu Wolde ◽

Andrew S. Ackerman ◽

Ann M. Fridlind ◽

...

Keyword(s):

Ice Crystals ◽

Liquid Drops ◽

Melting Layer ◽

Convective Systems ◽

Spatially Correlated ◽

Ice Particles ◽

Mesoscale Convective ◽

In Situ Observations ◽

Ice Production

Abstract. This study attempts identification of mechanisms of secondary ice production (SIP) based on the observation of small faceted ice crystals (hexagonal plates or columns) with characteristic sizes smaller than 100 μm. Due to their young age, such small ice crystals can be used as tracers for identifying the conditions for SIP. Observations reported here were conducted in oceanic tropical mesoscale convective systems (MCS) and mid-latitude frontal clouds in the temperature range from 0 °C to −15 °C heavily seeded by aged ice particles. It was found that both in MCSs and frontal clouds, SIP was observed right above the melting layer and extended to the higher altitudes with colder temperatures. It is proposed that the initiation of SIP above the melting layer is related to the circulation of liquid drops through the melting layer. Liquid drops formed via melting ice particles are advected by the convective updrafts above the melting layer, where they impact with aged ice, freeze and shatter. The ice splinters generated by shattering initiate the chain reaction of SIP. The size of the splinters generated during SIP were estimated as 10 μm or less. In most SIP cases, small secondary ice particles spatially correlated with liquid phase, vertical updrafts and aged rimed ice particles. However, in many cases neither graupel nor liquid drops were observed in the SIP regions, and therefore, the conditions for an active Hallett-Mossop process were not met. A principal conclusion of this work is that the freezing drop shattering mechanism is alone among established SIP mechanisms is plausibly accounting for the measured ice concentrations in the observed conditions. No other SIP mechanisms could be confidently identified from the airborne in-situ observations.

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Multiyear statistics of columnar ice production in stratiform clouds over Hyytiälä, Finland

10.5194/acp-2021-332 ◽

2021 ◽

Author(s):

Haoran Li ◽

Ottmar Möhler ◽

Tuukka Petäjä ◽

Dmitri Moisseev

Keyword(s):

Single Layer ◽

Number Concentration ◽

Ice Crystals ◽

Liquid Water Path ◽

Ice Particles ◽

Stratiform Clouds ◽

Shallow Clouds ◽

Linear Depolarization Ratio ◽

Generation Mechanisms ◽

Ice Production

Abstract. Formation of ice particles in clouds at the temperatures of −10 °C or warmer was documented by using ground-based remote sensing observations. At these temperatures, the number concentration of ice nucleating particles (INP) is not only expected to be small, but also this number is highly uncertain. In addition, there are a number of studies reporting that the observed number concentration of ice particles exceeds expected INP concentrations, indicating that other ice generation mechanisms, such as secondary ice production (SIP), may play an important role in such clouds. To identify the formation of ice crystals and report conditions in which they are generated, W-band cloud radar Doppler spectra observations collected at the Hyytiälä station for more than two years were used. Given that at these temperatures ice crystals grow mainly as columns, which have distinct linear depolarization ratio (LDR) values, spectral LDR was utilized to identify newly formed ice particles. Our results indicate that that the columnar ice production took place in 5 to 13 % of clouds, where cloud top temperatures were −12 °C or higher. For colder clouds, this percentage can be as high as 33 %. 40 ~ 50 % of columnar-ice-producing events last less than 1 hour, while 5 ~ 15 % can persist for more than 6 hours. By comparing clouds where columnar crystals were produced with the ones where these crystals were absent, we found that the columnar-ice-producing clouds tend to have larger values of liquid water path and precipitation intensity. The columnar-ice-producing clouds were subdivided into subcategories, using the temperature difference, Δ T, between the altitudes where columns are first detected and the cloud top altitude. The cases where Δ T is less than 2 °C are typically single-layer shallow clouds where needles are produced at the cloud top. In multilayered clouds, where Δ T > 2 °C, columns are produced in a layer that is seeded by ice particles falling from above. This classification allows to study potential impacts of various SIP mechanisms, such as Hallet-Mossop process or freezing breakup, on columnar ice production. To answer the question whether the observed ice particles are generated by SIP in the observed single-layer shallow clouds, ice particle number concentrations were retrieved and compared to several INP parameterizations. It was found that the ice number concentrations tend to be 1 ~ 3 orders of magnitude higher than the expected INP concentrations.

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