How frequent is natural cloud seeding from ice cloud layers ( &amp;lt; −35 °C) over Switzerland?

Proske, Ulrike; Bessenbacher, Verena; Dedekind, Zane; Lohmann, Ulrike; Neubauer, David

doi:10.5194/acp-21-5195-2021

Cited by 27 publications

(68 citation statements)

References 88 publications

(150 reference statements)

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“…While Doppler velocity alone could be used to identify certain types of particles (Mosimann, 1995;Kneifel and Moisseev, 2020), there are associated limitations. These limitations include uncertainties in hydrometeor classification due to similarities of terminal fall velocities of different particles (Locatelli and Hobbs, 1974;Barthazy and Schefold, 2006;Li et al, 2020), the presence of a mixture of ice particle populations within the radar volume (Zawadzki et al, 2001;Kalesse et al, 2019;Li and Moisseev, 2020) and impact of air motion on the observed MDV (Protat and Williams, 2011). By using radar Doppler spectra instead of MDV, contributions from different particle populations can be separated (e.g., Zawadzki et al, 2001;Kalesse et al, 2019;Radenz et al, 2019;Li and Moisseev, 2020;Luke et al, 2021).…”

Section: Methodsmentioning

confidence: 99%

“…The observed MDV is affected by vertical air motion. To at least partially mitigate this issue, the observed MDV is averaged over 20 min (Protat and Williams, 2011;Mosimann, 1995;Kneifel and Moisseev, 2020;Silber et al, 2020). While this step reduces the impact of air motion by averaging Doppler velocity over updrafts and downdrafts, the residual air motion is expected to widen the retrieved distribution of N needle .…”

Section: Lwpmentioning

confidence: 99%

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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

Möhler

Petäj̈ä

et al. 2021

Atmos. Chem. Phys.

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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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Section: Methodsmentioning

confidence: 99%

Section: Lwpmentioning

confidence: 99%

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

Möhler

Petäj̈ä

et al. 2021

Atmos. Chem. Phys.

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“…1). The separation between the seeder and feeder clouds is often nonexistent, meaning that ice seeding can occur either in layered clouds or internally within one cloud (Roe, 2005;Proske et al, 2021). In the first case, which seems to occur here as well, there can be vertical continuum of cloud condensates between the seeder and the feeder cloud due to precipitation of ice crystals from the higherlevel cloud (Fig.…”

Section: Conditions Favoring Br In the Two Considered Eventsmentioning

confidence: 96%

“…This means that the seeding ice crystals fall through subsaturated cloudfree air before reaching the feeder region of the cloud and might sublimate. A remote-sensing analysis to 11-year of data over Switzerland showed that in-cloud seeding occurs in 18% of the observations, while the external seeder-feeder mechanism is present 15% of the time (Proske et al, 2021) when the seeder is a cirrus cloud.…”

Section: Conditions Favoring Br In the Two Considered Eventsmentioning

confidence: 99%

“…This mechanism has been observed in several field studies (e.g., Reinking et al, 2000;Purdy et al, 2005;Mott et al, 2014;Ramelli et al, 2021) and refers to ice crystals falling from a high-level seeder cloud into a lower-level cloud (external seederfeeder event) or a lower-lying part of the same cloud (in-cloud seeder-feeder event), where they act as seeds for the glaciation of clouds. Satellite products covering the 11-year period between April 2006 and October 2017 indicated that seeding events are widespread over Switzerland, occurring with a frequency of 31% of the total observations (Proske et al, 2021). Despite these two mechanisms that can readily destabilize an orographic cloud, a high frequency of MPCs have been reported under high updraft velocity conditions prevailing over the complex mountainous terrain (e.g., in the Swiss Alps), where supercooled liquid droplets are generated faster than depleted by depositional ice growth and riming, leading to persistent mixed-phase conditions (Korolev and Isaac, 2003;Lohmann et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Secondary ice production processes in wintertime alpine mixed-phase clouds

Georgakaki¹,

Sotiropoulou

Vignon

et al. 2021

Preprint

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Abstract. Observations of orographic mixed-phase clouds (MPCs) have long shown that measured ice crystal number concentrations (ICNCs) can exceed the concentration of ice nucleating particles by orders of magnitude. Additionally, model simulations of alpine clouds are frequently found to underestimate the amount of ice compared with observations. Surface-based blowing snow, hoar frost and secondary ice production processes have been suggested as potential causes, but their relative importance and persistence remains highly uncertain. Here we study ice production mechanisms in wintertime orographic MPCs observed during the Cloud and Aerosol Characterization Experiment (CLACE) 2014 campaign at the Jungfraujoch site in the Swiss Alps with the Weather Research and Forecasting model (WRF). Simulations suggest that droplet shattering is not a significant source of ice crystals at this specific location – but break-up upon collisions between ice particles is quite active, elevating the predicted ICNCs by up to 3 orders of magnitude, which is consistent with observations. The initiation of the ice-ice collisional break-up mechanism is primarily associated with the occurrence of seeder-feeder events from higher precipitating cloud layers. The enhanced aggregation of snowflakes is found to drive secondary ice formation in the simulated clouds, the role of which is strengthened when the large hydrometeors interact with the primary ice crystals formed in the feeder cloud. Including a constant source of cloud ice crystals from blowing snow, through the action of the break-up mechanism, can episodically enhance ICNCs. Increases in secondary ice fragment generation can be counterbalanced by enhanced orographic precipitation, which seems to prevent explosive multiplication and cloud dissipation. These findings highlight the importance of secondary ice and "seeding" mechanisms – primarily falling ice from above and to a lesser degree blowing ice from the surface – which frequently enhance primary ice and determine the phase state and properties of MPCs.

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Natural Seeder‐Feeder Process Originating From Mixed‐Phase Clouds Observed With Polarization Lidar and Radiosonde at a Mid‐Latitude Plain Site

Liu

et al. 2022

JGR Atmospheres

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Natural seeder‐feeder processes play an essential role in the formation and enhancement of precipitation. However, the cloud‐seeding process from mixed‐phase clouds is still not well understood due to the lack of sufficient observations. Natural seeder‐feeder processes from mixed‐phase clouds (seeder clouds) to lower‐lying liquid clouds (feeder clouds) were observed on 19 occasions using ground‐based polarization lidar and radiosonde measurements from June 2018 to June 2020 at a mid‐latitude plain observatory in Wuhan (30.5°N, 114.4°E), China. Ice crystals originating from seeder clouds fell into feeder clouds located 0.2–2.2 km below. During the sedimentation between seeder and feeder clouds, ice crystals partly underwent sublimation when passing through the in‐between dry air layers. The feeder clouds inhibited those ice crystals from complete sublimation and grew them larger by riming or vapor deposition from a favorable liquid water supply. Subsequently, ice crystals were observed afresh falling from feeder clouds, forming ice virgae descending toward the surface. Owing to cloud seeding, feeder clouds with cloud‐top temperatures (CTTs) as warm as −0.2°C to −14.5°C could produce ice virgae, although these CTTs are generally considered somewhat insufficient to initiate primary ice nucleation. The observed optically thin feeder clouds prolonged the survival time/distance of falling ice crystals, indicating that denser feeder clouds may induce enhanced precipitation.

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How frequent is natural cloud seeding from ice cloud layers ( < −35 °C) over Switzerland?

Cited by 27 publications

References 88 publications

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

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

Secondary ice production processes in wintertime alpine mixed-phase clouds

Natural Seeder‐Feeder Process Originating From Mixed‐Phase Clouds Observed With Polarization Lidar and Radiosonde at a Mid‐Latitude Plain Site

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