Ice lollies: An ice particle generated in supercooled conveyor belts

Keppas, Stavros; Crosier, Jonathan; Bower, Keith

doi:10.1002/2017gl073441

Cited by 22 publications

(19 citation statements)

References 50 publications

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“…However, numerous recent in-situ measurements, which 220 applied the antishattering techniques, are in general consistent with the early SIP observations and they also showed that in many clouds, ice particle concentrations are still much higher than the INP concentration (e.g. Croiser et al 2011Croiser et al , 2014Crawford et al 2012;Stith et al 2014;Lawson et al, 2015;Lloyd et al 2015;Lasher-Trapp et al 2016;Keppas et al 2017;Ladino et al 2017;Sullivan et al, 2017Sullivan et al, , 2018and others) Most observations of an enhanced concentration of ice particles have been attributed to the HM-process. The list 225 of these studies extends over 30 publications, so we name only a few of them here (e.g.…”

Section: Spurious Enhancement Of Ice Concentration During Samplingsupporting

confidence: 60%

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

Korolev

Heckman

Wolde

et al. 2019

Preprint

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<p><strong>Abstract.</strong> 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&#8201;&#956;m. 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&#8201;&#176;C to &#8722;15&#8201;&#176;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&#8201;&#956;m 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.</p>

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Section: Spurious Enhancement Of Ice Concentration During Samplingsupporting

confidence: 60%

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

Korolev

Heckman

Wolde

et al. 2019

Preprint

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“…The observations show that multiple populations of ice particles may become visible in the dual-polarization radar observations of the precipitation ML. Given that the coexistence of multiple ice populations has been reported over various geographical areas, for example, the Arctic (Oue et al, 2015), North America (Korolev et al, 2020;Zawadzki et al, 2001), the United Kingdom (Hogan et al, 2002;Keppas et al, 2017), and China (Yang et al, 2014), more reports of this phenomenon are expected in the future. The distinctive polarimetric signals of small needles can be employed to determine the height of the top of the ML.…”

Section: Discussionmentioning

confidence: 99%

Two Layers of Melting Ice Particles Within a Single Radar Bright Band: Interpretation and Implications

Moisseev

2020

Geophysical Research Letters

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Dual‐frequency dual‐polarization radar observations of the melting of two ice populations in a stratiform rainfall event are presented. The observed phenomenon occurs as a two‐layer linear depolarization ratio (LDR) signature in a single radar bright band. Doppler spectra observations show that the upper LDR layer is caused by the melting of ice needles, potentially generated by the rime‐splintering process, while the lower one is mainly due to the melting of background ice particles formed at the cloud top. The melting signal of small needles acts as a unique benchmark for detecting the onset of melting and is used to verify the current methods for the identification of melting layer boundaries. The radar‐derived characteristics of the melting layer are found to be dependent on the radar variable and frequency used. The implications of the presented findings for radar‐based studies of precipitation properties in and above the melting layer are also discussed.

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“…Thermal-shock fragmentation (King and Fletcher, 1976) and the activation of INPs in transient supersaturation of freezing droplets both require precipitation-sized droplets to be active, while the fragmentation of sublimating ice can be important if cloud regions are affected by entrainment of dry air (Korolev and Leisner, 2020). Oraltay and observed no sublimation breakup for columnar and plate-like crystals, while breakup during melting only took place at relative humidities below 90 %.…”

Section: Secondary-ice Production Mechanismsmentioning

confidence: 99%

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

et al. 2021

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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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Ice lollies: An ice particle generated in supercooled conveyor belts

Cited by 22 publications

References 50 publications

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

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

Two Layers of Melting Ice Particles Within a Single Radar Bright Band: Interpretation and Implications

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

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