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Discussion papers
https://doi.org/10.5194/acp-2019-611
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-611
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 26 Jul 2019

Submitted as: research article | 26 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

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

Alexei Korolev1, Ivan Heckman1, Mengistu Wolde2, Andrew S. Ackerman3, Ann M. Fridlind3, Luis Ladino1,4, Paul Lawson5, Jason Milbrandt1, and Earle Williams6 Alexei Korolev et al.
  • 1Environment and Climate Change Canada, Toronto, ON, Canada
  • 2National Research Council, Ottawa, ON, Canada
  • 3NASA Goddard Institute for Space Studies, New York, NY, USA
  • 4Centro de Ciencias de la Atmósfera, Universidad Nacional Autonoma de Mexico, México City, Mexico
  • 5Stratton Park Engineering Company, Boulder, CO, USA
  • 6Massachusetts Institute of Technology, Boston, MA, USA

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.

Alexei Korolev et al.
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Alexei Korolev et al.
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Short summary
This study attempts identification of mechanisms of secondary ice production (SIP) based on the observation of small faceted ice crystals. It was found that both in mesoscale convective systems and frontal clouds, SIP was observed right above the melting layer and extended to the higher altitudes with colder temperatures. A principal conclusion of this work is that the freezing drop shattering mechanism is plausibly accounting for the measured ice concentrations in the observed conditions.
This study attempts identification of mechanisms of secondary ice production (SIP) based on the...
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