Ice multiplication as a long-standing question in cloud microphysics
Alexei
Kiselev
Karlsruhe Institute of Technology
Talk
(Invited)
Ice multiplication (IM) is one of the biggest unsolved problems in the field of atmospheric research. Ice crystal (IC) phase has a huge impact on cloud microphysics, as ice crystal size and number concentration are key for all other cloud process. Inability to accurately represent ice phase in cloud resolving models slows down further improvement of climate models, limits the precipitation forecast and decreases the reliability of future projections of the climate - cloud feedbacks.
The indirect signatures of ice multiplication have been reported by remote sensing studies (radar, lidar), in the aircraft-based in-situ observations (ice particles imaging with video probes, simultaneous or correlated measurements of ice crystals and INP), and in the lab experiments (droplet fragmentation upon freezing DF, Hallett-Mossop HM, ice-ice collisions, etc). Numeric model studies have repeatedly highlighted strong sensitivity of cloud microphysics to the representation of IM. However, the emerging consensus is such that none of these approaches taken alone can provide answers to the key questions:
1. What are cloud types and conditions where IM plays a crucial role in cloud evolution?
2. Is there a dominating IM mechanism or are several mechanisms (droplet fragmentation upon freezing (DF), riming-splintering or HM, sublimation break up, ice crystal collisions) necessary to explain the observations? Could several IM processes run in parallel or is there a spatial or temporal cascade hierarchy of IM processes?
3. What triggers the IM? How many INPs or primary IC are necessary to initiate the IM?
4. What are the exact physical processes underlying various IM processes?
5. What is the efficiency of the IM mechanisms (number of SIP per freezing event / per crystal collision / per mg rime)?
6. What are the key factors controlling the IM efficiency: temperature, droplet size distribution, updraft velocity, etc.?
In my talk, I will briefly review past and recent laboratory efforts aimed at characterization of various IM mechanisms, including rime-splintering, droplet fragmentation upon freezing, and ice-droplet collisions, among others. I will demonstrate the necessity to revise the current understanding of the "well-established" IM mechanisms, based on very recent experimental and in-situ cloud observations. I will emphasize the importance of combining research from the fields of in-situ cloud observations, remote sensing, and modeling, showcasing contributions from leading research groups. Such interdisciplinary approach is crucial for gaining comprehensive understanding of atmospheric ice multiplication on the global scale, with cloud modelling seen as a framework capable of combining the lab experimental data, remote sensing data and in-situ observations of IM.
The indirect signatures of ice multiplication have been reported by remote sensing studies (radar, lidar), in the aircraft-based in-situ observations (ice particles imaging with video probes, simultaneous or correlated measurements of ice crystals and INP), and in the lab experiments (droplet fragmentation upon freezing DF, Hallett-Mossop HM, ice-ice collisions, etc). Numeric model studies have repeatedly highlighted strong sensitivity of cloud microphysics to the representation of IM. However, the emerging consensus is such that none of these approaches taken alone can provide answers to the key questions:
1. What are cloud types and conditions where IM plays a crucial role in cloud evolution?
2. Is there a dominating IM mechanism or are several mechanisms (droplet fragmentation upon freezing (DF), riming-splintering or HM, sublimation break up, ice crystal collisions) necessary to explain the observations? Could several IM processes run in parallel or is there a spatial or temporal cascade hierarchy of IM processes?
3. What triggers the IM? How many INPs or primary IC are necessary to initiate the IM?
4. What are the exact physical processes underlying various IM processes?
5. What is the efficiency of the IM mechanisms (number of SIP per freezing event / per crystal collision / per mg rime)?
6. What are the key factors controlling the IM efficiency: temperature, droplet size distribution, updraft velocity, etc.?
In my talk, I will briefly review past and recent laboratory efforts aimed at characterization of various IM mechanisms, including rime-splintering, droplet fragmentation upon freezing, and ice-droplet collisions, among others. I will demonstrate the necessity to revise the current understanding of the "well-established" IM mechanisms, based on very recent experimental and in-situ cloud observations. I will emphasize the importance of combining research from the fields of in-situ cloud observations, remote sensing, and modeling, showcasing contributions from leading research groups. Such interdisciplinary approach is crucial for gaining comprehensive understanding of atmospheric ice multiplication on the global scale, with cloud modelling seen as a framework capable of combining the lab experimental data, remote sensing data and in-situ observations of IM.
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