Preprints
https://doi.org/10.5194/acp-2021-338
https://doi.org/10.5194/acp-2021-338

  09 Jun 2021

09 Jun 2021

Review status: this preprint is currently under review for the journal ACP.

Supercooled liquid water and secondary ice production in Kelvin–Helmholtz instability as revealed by radar Doppler spectra observations

Haoran Li1, Alexei Korolev2, and Dmitri Moisseev1,3 Haoran Li et al.
  • 1Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Finland
  • 2Environment and Climate Change Canada, Toronto, ON, Canada
  • 3Finnish Meteorological Institute, Helsinki, Finland

Abstract. Mixed-phase clouds are globally omnipresent and play a major role in the Earth's radiation budget and precipitation formation. The existence of liquid droplets in presence of ice particles is microphysically unstable and depends on a delicate balance of several competing processes. Understanding mechanisms that govern ice initiation and moisture supply are important to understand the life-cycle of such clouds. This study presents observations that reveal the onset of drizzle inside a ∼600 m deep mixed-phase layer embedded in a stratiform precipitation system. Using Doppler spectra analysis, we show how large supercooled liquid droplets are generated in Kelvin-Helmholtz (K-H) instability despite ice particles falling from upper cloud layers. The spectral width of supercooled liquid water mode in radar Doppler spectrum is used to identify a region of increased turbulence. The observations show that large liquid droplets, characterized by reflectivity values larger than −20 dBZ, are generated in this region. In addition to cloud droplets, Doppler spectral analysis reveals the production of the columnar ice crystals in the K-H billows. The modelling study estimates that the concentration of these ice crystals is 3 ∼ 8 L−1, which is at least one order of magnitude higher than that of primary ice nucleating particles. Given the detail of the observations, we show that multiple populations of secondary ice particles are generated in regions where larger cloud droplets are produced and not at some constant level within the cloud. It is therefore hypothesized that K-H instability provides conditions favorable for enhanced droplet growth and formation of secondary ice particles.

Haoran Li et al.

Status: open (until 21 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Haoran Li et al.

Haoran Li et al.

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Short summary
Kelvin-Helmholtz clouds embedded in a stratiform precipitation event were revealled by using radar doppler spectra analysis. Given the unprecedented detail of the observations, we show that multiple populations of secondary ice columns were generated in the pockets where larger cloud droplets are formed and not at some constant level within the cloud. Our observations indicate that the Kelvin-Helmholtz instability is favorable for droplet growth and secondary ice formation.
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