Evidence that ice forms primarily in supercooled liquid clouds at temperatures > -27C

Westbrook, C. D. ORCID: https://orcid.org/0000-0002-2889-8815 and Illingworth, A. J. ORCID: https://orcid.org/0000-0002-5774-8410 (2011) Evidence that ice forms primarily in supercooled liquid clouds at temperatures > -27C. Geophysical Research Letters, 38. L14808. ISSN 0094-8276 doi: 10.1029/2011GL048021

Abstract/Summary

Using 4 years of radar and lidar observations of layer clouds from the Chilbolton Observatory in the UK, we show that almost all (95%) ice particles formed at temperatures >-20°C appear to originate from supercooled liquid clouds. At colder temperatures, there is a monotonic decline in the fraction of liquid-topped ice clouds: 50% at -27°C, falling to zero at -37°C (where homogeneous freezing of water droplets occurs). This strongly suggests that deposition nucleation plays a relatively minor role in the initiation of ice in mid-level clouds. It also means that the initial growth of the ice particles occurs predominantly within a liquid cloud, a situation which promotes rapid production of precipitation via the Bergeron-Findeison mechanism.