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Volume 18, issue 20 | Copyright
Atmos. Chem. Phys., 18, 15329-15344, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Oct 2018

Research article | 25 Oct 2018

Observations of the microphysical evolution of convective clouds in the southwest of the United Kingdom

Robert Jackson1,a, Jeffrey R. French1, David C. Leon1,b, David M. Plummer1, Sonia Lasher-Trapp2, Alan M. Blyth3, and Alexei Korolev4 Robert Jackson et al.
  • 1University of Wyoming Department of Atmospheric Sciences, 1000 E. University Ave, Laramie, WY, USA
  • 2University of Illinois at Urbana-Champaign Department of Atmospheric Sciences, 105 S. Gregory St., Urbana, IL, USA
  • 3National Centre for Atmospheric Science, University of Leeds, Leeds, UK
  • 4Environment and Climate Change Canada, Cloud Physics and Severe Weather Section, Downsview, ON, USA
  • anow at: Argonne National Laboratory, Environmental Sciences Division, 9700 Cass Ave, Argonne, IL, USA
  • bnow at: Alpenglow Instruments, Laramie, WY, USA

Abstract. The COnvective Precipitation Experiment (COPE) was designed to investigate the origins of heavy convective precipitation over the southwestern UK, a region that experiences flash flooding due to heavy precipitation from slow-moving convective systems. In this study, the microphysical and dynamical characteristics of developing turrets during 4 days in July and August 2013 are analyzed. In situ cloud microphysical measurements from the University of Wyoming King Air and vertically pointing W-band radar measurements from Wyoming Cloud Radar are examined, together with data from the ground-based NXPol radar.

The 4 days presented here cover a range of environmental conditions in terms of wind shear and instability, resulting in a similarly wide variability in observed ice crystal concentrations, both across days as well as between clouds on individual days. The highest concentration of ice was observed on the days in which there was an active warm-rain process supplying precipitation-sized liquid drops. The high ice concentrations observed ( > 100L−1) are consistent with the production of secondary ice particles through the Hallett–Mossop process. Turrets that ascended through remnant cloud layers above the 0°C level had higher ice particle concentrations, suggesting that entrainment of ice particles from older clouds or previous thermals may have acted to aid in the production of secondary ice through the Hallett–Mossop process. Other mechanisms such as the shattering of frozen drops may be more important for producing ice in more isolated clouds.

Publications Copernicus
Short summary
This paper looks at microphysical observations of growing cumulus clouds in the southwest United Kingdom sampled during the COnvective Precipitation Experiment (COPE). Our results suggest that secondary ice production processes are contributing to the observed concentrations and that entrainment of particles from remnant cloud layers may have acted to aid in secondary ice production.
This paper looks at microphysical observations of growing cumulus clouds in the southwest United...