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Volume 14, issue 17
Atmos. Chem. Phys., 14, 9001–9012, 2014
https://doi.org/10.5194/acp-14-9001-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 14, 9001–9012, 2014
https://doi.org/10.5194/acp-14-9001-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Sep 2014

Research article | 01 Sep 2014

On transition-zone water clouds

E. Hirsch1,2, I. Koren1, Z. Levin3,4, O. Altaratz1, and E. Agassi2 E. Hirsch et al.
  • 1Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
  • 2Department of Environmental Physics, Israel Institute for Biological Research, Nes Ziona, Israel
  • 3Department of Geophysical, Atmospheric and Planetary Sciences, Tel-Aviv University, Tel-Aviv, Israel
  • 4The Energy, Environment and Water Research Center (EEWRC), The Cyprus Institute, Nicosia, Cyprus

Abstract. A recent field campaign was conducted to measure the properties of thin, warm convective clouds forming under conditions of weak updrafts. During the campaign, short-lived clouds (on the order of minutes) with droplets' effective radius of 1–2 μm and low liquid water path (~ 500 mg m–2) were measured. These low values are puzzling, since in most studies an effective radius of 4 μm is reported to serve as the lower bound for clouds. A theoretical cloud model designed to resolve the droplet-activation process suggested conditions that favor the formation of such clouds. Here we show that these clouds, which mark the transition from haze to cloud, are highly sensitive to the magnitude of the initial perturbation that initiated them. We define these clouds as "transition-zone clouds". The existence of such clouds poses a key challenge for the analysis of atmospheric observations and models, since they "further smooth" the transition from dry aerosol through haze pockets to cumulus clouds.

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