The relative dispersion of cloud droplets: its robustness with respect to key cloud properties
E. Tas1,2,A. Teller1,O. Altaratz1,D. Axisa3,R. Bruintjes3,Z. Levin4,5,and I. Koren1E. Tas et al. E. Tas1,2,A. Teller1,O. Altaratz1,D. Axisa3,R. Bruintjes3,Z. Levin4,5,and I. Koren1
1Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel
2Department of Soil and Water Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
3Research Applications Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
4Department of Geophysics and Planetary Science, Tel Aviv University, Israel
5The Energy, Environment and Water Research Center, the Cyprus Institute, Nicosia, Cyprus
1Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel
2Department of Soil and Water Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
3Research Applications Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
4Department of Geophysics and Planetary Science, Tel Aviv University, Israel
5The Energy, Environment and Water Research Center, the Cyprus Institute, Nicosia, Cyprus
Correspondence: I. Koren (ilan.koren@weizmann.ac.il)
Received: 25 Mar 2014 – Discussion started: 06 May 2014 – Revised: 28 Dec 2014 – Accepted: 23 Jan 2015 – Published: 24 Feb 2015
Abstract. Flight data measured in warm convective clouds near Istanbul in June 2008 were used to investigate the relative dispersion of cloud droplet size distribution. The relative dispersion (ϵ), defined as the ratio between the standard deviation (σ) of the cloud droplet size distribution and cloud droplet average radius (⟨r⟩), is a key factor in regional and global models. The relationship between ε and the clouds' microphysical and thermodynamic characteristics is examined. The results show that ε is constrained with average values in the range of ~0.25–0.35. ε is shown not to be correlated with cloud droplet concentration or liquid water content (LWC). However, ε variance is shown to be sensitive to droplet concentration and LWC, suggesting smaller variability of ϵ in the clouds' most adiabatic regions. A criterion for use of in situ airborne measurement data for calculations of statistical moments (used in bulk microphysical schemes), based on the evaluation of ϵ, is suggested.
