Comparison of collision velocity differences of drops and graupel particles in a very turbulent cloud

M. Pinsky*, A. Khain, D. Rosenfeld, A. Pokrovsky

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


The motion of water drops and graupel particles within a turbulent medium is analyzed. The turbulence is assumed to be homogeneous and isotropic. It is demonstrated that the inertia of drops and graupel particles falling within a turbulent flow leads to the formation of significant velocity deviations from the surrounding air, as well as to the formation of substantial relative velocity between drops and graupel particles. The results of calculations of the continuous growth of raindrops and graupel particles moving within a cloud of small droplets are presented both in a non-turbulent medium and within turbulent flows of different turbulence intensity. Continuous growth of a drop-collector was calculated with the coalescence efficient Eε = 1, as well as using Eε values provided by Beard and Ochs [Beard, K.V., Ochs, H.T., 1984. Collection and coalescence efficiencies for accretion. J. Geophys. Res., 89: 7165-7169. ranging from 0.5 to about 0.75 for different droplet sizes. In the case of graupel-droplet interaction Eε was assumed equal to 1. It is shown that in the case Eε = 1 in a non-turbulent medium, the growth rates of graupel and raindrops are close. Under turbulent conditions typical of mature convective clouds, graupel grows much faster than a raindrop. In the case Eε <1 the growth rate of a water drop slows down significantly, so that graupel grows faster than raindrops even under non-turbulent conditions. Turbulence greatly increases the difference between the growth rates of graupel and drop-collectors. Possible consequences of the faster growth of graupel in terms of cloud microphysics are discussed.

Original languageAmerican English
Pages (from-to)99-113
Number of pages15
JournalAtmospheric Research
Issue number2
StatePublished - Sep 1998

Bibliographical note

Funding Information:
The authors are grateful to the anonymous referees for their valuable comments on the manuscript. This study was partially supported by the Germany–Israel Science Foundation (grant 0407-008.08/95) and the Israel Science Foundation founded by the Israel Academy of Sciences and Humanities (grant 572/97).


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