Collisions between small precipitation drops. I: Laboratory measurements of bounce, coalescence, and temporary coalescence

Self-collection efficiencies were measured for isolated drop pairs falling at terminal velocity using orthogonal cameras to obtain the horizontal offset of the drops before collision and the collision outcome. Data were obtained on four different drop-size pairs over a range of impact Weber number (...

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Bibliographic Details
Published in:Journal of the atmospheric sciences 1995-06, Vol.52 (12), p.2258-2275
Main Authors: OCHS, H. T, BEARD, K. V, CZYS, R. R, LAIRD, N. F, SCHAUFELBERGER, D. E, HOLDRIDGE, D. J
Format: Article
Language:English
Subjects:
Cloud physics
Earth, ocean, space
Exact sciences and technology
External geophysics
Meteorology
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Summary:Self-collection efficiencies were measured for isolated drop pairs falling at terminal velocity using orthogonal cameras to obtain the horizontal offset of the drops before collision and the collision outcome. Data were obtained on four different drop-size pairs over a range of impact Weber number (1-10) and size ratio (0.45-0.73). Collision offsets and outcomes were recorded during 45 experiment runs as a function of drop charge. The collision results from all 4200 events were tabulated by offset and charge, and the coalescence efficiency was determined for each run as a function of charge. Collision results revealed a coalescence region for small offset and a bounce region at intermediate-to-large offset and low-to-intermediate charge. The critical offset that separated the regions of coalescence and bounce was independent of charge. At higher values of charge, increasing charge was found to induce permanent and/or temporary coalescence from smaller and larger offsets until bounce was completely eliminated. The production of satellite drops by colliding precipitation drops should provide precipitation embryos that would accelerate the accretion of cloud water in warm-base convective clouds. (Author)
ISSN:0022-4928
1520-0469