Effects of collision-induced breakup on drop size distributions in steady state rainshafts |
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| Authors: | J R Gillespie Roland List |
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| Institution: | (1) Department of Physics, University of Toronto, 60 St. George Street, M5S 1A7 Toronto, Ontario, Canada |
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| Abstract: | New equations and techniques for dealing with drop breakups are developed and applied to the modelling of the evolution of raindrop spectra in rainshafts. Breakup experiments byMcTaggart-Cowan andList (1975) served as data base.No matter what the original size distribution, the spectrum evolution will always lead to a Marshall-Palmer type equilibrium di tributionN=N
0e– D, with =constant andN
0 proportional to the rainfall rateR. (D stands for raindrop diameter.) ForR 29 mm h–1 and an original Marshall-Palmer distribution, the required fall height to reach equilibrium is  2 km.The equilibrium distributions are characterized by linear relationships betweenR, the radar reflectivity factorZ, the liquid water content LWC and theN
0 of the Marshall-Palmer distribution. Possible explanations for the discrepancy with observations are given.The fact that the all-water processes cannot produce drops withD2.5 mm (as confirmed by observations) leads to the conclusion that observed large raindrops withD 5 mm represent melted hailstones and have not yet reached an equilibrium distribution. These latter conclusions were reached within the original assumption of videspread, steady state precipitation. |
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| Keywords: | Drop breakup Drop size distribution Rain drops Drop collision |
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