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−ΛD, with Λ=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 withD≥2.5 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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Gillespie, J.R., List, R. Effects of collision-induced breakup on drop size distributions in steady state rainshafts. PAGEOPH 117, 599–626 (1978). https://doi.org/10.1007/BF00879971
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DOI: https://doi.org/10.1007/BF00879971