A New Representation of Collision-Induced Breakup of Raindrops and Its Implications for the Shapes of Raindrop Size Distributions

Abstract Using results of laboratory experiments on collision-induced raindrop breakup, Low and List (LL) developed a parameterization describing the fragment size distribution (FSD) produced by collisions of raindrops. An equilibrium raindrop size distribution (ED) is approached when this parameterization is used in numerical models of steady rain. Since scant observational evidence of such EDs exists, the need for a careful examination of the parameterization's foundation is evident. Using LL's experimental observations, an alternate parameterization is developed that alleviates three shortcomings of the original scheme, namely, ensuring mass conservation, the use of adequate uncertainty analysis, and the use of a more physical basis for deriving parameterized relationships. FSDs generated by raindrop collisions are represented by combinations of lognormal, Gaussian, and modified delta distributions for each of the three breakup types (filament, sheet, and disk) observed. The mode, width, and height of ...

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