Single-drop fragmentation determines size distribution of raindrops

Abstract

Like many natural objects, raindrops are distributed in size. By extension of what is known to occur inside the clouds, where small droplets grow by accretion of vapour and coalescence, raindrops in the falling rain at the ground level are believed to result from a complex mutual interaction with their neighbours. We show that the raindrops’ polydispersity, generically represented according to Marshall–Palmer’s law (1948), is quantitatively understood from the fragmentation products of non-interacting, isolated drops. Both the shape of the drops’ size distribution, and its parameters are related from first principles to the dynamics of a single drop deforming as it falls in air, ultimately breaking into a dispersion of smaller fragments containing the whole spectrum of sizes observed in rain. The topological change from a big drop into smaller stable fragments—the raindrops—is accomplished within a timescale much shorter than the typical collision time between the drops. The size-distribution profile of raindrops when they reach the ground was previously thought to be governed by complex interactions between neighbouring droplets as they fall. High-speed videos of falling water droplets suggest this is not the case, and that their size distribution can be explained by the fragmentation of individual droplets alone.

Cite this article

Villermaux, E., Bossa, B. Single-drop fragmentation determines size distribution of raindrops. Nature Phys 5, 697–702 (2009). https://doi.org/10.1038/nphys1340

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