Sometimes, the simplest physical events are the hardest to explain. Here is a hydrologic explanation of raindrop size heterogeneity.
The short lifetime of a raindrop is a complicated and explosive affair, physicists have revealed. Using high-speed video footage they have solved a longstanding conundrum of what determines the size of raindrops.
A century ago, physicists put out sheets of absorbent paper in showers to record raindrop size, and discovered a surprising variety. Most are under a millimetre across, but others span 5 mm – and providing rainfall level is constant, drops exhibit the same variation in every shower.
High-speed footage captured by Villermaux and colleague Benjamin Bossa at the University Institute of France in Paris suggests a more unexpected explanation. They think individual droplets inflate and then explode to create the smaller droplets so common at ground level.
The pair got the idea from the unusual but well known transformations of fuel droplets travelling at high speed in diesel engines. As they travel, drops flatten from a sphere into a pancake-like disc; this catches passing air and inflates like a liquid parachute that eventually explodes in a shower of smaller droplets.
Myth of raindrop formation exploded
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