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60-Second Earth

How Raindrops Calm the Wind

New research suggests the drag on falling precipitation helps slow atmospheric circulation. David Biello reports

Rain isn't just a soothing sound. It also helps calm the winds. How? Friction.

That's according to a new study published in Science on February 24.

Winds and even the atmospheric jet streams caused by the rotation of the planet dissipate much of their energy via friction already. Air molecules hurled hither, thither and yon rub together and warm up. But rain and other forms of precipitation rub against air molecules too, and produce a tiny bit of friction. That resistance slows each drop’s fall and also slows the winds themselves.

Raindrop drag hadn't been measured before, but, using satellites, scientists found that this friction averages 1.8 watts per square meter in the tropics. And that adds up on a global scale. Thanks to climate change even heavier downpours that originate higher in the sky are expected in the future. That means even more friction and, potentially, less of the wind that mixes the atmosphere.

Of course, the extra heat trapped by human greenhouse gas emissions is likely to play a bigger role than raindrop friction in any atmospheric changes. But it's going to be a more humid, wetter world. Better get a raincoat.

—David Biello

[The above text is a transcript of this podcast.]

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