Thank god for air friction. Without it, falling rain would smack into our heads at hundreds of miles per hour. But friction works both ways—falling raindrops also slow down the movement of air molecules in the atmosphere. A new paper in Science calculated that raindrops dissipate as much kinetic energy from the atmosphere as air turbulence. Granted, at 1.8 watts per square meter and 0.75% of the atmosphere’s total kinetic energy, that’s not very much. What’s surprising is that rain drops are pulling more than their weight, as they make up only 0.01% of the atmosphere’s mass.
Researchers calculated the kinetic energy dissipated by a single raindrop and put it together with precipitation rates around the world. Since satellite precipitation data also show the height from which rain started falling, the researchers could plug how far raindrops fell into their energy calculations. It all adds up across the whole globe: the researchers estimate the total rate of energy dissipation from rainfall to be 1015 Watts. That’s a lot of energy, but still unlikely to affect major weather phenomena like hurricanes or tornados.
[via Nature News]
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