Rain sucks energy out of world’s wind

By | February 27, 2012

Every time it rains, a little bit of energy gets wasted. For the first time we have an estimate of the amount of energy falling raindrops pull from the air.The team behind the calculations say that the atmosphere’s energy balance will drop as climate change increases rainfall, slightly weakening winds around the world.As a raindrop falls it is slowed by contact with the air. This friction takes energy away from the droplet, dissipating it in the atmosphere. The energy – originally from the sun – is not destroyed, but is converted into diffuse heat that cannot be used to generate winds.This is basic physics, but that doesn’t tell us how much energy is lost, says Olivier Pauluis of New York University. With Juliana Dias of the NOAA Earth System Research Laboratory in Boulder, Colorado, he set about finding out.We know roughly how much energy is dissipated by a single raindrop, so Pauluis just needed an estimate of total global rainfall. He got that from the TRMM Tropical Rainfall Measuring Mission satellite, which also told him how far each raindrop fell – a crucial point, as drops that fall further dissipate more energy. On average, 1.8 watts were dissipated for every square metre of atmosphere.That’s a lot, says Dargan Frierson of the University of Washington in Seattle. “Falling water droplets and ice crystals make up only a tiny fraction of the total mass of the atmosphere,” he says, but nevertheless they take out a lot of energy. Pauluis’s estimate may even be too low, as TRMM is thought to underestimate rainfall.

via Rain sucks energy out of world’s wind – environment – 23 February 2012 – New Scientist.

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