Flying rain dance.
Clouds are made of water droplets. Normal rainstorms occur when the water droplets collide and stick to one another. The small droplets combine to form heavier drops. The heaviest drops fall to Earth as rain. But the rain won't fall if the clouds evaporate before the drops have a chance to collide.
Scientists have tried for years to "seed" clouds to make them release their moisture. They shoot silver iodide particles into the clouds. The particles act as "seeds" around which ice crystals form. When they get heavy enough, the crystals fall to the ground as snow and hail.
But seeding for rain that way doesn't work well in warm climates. So, with the help of the Mexican government, NCAR's Dan Breed is trying a new approach.
First a radar instrument on the ground bounces radio waves off the cloud. That helps scientists measure the cloud's distance from Earth, as well as how fast and in which direction the cloud is moving. With the radar's guidance, an airplane with burning flares on its wings flies just below the cloud.
The flares are like emergency road flares, except they release salt as they burn. As the salty smoke floats into the clouds, the salt attracts water. That causes the cloud droplets to clump together. With this new technique, says Breed, up to 60 percent of the cloud's water falls to the ground.
Don't expect this flaming rain dance to prevent droughts, however. "It's not a magic bullet," Breed explains. "Drought periods are the worst time to do this." In a drought, with practically no water around, there are no clouds to seed.
But when rain is unpredictable, and clouds are plentiful, the flames in the sky could keep the water flowing -- and the crops growing -- here on Earth.
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|Title Annotation:||using radar and airplanes with burning flares on their wings to seed clouds for rain|
|Article Type:||Brief Article|
|Date:||Mar 21, 1997|
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