Magazine article Science News

Cosmic Rays Sow the Seeds of Cloud Growth

Magazine article Science News

Cosmic Rays Sow the Seeds of Cloud Growth

Article excerpt

The lowly raindrop that splatters on the ground may have an origin far loftier than the clouds. According to a new atmospheric theory, cosmic rays streaming in from distant reaches of our galaxy help form one of the necessary ingredients of cloud droplets.

Cosmic rays crash through the lower layers of the atmosphere like tiny tractor-trailers with broken brakes. Moving at close to the speed of light, these nuclear fragments smash into air molecules hard enough to knock electrons loose. This well-documented process creates negatively and positively charged ions.

Atmospheric researchers have often ignored the role of such ions because they are relatively rare. The new theory, however, suggests that ions play a central role in creating aerosols--the minute but important airborne particles that can serve as the cores of growing cloud droplets.

Richard P. Turco of the University of California, Los Angeles and his colleagues present this idea in the March 1 Geophysical Research Letters.

"If this mechanism works, and I think it does, it would be a major source of aerosols in Earth's atmosphere," says Turco.

Many aerosols are liquid droplets containing dissolved sea salt, sulfuric acid, organic molecules from trees, and other compounds. Over the continents, dust and soot are also aerosols. Both liquid and solid specks help clouds develop by encouraging the condensation of water vapor, which does not occur readily without an original seed particle of some sort in the air.

Despite the importance of aerosols, scientists remain uncertain about how they develop. …

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