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Constipated clouds.

Aerosols may be making thunderstorms bigger and more frequent. New research shows that an overabundance of aerosols--those tiny particles in the atmosphere that come from natural sources such as dust or volcanic eruptions, and from manmade sources like fossil fuel burning--can increase the lifespans of storm clouds by helping them grow larger and by delaying rainfall. The end result, according to a study led by climate scientists from the University of Texas, is more extreme storms when the rain finally does come.

"A cloud particle is basically water and aerosols. It's like a cell. The aerosol is the nucleus and the water is the cytoplasm," explains climate scientist Sudip Chakraborty, who led the study. "The more aerosols you have, the more cells you get. And if you have more water, you should get more rain."

But what the researchers found was that when there is an abundance of aerosols in the air, as happens in places with lots of industrial or agricultural pollution, the same amount of water vapor gets absorbed by a larger number of aerosols. This means a larger, stronger structure of connected particles that can better support the weight of water, which in turn allows the cloud system to last longer--by as much as 3 to 24 hours--and become more powerful before it begins to dissipate into rain.

The study, published in the Proceedings of the National Academy of Sciences in June, is the first to confirm the theory that aerosols can impact the lifespans of large thunderstorm systems called "mesoscale convective systems." These storms are complex, often violent systems that can span several hundred kilometers and are the primary source of rain over the tropics and the mid-latitudes.

The research team, which also included scientists from NASA's Jet Propulsion Laboratory and the University of Colorado, Boulder, analyzed data from 2,430 convective cloud systems and found that the amount of aerosols in the air could account for around 20 percent of the variability in a cloud system's lifetime over South Asia and Latin America.

The idea that aerosols and extreme storms could be connected "has long been proposed," the researchers noted, "but we have not known whether that increase is significant on global and regional scales."


Please note: Some tables or figures were omitted from this article.

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Title Annotation:FINDINGS; aerosols and thunderstorms
Publication:Earth Island Journal
Date:Sep 22, 2016
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