Pollution particles help clouds make snow

Atmospheric particles caused by pollution stimulate clouds on the windward side of mountains to make snow, a study has revealed. The findings could help weather forecasters, skiers and farmers.

Atmospheric particles caused by pollution promote cloud-building in the Central Valley and foothills of the Sierra Nevada Mountains in America.

When cloud drops form, latent heat is released that changes local circulation and strengthens the transport of moisture to the windward slope of the mountain, causing greater amounts of snow precipitation.

Clouds have a dual response when injected with numerous tiny pollution particles, as researchers from Pacific Northwest National Laboratory and Colorado State University have now found.

Their study, which discovered a new mechanism for how pollution-caused particles stimulate clouds, revealed that pollution particles near the Sierra Nevada Mountains ripen conditions for forming droplets and ice particles.

Although mountain-side precipitation initially decreases, when the particles reach a certain amount, snowfall dramatically increases over the mountain.

The team also found that high concentrations of pollution particles wafting into the area lead to many more shallow clouds, changing local circulation.

“When the pollution particles fill the mountain-side mixed-phase clouds it dramatically increases snow precipitation, and this finding is different from previous modeling studies,” commented study lead author Dr. Jiwen Fan.

The findings, which help in understanding when and how much snow and rain will fall, could be of benefit to weather forecasters, skiers, farmers and water managers.

The new mechanism also offers important insights for highly polluted mountainous regions in China and India.

Photo credit: jcookfisher/ CC BY 2.0

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