Rainy Days Driven by Traffic Patterns, Study Says

Richard A. Lovett
for National Geographic News
July 13, 2006

Think it rains only on the weekend? Not if you live in the Southeast United States.

Summer rainfall in this region of the country appears to mimic the highs and lows of air pollution from weekday commuters, says Thomas Bell of the NASA Goddard Space Flight Center in Greenbelt, Maryland.

At the May meeting of the American Geophysical Union in Baltimore, Maryland, Bell reported that afternoon thundershowers are more frequent and more intense on weekdays than on weekends.

Bell limited his study to summer thunderstorms, which, in theory, are most likely affected by changes in air pollution.

Meteorologists believe smog contains tiny particles that spur the formation of water droplets, which eventually become raindrops.

More smog, therefore, not only means more droplets, but also tinier ones—at least in the initial stages of storm formation.

These smaller droplets are carried higher into the air before falling as rain, which ultimately increases storm intensity.

(Related story: tornado chasers in National Geographic magazine.)

Wednesday Thunderstorms

Scientists have long speculated that pollution from weekday commuters might affect the storm cycle. But previous studies failed to detect a link.

Bell says that past studies tended to focus on individual cities, particularly those in coastal areas where other factors may also influence storms.

Seeking to examine the issue more broadly, Bell analyzed rainfall patterns from nine years of satellite data from the Southeast quadrant of the U.S.

Continued on Next Page >>


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