Satellite-generated rain maps show air pollution hinders rainfall
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Source: Virtual New York
Monday, 18 December 2000 22:51 (ET)
Satellite-generated rain maps show air pollution hinders rainfall
By KOREN CAPOZZA, UPI Science News
SAN FRANCISCO, Calif., Dec. 18 -- NASA researchers at the American
Geophysical Union meeting announced Monday that they discovered an important
link between air pollution and rainfall.
The Tropical Rainfall Measuring Mission, a joint U.S.-Japan effort,
collected rainfall data in the earth's tropics over three years. The highly
accurate images reveal that tropical rainfall can be significantly reduced
by man-made pollution.
"The large concentration of pollution particles redistribute the water
inside the clouds into a large number of very small droplets that are too
small to combine with each other in the available lifetime of the cloud,"
said Daniel Rosenfeld, TRMM Science Team researcher and professor of earth
sciences at Hebrew University of Jerusalem.
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The new information on tropical precipitation was revealed through TRMM
rain maps created with high-resolution microwave and precipitation radar
data. The satellite's advanced sensors enabled meteorologists to accurately
calibrate ground-based rain monitoring systems. The results show that
precipitation varies drastically between highly polluted and clean air days.
"Recently we found that clouds in the tropics produce as little as half
the rainfall as clean air clouds," said Rosenfeld. The findings suggest
that slash and burn agricultural practices and aerosol use in Brazil could
significantly affect precipitation in the tropical Amazon region. Rosenfeld
said that the trend is of particularly worrisome for communities in tropical
regions because they tend to be highly dependent on water for their
livelihood. "The most important implication is for our water resources that
we are so much dependent on. Here we show how, through air pollution, we
actually change precipitation processes in areas of the world where the
people are most dependent on that rainfall," said Rosenfeld. The
researchers also observed a seasonal and altitude shift in rain patterns.
"We believe we saw precipitation forming at lower altitudes on the clean
days compared to the dirty days. Then during the shoulder seasons, before
the rainy season really gets underway, the storms looked continental and
strong," said Robert Adler, the TRMM project scientist from NASA's Goddard
Space Flight Center.
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Adler noted that the global maps showed more lightening activity in Africa
than in South America. The reasons for the pattern are not yet clear but
Rosenfeld believes there may be a link with air pollution. "The message
here is that air pollution in the tropics is affecting the whole climate
system which is very sensitive to it," said Rosenfeld. While a great deal
remains to be learned about storms and rainfall, Adler says the new TRMM
findings shed light on the complicated processes involved in weather
patterns. "We are learning about storms on earth in a way that we've never
been able to before," said Adler.
Copyright 2000 by United Press International.
All rights reserved.
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