Spacecraft Shows Smoke Inhibits Rainfall
FOR
THE FIRST TIME, RESEARCHERS HAVE proven that smoke from forest fires
inhibits rainfall, which indicates changes in global precipitation
that affect human activities, such as crop production, and the global
rainfall weather pattern. More precise information about rainfall
and its variability is crucial to understanding the global climate
and predicting climate change.
Data from NASA's Tropical Rainfall Measuring Mission (TRMM) spacecraft
shows that the "warm rain" processes that often create
rain in tropical clouds are practically shut off when the clouds
are polluted with heavy smoke from forest fires. In these clouds,
scientists found, the cloud tops must grow considerably above the
freezing level (16,000 feet) in order for them to start producing
rain by an alternative mechanism.
"We've seen evidence of decreased precipitation in clouds
contaminated by smoke, but it wasn't until now that we had direct
evidence showing that smoke actually suppresses precipitation completely
from certain clouds," said Dr. Daniel Rosenfeld, a TRMM scientist
at the Institute of Earth Sciences at Hebrew University of Jerusalem.
Rosenfeld is also author of a paper on the findings published in
the October 15 issue of Geophysical Research Letters. The
findings are based on an extensive analysis of TRMM data.
Scientists have known for some time that smoke from burning vegetation
suppresses rainfall, but they did not know to what extent until
now. "It's important to note that this is not a unique case,"
said Rosenfeld. "We observed and documented several other cases
that showed similar behavior. In some instances even less severe
smoke concentration was found to have comparable impacts on clouds."
"Findings such as these are making the first inroads into
the difficult problem of understanding humanity's impacts on global
precipitation," said Dr. Christian Kummerow, TRMM project scientist
at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Raindrops in the atmosphere grow by two means. The "warm rain"
process is when a few cloud drops get large enough to start falling
and pick up other cloud drops along the way until they become big
enough to fall to Earth as raindrops. The second process requires
ice particles and water colder than 32 degrees Fahrenheit. Ice particles
surrounded by this "supercooled" water may grow extremely
rapidly as water freezes onto the ice core. As these large ice particles
fall, they eventually melt and become raindrops.
TRMM has produced continuous data since December 1997. It is a
U.S.-Japanese mission and part of NASA's Earth Science Enterprise,
a long-term research program designed to study Earth's land, oceans,
air, ice and life as a total system.
For more information, contact David E. Steitz at NASA Headquarters.
Call: 202/358-1730,
E-mail: dsteitz@mail.hq.nasa.gov Please mention you read
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