WASHINGTON -- For the first time, researchers have proven that smoke from forest fires inhibits rainfall. The findings, to be published in the October 15 issue of Geophysical Research Letters, are based on an extensive analysis of data taken from NASA's Tropical Rainfall Measuring Mission (TRMM) spacecraft.
The study 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 or 5,000 meters) 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, the paper's author and a TRMM scientist at the Institute of Earth Sciences, Hebrew University of Jerusalem.
Scientists have a keen interest in how changes in global precipitation 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.
In his paper, Rosenfeld highlights one specific area: Kalimantan, Indonesia. During the satellite's overpass on March 1, 1998, the southeastern portion of the island was engulfed in smoke, while the northwestern portion was relatively smoke free. The spacecraft's radar detected precipitation in smoke-free clouds, but almost none in the smoke-plagued clouds, showing the impact of smoke from fires on precipitation over the rainforest.
"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 conc
Contact: Harvey Leifert
American Geophysical Union