The doubling of the moisture content in the stratosphere over the last 50 years was caused, at least in part, by tropical biomass burning, a Yale researcher has concluded from examining satellite weather data.
Tropical biomass burning is any burning of plant material. In the tropics this is usually the clearing of forest or grassland for agricultural purposes, mostly before the growing season.
"In the stratosphere, there has been a cooling trend that is now believed to be contributing to milder winters in parts of the northern hemisphere; the cooling is caused as much by the increased humidity as by carbon dioxide," says Steven Sherwood, assistant professor of geology and geophysics whose article appears in this week's issue of the journal Science. "Higher humidity also helps catalyze the destruction of the ozone layer."
Cooling in the stratosphere causes changes to the jet stream that produce milder winters in North America and Europe, he explains. By contrast, he says, harsher winters result in the Arctic.
According to Sherwood, about half of the increased humidity in the stratosphere has been attributed to methane oxidation. It was not known, however, what caused the remaining added moisture, he notes.
In a study funded by the National Aeronautics and Space Administration, Sherwood examined a combination of data from a NASA satellite launched in the 1990s and operational weather satellite data archived at the Goddard Institute for Space Science in New York.
In particular, he studied monthly and yearly fluctuations of humidity in the stratosphere, relative humidity near the tropical tropopause, which is the place where air enters the stratosphere, ice crystal size in towering cumulus clouds, and aerosols associated with tropical biomass burning.
"More aerosols lead to smaller ice crystals and more water vapor entering the stratosphere," Sherwood said. "Aerosols are smoke from burning. They fluctuate seasonally and geographically. Over decades there have been increases linked to population growth."
-- By Jacqueline Weaver
T H I S
Bulletin Home
W E E K ' SS T O R I E S
Faculty cited for leadership in engineering
U.S. needs 'multi-faceted, multi-pronged' approach . . .
Building ties to the community is a core mission of AACC
Los Angeles bishop to serve as interim dean of Berkeley Divinity School
Weather changes linked to tropical plant burning
MEDICAL SCHOOL NEWSResearch shows impairment of self-control . . .
Prenatal exposure to cocaine can cause learning disabilities . . .
Team fine-tuning dosage of vaccine that can block cocaine users' euphoria
Research reveals how Legionnaire's disease takes root in the lungs
Conference and festival will explore Southeast Asia
Liman colloquium will explore the challenges related to . . .
Program to assess treatments for chronic wounds
Yale will cohost the 2004 Frozen Four championship
A look back at the University's Black History Month celebration
Pediatrician to discuss work on biological weapons as part of library series
Memorial service for Dr. Robert W. Berliner
|Visiting on Campus|Calendar of Events|In the News|Bulletin Board
Yale Scoreboard|Classified Ads|Search Archives|Deadlines
Bulletin Staff|Public Affairs Home|News Releases|
E-Mail Us|Yale Home Page