Sunday, November 6, 2011

Pollution may be fueling unusual desert cyclones

Bob Berwyn in the Summit County Citizens Voice: A buildup of atmospheric pollutants may be contributing to the intensification of tropical cyclones in the Arabian Sea, said a group of researchers who documented a shift in upper-air wind patterns over the region.

The scientists linked those changes to increased aerosols, possibly originating over the Indian subcontinent. A widespread brown cloud dampens the formation of monsoon-related shearing winds that historically have weakened cyclones in the region.

“We are showing that pollution from human activity – as simple as burning wood or driving a vehicle with a diesel engine – can actually change these massive atmospheric phenomena in a significant way,” said the study’s lead author, Amato Evan, an environmental scientist in the University of Virginia’s College of Arts & Sciences. “It underscores the importance of getting a handle on emissions in the region.”

“There has been a real uptick in the intensity of tropical cyclones in the Arabian Sea,” Evan said. “We wanted to understand why, and we think we found the reason.”

Traditionally, prevailing wind-shear patterns prevent cyclones in the Arabian Sea from becoming major storms. But changes in the winds aloft has enabled the formation of stronger cyclones in recent years – including storms in 2007 and 2010 that were the first recorded storms ever to enter the Gulf of Oman. Tropical Storm Keila just hit Oman a few days ago.

Until recent decades, cyclones in the Arabian Sea tended to be relatively weak storms. This was attributed to a naturally occurring vertical wind shear over the sea, which tended to weaken and ultimately break up developing storms.

The weakening wind patterns over the past 30 years have corresponded with a buildup of aerosols in the atmosphere over India, which deflect sunlight from the surface, creating dimming at ground level, the researchers said. The aerosol buildup creates formations known as “atmospheric brown clouds,” in which smog from diesel emissions, soot and other by-products of biomass burning accumulates and becomes widespread to a degree significant enough to be a climatic force....

Once a powerful Category 4 storm, Cyclone Phet had weakened to a Category 3 storm by the time it came ashore over Oman on June 4, 2010. Shot by NASA.

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