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The Honolulu Advertiser

Posted on: Monday, April 30, 2001

UH researchers study post-eruption climate

By Jan TenBruggencate
Advertiser Science Writer

Volcanoes do more than turn the night sky orange and send lava and mudflows through vulnerable villages. They also change the climate.

Researchers at the University of Hawai'i and elsewhere are building a computer model they hope will help predict those climate changes for future eruptions.

They have found evidence, for example, that an explosive eruption in tropical areas can alter the upper winds and cause mild winters in North America for as long as two years afterward.

"We've observed that after every volcanic eruption, and now we're trying to understand it," said Kevin Hamilton, a meteorologist with the University of Hawai'i's International Pacific Research Center.

It happened after the Mexican volcano El Chichon erupted in 1982, and again when the Philippine volcano Pinatubo spewed gas and volcanic particles into the upper atmosphere in 1991, providing the world with several years of brilliant sunsets caused by atmospheric contamination.

"Pinatubo is the best-observed eruption in the 20th century," said Georgiy Stenchikov, an applied mathematics expert who does climate modeling at Rutgers University.

But Pinatubo, occurring within sight of a galaxy of modern climate satellites and Earth-based climate-monitoring gear, provides weather researchers like Hamilton, Stenchikov and Rutgers meteorologist Alan Robock with a remarkable resource for testing their computer climate model.

"With Pinatubo, we have actual observations of the aerosols and we can use them to compare with our model," Hamilton said.

The appearance of volcanic sulfur gases in the stratosphere can heat that region of the atmosphere, and strengthen the jet stream. That can cause warmer winds to blow in from the south in the winter months, creating mild winters in certain areas, he said. Some parts of the world, however, experience cooler weather because of the volcanic output.

One of the things that's interesting is that global warming can cause similar effects, though for different reasons, Stenchikov said.

Because it is so involved in the chemistry and climate of the stratosphere, the researchers call their effort the SkyHi general circulation model. The stratosphere runs from about 18 to 50 kilometers above the Earth's surface. SkyHi is used to study forces that can influence climate.

Climate is a complex process, and the researchers are constantly tinkering with SkyHi to try to make it better predict actual climate processes. They have been able to reproduce winter warming in parts of North America, Europe and Asia. But is still far from perfect.

Robock said the team is now trying to figure out how the mysterious QBO — quasi-biennial oscillation — works. This is the term for winds that blow over the equator in the stratosphere at elevations of 18 to 40 kilometers above the surface. For 13 months, they blow east to west, and then change directions and blow west to east.

"So far, our model does not produce this result," Robock said.

They are also looking at volcanoes beyond the tropics. For instance, when Iceland's Laki volcano erupted in 1783, it generated a cloud over the polar ice cap and is believed to have produced temperate zone winters that were much colder than normal.

That volcano also provides a warning for the world, Robock said. It spat so much dust into the atmosphere that if it erupted with the same strength today, it would shut down aviation in the northern hemisphere for up to six months because of the damage to jet engines from volcanic particles in the air.

Hawaiian volcanoes generally are much quieter in their eruptions, and do not have the explosive events that drive gas and dust into the upper atmosphere.

The three researchers are working with financing and support from the National Science Foundation, NASA, Princeton's Geophysical Fluid Dynamics Lab and the National Oceanic and Atmospheric Administration.