U.Va. Environmental Scientist Looks for Link Between Volcanic Activity and Hurricane Frequency, Intensity

Listen to the UVA Today Radio Show report on this story by Fariss Samarrai:

June 1, 2010 — The Atlantic hurricane season began June 1, and the National Oceanic and Atmospheric Administration is projecting 14 to 23 named storms, of which three to seven could become major hurricanes.

But what would happen if a major volcano erupted in the tropics, altering the regional climate with a massive spewing of ash?

"We really don't know what would happen," said Amato Evan, an assistant professor of environmental sciences at the University of Virginia, who studies climate and how volcanic activity affects sea surface temperatures.

"We know from past eruptions – Mexico's El Chichón, in 1982, and Mount Pinatubo in the Philippines in 1991 – that storm activity in the Atlantic is altered by an eruption in the tropics, but we really need a better understanding of this interaction so we can predict with accuracy what might happen in the event of another major eruption."

Amato said previous eruptions altered world climate, particularly in the tropics, for a few years after each event, causing a clear reduction in the frequency and intensity of hurricane and tropical storm activity.

When a volcano erupts, it throws into the atmosphere millions of tons of fine ash and chemicals such as sulfur dioxide, as recently happened over northern Europe with the eruption of Iceland's Eyjafjallajökull. The ash, which is made up of fine shards of rock and glass, causes a short-term cooling effect by reflecting ultraviolet radiation from the sun back into space. A much longer-term effect is caused by sulfuric acid in the upper atmosphere – which is formed when the erupted sulfur dioxide combines with water vapor – further reflecting light to space.

This reduction in radiative heat cools the earth's surface, including the seas. Because warm seas fuel hurricanes, the number and intensity of hurricanes in a season are likely to be reduced as a result.

"Nobody really knows how much an eruption will affect storm activity, and how other factors will come into play," Evan said. "It's a complex mix."

 To better understand these processes, he uses a combination of satellite data and sophisticated numerical models to simulate the effect of a volcano on the temperatures of the Atlantic at its surface and to depths of as much as 100 meters.

"I'm trying to decipher how much previous eruptions changed the temperature of the ocean, and then to take that one step further, and to say, quantitatively, how much those changes in the temperature of the ocean affected hurricane activity," Evan said. "It is complicated in that a volcanic eruption doesn't simply cool the ocean everywhere; it makes the ocean cooler in different regions to different extents."

It is subtle changes, such as a cooler South Atlantic and warmer North Atlantic, that can have huge effects on how storms develop and behave following an eruption.

"I'm trying to parse out the details and relationships of ocean temperatures and wind speeds and circulation patterns, and ultimately be able to say with clarity, following an eruption, how much we can expect the Atlantic hurricane season to be reduced; how many fewer storms we can expect, and they will be less intense by some given amount," Evan said. "Right now, we really don't have a system for doing that, but we need one."

This is important, he said, to people, businesses and governments that lie in the path of tropical storms. People want to know in advance where storms are likely to hit, and how big a storm will be.

"The insurance industry in particular wants to be able to determine risk factors involving storms," Evan said, as possible storm paths, frequencies and intensities affect premiums.

Evan began thinking about this project several years ago as a graduate student at the University of Wisconsin. Last year, when he came to U.Va., he received startup funds from the Department of Environmental Sciences and the Office of the Dean of the College of Arts & Sciences.

Using $70,000 from these funds he built a large computer with which to do the required computer model simulations.

"Without the investment in the computational resources from the University, this work would not be possible," he said.

Evan began the detailed modeling work last fall. He currently is writing up the results and recently made a presentation to the American Meteorological Society's Conference on Hurricanes and Tropical Meteorology, where he received "great feedback" on the project from hurricane researchers/forecasters.

The work continues.

"I think I have identified the physical mechanisms by which large volcanic eruptions alter Atlantic hurricane activity," Evan said. "The next step will be to translate the theory into a set of numbers that will quantitatively describe changes in storm numbers and intensity given a future eruption. My goal is to use the current work as the basis for a proposal to the National Science Foundation in order to receive funding for a volcano-hurricane forecasting tool."

— By Fariss Samarrai