"Cyclones that traverse the Great Lakes have important impacts on the physical environment and human habitation in the region," said James Angel, a climatologist with the Survey. "There is a lot of development along the lakes, and when the water level is high -- as it is now -- the area becomes extremely vulnerable to shoreline damage from these storms. A better understanding of how the Great Lakes affect passing cyclones may allow better forecasting of these storms and their potential effects."

Cyclones are low-pressure storm centers, "often accompanied by high winds and heavy precipitation," said Scott Isard, a U. of I. professor of geography. "The ensuing storms can be huge, ranging in size from 800 to 1,500 miles in diameter."

To study the effect the Great Lakes have on passing cyclones, Angel and Isard examined the rates of movement and the changes in intensity for 583 cyclones that passed over the region between the years 1965 to 1990. The researchers' findings, published in the September issue of Monthly Weather Review, identify several important features regarding the lakes' influence on these storm systems.

"In general, we found that cyclones accelerated as they approached the Great Lakes region and increased in intensity over the lakes," Angel said. "This effect was most pronounced from September to November, when the surface waters of the lakes are warmer than the surrounding air and can provide a major source of both moisture and heat that energizes passing storms."

From January to March, when broken ice cover is generally present on the lakes, cyclones accelerated less and did not intensify, Angel said. However, cyclones that traversed the region during May and June did speed up and grow in strength.

"This surprised us, because the lakes are usually cooler than the overriding air mass during spring and summer, and have not generally been considered as an important energy source for cyclones at that time," Angel said. "We don't yet have a satisfactory explanation for this phenomenon."

In another study (to appear in the journal Climate), Angel and Isard analyzed trends in storm strength for the years 1900 to 1990. "We are seeing evidence of an increase in the number of stronger storms, particularly in the months of November and December," Angel said.

Historically, some of these cyclones have produced hurricane-force winds and caused extensive damage to shipping. The "great storm of 1913," for example, sank a dozen ships and claimed more than 250 lives. More recently, the ore carrier Edmund Fitzgerald -- popularized in a ballad by Canadian singer and songwriter Gordon Lightfoot -- sank in Lake Superior during a major storm on Nov. 10, 1975. All hands were lost.

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