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Freshwater can turn hurricanes into super storms

TEXAS A&M (US) — Hurricanes that pass over large areas of freshwater have the potential to intensify 50 percent faster than those that don’t, a new study shows.

Published in Proceedings of the National Academy of Sciences, the findings could benefit weather experts as they try to predict the path and strength of a hurricane, researchers say, noting that about 60 percent of the world’s population resides in areas that are prone to hurricanes or cyclones.

Scientists examined Tropical Cyclones for the decade 1998-2007, which includes about 587 storms, paying particular attention to Hurricane Omar—a Category 4 hurricane that formed in 2008 and eventually caused about $80 million in damages in the south Caribbean area.

They analyzed data from the oceanic region under the storm, including the salt and temperature structure of the water and other factors that played a part in the storm’s intensity.

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“We tested how the intensity of the storm and others increased over a 36-hour period,” says Ping Chang, professor of oceanography and atmospheric sciences at Texas A&M University and director of the Texas Center for Climate Studies. “We were looking for indications that the storm increased in intensity or weakened and compared it to other storms.

“This is near where the Amazon and Orinoco Rivers flow into the Atlantic Ocean, and there are immense amounts of freshwater in the region. We found that as a storm enters an area of freshwater, it can intensify 50 percent faster on average over a period of 36 hours when compared to storms that do not pass over such regions.”

The results could help in predicting a hurricane’s strength as it nears large river systems that flow into oceans, such as the Amazon in the Atlantic, the Ganges in the Indian Ocean, or even the Mississippi River into the Gulf of Mexico.

Hurricanes—called typhoons in the Pacific region and cyclones in the Indian region—are some of the most devastating natural hazards on Earth. A single storm, Cyclone Nargis in 2008, killed more than 138,000 people in Burma and caused $10 billion in damages.

“If we want to improve the accuracy of hurricane forecasting, we need to have a better understanding of not only the temperature, but also the salinity structure of the oceanic region under the storm,” Chang notes.

“If we know a hurricane’s likely path, we can project if it might become stronger when nearing freshwater regions. This is another tool to help us understand how a storm can intensify.”

Chang’s former student Karthik Balaguru, now at the Department of Energy’s Pacific Northwest National Laboratory, is a co-lead author of the paper.

Source: Texas A&M University

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