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November-December 2012

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Weather Front

Low Salt Heats Up Hurricanes

Hurricane forecasters may be wise to keep a closer eye on ocean salinity. According to a recent study, storms passing over an area of freshwater can intensify 50 percent faster on average over a period of 36 hours when compared to storms that do not pass over such regions.

Ping Chang of the Texas Center for Climate Studies and Karthik Balaguru of the United States Department of Energy examined almost 600 tropical cyclones that occurred between 1998 and 2007, and analyzed the salinity and temperature structure of the ocean water and other factors related to storm intensity. They were particularly concerned with Hurricane Omar, a Category 4 hurricane that caused nearly $80 million in damages in the Caribbean in 2008.

“We were looking for indications that the storm increased in intensity or weakened and compared it to other storms,” said Chang. “This is near where the Amazon and Orinoco Rivers flow into the Atlantic Ocean, and there are immense amounts of freshwater in the region.” Normally, as hurricane winds draw heat from the ocean surface, cooler water rises from the depths and slows the heat engine. But freshwater creates a barrier layer that prevents deeper, cooler ocean water from rising to the surface. The study found that tropical storms over thick barrier layers cooled 36 percent less than storms over areas lacking barrier layers, and barrier layer storms drew seven percent more heat from the ocean than other storms.

KIMBRA CUTLIP is a freelance writer and former assistant editor for Weatherwise.

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