Researchers at Purdue University in West Lafayette, Ind., said the evidence supports the hypothesis that rising temperatures of tropical waters � both on the surface and just below the surface - are causing more intense cyclones in the southern Pacific Ocean and hurricanes, their rotational opposites, in the Atlantic Ocean.

The research also supports a popular notion that warming global average temperatures are contributing to increasingly severe and more frequent tropical storms - such as Hurricane Katrina, a Category 4 storm that devastated New Orleans, La., and other parts of the U.S. Gulf Coast in 2005.

Their findings will appear in an upcoming issue of the journal Geophysical Research Letters.

"If you add up every puff of wind associated with tropical cyclones annually, that number has increased substantially,� said lead researcher Matthew Huber.

He said this means �that either the storms are getting stronger or there are more of them.� This is important, Huber continued, because tropical cyclonic storm activity has doubled over the 40 years, while ocean temperatures have increased by about a quarter-degree Celsius. Over the next century, he added, scientists expect two more degrees of ocean warming.

The research represents an independent confirmation of findings reported last year by Kerry Emanuel, a researcher at the Massachusetts Institute of Technology in Cambridge.

"We used a different technique and different data than Emanuel, who looked specifically at the Atlantic and western Pacific oceans, whereas we looked at the entire world," Huber said. "Nevertheless, we got the same results that he did, the same basic trends."

Huber�s team used wind and temperature data generated by computer models at the European Centre for Medium-Range Weather Forecasting�s Reanalysis 40 Year Project, which encompassed climate data and trends beginning in 1958.

The European scientists used simulations to reanalyze already known past weather events. From the reanalyzed data, the Purdue researchers then constructed a factor they call "globally integrated tropical cyclone power dissipation" �the total wind energy associated with tropical cyclones worldwide, representing the potential damage that could be caused by storms.

The power dissipation is a storm's overall surface wind velocity, cubed.

"Cubing the surface wind velocity tells us approximately how much damage would be caused by the winds produced by cyclones," Huber said. "The thing to keep in mind is that the quantities that we are calculating are actually over the ocean and just on the margins of land masses, so we are not actually calculating the dollar amount of damage.�

His team also is attempting to estimate a quantity that has been related to damage by other researchers. "This is the first time that anyone has made this particular calculation," he added.

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