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Severe Storms Getting Stronger, scientists find


Some of the most powerful storms on earth are getting stronger, according to new research published this week. VOA's Art Chimes reports.

Jim Elsner of Florida State University and his colleagues based their conclusion on 25 years of satellite data.

"If we look over the entire globe, we see that the strongest tropical cyclones are actually getting stronger. And this increase is most notable over the North Atlantic and also the northern Indian Oceans."

The researchers found that the top wind speeds in the strongest tropical cyclones have been increasing. And, the stronger the cyclone, the bigger the increase.

Scientists say these storms pick up energy from the warm water they pass over. Elsner says that's really a simplified version of what's happening.

"And this thermodynamic theory of hurricane intensification says that, with all else being equal, the warmer the ocean, the stronger the storms," he said in an interview. "So it stands to reason that if the theory is correct we should see increases in the intensity of the strongest storms with the warming ocean."

And that's exactly what they saw. For their study, Elsner and his colleagues examined the top wind speed in a range of storms, from weak to strong.

The weaker storms showed little or no increase in their maximum wind speed over 25 years of observations. But in the same period, the top wind speed in the strongest storms rose significantly.

"Generally the wind speed and how much power, destructive power, a hurricane has are very well correlated," Elsner said.

Although the storm data comes from satellites, Elsner says satellite instruments don't measure the wind speed directly.

"But what you can do is look at how the pattern of the satellite pictures [is] changing over time. If you see how the clouds change from one picture to the next, you can get some idea of motion. So if you look at where the clouds were at one time, then later, you get some idea of speed."

The effect the researchers observed was not evenly distributed around the world, probably because of different conditions in the various areas where tropical cyclones occur.

"Well, we speculate that has to do with the amount of warming we're seeing in the different basins," Elsner explained. "So basins that are marginally warm enough to support tropical cyclones on average and [where temperatures] are increasing, then we expect to see the effect stronger in those basins, and those include the North Atlantic and Indian Oceans."

So is this effect related to climate change? Elsner says his study looked at data from the past quarter-century, so he says it can't necessarily predict what's in the future. But warmer oceans could provide the energy to fuel stronger storms, and he says the data is consistent with the idea that global warming could affect sea temperatures.

"That gives us some confidence that if the seas continue to warm, we're likely to see the stronger storms getting stronger."

Jim Elsner of Florida State University. His paper appears this week in the journal Nature.

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