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From NPR News this is ALL THINGS CONSIDERED. I'm Audie Cornish. For several weeks now, two unmanned spy planes have been flying over the Atlantic on an unusual mission. They're gathering intelligence on tropical storms and hurricanes for NASA. Well, NPR's Jon Hamilton went on his own mission to find out what scientists are learning from those drones. He visited NASA's flight facility on Wallops Island, Virginia.

JON HAMILTON, BYLINE: On a runway at Wallops a graceful snow white aircraft is gathering speed for takeoff. It's destination? A tropical storm named Gabrielle. The Global Hawk has a Rolls Royce engine, the wingspan of a 737 and no pilot onboard. The pilots are sitting in front of computer screens in a nearby building. Chris Naftel is NASA's Global Hawk project manager.

CHRIS NAFTEL: Manned aircraft are limited by pilot endurance and that's typically eight to ten hours, at the most.

HAMILTON: Naftel says the drones can fly for more than 24 hours at a stretch.

NAFTEL: That gives us that ability to extend our time when we're looking at these science phenomena over a weather system.

HAMILTON: The Global Hawks also can fly miles higher than commercial aircraft and reach storms that would be much too far away for conventional planes. Naftel says that from the drone's usual home in California...

NAFTEL: We could take off, fly to New York and back, and do that again and back on one tank of fuel. So, incredible range. We can get to the coast of Africa and then come back to here at Wallops.

HAMILTON: Scientists took advantage of that range last year while studying an unusual hurricane named Nadine, which spent weeks meandering around the far reaches of the Northeast Atlantic. Scott Braun is the scientist in charge of NASA's five-year Hurricane and Severe Storm Sentinel Mission. He says Nadine was beyond the range of most U.S. aircraft but the Global Hawks were able to send back a huge amount of data as Nadine weakened to a tropical storm, then surprisingly began to regain hurricane strength.

SCOTT BRAUN: Nadine, at that point, was over fairly cold water and the winds were such that the storm should've been getting sheared apart and yet, it survived. So what was scientifically interesting about Nadine was its resilience despite very adverse surrounding conditions.

HAMILTON: Data from the Global Hawks turned up one possible explanation. Even though Nadine had traveled far north, it retained a mass of warm air at its core. That gave it the ability to re-strengthen quickly when conditions became more favorable. This year, scientists are using the drones to study something called the Saharan Air Layer, a mass of hot dry and dusty air that comes off the Sahara every few days.

Braun says the Saharan Air Layer interacts with waves of low pressure air that can turn into hurricanes as they head across the Atlantic.

BRAUN: Some have argued that the Saharan Air Layer is actually favorable for the growth of those waves and ultimately, for the development of tropical cyclones because it provides an energy source.

HAMILTON: Hot air, which is good for a hurricane; but the air is also dry, which is bad. So weather scientists think the Saharan Air Layer can actually kill a baby hurricane. The debate has been hard to settle because it involves weather thousands of miles from the U.S. Braun says having the Global Hawks should help with that problem.

BRAUN: It allows us to get the systems at that very early stage when the Saharan Air Layer is most interacting with storms. So we're getting to storms much earlier in their lifecycle than we would if we had to wait for them to get out to the Western Atlantic.

HAMILTON: Braun says the Global Hawks have spent much of the past couple of weeks flying over and around tropical storm Gabrielle as it churned up the east coast. He says detailed information about Gabrielle may eventually help scientists understand why some tropical storms quickly intensify into hurricanes while others don't. And the National Hurricane Center has already used data from the Global Hawks to help make forecasts about Gabrielle.

Gary Wick of the National Oceanic and Atmospheric Administration says that shows how drones could play an important role in weather forecasting.

GARY WICK: I really see the Global Hawk as bridging the gap between aircrafts and satellites. That you're now able to fly at altitudes, get coverage comparable to what you would with a satellite but really dwell over that system for an extended period of time, get some of those detailed measurements.

HAMILTON: At a cost. Global Hawks go for more than $100 million each, not counting research and development. Jon Hamilton, NPR News.

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