— The tiny aircraft weigh just 15 kilograms (33 pounds) or so and can be launched from atop a truck (Image: Aerosonde/NOAA)
Each aerosonde costs about $50,000 and can be reused, unless it drops into the sea (Image: Aerosonde/NOAA)
A small uncrewed aircraft is set to fly through the fierce winds surrounding the eye of a hurricane to take the first continuous data on how such storms gain their strength, according to a plan by NASA and the US National Oceanic and Atmospheric Association.
The craft, called an aerosonde, will measure the temperature, pressure, humidity and wind velocity inside the storm in an effort to crack the tough problem of predicting changes in hurricane intensity.
It will make the measurements when the hurricane is over the sea, where it builds in intensity. A hurricane is a giant heat engine, powered by the evaporation of warm seawater that then condenses inside the storm, releasing energy.
Unfortunately, understanding that process requires flying instruments a few hundred metres above the ocean, where wind speeds are highest. "It's far too dangerous to get there with manned aircraft," says Joe Cione of NOAA's National Hurricane Center in Miami, Florida, US.
NOAA and NASA now monitor hurricanes from satellites, and crewed hurricane-hunter planes fly through the upper layers of the storm. To measure near-surface conditions, though, the agencies drop 20 to 30 instrument packages called dropsondes into the storms.
Eye of the storm
Each $700 dropsonde takes measurements as it falls through the storm into the sea. But the method yields data on only scattered spots in a storm not enough information to forecast rapid changes in its intensity. In 2004, "Hurricane Charley went from Category 1 to Category 4 in six to eight hours," Cione told New Scientist. "We don't understand that at all."
Now, the agencies hope to shed light on this question by taking much longer observations with aerosondes developed by the Aerosonde Corporation of Wallops Island, Virginia, US. The $50,000 aircraft are launched from a rack on top of a small truck and can carry instrument packages that weigh just a couple of kilograms.
But they can fly for 18 hours at a time at altitudes of 150 to 600 metres. Plans call for them to transmit data in real time as they spiral inwards to the eye of the storm, then retrace their path back out again. By flying two aerosondes in succession, Cione hopes to monitor the transfer of energy from the ocean to the storm for 36 hours.
The key test will be flying the aerosonde into a hurricane, but no hurricanes have yet come within 500 kilometres of Florida's Key West Naval Air Station, where one of the aircraft is stored.
Key West is normally an ideal point for observing mature storms, and the test was scheduled for September, traditionally the busiest month of the hurricane season. "Mother Nature is laughing at us," says Cione. With additional funding, team members could keep trying to launch the aerosonde in October.
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