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Scientists glean turbulent lessons from titan |
| TheAllINeed.com |
(NC&T/APL) "Exactly the same physical processes are occurring on Titan and Earth, although under interestingly different conditions," notes planetary scientist Ralph Lorenz, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "Scientists who look at the Earth and those who study other planets, working together, can gain new insights into both places."
Turbulence is an important process in our weather, and can be more than an inconvenience—hundreds of injuries have occurred on commercial flights due to turbulence.
Giles Harrison, an atmospheric physicist in the Department of Meteorology at the University of Reading in the UK, devised an inexpensive way of measuring turbulence effects using weather balloons. The instrument package—a radiosonde—measures the Earth's magnetic field to detect turbulent motion. In a paper subtitled "A compass for a radiosonde," magnetic changes measured on the weather balloon were shown to arise from motions within cloud, using Earth's stable magnetic field for reference.
Lorenz found Harrison's results key to making sense of data from the Huygens probe, which descended by parachute through Titan's atmosphere in January 2005. The Surface Science Package on board Huygens included tilt sensors that measured motions of the probe during its descent. These tilt sensors act much like a drink in a glass, using a small slug of liquid to measure tilt angle. But as the probe plummeted at high speed on Titan, there was a lot of buffeting, even though the air itself was fairly still.
By knowing the particular signature of cloud-induced turbulence in Harrison's Earth balloon data, where nearby weather radar could document what was causing the turbulence, Lorenz was able to find this signal at Titan despite the buffeting during the Huygens descent. "The Huygens tilt history was just this long squiggly complex mess, but seeing the fingerprint of cloud turbulence in Harrison's work showed me what to look for," he says.
 | | Artist impression of the Huygens probe on Saturn's moon Titan. (Photo: ESA) |
Armed with that information, Lorenz found that a 20-minute period during Huygens' 2.5-hour descent, around an altitude of 20 kilometers, was affected by this kind of in-cloud turbulence.
Having experimented with instrumentation on small models, even Frisbees, to understand the dynamics of aerospace vehicles like the probe, Lorenz was familiar with the sensors Harrison used. His analysis helped identify a turbulent cloud layer in Titan's atmosphere—a significant result for the investigation of Titan's meteorology. In the process, he also found a way to improve Harrison's magnetic sensor arrangement on the weather balloon, simply by changing its orientation.
"We went to Titan to learn about that mysterious body and its atmosphere," he notes. "It's neat that there are lessons from Titan that can be usefully applied here on Earth."
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