Earth and Saturns moon Titan share the same turbulence

Turbulence in earths atmosphere often affects aeroplanes during a flight and this same phenomenon has now caused the NASA/ESA/ASI Cassini Huygens spacecraft to hitch a bumpy ride to Saturns moon, Titan, scientists have said.

London, Aug 29 : Turbulence in earth's atmosphere often affects aeroplanes during a flight and this same phenomenon has now caused the NASA/ESA/ASI Cassini Huygens spacecraft to hitch a bumpy ride to Saturn's moon, Titan, scientists have said.

As part of his research, Giles Harrison, an atmospheric physicist at the Department of Meteorology at the University of Reading in the UK, devised an inexpensive way of measuring turbulence effects in Earth's atmosphere, using weather balloons.

He extended the standard weather balloon instrument package to include a magnetic field sensor sensitive to Earth's magnetic field.

With colleague Robin Hogan, he compared magnetic observations made during a balloon ascent with cloud measurements of turbulence obtained using the nearby Doppler Cloud Radar at Chilbolton, Hampshire.

He found that turbulent regions observed using the Chilbolton radar coincided with where their balloon's measurements showed large magnetic changes.

"As the Earth's magnetic field is very stable, the measurements were showing that the balloon itself was moving violently, in response to air turbulence," said Harrison.

Planetary scientist Ralph Lorenz, at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, used Harrison's results to make sense of data generated by the ESA Huygens probe, which descended by parachute through Titan's atmosphere in January 2005.

An experiment led by The Open University in the UK, the Surface Science Package (SSP), included a set of tilt sensors, which measured the motions of the probe during its descent.

Scientists found that 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 the nearby weather radar could document what was causing the turbulence; Lorenz and his team were able to find this signal at Titan, despite the buffeting during the Huygens descent.

Armed with that information, Lorenz found that a 20-minute period of Huygens' 2.5-hour descent, around an altitude of 20km, was affected by this kind of in-cloud turbulence.

"We knew Huygens had a bumpy ride down to Titan's surface. Now, we can separate out twenty minutes of air turbulence probably due to a cloud layer- from other effects such as cross winds or air buffeting due to the irregular shape of the probe," said Mark Leese, Project Manager for the SSP on Huygens at The Open University.

Lorenz's analysis was recently published in the journal Planetary and Space Science. A discussion that took place between Lorenz and Harrison appears in the August 2007 issue of Journal of Atmospheric and Oceanic Technology.

ANI