Cassini Finds that Storms Power Saturn's Jet Streams
New Cassini research suggests eddies, or giant rotating storms, are the "engine" powering Saturn's jet stream winds.
"The new information about how Saturn's jet streams are powered is exactly the opposite
of what we thought prior to Cassini," said Anthony Del Genio of NASA's Goddard Institute
for Space Studies, New York, N.Y. Del Genio is a Cassini imaging team member and lead
author of a paper describing this research in press in the journal Icarus.
The image shows small-scale, sheared-out cloud features associated with turbulent eddies in the vicinity of one of Saturn's eastward flowing jet streams, or "jets."
Image credit: NASA/JPL/Space Science Institute
+ Full image and caption
Jet streams are motions in an atmosphere that carry clouds rapidly eastward or westward.
The eddies get fed into the jet streams, in much the same way that rotating gears can
power a conveyor belt.
"While we thought the conveyor belt--in this case, the jet streams--powered the rotating
eddies, we now think the opposite: the rotating eddies power the jet streams," said Del
"Intuition would say that the eddies take energy out of the jets, because of the friction and
tugging of the storms. Instead, what we find is that they are pumping energy into the jets,"
said Andrew Ingersoll, a Cassini imaging team member with the California Institute of
Technology, Pasadena, Calif. Ingersoll says that while this process has been known to
occur on Earth, it was only recently shown to operate on Jupiter and is a new idea for
Saturn, where data from the earlier Voyager missions had failed to detect the eddy-jet
The Cassini team analyzed, for the first time, how storms and eddies interact with Saturn's
jet streams. By tracking the movements of these cloud features in successive images
separated by about 10 hours (about one Saturn rotation), Cassini scientists have confirmed
that the eddies on either side of the jet give up their energy and momentum, which helps
keep the winds in the jet blowing.
"We knew the eddies were powering the jets because they were pointing in the same
direction and carrying momentum in that direction. If the eddies had been tapering the other
way, we would have concluded the opposite," added Ingersoll.
The analysis of Cassini images covering most of Saturn's southern hemisphere suggests
that similar processes are occurring all over the planet. This explains why Saturn's
alternating pattern of eastward and westward jets has remained constant over most of the
planet during the many decades that scientists have been able to observe it. The same
process was also recently found to occur on Jupiter, in data obtained when Cassini flew by
that planet on its way to Saturn. The process is a well known feature on Earth in the two jet
streams that circle the globe in the northern and southern hemisphere.
The findings suggest that traditional ideas about the banded clouds of Jupiter and Saturn
need to be revised.
"We used to assume that the bright cloud bands are regions where air rises and the dark
bands are where air sinks. But if the eddies power the jets in the way we observe, the
opposite must be true," said Del Genio. "And indeed, we find thunderstorms only in the
dark bands on both planets, which has to mean that the air is rising there."
An image from the study, showing cloud features near one of Saturn's jet streams, is
available at http://www.nasa.gov/cassini
The paper is available at http://www.sciencedirect.com
The Cassini-Huygens mission is a cooperative project of NASA, the European Space
Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of
Caltech, manages the Cassini-Huygens mission for NASA's Science Mission Directorate,
Washington. The Cassini orbiter and its two onboard cameras were designed, developed
and assembled at JPL. The imaging team is based at the Space Science Institute.
Media contact: Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
Preston Dyches 720-974-5859
Cassini Imaging Central Laboratory for Operations
Space Science Institute, Boulder, Colo.