NASAs Cassini finds that storms power Saturns jet streams

New observations by NASAs Cassini aircraft has revealed that giant storms or eddies power Saturns jet stream winds.

Washington, May 9 : New observations by NASA's Cassini aircraft has revealed that giant storms or eddies power Saturn's jet stream winds.

Researchers say this is exactly opposite to the earlier perception that the jet streams powered the giant storms.

"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.

Jet streams are motions in an atmosphere that carry clouds rapidly eastward or westward. Eddies are vortices or rotating storms. The storms get fed into the jet streams in much the same way rotating gears 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 Genio, a Cassini imaging team member and lead author of a paper describing the research.

"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," added Andrew Ingersoll, a Cassini imaging team member with the California Institute of Technology, Pasadena, California.

According to Ingersoll, while this process has been known to occur on Earth, it was only recently shown to operate on Jupiter, and is certainly a new idea for Saturn. Data from the earlier Voyager missions had failed to detect the eddy-jet interactions.

As part of the study, the Cassini team analyzed how storms and eddies interacted with Saturn's jet streams.

The team tracked the movements of these cloud features in successive images separated by about 10 hours (about one Saturn rotation), and confirmed that the eddies on either side of the jet gave up their energy and momentum to help 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," said Ingersoll.

Analysis of the images covering most of the planet's southern hemisphere further revealed that the similar process was 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, and is a well known feature on Earth in the two jet streams that circle the globe in the northern and southern hemisphere," Ingersoll added.

The researchers believe that traditional ideas about the banded clouds of Jupiter and Saturn now 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," he said.

The findings are due for publication in the journal Icarus.

ANI