March 14, 2012

Cassini Captures Jupiter Jet Stream Waves

New images from Cassini are giving scientists and amateur astronomers new insight into the jet streams of Jupiter. The team pieced together images taken from Cassini in 2000 to create a video, animating the wave that is disturbing Jupiter´s jet waves. These findings are part of an in-depth study that was published in the April 2012 issue of Icarus. Amy Simon-Miller is leading the research.

“This is the first time anyone has actually seen direct wave motion in one of Jupiter´s jet streams,” Simon-Miller told NASA.com. “And by comparing this type of interaction in Earth´s atmosphere to what happens on a planet as radically different as Jupiter, we can learn a lot about both planets.”

These jet streams are one of only a few ways the Earth and Jupiter are alike.  The strongest and most well-known jet streams on Earth circle the northern and southern poles. The winds blow from west to east, but sometimes sway a bit to the north and the south.

Rossby waves, strong and slow moving waves in the Earth´s atmosphere cause these jet streams to wander north and south. On occasion, these rossby waves are so strong that they can blow the jet streams far off course.

What makes the Jupiter jet streams different is how straight and narrow they travel. While these rossby waves were discovered on Jupiter around 20 years ago, the resulting wandering winds could not be traced. Even more confusing for astronomers was the fact that no evidence could be found of these rossby waves on the southern hemisphere of Jupiter.

NASA employed the Voyager spacecraft, the Hubble telescope, Cassini, and thousands of observations made by amateur astronomers to gain a better understanding of how these rossby waves affected Jupiter´s jet streams.

The images captured by Cassini gave the team the proof they were looking for. As the video put together using the images progresses, the well-ordered line of Jet Streams starts to ripple, a sure sign of rossby waves in effect.

“A planet´s atmosphere is a lot like the string of an instrument,” says co-author Michael D. Allison of the NASA Goddard Institute for Space Studies in New York. “If you pluck the string, it can resonate at different frequencies, which we hear as different notes. In the same way, an atmosphere can resonate with different modes, which is why we find different kinds of waves.”

By closely studying and characterizing these waves, the team move one step closer to understanding the deep and complex atmosphere of Jupiter.

In addition to the images and subsequent video of the waves, the raw information taken by Cassini is proving to be a treasure trove for team. Combining measurements from Cassini and measurements by the amateur astronomers on the ground, the team was able to calculate weed speeds and wind speed variations.

Using the information collected during this project, the team at NASA hopes to gain a better understanding about how atmospheres work.

“Understanding the emerging analogies between Earth and Jupiter, as well as the obviously profound differences, helps us learn fundamentally what an atmosphere is and how it can behave,” co-author Gianluigi Adamoli said.


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