MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 PHONE 818-354-5011
http://www.jpl.nasa.gov
Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov
Elizabeth Zubritsky 301-614-5438
Goddard Space Flight Center, Greenbelt, Md.
elizabeth.a.zubritsky@nasa.gov
News release: 2012-070 March 13, 2012
Cassini Spies Wave Rattling Jet Stream on Jupiter
The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-070&cid=release_2012-070
PASADENA, Calif. -- New movies of Jupiter are the first to catch an invisible wave shaking up
one of the giant planet's jet streams, an interaction that also takes place in Earth's atmosphere and
influences the weather. The movies, made from images taken by NASA's Cassini spacecraft
when it flew by Jupiter in 2000, are part of an in-depth study conducted by a team of scientists
and amateur astronomers led by Amy Simon-Miller at NASA's Goddard Space Flight Center in
Greenbelt, Md., and published in the April 2012 issue of Icarus.
"This is the first time anyone has actually seen direct wave motion in one of Jupiter's jet
streams," says Simon-Miller, the paper's lead author. "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."
Like Earth, Jupiter has several fast-moving jet streams that circle the globe. Earth's strongest and
best known jet streams are those near the north and south poles; as these winds blow west to east,
they take the scenic route, wandering north and south. What sets these jet streams on their
meandering paths—and sometimes makes them blast Florida and other warm places with frigid
air—are their encounters with slow-moving waves in Earth's atmosphere, called Rossby waves.
In contrast, Jupiter's jet streams "have always appeared to be straight and narrow," says co-author
John Rogers, who is the Jupiter Section Director of the British Astronomical Association,
London, U.K., and one of the amateur astronomers involved in this study.
Rossby waves were identified on Jupiter about 20 years ago, in the northern hemisphere. Even
so, the expected meandering winds could not be traced directly, and no evidence of them had
been found in the southern hemisphere, which puzzled planetary scientists.
To get a more complete view, the team analyzed images taken by NASA's Voyager spacecraft,
NASA's Hubble Space Telescope, and Cassini, as well as a decade's worth of observations made
by amateur astronomers and compiled by the JUPOS project.
The movies zoom in on a single jet stream in Jupiter's southern hemisphere. A line of small,
dark, v-shaped "chevrons" has formed along one edge of the jet stream and zips along west to
east with the wind. Later, the well-ordered line starts to ripple, with each chevron moving up and
down (north and south) in turn. And for the first time, it's clear that Jupiter's jet streams, like
Earth's, wander off course.
"That's the signature of the Rossby wave," says David Choi, the postdoctoral fellow at NASA
Goddard who strung together about a hundred Cassini images to make each time-lapse movie.
"The chevrons in the fast-moving jet stream interact with the slower-moving Rossby wave, and
that's when we see the chevrons oscillate."
The team's analysis also reveals that the chevrons are tied to a different type of wave in Jupiter's
atmosphere, called a gravity inertia wave. Earth also has gravity inertia waves, and under proper
conditions, these can be seen in repeating cloud patterns.
"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."
Characterizing these waves should offer important clues to the layering of the deep atmosphere
of Jupiter, which has so far been inaccessible to remote sensing, Allison adds.
Crucial to the study was the complementary information that the team was able to retrieve from
the detailed spacecraft images and the more complete visual record provided by amateur
astronomers. For example, the high resolution of the spacecraft images made it possible to
establish the top speed of the jet stream's wind, and then the amateur astronomers involved in the
study looked through the ground-based images to find variations in the wind speed.
The team also relied on images that amateur astronomers had been gathering of a large, transient
storm called the South Equatorial Disturbance. This visual record dates back to 1999, when
members of the community spotted the most recent recurrence of the storm just south of Jupiter's
equator. Analysis of these images revealed the dynamics of this storm and its impact on the
chevrons. The team now thinks this storm, together with the Great Red Spot, accounts for many
of the differences noted between the jet streams and Rossby waves on the two sides of Jupiter's
equator.
"We are just starting to investigate the long-term behavior of this alien atmosphere," says co-
author Gianluigi Adamoli, an amateur astronomer in Italy. "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."
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency,
and the Italian Space Agency. NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the
mission for NASA's Science Mission Directorate, Washington, D.C. JPL is a division of the
California Institute of Technology, Pasadena.
For information about Cassini, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .
-end-
To remove yourself from this mailing, please go to http://www.kintera.org/TR.asp?a=6pKHKUOsF6JIIVOHG&s=dnIOKMPlH9IALLOrGnH&m=mlL5KiMWKjLVJjI
To remove yourself from all mailings from NASA Jet Propulsion Laboratory, please go to http://www.kintera.org/TR.asp?a=9sINL3MEL9IOK5NUE&s=dnIOKMPlH9IALLOrGnH&m=mlL5KiMWKjLVJjI
No comments:
Post a Comment