Cassini Finds Saturn's Wind Change with Altitude and Small Storms Emerging Out Of Large Ones

http://ciclops.lpl.arizona.edu/view.php?id=894

CASSINI FIND SATURN'S WINDS CHANGE WITH ALTITUDE AND SMALL STORMS
EMERGING OUT OF LARGE ONES

MEDIA RELATIONS OFFICE
CASSINI IMAGING CENTRAL LABORATORY FOR OPERATIONS (CICLOPS)
SPACE SCIENCE INSTITUTE, BOULDER, COLORADO
http://ciclops.org


Preston Dyches (720) 974-5823
CICLOPS/Space Science Institute, Boulder, Colo.

For Immediate Release: February 24, 2005

CASSINI FIND SATURN'S WINDS CHANGE WITH ALTITUDE AND SMALL STORMS
EMERGING OUT OF LARGE ONES

The changing faces of Saturn's windy equatorial region and its
turbulent
southern mid-latitudes are revealed in the first Cassini Imaging Team
report on Saturn's atmosphere, to appear in the Feb. 25 issue of the
journal Science.

During NASA Voyager flybys of 1980-1981, winds in Saturn's equatorial
region were clocked at 470 meters per second (1,060 miles per hour),
ten
times the speed of Earth's jet stream, making Saturn's equator the
windiest place in the solar system.

During the 1990s, though, observations from NASA's Hubble Space
Telescope suggested that the equatorial jet had slowed down to about
275
meters per second (about 615 miles per hour). The Cassini imaging
experiment's suite of filters sense different altitudes in the
atmosphere and have made it possible to interpret this apparent slowing
of the wind.

By tracking the motions of cloud features seen through a spectral
filter
that senses deep in Saturn's atmosphere, imaging scientists have
measured equatorial wind speeds of about 325 to 400 meters per second
(725 to 895 miles per hour), between the Voyager and Hubble values. On
the other hand, measurements taken in a spectral region where methane
strongly absorbs, and therefore senses higher altitudes in the
atmosphere, suggest wind speeds consistent with the Hubble values.
These
observations imply that wind speeds decrease with height in Saturn's
equatorial region, and that the apparent slowing of the wind from the
Voyager epoch to the Hubble epoch may instead have been a result of
storms that raised cloud tops to higher levels where winds are slower.

Outside the equatorial region, winds have been remarkably stable from
the Voyager to Hubble to Cassini eras. A major question for Cassini
atmospheric scientists has been: What maintains the remarkably
energetic
winds on Saturn?

Cassini images have captured for the first time possible evidence of
processes that may act to maintain the jets. Early in the mission, the
region near 35 degrees South latitude as observed to be especially
active, with at least one long-lived thunderstorm erupting from time to
time, and a variety of more compact ovals appearing and merging. One
sequence captured dark spots arising from the upper level outflow of a
convective storm. These spots are of the same type that are seen to
merge with the jets and give up their energy to them. These
observations
are a possible first glimpse into the process by which energy is
transferred by convection from Saturn's interior to help sustain its
strong cloud-level winds.

An image associated with this release, and information about the
Cassini-Huygens mission, are available at http://ciclops.org,
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory, a division of the California Institute of Technology in
Pasadena, manages the Cassini-Huygens mission for NASA's Science
Mission
Directorate, Washington, D.C. 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, Boulder, Colo.