Organised Wind Chaos on Jupiter (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 11 Nov 2005 13:11:59 -0500 (EST)
Press and Public Relations Department
Max Planck Society for the Advancement of Science
Munich, Germany
Contact:
Dr Johannes Wicht
Max Planck Institute for Solar System Research, Katlenburg-Lindau
Tel.: +49 5556 979437
Fax: +49 5556 979240
November 9th, 2005
SP / 2005 (59)
Organised Wind Chaos on Jupiter
An international team of researchers, using new computer simulations,
explains the existence of banded wind structures on Jupiter
Jupiter's atmosphere is stirred by giant storms and high speed jets that
are mirrored in the planet's banded surface. Though the complex system of
alternating eastward and westward winds has been observed for more than a
hundred years, its true origin remained unclear. Scientists from the Max
Planck Institute for Solar System Research, the University of Alberta in
Edmonton, Canada, and the University of California, Los Angeles, have now
presented a new three-dimensional computer model that successfully
describes and explains all important characteristics of the banded flows
on Jupiter. The simulations suggest that the wind system may reach as deep
as 7000 km into the planet's atmosphere. Driving forces are smaller,
turbulent flows that are organised into the banded form by the planet's
curvature and rotation. The computer model also explains why there are two
jet classes: strong and wide jets near the equator, but narrow and weak
wind belts at higher latitudes. The reason is hidden deep in the planet,
where immense pressures cause the atmosphere to take on a metallic state.
(Nature, November 10, 2005)
Jupiter, the largest planet of our solar system, offers a fascinating
view. A number of bands of different coloured clouds seem to embrace the
planet like belts. These bands mirror a system of extremely strong and
stable jet winds, blowing both in easterly and westerly directions.
Comparisons between the measurements of the VOYAGER mission in 1979 and
the recent CASSINI spacecraft show that the system remained nearly
unchanged. The winds alternate direction in accordance with the clouds:
they blow eastward on the equator-facing side of the dark belts, and
westward on the pole-facing side. The strongest jet is centred on the
equator and blows with a speed of up to 170 metres per second in easterly
direction. The jets can be separated into two classes. Stronger, broader
winds are grouped around the equator while the jets at higher latitudes
are generally weaker and narrower.
The team of researchers from Germany, Canada, and the USA has presented
the first computer simulation that models all important characteristics of
Jupiter's wind system and explains its origin. Two groups of models for
the dynamics of Jupiter's atmosphere can be distinguished: shallow and
deep models. Supporters of the shallow approach apply techniques developed
in meteorology on Earth to Jupiter's atmosphere. Because the Earth's
atmosphere is very thin compared to the planet's radius, its spherical
form can be approximated with a simplified layer, which allows the
computer simulations to run considerably faster. The respective models
successfully produce several banded winds but fail otherwise: the
equatorial jet, the strongest on Jupiter, blows in the wrong direction,
and the distinction into the two classes is missing. All jets are similar.
In the 1970s Friedrich Busse, Professor Emeritus at the University of
Bayreuth, Germany, developed the first deep dynamical model. He pointed
out that there is an important difference between the atmospheres of
Jupiter and Earth: the Earth's atmosphere is bounded by the planets rocky
surface. Jupiter, on the other hand, is a gaseous planet. There simply is
no bottom that could restrict the winds to a thin layer.
Jupiter's atmosphere mainly consists of hydrogen and helium. The
atmospheric pressure increases with depth. At some point, the hydrogen
molecules are pressed so close together that they form a metallic,
electrically conductive state. Jupiter's strong magnetic field prevents
any faster movement in the electrically conductive deeper regions by a
mechanism that also works in an eddy current brake. This limits the fast
jet flows to the outer 10 percent of the planet's radius.
Based on ideas by Friedrich Busse, the new computer models the dynamics of
this outer layer, which still comprises 7000 km in depth. The computer
program has been developed by Johannes Wicht at the Max Planck Institute
for Solar System Research in Katlenburg-Lindau, Germany, and simulates the
convection-driven fluid flow in a rotating spherical shell. The results
offer a novel insight into how and why Jupiter's wind system has
developed.
On Earth, weather dynamics are driven by the heat coming from the sun. On
Jupiter, however, heat emerging from inside the planet plays a larger
role. This powerful energy source primarily drives small-scale turbulent
convective motion. But the dynamics of fluids in rotating systems -- like
planets -- exhibit some particular characteristics: these systems prefer
flows which do not change along the axis of rotation. Convective motions,
like tornadoes on earth, therefore try to organise themselves into
cylinder-shaped columns. The cylindrical geometry is in conflict with the
spherical shape of the planet.
The spherical curvature hardly affects smaller, turbulent vortex
structures. There is, however, a particular vortex size where its
influence becomes as important as the convective forcing. This
theoretically-derived size is known as the Rhines length, after Peter B
Rhines, a professor at the University of Washington, Seattle. When a
vortex diameter reaches the Rhines length, the planet's curvature starts
to organize the convective kinetic energy into the jet winds. The Rhines
length therefore determines not only the width but also the number of jets
that fill the planetary surface.
But why are there two different classes of jets? The computer models also
provide insight into this question, and confirm the theoretical principle
also proposed in the article in Nature. Jet winds around the equator reach
right through the planet spanning the northern as well as southern
hemisphere. This is not possible at higher latitudes where the winds are
in contact with the electrically conductive gas region. Here, the stronger
curvature of the inner boundary helps to organize the turbulent
convection. When incorporating this effect into a redefined Rhines length
theory, simulation, and observation all agree: these jets are narrower
than, and belong to a different class as, those around the equator.
Original work:
Moritz Heimpel, Jonathan Aurnou & Johannes Wicht
Simulation of equatorial and high-latitude jets on Jupiter in a deep
convection model
Nature, November 10, 2005
IMAGE CAPTIONS:
[Image 1:
http://www.mpg.de/bilderBerichteDokumente/multimedial/bilderWissenschaft/2005/11/Wicht0501/Web_Zoom.jpeg
(109KB)]
Jupiter¹s surface as imaged by the NASA probe CASSINI. The stripes are
colourful clouds of ammonia which reveal a system of strong easterly and
westerly winds.
Image: NASA
[Image 2:
http://www.mpg.de/bilderBerichteDokumente/multimedial/bilderWissenschaft/2005/11/Wicht0502/Web_Zoom.jpeg
(186KB)]
Comparison of wind speeds on Jupiter. The picture shows colour-coded wind
speeds in the computer simulation (red=easterly, blue=westerly), and
demonstrates that the winds pervade the entire outer gas layer. Deeper
inside, the magnetic field slows down the winds.
Image: Max Planck Institute for Solar System Research
.
- Prev by Date: Jupiter's Massive Winds Likely Generated From Deep Inside Its Interior, Scientists Report (Forwarded)
- Next by Date: Cassini Update - November 11, 2005
- Previous by thread: Jupiter's Massive Winds Likely Generated From Deep Inside Its Interior, Scientists Report (Forwarded)
- Next by thread: Cassini Update - November 11, 2005
- Index(es):
Relevant Pages
|
Loading
