http://www.esa.int/SPECIALS/Venus_Ex...N77DWZE_0.html

Tracking alien turbulences with Venus Express
European Space Agency
3 April 2007

New images and data from ESA's mission to Venus provide new insights
into the turbulent and noxious atmosphere of Earth's sister planet.
What
causes violent winds and turbulences? Is the surface topography
playing
a role in the complex global dynamics of the atmosphere? Venus Express
is on the case.

Venus' atmosphere represents a true puzzle for scientists. Winds are
so
powerful and fast that they circumnavigate the planet in only four
Earth
days - the atmospheric "super-rotation" - while the planet itself is
very slow in comparison, taking 243 Earth days to perform one full
rotation around its axis.

At the poles things get really complicated with huge double-eyed
vortices providing a truly dramatic view. In addition, a layer of
dense
clouds covers the whole planet as a thick curtain, preventing
observers
using conventional optical means from seeing what lies beneath.

Venus Express is on the contrary capable of looking through the
atmosphere at different depths, by probing it at different infrared
wavelengths. The Ultraviolet, Visible and Near-Infrared Mapping
Spectrometer (VIRTIS) on board is continuing its systematic
investigation of Venus' atmospheric layers to solve the riddle of the
causes for such turbulent and stormy atmosphere.

The images presented with this article focus on Venusian atmospheric
turbulences and cloud features, whose shape and size vary with
planetary
latitudes. At the equator, clouds are irregular and assume a peculiar
"bubble"-shape. At mid latitudes they are more regular and streaky,
running almost parallel to the direction of the super rotation with
speed reaching more than 400 kilometres per hour. Going higher up in
latitude, in the polar region, the clouds end up in entering a vortex
shape.

With its multi-wavelength eyes, VIRTIS can observe the atmosphere and
the cloud layers not only at different depths, but also both in the
day-
and night-side of the planet - a characteristic that allows an overall
assessment of the "environmental" causes that can be at the origin of
such an atmospheric complexity.

At the equator, the extremely violent winds of the super-rotation are
in
constant "battle" with other kinds of local turbulences, or "regional"
winds, creating very complex cloud structures.

One type of regional wind is due to the strong flux of radiation from
the Sun reaching the atmosphere of the planet on the day-side. This
flux
heats up the atmosphere creating convective cells, where masses of
warm
air move upwards and generate local turbulence and winds.

On the night-side there is obviously no flux from the Sun, but the
clouds' shape and the wind dynamics are somehow similar to that we see
on the day-side. So, scientists are currently trying to understand if
there is any mechanism other than "convection" responsible for the
equatorial turbulences, both on the day- and night-side of Venus.

For instance, VIRTIS imaged clouds over Alpha Regio, an area close to
the equator. This area is characterised by a series of troughs,
ridges,
and faults that are oriented in many directions, with surface features
that can be up to 4 kilometres high. There might be a connection
between
the surface topography and the local atmospheric turbulence which is
observed in this area. This and other hypotheses are being
investigated
by the Venus Express science teams using data from several
instruments.

Actually, the Venusian topography may play an important role also in
the
global atmospheric dynamics. Understanding this surface-atmosphere
connection is one of the major objectives of Venus Express - something
to be verified in the whole course of the mission.



For more information

Giuseppe Piccioni, VIRTIS co-Principal Investigator, IASF-INAF, Rome,
Italy
Email: giuseppe.piccioni @ iasf-roma.inaf.it

Pierre Drossart, VIRTIS co-Principal Investigator, Observatoire de
Paris, France
Email: pierre.drossart @ obspm.fr

Hakan Svedhem, ESA Venus Express Project Scientist
Email: hakan.svedhem @ esa.int