From 'macro' to 'micro' -- turbulence seen by Cluster (Forwarded)

ESA News
http://www.esa.int

10 August 2005

From 'macro' to 'micro' -- turbulence seen by Cluster

Thanks to measurements by ESA's Cluster mission, a team of European
scientists have identified 'micro'-vortices in Earth's magnetosphere.

Such small-scale vortex turbulence, whose existence was predicted
through mathematical models, has not been observed before in space. The
results are not only relevant for space physics, but also for other
applications like research on nuclear fusion.

On 9 March 2002, the four Cluster satellites, flying in tetrahedral
formation at 100 kilometres distance from each other, were crossing the
northern 'magnetic cusp' when they made their discovery. Magnetic cusps
are the regions over the magnetic poles where the magnetic field lines
surrounding Earth form a magnetic funnel.

The magnetic cusps are the two important regions in Earth's
magnetosphere where the 'solar wind' -- a constant flow of charged
particles generated by the Sun that crosses the whole Solar System --
can directly access the upper layer of Earth's atmosphere (the ionosphere).

Large amounts of plasma (a gas of charged particles) and energy are
transported through these and other 'accessible' regions, to penetrate
the magnetosphere -- Earth's natural protective shield. Only less than
one percent of all the energy carried by the solar wind and hitting the
Earth's magnetosphere actually manages to sneak through, but it still
can have a significant impact on earthly systems, like telecommunication
networks and power lines.

The solar material sneaking in generates turbulence in the plasma
surrounding Earth, similar to that in fluids but with more complex
forces involved. Such turbulence is generated for instance in the areas
of transition between layers of plasma of different density and
temperature, but its formation mechanisms are not completely clear yet.

The turbulence exists at different scales, from few thousand to few
kilometres across. With in situ 'multi-point' measurements, the four
Cluster satellites reported in the year 2004 the existence of large
scale turbulence -- vortices up to 40 000 kilometres wide, at the flank
of the 'magnetopause' (a boundary layer separating the magnetosphere
from free space). The new discovery of 'micro' turbulence, with vortices
of only 100 kilometres across, is a first in the study of the plasma
surrounding Earth.

Cluster: an unprecedented diagnostic tool

Such a discovery is very relevant. For example, it allows scientists to
start linking small and large-scale turbulence, and start questioning
how it is actually formed and what are the connections. For instance,
what are the basic mechanisms driving and shaping the turbulence? How
much do vortices contribute to the transport of mass and energy through
boundary layers? Are small vortices needed to generate large ones? Or,
on the other hand, do large vortices dissipate their energy and create a
cascade of smaller ones?

In trying to answer these questions, Cluster is an unprecedented
diagnostic tool for the first three-dimensional map of the near-Earth
environment, its exceptionality being given by its multi-spacecraft
simultaneous observations. Cluster is revolutionising our understanding
of the ways and the mechanisms by which solar activity affects Earth.

Besides, Cluster's study of the turbulence in Earth's plasma, with the
dynamics and the energies involved, is contributing to the advancement
of fundamental theories on plasma. This is not only important in
astrophysics, but also as far as the understanding and the handling of
plasma in laboratories is concerned, given the high energies involved.
This is particularly relevant for research on nuclear fusion.

For example, Cluster's data are complementing research on plasma physics
in the international ITER project, an experimental step involving
several research institutes around the world for tomorrow's
electricity-producing power plants. In this respect, by probing into the
magnetosphere, Cluster has free access to the only open 'natural
laboratory' for the study of plasma physics.

Notes to editors:

These findings are published in the 11 August issue of the scientific
journal Nature. The authors of the results a D. Sundkvist (CNRS,
Orleans, France/Swedish Institute of Space Physics, Uppsala, Sweden); V.
Krasnoselskikh (CNRS, Orleans, France); P.K. Shukla (Institut fur
Theoretische Physik IV, Bochum, Germany); A. Vaivads, M. Andre, S.
Buchert (Swedish Institute of Space Phyisics, Uppsala, Sweden); H. Reme
(CESR, Toulouse, France).

The discovery of the mentioned giant vortices was published in the 12
August 2004 issue of Nature, in a paper by H. Hasegawa, et al.

For more information:

David Sundkvist, Results lead author
Swedish Institute of Space Physics (IRF), Uppsala, Sweden
E-mail: david.sundkvist @ irfu.se

Philippe Escoubet, ESA Cluster Project Scientist
E-mail: philippe.escoubet @ esa.int

More about...

* Cluster factsheet
http://www.esa.int/esaSC/SEMYN5T1VED_index_0.html

Related articles

* Space weather
http://www.esa.int/esaSC/SEMLC2T1VED_index_0.html
* Cluster's new view of near-Earth space
http://www.esa.int/esaCP/ESA6VTTM5JC_index_0.html
* How the Sun affects us on Earth
http://www.esa.int/esaSC/SEML7BS1VED_foryou_0.html
* What are solar flares?
http://www.esa.int/esaSC/SEMHKP7O0MD_index_0.html
* Click here for a video of a 'Solar tantrum'
http://esamultimedia.esa.int/video/s...r_tantrums.mpg

Related links

* ESA's Space Weather pages
http://www.esa.int/spaceweather

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaCP/SEM18O808BE_index_1.html]
Artist's impression of the micro vortices observed in the Northern
magnetic cusp by Cluster. It is the first time ever that such phenomenon
is observed in space.

Credits: ESA

[Image 2:
http://www.esa.int/esaCP/SEM18O808BE...html#subhead1]
Magnetic turbulence are mainly created where the solar wind -- a
constant flow of charged pareticles generated by the Sun -- can directly
access the magnetosphere, the natural magnetic shield that surrounds and
protects our planet. Cluster is studying these phenomena in 3D.

Credits: ESA