Cluster monitors convection cells over the polar caps (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 9 Nov 2007 21:06:13 -0500
ESA News
http://www.esa.int
22 October 2007
Cluster monitors convection cells over the polar caps
Scientists have fully mapped convection cells in Earth's magnetic field for
the first time using Cluster data. Results show that the behaviour of the
cells is heavily linked to solar activity.
Convection cells, made of plasma, an ionised and highly variable gas, are
found at altitudes of hundreds kilometres over the polar caps. Their
behaviour pattern is intimately linked to the response of the Earth's
magnetic environment to solar activity.
Although Earth is largely protected from the hazards of interplanetary space
by the magnetosphere and atmosphere, they don't form an isolated bubble.
The solar wind, a stream of particles continuously blowing from the Sun,
compresses Earth's magnetosphere on the dayside and stretches it into a long
tail on the nightside. Most solar wind is deflected by the magnetosphere but
some material manages to enter. Understanding how this works is of crucial
importance to space-borne infrastructure (GPS, telecommunication satellites)
and for the safety of astronauts.
One way to monitor this interaction is to study the convection cells. In the
region, called the high-latitude ionosphere where they are located, the
behaviour of the plasma cells strongly depends on the response of the
magnetosphere to the orientation of the interplanetary magnetic field (IMF,
an extension of the solar magnetic field, carried by the solar wind). This
means that the behaviour of polar cap convection cells is a good tracer of
the Sun-Earth connection.
So far, convection maps have been produced using ground-based experiments or
by using in-situ measurements of low altitude satellites crossing the polar
caps. Mapping the region with radar is not possible in cases where the
geomagnetic field is disturbed, and it is also not possible to cover large
areas simultaneously.
For the first time, statistical maps of the convection cells under various
solar conditions were derived with six years of data from ESA's Cluster
mission. The results that used data from the Electron Drift Instrument (EDI)
on board Cluster show the presence of two radically different patterns of
convection cells -- the number of cells (two to four) changes depending on
the orientation of the IMF .
The orientation of the IMF and the solar wind conditions were also recorded
simultaneously by NASA's Advanced Composition Explorer (ACE) spacecraft
located in the solar wind, in between the Sun and Earth, at roughly 1.5
million km from Earth.
"The SuperDARN radar results and Cluster satellite-based results show an
excellent agreement. This confirms the hypothesis that magnetic field lines
are equipotentials," said Dr Stein Haaland, scientist at the
Max-Planck-Institut fur extraterrestrische Physik, Germany. It also means
that it will be possible to map the region at any altitude, under any
conditions with satellites, making our task easier.
"The results are a great achievement for the Cluster mission -- they show
data collected over years is helping deepen our understanding of the
Sun-Earth connection," commented Philippe Escoubet, ESA's Project Scientist
for Cluster and Double Star.
Notes for editors:
Dr. Haaland is the lead author of this statistical study published on 1
February 2007 in the journal Annales Geophysicae. A complementary paper led
by Dr. Forster from the GeoForschungsZentrum Potsdam, Germany was published
on 30 July 2007 in the same journal.
The article 'High-latitude plasma convection from Cluster EDI measurements:
method and IMF-dependence' by S. E. Haaland, G. Paschmann, M. Forster, J.M.
Quinn, R.B. Torbert, C.E. McIlwain, H. Vaith, P.A. Puhl-Quinn, and C.A.
Kletzing was published on 1 February 2007 in the Annales Geophysicae.
The article 'High-latitude plasma convection from Cluster EDI: variances and
solar wind correlations' is by M. Forster, G. Paschmann, S. E. Haaland, J.
M. Quinn, R. B. Torbert, H. Vaith, and C. A. Kletzing. It was published on
30 July 2007 in the Annales Geophysicae.
For more information:
Stein Haaland, Max-Planck-Institut fur extraterrestrische Physik
Email: Stein.Haaland @ mpe.mpg.de
Philippe Escoubet, ESA Cluster and Double Star Project Scientist
Email: Philippe.Escoubet @ esa.int
Matt Taylor, ESA Cluster and Double Star deputy Project Scientist
Email: Matthew.Taylor @ esa.int
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaSC/SEM48GJJX7F_index_1.html ]
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