Scientists weather a space storm to find its origin (Forwarded)

ESA News
http://www.esa.int

2 August 2005

Scientists weather a space storm to find its origin

A team of researchers from the UK and France used SOHO, ACE and the four
Cluster spacecraft to study a huge eruption on the Sun, tracing its
progress from birth to when it reached Earth.

The team, led by scientists from University College London, identified
the source of a 'coronal mass ejection' (CME) and analysed how its
magnetic field changes on its path to Earth.

Triggered by a massive explosion on the Sun with millions of times more
energy than a nuclear bomb, these CMEs are blasts of gas that could
engulf Earth. CMEs are caused by the collision of loop-like magnetic
field lines with different polarities on the Sun's surface.

"There's been much speculation about the shape of the magnetic field and
how it might change on its journey from the Sun to Earth. Using
complementary satellites we have been able to see that the magnetic
field changes very little on its journey," said Dr Louise Harra, of UCL
Mullard Space Science Laboratory.

Earth's magnetic field, forming the magnetosphere, protects the planet
from the full brunt of these blasts, but when the CME's fields collide
directly with it they can excite geomagnetic storms. In extreme cases
they cause electrical power outages and damage to communications
networks and satellites.

"If we are to successfully predict storms we need to be able to identify
an Earth-directed coronal mass ejection as it leaves the Sun and work
out how it evolves," said Dr Harra.

The CME was detected on 20 January 2004 by the ESA/NASA SOHO spacecraft
which was used to identify the source of the ejection.

Two days later, on its journey to Earth, the ejected magnetic field
passed ESA's four Cluster spacecraft. Their tetrahedral formation
allowed the sampling of the speed and direction of the field. Similar
measurements were made by NASA's ACE spacecraft.

"SOHO and Cluster spacecraft are ideally suited to working together --
SOHO 'sees' the explosions from the Sun and Cluster 'feels' them. Our
next step is to predict the eruption of storms on the Sun," said Dr Harra.

This direct measurement by SOHO, ACE and Cluster confirms previous
Earth-bound predictions and takes researchers a step closer to
forecasting these geomagnetic storms.

For more information:

Dr Louise Harra, UCL Mullard Space Laboratory
E-mail: lkh @ mssl.ucl.ac.uk

Judith Moore, UCL Media Relations
E-mail: judith.moore @ ucl.ac.uk

More about...

* SOHO overview
http://www.esa.int/esaSC/120373_index_0_m.html
* Cluster overview
http://www.esa.int/esaSC/120383_index_0_m.html

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IMAGE CAPTION:
[http://www.esa.int/esaCP/SEM5TK808BE_index_1.html]
This composite images is a snapshot of the solar explosion which took
place at 00:54 UT on 20 January 2004. The inner image was taken with the
SOHO EUV Imaging Telescope (EIT) and shows the solar disk in green as
seen in the EUV waveband. The southerly white region shows the regions
that flared, releasing energy. The outer image in blue taken with the
SOHO LASCO telescope shows white areas which are regions of high-density
gas and magnetic field leaving the Sun at a speed of over 900 km per second.

Credits: ESA/NASA