A team of researchers from the UK and France used SOHO, ACEand the four Cluster spacecraft to study a huge eruption on the Sun,tracing its progress from birth to when it reached Earth.
Theteam, led by scientists from University College London, identified thesource of a ‘coronal mass ejection’ (CME) and analysed how its magneticfield changes on its path to Earth.
Triggered by a massiveexplosion on the Sun with millions of times more energy than a nuclearbomb, these CMEs are blasts of gas that could engulf Earth. CMEs arecaused by the collision of loop-like magnetic field lines withdifferent polarities on the Sun’s surface.
“There’s been muchspeculation about the shape of the magnetic field and how it mightchange on its journey from the Sun to Earth. Using complementarysatellites we have been able to see that the magnetic field changesvery little on its journey,” said Dr Louise Harra, of UCL Mullard SpaceScience Laboratory.
Earth’s magnetic field, forming themagnetosphere, protects the planet from the full brunt of these blasts,but when the CME’s fields collide directly with it they can excitegeomagnetic storms. In extreme cases they cause electrical poweroutages and damage to communications networks and satellites.
“Ifwe are to successfully predict storms we need to be able to identify anEarth-directed coronal mass ejection as it leaves the Sun and work outhow 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.
Twodays later, on its journey to Earth, the ejected magnetic field passedESA’s four Cluster spacecraft. Their tetrahedral formation allowed thesampling of the speed and direction of the field. Similar measurementswere made by NASA’s ACE spacecraft.
“SOHO and Cluster spacecraftare ideally suited to working together - SOHO 'sees' the explosionsfrom the Sun and Cluster 'feels' them. Our next step is to predict theeruption of storms on the Sun,” said Dr Harra.
This directmeasurement by SOHO, ACE and Cluster confirms previous Earth-boundpredictions and takes researchers a step closer to forecasting thesegeomagnetic storms.
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