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Friday, 9 June, 2000, 12:15 GMT 13:15 UK
Siberian space light show
Nasa
The Northern Lights formed a ring around the magnetic pole
By BBC News Online science editor Dr David Whitehouse

Dramatic shows of the Northern Lights have illuminated Siberia, but the chances for further widespread aurorae over the Northern Hemisphere are declining.

The Earth's magnetosphere is now settling down after being disrupted by an interplanetary shock wave.

The shock wave began in an explosion on the surface of the Sun on 6 June. As well as an energetic solar flare, a mass of super-hot ionised gas was propelled towards the Earth.


Nasa
The Advanced Compositional Explorer
The first indications that the so-called coronal mass ejection (CME) were heading for the Earth was from the Soho Sun-monitoring satellite and the Advanced Composition Explorer (Ace) that are positioned closer to the Sun than the Earth.

Both recorded a jump in the speed of the solar wind from about 500 km per second (310 miles per second) to over 700 km per second (434 miles per second). The number of sub-atomic particles in the solar wind doubled.

The disturbance arrived at Earth about an hour later, triggering some intense auroras that were best seen from Northern Asia.

The charged particles from the CME were drawn towards the Earth by the planet's magnetic field and struck the upper atmosphere near the magnetic poles. Earth-orbiting satellites looking down on the polar regions detected a characteristic ring of auroral light.

The solar wind has now declined to pre-shock levels. Scientists say that the interplanetary magnetic field has also adopted a posture that is generally unfavourable for displays of aurora today.

Further flares are bound to occur on the solar surface as the Sun reaches its peak of activity this summer.

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08 Jun 00 | Sci/Tech
Sun sends a cloud our way
02 May 00 | Sci/Tech
Solar eruption may flood Earth
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