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The BBC's Sue Nelson
Scientists are testing a space weather prediction system
 real 28k

Tuesday, 22 February, 2000, 13:16 GMT
Solar storm just a wind up

Sun
Sun fails to penetrate Earth's defences


A solar storm that threatened to disrupt communications and power supplies on Earth appears to have passed harmlessly by.

A vast cloud of superheated gas thrown out of the Sun by what's called a coronal mass ejection (CME) was expected to collide with the Earth's magnetic field, creating a geomagnetic storm.

Radiation spike from the flare Radiation spike from the flare
Such storms may cause a display of aurorae, or Northern or Southern Lights. In extreme cases, they can also induce electric currents that damage electric power transmission equipment.

Normally, the Earth is protected from such storms by its magnetosphere, but solar material can break through if its own magnetic field is aligned in a certain way, with the South Pole dominating.

AB Light from the Aurora Borealis dances in the sky above Alaska
In this case, the magnetic field of the disturbance flipped northward only four hours after colliding with the Earth, and the storm slid by without penetrating the planet's "magnetic armour".

But it may be a little early to relax. A large coronal hole is just approaching the Sun's central meridian. Coronal holes are regions of low magnetic field strength where high-speed solar wind particles can escape into interplanetary space.

When the energetic wind stream reaches Earth, it can buffet the magnetosphere and trigger aurorae, so later this week or next we could be in for a dazzling display.

As the Sun reaches its maximum period of activity later this year, CME's and other solar events will become more common.

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See also:
19 Feb 00 |  Sci/Tech
Here comes the Sun
07 Feb 00 |  Sci/Tech
Major flare erupts on Sun
12 Nov 99 |  Sci/Tech
An active Sun

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