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BBC News Online: Sci/Tech

Thursday, 24 February, 2000, 11:30 GMT

Leaky Sun threatens disruption

X-ray picture shows the hole as a dark patch (centre)

Space weather forecasters have warned that gusts of solar wind could disrupt satellite operations and power grids until the end of February.

High-speed particles are streaming out of a hole in the Sun's corona - its higher "atmosphere". Coronal holes are easy to spot by looking at the Sun through an x-ray telescope. They appear as very dark areas that contrast with bright spots overlying sunspot groups.

Hot gas around sunspots is captured by magnetic fields that rise up out of one sunspot and bend back to reconnect at another spot nearby. These glowing 'magnetic bottles' shine brightly at x-ray wavelengths.

The magnetic fields around coronal holes are different. Instead of looping back to reconnect on the Sun's "surface", these magnetic fields are essentially open. They extend far out into the Solar System and no one knows exactly where they reconnect.

Hot gas

Rather than trapping the hot gas, the open field lines of a coronal hole allow high-speed solar wind particles to escape.

The solar wind flows away from the Sun in all directions, but the wind speed can be twice as great over holes, reaching up to 800 km/s (500 miles per second).

The higher-pressure streams from coronal holes squeeze the Earth's magnetic field, causing disruption to power grids and communications as well as spectacular aurorae, or Northern Lights and Southern Lights.

It is the second solar storm warning in a week. On Monday, fears that a solar eruption could cause similar problems proved groundless after the Earth's protective magnetosphere successfully deflected the storm front into space.

The best time to look for aurorae is around midnight, before the waning moon rises.

Related to this story:
Solar storm just a wind up (22 Feb 00 | Sci/Tech)
National grid gets space protection (19 Feb 00 | Washington 2000)
Space storm warnings on your wristwatch (19 Feb 00 | Washington 2000)
Major flare erupts on Sun (07 Feb 00 | Sci/Tech)

Internet Links: Nasa space weather centre
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