Sunspot storms threaten power supplies

Power lines and some radio communications could be disrupted today as a massive magnetic storm spawned by the sun reaches the Earth. The storm may also provide spectacular displays of the aurora borealis - the northern lights. The storm is one of a series being thrown out by the largest cluster of sunspots to appear on the face of the sun in a decade. The group measures more than 22 earth-diameters across and is sparking enormous explosions.

"I think it is the largest group to appear in 10 years," said Dr Ian Elliott, a solar physicist and member of the staff at Dunsink Observatory in Dublin. "It has emitted several large flares."

Sunspot activity rises and falls in 11-year cycles and we are just exiting a peak, known as a "solar maximum". There are 320 distinct sunspots visible on the solar disc, according to the latest satellite data.

Sunspots occur above distortions of the sun's enormously powerful magnetic field. The distortions slow the flow of heat from the sun's interior, keeping their surroundings cooler and causing the dark patches we know as sunspots.

The violent solar activity that accompanies sunspots is thought to be caused by the sudden cataclysmic release of magnetic energy.

The explosions are unbelievably large, releasing as much energy as a billion million tonnes of TNT. They cause "coronal mass ejections" (CMEs), clouds of electrified magnetic gas weighing billions of tonnes that are thrown into space at speeds of up to 2,000 km a second.

The magnetic fields around the CME disturb Earth's own magnetic fields.

A major magnetic storm knocked out transformers and blacked out the city of Quebec several years ago. Power companies, including the ESB, pay particular attention to these storms.

The shockwave produced at the front of the cloud can damage the sensitive electronics in orbiting satellites, putting satellite communications at risk, said Dr Elliott.

Shortwave radio broadcasts are also disrupted by magnetic storms.