A SUNSPOT that at its peak has been five times larger than Earth is likely to release fresh solar flares this week that could cripple satellites and black out radio communications.

Sunspot 798 has already fired seven enormous X-class eruptions of radiation at Earth since September 7, including one monstrous flare on Wednesday that was measured as the fourth largest on record.

While the sunspot has since shrunk a little, it is rotating across the Sun’s surface so as to line up with Earth, meaning that any activity this week is more likely to strike the planet head-on rather than catch a glancing blow. Yesterday astronomers predicted a 75 per cent chance of further flares this week, raising the possibility of serious disruptions to telecommunications.

There also remains a small risk from the streams of charged particles, known as a coronal mass ejection, which reach Earth about two days after a solar flare event. The particles linked with the eruption on Wednesday, which was measured at a magnitude of X-17, arrived over the weekend, causing spectacular displays of the aurora borealis.

The US National Oceanographic and Atmospheric Administration (NOAA) describes solar activity as at “very high levels”, and has already reported some problems on Earth as a result. Electrical power systems, spacecraft, high-frequency communications and satellites such as those operating the global positioning system “are experiencing impacts due to the strong-to-severe solar activity”, though none has been knocked out, the NOAA Space Environment Centre said.

Previous geomagnetic storms have proved more serious, such as the one triggered by the largest flare on record, in November 2003.

This eruption was measured at a magnitude of X-28 and disabled satellites and an instrument aboard a Mars-bound spacecraft. Earth was spared wider disruption as the flare caught a glancing blow.

A smaller flare that hit head-on in 1989 knocked out the electricity supply in the Canadian state of Quebec.

The recent solar flares have also triggered spectacular auroras borealis, or northern lights, which occur as streams of charged particles from the Sun excite molecules in the atmosphere to produce bright colours in the night sky.

Over the weekend, aurora effects, which are generally seen only at high latitudes, were sighted as far south as Arizona in the United States.

Sunspots are cooler and darker patches on the surface of the Sun caused by magnetic fields shaped like coiled tubes that rise from the interior of the star.

These loops, which contain charged particles known as plasma, can become disrupted by the surface pressures of the Sun and spew their contents outwards.

This causes a solar flare of radiation that reaches Earth in seven minutes and a coronal mass ejection, which takes a further two days to get here.

When the plasma particles strike the magnetic field around Earth, they pull it out of shape, leading to geomagnetic storms that cause interference with electrical equipment, particularly transformers, generators and radio networks. Such storms are also responsible for the aurora.

Solar activity occurs on an 11-year cycle, and the latest events associated with Sunspot 798 have surprised astronomers because the current cycle is on a downswing: the last peak occurred in 2001, and activity ought to be on the decline.

Another significant passage of solar activity, however, was also recorded in January, including one huge flare on January 20.

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