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Scientists Find Early Warning Signs of Violent Solar Storms

David Perlman, Chronicle Science Editor
  Wednesday, March 10, 1999

Scientists studying violent electrical storms that erupt from the surface of the sun say they have discovered the first warning signs that could help them prepare for the potentially destructive eruptions.

Hurling more than 10 billion tons of hot, electrically charged gases from the sun's surface, the storms carry the equivalent of a billion atom bombs and travel at speeds of up to 1 million mph.

If the powerful storms head toward Earth they can expose spacecraft crews to radiation, endanger sensitive electronics in unmanned satellites, trigger blackouts along electric power grids, and disrupt communications around the world.

The bursts from the sun's surface take nearly four days to reach Earth. But an international team of researchers reported yesterday that S- shaped structures that form in some storms on the solar surface can provide an extra three or four days of early warning before an eruption occurs.

The scientists reported that the S-shaped regions of electromagnetic activity -- called coronal mass ejections, because they originate from electrical storms in the sun's corona, or outer atmosphere -- are closely correlated with the most violent eruptions.

Another ``early warning'' of impending eruptions, they said, appears to be signaled when sunspots in the sun's inner atmosphere, the photosphere, are unusually large.

Storms on the solar surface that do not show the S-shaped sigmoids are very unlikely to erupt dangerously, as are sunspots of normal size, the researchers said.

The scientific team, headed by physicist Richard Canfield of the University of Montana, described its findings yesterday at a NASA press conference in Washington, D.C. A detailed report is also being published in the March 15 issue of the journal Geophysical Research Letters.

The sigmoids on the sun's surface were detected by an unmanned Japanese satellite whose instruments, developed by U.S., British and Japanese scientists, are tuned to X-ray frequencies. The researchers spent two years examining fiery images of all the coronal mass ejections from the sun taken by the satellite in the years 1993 and 1997.

If the storms appeared merely as irregularly shaped patches of storm activity, they did not turn into major eruptions, Canfield said. But when they assumed the sigmoid shape, they turned into far more violent blasts within three or four days, he said.

The S-shaped areas are huge: typically 50,000 to 100,00 miles long on the sun's surface, and 10 to 20 times larger than the average sunspot. They can remain on the surface for several months, observable month after month as the sun rotates on its axis.

``Those X-ray images will tell us when something is likely to happen,'' Canfield said. ``As soon as we can recognize that a region is S- shaped, we know that it is more likely to erupt. They could be developed into a powerful predictive tool, and we could go from three or four days of warning to six or seven days.''

Although power companies on Earth can usually protect their grids from the intense surges of energy caused by solar storms, many of the delicate electronic instruments aboard satellites can be extremely vulnerable to damage from the electromagnetic energy. And astronauts -- whether they fly in low-Earth orbit, as the crews of the U.S. space shuttle and the Russian Mir do, or head farther out to the moon and beyond -- can be endangered both by radiation from the solar blasts and by damage to their spacecraft.

The advance notice would allow satellite operators, for instance, to shut down high-voltage equipment that is vulnerable to the magnetic storms and give utility companies time to protect valuable transformers.

Not all the effects of coronal mass ejections are dangerous, however. The streams of charged particles from some of them can interact with the Earth's magnetic field to produce the aurora borealis and aurora australis -- the beautifully shimmering northern and southern lights that enchant residents of the far North as well as Alaska-bound tourists.

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