More Accurate Warnings of When Sun Spews Harmful Radiation

Solar scientists have made a breakthrough in their ability to forecast space storms that can damage satellites, threaten astronauts, and cause power failures on Earth.

New observing techniques and computer simulations give fresh insight into solar outbursts that cause these dangerous storms. And a new ability to see the outbursts of electrically charged particles coming at Earth has doubled the accuracy of forecasts of the trouble it may cause here.

Space physicists call these storms coronal mass ejections. They are massive outbursts of electrically charged particles from the sun's outer atmosphere, called the corona. They can spray Earth with dangerously energetic electrically charged protons. These outbursts are like having the mass of "a hundred thousand Nimitz-class aircraft carriers steaming out of the sun at of a million miles an hour," says Spiro Antiochos of the US Naval Research Laboratory in Washington. This causes storms of electrons and magnetic-field disruptions that damage satellites and disrupt power transmissions.

Dr. Antiochos says coronal material builds up pressure until it bursts free. Images from a National Aeronautics and Space Administration satellite show the material exploding outward.

Having the ability to predict these bursts is good news for astronauts, who will begin building the international space station next fall. Boston University space physicist Nancy Crooker explains that "we're practicing [forecasting] when [space storms] are not at their maximum." Solar activity will be moving into its maximum phase over the next few years. Because this solar radiation can be deadly to astronauts during a space walk, spacewalkers will need ample warning to take cover when a storm threatens.

SPACE-storm forecasters need to get their act together before then, Dr. Crooker says. The trick is to identify which solar outbursts actually threaten our planet and the spacecraft in orbit around it. Crooker explains that, using previous techniques, "if you could predict one storm in three, you were doing real good." In experimental forecasts made between December 1996 and June 1997 using the new techniques, scientists predicted 12 outbursts would cause storms at Earth. Nine of them actually did. That cut the false-alarm rate in half.

Crooker and several colleagues detailed their new insights to fellow scientists at a meeting of the American Geophysical Union here. They presented computer simulations and images gathered by sun and Earth-watching satellites that are part of the International Solar Terrestrial Physics program.

The essential point, Antiochos says, is that scientists now understand what is going on well enough to begin to base forecasts of threats to Earth on the physics involved. Charles Goodrich, an astrophysicist with the University of Maryland at College Park, showed computer-generated animations based on such knowledge depicting storms pounding Earth's magnetic shield.

The ability to do this is akin to progress made in weather forecasting on Earth over the past century. Meteorologists began with forecasts based on intuition and some very limited data. Now space weather forecasting has reached the stage meteorologists achieved 30 to 40 years ago - when computer-based weather forecasting began moving from research into practice.