EYES ON THE STORM-TOSSED SUN

By Dick Thompson/Washington

If you think hurricanes and tornadoes are powerful, take a look at the sun's periodic storms. Kicking up twisting arcs of fiery gases, solar eruptions from that great thermonuclear reactor in the sky can stretch as far as the distance from Earth to the moon. The most intense outbursts explode a billion tons of material off the sun's searing (11,000[degrees]F) surface at speeds of millions of miles an hour. If these electrically charged particles happen to slam against Earth's atmosphere, they can imperil astronauts, push satellites out of orbit or fry their circuitry. If they hit the ground, they can turn compass needles topsy-turvy, knock out electrical-power systems and possibly change the planetary climate. No wonder scientists dream of one day being able to predict storms on the sun with all the accuracy of terrestrial weather forecasts.

Last week they seemed a little closer to getting their wish. At a meeting of the International Astronomical Union in Kyoto, Japan, and at a special NASA briefing in Washington, solar physicists ecstatically reported results from a new generation of solar observatories--a NASA-European Space Agency satellite known as soho (for Solar and Heliospheric Observatory), which has been circling the sun since December 1995, and the National Science Foundation's global network of ground-based solar stations. By keeping a day-to-day eye on solar weather features such as the sun's "trade winds" and "jet streams," these new high-tech observatories are creating what the assembled researchers hailed as a revolution in their field. An exultant John Leibacher, director of the NSF solar program, said, "I have been [observing the sun] for 40 years, and I never had any hope that we would be able to see these things."

What they saw included an astonishing doughnut-shaped jet stream of hot gases circling the sun's "Arctic" region, like Earth's own circumpolar winds. The scientists were so taken aback by the fast-moving river of plasma, they said, that they dared not reveal their findings until they had rechecked their data several times. The scientists also got a close-up look at the sun's lower-latitude trade winds, whose existence they had hitherto only suspected. The new probes not only confirmed these suspicions but also showed that the winds--actually, great bands of plasma slightly warmer than neighboring solar gases--dive deep into the solar interior, itself a mass of gases, then flow back toward the equator, creating a circular gyre reminiscent of Earth's great ocean currents, such as those that sweep the Atlantic and Pacific. "We used to think the inside of the sun was fairly simple," says John Harvey, an astronomer at the Kitt Peak National Observatory near Tuscon, Ariz. "But that was before we had the capability to see into it."

The key that the scientists used to unlock that interior was provided by the sun itself: the great, sonic-boom-like explosions that constantly ripple its surface. Using computer techniques similar to those required to produce sonograms of the human body, the scientists followed the sun's sound waves as they raced through its interior and across its surface at speeds of 20,000 m.p.h. "It's a terrible din," says University of Cambridge astrophysicist Douglas Gough. But, he adds, since millions of explosions are taking place at any single moment, their waves can be plotted like a body scan to create a three-dimensional image of the sun's interior extending down to its huge core, which accounts for 70% of the star's volume.

In addition, scientists have begun to get a better understanding of the sun's magnetic properties, which may hold the answer to what generates solar storms. While Earth's north and south magnetic poles have remained in place for the past 30,000 years, the sun's poles flip-flop every 11 years--so that the needles of any would-be solar compasses would swing 180[degrees]. The reversal is preceded by a kind of magnetic sparkling across the sun's surface--as if it were suddenly the site of millions of toy magnets, each with its own poles.

The sparkling, in fact, gives rise to the sun's periodic magnetic storms, an activity that reaches a peak with the 11-year polar shifts. Huge pockets of gases form on the sun's surface, accompanied by sunspots, solar flares and great eruptions of gas. While this phenomenon has seemed to be limited to the sun's surface, the new probing shows that the magnetic storms are apparently stirred up by the shearing action of the winds as they press past slower moving gases, just as the eruptions of volcanoes on Earth are produced by the pressures created by motions of its great crustal plates rubbing against each other. By learning to track these winds, the researchers believe they can take a giant leap forward in the science of forecasting solar weather.

To bolster its solar-observing efforts, NASA last week launched another solar satellite--this one to measure the properties of the high-energy particles ("solar wind") blowing out from the star. That was good news to many scientists who feared that, for budget reasons, the space agency might pull the plug on its existing solar observatory. "One way or another, we will keep it operating," vows NASA official George Withbroe. A good thing too, since solar storms are expected to reach another peak in the year 2000 or 2001. Stay tuned--if your power remains on.

For more information on the new wave of space exploration, see time.com