Tracking a solar storm from `cradle to grave'
Space: For the first time, observatories help scientists follow an interplanetary weather event -- a space storm that carried a blast of high-energy particles from the sun to Earth.

By Frank D. Roylance

SUN STAFF

GREENBELT -- A space storm that erupted from the sun and swept across the solar system to Earth earlier this month has given scientists their best look yet at the details of these violent interplanetary weather events.

The blast of high-energy solar particles was born on the sun Jan. 6 and reached Earth on Jan. 10, where it began pumping vast amounts of energy into the Earth's space environment. It triggered auroral displays, disrupted some radio communications and may have played a role in the Jan. 11 failure of the $200 million Telstar 401 communications satellite.

It wasn't a big solar eruption as these things go. But it has delighted scientists because it is the first one ever recorded "from cradle to grave" by a battery of orbiting solar observatories.

"It was a very exciting moment," said Dr. John Dudeney, a researcher at the British Antarctic Survey. "For the first time, we were able to see the birth of a space storm and have sufficient instruments in the right places to follow its eff ects all the way from the explosion on the sun to the fi-

nal dumping of gigawatts of energy" into the Earth's atmosphere.

People on Earth are shielded by its magnetic field and face no direct hazard from such storms. But the crews of high-altitude aircraft, especially on polar routes, can receive significant amounts of radiation over time.

The storm's effect, if any, on NASA astronaut John Blaha and his Russian crew mates on board the space station Mir at the time, is not yet known. (The shuttle Atlantis was launched Jan. 13, after the storm had passed.)

Generally, astronauts in near-Earth orbit, where Mir and U.S. shuttles operate, are shielded well enough from harmful solar radiation by Earth's magnetic field. Those en route to the moon or Mars during such a storm would be in serious danger unless thei r spacecraft were heavily shielded.

The solar storm's eruption and impact on Earth were recorded by 20 unmanned satellites and 10 ground observatories. Scientists in 12 countries are assisting with data analysis -- a process expected to continue for months, perhaps even years.

Solar experts at the NASA Goddard Space Flight Center in Greenbelt said yesterday that the Jan. 6 event was a "coronal mass ejection." That's a magnetic phenomenon in which hydrogen and helium on the sun's surface, for reasons not well understo od, are thrown off as a huge bubble of hot gas and atomic particles, chiefly protons and electrons.

The material flies away from the sun into interplanetary space in an expanding, dome-shaped cloud front. When it reaches a planet with a magnetic field, like Earth, a portion of the cloud's electrically charged particles gets swept into that magnetic fie ld, charging it with vast amounts of electrical and magnetic energy.

If they are large enough, the surges can knock out satellites and induce electrical currents in oil pipelines, telephone and electric power lines.

NASA has received no reports of power outages caused by the latest event. Citing legal constraints, they declined to speculate on whether the storm caused the Telstar satellite's failure.

Coronal mass ejections occur as often as once a day. But its rare when big ones are aimed straight at Earth. It's happened only twice since the Solar and Heliospheric Observatory (SOHO) was launched two years ago.

The Jan. 6 eruption occurred just as NASA's International Solar-Terrestrial Physics program -- which oversees the solar observatories -- was convening a science workshop at Goddard.

Scientists at the meeting were told the magnetic cloud was headed for Earth at close to 1 million miles an hour. At that rate, it would reach Earth by Jan. 10. Scientists around the world began planning for several days of intensive data collection.

On Jan. 10, the speeding cloud front reached SOHO, 2 million miles sunward from Earth. As it did, SOHO's instruments noted that the speed of the solar wind -- particles that normally stream outward from the sun at 670,000 mph -- jumped suddenly to 962,00 0 mph.

A short time later, the cloud passed the Wind Laboratory, a satellite stationed halfway between Earth and SOHO. Wind reported a sharp increase in the density and temperature of the solar wind and changes in the intensity and direction of its magnetic fie ld.

Dr. Keith Ogilvie, project scientist for Wind, said it took the magnetic cloud most of a day to pass Wind's position in space, suggesting a thickness of at least 30 million miles -- about the distance from Earth's orbit to Venus'.

As the magnetic cloud swept past the Earth, it had multiple impacts, scientists said.

It pushed the sunward boundary of the Earth's magnetosphere -- the magnetic field that surrounds the planet and shields it from dangerous radiation -- closer to Earth. That left several satellites in geosynchronous orbits 22,000 miles above Earth briefly outside the magnetosphere's protection. A satellite in geosynchronous orbit remains over the same point on the globe.

Geosynchronous satellites on the other side of the Earth measured strong fluctuations in their electrical and magnetic environment ranging from 100 to 10,000 times normal readings.

The British Antarctic Survey at its South Pole Halley Research Station reported the storm disrupted high-frequency radio communications and shut down aircraft operations.

Auroral displays were reported over Alaska, Canada and Scandinavia as charged particles from the storm were swept toward the north magnetic pole and collided with molecules in the upper atmosphere, causing them to glow.

Small fluctuations in the Earth's magnetic field were recorded around the globe.