WASHINGTON (AP) - Solar waves that interfere with satellite transmissions - and were blamed for a power blackout in Canada in 1989 - have long eluded timely detection by scientists. Now, researchers have found telltale ripples from the sun that enable them to predict these disturbances weeks in advance.
Solar physicists analyzing data from the Solar and Heliospheric Observatory (SOHO) said measuring the speed of waves moving through the great gas ball of the sun lets them detect disturbances that start on the far side and then rotate into view.
''This gives a week to two weeks warning,'' said Douglas Braun, a solar physicist and co-author of a study appearing Friday in the journal Science. ''Such a prediction could be important because it would give time to warn the crew of a manned mission to Mars, or astronauts working outside the International Space Station.''
Powerful bursts of electromagnetic energy and particle radiation can erupt from the sun and send waves toward the Earth. The eruptions can disrupt radio communication and cause surges in electrical power transmissions systems on Earth. Some blackouts have occurred in the past. Unusually large solar flares were believed responsible for a huge blackout in March 1989 that left almost 6 million people in Quebec without heat or electricity.
These energy waves also pose a particular hazard to satellites, to spacewalking astronauts and, perhaps one day, to the crew of spacecraft en route to Mars.
Braun, a researcher with Northwest Research Associates in Boulder, Colo., said that right now, space weather predictions must wait until satellites detect the distinctive markings on the face of the sun that precede an eruption. These markings first appeared on the far side of the sun, but could not be seen. Having to wait until the active region is in view means there could be only a day or two of warning, he said.
With the new technique discovered by Braun and Charles Lindsey, a scientist with Solar Physics Research Corp. of Tucson, Ariz., it may be possible to forecast a solar up to two weeks in advance.
Braun said the SOHO satellite detects waves caused by acoustic pulses racing through the superheated plasma of the sun. He and Lindsey found that some of these waves had a pattern suggesting they were affected by disturbances on the far side of the sun.
''These waves are coming from all over the place,'' Braun said. ''The trick is pick out the ones that have gone all of the way to the other side and then bounced back.
''Measuring this travel time indicates if there is an active region on the other side,'' he said.
Because the sun rotates every 27 days, it could be weeks before a disturbance on the far side rotates into view and becomes a threat to Earth, he said.
The researchers, checking archived data from SOHO, found what could be the signature of waves affected by disturbances and then related this pattern to later views that showed active regions on the front face of the sun. Braun said the timing matched, proving that the ripple pattern they found on the near side was caused by activity on the far side.
Braun said the ripples seen on this side of the sun are caused by sound waves that flash through the center of the sun. Since the sun is, in effect, a dense and torrid ball of gas, he said, ''it is a perfect medium for sound waves.''
When the sound waves pulse through the sun, they create a visible motion in the plasma seen on this side of the sun. It is this visible motion that the researchers interpret, said Braun.
Braun said the study has proven that the solar weather prediction technique works, but to create a permanent advanced forecasting system would require changes in the way SOHO data is now handled, or, perhaps, a satellite dedicated to long range solar forecasting.
''This is really just a proof of concept study,'' he said. ''We have proved the procedure would work.''
SOHO is parked in what is known as the L1 point between the sun and the Earth. Objects placed here are in gravitational balance between the sun and Earth and will maintain the same position relative to those bodies. This enables the spacecraft to stare continuously at the sun, or, as planned for another NASA satellite, to look constantly at a sunlit Earth.
