WASHINGTON -- The Global Positioning System, relied on for everything from navigating cars and airplanes to transferring money between banks, may be threatened by powerful solar flares, a panel of scientists warned yesterday.

"Our increasingly technologically dependent society is becoming increasingly vulnerable to space weather," David L. Johnson, director of the National Weather Service, said at a briefing.

GPS receivers have become widely used in recent years, for satellite signals that navigate airplanes, ships, and automobiles and for cellphones, mining, surveying, and many other commercial uses.

Indeed, banks use the system to synchronize money transfers, "so space weather can affect all of us, right down to our wallet," said Anthea J. Coster, an atmospheric scientist at the Haystack Observatory of the Massachusetts Institute of Technology.

The cause for their concern, Johnson said, was an unexpected solar radio burst on Dec. 6 that affected virtually every GPS receiver on the lighted half of earth. Some receivers had a reduction in accuracy while others completely lost the ability to determine position, he said.

Solar activity rises and falls in 11-year cycles, with the next peak expected in 2011. If that increasing level of activity produces more such radio bursts, the GPS system could be seriously affected, the researchers said.

Protecting the system is no simple task, said Paul M. Kintner Jr., a professor of electrical engineering at Cornell University, who monitored the December event.

There are two possible ways to shield the system, he said, both very expensive: either alter all GPS antennas to screen out solar signals or replace all of the GPS satellites with ones that broadcast a stronger signal. That is why it is essential to learn more about the sun's behavior quickly in an effort to find ways to predict such events, the researchers said.

The December solar flare also induced unexpected currents in the electrical grid, Johnson said.

Patricia H. Doherty, co-director of the Institute for Scientific Research at Boston College, said the burst affected but did not shut down the Federal Aviation Administration's Wide Area Augmentation System, which uses GPS signals to assist in navigation.

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