A blast of particles from the sun hit the Earth just before 6 a.m. Wednesday, but the resulting geomagnetic storm didn't immediately cause any reported disruptions to GPS and power grids.
"So far, the orientation of the magnetic field has been opposite of what is needed to cause the strongest storming," the Space Weather Prediction Center of the U.S. National Oceanic and Atmospheric Administration reported around 6:30 a.m. ET. "As the event progresses, that field will continue to change."
The centre expected "strong" geomagnetic storm levels for some periods of the day, with the potential to cause power disruptions and intermittent satellite navigation and low-frequency radio navigation problems.
In addition, it said, solar radiation storm levels were strong, boosting the radiation exposure risk for passengers and crew in high-flying aircraft.
The storm, started with a massive solar flare earlier in the week and grew as it raced outward from the sun, expanding like a giant soap bubble, scientists said.
"It's hitting us right in the nose," said Joe Kunches, a scientist for the National Oceanic and Atmospheric Administration in Boulder, Colo.
The massive cloud of charged particles could disrupt utility grids, airline flights, satellite networks and GPS services, especially in northern areas. But the same blast could also paint colorful auroras farther from the poles than normal.
The effects could linger through Friday morning.
Astronomers say the sun has been relatively quiet for some time. And this storm, while strong, may seem fiercer because Earth has been lulled by several years of weak solar activity.
The storm is part of the sun's normal 11-year cycle, which is supposed to reach peak storminess next year. Solar storms don't harm people, but they do disrupt technology. And during the last peak around 2002, experts learned that GPS was vulnerable to solar outbursts.
Because new technology has flourished since then, scientists could discover that some new systems are also at risk, said Jeffrey Hughes, director of the Center for Integrated Space Weather Modeling at Boston University.
A decade ago, this type of solar storm happened a couple of times a year, Hughes said.
"This is a good-size event, but not the extreme type," said Bill Murtagh, program co-ordinator for the federal government's Space Weather Prediction Center.
The region of the sun that erupted can still send more blasts our way, Kunches said. He said another set of active sunspots is ready to aim at Earth right after this.
"This is a big sun spot group, particularly nasty," NASA solar physicist David Hathaway said. "Things are really twisted up and mixed up. It keeps flaring."
For North America, the good part of a solar storm — the one that creates more noticeable auroras or Northern Lights — will peak Thursday evening. Auroras could dip as far south as the Great Lakes states or lower, Kunches said, but a full moon will make them harder to see.
Auroras are "probably the treat we get when the sun erupts," Kunches said.
North American utilities are monitoring for abnormalities on their grids and have contingency plans, said Kimberly Mielcarek, spokeswoman for the North American Electric Reliability Corporation, a consortium of electricity grid operators.
In 1989, a strong solar storm knocked out the power grid in Quebec, causing six million people to lose power.
Solar storms can also make global positioning systems less accurate and cause GPS outages.
The storm could trigger communication problems and additional radiation around the north and south poles — a risk that will probably force airlines to reroute flights. Some already have done so, Kunches said.
Satellites could be affected, too. NASA spokesman Rob Navias said the space agency isn't taking any extra precautions to protect astronauts on the International Space Station from added radiation.
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