Associated Press Writer
BOULDER, Colo.—The sun may finally be awakening from its longest quiet period in about a century and powering up to solar maximum, when it could fling disruptive electromagnetic storms toward Earth.
But once the sun does ramp up, it could be a relatively quiet solar maximum, with a below-average number of eruptions, scientists say.
Some researchers argue the sun has begun to enter solar maximum; others say it's not there yet. They do agree the current quiet period, or solar minimum, is the longest since the early 1900s, but they don't know why.
"For the average person or for a technological society like ours, a hundred years is a pretty long time," said Dan Baker, director of the Laboratory for Atmospheric and Space Physics at the University of Colorado.
A solar cycle usually lasts about 11 years, measured from one low point to the next. The most recent started about 13 years ago, in 1996.
Scientists won't declare the quiet period over until after a sustained stretch of activity, generally about three months, said Frank Eparvier, a scientist at the space physics lab.
"We've increased a little bit and had some strong active regions," Eparvier said, but it hasn't been long enough to say solar maximum has begun.
The sun goes through fairly regular cycles of more and fewer eruptions, averaging as many as 180 per day during solar maximum and dipping as low as zero per day during solar minimum.
The magnetic fields that cause the eruptions are themselves influenced by a mix of internal solar motions, including rotation, shears, turbulence and global circulation similar to Earth's ocean currents.
Sarah Gibson, a scientist with the High Altitude Observatory at the National Center for Atmospheric Research in Boulder, calls it "a delicate mix of ordered and chaotic processes."
The consensus prediction for the next solar maximum is a small one, averaging about 90 or fewer sunspots a day in 2013, Eparvier said.
A panel of scientists convened by NASA, the National Oceanic and Atmospheric Administration and the International Space Environment Service reviewed more than 100 published forecasts and eventually coalesced around the small-maximum prediction.
Solar eruptions can send billions of tons of magnetically charged particles into space at high speed. If those particle clouds, called plasma, collide with the Earth's magnetic field, they can create dramatic effects ranging from a beautiful aurora borealis to a devastating electrical blackout.
The sun's volatile magnetic fields can become so severely twisted that they snap and then reconnect, producing a flash called a solar flare and a plasma eruption, Gibson said. If the plasma's magnetic field collides with the Earth's own magnetic field, they connect with another powerful snap.
That can add electrical current on power lines, overtax transformers and set off a rapid collapse of parts of the power grid. It can disrupt radio signals, cause Global Positioning System devices to be off by the distance of a football field and cut off communication between ground controllers and jetliners flying over polar regions. That forces airlines to send planes on longer routes that take more time and burn more fuel.
United Airlines diverted 26 flights from their normal polar routes in January 2005 to avoid communications blackouts during solar storms.
In March 1989, a geomagnetic storm triggered the collapse of a power grid in Quebec, leaving an estimated 6 million people without electricity for nine hours. And in 2006, a burst of solar radiation disoriented virtually all GPS receivers on the lighted half of the Earth, the National Weather Service said.
Baker said radiation from solar flares could be harmful to space travelers and even airline crews who are repeatedly exposed to it on flights over the Earth's poles.
Solar plasma can also physically compress the Earth's magnetic field so much that it's smaller than the orbit of some satellites. Without that magnetic field to orient themselves, those satellites can have trouble communicating with ground stations. Baker estimated that $200 billion worth of satellites are in orbits that leave them vulnerable to such disruptions.
Some satellites are more vulnerable to radiation damage than previous models. During the Cold War, many satellites were "hardened" against enemy radiation attacks, but when that threat passed, designers took fewer protective measures.
On the Net:
Laboratory for Atmospheric and Space Physics: http://lasp.colorado.edu/
High Altitude Observatory: http://www.hao.ucar.edu/
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