‘S’ marks the spot for solar storms

‘S’ marks the spot for solar storms

Key indicator for space weather
The Yohkoh satellite documented the rise of S-shaped patterns of solar activity (shown in the left image) that heralded the breakout of a potentially disruptive solar storm known as a coronal mass eruption. The right image shows the same area of the sun's surface after the eruption.

By Alan Boyle MSNBC


March 9 — Solar storms can cause headaches even on a cloudless day by disrupting communications and power grids here on Earth. But physicists say they may be able to predict the sun’s most violent explosions several days in advance by watching for a characteristic S-shaped pattern.


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		Montana State University physicist Richard Canfield narrates an animation explaining how coronal mass ejections affect Earth.

THE EXPLOSIONS, called coronal mass ejections, occur several times a day, packing the power of billion-megaton nuclear blasts. Such storms send out a hail of electrically charged particles at a million miles an hour —and if the blast happens to be pointed in Earth’s direction, it can affect radio communications, electrical power systems and satellites orbiting Earth.
“This event, although not common, is a disaster ... a very expensive event for the folks who rely on these systems,” said Richard Canfield, a physicist at Montana State University at Bozeman.
Scientists can spot a hazardous coronal mass ejection as it occurs, providing about four days of lead time to prepare for the storm. But Canfield said he and his colleagues have detected telltale warning signs that herald a coronal mass ejection two or three days before it even happens — which could give power companies and satellite operators extra time to cover their assets.
“We have here a tool that we expect would be very useful for predicting conditions in space weather,” he told reporters Tuesday at a NASA news briefing.

SOLAR SLEUTHS
The discovery is the subject of a paper to be published in the March 15 issue of Geophysical Research Letters.
Analyzing two years’ worth of X-ray images from the Japanese-American Yohkoh satellite, Canfield and his colleagues found a link between S-shaped structures of brightly glowing gas on the sun’s surface and the rise of a coronal mass eruption. About two-thirds of the sun’s big eruptions develop from such structures, known as sigmoids, said Alphonse Sterling, a solar physicist at Computational Physics Inc. in Virginia.



		Montana State University physicist Richard Canfield shows how sigmoids herald the onset of solar storms.

Scientists believe the S-shaped structure is actually the signature of a twisted magnetic field on the sun’s surface. “The magnetic field is what the plasma (superheated gas) is hanging on,” explained Cambridge University researcher Sarah Gibson.
She and her colleagues surmise that the twists build up tension like a twisted rubber band — magnetic flux that is released in the explosive eruptions.
Canfield said there was also a statistical correlation between the eruptions and sunspots, those relatively cool, dark areas that mottle the sun’s bright disk. If the S-shaped pattern is spotted in an area that has large sunspots, “the sigmoid is virtually certain to erupt as it passes across the disk,” he said.

WHAT IT ALL MEANS
The new findings are scientifically significant because they help flesh out theories on how the sun works and how the superstorms are created, experts said. “The idea that twisted structures should erupt is not a new idea. … This just brings a lot of specificity to that question,” Canfield said.
The findings also could lead the way to better forecasting of “space weather,” the scientists said. As it happens, the sun is headed toward the peak of an 11-year cycle of activity next year. During the last solar maximum, in 1989, a coronal mass ejection knocked out power to a wide area of Quebec for nine hours, noted George Withbroe, science director for NASA’s Sun-Earth Connection research theme. He also referred to last year’s failure of the Galaxy 4 satellite, which led to widespread communications outages.

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Such outages couldn’t be ruled out during the coming solar maximum, he said, although he acknowledged that they were more of a nuisance than a catastrophe.
With an extra couple of days of warning about solar storms, power companies could take further steps to protect transformers, and satellite operators could have more time to soften the brunt of the storm. However, Canfield said much more work needed to be done to turn sigmoid-spotting into a more precise predictive tool for coronal mass ejections.
“We need to get past simple classifications such as, ‘Is it sigmoidal or not, is the sunspot big or small,’ and get to quantitative measurements that answer ‘how twisted are the magnetic fields, how big is the spot,’” Canfield said. “As well, we want to know in which direction the CME is going to go and how many regions are likely to erupt.”
NASA is planning a mission that will make three-dimensional images of coronal mass ejections and the structures around them — called the Solar Terrestrial Relations Observatory, or STEREO — to answer these questions, he said.
Ultimately, Canfield said, the National Oceanic and Atmospheric Administration may be able to include warnings of coronal mass ejections in its space weather forecasts, in the same way that meteorologists make long-range forecasts on Earth. NOAA is building a Solar X-Ray Imager similar to that on Yohkoh that is scheduled for launch next year, he noted.



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