Observations Show that "S" Marks the Spot

BOZEMAN, MONT--Even though it's a lovely spring day today, gardeners will protect their new seedlings if a hard frost is forecast for tonight.

Similarly, a utility company will protect its $10-million transformers if officials know a burst of solar magnetism is speeding toward Earth at one million miles an hour. As powerful as billions of nuclear explosions, solar bursts have a reputation for destroying machinery and equipment sensitive to changes in solar weather.

Predicting those magnetic bursts, called coronal mass ejections, several days in advance may now be possible, according to a group of solar physicists in Montana and Japan.

The scientists have found a strong correlation between an S-shaped pattern on the sun, called a sigmoid, and the likelihood that an ejection will occur from that region within days. Each sigmoid is like a loaded gun that scientists now know has a high probability of going off.

The observation will be useful to the burgeoning science of space weather forecasting, which aims to predict solar activity and its impact on the Earth's environment.

"We've found that the S-shaped regions are the dangerous ones," said Richard Canfield, a research professor of physics at Montana State University-Bozeman and lead author on a paper to be published in the March 15 issue of Geophysical Research Letters. "As soon as we can recognize that a region is S-shaped, we know that it is more likely to erupt."

The sigmoid structures are likely the result of twisted solar magnetic fields. By contrast, other common magnetically disturbed regions have a symmetrical, butterfly shape and rarely erupt.

Canfield and several other scientists will present the discovery at a National Aeronautics and Space Administration "Space Science Update" at 1 p.m., EST, March 9 in Washington, D.C. The six-month study was sponsored by the space agency.

Coronal mass ejections (CMEs) are violent discharges of hot, electrically charged gas from the sun's corona or outer halo. The largest explosions in the solar system, CMEs hurl up to 11 billion tons of electrically charged gas into space. The outbursts occur several times a day, but only those shot toward Earth are potentially dangerous. They travel the 93 million miles between the sun and Earth in about four days and can damage satellites, disrupt communications networks and cause power outages.

Images from various space satellites have provided clues to when a CME had already erupted, but scientists have been interested for some time in knowing about them beforehand. Hugh Hudson and Alphonse Sterling, working at the Institute of Space and Astronautical Science in Japan, first observed a relationship between a sigmoid shape before a CME and a cusp or arcade shape afterwards. Later, Hudson and others found the same pattern in several other ejections.

That finding prompted Canfield, Hudson and David McKenzie, a research scientist at Montana State University, to look for a statistical correlation between the sigmoid shape and subsequent eruptions. They viewed two years' worth of daily X-ray images from the Japanese/US/UK satellite called Yohkoh. The composite pictures--50 images each day--were made into movies that the researchers analyzed on TV.

The study not only showed that "S" marks the spot of a likely eruption, it also revealed a statistical correlation between large sun spot areas and CMEs. Sun spots are cool, black areas on the otherwise bright solar disk.

Now Canfield said the goal is to transform the correlations into a more refined predictive tool. Utility and communications industries with millions of dollars at stake and NASA would benefit from warnings as far as possible in advance of the ionized gas reaching Earth.

"We need to get past simple classifications such as 'Is it sigmoidal or not, is the sun spot 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 CMEs and the structures around them, called the Solar TErrestrial RElations Observatory (STEREO), to answer these questions, he said.

Ultimately, Canfield continued, the National Oceanic and Atmospheric Administration may be able to include warnings of CMEs in its space weather forecasts in the same way meteorologists make long-range forecasts on Earth. The administration is building a Solar X-Ray Imager similar to that on Yohkoh that is scheduled for launch next year, he said.

For a copy of the Canfield et al. paper, journalists and science public information officers should contact Harvey Leifert of the American Geophysical Union at [email protected].

Note to Editors: Images and supporting material can be found on the internet at
http://solar.physics.montana.edu/press
http://solar.physics.montana.edu/YPOP/
http://www.isas.ac.jp/info/sat/yohkoh-e.html#Tag:0