Solar storms: Two breakthroughs could lead to better warnings

Intense solar storms can disrupt satellites, airline and electric-utility operations, and, in the case of astronauts on orbit, directly endanger lives.

Thursday, independent teams of researchers unveiled a pair of storm-tracking techniques that could significantly improve forecasts of "space weather" storms, the researchers say.

One team's approach tracks magnetic fields while they are still taking shape nearly 40,000 miles below the sun's surface, well before they form and corral groups of sunspots on the solar surface. These sunspot groups represent active regions that spawn coronal-mass ejections – outbursts that can send up to 1 billion tons of hot plasma hurtling through space at up to 1 million miles an hour.

The second team used a pair of sun-watching satellites to build detailed images of a coronal-mass ejection and its evolution as it traveled from the sun to Earth. Until now, researchers had been able to track these eruptions in detail for only about the first 20 percent of the trip, yet a cloud's structure and speed, among other traits, can change markedly across the missing 80 percent of the trip.

Between the two projects, the teams have developed tools to track some of the most severe types of space weather from gestation within the sun to delivery at Earth's doorstep.

"For the first time, we're beginning to see a complete, predictive system," says Craig DeForest, a solar physicist at the Southwest Research Institute in Boulder, Colo., who led one of the two teams.

For federal space-weather forecasters, these techniques could lead to substantial improvements in the accuracy of their forecasts.

The largest coronal-mass ejections most often come from active, sunspot-dotted regions of the solar surface. "It is pretty exciting to be able to look underneath the sun and try to predict when an active region will appear," says Alysha Reinard, a research scientist at the National Oceanic and Atmospheric Administration's Space Weather Prediction Center in Boulder, Colo.

With the new ability to track in detail a coronal-mass ejection along its complete trip, it should be possible to predict effects at Earth to within eight hours of its arrival, as opposed to today's 12- to 14-hour window, she says. Such an improvement could, for instance, allow airliners flying intercontinental routes to travel along the most fuel efficient routes longer before they have to change course to avoid air space subject to radio blackouts, which solar storms can bring.

The developments come as two scientists in Britain suggest that over the next several decades, solar storms could become a more significant problem than they are today. And it isn't just because of the spread of vulnerable technologies, such as power grids.

If the sun is entering a prolonged phase when the peak sunspot activity is relatively weak to nonexistent, solar storms would become fewer in number but more powerful when they do occur. Their conclusions appeared in the May 11 issues of the Journal of Geophysical Research and is based on Antarctic-ice-core reconstructions of past solar activity.

One of the two, Michael Lockwood of the University of Reading, has put the chance of the sun entering such a deep minimum, similar to the so-called Maunder minimum, at about 8 percent.

To spot the changes inside the sun that appear to herald a coming blossom of sunspots, a team led by Stanford University graduate student Stathis Ilonidis used data from the SOHO spacecraft, a collaboration between the European Space Agency and NASA. SOHO orbits the sun within a gravitational sweet spot that lies some 1.5 million miles from Earth, in the sun's direction. There, gravity from the sun and Earth in effect cancel each other, allowing the craft to stay put with few or no additional maneuvers needed.

Mr. Ilonidis and colleagues used an imager on SOHO that can detect changes in the intensity and direction of acoustic waves in the sun. These waves are generated by vigorous convection as the searing gases within the sun rise, cool, and sink again to be reheated by the star's nuclear furnace.

Scientists had long thought that the magnetic activity that generated sunspot regions originated deep within the sun. The results Ilonidis and colleagues are publishing in Friday's issue of the journal Science represent what he says are the first observations of this deep process.

The team looked at four different sunspot outbreaks and spotted the deep magnetic precursors for each. The strongest of their examples occurred Oct. 26, 2003. The next step is to look at a large number of sunspot outbreaks to see how consistently the precursor signals the team identified show up.

In addition to the Paul Revere-like "sunspots are coming" data SOHO provide, the team also says it's possible to estimate the intensity of a sunspot outbreak from the speed with which the magnetic fields responsible migrate up from deep in the sun.

Once an active region spawns a coronal-mass ejection, observations pioneered by Dr. DeForest's team could take over. The team used visible images from one of NASA's two STEREO spacecraft. The STEREO mission involves a pair of sun-watching orbiters traveling in opposite directions around the star but at the same distance as Earth.

Using new signal-processing techniques, the team was able to catch the full trip and evolution of a coronal-mass ejection by capturing the vanishingly faint sunlight that in effect glints off of the particles themselves.

Early in its travels, the massive cloud is dense and relatively compact, making it easy to see. But after it travels about 20 percent of the distance from the sun to Earth the cloud grows diffuse. By the time it reaches Earth three days later, it can arrive "as a 50-million-mile-tall wall of plasma," DeForest says.

As it travels, the plasma's interaction with the sun's extended magnetic field alters the cloud's shape and creates voids, filaments, and other features that make it increasingly difficult to detect.

DeForest's team used innovative image-processing techniques to tease out the light from the cloud. By the time the cloud reaches Earth, the light it reflects is about 10 billion times fainter than the light of a full moon, and some 10,000 times fainter than the stars within the spacecraft's field of view, but because of the way they processed the images they were able to see it.

The team, which described its research during a press briefing today, formally published its results recently in the Astrophysical Journal.