SOHO Consortium/ESA/NASA

False security? Even magnetic storms launched from the solar poles, like this one seen in 2000, can threaten Earth.

The Sun Can Lob Curveballs

Sandy Koufax has a solar equivalent. The great former Brooklyn and Los Angeles Dodgers pitcher was famous for his ferocious curveball. Now scientists have discovered that powerful bursts of magnetism emanating from sunspots near the poles of the sun can be arced back toward Earth by the solar magnetic field. The finding creates another potential headache for people who run or rely on GPS satellites, telecommunications networks, and power grids, but it also means more reliable warnings about these electromagnetic disturbances.

The sun's coronal mass ejections (CMEs) are of more than just scientific interest. When these gigantic bursts of electrically charged, extremely hot gas particles hit satellites, they can disrupt TV and radio transmissions, GPS signals, and cell phone calls. They can also overload electric power grids on the ground and pose a radiation hazard for astronauts in orbit. One recent U.S. National Academy of Sciences study of the potential hazards from a major CME hitting Earth estimated that the damage could total more than a trillion dollars and require up to 10 years to repair. Scientists have spent years attempting to track CMEs and provide enough warning to allow precautions, such as placing satellites in temporary safe modes.

So an international team analyzing data from NASA's twin STEREO spacecrafts, which provide three-dimensional observations of solar activity, made an important discovery when they noticed something that had been predicted but never observed: CMEs launched into space from the sun's high latitudes following trajectories that brought them back toward the solar system's equatorial plane—where Earth resides. "We were really surprised and thought something might be wrong with our algorithms," says solar physicist Peter Gallagher of Trinity College Dublin.

Further analyses revealed, however, that the curving solar storm tracks were accurate. CMEs emerging from sunspots located at latitudes of 60˚ or higher, north and south, can have their tracks bent by the sun's magnetic field and pushed out toward the planets by the 500-kilometer-per-second solar wind. Gallagher and colleagues report this week in Nature Communications that the magnetic fields of CMEs also affect their trajectories. These fields tend to rotate, and their rotation can either sharpen the curve of the trajectory or flatten it out, depending on whether the CME is traveling slower or faster than the solar wind at the moment. The result is that, just like the breaking curveballs by a Major League pitcher, the bent tracks of CMEs can vary.

Gallagher, who used to compile solar-activity warnings for NASA, says the findings mean that space-weather forecasters need to watch high-latitude ejections more carefully. The normal reaction when CMEs emerge from the polar regions has been to think "that they're going to miss us." The new data show that isn't the case.

The imaging process the researchers have developed to track CMEs is "quite innovative,” says Madhulika Guhathakurta, a solar physicist with NASA's STEREO mission in Washington, D.C. The ability to track even curving CMEs through space "is of great benefit to forecasters of space weather," adds Guhathakurta, who was not involved in the research.

The researchers have "clearly shown that [solar] storms launched initially at high latitudes can still affect us at Earth," says solar physicist William Thompson, a contractor for the STEREO mission at NASA's Goddard Space Flight center in Greenbelt, Maryland. Thompson adds that although scientists have long known solar storms can change directions while close to the sun, "it was surprising to find that this can still be the case farther along [in their] journey."

Posted in Physics