NASA
When you plan a picnic or a hike, you want an accurate weather forecast to warn you of possible storms. If you plan to use your global positioning system (GPS) to chart your course, you may want a solar weather forecast, as well. Recent news articles have reported that solar storms can interfere with GPS satellite transmissions. This could be a bit of a problem if you are relying on your car's onboard navigation system to tell you where to turn right. It could be a real problem if you are an airplane pilot trying to locate your position over the Pacific Ocean.
"A solar storm is a stream of charged particles—electrons and protons—that flows from the sun's surface at close to the speed of light," says Chris Palma, outreach fellow in the Penn State astronomy department. "There is a constant flow of charged particles from the sun, but during a solar storm, the intensity can increase immensely. The energy released during such a storm is equivalent to millions of times more than is released during a volcanic eruption on Earth." These particles affect the operation of satellites orbiting Earth, generating radio waves that interfere with the signals that transmit location information from those satellites to your GPS receiver.
What causes a solar storm? "The sun has a magnetic field, similar to that of Earth but a lot more complicated," says Palma. "Because the sun is made of plasma—flowing charged particles—the sun also has many local regions that generate very strong magnetic fields." These smaller fields can be observed from Earth as sunspots, which, according to Palma, generally occur in pairs and are the "footprint" of the magnetic field as it emerges from beneath the sun's surface. One spot marks the north pole of the field, he explains, and the other marks the south pole. Between these spots, gouts of superhot gas form huge loops out from the surface, following the magnetic field lines the same way that magnetic filings follow the field lines of a bar magnet in a grade-school science experiment.
The real fireworks begin when the direction of these magnetic fields reverses, switching the north and south poles. "These local fields can change almost instantaneously," Palma says. "Then the loop breaks and material is ejected into space at high speed, forming a solar flare, or as astronomers prefer to name it, a coronal mass ejection (CME). If this mass of charged particles is ejected toward Earth, we are bombarded with them." It is this bombardment that can momentarily shut down your GPS reception, your cell phone, even your television reception.
Earth's own magnetic field protects us from most solar storms. "The incoming particles are funneled toward the poles by the magnetic field," Palma explains. When they interact with atoms in the upper atmosphere, they form an aurora—a bright glow in the night sky. "Although this is generally a polar phenomenon, during a strong CME, auroras can sometimes be seen from the roof of Davey Lab, here at University Park" In a truly extreme case, a CME can even affect electrical systems on Earth's surface. A major solar storm in 1989 caused a nine-hour power outage in Quebec that affected 6 million people.
Solar storms can also create a problem for humans in space. Although the International Space Station is shielded to protect its residents from these storms, future space flights to the moon or Mars may leave astronauts more vulnerable to them, as the mass of an efficient shield may be too great to be practical on the type of spacecraft needed for these missions.
That brings us to weather forecasting. Although it is not yet possible to tell ahead of time when a CME will occur, we do know they are more common during the periodic reversals of the sun's overall magnetic field, which occur on an eleven year cycle, Palma says. "During these periods, the number of sunspots increases, causing more solar flares. At maximum activity, CMEs are possible as often as a few times a day. If these storm could be predicted, it might be possible to prepare for them and even take actions to reduce their effects." The last maximum activity phase occurred in 2001 and the next is predicted in 2012, he notes.
NASA's Solar and Heliospheric Observatory (SOHO) is a spacecraft designed to learn about the sun's magnetic field. Its goal is to make solar storms as predictable as storms on Earth. As an extra benefit to us, it also provides great photographs of the sun. The SOHO Web site, is updated, close to real time, with current pictures of the sun. It also has an archive of images, movies and slideshows, illustrating sunspots, loops that trace the magnetic fields, and the solar flares that cause storms.
Christopher Palma, Ph.D., is outreach fellow in astronomy in the Eberly College of Science. He can be reached at cxp137@psu.edu.