Slipping motion was first reported in coronal loops, not during flares.
"You need the right event," Janvier said. Such an event allows researchers to see not only the field lines but also the intensely heated regions of plasma that follow them, enabling scientists to confirm that what they observe is slipping field lines.
He further explained that spotting such flares requires good observations, where the brightness of the event doesn't overwhelm the event being observed.
"During a flare, the emission is so intense that it is difficult to see the refined structures of loops," Janvier said.
Finally, the events can occur too rapidly for either scientists or their equipment to notice them.
"The slipping motion can be very fast," Dudik said. "In my opinion, it is therefore easy to miss."
The Atmospheric Imaging Assembly (AIA) instrument on board the SDO spacecraft is the only one capable of capturing a video with the full detail required to spot the July 2012 event.
AIA captures an image every 12 seconds, whereas previous instruments, only captured an image every minute. The more-frequent images allow for a closer inspection of the fast-moving events on the surface of the sun, including the slipping motion of magnetic reconnection. In a smaller, less-energetic flare, the reconnecting action could be a greater challenge to spot, even for today's technology.
Speaking of how the the flare confirmed his research predicting the slipping motion, Janvier said, "That made the discovery very exciting, because suddenly what was still theoretical was really happening during flares."
The new paper was published in the Astrophysical Journal.
The dangers of space weather
Solar flares are often linked to powerful explosions of material from the sun known as coronal mass ejections (CMEs). When CMEs are directed toward Earth, they can damage satellites, affect airlines and knock out electricity grids.
Although the CME associated with the 2012 event faced Earth, Jaroslav said it "was a weak one, and therefore posed no threat."
Other CMEs have had more devastating effects. In 1989, a powerful solar flare and the resulting CME damaged a transformer in Canada, leaving over 6 million people without electricity for more than 12 hours.
That storm was only a fraction of the power of the "Carrington event" of 1859. The massive historic flare disrupted global telegraph communications, shocking some telegraph operators and even allowing some machines to run when disconnected from their power supplies.
Although solar flares and CMEs are related, they do not always occur together.
"The CME is a byproduct of the flare, similar to an ash cloud from a volcano, but it is not always present," Janvier said.
Magnetic slipping has only been seen in the most powerful, X-class flares, though it could happen in other, weaker types as well. The scientists intend to continue studying other types of flares for the slipping mechanism.
"It is unknown whether the phenomenon occurs in all flares. It is certainly predicted to be" present in all flares, Dudik said. "But we need to analyze other observations."
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