Space

First Sighting of Gigantic Energy Buildup Confirms Solar Flare Models

March 27, 2014 | by Janet Fang

Photo credit: The formation of a solar flare, courtesy of NASA/SDO and AIA
 
For the first time, scientists have witnessed the mechanism behind the creation of solar flares, finally confirming the theoretical models of space weather. 
 
“Human civilization is nowadays maintained by technology, and that technology is vulnerable to space weather,” lead author Jaroslav Dudik of University of Cambridge says in a press release. Coronal mass ejections can damage satellites or threaten airlines by disturbing Earth’s magnetic field. And very large flares can even create currents within electricity grids and knock out energy supplies. 
 
Back in 2012, for example, two solar eruptions collided into a superstorm that would have devastated our electronic lives if it happened just 9 days sooner, when the ignition point was aimed at Earth. With this new discovery, researchers are a big step closer to predicting when and where large solar flares will occur. 
 
There’s been a lot of developments theoretically, but scientists have never been able to tie them down with observations of gigantic energy buildups... until now. An international team of researchers put together footage showing how entangled magnetic field lines looping from the Sun’s surface slip around each other, leading up to an explosive release of magnetic energy into space -- an eruption 35 times the size of Earth. 
 
According to the standard 3D model of solar flares, these occur in places where the magnetic field is highly distorted: field lines continuously reconnect while slipping and flipping around each other, creating new magnetic structures. 
 
Long before the flare when magnetic energy levels are low, the non-entangled field lines appear in a smooth arc between two points on the Sun’s visible surface; these are called field line footpoints. Entanglement happens when footpoints move around each other as they’re jostled from below by currents rising and falling beneath the Sun’s surface. As the movement goes on, entangling field lines cause magnetic energy to build up.
 
Imagine twisting a bundle of straight cords. They’ll hold the energy until it becomes too difficult, and at that point, they’ll simply release it, straightening back to the lower energy state. Same with magnetic lines. “You build the stress slowly until a point where they are no longer sustainable. The field lines say they have had enough and ‘ping’, they go back to something simple,” explains study coauthor Helen Mason of Cambridge. That “ping” creates the solar flare and CME. 
 
This theory remained unconfirmed until Dudik reviewed footage created by NASA’s Solar Dynamics Observatory (SDO) satellite mission, which watches the Sun in ultraviolet with the Atmospheric Imaging Assembly (AIA) capturing hi-def images every 12 seconds. He realized that he was watching an ultraviolet dance caused by the magnetic field lines slipping around each other as the footpoints moved around on the surface. During the flare, the highly-ordered footpoint slipping motion is much faster than the random motions that are entangling the field beforehand.
 
 
Finally, some evidence of theory! It also helped that this particular flare was the most energetic kind: an X Class flare that took an hour to reach its maximum. The slipping motion that characterizes the magnetic reconnection may not have been visible with smaller flare. 
 
The work was published in Astrophysical Journal this week. 
 
 
Image: NASA/SDO and AIA via CC BY-NC-SA
 

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