For the first time, a massive solar flare revealed the process that created it, confirming new theories about flares and the explosive ejections of solar material often linked with them, a new study reports.
Understanding how solar flares form brings scientists a step closer to predicting them, along with the dangerous space weather that has the power to damage satellites and power grids on Earth, researchers said.
Captured by NASA's Solar Dynamics Observatory (SDO) spacecraft, the massive solar flare occurred on July 12, 2012 — less than a week after the publication of a new 3D model that suggested similar flares are driven by a process known as slipping reconnection, in which magnetic field lines disconnect and reconnect. [The Sun's Wrath: Worst Solar Storms in History]
"The 2D standard solar flare model captures much of the physics involved, but has the inherent limitation of being a 2D model," said study lead author Jaroslav Dudik of the University of Cambridge. "There can be no slipping reconnection in a 2D model, since it is missing the third dimension, in which the slipping motion occurs."
Bright Lights on the Sun
Solar flares — very intense brightenings of the sun's atmosphere — occur throughout the sun's 11-year activity cycle, with their frequency increasing as the cycle peaks, as it did around the 2012 event.
Flares are classified by the peak X-ray flux measured at Earth. Smaller C- and M-class flares are far more numerous, with dozens of C-class flares sometimes occurring daily during solar maximum, Dudik said.
But the most energetic type — X-class flares, like the July 12, 2012 event — are far more rare, occurring at a frequency of at most a few per month. In addition to being 35 times the size of Earth, the July 2012 flare lasted more than 12 hours, a duration that Dudik calls "somewhat unusual." [Anatomy of Sun Storms & Solar Flares (Infographic)]
In a study published less than a week before the event, a team led by Miho Janvier of the United Kingdom's University of Dundee provided a 3D simulation that showed how distortions in the sun's magnetic field can lead to solar flares.
"We have extended in 3D the standard model of solar flares that has been, and still is, used to explain solar eruptive flares," Janvier told Space.com by email regarding his earlier research. "All in all, we are just completing pieces of the puzzle."
Janvier also served as an author on Dudik's research examining the explosive flare. This was the first time the slipping motion had been seen in a solar flare.
Scientists can't observe the sun's magnetic field lines directly, because they are theoretical lines of force.
"However, it is possible to trace them with the material trapped in the magnetic field, similar to iron fillings you can put near a magnet," Janvier said. "One can observe the evolution of the solar corona's magnetic field by looking at the motion of the plasma trapped in the magnetic field."
Magnetic field lines on the sun start off smooth, stretching between two points on the visible surface known as field line footprints. As powerful convection currents rise and fall beneath them, the footprints move about, causing the field lines to twist and entangle in regions known as flux ropes.
Energy begins to build in the flux ropes until the lines snap and the energy is released, creating a solar flare and sometimes launching super-hot plasma into space. With their energy gone, the magnetic field lines return to straight, low-energy states.