Scientists may one day be able to predict dangerous solar flares just one day in advance using a new solar outburst model, a new study finds.
Solar flares are the largest explosions in the solar system. These giant eruptions from the solar corona — the sun's outer atmosphere — can not only prove harmful to astronauts and satellites in orbit, but the plumes of plasma that often accompany them can trigger so-called "geomagnetic storms" that can wreak havoc on Earth. For example, a solar flare blacked out the entire Canadian province of Quebec in 1989, nearly taking down U.S. power grids from the Eastern Seaboard to the Pacific Northwest.
Previous research found that these powerful explosions arise from the sudden release of magnetic energy from areas near-visible sunspots. However, much remains unknown about the specific triggers behind solar flares, which makes them particularly difficult to reliably forecast. Although computer models exist, which can help scientists explore the physics of these eruptions, these models are not useful when it comes to predicting when exactly a flare might happen.
"Flare forecasting is an interesting and very difficult subject, in large part because we have no way to measure magnetic fields in the corona," Astrid Veronig, a solar physicist at the University of Graz in Austria who did not take part in this research, told Space.com.
Scientists have long suspected that an effect known as magnetic reconnection underlies solar flares. This effect takes place when two magnetic regions with differently oriented field lines meet. When this happens, their magnetic field lines can break and reconnect with each other, explosively converting magnetic energy to heat and kinetic energy.
In the new study, researchers in Japan suggested magnetic reconnection can lead sheared magnetic loops to form unstable double-arc magnetic loops, which somewhat resemble the letter "m." As these double-arc instabilities grow, they move upward, shearing other magnetic loops and causing further magnetic reconnection, which, in turn, helps the double-arc magnetic loops to grow and eventually burst as flares.
Assuming that double-arc instabilities do trigger solar explosions, the scientists developed a model to predict when large solar flares might occur based on routine magnetic observations of the sun. The model can also identify where these flares might happen and how much energy they might release.
The researchers tested their model using data on the largest, so-called "X-class" flares, collected using NASA's Solar Dynamics Observatory from 2010 to 2017. Using this data with the model, they were able to identify the location of most large flares up to 24 hours in advance.
Previous methods for predicting large solar flares mostly try to predict the eruptions by looking at magnetic details of the sun's surface, without modeling what is actually happening in the corona to drive a flare, Veronig said. In contrast, this new method "is based on the physics of flares, and seems to identify when and where flares might start," said Veronig.
This model is likely still one or two years away from being applicable to forecasts, Veronig cautioned. To develop this research into a predictive tool comparable to existing techniques, it will have to show that it can accomplish tasks such as automatically checking solar data and making predictions on how likely a flare of a particular strength might occur and where it might happen say, 12 or 24 hours in advance, she said.
There are two large flares for which this model did not account, both of which are not accompanied by huge eruptions of plasma, known as coronal mass ejections. More than 90 percent of all large flares are linked to coronal mass ejections — the flares this model did not account for might have involved magnetic reconnection high up in the corona, or powerful magnetic fields that prevented coronal mass ejections from spewing outward, Veronig said.
"When something doesn't work, like this model when it comes to these two cases, we can still learn something more about the underlying physics involved," Veronig said.
The scientists detailed their findings in the July 31 issue of the journal Science.
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