New method detects emerging sunspots deep inside the sun, provides warning of dangerous solar flares
Researchers at Stanford University have developed a way to detect incipient sunspots as deep as 65,000 kilometers inside the sun, providing up to two days’ advance warning of a damaging solar flare.
The key to the new method is using acoustic waves generated inside the sun by the turbulent motion of plasma and gases in constant motion. In the near-surface region, small-scale convection cells —about the size of California — generate sound waves that travel to the interior of the sun and are refracted back to the surface.
The researchers got help from the Michelson Doppler Imager aboard NASA’s Solar and Heliospheric Observatory satellite, known as SOHO. The craft spent 15 years making detailed observations of the sound waves within the sun. It was superseded in 2010 with the launch of NASA’s Solar Dynamics Observatory satellite, which carries the Helioseismic and Magnetic Imager.
“We know enough about the structure of the sun that we can predict the travel path and travel time of an acoustic wave as it propagates through the interior of the sun,” said Junwei Zha, senior research scientist. ”Travel times get perturbed if there are magnetic fields located along the wave’s travel path.”
By measuring and comparing millions of pairs of points and the travel times between them, the researchers are able to home in on the anomalies that reveal the growing presence of magnetic flux associated with an incipient sunspot.
They found that sunspots that ultimately become large rise up to the surface more quickly than ones that stay small. The larger sunspots are the ones that spawn the biggest disruptions, and for those the warning time is roughly a day. The smaller ones can be found up to two days before they reach the surface.
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