Solar Seismology Boosts Flare Predictions

Abstract

Predicting when potentially dangerous solar flares will form has always entailed a lot of guesswork. Solar physicists compare active regions of the Sun with what happened after similar activity in the past to come up with forecasts. Now researchers at NOAA's Space Weather Prediction Center, in Boulder, Colo., have designed a new forecasting tool they say is twice as accurate as current methods. Solar flares blast into space highly energetic photons that can damage spacecraft, disrupt communications and navigation signals, and take out power grids on Earth. Government agencies and commercial entities would like as much advance warning as possible so they can take steps to mitigate potential adverse impacts. “Two or three days’ lead time can make the difference between safeguarding the advanced technologies we depend on every day…and the catastrophic loss of these capabilities and trillions of dollars in disrupted commerce,” Thomas Bogdan, director of the Space Weather Prediction Center, said in a statement about the new technique issued by NOAA in January. The new solar flare prediction tool is based on analysis of twisting magnetic fields beneath the surface of the Sun (Figure 1). Using solar seismic data collected from a network of ground stations, researchers initially noticed a region of magnetism that sped up and then suddenly slowed days before a massive flare was emitted. Curious if this was a coincidence, NOAA solar physicist Alysha Reinard began comparing the motions of magnetic fields with subsequent flares. She studied more than 1000 regions and saw a pattern emerge. “You get this faster, twisting motion [in the magnetic field] that then slows down to almost nothing and then the flare,” Reinard said. The reason for the slowdown is that the twisting magnetic field lines reach a point where they can't twist anymore, she explained. They then snap, creating a flare. The energetic difference between turbulence and quiet “tells us how big the flare is going to be,” Reinard added. Using the model, the team was able to accurately predict through hindcast studies between one third and one half of the solar flares that occurred between 2001 and 2007, the period for which the seismic data were available. The technique is being refined to improve the rate of false positives, which currently is about 60%. Researchers hope that real-time space weather forecasts will be possible once NASA's Solar Dynamics Observatory (SDO), a mission to study the Sun's magnetic field and magnetic energy, starts collecting and relaying seismic data full time. SDO launched on 11 February. “The forecasting group is pretty excited about this technique,” Reinard said. “Hopefully we can get to a stage where it's operational soon.” Irene Klotz is a freelance writer for the American Geophysical Union.