For decades, experts have searched for signs in the sun that could lead
to more accurate forecasts of solar flares — powerful blasts of energy
that can supercharge Earth's upper atmosphere and disrupt satellites and
the land-based technologies on which modern societies depend. Now a
scientist at NOAA's Space Weather Prediction Center and her colleagues
have found a technique for predicting solar flares two to three days in
advance with unprecedented accuracy.
The long-sought clue to prediction lies in changes in twisting magnetic
fields beneath the surface of the sun in the days leading up to a flare,
according to the authors. The findings will be published in
"Astrophysical Journal Letters" next month.
"For the first time, we can tell two to three days in advance when and
where a solar flare will occur and how large it will be," said lead
author Alysha Reinard, a solar physicist at NOAA's Space Weather
Prediction Center and the Cooperative Institute for Research in the
Environmental Sciences, a partnership between NOAA and the University of
Colorado.
The new technique is already twice as accurate as current methods,
according to the authors, and that number is expected to improve as they
refine their work over the next few years. With this technique, reliable
watches and warnings should be possible before the next solar sunspot
maximum, predicted to occur in 2013. Currently, forecasters see complex
sunspot regions and issue alerts that a large flare may erupt, but the
when-and-where eludes them.
Solar flares are sudden bursts of energy and light from sunspots'
magnetic fields. During a flare, photons travel at the speed of light in
all directions through space, arriving at Earth's upper atmosphere—93
million miles from the sun—in just eight minutes.
Almost instantly the photons can affect the high-orbiting satellites of
the Global Positioning System, or GPS, creating timing delays and
skewing positioning signals by as much as half a football field, risking
high-precision agriculture, oil drilling, military and airline
operations, financial transactions, navigation, disaster warnings, and
other critical functions relying on GPS accuracy.
"Two or three days lead time can make the difference between
safeguarding the advanced technologies we depend on every day for our
livelihood and security, and the catastrophic loss of these capabilities
and trillions of dollars in disrupted commerce," said Thomas Bogdan,
director of NOAA's Space Weather Prediction Center.
Reinard and NOAA intern Justin Henthorn of Ohio University pored over
detailed maps of more than 1,000 sunspot groups, called active regions.
The maps were constructed from solar sound-wave data from the National
Science Foundation's Global Oscillation Network Group.
Reinard and Henthorn found the same pattern in region after region:
magnetic twisting that tightened to the breaking point, burst into a
large flare, and vanished. They established that the pattern could be
used as a reliable tool for predicting a solar flare.
"These recurring motions of the magnetic field, playing out unseen
beneath the solar surface, are the clue we've needed to know that a
large flare is coming—and when," said Reinard.
Rudi Komm and Frank Hill of the National Solar Observatory contributed
to the research.
