Sun activity rises and falls in an 11-year-long cycle, such as this cycle from top left taken in early 1997 to bottom right, taken in early 2000.
Credit: NASA
SYDNEY: After a long silence, the Sun erupted in an unusual pattern of small solar flares, said an Australian astrophysicist, which may provide a unique opportunity to predict when bigger solar flares will erupt.
Solar flares are explosions in the Sun's atmosphere marked by a burst of X-rays. They increase or decrease in a roughly 11-year cycle — larger flares can reach tens of millions of degrees Celsius and interfere with communications satellites and affect astronauts' health.
The Sun has recently been in a calm phase — a solar minimum — which was the longest and quietest minimum since early last century.
Puzzling small flares in 2009
As it now moves into a new cycle, a flurry of rapid, small solar flares that occurred between October and November 2009 has puzzled astrophysicists who study the pattern of flares in order to predict their distribution.
Australian astrophysicist Mike Wheatland from the University of Sydney examined X-ray data of the unusual flares from the GOES (Geostationary Operational Environmental Satellite) system. The results will be published in an upcoming issue of The Astrophysical Journal.
He says what made the event unusual was the fact that the region was very small and yet solar flare intensive, with 73 flares occurring within one week. "And this region did not follow an observed rule," he adds.
Predicting sunspots is "like reading tea leaves"
"It was punching well above its weight in terms of production. It produced too many small flares and too few large flares," Wheatland says.
Wheatland says the observations could help to improve predictive models that forecast the energy of flares in active solar regions. Larger flares can interrupt radar and communications systems. Predicting when and where solar flares will occur is problematic, however.
"Unfortunately the prediction methods are statistical, and not entirely reliable — it is somewhat like reading tea leaves," Wheatland says.
Because the rest of the Sun was unusually quiet during his latest event, Wheatland was able to constrain the amount of energy that the region produced during the event. The result from this small region could then be 'scaled up' to test prediction models at larger scales, he says.
"Every active region produces flares in the same way," Wheatleand says.
Small region helps predict larger regions
"If you can see an upper limit then you've got a constraint on the total energy that's in that region. That's something we've not been able to do before."
Space weather physicist Phil Wilkinson, assistant director of the Australian Government's IPS (Ionospheric Prediction Service) Radio and Space Services, said it was an "interesting way of looking at the problem" of predicting solar flares and "had potential".
"We've tried all sorts of ways to get a measure of flare prediction and it's evasive," he said.
Ionosphere quiet for a few years
"There are not too many options in asking the question of when and where [a solar flare will next occur]."
He said the current "low" cycle meant that the ionosphere would be relatively quiet for the next few years, which is good news for spacecraft, but that didn't rule out the possibility of a big storm.
"It's rare to get one little region busily flaring and nothing else. It could mean we are looking at a very long, slow increase [in solar activity]," he said.
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