Solar flares can happen at any time and are difficult to predict, but a solar physicist at NASA’s Marshall Space Flight Center in Huntsville, Ala., has devised a better way to predict their frequency.
Every 11 years, the Sun spawns a flurry of sunspots, solar flares and other explosive events -- the result of cyclical shifts in the gaseous orb’s magnetic field. Such events can happen any time in the Sun’s 11-year cycle, which is akin to Earth’s year. But at the peak of the cycle, called "solar maximum" or "solar max," they’re particularly plentiful.
Using a new forecasting technique, Dr. David Hathaway, leader of the Marshall Center’s solar physics group, predicts "this cycle looks like it’s going to be bigger than average, but probably similar to the last two cycles or perhaps slightly smaller," he said.
Scientists have been watching and charting the Sun’s explosive activity since Galileo invented the telescope in the early 1600s. But while they’ve been able to followthe 11-year cycle, they’ve had little success predicting a cycle’s month-to-month intensity in terms of the number of sunspots. The sunspots are the precursors to solar flares and other events.
"If you look at it from day to day, the Sun’s activity fluctuates wildly over the course of a month," Hathaway said. "If you look at the monthly values, they fluctuate wildly, as well."
Prior to the Space Age, the most visible effect of solar activity was the showy aurora borealis, or Northern Lights, Hathaway said. "Because we’re more dependent on technology now -- in particular as we venture into space – it’s more important for us to understand solar activity and predict it reliably so people can take the necessary precautions."
For instance, during the solar max of 1989, such a "solar power surge" damaged transformers of the Hydro-Quebec power system, leaving 6 million people in Canada and the Northeast United States powerless for more than nine hours.
Scientists have worked for decades with dozens of prediction techniques, focusing on two methods to forecast sunspots: long-term predictions for the size of the next cycle and month-to-month forecasts within a given cycle. At best, their results have been mediocre. The long-term predictions, called precursor methods, only forecast a cycle’s general intensity. And the month-to-month forecasts were accurate only in the middle of a cycle.
Hathaway analyzed scores of techniques, combining the best of both methods. He took two precursor methods that generally scored much better than others and usually had offsetting errors, and combined them into a weighted value. These values were then used with a bell curve of monthly sunspot activity. When he aligned the low points of the curve with low points of the current solar activity cycle, he found the results were better than expected.
"Three out of the last four months have been right on what we have predicted," he said.
Hathaway predicts solar max 2000 will reach its peak in mid to late 2000, but high levels of activity will continue well into 2001. "The sunspot maximum is usually a broad peak," he said. "There is a two- or three-year period when activity is quite high." Still, he said, solar max 2000 will be "no record-breaker."
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