Astronauts, power grid operators, and satellite managers had better watch out come 2012. Based on a computer simulation of the sun's interior, solar scientists warned today that in 6 years the activity of dark spots on the surface will, with a single exception, be greater than it has been at any point since 1880. The accompanying solar storms could play havoc with satellite communications and threaten space station astronauts.
The key to an accurate prediction of solar activity is the realization that the sun's magnetic memory extends back not just one but up to three 11-year sunspot cycles, say solar physicists Mausumi Dikpati, Peter Gilman, and Giuliana de Toma of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. Predictions based on just the present strength of the magnetic field near the sun's poles--that is, the lingering remnants of the previous cycle's sunspots--call for an especially weak sun spot cycle.
But the NCAR researchers ran their new model of the solar interior fed with observations since 1880 to see how far back past cycles influence the coming one. They found that it takes roughly 20 years for the magnetic remnants of past sunspots to recirculate deep into the interior, to be amplified by the twisting action of the sun's rotation, and to rise back to the surface near the equator as the next cycle's sun spots. Given the model's impressively accurate "hindcasting" of the size and timing of past cycles, Dikpati told a media teleconference today that she is confident "predicting the next solar cycle will be 30% to 50% stronger than the last solar cycle." The next cycle will begin 6 to 12 months later than average, in late 2007 or early 2008, according to the model, and peak in 2012.
The model-based prediction "is exciting stuff, the first new thing to come along" in decades, says Ernest Hildner, the recently retired director of the Space Environment Center in Boulder, the federal group charged with forecasting solar activity. It's especially exhilarating, solar astronomer David Hathaway of NASA's Marshall Space Flight Center in Huntsville, Alabama, told the teleconference, because "it finally answers the 150-year-old question: What causes the sunspot cycle?"
If the sun is gearing up for an especially active maximum, managers of everything from the global positioning system--which solar storms can disrupt--to low-orbiting satellites--which storms can drag down--could begin taking the threat into account. But exciting as the forecast is, other promising techniques have failed their first test predicting the future, says Hildner: "You still have to wait and see."