Researchers predict that the next sunspot cycle will be much stronger than the last one, potentially causing more intense solar storms that disrupt electrical activity on Earth. The scientists made their forecast based on a new computer model they say will help societies plan for such disturbances far ahead of time.
As peaceful as the sun appears, it is really a ball of hot, churning gases. Scientists believe that turbulent gas flows below the surface of the sun cause a cycle of magnetic activity that grows and subsides over 11-year periods. When the sun's magnetic activity is at its peak, sunspots are numerous and solar storms are generally most intense, spewing out billions of tons of electrically charged particles toward Earth that can cause electrical blackouts and the failure of communications networks and satellites.
Scientists at the U.S. National Center for Atmospheric Research developed a computer model of the sun that follows its gas flows. They used telescopes to observe the growth, speed and trail of sunspots, areas of the strongest magnetism that track the gas movement beneath.
Center researcher Mausumi Dikpati says the computer model, combined with data about previous solar cycles, allows the first forecast of when and how strong the next solar cycle will be.
"We predict that the next solar cycle will be 30 to 50 percent stronger than the last cycle," she said. "Our model also predicted that the onset of the next cycle will be delayed by six to 12 months to late 2007 or early 2008."
Dikpati says her team's solar sunspot model simulated the strength of the past eight solar cycles with more than 98 percent accuracy, giving them a great deal of confidence in it as a forecasting tool.
Scientists have never been able to accurately predict the timing or intensity of maximum solar activity before. NASA sun researcher David Hathaway calls the new work exciting.
"First of all, it is based on sound physical principles, and secondly, it finally answers the 150-year-old question of what causes the 11-year sunspot cycle," added Hathaway.
The U.S. governments' chief solar storm forecaster, Joseph Kunches of the National Oceanic and Atmospheric Administration, says the findings will help his agency better advise operators of satellites, communications networks, and electrical power grids to anticipate the onslaught of charged solar particles that will require them to protect their systems.
"It's going to help us answer some very difficult questions that users of space weather systems ask us all the time," he noted. "You can think of this sort of like hurricane season forecasting. The kinds of questions posed to hurricane forecasters also come to us in terms of space weather - when is the next cycle going to start, how strong will it be, what are the effects going to be?"
Solar activity is currently at a low level in the 11-year cycle, with the last peak in 2001. David Hathaway of NASA agrees that the next period of high intensity will be significantly stronger. But he disagrees on the timing, suggesting that sunspot activity will pick up late this year or early next rather than late 2007 or early 2008.
"We have found that large cycles usually start early, and at this point we are anxiously awaiting the appearance of those first spots from the new cycle," he noted.
Even if Mausumi Dikpati is correct about when the solar cycle intensifies, her computer model does not predict specific solar storms linked to that intensity. In fact, huge storms can occur during periods of minimum intensity like we are in now, although the likelihood is less. Atmospheric researcher Richard Behnke of the U.S. National Science Foundation near Washington says the real need is for tools to forecast solar storms hours or even days ahead.
"So what we're working on with these models is individual forecasts of particular storms," said Behnke. "That would be what we're really pressed to look at now."