March 6, 2006 —Solar scientists have pinned down the cause of solar sunspot cycles and are now predicting the onset and intensity of the next surge of sunspot activity.

Researchers announced Monday a new computer model that incorporates the internal circulation patterns of the sun. The model forecasts that the next approximately 11-year solar cycle will be 30 to 50 percent stronger than the last cycle and commence a year late.

It also finally answers the 150-year-old question of what causes the sun's sunspot cycles.

"For the first time we can predict the strength of the 11-year solar activity cycle," said solar scientist Mausumi Dikpati of the High Altitude Observatory Division of the National Center for Atmospheric Research in Boulder, Colo.

Dikpati developed the model and spoke with reporters via teleconference. A paper describing the new sunspot forecast model also appears in the current issue of Geophysical Research Letters.

Dikpati's model treats about half of the sun's upper depths almost like circulating water, only with the added twist of it being magnetic plasma. The spinning of the sun moves the plasma at the sun's equator more quickly than the plasma at higher latitudes, causing something like magnetic eddies in the sun's mid-latitudes, where most sunspots are seen.

These eddies are then folded into deeper north-south currents that cycle into the sun's depths and move the magnetic eddies toward the poles. Deeper inside the sun the magnetic eddies then move toward the equator, altering magnetic polarity of the entire sun and serving as seeds for future sunspots.

The total recycling time of the magnetic eddy is about 22 years, or two solar cycles.

"This is the memory of its past magnetic fields," said Dikpati of the sunspot activity seen in each cycle.

"We're very excited about this work," said Joe Kunches, chief space weather forecaster at the Space Environment Center, operated by the National Oceanic and Atmospheric Administration.

"It will answer questions that users of space weather forecasting ask us all the time," he said, such as when will the next solar cycle begin, how strong will it be and how long will it last.

Space weather forecasts users include satellites operators and radio airlines and others requiring radio communications over the poles, GPS users and NASA. NASA needs to keep astronauts out of harm's way when sunspots are blasting near-Earth space with high doses of X-rays, heavy particle radiation and high-energy electrons.

NASA solar scientists also welcome Dikpati's model, but they are not certain she has the timing of the next solar cycle right, says David Hathaway of NASA's Marshall Space Flight Center.

"I'm really excited about this one," Hathaway. This behavior has been difficult to reproduce with other models, he said, adding that they agree with Dikpati's prediction of a 30 to 50 percent increasing in the next cycle. "But we disagree with her timing."

Hathaway points to other very active solar cycles of the past and notes that they get moving quickly, not a year late as Dikpati is expecting. Hathaway and his colleagues, on the other hand, expect the sun will begin ramping up sunspots as early as this year, he said.

The two opinions could make this next solar cycle one of the most closely watched ever.