Scientists predict solar cycle with “unprecedented” accuracy
and World Science staff
The next cycle of solar storms will be 30-50% stronger than the last one and begin as much as a year late, according to what scientists called a breakthrough forecast system.
The Sun goes through roughly 11-year cycles, from peak storm activity to quiet and back. Scientists have long tracked them without being able to predict their intensity or timing. Solar weather forecasting is far behind Earth weather forecasting in sophistication.
Predicting the Sun’s cycles could help societies plan for active bouts of solar storms, scientists say. These outbursts can shoot streams of particles toward Earth, which can slow satellite orbits, disrupt communications, and bring down power systems, though they don’t harm people on the planet.
For the new forecast, researchers at the National Center for Atmospheric Research in Boulder, Colo., used a newly developed computer model of solar activity. “This is a significant breakthrough with important applications, especially for satellite-dependent sectors of society,” said the center’s Peter Gilman.
In test runs, the newly developed model simulated the strength of the past eight solar cycles with more than 98% accuracy, the researchers said.
The forecasts are generated in part by analyzing sunspots, relatively cool, dark spots on the Sun’s surface associated with violent solar outbursts. The researchers conducted each test forecast by tracking the subsurface movements of the sunspot remnants of the previous two solar cycles.
The team is publishing its future forecast in the current issue of the research journal Geophysical Research Letters.
“Our model has demonstrated the necessary skill to be used as a forecasting tool,” said Mausumi Dikpati, the leader of the forecast team at center’s High Altitude Observatory.
Solar storms are linked to twisted magnetic fields—areas of magnetic activity—in the Sun that suddenly snap and release tremendous amounts of energy. They tend to occur near sunspots, where such fields concentrate.
The computer model, called the Predictive Flux-transport Dynamo Model, draws on research showing that sunspot evolution is caused by a current of plasma, or electrified gas, circulating between the Sun’s equator and its poles over a period of 17 to 22 years. This current acts like a conveyor belt of sunspots, the researchers said.
The sunspot process, they explained, begins with concentrated magnetic fields in a region called the convection zone, the outermost layer of the Sun’s interior. As the fields circulate in the current and approach the Sun’s equator, they become still more concentrated. They are also stretched and twisted by internal rotation in the star.
This eventually causes coiled-up magnetic fields to tear through the surface and create new sunspots, the researchers said.
The researchers drew the conclusions partly by using a relatively new technique, helioseismology, which tracks sound waves reverberating in the Sun to reveal details of its interior. This is similar to the way doctors use ultrasound to see inside patients.
The next solar cycle, known as Cycle 24, will produce sunspots across an area slightly larger than 2.5% of the Sun’s visible surface, the researchers said. They added that it will likely begin in late 2007 or early 2008, which is about 6 to 12 months later than a cycle would normally start. The cycle would reach its peak about 2012.
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