A new computer model which accurately simulates the Sun's past few solar cycles predicts that the next cycle will be up to 50 percent stronger than its predecessor and begin a year later than expected, scientists announced Monday.
The National Center for Atmospheric Research's (NCAR) Mausumi Dikpati and colleagues developed the model, which is detailed in the March 3 issue of Geophysical Research Letters, and announced their findings in a press conference today.
The model offers a possible solution to the 150-year-old mystery of what's behind the Sun's approximately 11-year cycle of activity. It could also lead to better planning for space weather, such as solar flares and coronal mass ejections, which can disrupt navigation and power systems and threaten astronauts in space.
The next cycle
The Sun goes through approximately 11-year cycles that range from peak activity to quiet and back again. We are near the low point of the current cycle.
Scientists have tracked the cycles for decades but have been unable to predict when their durations and intensity.
The new model, known as the Predictive Flux-transport Dynamo Model, has simulated the strength of the past eight solar cycles extending back to the early 1900s with 98 percent accuracy.
Using the model, researchers predict that the next solar cycle, known as Cycle 24, will produce sunspots across an area slightly larger than 2.5 percent of the visible surface of the Sun. They also expect that the cycle will begin in late 2007 or early 2008--about six to 12 months later than earlier predictions--and reach its peak in 2012.
The researchers attribute the accuracy of the new model to recent observations of how currents of electrical gas called plasma circulate between the Sun's equator and its pole, and how these currents are affected by the Sun's rotation.
Birth of a sunspot
The birth of a new sunspot begins with the death of an old one from a previous cycle. As an old sunspot decays, it leaves a magnetic "imprint" or signature on the flow of plasma moving between the Sun's equator and its poles.
As the plasma current approaches the poles, it sinks about 124,000 miles (200,000 kilometers) down into the Sun's interior and starts its return journey back to the equator.
These subsurface plasma flows have been verified with observations from NASA's Solar and Heliospheric Observatory (SOHO), which uses sound waves inside the Sun to reveal details about its interior.
Observations show that as the plasma currents move, they are affected by the Sun's rotation. Unlike the Earth, the Sun's equator moves more rapidly than its poles.
This differential rotation stretches and twists the moving plasma current, making it more unstable than surrounding plasma. Eventually, the warped plasma currents rise up and tear through the Sun's surface, creating a new sunspot. When the new sunspots begin to decay, the cycle begins anew.
David Hathaway, a NASA solar astronomer who was not involved in the study, said he is excited about the new model.
"It's based on sound physical principals and it finally answers the 150-year-old question of what causes the 11-year sun spot cycle," Hathaway said.
Hathaway's team agrees with Dikpati that Cycle 24 will be stronger than the last one, but disputes the claim that it will occur later than expected.
After reviewing the previous 12 solar cycles, Hathaway's team believes large cycles usually start early and that Cycle 24 will start sometime later this year or early next year.
The new predictions could mean that Earth could experience more intense solar flares and related space weather in upcoming years.
"This prediction suggests we're potentially looking at more communications and navigation disruptions, more satellite failures, possible disruptions of electrical grids and blackouts and more dangerous conditions for astronauts," said Richard Behnke, program director of the National Science Foundation's division of atmospheric sciences, which funded the research.
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