This is according to a study by researchers at the National Center for Atmospheric Research in the USA, who sought to find out why the sun was quiet for too long and only recently began to wake up
A new analysis of the longer than usual solar cycle that ended in 2008 indicates that one of the reasons for the cycle time could be the stretching of the solar conveyor belt, a stream of plasma that circulates between its equator and the poles. The results should help scientists better understand the factors that control the timing of solar cycles could lead to better predictions.
The study was conducted by Mausumi Dicapati, Peter Gilman, and Juliana De Toma, all of the National Center for Atmospheric Research (NCAR) High Latitude Observatory, and by Roger Ulrich of the University of California, Los Angeles. The article was published July 30 in Geophysical Research Letters.
The sun goes through cycles that last about 11 years, which include phases in which the magnetic activity is increased, more sunspots as well as more solar flares compared to phases in which the activity is less. The level of solar activity can affect navigation and communication systems on Earth. Puzzlingly, solar cycle 23, the one that ended in 2008, lasted longer than previous cycles, with a prolonged phase of low activity that scientists struggled to explain.
NCAR's new analysis suggests that one reason for the long cycle could be changes in the sun's conveyor belt. Just like Earth's global ocean currents that transport water and heat around the Earth, the Sun has a conveyor belt where plasma flows across the surface toward the poles, sinks, and returns toward the equator, carrying the magnetic flux along the way.
"The key to explaining the long duration of cycle 23 using our dynamo model is the observation of an exceptionally long conveyor belt in this cycle," Dikpati says. "The conveyor belt theory holds that shorter bands as observed in cycle 22 should be more common in the Sun."
Recent measurements collected and analyzed by Ulrich and his colleagues show that in solar cycle 23, the poleward flow of plasma did indeed make it all the way to the poles, whereas in the previous solar cycle the equatorward flow stopped at 60 degrees latitude. Moreover, as a result of the law of conservation of mass, the reflow was slower in cycle 23 than in previous cycles.
In their paper DiCapati, Gilman and De Thoma used simulation to model the plasma conveyor belt during the solar cycle. The researchers found that the longer the conveyor belt and the slower the return component, the longer the solar cycle, as in the case of cycle 23.
This study highlights the importance of monitoring and improving the measurement of the solar plasma flow," says Ulrich. "In order to improve predictions of the solar cycle, we need to put a strong effort into understanding the large-scale patterns of plasma motion in the Sun.