Data from an instrument on NASA's Solar Dynamics Observatory called the Helioseismic and Magnetic Imager show that, instead of a simple cycle of flow moving toward the poles near the sun's surface and then back to the equator, the material shows a double layer of circulation, NASA reported Wednesday.
The findings may help improve predictions of the intensity of the next solar cycle, scientists said.
"For decades people have known that the solar cycle depends on the poleward flow or material, changing the magnetic fields from one cycle to the next," said Philip Scherrer, principal investigator for the HMI instrument at Stanford University. "We mapped out what we believed to be the flow pattern in the 1990s, but the results didn't quite make sense."
Previous observations had detected material moving from the equators toward the poles within the top 20,000 miles of the sun's surface but the flow back toward the equator from the poles was not detected, leading to the assumption the equator-bound flow was much lower, only occurring at the bottom of the convection layer of the sun that houses these flows, about 125,000 miles down.
"Scientists have used this assumption to describe the solar dynamo," Junwei Zhao, a helioseismologist at Stanford University, said. "And now we have found that it isn't right. The flow patterns we have found are sharply different."
Flow toward the poles does indeed occur in a layer at near the sun's surface, the researchers said, but the return flow to the equator isn't at the bottom. Instead, the material seeps back toward the equator through the middle of the convection layer, while deep down inside the layer is a second stream of material moving toward the poles, making what the scientists refer to as a double-cell system in which two oblong flow systems are stacked on top of each other.
"This has important consequences for modeling the solar dynamo," Zhao said. "We hope our results on the sun's interior flow will provide a new opportunity to study the generation of solar magnetism and solar cycles."