New Study Reveals Clearer Picture of Sun's Inner Motions

NASA scientists have developed what they say is a more accurate model of how the Sun's writhing insides move from equator to pole and back again, paving the way to more precise predictions regarding the intensity of solar cycles.

Using the Solar Dynamics Observatory (SDO), a team of researchers show that, rather than a straightforward cycle of flow moving toward the poles and then back to the equator, the material instead creates a double layer of circulation in which two such cycles are layered on top of each other.

"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 HMI at Stanford University in Stanford, Calif. "We mapped out what we believed to be the flow pattern in the 1990s, but the results didn't quite make sense."

Researchers made the discovery using the SDO's Helioseismic and Magnetic Imager (HMI), which, unlike its predecessors, observes the Sun throughout the year and with 16 times more detail. In all, the researchers examined two years' worth of HMI data to come up with the new model that helped identify the long-sought equatorward flow inside the sun.

Specifically, the scientists found that while the flow toward the poles does in fact occur near the Sun's surface, the equatorward flow isn't relegated to the bottom. Rather, the study suggests, the material seeps back toward the equator through the middle of the convection layer. Meanwhile, deep inside the layer is a second stream of material moving toward the poles. The scientists have named the resulting model 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 in reference to the Sun's ever-changing magnetic current. "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."

Going forward, the researchers will determine whether these new models agree with the observations seen on the Sun and in what way it improves researchers' understanding of the constant dance of magnetism being played out on the Sun's surface.