Solar phenomena like sunspots and flares could be a product of a shallow magnetic field, according to surprising new findings that may help scientists predict space weather.
The sun’s surface dazzles with sunspots and flares, products of a solar magnetic field created by a mechanism known as dynamo action. Traditionally, astrophysicists believed that this magnetic field formed deep within the star. However, a study by
If the sun’s magnetic field does in fact arise from its outermost layers, this might give scientists a better chance at forecasting flares and geomagnetic storms that have the potential to damage satellites and telecommunications systems.
“We know the dynamo acts like a giant clock with many complex interacting parts,” says co-author Geoffrey Vasil, a researcher at the University of Edinburgh. “But we don’t know many of the pieces or how they fit together. This new idea of how the solar dynamo starts is essential to understanding and predicting it.”
The study’s co-authors also include Daniel Lecoanet and Kyle Augustson of
Rather than simulating the complex flow of plasma throughout the entire body of the sun, Burns and his colleagues wondered whether studying the stability of plasma flow near the surface might be enough to explain the origins of the dynamo process.
To explore this idea, the team first used data from the field of “helioseismology,” where scientists use observed vibrations on the sun’s surface to determine the average structure and flow of plasma beneath the surface.
“If you take a video of a drum and watch how it vibrates in slow motion, you can work out the drumhead’s shape and stiffness from the vibrational modes,” Burns says. “Similarly, we can use vibrations that we see on the solar surface to infer the average structure on the inside.”
Solar Onion
For their new study, the researchers collected models of the sun’s structure from helioseismic observations. “These average flows look sort like an onion, with different layers of plasma rotating past each other,” Burns explains. “Then we ask: Are there perturbations, or tiny changes in the flow of plasma, that we could superimpose on top of this average structure, that might grow to cause the sun’s magnetic field?”
To look for such patterns, the team utilized the Dedalus Project — a numerical framework that Burns developed that can simulate many types of fluid flows with high precision. The code has been applied to a wide range of problems, from modeling the dynamics inside individual cells, to ocean and atmospheric circulations.
“My collaborators have been thinking about the solar magnetism problem for years, and the capabilities of Dedalus have now reached the point where we could address it,” Burns says.
The team developed algorithms that they incorporated into Dedalus to find self-reinforcing changes in the sun’s average surface flows. The algorithm discovered new patterns that could grow and result in realistic solar activity. In particular, the team found patterns that match the locations and timescales of sunspots that have been have observed by astronomers since Galileo in 1612.
Sunspots are transient features on the surface of the sun that are thought to be shaped by the sun’s magnetic field. These relatively cooler regions appear as dark spots in relation to the rest of the sun’s white-hot surface. Astronomers have long observed that sunspots occur in a cyclical pattern, growing and receding every 11 years, and generally gravitating around the equator, rather than near the poles.
In the team’s simulations, they found that certain changes in the flow of plasma, within just the top 5 to 10 percent of the sun’s surface layers, were enough to generate magnetic structures in the same regions. In contrast, changes in deeper layers produce less realistic solar fields that are concentrated near the poles, rather than near the equator.
The team was motivated to take a closer look at flow patterns near the surface as conditions there resembled the unstable plasma flows in entirely different systems: the accretion disks around black holes. Accretion disks are massive disks of gas and stellar dust that rotate in towards a