Solar heartbeat

A magnetic “solar heartbeat” beats deep in the sun’s interior, generating energy that leads to solar flares and sunspots.

The sun’s periodic magnetic field reversals. Every 40 years, according to the model, the sun’s zonal magnetic field bands switch their orientation, or polarity.

That cycle is about four times longer than the 11-year sunspot cycle that governs the level of solar activity. Being able to model such a regular, long-term process is remarkable.

magnetic-fields-solar-maximum

Dissipating turbulence

Modeling the sun has been a sticky problem for decades. The first attempts in the 1980s captured only a rough approximation of the turbulence inside of the sun.

Turbulence, when it occurs, happens at both large and small scales. The large scales are easy to simulate, but in the sun, a small feature only about tens of miles across is just as important in understanding how fluid propagates.

When energy from turbulence dissipates, the turbulence flows into smaller and smaller whirlpool shapes, called vortices. You can see this for yourself, Charbonneau said, when swirling your hand in a full bathtub. The movement will produce a vortex in the water that will gradually break up into tinier ones that dissipate the energy.

On the sun, dissipation takes place at a scale of tens of yards. That’s extremely minute, compared with the size of the sun which is 1 million times larger than Earth. “There’s no way we can capture that in a simulation.

To approximate this process, scientists typically limit the resolution to about 6.2 miles (10 kilometers). This, however, creates an energy buildup in the simulation that will “blow up” the model before it can run for very long.

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Studying the sun’s brightness

Several science groups are now trying to model brightness changes in the sun. It’s been known for years that the sun is brighter when it’s more active.

The sun produces more dark sunspots during that time — which dim it somewhat — but it also creates small magnetic structures that brighten the surface.

How these structures form is still under investigation. Charbonneau and his team are examining how the magnetic field on the sun affects the transport of energy from the inside to the outside.

“There’s a link between convective energy transport and the magnetic cycle, and you can measure that through going through the simulation and pulling out the flows, the primary variables.

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