‘Beauty’ of sunspots revealed by supercomputers

An international team of scientists led by the National Center for Atmospheric Research (NCAR) has created the first-ever comprehensive computer model of sunspots. The resulting images capture the necessary scientific detail but highlight a remarkable, usually unseen beauty.

So far, scientists have determined that sunspots are linked with massive ejections of charged plasma that can cause extremely powerful geomagnetic storms that can disrupt communications and navigational systems.

Sunspots, first studied by Galileo, can also affect weather and influence subtle changes in climate patterns on Earth. Variations in solar output is also attributed to sunspots.

The high-resolution simulations of sunspot pairs will hopefully lead researchers to learn more about the vast mysterious dark patches on the sun's surface.

Scientists leading the research at NCAR and the Max Planck Institute for Solar System Research (MPS) in Germany, have published their findings.

"This is the first time we have a model of an entire sunspot," says lead author Matthias Rempel, a scientist at NCAR's High Altitude Observatory. "If you want to understand all the drivers of Earth's atmospheric system, you have to understand how sunspots emerge and evolve. Our simulations will advance research into the inner workings of the sun as well as connections between solar output and Earth's atmosphere."

"Understanding complexities in the solar magnetic field is key to 'space weather' forecasting," says Richard Behnke of NSF's Division of Atmospheric Sciences. "If we can model sunspots, we may be able to predict them and be better prepared for the potential serious consequences here on Earth of these violent storms on the sun." The sunspot research was supported by the National Science Foundation (NSF).

Outward flows from the center of sunspots were first discovered 100 years. Since then scientists have worked toward explaining their complex structures, whose number peaks and wanes during the 11-year solar cycle.

Before the latest generation of supercomputers, modeling in this detail has been impossible. Now scientists are able to capture the convective flow and movement of energy in the sunspots, which is not directly detectable by instruments.

The work was supported by the National Science Foundation, NCAR's sponsor. The research team improved a computer model, developed at MPS, that built upon numerical codes for magnetized fluids that had been created at the University of Chicago.

How it works

Scientists working on this project have developed new simulations that capture pairs of sunspots with opposite polarity. They reveal the dark central region, or umbra, with brighter umbral dots, as well as webs of elongated narrow filaments with flows of mass streaming away from the spots in the outer penumbral regions.

The authors conclude that there is a unified physical explanation for the structure of sunspots in umbra and penumbra that is the consequence of convection in a magnetic field with varying properties.

The model

The research team designed a virtual, three-dimensional domain that simulates an area on the sun measuring about 31,000 miles by 62,000 miles and about 3,700 miles in depth (which equals an expanse as long as eight times Earth's diameter and as deep as Earth's radius).

The scientists then used a series of equations involving fundamental physical laws of energy transfer, fluid dynamics, magnetic induction and feedback, and other phenomena to simulate sunspot dynamics at 1.8 billion points within the virtual expanse, each spaced about 10 to 20 miles apart. For weeks, they solved the equations on NCAR's new Bluefire supercomputer, an IBM machine that can perform 76 trillion calculations per second.

The accuracy of the modeling was verified by a large network of ground- and space-based instruments.

The new model is far more detailed and realistic than previous simulations that failed to capture the complexities of the outer penumbral region. The researchers noted, however, that even their new model does not accurately capture the lengths of the filaments in parts of the penumbra. This can only be completed when even more computing power is available.

"Advances in supercomputing power are enabling us to close in on some of the most fundamental processes of the sun," says Michael Knoelker, director of NCAR's High Altitude Observatory and a co-author of the paper. "With this breakthrough simulation, an overall comprehensive physical picture is emerging for everything that observers have associated with the appearance, formation, dynamics, and the decay of sunspots on the sun's surface."