Supercomputers Give Inside Look at Sunspots
The simulation shows the interface between a sunspot's umbra (dark center) and penumbra (outer region) shows a complex structure with narrow, almost horizontal (lighter to white) filaments embedded in a background with more vertical (darker to black) magnetic field.
Credit: UCAR/ Matthias Rempel, NCAR

The inner workings of sunspots ?those dark blotches that mark intense magnetic activity on the sun's surface ? have long been a mystery, but a new computer simulation is providing a more realistic look inside them.

Understanding the complex dynamics that drive sunspots could help scientists better understand and predict the potential impacts on communications systems and climate patterns of the geomagnetic storms produced by these solar blights.

"This is the first time we have a model of an entire sunspot," said one of the scientists who helped create the simulation, Matthias Rempel of the National Center for Atmospheric Research (NCAR) in Boulder, Colo. "If you want to understand all the drivers of Earth's atmospheric system, you have to understand how sunspots emerge and evolve."

Sunspots are areas where intense magnetic activity acts like a cap on the roiling material below. These splotches appear darker than the surrounding surface because they are cooler ? around 7,000 degrees Fahrenheit (4,000 Celsius) versus 10,000 F (5,500 C).

Solar flares and coronal mass ejections are typically found in magnetically active regions around groupings of sunspots. These plasma storms can buffet the Earth's atmosphere and disrupt power grids, satellites and other systems.

Sunspot activity peaks and wanes on a roughly 11-year cycle. That cycle is currently in its low period, so there now are few sunspots and little solar activity.

The new model simulates an area on the sun of about 31,000 by 62,000 miles (50,000 by 100,000 km) and 3,700 miles (6,000 km) in depth; within this area, the simulation captures pairs of sunspots with opposite magnetic polarity. The model reveals the details of the dark central region, or umbra, as well as the narrow filaments of mass that stream away from the spots in the outer, or penumbral, regions of the sunspot.

The simulations suggest that the magnetic fields within the sunspots need to be inclined in certain directions to create these complex structures. Rempel and his colleagues think that sunspot features can be explained as a consequence of convection in a magnetic field.

"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," said Michael Knoelker, also of NCAR.

The model was run on NCAR's new bluefire supercomputer ?and verified with the detailed observations made by ground- and space-based telescopes.

The research, detailed in the June 19 online issue of the journal Science, was funded by the National Science Foundation.

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