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Section site map: News |
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NewsA stellar performanceA new model allows far more detailed simulations of convection patterns deep inside the sun. Download a pdf of the print version.
Giant cell convection patterns beneath the surface of the sun, as revealed by the new model. Image by Mark Miesch, NCAR, ©UCAR. From deity to dynamo, the sun has been a source of inspiration and subject of study throughout human history. Thanks to a recently developed computer model, scientists are now able to peer deeper into the inner workings of the sun, which are hidden from any current observational technique. The model can simulate convection patterns in the deep interior of the sun in unprecedented detail. The patterns, known as giant cells, play a critical role in solar variability and influence magnetic storms that can reach all the way to Earth. Juri Toomre, a professor of astrophysics at the University of Colorado (CU) in Boulder, and graduate student Benjamin Brown are studying how stars build magnetic fields to run a so-called "stellar dynamo." They model the sun's magnetism and internal rotation using the Anelastic Spherical Harmonic (ASH) code. ASH is helping scientists investigate the origins of magnetic activity such as sunspots and coronal mass ejections, which can affect airline travel and disrupt satellite and communication systems on Earth. The team's simulations indicate that, at low solar latitudes, cooler and denser plasma sinks along north-south corridors, with corridors moving east relative to hotter plasma that rises. But at higher latitudes, rising and falling areas of plasma meet and create solar cyclones that last for several days. The findings have been submitted to the Astrophysical Journal and were presented at the American Astronomical Society meeting in May. Convection near the surface of the sun occurs as hot plasma rises and cooler, denser plasma sinks. This also happens deep beneath the surface, where scientists now suspect that these giant cells, or churning masses of plasma, may be up to 10 times larger than Earth. The giant cells also induce a global circulation pattern, moving plasma from the solar equator toward the poles near the surface, and then back toward the equator at greater depth. Coupled with convection and rotation, this circulation generates and organizes magnetic fields that cause magnetic activity like the 11-year sunspot cycle.
Snapshot of magnetic fields in an ASH dynamo simulation of a more rapidly rotating sun-like star. Strong, global-scale fields fill the bulk of the convection zone, with opposite toroidal polarities above and below the equator (red positive, blue negative, white neutral; color scale saturates at +- 10kG). This viewpoint, looking outward from the center of the star and encompassing latitudes from +-45 degrees, shows that the fields at the equator have significant connection with the high latitudes. Image courtesy of Benjamin Brown, University of Colorado. According to Mark Miesch, a scientist in the High Altitude Observatory of the National Center for Atmospheric Research (NCAR) who is a member of the ASH team, "stars are the building blocks of the universe, and understanding what goes on within them is critical to understanding diverse aspects of astrophysics. This model opens a window on a number of important solar processes, including the delicate balance of forces that causes the sun's equator to rotate faster than its poles." Miesch and colleagues used supercomputing resources like the TeraGrid to generate simulations of subsurface processes and the sun's unusual rotational pattern. The ASH simulations generate terabytes of data that reside at PSC and SDSC. Moving the data to CU and NCAR, where much of the analysis is being performed, would be a costly proposition. Instead, Brown has been exploring the data remotely using the Visualization and Analysis Platform for Ocean, Atmosphere, and Solar Researchers (VAPOR), a tool developed under an NSF grant by NCAR's Computational and Information System Laboratory, in partnership with UC Davis and Ohio State University. VAPOR allows researchers to probe three-dimensional volumes in detail, providing rich visualizations of the complex processes taking place. "Being able to render the simulations without having to move the data is a unique capability of the TeraGrid. From CU, we are able to connect remotely to NCAR, and then NCAR uses the TeraGrid backbone to connect to PSC and SDSC," Brown says. "TeraGrid resources are making these challenging three-dimensional simulations tractable," Toomre adds. In turn, such simulations are bringing scientists closer to understanding not only the processes taking place in our sun and other stars, but also how they might serve to advance science and technology applications on Earth.
Mark Miesch and Juri Toomre, High Altitude Observatory. More informationhttp://www.ucar.edu/news/releases/2007/solarmodel.shtml |
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