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NASA and NSF Computers Simulate Sun's Corona
June 26, 2006

For the first time, researchers have developed a computer simulation that can accurately create a model of the sun's outer atmosphere, or corona. Funded by NASA and the National Science Foundation, the computer model marks the beginning of a new era in space weather prediction.

Conceptual Model of the SunGreyscale Image of the SunLASCO Instrument image of the Sun

Images 1-3 above: Researchers set out to predict the view of the solar atmosphere, or corona, which is most easily observed during an eclipse. Images on the left and center show two representations from the model while the right image shows a composite of the eclipse using a photograph of the corona (gray) taken in Kastellorizo, Greece, by the Williams College Eclipse Expedition. The sun's surface and the solar plasma streaming out into space (both orange) come from the Solar and Heliospheric Observatory (SOHO) spacecraft. Click on images to download larger versions. Credit #1-2: SAIC/NASA/NSF. Credit #3: The Williams College Eclipse Expedition with support from NSF/NASA/National Geographic. (+ High Res .tif #1 | + High Res .tif #2 | + High Res .tif #3 | + More Prediction Information | + More Comparison/Observation Information)

By accurately simulating the behavior of the corona, scientists hope to eventually predict when it will produce flares and coronal mass ejections, huge clouds of hot plasma ejected from the sun. It's the same approach the National Weather Service uses to predict when the Earth's atmosphere will produce thunderstorms or hurricanes.

Such predictions will help protect astronauts against radiation from flares and coronal mass ejections, in addition to mitigating disruptions on orbiting satellites and land-based communications and power systems.

"This confirms that computer models can describe the physics of the solar corona," said Zoran Mikic of Science Applications International Corp, San Diego, Calif. The turbulent corona is threaded with magnetic fields generated beneath the visible solar surface. The evolution of these magnetic fields causes violent eruptions and solar storms originating in the corona.

The computer model was based on spacecraft observations of magnetic activity on the sun's surface, which affects and shapes the corona. The observations were made with the Michelson Doppler Imager instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft. The Science Applications International Corporation team released simulated "photographs" of the March 29 total solar eclipse 13 days before and again 5 days before the actual event.

Previous computer simulations were based on simplified models, so the calculations could be completed in a reasonable time. The new simulation is the first to base its calculations on the physics of how energy is transferred in the corona. Even using NASA and the National Science Foundation supercomputers, the calculations required four days to complete on about 700 computer processors.

During a total solar eclipse, the moon blocks direct light from the sun, so the much fainter corona is visible. This is the only time the corona is visible from Earth without special instruments, and it resembles a white, lacy veil surrounding the black disk of the moon. Because the corona is always changing, each eclipse looks different.

Since the physics of the corona is still not completely understood, the accuracy of the simulation will improve when our understanding of how energy flows through the corona improves. More detailed measurements of magnetic activity on the solar surface, like those expected from NASA's Solar Dynamics Observatory scheduled to launch in 2008, will also improve the accuracy of the simulation.

Researchers are presenting the findings today at the American Astronomical Society's Solar Physics Division Meeting in Durham, N.H. For additional information and graphics, visit:


This research was sponsored in part by National Science Foundation's Center for Integrated Space Weather Modeling program and NASA's Living With a Star and Sun-Earth Connection Theory Program. SOHO is a joint effort between NASA and the European Space Agency.

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