The University Record, June 11, 1997

U-M scientists simulate solar atmosphere on supercomputer

By Sally Pobojewski
News and Information Services

Using one of the world's most powerful supercomputers, U-M researchers are creating the first 3-D simulation of the sun's complex, dynamic, mysterious upper atmosphere called the heliosphere.

The heliosphere extends from the sun to the outer reaches of the solar system. Its major component is the solar wind---a constant stream of charged particles, magnetic fields and superheated ionized gas---which buffets the planets as it blasts by at speeds up to 500 miles per second.

"The U-M model is the first numerical code capable of duplicating the basic physics of how the heliosphere works in three dimensions," says Tamas I. Gombosi, professor of atmospheric, oceanic and space sciences and director of the research team.

"At this early point in its development, the simulation can only roughly mimic the portion of the heliosphere which extends from the solar surface to the orbit of Mercury. Even supercomputers are not powerful enough to allow us to precisely model the reality of a system so complex, but our goal is to get as close as possible."

At the American Geophysical Union meeting held in Boston in late May, several members of the U-M research team discussed the latest developments in the heliosphere simulation project---one of nine Grand Challenge Investigations funded by the NASA High Performance Computing and Communication Program's Earth and Space Sciences Project.

Clinton Groth, assistant research scientist in the Space Physics Research Laboratory, presented the team's model of the steady-state flow of the solar wind from the base of the solar corona to the orbit of Mercury during "quiet sun" conditions.

Darren L. DeZeeuw, also an assistant research scientist in the Space Physics Research Laboratory, presented images produced from the simulation showing a coronal mass ejection (CME) or magnetic cloud bursting out from the sun's surface into the inner heliosphere.

When complete, Gombosi believes the computer simulation may help scientists answer the many unresolved questions about the sun's atmosphere and how it affects life on Earth, including:

· How and why do solar flares and coronal mass ejections form on the sun's surface?

· What are the early warning signs of a solar magnetic storm?

· What causes the temperature of the solar corona to jump suddenly when it reaches a specific point above the sun's surface?

· How far does the heliosphere extend beyond the solar system?

The new supercomputer simulation model uses a technique called adaptive mesh refinement, which allows the computer program to adapt to the level of complexity existing in different areas of the simulation. "We can increase the resolution in areas where we know interesting phenomena will occur," explains DeZeeuw, who, along with associate research scientist Hal G. Marshall, wrote much of the original source code for the simulation. "This lets us focus the supercomputer's processing power on areas of greatest complexity and interest."

Other U-M researchers on the heliosphere simulation development team are Kenneth G. Powell, associate professor of aerospace engineering; Quentin F. Stout and Edward S. Davidson, professors of electrical engineering and computer science; Lennard A. Fisk, professor of atmospheric, oceanic and space sciences; Philip L. Roe and Bram van Leer, pro fessors of aerospace engineering; and graduate student Timur J. Linde.