Stein and Nordlund have used supercomputers to study the nature of the sun for more than 15 years, and a fair amount of their work has been done at NCSA. Their newest simulation on the Alliance's SGI Origin2000 at NCSA, however, is one of their largest undertakings to date. The simulation covers a swath of the sun that's 18,000 km square and runs from the surface to 9,000 km deep.

Rather than creating the simulation through a variety of modeling applications, the team uses a single, integrated code. Their code is based on the laws of conservation of mass, momentum, and energy as well as the forces of pressure, gravity, and the magnetic field. Solving the equations that represent these laws and forces allow the researchers to see the essential physics at work, the radiative cooling at the surface that drives convection and the turbulent motions that generate small-scale magnetic fields and shuffle them around, for example.

On four to six Origin2000 processors, it takes about one day to simulate 30 seconds of time on the sun. Eventually, they hope to simulate about one day on the sun.

The team has been using this code for many years, constantly updating and improving it. Past simulations have already helped the team make a great deal of sense out of the region near the surface of the sun. They have discovered that moderately powerful magnetic fields influence the patterns of convection-created granules, making them smaller and more irregular. They've also given other researchers a whole new way to look at the nature of solar convection in general. Previously, most solar researchers characterized convection patterns as a hierarchy of eddies of decreasing size. Through computer simulations, however, the team found that convection actually flows in cool, turbulent downdrafts that plunge through hot, smooth upflows.

The newest simulations promise similar discoveries. The team hopes to discover how much small scale magnetic flux is generated by convection, how larger-scale structures are related to granulation, and how to calibrate sound waves to observe phenomena near the solar surface.