The solar flare has always presented scientists an astronomical phenomenon that is visually fascinating but also equally mystifying, in trying to determine how and why they form and occur. Now, a team of scientists, led by National Center for Atmospheric Research (NCAR) and the Lockheed Martin Solar and Astrophysics Laboratory, have developed a single, cohesive computer model to simulate the entire life cycle of a solar flare.
The comprehensive new simulation traces the initial formation of the flare from the buildup of energy thousands of kilometers below the solar surface, to the emergence of tangled magnetic field lines, to the explosive release of energy in a brilliant flash. The model captures the formation of a solar flare in a more realistic way than previous efforts, and it includes the spectrum of light emissions known to be associated with flares.
The accomplishment, detailed in the journal Nature Astronomy, could set the stage for future solar models to realistically simulate the Sun’s own weather as it unfolds in real time, including the appearance of roiling sunspots, which sometimes produce flares and coronal mass ejections. These eruptions can have widespread impacts on Earth, from disrupting power grids and communications networks, to damaging satellites and endangering astronauts.
“This work allows us to provide an explanation for why flares look like the way they do, not just at a single wavelength, but in visible wavelengths, in ultraviolet and extreme ultraviolet wavelengths, and in X-rays,” says Mark Cheung, a staff physicist at Lockheed Martin Solar and Astrophysics Laboratory and a visiting scholar at Stanford University. “We are explaining the many colors of solar flares.”
For the new study, the scientists had to build a solar model that could stretch across multiple regions of the Sun, capturing the complex and unique physical behavior of each one.
The resulting model begins in the upper part of the convection zone—about 10,000 kilometers below the Sun’s surface—rises through the solar surface, and pushes out 40,000 kilometers into the solar atmosphere, known as the corona. The differences in gas density, pressure, and other characteristics of the Sun represented across the model are vast (see video).
To successfully simulate a solar flare from emergence to energy release, the scientists needed to add detailed equations to the model that could allow each region to contribute to the solar flare evolution in a realistic way. But they also had to be careful not to make the model so complicated that it would no longer be practical to run with available supercomputing resources.
“We have a model that covers a big range of physical conditions, which makes it very challenging,” says NCAR scientist Matthias Rempel. “This kind of realism requires innovative solutions.”
To address the challenges, Rempel borrowed a mathematical technique historically used by researchers studying the magnetospheres of Earth and other planets. The technique, which allowed the scientists to compress the difference in time scales between the layers without losing accuracy, enabled the research team to create a model that was both realistic and computationally efficient.