If you didn’t know, there will be a total solar eclipse of the Sun on Monday, August 21st, 2017. Honestly, if you didn’t know you probably live under a rock. The eclipse will spread out across a 70-mile-wide band across 14 states. People are very excited about it and have even planned vacation trips to the areas where the total eclipse can be seen.
Solar eclipses help astronomers understand and study the sun better, from its structure, inner working, and the space weather that it generates. Eclipses also provide researchers who study solar science with an opportunity to forecast how the Sun will look during the eclipse.
A team from Predictive Science Inc. (PSI), in San Diego is one of the groups taking advantage of this eclipse. Starting on July 28, 2017, the team started a large-scale simulation of the Sun’s surface to prepare for a prediction of what the solar corona will look like during the eclipse. The solar corona is the aura of plasma that surrounds the sun and extends millions of kilometers into space. The team had support from NASA and the Air Force Foundation Office of Scientific Research and National Science Foundation.
The team used massive supercomputers, including Stampede2 that is housed at the Texas Advanced Computing Center (TACC), Comet at the San Diego Supercomputer Center (SDSC) and NASA’s Pleiades supercomputer to conduct the research. The researchers completed a series of highly-detailed solar simulations timed to the moment of the eclipse.
"Advanced computational resources are crucial to developing detailed physical models of the solar corona and solar wind," says Jon Linker, president and senior research scientist of PSI. "The growth in the power of these resources in recent years has fueled an increase in not only the resolution of these models, but the sophistication of the way the models treat the underlying physical processes as well."
The team used data that was collected by the Helioseismic and Magnetic Imager (HMI) on NASA’s Solar Dynamics Observatory (SDO), as well as magnetic field maps, solar rotation rates and math models of how magnetohydrodynamics impact of the corona. Time on Sampede2 and Comet was provided by Extreme Science and Engineering Discovery Environment (XSEDE).
The magnetohydrodynamic model of the solar corona that the researchers used had an improved treatment of energy transport. Previous predictions in 2006 and in 2008 used a simplistic heating formalism, but PSI’s researchers applied a wave turbulence-driven methodology to heat the corona. This model better reproduces the underlying physical processes in the corona and has potential to produce a more accurate eclipse prediction.
For the final prediction, they introduced magnetic shear, a well-known feature of large-scale coronal magnetic fields that previous predictions did not account for. The inclusion of shear qualitatively changes the shape of the streamers and the connectivity of the underlying fields and increases free magnetic energy the of the corona.
One of the simulations produced a coronal mass ejection from an active region that will exist near the east limb of the Sun on eclipse day.
The simulations are some of the largest the research group has performed with 65 million grid points to provide greater accuracy and realism.
When the research was completed, the researchers converted their computer simulations into scientific visualizations that approximate what a human eye might see during the solar eclipse.
"The Solar eclipse allows us to see levels of the solar corona not possible even with the most powerful telescopes and spacecraft," says Niall Gaffney, a former Hubble scientist and director of Data Intensive Computing at the Texas Advanced Computing Center. "It also gives high performance computing researchers who model high energy plasmas the unique ability to test our understanding of magnetohydrodynamics at a scale and environment not possible anywhere else."
Making predictions about the corona’s appearance during an eclipse is a way to test complex three-dimensional computational models of the sun against visible reality.
This endeavor has a practical purpose beyond just the eclipse. Accurate predictions of space weather can potential help authorities stop the worst impacts of a powerful solar storm.
According to a 2008 report by the National Academy of Sciences, if a solar storm were to hit the Earth today, it could cause more than $2 trillion in damages. By predicting a solar storm in advance, people can implement damage prevention steps by taking critical electronic infrastructure offline. Doing this means understanding how the visible surface of the sun relates to the mass injections of plasma that can cause space weather.
Solar storms are not an imminent threat, but problems with space weather are not imagined. In an article published in Space Weather in 2012, Pete Riley, a senior scientist at PSI put the odds of a space weather event in 2020 at 1 in 8.
"The ability to more accurately model solar plasmas, helps reduce the impacts of space weather on key pieces of infrastructure that drive today's digital world," Gaffney says.
The team completed their initial forecasts on July 31, 2017. They published their final predictions using newer magnetic field data on their website on August 15, 2017. They will present the results at the Solar Physics Division (SPD) meeting of the American Astronomical Society (AAS) from August 22-24.