NCCS-Hosted Simulations Bring to Light
a New Type of Coupled Eruption from the Sun

The visualization shows the configuration and speed (in kilometers per second) of the solar wind and magnetic field lines during a streamer-blowout eruption and coronal mass ejection from the Sun. See below a movie showing the entire coupled eruption. Figure from Wyper et al., 2021.

Using the NASA Center for Climate Simulation (NCCS) Discover supercomputer, scientists simulated complex interactions between large structures in our Sun’s atmosphere that unexpectedly produced a new type of “coupled eruption.”

Peter Wyper, Durham University.
Photo by NASA/Kelly Ramos.

Eclipse and satellite images of the Sun reveal large, tapered structures called streamers that stretch out into space from the solar atmosphere, or corona. “Differences in the underlying magnetic field distinguish broad ‘helmet streamers’ from narrow ‘pseudostreamers,’” explained Peter Wyper, assistant professor, Department of Mathematical Sciences, Durham University. “From beneath these tapered canopies, snaking structures known as filaments erupt and expel millions of tons of plasma at high speed into the solar wind.”

Wyper and his colleagues at the NASA Goddard Space Flight Center and University of California, Berkeley describe these first-of-a-kind simulations in a paper recently published in The Astrophysical Journal.

The European Space Agency PROBA2 micro-satellite’s SWAP (Sun Watcher using Active Pixel System detector and Image Processing) imager observed this pseudostreamer emerging from the Sun’s atmosphere. “Filament” marks the snaking structure harbored by the pseudostreamer. “NP” marks the apparent null point at the top of the pseudostreamer. Figure from Wyper at al. 2021.

In the research team’s simulations, placing a filament eruption from a pseudostreamer next to a helmet streamer led to the latter blowing its top in a “streamer-blowout eruption" accompanied by a bubble-shaped coronal mass ejection. Scientists have previously seen coupled eruptions involving paired filament ejections that originate beneath a single helmet streamer but not this particular coupling before. “This unexpected coupling produced quite complex internal structure in the ejected bubble and strongly deflected the filament material from its original outward path,” Wyper said.

Simulating this complexity was a task for the 3D Adaptively Refined Magnetohydrodynamics Solver (ARMS) software developed by paper co-authors Spiro Antiochos and Rick DeVore of NASA Goddard’s Heliophysics Science Division and collaborators. To capture the vast differences in spatial scales, ARMS used four refinement levels with each higher level doubling the computational grid resolution.

Simulation grid (left) on the Sun’s surface, with magnetic field lines from the pseudostreamer null points drawn for context, and (right) in a plane of constant longitude, showing how the adaptive refinement localizes the grid to the erupting magnetic structure. Colors show (left) magnetic field strength in Gauss and (right) solar plasma velocity in kilometers per second. Figure from Wyper at al. 2021.

Dozens of ARMS simulations — including four production runs testing different configurations — used nearly 1.8 million core-hours on the NCCS Discover supercomputer. The simulations produced 162 gigabytes of data, initially saved to Discover’s "nobackup" disk and then archived in mass storage.

“The global, coupled nature of the eruptions that we studied requires simulating nearly the entire solar atmosphere, including the inner solar wind,” Wyper noted. “Access to NCCS supercomputing facilities was critical for obtaining our results, as without those resources, simulations of this scale and ambition would have been difficult to perform and analyze.”

Impact: Large-scale numerical simulations revealed the existence of a previously unrecognized type of coupled eruption and demonstrated the important role played by the global magnetic field in guiding and shaping coronal mass ejections from the Sun.

The team made synthetic observations from the simulation data, and the morphology and acceleration of the simulated bubble-like coronal mass ejection compare well with satellite observations.

Moreover, the simulation results highlight the sometimes-interconnected nature of eruptions from our Sun. To fully understand and predict the path of eruptions, scientists need to consider how the erupting structure might couple with the larger-scale magnetic field that surrounds it.

“Although we focused on this coupling in the paper, we actually were surprised that we obtained a coupled eruption,” Wyper explained. “We were not intending to study this aspect of the Sun; our original plan was purely to study the first part of the event, a simple eruption. The subsequent coupling with the global magnetic field was unexpected and new.”

In this movie, magnetic field lines of the solar wind at the interface between the pseudostreamer and helmet streamer (red traces) and at the far edge of the helmet streamer (yellow traces) become disturbed as the pseudostreamer’s low-lying inner field lines (cyan traces) begin to erupt outward. The magnetic connections change rapidly as the eruption proceeds, entwining field lines (yellow and cyan traces) to form the growing, bubble-shaped coronal mass ejection. The color shading in the background shows the solar-wind speed early and the very high speeds attained by the ejecta during the eruption later on. At the end of the movie, field lines that were closed to the Sun at both ends before the event are open to interplanetary space after the event (yellow and cyan traces). Movie from Wyper at al. 2021. Caption by C. Richard DeVore, NASA Goddard Space Flight Center.

Related Link

Jarrett Cohen, NASA Goddard Space Flight Center