NCCS-Hosted Simulations Validate New Method of
Simulating Solar Processes that Birth Space Weather
This gigantic coronal mass ejection blew out from the Sun over June 17–18, 2015. NASA’s Solar Dynamics Observatory caught the action in the 304 Angstrom wavelength of extreme ultraviolet light. While some of the plasma falls back into the Sun, a look at the coronagraph instrument on the Solar and Heliospheric Observatory shows a large cloud of particles heading into space. Image by Solar Dynamics Observatory, NASA.
The NASA Center for Climate Simulation (NCCS) Discover supercomputer hosted simulations validating a new, computationally efficient method for capturing the complex magnetic processes that spawn coronal mass ejections and other space weather phenomena. If they hit Earth in the right locations, such space weather events can disrupt satellite communications and electric power grids, among other hazards.
NASA Goddard Space Flight Center scientists created the STatistical InjecTion of Condensed Helicity (STITCH) computer model to represent the essential physics of “helicity condensation.” This process takes place in the Sun’s corona (outer atmosphere) when magnetic reconnection causes magnetic field structures, which have been twisted by “vortical” (whirling) motions at the Sun’s surface, to successively merge with their neighbors and build up enough energy to erupt.
“The generalized tangling of magnetic field structures can be described by a mathematical quantity known as 'helicity,' and the merging process can be thought of as the 'condensation' of the tangling into coherent, eruptive structures,” explained Joel Dahlin, Assistant Research Scientist, Heliophysics Science Division, NASA Goddard Space Flight Center and the University of Maryland at College Park. “We developed STITCH because we wanted to include the essential physics of helicity condensation in our simulations of solar eruptive events without untenable computational expense.” Dahlin was lead author on the study recently published in the Astrophysical Journal.
Paper co-authors were (left to right) Joel Dahlin, Rick DeVore, and Spiro Antiochos, all of NASA Goddard Space Flight Center. Photos by NASA and Jay Friedlander, NASA Goddard.
STITCH is a new component of the 3D Adaptively Refined Magnetohydrodynamics Solver (ARMS) software developed by paper co-authors Rick DeVore and Spiro Antiochos of NASA Goddard’s Heliophysics Science Division and collaborators.
The NCCS Discover supercomputer hosted a variety of ARMS simulations comparing STITCH to “full helicity condensation” methods; the latter solve equations for the full range of physical and magnetic processes involved in helicity condensation. “STITCH is much easier to set up than full helicity condensation, where we have to ‘hand-place’ vortical motions and avoid tangling them with each other or certain magnetic boundaries,” Dahlin said. “For STITCH we instead simply select a region over which we wish to introduce ‘condensed helicity’ and choose the rate of helicity injection.”
Impact: A new numerical method for generating the magnetic structures that birth coronal mass ejections — and benchmarked against large-scale simulations — captures the essential physics of energy build-up on the Sun in a much simpler and less computationally expensive implementation than previous methods.
For the study, Dahlin and collaborators ran four ARMS simulations on Discover. Three simulations had a simple initial magnetic field profile: full helicity condensation, spatially uniform STITCH, and spatially localized STITCH. The fourth simulation combined STITCH with a more complex magnetic field to mimic an active region on the Sun. Running on 500 computing cores each, the STITCH simulations finished in 5–6 days compared to 2 months for the full helicity condensation simulation.
“To ‘benchmark’ the new method, we needed to perform detailed calculations of the full helicity condensation process, which could not have been performed without access to the Discover supercomputer,” Dahlin said. “Testing our new method against these computationally expensive simulations was critical to show that STITCH captured the essential physics of the process at far lower cost.”
Full helicity condensation (top) and spatially uniform STITCH (bottom) simulations both capture the essential physics of energy build-up and eruption of a flare from the Sun, as shown in the images and their linked videos. Click on each image to play the linked video.
Top: The full helicity condensation images show the (a) the energy build-up phase and (b) the eruptive phase. The video consecutively displays animations of the energy build-up and eruptive phases.
Bottom: The spatially uniform STITCH images show the (a) the energy build-up phase and (b) the eruptive phase. The video displays animations of (a) the energy build-up and (b) eruptive phases simultaneously since STITCH’s computational efficiency enables significantly shortening the energy build-up phase.
Color key and credits: In both the (a) and (b) panels, surface gray shading indicates the sign and strength of the radial magnetic field component (Br), while magnetic field lines are colored according to location and function. In the (b) panel, red shading indicates velocities (Vr) more than 500 kilometers per second (km/s) outward from the Sun. Images and videos from Dahlin et al., 2022.
The benchmark results indicate that the STITCH method generated a magnetic field consistent with observations of the magnetic structures from which coronal mass ejections originate. Moreover, “if anything STITCH showed that it had even more favorable qualities than we had thought,” Dahlin said. “For example, we could easily create very narrow structures with STITCH that wouldn’t be feasible with the full helicity condensation model.”
STITCH’s simplicity, flexibility, and computational efficiency make it a promising tool for space weather modeling, which is “a race against time,” Dahlin said. “Every computational expense saved in the simulations can be crucial to producing timely predictions. Solar eruptive events such as those modeled with STITCH represent a significant space weather hazard, threatening spaceborne astronauts and satellites and disrupting communications on the ground.”
Accordingly, next steps for STITCH development include collaborating with other research groups to implement the same method in space weather modeling codes such as those hosted at NASA’s Community Coordinated Modeling Center (CCMC).
The panels visualize the STITCH simulation method for a complex active region like those observed on the Sun. The top panels show the initial configuration (a) from above and (c) from the side. The bottom panels show (b) the energized magnetic field structure generated by STITCH and (d) the resulting coronal mass ejection. Colors are as in the previous set of images. Figure from Dahlin et al., 2022.
Related Links
- Dahlin, J.T., C.R. DeVore, and S.K. Antiochos, 2022: STITCH: A Subgrid-scale Model for Energy Buildup in the Solar Corona. Astrophysical Journal, 941, 79, doi:10.3847/1538-4357/ac9e5a.
- NASA Scientific Visualization Studio: Space Weather Gallery.
- NASA eClips: Real World: Space Weather.
Jarrett Cohen, NASA Goddard Space Flight Center
March 29, 2023
