A New Solar Model Filters Out “Ghost” Activity on the Sun’s Far Side

Half of the Sun is hidden from Earth at any moment, leaving an awkward gap in efforts to track its changing magnetic field. A Southwest Research Institute team has developed a way to improve those maps while screening out misleading signals from the unseen hemisphere.

The work, announced by SwRI on October 13, uses helioseismology: the study of waves traveling through the Sun. Those waves carry clues about magnetic activity beyond direct view. Some apparent active regions, however, turn out to be false detections, known as “ghost” regions.

Rather than treating every signal equally, the team assigns candidate regions a probability of being real. The aim is to improve surface flux transport models, which follow how magnetic activity changes across the solar surface. Such maps support research into solar cycles and the space weather that can affect Earth.

A clearer map, with a measurable trade-off

The research paper describes a comparison of helioseismic maps with STEREO ultraviolet observations collected between May 2010 and August 2014. Properties including magnetic flux, field strength and location help the method distinguish likely active regions from false signals.

At the selected threshold, 93 percent of regions classified as real were genuine in the evaluation sample, while roughly 90 percent of ghost regions were rejected. That precision comes with a trade-off: the method recovered about 52 percent of genuine regions in the same test. It is a selective filter rather than a complete inventory.

The authors also found that their conventional, near-side-driven simulations missed roughly 10 to 20 percent of the Sun’s total unsigned magnetic flux compared with the far-side-informed reconstruction. Incorporating the additional information produced more realistic magnetic evolution across successive rotations.

The immediate result is a better-supported input to solar modeling. It does not mean the team can now predict every flare or Earth-directed eruption. Turning improved magnetic maps into dependable warnings still requires the other physical models and observations used in space-weather forecasting.