By Stephanie Dwilson | 2025-08-21

Coronal loops are mysterious, arcing ropes of plasma in the sun's atmosphere that may one day serve as a powerful early warning system for predicting strong solar flares, scientists say.

These electrified plasma structures frequently arc over the surface of the sun, following magnetic fields in its outer atmosphere. The magnetic fields arc back toward the sun’s surface, giving the ropes their characteristic "loop" shape.

Coronal loops tend to arc between sunspots that have opposite magnetic poles. Some loops can last for days or even weeks. They sometimes grow so large they could theoretically cover the entire Earth.

While these arcs of plasma are commonly referred to as loops, some scientists believe they are not loops at all.

A 2022 study by the National Center for Atmospheric Research’s High Altitude Observatory suggested the "loop" shape could be an optical illusion. Instead, the loops might be "wrinkles" within sheets of plasma.

Potential to predict solar flares

Late last year, a research team led by heliophysicist Emily Mason of Predictive Sciences Inc. discovered that coronal loops’ ultraviolet brightness varies just before a flare.

Solar flares are eruptions of electromagnetic radiation from the sun. Being able to more accurately predict their timing could prove useful.

Using NASA’s Solar Dynamics Observatory, Mason's team studied 50 strong solar flares and the way coronal loops acted around them. They found that coronal loops tend to flicker erratically for a few hours before a solar flare occurs.

The findings of the open-access study, "131 and 304 Å emission variability increases hours prior to solar flare onset," were published in December in the Astrophysical Journal Letters.

"We find that searching for periods of 'chaotic' behavior in the coronal loop emission, rather than specific trends, provide a much more consistent metric," said the study's lead author, Kara Kniezewski.

This also may correlate with how strong a flare will be, said Kniezewski, who is a graduate student at the Air Force Institute of Technology in the United States.

Early warning could be useful

Solar flares are classified on a five-level scale according to their intensity: A, B, C, M, and X. A is the weakest level and X is the strongest.

Each level represents a tenfold increase in energy, with an X flare 100 times stronger than a C flare, for example.

The energy from solar flares reaches the Earth at the speed of light -- about eight minutes after they occur -- with most of the energy arriving by the time it can be observed.

While the Earth’s atmosphere and magnetic field shield provide some protection from a flare’s radiation, that doesn’t mean it can’t do any damage.

Flares on the stronger end of the scale can disrupt radio communications, power grids, GPS navigation signals and damage satellites or spacecraft.

Receiving an earlier warning about solar flares could improve the level of preparedness for potential blackouts or other impacts.