Peking University researchers found 2,318 transverse waves in polar coronal plumes, about four times as many as a lower-resolution NASA instrument detected, carrying an estimated 2.6 times more energy.

The Sun constantly blows a stream of charged particles into space. This solar wind fills the solar system, shapes the magnetic bubble around Earth and can disturb satellites and power grids. Part of it, the fast solar wind, races outward at hundreds of kilometers per second, mostly from dark regions near the Sun’s poles called coronal holes.

Exactly how that wind gets its energy has been a long-standing puzzle. One leading idea is that waves carry energy up from the Sun’s lower atmosphere into the corona, where they heat the plasma and push the wind outward. But direct evidence that these waves carry enough energy has been scarce.

A new study adds important support. Researchers at Peking University led by Professor Hui Tian and Dr. Yuhang Gao used high-resolution images from the European Space Agency’s Solar Orbiter spacecraft to find large numbers of high-frequency waves in the Sun’s polar corona. Their results appear in National Science Review.

A hot mystery

The corona, the Sun’s outer atmosphere, is one of astronomy’s great puzzles. Its temperature reaches more than a million degrees Celsius, while the visible surface below is only about 5,500 degrees. Something must be pumping energy upward, and the same processes are thought to drive the fast solar wind.

One candidate is Alfvén waves, named for the Swedish physicist Hannes Alfvén, who won the 1970 Nobel Prize in Physics in part for describing them. These waves travel along magnetic field lines like vibrations along a plucked string. Transverse waves of this kind, in which the field lines sway sideways, have been observed in the corona for years.

Theoretical models suggest that high-frequency waves are especially important, because they dissipate their energy more efficiently and could therefore heat the corona and accelerate the wind more effectively. But most earlier observations detected mainly longer-period waves.

A sharper view of the poles

The Peking University team analyzed observations from Solar Orbiter’s Extreme Ultraviolet Imager taken on 14 September 2021. They targeted a coronal hole over the Sun’s north pole, where open magnetic field lines allow plasma and waves to escape into space.

Within the coronal hole, they focused on plumes, bright ray-like structures that can guide waves outward.

The instrument’s capabilities were key. It took images every 5 seconds with a pixel scale of roughly 210 kilometers on the Sun, fine and fast enough to resolve rapidly changing plume structures. Using time-distance maps and an automated wave-tracking method, the team identified 2,318 propagating transverse wave events.

Solar Orbiter, a mission led by the European Space Agency in collaboration with NASA, launched in February 2020. Its orbit carries it closer to the Sun than Mercury, allowing its cameras to see fine details in the solar atmosphere.

Four times as many waves

For comparison, the researchers ran the same analysis on simultaneous observations from the Atmospheric Imaging Assembly on NASA’s Solar Dynamics Observatory, which has watched the Sun since 2010 at lower resolution. That data set yielded 560 wave events.

The difference was largest for the fastest waves. Thirty-eight percent of the waves found by Solar Orbiter had periods shorter than 100 seconds, compared with 9 percent in the Solar Dynamics Observatory data.

Power-spectrum analysis showed much stronger wave power at frequencies above about 10 millihertz than lower-resolution data had suggested. Power between 10 and 30 millihertz was more than twice that between 2 and 10 millihertz. The estimated wave energy flux was about 2.6 times the value derived from the Solar Dynamics Observatory data.

“The new findings help bridge the gap between models that require high-frequency waves and previous observations that mainly detected longer-period waves,” Gao said.

A view from above

The study has a built-in limitation. At the time of these observations, Solar Orbiter, like nearly all solar observatories, viewed the Sun’s pole from close to the plane in which the planets orbit. Looking at the pole edge-on means that structures overlap along the line of sight, making it hard to trace where waves originate.

Tian points to future missions designed to solve that problem. “Future missions such as China’s planned Solar Polar-orbit Observatory will provide a more direct view of the Sun’s polar regions, together with imaging, magnetic-field measurements, and in-situ solar wind observations,” he said. “Such observations will be crucial for understanding where these high-frequency waves are generated, how they propagate and dissipate, and how they contribute to the acceleration of the fast solar wind.”

The results come from a single day of observations of one coronal hole. The release does not give the paper’s title, full author list or funders.

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Notes

1. National Science Review, 2026. DOI: 10.1093/nsr/nwag370.
2. Science China Press. “Hidden high-frequency waves found in the Sun’s polar corona may help power the fast solar wind.” EurekAlert!, 2 August 2026. https://www.eurekalert.org/news-releases/1138521.