Solar Orbiter circles the sun roughly every six months and can image the far side that ground- and Earth-orbiting instruments cannot see. Between April and July 2024, the spacecraft monitored one of the most active solar regions of the past twenty years, designated NOAA 13664, as it evolved over three rotations.

When NOAA 13664 rotated onto the Earth-facing side in May 2024, it produced the strongest geomagnetic storms recorded since 2003. "This region caused the spectacular aurora borealis that was visible as far south as Switzerland," says Louise Harra, professor at ETH Zurich and director of the Davos Physical Meteorological Observatory.

To investigate how such superactive regions form, evolve and affect space weather, Harra and Kontogiannis assembled an international research team. The group combined Solar Orbiter observations of NOAA 13664 on the far side with data from NASA's Solar Dynamics Observatory, which sits near the Earth - sun line and monitors the near side.

This coordinated campaign allowed the scientists to track NOAA 13664 almost continuously for 94 days. "This is the longest continuous series of images ever created for a single active region: it's a milestone in solar physics," says Kontogiannis, adding that the team followed the region from its emergence on 16 April 2024 on the far side through its decay after 18 July 2024.

Active regions on the sun host strong and complex magnetic fields that arise when highly magnetised plasma rises to the surface. These fields can drive powerful solar storms that emit intense electromagnetic radiation in the form of flares, eject plasma from the solar atmosphere, and launch high-energy particles into space.

Beyond creating auroras, major solar storms can damage or disrupt modern technological systems on and around Earth. They can trigger power outages, interfere with communication links, increase radiation exposure for aircraft crews and force satellites to reenter, as occurred in February 2022 when 38 of 49 newly launched Starlink satellites were lost within two days.

"Even signals on railway lines can be affected and switch from red to green or vice versa," says Harra. NOAA 13664 also generated problems in May 2024, when "modern digital agriculture was particularly affected," she explains, as signals from satellites, drones and sensors were disturbed, causing lost working days for farmers and crop failures with significant economic impact.

"It's a good reminder that the sun is the only star that influences our activities," adds Kontogiannis. "We live with this star, so it's really important we observe it and try to understand how it works and how it affects our environment."

Using data from multiple space probes, the researchers followed three full solar rotations and documented how the magnetic field in the superactive region developed over several stages, becoming more intricate with time. The analysis shows that an intertwined magnetic structure formed before the most powerful flare of the past twenty years erupted from the far side of the sun on 20 May 2024.

The team expects these results to sharpen understanding of how solar storms arise and what impacts they may have on Earth. Their goal is to improve space-weather forecasting so that vulnerable infrastructure and technologies can be better protected.

"When we see a region on the sun with an extremely complex magnetic field, we can assume that there is a large amount of energy there that will have to be released as solar storms," explains Harra. At present, however, models cannot yet predict how large any given eruption will be, whether a region will unleash one major event or a sequence of smaller ones, or precisely when such eruptions will occur.

"We're not there yet. But we're currently developing a new space probe at ESA called Vigil which will be dedicated exclusively to improving our understanding of space weather," says Harra. The Vigil mission is scheduled for launch in 2031 and will focus on monitoring solar activity relevant to space-weather hazards.

Research Report: Near-continuous tracking of solar active region NOAA 13664 over three solar rotations

Related Links
ETH Zurich
Solar Science News at SpaceDaily