Geomagnetic Storm Watch Issued as Sun Unleashes Strongest Solar Flare Since 2017

A solar flare, the bright flash at right, on May 14, 2024. NASA/SDO via AP

The sun emitted a powerful solar flare on Oct. 3, according to NASA, prompting the Space Weather Prediction Center to issue a Geomagnetic Storm Watch due to the forecasted arrival of coronal mass ejections.

NASA stated that its Solar Dynamics Observatory, which constantly monitors the sun, captured the flare on Thursday morning. This was the second intense flare this year and the most powerful since 2017.

Solar flares are bursts of energy that can last from several minutes to a few hours, according to the National Oceanic and Atmospheric Administration (NOAA).

They occur when the powerful magnetic fields in and around the sun reconnect and are usually associated with active regions, often visible as sunspots, where the magnetic fields are strongest, according to NASA.

Their strengths are classified on a scale ranging from the lowest B-class to C-class, followed by M-class, and then the largest, X-class, with each letter representing a tenfold increase in energy output.

“This flare is classified as an X9.0 flare. X-class denotes the most intense flares, while the number provides more information about its strength,” NASA said in the Oct 3. blog post.

The Oct. 3 flare was the second strongest in Solar Cycle 25, following an X8.7 flare on May 14. It also marked the strongest since 2017, when the sun emitted two powerful flares measuring X13.3 and X11.8, according to Space Weather Watch.

Solar flares can affect radio communications, electrical power grids, and navigation signals. NASA stated that flares also pose risks to spacecraft and astronauts.

Radiation from the recent flare could lead to “strong degradation or signal loss in high-frequency (HF) communication bands over much of the sunlit side of Earth,” according to the NOAA.

The agency stated that users of high-frequency radio signals in affected areas might experience loss of contact or major disruptions lasting for several minutes to a couple of hours.

Solar flares are also often accompanied by coronal mass ejection (CME), during which a large mass of plasma and highly magnetized particles is violently ejected from the sun.

NOAA’s Space Weather Prediction Center (SWPC) issued a Geomagnetic Storm Watch from Oct. 4 to Oct. 6 due to a pair of coronal mass ejections that are anticipated to arrive over the next three days.

“A CME is anticipated to reach and impact Earth with elevated geomagnetic response and dependent upon the orientation of the embedded magnetic field, potential exists for Strong Storm levels,” it said.

The SWPC stated that there may be “limited, minor effects to some technological infrastructure” resulting from the anticipated geomagnetic storm but that they are “mainly mitigatable.”

Northern lights or aurora borealis illuminate the night sky over a camper's tent north of San Francisco in Middletown, Calif., on May 11, 2024. Josh Edelson/AFP via Getty Images

Geomagnetic storms are often accompanied by aurora borealis and aurora australis light shows that can be seen from the ground.

NOAA said that aurora lights may be visible “over many of the northern states and some of the lower Midwest to Oregon.”

Katabella Roberts contributed to this report.