The U.S. Space Weather Prediction Center (SWPC) has issued a G4 geomagnetic storm watch, on a scale of 5.

"A series of coronal mass ejections, which are explosions of energetic particles and magnetic fields from the sun, are headed toward Earth," explained Shawn Dahl, a scientist with the center, part of the U.S. National Oceanic and Atmospheric Administration (NOAA).

The first of these "very strong" explosions reached Earth around 5:30 p.m. EST Friday, the agency said.

"There could be impacts to infrastructure," Dahl warned, calling the event "fairly rare" and saying it was likely to persist through the weekend.

"We've notified all the operators that we work with, such as satellite, communications, and of course the power grid operators in North America," he added.

The sun is currently near the peak of its activity cycle, which recurs about every 11 years.

The coronal mass ejections — at least seven of which have been observed heading toward Earth — are coming from a sunspot roughly 16 times the diameter of Earth. The material they expel travels at hundreds of kilometers per second.

Dahl advised residents to equip themselves with generators, as they would for any other storm warning.

But electric utilities have worked for a decade to better protect their grids, said SWPC scientist Rob Steenburgh.

GPS signals could also be affected, he said, adding that his agency was in close contact with NASA, which is responsible for the safety of astronauts on the International Space Station, who are more vulnerable to solar radiation.

A radiation alert has also been issued, but it is only a 1 on a scale of 5, and is not a major concern at this time.

As for air travel, the Federal Aviation Administration (FAA) said it "does not anticipate significant impacts."

However, geomagnetic storms can disrupt navigation tools and high-frequency radio communications, the U.S. aviation regulator explained, adding that it had advised airlines and pilots to be prepared for potential disruptions.

The last time a G4 geomagnetic storm watch was issued was in 2005. Such a watch precedes a warning, which is issued when a storm is actually observed.

The current event is expected to be of a lesser magnitude, though still significant. The most powerful solar storm on record, according to NASA, was the so-called Carrington Event of 1859.

Also a G5 event, it severely disrupted telegraph communications.

This type of storm particularly affects northern and southern latitudes, around the poles, Mathew Owens, a professor of space physics at the University of Reading, explained to AFP.

The event is therefore likely to produce auroras as far south as the northern United States and as far north as southern Australia.

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