Watch out, Earth: There's another strong geomagnetic storm headed our way from the Sun, following the G5-class one that hit back in May.

The US National Oceanic and Atmospheric Administration's Space Weather Prediction Center (SWPC) warned today that a coronal mass ejection (CME) detected on October 8 is moving fast - somewhere between 1,200 and 1,300 kilometers per second - and will likely strike Earth sometime early tomorrow, October 10. 

According to SWPC, the storm has the potential to reach G4 levels upon its arrival, putting it at just shy of the G5 maximum for geomagnetic storms.

At G4 strength, the center noted effects may include widespread voltage control problems, interference with spacecraft operations, aurora borealis at lower altitudes than expected, and interruption to terrestrial communications.

Along with the G4 storm, the SWPC said the CME headed for Earth will also bring with it an S3-level solar radiation storm, which could harm astronauts and passengers on high-flying aircraft, disrupt solar panel efficiency, and degrade radio and navigation signal propagation. An R3-level radio blackout is also expected from the CME that originated with yesterday's X1.8 solar flare (relatively low in strength, but potentially disruptive due to its direct path toward Earth), potentially causing loss of high-frequency radio and degradation of low-frequency signals that could last for tens of minutes. 

Hey, Sun - knock it off?

It's been a busy year for our star, with a massive X6.3 solar flare in February, and Earth being hit by a G5-level geomagnetic storm in May. If you're hoping things will calm down in the near future - sorry, we still have some more solar activity to endure. 

We're approaching the peak of solar cycle 25, which began in December 2019 and is expected to peak next July. The NOAA previously predicted that cycle 25 would be a relatively calm one, but said during a press briefing today that it's already revised its prediction upward given the previous May storm. Instead of predicting between 137 and 166 sunspots (which give birth to CMEs), the SWPC believes we'll see between 165 and 186 of them. 

"We have a good number [of G4 events] through the maximum of a solar cycle," SWPC service coordinator Shawn Dahl said during the briefing. G5-level storms, however, are rare. The October CME has the potential to reach G5, Dahl said, and if it does that would mark a rare moment when two G5 storms occurred within months of each other. 

"We went through the entire previous cycle without reaching G5," Dahl noted. The May event, Dahl said, was the first G5 storm since 2003.

The SWPC said it won't know the storm's true strength until it gets within one million miles of Earth, which is expected early tomorrow, about 15 to 30 minutes before reaching Earth.

But while this storm has the potential to be worse than our previous brush with a CME, Dahl said it likely won't reach the severity of the May storm.

"During the one in May, we had a series of CMEs that swept everything together and enhanced the effect," Dahl said. "This time we only have one." 

The peak of solar activity in this busy cycle is coming next year, but that doesn't mean the solar maximum is over, Dahl said. Storms after the peak of a solar maximum can be even worse than earlier ones because of the position of sunspots. 

Early in a maximum, sunspots form closer to the Sun's poles before slowly migrating toward its equator. We still have around ten degrees to go before the Sun's many spots reach the equatorial region, Dahl said. 

In short, we'll likely see plenty of storms, and southerly auroras, in the next year, but this one might be a slight disappointment for space weather watchers. Either way, keep an eye on the SWPC space weather forecast tomorrow morning to ensure this one won't disrupt your day. ®

https://www.theregister.com//2024/10/09/g4_solar_storm/