“This is definitely the season for big solar storms,” explained Kelly Korreck, a program scientist with NASA’s heliophysics division. That season gets to a climactic point this week, when a strong coronal mass ejection (CME) hurtles towards Earth at an estimated 2 million miles per hour and potentially lights auroras far from their typical haunts. Predictions from the U.S. National Oceanic and Atmospheric Administration Space Weather Prediction Center (SWPC) indicates that later in the night of Monday, skies as far south as Oregon, Illinois, and upstate New York may glow with green, purple, and blue light. From across the Atlantic, the UK Met Office predicts “across much of the UK, potentially without the need for photographic equipment.”
The cause of this spectacle is a CME that burst from the outer atmosphere of the Sun on Saturday, sending a huge cloud of ionized plasma and knotted magnetic fields hurtling straight towards Earth. When such material crashes into the planet’s magnetosphere, charged particles follow magnetic field lines spiraling towards the poles, impacting atmospheric oxygen and nitrogen. Oxygen emissions give the sky its green hue; nitrogen emits blues and violets. This week’s event might briefly qualify as a rare G4 geomagnetic storm level a notch below the most intense G5 a level not usually reached outside the solar cycle’s most active years.
That 11-year cycle is currently at its “solar maximum,” when sunspot counts spike and eruptions occur daily and vigorously. Sunspots are cooler, magnetically active areas that can release both flares and CMEs. “During solar maximum, the number of sunspots, and therefore, the amount of solar activity, increases,” said Jamie Favors, the director of NASA’s Space Weather Program. Already this year there have been a number of prominent storms, such as a May 2024 G5 storm that extended auroras to Florida and led to GPS disruptions worth more than $500 million to US farmers.
While the visual display is perhaps most heralded, the electromagnetic disturbances from the storm can propagate through current infrastructure. Geomagnetically induced currents can saturate transformers, hinder radio communication, and blur GPS signals. The SWPC predicts “limited, minor effects to some technological infrastructure,” but even moderate storms have prompted airlines to reroute flights over the poles, satellite operators to hold maneuvers, and utilities to prepare for grid shocks. Oregon State University’s recent 3D map of the U.S. crust and mantle, which used supercomputer models and surveys of seismic activity, pointed out East Coast areas from Washington D.C. to Georgia as most susceptible to such currents.
The potential to predict these effects relies on a constellation of observatories and satellites. NASA’s Parker Solar Probe, currently diving just 3.86 million miles from the Sun, is directly sampling the corona, while NOAA’s DSCOVR satellite, located at the Earth-Sun Lagrange Point 1, offers real-time solar wind observations some 20 to 50 minutes in advance of impact. Future missions, like NOAA’s SWFO-L1, will improve early detection, and coronagraphs on the GOES-U spacecraft will provide uninterrupted images of the Sun’s tenuous outer atmosphere “the equivalent of a total solar eclipse every 30 minutes,” NOAA space weather director Elsayed Talaat said.
Even with these new technologies, it is still hard to estimate the precise strength of a CME until it is almost on top of Earth. “We think there is a chance for G4 if the CME magnetic field is strong enough and favorable but we won’t know that until it arrives 1 million miles from Earth at our solar wind observatory,” said SWPC forecaster Shawn Dahl. That uncertainty puts both scientists and infrastructure operators on their toes.
For observers, the peak viewing will be in the wee hours of Tuesday, 2 a.m. to 5 a.m. Eastern time, distant from city lights. A waxing gibbous Moon would likely overpower some of the softer hues, but the brightness of a G4 storm might create dramatic curtains of light far beyond the Arctic Circle. For forecasters and engineers, tonight will be more watchful and less showy a reminder that the Sun’s splendor and its destructive capability can come in the same flash of light.
