Why we’ve been seeing the northern lights so often lately

Fresh waves of green and purple auroras may shimmer in the night sky tonight over parts of the continental United States, visible as far south as Iowa, Pennsylvania, and Oregon as a strong geomagnetic storm strikes Earth. It’s the latest display in an already rambunctious year for space weather.
NOAA’s Space Weather Prediction Center issued a geomagnetic storm watch for September 16, 2024, noting that the storm could reach G3, or “strong,” strength. That’s the level at which power systems at high latitudes could set off high-voltage alarms, where navigation instruments will have to account for interference, and spacecraft may need to make adjustments to stay aloft. The wave of solar wind will also extend the reach of auroras.
The current wave of celestial activity began last week 93 million miles away at a huge sunspot on our friendly neighborhood star. Sunspots are patches of the sun’s surface with unusually strong magnetic fields and they appear as dark spots. The boundaries of these spots are ripe for storms that trigger solar flares, large eruptions of radiation. They also foment coronal mass ejections, bursts of magnetized plasma from the sun’s corona, its outermost layer.
The sunspot set off a massive flare that sprayed the solar system with high-energy particles. When these particles collide with the Earth’s atmosphere, they create a phenomenon similar to how neon lights work, exciting gasses in the atmosphere and making them glow, creating auroras.
They typically cluster near the Earth’s poles (hence “northern lights”), but if enough energetic solar particles charge up the sky, auroras can reach much closer to the equator, which is why we’ve been seeing them all over the globe lately.
This year, the sun is at the peak of its activity cycle.
Roughly every 11 years, the sun’s magnetic poles reverse and as that flip approaches, there tends to be much more magnetic activity and thus more sunspots at the surface.
Anticipating how this activity will ripple toward our home planet is an important task, not just so we Earthlings can get our cameras ready and ooh and aah at the nighttime colors; space weather can create problems for communication, navigation, and the power grid.
Michael Wiltberger, deputy director of the High Altitude Observatory at the National Science Foundation’s National Center for Atmospheric Research, noted that predicting space weather is a lot like forecasting terrestrial weather. The weather we typically experience on the ground is driven by heat, moisture, and wind while space weather is driven by the electromagnetism of stars and planets. But both space and terrestrial weather emerge at the confluence of short- and long-term drivers playing out over a variety of different regions. While we don’t usually experience space weather on the ground, it generates a constant burbling mix of subtle and severe influences on the tools of our modern world.
“There’s stuff going on all the time that affects a wide range of things from radio communications to lifetimes of satellites to radiation risks to astronauts in space,” Wiltberger said.
And like your local TV weather experts, scientists studying space weather draw on a variety of instruments and models to generate useful forecasts with bulletins and visuals. On its website, the Space Weather Prediction Center produces predictions for “essential space weather communities” like aviation, emergency management, satellites, and space weather enthusiasts.
The key tools for space weather forecasting are spacecraft that monitor the flow of solar wind and the direction of the magnetic field. “It’s important because if it’s aligned in the direction of the Earth’s magnetic field, we’re not going to get a lot of energy dumped into the system,” Wiltberger said. “But if it’s in the opposite direction then the magnetic fields can interact and get more energy and more direct coupling during these geomagnetic storms.”
These measurements are then coupled with readings from ground-based cameras and magnetometers and fed into models to figure out how a rowdy sun will light up the Earth.
Right now, one of the main goals is to extend the lead time for forecasts of how disruptive a geomagnetic storm will be. While scientists can see coronal mass ejections days before they start to impact Earth, they can’t easily figure out the strength and direction of the magnetic field, which, again, is the key factor in how much energy the Earth suddenly absorbs.
Even small hits from the sun can be impactful. GPS, for example, relies on timing signals between satellites to pinpoint locations on the ground. A geomagnetic storm can create delays in these signals, throwing off critical measurements. “If you’re driving your car, probably not a big deal,” Wiltberger said. “But if you’re doing precision agriculture and you’re trying to use it to tell you where to put the water on the seed that you just planted and you need really good accuracy, it’s a concern.”
Satellites can be vulnerable to solar storms in other ways as well. On February 3, 2022, SpaceX launched 49 Starlink internet satellites into low Earth orbit, but a geomagnetic storm struck the next day. The storm increased the density of the atmosphere, creating unexpected drag and forcing most of the satellites to re-enter and burn up in the Earth’s atmosphere.
The company said the nearly 6,000-strong Starlink satellite fleet weathered the recent storms just fine.
One of the biggest concerns is what a strong solar storm could do to electricity systems. Wiltberger said one could imagine a gargantuan, fast-moving coronal mass ejection that hits the Earth just 24 hours after leaving the sun.
If the magnetic field in this ejection happens to line up in the opposite direction of the Earth’s, it will create a big shift in the Earth’s magnetic field. A changing magnetic field, you may recall from your electromagnetism classes, can induce a current in a conductor, like, say, power transmission lines. That can then disrupt power delivery or cause parts of the grid to trip offline.
Still, even a severe coronal mass ejection is unlikely to trigger a civilization-stopping blackout. “We’re probably not going to lose the power grid, but the power grid may actually have to take steps to bring more power generation capability online, defer maintenance, do those types of things,” Wiltberger said.
And perhaps losing a few lights on the ground for a while isn’t such a bad thing when the night sky lights up.
Update, September 16, 2:20 pm: This story was originally published on May 14, 2024, and has been updated to include details about aurora visibility following another geomagnetic storm.