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Northern U.S. could see dazzling aurora Wednesday night

A sunspot produced a cannibal CME, which is expected to bring a strong geomagnetic storm and beautiful aurora

The sun on March 29 showing active sunspot 2975 that produced multiple M-class solar flares. (SDO/HMI via
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It’s a good time to look up at the night sky.

Sky watchers at northern latitudes could be treated to a beautiful aurora Wednesday night into early Thursday, after the sun unleashed two large bursts of energy toward Earth. Activity is expected to peak in the early morning Thursday as a strong geomagnetic storm (rated 3 out of 5) reaches Earth’s magnetic field.

In the United States, the northern lights may be seen as far south as Oregon, Pennsylvania, Iowa and Massachusetts. Cloud cover from parts of the Upper Midwest into the interior Northeast may impede viewing, but skies should be clear across much of the Northern Plains through the northern Rockies. Sky cover will vary in the Pacific Northwest.

The geomagnetic activity began around Monday when one angry sunspot spurred a flurry of activity. Appearing as a dark spot, a sunspot is a region where the magnetic field is particularly strong on the sun. When the magnetic field lines tangle or cross, it can cause an explosion of energy called a solar flare. In this case, sunspot 2975 produced more than a dozen solar flares in 24 hours, impressing solar physicists.

On Monday, one of the larger solar flares, occurring around 7:28 a.m. Eastern time, caused a minor high-frequency radio blackout over Africa. A coronal mass ejection (CME), or a large plume of the sun’s plasma and magnetic field, also occurred toward Earth. Such magnetic clouds from the sun can jostle the magnetic field of the Earth, creating electrical currents in the upper atmosphere and exciting particles to create auroras.

But the sunspot wasn’t done. It spawned another moderately sized solar flare later that day at 3:23 p.m. Eastern. A second, faster CME associated with the flare also erupted. Moving at around 2 million miles per hour (841 km/s), this CME is expected to catch up with the first CME and merge into one — what scientists call a cannibal CME.

“Because these two have merged together or are merging together, that’s often an indication that the CME will be a bit stronger. It’s more stuff coming,” said Alex Young, a solar astrophysicist at the NASA Goddard Space Flight Center. “Also, it means that there’s a better chance that the magnetic field will disturb the Earth’s magnetic field.

Young said this CME activity was also accompanied by a “solar tsunami” (also known as an EIT wave, so named for its discovery using the EUV Imaging Telescope), a shock wave that typically indicates an energetic CME. Satellite data show the shock wave propagating across the sun.

The Space Weather Prediction Center forecast that the cannibal CME could arrive in the wee hours on Thursday as a strong (G3) geomagnetic storm. It also issued a moderate (G2) geomagnetic storm watch on Friday as weaker CME activity could continue toward Earth.

There may be a decent show Wednesday night into Thursday in northern New England; Michigan, especially in the Upper Peninsula; and northern parts of the Intermountain West and Northern Tier. Canada will also likely be treated to a good show. Outside of cloud coverage, light interference from the moon should be minimal, as a new moon appears Friday.

Otherwise, areas more than 150 miles or so from the U.S.-Canada border probably won’t have anything to look at with the naked eye, the only photographs coming from long exposures on sensitive DSLR cameras.

The Space Weather Prediction Center also said spacecraft, high-frequency radios and satellite GPS navigation systems may experience intermittent problems. During G3 geomagnetic storms, voltage irregularities may occur on some power systems at high latitudes. This would be most prevalent in the Arctic and Antarctic. Space junk and satellites in low Earth orbit can experience increased drag, and various issues with high-frequency radios and GPS signals can be expected.

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Young said there is a possibility this event could end up as a “dud.” For instance, he said, think of Earth’s magnetic field and the incoming CME as two bar magnets. If the bar magnets are oriented in opposite directions, the two click in harmony.

In this case, Young explained, Earth’s magnetic field at the front is oriented northward, or up and down. If the incoming CME has a magnetic field in the opposite orientation, Young said, the two could click and more energy could be transferred into the Earth’s magnetic field to create a stronger geomagnetic storm — and beautiful aurora.

If the orientation of the incoming CME isn’t quite right, there still may be some impact but just not as much, he said. Unfortunately, scientists won’t know the real-time solar wind changes until around 30 minutes before it reaches Earth, as it passes in front of the DSCOVR satellite.

Even if everything does work out, it’s important to remember that what you see online with regard to the northern lights is not usually what you get in person. Bona fide displays are breathtaking, but being outside the “auroral oval” means you might notice only some white hues or pillars on the horizon.

Overall, G3 geomagnetic storms aren’t terribly rare, occurring on average about 130 days out of every 11-year solar cycle. During the peak of a solar cycle, when sunspots are more numerous, G3 storms may occur a couple of times per month. We’re currently coming out of solar minimum as Solar Cycle 25 builds, hitting its peak around 2025.

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These events are “very normal for leading into a solar maximum, so we’ll see more of them,” said Young. “There’s just potential energy, and the more potential energy that’s built up, the more possibility you have for an eruption.”

With more pent-up energy, he added, big flares may be followed by other large flares as we head into a solar maximum. And that could happen in this case as well.

“As we watch these sunspot groups, we’ll start to see if they start to deteriorate,” said Young. “There’s still some fuel left there.”

On Wednesday, the sunspot fired off a X-class solar flare, the most intense solar flare class. The Space Weather Prediction Center data indicated potential strong radio blackouts occurred over North and South America. The flare was also likely associated with a new CME, which forecasters are currently analyzing to determine if it is directed towards Earth for another potential lightshow.