The fastest-moving solar storm in years sparked a beautiful green and purple aurora

In Finland, self-described “aurora hunter” Alexander Kuznetsov wrote that “the aurora did a wonderful dance after darkness fell.” SpaceWeather.com. “It started as a sharp dancing arc on the southern horizon that quickly moved up, producing the most vibrant red and purple auroras I've ever seen in my entire aurora hunting career!”

Matti Helin, another aurora observer in southwestern Finland, said A “good scene” lasted only 20 minutes.

Strong solar storms and brilliant light displays come when the Sun is at its most active in two decades. Scientists expect auroral activity to be high in the coming years, including the coming months.

Fierce eruptions on the Sun

Auroras are initiated when the Sun sends a plume of solar particles towards Earth and disturbs our magnetic field – creating a geomagnetic storm. Solar particles excite oxygen and nitrogen molecules in our upper atmosphere and emit photons of light, which we see as the aurora.

Geomagnetic storms are rated on a scale of 1 (minor) to 5 (intense) by NOAA's Space Weather Prediction Center. The geomagnetic storm reached G4 on Sunday, but weakened to G2 and G1 levels a few hours later.

A fast stream of solar particles followed Earth's magnetic field Monday morning at twice its normal speed. But the potential for strong aurora activity has decreased as geomagnetic activity has weakened, said Bill Murdock, program coordinator for NOAA's Space Weather Prediction Center.

In parts of Europe and the Southern Hemisphere the best auroral displays occurred when G4 activity coincided with evening or nighttime. Unfortunately, G4 conditions occurred during the day for the U.S., when our sun obscured the light scene, but northern parts of the country still saw some dancing lights during a weak geomagnetic storm at night.

New Zealand was well-positioned for an aurora display where it was dawn when the solar storm hit.

“While clouds obstructed the view, the aurora was strong despite the full moon,” wrote Ian Griffin, a photographer based in New Zealand's Otago Peninsula. SpaceWeather.com.

Scientists detected geomagnetic activity last week in sunspots, or groups of dark, cold regions on the Sun. Sunspots are regions where the Sun's magnetic field is strongest. Magnetic field lines near sunspots are often entangled, crossed and realigned until pressure builds up and releases a great deal of energy, Murdoch said.

Activity around sunspots erupted on Friday evening. One event was a solar flare that sent an intense wave of electromagnetic radiation to Earth. According to a space meteorologist, the solar flare event lasted for several hours and hammered radio communications Tamita forest.

At the same time, another explosion occurred on the surface of the Sun, Murdoch said. The explosion, or coronal mass ejection, was lifted from the center of the Sun and sent a plume of solar particles directly toward Earth. The explosion was moving Incredibly fast It arrived at Earth at about 1.7 million mph and about 10 hours earlier than expected — the fastest-moving burst of the current solar cycle, Murdoch said.

“How fast we calculated [the eruption] “It took over 37 hours to get from the Sun to Earth,” Murdoch said. Anything you see in less than 40 hours is pretty fast.

Why did aurora activity decline so quickly?

But even a strong direct impact from a fast-moving coronal mass ejection is insufficient to guarantee widespread beautiful auroras. For strong coupling, such as clicking two bar magnets together, the magnetic orientation of the coronal mass ejection must also be perfectly aligned with Earth.

“We often talk about magnetic orientation [coronal mass ejection], how it interacts with the Earth's magnetic field,” Murdoch said. “What we saw was a strong response initially … but it lasted for a relatively short period of time.”

The initial wave of the coronal mass ejection is strongly coupled to the Earth's magnetic field, appearing in a strong southward direction to connect with the Earth—recorded as a G4 storm. Where the sky was dark, people could see the beautiful aurora. Murdoch received reports from grid operators in Quebec, British Columbia, who reported voltage irregularities but were able to manage them.

But when the bulk of the coronal mass ejection reached Earth several hours later, the magnetic orientation was flipped — like a baseball spinning in the wind. The coronal mass ejection now acquired a northward orientation, weakening its coupling with Earth's magnetic field. The geomagnetic storm then weakened to G1 and G2 levels overnight, Murdoch said.

Despite the weakening of the geomagnetic storm, some skywatchers in northern latitudes were still able to catch the dancing lights.

But if you missed Sunday's activity because you were sleeping or it was daylight, don't worry. The Sun's activity fluctuates every 11 years or so, which is called a solar cycle. In the coming months, scientists predict that the Sun will hit the peak of its current solar cycle.

“Hold on. There's more to come,” Murdoch said. “We'll see more of these eruptions in the coming months because of the phase of the solar cycle.”

Jason Samenow contributed to this report.