James Reynolds was sitting at home scrolling through Twitter on Thursday night, when photos of the aurora borealis started to flood his timeline.
Mr. Reynolds, a professional photographer who lives just outside Asheville, N.C., decided to load up his equipment and to drive with his wife and 10-year-old son to the Blue Ridge Parkway, a popular, scenic road about an hour from his home.
After getting set up there and snapping a few shots, Mr. Reynolds finally spotted it: purple hues dancing in the sky.
“It felt like the sky was alive,” said Mr. Reynolds, 45. “It was a joyful moment to see it with the Blue Ridge Mountains and my familiar home environment in the background, where you would never expect to see something like that.”
The colorful streaks in the sky, also known as the northern lights, are often visible from places like Alaska, Canada and Iceland. But on Thursday night, a “severe” geomagnetic storm brought the auroras to Minnesota, New York and Virginia, and the views even moved as far south as Arizona and North Carolina. The Space Weather Prediction Center at the National Oceanic and Atmospheric Administration rated the geomagnetic storm’s severity a Level 4 on its five-tier scale.
Catching a glimpse of the auroras requires electrons from solar wind to hit the electrons that are already trapped around earth’s magnetic field, which then acts like a slingshot, said C. Alex Young, the associate director for science in the Heliophysics Science Division at NASA’s Goddard Space Flight Center. The energy comes from a coronal mass ejection, a large expulsion of plasma from the sun, which causes the magnetic field around Earth to shake. That creates geomagnetic storms that produce the aurora.
The colors seen in the sky are dictated by where in the atmosphere the oxygen and nitrogen hit, Dr. Young said. Green and red largely come from oxygen, and blue stems from nitrogen.
Mostly, that energy is driven to the Earth’s North and South Poles, but the stronger the storm is, the more likely it is to be seen in lower latitudes like the southern United States.
At first, Dr. Young said, Thursday’s geomagnetic storms were forecast to potentially reach only a Level 3. In the days prior, the sun had several small coronal mass ejections, but forecasters believed their impact had largely brushed past Earth. As it turned out, he said, there had been two ejections that got closer to Earth, helping to “give it an extra kick to the Earth” when the electrons reached the magnetic field.
“It only lasted for a couple hours, but that’s why people were seeing it on the horizon so much further south than usual,” he said. “It’s been so exciting and quite spectacular.”
It’s difficult to pinpoint how often strong geomagnetic storms like this one occur, Dr. Young said. Typically, anywhere from 50 to 100 storms of this magnitude may occur over an 11-year solar cycle, and they become more likely as the end of the cycle nears in 2025.