By GARLAND KENNEDY
Sentinel Staff Writer
Alaskans who stepped outdoors after sunset Sunday witnessed a spectacular display of the aurora borealis, thanks to a large solar storm that illuminated the night sky across Alaska and far into the Lower 48.
The brilliant display of green and red light was one of the largest shows of northern lights in years, University of Alaska Fairbanks associate professor Donald Hampton told the Sentinel Monday.
“This was definitely one of the larger storms we’ve seen in a while… I think it’s the best one we’ve had since the last solar cycle,” Hampton said over the phone. “The sun goes through an 11-year cycle with the sunspots as it changes its magnetic field, and during solar maximum conditions is when we get coronal mass ejections that create these very large solar storms like what we saw (Sunday) night. This is the first big one we’ve had for this solar cycle.”
Hampton works at UAF’s geophysical institute and specializes in atmospheric and space science.
The current solar cycle began with a low point in 2019, and solar activity will continue to build up for the next three years, he said.
“The aurora is always driven by the sun and primarily through the solar wind, which is a stream of charged particles that come off the sun. Those charged particles and that solar wind will interact with our magnetic field and produce all the processes that create the aurora,” he said.
Sunday night, the aurora became active above Sitka not long after sunset. By 9 p.m., curtains of shimmering green and sometimes red light hung in the sky and remained there for hours.
Sitkans piled into their cars to find viewpoints, from Starrigavan to Silver Bay. The lights were clearly visible from downtown despite the light pollution. But parking spaces north of town at Old Sitka were full as carloads of watchers sought viewing sites less affected by lights in town. Skies over the region were almost entirely clear, and while the first quarter moon was bright, it did little to dim the northern lights.
The aurora was active over all of Alaska Sunday, but social media reported sightings as far south as Wyoming.
A coronal mass ejection caused the light show, Hampton said.
“This one was a fairly large one,” he said, “and it happened to be aimed right at Earth. And so that’s why we got this large storm.”
In Colorado, where NOAA’s Space Weather Prediction Center monitors solar activity, the office’s lead forecaster, Rob Steenburgh, said not one but two mass ejections from the sun, on Friday and Saturday, triggered the spectacular light show that followed.
In a phone interview, he described a coronal mass ejection as “a big blob of plasma from the sun that erupts and escapes the sun’s gravity and moves through interplanetary space, and sometimes, it runs into Earth, and our magnetosphere. The big blob of plasma carries its own magnetic field, and that magnetic field interacts with Earth’s magnetic fields. And it’s in that interaction that you can drive storms like this.”
While a green aurora is not uncommon above Alaska, Hampton said, red coloration is less typical. The UAF scientist said green and red lights occur because of solar wind interacting with atomic oxygen in the ionosphere, but the pink fringes that added depth to Sunday’s aurora are caused by nitrogen.
“That early display, about 9 p.m., 9:30 p.m. Alaska time, was really particularly bright, from here (Fairbanks) to Sitka, just the extent and the total energy that went into it… there was a lot of red that people could see, and that’s not as common.”
The strength of the northern lights can be measured on the Planetary Kennziffer, or KP index, which calculates disturbances of the planet’s magnetic field on a logarithmic scale. UAF maintains an aurora forecast online at https://www.gi.alaska.edu/monitors/aurora-forecast.
The NOAA Space Weather Prediction Center posts information at https://www.swpc.noaa.gov/.
The beauty of an active aurora, Hampton recalled, is part of what drew him from his home state of Texas to Alaska years ago as a graduate student.
“I got up here and that fall, went outside one night and watched the aurora and I said, ‘Well, I think I need to study that,’ because it was just so spectacular and so intriguing,” he said. “So yeah, I’ve been working on that ever since.”
