Here we are in 12,003 BCE somewhere along a featureless tundric landscape…
54.6 miles from the nearest human…
3.9 miles from the nearest musk ox…
Oh, drat. We were only supposed to go back to October 30, 2003. Forgive me; I’m still contending with these pesky time zone adjustments. All the same, it’s not all a loss. Look up! Yes, that’s right. We’re observing a gobstoppingly gorgeous green aurora. The souls of the ancestors caught in a bacchanal frenzy in profoundly silent, star-adorned Arctic skies. If only we could lapse into delta sleep we’d be able to dance with them. Not, of course, that we’d remember.
Or, if you insist, we’re observing the excitation of oxygen molecules between 60 to 190 miles above us. Whatever explanation you prefer, the point of staring up is to observe the light. Notice it? Never mind the ethereal beauty and aching soul balderdash. Notice the motion? See the shimmering sheets of emerald green as they pulse and shift and slither with a strange serpentine grace across the firmament? That’s how aurorae generally behave.
Now, if, well, I’d known what I was doing and we’d ended up 14,006 years in the future, in October 2003 in Newfoundland, we would have seen an early-evening sky glowing crimson under an auroral sheath that literally covered the sky. More excited oxygen, but higher up: around 200 – 240 miles. Under that sky, we would have observed the pulsating peaks of reddish light encircling us. As is true with this 12,003 BCE aurora, which only an unsleeping mother and her three bedazzled and fatigued children will see well beyond our personal horizon, the one far in the future will also shimmer and move.
Now, let’s travel to 2022:
We’re back in the Arctic.
December 25 – 26th
1.2 miles from the next nearest human
Would you look at that? Another emerald aurora extending across the entire sky. It is almost as though we could pivot by a single degree and find ourselves back in 12,003 BCE… except it’s faint. It’s also not moving. No shimmering. No pulsations. Nothing but a steady greenish glow. Very strange, indeed. In fact, a type of aurora that nobody on Earth’s surface had ever seen before. The coterie of departed souls stands inert. How can this phenomenon be explained?
The mystery of the faint, stagnant aurora was solved by a research team led by Keisuke Hosokawa from the Center for Space Science and Radio Engineering at the University of Electronic Communications in Tokyo. Dr. Hosokawa used data collected by the Special Sensor Ultraviolet Scanning Imager (SSUSI) on the Polar Orbiting Defense Meteorological Satellite Program (DMSP). (Unlike in 12,003 BCE, our sky today is a veritable autobahn of satellites.) Much to their shock and delight, members of this research team realized that the Christmas 2022 event was a “polar rain aurora,” the very first ever observed on Earth. Others have been seen from outer space. Such events are as rare as they are underwhelming: one of those astronomical events that raise more eyebrows than spirits.
So, what is a polar rain aurora, exactly? First, let’s discuss the “regular” aurora. Charged particles stream radially away from the Sun along a nearly incessant outflow called “the solar wind.” When these particles reach Earth, the magnetosphere enclosing our planet directs them toward the two magnetic poles: one in the northern hemisphere and another in the south. The resultant excitation of the atmospheric gases produces the shimmering, ever-changing aurora.
However, the Christmas 2022 aurora’s provenance was different. What one might call the regular solar wind generally travels about 250 miles per second.* However, around coronal holes (gaps within the Sun’s extremely hot, yet rarefied outer atmosphere) the solar wind can move at more than twice that velocity. Around these gaps the Sun’s magnetic field is wide open and allows a constant stream of high-energy electrons to flow out of it without any impedance. Most of the time these gaps form at higher solar latitudes and so the stream is directed away from Earth, but in December 2022 these holes formed at a lower solar latitude and the high-energy electrons did flow toward our planet.
Also, by the luckiest coincidence, at the same time we experienced the usually active solar wind diminished almost to nothing. Ordinarily, these high-energy coronal hole electrons would have been swept into the solar wind maelstrom and become part of the aurora-inducing storms. This time, however, the lack of solar wind pressure allowed these electrons to reach Earth in a full-blown torrent. Moreover, the diameter of the magnetic funnel directing these electrons toward the planet extended over 4,500 miles, hence the smoothness and lack of motion in the aurora. No change in flux and flow, at least until the particle density diminished enough so as to no longer produce the aurora. Researchers have been able to study the phenomenon of polar-rain electrons through satellite observations. For the first time, the effect was visible on Earth’s surface. It might not have been seen by many up there in the remote Arctic wilds, but it was seen by some: a rare sight caused by a quiet solar wind, a stream of high energy electrons, and a bit of luck.
*This speed, though fast, is much slower than that of light. Consequently, we can see a dramatic solar event such as a coronal mass ejection within minutes of its occurrence, because the Sun is about 8.3 light minutes away. However, the material spewing away from such ejections requires 2 – 4 days to arrive. This lapse gives us some time to warn others of impending aurora events or other solar-storm-related disruptions.
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