The science behind nature’s beauty
Last week, while traveling through Fairbanks, Alaska, I was treated to a spectacular double feature in the sky. Aurora danced overhead in pale pastel hues, while pillars of light anchored to the ground beamed into the night sky.
It was an awe-inspiring 24 hours in the Last Frontier.
At the time of the two shows, temperatures were in the single digits above zero, with intermittent flurries and a confetti of ice crystals known as “diamond dust” glimmering in the predawn sky.
From the ground north of Fairbanks, columns extended upward from city lights, reaching hundreds of feet into the air. The shafts of light resembled those accompanying popular monuments and memorials, luminous pillars piercing into the overcast night sky.
The phenomenon, known as light pillars, is rare at the lower latitudes, and it occurs infrequently even in the Arctic. Light pillar development requires the perfect combination of temperature, moisture and wind conditions.
At sufficiently low temperatures, trace amounts of moisture in the air freeze as hexagonal ice crystals. Diamond dust requires nuclei, or small particulates in the air, for ice crystals to form when temperatures are above 10 or 15 degrees.
The diamond dust in the air Friday morning probably was enhanced by the ashy soot and aerosols originating from vehicle traffic and industry in Fairbanks.
Each of the small ice crystals acts as a mirror, such that light shining on from the ground up into the sky is reflected back toward the surface in the direction of an observer. Ice crystals at different heights bounce back different beams of light, allowing a vertical column of luminance to form over natural light sources or those of human origin.
There were also patches of light-to-moderate snow falling at the time beneath a mostly clear sky, courtesy of moisture trapped beneath a low-level inversion, or an uptick in temperature with height.
While I was photographing light pillars, I noticed a band of aurora becoming increasingly bright overhead. The colors were not overly vibrant yet, but I bet on its appearance signifying a more dramatic show to come. I decided to drive west of Fairbanks to escape snow showers in the Tanana valley.
Much like my friend and I had done earlier in the week, we set up shop in the town of Ester, about a 20 minute drive west of Fairbanks, where we took advantage of clear skies brightened only by the aurora and a waxing crescent moon. The show was fun to watch, but it paled in comparison to what would arrive 20 hours later.
On Friday night, a spurt of swift solar wind hit Rarth’s magnetic field, or magnetosphere. The solar wind, which carries high-energy particles from the surface of the sun into space, can interact with the magnetosphere to induce epic displays of the northern and southern lights. The aurora are more prominent around the time of the equinox thanks to something called the Russell-McPherron effect.
By midnight Friday Alaska time, there was a full fledged geomagnetic storm; glimpses of the aurora borealis dipped all the way into the Northern Tier of the Lower 48 and shone brightly over Alberta, Manitoba and Saskatchewan in Canada.
I had planned my return flight from Alaska to maximize my chances of flying beneath the aurora, which coincided perfectly with the solar storm. Because the flight passed directly beneath the auroral oval, which had swollen south thanks to the arrival of an enhanced solar wind, I was not just witnessing an emerald glow on the horizon — the aurora was dancing directly overhead.
It appeared as bright columns of light delivering pinpricks to the sky overhead while rippling like laundry strung out in the wind. Occasional eddies of glowing plasma swirled through the sky, the display unlike any of the comparatively meager shows I had witnessed in days prior.
The intensity of the geomagnetic storm surprised even forecasters at the Space Weather Prediction Center in Boulder, Colo., who had expected a G1 storm. Geomagnetic storms are ranked on a 1 to 5 scale. Friday’s episode was a G2.
The most dramatic display lasted only 15 minutes, but it produced a sight beyond words.