Spotless sun sparks pink auroras


On Feb. 23rd the sun was completely blank (no sunspots) and NOAA classified solar activity as "very low." Nevertheless, this happened:

"Despite the blank sun, we witnessed a beautiful display of auroras," reports photographer Andrei Andritcu from Tromso, Norway. In addition to the usual green, the lights contained a splash of pink.

In auroras, pink is a sign of nitrogen. Ordinary green auroras are caused by energetic particles from space hitting oxygen atoms 100 km to 300 km above Earth's surface. Pink appears when the energetic particles descend lower than usual, striking nitrogen molecules at the 100 km level and below.

Recent displays of pink and white auroras have coincided with spotless suns often enough to make observers wonder if there is a connection. E.g. perhaps solar wind emerging from the spotless sun is unusually penetrating. If so, we can expect to see more nitrogenous auroras in the years ahead. The sun is descending into a deep Solar Minimum, and the nadir could be colored pink.


Frankie Lucena of Puerto Rico frequently scans the automated Gemini webcam on Hawaii's Mauna Kea volcano, looking for sprites and other forms of exotic lightning. On Feb. 13th he saw something--but it wasn't lightning. "It was a rare Hawaiian light pillar," he says. Here is one frame from the complete video:
light pillar hawaii
"I was searching for thunderstorms and just happened to come across this rarely seen event in this part of the world," says Lucena. "Light pillars usually occur in cold climates like Canada so to see them this far south is unusual."

Light pillars appear when urban lights reflect from the flat faces of ice crystals fluttering down from high freezing clouds. The source of the crystals, in this case, was probably a bank of altostratus/cumulus clouds shown in the video. "I do not recall seeing examples of these pillars so far south or in a location like Hawaii," says atmospheric optics expert Les Cowley. "So these are very rare indeed."