Nov. 23, 2017: On Nov. 22nd, the face of the sun was unblemished by sunspots, and NOAA classified solar activity as “very low.” Nevertheless, the skies above Tromsø, Norway, exploded with a remarkable outburst of pink auroras. “Suddenly, the whole valley turned white (with a hint of pink),” says Frank Meissner, who witnessed and photographed the display. “It was over after about 20 seconds.”
How bright was it? “The brightness of the auroras may be compared to the car lights in the background of my photo,” points out Meissner.
In nearby Kvaløya, aurora tour guide Marianne Bergli witnessed a surge of pink that was, if anything, even more dramatic:
“Ironically, our guests stopped taking pictures,” says Bergli. “They were awestruck and frozen to the spot by the incredible pink and green lights overhead.”
This outburst was powered by a stream of solar wind flowing from a hole in the sun’s atmosphere. Such holes are common during Solar Minimum, and they require no sunspots to form. That’s why auroras continue throughout the 11-year solar cycle.
The pink color of the outburst tells us something interesting about the solar wind on Nov. 22nd: it seems to have been unusually penetrating. Most auroras are green–a verdant glow 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.
In recent winters, big displays of pink and white auroras have coincided with spotless suns often enough to make observers wonder if there is a connection. If so, more outbursts are in the offing as the sun continues its plunge toward a deep Solar Minimum. Stay tuned for pink!