#AURORA DUNES SEEN DURING EXTREME STORM: Lots of unusual things were seen during last week's extreme geomagnetic storm. Alan Dyer of Gleichen, Alberta, photographed one of them, shown here in a deep twilight photo at te onsett of the storm:

"I captured some 'aurora dunes,'" Dyer says. "They are the horizontal green ripples to the left of Venus and the Moon."

Aurora dunes are a recently identified form of Northern Lights named after their resemblence to ripples in desert sand. Researchers first explained them in a paper published only a few years ago. The dunes are a "mesospheric bore," a type of atmospheric gravity wave that springs up from Earth's surface and gets caught in a thermal waveguide ~100 km high. When solar wind particles rain down on the bore, they illuminate its rippling structure.

https://spaceweather.com/