aurora wave
A rare image of the aurora. The view highlight the wave in the middle of the frame. It’s still a hot topic for the experts. The specialist told me that the formation of these curl-like structures may be connected with flow shear driven by ultra-low frequency waves. These curls are fine structures in the poleward boundary of multiple arcs formed by longitudinal-arranged field-aligned current pairs. It look like to the Auroral Undulations Triggered by Kelvin-Helmholtz Waves. The view was captured when the aurora appears in the zenith which exists just several minutes. I also captured a timelapse video at that moment. Photo taken at Kerid Crater, Iceland on Jan 16th. 2024. Photographer's website: https://twanight.org/dai
Regular readers may recall how we have occasionally reported on magnetic sine waves rippling through Earth's magnetic field, causing the magnetosphere to ring like a bell. On Jan. 16th, Jeff Dai looked up and actually saw one of those waves over the Kerid Crater in Iceland:

"I captured this rare image of 'aurora curls," says Dai. "They rippled across the zenith for several minutes."

Dai, who is vacationing in Iceland from China, asked Xing-Yu Li of Peking University's Institute of Space Physics and Applied Technology for help in understanding the aurora curls. "Imagine that Earth's magnetic field is like a guitar string," says Li. "In Jeff Dai's picture we are seeing vibrations in that string." Their wavelength, Li estimates, is several kilometers.

Normally this kind of magnetic pulsation is seen only as a squiggle on a chart recorder. In this case, however, energetic particles from space flowed down the rippling geomagnetic field, causing it to glow with auroral light and write the wave across the night sky. It was a very rare sighting, indeed.