Auroras still have the capacity to surprise. On April 16th, Matthew Wheeler, an experienced aurora-watcher in Robson Valley, British Columbia, saw a green glow forming in the north--then he noticed something odd. "Horizontal lines caught my attention", he says. "There appeared to be ripples in the aurora." Six of them are labeled in this 1/2 second exposure:
A video captured by Wheeler shows their dynamics over a 20-minute period: watch it.
These are "dunes", a newly recognized form of aurora named after their resemblance to desert sand dunes. A team of researchers first explained them in a paper published just last year. 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.
These are "dunes", a newly recognized form of aurora named after their resemblance to desert sand dunes. A team of researchers first explained them in a paper published just last year. 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.
Sky watchers in the Arctic have been seeing Dunes for years without understanding what they were. A breakthrough came on Oct. 7, 2018, when multiple groups photographed dunes from widely separated locations in Finland. Triangulation revealed the dunes to be ~100 km high with a pure, monochromatic wavelength of about 45 km.
This is a new field of study with potential for discovery. Monitoring aurora dunes may reveal previously hidden waves and waveguides at the boundary between Earth and space.
www.spaceweather.com
This is a new field of study with potential for discovery. Monitoring aurora dunes may reveal previously hidden waves and waveguides at the boundary between Earth and space.
www.spaceweather.com
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