The Thanksgiving Storm across 900km of Latitude

AAC

The Alberta Aurora Chasers Facebook Group is one of the most active places for aurora spotters to post their sighting in the sub-auroral zone. This past October 11-12, a G2 storm produced some amazing displays overhead of Alberta, captured by a range of cameras from large to smartphone. 

One post in the AAC channel requested that participants post images from a specific time of a very distinct 'ring' formation seen around 10:15pm MST, along with general location.

Putting together the data

This provided the opportunity to make an animation of 'flying' under that aurora in a one second - a north-south distance of about 900km from Lethbridge to Fort MacMurray, about 100 times the ground speed of the International Space Station.

The result of arranging these credited images by latitude gives a perspective of the size and 3D structure of the aurora at that moment, and is only possible by community cooperation and the prevalence of smartphones that can capture reasonable aurora imagery.

Credit

All photos are from the AAC Facebook group feed and are credited to their respective photographers, along with the approximate location they shared.

Process

They are edited for relative framing position, lens perspective, and some frames are corrected for colour balance. They are aligned approximately on the horizon point, after experimentation with alignment using stars like the Pleiades cluster.

Analysis

The animation shows what potentially appears to be the 'Dunes' formation, especially from images taken in the South (near the left side of the animation frame on the closed side of the auroral rings)

Although the rings appear to be separated, they are likely connected and just brighter on one side. This periodic pattern when seen in fluids is referred to as a 'Kelvin-Helmholtz Instability' and although that may not be the phenomena seen here, it does have a similar periodic structure

KHI Seen Elsewhere

This Kelvin-Helmholtz Instability structure was also seen in Dawson City, YT on September 8, 2021, about a month before, seen here on the leftmost curtain. The rings or waves seem to move at the same velocity along the curtain, maintaining distance and relative scale for some time.