Best guess, high altitude atomic oxygen.

Based on the wikipedia aurora article it sounds like the lower atmosphere has a more mixed bag of gasses, so it glows white, while in the upper atmosphere atomic oxygen(note that oxygen lower down is all diatomic and glows green) is able to showcase it's characteristic red glow.

https://en.wikipedia.org/wiki/Aurora#Colours_and_wavelengths...

But now I am wondering about the green(oxygen?) and yellow(sodium?) atmospheric bands visable. The green one is interesting because it may tear apart my atomic oxygen theory. why would a green diatomic band be above the red atomic sprite flare?

PecosHank on YouTube has a great video on TLEs and how to photograph them from the ground. I think the green is oxygen and the red is nitrogen, same as in the aurora.