The SAR and the Milky Way (Astronomy Picture of the Day)
Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2023 November 11
See Explanation. Clicking on the picture [at link] will download the highest resolution version available.
Image Credit & Copyright: Julien Looten
Explanation: This broad, luminous red arc was a surprising visitor to partly cloudy evening skies over northern France. Captured extending toward the zenith in a west-to-east mosaic of images from November 5, the faint atmospheric ribbon of light is an example of a Stable Auroral Red (SAR) arc. The rare night sky phenomenon was also spotted at unusually low latitudes around world, along with more dynamic auroral displays during an intense geomagnetic storm. SAR arcs and their relation to auroral emission have been explored by citizen science and satellite investigations. From altitudes substantially above the normal auroral glow, the deep red SAR emission is thought to be caused by strong heating due to currents flowing in planet Earth's inner magnetosphere. Beyond this SAR, the Milky Way arcs above the cloud banks along the horizon, a regular visitor to night skies over northern France.
= new reply since forum marked as read
It is now set as my background! 
Since it seems as though SAR are consistently described as "Stable Auroral Red arc," SARA would seem to me a better acronym—one which would nicely balance another aurora associated phenomenon STEVE (Strong Thermal Emission Velocity Enhancement).
Here is another SARA, this over India
STEVEs were also seen in the auroral event which caused the APOD. Although generally purple, these were multicolored. Well, multicoloured since they were over the UK.
SARA were first noted in the scientific literature only in 1956. STEVE was not scientifically described until 2015 by Canadian aurora photographers—not by astronomers! Recently it was learned that SARAs can evolve into STEVEs.
Going further down into the interweb pipes (avoiding those choked with cats) this morning, it seems that both SARA and STEVE are actually SAIDs (SubAuroral Ion Drift) which are streams of glowing very hot particles apparently arising from our atmosphere. This is unlike the aurorae which glow because of electric discharges caused directly by the incoming particles from the sun. That, at least, is my understanding.
To add confusion, though SAIDs are called "SubAuroral" they are actually at a HIGHER altitude from the earth's surface than are the aurorae. In this context "SubAuroral" means at a Lower Latitude (closer to the equator on the globe) than the auroral displays.
There is so much yet to learn, so much yet to discover. Hopefully, we will have the time, talent and will to do so. 
Thankk you for the pictures and explanations. I am learning so much today.
It was nice of you to think of our British friends, too. They do seem fond of that superfluous "u".
